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Invariant Sections being "Funding Free Software", the Front-Cover Texts
being (a) (see below), and with the Back-Cover Texts being (b) (see
below).  A copy of the license is included in the section entitled "GNU
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INFO-DIR-SECTION Software development
START-INFO-DIR-ENTRY
* gcc: (gcc).                  The GNU Compiler Collection.
* g++: (gcc).                  The GNU C++ compiler.
* gcov: (gcc) Gcov.            ‘gcov’--a test coverage program.
* gcov-tool: (gcc) Gcov-tool.  ‘gcov-tool’--an offline gcda profile processing program.
* gcov-dump: (gcc) Gcov-dump.  ‘gcov-dump’--an offline gcda and gcno profile dump tool.
* lto-dump: (gcc) lto-dump.    ‘lto-dump’--Tool for
dumping LTO object files.
END-INFO-DIR-ENTRY

 This file documents the use of the GNU compilers.

 Copyright © 1988-2022 Free Software Foundation, Inc.

 Permission is granted to copy, distribute and/or modify this document
under the terms of the GNU Free Documentation License, Version 1.3 or
any later version published by the Free Software Foundation; with the
Invariant Sections being "Funding Free Software", the Front-Cover Texts
being (a) (see below), and with the Back-Cover Texts being (b) (see
below).  A copy of the license is included in the section entitled "GNU
Free Documentation License".

 (a) The FSF's Front-Cover Text is:

 A GNU Manual

 (b) The FSF's Back-Cover Text is:

 You have freedom to copy and modify this GNU Manual, like GNU software.
Copies published by the Free Software Foundation raise funds for GNU
development.


File: gcc.info,  Node: Top,  Next: G++ and GCC,  Up: (dir)

Introduction
************

This manual documents how to use the GNU compilers, as well as their
features and incompatibilities, and how to report bugs.  It corresponds
to the compilers (GCC) version 12.2.0.  The internals of the GNU
compilers, including how to port them to new targets and some
information about how to write front ends for new languages, are
documented in a separate manual.  *Note Introduction: (gccint)Top.

* Menu:

* G++ and GCC::     You can compile C or C++ programs.
* Standards::       Language standards supported by GCC.
* Invoking GCC::    Command options supported by ‘gcc’.
* C Implementation:: How GCC implements the ISO C specification.
* C++ Implementation:: How GCC implements the ISO C++ specification.
* C Extensions::    GNU extensions to the C language family.
* C++ Extensions::  GNU extensions to the C++ language.
* Objective-C::     GNU Objective-C runtime features.
* Compatibility::   Binary Compatibility
* Gcov::            ‘gcov’--a test coverage program.
* Gcov-tool::       ‘gcov-tool’--an offline gcda profile processing program.
* Gcov-dump::       ‘gcov-dump’--an offline gcda and gcno profile dump tool.
* lto-dump::        ‘lto-dump’--Tool for dumping LTO
object files.
* Trouble::         If you have trouble using GCC.
* Bugs::            How, why and where to report bugs.
* Service::         How To Get Help with GCC
* Contributing::    How to contribute to testing and developing GCC.

* Funding::         How to help assure funding for free software.
* GNU Project::     The GNU Project and GNU/Linux.

* Copying::         GNU General Public License says
                    how you can copy and share GCC.
* GNU Free Documentation License:: How you can copy and share this manual.
* Contributors::    People who have contributed to GCC.

* Option Index::    Index to command line options.
* Keyword Index::   Index of concepts and symbol names.


File: gcc.info,  Node: G++ and GCC,  Next: Standards,  Up: Top

1 Programming Languages Supported by GCC
****************************************

GCC stands for "GNU Compiler Collection".  GCC is an integrated
distribution of compilers for several major programming languages.
These languages currently include C, C++, Objective-C, Objective-C++,
Fortran, Ada, D, and Go.

 The abbreviation “GCC” has multiple meanings in common use.  The
current official meaning is "GNU Compiler Collection", which refers
generically to the complete suite of tools.  The name historically stood
for "GNU C Compiler", and this usage is still common when the emphasis
is on compiling C programs.  Finally, the name is also used when
speaking of the “language-independent” component of GCC: code shared
among the compilers for all supported languages.

 The language-independent component of GCC includes the majority of the
optimizers, as well as the "back ends" that generate machine code for
various processors.

 The part of a compiler that is specific to a particular language is
called the "front end".  In addition to the front ends that are
integrated components of GCC, there are several other front ends that
are maintained separately.  These support languages such as Mercury, and
COBOL.  To use these, they must be built together with GCC proper.

 Most of the compilers for languages other than C have their own names.
The C++ compiler is G++, the Ada compiler is GNAT, and so on.  When we
talk about compiling one of those languages, we might refer to that
compiler by its own name, or as GCC.  Either is correct.

 Historically, compilers for many languages, including C++ and Fortran,
have been implemented as "preprocessors" which emit another high level
language such as C.  None of the compilers included in GCC are
implemented this way; they all generate machine code directly.  This
sort of preprocessor should not be confused with the “C preprocessor”,
which is an integral feature of the C, C++, Objective-C and
Objective-C++ languages.


File: gcc.info,  Node: Standards,  Next: Invoking GCC,  Prev: G++ and GCC,  Up: Top

2 Language Standards Supported by GCC
*************************************

For each language compiled by GCC for which there is a standard, GCC
attempts to follow one or more versions of that standard, possibly with
some exceptions, and possibly with some extensions.

2.1 C Language
==============

The original ANSI C standard (X3.159-1989) was ratified in 1989 and
published in 1990.  This standard was ratified as an ISO standard
(ISO/IEC 9899:1990) later in 1990.  There were no technical differences
between these publications, although the sections of the ANSI standard
were renumbered and became clauses in the ISO standard.  The ANSI
standard, but not the ISO standard, also came with a Rationale document.
This standard, in both its forms, is commonly known as “C89”, or
occasionally as “C90”, from the dates of ratification.  To select this
standard in GCC, use one of the options ‘-ansi’, ‘-std=c90’ or
‘-std=iso9899:1990’; to obtain all the diagnostics required by the
standard, you should also specify ‘-pedantic’ (or ‘-pedantic-errors’ if
you want them to be errors rather than warnings).  *Note Options
Controlling C Dialect: C Dialect Options.

 Errors in the 1990 ISO C standard were corrected in two Technical
Corrigenda published in 1994 and 1996.  GCC does not support the
uncorrected version.

 An amendment to the 1990 standard was published in 1995.  This
amendment added digraphs and ‘__STDC_VERSION__’ to the language, but
otherwise concerned the library.  This amendment is commonly known as
“AMD1”; the amended standard is sometimes known as “C94” or “C95”.  To
select this standard in GCC, use the option ‘-std=iso9899:199409’ (with,
as for other standard versions, ‘-pedantic’ to receive all required
diagnostics).

 A new edition of the ISO C standard was published in 1999 as ISO/IEC
9899:1999, and is commonly known as “C99”.  (While in development,
drafts of this standard version were referred to as “C9X”.) GCC has
substantially complete support for this standard version; see
<https://gcc.gnu.org/c99status.html> for details.  To select this
standard, use ‘-std=c99’ or ‘-std=iso9899:1999’.

 Errors in the 1999 ISO C standard were corrected in three Technical
Corrigenda published in 2001, 2004 and 2007.  GCC does not support the
uncorrected version.

 A fourth version of the C standard, known as “C11”, was published in
2011 as ISO/IEC 9899:2011.  (While in development, drafts of this
standard version were referred to as “C1X”.) GCC has substantially
complete support for this standard, enabled with ‘-std=c11’ or
‘-std=iso9899:2011’.  A version with corrections integrated was prepared
in 2017 and published in 2018 as ISO/IEC 9899:2018; it is known as “C17”
and is supported with ‘-std=c17’ or ‘-std=iso9899:2017’; the corrections
are also applied with ‘-std=c11’, and the only difference between the
options is the value of ‘__STDC_VERSION__’.

 A further version of the C standard, known as “C2X”, is under
development; experimental and incomplete support for this is enabled
with ‘-std=c2x’.

 By default, GCC provides some extensions to the C language that, on
rare occasions conflict with the C standard.  *Note Extensions to the C
Language Family: C Extensions.  Some features that are part of the C99
standard are accepted as extensions in C90 mode, and some features that
are part of the C11 standard are accepted as extensions in C90 and C99
modes.  Use of the ‘-std’ options listed above disables these extensions
where they conflict with the C standard version selected.  You may also
select an extended version of the C language explicitly with
‘-std=gnu90’ (for C90 with GNU extensions), ‘-std=gnu99’ (for C99 with
GNU extensions) or ‘-std=gnu11’ (for C11 with GNU extensions).

 The default, if no C language dialect options are given, is
‘-std=gnu17’.

 The ISO C standard defines (in clause 4) two classes of conforming
implementation.  A “conforming hosted implementation” supports the whole
standard including all the library facilities; a “conforming
freestanding implementation” is only required to provide certain library
facilities: those in ‘<float.h>’, ‘<limits.h>’, ‘<stdarg.h>’, and
‘<stddef.h>’; since AMD1, also those in ‘<iso646.h>’; since C99, also
those in ‘<stdbool.h>’ and ‘<stdint.h>’; and since C11, also those in
‘<stdalign.h>’ and ‘<stdnoreturn.h>’.  In addition, complex types, added
in C99, are not required for freestanding implementations.

 The standard also defines two environments for programs, a
“freestanding environment”, required of all implementations and which
may not have library facilities beyond those required of freestanding
implementations, where the handling of program startup and termination
are implementation-defined; and a “hosted environment”, which is not
required, in which all the library facilities are provided and startup
is through a function ‘int main (void)’ or ‘int main (int, char *[])’.
An OS kernel is an example of a program running in a freestanding
environment; a program using the facilities of an operating system is an
example of a program running in a hosted environment.

 GCC aims towards being usable as a conforming freestanding
implementation, or as the compiler for a conforming hosted
implementation.  By default, it acts as the compiler for a hosted
implementation, defining ‘__STDC_HOSTED__’ as ‘1’ and presuming that
when the names of ISO C functions are used, they have the semantics
defined in the standard.  To make it act as a conforming freestanding
implementation for a freestanding environment, use the option
‘-ffreestanding’; it then defines ‘__STDC_HOSTED__’ to ‘0’ and does not
make assumptions about the meanings of function names from the standard
library, with exceptions noted below.  To build an OS kernel, you may
well still need to make your own arrangements for linking and startup.
*Note Options Controlling C Dialect: C Dialect Options.

 GCC does not provide the library facilities required only of hosted
implementations, nor yet all the facilities required by C99 of
freestanding implementations on all platforms.  To use the facilities of
a hosted environment, you need to find them elsewhere (for example, in
the GNU C library).  *Note Standard Libraries: Standard Libraries.

 Most of the compiler support routines used by GCC are present in
‘libgcc’, but there are a few exceptions.  GCC requires the freestanding
environment provide ‘memcpy’, ‘memmove’, ‘memset’ and ‘memcmp’.
Finally, if ‘__builtin_trap’ is used, and the target does not implement
the ‘trap’ pattern, then GCC emits a call to ‘abort’.

 For references to Technical Corrigenda, Rationale documents and
information concerning the history of C that is available online, see
<https://gcc.gnu.org/readings.html>

2.2 C++ Language
================

GCC supports the original ISO C++ standard published in 1998, and the
2011, 2014, 2017 and mostly 2020 revisions.

 The original ISO C++ standard was published as the ISO standard
(ISO/IEC 14882:1998) and amended by a Technical Corrigenda published in
2003 (ISO/IEC 14882:2003).  These standards are referred to as C++98 and
C++03, respectively.  GCC implements the majority of C++98 (‘export’ is
a notable exception) and most of the changes in C++03.  To select this
standard in GCC, use one of the options ‘-ansi’, ‘-std=c++98’, or
‘-std=c++03’; to obtain all the diagnostics required by the standard,
you should also specify ‘-pedantic’ (or ‘-pedantic-errors’ if you want
them to be errors rather than warnings).

 A revised ISO C++ standard was published in 2011 as ISO/IEC 14882:2011,
and is referred to as C++11; before its publication it was commonly
referred to as C++0x.  C++11 contains several changes to the C++
language, all of which have been implemented in GCC.  For details see
<https://gcc.gnu.org/projects/cxx-status.html#cxx11>.  To select this
standard in GCC, use the option ‘-std=c++11’.

 Another revised ISO C++ standard was published in 2014 as ISO/IEC
14882:2014, and is referred to as C++14; before its publication it was
sometimes referred to as C++1y.  C++14 contains several further changes
to the C++ language, all of which have been implemented in GCC.  For
details see <https://gcc.gnu.org/projects/cxx-status.html#cxx14>.  To
select this standard in GCC, use the option ‘-std=c++14’.

 The C++ language was further revised in 2017 and ISO/IEC 14882:2017 was
published.  This is referred to as C++17, and before publication was
often referred to as C++1z.  GCC supports all the changes in that
specification.  For further details see
<https://gcc.gnu.org/projects/cxx-status.html#cxx17>.  Use the option
‘-std=c++17’ to select this variant of C++.

 Another revised ISO C++ standard was published in 2020 as ISO/IEC
14882:2020, and is referred to as C++20; before its publication it was
sometimes referred to as C++2a.  GCC supports most of the changes in the
new specification.  For further details see
<https://gcc.gnu.org/projects/cxx-status.html#cxx20>.  To select this
standard in GCC, use the option ‘-std=c++20’.

 More information about the C++ standards is available on the ISO C++
committee's web site at <http://www.open-std.org/jtc1/sc22/wg21/>.

 To obtain all the diagnostics required by any of the standard versions
described above you should specify ‘-pedantic’ or ‘-pedantic-errors’,
otherwise GCC will allow some non-ISO C++ features as extensions.  *Note
Warning Options::.

 By default, GCC also provides some additional extensions to the C++
language that on rare occasions conflict with the C++ standard.  *Note
Options Controlling C++ Dialect: C++ Dialect Options.  Use of the ‘-std’
options listed above disables these extensions where they they conflict
with the C++ standard version selected.  You may also select an extended
version of the C++ language explicitly with ‘-std=gnu++98’ (for C++98
with GNU extensions), or ‘-std=gnu++11’ (for C++11 with GNU extensions),
or ‘-std=gnu++14’ (for C++14 with GNU extensions), or ‘-std=gnu++17’
(for C++17 with GNU extensions), or ‘-std=gnu++20’ (for C++20 with GNU
extensions).

 The default, if no C++ language dialect options are given, is
‘-std=gnu++17’.

2.3 Objective-C and Objective-C++ Languages
===========================================

GCC supports "traditional" Objective-C (also known as "Objective-C 1.0")
and contains support for the Objective-C exception and synchronization
syntax.  It has also support for a number of "Objective-C 2.0" language
extensions, including properties, fast enumeration (only for
Objective-C), method attributes and the @optional and @required keywords
in protocols.  GCC supports Objective-C++ and features available in
Objective-C are also available in Objective-C++.

 GCC by default uses the GNU Objective-C runtime library, which is part
of GCC and is not the same as the Apple/NeXT Objective-C runtime library
used on Apple systems.  There are a number of differences documented in
this manual.  The options ‘-fgnu-runtime’ and ‘-fnext-runtime’ allow you
to switch between producing output that works with the GNU Objective-C
runtime library and output that works with the Apple/NeXT Objective-C
runtime library.

 There is no formal written standard for Objective-C or Objective-C++.
The authoritative manual on traditional Objective-C (1.0) is
"Object-Oriented Programming and the Objective-C Language":
<http://www.gnustep.org/resources/documentation/ObjectivCBook.pdf> is
the original NeXTstep document.

 The Objective-C exception and synchronization syntax (that is, the
keywords ‘@try’, ‘@throw’, ‘@catch’, ‘@finally’ and ‘@synchronized’) is
supported by GCC and is enabled with the option ‘-fobjc-exceptions’.
The syntax is briefly documented in this manual and in the Objective-C
2.0 manuals from Apple.

 The Objective-C 2.0 language extensions and features are automatically
enabled; they include properties (via the ‘@property’, ‘@synthesize’ and
‘@dynamic keywords’), fast enumeration (not available in Objective-C++),
attributes for methods (such as ‘deprecated’, ‘noreturn’, ‘sentinel’,
‘format’), the ‘unused’ attribute for method arguments, the ‘@package’
keyword for instance variables and the ‘@optional’ and ‘@required’
keywords in protocols.  You can disable all these Objective-C 2.0
language extensions with the option ‘-fobjc-std=objc1’, which causes the
compiler to recognize the same Objective-C language syntax recognized by
GCC 4.0, and to produce an error if one of the new features is used.

 GCC has currently no support for non-fragile instance variables.

 The authoritative manual on Objective-C 2.0 is available from Apple:
   • 
     <https://developer.apple.com/library/archive/documentation/Cocoa/Conceptual/ProgrammingWithObjectiveC/Introduction/Introduction.html>

 For more information concerning the history of Objective-C that is
available online, see <https://gcc.gnu.org/readings.html>

2.4 Go Language
===============

As of the GCC 4.7.1 release, GCC supports the Go 1 language standard,
described at <https://golang.org/doc/go1>.

2.5 D language
==============

GCC supports the D 2.0 programming language.  The D language itself is
currently defined by its reference implementation and supporting
language specification, described at <https://dlang.org/spec/spec.html>.

2.6 References for Other Languages
==================================

*Note GNAT Reference Manual: (gnat_rm)Top, for information on standard
conformance and compatibility of the Ada compiler.

 *Note Standards: (gfortran)Standards, for details of standards
supported by GNU Fortran.


File: gcc.info,  Node: Invoking GCC,  Next: C Implementation,  Prev: Standards,  Up: Top

3 GCC Command Options
*********************

When you invoke GCC, it normally does preprocessing, compilation,
assembly and linking.  The "overall options" allow you to stop this
process at an intermediate stage.  For example, the ‘-c’ option says not
to run the linker.  Then the output consists of object files output by
the assembler.  *Note Options Controlling the Kind of Output: Overall
Options.

 Other options are passed on to one or more stages of processing.  Some
options control the preprocessor and others the compiler itself.  Yet
other options control the assembler and linker; most of these are not
documented here, since you rarely need to use any of them.

 Most of the command-line options that you can use with GCC are useful
for C programs; when an option is only useful with another language
(usually C++), the explanation says so explicitly.  If the description
for a particular option does not mention a source language, you can use
that option with all supported languages.

 The usual way to run GCC is to run the executable called ‘gcc’, or
‘MACHINE-gcc’ when cross-compiling, or ‘MACHINE-gcc-VERSION’ to run a
specific version of GCC. When you compile C++ programs, you should
invoke GCC as ‘g++’ instead.  *Note Compiling C++ Programs: Invoking
G++, for information about the differences in behavior between ‘gcc’ and
‘g++’ when compiling C++ programs.

 The ‘gcc’ program accepts options and file names as operands.  Many
options have multi-letter names; therefore multiple single-letter
options may _not_ be grouped: ‘-dv’ is very different from ‘-d -v’.

 You can mix options and other arguments.  For the most part, the order
you use doesn't matter.  Order does matter when you use several options
of the same kind; for example, if you specify ‘-L’ more than once, the
directories are searched in the order specified.  Also, the placement of
the ‘-l’ option is significant.

 Many options have long names starting with ‘-f’ or with ‘-W’--for
example, ‘-fmove-loop-invariants’, ‘-Wformat’ and so on.  Most of these
have both positive and negative forms; the negative form of ‘-ffoo’ is
‘-fno-foo’.  This manual documents only one of these two forms,
whichever one is not the default.

 Some options take one or more arguments typically separated either by a
space or by the equals sign (‘=’) from the option name.  Unless
documented otherwise, an argument can be either numeric or a string.
Numeric arguments must typically be small unsigned decimal or
hexadecimal integers.  Hexadecimal arguments must begin with the ‘0x’
prefix.  Arguments to options that specify a size threshold of some sort
may be arbitrarily large decimal or hexadecimal integers followed by a
byte size suffix designating a multiple of bytes such as ‘kB’ and ‘KiB’
for kilobyte and kibibyte, respectively, ‘MB’ and ‘MiB’ for megabyte and
mebibyte, ‘GB’ and ‘GiB’ for gigabyte and gigibyte, and so on.  Such
arguments are designated by BYTE-SIZE in the following text.  Refer to
the NIST, IEC, and other relevant national and international standards
for the full listing and explanation of the binary and decimal byte size
prefixes.

 *Note Option Index::, for an index to GCC's options.

* Menu:

* Option Summary::      Brief list of all options, without explanations.
* Overall Options::     Controlling the kind of output:
                        an executable, object files, assembler files,
                        or preprocessed source.
* Invoking G++::        Compiling C++ programs.
* C Dialect Options::   Controlling the variant of C language compiled.
* C++ Dialect Options:: Variations on C++.
* Objective-C and Objective-C++ Dialect Options:: Variations on Objective-C
                        and Objective-C++.
* Diagnostic Message Formatting Options:: Controlling how diagnostics should
                        be formatted.
* Warning Options::     How picky should the compiler be?
* Static Analyzer Options:: More expensive warnings.
* Debugging Options::   Producing debuggable code.
* Optimize Options::    How much optimization?
* Instrumentation Options:: Enabling profiling and extra run-time error checking.
* Preprocessor Options:: Controlling header files and macro definitions.
                         Also, getting dependency information for Make.
* Assembler Options::   Passing options to the assembler.
* Link Options::        Specifying libraries and so on.
* Directory Options::   Where to find header files and libraries.
                        Where to find the compiler executable files.
* Code Gen Options::    Specifying conventions for function calls, data layout
                        and register usage.
* Developer Options::   Printing GCC configuration info, statistics, and
                        debugging dumps.
* Submodel Options::    Target-specific options, such as compiling for a
                        specific processor variant.
* Spec Files::          How to pass switches to sub-processes.
* Environment Variables:: Env vars that affect GCC.
* Precompiled Headers:: Compiling a header once, and using it many times.
* C++ Modules::		Experimental C++20 module system.


File: gcc.info,  Node: Option Summary,  Next: Overall Options,  Up: Invoking GCC

3.1 Option Summary
==================

Here is a summary of all the options, grouped by type.  Explanations are
in the following sections.

_Overall Options_
     *Note Options Controlling the Kind of Output: Overall Options.
          -c  -S  -E  -o FILE
          -dumpbase DUMPBASE  -dumpbase-ext AUXDROPSUF
          -dumpdir DUMPPFX  -x LANGUAGE
          -v  -###  --help[=CLASS[,...]]  --target-help  --version
          -pass-exit-codes  -pipe  -specs=FILE  -wrapper
          @FILE  -ffile-prefix-map=OLD=NEW
          -fplugin=FILE  -fplugin-arg-NAME=ARG
          -fdump-ada-spec[-slim]  -fada-spec-parent=UNIT  -fdump-go-spec=FILE

_C Language Options_
     *Note Options Controlling C Dialect: C Dialect Options.
          -ansi  -std=STANDARD  -aux-info FILENAME
          -fallow-parameterless-variadic-functions  -fno-asm
          -fno-builtin  -fno-builtin-FUNCTION  -fcond-mismatch
          -ffreestanding  -fgimple  -fgnu-tm  -fgnu89-inline  -fhosted
          -flax-vector-conversions  -fms-extensions
          -foffload=ARG  -foffload-options=ARG
          -fopenacc  -fopenacc-dim=GEOM
          -fopenmp  -fopenmp-simd
          -fpermitted-flt-eval-methods=STANDARD
          -fplan9-extensions  -fsigned-bitfields  -funsigned-bitfields
          -fsigned-char  -funsigned-char  -fsso-struct=ENDIANNESS

_C++ Language Options_
     *Note Options Controlling C++ Dialect: C++ Dialect Options.
          -fabi-version=N  -fno-access-control
          -faligned-new=N  -fargs-in-order=N  -fchar8_t  -fcheck-new
          -fconstexpr-depth=N  -fconstexpr-cache-depth=N
          -fconstexpr-loop-limit=N  -fconstexpr-ops-limit=N
          -fno-elide-constructors
          -fno-enforce-eh-specs
          -fno-gnu-keywords
          -fno-implicit-templates
          -fno-implicit-inline-templates
          -fno-implement-inlines
          -fmodule-header[=KIND] -fmodule-only -fmodules-ts
          -fmodule-implicit-inline
          -fno-module-lazy
          -fmodule-mapper=SPECIFICATION
          -fmodule-version-ignore
          -fms-extensions
          -fnew-inheriting-ctors
          -fnew-ttp-matching
          -fno-nonansi-builtins  -fnothrow-opt  -fno-operator-names
          -fno-optional-diags  -fpermissive
          -fno-pretty-templates
          -fno-rtti  -fsized-deallocation
          -ftemplate-backtrace-limit=N
          -ftemplate-depth=N
          -fno-threadsafe-statics  -fuse-cxa-atexit
          -fno-weak  -nostdinc++
          -fvisibility-inlines-hidden
          -fvisibility-ms-compat
          -fext-numeric-literals
          -flang-info-include-translate[=HEADER]
          -flang-info-include-translate-not
          -flang-info-module-cmi[=MODULE]
          -stdlib=LIBSTDC++,LIBC++
          -Wabi-tag  -Wcatch-value  -Wcatch-value=N
          -Wno-class-conversion  -Wclass-memaccess
          -Wcomma-subscript  -Wconditionally-supported
          -Wno-conversion-null  -Wctad-maybe-unsupported
          -Wctor-dtor-privacy  -Wno-delete-incomplete
          -Wdelete-non-virtual-dtor  -Wno-deprecated-array-compare
          -Wdeprecated-copy -Wdeprecated-copy-dtor
          -Wno-deprecated-enum-enum-conversion -Wno-deprecated-enum-float-conversion
          -Weffc++  -Wno-exceptions -Wextra-semi  -Wno-inaccessible-base
          -Wno-inherited-variadic-ctor  -Wno-init-list-lifetime
          -Winvalid-imported-macros
          -Wno-invalid-offsetof  -Wno-literal-suffix
          -Wmismatched-new-delete -Wmismatched-tags
          -Wmultiple-inheritance  -Wnamespaces  -Wnarrowing
          -Wnoexcept  -Wnoexcept-type  -Wnon-virtual-dtor
          -Wpessimizing-move  -Wno-placement-new  -Wplacement-new=N
          -Wrange-loop-construct -Wredundant-move -Wredundant-tags
          -Wreorder  -Wregister
          -Wstrict-null-sentinel  -Wno-subobject-linkage  -Wtemplates
          -Wno-non-template-friend  -Wold-style-cast
          -Woverloaded-virtual  -Wno-pmf-conversions -Wsign-promo
          -Wsized-deallocation  -Wsuggest-final-methods
          -Wsuggest-final-types  -Wsuggest-override
          -Wno-terminate  -Wuseless-cast  -Wno-vexing-parse
          -Wvirtual-inheritance
          -Wno-virtual-move-assign  -Wvolatile  -Wzero-as-null-pointer-constant

_Objective-C and Objective-C++ Language Options_
     *Note Options Controlling Objective-C and Objective-C++ Dialects:
     Objective-C and Objective-C++ Dialect Options.
          -fconstant-string-class=CLASS-NAME
          -fgnu-runtime  -fnext-runtime
          -fno-nil-receivers
          -fobjc-abi-version=N
          -fobjc-call-cxx-cdtors
          -fobjc-direct-dispatch
          -fobjc-exceptions
          -fobjc-gc
          -fobjc-nilcheck
          -fobjc-std=objc1
          -fno-local-ivars
          -fivar-visibility=[public|protected|private|package]
          -freplace-objc-classes
          -fzero-link
          -gen-decls
          -Wassign-intercept  -Wno-property-assign-default
          -Wno-protocol -Wobjc-root-class -Wselector
          -Wstrict-selector-match
          -Wundeclared-selector

_Diagnostic Message Formatting Options_
     *Note Options to Control Diagnostic Messages Formatting: Diagnostic
     Message Formatting Options.
          -fmessage-length=N
          -fdiagnostics-plain-output
          -fdiagnostics-show-location=[once|every-line]
          -fdiagnostics-color=[auto|never|always]
          -fdiagnostics-urls=[auto|never|always]
          -fdiagnostics-format=[text|json]
          -fno-diagnostics-show-option  -fno-diagnostics-show-caret
          -fno-diagnostics-show-labels  -fno-diagnostics-show-line-numbers
          -fno-diagnostics-show-cwe
          -fdiagnostics-minimum-margin-width=WIDTH
          -fdiagnostics-parseable-fixits  -fdiagnostics-generate-patch
          -fdiagnostics-show-template-tree  -fno-elide-type
          -fdiagnostics-path-format=[none|separate-events|inline-events]
          -fdiagnostics-show-path-depths
          -fno-show-column
          -fdiagnostics-column-unit=[display|byte]
          -fdiagnostics-column-origin=ORIGIN
          -fdiagnostics-escape-format=[unicode|bytes]

_Warning Options_
     *Note Options to Request or Suppress Warnings: Warning Options.
          -fsyntax-only  -fmax-errors=N  -Wpedantic
          -pedantic-errors
          -w  -Wextra  -Wall  -Wabi=N
          -Waddress  -Wno-address-of-packed-member  -Waggregate-return
          -Walloc-size-larger-than=BYTE-SIZE  -Walloc-zero
          -Walloca  -Walloca-larger-than=BYTE-SIZE
          -Wno-aggressive-loop-optimizations
          -Warith-conversion
          -Warray-bounds  -Warray-bounds=N  -Warray-compare
          -Wno-attributes  -Wattribute-alias=N -Wno-attribute-alias
          -Wno-attribute-warning
          -Wbidi-chars=[none|unpaired|any|ucn]
          -Wbool-compare  -Wbool-operation
          -Wno-builtin-declaration-mismatch
          -Wno-builtin-macro-redefined  -Wc90-c99-compat  -Wc99-c11-compat
          -Wc11-c2x-compat
          -Wc++-compat  -Wc++11-compat  -Wc++14-compat  -Wc++17-compat
          -Wc++20-compat
          -Wno-c++11-extensions  -Wno-c++14-extensions -Wno-c++17-extensions
          -Wno-c++20-extensions  -Wno-c++23-extensions
          -Wcast-align  -Wcast-align=strict  -Wcast-function-type  -Wcast-qual
          -Wchar-subscripts
          -Wclobbered  -Wcomment
          -Wconversion  -Wno-coverage-mismatch  -Wno-cpp
          -Wdangling-else  -Wdangling-pointer  -Wdangling-pointer=N
          -Wdate-time
          -Wno-deprecated  -Wno-deprecated-declarations  -Wno-designated-init
          -Wdisabled-optimization
          -Wno-discarded-array-qualifiers  -Wno-discarded-qualifiers
          -Wno-div-by-zero  -Wdouble-promotion
          -Wduplicated-branches  -Wduplicated-cond
          -Wempty-body  -Wno-endif-labels  -Wenum-compare  -Wenum-conversion
          -Werror  -Werror=*  -Wexpansion-to-defined  -Wfatal-errors
          -Wfloat-conversion  -Wfloat-equal  -Wformat  -Wformat=2
          -Wno-format-contains-nul  -Wno-format-extra-args
          -Wformat-nonliteral  -Wformat-overflow=N
          -Wformat-security  -Wformat-signedness  -Wformat-truncation=N
          -Wformat-y2k  -Wframe-address
          -Wframe-larger-than=BYTE-SIZE  -Wno-free-nonheap-object
          -Wno-if-not-aligned  -Wno-ignored-attributes
          -Wignored-qualifiers  -Wno-incompatible-pointer-types
          -Wimplicit  -Wimplicit-fallthrough  -Wimplicit-fallthrough=N
          -Wno-implicit-function-declaration  -Wno-implicit-int
          -Winfinite-recursion
          -Winit-self  -Winline  -Wno-int-conversion  -Wint-in-bool-context
          -Wno-int-to-pointer-cast  -Wno-invalid-memory-model
          -Winvalid-pch  -Wjump-misses-init  -Wlarger-than=BYTE-SIZE
          -Wlogical-not-parentheses  -Wlogical-op  -Wlong-long
          -Wno-lto-type-mismatch -Wmain  -Wmaybe-uninitialized
          -Wmemset-elt-size  -Wmemset-transposed-args
          -Wmisleading-indentation  -Wmissing-attributes  -Wmissing-braces
          -Wmissing-field-initializers  -Wmissing-format-attribute
          -Wmissing-include-dirs  -Wmissing-noreturn  -Wno-missing-profile
          -Wno-multichar  -Wmultistatement-macros  -Wnonnull  -Wnonnull-compare
          -Wnormalized=[none|id|nfc|nfkc]
          -Wnull-dereference  -Wno-odr
          -Wopenacc-parallelism
          -Wopenmp-simd
          -Wno-overflow  -Woverlength-strings  -Wno-override-init-side-effects
          -Wpacked  -Wno-packed-bitfield-compat  -Wpacked-not-aligned  -Wpadded
          -Wparentheses  -Wno-pedantic-ms-format
          -Wpointer-arith  -Wno-pointer-compare  -Wno-pointer-to-int-cast
          -Wno-pragmas  -Wno-prio-ctor-dtor  -Wredundant-decls
          -Wrestrict  -Wno-return-local-addr  -Wreturn-type
          -Wno-scalar-storage-order  -Wsequence-point
          -Wshadow  -Wshadow=global  -Wshadow=local  -Wshadow=compatible-local
          -Wno-shadow-ivar
          -Wno-shift-count-negative  -Wno-shift-count-overflow  -Wshift-negative-value
          -Wno-shift-overflow  -Wshift-overflow=N
          -Wsign-compare  -Wsign-conversion
          -Wno-sizeof-array-argument
          -Wsizeof-array-div
          -Wsizeof-pointer-div  -Wsizeof-pointer-memaccess
          -Wstack-protector  -Wstack-usage=BYTE-SIZE  -Wstrict-aliasing
          -Wstrict-aliasing=n  -Wstrict-overflow  -Wstrict-overflow=N
          -Wstring-compare
          -Wno-stringop-overflow -Wno-stringop-overread
          -Wno-stringop-truncation
          -Wsuggest-attribute=[pure|const|noreturn|format|malloc]
          -Wswitch  -Wno-switch-bool  -Wswitch-default  -Wswitch-enum
          -Wno-switch-outside-range  -Wno-switch-unreachable  -Wsync-nand
          -Wsystem-headers  -Wtautological-compare  -Wtrampolines  -Wtrigraphs
          -Wtrivial-auto-var-init -Wtsan -Wtype-limits  -Wundef
          -Wuninitialized  -Wunknown-pragmas
          -Wunsuffixed-float-constants  -Wunused
          -Wunused-but-set-parameter  -Wunused-but-set-variable
          -Wunused-const-variable  -Wunused-const-variable=N
          -Wunused-function  -Wunused-label  -Wunused-local-typedefs
          -Wunused-macros
          -Wunused-parameter  -Wno-unused-result
          -Wunused-value  -Wunused-variable
          -Wno-varargs  -Wvariadic-macros
          -Wvector-operation-performance
          -Wvla  -Wvla-larger-than=BYTE-SIZE  -Wno-vla-larger-than
          -Wvolatile-register-var  -Wwrite-strings
          -Wzero-length-bounds

_Static Analyzer Options_
          -fanalyzer
          -fanalyzer-call-summaries
          -fanalyzer-checker=NAME
          -fno-analyzer-feasibility
          -fanalyzer-fine-grained
          -fno-analyzer-state-merge
          -fno-analyzer-state-purge
          -fanalyzer-transitivity
          -fanalyzer-verbose-edges
          -fanalyzer-verbose-state-changes
          -fanalyzer-verbosity=LEVEL
          -fdump-analyzer
          -fdump-analyzer-callgraph
          -fdump-analyzer-exploded-graph
          -fdump-analyzer-exploded-nodes
          -fdump-analyzer-exploded-nodes-2
          -fdump-analyzer-exploded-nodes-3
          -fdump-analyzer-exploded-paths
          -fdump-analyzer-feasibility
          -fdump-analyzer-json
          -fdump-analyzer-state-purge
          -fdump-analyzer-stderr
          -fdump-analyzer-supergraph
          -fdump-analyzer-untracked
          -Wno-analyzer-double-fclose
          -Wno-analyzer-double-free
          -Wno-analyzer-exposure-through-output-file
          -Wno-analyzer-file-leak
          -Wno-analyzer-free-of-non-heap
          -Wno-analyzer-malloc-leak
          -Wno-analyzer-mismatching-deallocation
          -Wno-analyzer-null-argument
          -Wno-analyzer-null-dereference
          -Wno-analyzer-possible-null-argument
          -Wno-analyzer-possible-null-dereference
          -Wno-analyzer-shift-count-negative
          -Wno-analyzer-shift-count-overflow
          -Wno-analyzer-stale-setjmp-buffer
          -Wno-analyzer-tainted-allocation-size
          -Wno-analyzer-tainted-array-index
          -Wno-analyzer-tainted-divisor
          -Wno-analyzer-tainted-offset
          -Wno-analyzer-tainted-size
          -Wanalyzer-too-complex
          -Wno-analyzer-unsafe-call-within-signal-handler
          -Wno-analyzer-use-after-free
          -Wno-analyzer-use-of-pointer-in-stale-stack-frame
          -Wno-analyzer-use-of-uninitialized-value
          -Wno-analyzer-write-to-const
          -Wno-analyzer-write-to-string-literal

_C and Objective-C-only Warning Options_
          -Wbad-function-cast  -Wmissing-declarations
          -Wmissing-parameter-type  -Wmissing-prototypes  -Wnested-externs
          -Wold-style-declaration  -Wold-style-definition
          -Wstrict-prototypes  -Wtraditional  -Wtraditional-conversion
          -Wdeclaration-after-statement  -Wpointer-sign

_Debugging Options_
     *Note Options for Debugging Your Program: Debugging Options.
          -g  -gLEVEL  -gdwarf  -gdwarf-VERSION
          -gbtf -gctf  -gctfLEVEL
          -ggdb  -grecord-gcc-switches  -gno-record-gcc-switches
          -gstabs  -gstabs+  -gstrict-dwarf  -gno-strict-dwarf
          -gas-loc-support  -gno-as-loc-support
          -gas-locview-support  -gno-as-locview-support
          -gcolumn-info  -gno-column-info  -gdwarf32  -gdwarf64
          -gstatement-frontiers  -gno-statement-frontiers
          -gvariable-location-views  -gno-variable-location-views
          -ginternal-reset-location-views  -gno-internal-reset-location-views
          -ginline-points  -gno-inline-points
          -gvms  -gxcoff  -gxcoff+  -gz[=TYPE]
          -gsplit-dwarf  -gdescribe-dies  -gno-describe-dies
          -fdebug-prefix-map=OLD=NEW  -fdebug-types-section
          -fno-eliminate-unused-debug-types
          -femit-struct-debug-baseonly  -femit-struct-debug-reduced
          -femit-struct-debug-detailed[=SPEC-LIST]
          -fno-eliminate-unused-debug-symbols  -femit-class-debug-always
          -fno-merge-debug-strings  -fno-dwarf2-cfi-asm
          -fvar-tracking  -fvar-tracking-assignments

_Optimization Options_
     *Note Options that Control Optimization: Optimize Options.
          -faggressive-loop-optimizations
          -falign-functions[=N[:M:[N2[:M2]]]]
          -falign-jumps[=N[:M:[N2[:M2]]]]
          -falign-labels[=N[:M:[N2[:M2]]]]
          -falign-loops[=N[:M:[N2[:M2]]]]
          -fno-allocation-dce -fallow-store-data-races
          -fassociative-math  -fauto-profile  -fauto-profile[=PATH]
          -fauto-inc-dec  -fbranch-probabilities
          -fcaller-saves
          -fcombine-stack-adjustments  -fconserve-stack
          -fcompare-elim  -fcprop-registers  -fcrossjumping
          -fcse-follow-jumps  -fcse-skip-blocks  -fcx-fortran-rules
          -fcx-limited-range
          -fdata-sections  -fdce  -fdelayed-branch
          -fdelete-null-pointer-checks  -fdevirtualize  -fdevirtualize-speculatively
          -fdevirtualize-at-ltrans  -fdse
          -fearly-inlining  -fipa-sra  -fexpensive-optimizations  -ffat-lto-objects
          -ffast-math  -ffinite-math-only  -ffloat-store  -fexcess-precision=STYLE
          -ffinite-loops
          -fforward-propagate  -ffp-contract=STYLE  -ffunction-sections
          -fgcse  -fgcse-after-reload  -fgcse-las  -fgcse-lm  -fgraphite-identity
          -fgcse-sm  -fhoist-adjacent-loads  -fif-conversion
          -fif-conversion2  -findirect-inlining
          -finline-functions  -finline-functions-called-once  -finline-limit=N
          -finline-small-functions -fipa-modref -fipa-cp  -fipa-cp-clone
          -fipa-bit-cp  -fipa-vrp  -fipa-pta  -fipa-profile  -fipa-pure-const
          -fipa-reference  -fipa-reference-addressable
          -fipa-stack-alignment  -fipa-icf  -fira-algorithm=ALGORITHM
          -flive-patching=LEVEL
          -fira-region=REGION  -fira-hoist-pressure
          -fira-loop-pressure  -fno-ira-share-save-slots
          -fno-ira-share-spill-slots
          -fisolate-erroneous-paths-dereference  -fisolate-erroneous-paths-attribute
          -fivopts  -fkeep-inline-functions  -fkeep-static-functions
          -fkeep-static-consts  -flimit-function-alignment  -flive-range-shrinkage
          -floop-block  -floop-interchange  -floop-strip-mine
          -floop-unroll-and-jam  -floop-nest-optimize
          -floop-parallelize-all  -flra-remat  -flto  -flto-compression-level
          -flto-partition=ALG  -fmerge-all-constants
          -fmerge-constants  -fmodulo-sched  -fmodulo-sched-allow-regmoves
          -fmove-loop-invariants  -fmove-loop-stores  -fno-branch-count-reg
          -fno-defer-pop  -fno-fp-int-builtin-inexact  -fno-function-cse
          -fno-guess-branch-probability  -fno-inline  -fno-math-errno  -fno-peephole
          -fno-peephole2  -fno-printf-return-value  -fno-sched-interblock
          -fno-sched-spec  -fno-signed-zeros
          -fno-toplevel-reorder  -fno-trapping-math  -fno-zero-initialized-in-bss
          -fomit-frame-pointer  -foptimize-sibling-calls
          -fpartial-inlining  -fpeel-loops  -fpredictive-commoning
          -fprefetch-loop-arrays
          -fprofile-correction
          -fprofile-use  -fprofile-use=PATH -fprofile-partial-training
          -fprofile-values -fprofile-reorder-functions
          -freciprocal-math  -free  -frename-registers  -freorder-blocks
          -freorder-blocks-algorithm=ALGORITHM
          -freorder-blocks-and-partition  -freorder-functions
          -frerun-cse-after-loop  -freschedule-modulo-scheduled-loops
          -frounding-math  -fsave-optimization-record
          -fsched2-use-superblocks  -fsched-pressure
          -fsched-spec-load  -fsched-spec-load-dangerous
          -fsched-stalled-insns-dep[=N]  -fsched-stalled-insns[=N]
          -fsched-group-heuristic  -fsched-critical-path-heuristic
          -fsched-spec-insn-heuristic  -fsched-rank-heuristic
          -fsched-last-insn-heuristic  -fsched-dep-count-heuristic
          -fschedule-fusion
          -fschedule-insns  -fschedule-insns2  -fsection-anchors
          -fselective-scheduling  -fselective-scheduling2
          -fsel-sched-pipelining  -fsel-sched-pipelining-outer-loops
          -fsemantic-interposition  -fshrink-wrap  -fshrink-wrap-separate
          -fsignaling-nans
          -fsingle-precision-constant  -fsplit-ivs-in-unroller  -fsplit-loops
          -fsplit-paths
          -fsplit-wide-types  -fsplit-wide-types-early  -fssa-backprop  -fssa-phiopt
          -fstdarg-opt  -fstore-merging  -fstrict-aliasing -fipa-strict-aliasing
          -fthread-jumps  -ftracer  -ftree-bit-ccp
          -ftree-builtin-call-dce  -ftree-ccp  -ftree-ch
          -ftree-coalesce-vars  -ftree-copy-prop  -ftree-dce  -ftree-dominator-opts
          -ftree-dse  -ftree-forwprop  -ftree-fre  -fcode-hoisting
          -ftree-loop-if-convert  -ftree-loop-im
          -ftree-phiprop  -ftree-loop-distribution  -ftree-loop-distribute-patterns
          -ftree-loop-ivcanon  -ftree-loop-linear  -ftree-loop-optimize
          -ftree-loop-vectorize
          -ftree-parallelize-loops=N  -ftree-pre  -ftree-partial-pre  -ftree-pta
          -ftree-reassoc  -ftree-scev-cprop  -ftree-sink  -ftree-slsr  -ftree-sra
          -ftree-switch-conversion  -ftree-tail-merge
          -ftree-ter  -ftree-vectorize  -ftree-vrp  -ftrivial-auto-var-init
          -funconstrained-commons -funit-at-a-time  -funroll-all-loops
          -funroll-loops -funsafe-math-optimizations  -funswitch-loops
          -fipa-ra  -fvariable-expansion-in-unroller  -fvect-cost-model  -fvpt
          -fweb  -fwhole-program  -fwpa  -fuse-linker-plugin -fzero-call-used-regs
          --param NAME=VALUE
          -O  -O0  -O1  -O2  -O3  -Os  -Ofast  -Og  -Oz

_Program Instrumentation Options_
     *Note Program Instrumentation Options: Instrumentation Options.
          -p  -pg  -fprofile-arcs  --coverage  -ftest-coverage
          -fprofile-abs-path
          -fprofile-dir=PATH  -fprofile-generate  -fprofile-generate=PATH
          -fprofile-info-section  -fprofile-info-section=NAME
          -fprofile-note=PATH -fprofile-prefix-path=PATH
          -fprofile-update=METHOD -fprofile-filter-files=REGEX
          -fprofile-exclude-files=REGEX
          -fprofile-reproducible=[multithreaded|parallel-runs|serial]
          -fsanitize=STYLE  -fsanitize-recover  -fsanitize-recover=STYLE
          -fasan-shadow-offset=NUMBER  -fsanitize-sections=S1,S2,...
          -fsanitize-undefined-trap-on-error  -fbounds-check
          -fcf-protection=[full|branch|return|none|check]
          -fharden-compares -fharden-conditional-branches
          -fstack-protector  -fstack-protector-all  -fstack-protector-strong
          -fstack-protector-explicit  -fstack-check
          -fstack-limit-register=REG  -fstack-limit-symbol=SYM
          -fno-stack-limit  -fsplit-stack
          -fvtable-verify=[std|preinit|none]
          -fvtv-counts  -fvtv-debug
          -finstrument-functions
          -finstrument-functions-exclude-function-list=SYM,SYM,...
          -finstrument-functions-exclude-file-list=FILE,FILE,...
     -fprofile-prefix-map=OLD=NEW

_Preprocessor Options_
     *Note Options Controlling the Preprocessor: Preprocessor Options.
          -AQUESTION=ANSWER
          -A-QUESTION[=ANSWER]
          -C  -CC  -DMACRO[=DEFN]
          -dD  -dI  -dM  -dN  -dU
          -fdebug-cpp  -fdirectives-only  -fdollars-in-identifiers
          -fexec-charset=CHARSET  -fextended-identifiers
          -finput-charset=CHARSET  -flarge-source-files
          -fmacro-prefix-map=OLD=NEW -fmax-include-depth=DEPTH
          -fno-canonical-system-headers  -fpch-deps  -fpch-preprocess
          -fpreprocessed  -ftabstop=WIDTH  -ftrack-macro-expansion
          -fwide-exec-charset=CHARSET  -fworking-directory
          -H  -imacros FILE  -include FILE
          -M  -MD  -MF  -MG  -MM  -MMD  -MP  -MQ  -MT -Mno-modules
          -no-integrated-cpp  -P  -pthread  -remap
          -traditional  -traditional-cpp  -trigraphs
          -UMACRO  -undef
          -Wp,OPTION  -Xpreprocessor OPTION

_Assembler Options_
     *Note Passing Options to the Assembler: Assembler Options.
          -Wa,OPTION  -Xassembler OPTION

_Linker Options_
     *Note Options for Linking: Link Options.
          OBJECT-FILE-NAME  -fuse-ld=LINKER  -lLIBRARY
          -nostartfiles  -nodefaultlibs  -nolibc  -nostdlib
          -e ENTRY  --entry=ENTRY
          -pie  -pthread  -r  -rdynamic
          -s  -static  -static-pie  -static-libgcc  -static-libstdc++
          -static-libasan  -static-libtsan  -static-liblsan  -static-libubsan
          -shared  -shared-libgcc  -symbolic
          -T SCRIPT  -Wl,OPTION  -Xlinker OPTION
          -u SYMBOL  -z KEYWORD

_Directory Options_
     *Note Options for Directory Search: Directory Options.
          -BPREFIX  -IDIR  -I-
          -idirafter DIR
          -imacros FILE  -imultilib DIR
          -iplugindir=DIR  -iprefix FILE
          -iquote DIR  -isysroot DIR  -isystem DIR
          -iwithprefix DIR  -iwithprefixbefore DIR
          -LDIR  -no-canonical-prefixes  --no-sysroot-suffix
          -nostdinc  -nostdinc++  --sysroot=DIR

_Code Generation Options_
     *Note Options for Code Generation Conventions: Code Gen Options.
          -fcall-saved-REG  -fcall-used-REG
          -ffixed-REG  -fexceptions
          -fnon-call-exceptions  -fdelete-dead-exceptions  -funwind-tables
          -fasynchronous-unwind-tables
          -fno-gnu-unique
          -finhibit-size-directive  -fcommon  -fno-ident
          -fpcc-struct-return  -fpic  -fPIC  -fpie  -fPIE  -fno-plt
          -fno-jump-tables -fno-bit-tests
          -frecord-gcc-switches
          -freg-struct-return  -fshort-enums  -fshort-wchar
          -fverbose-asm  -fpack-struct[=N]
          -fleading-underscore  -ftls-model=MODEL
          -fstack-reuse=REUSE_LEVEL
          -ftrampolines  -ftrapv  -fwrapv
          -fvisibility=[default|internal|hidden|protected]
          -fstrict-volatile-bitfields  -fsync-libcalls

_Developer Options_
     *Note GCC Developer Options: Developer Options.
          -dLETTERS  -dumpspecs  -dumpmachine  -dumpversion
          -dumpfullversion  -fcallgraph-info[=su,da]
          -fchecking  -fchecking=N
          -fdbg-cnt-list   -fdbg-cnt=COUNTER-VALUE-LIST
          -fdisable-ipa-PASS_NAME
          -fdisable-rtl-PASS_NAME
          -fdisable-rtl-PASS-NAME=RANGE-LIST
          -fdisable-tree-PASS_NAME
          -fdisable-tree-PASS-NAME=RANGE-LIST
          -fdump-debug  -fdump-earlydebug
          -fdump-noaddr  -fdump-unnumbered  -fdump-unnumbered-links
          -fdump-final-insns[=FILE]
          -fdump-ipa-all  -fdump-ipa-cgraph  -fdump-ipa-inline
          -fdump-lang-all
          -fdump-lang-SWITCH
          -fdump-lang-SWITCH-OPTIONS
          -fdump-lang-SWITCH-OPTIONS=FILENAME
          -fdump-passes
          -fdump-rtl-PASS  -fdump-rtl-PASS=FILENAME
          -fdump-statistics
          -fdump-tree-all
          -fdump-tree-SWITCH
          -fdump-tree-SWITCH-OPTIONS
          -fdump-tree-SWITCH-OPTIONS=FILENAME
          -fcompare-debug[=OPTS]  -fcompare-debug-second
          -fenable-KIND-PASS
          -fenable-KIND-PASS=RANGE-LIST
          -fira-verbose=N
          -flto-report  -flto-report-wpa  -fmem-report-wpa
          -fmem-report  -fpre-ipa-mem-report  -fpost-ipa-mem-report
          -fopt-info  -fopt-info-OPTIONS[=FILE]
          -fprofile-report
          -frandom-seed=STRING  -fsched-verbose=N
          -fsel-sched-verbose  -fsel-sched-dump-cfg  -fsel-sched-pipelining-verbose
          -fstats  -fstack-usage  -ftime-report  -ftime-report-details
          -fvar-tracking-assignments-toggle  -gtoggle
          -print-file-name=LIBRARY  -print-libgcc-file-name
          -print-multi-directory  -print-multi-lib  -print-multi-os-directory
          -print-prog-name=PROGRAM  -print-search-dirs  -Q
          -print-sysroot  -print-sysroot-headers-suffix
          -save-temps  -save-temps=cwd  -save-temps=obj  -time[=FILE]

_Machine-Dependent Options_
     *Note Machine-Dependent Options: Submodel Options.

     _AArch64 Options_
          -mabi=NAME  -mbig-endian  -mlittle-endian
          -mgeneral-regs-only
          -mcmodel=tiny  -mcmodel=small  -mcmodel=large
          -mstrict-align  -mno-strict-align
          -momit-leaf-frame-pointer
          -mtls-dialect=desc  -mtls-dialect=traditional
          -mtls-size=SIZE
          -mfix-cortex-a53-835769  -mfix-cortex-a53-843419
          -mlow-precision-recip-sqrt  -mlow-precision-sqrt  -mlow-precision-div
          -mpc-relative-literal-loads
          -msign-return-address=SCOPE
          -mbranch-protection=NONE|STANDARD|PAC-RET[+LEAF
          +B-KEY]|BTI
          -mharden-sls=OPTS
          -march=NAME  -mcpu=NAME  -mtune=NAME
          -moverride=STRING  -mverbose-cost-dump
          -mstack-protector-guard=GUARD -mstack-protector-guard-reg=SYSREG
          -mstack-protector-guard-offset=OFFSET -mtrack-speculation
          -moutline-atomics

     _Adapteva Epiphany Options_
          -mhalf-reg-file  -mprefer-short-insn-regs
          -mbranch-cost=NUM  -mcmove  -mnops=NUM  -msoft-cmpsf
          -msplit-lohi  -mpost-inc  -mpost-modify  -mstack-offset=NUM
          -mround-nearest  -mlong-calls  -mshort-calls  -msmall16
          -mfp-mode=MODE  -mvect-double  -max-vect-align=NUM
          -msplit-vecmove-early  -m1reg-REG

     _AMD GCN Options_
          -march=GPU -mtune=GPU -mstack-size=BYTES

     _ARC Options_
          -mbarrel-shifter  -mjli-always
          -mcpu=CPU  -mA6  -mARC600  -mA7  -mARC700
          -mdpfp  -mdpfp-compact  -mdpfp-fast  -mno-dpfp-lrsr
          -mea  -mno-mpy  -mmul32x16  -mmul64  -matomic
          -mnorm  -mspfp  -mspfp-compact  -mspfp-fast  -msimd  -msoft-float  -mswap
          -mcrc  -mdsp-packa  -mdvbf  -mlock  -mmac-d16  -mmac-24  -mrtsc  -mswape
          -mtelephony  -mxy  -misize  -mannotate-align  -marclinux  -marclinux_prof
          -mlong-calls  -mmedium-calls  -msdata  -mirq-ctrl-saved
          -mrgf-banked-regs  -mlpc-width=WIDTH  -G NUM
          -mvolatile-cache  -mtp-regno=REGNO
          -malign-call  -mauto-modify-reg  -mbbit-peephole  -mno-brcc
          -mcase-vector-pcrel  -mcompact-casesi  -mno-cond-exec  -mearly-cbranchsi
          -mexpand-adddi  -mindexed-loads  -mlra  -mlra-priority-none
          -mlra-priority-compact -mlra-priority-noncompact  -mmillicode
          -mmixed-code  -mq-class  -mRcq  -mRcw  -msize-level=LEVEL
          -mtune=CPU  -mmultcost=NUM  -mcode-density-frame
          -munalign-prob-threshold=PROBABILITY  -mmpy-option=MULTO
          -mdiv-rem  -mcode-density  -mll64  -mfpu=FPU  -mrf16  -mbranch-index

     _ARM Options_
          -mapcs-frame  -mno-apcs-frame
          -mabi=NAME
          -mapcs-stack-check  -mno-apcs-stack-check
          -mapcs-reentrant  -mno-apcs-reentrant
          -mgeneral-regs-only
          -msched-prolog  -mno-sched-prolog
          -mlittle-endian  -mbig-endian
          -mbe8  -mbe32
          -mfloat-abi=NAME
          -mfp16-format=NAME
          -mthumb-interwork  -mno-thumb-interwork
          -mcpu=NAME  -march=NAME  -mfpu=NAME
          -mtune=NAME  -mprint-tune-info
          -mstructure-size-boundary=N
          -mabort-on-noreturn
          -mlong-calls  -mno-long-calls
          -msingle-pic-base  -mno-single-pic-base
          -mpic-register=REG
          -mnop-fun-dllimport
          -mpoke-function-name
          -mthumb  -marm  -mflip-thumb
          -mtpcs-frame  -mtpcs-leaf-frame
          -mcaller-super-interworking  -mcallee-super-interworking
          -mtp=NAME  -mtls-dialect=DIALECT
          -mword-relocations
          -mfix-cortex-m3-ldrd
          -mfix-cortex-a57-aes-1742098
          -mfix-cortex-a72-aes-1655431
          -munaligned-access
          -mneon-for-64bits
          -mslow-flash-data
          -masm-syntax-unified
          -mrestrict-it
          -mverbose-cost-dump
          -mpure-code
          -mcmse
          -mfix-cmse-cve-2021-35465
          -mstack-protector-guard=GUARD -mstack-protector-guard-offset=OFFSET
          -mfdpic

     _AVR Options_
          -mmcu=MCU  -mabsdata  -maccumulate-args
          -mbranch-cost=COST
          -mcall-prologues  -mgas-isr-prologues  -mint8
          -mdouble=BITS -mlong-double=BITS
          -mn_flash=SIZE  -mno-interrupts
          -mmain-is-OS_task  -mrelax  -mrmw  -mstrict-X  -mtiny-stack
          -mfract-convert-truncate
          -mshort-calls  -nodevicelib  -nodevicespecs
          -Waddr-space-convert  -Wmisspelled-isr

     _Blackfin Options_
          -mcpu=CPU[-SIREVISION]
          -msim  -momit-leaf-frame-pointer  -mno-omit-leaf-frame-pointer
          -mspecld-anomaly  -mno-specld-anomaly  -mcsync-anomaly  -mno-csync-anomaly
          -mlow-64k  -mno-low64k  -mstack-check-l1  -mid-shared-library
          -mno-id-shared-library  -mshared-library-id=N
          -mleaf-id-shared-library  -mno-leaf-id-shared-library
          -msep-data  -mno-sep-data  -mlong-calls  -mno-long-calls
          -mfast-fp  -minline-plt  -mmulticore  -mcorea  -mcoreb  -msdram
          -micplb

     _C6X Options_
          -mbig-endian  -mlittle-endian  -march=CPU
          -msim  -msdata=SDATA-TYPE

     _CRIS Options_
          -mcpu=CPU  -march=CPU
          -mtune=CPU -mmax-stack-frame=N
          -metrax4  -metrax100  -mpdebug  -mcc-init  -mno-side-effects
          -mstack-align  -mdata-align  -mconst-align
          -m32-bit  -m16-bit  -m8-bit  -mno-prologue-epilogue
          -melf  -maout  -sim  -sim2
          -mmul-bug-workaround  -mno-mul-bug-workaround

     _CR16 Options_
          -mmac
          -mcr16cplus  -mcr16c
          -msim  -mint32  -mbit-ops
          -mdata-model=MODEL

     _C-SKY Options_
          -march=ARCH  -mcpu=CPU
          -mbig-endian  -EB  -mlittle-endian  -EL
          -mhard-float  -msoft-float  -mfpu=FPU  -mdouble-float  -mfdivdu
          -mfloat-abi=NAME
          -melrw  -mistack  -mmp  -mcp  -mcache  -msecurity  -mtrust
          -mdsp  -medsp  -mvdsp
          -mdiv  -msmart  -mhigh-registers  -manchor
          -mpushpop  -mmultiple-stld  -mconstpool  -mstack-size  -mccrt
          -mbranch-cost=N  -mcse-cc  -msched-prolog -msim

     _Darwin Options_
          -all_load  -allowable_client  -arch  -arch_errors_fatal
          -arch_only  -bind_at_load  -bundle  -bundle_loader
          -client_name  -compatibility_version  -current_version
          -dead_strip
          -dependency-file  -dylib_file  -dylinker_install_name
          -dynamic  -dynamiclib  -exported_symbols_list
          -filelist  -flat_namespace  -force_cpusubtype_ALL
          -force_flat_namespace  -headerpad_max_install_names
          -iframework
          -image_base  -init  -install_name  -keep_private_externs
          -multi_module  -multiply_defined  -multiply_defined_unused
          -noall_load   -no_dead_strip_inits_and_terms
          -nofixprebinding  -nomultidefs  -noprebind  -noseglinkedit
          -pagezero_size  -prebind  -prebind_all_twolevel_modules
          -private_bundle  -read_only_relocs  -sectalign
          -sectobjectsymbols  -whyload  -seg1addr
          -sectcreate  -sectobjectsymbols  -sectorder
          -segaddr  -segs_read_only_addr  -segs_read_write_addr
          -seg_addr_table  -seg_addr_table_filename  -seglinkedit
          -segprot  -segs_read_only_addr  -segs_read_write_addr
          -single_module  -static  -sub_library  -sub_umbrella
          -twolevel_namespace  -umbrella  -undefined
          -unexported_symbols_list  -weak_reference_mismatches
          -whatsloaded  -F  -gused  -gfull  -mmacosx-version-min=VERSION
          -mkernel  -mone-byte-bool

     _DEC Alpha Options_
          -mno-fp-regs  -msoft-float
          -mieee  -mieee-with-inexact  -mieee-conformant
          -mfp-trap-mode=MODE  -mfp-rounding-mode=MODE
          -mtrap-precision=MODE  -mbuild-constants
          -mcpu=CPU-TYPE  -mtune=CPU-TYPE
          -mbwx  -mmax  -mfix  -mcix
          -mfloat-vax  -mfloat-ieee
          -mexplicit-relocs  -msmall-data  -mlarge-data
          -msmall-text  -mlarge-text
          -mmemory-latency=TIME

     _eBPF Options_
          -mbig-endian -mlittle-endian -mkernel=VERSION
          -mframe-limit=BYTES -mxbpf -mco-re -mno-co-re
          -mjmpext -mjmp32 -malu32 -mcpu=VERSION

     _FR30 Options_
          -msmall-model  -mno-lsim

     _FT32 Options_
          -msim  -mlra  -mnodiv  -mft32b  -mcompress  -mnopm

     _FRV Options_
          -mgpr-32  -mgpr-64  -mfpr-32  -mfpr-64
          -mhard-float  -msoft-float
          -malloc-cc  -mfixed-cc  -mdword  -mno-dword
          -mdouble  -mno-double
          -mmedia  -mno-media  -mmuladd  -mno-muladd
          -mfdpic  -minline-plt  -mgprel-ro  -multilib-library-pic
          -mlinked-fp  -mlong-calls  -malign-labels
          -mlibrary-pic  -macc-4  -macc-8
          -mpack  -mno-pack  -mno-eflags  -mcond-move  -mno-cond-move
          -moptimize-membar  -mno-optimize-membar
          -mscc  -mno-scc  -mcond-exec  -mno-cond-exec
          -mvliw-branch  -mno-vliw-branch
          -mmulti-cond-exec  -mno-multi-cond-exec  -mnested-cond-exec
          -mno-nested-cond-exec  -mtomcat-stats
          -mTLS  -mtls
          -mcpu=CPU

     _GNU/Linux Options_
          -mglibc  -muclibc  -mmusl  -mbionic  -mandroid
          -tno-android-cc  -tno-android-ld

     _H8/300 Options_
          -mrelax  -mh  -ms  -mn  -mexr  -mno-exr  -mint32  -malign-300

     _HPPA Options_
          -march=ARCHITECTURE-TYPE
          -mcaller-copies  -mdisable-fpregs  -mdisable-indexing
          -mfast-indirect-calls  -mgas  -mgnu-ld   -mhp-ld
          -mfixed-range=REGISTER-RANGE
          -mjump-in-delay  -mlinker-opt  -mlong-calls
          -mlong-load-store  -mno-disable-fpregs
          -mno-disable-indexing  -mno-fast-indirect-calls  -mno-gas
          -mno-jump-in-delay  -mno-long-load-store
          -mno-portable-runtime  -mno-soft-float
          -mno-space-regs  -msoft-float  -mpa-risc-1-0
          -mpa-risc-1-1  -mpa-risc-2-0  -mportable-runtime
          -mschedule=CPU-TYPE  -mspace-regs  -msio  -mwsio
          -munix=UNIX-STD  -nolibdld  -static  -threads

     _IA-64 Options_
          -mbig-endian  -mlittle-endian  -mgnu-as  -mgnu-ld  -mno-pic
          -mvolatile-asm-stop  -mregister-names  -msdata  -mno-sdata
          -mconstant-gp  -mauto-pic  -mfused-madd
          -minline-float-divide-min-latency
          -minline-float-divide-max-throughput
          -mno-inline-float-divide
          -minline-int-divide-min-latency
          -minline-int-divide-max-throughput
          -mno-inline-int-divide
          -minline-sqrt-min-latency  -minline-sqrt-max-throughput
          -mno-inline-sqrt
          -mdwarf2-asm  -mearly-stop-bits
          -mfixed-range=REGISTER-RANGE  -mtls-size=TLS-SIZE
          -mtune=CPU-TYPE  -milp32  -mlp64
          -msched-br-data-spec  -msched-ar-data-spec  -msched-control-spec
          -msched-br-in-data-spec  -msched-ar-in-data-spec  -msched-in-control-spec
          -msched-spec-ldc  -msched-spec-control-ldc
          -msched-prefer-non-data-spec-insns  -msched-prefer-non-control-spec-insns
          -msched-stop-bits-after-every-cycle  -msched-count-spec-in-critical-path
          -msel-sched-dont-check-control-spec  -msched-fp-mem-deps-zero-cost
          -msched-max-memory-insns-hard-limit  -msched-max-memory-insns=MAX-INSNS

     _LM32 Options_
          -mbarrel-shift-enabled  -mdivide-enabled  -mmultiply-enabled
          -msign-extend-enabled  -muser-enabled

     _LoongArch Options_
          -march=CPU-TYPE  -mtune=CPU-TYPE -mabi=BASE-ABI-TYPE
          -mfpu=FPU-TYPE -msoft-float -msingle-float -mdouble-float
          -mbranch-cost=N  -mcheck-zero-division -mno-check-zero-division
          -mcond-move-int  -mno-cond-move-int
          -mcond-move-float  -mno-cond-move-float
          -memcpy  -mno-memcpy -mstrict-align -mno-strict-align
          -mmax-inline-memcpy-size=N
          -mcmodel=CODE-MODEL

     _M32R/D Options_
          -m32r2  -m32rx  -m32r
          -mdebug
          -malign-loops  -mno-align-loops
          -missue-rate=NUMBER
          -mbranch-cost=NUMBER
          -mmodel=CODE-SIZE-MODEL-TYPE
          -msdata=SDATA-TYPE
          -mno-flush-func  -mflush-func=NAME
          -mno-flush-trap  -mflush-trap=NUMBER
          -G NUM

     _M32C Options_
          -mcpu=CPU  -msim  -memregs=NUMBER

     _M680x0 Options_
          -march=ARCH  -mcpu=CPU  -mtune=TUNE
          -m68000  -m68020  -m68020-40  -m68020-60  -m68030  -m68040
          -m68060  -mcpu32  -m5200  -m5206e  -m528x  -m5307  -m5407
          -mcfv4e  -mbitfield  -mno-bitfield  -mc68000  -mc68020
          -mnobitfield  -mrtd  -mno-rtd  -mdiv  -mno-div  -mshort
          -mno-short  -mhard-float  -m68881  -msoft-float  -mpcrel
          -malign-int  -mstrict-align  -msep-data  -mno-sep-data
          -mshared-library-id=n  -mid-shared-library  -mno-id-shared-library
          -mxgot  -mno-xgot  -mlong-jump-table-offsets

     _MCore Options_
          -mhardlit  -mno-hardlit  -mdiv  -mno-div  -mrelax-immediates
          -mno-relax-immediates  -mwide-bitfields  -mno-wide-bitfields
          -m4byte-functions  -mno-4byte-functions  -mcallgraph-data
          -mno-callgraph-data  -mslow-bytes  -mno-slow-bytes  -mno-lsim
          -mlittle-endian  -mbig-endian  -m210  -m340  -mstack-increment

     _MeP Options_
          -mabsdiff  -mall-opts  -maverage  -mbased=N  -mbitops
          -mc=N  -mclip  -mconfig=NAME  -mcop  -mcop32  -mcop64  -mivc2
          -mdc  -mdiv  -meb  -mel  -mio-volatile  -ml  -mleadz  -mm  -mminmax
          -mmult  -mno-opts  -mrepeat  -ms  -msatur  -msdram  -msim  -msimnovec  -mtf
          -mtiny=N

     _MicroBlaze Options_
          -msoft-float  -mhard-float  -msmall-divides  -mcpu=CPU
          -mmemcpy  -mxl-soft-mul  -mxl-soft-div  -mxl-barrel-shift
          -mxl-pattern-compare  -mxl-stack-check  -mxl-gp-opt  -mno-clearbss
          -mxl-multiply-high  -mxl-float-convert  -mxl-float-sqrt
          -mbig-endian  -mlittle-endian  -mxl-reorder  -mxl-mode-APP-MODEL
          -mpic-data-is-text-relative

     _MIPS Options_
          -EL  -EB  -march=ARCH  -mtune=ARCH
          -mips1  -mips2  -mips3  -mips4  -mips32  -mips32r2  -mips32r3  -mips32r5
          -mips32r6  -mips64  -mips64r2  -mips64r3  -mips64r5  -mips64r6
          -mips16  -mno-mips16  -mflip-mips16
          -minterlink-compressed  -mno-interlink-compressed
          -minterlink-mips16  -mno-interlink-mips16
          -mabi=ABI  -mabicalls  -mno-abicalls
          -mshared  -mno-shared  -mplt  -mno-plt  -mxgot  -mno-xgot
          -mgp32  -mgp64  -mfp32  -mfpxx  -mfp64  -mhard-float  -msoft-float
          -mno-float  -msingle-float  -mdouble-float
          -modd-spreg  -mno-odd-spreg
          -mabs=MODE  -mnan=ENCODING
          -mdsp  -mno-dsp  -mdspr2  -mno-dspr2
          -mmcu  -mmno-mcu
          -meva  -mno-eva
          -mvirt  -mno-virt
          -mxpa  -mno-xpa
          -mcrc  -mno-crc
          -mginv  -mno-ginv
          -mmicromips  -mno-micromips
          -mmsa  -mno-msa
          -mloongson-mmi  -mno-loongson-mmi
          -mloongson-ext  -mno-loongson-ext
          -mloongson-ext2  -mno-loongson-ext2
          -mfpu=FPU-TYPE
          -msmartmips  -mno-smartmips
          -mpaired-single  -mno-paired-single  -mdmx  -mno-mdmx
          -mips3d  -mno-mips3d  -mmt  -mno-mt  -mllsc  -mno-llsc
          -mlong64  -mlong32  -msym32  -mno-sym32
          -GNUM  -mlocal-sdata  -mno-local-sdata
          -mextern-sdata  -mno-extern-sdata  -mgpopt  -mno-gopt
          -membedded-data  -mno-embedded-data
          -muninit-const-in-rodata  -mno-uninit-const-in-rodata
          -mcode-readable=SETTING
          -msplit-addresses  -mno-split-addresses
          -mexplicit-relocs  -mno-explicit-relocs
          -mcheck-zero-division  -mno-check-zero-division
          -mdivide-traps  -mdivide-breaks
          -mload-store-pairs  -mno-load-store-pairs
          -munaligned-access  -mno-unaligned-access
          -mmemcpy  -mno-memcpy  -mlong-calls  -mno-long-calls
          -mmad  -mno-mad  -mimadd  -mno-imadd  -mfused-madd  -mno-fused-madd  -nocpp
          -mfix-24k  -mno-fix-24k
          -mfix-r4000  -mno-fix-r4000  -mfix-r4400  -mno-fix-r4400
          -mfix-r5900  -mno-fix-r5900
          -mfix-r10000  -mno-fix-r10000  -mfix-rm7000  -mno-fix-rm7000
          -mfix-vr4120  -mno-fix-vr4120
          -mfix-vr4130  -mno-fix-vr4130  -mfix-sb1  -mno-fix-sb1
          -mflush-func=FUNC  -mno-flush-func
          -mbranch-cost=NUM  -mbranch-likely  -mno-branch-likely
          -mcompact-branches=POLICY
          -mfp-exceptions  -mno-fp-exceptions
          -mvr4130-align  -mno-vr4130-align  -msynci  -mno-synci
          -mlxc1-sxc1  -mno-lxc1-sxc1  -mmadd4  -mno-madd4
          -mrelax-pic-calls  -mno-relax-pic-calls  -mmcount-ra-address
          -mframe-header-opt  -mno-frame-header-opt

     _MMIX Options_
          -mlibfuncs  -mno-libfuncs  -mepsilon  -mno-epsilon  -mabi=gnu
          -mabi=mmixware  -mzero-extend  -mknuthdiv  -mtoplevel-symbols
          -melf  -mbranch-predict  -mno-branch-predict  -mbase-addresses
          -mno-base-addresses  -msingle-exit  -mno-single-exit

     _MN10300 Options_
          -mmult-bug  -mno-mult-bug
          -mno-am33  -mam33  -mam33-2  -mam34
          -mtune=CPU-TYPE
          -mreturn-pointer-on-d0
          -mno-crt0  -mrelax  -mliw  -msetlb

     _Moxie Options_
          -meb  -mel  -mmul.x  -mno-crt0

     _MSP430 Options_
          -msim  -masm-hex  -mmcu=  -mcpu=  -mlarge  -msmall  -mrelax
          -mwarn-mcu
          -mcode-region=  -mdata-region=
          -msilicon-errata=  -msilicon-errata-warn=
          -mhwmult=  -minrt  -mtiny-printf  -mmax-inline-shift=

     _NDS32 Options_
          -mbig-endian  -mlittle-endian
          -mreduced-regs  -mfull-regs
          -mcmov  -mno-cmov
          -mext-perf  -mno-ext-perf
          -mext-perf2  -mno-ext-perf2
          -mext-string  -mno-ext-string
          -mv3push  -mno-v3push
          -m16bit  -mno-16bit
          -misr-vector-size=NUM
          -mcache-block-size=NUM
          -march=ARCH
          -mcmodel=CODE-MODEL
          -mctor-dtor  -mrelax

     _Nios II Options_
          -G NUM  -mgpopt=OPTION  -mgpopt  -mno-gpopt
          -mgprel-sec=REGEXP  -mr0rel-sec=REGEXP
          -mel  -meb
          -mno-bypass-cache  -mbypass-cache
          -mno-cache-volatile  -mcache-volatile
          -mno-fast-sw-div  -mfast-sw-div
          -mhw-mul  -mno-hw-mul  -mhw-mulx  -mno-hw-mulx  -mno-hw-div  -mhw-div
          -mcustom-INSN=N  -mno-custom-INSN
          -mcustom-fpu-cfg=NAME
          -mhal  -msmallc  -msys-crt0=NAME  -msys-lib=NAME
          -march=ARCH  -mbmx  -mno-bmx  -mcdx  -mno-cdx

     _Nvidia PTX Options_
          -m64  -mmainkernel  -moptimize

     _OpenRISC Options_
          -mboard=NAME  -mnewlib  -mhard-mul  -mhard-div
          -msoft-mul  -msoft-div
          -msoft-float  -mhard-float  -mdouble-float -munordered-float
          -mcmov  -mror  -mrori  -msext  -msfimm  -mshftimm
          -mcmodel=CODE-MODEL

     _PDP-11 Options_
          -mfpu  -msoft-float  -mac0  -mno-ac0  -m40  -m45  -m10
          -mint32  -mno-int16  -mint16  -mno-int32
          -msplit  -munix-asm  -mdec-asm  -mgnu-asm  -mlra

     _picoChip Options_
          -mae=AE_TYPE  -mvliw-lookahead=N
          -msymbol-as-address  -mno-inefficient-warnings

     _PowerPC Options_ See RS/6000 and PowerPC Options.

     _PRU Options_
          -mmcu=MCU  -minrt  -mno-relax  -mloop
          -mabi=VARIANT

     _RISC-V Options_
          -mbranch-cost=N-INSTRUCTION
          -mplt  -mno-plt
          -mabi=ABI-STRING
          -mfdiv  -mno-fdiv
          -mdiv  -mno-div
          -misa-spec=ISA-SPEC-STRING
          -march=ISA-STRING
          -mtune=PROCESSOR-STRING
          -mpreferred-stack-boundary=NUM
          -msmall-data-limit=N-BYTES
          -msave-restore  -mno-save-restore
          -mshorten-memrefs  -mno-shorten-memrefs
          -mstrict-align  -mno-strict-align
          -mcmodel=medlow  -mcmodel=medany
          -mexplicit-relocs  -mno-explicit-relocs
          -mrelax  -mno-relax
          -mriscv-attribute  -mmo-riscv-attribute
          -malign-data=TYPE
          -mbig-endian  -mlittle-endian
          -mstack-protector-guard=GUARD -mstack-protector-guard-reg=REG
          -mstack-protector-guard-offset=OFFSET

     _RL78 Options_
          -msim  -mmul=none  -mmul=g13  -mmul=g14  -mallregs
          -mcpu=g10  -mcpu=g13  -mcpu=g14  -mg10  -mg13  -mg14
          -m64bit-doubles  -m32bit-doubles  -msave-mduc-in-interrupts

     _RS/6000 and PowerPC Options_
          -mcpu=CPU-TYPE
          -mtune=CPU-TYPE
          -mcmodel=CODE-MODEL
          -mpowerpc64
          -maltivec  -mno-altivec
          -mpowerpc-gpopt  -mno-powerpc-gpopt
          -mpowerpc-gfxopt  -mno-powerpc-gfxopt
          -mmfcrf  -mno-mfcrf  -mpopcntb  -mno-popcntb  -mpopcntd  -mno-popcntd
          -mfprnd  -mno-fprnd
          -mcmpb  -mno-cmpb  -mhard-dfp  -mno-hard-dfp
          -mfull-toc   -mminimal-toc  -mno-fp-in-toc  -mno-sum-in-toc
          -m64  -m32  -mxl-compat  -mno-xl-compat  -mpe
          -malign-power  -malign-natural
          -msoft-float  -mhard-float  -mmultiple  -mno-multiple
          -mupdate  -mno-update
          -mavoid-indexed-addresses  -mno-avoid-indexed-addresses
          -mfused-madd  -mno-fused-madd  -mbit-align  -mno-bit-align
          -mstrict-align  -mno-strict-align  -mrelocatable
          -mno-relocatable  -mrelocatable-lib  -mno-relocatable-lib
          -mtoc  -mno-toc  -mlittle  -mlittle-endian  -mbig  -mbig-endian
          -mdynamic-no-pic  -mswdiv  -msingle-pic-base
          -mprioritize-restricted-insns=PRIORITY
          -msched-costly-dep=DEPENDENCE_TYPE
          -minsert-sched-nops=SCHEME
          -mcall-aixdesc  -mcall-eabi  -mcall-freebsd
          -mcall-linux  -mcall-netbsd  -mcall-openbsd
          -mcall-sysv  -mcall-sysv-eabi  -mcall-sysv-noeabi
          -mtraceback=TRACEBACK_TYPE
          -maix-struct-return  -msvr4-struct-return
          -mabi=ABI-TYPE  -msecure-plt  -mbss-plt
          -mlongcall  -mno-longcall  -mpltseq  -mno-pltseq
          -mblock-move-inline-limit=NUM
          -mblock-compare-inline-limit=NUM
          -mblock-compare-inline-loop-limit=NUM
          -mno-block-ops-unaligned-vsx
          -mstring-compare-inline-limit=NUM
          -misel  -mno-isel
          -mvrsave  -mno-vrsave
          -mmulhw  -mno-mulhw
          -mdlmzb  -mno-dlmzb
          -mprototype  -mno-prototype
          -msim  -mmvme  -mads  -myellowknife  -memb  -msdata
          -msdata=OPT  -mreadonly-in-sdata  -mvxworks  -G NUM
          -mrecip  -mrecip=OPT  -mno-recip  -mrecip-precision
          -mno-recip-precision
          -mveclibabi=TYPE  -mfriz  -mno-friz
          -mpointers-to-nested-functions  -mno-pointers-to-nested-functions
          -msave-toc-indirect  -mno-save-toc-indirect
          -mpower8-fusion  -mno-mpower8-fusion  -mpower8-vector  -mno-power8-vector
          -mcrypto  -mno-crypto  -mhtm  -mno-htm
          -mquad-memory  -mno-quad-memory
          -mquad-memory-atomic  -mno-quad-memory-atomic
          -mcompat-align-parm  -mno-compat-align-parm
          -mfloat128  -mno-float128  -mfloat128-hardware  -mno-float128-hardware
          -mgnu-attribute  -mno-gnu-attribute
          -mstack-protector-guard=GUARD -mstack-protector-guard-reg=REG
          -mstack-protector-guard-offset=OFFSET -mprefixed -mno-prefixed
          -mpcrel -mno-pcrel -mmma -mno-mmma -mrop-protect -mno-rop-protect
          -mprivileged -mno-privileged

     _RX Options_
          -m64bit-doubles  -m32bit-doubles  -fpu  -nofpu
          -mcpu=
          -mbig-endian-data  -mlittle-endian-data
          -msmall-data
          -msim  -mno-sim
          -mas100-syntax  -mno-as100-syntax
          -mrelax
          -mmax-constant-size=
          -mint-register=
          -mpid
          -mallow-string-insns  -mno-allow-string-insns
          -mjsr
          -mno-warn-multiple-fast-interrupts
          -msave-acc-in-interrupts

     _S/390 and zSeries Options_
          -mtune=CPU-TYPE  -march=CPU-TYPE
          -mhard-float  -msoft-float  -mhard-dfp  -mno-hard-dfp
          -mlong-double-64  -mlong-double-128
          -mbackchain  -mno-backchain  -mpacked-stack  -mno-packed-stack
          -msmall-exec  -mno-small-exec  -mmvcle  -mno-mvcle
          -m64  -m31  -mdebug  -mno-debug  -mesa  -mzarch
          -mhtm  -mvx  -mzvector
          -mtpf-trace  -mno-tpf-trace  -mtpf-trace-skip  -mno-tpf-trace-skip
          -mfused-madd  -mno-fused-madd
          -mwarn-framesize  -mwarn-dynamicstack  -mstack-size  -mstack-guard
          -mhotpatch=HALFWORDS,HALFWORDS

     _Score Options_
          -meb  -mel
          -mnhwloop
          -muls
          -mmac
          -mscore5  -mscore5u  -mscore7  -mscore7d

     _SH Options_
          -m1  -m2  -m2e
          -m2a-nofpu  -m2a-single-only  -m2a-single  -m2a
          -m3  -m3e
          -m4-nofpu  -m4-single-only  -m4-single  -m4
          -m4a-nofpu  -m4a-single-only  -m4a-single  -m4a  -m4al
          -mb  -ml  -mdalign  -mrelax
          -mbigtable  -mfmovd  -mrenesas  -mno-renesas  -mnomacsave
          -mieee  -mno-ieee  -mbitops  -misize  -minline-ic_invalidate  -mpadstruct
          -mprefergot  -musermode  -multcost=NUMBER  -mdiv=STRATEGY
          -mdivsi3_libfunc=NAME  -mfixed-range=REGISTER-RANGE
          -maccumulate-outgoing-args
          -matomic-model=ATOMIC-MODEL
          -mbranch-cost=NUM  -mzdcbranch  -mno-zdcbranch
          -mcbranch-force-delay-slot
          -mfused-madd  -mno-fused-madd  -mfsca  -mno-fsca  -mfsrra  -mno-fsrra
          -mpretend-cmove  -mtas

     _Solaris 2 Options_
          -mclear-hwcap  -mno-clear-hwcap  -mimpure-text  -mno-impure-text
          -pthreads

     _SPARC Options_
          -mcpu=CPU-TYPE
          -mtune=CPU-TYPE
          -mcmodel=CODE-MODEL
          -mmemory-model=MEM-MODEL
          -m32  -m64  -mapp-regs  -mno-app-regs
          -mfaster-structs  -mno-faster-structs  -mflat  -mno-flat
          -mfpu  -mno-fpu  -mhard-float  -msoft-float
          -mhard-quad-float  -msoft-quad-float
          -mstack-bias  -mno-stack-bias
          -mstd-struct-return  -mno-std-struct-return
          -munaligned-doubles  -mno-unaligned-doubles
          -muser-mode  -mno-user-mode
          -mv8plus  -mno-v8plus  -mvis  -mno-vis
          -mvis2  -mno-vis2  -mvis3  -mno-vis3
          -mvis4  -mno-vis4  -mvis4b  -mno-vis4b
          -mcbcond  -mno-cbcond  -mfmaf  -mno-fmaf  -mfsmuld  -mno-fsmuld
          -mpopc  -mno-popc  -msubxc  -mno-subxc
          -mfix-at697f  -mfix-ut699  -mfix-ut700  -mfix-gr712rc
          -mlra  -mno-lra

     _System V Options_
          -Qy  -Qn  -YP,PATHS  -Ym,DIR

     _TILE-Gx Options_
          -mcpu=CPU  -m32  -m64  -mbig-endian  -mlittle-endian
          -mcmodel=CODE-MODEL

     _TILEPro Options_
          -mcpu=CPU  -m32

     _V850 Options_
          -mlong-calls  -mno-long-calls  -mep  -mno-ep
          -mprolog-function  -mno-prolog-function  -mspace
          -mtda=N  -msda=N  -mzda=N
          -mapp-regs  -mno-app-regs
          -mdisable-callt  -mno-disable-callt
          -mv850e2v3  -mv850e2  -mv850e1  -mv850es
          -mv850e  -mv850  -mv850e3v5
          -mloop
          -mrelax
          -mlong-jumps
          -msoft-float
          -mhard-float
          -mgcc-abi
          -mrh850-abi
          -mbig-switch

     _VAX Options_
          -mg  -mgnu  -munix  -mlra

     _Visium Options_
          -mdebug  -msim  -mfpu  -mno-fpu  -mhard-float  -msoft-float
          -mcpu=CPU-TYPE  -mtune=CPU-TYPE  -msv-mode  -muser-mode

     _VMS Options_
          -mvms-return-codes  -mdebug-main=PREFIX  -mmalloc64
          -mpointer-size=SIZE

     _VxWorks Options_
          -mrtp  -non-static  -Bstatic  -Bdynamic
          -Xbind-lazy  -Xbind-now

     _x86 Options_
          -mtune=CPU-TYPE  -march=CPU-TYPE
          -mtune-ctrl=FEATURE-LIST  -mdump-tune-features  -mno-default
          -mfpmath=UNIT
          -masm=DIALECT  -mno-fancy-math-387
          -mno-fp-ret-in-387  -m80387  -mhard-float  -msoft-float
          -mno-wide-multiply  -mrtd  -malign-double
          -mpreferred-stack-boundary=NUM
          -mincoming-stack-boundary=NUM
          -mcld  -mcx16  -msahf  -mmovbe  -mcrc32 -mmwait
          -mrecip  -mrecip=OPT
          -mvzeroupper  -mprefer-avx128  -mprefer-vector-width=OPT
          -mmove-max=BITS -mstore-max=BITS
          -mmmx  -msse  -msse2  -msse3  -mssse3  -msse4.1  -msse4.2  -msse4  -mavx
          -mavx2  -mavx512f  -mavx512pf  -mavx512er  -mavx512cd  -mavx512vl
          -mavx512bw  -mavx512dq  -mavx512ifma  -mavx512vbmi  -msha  -maes
          -mpclmul  -mfsgsbase  -mrdrnd  -mf16c  -mfma  -mpconfig  -mwbnoinvd
          -mptwrite  -mprefetchwt1  -mclflushopt  -mclwb  -mxsavec  -mxsaves
          -msse4a  -m3dnow  -m3dnowa  -mpopcnt  -mabm  -mbmi  -mtbm  -mfma4  -mxop
          -madx  -mlzcnt  -mbmi2  -mfxsr  -mxsave  -mxsaveopt  -mrtm  -mhle  -mlwp
          -mmwaitx  -mclzero  -mpku  -mthreads  -mgfni  -mvaes  -mwaitpkg
          -mshstk -mmanual-endbr -mforce-indirect-call  -mavx512vbmi2 -mavx512bf16 -menqcmd
          -mvpclmulqdq  -mavx512bitalg  -mmovdiri  -mmovdir64b  -mavx512vpopcntdq
          -mavx5124fmaps  -mavx512vnni  -mavx5124vnniw  -mprfchw  -mrdpid
          -mrdseed  -msgx -mavx512vp2intersect -mserialize -mtsxldtrk
          -mamx-tile  -mamx-int8  -mamx-bf16 -muintr -mhreset -mavxvnni
          -mavx512fp16
          -mcldemote  -mms-bitfields  -mno-align-stringops  -minline-all-stringops
          -minline-stringops-dynamically  -mstringop-strategy=ALG
          -mkl -mwidekl
          -mmemcpy-strategy=STRATEGY  -mmemset-strategy=STRATEGY
          -mpush-args  -maccumulate-outgoing-args  -m128bit-long-double
          -m96bit-long-double  -mlong-double-64  -mlong-double-80  -mlong-double-128
          -mregparm=NUM  -msseregparm
          -mveclibabi=TYPE  -mvect8-ret-in-mem
          -mpc32  -mpc64  -mpc80  -mstackrealign
          -momit-leaf-frame-pointer  -mno-red-zone  -mno-tls-direct-seg-refs
          -mcmodel=CODE-MODEL  -mabi=NAME  -maddress-mode=MODE
          -m32  -m64  -mx32  -m16  -miamcu  -mlarge-data-threshold=NUM
          -msse2avx  -mfentry  -mrecord-mcount  -mnop-mcount  -m8bit-idiv
          -minstrument-return=TYPE -mfentry-name=NAME -mfentry-section=NAME
          -mavx256-split-unaligned-load  -mavx256-split-unaligned-store
          -malign-data=TYPE  -mstack-protector-guard=GUARD
          -mstack-protector-guard-reg=REG
          -mstack-protector-guard-offset=OFFSET
          -mstack-protector-guard-symbol=SYMBOL
          -mgeneral-regs-only  -mcall-ms2sysv-xlogues -mrelax-cmpxchg-loop
          -mindirect-branch=CHOICE  -mfunction-return=CHOICE
          -mindirect-branch-register -mharden-sls=CHOICE
          -mindirect-branch-cs-prefix -mneeded -mno-direct-extern-access

     _x86 Windows Options_
          -mconsole  -mcygwin  -mno-cygwin  -mdll
          -mnop-fun-dllimport  -mthread
          -municode  -mwin32  -mwindows  -fno-set-stack-executable

     _Xstormy16 Options_
          -msim

     _Xtensa Options_
          -mconst16  -mno-const16
          -mfused-madd  -mno-fused-madd
          -mforce-no-pic
          -mserialize-volatile  -mno-serialize-volatile
          -mtext-section-literals  -mno-text-section-literals
          -mauto-litpools  -mno-auto-litpools
          -mtarget-align  -mno-target-align
          -mlongcalls  -mno-longcalls
          -mabi=ABI-TYPE

     _zSeries Options_ See S/390 and zSeries Options.


File: gcc.info,  Node: Overall Options,  Next: Invoking G++,  Prev: Option Summary,  Up: Invoking GCC

3.2 Options Controlling the Kind of Output
==========================================

Compilation can involve up to four stages: preprocessing, compilation
proper, assembly and linking, always in that order.  GCC is capable of
preprocessing and compiling several files either into several assembler
input files, or into one assembler input file; then each assembler input
file produces an object file, and linking combines all the object files
(those newly compiled, and those specified as input) into an executable
file.

 For any given input file, the file name suffix determines what kind of
compilation is done:

‘FILE.c’
     C source code that must be preprocessed.

‘FILE.i’
     C source code that should not be preprocessed.

‘FILE.ii’
     C++ source code that should not be preprocessed.

‘FILE.m’
     Objective-C source code.  Note that you must link with the
     ‘libobjc’ library to make an Objective-C program work.

‘FILE.mi’
     Objective-C source code that should not be preprocessed.

‘FILE.mm’
‘FILE.M’
     Objective-C++ source code.  Note that you must link with the
     ‘libobjc’ library to make an Objective-C++ program work.  Note that
     ‘.M’ refers to a literal capital M.

‘FILE.mii’
     Objective-C++ source code that should not be preprocessed.

‘FILE.h’
     C, C++, Objective-C or Objective-C++ header file to be turned into
     a precompiled header (default), or C, C++ header file to be turned
     into an Ada spec (via the ‘-fdump-ada-spec’ switch).

‘FILE.cc’
‘FILE.cp’
‘FILE.cxx’
‘FILE.cpp’
‘FILE.CPP’
‘FILE.c++’
‘FILE.C’
     C++ source code that must be preprocessed.  Note that in ‘.cxx’,
     the last two letters must both be literally ‘x’.  Likewise, ‘.C’
     refers to a literal capital C.

‘FILE.mm’
‘FILE.M’
     Objective-C++ source code that must be preprocessed.

‘FILE.mii’
     Objective-C++ source code that should not be preprocessed.

‘FILE.hh’
‘FILE.H’
‘FILE.hp’
‘FILE.hxx’
‘FILE.hpp’
‘FILE.HPP’
‘FILE.h++’
‘FILE.tcc’
     C++ header file to be turned into a precompiled header or Ada spec.

‘FILE.f’
‘FILE.for’
‘FILE.ftn’
     Fixed form Fortran source code that should not be preprocessed.

‘FILE.F’
‘FILE.FOR’
‘FILE.fpp’
‘FILE.FPP’
‘FILE.FTN’
     Fixed form Fortran source code that must be preprocessed (with the
     traditional preprocessor).

‘FILE.f90’
‘FILE.f95’
‘FILE.f03’
‘FILE.f08’
     Free form Fortran source code that should not be preprocessed.

‘FILE.F90’
‘FILE.F95’
‘FILE.F03’
‘FILE.F08’
     Free form Fortran source code that must be preprocessed (with the
     traditional preprocessor).

‘FILE.go’
     Go source code.

‘FILE.d’
     D source code.

‘FILE.di’
     D interface file.

‘FILE.dd’
     D documentation code (Ddoc).

‘FILE.ads’
     Ada source code file that contains a library unit declaration (a
     declaration of a package, subprogram, or generic, or a generic
     instantiation), or a library unit renaming declaration (a package,
     generic, or subprogram renaming declaration).  Such files are also
     called “specs”.

‘FILE.adb’
     Ada source code file containing a library unit body (a subprogram
     or package body).  Such files are also called “bodies”.

‘FILE.s’
     Assembler code.

‘FILE.S’
‘FILE.sx’
     Assembler code that must be preprocessed.

‘OTHER’
     An object file to be fed straight into linking.  Any file name with
     no recognized suffix is treated this way.

 You can specify the input language explicitly with the ‘-x’ option:

‘-x LANGUAGE’
     Specify explicitly the LANGUAGE for the following input files
     (rather than letting the compiler choose a default based on the
     file name suffix).  This option applies to all following input
     files until the next ‘-x’ option.  Possible values for LANGUAGE
     are:
          c  c-header  cpp-output
          c++  c++-header  c++-system-header c++-user-header c++-cpp-output
          objective-c  objective-c-header  objective-c-cpp-output
          objective-c++ objective-c++-header objective-c++-cpp-output
          assembler  assembler-with-cpp
          ada
          d
          f77  f77-cpp-input f95  f95-cpp-input
          go

‘-x none’
     Turn off any specification of a language, so that subsequent files
     are handled according to their file name suffixes (as they are if
     ‘-x’ has not been used at all).

 If you only want some of the stages of compilation, you can use ‘-x’
(or filename suffixes) to tell ‘gcc’ where to start, and one of the
options ‘-c’, ‘-S’, or ‘-E’ to say where ‘gcc’ is to stop.  Note that
some combinations (for example, ‘-x cpp-output -E’) instruct ‘gcc’ to do
nothing at all.

‘-c’
     Compile or assemble the source files, but do not link.  The linking
     stage simply is not done.  The ultimate output is in the form of an
     object file for each source file.

     By default, the object file name for a source file is made by
     replacing the suffix ‘.c’, ‘.i’, ‘.s’, etc., with ‘.o’.

     Unrecognized input files, not requiring compilation or assembly,
     are ignored.

‘-S’
     Stop after the stage of compilation proper; do not assemble.  The
     output is in the form of an assembler code file for each
     non-assembler input file specified.

     By default, the assembler file name for a source file is made by
     replacing the suffix ‘.c’, ‘.i’, etc., with ‘.s’.

     Input files that don't require compilation are ignored.

‘-E’
     Stop after the preprocessing stage; do not run the compiler proper.
     The output is in the form of preprocessed source code, which is
     sent to the standard output.

     Input files that don't require preprocessing are ignored.

‘-o FILE’
     Place the primary output in file FILE.  This applies to whatever
     sort of output is being produced, whether it be an executable file,
     an object file, an assembler file or preprocessed C code.

     If ‘-o’ is not specified, the default is to put an executable file
     in ‘a.out’, the object file for ‘SOURCE.SUFFIX’ in ‘SOURCE.o’, its
     assembler file in ‘SOURCE.s’, a precompiled header file in
     ‘SOURCE.SUFFIX.gch’, and all preprocessed C source on standard
     output.

     Though ‘-o’ names only the primary output, it also affects the
     naming of auxiliary and dump outputs.  See the examples below.
     Unless overridden, both auxiliary outputs and dump outputs are
     placed in the same directory as the primary output.  In auxiliary
     outputs, the suffix of the input file is replaced with that of the
     auxiliary output file type; in dump outputs, the suffix of the dump
     file is appended to the input file suffix.  In compilation
     commands, the base name of both auxiliary and dump outputs is that
     of the primary output; in compile and link commands, the primary
     output name, minus the executable suffix, is combined with the
     input file name.  If both share the same base name, disregarding
     the suffix, the result of the combination is that base name,
     otherwise, they are concatenated, separated by a dash.

          gcc -c foo.c ...

     will use ‘foo.o’ as the primary output, and place aux outputs and
     dumps next to it, e.g., aux file ‘foo.dwo’ for ‘-gsplit-dwarf’, and
     dump file ‘foo.c.???r.final’ for ‘-fdump-rtl-final’.

     If a non-linker output file is explicitly specified, aux and dump
     files by default take the same base name:

          gcc -c foo.c -o dir/foobar.o ...

     will name aux outputs ‘dir/foobar.*’ and dump outputs
     ‘dir/foobar.c.*’.

     A linker output will instead prefix aux and dump outputs:

          gcc foo.c bar.c -o dir/foobar ...

     will generally name aux outputs ‘dir/foobar-foo.*’ and
     ‘dir/foobar-bar.*’, and dump outputs ‘dir/foobar-foo.c.*’ and
     ‘dir/foobar-bar.c.*’.

     The one exception to the above is when the executable shares the
     base name with the single input:

          gcc foo.c -o dir/foo ...

     in which case aux outputs are named ‘dir/foo.*’ and dump outputs
     named ‘dir/foo.c.*’.

     The location and the names of auxiliary and dump outputs can be
     adjusted by the options ‘-dumpbase’, ‘-dumpbase-ext’, ‘-dumpdir’,
     ‘-save-temps=cwd’, and ‘-save-temps=obj’.

‘-dumpbase DUMPBASE’
     This option sets the base name for auxiliary and dump output files.
     It does not affect the name of the primary output file.
     Intermediate outputs, when preserved, are not regarded as primary
     outputs, but as auxiliary outputs:

          gcc -save-temps -S foo.c

     saves the (no longer) temporary preprocessed file in ‘foo.i’, and
     then compiles to the (implied) output file ‘foo.s’, whereas:

          gcc -save-temps -dumpbase save-foo -c foo.c

     preprocesses to in ‘save-foo.i’, compiles to ‘save-foo.s’ (now an
     intermediate, thus auxiliary output), and then assembles to the
     (implied) output file ‘foo.o’.

     Absent this option, dump and aux files take their names from the
     input file, or from the (non-linker) output file, if one is
     explicitly specified: dump output files (e.g.  those requested by
     ‘-fdump-*’ options) with the input name suffix, and aux output
     files (those requested by other non-dump options, e.g.
     ‘-save-temps’, ‘-gsplit-dwarf’, ‘-fcallgraph-info’) without it.

     Similar suffix differentiation of dump and aux outputs can be
     attained for explicitly-given ‘-dumpbase basename.suf’ by also
     specifying ‘-dumpbase-ext .suf’.

     If DUMPBASE is explicitly specified with any directory component,
     any DUMPPFX specification (e.g.  ‘-dumpdir’ or ‘-save-temps=*’) is
     ignored, and instead of appending to it, DUMPBASE fully overrides
     it:

          gcc foo.c -c -o dir/foo.o -dumpbase alt/foo \
            -dumpdir pfx- -save-temps=cwd ...

     creates auxiliary and dump outputs named ‘alt/foo.*’, disregarding
     ‘dir/’ in ‘-o’, the ‘./’ prefix implied by ‘-save-temps=cwd’, and
     ‘pfx-’ in ‘-dumpdir’.

     When ‘-dumpbase’ is specified in a command that compiles multiple
     inputs, or that compiles and then links, it may be combined with
     DUMPPFX, as specified under ‘-dumpdir’.  Then, each input file is
     compiled using the combined DUMPPFX, and default values for
     DUMPBASE and AUXDROPSUF are computed for each input file:

          gcc foo.c bar.c -c -dumpbase main ...

     creates ‘foo.o’ and ‘bar.o’ as primary outputs, and avoids
     overwriting the auxiliary and dump outputs by using the DUMPBASE as
     a prefix, creating auxiliary and dump outputs named ‘main-foo.*’
     and ‘main-bar.*’.

     An empty string specified as DUMPBASE avoids the influence of the
     output basename in the naming of auxiliary and dump outputs during
     compilation, computing default values :

          gcc -c foo.c -o dir/foobar.o -dumpbase '' ...

     will name aux outputs ‘dir/foo.*’ and dump outputs ‘dir/foo.c.*’.
     Note how their basenames are taken from the input name, but the
     directory still defaults to that of the output.

     The empty-string dumpbase does not prevent the use of the output
     basename for outputs during linking:

          gcc foo.c bar.c -o dir/foobar -dumpbase '' -flto ...

     The compilation of the source files will name auxiliary outputs
     ‘dir/foo.*’ and ‘dir/bar.*’, and dump outputs ‘dir/foo.c.*’ and
     ‘dir/bar.c.*’.  LTO recompilation during linking will use
     ‘dir/foobar.’ as the prefix for dumps and auxiliary files.

‘-dumpbase-ext AUXDROPSUF’
     When forming the name of an auxiliary (but not a dump) output file,
     drop trailing AUXDROPSUF from DUMPBASE before appending any
     suffixes.  If not specified, this option defaults to the suffix of
     a default DUMPBASE, i.e., the suffix of the input file when
     ‘-dumpbase’ is not present in the command line, or DUMPBASE is
     combined with DUMPPFX.

          gcc foo.c -c -o dir/foo.o -dumpbase x-foo.c -dumpbase-ext .c ...

     creates ‘dir/foo.o’ as the main output, and generates auxiliary
     outputs in ‘dir/x-foo.*’, taking the location of the primary
     output, and dropping the ‘.c’ suffix from the DUMPBASE.  Dump
     outputs retain the suffix: ‘dir/x-foo.c.*’.

     This option is disregarded if it does not match the suffix of a
     specified DUMPBASE, except as an alternative to the executable
     suffix when appending the linker output base name to DUMPPFX, as
     specified below:

          gcc foo.c bar.c -o main.out -dumpbase-ext .out ...

     creates ‘main.out’ as the primary output, and avoids overwriting
     the auxiliary and dump outputs by using the executable name minus
     AUXDROPSUF as a prefix, creating auxiliary outputs named
     ‘main-foo.*’ and ‘main-bar.*’ and dump outputs named ‘main-foo.c.*’
     and ‘main-bar.c.*’.

‘-dumpdir DUMPPFX’
     When forming the name of an auxiliary or dump output file, use
     DUMPPFX as a prefix:

          gcc -dumpdir pfx- -c foo.c ...

     creates ‘foo.o’ as the primary output, and auxiliary outputs named
     ‘pfx-foo.*’, combining the given DUMPPFX with the default DUMPBASE
     derived from the default primary output, derived in turn from the
     input name.  Dump outputs also take the input name suffix:
     ‘pfx-foo.c.*’.

     If DUMPPFX is to be used as a directory name, it must end with a
     directory separator:

          gcc -dumpdir dir/ -c foo.c -o obj/bar.o ...

     creates ‘obj/bar.o’ as the primary output, and auxiliary outputs
     named ‘dir/bar.*’, combining the given DUMPPFX with the default
     DUMPBASE derived from the primary output name.  Dump outputs also
     take the input name suffix: ‘dir/bar.c.*’.

     It defaults to the location of the output file, unless the output
     file is a special file like ‘/dev/null’.  Options ‘-save-temps=cwd’
     and ‘-save-temps=obj’ override this default, just like an explicit
     ‘-dumpdir’ option.  In case multiple such options are given, the
     last one prevails:

          gcc -dumpdir pfx- -c foo.c -save-temps=obj ...

     outputs ‘foo.o’, with auxiliary outputs named ‘foo.*’ because
     ‘-save-temps=*’ overrides the DUMPPFX given by the earlier
     ‘-dumpdir’ option.  It does not matter that ‘=obj’ is the default
     for ‘-save-temps’, nor that the output directory is implicitly the
     current directory.  Dump outputs are named ‘foo.c.*’.

     When compiling from multiple input files, if ‘-dumpbase’ is
     specified, DUMPBASE, minus a AUXDROPSUF suffix, and a dash are
     appended to (or override, if containing any directory components)
     an explicit or defaulted DUMPPFX, so that each of the multiple
     compilations gets differently-named aux and dump outputs.

          gcc foo.c bar.c -c -dumpdir dir/pfx- -dumpbase main ...

     outputs auxiliary dumps to ‘dir/pfx-main-foo.*’ and
     ‘dir/pfx-main-bar.*’, appending DUMPBASE- to DUMPPFX.  Dump outputs
     retain the input file suffix: ‘dir/pfx-main-foo.c.*’ and
     ‘dir/pfx-main-bar.c.*’, respectively.  Contrast with the
     single-input compilation:

          gcc foo.c -c -dumpdir dir/pfx- -dumpbase main ...

     that, applying ‘-dumpbase’ to a single source, does not compute and
     append a separate DUMPBASE per input file.  Its auxiliary and dump
     outputs go in ‘dir/pfx-main.*’.

     When compiling and then linking from multiple input files, a
     defaulted or explicitly specified DUMPPFX also undergoes the
     DUMPBASE- transformation above (e.g.  the compilation of ‘foo.c’
     and ‘bar.c’ above, but without ‘-c’).  If neither ‘-dumpdir’ nor
     ‘-dumpbase’ are given, the linker output base name, minus
     AUXDROPSUF, if specified, or the executable suffix otherwise, plus
     a dash is appended to the default DUMPPFX instead.  Note, however,
     that unlike earlier cases of linking:

          gcc foo.c bar.c -dumpdir dir/pfx- -o main ...

     does not append the output name ‘main’ to DUMPPFX, because
     ‘-dumpdir’ is explicitly specified.  The goal is that the
     explicitly-specified DUMPPFX may contain the specified output name
     as part of the prefix, if desired; only an explicitly-specified
     ‘-dumpbase’ would be combined with it, in order to avoid simply
     discarding a meaningful option.

     When compiling and then linking from a single input file, the
     linker output base name will only be appended to the default
     DUMPPFX as above if it does not share the base name with the single
     input file name.  This has been covered in single-input linking
     cases above, but not with an explicit ‘-dumpdir’ that inhibits the
     combination, even if overridden by ‘-save-temps=*’:

          gcc foo.c -dumpdir alt/pfx- -o dir/main.exe -save-temps=cwd ...

     Auxiliary outputs are named ‘foo.*’, and dump outputs ‘foo.c.*’, in
     the current working directory as ultimately requested by
     ‘-save-temps=cwd’.

     Summing it all up for an intuitive though slightly imprecise data
     flow: the primary output name is broken into a directory part and a
     basename part; DUMPPFX is set to the former, unless overridden by
     ‘-dumpdir’ or ‘-save-temps=*’, and DUMPBASE is set to the latter,
     unless overriden by ‘-dumpbase’.  If there are multiple inputs or
     linking, this DUMPBASE may be combined with DUMPPFX and taken from
     each input file.  Auxiliary output names for each input are formed
     by combining DUMPPFX, DUMPBASE minus suffix, and the auxiliary
     output suffix; dump output names are only different in that the
     suffix from DUMPBASE is retained.

     When it comes to auxiliary and dump outputs created during LTO
     recompilation, a combination of DUMPPFX and DUMPBASE, as given or
     as derived from the linker output name but not from inputs, even in
     cases in which this combination would not otherwise be used as
     such, is passed down with a trailing period replacing the
     compiler-added dash, if any, as a ‘-dumpdir’ option to
     ‘lto-wrapper’; being involved in linking, this program does not
     normally get any ‘-dumpbase’ and ‘-dumpbase-ext’, and it ignores
     them.

     When running sub-compilers, ‘lto-wrapper’ appends LTO stage names
     to the received DUMPPFX, ensures it contains a directory component
     so that it overrides any ‘-dumpdir’, and passes that as ‘-dumpbase’
     to sub-compilers.

‘-v’
     Print (on standard error output) the commands executed to run the
     stages of compilation.  Also print the version number of the
     compiler driver program and of the preprocessor and the compiler
     proper.

‘-###’
     Like ‘-v’ except the commands are not executed and arguments are
     quoted unless they contain only alphanumeric characters or ‘./-_’.
     This is useful for shell scripts to capture the driver-generated
     command lines.

‘--help’
     Print (on the standard output) a description of the command-line
     options understood by ‘gcc’.  If the ‘-v’ option is also specified
     then ‘--help’ is also passed on to the various processes invoked by
     ‘gcc’, so that they can display the command-line options they
     accept.  If the ‘-Wextra’ option has also been specified (prior to
     the ‘--help’ option), then command-line options that have no
     documentation associated with them are also displayed.

‘--target-help’
     Print (on the standard output) a description of target-specific
     command-line options for each tool.  For some targets extra
     target-specific information may also be printed.

‘--help={CLASS|[^]QUALIFIER}[,...]’
     Print (on the standard output) a description of the command-line
     options understood by the compiler that fit into all specified
     classes and qualifiers.  These are the supported classes:

     ‘optimizers’
          Display all of the optimization options supported by the
          compiler.

     ‘warnings’
          Display all of the options controlling warning messages
          produced by the compiler.

     ‘target’
          Display target-specific options.  Unlike the ‘--target-help’
          option however, target-specific options of the linker and
          assembler are not displayed.  This is because those tools do
          not currently support the extended ‘--help=’ syntax.

     ‘params’
          Display the values recognized by the ‘--param’ option.

     LANGUAGE
          Display the options supported for LANGUAGE, where LANGUAGE is
          the name of one of the languages supported in this version of
          GCC.  If an option is supported by all languages, one needs to
          select ‘common’ class.

     ‘common’
          Display the options that are common to all languages.

     These are the supported qualifiers:

     ‘undocumented’
          Display only those options that are undocumented.

     ‘joined’
          Display options taking an argument that appears after an equal
          sign in the same continuous piece of text, such as:
          ‘--help=target’.

     ‘separate’
          Display options taking an argument that appears as a separate
          word following the original option, such as: ‘-o output-file’.

     Thus for example to display all the undocumented target-specific
     switches supported by the compiler, use:

          --help=target,undocumented

     The sense of a qualifier can be inverted by prefixing it with the
     ‘^’ character, so for example to display all binary warning options
     (i.e., ones that are either on or off and that do not take an
     argument) that have a description, use:

          --help=warnings,^joined,^undocumented

     The argument to ‘--help=’ should not consist solely of inverted
     qualifiers.

     Combining several classes is possible, although this usually
     restricts the output so much that there is nothing to display.  One
     case where it does work, however, is when one of the classes is
     TARGET.  For example, to display all the target-specific
     optimization options, use:

          --help=target,optimizers

     The ‘--help=’ option can be repeated on the command line.  Each
     successive use displays its requested class of options, skipping
     those that have already been displayed.  If ‘--help’ is also
     specified anywhere on the command line then this takes precedence
     over any ‘--help=’ option.

     If the ‘-Q’ option appears on the command line before the ‘--help=’
     option, then the descriptive text displayed by ‘--help=’ is
     changed.  Instead of describing the displayed options, an
     indication is given as to whether the option is enabled, disabled
     or set to a specific value (assuming that the compiler knows this
     at the point where the ‘--help=’ option is used).

     Here is a truncated example from the ARM port of ‘gcc’:

            % gcc -Q -mabi=2 --help=target -c
            The following options are target specific:
            -mabi=                                2
            -mabort-on-noreturn                   [disabled]
            -mapcs                                [disabled]

     The output is sensitive to the effects of previous command-line
     options, so for example it is possible to find out which
     optimizations are enabled at ‘-O2’ by using:

          -Q -O2 --help=optimizers

     Alternatively you can discover which binary optimizations are
     enabled by ‘-O3’ by using:

          gcc -c -Q -O3 --help=optimizers > /tmp/O3-opts
          gcc -c -Q -O2 --help=optimizers > /tmp/O2-opts
          diff /tmp/O2-opts /tmp/O3-opts | grep enabled

‘--version’
     Display the version number and copyrights of the invoked GCC.

‘-pass-exit-codes’
     Normally the ‘gcc’ program exits with the code of 1 if any phase of
     the compiler returns a non-success return code.  If you specify
     ‘-pass-exit-codes’, the ‘gcc’ program instead returns with the
     numerically highest error produced by any phase returning an error
     indication.  The C, C++, and Fortran front ends return 4 if an
     internal compiler error is encountered.

‘-pipe’
     Use pipes rather than temporary files for communication between the
     various stages of compilation.  This fails to work on some systems
     where the assembler is unable to read from a pipe; but the GNU
     assembler has no trouble.

‘-specs=FILE’
     Process FILE after the compiler reads in the standard ‘specs’ file,
     in order to override the defaults which the ‘gcc’ driver program
     uses when determining what switches to pass to ‘cc1’, ‘cc1plus’,
     ‘as’, ‘ld’, etc.  More than one ‘-specs=FILE’ can be specified on
     the command line, and they are processed in order, from left to
     right.  *Note Spec Files::, for information about the format of the
     FILE.

‘-wrapper’
     Invoke all subcommands under a wrapper program.  The name of the
     wrapper program and its parameters are passed as a comma separated
     list.

          gcc -c t.c -wrapper gdb,--args

     This invokes all subprograms of ‘gcc’ under ‘gdb --args’, thus the
     invocation of ‘cc1’ is ‘gdb --args cc1 ...’.

‘-ffile-prefix-map=OLD=NEW’
     When compiling files residing in directory ‘OLD’, record any
     references to them in the result of the compilation as if the files
     resided in directory ‘NEW’ instead.  Specifying this option is
     equivalent to specifying all the individual ‘-f*-prefix-map’
     options.  This can be used to make reproducible builds that are
     location independent.  See also ‘-fmacro-prefix-map’,
     ‘-fdebug-prefix-map’ and ‘-fprofile-prefix-map’.

‘-fplugin=NAME.so’
     Load the plugin code in file NAME.so, assumed to be a shared object
     to be dlopen'd by the compiler.  The base name of the shared object
     file is used to identify the plugin for the purposes of argument
     parsing (See ‘-fplugin-arg-NAME-KEY=VALUE’ below).  Each plugin
     should define the callback functions specified in the Plugins API.

‘-fplugin-arg-NAME-KEY=VALUE’
     Define an argument called KEY with a value of VALUE for the plugin
     called NAME.

‘-fdump-ada-spec[-slim]’
     For C and C++ source and include files, generate corresponding Ada
     specs.  *Note (gnat_ugn)Generating Ada Bindings for C and C++
     headers::, which provides detailed documentation on this feature.

‘-fada-spec-parent=UNIT’
     In conjunction with ‘-fdump-ada-spec[-slim]’ above, generate Ada
     specs as child units of parent UNIT.

‘-fdump-go-spec=FILE’
     For input files in any language, generate corresponding Go
     declarations in FILE.  This generates Go ‘const’, ‘type’, ‘var’,
     and ‘func’ declarations which may be a useful way to start writing
     a Go interface to code written in some other language.

‘@FILE’
     Read command-line options from FILE.  The options read are inserted
     in place of the original @FILE option.  If FILE does not exist, or
     cannot be read, then the option will be treated literally, and not
     removed.

     Options in FILE are separated by whitespace.  A whitespace
     character may be included in an option by surrounding the entire
     option in either single or double quotes.  Any character (including
     a backslash) may be included by prefixing the character to be
     included with a backslash.  The FILE may itself contain additional
     @FILE options; any such options will be processed recursively.


File: gcc.info,  Node: Invoking G++,  Next: C Dialect Options,  Prev: Overall Options,  Up: Invoking GCC

3.3 Compiling C++ Programs
==========================

C++ source files conventionally use one of the suffixes ‘.C’, ‘.cc’,
‘.cpp’, ‘.CPP’, ‘.c++’, ‘.cp’, or ‘.cxx’; C++ header files often use
‘.hh’, ‘.hpp’, ‘.H’, or (for shared template code) ‘.tcc’; and
preprocessed C++ files use the suffix ‘.ii’.  GCC recognizes files with
these names and compiles them as C++ programs even if you call the
compiler the same way as for compiling C programs (usually with the name
‘gcc’).

 However, the use of ‘gcc’ does not add the C++ library.  ‘g++’ is a
program that calls GCC and automatically specifies linking against the
C++ library.  It treats ‘.c’, ‘.h’ and ‘.i’ files as C++ source files
instead of C source files unless ‘-x’ is used.  This program is also
useful when precompiling a C header file with a ‘.h’ extension for use
in C++ compilations.  On many systems, ‘g++’ is also installed with the
name ‘c++’.

 When you compile C++ programs, you may specify many of the same
command-line options that you use for compiling programs in any
language; or command-line options meaningful for C and related
languages; or options that are meaningful only for C++ programs.  *Note
Options Controlling C Dialect: C Dialect Options, for explanations of
options for languages related to C.  *Note Options Controlling C++
Dialect: C++ Dialect Options, for explanations of options that are
meaningful only for C++ programs.


File: gcc.info,  Node: C Dialect Options,  Next: C++ Dialect Options,  Prev: Invoking G++,  Up: Invoking GCC

3.4 Options Controlling C Dialect
=================================

The following options control the dialect of C (or languages derived
from C, such as C++, Objective-C and Objective-C++) that the compiler
accepts:

‘-ansi’
     In C mode, this is equivalent to ‘-std=c90’.  In C++ mode, it is
     equivalent to ‘-std=c++98’.

     This turns off certain features of GCC that are incompatible with
     ISO C90 (when compiling C code), or of standard C++ (when compiling
     C++ code), such as the ‘asm’ and ‘typeof’ keywords, and predefined
     macros such as ‘unix’ and ‘vax’ that identify the type of system
     you are using.  It also enables the undesirable and rarely used ISO
     trigraph feature.  For the C compiler, it disables recognition of
     C++ style ‘//’ comments as well as the ‘inline’ keyword.

     The alternate keywords ‘__asm__’, ‘__extension__’, ‘__inline__’ and
     ‘__typeof__’ continue to work despite ‘-ansi’.  You would not want
     to use them in an ISO C program, of course, but it is useful to put
     them in header files that might be included in compilations done
     with ‘-ansi’.  Alternate predefined macros such as ‘__unix__’ and
     ‘__vax__’ are also available, with or without ‘-ansi’.

     The ‘-ansi’ option does not cause non-ISO programs to be rejected
     gratuitously.  For that, ‘-Wpedantic’ is required in addition to
     ‘-ansi’.  *Note Warning Options::.

     The macro ‘__STRICT_ANSI__’ is predefined when the ‘-ansi’ option
     is used.  Some header files may notice this macro and refrain from
     declaring certain functions or defining certain macros that the ISO
     standard doesn't call for; this is to avoid interfering with any
     programs that might use these names for other things.

     Functions that are normally built in but do not have semantics
     defined by ISO C (such as ‘alloca’ and ‘ffs’) are not built-in
     functions when ‘-ansi’ is used.  *Note Other built-in functions
     provided by GCC: Other Builtins, for details of the functions
     affected.

‘-std=’
     Determine the language standard.  *Note Language Standards
     Supported by GCC: Standards, for details of these standard
     versions.  This option is currently only supported when compiling C
     or C++.

     The compiler can accept several base standards, such as ‘c90’ or
     ‘c++98’, and GNU dialects of those standards, such as ‘gnu90’ or
     ‘gnu++98’.  When a base standard is specified, the compiler accepts
     all programs following that standard plus those using GNU
     extensions that do not contradict it.  For example, ‘-std=c90’
     turns off certain features of GCC that are incompatible with ISO
     C90, such as the ‘asm’ and ‘typeof’ keywords, but not other GNU
     extensions that do not have a meaning in ISO C90, such as omitting
     the middle term of a ‘?:’ expression.  On the other hand, when a
     GNU dialect of a standard is specified, all features supported by
     the compiler are enabled, even when those features change the
     meaning of the base standard.  As a result, some strict-conforming
     programs may be rejected.  The particular standard is used by
     ‘-Wpedantic’ to identify which features are GNU extensions given
     that version of the standard.  For example ‘-std=gnu90 -Wpedantic’
     warns about C++ style ‘//’ comments, while ‘-std=gnu99 -Wpedantic’
     does not.

     A value for this option must be provided; possible values are

     ‘c90’
     ‘c89’
     ‘iso9899:1990’
          Support all ISO C90 programs (certain GNU extensions that
          conflict with ISO C90 are disabled).  Same as ‘-ansi’ for C
          code.

     ‘iso9899:199409’
          ISO C90 as modified in amendment 1.

     ‘c99’
     ‘c9x’
     ‘iso9899:1999’
     ‘iso9899:199x’
          ISO C99.  This standard is substantially completely supported,
          modulo bugs and floating-point issues (mainly but not entirely
          relating to optional C99 features from Annexes F and G). See
          <https://gcc.gnu.org/c99status.html> for more information.
          The names ‘c9x’ and ‘iso9899:199x’ are deprecated.

     ‘c11’
     ‘c1x’
     ‘iso9899:2011’
          ISO C11, the 2011 revision of the ISO C standard.  This
          standard is substantially completely supported, modulo bugs,
          floating-point issues (mainly but not entirely relating to
          optional C11 features from Annexes F and G) and the optional
          Annexes K (Bounds-checking interfaces) and L (Analyzability).
          The name ‘c1x’ is deprecated.

     ‘c17’
     ‘c18’
     ‘iso9899:2017’
     ‘iso9899:2018’
          ISO C17, the 2017 revision of the ISO C standard (published in
          2018).  This standard is same as C11 except for corrections of
          defects (all of which are also applied with ‘-std=c11’) and a
          new value of ‘__STDC_VERSION__’, and so is supported to the
          same extent as C11.

     ‘c2x’
          The next version of the ISO C standard, still under
          development.  The support for this version is experimental and
          incomplete.

     ‘gnu90’
     ‘gnu89’
          GNU dialect of ISO C90 (including some C99 features).

     ‘gnu99’
     ‘gnu9x’
          GNU dialect of ISO C99.  The name ‘gnu9x’ is deprecated.

     ‘gnu11’
     ‘gnu1x’
          GNU dialect of ISO C11.  The name ‘gnu1x’ is deprecated.

     ‘gnu17’
     ‘gnu18’
          GNU dialect of ISO C17.  This is the default for C code.

     ‘gnu2x’
          The next version of the ISO C standard, still under
          development, plus GNU extensions.  The support for this
          version is experimental and incomplete.

     ‘c++98’
     ‘c++03’
          The 1998 ISO C++ standard plus the 2003 technical corrigendum
          and some additional defect reports.  Same as ‘-ansi’ for C++
          code.

     ‘gnu++98’
     ‘gnu++03’
          GNU dialect of ‘-std=c++98’.

     ‘c++11’
     ‘c++0x’
          The 2011 ISO C++ standard plus amendments.  The name ‘c++0x’
          is deprecated.

     ‘gnu++11’
     ‘gnu++0x’
          GNU dialect of ‘-std=c++11’.  The name ‘gnu++0x’ is
          deprecated.

     ‘c++14’
     ‘c++1y’
          The 2014 ISO C++ standard plus amendments.  The name ‘c++1y’
          is deprecated.

     ‘gnu++14’
     ‘gnu++1y’
          GNU dialect of ‘-std=c++14’.  The name ‘gnu++1y’ is
          deprecated.

     ‘c++17’
     ‘c++1z’
          The 2017 ISO C++ standard plus amendments.  The name ‘c++1z’
          is deprecated.

     ‘gnu++17’
     ‘gnu++1z’
          GNU dialect of ‘-std=c++17’.  This is the default for C++
          code.  The name ‘gnu++1z’ is deprecated.

     ‘c++20’
     ‘c++2a’
          The 2020 ISO C++ standard plus amendments.  Support is
          experimental, and could change in incompatible ways in future
          releases.  The name ‘c++2a’ is deprecated.

     ‘gnu++20’
     ‘gnu++2a’
          GNU dialect of ‘-std=c++20’.  Support is experimental, and
          could change in incompatible ways in future releases.  The
          name ‘gnu++2a’ is deprecated.

     ‘c++2b’
     ‘c++23’
          The next revision of the ISO C++ standard, planned for 2023.
          Support is highly experimental, and will almost certainly
          change in incompatible ways in future releases.

     ‘gnu++2b’
     ‘gnu++23’
          GNU dialect of ‘-std=c++2b’.  Support is highly experimental,
          and will almost certainly change in incompatible ways in
          future releases.

‘-aux-info FILENAME’
     Output to the given filename prototyped declarations for all
     functions declared and/or defined in a translation unit, including
     those in header files.  This option is silently ignored in any
     language other than C.

     Besides declarations, the file indicates, in comments, the origin
     of each declaration (source file and line), whether the declaration
     was implicit, prototyped or unprototyped (‘I’, ‘N’ for new or ‘O’
     for old, respectively, in the first character after the line number
     and the colon), and whether it came from a declaration or a
     definition (‘C’ or ‘F’, respectively, in the following character).
     In the case of function definitions, a K&R-style list of arguments
     followed by their declarations is also provided, inside comments,
     after the declaration.

‘-fallow-parameterless-variadic-functions’
     Accept variadic functions without named parameters.

     Although it is possible to define such a function, this is not very
     useful as it is not possible to read the arguments.  This is only
     supported for C as this construct is allowed by C++.

‘-fno-asm’
     Do not recognize ‘asm’, ‘inline’ or ‘typeof’ as a keyword, so that
     code can use these words as identifiers.  You can use the keywords
     ‘__asm__’, ‘__inline__’ and ‘__typeof__’ instead.  In C, ‘-ansi’
     implies ‘-fno-asm’.

     In C++, ‘inline’ is a standard keyword and is not affected by this
     switch.  You may want to use the ‘-fno-gnu-keywords’ flag instead,
     which disables ‘typeof’ but not ‘asm’ and ‘inline’.  In C99 mode
     (‘-std=c99’ or ‘-std=gnu99’), this switch only affects the ‘asm’
     and ‘typeof’ keywords, since ‘inline’ is a standard keyword in ISO
     C99.

‘-fno-builtin’
‘-fno-builtin-FUNCTION’
     Don't recognize built-in functions that do not begin with
     ‘__builtin_’ as prefix.  *Note Other built-in functions provided by
     GCC: Other Builtins, for details of the functions affected,
     including those which are not built-in functions when ‘-ansi’ or
     ‘-std’ options for strict ISO C conformance are used because they
     do not have an ISO standard meaning.

     GCC normally generates special code to handle certain built-in
     functions more efficiently; for instance, calls to ‘alloca’ may
     become single instructions which adjust the stack directly, and
     calls to ‘memcpy’ may become inline copy loops.  The resulting code
     is often both smaller and faster, but since the function calls no
     longer appear as such, you cannot set a breakpoint on those calls,
     nor can you change the behavior of the functions by linking with a
     different library.  In addition, when a function is recognized as a
     built-in function, GCC may use information about that function to
     warn about problems with calls to that function, or to generate
     more efficient code, even if the resulting code still contains
     calls to that function.  For example, warnings are given with
     ‘-Wformat’ for bad calls to ‘printf’ when ‘printf’ is built in and
     ‘strlen’ is known not to modify global memory.

     With the ‘-fno-builtin-FUNCTION’ option only the built-in function
     FUNCTION is disabled.  FUNCTION must not begin with ‘__builtin_’.
     If a function is named that is not built-in in this version of GCC,
     this option is ignored.  There is no corresponding
     ‘-fbuiltin-FUNCTION’ option; if you wish to enable built-in
     functions selectively when using ‘-fno-builtin’ or
     ‘-ffreestanding’, you may define macros such as:

          #define abs(n)          __builtin_abs ((n))
          #define strcpy(d, s)    __builtin_strcpy ((d), (s))

‘-fcond-mismatch’
     Allow conditional expressions with mismatched types in the second
     and third arguments.  The value of such an expression is void.
     This option is not supported for C++.

‘-ffreestanding’

     Assert that compilation targets a freestanding environment.  This
     implies ‘-fno-builtin’.  A freestanding environment is one in which
     the standard library may not exist, and program startup may not
     necessarily be at ‘main’.  The most obvious example is an OS
     kernel.  This is equivalent to ‘-fno-hosted’.

     *Note Language Standards Supported by GCC: Standards, for details
     of freestanding and hosted environments.

‘-fgimple’

     Enable parsing of function definitions marked with ‘__GIMPLE’.
     This is an experimental feature that allows unit testing of GIMPLE
     passes.

‘-fgnu-tm’
     When the option ‘-fgnu-tm’ is specified, the compiler generates
     code for the Linux variant of Intel's current Transactional Memory
     ABI specification document (Revision 1.1, May 6 2009).  This is an
     experimental feature whose interface may change in future versions
     of GCC, as the official specification changes.  Please note that
     not all architectures are supported for this feature.

     For more information on GCC's support for transactional memory,
     *Note The GNU Transactional Memory Library: (libitm)Enabling
     libitm.

     Note that the transactional memory feature is not supported with
     non-call exceptions (‘-fnon-call-exceptions’).

‘-fgnu89-inline’
     The option ‘-fgnu89-inline’ tells GCC to use the traditional GNU
     semantics for ‘inline’ functions when in C99 mode.  *Note An Inline
     Function is As Fast As a Macro: Inline.  Using this option is
     roughly equivalent to adding the ‘gnu_inline’ function attribute to
     all inline functions (*note Function Attributes::).

     The option ‘-fno-gnu89-inline’ explicitly tells GCC to use the C99
     semantics for ‘inline’ when in C99 or gnu99 mode (i.e., it
     specifies the default behavior).  This option is not supported in
     ‘-std=c90’ or ‘-std=gnu90’ mode.

     The preprocessor macros ‘__GNUC_GNU_INLINE__’ and
     ‘__GNUC_STDC_INLINE__’ may be used to check which semantics are in
     effect for ‘inline’ functions.  *Note (cpp)Common Predefined
     Macros::.

‘-fhosted’

     Assert that compilation targets a hosted environment.  This implies
     ‘-fbuiltin’.  A hosted environment is one in which the entire
     standard library is available, and in which ‘main’ has a return
     type of ‘int’.  Examples are nearly everything except a kernel.
     This is equivalent to ‘-fno-freestanding’.

‘-flax-vector-conversions’
     Allow implicit conversions between vectors with differing numbers
     of elements and/or incompatible element types.  This option should
     not be used for new code.

‘-fms-extensions’
     Accept some non-standard constructs used in Microsoft header files.

     In C++ code, this allows member names in structures to be similar
     to previous types declarations.

          typedef int UOW;
          struct ABC {
            UOW UOW;
          };

     Some cases of unnamed fields in structures and unions are only
     accepted with this option.  *Note Unnamed struct/union fields
     within structs/unions: Unnamed Fields, for details.

     Note that this option is off for all targets except for x86 targets
     using ms-abi.

‘-foffload=disable’
‘-foffload=default’
‘-foffload=TARGET-LIST’
     Specify for which OpenMP and OpenACC offload targets code should be
     generated.  The default behavior, equivalent to
     ‘-foffload=default’, is to generate code for all supported offload
     targets.  The ‘-foffload=disable’ form generates code only for the
     host fallback, while ‘-foffload=TARGET-LIST’ generates code only
     for the specified comma-separated list of offload targets.

     Offload targets are specified in GCC's internal target-triplet
     format.  You can run the compiler with ‘-v’ to show the list of
     configured offload targets under ‘OFFLOAD_TARGET_NAMES’.

‘-foffload-options=OPTIONS’
‘-foffload-options=TARGET-TRIPLET-LIST=OPTIONS’

     With ‘-foffload-options=OPTIONS’, GCC passes the specified OPTIONS
     to the compilers for all enabled offloading targets.  You can
     specify options that apply only to a specific target or targets by
     using the ‘-foffload-options=TARGET-LIST=OPTIONS’ form.  The
     TARGET-LIST is a comma-separated list in the same format as for the
     ‘-foffload=’ option.

     Typical command lines are

          -foffload-options=-lgfortran -foffload-options=-lm
          -foffload-options="-lgfortran -lm" -foffload-options=nvptx-none=-latomic
          -foffload-options=amdgcn-amdhsa=-march=gfx906 -foffload-options=-lm

‘-fopenacc’
     Enable handling of OpenACC directives ‘#pragma acc’ in C/C++ and
     ‘!$acc’ in Fortran.  When ‘-fopenacc’ is specified, the compiler
     generates accelerated code according to the OpenACC Application
     Programming Interface v2.6 <https://www.openacc.org>.  This option
     implies ‘-pthread’, and thus is only supported on targets that have
     support for ‘-pthread’.

‘-fopenacc-dim=GEOM’
     Specify default compute dimensions for parallel offload regions
     that do not explicitly specify.  The GEOM value is a triple of
     ':'-separated sizes, in order 'gang', 'worker' and, 'vector'.  A
     size can be omitted, to use a target-specific default value.

‘-fopenmp’
     Enable handling of OpenMP directives ‘#pragma omp’ in C/C++ and
     ‘!$omp’ in Fortran.  When ‘-fopenmp’ is specified, the compiler
     generates parallel code according to the OpenMP Application Program
     Interface v4.5 <https://www.openmp.org>.  This option implies
     ‘-pthread’, and thus is only supported on targets that have support
     for ‘-pthread’.  ‘-fopenmp’ implies ‘-fopenmp-simd’.

‘-fopenmp-simd’
     Enable handling of OpenMP's SIMD directives with ‘#pragma omp’ in
     C/C++ and ‘!$omp’ in Fortran.  Other OpenMP directives are ignored.

‘-fpermitted-flt-eval-methods=STYLE’
     ISO/IEC TS 18661-3 defines new permissible values for
     ‘FLT_EVAL_METHOD’ that indicate that operations and constants with
     a semantic type that is an interchange or extended format should be
     evaluated to the precision and range of that type.  These new
     values are a superset of those permitted under C99/C11, which does
     not specify the meaning of other positive values of
     ‘FLT_EVAL_METHOD’.  As such, code conforming to C11 may not have
     been written expecting the possibility of the new values.

     ‘-fpermitted-flt-eval-methods’ specifies whether the compiler
     should allow only the values of ‘FLT_EVAL_METHOD’ specified in
     C99/C11, or the extended set of values specified in ISO/IEC TS
     18661-3.

     STYLE is either ‘c11’ or ‘ts-18661-3’ as appropriate.

     The default when in a standards compliant mode (‘-std=c11’ or
     similar) is ‘-fpermitted-flt-eval-methods=c11’.  The default when
     in a GNU dialect (‘-std=gnu11’ or similar) is
     ‘-fpermitted-flt-eval-methods=ts-18661-3’.

‘-fplan9-extensions’
     Accept some non-standard constructs used in Plan 9 code.

     This enables ‘-fms-extensions’, permits passing pointers to
     structures with anonymous fields to functions that expect pointers
     to elements of the type of the field, and permits referring to
     anonymous fields declared using a typedef.  *Note Unnamed
     struct/union fields within structs/unions: Unnamed Fields, for
     details.  This is only supported for C, not C++.

‘-fsigned-bitfields’
‘-funsigned-bitfields’
‘-fno-signed-bitfields’
‘-fno-unsigned-bitfields’
     These options control whether a bit-field is signed or unsigned,
     when the declaration does not use either ‘signed’ or ‘unsigned’.
     By default, such a bit-field is signed, because this is consistent:
     the basic integer types such as ‘int’ are signed types.

‘-fsigned-char’
     Let the type ‘char’ be signed, like ‘signed char’.

     Note that this is equivalent to ‘-fno-unsigned-char’, which is the
     negative form of ‘-funsigned-char’.  Likewise, the option
     ‘-fno-signed-char’ is equivalent to ‘-funsigned-char’.

‘-funsigned-char’
     Let the type ‘char’ be unsigned, like ‘unsigned char’.

     Each kind of machine has a default for what ‘char’ should be.  It
     is either like ‘unsigned char’ by default or like ‘signed char’ by
     default.

     Ideally, a portable program should always use ‘signed char’ or
     ‘unsigned char’ when it depends on the signedness of an object.
     But many programs have been written to use plain ‘char’ and expect
     it to be signed, or expect it to be unsigned, depending on the
     machines they were written for.  This option, and its inverse, let
     you make such a program work with the opposite default.

     The type ‘char’ is always a distinct type from each of ‘signed
     char’ or ‘unsigned char’, even though its behavior is always just
     like one of those two.

‘-fsso-struct=ENDIANNESS’
     Set the default scalar storage order of structures and unions to
     the specified endianness.  The accepted values are ‘big-endian’,
     ‘little-endian’ and ‘native’ for the native endianness of the
     target (the default).  This option is not supported for C++.

     *Warning:* the ‘-fsso-struct’ switch causes GCC to generate code
     that is not binary compatible with code generated without it if the
     specified endianness is not the native endianness of the target.


File: gcc.info,  Node: C++ Dialect Options,  Next: Objective-C and Objective-C++ Dialect Options,  Prev: C Dialect Options,  Up: Invoking GCC

3.5 Options Controlling C++ Dialect
===================================

This section describes the command-line options that are only meaningful
for C++ programs.  You can also use most of the GNU compiler options
regardless of what language your program is in.  For example, you might
compile a file ‘firstClass.C’ like this:

     g++ -g -fstrict-enums -O -c firstClass.C

In this example, only ‘-fstrict-enums’ is an option meant only for C++
programs; you can use the other options with any language supported by
GCC.

 Some options for compiling C programs, such as ‘-std’, are also
relevant for C++ programs.  *Note Options Controlling C Dialect: C
Dialect Options.

 Here is a list of options that are _only_ for compiling C++ programs:

‘-fabi-version=N’
     Use version N of the C++ ABI.  The default is version 0.

     Version 0 refers to the version conforming most closely to the C++
     ABI specification.  Therefore, the ABI obtained using version 0
     will change in different versions of G++ as ABI bugs are fixed.

     Version 1 is the version of the C++ ABI that first appeared in G++
     3.2.

     Version 2 is the version of the C++ ABI that first appeared in G++
     3.4, and was the default through G++ 4.9.

     Version 3 corrects an error in mangling a constant address as a
     template argument.

     Version 4, which first appeared in G++ 4.5, implements a standard
     mangling for vector types.

     Version 5, which first appeared in G++ 4.6, corrects the mangling
     of attribute const/volatile on function pointer types, decltype of
     a plain decl, and use of a function parameter in the declaration of
     another parameter.

     Version 6, which first appeared in G++ 4.7, corrects the promotion
     behavior of C++11 scoped enums and the mangling of template
     argument packs, const/static_cast, prefix ++ and -, and a class
     scope function used as a template argument.

     Version 7, which first appeared in G++ 4.8, that treats nullptr_t
     as a builtin type and corrects the mangling of lambdas in default
     argument scope.

     Version 8, which first appeared in G++ 4.9, corrects the
     substitution behavior of function types with
     function-cv-qualifiers.

     Version 9, which first appeared in G++ 5.2, corrects the alignment
     of ‘nullptr_t’.

     Version 10, which first appeared in G++ 6.1, adds mangling of
     attributes that affect type identity, such as ia32 calling
     convention attributes (e.g. ‘stdcall’).

     Version 11, which first appeared in G++ 7, corrects the mangling of
     sizeof...  expressions and operator names.  For multiple entities
     with the same name within a function, that are declared in
     different scopes, the mangling now changes starting with the
     twelfth occurrence.  It also implies ‘-fnew-inheriting-ctors’.

     Version 12, which first appeared in G++ 8, corrects the calling
     conventions for empty classes on the x86_64 target and for classes
     with only deleted copy/move constructors.  It accidentally changes
     the calling convention for classes with a deleted copy constructor
     and a trivial move constructor.

     Version 13, which first appeared in G++ 8.2, fixes the accidental
     change in version 12.

     Version 14, which first appeared in G++ 10, corrects the mangling
     of the nullptr expression.

     Version 15, which first appeared in G++ 11, changes the mangling of
     ‘__alignof__’ to be distinct from that of ‘alignof’, and dependent
     operator names.

     See also ‘-Wabi’.

‘-fabi-compat-version=N’
     On targets that support strong aliases, G++ works around mangling
     changes by creating an alias with the correct mangled name when
     defining a symbol with an incorrect mangled name.  This switch
     specifies which ABI version to use for the alias.

     With ‘-fabi-version=0’ (the default), this defaults to 11 (GCC 7
     compatibility).  If another ABI version is explicitly selected,
     this defaults to 0.  For compatibility with GCC versions 3.2
     through 4.9, use ‘-fabi-compat-version=2’.

     If this option is not provided but ‘-Wabi=N’ is, that version is
     used for compatibility aliases.  If this option is provided along
     with ‘-Wabi’ (without the version), the version from this option is
     used for the warning.

‘-fno-access-control’
     Turn off all access checking.  This switch is mainly useful for
     working around bugs in the access control code.

‘-faligned-new’
     Enable support for C++17 ‘new’ of types that require more alignment
     than ‘void* ::operator new(std::size_t)’ provides.  A numeric
     argument such as ‘-faligned-new=32’ can be used to specify how much
     alignment (in bytes) is provided by that function, but few users
     will need to override the default of ‘alignof(std::max_align_t)’.

     This flag is enabled by default for ‘-std=c++17’.

‘-fchar8_t’
‘-fno-char8_t’
     Enable support for ‘char8_t’ as adopted for C++20.  This includes
     the addition of a new ‘char8_t’ fundamental type, changes to the
     types of UTF-8 string and character literals, new signatures for
     user-defined literals, associated standard library updates, and new
     ‘__cpp_char8_t’ and ‘__cpp_lib_char8_t’ feature test macros.

     This option enables functions to be overloaded for ordinary and
     UTF-8 strings:

          int f(const char *);    // #1
          int f(const char8_t *); // #2
          int v1 = f("text");     // Calls #1
          int v2 = f(u8"text");   // Calls #2

     and introduces new signatures for user-defined literals:

          int operator""_udl1(char8_t);
          int v3 = u8'x'_udl1;
          int operator""_udl2(const char8_t*, std::size_t);
          int v4 = u8"text"_udl2;
          template<typename T, T...> int operator""_udl3();
          int v5 = u8"text"_udl3;

     The change to the types of UTF-8 string and character literals
     introduces incompatibilities with ISO C++11 and later standards.
     For example, the following code is well-formed under ISO C++11, but
     is ill-formed when ‘-fchar8_t’ is specified.

          char ca[] = u8"xx";     // error: char-array initialized from wide
                                  //        string
          const char *cp = u8"xx";// error: invalid conversion from
                                  //        `const char8_t*' to `const char*'
          int f(const char*);
          auto v = f(u8"xx");     // error: invalid conversion from
                                  //        `const char8_t*' to `const char*'
          std::string s{u8"xx"};  // error: no matching function for call to
                                  //        `std::basic_string<char>::basic_string()'
          using namespace std::literals;
          s = u8"xx"s;            // error: conversion from
                                  //        `basic_string<char8_t>' to non-scalar
                                  //        type `basic_string<char>' requested

‘-fcheck-new’
     Check that the pointer returned by ‘operator new’ is non-null
     before attempting to modify the storage allocated.  This check is
     normally unnecessary because the C++ standard specifies that
     ‘operator new’ only returns ‘0’ if it is declared ‘throw()’, in
     which case the compiler always checks the return value even without
     this option.  In all other cases, when ‘operator new’ has a
     non-empty exception specification, memory exhaustion is signalled
     by throwing ‘std::bad_alloc’.  See also ‘new (nothrow)’.

‘-fconcepts’
‘-fconcepts-ts’
     Below ‘-std=c++20’, ‘-fconcepts’ enables support for the C++
     Extensions for Concepts Technical Specification, ISO 19217 (2015).

     With ‘-std=c++20’ and above, Concepts are part of the language
     standard, so ‘-fconcepts’ defaults to on.  But the standard
     specification of Concepts differs significantly from the TS, so
     some constructs that were allowed in the TS but didn't make it into
     the standard can still be enabled by ‘-fconcepts-ts’.

‘-fconstexpr-depth=N’
     Set the maximum nested evaluation depth for C++11 constexpr
     functions to N.  A limit is needed to detect endless recursion
     during constant expression evaluation.  The minimum specified by
     the standard is 512.

‘-fconstexpr-cache-depth=N’
     Set the maximum level of nested evaluation depth for C++11
     constexpr functions that will be cached to N.  This is a heuristic
     that trades off compilation speed (when the cache avoids repeated
     calculations) against memory consumption (when the cache grows very
     large from highly recursive evaluations).  The default is 8.  Very
     few users are likely to want to adjust it, but if your code does
     heavy constexpr calculations you might want to experiment to find
     which value works best for you.

‘-fconstexpr-fp-except’
     Annex F of the C standard specifies that IEC559 floating point
     exceptions encountered at compile time should not stop compilation.
     C++ compilers have historically not followed this guidance, instead
     treating floating point division by zero as non-constant even
     though it has a well defined value.  This flag tells the compiler
     to give Annex F priority over other rules saying that a particular
     operation is undefined.

          constexpr float inf = 1./0.; // OK with -fconstexpr-fp-except

‘-fconstexpr-loop-limit=N’
     Set the maximum number of iterations for a loop in C++14 constexpr
     functions to N.  A limit is needed to detect infinite loops during
     constant expression evaluation.  The default is 262144 (1<<18).

‘-fconstexpr-ops-limit=N’
     Set the maximum number of operations during a single constexpr
     evaluation.  Even when number of iterations of a single loop is
     limited with the above limit, if there are several nested loops and
     each of them has many iterations but still smaller than the above
     limit, or if in a body of some loop or even outside of a loop too
     many expressions need to be evaluated, the resulting constexpr
     evaluation might take too long.  The default is 33554432 (1<<25).

‘-fcoroutines’
     Enable support for the C++ coroutines extension (experimental).

‘-fno-elide-constructors’
     The C++ standard allows an implementation to omit creating a
     temporary that is only used to initialize another object of the
     same type.  Specifying this option disables that optimization, and
     forces G++ to call the copy constructor in all cases.  This option
     also causes G++ to call trivial member functions which otherwise
     would be expanded inline.

     In C++17, the compiler is required to omit these temporaries, but
     this option still affects trivial member functions.

‘-fno-enforce-eh-specs’
     Don't generate code to check for violation of exception
     specifications at run time.  This option violates the C++ standard,
     but may be useful for reducing code size in production builds, much
     like defining ‘NDEBUG’.  This does not give user code permission to
     throw exceptions in violation of the exception specifications; the
     compiler still optimizes based on the specifications, so throwing
     an unexpected exception results in undefined behavior at run time.

‘-fextern-tls-init’
‘-fno-extern-tls-init’
     The C++11 and OpenMP standards allow ‘thread_local’ and
     ‘threadprivate’ variables to have dynamic (runtime) initialization.
     To support this, any use of such a variable goes through a wrapper
     function that performs any necessary initialization.  When the use
     and definition of the variable are in the same translation unit,
     this overhead can be optimized away, but when the use is in a
     different translation unit there is significant overhead even if
     the variable doesn't actually need dynamic initialization.  If the
     programmer can be sure that no use of the variable in a
     non-defining TU needs to trigger dynamic initialization (either
     because the variable is statically initialized, or a use of the
     variable in the defining TU will be executed before any uses in
     another TU), they can avoid this overhead with the
     ‘-fno-extern-tls-init’ option.

     On targets that support symbol aliases, the default is
     ‘-fextern-tls-init’.  On targets that do not support symbol
     aliases, the default is ‘-fno-extern-tls-init’.

‘-ffold-simple-inlines’
‘-fno-fold-simple-inlines’
     Permit the C++ frontend to fold calls to ‘std::move’,
     ‘std::forward’, ‘std::addressof’ and ‘std::as_const’.  In contrast
     to inlining, this means no debug information will be generated for
     such calls.  Since these functions are rarely interesting to debug,
     this flag is enabled by default unless ‘-fno-inline’ is active.

‘-fno-gnu-keywords’
     Do not recognize ‘typeof’ as a keyword, so that code can use this
     word as an identifier.  You can use the keyword ‘__typeof__’
     instead.  This option is implied by the strict ISO C++ dialects:
     ‘-ansi’, ‘-std=c++98’, ‘-std=c++11’, etc.

‘-fimplicit-constexpr’
     Make inline functions implicitly constexpr, if they satisfy the
     requirements for a constexpr function.  This option can be used in
     C++14 mode or later.  This can result in initialization changing
     from dynamic to static and other optimizations.

‘-fno-implicit-templates’
     Never emit code for non-inline templates that are instantiated
     implicitly (i.e. by use); only emit code for explicit
     instantiations.  If you use this option, you must take care to
     structure your code to include all the necessary explicit
     instantiations to avoid getting undefined symbols at link time.
     *Note Template Instantiation::, for more information.

‘-fno-implicit-inline-templates’
     Don't emit code for implicit instantiations of inline templates,
     either.  The default is to handle inlines differently so that
     compiles with and without optimization need the same set of
     explicit instantiations.

‘-fno-implement-inlines’
     To save space, do not emit out-of-line copies of inline functions
     controlled by ‘#pragma implementation’.  This causes linker errors
     if these functions are not inlined everywhere they are called.

‘-fmodules-ts’
‘-fno-modules-ts’
     Enable support for C++20 modules (*note C++ Modules::).  The
     ‘-fno-modules-ts’ is usually not needed, as that is the default.
     Even though this is a C++20 feature, it is not currently implicitly
     enabled by selecting that standard version.

‘-fmodule-header’
‘-fmodule-header=user’
‘-fmodule-header=system’
     Compile a header file to create an importable header unit.

‘-fmodule-implicit-inline’
     Member functions defined in their class definitions are not
     implicitly inline for modular code.  This is different to
     traditional C++ behavior, for good reasons.  However, it may result
     in a difficulty during code porting.  This option makes such
     function definitions implicitly inline.  It does however generate
     an ABI incompatibility, so you must use it everywhere or nowhere.
     (Such definitions outside of a named module remain implicitly
     inline, regardless.)

‘-fno-module-lazy’
     Disable lazy module importing and module mapper creation.

‘-fmodule-mapper=[HOSTNAME]:PORT[?IDENT]’
‘-fmodule-mapper=|PROGRAM[?IDENT] ARGS...’
‘-fmodule-mapper==SOCKET[?IDENT]’
‘-fmodule-mapper=<>[INOUT][?IDENT]’
‘-fmodule-mapper=<IN>OUT[?IDENT]’
‘-fmodule-mapper=FILE[?IDENT]’
     An oracle to query for module name to filename mappings.  If
     unspecified the ‘CXX_MODULE_MAPPER’ environment variable is used,
     and if that is unset, an in-process default is provided.

‘-fmodule-only’
     Only emit the Compiled Module Interface, inhibiting any object
     file.

‘-fms-extensions’
     Disable Wpedantic warnings about constructs used in MFC, such as
     implicit int and getting a pointer to member function via
     non-standard syntax.

‘-fnew-inheriting-ctors’
     Enable the P0136 adjustment to the semantics of C++11 constructor
     inheritance.  This is part of C++17 but also considered to be a
     Defect Report against C++11 and C++14.  This flag is enabled by
     default unless ‘-fabi-version=10’ or lower is specified.

‘-fnew-ttp-matching’
     Enable the P0522 resolution to Core issue 150, template template
     parameters and default arguments: this allows a template with
     default template arguments as an argument for a template template
     parameter with fewer template parameters.  This flag is enabled by
     default for ‘-std=c++17’.

‘-fno-nonansi-builtins’
     Disable built-in declarations of functions that are not mandated by
     ANSI/ISO C.  These include ‘ffs’, ‘alloca’, ‘_exit’, ‘index’,
     ‘bzero’, ‘conjf’, and other related functions.

‘-fnothrow-opt’
     Treat a ‘throw()’ exception specification as if it were a
     ‘noexcept’ specification to reduce or eliminate the text size
     overhead relative to a function with no exception specification.
     If the function has local variables of types with non-trivial
     destructors, the exception specification actually makes the
     function smaller because the EH cleanups for those variables can be
     optimized away.  The semantic effect is that an exception thrown
     out of a function with such an exception specification results in a
     call to ‘terminate’ rather than ‘unexpected’.

‘-fno-operator-names’
     Do not treat the operator name keywords ‘and’, ‘bitand’, ‘bitor’,
     ‘compl’, ‘not’, ‘or’ and ‘xor’ as synonyms as keywords.

‘-fno-optional-diags’
     Disable diagnostics that the standard says a compiler does not need
     to issue.  Currently, the only such diagnostic issued by G++ is the
     one for a name having multiple meanings within a class.

‘-fpermissive’
     Downgrade some diagnostics about nonconformant code from errors to
     warnings.  Thus, using ‘-fpermissive’ allows some nonconforming
     code to compile.

‘-fno-pretty-templates’
     When an error message refers to a specialization of a function
     template, the compiler normally prints the signature of the
     template followed by the template arguments and any typedefs or
     typenames in the signature (e.g. ‘void f(T) [with T = int]’ rather
     than ‘void f(int)’) so that it's clear which template is involved.
     When an error message refers to a specialization of a class
     template, the compiler omits any template arguments that match the
     default template arguments for that template.  If either of these
     behaviors make it harder to understand the error message rather
     than easier, you can use ‘-fno-pretty-templates’ to disable them.

‘-fno-rtti’
     Disable generation of information about every class with virtual
     functions for use by the C++ run-time type identification features
     (‘dynamic_cast’ and ‘typeid’).  If you don't use those parts of the
     language, you can save some space by using this flag.  Note that
     exception handling uses the same information, but G++ generates it
     as needed.  The ‘dynamic_cast’ operator can still be used for casts
     that do not require run-time type information, i.e. casts to ‘void
     *’ or to unambiguous base classes.

     Mixing code compiled with ‘-frtti’ with that compiled with
     ‘-fno-rtti’ may not work.  For example, programs may fail to link
     if a class compiled with ‘-fno-rtti’ is used as a base for a class
     compiled with ‘-frtti’.

‘-fsized-deallocation’
     Enable the built-in global declarations
          void operator delete (void *, std::size_t) noexcept;
          void operator delete[] (void *, std::size_t) noexcept;
     as introduced in C++14.  This is useful for user-defined
     replacement deallocation functions that, for example, use the size
     of the object to make deallocation faster.  Enabled by default
     under ‘-std=c++14’ and above.  The flag ‘-Wsized-deallocation’
     warns about places that might want to add a definition.

‘-fstrict-enums’
     Allow the compiler to optimize using the assumption that a value of
     enumerated type can only be one of the values of the enumeration
     (as defined in the C++ standard; basically, a value that can be
     represented in the minimum number of bits needed to represent all
     the enumerators).  This assumption may not be valid if the program
     uses a cast to convert an arbitrary integer value to the enumerated
     type.

‘-fstrong-eval-order’
     Evaluate member access, array subscripting, and shift expressions
     in left-to-right order, and evaluate assignment in right-to-left
     order, as adopted for C++17.  Enabled by default with ‘-std=c++17’.
     ‘-fstrong-eval-order=some’ enables just the ordering of member
     access and shift expressions, and is the default without
     ‘-std=c++17’.

‘-ftemplate-backtrace-limit=N’
     Set the maximum number of template instantiation notes for a single
     warning or error to N.  The default value is 10.

‘-ftemplate-depth=N’
     Set the maximum instantiation depth for template classes to N.  A
     limit on the template instantiation depth is needed to detect
     endless recursions during template class instantiation.  ANSI/ISO
     C++ conforming programs must not rely on a maximum depth greater
     than 17 (changed to 1024 in C++11).  The default value is 900, as
     the compiler can run out of stack space before hitting 1024 in some
     situations.

‘-fno-threadsafe-statics’
     Do not emit the extra code to use the routines specified in the C++
     ABI for thread-safe initialization of local statics.  You can use
     this option to reduce code size slightly in code that doesn't need
     to be thread-safe.

‘-fuse-cxa-atexit’
     Register destructors for objects with static storage duration with
     the ‘__cxa_atexit’ function rather than the ‘atexit’ function.
     This option is required for fully standards-compliant handling of
     static destructors, but only works if your C library supports
     ‘__cxa_atexit’.

‘-fno-use-cxa-get-exception-ptr’
     Don't use the ‘__cxa_get_exception_ptr’ runtime routine.  This
     causes ‘std::uncaught_exception’ to be incorrect, but is necessary
     if the runtime routine is not available.

‘-fvisibility-inlines-hidden’
     This switch declares that the user does not attempt to compare
     pointers to inline functions or methods where the addresses of the
     two functions are taken in different shared objects.

     The effect of this is that GCC may, effectively, mark inline
     methods with ‘__attribute__ ((visibility ("hidden")))’ so that they
     do not appear in the export table of a DSO and do not require a PLT
     indirection when used within the DSO.  Enabling this option can
     have a dramatic effect on load and link times of a DSO as it
     massively reduces the size of the dynamic export table when the
     library makes heavy use of templates.

     The behavior of this switch is not quite the same as marking the
     methods as hidden directly, because it does not affect static
     variables local to the function or cause the compiler to deduce
     that the function is defined in only one shared object.

     You may mark a method as having a visibility explicitly to negate
     the effect of the switch for that method.  For example, if you do
     want to compare pointers to a particular inline method, you might
     mark it as having default visibility.  Marking the enclosing class
     with explicit visibility has no effect.

     Explicitly instantiated inline methods are unaffected by this
     option as their linkage might otherwise cross a shared library
     boundary.  *Note Template Instantiation::.

‘-fvisibility-ms-compat’
     This flag attempts to use visibility settings to make GCC's C++
     linkage model compatible with that of Microsoft Visual Studio.

     The flag makes these changes to GCC's linkage model:

       1. It sets the default visibility to ‘hidden’, like
          ‘-fvisibility=hidden’.

       2. Types, but not their members, are not hidden by default.

       3. The One Definition Rule is relaxed for types without explicit
          visibility specifications that are defined in more than one
          shared object: those declarations are permitted if they are
          permitted when this option is not used.

     In new code it is better to use ‘-fvisibility=hidden’ and export
     those classes that are intended to be externally visible.
     Unfortunately it is possible for code to rely, perhaps
     accidentally, on the Visual Studio behavior.

     Among the consequences of these changes are that static data
     members of the same type with the same name but defined in
     different shared objects are different, so changing one does not
     change the other; and that pointers to function members defined in
     different shared objects may not compare equal.  When this flag is
     given, it is a violation of the ODR to define types with the same
     name differently.

‘-fno-weak’
     Do not use weak symbol support, even if it is provided by the
     linker.  By default, G++ uses weak symbols if they are available.
     This option exists only for testing, and should not be used by
     end-users; it results in inferior code and has no benefits.  This
     option may be removed in a future release of G++.

‘-fext-numeric-literals (C++ and Objective-C++ only)’
     Accept imaginary, fixed-point, or machine-defined literal number
     suffixes as GNU extensions.  When this option is turned off these
     suffixes are treated as C++11 user-defined literal numeric
     suffixes.  This is on by default for all pre-C++11 dialects and all
     GNU dialects: ‘-std=c++98’, ‘-std=gnu++98’, ‘-std=gnu++11’,
     ‘-std=gnu++14’.  This option is off by default for ISO C++11
     onwards (‘-std=c++11’, ...).

‘-nostdinc++’
     Do not search for header files in the standard directories specific
     to C++, but do still search the other standard directories.  (This
     option is used when building the C++ library.)

‘-flang-info-include-translate’
‘-flang-info-include-translate-not’
‘-flang-info-include-translate=HEADER’
     Inform of include translation events.  The first will note accepted
     include translations, the second will note declined include
     translations.  The HEADER form will inform of include translations
     relating to that specific header.  If HEADER is of the form
     ‘"user"’ or ‘<system>’ it will be resolved to a specific user or
     system header using the include path.

‘-flang-info-module-cmi’
‘-flang-info-module-cmi=MODULE’
     Inform of Compiled Module Interface pathnames.  The first will note
     all read CMI pathnames.  The MODULE form will not reading a
     specific module's CMI. MODULE may be a named module or a
     header-unit (the latter indicated by either being a pathname
     containing directory separators or enclosed in ‘<>’ or ‘""’).

‘-stdlib=LIBSTDC++,LIBC++’
     When G++ is configured to support this option, it allows
     specification of alternate C++ runtime libraries.  Two options are
     available: LIBSTDC++ (the default, native C++ runtime for G++) and
     LIBC++ which is the C++ runtime installed on some operating systems
     (e.g.  Darwin versions from Darwin11 onwards).  The option switches
     G++ to use the headers from the specified library and to emit
     ‘-lstdc++’ or ‘-lc++’ respectively, when a C++ runtime is required
     for linking.

 In addition, these warning options have meanings only for C++ programs:

‘-Wabi-tag (C++ and Objective-C++ only)’
     Warn when a type with an ABI tag is used in a context that does not
     have that ABI tag.  See *note C++ Attributes:: for more information
     about ABI tags.

‘-Wcomma-subscript (C++ and Objective-C++ only)’
     Warn about uses of a comma expression within a subscripting
     expression.  This usage was deprecated in C++20 and is going to be
     removed in C++23.  However, a comma expression wrapped in ‘( )’ is
     not deprecated.  Example:

          void f(int *a, int b, int c) {
              a[b,c];     // deprecated in C++20, invalid in C++23
              a[(b,c)];   // OK
          }

     In C++23 it is valid to have comma separated expressions in a
     subscript when an overloaded subscript operator is found and
     supports the right number and types of arguments.  G++ will accept
     the formerly valid syntax for code that is not valid in C++23 but
     used to be valid but deprecated in C++20 with a pedantic warning
     that can be disabled with ‘-Wno-comma-subscript’.

     Enabled by default with ‘-std=c++20’ unless ‘-Wno-deprecated’, and
     with ‘-std=c++23’ regardless of ‘-Wno-deprecated’.

‘-Wctad-maybe-unsupported (C++ and Objective-C++ only)’
     Warn when performing class template argument deduction (CTAD) on a
     type with no explicitly written deduction guides.  This warning
     will point out cases where CTAD succeeded only because the compiler
     synthesized the implicit deduction guides, which might not be what
     the programmer intended.  Certain style guides allow CTAD only on
     types that specifically "opt-in"; i.e., on types that are designed
     to support CTAD. This warning can be suppressed with the following
     pattern:

          struct allow_ctad_t; // any name works
          template <typename T> struct S {
            S(T) { }
          };
          S(allow_ctad_t) -> S<void>; // guide with incomplete parameter type will never be considered

‘-Wctor-dtor-privacy (C++ and Objective-C++ only)’
     Warn when a class seems unusable because all the constructors or
     destructors in that class are private, and it has neither friends
     nor public static member functions.  Also warn if there are no
     non-private methods, and there's at least one private member
     function that isn't a constructor or destructor.

‘-Wdelete-non-virtual-dtor (C++ and Objective-C++ only)’
     Warn when ‘delete’ is used to destroy an instance of a class that
     has virtual functions and non-virtual destructor.  It is unsafe to
     delete an instance of a derived class through a pointer to a base
     class if the base class does not have a virtual destructor.  This
     warning is enabled by ‘-Wall’.

‘-Wdeprecated-copy (C++ and Objective-C++ only)’
     Warn that the implicit declaration of a copy constructor or copy
     assignment operator is deprecated if the class has a user-provided
     copy constructor or copy assignment operator, in C++11 and up.
     This warning is enabled by ‘-Wextra’.  With
     ‘-Wdeprecated-copy-dtor’, also deprecate if the class has a
     user-provided destructor.

‘-Wno-deprecated-enum-enum-conversion (C++ and Objective-C++ only)’
     Disable the warning about the case when the usual arithmetic
     conversions are applied on operands where one is of enumeration
     type and the other is of a different enumeration type.  This
     conversion was deprecated in C++20.  For example:

          enum E1 { e };
          enum E2 { f };
          int k = f - e;

     ‘-Wdeprecated-enum-enum-conversion’ is enabled by default with
     ‘-std=c++20’.  In pre-C++20 dialects, this warning can be enabled
     by ‘-Wenum-conversion’.

‘-Wno-deprecated-enum-float-conversion (C++ and Objective-C++ only)’
     Disable the warning about the case when the usual arithmetic
     conversions are applied on operands where one is of enumeration
     type and the other is of a floating-point type.  This conversion
     was deprecated in C++20.  For example:

          enum E1 { e };
          enum E2 { f };
          bool b = e <= 3.7;

     ‘-Wdeprecated-enum-float-conversion’ is enabled by default with
     ‘-std=c++20’.  In pre-C++20 dialects, this warning can be enabled
     by ‘-Wenum-conversion’.

‘-Wno-init-list-lifetime (C++ and Objective-C++ only)’
     Do not warn about uses of ‘std::initializer_list’ that are likely
     to result in dangling pointers.  Since the underlying array for an
     ‘initializer_list’ is handled like a normal C++ temporary object,
     it is easy to inadvertently keep a pointer to the array past the
     end of the array's lifetime.  For example:

        • If a function returns a temporary ‘initializer_list’, or a
          local ‘initializer_list’ variable, the array's lifetime ends
          at the end of the return statement, so the value returned has
          a dangling pointer.

        • If a new-expression creates an ‘initializer_list’, the array
          only lives until the end of the enclosing full-expression, so
          the ‘initializer_list’ in the heap has a dangling pointer.

        • When an ‘initializer_list’ variable is assigned from a
          brace-enclosed initializer list, the temporary array created
          for the right side of the assignment only lives until the end
          of the full-expression, so at the next statement the
          ‘initializer_list’ variable has a dangling pointer.

               // li's initial underlying array lives as long as li
               std::initializer_list<int> li = { 1,2,3 };
               // assignment changes li to point to a temporary array
               li = { 4, 5 };
               // now the temporary is gone and li has a dangling pointer
               int i = li.begin()[0] // undefined behavior

        • When a list constructor stores the ‘begin’ pointer from the
          ‘initializer_list’ argument, this doesn't extend the lifetime
          of the array, so if a class variable is constructed from a
          temporary ‘initializer_list’, the pointer is left dangling by
          the end of the variable declaration statement.

‘-Winvalid-imported-macros’
     Verify all imported macro definitions are valid at the end of
     compilation.  This is not enabled by default, as it requires
     additional processing to determine.  It may be useful when
     preparing sets of header-units to ensure consistent macros.

‘-Wno-literal-suffix (C++ and Objective-C++ only)’
     Do not warn when a string or character literal is followed by a
     ud-suffix which does not begin with an underscore.  As a conforming
     extension, GCC treats such suffixes as separate preprocessing
     tokens in order to maintain backwards compatibility with code that
     uses formatting macros from ‘<inttypes.h>’.  For example:

          #define __STDC_FORMAT_MACROS
          #include <inttypes.h>
          #include <stdio.h>

          int main() {
            int64_t i64 = 123;
            printf("My int64: %" PRId64"\n", i64);
          }

     In this case, ‘PRId64’ is treated as a separate preprocessing
     token.

     This option also controls warnings when a user-defined literal
     operator is declared with a literal suffix identifier that doesn't
     begin with an underscore.  Literal suffix identifiers that don't
     begin with an underscore are reserved for future standardization.

     These warnings are enabled by default.

‘-Wno-narrowing (C++ and Objective-C++ only)’
     For C++11 and later standards, narrowing conversions are diagnosed
     by default, as required by the standard.  A narrowing conversion
     from a constant produces an error, and a narrowing conversion from
     a non-constant produces a warning, but ‘-Wno-narrowing’ suppresses
     the diagnostic.  Note that this does not affect the meaning of
     well-formed code; narrowing conversions are still considered
     ill-formed in SFINAE contexts.

     With ‘-Wnarrowing’ in C++98, warn when a narrowing conversion
     prohibited by C++11 occurs within ‘{ }’, e.g.

          int i = { 2.2 }; // error: narrowing from double to int

     This flag is included in ‘-Wall’ and ‘-Wc++11-compat’.

‘-Wnoexcept (C++ and Objective-C++ only)’
     Warn when a noexcept-expression evaluates to false because of a
     call to a function that does not have a non-throwing exception
     specification (i.e.  ‘throw()’ or ‘noexcept’) but is known by the
     compiler to never throw an exception.

‘-Wnoexcept-type (C++ and Objective-C++ only)’
     Warn if the C++17 feature making ‘noexcept’ part of a function type
     changes the mangled name of a symbol relative to C++14.  Enabled by
     ‘-Wabi’ and ‘-Wc++17-compat’.

     As an example:

          template <class T> void f(T t) { t(); };
          void g() noexcept;
          void h() { f(g); }

     In C++14, ‘f’ calls ‘f<void(*)()>’, but in C++17 it calls
     ‘f<void(*)()noexcept>’.

‘-Wclass-memaccess (C++ and Objective-C++ only)’
     Warn when the destination of a call to a raw memory function such
     as ‘memset’ or ‘memcpy’ is an object of class type, and when
     writing into such an object might bypass the class non-trivial or
     deleted constructor or copy assignment, violate const-correctness
     or encapsulation, or corrupt virtual table pointers.  Modifying the
     representation of such objects may violate invariants maintained by
     member functions of the class.  For example, the call to ‘memset’
     below is undefined because it modifies a non-trivial class object
     and is, therefore, diagnosed.  The safe way to either initialize or
     clear the storage of objects of such types is by using the
     appropriate constructor or assignment operator, if one is
     available.
          std::string str = "abc";
          memset (&str, 0, sizeof str);
     The ‘-Wclass-memaccess’ option is enabled by ‘-Wall’.  Explicitly
     casting the pointer to the class object to ‘void *’ or to a type
     that can be safely accessed by the raw memory function suppresses
     the warning.

‘-Wnon-virtual-dtor (C++ and Objective-C++ only)’
     Warn when a class has virtual functions and an accessible
     non-virtual destructor itself or in an accessible polymorphic base
     class, in which case it is possible but unsafe to delete an
     instance of a derived class through a pointer to the class itself
     or base class.  This warning is automatically enabled if ‘-Weffc++’
     is specified.

‘-Wregister (C++ and Objective-C++ only)’
     Warn on uses of the ‘register’ storage class specifier, except when
     it is part of the GNU *note Explicit Register Variables::
     extension.  The use of the ‘register’ keyword as storage class
     specifier has been deprecated in C++11 and removed in C++17.
     Enabled by default with ‘-std=c++17’.

‘-Wreorder (C++ and Objective-C++ only)’
     Warn when the order of member initializers given in the code does
     not match the order in which they must be executed.  For instance:

          struct A {
            int i;
            int j;
            A(): j (0), i (1) { }
          };

     The compiler rearranges the member initializers for ‘i’ and ‘j’ to
     match the declaration order of the members, emitting a warning to
     that effect.  This warning is enabled by ‘-Wall’.

‘-Wno-pessimizing-move (C++ and Objective-C++ only)’
     This warning warns when a call to ‘std::move’ prevents copy
     elision.  A typical scenario when copy elision can occur is when
     returning in a function with a class return type, when the
     expression being returned is the name of a non-volatile automatic
     object, and is not a function parameter, and has the same type as
     the function return type.

          struct T {
          ...
          };
          T fn()
          {
            T t;
            ...
            return std::move (t);
          }

     But in this example, the ‘std::move’ call prevents copy elision.

     This warning is enabled by ‘-Wall’.

‘-Wno-redundant-move (C++ and Objective-C++ only)’
     This warning warns about redundant calls to ‘std::move’; that is,
     when a move operation would have been performed even without the
     ‘std::move’ call.  This happens because the compiler is forced to
     treat the object as if it were an rvalue in certain situations such
     as returning a local variable, where copy elision isn't applicable.
     Consider:

          struct T {
          ...
          };
          T fn(T t)
          {
            ...
            return std::move (t);
          }

     Here, the ‘std::move’ call is redundant.  Because G++ implements
     Core Issue 1579, another example is:

          struct T { // convertible to U
          ...
          };
          struct U {
          ...
          };
          U fn()
          {
            T t;
            ...
            return std::move (t);
          }
     In this example, copy elision isn't applicable because the type of
     the expression being returned and the function return type differ,
     yet G++ treats the return value as if it were designated by an
     rvalue.

     This warning is enabled by ‘-Wextra’.

‘-Wrange-loop-construct (C++ and Objective-C++ only)’
     This warning warns when a C++ range-based for-loop is creating an
     unnecessary copy.  This can happen when the range declaration is
     not a reference, but probably should be.  For example:

          struct S { char arr[128]; };
          void fn () {
            S arr[5];
            for (const auto x : arr) { ... }
          }

     It does not warn when the type being copied is a trivially-copyable
     type whose size is less than 64 bytes.

     This warning also warns when a loop variable in a range-based
     for-loop is initialized with a value of a different type resulting
     in a copy.  For example:

          void fn() {
            int arr[10];
            for (const double &x : arr) { ... }
          }

     In the example above, in every iteration of the loop a temporary
     value of type ‘double’ is created and destroyed, to which the
     reference ‘const double &’ is bound.

     This warning is enabled by ‘-Wall’.

‘-Wredundant-tags (C++ and Objective-C++ only)’
     Warn about redundant class-key and enum-key in references to class
     types and enumerated types in contexts where the key can be
     eliminated without causing an ambiguity.  For example:

          struct foo;
          struct foo *p;   // warn that keyword struct can be eliminated

     On the other hand, in this example there is no warning:

          struct foo;
          void foo ();   // "hides" struct foo
          void bar (struct foo&);  // no warning, keyword struct is necessary

‘-Wno-subobject-linkage (C++ and Objective-C++ only)’
     Do not warn if a class type has a base or a field whose type uses
     the anonymous namespace or depends on a type with no linkage.  If a
     type A depends on a type B with no or internal linkage, defining it
     in multiple translation units would be an ODR violation because the
     meaning of B is different in each translation unit.  If A only
     appears in a single translation unit, the best way to silence the
     warning is to give it internal linkage by putting it in an
     anonymous namespace as well.  The compiler doesn't give this
     warning for types defined in the main .C file, as those are
     unlikely to have multiple definitions.  ‘-Wsubobject-linkage’ is
     enabled by default.

‘-Weffc++ (C++ and Objective-C++ only)’
     Warn about violations of the following style guidelines from Scott
     Meyers' ‘Effective C++’ series of books:

        • Define a copy constructor and an assignment operator for
          classes with dynamically-allocated memory.

        • Prefer initialization to assignment in constructors.

        • Have ‘operator=’ return a reference to ‘*this’.

        • Don't try to return a reference when you must return an
          object.

        • Distinguish between prefix and postfix forms of increment and
          decrement operators.

        • Never overload ‘&&’, ‘||’, or ‘,’.

     This option also enables ‘-Wnon-virtual-dtor’, which is also one of
     the effective C++ recommendations.  However, the check is extended
     to warn about the lack of virtual destructor in accessible
     non-polymorphic bases classes too.

     When selecting this option, be aware that the standard library
     headers do not obey all of these guidelines; use ‘grep -v’ to
     filter out those warnings.

‘-Wno-exceptions (C++ and Objective-C++ only)’
     Disable the warning about the case when an exception handler is
     shadowed by another handler, which can point out a wrong ordering
     of exception handlers.

‘-Wstrict-null-sentinel (C++ and Objective-C++ only)’
     Warn about the use of an uncasted ‘NULL’ as sentinel.  When
     compiling only with GCC this is a valid sentinel, as ‘NULL’ is
     defined to ‘__null’.  Although it is a null pointer constant rather
     than a null pointer, it is guaranteed to be of the same size as a
     pointer.  But this use is not portable across different compilers.

‘-Wno-non-template-friend (C++ and Objective-C++ only)’
     Disable warnings when non-template friend functions are declared
     within a template.  In very old versions of GCC that predate
     implementation of the ISO standard, declarations such as ‘friend
     int foo(int)’, where the name of the friend is an unqualified-id,
     could be interpreted as a particular specialization of a template
     function; the warning exists to diagnose compatibility problems,
     and is enabled by default.

‘-Wold-style-cast (C++ and Objective-C++ only)’
     Warn if an old-style (C-style) cast to a non-void type is used
     within a C++ program.  The new-style casts (‘dynamic_cast’,
     ‘static_cast’, ‘reinterpret_cast’, and ‘const_cast’) are less
     vulnerable to unintended effects and much easier to search for.

‘-Woverloaded-virtual (C++ and Objective-C++ only)’
     Warn when a function declaration hides virtual functions from a
     base class.  For example, in:

          struct A {
            virtual void f();
          };

          struct B: public A {
            void f(int);
          };

     the ‘A’ class version of ‘f’ is hidden in ‘B’, and code like:

          B* b;
          b->f();

     fails to compile.

‘-Wno-pmf-conversions (C++ and Objective-C++ only)’
     Disable the diagnostic for converting a bound pointer to member
     function to a plain pointer.

‘-Wsign-promo (C++ and Objective-C++ only)’
     Warn when overload resolution chooses a promotion from unsigned or
     enumerated type to a signed type, over a conversion to an unsigned
     type of the same size.  Previous versions of G++ tried to preserve
     unsignedness, but the standard mandates the current behavior.

‘-Wtemplates (C++ and Objective-C++ only)’
     Warn when a primary template declaration is encountered.  Some
     coding rules disallow templates, and this may be used to enforce
     that rule.  The warning is inactive inside a system header file,
     such as the STL, so one can still use the STL. One may also
     instantiate or specialize templates.

‘-Wmismatched-new-delete (C++ and Objective-C++ only)’
     Warn for mismatches between calls to ‘operator new’ or ‘operator
     delete’ and the corresponding call to the allocation or
     deallocation function.  This includes invocations of C++ ‘operator
     delete’ with pointers returned from either mismatched forms of
     ‘operator new’, or from other functions that allocate objects for
     which the ‘operator delete’ isn't a suitable deallocator, as well
     as calls to other deallocation functions with pointers returned
     from ‘operator new’ for which the deallocation function isn't
     suitable.

     For example, the ‘delete’ expression in the function below is
     diagnosed because it doesn't match the array form of the ‘new’
     expression the pointer argument was returned from.  Similarly, the
     call to ‘free’ is also diagnosed.

          void f ()
          {
            int *a = new int[n];
            delete a;   // warning: mismatch in array forms of expressions

            char *p = new char[n];
            free (p);   // warning: mismatch between new and free
          }

     The related option ‘-Wmismatched-dealloc’ diagnoses mismatches
     involving allocation and deallocation functions other than
     ‘operator new’ and ‘operator delete’.

     ‘-Wmismatched-new-delete’ is included in ‘-Wall’.

‘-Wmismatched-tags (C++ and Objective-C++ only)’
     Warn for declarations of structs, classes, and class templates and
     their specializations with a class-key that does not match either
     the definition or the first declaration if no definition is
     provided.

     For example, the declaration of ‘struct Object’ in the argument
     list of ‘draw’ triggers the warning.  To avoid it, either remove
     the redundant class-key ‘struct’ or replace it with ‘class’ to
     match its definition.
          class Object {
          public:
            virtual ~Object () = 0;
          };
          void draw (struct Object*);

     It is not wrong to declare a class with the class-key ‘struct’ as
     the example above shows.  The ‘-Wmismatched-tags’ option is
     intended to help achieve a consistent style of class declarations.
     In code that is intended to be portable to Windows-based compilers
     the warning helps prevent unresolved references due to the
     difference in the mangling of symbols declared with different
     class-keys.  The option can be used either on its own or in
     conjunction with ‘-Wredundant-tags’.

‘-Wmultiple-inheritance (C++ and Objective-C++ only)’
     Warn when a class is defined with multiple direct base classes.
     Some coding rules disallow multiple inheritance, and this may be
     used to enforce that rule.  The warning is inactive inside a system
     header file, such as the STL, so one can still use the STL. One may
     also define classes that indirectly use multiple inheritance.

‘-Wvirtual-inheritance’
     Warn when a class is defined with a virtual direct base class.
     Some coding rules disallow multiple inheritance, and this may be
     used to enforce that rule.  The warning is inactive inside a system
     header file, such as the STL, so one can still use the STL. One may
     also define classes that indirectly use virtual inheritance.

‘-Wno-virtual-move-assign’
     Suppress warnings about inheriting from a virtual base with a
     non-trivial C++11 move assignment operator.  This is dangerous
     because if the virtual base is reachable along more than one path,
     it is moved multiple times, which can mean both objects end up in
     the moved-from state.  If the move assignment operator is written
     to avoid moving from a moved-from object, this warning can be
     disabled.

‘-Wnamespaces’
     Warn when a namespace definition is opened.  Some coding rules
     disallow namespaces, and this may be used to enforce that rule.
     The warning is inactive inside a system header file, such as the
     STL, so one can still use the STL. One may also use using
     directives and qualified names.

‘-Wno-terminate (C++ and Objective-C++ only)’
     Disable the warning about a throw-expression that will immediately
     result in a call to ‘terminate’.

‘-Wno-vexing-parse (C++ and Objective-C++ only)’
     Warn about the most vexing parse syntactic ambiguity.  This warns
     about the cases when a declaration looks like a variable
     definition, but the C++ language requires it to be interpreted as a
     function declaration.  For instance:

          void f(double a) {
            int i();        // extern int i (void);
            int n(int(a));  // extern int n (int);
          }

     Another example:

          struct S { S(int); };
          void f(double a) {
            S x(int(a));   // extern struct S x (int);
            S y(int());    // extern struct S y (int (*) (void));
            S z();         // extern struct S z (void);
          }

     The warning will suggest options how to deal with such an
     ambiguity; e.g., it can suggest removing the parentheses or using
     braces instead.

     This warning is enabled by default.

‘-Wno-class-conversion (C++ and Objective-C++ only)’
     Do not warn when a conversion function converts an object to the
     same type, to a base class of that type, or to void; such a
     conversion function will never be called.

‘-Wvolatile (C++ and Objective-C++ only)’
     Warn about deprecated uses of the ‘volatile’ qualifier.  This
     includes postfix and prefix ‘++’ and ‘--’ expressions of
     ‘volatile’-qualified types, using simple assignments where the left
     operand is a ‘volatile’-qualified non-class type for their value,
     compound assignments where the left operand is a
     ‘volatile’-qualified non-class type, ‘volatile’-qualified function
     return type, ‘volatile’-qualified parameter type, and structured
     bindings of a ‘volatile’-qualified type.  This usage was deprecated
     in C++20.

     Enabled by default with ‘-std=c++20’.

‘-Wzero-as-null-pointer-constant (C++ and Objective-C++ only)’
     Warn when a literal ‘0’ is used as null pointer constant.  This can
     be useful to facilitate the conversion to ‘nullptr’ in C++11.

‘-Waligned-new’
     Warn about a new-expression of a type that requires greater
     alignment than the ‘alignof(std::max_align_t)’ but uses an
     allocation function without an explicit alignment parameter.  This
     option is enabled by ‘-Wall’.

     Normally this only warns about global allocation functions, but
     ‘-Waligned-new=all’ also warns about class member allocation
     functions.

‘-Wno-placement-new’
‘-Wplacement-new=N’
     Warn about placement new expressions with undefined behavior, such
     as constructing an object in a buffer that is smaller than the type
     of the object.  For example, the placement new expression below is
     diagnosed because it attempts to construct an array of 64 integers
     in a buffer only 64 bytes large.
          char buf [64];
          new (buf) int[64];
     This warning is enabled by default.

     ‘-Wplacement-new=1’
          This is the default warning level of ‘-Wplacement-new’.  At
          this level the warning is not issued for some strictly
          undefined constructs that GCC allows as extensions for
          compatibility with legacy code.  For example, the following
          ‘new’ expression is not diagnosed at this level even though it
          has undefined behavior according to the C++ standard because
          it writes past the end of the one-element array.
               struct S { int n, a[1]; };
               S *s = (S *)malloc (sizeof *s + 31 * sizeof s->a[0]);
               new (s->a)int [32]();

     ‘-Wplacement-new=2’
          At this level, in addition to diagnosing all the same
          constructs as at level 1, a diagnostic is also issued for
          placement new expressions that construct an object in the last
          member of structure whose type is an array of a single element
          and whose size is less than the size of the object being
          constructed.  While the previous example would be diagnosed,
          the following construct makes use of the flexible member array
          extension to avoid the warning at level 2.
               struct S { int n, a[]; };
               S *s = (S *)malloc (sizeof *s + 32 * sizeof s->a[0]);
               new (s->a)int [32]();

‘-Wcatch-value’
‘-Wcatch-value=N (C++ and Objective-C++ only)’
     Warn about catch handlers that do not catch via reference.  With
     ‘-Wcatch-value=1’ (or ‘-Wcatch-value’ for short) warn about
     polymorphic class types that are caught by value.  With
     ‘-Wcatch-value=2’ warn about all class types that are caught by
     value.  With ‘-Wcatch-value=3’ warn about all types that are not
     caught by reference.  ‘-Wcatch-value’ is enabled by ‘-Wall’.

‘-Wconditionally-supported (C++ and Objective-C++ only)’
     Warn for conditionally-supported (C++11 [intro.defs]) constructs.

‘-Wno-delete-incomplete (C++ and Objective-C++ only)’
     Do not warn when deleting a pointer to incomplete type, which may
     cause undefined behavior at runtime.  This warning is enabled by
     default.

‘-Wextra-semi (C++, Objective-C++ only)’
     Warn about redundant semicolons after in-class function
     definitions.

‘-Wno-inaccessible-base (C++, Objective-C++ only)’
     This option controls warnings when a base class is inaccessible in
     a class derived from it due to ambiguity.  The warning is enabled
     by default.  Note that the warning for ambiguous virtual bases is
     enabled by the ‘-Wextra’ option.
          struct A { int a; };

          struct B : A { };

          struct C : B, A { };

‘-Wno-inherited-variadic-ctor’
     Suppress warnings about use of C++11 inheriting constructors when
     the base class inherited from has a C variadic constructor; the
     warning is on by default because the ellipsis is not inherited.

‘-Wno-invalid-offsetof (C++ and Objective-C++ only)’
     Suppress warnings from applying the ‘offsetof’ macro to a non-POD
     type.  According to the 2014 ISO C++ standard, applying ‘offsetof’
     to a non-standard-layout type is undefined.  In existing C++
     implementations, however, ‘offsetof’ typically gives meaningful
     results.  This flag is for users who are aware that they are
     writing nonportable code and who have deliberately chosen to ignore
     the warning about it.

     The restrictions on ‘offsetof’ may be relaxed in a future version
     of the C++ standard.

‘-Wsized-deallocation (C++ and Objective-C++ only)’
     Warn about a definition of an unsized deallocation function
          void operator delete (void *) noexcept;
          void operator delete[] (void *) noexcept;
     without a definition of the corresponding sized deallocation
     function
          void operator delete (void *, std::size_t) noexcept;
          void operator delete[] (void *, std::size_t) noexcept;
     or vice versa.  Enabled by ‘-Wextra’ along with
     ‘-fsized-deallocation’.

‘-Wsuggest-final-types’
     Warn about types with virtual methods where code quality would be
     improved if the type were declared with the C++11 ‘final’
     specifier, or, if possible, declared in an anonymous namespace.
     This allows GCC to more aggressively devirtualize the polymorphic
     calls.  This warning is more effective with link-time optimization,
     where the information about the class hierarchy graph is more
     complete.

‘-Wsuggest-final-methods’
     Warn about virtual methods where code quality would be improved if
     the method were declared with the C++11 ‘final’ specifier, or, if
     possible, its type were declared in an anonymous namespace or with
     the ‘final’ specifier.  This warning is more effective with
     link-time optimization, where the information about the class
     hierarchy graph is more complete.  It is recommended to first
     consider suggestions of ‘-Wsuggest-final-types’ and then rebuild
     with new annotations.

‘-Wsuggest-override’
     Warn about overriding virtual functions that are not marked with
     the ‘override’ keyword.

‘-Wuse-after-free’
‘-Wuse-after-free=N’
     Warn about uses of pointers to dynamically allocated objects that
     have been rendered indeterminate by a call to a deallocation
     function.  The warning is enabled at all optimization levels but
     may yield different results with optimization than without.

     ‘-Wuse-after-free=1’
          At level 1 the warning attempts to diagnose only unconditional
          uses of pointers made indeterminate by a deallocation call or
          a successful call to ‘realloc’, regardless of whether or not
          the call resulted in an actual reallocatio of memory.  This
          includes double-‘free’ calls as well as uses in arithmetic and
          relational expressions.  Although undefined, uses of
          indeterminate pointers in equality (or inequality) expressions
          are not diagnosed at this level.
     ‘-Wuse-after-free=2’
          At level 2, in addition to unconditional uses, the warning
          also diagnoses conditional uses of pointers made indeterminate
          by a deallocation call.  As at level 2, uses in equality (or
          inequality) expressions are not diagnosed.  For example, the
          second call to ‘free’ in the following function is diagnosed
          at this level:
               struct A { int refcount; void *data; };

               void release (struct A *p)
               {
                 int refcount = --p->refcount;
                 free (p);
                 if (refcount == 0)
                   free (p->data);   // warning: p may be used after free
               }
     ‘-Wuse-after-free=3’
          At level 3, the warning also diagnoses uses of indeterminate
          pointers in equality expressions.  All uses of indeterminate
          pointers are undefined but equality tests sometimes appear
          after calls to ‘realloc’ as an attempt to determine whether
          the call resulted in relocating the object to a different
          address.  They are diagnosed at a separate level to aid legacy
          code gradually transition to safe alternatives.  For example,
          the equality test in the function below is diagnosed at this
          level:
               void adjust_pointers (int**, int);

               void grow (int **p, int n)
               {
                 int **q = (int**)realloc (p, n *= 2);
                 if (q == p)
                   return;
                 adjust_pointers ((int**)q, n);
               }
          To avoid the warning at this level, store offsets into
          allocated memory instead of pointers.  This approach obviates
          needing to adjust the stored pointers after reallocation.

     ‘-Wuse-after-free=2’ is included in ‘-Wall’.

‘-Wuseless-cast (C++ and Objective-C++ only)’
     Warn when an expression is casted to its own type.

‘-Wno-conversion-null (C++ and Objective-C++ only)’
     Do not warn for conversions between ‘NULL’ and non-pointer types.
     ‘-Wconversion-null’ is enabled by default.


File: gcc.info,  Node: Objective-C and Objective-C++ Dialect Options,  Next: Diagnostic Message Formatting Options,  Prev: C++ Dialect Options,  Up: Invoking GCC

3.6 Options Controlling Objective-C and Objective-C++ Dialects
==============================================================

(NOTE: This manual does not describe the Objective-C and Objective-C++
languages themselves.  *Note Language Standards Supported by GCC:
Standards, for references.)

 This section describes the command-line options that are only
meaningful for Objective-C and Objective-C++ programs.  You can also use
most of the language-independent GNU compiler options.  For example, you
might compile a file ‘some_class.m’ like this:

     gcc -g -fgnu-runtime -O -c some_class.m

In this example, ‘-fgnu-runtime’ is an option meant only for Objective-C
and Objective-C++ programs; you can use the other options with any
language supported by GCC.

 Note that since Objective-C is an extension of the C language,
Objective-C compilations may also use options specific to the C
front-end (e.g., ‘-Wtraditional’).  Similarly, Objective-C++
compilations may use C++-specific options (e.g., ‘-Wabi’).

 Here is a list of options that are _only_ for compiling Objective-C and
Objective-C++ programs:

‘-fconstant-string-class=CLASS-NAME’
     Use CLASS-NAME as the name of the class to instantiate for each
     literal string specified with the syntax ‘@"..."’.  The default
     class name is ‘NXConstantString’ if the GNU runtime is being used,
     and ‘NSConstantString’ if the NeXT runtime is being used (see
     below).  The ‘-fconstant-cfstrings’ option, if also present,
     overrides the ‘-fconstant-string-class’ setting and cause ‘@"..."’
     literals to be laid out as constant CoreFoundation strings.

‘-fgnu-runtime’
     Generate object code compatible with the standard GNU Objective-C
     runtime.  This is the default for most types of systems.

‘-fnext-runtime’
     Generate output compatible with the NeXT runtime.  This is the
     default for NeXT-based systems, including Darwin and Mac OS X.  The
     macro ‘__NEXT_RUNTIME__’ is predefined if (and only if) this option
     is used.

‘-fno-nil-receivers’
     Assume that all Objective-C message dispatches (‘[receiver
     message:arg]’) in this translation unit ensure that the receiver is
     not ‘nil’.  This allows for more efficient entry points in the
     runtime to be used.  This option is only available in conjunction
     with the NeXT runtime and ABI version 0 or 1.

‘-fobjc-abi-version=N’
     Use version N of the Objective-C ABI for the selected runtime.
     This option is currently supported only for the NeXT runtime.  In
     that case, Version 0 is the traditional (32-bit) ABI without
     support for properties and other Objective-C 2.0 additions.
     Version 1 is the traditional (32-bit) ABI with support for
     properties and other Objective-C 2.0 additions.  Version 2 is the
     modern (64-bit) ABI. If nothing is specified, the default is
     Version 0 on 32-bit target machines, and Version 2 on 64-bit target
     machines.

‘-fobjc-call-cxx-cdtors’
     For each Objective-C class, check if any of its instance variables
     is a C++ object with a non-trivial default constructor.  If so,
     synthesize a special ‘- (id) .cxx_construct’ instance method which
     runs non-trivial default constructors on any such instance
     variables, in order, and then return ‘self’.  Similarly, check if
     any instance variable is a C++ object with a non-trivial
     destructor, and if so, synthesize a special ‘- (void)
     .cxx_destruct’ method which runs all such default destructors, in
     reverse order.

     The ‘- (id) .cxx_construct’ and ‘- (void) .cxx_destruct’ methods
     thusly generated only operate on instance variables declared in the
     current Objective-C class, and not those inherited from
     superclasses.  It is the responsibility of the Objective-C runtime
     to invoke all such methods in an object's inheritance hierarchy.
     The ‘- (id) .cxx_construct’ methods are invoked by the runtime
     immediately after a new object instance is allocated; the ‘- (void)
     .cxx_destruct’ methods are invoked immediately before the runtime
     deallocates an object instance.

     As of this writing, only the NeXT runtime on Mac OS X 10.4 and
     later has support for invoking the ‘- (id) .cxx_construct’ and ‘-
     (void) .cxx_destruct’ methods.

‘-fobjc-direct-dispatch’
     Allow fast jumps to the message dispatcher.  On Darwin this is
     accomplished via the comm page.

‘-fobjc-exceptions’
     Enable syntactic support for structured exception handling in
     Objective-C, similar to what is offered by C++.  This option is
     required to use the Objective-C keywords ‘@try’, ‘@throw’,
     ‘@catch’, ‘@finally’ and ‘@synchronized’.  This option is available
     with both the GNU runtime and the NeXT runtime (but not available
     in conjunction with the NeXT runtime on Mac OS X 10.2 and earlier).

‘-fobjc-gc’
     Enable garbage collection (GC) in Objective-C and Objective-C++
     programs.  This option is only available with the NeXT runtime; the
     GNU runtime has a different garbage collection implementation that
     does not require special compiler flags.

‘-fobjc-nilcheck’
     For the NeXT runtime with version 2 of the ABI, check for a nil
     receiver in method invocations before doing the actual method call.
     This is the default and can be disabled using ‘-fno-objc-nilcheck’.
     Class methods and super calls are never checked for nil in this way
     no matter what this flag is set to.  Currently this flag does
     nothing when the GNU runtime, or an older version of the NeXT
     runtime ABI, is used.

‘-fobjc-std=objc1’
     Conform to the language syntax of Objective-C 1.0, the language
     recognized by GCC 4.0.  This only affects the Objective-C additions
     to the C/C++ language; it does not affect conformance to C/C++
     standards, which is controlled by the separate C/C++ dialect option
     flags.  When this option is used with the Objective-C or
     Objective-C++ compiler, any Objective-C syntax that is not
     recognized by GCC 4.0 is rejected.  This is useful if you need to
     make sure that your Objective-C code can be compiled with older
     versions of GCC.

‘-freplace-objc-classes’
     Emit a special marker instructing ‘ld(1)’ not to statically link in
     the resulting object file, and allow ‘dyld(1)’ to load it in at run
     time instead.  This is used in conjunction with the
     Fix-and-Continue debugging mode, where the object file in question
     may be recompiled and dynamically reloaded in the course of program
     execution, without the need to restart the program itself.
     Currently, Fix-and-Continue functionality is only available in
     conjunction with the NeXT runtime on Mac OS X 10.3 and later.

‘-fzero-link’
     When compiling for the NeXT runtime, the compiler ordinarily
     replaces calls to ‘objc_getClass("...")’ (when the name of the
     class is known at compile time) with static class references that
     get initialized at load time, which improves run-time performance.
     Specifying the ‘-fzero-link’ flag suppresses this behavior and
     causes calls to ‘objc_getClass("...")’ to be retained.  This is
     useful in Zero-Link debugging mode, since it allows for individual
     class implementations to be modified during program execution.  The
     GNU runtime currently always retains calls to
     ‘objc_get_class("...")’ regardless of command-line options.

‘-fno-local-ivars’
     By default instance variables in Objective-C can be accessed as if
     they were local variables from within the methods of the class
     they're declared in.  This can lead to shadowing between instance
     variables and other variables declared either locally inside a
     class method or globally with the same name.  Specifying the
     ‘-fno-local-ivars’ flag disables this behavior thus avoiding
     variable shadowing issues.

‘-fivar-visibility=[public|protected|private|package]’
     Set the default instance variable visibility to the specified
     option so that instance variables declared outside the scope of any
     access modifier directives default to the specified visibility.

‘-gen-decls’
     Dump interface declarations for all classes seen in the source file
     to a file named ‘SOURCENAME.decl’.

‘-Wassign-intercept (Objective-C and Objective-C++ only)’
     Warn whenever an Objective-C assignment is being intercepted by the
     garbage collector.

‘-Wno-property-assign-default (Objective-C and Objective-C++ only)’
     Do not warn if a property for an Objective-C object has no assign
     semantics specified.

‘-Wno-protocol (Objective-C and Objective-C++ only)’
     If a class is declared to implement a protocol, a warning is issued
     for every method in the protocol that is not implemented by the
     class.  The default behavior is to issue a warning for every method
     not explicitly implemented in the class, even if a method
     implementation is inherited from the superclass.  If you use the
     ‘-Wno-protocol’ option, then methods inherited from the superclass
     are considered to be implemented, and no warning is issued for
     them.

‘-Wobjc-root-class (Objective-C and Objective-C++ only)’
     Warn if a class interface lacks a superclass.  Most classes will
     inherit from ‘NSObject’ (or ‘Object’) for example.  When declaring
     classes intended to be root classes, the warning can be suppressed
     by marking their interfaces with
     ‘__attribute__((objc_root_class))’.

‘-Wselector (Objective-C and Objective-C++ only)’
     Warn if multiple methods of different types for the same selector
     are found during compilation.  The check is performed on the list
     of methods in the final stage of compilation.  Additionally, a
     check is performed for each selector appearing in a
     ‘@selector(...)’ expression, and a corresponding method for that
     selector has been found during compilation.  Because these checks
     scan the method table only at the end of compilation, these
     warnings are not produced if the final stage of compilation is not
     reached, for example because an error is found during compilation,
     or because the ‘-fsyntax-only’ option is being used.

‘-Wstrict-selector-match (Objective-C and Objective-C++ only)’
     Warn if multiple methods with differing argument and/or return
     types are found for a given selector when attempting to send a
     message using this selector to a receiver of type ‘id’ or ‘Class’.
     When this flag is off (which is the default behavior), the compiler
     omits such warnings if any differences found are confined to types
     that share the same size and alignment.

‘-Wundeclared-selector (Objective-C and Objective-C++ only)’
     Warn if a ‘@selector(...)’ expression referring to an undeclared
     selector is found.  A selector is considered undeclared if no
     method with that name has been declared before the ‘@selector(...)’
     expression, either explicitly in an ‘@interface’ or ‘@protocol’
     declaration, or implicitly in an ‘@implementation’ section.  This
     option always performs its checks as soon as a ‘@selector(...)’
     expression is found, while ‘-Wselector’ only performs its checks in
     the final stage of compilation.  This also enforces the coding
     style convention that methods and selectors must be declared before
     being used.

‘-print-objc-runtime-info’
     Generate C header describing the largest structure that is passed
     by value, if any.


File: gcc.info,  Node: Diagnostic Message Formatting Options,  Next: Warning Options,  Prev: Objective-C and Objective-C++ Dialect Options,  Up: Invoking GCC

3.7 Options to Control Diagnostic Messages Formatting
=====================================================

Traditionally, diagnostic messages have been formatted irrespective of
the output device's aspect (e.g. its width, ...).  You can use the
options described below to control the formatting algorithm for
diagnostic messages, e.g. how many characters per line, how often source
location information should be reported.  Note that some language front
ends may not honor these options.

‘-fmessage-length=N’
     Try to format error messages so that they fit on lines of about N
     characters.  If N is zero, then no line-wrapping is done; each
     error message appears on a single line.  This is the default for
     all front ends.

     Note - this option also affects the display of the ‘#error’ and
     ‘#warning’ pre-processor directives, and the ‘deprecated’
     function/type/variable attribute.  It does not however affect the
     ‘pragma GCC warning’ and ‘pragma GCC error’ pragmas.

‘-fdiagnostics-plain-output’
     This option requests that diagnostic output look as plain as
     possible, which may be useful when running ‘dejagnu’ or other
     utilities that need to parse diagnostics output and prefer that it
     remain more stable over time.  ‘-fdiagnostics-plain-output’ is
     currently equivalent to the following options:
          -fno-diagnostics-show-caret
          -fno-diagnostics-show-line-numbers
          -fdiagnostics-color=never
          -fdiagnostics-urls=never
          -fdiagnostics-path-format=separate-events
     In the future, if GCC changes the default appearance of its
     diagnostics, the corresponding option to disable the new behavior
     will be added to this list.

‘-fdiagnostics-show-location=once’
     Only meaningful in line-wrapping mode.  Instructs the diagnostic
     messages reporter to emit source location information _once_; that
     is, in case the message is too long to fit on a single physical
     line and has to be wrapped, the source location won't be emitted
     (as prefix) again, over and over, in subsequent continuation lines.
     This is the default behavior.

‘-fdiagnostics-show-location=every-line’
     Only meaningful in line-wrapping mode.  Instructs the diagnostic
     messages reporter to emit the same source location information (as
     prefix) for physical lines that result from the process of breaking
     a message which is too long to fit on a single line.

‘-fdiagnostics-color[=WHEN]’
‘-fno-diagnostics-color’
     Use color in diagnostics.  WHEN is ‘never’, ‘always’, or ‘auto’.
     The default depends on how the compiler has been configured, it can
     be any of the above WHEN options or also ‘never’ if ‘GCC_COLORS’
     environment variable isn't present in the environment, and ‘auto’
     otherwise.  ‘auto’ makes GCC use color only when the standard error
     is a terminal, and when not executing in an emacs shell.  The forms
     ‘-fdiagnostics-color’ and ‘-fno-diagnostics-color’ are aliases for
     ‘-fdiagnostics-color=always’ and ‘-fdiagnostics-color=never’,
     respectively.

     The colors are defined by the environment variable ‘GCC_COLORS’.
     Its value is a colon-separated list of capabilities and Select
     Graphic Rendition (SGR) substrings.  SGR commands are interpreted
     by the terminal or terminal emulator.  (See the section in the
     documentation of your text terminal for permitted values and their
     meanings as character attributes.)  These substring values are
     integers in decimal representation and can be concatenated with
     semicolons.  Common values to concatenate include ‘1’ for bold, ‘4’
     for underline, ‘5’ for blink, ‘7’ for inverse, ‘39’ for default
     foreground color, ‘30’ to ‘37’ for foreground colors, ‘90’ to ‘97’
     for 16-color mode foreground colors, ‘38;5;0’ to ‘38;5;255’ for
     88-color and 256-color modes foreground colors, ‘49’ for default
     background color, ‘40’ to ‘47’ for background colors, ‘100’ to
     ‘107’ for 16-color mode background colors, and ‘48;5;0’ to
     ‘48;5;255’ for 88-color and 256-color modes background colors.

     The default ‘GCC_COLORS’ is
          error=01;31:warning=01;35:note=01;36:range1=32:range2=34:locus=01:\
          quote=01:path=01;36:fixit-insert=32:fixit-delete=31:\
          diff-filename=01:diff-hunk=32:diff-delete=31:diff-insert=32:\
          type-diff=01;32
     where ‘01;31’ is bold red, ‘01;35’ is bold magenta, ‘01;36’ is bold
     cyan, ‘32’ is green, ‘34’ is blue, ‘01’ is bold, and ‘31’ is red.
     Setting ‘GCC_COLORS’ to the empty string disables colors.
     Supported capabilities are as follows.

     ‘error=’
          SGR substring for error: markers.

     ‘warning=’
          SGR substring for warning: markers.

     ‘note=’
          SGR substring for note: markers.

     ‘path=’
          SGR substring for colorizing paths of control-flow events as
          printed via ‘-fdiagnostics-path-format=’, such as the
          identifiers of individual events and lines indicating
          interprocedural calls and returns.

     ‘range1=’
          SGR substring for first additional range.

     ‘range2=’
          SGR substring for second additional range.

     ‘locus=’
          SGR substring for location information, ‘file:line’ or
          ‘file:line:column’ etc.

     ‘quote=’
          SGR substring for information printed within quotes.

     ‘fixit-insert=’
          SGR substring for fix-it hints suggesting text to be inserted
          or replaced.

     ‘fixit-delete=’
          SGR substring for fix-it hints suggesting text to be deleted.

     ‘diff-filename=’
          SGR substring for filename headers within generated patches.

     ‘diff-hunk=’
          SGR substring for the starts of hunks within generated
          patches.

     ‘diff-delete=’
          SGR substring for deleted lines within generated patches.

     ‘diff-insert=’
          SGR substring for inserted lines within generated patches.

     ‘type-diff=’
          SGR substring for highlighting mismatching types within
          template arguments in the C++ frontend.

‘-fdiagnostics-urls[=WHEN]’
     Use escape sequences to embed URLs in diagnostics.  For example,
     when ‘-fdiagnostics-show-option’ emits text showing the
     command-line option controlling a diagnostic, embed a URL for
     documentation of that option.

     WHEN is ‘never’, ‘always’, or ‘auto’.  ‘auto’ makes GCC use URL
     escape sequences only when the standard error is a terminal, and
     when not executing in an emacs shell or any graphical terminal
     which is known to be incompatible with this feature, see below.

     The default depends on how the compiler has been configured.  It
     can be any of the above WHEN options.

     GCC can also be configured (via the
     ‘--with-diagnostics-urls=auto-if-env’ configure-time option) so
     that the default is affected by environment variables.  Under such
     a configuration, GCC defaults to using ‘auto’ if either ‘GCC_URLS’
     or ‘TERM_URLS’ environment variables are present and non-empty in
     the environment of the compiler, or ‘never’ if neither are.

     However, even with ‘-fdiagnostics-urls=always’ the behavior is
     dependent on those environment variables: If ‘GCC_URLS’ is set to
     empty or ‘no’, do not embed URLs in diagnostics.  If set to ‘st’,
     URLs use ST escape sequences.  If set to ‘bel’, the default, URLs
     use BEL escape sequences.  Any other non-empty value enables the
     feature.  If ‘GCC_URLS’ is not set, use ‘TERM_URLS’ as a fallback.
     Note: ST is an ANSI escape sequence, string terminator ‘ESC \’, BEL
     is an ASCII character, CTRL-G that usually sounds like a beep.

     At this time GCC tries to detect also a few terminals that are
     known to not implement the URL feature, and have bugs or at least
     had bugs in some versions that are still in use, where the URL
     escapes are likely to misbehave, i.e.  print garbage on the screen.
     That list is currently xfce4-terminal, certain known to be buggy
     gnome-terminal versions, the linux console, and mingw.  This check
     can be skipped with the ‘-fdiagnostics-urls=always’.

‘-fno-diagnostics-show-option’
     By default, each diagnostic emitted includes text indicating the
     command-line option that directly controls the diagnostic (if such
     an option is known to the diagnostic machinery).  Specifying the
     ‘-fno-diagnostics-show-option’ flag suppresses that behavior.

‘-fno-diagnostics-show-caret’
     By default, each diagnostic emitted includes the original source
     line and a caret ‘^’ indicating the column.  This option suppresses
     this information.  The source line is truncated to N characters, if
     the ‘-fmessage-length=n’ option is given.  When the output is done
     to the terminal, the width is limited to the width given by the
     ‘COLUMNS’ environment variable or, if not set, to the terminal
     width.

‘-fno-diagnostics-show-labels’
     By default, when printing source code (via
     ‘-fdiagnostics-show-caret’), diagnostics can label ranges of source
     code with pertinent information, such as the types of expressions:

              printf ("foo %s bar", long_i + long_j);
                           ~^       ~~~~~~~~~~~~~~~
                            |              |
                            char *         long int

     This option suppresses the printing of these labels (in the example
     above, the vertical bars and the "char *" and "long int" text).

‘-fno-diagnostics-show-cwe’
     Diagnostic messages can optionally have an associated CWE
     (https://cwe.mitre.org/index.html) identifier.  GCC itself only
     provides such metadata for some of the ‘-fanalyzer’ diagnostics.
     GCC plugins may also provide diagnostics with such metadata.  By
     default, if this information is present, it will be printed with
     the diagnostic.  This option suppresses the printing of this
     metadata.

‘-fno-diagnostics-show-line-numbers’
     By default, when printing source code (via
     ‘-fdiagnostics-show-caret’), a left margin is printed, showing line
     numbers.  This option suppresses this left margin.

‘-fdiagnostics-minimum-margin-width=WIDTH’
     This option controls the minimum width of the left margin printed
     by ‘-fdiagnostics-show-line-numbers’.  It defaults to 6.

‘-fdiagnostics-parseable-fixits’
     Emit fix-it hints in a machine-parseable format, suitable for
     consumption by IDEs.  For each fix-it, a line will be printed after
     the relevant diagnostic, starting with the string "fix-it:".  For
     example:

          fix-it:"test.c":{45:3-45:21}:"gtk_widget_show_all"

     The location is expressed as a half-open range, expressed as a
     count of bytes, starting at byte 1 for the initial column.  In the
     above example, bytes 3 through 20 of line 45 of "test.c" are to be
     replaced with the given string:

          00000000011111111112222222222
          12345678901234567890123456789
            gtk_widget_showall (dlg);
            ^^^^^^^^^^^^^^^^^^
            gtk_widget_show_all

     The filename and replacement string escape backslash as "\\", tab
     as "\t", newline as "\n", double quotes as "\"", non-printable
     characters as octal (e.g.  vertical tab as "\013").

     An empty replacement string indicates that the given range is to be
     removed.  An empty range (e.g.  "45:3-45:3") indicates that the
     string is to be inserted at the given position.

‘-fdiagnostics-generate-patch’
     Print fix-it hints to stderr in unified diff format, after any
     diagnostics are printed.  For example:

          --- test.c
          +++ test.c
          @ -42,5 +42,5 @

           void show_cb(GtkDialog *dlg)
           {
          -  gtk_widget_showall(dlg);
          +  gtk_widget_show_all(dlg);
           }

     The diff may or may not be colorized, following the same rules as
     for diagnostics (see ‘-fdiagnostics-color’).

‘-fdiagnostics-show-template-tree’

     In the C++ frontend, when printing diagnostics showing mismatching
     template types, such as:

            could not convert 'std::map<int, std::vector<double> >()'
              from 'map<[...],vector<double>>' to 'map<[...],vector<float>>

     the ‘-fdiagnostics-show-template-tree’ flag enables printing a
     tree-like structure showing the common and differing parts of the
     types, such as:

            map<
              [...],
              vector<
                [double != float]>>

     The parts that differ are highlighted with color ("double" and
     "float" in this case).

‘-fno-elide-type’
     By default when the C++ frontend prints diagnostics showing
     mismatching template types, common parts of the types are printed
     as "[...]"  to simplify the error message.  For example:

            could not convert 'std::map<int, std::vector<double> >()'
              from 'map<[...],vector<double>>' to 'map<[...],vector<float>>

     Specifying the ‘-fno-elide-type’ flag suppresses that behavior.
     This flag also affects the output of the
     ‘-fdiagnostics-show-template-tree’ flag.

‘-fdiagnostics-path-format=KIND’
     Specify how to print paths of control-flow events for diagnostics
     that have such a path associated with them.

     KIND is ‘none’, ‘separate-events’, or ‘inline-events’, the default.

     ‘none’ means to not print diagnostic paths.

     ‘separate-events’ means to print a separate "note" diagnostic for
     each event within the diagnostic.  For example:

          test.c:29:5: error: passing NULL as argument 1 to 'PyList_Append' which requires a non-NULL parameter
          test.c:25:10: note: (1) when 'PyList_New' fails, returning NULL
          test.c:27:3: note: (2) when 'i < count'
          test.c:29:5: note: (3) when calling 'PyList_Append', passing NULL from (1) as argument 1

     ‘inline-events’ means to print the events "inline" within the
     source code.  This view attempts to consolidate the events into
     runs of sufficiently-close events, printing them as labelled ranges
     within the source.

     For example, the same events as above might be printed as:

            'test': events 1-3
              |
              |   25 |   list = PyList_New(0);
              |      |          ^~~~~~~~~~~~~
              |      |          |
              |      |          (1) when 'PyList_New' fails, returning NULL
              |   26 |
              |   27 |   for (i = 0; i < count; i++) {
              |      |   ~~~
              |      |   |
              |      |   (2) when 'i < count'
              |   28 |     item = PyLong_FromLong(random());
              |   29 |     PyList_Append(list, item);
              |      |     ~~~~~~~~~~~~~~~~~~~~~~~~~
              |      |     |
              |      |     (3) when calling 'PyList_Append', passing NULL from (1) as argument 1
              |

     Interprocedural control flow is shown by grouping the events by
     stack frame, and using indentation to show how stack frames are
     nested, pushed, and popped.

     For example:

            'test': events 1-2
              |
              |  133 | {
              |      | ^
              |      | |
              |      | (1) entering 'test'
              |  134 |   boxed_int *obj = make_boxed_int (i);
              |      |                    ~~~~~~~~~~~~~~~~~~
              |      |                    |
              |      |                    (2) calling 'make_boxed_int'
              |
              +--> 'make_boxed_int': events 3-4
                     |
                     |  120 | {
                     |      | ^
                     |      | |
                     |      | (3) entering 'make_boxed_int'
                     |  121 |   boxed_int *result = (boxed_int *)wrapped_malloc (sizeof (boxed_int));
                     |      |                                    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
                     |      |                                    |
                     |      |                                    (4) calling 'wrapped_malloc'
                     |
                     +--> 'wrapped_malloc': events 5-6
                            |
                            |    7 | {
                            |      | ^
                            |      | |
                            |      | (5) entering 'wrapped_malloc'
                            |    8 |   return malloc (size);
                            |      |          ~~~~~~~~~~~~~
                            |      |          |
                            |      |          (6) calling 'malloc'
                            |
              <-------------+
              |
           'test': event 7
              |
              |  138 |   free_boxed_int (obj);
              |      |   ^~~~~~~~~~~~~~~~~~~~
              |      |   |
              |      |   (7) calling 'free_boxed_int'
              |
          (etc)

‘-fdiagnostics-show-path-depths’
     This option provides additional information when printing
     control-flow paths associated with a diagnostic.

     If this is option is provided then the stack depth will be printed
     for each run of events within
     ‘-fdiagnostics-path-format=separate-events’.

     This is intended for use by GCC developers and plugin developers
     when debugging diagnostics that report interprocedural control
     flow.

‘-fno-show-column’
     Do not print column numbers in diagnostics.  This may be necessary
     if diagnostics are being scanned by a program that does not
     understand the column numbers, such as ‘dejagnu’.

‘-fdiagnostics-column-unit=UNIT’
     Select the units for the column number.  This affects traditional
     diagnostics (in the absence of ‘-fno-show-column’), as well as JSON
     format diagnostics if requested.

     The default UNIT, ‘display’, considers the number of display
     columns occupied by each character.  This may be larger than the
     number of bytes required to encode the character, in the case of
     tab characters, or it may be smaller, in the case of multibyte
     characters.  For example, the character "GREEK SMALL LETTER PI
     (U+03C0)" occupies one display column, and its UTF-8 encoding
     requires two bytes; the character "SLIGHTLY SMILING FACE (U+1F642)"
     occupies two display columns, and its UTF-8 encoding requires four
     bytes.

     Setting UNIT to ‘byte’ changes the column number to the raw byte
     count in all cases, as was traditionally output by GCC prior to
     version 11.1.0.

‘-fdiagnostics-column-origin=ORIGIN’
     Select the origin for column numbers, i.e.  the column number
     assigned to the first column.  The default value of 1 corresponds
     to traditional GCC behavior and to the GNU style guide.  Some
     utilities may perform better with an origin of 0; any non-negative
     value may be specified.

‘-fdiagnostics-escape-format=FORMAT’
     When GCC prints pertinent source lines for a diagnostic it normally
     attempts to print the source bytes directly.  However, some
     diagnostics relate to encoding issues in the source file, such as
     malformed UTF-8, or issues with Unicode normalization.  These
     diagnostics are flagged so that GCC will escape bytes that are not
     printable ASCII when printing their pertinent source lines.

     This option controls how such bytes should be escaped.

     The default FORMAT, ‘unicode’ displays Unicode characters that are
     not printable ASCII in the form ‘<U+XXXX>’, and bytes that do not
     correspond to a Unicode character validly-encoded in UTF-8-encoded
     will be displayed as hexadecimal in the form ‘<XX>’.

     For example, a source line containing the string ‘before’ followed
     by the Unicode character U+03C0 ("GREEK SMALL LETTER PI", with
     UTF-8 encoding 0xCF 0x80) followed by the byte 0xBF (a stray UTF-8
     trailing byte), followed by the string ‘after’ will be printed for
     such a diagnostic as:

           before<U+03C0><BF>after

     Setting FORMAT to ‘bytes’ will display all non-printable-ASCII
     bytes in the form ‘<XX>’, thus showing the underlying encoding of
     non-ASCII Unicode characters.  For the example above, the following
     will be printed:

           before<CF><80><BF>after

‘-fdiagnostics-format=FORMAT’
     Select a different format for printing diagnostics.  FORMAT is
     ‘text’ or ‘json’.  The default is ‘text’.

     The ‘json’ format consists of a top-level JSON array containing
     JSON objects representing the diagnostics.

     The JSON is emitted as one line, without formatting; the examples
     below have been formatted for clarity.

     Diagnostics can have child diagnostics.  For example, this error
     and note:

          misleading-indentation.c:15:3: warning: this 'if' clause does not
            guard... [-Wmisleading-indentation]
             15 |   if (flag)
                |   ^~
          misleading-indentation.c:17:5: note: ...this statement, but the latter
            is misleadingly indented as if it were guarded by the 'if'
             17 |     y = 2;
                |     ^

     might be printed in JSON form (after formatting) like this:

          [
              {
                  "kind": "warning",
                  "locations": [
                      {
                          "caret": {
          		    "display-column": 3,
          		    "byte-column": 3,
                              "column": 3,
                              "file": "misleading-indentation.c",
                              "line": 15
                          },
                          "finish": {
          		    "display-column": 4,
          		    "byte-column": 4,
                              "column": 4,
                              "file": "misleading-indentation.c",
                              "line": 15
                          }
                      }
                  ],
                  "message": "this \u2018if\u2019 clause does not guard...",
                  "option": "-Wmisleading-indentation",
                  "option_url": "https://gcc.gnu.org/onlinedocs/gcc/Warning-Options.html#index-Wmisleading-indentation",
                  "children": [
                      {
                          "kind": "note",
                          "locations": [
                              {
                                  "caret": {
          			    "display-column": 5,
          			    "byte-column": 5,
                                      "column": 5,
                                      "file": "misleading-indentation.c",
                                      "line": 17
                                  }
                              }
                          ],
                          "escape-source": false,
                          "message": "...this statement, but the latter is ..."
                      }
                  ]
          	"escape-source": false,
          	"column-origin": 1,
              }
          ]

     where the ‘note’ is a child of the ‘warning’.

     A diagnostic has a ‘kind’.  If this is ‘warning’, then there is an
     ‘option’ key describing the command-line option controlling the
     warning.

     A diagnostic can contain zero or more locations.  Each location has
     an optional ‘label’ string and up to three positions within it: a
     ‘caret’ position and optional ‘start’ and ‘finish’ positions.  A
     position is described by a ‘file’ name, a ‘line’ number, and three
     numbers indicating a column position:

        • ‘display-column’ counts display columns, accounting for tabs
          and multibyte characters.

        • ‘byte-column’ counts raw bytes.

        • ‘column’ is equal to one of the previous two, as dictated by
          the ‘-fdiagnostics-column-unit’ option.

     All three columns are relative to the origin specified by
     ‘-fdiagnostics-column-origin’, which is typically equal to 1 but
     may be set, for instance, to 0 for compatibility with other
     utilities that number columns from 0.  The column origin is
     recorded in the JSON output in the ‘column-origin’ tag.  In the
     remaining examples below, the extra column number outputs have been
     omitted for brevity.

     For example, this error:

          bad-binary-ops.c:64:23: error: invalid operands to binary + (have 'S' {aka
             'struct s'} and 'T' {aka 'struct t'})
             64 |   return callee_4a () + callee_4b ();
                |          ~~~~~~~~~~~~ ^ ~~~~~~~~~~~~
                |          |              |
                |          |              T {aka struct t}
                |          S {aka struct s}

     has three locations.  Its primary location is at the "+" token at
     column 23.  It has two secondary locations, describing the left and
     right-hand sides of the expression, which have labels.  It might be
     printed in JSON form as:

              {
                  "children": [],
                  "kind": "error",
                  "locations": [
                      {
                          "caret": {
                              "column": 23, "file": "bad-binary-ops.c", "line": 64
                          }
                      },
                      {
                          "caret": {
                              "column": 10, "file": "bad-binary-ops.c", "line": 64
                          },
                          "finish": {
                              "column": 21, "file": "bad-binary-ops.c", "line": 64
                          },
                          "label": "S {aka struct s}"
                      },
                      {
                          "caret": {
                              "column": 25, "file": "bad-binary-ops.c", "line": 64
                          },
                          "finish": {
                              "column": 36, "file": "bad-binary-ops.c", "line": 64
                          },
                          "label": "T {aka struct t}"
                      }
                  ],
                  "escape-source": false,
                  "message": "invalid operands to binary + ..."
              }

     If a diagnostic contains fix-it hints, it has a ‘fixits’ array,
     consisting of half-open intervals, similar to the output of
     ‘-fdiagnostics-parseable-fixits’.  For example, this diagnostic
     with a replacement fix-it hint:

          demo.c:8:15: error: 'struct s' has no member named 'colour'; did you
            mean 'color'?
              8 |   return ptr->colour;
                |               ^~~~~~
                |               color

     might be printed in JSON form as:

              {
                  "children": [],
                  "fixits": [
                      {
                          "next": {
                              "column": 21,
                              "file": "demo.c",
                              "line": 8
                          },
                          "start": {
                              "column": 15,
                              "file": "demo.c",
                              "line": 8
                          },
                          "string": "color"
                      }
                  ],
                  "kind": "error",
                  "locations": [
                      {
                          "caret": {
                              "column": 15,
                              "file": "demo.c",
                              "line": 8
                          },
                          "finish": {
                              "column": 20,
                              "file": "demo.c",
                              "line": 8
                          }
                      }
                  ],
                  "escape-source": false,
                  "message": "\u2018struct s\u2019 has no member named ..."
              }

     where the fix-it hint suggests replacing the text from ‘start’ up
     to but not including ‘next’ with ‘string’'s value.  Deletions are
     expressed via an empty value for ‘string’, insertions by having
     ‘start’ equal ‘next’.

     If the diagnostic has a path of control-flow events associated with
     it, it has a ‘path’ array of objects representing the events.  Each
     event object has a ‘description’ string, a ‘location’ object, along
     with a ‘function’ string and a ‘depth’ number for representing
     interprocedural paths.  The ‘function’ represents the current
     function at that event, and the ‘depth’ represents the stack depth
     relative to some baseline: the higher, the more frames are within
     the stack.

     For example, the intraprocedural example shown for
     ‘-fdiagnostics-path-format=’ might have this JSON for its path:

              "path": [
                  {
                      "depth": 0,
                      "description": "when 'PyList_New' fails, returning NULL",
                      "function": "test",
                      "location": {
                          "column": 10,
                          "file": "test.c",
                          "line": 25
                      }
                  },
                  {
                      "depth": 0,
                      "description": "when 'i < count'",
                      "function": "test",
                      "location": {
                          "column": 3,
                          "file": "test.c",
                          "line": 27
                      }
                  },
                  {
                      "depth": 0,
                      "description": "when calling 'PyList_Append', passing NULL from (1) as argument 1",
                      "function": "test",
                      "location": {
                          "column": 5,
                          "file": "test.c",
                          "line": 29
                      }
                  }
              ]

     Diagnostics have a boolean attribute ‘escape-source’, hinting
     whether non-ASCII bytes should be escaped when printing the
     pertinent lines of source code (‘true’ for diagnostics involving
     source encoding issues).


File: gcc.info,  Node: Warning Options,  Next: Static Analyzer Options,  Prev: Diagnostic Message Formatting Options,  Up: Invoking GCC

3.8 Options to Request or Suppress Warnings
===========================================

Warnings are diagnostic messages that report constructions that are not
inherently erroneous but that are risky or suggest there may have been
an error.

 The following language-independent options do not enable specific
warnings but control the kinds of diagnostics produced by GCC.

‘-fsyntax-only’
     Check the code for syntax errors, but don't do anything beyond
     that.

‘-fmax-errors=N’
     Limits the maximum number of error messages to N, at which point
     GCC bails out rather than attempting to continue processing the
     source code.  If N is 0 (the default), there is no limit on the
     number of error messages produced.  If ‘-Wfatal-errors’ is also
     specified, then ‘-Wfatal-errors’ takes precedence over this option.

‘-w’
     Inhibit all warning messages.

‘-Werror’
     Make all warnings into errors.

‘-Werror=’
     Make the specified warning into an error.  The specifier for a
     warning is appended; for example ‘-Werror=switch’ turns the
     warnings controlled by ‘-Wswitch’ into errors.  This switch takes a
     negative form, to be used to negate ‘-Werror’ for specific
     warnings; for example ‘-Wno-error=switch’ makes ‘-Wswitch’ warnings
     not be errors, even when ‘-Werror’ is in effect.

     The warning message for each controllable warning includes the
     option that controls the warning.  That option can then be used
     with ‘-Werror=’ and ‘-Wno-error=’ as described above.  (Printing of
     the option in the warning message can be disabled using the
     ‘-fno-diagnostics-show-option’ flag.)

     Note that specifying ‘-Werror=’FOO automatically implies ‘-W’FOO.
     However, ‘-Wno-error=’FOO does not imply anything.

‘-Wfatal-errors’
     This option causes the compiler to abort compilation on the first
     error occurred rather than trying to keep going and printing
     further error messages.

 You can request many specific warnings with options beginning with
‘-W’, for example ‘-Wimplicit’ to request warnings on implicit
declarations.  Each of these specific warning options also has a
negative form beginning ‘-Wno-’ to turn off warnings; for example,
‘-Wno-implicit’.  This manual lists only one of the two forms, whichever
is not the default.  For further language-specific options also refer to
*note C++ Dialect Options:: and *note Objective-C and Objective-C++
Dialect Options::.  Additional warnings can be produced by enabling the
static analyzer; *Note Static Analyzer Options::.

 Some options, such as ‘-Wall’ and ‘-Wextra’, turn on other options,
such as ‘-Wunused’, which may turn on further options, such as
‘-Wunused-value’.  The combined effect of positive and negative forms is
that more specific options have priority over less specific ones,
independently of their position in the command-line.  For options of the
same specificity, the last one takes effect.  Options enabled or
disabled via pragmas (*note Diagnostic Pragmas::) take effect as if they
appeared at the end of the command-line.

 When an unrecognized warning option is requested (e.g.,
‘-Wunknown-warning’), GCC emits a diagnostic stating that the option is
not recognized.  However, if the ‘-Wno-’ form is used, the behavior is
slightly different: no diagnostic is produced for ‘-Wno-unknown-warning’
unless other diagnostics are being produced.  This allows the use of new
‘-Wno-’ options with old compilers, but if something goes wrong, the
compiler warns that an unrecognized option is present.

 The effectiveness of some warnings depends on optimizations also being
enabled.  For example ‘-Wsuggest-final-types’ is more effective with
link-time optimization and some instances of other warnings may not be
issued at all unless optimization is enabled.  While optimization in
general improves the efficacy of control and data flow sensitive
warnings, in some cases it may also cause false positives.

‘-Wpedantic’
‘-pedantic’
     Issue all the warnings demanded by strict ISO C and ISO C++; reject
     all programs that use forbidden extensions, and some other programs
     that do not follow ISO C and ISO C++.  For ISO C, follows the
     version of the ISO C standard specified by any ‘-std’ option used.

     Valid ISO C and ISO C++ programs should compile properly with or
     without this option (though a rare few require ‘-ansi’ or a ‘-std’
     option specifying the required version of ISO C).  However, without
     this option, certain GNU extensions and traditional C and C++
     features are supported as well.  With this option, they are
     rejected.

     ‘-Wpedantic’ does not cause warning messages for use of the
     alternate keywords whose names begin and end with ‘__’.  This
     alternate format can also be used to disable warnings for non-ISO
     ‘__intN’ types, i.e.  ‘__intN__’.  Pedantic warnings are also
     disabled in the expression that follows ‘__extension__’.  However,
     only system header files should use these escape routes;
     application programs should avoid them.  *Note Alternate
     Keywords::.

     Some users try to use ‘-Wpedantic’ to check programs for strict ISO
     C conformance.  They soon find that it does not do quite what they
     want: it finds some non-ISO practices, but not all--only those for
     which ISO C _requires_ a diagnostic, and some others for which
     diagnostics have been added.

     A feature to report any failure to conform to ISO C might be useful
     in some instances, but would require considerable additional work
     and would be quite different from ‘-Wpedantic’.  We don't have
     plans to support such a feature in the near future.

     Where the standard specified with ‘-std’ represents a GNU extended
     dialect of C, such as ‘gnu90’ or ‘gnu99’, there is a corresponding
     “base standard”, the version of ISO C on which the GNU extended
     dialect is based.  Warnings from ‘-Wpedantic’ are given where they
     are required by the base standard.  (It does not make sense for
     such warnings to be given only for features not in the specified
     GNU C dialect, since by definition the GNU dialects of C include
     all features the compiler supports with the given option, and there
     would be nothing to warn about.)

‘-pedantic-errors’
     Give an error whenever the “base standard” (see ‘-Wpedantic’)
     requires a diagnostic, in some cases where there is undefined
     behavior at compile-time and in some other cases that do not
     prevent compilation of programs that are valid according to the
     standard.  This is not equivalent to ‘-Werror=pedantic’, since
     there are errors enabled by this option and not enabled by the
     latter and vice versa.

‘-Wall’
     This enables all the warnings about constructions that some users
     consider questionable, and that are easy to avoid (or modify to
     prevent the warning), even in conjunction with macros.  This also
     enables some language-specific warnings described in *note C++
     Dialect Options:: and *note Objective-C and Objective-C++ Dialect
     Options::.

     ‘-Wall’ turns on the following warning flags:

          -Waddress
          -Warray-bounds=1 (only with -O2)
          -Warray-compare
          -Warray-parameter=2 (C and Objective-C only)
          -Wbool-compare
          -Wbool-operation
          -Wc++11-compat  -Wc++14-compat
          -Wcatch-value (C++ and Objective-C++ only)
          -Wchar-subscripts
          -Wcomment
          -Wdangling-pointer=2
          -Wduplicate-decl-specifier (C and Objective-C only)
          -Wenum-compare (in C/ObjC; this is on by default in C++)
          -Wformat
          -Wformat-overflow
          -Wformat-truncation
          -Wint-in-bool-context
          -Wimplicit (C and Objective-C only)
          -Wimplicit-int (C and Objective-C only)
          -Wimplicit-function-declaration (C and Objective-C only)
          -Winit-self (only for C++)
          -Wlogical-not-parentheses
          -Wmain (only for C/ObjC and unless -ffreestanding)
          -Wmaybe-uninitialized
          -Wmemset-elt-size
          -Wmemset-transposed-args
          -Wmisleading-indentation (only for C/C++)
          -Wmismatched-dealloc
          -Wmismatched-new-delete (only for C/C++)
          -Wmissing-attributes
          -Wmissing-braces (only for C/ObjC)
          -Wmultistatement-macros
          -Wnarrowing (only for C++)
          -Wnonnull
          -Wnonnull-compare
          -Wopenmp-simd
          -Wparentheses
          -Wpessimizing-move (only for C++)
          -Wpointer-sign
          -Wrange-loop-construct (only for C++)
          -Wreorder
          -Wrestrict
          -Wreturn-type
          -Wsequence-point
          -Wsign-compare (only in C++)
          -Wsizeof-array-div
          -Wsizeof-pointer-div
          -Wsizeof-pointer-memaccess
          -Wstrict-aliasing
          -Wstrict-overflow=1
          -Wswitch
          -Wtautological-compare
          -Wtrigraphs
          -Wuninitialized
          -Wunknown-pragmas
          -Wunused-function
          -Wunused-label
          -Wunused-value
          -Wunused-variable
          -Wuse-after-free=3
          -Wvla-parameter (C and Objective-C only)
          -Wvolatile-register-var
          -Wzero-length-bounds

     Note that some warning flags are not implied by ‘-Wall’.  Some of
     them warn about constructions that users generally do not consider
     questionable, but which occasionally you might wish to check for;
     others warn about constructions that are necessary or hard to avoid
     in some cases, and there is no simple way to modify the code to
     suppress the warning.  Some of them are enabled by ‘-Wextra’ but
     many of them must be enabled individually.

‘-Wextra’
     This enables some extra warning flags that are not enabled by
     ‘-Wall’.  (This option used to be called ‘-W’.  The older name is
     still supported, but the newer name is more descriptive.)

          -Wclobbered
          -Wcast-function-type
          -Wdeprecated-copy (C++ only)
          -Wempty-body
          -Wenum-conversion (C only)
          -Wignored-qualifiers
          -Wimplicit-fallthrough=3
          -Wmissing-field-initializers
          -Wmissing-parameter-type (C only)
          -Wold-style-declaration (C only)
          -Woverride-init
          -Wsign-compare (C only)
          -Wstring-compare
          -Wredundant-move (only for C++)
          -Wtype-limits
          -Wuninitialized
          -Wshift-negative-value (in C++11 to C++17 and in C99 and newer)
          -Wunused-parameter (only with -Wunused or -Wall)
          -Wunused-but-set-parameter (only with -Wunused or -Wall)

     The option ‘-Wextra’ also prints warning messages for the following
     cases:

        • A pointer is compared against integer zero with ‘<’, ‘<=’,
          ‘>’, or ‘>=’.

        • (C++ only) An enumerator and a non-enumerator both appear in a
          conditional expression.

        • (C++ only) Ambiguous virtual bases.

        • (C++ only) Subscripting an array that has been declared
          ‘register’.

        • (C++ only) Taking the address of a variable that has been
          declared ‘register’.

        • (C++ only) A base class is not initialized in the copy
          constructor of a derived class.

‘-Wabi (C, Objective-C, C++ and Objective-C++ only)’

     Warn about code affected by ABI changes.  This includes code that
     may not be compatible with the vendor-neutral C++ ABI as well as
     the psABI for the particular target.

     Since G++ now defaults to updating the ABI with each major release,
     normally ‘-Wabi’ warns only about C++ ABI compatibility problems if
     there is a check added later in a release series for an ABI issue
     discovered since the initial release.  ‘-Wabi’ warns about more
     things if an older ABI version is selected (with
     ‘-fabi-version=N’).

     ‘-Wabi’ can also be used with an explicit version number to warn
     about C++ ABI compatibility with a particular ‘-fabi-version’
     level, e.g. ‘-Wabi=2’ to warn about changes relative to
     ‘-fabi-version=2’.

     If an explicit version number is provided and
     ‘-fabi-compat-version’ is not specified, the version number from
     this option is used for compatibility aliases.  If no explicit
     version number is provided with this option, but
     ‘-fabi-compat-version’ is specified, that version number is used
     for C++ ABI warnings.

     Although an effort has been made to warn about all such cases,
     there are probably some cases that are not warned about, even
     though G++ is generating incompatible code.  There may also be
     cases where warnings are emitted even though the code that is
     generated is compatible.

     You should rewrite your code to avoid these warnings if you are
     concerned about the fact that code generated by G++ may not be
     binary compatible with code generated by other compilers.

     Known incompatibilities in ‘-fabi-version=2’ (which was the default
     from GCC 3.4 to 4.9) include:

        • A template with a non-type template parameter of reference
          type was mangled incorrectly:
               extern int N;
               template <int &> struct S {};
               void n (S<N>) {2}

          This was fixed in ‘-fabi-version=3’.

        • SIMD vector types declared using ‘__attribute ((vector_size))’
          were mangled in a non-standard way that does not allow for
          overloading of functions taking vectors of different sizes.

          The mangling was changed in ‘-fabi-version=4’.

        • ‘__attribute ((const))’ and ‘noreturn’ were mangled as type
          qualifiers, and ‘decltype’ of a plain declaration was folded
          away.

          These mangling issues were fixed in ‘-fabi-version=5’.

        • Scoped enumerators passed as arguments to a variadic function
          are promoted like unscoped enumerators, causing ‘va_arg’ to
          complain.  On most targets this does not actually affect the
          parameter passing ABI, as there is no way to pass an argument
          smaller than ‘int’.

          Also, the ABI changed the mangling of template argument packs,
          ‘const_cast’, ‘static_cast’, prefix increment/decrement, and a
          class scope function used as a template argument.

          These issues were corrected in ‘-fabi-version=6’.

        • Lambdas in default argument scope were mangled incorrectly,
          and the ABI changed the mangling of ‘nullptr_t’.

          These issues were corrected in ‘-fabi-version=7’.

        • When mangling a function type with function-cv-qualifiers, the
          un-qualified function type was incorrectly treated as a
          substitution candidate.

          This was fixed in ‘-fabi-version=8’, the default for GCC 5.1.

        • ‘decltype(nullptr)’ incorrectly had an alignment of 1, leading
          to unaligned accesses.  Note that this did not affect the ABI
          of a function with a ‘nullptr_t’ parameter, as parameters have
          a minimum alignment.

          This was fixed in ‘-fabi-version=9’, the default for GCC 5.2.

        • Target-specific attributes that affect the identity of a type,
          such as ia32 calling conventions on a function type (stdcall,
          regparm, etc.), did not affect the mangled name, leading to
          name collisions when function pointers were used as template
          arguments.

          This was fixed in ‘-fabi-version=10’, the default for GCC 6.1.

     This option also enables warnings about psABI-related changes.  The
     known psABI changes at this point include:

        • For SysV/x86-64, unions with ‘long double’ members are passed
          in memory as specified in psABI. Prior to GCC 4.4, this was
          not the case.  For example:

               union U {
                 long double ld;
                 int i;
               };

          ‘union U’ is now always passed in memory.

‘-Wchar-subscripts’
     Warn if an array subscript has type ‘char’.  This is a common cause
     of error, as programmers often forget that this type is signed on
     some machines.  This warning is enabled by ‘-Wall’.

‘-Wno-coverage-mismatch’
     Warn if feedback profiles do not match when using the
     ‘-fprofile-use’ option.  If a source file is changed between
     compiling with ‘-fprofile-generate’ and with ‘-fprofile-use’, the
     files with the profile feedback can fail to match the source file
     and GCC cannot use the profile feedback information.  By default,
     this warning is enabled and is treated as an error.
     ‘-Wno-coverage-mismatch’ can be used to disable the warning or
     ‘-Wno-error=coverage-mismatch’ can be used to disable the error.
     Disabling the error for this warning can result in poorly optimized
     code and is useful only in the case of very minor changes such as
     bug fixes to an existing code-base.  Completely disabling the
     warning is not recommended.

‘-Wno-coverage-invalid-line-number’
     Warn in case a function ends earlier than it begins due to an
     invalid linenum macros.  The warning is emitted only with
     ‘--coverage’ enabled.

     By default, this warning is enabled and is treated as an error.
     ‘-Wno-coverage-invalid-line-number’ can be used to disable the
     warning or ‘-Wno-error=coverage-invalid-line-number’ can be used to
     disable the error.

‘-Wno-cpp (C, Objective-C, C++, Objective-C++ and Fortran only)’
     Suppress warning messages emitted by ‘#warning’ directives.

‘-Wdouble-promotion (C, C++, Objective-C and Objective-C++ only)’
     Give a warning when a value of type ‘float’ is implicitly promoted
     to ‘double’.  CPUs with a 32-bit "single-precision" floating-point
     unit implement ‘float’ in hardware, but emulate ‘double’ in
     software.  On such a machine, doing computations using ‘double’
     values is much more expensive because of the overhead required for
     software emulation.

     It is easy to accidentally do computations with ‘double’ because
     floating-point literals are implicitly of type ‘double’.  For
     example, in:
          float area(float radius)
          {
             return 3.14159 * radius * radius;
          }
     the compiler performs the entire computation with ‘double’ because
     the floating-point literal is a ‘double’.

‘-Wduplicate-decl-specifier (C and Objective-C only)’
     Warn if a declaration has duplicate ‘const’, ‘volatile’, ‘restrict’
     or ‘_Atomic’ specifier.  This warning is enabled by ‘-Wall’.

‘-Wformat’
‘-Wformat=N’
     Check calls to ‘printf’ and ‘scanf’, etc., to make sure that the
     arguments supplied have types appropriate to the format string
     specified, and that the conversions specified in the format string
     make sense.  This includes standard functions, and others specified
     by format attributes (*note Function Attributes::), in the
     ‘printf’, ‘scanf’, ‘strftime’ and ‘strfmon’ (an X/Open extension,
     not in the C standard) families (or other target-specific
     families).  Which functions are checked without format attributes
     having been specified depends on the standard version selected, and
     such checks of functions without the attribute specified are
     disabled by ‘-ffreestanding’ or ‘-fno-builtin’.

     The formats are checked against the format features supported by
     GNU libc version 2.2.  These include all ISO C90 and C99 features,
     as well as features from the Single Unix Specification and some BSD
     and GNU extensions.  Other library implementations may not support
     all these features; GCC does not support warning about features
     that go beyond a particular library's limitations.  However, if
     ‘-Wpedantic’ is used with ‘-Wformat’, warnings are given about
     format features not in the selected standard version (but not for
     ‘strfmon’ formats, since those are not in any version of the C
     standard).  *Note Options Controlling C Dialect: C Dialect Options.

     ‘-Wformat=1’
     ‘-Wformat’
          Option ‘-Wformat’ is equivalent to ‘-Wformat=1’, and
          ‘-Wno-format’ is equivalent to ‘-Wformat=0’.  Since ‘-Wformat’
          also checks for null format arguments for several functions,
          ‘-Wformat’ also implies ‘-Wnonnull’.  Some aspects of this
          level of format checking can be disabled by the options:
          ‘-Wno-format-contains-nul’, ‘-Wno-format-extra-args’, and
          ‘-Wno-format-zero-length’.  ‘-Wformat’ is enabled by ‘-Wall’.

     ‘-Wformat=2’
          Enable ‘-Wformat’ plus additional format checks.  Currently
          equivalent to ‘-Wformat -Wformat-nonliteral -Wformat-security
          -Wformat-y2k’.

‘-Wno-format-contains-nul’
     If ‘-Wformat’ is specified, do not warn about format strings that
     contain NUL bytes.

‘-Wno-format-extra-args’
     If ‘-Wformat’ is specified, do not warn about excess arguments to a
     ‘printf’ or ‘scanf’ format function.  The C standard specifies that
     such arguments are ignored.

     Where the unused arguments lie between used arguments that are
     specified with ‘$’ operand number specifications, normally warnings
     are still given, since the implementation could not know what type
     to pass to ‘va_arg’ to skip the unused arguments.  However, in the
     case of ‘scanf’ formats, this option suppresses the warning if the
     unused arguments are all pointers, since the Single Unix
     Specification says that such unused arguments are allowed.

‘-Wformat-overflow’
‘-Wformat-overflow=LEVEL’
     Warn about calls to formatted input/output functions such as
     ‘sprintf’ and ‘vsprintf’ that might overflow the destination
     buffer.  When the exact number of bytes written by a format
     directive cannot be determined at compile-time it is estimated
     based on heuristics that depend on the LEVEL argument and on
     optimization.  While enabling optimization will in most cases
     improve the accuracy of the warning, it may also result in false
     positives.

     ‘-Wformat-overflow’
     ‘-Wformat-overflow=1’
          Level 1 of ‘-Wformat-overflow’ enabled by ‘-Wformat’ employs a
          conservative approach that warns only about calls that most
          likely overflow the buffer.  At this level, numeric arguments
          to format directives with unknown values are assumed to have
          the value of one, and strings of unknown length to be empty.
          Numeric arguments that are known to be bounded to a subrange
          of their type, or string arguments whose output is bounded
          either by their directive's precision or by a finite set of
          string literals, are assumed to take on the value within the
          range that results in the most bytes on output.  For example,
          the call to ‘sprintf’ below is diagnosed because even with
          both A and B equal to zero, the terminating NUL character
          (‘'\0'’) appended by the function to the destination buffer
          will be written past its end.  Increasing the size of the
          buffer by a single byte is sufficient to avoid the warning,
          though it may not be sufficient to avoid the overflow.

               void f (int a, int b)
               {
                 char buf [13];
                 sprintf (buf, "a = %i, b = %i\n", a, b);
               }

     ‘-Wformat-overflow=2’
          Level 2 warns also about calls that might overflow the
          destination buffer given an argument of sufficient length or
          magnitude.  At level 2, unknown numeric arguments are assumed
          to have the minimum representable value for signed types with
          a precision greater than 1, and the maximum representable
          value otherwise.  Unknown string arguments whose length cannot
          be assumed to be bounded either by the directive's precision,
          or by a finite set of string literals they may evaluate to, or
          the character array they may point to, are assumed to be 1
          character long.

          At level 2, the call in the example above is again diagnosed,
          but this time because with A equal to a 32-bit ‘INT_MIN’ the
          first ‘%i’ directive will write some of its digits beyond the
          end of the destination buffer.  To make the call safe
          regardless of the values of the two variables, the size of the
          destination buffer must be increased to at least 34 bytes.
          GCC includes the minimum size of the buffer in an
          informational note following the warning.

          An alternative to increasing the size of the destination
          buffer is to constrain the range of formatted values.  The
          maximum length of string arguments can be bounded by
          specifying the precision in the format directive.  When
          numeric arguments of format directives can be assumed to be
          bounded by less than the precision of their type, choosing an
          appropriate length modifier to the format specifier will
          reduce the required buffer size.  For example, if A and B in
          the example above can be assumed to be within the precision of
          the ‘short int’ type then using either the ‘%hi’ format
          directive or casting the argument to ‘short’ reduces the
          maximum required size of the buffer to 24 bytes.

               void f (int a, int b)
               {
                 char buf [23];
                 sprintf (buf, "a = %hi, b = %i\n", a, (short)b);
               }

‘-Wno-format-zero-length’
     If ‘-Wformat’ is specified, do not warn about zero-length formats.
     The C standard specifies that zero-length formats are allowed.

‘-Wformat-nonliteral’
     If ‘-Wformat’ is specified, also warn if the format string is not a
     string literal and so cannot be checked, unless the format function
     takes its format arguments as a ‘va_list’.

‘-Wformat-security’
     If ‘-Wformat’ is specified, also warn about uses of format
     functions that represent possible security problems.  At present,
     this warns about calls to ‘printf’ and ‘scanf’ functions where the
     format string is not a string literal and there are no format
     arguments, as in ‘printf (foo);’.  This may be a security hole if
     the format string came from untrusted input and contains ‘%n’.
     (This is currently a subset of what ‘-Wformat-nonliteral’ warns
     about, but in future warnings may be added to ‘-Wformat-security’
     that are not included in ‘-Wformat-nonliteral’.)

‘-Wformat-signedness’
     If ‘-Wformat’ is specified, also warn if the format string requires
     an unsigned argument and the argument is signed and vice versa.

‘-Wformat-truncation’
‘-Wformat-truncation=LEVEL’
     Warn about calls to formatted input/output functions such as
     ‘snprintf’ and ‘vsnprintf’ that might result in output truncation.
     When the exact number of bytes written by a format directive cannot
     be determined at compile-time it is estimated based on heuristics
     that depend on the LEVEL argument and on optimization.  While
     enabling optimization will in most cases improve the accuracy of
     the warning, it may also result in false positives.  Except as
     noted otherwise, the option uses the same logic
     ‘-Wformat-overflow’.

     ‘-Wformat-truncation’
     ‘-Wformat-truncation=1’
          Level 1 of ‘-Wformat-truncation’ enabled by ‘-Wformat’ employs
          a conservative approach that warns only about calls to bounded
          functions whose return value is unused and that will most
          likely result in output truncation.

     ‘-Wformat-truncation=2’
          Level 2 warns also about calls to bounded functions whose
          return value is used and that might result in truncation given
          an argument of sufficient length or magnitude.

‘-Wformat-y2k’
     If ‘-Wformat’ is specified, also warn about ‘strftime’ formats that
     may yield only a two-digit year.

‘-Wnonnull’
     Warn about passing a null pointer for arguments marked as requiring
     a non-null value by the ‘nonnull’ function attribute.

     ‘-Wnonnull’ is included in ‘-Wall’ and ‘-Wformat’.  It can be
     disabled with the ‘-Wno-nonnull’ option.

‘-Wnonnull-compare’
     Warn when comparing an argument marked with the ‘nonnull’ function
     attribute against null inside the function.

     ‘-Wnonnull-compare’ is included in ‘-Wall’.  It can be disabled
     with the ‘-Wno-nonnull-compare’ option.

‘-Wnull-dereference’
     Warn if the compiler detects paths that trigger erroneous or
     undefined behavior due to dereferencing a null pointer.  This
     option is only active when ‘-fdelete-null-pointer-checks’ is
     active, which is enabled by optimizations in most targets.  The
     precision of the warnings depends on the optimization options used.

‘-Winfinite-recursion’
     Warn about infinitely recursive calls.  The warning is effective at
     all optimization levels but requires optimization in order to
     detect infinite recursion in calls between two or more functions.
     ‘-Winfinite-recursion’ is included in ‘-Wall’.

‘-Winit-self (C, C++, Objective-C and Objective-C++ only)’
     Warn about uninitialized variables that are initialized with
     themselves.  Note this option can only be used with the
     ‘-Wuninitialized’ option.

     For example, GCC warns about ‘i’ being uninitialized in the
     following snippet only when ‘-Winit-self’ has been specified:
          int f()
          {
            int i = i;
            return i;
          }

     This warning is enabled by ‘-Wall’ in C++.

‘-Wno-implicit-int (C and Objective-C only)’
     This option controls warnings when a declaration does not specify a
     type.  This warning is enabled by default in C99 and later dialects
     of C, and also by ‘-Wall’.

‘-Wno-implicit-function-declaration (C and Objective-C only)’
     This option controls warnings when a function is used before being
     declared.  This warning is enabled by default in C99 and later
     dialects of C, and also by ‘-Wall’.  The warning is made into an
     error by ‘-pedantic-errors’.

‘-Wimplicit (C and Objective-C only)’
     Same as ‘-Wimplicit-int’ and ‘-Wimplicit-function-declaration’.
     This warning is enabled by ‘-Wall’.

‘-Wimplicit-fallthrough’
     ‘-Wimplicit-fallthrough’ is the same as ‘-Wimplicit-fallthrough=3’
     and ‘-Wno-implicit-fallthrough’ is the same as
     ‘-Wimplicit-fallthrough=0’.

‘-Wimplicit-fallthrough=N’
     Warn when a switch case falls through.  For example:

          switch (cond)
            {
            case 1:
              a = 1;
              break;
            case 2:
              a = 2;
            case 3:
              a = 3;
              break;
            }

     This warning does not warn when the last statement of a case cannot
     fall through, e.g.  when there is a return statement or a call to
     function declared with the noreturn attribute.
     ‘-Wimplicit-fallthrough=’ also takes into account control flow
     statements, such as ifs, and only warns when appropriate.  E.g.

          switch (cond)
            {
            case 1:
              if (i > 3) {
                bar (5);
                break;
              } else if (i < 1) {
                bar (0);
              } else
                return;
            default:
              ...
            }

     Since there are occasions where a switch case fall through is
     desirable, GCC provides an attribute, ‘__attribute__
     ((fallthrough))’, that is to be used along with a null statement to
     suppress this warning that would normally occur:

          switch (cond)
            {
            case 1:
              bar (0);
              __attribute__ ((fallthrough));
            default:
              ...
            }

     C++17 provides a standard way to suppress the
     ‘-Wimplicit-fallthrough’ warning using ‘[[fallthrough]];’ instead
     of the GNU attribute.  In C++11 or C++14 users can use
     ‘[[gnu::fallthrough]];’, which is a GNU extension.  Instead of
     these attributes, it is also possible to add a fallthrough comment
     to silence the warning.  The whole body of the C or C++ style
     comment should match the given regular expressions listed below.
     The option argument N specifies what kind of comments are accepted:

        • ‘-Wimplicit-fallthrough=0’ disables the warning altogether.

        • ‘-Wimplicit-fallthrough=1’ matches ‘.*’ regular expression,
          any comment is used as fallthrough comment.

        • ‘-Wimplicit-fallthrough=2’ case insensitively matches
          ‘.*falls?[ \t-]*thr(ough|u).*’ regular expression.

        • ‘-Wimplicit-fallthrough=3’ case sensitively matches one of the
          following regular expressions:

             • ‘-fallthrough’

             • ‘@fallthrough@’

             • ‘lint -fallthrough[ \t]*’

             • ‘[ \t.!]*(ELSE,? |INTENTIONAL(LY)? )?
               FALL(S | |-)?THR(OUGH|U)[ \t.!]*(-[^\n\r]*)?’

             • ‘[ \t.!]*(Else,? |Intentional(ly)? )?
               Fall((s | |-)[Tt]|t)hr(ough|u)[ \t.!]*(-[^\n\r]*)?’

             • ‘[ \t.!]*([Ee]lse,? |[Ii]ntentional(ly)? )?
               fall(s | |-)?thr(ough|u)[ \t.!]*(-[^\n\r]*)?’

        • ‘-Wimplicit-fallthrough=4’ case sensitively matches one of the
          following regular expressions:

             • ‘-fallthrough’

             • ‘@fallthrough@’

             • ‘lint -fallthrough[ \t]*’

             • ‘[ \t]*FALLTHR(OUGH|U)[ \t]*’

        • ‘-Wimplicit-fallthrough=5’ doesn't recognize any comments as
          fallthrough comments, only attributes disable the warning.

     The comment needs to be followed after optional whitespace and
     other comments by ‘case’ or ‘default’ keywords or by a user label
     that precedes some ‘case’ or ‘default’ label.

          switch (cond)
            {
            case 1:
              bar (0);
              /* FALLTHRU */
            default:
              ...
            }

     The ‘-Wimplicit-fallthrough=3’ warning is enabled by ‘-Wextra’.

‘-Wno-if-not-aligned (C, C++, Objective-C and Objective-C++ only)’
     Control if warnings triggered by the ‘warn_if_not_aligned’
     attribute should be issued.  These warnings are enabled by default.

‘-Wignored-qualifiers (C and C++ only)’
     Warn if the return type of a function has a type qualifier such as
     ‘const’.  For ISO C such a type qualifier has no effect, since the
     value returned by a function is not an lvalue.  For C++, the
     warning is only emitted for scalar types or ‘void’.  ISO C
     prohibits qualified ‘void’ return types on function definitions, so
     such return types always receive a warning even without this
     option.

     This warning is also enabled by ‘-Wextra’.

‘-Wno-ignored-attributes (C and C++ only)’
     This option controls warnings when an attribute is ignored.  This
     is different from the ‘-Wattributes’ option in that it warns
     whenever the compiler decides to drop an attribute, not that the
     attribute is either unknown, used in a wrong place, etc.  This
     warning is enabled by default.

‘-Wmain’
     Warn if the type of ‘main’ is suspicious.  ‘main’ should be a
     function with external linkage, returning int, taking either zero
     arguments, two, or three arguments of appropriate types.  This
     warning is enabled by default in C++ and is enabled by either
     ‘-Wall’ or ‘-Wpedantic’.

‘-Wmisleading-indentation (C and C++ only)’
     Warn when the indentation of the code does not reflect the block
     structure.  Specifically, a warning is issued for ‘if’, ‘else’,
     ‘while’, and ‘for’ clauses with a guarded statement that does not
     use braces, followed by an unguarded statement with the same
     indentation.

     In the following example, the call to "bar" is misleadingly
     indented as if it were guarded by the "if" conditional.

            if (some_condition ())
              foo ();
              bar ();  /* Gotcha: this is not guarded by the "if".  */

     In the case of mixed tabs and spaces, the warning uses the
     ‘-ftabstop=’ option to determine if the statements line up
     (defaulting to 8).

     The warning is not issued for code involving multiline preprocessor
     logic such as the following example.

            if (flagA)
              foo (0);
          #if SOME_CONDITION_THAT_DOES_NOT_HOLD
            if (flagB)
          #endif
              foo (1);

     The warning is not issued after a ‘#line’ directive, since this
     typically indicates autogenerated code, and no assumptions can be
     made about the layout of the file that the directive references.

     This warning is enabled by ‘-Wall’ in C and C++.

‘-Wmissing-attributes’
     Warn when a declaration of a function is missing one or more
     attributes that a related function is declared with and whose
     absence may adversely affect the correctness or efficiency of
     generated code.  For example, the warning is issued for
     declarations of aliases that use attributes to specify less
     restrictive requirements than those of their targets.  This
     typically represents a potential optimization opportunity.  By
     contrast, the ‘-Wattribute-alias=2’ option controls warnings issued
     when the alias is more restrictive than the target, which could
     lead to incorrect code generation.  Attributes considered include
     ‘alloc_align’, ‘alloc_size’, ‘cold’, ‘const’, ‘hot’, ‘leaf’,
     ‘malloc’, ‘nonnull’, ‘noreturn’, ‘nothrow’, ‘pure’,
     ‘returns_nonnull’, and ‘returns_twice’.

     In C++, the warning is issued when an explicit specialization of a
     primary template declared with attribute ‘alloc_align’,
     ‘alloc_size’, ‘assume_aligned’, ‘format’, ‘format_arg’, ‘malloc’,
     or ‘nonnull’ is declared without it.  Attributes ‘deprecated’,
     ‘error’, and ‘warning’ suppress the warning.  (*note Function
     Attributes::).

     You can use the ‘copy’ attribute to apply the same set of
     attributes to a declaration as that on another declaration without
     explicitly enumerating the attributes.  This attribute can be
     applied to declarations of functions (*note Common Function
     Attributes::), variables (*note Common Variable Attributes::), or
     types (*note Common Type Attributes::).

     ‘-Wmissing-attributes’ is enabled by ‘-Wall’.

     For example, since the declaration of the primary function template
     below makes use of both attribute ‘malloc’ and ‘alloc_size’ the
     declaration of the explicit specialization of the template is
     diagnosed because it is missing one of the attributes.

          template <class T>
          T* __attribute__ ((malloc, alloc_size (1)))
          allocate (size_t);

          template <>
          void* __attribute__ ((malloc))   // missing alloc_size
          allocate<void> (size_t);

‘-Wmissing-braces’
     Warn if an aggregate or union initializer is not fully bracketed.
     In the following example, the initializer for ‘a’ is not fully
     bracketed, but that for ‘b’ is fully bracketed.

          int a[2][2] = { 0, 1, 2, 3 };
          int b[2][2] = { { 0, 1 }, { 2, 3 } };

     This warning is enabled by ‘-Wall’.

‘-Wmissing-include-dirs (C, C++, Objective-C, Objective-C++ and Fortran only)’
     Warn if a user-supplied include directory does not exist.  This
     opions is disabled by default for C, C++, Objective-C and
     Objective-C++.  For Fortran, it is partially enabled by default by
     warning for -I and -J, only.

‘-Wno-missing-profile’
     This option controls warnings if feedback profiles are missing when
     using the ‘-fprofile-use’ option.  This option diagnoses those
     cases where a new function or a new file is added between compiling
     with ‘-fprofile-generate’ and with ‘-fprofile-use’, without
     regenerating the profiles.  In these cases, the profile feedback
     data files do not contain any profile feedback information for the
     newly added function or file respectively.  Also, in the case when
     profile count data (.gcda) files are removed, GCC cannot use any
     profile feedback information.  In all these cases, warnings are
     issued to inform you that a profile generation step is due.
     Ignoring the warning can result in poorly optimized code.
     ‘-Wno-missing-profile’ can be used to disable the warning, but this
     is not recommended and should be done only when non-existent
     profile data is justified.

‘-Wmismatched-dealloc’

     Warn for calls to deallocation functions with pointer arguments
     returned from from allocations functions for which the former isn't
     a suitable deallocator.  A pair of functions can be associated as
     matching allocators and deallocators by use of attribute ‘malloc’.
     Unless disabled by the ‘-fno-builtin’ option the standard functions
     ‘calloc’, ‘malloc’, ‘realloc’, and ‘free’, as well as the
     corresponding forms of C++ ‘operator new’ and ‘operator delete’ are
     implicitly associated as matching allocators and deallocators.  In
     the following example ‘mydealloc’ is the deallocator for pointers
     returned from ‘myalloc’.

          void mydealloc (void*);

          __attribute__ ((malloc (mydealloc, 1))) void*
          myalloc (size_t);

          void f (void)
          {
            void *p = myalloc (32);
            // ...use p...
            free (p);   // warning: not a matching deallocator for myalloc
            mydealloc (p);   // ok
          }

     In C++, the related option ‘-Wmismatched-new-delete’ diagnoses
     mismatches involving either ‘operator new’ or ‘operator delete’.

     Option ‘-Wmismatched-dealloc’ is included in ‘-Wall’.

‘-Wmultistatement-macros’
     Warn about unsafe multiple statement macros that appear to be
     guarded by a clause such as ‘if’, ‘else’, ‘for’, ‘switch’, or
     ‘while’, in which only the first statement is actually guarded
     after the macro is expanded.

     For example:

          #define DOIT x++; y++
          if (c)
            DOIT;

     will increment ‘y’ unconditionally, not just when ‘c’ holds.  The
     can usually be fixed by wrapping the macro in a do-while loop:
          #define DOIT do { x++; y++; } while (0)
          if (c)
            DOIT;

     This warning is enabled by ‘-Wall’ in C and C++.

‘-Wparentheses’
     Warn if parentheses are omitted in certain contexts, such as when
     there is an assignment in a context where a truth value is
     expected, or when operators are nested whose precedence people
     often get confused about.

     Also warn if a comparison like ‘x<=y<=z’ appears; this is
     equivalent to ‘(x<=y ? 1 : 0) <= z’, which is a different
     interpretation from that of ordinary mathematical notation.

     Also warn for dangerous uses of the GNU extension to ‘?:’ with
     omitted middle operand.  When the condition in the ‘?’: operator is
     a boolean expression, the omitted value is always 1.  Often
     programmers expect it to be a value computed inside the conditional
     expression instead.

     For C++ this also warns for some cases of unnecessary parentheses
     in declarations, which can indicate an attempt at a function call
     instead of a declaration:
          {
            // Declares a local variable called mymutex.
            std::unique_lock<std::mutex> (mymutex);
            // User meant std::unique_lock<std::mutex> lock (mymutex);
          }

     This warning is enabled by ‘-Wall’.

‘-Wsequence-point’
     Warn about code that may have undefined semantics because of
     violations of sequence point rules in the C and C++ standards.

     The C and C++ standards define the order in which expressions in a
     C/C++ program are evaluated in terms of “sequence points”, which
     represent a partial ordering between the execution of parts of the
     program: those executed before the sequence point, and those
     executed after it.  These occur after the evaluation of a full
     expression (one which is not part of a larger expression), after
     the evaluation of the first operand of a ‘&&’, ‘||’, ‘? :’ or ‘,’
     (comma) operator, before a function is called (but after the
     evaluation of its arguments and the expression denoting the called
     function), and in certain other places.  Other than as expressed by
     the sequence point rules, the order of evaluation of subexpressions
     of an expression is not specified.  All these rules describe only a
     partial order rather than a total order, since, for example, if two
     functions are called within one expression with no sequence point
     between them, the order in which the functions are called is not
     specified.  However, the standards committee have ruled that
     function calls do not overlap.

     It is not specified when between sequence points modifications to
     the values of objects take effect.  Programs whose behavior depends
     on this have undefined behavior; the C and C++ standards specify
     that "Between the previous and next sequence point an object shall
     have its stored value modified at most once by the evaluation of an
     expression.  Furthermore, the prior value shall be read only to
     determine the value to be stored.".  If a program breaks these
     rules, the results on any particular implementation are entirely
     unpredictable.

     Examples of code with undefined behavior are ‘a = a++;’, ‘a[n] =
     b[n++]’ and ‘a[i++] = i;’.  Some more complicated cases are not
     diagnosed by this option, and it may give an occasional false
     positive result, but in general it has been found fairly effective
     at detecting this sort of problem in programs.

     The C++17 standard will define the order of evaluation of operands
     in more cases: in particular it requires that the right-hand side
     of an assignment be evaluated before the left-hand side, so the
     above examples are no longer undefined.  But this option will still
     warn about them, to help people avoid writing code that is
     undefined in C and earlier revisions of C++.

     The standard is worded confusingly, therefore there is some debate
     over the precise meaning of the sequence point rules in subtle
     cases.  Links to discussions of the problem, including proposed
     formal definitions, may be found on the GCC readings page, at
     <https://gcc.gnu.org/readings.html>.

     This warning is enabled by ‘-Wall’ for C and C++.

‘-Wno-return-local-addr’
     Do not warn about returning a pointer (or in C++, a reference) to a
     variable that goes out of scope after the function returns.

‘-Wreturn-type’
     Warn whenever a function is defined with a return type that
     defaults to ‘int’.  Also warn about any ‘return’ statement with no
     return value in a function whose return type is not ‘void’ (falling
     off the end of the function body is considered returning without a
     value).

     For C only, warn about a ‘return’ statement with an expression in a
     function whose return type is ‘void’, unless the expression type is
     also ‘void’.  As a GNU extension, the latter case is accepted
     without a warning unless ‘-Wpedantic’ is used.  Attempting to use
     the return value of a non-‘void’ function other than ‘main’ that
     flows off the end by reaching the closing curly brace that
     terminates the function is undefined.

     Unlike in C, in C++, flowing off the end of a non-‘void’ function
     other than ‘main’ results in undefined behavior even when the value
     of the function is not used.

     This warning is enabled by default in C++ and by ‘-Wall’ otherwise.

‘-Wno-shift-count-negative’
     Controls warnings if a shift count is negative.  This warning is
     enabled by default.

‘-Wno-shift-count-overflow’
     Controls warnings if a shift count is greater than or equal to the
     bit width of the type.  This warning is enabled by default.

‘-Wshift-negative-value’
     Warn if left shifting a negative value.  This warning is enabled by
     ‘-Wextra’ in C99 (and newer) and C++11 to C++17 modes.

‘-Wno-shift-overflow’
‘-Wshift-overflow=N’
     These options control warnings about left shift overflows.

     ‘-Wshift-overflow=1’
          This is the warning level of ‘-Wshift-overflow’ and is enabled
          by default in C99 and C++11 modes (and newer).  This warning
          level does not warn about left-shifting 1 into the sign bit.
          (However, in C, such an overflow is still rejected in contexts
          where an integer constant expression is required.)  No warning
          is emitted in C++20 mode (and newer), as signed left shifts
          always wrap.

     ‘-Wshift-overflow=2’
          This warning level also warns about left-shifting 1 into the
          sign bit, unless C++14 mode (or newer) is active.

‘-Wswitch’
     Warn whenever a ‘switch’ statement has an index of enumerated type
     and lacks a ‘case’ for one or more of the named codes of that
     enumeration.  (The presence of a ‘default’ label prevents this
     warning.)  ‘case’ labels outside the enumeration range also provoke
     warnings when this option is used (even if there is a ‘default’
     label).  This warning is enabled by ‘-Wall’.

‘-Wswitch-default’
     Warn whenever a ‘switch’ statement does not have a ‘default’ case.

‘-Wswitch-enum’
     Warn whenever a ‘switch’ statement has an index of enumerated type
     and lacks a ‘case’ for one or more of the named codes of that
     enumeration.  ‘case’ labels outside the enumeration range also
     provoke warnings when this option is used.  The only difference
     between ‘-Wswitch’ and this option is that this option gives a
     warning about an omitted enumeration code even if there is a
     ‘default’ label.

‘-Wno-switch-bool’
     Do not warn when a ‘switch’ statement has an index of boolean type
     and the case values are outside the range of a boolean type.  It is
     possible to suppress this warning by casting the controlling
     expression to a type other than ‘bool’.  For example:
          switch ((int) (a == 4))
            {
            ...
            }
     This warning is enabled by default for C and C++ programs.

‘-Wno-switch-outside-range’
     This option controls warnings when a ‘switch’ case has a value that
     is outside of its respective type range.  This warning is enabled
     by default for C and C++ programs.

‘-Wno-switch-unreachable’
     Do not warn when a ‘switch’ statement contains statements between
     the controlling expression and the first case label, which will
     never be executed.  For example:
          switch (cond)
            {
             i = 15;
            ...
             case 5:
            ...
            }
     ‘-Wswitch-unreachable’ does not warn if the statement between the
     controlling expression and the first case label is just a
     declaration:
          switch (cond)
            {
             int i;
            ...
             case 5:
             i = 5;
            ...
            }
     This warning is enabled by default for C and C++ programs.

‘-Wsync-nand (C and C++ only)’
     Warn when ‘__sync_fetch_and_nand’ and ‘__sync_nand_and_fetch’
     built-in functions are used.  These functions changed semantics in
     GCC 4.4.

‘-Wtrivial-auto-var-init’
     Warn when ‘-ftrivial-auto-var-init’ cannot initialize the automatic
     variable.  A common situation is an automatic variable that is
     declared between the controlling expression and the first case
     label of a ‘switch’ statement.

‘-Wunused-but-set-parameter’
     Warn whenever a function parameter is assigned to, but otherwise
     unused (aside from its declaration).

     To suppress this warning use the ‘unused’ attribute (*note Variable
     Attributes::).

     This warning is also enabled by ‘-Wunused’ together with ‘-Wextra’.

‘-Wunused-but-set-variable’
     Warn whenever a local variable is assigned to, but otherwise unused
     (aside from its declaration).  This warning is enabled by ‘-Wall’.

     To suppress this warning use the ‘unused’ attribute (*note Variable
     Attributes::).

     This warning is also enabled by ‘-Wunused’, which is enabled by
     ‘-Wall’.

‘-Wunused-function’
     Warn whenever a static function is declared but not defined or a
     non-inline static function is unused.  This warning is enabled by
     ‘-Wall’.

‘-Wunused-label’
     Warn whenever a label is declared but not used.  This warning is
     enabled by ‘-Wall’.

     To suppress this warning use the ‘unused’ attribute (*note Variable
     Attributes::).

‘-Wunused-local-typedefs (C, Objective-C, C++ and Objective-C++ only)’
     Warn when a typedef locally defined in a function is not used.
     This warning is enabled by ‘-Wall’.

‘-Wunused-parameter’
     Warn whenever a function parameter is unused aside from its
     declaration.

     To suppress this warning use the ‘unused’ attribute (*note Variable
     Attributes::).

‘-Wno-unused-result’
     Do not warn if a caller of a function marked with attribute
     ‘warn_unused_result’ (*note Function Attributes::) does not use its
     return value.  The default is ‘-Wunused-result’.

‘-Wunused-variable’
     Warn whenever a local or static variable is unused aside from its
     declaration.  This option implies ‘-Wunused-const-variable=1’ for
     C, but not for C++.  This warning is enabled by ‘-Wall’.

     To suppress this warning use the ‘unused’ attribute (*note Variable
     Attributes::).

‘-Wunused-const-variable’
‘-Wunused-const-variable=N’
     Warn whenever a constant static variable is unused aside from its
     declaration.  ‘-Wunused-const-variable=1’ is enabled by
     ‘-Wunused-variable’ for C, but not for C++.  In C this declares
     variable storage, but in C++ this is not an error since const
     variables take the place of ‘#define’s.

     To suppress this warning use the ‘unused’ attribute (*note Variable
     Attributes::).

     ‘-Wunused-const-variable=1’
          This is the warning level that is enabled by
          ‘-Wunused-variable’ for C. It warns only about unused static
          const variables defined in the main compilation unit, but not
          about static const variables declared in any header included.

     ‘-Wunused-const-variable=2’
          This warning level also warns for unused constant static
          variables in headers (excluding system headers).  This is the
          warning level of ‘-Wunused-const-variable’ and must be
          explicitly requested since in C++ this isn't an error and in C
          it might be harder to clean up all headers included.

‘-Wunused-value’
     Warn whenever a statement computes a result that is explicitly not
     used.  To suppress this warning cast the unused expression to
     ‘void’.  This includes an expression-statement or the left-hand
     side of a comma expression that contains no side effects.  For
     example, an expression such as ‘x[i,j]’ causes a warning, while
     ‘x[(void)i,j]’ does not.

     This warning is enabled by ‘-Wall’.

‘-Wunused’
     All the above ‘-Wunused’ options combined.

     In order to get a warning about an unused function parameter, you
     must either specify ‘-Wextra -Wunused’ (note that ‘-Wall’ implies
     ‘-Wunused’), or separately specify ‘-Wunused-parameter’.

‘-Wuninitialized’
     Warn if an object with automatic or allocated storage duration is
     used without having been initialized.  In C++, also warn if a
     non-static reference or non-static ‘const’ member appears in a
     class without constructors.

     In addition, passing a pointer (or in C++, a reference) to an
     uninitialized object to a ‘const’-qualified argument of a built-in
     function known to read the object is also diagnosed by this
     warning.  (‘-Wmaybe-uninitialized’ is issued for ordinary
     functions.)

     If you want to warn about code that uses the uninitialized value of
     the variable in its own initializer, use the ‘-Winit-self’ option.

     These warnings occur for individual uninitialized elements of
     structure, union or array variables as well as for variables that
     are uninitialized as a whole.  They do not occur for variables or
     elements declared ‘volatile’.  Because these warnings depend on
     optimization, the exact variables or elements for which there are
     warnings depend on the precise optimization options and version of
     GCC used.

     Note that there may be no warning about a variable that is used
     only to compute a value that itself is never used, because such
     computations may be deleted by data flow analysis before the
     warnings are printed.

     In C++, this warning also warns about using uninitialized objects
     in member-initializer-lists.  For example, GCC warns about ‘b’
     being uninitialized in the following snippet:

          struct A {
            int a;
            int b;
            A() : a(b) { }
          };

‘-Wno-invalid-memory-model’
     This option controls warnings for invocations of *note __atomic
     Builtins::, *note __sync Builtins::, and the C11 atomic generic
     functions with a memory consistency argument that is either invalid
     for the operation or outside the range of values of the
     ‘memory_order’ enumeration.  For example, since the
     ‘__atomic_store’ and ‘__atomic_store_n’ built-ins are only defined
     for the relaxed, release, and sequentially consistent memory orders
     the following code is diagnosed:

          void store (int *i)
          {
            __atomic_store_n (i, 0, memory_order_consume);
          }

     ‘-Winvalid-memory-model’ is enabled by default.

‘-Wmaybe-uninitialized’
     For an object with automatic or allocated storage duration, if
     there exists a path from the function entry to a use of the object
     that is initialized, but there exist some other paths for which the
     object is not initialized, the compiler emits a warning if it
     cannot prove the uninitialized paths are not executed at run time.

     In addition, passing a pointer (or in C++, a reference) to an
     uninitialized object to a ‘const’-qualified function argument is
     also diagnosed by this warning.  (‘-Wuninitialized’ is issued for
     built-in functions known to read the object.)  Annotating the
     function with attribute ‘access (none)’ indicates that the argument
     isn't used to access the object and avoids the warning (*note
     Common Function Attributes::).

     These warnings are only possible in optimizing compilation, because
     otherwise GCC does not keep track of the state of variables.

     These warnings are made optional because GCC may not be able to
     determine when the code is correct in spite of appearing to have an
     error.  Here is one example of how this can happen:

          {
            int x;
            switch (y)
              {
              case 1: x = 1;
                break;
              case 2: x = 4;
                break;
              case 3: x = 5;
              }
            foo (x);
          }

     If the value of ‘y’ is always 1, 2 or 3, then ‘x’ is always
     initialized, but GCC doesn't know this.  To suppress the warning,
     you need to provide a default case with assert(0) or similar code.

     This option also warns when a non-volatile automatic variable might
     be changed by a call to ‘longjmp’.  The compiler sees only the
     calls to ‘setjmp’.  It cannot know where ‘longjmp’ will be called;
     in fact, a signal handler could call it at any point in the code.
     As a result, you may get a warning even when there is in fact no
     problem because ‘longjmp’ cannot in fact be called at the place
     that would cause a problem.

     Some spurious warnings can be avoided if you declare all the
     functions you use that never return as ‘noreturn’.  *Note Function
     Attributes::.

     This warning is enabled by ‘-Wall’ or ‘-Wextra’.

‘-Wunknown-pragmas’
     Warn when a ‘#pragma’ directive is encountered that is not
     understood by GCC.  If this command-line option is used, warnings
     are even issued for unknown pragmas in system header files.  This
     is not the case if the warnings are only enabled by the ‘-Wall’
     command-line option.

‘-Wno-pragmas’
     Do not warn about misuses of pragmas, such as incorrect parameters,
     invalid syntax, or conflicts between pragmas.  See also
     ‘-Wunknown-pragmas’.

‘-Wno-prio-ctor-dtor’
     Do not warn if a priority from 0 to 100 is used for constructor or
     destructor.  The use of constructor and destructor attributes allow
     you to assign a priority to the constructor/destructor to control
     its order of execution before ‘main’ is called or after it returns.
     The priority values must be greater than 100 as the compiler
     reserves priority values between 0-100 for the implementation.

‘-Wstrict-aliasing’
     This option is only active when ‘-fstrict-aliasing’ is active.  It
     warns about code that might break the strict aliasing rules that
     the compiler is using for optimization.  The warning does not catch
     all cases, but does attempt to catch the more common pitfalls.  It
     is included in ‘-Wall’.  It is equivalent to ‘-Wstrict-aliasing=3’

‘-Wstrict-aliasing=n’
     This option is only active when ‘-fstrict-aliasing’ is active.  It
     warns about code that might break the strict aliasing rules that
     the compiler is using for optimization.  Higher levels correspond
     to higher accuracy (fewer false positives).  Higher levels also
     correspond to more effort, similar to the way ‘-O’ works.
     ‘-Wstrict-aliasing’ is equivalent to ‘-Wstrict-aliasing=3’.

     Level 1: Most aggressive, quick, least accurate.  Possibly useful
     when higher levels do not warn but ‘-fstrict-aliasing’ still breaks
     the code, as it has very few false negatives.  However, it has many
     false positives.  Warns for all pointer conversions between
     possibly incompatible types, even if never dereferenced.  Runs in
     the front end only.

     Level 2: Aggressive, quick, not too precise.  May still have many
     false positives (not as many as level 1 though), and few false
     negatives (but possibly more than level 1).  Unlike level 1, it
     only warns when an address is taken.  Warns about incomplete types.
     Runs in the front end only.

     Level 3 (default for ‘-Wstrict-aliasing’): Should have very few
     false positives and few false negatives.  Slightly slower than
     levels 1 or 2 when optimization is enabled.  Takes care of the
     common pun+dereference pattern in the front end:
     ‘*(int*)&some_float’.  If optimization is enabled, it also runs in
     the back end, where it deals with multiple statement cases using
     flow-sensitive points-to information.  Only warns when the
     converted pointer is dereferenced.  Does not warn about incomplete
     types.

‘-Wstrict-overflow’
‘-Wstrict-overflow=N’
     This option is only active when signed overflow is undefined.  It
     warns about cases where the compiler optimizes based on the
     assumption that signed overflow does not occur.  Note that it does
     not warn about all cases where the code might overflow: it only
     warns about cases where the compiler implements some optimization.
     Thus this warning depends on the optimization level.

     An optimization that assumes that signed overflow does not occur is
     perfectly safe if the values of the variables involved are such
     that overflow never does, in fact, occur.  Therefore this warning
     can easily give a false positive: a warning about code that is not
     actually a problem.  To help focus on important issues, several
     warning levels are defined.  No warnings are issued for the use of
     undefined signed overflow when estimating how many iterations a
     loop requires, in particular when determining whether a loop will
     be executed at all.

     ‘-Wstrict-overflow=1’
          Warn about cases that are both questionable and easy to avoid.
          For example the compiler simplifies ‘x + 1 > x’ to ‘1’.  This
          level of ‘-Wstrict-overflow’ is enabled by ‘-Wall’; higher
          levels are not, and must be explicitly requested.

     ‘-Wstrict-overflow=2’
          Also warn about other cases where a comparison is simplified
          to a constant.  For example: ‘abs (x) >= 0’.  This can only be
          simplified when signed integer overflow is undefined, because
          ‘abs (INT_MIN)’ overflows to ‘INT_MIN’, which is less than
          zero.  ‘-Wstrict-overflow’ (with no level) is the same as
          ‘-Wstrict-overflow=2’.

     ‘-Wstrict-overflow=3’
          Also warn about other cases where a comparison is simplified.
          For example: ‘x + 1 > 1’ is simplified to ‘x > 0’.

     ‘-Wstrict-overflow=4’
          Also warn about other simplifications not covered by the above
          cases.  For example: ‘(x * 10) / 5’ is simplified to ‘x * 2’.

     ‘-Wstrict-overflow=5’
          Also warn about cases where the compiler reduces the magnitude
          of a constant involved in a comparison.  For example: ‘x + 2 >
          y’ is simplified to ‘x + 1 >= y’.  This is reported only at
          the highest warning level because this simplification applies
          to many comparisons, so this warning level gives a very large
          number of false positives.

‘-Wstring-compare’
     Warn for calls to ‘strcmp’ and ‘strncmp’ whose result is determined
     to be either zero or non-zero in tests for such equality owing to
     the length of one argument being greater than the size of the array
     the other argument is stored in (or the bound in the case of
     ‘strncmp’).  Such calls could be mistakes.  For example, the call
     to ‘strcmp’ below is diagnosed because its result is necessarily
     non-zero irrespective of the contents of the array ‘a’.

          extern char a[4];
          void f (char *d)
          {
            strcpy (d, "string");
            ...
            if (0 == strcmp (a, d))   // cannot be true
              puts ("a and d are the same");
          }

     ‘-Wstring-compare’ is enabled by ‘-Wextra’.

‘-Wno-stringop-overflow’
‘-Wstringop-overflow’
‘-Wstringop-overflow=TYPE’
     Warn for calls to string manipulation functions such as ‘memcpy’
     and ‘strcpy’ that are determined to overflow the destination
     buffer.  The optional argument is one greater than the type of
     Object Size Checking to perform to determine the size of the
     destination.  *Note Object Size Checking::.  The argument is
     meaningful only for functions that operate on character arrays but
     not for raw memory functions like ‘memcpy’ which always make use of
     Object Size type-0.  The option also warns for calls that specify a
     size in excess of the largest possible object or at most ‘SIZE_MAX
     / 2’ bytes.  The option produces the best results with optimization
     enabled but can detect a small subset of simple buffer overflows
     even without optimization in calls to the GCC built-in functions
     like ‘__builtin_memcpy’ that correspond to the standard functions.
     In any case, the option warns about just a subset of buffer
     overflows detected by the corresponding overflow checking
     built-ins.  For example, the option issues a warning for the
     ‘strcpy’ call below because it copies at least 5 characters (the
     string ‘"blue"’ including the terminating NUL) into the buffer of
     size 4.

          enum Color { blue, purple, yellow };
          const char* f (enum Color clr)
          {
            static char buf [4];
            const char *str;
            switch (clr)
              {
                case blue: str = "blue"; break;
                case purple: str = "purple"; break;
                case yellow: str = "yellow"; break;
              }

            return strcpy (buf, str);   // warning here
          }

     Option ‘-Wstringop-overflow=2’ is enabled by default.

     ‘-Wstringop-overflow’
     ‘-Wstringop-overflow=1’
          The ‘-Wstringop-overflow=1’ option uses type-zero Object Size
          Checking to determine the sizes of destination objects.  At
          this setting the option does not warn for writes past the end
          of subobjects of larger objects accessed by pointers unless
          the size of the largest surrounding object is known.  When the
          destination may be one of several objects it is assumed to be
          the largest one of them.  On Linux systems, when optimization
          is enabled at this setting the option warns for the same code
          as when the ‘_FORTIFY_SOURCE’ macro is defined to a non-zero
          value.

     ‘-Wstringop-overflow=2’
          The ‘-Wstringop-overflow=2’ option uses type-one Object Size
          Checking to determine the sizes of destination objects.  At
          this setting the option warns about overflows when writing to
          members of the largest complete objects whose exact size is
          known.  However, it does not warn for excessive writes to the
          same members of unknown objects referenced by pointers since
          they may point to arrays containing unknown numbers of
          elements.  This is the default setting of the option.

     ‘-Wstringop-overflow=3’
          The ‘-Wstringop-overflow=3’ option uses type-two Object Size
          Checking to determine the sizes of destination objects.  At
          this setting the option warns about overflowing the smallest
          object or data member.  This is the most restrictive setting
          of the option that may result in warnings for safe code.

     ‘-Wstringop-overflow=4’
          The ‘-Wstringop-overflow=4’ option uses type-three Object Size
          Checking to determine the sizes of destination objects.  At
          this setting the option warns about overflowing any data
          members, and when the destination is one of several objects it
          uses the size of the largest of them to decide whether to
          issue a warning.  Similarly to ‘-Wstringop-overflow=3’ this
          setting of the option may result in warnings for benign code.

‘-Wno-stringop-overread’
     Warn for calls to string manipulation functions such as ‘memchr’,
     or ‘strcpy’ that are determined to read past the end of the source
     sequence.

     Option ‘-Wstringop-overread’ is enabled by default.

‘-Wno-stringop-truncation’
     Do not warn for calls to bounded string manipulation functions such
     as ‘strncat’, ‘strncpy’, and ‘stpncpy’ that may either truncate the
     copied string or leave the destination unchanged.

     In the following example, the call to ‘strncat’ specifies a bound
     that is less than the length of the source string.  As a result,
     the copy of the source will be truncated and so the call is
     diagnosed.  To avoid the warning use ‘bufsize - strlen (buf) - 1)’
     as the bound.

          void append (char *buf, size_t bufsize)
          {
            strncat (buf, ".txt", 3);
          }

     As another example, the following call to ‘strncpy’ results in
     copying to ‘d’ just the characters preceding the terminating NUL,
     without appending the NUL to the end.  Assuming the result of
     ‘strncpy’ is necessarily a NUL-terminated string is a common
     mistake, and so the call is diagnosed.  To avoid the warning when
     the result is not expected to be NUL-terminated, call ‘memcpy’
     instead.

          void copy (char *d, const char *s)
          {
            strncpy (d, s, strlen (s));
          }

     In the following example, the call to ‘strncpy’ specifies the size
     of the destination buffer as the bound.  If the length of the
     source string is equal to or greater than this size the result of
     the copy will not be NUL-terminated.  Therefore, the call is also
     diagnosed.  To avoid the warning, specify ‘sizeof buf - 1’ as the
     bound and set the last element of the buffer to ‘NUL’.

          void copy (const char *s)
          {
            char buf[80];
            strncpy (buf, s, sizeof buf);
            ...
          }

     In situations where a character array is intended to store a
     sequence of bytes with no terminating ‘NUL’ such an array may be
     annotated with attribute ‘nonstring’ to avoid this warning.  Such
     arrays, however, are not suitable arguments to functions that
     expect ‘NUL’-terminated strings.  To help detect accidental misuses
     of such arrays GCC issues warnings unless it can prove that the use
     is safe.  *Note Common Variable Attributes::.

‘-Wsuggest-attribute=[pure|const|noreturn|format|cold|malloc]’
     Warn for cases where adding an attribute may be beneficial.  The
     attributes currently supported are listed below.

     ‘-Wsuggest-attribute=pure’
     ‘-Wsuggest-attribute=const’
     ‘-Wsuggest-attribute=noreturn’
     ‘-Wmissing-noreturn’
     ‘-Wsuggest-attribute=malloc’

          Warn about functions that might be candidates for attributes
          ‘pure’, ‘const’ or ‘noreturn’ or ‘malloc’.  The compiler only
          warns for functions visible in other compilation units or (in
          the case of ‘pure’ and ‘const’) if it cannot prove that the
          function returns normally.  A function returns normally if it
          doesn't contain an infinite loop or return abnormally by
          throwing, calling ‘abort’ or trapping.  This analysis requires
          option ‘-fipa-pure-const’, which is enabled by default at ‘-O’
          and higher.  Higher optimization levels improve the accuracy
          of the analysis.

     ‘-Wsuggest-attribute=format’
     ‘-Wmissing-format-attribute’

          Warn about function pointers that might be candidates for
          ‘format’ attributes.  Note these are only possible candidates,
          not absolute ones.  GCC guesses that function pointers with
          ‘format’ attributes that are used in assignment,
          initialization, parameter passing or return statements should
          have a corresponding ‘format’ attribute in the resulting type.
          I.e. the left-hand side of the assignment or initialization,
          the type of the parameter variable, or the return type of the
          containing function respectively should also have a ‘format’
          attribute to avoid the warning.

          GCC also warns about function definitions that might be
          candidates for ‘format’ attributes.  Again, these are only
          possible candidates.  GCC guesses that ‘format’ attributes
          might be appropriate for any function that calls a function
          like ‘vprintf’ or ‘vscanf’, but this might not always be the
          case, and some functions for which ‘format’ attributes are
          appropriate may not be detected.

     ‘-Wsuggest-attribute=cold’

          Warn about functions that might be candidates for ‘cold’
          attribute.  This is based on static detection and generally
          only warns about functions which always leads to a call to
          another ‘cold’ function such as wrappers of C++ ‘throw’ or
          fatal error reporting functions leading to ‘abort’.

‘-Walloc-zero’
     Warn about calls to allocation functions decorated with attribute
     ‘alloc_size’ that specify zero bytes, including those to the
     built-in forms of the functions ‘aligned_alloc’, ‘alloca’,
     ‘calloc’, ‘malloc’, and ‘realloc’.  Because the behavior of these
     functions when called with a zero size differs among
     implementations (and in the case of ‘realloc’ has been deprecated)
     relying on it may result in subtle portability bugs and should be
     avoided.

‘-Walloc-size-larger-than=BYTE-SIZE’
     Warn about calls to functions decorated with attribute ‘alloc_size’
     that attempt to allocate objects larger than the specified number
     of bytes, or where the result of the size computation in an integer
     type with infinite precision would exceed the value of
     ‘PTRDIFF_MAX’ on the target.
     ‘-Walloc-size-larger-than=’‘PTRDIFF_MAX’ is enabled by default.
     Warnings controlled by the option can be disabled either by
     specifying BYTE-SIZE of ‘SIZE_MAX’ or more or by
     ‘-Wno-alloc-size-larger-than’.  *Note Function Attributes::.

‘-Wno-alloc-size-larger-than’
     Disable ‘-Walloc-size-larger-than=’ warnings.  The option is
     equivalent to ‘-Walloc-size-larger-than=’‘SIZE_MAX’ or larger.

‘-Walloca’
     This option warns on all uses of ‘alloca’ in the source.

‘-Walloca-larger-than=BYTE-SIZE’
     This option warns on calls to ‘alloca’ with an integer argument
     whose value is either zero, or that is not bounded by a controlling
     predicate that limits its value to at most BYTE-SIZE.  It also
     warns for calls to ‘alloca’ where the bound value is unknown.
     Arguments of non-integer types are considered unbounded even if
     they appear to be constrained to the expected range.

     For example, a bounded case of ‘alloca’ could be:

          void func (size_t n)
          {
            void *p;
            if (n <= 1000)
              p = alloca (n);
            else
              p = malloc (n);
            f (p);
          }

     In the above example, passing ‘-Walloca-larger-than=1000’ would not
     issue a warning because the call to ‘alloca’ is known to be at most
     1000 bytes.  However, if ‘-Walloca-larger-than=500’ were passed,
     the compiler would emit a warning.

     Unbounded uses, on the other hand, are uses of ‘alloca’ with no
     controlling predicate constraining its integer argument.  For
     example:

          void func ()
          {
            void *p = alloca (n);
            f (p);
          }

     If ‘-Walloca-larger-than=500’ were passed, the above would trigger
     a warning, but this time because of the lack of bounds checking.

     Note, that even seemingly correct code involving signed integers
     could cause a warning:

          void func (signed int n)
          {
            if (n < 500)
              {
                p = alloca (n);
                f (p);
              }
          }

     In the above example, N could be negative, causing a larger than
     expected argument to be implicitly cast into the ‘alloca’ call.

     This option also warns when ‘alloca’ is used in a loop.

     ‘-Walloca-larger-than=’‘PTRDIFF_MAX’ is enabled by default but is
     usually only effective when ‘-ftree-vrp’ is active (default for
     ‘-O2’ and above).

     See also ‘-Wvla-larger-than=’‘byte-size’.

‘-Wno-alloca-larger-than’
     Disable ‘-Walloca-larger-than=’ warnings.  The option is equivalent
     to ‘-Walloca-larger-than=’‘SIZE_MAX’ or larger.

‘-Warith-conversion’
     Do warn about implicit conversions from arithmetic operations even
     when conversion of the operands to the same type cannot change
     their values.  This affects warnings from ‘-Wconversion’,
     ‘-Wfloat-conversion’, and ‘-Wsign-conversion’.

          void f (char c, int i)
          {
            c = c + i; // warns with -Wconversion
            c = c + 1; // only warns with -Warith-conversion
          }

‘-Warray-bounds’
‘-Warray-bounds=N’
     Warn about out of bounds subscripts or offsets into arrays.  This
     warning is enabled by ‘-Wall’.  It is more effective when
     ‘-ftree-vrp’ is active (the default for ‘-O2’ and above) but a
     subset of instances are issued even without optimization.

     ‘-Warray-bounds=1’
          This is the default warning level of ‘-Warray-bounds’ and is
          enabled by ‘-Wall’; higher levels are not, and must be
          explicitly requested.

     ‘-Warray-bounds=2’
          This warning level also warns about out of bounds accesses to
          trailing struct members of one-element array types (*note Zero
          Length::) and about the intermediate results of pointer
          arithmetic that may yield out of bounds values.  This warning
          level may give a larger number of false positives and is
          deactivated by default.

‘-Warray-compare’
     Warn about equality and relational comparisons between two operands
     of array type.  This comparison was deprecated in C++20.  For
     example:

          int arr1[5];
          int arr2[5];
          bool same = arr1 == arr2;

     ‘-Warray-compare’ is enabled by ‘-Wall’.

‘-Warray-parameter’
‘-Warray-parameter=N’
     Warn about redeclarations of functions involving arguments of array
     or pointer types of inconsistent kinds or forms, and enable the
     detection of out-of-bounds accesses to such parameters by warnings
     such as ‘-Warray-bounds’.

     If the first function declaration uses the array form the bound
     specified in the array is assumed to be the minimum number of
     elements expected to be provided in calls to the function and the
     maximum number of elements accessed by it.  Failing to provide
     arguments of sufficient size or accessing more than the maximum
     number of elements may be diagnosed by warnings such as
     ‘-Warray-bounds’.  At level 1 the warning diagnoses inconsistencies
     involving array parameters declared using the ‘T[static N]’ form.

     For example, the warning triggers for the following redeclarations
     because the first one allows an array of any size to be passed to
     ‘f’ while the second one with the keyword ‘static’ specifies that
     the array argument must have at least four elements.

          void f (int[static 4]);
          void f (int[]);           // warning (inconsistent array form)

          void g (void)
          {
            int *p = (int *)malloc (4);
            f (p);                  // warning (array too small)
            ...
          }

     At level 2 the warning also triggers for redeclarations involving
     any other inconsistency in array or pointer argument forms denoting
     array sizes.  Pointers and arrays of unspecified bound are
     considered equivalent and do not trigger a warning.

          void g (int*);
          void g (int[]);     // no warning
          void g (int[8]);    // warning (inconsistent array bound)

     ‘-Warray-parameter=2’ is included in ‘-Wall’.  The
     ‘-Wvla-parameter’ option triggers warnings for similar
     inconsistencies involving Variable Length Array arguments.

‘-Wattribute-alias=N’
‘-Wno-attribute-alias’
     Warn about declarations using the ‘alias’ and similar attributes
     whose target is incompatible with the type of the alias.  *Note
     Declaring Attributes of Functions: Function Attributes.

     ‘-Wattribute-alias=1’
          The default warning level of the ‘-Wattribute-alias’ option
          diagnoses incompatibilities between the type of the alias
          declaration and that of its target.  Such incompatibilities
          are typically indicative of bugs.

     ‘-Wattribute-alias=2’

          At this level ‘-Wattribute-alias’ also diagnoses cases where
          the attributes of the alias declaration are more restrictive
          than the attributes applied to its target.  These mismatches
          can potentially result in incorrect code generation.  In other
          cases they may be benign and could be resolved simply by
          adding the missing attribute to the target.  For comparison,
          see the ‘-Wmissing-attributes’ option, which controls
          diagnostics when the alias declaration is less restrictive
          than the target, rather than more restrictive.

          Attributes considered include ‘alloc_align’, ‘alloc_size’,
          ‘cold’, ‘const’, ‘hot’, ‘leaf’, ‘malloc’, ‘nonnull’,
          ‘noreturn’, ‘nothrow’, ‘pure’, ‘returns_nonnull’, and
          ‘returns_twice’.

     ‘-Wattribute-alias’ is equivalent to ‘-Wattribute-alias=1’.  This
     is the default.  You can disable these warnings with either
     ‘-Wno-attribute-alias’ or ‘-Wattribute-alias=0’.

‘-Wbidi-chars=[none|unpaired|any|ucn]’
     Warn about possibly misleading UTF-8 bidirectional control
     characters in comments, string literals, character constants, and
     identifiers.  Such characters can change left-to-right writing
     direction into right-to-left (and vice versa), which can cause
     confusion between the logical order and visual order.  This may be
     dangerous; for instance, it may seem that a piece of code is not
     commented out, whereas it in fact is.

     There are three levels of warning supported by GCC.  The default is
     ‘-Wbidi-chars=unpaired’, which warns about improperly terminated
     bidi contexts.  ‘-Wbidi-chars=none’ turns the warning off.
     ‘-Wbidi-chars=any’ warns about any use of bidirectional control
     characters.

     By default, this warning does not warn about UCNs.  It is, however,
     possible to turn on such checking by using
     ‘-Wbidi-chars=unpaired,ucn’ or ‘-Wbidi-chars=any,ucn’.  Using
     ‘-Wbidi-chars=ucn’ is valid, and is equivalent to
     ‘-Wbidi-chars=unpaired,ucn’, if no previous ‘-Wbidi-chars=any’ was
     specified.

‘-Wbool-compare’
     Warn about boolean expression compared with an integer value
     different from ‘true’/‘false’.  For instance, the following
     comparison is always false:
          int n = 5;
          ...
          if ((n > 1) == 2) { ... }
     This warning is enabled by ‘-Wall’.

‘-Wbool-operation’
     Warn about suspicious operations on expressions of a boolean type.
     For instance, bitwise negation of a boolean is very likely a bug in
     the program.  For C, this warning also warns about incrementing or
     decrementing a boolean, which rarely makes sense.  (In C++,
     decrementing a boolean is always invalid.  Incrementing a boolean
     is invalid in C++17, and deprecated otherwise.)

     This warning is enabled by ‘-Wall’.

‘-Wduplicated-branches’
     Warn when an if-else has identical branches.  This warning detects
     cases like
          if (p != NULL)
            return 0;
          else
            return 0;
     It doesn't warn when both branches contain just a null statement.
     This warning also warn for conditional operators:
            int i = x ? *p : *p;

‘-Wduplicated-cond’
     Warn about duplicated conditions in an if-else-if chain.  For
     instance, warn for the following code:
          if (p->q != NULL) { ... }
          else if (p->q != NULL) { ... }

‘-Wframe-address’
     Warn when the ‘__builtin_frame_address’ or
     ‘__builtin_return_address’ is called with an argument greater than
     0.  Such calls may return indeterminate values or crash the
     program.  The warning is included in ‘-Wall’.

‘-Wno-discarded-qualifiers (C and Objective-C only)’
     Do not warn if type qualifiers on pointers are being discarded.
     Typically, the compiler warns if a ‘const char *’ variable is
     passed to a function that takes a ‘char *’ parameter.  This option
     can be used to suppress such a warning.

‘-Wno-discarded-array-qualifiers (C and Objective-C only)’
     Do not warn if type qualifiers on arrays which are pointer targets
     are being discarded.  Typically, the compiler warns if a ‘const int
     (*)[]’ variable is passed to a function that takes a ‘int (*)[]’
     parameter.  This option can be used to suppress such a warning.

‘-Wno-incompatible-pointer-types (C and Objective-C only)’
     Do not warn when there is a conversion between pointers that have
     incompatible types.  This warning is for cases not covered by
     ‘-Wno-pointer-sign’, which warns for pointer argument passing or
     assignment with different signedness.

‘-Wno-int-conversion (C and Objective-C only)’
     Do not warn about incompatible integer to pointer and pointer to
     integer conversions.  This warning is about implicit conversions;
     for explicit conversions the warnings ‘-Wno-int-to-pointer-cast’
     and ‘-Wno-pointer-to-int-cast’ may be used.

‘-Wzero-length-bounds’
     Warn about accesses to elements of zero-length array members that
     might overlap other members of the same object.  Declaring interior
     zero-length arrays is discouraged because accesses to them are
     undefined.  See *Note Zero Length::.

     For example, the first two stores in function ‘bad’ are diagnosed
     because the array elements overlap the subsequent members ‘b’ and
     ‘c’.  The third store is diagnosed by ‘-Warray-bounds’ because it
     is beyond the bounds of the enclosing object.

          struct X { int a[0]; int b, c; };
          struct X x;

          void bad (void)
          {
            x.a[0] = 0;   // -Wzero-length-bounds
            x.a[1] = 1;   // -Wzero-length-bounds
            x.a[2] = 2;   // -Warray-bounds
          }

     Option ‘-Wzero-length-bounds’ is enabled by ‘-Warray-bounds’.

‘-Wno-div-by-zero’
     Do not warn about compile-time integer division by zero.
     Floating-point division by zero is not warned about, as it can be a
     legitimate way of obtaining infinities and NaNs.

‘-Wsystem-headers’
     Print warning messages for constructs found in system header files.
     Warnings from system headers are normally suppressed, on the
     assumption that they usually do not indicate real problems and
     would only make the compiler output harder to read.  Using this
     command-line option tells GCC to emit warnings from system headers
     as if they occurred in user code.  However, note that using ‘-Wall’
     in conjunction with this option does _not_ warn about unknown
     pragmas in system headers--for that, ‘-Wunknown-pragmas’ must also
     be used.

‘-Wtautological-compare’
     Warn if a self-comparison always evaluates to true or false.  This
     warning detects various mistakes such as:
          int i = 1;
          ...
          if (i > i) { ... }

     This warning also warns about bitwise comparisons that always
     evaluate to true or false, for instance:
          if ((a & 16) == 10) { ... }
     will always be false.

     This warning is enabled by ‘-Wall’.

‘-Wtrampolines’
     Warn about trampolines generated for pointers to nested functions.
     A trampoline is a small piece of data or code that is created at
     run time on the stack when the address of a nested function is
     taken, and is used to call the nested function indirectly.  For
     some targets, it is made up of data only and thus requires no
     special treatment.  But, for most targets, it is made up of code
     and thus requires the stack to be made executable in order for the
     program to work properly.

‘-Wfloat-equal’
     Warn if floating-point values are used in equality comparisons.

     The idea behind this is that sometimes it is convenient (for the
     programmer) to consider floating-point values as approximations to
     infinitely precise real numbers.  If you are doing this, then you
     need to compute (by analyzing the code, or in some other way) the
     maximum or likely maximum error that the computation introduces,
     and allow for it when performing comparisons (and when producing
     output, but that's a different problem).  In particular, instead of
     testing for equality, you should check to see whether the two
     values have ranges that overlap; and this is done with the
     relational operators, so equality comparisons are probably
     mistaken.

‘-Wtraditional (C and Objective-C only)’
     Warn about certain constructs that behave differently in
     traditional and ISO C.  Also warn about ISO C constructs that have
     no traditional C equivalent, and/or problematic constructs that
     should be avoided.

        • Macro parameters that appear within string literals in the
          macro body.  In traditional C macro replacement takes place
          within string literals, but in ISO C it does not.

        • In traditional C, some preprocessor directives did not exist.
          Traditional preprocessors only considered a line to be a
          directive if the ‘#’ appeared in column 1 on the line.
          Therefore ‘-Wtraditional’ warns about directives that
          traditional C understands but ignores because the ‘#’ does not
          appear as the first character on the line.  It also suggests
          you hide directives like ‘#pragma’ not understood by
          traditional C by indenting them.  Some traditional
          implementations do not recognize ‘#elif’, so this option
          suggests avoiding it altogether.

        • A function-like macro that appears without arguments.

        • The unary plus operator.

        • The ‘U’ integer constant suffix, or the ‘F’ or ‘L’
          floating-point constant suffixes.  (Traditional C does support
          the ‘L’ suffix on integer constants.)  Note, these suffixes
          appear in macros defined in the system headers of most modern
          systems, e.g. the ‘_MIN’/‘_MAX’ macros in ‘<limits.h>’.  Use
          of these macros in user code might normally lead to spurious
          warnings, however GCC's integrated preprocessor has enough
          context to avoid warning in these cases.

        • A function declared external in one block and then used after
          the end of the block.

        • A ‘switch’ statement has an operand of type ‘long’.

        • A non-‘static’ function declaration follows a ‘static’ one.
          This construct is not accepted by some traditional C
          compilers.

        • The ISO type of an integer constant has a different width or
          signedness from its traditional type.  This warning is only
          issued if the base of the constant is ten.  I.e. hexadecimal
          or octal values, which typically represent bit patterns, are
          not warned about.

        • Usage of ISO string concatenation is detected.

        • Initialization of automatic aggregates.

        • Identifier conflicts with labels.  Traditional C lacks a
          separate namespace for labels.

        • Initialization of unions.  If the initializer is zero, the
          warning is omitted.  This is done under the assumption that
          the zero initializer in user code appears conditioned on e.g.
          ‘__STDC__’ to avoid missing initializer warnings and relies on
          default initialization to zero in the traditional C case.

        • Conversions by prototypes between fixed/floating-point values
          and vice versa.  The absence of these prototypes when
          compiling with traditional C causes serious problems.  This is
          a subset of the possible conversion warnings; for the full set
          use ‘-Wtraditional-conversion’.

        • Use of ISO C style function definitions.  This warning
          intentionally is _not_ issued for prototype declarations or
          variadic functions because these ISO C features appear in your
          code when using libiberty's traditional C compatibility
          macros, ‘PARAMS’ and ‘VPARAMS’.  This warning is also bypassed
          for nested functions because that feature is already a GCC
          extension and thus not relevant to traditional C
          compatibility.

‘-Wtraditional-conversion (C and Objective-C only)’
     Warn if a prototype causes a type conversion that is different from
     what would happen to the same argument in the absence of a
     prototype.  This includes conversions of fixed point to floating
     and vice versa, and conversions changing the width or signedness of
     a fixed-point argument except when the same as the default
     promotion.

‘-Wdeclaration-after-statement (C and Objective-C only)’
     Warn when a declaration is found after a statement in a block.
     This construct, known from C++, was introduced with ISO C99 and is
     by default allowed in GCC.  It is not supported by ISO C90.  *Note
     Mixed Labels and Declarations::.

‘-Wshadow’
     Warn whenever a local variable or type declaration shadows another
     variable, parameter, type, class member (in C++), or instance
     variable (in Objective-C) or whenever a built-in function is
     shadowed.  Note that in C++, the compiler warns if a local variable
     shadows an explicit typedef, but not if it shadows a
     struct/class/enum.  If this warning is enabled, it includes also
     all instances of local shadowing.  This means that
     ‘-Wno-shadow=local’ and ‘-Wno-shadow=compatible-local’ are ignored
     when ‘-Wshadow’ is used.  Same as ‘-Wshadow=global’.

‘-Wno-shadow-ivar (Objective-C only)’
     Do not warn whenever a local variable shadows an instance variable
     in an Objective-C method.

‘-Wshadow=global’
     Warn for any shadowing.  Same as ‘-Wshadow’.

‘-Wshadow=local’
     Warn when a local variable shadows another local variable or
     parameter.

‘-Wshadow=compatible-local’
     Warn when a local variable shadows another local variable or
     parameter whose type is compatible with that of the shadowing
     variable.  In C++, type compatibility here means the type of the
     shadowing variable can be converted to that of the shadowed
     variable.  The creation of this flag (in addition to
     ‘-Wshadow=local’) is based on the idea that when a local variable
     shadows another one of incompatible type, it is most likely
     intentional, not a bug or typo, as shown in the following example:

          for (SomeIterator i = SomeObj.begin(); i != SomeObj.end(); ++i)
          {
            for (int i = 0; i < N; ++i)
            {
              ...
            }
            ...
          }

     Since the two variable ‘i’ in the example above have incompatible
     types, enabling only ‘-Wshadow=compatible-local’ does not emit a
     warning.  Because their types are incompatible, if a programmer
     accidentally uses one in place of the other, type checking is
     expected to catch that and emit an error or warning.  Use of this
     flag instead of ‘-Wshadow=local’ can possibly reduce the number of
     warnings triggered by intentional shadowing.  Note that this also
     means that shadowing ‘const char *i’ by ‘char *i’ does not emit a
     warning.

     This warning is also enabled by ‘-Wshadow=local’.

‘-Wlarger-than=BYTE-SIZE’
     Warn whenever an object is defined whose size exceeds BYTE-SIZE.
     ‘-Wlarger-than=’‘PTRDIFF_MAX’ is enabled by default.  Warnings
     controlled by the option can be disabled either by specifying
     BYTE-SIZE of ‘SIZE_MAX’ or more or by ‘-Wno-larger-than’.

     Also warn for calls to bounded functions such as ‘memchr’ or
     ‘strnlen’ that specify a bound greater than the largest possible
     object, which is ‘PTRDIFF_MAX’ bytes by default.  These warnings
     can only be disabled by ‘-Wno-larger-than’.

‘-Wno-larger-than’
     Disable ‘-Wlarger-than=’ warnings.  The option is equivalent to
     ‘-Wlarger-than=’‘SIZE_MAX’ or larger.

‘-Wframe-larger-than=BYTE-SIZE’
     Warn if the size of a function frame exceeds BYTE-SIZE.  The
     computation done to determine the stack frame size is approximate
     and not conservative.  The actual requirements may be somewhat
     greater than BYTE-SIZE even if you do not get a warning.  In
     addition, any space allocated via ‘alloca’, variable-length arrays,
     or related constructs is not included by the compiler when
     determining whether or not to issue a warning.
     ‘-Wframe-larger-than=’‘PTRDIFF_MAX’ is enabled by default.
     Warnings controlled by the option can be disabled either by
     specifying BYTE-SIZE of ‘SIZE_MAX’ or more or by
     ‘-Wno-frame-larger-than’.

‘-Wno-frame-larger-than’
     Disable ‘-Wframe-larger-than=’ warnings.  The option is equivalent
     to ‘-Wframe-larger-than=’‘SIZE_MAX’ or larger.

‘-Wfree-nonheap-object’
     Warn when attempting to deallocate an object that was either not
     allocated on the heap, or by using a pointer that was not returned
     from a prior call to the corresponding allocation function.  For
     example, because the call to ‘stpcpy’ returns a pointer to the
     terminating nul character and not to the beginning of the object,
     the call to ‘free’ below is diagnosed.

          void f (char *p)
          {
            p = stpcpy (p, "abc");
            // ...
            free (p);   // warning
          }

     ‘-Wfree-nonheap-object’ is included in ‘-Wall’.

‘-Wstack-usage=BYTE-SIZE’
     Warn if the stack usage of a function might exceed BYTE-SIZE.  The
     computation done to determine the stack usage is conservative.  Any
     space allocated via ‘alloca’, variable-length arrays, or related
     constructs is included by the compiler when determining whether or
     not to issue a warning.

     The message is in keeping with the output of ‘-fstack-usage’.

        • If the stack usage is fully static but exceeds the specified
          amount, it's:

                 warning: stack usage is 1120 bytes
        • If the stack usage is (partly) dynamic but bounded, it's:

                 warning: stack usage might be 1648 bytes
        • If the stack usage is (partly) dynamic and not bounded, it's:

                 warning: stack usage might be unbounded

     ‘-Wstack-usage=’‘PTRDIFF_MAX’ is enabled by default.  Warnings
     controlled by the option can be disabled either by specifying
     BYTE-SIZE of ‘SIZE_MAX’ or more or by ‘-Wno-stack-usage’.

‘-Wno-stack-usage’
     Disable ‘-Wstack-usage=’ warnings.  The option is equivalent to
     ‘-Wstack-usage=’‘SIZE_MAX’ or larger.

‘-Wunsafe-loop-optimizations’
     Warn if the loop cannot be optimized because the compiler cannot
     assume anything on the bounds of the loop indices.  With
     ‘-funsafe-loop-optimizations’ warn if the compiler makes such
     assumptions.

‘-Wno-pedantic-ms-format (MinGW targets only)’
     When used in combination with ‘-Wformat’ and ‘-pedantic’ without
     GNU extensions, this option disables the warnings about non-ISO
     ‘printf’ / ‘scanf’ format width specifiers ‘I32’, ‘I64’, and ‘I’
     used on Windows targets, which depend on the MS runtime.

‘-Wpointer-arith’
     Warn about anything that depends on the "size of" a function type
     or of ‘void’.  GNU C assigns these types a size of 1, for
     convenience in calculations with ‘void *’ pointers and pointers to
     functions.  In C++, warn also when an arithmetic operation involves
     ‘NULL’.  This warning is also enabled by ‘-Wpedantic’.

‘-Wno-pointer-compare’
     Do not warn if a pointer is compared with a zero character
     constant.  This usually means that the pointer was meant to be
     dereferenced.  For example:

          const char *p = foo ();
          if (p == '\0')
            return 42;

     Note that the code above is invalid in C++11.

     This warning is enabled by default.

‘-Wtsan’
     Warn about unsupported features in ThreadSanitizer.

     ThreadSanitizer does not support ‘std::atomic_thread_fence’ and can
     report false positives.

     This warning is enabled by default.

‘-Wtype-limits’
     Warn if a comparison is always true or always false due to the
     limited range of the data type, but do not warn for constant
     expressions.  For example, warn if an unsigned variable is compared
     against zero with ‘<’ or ‘>=’.  This warning is also enabled by
     ‘-Wextra’.

‘-Wabsolute-value (C and Objective-C only)’
     Warn for calls to standard functions that compute the absolute
     value of an argument when a more appropriate standard function is
     available.  For example, calling ‘abs(3.14)’ triggers the warning
     because the appropriate function to call to compute the absolute
     value of a double argument is ‘fabs’.  The option also triggers
     warnings when the argument in a call to such a function has an
     unsigned type.  This warning can be suppressed with an explicit
     type cast and it is also enabled by ‘-Wextra’.

‘-Wcomment’
‘-Wcomments’
     Warn whenever a comment-start sequence ‘/*’ appears in a ‘/*’
     comment, or whenever a backslash-newline appears in a ‘//’ comment.
     This warning is enabled by ‘-Wall’.

‘-Wtrigraphs’
     Warn if any trigraphs are encountered that might change the meaning
     of the program.  Trigraphs within comments are not warned about,
     except those that would form escaped newlines.

     This option is implied by ‘-Wall’.  If ‘-Wall’ is not given, this
     option is still enabled unless trigraphs are enabled.  To get
     trigraph conversion without warnings, but get the other ‘-Wall’
     warnings, use ‘-trigraphs -Wall -Wno-trigraphs’.

‘-Wundef’
     Warn if an undefined identifier is evaluated in an ‘#if’ directive.
     Such identifiers are replaced with zero.

‘-Wexpansion-to-defined’
     Warn whenever ‘defined’ is encountered in the expansion of a macro
     (including the case where the macro is expanded by an ‘#if’
     directive).  Such usage is not portable.  This warning is also
     enabled by ‘-Wpedantic’ and ‘-Wextra’.

‘-Wunused-macros’
     Warn about macros defined in the main file that are unused.  A
     macro is “used” if it is expanded or tested for existence at least
     once.  The preprocessor also warns if the macro has not been used
     at the time it is redefined or undefined.

     Built-in macros, macros defined on the command line, and macros
     defined in include files are not warned about.

     _Note:_ If a macro is actually used, but only used in skipped
     conditional blocks, then the preprocessor reports it as unused.  To
     avoid the warning in such a case, you might improve the scope of
     the macro's definition by, for example, moving it into the first
     skipped block.  Alternatively, you could provide a dummy use with
     something like:

          #if defined the_macro_causing_the_warning
          #endif

‘-Wno-endif-labels’
     Do not warn whenever an ‘#else’ or an ‘#endif’ are followed by
     text.  This sometimes happens in older programs with code of the
     form

          #if FOO
          ...
          #else FOO
          ...
          #endif FOO

     The second and third ‘FOO’ should be in comments.  This warning is
     on by default.

‘-Wbad-function-cast (C and Objective-C only)’
     Warn when a function call is cast to a non-matching type.  For
     example, warn if a call to a function returning an integer type is
     cast to a pointer type.

‘-Wc90-c99-compat (C and Objective-C only)’
     Warn about features not present in ISO C90, but present in ISO C99.
     For instance, warn about use of variable length arrays, ‘long long’
     type, ‘bool’ type, compound literals, designated initializers, and
     so on.  This option is independent of the standards mode.  Warnings
     are disabled in the expression that follows ‘__extension__’.

‘-Wc99-c11-compat (C and Objective-C only)’
     Warn about features not present in ISO C99, but present in ISO C11.
     For instance, warn about use of anonymous structures and unions,
     ‘_Atomic’ type qualifier, ‘_Thread_local’ storage-class specifier,
     ‘_Alignas’ specifier, ‘Alignof’ operator, ‘_Generic’ keyword, and
     so on.  This option is independent of the standards mode.  Warnings
     are disabled in the expression that follows ‘__extension__’.

‘-Wc11-c2x-compat (C and Objective-C only)’
     Warn about features not present in ISO C11, but present in ISO C2X.
     For instance, warn about omitting the string in ‘_Static_assert’,
     use of ‘[[]]’ syntax for attributes, use of decimal floating-point
     types, and so on.  This option is independent of the standards
     mode.  Warnings are disabled in the expression that follows
     ‘__extension__’.

‘-Wc++-compat (C and Objective-C only)’
     Warn about ISO C constructs that are outside of the common subset
     of ISO C and ISO C++, e.g. request for implicit conversion from
     ‘void *’ to a pointer to non-‘void’ type.

‘-Wc++11-compat (C++ and Objective-C++ only)’
     Warn about C++ constructs whose meaning differs between ISO C++
     1998 and ISO C++ 2011, e.g., identifiers in ISO C++ 1998 that are
     keywords in ISO C++ 2011.  This warning turns on ‘-Wnarrowing’ and
     is enabled by ‘-Wall’.

‘-Wc++14-compat (C++ and Objective-C++ only)’
     Warn about C++ constructs whose meaning differs between ISO C++
     2011 and ISO C++ 2014.  This warning is enabled by ‘-Wall’.

‘-Wc++17-compat (C++ and Objective-C++ only)’
     Warn about C++ constructs whose meaning differs between ISO C++
     2014 and ISO C++ 2017.  This warning is enabled by ‘-Wall’.

‘-Wc++20-compat (C++ and Objective-C++ only)’
     Warn about C++ constructs whose meaning differs between ISO C++
     2017 and ISO C++ 2020.  This warning is enabled by ‘-Wall’.

‘-Wno-c++11-extensions (C++ and Objective-C++ only)’
     Do not warn about C++11 constructs in code being compiled using an
     older C++ standard.  Even without this option, some C++11
     constructs will only be diagnosed if ‘-Wpedantic’ is used.

‘-Wno-c++14-extensions (C++ and Objective-C++ only)’
     Do not warn about C++14 constructs in code being compiled using an
     older C++ standard.  Even without this option, some C++14
     constructs will only be diagnosed if ‘-Wpedantic’ is used.

‘-Wno-c++17-extensions (C++ and Objective-C++ only)’
     Do not warn about C++17 constructs in code being compiled using an
     older C++ standard.  Even without this option, some C++17
     constructs will only be diagnosed if ‘-Wpedantic’ is used.

‘-Wno-c++20-extensions (C++ and Objective-C++ only)’
     Do not warn about C++20 constructs in code being compiled using an
     older C++ standard.  Even without this option, some C++20
     constructs will only be diagnosed if ‘-Wpedantic’ is used.

‘-Wno-c++23-extensions (C++ and Objective-C++ only)’
     Do not warn about C++23 constructs in code being compiled using an
     older C++ standard.  Even without this option, some C++23
     constructs will only be diagnosed if ‘-Wpedantic’ is used.

‘-Wcast-qual’
     Warn whenever a pointer is cast so as to remove a type qualifier
     from the target type.  For example, warn if a ‘const char *’ is
     cast to an ordinary ‘char *’.

     Also warn when making a cast that introduces a type qualifier in an
     unsafe way.  For example, casting ‘char **’ to ‘const char **’ is
     unsafe, as in this example:

            /* p is char ** value.  */
            const char **q = (const char **) p;
            /* Assignment of readonly string to const char * is OK.  */
            *q = "string";
            /* Now char** pointer points to read-only memory.  */
            **p = 'b';

‘-Wcast-align’
     Warn whenever a pointer is cast such that the required alignment of
     the target is increased.  For example, warn if a ‘char *’ is cast
     to an ‘int *’ on machines where integers can only be accessed at
     two- or four-byte boundaries.

‘-Wcast-align=strict’
     Warn whenever a pointer is cast such that the required alignment of
     the target is increased.  For example, warn if a ‘char *’ is cast
     to an ‘int *’ regardless of the target machine.

‘-Wcast-function-type’
     Warn when a function pointer is cast to an incompatible function
     pointer.  In a cast involving function types with a variable
     argument list only the types of initial arguments that are provided
     are considered.  Any parameter of pointer-type matches any other
     pointer-type.  Any benign differences in integral types are
     ignored, like ‘int’ vs. ‘long’ on ILP32 targets.  Likewise type
     qualifiers are ignored.  The function type ‘void (*) (void)’ is
     special and matches everything, which can be used to suppress this
     warning.  In a cast involving pointer to member types this warning
     warns whenever the type cast is changing the pointer to member
     type.  This warning is enabled by ‘-Wextra’.

‘-Wwrite-strings’
     When compiling C, give string constants the type ‘const
     char[LENGTH]’ so that copying the address of one into a non-‘const’
     ‘char *’ pointer produces a warning.  These warnings help you find
     at compile time code that can try to write into a string constant,
     but only if you have been very careful about using ‘const’ in
     declarations and prototypes.  Otherwise, it is just a nuisance.
     This is why we did not make ‘-Wall’ request these warnings.

     When compiling C++, warn about the deprecated conversion from
     string literals to ‘char *’.  This warning is enabled by default
     for C++ programs.

‘-Wclobbered’
     Warn for variables that might be changed by ‘longjmp’ or ‘vfork’.
     This warning is also enabled by ‘-Wextra’.

‘-Wconversion’
     Warn for implicit conversions that may alter a value.  This
     includes conversions between real and integer, like ‘abs (x)’ when
     ‘x’ is ‘double’; conversions between signed and unsigned, like
     ‘unsigned ui = -1’; and conversions to smaller types, like ‘sqrtf
     (M_PI)’.  Do not warn for explicit casts like ‘abs ((int) x)’ and
     ‘ui = (unsigned) -1’, or if the value is not changed by the
     conversion like in ‘abs (2.0)’.  Warnings about conversions between
     signed and unsigned integers can be disabled by using
     ‘-Wno-sign-conversion’.

     For C++, also warn for confusing overload resolution for
     user-defined conversions; and conversions that never use a type
     conversion operator: conversions to ‘void’, the same type, a base
     class or a reference to them.  Warnings about conversions between
     signed and unsigned integers are disabled by default in C++ unless
     ‘-Wsign-conversion’ is explicitly enabled.

     Warnings about conversion from arithmetic on a small type back to
     that type are only given with ‘-Warith-conversion’.

‘-Wdangling-else’
     Warn about constructions where there may be confusion to which ‘if’
     statement an ‘else’ branch belongs.  Here is an example of such a
     case:

          {
            if (a)
              if (b)
                foo ();
            else
              bar ();
          }

     In C/C++, every ‘else’ branch belongs to the innermost possible
     ‘if’ statement, which in this example is ‘if (b)’.  This is often
     not what the programmer expected, as illustrated in the above
     example by indentation the programmer chose.  When there is the
     potential for this confusion, GCC issues a warning when this flag
     is specified.  To eliminate the warning, add explicit braces around
     the innermost ‘if’ statement so there is no way the ‘else’ can
     belong to the enclosing ‘if’.  The resulting code looks like this:

          {
            if (a)
              {
                if (b)
                  foo ();
                else
                  bar ();
              }
          }

     This warning is enabled by ‘-Wparentheses’.

‘-Wdangling-pointer’
‘-Wdangling-pointer=N’
     Warn about uses of pointers (or C++ references) to objects with
     automatic storage duration after their lifetime has ended.  This
     includes local variables declared in nested blocks, compound
     literals and other unnamed temporary objects.  In addition, warn
     about storing the address of such objects in escaped pointers.  The
     warning is enabled at all optimization levels but may yield
     different results with optimization than without.

     ‘-Wdangling-pointer=1’
          At level 1 the warning diagnoses only unconditional uses of
          dangling pointers.  For example
               int f (int c1, int c2, x)
               {
                 char *p = strchr ((char[]){ c1, c2 }, c3);
                 return p ? *p : 'x';   // warning: dangling pointer to a compound literal
               }
          In the following function the store of the address of the
          local variable ‘x’ in the escaped pointer ‘*p’ also triggers
          the warning.
               void g (int **p)
               {
                 int x = 7;
                 *p = &x;   // warning: storing the address of a local variable in *p
               }

     ‘-Wdangling-pointer=2’
          At level 2, in addition to unconditional uses the warning also
          diagnoses conditional uses of dangling pointers.

          For example, because the array A in the following function is
          out of scope when the pointer S that was set to point is used,
          the warning triggers at this level.

               void f (char *s)
               {
                 if (!s)
                   {
                     char a[12] = "tmpname";
                     s = a;
                   }
                 strcat (s, ".tmp");   // warning: dangling pointer to a may be used
                 ...
               }

     ‘-Wdangling-pointer=2’ is included in ‘-Wall’.

‘-Wdate-time’
     Warn when macros ‘__TIME__’, ‘__DATE__’ or ‘__TIMESTAMP__’ are
     encountered as they might prevent bit-wise-identical reproducible
     compilations.

‘-Wempty-body’
     Warn if an empty body occurs in an ‘if’, ‘else’ or ‘do while’
     statement.  This warning is also enabled by ‘-Wextra’.

‘-Wno-endif-labels’
     Do not warn about stray tokens after ‘#else’ and ‘#endif’.

‘-Wenum-compare’
     Warn about a comparison between values of different enumerated
     types.  In C++ enumerated type mismatches in conditional
     expressions are also diagnosed and the warning is enabled by
     default.  In C this warning is enabled by ‘-Wall’.

‘-Wenum-conversion’
     Warn when a value of enumerated type is implicitly converted to a
     different enumerated type.  This warning is enabled by ‘-Wextra’ in
     C.

‘-Wjump-misses-init (C, Objective-C only)’
     Warn if a ‘goto’ statement or a ‘switch’ statement jumps forward
     across the initialization of a variable, or jumps backward to a
     label after the variable has been initialized.  This only warns
     about variables that are initialized when they are declared.  This
     warning is only supported for C and Objective-C; in C++ this sort
     of branch is an error in any case.

     ‘-Wjump-misses-init’ is included in ‘-Wc++-compat’.  It can be
     disabled with the ‘-Wno-jump-misses-init’ option.

‘-Wsign-compare’
     Warn when a comparison between signed and unsigned values could
     produce an incorrect result when the signed value is converted to
     unsigned.  In C++, this warning is also enabled by ‘-Wall’.  In C,
     it is also enabled by ‘-Wextra’.

‘-Wsign-conversion’
     Warn for implicit conversions that may change the sign of an
     integer value, like assigning a signed integer expression to an
     unsigned integer variable.  An explicit cast silences the warning.
     In C, this option is enabled also by ‘-Wconversion’.

‘-Wfloat-conversion’
     Warn for implicit conversions that reduce the precision of a real
     value.  This includes conversions from real to integer, and from
     higher precision real to lower precision real values.  This option
     is also enabled by ‘-Wconversion’.

‘-Wno-scalar-storage-order’
     Do not warn on suspicious constructs involving reverse scalar
     storage order.

‘-Wsizeof-array-div’
     Warn about divisions of two sizeof operators when the first one is
     applied to an array and the divisor does not equal the size of the
     array element.  In such a case, the computation will not yield the
     number of elements in the array, which is likely what the user
     intended.  This warning warns e.g.  about
          int fn ()
          {
            int arr[10];
            return sizeof (arr) / sizeof (short);
          }

     This warning is enabled by ‘-Wall’.

‘-Wsizeof-pointer-div’
     Warn for suspicious divisions of two sizeof expressions that divide
     the pointer size by the element size, which is the usual way to
     compute the array size but won't work out correctly with pointers.
     This warning warns e.g. about ‘sizeof (ptr) / sizeof (ptr[0])’ if
     ‘ptr’ is not an array, but a pointer.  This warning is enabled by
     ‘-Wall’.

‘-Wsizeof-pointer-memaccess’
     Warn for suspicious length parameters to certain string and memory
     built-in functions if the argument uses ‘sizeof’.  This warning
     triggers for example for ‘memset (ptr, 0, sizeof (ptr));’ if ‘ptr’
     is not an array, but a pointer, and suggests a possible fix, or
     about ‘memcpy (&foo, ptr, sizeof (&foo));’.
     ‘-Wsizeof-pointer-memaccess’ also warns about calls to bounded
     string copy functions like ‘strncat’ or ‘strncpy’ that specify as
     the bound a ‘sizeof’ expression of the source array.  For example,
     in the following function the call to ‘strncat’ specifies the size
     of the source string as the bound.  That is almost certainly a
     mistake and so the call is diagnosed.
          void make_file (const char *name)
          {
            char path[PATH_MAX];
            strncpy (path, name, sizeof path - 1);
            strncat (path, ".text", sizeof ".text");
            ...
          }

     The ‘-Wsizeof-pointer-memaccess’ option is enabled by ‘-Wall’.

‘-Wno-sizeof-array-argument’
     Do not warn when the ‘sizeof’ operator is applied to a parameter
     that is declared as an array in a function definition.  This
     warning is enabled by default for C and C++ programs.

‘-Wmemset-elt-size’
     Warn for suspicious calls to the ‘memset’ built-in function, if the
     first argument references an array, and the third argument is a
     number equal to the number of elements, but not equal to the size
     of the array in memory.  This indicates that the user has omitted a
     multiplication by the element size.  This warning is enabled by
     ‘-Wall’.

‘-Wmemset-transposed-args’
     Warn for suspicious calls to the ‘memset’ built-in function where
     the second argument is not zero and the third argument is zero.
     For example, the call ‘memset (buf, sizeof buf, 0)’ is diagnosed
     because ‘memset (buf, 0, sizeof buf)’ was meant instead.  The
     diagnostic is only emitted if the third argument is a literal zero.
     Otherwise, if it is an expression that is folded to zero, or a cast
     of zero to some type, it is far less likely that the arguments have
     been mistakenly transposed and no warning is emitted.  This warning
     is enabled by ‘-Wall’.

‘-Waddress’
     Warn about suspicious uses of address expressions.  These include
     comparing the address of a function or a declared object to the
     null pointer constant such as in
          void f (void);
          void g (void)
          {
            if (!func)   // warning: expression evaluates to false
              abort ();
          }
     comparisons of a pointer to a string literal, such as in
          void f (const char *x)
          {
            if (x == "abc")   // warning: expression evaluates to false
              puts ("equal");
          }
     and tests of the results of pointer addition or subtraction for
     equality to null, such as in
          void f (const int *p, int i)
          {
            return p + i == NULL;
          }
     Such uses typically indicate a programmer error: the address of
     most functions and objects necessarily evaluates to true (the
     exception are weak symbols), so their use in a conditional might
     indicate missing parentheses in a function call or a missing
     dereference in an array expression.  The subset of the warning for
     object pointers can be suppressed by casting the pointer operand to
     an integer type such as ‘inptr_t’ or ‘uinptr_t’.  Comparisons
     against string literals result in unspecified behavior and are not
     portable, and suggest the intent was to call ‘strcmp’.  The warning
     is suppressed if the suspicious expression is the result of macro
     expansion.  ‘-Waddress’ warning is enabled by ‘-Wall’.

‘-Wno-address-of-packed-member’
     Do not warn when the address of packed member of struct or union is
     taken, which usually results in an unaligned pointer value.  This
     is enabled by default.

‘-Wlogical-op’
     Warn about suspicious uses of logical operators in expressions.
     This includes using logical operators in contexts where a bit-wise
     operator is likely to be expected.  Also warns when the operands of
     a logical operator are the same:
          extern int a;
          if (a < 0 && a < 0) { ... }

‘-Wlogical-not-parentheses’
     Warn about logical not used on the left hand side operand of a
     comparison.  This option does not warn if the right operand is
     considered to be a boolean expression.  Its purpose is to detect
     suspicious code like the following:
          int a;
          ...
          if (!a > 1) { ... }

     It is possible to suppress the warning by wrapping the LHS into
     parentheses:
          if ((!a) > 1) { ... }

     This warning is enabled by ‘-Wall’.

‘-Waggregate-return’
     Warn if any functions that return structures or unions are defined
     or called.  (In languages where you can return an array, this also
     elicits a warning.)

‘-Wno-aggressive-loop-optimizations’
     Warn if in a loop with constant number of iterations the compiler
     detects undefined behavior in some statement during one or more of
     the iterations.

‘-Wno-attributes’
     Do not warn if an unexpected ‘__attribute__’ is used, such as
     unrecognized attributes, function attributes applied to variables,
     etc.  This does not stop errors for incorrect use of supported
     attributes.

     Additionally, using ‘-Wno-attributes=’, it is possible to suppress
     warnings about unknown scoped attributes (in C++11 and C2X). For
     example, ‘-Wno-attributes=vendor::attr’ disables warning about the
     following declaration:

          [[vendor::attr]] void f();

     It is also possible to disable warning about all attributes in a
     namespace using ‘-Wno-attributes=vendor::’ which prevents warning
     about both of these declarations:

          [[vendor::safe]] void f();
          [[vendor::unsafe]] void f2();

     Note that ‘-Wno-attributes=’ does not imply ‘-Wno-attributes’.

‘-Wno-builtin-declaration-mismatch’
     Warn if a built-in function is declared with an incompatible
     signature or as a non-function, or when a built-in function
     declared with a type that does not include a prototype is called
     with arguments whose promoted types do not match those expected by
     the function.  When ‘-Wextra’ is specified, also warn when a
     built-in function that takes arguments is declared without a
     prototype.  The ‘-Wbuiltin-declaration-mismatch’ warning is enabled
     by default.  To avoid the warning include the appropriate header to
     bring the prototypes of built-in functions into scope.

     For example, the call to ‘memset’ below is diagnosed by the warning
     because the function expects a value of type ‘size_t’ as its
     argument but the type of ‘32’ is ‘int’.  With ‘-Wextra’, the
     declaration of the function is diagnosed as well.
          extern void* memset ();
          void f (void *d)
          {
            memset (d, '\0', 32);
          }

‘-Wno-builtin-macro-redefined’
     Do not warn if certain built-in macros are redefined.  This
     suppresses warnings for redefinition of ‘__TIMESTAMP__’,
     ‘__TIME__’, ‘__DATE__’, ‘__FILE__’, and ‘__BASE_FILE__’.

‘-Wstrict-prototypes (C and Objective-C only)’
     Warn if a function is declared or defined without specifying the
     argument types.  (An old-style function definition is permitted
     without a warning if preceded by a declaration that specifies the
     argument types.)

‘-Wold-style-declaration (C and Objective-C only)’
     Warn for obsolescent usages, according to the C Standard, in a
     declaration.  For example, warn if storage-class specifiers like
     ‘static’ are not the first things in a declaration.  This warning
     is also enabled by ‘-Wextra’.

‘-Wold-style-definition (C and Objective-C only)’
     Warn if an old-style function definition is used.  A warning is
     given even if there is a previous prototype.  A definition using
     ‘()’ is not considered an old-style definition in C2X mode, because
     it is equivalent to ‘(void)’ in that case, but is considered an
     old-style definition for older standards.

‘-Wmissing-parameter-type (C and Objective-C only)’
     A function parameter is declared without a type specifier in
     K&R-style functions:

          void foo(bar) { }

     This warning is also enabled by ‘-Wextra’.

‘-Wmissing-prototypes (C and Objective-C only)’
     Warn if a global function is defined without a previous prototype
     declaration.  This warning is issued even if the definition itself
     provides a prototype.  Use this option to detect global functions
     that do not have a matching prototype declaration in a header file.
     This option is not valid for C++ because all function declarations
     provide prototypes and a non-matching declaration declares an
     overload rather than conflict with an earlier declaration.  Use
     ‘-Wmissing-declarations’ to detect missing declarations in C++.

‘-Wmissing-declarations’
     Warn if a global function is defined without a previous
     declaration.  Do so even if the definition itself provides a
     prototype.  Use this option to detect global functions that are not
     declared in header files.  In C, no warnings are issued for
     functions with previous non-prototype declarations; use
     ‘-Wmissing-prototypes’ to detect missing prototypes.  In C++, no
     warnings are issued for function templates, or for inline
     functions, or for functions in anonymous namespaces.

‘-Wmissing-field-initializers’
     Warn if a structure's initializer has some fields missing.  For
     example, the following code causes such a warning, because ‘x.h’ is
     implicitly zero:

          struct s { int f, g, h; };
          struct s x = { 3, 4 };

     This option does not warn about designated initializers, so the
     following modification does not trigger a warning:

          struct s { int f, g, h; };
          struct s x = { .f = 3, .g = 4 };

     In C this option does not warn about the universal zero initializer
     ‘{ 0 }’:

          struct s { int f, g, h; };
          struct s x = { 0 };

     Likewise, in C++ this option does not warn about the empty { }
     initializer, for example:

          struct s { int f, g, h; };
          s x = { };

     This warning is included in ‘-Wextra’.  To get other ‘-Wextra’
     warnings without this one, use ‘-Wextra
     -Wno-missing-field-initializers’.

‘-Wno-missing-requires’

     By default, the compiler warns about a concept-id appearing as a
     C++20 simple-requirement:

          bool satisfied = requires { C<T> };

     Here ‘satisfied’ will be true if ‘C<T>’ is a valid expression,
     which it is for all T. Presumably the user meant to write

          bool satisfied = requires { requires C<T> };

     so ‘satisfied’ is only true if concept ‘C’ is satisfied for type
     ‘T’.

     This warning can be disabled with ‘-Wno-missing-requires’.

‘-Wno-missing-template-keyword’

     The member access tokens ., -> and :: must be followed by the
     ‘template’ keyword if the parent object is dependent and the member
     being named is a template.

          template <class X>
          void DoStuff (X x)
          {
            x.template DoSomeOtherStuff<X>(); // Good.
            x.DoMoreStuff<X>(); // Warning, x is dependent.
          }

     In rare cases it is possible to get false positives.  To silence
     this, wrap the expression in parentheses.  For example, the
     following is treated as a template, even where m and N are
     integers:

          void NotATemplate (my_class t)
          {
            int N = 5;

            bool test = t.m < N > (0); // Treated as a template.
            test = (t.m < N) > (0); // Same meaning, but not treated as a template.
          }

     This warning can be disabled with ‘-Wno-missing-template-keyword’.

‘-Wno-multichar’
     Do not warn if a multicharacter constant (‘'FOOF'’) is used.
     Usually they indicate a typo in the user's code, as they have
     implementation-defined values, and should not be used in portable
     code.

‘-Wnormalized=[none|id|nfc|nfkc]’
     In ISO C and ISO C++, two identifiers are different if they are
     different sequences of characters.  However, sometimes when
     characters outside the basic ASCII character set are used, you can
     have two different character sequences that look the same.  To
     avoid confusion, the ISO 10646 standard sets out some
     “normalization rules” which when applied ensure that two sequences
     that look the same are turned into the same sequence.  GCC can warn
     you if you are using identifiers that have not been normalized;
     this option controls that warning.

     There are four levels of warning supported by GCC.  The default is
     ‘-Wnormalized=nfc’, which warns about any identifier that is not in
     the ISO 10646 "C" normalized form, “NFC”. NFC is the recommended
     form for most uses.  It is equivalent to ‘-Wnormalized’.

     Unfortunately, there are some characters allowed in identifiers by
     ISO C and ISO C++ that, when turned into NFC, are not allowed in
     identifiers.  That is, there's no way to use these symbols in
     portable ISO C or C++ and have all your identifiers in NFC.
     ‘-Wnormalized=id’ suppresses the warning for these characters.  It
     is hoped that future versions of the standards involved will
     correct this, which is why this option is not the default.

     You can switch the warning off for all characters by writing
     ‘-Wnormalized=none’ or ‘-Wno-normalized’.  You should only do this
     if you are using some other normalization scheme (like "D"),
     because otherwise you can easily create bugs that are literally
     impossible to see.

     Some characters in ISO 10646 have distinct meanings but look
     identical in some fonts or display methodologies, especially once
     formatting has been applied.  For instance ‘\u207F’, "SUPERSCRIPT
     LATIN SMALL LETTER N", displays just like a regular ‘n’ that has
     been placed in a superscript.  ISO 10646 defines the “NFKC”
     normalization scheme to convert all these into a standard form as
     well, and GCC warns if your code is not in NFKC if you use
     ‘-Wnormalized=nfkc’.  This warning is comparable to warning about
     every identifier that contains the letter O because it might be
     confused with the digit 0, and so is not the default, but may be
     useful as a local coding convention if the programming environment
     cannot be fixed to display these characters distinctly.

‘-Wno-attribute-warning’
     Do not warn about usage of functions (*note Function Attributes::)
     declared with ‘warning’ attribute.  By default, this warning is
     enabled.  ‘-Wno-attribute-warning’ can be used to disable the
     warning or ‘-Wno-error=attribute-warning’ can be used to disable
     the error when compiled with ‘-Werror’ flag.

‘-Wno-deprecated’
     Do not warn about usage of deprecated features.  *Note Deprecated
     Features::.

‘-Wno-deprecated-declarations’
     Do not warn about uses of functions (*note Function Attributes::),
     variables (*note Variable Attributes::), and types (*note Type
     Attributes::) marked as deprecated by using the ‘deprecated’
     attribute.

‘-Wno-overflow’
     Do not warn about compile-time overflow in constant expressions.

‘-Wno-odr’
     Warn about One Definition Rule violations during link-time
     optimization.  Enabled by default.

‘-Wopenacc-parallelism’
     Warn about potentially suboptimal choices related to OpenACC
     parallelism.

‘-Wopenmp-simd’
     Warn if the vectorizer cost model overrides the OpenMP simd
     directive set by user.  The ‘-fsimd-cost-model=unlimited’ option
     can be used to relax the cost model.

‘-Woverride-init (C and Objective-C only)’
     Warn if an initialized field without side effects is overridden
     when using designated initializers (*note Designated Initializers:
     Designated Inits.).

     This warning is included in ‘-Wextra’.  To get other ‘-Wextra’
     warnings without this one, use ‘-Wextra -Wno-override-init’.

‘-Wno-override-init-side-effects (C and Objective-C only)’
     Do not warn if an initialized field with side effects is overridden
     when using designated initializers (*note Designated Initializers:
     Designated Inits.).  This warning is enabled by default.

‘-Wpacked’
     Warn if a structure is given the packed attribute, but the packed
     attribute has no effect on the layout or size of the structure.
     Such structures may be mis-aligned for little benefit.  For
     instance, in this code, the variable ‘f.x’ in ‘struct bar’ is
     misaligned even though ‘struct bar’ does not itself have the packed
     attribute:

          struct foo {
            int x;
            char a, b, c, d;
          } __attribute__((packed));
          struct bar {
            char z;
            struct foo f;
          };

‘-Wnopacked-bitfield-compat’
     The 4.1, 4.2 and 4.3 series of GCC ignore the ‘packed’ attribute on
     bit-fields of type ‘char’.  This was fixed in GCC 4.4 but the
     change can lead to differences in the structure layout.  GCC
     informs you when the offset of such a field has changed in GCC 4.4.
     For example there is no longer a 4-bit padding between field ‘a’
     and ‘b’ in this structure:

          struct foo
          {
            char a:4;
            char b:8;
          } __attribute__ ((packed));

     This warning is enabled by default.  Use
     ‘-Wno-packed-bitfield-compat’ to disable this warning.

‘-Wpacked-not-aligned (C, C++, Objective-C and Objective-C++ only)’
     Warn if a structure field with explicitly specified alignment in a
     packed struct or union is misaligned.  For example, a warning will
     be issued on ‘struct S’, like, ‘warning: alignment 1 of 'struct S'
     is less than 8’, in this code:

          struct __attribute__ ((aligned (8))) S8 { char a[8]; };
          struct __attribute__ ((packed)) S {
            struct S8 s8;
          };

     This warning is enabled by ‘-Wall’.

‘-Wpadded’
     Warn if padding is included in a structure, either to align an
     element of the structure or to align the whole structure.
     Sometimes when this happens it is possible to rearrange the fields
     of the structure to reduce the padding and so make the structure
     smaller.

‘-Wredundant-decls’
     Warn if anything is declared more than once in the same scope, even
     in cases where multiple declaration is valid and changes nothing.

‘-Wrestrict’
     Warn when an object referenced by a ‘restrict’-qualified parameter
     (or, in C++, a ‘__restrict’-qualified parameter) is aliased by
     another argument, or when copies between such objects overlap.  For
     example, the call to the ‘strcpy’ function below attempts to
     truncate the string by replacing its initial characters with the
     last four.  However, because the call writes the terminating NUL
     into ‘a[4]’, the copies overlap and the call is diagnosed.

          void foo (void)
          {
            char a[] = "abcd1234";
            strcpy (a, a + 4);
            ...
          }
     The ‘-Wrestrict’ option detects some instances of simple overlap
     even without optimization but works best at ‘-O2’ and above.  It is
     included in ‘-Wall’.

‘-Wnested-externs (C and Objective-C only)’
     Warn if an ‘extern’ declaration is encountered within a function.

‘-Winline’
     Warn if a function that is declared as inline cannot be inlined.
     Even with this option, the compiler does not warn about failures to
     inline functions declared in system headers.

     The compiler uses a variety of heuristics to determine whether or
     not to inline a function.  For example, the compiler takes into
     account the size of the function being inlined and the amount of
     inlining that has already been done in the current function.
     Therefore, seemingly insignificant changes in the source program
     can cause the warnings produced by ‘-Winline’ to appear or
     disappear.

‘-Winterference-size’
     Warn about use of C++17
     ‘std::hardware_destructive_interference_size’ without specifying
     its value with ‘--param destructive-interference-size’.  Also warn
     about questionable values for that option.

     This variable is intended to be used for controlling class layout,
     to avoid false sharing in concurrent code:

          struct independent_fields {
            alignas(std::hardware_destructive_interference_size) std::atomic<int> one;
            alignas(std::hardware_destructive_interference_size) std::atomic<int> two;
          };

     Here ‘one’ and ‘two’ are intended to be far enough apart that
     stores to one won't require accesses to the other to reload the
     cache line.

     By default, ‘--param destructive-interference-size’ and ‘--param
     constructive-interference-size’ are set based on the current
     ‘-mtune’ option, typically to the L1 cache line size for the
     particular target CPU, sometimes to a range if tuning for a generic
     target.  So all translation units that depend on ABI compatibility
     for the use of these variables must be compiled with the same
     ‘-mtune’ (or ‘-mcpu’).

     If ABI stability is important, such as if the use is in a header
     for a library, you should probably not use the hardware
     interference size variables at all.  Alternatively, you can force a
     particular value with ‘--param’.

     If you are confident that your use of the variable does not affect
     ABI outside a single build of your project, you can turn off the
     warning with ‘-Wno-interference-size’.

‘-Wint-in-bool-context’
     Warn for suspicious use of integer values where boolean values are
     expected, such as conditional expressions (?:) using non-boolean
     integer constants in boolean context, like ‘if (a <= b ? 2 : 3)’.
     Or left shifting of signed integers in boolean context, like ‘for
     (a = 0; 1 << a; a++);’.  Likewise for all kinds of multiplications
     regardless of the data type.  This warning is enabled by ‘-Wall’.

‘-Wno-int-to-pointer-cast’
     Suppress warnings from casts to pointer type of an integer of a
     different size.  In C++, casting to a pointer type of smaller size
     is an error.  ‘Wint-to-pointer-cast’ is enabled by default.

‘-Wno-pointer-to-int-cast (C and Objective-C only)’
     Suppress warnings from casts from a pointer to an integer type of a
     different size.

‘-Winvalid-pch’
     Warn if a precompiled header (*note Precompiled Headers::) is found
     in the search path but cannot be used.

‘-Wlong-long’
     Warn if ‘long long’ type is used.  This is enabled by either
     ‘-Wpedantic’ or ‘-Wtraditional’ in ISO C90 and C++98 modes.  To
     inhibit the warning messages, use ‘-Wno-long-long’.

‘-Wvariadic-macros’
     Warn if variadic macros are used in ISO C90 mode, or if the GNU
     alternate syntax is used in ISO C99 mode.  This is enabled by
     either ‘-Wpedantic’ or ‘-Wtraditional’.  To inhibit the warning
     messages, use ‘-Wno-variadic-macros’.

‘-Wno-varargs’
     Do not warn upon questionable usage of the macros used to handle
     variable arguments like ‘va_start’.  These warnings are enabled by
     default.

‘-Wvector-operation-performance’
     Warn if vector operation is not implemented via SIMD capabilities
     of the architecture.  Mainly useful for the performance tuning.
     Vector operation can be implemented ‘piecewise’, which means that
     the scalar operation is performed on every vector element; ‘in
     parallel’, which means that the vector operation is implemented
     using scalars of wider type, which normally is more performance
     efficient; and ‘as a single scalar’, which means that vector fits
     into a scalar type.

‘-Wvla’
     Warn if a variable-length array is used in the code.  ‘-Wno-vla’
     prevents the ‘-Wpedantic’ warning of the variable-length array.

‘-Wvla-larger-than=BYTE-SIZE’
     If this option is used, the compiler warns for declarations of
     variable-length arrays whose size is either unbounded, or bounded
     by an argument that allows the array size to exceed BYTE-SIZE
     bytes.  This is similar to how ‘-Walloca-larger-than=’BYTE-SIZE
     works, but with variable-length arrays.

     Note that GCC may optimize small variable-length arrays of a known
     value into plain arrays, so this warning may not get triggered for
     such arrays.

     ‘-Wvla-larger-than=’‘PTRDIFF_MAX’ is enabled by default but is
     typically only effective when ‘-ftree-vrp’ is active (default for
     ‘-O2’ and above).

     See also ‘-Walloca-larger-than=BYTE-SIZE’.

‘-Wno-vla-larger-than’
     Disable ‘-Wvla-larger-than=’ warnings.  The option is equivalent to
     ‘-Wvla-larger-than=’‘SIZE_MAX’ or larger.

‘-Wvla-parameter’
     Warn about redeclarations of functions involving arguments of
     Variable Length Array types of inconsistent kinds or forms, and
     enable the detection of out-of-bounds accesses to such parameters
     by warnings such as ‘-Warray-bounds’.

     If the first function declaration uses the VLA form the bound
     specified in the array is assumed to be the minimum number of
     elements expected to be provided in calls to the function and the
     maximum number of elements accessed by it.  Failing to provide
     arguments of sufficient size or accessing more than the maximum
     number of elements may be diagnosed.

     For example, the warning triggers for the following redeclarations
     because the first one allows an array of any size to be passed to
     ‘f’ while the second one specifies that the array argument must
     have at least ‘n’ elements.  In addition, calling ‘f’ with the
     associated VLA bound parameter in excess of the actual VLA bound
     triggers a warning as well.

          void f (int n, int[n]);
          void f (int, int[]);     // warning: argument 2 previously declared as a VLA

          void g (int n)
          {
              if (n > 4)
                return;
              int a[n];
              f (sizeof a, a);     // warning: access to a by f may be out of bounds
            ...
          }

     ‘-Wvla-parameter’ is included in ‘-Wall’.  The ‘-Warray-parameter’
     option triggers warnings for similar problems involving ordinary
     array arguments.

‘-Wvolatile-register-var’
     Warn if a register variable is declared volatile.  The volatile
     modifier does not inhibit all optimizations that may eliminate
     reads and/or writes to register variables.  This warning is enabled
     by ‘-Wall’.

‘-Wdisabled-optimization’
     Warn if a requested optimization pass is disabled.  This warning
     does not generally indicate that there is anything wrong with your
     code; it merely indicates that GCC's optimizers are unable to
     handle the code effectively.  Often, the problem is that your code
     is too big or too complex; GCC refuses to optimize programs when
     the optimization itself is likely to take inordinate amounts of
     time.

‘-Wpointer-sign (C and Objective-C only)’
     Warn for pointer argument passing or assignment with different
     signedness.  This option is only supported for C and Objective-C.
     It is implied by ‘-Wall’ and by ‘-Wpedantic’, which can be disabled
     with ‘-Wno-pointer-sign’.

‘-Wstack-protector’
     This option is only active when ‘-fstack-protector’ is active.  It
     warns about functions that are not protected against stack
     smashing.

‘-Woverlength-strings’
     Warn about string constants that are longer than the "minimum
     maximum" length specified in the C standard.  Modern compilers
     generally allow string constants that are much longer than the
     standard's minimum limit, but very portable programs should avoid
     using longer strings.

     The limit applies _after_ string constant concatenation, and does
     not count the trailing NUL.  In C90, the limit was 509 characters;
     in C99, it was raised to 4095.  C++98 does not specify a normative
     minimum maximum, so we do not diagnose overlength strings in C++.

     This option is implied by ‘-Wpedantic’, and can be disabled with
     ‘-Wno-overlength-strings’.

‘-Wunsuffixed-float-constants (C and Objective-C only)’

     Issue a warning for any floating constant that does not have a
     suffix.  When used together with ‘-Wsystem-headers’ it warns about
     such constants in system header files.  This can be useful when
     preparing code to use with the ‘FLOAT_CONST_DECIMAL64’ pragma from
     the decimal floating-point extension to C99.

‘-Wno-lto-type-mismatch’

     During the link-time optimization, do not warn about type
     mismatches in global declarations from different compilation units.
     Requires ‘-flto’ to be enabled.  Enabled by default.

‘-Wno-designated-init (C and Objective-C only)’
     Suppress warnings when a positional initializer is used to
     initialize a structure that has been marked with the
     ‘designated_init’ attribute.


File: gcc.info,  Node: Static Analyzer Options,  Next: Debugging Options,  Prev: Warning Options,  Up: Invoking GCC

3.9 Options That Control Static Analysis
========================================

‘-fanalyzer’
     This option enables an static analysis of program flow which looks
     for "interesting" interprocedural paths through the code, and
     issues warnings for problems found on them.

     This analysis is much more expensive than other GCC warnings.

     Enabling this option effectively enables the following warnings:


          -Wanalyzer-double-fclose
          -Wanalyzer-double-free
          -Wanalyzer-exposure-through-output-file
          -Wanalyzer-file-leak
          -Wanalyzer-free-of-non-heap
          -Wanalyzer-malloc-leak
          -Wanalyzer-mismatching-deallocation
          -Wanalyzer-null-argument
          -Wanalyzer-null-dereference
          -Wanalyzer-possible-null-argument
          -Wanalyzer-possible-null-dereference
          -Wanalyzer-shift-count-negative
          -Wanalyzer-shift-count-overflow
          -Wanalyzer-stale-setjmp-buffer
          -Wanalyzer-unsafe-call-within-signal-handler
          -Wanalyzer-use-after-free
          -Wanalyzer-use-of-pointer-in-stale-stack-frame
          -Wanalyzer-use-of-uninitialized-value
          -Wanalyzer-write-to-const
          -Wanalyzer-write-to-string-literal

     This option is only available if GCC was configured with analyzer
     support enabled.

‘-Wanalyzer-too-complex’
     If ‘-fanalyzer’ is enabled, the analyzer uses various heuristics to
     attempt to explore the control flow and data flow in the program,
     but these can be defeated by sufficiently complicated code.

     By default, the analysis silently stops if the code is too
     complicated for the analyzer to fully explore and it reaches an
     internal limit.  The ‘-Wanalyzer-too-complex’ option warns if this
     occurs.

‘-Wno-analyzer-double-fclose’
     This warning requires ‘-fanalyzer’, which enables it; use
     ‘-Wno-analyzer-double-fclose’ to disable it.

     This diagnostic warns for paths through the code in which a ‘FILE
     *’ can have ‘fclose’ called on it more than once.

‘-Wno-analyzer-double-free’
     This warning requires ‘-fanalyzer’, which enables it; use
     ‘-Wno-analyzer-double-free’ to disable it.

     This diagnostic warns for paths through the code in which a pointer
     can have a deallocator called on it more than once, either ‘free’,
     or a deallocator referenced by attribute ‘malloc’.

‘-Wno-analyzer-exposure-through-output-file’
     This warning requires ‘-fanalyzer’, which enables it; use
     ‘-Wno-analyzer-exposure-through-output-file’ to disable it.

     This diagnostic warns for paths through the code in which a
     security-sensitive value is written to an output file (such as
     writing a password to a log file).

‘-Wno-analyzer-file-leak’
     This warning requires ‘-fanalyzer’, which enables it; use
     ‘-Wno-analyzer-file-leak’ to disable it.

     This diagnostic warns for paths through the code in which a
     ‘<stdio.h>’ ‘FILE *’ stream object is leaked.

‘-Wno-analyzer-free-of-non-heap’
     This warning requires ‘-fanalyzer’, which enables it; use
     ‘-Wno-analyzer-free-of-non-heap’ to disable it.

     This diagnostic warns for paths through the code in which ‘free’ is
     called on a non-heap pointer (e.g.  an on-stack buffer, or a
     global).

‘-Wno-analyzer-malloc-leak’
     This warning requires ‘-fanalyzer’, which enables it; use
     ‘-Wno-analyzer-malloc-leak’ to disable it.

     This diagnostic warns for paths through the code in which a pointer
     allocated via an allocator is leaked: either ‘malloc’, or a
     function marked with attribute ‘malloc’.

‘-Wno-analyzer-mismatching-deallocation’
     This warning requires ‘-fanalyzer’, which enables it; use
     ‘-Wno-analyzer-mismatching-deallocation’ to disable it.

     This diagnostic warns for paths through the code in which the wrong
     deallocation function is called on a pointer value, based on which
     function was used to allocate the pointer value.  The diagnostic
     will warn about mismatches between ‘free’, scalar ‘delete’ and
     vector ‘delete[]’, and those marked as allocator/deallocator pairs
     using attribute ‘malloc’.

‘-Wno-analyzer-possible-null-argument’
     This warning requires ‘-fanalyzer’, which enables it; use
     ‘-Wno-analyzer-possible-null-argument’ to disable it.

     This diagnostic warns for paths through the code in which a
     possibly-NULL value is passed to a function argument marked with
     ‘__attribute__((nonnull))’ as requiring a non-NULL value.

‘-Wno-analyzer-possible-null-dereference’
     This warning requires ‘-fanalyzer’, which enables it; use
     ‘-Wno-analyzer-possible-null-dereference’ to disable it.

     This diagnostic warns for paths through the code in which a
     possibly-NULL value is dereferenced.

‘-Wno-analyzer-null-argument’
     This warning requires ‘-fanalyzer’, which enables it; use
     ‘-Wno-analyzer-null-argument’ to disable it.

     This diagnostic warns for paths through the code in which a value
     known to be NULL is passed to a function argument marked with
     ‘__attribute__((nonnull))’ as requiring a non-NULL value.

‘-Wno-analyzer-null-dereference’
     This warning requires ‘-fanalyzer’, which enables it; use
     ‘-Wno-analyzer-null-dereference’ to disable it.

     This diagnostic warns for paths through the code in which a value
     known to be NULL is dereferenced.

‘-Wno-analyzer-shift-count-negative’
     This warning requires ‘-fanalyzer’, which enables it; use
     ‘-Wno-analyzer-shift-count-negative’ to disable it.

     This diagnostic warns for paths through the code in which a shift
     is attempted with a negative count.  It is analogous to the
     ‘-Wshift-count-negative’ diagnostic implemented in the C/C++ front
     ends, but is implemented based on analyzing interprocedural paths,
     rather than merely parsing the syntax tree.  However, the analyzer
     does not prioritize detection of such paths, so false negatives are
     more likely relative to other warnings.

‘-Wno-analyzer-shift-count-overflow’
     This warning requires ‘-fanalyzer’, which enables it; use
     ‘-Wno-analyzer-shift-count-overflow’ to disable it.

     This diagnostic warns for paths through the code in which a shift
     is attempted with a count greater than or equal to the precision of
     the operand's type.  It is analogous to the
     ‘-Wshift-count-overflow’ diagnostic implemented in the C/C++ front
     ends, but is implemented based on analyzing interprocedural paths,
     rather than merely parsing the syntax tree.  However, the analyzer
     does not prioritize detection of such paths, so false negatives are
     more likely relative to other warnings.

‘-Wno-analyzer-stale-setjmp-buffer’
     This warning requires ‘-fanalyzer’, which enables it; use
     ‘-Wno-analyzer-stale-setjmp-buffer’ to disable it.

     This diagnostic warns for paths through the code in which ‘longjmp’
     is called to rewind to a ‘jmp_buf’ relating to a ‘setjmp’ call in a
     function that has returned.

     When ‘setjmp’ is called on a ‘jmp_buf’ to record a rewind location,
     it records the stack frame.  The stack frame becomes invalid when
     the function containing the ‘setjmp’ call returns.  Attempting to
     rewind to it via ‘longjmp’ would reference a stack frame that no
     longer exists, and likely lead to a crash (or worse).

‘-Wno-analyzer-tainted-allocation-size’
     This warning requires both ‘-fanalyzer’ and
     ‘-fanalyzer-checker=taint’ to enable it; use
     ‘-Wno-analyzer-tainted-allocation-size’ to disable it.

     This diagnostic warns for paths through the code in which a value
     that could be under an attacker's control is used as the size of an
     allocation without being sanitized, so that an attacker could
     inject an excessively large allocation and potentially cause a
     denial of service attack.

     See CWE-789: Memory Allocation with Excessive Size Value
     (https://cwe.mitre.org/data/definitions/789.html).

‘-Wno-analyzer-tainted-array-index’
     This warning requires both ‘-fanalyzer’ and
     ‘-fanalyzer-checker=taint’ to enable it; use
     ‘-Wno-analyzer-tainted-array-index’ to disable it.

     This diagnostic warns for paths through the code in which a value
     that could be under an attacker's control is used as the index of
     an array access without being sanitized, so that an attacker could
     inject an out-of-bounds access.

     See CWE-129: Improper Validation of Array Index
     (https://cwe.mitre.org/data/definitions/129.html).

‘-Wno-analyzer-tainted-divisor’
     This warning requires both ‘-fanalyzer’ and
     ‘-fanalyzer-checker=taint’ to enable it; use
     ‘-Wno-analyzer-tainted-divisor’ to disable it.

     This diagnostic warns for paths through the code in which a value
     that could be under an attacker's control is used as the divisor in
     a division or modulus operation without being sanitized, so that an
     attacker could inject a division-by-zero.

‘-Wno-analyzer-tainted-offset’
     This warning requires both ‘-fanalyzer’ and
     ‘-fanalyzer-checker=taint’ to enable it; use
     ‘-Wno-analyzer-tainted-offset’ to disable it.

     This diagnostic warns for paths through the code in which a value
     that could be under an attacker's control is used as a pointer
     offset without being sanitized, so that an attacker could inject an
     out-of-bounds access.

     See CWE-823: Use of Out-of-range Pointer Offset
     (https://cwe.mitre.org/data/definitions/823.html).

‘-Wno-analyzer-tainted-size’
     This warning requires both ‘-fanalyzer’ and
     ‘-fanalyzer-checker=taint’ to enable it; use
     ‘-Wno-analyzer-tainted-size’ to disable it.

     This diagnostic warns for paths through the code in which a value
     that could be under an attacker's control is used as the size of an
     operation such as ‘memset’ without being sanitized, so that an
     attacker could inject an out-of-bounds access.

‘-Wno-analyzer-unsafe-call-within-signal-handler’
     This warning requires ‘-fanalyzer’, which enables it; use
     ‘-Wno-analyzer-unsafe-call-within-signal-handler’ to disable it.

     This diagnostic warns for paths through the code in which a
     function known to be async-signal-unsafe (such as ‘fprintf’) is
     called from a signal handler.

‘-Wno-analyzer-use-after-free’
     This warning requires ‘-fanalyzer’, which enables it; use
     ‘-Wno-analyzer-use-after-free’ to disable it.

     This diagnostic warns for paths through the code in which a pointer
     is used after a deallocator is called on it: either ‘free’, or a
     deallocator referenced by attribute ‘malloc’.

‘-Wno-analyzer-use-of-pointer-in-stale-stack-frame’
     This warning requires ‘-fanalyzer’, which enables it; use
     ‘-Wno-analyzer-use-of-pointer-in-stale-stack-frame’ to disable it.

     This diagnostic warns for paths through the code in which a pointer
     is dereferenced that points to a variable in a stale stack frame.

‘-Wno-analyzer-write-to-const’
     This warning requires ‘-fanalyzer’, which enables it; use
     ‘-Wno-analyzer-write-to-const’ to disable it.

     This diagnostic warns for paths through the code in which the
     analyzer detects an attempt to write through a pointer to a ‘const’
     object.  However, the analyzer does not prioritize detection of
     such paths, so false negatives are more likely relative to other
     warnings.

‘-Wno-analyzer-write-to-string-literal’
     This warning requires ‘-fanalyzer’, which enables it; use
     ‘-Wno-analyzer-write-to-string-literal’ to disable it.

     This diagnostic warns for paths through the code in which the
     analyzer detects an attempt to write through a pointer to a string
     literal.  However, the analyzer does not prioritize detection of
     such paths, so false negatives are more likely relative to other
     warnings.

‘-Wno-analyzer-use-of-uninitialized-value’
     This warning requires ‘-fanalyzer’, which enables it; use
     ‘-Wno-analyzer-use-of-uninitialized-value’ to disable it.

     This diagnostic warns for paths through the code in which an
     uninitialized value is used.

 Pertinent parameters for controlling the exploration are: ‘--param
analyzer-bb-explosion-factor=VALUE’, ‘--param
analyzer-max-enodes-per-program-point=VALUE’, ‘--param
analyzer-max-recursion-depth=VALUE’, and ‘--param
analyzer-min-snodes-for-call-summary=VALUE’.

 The following options control the analyzer.

‘-fanalyzer-call-summaries’
     Simplify interprocedural analysis by computing the effect of
     certain calls, rather than exploring all paths through the function
     from callsite to each possible return.

     If enabled, call summaries are only used for functions with more
     than one call site, and that are sufficiently complicated (as per
     ‘--param analyzer-min-snodes-for-call-summary=VALUE’).

‘-fanalyzer-checker=NAME’
     Restrict the analyzer to run just the named checker, and enable it.

     Some checkers are disabled by default (even with ‘-fanalyzer’),
     such as the ‘taint’ checker that implements
     ‘-Wanalyzer-tainted-array-index’, and this option is required to
     enable them.

     _Note:_ currently, ‘-fanalyzer-checker=taint’ disables the
     following warnings from ‘-fanalyzer’:


          -Wanalyzer-double-fclose
          -Wanalyzer-double-free
          -Wanalyzer-exposure-through-output-file
          -Wanalyzer-file-leak
          -Wanalyzer-free-of-non-heap
          -Wanalyzer-malloc-leak
          -Wanalyzer-mismatching-deallocation
          -Wanalyzer-null-argument
          -Wanalyzer-null-dereference
          -Wanalyzer-possible-null-argument
          -Wanalyzer-possible-null-dereference
          -Wanalyzer-unsafe-call-within-signal-handler
          -Wanalyzer-use-after-free

‘-fno-analyzer-feasibility’
     This option is intended for analyzer developers.

     By default the analyzer verifies that there is a feasible control
     flow path for each diagnostic it emits: that the conditions that
     hold are not mutually exclusive.  Diagnostics for which no feasible
     path can be found are rejected.  This filtering can be suppressed
     with ‘-fno-analyzer-feasibility’, for debugging issues in this
     code.

‘-fanalyzer-fine-grained’
     This option is intended for analyzer developers.

     Internally the analyzer builds an "exploded graph" that combines
     control flow graphs with data flow information.

     By default, an edge in this graph can contain the effects of a run
     of multiple statements within a basic block.  With
     ‘-fanalyzer-fine-grained’, each statement gets its own edge.

‘-fanalyzer-show-duplicate-count’
     This option is intended for analyzer developers: if multiple
     diagnostics have been detected as being duplicates of each other,
     it emits a note when reporting the best diagnostic, giving the
     number of additional diagnostics that were suppressed by the
     deduplication logic.

‘-fno-analyzer-state-merge’
     This option is intended for analyzer developers.

     By default the analyzer attempts to simplify analysis by merging
     sufficiently similar states at each program point as it builds its
     "exploded graph".  With ‘-fno-analyzer-state-merge’ this merging
     can be suppressed, for debugging state-handling issues.

‘-fno-analyzer-state-purge’
     This option is intended for analyzer developers.

     By default the analyzer attempts to simplify analysis by purging
     aspects of state at a program point that appear to no longer be
     relevant e.g.  the values of locals that aren't accessed later in
     the function and which aren't relevant to leak analysis.

     With ‘-fno-analyzer-state-purge’ this purging of state can be
     suppressed, for debugging state-handling issues.

‘-fanalyzer-transitivity’
     This option enables transitivity of constraints within the
     analyzer.

‘-fanalyzer-verbose-edges’
     This option is intended for analyzer developers.  It enables more
     verbose, lower-level detail in the descriptions of control flow
     within diagnostic paths.

‘-fanalyzer-verbose-state-changes’
     This option is intended for analyzer developers.  It enables more
     verbose, lower-level detail in the descriptions of events relating
     to state machines within diagnostic paths.

‘-fanalyzer-verbosity=LEVEL’
     This option controls the complexity of the control flow paths that
     are emitted for analyzer diagnostics.

     The LEVEL can be one of:

     ‘0’
          At this level, interprocedural call and return events are
          displayed, along with the most pertinent state-change events
          relating to a diagnostic.  For example, for a double-‘free’
          diagnostic, both calls to ‘free’ will be shown.

     ‘1’
          As per the previous level, but also show events for the entry
          to each function.

     ‘2’
          As per the previous level, but also show events relating to
          control flow that are significant to triggering the issue
          (e.g.  "true path taken" at a conditional).

          This level is the default.

     ‘3’
          As per the previous level, but show all control flow events,
          not just significant ones.

     ‘4’
          This level is intended for analyzer developers; it adds
          various other events intended for debugging the analyzer.

‘-fdump-analyzer’
     Dump internal details about what the analyzer is doing to
     ‘FILE.analyzer.txt’.  This option is overridden by
     ‘-fdump-analyzer-stderr’.

‘-fdump-analyzer-stderr’
     Dump internal details about what the analyzer is doing to stderr.
     This option overrides ‘-fdump-analyzer’.

‘-fdump-analyzer-callgraph’
     Dump a representation of the call graph suitable for viewing with
     GraphViz to ‘FILE.callgraph.dot’.

‘-fdump-analyzer-exploded-graph’
     Dump a representation of the "exploded graph" suitable for viewing
     with GraphViz to ‘FILE.eg.dot’.  Nodes are color-coded based on
     state-machine states to emphasize state changes.

‘-fdump-analyzer-exploded-nodes’
     Emit diagnostics showing where nodes in the "exploded graph" are in
     relation to the program source.

‘-fdump-analyzer-exploded-nodes-2’
     Dump a textual representation of the "exploded graph" to
     ‘FILE.eg.txt’.

‘-fdump-analyzer-exploded-nodes-3’
     Dump a textual representation of the "exploded graph" to one dump
     file per node, to ‘FILE.eg-ID.txt’.  This is typically a large
     number of dump files.

‘-fdump-analyzer-exploded-paths’
     Dump a textual representation of the "exploded path" for each
     diagnostic to ‘FILE.IDX.KIND.epath.txt’.

‘-fdump-analyzer-feasibility’
     Dump internal details about the analyzer's search for feasible
     paths.  The details are written in a form suitable for viewing with
     GraphViz to filenames of the form ‘FILE.*.fg.dot’, ‘FILE.*.tg.dot’,
     and ‘FILE.*.fpath.txt’.

‘-fdump-analyzer-json’
     Dump a compressed JSON representation of analyzer internals to
     ‘FILE.analyzer.json.gz’.  The precise format is subject to change.

‘-fdump-analyzer-state-purge’
     As per ‘-fdump-analyzer-supergraph’, dump a representation of the
     "supergraph" suitable for viewing with GraphViz, but annotate the
     graph with information on what state will be purged at each node.
     The graph is written to ‘FILE.state-purge.dot’.

‘-fdump-analyzer-supergraph’
     Dump representations of the "supergraph" suitable for viewing with
     GraphViz to ‘FILE.supergraph.dot’ and to ‘FILE.supergraph-eg.dot’.
     These show all of the control flow graphs in the program, with
     interprocedural edges for calls and returns.  The second dump
     contains annotations showing nodes in the "exploded graph" and
     diagnostics associated with them.

‘-fdump-analyzer-untracked’
     Emit custom warnings with internal details intended for analyzer
     developers.


File: gcc.info,  Node: Debugging Options,  Next: Optimize Options,  Prev: Static Analyzer Options,  Up: Invoking GCC

3.10 Options for Debugging Your Program
=======================================

To tell GCC to emit extra information for use by a debugger, in almost
all cases you need only to add ‘-g’ to your other options.  Some debug
formats can co-exist (like DWARF with CTF) when each of them is enabled
explicitly by adding the respective command line option to your other
options.

 GCC allows you to use ‘-g’ with ‘-O’.  The shortcuts taken by optimized
code may occasionally be surprising: some variables you declared may not
exist at all; flow of control may briefly move where you did not expect
it; some statements may not be executed because they compute constant
results or their values are already at hand; some statements may execute
in different places because they have been moved out of loops.
Nevertheless it is possible to debug optimized output.  This makes it
reasonable to use the optimizer for programs that might have bugs.

 If you are not using some other optimization option, consider using
‘-Og’ (*note Optimize Options::) with ‘-g’.  With no ‘-O’ option at all,
some compiler passes that collect information useful for debugging do
not run at all, so that ‘-Og’ may result in a better debugging
experience.

‘-g’
     Produce debugging information in the operating system's native
     format (stabs, COFF, XCOFF, or DWARF).  GDB can work with this
     debugging information.

     On most systems that use stabs format, ‘-g’ enables use of extra
     debugging information that only GDB can use; this extra information
     makes debugging work better in GDB but probably makes other
     debuggers crash or refuse to read the program.  If you want to
     control for certain whether to generate the extra information, use
     ‘-gstabs+’, ‘-gstabs’, ‘-gxcoff+’, ‘-gxcoff’, or ‘-gvms’ (see
     below).

‘-ggdb’
     Produce debugging information for use by GDB.  This means to use
     the most expressive format available (DWARF, stabs, or the native
     format if neither of those are supported), including GDB extensions
     if at all possible.

‘-gdwarf’
‘-gdwarf-VERSION’
     Produce debugging information in DWARF format (if that is
     supported).  The value of VERSION may be either 2, 3, 4 or 5; the
     default version for most targets is 5 (with the exception of
     VxWorks, TPF and Darwin/Mac OS X, which default to version 2, and
     AIX, which defaults to version 4).

     Note that with DWARF Version 2, some ports require and always use
     some non-conflicting DWARF 3 extensions in the unwind tables.

     Version 4 may require GDB 7.0 and ‘-fvar-tracking-assignments’ for
     maximum benefit.  Version 5 requires GDB 8.0 or higher.

     GCC no longer supports DWARF Version 1, which is substantially
     different than Version 2 and later.  For historical reasons, some
     other DWARF-related options such as ‘-fno-dwarf2-cfi-asm’) retain a
     reference to DWARF Version 2 in their names, but apply to all
     currently-supported versions of DWARF.

‘-gbtf’
     Request BTF debug information.  BTF is the default debugging format
     for the eBPF target.  On other targets, like x86, BTF debug
     information can be generated along with DWARF debug information
     when both of the debug formats are enabled explicitly via their
     respective command line options.

‘-gctf’
‘-gctfLEVEL’
     Request CTF debug information and use level to specify how much CTF
     debug information should be produced.  If ‘-gctf’ is specified
     without a value for level, the default level of CTF debug
     information is 2.

     CTF debug information can be generated along with DWARF debug
     information when both of the debug formats are enabled explicitly
     via their respective command line options.

     Level 0 produces no CTF debug information at all.  Thus, ‘-gctf0’
     negates ‘-gctf’.

     Level 1 produces CTF information for tracebacks only.  This
     includes callsite information, but does not include type
     information.

     Level 2 produces type information for entities (functions, data
     objects etc.)  at file-scope or global-scope only.

‘-gstabs’
     Produce debugging information in stabs format (if that is
     supported), without GDB extensions.  This is the format used by DBX
     on most BSD systems.  On MIPS, Alpha and System V Release 4 systems
     this option produces stabs debugging output that is not understood
     by DBX.  On System V Release 4 systems this option requires the GNU
     assembler.

‘-gstabs+’
     Produce debugging information in stabs format (if that is
     supported), using GNU extensions understood only by the GNU
     debugger (GDB).  The use of these extensions is likely to make
     other debuggers crash or refuse to read the program.

‘-gxcoff’
     Produce debugging information in XCOFF format (if that is
     supported).  This is the format used by the DBX debugger on IBM
     RS/6000 systems.

‘-gxcoff+’
     Produce debugging information in XCOFF format (if that is
     supported), using GNU extensions understood only by the GNU
     debugger (GDB).  The use of these extensions is likely to make
     other debuggers crash or refuse to read the program, and may cause
     assemblers other than the GNU assembler (GAS) to fail with an
     error.

‘-gvms’
     Produce debugging information in Alpha/VMS debug format (if that is
     supported).  This is the format used by DEBUG on Alpha/VMS systems.

‘-gLEVEL’
‘-ggdbLEVEL’
‘-gstabsLEVEL’
‘-gxcoffLEVEL’
‘-gvmsLEVEL’
     Request debugging information and also use LEVEL to specify how
     much information.  The default level is 2.

     Level 0 produces no debug information at all.  Thus, ‘-g0’ negates
     ‘-g’.

     Level 1 produces minimal information, enough for making backtraces
     in parts of the program that you don't plan to debug.  This
     includes descriptions of functions and external variables, and line
     number tables, but no information about local variables.

     Level 3 includes extra information, such as all the macro
     definitions present in the program.  Some debuggers support macro
     expansion when you use ‘-g3’.

     If you use multiple ‘-g’ options, with or without level numbers,
     the last such option is the one that is effective.

     ‘-gdwarf’ does not accept a concatenated debug level, to avoid
     confusion with ‘-gdwarf-LEVEL’.  Instead use an additional
     ‘-gLEVEL’ option to change the debug level for DWARF.

‘-fno-eliminate-unused-debug-symbols’
     By default, no debug information is produced for symbols that are
     not actually used.  Use this option if you want debug information
     for all symbols.

‘-femit-class-debug-always’
     Instead of emitting debugging information for a C++ class in only
     one object file, emit it in all object files using the class.  This
     option should be used only with debuggers that are unable to handle
     the way GCC normally emits debugging information for classes
     because using this option increases the size of debugging
     information by as much as a factor of two.

‘-fno-merge-debug-strings’
     Direct the linker to not merge together strings in the debugging
     information that are identical in different object files.  Merging
     is not supported by all assemblers or linkers.  Merging decreases
     the size of the debug information in the output file at the cost of
     increasing link processing time.  Merging is enabled by default.

‘-fdebug-prefix-map=OLD=NEW’
     When compiling files residing in directory ‘OLD’, record debugging
     information describing them as if the files resided in directory
     ‘NEW’ instead.  This can be used to replace a build-time path with
     an install-time path in the debug info.  It can also be used to
     change an absolute path to a relative path by using ‘.’ for NEW.
     This can give more reproducible builds, which are location
     independent, but may require an extra command to tell GDB where to
     find the source files.  See also ‘-ffile-prefix-map’.

‘-fvar-tracking’
     Run variable tracking pass.  It computes where variables are stored
     at each position in code.  Better debugging information is then
     generated (if the debugging information format supports this
     information).

     It is enabled by default when compiling with optimization (‘-Os’,
     ‘-O’, ‘-O2’, ...), debugging information (‘-g’) and the debug info
     format supports it.

‘-fvar-tracking-assignments’
     Annotate assignments to user variables early in the compilation and
     attempt to carry the annotations over throughout the compilation
     all the way to the end, in an attempt to improve debug information
     while optimizing.  Use of ‘-gdwarf-4’ is recommended along with it.

     It can be enabled even if var-tracking is disabled, in which case
     annotations are created and maintained, but discarded at the end.
     By default, this flag is enabled together with ‘-fvar-tracking’,
     except when selective scheduling is enabled.

‘-gsplit-dwarf’
     If DWARF debugging information is enabled, separate as much
     debugging information as possible into a separate output file with
     the extension ‘.dwo’.  This option allows the build system to avoid
     linking files with debug information.  To be useful, this option
     requires a debugger capable of reading ‘.dwo’ files.

‘-gdwarf32’
‘-gdwarf64’
     If DWARF debugging information is enabled, the ‘-gdwarf32’ selects
     the 32-bit DWARF format and the ‘-gdwarf64’ selects the 64-bit
     DWARF format.  The default is target specific, on most targets it
     is ‘-gdwarf32’ though.  The 32-bit DWARF format is smaller, but
     can't support more than 2GiB of debug information in any of the
     DWARF debug information sections.  The 64-bit DWARF format allows
     larger debug information and might not be well supported by all
     consumers yet.

‘-gdescribe-dies’
     Add description attributes to some DWARF DIEs that have no name
     attribute, such as artificial variables, external references and
     call site parameter DIEs.

‘-gpubnames’
     Generate DWARF ‘.debug_pubnames’ and ‘.debug_pubtypes’ sections.

‘-ggnu-pubnames’
     Generate ‘.debug_pubnames’ and ‘.debug_pubtypes’ sections in a
     format suitable for conversion into a GDB index.  This option is
     only useful with a linker that can produce GDB index version 7.

‘-fdebug-types-section’
     When using DWARF Version 4 or higher, type DIEs can be put into
     their own ‘.debug_types’ section instead of making them part of the
     ‘.debug_info’ section.  It is more efficient to put them in a
     separate comdat section since the linker can then remove
     duplicates.  But not all DWARF consumers support ‘.debug_types’
     sections yet and on some objects ‘.debug_types’ produces larger
     instead of smaller debugging information.

‘-grecord-gcc-switches’
‘-gno-record-gcc-switches’
     This switch causes the command-line options used to invoke the
     compiler that may affect code generation to be appended to the
     DW_AT_producer attribute in DWARF debugging information.  The
     options are concatenated with spaces separating them from each
     other and from the compiler version.  It is enabled by default.
     See also ‘-frecord-gcc-switches’ for another way of storing
     compiler options into the object file.

‘-gstrict-dwarf’
     Disallow using extensions of later DWARF standard version than
     selected with ‘-gdwarf-VERSION’.  On most targets using
     non-conflicting DWARF extensions from later standard versions is
     allowed.

‘-gno-strict-dwarf’
     Allow using extensions of later DWARF standard version than
     selected with ‘-gdwarf-VERSION’.

‘-gas-loc-support’
     Inform the compiler that the assembler supports ‘.loc’ directives.
     It may then use them for the assembler to generate DWARF2+ line
     number tables.

     This is generally desirable, because assembler-generated
     line-number tables are a lot more compact than those the compiler
     can generate itself.

     This option will be enabled by default if, at GCC configure time,
     the assembler was found to support such directives.

‘-gno-as-loc-support’
     Force GCC to generate DWARF2+ line number tables internally, if
     DWARF2+ line number tables are to be generated.

‘-gas-locview-support’
     Inform the compiler that the assembler supports ‘view’ assignment
     and reset assertion checking in ‘.loc’ directives.

     This option will be enabled by default if, at GCC configure time,
     the assembler was found to support them.

‘-gno-as-locview-support’
     Force GCC to assign view numbers internally, if
     ‘-gvariable-location-views’ are explicitly requested.

‘-gcolumn-info’
‘-gno-column-info’
     Emit location column information into DWARF debugging information,
     rather than just file and line.  This option is enabled by default.

‘-gstatement-frontiers’
‘-gno-statement-frontiers’
     This option causes GCC to create markers in the internal
     representation at the beginning of statements, and to keep them
     roughly in place throughout compilation, using them to guide the
     output of ‘is_stmt’ markers in the line number table.  This is
     enabled by default when compiling with optimization (‘-Os’, ‘-O1’,
     ‘-O2’, ...), and outputting DWARF 2 debug information at the normal
     level.

‘-gvariable-location-views’
‘-gvariable-location-views=incompat5’
‘-gno-variable-location-views’
     Augment variable location lists with progressive view numbers
     implied from the line number table.  This enables debug information
     consumers to inspect state at certain points of the program, even
     if no instructions associated with the corresponding source
     locations are present at that point.  If the assembler lacks
     support for view numbers in line number tables, this will cause the
     compiler to emit the line number table, which generally makes them
     somewhat less compact.  The augmented line number tables and
     location lists are fully backward-compatible, so they can be
     consumed by debug information consumers that are not aware of these
     augmentations, but they won't derive any benefit from them either.

     This is enabled by default when outputting DWARF 2 debug
     information at the normal level, as long as there is assembler
     support, ‘-fvar-tracking-assignments’ is enabled and
     ‘-gstrict-dwarf’ is not.  When assembler support is not available,
     this may still be enabled, but it will force GCC to output internal
     line number tables, and if ‘-ginternal-reset-location-views’ is not
     enabled, that will most certainly lead to silently mismatching
     location views.

     There is a proposed representation for view numbers that is not
     backward compatible with the location list format introduced in
     DWARF 5, that can be enabled with
     ‘-gvariable-location-views=incompat5’.  This option may be removed
     in the future, is only provided as a reference implementation of
     the proposed representation.  Debug information consumers are not
     expected to support this extended format, and they would be
     rendered unable to decode location lists using it.

‘-ginternal-reset-location-views’
‘-gno-internal-reset-location-views’
     Attempt to determine location views that can be omitted from
     location view lists.  This requires the compiler to have very
     accurate insn length estimates, which isn't always the case, and it
     may cause incorrect view lists to be generated silently when using
     an assembler that does not support location view lists.  The GNU
     assembler will flag any such error as a ‘view number mismatch’.
     This is only enabled on ports that define a reliable estimation
     function.

‘-ginline-points’
‘-gno-inline-points’
     Generate extended debug information for inlined functions.
     Location view tracking markers are inserted at inlined entry
     points, so that address and view numbers can be computed and output
     in debug information.  This can be enabled independently of
     location views, in which case the view numbers won't be output, but
     it can only be enabled along with statement frontiers, and it is
     only enabled by default if location views are enabled.

‘-gz[=TYPE]’
     Produce compressed debug sections in DWARF format, if that is
     supported.  If TYPE is not given, the default type depends on the
     capabilities of the assembler and linker used.  TYPE may be one of
     ‘none’ (don't compress debug sections), ‘zlib’ (use zlib
     compression in ELF gABI format), or ‘zlib-gnu’ (use zlib
     compression in traditional GNU format).  If the linker doesn't
     support writing compressed debug sections, the option is rejected.
     Otherwise, if the assembler does not support them, ‘-gz’ is
     silently ignored when producing object files.

‘-femit-struct-debug-baseonly’
     Emit debug information for struct-like types only when the base
     name of the compilation source file matches the base name of file
     in which the struct is defined.

     This option substantially reduces the size of debugging
     information, but at significant potential loss in type information
     to the debugger.  See ‘-femit-struct-debug-reduced’ for a less
     aggressive option.  See ‘-femit-struct-debug-detailed’ for more
     detailed control.

     This option works only with DWARF debug output.

‘-femit-struct-debug-reduced’
     Emit debug information for struct-like types only when the base
     name of the compilation source file matches the base name of file
     in which the type is defined, unless the struct is a template or
     defined in a system header.

     This option significantly reduces the size of debugging
     information, with some potential loss in type information to the
     debugger.  See ‘-femit-struct-debug-baseonly’ for a more aggressive
     option.  See ‘-femit-struct-debug-detailed’ for more detailed
     control.

     This option works only with DWARF debug output.

‘-femit-struct-debug-detailed[=SPEC-LIST]’
     Specify the struct-like types for which the compiler generates
     debug information.  The intent is to reduce duplicate struct debug
     information between different object files within the same program.

     This option is a detailed version of ‘-femit-struct-debug-reduced’
     and ‘-femit-struct-debug-baseonly’, which serves for most needs.

     A specification has the syntax
     [‘dir:’|‘ind:’][‘ord:’|‘gen:’](‘any’|‘sys’|‘base’|‘none’)

     The optional first word limits the specification to structs that
     are used directly (‘dir:’) or used indirectly (‘ind:’).  A struct
     type is used directly when it is the type of a variable, member.
     Indirect uses arise through pointers to structs.  That is, when use
     of an incomplete struct is valid, the use is indirect.  An example
     is ‘struct one direct; struct two * indirect;’.

     The optional second word limits the specification to ordinary
     structs (‘ord:’) or generic structs (‘gen:’).  Generic structs are
     a bit complicated to explain.  For C++, these are non-explicit
     specializations of template classes, or non-template classes within
     the above.  Other programming languages have generics, but
     ‘-femit-struct-debug-detailed’ does not yet implement them.

     The third word specifies the source files for those structs for
     which the compiler should emit debug information.  The values
     ‘none’ and ‘any’ have the normal meaning.  The value ‘base’ means
     that the base of name of the file in which the type declaration
     appears must match the base of the name of the main compilation
     file.  In practice, this means that when compiling ‘foo.c’, debug
     information is generated for types declared in that file and
     ‘foo.h’, but not other header files.  The value ‘sys’ means those
     types satisfying ‘base’ or declared in system or compiler headers.

     You may need to experiment to determine the best settings for your
     application.

     The default is ‘-femit-struct-debug-detailed=all’.

     This option works only with DWARF debug output.

‘-fno-dwarf2-cfi-asm’
     Emit DWARF unwind info as compiler generated ‘.eh_frame’ section
     instead of using GAS ‘.cfi_*’ directives.

‘-fno-eliminate-unused-debug-types’
     Normally, when producing DWARF output, GCC avoids producing debug
     symbol output for types that are nowhere used in the source file
     being compiled.  Sometimes it is useful to have GCC emit debugging
     information for all types declared in a compilation unit,
     regardless of whether or not they are actually used in that
     compilation unit, for example if, in the debugger, you want to cast
     a value to a type that is not actually used in your program (but is
     declared).  More often, however, this results in a significant
     amount of wasted space.


File: gcc.info,  Node: Optimize Options,  Next: Instrumentation Options,  Prev: Debugging Options,  Up: Invoking GCC

3.11 Options That Control Optimization
======================================

These options control various sorts of optimizations.

 Without any optimization option, the compiler's goal is to reduce the
cost of compilation and to make debugging produce the expected results.
Statements are independent: if you stop the program with a breakpoint
between statements, you can then assign a new value to any variable or
change the program counter to any other statement in the function and
get exactly the results you expect from the source code.

 Turning on optimization flags makes the compiler attempt to improve the
performance and/or code size at the expense of compilation time and
possibly the ability to debug the program.

 The compiler performs optimization based on the knowledge it has of the
program.  Compiling multiple files at once to a single output file mode
allows the compiler to use information gained from all of the files when
compiling each of them.

 Not all optimizations are controlled directly by a flag.  Only
optimizations that have a flag are listed in this section.

 Most optimizations are completely disabled at ‘-O0’ or if an ‘-O’ level
is not set on the command line, even if individual optimization flags
are specified.  Similarly, ‘-Og’ suppresses many optimization passes.

 Depending on the target and how GCC was configured, a slightly
different set of optimizations may be enabled at each ‘-O’ level than
those listed here.  You can invoke GCC with ‘-Q --help=optimizers’ to
find out the exact set of optimizations that are enabled at each level.
*Note Overall Options::, for examples.

‘-O’
‘-O1’
     Optimize.  Optimizing compilation takes somewhat more time, and a
     lot more memory for a large function.

     With ‘-O’, the compiler tries to reduce code size and execution
     time, without performing any optimizations that take a great deal
     of compilation time.

     ‘-O’ turns on the following optimization flags:

          -fauto-inc-dec
          -fbranch-count-reg
          -fcombine-stack-adjustments
          -fcompare-elim
          -fcprop-registers
          -fdce
          -fdefer-pop
          -fdelayed-branch
          -fdse
          -fforward-propagate
          -fguess-branch-probability
          -fif-conversion
          -fif-conversion2
          -finline-functions-called-once
          -fipa-modref
          -fipa-profile
          -fipa-pure-const
          -fipa-reference
          -fipa-reference-addressable
          -fmerge-constants
          -fmove-loop-invariants
          -fmove-loop-stores
          -fomit-frame-pointer
          -freorder-blocks
          -fshrink-wrap
          -fshrink-wrap-separate
          -fsplit-wide-types
          -fssa-backprop
          -fssa-phiopt
          -ftree-bit-ccp
          -ftree-ccp
          -ftree-ch
          -ftree-coalesce-vars
          -ftree-copy-prop
          -ftree-dce
          -ftree-dominator-opts
          -ftree-dse
          -ftree-forwprop
          -ftree-fre
          -ftree-phiprop
          -ftree-pta
          -ftree-scev-cprop
          -ftree-sink
          -ftree-slsr
          -ftree-sra
          -ftree-ter
          -funit-at-a-time

‘-O2’
     Optimize even more.  GCC performs nearly all supported
     optimizations that do not involve a space-speed tradeoff.  As
     compared to ‘-O’, this option increases both compilation time and
     the performance of the generated code.

     ‘-O2’ turns on all optimization flags specified by ‘-O1’.  It also
     turns on the following optimization flags:

          -falign-functions  -falign-jumps
          -falign-labels  -falign-loops
          -fcaller-saves
          -fcode-hoisting
          -fcrossjumping
          -fcse-follow-jumps  -fcse-skip-blocks
          -fdelete-null-pointer-checks
          -fdevirtualize  -fdevirtualize-speculatively
          -fexpensive-optimizations
          -ffinite-loops
          -fgcse  -fgcse-lm
          -fhoist-adjacent-loads
          -finline-functions
          -finline-small-functions
          -findirect-inlining
          -fipa-bit-cp  -fipa-cp  -fipa-icf
          -fipa-ra  -fipa-sra  -fipa-vrp
          -fisolate-erroneous-paths-dereference
          -flra-remat
          -foptimize-sibling-calls
          -foptimize-strlen
          -fpartial-inlining
          -fpeephole2
          -freorder-blocks-algorithm=stc
          -freorder-blocks-and-partition  -freorder-functions
          -frerun-cse-after-loop
          -fschedule-insns  -fschedule-insns2
          -fsched-interblock  -fsched-spec
          -fstore-merging
          -fstrict-aliasing
          -fthread-jumps
          -ftree-builtin-call-dce
          -ftree-loop-vectorize
          -ftree-pre
          -ftree-slp-vectorize
          -ftree-switch-conversion  -ftree-tail-merge
          -ftree-vrp
          -fvect-cost-model=very-cheap

     Please note the warning under ‘-fgcse’ about invoking ‘-O2’ on
     programs that use computed gotos.

‘-O3’
     Optimize yet more.  ‘-O3’ turns on all optimizations specified by
     ‘-O2’ and also turns on the following optimization flags:

          -fgcse-after-reload
          -fipa-cp-clone
          -floop-interchange
          -floop-unroll-and-jam
          -fpeel-loops
          -fpredictive-commoning
          -fsplit-loops
          -fsplit-paths
          -ftree-loop-distribution
          -ftree-partial-pre
          -funswitch-loops
          -fvect-cost-model=dynamic
          -fversion-loops-for-strides

‘-O0’
     Reduce compilation time and make debugging produce the expected
     results.  This is the default.

‘-Os’
     Optimize for size.  ‘-Os’ enables all ‘-O2’ optimizations except
     those that often increase code size:

          -falign-functions  -falign-jumps
          -falign-labels  -falign-loops
          -fprefetch-loop-arrays  -freorder-blocks-algorithm=stc

     It also enables ‘-finline-functions’, causes the compiler to tune
     for code size rather than execution speed, and performs further
     optimizations designed to reduce code size.

‘-Ofast’
     Disregard strict standards compliance.  ‘-Ofast’ enables all ‘-O3’
     optimizations.  It also enables optimizations that are not valid
     for all standard-compliant programs.  It turns on ‘-ffast-math’,
     ‘-fallow-store-data-races’ and the Fortran-specific
     ‘-fstack-arrays’, unless ‘-fmax-stack-var-size’ is specified, and
     ‘-fno-protect-parens’.  It turns off ‘-fsemantic-interposition’.

‘-Og’
     Optimize debugging experience.  ‘-Og’ should be the optimization
     level of choice for the standard edit-compile-debug cycle, offering
     a reasonable level of optimization while maintaining fast
     compilation and a good debugging experience.  It is a better choice
     than ‘-O0’ for producing debuggable code because some compiler
     passes that collect debug information are disabled at ‘-O0’.

     Like ‘-O0’, ‘-Og’ completely disables a number of optimization
     passes so that individual options controlling them have no effect.
     Otherwise ‘-Og’ enables all ‘-O1’ optimization flags except for
     those that may interfere with debugging:

          -fbranch-count-reg  -fdelayed-branch
          -fdse  -fif-conversion  -fif-conversion2
          -finline-functions-called-once
          -fmove-loop-invariants  -fmove-loop-stores  -fssa-phiopt
          -ftree-bit-ccp  -ftree-dse  -ftree-pta  -ftree-sra

‘-Oz’
     Optimize aggressively for size rather than speed.  This may
     increase the number of instructions executed if those instructions
     require fewer bytes to encode.  ‘-Oz’ behaves similarly to ‘-Os’
     including enabling most ‘-O2’ optimizations.

 If you use multiple ‘-O’ options, with or without level numbers, the
last such option is the one that is effective.

 Options of the form ‘-fFLAG’ specify machine-independent flags.  Most
flags have both positive and negative forms; the negative form of
‘-ffoo’ is ‘-fno-foo’.  In the table below, only one of the forms is
listed--the one you typically use.  You can figure out the other form by
either removing ‘no-’ or adding it.

 The following options control specific optimizations.  They are either
activated by ‘-O’ options or are related to ones that are.  You can use
the following flags in the rare cases when "fine-tuning" of
optimizations to be performed is desired.

‘-fno-defer-pop’
     For machines that must pop arguments after a function call, always
     pop the arguments as soon as each function returns.  At levels
     ‘-O1’ and higher, ‘-fdefer-pop’ is the default; this allows the
     compiler to let arguments accumulate on the stack for several
     function calls and pop them all at once.

‘-fforward-propagate’
     Perform a forward propagation pass on RTL.  The pass tries to
     combine two instructions and checks if the result can be
     simplified.  If loop unrolling is active, two passes are performed
     and the second is scheduled after loop unrolling.

     This option is enabled by default at optimization levels ‘-O1’,
     ‘-O2’, ‘-O3’, ‘-Os’.

‘-ffp-contract=STYLE’
     ‘-ffp-contract=off’ disables floating-point expression contraction.
     ‘-ffp-contract=fast’ enables floating-point expression contraction
     such as forming of fused multiply-add operations if the target has
     native support for them.  ‘-ffp-contract=on’ enables floating-point
     expression contraction if allowed by the language standard.  This
     is currently not implemented and treated equal to
     ‘-ffp-contract=off’.

     The default is ‘-ffp-contract=fast’.

‘-fomit-frame-pointer’
     Omit the frame pointer in functions that don't need one.  This
     avoids the instructions to save, set up and restore the frame
     pointer; on many targets it also makes an extra register available.

     On some targets this flag has no effect because the standard
     calling sequence always uses a frame pointer, so it cannot be
     omitted.

     Note that ‘-fno-omit-frame-pointer’ doesn't guarantee the frame
     pointer is used in all functions.  Several targets always omit the
     frame pointer in leaf functions.

     Enabled by default at ‘-O1’ and higher.

‘-foptimize-sibling-calls’
     Optimize sibling and tail recursive calls.

     Enabled at levels ‘-O2’, ‘-O3’, ‘-Os’.

‘-foptimize-strlen’
     Optimize various standard C string functions (e.g. ‘strlen’,
     ‘strchr’ or ‘strcpy’) and their ‘_FORTIFY_SOURCE’ counterparts into
     faster alternatives.

     Enabled at levels ‘-O2’, ‘-O3’.

‘-fno-inline’
     Do not expand any functions inline apart from those marked with the
     ‘always_inline’ attribute.  This is the default when not
     optimizing.

     Single functions can be exempted from inlining by marking them with
     the ‘noinline’ attribute.

‘-finline-small-functions’
     Integrate functions into their callers when their body is smaller
     than expected function call code (so overall size of program gets
     smaller).  The compiler heuristically decides which functions are
     simple enough to be worth integrating in this way.  This inlining
     applies to all functions, even those not declared inline.

     Enabled at levels ‘-O2’, ‘-O3’, ‘-Os’.

‘-findirect-inlining’
     Inline also indirect calls that are discovered to be known at
     compile time thanks to previous inlining.  This option has any
     effect only when inlining itself is turned on by the
     ‘-finline-functions’ or ‘-finline-small-functions’ options.

     Enabled at levels ‘-O2’, ‘-O3’, ‘-Os’.

‘-finline-functions’
     Consider all functions for inlining, even if they are not declared
     inline.  The compiler heuristically decides which functions are
     worth integrating in this way.

     If all calls to a given function are integrated, and the function
     is declared ‘static’, then the function is normally not output as
     assembler code in its own right.

     Enabled at levels ‘-O2’, ‘-O3’, ‘-Os’.  Also enabled by
     ‘-fprofile-use’ and ‘-fauto-profile’.

‘-finline-functions-called-once’
     Consider all ‘static’ functions called once for inlining into their
     caller even if they are not marked ‘inline’.  If a call to a given
     function is integrated, then the function is not output as
     assembler code in its own right.

     Enabled at levels ‘-O1’, ‘-O2’, ‘-O3’ and ‘-Os’, but not ‘-Og’.

‘-fearly-inlining’
     Inline functions marked by ‘always_inline’ and functions whose body
     seems smaller than the function call overhead early before doing
     ‘-fprofile-generate’ instrumentation and real inlining pass.  Doing
     so makes profiling significantly cheaper and usually inlining
     faster on programs having large chains of nested wrapper functions.

     Enabled by default.

‘-fipa-sra’
     Perform interprocedural scalar replacement of aggregates, removal
     of unused parameters and replacement of parameters passed by
     reference by parameters passed by value.

     Enabled at levels ‘-O2’, ‘-O3’ and ‘-Os’.

‘-finline-limit=N’
     By default, GCC limits the size of functions that can be inlined.
     This flag allows coarse control of this limit.  N is the size of
     functions that can be inlined in number of pseudo instructions.

     Inlining is actually controlled by a number of parameters, which
     may be specified individually by using ‘--param NAME=VALUE’.  The
     ‘-finline-limit=N’ option sets some of these parameters as follows:

     ‘max-inline-insns-single’
          is set to N/2.
     ‘max-inline-insns-auto’
          is set to N/2.

     See below for a documentation of the individual parameters
     controlling inlining and for the defaults of these parameters.

     _Note:_ there may be no value to ‘-finline-limit’ that results in
     default behavior.

     _Note:_ pseudo instruction represents, in this particular context,
     an abstract measurement of function's size.  In no way does it
     represent a count of assembly instructions and as such its exact
     meaning might change from one release to an another.

‘-fno-keep-inline-dllexport’
     This is a more fine-grained version of ‘-fkeep-inline-functions’,
     which applies only to functions that are declared using the
     ‘dllexport’ attribute or declspec.  *Note Declaring Attributes of
     Functions: Function Attributes.

‘-fkeep-inline-functions’
     In C, emit ‘static’ functions that are declared ‘inline’ into the
     object file, even if the function has been inlined into all of its
     callers.  This switch does not affect functions using the ‘extern
     inline’ extension in GNU C90.  In C++, emit any and all inline
     functions into the object file.

‘-fkeep-static-functions’
     Emit ‘static’ functions into the object file, even if the function
     is never used.

‘-fkeep-static-consts’
     Emit variables declared ‘static const’ when optimization isn't
     turned on, even if the variables aren't referenced.

     GCC enables this option by default.  If you want to force the
     compiler to check if a variable is referenced, regardless of
     whether or not optimization is turned on, use the
     ‘-fno-keep-static-consts’ option.

‘-fmerge-constants’
     Attempt to merge identical constants (string constants and
     floating-point constants) across compilation units.

     This option is the default for optimized compilation if the
     assembler and linker support it.  Use ‘-fno-merge-constants’ to
     inhibit this behavior.

     Enabled at levels ‘-O1’, ‘-O2’, ‘-O3’, ‘-Os’.

‘-fmerge-all-constants’
     Attempt to merge identical constants and identical variables.

     This option implies ‘-fmerge-constants’.  In addition to
     ‘-fmerge-constants’ this considers e.g. even constant initialized
     arrays or initialized constant variables with integral or
     floating-point types.  Languages like C or C++ require each
     variable, including multiple instances of the same variable in
     recursive calls, to have distinct locations, so using this option
     results in non-conforming behavior.

‘-fmodulo-sched’
     Perform swing modulo scheduling immediately before the first
     scheduling pass.  This pass looks at innermost loops and reorders
     their instructions by overlapping different iterations.

‘-fmodulo-sched-allow-regmoves’
     Perform more aggressive SMS-based modulo scheduling with register
     moves allowed.  By setting this flag certain anti-dependences edges
     are deleted, which triggers the generation of reg-moves based on
     the life-range analysis.  This option is effective only with
     ‘-fmodulo-sched’ enabled.

‘-fno-branch-count-reg’
     Disable the optimization pass that scans for opportunities to use
     "decrement and branch" instructions on a count register instead of
     instruction sequences that decrement a register, compare it against
     zero, and then branch based upon the result.  This option is only
     meaningful on architectures that support such instructions, which
     include x86, PowerPC, IA-64 and S/390.  Note that the
     ‘-fno-branch-count-reg’ option doesn't remove the decrement and
     branch instructions from the generated instruction stream
     introduced by other optimization passes.

     The default is ‘-fbranch-count-reg’ at ‘-O1’ and higher, except for
     ‘-Og’.

‘-fno-function-cse’
     Do not put function addresses in registers; make each instruction
     that calls a constant function contain the function's address
     explicitly.

     This option results in less efficient code, but some strange hacks
     that alter the assembler output may be confused by the
     optimizations performed when this option is not used.

     The default is ‘-ffunction-cse’

‘-fno-zero-initialized-in-bss’
     If the target supports a BSS section, GCC by default puts variables
     that are initialized to zero into BSS.  This can save space in the
     resulting code.

     This option turns off this behavior because some programs
     explicitly rely on variables going to the data section--e.g., so
     that the resulting executable can find the beginning of that
     section and/or make assumptions based on that.

     The default is ‘-fzero-initialized-in-bss’.

‘-fthread-jumps’
     Perform optimizations that check to see if a jump branches to a
     location where another comparison subsumed by the first is found.
     If so, the first branch is redirected to either the destination of
     the second branch or a point immediately following it, depending on
     whether the condition is known to be true or false.

     Enabled at levels ‘-O1’, ‘-O2’, ‘-O3’, ‘-Os’.

‘-fsplit-wide-types’
     When using a type that occupies multiple registers, such as ‘long
     long’ on a 32-bit system, split the registers apart and allocate
     them independently.  This normally generates better code for those
     types, but may make debugging more difficult.

     Enabled at levels ‘-O1’, ‘-O2’, ‘-O3’, ‘-Os’.

‘-fsplit-wide-types-early’
     Fully split wide types early, instead of very late.  This option
     has no effect unless ‘-fsplit-wide-types’ is turned on.

     This is the default on some targets.

‘-fcse-follow-jumps’
     In common subexpression elimination (CSE), scan through jump
     instructions when the target of the jump is not reached by any
     other path.  For example, when CSE encounters an ‘if’ statement
     with an ‘else’ clause, CSE follows the jump when the condition
     tested is false.

     Enabled at levels ‘-O2’, ‘-O3’, ‘-Os’.

‘-fcse-skip-blocks’
     This is similar to ‘-fcse-follow-jumps’, but causes CSE to follow
     jumps that conditionally skip over blocks.  When CSE encounters a
     simple ‘if’ statement with no else clause, ‘-fcse-skip-blocks’
     causes CSE to follow the jump around the body of the ‘if’.

     Enabled at levels ‘-O2’, ‘-O3’, ‘-Os’.

‘-frerun-cse-after-loop’
     Re-run common subexpression elimination after loop optimizations
     are performed.

     Enabled at levels ‘-O2’, ‘-O3’, ‘-Os’.

‘-fgcse’
     Perform a global common subexpression elimination pass.  This pass
     also performs global constant and copy propagation.

     _Note:_ When compiling a program using computed gotos, a GCC
     extension, you may get better run-time performance if you disable
     the global common subexpression elimination pass by adding
     ‘-fno-gcse’ to the command line.

     Enabled at levels ‘-O2’, ‘-O3’, ‘-Os’.

‘-fgcse-lm’
     When ‘-fgcse-lm’ is enabled, global common subexpression
     elimination attempts to move loads that are only killed by stores
     into themselves.  This allows a loop containing a load/store
     sequence to be changed to a load outside the loop, and a copy/store
     within the loop.

     Enabled by default when ‘-fgcse’ is enabled.

‘-fgcse-sm’
     When ‘-fgcse-sm’ is enabled, a store motion pass is run after
     global common subexpression elimination.  This pass attempts to
     move stores out of loops.  When used in conjunction with
     ‘-fgcse-lm’, loops containing a load/store sequence can be changed
     to a load before the loop and a store after the loop.

     Not enabled at any optimization level.

‘-fgcse-las’
     When ‘-fgcse-las’ is enabled, the global common subexpression
     elimination pass eliminates redundant loads that come after stores
     to the same memory location (both partial and full redundancies).

     Not enabled at any optimization level.

‘-fgcse-after-reload’
     When ‘-fgcse-after-reload’ is enabled, a redundant load elimination
     pass is performed after reload.  The purpose of this pass is to
     clean up redundant spilling.

     Enabled by ‘-O3’, ‘-fprofile-use’ and ‘-fauto-profile’.

‘-faggressive-loop-optimizations’
     This option tells the loop optimizer to use language constraints to
     derive bounds for the number of iterations of a loop.  This assumes
     that loop code does not invoke undefined behavior by for example
     causing signed integer overflows or out-of-bound array accesses.
     The bounds for the number of iterations of a loop are used to guide
     loop unrolling and peeling and loop exit test optimizations.  This
     option is enabled by default.

‘-funconstrained-commons’
     This option tells the compiler that variables declared in common
     blocks (e.g. Fortran) may later be overridden with longer trailing
     arrays.  This prevents certain optimizations that depend on knowing
     the array bounds.

‘-fcrossjumping’
     Perform cross-jumping transformation.  This transformation unifies
     equivalent code and saves code size.  The resulting code may or may
     not perform better than without cross-jumping.

     Enabled at levels ‘-O2’, ‘-O3’, ‘-Os’.

‘-fauto-inc-dec’
     Combine increments or decrements of addresses with memory accesses.
     This pass is always skipped on architectures that do not have
     instructions to support this.  Enabled by default at ‘-O1’ and
     higher on architectures that support this.

‘-fdce’
     Perform dead code elimination (DCE) on RTL.  Enabled by default at
     ‘-O1’ and higher.

‘-fdse’
     Perform dead store elimination (DSE) on RTL.  Enabled by default at
     ‘-O1’ and higher.

‘-fif-conversion’
     Attempt to transform conditional jumps into branch-less
     equivalents.  This includes use of conditional moves, min, max, set
     flags and abs instructions, and some tricks doable by standard
     arithmetics.  The use of conditional execution on chips where it is
     available is controlled by ‘-fif-conversion2’.

     Enabled at levels ‘-O1’, ‘-O2’, ‘-O3’, ‘-Os’, but not with ‘-Og’.

‘-fif-conversion2’
     Use conditional execution (where available) to transform
     conditional jumps into branch-less equivalents.

     Enabled at levels ‘-O1’, ‘-O2’, ‘-O3’, ‘-Os’, but not with ‘-Og’.

‘-fdeclone-ctor-dtor’
     The C++ ABI requires multiple entry points for constructors and
     destructors: one for a base subobject, one for a complete object,
     and one for a virtual destructor that calls operator delete
     afterwards.  For a hierarchy with virtual bases, the base and
     complete variants are clones, which means two copies of the
     function.  With this option, the base and complete variants are
     changed to be thunks that call a common implementation.

     Enabled by ‘-Os’.

‘-fdelete-null-pointer-checks’
     Assume that programs cannot safely dereference null pointers, and
     that no code or data element resides at address zero.  This option
     enables simple constant folding optimizations at all optimization
     levels.  In addition, other optimization passes in GCC use this
     flag to control global dataflow analyses that eliminate useless
     checks for null pointers; these assume that a memory access to
     address zero always results in a trap, so that if a pointer is
     checked after it has already been dereferenced, it cannot be null.

     Note however that in some environments this assumption is not true.
     Use ‘-fno-delete-null-pointer-checks’ to disable this optimization
     for programs that depend on that behavior.

     This option is enabled by default on most targets.  On Nios II ELF,
     it defaults to off.  On AVR, CR16, and MSP430, this option is
     completely disabled.

     Passes that use the dataflow information are enabled independently
     at different optimization levels.

‘-fdevirtualize’
     Attempt to convert calls to virtual functions to direct calls.
     This is done both within a procedure and interprocedurally as part
     of indirect inlining (‘-findirect-inlining’) and interprocedural
     constant propagation (‘-fipa-cp’).  Enabled at levels ‘-O2’, ‘-O3’,
     ‘-Os’.

‘-fdevirtualize-speculatively’
     Attempt to convert calls to virtual functions to speculative direct
     calls.  Based on the analysis of the type inheritance graph,
     determine for a given call the set of likely targets.  If the set
     is small, preferably of size 1, change the call into a conditional
     deciding between direct and indirect calls.  The speculative calls
     enable more optimizations, such as inlining.  When they seem
     useless after further optimization, they are converted back into
     original form.

‘-fdevirtualize-at-ltrans’
     Stream extra information needed for aggressive devirtualization
     when running the link-time optimizer in local transformation mode.
     This option enables more devirtualization but significantly
     increases the size of streamed data.  For this reason it is
     disabled by default.

‘-fexpensive-optimizations’
     Perform a number of minor optimizations that are relatively
     expensive.

     Enabled at levels ‘-O2’, ‘-O3’, ‘-Os’.

‘-free’
     Attempt to remove redundant extension instructions.  This is
     especially helpful for the x86-64 architecture, which implicitly
     zero-extends in 64-bit registers after writing to their lower
     32-bit half.

     Enabled for Alpha, AArch64 and x86 at levels ‘-O2’, ‘-O3’, ‘-Os’.

‘-fno-lifetime-dse’
     In C++ the value of an object is only affected by changes within
     its lifetime: when the constructor begins, the object has an
     indeterminate value, and any changes during the lifetime of the
     object are dead when the object is destroyed.  Normally dead store
     elimination will take advantage of this; if your code relies on the
     value of the object storage persisting beyond the lifetime of the
     object, you can use this flag to disable this optimization.  To
     preserve stores before the constructor starts (e.g. because your
     operator new clears the object storage) but still treat the object
     as dead after the destructor, you can use ‘-flifetime-dse=1’.  The
     default behavior can be explicitly selected with
     ‘-flifetime-dse=2’.  ‘-flifetime-dse=0’ is equivalent to
     ‘-fno-lifetime-dse’.

‘-flive-range-shrinkage’
     Attempt to decrease register pressure through register live range
     shrinkage.  This is helpful for fast processors with small or
     moderate size register sets.

‘-fira-algorithm=ALGORITHM’
     Use the specified coloring algorithm for the integrated register
     allocator.  The ALGORITHM argument can be ‘priority’, which
     specifies Chow's priority coloring, or ‘CB’, which specifies
     Chaitin-Briggs coloring.  Chaitin-Briggs coloring is not
     implemented for all architectures, but for those targets that do
     support it, it is the default because it generates better code.

‘-fira-region=REGION’
     Use specified regions for the integrated register allocator.  The
     REGION argument should be one of the following:

     ‘all’
          Use all loops as register allocation regions.  This can give
          the best results for machines with a small and/or irregular
          register set.

     ‘mixed’
          Use all loops except for loops with small register pressure as
          the regions.  This value usually gives the best results in
          most cases and for most architectures, and is enabled by
          default when compiling with optimization for speed (‘-O’,
          ‘-O2’, ...).

     ‘one’
          Use all functions as a single region.  This typically results
          in the smallest code size, and is enabled by default for ‘-Os’
          or ‘-O0’.

‘-fira-hoist-pressure’
     Use IRA to evaluate register pressure in the code hoisting pass for
     decisions to hoist expressions.  This option usually results in
     smaller code, but it can slow the compiler down.

     This option is enabled at level ‘-Os’ for all targets.

‘-fira-loop-pressure’
     Use IRA to evaluate register pressure in loops for decisions to
     move loop invariants.  This option usually results in generation of
     faster and smaller code on machines with large register files (>=
     32 registers), but it can slow the compiler down.

     This option is enabled at level ‘-O3’ for some targets.

‘-fno-ira-share-save-slots’
     Disable sharing of stack slots used for saving call-used hard
     registers living through a call.  Each hard register gets a
     separate stack slot, and as a result function stack frames are
     larger.

‘-fno-ira-share-spill-slots’
     Disable sharing of stack slots allocated for pseudo-registers.
     Each pseudo-register that does not get a hard register gets a
     separate stack slot, and as a result function stack frames are
     larger.

‘-flra-remat’
     Enable CFG-sensitive rematerialization in LRA. Instead of loading
     values of spilled pseudos, LRA tries to rematerialize (recalculate)
     values if it is profitable.

     Enabled at levels ‘-O2’, ‘-O3’, ‘-Os’.

‘-fdelayed-branch’
     If supported for the target machine, attempt to reorder
     instructions to exploit instruction slots available after delayed
     branch instructions.

     Enabled at levels ‘-O1’, ‘-O2’, ‘-O3’, ‘-Os’, but not at ‘-Og’.

‘-fschedule-insns’
     If supported for the target machine, attempt to reorder
     instructions to eliminate execution stalls due to required data
     being unavailable.  This helps machines that have slow floating
     point or memory load instructions by allowing other instructions to
     be issued until the result of the load or floating-point
     instruction is required.

     Enabled at levels ‘-O2’, ‘-O3’.

‘-fschedule-insns2’
     Similar to ‘-fschedule-insns’, but requests an additional pass of
     instruction scheduling after register allocation has been done.
     This is especially useful on machines with a relatively small
     number of registers and where memory load instructions take more
     than one cycle.

     Enabled at levels ‘-O2’, ‘-O3’, ‘-Os’.

‘-fno-sched-interblock’
     Disable instruction scheduling across basic blocks, which is
     normally enabled when scheduling before register allocation, i.e.
     with ‘-fschedule-insns’ or at ‘-O2’ or higher.

‘-fno-sched-spec’
     Disable speculative motion of non-load instructions, which is
     normally enabled when scheduling before register allocation, i.e.
     with ‘-fschedule-insns’ or at ‘-O2’ or higher.

‘-fsched-pressure’
     Enable register pressure sensitive insn scheduling before register
     allocation.  This only makes sense when scheduling before register
     allocation is enabled, i.e. with ‘-fschedule-insns’ or at ‘-O2’ or
     higher.  Usage of this option can improve the generated code and
     decrease its size by preventing register pressure increase above
     the number of available hard registers and subsequent spills in
     register allocation.

‘-fsched-spec-load’
     Allow speculative motion of some load instructions.  This only
     makes sense when scheduling before register allocation, i.e. with
     ‘-fschedule-insns’ or at ‘-O2’ or higher.

‘-fsched-spec-load-dangerous’
     Allow speculative motion of more load instructions.  This only
     makes sense when scheduling before register allocation, i.e. with
     ‘-fschedule-insns’ or at ‘-O2’ or higher.

‘-fsched-stalled-insns’
‘-fsched-stalled-insns=N’
     Define how many insns (if any) can be moved prematurely from the
     queue of stalled insns into the ready list during the second
     scheduling pass.  ‘-fno-sched-stalled-insns’ means that no insns
     are moved prematurely, ‘-fsched-stalled-insns=0’ means there is no
     limit on how many queued insns can be moved prematurely.
     ‘-fsched-stalled-insns’ without a value is equivalent to
     ‘-fsched-stalled-insns=1’.

‘-fsched-stalled-insns-dep’
‘-fsched-stalled-insns-dep=N’
     Define how many insn groups (cycles) are examined for a dependency
     on a stalled insn that is a candidate for premature removal from
     the queue of stalled insns.  This has an effect only during the
     second scheduling pass, and only if ‘-fsched-stalled-insns’ is
     used.  ‘-fno-sched-stalled-insns-dep’ is equivalent to
     ‘-fsched-stalled-insns-dep=0’.  ‘-fsched-stalled-insns-dep’ without
     a value is equivalent to ‘-fsched-stalled-insns-dep=1’.

‘-fsched2-use-superblocks’
     When scheduling after register allocation, use superblock
     scheduling.  This allows motion across basic block boundaries,
     resulting in faster schedules.  This option is experimental, as not
     all machine descriptions used by GCC model the CPU closely enough
     to avoid unreliable results from the algorithm.

     This only makes sense when scheduling after register allocation,
     i.e. with ‘-fschedule-insns2’ or at ‘-O2’ or higher.

‘-fsched-group-heuristic’
     Enable the group heuristic in the scheduler.  This heuristic favors
     the instruction that belongs to a schedule group.  This is enabled
     by default when scheduling is enabled, i.e. with ‘-fschedule-insns’
     or ‘-fschedule-insns2’ or at ‘-O2’ or higher.

‘-fsched-critical-path-heuristic’
     Enable the critical-path heuristic in the scheduler.  This
     heuristic favors instructions on the critical path.  This is
     enabled by default when scheduling is enabled, i.e. with
     ‘-fschedule-insns’ or ‘-fschedule-insns2’ or at ‘-O2’ or higher.

‘-fsched-spec-insn-heuristic’
     Enable the speculative instruction heuristic in the scheduler.
     This heuristic favors speculative instructions with greater
     dependency weakness.  This is enabled by default when scheduling is
     enabled, i.e. with ‘-fschedule-insns’ or ‘-fschedule-insns2’ or at
     ‘-O2’ or higher.

‘-fsched-rank-heuristic’
     Enable the rank heuristic in the scheduler.  This heuristic favors
     the instruction belonging to a basic block with greater size or
     frequency.  This is enabled by default when scheduling is enabled,
     i.e. with ‘-fschedule-insns’ or ‘-fschedule-insns2’ or at ‘-O2’ or
     higher.

‘-fsched-last-insn-heuristic’
     Enable the last-instruction heuristic in the scheduler.  This
     heuristic favors the instruction that is less dependent on the last
     instruction scheduled.  This is enabled by default when scheduling
     is enabled, i.e. with ‘-fschedule-insns’ or ‘-fschedule-insns2’ or
     at ‘-O2’ or higher.

‘-fsched-dep-count-heuristic’
     Enable the dependent-count heuristic in the scheduler.  This
     heuristic favors the instruction that has more instructions
     depending on it.  This is enabled by default when scheduling is
     enabled, i.e. with ‘-fschedule-insns’ or ‘-fschedule-insns2’ or at
     ‘-O2’ or higher.

‘-freschedule-modulo-scheduled-loops’
     Modulo scheduling is performed before traditional scheduling.  If a
     loop is modulo scheduled, later scheduling passes may change its
     schedule.  Use this option to control that behavior.

‘-fselective-scheduling’
     Schedule instructions using selective scheduling algorithm.
     Selective scheduling runs instead of the first scheduler pass.

‘-fselective-scheduling2’
     Schedule instructions using selective scheduling algorithm.
     Selective scheduling runs instead of the second scheduler pass.

‘-fsel-sched-pipelining’
     Enable software pipelining of innermost loops during selective
     scheduling.  This option has no effect unless one of
     ‘-fselective-scheduling’ or ‘-fselective-scheduling2’ is turned on.

‘-fsel-sched-pipelining-outer-loops’
     When pipelining loops during selective scheduling, also pipeline
     outer loops.  This option has no effect unless
     ‘-fsel-sched-pipelining’ is turned on.

‘-fsemantic-interposition’
     Some object formats, like ELF, allow interposing of symbols by the
     dynamic linker.  This means that for symbols exported from the DSO,
     the compiler cannot perform interprocedural propagation, inlining
     and other optimizations in anticipation that the function or
     variable in question may change.  While this feature is useful, for
     example, to rewrite memory allocation functions by a debugging
     implementation, it is expensive in the terms of code quality.  With
     ‘-fno-semantic-interposition’ the compiler assumes that if
     interposition happens for functions the overwriting function will
     have precisely the same semantics (and side effects).  Similarly if
     interposition happens for variables, the constructor of the
     variable will be the same.  The flag has no effect for functions
     explicitly declared inline (where it is never allowed for
     interposition to change semantics) and for symbols explicitly
     declared weak.

‘-fshrink-wrap’
     Emit function prologues only before parts of the function that need
     it, rather than at the top of the function.  This flag is enabled
     by default at ‘-O’ and higher.

‘-fshrink-wrap-separate’
     Shrink-wrap separate parts of the prologue and epilogue separately,
     so that those parts are only executed when needed.  This option is
     on by default, but has no effect unless ‘-fshrink-wrap’ is also
     turned on and the target supports this.

‘-fcaller-saves’
     Enable allocation of values to registers that are clobbered by
     function calls, by emitting extra instructions to save and restore
     the registers around such calls.  Such allocation is done only when
     it seems to result in better code.

     This option is always enabled by default on certain machines,
     usually those which have no call-preserved registers to use
     instead.

     Enabled at levels ‘-O2’, ‘-O3’, ‘-Os’.

‘-fcombine-stack-adjustments’
     Tracks stack adjustments (pushes and pops) and stack memory
     references and then tries to find ways to combine them.

     Enabled by default at ‘-O1’ and higher.

‘-fipa-ra’
     Use caller save registers for allocation if those registers are not
     used by any called function.  In that case it is not necessary to
     save and restore them around calls.  This is only possible if
     called functions are part of same compilation unit as current
     function and they are compiled before it.

     Enabled at levels ‘-O2’, ‘-O3’, ‘-Os’, however the option is
     disabled if generated code will be instrumented for profiling
     (‘-p’, or ‘-pg’) or if callee's register usage cannot be known
     exactly (this happens on targets that do not expose prologues and
     epilogues in RTL).

‘-fconserve-stack’
     Attempt to minimize stack usage.  The compiler attempts to use less
     stack space, even if that makes the program slower.  This option
     implies setting the ‘large-stack-frame’ parameter to 100 and the
     ‘large-stack-frame-growth’ parameter to 400.

‘-ftree-reassoc’
     Perform reassociation on trees.  This flag is enabled by default at
     ‘-O1’ and higher.

‘-fcode-hoisting’
     Perform code hoisting.  Code hoisting tries to move the evaluation
     of expressions executed on all paths to the function exit as early
     as possible.  This is especially useful as a code size
     optimization, but it often helps for code speed as well.  This flag
     is enabled by default at ‘-O2’ and higher.

‘-ftree-pre’
     Perform partial redundancy elimination (PRE) on trees.  This flag
     is enabled by default at ‘-O2’ and ‘-O3’.

‘-ftree-partial-pre’
     Make partial redundancy elimination (PRE) more aggressive.  This
     flag is enabled by default at ‘-O3’.

‘-ftree-forwprop’
     Perform forward propagation on trees.  This flag is enabled by
     default at ‘-O1’ and higher.

‘-ftree-fre’
     Perform full redundancy elimination (FRE) on trees.  The difference
     between FRE and PRE is that FRE only considers expressions that are
     computed on all paths leading to the redundant computation.  This
     analysis is faster than PRE, though it exposes fewer redundancies.
     This flag is enabled by default at ‘-O1’ and higher.

‘-ftree-phiprop’
     Perform hoisting of loads from conditional pointers on trees.  This
     pass is enabled by default at ‘-O1’ and higher.

‘-fhoist-adjacent-loads’
     Speculatively hoist loads from both branches of an if-then-else if
     the loads are from adjacent locations in the same structure and the
     target architecture has a conditional move instruction.  This flag
     is enabled by default at ‘-O2’ and higher.

‘-ftree-copy-prop’
     Perform copy propagation on trees.  This pass eliminates
     unnecessary copy operations.  This flag is enabled by default at
     ‘-O1’ and higher.

‘-fipa-pure-const’
     Discover which functions are pure or constant.  Enabled by default
     at ‘-O1’ and higher.

‘-fipa-reference’
     Discover which static variables do not escape the compilation unit.
     Enabled by default at ‘-O1’ and higher.

‘-fipa-reference-addressable’
     Discover read-only, write-only and non-addressable static
     variables.  Enabled by default at ‘-O1’ and higher.

‘-fipa-stack-alignment’
     Reduce stack alignment on call sites if possible.  Enabled by
     default.

‘-fipa-pta’
     Perform interprocedural pointer analysis and interprocedural
     modification and reference analysis.  This option can cause
     excessive memory and compile-time usage on large compilation units.
     It is not enabled by default at any optimization level.

‘-fipa-profile’
     Perform interprocedural profile propagation.  The functions called
     only from cold functions are marked as cold.  Also functions
     executed once (such as ‘cold’, ‘noreturn’, static constructors or
     destructors) are identified.  Cold functions and loop less parts of
     functions executed once are then optimized for size.  Enabled by
     default at ‘-O1’ and higher.

‘-fipa-modref’
     Perform interprocedural mod/ref analysis.  This optimization
     analyzes the side effects of functions (memory locations that are
     modified or referenced) and enables better optimization across the
     function call boundary.  This flag is enabled by default at ‘-O1’
     and higher.

‘-fipa-cp’
     Perform interprocedural constant propagation.  This optimization
     analyzes the program to determine when values passed to functions
     are constants and then optimizes accordingly.  This optimization
     can substantially increase performance if the application has
     constants passed to functions.  This flag is enabled by default at
     ‘-O2’, ‘-Os’ and ‘-O3’.  It is also enabled by ‘-fprofile-use’ and
     ‘-fauto-profile’.

‘-fipa-cp-clone’
     Perform function cloning to make interprocedural constant
     propagation stronger.  When enabled, interprocedural constant
     propagation performs function cloning when externally visible
     function can be called with constant arguments.  Because this
     optimization can create multiple copies of functions, it may
     significantly increase code size (see ‘--param
     ipa-cp-unit-growth=VALUE’).  This flag is enabled by default at
     ‘-O3’.  It is also enabled by ‘-fprofile-use’ and ‘-fauto-profile’.

‘-fipa-bit-cp’
     When enabled, perform interprocedural bitwise constant propagation.
     This flag is enabled by default at ‘-O2’ and by ‘-fprofile-use’ and
     ‘-fauto-profile’.  It requires that ‘-fipa-cp’ is enabled.

‘-fipa-vrp’
     When enabled, perform interprocedural propagation of value ranges.
     This flag is enabled by default at ‘-O2’.  It requires that
     ‘-fipa-cp’ is enabled.

‘-fipa-icf’
     Perform Identical Code Folding for functions and read-only
     variables.  The optimization reduces code size and may disturb
     unwind stacks by replacing a function by equivalent one with a
     different name.  The optimization works more effectively with
     link-time optimization enabled.

     Although the behavior is similar to the Gold Linker's ICF
     optimization, GCC ICF works on different levels and thus the
     optimizations are not same - there are equivalences that are found
     only by GCC and equivalences found only by Gold.

     This flag is enabled by default at ‘-O2’ and ‘-Os’.

‘-flive-patching=LEVEL’
     Control GCC's optimizations to produce output suitable for
     live-patching.

     If the compiler's optimization uses a function's body or
     information extracted from its body to optimize/change another
     function, the latter is called an impacted function of the former.
     If a function is patched, its impacted functions should be patched
     too.

     The impacted functions are determined by the compiler's
     interprocedural optimizations.  For example, a caller is impacted
     when inlining a function into its caller, cloning a function and
     changing its caller to call this new clone, or extracting a
     function's pureness/constness information to optimize its direct or
     indirect callers, etc.

     Usually, the more IPA optimizations enabled, the larger the number
     of impacted functions for each function.  In order to control the
     number of impacted functions and more easily compute the list of
     impacted function, IPA optimizations can be partially enabled at
     two different levels.

     The LEVEL argument should be one of the following:

     ‘inline-clone’

          Only enable inlining and cloning optimizations, which includes
          inlining, cloning, interprocedural scalar replacement of
          aggregates and partial inlining.  As a result, when patching a
          function, all its callers and its clones' callers are
          impacted, therefore need to be patched as well.

          ‘-flive-patching=inline-clone’ disables the following
          optimization flags:
               -fwhole-program  -fipa-pta  -fipa-reference  -fipa-ra
               -fipa-icf  -fipa-icf-functions  -fipa-icf-variables
               -fipa-bit-cp  -fipa-vrp  -fipa-pure-const  -fipa-reference-addressable
               -fipa-stack-alignment -fipa-modref

     ‘inline-only-static’

          Only enable inlining of static functions.  As a result, when
          patching a static function, all its callers are impacted and
          so need to be patched as well.

          In addition to all the flags that
          ‘-flive-patching=inline-clone’ disables,
          ‘-flive-patching=inline-only-static’ disables the following
          additional optimization flags:
               -fipa-cp-clone  -fipa-sra  -fpartial-inlining  -fipa-cp

     When ‘-flive-patching’ is specified without any value, the default
     value is INLINE-CLONE.

     This flag is disabled by default.

     Note that ‘-flive-patching’ is not supported with link-time
     optimization (‘-flto’).

‘-fisolate-erroneous-paths-dereference’
     Detect paths that trigger erroneous or undefined behavior due to
     dereferencing a null pointer.  Isolate those paths from the main
     control flow and turn the statement with erroneous or undefined
     behavior into a trap.  This flag is enabled by default at ‘-O2’ and
     higher and depends on ‘-fdelete-null-pointer-checks’ also being
     enabled.

‘-fisolate-erroneous-paths-attribute’
     Detect paths that trigger erroneous or undefined behavior due to a
     null value being used in a way forbidden by a ‘returns_nonnull’ or
     ‘nonnull’ attribute.  Isolate those paths from the main control
     flow and turn the statement with erroneous or undefined behavior
     into a trap.  This is not currently enabled, but may be enabled by
     ‘-O2’ in the future.

‘-ftree-sink’
     Perform forward store motion on trees.  This flag is enabled by
     default at ‘-O1’ and higher.

‘-ftree-bit-ccp’
     Perform sparse conditional bit constant propagation on trees and
     propagate pointer alignment information.  This pass only operates
     on local scalar variables and is enabled by default at ‘-O1’ and
     higher, except for ‘-Og’.  It requires that ‘-ftree-ccp’ is
     enabled.

‘-ftree-ccp’
     Perform sparse conditional constant propagation (CCP) on trees.
     This pass only operates on local scalar variables and is enabled by
     default at ‘-O1’ and higher.

‘-fssa-backprop’
     Propagate information about uses of a value up the definition chain
     in order to simplify the definitions.  For example, this pass
     strips sign operations if the sign of a value never matters.  The
     flag is enabled by default at ‘-O1’ and higher.

‘-fssa-phiopt’
     Perform pattern matching on SSA PHI nodes to optimize conditional
     code.  This pass is enabled by default at ‘-O1’ and higher, except
     for ‘-Og’.

‘-ftree-switch-conversion’
     Perform conversion of simple initializations in a switch to
     initializations from a scalar array.  This flag is enabled by
     default at ‘-O2’ and higher.

‘-ftree-tail-merge’
     Look for identical code sequences.  When found, replace one with a
     jump to the other.  This optimization is known as tail merging or
     cross jumping.  This flag is enabled by default at ‘-O2’ and
     higher.  The compilation time in this pass can be limited using
     ‘max-tail-merge-comparisons’ parameter and
     ‘max-tail-merge-iterations’ parameter.

‘-ftree-dce’
     Perform dead code elimination (DCE) on trees.  This flag is enabled
     by default at ‘-O1’ and higher.

‘-ftree-builtin-call-dce’
     Perform conditional dead code elimination (DCE) for calls to
     built-in functions that may set ‘errno’ but are otherwise free of
     side effects.  This flag is enabled by default at ‘-O2’ and higher
     if ‘-Os’ is not also specified.

‘-ffinite-loops’
     Assume that a loop with an exit will eventually take the exit and
     not loop indefinitely.  This allows the compiler to remove loops
     that otherwise have no side-effects, not considering eventual
     endless looping as such.

     This option is enabled by default at ‘-O2’ for C++ with -std=c++11
     or higher.

‘-ftree-dominator-opts’
     Perform a variety of simple scalar cleanups (constant/copy
     propagation, redundancy elimination, range propagation and
     expression simplification) based on a dominator tree traversal.
     This also performs jump threading (to reduce jumps to jumps).  This
     flag is enabled by default at ‘-O1’ and higher.

‘-ftree-dse’
     Perform dead store elimination (DSE) on trees.  A dead store is a
     store into a memory location that is later overwritten by another
     store without any intervening loads.  In this case the earlier
     store can be deleted.  This flag is enabled by default at ‘-O1’ and
     higher.

‘-ftree-ch’
     Perform loop header copying on trees.  This is beneficial since it
     increases effectiveness of code motion optimizations.  It also
     saves one jump.  This flag is enabled by default at ‘-O1’ and
     higher.  It is not enabled for ‘-Os’, since it usually increases
     code size.

‘-ftree-loop-optimize’
     Perform loop optimizations on trees.  This flag is enabled by
     default at ‘-O1’ and higher.

‘-ftree-loop-linear’
‘-floop-strip-mine’
‘-floop-block’
     Perform loop nest optimizations.  Same as ‘-floop-nest-optimize’.
     To use this code transformation, GCC has to be configured with
     ‘--with-isl’ to enable the Graphite loop transformation
     infrastructure.

‘-fgraphite-identity’
     Enable the identity transformation for graphite.  For every SCoP we
     generate the polyhedral representation and transform it back to
     gimple.  Using ‘-fgraphite-identity’ we can check the costs or
     benefits of the GIMPLE -> GRAPHITE -> GIMPLE transformation.  Some
     minimal optimizations are also performed by the code generator isl,
     like index splitting and dead code elimination in loops.

‘-floop-nest-optimize’
     Enable the isl based loop nest optimizer.  This is a generic loop
     nest optimizer based on the Pluto optimization algorithms.  It
     calculates a loop structure optimized for data-locality and
     parallelism.  This option is experimental.

‘-floop-parallelize-all’
     Use the Graphite data dependence analysis to identify loops that
     can be parallelized.  Parallelize all the loops that can be
     analyzed to not contain loop carried dependences without checking
     that it is profitable to parallelize the loops.

‘-ftree-coalesce-vars’
     While transforming the program out of the SSA representation,
     attempt to reduce copying by coalescing versions of different
     user-defined variables, instead of just compiler temporaries.  This
     may severely limit the ability to debug an optimized program
     compiled with ‘-fno-var-tracking-assignments’.  In the negated
     form, this flag prevents SSA coalescing of user variables.  This
     option is enabled by default if optimization is enabled, and it
     does very little otherwise.

‘-ftree-loop-if-convert’
     Attempt to transform conditional jumps in the innermost loops to
     branch-less equivalents.  The intent is to remove control-flow from
     the innermost loops in order to improve the ability of the
     vectorization pass to handle these loops.  This is enabled by
     default if vectorization is enabled.

‘-ftree-loop-distribution’
     Perform loop distribution.  This flag can improve cache performance
     on big loop bodies and allow further loop optimizations, like
     parallelization or vectorization, to take place.  For example, the
     loop
          DO I = 1, N
            A(I) = B(I) + C
            D(I) = E(I) * F
          ENDDO
     is transformed to
          DO I = 1, N
             A(I) = B(I) + C
          ENDDO
          DO I = 1, N
             D(I) = E(I) * F
          ENDDO
     This flag is enabled by default at ‘-O3’.  It is also enabled by
     ‘-fprofile-use’ and ‘-fauto-profile’.

‘-ftree-loop-distribute-patterns’
     Perform loop distribution of patterns that can be code generated
     with calls to a library.  This flag is enabled by default at ‘-O2’
     and higher, and by ‘-fprofile-use’ and ‘-fauto-profile’.

     This pass distributes the initialization loops and generates a call
     to memset zero.  For example, the loop
          DO I = 1, N
            A(I) = 0
            B(I) = A(I) + I
          ENDDO
     is transformed to
          DO I = 1, N
             A(I) = 0
          ENDDO
          DO I = 1, N
             B(I) = A(I) + I
          ENDDO
     and the initialization loop is transformed into a call to memset
     zero.  This flag is enabled by default at ‘-O3’.  It is also
     enabled by ‘-fprofile-use’ and ‘-fauto-profile’.

‘-floop-interchange’
     Perform loop interchange outside of graphite.  This flag can
     improve cache performance on loop nest and allow further loop
     optimizations, like vectorization, to take place.  For example, the
     loop
          for (int i = 0; i < N; i++)
            for (int j = 0; j < N; j++)
              for (int k = 0; k < N; k++)
                c[i][j] = c[i][j] + a[i][k]*b[k][j];
     is transformed to
          for (int i = 0; i < N; i++)
            for (int k = 0; k < N; k++)
              for (int j = 0; j < N; j++)
                c[i][j] = c[i][j] + a[i][k]*b[k][j];
     This flag is enabled by default at ‘-O3’.  It is also enabled by
     ‘-fprofile-use’ and ‘-fauto-profile’.

‘-floop-unroll-and-jam’
     Apply unroll and jam transformations on feasible loops.  In a loop
     nest this unrolls the outer loop by some factor and fuses the
     resulting multiple inner loops.  This flag is enabled by default at
     ‘-O3’.  It is also enabled by ‘-fprofile-use’ and ‘-fauto-profile’.

‘-ftree-loop-im’
     Perform loop invariant motion on trees.  This pass moves only
     invariants that are hard to handle at RTL level (function calls,
     operations that expand to nontrivial sequences of insns).  With
     ‘-funswitch-loops’ it also moves operands of conditions that are
     invariant out of the loop, so that we can use just trivial
     invariantness analysis in loop unswitching.  The pass also includes
     store motion.

‘-ftree-loop-ivcanon’
     Create a canonical counter for number of iterations in loops for
     which determining number of iterations requires complicated
     analysis.  Later optimizations then may determine the number
     easily.  Useful especially in connection with unrolling.

‘-ftree-scev-cprop’
     Perform final value replacement.  If a variable is modified in a
     loop in such a way that its value when exiting the loop can be
     determined using only its initial value and the number of loop
     iterations, replace uses of the final value by such a computation,
     provided it is sufficiently cheap.  This reduces data dependencies
     and may allow further simplifications.  Enabled by default at ‘-O1’
     and higher.

‘-fivopts’
     Perform induction variable optimizations (strength reduction,
     induction variable merging and induction variable elimination) on
     trees.

‘-ftree-parallelize-loops=n’
     Parallelize loops, i.e., split their iteration space to run in n
     threads.  This is only possible for loops whose iterations are
     independent and can be arbitrarily reordered.  The optimization is
     only profitable on multiprocessor machines, for loops that are
     CPU-intensive, rather than constrained e.g. by memory bandwidth.
     This option implies ‘-pthread’, and thus is only supported on
     targets that have support for ‘-pthread’.

‘-ftree-pta’
     Perform function-local points-to analysis on trees.  This flag is
     enabled by default at ‘-O1’ and higher, except for ‘-Og’.

‘-ftree-sra’
     Perform scalar replacement of aggregates.  This pass replaces
     structure references with scalars to prevent committing structures
     to memory too early.  This flag is enabled by default at ‘-O1’ and
     higher, except for ‘-Og’.

‘-fstore-merging’
     Perform merging of narrow stores to consecutive memory addresses.
     This pass merges contiguous stores of immediate values narrower
     than a word into fewer wider stores to reduce the number of
     instructions.  This is enabled by default at ‘-O2’ and higher as
     well as ‘-Os’.

‘-ftree-ter’
     Perform temporary expression replacement during the SSA->normal
     phase.  Single use/single def temporaries are replaced at their use
     location with their defining expression.  This results in
     non-GIMPLE code, but gives the expanders much more complex trees to
     work on resulting in better RTL generation.  This is enabled by
     default at ‘-O1’ and higher.

‘-ftree-slsr’
     Perform straight-line strength reduction on trees.  This recognizes
     related expressions involving multiplications and replaces them by
     less expensive calculations when possible.  This is enabled by
     default at ‘-O1’ and higher.

‘-ftree-vectorize’
     Perform vectorization on trees.  This flag enables
     ‘-ftree-loop-vectorize’ and ‘-ftree-slp-vectorize’ if not
     explicitly specified.

‘-ftree-loop-vectorize’
     Perform loop vectorization on trees.  This flag is enabled by
     default at ‘-O2’ and by ‘-ftree-vectorize’, ‘-fprofile-use’, and
     ‘-fauto-profile’.

‘-ftree-slp-vectorize’
     Perform basic block vectorization on trees.  This flag is enabled
     by default at ‘-O2’ and by ‘-ftree-vectorize’, ‘-fprofile-use’, and
     ‘-fauto-profile’.

‘-ftrivial-auto-var-init=CHOICE’
     Initialize automatic variables with either a pattern or with zeroes
     to increase the security and predictability of a program by
     preventing uninitialized memory disclosure and use.  GCC still
     considers an automatic variable that doesn't have an explicit
     initializer as uninitialized, ‘-Wuninitialized’ and
     ‘-Wanalyzer-use-of-uninitialized-value’ will still report warning
     messages on such automatic variables.  With this option, GCC will
     also initialize any padding of automatic variables that have
     structure or union types to zeroes.  However, the current
     implementation cannot initialize automatic variables that are
     declared between the controlling expression and the first case of a
     ‘switch’ statement.  Using ‘-Wtrivial-auto-var-init’ to report all
     such cases.

     The three values of CHOICE are:

        • ‘uninitialized’ doesn't initialize any automatic variables.
          This is C and C++'s default.

        • ‘pattern’ Initialize automatic variables with values which
          will likely transform logic bugs into crashes down the line,
          are easily recognized in a crash dump and without being values
          that programmers can rely on for useful program semantics.
          The current value is byte-repeatable pattern with byte "0xFE".
          The values used for pattern initialization might be changed in
          the future.

        • ‘zero’ Initialize automatic variables with zeroes.

     The default is ‘uninitialized’.

     You can control this behavior for a specific variable by using the
     variable attribute ‘uninitialized’ (*note Variable Attributes::).

‘-fvect-cost-model=MODEL’
     Alter the cost model used for vectorization.  The MODEL argument
     should be one of ‘unlimited’, ‘dynamic’, ‘cheap’ or ‘very-cheap’.
     With the ‘unlimited’ model the vectorized code-path is assumed to
     be profitable while with the ‘dynamic’ model a runtime check guards
     the vectorized code-path to enable it only for iteration counts
     that will likely execute faster than when executing the original
     scalar loop.  The ‘cheap’ model disables vectorization of loops
     where doing so would be cost prohibitive for example due to
     required runtime checks for data dependence or alignment but
     otherwise is equal to the ‘dynamic’ model.  The ‘very-cheap’ model
     only allows vectorization if the vector code would entirely replace
     the scalar code that is being vectorized.  For example, if each
     iteration of a vectorized loop would only be able to handle exactly
     four iterations of the scalar loop, the ‘very-cheap’ model would
     only allow vectorization if the scalar iteration count is known to
     be a multiple of four.

     The default cost model depends on other optimization flags and is
     either ‘dynamic’ or ‘cheap’.

‘-fsimd-cost-model=MODEL’
     Alter the cost model used for vectorization of loops marked with
     the OpenMP simd directive.  The MODEL argument should be one of
     ‘unlimited’, ‘dynamic’, ‘cheap’.  All values of MODEL have the same
     meaning as described in ‘-fvect-cost-model’ and by default a cost
     model defined with ‘-fvect-cost-model’ is used.

‘-ftree-vrp’
     Perform Value Range Propagation on trees.  This is similar to the
     constant propagation pass, but instead of values, ranges of values
     are propagated.  This allows the optimizers to remove unnecessary
     range checks like array bound checks and null pointer checks.  This
     is enabled by default at ‘-O2’ and higher.  Null pointer check
     elimination is only done if ‘-fdelete-null-pointer-checks’ is
     enabled.

‘-fsplit-paths’
     Split paths leading to loop backedges.  This can improve dead code
     elimination and common subexpression elimination.  This is enabled
     by default at ‘-O3’ and above.

‘-fsplit-ivs-in-unroller’
     Enables expression of values of induction variables in later
     iterations of the unrolled loop using the value in the first
     iteration.  This breaks long dependency chains, thus improving
     efficiency of the scheduling passes.

     A combination of ‘-fweb’ and CSE is often sufficient to obtain the
     same effect.  However, that is not reliable in cases where the loop
     body is more complicated than a single basic block.  It also does
     not work at all on some architectures due to restrictions in the
     CSE pass.

     This optimization is enabled by default.

‘-fvariable-expansion-in-unroller’
     With this option, the compiler creates multiple copies of some
     local variables when unrolling a loop, which can result in superior
     code.

     This optimization is enabled by default for PowerPC targets, but
     disabled by default otherwise.

‘-fpartial-inlining’
     Inline parts of functions.  This option has any effect only when
     inlining itself is turned on by the ‘-finline-functions’ or
     ‘-finline-small-functions’ options.

     Enabled at levels ‘-O2’, ‘-O3’, ‘-Os’.

‘-fpredictive-commoning’
     Perform predictive commoning optimization, i.e., reusing
     computations (especially memory loads and stores) performed in
     previous iterations of loops.

     This option is enabled at level ‘-O3’.  It is also enabled by
     ‘-fprofile-use’ and ‘-fauto-profile’.

‘-fprefetch-loop-arrays’
     If supported by the target machine, generate instructions to
     prefetch memory to improve the performance of loops that access
     large arrays.

     This option may generate better or worse code; results are highly
     dependent on the structure of loops within the source code.

     Disabled at level ‘-Os’.

‘-fno-printf-return-value’
     Do not substitute constants for known return value of formatted
     output functions such as ‘sprintf’, ‘snprintf’, ‘vsprintf’, and
     ‘vsnprintf’ (but not ‘printf’ of ‘fprintf’).  This transformation
     allows GCC to optimize or even eliminate branches based on the
     known return value of these functions called with arguments that
     are either constant, or whose values are known to be in a range
     that makes determining the exact return value possible.  For
     example, when ‘-fprintf-return-value’ is in effect, both the branch
     and the body of the ‘if’ statement (but not the call to ‘snprint’)
     can be optimized away when ‘i’ is a 32-bit or smaller integer
     because the return value is guaranteed to be at most 8.

          char buf[9];
          if (snprintf (buf, "%08x", i) >= sizeof buf)
            ...

     The ‘-fprintf-return-value’ option relies on other optimizations
     and yields best results with ‘-O2’ and above.  It works in tandem
     with the ‘-Wformat-overflow’ and ‘-Wformat-truncation’ options.
     The ‘-fprintf-return-value’ option is enabled by default.

‘-fno-peephole’
‘-fno-peephole2’
     Disable any machine-specific peephole optimizations.  The
     difference between ‘-fno-peephole’ and ‘-fno-peephole2’ is in how
     they are implemented in the compiler; some targets use one, some
     use the other, a few use both.

     ‘-fpeephole’ is enabled by default.  ‘-fpeephole2’ enabled at
     levels ‘-O2’, ‘-O3’, ‘-Os’.

‘-fno-guess-branch-probability’
     Do not guess branch probabilities using heuristics.

     GCC uses heuristics to guess branch probabilities if they are not
     provided by profiling feedback (‘-fprofile-arcs’).  These
     heuristics are based on the control flow graph.  If some branch
     probabilities are specified by ‘__builtin_expect’, then the
     heuristics are used to guess branch probabilities for the rest of
     the control flow graph, taking the ‘__builtin_expect’ info into
     account.  The interactions between the heuristics and
     ‘__builtin_expect’ can be complex, and in some cases, it may be
     useful to disable the heuristics so that the effects of
     ‘__builtin_expect’ are easier to understand.

     It is also possible to specify expected probability of the
     expression with ‘__builtin_expect_with_probability’ built-in
     function.

     The default is ‘-fguess-branch-probability’ at levels ‘-O’, ‘-O2’,
     ‘-O3’, ‘-Os’.

‘-freorder-blocks’
     Reorder basic blocks in the compiled function in order to reduce
     number of taken branches and improve code locality.

     Enabled at levels ‘-O1’, ‘-O2’, ‘-O3’, ‘-Os’.

‘-freorder-blocks-algorithm=ALGORITHM’
     Use the specified algorithm for basic block reordering.  The
     ALGORITHM argument can be ‘simple’, which does not increase code
     size (except sometimes due to secondary effects like alignment), or
     ‘stc’, the "software trace cache" algorithm, which tries to put all
     often executed code together, minimizing the number of branches
     executed by making extra copies of code.

     The default is ‘simple’ at levels ‘-O1’, ‘-Os’, and ‘stc’ at levels
     ‘-O2’, ‘-O3’.

‘-freorder-blocks-and-partition’
     In addition to reordering basic blocks in the compiled function, in
     order to reduce number of taken branches, partitions hot and cold
     basic blocks into separate sections of the assembly and ‘.o’ files,
     to improve paging and cache locality performance.

     This optimization is automatically turned off in the presence of
     exception handling or unwind tables (on targets using
     setjump/longjump or target specific scheme), for linkonce sections,
     for functions with a user-defined section attribute and on any
     architecture that does not support named sections.  When
     ‘-fsplit-stack’ is used this option is not enabled by default (to
     avoid linker errors), but may be enabled explicitly (if using a
     working linker).

     Enabled for x86 at levels ‘-O2’, ‘-O3’, ‘-Os’.

‘-freorder-functions’
     Reorder functions in the object file in order to improve code
     locality.  This is implemented by using special subsections
     ‘.text.hot’ for most frequently executed functions and
     ‘.text.unlikely’ for unlikely executed functions.  Reordering is
     done by the linker so object file format must support named
     sections and linker must place them in a reasonable way.

     This option isn't effective unless you either provide profile
     feedback (see ‘-fprofile-arcs’ for details) or manually annotate
     functions with ‘hot’ or ‘cold’ attributes (*note Common Function
     Attributes::).

     Enabled at levels ‘-O2’, ‘-O3’, ‘-Os’.

‘-fstrict-aliasing’
     Allow the compiler to assume the strictest aliasing rules
     applicable to the language being compiled.  For C (and C++), this
     activates optimizations based on the type of expressions.  In
     particular, an object of one type is assumed never to reside at the
     same address as an object of a different type, unless the types are
     almost the same.  For example, an ‘unsigned int’ can alias an
     ‘int’, but not a ‘void*’ or a ‘double’.  A character type may alias
     any other type.

     Pay special attention to code like this:
          union a_union {
            int i;
            double d;
          };

          int f() {
            union a_union t;
            t.d = 3.0;
            return t.i;
          }
     The practice of reading from a different union member than the one
     most recently written to (called "type-punning") is common.  Even
     with ‘-fstrict-aliasing’, type-punning is allowed, provided the
     memory is accessed through the union type.  So, the code above
     works as expected.  *Note Structures unions enumerations and
     bit-fields implementation::.  However, this code might not:
          int f() {
            union a_union t;
            int* ip;
            t.d = 3.0;
            ip = &t.i;
            return *ip;
          }

     Similarly, access by taking the address, casting the resulting
     pointer and dereferencing the result has undefined behavior, even
     if the cast uses a union type, e.g.:
          int f() {
            double d = 3.0;
            return ((union a_union *) &d)->i;
          }

     The ‘-fstrict-aliasing’ option is enabled at levels ‘-O2’, ‘-O3’,
     ‘-Os’.

‘-fipa-strict-aliasing’
     Controls whether rules of ‘-fstrict-aliasing’ are applied across
     function boundaries.  Note that if multiple functions gets inlined
     into a single function the memory accesses are no longer considered
     to be crossing a function boundary.

     The ‘-fipa-strict-aliasing’ option is enabled by default and is
     effective only in combination with ‘-fstrict-aliasing’.

‘-falign-functions’
‘-falign-functions=N’
‘-falign-functions=N:M’
‘-falign-functions=N:M:N2’
‘-falign-functions=N:M:N2:M2’
     Align the start of functions to the next power-of-two greater than
     or equal to N, skipping up to M-1 bytes.  This ensures that at
     least the first M bytes of the function can be fetched by the CPU
     without crossing an N-byte alignment boundary.

     If M is not specified, it defaults to N.

     Examples: ‘-falign-functions=32’ aligns functions to the next
     32-byte boundary, ‘-falign-functions=24’ aligns to the next 32-byte
     boundary only if this can be done by skipping 23 bytes or less,
     ‘-falign-functions=32:7’ aligns to the next 32-byte boundary only
     if this can be done by skipping 6 bytes or less.

     The second pair of N2:M2 values allows you to specify a secondary
     alignment: ‘-falign-functions=64:7:32:3’ aligns to the next 64-byte
     boundary if this can be done by skipping 6 bytes or less, otherwise
     aligns to the next 32-byte boundary if this can be done by skipping
     2 bytes or less.  If M2 is not specified, it defaults to N2.

     Some assemblers only support this flag when N is a power of two; in
     that case, it is rounded up.

     ‘-fno-align-functions’ and ‘-falign-functions=1’ are equivalent and
     mean that functions are not aligned.

     If N is not specified or is zero, use a machine-dependent default.
     The maximum allowed N option value is 65536.

     Enabled at levels ‘-O2’, ‘-O3’.

‘-flimit-function-alignment’
     If this option is enabled, the compiler tries to avoid
     unnecessarily overaligning functions.  It attempts to instruct the
     assembler to align by the amount specified by ‘-falign-functions’,
     but not to skip more bytes than the size of the function.

‘-falign-labels’
‘-falign-labels=N’
‘-falign-labels=N:M’
‘-falign-labels=N:M:N2’
‘-falign-labels=N:M:N2:M2’
     Align all branch targets to a power-of-two boundary.

     Parameters of this option are analogous to the ‘-falign-functions’
     option.  ‘-fno-align-labels’ and ‘-falign-labels=1’ are equivalent
     and mean that labels are not aligned.

     If ‘-falign-loops’ or ‘-falign-jumps’ are applicable and are
     greater than this value, then their values are used instead.

     If N is not specified or is zero, use a machine-dependent default
     which is very likely to be ‘1’, meaning no alignment.  The maximum
     allowed N option value is 65536.

     Enabled at levels ‘-O2’, ‘-O3’.

‘-falign-loops’
‘-falign-loops=N’
‘-falign-loops=N:M’
‘-falign-loops=N:M:N2’
‘-falign-loops=N:M:N2:M2’
     Align loops to a power-of-two boundary.  If the loops are executed
     many times, this makes up for any execution of the dummy padding
     instructions.

     If ‘-falign-labels’ is greater than this value, then its value is
     used instead.

     Parameters of this option are analogous to the ‘-falign-functions’
     option.  ‘-fno-align-loops’ and ‘-falign-loops=1’ are equivalent
     and mean that loops are not aligned.  The maximum allowed N option
     value is 65536.

     If N is not specified or is zero, use a machine-dependent default.

     Enabled at levels ‘-O2’, ‘-O3’.

‘-falign-jumps’
‘-falign-jumps=N’
‘-falign-jumps=N:M’
‘-falign-jumps=N:M:N2’
‘-falign-jumps=N:M:N2:M2’
     Align branch targets to a power-of-two boundary, for branch targets
     where the targets can only be reached by jumping.  In this case, no
     dummy operations need be executed.

     If ‘-falign-labels’ is greater than this value, then its value is
     used instead.

     Parameters of this option are analogous to the ‘-falign-functions’
     option.  ‘-fno-align-jumps’ and ‘-falign-jumps=1’ are equivalent
     and mean that loops are not aligned.

     If N is not specified or is zero, use a machine-dependent default.
     The maximum allowed N option value is 65536.

     Enabled at levels ‘-O2’, ‘-O3’.

‘-fno-allocation-dce’
     Do not remove unused C++ allocations in dead code elimination.

‘-fallow-store-data-races’
     Allow the compiler to perform optimizations that may introduce new
     data races on stores, without proving that the variable cannot be
     concurrently accessed by other threads.  Does not affect
     optimization of local data.  It is safe to use this option if it is
     known that global data will not be accessed by multiple threads.

     Examples of optimizations enabled by ‘-fallow-store-data-races’
     include hoisting or if-conversions that may cause a value that was
     already in memory to be re-written with that same value.  Such
     re-writing is safe in a single threaded context but may be unsafe
     in a multi-threaded context.  Note that on some processors,
     if-conversions may be required in order to enable vectorization.

     Enabled at level ‘-Ofast’.

‘-funit-at-a-time’
     This option is left for compatibility reasons.  ‘-funit-at-a-time’
     has no effect, while ‘-fno-unit-at-a-time’ implies
     ‘-fno-toplevel-reorder’ and ‘-fno-section-anchors’.

     Enabled by default.

‘-fno-toplevel-reorder’
     Do not reorder top-level functions, variables, and ‘asm’
     statements.  Output them in the same order that they appear in the
     input file.  When this option is used, unreferenced static
     variables are not removed.  This option is intended to support
     existing code that relies on a particular ordering.  For new code,
     it is better to use attributes when possible.

     ‘-ftoplevel-reorder’ is the default at ‘-O1’ and higher, and also
     at ‘-O0’ if ‘-fsection-anchors’ is explicitly requested.
     Additionally ‘-fno-toplevel-reorder’ implies
     ‘-fno-section-anchors’.

‘-fweb’
     Constructs webs as commonly used for register allocation purposes
     and assign each web individual pseudo register.  This allows the
     register allocation pass to operate on pseudos directly, but also
     strengthens several other optimization passes, such as CSE, loop
     optimizer and trivial dead code remover.  It can, however, make
     debugging impossible, since variables no longer stay in a "home
     register".

     Enabled by default with ‘-funroll-loops’.

‘-fwhole-program’
     Assume that the current compilation unit represents the whole
     program being compiled.  All public functions and variables with
     the exception of ‘main’ and those merged by attribute
     ‘externally_visible’ become static functions and in effect are
     optimized more aggressively by interprocedural optimizers.

     This option should not be used in combination with ‘-flto’.
     Instead relying on a linker plugin should provide safer and more
     precise information.

‘-flto[=N]’
     This option runs the standard link-time optimizer.  When invoked
     with source code, it generates GIMPLE (one of GCC's internal
     representations) and writes it to special ELF sections in the
     object file.  When the object files are linked together, all the
     function bodies are read from these ELF sections and instantiated
     as if they had been part of the same translation unit.

     To use the link-time optimizer, ‘-flto’ and optimization options
     should be specified at compile time and during the final link.  It
     is recommended that you compile all the files participating in the
     same link with the same options and also specify those options at
     link time.  For example:

          gcc -c -O2 -flto foo.c
          gcc -c -O2 -flto bar.c
          gcc -o myprog -flto -O2 foo.o bar.o

     The first two invocations to GCC save a bytecode representation of
     GIMPLE into special ELF sections inside ‘foo.o’ and ‘bar.o’.  The
     final invocation reads the GIMPLE bytecode from ‘foo.o’ and
     ‘bar.o’, merges the two files into a single internal image, and
     compiles the result as usual.  Since both ‘foo.o’ and ‘bar.o’ are
     merged into a single image, this causes all the interprocedural
     analyses and optimizations in GCC to work across the two files as
     if they were a single one.  This means, for example, that the
     inliner is able to inline functions in ‘bar.o’ into functions in
     ‘foo.o’ and vice-versa.

     Another (simpler) way to enable link-time optimization is:

          gcc -o myprog -flto -O2 foo.c bar.c

     The above generates bytecode for ‘foo.c’ and ‘bar.c’, merges them
     together into a single GIMPLE representation and optimizes them as
     usual to produce ‘myprog’.

     The important thing to keep in mind is that to enable link-time
     optimizations you need to use the GCC driver to perform the link
     step.  GCC automatically performs link-time optimization if any of
     the objects involved were compiled with the ‘-flto’ command-line
     option.  You can always override the automatic decision to do
     link-time optimization by passing ‘-fno-lto’ to the link command.

     To make whole program optimization effective, it is necessary to
     make certain whole program assumptions.  The compiler needs to know
     what functions and variables can be accessed by libraries and
     runtime outside of the link-time optimized unit.  When supported by
     the linker, the linker plugin (see ‘-fuse-linker-plugin’) passes
     information to the compiler about used and externally visible
     symbols.  When the linker plugin is not available,
     ‘-fwhole-program’ should be used to allow the compiler to make
     these assumptions, which leads to more aggressive optimization
     decisions.

     When a file is compiled with ‘-flto’ without ‘-fuse-linker-plugin’,
     the generated object file is larger than a regular object file
     because it contains GIMPLE bytecodes and the usual final code (see
     ‘-ffat-lto-objects’).  This means that object files with LTO
     information can be linked as normal object files; if ‘-fno-lto’ is
     passed to the linker, no interprocedural optimizations are applied.
     Note that when ‘-fno-fat-lto-objects’ is enabled the compile stage
     is faster but you cannot perform a regular, non-LTO link on them.

     When producing the final binary, GCC only applies link-time
     optimizations to those files that contain bytecode.  Therefore, you
     can mix and match object files and libraries with GIMPLE bytecodes
     and final object code.  GCC automatically selects which files to
     optimize in LTO mode and which files to link without further
     processing.

     Generally, options specified at link time override those specified
     at compile time, although in some cases GCC attempts to infer
     link-time options from the settings used to compile the input
     files.

     If you do not specify an optimization level option ‘-O’ at link
     time, then GCC uses the highest optimization level used when
     compiling the object files.  Note that it is generally ineffective
     to specify an optimization level option only at link time and not
     at compile time, for two reasons.  First, compiling without
     optimization suppresses compiler passes that gather information
     needed for effective optimization at link time.  Second, some early
     optimization passes can be performed only at compile time and not
     at link time.

     There are some code generation flags preserved by GCC when
     generating bytecodes, as they need to be used during the final
     link.  Currently, the following options and their settings are
     taken from the first object file that explicitly specifies them:
     ‘-fcommon’, ‘-fexceptions’, ‘-fnon-call-exceptions’, ‘-fgnu-tm’ and
     all the ‘-m’ target flags.

     The following options ‘-fPIC’, ‘-fpic’, ‘-fpie’ and ‘-fPIE’ are
     combined based on the following scheme:

          -fPIC + -fpic = -fpic
          -fPIC + -fno-pic = -fno-pic
          -fpic/-fPIC + (no option) = (no option)
          -fPIC + -fPIE = -fPIE
          -fpic + -fPIE = -fpie
          -fPIC/-fpic + -fpie = -fpie

     Certain ABI-changing flags are required to match in all compilation
     units, and trying to override this at link time with a conflicting
     value is ignored.  This includes options such as
     ‘-freg-struct-return’ and ‘-fpcc-struct-return’.

     Other options such as ‘-ffp-contract’, ‘-fno-strict-overflow’,
     ‘-fwrapv’, ‘-fno-trapv’ or ‘-fno-strict-aliasing’ are passed
     through to the link stage and merged conservatively for conflicting
     translation units.  Specifically ‘-fno-strict-overflow’, ‘-fwrapv’
     and ‘-fno-trapv’ take precedence; and for example
     ‘-ffp-contract=off’ takes precedence over ‘-ffp-contract=fast’.
     You can override them at link time.

     Diagnostic options such as ‘-Wstringop-overflow’ are passed through
     to the link stage and their setting matches that of the
     compile-step at function granularity.  Note that this matters only
     for diagnostics emitted during optimization.  Note that code
     transforms such as inlining can lead to warnings being enabled or
     disabled for regions if code not consistent with the setting at
     compile time.

     When you need to pass options to the assembler via ‘-Wa’ or
     ‘-Xassembler’ make sure to either compile such translation units
     with ‘-fno-lto’ or consistently use the same assembler options on
     all translation units.  You can alternatively also specify
     assembler options at LTO link time.

     To enable debug info generation you need to supply ‘-g’ at compile
     time.  If any of the input files at link time were built with debug
     info generation enabled the link will enable debug info generation
     as well.  Any elaborate debug info settings like the dwarf level
     ‘-gdwarf-5’ need to be explicitly repeated at the linker command
     line and mixing different settings in different translation units
     is discouraged.

     If LTO encounters objects with C linkage declared with incompatible
     types in separate translation units to be linked together
     (undefined behavior according to ISO C99 6.2.7), a non-fatal
     diagnostic may be issued.  The behavior is still undefined at run
     time.  Similar diagnostics may be raised for other languages.

     Another feature of LTO is that it is possible to apply
     interprocedural optimizations on files written in different
     languages:

          gcc -c -flto foo.c
          g++ -c -flto bar.cc
          gfortran -c -flto baz.f90
          g++ -o myprog -flto -O3 foo.o bar.o baz.o -lgfortran

     Notice that the final link is done with ‘g++’ to get the C++
     runtime libraries and ‘-lgfortran’ is added to get the Fortran
     runtime libraries.  In general, when mixing languages in LTO mode,
     you should use the same link command options as when mixing
     languages in a regular (non-LTO) compilation.

     If object files containing GIMPLE bytecode are stored in a library
     archive, say ‘libfoo.a’, it is possible to extract and use them in
     an LTO link if you are using a linker with plugin support.  To
     create static libraries suitable for LTO, use ‘gcc-ar’ and
     ‘gcc-ranlib’ instead of ‘ar’ and ‘ranlib’; to show the symbols of
     object files with GIMPLE bytecode, use ‘gcc-nm’.  Those commands
     require that ‘ar’, ‘ranlib’ and ‘nm’ have been compiled with plugin
     support.  At link time, use the flag ‘-fuse-linker-plugin’ to
     ensure that the library participates in the LTO optimization
     process:

          gcc -o myprog -O2 -flto -fuse-linker-plugin a.o b.o -lfoo

     With the linker plugin enabled, the linker extracts the needed
     GIMPLE files from ‘libfoo.a’ and passes them on to the running GCC
     to make them part of the aggregated GIMPLE image to be optimized.

     If you are not using a linker with plugin support and/or do not
     enable the linker plugin, then the objects inside ‘libfoo.a’ are
     extracted and linked as usual, but they do not participate in the
     LTO optimization process.  In order to make a static library
     suitable for both LTO optimization and usual linkage, compile its
     object files with ‘-flto’ ‘-ffat-lto-objects’.

     Link-time optimizations do not require the presence of the whole
     program to operate.  If the program does not require any symbols to
     be exported, it is possible to combine ‘-flto’ and
     ‘-fwhole-program’ to allow the interprocedural optimizers to use
     more aggressive assumptions which may lead to improved optimization
     opportunities.  Use of ‘-fwhole-program’ is not needed when linker
     plugin is active (see ‘-fuse-linker-plugin’).

     The current implementation of LTO makes no attempt to generate
     bytecode that is portable between different types of hosts.  The
     bytecode files are versioned and there is a strict version check,
     so bytecode files generated in one version of GCC do not work with
     an older or newer version of GCC.

     Link-time optimization does not work well with generation of
     debugging information on systems other than those using a
     combination of ELF and DWARF.

     If you specify the optional N, the optimization and code generation
     done at link time is executed in parallel using N parallel jobs by
     utilizing an installed ‘make’ program.  The environment variable
     ‘MAKE’ may be used to override the program used.

     You can also specify ‘-flto=jobserver’ to use GNU make's job server
     mode to determine the number of parallel jobs.  This is useful when
     the Makefile calling GCC is already executing in parallel.  You
     must prepend a ‘+’ to the command recipe in the parent Makefile for
     this to work.  This option likely only works if ‘MAKE’ is GNU make.
     Even without the option value, GCC tries to automatically detect a
     running GNU make's job server.

     Use ‘-flto=auto’ to use GNU make's job server, if available, or
     otherwise fall back to autodetection of the number of CPU threads
     present in your system.

‘-flto-partition=ALG’
     Specify the partitioning algorithm used by the link-time optimizer.
     The value is either ‘1to1’ to specify a partitioning mirroring the
     original source files or ‘balanced’ to specify partitioning into
     equally sized chunks (whenever possible) or ‘max’ to create new
     partition for every symbol where possible.  Specifying ‘none’ as an
     algorithm disables partitioning and streaming completely.  The
     default value is ‘balanced’.  While ‘1to1’ can be used as an
     workaround for various code ordering issues, the ‘max’ partitioning
     is intended for internal testing only.  The value ‘one’ specifies
     that exactly one partition should be used while the value ‘none’
     bypasses partitioning and executes the link-time optimization step
     directly from the WPA phase.

‘-flto-compression-level=N’
     This option specifies the level of compression used for
     intermediate language written to LTO object files, and is only
     meaningful in conjunction with LTO mode (‘-flto’).  GCC currently
     supports two LTO compression algorithms.  For zstd, valid values
     are 0 (no compression) to 19 (maximum compression), while zlib
     supports values from 0 to 9.  Values outside this range are clamped
     to either minimum or maximum of the supported values.  If the
     option is not given, a default balanced compression setting is
     used.

‘-fuse-linker-plugin’
     Enables the use of a linker plugin during link-time optimization.
     This option relies on plugin support in the linker, which is
     available in gold or in GNU ld 2.21 or newer.

     This option enables the extraction of object files with GIMPLE
     bytecode out of library archives.  This improves the quality of
     optimization by exposing more code to the link-time optimizer.
     This information specifies what symbols can be accessed externally
     (by non-LTO object or during dynamic linking).  Resulting code
     quality improvements on binaries (and shared libraries that use
     hidden visibility) are similar to ‘-fwhole-program’.  See ‘-flto’
     for a description of the effect of this flag and how to use it.

     This option is enabled by default when LTO support in GCC is
     enabled and GCC was configured for use with a linker supporting
     plugins (GNU ld 2.21 or newer or gold).

‘-ffat-lto-objects’
     Fat LTO objects are object files that contain both the intermediate
     language and the object code.  This makes them usable for both LTO
     linking and normal linking.  This option is effective only when
     compiling with ‘-flto’ and is ignored at link time.

     ‘-fno-fat-lto-objects’ improves compilation time over plain LTO,
     but requires the complete toolchain to be aware of LTO. It requires
     a linker with linker plugin support for basic functionality.
     Additionally, ‘nm’, ‘ar’ and ‘ranlib’ need to support linker
     plugins to allow a full-featured build environment (capable of
     building static libraries etc).  GCC provides the ‘gcc-ar’,
     ‘gcc-nm’, ‘gcc-ranlib’ wrappers to pass the right options to these
     tools.  With non fat LTO makefiles need to be modified to use them.

     Note that modern binutils provide plugin auto-load mechanism.
     Installing the linker plugin into ‘$libdir/bfd-plugins’ has the
     same effect as usage of the command wrappers (‘gcc-ar’, ‘gcc-nm’
     and ‘gcc-ranlib’).

     The default is ‘-fno-fat-lto-objects’ on targets with linker plugin
     support.

‘-fcompare-elim’
     After register allocation and post-register allocation instruction
     splitting, identify arithmetic instructions that compute processor
     flags similar to a comparison operation based on that arithmetic.
     If possible, eliminate the explicit comparison operation.

     This pass only applies to certain targets that cannot explicitly
     represent the comparison operation before register allocation is
     complete.

     Enabled at levels ‘-O1’, ‘-O2’, ‘-O3’, ‘-Os’.

‘-fcprop-registers’
     After register allocation and post-register allocation instruction
     splitting, perform a copy-propagation pass to try to reduce
     scheduling dependencies and occasionally eliminate the copy.

     Enabled at levels ‘-O1’, ‘-O2’, ‘-O3’, ‘-Os’.

‘-fprofile-correction’
     Profiles collected using an instrumented binary for multi-threaded
     programs may be inconsistent due to missed counter updates.  When
     this option is specified, GCC uses heuristics to correct or smooth
     out such inconsistencies.  By default, GCC emits an error message
     when an inconsistent profile is detected.

     This option is enabled by ‘-fauto-profile’.

‘-fprofile-partial-training’
     With ‘-fprofile-use’ all portions of programs not executed during
     train run are optimized agressively for size rather than speed.  In
     some cases it is not practical to train all possible hot paths in
     the program.  (For example, program may contain functions specific
     for a given hardware and trianing may not cover all hardware
     configurations program is run on.)  With
     ‘-fprofile-partial-training’ profile feedback will be ignored for
     all functions not executed during the train run leading them to be
     optimized as if they were compiled without profile feedback.  This
     leads to better performance when train run is not representative
     but also leads to significantly bigger code.

‘-fprofile-use’
‘-fprofile-use=PATH’
     Enable profile feedback-directed optimizations, and the following
     optimizations, many of which are generally profitable only with
     profile feedback available:

          -fbranch-probabilities  -fprofile-values
          -funroll-loops  -fpeel-loops  -ftracer  -fvpt
          -finline-functions  -fipa-cp  -fipa-cp-clone  -fipa-bit-cp
          -fpredictive-commoning  -fsplit-loops  -funswitch-loops
          -fgcse-after-reload  -ftree-loop-vectorize  -ftree-slp-vectorize
          -fvect-cost-model=dynamic  -ftree-loop-distribute-patterns
          -fprofile-reorder-functions

     Before you can use this option, you must first generate profiling
     information.  *Note Instrumentation Options::, for information
     about the ‘-fprofile-generate’ option.

     By default, GCC emits an error message if the feedback profiles do
     not match the source code.  This error can be turned into a warning
     by using ‘-Wno-error=coverage-mismatch’.  Note this may result in
     poorly optimized code.  Additionally, by default, GCC also emits a
     warning message if the feedback profiles do not exist (see
     ‘-Wmissing-profile’).

     If PATH is specified, GCC looks at the PATH to find the profile
     feedback data files.  See ‘-fprofile-dir’.

‘-fauto-profile’
‘-fauto-profile=PATH’
     Enable sampling-based feedback-directed optimizations, and the
     following optimizations, many of which are generally profitable
     only with profile feedback available:

          -fbranch-probabilities  -fprofile-values
          -funroll-loops  -fpeel-loops  -ftracer  -fvpt
          -finline-functions  -fipa-cp  -fipa-cp-clone  -fipa-bit-cp
          -fpredictive-commoning  -fsplit-loops  -funswitch-loops
          -fgcse-after-reload  -ftree-loop-vectorize  -ftree-slp-vectorize
          -fvect-cost-model=dynamic  -ftree-loop-distribute-patterns
          -fprofile-correction

     PATH is the name of a file containing AutoFDO profile information.
     If omitted, it defaults to ‘fbdata.afdo’ in the current directory.

     Producing an AutoFDO profile data file requires running your
     program with the ‘perf’ utility on a supported GNU/Linux target
     system.  For more information, see <https://perf.wiki.kernel.org/>.

     E.g.
          perf record -e br_inst_retired:near_taken -b -o perf.data \
              -- your_program

     Then use the ‘create_gcov’ tool to convert the raw profile data to
     a format that can be used by GCC.  You must also supply the
     unstripped binary for your program to this tool.  See
     <https://github.com/google/autofdo>.

     E.g.
          create_gcov --binary=your_program.unstripped --profile=perf.data \
              --gcov=profile.afdo

 The following options control compiler behavior regarding
floating-point arithmetic.  These options trade off between speed and
correctness.  All must be specifically enabled.

‘-ffloat-store’
     Do not store floating-point variables in registers, and inhibit
     other options that might change whether a floating-point value is
     taken from a register or memory.

     This option prevents undesirable excess precision on machines such
     as the 68000 where the floating registers (of the 68881) keep more
     precision than a ‘double’ is supposed to have.  Similarly for the
     x86 architecture.  For most programs, the excess precision does
     only good, but a few programs rely on the precise definition of
     IEEE floating point.  Use ‘-ffloat-store’ for such programs, after
     modifying them to store all pertinent intermediate computations
     into variables.

‘-fexcess-precision=STYLE’
     This option allows further control over excess precision on
     machines where floating-point operations occur in a format with
     more precision or range than the IEEE standard and interchange
     floating-point types.  By default, ‘-fexcess-precision=fast’ is in
     effect; this means that operations may be carried out in a wider
     precision than the types specified in the source if that would
     result in faster code, and it is unpredictable when rounding to the
     types specified in the source code takes place.  When compiling C,
     if ‘-fexcess-precision=standard’ is specified then excess precision
     follows the rules specified in ISO C99; in particular, both casts
     and assignments cause values to be rounded to their semantic types
     (whereas ‘-ffloat-store’ only affects assignments).  This option is
     enabled by default for C if a strict conformance option such as
     ‘-std=c99’ is used.  ‘-ffast-math’ enables
     ‘-fexcess-precision=fast’ by default regardless of whether a strict
     conformance option is used.

     ‘-fexcess-precision=standard’ is not implemented for languages
     other than C. On the x86, it has no effect if ‘-mfpmath=sse’ or
     ‘-mfpmath=sse+387’ is specified; in the former case, IEEE semantics
     apply without excess precision, and in the latter, rounding is
     unpredictable.

‘-ffast-math’
     Sets the options ‘-fno-math-errno’, ‘-funsafe-math-optimizations’,
     ‘-ffinite-math-only’, ‘-fno-rounding-math’, ‘-fno-signaling-nans’,
     ‘-fcx-limited-range’ and ‘-fexcess-precision=fast’.

     This option causes the preprocessor macro ‘__FAST_MATH__’ to be
     defined.

     This option is not turned on by any ‘-O’ option besides ‘-Ofast’
     since it can result in incorrect output for programs that depend on
     an exact implementation of IEEE or ISO rules/specifications for
     math functions.  It may, however, yield faster code for programs
     that do not require the guarantees of these specifications.

‘-fno-math-errno’
     Do not set ‘errno’ after calling math functions that are executed
     with a single instruction, e.g., ‘sqrt’.  A program that relies on
     IEEE exceptions for math error handling may want to use this flag
     for speed while maintaining IEEE arithmetic compatibility.

     This option is not turned on by any ‘-O’ option since it can result
     in incorrect output for programs that depend on an exact
     implementation of IEEE or ISO rules/specifications for math
     functions.  It may, however, yield faster code for programs that do
     not require the guarantees of these specifications.

     The default is ‘-fmath-errno’.

     On Darwin systems, the math library never sets ‘errno’.  There is
     therefore no reason for the compiler to consider the possibility
     that it might, and ‘-fno-math-errno’ is the default.

‘-funsafe-math-optimizations’

     Allow optimizations for floating-point arithmetic that (a) assume
     that arguments and results are valid and (b) may violate IEEE or
     ANSI standards.  When used at link time, it may include libraries
     or startup files that change the default FPU control word or other
     similar optimizations.

     This option is not turned on by any ‘-O’ option since it can result
     in incorrect output for programs that depend on an exact
     implementation of IEEE or ISO rules/specifications for math
     functions.  It may, however, yield faster code for programs that do
     not require the guarantees of these specifications.  Enables
     ‘-fno-signed-zeros’, ‘-fno-trapping-math’, ‘-fassociative-math’ and
     ‘-freciprocal-math’.

     The default is ‘-fno-unsafe-math-optimizations’.

‘-fassociative-math’

     Allow re-association of operands in series of floating-point
     operations.  This violates the ISO C and C++ language standard by
     possibly changing computation result.  NOTE: re-ordering may change
     the sign of zero as well as ignore NaNs and inhibit or create
     underflow or overflow (and thus cannot be used on code that relies
     on rounding behavior like ‘(x + 2**52) - 2**52’.  May also reorder
     floating-point comparisons and thus may not be used when ordered
     comparisons are required.  This option requires that both
     ‘-fno-signed-zeros’ and ‘-fno-trapping-math’ be in effect.
     Moreover, it doesn't make much sense with ‘-frounding-math’.  For
     Fortran the option is automatically enabled when both
     ‘-fno-signed-zeros’ and ‘-fno-trapping-math’ are in effect.

     The default is ‘-fno-associative-math’.

‘-freciprocal-math’

     Allow the reciprocal of a value to be used instead of dividing by
     the value if this enables optimizations.  For example ‘x / y’ can
     be replaced with ‘x * (1/y)’, which is useful if ‘(1/y)’ is subject
     to common subexpression elimination.  Note that this loses
     precision and increases the number of flops operating on the value.

     The default is ‘-fno-reciprocal-math’.

‘-ffinite-math-only’
     Allow optimizations for floating-point arithmetic that assume that
     arguments and results are not NaNs or +-Infs.

     This option is not turned on by any ‘-O’ option since it can result
     in incorrect output for programs that depend on an exact
     implementation of IEEE or ISO rules/specifications for math
     functions.  It may, however, yield faster code for programs that do
     not require the guarantees of these specifications.

     The default is ‘-fno-finite-math-only’.

‘-fno-signed-zeros’
     Allow optimizations for floating-point arithmetic that ignore the
     signedness of zero.  IEEE arithmetic specifies the behavior of
     distinct +0.0 and −0.0 values, which then prohibits simplification
     of expressions such as x+0.0 or 0.0*x (even with
     ‘-ffinite-math-only’).  This option implies that the sign of a zero
     result isn't significant.

     The default is ‘-fsigned-zeros’.

‘-fno-trapping-math’
     Compile code assuming that floating-point operations cannot
     generate user-visible traps.  These traps include division by zero,
     overflow, underflow, inexact result and invalid operation.  This
     option requires that ‘-fno-signaling-nans’ be in effect.  Setting
     this option may allow faster code if one relies on "non-stop" IEEE
     arithmetic, for example.

     This option should never be turned on by any ‘-O’ option since it
     can result in incorrect output for programs that depend on an exact
     implementation of IEEE or ISO rules/specifications for math
     functions.

     The default is ‘-ftrapping-math’.

‘-frounding-math’
     Disable transformations and optimizations that assume default
     floating-point rounding behavior.  This is round-to-zero for all
     floating point to integer conversions, and round-to-nearest for all
     other arithmetic truncations.  This option should be specified for
     programs that change the FP rounding mode dynamically, or that may
     be executed with a non-default rounding mode.  This option disables
     constant folding of floating-point expressions at compile time
     (which may be affected by rounding mode) and arithmetic
     transformations that are unsafe in the presence of sign-dependent
     rounding modes.

     The default is ‘-fno-rounding-math’.

     This option is experimental and does not currently guarantee to
     disable all GCC optimizations that are affected by rounding mode.
     Future versions of GCC may provide finer control of this setting
     using C99's ‘FENV_ACCESS’ pragma.  This command-line option will be
     used to specify the default state for ‘FENV_ACCESS’.

‘-fsignaling-nans’
     Compile code assuming that IEEE signaling NaNs may generate
     user-visible traps during floating-point operations.  Setting this
     option disables optimizations that may change the number of
     exceptions visible with signaling NaNs.  This option implies
     ‘-ftrapping-math’.

     This option causes the preprocessor macro ‘__SUPPORT_SNAN__’ to be
     defined.

     The default is ‘-fno-signaling-nans’.

     This option is experimental and does not currently guarantee to
     disable all GCC optimizations that affect signaling NaN behavior.

‘-fno-fp-int-builtin-inexact’
     Do not allow the built-in functions ‘ceil’, ‘floor’, ‘round’ and
     ‘trunc’, and their ‘float’ and ‘long double’ variants, to generate
     code that raises the "inexact" floating-point exception for
     noninteger arguments.  ISO C99 and C11 allow these functions to
     raise the "inexact" exception, but ISO/IEC TS 18661-1:2014, the C
     bindings to IEEE 754-2008, as integrated into ISO C2X, does not
     allow these functions to do so.

     The default is ‘-ffp-int-builtin-inexact’, allowing the exception
     to be raised, unless C2X or a later C standard is selected.  This
     option does nothing unless ‘-ftrapping-math’ is in effect.

     Even if ‘-fno-fp-int-builtin-inexact’ is used, if the functions
     generate a call to a library function then the "inexact" exception
     may be raised if the library implementation does not follow TS
     18661.

‘-fsingle-precision-constant’
     Treat floating-point constants as single precision instead of
     implicitly converting them to double-precision constants.

‘-fcx-limited-range’
     When enabled, this option states that a range reduction step is not
     needed when performing complex division.  Also, there is no
     checking whether the result of a complex multiplication or division
     is ‘NaN + I*NaN’, with an attempt to rescue the situation in that
     case.  The default is ‘-fno-cx-limited-range’, but is enabled by
     ‘-ffast-math’.

     This option controls the default setting of the ISO C99
     ‘CX_LIMITED_RANGE’ pragma.  Nevertheless, the option applies to all
     languages.

‘-fcx-fortran-rules’
     Complex multiplication and division follow Fortran rules.  Range
     reduction is done as part of complex division, but there is no
     checking whether the result of a complex multiplication or division
     is ‘NaN + I*NaN’, with an attempt to rescue the situation in that
     case.

     The default is ‘-fno-cx-fortran-rules’.

 The following options control optimizations that may improve
performance, but are not enabled by any ‘-O’ options.  This section
includes experimental options that may produce broken code.

‘-fbranch-probabilities’
     After running a program compiled with ‘-fprofile-arcs’ (*note
     Instrumentation Options::), you can compile it a second time using
     ‘-fbranch-probabilities’, to improve optimizations based on the
     number of times each branch was taken.  When a program compiled
     with ‘-fprofile-arcs’ exits, it saves arc execution counts to a
     file called ‘SOURCENAME.gcda’ for each source file.  The
     information in this data file is very dependent on the structure of
     the generated code, so you must use the same source code and the
     same optimization options for both compilations.  See details about
     the file naming in ‘-fprofile-arcs’.

     With ‘-fbranch-probabilities’, GCC puts a ‘REG_BR_PROB’ note on
     each ‘JUMP_INSN’ and ‘CALL_INSN’.  These can be used to improve
     optimization.  Currently, they are only used in one place: in
     ‘reorg.cc’, instead of guessing which path a branch is most likely
     to take, the ‘REG_BR_PROB’ values are used to exactly determine
     which path is taken more often.

     Enabled by ‘-fprofile-use’ and ‘-fauto-profile’.

‘-fprofile-values’
     If combined with ‘-fprofile-arcs’, it adds code so that some data
     about values of expressions in the program is gathered.

     With ‘-fbranch-probabilities’, it reads back the data gathered from
     profiling values of expressions for usage in optimizations.

     Enabled by ‘-fprofile-generate’, ‘-fprofile-use’, and
     ‘-fauto-profile’.

‘-fprofile-reorder-functions’
     Function reordering based on profile instrumentation collects first
     time of execution of a function and orders these functions in
     ascending order.

     Enabled with ‘-fprofile-use’.

‘-fvpt’
     If combined with ‘-fprofile-arcs’, this option instructs the
     compiler to add code to gather information about values of
     expressions.

     With ‘-fbranch-probabilities’, it reads back the data gathered and
     actually performs the optimizations based on them.  Currently the
     optimizations include specialization of division operations using
     the knowledge about the value of the denominator.

     Enabled with ‘-fprofile-use’ and ‘-fauto-profile’.

‘-frename-registers’
     Attempt to avoid false dependencies in scheduled code by making use
     of registers left over after register allocation.  This
     optimization most benefits processors with lots of registers.
     Depending on the debug information format adopted by the target,
     however, it can make debugging impossible, since variables no
     longer stay in a "home register".

     Enabled by default with ‘-funroll-loops’.

‘-fschedule-fusion’
     Performs a target dependent pass over the instruction stream to
     schedule instructions of same type together because target machine
     can execute them more efficiently if they are adjacent to each
     other in the instruction flow.

     Enabled at levels ‘-O2’, ‘-O3’, ‘-Os’.

‘-ftracer’
     Perform tail duplication to enlarge superblock size.  This
     transformation simplifies the control flow of the function allowing
     other optimizations to do a better job.

     Enabled by ‘-fprofile-use’ and ‘-fauto-profile’.

‘-funroll-loops’
     Unroll loops whose number of iterations can be determined at
     compile time or upon entry to the loop.  ‘-funroll-loops’ implies
     ‘-frerun-cse-after-loop’, ‘-fweb’ and ‘-frename-registers’.  It
     also turns on complete loop peeling (i.e. complete removal of loops
     with a small constant number of iterations).  This option makes
     code larger, and may or may not make it run faster.

     Enabled by ‘-fprofile-use’ and ‘-fauto-profile’.

‘-funroll-all-loops’
     Unroll all loops, even if their number of iterations is uncertain
     when the loop is entered.  This usually makes programs run more
     slowly.  ‘-funroll-all-loops’ implies the same options as
     ‘-funroll-loops’.

‘-fpeel-loops’
     Peels loops for which there is enough information that they do not
     roll much (from profile feedback or static analysis).  It also
     turns on complete loop peeling (i.e. complete removal of loops with
     small constant number of iterations).

     Enabled by ‘-O3’, ‘-fprofile-use’, and ‘-fauto-profile’.

‘-fmove-loop-invariants’
     Enables the loop invariant motion pass in the RTL loop optimizer.
     Enabled at level ‘-O1’ and higher, except for ‘-Og’.

‘-fmove-loop-stores’
     Enables the loop store motion pass in the GIMPLE loop optimizer.
     This moves invariant stores to after the end of the loop in
     exchange for carrying the stored value in a register across the
     iteration.  Note for this option to have an effect ‘-ftree-loop-im’
     has to be enabled as well.  Enabled at level ‘-O1’ and higher,
     except for ‘-Og’.

‘-fsplit-loops’
     Split a loop into two if it contains a condition that's always true
     for one side of the iteration space and false for the other.

     Enabled by ‘-fprofile-use’ and ‘-fauto-profile’.

‘-funswitch-loops’
     Move branches with loop invariant conditions out of the loop, with
     duplicates of the loop on both branches (modified according to
     result of the condition).

     Enabled by ‘-fprofile-use’ and ‘-fauto-profile’.

‘-fversion-loops-for-strides’
     If a loop iterates over an array with a variable stride, create
     another version of the loop that assumes the stride is always one.
     For example:

          for (int i = 0; i < n; ++i)
            x[i * stride] = ...;

     becomes:

          if (stride == 1)
            for (int i = 0; i < n; ++i)
              x[i] = ...;
          else
            for (int i = 0; i < n; ++i)
              x[i * stride] = ...;

     This is particularly useful for assumed-shape arrays in Fortran
     where (for example) it allows better vectorization assuming
     contiguous accesses.  This flag is enabled by default at ‘-O3’.  It
     is also enabled by ‘-fprofile-use’ and ‘-fauto-profile’.

‘-ffunction-sections’
‘-fdata-sections’
     Place each function or data item into its own section in the output
     file if the target supports arbitrary sections.  The name of the
     function or the name of the data item determines the section's name
     in the output file.

     Use these options on systems where the linker can perform
     optimizations to improve locality of reference in the instruction
     space.  Most systems using the ELF object format have linkers with
     such optimizations.  On AIX, the linker rearranges sections
     (CSECTs) based on the call graph.  The performance impact varies.

     Together with a linker garbage collection (linker ‘--gc-sections’
     option) these options may lead to smaller statically-linked
     executables (after stripping).

     On ELF/DWARF systems these options do not degenerate the quality of
     the debug information.  There could be issues with other object
     files/debug info formats.

     Only use these options when there are significant benefits from
     doing so.  When you specify these options, the assembler and linker
     create larger object and executable files and are also slower.
     These options affect code generation.  They prevent optimizations
     by the compiler and assembler using relative locations inside a
     translation unit since the locations are unknown until link time.
     An example of such an optimization is relaxing calls to short call
     instructions.

‘-fstdarg-opt’
     Optimize the prologue of variadic argument functions with respect
     to usage of those arguments.

‘-fsection-anchors’
     Try to reduce the number of symbolic address calculations by using
     shared "anchor" symbols to address nearby objects.  This
     transformation can help to reduce the number of GOT entries and GOT
     accesses on some targets.

     For example, the implementation of the following function ‘foo’:

          static int a, b, c;
          int foo (void) { return a + b + c; }

     usually calculates the addresses of all three variables, but if you
     compile it with ‘-fsection-anchors’, it accesses the variables from
     a common anchor point instead.  The effect is similar to the
     following pseudocode (which isn't valid C):

          int foo (void)
          {
            register int *xr = &x;
            return xr[&a - &x] + xr[&b - &x] + xr[&c - &x];
          }

     Not all targets support this option.

‘-fzero-call-used-regs=CHOICE’
     Zero call-used registers at function return to increase program
     security by either mitigating Return-Oriented Programming (ROP)
     attacks or preventing information leakage through registers.

     The possible values of CHOICE are the same as for the
     ‘zero_call_used_regs’ attribute (*note Function Attributes::).  The
     default is ‘skip’.

     You can control this behavior for a specific function by using the
     function attribute ‘zero_call_used_regs’ (*note Function
     Attributes::).

‘--param NAME=VALUE’
     In some places, GCC uses various constants to control the amount of
     optimization that is done.  For example, GCC does not inline
     functions that contain more than a certain number of instructions.
     You can control some of these constants on the command line using
     the ‘--param’ option.

     The names of specific parameters, and the meaning of the values,
     are tied to the internals of the compiler, and are subject to
     change without notice in future releases.

     In order to get minimal, maximal and default value of a parameter,
     one can use ‘--help=param -Q’ options.

     In each case, the VALUE is an integer.  The following choices of
     NAME are recognized for all targets:

     ‘predictable-branch-outcome’
          When branch is predicted to be taken with probability lower
          than this threshold (in percent), then it is considered well
          predictable.

     ‘max-rtl-if-conversion-insns’
          RTL if-conversion tries to remove conditional branches around
          a block and replace them with conditionally executed
          instructions.  This parameter gives the maximum number of
          instructions in a block which should be considered for
          if-conversion.  The compiler will also use other heuristics to
          decide whether if-conversion is likely to be profitable.

     ‘max-rtl-if-conversion-predictable-cost’
          RTL if-conversion will try to remove conditional branches
          around a block and replace them with conditionally executed
          instructions.  These parameters give the maximum permissible
          cost for the sequence that would be generated by if-conversion
          depending on whether the branch is statically determined to be
          predictable or not.  The units for this parameter are the same
          as those for the GCC internal seq_cost metric.  The compiler
          will try to provide a reasonable default for this parameter
          using the BRANCH_COST target macro.

     ‘max-crossjump-edges’
          The maximum number of incoming edges to consider for
          cross-jumping.  The algorithm used by ‘-fcrossjumping’ is
          O(N^2) in the number of edges incoming to each block.
          Increasing values mean more aggressive optimization, making
          the compilation time increase with probably small improvement
          in executable size.

     ‘min-crossjump-insns’
          The minimum number of instructions that must be matched at the
          end of two blocks before cross-jumping is performed on them.
          This value is ignored in the case where all instructions in
          the block being cross-jumped from are matched.

     ‘max-grow-copy-bb-insns’
          The maximum code size expansion factor when copying basic
          blocks instead of jumping.  The expansion is relative to a
          jump instruction.

     ‘max-goto-duplication-insns’
          The maximum number of instructions to duplicate to a block
          that jumps to a computed goto.  To avoid O(N^2) behavior in a
          number of passes, GCC factors computed gotos early in the
          compilation process, and unfactors them as late as possible.
          Only computed jumps at the end of a basic blocks with no more
          than max-goto-duplication-insns are unfactored.

     ‘max-delay-slot-insn-search’
          The maximum number of instructions to consider when looking
          for an instruction to fill a delay slot.  If more than this
          arbitrary number of instructions are searched, the time
          savings from filling the delay slot are minimal, so stop
          searching.  Increasing values mean more aggressive
          optimization, making the compilation time increase with
          probably small improvement in execution time.

     ‘max-delay-slot-live-search’
          When trying to fill delay slots, the maximum number of
          instructions to consider when searching for a block with valid
          live register information.  Increasing this arbitrarily chosen
          value means more aggressive optimization, increasing the
          compilation time.  This parameter should be removed when the
          delay slot code is rewritten to maintain the control-flow
          graph.

     ‘max-gcse-memory’
          The approximate maximum amount of memory in ‘kB’ that can be
          allocated in order to perform the global common subexpression
          elimination optimization.  If more memory than specified is
          required, the optimization is not done.

     ‘max-gcse-insertion-ratio’
          If the ratio of expression insertions to deletions is larger
          than this value for any expression, then RTL PRE inserts or
          removes the expression and thus leaves partially redundant
          computations in the instruction stream.

     ‘max-pending-list-length’
          The maximum number of pending dependencies scheduling allows
          before flushing the current state and starting over.  Large
          functions with few branches or calls can create excessively
          large lists which needlessly consume memory and resources.

     ‘max-modulo-backtrack-attempts’
          The maximum number of backtrack attempts the scheduler should
          make when modulo scheduling a loop.  Larger values can
          exponentially increase compilation time.

     ‘max-inline-functions-called-once-loop-depth’
          Maximal loop depth of a call considered by inline heuristics
          that tries to inline all functions called once.

     ‘max-inline-functions-called-once-insns’
          Maximal estimated size of functions produced while inlining
          functions called once.

     ‘max-inline-insns-single’
          Several parameters control the tree inliner used in GCC.  This
          number sets the maximum number of instructions (counted in
          GCC's internal representation) in a single function that the
          tree inliner considers for inlining.  This only affects
          functions declared inline and methods implemented in a class
          declaration (C++).

     ‘max-inline-insns-auto’
          When you use ‘-finline-functions’ (included in ‘-O3’), a lot
          of functions that would otherwise not be considered for
          inlining by the compiler are investigated.  To those
          functions, a different (more restrictive) limit compared to
          functions declared inline can be applied (‘--param
          max-inline-insns-auto’).

     ‘max-inline-insns-small’
          This is bound applied to calls which are considered relevant
          with ‘-finline-small-functions’.

     ‘max-inline-insns-size’
          This is bound applied to calls which are optimized for size.
          Small growth may be desirable to anticipate optimization
          oppurtunities exposed by inlining.

     ‘uninlined-function-insns’
          Number of instructions accounted by inliner for function
          overhead such as function prologue and epilogue.

     ‘uninlined-function-time’
          Extra time accounted by inliner for function overhead such as
          time needed to execute function prologue and epilogue.

     ‘inline-heuristics-hint-percent’
          The scale (in percents) applied to ‘inline-insns-single’,
          ‘inline-insns-single-O2’, ‘inline-insns-auto’ when inline
          heuristics hints that inlining is very profitable (will enable
          later optimizations).

     ‘uninlined-thunk-insns’
     ‘uninlined-thunk-time’
          Same as ‘--param uninlined-function-insns’ and ‘--param
          uninlined-function-time’ but applied to function thunks.

     ‘inline-min-speedup’
          When estimated performance improvement of caller + callee
          runtime exceeds this threshold (in percent), the function can
          be inlined regardless of the limit on ‘--param
          max-inline-insns-single’ and ‘--param max-inline-insns-auto’.

     ‘large-function-insns’
          The limit specifying really large functions.  For functions
          larger than this limit after inlining, inlining is constrained
          by ‘--param large-function-growth’.  This parameter is useful
          primarily to avoid extreme compilation time caused by
          non-linear algorithms used by the back end.

     ‘large-function-growth’
          Specifies maximal growth of large function caused by inlining
          in percents.  For example, parameter value 100 limits large
          function growth to 2.0 times the original size.

     ‘large-unit-insns’
          The limit specifying large translation unit.  Growth caused by
          inlining of units larger than this limit is limited by
          ‘--param inline-unit-growth’.  For small units this might be
          too tight.  For example, consider a unit consisting of
          function A that is inline and B that just calls A three times.
          If B is small relative to A, the growth of unit is 300\% and
          yet such inlining is very sane.  For very large units
          consisting of small inlineable functions, however, the overall
          unit growth limit is needed to avoid exponential explosion of
          code size.  Thus for smaller units, the size is increased to
          ‘--param large-unit-insns’ before applying ‘--param
          inline-unit-growth’.

     ‘lazy-modules’
          Maximum number of concurrently open C++ module files when lazy
          loading.

     ‘inline-unit-growth’
          Specifies maximal overall growth of the compilation unit
          caused by inlining.  For example, parameter value 20 limits
          unit growth to 1.2 times the original size.  Cold functions
          (either marked cold via an attribute or by profile feedback)
          are not accounted into the unit size.

     ‘ipa-cp-unit-growth’
          Specifies maximal overall growth of the compilation unit
          caused by interprocedural constant propagation.  For example,
          parameter value 10 limits unit growth to 1.1 times the
          original size.

     ‘ipa-cp-large-unit-insns’
          The size of translation unit that IPA-CP pass considers large.

     ‘large-stack-frame’
          The limit specifying large stack frames.  While inlining the
          algorithm is trying to not grow past this limit too much.

     ‘large-stack-frame-growth’
          Specifies maximal growth of large stack frames caused by
          inlining in percents.  For example, parameter value 1000
          limits large stack frame growth to 11 times the original size.

     ‘max-inline-insns-recursive’
     ‘max-inline-insns-recursive-auto’
          Specifies the maximum number of instructions an out-of-line
          copy of a self-recursive inline function can grow into by
          performing recursive inlining.

          ‘--param max-inline-insns-recursive’ applies to functions
          declared inline.  For functions not declared inline, recursive
          inlining happens only when ‘-finline-functions’ (included in
          ‘-O3’) is enabled; ‘--param max-inline-insns-recursive-auto’
          applies instead.

     ‘max-inline-recursive-depth’
     ‘max-inline-recursive-depth-auto’
          Specifies the maximum recursion depth used for recursive
          inlining.

          ‘--param max-inline-recursive-depth’ applies to functions
          declared inline.  For functions not declared inline, recursive
          inlining happens only when ‘-finline-functions’ (included in
          ‘-O3’) is enabled; ‘--param max-inline-recursive-depth-auto’
          applies instead.

     ‘min-inline-recursive-probability’
          Recursive inlining is profitable only for function having deep
          recursion in average and can hurt for function having little
          recursion depth by increasing the prologue size or complexity
          of function body to other optimizers.

          When profile feedback is available (see ‘-fprofile-generate’)
          the actual recursion depth can be guessed from the probability
          that function recurses via a given call expression.  This
          parameter limits inlining only to call expressions whose
          probability exceeds the given threshold (in percents).

     ‘early-inlining-insns’
          Specify growth that the early inliner can make.  In effect it
          increases the amount of inlining for code having a large
          abstraction penalty.

     ‘max-early-inliner-iterations’
          Limit of iterations of the early inliner.  This basically
          bounds the number of nested indirect calls the early inliner
          can resolve.  Deeper chains are still handled by late
          inlining.

     ‘comdat-sharing-probability’
          Probability (in percent) that C++ inline function with comdat
          visibility are shared across multiple compilation units.

     ‘modref-max-bases’
     ‘modref-max-refs’
     ‘modref-max-accesses’
          Specifies the maximal number of base pointers, references and
          accesses stored for a single function by mod/ref analysis.

     ‘modref-max-tests’
          Specifies the maxmal number of tests alias oracle can perform
          to disambiguate memory locations using the mod/ref
          information.  This parameter ought to be bigger than ‘--param
          modref-max-bases’ and ‘--param modref-max-refs’.

     ‘modref-max-depth’
          Specifies the maximum depth of DFS walk used by modref escape
          analysis.  Setting to 0 disables the analysis completely.

     ‘modref-max-escape-points’
          Specifies the maximum number of escape points tracked by
          modref per SSA-name.

     ‘modref-max-adjustments’
          Specifies the maximum number the access range is enlarged
          during modref dataflow analysis.

     ‘profile-func-internal-id’
          A parameter to control whether to use function internal id in
          profile database lookup.  If the value is 0, the compiler uses
          an id that is based on function assembler name and filename,
          which makes old profile data more tolerant to source changes
          such as function reordering etc.

     ‘min-vect-loop-bound’
          The minimum number of iterations under which loops are not
          vectorized when ‘-ftree-vectorize’ is used.  The number of
          iterations after vectorization needs to be greater than the
          value specified by this option to allow vectorization.

     ‘gcse-cost-distance-ratio’
          Scaling factor in calculation of maximum distance an
          expression can be moved by GCSE optimizations.  This is
          currently supported only in the code hoisting pass.  The
          bigger the ratio, the more aggressive code hoisting is with
          simple expressions, i.e., the expressions that have cost less
          than ‘gcse-unrestricted-cost’.  Specifying 0 disables hoisting
          of simple expressions.

     ‘gcse-unrestricted-cost’
          Cost, roughly measured as the cost of a single typical machine
          instruction, at which GCSE optimizations do not constrain the
          distance an expression can travel.  This is currently
          supported only in the code hoisting pass.  The lesser the
          cost, the more aggressive code hoisting is.  Specifying 0
          allows all expressions to travel unrestricted distances.

     ‘max-hoist-depth’
          The depth of search in the dominator tree for expressions to
          hoist.  This is used to avoid quadratic behavior in hoisting
          algorithm.  The value of 0 does not limit on the search, but
          may slow down compilation of huge functions.

     ‘max-tail-merge-comparisons’
          The maximum amount of similar bbs to compare a bb with.  This
          is used to avoid quadratic behavior in tree tail merging.

     ‘max-tail-merge-iterations’
          The maximum amount of iterations of the pass over the
          function.  This is used to limit compilation time in tree tail
          merging.

     ‘store-merging-allow-unaligned’
          Allow the store merging pass to introduce unaligned stores if
          it is legal to do so.

     ‘max-stores-to-merge’
          The maximum number of stores to attempt to merge into wider
          stores in the store merging pass.

     ‘max-store-chains-to-track’
          The maximum number of store chains to track at the same time
          in the attempt to merge them into wider stores in the store
          merging pass.

     ‘max-stores-to-track’
          The maximum number of stores to track at the same time in the
          attemt to to merge them into wider stores in the store merging
          pass.

     ‘max-unrolled-insns’
          The maximum number of instructions that a loop may have to be
          unrolled.  If a loop is unrolled, this parameter also
          determines how many times the loop code is unrolled.

     ‘max-average-unrolled-insns’
          The maximum number of instructions biased by probabilities of
          their execution that a loop may have to be unrolled.  If a
          loop is unrolled, this parameter also determines how many
          times the loop code is unrolled.

     ‘max-unroll-times’
          The maximum number of unrollings of a single loop.

     ‘max-peeled-insns’
          The maximum number of instructions that a loop may have to be
          peeled.  If a loop is peeled, this parameter also determines
          how many times the loop code is peeled.

     ‘max-peel-times’
          The maximum number of peelings of a single loop.

     ‘max-peel-branches’
          The maximum number of branches on the hot path through the
          peeled sequence.

     ‘max-completely-peeled-insns’
          The maximum number of insns of a completely peeled loop.

     ‘max-completely-peel-times’
          The maximum number of iterations of a loop to be suitable for
          complete peeling.

     ‘max-completely-peel-loop-nest-depth’
          The maximum depth of a loop nest suitable for complete
          peeling.

     ‘max-unswitch-insns’
          The maximum number of insns of an unswitched loop.

     ‘max-unswitch-level’
          The maximum number of branches unswitched in a single loop.

     ‘lim-expensive’
          The minimum cost of an expensive expression in the loop
          invariant motion.

     ‘min-loop-cond-split-prob’
          When FDO profile information is available,
          ‘min-loop-cond-split-prob’ specifies minimum threshold for
          probability of semi-invariant condition statement to trigger
          loop split.

     ‘iv-consider-all-candidates-bound’
          Bound on number of candidates for induction variables, below
          which all candidates are considered for each use in induction
          variable optimizations.  If there are more candidates than
          this, only the most relevant ones are considered to avoid
          quadratic time complexity.

     ‘iv-max-considered-uses’
          The induction variable optimizations give up on loops that
          contain more induction variable uses.

     ‘iv-always-prune-cand-set-bound’
          If the number of candidates in the set is smaller than this
          value, always try to remove unnecessary ivs from the set when
          adding a new one.

     ‘avg-loop-niter’
          Average number of iterations of a loop.

     ‘dse-max-object-size’
          Maximum size (in bytes) of objects tracked bytewise by dead
          store elimination.  Larger values may result in larger
          compilation times.

     ‘dse-max-alias-queries-per-store’
          Maximum number of queries into the alias oracle per store.
          Larger values result in larger compilation times and may
          result in more removed dead stores.

     ‘scev-max-expr-size’
          Bound on size of expressions used in the scalar evolutions
          analyzer.  Large expressions slow the analyzer.

     ‘scev-max-expr-complexity’
          Bound on the complexity of the expressions in the scalar
          evolutions analyzer.  Complex expressions slow the analyzer.

     ‘max-tree-if-conversion-phi-args’
          Maximum number of arguments in a PHI supported by TREE if
          conversion unless the loop is marked with simd pragma.

     ‘vect-max-version-for-alignment-checks’
          The maximum number of run-time checks that can be performed
          when doing loop versioning for alignment in the vectorizer.

     ‘vect-max-version-for-alias-checks’
          The maximum number of run-time checks that can be performed
          when doing loop versioning for alias in the vectorizer.

     ‘vect-max-peeling-for-alignment’
          The maximum number of loop peels to enhance access alignment
          for vectorizer.  Value -1 means no limit.

     ‘max-iterations-to-track’
          The maximum number of iterations of a loop the brute-force
          algorithm for analysis of the number of iterations of the loop
          tries to evaluate.

     ‘hot-bb-count-fraction’
          The denominator n of fraction 1/n of the maximal execution
          count of a basic block in the entire program that a basic
          block needs to at least have in order to be considered hot.
          The default is 10000, which means that a basic block is
          considered hot if its execution count is greater than 1/10000
          of the maximal execution count.  0 means that it is never
          considered hot.  Used in non-LTO mode.

     ‘hot-bb-count-ws-permille’
          The number of most executed permilles, ranging from 0 to 1000,
          of the profiled execution of the entire program to which the
          execution count of a basic block must be part of in order to
          be considered hot.  The default is 990, which means that a
          basic block is considered hot if its execution count
          contributes to the upper 990 permilles, or 99.0%, of the
          profiled execution of the entire program.  0 means that it is
          never considered hot.  Used in LTO mode.

     ‘hot-bb-frequency-fraction’
          The denominator n of fraction 1/n of the execution frequency
          of the entry block of a function that a basic block of this
          function needs to at least have in order to be considered hot.
          The default is 1000, which means that a basic block is
          considered hot in a function if it is executed more frequently
          than 1/1000 of the frequency of the entry block of the
          function.  0 means that it is never considered hot.

     ‘unlikely-bb-count-fraction’
          The denominator n of fraction 1/n of the number of profiled
          runs of the entire program below which the execution count of
          a basic block must be in order for the basic block to be
          considered unlikely executed.  The default is 20, which means
          that a basic block is considered unlikely executed if it is
          executed in fewer than 1/20, or 5%, of the runs of the
          program.  0 means that it is always considered unlikely
          executed.

     ‘max-predicted-iterations’
          The maximum number of loop iterations we predict statically.
          This is useful in cases where a function contains a single
          loop with known bound and another loop with unknown bound.
          The known number of iterations is predicted correctly, while
          the unknown number of iterations average to roughly 10.  This
          means that the loop without bounds appears artificially cold
          relative to the other one.

     ‘builtin-expect-probability’
          Control the probability of the expression having the specified
          value.  This parameter takes a percentage (i.e. 0 ...  100) as
          input.

     ‘builtin-string-cmp-inline-length’
          The maximum length of a constant string for a builtin string
          cmp call eligible for inlining.

     ‘align-threshold’

          Select fraction of the maximal frequency of executions of a
          basic block in a function to align the basic block.

     ‘align-loop-iterations’

          A loop expected to iterate at least the selected number of
          iterations is aligned.

     ‘tracer-dynamic-coverage’
     ‘tracer-dynamic-coverage-feedback’

          This value is used to limit superblock formation once the
          given percentage of executed instructions is covered.  This
          limits unnecessary code size expansion.

          The ‘tracer-dynamic-coverage-feedback’ parameter is used only
          when profile feedback is available.  The real profiles (as
          opposed to statically estimated ones) are much less balanced
          allowing the threshold to be larger value.

     ‘tracer-max-code-growth’
          Stop tail duplication once code growth has reached given
          percentage.  This is a rather artificial limit, as most of the
          duplicates are eliminated later in cross jumping, so it may be
          set to much higher values than is the desired code growth.

     ‘tracer-min-branch-ratio’

          Stop reverse growth when the reverse probability of best edge
          is less than this threshold (in percent).

     ‘tracer-min-branch-probability’
     ‘tracer-min-branch-probability-feedback’

          Stop forward growth if the best edge has probability lower
          than this threshold.

          Similarly to ‘tracer-dynamic-coverage’ two parameters are
          provided.  ‘tracer-min-branch-probability-feedback’ is used
          for compilation with profile feedback and
          ‘tracer-min-branch-probability’ compilation without.  The
          value for compilation with profile feedback needs to be more
          conservative (higher) in order to make tracer effective.

     ‘stack-clash-protection-guard-size’
          Specify the size of the operating system provided stack guard
          as 2 raised to NUM bytes.  Higher values may reduce the number
          of explicit probes, but a value larger than the operating
          system provided guard will leave code vulnerable to stack
          clash style attacks.

     ‘stack-clash-protection-probe-interval’
          Stack clash protection involves probing stack space as it is
          allocated.  This param controls the maximum distance between
          probes into the stack as 2 raised to NUM bytes.  Higher values
          may reduce the number of explicit probes, but a value larger
          than the operating system provided guard will leave code
          vulnerable to stack clash style attacks.

     ‘max-cse-path-length’

          The maximum number of basic blocks on path that CSE considers.

     ‘max-cse-insns’
          The maximum number of instructions CSE processes before
          flushing.

     ‘ggc-min-expand’

          GCC uses a garbage collector to manage its own memory
          allocation.  This parameter specifies the minimum percentage
          by which the garbage collector's heap should be allowed to
          expand between collections.  Tuning this may improve
          compilation speed; it has no effect on code generation.

          The default is 30% + 70% * (RAM/1GB) with an upper bound of
          100% when RAM >= 1GB.  If ‘getrlimit’ is available, the notion
          of "RAM" is the smallest of actual RAM and ‘RLIMIT_DATA’ or
          ‘RLIMIT_AS’.  If GCC is not able to calculate RAM on a
          particular platform, the lower bound of 30% is used.  Setting
          this parameter and ‘ggc-min-heapsize’ to zero causes a full
          collection to occur at every opportunity.  This is extremely
          slow, but can be useful for debugging.

     ‘ggc-min-heapsize’

          Minimum size of the garbage collector's heap before it begins
          bothering to collect garbage.  The first collection occurs
          after the heap expands by ‘ggc-min-expand’% beyond
          ‘ggc-min-heapsize’.  Again, tuning this may improve
          compilation speed, and has no effect on code generation.

          The default is the smaller of RAM/8, RLIMIT_RSS, or a limit
          that tries to ensure that RLIMIT_DATA or RLIMIT_AS are not
          exceeded, but with a lower bound of 4096 (four megabytes) and
          an upper bound of 131072 (128 megabytes).  If GCC is not able
          to calculate RAM on a particular platform, the lower bound is
          used.  Setting this parameter very large effectively disables
          garbage collection.  Setting this parameter and
          ‘ggc-min-expand’ to zero causes a full collection to occur at
          every opportunity.

     ‘max-reload-search-insns’
          The maximum number of instruction reload should look backward
          for equivalent register.  Increasing values mean more
          aggressive optimization, making the compilation time increase
          with probably slightly better performance.

     ‘max-cselib-memory-locations’
          The maximum number of memory locations cselib should take into
          account.  Increasing values mean more aggressive optimization,
          making the compilation time increase with probably slightly
          better performance.

     ‘max-sched-ready-insns’
          The maximum number of instructions ready to be issued the
          scheduler should consider at any given time during the first
          scheduling pass.  Increasing values mean more thorough
          searches, making the compilation time increase with probably
          little benefit.

     ‘max-sched-region-blocks’
          The maximum number of blocks in a region to be considered for
          interblock scheduling.

     ‘max-pipeline-region-blocks’
          The maximum number of blocks in a region to be considered for
          pipelining in the selective scheduler.

     ‘max-sched-region-insns’
          The maximum number of insns in a region to be considered for
          interblock scheduling.

     ‘max-pipeline-region-insns’
          The maximum number of insns in a region to be considered for
          pipelining in the selective scheduler.

     ‘min-spec-prob’
          The minimum probability (in percents) of reaching a source
          block for interblock speculative scheduling.

     ‘max-sched-extend-regions-iters’
          The maximum number of iterations through CFG to extend
          regions.  A value of 0 disables region extensions.

     ‘max-sched-insn-conflict-delay’
          The maximum conflict delay for an insn to be considered for
          speculative motion.

     ‘sched-spec-prob-cutoff’
          The minimal probability of speculation success (in percents),
          so that speculative insns are scheduled.

     ‘sched-state-edge-prob-cutoff’
          The minimum probability an edge must have for the scheduler to
          save its state across it.

     ‘sched-mem-true-dep-cost’
          Minimal distance (in CPU cycles) between store and load
          targeting same memory locations.

     ‘selsched-max-lookahead’
          The maximum size of the lookahead window of selective
          scheduling.  It is a depth of search for available
          instructions.

     ‘selsched-max-sched-times’
          The maximum number of times that an instruction is scheduled
          during selective scheduling.  This is the limit on the number
          of iterations through which the instruction may be pipelined.

     ‘selsched-insns-to-rename’
          The maximum number of best instructions in the ready list that
          are considered for renaming in the selective scheduler.

     ‘sms-min-sc’
          The minimum value of stage count that swing modulo scheduler
          generates.

     ‘max-last-value-rtl’
          The maximum size measured as number of RTLs that can be
          recorded in an expression in combiner for a pseudo register as
          last known value of that register.

     ‘max-combine-insns’
          The maximum number of instructions the RTL combiner tries to
          combine.

     ‘integer-share-limit’
          Small integer constants can use a shared data structure,
          reducing the compiler's memory usage and increasing its speed.
          This sets the maximum value of a shared integer constant.

     ‘ssp-buffer-size’
          The minimum size of buffers (i.e. arrays) that receive stack
          smashing protection when ‘-fstack-protector’ is used.

     ‘min-size-for-stack-sharing’
          The minimum size of variables taking part in stack slot
          sharing when not optimizing.

     ‘max-jump-thread-duplication-stmts’
          Maximum number of statements allowed in a block that needs to
          be duplicated when threading jumps.

     ‘max-fields-for-field-sensitive’
          Maximum number of fields in a structure treated in a field
          sensitive manner during pointer analysis.

     ‘prefetch-latency’
          Estimate on average number of instructions that are executed
          before prefetch finishes.  The distance prefetched ahead is
          proportional to this constant.  Increasing this number may
          also lead to less streams being prefetched (see
          ‘simultaneous-prefetches’).

     ‘simultaneous-prefetches’
          Maximum number of prefetches that can run at the same time.

     ‘l1-cache-line-size’
          The size of cache line in L1 data cache, in bytes.

     ‘l1-cache-size’
          The size of L1 data cache, in kilobytes.

     ‘l2-cache-size’
          The size of L2 data cache, in kilobytes.

     ‘prefetch-dynamic-strides’
          Whether the loop array prefetch pass should issue software
          prefetch hints for strides that are non-constant.  In some
          cases this may be beneficial, though the fact the stride is
          non-constant may make it hard to predict when there is clear
          benefit to issuing these hints.

          Set to 1 if the prefetch hints should be issued for
          non-constant strides.  Set to 0 if prefetch hints should be
          issued only for strides that are known to be constant and
          below ‘prefetch-minimum-stride’.

     ‘prefetch-minimum-stride’
          Minimum constant stride, in bytes, to start using prefetch
          hints for.  If the stride is less than this threshold,
          prefetch hints will not be issued.

          This setting is useful for processors that have hardware
          prefetchers, in which case there may be conflicts between the
          hardware prefetchers and the software prefetchers.  If the
          hardware prefetchers have a maximum stride they can handle, it
          should be used here to improve the use of software
          prefetchers.

          A value of -1 means we don't have a threshold and therefore
          prefetch hints can be issued for any constant stride.

          This setting is only useful for strides that are known and
          constant.

     ‘destructive-interference-size’
     ‘constructive-interference-size’
          The values for the C++17 variables
          ‘std::hardware_destructive_interference_size’ and
          ‘std::hardware_constructive_interference_size’.  The
          destructive interference size is the minimum recommended
          offset between two independent concurrently-accessed objects;
          the constructive interference size is the maximum recommended
          size of contiguous memory accessed together.  Typically both
          will be the size of an L1 cache line for the target, in bytes.
          For a generic target covering a range of L1 cache line sizes,
          typically the constructive interference size will be the small
          end of the range and the destructive size will be the large
          end.

          The destructive interference size is intended to be used for
          layout, and thus has ABI impact.  The default value is not
          expected to be stable, and on some targets varies with
          ‘-mtune’, so use of this variable in a context where ABI
          stability is important, such as the public interface of a
          library, is strongly discouraged; if it is used in that
          context, users can stabilize the value using this option.

          The constructive interference size is less sensitive, as it is
          typically only used in a ‘static_assert’ to make sure that a
          type fits within a cache line.

          See also ‘-Winterference-size’.

     ‘loop-interchange-max-num-stmts’
          The maximum number of stmts in a loop to be interchanged.

     ‘loop-interchange-stride-ratio’
          The minimum ratio between stride of two loops for interchange
          to be profitable.

     ‘min-insn-to-prefetch-ratio’
          The minimum ratio between the number of instructions and the
          number of prefetches to enable prefetching in a loop.

     ‘prefetch-min-insn-to-mem-ratio’
          The minimum ratio between the number of instructions and the
          number of memory references to enable prefetching in a loop.

     ‘use-canonical-types’
          Whether the compiler should use the "canonical" type system.
          Should always be 1, which uses a more efficient internal
          mechanism for comparing types in C++ and Objective-C++.
          However, if bugs in the canonical type system are causing
          compilation failures, set this value to 0 to disable canonical
          types.

     ‘switch-conversion-max-branch-ratio’
          Switch initialization conversion refuses to create arrays that
          are bigger than ‘switch-conversion-max-branch-ratio’ times the
          number of branches in the switch.

     ‘max-partial-antic-length’
          Maximum length of the partial antic set computed during the
          tree partial redundancy elimination optimization
          (‘-ftree-pre’) when optimizing at ‘-O3’ and above.  For some
          sorts of source code the enhanced partial redundancy
          elimination optimization can run away, consuming all of the
          memory available on the host machine.  This parameter sets a
          limit on the length of the sets that are computed, which
          prevents the runaway behavior.  Setting a value of 0 for this
          parameter allows an unlimited set length.

     ‘rpo-vn-max-loop-depth’
          Maximum loop depth that is value-numbered optimistically.
          When the limit hits the innermost RPO-VN-MAX-LOOP-DEPTH loops
          and the outermost loop in the loop nest are value-numbered
          optimistically and the remaining ones not.

     ‘sccvn-max-alias-queries-per-access’
          Maximum number of alias-oracle queries we perform when looking
          for redundancies for loads and stores.  If this limit is hit
          the search is aborted and the load or store is not considered
          redundant.  The number of queries is algorithmically limited
          to the number of stores on all paths from the load to the
          function entry.

     ‘ira-max-loops-num’
          IRA uses regional register allocation by default.  If a
          function contains more loops than the number given by this
          parameter, only at most the given number of the most
          frequently-executed loops form regions for regional register
          allocation.

     ‘ira-max-conflict-table-size’
          Although IRA uses a sophisticated algorithm to compress the
          conflict table, the table can still require excessive amounts
          of memory for huge functions.  If the conflict table for a
          function could be more than the size in MB given by this
          parameter, the register allocator instead uses a faster,
          simpler, and lower-quality algorithm that does not require
          building a pseudo-register conflict table.

     ‘ira-loop-reserved-regs’
          IRA can be used to evaluate more accurate register pressure in
          loops for decisions to move loop invariants (see ‘-O3’).  The
          number of available registers reserved for some other purposes
          is given by this parameter.  Default of the parameter is the
          best found from numerous experiments.

     ‘ira-consider-dup-in-all-alts’
          Make IRA to consider matching constraint (duplicated operand
          number) heavily in all available alternatives for preferred
          register class.  If it is set as zero, it means IRA only
          respects the matching constraint when it's in the only
          available alternative with an appropriate register class.
          Otherwise, it means IRA will check all available alternatives
          for preferred register class even if it has found some choice
          with an appropriate register class and respect the found
          qualified matching constraint.

     ‘lra-inheritance-ebb-probability-cutoff’
          LRA tries to reuse values reloaded in registers in subsequent
          insns.  This optimization is called inheritance.  EBB is used
          as a region to do this optimization.  The parameter defines a
          minimal fall-through edge probability in percentage used to
          add BB to inheritance EBB in LRA. The default value was chosen
          from numerous runs of SPEC2000 on x86-64.

     ‘loop-invariant-max-bbs-in-loop’
          Loop invariant motion can be very expensive, both in
          compilation time and in amount of needed compile-time memory,
          with very large loops.  Loops with more basic blocks than this
          parameter won't have loop invariant motion optimization
          performed on them.

     ‘loop-max-datarefs-for-datadeps’
          Building data dependencies is expensive for very large loops.
          This parameter limits the number of data references in loops
          that are considered for data dependence analysis.  These large
          loops are no handled by the optimizations using loop data
          dependencies.

     ‘max-vartrack-size’
          Sets a maximum number of hash table slots to use during
          variable tracking dataflow analysis of any function.  If this
          limit is exceeded with variable tracking at assignments
          enabled, analysis for that function is retried without it,
          after removing all debug insns from the function.  If the
          limit is exceeded even without debug insns, var tracking
          analysis is completely disabled for the function.  Setting the
          parameter to zero makes it unlimited.

     ‘max-vartrack-expr-depth’
          Sets a maximum number of recursion levels when attempting to
          map variable names or debug temporaries to value expressions.
          This trades compilation time for more complete debug
          information.  If this is set too low, value expressions that
          are available and could be represented in debug information
          may end up not being used; setting this higher may enable the
          compiler to find more complex debug expressions, but compile
          time and memory use may grow.

     ‘max-debug-marker-count’
          Sets a threshold on the number of debug markers (e.g. begin
          stmt markers) to avoid complexity explosion at inlining or
          expanding to RTL. If a function has more such gimple stmts
          than the set limit, such stmts will be dropped from the
          inlined copy of a function, and from its RTL expansion.

     ‘min-nondebug-insn-uid’
          Use uids starting at this parameter for nondebug insns.  The
          range below the parameter is reserved exclusively for debug
          insns created by ‘-fvar-tracking-assignments’, but debug insns
          may get (non-overlapping) uids above it if the reserved range
          is exhausted.

     ‘ipa-sra-ptr-growth-factor’
          IPA-SRA replaces a pointer to an aggregate with one or more
          new parameters only when their cumulative size is less or
          equal to ‘ipa-sra-ptr-growth-factor’ times the size of the
          original pointer parameter.

     ‘ipa-sra-max-replacements’
          Maximum pieces of an aggregate that IPA-SRA tracks.  As a
          consequence, it is also the maximum number of replacements of
          a formal parameter.

     ‘sra-max-scalarization-size-Ospeed’
     ‘sra-max-scalarization-size-Osize’
          The two Scalar Reduction of Aggregates passes (SRA and
          IPA-SRA) aim to replace scalar parts of aggregates with uses
          of independent scalar variables.  These parameters control the
          maximum size, in storage units, of aggregate which is
          considered for replacement when compiling for speed
          (‘sra-max-scalarization-size-Ospeed’) or size
          (‘sra-max-scalarization-size-Osize’) respectively.

     ‘sra-max-propagations’
          The maximum number of artificial accesses that Scalar
          Replacement of Aggregates (SRA) will track, per one local
          variable, in order to facilitate copy propagation.

     ‘tm-max-aggregate-size’
          When making copies of thread-local variables in a transaction,
          this parameter specifies the size in bytes after which
          variables are saved with the logging functions as opposed to
          save/restore code sequence pairs.  This option only applies
          when using ‘-fgnu-tm’.

     ‘graphite-max-nb-scop-params’
          To avoid exponential effects in the Graphite loop transforms,
          the number of parameters in a Static Control Part (SCoP) is
          bounded.  A value of zero can be used to lift the bound.  A
          variable whose value is unknown at compilation time and
          defined outside a SCoP is a parameter of the SCoP.

     ‘loop-block-tile-size’
          Loop blocking or strip mining transforms, enabled with
          ‘-floop-block’ or ‘-floop-strip-mine’, strip mine each loop in
          the loop nest by a given number of iterations.  The strip
          length can be changed using the ‘loop-block-tile-size’
          parameter.

     ‘ipa-jump-function-lookups’
          Specifies number of statements visited during jump function
          offset discovery.

     ‘ipa-cp-value-list-size’
          IPA-CP attempts to track all possible values and types passed
          to a function's parameter in order to propagate them and
          perform devirtualization.  ‘ipa-cp-value-list-size’ is the
          maximum number of values and types it stores per one formal
          parameter of a function.

     ‘ipa-cp-eval-threshold’
          IPA-CP calculates its own score of cloning profitability
          heuristics and performs those cloning opportunities with
          scores that exceed ‘ipa-cp-eval-threshold’.

     ‘ipa-cp-max-recursive-depth’
          Maximum depth of recursive cloning for self-recursive
          function.

     ‘ipa-cp-min-recursive-probability’
          Recursive cloning only when the probability of call being
          executed exceeds the parameter.

     ‘ipa-cp-profile-count-base’
          When using ‘-fprofile-use’ option, IPA-CP will consider the
          measured execution count of a call graph edge at this
          percentage position in their histogram as the basis for its
          heuristics calculation.

     ‘ipa-cp-recursive-freq-factor’
          The number of times interprocedural copy propagation expects
          recursive functions to call themselves.

     ‘ipa-cp-recursion-penalty’
          Percentage penalty the recursive functions will receive when
          they are evaluated for cloning.

     ‘ipa-cp-single-call-penalty’
          Percentage penalty functions containing a single call to
          another function will receive when they are evaluated for
          cloning.

     ‘ipa-max-agg-items’
          IPA-CP is also capable to propagate a number of scalar values
          passed in an aggregate.  ‘ipa-max-agg-items’ controls the
          maximum number of such values per one parameter.

     ‘ipa-cp-loop-hint-bonus’
          When IPA-CP determines that a cloning candidate would make the
          number of iterations of a loop known, it adds a bonus of
          ‘ipa-cp-loop-hint-bonus’ to the profitability score of the
          candidate.

     ‘ipa-max-loop-predicates’
          The maximum number of different predicates IPA will use to
          describe when loops in a function have known properties.

     ‘ipa-max-aa-steps’
          During its analysis of function bodies, IPA-CP employs alias
          analysis in order to track values pointed to by function
          parameters.  In order not spend too much time analyzing huge
          functions, it gives up and consider all memory clobbered after
          examining ‘ipa-max-aa-steps’ statements modifying memory.

     ‘ipa-max-switch-predicate-bounds’
          Maximal number of boundary endpoints of case ranges of switch
          statement.  For switch exceeding this limit, IPA-CP will not
          construct cloning cost predicate, which is used to estimate
          cloning benefit, for default case of the switch statement.

     ‘ipa-max-param-expr-ops’
          IPA-CP will analyze conditional statement that references some
          function parameter to estimate benefit for cloning upon
          certain constant value.  But if number of operations in a
          parameter expression exceeds ‘ipa-max-param-expr-ops’, the
          expression is treated as complicated one, and is not handled
          by IPA analysis.

     ‘lto-partitions’
          Specify desired number of partitions produced during WHOPR
          compilation.  The number of partitions should exceed the
          number of CPUs used for compilation.

     ‘lto-min-partition’
          Size of minimal partition for WHOPR (in estimated
          instructions).  This prevents expenses of splitting very small
          programs into too many partitions.

     ‘lto-max-partition’
          Size of max partition for WHOPR (in estimated instructions).
          to provide an upper bound for individual size of partition.
          Meant to be used only with balanced partitioning.

     ‘lto-max-streaming-parallelism’
          Maximal number of parallel processes used for LTO streaming.

     ‘cxx-max-namespaces-for-diagnostic-help’
          The maximum number of namespaces to consult for suggestions
          when C++ name lookup fails for an identifier.

     ‘sink-frequency-threshold’
          The maximum relative execution frequency (in percents) of the
          target block relative to a statement's original block to allow
          statement sinking of a statement.  Larger numbers result in
          more aggressive statement sinking.  A small positive
          adjustment is applied for statements with memory operands as
          those are even more profitable so sink.

     ‘max-stores-to-sink’
          The maximum number of conditional store pairs that can be
          sunk.  Set to 0 if either vectorization (‘-ftree-vectorize’)
          or if-conversion (‘-ftree-loop-if-convert’) is disabled.

     ‘case-values-threshold’
          The smallest number of different values for which it is best
          to use a jump-table instead of a tree of conditional branches.
          If the value is 0, use the default for the machine.

     ‘jump-table-max-growth-ratio-for-size’
          The maximum code size growth ratio when expanding into a jump
          table (in percent).  The parameter is used when optimizing for
          size.

     ‘jump-table-max-growth-ratio-for-speed’
          The maximum code size growth ratio when expanding into a jump
          table (in percent).  The parameter is used when optimizing for
          speed.

     ‘tree-reassoc-width’
          Set the maximum number of instructions executed in parallel in
          reassociated tree.  This parameter overrides target dependent
          heuristics used by default if has non zero value.

     ‘sched-pressure-algorithm’
          Choose between the two available implementations of
          ‘-fsched-pressure’.  Algorithm 1 is the original
          implementation and is the more likely to prevent instructions
          from being reordered.  Algorithm 2 was designed to be a
          compromise between the relatively conservative approach taken
          by algorithm 1 and the rather aggressive approach taken by the
          default scheduler.  It relies more heavily on having a regular
          register file and accurate register pressure classes.  See
          ‘haifa-sched.cc’ in the GCC sources for more details.

          The default choice depends on the target.

     ‘max-slsr-cand-scan’
          Set the maximum number of existing candidates that are
          considered when seeking a basis for a new straight-line
          strength reduction candidate.

     ‘asan-globals’
          Enable buffer overflow detection for global objects.  This
          kind of protection is enabled by default if you are using
          ‘-fsanitize=address’ option.  To disable global objects
          protection use ‘--param asan-globals=0’.

     ‘asan-stack’
          Enable buffer overflow detection for stack objects.  This kind
          of protection is enabled by default when using
          ‘-fsanitize=address’.  To disable stack protection use
          ‘--param asan-stack=0’ option.

     ‘asan-instrument-reads’
          Enable buffer overflow detection for memory reads.  This kind
          of protection is enabled by default when using
          ‘-fsanitize=address’.  To disable memory reads protection use
          ‘--param asan-instrument-reads=0’.

     ‘asan-instrument-writes’
          Enable buffer overflow detection for memory writes.  This kind
          of protection is enabled by default when using
          ‘-fsanitize=address’.  To disable memory writes protection use
          ‘--param asan-instrument-writes=0’ option.

     ‘asan-memintrin’
          Enable detection for built-in functions.  This kind of
          protection is enabled by default when using
          ‘-fsanitize=address’.  To disable built-in functions
          protection use ‘--param asan-memintrin=0’.

     ‘asan-use-after-return’
          Enable detection of use-after-return.  This kind of protection
          is enabled by default when using the ‘-fsanitize=address’
          option.  To disable it use ‘--param asan-use-after-return=0’.

          Note: By default the check is disabled at run time.  To enable
          it, add ‘detect_stack_use_after_return=1’ to the environment
          variable ‘ASAN_OPTIONS’.

     ‘asan-instrumentation-with-call-threshold’
          If number of memory accesses in function being instrumented is
          greater or equal to this number, use callbacks instead of
          inline checks.  E.g.  to disable inline code use ‘--param
          asan-instrumentation-with-call-threshold=0’.

     ‘hwasan-instrument-stack’
          Enable hwasan instrumentation of statically sized
          stack-allocated variables.  This kind of instrumentation is
          enabled by default when using ‘-fsanitize=hwaddress’ and
          disabled by default when using ‘-fsanitize=kernel-hwaddress’.
          To disable stack instrumentation use ‘--param
          hwasan-instrument-stack=0’, and to enable it use ‘--param
          hwasan-instrument-stack=1’.

     ‘hwasan-random-frame-tag’
          When using stack instrumentation, decide tags for stack
          variables using a deterministic sequence beginning at a random
          tag for each frame.  With this parameter unset tags are chosen
          using the same sequence but beginning from 1.  This is enabled
          by default for ‘-fsanitize=hwaddress’ and unavailable for
          ‘-fsanitize=kernel-hwaddress’.  To disable it use ‘--param
          hwasan-random-frame-tag=0’.

     ‘hwasan-instrument-allocas’
          Enable hwasan instrumentation of dynamically sized
          stack-allocated variables.  This kind of instrumentation is
          enabled by default when using ‘-fsanitize=hwaddress’ and
          disabled by default when using ‘-fsanitize=kernel-hwaddress’.
          To disable instrumentation of such variables use ‘--param
          hwasan-instrument-allocas=0’, and to enable it use ‘--param
          hwasan-instrument-allocas=1’.

     ‘hwasan-instrument-reads’
          Enable hwasan checks on memory reads.  Instrumentation of
          reads is enabled by default for both ‘-fsanitize=hwaddress’
          and ‘-fsanitize=kernel-hwaddress’.  To disable checking memory
          reads use ‘--param hwasan-instrument-reads=0’.

     ‘hwasan-instrument-writes’
          Enable hwasan checks on memory writes.  Instrumentation of
          writes is enabled by default for both ‘-fsanitize=hwaddress’
          and ‘-fsanitize=kernel-hwaddress’.  To disable checking memory
          writes use ‘--param hwasan-instrument-writes=0’.

     ‘hwasan-instrument-mem-intrinsics’
          Enable hwasan instrumentation of builtin functions.
          Instrumentation of these builtin functions is enabled by
          default for both ‘-fsanitize=hwaddress’ and
          ‘-fsanitize=kernel-hwaddress’.  To disable instrumentation of
          builtin functions use ‘--param
          hwasan-instrument-mem-intrinsics=0’.

     ‘use-after-scope-direct-emission-threshold’
          If the size of a local variable in bytes is smaller or equal
          to this number, directly poison (or unpoison) shadow memory
          instead of using run-time callbacks.

     ‘tsan-distinguish-volatile’
          Emit special instrumentation for accesses to volatiles.

     ‘tsan-instrument-func-entry-exit’
          Emit instrumentation calls to __tsan_func_entry() and
          __tsan_func_exit().

     ‘max-fsm-thread-path-insns’
          Maximum number of instructions to copy when duplicating blocks
          on a finite state automaton jump thread path.

     ‘max-fsm-thread-length’
          Maximum number of basic blocks on a jump thread path.

     ‘threader-debug’
          threader-debug=[none|all] Enables verbose dumping of the
          threader solver.

     ‘parloops-chunk-size’
          Chunk size of omp schedule for loops parallelized by parloops.

     ‘parloops-schedule’
          Schedule type of omp schedule for loops parallelized by
          parloops (static, dynamic, guided, auto, runtime).

     ‘parloops-min-per-thread’
          The minimum number of iterations per thread of an innermost
          parallelized loop for which the parallelized variant is
          preferred over the single threaded one.  Note that for a
          parallelized loop nest the minimum number of iterations of the
          outermost loop per thread is two.

     ‘max-ssa-name-query-depth’
          Maximum depth of recursion when querying properties of SSA
          names in things like fold routines.  One level of recursion
          corresponds to following a use-def chain.

     ‘max-speculative-devirt-maydefs’
          The maximum number of may-defs we analyze when looking for a
          must-def specifying the dynamic type of an object that invokes
          a virtual call we may be able to devirtualize speculatively.

     ‘max-vrp-switch-assertions’
          The maximum number of assertions to add along the default edge
          of a switch statement during VRP.

     ‘evrp-sparse-threshold’
          Maximum number of basic blocks before EVRP uses a sparse
          cache.

     ‘evrp-mode’
          Specifies the mode Early VRP should operate in.

     ‘vrp1-mode’
          Specifies the mode VRP pass 1 should operate in.

     ‘vrp2-mode’
          Specifies the mode VRP pass 2 should operate in.

     ‘ranger-debug’
          Specifies the type of debug output to be issued for ranges.

     ‘evrp-switch-limit’
          Specifies the maximum number of switch cases before EVRP
          ignores a switch.

     ‘unroll-jam-min-percent’
          The minimum percentage of memory references that must be
          optimized away for the unroll-and-jam transformation to be
          considered profitable.

     ‘unroll-jam-max-unroll’
          The maximum number of times the outer loop should be unrolled
          by the unroll-and-jam transformation.

     ‘max-rtl-if-conversion-unpredictable-cost’
          Maximum permissible cost for the sequence that would be
          generated by the RTL if-conversion pass for a branch that is
          considered unpredictable.

     ‘max-variable-expansions-in-unroller’
          If ‘-fvariable-expansion-in-unroller’ is used, the maximum
          number of times that an individual variable will be expanded
          during loop unrolling.

     ‘partial-inlining-entry-probability’
          Maximum probability of the entry BB of split region (in
          percent relative to entry BB of the function) to make partial
          inlining happen.

     ‘max-tracked-strlens’
          Maximum number of strings for which strlen optimization pass
          will track string lengths.

     ‘gcse-after-reload-partial-fraction’
          The threshold ratio for performing partial redundancy
          elimination after reload.

     ‘gcse-after-reload-critical-fraction’
          The threshold ratio of critical edges execution count that
          permit performing redundancy elimination after reload.

     ‘max-loop-header-insns’
          The maximum number of insns in loop header duplicated by the
          copy loop headers pass.

     ‘vect-epilogues-nomask’
          Enable loop epilogue vectorization using smaller vector size.

     ‘vect-partial-vector-usage’
          Controls when the loop vectorizer considers using partial
          vector loads and stores as an alternative to falling back to
          scalar code.  0 stops the vectorizer from ever using partial
          vector loads and stores.  1 allows partial vector loads and
          stores if vectorization removes the need for the code to
          iterate.  2 allows partial vector loads and stores in all
          loops.  The parameter only has an effect on targets that
          support partial vector loads and stores.

     ‘vect-inner-loop-cost-factor’
          The maximum factor which the loop vectorizer applies to the
          cost of statements in an inner loop relative to the loop being
          vectorized.  The factor applied is the maximum of the
          estimated number of iterations of the inner loop and this
          parameter.  The default value of this parameter is 50.

     ‘vect-induction-float’
          Enable loop vectorization of floating point inductions.

     ‘avoid-fma-max-bits’
          Maximum number of bits for which we avoid creating FMAs.

     ‘sms-loop-average-count-threshold’
          A threshold on the average loop count considered by the swing
          modulo scheduler.

     ‘sms-dfa-history’
          The number of cycles the swing modulo scheduler considers when
          checking conflicts using DFA.

     ‘graphite-allow-codegen-errors’
          Whether codegen errors should be ICEs when ‘-fchecking’.

     ‘sms-max-ii-factor’
          A factor for tuning the upper bound that swing modulo
          scheduler uses for scheduling a loop.

     ‘lra-max-considered-reload-pseudos’
          The max number of reload pseudos which are considered during
          spilling a non-reload pseudo.

     ‘max-pow-sqrt-depth’
          Maximum depth of sqrt chains to use when synthesizing
          exponentiation by a real constant.

     ‘max-dse-active-local-stores’
          Maximum number of active local stores in RTL dead store
          elimination.

     ‘asan-instrument-allocas’
          Enable asan allocas/VLAs protection.

     ‘max-iterations-computation-cost’
          Bound on the cost of an expression to compute the number of
          iterations.

     ‘max-isl-operations’
          Maximum number of isl operations, 0 means unlimited.

     ‘graphite-max-arrays-per-scop’
          Maximum number of arrays per scop.

     ‘max-vartrack-reverse-op-size’
          Max.  size of loc list for which reverse ops should be added.

     ‘fsm-scale-path-stmts’
          Scale factor to apply to the number of statements in a
          threading path when comparing to the number of (scaled)
          blocks.

     ‘uninit-control-dep-attempts’
          Maximum number of nested calls to search for control
          dependencies during uninitialized variable analysis.

     ‘fsm-scale-path-blocks’
          Scale factor to apply to the number of blocks in a threading
          path when comparing to the number of (scaled) statements.

     ‘sched-autopref-queue-depth’
          Hardware autoprefetcher scheduler model control flag.  Number
          of lookahead cycles the model looks into; at ' ' only enable
          instruction sorting heuristic.

     ‘loop-versioning-max-inner-insns’
          The maximum number of instructions that an inner loop can have
          before the loop versioning pass considers it too big to copy.

     ‘loop-versioning-max-outer-insns’
          The maximum number of instructions that an outer loop can have
          before the loop versioning pass considers it too big to copy,
          discounting any instructions in inner loops that directly
          benefit from versioning.

     ‘ssa-name-def-chain-limit’
          The maximum number of SSA_NAME assignments to follow in
          determining a property of a variable such as its value.  This
          limits the number of iterations or recursive calls GCC
          performs when optimizing certain statements or when
          determining their validity prior to issuing diagnostics.

     ‘store-merging-max-size’
          Maximum size of a single store merging region in bytes.

     ‘hash-table-verification-limit’
          The number of elements for which hash table verification is
          done for each searched element.

     ‘max-find-base-term-values’
          Maximum number of VALUEs handled during a single
          find_base_term call.

     ‘analyzer-max-enodes-per-program-point’
          The maximum number of exploded nodes per program point within
          the analyzer, before terminating analysis of that point.

     ‘analyzer-max-constraints’
          The maximum number of constraints per state.

     ‘analyzer-min-snodes-for-call-summary’
          The minimum number of supernodes within a function for the
          analyzer to consider summarizing its effects at call sites.

     ‘analyzer-max-enodes-for-full-dump’
          The maximum depth of exploded nodes that should appear in a
          dot dump before switching to a less verbose format.

     ‘analyzer-max-recursion-depth’
          The maximum number of times a callsite can appear in a call
          stack within the analyzer, before terminating analysis of a
          call that would recurse deeper.

     ‘analyzer-max-svalue-depth’
          The maximum depth of a symbolic value, before approximating
          the value as unknown.

     ‘analyzer-max-infeasible-edges’
          The maximum number of infeasible edges to reject before
          declaring a diagnostic as infeasible.

     ‘gimple-fe-computed-hot-bb-threshold’
          The number of executions of a basic block which is considered
          hot.  The parameter is used only in GIMPLE FE.

     ‘analyzer-bb-explosion-factor’
          The maximum number of 'after supernode' exploded nodes within
          the analyzer per supernode, before terminating analysis.

     ‘ranger-logical-depth’
          Maximum depth of logical expression evaluation ranger will
          look through when evaluating outgoing edge ranges.

     ‘relation-block-limit’
          Maximum number of relations the oracle will register in a
          basic block.

     ‘min-pagesize’
          Minimum page size for warning purposes.

     ‘openacc-kernels’
          Specify mode of OpenACC 'kernels' constructs handling.  With
          ‘--param=openacc-kernels=decompose’, OpenACC 'kernels'
          constructs are decomposed into parts, a sequence of compute
          constructs, each then handled individually.  This is work in
          progress.  With ‘--param=openacc-kernels=parloops’, OpenACC
          'kernels' constructs are handled by the ‘parloops’ pass, en
          bloc.  This is the current default.

     ‘openacc-privatization’
          Specify mode of OpenACC privatization diagnostics for
          ‘-fopt-info-omp-note’ and applicable ‘-fdump-tree-*-details’.
          With ‘--param=openacc-privatization=quiet’, don't diagnose.
          This is the current default.  With
          ‘--param=openacc-privatization=noisy’, do diagnose.

     The following choices of NAME are available on AArch64 targets:

     ‘aarch64-sve-compare-costs’
          When vectorizing for SVE, consider using "unpacked" vectors
          for smaller elements and use the cost model to pick the
          cheapest approach.  Also use the cost model to choose between
          SVE and Advanced SIMD vectorization.

          Using unpacked vectors includes storing smaller elements in
          larger containers and accessing elements with extending loads
          and truncating stores.

     ‘aarch64-float-recp-precision’
          The number of Newton iterations for calculating the reciprocal
          for float type.  The precision of division is proportional to
          this param when division approximation is enabled.  The
          default value is 1.

     ‘aarch64-double-recp-precision’
          The number of Newton iterations for calculating the reciprocal
          for double type.  The precision of division is propotional to
          this param when division approximation is enabled.  The
          default value is 2.

     ‘aarch64-autovec-preference’
          Force an ISA selection strategy for auto-vectorization.
          Accepts values from 0 to 4, inclusive.
          ‘0’
               Use the default heuristics.
          ‘1’
               Use only Advanced SIMD for auto-vectorization.
          ‘2’
               Use only SVE for auto-vectorization.
          ‘3’
               Use both Advanced SIMD and SVE. Prefer Advanced SIMD when
               the costs are deemed equal.
          ‘4’
               Use both Advanced SIMD and SVE. Prefer SVE when the costs
               are deemed equal.
          The default value is 0.

     ‘aarch64-loop-vect-issue-rate-niters’
          The tuning for some AArch64 CPUs tries to take both latencies
          and issue rates into account when deciding whether a loop
          should be vectorized using SVE, vectorized using Advanced
          SIMD, or not vectorized at all.  If this parameter is set to
          N, GCC will not use this heuristic for loops that are known to
          execute in fewer than N Advanced SIMD iterations.

     ‘aarch64-vect-unroll-limit’
          The vectorizer will use available tuning information to
          determine whether it would be beneficial to unroll the main
          vectorized loop and by how much.  This parameter set's the
          upper bound of how much the vectorizer will unroll the main
          loop.  The default value is four.

     The following choices of NAME are available on i386 and x86_64
     targets:

     ‘x86-stlf-window-ninsns’
          Instructions number above which STFL stall penalty can be
          compensated.


File: gcc.info,  Node: Instrumentation Options,  Next: Preprocessor Options,  Prev: Optimize Options,  Up: Invoking GCC

3.12 Program Instrumentation Options
====================================

GCC supports a number of command-line options that control adding
run-time instrumentation to the code it normally generates.  For
example, one purpose of instrumentation is collect profiling statistics
for use in finding program hot spots, code coverage analysis, or
profile-guided optimizations.  Another class of program instrumentation
is adding run-time checking to detect programming errors like invalid
pointer dereferences or out-of-bounds array accesses, as well as
deliberately hostile attacks such as stack smashing or C++ vtable
hijacking.  There is also a general hook which can be used to implement
other forms of tracing or function-level instrumentation for debug or
program analysis purposes.

‘-p’
‘-pg’
     Generate extra code to write profile information suitable for the
     analysis program ‘prof’ (for ‘-p’) or ‘gprof’ (for ‘-pg’).  You
     must use this option when compiling the source files you want data
     about, and you must also use it when linking.

     You can use the function attribute ‘no_instrument_function’ to
     suppress profiling of individual functions when compiling with
     these options.  *Note Common Function Attributes::.

‘-fprofile-arcs’
     Add code so that program flow “arcs” are instrumented.  During
     execution the program records how many times each branch and call
     is executed and how many times it is taken or returns.  On targets
     that support constructors with priority support, profiling properly
     handles constructors, destructors and C++ constructors (and
     destructors) of classes which are used as a type of a global
     variable.

     When the compiled program exits it saves this data to a file called
     ‘AUXNAME.gcda’ for each source file.  The data may be used for
     profile-directed optimizations (‘-fbranch-probabilities’), or for
     test coverage analysis (‘-ftest-coverage’).  Each object file's
     AUXNAME is generated from the name of the output file, if
     explicitly specified and it is not the final executable, otherwise
     it is the basename of the source file.  In both cases any suffix is
     removed (e.g. ‘foo.gcda’ for input file ‘dir/foo.c’, or
     ‘dir/foo.gcda’ for output file specified as ‘-o dir/foo.o’).

     Note that if a command line directly links source files, the
     corresponding .GCDA files will be prefixed with the unsuffixed name
     of the output file.  E.g.  ‘gcc a.c b.c -o binary’ would generate
     ‘binary-a.gcda’ and ‘binary-b.gcda’ files.

     *Note Cross-profiling::.

‘--coverage’

     This option is used to compile and link code instrumented for
     coverage analysis.  The option is a synonym for ‘-fprofile-arcs’
     ‘-ftest-coverage’ (when compiling) and ‘-lgcov’ (when linking).
     See the documentation for those options for more details.

        • Compile the source files with ‘-fprofile-arcs’ plus
          optimization and code generation options.  For test coverage
          analysis, use the additional ‘-ftest-coverage’ option.  You do
          not need to profile every source file in a program.

        • Compile the source files additionally with
          ‘-fprofile-abs-path’ to create absolute path names in the
          ‘.gcno’ files.  This allows ‘gcov’ to find the correct sources
          in projects where compilations occur with different working
          directories.

        • Link your object files with ‘-lgcov’ or ‘-fprofile-arcs’ (the
          latter implies the former).

        • Run the program on a representative workload to generate the
          arc profile information.  This may be repeated any number of
          times.  You can run concurrent instances of your program, and
          provided that the file system supports locking, the data files
          will be correctly updated.  Unless a strict ISO C dialect
          option is in effect, ‘fork’ calls are detected and correctly
          handled without double counting.

          Moreover, an object file can be recompiled multiple times and
          the corresponding ‘.gcda’ file merges as long as the source
          file and the compiler options are unchanged.

        • For profile-directed optimizations, compile the source files
          again with the same optimization and code generation options
          plus ‘-fbranch-probabilities’ (*note Options that Control
          Optimization: Optimize Options.).

        • For test coverage analysis, use ‘gcov’ to produce human
          readable information from the ‘.gcno’ and ‘.gcda’ files.
          Refer to the ‘gcov’ documentation for further information.

     With ‘-fprofile-arcs’, for each function of your program GCC
     creates a program flow graph, then finds a spanning tree for the
     graph.  Only arcs that are not on the spanning tree have to be
     instrumented: the compiler adds code to count the number of times
     that these arcs are executed.  When an arc is the only exit or only
     entrance to a block, the instrumentation code can be added to the
     block; otherwise, a new basic block must be created to hold the
     instrumentation code.

‘-ftest-coverage’
     Produce a notes file that the ‘gcov’ code-coverage utility (*note
     ‘gcov’--a Test Coverage Program: Gcov.) can use to show program
     coverage.  Each source file's note file is called ‘AUXNAME.gcno’.
     Refer to the ‘-fprofile-arcs’ option above for a description of
     AUXNAME and instructions on how to generate test coverage data.
     Coverage data matches the source files more closely if you do not
     optimize.

‘-fprofile-abs-path’
     Automatically convert relative source file names to absolute path
     names in the ‘.gcno’ files.  This allows ‘gcov’ to find the correct
     sources in projects where compilations occur with different working
     directories.

‘-fprofile-dir=PATH’

     Set the directory to search for the profile data files in to PATH.
     This option affects only the profile data generated by
     ‘-fprofile-generate’, ‘-ftest-coverage’, ‘-fprofile-arcs’ and used
     by ‘-fprofile-use’ and ‘-fbranch-probabilities’ and its related
     options.  Both absolute and relative paths can be used.  By
     default, GCC uses the current directory as PATH, thus the profile
     data file appears in the same directory as the object file.  In
     order to prevent the file name clashing, if the object file name is
     not an absolute path, we mangle the absolute path of the
     ‘SOURCENAME.gcda’ file and use it as the file name of a ‘.gcda’
     file.  See details about the file naming in ‘-fprofile-arcs’.  See
     similar option ‘-fprofile-note’.

     When an executable is run in a massive parallel environment, it is
     recommended to save profile to different folders.  That can be done
     with variables in PATH that are exported during run-time:

     ‘%p’
          process ID.

     ‘%q{VAR}’
          value of environment variable VAR

‘-fprofile-generate’
‘-fprofile-generate=PATH’

     Enable options usually used for instrumenting application to
     produce profile useful for later recompilation with profile
     feedback based optimization.  You must use ‘-fprofile-generate’
     both when compiling and when linking your program.

     The following options are enabled: ‘-fprofile-arcs’,
     ‘-fprofile-values’, ‘-finline-functions’, and ‘-fipa-bit-cp’.

     If PATH is specified, GCC looks at the PATH to find the profile
     feedback data files.  See ‘-fprofile-dir’.

     To optimize the program based on the collected profile information,
     use ‘-fprofile-use’.  *Note Optimize Options::, for more
     information.

‘-fprofile-info-section’
‘-fprofile-info-section=NAME’

     Register the profile information in the specified section instead
     of using a constructor/destructor.  The section name is NAME if it
     is specified, otherwise the section name defaults to ‘.gcov_info’.
     A pointer to the profile information generated by ‘-fprofile-arcs’
     is placed in the specified section for each translation unit.  This
     option disables the profile information registration through a
     constructor and it disables the profile information processing
     through a destructor.  This option is not intended to be used in
     hosted environments such as GNU/Linux.  It targets free-standing
     environments (for example embedded systems) with limited resources
     which do not support constructors/destructors or the C library file
     I/O.

     The linker could collect the input sections in a continuous memory
     block and define start and end symbols.  A GNU linker script
     example which defines a linker output section follows:

            .gcov_info      :
            {
              PROVIDE (__gcov_info_start = .);
              KEEP (*(.gcov_info))
              PROVIDE (__gcov_info_end = .);
            }

     The program could dump the profiling information registered in this
     linker set for example like this:

          #include <gcov.h>
          #include <stdio.h>
          #include <stdlib.h>

          extern const struct gcov_info *__gcov_info_start[];
          extern const struct gcov_info *__gcov_info_end[];

          static void
          filename (const char *f, void *arg)
          {
            puts (f);
          }

          static void
          dump (const void *d, unsigned n, void *arg)
          {
            const unsigned char *c = d;

            for (unsigned i = 0; i < n; ++i)
              printf ("%02x", c[i]);
          }

          static void *
          allocate (unsigned length, void *arg)
          {
            return malloc (length);
          }

          static void
          dump_gcov_info (void)
          {
            const struct gcov_info **info = __gcov_info_start;
            const struct gcov_info **end = __gcov_info_end;

            /* Obfuscate variable to prevent compiler optimizations.  */
            __asm__ ("" : "+r" (info));

            while (info != end)
            {
              void *arg = NULL;
              __gcov_info_to_gcda (*info, filename, dump, allocate, arg);
              putchar ('\n');
              ++info;
            }
          }

          int
          main()
          {
            dump_gcov_info();
            return 0;
          }

‘-fprofile-note=PATH’

     If PATH is specified, GCC saves ‘.gcno’ file into PATH location.
     If you combine the option with multiple source files, the ‘.gcno’
     file will be overwritten.

‘-fprofile-prefix-path=PATH’

     This option can be used in combination with
     ‘profile-generate=’PROFILE_DIR and ‘profile-use=’PROFILE_DIR to
     inform GCC where is the base directory of built source tree.  By
     default PROFILE_DIR will contain files with mangled absolute paths
     of all object files in the built project.  This is not desirable
     when directory used to build the instrumented binary differs from
     the directory used to build the binary optimized with profile
     feedback because the profile data will not be found during the
     optimized build.  In such setups ‘-fprofile-prefix-path=’PATH with
     PATH pointing to the base directory of the build can be used to
     strip the irrelevant part of the path and keep all file names
     relative to the main build directory.

‘-fprofile-prefix-map=OLD=NEW’
     When compiling files residing in directory ‘OLD’, record profiling
     information (with ‘--coverage’) describing them as if the files
     resided in directory ‘NEW’ instead.  See also ‘-ffile-prefix-map’.

‘-fprofile-update=METHOD’

     Alter the update method for an application instrumented for profile
     feedback based optimization.  The METHOD argument should be one of
     ‘single’, ‘atomic’ or ‘prefer-atomic’.  The first one is useful for
     single-threaded applications, while the second one prevents profile
     corruption by emitting thread-safe code.

     *Warning:* When an application does not properly join all threads
     (or creates an detached thread), a profile file can be still
     corrupted.

     Using ‘prefer-atomic’ would be transformed either to ‘atomic’, when
     supported by a target, or to ‘single’ otherwise.  The GCC driver
     automatically selects ‘prefer-atomic’ when ‘-pthread’ is present in
     the command line.

‘-fprofile-filter-files=REGEX’

     Instrument only functions from files whose name matches any of the
     regular expressions (separated by semi-colons).

     For example, ‘-fprofile-filter-files=main\.c;module.*\.c’ will
     instrument only ‘main.c’ and all C files starting with 'module'.

‘-fprofile-exclude-files=REGEX’

     Instrument only functions from files whose name does not match any
     of the regular expressions (separated by semi-colons).

     For example, ‘-fprofile-exclude-files=/usr/.*’ will prevent
     instrumentation of all files that are located in the ‘/usr/’
     folder.

‘-fprofile-reproducible=[multithreaded|parallel-runs|serial]’
     Control level of reproducibility of profile gathered by
     ‘-fprofile-generate’.  This makes it possible to rebuild program
     with same outcome which is useful, for example, for distribution
     packages.

     With ‘-fprofile-reproducible=serial’ the profile gathered by
     ‘-fprofile-generate’ is reproducible provided the trained program
     behaves the same at each invocation of the train run, it is not
     multi-threaded and profile data streaming is always done in the
     same order.  Note that profile streaming happens at the end of
     program run but also before ‘fork’ function is invoked.

     Note that it is quite common that execution counts of some part of
     programs depends, for example, on length of temporary file names or
     memory space randomization (that may affect hash-table collision
     rate).  Such non-reproducible part of programs may be annotated by
     ‘no_instrument_function’ function attribute.  ‘gcov-dump’ with ‘-l’
     can be used to dump gathered data and verify that they are indeed
     reproducible.

     With ‘-fprofile-reproducible=parallel-runs’ collected profile stays
     reproducible regardless the order of streaming of the data into
     gcda files.  This setting makes it possible to run multiple
     instances of instrumented program in parallel (such as with ‘make
     -j’).  This reduces quality of gathered data, in particular of
     indirect call profiling.

‘-fsanitize=address’
     Enable AddressSanitizer, a fast memory error detector.  Memory
     access instructions are instrumented to detect out-of-bounds and
     use-after-free bugs.  The option enables
     ‘-fsanitize-address-use-after-scope’.  See
     <https://github.com/google/sanitizers/wiki/AddressSanitizer> for
     more details.  The run-time behavior can be influenced using the
     ‘ASAN_OPTIONS’ environment variable.  When set to ‘help=1’, the
     available options are shown at startup of the instrumented program.
     See
     <https://github.com/google/sanitizers/wiki/AddressSanitizerFlags#run-time-flags>
     for a list of supported options.  The option cannot be combined
     with ‘-fsanitize=thread’ or ‘-fsanitize=hwaddress’.  Note that the
     only target ‘-fsanitize=hwaddress’ is currently supported on is
     AArch64.

‘-fsanitize=kernel-address’
     Enable AddressSanitizer for Linux kernel.  See
     <https://github.com/google/kasan> for more details.

‘-fsanitize=hwaddress’
     Enable Hardware-assisted AddressSanitizer, which uses a hardware
     ability to ignore the top byte of a pointer to allow the detection
     of memory errors with a low memory overhead.  Memory access
     instructions are instrumented to detect out-of-bounds and
     use-after-free bugs.  The option enables
     ‘-fsanitize-address-use-after-scope’.  See
     <https://clang.llvm.org/docs/HardwareAssistedAddressSanitizerDesign.html>
     for more details.  The run-time behavior can be influenced using
     the ‘HWASAN_OPTIONS’ environment variable.  When set to ‘help=1’,
     the available options are shown at startup of the instrumented
     program.  The option cannot be combined with ‘-fsanitize=thread’ or
     ‘-fsanitize=address’, and is currently only available on AArch64.

‘-fsanitize=kernel-hwaddress’
     Enable Hardware-assisted AddressSanitizer for compilation of the
     Linux kernel.  Similar to ‘-fsanitize=kernel-address’ but using an
     alternate instrumentation method, and similar to
     ‘-fsanitize=hwaddress’ but with instrumentation differences
     necessary for compiling the Linux kernel.  These differences are to
     avoid hwasan library initialization calls and to account for the
     stack pointer having a different value in its top byte.

     _Note:_ This option has different defaults to the
     ‘-fsanitize=hwaddress’.  Instrumenting the stack and alloca calls
     are not on by default but are still possible by specifying the
     command-line options ‘--param hwasan-instrument-stack=1’ and
     ‘--param hwasan-instrument-allocas=1’ respectively.  Using a random
     frame tag is not implemented for kernel instrumentation.

‘-fsanitize=pointer-compare’
     Instrument comparison operation (<, <=, >, >=) with pointer
     operands.  The option must be combined with either
     ‘-fsanitize=kernel-address’ or ‘-fsanitize=address’ The option
     cannot be combined with ‘-fsanitize=thread’.  Note: By default the
     check is disabled at run time.  To enable it, add
     ‘detect_invalid_pointer_pairs=2’ to the environment variable
     ‘ASAN_OPTIONS’.  Using ‘detect_invalid_pointer_pairs=1’ detects
     invalid operation only when both pointers are non-null.

‘-fsanitize=pointer-subtract’
     Instrument subtraction with pointer operands.  The option must be
     combined with either ‘-fsanitize=kernel-address’ or
     ‘-fsanitize=address’ The option cannot be combined with
     ‘-fsanitize=thread’.  Note: By default the check is disabled at run
     time.  To enable it, add ‘detect_invalid_pointer_pairs=2’ to the
     environment variable ‘ASAN_OPTIONS’.  Using
     ‘detect_invalid_pointer_pairs=1’ detects invalid operation only
     when both pointers are non-null.

‘-fsanitize=shadow-call-stack’
     Enable ShadowCallStack, a security enhancement mechanism used to
     protect programs against return address overwrites (e.g.  stack
     buffer overflows.)  It works by saving a function's return address
     to a separately allocated shadow call stack in the function
     prologue and restoring the return address from the shadow call
     stack in the function epilogue.  Instrumentation only occurs in
     functions that need to save the return address to the stack.

     Currently it only supports the aarch64 platform.  It is
     specifically designed for linux kernels that enable the
     CONFIG_SHADOW_CALL_STACK option.  For the user space programs,
     runtime support is not currently provided in libc and libgcc.
     Users who want to use this feature in user space need to provide
     their own support for the runtime.  It should be noted that this
     may cause the ABI rules to be broken.

     On aarch64, the instrumentation makes use of the platform register
     ‘x18’.  This generally means that any code that may run on the same
     thread as code compiled with ShadowCallStack must be compiled with
     the flag ‘-ffixed-x18’, otherwise functions compiled without
     ‘-ffixed-x18’ might clobber ‘x18’ and so corrupt the shadow stack
     pointer.

     Also, because there is no userspace runtime support, code compiled
     with ShadowCallStack cannot use exception handling.  Use
     ‘-fno-exceptions’ to turn off exceptions.

     See <https://clang.llvm.org/docs/ShadowCallStack.html> for more
     details.

‘-fsanitize=thread’
     Enable ThreadSanitizer, a fast data race detector.  Memory access
     instructions are instrumented to detect data race bugs.  See
     <https://github.com/google/sanitizers/wiki#threadsanitizer> for
     more details.  The run-time behavior can be influenced using the
     ‘TSAN_OPTIONS’ environment variable; see
     <https://github.com/google/sanitizers/wiki/ThreadSanitizerFlags>
     for a list of supported options.  The option cannot be combined
     with ‘-fsanitize=address’, ‘-fsanitize=leak’.

     Note that sanitized atomic builtins cannot throw exceptions when
     operating on invalid memory addresses with non-call exceptions
     (‘-fnon-call-exceptions’).

‘-fsanitize=leak’
     Enable LeakSanitizer, a memory leak detector.  This option only
     matters for linking of executables and the executable is linked
     against a library that overrides ‘malloc’ and other allocator
     functions.  See
     <https://github.com/google/sanitizers/wiki/AddressSanitizerLeakSanitizer>
     for more details.  The run-time behavior can be influenced using
     the ‘LSAN_OPTIONS’ environment variable.  The option cannot be
     combined with ‘-fsanitize=thread’.

‘-fsanitize=undefined’
     Enable UndefinedBehaviorSanitizer, a fast undefined behavior
     detector.  Various computations are instrumented to detect
     undefined behavior at runtime.  See
     <https://clang.llvm.org/docs/UndefinedBehaviorSanitizer.html> for
     more details.  The run-time behavior can be influenced using the
     ‘UBSAN_OPTIONS’ environment variable.  Current suboptions are:

     ‘-fsanitize=shift’
          This option enables checking that the result of a shift
          operation is not undefined.  Note that what exactly is
          considered undefined differs slightly between C and C++, as
          well as between ISO C90 and C99, etc.  This option has two
          suboptions, ‘-fsanitize=shift-base’ and
          ‘-fsanitize=shift-exponent’.

     ‘-fsanitize=shift-exponent’
          This option enables checking that the second argument of a
          shift operation is not negative and is smaller than the
          precision of the promoted first argument.

     ‘-fsanitize=shift-base’
          If the second argument of a shift operation is within range,
          check that the result of a shift operation is not undefined.
          Note that what exactly is considered undefined differs
          slightly between C and C++, as well as between ISO C90 and
          C99, etc.

     ‘-fsanitize=integer-divide-by-zero’
          Detect integer division by zero.

     ‘-fsanitize=unreachable’
          With this option, the compiler turns the
          ‘__builtin_unreachable’ call into a diagnostics message call
          instead.  When reaching the ‘__builtin_unreachable’ call, the
          behavior is undefined.

     ‘-fsanitize=vla-bound’
          This option instructs the compiler to check that the size of a
          variable length array is positive.

     ‘-fsanitize=null’
          This option enables pointer checking.  Particularly, the
          application built with this option turned on will issue an
          error message when it tries to dereference a NULL pointer, or
          if a reference (possibly an rvalue reference) is bound to a
          NULL pointer, or if a method is invoked on an object pointed
          by a NULL pointer.

     ‘-fsanitize=return’
          This option enables return statement checking.  Programs built
          with this option turned on will issue an error message when
          the end of a non-void function is reached without actually
          returning a value.  This option works in C++ only.

     ‘-fsanitize=signed-integer-overflow’
          This option enables signed integer overflow checking.  We
          check that the result of ‘+’, ‘*’, and both unary and binary
          ‘-’ does not overflow in the signed arithmetics.  This also
          detects ‘INT_MIN / -1’ signed division.  Note, integer
          promotion rules must be taken into account.  That is, the
          following is not an overflow:
               signed char a = SCHAR_MAX;
               a++;

     ‘-fsanitize=bounds’
          This option enables instrumentation of array bounds.  Various
          out of bounds accesses are detected.  Flexible array members,
          flexible array member-like arrays, and initializers of
          variables with static storage are not instrumented.

     ‘-fsanitize=bounds-strict’
          This option enables strict instrumentation of array bounds.
          Most out of bounds accesses are detected, including flexible
          array members and flexible array member-like arrays.
          Initializers of variables with static storage are not
          instrumented.

     ‘-fsanitize=alignment’

          This option enables checking of alignment of pointers when
          they are dereferenced, or when a reference is bound to
          insufficiently aligned target, or when a method or constructor
          is invoked on insufficiently aligned object.

     ‘-fsanitize=object-size’
          This option enables instrumentation of memory references using
          the ‘__builtin_object_size’ function.  Various out of bounds
          pointer accesses are detected.

     ‘-fsanitize=float-divide-by-zero’
          Detect floating-point division by zero.  Unlike other similar
          options, ‘-fsanitize=float-divide-by-zero’ is not enabled by
          ‘-fsanitize=undefined’, since floating-point division by zero
          can be a legitimate way of obtaining infinities and NaNs.

     ‘-fsanitize=float-cast-overflow’
          This option enables floating-point type to integer conversion
          checking.  We check that the result of the conversion does not
          overflow.  Unlike other similar options,
          ‘-fsanitize=float-cast-overflow’ is not enabled by
          ‘-fsanitize=undefined’.  This option does not work well with
          ‘FE_INVALID’ exceptions enabled.

     ‘-fsanitize=nonnull-attribute’

          This option enables instrumentation of calls, checking whether
          null values are not passed to arguments marked as requiring a
          non-null value by the ‘nonnull’ function attribute.

     ‘-fsanitize=returns-nonnull-attribute’

          This option enables instrumentation of return statements in
          functions marked with ‘returns_nonnull’ function attribute, to
          detect returning of null values from such functions.

     ‘-fsanitize=bool’

          This option enables instrumentation of loads from bool.  If a
          value other than 0/1 is loaded, a run-time error is issued.

     ‘-fsanitize=enum’

          This option enables instrumentation of loads from an enum
          type.  If a value outside the range of values for the enum
          type is loaded, a run-time error is issued.

     ‘-fsanitize=vptr’

          This option enables instrumentation of C++ member function
          calls, member accesses and some conversions between pointers
          to base and derived classes, to verify the referenced object
          has the correct dynamic type.

     ‘-fsanitize=pointer-overflow’

          This option enables instrumentation of pointer arithmetics.
          If the pointer arithmetics overflows, a run-time error is
          issued.

     ‘-fsanitize=builtin’

          This option enables instrumentation of arguments to selected
          builtin functions.  If an invalid value is passed to such
          arguments, a run-time error is issued.  E.g. passing 0 as the
          argument to ‘__builtin_ctz’ or ‘__builtin_clz’ invokes
          undefined behavior and is diagnosed by this option.

     While ‘-ftrapv’ causes traps for signed overflows to be emitted,
     ‘-fsanitize=undefined’ gives a diagnostic message.  This currently
     works only for the C family of languages.

‘-fno-sanitize=all’

     This option disables all previously enabled sanitizers.
     ‘-fsanitize=all’ is not allowed, as some sanitizers cannot be used
     together.

‘-fasan-shadow-offset=NUMBER’
     This option forces GCC to use custom shadow offset in
     AddressSanitizer checks.  It is useful for experimenting with
     different shadow memory layouts in Kernel AddressSanitizer.

‘-fsanitize-sections=S1,S2,...’
     Sanitize global variables in selected user-defined sections.  SI
     may contain wildcards.

‘-fsanitize-recover[=OPTS]’
     ‘-fsanitize-recover=’ controls error recovery mode for sanitizers
     mentioned in comma-separated list of OPTS.  Enabling this option
     for a sanitizer component causes it to attempt to continue running
     the program as if no error happened.  This means multiple runtime
     errors can be reported in a single program run, and the exit code
     of the program may indicate success even when errors have been
     reported.  The ‘-fno-sanitize-recover=’ option can be used to alter
     this behavior: only the first detected error is reported and
     program then exits with a non-zero exit code.

     Currently this feature only works for ‘-fsanitize=undefined’ (and
     its suboptions except for ‘-fsanitize=unreachable’ and
     ‘-fsanitize=return’), ‘-fsanitize=float-cast-overflow’,
     ‘-fsanitize=float-divide-by-zero’, ‘-fsanitize=bounds-strict’,
     ‘-fsanitize=kernel-address’ and ‘-fsanitize=address’.  For these
     sanitizers error recovery is turned on by default, except
     ‘-fsanitize=address’, for which this feature is experimental.
     ‘-fsanitize-recover=all’ and ‘-fno-sanitize-recover=all’ is also
     accepted, the former enables recovery for all sanitizers that
     support it, the latter disables recovery for all sanitizers that
     support it.

     Even if a recovery mode is turned on the compiler side, it needs to
     be also enabled on the runtime library side, otherwise the failures
     are still fatal.  The runtime library defaults to ‘halt_on_error=0’
     for ThreadSanitizer and UndefinedBehaviorSanitizer, while default
     value for AddressSanitizer is ‘halt_on_error=1’.  This can be
     overridden through setting the ‘halt_on_error’ flag in the
     corresponding environment variable.

     Syntax without an explicit OPTS parameter is deprecated.  It is
     equivalent to specifying an OPTS list of:

          undefined,float-cast-overflow,float-divide-by-zero,bounds-strict

‘-fsanitize-address-use-after-scope’
     Enable sanitization of local variables to detect use-after-scope
     bugs.  The option sets ‘-fstack-reuse’ to ‘none’.

‘-fsanitize-undefined-trap-on-error’
     The ‘-fsanitize-undefined-trap-on-error’ option instructs the
     compiler to report undefined behavior using ‘__builtin_trap’ rather
     than a ‘libubsan’ library routine.  The advantage of this is that
     the ‘libubsan’ library is not needed and is not linked in, so this
     is usable even in freestanding environments.

‘-fsanitize-coverage=trace-pc’
     Enable coverage-guided fuzzing code instrumentation.  Inserts a
     call to ‘__sanitizer_cov_trace_pc’ into every basic block.

‘-fsanitize-coverage=trace-cmp’
     Enable dataflow guided fuzzing code instrumentation.  Inserts a
     call to ‘__sanitizer_cov_trace_cmp1’, ‘__sanitizer_cov_trace_cmp2’,
     ‘__sanitizer_cov_trace_cmp4’ or ‘__sanitizer_cov_trace_cmp8’ for
     integral comparison with both operands variable or
     ‘__sanitizer_cov_trace_const_cmp1’,
     ‘__sanitizer_cov_trace_const_cmp2’,
     ‘__sanitizer_cov_trace_const_cmp4’ or
     ‘__sanitizer_cov_trace_const_cmp8’ for integral comparison with one
     operand constant, ‘__sanitizer_cov_trace_cmpf’ or
     ‘__sanitizer_cov_trace_cmpd’ for float or double comparisons and
     ‘__sanitizer_cov_trace_switch’ for switch statements.

‘-fcf-protection=[full|branch|return|none|check]’
     Enable code instrumentation of control-flow transfers to increase
     program security by checking that target addresses of control-flow
     transfer instructions (such as indirect function call, function
     return, indirect jump) are valid.  This prevents diverting the flow
     of control to an unexpected target.  This is intended to protect
     against such threats as Return-oriented Programming (ROP), and
     similarly call/jmp-oriented programming (COP/JOP).

     The value ‘branch’ tells the compiler to implement checking of
     validity of control-flow transfer at the point of indirect branch
     instructions, i.e. call/jmp instructions.  The value ‘return’
     implements checking of validity at the point of returning from a
     function.  The value ‘full’ is an alias for specifying both
     ‘branch’ and ‘return’.  The value ‘none’ turns off instrumentation.

     The value ‘check’ is used for the final link with link-time
     optimization (LTO). An error is issued if LTO object files are
     compiled with different ‘-fcf-protection’ values.  The value
     ‘check’ is ignored at the compile time.

     The macro ‘__CET__’ is defined when ‘-fcf-protection’ is used.  The
     first bit of ‘__CET__’ is set to 1 for the value ‘branch’ and the
     second bit of ‘__CET__’ is set to 1 for the ‘return’.

     You can also use the ‘nocf_check’ attribute to identify which
     functions and calls should be skipped from instrumentation (*note
     Function Attributes::).

     Currently the x86 GNU/Linux target provides an implementation based
     on Intel Control-flow Enforcement Technology (CET) which works for
     i686 processor or newer.

‘-fharden-compares’
     For every logical test that survives gimple optimizations and is
     _not_ the condition in a conditional branch (for example,
     conditions tested for conditional moves, or to store in boolean
     variables), emit extra code to compute and verify the reversed
     condition, and to call ‘__builtin_trap’ if the results do not
     match.  Use with ‘-fharden-conditional-branches’ to cover all
     conditionals.

‘-fharden-conditional-branches’
     For every non-vectorized conditional branch that survives gimple
     optimizations, emit extra code to compute and verify the reversed
     condition, and to call ‘__builtin_trap’ if the result is
     unexpected.  Use with ‘-fharden-compares’ to cover all
     conditionals.

‘-fstack-protector’
     Emit extra code to check for buffer overflows, such as stack
     smashing attacks.  This is done by adding a guard variable to
     functions with vulnerable objects.  This includes functions that
     call ‘alloca’, and functions with buffers larger than or equal to 8
     bytes.  The guards are initialized when a function is entered and
     then checked when the function exits.  If a guard check fails, an
     error message is printed and the program exits.  Only variables
     that are actually allocated on the stack are considered, optimized
     away variables or variables allocated in registers don't count.

‘-fstack-protector-all’
     Like ‘-fstack-protector’ except that all functions are protected.

‘-fstack-protector-strong’
     Like ‘-fstack-protector’ but includes additional functions to be
     protected -- those that have local array definitions, or have
     references to local frame addresses.  Only variables that are
     actually allocated on the stack are considered, optimized away
     variables or variables allocated in registers don't count.

‘-fstack-protector-explicit’
     Like ‘-fstack-protector’ but only protects those functions which
     have the ‘stack_protect’ attribute.

‘-fstack-check’
     Generate code to verify that you do not go beyond the boundary of
     the stack.  You should specify this flag if you are running in an
     environment with multiple threads, but you only rarely need to
     specify it in a single-threaded environment since stack overflow is
     automatically detected on nearly all systems if there is only one
     stack.

     Note that this switch does not actually cause checking to be done;
     the operating system or the language runtime must do that.  The
     switch causes generation of code to ensure that they see the stack
     being extended.

     You can additionally specify a string parameter: ‘no’ means no
     checking, ‘generic’ means force the use of old-style checking,
     ‘specific’ means use the best checking method and is equivalent to
     bare ‘-fstack-check’.

     Old-style checking is a generic mechanism that requires no specific
     target support in the compiler but comes with the following
     drawbacks:

       1. Modified allocation strategy for large objects: they are
          always allocated dynamically if their size exceeds a fixed
          threshold.  Note this may change the semantics of some code.

       2. Fixed limit on the size of the static frame of functions: when
          it is topped by a particular function, stack checking is not
          reliable and a warning is issued by the compiler.

       3. Inefficiency: because of both the modified allocation strategy
          and the generic implementation, code performance is hampered.

     Note that old-style stack checking is also the fallback method for
     ‘specific’ if no target support has been added in the compiler.

     ‘-fstack-check=’ is designed for Ada's needs to detect infinite
     recursion and stack overflows.  ‘specific’ is an excellent choice
     when compiling Ada code.  It is not generally sufficient to protect
     against stack-clash attacks.  To protect against those you want
     ‘-fstack-clash-protection’.

‘-fstack-clash-protection’
     Generate code to prevent stack clash style attacks.  When this
     option is enabled, the compiler will only allocate one page of
     stack space at a time and each page is accessed immediately after
     allocation.  Thus, it prevents allocations from jumping over any
     stack guard page provided by the operating system.

     Most targets do not fully support stack clash protection.  However,
     on those targets ‘-fstack-clash-protection’ will protect dynamic
     stack allocations.  ‘-fstack-clash-protection’ may also provide
     limited protection for static stack allocations if the target
     supports ‘-fstack-check=specific’.

‘-fstack-limit-register=REG’
‘-fstack-limit-symbol=SYM’
‘-fno-stack-limit’
     Generate code to ensure that the stack does not grow beyond a
     certain value, either the value of a register or the address of a
     symbol.  If a larger stack is required, a signal is raised at run
     time.  For most targets, the signal is raised before the stack
     overruns the boundary, so it is possible to catch the signal
     without taking special precautions.

     For instance, if the stack starts at absolute address ‘0x80000000’
     and grows downwards, you can use the flags
     ‘-fstack-limit-symbol=__stack_limit’ and
     ‘-Wl,--defsym,__stack_limit=0x7ffe0000’ to enforce a stack limit of
     128KB.  Note that this may only work with the GNU linker.

     You can locally override stack limit checking by using the
     ‘no_stack_limit’ function attribute (*note Function Attributes::).

‘-fsplit-stack’
     Generate code to automatically split the stack before it overflows.
     The resulting program has a discontiguous stack which can only
     overflow if the program is unable to allocate any more memory.
     This is most useful when running threaded programs, as it is no
     longer necessary to calculate a good stack size to use for each
     thread.  This is currently only implemented for the x86 targets
     running GNU/Linux.

     When code compiled with ‘-fsplit-stack’ calls code compiled without
     ‘-fsplit-stack’, there may not be much stack space available for
     the latter code to run.  If compiling all code, including library
     code, with ‘-fsplit-stack’ is not an option, then the linker can
     fix up these calls so that the code compiled without
     ‘-fsplit-stack’ always has a large stack.  Support for this is
     implemented in the gold linker in GNU binutils release 2.21 and
     later.

‘-fvtable-verify=[std|preinit|none]’
     This option is only available when compiling C++ code.  It turns on
     (or off, if using ‘-fvtable-verify=none’) the security feature that
     verifies at run time, for every virtual call, that the vtable
     pointer through which the call is made is valid for the type of the
     object, and has not been corrupted or overwritten.  If an invalid
     vtable pointer is detected at run time, an error is reported and
     execution of the program is immediately halted.

     This option causes run-time data structures to be built at program
     startup, which are used for verifying the vtable pointers.  The
     options ‘std’ and ‘preinit’ control the timing of when these data
     structures are built.  In both cases the data structures are built
     before execution reaches ‘main’.  Using ‘-fvtable-verify=std’
     causes the data structures to be built after shared libraries have
     been loaded and initialized.  ‘-fvtable-verify=preinit’ causes them
     to be built before shared libraries have been loaded and
     initialized.

     If this option appears multiple times in the command line with
     different values specified, ‘none’ takes highest priority over both
     ‘std’ and ‘preinit’; ‘preinit’ takes priority over ‘std’.

‘-fvtv-debug’
     When used in conjunction with ‘-fvtable-verify=std’ or
     ‘-fvtable-verify=preinit’, causes debug versions of the runtime
     functions for the vtable verification feature to be called.  This
     flag also causes the compiler to log information about which vtable
     pointers it finds for each class.  This information is written to a
     file named ‘vtv_set_ptr_data.log’ in the directory named by the
     environment variable ‘VTV_LOGS_DIR’ if that is defined or the
     current working directory otherwise.

     Note: This feature _appends_ data to the log file.  If you want a
     fresh log file, be sure to delete any existing one.

‘-fvtv-counts’
     This is a debugging flag.  When used in conjunction with
     ‘-fvtable-verify=std’ or ‘-fvtable-verify=preinit’, this causes the
     compiler to keep track of the total number of virtual calls it
     encounters and the number of verifications it inserts.  It also
     counts the number of calls to certain run-time library functions
     that it inserts and logs this information for each compilation
     unit.  The compiler writes this information to a file named
     ‘vtv_count_data.log’ in the directory named by the environment
     variable ‘VTV_LOGS_DIR’ if that is defined or the current working
     directory otherwise.  It also counts the size of the vtable pointer
     sets for each class, and writes this information to
     ‘vtv_class_set_sizes.log’ in the same directory.

     Note: This feature _appends_ data to the log files.  To get fresh
     log files, be sure to delete any existing ones.

‘-finstrument-functions’
     Generate instrumentation calls for entry and exit to functions.
     Just after function entry and just before function exit, the
     following profiling functions are called with the address of the
     current function and its call site.  (On some platforms,
     ‘__builtin_return_address’ does not work beyond the current
     function, so the call site information may not be available to the
     profiling functions otherwise.)

          void __cyg_profile_func_enter (void *this_fn,
                                         void *call_site);
          void __cyg_profile_func_exit  (void *this_fn,
                                         void *call_site);

     The first argument is the address of the start of the current
     function, which may be looked up exactly in the symbol table.

     This instrumentation is also done for functions expanded inline in
     other functions.  The profiling calls indicate where, conceptually,
     the inline function is entered and exited.  This means that
     addressable versions of such functions must be available.  If all
     your uses of a function are expanded inline, this may mean an
     additional expansion of code size.  If you use ‘extern inline’ in
     your C code, an addressable version of such functions must be
     provided.  (This is normally the case anyway, but if you get lucky
     and the optimizer always expands the functions inline, you might
     have gotten away without providing static copies.)

     A function may be given the attribute ‘no_instrument_function’, in
     which case this instrumentation is not done.  This can be used, for
     example, for the profiling functions listed above, high-priority
     interrupt routines, and any functions from which the profiling
     functions cannot safely be called (perhaps signal handlers, if the
     profiling routines generate output or allocate memory).  *Note
     Common Function Attributes::.

‘-finstrument-functions-exclude-file-list=FILE,FILE,...’

     Set the list of functions that are excluded from instrumentation
     (see the description of ‘-finstrument-functions’).  If the file
     that contains a function definition matches with one of FILE, then
     that function is not instrumented.  The match is done on
     substrings: if the FILE parameter is a substring of the file name,
     it is considered to be a match.

     For example:

          -finstrument-functions-exclude-file-list=/bits/stl,include/sys

     excludes any inline function defined in files whose pathnames
     contain ‘/bits/stl’ or ‘include/sys’.

     If, for some reason, you want to include letter ‘,’ in one of SYM,
     write ‘\,’.  For example,
     ‘-finstrument-functions-exclude-file-list='\,\,tmp'’ (note the
     single quote surrounding the option).

‘-finstrument-functions-exclude-function-list=SYM,SYM,...’

     This is similar to ‘-finstrument-functions-exclude-file-list’, but
     this option sets the list of function names to be excluded from
     instrumentation.  The function name to be matched is its
     user-visible name, such as ‘vector<int> blah(const vector<int> &)’,
     not the internal mangled name (e.g., ‘_Z4blahRSt6vectorIiSaIiEE’).
     The match is done on substrings: if the SYM parameter is a
     substring of the function name, it is considered to be a match.
     For C99 and C++ extended identifiers, the function name must be
     given in UTF-8, not using universal character names.

‘-fpatchable-function-entry=N[,M]’
     Generate N NOPs right at the beginning of each function, with the
     function entry point before the Mth NOP. If M is omitted, it
     defaults to ‘0’ so the function entry points to the address just at
     the first NOP. The NOP instructions reserve extra space which can
     be used to patch in any desired instrumentation at run time,
     provided that the code segment is writable.  The amount of space is
     controllable indirectly via the number of NOPs; the NOP instruction
     used corresponds to the instruction emitted by the internal GCC
     back-end interface ‘gen_nop’.  This behavior is target-specific and
     may also depend on the architecture variant and/or other
     compilation options.

     For run-time identification, the starting addresses of these areas,
     which correspond to their respective function entries minus M, are
     additionally collected in the ‘__patchable_function_entries’
     section of the resulting binary.

     Note that the value of ‘__attribute__ ((patchable_function_entry
     (N,M)))’ takes precedence over command-line option
     ‘-fpatchable-function-entry=N,M’.  This can be used to increase the
     area size or to remove it completely on a single function.  If
     ‘N=0’, no pad location is recorded.

     The NOP instructions are inserted at--and maybe before, depending
     on M--the function entry address, even before the prologue.

     The maximum value of N and M is 65535.


File: gcc.info,  Node: Preprocessor Options,  Next: Assembler Options,  Prev: Instrumentation Options,  Up: Invoking GCC

3.13 Options Controlling the Preprocessor
=========================================

These options control the C preprocessor, which is run on each C source
file before actual compilation.

 If you use the ‘-E’ option, nothing is done except preprocessing.  Some
of these options make sense only together with ‘-E’ because they cause
the preprocessor output to be unsuitable for actual compilation.

 In addition to the options listed here, there are a number of options
to control search paths for include files documented in *note Directory
Options::.  Options to control preprocessor diagnostics are listed in
*note Warning Options::.

‘-D NAME’
     Predefine NAME as a macro, with definition ‘1’.

‘-D NAME=DEFINITION’
     The contents of DEFINITION are tokenized and processed as if they
     appeared during translation phase three in a ‘#define’ directive.
     In particular, the definition is truncated by embedded newline
     characters.

     If you are invoking the preprocessor from a shell or shell-like
     program you may need to use the shell's quoting syntax to protect
     characters such as spaces that have a meaning in the shell syntax.

     If you wish to define a function-like macro on the command line,
     write its argument list with surrounding parentheses before the
     equals sign (if any).  Parentheses are meaningful to most shells,
     so you should quote the option.  With ‘sh’ and ‘csh’,
     ‘-D'NAME(ARGS...)=DEFINITION'’ works.

     ‘-D’ and ‘-U’ options are processed in the order they are given on
     the command line.  All ‘-imacros FILE’ and ‘-include FILE’ options
     are processed after all ‘-D’ and ‘-U’ options.

‘-U NAME’
     Cancel any previous definition of NAME, either built in or provided
     with a ‘-D’ option.

‘-include FILE’
     Process FILE as if ‘#include "file"’ appeared as the first line of
     the primary source file.  However, the first directory searched for
     FILE is the preprocessor's working directory _instead of_ the
     directory containing the main source file.  If not found there, it
     is searched for in the remainder of the ‘#include "..."’ search
     chain as normal.

     If multiple ‘-include’ options are given, the files are included in
     the order they appear on the command line.

‘-imacros FILE’
     Exactly like ‘-include’, except that any output produced by
     scanning FILE is thrown away.  Macros it defines remain defined.
     This allows you to acquire all the macros from a header without
     also processing its declarations.

     All files specified by ‘-imacros’ are processed before all files
     specified by ‘-include’.

‘-undef’
     Do not predefine any system-specific or GCC-specific macros.  The
     standard predefined macros remain defined.

‘-pthread’
     Define additional macros required for using the POSIX threads
     library.  You should use this option consistently for both
     compilation and linking.  This option is supported on GNU/Linux
     targets, most other Unix derivatives, and also on x86 Cygwin and
     MinGW targets.

‘-M’
     Instead of outputting the result of preprocessing, output a rule
     suitable for ‘make’ describing the dependencies of the main source
     file.  The preprocessor outputs one ‘make’ rule containing the
     object file name for that source file, a colon, and the names of
     all the included files, including those coming from ‘-include’ or
     ‘-imacros’ command-line options.

     Unless specified explicitly (with ‘-MT’ or ‘-MQ’), the object file
     name consists of the name of the source file with any suffix
     replaced with object file suffix and with any leading directory
     parts removed.  If there are many included files then the rule is
     split into several lines using ‘\’-newline.  The rule has no
     commands.

     This option does not suppress the preprocessor's debug output, such
     as ‘-dM’.  To avoid mixing such debug output with the dependency
     rules you should explicitly specify the dependency output file with
     ‘-MF’, or use an environment variable like ‘DEPENDENCIES_OUTPUT’
     (*note Environment Variables::).  Debug output is still sent to the
     regular output stream as normal.

     Passing ‘-M’ to the driver implies ‘-E’, and suppresses warnings
     with an implicit ‘-w’.

‘-MM’
     Like ‘-M’ but do not mention header files that are found in system
     header directories, nor header files that are included, directly or
     indirectly, from such a header.

     This implies that the choice of angle brackets or double quotes in
     an ‘#include’ directive does not in itself determine whether that
     header appears in ‘-MM’ dependency output.

‘-MF FILE’
     When used with ‘-M’ or ‘-MM’, specifies a file to write the
     dependencies to.  If no ‘-MF’ switch is given the preprocessor
     sends the rules to the same place it would send preprocessed
     output.

     When used with the driver options ‘-MD’ or ‘-MMD’, ‘-MF’ overrides
     the default dependency output file.

     If FILE is ‘-’, then the dependencies are written to ‘stdout’.

‘-MG’
     In conjunction with an option such as ‘-M’ requesting dependency
     generation, ‘-MG’ assumes missing header files are generated files
     and adds them to the dependency list without raising an error.  The
     dependency filename is taken directly from the ‘#include’ directive
     without prepending any path.  ‘-MG’ also suppresses preprocessed
     output, as a missing header file renders this useless.

     This feature is used in automatic updating of makefiles.

‘-Mno-modules’
     Disable dependency generation for compiled module interfaces.

‘-MP’
     This option instructs CPP to add a phony target for each dependency
     other than the main file, causing each to depend on nothing.  These
     dummy rules work around errors ‘make’ gives if you remove header
     files without updating the ‘Makefile’ to match.

     This is typical output:

          test.o: test.c test.h

          test.h:

‘-MT TARGET’

     Change the target of the rule emitted by dependency generation.  By
     default CPP takes the name of the main input file, deletes any
     directory components and any file suffix such as ‘.c’, and appends
     the platform's usual object suffix.  The result is the target.

     An ‘-MT’ option sets the target to be exactly the string you
     specify.  If you want multiple targets, you can specify them as a
     single argument to ‘-MT’, or use multiple ‘-MT’ options.

     For example, ‘-MT '$(objpfx)foo.o'’ might give

          $(objpfx)foo.o: foo.c

‘-MQ TARGET’

     Same as ‘-MT’, but it quotes any characters which are special to
     Make.  ‘-MQ '$(objpfx)foo.o'’ gives

          $$(objpfx)foo.o: foo.c

     The default target is automatically quoted, as if it were given
     with ‘-MQ’.

‘-MD’
     ‘-MD’ is equivalent to ‘-M -MF FILE’, except that ‘-E’ is not
     implied.  The driver determines FILE based on whether an ‘-o’
     option is given.  If it is, the driver uses its argument but with a
     suffix of ‘.d’, otherwise it takes the name of the input file,
     removes any directory components and suffix, and applies a ‘.d’
     suffix.

     If ‘-MD’ is used in conjunction with ‘-E’, any ‘-o’ switch is
     understood to specify the dependency output file (*note -MF:
     dashMF.), but if used without ‘-E’, each ‘-o’ is understood to
     specify a target object file.

     Since ‘-E’ is not implied, ‘-MD’ can be used to generate a
     dependency output file as a side effect of the compilation process.

‘-MMD’
     Like ‘-MD’ except mention only user header files, not system header
     files.

‘-fpreprocessed’
     Indicate to the preprocessor that the input file has already been
     preprocessed.  This suppresses things like macro expansion,
     trigraph conversion, escaped newline splicing, and processing of
     most directives.  The preprocessor still recognizes and removes
     comments, so that you can pass a file preprocessed with ‘-C’ to the
     compiler without problems.  In this mode the integrated
     preprocessor is little more than a tokenizer for the front ends.

     ‘-fpreprocessed’ is implicit if the input file has one of the
     extensions ‘.i’, ‘.ii’ or ‘.mi’.  These are the extensions that GCC
     uses for preprocessed files created by ‘-save-temps’.

‘-fdirectives-only’
     When preprocessing, handle directives, but do not expand macros.

     The option's behavior depends on the ‘-E’ and ‘-fpreprocessed’
     options.

     With ‘-E’, preprocessing is limited to the handling of directives
     such as ‘#define’, ‘#ifdef’, and ‘#error’.  Other preprocessor
     operations, such as macro expansion and trigraph conversion are not
     performed.  In addition, the ‘-dD’ option is implicitly enabled.

     With ‘-fpreprocessed’, predefinition of command line and most
     builtin macros is disabled.  Macros such as ‘__LINE__’, which are
     contextually dependent, are handled normally.  This enables
     compilation of files previously preprocessed with ‘-E
     -fdirectives-only’.

     With both ‘-E’ and ‘-fpreprocessed’, the rules for ‘-fpreprocessed’
     take precedence.  This enables full preprocessing of files
     previously preprocessed with ‘-E -fdirectives-only’.

‘-fdollars-in-identifiers’
     Accept ‘$’ in identifiers.

‘-fextended-identifiers’
     Accept universal character names and extended characters in
     identifiers.  This option is enabled by default for C99 (and later
     C standard versions) and C++.

‘-fno-canonical-system-headers’
     When preprocessing, do not shorten system header paths with
     canonicalization.

‘-fmax-include-depth=DEPTH’
     Set the maximum depth of the nested #include.  The default is 200.

‘-ftabstop=WIDTH’
     Set the distance between tab stops.  This helps the preprocessor
     report correct column numbers in warnings or errors, even if tabs
     appear on the line.  If the value is less than 1 or greater than
     100, the option is ignored.  The default is 8.

‘-ftrack-macro-expansion[=LEVEL]’
     Track locations of tokens across macro expansions.  This allows the
     compiler to emit diagnostic about the current macro expansion stack
     when a compilation error occurs in a macro expansion.  Using this
     option makes the preprocessor and the compiler consume more memory.
     The LEVEL parameter can be used to choose the level of precision of
     token location tracking thus decreasing the memory consumption if
     necessary.  Value ‘0’ of LEVEL de-activates this option.  Value ‘1’
     tracks tokens locations in a degraded mode for the sake of minimal
     memory overhead.  In this mode all tokens resulting from the
     expansion of an argument of a function-like macro have the same
     location.  Value ‘2’ tracks tokens locations completely.  This
     value is the most memory hungry.  When this option is given no
     argument, the default parameter value is ‘2’.

     Note that ‘-ftrack-macro-expansion=2’ is activated by default.

‘-fmacro-prefix-map=OLD=NEW’
     When preprocessing files residing in directory ‘OLD’, expand the
     ‘__FILE__’ and ‘__BASE_FILE__’ macros as if the files resided in
     directory ‘NEW’ instead.  This can be used to change an absolute
     path to a relative path by using ‘.’ for NEW which can result in
     more reproducible builds that are location independent.  This
     option also affects ‘__builtin_FILE()’ during compilation.  See
     also ‘-ffile-prefix-map’.

‘-fexec-charset=CHARSET’
     Set the execution character set, used for string and character
     constants.  The default is UTF-8.  CHARSET can be any encoding
     supported by the system's ‘iconv’ library routine.

‘-fwide-exec-charset=CHARSET’
     Set the wide execution character set, used for wide string and
     character constants.  The default is UTF-32 or UTF-16, whichever
     corresponds to the width of ‘wchar_t’.  As with ‘-fexec-charset’,
     CHARSET can be any encoding supported by the system's ‘iconv’
     library routine; however, you will have problems with encodings
     that do not fit exactly in ‘wchar_t’.

‘-finput-charset=CHARSET’
     Set the input character set, used for translation from the
     character set of the input file to the source character set used by
     GCC.  If the locale does not specify, or GCC cannot get this
     information from the locale, the default is UTF-8.  This can be
     overridden by either the locale or this command-line option.
     Currently the command-line option takes precedence if there's a
     conflict.  CHARSET can be any encoding supported by the system's
     ‘iconv’ library routine.

‘-fpch-deps’
     When using precompiled headers (*note Precompiled Headers::), this
     flag causes the dependency-output flags to also list the files from
     the precompiled header's dependencies.  If not specified, only the
     precompiled header are listed and not the files that were used to
     create it, because those files are not consulted when a precompiled
     header is used.

‘-fpch-preprocess’
     This option allows use of a precompiled header (*note Precompiled
     Headers::) together with ‘-E’.  It inserts a special ‘#pragma’,
     ‘#pragma GCC pch_preprocess "FILENAME"’ in the output to mark the
     place where the precompiled header was found, and its FILENAME.
     When ‘-fpreprocessed’ is in use, GCC recognizes this ‘#pragma’ and
     loads the PCH.

     This option is off by default, because the resulting preprocessed
     output is only really suitable as input to GCC.  It is switched on
     by ‘-save-temps’.

     You should not write this ‘#pragma’ in your own code, but it is
     safe to edit the filename if the PCH file is available in a
     different location.  The filename may be absolute or it may be
     relative to GCC's current directory.

‘-fworking-directory’
     Enable generation of linemarkers in the preprocessor output that
     let the compiler know the current working directory at the time of
     preprocessing.  When this option is enabled, the preprocessor
     emits, after the initial linemarker, a second linemarker with the
     current working directory followed by two slashes.  GCC uses this
     directory, when it's present in the preprocessed input, as the
     directory emitted as the current working directory in some
     debugging information formats.  This option is implicitly enabled
     if debugging information is enabled, but this can be inhibited with
     the negated form ‘-fno-working-directory’.  If the ‘-P’ flag is
     present in the command line, this option has no effect, since no
     ‘#line’ directives are emitted whatsoever.

‘-A PREDICATE=ANSWER’
     Make an assertion with the predicate PREDICATE and answer ANSWER.
     This form is preferred to the older form ‘-A PREDICATE(ANSWER)’,
     which is still supported, because it does not use shell special
     characters.

‘-A -PREDICATE=ANSWER’
     Cancel an assertion with the predicate PREDICATE and answer ANSWER.

‘-C’
     Do not discard comments.  All comments are passed through to the
     output file, except for comments in processed directives, which are
     deleted along with the directive.

     You should be prepared for side effects when using ‘-C’; it causes
     the preprocessor to treat comments as tokens in their own right.
     For example, comments appearing at the start of what would be a
     directive line have the effect of turning that line into an
     ordinary source line, since the first token on the line is no
     longer a ‘#’.

‘-CC’
     Do not discard comments, including during macro expansion.  This is
     like ‘-C’, except that comments contained within macros are also
     passed through to the output file where the macro is expanded.

     In addition to the side effects of the ‘-C’ option, the ‘-CC’
     option causes all C++-style comments inside a macro to be converted
     to C-style comments.  This is to prevent later use of that macro
     from inadvertently commenting out the remainder of the source line.

     The ‘-CC’ option is generally used to support lint comments.

‘-P’
     Inhibit generation of linemarkers in the output from the
     preprocessor.  This might be useful when running the preprocessor
     on something that is not C code, and will be sent to a program
     which might be confused by the linemarkers.

‘-traditional’
‘-traditional-cpp’

     Try to imitate the behavior of pre-standard C preprocessors, as
     opposed to ISO C preprocessors.  See the GNU CPP manual for
     details.

     Note that GCC does not otherwise attempt to emulate a pre-standard
     C compiler, and these options are only supported with the ‘-E’
     switch, or when invoking CPP explicitly.

‘-trigraphs’
     Support ISO C trigraphs.  These are three-character sequences, all
     starting with ‘??’, that are defined by ISO C to stand for single
     characters.  For example, ‘??/’ stands for ‘\’, so ‘'??/n'’ is a
     character constant for a newline.

     The nine trigraphs and their replacements are

          Trigraph:       ??(  ??)  ??<  ??>  ??=  ??/  ??'  ??!  ??-
          Replacement:      [    ]    {    }    #    \    ^    |    ~

     By default, GCC ignores trigraphs, but in standard-conforming modes
     it converts them.  See the ‘-std’ and ‘-ansi’ options.

‘-remap’
     Enable special code to work around file systems which only permit
     very short file names, such as MS-DOS.

‘-H’
     Print the name of each header file used, in addition to other
     normal activities.  Each name is indented to show how deep in the
     ‘#include’ stack it is.  Precompiled header files are also printed,
     even if they are found to be invalid; an invalid precompiled header
     file is printed with ‘...x’ and a valid one with ‘...!’ .

‘-dLETTERS’
     Says to make debugging dumps during compilation as specified by
     LETTERS.  The flags documented here are those relevant to the
     preprocessor.  Other LETTERS are interpreted by the compiler
     proper, or reserved for future versions of GCC, and so are silently
     ignored.  If you specify LETTERS whose behavior conflicts, the
     result is undefined.  *Note Developer Options::, for more
     information.

     ‘-dM’
          Instead of the normal output, generate a list of ‘#define’
          directives for all the macros defined during the execution of
          the preprocessor, including predefined macros.  This gives you
          a way of finding out what is predefined in your version of the
          preprocessor.  Assuming you have no file ‘foo.h’, the command

               touch foo.h; cpp -dM foo.h

          shows all the predefined macros.

          If you use ‘-dM’ without the ‘-E’ option, ‘-dM’ is interpreted
          as a synonym for ‘-fdump-rtl-mach’.  *Note (gcc)Developer
          Options::.

     ‘-dD’
          Like ‘-dM’ except in two respects: it does _not_ include the
          predefined macros, and it outputs _both_ the ‘#define’
          directives and the result of preprocessing.  Both kinds of
          output go to the standard output file.

     ‘-dN’
          Like ‘-dD’, but emit only the macro names, not their
          expansions.

     ‘-dI’
          Output ‘#include’ directives in addition to the result of
          preprocessing.

     ‘-dU’
          Like ‘-dD’ except that only macros that are expanded, or whose
          definedness is tested in preprocessor directives, are output;
          the output is delayed until the use or test of the macro; and
          ‘#undef’ directives are also output for macros tested but
          undefined at the time.

‘-fdebug-cpp’
     This option is only useful for debugging GCC. When used from CPP or
     with ‘-E’, it dumps debugging information about location maps.
     Every token in the output is preceded by the dump of the map its
     location belongs to.

     When used from GCC without ‘-E’, this option has no effect.

‘-Wp,OPTION’
     You can use ‘-Wp,OPTION’ to bypass the compiler driver and pass
     OPTION directly through to the preprocessor.  If OPTION contains
     commas, it is split into multiple options at the commas.  However,
     many options are modified, translated or interpreted by the
     compiler driver before being passed to the preprocessor, and ‘-Wp’
     forcibly bypasses this phase.  The preprocessor's direct interface
     is undocumented and subject to change, so whenever possible you
     should avoid using ‘-Wp’ and let the driver handle the options
     instead.

‘-Xpreprocessor OPTION’
     Pass OPTION as an option to the preprocessor.  You can use this to
     supply system-specific preprocessor options that GCC does not
     recognize.

     If you want to pass an option that takes an argument, you must use
     ‘-Xpreprocessor’ twice, once for the option and once for the
     argument.

‘-no-integrated-cpp’
     Perform preprocessing as a separate pass before compilation.  By
     default, GCC performs preprocessing as an integrated part of input
     tokenization and parsing.  If this option is provided, the
     appropriate language front end (‘cc1’, ‘cc1plus’, or ‘cc1obj’ for
     C, C++, and Objective-C, respectively) is instead invoked twice,
     once for preprocessing only and once for actual compilation of the
     preprocessed input.  This option may be useful in conjunction with
     the ‘-B’ or ‘-wrapper’ options to specify an alternate preprocessor
     or perform additional processing of the program source between
     normal preprocessing and compilation.

‘-flarge-source-files’
     Adjust GCC to expect large source files, at the expense of slower
     compilation and higher memory usage.

     Specifically, GCC normally tracks both column numbers and line
     numbers within source files and it normally prints both of these
     numbers in diagnostics.  However, once it has processed a certain
     number of source lines, it stops tracking column numbers and only
     tracks line numbers.  This means that diagnostics for later lines
     do not include column numbers.  It also means that options like
     ‘-Wmisleading-indentation’ cease to work at that point, although
     the compiler prints a note if this happens.  Passing
     ‘-flarge-source-files’ significantly increases the number of source
     lines that GCC can process before it stops tracking columns.


File: gcc.info,  Node: Assembler Options,  Next: Link Options,  Prev: Preprocessor Options,  Up: Invoking GCC

3.14 Passing Options to the Assembler
=====================================

You can pass options to the assembler.

‘-Wa,OPTION’
     Pass OPTION as an option to the assembler.  If OPTION contains
     commas, it is split into multiple options at the commas.

‘-Xassembler OPTION’
     Pass OPTION as an option to the assembler.  You can use this to
     supply system-specific assembler options that GCC does not
     recognize.

     If you want to pass an option that takes an argument, you must use
     ‘-Xassembler’ twice, once for the option and once for the argument.


File: gcc.info,  Node: Link Options,  Next: Directory Options,  Prev: Assembler Options,  Up: Invoking GCC

3.15 Options for Linking
========================

These options come into play when the compiler links object files into
an executable output file.  They are meaningless if the compiler is not
doing a link step.

‘OBJECT-FILE-NAME’
     A file name that does not end in a special recognized suffix is
     considered to name an object file or library.  (Object files are
     distinguished from libraries by the linker according to the file
     contents.)  If linking is done, these object files are used as
     input to the linker.

‘-c’
‘-S’
‘-E’
     If any of these options is used, then the linker is not run, and
     object file names should not be used as arguments.  *Note Overall
     Options::.

‘-flinker-output=TYPE’
     This option controls code generation of the link-time optimizer.
     By default the linker output is automatically determined by the
     linker plugin.  For debugging the compiler and if incremental
     linking with a non-LTO object file is desired, it may be useful to
     control the type manually.

     If TYPE is ‘exec’, code generation produces a static binary.  In
     this case ‘-fpic’ and ‘-fpie’ are both disabled.

     If TYPE is ‘dyn’, code generation produces a shared library.  In
     this case ‘-fpic’ or ‘-fPIC’ is preserved, but not enabled
     automatically.  This allows to build shared libraries without
     position-independent code on architectures where this is possible,
     i.e. on x86.

     If TYPE is ‘pie’, code generation produces an ‘-fpie’ executable.
     This results in similar optimizations as ‘exec’ except that ‘-fpie’
     is not disabled if specified at compilation time.

     If TYPE is ‘rel’, the compiler assumes that incremental linking is
     done.  The sections containing intermediate code for link-time
     optimization are merged, pre-optimized, and output to the resulting
     object file.  In addition, if ‘-ffat-lto-objects’ is specified,
     binary code is produced for future non-LTO linking.  The object
     file produced by incremental linking is smaller than a static
     library produced from the same object files.  At link time the
     result of incremental linking also loads faster than a static
     library assuming that the majority of objects in the library are
     used.

     Finally ‘nolto-rel’ configures the compiler for incremental linking
     where code generation is forced, a final binary is produced, and
     the intermediate code for later link-time optimization is stripped.
     When multiple object files are linked together the resulting code
     is better optimized than with link-time optimizations disabled (for
     example, cross-module inlining happens), but most of benefits of
     whole program optimizations are lost.

     During the incremental link (by ‘-r’) the linker plugin defaults to
     ‘rel’.  With current interfaces to GNU Binutils it is however not
     possible to incrementally link LTO objects and non-LTO objects into
     a single mixed object file.  If any of object files in incremental
     link cannot be used for link-time optimization, the linker plugin
     issues a warning and uses ‘nolto-rel’.  To maintain whole program
     optimization, it is recommended to link such objects into static
     library instead.  Alternatively it is possible to use H.J. Lu's
     binutils with support for mixed objects.

‘-fuse-ld=bfd’
     Use the ‘bfd’ linker instead of the default linker.

‘-fuse-ld=gold’
     Use the ‘gold’ linker instead of the default linker.

‘-fuse-ld=lld’
     Use the LLVM ‘lld’ linker instead of the default linker.

‘-fuse-ld=mold’
     Use the Modern Linker (‘mold’) instead of the default linker.

‘-lLIBRARY’
‘-l LIBRARY’
     Search the library named LIBRARY when linking.  (The second
     alternative with the library as a separate argument is only for
     POSIX compliance and is not recommended.)

     The ‘-l’ option is passed directly to the linker by GCC. Refer to
     your linker documentation for exact details.  The general
     description below applies to the GNU linker.

     The linker searches a standard list of directories for the library.
     The directories searched include several standard system
     directories plus any that you specify with ‘-L’.

     Static libraries are archives of object files, and have file names
     like ‘libLIBRARY.a’.  Some targets also support shared libraries,
     which typically have names like ‘libLIBRARY.so’.  If both static
     and shared libraries are found, the linker gives preference to
     linking with the shared library unless the ‘-static’ option is
     used.

     It makes a difference where in the command you write this option;
     the linker searches and processes libraries and object files in the
     order they are specified.  Thus, ‘foo.o -lz bar.o’ searches library
     ‘z’ after file ‘foo.o’ but before ‘bar.o’.  If ‘bar.o’ refers to
     functions in ‘z’, those functions may not be loaded.

‘-lobjc’
     You need this special case of the ‘-l’ option in order to link an
     Objective-C or Objective-C++ program.

‘-nostartfiles’
     Do not use the standard system startup files when linking.  The
     standard system libraries are used normally, unless ‘-nostdlib’,
     ‘-nolibc’, or ‘-nodefaultlibs’ is used.

‘-nodefaultlibs’
     Do not use the standard system libraries when linking.  Only the
     libraries you specify are passed to the linker, and options
     specifying linkage of the system libraries, such as
     ‘-static-libgcc’ or ‘-shared-libgcc’, are ignored.  The standard
     startup files are used normally, unless ‘-nostartfiles’ is used.

     The compiler may generate calls to ‘memcmp’, ‘memset’, ‘memcpy’ and
     ‘memmove’.  These entries are usually resolved by entries in libc.
     These entry points should be supplied through some other mechanism
     when this option is specified.

‘-nolibc’
     Do not use the C library or system libraries tightly coupled with
     it when linking.  Still link with the startup files, ‘libgcc’ or
     toolchain provided language support libraries such as ‘libgnat’,
     ‘libgfortran’ or ‘libstdc++’ unless options preventing their
     inclusion are used as well.  This typically removes ‘-lc’ from the
     link command line, as well as system libraries that normally go
     with it and become meaningless when absence of a C library is
     assumed, for example ‘-lpthread’ or ‘-lm’ in some configurations.
     This is intended for bare-board targets when there is indeed no C
     library available.

‘-nostdlib’
     Do not use the standard system startup files or libraries when
     linking.  No startup files and only the libraries you specify are
     passed to the linker, and options specifying linkage of the system
     libraries, such as ‘-static-libgcc’ or ‘-shared-libgcc’, are
     ignored.

     The compiler may generate calls to ‘memcmp’, ‘memset’, ‘memcpy’ and
     ‘memmove’.  These entries are usually resolved by entries in libc.
     These entry points should be supplied through some other mechanism
     when this option is specified.

     One of the standard libraries bypassed by ‘-nostdlib’ and
     ‘-nodefaultlibs’ is ‘libgcc.a’, a library of internal subroutines
     which GCC uses to overcome shortcomings of particular machines, or
     special needs for some languages.  (*Note Interfacing to GCC
     Output: (gccint)Interface, for more discussion of ‘libgcc.a’.)  In
     most cases, you need ‘libgcc.a’ even when you want to avoid other
     standard libraries.  In other words, when you specify ‘-nostdlib’
     or ‘-nodefaultlibs’ you should usually specify ‘-lgcc’ as well.
     This ensures that you have no unresolved references to internal GCC
     library subroutines.  (An example of such an internal subroutine is
     ‘__main’, used to ensure C++ constructors are called; *note
     ‘collect2’: (gccint)Collect2.)

‘-e ENTRY’
‘--entry=ENTRY’

     Specify that the program entry point is ENTRY.  The argument is
     interpreted by the linker; the GNU linker accepts either a symbol
     name or an address.

‘-pie’
     Produce a dynamically linked position independent executable on
     targets that support it.  For predictable results, you must also
     specify the same set of options used for compilation (‘-fpie’,
     ‘-fPIE’, or model suboptions) when you specify this linker option.

‘-no-pie’
     Don't produce a dynamically linked position independent executable.

‘-static-pie’
     Produce a static position independent executable on targets that
     support it.  A static position independent executable is similar to
     a static executable, but can be loaded at any address without a
     dynamic linker.  For predictable results, you must also specify the
     same set of options used for compilation (‘-fpie’, ‘-fPIE’, or
     model suboptions) when you specify this linker option.

‘-pthread’
     Link with the POSIX threads library.  This option is supported on
     GNU/Linux targets, most other Unix derivatives, and also on x86
     Cygwin and MinGW targets.  On some targets this option also sets
     flags for the preprocessor, so it should be used consistently for
     both compilation and linking.

‘-r’
     Produce a relocatable object as output.  This is also known as
     partial linking.

‘-rdynamic’
     Pass the flag ‘-export-dynamic’ to the ELF linker, on targets that
     support it.  This instructs the linker to add all symbols, not only
     used ones, to the dynamic symbol table.  This option is needed for
     some uses of ‘dlopen’ or to allow obtaining backtraces from within
     a program.

‘-s’
     Remove all symbol table and relocation information from the
     executable.

‘-static’
     On systems that support dynamic linking, this overrides ‘-pie’ and
     prevents linking with the shared libraries.  On other systems, this
     option has no effect.

‘-shared’
     Produce a shared object which can then be linked with other objects
     to form an executable.  Not all systems support this option.  For
     predictable results, you must also specify the same set of options
     used for compilation (‘-fpic’, ‘-fPIC’, or model suboptions) when
     you specify this linker option.(1)

‘-shared-libgcc’
‘-static-libgcc’
     On systems that provide ‘libgcc’ as a shared library, these options
     force the use of either the shared or static version, respectively.
     If no shared version of ‘libgcc’ was built when the compiler was
     configured, these options have no effect.

     There are several situations in which an application should use the
     shared ‘libgcc’ instead of the static version.  The most common of
     these is when the application wishes to throw and catch exceptions
     across different shared libraries.  In that case, each of the
     libraries as well as the application itself should use the shared
     ‘libgcc’.

     Therefore, the G++ driver automatically adds ‘-shared-libgcc’
     whenever you build a shared library or a main executable, because
     C++ programs typically use exceptions, so this is the right thing
     to do.

     If, instead, you use the GCC driver to create shared libraries, you
     may find that they are not always linked with the shared ‘libgcc’.
     If GCC finds, at its configuration time, that you have a non-GNU
     linker or a GNU linker that does not support option
     ‘--eh-frame-hdr’, it links the shared version of ‘libgcc’ into
     shared libraries by default.  Otherwise, it takes advantage of the
     linker and optimizes away the linking with the shared version of
     ‘libgcc’, linking with the static version of libgcc by default.
     This allows exceptions to propagate through such shared libraries,
     without incurring relocation costs at library load time.

     However, if a library or main executable is supposed to throw or
     catch exceptions, you must link it using the G++ driver, or using
     the option ‘-shared-libgcc’, such that it is linked with the shared
     ‘libgcc’.

‘-static-libasan’
     When the ‘-fsanitize=address’ option is used to link a program, the
     GCC driver automatically links against ‘libasan’.  If ‘libasan’ is
     available as a shared library, and the ‘-static’ option is not
     used, then this links against the shared version of ‘libasan’.  The
     ‘-static-libasan’ option directs the GCC driver to link ‘libasan’
     statically, without necessarily linking other libraries statically.

‘-static-libtsan’
     When the ‘-fsanitize=thread’ option is used to link a program, the
     GCC driver automatically links against ‘libtsan’.  If ‘libtsan’ is
     available as a shared library, and the ‘-static’ option is not
     used, then this links against the shared version of ‘libtsan’.  The
     ‘-static-libtsan’ option directs the GCC driver to link ‘libtsan’
     statically, without necessarily linking other libraries statically.

‘-static-liblsan’
     When the ‘-fsanitize=leak’ option is used to link a program, the
     GCC driver automatically links against ‘liblsan’.  If ‘liblsan’ is
     available as a shared library, and the ‘-static’ option is not
     used, then this links against the shared version of ‘liblsan’.  The
     ‘-static-liblsan’ option directs the GCC driver to link ‘liblsan’
     statically, without necessarily linking other libraries statically.

‘-static-libubsan’
     When the ‘-fsanitize=undefined’ option is used to link a program,
     the GCC driver automatically links against ‘libubsan’.  If
     ‘libubsan’ is available as a shared library, and the ‘-static’
     option is not used, then this links against the shared version of
     ‘libubsan’.  The ‘-static-libubsan’ option directs the GCC driver
     to link ‘libubsan’ statically, without necessarily linking other
     libraries statically.

‘-static-libstdc++’
     When the ‘g++’ program is used to link a C++ program, it normally
     automatically links against ‘libstdc++’.  If ‘libstdc++’ is
     available as a shared library, and the ‘-static’ option is not
     used, then this links against the shared version of ‘libstdc++’.
     That is normally fine.  However, it is sometimes useful to freeze
     the version of ‘libstdc++’ used by the program without going all
     the way to a fully static link.  The ‘-static-libstdc++’ option
     directs the ‘g++’ driver to link ‘libstdc++’ statically, without
     necessarily linking other libraries statically.

‘-symbolic’
     Bind references to global symbols when building a shared object.
     Warn about any unresolved references (unless overridden by the link
     editor option ‘-Xlinker -z -Xlinker defs’).  Only a few systems
     support this option.

‘-T SCRIPT’
     Use SCRIPT as the linker script.  This option is supported by most
     systems using the GNU linker.  On some targets, such as bare-board
     targets without an operating system, the ‘-T’ option may be
     required when linking to avoid references to undefined symbols.

‘-Xlinker OPTION’
     Pass OPTION as an option to the linker.  You can use this to supply
     system-specific linker options that GCC does not recognize.

     If you want to pass an option that takes a separate argument, you
     must use ‘-Xlinker’ twice, once for the option and once for the
     argument.  For example, to pass ‘-assert definitions’, you must
     write ‘-Xlinker -assert -Xlinker definitions’.  It does not work to
     write ‘-Xlinker "-assert definitions"’, because this passes the
     entire string as a single argument, which is not what the linker
     expects.

     When using the GNU linker, it is usually more convenient to pass
     arguments to linker options using the ‘OPTION=VALUE’ syntax than as
     separate arguments.  For example, you can specify ‘-Xlinker
     -Map=output.map’ rather than ‘-Xlinker -Map -Xlinker output.map’.
     Other linkers may not support this syntax for command-line options.

‘-Wl,OPTION’
     Pass OPTION as an option to the linker.  If OPTION contains commas,
     it is split into multiple options at the commas.  You can use this
     syntax to pass an argument to the option.  For example,
     ‘-Wl,-Map,output.map’ passes ‘-Map output.map’ to the linker.  When
     using the GNU linker, you can also get the same effect with
     ‘-Wl,-Map=output.map’.

‘-u SYMBOL’
     Pretend the symbol SYMBOL is undefined, to force linking of library
     modules to define it.  You can use ‘-u’ multiple times with
     different symbols to force loading of additional library modules.

‘-z KEYWORD’
     ‘-z’ is passed directly on to the linker along with the keyword
     KEYWORD.  See the section in the documentation of your linker for
     permitted values and their meanings.

   ---------- Footnotes ----------

   (1) On some systems, ‘gcc -shared’ needs to build supplementary stub
code for constructors to work.  On multi-libbed systems, ‘gcc -shared’
must select the correct support libraries to link against.  Failing to
supply the correct flags may lead to subtle defects.  Supplying them in
cases where they are not necessary is innocuous.


File: gcc.info,  Node: Directory Options,  Next: Code Gen Options,  Prev: Link Options,  Up: Invoking GCC

3.16 Options for Directory Search
=================================

These options specify directories to search for header files, for
libraries and for parts of the compiler:

‘-I DIR’
‘-iquote DIR’
‘-isystem DIR’
‘-idirafter DIR’
     Add the directory DIR to the list of directories to be searched for
     header files during preprocessing.  If DIR begins with ‘=’ or
     ‘$SYSROOT’, then the ‘=’ or ‘$SYSROOT’ is replaced by the sysroot
     prefix; see ‘--sysroot’ and ‘-isysroot’.

     Directories specified with ‘-iquote’ apply only to the quote form
     of the directive, ‘#include "FILE"’.  Directories specified with
     ‘-I’, ‘-isystem’, or ‘-idirafter’ apply to lookup for both the
     ‘#include "FILE"’ and ‘#include <FILE>’ directives.

     You can specify any number or combination of these options on the
     command line to search for header files in several directories.
     The lookup order is as follows:

       1. For the quote form of the include directive, the directory of
          the current file is searched first.

       2. For the quote form of the include directive, the directories
          specified by ‘-iquote’ options are searched in left-to-right
          order, as they appear on the command line.

       3. Directories specified with ‘-I’ options are scanned in
          left-to-right order.

       4. Directories specified with ‘-isystem’ options are scanned in
          left-to-right order.

       5. Standard system directories are scanned.

       6. Directories specified with ‘-idirafter’ options are scanned in
          left-to-right order.

     You can use ‘-I’ to override a system header file, substituting
     your own version, since these directories are searched before the
     standard system header file directories.  However, you should not
     use this option to add directories that contain vendor-supplied
     system header files; use ‘-isystem’ for that.

     The ‘-isystem’ and ‘-idirafter’ options also mark the directory as
     a system directory, so that it gets the same special treatment that
     is applied to the standard system directories.

     If a standard system include directory, or a directory specified
     with ‘-isystem’, is also specified with ‘-I’, the ‘-I’ option is
     ignored.  The directory is still searched but as a system directory
     at its normal position in the system include chain.  This is to
     ensure that GCC's procedure to fix buggy system headers and the
     ordering for the ‘#include_next’ directive are not inadvertently
     changed.  If you really need to change the search order for system
     directories, use the ‘-nostdinc’ and/or ‘-isystem’ options.

‘-I-’
     Split the include path.  This option has been deprecated.  Please
     use ‘-iquote’ instead for ‘-I’ directories before the ‘-I-’ and
     remove the ‘-I-’ option.

     Any directories specified with ‘-I’ options before ‘-I-’ are
     searched only for headers requested with ‘#include "FILE"’; they
     are not searched for ‘#include <FILE>’.  If additional directories
     are specified with ‘-I’ options after the ‘-I-’, those directories
     are searched for all ‘#include’ directives.

     In addition, ‘-I-’ inhibits the use of the directory of the current
     file directory as the first search directory for ‘#include "FILE"’.
     There is no way to override this effect of ‘-I-’.

‘-iprefix PREFIX’
     Specify PREFIX as the prefix for subsequent ‘-iwithprefix’ options.
     If the prefix represents a directory, you should include the final
     ‘/’.

‘-iwithprefix DIR’
‘-iwithprefixbefore DIR’
     Append DIR to the prefix specified previously with ‘-iprefix’, and
     add the resulting directory to the include search path.
     ‘-iwithprefixbefore’ puts it in the same place ‘-I’ would;
     ‘-iwithprefix’ puts it where ‘-idirafter’ would.

‘-isysroot DIR’
     This option is like the ‘--sysroot’ option, but applies only to
     header files (except for Darwin targets, where it applies to both
     header files and libraries).  See the ‘--sysroot’ option for more
     information.

‘-imultilib DIR’
     Use DIR as a subdirectory of the directory containing
     target-specific C++ headers.

‘-nostdinc’
     Do not search the standard system directories for header files.
     Only the directories explicitly specified with ‘-I’, ‘-iquote’,
     ‘-isystem’, and/or ‘-idirafter’ options (and the directory of the
     current file, if appropriate) are searched.

‘-nostdinc++’
     Do not search for header files in the C++-specific standard
     directories, but do still search the other standard directories.
     (This option is used when building the C++ library.)

‘-iplugindir=DIR’
     Set the directory to search for plugins that are passed by
     ‘-fplugin=NAME’ instead of ‘-fplugin=PATH/NAME.so’.  This option is
     not meant to be used by the user, but only passed by the driver.

‘-LDIR’
     Add directory DIR to the list of directories to be searched for
     ‘-l’.

‘-BPREFIX’
     This option specifies where to find the executables, libraries,
     include files, and data files of the compiler itself.

     The compiler driver program runs one or more of the subprograms
     ‘cpp’, ‘cc1’, ‘as’ and ‘ld’.  It tries PREFIX as a prefix for each
     program it tries to run, both with and without ‘MACHINE/VERSION/’
     for the corresponding target machine and compiler version.

     For each subprogram to be run, the compiler driver first tries the
     ‘-B’ prefix, if any.  If that name is not found, or if ‘-B’ is not
     specified, the driver tries two standard prefixes, ‘/usr/lib/gcc/’
     and ‘/usr/local/lib/gcc/’.  If neither of those results in a file
     name that is found, the unmodified program name is searched for
     using the directories specified in your ‘PATH’ environment
     variable.

     The compiler checks to see if the path provided by ‘-B’ refers to a
     directory, and if necessary it adds a directory separator character
     at the end of the path.

     ‘-B’ prefixes that effectively specify directory names also apply
     to libraries in the linker, because the compiler translates these
     options into ‘-L’ options for the linker.  They also apply to
     include files in the preprocessor, because the compiler translates
     these options into ‘-isystem’ options for the preprocessor.  In
     this case, the compiler appends ‘include’ to the prefix.

     The runtime support file ‘libgcc.a’ can also be searched for using
     the ‘-B’ prefix, if needed.  If it is not found there, the two
     standard prefixes above are tried, and that is all.  The file is
     left out of the link if it is not found by those means.

     Another way to specify a prefix much like the ‘-B’ prefix is to use
     the environment variable ‘GCC_EXEC_PREFIX’.  *Note Environment
     Variables::.

     As a special kludge, if the path provided by ‘-B’ is
     ‘[dir/]stageN/’, where N is a number in the range 0 to 9, then it
     is replaced by ‘[dir/]include’.  This is to help with
     boot-strapping the compiler.

‘-no-canonical-prefixes’
     Do not expand any symbolic links, resolve references to ‘/../’ or
     ‘/./’, or make the path absolute when generating a relative prefix.

‘--sysroot=DIR’
     Use DIR as the logical root directory for headers and libraries.
     For example, if the compiler normally searches for headers in
     ‘/usr/include’ and libraries in ‘/usr/lib’, it instead searches
     ‘DIR/usr/include’ and ‘DIR/usr/lib’.

     If you use both this option and the ‘-isysroot’ option, then the
     ‘--sysroot’ option applies to libraries, but the ‘-isysroot’ option
     applies to header files.

     The GNU linker (beginning with version 2.16) has the necessary
     support for this option.  If your linker does not support this
     option, the header file aspect of ‘--sysroot’ still works, but the
     library aspect does not.

‘--no-sysroot-suffix’
     For some targets, a suffix is added to the root directory specified
     with ‘--sysroot’, depending on the other options used, so that
     headers may for example be found in ‘DIR/SUFFIX/usr/include’
     instead of ‘DIR/usr/include’.  This option disables the addition of
     such a suffix.


File: gcc.info,  Node: Code Gen Options,  Next: Developer Options,  Prev: Directory Options,  Up: Invoking GCC

3.17 Options for Code Generation Conventions
============================================

These machine-independent options control the interface conventions used
in code generation.

 Most of them have both positive and negative forms; the negative form
of ‘-ffoo’ is ‘-fno-foo’.  In the table below, only one of the forms is
listed--the one that is not the default.  You can figure out the other
form by either removing ‘no-’ or adding it.

‘-fstack-reuse=REUSE-LEVEL’
     This option controls stack space reuse for user declared local/auto
     variables and compiler generated temporaries.  REUSE_LEVEL can be
     ‘all’, ‘named_vars’, or ‘none’.  ‘all’ enables stack reuse for all
     local variables and temporaries, ‘named_vars’ enables the reuse
     only for user defined local variables with names, and ‘none’
     disables stack reuse completely.  The default value is ‘all’.  The
     option is needed when the program extends the lifetime of a scoped
     local variable or a compiler generated temporary beyond the end
     point defined by the language.  When a lifetime of a variable ends,
     and if the variable lives in memory, the optimizing compiler has
     the freedom to reuse its stack space with other temporaries or
     scoped local variables whose live range does not overlap with it.
     Legacy code extending local lifetime is likely to break with the
     stack reuse optimization.

     For example,

             int *p;
             {
               int local1;

               p = &local1;
               local1 = 10;
               ....
             }
             {
                int local2;
                local2 = 20;
                ...
             }

             if (*p == 10)  // out of scope use of local1
               {

               }

     Another example:

             struct A
             {
                 A(int k) : i(k), j(k) { }
                 int i;
                 int j;
             };

             A *ap;

             void foo(const A& ar)
             {
                ap = &ar;
             }

             void bar()
             {
                foo(A(10)); // temp object's lifetime ends when foo returns

                {
                  A a(20);
                  ....
                }
                ap->i+= 10;  // ap references out of scope temp whose space
                             // is reused with a. What is the value of ap->i?
             }

     The lifetime of a compiler generated temporary is well defined by
     the C++ standard.  When a lifetime of a temporary ends, and if the
     temporary lives in memory, the optimizing compiler has the freedom
     to reuse its stack space with other temporaries or scoped local
     variables whose live range does not overlap with it.  However some
     of the legacy code relies on the behavior of older compilers in
     which temporaries' stack space is not reused, the aggressive stack
     reuse can lead to runtime errors.  This option is used to control
     the temporary stack reuse optimization.

‘-ftrapv’
     This option generates traps for signed overflow on addition,
     subtraction, multiplication operations.  The options ‘-ftrapv’ and
     ‘-fwrapv’ override each other, so using ‘-ftrapv’ ‘-fwrapv’ on the
     command-line results in ‘-fwrapv’ being effective.  Note that only
     active options override, so using ‘-ftrapv’ ‘-fwrapv’ ‘-fno-wrapv’
     on the command-line results in ‘-ftrapv’ being effective.

‘-fwrapv’
     This option instructs the compiler to assume that signed arithmetic
     overflow of addition, subtraction and multiplication wraps around
     using twos-complement representation.  This flag enables some
     optimizations and disables others.  The options ‘-ftrapv’ and
     ‘-fwrapv’ override each other, so using ‘-ftrapv’ ‘-fwrapv’ on the
     command-line results in ‘-fwrapv’ being effective.  Note that only
     active options override, so using ‘-ftrapv’ ‘-fwrapv’ ‘-fno-wrapv’
     on the command-line results in ‘-ftrapv’ being effective.

‘-fwrapv-pointer’
     This option instructs the compiler to assume that pointer
     arithmetic overflow on addition and subtraction wraps around using
     twos-complement representation.  This flag disables some
     optimizations which assume pointer overflow is invalid.

‘-fstrict-overflow’
     This option implies ‘-fno-wrapv’ ‘-fno-wrapv-pointer’ and when
     negated implies ‘-fwrapv’ ‘-fwrapv-pointer’.

‘-fexceptions’
     Enable exception handling.  Generates extra code needed to
     propagate exceptions.  For some targets, this implies GCC generates
     frame unwind information for all functions, which can produce
     significant data size overhead, although it does not affect
     execution.  If you do not specify this option, GCC enables it by
     default for languages like C++ that normally require exception
     handling, and disables it for languages like C that do not normally
     require it.  However, you may need to enable this option when
     compiling C code that needs to interoperate properly with exception
     handlers written in C++.  You may also wish to disable this option
     if you are compiling older C++ programs that don't use exception
     handling.

‘-fnon-call-exceptions’
     Generate code that allows trapping instructions to throw
     exceptions.  Note that this requires platform-specific runtime
     support that does not exist everywhere.  Moreover, it only allows
     _trapping_ instructions to throw exceptions, i.e. memory references
     or floating-point instructions.  It does not allow exceptions to be
     thrown from arbitrary signal handlers such as ‘SIGALRM’.  This
     enables ‘-fexceptions’.

‘-fdelete-dead-exceptions’
     Consider that instructions that may throw exceptions but don't
     otherwise contribute to the execution of the program can be
     optimized away.  This does not affect calls to functions except
     those with the ‘pure’ or ‘const’ attributes.  This option is
     enabled by default for the Ada and C++ compilers, as permitted by
     the language specifications.  Optimization passes that cause dead
     exceptions to be removed are enabled independently at different
     optimization levels.

‘-funwind-tables’
     Similar to ‘-fexceptions’, except that it just generates any needed
     static data, but does not affect the generated code in any other
     way.  You normally do not need to enable this option; instead, a
     language processor that needs this handling enables it on your
     behalf.

‘-fasynchronous-unwind-tables’
     Generate unwind table in DWARF format, if supported by target
     machine.  The table is exact at each instruction boundary, so it
     can be used for stack unwinding from asynchronous events (such as
     debugger or garbage collector).

‘-fno-gnu-unique’
     On systems with recent GNU assembler and C library, the C++
     compiler uses the ‘STB_GNU_UNIQUE’ binding to make sure that
     definitions of template static data members and static local
     variables in inline functions are unique even in the presence of
     ‘RTLD_LOCAL’; this is necessary to avoid problems with a library
     used by two different ‘RTLD_LOCAL’ plugins depending on a
     definition in one of them and therefore disagreeing with the other
     one about the binding of the symbol.  But this causes ‘dlclose’ to
     be ignored for affected DSOs; if your program relies on
     reinitialization of a DSO via ‘dlclose’ and ‘dlopen’, you can use
     ‘-fno-gnu-unique’.

‘-fpcc-struct-return’
     Return "short" ‘struct’ and ‘union’ values in memory like longer
     ones, rather than in registers.  This convention is less efficient,
     but it has the advantage of allowing intercallability between
     GCC-compiled files and files compiled with other compilers,
     particularly the Portable C Compiler (pcc).

     The precise convention for returning structures in memory depends
     on the target configuration macros.

     Short structures and unions are those whose size and alignment
     match that of some integer type.

     *Warning:* code compiled with the ‘-fpcc-struct-return’ switch is
     not binary compatible with code compiled with the
     ‘-freg-struct-return’ switch.  Use it to conform to a non-default
     application binary interface.

‘-freg-struct-return’
     Return ‘struct’ and ‘union’ values in registers when possible.
     This is more efficient for small structures than
     ‘-fpcc-struct-return’.

     If you specify neither ‘-fpcc-struct-return’ nor
     ‘-freg-struct-return’, GCC defaults to whichever convention is
     standard for the target.  If there is no standard convention, GCC
     defaults to ‘-fpcc-struct-return’, except on targets where GCC is
     the principal compiler.  In those cases, we can choose the
     standard, and we chose the more efficient register return
     alternative.

     *Warning:* code compiled with the ‘-freg-struct-return’ switch is
     not binary compatible with code compiled with the
     ‘-fpcc-struct-return’ switch.  Use it to conform to a non-default
     application binary interface.

‘-fshort-enums’
     Allocate to an ‘enum’ type only as many bytes as it needs for the
     declared range of possible values.  Specifically, the ‘enum’ type
     is equivalent to the smallest integer type that has enough room.

     *Warning:* the ‘-fshort-enums’ switch causes GCC to generate code
     that is not binary compatible with code generated without that
     switch.  Use it to conform to a non-default application binary
     interface.

‘-fshort-wchar’
     Override the underlying type for ‘wchar_t’ to be ‘short unsigned
     int’ instead of the default for the target.  This option is useful
     for building programs to run under WINE.

     *Warning:* the ‘-fshort-wchar’ switch causes GCC to generate code
     that is not binary compatible with code generated without that
     switch.  Use it to conform to a non-default application binary
     interface.

‘-fcommon’
     In C code, this option controls the placement of global variables
     defined without an initializer, known as “tentative definitions” in
     the C standard.  Tentative definitions are distinct from
     declarations of a variable with the ‘extern’ keyword, which do not
     allocate storage.

     The default is ‘-fno-common’, which specifies that the compiler
     places uninitialized global variables in the BSS section of the
     object file.  This inhibits the merging of tentative definitions by
     the linker so you get a multiple-definition error if the same
     variable is accidentally defined in more than one compilation unit.

     The ‘-fcommon’ places uninitialized global variables in a common
     block.  This allows the linker to resolve all tentative definitions
     of the same variable in different compilation units to the same
     object, or to a non-tentative definition.  This behavior is
     inconsistent with C++, and on many targets implies a speed and code
     size penalty on global variable references.  It is mainly useful to
     enable legacy code to link without errors.

‘-fno-ident’
     Ignore the ‘#ident’ directive.

‘-finhibit-size-directive’
     Don't output a ‘.size’ assembler directive, or anything else that
     would cause trouble if the function is split in the middle, and the
     two halves are placed at locations far apart in memory.  This
     option is used when compiling ‘crtstuff.c’; you should not need to
     use it for anything else.

‘-fverbose-asm’
     Put extra commentary information in the generated assembly code to
     make it more readable.  This option is generally only of use to
     those who actually need to read the generated assembly code
     (perhaps while debugging the compiler itself).

     ‘-fno-verbose-asm’, the default, causes the extra information to be
     omitted and is useful when comparing two assembler files.

     The added comments include:

        • information on the compiler version and command-line options,

        • the source code lines associated with the assembly
          instructions, in the form FILENAME:LINENUMBER:CONTENT OF LINE,

        • hints on which high-level expressions correspond to the
          various assembly instruction operands.

     For example, given this C source file:

          int test (int n)
          {
            int i;
            int total = 0;

            for (i = 0; i < n; i++)
              total += i * i;

            return total;
          }

     compiling to (x86_64) assembly via ‘-S’ and emitting the result
     direct to stdout via ‘-o’ ‘-’

          gcc -S test.c -fverbose-asm -Os -o -

     gives output similar to this:

          	.file	"test.c"
          # GNU C11 (GCC) version 7.0.0 20160809 (experimental) (x86_64-pc-linux-gnu)
            [...snip...]
          # options passed:
            [...snip...]

          	.text
          	.globl	test
          	.type	test, @function
          test:
          .LFB0:
          	.cfi_startproc
          # test.c:4:   int total = 0;
          	xorl	%eax, %eax	# <retval>
          # test.c:6:   for (i = 0; i < n; i++)
          	xorl	%edx, %edx	# i
          .L2:
          # test.c:6:   for (i = 0; i < n; i++)
          	cmpl	%edi, %edx	# n, i
          	jge	.L5	#,
          # test.c:7:     total += i * i;
          	movl	%edx, %ecx	# i, tmp92
          	imull	%edx, %ecx	# i, tmp92
          # test.c:6:   for (i = 0; i < n; i++)
          	incl	%edx	# i
          # test.c:7:     total += i * i;
          	addl	%ecx, %eax	# tmp92, <retval>
          	jmp	.L2	#
          .L5:
          # test.c:10: }
          	ret
          	.cfi_endproc
          .LFE0:
          	.size	test, .-test
          	.ident	"GCC: (GNU) 7.0.0 20160809 (experimental)"
          	.section	.note.GNU-stack,"",@progbits

     The comments are intended for humans rather than machines and hence
     the precise format of the comments is subject to change.

‘-frecord-gcc-switches’
     This switch causes the command line used to invoke the compiler to
     be recorded into the object file that is being created.  This
     switch is only implemented on some targets and the exact format of
     the recording is target and binary file format dependent, but it
     usually takes the form of a section containing ASCII text.  This
     switch is related to the ‘-fverbose-asm’ switch, but that switch
     only records information in the assembler output file as comments,
     so it never reaches the object file.  See also
     ‘-grecord-gcc-switches’ for another way of storing compiler options
     into the object file.

‘-fpic’
     Generate position-independent code (PIC) suitable for use in a
     shared library, if supported for the target machine.  Such code
     accesses all constant addresses through a global offset table
     (GOT).  The dynamic loader resolves the GOT entries when the
     program starts (the dynamic loader is not part of GCC; it is part
     of the operating system).  If the GOT size for the linked
     executable exceeds a machine-specific maximum size, you get an
     error message from the linker indicating that ‘-fpic’ does not
     work; in that case, recompile with ‘-fPIC’ instead.  (These
     maximums are 8k on the SPARC, 28k on AArch64 and 32k on the m68k
     and RS/6000.  The x86 has no such limit.)

     Position-independent code requires special support, and therefore
     works only on certain machines.  For the x86, GCC supports PIC for
     System V but not for the Sun 386i.  Code generated for the IBM
     RS/6000 is always position-independent.

     When this flag is set, the macros ‘__pic__’ and ‘__PIC__’ are
     defined to 1.

‘-fPIC’
     If supported for the target machine, emit position-independent
     code, suitable for dynamic linking and avoiding any limit on the
     size of the global offset table.  This option makes a difference on
     AArch64, m68k, PowerPC and SPARC.

     Position-independent code requires special support, and therefore
     works only on certain machines.

     When this flag is set, the macros ‘__pic__’ and ‘__PIC__’ are
     defined to 2.

‘-fpie’
‘-fPIE’
     These options are similar to ‘-fpic’ and ‘-fPIC’, but the generated
     position-independent code can be only linked into executables.
     Usually these options are used to compile code that will be linked
     using the ‘-pie’ GCC option.

     ‘-fpie’ and ‘-fPIE’ both define the macros ‘__pie__’ and ‘__PIE__’.
     The macros have the value 1 for ‘-fpie’ and 2 for ‘-fPIE’.

‘-fno-plt’
     Do not use the PLT for external function calls in
     position-independent code.  Instead, load the callee address at
     call sites from the GOT and branch to it.  This leads to more
     efficient code by eliminating PLT stubs and exposing GOT loads to
     optimizations.  On architectures such as 32-bit x86 where PLT stubs
     expect the GOT pointer in a specific register, this gives more
     register allocation freedom to the compiler.  Lazy binding requires
     use of the PLT; with ‘-fno-plt’ all external symbols are resolved
     at load time.

     Alternatively, the function attribute ‘noplt’ can be used to avoid
     calls through the PLT for specific external functions.

     In position-dependent code, a few targets also convert calls to
     functions that are marked to not use the PLT to use the GOT
     instead.

‘-fno-jump-tables’
     Do not use jump tables for switch statements even where it would be
     more efficient than other code generation strategies.  This option
     is of use in conjunction with ‘-fpic’ or ‘-fPIC’ for building code
     that forms part of a dynamic linker and cannot reference the
     address of a jump table.  On some targets, jump tables do not
     require a GOT and this option is not needed.

‘-fno-bit-tests’
     Do not use bit tests for switch statements even where it would be
     more efficient than other code generation strategies.

‘-ffixed-REG’
     Treat the register named REG as a fixed register; generated code
     should never refer to it (except perhaps as a stack pointer, frame
     pointer or in some other fixed role).

     REG must be the name of a register.  The register names accepted
     are machine-specific and are defined in the ‘REGISTER_NAMES’ macro
     in the machine description macro file.

     This flag does not have a negative form, because it specifies a
     three-way choice.

‘-fcall-used-REG’
     Treat the register named REG as an allocable register that is
     clobbered by function calls.  It may be allocated for temporaries
     or variables that do not live across a call.  Functions compiled
     this way do not save and restore the register REG.

     It is an error to use this flag with the frame pointer or stack
     pointer.  Use of this flag for other registers that have fixed
     pervasive roles in the machine's execution model produces
     disastrous results.

     This flag does not have a negative form, because it specifies a
     three-way choice.

‘-fcall-saved-REG’
     Treat the register named REG as an allocable register saved by
     functions.  It may be allocated even for temporaries or variables
     that live across a call.  Functions compiled this way save and
     restore the register REG if they use it.

     It is an error to use this flag with the frame pointer or stack
     pointer.  Use of this flag for other registers that have fixed
     pervasive roles in the machine's execution model produces
     disastrous results.

     A different sort of disaster results from the use of this flag for
     a register in which function values may be returned.

     This flag does not have a negative form, because it specifies a
     three-way choice.

‘-fpack-struct[=N]’
     Without a value specified, pack all structure members together
     without holes.  When a value is specified (which must be a small
     power of two), pack structure members according to this value,
     representing the maximum alignment (that is, objects with default
     alignment requirements larger than this are output potentially
     unaligned at the next fitting location.

     *Warning:* the ‘-fpack-struct’ switch causes GCC to generate code
     that is not binary compatible with code generated without that
     switch.  Additionally, it makes the code suboptimal.  Use it to
     conform to a non-default application binary interface.

‘-fleading-underscore’
     This option and its counterpart, ‘-fno-leading-underscore’,
     forcibly change the way C symbols are represented in the object
     file.  One use is to help link with legacy assembly code.

     *Warning:* the ‘-fleading-underscore’ switch causes GCC to generate
     code that is not binary compatible with code generated without that
     switch.  Use it to conform to a non-default application binary
     interface.  Not all targets provide complete support for this
     switch.

‘-ftls-model=MODEL’
     Alter the thread-local storage model to be used (*note
     Thread-Local::).  The MODEL argument should be one of
     ‘global-dynamic’, ‘local-dynamic’, ‘initial-exec’ or ‘local-exec’.
     Note that the choice is subject to optimization: the compiler may
     use a more efficient model for symbols not visible outside of the
     translation unit, or if ‘-fpic’ is not given on the command line.

     The default without ‘-fpic’ is ‘initial-exec’; with ‘-fpic’ the
     default is ‘global-dynamic’.

‘-ftrampolines’
     For targets that normally need trampolines for nested functions,
     always generate them instead of using descriptors.  Otherwise, for
     targets that do not need them, like for example HP-PA or IA-64, do
     nothing.

     A trampoline is a small piece of code that is created at run time
     on the stack when the address of a nested function is taken, and is
     used to call the nested function indirectly.  Therefore, it
     requires the stack to be made executable in order for the program
     to work properly.

     ‘-fno-trampolines’ is enabled by default on a language by language
     basis to let the compiler avoid generating them, if it computes
     that this is safe, and replace them with descriptors.  Descriptors
     are made up of data only, but the generated code must be prepared
     to deal with them.  As of this writing, ‘-fno-trampolines’ is
     enabled by default only for Ada.

     Moreover, code compiled with ‘-ftrampolines’ and code compiled with
     ‘-fno-trampolines’ are not binary compatible if nested functions
     are present.  This option must therefore be used on a program-wide
     basis and be manipulated with extreme care.

     For languages other than Ada, the ‘-ftrampolines’ and
     ‘-fno-trampolines’ options currently have no effect, and
     trampolines are always generated on platforms that need them for
     nested functions.

‘-fvisibility=[default|internal|hidden|protected]’
     Set the default ELF image symbol visibility to the specified
     option--all symbols are marked with this unless overridden within
     the code.  Using this feature can very substantially improve
     linking and load times of shared object libraries, produce more
     optimized code, provide near-perfect API export and prevent symbol
     clashes.  It is *strongly* recommended that you use this in any
     shared objects you distribute.

     Despite the nomenclature, ‘default’ always means public; i.e.,
     available to be linked against from outside the shared object.
     ‘protected’ and ‘internal’ are pretty useless in real-world usage
     so the only other commonly used option is ‘hidden’.  The default if
     ‘-fvisibility’ isn't specified is ‘default’, i.e., make every
     symbol public.

     A good explanation of the benefits offered by ensuring ELF symbols
     have the correct visibility is given by "How To Write Shared
     Libraries" by Ulrich Drepper (which can be found at
     <https://www.akkadia.org/drepper/>)--however a superior solution
     made possible by this option to marking things hidden when the
     default is public is to make the default hidden and mark things
     public.  This is the norm with DLLs on Windows and with
     ‘-fvisibility=hidden’ and ‘__attribute__ ((visibility("default")))’
     instead of ‘__declspec(dllexport)’ you get almost identical
     semantics with identical syntax.  This is a great boon to those
     working with cross-platform projects.

     For those adding visibility support to existing code, you may find
     ‘#pragma GCC visibility’ of use.  This works by you enclosing the
     declarations you wish to set visibility for with (for example)
     ‘#pragma GCC visibility push(hidden)’ and ‘#pragma GCC visibility
     pop’.  Bear in mind that symbol visibility should be viewed *as
     part of the API interface contract* and thus all new code should
     always specify visibility when it is not the default; i.e.,
     declarations only for use within the local DSO should *always* be
     marked explicitly as hidden as so to avoid PLT indirection
     overheads--making this abundantly clear also aids readability and
     self-documentation of the code.  Note that due to ISO C++
     specification requirements, ‘operator new’ and ‘operator delete’
     must always be of default visibility.

     Be aware that headers from outside your project, in particular
     system headers and headers from any other library you use, may not
     be expecting to be compiled with visibility other than the default.
     You may need to explicitly say ‘#pragma GCC visibility
     push(default)’ before including any such headers.

     ‘extern’ declarations are not affected by ‘-fvisibility’, so a lot
     of code can be recompiled with ‘-fvisibility=hidden’ with no
     modifications.  However, this means that calls to ‘extern’
     functions with no explicit visibility use the PLT, so it is more
     effective to use ‘__attribute ((visibility))’ and/or ‘#pragma GCC
     visibility’ to tell the compiler which ‘extern’ declarations should
     be treated as hidden.

     Note that ‘-fvisibility’ does affect C++ vague linkage entities.
     This means that, for instance, an exception class that is be thrown
     between DSOs must be explicitly marked with default visibility so
     that the ‘type_info’ nodes are unified between the DSOs.

     An overview of these techniques, their benefits and how to use them
     is at <https://gcc.gnu.org/wiki/Visibility>.

‘-fstrict-volatile-bitfields’
     This option should be used if accesses to volatile bit-fields (or
     other structure fields, although the compiler usually honors those
     types anyway) should use a single access of the width of the
     field's type, aligned to a natural alignment if possible.  For
     example, targets with memory-mapped peripheral registers might
     require all such accesses to be 16 bits wide; with this flag you
     can declare all peripheral bit-fields as ‘unsigned short’ (assuming
     short is 16 bits on these targets) to force GCC to use 16-bit
     accesses instead of, perhaps, a more efficient 32-bit access.

     If this option is disabled, the compiler uses the most efficient
     instruction.  In the previous example, that might be a 32-bit load
     instruction, even though that accesses bytes that do not contain
     any portion of the bit-field, or memory-mapped registers unrelated
     to the one being updated.

     In some cases, such as when the ‘packed’ attribute is applied to a
     structure field, it may not be possible to access the field with a
     single read or write that is correctly aligned for the target
     machine.  In this case GCC falls back to generating multiple
     accesses rather than code that will fault or truncate the result at
     run time.

     Note: Due to restrictions of the C/C++11 memory model, write
     accesses are not allowed to touch non bit-field members.  It is
     therefore recommended to define all bits of the field's type as
     bit-field members.

     The default value of this option is determined by the application
     binary interface for the target processor.

‘-fsync-libcalls’
     This option controls whether any out-of-line instance of the
     ‘__sync’ family of functions may be used to implement the C++11
     ‘__atomic’ family of functions.

     The default value of this option is enabled, thus the only useful
     form of the option is ‘-fno-sync-libcalls’.  This option is used in
     the implementation of the ‘libatomic’ runtime library.


File: gcc.info,  Node: Developer Options,  Next: Submodel Options,  Prev: Code Gen Options,  Up: Invoking GCC

3.18 GCC Developer Options
==========================

This section describes command-line options that are primarily of
interest to GCC developers, including options to support compiler
testing and investigation of compiler bugs and compile-time performance
problems.  This includes options that produce debug dumps at various
points in the compilation; that print statistics such as memory use and
execution time; and that print information about GCC's configuration,
such as where it searches for libraries.  You should rarely need to use
any of these options for ordinary compilation and linking tasks.

 Many developer options that cause GCC to dump output to a file take an
optional ‘=FILENAME’ suffix.  You can specify ‘stdout’ or ‘-’ to dump to
standard output, and ‘stderr’ for standard error.

 If ‘=FILENAME’ is omitted, a default dump file name is constructed by
concatenating the base dump file name, a pass number, phase letter, and
pass name.  The base dump file name is the name of output file produced
by the compiler if explicitly specified and not an executable; otherwise
it is the source file name.  The pass number is determined by the order
passes are registered with the compiler's pass manager.  This is
generally the same as the order of execution, but passes registered by
plugins, target-specific passes, or passes that are otherwise registered
late are numbered higher than the pass named ‘final’, even if they are
executed earlier.  The phase letter is one of ‘i’ (inter-procedural
analysis), ‘l’ (language-specific), ‘r’ (RTL), or ‘t’ (tree).  The files
are created in the directory of the output file.

‘-fcallgraph-info’
‘-fcallgraph-info=MARKERS’
     Makes the compiler output callgraph information for the program, on
     a per-object-file basis.  The information is generated in the
     common VCG format.  It can be decorated with additional, per-node
     and/or per-edge information, if a list of comma-separated markers
     is additionally specified.  When the ‘su’ marker is specified, the
     callgraph is decorated with stack usage information; it is
     equivalent to ‘-fstack-usage’.  When the ‘da’ marker is specified,
     the callgraph is decorated with information about dynamically
     allocated objects.

     When compiling with ‘-flto’, no callgraph information is output
     along with the object file.  At LTO link time, ‘-fcallgraph-info’
     may generate multiple callgraph information files next to
     intermediate LTO output files.

‘-dLETTERS’
‘-fdump-rtl-PASS’
‘-fdump-rtl-PASS=FILENAME’
     Says to make debugging dumps during compilation at times specified
     by LETTERS.  This is used for debugging the RTL-based passes of the
     compiler.

     Some ‘-dLETTERS’ switches have different meaning when ‘-E’ is used
     for preprocessing.  *Note Preprocessor Options::, for information
     about preprocessor-specific dump options.

     Debug dumps can be enabled with a ‘-fdump-rtl’ switch or some ‘-d’
     option LETTERS.  Here are the possible letters for use in PASS and
     LETTERS, and their meanings:

     ‘-fdump-rtl-alignments’
          Dump after branch alignments have been computed.

     ‘-fdump-rtl-asmcons’
          Dump after fixing rtl statements that have unsatisfied in/out
          constraints.

     ‘-fdump-rtl-auto_inc_dec’
          Dump after auto-inc-dec discovery.  This pass is only run on
          architectures that have auto inc or auto dec instructions.

     ‘-fdump-rtl-barriers’
          Dump after cleaning up the barrier instructions.

     ‘-fdump-rtl-bbpart’
          Dump after partitioning hot and cold basic blocks.

     ‘-fdump-rtl-bbro’
          Dump after block reordering.

     ‘-fdump-rtl-btl1’
     ‘-fdump-rtl-btl2’
          ‘-fdump-rtl-btl1’ and ‘-fdump-rtl-btl2’ enable dumping after
          the two branch target load optimization passes.

     ‘-fdump-rtl-bypass’
          Dump after jump bypassing and control flow optimizations.

     ‘-fdump-rtl-combine’
          Dump after the RTL instruction combination pass.

     ‘-fdump-rtl-compgotos’
          Dump after duplicating the computed gotos.

     ‘-fdump-rtl-ce1’
     ‘-fdump-rtl-ce2’
     ‘-fdump-rtl-ce3’
          ‘-fdump-rtl-ce1’, ‘-fdump-rtl-ce2’, and ‘-fdump-rtl-ce3’
          enable dumping after the three if conversion passes.

     ‘-fdump-rtl-cprop_hardreg’
          Dump after hard register copy propagation.

     ‘-fdump-rtl-csa’
          Dump after combining stack adjustments.

     ‘-fdump-rtl-cse1’
     ‘-fdump-rtl-cse2’
          ‘-fdump-rtl-cse1’ and ‘-fdump-rtl-cse2’ enable dumping after
          the two common subexpression elimination passes.

     ‘-fdump-rtl-dce’
          Dump after the standalone dead code elimination passes.

     ‘-fdump-rtl-dbr’
          Dump after delayed branch scheduling.

     ‘-fdump-rtl-dce1’
     ‘-fdump-rtl-dce2’
          ‘-fdump-rtl-dce1’ and ‘-fdump-rtl-dce2’ enable dumping after
          the two dead store elimination passes.

     ‘-fdump-rtl-eh’
          Dump after finalization of EH handling code.

     ‘-fdump-rtl-eh_ranges’
          Dump after conversion of EH handling range regions.

     ‘-fdump-rtl-expand’
          Dump after RTL generation.

     ‘-fdump-rtl-fwprop1’
     ‘-fdump-rtl-fwprop2’
          ‘-fdump-rtl-fwprop1’ and ‘-fdump-rtl-fwprop2’ enable dumping
          after the two forward propagation passes.

     ‘-fdump-rtl-gcse1’
     ‘-fdump-rtl-gcse2’
          ‘-fdump-rtl-gcse1’ and ‘-fdump-rtl-gcse2’ enable dumping after
          global common subexpression elimination.

     ‘-fdump-rtl-init-regs’
          Dump after the initialization of the registers.

     ‘-fdump-rtl-initvals’
          Dump after the computation of the initial value sets.

     ‘-fdump-rtl-into_cfglayout’
          Dump after converting to cfglayout mode.

     ‘-fdump-rtl-ira’
          Dump after iterated register allocation.

     ‘-fdump-rtl-jump’
          Dump after the second jump optimization.

     ‘-fdump-rtl-loop2’
          ‘-fdump-rtl-loop2’ enables dumping after the rtl loop
          optimization passes.

     ‘-fdump-rtl-mach’
          Dump after performing the machine dependent reorganization
          pass, if that pass exists.

     ‘-fdump-rtl-mode_sw’
          Dump after removing redundant mode switches.

     ‘-fdump-rtl-rnreg’
          Dump after register renumbering.

     ‘-fdump-rtl-outof_cfglayout’
          Dump after converting from cfglayout mode.

     ‘-fdump-rtl-peephole2’
          Dump after the peephole pass.

     ‘-fdump-rtl-postreload’
          Dump after post-reload optimizations.

     ‘-fdump-rtl-pro_and_epilogue’
          Dump after generating the function prologues and epilogues.

     ‘-fdump-rtl-sched1’
     ‘-fdump-rtl-sched2’
          ‘-fdump-rtl-sched1’ and ‘-fdump-rtl-sched2’ enable dumping
          after the basic block scheduling passes.

     ‘-fdump-rtl-ree’
          Dump after sign/zero extension elimination.

     ‘-fdump-rtl-seqabstr’
          Dump after common sequence discovery.

     ‘-fdump-rtl-shorten’
          Dump after shortening branches.

     ‘-fdump-rtl-sibling’
          Dump after sibling call optimizations.

     ‘-fdump-rtl-split1’
     ‘-fdump-rtl-split2’
     ‘-fdump-rtl-split3’
     ‘-fdump-rtl-split4’
     ‘-fdump-rtl-split5’
          These options enable dumping after five rounds of instruction
          splitting.

     ‘-fdump-rtl-sms’
          Dump after modulo scheduling.  This pass is only run on some
          architectures.

     ‘-fdump-rtl-stack’
          Dump after conversion from GCC's "flat register file"
          registers to the x87's stack-like registers.  This pass is
          only run on x86 variants.

     ‘-fdump-rtl-subreg1’
     ‘-fdump-rtl-subreg2’
          ‘-fdump-rtl-subreg1’ and ‘-fdump-rtl-subreg2’ enable dumping
          after the two subreg expansion passes.

     ‘-fdump-rtl-unshare’
          Dump after all rtl has been unshared.

     ‘-fdump-rtl-vartrack’
          Dump after variable tracking.

     ‘-fdump-rtl-vregs’
          Dump after converting virtual registers to hard registers.

     ‘-fdump-rtl-web’
          Dump after live range splitting.

     ‘-fdump-rtl-regclass’
     ‘-fdump-rtl-subregs_of_mode_init’
     ‘-fdump-rtl-subregs_of_mode_finish’
     ‘-fdump-rtl-dfinit’
     ‘-fdump-rtl-dfinish’
          These dumps are defined but always produce empty files.

     ‘-da’
     ‘-fdump-rtl-all’
          Produce all the dumps listed above.

     ‘-dA’
          Annotate the assembler output with miscellaneous debugging
          information.

     ‘-dD’
          Dump all macro definitions, at the end of preprocessing, in
          addition to normal output.

     ‘-dH’
          Produce a core dump whenever an error occurs.

     ‘-dp’
          Annotate the assembler output with a comment indicating which
          pattern and alternative is used.  The length and cost of each
          instruction are also printed.

     ‘-dP’
          Dump the RTL in the assembler output as a comment before each
          instruction.  Also turns on ‘-dp’ annotation.

     ‘-dx’
          Just generate RTL for a function instead of compiling it.
          Usually used with ‘-fdump-rtl-expand’.

‘-fdump-debug’
     Dump debugging information generated during the debug generation
     phase.

‘-fdump-earlydebug’
     Dump debugging information generated during the early debug
     generation phase.

‘-fdump-noaddr’
     When doing debugging dumps, suppress address output.  This makes it
     more feasible to use diff on debugging dumps for compiler
     invocations with different compiler binaries and/or different text
     / bss / data / heap / stack / dso start locations.

‘-freport-bug’
     Collect and dump debug information into a temporary file if an
     internal compiler error (ICE) occurs.

‘-fdump-unnumbered’
     When doing debugging dumps, suppress instruction numbers and
     address output.  This makes it more feasible to use diff on
     debugging dumps for compiler invocations with different options, in
     particular with and without ‘-g’.

‘-fdump-unnumbered-links’
     When doing debugging dumps (see ‘-d’ option above), suppress
     instruction numbers for the links to the previous and next
     instructions in a sequence.

‘-fdump-ipa-SWITCH’
‘-fdump-ipa-SWITCH-OPTIONS’
     Control the dumping at various stages of inter-procedural analysis
     language tree to a file.  The file name is generated by appending a
     switch specific suffix to the source file name, and the file is
     created in the same directory as the output file.  The following
     dumps are possible:

     ‘all’
          Enables all inter-procedural analysis dumps.

     ‘cgraph’
          Dumps information about call-graph optimization, unused
          function removal, and inlining decisions.

     ‘inline’
          Dump after function inlining.

     Additionally, the options ‘-optimized’, ‘-missed’, ‘-note’, and
     ‘-all’ can be provided, with the same meaning as for ‘-fopt-info’,
     defaulting to ‘-optimized’.

     For example, ‘-fdump-ipa-inline-optimized-missed’ will emit
     information on callsites that were inlined, along with callsites
     that were not inlined.

     By default, the dump will contain messages about successful
     optimizations (equivalent to ‘-optimized’) together with low-level
     details about the analysis.

‘-fdump-lang’
     Dump language-specific information.  The file name is made by
     appending ‘.lang’ to the source file name.

‘-fdump-lang-all’
‘-fdump-lang-SWITCH’
‘-fdump-lang-SWITCH-OPTIONS’
‘-fdump-lang-SWITCH-OPTIONS=FILENAME’
     Control the dumping of language-specific information.  The OPTIONS
     and FILENAME portions behave as described in the ‘-fdump-tree’
     option.  The following SWITCH values are accepted:

     ‘all’

          Enable all language-specific dumps.

     ‘class’
          Dump class hierarchy information.  Virtual table information
          is emitted unless '‘slim’' is specified.  This option is
          applicable to C++ only.

     ‘module’
          Dump module information.  Options ‘lineno’ (locations),
          ‘graph’ (reachability), ‘blocks’ (clusters), ‘uid’
          (serialization), ‘alias’ (mergeable), ‘asmname’ (Elrond), ‘eh’
          (mapper) & ‘vops’ (macros) may provide additional information.
          This option is applicable to C++ only.

     ‘raw’
          Dump the raw internal tree data.  This option is applicable to
          C++ only.

‘-fdump-passes’
     Print on ‘stderr’ the list of optimization passes that are turned
     on and off by the current command-line options.

‘-fdump-statistics-OPTION’
     Enable and control dumping of pass statistics in a separate file.
     The file name is generated by appending a suffix ending in
     ‘.statistics’ to the source file name, and the file is created in
     the same directory as the output file.  If the ‘-OPTION’ form is
     used, ‘-stats’ causes counters to be summed over the whole
     compilation unit while ‘-details’ dumps every event as the passes
     generate them.  The default with no option is to sum counters for
     each function compiled.

‘-fdump-tree-all’
‘-fdump-tree-SWITCH’
‘-fdump-tree-SWITCH-OPTIONS’
‘-fdump-tree-SWITCH-OPTIONS=FILENAME’
     Control the dumping at various stages of processing the
     intermediate language tree to a file.  If the ‘-OPTIONS’ form is
     used, OPTIONS is a list of ‘-’ separated options which control the
     details of the dump.  Not all options are applicable to all dumps;
     those that are not meaningful are ignored.  The following options
     are available

     ‘address’
          Print the address of each node.  Usually this is not
          meaningful as it changes according to the environment and
          source file.  Its primary use is for tying up a dump file with
          a debug environment.
     ‘asmname’
          If ‘DECL_ASSEMBLER_NAME’ has been set for a given decl, use
          that in the dump instead of ‘DECL_NAME’.  Its primary use is
          ease of use working backward from mangled names in the
          assembly file.
     ‘slim’
          When dumping front-end intermediate representations, inhibit
          dumping of members of a scope or body of a function merely
          because that scope has been reached.  Only dump such items
          when they are directly reachable by some other path.

          When dumping pretty-printed trees, this option inhibits
          dumping the bodies of control structures.

          When dumping RTL, print the RTL in slim (condensed) form
          instead of the default LISP-like representation.
     ‘raw’
          Print a raw representation of the tree.  By default, trees are
          pretty-printed into a C-like representation.
     ‘details’
          Enable more detailed dumps (not honored by every dump option).
          Also include information from the optimization passes.
     ‘stats’
          Enable dumping various statistics about the pass (not honored
          by every dump option).
     ‘blocks’
          Enable showing basic block boundaries (disabled in raw dumps).
     ‘graph’
          For each of the other indicated dump files
          (‘-fdump-rtl-PASS’), dump a representation of the control flow
          graph suitable for viewing with GraphViz to
          ‘FILE.PASSID.PASS.dot’.  Each function in the file is
          pretty-printed as a subgraph, so that GraphViz can render them
          all in a single plot.

          This option currently only works for RTL dumps, and the RTL is
          always dumped in slim form.
     ‘vops’
          Enable showing virtual operands for every statement.
     ‘lineno’
          Enable showing line numbers for statements.
     ‘uid’
          Enable showing the unique ID (‘DECL_UID’) for each variable.
     ‘verbose’
          Enable showing the tree dump for each statement.
     ‘eh’
          Enable showing the EH region number holding each statement.
     ‘scev’
          Enable showing scalar evolution analysis details.
     ‘optimized’
          Enable showing optimization information (only available in
          certain passes).
     ‘missed’
          Enable showing missed optimization information (only available
          in certain passes).
     ‘note’
          Enable other detailed optimization information (only available
          in certain passes).
     ‘all’
          Turn on all options, except ‘raw’, ‘slim’, ‘verbose’ and
          ‘lineno’.
     ‘optall’
          Turn on all optimization options, i.e., ‘optimized’, ‘missed’,
          and ‘note’.

     To determine what tree dumps are available or find the dump for a
     pass of interest follow the steps below.

       1. Invoke GCC with ‘-fdump-passes’ and in the ‘stderr’ output
          look for a code that corresponds to the pass you are
          interested in.  For example, the codes ‘tree-evrp’,
          ‘tree-vrp1’, and ‘tree-vrp2’ correspond to the three Value
          Range Propagation passes.  The number at the end distinguishes
          distinct invocations of the same pass.
       2. To enable the creation of the dump file, append the pass code
          to the ‘-fdump-’ option prefix and invoke GCC with it.  For
          example, to enable the dump from the Early Value Range
          Propagation pass, invoke GCC with the ‘-fdump-tree-evrp’
          option.  Optionally, you may specify the name of the dump
          file.  If you don't specify one, GCC creates as described
          below.
       3. Find the pass dump in a file whose name is composed of three
          components separated by a period: the name of the source file
          GCC was invoked to compile, a numeric suffix indicating the
          pass number followed by the letter ‘t’ for tree passes (and
          the letter ‘r’ for RTL passes), and finally the pass code.
          For example, the Early VRP pass dump might be in a file named
          ‘myfile.c.038t.evrp’ in the current working directory.  Note
          that the numeric codes are not stable and may change from one
          version of GCC to another.

‘-fopt-info’
‘-fopt-info-OPTIONS’
‘-fopt-info-OPTIONS=FILENAME’
     Controls optimization dumps from various optimization passes.  If
     the ‘-OPTIONS’ form is used, OPTIONS is a list of ‘-’ separated
     option keywords to select the dump details and optimizations.

     The OPTIONS can be divided into three groups:
       1. options describing what kinds of messages should be emitted,
       2. options describing the verbosity of the dump, and
       3. options describing which optimizations should be included.
     The options from each group can be freely mixed as they are
     non-overlapping.  However, in case of any conflicts, the later
     options override the earlier options on the command line.

     The following options control which kinds of messages should be
     emitted:

     ‘optimized’
          Print information when an optimization is successfully
          applied.  It is up to a pass to decide which information is
          relevant.  For example, the vectorizer passes print the source
          location of loops which are successfully vectorized.
     ‘missed’
          Print information about missed optimizations.  Individual
          passes control which information to include in the output.
     ‘note’
          Print verbose information about optimizations, such as certain
          transformations, more detailed messages about decisions etc.
     ‘all’
          Print detailed optimization information.  This includes
          ‘optimized’, ‘missed’, and ‘note’.

     The following option controls the dump verbosity:

     ‘internals’
          By default, only "high-level" messages are emitted.  This
          option enables additional, more detailed, messages, which are
          likely to only be of interest to GCC developers.

     One or more of the following option keywords can be used to
     describe a group of optimizations:

     ‘ipa’
          Enable dumps from all interprocedural optimizations.
     ‘loop’
          Enable dumps from all loop optimizations.
     ‘inline’
          Enable dumps from all inlining optimizations.
     ‘omp’
          Enable dumps from all OMP (Offloading and Multi Processing)
          optimizations.
     ‘vec’
          Enable dumps from all vectorization optimizations.
     ‘optall’
          Enable dumps from all optimizations.  This is a superset of
          the optimization groups listed above.

     If OPTIONS is omitted, it defaults to ‘optimized-optall’, which
     means to dump messages about successful optimizations from all the
     passes, omitting messages that are treated as "internals".

     If the FILENAME is provided, then the dumps from all the applicable
     optimizations are concatenated into the FILENAME.  Otherwise the
     dump is output onto ‘stderr’.  Though multiple ‘-fopt-info’ options
     are accepted, only one of them can include a FILENAME.  If other
     filenames are provided then all but the first such option are
     ignored.

     Note that the output FILENAME is overwritten in case of multiple
     translation units.  If a combined output from multiple translation
     units is desired, ‘stderr’ should be used instead.

     In the following example, the optimization info is output to
     ‘stderr’:

          gcc -O3 -fopt-info

     This example:
          gcc -O3 -fopt-info-missed=missed.all

     outputs missed optimization report from all the passes into
     ‘missed.all’, and this one:

          gcc -O2 -ftree-vectorize -fopt-info-vec-missed

     prints information about missed optimization opportunities from
     vectorization passes on ‘stderr’.  Note that
     ‘-fopt-info-vec-missed’ is equivalent to ‘-fopt-info-missed-vec’.
     The order of the optimization group names and message types listed
     after ‘-fopt-info’ does not matter.

     As another example,
          gcc -O3 -fopt-info-inline-optimized-missed=inline.txt

     outputs information about missed optimizations as well as optimized
     locations from all the inlining passes into ‘inline.txt’.

     Finally, consider:

          gcc -fopt-info-vec-missed=vec.miss -fopt-info-loop-optimized=loop.opt

     Here the two output filenames ‘vec.miss’ and ‘loop.opt’ are in
     conflict since only one output file is allowed.  In this case, only
     the first option takes effect and the subsequent options are
     ignored.  Thus only ‘vec.miss’ is produced which contains dumps
     from the vectorizer about missed opportunities.

‘-fsave-optimization-record’
     Write a SRCFILE.opt-record.json.gz file detailing what
     optimizations were performed, for those optimizations that support
     ‘-fopt-info’.

     This option is experimental and the format of the data within the
     compressed JSON file is subject to change.

     It is roughly equivalent to a machine-readable version of
     ‘-fopt-info-all’, as a collection of messages with source file,
     line number and column number, with the following additional data
     for each message:

        • the execution count of the code being optimized, along with
          metadata about whether this was from actual profile data, or
          just an estimate, allowing consumers to prioritize messages by
          code hotness,

        • the function name of the code being optimized, where
          applicable,

        • the "inlining chain" for the code being optimized, so that
          when a function is inlined into several different places
          (which might themselves be inlined), the reader can
          distinguish between the copies,

        • objects identifying those parts of the message that refer to
          expressions, statements or symbol-table nodes, which of these
          categories they are, and, when available, their source code
          location,

        • the GCC pass that emitted the message, and

        • the location in GCC's own code from which the message was
          emitted

     Additionally, some messages are logically nested within other
     messages, reflecting implementation details of the optimization
     passes.

‘-fsched-verbose=N’
     On targets that use instruction scheduling, this option controls
     the amount of debugging output the scheduler prints to the dump
     files.

     For N greater than zero, ‘-fsched-verbose’ outputs the same
     information as ‘-fdump-rtl-sched1’ and ‘-fdump-rtl-sched2’.  For N
     greater than one, it also output basic block probabilities,
     detailed ready list information and unit/insn info.  For N greater
     than two, it includes RTL at abort point, control-flow and regions
     info.  And for N over four, ‘-fsched-verbose’ also includes
     dependence info.

‘-fenable-KIND-PASS’
‘-fdisable-KIND-PASS=RANGE-LIST’

     This is a set of options that are used to explicitly disable/enable
     optimization passes.  These options are intended for use for
     debugging GCC. Compiler users should use regular options for
     enabling/disabling passes instead.

     ‘-fdisable-ipa-PASS’
          Disable IPA pass PASS.  PASS is the pass name.  If the same
          pass is statically invoked in the compiler multiple times, the
          pass name should be appended with a sequential number starting
          from 1.

     ‘-fdisable-rtl-PASS’
     ‘-fdisable-rtl-PASS=RANGE-LIST’
          Disable RTL pass PASS.  PASS is the pass name.  If the same
          pass is statically invoked in the compiler multiple times, the
          pass name should be appended with a sequential number starting
          from 1.  RANGE-LIST is a comma-separated list of function
          ranges or assembler names.  Each range is a number pair
          separated by a colon.  The range is inclusive in both ends.
          If the range is trivial, the number pair can be simplified as
          a single number.  If the function's call graph node's UID
          falls within one of the specified ranges, the PASS is disabled
          for that function.  The UID is shown in the function header of
          a dump file, and the pass names can be dumped by using option
          ‘-fdump-passes’.

     ‘-fdisable-tree-PASS’
     ‘-fdisable-tree-PASS=RANGE-LIST’
          Disable tree pass PASS.  See ‘-fdisable-rtl’ for the
          description of option arguments.

     ‘-fenable-ipa-PASS’
          Enable IPA pass PASS.  PASS is the pass name.  If the same
          pass is statically invoked in the compiler multiple times, the
          pass name should be appended with a sequential number starting
          from 1.

     ‘-fenable-rtl-PASS’
     ‘-fenable-rtl-PASS=RANGE-LIST’
          Enable RTL pass PASS.  See ‘-fdisable-rtl’ for option argument
          description and examples.

     ‘-fenable-tree-PASS’
     ‘-fenable-tree-PASS=RANGE-LIST’
          Enable tree pass PASS.  See ‘-fdisable-rtl’ for the
          description of option arguments.

     Here are some examples showing uses of these options.


          # disable ccp1 for all functions
             -fdisable-tree-ccp1
          # disable complete unroll for function whose cgraph node uid is 1
             -fenable-tree-cunroll=1
          # disable gcse2 for functions at the following ranges [1,1],
          # [300,400], and [400,1000]
          # disable gcse2 for functions foo and foo2
             -fdisable-rtl-gcse2=foo,foo2
          # disable early inlining
             -fdisable-tree-einline
          # disable ipa inlining
             -fdisable-ipa-inline
          # enable tree full unroll
             -fenable-tree-unroll

‘-fchecking’
‘-fchecking=N’
     Enable internal consistency checking.  The default depends on the
     compiler configuration.  ‘-fchecking=2’ enables further internal
     consistency checking that might affect code generation.

‘-frandom-seed=STRING’
     This option provides a seed that GCC uses in place of random
     numbers in generating certain symbol names that have to be
     different in every compiled file.  It is also used to place unique
     stamps in coverage data files and the object files that produce
     them.  You can use the ‘-frandom-seed’ option to produce
     reproducibly identical object files.

     The STRING can either be a number (decimal, octal or hex) or an
     arbitrary string (in which case it's converted to a number by
     computing CRC32).

     The STRING should be different for every file you compile.

‘-save-temps’
     Store the usual "temporary" intermediate files permanently; name
     them as auxiliary output files, as specified described under
     ‘-dumpbase’ and ‘-dumpdir’.

     When used in combination with the ‘-x’ command-line option,
     ‘-save-temps’ is sensible enough to avoid overwriting an input
     source file with the same extension as an intermediate file.  The
     corresponding intermediate file may be obtained by renaming the
     source file before using ‘-save-temps’.

‘-save-temps=cwd’
     Equivalent to ‘-save-temps -dumpdir ./’.

‘-save-temps=obj’
     Equivalent to ‘-save-temps -dumpdir outdir/’, where ‘outdir/’ is
     the directory of the output file specified after the ‘-o’ option,
     including any directory separators.  If the ‘-o’ option is not
     used, the ‘-save-temps=obj’ switch behaves like ‘-save-temps=cwd’.

‘-time[=FILE]’
     Report the CPU time taken by each subprocess in the compilation
     sequence.  For C source files, this is the compiler proper and
     assembler (plus the linker if linking is done).

     Without the specification of an output file, the output looks like
     this:

          # cc1 0.12 0.01
          # as 0.00 0.01

     The first number on each line is the "user time", that is time
     spent executing the program itself.  The second number is "system
     time", time spent executing operating system routines on behalf of
     the program.  Both numbers are in seconds.

     With the specification of an output file, the output is appended to
     the named file, and it looks like this:

          0.12 0.01 cc1 OPTIONS
          0.00 0.01 as OPTIONS

     The "user time" and the "system time" are moved before the program
     name, and the options passed to the program are displayed, so that
     one can later tell what file was being compiled, and with which
     options.

‘-fdump-final-insns[=FILE]’
     Dump the final internal representation (RTL) to FILE.  If the
     optional argument is omitted (or if FILE is ‘.’), the name of the
     dump file is determined by appending ‘.gkd’ to the dump base name,
     see ‘-dumpbase’.

‘-fcompare-debug[=OPTS]’
     If no error occurs during compilation, run the compiler a second
     time, adding OPTS and ‘-fcompare-debug-second’ to the arguments
     passed to the second compilation.  Dump the final internal
     representation in both compilations, and print an error if they
     differ.

     If the equal sign is omitted, the default ‘-gtoggle’ is used.

     The environment variable ‘GCC_COMPARE_DEBUG’, if defined, non-empty
     and nonzero, implicitly enables ‘-fcompare-debug’.  If
     ‘GCC_COMPARE_DEBUG’ is defined to a string starting with a dash,
     then it is used for OPTS, otherwise the default ‘-gtoggle’ is used.

     ‘-fcompare-debug=’, with the equal sign but without OPTS, is
     equivalent to ‘-fno-compare-debug’, which disables the dumping of
     the final representation and the second compilation, preventing
     even ‘GCC_COMPARE_DEBUG’ from taking effect.

     To verify full coverage during ‘-fcompare-debug’ testing, set
     ‘GCC_COMPARE_DEBUG’ to say ‘-fcompare-debug-not-overridden’, which
     GCC rejects as an invalid option in any actual compilation (rather
     than preprocessing, assembly or linking).  To get just a warning,
     setting ‘GCC_COMPARE_DEBUG’ to ‘-w%n-fcompare-debug not overridden’
     will do.

‘-fcompare-debug-second’
     This option is implicitly passed to the compiler for the second
     compilation requested by ‘-fcompare-debug’, along with options to
     silence warnings, and omitting other options that would cause the
     compiler to produce output to files or to standard output as a side
     effect.  Dump files and preserved temporary files are renamed so as
     to contain the ‘.gk’ additional extension during the second
     compilation, to avoid overwriting those generated by the first.

     When this option is passed to the compiler driver, it causes the
     _first_ compilation to be skipped, which makes it useful for little
     other than debugging the compiler proper.

‘-gtoggle’
     Turn off generation of debug info, if leaving out this option
     generates it, or turn it on at level 2 otherwise.  The position of
     this argument in the command line does not matter; it takes effect
     after all other options are processed, and it does so only once, no
     matter how many times it is given.  This is mainly intended to be
     used with ‘-fcompare-debug’.

‘-fvar-tracking-assignments-toggle’
     Toggle ‘-fvar-tracking-assignments’, in the same way that
     ‘-gtoggle’ toggles ‘-g’.

‘-Q’
     Makes the compiler print out each function name as it is compiled,
     and print some statistics about each pass when it finishes.

‘-ftime-report’
     Makes the compiler print some statistics about the time consumed by
     each pass when it finishes.

‘-ftime-report-details’
     Record the time consumed by infrastructure parts separately for
     each pass.

‘-fira-verbose=N’
     Control the verbosity of the dump file for the integrated register
     allocator.  The default value is 5.  If the value N is greater or
     equal to 10, the dump output is sent to stderr using the same
     format as N minus 10.

‘-flto-report’
     Prints a report with internal details on the workings of the
     link-time optimizer.  The contents of this report vary from version
     to version.  It is meant to be useful to GCC developers when
     processing object files in LTO mode (via ‘-flto’).

     Disabled by default.

‘-flto-report-wpa’
     Like ‘-flto-report’, but only print for the WPA phase of link-time
     optimization.

‘-fmem-report’
     Makes the compiler print some statistics about permanent memory
     allocation when it finishes.

‘-fmem-report-wpa’
     Makes the compiler print some statistics about permanent memory
     allocation for the WPA phase only.

‘-fpre-ipa-mem-report’
‘-fpost-ipa-mem-report’
     Makes the compiler print some statistics about permanent memory
     allocation before or after interprocedural optimization.

‘-fprofile-report’
     Makes the compiler print some statistics about consistency of the
     (estimated) profile and effect of individual passes.

‘-fstack-usage’
     Makes the compiler output stack usage information for the program,
     on a per-function basis.  The filename for the dump is made by
     appending ‘.su’ to the AUXNAME.  AUXNAME is generated from the name
     of the output file, if explicitly specified and it is not an
     executable, otherwise it is the basename of the source file.  An
     entry is made up of three fields:

        • The name of the function.
        • A number of bytes.
        • One or more qualifiers: ‘static’, ‘dynamic’, ‘bounded’.

     The qualifier ‘static’ means that the function manipulates the
     stack statically: a fixed number of bytes are allocated for the
     frame on function entry and released on function exit; no stack
     adjustments are otherwise made in the function.  The second field
     is this fixed number of bytes.

     The qualifier ‘dynamic’ means that the function manipulates the
     stack dynamically: in addition to the static allocation described
     above, stack adjustments are made in the body of the function, for
     example to push/pop arguments around function calls.  If the
     qualifier ‘bounded’ is also present, the amount of these
     adjustments is bounded at compile time and the second field is an
     upper bound of the total amount of stack used by the function.  If
     it is not present, the amount of these adjustments is not bounded
     at compile time and the second field only represents the bounded
     part.

‘-fstats’
     Emit statistics about front-end processing at the end of the
     compilation.  This option is supported only by the C++ front end,
     and the information is generally only useful to the G++ development
     team.

‘-fdbg-cnt-list’
     Print the name and the counter upper bound for all debug counters.

‘-fdbg-cnt=COUNTER-VALUE-LIST’
     Set the internal debug counter lower and upper bound.
     COUNTER-VALUE-LIST is a comma-separated list of
     NAME:LOWER_BOUND1-UPPER_BOUND1 [:LOWER_BOUND2-UPPER_BOUND2...]
     tuples which sets the name of the counter and list of closed
     intervals.  The LOWER_BOUND is optional and is zero initialized if
     not set.  For example, with ‘-fdbg-cnt=dce:2-4:10-11,tail_call:10’,
     ‘dbg_cnt(dce)’ returns true only for second, third, fourth, tenth
     and eleventh invocation.  For ‘dbg_cnt(tail_call)’ true is returned
     for first 10 invocations.

‘-print-file-name=LIBRARY’
     Print the full absolute name of the library file LIBRARY that would
     be used when linking--and don't do anything else.  With this
     option, GCC does not compile or link anything; it just prints the
     file name.

‘-print-multi-directory’
     Print the directory name corresponding to the multilib selected by
     any other switches present in the command line.  This directory is
     supposed to exist in ‘GCC_EXEC_PREFIX’.

‘-print-multi-lib’
     Print the mapping from multilib directory names to compiler
     switches that enable them.  The directory name is separated from
     the switches by ‘;’, and each switch starts with an ‘@’ instead of
     the ‘-’, without spaces between multiple switches.  This is
     supposed to ease shell processing.

‘-print-multi-os-directory’
     Print the path to OS libraries for the selected multilib, relative
     to some ‘lib’ subdirectory.  If OS libraries are present in the
     ‘lib’ subdirectory and no multilibs are used, this is usually just
     ‘.’, if OS libraries are present in ‘libSUFFIX’ sibling directories
     this prints e.g. ‘../lib64’, ‘../lib’ or ‘../lib32’, or if OS
     libraries are present in ‘lib/SUBDIR’ subdirectories it prints e.g.
     ‘amd64’, ‘sparcv9’ or ‘ev6’.

‘-print-multiarch’
     Print the path to OS libraries for the selected multiarch, relative
     to some ‘lib’ subdirectory.

‘-print-prog-name=PROGRAM’
     Like ‘-print-file-name’, but searches for a program such as ‘cpp’.

‘-print-libgcc-file-name’
     Same as ‘-print-file-name=libgcc.a’.

     This is useful when you use ‘-nostdlib’ or ‘-nodefaultlibs’ but you
     do want to link with ‘libgcc.a’.  You can do:

          gcc -nostdlib FILES... `gcc -print-libgcc-file-name`

‘-print-search-dirs’
     Print the name of the configured installation directory and a list
     of program and library directories ‘gcc’ searches--and don't do
     anything else.

     This is useful when ‘gcc’ prints the error message ‘installation
     problem, cannot exec cpp0: No such file or directory’.  To resolve
     this you either need to put ‘cpp0’ and the other compiler
     components where ‘gcc’ expects to find them, or you can set the
     environment variable ‘GCC_EXEC_PREFIX’ to the directory where you
     installed them.  Don't forget the trailing ‘/’.  *Note Environment
     Variables::.

‘-print-sysroot’
     Print the target sysroot directory that is used during compilation.
     This is the target sysroot specified either at configure time or
     using the ‘--sysroot’ option, possibly with an extra suffix that
     depends on compilation options.  If no target sysroot is specified,
     the option prints nothing.

‘-print-sysroot-headers-suffix’
     Print the suffix added to the target sysroot when searching for
     headers, or give an error if the compiler is not configured with
     such a suffix--and don't do anything else.

‘-dumpmachine’
     Print the compiler's target machine (for example,
     ‘i686-pc-linux-gnu’)--and don't do anything else.

‘-dumpversion’
     Print the compiler version (for example, ‘3.0’, ‘6.3.0’ or
     ‘7’)--and don't do anything else.  This is the compiler version
     used in filesystem paths and specs.  Depending on how the compiler
     has been configured it can be just a single number (major version),
     two numbers separated by a dot (major and minor version) or three
     numbers separated by dots (major, minor and patchlevel version).

‘-dumpfullversion’
     Print the full compiler version--and don't do anything else.  The
     output is always three numbers separated by dots, major, minor and
     patchlevel version.

‘-dumpspecs’
     Print the compiler's built-in specs--and don't do anything else.
     (This is used when GCC itself is being built.)  *Note Spec Files::.


File: gcc.info,  Node: Submodel Options,  Next: Spec Files,  Prev: Developer Options,  Up: Invoking GCC

3.19 Machine-Dependent Options
==============================

Each target machine supported by GCC can have its own options--for
example, to allow you to compile for a particular processor variant or
ABI, or to control optimizations specific to that machine.  By
convention, the names of machine-specific options start with ‘-m’.

 Some configurations of the compiler also support additional
target-specific options, usually for compatibility with other compilers
on the same platform.

* Menu:

* AArch64 Options::
* Adapteva Epiphany Options::
* AMD GCN Options::
* ARC Options::
* ARM Options::
* AVR Options::
* Blackfin Options::
* C6X Options::
* CRIS Options::
* CR16 Options::
* C-SKY Options::
* Darwin Options::
* DEC Alpha Options::
* eBPF Options::
* FR30 Options::
* FT32 Options::
* FRV Options::
* GNU/Linux Options::
* H8/300 Options::
* HPPA Options::
* IA-64 Options::
* LM32 Options::
* LoongArch Options::
* M32C Options::
* M32R/D Options::
* M680x0 Options::
* MCore Options::
* MeP Options::
* MicroBlaze Options::
* MIPS Options::
* MMIX Options::
* MN10300 Options::
* Moxie Options::
* MSP430 Options::
* NDS32 Options::
* Nios II Options::
* Nvidia PTX Options::
* OpenRISC Options::
* PDP-11 Options::
* picoChip Options::
* PowerPC Options::
* PRU Options::
* RISC-V Options::
* RL78 Options::
* RS/6000 and PowerPC Options::
* RX Options::
* S/390 and zSeries Options::
* Score Options::
* SH Options::
* Solaris 2 Options::
* SPARC Options::
* System V Options::
* TILE-Gx Options::
* TILEPro Options::
* V850 Options::
* VAX Options::
* Visium Options::
* VMS Options::
* VxWorks Options::
* x86 Options::
* x86 Windows Options::
* Xstormy16 Options::
* Xtensa Options::
* zSeries Options::


File: gcc.info,  Node: AArch64 Options,  Next: Adapteva Epiphany Options,  Up: Submodel Options

3.19.1 AArch64 Options
----------------------

These options are defined for AArch64 implementations:

‘-mabi=NAME’
     Generate code for the specified data model.  Permissible values are
     ‘ilp32’ for SysV-like data model where int, long int and pointers
     are 32 bits, and ‘lp64’ for SysV-like data model where int is 32
     bits, but long int and pointers are 64 bits.

     The default depends on the specific target configuration.  Note
     that the LP64 and ILP32 ABIs are not link-compatible; you must
     compile your entire program with the same ABI, and link with a
     compatible set of libraries.

‘-mbig-endian’
     Generate big-endian code.  This is the default when GCC is
     configured for an ‘aarch64_be-*-*’ target.

‘-mgeneral-regs-only’
     Generate code which uses only the general-purpose registers.  This
     will prevent the compiler from using floating-point and Advanced
     SIMD registers but will not impose any restrictions on the
     assembler.

‘-mlittle-endian’
     Generate little-endian code.  This is the default when GCC is
     configured for an ‘aarch64-*-*’ but not an ‘aarch64_be-*-*’ target.

‘-mcmodel=tiny’
     Generate code for the tiny code model.  The program and its
     statically defined symbols must be within 1MB of each other.
     Programs can be statically or dynamically linked.

‘-mcmodel=small’
     Generate code for the small code model.  The program and its
     statically defined symbols must be within 4GB of each other.
     Programs can be statically or dynamically linked.  This is the
     default code model.

‘-mcmodel=large’
     Generate code for the large code model.  This makes no assumptions
     about addresses and sizes of sections.  Programs can be statically
     linked only.  The ‘-mcmodel=large’ option is incompatible with
     ‘-mabi=ilp32’, ‘-fpic’ and ‘-fPIC’.

‘-mstrict-align’
‘-mno-strict-align’
     Avoid or allow generating memory accesses that may not be aligned
     on a natural object boundary as described in the architecture
     specification.

‘-momit-leaf-frame-pointer’
‘-mno-omit-leaf-frame-pointer’
     Omit or keep the frame pointer in leaf functions.  The former
     behavior is the default.

‘-mstack-protector-guard=GUARD’
‘-mstack-protector-guard-reg=REG’
‘-mstack-protector-guard-offset=OFFSET’
     Generate stack protection code using canary at GUARD.  Supported
     locations are ‘global’ for a global canary or ‘sysreg’ for a canary
     in an appropriate system register.

     With the latter choice the options
     ‘-mstack-protector-guard-reg=REG’ and
     ‘-mstack-protector-guard-offset=OFFSET’ furthermore specify which
     system register to use as base register for reading the canary, and
     from what offset from that base register.  There is no default
     register or offset as this is entirely for use within the Linux
     kernel.

‘-mtls-dialect=desc’
     Use TLS descriptors as the thread-local storage mechanism for
     dynamic accesses of TLS variables.  This is the default.

‘-mtls-dialect=traditional’
     Use traditional TLS as the thread-local storage mechanism for
     dynamic accesses of TLS variables.

‘-mtls-size=SIZE’
     Specify bit size of immediate TLS offsets.  Valid values are 12,
     24, 32, 48.  This option requires binutils 2.26 or newer.

‘-mfix-cortex-a53-835769’
‘-mno-fix-cortex-a53-835769’
     Enable or disable the workaround for the ARM Cortex-A53 erratum
     number 835769.  This involves inserting a NOP instruction between
     memory instructions and 64-bit integer multiply-accumulate
     instructions.

‘-mfix-cortex-a53-843419’
‘-mno-fix-cortex-a53-843419’
     Enable or disable the workaround for the ARM Cortex-A53 erratum
     number 843419.  This erratum workaround is made at link time and
     this will only pass the corresponding flag to the linker.

‘-mlow-precision-recip-sqrt’
‘-mno-low-precision-recip-sqrt’
     Enable or disable the reciprocal square root approximation.  This
     option only has an effect if ‘-ffast-math’ or
     ‘-funsafe-math-optimizations’ is used as well.  Enabling this
     reduces precision of reciprocal square root results to about 16
     bits for single precision and to 32 bits for double precision.

‘-mlow-precision-sqrt’
‘-mno-low-precision-sqrt’
     Enable or disable the square root approximation.  This option only
     has an effect if ‘-ffast-math’ or ‘-funsafe-math-optimizations’ is
     used as well.  Enabling this reduces precision of square root
     results to about 16 bits for single precision and to 32 bits for
     double precision.  If enabled, it implies
     ‘-mlow-precision-recip-sqrt’.

‘-mlow-precision-div’
‘-mno-low-precision-div’
     Enable or disable the division approximation.  This option only has
     an effect if ‘-ffast-math’ or ‘-funsafe-math-optimizations’ is used
     as well.  Enabling this reduces precision of division results to
     about 16 bits for single precision and to 32 bits for double
     precision.

‘-mtrack-speculation’
‘-mno-track-speculation’
     Enable or disable generation of additional code to track
     speculative execution through conditional branches.  The tracking
     state can then be used by the compiler when expanding calls to
     ‘__builtin_speculation_safe_copy’ to permit a more efficient code
     sequence to be generated.

‘-moutline-atomics’
‘-mno-outline-atomics’
     Enable or disable calls to out-of-line helpers to implement atomic
     operations.  These helpers will, at runtime, determine if the LSE
     instructions from ARMv8.1-A can be used; if not, they will use the
     load/store-exclusive instructions that are present in the base
     ARMv8.0 ISA.

     This option is only applicable when compiling for the base ARMv8.0
     instruction set.  If using a later revision, e.g.
     ‘-march=armv8.1-a’ or ‘-march=armv8-a+lse’, the ARMv8.1-Atomics
     instructions will be used directly.  The same applies when using
     ‘-mcpu=’ when the selected cpu supports the ‘lse’ feature.  This
     option is on by default.

‘-march=NAME’
     Specify the name of the target architecture and, optionally, one or
     more feature modifiers.  This option has the form
     ‘-march=ARCH{+[no]FEATURE}*’.

     The table below summarizes the permissible values for ARCH and the
     features that they enable by default:

     ARCH value     Architecture   Includes by default
     --------------------------------------------------------------------------
     ‘armv8-a’      Armv8-A        ‘+fp’, ‘+simd’
     ‘armv8.1-a’    Armv8.1-A      ‘armv8-a’, ‘+crc’, ‘+lse’, ‘+rdma’
     ‘armv8.2-a’    Armv8.2-A      ‘armv8.1-a’
     ‘armv8.3-a’    Armv8.3-A      ‘armv8.2-a’, ‘+pauth’
     ‘armv8.4-a’    Armv8.4-A      ‘armv8.3-a’, ‘+flagm’, ‘+fp16fml’,
                                   ‘+dotprod’
     ‘armv8.5-a’    Armv8.5-A      ‘armv8.4-a’, ‘+sb’, ‘+ssbs’, ‘+predres’
     ‘armv8.6-a’    Armv8.6-A      ‘armv8.5-a’, ‘+bf16’, ‘+i8mm’
     ‘armv8.7-a’    Armv8.7-A      ‘armv8.6-a’, ‘+ls64’
     ‘armv8.8-a’    Armv8.8-a      ‘armv8.7-a’, ‘+mops’
     ‘armv9-a’      Armv9-A        ‘armv8.5-a’, ‘+sve’, ‘+sve2’
     ‘armv8-r’      Armv8-R        ‘armv8-r’

     The value ‘native’ is available on native AArch64 GNU/Linux and
     causes the compiler to pick the architecture of the host system.
     This option has no effect if the compiler is unable to recognize
     the architecture of the host system,

     The permissible values for FEATURE are listed in the sub-section on
     *note ‘-march’ and ‘-mcpu’ Feature Modifiers:
     aarch64-feature-modifiers.  Where conflicting feature modifiers are
     specified, the right-most feature is used.

     GCC uses NAME to determine what kind of instructions it can emit
     when generating assembly code.  If ‘-march’ is specified without
     either of ‘-mtune’ or ‘-mcpu’ also being specified, the code is
     tuned to perform well across a range of target processors
     implementing the target architecture.

‘-mtune=NAME’
     Specify the name of the target processor for which GCC should tune
     the performance of the code.  Permissible values for this option
     are: ‘generic’, ‘cortex-a35’, ‘cortex-a53’, ‘cortex-a55’,
     ‘cortex-a57’, ‘cortex-a72’, ‘cortex-a73’, ‘cortex-a75’,
     ‘cortex-a76’, ‘cortex-a76ae’, ‘cortex-a77’, ‘cortex-a65’,
     ‘cortex-a65ae’, ‘cortex-a34’, ‘cortex-a78’, ‘cortex-a78ae’,
     ‘cortex-a78c’, ‘ares’, ‘exynos-m1’, ‘emag’, ‘falkor’,
     ‘neoverse-512tvb’, ‘neoverse-e1’, ‘neoverse-n1’, ‘neoverse-n2’,
     ‘neoverse-v1’, ‘qdf24xx’, ‘saphira’, ‘phecda’, ‘xgene1’, ‘vulcan’,
     ‘octeontx’, ‘octeontx81’, ‘octeontx83’, ‘octeontx2’,
     ‘octeontx2t98’, ‘octeontx2t96’ ‘octeontx2t93’, ‘octeontx2f95’,
     ‘octeontx2f95n’, ‘octeontx2f95mm’, ‘a64fx’, ‘thunderx’,
     ‘thunderxt88’, ‘thunderxt88p1’, ‘thunderxt81’, ‘tsv110’,
     ‘thunderxt83’, ‘thunderx2t99’, ‘thunderx3t110’, ‘zeus’,
     ‘cortex-a57.cortex-a53’, ‘cortex-a72.cortex-a53’,
     ‘cortex-a73.cortex-a35’, ‘cortex-a73.cortex-a53’,
     ‘cortex-a75.cortex-a55’, ‘cortex-a76.cortex-a55’, ‘cortex-r82’,
     ‘cortex-x1’, ‘cortex-x2’, ‘cortex-a510’, ‘cortex-a710’, ‘ampere1’,
     ‘native’.

     The values ‘cortex-a57.cortex-a53’, ‘cortex-a72.cortex-a53’,
     ‘cortex-a73.cortex-a35’, ‘cortex-a73.cortex-a53’,
     ‘cortex-a75.cortex-a55’, ‘cortex-a76.cortex-a55’ specify that GCC
     should tune for a big.LITTLE system.

     The value ‘neoverse-512tvb’ specifies that GCC should tune for
     Neoverse cores that (a) implement SVE and (b) have a total vector
     bandwidth of 512 bits per cycle.  In other words, the option tells
     GCC to tune for Neoverse cores that can execute 4 128-bit Advanced
     SIMD arithmetic instructions a cycle and that can execute an
     equivalent number of SVE arithmetic instructions per cycle (2 for
     256-bit SVE, 4 for 128-bit SVE). This is more general than tuning
     for a specific core like Neoverse V1 but is more specific than the
     default tuning described below.

     Additionally on native AArch64 GNU/Linux systems the value ‘native’
     tunes performance to the host system.  This option has no effect if
     the compiler is unable to recognize the processor of the host
     system.

     Where none of ‘-mtune=’, ‘-mcpu=’ or ‘-march=’ are specified, the
     code is tuned to perform well across a range of target processors.

     This option cannot be suffixed by feature modifiers.

‘-mcpu=NAME’
     Specify the name of the target processor, optionally suffixed by
     one or more feature modifiers.  This option has the form
     ‘-mcpu=CPU{+[no]FEATURE}*’, where the permissible values for CPU
     are the same as those available for ‘-mtune’.  The permissible
     values for FEATURE are documented in the sub-section on *note
     ‘-march’ and ‘-mcpu’ Feature Modifiers: aarch64-feature-modifiers.
     Where conflicting feature modifiers are specified, the right-most
     feature is used.

     GCC uses NAME to determine what kind of instructions it can emit
     when generating assembly code (as if by ‘-march’) and to determine
     the target processor for which to tune for performance (as if by
     ‘-mtune’).  Where this option is used in conjunction with ‘-march’
     or ‘-mtune’, those options take precedence over the appropriate
     part of this option.

     ‘-mcpu=neoverse-512tvb’ is special in that it does not refer to a
     specific core, but instead refers to all Neoverse cores that (a)
     implement SVE and (b) have a total vector bandwidth of 512 bits a
     cycle.  Unless overridden by ‘-march’, ‘-mcpu=neoverse-512tvb’
     generates code that can run on a Neoverse V1 core, since Neoverse
     V1 is the first Neoverse core with these properties.  Unless
     overridden by ‘-mtune’, ‘-mcpu=neoverse-512tvb’ tunes code in the
     same way as for ‘-mtune=neoverse-512tvb’.

‘-moverride=STRING’
     Override tuning decisions made by the back-end in response to a
     ‘-mtune=’ switch.  The syntax, semantics, and accepted values for
     STRING in this option are not guaranteed to be consistent across
     releases.

     This option is only intended to be useful when developing GCC.

‘-mverbose-cost-dump’
     Enable verbose cost model dumping in the debug dump files.  This
     option is provided for use in debugging the compiler.

‘-mpc-relative-literal-loads’
‘-mno-pc-relative-literal-loads’
     Enable or disable PC-relative literal loads.  With this option
     literal pools are accessed using a single instruction and emitted
     after each function.  This limits the maximum size of functions to
     1MB.  This is enabled by default for ‘-mcmodel=tiny’.

‘-msign-return-address=SCOPE’
     Select the function scope on which return address signing will be
     applied.  Permissible values are ‘none’, which disables return
     address signing, ‘non-leaf’, which enables pointer signing for
     functions which are not leaf functions, and ‘all’, which enables
     pointer signing for all functions.  The default value is ‘none’.
     This option has been deprecated by -mbranch-protection.

‘-mbranch-protection=NONE|STANDARD|PAC-RET[+LEAF+B-KEY]|BTI’
     Select the branch protection features to use.  ‘none’ is the
     default and turns off all types of branch protection.  ‘standard’
     turns on all types of branch protection features.  If a feature has
     additional tuning options, then ‘standard’ sets it to its standard
     level.  ‘pac-ret[+LEAF]’ turns on return address signing to its
     standard level: signing functions that save the return address to
     memory (non-leaf functions will practically always do this) using
     the a-key.  The optional argument ‘leaf’ can be used to extend the
     signing to include leaf functions.  The optional argument ‘b-key’
     can be used to sign the functions with the B-key instead of the
     A-key.  ‘bti’ turns on branch target identification mechanism.

‘-mharden-sls=OPTS’
     Enable compiler hardening against straight line speculation (SLS).
     OPTS is a comma-separated list of the following options:
     ‘retbr’
     ‘blr’
     In addition, ‘-mharden-sls=all’ enables all SLS hardening while
     ‘-mharden-sls=none’ disables all SLS hardening.

‘-msve-vector-bits=BITS’
     Specify the number of bits in an SVE vector register.  This option
     only has an effect when SVE is enabled.

     GCC supports two forms of SVE code generation: "vector-length
     agnostic" output that works with any size of vector register and
     "vector-length specific" output that allows GCC to make assumptions
     about the vector length when it is useful for optimization reasons.
     The possible values of ‘bits’ are: ‘scalable’, ‘128’, ‘256’, ‘512’,
     ‘1024’ and ‘2048’.  Specifying ‘scalable’ selects vector-length
     agnostic output.  At present ‘-msve-vector-bits=128’ also generates
     vector-length agnostic output for big-endian targets.  All other
     values generate vector-length specific code.  The behavior of these
     values may change in future releases and no value except ‘scalable’
     should be relied on for producing code that is portable across
     different hardware SVE vector lengths.

     The default is ‘-msve-vector-bits=scalable’, which produces
     vector-length agnostic code.

3.19.1.1 ‘-march’ and ‘-mcpu’ Feature Modifiers
...............................................

Feature modifiers used with ‘-march’ and ‘-mcpu’ can be any of the
following and their inverses ‘noFEATURE’:

‘crc’
     Enable CRC extension.  This is on by default for
     ‘-march=armv8.1-a’.
‘crypto’
     Enable Crypto extension.  This also enables Advanced SIMD and
     floating-point instructions.
‘fp’
     Enable floating-point instructions.  This is on by default for all
     possible values for options ‘-march’ and ‘-mcpu’.
‘simd’
     Enable Advanced SIMD instructions.  This also enables
     floating-point instructions.  This is on by default for all
     possible values for options ‘-march’ and ‘-mcpu’.
‘sve’
     Enable Scalable Vector Extension instructions.  This also enables
     Advanced SIMD and floating-point instructions.
‘lse’
     Enable Large System Extension instructions.  This is on by default
     for ‘-march=armv8.1-a’.
‘rdma’
     Enable Round Double Multiply Accumulate instructions.  This is on
     by default for ‘-march=armv8.1-a’.
‘fp16’
     Enable FP16 extension.  This also enables floating-point
     instructions.
‘fp16fml’
     Enable FP16 fmla extension.  This also enables FP16 extensions and
     floating-point instructions.  This option is enabled by default for
     ‘-march=armv8.4-a’.  Use of this option with architectures prior to
     Armv8.2-A is not supported.

‘rcpc’
     Enable the RcPc extension.  This does not change code generation
     from GCC, but is passed on to the assembler, enabling inline asm
     statements to use instructions from the RcPc extension.
‘dotprod’
     Enable the Dot Product extension.  This also enables Advanced SIMD
     instructions.
‘aes’
     Enable the Armv8-a aes and pmull crypto extension.  This also
     enables Advanced SIMD instructions.
‘sha2’
     Enable the Armv8-a sha2 crypto extension.  This also enables
     Advanced SIMD instructions.
‘sha3’
     Enable the sha512 and sha3 crypto extension.  This also enables
     Advanced SIMD instructions.  Use of this option with architectures
     prior to Armv8.2-A is not supported.
‘sm4’
     Enable the sm3 and sm4 crypto extension.  This also enables
     Advanced SIMD instructions.  Use of this option with architectures
     prior to Armv8.2-A is not supported.
‘profile’
     Enable the Statistical Profiling extension.  This option is only to
     enable the extension at the assembler level and does not affect
     code generation.
‘rng’
     Enable the Armv8.5-a Random Number instructions.  This option is
     only to enable the extension at the assembler level and does not
     affect code generation.
‘memtag’
     Enable the Armv8.5-a Memory Tagging Extensions.  Use of this option
     with architectures prior to Armv8.5-A is not supported.
‘sb’
     Enable the Armv8-a Speculation Barrier instruction.  This option is
     only to enable the extension at the assembler level and does not
     affect code generation.  This option is enabled by default for
     ‘-march=armv8.5-a’.
‘ssbs’
     Enable the Armv8-a Speculative Store Bypass Safe instruction.  This
     option is only to enable the extension at the assembler level and
     does not affect code generation.  This option is enabled by default
     for ‘-march=armv8.5-a’.
‘predres’
     Enable the Armv8-a Execution and Data Prediction Restriction
     instructions.  This option is only to enable the extension at the
     assembler level and does not affect code generation.  This option
     is enabled by default for ‘-march=armv8.5-a’.
‘sve2’
     Enable the Armv8-a Scalable Vector Extension 2.  This also enables
     SVE instructions.
‘sve2-bitperm’
     Enable SVE2 bitperm instructions.  This also enables SVE2
     instructions.
‘sve2-sm4’
     Enable SVE2 sm4 instructions.  This also enables SVE2 instructions.
‘sve2-aes’
     Enable SVE2 aes instructions.  This also enables SVE2 instructions.
‘sve2-sha3’
     Enable SVE2 sha3 instructions.  This also enables SVE2
     instructions.
‘tme’
     Enable the Transactional Memory Extension.
‘i8mm’
     Enable 8-bit Integer Matrix Multiply instructions.  This also
     enables Advanced SIMD and floating-point instructions.  This option
     is enabled by default for ‘-march=armv8.6-a’.  Use of this option
     with architectures prior to Armv8.2-A is not supported.
‘f32mm’
     Enable 32-bit Floating point Matrix Multiply instructions.  This
     also enables SVE instructions.  Use of this option with
     architectures prior to Armv8.2-A is not supported.
‘f64mm’
     Enable 64-bit Floating point Matrix Multiply instructions.  This
     also enables SVE instructions.  Use of this option with
     architectures prior to Armv8.2-A is not supported.
‘bf16’
     Enable brain half-precision floating-point instructions.  This also
     enables Advanced SIMD and floating-point instructions.  This option
     is enabled by default for ‘-march=armv8.6-a’.  Use of this option
     with architectures prior to Armv8.2-A is not supported.
‘ls64’
     Enable the 64-byte atomic load and store instructions for
     accelerators.  This option is enabled by default for
     ‘-march=armv8.7-a’.
‘mops’
     Enable the instructions to accelerate memory operations like
     ‘memcpy’, ‘memmove’, ‘memset’.  This option is enabled by default
     for ‘-march=armv8.8-a’
‘flagm’
     Enable the Flag Manipulation instructions Extension.
‘pauth’
     Enable the Pointer Authentication Extension.

 Feature ‘crypto’ implies ‘aes’, ‘sha2’, and ‘simd’, which implies ‘fp’.
Conversely, ‘nofp’ implies ‘nosimd’, which implies ‘nocrypto’, ‘noaes’
and ‘nosha2’.


File: gcc.info,  Node: Adapteva Epiphany Options,  Next: AMD GCN Options,  Prev: AArch64 Options,  Up: Submodel Options

3.19.2 Adapteva Epiphany Options
--------------------------------

These ‘-m’ options are defined for Adapteva Epiphany:

‘-mhalf-reg-file’
     Don't allocate any register in the range ‘r32’...‘r63’.  That
     allows code to run on hardware variants that lack these registers.

‘-mprefer-short-insn-regs’
     Preferentially allocate registers that allow short instruction
     generation.  This can result in increased instruction count, so
     this may either reduce or increase overall code size.

‘-mbranch-cost=NUM’
     Set the cost of branches to roughly NUM "simple" instructions.
     This cost is only a heuristic and is not guaranteed to produce
     consistent results across releases.

‘-mcmove’
     Enable the generation of conditional moves.

‘-mnops=NUM’
     Emit NUM NOPs before every other generated instruction.

‘-mno-soft-cmpsf’
     For single-precision floating-point comparisons, emit an ‘fsub’
     instruction and test the flags.  This is faster than a software
     comparison, but can get incorrect results in the presence of NaNs,
     or when two different small numbers are compared such that their
     difference is calculated as zero.  The default is ‘-msoft-cmpsf’,
     which uses slower, but IEEE-compliant, software comparisons.

‘-mstack-offset=NUM’
     Set the offset between the top of the stack and the stack pointer.
     E.g., a value of 8 means that the eight bytes in the range
     ‘sp+0...sp+7’ can be used by leaf functions without stack
     allocation.  Values other than ‘8’ or ‘16’ are untested and
     unlikely to work.  Note also that this option changes the ABI;
     compiling a program with a different stack offset than the
     libraries have been compiled with generally does not work.  This
     option can be useful if you want to evaluate if a different stack
     offset would give you better code, but to actually use a different
     stack offset to build working programs, it is recommended to
     configure the toolchain with the appropriate
     ‘--with-stack-offset=NUM’ option.

‘-mno-round-nearest’
     Make the scheduler assume that the rounding mode has been set to
     truncating.  The default is ‘-mround-nearest’.

‘-mlong-calls’
     If not otherwise specified by an attribute, assume all calls might
     be beyond the offset range of the ‘b’ / ‘bl’ instructions, and
     therefore load the function address into a register before
     performing a (otherwise direct) call.  This is the default.

‘-mshort-calls’
     If not otherwise specified by an attribute, assume all direct calls
     are in the range of the ‘b’ / ‘bl’ instructions, so use these
     instructions for direct calls.  The default is ‘-mlong-calls’.

‘-msmall16’
     Assume addresses can be loaded as 16-bit unsigned values.  This
     does not apply to function addresses for which ‘-mlong-calls’
     semantics are in effect.

‘-mfp-mode=MODE’
     Set the prevailing mode of the floating-point unit.  This
     determines the floating-point mode that is provided and expected at
     function call and return time.  Making this mode match the mode you
     predominantly need at function start can make your programs smaller
     and faster by avoiding unnecessary mode switches.

     MODE can be set to one the following values:

     ‘caller’
          Any mode at function entry is valid, and retained or restored
          when the function returns, and when it calls other functions.
          This mode is useful for compiling libraries or other
          compilation units you might want to incorporate into different
          programs with different prevailing FPU modes, and the
          convenience of being able to use a single object file
          outweighs the size and speed overhead for any extra mode
          switching that might be needed, compared with what would be
          needed with a more specific choice of prevailing FPU mode.

     ‘truncate’
          This is the mode used for floating-point calculations with
          truncating (i.e. round towards zero) rounding mode.  That
          includes conversion from floating point to integer.

     ‘round-nearest’
          This is the mode used for floating-point calculations with
          round-to-nearest-or-even rounding mode.

     ‘int’
          This is the mode used to perform integer calculations in the
          FPU, e.g. integer multiply, or integer
          multiply-and-accumulate.

     The default is ‘-mfp-mode=caller’

‘-mno-split-lohi’
‘-mno-postinc’
‘-mno-postmodify’
     Code generation tweaks that disable, respectively, splitting of
     32-bit loads, generation of post-increment addresses, and
     generation of post-modify addresses.  The defaults are
     ‘msplit-lohi’, ‘-mpost-inc’, and ‘-mpost-modify’.

‘-mnovect-double’
     Change the preferred SIMD mode to SImode.  The default is
     ‘-mvect-double’, which uses DImode as preferred SIMD mode.

‘-max-vect-align=NUM’
     The maximum alignment for SIMD vector mode types.  NUM may be 4 or
     8.  The default is 8.  Note that this is an ABI change, even though
     many library function interfaces are unaffected if they don't use
     SIMD vector modes in places that affect size and/or alignment of
     relevant types.

‘-msplit-vecmove-early’
     Split vector moves into single word moves before reload.  In theory
     this can give better register allocation, but so far the reverse
     seems to be generally the case.

‘-m1reg-REG’
     Specify a register to hold the constant −1, which makes loading
     small negative constants and certain bitmasks faster.  Allowable
     values for REG are ‘r43’ and ‘r63’, which specify use of that
     register as a fixed register, and ‘none’, which means that no
     register is used for this purpose.  The default is ‘-m1reg-none’.


File: gcc.info,  Node: AMD GCN Options,  Next: ARC Options,  Prev: Adapteva Epiphany Options,  Up: Submodel Options

3.19.3 AMD GCN Options
----------------------

These options are defined specifically for the AMD GCN port.

‘-march=GPU’
‘-mtune=GPU’
     Set architecture type or tuning for GPU.  Supported values for GPU
     are

     ‘fiji’
          Compile for GCN3 Fiji devices (gfx803).

     ‘gfx900’
          Compile for GCN5 Vega 10 devices (gfx900).

     ‘gfx906’
          Compile for GCN5 Vega 20 devices (gfx906).

‘-msram-ecc=on’
‘-msram-ecc=off’
‘-msram-ecc=any’
     Compile binaries suitable for devices with the SRAM-ECC feature
     enabled, disabled, or either mode.  This feature can be enabled
     per-process on some devices.  The compiled code must match the
     device mode.  The default is ‘any’, for devices that support it.

‘-mstack-size=BYTES’
     Specify how many BYTES of stack space will be requested for each
     GPU thread (wave-front).  Beware that there may be many threads and
     limited memory available.  The size of the stack allocation may
     also have an impact on run-time performance.  The default is 32KB
     when using OpenACC or OpenMP, and 1MB otherwise.

‘-mxnack’
     Compile binaries suitable for devices with the XNACK feature
     enabled.  Some devices always require XNACK and some allow the user
     to configure XNACK. The compiled code must match the device mode.
     The default is ‘-mno-xnack’.  At present this option is a
     placeholder for support that is not yet implemented.


File: gcc.info,  Node: ARC Options,  Next: ARM Options,  Prev: AMD GCN Options,  Up: Submodel Options

3.19.4 ARC Options
------------------

The following options control the architecture variant for which code is
being compiled:

‘-mbarrel-shifter’
     Generate instructions supported by barrel shifter.  This is the
     default unless ‘-mcpu=ARC601’ or ‘-mcpu=ARCEM’ is in effect.

‘-mjli-always’
     Force to call a function using jli_s instruction.  This option is
     valid only for ARCv2 architecture.

‘-mcpu=CPU’
     Set architecture type, register usage, and instruction scheduling
     parameters for CPU.  There are also shortcut alias options
     available for backward compatibility and convenience.  Supported
     values for CPU are

     ‘arc600’
          Compile for ARC600.  Aliases: ‘-mA6’, ‘-mARC600’.

     ‘arc601’
          Compile for ARC601.  Alias: ‘-mARC601’.

     ‘arc700’
          Compile for ARC700.  Aliases: ‘-mA7’, ‘-mARC700’.  This is the
          default when configured with ‘--with-cpu=arc700’.

     ‘arcem’
          Compile for ARC EM.

     ‘archs’
          Compile for ARC HS.

     ‘em’
          Compile for ARC EM CPU with no hardware extensions.

     ‘em4’
          Compile for ARC EM4 CPU.

     ‘em4_dmips’
          Compile for ARC EM4 DMIPS CPU.

     ‘em4_fpus’
          Compile for ARC EM4 DMIPS CPU with the single-precision
          floating-point extension.

     ‘em4_fpuda’
          Compile for ARC EM4 DMIPS CPU with single-precision
          floating-point and double assist instructions.

     ‘hs’
          Compile for ARC HS CPU with no hardware extensions except the
          atomic instructions.

     ‘hs34’
          Compile for ARC HS34 CPU.

     ‘hs38’
          Compile for ARC HS38 CPU.

     ‘hs38_linux’
          Compile for ARC HS38 CPU with all hardware extensions on.

     ‘arc600_norm’
          Compile for ARC 600 CPU with ‘norm’ instructions enabled.

     ‘arc600_mul32x16’
          Compile for ARC 600 CPU with ‘norm’ and 32x16-bit multiply
          instructions enabled.

     ‘arc600_mul64’
          Compile for ARC 600 CPU with ‘norm’ and ‘mul64’-family
          instructions enabled.

     ‘arc601_norm’
          Compile for ARC 601 CPU with ‘norm’ instructions enabled.

     ‘arc601_mul32x16’
          Compile for ARC 601 CPU with ‘norm’ and 32x16-bit multiply
          instructions enabled.

     ‘arc601_mul64’
          Compile for ARC 601 CPU with ‘norm’ and ‘mul64’-family
          instructions enabled.

     ‘nps400’
          Compile for ARC 700 on NPS400 chip.

     ‘em_mini’
          Compile for ARC EM minimalist configuration featuring reduced
          register set.

‘-mdpfp’
‘-mdpfp-compact’
     Generate double-precision FPX instructions, tuned for the compact
     implementation.

‘-mdpfp-fast’
     Generate double-precision FPX instructions, tuned for the fast
     implementation.

‘-mno-dpfp-lrsr’
     Disable ‘lr’ and ‘sr’ instructions from using FPX extension aux
     registers.

‘-mea’
     Generate extended arithmetic instructions.  Currently only ‘divaw’,
     ‘adds’, ‘subs’, and ‘sat16’ are supported.  Only valid for
     ‘-mcpu=ARC700’.

‘-mno-mpy’
     Do not generate ‘mpy’-family instructions for ARC700.  This option
     is deprecated.

‘-mmul32x16’
     Generate 32x16-bit multiply and multiply-accumulate instructions.

‘-mmul64’
     Generate ‘mul64’ and ‘mulu64’ instructions.  Only valid for
     ‘-mcpu=ARC600’.

‘-mnorm’
     Generate ‘norm’ instructions.  This is the default if
     ‘-mcpu=ARC700’ is in effect.

‘-mspfp’
‘-mspfp-compact’
     Generate single-precision FPX instructions, tuned for the compact
     implementation.

‘-mspfp-fast’
     Generate single-precision FPX instructions, tuned for the fast
     implementation.

‘-msimd’
     Enable generation of ARC SIMD instructions via target-specific
     builtins.  Only valid for ‘-mcpu=ARC700’.

‘-msoft-float’
     This option ignored; it is provided for compatibility purposes
     only.  Software floating-point code is emitted by default, and this
     default can overridden by FPX options; ‘-mspfp’, ‘-mspfp-compact’,
     or ‘-mspfp-fast’ for single precision, and ‘-mdpfp’,
     ‘-mdpfp-compact’, or ‘-mdpfp-fast’ for double precision.

‘-mswap’
     Generate ‘swap’ instructions.

‘-matomic’
     This enables use of the locked load/store conditional extension to
     implement atomic memory built-in functions.  Not available for ARC
     6xx or ARC EM cores.

‘-mdiv-rem’
     Enable ‘div’ and ‘rem’ instructions for ARCv2 cores.

‘-mcode-density’
     Enable code density instructions for ARC EM. This option is on by
     default for ARC HS.

‘-mll64’
     Enable double load/store operations for ARC HS cores.

‘-mtp-regno=REGNO’
     Specify thread pointer register number.

‘-mmpy-option=MULTO’
     Compile ARCv2 code with a multiplier design option.  You can
     specify the option using either a string or numeric value for
     MULTO.  ‘wlh1’ is the default value.  The recognized values are:

     ‘0’
     ‘none’
          No multiplier available.

     ‘1’
     ‘w’
          16x16 multiplier, fully pipelined.  The following instructions
          are enabled: ‘mpyw’ and ‘mpyuw’.

     ‘2’
     ‘wlh1’
          32x32 multiplier, fully pipelined (1 stage).  The following
          instructions are additionally enabled: ‘mpy’, ‘mpyu’, ‘mpym’,
          ‘mpymu’, and ‘mpy_s’.

     ‘3’
     ‘wlh2’
          32x32 multiplier, fully pipelined (2 stages).  The following
          instructions are additionally enabled: ‘mpy’, ‘mpyu’, ‘mpym’,
          ‘mpymu’, and ‘mpy_s’.

     ‘4’
     ‘wlh3’
          Two 16x16 multipliers, blocking, sequential.  The following
          instructions are additionally enabled: ‘mpy’, ‘mpyu’, ‘mpym’,
          ‘mpymu’, and ‘mpy_s’.

     ‘5’
     ‘wlh4’
          One 16x16 multiplier, blocking, sequential.  The following
          instructions are additionally enabled: ‘mpy’, ‘mpyu’, ‘mpym’,
          ‘mpymu’, and ‘mpy_s’.

     ‘6’
     ‘wlh5’
          One 32x4 multiplier, blocking, sequential.  The following
          instructions are additionally enabled: ‘mpy’, ‘mpyu’, ‘mpym’,
          ‘mpymu’, and ‘mpy_s’.

     ‘7’
     ‘plus_dmpy’
          ARC HS SIMD support.

     ‘8’
     ‘plus_macd’
          ARC HS SIMD support.

     ‘9’
     ‘plus_qmacw’
          ARC HS SIMD support.

     This option is only available for ARCv2 cores.

‘-mfpu=FPU’
     Enables support for specific floating-point hardware extensions for
     ARCv2 cores.  Supported values for FPU are:

     ‘fpus’
          Enables support for single-precision floating-point hardware
          extensions.

     ‘fpud’
          Enables support for double-precision floating-point hardware
          extensions.  The single-precision floating-point extension is
          also enabled.  Not available for ARC EM.

     ‘fpuda’
          Enables support for double-precision floating-point hardware
          extensions using double-precision assist instructions.  The
          single-precision floating-point extension is also enabled.
          This option is only available for ARC EM.

     ‘fpuda_div’
          Enables support for double-precision floating-point hardware
          extensions using double-precision assist instructions.  The
          single-precision floating-point, square-root, and divide
          extensions are also enabled.  This option is only available
          for ARC EM.

     ‘fpuda_fma’
          Enables support for double-precision floating-point hardware
          extensions using double-precision assist instructions.  The
          single-precision floating-point and fused multiply and add
          hardware extensions are also enabled.  This option is only
          available for ARC EM.

     ‘fpuda_all’
          Enables support for double-precision floating-point hardware
          extensions using double-precision assist instructions.  All
          single-precision floating-point hardware extensions are also
          enabled.  This option is only available for ARC EM.

     ‘fpus_div’
          Enables support for single-precision floating-point,
          square-root and divide hardware extensions.

     ‘fpud_div’
          Enables support for double-precision floating-point,
          square-root and divide hardware extensions.  This option
          includes option ‘fpus_div’.  Not available for ARC EM.

     ‘fpus_fma’
          Enables support for single-precision floating-point and fused
          multiply and add hardware extensions.

     ‘fpud_fma’
          Enables support for double-precision floating-point and fused
          multiply and add hardware extensions.  This option includes
          option ‘fpus_fma’.  Not available for ARC EM.

     ‘fpus_all’
          Enables support for all single-precision floating-point
          hardware extensions.

     ‘fpud_all’
          Enables support for all single- and double-precision
          floating-point hardware extensions.  Not available for ARC EM.

‘-mirq-ctrl-saved=REGISTER-RANGE, BLINK, LP_COUNT’
     Specifies general-purposes registers that the processor
     automatically saves/restores on interrupt entry and exit.
     REGISTER-RANGE is specified as two registers separated by a dash.
     The register range always starts with ‘r0’, the upper limit is ‘fp’
     register.  BLINK and LP_COUNT are optional.  This option is only
     valid for ARC EM and ARC HS cores.

‘-mrgf-banked-regs=NUMBER’
     Specifies the number of registers replicated in second register
     bank on entry to fast interrupt.  Fast interrupts are interrupts
     with the highest priority level P0.  These interrupts save only PC
     and STATUS32 registers to avoid memory transactions during
     interrupt entry and exit sequences.  Use this option when you are
     using fast interrupts in an ARC V2 family processor.  Permitted
     values are 4, 8, 16, and 32.

‘-mlpc-width=WIDTH’
     Specify the width of the ‘lp_count’ register.  Valid values for
     WIDTH are 8, 16, 20, 24, 28 and 32 bits.  The default width is
     fixed to 32 bits.  If the width is less than 32, the compiler does
     not attempt to transform loops in your program to use the
     zero-delay loop mechanism unless it is known that the ‘lp_count’
     register can hold the required loop-counter value.  Depending on
     the width specified, the compiler and run-time library might
     continue to use the loop mechanism for various needs.  This option
     defines macro ‘__ARC_LPC_WIDTH__’ with the value of WIDTH.

‘-mrf16’
     This option instructs the compiler to generate code for a 16-entry
     register file.  This option defines the ‘__ARC_RF16__’ preprocessor
     macro.

‘-mbranch-index’
     Enable use of ‘bi’ or ‘bih’ instructions to implement jump tables.

 The following options are passed through to the assembler, and also
define preprocessor macro symbols.

‘-mdsp-packa’
     Passed down to the assembler to enable the DSP Pack A extensions.
     Also sets the preprocessor symbol ‘__Xdsp_packa’.  This option is
     deprecated.

‘-mdvbf’
     Passed down to the assembler to enable the dual Viterbi butterfly
     extension.  Also sets the preprocessor symbol ‘__Xdvbf’.  This
     option is deprecated.

‘-mlock’
     Passed down to the assembler to enable the locked load/store
     conditional extension.  Also sets the preprocessor symbol
     ‘__Xlock’.

‘-mmac-d16’
     Passed down to the assembler.  Also sets the preprocessor symbol
     ‘__Xxmac_d16’.  This option is deprecated.

‘-mmac-24’
     Passed down to the assembler.  Also sets the preprocessor symbol
     ‘__Xxmac_24’.  This option is deprecated.

‘-mrtsc’
     Passed down to the assembler to enable the 64-bit time-stamp
     counter extension instruction.  Also sets the preprocessor symbol
     ‘__Xrtsc’.  This option is deprecated.

‘-mswape’
     Passed down to the assembler to enable the swap byte ordering
     extension instruction.  Also sets the preprocessor symbol
     ‘__Xswape’.

‘-mtelephony’
     Passed down to the assembler to enable dual- and single-operand
     instructions for telephony.  Also sets the preprocessor symbol
     ‘__Xtelephony’.  This option is deprecated.

‘-mxy’
     Passed down to the assembler to enable the XY memory extension.
     Also sets the preprocessor symbol ‘__Xxy’.

 The following options control how the assembly code is annotated:

‘-misize’
     Annotate assembler instructions with estimated addresses.

‘-mannotate-align’
     Explain what alignment considerations lead to the decision to make
     an instruction short or long.

 The following options are passed through to the linker:

‘-marclinux’
     Passed through to the linker, to specify use of the ‘arclinux’
     emulation.  This option is enabled by default in tool chains built
     for ‘arc-linux-uclibc’ and ‘arceb-linux-uclibc’ targets when
     profiling is not requested.

‘-marclinux_prof’
     Passed through to the linker, to specify use of the ‘arclinux_prof’
     emulation.  This option is enabled by default in tool chains built
     for ‘arc-linux-uclibc’ and ‘arceb-linux-uclibc’ targets when
     profiling is requested.

 The following options control the semantics of generated code:

‘-mlong-calls’
     Generate calls as register indirect calls, thus providing access to
     the full 32-bit address range.

‘-mmedium-calls’
     Don't use less than 25-bit addressing range for calls, which is the
     offset available for an unconditional branch-and-link instruction.
     Conditional execution of function calls is suppressed, to allow use
     of the 25-bit range, rather than the 21-bit range with conditional
     branch-and-link.  This is the default for tool chains built for
     ‘arc-linux-uclibc’ and ‘arceb-linux-uclibc’ targets.

‘-G NUM’
     Put definitions of externally-visible data in a small data section
     if that data is no bigger than NUM bytes.  The default value of NUM
     is 4 for any ARC configuration, or 8 when we have double load/store
     operations.

‘-mno-sdata’
     Do not generate sdata references.  This is the default for tool
     chains built for ‘arc-linux-uclibc’ and ‘arceb-linux-uclibc’
     targets.

‘-mvolatile-cache’
     Use ordinarily cached memory accesses for volatile references.
     This is the default.

‘-mno-volatile-cache’
     Enable cache bypass for volatile references.

 The following options fine tune code generation:
‘-malign-call’
     Does nothing.  Preserved for backward compatibility.

‘-mauto-modify-reg’
     Enable the use of pre/post modify with register displacement.

‘-mbbit-peephole’
     Enable bbit peephole2.

‘-mno-brcc’
     This option disables a target-specific pass in ‘arc_reorg’ to
     generate compare-and-branch (‘brCC’) instructions.  It has no
     effect on generation of these instructions driven by the combiner
     pass.

‘-mcase-vector-pcrel’
     Use PC-relative switch case tables to enable case table shortening.
     This is the default for ‘-Os’.

‘-mcompact-casesi’
     Enable compact ‘casesi’ pattern.  This is the default for ‘-Os’,
     and only available for ARCv1 cores.  This option is deprecated.

‘-mno-cond-exec’
     Disable the ARCompact-specific pass to generate conditional
     execution instructions.

     Due to delay slot scheduling and interactions between operand
     numbers, literal sizes, instruction lengths, and the support for
     conditional execution, the target-independent pass to generate
     conditional execution is often lacking, so the ARC port has kept a
     special pass around that tries to find more conditional execution
     generation opportunities after register allocation, branch
     shortening, and delay slot scheduling have been done.  This pass
     generally, but not always, improves performance and code size, at
     the cost of extra compilation time, which is why there is an option
     to switch it off.  If you have a problem with call instructions
     exceeding their allowable offset range because they are
     conditionalized, you should consider using ‘-mmedium-calls’
     instead.

‘-mearly-cbranchsi’
     Enable pre-reload use of the ‘cbranchsi’ pattern.

‘-mexpand-adddi’
     Expand ‘adddi3’ and ‘subdi3’ at RTL generation time into ‘add.f’,
     ‘adc’ etc.  This option is deprecated.

‘-mindexed-loads’
     Enable the use of indexed loads.  This can be problematic because
     some optimizers then assume that indexed stores exist, which is not
     the case.

‘-mlra’
     Enable Local Register Allocation.  This is still experimental for
     ARC, so by default the compiler uses standard reload (i.e.
     ‘-mno-lra’).

‘-mlra-priority-none’
     Don't indicate any priority for target registers.

‘-mlra-priority-compact’
     Indicate target register priority for r0..r3 / r12..r15.

‘-mlra-priority-noncompact’
     Reduce target register priority for r0..r3 / r12..r15.

‘-mmillicode’
     When optimizing for size (using ‘-Os’), prologues and epilogues
     that have to save or restore a large number of registers are often
     shortened by using call to a special function in libgcc; this is
     referred to as a _millicode_ call.  As these calls can pose
     performance issues, and/or cause linking issues when linking in a
     nonstandard way, this option is provided to turn on or off
     millicode call generation.

‘-mcode-density-frame’
     This option enable the compiler to emit ‘enter’ and ‘leave’
     instructions.  These instructions are only valid for CPUs with
     code-density feature.

‘-mmixed-code’
     Does nothing.  Preserved for backward compatibility.

‘-mq-class’
     Ths option is deprecated.  Enable ‘q’ instruction alternatives.
     This is the default for ‘-Os’.

‘-mRcq’
     Enable ‘Rcq’ constraint handling.  Most short code generation
     depends on this.  This is the default.

‘-mRcw’
     Enable ‘Rcw’ constraint handling.  Most ccfsm condexec mostly
     depends on this.  This is the default.

‘-msize-level=LEVEL’
     Fine-tune size optimization with regards to instruction lengths and
     alignment.  The recognized values for LEVEL are:
     ‘0’
          No size optimization.  This level is deprecated and treated
          like ‘1’.

     ‘1’
          Short instructions are used opportunistically.

     ‘2’
          In addition, alignment of loops and of code after barriers are
          dropped.

     ‘3’
          In addition, optional data alignment is dropped, and the
          option ‘Os’ is enabled.

     This defaults to ‘3’ when ‘-Os’ is in effect.  Otherwise, the
     behavior when this is not set is equivalent to level ‘1’.

‘-mtune=CPU’
     Set instruction scheduling parameters for CPU, overriding any
     implied by ‘-mcpu=’.

     Supported values for CPU are

     ‘ARC600’
          Tune for ARC600 CPU.

     ‘ARC601’
          Tune for ARC601 CPU.

     ‘ARC700’
          Tune for ARC700 CPU with standard multiplier block.

     ‘ARC700-xmac’
          Tune for ARC700 CPU with XMAC block.

     ‘ARC725D’
          Tune for ARC725D CPU.

     ‘ARC750D’
          Tune for ARC750D CPU.

‘-mmultcost=NUM’
     Cost to assume for a multiply instruction, with ‘4’ being equal to
     a normal instruction.

‘-munalign-prob-threshold=PROBABILITY’
     Does nothing.  Preserved for backward compatibility.

 The following options are maintained for backward compatibility, but
are now deprecated and will be removed in a future release:

‘-margonaut’
     Obsolete FPX.

‘-mbig-endian’
‘-EB’
     Compile code for big-endian targets.  Use of these options is now
     deprecated.  Big-endian code is supported by configuring GCC to
     build ‘arceb-elf32’ and ‘arceb-linux-uclibc’ targets, for which big
     endian is the default.

‘-mlittle-endian’
‘-EL’
     Compile code for little-endian targets.  Use of these options is
     now deprecated.  Little-endian code is supported by configuring GCC
     to build ‘arc-elf32’ and ‘arc-linux-uclibc’ targets, for which
     little endian is the default.

‘-mbarrel_shifter’
     Replaced by ‘-mbarrel-shifter’.

‘-mdpfp_compact’
     Replaced by ‘-mdpfp-compact’.

‘-mdpfp_fast’
     Replaced by ‘-mdpfp-fast’.

‘-mdsp_packa’
     Replaced by ‘-mdsp-packa’.

‘-mEA’
     Replaced by ‘-mea’.

‘-mmac_24’
     Replaced by ‘-mmac-24’.

‘-mmac_d16’
     Replaced by ‘-mmac-d16’.

‘-mspfp_compact’
     Replaced by ‘-mspfp-compact’.

‘-mspfp_fast’
     Replaced by ‘-mspfp-fast’.

‘-mtune=CPU’
     Values ‘arc600’, ‘arc601’, ‘arc700’ and ‘arc700-xmac’ for CPU are
     replaced by ‘ARC600’, ‘ARC601’, ‘ARC700’ and ‘ARC700-xmac’
     respectively.

‘-multcost=NUM’
     Replaced by ‘-mmultcost’.


File: gcc.info,  Node: ARM Options,  Next: AVR Options,  Prev: ARC Options,  Up: Submodel Options

3.19.5 ARM Options
------------------

These ‘-m’ options are defined for the ARM port:

‘-mabi=NAME’
     Generate code for the specified ABI.  Permissible values are:
     ‘apcs-gnu’, ‘atpcs’, ‘aapcs’, ‘aapcs-linux’ and ‘iwmmxt’.

‘-mapcs-frame’
     Generate a stack frame that is compliant with the ARM Procedure
     Call Standard for all functions, even if this is not strictly
     necessary for correct execution of the code.  Specifying
     ‘-fomit-frame-pointer’ with this option causes the stack frames not
     to be generated for leaf functions.  The default is
     ‘-mno-apcs-frame’.  This option is deprecated.

‘-mapcs’
     This is a synonym for ‘-mapcs-frame’ and is deprecated.

‘-mthumb-interwork’
     Generate code that supports calling between the ARM and Thumb
     instruction sets.  Without this option, on pre-v5 architectures,
     the two instruction sets cannot be reliably used inside one
     program.  The default is ‘-mno-thumb-interwork’, since slightly
     larger code is generated when ‘-mthumb-interwork’ is specified.  In
     AAPCS configurations this option is meaningless.

‘-mno-sched-prolog’
     Prevent the reordering of instructions in the function prologue, or
     the merging of those instruction with the instructions in the
     function's body.  This means that all functions start with a
     recognizable set of instructions (or in fact one of a choice from a
     small set of different function prologues), and this information
     can be used to locate the start of functions inside an executable
     piece of code.  The default is ‘-msched-prolog’.

‘-mfloat-abi=NAME’
     Specifies which floating-point ABI to use.  Permissible values are:
     ‘soft’, ‘softfp’ and ‘hard’.

     Specifying ‘soft’ causes GCC to generate output containing library
     calls for floating-point operations.  ‘softfp’ allows the
     generation of code using hardware floating-point instructions, but
     still uses the soft-float calling conventions.  ‘hard’ allows
     generation of floating-point instructions and uses FPU-specific
     calling conventions.

     The default depends on the specific target configuration.  Note
     that the hard-float and soft-float ABIs are not link-compatible;
     you must compile your entire program with the same ABI, and link
     with a compatible set of libraries.

‘-mgeneral-regs-only’
     Generate code which uses only the general-purpose registers.  This
     will prevent the compiler from using floating-point and Advanced
     SIMD registers but will not impose any restrictions on the
     assembler.

‘-mlittle-endian’
     Generate code for a processor running in little-endian mode.  This
     is the default for all standard configurations.

‘-mbig-endian’
     Generate code for a processor running in big-endian mode; the
     default is to compile code for a little-endian processor.

‘-mbe8’
‘-mbe32’
     When linking a big-endian image select between BE8 and BE32
     formats.  The option has no effect for little-endian images and is
     ignored.  The default is dependent on the selected target
     architecture.  For ARMv6 and later architectures the default is
     BE8, for older architectures the default is BE32.  BE32 format has
     been deprecated by ARM.

‘-march=NAME[+extension...]’
     This specifies the name of the target ARM architecture.  GCC uses
     this name to determine what kind of instructions it can emit when
     generating assembly code.  This option can be used in conjunction
     with or instead of the ‘-mcpu=’ option.

     Permissible names are: ‘armv4t’, ‘armv5t’, ‘armv5te’, ‘armv6’,
     ‘armv6j’, ‘armv6k’, ‘armv6kz’, ‘armv6t2’, ‘armv6z’, ‘armv6zk’,
     ‘armv7’, ‘armv7-a’, ‘armv7ve’, ‘armv8-a’, ‘armv8.1-a’, ‘armv8.2-a’,
     ‘armv8.3-a’, ‘armv8.4-a’, ‘armv8.5-a’, ‘armv8.6-a’, ‘armv9-a’,
     ‘armv7-r’, ‘armv8-r’, ‘armv6-m’, ‘armv6s-m’, ‘armv7-m’, ‘armv7e-m’,
     ‘armv8-m.base’, ‘armv8-m.main’, ‘armv8.1-m.main’, ‘armv9-a’,
     ‘iwmmxt’ and ‘iwmmxt2’.

     Additionally, the following architectures, which lack support for
     the Thumb execution state, are recognized but support is
     deprecated: ‘armv4’.

     Many of the architectures support extensions.  These can be added
     by appending ‘+EXTENSION’ to the architecture name.  Extension
     options are processed in order and capabilities accumulate.  An
     extension will also enable any necessary base extensions upon which
     it depends.  For example, the ‘+crypto’ extension will always
     enable the ‘+simd’ extension.  The exception to the additive
     construction is for extensions that are prefixed with ‘+no...’:
     these extensions disable the specified option and any other
     extensions that may depend on the presence of that extension.

     For example, ‘-march=armv7-a+simd+nofp+vfpv4’ is equivalent to
     writing ‘-march=armv7-a+vfpv4’ since the ‘+simd’ option is entirely
     disabled by the ‘+nofp’ option that follows it.

     Most extension names are generically named, but have an effect that
     is dependent upon the architecture to which it is applied.  For
     example, the ‘+simd’ option can be applied to both ‘armv7-a’ and
     ‘armv8-a’ architectures, but will enable the original ARMv7-A
     Advanced SIMD (Neon) extensions for ‘armv7-a’ and the ARMv8-A
     variant for ‘armv8-a’.

     The table below lists the supported extensions for each
     architecture.  Architectures not mentioned do not support any
     extensions.

     ‘armv5te’
     ‘armv6’
     ‘armv6j’
     ‘armv6k’
     ‘armv6kz’
     ‘armv6t2’
     ‘armv6z’
     ‘armv6zk’
          ‘+fp’
               The VFPv2 floating-point instructions.  The extension
               ‘+vfpv2’ can be used as an alias for this extension.

          ‘+nofp’
               Disable the floating-point instructions.

     ‘armv7’
          The common subset of the ARMv7-A, ARMv7-R and ARMv7-M
          architectures.
          ‘+fp’
               The VFPv3 floating-point instructions, with 16
               double-precision registers.  The extension ‘+vfpv3-d16’
               can be used as an alias for this extension.  Note that
               floating-point is not supported by the base ARMv7-M
               architecture, but is compatible with both the ARMv7-A and
               ARMv7-R architectures.

          ‘+nofp’
               Disable the floating-point instructions.

     ‘armv7-a’
          ‘+mp’
               The multiprocessing extension.

          ‘+sec’
               The security extension.

          ‘+fp’
               The VFPv3 floating-point instructions, with 16
               double-precision registers.  The extension ‘+vfpv3-d16’
               can be used as an alias for this extension.

          ‘+simd’
               The Advanced SIMD (Neon) v1 and the VFPv3 floating-point
               instructions.  The extensions ‘+neon’ and ‘+neon-vfpv3’
               can be used as aliases for this extension.

          ‘+vfpv3’
               The VFPv3 floating-point instructions, with 32
               double-precision registers.

          ‘+vfpv3-d16-fp16’
               The VFPv3 floating-point instructions, with 16
               double-precision registers and the half-precision
               floating-point conversion operations.

          ‘+vfpv3-fp16’
               The VFPv3 floating-point instructions, with 32
               double-precision registers and the half-precision
               floating-point conversion operations.

          ‘+vfpv4-d16’
               The VFPv4 floating-point instructions, with 16
               double-precision registers.

          ‘+vfpv4’
               The VFPv4 floating-point instructions, with 32
               double-precision registers.

          ‘+neon-fp16’
               The Advanced SIMD (Neon) v1 and the VFPv3 floating-point
               instructions, with the half-precision floating-point
               conversion operations.

          ‘+neon-vfpv4’
               The Advanced SIMD (Neon) v2 and the VFPv4 floating-point
               instructions.

          ‘+nosimd’
               Disable the Advanced SIMD instructions (does not disable
               floating point).

          ‘+nofp’
               Disable the floating-point and Advanced SIMD
               instructions.

     ‘armv7ve’
          The extended version of the ARMv7-A architecture with support
          for virtualization.
          ‘+fp’
               The VFPv4 floating-point instructions, with 16
               double-precision registers.  The extension ‘+vfpv4-d16’
               can be used as an alias for this extension.

          ‘+simd’
               The Advanced SIMD (Neon) v2 and the VFPv4 floating-point
               instructions.  The extension ‘+neon-vfpv4’ can be used as
               an alias for this extension.

          ‘+vfpv3-d16’
               The VFPv3 floating-point instructions, with 16
               double-precision registers.

          ‘+vfpv3’
               The VFPv3 floating-point instructions, with 32
               double-precision registers.

          ‘+vfpv3-d16-fp16’
               The VFPv3 floating-point instructions, with 16
               double-precision registers and the half-precision
               floating-point conversion operations.

          ‘+vfpv3-fp16’
               The VFPv3 floating-point instructions, with 32
               double-precision registers and the half-precision
               floating-point conversion operations.

          ‘+vfpv4-d16’
               The VFPv4 floating-point instructions, with 16
               double-precision registers.

          ‘+vfpv4’
               The VFPv4 floating-point instructions, with 32
               double-precision registers.

          ‘+neon’
               The Advanced SIMD (Neon) v1 and the VFPv3 floating-point
               instructions.  The extension ‘+neon-vfpv3’ can be used as
               an alias for this extension.

          ‘+neon-fp16’
               The Advanced SIMD (Neon) v1 and the VFPv3 floating-point
               instructions, with the half-precision floating-point
               conversion operations.

          ‘+nosimd’
               Disable the Advanced SIMD instructions (does not disable
               floating point).

          ‘+nofp’
               Disable the floating-point and Advanced SIMD
               instructions.

     ‘armv8-a’
          ‘+crc’
               The Cyclic Redundancy Check (CRC) instructions.
          ‘+simd’
               The ARMv8-A Advanced SIMD and floating-point
               instructions.
          ‘+crypto’
               The cryptographic instructions.
          ‘+nocrypto’
               Disable the cryptographic instructions.
          ‘+nofp’
               Disable the floating-point, Advanced SIMD and
               cryptographic instructions.
          ‘+sb’
               Speculation Barrier Instruction.
          ‘+predres’
               Execution and Data Prediction Restriction Instructions.

     ‘armv8.1-a’
          ‘+simd’
               The ARMv8.1-A Advanced SIMD and floating-point
               instructions.

          ‘+crypto’
               The cryptographic instructions.  This also enables the
               Advanced SIMD and floating-point instructions.

          ‘+nocrypto’
               Disable the cryptographic instructions.

          ‘+nofp’
               Disable the floating-point, Advanced SIMD and
               cryptographic instructions.

          ‘+sb’
               Speculation Barrier Instruction.

          ‘+predres’
               Execution and Data Prediction Restriction Instructions.

     ‘armv8.2-a’
     ‘armv8.3-a’
          ‘+fp16’
               The half-precision floating-point data processing
               instructions.  This also enables the Advanced SIMD and
               floating-point instructions.

          ‘+fp16fml’
               The half-precision floating-point fmla extension.  This
               also enables the half-precision floating-point extension
               and Advanced SIMD and floating-point instructions.

          ‘+simd’
               The ARMv8.1-A Advanced SIMD and floating-point
               instructions.

          ‘+crypto’
               The cryptographic instructions.  This also enables the
               Advanced SIMD and floating-point instructions.

          ‘+dotprod’
               Enable the Dot Product extension.  This also enables
               Advanced SIMD instructions.

          ‘+nocrypto’
               Disable the cryptographic extension.

          ‘+nofp’
               Disable the floating-point, Advanced SIMD and
               cryptographic instructions.

          ‘+sb’
               Speculation Barrier Instruction.

          ‘+predres’
               Execution and Data Prediction Restriction Instructions.

          ‘+i8mm’
               8-bit Integer Matrix Multiply instructions.  This also
               enables Advanced SIMD and floating-point instructions.

          ‘+bf16’
               Brain half-precision floating-point instructions.  This
               also enables Advanced SIMD and floating-point
               instructions.

     ‘armv8.4-a’
          ‘+fp16’
               The half-precision floating-point data processing
               instructions.  This also enables the Advanced SIMD and
               floating-point instructions as well as the Dot Product
               extension and the half-precision floating-point fmla
               extension.

          ‘+simd’
               The ARMv8.3-A Advanced SIMD and floating-point
               instructions as well as the Dot Product extension.

          ‘+crypto’
               The cryptographic instructions.  This also enables the
               Advanced SIMD and floating-point instructions as well as
               the Dot Product extension.

          ‘+nocrypto’
               Disable the cryptographic extension.

          ‘+nofp’
               Disable the floating-point, Advanced SIMD and
               cryptographic instructions.

          ‘+sb’
               Speculation Barrier Instruction.

          ‘+predres’
               Execution and Data Prediction Restriction Instructions.

          ‘+i8mm’
               8-bit Integer Matrix Multiply instructions.  This also
               enables Advanced SIMD and floating-point instructions.

          ‘+bf16’
               Brain half-precision floating-point instructions.  This
               also enables Advanced SIMD and floating-point
               instructions.

     ‘armv8.5-a’
          ‘+fp16’
               The half-precision floating-point data processing
               instructions.  This also enables the Advanced SIMD and
               floating-point instructions as well as the Dot Product
               extension and the half-precision floating-point fmla
               extension.

          ‘+simd’
               The ARMv8.3-A Advanced SIMD and floating-point
               instructions as well as the Dot Product extension.

          ‘+crypto’
               The cryptographic instructions.  This also enables the
               Advanced SIMD and floating-point instructions as well as
               the Dot Product extension.

          ‘+nocrypto’
               Disable the cryptographic extension.

          ‘+nofp’
               Disable the floating-point, Advanced SIMD and
               cryptographic instructions.

          ‘+i8mm’
               8-bit Integer Matrix Multiply instructions.  This also
               enables Advanced SIMD and floating-point instructions.

          ‘+bf16’
               Brain half-precision floating-point instructions.  This
               also enables Advanced SIMD and floating-point
               instructions.

     ‘armv8.6-a’
          ‘+fp16’
               The half-precision floating-point data processing
               instructions.  This also enables the Advanced SIMD and
               floating-point instructions as well as the Dot Product
               extension and the half-precision floating-point fmla
               extension.

          ‘+simd’
               The ARMv8.3-A Advanced SIMD and floating-point
               instructions as well as the Dot Product extension.

          ‘+crypto’
               The cryptographic instructions.  This also enables the
               Advanced SIMD and floating-point instructions as well as
               the Dot Product extension.

          ‘+nocrypto’
               Disable the cryptographic extension.

          ‘+nofp’
               Disable the floating-point, Advanced SIMD and
               cryptographic instructions.

          ‘+i8mm’
               8-bit Integer Matrix Multiply instructions.  This also
               enables Advanced SIMD and floating-point instructions.

          ‘+bf16’
               Brain half-precision floating-point instructions.  This
               also enables Advanced SIMD and floating-point
               instructions.

     ‘armv7-r’
          ‘+fp.sp’
               The single-precision VFPv3 floating-point instructions.
               The extension ‘+vfpv3xd’ can be used as an alias for this
               extension.

          ‘+fp’
               The VFPv3 floating-point instructions with 16
               double-precision registers.  The extension +vfpv3-d16 can
               be used as an alias for this extension.

          ‘+vfpv3xd-d16-fp16’
               The single-precision VFPv3 floating-point instructions
               with 16 double-precision registers and the half-precision
               floating-point conversion operations.

          ‘+vfpv3-d16-fp16’
               The VFPv3 floating-point instructions with 16
               double-precision registers and the half-precision
               floating-point conversion operations.

          ‘+nofp’
               Disable the floating-point extension.

          ‘+idiv’
               The ARM-state integer division instructions.

          ‘+noidiv’
               Disable the ARM-state integer division extension.

     ‘armv7e-m’
          ‘+fp’
               The single-precision VFPv4 floating-point instructions.

          ‘+fpv5’
               The single-precision FPv5 floating-point instructions.

          ‘+fp.dp’
               The single- and double-precision FPv5 floating-point
               instructions.

          ‘+nofp’
               Disable the floating-point extensions.

     ‘armv8.1-m.main’

          ‘+dsp’
               The DSP instructions.

          ‘+mve’
               The M-Profile Vector Extension (MVE) integer
               instructions.

          ‘+mve.fp’
               The M-Profile Vector Extension (MVE) integer and single
               precision floating-point instructions.

          ‘+fp’
               The single-precision floating-point instructions.

          ‘+fp.dp’
               The single- and double-precision floating-point
               instructions.

          ‘+nofp’
               Disable the floating-point extension.

          ‘+cdecp0, +cdecp1, ... , +cdecp7’
               Enable the Custom Datapath Extension (CDE) on selected
               coprocessors according to the numbers given in the
               options in the range 0 to 7.

     ‘armv8-m.main’
          ‘+dsp’
               The DSP instructions.

          ‘+nodsp’
               Disable the DSP extension.

          ‘+fp’
               The single-precision floating-point instructions.

          ‘+fp.dp’
               The single- and double-precision floating-point
               instructions.

          ‘+nofp’
               Disable the floating-point extension.

          ‘+cdecp0, +cdecp1, ... , +cdecp7’
               Enable the Custom Datapath Extension (CDE) on selected
               coprocessors according to the numbers given in the
               options in the range 0 to 7.

     ‘armv8-r’
          ‘+crc’
               The Cyclic Redundancy Check (CRC) instructions.
          ‘+fp.sp’
               The single-precision FPv5 floating-point instructions.
          ‘+simd’
               The ARMv8-A Advanced SIMD and floating-point
               instructions.
          ‘+crypto’
               The cryptographic instructions.
          ‘+nocrypto’
               Disable the cryptographic instructions.
          ‘+nofp’
               Disable the floating-point, Advanced SIMD and
               cryptographic instructions.

     ‘-march=native’ causes the compiler to auto-detect the architecture
     of the build computer.  At present, this feature is only supported
     on GNU/Linux, and not all architectures are recognized.  If the
     auto-detect is unsuccessful the option has no effect.

‘-mtune=NAME’
     This option specifies the name of the target ARM processor for
     which GCC should tune the performance of the code.  For some ARM
     implementations better performance can be obtained by using this
     option.  Permissible names are: ‘arm7tdmi’, ‘arm7tdmi-s’,
     ‘arm710t’, ‘arm720t’, ‘arm740t’, ‘strongarm’, ‘strongarm110’,
     ‘strongarm1100’, ‘strongarm1110’, ‘arm8’, ‘arm810’, ‘arm9’,
     ‘arm9e’, ‘arm920’, ‘arm920t’, ‘arm922t’, ‘arm946e-s’, ‘arm966e-s’,
     ‘arm968e-s’, ‘arm926ej-s’, ‘arm940t’, ‘arm9tdmi’, ‘arm10tdmi’,
     ‘arm1020t’, ‘arm1026ej-s’, ‘arm10e’, ‘arm1020e’, ‘arm1022e’,
     ‘arm1136j-s’, ‘arm1136jf-s’, ‘mpcore’, ‘mpcorenovfp’,
     ‘arm1156t2-s’, ‘arm1156t2f-s’, ‘arm1176jz-s’, ‘arm1176jzf-s’,
     ‘generic-armv7-a’, ‘cortex-a5’, ‘cortex-a7’, ‘cortex-a8’,
     ‘cortex-a9’, ‘cortex-a12’, ‘cortex-a15’, ‘cortex-a17’,
     ‘cortex-a32’, ‘cortex-a35’, ‘cortex-a53’, ‘cortex-a55’,
     ‘cortex-a57’, ‘cortex-a72’, ‘cortex-a73’, ‘cortex-a75’,
     ‘cortex-a76’, ‘cortex-a76ae’, ‘cortex-a77’, ‘cortex-a78’,
     ‘cortex-a78ae’, ‘cortex-a78c’, ‘cortex-a710’, ‘ares’, ‘cortex-r4’,
     ‘cortex-r4f’, ‘cortex-r5’, ‘cortex-r7’, ‘cortex-r8’, ‘cortex-r52’,
     ‘cortex-r52plus’, ‘cortex-m0’, ‘cortex-m0plus’, ‘cortex-m1’,
     ‘cortex-m3’, ‘cortex-m4’, ‘cortex-m7’, ‘cortex-m23’, ‘cortex-m33’,
     ‘cortex-m35p’, ‘cortex-m55’, ‘cortex-x1’,
     ‘cortex-m1.small-multiply’, ‘cortex-m0.small-multiply’,
     ‘cortex-m0plus.small-multiply’, ‘exynos-m1’, ‘marvell-pj4’,
     ‘neoverse-n1’, ‘neoverse-n2’, ‘neoverse-v1’, ‘xscale’, ‘iwmmxt’,
     ‘iwmmxt2’, ‘ep9312’, ‘fa526’, ‘fa626’, ‘fa606te’, ‘fa626te’,
     ‘fmp626’, ‘fa726te’, ‘xgene1’.

     Additionally, this option can specify that GCC should tune the
     performance of the code for a big.LITTLE system.  Permissible names
     are: ‘cortex-a15.cortex-a7’, ‘cortex-a17.cortex-a7’,
     ‘cortex-a57.cortex-a53’, ‘cortex-a72.cortex-a53’,
     ‘cortex-a72.cortex-a35’, ‘cortex-a73.cortex-a53’,
     ‘cortex-a75.cortex-a55’, ‘cortex-a76.cortex-a55’.

     ‘-mtune=generic-ARCH’ specifies that GCC should tune the
     performance for a blend of processors within architecture ARCH.
     The aim is to generate code that run well on the current most
     popular processors, balancing between optimizations that benefit
     some CPUs in the range, and avoiding performance pitfalls of other
     CPUs.  The effects of this option may change in future GCC versions
     as CPU models come and go.

     ‘-mtune’ permits the same extension options as ‘-mcpu’, but the
     extension options do not affect the tuning of the generated code.

     ‘-mtune=native’ causes the compiler to auto-detect the CPU of the
     build computer.  At present, this feature is only supported on
     GNU/Linux, and not all architectures are recognized.  If the
     auto-detect is unsuccessful the option has no effect.

‘-mcpu=NAME[+extension...]’
     This specifies the name of the target ARM processor.  GCC uses this
     name to derive the name of the target ARM architecture (as if
     specified by ‘-march’) and the ARM processor type for which to tune
     for performance (as if specified by ‘-mtune’).  Where this option
     is used in conjunction with ‘-march’ or ‘-mtune’, those options
     take precedence over the appropriate part of this option.

     Many of the supported CPUs implement optional architectural
     extensions.  Where this is so the architectural extensions are
     normally enabled by default.  If implementations that lack the
     extension exist, then the extension syntax can be used to disable
     those extensions that have been omitted.  For floating-point and
     Advanced SIMD (Neon) instructions, the settings of the options
     ‘-mfloat-abi’ and ‘-mfpu’ must also be considered: floating-point
     and Advanced SIMD instructions will only be used if ‘-mfloat-abi’
     is not set to ‘soft’; and any setting of ‘-mfpu’ other than ‘auto’
     will override the available floating-point and SIMD extension
     instructions.

     For example, ‘cortex-a9’ can be found in three major
     configurations: integer only, with just a floating-point unit or
     with floating-point and Advanced SIMD. The default is to enable all
     the instructions, but the extensions ‘+nosimd’ and ‘+nofp’ can be
     used to disable just the SIMD or both the SIMD and floating-point
     instructions respectively.

     Permissible names for this option are the same as those for
     ‘-mtune’.

     The following extension options are common to the listed CPUs:

     ‘+nodsp’
          Disable the DSP instructions on ‘cortex-m33’, ‘cortex-m35p’.

     ‘+nofp’
          Disables the floating-point instructions on ‘arm9e’,
          ‘arm946e-s’, ‘arm966e-s’, ‘arm968e-s’, ‘arm10e’, ‘arm1020e’,
          ‘arm1022e’, ‘arm926ej-s’, ‘arm1026ej-s’, ‘cortex-r5’,
          ‘cortex-r7’, ‘cortex-r8’, ‘cortex-m4’, ‘cortex-m7’,
          ‘cortex-m33’ and ‘cortex-m35p’.  Disables the floating-point
          and SIMD instructions on ‘generic-armv7-a’, ‘cortex-a5’,
          ‘cortex-a7’, ‘cortex-a8’, ‘cortex-a9’, ‘cortex-a12’,
          ‘cortex-a15’, ‘cortex-a17’, ‘cortex-a15.cortex-a7’,
          ‘cortex-a17.cortex-a7’, ‘cortex-a32’, ‘cortex-a35’,
          ‘cortex-a53’ and ‘cortex-a55’.

     ‘+nofp.dp’
          Disables the double-precision component of the floating-point
          instructions on ‘cortex-r5’, ‘cortex-r7’, ‘cortex-r8’,
          ‘cortex-r52’, ‘cortex-r52plus’ and ‘cortex-m7’.

     ‘+nosimd’
          Disables the SIMD (but not floating-point) instructions on
          ‘generic-armv7-a’, ‘cortex-a5’, ‘cortex-a7’ and ‘cortex-a9’.

     ‘+crypto’
          Enables the cryptographic instructions on ‘cortex-a32’,
          ‘cortex-a35’, ‘cortex-a53’, ‘cortex-a55’, ‘cortex-a57’,
          ‘cortex-a72’, ‘cortex-a73’, ‘cortex-a75’, ‘exynos-m1’,
          ‘xgene1’, ‘cortex-a57.cortex-a53’, ‘cortex-a72.cortex-a53’,
          ‘cortex-a73.cortex-a35’, ‘cortex-a73.cortex-a53’ and
          ‘cortex-a75.cortex-a55’.

     Additionally the ‘generic-armv7-a’ pseudo target defaults to VFPv3
     with 16 double-precision registers.  It supports the following
     extension options: ‘mp’, ‘sec’, ‘vfpv3-d16’, ‘vfpv3’,
     ‘vfpv3-d16-fp16’, ‘vfpv3-fp16’, ‘vfpv4-d16’, ‘vfpv4’, ‘neon’,
     ‘neon-vfpv3’, ‘neon-fp16’, ‘neon-vfpv4’.  The meanings are the same
     as for the extensions to ‘-march=armv7-a’.

     ‘-mcpu=generic-ARCH’ is also permissible, and is equivalent to
     ‘-march=ARCH -mtune=generic-ARCH’.  See ‘-mtune’ for more
     information.

     ‘-mcpu=native’ causes the compiler to auto-detect the CPU of the
     build computer.  At present, this feature is only supported on
     GNU/Linux, and not all architectures are recognized.  If the
     auto-detect is unsuccessful the option has no effect.

‘-mfpu=NAME’
     This specifies what floating-point hardware (or hardware emulation)
     is available on the target.  Permissible names are: ‘auto’,
     ‘vfpv2’, ‘vfpv3’, ‘vfpv3-fp16’, ‘vfpv3-d16’, ‘vfpv3-d16-fp16’,
     ‘vfpv3xd’, ‘vfpv3xd-fp16’, ‘neon-vfpv3’, ‘neon-fp16’, ‘vfpv4’,
     ‘vfpv4-d16’, ‘fpv4-sp-d16’, ‘neon-vfpv4’, ‘fpv5-d16’,
     ‘fpv5-sp-d16’, ‘fp-armv8’, ‘neon-fp-armv8’ and
     ‘crypto-neon-fp-armv8’.  Note that ‘neon’ is an alias for
     ‘neon-vfpv3’ and ‘vfp’ is an alias for ‘vfpv2’.

     The setting ‘auto’ is the default and is special.  It causes the
     compiler to select the floating-point and Advanced SIMD
     instructions based on the settings of ‘-mcpu’ and ‘-march’.

     If the selected floating-point hardware includes the NEON extension
     (e.g. ‘-mfpu=neon’), note that floating-point operations are not
     generated by GCC's auto-vectorization pass unless
     ‘-funsafe-math-optimizations’ is also specified.  This is because
     NEON hardware does not fully implement the IEEE 754 standard for
     floating-point arithmetic (in particular denormal values are
     treated as zero), so the use of NEON instructions may lead to a
     loss of precision.

     You can also set the fpu name at function level by using the
     ‘target("fpu=")’ function attributes (*note ARM Function
     Attributes::) or pragmas (*note Function Specific Option
     Pragmas::).

‘-mfp16-format=NAME’
     Specify the format of the ‘__fp16’ half-precision floating-point
     type.  Permissible names are ‘none’, ‘ieee’, and ‘alternative’; the
     default is ‘none’, in which case the ‘__fp16’ type is not defined.
     *Note Half-Precision::, for more information.

‘-mstructure-size-boundary=N’
     The sizes of all structures and unions are rounded up to a multiple
     of the number of bits set by this option.  Permissible values are
     8, 32 and 64.  The default value varies for different toolchains.
     For the COFF targeted toolchain the default value is 8.  A value of
     64 is only allowed if the underlying ABI supports it.

     Specifying a larger number can produce faster, more efficient code,
     but can also increase the size of the program.  Different values
     are potentially incompatible.  Code compiled with one value cannot
     necessarily expect to work with code or libraries compiled with
     another value, if they exchange information using structures or
     unions.

     This option is deprecated.

‘-mabort-on-noreturn’
     Generate a call to the function ‘abort’ at the end of a ‘noreturn’
     function.  It is executed if the function tries to return.

‘-mlong-calls’
‘-mno-long-calls’
     Tells the compiler to perform function calls by first loading the
     address of the function into a register and then performing a
     subroutine call on this register.  This switch is needed if the
     target function lies outside of the 64-megabyte addressing range of
     the offset-based version of subroutine call instruction.

     Even if this switch is enabled, not all function calls are turned
     into long calls.  The heuristic is that static functions, functions
     that have the ‘short_call’ attribute, functions that are inside the
     scope of a ‘#pragma no_long_calls’ directive, and functions whose
     definitions have already been compiled within the current
     compilation unit are not turned into long calls.  The exceptions to
     this rule are that weak function definitions, functions with the
     ‘long_call’ attribute or the ‘section’ attribute, and functions
     that are within the scope of a ‘#pragma long_calls’ directive are
     always turned into long calls.

     This feature is not enabled by default.  Specifying
     ‘-mno-long-calls’ restores the default behavior, as does placing
     the function calls within the scope of a ‘#pragma long_calls_off’
     directive.  Note these switches have no effect on how the compiler
     generates code to handle function calls via function pointers.

‘-msingle-pic-base’
     Treat the register used for PIC addressing as read-only, rather
     than loading it in the prologue for each function.  The runtime
     system is responsible for initializing this register with an
     appropriate value before execution begins.

‘-mpic-register=REG’
     Specify the register to be used for PIC addressing.  For standard
     PIC base case, the default is any suitable register determined by
     compiler.  For single PIC base case, the default is ‘R9’ if target
     is EABI based or stack-checking is enabled, otherwise the default
     is ‘R10’.

‘-mpic-data-is-text-relative’
     Assume that the displacement between the text and data segments is
     fixed at static link time.  This permits using PC-relative
     addressing operations to access data known to be in the data
     segment.  For non-VxWorks RTP targets, this option is enabled by
     default.  When disabled on such targets, it will enable
     ‘-msingle-pic-base’ by default.

‘-mpoke-function-name’
     Write the name of each function into the text section, directly
     preceding the function prologue.  The generated code is similar to
     this:

               t0
                   .ascii "arm_poke_function_name", 0
                   .align
               t1
                   .word 0xff000000 + (t1 - t0)
               arm_poke_function_name
                   mov     ip, sp
                   stmfd   sp!, {fp, ip, lr, pc}
                   sub     fp, ip, #4

     When performing a stack backtrace, code can inspect the value of
     ‘pc’ stored at ‘fp + 0’.  If the trace function then looks at
     location ‘pc - 12’ and the top 8 bits are set, then we know that
     there is a function name embedded immediately preceding this
     location and has length ‘((pc[-3]) & 0xff000000)’.

‘-mthumb’
‘-marm’

     Select between generating code that executes in ARM and Thumb
     states.  The default for most configurations is to generate code
     that executes in ARM state, but the default can be changed by
     configuring GCC with the ‘--with-mode=’STATE configure option.

     You can also override the ARM and Thumb mode for each function by
     using the ‘target("thumb")’ and ‘target("arm")’ function attributes
     (*note ARM Function Attributes::) or pragmas (*note Function
     Specific Option Pragmas::).

‘-mflip-thumb’
     Switch ARM/Thumb modes on alternating functions.  This option is
     provided for regression testing of mixed Thumb/ARM code generation,
     and is not intended for ordinary use in compiling code.

‘-mtpcs-frame’
     Generate a stack frame that is compliant with the Thumb Procedure
     Call Standard for all non-leaf functions.  (A leaf function is one
     that does not call any other functions.)  The default is
     ‘-mno-tpcs-frame’.

‘-mtpcs-leaf-frame’
     Generate a stack frame that is compliant with the Thumb Procedure
     Call Standard for all leaf functions.  (A leaf function is one that
     does not call any other functions.)  The default is
     ‘-mno-apcs-leaf-frame’.

‘-mcallee-super-interworking’
     Gives all externally visible functions in the file being compiled
     an ARM instruction set header which switches to Thumb mode before
     executing the rest of the function.  This allows these functions to
     be called from non-interworking code.  This option is not valid in
     AAPCS configurations because interworking is enabled by default.

‘-mcaller-super-interworking’
     Allows calls via function pointers (including virtual functions) to
     execute correctly regardless of whether the target code has been
     compiled for interworking or not.  There is a small overhead in the
     cost of executing a function pointer if this option is enabled.
     This option is not valid in AAPCS configurations because
     interworking is enabled by default.

‘-mtp=NAME’
     Specify the access model for the thread local storage pointer.  The
     valid models are ‘soft’, which generates calls to
     ‘__aeabi_read_tp’, ‘cp15’, which fetches the thread pointer from
     ‘cp15’ directly (supported in the arm6k architecture), and ‘auto’,
     which uses the best available method for the selected processor.
     The default setting is ‘auto’.

‘-mtls-dialect=DIALECT’
     Specify the dialect to use for accessing thread local storage.  Two
     DIALECTs are supported--‘gnu’ and ‘gnu2’.  The ‘gnu’ dialect
     selects the original GNU scheme for supporting local and global
     dynamic TLS models.  The ‘gnu2’ dialect selects the GNU descriptor
     scheme, which provides better performance for shared libraries.
     The GNU descriptor scheme is compatible with the original scheme,
     but does require new assembler, linker and library support.
     Initial and local exec TLS models are unaffected by this option and
     always use the original scheme.

‘-mword-relocations’
     Only generate absolute relocations on word-sized values (i.e.
     R_ARM_ABS32).  This is enabled by default on targets (uClinux,
     SymbianOS) where the runtime loader imposes this restriction, and
     when ‘-fpic’ or ‘-fPIC’ is specified.  This option conflicts with
     ‘-mslow-flash-data’.

‘-mfix-cortex-m3-ldrd’
     Some Cortex-M3 cores can cause data corruption when ‘ldrd’
     instructions with overlapping destination and base registers are
     used.  This option avoids generating these instructions.  This
     option is enabled by default when ‘-mcpu=cortex-m3’ is specified.

‘-mfix-cortex-a57-aes-1742098’
‘-mno-fix-cortex-a57-aes-1742098’
‘-mfix-cortex-a72-aes-1655431’
‘-mno-fix-cortex-a72-aes-1655431’
     Enable (disable) mitigation for an erratum on Cortex-A57 and
     Cortex-A72 that affects the AES cryptographic instructions.  This
     option is enabled by default when either ‘-mcpu=cortex-a57’ or
     ‘-mcpu=cortex-a72’ is specified.

‘-munaligned-access’
‘-mno-unaligned-access’
     Enables (or disables) reading and writing of 16- and 32- bit values
     from addresses that are not 16- or 32- bit aligned.  By default
     unaligned access is disabled for all pre-ARMv6, all ARMv6-M and for
     ARMv8-M Baseline architectures, and enabled for all other
     architectures.  If unaligned access is not enabled then words in
     packed data structures are accessed a byte at a time.

     The ARM attribute ‘Tag_CPU_unaligned_access’ is set in the
     generated object file to either true or false, depending upon the
     setting of this option.  If unaligned access is enabled then the
     preprocessor symbol ‘__ARM_FEATURE_UNALIGNED’ is also defined.

‘-mneon-for-64bits’
     This option is deprecated and has no effect.

‘-mslow-flash-data’
     Assume loading data from flash is slower than fetching instruction.
     Therefore literal load is minimized for better performance.  This
     option is only supported when compiling for ARMv7 M-profile and off
     by default.  It conflicts with ‘-mword-relocations’.

‘-masm-syntax-unified’
     Assume inline assembler is using unified asm syntax.  The default
     is currently off which implies divided syntax.  This option has no
     impact on Thumb2.  However, this may change in future releases of
     GCC.  Divided syntax should be considered deprecated.

‘-mrestrict-it’
     Restricts generation of IT blocks to conform to the rules of
     ARMv8-A.  IT blocks can only contain a single 16-bit instruction
     from a select set of instructions.  This option is on by default
     for ARMv8-A Thumb mode.

‘-mprint-tune-info’
     Print CPU tuning information as comment in assembler file.  This is
     an option used only for regression testing of the compiler and not
     intended for ordinary use in compiling code.  This option is
     disabled by default.

‘-mverbose-cost-dump’
     Enable verbose cost model dumping in the debug dump files.  This
     option is provided for use in debugging the compiler.

‘-mpure-code’
     Do not allow constant data to be placed in code sections.
     Additionally, when compiling for ELF object format give all text
     sections the ELF processor-specific section attribute
     ‘SHF_ARM_PURECODE’.  This option is only available when generating
     non-pic code for M-profile targets.

‘-mcmse’
     Generate secure code as per the "ARMv8-M Security Extensions:
     Requirements on Development Tools Engineering Specification", which
     can be found on
     <https://developer.arm.com/documentation/ecm0359818/latest/>.

‘-mfix-cmse-cve-2021-35465’
     Mitigate against a potential security issue with the ‘VLLDM’
     instruction in some M-profile devices when using CMSE
     (CVE-2021-365465).  This option is enabled by default when the
     option ‘-mcpu=’ is used with ‘cortex-m33’, ‘cortex-m35p’ or
     ‘cortex-m55’.  The option ‘-mno-fix-cmse-cve-2021-35465’ can be
     used to disable the mitigation.

‘-mstack-protector-guard=GUARD’
‘-mstack-protector-guard-offset=OFFSET’
     Generate stack protection code using canary at GUARD.  Supported
     locations are ‘global’ for a global canary or ‘tls’ for a canary
     accessible via the TLS register.  The option
     ‘-mstack-protector-guard-offset=’ is for use with
     ‘-fstack-protector-guard=tls’ and not for use in user-land code.

‘-mfdpic’
‘-mno-fdpic’
     Select the FDPIC ABI, which uses 64-bit function descriptors to
     represent pointers to functions.  When the compiler is configured
     for ‘arm-*-uclinuxfdpiceabi’ targets, this option is on by default
     and implies ‘-fPIE’ if none of the PIC/PIE-related options is
     provided.  On other targets, it only enables the FDPIC-specific
     code generation features, and the user should explicitly provide
     the PIC/PIE-related options as needed.

     Note that static linking is not supported because it would still
     involve the dynamic linker when the program self-relocates.  If
     such behavior is acceptable, use -static and -Wl,-dynamic-linker
     options.

     The opposite ‘-mno-fdpic’ option is useful (and required) to build
     the Linux kernel using the same (‘arm-*-uclinuxfdpiceabi’)
     toolchain as the one used to build the userland programs.


File: gcc.info,  Node: AVR Options,  Next: Blackfin Options,  Prev: ARM Options,  Up: Submodel Options

3.19.6 AVR Options
------------------

These options are defined for AVR implementations:

‘-mmcu=MCU’
     Specify Atmel AVR instruction set architectures (ISA) or MCU type.

     The default for this option is ‘avr2’.

     GCC supports the following AVR devices and ISAs:

     ‘avr2’
          "Classic" devices with up to 8 KiB of program memory.
          MCU = ‘attiny22’, ‘attiny26’, ‘at90s2313’, ‘at90s2323’,
          ‘at90s2333’, ‘at90s2343’, ‘at90s4414’, ‘at90s4433’,
          ‘at90s4434’, ‘at90c8534’, ‘at90s8515’, ‘at90s8535’.

     ‘avr25’
          "Classic" devices with up to 8 KiB of program memory and with
          the ‘MOVW’ instruction.
          MCU = ‘attiny13’, ‘attiny13a’, ‘attiny24’, ‘attiny24a’,
          ‘attiny25’, ‘attiny261’, ‘attiny261a’, ‘attiny2313’,
          ‘attiny2313a’, ‘attiny43u’, ‘attiny44’, ‘attiny44a’,
          ‘attiny45’, ‘attiny48’, ‘attiny441’, ‘attiny461’,
          ‘attiny461a’, ‘attiny4313’, ‘attiny84’, ‘attiny84a’,
          ‘attiny85’, ‘attiny87’, ‘attiny88’, ‘attiny828’, ‘attiny841’,
          ‘attiny861’, ‘attiny861a’, ‘ata5272’, ‘ata6616c’, ‘at86rf401’.

     ‘avr3’
          "Classic" devices with 16 KiB up to 64 KiB of program memory.

          MCU = ‘at76c711’, ‘at43usb355’.

     ‘avr31’
          "Classic" devices with 128 KiB of program memory.
          MCU = ‘atmega103’, ‘at43usb320’.

     ‘avr35’
          "Classic" devices with 16 KiB up to 64 KiB of program memory
          and with the ‘MOVW’ instruction.
          MCU = ‘attiny167’, ‘attiny1634’, ‘atmega8u2’, ‘atmega16u2’,
          ‘atmega32u2’, ‘ata5505’, ‘ata6617c’, ‘ata664251’, ‘at90usb82’,
          ‘at90usb162’.

     ‘avr4’
          "Enhanced" devices with up to 8 KiB of program memory.
          MCU = ‘atmega48’, ‘atmega48a’, ‘atmega48p’, ‘atmega48pa’,
          ‘atmega48pb’, ‘atmega8’, ‘atmega8a’, ‘atmega8hva’, ‘atmega88’,
          ‘atmega88a’, ‘atmega88p’, ‘atmega88pa’, ‘atmega88pb’,
          ‘atmega8515’, ‘atmega8535’, ‘ata6285’, ‘ata6286’, ‘ata6289’,
          ‘ata6612c’, ‘at90pwm1’, ‘at90pwm2’, ‘at90pwm2b’, ‘at90pwm3’,
          ‘at90pwm3b’, ‘at90pwm81’.

     ‘avr5’
          "Enhanced" devices with 16 KiB up to 64 KiB of program memory.

          MCU = ‘atmega16’, ‘atmega16a’, ‘atmega16hva’, ‘atmega16hva2’,
          ‘atmega16hvb’, ‘atmega16hvbrevb’, ‘atmega16m1’, ‘atmega16u4’,
          ‘atmega161’, ‘atmega162’, ‘atmega163’, ‘atmega164a’,
          ‘atmega164p’, ‘atmega164pa’, ‘atmega165’, ‘atmega165a’,
          ‘atmega165p’, ‘atmega165pa’, ‘atmega168’, ‘atmega168a’,
          ‘atmega168p’, ‘atmega168pa’, ‘atmega168pb’, ‘atmega169’,
          ‘atmega169a’, ‘atmega169p’, ‘atmega169pa’, ‘atmega32’,
          ‘atmega32a’, ‘atmega32c1’, ‘atmega32hvb’, ‘atmega32hvbrevb’,
          ‘atmega32m1’, ‘atmega32u4’, ‘atmega32u6’, ‘atmega323’,
          ‘atmega324a’, ‘atmega324p’, ‘atmega324pa’, ‘atmega324pb’,
          ‘atmega325’, ‘atmega325a’, ‘atmega325p’, ‘atmega325pa’,
          ‘atmega328’, ‘atmega328p’, ‘atmega328pb’, ‘atmega329’,
          ‘atmega329a’, ‘atmega329p’, ‘atmega329pa’, ‘atmega3250’,
          ‘atmega3250a’, ‘atmega3250p’, ‘atmega3250pa’, ‘atmega3290’,
          ‘atmega3290a’, ‘atmega3290p’, ‘atmega3290pa’, ‘atmega406’,
          ‘atmega64’, ‘atmega64a’, ‘atmega64c1’, ‘atmega64hve’,
          ‘atmega64hve2’, ‘atmega64m1’, ‘atmega64rfr2’, ‘atmega640’,
          ‘atmega644’, ‘atmega644a’, ‘atmega644p’, ‘atmega644pa’,
          ‘atmega644rfr2’, ‘atmega645’, ‘atmega645a’, ‘atmega645p’,
          ‘atmega649’, ‘atmega649a’, ‘atmega649p’, ‘atmega6450’,
          ‘atmega6450a’, ‘atmega6450p’, ‘atmega6490’, ‘atmega6490a’,
          ‘atmega6490p’, ‘ata5795’, ‘ata5790’, ‘ata5790n’, ‘ata5791’,
          ‘ata6613c’, ‘ata6614q’, ‘ata5782’, ‘ata5831’, ‘ata8210’,
          ‘ata8510’, ‘ata5702m322’, ‘at90pwm161’, ‘at90pwm216’,
          ‘at90pwm316’, ‘at90can32’, ‘at90can64’, ‘at90scr100’,
          ‘at90usb646’, ‘at90usb647’, ‘at94k’, ‘m3000’.

     ‘avr51’
          "Enhanced" devices with 128 KiB of program memory.
          MCU = ‘atmega128’, ‘atmega128a’, ‘atmega128rfa1’,
          ‘atmega128rfr2’, ‘atmega1280’, ‘atmega1281’, ‘atmega1284’,
          ‘atmega1284p’, ‘atmega1284rfr2’, ‘at90can128’, ‘at90usb1286’,
          ‘at90usb1287’.

     ‘avr6’
          "Enhanced" devices with 3-byte PC, i.e. with more than 128 KiB
          of program memory.
          MCU = ‘atmega256rfr2’, ‘atmega2560’, ‘atmega2561’,
          ‘atmega2564rfr2’.

     ‘avrxmega2’
          "XMEGA" devices with more than 8 KiB and up to 64 KiB of
          program memory.
          MCU = ‘atxmega8e5’, ‘atxmega16a4’, ‘atxmega16a4u’,
          ‘atxmega16c4’, ‘atxmega16d4’, ‘atxmega16e5’, ‘atxmega32a4’,
          ‘atxmega32a4u’, ‘atxmega32c3’, ‘atxmega32c4’, ‘atxmega32d3’,
          ‘atxmega32d4’, ‘atxmega32e5’.

     ‘avrxmega3’
          "XMEGA" devices with up to 64 KiB of combined program memory
          and RAM, and with program memory visible in the RAM address
          space.
          MCU = ‘attiny202’, ‘attiny204’, ‘attiny212’, ‘attiny214’,
          ‘attiny402’, ‘attiny404’, ‘attiny406’, ‘attiny412’,
          ‘attiny414’, ‘attiny416’, ‘attiny417’, ‘attiny804’,
          ‘attiny806’, ‘attiny807’, ‘attiny814’, ‘attiny816’,
          ‘attiny817’, ‘attiny1604’, ‘attiny1606’, ‘attiny1607’,
          ‘attiny1614’, ‘attiny1616’, ‘attiny1617’, ‘attiny3214’,
          ‘attiny3216’, ‘attiny3217’, ‘atmega808’, ‘atmega809’,
          ‘atmega1608’, ‘atmega1609’, ‘atmega3208’, ‘atmega3209’,
          ‘atmega4808’, ‘atmega4809’.

     ‘avrxmega4’
          "XMEGA" devices with more than 64 KiB and up to 128 KiB of
          program memory.
          MCU = ‘atxmega64a3’, ‘atxmega64a3u’, ‘atxmega64a4u’,
          ‘atxmega64b1’, ‘atxmega64b3’, ‘atxmega64c3’, ‘atxmega64d3’,
          ‘atxmega64d4’.

     ‘avrxmega5’
          "XMEGA" devices with more than 64 KiB and up to 128 KiB of
          program memory and more than 64 KiB of RAM.
          MCU = ‘atxmega64a1’, ‘atxmega64a1u’.

     ‘avrxmega6’
          "XMEGA" devices with more than 128 KiB of program memory.
          MCU = ‘atxmega128a3’, ‘atxmega128a3u’, ‘atxmega128b1’,
          ‘atxmega128b3’, ‘atxmega128c3’, ‘atxmega128d3’,
          ‘atxmega128d4’, ‘atxmega192a3’, ‘atxmega192a3u’,
          ‘atxmega192c3’, ‘atxmega192d3’, ‘atxmega256a3’,
          ‘atxmega256a3b’, ‘atxmega256a3bu’, ‘atxmega256a3u’,
          ‘atxmega256c3’, ‘atxmega256d3’, ‘atxmega384c3’,
          ‘atxmega384d3’.

     ‘avrxmega7’
          "XMEGA" devices with more than 128 KiB of program memory and
          more than 64 KiB of RAM.
          MCU = ‘atxmega128a1’, ‘atxmega128a1u’, ‘atxmega128a4u’.

     ‘avrtiny’
          "TINY" Tiny core devices with 512 B up to 4 KiB of program
          memory.
          MCU = ‘attiny4’, ‘attiny5’, ‘attiny9’, ‘attiny10’, ‘attiny20’,
          ‘attiny40’.

     ‘avr1’
          This ISA is implemented by the minimal AVR core and supported
          for assembler only.
          MCU = ‘attiny11’, ‘attiny12’, ‘attiny15’, ‘attiny28’,
          ‘at90s1200’.

‘-mabsdata’

     Assume that all data in static storage can be accessed by LDS / STS
     instructions.  This option has only an effect on reduced Tiny
     devices like ATtiny40.  See also the ‘absdata’ *note variable
     attribute: AVR Variable Attributes.

‘-maccumulate-args’
     Accumulate outgoing function arguments and acquire/release the
     needed stack space for outgoing function arguments once in function
     prologue/epilogue.  Without this option, outgoing arguments are
     pushed before calling a function and popped afterwards.

     Popping the arguments after the function call can be expensive on
     AVR so that accumulating the stack space might lead to smaller
     executables because arguments need not be removed from the stack
     after such a function call.

     This option can lead to reduced code size for functions that
     perform several calls to functions that get their arguments on the
     stack like calls to printf-like functions.

‘-mbranch-cost=COST’
     Set the branch costs for conditional branch instructions to COST.
     Reasonable values for COST are small, non-negative integers.  The
     default branch cost is 0.

‘-mcall-prologues’
     Functions prologues/epilogues are expanded as calls to appropriate
     subroutines.  Code size is smaller.

‘-mdouble=BITS’
‘-mlong-double=BITS’
     Set the size (in bits) of the ‘double’ or ‘long double’ type,
     respectively.  Possible values for BITS are 32 and 64.  Whether or
     not a specific value for BITS is allowed depends on the
     ‘--with-double=’ and ‘--with-long-double=’
     configure options (https://gcc.gnu.org/install/configure.html#avr),
     and the same applies for the default values of the options.

‘-mgas-isr-prologues’
     Interrupt service routines (ISRs) may use the ‘__gcc_isr’ pseudo
     instruction supported by GNU Binutils.  If this option is on, the
     feature can still be disabled for individual ISRs by means of the
     *note ‘no_gccisr’: AVR Function Attributes. function attribute.
     This feature is activated per default if optimization is on (but
     not with ‘-Og’, *note Optimize Options::), and if GNU Binutils
     support PR21683 (https://sourceware.org/PR21683).

‘-mint8’
     Assume ‘int’ to be 8-bit integer.  This affects the sizes of all
     types: a ‘char’ is 1 byte, an ‘int’ is 1 byte, a ‘long’ is 2 bytes,
     and ‘long long’ is 4 bytes.  Please note that this option does not
     conform to the C standards, but it results in smaller code size.

‘-mmain-is-OS_task’
     Do not save registers in ‘main’.  The effect is the same like
     attaching attribute *note ‘OS_task’: AVR Function Attributes. to
     ‘main’.  It is activated per default if optimization is on.

‘-mn-flash=NUM’
     Assume that the flash memory has a size of NUM times 64 KiB.

‘-mno-interrupts’
     Generated code is not compatible with hardware interrupts.  Code
     size is smaller.

‘-mrelax’
     Try to replace ‘CALL’ resp. ‘JMP’ instruction by the shorter
     ‘RCALL’ resp. ‘RJMP’ instruction if applicable.  Setting ‘-mrelax’
     just adds the ‘--mlink-relax’ option to the assembler's command
     line and the ‘--relax’ option to the linker's command line.

     Jump relaxing is performed by the linker because jump offsets are
     not known before code is located.  Therefore, the assembler code
     generated by the compiler is the same, but the instructions in the
     executable may differ from instructions in the assembler code.

     Relaxing must be turned on if linker stubs are needed, see the
     section on ‘EIND’ and linker stubs below.

‘-mrmw’
     Assume that the device supports the Read-Modify-Write instructions
     ‘XCH’, ‘LAC’, ‘LAS’ and ‘LAT’.

‘-mshort-calls’

     Assume that ‘RJMP’ and ‘RCALL’ can target the whole program memory.

     This option is used internally for multilib selection.  It is not
     an optimization option, and you don't need to set it by hand.

‘-msp8’
     Treat the stack pointer register as an 8-bit register, i.e. assume
     the high byte of the stack pointer is zero.  In general, you don't
     need to set this option by hand.

     This option is used internally by the compiler to select and build
     multilibs for architectures ‘avr2’ and ‘avr25’.  These
     architectures mix devices with and without ‘SPH’.  For any setting
     other than ‘-mmcu=avr2’ or ‘-mmcu=avr25’ the compiler driver adds
     or removes this option from the compiler proper's command line,
     because the compiler then knows if the device or architecture has
     an 8-bit stack pointer and thus no ‘SPH’ register or not.

‘-mstrict-X’
     Use address register ‘X’ in a way proposed by the hardware.  This
     means that ‘X’ is only used in indirect, post-increment or
     pre-decrement addressing.

     Without this option, the ‘X’ register may be used in the same way
     as ‘Y’ or ‘Z’ which then is emulated by additional instructions.
     For example, loading a value with ‘X+const’ addressing with a small
     non-negative ‘const < 64’ to a register RN is performed as

          adiw r26, const   ; X += const
          ld   RN, X        ; RN = *X
          sbiw r26, const   ; X -= const

‘-mtiny-stack’
     Only change the lower 8 bits of the stack pointer.

‘-mfract-convert-truncate’
     Allow to use truncation instead of rounding towards zero for
     fractional fixed-point types.

‘-nodevicelib’
     Don't link against AVR-LibC's device specific library ‘lib<mcu>.a’.

‘-nodevicespecs’
     Don't add ‘-specs=device-specs/specs-MCU’ to the compiler driver's
     command line.  The user takes responsibility for supplying the
     sub-processes like compiler proper, assembler and linker with
     appropriate command line options.  This means that the user has to
     supply her private device specs file by means of
     ‘-specs=PATH-TO-SPECS-FILE’.  There is no more need for option
     ‘-mmcu=MCU’.

     This option can also serve as a replacement for the older way of
     specifying custom device-specs files that needed ‘-B SOME-PATH’ to
     point to a directory which contains a folder named ‘device-specs’
     which contains a specs file named ‘specs-MCU’, where MCU was
     specified by ‘-mmcu=MCU’.

‘-Waddr-space-convert’
     Warn about conversions between address spaces in the case where the
     resulting address space is not contained in the incoming address
     space.

‘-Wmisspelled-isr’
     Warn if the ISR is misspelled, i.e. without __vector prefix.
     Enabled by default.

3.19.6.1 ‘EIND’ and Devices with More Than 128 Ki Bytes of Flash
................................................................

Pointers in the implementation are 16 bits wide.  The address of a
function or label is represented as word address so that indirect jumps
and calls can target any code address in the range of 64 Ki words.

 In order to facilitate indirect jump on devices with more than 128 Ki
bytes of program memory space, there is a special function register
called ‘EIND’ that serves as most significant part of the target address
when ‘EICALL’ or ‘EIJMP’ instructions are used.

 Indirect jumps and calls on these devices are handled as follows by the
compiler and are subject to some limitations:

   • The compiler never sets ‘EIND’.

   • The compiler uses ‘EIND’ implicitly in ‘EICALL’/‘EIJMP’
     instructions or might read ‘EIND’ directly in order to emulate an
     indirect call/jump by means of a ‘RET’ instruction.

   • The compiler assumes that ‘EIND’ never changes during the startup
     code or during the application.  In particular, ‘EIND’ is not
     saved/restored in function or interrupt service routine
     prologue/epilogue.

   • For indirect calls to functions and computed goto, the linker
     generates _stubs_.  Stubs are jump pads sometimes also called
     _trampolines_.  Thus, the indirect call/jump jumps to such a stub.
     The stub contains a direct jump to the desired address.

   • Linker relaxation must be turned on so that the linker generates
     the stubs correctly in all situations.  See the compiler option
     ‘-mrelax’ and the linker option ‘--relax’.  There are corner cases
     where the linker is supposed to generate stubs but aborts without
     relaxation and without a helpful error message.

   • The default linker script is arranged for code with ‘EIND = 0’.  If
     code is supposed to work for a setup with ‘EIND != 0’, a custom
     linker script has to be used in order to place the sections whose
     name start with ‘.trampolines’ into the segment where ‘EIND’ points
     to.

   • The startup code from libgcc never sets ‘EIND’.  Notice that
     startup code is a blend of code from libgcc and AVR-LibC. For the
     impact of AVR-LibC on ‘EIND’, see the
     AVR-LibC user manual (http://nongnu.org/avr-libc/user-manual/).

   • It is legitimate for user-specific startup code to set up ‘EIND’
     early, for example by means of initialization code located in
     section ‘.init3’.  Such code runs prior to general startup code
     that initializes RAM and calls constructors, but after the bit of
     startup code from AVR-LibC that sets ‘EIND’ to the segment where
     the vector table is located.
          #include <avr/io.h>

          static void
          __attribute__((section(".init3"),naked,used,no_instrument_function))
          init3_set_eind (void)
          {
            __asm volatile ("ldi r24,pm_hh8(__trampolines_start)\n\t"
                            "out %i0,r24" :: "n" (&EIND) : "r24","memory");
          }

     The ‘__trampolines_start’ symbol is defined in the linker script.

   • Stubs are generated automatically by the linker if the following
     two conditions are met:

        − The address of a label is taken by means of the ‘gs’ modifier
          (short for _generate stubs_) like so:
               LDI r24, lo8(gs(FUNC))
               LDI r25, hi8(gs(FUNC))
        − The final location of that label is in a code segment
          _outside_ the segment where the stubs are located.

   • The compiler emits such ‘gs’ modifiers for code labels in the
     following situations:
        − Taking address of a function or code label.
        − Computed goto.
        − If prologue-save function is used, see ‘-mcall-prologues’
          command-line option.
        − Switch/case dispatch tables.  If you do not want such dispatch
          tables you can specify the ‘-fno-jump-tables’ command-line
          option.
        − C and C++ constructors/destructors called during
          startup/shutdown.
        − If the tools hit a ‘gs()’ modifier explained above.

   • Jumping to non-symbolic addresses like so is _not_ supported:

          int main (void)
          {
              /* Call function at word address 0x2 */
              return ((int(*)(void)) 0x2)();
          }

     Instead, a stub has to be set up, i.e. the function has to be
     called through a symbol (‘func_4’ in the example):

          int main (void)
          {
              extern int func_4 (void);

              /* Call function at byte address 0x4 */
              return func_4();
          }

     and the application be linked with ‘-Wl,--defsym,func_4=0x4’.
     Alternatively, ‘func_4’ can be defined in the linker script.

3.19.6.2 Handling of the ‘RAMPD’, ‘RAMPX’, ‘RAMPY’ and ‘RAMPZ’ Special Function Registers
.........................................................................................

Some AVR devices support memories larger than the 64 KiB range that can
be accessed with 16-bit pointers.  To access memory locations outside
this 64 KiB range, the content of a ‘RAMP’ register is used as high part
of the address: The ‘X’, ‘Y’, ‘Z’ address register is concatenated with
the ‘RAMPX’, ‘RAMPY’, ‘RAMPZ’ special function register, respectively,
to get a wide address.  Similarly, ‘RAMPD’ is used together with direct
addressing.

   • The startup code initializes the ‘RAMP’ special function registers
     with zero.

   • If a *note named address space: AVR Named Address Spaces. other
     than generic or ‘__flash’ is used, then ‘RAMPZ’ is set as needed
     before the operation.

   • If the device supports RAM larger than 64 KiB and the compiler
     needs to change ‘RAMPZ’ to accomplish an operation, ‘RAMPZ’ is
     reset to zero after the operation.

   • If the device comes with a specific ‘RAMP’ register, the ISR
     prologue/epilogue saves/restores that SFR and initializes it with
     zero in case the ISR code might (implicitly) use it.

   • RAM larger than 64 KiB is not supported by GCC for AVR targets.  If
     you use inline assembler to read from locations outside the 16-bit
     address range and change one of the ‘RAMP’ registers, you must
     reset it to zero after the access.

3.19.6.3 AVR Built-in Macros
............................

GCC defines several built-in macros so that the user code can test for
the presence or absence of features.  Almost any of the following
built-in macros are deduced from device capabilities and thus triggered
by the ‘-mmcu=’ command-line option.

 For even more AVR-specific built-in macros see *note AVR Named Address
Spaces:: and *note AVR Built-in Functions::.

‘__AVR_ARCH__’
     Build-in macro that resolves to a decimal number that identifies
     the architecture and depends on the ‘-mmcu=MCU’ option.  Possible
     values are:

     ‘2’, ‘25’, ‘3’, ‘31’, ‘35’, ‘4’, ‘5’, ‘51’, ‘6’

     for MCU=‘avr2’, ‘avr25’, ‘avr3’, ‘avr31’, ‘avr35’, ‘avr4’, ‘avr5’,
     ‘avr51’, ‘avr6’,

     respectively and

     ‘100’, ‘102’, ‘103’, ‘104’, ‘105’, ‘106’, ‘107’

     for MCU=‘avrtiny’, ‘avrxmega2’, ‘avrxmega3’, ‘avrxmega4’,
     ‘avrxmega5’, ‘avrxmega6’, ‘avrxmega7’, respectively.  If MCU
     specifies a device, this built-in macro is set accordingly.  For
     example, with ‘-mmcu=atmega8’ the macro is defined to ‘4’.

‘__AVR_DEVICE__’
     Setting ‘-mmcu=DEVICE’ defines this built-in macro which reflects
     the device's name.  For example, ‘-mmcu=atmega8’ defines the
     built-in macro ‘__AVR_ATmega8__’, ‘-mmcu=attiny261a’ defines
     ‘__AVR_ATtiny261A__’, etc.

     The built-in macros' names follow the scheme ‘__AVR_DEVICE__’ where
     DEVICE is the device name as from the AVR user manual.  The
     difference between DEVICE in the built-in macro and DEVICE in
     ‘-mmcu=DEVICE’ is that the latter is always lowercase.

     If DEVICE is not a device but only a core architecture like
     ‘avr51’, this macro is not defined.

‘__AVR_DEVICE_NAME__’
     Setting ‘-mmcu=DEVICE’ defines this built-in macro to the device's
     name.  For example, with ‘-mmcu=atmega8’ the macro is defined to
     ‘atmega8’.

     If DEVICE is not a device but only a core architecture like
     ‘avr51’, this macro is not defined.

‘__AVR_XMEGA__’
     The device / architecture belongs to the XMEGA family of devices.

‘__AVR_HAVE_ELPM__’
     The device has the ‘ELPM’ instruction.

‘__AVR_HAVE_ELPMX__’
     The device has the ‘ELPM RN,Z’ and ‘ELPM RN,Z+’ instructions.

‘__AVR_HAVE_MOVW__’
     The device has the ‘MOVW’ instruction to perform 16-bit
     register-register moves.

‘__AVR_HAVE_LPMX__’
     The device has the ‘LPM RN,Z’ and ‘LPM RN,Z+’ instructions.

‘__AVR_HAVE_MUL__’
     The device has a hardware multiplier.

‘__AVR_HAVE_JMP_CALL__’
     The device has the ‘JMP’ and ‘CALL’ instructions.  This is the case
     for devices with more than 8 KiB of program memory.

‘__AVR_HAVE_EIJMP_EICALL__’
‘__AVR_3_BYTE_PC__’
     The device has the ‘EIJMP’ and ‘EICALL’ instructions.  This is the
     case for devices with more than 128 KiB of program memory.  This
     also means that the program counter (PC) is 3 bytes wide.

‘__AVR_2_BYTE_PC__’
     The program counter (PC) is 2 bytes wide.  This is the case for
     devices with up to 128 KiB of program memory.

‘__AVR_HAVE_8BIT_SP__’
‘__AVR_HAVE_16BIT_SP__’
     The stack pointer (SP) register is treated as 8-bit respectively
     16-bit register by the compiler.  The definition of these macros is
     affected by ‘-mtiny-stack’.

‘__AVR_HAVE_SPH__’
‘__AVR_SP8__’
     The device has the SPH (high part of stack pointer) special
     function register or has an 8-bit stack pointer, respectively.  The
     definition of these macros is affected by ‘-mmcu=’ and in the cases
     of ‘-mmcu=avr2’ and ‘-mmcu=avr25’ also by ‘-msp8’.

‘__AVR_HAVE_RAMPD__’
‘__AVR_HAVE_RAMPX__’
‘__AVR_HAVE_RAMPY__’
‘__AVR_HAVE_RAMPZ__’
     The device has the ‘RAMPD’, ‘RAMPX’, ‘RAMPY’, ‘RAMPZ’ special
     function register, respectively.

‘__NO_INTERRUPTS__’
     This macro reflects the ‘-mno-interrupts’ command-line option.

‘__AVR_ERRATA_SKIP__’
‘__AVR_ERRATA_SKIP_JMP_CALL__’
     Some AVR devices (AT90S8515, ATmega103) must not skip 32-bit
     instructions because of a hardware erratum.  Skip instructions are
     ‘SBRS’, ‘SBRC’, ‘SBIS’, ‘SBIC’ and ‘CPSE’.  The second macro is
     only defined if ‘__AVR_HAVE_JMP_CALL__’ is also set.

‘__AVR_ISA_RMW__’
     The device has Read-Modify-Write instructions (XCH, LAC, LAS and
     LAT).

‘__AVR_SFR_OFFSET__=OFFSET’
     Instructions that can address I/O special function registers
     directly like ‘IN’, ‘OUT’, ‘SBI’, etc. may use a different address
     as if addressed by an instruction to access RAM like ‘LD’ or ‘STS’.
     This offset depends on the device architecture and has to be
     subtracted from the RAM address in order to get the respective
     I/O address.

‘__AVR_SHORT_CALLS__’
     The ‘-mshort-calls’ command line option is set.

‘__AVR_PM_BASE_ADDRESS__=ADDR’
     Some devices support reading from flash memory by means of ‘LD*’
     instructions.  The flash memory is seen in the data address space
     at an offset of ‘__AVR_PM_BASE_ADDRESS__’.  If this macro is not
     defined, this feature is not available.  If defined, the address
     space is linear and there is no need to put ‘.rodata’ into RAM.
     This is handled by the default linker description file, and is
     currently available for ‘avrtiny’ and ‘avrxmega3’.  Even more
     convenient, there is no need to use address spaces like ‘__flash’
     or features like attribute ‘progmem’ and ‘pgm_read_*’.

‘__WITH_AVRLIBC__’
     The compiler is configured to be used together with AVR-Libc.  See
     the ‘--with-avrlibc’ configure option.

‘__HAVE_DOUBLE_MULTILIB__’
     Defined if ‘-mdouble=’ acts as a multilib option.

‘__HAVE_DOUBLE32__’
‘__HAVE_DOUBLE64__’
     Defined if the compiler supports 32-bit double resp.  64-bit
     double.  The actual layout is specified by option ‘-mdouble=’.

‘__DEFAULT_DOUBLE__’
     The size in bits of ‘double’ if ‘-mdouble=’ is not set.  To test
     the layout of ‘double’ in a program, use the built-in macro
     ‘__SIZEOF_DOUBLE__’.

‘__HAVE_LONG_DOUBLE32__’
‘__HAVE_LONG_DOUBLE64__’
‘__HAVE_LONG_DOUBLE_MULTILIB__’
‘__DEFAULT_LONG_DOUBLE__’
     Same as above, but for ‘long double’ instead of ‘double’.

‘__WITH_DOUBLE_COMPARISON__’
     Reflects the ‘--with-double-comparison={tristate|bool|libf7}’
     configure option (https://gcc.gnu.org/install/configure.html#avr)
     and is defined to ‘2’ or ‘3’.

‘__WITH_LIBF7_LIBGCC__’
‘__WITH_LIBF7_MATH__’
‘__WITH_LIBF7_MATH_SYMBOLS__’
     Reflects the ‘--with-libf7={libgcc|math|math-symbols}’
     configure option (https://gcc.gnu.org/install/configure.html#avr).


File: gcc.info,  Node: Blackfin Options,  Next: C6X Options,  Prev: AVR Options,  Up: Submodel Options

3.19.7 Blackfin Options
-----------------------

‘-mcpu=CPU[-SIREVISION]’
     Specifies the name of the target Blackfin processor.  Currently,
     CPU can be one of ‘bf512’, ‘bf514’, ‘bf516’, ‘bf518’, ‘bf522’,
     ‘bf523’, ‘bf524’, ‘bf525’, ‘bf526’, ‘bf527’, ‘bf531’, ‘bf532’,
     ‘bf533’, ‘bf534’, ‘bf536’, ‘bf537’, ‘bf538’, ‘bf539’, ‘bf542’,
     ‘bf544’, ‘bf547’, ‘bf548’, ‘bf549’, ‘bf542m’, ‘bf544m’, ‘bf547m’,
     ‘bf548m’, ‘bf549m’, ‘bf561’, ‘bf592’.

     The optional SIREVISION specifies the silicon revision of the
     target Blackfin processor.  Any workarounds available for the
     targeted silicon revision are enabled.  If SIREVISION is ‘none’, no
     workarounds are enabled.  If SIREVISION is ‘any’, all workarounds
     for the targeted processor are enabled.  The ‘__SILICON_REVISION__’
     macro is defined to two hexadecimal digits representing the major
     and minor numbers in the silicon revision.  If SIREVISION is
     ‘none’, the ‘__SILICON_REVISION__’ is not defined.  If SIREVISION
     is ‘any’, the ‘__SILICON_REVISION__’ is defined to be ‘0xffff’.  If
     this optional SIREVISION is not used, GCC assumes the latest known
     silicon revision of the targeted Blackfin processor.

     GCC defines a preprocessor macro for the specified CPU.  For the
     ‘bfin-elf’ toolchain, this option causes the hardware BSP provided
     by libgloss to be linked in if ‘-msim’ is not given.

     Without this option, ‘bf532’ is used as the processor by default.

     Note that support for ‘bf561’ is incomplete.  For ‘bf561’, only the
     preprocessor macro is defined.

‘-msim’
     Specifies that the program will be run on the simulator.  This
     causes the simulator BSP provided by libgloss to be linked in.
     This option has effect only for ‘bfin-elf’ toolchain.  Certain
     other options, such as ‘-mid-shared-library’ and ‘-mfdpic’, imply
     ‘-msim’.

‘-momit-leaf-frame-pointer’
     Don't keep the frame pointer in a register for leaf functions.
     This avoids the instructions to save, set up and restore frame
     pointers and makes an extra register available in leaf functions.

‘-mspecld-anomaly’
     When enabled, the compiler ensures that the generated code does not
     contain speculative loads after jump instructions.  If this option
     is used, ‘__WORKAROUND_SPECULATIVE_LOADS’ is defined.

‘-mno-specld-anomaly’
     Don't generate extra code to prevent speculative loads from
     occurring.

‘-mcsync-anomaly’
     When enabled, the compiler ensures that the generated code does not
     contain CSYNC or SSYNC instructions too soon after conditional
     branches.  If this option is used, ‘__WORKAROUND_SPECULATIVE_SYNCS’
     is defined.

‘-mno-csync-anomaly’
     Don't generate extra code to prevent CSYNC or SSYNC instructions
     from occurring too soon after a conditional branch.

‘-mlow64k’
     When enabled, the compiler is free to take advantage of the
     knowledge that the entire program fits into the low 64k of memory.

‘-mno-low64k’
     Assume that the program is arbitrarily large.  This is the default.

‘-mstack-check-l1’
     Do stack checking using information placed into L1 scratchpad
     memory by the uClinux kernel.

‘-mid-shared-library’
     Generate code that supports shared libraries via the library ID
     method.  This allows for execute in place and shared libraries in
     an environment without virtual memory management.  This option
     implies ‘-fPIC’.  With a ‘bfin-elf’ target, this option implies
     ‘-msim’.

‘-mno-id-shared-library’
     Generate code that doesn't assume ID-based shared libraries are
     being used.  This is the default.

‘-mleaf-id-shared-library’
     Generate code that supports shared libraries via the library ID
     method, but assumes that this library or executable won't link
     against any other ID shared libraries.  That allows the compiler to
     use faster code for jumps and calls.

‘-mno-leaf-id-shared-library’
     Do not assume that the code being compiled won't link against any
     ID shared libraries.  Slower code is generated for jump and call
     insns.

‘-mshared-library-id=n’
     Specifies the identification number of the ID-based shared library
     being compiled.  Specifying a value of 0 generates more compact
     code; specifying other values forces the allocation of that number
     to the current library but is no more space- or time-efficient than
     omitting this option.

‘-msep-data’
     Generate code that allows the data segment to be located in a
     different area of memory from the text segment.  This allows for
     execute in place in an environment without virtual memory
     management by eliminating relocations against the text section.

‘-mno-sep-data’
     Generate code that assumes that the data segment follows the text
     segment.  This is the default.

‘-mlong-calls’
‘-mno-long-calls’
     Tells the compiler to perform function calls by first loading the
     address of the function into a register and then performing a
     subroutine call on this register.  This switch is needed if the
     target function lies outside of the 24-bit addressing range of the
     offset-based version of subroutine call instruction.

     This feature is not enabled by default.  Specifying
     ‘-mno-long-calls’ restores the default behavior.  Note these
     switches have no effect on how the compiler generates code to
     handle function calls via function pointers.

‘-mfast-fp’
     Link with the fast floating-point library.  This library relaxes
     some of the IEEE floating-point standard's rules for checking
     inputs against Not-a-Number (NAN), in the interest of performance.

‘-minline-plt’
     Enable inlining of PLT entries in function calls to functions that
     are not known to bind locally.  It has no effect without ‘-mfdpic’.

‘-mmulticore’
     Build a standalone application for multicore Blackfin processors.
     This option causes proper start files and link scripts supporting
     multicore to be used, and defines the macro ‘__BFIN_MULTICORE’.  It
     can only be used with ‘-mcpu=bf561[-SIREVISION]’.

     This option can be used with ‘-mcorea’ or ‘-mcoreb’, which selects
     the one-application-per-core programming model.  Without ‘-mcorea’
     or ‘-mcoreb’, the single-application/dual-core programming model is
     used.  In this model, the main function of Core B should be named
     as ‘coreb_main’.

     If this option is not used, the single-core application programming
     model is used.

‘-mcorea’
     Build a standalone application for Core A of BF561 when using the
     one-application-per-core programming model.  Proper start files and
     link scripts are used to support Core A, and the macro
     ‘__BFIN_COREA’ is defined.  This option can only be used in
     conjunction with ‘-mmulticore’.

‘-mcoreb’
     Build a standalone application for Core B of BF561 when using the
     one-application-per-core programming model.  Proper start files and
     link scripts are used to support Core B, and the macro
     ‘__BFIN_COREB’ is defined.  When this option is used, ‘coreb_main’
     should be used instead of ‘main’.  This option can only be used in
     conjunction with ‘-mmulticore’.

‘-msdram’
     Build a standalone application for SDRAM. Proper start files and
     link scripts are used to put the application into SDRAM, and the
     macro ‘__BFIN_SDRAM’ is defined.  The loader should initialize
     SDRAM before loading the application.

‘-micplb’
     Assume that ICPLBs are enabled at run time.  This has an effect on
     certain anomaly workarounds.  For Linux targets, the default is to
     assume ICPLBs are enabled; for standalone applications the default
     is off.


File: gcc.info,  Node: C6X Options,  Next: CRIS Options,  Prev: Blackfin Options,  Up: Submodel Options

3.19.8 C6X Options
------------------

‘-march=NAME’
     This specifies the name of the target architecture.  GCC uses this
     name to determine what kind of instructions it can emit when
     generating assembly code.  Permissible names are: ‘c62x’, ‘c64x’,
     ‘c64x+’, ‘c67x’, ‘c67x+’, ‘c674x’.

‘-mbig-endian’
     Generate code for a big-endian target.

‘-mlittle-endian’
     Generate code for a little-endian target.  This is the default.

‘-msim’
     Choose startup files and linker script suitable for the simulator.

‘-msdata=default’
     Put small global and static data in the ‘.neardata’ section, which
     is pointed to by register ‘B14’.  Put small uninitialized global
     and static data in the ‘.bss’ section, which is adjacent to the
     ‘.neardata’ section.  Put small read-only data into the ‘.rodata’
     section.  The corresponding sections used for large pieces of data
     are ‘.fardata’, ‘.far’ and ‘.const’.

‘-msdata=all’
     Put all data, not just small objects, into the sections reserved
     for small data, and use addressing relative to the ‘B14’ register
     to access them.

‘-msdata=none’
     Make no use of the sections reserved for small data, and use
     absolute addresses to access all data.  Put all initialized global
     and static data in the ‘.fardata’ section, and all uninitialized
     data in the ‘.far’ section.  Put all constant data into the
     ‘.const’ section.


File: gcc.info,  Node: CRIS Options,  Next: CR16 Options,  Prev: C6X Options,  Up: Submodel Options

3.19.9 CRIS Options
-------------------

These options are defined specifically for the CRIS ports.

‘-march=ARCHITECTURE-TYPE’
‘-mcpu=ARCHITECTURE-TYPE’
     Generate code for the specified architecture.  The choices for
     ARCHITECTURE-TYPE are ‘v3’, ‘v8’ and ‘v10’ for respectively
     ETRAX 4, ETRAX 100, and ETRAX 100 LX.  Default is ‘v0’.

‘-mtune=ARCHITECTURE-TYPE’
     Tune to ARCHITECTURE-TYPE everything applicable about the generated
     code, except for the ABI and the set of available instructions.
     The choices for ARCHITECTURE-TYPE are the same as for
     ‘-march=ARCHITECTURE-TYPE’.

‘-mmax-stack-frame=N’
     Warn when the stack frame of a function exceeds N bytes.

‘-metrax4’
‘-metrax100’
     The options ‘-metrax4’ and ‘-metrax100’ are synonyms for
     ‘-march=v3’ and ‘-march=v8’ respectively.

‘-mmul-bug-workaround’
‘-mno-mul-bug-workaround’
     Work around a bug in the ‘muls’ and ‘mulu’ instructions for CPU
     models where it applies.  This option is disabled by default.

‘-mpdebug’
     Enable CRIS-specific verbose debug-related information in the
     assembly code.  This option also has the effect of turning off the
     ‘#NO_APP’ formatted-code indicator to the assembler at the
     beginning of the assembly file.

‘-mcc-init’
     Do not use condition-code results from previous instruction; always
     emit compare and test instructions before use of condition codes.

‘-mno-side-effects’
     Do not emit instructions with side effects in addressing modes
     other than post-increment.

‘-mstack-align’
‘-mno-stack-align’
‘-mdata-align’
‘-mno-data-align’
‘-mconst-align’
‘-mno-const-align’
     These options (‘no-’ options) arrange (eliminate arrangements) for
     the stack frame, individual data and constants to be aligned for
     the maximum single data access size for the chosen CPU model.  The
     default is to arrange for 32-bit alignment.  ABI details such as
     structure layout are not affected by these options.

‘-m32-bit’
‘-m16-bit’
‘-m8-bit’
     Similar to the stack- data- and const-align options above, these
     options arrange for stack frame, writable data and constants to all
     be 32-bit, 16-bit or 8-bit aligned.  The default is 32-bit
     alignment.

‘-mno-prologue-epilogue’
‘-mprologue-epilogue’
     With ‘-mno-prologue-epilogue’, the normal function prologue and
     epilogue which set up the stack frame are omitted and no return
     instructions or return sequences are generated in the code.  Use
     this option only together with visual inspection of the compiled
     code: no warnings or errors are generated when call-saved registers
     must be saved, or storage for local variables needs to be
     allocated.

‘-melf’
     Legacy no-op option.

‘-sim’
     This option arranges to link with input-output functions from a
     simulator library.  Code, initialized data and zero-initialized
     data are allocated consecutively.

‘-sim2’
     Like ‘-sim’, but pass linker options to locate initialized data at
     0x40000000 and zero-initialized data at 0x80000000.


File: gcc.info,  Node: CR16 Options,  Next: C-SKY Options,  Prev: CRIS Options,  Up: Submodel Options

3.19.10 CR16 Options
--------------------

These options are defined specifically for the CR16 ports.

‘-mmac’
     Enable the use of multiply-accumulate instructions.  Disabled by
     default.

‘-mcr16cplus’
‘-mcr16c’
     Generate code for CR16C or CR16C+ architecture.  CR16C+
     architecture is default.

‘-msim’
     Links the library libsim.a which is in compatible with simulator.
     Applicable to ELF compiler only.

‘-mint32’
     Choose integer type as 32-bit wide.

‘-mbit-ops’
     Generates ‘sbit’/‘cbit’ instructions for bit manipulations.

‘-mdata-model=MODEL’
     Choose a data model.  The choices for MODEL are ‘near’, ‘far’ or
     ‘medium’.  ‘medium’ is default.  However, ‘far’ is not valid with
     ‘-mcr16c’, as the CR16C architecture does not support the far data
     model.


File: gcc.info,  Node: C-SKY Options,  Next: Darwin Options,  Prev: CR16 Options,  Up: Submodel Options

3.19.11 C-SKY Options
---------------------

GCC supports these options when compiling for C-SKY V2 processors.

‘-march=ARCH’
     Specify the C-SKY target architecture.  Valid values for ARCH are:
     ‘ck801’, ‘ck802’, ‘ck803’, ‘ck807’, and ‘ck810’.  The default is
     ‘ck810’.

‘-mcpu=CPU’
     Specify the C-SKY target processor.  Valid values for CPU are:
     ‘ck801’, ‘ck801t’, ‘ck802’, ‘ck802t’, ‘ck802j’, ‘ck803’, ‘ck803h’,
     ‘ck803t’, ‘ck803ht’, ‘ck803f’, ‘ck803fh’, ‘ck803e’, ‘ck803eh’,
     ‘ck803et’, ‘ck803eht’, ‘ck803ef’, ‘ck803efh’, ‘ck803ft’,
     ‘ck803eft’, ‘ck803efht’, ‘ck803r1’, ‘ck803hr1’, ‘ck803tr1’,
     ‘ck803htr1’, ‘ck803fr1’, ‘ck803fhr1’, ‘ck803er1’, ‘ck803ehr1’,
     ‘ck803etr1’, ‘ck803ehtr1’, ‘ck803efr1’, ‘ck803efhr1’, ‘ck803ftr1’,
     ‘ck803eftr1’, ‘ck803efhtr1’, ‘ck803s’, ‘ck803st’, ‘ck803se’,
     ‘ck803sf’, ‘ck803sef’, ‘ck803seft’, ‘ck807e’, ‘ck807ef’, ‘ck807’,
     ‘ck807f’, ‘ck810e’, ‘ck810et’, ‘ck810ef’, ‘ck810eft’, ‘ck810’,
     ‘ck810v’, ‘ck810f’, ‘ck810t’, ‘ck810fv’, ‘ck810tv’, ‘ck810ft’, and
     ‘ck810ftv’.

‘-mbig-endian’
‘-EB’
‘-mlittle-endian’
‘-EL’

     Select big- or little-endian code.  The default is little-endian.

‘-mfloat-abi=NAME’
     Specifies which floating-point ABI to use.  Permissible values are:
     ‘soft’, ‘softfp’ and ‘hard’.

     Specifying ‘soft’ causes GCC to generate output containing library
     calls for floating-point operations.  ‘softfp’ allows the
     generation of code using hardware floating-point instructions, but
     still uses the soft-float calling conventions.  ‘hard’ allows
     generation of floating-point instructions and uses FPU-specific
     calling conventions.

     The default depends on the specific target configuration.  Note
     that the hard-float and soft-float ABIs are not link-compatible;
     you must compile your entire program with the same ABI, and link
     with a compatible set of libraries.

‘-mhard-float’
‘-msoft-float’

     Select hardware or software floating-point implementations.  The
     default is soft float.

‘-mdouble-float’
‘-mno-double-float’
     When ‘-mhard-float’ is in effect, enable generation of
     double-precision float instructions.  This is the default except
     when compiling for CK803.

‘-mfdivdu’
‘-mno-fdivdu’
     When ‘-mhard-float’ is in effect, enable generation of ‘frecipd’,
     ‘fsqrtd’, and ‘fdivd’ instructions.  This is the default except
     when compiling for CK803.

‘-mfpu=FPU’
     Select the floating-point processor.  This option can only be used
     with ‘-mhard-float’.  Values for FPU are ‘fpv2_sf’ (equivalent to
     ‘-mno-double-float -mno-fdivdu’), ‘fpv2’ (‘-mdouble-float
     -mno-divdu’), and ‘fpv2_divd’ (‘-mdouble-float -mdivdu’).

‘-melrw’
‘-mno-elrw’
     Enable the extended ‘lrw’ instruction.  This option defaults to on
     for CK801 and off otherwise.

‘-mistack’
‘-mno-istack’
     Enable interrupt stack instructions; the default is off.

     The ‘-mistack’ option is required to handle the ‘interrupt’ and
     ‘isr’ function attributes (*note C-SKY Function Attributes::).

‘-mmp’
     Enable multiprocessor instructions; the default is off.

‘-mcp’
     Enable coprocessor instructions; the default is off.

‘-mcache’
     Enable coprocessor instructions; the default is off.

‘-msecurity’
     Enable C-SKY security instructions; the default is off.

‘-mtrust’
     Enable C-SKY trust instructions; the default is off.

‘-mdsp’
‘-medsp’
‘-mvdsp’
     Enable C-SKY DSP, Enhanced DSP, or Vector DSP instructions,
     respectively.  All of these options default to off.

‘-mdiv’
‘-mno-div’
     Generate divide instructions.  Default is off.

‘-msmart’
‘-mno-smart’
     Generate code for Smart Mode, using only registers numbered 0-7 to
     allow use of 16-bit instructions.  This option is ignored for CK801
     where this is the required behavior, and it defaults to on for
     CK802.  For other targets, the default is off.

‘-mhigh-registers’
‘-mno-high-registers’
     Generate code using the high registers numbered 16-31.  This option
     is not supported on CK801, CK802, or CK803, and is enabled by
     default for other processors.

‘-manchor’
‘-mno-anchor’
     Generate code using global anchor symbol addresses.

‘-mpushpop’
‘-mno-pushpop’
     Generate code using ‘push’ and ‘pop’ instructions.  This option
     defaults to on.

‘-mmultiple-stld’
‘-mstm’
‘-mno-multiple-stld’
‘-mno-stm’
     Generate code using ‘stm’ and ‘ldm’ instructions.  This option
     isn't supported on CK801 but is enabled by default on other
     processors.

‘-mconstpool’
‘-mno-constpool’
     Create constant pools in the compiler instead of deferring it to
     the assembler.  This option is the default and required for correct
     code generation on CK801 and CK802, and is optional on other
     processors.

‘-mstack-size’
‘-mno-stack-size’
     Emit ‘.stack_size’ directives for each function in the assembly
     output.  This option defaults to off.

‘-mccrt’
‘-mno-ccrt’
     Generate code for the C-SKY compiler runtime instead of libgcc.
     This option defaults to off.

‘-mbranch-cost=N’
     Set the branch costs to roughly ‘n’ instructions.  The default is
     1.

‘-msched-prolog’
‘-mno-sched-prolog’
     Permit scheduling of function prologue and epilogue sequences.
     Using this option can result in code that is not compliant with the
     C-SKY V2 ABI prologue requirements and that cannot be debugged or
     backtraced.  It is disabled by default.

‘-msim’
     Links the library libsemi.a which is in compatible with simulator.
     Applicable to ELF compiler only.


File: gcc.info,  Node: Darwin Options,  Next: DEC Alpha Options,  Prev: C-SKY Options,  Up: Submodel Options

3.19.12 Darwin Options
----------------------

These options are defined for all architectures running the Darwin
operating system.

 FSF GCC on Darwin does not create "fat" object files; it creates an
object file for the single architecture that GCC was built to target.
Apple's GCC on Darwin does create "fat" files if multiple ‘-arch’
options are used; it does so by running the compiler or linker multiple
times and joining the results together with ‘lipo’.

 The subtype of the file created (like ‘ppc7400’ or ‘ppc970’ or ‘i686’)
is determined by the flags that specify the ISA that GCC is targeting,
like ‘-mcpu’ or ‘-march’.  The ‘-force_cpusubtype_ALL’ option can be
used to override this.

 The Darwin tools vary in their behavior when presented with an ISA
mismatch.  The assembler, ‘as’, only permits instructions to be used
that are valid for the subtype of the file it is generating, so you
cannot put 64-bit instructions in a ‘ppc750’ object file.  The linker
for shared libraries, ‘/usr/bin/libtool’, fails and prints an error if
asked to create a shared library with a less restrictive subtype than
its input files (for instance, trying to put a ‘ppc970’ object file in a
‘ppc7400’ library).  The linker for executables, ‘ld’, quietly gives the
executable the most restrictive subtype of any of its input files.

‘-FDIR’
     Add the framework directory DIR to the head of the list of
     directories to be searched for header files.  These directories are
     interleaved with those specified by ‘-I’ options and are scanned in
     a left-to-right order.

     A framework directory is a directory with frameworks in it.  A
     framework is a directory with a ‘Headers’ and/or ‘PrivateHeaders’
     directory contained directly in it that ends in ‘.framework’.  The
     name of a framework is the name of this directory excluding the
     ‘.framework’.  Headers associated with the framework are found in
     one of those two directories, with ‘Headers’ being searched first.
     A subframework is a framework directory that is in a framework's
     ‘Frameworks’ directory.  Includes of subframework headers can only
     appear in a header of a framework that contains the subframework,
     or in a sibling subframework header.  Two subframeworks are
     siblings if they occur in the same framework.  A subframework
     should not have the same name as a framework; a warning is issued
     if this is violated.  Currently a subframework cannot have
     subframeworks; in the future, the mechanism may be extended to
     support this.  The standard frameworks can be found in
     ‘/System/Library/Frameworks’ and ‘/Library/Frameworks’.  An example
     include looks like ‘#include <Framework/header.h>’, where
     ‘Framework’ denotes the name of the framework and ‘header.h’ is
     found in the ‘PrivateHeaders’ or ‘Headers’ directory.

‘-iframeworkDIR’
     Like ‘-F’ except the directory is a treated as a system directory.
     The main difference between this ‘-iframework’ and ‘-F’ is that
     with ‘-iframework’ the compiler does not warn about constructs
     contained within header files found via DIR.  This option is valid
     only for the C family of languages.

‘-gused’
     Emit debugging information for symbols that are used.  For stabs
     debugging format, this enables ‘-feliminate-unused-debug-symbols’.
     This is by default ON.

‘-gfull’
     Emit debugging information for all symbols and types.

‘-mmacosx-version-min=VERSION’
     The earliest version of MacOS X that this executable will run on is
     VERSION.  Typical values of VERSION include ‘10.1’, ‘10.2’, and
     ‘10.3.9’.

     If the compiler was built to use the system's headers by default,
     then the default for this option is the system version on which the
     compiler is running, otherwise the default is to make choices that
     are compatible with as many systems and code bases as possible.

‘-mkernel’
     Enable kernel development mode.  The ‘-mkernel’ option sets
     ‘-static’, ‘-fno-common’, ‘-fno-use-cxa-atexit’, ‘-fno-exceptions’,
     ‘-fno-non-call-exceptions’, ‘-fapple-kext’, ‘-fno-weak’ and
     ‘-fno-rtti’ where applicable.  This mode also sets ‘-mno-altivec’,
     ‘-msoft-float’, ‘-fno-builtin’ and ‘-mlong-branch’ for PowerPC
     targets.

‘-mone-byte-bool’
     Override the defaults for ‘bool’ so that ‘sizeof(bool)==1’.  By
     default ‘sizeof(bool)’ is ‘4’ when compiling for Darwin/PowerPC and
     ‘1’ when compiling for Darwin/x86, so this option has no effect on
     x86.

     *Warning:* The ‘-mone-byte-bool’ switch causes GCC to generate code
     that is not binary compatible with code generated without that
     switch.  Using this switch may require recompiling all other
     modules in a program, including system libraries.  Use this switch
     to conform to a non-default data model.

‘-mfix-and-continue’
‘-ffix-and-continue’
‘-findirect-data’
     Generate code suitable for fast turnaround development, such as to
     allow GDB to dynamically load ‘.o’ files into already-running
     programs.  ‘-findirect-data’ and ‘-ffix-and-continue’ are provided
     for backwards compatibility.

‘-all_load’
     Loads all members of static archive libraries.  See man ld(1) for
     more information.

‘-arch_errors_fatal’
     Cause the errors having to do with files that have the wrong
     architecture to be fatal.

‘-bind_at_load’
     Causes the output file to be marked such that the dynamic linker
     will bind all undefined references when the file is loaded or
     launched.

‘-bundle’
     Produce a Mach-o bundle format file.  See man ld(1) for more
     information.

‘-bundle_loader EXECUTABLE’
     This option specifies the EXECUTABLE that will load the build
     output file being linked.  See man ld(1) for more information.

‘-dynamiclib’
     When passed this option, GCC produces a dynamic library instead of
     an executable when linking, using the Darwin ‘libtool’ command.

‘-force_cpusubtype_ALL’
     This causes GCC's output file to have the ‘ALL’ subtype, instead of
     one controlled by the ‘-mcpu’ or ‘-march’ option.

‘-allowable_client CLIENT_NAME’
‘-client_name’
‘-compatibility_version’
‘-current_version’
‘-dead_strip’
‘-dependency-file’
‘-dylib_file’
‘-dylinker_install_name’
‘-dynamic’
‘-exported_symbols_list’
‘-filelist’
‘-flat_namespace’
‘-force_flat_namespace’
‘-headerpad_max_install_names’
‘-image_base’
‘-init’
‘-install_name’
‘-keep_private_externs’
‘-multi_module’
‘-multiply_defined’
‘-multiply_defined_unused’
‘-noall_load’
‘-no_dead_strip_inits_and_terms’
‘-nofixprebinding’
‘-nomultidefs’
‘-noprebind’
‘-noseglinkedit’
‘-pagezero_size’
‘-prebind’
‘-prebind_all_twolevel_modules’
‘-private_bundle’
‘-read_only_relocs’
‘-sectalign’
‘-sectobjectsymbols’
‘-whyload’
‘-seg1addr’
‘-sectcreate’
‘-sectobjectsymbols’
‘-sectorder’
‘-segaddr’
‘-segs_read_only_addr’
‘-segs_read_write_addr’
‘-seg_addr_table’
‘-seg_addr_table_filename’
‘-seglinkedit’
‘-segprot’
‘-segs_read_only_addr’
‘-segs_read_write_addr’
‘-single_module’
‘-static’
‘-sub_library’
‘-sub_umbrella’
‘-twolevel_namespace’
‘-umbrella’
‘-undefined’
‘-unexported_symbols_list’
‘-weak_reference_mismatches’
‘-whatsloaded’
     These options are passed to the Darwin linker.  The Darwin linker
     man page describes them in detail.


File: gcc.info,  Node: DEC Alpha Options,  Next: eBPF Options,  Prev: Darwin Options,  Up: Submodel Options

3.19.13 DEC Alpha Options
-------------------------

These ‘-m’ options are defined for the DEC Alpha implementations:

‘-mno-soft-float’
‘-msoft-float’
     Use (do not use) the hardware floating-point instructions for
     floating-point operations.  When ‘-msoft-float’ is specified,
     functions in ‘libgcc.a’ are used to perform floating-point
     operations.  Unless they are replaced by routines that emulate the
     floating-point operations, or compiled in such a way as to call
     such emulations routines, these routines issue floating-point
     operations.  If you are compiling for an Alpha without
     floating-point operations, you must ensure that the library is
     built so as not to call them.

     Note that Alpha implementations without floating-point operations
     are required to have floating-point registers.

‘-mfp-reg’
‘-mno-fp-regs’
     Generate code that uses (does not use) the floating-point register
     set.  ‘-mno-fp-regs’ implies ‘-msoft-float’.  If the floating-point
     register set is not used, floating-point operands are passed in
     integer registers as if they were integers and floating-point
     results are passed in ‘$0’ instead of ‘$f0’.  This is a
     non-standard calling sequence, so any function with a
     floating-point argument or return value called by code compiled
     with ‘-mno-fp-regs’ must also be compiled with that option.

     A typical use of this option is building a kernel that does not
     use, and hence need not save and restore, any floating-point
     registers.

‘-mieee’
     The Alpha architecture implements floating-point hardware optimized
     for maximum performance.  It is mostly compliant with the IEEE
     floating-point standard.  However, for full compliance, software
     assistance is required.  This option generates code fully
     IEEE-compliant code _except_ that the INEXACT-FLAG is not
     maintained (see below).  If this option is turned on, the
     preprocessor macro ‘_IEEE_FP’ is defined during compilation.  The
     resulting code is less efficient but is able to correctly support
     denormalized numbers and exceptional IEEE values such as
     not-a-number and plus/minus infinity.  Other Alpha compilers call
     this option ‘-ieee_with_no_inexact’.

‘-mieee-with-inexact’
     This is like ‘-mieee’ except the generated code also maintains the
     IEEE INEXACT-FLAG.  Turning on this option causes the generated
     code to implement fully-compliant IEEE math.  In addition to
     ‘_IEEE_FP’, ‘_IEEE_FP_EXACT’ is defined as a preprocessor macro.
     On some Alpha implementations the resulting code may execute
     significantly slower than the code generated by default.  Since
     there is very little code that depends on the INEXACT-FLAG, you
     should normally not specify this option.  Other Alpha compilers
     call this option ‘-ieee_with_inexact’.

‘-mfp-trap-mode=TRAP-MODE’
     This option controls what floating-point related traps are enabled.
     Other Alpha compilers call this option ‘-fptm TRAP-MODE’.  The trap
     mode can be set to one of four values:

     ‘n’
          This is the default (normal) setting.  The only traps that are
          enabled are the ones that cannot be disabled in software
          (e.g., division by zero trap).

     ‘u’
          In addition to the traps enabled by ‘n’, underflow traps are
          enabled as well.

     ‘su’
          Like ‘u’, but the instructions are marked to be safe for
          software completion (see Alpha architecture manual for
          details).

     ‘sui’
          Like ‘su’, but inexact traps are enabled as well.

‘-mfp-rounding-mode=ROUNDING-MODE’
     Selects the IEEE rounding mode.  Other Alpha compilers call this
     option ‘-fprm ROUNDING-MODE’.  The ROUNDING-MODE can be one of:

     ‘n’
          Normal IEEE rounding mode.  Floating-point numbers are rounded
          towards the nearest machine number or towards the even machine
          number in case of a tie.

     ‘m’
          Round towards minus infinity.

     ‘c’
          Chopped rounding mode.  Floating-point numbers are rounded
          towards zero.

     ‘d’
          Dynamic rounding mode.  A field in the floating-point control
          register (FPCR, see Alpha architecture reference manual)
          controls the rounding mode in effect.  The C library
          initializes this register for rounding towards plus infinity.
          Thus, unless your program modifies the FPCR, ‘d’ corresponds
          to round towards plus infinity.

‘-mtrap-precision=TRAP-PRECISION’
     In the Alpha architecture, floating-point traps are imprecise.
     This means without software assistance it is impossible to recover
     from a floating trap and program execution normally needs to be
     terminated.  GCC can generate code that can assist operating system
     trap handlers in determining the exact location that caused a
     floating-point trap.  Depending on the requirements of an
     application, different levels of precisions can be selected:

     ‘p’
          Program precision.  This option is the default and means a
          trap handler can only identify which program caused a
          floating-point exception.

     ‘f’
          Function precision.  The trap handler can determine the
          function that caused a floating-point exception.

     ‘i’
          Instruction precision.  The trap handler can determine the
          exact instruction that caused a floating-point exception.

     Other Alpha compilers provide the equivalent options called
     ‘-scope_safe’ and ‘-resumption_safe’.

‘-mieee-conformant’
     This option marks the generated code as IEEE conformant.  You must
     not use this option unless you also specify ‘-mtrap-precision=i’
     and either ‘-mfp-trap-mode=su’ or ‘-mfp-trap-mode=sui’.  Its only
     effect is to emit the line ‘.eflag 48’ in the function prologue of
     the generated assembly file.

‘-mbuild-constants’
     Normally GCC examines a 32- or 64-bit integer constant to see if it
     can construct it from smaller constants in two or three
     instructions.  If it cannot, it outputs the constant as a literal
     and generates code to load it from the data segment at run time.

     Use this option to require GCC to construct _all_ integer constants
     using code, even if it takes more instructions (the maximum is
     six).

     You typically use this option to build a shared library dynamic
     loader.  Itself a shared library, it must relocate itself in memory
     before it can find the variables and constants in its own data
     segment.

‘-mbwx’
‘-mno-bwx’
‘-mcix’
‘-mno-cix’
‘-mfix’
‘-mno-fix’
‘-mmax’
‘-mno-max’
     Indicate whether GCC should generate code to use the optional BWX,
     CIX, FIX and MAX instruction sets.  The default is to use the
     instruction sets supported by the CPU type specified via ‘-mcpu=’
     option or that of the CPU on which GCC was built if none is
     specified.

‘-mfloat-vax’
‘-mfloat-ieee’
     Generate code that uses (does not use) VAX F and G floating-point
     arithmetic instead of IEEE single and double precision.

‘-mexplicit-relocs’
‘-mno-explicit-relocs’
     Older Alpha assemblers provided no way to generate symbol
     relocations except via assembler macros.  Use of these macros does
     not allow optimal instruction scheduling.  GNU binutils as of
     version 2.12 supports a new syntax that allows the compiler to
     explicitly mark which relocations should apply to which
     instructions.  This option is mostly useful for debugging, as GCC
     detects the capabilities of the assembler when it is built and sets
     the default accordingly.

‘-msmall-data’
‘-mlarge-data’
     When ‘-mexplicit-relocs’ is in effect, static data is accessed via
     “gp-relative” relocations.  When ‘-msmall-data’ is used, objects 8
     bytes long or smaller are placed in a “small data area” (the
     ‘.sdata’ and ‘.sbss’ sections) and are accessed via 16-bit
     relocations off of the ‘$gp’ register.  This limits the size of the
     small data area to 64KB, but allows the variables to be directly
     accessed via a single instruction.

     The default is ‘-mlarge-data’.  With this option the data area is
     limited to just below 2GB.  Programs that require more than 2GB of
     data must use ‘malloc’ or ‘mmap’ to allocate the data in the heap
     instead of in the program's data segment.

     When generating code for shared libraries, ‘-fpic’ implies
     ‘-msmall-data’ and ‘-fPIC’ implies ‘-mlarge-data’.

‘-msmall-text’
‘-mlarge-text’
     When ‘-msmall-text’ is used, the compiler assumes that the code of
     the entire program (or shared library) fits in 4MB, and is thus
     reachable with a branch instruction.  When ‘-msmall-data’ is used,
     the compiler can assume that all local symbols share the same ‘$gp’
     value, and thus reduce the number of instructions required for a
     function call from 4 to 1.

     The default is ‘-mlarge-text’.

‘-mcpu=CPU_TYPE’
     Set the instruction set and instruction scheduling parameters for
     machine type CPU_TYPE.  You can specify either the ‘EV’ style name
     or the corresponding chip number.  GCC supports scheduling
     parameters for the EV4, EV5 and EV6 family of processors and
     chooses the default values for the instruction set from the
     processor you specify.  If you do not specify a processor type, GCC
     defaults to the processor on which the compiler was built.

     Supported values for CPU_TYPE are

     ‘ev4’
     ‘ev45’
     ‘21064’
          Schedules as an EV4 and has no instruction set extensions.

     ‘ev5’
     ‘21164’
          Schedules as an EV5 and has no instruction set extensions.

     ‘ev56’
     ‘21164a’
          Schedules as an EV5 and supports the BWX extension.

     ‘pca56’
     ‘21164pc’
     ‘21164PC’
          Schedules as an EV5 and supports the BWX and MAX extensions.

     ‘ev6’
     ‘21264’
          Schedules as an EV6 and supports the BWX, FIX, and MAX
          extensions.

     ‘ev67’
     ‘21264a’
          Schedules as an EV6 and supports the BWX, CIX, FIX, and MAX
          extensions.

     Native toolchains also support the value ‘native’, which selects
     the best architecture option for the host processor.
     ‘-mcpu=native’ has no effect if GCC does not recognize the
     processor.

‘-mtune=CPU_TYPE’
     Set only the instruction scheduling parameters for machine type
     CPU_TYPE.  The instruction set is not changed.

     Native toolchains also support the value ‘native’, which selects
     the best architecture option for the host processor.
     ‘-mtune=native’ has no effect if GCC does not recognize the
     processor.

‘-mmemory-latency=TIME’
     Sets the latency the scheduler should assume for typical memory
     references as seen by the application.  This number is highly
     dependent on the memory access patterns used by the application and
     the size of the external cache on the machine.

     Valid options for TIME are

     ‘NUMBER’
          A decimal number representing clock cycles.

     ‘L1’
     ‘L2’
     ‘L3’
     ‘main’
          The compiler contains estimates of the number of clock cycles
          for "typical" EV4 & EV5 hardware for the Level 1, 2 & 3 caches
          (also called Dcache, Scache, and Bcache), as well as to main
          memory.  Note that L3 is only valid for EV5.


File: gcc.info,  Node: eBPF Options,  Next: FR30 Options,  Prev: DEC Alpha Options,  Up: Submodel Options

3.19.14 eBPF Options
--------------------

‘-mframe-limit=BYTES’
     This specifies the hard limit for frame sizes, in bytes.
     Currently, the value that can be specified should be less than or
     equal to ‘32767’.  Defaults to whatever limit is imposed by the
     version of the Linux kernel targeted.

‘-mkernel=VERSION’
     This specifies the minimum version of the kernel that will run the
     compiled program.  GCC uses this version to determine which
     instructions to use, what kernel helpers to allow, etc.  Currently,
     VERSION can be one of ‘4.0’, ‘4.1’, ‘4.2’, ‘4.3’, ‘4.4’, ‘4.5’,
     ‘4.6’, ‘4.7’, ‘4.8’, ‘4.9’, ‘4.10’, ‘4.11’, ‘4.12’, ‘4.13’, ‘4.14’,
     ‘4.15’, ‘4.16’, ‘4.17’, ‘4.18’, ‘4.19’, ‘4.20’, ‘5.0’, ‘5.1’,
     ‘5.2’, ‘latest’ and ‘native’.

‘-mbig-endian’
     Generate code for a big-endian target.

‘-mlittle-endian’
     Generate code for a little-endian target.  This is the default.

‘-mjmpext’
     Enable generation of extra conditional-branch instructions.
     Enabled for CPU v2 and above.

‘-mjmp32’
     Enable 32-bit jump instructions.  Enabled for CPU v3 and above.

‘-malu32’
     Enable 32-bit ALU instructions.  Enabled for CPU v3 and above.

‘-mcpu=VERSION’
     This specifies which version of the eBPF ISA to target.  Newer
     versions may not be supported by all kernels.  The default is ‘v3’.

     Supported values for VERSION are:

     ‘v1’
          The first stable eBPF ISA with no special features or
          extensions.

     ‘v2’
          Supports the jump extensions, as in ‘-mjmpext’.

     ‘v3’
          All features of v2, plus:
             − 32-bit jump operations, as in ‘-mjmp32’
             − 32-bit ALU operations, as in ‘-malu32’

‘-mco-re’
     Enable BPF Compile Once - Run Everywhere (CO-RE) support.  Requires
     and is implied by ‘-gbtf’.

‘-mno-co-re’
     Disable BPF Compile Once - Run Everywhere (CO-RE) support.  BPF
     CO-RE support is enabled by default when generating BTF debug
     information for the BPF target.

‘-mxbpf’
     Generate code for an expanded version of BPF, which relaxes some of
     the restrictions imposed by the BPF architecture:
        − Save and restore callee-saved registers at function entry and
          exit, respectively.


File: gcc.info,  Node: FR30 Options,  Next: FT32 Options,  Prev: eBPF Options,  Up: Submodel Options

3.19.15 FR30 Options
--------------------

These options are defined specifically for the FR30 port.

‘-msmall-model’
     Use the small address space model.  This can produce smaller code,
     but it does assume that all symbolic values and addresses fit into
     a 20-bit range.

‘-mno-lsim’
     Assume that runtime support has been provided and so there is no
     need to include the simulator library (‘libsim.a’) on the linker
     command line.


File: gcc.info,  Node: FT32 Options,  Next: FRV Options,  Prev: FR30 Options,  Up: Submodel Options

3.19.16 FT32 Options
--------------------

These options are defined specifically for the FT32 port.

‘-msim’
     Specifies that the program will be run on the simulator.  This
     causes an alternate runtime startup and library to be linked.  You
     must not use this option when generating programs that will run on
     real hardware; you must provide your own runtime library for
     whatever I/O functions are needed.

‘-mlra’
     Enable Local Register Allocation.  This is still experimental for
     FT32, so by default the compiler uses standard reload.

‘-mnodiv’
     Do not use div and mod instructions.

‘-mft32b’
     Enable use of the extended instructions of the FT32B processor.

‘-mcompress’
     Compress all code using the Ft32B code compression scheme.

‘-mnopm’
     Do not generate code that reads program memory.


File: gcc.info,  Node: FRV Options,  Next: GNU/Linux Options,  Prev: FT32 Options,  Up: Submodel Options

3.19.17 FRV Options
-------------------

‘-mgpr-32’

     Only use the first 32 general-purpose registers.

‘-mgpr-64’

     Use all 64 general-purpose registers.

‘-mfpr-32’

     Use only the first 32 floating-point registers.

‘-mfpr-64’

     Use all 64 floating-point registers.

‘-mhard-float’

     Use hardware instructions for floating-point operations.

‘-msoft-float’

     Use library routines for floating-point operations.

‘-malloc-cc’

     Dynamically allocate condition code registers.

‘-mfixed-cc’

     Do not try to dynamically allocate condition code registers, only
     use ‘icc0’ and ‘fcc0’.

‘-mdword’

     Change ABI to use double word insns.

‘-mno-dword’

     Do not use double word instructions.

‘-mdouble’

     Use floating-point double instructions.

‘-mno-double’

     Do not use floating-point double instructions.

‘-mmedia’

     Use media instructions.

‘-mno-media’

     Do not use media instructions.

‘-mmuladd’

     Use multiply and add/subtract instructions.

‘-mno-muladd’

     Do not use multiply and add/subtract instructions.

‘-mfdpic’

     Select the FDPIC ABI, which uses function descriptors to represent
     pointers to functions.  Without any PIC/PIE-related options, it
     implies ‘-fPIE’.  With ‘-fpic’ or ‘-fpie’, it assumes GOT entries
     and small data are within a 12-bit range from the GOT base address;
     with ‘-fPIC’ or ‘-fPIE’, GOT offsets are computed with 32 bits.
     With a ‘bfin-elf’ target, this option implies ‘-msim’.

‘-minline-plt’

     Enable inlining of PLT entries in function calls to functions that
     are not known to bind locally.  It has no effect without ‘-mfdpic’.
     It's enabled by default if optimizing for speed and compiling for
     shared libraries (i.e., ‘-fPIC’ or ‘-fpic’), or when an
     optimization option such as ‘-O3’ or above is present in the
     command line.

‘-mTLS’

     Assume a large TLS segment when generating thread-local code.

‘-mtls’

     Do not assume a large TLS segment when generating thread-local
     code.

‘-mgprel-ro’

     Enable the use of ‘GPREL’ relocations in the FDPIC ABI for data
     that is known to be in read-only sections.  It's enabled by
     default, except for ‘-fpic’ or ‘-fpie’: even though it may help
     make the global offset table smaller, it trades 1 instruction for
     4.  With ‘-fPIC’ or ‘-fPIE’, it trades 3 instructions for 4, one of
     which may be shared by multiple symbols, and it avoids the need for
     a GOT entry for the referenced symbol, so it's more likely to be a
     win.  If it is not, ‘-mno-gprel-ro’ can be used to disable it.

‘-multilib-library-pic’

     Link with the (library, not FD) pic libraries.  It's implied by
     ‘-mlibrary-pic’, as well as by ‘-fPIC’ and ‘-fpic’ without
     ‘-mfdpic’.  You should never have to use it explicitly.

‘-mlinked-fp’

     Follow the EABI requirement of always creating a frame pointer
     whenever a stack frame is allocated.  This option is enabled by
     default and can be disabled with ‘-mno-linked-fp’.

‘-mlong-calls’

     Use indirect addressing to call functions outside the current
     compilation unit.  This allows the functions to be placed anywhere
     within the 32-bit address space.

‘-malign-labels’

     Try to align labels to an 8-byte boundary by inserting NOPs into
     the previous packet.  This option only has an effect when VLIW
     packing is enabled.  It doesn't create new packets; it merely adds
     NOPs to existing ones.

‘-mlibrary-pic’

     Generate position-independent EABI code.

‘-macc-4’

     Use only the first four media accumulator registers.

‘-macc-8’

     Use all eight media accumulator registers.

‘-mpack’

     Pack VLIW instructions.

‘-mno-pack’

     Do not pack VLIW instructions.

‘-mno-eflags’

     Do not mark ABI switches in e_flags.

‘-mcond-move’

     Enable the use of conditional-move instructions (default).

     This switch is mainly for debugging the compiler and will likely be
     removed in a future version.

‘-mno-cond-move’

     Disable the use of conditional-move instructions.

     This switch is mainly for debugging the compiler and will likely be
     removed in a future version.

‘-mscc’

     Enable the use of conditional set instructions (default).

     This switch is mainly for debugging the compiler and will likely be
     removed in a future version.

‘-mno-scc’

     Disable the use of conditional set instructions.

     This switch is mainly for debugging the compiler and will likely be
     removed in a future version.

‘-mcond-exec’

     Enable the use of conditional execution (default).

     This switch is mainly for debugging the compiler and will likely be
     removed in a future version.

‘-mno-cond-exec’

     Disable the use of conditional execution.

     This switch is mainly for debugging the compiler and will likely be
     removed in a future version.

‘-mvliw-branch’

     Run a pass to pack branches into VLIW instructions (default).

     This switch is mainly for debugging the compiler and will likely be
     removed in a future version.

‘-mno-vliw-branch’

     Do not run a pass to pack branches into VLIW instructions.

     This switch is mainly for debugging the compiler and will likely be
     removed in a future version.

‘-mmulti-cond-exec’

     Enable optimization of ‘&&’ and ‘||’ in conditional execution
     (default).

     This switch is mainly for debugging the compiler and will likely be
     removed in a future version.

‘-mno-multi-cond-exec’

     Disable optimization of ‘&&’ and ‘||’ in conditional execution.

     This switch is mainly for debugging the compiler and will likely be
     removed in a future version.

‘-mnested-cond-exec’

     Enable nested conditional execution optimizations (default).

     This switch is mainly for debugging the compiler and will likely be
     removed in a future version.

‘-mno-nested-cond-exec’

     Disable nested conditional execution optimizations.

     This switch is mainly for debugging the compiler and will likely be
     removed in a future version.

‘-moptimize-membar’

     This switch removes redundant ‘membar’ instructions from the
     compiler-generated code.  It is enabled by default.

‘-mno-optimize-membar’

     This switch disables the automatic removal of redundant ‘membar’
     instructions from the generated code.

‘-mtomcat-stats’

     Cause gas to print out tomcat statistics.

‘-mcpu=CPU’

     Select the processor type for which to generate code.  Possible
     values are ‘frv’, ‘fr550’, ‘tomcat’, ‘fr500’, ‘fr450’, ‘fr405’,
     ‘fr400’, ‘fr300’ and ‘simple’.


File: gcc.info,  Node: GNU/Linux Options,  Next: H8/300 Options,  Prev: FRV Options,  Up: Submodel Options

3.19.18 GNU/Linux Options
-------------------------

These ‘-m’ options are defined for GNU/Linux targets:

‘-mglibc’
     Use the GNU C library.  This is the default except on
     ‘*-*-linux-*uclibc*’, ‘*-*-linux-*musl*’ and ‘*-*-linux-*android*’
     targets.

‘-muclibc’
     Use uClibc C library.  This is the default on ‘*-*-linux-*uclibc*’
     targets.

‘-mmusl’
     Use the musl C library.  This is the default on ‘*-*-linux-*musl*’
     targets.

‘-mbionic’
     Use Bionic C library.  This is the default on ‘*-*-linux-*android*’
     targets.

‘-mandroid’
     Compile code compatible with Android platform.  This is the default
     on ‘*-*-linux-*android*’ targets.

     When compiling, this option enables ‘-mbionic’, ‘-fPIC’,
     ‘-fno-exceptions’ and ‘-fno-rtti’ by default.  When linking, this
     option makes the GCC driver pass Android-specific options to the
     linker.  Finally, this option causes the preprocessor macro
     ‘__ANDROID__’ to be defined.

‘-tno-android-cc’
     Disable compilation effects of ‘-mandroid’, i.e., do not enable
     ‘-mbionic’, ‘-fPIC’, ‘-fno-exceptions’ and ‘-fno-rtti’ by default.

‘-tno-android-ld’
     Disable linking effects of ‘-mandroid’, i.e., pass standard Linux
     linking options to the linker.


File: gcc.info,  Node: H8/300 Options,  Next: HPPA Options,  Prev: GNU/Linux Options,  Up: Submodel Options

3.19.19 H8/300 Options
----------------------

These ‘-m’ options are defined for the H8/300 implementations:

‘-mrelax’
     Shorten some address references at link time, when possible; uses
     the linker option ‘-relax’.  *Note ‘ld’ and the H8/300: (ld)H8/300,
     for a fuller description.

‘-mh’
     Generate code for the H8/300H.

‘-ms’
     Generate code for the H8S.

‘-mn’
     Generate code for the H8S and H8/300H in the normal mode.  This
     switch must be used either with ‘-mh’ or ‘-ms’.

‘-ms2600’
     Generate code for the H8S/2600.  This switch must be used with
     ‘-ms’.

‘-mexr’
     Extended registers are stored on stack before execution of function
     with monitor attribute.  Default option is ‘-mexr’.  This option is
     valid only for H8S targets.

‘-mno-exr’
     Extended registers are not stored on stack before execution of
     function with monitor attribute.  Default option is ‘-mno-exr’.
     This option is valid only for H8S targets.

‘-mint32’
     Make ‘int’ data 32 bits by default.

‘-malign-300’
     On the H8/300H and H8S, use the same alignment rules as for the
     H8/300.  The default for the H8/300H and H8S is to align longs and
     floats on 4-byte boundaries.  ‘-malign-300’ causes them to be
     aligned on 2-byte boundaries.  This option has no effect on the
     H8/300.


File: gcc.info,  Node: HPPA Options,  Next: IA-64 Options,  Prev: H8/300 Options,  Up: Submodel Options

3.19.20 HPPA Options
--------------------

These ‘-m’ options are defined for the HPPA family of computers:

‘-march=ARCHITECTURE-TYPE’
     Generate code for the specified architecture.  The choices for
     ARCHITECTURE-TYPE are ‘1.0’ for PA 1.0, ‘1.1’ for PA 1.1, and ‘2.0’
     for PA 2.0 processors.  Refer to ‘/usr/lib/sched.models’ on an
     HP-UX system to determine the proper architecture option for your
     machine.  Code compiled for lower numbered architectures runs on
     higher numbered architectures, but not the other way around.

‘-mpa-risc-1-0’
‘-mpa-risc-1-1’
‘-mpa-risc-2-0’
     Synonyms for ‘-march=1.0’, ‘-march=1.1’, and ‘-march=2.0’
     respectively.

‘-mcaller-copies’
     The caller copies function arguments passed by hidden reference.
     This option should be used with care as it is not compatible with
     the default 32-bit runtime.  However, only aggregates larger than
     eight bytes are passed by hidden reference and the option provides
     better compatibility with OpenMP.

‘-mjump-in-delay’
     This option is ignored and provided for compatibility purposes
     only.

‘-mdisable-fpregs’
     Prevent floating-point registers from being used in any manner.
     This is necessary for compiling kernels that perform lazy context
     switching of floating-point registers.  If you use this option and
     attempt to perform floating-point operations, the compiler aborts.

‘-mdisable-indexing’
     Prevent the compiler from using indexing address modes.  This
     avoids some rather obscure problems when compiling MIG generated
     code under MACH.

‘-mno-space-regs’
     Generate code that assumes the target has no space registers.  This
     allows GCC to generate faster indirect calls and use unscaled index
     address modes.

     Such code is suitable for level 0 PA systems and kernels.

‘-mfast-indirect-calls’
     Generate code that assumes calls never cross space boundaries.
     This allows GCC to emit code that performs faster indirect calls.

     This option does not work in the presence of shared libraries or
     nested functions.

‘-mfixed-range=REGISTER-RANGE’
     Generate code treating the given register range as fixed registers.
     A fixed register is one that the register allocator cannot use.
     This is useful when compiling kernel code.  A register range is
     specified as two registers separated by a dash.  Multiple register
     ranges can be specified separated by a comma.

‘-mlong-load-store’
     Generate 3-instruction load and store sequences as sometimes
     required by the HP-UX 10 linker.  This is equivalent to the ‘+k’
     option to the HP compilers.

‘-mportable-runtime’
     Use the portable calling conventions proposed by HP for ELF
     systems.

‘-mgas’
     Enable the use of assembler directives only GAS understands.

‘-mschedule=CPU-TYPE’
     Schedule code according to the constraints for the machine type
     CPU-TYPE.  The choices for CPU-TYPE are ‘700’ ‘7100’, ‘7100LC’,
     ‘7200’, ‘7300’ and ‘8000’.  Refer to ‘/usr/lib/sched.models’ on an
     HP-UX system to determine the proper scheduling option for your
     machine.  The default scheduling is ‘8000’.

‘-mlinker-opt’
     Enable the optimization pass in the HP-UX linker.  Note this makes
     symbolic debugging impossible.  It also triggers a bug in the HP-UX
     8 and HP-UX 9 linkers in which they give bogus error messages when
     linking some programs.

‘-msoft-float’
     Generate output containing library calls for floating point.
     *Warning:* the requisite libraries are not available for all HPPA
     targets.  Normally the facilities of the machine's usual C compiler
     are used, but this cannot be done directly in cross-compilation.
     You must make your own arrangements to provide suitable library
     functions for cross-compilation.

     ‘-msoft-float’ changes the calling convention in the output file;
     therefore, it is only useful if you compile _all_ of a program with
     this option.  In particular, you need to compile ‘libgcc.a’, the
     library that comes with GCC, with ‘-msoft-float’ in order for this
     to work.

‘-msio’
     Generate the predefine, ‘_SIO’, for server IO.  The default is
     ‘-mwsio’.  This generates the predefines, ‘__hp9000s700’,
     ‘__hp9000s700__’ and ‘_WSIO’, for workstation IO.  These options
     are available under HP-UX and HI-UX.

‘-mgnu-ld’
     Use options specific to GNU ‘ld’.  This passes ‘-shared’ to ‘ld’
     when building a shared library.  It is the default when GCC is
     configured, explicitly or implicitly, with the GNU linker.  This
     option does not affect which ‘ld’ is called; it only changes what
     parameters are passed to that ‘ld’.  The ‘ld’ that is called is
     determined by the ‘--with-ld’ configure option, GCC's program
     search path, and finally by the user's ‘PATH’.  The linker used by
     GCC can be printed using ‘which `gcc -print-prog-name=ld`’.  This
     option is only available on the 64-bit HP-UX GCC, i.e. configured
     with ‘hppa*64*-*-hpux*’.

‘-mhp-ld’
     Use options specific to HP ‘ld’.  This passes ‘-b’ to ‘ld’ when
     building a shared library and passes ‘+Accept TypeMismatch’ to ‘ld’
     on all links.  It is the default when GCC is configured, explicitly
     or implicitly, with the HP linker.  This option does not affect
     which ‘ld’ is called; it only changes what parameters are passed to
     that ‘ld’.  The ‘ld’ that is called is determined by the
     ‘--with-ld’ configure option, GCC's program search path, and
     finally by the user's ‘PATH’.  The linker used by GCC can be
     printed using ‘which `gcc -print-prog-name=ld`’.  This option is
     only available on the 64-bit HP-UX GCC, i.e. configured with
     ‘hppa*64*-*-hpux*’.

‘-mlong-calls’
     Generate code that uses long call sequences.  This ensures that a
     call is always able to reach linker generated stubs.  The default
     is to generate long calls only when the distance from the call site
     to the beginning of the function or translation unit, as the case
     may be, exceeds a predefined limit set by the branch type being
     used.  The limits for normal calls are 7,600,000 and 240,000 bytes,
     respectively for the PA 2.0 and PA 1.X architectures.  Sibcalls are
     always limited at 240,000 bytes.

     Distances are measured from the beginning of functions when using
     the ‘-ffunction-sections’ option, or when using the ‘-mgas’ and
     ‘-mno-portable-runtime’ options together under HP-UX with the SOM
     linker.

     It is normally not desirable to use this option as it degrades
     performance.  However, it may be useful in large applications,
     particularly when partial linking is used to build the application.

     The types of long calls used depends on the capabilities of the
     assembler and linker, and the type of code being generated.  The
     impact on systems that support long absolute calls, and long pic
     symbol-difference or pc-relative calls should be relatively small.
     However, an indirect call is used on 32-bit ELF systems in pic code
     and it is quite long.

‘-munix=UNIX-STD’
     Generate compiler predefines and select a startfile for the
     specified UNIX standard.  The choices for UNIX-STD are ‘93’, ‘95’
     and ‘98’.  ‘93’ is supported on all HP-UX versions.  ‘95’ is
     available on HP-UX 10.10 and later.  ‘98’ is available on HP-UX
     11.11 and later.  The default values are ‘93’ for HP-UX 10.00, ‘95’
     for HP-UX 10.10 though to 11.00, and ‘98’ for HP-UX 11.11 and
     later.

     ‘-munix=93’ provides the same predefines as GCC 3.3 and 3.4.
     ‘-munix=95’ provides additional predefines for ‘XOPEN_UNIX’ and
     ‘_XOPEN_SOURCE_EXTENDED’, and the startfile ‘unix95.o’.
     ‘-munix=98’ provides additional predefines for ‘_XOPEN_UNIX’,
     ‘_XOPEN_SOURCE_EXTENDED’, ‘_INCLUDE__STDC_A1_SOURCE’ and
     ‘_INCLUDE_XOPEN_SOURCE_500’, and the startfile ‘unix98.o’.

     It is _important_ to note that this option changes the interfaces
     for various library routines.  It also affects the operational
     behavior of the C library.  Thus, _extreme_ care is needed in using
     this option.

     Library code that is intended to operate with more than one UNIX
     standard must test, set and restore the variable
     ‘__xpg4_extended_mask’ as appropriate.  Most GNU software doesn't
     provide this capability.

‘-nolibdld’
     Suppress the generation of link options to search libdld.sl when
     the ‘-static’ option is specified on HP-UX 10 and later.

‘-static’
     The HP-UX implementation of setlocale in libc has a dependency on
     libdld.sl.  There isn't an archive version of libdld.sl.  Thus,
     when the ‘-static’ option is specified, special link options are
     needed to resolve this dependency.

     On HP-UX 10 and later, the GCC driver adds the necessary options to
     link with libdld.sl when the ‘-static’ option is specified.  This
     causes the resulting binary to be dynamic.  On the 64-bit port, the
     linkers generate dynamic binaries by default in any case.  The
     ‘-nolibdld’ option can be used to prevent the GCC driver from
     adding these link options.

‘-threads’
     Add support for multithreading with the “dce thread” library under
     HP-UX.  This option sets flags for both the preprocessor and
     linker.


File: gcc.info,  Node: IA-64 Options,  Next: LM32 Options,  Prev: HPPA Options,  Up: Submodel Options

3.19.21 IA-64 Options
---------------------

These are the ‘-m’ options defined for the Intel IA-64 architecture.

‘-mbig-endian’
     Generate code for a big-endian target.  This is the default for
     HP-UX.

‘-mlittle-endian’
     Generate code for a little-endian target.  This is the default for
     AIX5 and GNU/Linux.

‘-mgnu-as’
‘-mno-gnu-as’
     Generate (or don't) code for the GNU assembler.  This is the
     default.

‘-mgnu-ld’
‘-mno-gnu-ld’
     Generate (or don't) code for the GNU linker.  This is the default.

‘-mno-pic’
     Generate code that does not use a global pointer register.  The
     result is not position independent code, and violates the IA-64
     ABI.

‘-mvolatile-asm-stop’
‘-mno-volatile-asm-stop’
     Generate (or don't) a stop bit immediately before and after
     volatile asm statements.

‘-mregister-names’
‘-mno-register-names’
     Generate (or don't) ‘in’, ‘loc’, and ‘out’ register names for the
     stacked registers.  This may make assembler output more readable.

‘-mno-sdata’
‘-msdata’
     Disable (or enable) optimizations that use the small data section.
     This may be useful for working around optimizer bugs.

‘-mconstant-gp’
     Generate code that uses a single constant global pointer value.
     This is useful when compiling kernel code.

‘-mauto-pic’
     Generate code that is self-relocatable.  This implies
     ‘-mconstant-gp’.  This is useful when compiling firmware code.

‘-minline-float-divide-min-latency’
     Generate code for inline divides of floating-point values using the
     minimum latency algorithm.

‘-minline-float-divide-max-throughput’
     Generate code for inline divides of floating-point values using the
     maximum throughput algorithm.

‘-mno-inline-float-divide’
     Do not generate inline code for divides of floating-point values.

‘-minline-int-divide-min-latency’
     Generate code for inline divides of integer values using the
     minimum latency algorithm.

‘-minline-int-divide-max-throughput’
     Generate code for inline divides of integer values using the
     maximum throughput algorithm.

‘-mno-inline-int-divide’
     Do not generate inline code for divides of integer values.

‘-minline-sqrt-min-latency’
     Generate code for inline square roots using the minimum latency
     algorithm.

‘-minline-sqrt-max-throughput’
     Generate code for inline square roots using the maximum throughput
     algorithm.

‘-mno-inline-sqrt’
     Do not generate inline code for ‘sqrt’.

‘-mfused-madd’
‘-mno-fused-madd’
     Do (don't) generate code that uses the fused multiply/add or
     multiply/subtract instructions.  The default is to use these
     instructions.

‘-mno-dwarf2-asm’
‘-mdwarf2-asm’
     Don't (or do) generate assembler code for the DWARF line number
     debugging info.  This may be useful when not using the GNU
     assembler.

‘-mearly-stop-bits’
‘-mno-early-stop-bits’
     Allow stop bits to be placed earlier than immediately preceding the
     instruction that triggered the stop bit.  This can improve
     instruction scheduling, but does not always do so.

‘-mfixed-range=REGISTER-RANGE’
     Generate code treating the given register range as fixed registers.
     A fixed register is one that the register allocator cannot use.
     This is useful when compiling kernel code.  A register range is
     specified as two registers separated by a dash.  Multiple register
     ranges can be specified separated by a comma.

‘-mtls-size=TLS-SIZE’
     Specify bit size of immediate TLS offsets.  Valid values are 14,
     22, and 64.

‘-mtune=CPU-TYPE’
     Tune the instruction scheduling for a particular CPU, Valid values
     are ‘itanium’, ‘itanium1’, ‘merced’, ‘itanium2’, and ‘mckinley’.

‘-milp32’
‘-mlp64’
     Generate code for a 32-bit or 64-bit environment.  The 32-bit
     environment sets int, long and pointer to 32 bits.  The 64-bit
     environment sets int to 32 bits and long and pointer to 64 bits.
     These are HP-UX specific flags.

‘-mno-sched-br-data-spec’
‘-msched-br-data-spec’
     (Dis/En)able data speculative scheduling before reload.  This
     results in generation of ‘ld.a’ instructions and the corresponding
     check instructions (‘ld.c’ / ‘chk.a’).  The default setting is
     disabled.

‘-msched-ar-data-spec’
‘-mno-sched-ar-data-spec’
     (En/Dis)able data speculative scheduling after reload.  This
     results in generation of ‘ld.a’ instructions and the corresponding
     check instructions (‘ld.c’ / ‘chk.a’).  The default setting is
     enabled.

‘-mno-sched-control-spec’
‘-msched-control-spec’
     (Dis/En)able control speculative scheduling.  This feature is
     available only during region scheduling (i.e. before reload).  This
     results in generation of the ‘ld.s’ instructions and the
     corresponding check instructions ‘chk.s’.  The default setting is
     disabled.

‘-msched-br-in-data-spec’
‘-mno-sched-br-in-data-spec’
     (En/Dis)able speculative scheduling of the instructions that are
     dependent on the data speculative loads before reload.  This is
     effective only with ‘-msched-br-data-spec’ enabled.  The default
     setting is enabled.

‘-msched-ar-in-data-spec’
‘-mno-sched-ar-in-data-spec’
     (En/Dis)able speculative scheduling of the instructions that are
     dependent on the data speculative loads after reload.  This is
     effective only with ‘-msched-ar-data-spec’ enabled.  The default
     setting is enabled.

‘-msched-in-control-spec’
‘-mno-sched-in-control-spec’
     (En/Dis)able speculative scheduling of the instructions that are
     dependent on the control speculative loads.  This is effective only
     with ‘-msched-control-spec’ enabled.  The default setting is
     enabled.

‘-mno-sched-prefer-non-data-spec-insns’
‘-msched-prefer-non-data-spec-insns’
     If enabled, data-speculative instructions are chosen for schedule
     only if there are no other choices at the moment.  This makes the
     use of the data speculation much more conservative.  The default
     setting is disabled.

‘-mno-sched-prefer-non-control-spec-insns’
‘-msched-prefer-non-control-spec-insns’
     If enabled, control-speculative instructions are chosen for
     schedule only if there are no other choices at the moment.  This
     makes the use of the control speculation much more conservative.
     The default setting is disabled.

‘-mno-sched-count-spec-in-critical-path’
‘-msched-count-spec-in-critical-path’
     If enabled, speculative dependencies are considered during
     computation of the instructions priorities.  This makes the use of
     the speculation a bit more conservative.  The default setting is
     disabled.

‘-msched-spec-ldc’
     Use a simple data speculation check.  This option is on by default.

‘-msched-control-spec-ldc’
     Use a simple check for control speculation.  This option is on by
     default.

‘-msched-stop-bits-after-every-cycle’
     Place a stop bit after every cycle when scheduling.  This option is
     on by default.

‘-msched-fp-mem-deps-zero-cost’
     Assume that floating-point stores and loads are not likely to cause
     a conflict when placed into the same instruction group.  This
     option is disabled by default.

‘-msel-sched-dont-check-control-spec’
     Generate checks for control speculation in selective scheduling.
     This flag is disabled by default.

‘-msched-max-memory-insns=MAX-INSNS’
     Limit on the number of memory insns per instruction group, giving
     lower priority to subsequent memory insns attempting to schedule in
     the same instruction group.  Frequently useful to prevent cache
     bank conflicts.  The default value is 1.

‘-msched-max-memory-insns-hard-limit’
     Makes the limit specified by ‘msched-max-memory-insns’ a hard
     limit, disallowing more than that number in an instruction group.
     Otherwise, the limit is "soft", meaning that non-memory operations
     are preferred when the limit is reached, but memory operations may
     still be scheduled.


File: gcc.info,  Node: LM32 Options,  Next: LoongArch Options,  Prev: IA-64 Options,  Up: Submodel Options

3.19.22 LM32 Options
--------------------

These ‘-m’ options are defined for the LatticeMico32 architecture:

‘-mbarrel-shift-enabled’
     Enable barrel-shift instructions.

‘-mdivide-enabled’
     Enable divide and modulus instructions.

‘-mmultiply-enabled’
     Enable multiply instructions.

‘-msign-extend-enabled’
     Enable sign extend instructions.

‘-muser-enabled’
     Enable user-defined instructions.


File: gcc.info,  Node: LoongArch Options,  Next: M32C Options,  Prev: LM32 Options,  Up: Submodel Options

3.19.23 LoongArch Options
-------------------------

These command-line options are defined for LoongArch targets:

‘-march=CPU-TYPE’
     Generate instructions for the machine type CPU-TYPE.  In contrast
     to ‘-mtune=CPU-TYPE’, which merely tunes the generated code for the
     specified CPU-TYPE, ‘-march=CPU-TYPE’ allows GCC to generate code
     that may not run at all on processors other than the one indicated.
     Specifying ‘-march=CPU-TYPE’ implies ‘-mtune=CPU-TYPE’, except
     where noted otherwise.

     The choices for CPU-TYPE are:

     ‘native’
          This selects the CPU to generate code for at compilation time
          by determining the processor type of the compiling machine.
          Using ‘-march=native’ enables all instruction subsets
          supported by the local machine (hence the result might not run
          on different machines).  Using ‘-mtune=native’ produces code
          optimized for the local machine under the constraints of the
          selected instruction set.
     ‘loongarch64’
          A generic CPU with 64-bit extensions.
     ‘la464’
          LoongArch LA464 CPU with LBT, LSX, LASX, LVZ.

‘-mtune=CPU-TYPE’
     Optimize the output for the given processor, specified by
     microarchitecture name.

‘-mabi=BASE-ABI-TYPE’
     Generate code for the specified calling convention.  BASE-ABI-TYPE
     can be one of:
     ‘lp64d’
          Uses 64-bit general purpose registers and 32/64-bit
          floating-point registers for parameter passing.  Data model is
          LP64, where ‘int’ is 32 bits, while ‘long int’ and pointers
          are 64 bits.
     ‘lp64f’
          Uses 64-bit general purpose registers and 32-bit
          floating-point registers for parameter passing.  Data model is
          LP64, where ‘int’ is 32 bits, while ‘long int’ and pointers
          are 64 bits.
     ‘lp64s’
          Uses 64-bit general purpose registers and no floating-point
          registers for parameter passing.  Data model is LP64, where
          ‘int’ is 32 bits, while ‘long int’ and pointers are 64 bits.

‘-mfpu=FPU-TYPE’
     Generate code for the specified FPU type, which can be one of:
     ‘64’
          Allow the use of hardware floating-point instructions for
          32-bit and 64-bit operations.
     ‘32’
          Allow the use of hardware floating-point instructions for
          32-bit operations.
     ‘none’
     ‘0’
          Prevent the use of hardware floating-point instructions.

‘-msoft-float’
     Force ‘-mfpu=none’ and prevents the use of floating-point registers
     for parameter passing.  This option may change the target ABI.

‘-msingle-float’
     Force ‘-mfpu=32’ and allow the use of 32-bit floating-point
     registers for parameter passing.  This option may change the target
     ABI.

‘-mdouble-float’
     Force ‘-mfpu=64’ and allow the use of 32/64-bit floating-point
     registers for parameter passing.  This option may change the target
     ABI.

‘-mbranch-cost=N’
     Set the cost of branches to roughly N instructions.

‘-mcheck-zero-division’
‘-mno-check-zero-divison’
     Trap (do not trap) on integer division by zero.  The default is
     ‘-mcheck-zero-division’ for ‘-O0’ or ‘-Og’, and
     ‘-mno-check-zero-division’ for other optimization levels.

‘-mcond-move-int’
‘-mno-cond-move-int’
     Conditional moves for integral data in general-purpose registers
     are enabled (disabled).  The default is ‘-mcond-move-int’.

‘-mcond-move-float’
‘-mno-cond-move-float’
     Conditional moves for floating-point registers are enabled
     (disabled).  The default is ‘-mcond-move-float’.

‘-mmemcpy’
‘-mno-memcpy’
     Force (do not force) the use of ‘memcpy’ for non-trivial block
     moves.  The default is ‘-mno-memcpy’, which allows GCC to inline
     most constant-sized copies.  Setting optimization level to ‘-Os’
     also forces the use of ‘memcpy’, but ‘-mno-memcpy’ may override
     this behavior if explicitly specified, regardless of the order
     these options on the command line.

‘-mstrict-align’
‘-mno-strict-align’
     Avoid or allow generating memory accesses that may not be aligned
     on a natural object boundary as described in the architecture
     specification.  The default is ‘-mno-strict-align’.

‘-msmall-data-limit=NUMBER’
     Put global and static data smaller than NUMBER bytes into a special
     section (on some targets).  The default value is 0.

‘-mmax-inline-memcpy-size=N’
     Inline all block moves (such as calls to ‘memcpy’ or structure
     copies) less than or equal to N bytes.  The default value of N is
     1024.

‘-mcmodel=CODE-MODEL’
     Set the code model to one of:
     ‘tiny-static’
             • local symbol and global strong symbol: The data section
               must be within +/-2MiB addressing space.  The text
               section must be within +/-128MiB addressing space.
             • global weak symbol: The got table must be within +/-2GiB
               addressing space.

     ‘tiny’
             • local symbol: The data section must be within +/-2MiB
               addressing space.  The text section must be within
               +/-128MiB addressing space.
             • global symbol: The got table must be within +/-2GiB
               addressing space.

     ‘normal’
             • local symbol: The data section must be within +/-2GiB
               addressing space.  The text section must be within
               +/-128MiB addressing space.
             • global symbol: The got table must be within +/-2GiB
               addressing space.

     ‘large’
             • local symbol: The data section must be within +/-2GiB
               addressing space.  The text section must be within
               +/-128GiB addressing space.
             • global symbol: The got table must be within +/-2GiB
               addressing space.

     ‘extreme(Not implemented yet)’
             • local symbol: The data and text section must be within
               +/-8EiB addressing space.
             • global symbol: The data got table must be within +/-8EiB
               addressing space.
     The default code model is ‘normal’.


File: gcc.info,  Node: M32C Options,  Next: M32R/D Options,  Prev: LoongArch Options,  Up: Submodel Options

3.19.24 M32C Options
--------------------

‘-mcpu=NAME’
     Select the CPU for which code is generated.  NAME may be one of
     ‘r8c’ for the R8C/Tiny series, ‘m16c’ for the M16C (up to /60)
     series, ‘m32cm’ for the M16C/80 series, or ‘m32c’ for the M32C/80
     series.

‘-msim’
     Specifies that the program will be run on the simulator.  This
     causes an alternate runtime library to be linked in which supports,
     for example, file I/O.  You must not use this option when
     generating programs that will run on real hardware; you must
     provide your own runtime library for whatever I/O functions are
     needed.

‘-memregs=NUMBER’
     Specifies the number of memory-based pseudo-registers GCC uses
     during code generation.  These pseudo-registers are used like real
     registers, so there is a tradeoff between GCC's ability to fit the
     code into available registers, and the performance penalty of using
     memory instead of registers.  Note that all modules in a program
     must be compiled with the same value for this option.  Because of
     that, you must not use this option with GCC's default runtime
     libraries.


File: gcc.info,  Node: M32R/D Options,  Next: M680x0 Options,  Prev: M32C Options,  Up: Submodel Options

3.19.25 M32R/D Options
----------------------

These ‘-m’ options are defined for Renesas M32R/D architectures:

‘-m32r2’
     Generate code for the M32R/2.

‘-m32rx’
     Generate code for the M32R/X.

‘-m32r’
     Generate code for the M32R.  This is the default.

‘-mmodel=small’
     Assume all objects live in the lower 16MB of memory (so that their
     addresses can be loaded with the ‘ld24’ instruction), and assume
     all subroutines are reachable with the ‘bl’ instruction.  This is
     the default.

     The addressability of a particular object can be set with the
     ‘model’ attribute.

‘-mmodel=medium’
     Assume objects may be anywhere in the 32-bit address space (the
     compiler generates ‘seth/add3’ instructions to load their
     addresses), and assume all subroutines are reachable with the ‘bl’
     instruction.

‘-mmodel=large’
     Assume objects may be anywhere in the 32-bit address space (the
     compiler generates ‘seth/add3’ instructions to load their
     addresses), and assume subroutines may not be reachable with the
     ‘bl’ instruction (the compiler generates the much slower
     ‘seth/add3/jl’ instruction sequence).

‘-msdata=none’
     Disable use of the small data area.  Variables are put into one of
     ‘.data’, ‘.bss’, or ‘.rodata’ (unless the ‘section’ attribute has
     been specified).  This is the default.

     The small data area consists of sections ‘.sdata’ and ‘.sbss’.
     Objects may be explicitly put in the small data area with the
     ‘section’ attribute using one of these sections.

‘-msdata=sdata’
     Put small global and static data in the small data area, but do not
     generate special code to reference them.

‘-msdata=use’
     Put small global and static data in the small data area, and
     generate special instructions to reference them.

‘-G NUM’
     Put global and static objects less than or equal to NUM bytes into
     the small data or BSS sections instead of the normal data or BSS
     sections.  The default value of NUM is 8.  The ‘-msdata’ option
     must be set to one of ‘sdata’ or ‘use’ for this option to have any
     effect.

     All modules should be compiled with the same ‘-G NUM’ value.
     Compiling with different values of NUM may or may not work; if it
     doesn't the linker gives an error message--incorrect code is not
     generated.

‘-mdebug’
     Makes the M32R-specific code in the compiler display some
     statistics that might help in debugging programs.

‘-malign-loops’
     Align all loops to a 32-byte boundary.

‘-mno-align-loops’
     Do not enforce a 32-byte alignment for loops.  This is the default.

‘-missue-rate=NUMBER’
     Issue NUMBER instructions per cycle.  NUMBER can only be 1 or 2.

‘-mbranch-cost=NUMBER’
     NUMBER can only be 1 or 2.  If it is 1 then branches are preferred
     over conditional code, if it is 2, then the opposite applies.

‘-mflush-trap=NUMBER’
     Specifies the trap number to use to flush the cache.  The default
     is 12.  Valid numbers are between 0 and 15 inclusive.

‘-mno-flush-trap’
     Specifies that the cache cannot be flushed by using a trap.

‘-mflush-func=NAME’
     Specifies the name of the operating system function to call to
     flush the cache.  The default is ‘_flush_cache’, but a function
     call is only used if a trap is not available.

‘-mno-flush-func’
     Indicates that there is no OS function for flushing the cache.


File: gcc.info,  Node: M680x0 Options,  Next: MCore Options,  Prev: M32R/D Options,  Up: Submodel Options

3.19.26 M680x0 Options
----------------------

These are the ‘-m’ options defined for M680x0 and ColdFire processors.
The default settings depend on which architecture was selected when the
compiler was configured; the defaults for the most common choices are
given below.

‘-march=ARCH’
     Generate code for a specific M680x0 or ColdFire instruction set
     architecture.  Permissible values of ARCH for M680x0 architectures
     are: ‘68000’, ‘68010’, ‘68020’, ‘68030’, ‘68040’, ‘68060’ and
     ‘cpu32’.  ColdFire architectures are selected according to
     Freescale's ISA classification and the permissible values are:
     ‘isaa’, ‘isaaplus’, ‘isab’ and ‘isac’.

     GCC defines a macro ‘__mcfARCH__’ whenever it is generating code
     for a ColdFire target.  The ARCH in this macro is one of the
     ‘-march’ arguments given above.

     When used together, ‘-march’ and ‘-mtune’ select code that runs on
     a family of similar processors but that is optimized for a
     particular microarchitecture.

‘-mcpu=CPU’
     Generate code for a specific M680x0 or ColdFire processor.  The
     M680x0 CPUs are: ‘68000’, ‘68010’, ‘68020’, ‘68030’, ‘68040’,
     ‘68060’, ‘68302’, ‘68332’ and ‘cpu32’.  The ColdFire CPUs are given
     by the table below, which also classifies the CPUs into families:

     *Family*       *‘-mcpu’ arguments*
     --------------------------------------------------------------------------
     ‘51’           ‘51’ ‘51ac’ ‘51ag’ ‘51cn’ ‘51em’ ‘51je’ ‘51jf’ ‘51jg’
                    ‘51jm’ ‘51mm’ ‘51qe’ ‘51qm’
     ‘5206’         ‘5202’ ‘5204’ ‘5206’
     ‘5206e’        ‘5206e’
     ‘5208’         ‘5207’ ‘5208’
     ‘5211a’        ‘5210a’ ‘5211a’
     ‘5213’         ‘5211’ ‘5212’ ‘5213’
     ‘5216’         ‘5214’ ‘5216’
     ‘52235’        ‘52230’ ‘52231’ ‘52232’ ‘52233’ ‘52234’ ‘52235’
     ‘5225’         ‘5224’ ‘5225’
     ‘52259’        ‘52252’ ‘52254’ ‘52255’ ‘52256’ ‘52258’ ‘52259’
     ‘5235’         ‘5232’ ‘5233’ ‘5234’ ‘5235’ ‘523x’
     ‘5249’         ‘5249’
     ‘5250’         ‘5250’
     ‘5271’         ‘5270’ ‘5271’
     ‘5272’         ‘5272’
     ‘5275’         ‘5274’ ‘5275’
     ‘5282’         ‘5280’ ‘5281’ ‘5282’ ‘528x’
     ‘53017’        ‘53011’ ‘53012’ ‘53013’ ‘53014’ ‘53015’ ‘53016’ ‘53017’
     ‘5307’         ‘5307’
     ‘5329’         ‘5327’ ‘5328’ ‘5329’ ‘532x’
     ‘5373’         ‘5372’ ‘5373’ ‘537x’
     ‘5407’         ‘5407’
     ‘5475’         ‘5470’ ‘5471’ ‘5472’ ‘5473’ ‘5474’ ‘5475’ ‘547x’ ‘5480’
                    ‘5481’ ‘5482’ ‘5483’ ‘5484’ ‘5485’

     ‘-mcpu=CPU’ overrides ‘-march=ARCH’ if ARCH is compatible with CPU.
     Other combinations of ‘-mcpu’ and ‘-march’ are rejected.

     GCC defines the macro ‘__mcf_cpu_CPU’ when ColdFire target CPU is
     selected.  It also defines ‘__mcf_family_FAMILY’, where the value
     of FAMILY is given by the table above.

‘-mtune=TUNE’
     Tune the code for a particular microarchitecture within the
     constraints set by ‘-march’ and ‘-mcpu’.  The M680x0
     microarchitectures are: ‘68000’, ‘68010’, ‘68020’, ‘68030’,
     ‘68040’, ‘68060’ and ‘cpu32’.  The ColdFire microarchitectures are:
     ‘cfv1’, ‘cfv2’, ‘cfv3’, ‘cfv4’ and ‘cfv4e’.

     You can also use ‘-mtune=68020-40’ for code that needs to run
     relatively well on 68020, 68030 and 68040 targets.
     ‘-mtune=68020-60’ is similar but includes 68060 targets as well.
     These two options select the same tuning decisions as ‘-m68020-40’
     and ‘-m68020-60’ respectively.

     GCC defines the macros ‘__mcARCH’ and ‘__mcARCH__’ when tuning for
     680x0 architecture ARCH.  It also defines ‘mcARCH’ unless either
     ‘-ansi’ or a non-GNU ‘-std’ option is used.  If GCC is tuning for a
     range of architectures, as selected by ‘-mtune=68020-40’ or
     ‘-mtune=68020-60’, it defines the macros for every architecture in
     the range.

     GCC also defines the macro ‘__mUARCH__’ when tuning for ColdFire
     microarchitecture UARCH, where UARCH is one of the arguments given
     above.

‘-m68000’
‘-mc68000’
     Generate output for a 68000.  This is the default when the compiler
     is configured for 68000-based systems.  It is equivalent to
     ‘-march=68000’.

     Use this option for microcontrollers with a 68000 or EC000 core,
     including the 68008, 68302, 68306, 68307, 68322, 68328 and 68356.

‘-m68010’
     Generate output for a 68010.  This is the default when the compiler
     is configured for 68010-based systems.  It is equivalent to
     ‘-march=68010’.

‘-m68020’
‘-mc68020’
     Generate output for a 68020.  This is the default when the compiler
     is configured for 68020-based systems.  It is equivalent to
     ‘-march=68020’.

‘-m68030’
     Generate output for a 68030.  This is the default when the compiler
     is configured for 68030-based systems.  It is equivalent to
     ‘-march=68030’.

‘-m68040’
     Generate output for a 68040.  This is the default when the compiler
     is configured for 68040-based systems.  It is equivalent to
     ‘-march=68040’.

     This option inhibits the use of 68881/68882 instructions that have
     to be emulated by software on the 68040.  Use this option if your
     68040 does not have code to emulate those instructions.

‘-m68060’
     Generate output for a 68060.  This is the default when the compiler
     is configured for 68060-based systems.  It is equivalent to
     ‘-march=68060’.

     This option inhibits the use of 68020 and 68881/68882 instructions
     that have to be emulated by software on the 68060.  Use this option
     if your 68060 does not have code to emulate those instructions.

‘-mcpu32’
     Generate output for a CPU32.  This is the default when the compiler
     is configured for CPU32-based systems.  It is equivalent to
     ‘-march=cpu32’.

     Use this option for microcontrollers with a CPU32 or CPU32+ core,
     including the 68330, 68331, 68332, 68333, 68334, 68336, 68340,
     68341, 68349 and 68360.

‘-m5200’
     Generate output for a 520X ColdFire CPU.  This is the default when
     the compiler is configured for 520X-based systems.  It is
     equivalent to ‘-mcpu=5206’, and is now deprecated in favor of that
     option.

     Use this option for microcontroller with a 5200 core, including the
     MCF5202, MCF5203, MCF5204 and MCF5206.

‘-m5206e’
     Generate output for a 5206e ColdFire CPU.  The option is now
     deprecated in favor of the equivalent ‘-mcpu=5206e’.

‘-m528x’
     Generate output for a member of the ColdFire 528X family.  The
     option is now deprecated in favor of the equivalent ‘-mcpu=528x’.

‘-m5307’
     Generate output for a ColdFire 5307 CPU.  The option is now
     deprecated in favor of the equivalent ‘-mcpu=5307’.

‘-m5407’
     Generate output for a ColdFire 5407 CPU.  The option is now
     deprecated in favor of the equivalent ‘-mcpu=5407’.

‘-mcfv4e’
     Generate output for a ColdFire V4e family CPU (e.g. 547x/548x).
     This includes use of hardware floating-point instructions.  The
     option is equivalent to ‘-mcpu=547x’, and is now deprecated in
     favor of that option.

‘-m68020-40’
     Generate output for a 68040, without using any of the new
     instructions.  This results in code that can run relatively
     efficiently on either a 68020/68881 or a 68030 or a 68040.  The
     generated code does use the 68881 instructions that are emulated on
     the 68040.

     The option is equivalent to ‘-march=68020’ ‘-mtune=68020-40’.

‘-m68020-60’
     Generate output for a 68060, without using any of the new
     instructions.  This results in code that can run relatively
     efficiently on either a 68020/68881 or a 68030 or a 68040.  The
     generated code does use the 68881 instructions that are emulated on
     the 68060.

     The option is equivalent to ‘-march=68020’ ‘-mtune=68020-60’.

‘-mhard-float’
‘-m68881’
     Generate floating-point instructions.  This is the default for
     68020 and above, and for ColdFire devices that have an FPU.  It
     defines the macro ‘__HAVE_68881__’ on M680x0 targets and
     ‘__mcffpu__’ on ColdFire targets.

‘-msoft-float’
     Do not generate floating-point instructions; use library calls
     instead.  This is the default for 68000, 68010, and 68832 targets.
     It is also the default for ColdFire devices that have no FPU.

‘-mdiv’
‘-mno-div’
     Generate (do not generate) ColdFire hardware divide and remainder
     instructions.  If ‘-march’ is used without ‘-mcpu’, the default is
     "on" for ColdFire architectures and "off" for M680x0 architectures.
     Otherwise, the default is taken from the target CPU (either the
     default CPU, or the one specified by ‘-mcpu’).  For example, the
     default is "off" for ‘-mcpu=5206’ and "on" for ‘-mcpu=5206e’.

     GCC defines the macro ‘__mcfhwdiv__’ when this option is enabled.

‘-mshort’
     Consider type ‘int’ to be 16 bits wide, like ‘short int’.
     Additionally, parameters passed on the stack are also aligned to a
     16-bit boundary even on targets whose API mandates promotion to
     32-bit.

‘-mno-short’
     Do not consider type ‘int’ to be 16 bits wide.  This is the
     default.

‘-mnobitfield’
‘-mno-bitfield’
     Do not use the bit-field instructions.  The ‘-m68000’, ‘-mcpu32’
     and ‘-m5200’ options imply ‘-mnobitfield’.

‘-mbitfield’
     Do use the bit-field instructions.  The ‘-m68020’ option implies
     ‘-mbitfield’.  This is the default if you use a configuration
     designed for a 68020.

‘-mrtd’
     Use a different function-calling convention, in which functions
     that take a fixed number of arguments return with the ‘rtd’
     instruction, which pops their arguments while returning.  This
     saves one instruction in the caller since there is no need to pop
     the arguments there.

     This calling convention is incompatible with the one normally used
     on Unix, so you cannot use it if you need to call libraries
     compiled with the Unix compiler.

     Also, you must provide function prototypes for all functions that
     take variable numbers of arguments (including ‘printf’); otherwise
     incorrect code is generated for calls to those functions.

     In addition, seriously incorrect code results if you call a
     function with too many arguments.  (Normally, extra arguments are
     harmlessly ignored.)

     The ‘rtd’ instruction is supported by the 68010, 68020, 68030,
     68040, 68060 and CPU32 processors, but not by the 68000 or 5200.

     The default is ‘-mno-rtd’.

‘-malign-int’
‘-mno-align-int’
     Control whether GCC aligns ‘int’, ‘long’, ‘long long’, ‘float’,
     ‘double’, and ‘long double’ variables on a 32-bit boundary
     (‘-malign-int’) or a 16-bit boundary (‘-mno-align-int’).  Aligning
     variables on 32-bit boundaries produces code that runs somewhat
     faster on processors with 32-bit busses at the expense of more
     memory.

     *Warning:* if you use the ‘-malign-int’ switch, GCC aligns
     structures containing the above types differently than most
     published application binary interface specifications for the m68k.

     Use the pc-relative addressing mode of the 68000 directly, instead
     of using a global offset table.  At present, this option implies
     ‘-fpic’, allowing at most a 16-bit offset for pc-relative
     addressing.  ‘-fPIC’ is not presently supported with ‘-mpcrel’,
     though this could be supported for 68020 and higher processors.

‘-mno-strict-align’
‘-mstrict-align’
     Do not (do) assume that unaligned memory references are handled by
     the system.

‘-msep-data’
     Generate code that allows the data segment to be located in a
     different area of memory from the text segment.  This allows for
     execute-in-place in an environment without virtual memory
     management.  This option implies ‘-fPIC’.

‘-mno-sep-data’
     Generate code that assumes that the data segment follows the text
     segment.  This is the default.

‘-mid-shared-library’
     Generate code that supports shared libraries via the library ID
     method.  This allows for execute-in-place and shared libraries in
     an environment without virtual memory management.  This option
     implies ‘-fPIC’.

‘-mno-id-shared-library’
     Generate code that doesn't assume ID-based shared libraries are
     being used.  This is the default.

‘-mshared-library-id=n’
     Specifies the identification number of the ID-based shared library
     being compiled.  Specifying a value of 0 generates more compact
     code; specifying other values forces the allocation of that number
     to the current library, but is no more space- or time-efficient
     than omitting this option.

‘-mxgot’
‘-mno-xgot’
     When generating position-independent code for ColdFire, generate
     code that works if the GOT has more than 8192 entries.  This code
     is larger and slower than code generated without this option.  On
     M680x0 processors, this option is not needed; ‘-fPIC’ suffices.

     GCC normally uses a single instruction to load values from the GOT.
     While this is relatively efficient, it only works if the GOT is
     smaller than about 64k.  Anything larger causes the linker to
     report an error such as:

          relocation truncated to fit: R_68K_GOT16O foobar

     If this happens, you should recompile your code with ‘-mxgot’.  It
     should then work with very large GOTs.  However, code generated
     with ‘-mxgot’ is less efficient, since it takes 4 instructions to
     fetch the value of a global symbol.

     Note that some linkers, including newer versions of the GNU linker,
     can create multiple GOTs and sort GOT entries.  If you have such a
     linker, you should only need to use ‘-mxgot’ when compiling a
     single object file that accesses more than 8192 GOT entries.  Very
     few do.

     These options have no effect unless GCC is generating
     position-independent code.

‘-mlong-jump-table-offsets’
     Use 32-bit offsets in ‘switch’ tables.  The default is to use
     16-bit offsets.


File: gcc.info,  Node: MCore Options,  Next: MeP Options,  Prev: M680x0 Options,  Up: Submodel Options

3.19.27 MCore Options
---------------------

These are the ‘-m’ options defined for the Motorola M*Core processors.

‘-mhardlit’
‘-mno-hardlit’
     Inline constants into the code stream if it can be done in two
     instructions or less.

‘-mdiv’
‘-mno-div’
     Use the divide instruction.  (Enabled by default).

‘-mrelax-immediate’
‘-mno-relax-immediate’
     Allow arbitrary-sized immediates in bit operations.

‘-mwide-bitfields’
‘-mno-wide-bitfields’
     Always treat bit-fields as ‘int’-sized.

‘-m4byte-functions’
‘-mno-4byte-functions’
     Force all functions to be aligned to a 4-byte boundary.

‘-mcallgraph-data’
‘-mno-callgraph-data’
     Emit callgraph information.

‘-mslow-bytes’
‘-mno-slow-bytes’
     Prefer word access when reading byte quantities.

‘-mlittle-endian’
‘-mbig-endian’
     Generate code for a little-endian target.

‘-m210’
‘-m340’
     Generate code for the 210 processor.

‘-mno-lsim’
     Assume that runtime support has been provided and so omit the
     simulator library (‘libsim.a)’ from the linker command line.

‘-mstack-increment=SIZE’
     Set the maximum amount for a single stack increment operation.
     Large values can increase the speed of programs that contain
     functions that need a large amount of stack space, but they can
     also trigger a segmentation fault if the stack is extended too
     much.  The default value is 0x1000.


File: gcc.info,  Node: MeP Options,  Next: MicroBlaze Options,  Prev: MCore Options,  Up: Submodel Options

3.19.28 MeP Options
-------------------

‘-mabsdiff’
     Enables the ‘abs’ instruction, which is the absolute difference
     between two registers.

‘-mall-opts’
     Enables all the optional instructions--average, multiply, divide,
     bit operations, leading zero, absolute difference, min/max, clip,
     and saturation.

‘-maverage’
     Enables the ‘ave’ instruction, which computes the average of two
     registers.

‘-mbased=N’
     Variables of size N bytes or smaller are placed in the ‘.based’
     section by default.  Based variables use the ‘$tp’ register as a
     base register, and there is a 128-byte limit to the ‘.based’
     section.

‘-mbitops’
     Enables the bit operation instructions--bit test (‘btstm’), set
     (‘bsetm’), clear (‘bclrm’), invert (‘bnotm’), and test-and-set
     (‘tas’).

‘-mc=NAME’
     Selects which section constant data is placed in.  NAME may be
     ‘tiny’, ‘near’, or ‘far’.

‘-mclip’
     Enables the ‘clip’ instruction.  Note that ‘-mclip’ is not useful
     unless you also provide ‘-mminmax’.

‘-mconfig=NAME’
     Selects one of the built-in core configurations.  Each MeP chip has
     one or more modules in it; each module has a core CPU and a variety
     of coprocessors, optional instructions, and peripherals.  The
     ‘MeP-Integrator’ tool, not part of GCC, provides these
     configurations through this option; using this option is the same
     as using all the corresponding command-line options.  The default
     configuration is ‘default’.

‘-mcop’
     Enables the coprocessor instructions.  By default, this is a 32-bit
     coprocessor.  Note that the coprocessor is normally enabled via the
     ‘-mconfig=’ option.

‘-mcop32’
     Enables the 32-bit coprocessor's instructions.

‘-mcop64’
     Enables the 64-bit coprocessor's instructions.

‘-mivc2’
     Enables IVC2 scheduling.  IVC2 is a 64-bit VLIW coprocessor.

‘-mdc’
     Causes constant variables to be placed in the ‘.near’ section.

‘-mdiv’
     Enables the ‘div’ and ‘divu’ instructions.

‘-meb’
     Generate big-endian code.

‘-mel’
     Generate little-endian code.

‘-mio-volatile’
     Tells the compiler that any variable marked with the ‘io’ attribute
     is to be considered volatile.

‘-ml’
     Causes variables to be assigned to the ‘.far’ section by default.

‘-mleadz’
     Enables the ‘leadz’ (leading zero) instruction.

‘-mm’
     Causes variables to be assigned to the ‘.near’ section by default.

‘-mminmax’
     Enables the ‘min’ and ‘max’ instructions.

‘-mmult’
     Enables the multiplication and multiply-accumulate instructions.

‘-mno-opts’
     Disables all the optional instructions enabled by ‘-mall-opts’.

‘-mrepeat’
     Enables the ‘repeat’ and ‘erepeat’ instructions, used for
     low-overhead looping.

‘-ms’
     Causes all variables to default to the ‘.tiny’ section.  Note that
     there is a 65536-byte limit to this section.  Accesses to these
     variables use the ‘%gp’ base register.

‘-msatur’
     Enables the saturation instructions.  Note that the compiler does
     not currently generate these itself, but this option is included
     for compatibility with other tools, like ‘as’.

‘-msdram’
     Link the SDRAM-based runtime instead of the default ROM-based
     runtime.

‘-msim’
     Link the simulator run-time libraries.

‘-msimnovec’
     Link the simulator runtime libraries, excluding built-in support
     for reset and exception vectors and tables.

‘-mtf’
     Causes all functions to default to the ‘.far’ section.  Without
     this option, functions default to the ‘.near’ section.

‘-mtiny=N’
     Variables that are N bytes or smaller are allocated to the ‘.tiny’
     section.  These variables use the ‘$gp’ base register.  The default
     for this option is 4, but note that there's a 65536-byte limit to
     the ‘.tiny’ section.


File: gcc.info,  Node: MicroBlaze Options,  Next: MIPS Options,  Prev: MeP Options,  Up: Submodel Options

3.19.29 MicroBlaze Options
--------------------------

‘-msoft-float’
     Use software emulation for floating point (default).

‘-mhard-float’
     Use hardware floating-point instructions.

‘-mmemcpy’
     Do not optimize block moves, use ‘memcpy’.

‘-mno-clearbss’
     This option is deprecated.  Use ‘-fno-zero-initialized-in-bss’
     instead.

‘-mcpu=CPU-TYPE’
     Use features of, and schedule code for, the given CPU. Supported
     values are in the format ‘vX.YY.Z’, where X is a major version, YY
     is the minor version, and Z is compatibility code.  Example values
     are ‘v3.00.a’, ‘v4.00.b’, ‘v5.00.a’, ‘v5.00.b’, ‘v6.00.a’.

‘-mxl-soft-mul’
     Use software multiply emulation (default).

‘-mxl-soft-div’
     Use software emulation for divides (default).

‘-mxl-barrel-shift’
     Use the hardware barrel shifter.

‘-mxl-pattern-compare’
     Use pattern compare instructions.

‘-msmall-divides’
     Use table lookup optimization for small signed integer divisions.

‘-mxl-stack-check’
     This option is deprecated.  Use ‘-fstack-check’ instead.

‘-mxl-gp-opt’
     Use GP-relative ‘.sdata’/‘.sbss’ sections.

‘-mxl-multiply-high’
     Use multiply high instructions for high part of 32x32 multiply.

‘-mxl-float-convert’
     Use hardware floating-point conversion instructions.

‘-mxl-float-sqrt’
     Use hardware floating-point square root instruction.

‘-mbig-endian’
     Generate code for a big-endian target.

‘-mlittle-endian’
     Generate code for a little-endian target.

‘-mxl-reorder’
     Use reorder instructions (swap and byte reversed load/store).

‘-mxl-mode-APP-MODEL’
     Select application model APP-MODEL.  Valid models are
     ‘executable’
          normal executable (default), uses startup code ‘crt0.o’.

     ‘xmdstub’
          for use with Xilinx Microprocessor Debugger (XMD) based
          software intrusive debug agent called xmdstub.  This uses
          startup file ‘crt1.o’ and sets the start address of the
          program to 0x800.

     ‘bootstrap’
          for applications that are loaded using a bootloader.  This
          model uses startup file ‘crt2.o’ which does not contain a
          processor reset vector handler.  This is suitable for
          transferring control on a processor reset to the bootloader
          rather than the application.

     ‘novectors’
          for applications that do not require any of the MicroBlaze
          vectors.  This option may be useful for applications running
          within a monitoring application.  This model uses ‘crt3.o’ as
          a startup file.

     Option ‘-xl-mode-APP-MODEL’ is a deprecated alias for
     ‘-mxl-mode-APP-MODEL’.

‘-mpic-data-is-text-relative’
     Assume that the displacement between the text and data segments is
     fixed at static link time.  This allows data to be referenced by
     offset from start of text address instead of GOT since PC-relative
     addressing is not supported.


File: gcc.info,  Node: MIPS Options,  Next: MMIX Options,  Prev: MicroBlaze Options,  Up: Submodel Options

3.19.30 MIPS Options
--------------------

‘-EB’
     Generate big-endian code.

‘-EL’
     Generate little-endian code.  This is the default for ‘mips*el-*-*’
     configurations.

‘-march=ARCH’
     Generate code that runs on ARCH, which can be the name of a generic
     MIPS ISA, or the name of a particular processor.  The ISA names
     are: ‘mips1’, ‘mips2’, ‘mips3’, ‘mips4’, ‘mips32’, ‘mips32r2’,
     ‘mips32r3’, ‘mips32r5’, ‘mips32r6’, ‘mips64’, ‘mips64r2’,
     ‘mips64r3’, ‘mips64r5’ and ‘mips64r6’.  The processor names are:
     ‘4kc’, ‘4km’, ‘4kp’, ‘4ksc’, ‘4kec’, ‘4kem’, ‘4kep’, ‘4ksd’, ‘5kc’,
     ‘5kf’, ‘20kc’, ‘24kc’, ‘24kf2_1’, ‘24kf1_1’, ‘24kec’, ‘24kef2_1’,
     ‘24kef1_1’, ‘34kc’, ‘34kf2_1’, ‘34kf1_1’, ‘34kn’, ‘74kc’,
     ‘74kf2_1’, ‘74kf1_1’, ‘74kf3_2’, ‘1004kc’, ‘1004kf2_1’,
     ‘1004kf1_1’, ‘i6400’, ‘i6500’, ‘interaptiv’, ‘loongson2e’,
     ‘loongson2f’, ‘loongson3a’, ‘gs464’, ‘gs464e’, ‘gs264e’, ‘m4k’,
     ‘m14k’, ‘m14kc’, ‘m14ke’, ‘m14kec’, ‘m5100’, ‘m5101’, ‘octeon’,
     ‘octeon+’, ‘octeon2’, ‘octeon3’, ‘orion’, ‘p5600’, ‘p6600’,
     ‘r2000’, ‘r3000’, ‘r3900’, ‘r4000’, ‘r4400’, ‘r4600’, ‘r4650’,
     ‘r4700’, ‘r5900’, ‘r6000’, ‘r8000’, ‘rm7000’, ‘rm9000’, ‘r10000’,
     ‘r12000’, ‘r14000’, ‘r16000’, ‘sb1’, ‘sr71000’, ‘vr4100’, ‘vr4111’,
     ‘vr4120’, ‘vr4130’, ‘vr4300’, ‘vr5000’, ‘vr5400’, ‘vr5500’, ‘xlr’
     and ‘xlp’.  The special value ‘from-abi’ selects the most
     compatible architecture for the selected ABI (that is, ‘mips1’ for
     32-bit ABIs and ‘mips3’ for 64-bit ABIs).

     The native Linux/GNU toolchain also supports the value ‘native’,
     which selects the best architecture option for the host processor.
     ‘-march=native’ has no effect if GCC does not recognize the
     processor.

     In processor names, a final ‘000’ can be abbreviated as ‘k’ (for
     example, ‘-march=r2k’).  Prefixes are optional, and ‘vr’ may be
     written ‘r’.

     Names of the form ‘Nf2_1’ refer to processors with FPUs clocked at
     half the rate of the core, names of the form ‘Nf1_1’ refer to
     processors with FPUs clocked at the same rate as the core, and
     names of the form ‘Nf3_2’ refer to processors with FPUs clocked a
     ratio of 3:2 with respect to the core.  For compatibility reasons,
     ‘Nf’ is accepted as a synonym for ‘Nf2_1’ while ‘Nx’ and ‘Bfx’ are
     accepted as synonyms for ‘Nf1_1’.

     GCC defines two macros based on the value of this option.  The
     first is ‘_MIPS_ARCH’, which gives the name of target architecture,
     as a string.  The second has the form ‘_MIPS_ARCH_FOO’, where FOO
     is the capitalized value of ‘_MIPS_ARCH’.  For example,
     ‘-march=r2000’ sets ‘_MIPS_ARCH’ to ‘"r2000"’ and defines the macro
     ‘_MIPS_ARCH_R2000’.

     Note that the ‘_MIPS_ARCH’ macro uses the processor names given
     above.  In other words, it has the full prefix and does not
     abbreviate ‘000’ as ‘k’.  In the case of ‘from-abi’, the macro
     names the resolved architecture (either ‘"mips1"’ or ‘"mips3"’).
     It names the default architecture when no ‘-march’ option is given.

‘-mtune=ARCH’
     Optimize for ARCH.  Among other things, this option controls the
     way instructions are scheduled, and the perceived cost of
     arithmetic operations.  The list of ARCH values is the same as for
     ‘-march’.

     When this option is not used, GCC optimizes for the processor
     specified by ‘-march’.  By using ‘-march’ and ‘-mtune’ together, it
     is possible to generate code that runs on a family of processors,
     but optimize the code for one particular member of that family.

     ‘-mtune’ defines the macros ‘_MIPS_TUNE’ and ‘_MIPS_TUNE_FOO’,
     which work in the same way as the ‘-march’ ones described above.

‘-mips1’
     Equivalent to ‘-march=mips1’.

‘-mips2’
     Equivalent to ‘-march=mips2’.

‘-mips3’
     Equivalent to ‘-march=mips3’.

‘-mips4’
     Equivalent to ‘-march=mips4’.

‘-mips32’
     Equivalent to ‘-march=mips32’.

‘-mips32r3’
     Equivalent to ‘-march=mips32r3’.

‘-mips32r5’
     Equivalent to ‘-march=mips32r5’.

‘-mips32r6’
     Equivalent to ‘-march=mips32r6’.

‘-mips64’
     Equivalent to ‘-march=mips64’.

‘-mips64r2’
     Equivalent to ‘-march=mips64r2’.

‘-mips64r3’
     Equivalent to ‘-march=mips64r3’.

‘-mips64r5’
     Equivalent to ‘-march=mips64r5’.

‘-mips64r6’
     Equivalent to ‘-march=mips64r6’.

‘-mips16’
‘-mno-mips16’
     Generate (do not generate) MIPS16 code.  If GCC is targeting a
     MIPS32 or MIPS64 architecture, it makes use of the MIPS16e ASE.

     MIPS16 code generation can also be controlled on a per-function
     basis by means of ‘mips16’ and ‘nomips16’ attributes.  *Note
     Function Attributes::, for more information.

‘-mflip-mips16’
     Generate MIPS16 code on alternating functions.  This option is
     provided for regression testing of mixed MIPS16/non-MIPS16 code
     generation, and is not intended for ordinary use in compiling user
     code.

‘-minterlink-compressed’
‘-mno-interlink-compressed’
     Require (do not require) that code using the standard
     (uncompressed) MIPS ISA be link-compatible with MIPS16 and
     microMIPS code, and vice versa.

     For example, code using the standard ISA encoding cannot jump
     directly to MIPS16 or microMIPS code; it must either use a call or
     an indirect jump.  ‘-minterlink-compressed’ therefore disables
     direct jumps unless GCC knows that the target of the jump is not
     compressed.

‘-minterlink-mips16’
‘-mno-interlink-mips16’
     Aliases of ‘-minterlink-compressed’ and
     ‘-mno-interlink-compressed’.  These options predate the microMIPS
     ASE and are retained for backwards compatibility.

‘-mabi=32’
‘-mabi=o64’
‘-mabi=n32’
‘-mabi=64’
‘-mabi=eabi’
     Generate code for the given ABI.

     Note that the EABI has a 32-bit and a 64-bit variant.  GCC normally
     generates 64-bit code when you select a 64-bit architecture, but
     you can use ‘-mgp32’ to get 32-bit code instead.

     For information about the O64 ABI, see
     <https://gcc.gnu.org/projects/mipso64-abi.html>.

     GCC supports a variant of the o32 ABI in which floating-point
     registers are 64 rather than 32 bits wide.  You can select this
     combination with ‘-mabi=32’ ‘-mfp64’.  This ABI relies on the
     ‘mthc1’ and ‘mfhc1’ instructions and is therefore only supported
     for MIPS32R2, MIPS32R3 and MIPS32R5 processors.

     The register assignments for arguments and return values remain the
     same, but each scalar value is passed in a single 64-bit register
     rather than a pair of 32-bit registers.  For example, scalar
     floating-point values are returned in ‘$f0’ only, not a ‘$f0’/‘$f1’
     pair.  The set of call-saved registers also remains the same in
     that the even-numbered double-precision registers are saved.

     Two additional variants of the o32 ABI are supported to enable a
     transition from 32-bit to 64-bit registers.  These are FPXX
     (‘-mfpxx’) and FP64A (‘-mfp64’ ‘-mno-odd-spreg’).  The FPXX
     extension mandates that all code must execute correctly when run
     using 32-bit or 64-bit registers.  The code can be interlinked with
     either FP32 or FP64, but not both.  The FP64A extension is similar
     to the FP64 extension but forbids the use of odd-numbered
     single-precision registers.  This can be used in conjunction with
     the ‘FRE’ mode of FPUs in MIPS32R5 processors and allows both FP32
     and FP64A code to interlink and run in the same process without
     changing FPU modes.

‘-mabicalls’
‘-mno-abicalls’
     Generate (do not generate) code that is suitable for SVR4-style
     dynamic objects.  ‘-mabicalls’ is the default for SVR4-based
     systems.

‘-mshared’
‘-mno-shared’
     Generate (do not generate) code that is fully position-independent,
     and that can therefore be linked into shared libraries.  This
     option only affects ‘-mabicalls’.

     All ‘-mabicalls’ code has traditionally been position-independent,
     regardless of options like ‘-fPIC’ and ‘-fpic’.  However, as an
     extension, the GNU toolchain allows executables to use absolute
     accesses for locally-binding symbols.  It can also use shorter GP
     initialization sequences and generate direct calls to
     locally-defined functions.  This mode is selected by ‘-mno-shared’.

     ‘-mno-shared’ depends on binutils 2.16 or higher and generates
     objects that can only be linked by the GNU linker.  However, the
     option does not affect the ABI of the final executable; it only
     affects the ABI of relocatable objects.  Using ‘-mno-shared’
     generally makes executables both smaller and quicker.

     ‘-mshared’ is the default.

‘-mplt’
‘-mno-plt’
     Assume (do not assume) that the static and dynamic linkers support
     PLTs and copy relocations.  This option only affects ‘-mno-shared
     -mabicalls’.  For the n64 ABI, this option has no effect without
     ‘-msym32’.

     You can make ‘-mplt’ the default by configuring GCC with
     ‘--with-mips-plt’.  The default is ‘-mno-plt’ otherwise.

‘-mxgot’
‘-mno-xgot’
     Lift (do not lift) the usual restrictions on the size of the global
     offset table.

     GCC normally uses a single instruction to load values from the GOT.
     While this is relatively efficient, it only works if the GOT is
     smaller than about 64k.  Anything larger causes the linker to
     report an error such as:

          relocation truncated to fit: R_MIPS_GOT16 foobar

     If this happens, you should recompile your code with ‘-mxgot’.
     This works with very large GOTs, although the code is also less
     efficient, since it takes three instructions to fetch the value of
     a global symbol.

     Note that some linkers can create multiple GOTs.  If you have such
     a linker, you should only need to use ‘-mxgot’ when a single object
     file accesses more than 64k's worth of GOT entries.  Very few do.

     These options have no effect unless GCC is generating position
     independent code.

‘-mgp32’
     Assume that general-purpose registers are 32 bits wide.

‘-mgp64’
     Assume that general-purpose registers are 64 bits wide.

‘-mfp32’
     Assume that floating-point registers are 32 bits wide.

‘-mfp64’
     Assume that floating-point registers are 64 bits wide.

‘-mfpxx’
     Do not assume the width of floating-point registers.

‘-mhard-float’
     Use floating-point coprocessor instructions.

‘-msoft-float’
     Do not use floating-point coprocessor instructions.  Implement
     floating-point calculations using library calls instead.

‘-mno-float’
     Equivalent to ‘-msoft-float’, but additionally asserts that the
     program being compiled does not perform any floating-point
     operations.  This option is presently supported only by some
     bare-metal MIPS configurations, where it may select a special set
     of libraries that lack all floating-point support (including, for
     example, the floating-point ‘printf’ formats).  If code compiled
     with ‘-mno-float’ accidentally contains floating-point operations,
     it is likely to suffer a link-time or run-time failure.

‘-msingle-float’
     Assume that the floating-point coprocessor only supports
     single-precision operations.

‘-mdouble-float’
     Assume that the floating-point coprocessor supports
     double-precision operations.  This is the default.

‘-modd-spreg’
‘-mno-odd-spreg’
     Enable the use of odd-numbered single-precision floating-point
     registers for the o32 ABI. This is the default for processors that
     are known to support these registers.  When using the o32 FPXX ABI,
     ‘-mno-odd-spreg’ is set by default.

‘-mabs=2008’
‘-mabs=legacy’
     These options control the treatment of the special not-a-number
     (NaN) IEEE 754 floating-point data with the ‘abs.fmt’ and ‘neg.fmt’
     machine instructions.

     By default or when ‘-mabs=legacy’ is used the legacy treatment is
     selected.  In this case these instructions are considered
     arithmetic and avoided where correct operation is required and the
     input operand might be a NaN. A longer sequence of instructions
     that manipulate the sign bit of floating-point datum manually is
     used instead unless the ‘-ffinite-math-only’ option has also been
     specified.

     The ‘-mabs=2008’ option selects the IEEE 754-2008 treatment.  In
     this case these instructions are considered non-arithmetic and
     therefore operating correctly in all cases, including in particular
     where the input operand is a NaN. These instructions are therefore
     always used for the respective operations.

‘-mnan=2008’
‘-mnan=legacy’
     These options control the encoding of the special not-a-number
     (NaN) IEEE 754 floating-point data.

     The ‘-mnan=legacy’ option selects the legacy encoding.  In this
     case quiet NaNs (qNaNs) are denoted by the first bit of their
     trailing significand field being 0, whereas signaling NaNs (sNaNs)
     are denoted by the first bit of their trailing significand field
     being 1.

     The ‘-mnan=2008’ option selects the IEEE 754-2008 encoding.  In
     this case qNaNs are denoted by the first bit of their trailing
     significand field being 1, whereas sNaNs are denoted by the first
     bit of their trailing significand field being 0.

     The default is ‘-mnan=legacy’ unless GCC has been configured with
     ‘--with-nan=2008’.

‘-mllsc’
‘-mno-llsc’
     Use (do not use) ‘ll’, ‘sc’, and ‘sync’ instructions to implement
     atomic memory built-in functions.  When neither option is
     specified, GCC uses the instructions if the target architecture
     supports them.

     ‘-mllsc’ is useful if the runtime environment can emulate the
     instructions and ‘-mno-llsc’ can be useful when compiling for
     nonstandard ISAs.  You can make either option the default by
     configuring GCC with ‘--with-llsc’ and ‘--without-llsc’
     respectively.  ‘--with-llsc’ is the default for some
     configurations; see the installation documentation for details.

‘-mdsp’
‘-mno-dsp’
     Use (do not use) revision 1 of the MIPS DSP ASE.  *Note MIPS DSP
     Built-in Functions::.  This option defines the preprocessor macro
     ‘__mips_dsp’.  It also defines ‘__mips_dsp_rev’ to 1.

‘-mdspr2’
‘-mno-dspr2’
     Use (do not use) revision 2 of the MIPS DSP ASE.  *Note MIPS DSP
     Built-in Functions::.  This option defines the preprocessor macros
     ‘__mips_dsp’ and ‘__mips_dspr2’.  It also defines ‘__mips_dsp_rev’
     to 2.

‘-msmartmips’
‘-mno-smartmips’
     Use (do not use) the MIPS SmartMIPS ASE.

‘-mpaired-single’
‘-mno-paired-single’
     Use (do not use) paired-single floating-point instructions.  *Note
     MIPS Paired-Single Support::.  This option requires hardware
     floating-point support to be enabled.

‘-mdmx’
‘-mno-mdmx’
     Use (do not use) MIPS Digital Media Extension instructions.  This
     option can only be used when generating 64-bit code and requires
     hardware floating-point support to be enabled.

‘-mips3d’
‘-mno-mips3d’
     Use (do not use) the MIPS-3D ASE.  *Note MIPS-3D Built-in
     Functions::.  The option ‘-mips3d’ implies ‘-mpaired-single’.

‘-mmicromips’
‘-mno-micromips’
     Generate (do not generate) microMIPS code.

     MicroMIPS code generation can also be controlled on a per-function
     basis by means of ‘micromips’ and ‘nomicromips’ attributes.  *Note
     Function Attributes::, for more information.

‘-mmt’
‘-mno-mt’
     Use (do not use) MT Multithreading instructions.

‘-mmcu’
‘-mno-mcu’
     Use (do not use) the MIPS MCU ASE instructions.

‘-meva’
‘-mno-eva’
     Use (do not use) the MIPS Enhanced Virtual Addressing instructions.

‘-mvirt’
‘-mno-virt’
     Use (do not use) the MIPS Virtualization (VZ) instructions.

‘-mxpa’
‘-mno-xpa’
     Use (do not use) the MIPS eXtended Physical Address (XPA)
     instructions.

‘-mcrc’
‘-mno-crc’
     Use (do not use) the MIPS Cyclic Redundancy Check (CRC)
     instructions.

‘-mginv’
‘-mno-ginv’
     Use (do not use) the MIPS Global INValidate (GINV) instructions.

‘-mloongson-mmi’
‘-mno-loongson-mmi’
     Use (do not use) the MIPS Loongson MultiMedia extensions
     Instructions (MMI).

‘-mloongson-ext’
‘-mno-loongson-ext’
     Use (do not use) the MIPS Loongson EXTensions (EXT) instructions.

‘-mloongson-ext2’
‘-mno-loongson-ext2’
     Use (do not use) the MIPS Loongson EXTensions r2 (EXT2)
     instructions.

‘-mlong64’
     Force ‘long’ types to be 64 bits wide.  See ‘-mlong32’ for an
     explanation of the default and the way that the pointer size is
     determined.

‘-mlong32’
     Force ‘long’, ‘int’, and pointer types to be 32 bits wide.

     The default size of ‘int’s, ‘long’s and pointers depends on the
     ABI.  All the supported ABIs use 32-bit ‘int’s.  The n64 ABI uses
     64-bit ‘long’s, as does the 64-bit EABI; the others use 32-bit
     ‘long’s.  Pointers are the same size as ‘long’s, or the same size
     as integer registers, whichever is smaller.

‘-msym32’
‘-mno-sym32’
     Assume (do not assume) that all symbols have 32-bit values,
     regardless of the selected ABI.  This option is useful in
     combination with ‘-mabi=64’ and ‘-mno-abicalls’ because it allows
     GCC to generate shorter and faster references to symbolic
     addresses.

‘-G NUM’
     Put definitions of externally-visible data in a small data section
     if that data is no bigger than NUM bytes.  GCC can then generate
     more efficient accesses to the data; see ‘-mgpopt’ for details.

     The default ‘-G’ option depends on the configuration.

‘-mlocal-sdata’
‘-mno-local-sdata’
     Extend (do not extend) the ‘-G’ behavior to local data too, such as
     to static variables in C.  ‘-mlocal-sdata’ is the default for all
     configurations.

     If the linker complains that an application is using too much small
     data, you might want to try rebuilding the less
     performance-critical parts with ‘-mno-local-sdata’.  You might also
     want to build large libraries with ‘-mno-local-sdata’, so that the
     libraries leave more room for the main program.

‘-mextern-sdata’
‘-mno-extern-sdata’
     Assume (do not assume) that externally-defined data is in a small
     data section if the size of that data is within the ‘-G’ limit.
     ‘-mextern-sdata’ is the default for all configurations.

     If you compile a module MOD with ‘-mextern-sdata’ ‘-G NUM’
     ‘-mgpopt’, and MOD references a variable VAR that is no bigger than
     NUM bytes, you must make sure that VAR is placed in a small data
     section.  If VAR is defined by another module, you must either
     compile that module with a high-enough ‘-G’ setting or attach a
     ‘section’ attribute to VAR's definition.  If VAR is common, you
     must link the application with a high-enough ‘-G’ setting.

     The easiest way of satisfying these restrictions is to compile and
     link every module with the same ‘-G’ option.  However, you may wish
     to build a library that supports several different small data
     limits.  You can do this by compiling the library with the highest
     supported ‘-G’ setting and additionally using ‘-mno-extern-sdata’
     to stop the library from making assumptions about
     externally-defined data.

‘-mgpopt’
‘-mno-gpopt’
     Use (do not use) GP-relative accesses for symbols that are known to
     be in a small data section; see ‘-G’, ‘-mlocal-sdata’ and
     ‘-mextern-sdata’.  ‘-mgpopt’ is the default for all configurations.

     ‘-mno-gpopt’ is useful for cases where the ‘$gp’ register might not
     hold the value of ‘_gp’.  For example, if the code is part of a
     library that might be used in a boot monitor, programs that call
     boot monitor routines pass an unknown value in ‘$gp’.  (In such
     situations, the boot monitor itself is usually compiled with
     ‘-G0’.)

     ‘-mno-gpopt’ implies ‘-mno-local-sdata’ and ‘-mno-extern-sdata’.

‘-membedded-data’
‘-mno-embedded-data’
     Allocate variables to the read-only data section first if possible,
     then next in the small data section if possible, otherwise in data.
     This gives slightly slower code than the default, but reduces the
     amount of RAM required when executing, and thus may be preferred
     for some embedded systems.

‘-muninit-const-in-rodata’
‘-mno-uninit-const-in-rodata’
     Put uninitialized ‘const’ variables in the read-only data section.
     This option is only meaningful in conjunction with
     ‘-membedded-data’.

‘-mcode-readable=SETTING’
     Specify whether GCC may generate code that reads from executable
     sections.  There are three possible settings:

     ‘-mcode-readable=yes’
          Instructions may freely access executable sections.  This is
          the default setting.

     ‘-mcode-readable=pcrel’
          MIPS16 PC-relative load instructions can access executable
          sections, but other instructions must not do so.  This option
          is useful on 4KSc and 4KSd processors when the code TLBs have
          the Read Inhibit bit set.  It is also useful on processors
          that can be configured to have a dual instruction/data SRAM
          interface and that, like the M4K, automatically redirect
          PC-relative loads to the instruction RAM.

     ‘-mcode-readable=no’
          Instructions must not access executable sections.  This option
          can be useful on targets that are configured to have a dual
          instruction/data SRAM interface but that (unlike the M4K) do
          not automatically redirect PC-relative loads to the
          instruction RAM.

‘-msplit-addresses’
‘-mno-split-addresses’
     Enable (disable) use of the ‘%hi()’ and ‘%lo()’ assembler
     relocation operators.  This option has been superseded by
     ‘-mexplicit-relocs’ but is retained for backwards compatibility.

‘-mexplicit-relocs’
‘-mno-explicit-relocs’
     Use (do not use) assembler relocation operators when dealing with
     symbolic addresses.  The alternative, selected by
     ‘-mno-explicit-relocs’, is to use assembler macros instead.

     ‘-mexplicit-relocs’ is the default if GCC was configured to use an
     assembler that supports relocation operators.

‘-mcheck-zero-division’
‘-mno-check-zero-division’
     Trap (do not trap) on integer division by zero.

     The default is ‘-mcheck-zero-division’.

‘-mdivide-traps’
‘-mdivide-breaks’
     MIPS systems check for division by zero by generating either a
     conditional trap or a break instruction.  Using traps results in
     smaller code, but is only supported on MIPS II and later.  Also,
     some versions of the Linux kernel have a bug that prevents trap
     from generating the proper signal (‘SIGFPE’).  Use ‘-mdivide-traps’
     to allow conditional traps on architectures that support them and
     ‘-mdivide-breaks’ to force the use of breaks.

     The default is usually ‘-mdivide-traps’, but this can be overridden
     at configure time using ‘--with-divide=breaks’.  Divide-by-zero
     checks can be completely disabled using ‘-mno-check-zero-division’.

‘-mload-store-pairs’
‘-mno-load-store-pairs’
     Enable (disable) an optimization that pairs consecutive load or
     store instructions to enable load/store bonding.  This option is
     enabled by default but only takes effect when the selected
     architecture is known to support bonding.

‘-munaligned-access’
‘-mno-unaligned-access’
     Enable (disable) direct unaligned access for MIPS Release 6.
     MIPSr6 requires load/store unaligned-access support, by hardware or
     trap&emulate.  So ‘-mno-unaligned-access’ may be needed by kernel.

‘-mmemcpy’
‘-mno-memcpy’
     Force (do not force) the use of ‘memcpy’ for non-trivial block
     moves.  The default is ‘-mno-memcpy’, which allows GCC to inline
     most constant-sized copies.

‘-mlong-calls’
‘-mno-long-calls’
     Disable (do not disable) use of the ‘jal’ instruction.  Calling
     functions using ‘jal’ is more efficient but requires the caller and
     callee to be in the same 256 megabyte segment.

     This option has no effect on abicalls code.  The default is
     ‘-mno-long-calls’.

‘-mmad’
‘-mno-mad’
     Enable (disable) use of the ‘mad’, ‘madu’ and ‘mul’ instructions,
     as provided by the R4650 ISA.

‘-mimadd’
‘-mno-imadd’
     Enable (disable) use of the ‘madd’ and ‘msub’ integer instructions.
     The default is ‘-mimadd’ on architectures that support ‘madd’ and
     ‘msub’ except for the 74k architecture where it was found to
     generate slower code.

‘-mfused-madd’
‘-mno-fused-madd’
     Enable (disable) use of the floating-point multiply-accumulate
     instructions, when they are available.  The default is
     ‘-mfused-madd’.

     On the R8000 CPU when multiply-accumulate instructions are used,
     the intermediate product is calculated to infinite precision and is
     not subject to the FCSR Flush to Zero bit.  This may be undesirable
     in some circumstances.  On other processors the result is
     numerically identical to the equivalent computation using separate
     multiply, add, subtract and negate instructions.

‘-nocpp’
     Tell the MIPS assembler to not run its preprocessor over user
     assembler files (with a ‘.s’ suffix) when assembling them.

‘-mfix-24k’
‘-mno-fix-24k’
     Work around the 24K E48 (lost data on stores during refill) errata.
     The workarounds are implemented by the assembler rather than by
     GCC.

‘-mfix-r4000’
‘-mno-fix-r4000’
     Work around certain R4000 CPU errata:
        − A double-word or a variable shift may give an incorrect result
          if executed immediately after starting an integer division.
        − A double-word or a variable shift may give an incorrect result
          if executed while an integer multiplication is in progress.
        − An integer division may give an incorrect result if started in
          a delay slot of a taken branch or a jump.

‘-mfix-r4400’
‘-mno-fix-r4400’
     Work around certain R4400 CPU errata:
        − A double-word or a variable shift may give an incorrect result
          if executed immediately after starting an integer division.

‘-mfix-r10000’
‘-mno-fix-r10000’
     Work around certain R10000 errata:
        − ‘ll’/‘sc’ sequences may not behave atomically on revisions
          prior to 3.0.  They may deadlock on revisions 2.6 and earlier.

     This option can only be used if the target architecture supports
     branch-likely instructions.  ‘-mfix-r10000’ is the default when
     ‘-march=r10000’ is used; ‘-mno-fix-r10000’ is the default
     otherwise.

‘-mfix-r5900’
‘-mno-fix-r5900’
     Do not attempt to schedule the preceding instruction into the delay
     slot of a branch instruction placed at the end of a short loop of
     six instructions or fewer and always schedule a ‘nop’ instruction
     there instead.  The short loop bug under certain conditions causes
     loops to execute only once or twice, due to a hardware bug in the
     R5900 chip.  The workaround is implemented by the assembler rather
     than by GCC.

‘-mfix-rm7000’
‘-mno-fix-rm7000’
     Work around the RM7000 ‘dmult’/‘dmultu’ errata.  The workarounds
     are implemented by the assembler rather than by GCC.

‘-mfix-vr4120’
‘-mno-fix-vr4120’
     Work around certain VR4120 errata:
        − ‘dmultu’ does not always produce the correct result.
        − ‘div’ and ‘ddiv’ do not always produce the correct result if
          one of the operands is negative.
     The workarounds for the division errata rely on special functions
     in ‘libgcc.a’.  At present, these functions are only provided by
     the ‘mips64vr*-elf’ configurations.

     Other VR4120 errata require a NOP to be inserted between certain
     pairs of instructions.  These errata are handled by the assembler,
     not by GCC itself.

‘-mfix-vr4130’
     Work around the VR4130 ‘mflo’/‘mfhi’ errata.  The workarounds are
     implemented by the assembler rather than by GCC, although GCC
     avoids using ‘mflo’ and ‘mfhi’ if the VR4130 ‘macc’, ‘macchi’,
     ‘dmacc’ and ‘dmacchi’ instructions are available instead.

‘-mfix-sb1’
‘-mno-fix-sb1’
     Work around certain SB-1 CPU core errata.  (This flag currently
     works around the SB-1 revision 2 "F1" and "F2" floating-point
     errata.)

‘-mr10k-cache-barrier=SETTING’
     Specify whether GCC should insert cache barriers to avoid the side
     effects of speculation on R10K processors.

     In common with many processors, the R10K tries to predict the
     outcome of a conditional branch and speculatively executes
     instructions from the "taken" branch.  It later aborts these
     instructions if the predicted outcome is wrong.  However, on the
     R10K, even aborted instructions can have side effects.

     This problem only affects kernel stores and, depending on the
     system, kernel loads.  As an example, a speculatively-executed
     store may load the target memory into cache and mark the cache line
     as dirty, even if the store itself is later aborted.  If a DMA
     operation writes to the same area of memory before the "dirty" line
     is flushed, the cached data overwrites the DMA-ed data.  See the
     R10K processor manual for a full description, including other
     potential problems.

     One workaround is to insert cache barrier instructions before every
     memory access that might be speculatively executed and that might
     have side effects even if aborted.  ‘-mr10k-cache-barrier=SETTING’
     controls GCC's implementation of this workaround.  It assumes that
     aborted accesses to any byte in the following regions does not have
     side effects:

       1. the memory occupied by the current function's stack frame;

       2. the memory occupied by an incoming stack argument;

       3. the memory occupied by an object with a link-time-constant
          address.

     It is the kernel's responsibility to ensure that speculative
     accesses to these regions are indeed safe.

     If the input program contains a function declaration such as:

          void foo (void);

     then the implementation of ‘foo’ must allow ‘j foo’ and ‘jal foo’
     to be executed speculatively.  GCC honors this restriction for
     functions it compiles itself.  It expects non-GCC functions (such
     as hand-written assembly code) to do the same.

     The option has three forms:

     ‘-mr10k-cache-barrier=load-store’
          Insert a cache barrier before a load or store that might be
          speculatively executed and that might have side effects even
          if aborted.

     ‘-mr10k-cache-barrier=store’
          Insert a cache barrier before a store that might be
          speculatively executed and that might have side effects even
          if aborted.

     ‘-mr10k-cache-barrier=none’
          Disable the insertion of cache barriers.  This is the default
          setting.

‘-mflush-func=FUNC’
‘-mno-flush-func’
     Specifies the function to call to flush the I and D caches, or to
     not call any such function.  If called, the function must take the
     same arguments as the common ‘_flush_func’, that is, the address of
     the memory range for which the cache is being flushed, the size of
     the memory range, and the number 3 (to flush both caches).  The
     default depends on the target GCC was configured for, but commonly
     is either ‘_flush_func’ or ‘__cpu_flush’.

‘mbranch-cost=NUM’
     Set the cost of branches to roughly NUM "simple" instructions.
     This cost is only a heuristic and is not guaranteed to produce
     consistent results across releases.  A zero cost redundantly
     selects the default, which is based on the ‘-mtune’ setting.

‘-mbranch-likely’
‘-mno-branch-likely’
     Enable or disable use of Branch Likely instructions, regardless of
     the default for the selected architecture.  By default, Branch
     Likely instructions may be generated if they are supported by the
     selected architecture.  An exception is for the MIPS32 and MIPS64
     architectures and processors that implement those architectures;
     for those, Branch Likely instructions are not be generated by
     default because the MIPS32 and MIPS64 architectures specifically
     deprecate their use.

‘-mcompact-branches=never’
‘-mcompact-branches=optimal’
‘-mcompact-branches=always’
     These options control which form of branches will be generated.
     The default is ‘-mcompact-branches=optimal’.

     The ‘-mcompact-branches=never’ option ensures that compact branch
     instructions will never be generated.

     The ‘-mcompact-branches=always’ option ensures that a compact
     branch instruction will be generated if available.  If a compact
     branch instruction is not available, a delay slot form of the
     branch will be used instead.

     This option is supported from MIPS Release 6 onwards.

     The ‘-mcompact-branches=optimal’ option will cause a delay slot
     branch to be used if one is available in the current ISA and the
     delay slot is successfully filled.  If the delay slot is not
     filled, a compact branch will be chosen if one is available.

‘-mfp-exceptions’
‘-mno-fp-exceptions’
     Specifies whether FP exceptions are enabled.  This affects how FP
     instructions are scheduled for some processors.  The default is
     that FP exceptions are enabled.

     For instance, on the SB-1, if FP exceptions are disabled, and we
     are emitting 64-bit code, then we can use both FP pipes.
     Otherwise, we can only use one FP pipe.

‘-mvr4130-align’
‘-mno-vr4130-align’
     The VR4130 pipeline is two-way superscalar, but can only issue two
     instructions together if the first one is 8-byte aligned.  When
     this option is enabled, GCC aligns pairs of instructions that it
     thinks should execute in parallel.

     This option only has an effect when optimizing for the VR4130.  It
     normally makes code faster, but at the expense of making it bigger.
     It is enabled by default at optimization level ‘-O3’.

‘-msynci’
‘-mno-synci’
     Enable (disable) generation of ‘synci’ instructions on
     architectures that support it.  The ‘synci’ instructions (if
     enabled) are generated when ‘__builtin___clear_cache’ is compiled.

     This option defaults to ‘-mno-synci’, but the default can be
     overridden by configuring GCC with ‘--with-synci’.

     When compiling code for single processor systems, it is generally
     safe to use ‘synci’.  However, on many multi-core (SMP) systems, it
     does not invalidate the instruction caches on all cores and may
     lead to undefined behavior.

‘-mrelax-pic-calls’
‘-mno-relax-pic-calls’
     Try to turn PIC calls that are normally dispatched via register
     ‘$25’ into direct calls.  This is only possible if the linker can
     resolve the destination at link time and if the destination is
     within range for a direct call.

     ‘-mrelax-pic-calls’ is the default if GCC was configured to use an
     assembler and a linker that support the ‘.reloc’ assembly directive
     and ‘-mexplicit-relocs’ is in effect.  With ‘-mno-explicit-relocs’,
     this optimization can be performed by the assembler and the linker
     alone without help from the compiler.

‘-mmcount-ra-address’
‘-mno-mcount-ra-address’
     Emit (do not emit) code that allows ‘_mcount’ to modify the calling
     function's return address.  When enabled, this option extends the
     usual ‘_mcount’ interface with a new RA-ADDRESS parameter, which
     has type ‘intptr_t *’ and is passed in register ‘$12’.  ‘_mcount’
     can then modify the return address by doing both of the following:
        • Returning the new address in register ‘$31’.
        • Storing the new address in ‘*RA-ADDRESS’, if RA-ADDRESS is
          nonnull.

     The default is ‘-mno-mcount-ra-address’.

‘-mframe-header-opt’
‘-mno-frame-header-opt’
     Enable (disable) frame header optimization in the o32 ABI. When
     using the o32 ABI, calling functions will allocate 16 bytes on the
     stack for the called function to write out register arguments.
     When enabled, this optimization will suppress the allocation of the
     frame header if it can be determined that it is unused.

     This optimization is off by default at all optimization levels.

‘-mlxc1-sxc1’
‘-mno-lxc1-sxc1’
     When applicable, enable (disable) the generation of ‘lwxc1’,
     ‘swxc1’, ‘ldxc1’, ‘sdxc1’ instructions.  Enabled by default.

‘-mmadd4’
‘-mno-madd4’
     When applicable, enable (disable) the generation of 4-operand
     ‘madd.s’, ‘madd.d’ and related instructions.  Enabled by default.


File: gcc.info,  Node: MMIX Options,  Next: MN10300 Options,  Prev: MIPS Options,  Up: Submodel Options

3.19.31 MMIX Options
--------------------

These options are defined for the MMIX:

‘-mlibfuncs’
‘-mno-libfuncs’
     Specify that intrinsic library functions are being compiled,
     passing all values in registers, no matter the size.

‘-mepsilon’
‘-mno-epsilon’
     Generate floating-point comparison instructions that compare with
     respect to the ‘rE’ epsilon register.

‘-mabi=mmixware’
‘-mabi=gnu’
     Generate code that passes function parameters and return values
     that (in the called function) are seen as registers ‘$0’ and up, as
     opposed to the GNU ABI which uses global registers ‘$231’ and up.

‘-mzero-extend’
‘-mno-zero-extend’
     When reading data from memory in sizes shorter than 64 bits, use
     (do not use) zero-extending load instructions by default, rather
     than sign-extending ones.

‘-mknuthdiv’
‘-mno-knuthdiv’
     Make the result of a division yielding a remainder have the same
     sign as the divisor.  With the default, ‘-mno-knuthdiv’, the sign
     of the remainder follows the sign of the dividend.  Both methods
     are arithmetically valid, the latter being almost exclusively used.

‘-mtoplevel-symbols’
‘-mno-toplevel-symbols’
     Prepend (do not prepend) a ‘:’ to all global symbols, so the
     assembly code can be used with the ‘PREFIX’ assembly directive.

‘-melf’
     Generate an executable in the ELF format, rather than the default
     ‘mmo’ format used by the ‘mmix’ simulator.

‘-mbranch-predict’
‘-mno-branch-predict’
     Use (do not use) the probable-branch instructions, when static
     branch prediction indicates a probable branch.

‘-mbase-addresses’
‘-mno-base-addresses’
     Generate (do not generate) code that uses _base addresses_.  Using
     a base address automatically generates a request (handled by the
     assembler and the linker) for a constant to be set up in a global
     register.  The register is used for one or more base address
     requests within the range 0 to 255 from the value held in the
     register.  The generally leads to short and fast code, but the
     number of different data items that can be addressed is limited.
     This means that a program that uses lots of static data may require
     ‘-mno-base-addresses’.

‘-msingle-exit’
‘-mno-single-exit’
     Force (do not force) generated code to have a single exit point in
     each function.


File: gcc.info,  Node: MN10300 Options,  Next: Moxie Options,  Prev: MMIX Options,  Up: Submodel Options

3.19.32 MN10300 Options
-----------------------

These ‘-m’ options are defined for Matsushita MN10300 architectures:

‘-mmult-bug’
     Generate code to avoid bugs in the multiply instructions for the
     MN10300 processors.  This is the default.

‘-mno-mult-bug’
     Do not generate code to avoid bugs in the multiply instructions for
     the MN10300 processors.

‘-mam33’
     Generate code using features specific to the AM33 processor.

‘-mno-am33’
     Do not generate code using features specific to the AM33 processor.
     This is the default.

‘-mam33-2’
     Generate code using features specific to the AM33/2.0 processor.

‘-mam34’
     Generate code using features specific to the AM34 processor.

‘-mtune=CPU-TYPE’
     Use the timing characteristics of the indicated CPU type when
     scheduling instructions.  This does not change the targeted
     processor type.  The CPU type must be one of ‘mn10300’, ‘am33’,
     ‘am33-2’ or ‘am34’.

‘-mreturn-pointer-on-d0’
     When generating a function that returns a pointer, return the
     pointer in both ‘a0’ and ‘d0’.  Otherwise, the pointer is returned
     only in ‘a0’, and attempts to call such functions without a
     prototype result in errors.  Note that this option is on by
     default; use ‘-mno-return-pointer-on-d0’ to disable it.

‘-mno-crt0’
     Do not link in the C run-time initialization object file.

‘-mrelax’
     Indicate to the linker that it should perform a relaxation
     optimization pass to shorten branches, calls and absolute memory
     addresses.  This option only has an effect when used on the command
     line for the final link step.

     This option makes symbolic debugging impossible.

‘-mliw’
     Allow the compiler to generate _Long Instruction Word_ instructions
     if the target is the ‘AM33’ or later.  This is the default.  This
     option defines the preprocessor macro ‘__LIW__’.

‘-mno-liw’
     Do not allow the compiler to generate _Long Instruction Word_
     instructions.  This option defines the preprocessor macro
     ‘__NO_LIW__’.

‘-msetlb’
     Allow the compiler to generate the _SETLB_ and _Lcc_ instructions
     if the target is the ‘AM33’ or later.  This is the default.  This
     option defines the preprocessor macro ‘__SETLB__’.

‘-mno-setlb’
     Do not allow the compiler to generate _SETLB_ or _Lcc_
     instructions.  This option defines the preprocessor macro
     ‘__NO_SETLB__’.


File: gcc.info,  Node: Moxie Options,  Next: MSP430 Options,  Prev: MN10300 Options,  Up: Submodel Options

3.19.33 Moxie Options
---------------------

‘-meb’
     Generate big-endian code.  This is the default for ‘moxie-*-*’
     configurations.

‘-mel’
     Generate little-endian code.

‘-mmul.x’
     Generate mul.x and umul.x instructions.  This is the default for
     ‘moxiebox-*-*’ configurations.

‘-mno-crt0’
     Do not link in the C run-time initialization object file.


File: gcc.info,  Node: MSP430 Options,  Next: NDS32 Options,  Prev: Moxie Options,  Up: Submodel Options

3.19.34 MSP430 Options
----------------------

These options are defined for the MSP430:

‘-masm-hex’
     Force assembly output to always use hex constants.  Normally such
     constants are signed decimals, but this option is available for
     testsuite and/or aesthetic purposes.

‘-mmcu=’
     Select the MCU to target.  This is used to create a C preprocessor
     symbol based upon the MCU name, converted to upper case and pre-
     and post-fixed with ‘__’.  This in turn is used by the ‘msp430.h’
     header file to select an MCU-specific supplementary header file.

     The option also sets the ISA to use.  If the MCU name is one that
     is known to only support the 430 ISA then that is selected,
     otherwise the 430X ISA is selected.  A generic MCU name of ‘msp430’
     can also be used to select the 430 ISA. Similarly the generic
     ‘msp430x’ MCU name selects the 430X ISA.

     In addition an MCU-specific linker script is added to the linker
     command line.  The script's name is the name of the MCU with ‘.ld’
     appended.  Thus specifying ‘-mmcu=xxx’ on the ‘gcc’ command line
     defines the C preprocessor symbol ‘__XXX__’ and cause the linker to
     search for a script called ‘xxx.ld’.

     The ISA and hardware multiply supported for the different MCUs is
     hard-coded into GCC. However, an external ‘devices.csv’ file can be
     used to extend device support beyond those that have been
     hard-coded.

     GCC searches for the ‘devices.csv’ file using the following methods
     in the given precedence order, where the first method takes
     precendence over the second which takes precedence over the third.

     Include path specified with ‘-I’ and ‘-L’
          ‘devices.csv’ will be searched for in each of the directories
          specified by include paths and linker library search paths.
     Path specified by the environment variable ‘MSP430_GCC_INCLUDE_DIR’
          Define the value of the global environment variable
          ‘MSP430_GCC_INCLUDE_DIR’ to the full path to the directory
          containing devices.csv, and GCC will search this directory for
          devices.csv.  If devices.csv is found, this directory will
          also be registered as an include path, and linker library
          path.  Header files and linker scripts in this directory can
          therefore be used without manually specifying ‘-I’ and ‘-L’ on
          the command line.
     The ‘msp430-elf{,bare}/include/devices’ directory
          Finally, GCC will examine ‘msp430-elf{,bare}/include/devices’
          from the toolchain root directory.  This directory does not
          exist in a default installation, but if the user has created
          it and copied ‘devices.csv’ there, then the MCU data will be
          read.  As above, this directory will also be registered as an
          include path, and linker library path.

     If none of the above search methods find ‘devices.csv’, then the
     hard-coded MCU data is used.

‘-mwarn-mcu’
‘-mno-warn-mcu’
     This option enables or disables warnings about conflicts between
     the MCU name specified by the ‘-mmcu’ option and the ISA set by the
     ‘-mcpu’ option and/or the hardware multiply support set by the
     ‘-mhwmult’ option.  It also toggles warnings about unrecognized MCU
     names.  This option is on by default.

‘-mcpu=’
     Specifies the ISA to use.  Accepted values are ‘msp430’, ‘msp430x’
     and ‘msp430xv2’.  This option is deprecated.  The ‘-mmcu=’ option
     should be used to select the ISA.

‘-msim’
     Link to the simulator runtime libraries and linker script.
     Overrides any scripts that would be selected by the ‘-mmcu=’
     option.

‘-mlarge’
     Use large-model addressing (20-bit pointers, 20-bit ‘size_t’).

‘-msmall’
     Use small-model addressing (16-bit pointers, 16-bit ‘size_t’).

‘-mrelax’
     This option is passed to the assembler and linker, and allows the
     linker to perform certain optimizations that cannot be done until
     the final link.

‘mhwmult=’
     Describes the type of hardware multiply supported by the target.
     Accepted values are ‘none’ for no hardware multiply, ‘16bit’ for
     the original 16-bit-only multiply supported by early MCUs.  ‘32bit’
     for the 16/32-bit multiply supported by later MCUs and ‘f5series’
     for the 16/32-bit multiply supported by F5-series MCUs.  A value of
     ‘auto’ can also be given.  This tells GCC to deduce the hardware
     multiply support based upon the MCU name provided by the ‘-mmcu’
     option.  If no ‘-mmcu’ option is specified or if the MCU name is
     not recognized then no hardware multiply support is assumed.
     ‘auto’ is the default setting.

     Hardware multiplies are normally performed by calling a library
     routine.  This saves space in the generated code.  When compiling
     at ‘-O3’ or higher however the hardware multiplier is invoked
     inline.  This makes for bigger, but faster code.

     The hardware multiply routines disable interrupts whilst running
     and restore the previous interrupt state when they finish.  This
     makes them safe to use inside interrupt handlers as well as in
     normal code.

‘-minrt’
     Enable the use of a minimum runtime environment - no static
     initializers or constructors.  This is intended for
     memory-constrained devices.  The compiler includes special symbols
     in some objects that tell the linker and runtime which code
     fragments are required.

‘-mtiny-printf’
     Enable reduced code size ‘printf’ and ‘puts’ library functions.
     The ‘tiny’ implementations of these functions are not reentrant, so
     must be used with caution in multi-threaded applications.

     Support for streams has been removed and the string to be printed
     will always be sent to stdout via the ‘write’ syscall.  The string
     is not buffered before it is sent to write.

     This option requires Newlib Nano IO, so GCC must be configured with
     ‘--enable-newlib-nano-formatted-io’.

‘-mmax-inline-shift=’
     This option takes an integer between 0 and 64 inclusive, and sets
     the maximum number of inline shift instructions which should be
     emitted to perform a shift operation by a constant amount.  When
     this value needs to be exceeded, an mspabi helper function is used
     instead.  The default value is 4.

     This only affects cases where a shift by multiple positions cannot
     be completed with a single instruction (e.g.  all shifts >1 on the
     430 ISA).

     Shifts of a 32-bit value are at least twice as costly, so the value
     passed for this option is divided by 2 and the resulting value used
     instead.

‘-mcode-region=’
‘-mdata-region=’
     These options tell the compiler where to place functions and data
     that do not have one of the ‘lower’, ‘upper’, ‘either’ or ‘section’
     attributes.  Possible values are ‘lower’, ‘upper’, ‘either’ or
     ‘any’.  The first three behave like the corresponding attribute.
     The fourth possible value - ‘any’ - is the default.  It leaves
     placement entirely up to the linker script and how it assigns the
     standard sections (‘.text’, ‘.data’, etc) to the memory regions.

‘-msilicon-errata=’
     This option passes on a request to assembler to enable the fixes
     for the named silicon errata.

‘-msilicon-errata-warn=’
     This option passes on a request to the assembler to enable warning
     messages when a silicon errata might need to be applied.

‘-mwarn-devices-csv’
‘-mno-warn-devices-csv’
     Warn if ‘devices.csv’ is not found or there are problem parsing it
     (default: on).


File: gcc.info,  Node: NDS32 Options,  Next: Nios II Options,  Prev: MSP430 Options,  Up: Submodel Options

3.19.35 NDS32 Options
---------------------

These options are defined for NDS32 implementations:

‘-mbig-endian’
     Generate code in big-endian mode.

‘-mlittle-endian’
     Generate code in little-endian mode.

‘-mreduced-regs’
     Use reduced-set registers for register allocation.

‘-mfull-regs’
     Use full-set registers for register allocation.

‘-mcmov’
     Generate conditional move instructions.

‘-mno-cmov’
     Do not generate conditional move instructions.

‘-mext-perf’
     Generate performance extension instructions.

‘-mno-ext-perf’
     Do not generate performance extension instructions.

‘-mext-perf2’
     Generate performance extension 2 instructions.

‘-mno-ext-perf2’
     Do not generate performance extension 2 instructions.

‘-mext-string’
     Generate string extension instructions.

‘-mno-ext-string’
     Do not generate string extension instructions.

‘-mv3push’
     Generate v3 push25/pop25 instructions.

‘-mno-v3push’
     Do not generate v3 push25/pop25 instructions.

‘-m16-bit’
     Generate 16-bit instructions.

‘-mno-16-bit’
     Do not generate 16-bit instructions.

‘-misr-vector-size=NUM’
     Specify the size of each interrupt vector, which must be 4 or 16.

‘-mcache-block-size=NUM’
     Specify the size of each cache block, which must be a power of 2
     between 4 and 512.

‘-march=ARCH’
     Specify the name of the target architecture.

‘-mcmodel=CODE-MODEL’
     Set the code model to one of
     ‘small’
          All the data and read-only data segments must be within 512KB
          addressing space.  The text segment must be within 16MB
          addressing space.
     ‘medium’
          The data segment must be within 512KB while the read-only data
          segment can be within 4GB addressing space.  The text segment
          should be still within 16MB addressing space.
     ‘large’
          All the text and data segments can be within 4GB addressing
          space.

‘-mctor-dtor’
     Enable constructor/destructor feature.

‘-mrelax’
     Guide linker to relax instructions.


File: gcc.info,  Node: Nios II Options,  Next: Nvidia PTX Options,  Prev: NDS32 Options,  Up: Submodel Options

3.19.36 Nios II Options
-----------------------

These are the options defined for the Altera Nios II processor.

‘-G NUM’
     Put global and static objects less than or equal to NUM bytes into
     the small data or BSS sections instead of the normal data or BSS
     sections.  The default value of NUM is 8.

‘-mgpopt=OPTION’
‘-mgpopt’
‘-mno-gpopt’
     Generate (do not generate) GP-relative accesses.  The following
     OPTION names are recognized:

     ‘none’
          Do not generate GP-relative accesses.

     ‘local’
          Generate GP-relative accesses for small data objects that are
          not external, weak, or uninitialized common symbols.  Also use
          GP-relative addressing for objects that have been explicitly
          placed in a small data section via a ‘section’ attribute.

     ‘global’
          As for ‘local’, but also generate GP-relative accesses for
          small data objects that are external, weak, or common.  If you
          use this option, you must ensure that all parts of your
          program (including libraries) are compiled with the same ‘-G’
          setting.

     ‘data’
          Generate GP-relative accesses for all data objects in the
          program.  If you use this option, the entire data and BSS
          segments of your program must fit in 64K of memory and you
          must use an appropriate linker script to allocate them within
          the addressable range of the global pointer.

     ‘all’
          Generate GP-relative addresses for function pointers as well
          as data pointers.  If you use this option, the entire text,
          data, and BSS segments of your program must fit in 64K of
          memory and you must use an appropriate linker script to
          allocate them within the addressable range of the global
          pointer.

     ‘-mgpopt’ is equivalent to ‘-mgpopt=local’, and ‘-mno-gpopt’ is
     equivalent to ‘-mgpopt=none’.

     The default is ‘-mgpopt’ except when ‘-fpic’ or ‘-fPIC’ is
     specified to generate position-independent code.  Note that the
     Nios II ABI does not permit GP-relative accesses from shared
     libraries.

     You may need to specify ‘-mno-gpopt’ explicitly when building
     programs that include large amounts of small data, including large
     GOT data sections.  In this case, the 16-bit offset for GP-relative
     addressing may not be large enough to allow access to the entire
     small data section.

‘-mgprel-sec=REGEXP’
     This option specifies additional section names that can be accessed
     via GP-relative addressing.  It is most useful in conjunction with
     ‘section’ attributes on variable declarations (*note Common
     Variable Attributes::) and a custom linker script.  The REGEXP is a
     POSIX Extended Regular Expression.

     This option does not affect the behavior of the ‘-G’ option, and
     the specified sections are in addition to the standard ‘.sdata’ and
     ‘.sbss’ small-data sections that are recognized by ‘-mgpopt’.

‘-mr0rel-sec=REGEXP’
     This option specifies names of sections that can be accessed via a
     16-bit offset from ‘r0’; that is, in the low 32K or high 32K of the
     32-bit address space.  It is most useful in conjunction with
     ‘section’ attributes on variable declarations (*note Common
     Variable Attributes::) and a custom linker script.  The REGEXP is a
     POSIX Extended Regular Expression.

     In contrast to the use of GP-relative addressing for small data,
     zero-based addressing is never generated by default and there are
     no conventional section names used in standard linker scripts for
     sections in the low or high areas of memory.

‘-mel’
‘-meb’
     Generate little-endian (default) or big-endian (experimental) code,
     respectively.

‘-march=ARCH’
     This specifies the name of the target Nios II architecture.  GCC
     uses this name to determine what kind of instructions it can emit
     when generating assembly code.  Permissible names are: ‘r1’, ‘r2’.

     The preprocessor macro ‘__nios2_arch__’ is available to programs,
     with value 1 or 2, indicating the targeted ISA level.

‘-mbypass-cache’
‘-mno-bypass-cache’
     Force all load and store instructions to always bypass cache by
     using I/O variants of the instructions.  The default is not to
     bypass the cache.

‘-mno-cache-volatile’
‘-mcache-volatile’
     Volatile memory access bypass the cache using the I/O variants of
     the load and store instructions.  The default is not to bypass the
     cache.

‘-mno-fast-sw-div’
‘-mfast-sw-div’
     Do not use table-based fast divide for small numbers.  The default
     is to use the fast divide at ‘-O3’ and above.

‘-mno-hw-mul’
‘-mhw-mul’
‘-mno-hw-mulx’
‘-mhw-mulx’
‘-mno-hw-div’
‘-mhw-div’
     Enable or disable emitting ‘mul’, ‘mulx’ and ‘div’ family of
     instructions by the compiler.  The default is to emit ‘mul’ and not
     emit ‘div’ and ‘mulx’.

‘-mbmx’
‘-mno-bmx’
‘-mcdx’
‘-mno-cdx’
     Enable or disable generation of Nios II R2 BMX (bit manipulation)
     and CDX (code density) instructions.  Enabling these instructions
     also requires ‘-march=r2’.  Since these instructions are optional
     extensions to the R2 architecture, the default is not to emit them.

‘-mcustom-INSN=N’
‘-mno-custom-INSN’
     Each ‘-mcustom-INSN=N’ option enables use of a custom instruction
     with encoding N when generating code that uses INSN.  For example,
     ‘-mcustom-fadds=253’ generates custom instruction 253 for
     single-precision floating-point add operations instead of the
     default behavior of using a library call.

     The following values of INSN are supported.  Except as otherwise
     noted, floating-point operations are expected to be implemented
     with normal IEEE 754 semantics and correspond directly to the C
     operators or the equivalent GCC built-in functions (*note Other
     Builtins::).

     Single-precision floating point:

     ‘fadds’, ‘fsubs’, ‘fdivs’, ‘fmuls’
          Binary arithmetic operations.

     ‘fnegs’
          Unary negation.

     ‘fabss’
          Unary absolute value.

     ‘fcmpeqs’, ‘fcmpges’, ‘fcmpgts’, ‘fcmples’, ‘fcmplts’, ‘fcmpnes’
          Comparison operations.

     ‘fmins’, ‘fmaxs’
          Floating-point minimum and maximum.  These instructions are
          only generated if ‘-ffinite-math-only’ is specified.

     ‘fsqrts’
          Unary square root operation.

     ‘fcoss’, ‘fsins’, ‘ftans’, ‘fatans’, ‘fexps’, ‘flogs’
          Floating-point trigonometric and exponential functions.  These
          instructions are only generated if
          ‘-funsafe-math-optimizations’ is also specified.

     Double-precision floating point:

     ‘faddd’, ‘fsubd’, ‘fdivd’, ‘fmuld’
          Binary arithmetic operations.

     ‘fnegd’
          Unary negation.

     ‘fabsd’
          Unary absolute value.

     ‘fcmpeqd’, ‘fcmpged’, ‘fcmpgtd’, ‘fcmpled’, ‘fcmpltd’, ‘fcmpned’
          Comparison operations.

     ‘fmind’, ‘fmaxd’
          Double-precision minimum and maximum.  These instructions are
          only generated if ‘-ffinite-math-only’ is specified.

     ‘fsqrtd’
          Unary square root operation.

     ‘fcosd’, ‘fsind’, ‘ftand’, ‘fatand’, ‘fexpd’, ‘flogd’
          Double-precision trigonometric and exponential functions.
          These instructions are only generated if
          ‘-funsafe-math-optimizations’ is also specified.

     Conversions:
     ‘fextsd’
          Conversion from single precision to double precision.

     ‘ftruncds’
          Conversion from double precision to single precision.

     ‘fixsi’, ‘fixsu’, ‘fixdi’, ‘fixdu’
          Conversion from floating point to signed or unsigned integer
          types, with truncation towards zero.

     ‘round’
          Conversion from single-precision floating point to signed
          integer, rounding to the nearest integer and ties away from
          zero.  This corresponds to the ‘__builtin_lroundf’ function
          when ‘-fno-math-errno’ is used.

     ‘floatis’, ‘floatus’, ‘floatid’, ‘floatud’
          Conversion from signed or unsigned integer types to
          floating-point types.

     In addition, all of the following transfer instructions for
     internal registers X and Y must be provided to use any of the
     double-precision floating-point instructions.  Custom instructions
     taking two double-precision source operands expect the first
     operand in the 64-bit register X. The other operand (or only
     operand of a unary operation) is given to the custom arithmetic
     instruction with the least significant half in source register SRC1
     and the most significant half in SRC2.  A custom instruction that
     returns a double-precision result returns the most significant 32
     bits in the destination register and the other half in 32-bit
     register Y. GCC automatically generates the necessary code
     sequences to write register X and/or read register Y when
     double-precision floating-point instructions are used.

     ‘fwrx’
          Write SRC1 into the least significant half of X and SRC2 into
          the most significant half of X.

     ‘fwry’
          Write SRC1 into Y.

     ‘frdxhi’, ‘frdxlo’
          Read the most or least (respectively) significant half of X
          and store it in DEST.

     ‘frdy’
          Read the value of Y and store it into DEST.

     Note that you can gain more local control over generation of Nios
     II custom instructions by using the ‘target("custom-INSN=N")’ and
     ‘target("no-custom-INSN")’ function attributes (*note Function
     Attributes::) or pragmas (*note Function Specific Option
     Pragmas::).

‘-mcustom-fpu-cfg=NAME’

     This option enables a predefined, named set of custom instruction
     encodings (see ‘-mcustom-INSN’ above).  Currently, the following
     sets are defined:

     ‘-mcustom-fpu-cfg=60-1’ is equivalent to:
          -mcustom-fmuls=252
          -mcustom-fadds=253
          -mcustom-fsubs=254
          -fsingle-precision-constant

     ‘-mcustom-fpu-cfg=60-2’ is equivalent to:
          -mcustom-fmuls=252
          -mcustom-fadds=253
          -mcustom-fsubs=254
          -mcustom-fdivs=255
          -fsingle-precision-constant

     ‘-mcustom-fpu-cfg=72-3’ is equivalent to:
          -mcustom-floatus=243
          -mcustom-fixsi=244
          -mcustom-floatis=245
          -mcustom-fcmpgts=246
          -mcustom-fcmples=249
          -mcustom-fcmpeqs=250
          -mcustom-fcmpnes=251
          -mcustom-fmuls=252
          -mcustom-fadds=253
          -mcustom-fsubs=254
          -mcustom-fdivs=255
          -fsingle-precision-constant

     ‘-mcustom-fpu-cfg=fph2’ is equivalent to:
          -mcustom-fabss=224
          -mcustom-fnegs=225
          -mcustom-fcmpnes=226
          -mcustom-fcmpeqs=227
          -mcustom-fcmpges=228
          -mcustom-fcmpgts=229
          -mcustom-fcmples=230
          -mcustom-fcmplts=231
          -mcustom-fmaxs=232
          -mcustom-fmins=233
          -mcustom-round=248
          -mcustom-fixsi=249
          -mcustom-floatis=250
          -mcustom-fsqrts=251
          -mcustom-fmuls=252
          -mcustom-fadds=253
          -mcustom-fsubs=254
          -mcustom-fdivs=255

     Custom instruction assignments given by individual ‘-mcustom-INSN=’
     options override those given by ‘-mcustom-fpu-cfg=’, regardless of
     the order of the options on the command line.

     Note that you can gain more local control over selection of a FPU
     configuration by using the ‘target("custom-fpu-cfg=NAME")’ function
     attribute (*note Function Attributes::) or pragma (*note Function
     Specific Option Pragmas::).

     The name FPH2 is an abbreviation for _Nios II Floating Point
     Hardware 2 Component_.  Please note that the custom instructions
     enabled by ‘-mcustom-fmins=233’ and ‘-mcustom-fmaxs=234’ are only
     generated if ‘-ffinite-math-only’ is specified.  The custom
     instruction enabled by ‘-mcustom-round=248’ is only generated if
     ‘-fno-math-errno’ is specified.  In contrast to the other
     configurations, ‘-fsingle-precision-constant’ is not set.

 These additional ‘-m’ options are available for the Altera Nios II ELF
(bare-metal) target:

‘-mhal’
     Link with HAL BSP. This suppresses linking with the GCC-provided C
     runtime startup and termination code, and is typically used in
     conjunction with ‘-msys-crt0=’ to specify the location of the
     alternate startup code provided by the HAL BSP.

‘-msmallc’
     Link with a limited version of the C library, ‘-lsmallc’, rather
     than Newlib.

‘-msys-crt0=STARTFILE’
     STARTFILE is the file name of the startfile (crt0) to use when
     linking.  This option is only useful in conjunction with ‘-mhal’.

‘-msys-lib=SYSTEMLIB’
     SYSTEMLIB is the library name of the library that provides
     low-level system calls required by the C library, e.g. ‘read’ and
     ‘write’.  This option is typically used to link with a library
     provided by a HAL BSP.


File: gcc.info,  Node: Nvidia PTX Options,  Next: OpenRISC Options,  Prev: Nios II Options,  Up: Submodel Options

3.19.37 Nvidia PTX Options
--------------------------

These options are defined for Nvidia PTX:

‘-m64’
     Ignored, but preserved for backward compatibility.  Only 64-bit ABI
     is supported.

‘-march=ARCHITECTURE-STRING’
     Generate code for the specified PTX ISA target architecture (e.g.
     ‘sm_35’).  Valid architecture strings are ‘sm_30’, ‘sm_35’,
     ‘sm_53’, ‘sm_70’, ‘sm_75’ and ‘sm_80’.  The default target
     architecture is sm_30.

     This option sets the value of the preprocessor macro ‘__PTX_SM__’;
     for instance, for ‘sm_35’, it has the value ‘350’.

‘-misa=ARCHITECTURE-STRING’
     Alias of ‘-march=’.

‘-march-map=ARCHITECTURE-STRING’
     Select the closest available ‘-march=’ value that is not more
     capable.  For instance, for ‘-march-map=sm_50’ select
     ‘-march=sm_35’, and for ‘-march-map=sm_53’ select ‘-march=sm_53’.

‘-mptx=VERSION-STRING’
     Generate code for the specified PTX ISA version (e.g. ‘7.0’).
     Valid version strings include ‘3.1’, ‘6.0’, ‘6.3’, and ‘7.0’.  The
     default PTX ISA version is 6.0, unless a higher version is required
     for specified PTX ISA target architecture via option ‘-march=’.

     This option sets the values of the preprocessor macros
     ‘__PTX_ISA_VERSION_MAJOR__’ and ‘__PTX_ISA_VERSION_MINOR__’; for
     instance, for ‘3.1’ the macros have the values ‘3’ and ‘1’,
     respectively.

‘-mmainkernel’
     Link in code for a __main kernel.  This is for stand-alone instead
     of offloading execution.

‘-moptimize’
     Apply partitioned execution optimizations.  This is the default
     when any level of optimization is selected.

‘-msoft-stack’
     Generate code that does not use ‘.local’ memory directly for stack
     storage.  Instead, a per-warp stack pointer is maintained
     explicitly.  This enables variable-length stack allocation (with
     variable-length arrays or ‘alloca’), and when global memory is used
     for underlying storage, makes it possible to access automatic
     variables from other threads, or with atomic instructions.  This
     code generation variant is used for OpenMP offloading, but the
     option is exposed on its own for the purpose of testing the
     compiler; to generate code suitable for linking into programs using
     OpenMP offloading, use option ‘-mgomp’.

‘-muniform-simt’
     Switch to code generation variant that allows to execute all
     threads in each warp, while maintaining memory state and side
     effects as if only one thread in each warp was active outside of
     OpenMP SIMD regions.  All atomic operations and calls to runtime
     (malloc, free, vprintf) are conditionally executed (iff current
     lane index equals the master lane index), and the register being
     assigned is copied via a shuffle instruction from the master lane.
     Outside of SIMD regions lane 0 is the master; inside, each thread
     sees itself as the master.  Shared memory array ‘int __nvptx_uni[]’
     stores all-zeros or all-ones bitmasks for each warp, indicating
     current mode (0 outside of SIMD regions).  Each thread can
     bitwise-and the bitmask at position ‘tid.y’ with current lane index
     to compute the master lane index.

‘-mgomp’
     Generate code for use in OpenMP offloading: enables ‘-msoft-stack’
     and ‘-muniform-simt’ options, and selects corresponding multilib
     variant.


File: gcc.info,  Node: OpenRISC Options,  Next: PDP-11 Options,  Prev: Nvidia PTX Options,  Up: Submodel Options

3.19.38 OpenRISC Options
------------------------

These options are defined for OpenRISC:

‘-mboard=NAME’
     Configure a board specific runtime.  This will be passed to the
     linker for newlib board library linking.  The default is ‘or1ksim’.

‘-mnewlib’
     This option is ignored; it is for compatibility purposes only.
     This used to select linker and preprocessor options for use with
     newlib.

‘-msoft-div’
‘-mhard-div’
     Select software or hardware divide (‘l.div’, ‘l.divu’)
     instructions.  This default is hardware divide.

‘-msoft-mul’
‘-mhard-mul’
     Select software or hardware multiply (‘l.mul’, ‘l.muli’)
     instructions.  This default is hardware multiply.

‘-msoft-float’
‘-mhard-float’
     Select software or hardware for floating point operations.  The
     default is software.

‘-mdouble-float’
     When ‘-mhard-float’ is selected, enables generation of
     double-precision floating point instructions.  By default functions
     from ‘libgcc’ are used to perform double-precision floating point
     operations.

‘-munordered-float’
     When ‘-mhard-float’ is selected, enables generation of unordered
     floating point compare and set flag (‘lf.sfun*’) instructions.  By
     default functions from ‘libgcc’ are used to perform unordered
     floating point compare and set flag operations.

‘-mcmov’
     Enable generation of conditional move (‘l.cmov’) instructions.  By
     default the equivalent will be generated using set and branch.

‘-mror’
     Enable generation of rotate right (‘l.ror’) instructions.  By
     default functions from ‘libgcc’ are used to perform rotate right
     operations.

‘-mrori’
     Enable generation of rotate right with immediate (‘l.rori’)
     instructions.  By default functions from ‘libgcc’ are used to
     perform rotate right with immediate operations.

‘-msext’
     Enable generation of sign extension (‘l.ext*’) instructions.  By
     default memory loads are used to perform sign extension.

‘-msfimm’
     Enable generation of compare and set flag with immediate (‘l.sf*i’)
     instructions.  By default extra instructions will be generated to
     store the immediate to a register first.

‘-mshftimm’
     Enable generation of shift with immediate (‘l.srai’, ‘l.srli’,
     ‘l.slli’) instructions.  By default extra instructions will be
     generated to store the immediate to a register first.

‘-mcmodel=small’
     Generate OpenRISC code for the small model: The GOT is limited to
     64k.  This is the default model.

‘-mcmodel=large’
     Generate OpenRISC code for the large model: The GOT may grow up to
     4G in size.


File: gcc.info,  Node: PDP-11 Options,  Next: picoChip Options,  Prev: OpenRISC Options,  Up: Submodel Options

3.19.39 PDP-11 Options
----------------------

These options are defined for the PDP-11:

‘-mfpu’
     Use hardware FPP floating point.  This is the default.  (FIS
     floating point on the PDP-11/40 is not supported.)  Implies -m45.

‘-msoft-float’
     Do not use hardware floating point.

‘-mac0’
     Return floating-point results in ac0 (fr0 in Unix assembler
     syntax).

‘-mno-ac0’
     Return floating-point results in memory.  This is the default.

‘-m40’
     Generate code for a PDP-11/40.  Implies -msoft-float -mno-split.

‘-m45’
     Generate code for a PDP-11/45.  This is the default.

‘-m10’
     Generate code for a PDP-11/10.  Implies -msoft-float -mno-split.

‘-mint16’
‘-mno-int32’
     Use 16-bit ‘int’.  This is the default.

‘-mint32’
‘-mno-int16’
     Use 32-bit ‘int’.

‘-msplit’
     Target has split instruction and data space.  Implies -m45.

‘-munix-asm’
     Use Unix assembler syntax.

‘-mdec-asm’
     Use DEC assembler syntax.

‘-mgnu-asm’
     Use GNU assembler syntax.  This is the default.

‘-mlra’
     Use the new LRA register allocator.  By default, the old "reload"
     allocator is used.


File: gcc.info,  Node: picoChip Options,  Next: PowerPC Options,  Prev: PDP-11 Options,  Up: Submodel Options

3.19.40 picoChip Options
------------------------

These ‘-m’ options are defined for picoChip implementations:

‘-mae=AE_TYPE’
     Set the instruction set, register set, and instruction scheduling
     parameters for array element type AE_TYPE.  Supported values for
     AE_TYPE are ‘ANY’, ‘MUL’, and ‘MAC’.

     ‘-mae=ANY’ selects a completely generic AE type.  Code generated
     with this option runs on any of the other AE types.  The code is
     not as efficient as it would be if compiled for a specific AE type,
     and some types of operation (e.g., multiplication) do not work
     properly on all types of AE.

     ‘-mae=MUL’ selects a MUL AE type.  This is the most useful AE type
     for compiled code, and is the default.

     ‘-mae=MAC’ selects a DSP-style MAC AE. Code compiled with this
     option may suffer from poor performance of byte (char)
     manipulation, since the DSP AE does not provide hardware support
     for byte load/stores.

‘-msymbol-as-address’
     Enable the compiler to directly use a symbol name as an address in
     a load/store instruction, without first loading it into a register.
     Typically, the use of this option generates larger programs, which
     run faster than when the option isn't used.  However, the results
     vary from program to program, so it is left as a user option,
     rather than being permanently enabled.

‘-mno-inefficient-warnings’
     Disables warnings about the generation of inefficient code.  These
     warnings can be generated, for example, when compiling code that
     performs byte-level memory operations on the MAC AE type.  The MAC
     AE has no hardware support for byte-level memory operations, so all
     byte load/stores must be synthesized from word load/store
     operations.  This is inefficient and a warning is generated to
     indicate that you should rewrite the code to avoid byte operations,
     or to target an AE type that has the necessary hardware support.
     This option disables these warnings.


File: gcc.info,  Node: PowerPC Options,  Next: PRU Options,  Prev: picoChip Options,  Up: Submodel Options

3.19.41 PowerPC Options
-----------------------

These are listed under *Note RS/6000 and PowerPC Options::.


File: gcc.info,  Node: PRU Options,  Next: RISC-V Options,  Prev: PowerPC Options,  Up: Submodel Options

3.19.42 PRU Options
-------------------

These command-line options are defined for PRU target:

‘-minrt’
     Link with a minimum runtime environment, with no support for static
     initializers and constructors.  Using this option can significantly
     reduce the size of the final ELF binary.  Beware that the compiler
     could still generate code with static initializers and
     constructors.  It is up to the programmer to ensure that the source
     program will not use those features.

‘-mmcu=MCU’
     Specify the PRU MCU variant to use.  Check Newlib for the exact
     list of supported MCUs.

‘-mno-relax’
     Make GCC pass the ‘--no-relax’ command-line option to the linker
     instead of the ‘--relax’ option.

‘-mloop’
     Allow (or do not allow) GCC to use the LOOP instruction.

‘-mabi=VARIANT’
     Specify the ABI variant to output code for.  ‘-mabi=ti’ selects the
     unmodified TI ABI while ‘-mabi=gnu’ selects a GNU variant that
     copes more naturally with certain GCC assumptions.  These are the
     differences:

     ‘Function Pointer Size’
          TI ABI specifies that function (code) pointers are 16-bit,
          whereas GNU supports only 32-bit data and code pointers.

     ‘Optional Return Value Pointer’
          Function return values larger than 64 bits are passed by using
          a hidden pointer as the first argument of the function.  TI
          ABI, though, mandates that the pointer can be NULL in case the
          caller is not using the returned value.  GNU always passes and
          expects a valid return value pointer.

     The current ‘-mabi=ti’ implementation simply raises a compile error
     when any of the above code constructs is detected.  As a
     consequence the standard C library cannot be built and it is
     omitted when linking with ‘-mabi=ti’.

     Relaxation is a GNU feature and for safety reasons is disabled when
     using ‘-mabi=ti’.  The TI toolchain does not emit relocations for
     QBBx instructions, so the GNU linker cannot adjust them when
     shortening adjacent LDI32 pseudo instructions.


File: gcc.info,  Node: RISC-V Options,  Next: RL78 Options,  Prev: PRU Options,  Up: Submodel Options

3.19.43 RISC-V Options
----------------------

These command-line options are defined for RISC-V targets:

‘-mbranch-cost=N’
     Set the cost of branches to roughly N instructions.

‘-mplt’
‘-mno-plt’
     When generating PIC code, do or don't allow the use of PLTs.
     Ignored for non-PIC. The default is ‘-mplt’.

‘-mabi=ABI-STRING’
     Specify integer and floating-point calling convention.  ABI-STRING
     contains two parts: the size of integer types and the registers
     used for floating-point types.  For example ‘-march=rv64ifd
     -mabi=lp64d’ means that ‘long’ and pointers are 64-bit (implicitly
     defining ‘int’ to be 32-bit), and that floating-point values up to
     64 bits wide are passed in F registers.  Contrast this with
     ‘-march=rv64ifd -mabi=lp64f’, which still allows the compiler to
     generate code that uses the F and D extensions but only allows
     floating-point values up to 32 bits long to be passed in registers;
     or ‘-march=rv64ifd -mabi=lp64’, in which no floating-point
     arguments will be passed in registers.

     The default for this argument is system dependent, users who want a
     specific calling convention should specify one explicitly.  The
     valid calling conventions are: ‘ilp32’, ‘ilp32f’, ‘ilp32d’, ‘lp64’,
     ‘lp64f’, and ‘lp64d’.  Some calling conventions are impossible to
     implement on some ISAs: for example, ‘-march=rv32if -mabi=ilp32d’
     is invalid because the ABI requires 64-bit values be passed in F
     registers, but F registers are only 32 bits wide.  There is also
     the ‘ilp32e’ ABI that can only be used with the ‘rv32e’
     architecture.  This ABI is not well specified at present, and is
     subject to change.

‘-mfdiv’
‘-mno-fdiv’
     Do or don't use hardware floating-point divide and square root
     instructions.  This requires the F or D extensions for
     floating-point registers.  The default is to use them if the
     specified architecture has these instructions.

‘-mdiv’
‘-mno-div’
     Do or don't use hardware instructions for integer division.  This
     requires the M extension.  The default is to use them if the
     specified architecture has these instructions.

‘-misa-spec=ISA-SPEC-STRING’
     Specify the version of the RISC-V Unprivileged (formerly
     User-Level) ISA specification to produce code conforming to.  The
     possibilities for ISA-SPEC-STRING are:
     ‘2.2’
          Produce code conforming to version 2.2.
     ‘20190608’
          Produce code conforming to version 20190608.
     ‘20191213’
          Produce code conforming to version 20191213.
     The default is ‘-misa-spec=20191213’ unless GCC has been configured
     with ‘--with-isa-spec=’ specifying a different default version.

‘-march=ISA-STRING’
     Generate code for given RISC-V ISA (e.g. ‘rv64im’).  ISA strings
     must be lower-case.  Examples include ‘rv64i’, ‘rv32g’, ‘rv32e’,
     and ‘rv32imaf’.

     When ‘-march=’ is not specified, use the setting from ‘-mcpu’.

     If both ‘-march’ and ‘-mcpu=’ are not specified, the default for
     this argument is system dependent, users who want a specific
     architecture extensions should specify one explicitly.

‘-mcpu=PROCESSOR-STRING’
     Use architecture of and optimize the output for the given
     processor, specified by particular CPU name.  Permissible values
     for this option are: ‘sifive-e20’, ‘sifive-e21’, ‘sifive-e24’,
     ‘sifive-e31’, ‘sifive-e34’, ‘sifive-e76’, ‘sifive-s21’,
     ‘sifive-s51’, ‘sifive-s54’, ‘sifive-s76’, ‘sifive-u54’, and
     ‘sifive-u74’.

‘-mtune=PROCESSOR-STRING’
     Optimize the output for the given processor, specified by
     microarchitecture or particular CPU name.  Permissible values for
     this option are: ‘rocket’, ‘sifive-3-series’, ‘sifive-5-series’,
     ‘sifive-7-series’, ‘size’, and all valid options for ‘-mcpu=’.

     When ‘-mtune=’ is not specified, use the setting from ‘-mcpu’, the
     default is ‘rocket’ if both are not specified.

     The ‘size’ choice is not intended for use by end-users.  This is
     used when ‘-Os’ is specified.  It overrides the instruction cost
     info provided by ‘-mtune=’, but does not override the pipeline
     info.  This helps reduce code size while still giving good
     performance.

‘-mpreferred-stack-boundary=NUM’
     Attempt to keep the stack boundary aligned to a 2 raised to NUM
     byte boundary.  If ‘-mpreferred-stack-boundary’ is not specified,
     the default is 4 (16 bytes or 128-bits).

     *Warning:* If you use this switch, then you must build all modules
     with the same value, including any libraries.  This includes the
     system libraries and startup modules.

‘-msmall-data-limit=N’
     Put global and static data smaller than N bytes into a special
     section (on some targets).

‘-msave-restore’
‘-mno-save-restore’
     Do or don't use smaller but slower prologue and epilogue code that
     uses library function calls.  The default is to use fast inline
     prologues and epilogues.

‘-mshorten-memrefs’
‘-mno-shorten-memrefs’
     Do or do not attempt to make more use of compressed load/store
     instructions by replacing a load/store of 'base register + large
     offset' with a new load/store of 'new base + small offset'.  If the
     new base gets stored in a compressed register, then the new
     load/store can be compressed.  Currently targets 32-bit integer
     load/stores only.

‘-mstrict-align’
‘-mno-strict-align’
     Do not or do generate unaligned memory accesses.  The default is
     set depending on whether the processor we are optimizing for
     supports fast unaligned access or not.

‘-mcmodel=medlow’
     Generate code for the medium-low code model.  The program and its
     statically defined symbols must lie within a single 2 GiB address
     range and must lie between absolute addresses −2 GiB and +2 GiB.
     Programs can be statically or dynamically linked.  This is the
     default code model.

‘-mcmodel=medany’
     Generate code for the medium-any code model.  The program and its
     statically defined symbols must be within any single 2 GiB address
     range.  Programs can be statically or dynamically linked.

     The code generated by the medium-any code model is
     position-independent, but is not guaranteed to function correctly
     when linked into position-independent executables or libraries.

‘-mexplicit-relocs’
‘-mno-exlicit-relocs’
     Use or do not use assembler relocation operators when dealing with
     symbolic addresses.  The alternative is to use assembler macros
     instead, which may limit optimization.

‘-mrelax’
‘-mno-relax’
     Take advantage of linker relaxations to reduce the number of
     instructions required to materialize symbol addresses.  The default
     is to take advantage of linker relaxations.

‘-memit-attribute’
‘-mno-emit-attribute’
     Emit (do not emit) RISC-V attribute to record extra information
     into ELF objects.  This feature requires at least binutils 2.32.

‘-malign-data=TYPE’
     Control how GCC aligns variables and constants of array, structure,
     or union types.  Supported values for TYPE are ‘xlen’ which uses x
     register width as the alignment value, and ‘natural’ which uses
     natural alignment.  ‘xlen’ is the default.

‘-mbig-endian’
     Generate big-endian code.  This is the default when GCC is
     configured for a ‘riscv64be-*-*’ or ‘riscv32be-*-*’ target.

‘-mlittle-endian’
     Generate little-endian code.  This is the default when GCC is
     configured for a ‘riscv64-*-*’ or ‘riscv32-*-*’ but not a
     ‘riscv64be-*-*’ or ‘riscv32be-*-*’ target.

‘-mstack-protector-guard=GUARD’
‘-mstack-protector-guard-reg=REG’
‘-mstack-protector-guard-offset=OFFSET’
     Generate stack protection code using canary at GUARD.  Supported
     locations are ‘global’ for a global canary or ‘tls’ for per-thread
     canary in the TLS block.

     With the latter choice the options
     ‘-mstack-protector-guard-reg=REG’ and
     ‘-mstack-protector-guard-offset=OFFSET’ furthermore specify which
     register to use as base register for reading the canary, and from
     what offset from that base register.  There is no default register
     or offset as this is entirely for use within the Linux kernel.


File: gcc.info,  Node: RL78 Options,  Next: RS/6000 and PowerPC Options,  Prev: RISC-V Options,  Up: Submodel Options

3.19.44 RL78 Options
--------------------

‘-msim’
     Links in additional target libraries to support operation within a
     simulator.

‘-mmul=none’
‘-mmul=g10’
‘-mmul=g13’
‘-mmul=g14’
‘-mmul=rl78’
     Specifies the type of hardware multiplication and division support
     to be used.  The simplest is ‘none’, which uses software for both
     multiplication and division.  This is the default.  The ‘g13’ value
     is for the hardware multiply/divide peripheral found on the
     RL78/G13 (S2 core) targets.  The ‘g14’ value selects the use of the
     multiplication and division instructions supported by the RL78/G14
     (S3 core) parts.  The value ‘rl78’ is an alias for ‘g14’ and the
     value ‘mg10’ is an alias for ‘none’.

     In addition a C preprocessor macro is defined, based upon the
     setting of this option.  Possible values are: ‘__RL78_MUL_NONE__’,
     ‘__RL78_MUL_G13__’ or ‘__RL78_MUL_G14__’.

‘-mcpu=g10’
‘-mcpu=g13’
‘-mcpu=g14’
‘-mcpu=rl78’
     Specifies the RL78 core to target.  The default is the G14 core,
     also known as an S3 core or just RL78.  The G13 or S2 core does not
     have multiply or divide instructions, instead it uses a hardware
     peripheral for these operations.  The G10 or S1 core does not have
     register banks, so it uses a different calling convention.

     If this option is set it also selects the type of hardware multiply
     support to use, unless this is overridden by an explicit
     ‘-mmul=none’ option on the command line.  Thus specifying
     ‘-mcpu=g13’ enables the use of the G13 hardware multiply peripheral
     and specifying ‘-mcpu=g10’ disables the use of hardware
     multiplications altogether.

     Note, although the RL78/G14 core is the default target, specifying
     ‘-mcpu=g14’ or ‘-mcpu=rl78’ on the command line does change the
     behavior of the toolchain since it also enables G14 hardware
     multiply support.  If these options are not specified on the
     command line then software multiplication routines will be used
     even though the code targets the RL78 core.  This is for backwards
     compatibility with older toolchains which did not have hardware
     multiply and divide support.

     In addition a C preprocessor macro is defined, based upon the
     setting of this option.  Possible values are: ‘__RL78_G10__’,
     ‘__RL78_G13__’ or ‘__RL78_G14__’.

‘-mg10’
‘-mg13’
‘-mg14’
‘-mrl78’
     These are aliases for the corresponding ‘-mcpu=’ option.  They are
     provided for backwards compatibility.

‘-mallregs’
     Allow the compiler to use all of the available registers.  By
     default registers ‘r24..r31’ are reserved for use in interrupt
     handlers.  With this option enabled these registers can be used in
     ordinary functions as well.

‘-m64bit-doubles’
‘-m32bit-doubles’
     Make the ‘double’ data type be 64 bits (‘-m64bit-doubles’) or 32
     bits (‘-m32bit-doubles’) in size.  The default is
     ‘-m32bit-doubles’.

‘-msave-mduc-in-interrupts’
‘-mno-save-mduc-in-interrupts’
     Specifies that interrupt handler functions should preserve the MDUC
     registers.  This is only necessary if normal code might use the
     MDUC registers, for example because it performs multiplication and
     division operations.  The default is to ignore the MDUC registers
     as this makes the interrupt handlers faster.  The target option
     -mg13 needs to be passed for this to work as this feature is only
     available on the G13 target (S2 core).  The MDUC registers will
     only be saved if the interrupt handler performs a multiplication or
     division operation or it calls another function.


File: gcc.info,  Node: RS/6000 and PowerPC Options,  Next: RX Options,  Prev: RL78 Options,  Up: Submodel Options

3.19.45 IBM RS/6000 and PowerPC Options
---------------------------------------

These ‘-m’ options are defined for the IBM RS/6000 and PowerPC:
‘-mpowerpc-gpopt’
‘-mno-powerpc-gpopt’
‘-mpowerpc-gfxopt’
‘-mno-powerpc-gfxopt’
‘-mpowerpc64’
‘-mno-powerpc64’
‘-mmfcrf’
‘-mno-mfcrf’
‘-mpopcntb’
‘-mno-popcntb’
‘-mpopcntd’
‘-mno-popcntd’
‘-mfprnd’
‘-mno-fprnd’
‘-mcmpb’
‘-mno-cmpb’
‘-mhard-dfp’
‘-mno-hard-dfp’
     You use these options to specify which instructions are available
     on the processor you are using.  The default value of these options
     is determined when configuring GCC.  Specifying the
     ‘-mcpu=CPU_TYPE’ overrides the specification of these options.  We
     recommend you use the ‘-mcpu=CPU_TYPE’ option rather than the
     options listed above.

     Specifying ‘-mpowerpc-gpopt’ allows GCC to use the optional PowerPC
     architecture instructions in the General Purpose group, including
     floating-point square root.  Specifying ‘-mpowerpc-gfxopt’ allows
     GCC to use the optional PowerPC architecture instructions in the
     Graphics group, including floating-point select.

     The ‘-mmfcrf’ option allows GCC to generate the move from condition
     register field instruction implemented on the POWER4 processor and
     other processors that support the PowerPC V2.01 architecture.  The
     ‘-mpopcntb’ option allows GCC to generate the popcount and
     double-precision FP reciprocal estimate instruction implemented on
     the POWER5 processor and other processors that support the PowerPC
     V2.02 architecture.  The ‘-mpopcntd’ option allows GCC to generate
     the popcount instruction implemented on the POWER7 processor and
     other processors that support the PowerPC V2.06 architecture.  The
     ‘-mfprnd’ option allows GCC to generate the FP round to integer
     instructions implemented on the POWER5+ processor and other
     processors that support the PowerPC V2.03 architecture.  The
     ‘-mcmpb’ option allows GCC to generate the compare bytes
     instruction implemented on the POWER6 processor and other
     processors that support the PowerPC V2.05 architecture.  The
     ‘-mhard-dfp’ option allows GCC to generate the decimal
     floating-point instructions implemented on some POWER processors.

     The ‘-mpowerpc64’ option allows GCC to generate the additional
     64-bit instructions that are found in the full PowerPC64
     architecture and to treat GPRs as 64-bit, doubleword quantities.
     GCC defaults to ‘-mno-powerpc64’.

‘-mcpu=CPU_TYPE’
     Set architecture type, register usage, and instruction scheduling
     parameters for machine type CPU_TYPE.  Supported values for
     CPU_TYPE are ‘401’, ‘403’, ‘405’, ‘405fp’, ‘440’, ‘440fp’, ‘464’,
     ‘464fp’, ‘476’, ‘476fp’, ‘505’, ‘601’, ‘602’, ‘603’, ‘603e’, ‘604’,
     ‘604e’, ‘620’, ‘630’, ‘740’, ‘7400’, ‘7450’, ‘750’, ‘801’, ‘821’,
     ‘823’, ‘860’, ‘970’, ‘8540’, ‘a2’, ‘e300c2’, ‘e300c3’, ‘e500mc’,
     ‘e500mc64’, ‘e5500’, ‘e6500’, ‘ec603e’, ‘G3’, ‘G4’, ‘G5’, ‘titan’,
     ‘power3’, ‘power4’, ‘power5’, ‘power5+’, ‘power6’, ‘power6x’,
     ‘power7’, ‘power8’, ‘power9’, ‘power10’, ‘powerpc’, ‘powerpc64’,
     ‘powerpc64le’, ‘rs64’, and ‘native’.

     ‘-mcpu=powerpc’, ‘-mcpu=powerpc64’, and ‘-mcpu=powerpc64le’ specify
     pure 32-bit PowerPC (either endian), 64-bit big endian PowerPC and
     64-bit little endian PowerPC architecture machine types, with an
     appropriate, generic processor model assumed for scheduling
     purposes.

     Specifying ‘native’ as cpu type detects and selects the
     architecture option that corresponds to the host processor of the
     system performing the compilation.  ‘-mcpu=native’ has no effect if
     GCC does not recognize the processor.

     The other options specify a specific processor.  Code generated
     under those options runs best on that processor, and may not run at
     all on others.

     The ‘-mcpu’ options automatically enable or disable the following
     options:

          -maltivec  -mfprnd  -mhard-float  -mmfcrf  -mmultiple
          -mpopcntb  -mpopcntd  -mpowerpc64
          -mpowerpc-gpopt  -mpowerpc-gfxopt
          -mmulhw  -mdlmzb  -mmfpgpr  -mvsx
          -mcrypto  -mhtm  -mpower8-fusion  -mpower8-vector
          -mquad-memory  -mquad-memory-atomic  -mfloat128
          -mfloat128-hardware -mprefixed -mpcrel -mmma
          -mrop-protect

     The particular options set for any particular CPU varies between
     compiler versions, depending on what setting seems to produce
     optimal code for that CPU; it doesn't necessarily reflect the
     actual hardware's capabilities.  If you wish to set an individual
     option to a particular value, you may specify it after the ‘-mcpu’
     option, like ‘-mcpu=970 -mno-altivec’.

     On AIX, the ‘-maltivec’ and ‘-mpowerpc64’ options are not enabled
     or disabled by the ‘-mcpu’ option at present because AIX does not
     have full support for these options.  You may still enable or
     disable them individually if you're sure it'll work in your
     environment.

‘-mtune=CPU_TYPE’
     Set the instruction scheduling parameters for machine type
     CPU_TYPE, but do not set the architecture type or register usage,
     as ‘-mcpu=CPU_TYPE’ does.  The same values for CPU_TYPE are used
     for ‘-mtune’ as for ‘-mcpu’.  If both are specified, the code
     generated uses the architecture and registers set by ‘-mcpu’, but
     the scheduling parameters set by ‘-mtune’.

‘-mcmodel=small’
     Generate PowerPC64 code for the small model: The TOC is limited to
     64k.

‘-mcmodel=medium’
     Generate PowerPC64 code for the medium model: The TOC and other
     static data may be up to a total of 4G in size.  This is the
     default for 64-bit Linux.

‘-mcmodel=large’
     Generate PowerPC64 code for the large model: The TOC may be up to
     4G in size.  Other data and code is only limited by the 64-bit
     address space.

‘-maltivec’
‘-mno-altivec’
     Generate code that uses (does not use) AltiVec instructions, and
     also enable the use of built-in functions that allow more direct
     access to the AltiVec instruction set.  You may also need to set
     ‘-mabi=altivec’ to adjust the current ABI with AltiVec ABI
     enhancements.

     When ‘-maltivec’ is used, the element order for AltiVec intrinsics
     such as ‘vec_splat’, ‘vec_extract’, and ‘vec_insert’ match array
     element order corresponding to the endianness of the target.  That
     is, element zero identifies the leftmost element in a vector
     register when targeting a big-endian platform, and identifies the
     rightmost element in a vector register when targeting a
     little-endian platform.

‘-mvrsave’
‘-mno-vrsave’
     Generate VRSAVE instructions when generating AltiVec code.

‘-msecure-plt’
     Generate code that allows ‘ld’ and ‘ld.so’ to build executables and
     shared libraries with non-executable ‘.plt’ and ‘.got’ sections.
     This is a PowerPC 32-bit SYSV ABI option.

‘-mbss-plt’
     Generate code that uses a BSS ‘.plt’ section that ‘ld.so’ fills in,
     and requires ‘.plt’ and ‘.got’ sections that are both writable and
     executable.  This is a PowerPC 32-bit SYSV ABI option.

‘-misel’
‘-mno-isel’
     This switch enables or disables the generation of ISEL
     instructions.

‘-mvsx’
‘-mno-vsx’
     Generate code that uses (does not use) vector/scalar (VSX)
     instructions, and also enable the use of built-in functions that
     allow more direct access to the VSX instruction set.

‘-mcrypto’
‘-mno-crypto’
     Enable the use (disable) of the built-in functions that allow
     direct access to the cryptographic instructions that were added in
     version 2.07 of the PowerPC ISA.

‘-mhtm’
‘-mno-htm’
     Enable (disable) the use of the built-in functions that allow
     direct access to the Hardware Transactional Memory (HTM)
     instructions that were added in version 2.07 of the PowerPC ISA.

‘-mpower8-fusion’
‘-mno-power8-fusion’
     Generate code that keeps (does not keeps) some integer operations
     adjacent so that the instructions can be fused together on power8
     and later processors.

‘-mpower8-vector’
‘-mno-power8-vector’
     Generate code that uses (does not use) the vector and scalar
     instructions that were added in version 2.07 of the PowerPC ISA.
     Also enable the use of built-in functions that allow more direct
     access to the vector instructions.

‘-mquad-memory’
‘-mno-quad-memory’
     Generate code that uses (does not use) the non-atomic quad word
     memory instructions.  The ‘-mquad-memory’ option requires use of
     64-bit mode.

‘-mquad-memory-atomic’
‘-mno-quad-memory-atomic’
     Generate code that uses (does not use) the atomic quad word memory
     instructions.  The ‘-mquad-memory-atomic’ option requires use of
     64-bit mode.

‘-mfloat128’
‘-mno-float128’
     Enable/disable the __FLOAT128 keyword for IEEE 128-bit floating
     point and use either software emulation for IEEE 128-bit floating
     point or hardware instructions.

     The VSX instruction set (‘-mvsx’) must be enabled to use the IEEE
     128-bit floating point support.  The IEEE 128-bit floating point is
     only supported on Linux.

     The default for ‘-mfloat128’ is enabled on PowerPC Linux systems
     using the VSX instruction set, and disabled on other systems.

     If you use the ISA 3.0 instruction set (‘-mpower9-vector’ or
     ‘-mcpu=power9’) on a 64-bit system, the IEEE 128-bit floating point
     support will also enable the generation of ISA 3.0 IEEE 128-bit
     floating point instructions.  Otherwise, if you do not specify to
     generate ISA 3.0 instructions or you are targeting a 32-bit big
     endian system, IEEE 128-bit floating point will be done with
     software emulation.

‘-mfloat128-hardware’
‘-mno-float128-hardware’
     Enable/disable using ISA 3.0 hardware instructions to support the
     __FLOAT128 data type.

     The default for ‘-mfloat128-hardware’ is enabled on PowerPC Linux
     systems using the ISA 3.0 instruction set, and disabled on other
     systems.

‘-m32’
‘-m64’
     Generate code for 32-bit or 64-bit environments of Darwin and SVR4
     targets (including GNU/Linux).  The 32-bit environment sets int,
     long and pointer to 32 bits and generates code that runs on any
     PowerPC variant.  The 64-bit environment sets int to 32 bits and
     long and pointer to 64 bits, and generates code for PowerPC64, as
     for ‘-mpowerpc64’.

‘-mfull-toc’
‘-mno-fp-in-toc’
‘-mno-sum-in-toc’
‘-mminimal-toc’
     Modify generation of the TOC (Table Of Contents), which is created
     for every executable file.  The ‘-mfull-toc’ option is selected by
     default.  In that case, GCC allocates at least one TOC entry for
     each unique non-automatic variable reference in your program.  GCC
     also places floating-point constants in the TOC.  However, only
     16,384 entries are available in the TOC.

     If you receive a linker error message that saying you have
     overflowed the available TOC space, you can reduce the amount of
     TOC space used with the ‘-mno-fp-in-toc’ and ‘-mno-sum-in-toc’
     options.  ‘-mno-fp-in-toc’ prevents GCC from putting floating-point
     constants in the TOC and ‘-mno-sum-in-toc’ forces GCC to generate
     code to calculate the sum of an address and a constant at run time
     instead of putting that sum into the TOC.  You may specify one or
     both of these options.  Each causes GCC to produce very slightly
     slower and larger code at the expense of conserving TOC space.

     If you still run out of space in the TOC even when you specify both
     of these options, specify ‘-mminimal-toc’ instead.  This option
     causes GCC to make only one TOC entry for every file.  When you
     specify this option, GCC produces code that is slower and larger
     but which uses extremely little TOC space.  You may wish to use
     this option only on files that contain less frequently-executed
     code.

‘-maix64’
‘-maix32’
     Enable 64-bit AIX ABI and calling convention: 64-bit pointers,
     64-bit ‘long’ type, and the infrastructure needed to support them.
     Specifying ‘-maix64’ implies ‘-mpowerpc64’, while ‘-maix32’
     disables the 64-bit ABI and implies ‘-mno-powerpc64’.  GCC defaults
     to ‘-maix32’.

‘-mxl-compat’
‘-mno-xl-compat’
     Produce code that conforms more closely to IBM XL compiler
     semantics when using AIX-compatible ABI.  Pass floating-point
     arguments to prototyped functions beyond the register save area
     (RSA) on the stack in addition to argument FPRs.  Do not assume
     that most significant double in 128-bit long double value is
     properly rounded when comparing values and converting to double.
     Use XL symbol names for long double support routines.

     The AIX calling convention was extended but not initially
     documented to handle an obscure K&R C case of calling a function
     that takes the address of its arguments with fewer arguments than
     declared.  IBM XL compilers access floating-point arguments that do
     not fit in the RSA from the stack when a subroutine is compiled
     without optimization.  Because always storing floating-point
     arguments on the stack is inefficient and rarely needed, this
     option is not enabled by default and only is necessary when calling
     subroutines compiled by IBM XL compilers without optimization.

‘-mpe’
     Support “IBM RS/6000 SP” “Parallel Environment” (PE).  Link an
     application written to use message passing with special startup
     code to enable the application to run.  The system must have PE
     installed in the standard location (‘/usr/lpp/ppe.poe/’), or the
     ‘specs’ file must be overridden with the ‘-specs=’ option to
     specify the appropriate directory location.  The Parallel
     Environment does not support threads, so the ‘-mpe’ option and the
     ‘-pthread’ option are incompatible.

‘-malign-natural’
‘-malign-power’
     On AIX, 32-bit Darwin, and 64-bit PowerPC GNU/Linux, the option
     ‘-malign-natural’ overrides the ABI-defined alignment of larger
     types, such as floating-point doubles, on their natural size-based
     boundary.  The option ‘-malign-power’ instructs GCC to follow the
     ABI-specified alignment rules.  GCC defaults to the standard
     alignment defined in the ABI.

     On 64-bit Darwin, natural alignment is the default, and
     ‘-malign-power’ is not supported.

‘-msoft-float’
‘-mhard-float’
     Generate code that does not use (uses) the floating-point register
     set.  Software floating-point emulation is provided if you use the
     ‘-msoft-float’ option, and pass the option to GCC when linking.

‘-mmultiple’
‘-mno-multiple’
     Generate code that uses (does not use) the load multiple word
     instructions and the store multiple word instructions.  These
     instructions are generated by default on POWER systems, and not
     generated on PowerPC systems.  Do not use ‘-mmultiple’ on
     little-endian PowerPC systems, since those instructions do not work
     when the processor is in little-endian mode.  The exceptions are
     PPC740 and PPC750 which permit these instructions in little-endian
     mode.

‘-mupdate’
‘-mno-update’
     Generate code that uses (does not use) the load or store
     instructions that update the base register to the address of the
     calculated memory location.  These instructions are generated by
     default.  If you use ‘-mno-update’, there is a small window between
     the time that the stack pointer is updated and the address of the
     previous frame is stored, which means code that walks the stack
     frame across interrupts or signals may get corrupted data.

‘-mavoid-indexed-addresses’
‘-mno-avoid-indexed-addresses’
     Generate code that tries to avoid (not avoid) the use of indexed
     load or store instructions.  These instructions can incur a
     performance penalty on Power6 processors in certain situations,
     such as when stepping through large arrays that cross a 16M
     boundary.  This option is enabled by default when targeting Power6
     and disabled otherwise.

‘-mfused-madd’
‘-mno-fused-madd’
     Generate code that uses (does not use) the floating-point multiply
     and accumulate instructions.  These instructions are generated by
     default if hardware floating point is used.  The machine-dependent
     ‘-mfused-madd’ option is now mapped to the machine-independent
     ‘-ffp-contract=fast’ option, and ‘-mno-fused-madd’ is mapped to
     ‘-ffp-contract=off’.

‘-mmulhw’
‘-mno-mulhw’
     Generate code that uses (does not use) the half-word multiply and
     multiply-accumulate instructions on the IBM 405, 440, 464 and 476
     processors.  These instructions are generated by default when
     targeting those processors.

‘-mdlmzb’
‘-mno-dlmzb’
     Generate code that uses (does not use) the string-search ‘dlmzb’
     instruction on the IBM 405, 440, 464 and 476 processors.  This
     instruction is generated by default when targeting those
     processors.

‘-mno-bit-align’
‘-mbit-align’
     On System V.4 and embedded PowerPC systems do not (do) force
     structures and unions that contain bit-fields to be aligned to the
     base type of the bit-field.

     For example, by default a structure containing nothing but 8
     ‘unsigned’ bit-fields of length 1 is aligned to a 4-byte boundary
     and has a size of 4 bytes.  By using ‘-mno-bit-align’, the
     structure is aligned to a 1-byte boundary and is 1 byte in size.

‘-mno-strict-align’
‘-mstrict-align’
     On System V.4 and embedded PowerPC systems do not (do) assume that
     unaligned memory references are handled by the system.

‘-mrelocatable’
‘-mno-relocatable’
     Generate code that allows (does not allow) a static executable to
     be relocated to a different address at run time.  A simple embedded
     PowerPC system loader should relocate the entire contents of
     ‘.got2’ and 4-byte locations listed in the ‘.fixup’ section, a
     table of 32-bit addresses generated by this option.  For this to
     work, all objects linked together must be compiled with
     ‘-mrelocatable’ or ‘-mrelocatable-lib’.  ‘-mrelocatable’ code
     aligns the stack to an 8-byte boundary.

‘-mrelocatable-lib’
‘-mno-relocatable-lib’
     Like ‘-mrelocatable’, ‘-mrelocatable-lib’ generates a ‘.fixup’
     section to allow static executables to be relocated at run time,
     but ‘-mrelocatable-lib’ does not use the smaller stack alignment of
     ‘-mrelocatable’.  Objects compiled with ‘-mrelocatable-lib’ may be
     linked with objects compiled with any combination of the
     ‘-mrelocatable’ options.

‘-mno-toc’
‘-mtoc’
     On System V.4 and embedded PowerPC systems do not (do) assume that
     register 2 contains a pointer to a global area pointing to the
     addresses used in the program.

‘-mlittle’
‘-mlittle-endian’
     On System V.4 and embedded PowerPC systems compile code for the
     processor in little-endian mode.  The ‘-mlittle-endian’ option is
     the same as ‘-mlittle’.

‘-mbig’
‘-mbig-endian’
     On System V.4 and embedded PowerPC systems compile code for the
     processor in big-endian mode.  The ‘-mbig-endian’ option is the
     same as ‘-mbig’.

‘-mdynamic-no-pic’
     On Darwin and Mac OS X systems, compile code so that it is not
     relocatable, but that its external references are relocatable.  The
     resulting code is suitable for applications, but not shared
     libraries.

‘-msingle-pic-base’
     Treat the register used for PIC addressing as read-only, rather
     than loading it in the prologue for each function.  The runtime
     system is responsible for initializing this register with an
     appropriate value before execution begins.

‘-mprioritize-restricted-insns=PRIORITY’
     This option controls the priority that is assigned to dispatch-slot
     restricted instructions during the second scheduling pass.  The
     argument PRIORITY takes the value ‘0’, ‘1’, or ‘2’ to assign no,
     highest, or second-highest (respectively) priority to dispatch-slot
     restricted instructions.

‘-msched-costly-dep=DEPENDENCE_TYPE’
     This option controls which dependences are considered costly by the
     target during instruction scheduling.  The argument DEPENDENCE_TYPE
     takes one of the following values:

     ‘no’
          No dependence is costly.

     ‘all’
          All dependences are costly.

     ‘true_store_to_load’
          A true dependence from store to load is costly.

     ‘store_to_load’
          Any dependence from store to load is costly.

     NUMBER
          Any dependence for which the latency is greater than or equal
          to NUMBER is costly.

‘-minsert-sched-nops=SCHEME’
     This option controls which NOP insertion scheme is used during the
     second scheduling pass.  The argument SCHEME takes one of the
     following values:

     ‘no’
          Don't insert NOPs.

     ‘pad’
          Pad with NOPs any dispatch group that has vacant issue slots,
          according to the scheduler's grouping.

     ‘regroup_exact’
          Insert NOPs to force costly dependent insns into separate
          groups.  Insert exactly as many NOPs as needed to force an
          insn to a new group, according to the estimated processor
          grouping.

     NUMBER
          Insert NOPs to force costly dependent insns into separate
          groups.  Insert NUMBER NOPs to force an insn to a new group.

‘-mcall-sysv’
     On System V.4 and embedded PowerPC systems compile code using
     calling conventions that adhere to the March 1995 draft of the
     System V Application Binary Interface, PowerPC processor
     supplement.  This is the default unless you configured GCC using
     ‘powerpc-*-eabiaix’.

‘-mcall-sysv-eabi’
‘-mcall-eabi’
     Specify both ‘-mcall-sysv’ and ‘-meabi’ options.

‘-mcall-sysv-noeabi’
     Specify both ‘-mcall-sysv’ and ‘-mno-eabi’ options.

‘-mcall-aixdesc’
     On System V.4 and embedded PowerPC systems compile code for the AIX
     operating system.

‘-mcall-linux’
     On System V.4 and embedded PowerPC systems compile code for the
     Linux-based GNU system.

‘-mcall-freebsd’
     On System V.4 and embedded PowerPC systems compile code for the
     FreeBSD operating system.

‘-mcall-netbsd’
     On System V.4 and embedded PowerPC systems compile code for the
     NetBSD operating system.

‘-mcall-openbsd’
     On System V.4 and embedded PowerPC systems compile code for the
     OpenBSD operating system.

‘-mtraceback=TRACEBACK_TYPE’
     Select the type of traceback table.  Valid values for
     TRACEBACK_TYPE are ‘full’, ‘part’, and ‘no’.

‘-maix-struct-return’
     Return all structures in memory (as specified by the AIX ABI).

‘-msvr4-struct-return’
     Return structures smaller than 8 bytes in registers (as specified
     by the SVR4 ABI).

‘-mabi=ABI-TYPE’
     Extend the current ABI with a particular extension, or remove such
     extension.  Valid values are: ‘altivec’, ‘no-altivec’,
     ‘ibmlongdouble’, ‘ieeelongdouble’, ‘elfv1’, ‘elfv2’, and for AIX:
     ‘vec-extabi’, ‘vec-default’.

‘-mabi=ibmlongdouble’
     Change the current ABI to use IBM extended-precision long double.
     This is not likely to work if your system defaults to using IEEE
     extended-precision long double.  If you change the long double type
     from IEEE extended-precision, the compiler will issue a warning
     unless you use the ‘-Wno-psabi’ option.  Requires
     ‘-mlong-double-128’ to be enabled.

‘-mabi=ieeelongdouble’
     Change the current ABI to use IEEE extended-precision long double.
     This is not likely to work if your system defaults to using IBM
     extended-precision long double.  If you change the long double type
     from IBM extended-precision, the compiler will issue a warning
     unless you use the ‘-Wno-psabi’ option.  Requires
     ‘-mlong-double-128’ to be enabled.

‘-mabi=elfv1’
     Change the current ABI to use the ELFv1 ABI. This is the default
     ABI for big-endian PowerPC 64-bit Linux.  Overriding the default
     ABI requires special system support and is likely to fail in
     spectacular ways.

‘-mabi=elfv2’
     Change the current ABI to use the ELFv2 ABI. This is the default
     ABI for little-endian PowerPC 64-bit Linux.  Overriding the default
     ABI requires special system support and is likely to fail in
     spectacular ways.

‘-mgnu-attribute’
‘-mno-gnu-attribute’
     Emit .gnu_attribute assembly directives to set tag/value pairs in a
     .gnu.attributes section that specify ABI variations in function
     parameters or return values.

‘-mprototype’
‘-mno-prototype’
     On System V.4 and embedded PowerPC systems assume that all calls to
     variable argument functions are properly prototyped.  Otherwise,
     the compiler must insert an instruction before every non-prototyped
     call to set or clear bit 6 of the condition code register (‘CR’) to
     indicate whether floating-point values are passed in the
     floating-point registers in case the function takes variable
     arguments.  With ‘-mprototype’, only calls to prototyped variable
     argument functions set or clear the bit.

‘-msim’
     On embedded PowerPC systems, assume that the startup module is
     called ‘sim-crt0.o’ and that the standard C libraries are
     ‘libsim.a’ and ‘libc.a’.  This is the default for
     ‘powerpc-*-eabisim’ configurations.

‘-mmvme’
     On embedded PowerPC systems, assume that the startup module is
     called ‘crt0.o’ and the standard C libraries are ‘libmvme.a’ and
     ‘libc.a’.

‘-mads’
     On embedded PowerPC systems, assume that the startup module is
     called ‘crt0.o’ and the standard C libraries are ‘libads.a’ and
     ‘libc.a’.

‘-myellowknife’
     On embedded PowerPC systems, assume that the startup module is
     called ‘crt0.o’ and the standard C libraries are ‘libyk.a’ and
     ‘libc.a’.

‘-mvxworks’
     On System V.4 and embedded PowerPC systems, specify that you are
     compiling for a VxWorks system.

‘-memb’
     On embedded PowerPC systems, set the ‘PPC_EMB’ bit in the ELF flags
     header to indicate that ‘eabi’ extended relocations are used.

‘-meabi’
‘-mno-eabi’
     On System V.4 and embedded PowerPC systems do (do not) adhere to
     the Embedded Applications Binary Interface (EABI), which is a set
     of modifications to the System V.4 specifications.  Selecting
     ‘-meabi’ means that the stack is aligned to an 8-byte boundary, a
     function ‘__eabi’ is called from ‘main’ to set up the EABI
     environment, and the ‘-msdata’ option can use both ‘r2’ and ‘r13’
     to point to two separate small data areas.  Selecting ‘-mno-eabi’
     means that the stack is aligned to a 16-byte boundary, no EABI
     initialization function is called from ‘main’, and the ‘-msdata’
     option only uses ‘r13’ to point to a single small data area.  The
     ‘-meabi’ option is on by default if you configured GCC using one of
     the ‘powerpc*-*-eabi*’ options.

‘-msdata=eabi’
     On System V.4 and embedded PowerPC systems, put small initialized
     ‘const’ global and static data in the ‘.sdata2’ section, which is
     pointed to by register ‘r2’.  Put small initialized non-‘const’
     global and static data in the ‘.sdata’ section, which is pointed to
     by register ‘r13’.  Put small uninitialized global and static data
     in the ‘.sbss’ section, which is adjacent to the ‘.sdata’ section.
     The ‘-msdata=eabi’ option is incompatible with the ‘-mrelocatable’
     option.  The ‘-msdata=eabi’ option also sets the ‘-memb’ option.

‘-msdata=sysv’
     On System V.4 and embedded PowerPC systems, put small global and
     static data in the ‘.sdata’ section, which is pointed to by
     register ‘r13’.  Put small uninitialized global and static data in
     the ‘.sbss’ section, which is adjacent to the ‘.sdata’ section.
     The ‘-msdata=sysv’ option is incompatible with the ‘-mrelocatable’
     option.

‘-msdata=default’
‘-msdata’
     On System V.4 and embedded PowerPC systems, if ‘-meabi’ is used,
     compile code the same as ‘-msdata=eabi’, otherwise compile code the
     same as ‘-msdata=sysv’.

‘-msdata=data’
     On System V.4 and embedded PowerPC systems, put small global data
     in the ‘.sdata’ section.  Put small uninitialized global data in
     the ‘.sbss’ section.  Do not use register ‘r13’ to address small
     data however.  This is the default behavior unless other ‘-msdata’
     options are used.

‘-msdata=none’
‘-mno-sdata’
     On embedded PowerPC systems, put all initialized global and static
     data in the ‘.data’ section, and all uninitialized data in the
     ‘.bss’ section.

‘-mreadonly-in-sdata’
     Put read-only objects in the ‘.sdata’ section as well.  This is the
     default.

‘-mblock-move-inline-limit=NUM’
     Inline all block moves (such as calls to ‘memcpy’ or structure
     copies) less than or equal to NUM bytes.  The minimum value for NUM
     is 32 bytes on 32-bit targets and 64 bytes on 64-bit targets.  The
     default value is target-specific.

‘-mblock-compare-inline-limit=NUM’
     Generate non-looping inline code for all block compares (such as
     calls to ‘memcmp’ or structure compares) less than or equal to NUM
     bytes.  If NUM is 0, all inline expansion (non-loop and loop) of
     block compare is disabled.  The default value is target-specific.

‘-mblock-compare-inline-loop-limit=NUM’
     Generate an inline expansion using loop code for all block compares
     that are less than or equal to NUM bytes, but greater than the
     limit for non-loop inline block compare expansion.  If the block
     length is not constant, at most NUM bytes will be compared before
     ‘memcmp’ is called to compare the remainder of the block.  The
     default value is target-specific.

‘-mstring-compare-inline-limit=NUM’
     Compare at most NUM string bytes with inline code.  If the
     difference or end of string is not found at the end of the inline
     compare a call to ‘strcmp’ or ‘strncmp’ will take care of the rest
     of the comparison.  The default is 64 bytes.

‘-G NUM’
     On embedded PowerPC systems, put global and static items less than
     or equal to NUM bytes into the small data or BSS sections instead
     of the normal data or BSS section.  By default, NUM is 8.  The ‘-G
     NUM’ switch is also passed to the linker.  All modules should be
     compiled with the same ‘-G NUM’ value.

‘-mregnames’
‘-mno-regnames’
     On System V.4 and embedded PowerPC systems do (do not) emit
     register names in the assembly language output using symbolic
     forms.

‘-mlongcall’
‘-mno-longcall’
     By default assume that all calls are far away so that a longer and
     more expensive calling sequence is required.  This is required for
     calls farther than 32 megabytes (33,554,432 bytes) from the current
     location.  A short call is generated if the compiler knows the call
     cannot be that far away.  This setting can be overridden by the
     ‘shortcall’ function attribute, or by ‘#pragma longcall(0)’.

     Some linkers are capable of detecting out-of-range calls and
     generating glue code on the fly.  On these systems, long calls are
     unnecessary and generate slower code.  As of this writing, the AIX
     linker can do this, as can the GNU linker for PowerPC/64.  It is
     planned to add this feature to the GNU linker for 32-bit PowerPC
     systems as well.

     On PowerPC64 ELFv2 and 32-bit PowerPC systems with newer GNU
     linkers, GCC can generate long calls using an inline PLT call
     sequence (see ‘-mpltseq’).  PowerPC with ‘-mbss-plt’ and PowerPC64
     ELFv1 (big-endian) do not support inline PLT calls.

     On Darwin/PPC systems, ‘#pragma longcall’ generates ‘jbsr callee,
     L42’, plus a “branch island” (glue code).  The two target addresses
     represent the callee and the branch island.  The Darwin/PPC linker
     prefers the first address and generates a ‘bl callee’ if the PPC
     ‘bl’ instruction reaches the callee directly; otherwise, the linker
     generates ‘bl L42’ to call the branch island.  The branch island is
     appended to the body of the calling function; it computes the full
     32-bit address of the callee and jumps to it.

     On Mach-O (Darwin) systems, this option directs the compiler emit
     to the glue for every direct call, and the Darwin linker decides
     whether to use or discard it.

     In the future, GCC may ignore all longcall specifications when the
     linker is known to generate glue.

‘-mpltseq’
‘-mno-pltseq’
     Implement (do not implement) -fno-plt and long calls using an
     inline PLT call sequence that supports lazy linking and long calls
     to functions in dlopen'd shared libraries.  Inline PLT calls are
     only supported on PowerPC64 ELFv2 and 32-bit PowerPC systems with
     newer GNU linkers, and are enabled by default if the support is
     detected when configuring GCC, and, in the case of 32-bit PowerPC,
     if GCC is configured with ‘--enable-secureplt’.  ‘-mpltseq’ code
     and ‘-mbss-plt’ 32-bit PowerPC relocatable objects may not be
     linked together.

‘-mtls-markers’
‘-mno-tls-markers’
     Mark (do not mark) calls to ‘__tls_get_addr’ with a relocation
     specifying the function argument.  The relocation allows the linker
     to reliably associate function call with argument setup
     instructions for TLS optimization, which in turn allows GCC to
     better schedule the sequence.

‘-mrecip’
‘-mno-recip’
     This option enables use of the reciprocal estimate and reciprocal
     square root estimate instructions with additional Newton-Raphson
     steps to increase precision instead of doing a divide or square
     root and divide for floating-point arguments.  You should use the
     ‘-ffast-math’ option when using ‘-mrecip’ (or at least
     ‘-funsafe-math-optimizations’, ‘-ffinite-math-only’,
     ‘-freciprocal-math’ and ‘-fno-trapping-math’).  Note that while the
     throughput of the sequence is generally higher than the throughput
     of the non-reciprocal instruction, the precision of the sequence
     can be decreased by up to 2 ulp (i.e. the inverse of 1.0 equals
     0.99999994) for reciprocal square roots.

‘-mrecip=OPT’
     This option controls which reciprocal estimate instructions may be
     used.  OPT is a comma-separated list of options, which may be
     preceded by a ‘!’ to invert the option:

     ‘all’
          Enable all estimate instructions.

     ‘default’
          Enable the default instructions, equivalent to ‘-mrecip’.

     ‘none’
          Disable all estimate instructions, equivalent to ‘-mno-recip’.

     ‘div’
          Enable the reciprocal approximation instructions for both
          single and double precision.

     ‘divf’
          Enable the single-precision reciprocal approximation
          instructions.

     ‘divd’
          Enable the double-precision reciprocal approximation
          instructions.

     ‘rsqrt’
          Enable the reciprocal square root approximation instructions
          for both single and double precision.

     ‘rsqrtf’
          Enable the single-precision reciprocal square root
          approximation instructions.

     ‘rsqrtd’
          Enable the double-precision reciprocal square root
          approximation instructions.

     So, for example, ‘-mrecip=all,!rsqrtd’ enables all of the
     reciprocal estimate instructions, except for the ‘FRSQRTE’,
     ‘XSRSQRTEDP’, and ‘XVRSQRTEDP’ instructions which handle the
     double-precision reciprocal square root calculations.

‘-mrecip-precision’
‘-mno-recip-precision’
     Assume (do not assume) that the reciprocal estimate instructions
     provide higher-precision estimates than is mandated by the PowerPC
     ABI.  Selecting ‘-mcpu=power6’, ‘-mcpu=power7’ or ‘-mcpu=power8’
     automatically selects ‘-mrecip-precision’.  The double-precision
     square root estimate instructions are not generated by default on
     low-precision machines, since they do not provide an estimate that
     converges after three steps.

‘-mveclibabi=TYPE’
     Specifies the ABI type to use for vectorizing intrinsics using an
     external library.  The only type supported at present is ‘mass’,
     which specifies to use IBM's Mathematical Acceleration Subsystem
     (MASS) libraries for vectorizing intrinsics using external
     libraries.  GCC currently emits calls to ‘acosd2’, ‘acosf4’,
     ‘acoshd2’, ‘acoshf4’, ‘asind2’, ‘asinf4’, ‘asinhd2’, ‘asinhf4’,
     ‘atan2d2’, ‘atan2f4’, ‘atand2’, ‘atanf4’, ‘atanhd2’, ‘atanhf4’,
     ‘cbrtd2’, ‘cbrtf4’, ‘cosd2’, ‘cosf4’, ‘coshd2’, ‘coshf4’, ‘erfcd2’,
     ‘erfcf4’, ‘erfd2’, ‘erff4’, ‘exp2d2’, ‘exp2f4’, ‘expd2’, ‘expf4’,
     ‘expm1d2’, ‘expm1f4’, ‘hypotd2’, ‘hypotf4’, ‘lgammad2’, ‘lgammaf4’,
     ‘log10d2’, ‘log10f4’, ‘log1pd2’, ‘log1pf4’, ‘log2d2’, ‘log2f4’,
     ‘logd2’, ‘logf4’, ‘powd2’, ‘powf4’, ‘sind2’, ‘sinf4’, ‘sinhd2’,
     ‘sinhf4’, ‘sqrtd2’, ‘sqrtf4’, ‘tand2’, ‘tanf4’, ‘tanhd2’, and
     ‘tanhf4’ when generating code for power7.  Both ‘-ftree-vectorize’
     and ‘-funsafe-math-optimizations’ must also be enabled.  The MASS
     libraries must be specified at link time.

‘-mfriz’
‘-mno-friz’
     Generate (do not generate) the ‘friz’ instruction when the
     ‘-funsafe-math-optimizations’ option is used to optimize rounding
     of floating-point values to 64-bit integer and back to floating
     point.  The ‘friz’ instruction does not return the same value if
     the floating-point number is too large to fit in an integer.

‘-mpointers-to-nested-functions’
‘-mno-pointers-to-nested-functions’
     Generate (do not generate) code to load up the static chain
     register (‘r11’) when calling through a pointer on AIX and 64-bit
     Linux systems where a function pointer points to a 3-word
     descriptor giving the function address, TOC value to be loaded in
     register ‘r2’, and static chain value to be loaded in register
     ‘r11’.  The ‘-mpointers-to-nested-functions’ is on by default.  You
     cannot call through pointers to nested functions or pointers to
     functions compiled in other languages that use the static chain if
     you use ‘-mno-pointers-to-nested-functions’.

‘-msave-toc-indirect’
‘-mno-save-toc-indirect’
     Generate (do not generate) code to save the TOC value in the
     reserved stack location in the function prologue if the function
     calls through a pointer on AIX and 64-bit Linux systems.  If the
     TOC value is not saved in the prologue, it is saved just before the
     call through the pointer.  The ‘-mno-save-toc-indirect’ option is
     the default.

‘-mcompat-align-parm’
‘-mno-compat-align-parm’
     Generate (do not generate) code to pass structure parameters with a
     maximum alignment of 64 bits, for compatibility with older versions
     of GCC.

     Older versions of GCC (prior to 4.9.0) incorrectly did not align a
     structure parameter on a 128-bit boundary when that structure
     contained a member requiring 128-bit alignment.  This is corrected
     in more recent versions of GCC. This option may be used to generate
     code that is compatible with functions compiled with older versions
     of GCC.

     The ‘-mno-compat-align-parm’ option is the default.

‘-mstack-protector-guard=GUARD’
‘-mstack-protector-guard-reg=REG’
‘-mstack-protector-guard-offset=OFFSET’
‘-mstack-protector-guard-symbol=SYMBOL’
     Generate stack protection code using canary at GUARD.  Supported
     locations are ‘global’ for global canary or ‘tls’ for per-thread
     canary in the TLS block (the default with GNU libc version 2.4 or
     later).

     With the latter choice the options
     ‘-mstack-protector-guard-reg=REG’ and
     ‘-mstack-protector-guard-offset=OFFSET’ furthermore specify which
     register to use as base register for reading the canary, and from
     what offset from that base register.  The default for those is as
     specified in the relevant ABI.
     ‘-mstack-protector-guard-symbol=SYMBOL’ overrides the offset with a
     symbol reference to a canary in the TLS block.

‘-mpcrel’
‘-mno-pcrel’
     Generate (do not generate) pc-relative addressing.  The ‘-mpcrel’
     option requires that the medium code model (‘-mcmodel=medium’) and
     prefixed addressing (‘-mprefixed’) options are enabled.

‘-mprefixed’
‘-mno-prefixed’
     Generate (do not generate) addressing modes using prefixed load and
     store instructions.  The ‘-mprefixed’ option requires that the
     option ‘-mcpu=power10’ (or later) is enabled.

‘-mmma’
‘-mno-mma’
     Generate (do not generate) the MMA instructions.  The ‘-mma’ option
     requires that the option ‘-mcpu=power10’ (or later) is enabled.

‘-mrop-protect’
‘-mno-rop-protect’
     Generate (do not generate) ROP protection instructions when the
     target processor supports them.  Currently this option disables the
     shrink-wrap optimization (‘-fshrink-wrap’).

‘-mprivileged’
‘-mno-privileged’
     Generate (do not generate) code that will run in privileged state.

‘-mblock-ops-unaligned-vsx’
‘-mno-block-ops-unaligned-vsx’
     Generate (do not generate) unaligned vsx loads and stores for
     inline expansion of ‘memcpy’ and ‘memmove’.


File: gcc.info,  Node: RX Options,  Next: S/390 and zSeries Options,  Prev: RS/6000 and PowerPC Options,  Up: Submodel Options

3.19.46 RX Options
------------------

These command-line options are defined for RX targets:

‘-m64bit-doubles’
‘-m32bit-doubles’
     Make the ‘double’ data type be 64 bits (‘-m64bit-doubles’) or 32
     bits (‘-m32bit-doubles’) in size.  The default is
     ‘-m32bit-doubles’.  _Note_ RX floating-point hardware only works on
     32-bit values, which is why the default is ‘-m32bit-doubles’.

‘-fpu’
‘-nofpu’
     Enables (‘-fpu’) or disables (‘-nofpu’) the use of RX
     floating-point hardware.  The default is enabled for the RX600
     series and disabled for the RX200 series.

     Floating-point instructions are only generated for 32-bit
     floating-point values, however, so the FPU hardware is not used for
     doubles if the ‘-m64bit-doubles’ option is used.

     _Note_ If the ‘-fpu’ option is enabled then
     ‘-funsafe-math-optimizations’ is also enabled automatically.  This
     is because the RX FPU instructions are themselves unsafe.

‘-mcpu=NAME’
     Selects the type of RX CPU to be targeted.  Currently three types
     are supported, the generic ‘RX600’ and ‘RX200’ series hardware and
     the specific ‘RX610’ CPU. The default is ‘RX600’.

     The only difference between ‘RX600’ and ‘RX610’ is that the ‘RX610’
     does not support the ‘MVTIPL’ instruction.

     The ‘RX200’ series does not have a hardware floating-point unit and
     so ‘-nofpu’ is enabled by default when this type is selected.

‘-mbig-endian-data’
‘-mlittle-endian-data’
     Store data (but not code) in the big-endian format.  The default is
     ‘-mlittle-endian-data’, i.e. to store data in the little-endian
     format.

‘-msmall-data-limit=N’
     Specifies the maximum size in bytes of global and static variables
     which can be placed into the small data area.  Using the small data
     area can lead to smaller and faster code, but the size of area is
     limited and it is up to the programmer to ensure that the area does
     not overflow.  Also when the small data area is used one of the
     RX's registers (usually ‘r13’) is reserved for use pointing to this
     area, so it is no longer available for use by the compiler.  This
     could result in slower and/or larger code if variables are pushed
     onto the stack instead of being held in this register.

     Note, common variables (variables that have not been initialized)
     and constants are not placed into the small data area as they are
     assigned to other sections in the output executable.

     The default value is zero, which disables this feature.  Note, this
     feature is not enabled by default with higher optimization levels
     (‘-O2’ etc) because of the potentially detrimental effects of
     reserving a register.  It is up to the programmer to experiment and
     discover whether this feature is of benefit to their program.  See
     the description of the ‘-mpid’ option for a description of how the
     actual register to hold the small data area pointer is chosen.

‘-msim’
‘-mno-sim’
     Use the simulator runtime.  The default is to use the libgloss
     board-specific runtime.

‘-mas100-syntax’
‘-mno-as100-syntax’
     When generating assembler output use a syntax that is compatible
     with Renesas's AS100 assembler.  This syntax can also be handled by
     the GAS assembler, but it has some restrictions so it is not
     generated by default.

‘-mmax-constant-size=N’
     Specifies the maximum size, in bytes, of a constant that can be
     used as an operand in a RX instruction.  Although the RX
     instruction set does allow constants of up to 4 bytes in length to
     be used in instructions, a longer value equates to a longer
     instruction.  Thus in some circumstances it can be beneficial to
     restrict the size of constants that are used in instructions.
     Constants that are too big are instead placed into a constant pool
     and referenced via register indirection.

     The value N can be between 0 and 4.  A value of 0 (the default) or
     4 means that constants of any size are allowed.

‘-mrelax’
     Enable linker relaxation.  Linker relaxation is a process whereby
     the linker attempts to reduce the size of a program by finding
     shorter versions of various instructions.  Disabled by default.

‘-mint-register=N’
     Specify the number of registers to reserve for fast interrupt
     handler functions.  The value N can be between 0 and 4.  A value of
     1 means that register ‘r13’ is reserved for the exclusive use of
     fast interrupt handlers.  A value of 2 reserves ‘r13’ and ‘r12’.  A
     value of 3 reserves ‘r13’, ‘r12’ and ‘r11’, and a value of 4
     reserves ‘r13’ through ‘r10’.  A value of 0, the default, does not
     reserve any registers.

‘-msave-acc-in-interrupts’
     Specifies that interrupt handler functions should preserve the
     accumulator register.  This is only necessary if normal code might
     use the accumulator register, for example because it performs
     64-bit multiplications.  The default is to ignore the accumulator
     as this makes the interrupt handlers faster.

‘-mpid’
‘-mno-pid’
     Enables the generation of position independent data.  When enabled
     any access to constant data is done via an offset from a base
     address held in a register.  This allows the location of constant
     data to be determined at run time without requiring the executable
     to be relocated, which is a benefit to embedded applications with
     tight memory constraints.  Data that can be modified is not
     affected by this option.

     Note, using this feature reserves a register, usually ‘r13’, for
     the constant data base address.  This can result in slower and/or
     larger code, especially in complicated functions.

     The actual register chosen to hold the constant data base address
     depends upon whether the ‘-msmall-data-limit’ and/or the
     ‘-mint-register’ command-line options are enabled.  Starting with
     register ‘r13’ and proceeding downwards, registers are allocated
     first to satisfy the requirements of ‘-mint-register’, then ‘-mpid’
     and finally ‘-msmall-data-limit’.  Thus it is possible for the
     small data area register to be ‘r8’ if both ‘-mint-register=4’ and
     ‘-mpid’ are specified on the command line.

     By default this feature is not enabled.  The default can be
     restored via the ‘-mno-pid’ command-line option.

‘-mno-warn-multiple-fast-interrupts’
‘-mwarn-multiple-fast-interrupts’
     Prevents GCC from issuing a warning message if it finds more than
     one fast interrupt handler when it is compiling a file.  The
     default is to issue a warning for each extra fast interrupt handler
     found, as the RX only supports one such interrupt.

‘-mallow-string-insns’
‘-mno-allow-string-insns’
     Enables or disables the use of the string manipulation instructions
     ‘SMOVF’, ‘SCMPU’, ‘SMOVB’, ‘SMOVU’, ‘SUNTIL’ ‘SWHILE’ and also the
     ‘RMPA’ instruction.  These instructions may prefetch data, which is
     not safe to do if accessing an I/O register.  (See section 12.2.7
     of the RX62N Group User's Manual for more information).

     The default is to allow these instructions, but it is not possible
     for GCC to reliably detect all circumstances where a string
     instruction might be used to access an I/O register, so their use
     cannot be disabled automatically.  Instead it is reliant upon the
     programmer to use the ‘-mno-allow-string-insns’ option if their
     program accesses I/O space.

     When the instructions are enabled GCC defines the C preprocessor
     symbol ‘__RX_ALLOW_STRING_INSNS__’, otherwise it defines the symbol
     ‘__RX_DISALLOW_STRING_INSNS__’.

‘-mjsr’
‘-mno-jsr’
     Use only (or not only) ‘JSR’ instructions to access functions.
     This option can be used when code size exceeds the range of ‘BSR’
     instructions.  Note that ‘-mno-jsr’ does not mean to not use ‘JSR’
     but instead means that any type of branch may be used.

 _Note:_ The generic GCC command-line option ‘-ffixed-REG’ has special
significance to the RX port when used with the ‘interrupt’ function
attribute.  This attribute indicates a function intended to process fast
interrupts.  GCC ensures that it only uses the registers ‘r10’, ‘r11’,
‘r12’ and/or ‘r13’ and only provided that the normal use of the
corresponding registers have been restricted via the ‘-ffixed-REG’ or
‘-mint-register’ command-line options.


File: gcc.info,  Node: S/390 and zSeries Options,  Next: Score Options,  Prev: RX Options,  Up: Submodel Options

3.19.47 S/390 and zSeries Options
---------------------------------

These are the ‘-m’ options defined for the S/390 and zSeries
architecture.

‘-mhard-float’
‘-msoft-float’
     Use (do not use) the hardware floating-point instructions and
     registers for floating-point operations.  When ‘-msoft-float’ is
     specified, functions in ‘libgcc.a’ are used to perform
     floating-point operations.  When ‘-mhard-float’ is specified, the
     compiler generates IEEE floating-point instructions.  This is the
     default.

‘-mhard-dfp’
‘-mno-hard-dfp’
     Use (do not use) the hardware decimal-floating-point instructions
     for decimal-floating-point operations.  When ‘-mno-hard-dfp’ is
     specified, functions in ‘libgcc.a’ are used to perform
     decimal-floating-point operations.  When ‘-mhard-dfp’ is specified,
     the compiler generates decimal-floating-point hardware
     instructions.  This is the default for ‘-march=z9-ec’ or higher.

‘-mlong-double-64’
‘-mlong-double-128’
     These switches control the size of ‘long double’ type.  A size of
     64 bits makes the ‘long double’ type equivalent to the ‘double’
     type.  This is the default.

‘-mbackchain’
‘-mno-backchain’
     Store (do not store) the address of the caller's frame as backchain
     pointer into the callee's stack frame.  A backchain may be needed
     to allow debugging using tools that do not understand DWARF call
     frame information.  When ‘-mno-packed-stack’ is in effect, the
     backchain pointer is stored at the bottom of the stack frame; when
     ‘-mpacked-stack’ is in effect, the backchain is placed into the
     topmost word of the 96/160 byte register save area.

     In general, code compiled with ‘-mbackchain’ is call-compatible
     with code compiled with ‘-mno-backchain’; however, use of the
     backchain for debugging purposes usually requires that the whole
     binary is built with ‘-mbackchain’.  Note that the combination of
     ‘-mbackchain’, ‘-mpacked-stack’ and ‘-mhard-float’ is not
     supported.  In order to build a linux kernel use ‘-msoft-float’.

     The default is to not maintain the backchain.

‘-mpacked-stack’
‘-mno-packed-stack’
     Use (do not use) the packed stack layout.  When ‘-mno-packed-stack’
     is specified, the compiler uses the all fields of the 96/160 byte
     register save area only for their default purpose; unused fields
     still take up stack space.  When ‘-mpacked-stack’ is specified,
     register save slots are densely packed at the top of the register
     save area; unused space is reused for other purposes, allowing for
     more efficient use of the available stack space.  However, when
     ‘-mbackchain’ is also in effect, the topmost word of the save area
     is always used to store the backchain, and the return address
     register is always saved two words below the backchain.

     As long as the stack frame backchain is not used, code generated
     with ‘-mpacked-stack’ is call-compatible with code generated with
     ‘-mno-packed-stack’.  Note that some non-FSF releases of GCC 2.95
     for S/390 or zSeries generated code that uses the stack frame
     backchain at run time, not just for debugging purposes.  Such code
     is not call-compatible with code compiled with ‘-mpacked-stack’.
     Also, note that the combination of ‘-mbackchain’, ‘-mpacked-stack’
     and ‘-mhard-float’ is not supported.  In order to build a linux
     kernel use ‘-msoft-float’.

     The default is to not use the packed stack layout.

‘-msmall-exec’
‘-mno-small-exec’
     Generate (or do not generate) code using the ‘bras’ instruction to
     do subroutine calls.  This only works reliably if the total
     executable size does not exceed 64k.  The default is to use the
     ‘basr’ instruction instead, which does not have this limitation.

‘-m64’
‘-m31’
     When ‘-m31’ is specified, generate code compliant to the GNU/Linux
     for S/390 ABI.  When ‘-m64’ is specified, generate code compliant
     to the GNU/Linux for zSeries ABI.  This allows GCC in particular to
     generate 64-bit instructions.  For the ‘s390’ targets, the default
     is ‘-m31’, while the ‘s390x’ targets default to ‘-m64’.

‘-mzarch’
‘-mesa’
     When ‘-mzarch’ is specified, generate code using the instructions
     available on z/Architecture.  When ‘-mesa’ is specified, generate
     code using the instructions available on ESA/390.  Note that
     ‘-mesa’ is not possible with ‘-m64’.  When generating code
     compliant to the GNU/Linux for S/390 ABI, the default is ‘-mesa’.
     When generating code compliant to the GNU/Linux for zSeries ABI,
     the default is ‘-mzarch’.

‘-mhtm’
‘-mno-htm’
     The ‘-mhtm’ option enables a set of builtins making use of
     instructions available with the transactional execution facility
     introduced with the IBM zEnterprise EC12 machine generation *note
     S/390 System z Built-in Functions::.  ‘-mhtm’ is enabled by default
     when using ‘-march=zEC12’.

‘-mvx’
‘-mno-vx’
     When ‘-mvx’ is specified, generate code using the instructions
     available with the vector extension facility introduced with the
     IBM z13 machine generation.  This option changes the ABI for some
     vector type values with regard to alignment and calling
     conventions.  In case vector type values are being used in an
     ABI-relevant context a GAS ‘.gnu_attribute’ command will be added
     to mark the resulting binary with the ABI used.  ‘-mvx’ is enabled
     by default when using ‘-march=z13’.

‘-mzvector’
‘-mno-zvector’
     The ‘-mzvector’ option enables vector language extensions and
     builtins using instructions available with the vector extension
     facility introduced with the IBM z13 machine generation.  This
     option adds support for ‘vector’ to be used as a keyword to define
     vector type variables and arguments.  ‘vector’ is only available
     when GNU extensions are enabled.  It will not be expanded when
     requesting strict standard compliance e.g. with ‘-std=c99’.  In
     addition to the GCC low-level builtins ‘-mzvector’ enables a set of
     builtins added for compatibility with AltiVec-style implementations
     like Power and Cell.  In order to make use of these builtins the
     header file ‘vecintrin.h’ needs to be included.  ‘-mzvector’ is
     disabled by default.

‘-mmvcle’
‘-mno-mvcle’
     Generate (or do not generate) code using the ‘mvcle’ instruction to
     perform block moves.  When ‘-mno-mvcle’ is specified, use a ‘mvc’
     loop instead.  This is the default unless optimizing for size.

‘-mdebug’
‘-mno-debug’
     Print (or do not print) additional debug information when
     compiling.  The default is to not print debug information.

‘-march=CPU-TYPE’
     Generate code that runs on CPU-TYPE, which is the name of a system
     representing a certain processor type.  Possible values for
     CPU-TYPE are ‘z900’/‘arch5’, ‘z990’/‘arch6’, ‘z9-109’,
     ‘z9-ec’/‘arch7’, ‘z10’/‘arch8’, ‘z196’/‘arch9’, ‘zEC12’,
     ‘z13’/‘arch11’, ‘z14’/‘arch12’, ‘z15’/‘arch13’, ‘z16’/‘arch14’, and
     ‘native’.

     The default is ‘-march=z900’.

     Specifying ‘native’ as cpu type can be used to select the best
     architecture option for the host processor.  ‘-march=native’ has no
     effect if GCC does not recognize the processor.

‘-mtune=CPU-TYPE’
     Tune to CPU-TYPE everything applicable about the generated code,
     except for the ABI and the set of available instructions.  The list
     of CPU-TYPE values is the same as for ‘-march’.  The default is the
     value used for ‘-march’.

‘-mtpf-trace’
‘-mno-tpf-trace’
     Generate code that adds (does not add) in TPF OS specific branches
     to trace routines in the operating system.  This option is off by
     default, even when compiling for the TPF OS.

‘-mtpf-trace-skip’
‘-mno-tpf-trace-skip’
     Generate code that changes (does not change) the default branch
     targets enabled by ‘-mtpf-trace’ to point to specialized trace
     routines providing the ability of selectively skipping function
     trace entries for the TPF OS. This option is off by default, even
     when compiling for the TPF OS and specifying ‘-mtpf-trace’.

‘-mfused-madd’
‘-mno-fused-madd’
     Generate code that uses (does not use) the floating-point multiply
     and accumulate instructions.  These instructions are generated by
     default if hardware floating point is used.

‘-mwarn-framesize=FRAMESIZE’
     Emit a warning if the current function exceeds the given frame
     size.  Because this is a compile-time check it doesn't need to be a
     real problem when the program runs.  It is intended to identify
     functions that most probably cause a stack overflow.  It is useful
     to be used in an environment with limited stack size e.g. the linux
     kernel.

‘-mwarn-dynamicstack’
     Emit a warning if the function calls ‘alloca’ or uses
     dynamically-sized arrays.  This is generally a bad idea with a
     limited stack size.

‘-mstack-guard=STACK-GUARD’
‘-mstack-size=STACK-SIZE’
     If these options are provided the S/390 back end emits additional
     instructions in the function prologue that trigger a trap if the
     stack size is STACK-GUARD bytes above the STACK-SIZE (remember that
     the stack on S/390 grows downward).  If the STACK-GUARD option is
     omitted the smallest power of 2 larger than the frame size of the
     compiled function is chosen.  These options are intended to be used
     to help debugging stack overflow problems.  The additionally
     emitted code causes only little overhead and hence can also be used
     in production-like systems without greater performance degradation.
     The given values have to be exact powers of 2 and STACK-SIZE has to
     be greater than STACK-GUARD without exceeding 64k.  In order to be
     efficient the extra code makes the assumption that the stack starts
     at an address aligned to the value given by STACK-SIZE.  The
     STACK-GUARD option can only be used in conjunction with STACK-SIZE.

‘-mhotpatch=PRE-HALFWORDS,POST-HALFWORDS’
     If the hotpatch option is enabled, a "hot-patching" function
     prologue is generated for all functions in the compilation unit.
     The funtion label is prepended with the given number of two-byte
     NOP instructions (PRE-HALFWORDS, maximum 1000000).  After the
     label, 2 * POST-HALFWORDS bytes are appended, using the largest NOP
     like instructions the architecture allows (maximum 1000000).

     If both arguments are zero, hotpatching is disabled.

     This option can be overridden for individual functions with the
     ‘hotpatch’ attribute.


File: gcc.info,  Node: Score Options,  Next: SH Options,  Prev: S/390 and zSeries Options,  Up: Submodel Options

3.19.48 Score Options
---------------------

These options are defined for Score implementations:

‘-meb’
     Compile code for big-endian mode.  This is the default.

‘-mel’
     Compile code for little-endian mode.

‘-mnhwloop’
     Disable generation of ‘bcnz’ instructions.

‘-muls’
     Enable generation of unaligned load and store instructions.

‘-mmac’
     Enable the use of multiply-accumulate instructions.  Disabled by
     default.

‘-mscore5’
     Specify the SCORE5 as the target architecture.

‘-mscore5u’
     Specify the SCORE5U of the target architecture.

‘-mscore7’
     Specify the SCORE7 as the target architecture.  This is the
     default.

‘-mscore7d’
     Specify the SCORE7D as the target architecture.


File: gcc.info,  Node: SH Options,  Next: Solaris 2 Options,  Prev: Score Options,  Up: Submodel Options

3.19.49 SH Options
------------------

These ‘-m’ options are defined for the SH implementations:

‘-m1’
     Generate code for the SH1.

‘-m2’
     Generate code for the SH2.

‘-m2e’
     Generate code for the SH2e.

‘-m2a-nofpu’
     Generate code for the SH2a without FPU, or for a SH2a-FPU in such a
     way that the floating-point unit is not used.

‘-m2a-single-only’
     Generate code for the SH2a-FPU, in such a way that no
     double-precision floating-point operations are used.

‘-m2a-single’
     Generate code for the SH2a-FPU assuming the floating-point unit is
     in single-precision mode by default.

‘-m2a’
     Generate code for the SH2a-FPU assuming the floating-point unit is
     in double-precision mode by default.

‘-m3’
     Generate code for the SH3.

‘-m3e’
     Generate code for the SH3e.

‘-m4-nofpu’
     Generate code for the SH4 without a floating-point unit.

‘-m4-single-only’
     Generate code for the SH4 with a floating-point unit that only
     supports single-precision arithmetic.

‘-m4-single’
     Generate code for the SH4 assuming the floating-point unit is in
     single-precision mode by default.

‘-m4’
     Generate code for the SH4.

‘-m4-100’
     Generate code for SH4-100.

‘-m4-100-nofpu’
     Generate code for SH4-100 in such a way that the floating-point
     unit is not used.

‘-m4-100-single’
     Generate code for SH4-100 assuming the floating-point unit is in
     single-precision mode by default.

‘-m4-100-single-only’
     Generate code for SH4-100 in such a way that no double-precision
     floating-point operations are used.

‘-m4-200’
     Generate code for SH4-200.

‘-m4-200-nofpu’
     Generate code for SH4-200 without in such a way that the
     floating-point unit is not used.

‘-m4-200-single’
     Generate code for SH4-200 assuming the floating-point unit is in
     single-precision mode by default.

‘-m4-200-single-only’
     Generate code for SH4-200 in such a way that no double-precision
     floating-point operations are used.

‘-m4-300’
     Generate code for SH4-300.

‘-m4-300-nofpu’
     Generate code for SH4-300 without in such a way that the
     floating-point unit is not used.

‘-m4-300-single’
     Generate code for SH4-300 in such a way that no double-precision
     floating-point operations are used.

‘-m4-300-single-only’
     Generate code for SH4-300 in such a way that no double-precision
     floating-point operations are used.

‘-m4-340’
     Generate code for SH4-340 (no MMU, no FPU).

‘-m4-500’
     Generate code for SH4-500 (no FPU). Passes ‘-isa=sh4-nofpu’ to the
     assembler.

‘-m4a-nofpu’
     Generate code for the SH4al-dsp, or for a SH4a in such a way that
     the floating-point unit is not used.

‘-m4a-single-only’
     Generate code for the SH4a, in such a way that no double-precision
     floating-point operations are used.

‘-m4a-single’
     Generate code for the SH4a assuming the floating-point unit is in
     single-precision mode by default.

‘-m4a’
     Generate code for the SH4a.

‘-m4al’
     Same as ‘-m4a-nofpu’, except that it implicitly passes ‘-dsp’ to
     the assembler.  GCC doesn't generate any DSP instructions at the
     moment.

‘-mb’
     Compile code for the processor in big-endian mode.

‘-ml’
     Compile code for the processor in little-endian mode.

‘-mdalign’
     Align doubles at 64-bit boundaries.  Note that this changes the
     calling conventions, and thus some functions from the standard C
     library do not work unless you recompile it first with ‘-mdalign’.

‘-mrelax’
     Shorten some address references at link time, when possible; uses
     the linker option ‘-relax’.

‘-mbigtable’
     Use 32-bit offsets in ‘switch’ tables.  The default is to use
     16-bit offsets.

‘-mbitops’
     Enable the use of bit manipulation instructions on SH2A.

‘-mfmovd’
     Enable the use of the instruction ‘fmovd’.  Check ‘-mdalign’ for
     alignment constraints.

‘-mrenesas’
     Comply with the calling conventions defined by Renesas.

‘-mno-renesas’
     Comply with the calling conventions defined for GCC before the
     Renesas conventions were available.  This option is the default for
     all targets of the SH toolchain.

‘-mnomacsave’
     Mark the ‘MAC’ register as call-clobbered, even if ‘-mrenesas’ is
     given.

‘-mieee’
‘-mno-ieee’
     Control the IEEE compliance of floating-point comparisons, which
     affects the handling of cases where the result of a comparison is
     unordered.  By default ‘-mieee’ is implicitly enabled.  If
     ‘-ffinite-math-only’ is enabled ‘-mno-ieee’ is implicitly set,
     which results in faster floating-point greater-equal and less-equal
     comparisons.  The implicit settings can be overridden by specifying
     either ‘-mieee’ or ‘-mno-ieee’.

‘-minline-ic_invalidate’
     Inline code to invalidate instruction cache entries after setting
     up nested function trampolines.  This option has no effect if
     ‘-musermode’ is in effect and the selected code generation option
     (e.g. ‘-m4’) does not allow the use of the ‘icbi’ instruction.  If
     the selected code generation option does not allow the use of the
     ‘icbi’ instruction, and ‘-musermode’ is not in effect, the inlined
     code manipulates the instruction cache address array directly with
     an associative write.  This not only requires privileged mode at
     run time, but it also fails if the cache line had been mapped via
     the TLB and has become unmapped.

‘-misize’
     Dump instruction size and location in the assembly code.

‘-mpadstruct’
     This option is deprecated.  It pads structures to multiple of 4
     bytes, which is incompatible with the SH ABI.

‘-matomic-model=MODEL’
     Sets the model of atomic operations and additional parameters as a
     comma separated list.  For details on the atomic built-in functions
     see *note __atomic Builtins::.  The following models and parameters
     are supported:

     ‘none’
          Disable compiler generated atomic sequences and emit library
          calls for atomic operations.  This is the default if the
          target is not ‘sh*-*-linux*’.

     ‘soft-gusa’
          Generate GNU/Linux compatible gUSA software atomic sequences
          for the atomic built-in functions.  The generated atomic
          sequences require additional support from the
          interrupt/exception handling code of the system and are only
          suitable for SH3* and SH4* single-core systems.  This option
          is enabled by default when the target is ‘sh*-*-linux*’ and
          SH3* or SH4*.  When the target is SH4A, this option also
          partially utilizes the hardware atomic instructions ‘movli.l’
          and ‘movco.l’ to create more efficient code, unless ‘strict’
          is specified.

     ‘soft-tcb’
          Generate software atomic sequences that use a variable in the
          thread control block.  This is a variation of the gUSA
          sequences which can also be used on SH1* and SH2* targets.
          The generated atomic sequences require additional support from
          the interrupt/exception handling code of the system and are
          only suitable for single-core systems.  When using this model,
          the ‘gbr-offset=’ parameter has to be specified as well.

     ‘soft-imask’
          Generate software atomic sequences that temporarily disable
          interrupts by setting ‘SR.IMASK = 1111’.  This model works
          only when the program runs in privileged mode and is only
          suitable for single-core systems.  Additional support from the
          interrupt/exception handling code of the system is not
          required.  This model is enabled by default when the target is
          ‘sh*-*-linux*’ and SH1* or SH2*.

     ‘hard-llcs’
          Generate hardware atomic sequences using the ‘movli.l’ and
          ‘movco.l’ instructions only.  This is only available on SH4A
          and is suitable for multi-core systems.  Since the hardware
          instructions support only 32 bit atomic variables access to 8
          or 16 bit variables is emulated with 32 bit accesses.  Code
          compiled with this option is also compatible with other
          software atomic model interrupt/exception handling systems if
          executed on an SH4A system.  Additional support from the
          interrupt/exception handling code of the system is not
          required for this model.

     ‘gbr-offset=’
          This parameter specifies the offset in bytes of the variable
          in the thread control block structure that should be used by
          the generated atomic sequences when the ‘soft-tcb’ model has
          been selected.  For other models this parameter is ignored.
          The specified value must be an integer multiple of four and in
          the range 0-1020.

     ‘strict’
          This parameter prevents mixed usage of multiple atomic models,
          even if they are compatible, and makes the compiler generate
          atomic sequences of the specified model only.

‘-mtas’
     Generate the ‘tas.b’ opcode for ‘__atomic_test_and_set’.  Notice
     that depending on the particular hardware and software
     configuration this can degrade overall performance due to the
     operand cache line flushes that are implied by the ‘tas.b’
     instruction.  On multi-core SH4A processors the ‘tas.b’ instruction
     must be used with caution since it can result in data corruption
     for certain cache configurations.

‘-mprefergot’
     When generating position-independent code, emit function calls
     using the Global Offset Table instead of the Procedure Linkage
     Table.

‘-musermode’
‘-mno-usermode’
     Don't allow (allow) the compiler generating privileged mode code.
     Specifying ‘-musermode’ also implies ‘-mno-inline-ic_invalidate’ if
     the inlined code would not work in user mode.  ‘-musermode’ is the
     default when the target is ‘sh*-*-linux*’.  If the target is SH1*
     or SH2* ‘-musermode’ has no effect, since there is no user mode.

‘-multcost=NUMBER’
     Set the cost to assume for a multiply insn.

‘-mdiv=STRATEGY’
     Set the division strategy to be used for integer division
     operations.  STRATEGY can be one of:

     ‘call-div1’
          Calls a library function that uses the single-step division
          instruction ‘div1’ to perform the operation.  Division by zero
          calculates an unspecified result and does not trap.  This is
          the default except for SH4, SH2A and SHcompact.

     ‘call-fp’
          Calls a library function that performs the operation in double
          precision floating point.  Division by zero causes a
          floating-point exception.  This is the default for SHcompact
          with FPU. Specifying this for targets that do not have a
          double precision FPU defaults to ‘call-div1’.

     ‘call-table’
          Calls a library function that uses a lookup table for small
          divisors and the ‘div1’ instruction with case distinction for
          larger divisors.  Division by zero calculates an unspecified
          result and does not trap.  This is the default for SH4.
          Specifying this for targets that do not have dynamic shift
          instructions defaults to ‘call-div1’.

     When a division strategy has not been specified the default
     strategy is selected based on the current target.  For SH2A the
     default strategy is to use the ‘divs’ and ‘divu’ instructions
     instead of library function calls.

‘-maccumulate-outgoing-args’
     Reserve space once for outgoing arguments in the function prologue
     rather than around each call.  Generally beneficial for performance
     and size.  Also needed for unwinding to avoid changing the stack
     frame around conditional code.

‘-mdivsi3_libfunc=NAME’
     Set the name of the library function used for 32-bit signed
     division to NAME.  This only affects the name used in the ‘call’
     division strategies, and the compiler still expects the same sets
     of input/output/clobbered registers as if this option were not
     present.

‘-mfixed-range=REGISTER-RANGE’
     Generate code treating the given register range as fixed registers.
     A fixed register is one that the register allocator cannot use.
     This is useful when compiling kernel code.  A register range is
     specified as two registers separated by a dash.  Multiple register
     ranges can be specified separated by a comma.

‘-mbranch-cost=NUM’
     Assume NUM to be the cost for a branch instruction.  Higher numbers
     make the compiler try to generate more branch-free code if
     possible.  If not specified the value is selected depending on the
     processor type that is being compiled for.

‘-mzdcbranch’
‘-mno-zdcbranch’
     Assume (do not assume) that zero displacement conditional branch
     instructions ‘bt’ and ‘bf’ are fast.  If ‘-mzdcbranch’ is
     specified, the compiler prefers zero displacement branch code
     sequences.  This is enabled by default when generating code for SH4
     and SH4A. It can be explicitly disabled by specifying
     ‘-mno-zdcbranch’.

‘-mcbranch-force-delay-slot’
     Force the usage of delay slots for conditional branches, which
     stuffs the delay slot with a ‘nop’ if a suitable instruction cannot
     be found.  By default this option is disabled.  It can be enabled
     to work around hardware bugs as found in the original SH7055.

‘-mfused-madd’
‘-mno-fused-madd’
     Generate code that uses (does not use) the floating-point multiply
     and accumulate instructions.  These instructions are generated by
     default if hardware floating point is used.  The machine-dependent
     ‘-mfused-madd’ option is now mapped to the machine-independent
     ‘-ffp-contract=fast’ option, and ‘-mno-fused-madd’ is mapped to
     ‘-ffp-contract=off’.

‘-mfsca’
‘-mno-fsca’
     Allow or disallow the compiler to emit the ‘fsca’ instruction for
     sine and cosine approximations.  The option ‘-mfsca’ must be used
     in combination with ‘-funsafe-math-optimizations’.  It is enabled
     by default when generating code for SH4A. Using ‘-mno-fsca’
     disables sine and cosine approximations even if
     ‘-funsafe-math-optimizations’ is in effect.

‘-mfsrra’
‘-mno-fsrra’
     Allow or disallow the compiler to emit the ‘fsrra’ instruction for
     reciprocal square root approximations.  The option ‘-mfsrra’ must
     be used in combination with ‘-funsafe-math-optimizations’ and
     ‘-ffinite-math-only’.  It is enabled by default when generating
     code for SH4A. Using ‘-mno-fsrra’ disables reciprocal square root
     approximations even if ‘-funsafe-math-optimizations’ and
     ‘-ffinite-math-only’ are in effect.

‘-mpretend-cmove’
     Prefer zero-displacement conditional branches for conditional move
     instruction patterns.  This can result in faster code on the SH4
     processor.

‘-mfdpic’
     Generate code using the FDPIC ABI.


File: gcc.info,  Node: Solaris 2 Options,  Next: SPARC Options,  Prev: SH Options,  Up: Submodel Options

3.19.50 Solaris 2 Options
-------------------------

These ‘-m’ options are supported on Solaris 2:

‘-mclear-hwcap’
     ‘-mclear-hwcap’ tells the compiler to remove the hardware
     capabilities generated by the Solaris assembler.  This is only
     necessary when object files use ISA extensions not supported by the
     current machine, but check at runtime whether or not to use them.

‘-mimpure-text’
     ‘-mimpure-text’, used in addition to ‘-shared’, tells the compiler
     to not pass ‘-z text’ to the linker when linking a shared object.
     Using this option, you can link position-dependent code into a
     shared object.

     ‘-mimpure-text’ suppresses the "relocations remain against
     allocatable but non-writable sections" linker error message.
     However, the necessary relocations trigger copy-on-write, and the
     shared object is not actually shared across processes.  Instead of
     using ‘-mimpure-text’, you should compile all source code with
     ‘-fpic’ or ‘-fPIC’.

 These switches are supported in addition to the above on Solaris 2:

‘-pthreads’
     This is a synonym for ‘-pthread’.


File: gcc.info,  Node: SPARC Options,  Next: System V Options,  Prev: Solaris 2 Options,  Up: Submodel Options

3.19.51 SPARC Options
---------------------

These ‘-m’ options are supported on the SPARC:

‘-mno-app-regs’
‘-mapp-regs’
     Specify ‘-mapp-regs’ to generate output using the global registers
     2 through 4, which the SPARC SVR4 ABI reserves for applications.
     Like the global register 1, each global register 2 through 4 is
     then treated as an allocable register that is clobbered by function
     calls.  This is the default.

     To be fully SVR4 ABI-compliant at the cost of some performance
     loss, specify ‘-mno-app-regs’.  You should compile libraries and
     system software with this option.

‘-mflat’
‘-mno-flat’
     With ‘-mflat’, the compiler does not generate save/restore
     instructions and uses a "flat" or single register window model.
     This model is compatible with the regular register window model.
     The local registers and the input registers (0-5) are still treated
     as "call-saved" registers and are saved on the stack as needed.

     With ‘-mno-flat’ (the default), the compiler generates save/restore
     instructions (except for leaf functions).  This is the normal
     operating mode.

‘-mfpu’
‘-mhard-float’
     Generate output containing floating-point instructions.  This is
     the default.

‘-mno-fpu’
‘-msoft-float’
     Generate output containing library calls for floating point.
     *Warning:* the requisite libraries are not available for all SPARC
     targets.  Normally the facilities of the machine's usual C compiler
     are used, but this cannot be done directly in cross-compilation.
     You must make your own arrangements to provide suitable library
     functions for cross-compilation.  The embedded targets
     ‘sparc-*-aout’ and ‘sparclite-*-*’ do provide software
     floating-point support.

     ‘-msoft-float’ changes the calling convention in the output file;
     therefore, it is only useful if you compile _all_ of a program with
     this option.  In particular, you need to compile ‘libgcc.a’, the
     library that comes with GCC, with ‘-msoft-float’ in order for this
     to work.

‘-mhard-quad-float’
     Generate output containing quad-word (long double) floating-point
     instructions.

‘-msoft-quad-float’
     Generate output containing library calls for quad-word (long
     double) floating-point instructions.  The functions called are
     those specified in the SPARC ABI.  This is the default.

     As of this writing, there are no SPARC implementations that have
     hardware support for the quad-word floating-point instructions.
     They all invoke a trap handler for one of these instructions, and
     then the trap handler emulates the effect of the instruction.
     Because of the trap handler overhead, this is much slower than
     calling the ABI library routines.  Thus the ‘-msoft-quad-float’
     option is the default.

‘-mno-unaligned-doubles’
‘-munaligned-doubles’
     Assume that doubles have 8-byte alignment.  This is the default.

     With ‘-munaligned-doubles’, GCC assumes that doubles have 8-byte
     alignment only if they are contained in another type, or if they
     have an absolute address.  Otherwise, it assumes they have 4-byte
     alignment.  Specifying this option avoids some rare compatibility
     problems with code generated by other compilers.  It is not the
     default because it results in a performance loss, especially for
     floating-point code.

‘-muser-mode’
‘-mno-user-mode’
     Do not generate code that can only run in supervisor mode.  This is
     relevant only for the ‘casa’ instruction emitted for the LEON3
     processor.  This is the default.

‘-mfaster-structs’
‘-mno-faster-structs’
     With ‘-mfaster-structs’, the compiler assumes that structures
     should have 8-byte alignment.  This enables the use of pairs of
     ‘ldd’ and ‘std’ instructions for copies in structure assignment, in
     place of twice as many ‘ld’ and ‘st’ pairs.  However, the use of
     this changed alignment directly violates the SPARC ABI.  Thus, it's
     intended only for use on targets where the developer acknowledges
     that their resulting code is not directly in line with the rules of
     the ABI.

‘-mstd-struct-return’
‘-mno-std-struct-return’
     With ‘-mstd-struct-return’, the compiler generates checking code in
     functions returning structures or unions to detect size mismatches
     between the two sides of function calls, as per the 32-bit ABI.

     The default is ‘-mno-std-struct-return’.  This option has no effect
     in 64-bit mode.

‘-mlra’
‘-mno-lra’
     Enable Local Register Allocation.  This is the default for SPARC
     since GCC 7 so ‘-mno-lra’ needs to be passed to get old Reload.

‘-mcpu=CPU_TYPE’
     Set the instruction set, register set, and instruction scheduling
     parameters for machine type CPU_TYPE.  Supported values for
     CPU_TYPE are ‘v7’, ‘cypress’, ‘v8’, ‘supersparc’, ‘hypersparc’,
     ‘leon’, ‘leon3’, ‘leon3v7’, ‘leon5’, ‘sparclite’, ‘f930’, ‘f934’,
     ‘sparclite86x’, ‘sparclet’, ‘tsc701’, ‘v9’, ‘ultrasparc’,
     ‘ultrasparc3’, ‘niagara’, ‘niagara2’, ‘niagara3’, ‘niagara4’,
     ‘niagara7’ and ‘m8’.

     Native Solaris and GNU/Linux toolchains also support the value
     ‘native’, which selects the best architecture option for the host
     processor.  ‘-mcpu=native’ has no effect if GCC does not recognize
     the processor.

     Default instruction scheduling parameters are used for values that
     select an architecture and not an implementation.  These are ‘v7’,
     ‘v8’, ‘sparclite’, ‘sparclet’, ‘v9’.

     Here is a list of each supported architecture and their supported
     implementations.

     v7
          cypress, leon3v7

     v8
          supersparc, hypersparc, leon, leon3, leon5

     sparclite
          f930, f934, sparclite86x

     sparclet
          tsc701

     v9
          ultrasparc, ultrasparc3, niagara, niagara2, niagara3,
          niagara4, niagara7, m8

     By default (unless configured otherwise), GCC generates code for
     the V7 variant of the SPARC architecture.  With ‘-mcpu=cypress’,
     the compiler additionally optimizes it for the Cypress CY7C602
     chip, as used in the SPARCStation/SPARCServer 3xx series.  This is
     also appropriate for the older SPARCStation 1, 2, IPX etc.

     With ‘-mcpu=v8’, GCC generates code for the V8 variant of the SPARC
     architecture.  The only difference from V7 code is that the
     compiler emits the integer multiply and integer divide instructions
     which exist in SPARC-V8 but not in SPARC-V7.  With
     ‘-mcpu=supersparc’, the compiler additionally optimizes it for the
     SuperSPARC chip, as used in the SPARCStation 10, 1000 and 2000
     series.

     With ‘-mcpu=sparclite’, GCC generates code for the SPARClite
     variant of the SPARC architecture.  This adds the integer multiply,
     integer divide step and scan (‘ffs’) instructions which exist in
     SPARClite but not in SPARC-V7.  With ‘-mcpu=f930’, the compiler
     additionally optimizes it for the Fujitsu MB86930 chip, which is
     the original SPARClite, with no FPU.  With ‘-mcpu=f934’, the
     compiler additionally optimizes it for the Fujitsu MB86934 chip,
     which is the more recent SPARClite with FPU.

     With ‘-mcpu=sparclet’, GCC generates code for the SPARClet variant
     of the SPARC architecture.  This adds the integer multiply,
     multiply/accumulate, integer divide step and scan (‘ffs’)
     instructions which exist in SPARClet but not in SPARC-V7.  With
     ‘-mcpu=tsc701’, the compiler additionally optimizes it for the
     TEMIC SPARClet chip.

     With ‘-mcpu=v9’, GCC generates code for the V9 variant of the SPARC
     architecture.  This adds 64-bit integer and floating-point move
     instructions, 3 additional floating-point condition code registers
     and conditional move instructions.  With ‘-mcpu=ultrasparc’, the
     compiler additionally optimizes it for the Sun UltraSPARC I/II/IIi
     chips.  With ‘-mcpu=ultrasparc3’, the compiler additionally
     optimizes it for the Sun UltraSPARC III/III+/IIIi/IIIi+/IV/IV+
     chips.  With ‘-mcpu=niagara’, the compiler additionally optimizes
     it for Sun UltraSPARC T1 chips.  With ‘-mcpu=niagara2’, the
     compiler additionally optimizes it for Sun UltraSPARC T2 chips.
     With ‘-mcpu=niagara3’, the compiler additionally optimizes it for
     Sun UltraSPARC T3 chips.  With ‘-mcpu=niagara4’, the compiler
     additionally optimizes it for Sun UltraSPARC T4 chips.  With
     ‘-mcpu=niagara7’, the compiler additionally optimizes it for Oracle
     SPARC M7 chips.  With ‘-mcpu=m8’, the compiler additionally
     optimizes it for Oracle M8 chips.

‘-mtune=CPU_TYPE’
     Set the instruction scheduling parameters for machine type
     CPU_TYPE, but do not set the instruction set or register set that
     the option ‘-mcpu=CPU_TYPE’ does.

     The same values for ‘-mcpu=CPU_TYPE’ can be used for
     ‘-mtune=CPU_TYPE’, but the only useful values are those that select
     a particular CPU implementation.  Those are ‘cypress’,
     ‘supersparc’, ‘hypersparc’, ‘leon’, ‘leon3’, ‘leon3v7’, ‘leon5’,
     ‘f930’, ‘f934’, ‘sparclite86x’, ‘tsc701’, ‘ultrasparc’,
     ‘ultrasparc3’, ‘niagara’, ‘niagara2’, ‘niagara3’, ‘niagara4’,
     ‘niagara7’ and ‘m8’.  With native Solaris and GNU/Linux toolchains,
     ‘native’ can also be used.

‘-mv8plus’
‘-mno-v8plus’
     With ‘-mv8plus’, GCC generates code for the SPARC-V8+ ABI.  The
     difference from the V8 ABI is that the global and out registers are
     considered 64 bits wide.  This is enabled by default on Solaris in
     32-bit mode for all SPARC-V9 processors.

‘-mvis’
‘-mno-vis’
     With ‘-mvis’, GCC generates code that takes advantage of the
     UltraSPARC Visual Instruction Set extensions.  The default is
     ‘-mno-vis’.

‘-mvis2’
‘-mno-vis2’
     With ‘-mvis2’, GCC generates code that takes advantage of version
     2.0 of the UltraSPARC Visual Instruction Set extensions.  The
     default is ‘-mvis2’ when targeting a cpu that supports such
     instructions, such as UltraSPARC-III and later.  Setting ‘-mvis2’
     also sets ‘-mvis’.

‘-mvis3’
‘-mno-vis3’
     With ‘-mvis3’, GCC generates code that takes advantage of version
     3.0 of the UltraSPARC Visual Instruction Set extensions.  The
     default is ‘-mvis3’ when targeting a cpu that supports such
     instructions, such as niagara-3 and later.  Setting ‘-mvis3’ also
     sets ‘-mvis2’ and ‘-mvis’.

‘-mvis4’
‘-mno-vis4’
     With ‘-mvis4’, GCC generates code that takes advantage of version
     4.0 of the UltraSPARC Visual Instruction Set extensions.  The
     default is ‘-mvis4’ when targeting a cpu that supports such
     instructions, such as niagara-7 and later.  Setting ‘-mvis4’ also
     sets ‘-mvis3’, ‘-mvis2’ and ‘-mvis’.

‘-mvis4b’
‘-mno-vis4b’
     With ‘-mvis4b’, GCC generates code that takes advantage of version
     4.0 of the UltraSPARC Visual Instruction Set extensions, plus the
     additional VIS instructions introduced in the Oracle SPARC
     Architecture 2017.  The default is ‘-mvis4b’ when targeting a cpu
     that supports such instructions, such as m8 and later.  Setting
     ‘-mvis4b’ also sets ‘-mvis4’, ‘-mvis3’, ‘-mvis2’ and ‘-mvis’.

‘-mcbcond’
‘-mno-cbcond’
     With ‘-mcbcond’, GCC generates code that takes advantage of the
     UltraSPARC Compare-and-Branch-on-Condition instructions.  The
     default is ‘-mcbcond’ when targeting a CPU that supports such
     instructions, such as Niagara-4 and later.

‘-mfmaf’
‘-mno-fmaf’
     With ‘-mfmaf’, GCC generates code that takes advantage of the
     UltraSPARC Fused Multiply-Add Floating-point instructions.  The
     default is ‘-mfmaf’ when targeting a CPU that supports such
     instructions, such as Niagara-3 and later.

‘-mfsmuld’
‘-mno-fsmuld’
     With ‘-mfsmuld’, GCC generates code that takes advantage of the
     Floating-point Multiply Single to Double (FsMULd) instruction.  The
     default is ‘-mfsmuld’ when targeting a CPU supporting the
     architecture versions V8 or V9 with FPU except ‘-mcpu=leon’.

‘-mpopc’
‘-mno-popc’
     With ‘-mpopc’, GCC generates code that takes advantage of the
     UltraSPARC Population Count instruction.  The default is ‘-mpopc’
     when targeting a CPU that supports such an instruction, such as
     Niagara-2 and later.

‘-msubxc’
‘-mno-subxc’
     With ‘-msubxc’, GCC generates code that takes advantage of the
     UltraSPARC Subtract-Extended-with-Carry instruction.  The default
     is ‘-msubxc’ when targeting a CPU that supports such an
     instruction, such as Niagara-7 and later.

‘-mfix-at697f’
     Enable the documented workaround for the single erratum of the
     Atmel AT697F processor (which corresponds to erratum #13 of the
     AT697E processor).

‘-mfix-ut699’
     Enable the documented workarounds for the floating-point errata and
     the data cache nullify errata of the UT699 processor.

‘-mfix-ut700’
     Enable the documented workaround for the back-to-back store errata
     of the UT699E/UT700 processor.

‘-mfix-gr712rc’
     Enable the documented workaround for the back-to-back store errata
     of the GR712RC processor.

 These ‘-m’ options are supported in addition to the above on SPARC-V9
processors in 64-bit environments:

‘-m32’
‘-m64’
     Generate code for a 32-bit or 64-bit environment.  The 32-bit
     environment sets int, long and pointer to 32 bits.  The 64-bit
     environment sets int to 32 bits and long and pointer to 64 bits.

‘-mcmodel=WHICH’
     Set the code model to one of

     ‘medlow’
          The Medium/Low code model: 64-bit addresses, programs must be
          linked in the low 32 bits of memory.  Programs can be
          statically or dynamically linked.

     ‘medmid’
          The Medium/Middle code model: 64-bit addresses, programs must
          be linked in the low 44 bits of memory, the text and data
          segments must be less than 2GB in size and the data segment
          must be located within 2GB of the text segment.

     ‘medany’
          The Medium/Anywhere code model: 64-bit addresses, programs may
          be linked anywhere in memory, the text and data segments must
          be less than 2GB in size and the data segment must be located
          within 2GB of the text segment.

     ‘embmedany’
          The Medium/Anywhere code model for embedded systems: 64-bit
          addresses, the text and data segments must be less than 2GB in
          size, both starting anywhere in memory (determined at link
          time).  The global register %g4 points to the base of the data
          segment.  Programs are statically linked and PIC is not
          supported.

‘-mmemory-model=MEM-MODEL’
     Set the memory model in force on the processor to one of

     ‘default’
          The default memory model for the processor and operating
          system.

     ‘rmo’
          Relaxed Memory Order

     ‘pso’
          Partial Store Order

     ‘tso’
          Total Store Order

     ‘sc’
          Sequential Consistency

     These memory models are formally defined in Appendix D of the
     SPARC-V9 architecture manual, as set in the processor's ‘PSTATE.MM’
     field.

‘-mstack-bias’
‘-mno-stack-bias’
     With ‘-mstack-bias’, GCC assumes that the stack pointer, and frame
     pointer if present, are offset by −2047 which must be added back
     when making stack frame references.  This is the default in 64-bit
     mode.  Otherwise, assume no such offset is present.


File: gcc.info,  Node: System V Options,  Next: TILE-Gx Options,  Prev: SPARC Options,  Up: Submodel Options

3.19.52 Options for System V
----------------------------

These additional options are available on System V Release 4 for
compatibility with other compilers on those systems:

‘-G’
     Create a shared object.  It is recommended that ‘-symbolic’ or
     ‘-shared’ be used instead.

‘-Qy’
     Identify the versions of each tool used by the compiler, in a
     ‘.ident’ assembler directive in the output.

‘-Qn’
     Refrain from adding ‘.ident’ directives to the output file (this is
     the default).

‘-YP,DIRS’
     Search the directories DIRS, and no others, for libraries specified
     with ‘-l’.

‘-Ym,DIR’
     Look in the directory DIR to find the M4 preprocessor.  The
     assembler uses this option.


File: gcc.info,  Node: TILE-Gx Options,  Next: TILEPro Options,  Prev: System V Options,  Up: Submodel Options

3.19.53 TILE-Gx Options
-----------------------

These ‘-m’ options are supported on the TILE-Gx:

‘-mcmodel=small’
     Generate code for the small model.  The distance for direct calls
     is limited to 500M in either direction.  PC-relative addresses are
     32 bits.  Absolute addresses support the full address range.

‘-mcmodel=large’
     Generate code for the large model.  There is no limitation on call
     distance, pc-relative addresses, or absolute addresses.

‘-mcpu=NAME’
     Selects the type of CPU to be targeted.  Currently the only
     supported type is ‘tilegx’.

‘-m32’
‘-m64’
     Generate code for a 32-bit or 64-bit environment.  The 32-bit
     environment sets int, long, and pointer to 32 bits.  The 64-bit
     environment sets int to 32 bits and long and pointer to 64 bits.

‘-mbig-endian’
‘-mlittle-endian’
     Generate code in big/little endian mode, respectively.


File: gcc.info,  Node: TILEPro Options,  Next: V850 Options,  Prev: TILE-Gx Options,  Up: Submodel Options

3.19.54 TILEPro Options
-----------------------

These ‘-m’ options are supported on the TILEPro:

‘-mcpu=NAME’
     Selects the type of CPU to be targeted.  Currently the only
     supported type is ‘tilepro’.

‘-m32’
     Generate code for a 32-bit environment, which sets int, long, and
     pointer to 32 bits.  This is the only supported behavior so the
     flag is essentially ignored.


File: gcc.info,  Node: V850 Options,  Next: VAX Options,  Prev: TILEPro Options,  Up: Submodel Options

3.19.55 V850 Options
--------------------

These ‘-m’ options are defined for V850 implementations:

‘-mlong-calls’
‘-mno-long-calls’
     Treat all calls as being far away (near).  If calls are assumed to
     be far away, the compiler always loads the function's address into
     a register, and calls indirect through the pointer.

‘-mno-ep’
‘-mep’
     Do not optimize (do optimize) basic blocks that use the same index
     pointer 4 or more times to copy pointer into the ‘ep’ register, and
     use the shorter ‘sld’ and ‘sst’ instructions.  The ‘-mep’ option is
     on by default if you optimize.

‘-mno-prolog-function’
‘-mprolog-function’
     Do not use (do use) external functions to save and restore
     registers at the prologue and epilogue of a function.  The external
     functions are slower, but use less code space if more than one
     function saves the same number of registers.  The
     ‘-mprolog-function’ option is on by default if you optimize.

‘-mspace’
     Try to make the code as small as possible.  At present, this just
     turns on the ‘-mep’ and ‘-mprolog-function’ options.

‘-mtda=N’
     Put static or global variables whose size is N bytes or less into
     the tiny data area that register ‘ep’ points to.  The tiny data
     area can hold up to 256 bytes in total (128 bytes for byte
     references).

‘-msda=N’
     Put static or global variables whose size is N bytes or less into
     the small data area that register ‘gp’ points to.  The small data
     area can hold up to 64 kilobytes.

‘-mzda=N’
     Put static or global variables whose size is N bytes or less into
     the first 32 kilobytes of memory.

‘-mv850’
     Specify that the target processor is the V850.

‘-mv850e3v5’
     Specify that the target processor is the V850E3V5.  The
     preprocessor constant ‘__v850e3v5__’ is defined if this option is
     used.

‘-mv850e2v4’
     Specify that the target processor is the V850E3V5.  This is an
     alias for the ‘-mv850e3v5’ option.

‘-mv850e2v3’
     Specify that the target processor is the V850E2V3.  The
     preprocessor constant ‘__v850e2v3__’ is defined if this option is
     used.

‘-mv850e2’
     Specify that the target processor is the V850E2.  The preprocessor
     constant ‘__v850e2__’ is defined if this option is used.

‘-mv850e1’
     Specify that the target processor is the V850E1.  The preprocessor
     constants ‘__v850e1__’ and ‘__v850e__’ are defined if this option
     is used.

‘-mv850es’
     Specify that the target processor is the V850ES. This is an alias
     for the ‘-mv850e1’ option.

‘-mv850e’
     Specify that the target processor is the V850E.  The preprocessor
     constant ‘__v850e__’ is defined if this option is used.

     If neither ‘-mv850’ nor ‘-mv850e’ nor ‘-mv850e1’ nor ‘-mv850e2’ nor
     ‘-mv850e2v3’ nor ‘-mv850e3v5’ are defined then a default target
     processor is chosen and the relevant ‘__v850*__’ preprocessor
     constant is defined.

     The preprocessor constants ‘__v850’ and ‘__v851__’ are always
     defined, regardless of which processor variant is the target.

‘-mdisable-callt’
‘-mno-disable-callt’
     This option suppresses generation of the ‘CALLT’ instruction for
     the v850e, v850e1, v850e2, v850e2v3 and v850e3v5 flavors of the
     v850 architecture.

     This option is enabled by default when the RH850 ABI is in use (see
     ‘-mrh850-abi’), and disabled by default when the GCC ABI is in use.
     If ‘CALLT’ instructions are being generated then the C preprocessor
     symbol ‘__V850_CALLT__’ is defined.

‘-mrelax’
‘-mno-relax’
     Pass on (or do not pass on) the ‘-mrelax’ command-line option to
     the assembler.

‘-mlong-jumps’
‘-mno-long-jumps’
     Disable (or re-enable) the generation of PC-relative jump
     instructions.

‘-msoft-float’
‘-mhard-float’
     Disable (or re-enable) the generation of hardware floating point
     instructions.  This option is only significant when the target
     architecture is ‘V850E2V3’ or higher.  If hardware floating point
     instructions are being generated then the C preprocessor symbol
     ‘__FPU_OK__’ is defined, otherwise the symbol ‘__NO_FPU__’ is
     defined.

‘-mloop’
     Enables the use of the e3v5 LOOP instruction.  The use of this
     instruction is not enabled by default when the e3v5 architecture is
     selected because its use is still experimental.

‘-mrh850-abi’
‘-mghs’
     Enables support for the RH850 version of the V850 ABI. This is the
     default.  With this version of the ABI the following rules apply:

        • Integer sized structures and unions are returned via a memory
          pointer rather than a register.

        • Large structures and unions (more than 8 bytes in size) are
          passed by value.

        • Functions are aligned to 16-bit boundaries.

        • The ‘-m8byte-align’ command-line option is supported.

        • The ‘-mdisable-callt’ command-line option is enabled by
          default.  The ‘-mno-disable-callt’ command-line option is not
          supported.

     When this version of the ABI is enabled the C preprocessor symbol
     ‘__V850_RH850_ABI__’ is defined.

‘-mgcc-abi’
     Enables support for the old GCC version of the V850 ABI. With this
     version of the ABI the following rules apply:

        • Integer sized structures and unions are returned in register
          ‘r10’.

        • Large structures and unions (more than 8 bytes in size) are
          passed by reference.

        • Functions are aligned to 32-bit boundaries, unless optimizing
          for size.

        • The ‘-m8byte-align’ command-line option is not supported.

        • The ‘-mdisable-callt’ command-line option is supported but not
          enabled by default.

     When this version of the ABI is enabled the C preprocessor symbol
     ‘__V850_GCC_ABI__’ is defined.

‘-m8byte-align’
‘-mno-8byte-align’
     Enables support for ‘double’ and ‘long long’ types to be aligned on
     8-byte boundaries.  The default is to restrict the alignment of all
     objects to at most 4-bytes.  When ‘-m8byte-align’ is in effect the
     C preprocessor symbol ‘__V850_8BYTE_ALIGN__’ is defined.

‘-mbig-switch’
     Generate code suitable for big switch tables.  Use this option only
     if the assembler/linker complain about out of range branches within
     a switch table.

‘-mapp-regs’
     This option causes r2 and r5 to be used in the code generated by
     the compiler.  This setting is the default.

‘-mno-app-regs’
     This option causes r2 and r5 to be treated as fixed registers.


File: gcc.info,  Node: VAX Options,  Next: Visium Options,  Prev: V850 Options,  Up: Submodel Options

3.19.56 VAX Options
-------------------

These ‘-m’ options are defined for the VAX:

‘-munix’
     Do not output certain jump instructions (‘aobleq’ and so on) that
     the Unix assembler for the VAX cannot handle across long ranges.

‘-mgnu’
     Do output those jump instructions, on the assumption that the GNU
     assembler is being used.

‘-mg’
     Output code for G-format floating-point numbers instead of
     D-format.

‘-mlra’
‘-mno-lra’
     Enable Local Register Allocation.  This is still experimental for
     the VAX, so by default the compiler uses standard reload.


File: gcc.info,  Node: Visium Options,  Next: VMS Options,  Prev: VAX Options,  Up: Submodel Options

3.19.57 Visium Options
----------------------

‘-mdebug’
     A program which performs file I/O and is destined to run on an MCM
     target should be linked with this option.  It causes the libraries
     libc.a and libdebug.a to be linked.  The program should be run on
     the target under the control of the GDB remote debugging stub.

‘-msim’
     A program which performs file I/O and is destined to run on the
     simulator should be linked with option.  This causes libraries
     libc.a and libsim.a to be linked.

‘-mfpu’
‘-mhard-float’
     Generate code containing floating-point instructions.  This is the
     default.

‘-mno-fpu’
‘-msoft-float’
     Generate code containing library calls for floating-point.

     ‘-msoft-float’ changes the calling convention in the output file;
     therefore, it is only useful if you compile _all_ of a program with
     this option.  In particular, you need to compile ‘libgcc.a’, the
     library that comes with GCC, with ‘-msoft-float’ in order for this
     to work.

‘-mcpu=CPU_TYPE’
     Set the instruction set, register set, and instruction scheduling
     parameters for machine type CPU_TYPE.  Supported values for
     CPU_TYPE are ‘mcm’, ‘gr5’ and ‘gr6’.

     ‘mcm’ is a synonym of ‘gr5’ present for backward compatibility.

     By default (unless configured otherwise), GCC generates code for
     the GR5 variant of the Visium architecture.

     With ‘-mcpu=gr6’, GCC generates code for the GR6 variant of the
     Visium architecture.  The only difference from GR5 code is that the
     compiler will generate block move instructions.

‘-mtune=CPU_TYPE’
     Set the instruction scheduling parameters for machine type
     CPU_TYPE, but do not set the instruction set or register set that
     the option ‘-mcpu=CPU_TYPE’ would.

‘-msv-mode’
     Generate code for the supervisor mode, where there are no
     restrictions on the access to general registers.  This is the
     default.

‘-muser-mode’
     Generate code for the user mode, where the access to some general
     registers is forbidden: on the GR5, registers r24 to r31 cannot be
     accessed in this mode; on the GR6, only registers r29 to r31 are
     affected.


File: gcc.info,  Node: VMS Options,  Next: VxWorks Options,  Prev: Visium Options,  Up: Submodel Options

3.19.58 VMS Options
-------------------

These ‘-m’ options are defined for the VMS implementations:

‘-mvms-return-codes’
     Return VMS condition codes from ‘main’.  The default is to return
     POSIX-style condition (e.g. error) codes.

‘-mdebug-main=PREFIX’
     Flag the first routine whose name starts with PREFIX as the main
     routine for the debugger.

‘-mmalloc64’
     Default to 64-bit memory allocation routines.

‘-mpointer-size=SIZE’
     Set the default size of pointers.  Possible options for SIZE are
     ‘32’ or ‘short’ for 32 bit pointers, ‘64’ or ‘long’ for 64 bit
     pointers, and ‘no’ for supporting only 32 bit pointers.  The later
     option disables ‘pragma pointer_size’.


File: gcc.info,  Node: VxWorks Options,  Next: x86 Options,  Prev: VMS Options,  Up: Submodel Options

3.19.59 VxWorks Options
-----------------------

The options in this section are defined for all VxWorks targets.
Options specific to the target hardware are listed with the other
options for that target.

‘-mrtp’
     GCC can generate code for both VxWorks kernels and real time
     processes (RTPs).  This option switches from the former to the
     latter.  It also defines the preprocessor macro ‘__RTP__’.

‘-non-static’
     Link an RTP executable against shared libraries rather than static
     libraries.  The options ‘-static’ and ‘-shared’ can also be used
     for RTPs (*note Link Options::); ‘-static’ is the default.

‘-Bstatic’
‘-Bdynamic’
     These options are passed down to the linker.  They are defined for
     compatibility with Diab.

‘-Xbind-lazy’
     Enable lazy binding of function calls.  This option is equivalent
     to ‘-Wl,-z,now’ and is defined for compatibility with Diab.

‘-Xbind-now’
     Disable lazy binding of function calls.  This option is the default
     and is defined for compatibility with Diab.


File: gcc.info,  Node: x86 Options,  Next: x86 Windows Options,  Prev: VxWorks Options,  Up: Submodel Options

3.19.60 x86 Options
-------------------

These ‘-m’ options are defined for the x86 family of computers.

‘-march=CPU-TYPE’
     Generate instructions for the machine type CPU-TYPE.  In contrast
     to ‘-mtune=CPU-TYPE’, which merely tunes the generated code for the
     specified CPU-TYPE, ‘-march=CPU-TYPE’ allows GCC to generate code
     that may not run at all on processors other than the one indicated.
     Specifying ‘-march=CPU-TYPE’ implies ‘-mtune=CPU-TYPE’, except
     where noted otherwise.

     The choices for CPU-TYPE are:

     ‘native’
          This selects the CPU to generate code for at compilation time
          by determining the processor type of the compiling machine.
          Using ‘-march=native’ enables all instruction subsets
          supported by the local machine (hence the result might not run
          on different machines).  Using ‘-mtune=native’ produces code
          optimized for the local machine under the constraints of the
          selected instruction set.

     ‘x86-64’
          A generic CPU with 64-bit extensions.

     ‘x86-64-v2’
     ‘x86-64-v3’
     ‘x86-64-v4’
          These choices for CPU-TYPE select the corresponding
          micro-architecture level from the x86-64 psABI. On ABIs other
          than the x86-64 psABI they select the same CPU features as the
          x86-64 psABI documents for the particular micro-architecture
          level.

          Since these CPU-TYPE values do not have a corresponding
          ‘-mtune’ setting, using ‘-march’ with these values enables
          generic tuning.  Specific tuning can be enabled using the
          ‘-mtune=OTHER-CPU-TYPE’ option with an appropriate
          OTHER-CPU-TYPE value.

     ‘i386’
          Original Intel i386 CPU.

     ‘i486’
          Intel i486 CPU.  (No scheduling is implemented for this chip.)

     ‘i586’
     ‘pentium’
          Intel Pentium CPU with no MMX support.

     ‘lakemont’
          Intel Lakemont MCU, based on Intel Pentium CPU.

     ‘pentium-mmx’
          Intel Pentium MMX CPU, based on Pentium core with MMX
          instruction set support.

     ‘pentiumpro’
          Intel Pentium Pro CPU.

     ‘i686’
          When used with ‘-march’, the Pentium Pro instruction set is
          used, so the code runs on all i686 family chips.  When used
          with ‘-mtune’, it has the same meaning as ‘generic’.

     ‘pentium2’
          Intel Pentium II CPU, based on Pentium Pro core with MMX and
          FXSR instruction set support.

     ‘pentium3’
     ‘pentium3m’
          Intel Pentium III CPU, based on Pentium Pro core with MMX,
          FXSR and SSE instruction set support.

     ‘pentium-m’
          Intel Pentium M; low-power version of Intel Pentium III CPU
          with MMX, SSE, SSE2 and FXSR instruction set support.  Used by
          Centrino notebooks.

     ‘pentium4’
     ‘pentium4m’
          Intel Pentium 4 CPU with MMX, SSE, SSE2 and FXSR instruction
          set support.

     ‘prescott’
          Improved version of Intel Pentium 4 CPU with MMX, SSE, SSE2,
          SSE3 and FXSR instruction set support.

     ‘nocona’
          Improved version of Intel Pentium 4 CPU with 64-bit
          extensions, MMX, SSE, SSE2, SSE3 and FXSR instruction set
          support.

     ‘core2’
          Intel Core 2 CPU with 64-bit extensions, MMX, SSE, SSE2, SSE3,
          SSSE3, CX16, SAHF and FXSR instruction set support.

     ‘nehalem’
          Intel Nehalem CPU with 64-bit extensions, MMX, SSE, SSE2,
          SSE3, SSSE3, SSE4.1, SSE4.2, POPCNT, CX16, SAHF and FXSR
          instruction set support.

     ‘westmere’
          Intel Westmere CPU with 64-bit extensions, MMX, SSE, SSE2,
          SSE3, SSSE3, SSE4.1, SSE4.2, POPCNT, CX16, SAHF, FXSR and
          PCLMUL instruction set support.

     ‘sandybridge’
          Intel Sandy Bridge CPU with 64-bit extensions, MMX, SSE, SSE2,
          SSE3, SSSE3, SSE4.1, SSE4.2, POPCNT, CX16, SAHF, FXSR, AVX,
          XSAVE and PCLMUL instruction set support.

     ‘ivybridge’
          Intel Ivy Bridge CPU with 64-bit extensions, MMX, SSE, SSE2,
          SSE3, SSSE3, SSE4.1, SSE4.2, POPCNT, CX16, SAHF, FXSR, AVX,
          XSAVE, PCLMUL, FSGSBASE, RDRND and F16C instruction set
          support.

     ‘haswell’
          Intel Haswell CPU with 64-bit extensions, MOVBE, MMX, SSE,
          SSE2, SSE3, SSSE3, SSE4.1, SSE4.2, POPCNT, CX16, SAHF, FXSR,
          AVX, XSAVE, PCLMUL, FSGSBASE, RDRND, F16C, AVX2, BMI, BMI2,
          LZCNT, FMA, MOVBE and HLE instruction set support.

     ‘broadwell’
          Intel Broadwell CPU with 64-bit extensions, MOVBE, MMX, SSE,
          SSE2, SSE3, SSSE3, SSE4.1, SSE4.2, POPCNT, CX16, SAHF, FXSR,
          AVX, XSAVE, PCLMUL, FSGSBASE, RDRND, F16C, AVX2, BMI, BMI2,
          LZCNT, FMA, MOVBE, HLE, RDSEED, ADCX and PREFETCHW instruction
          set support.

     ‘skylake’
          Intel Skylake CPU with 64-bit extensions, MOVBE, MMX, SSE,
          SSE2, SSE3, SSSE3, SSE4.1, SSE4.2, POPCNT, CX16, SAHF, FXSR,
          AVX, XSAVE, PCLMUL, FSGSBASE, RDRND, F16C, AVX2, BMI, BMI2,
          LZCNT, FMA, MOVBE, HLE, RDSEED, ADCX, PREFETCHW, AES,
          CLFLUSHOPT, XSAVEC, XSAVES and SGX instruction set support.

     ‘bonnell’
          Intel Bonnell CPU with 64-bit extensions, MOVBE, MMX, SSE,
          SSE2, SSE3 and SSSE3 instruction set support.

     ‘silvermont’
          Intel Silvermont CPU with 64-bit extensions, MOVBE, MMX, SSE,
          SSE2, SSE3, SSSE3, SSE4.1, SSE4.2, POPCNT, CX16, SAHF, FXSR,
          PCLMUL, PREFETCHW and RDRND instruction set support.

     ‘goldmont’
          Intel Goldmont CPU with 64-bit extensions, MOVBE, MMX, SSE,
          SSE2, SSE3, SSSE3, SSE4.1, SSE4.2, POPCNT, CX16, SAHF, FXSR,
          PCLMUL, PREFETCHW, RDRND, AES, SHA, RDSEED, XSAVE, XSAVEC,
          XSAVES, XSAVEOPT, CLFLUSHOPT and FSGSBASE instruction set
          support.

     ‘goldmont-plus’
          Intel Goldmont Plus CPU with 64-bit extensions, MOVBE, MMX,
          SSE, SSE2, SSE3, SSSE3, SSE4.1, SSE4.2, POPCNT, CX16, SAHF,
          FXSR, PCLMUL, PREFETCHW, RDRND, AES, SHA, RDSEED, XSAVE,
          XSAVEC, XSAVES, XSAVEOPT, CLFLUSHOPT, FSGSBASE, PTWRITE, RDPID
          and SGX instruction set support.

     ‘tremont’
          Intel Tremont CPU with 64-bit extensions, MOVBE, MMX, SSE,
          SSE2, SSE3, SSSE3, SSE4.1, SSE4.2, POPCNT, CX16, SAHF, FXSR,
          PCLMUL, PREFETCHW, RDRND, AES, SHA, RDSEED, XSAVE, XSAVEC,
          XSAVES, XSAVEOPT, CLFLUSHOPT, FSGSBASE, PTWRITE, RDPID, SGX,
          CLWB, GFNI-SSE, MOVDIRI, MOVDIR64B, CLDEMOTE and WAITPKG
          instruction set support.

     ‘knl’
          Intel Knight's Landing CPU with 64-bit extensions, MOVBE, MMX,
          SSE, SSE2, SSE3, SSSE3, SSE4.1, SSE4.2, POPCNT, CX16, SAHF,
          FXSR, AVX, XSAVE, PCLMUL, FSGSBASE, RDRND, F16C, AVX2, BMI,
          BMI2, LZCNT, FMA, MOVBE, HLE, RDSEED, ADCX, PREFETCHW,
          AVX512PF, AVX512ER, AVX512F, AVX512CD and PREFETCHWT1
          instruction set support.

     ‘knm’
          Intel Knights Mill CPU with 64-bit extensions, MOVBE, MMX,
          SSE, SSE2, SSE3, SSSE3, SSE4.1, SSE4.2, POPCNT, CX16, SAHF,
          FXSR, AVX, XSAVE, PCLMUL, FSGSBASE, RDRND, F16C, AVX2, BMI,
          BMI2, LZCNT, FMA, MOVBE, HLE, RDSEED, ADCX, PREFETCHW,
          AVX512PF, AVX512ER, AVX512F, AVX512CD and PREFETCHWT1,
          AVX5124VNNIW, AVX5124FMAPS and AVX512VPOPCNTDQ instruction set
          support.

     ‘skylake-avx512’
          Intel Skylake Server CPU with 64-bit extensions, MOVBE, MMX,
          SSE, SSE2, SSE3, SSSE3, SSE4.1, SSE4.2, POPCNT, CX16, SAHF,
          FXSR, AVX, XSAVE, PCLMUL, FSGSBASE, RDRND, F16C, AVX2, BMI,
          BMI2, LZCNT, FMA, MOVBE, HLE, RDSEED, ADCX, PREFETCHW, AES,
          CLFLUSHOPT, XSAVEC, XSAVES, SGX, AVX512F, CLWB, AVX512VL,
          AVX512BW, AVX512DQ and AVX512CD instruction set support.

     ‘cannonlake’
          Intel Cannonlake Server CPU with 64-bit extensions, MOVBE,
          MMX, SSE, SSE2, SSE3, SSSE3, SSE4.1, SSE4.2, POPCNT, CX16,
          SAHF, FXSR, AVX, XSAVE, PCLMUL, FSGSBASE, RDRND, F16C, AVX2,
          BMI, BMI2, LZCNT, FMA, MOVBE, HLE, RDSEED, ADCX, PREFETCHW,
          AES, CLFLUSHOPT, XSAVEC, XSAVES, SGX, AVX512F, AVX512VL,
          AVX512BW, AVX512DQ, AVX512CD, PKU, AVX512VBMI, AVX512IFMA and
          SHA instruction set support.

     ‘icelake-client’
          Intel Icelake Client CPU with 64-bit extensions, MOVBE, MMX,
          SSE, SSE2, SSE3, SSSE3, SSE4.1, SSE4.2, POPCNT, CX16, SAHF,
          FXSR, AVX, XSAVE, PCLMUL, FSGSBASE, RDRND, F16C, AVX2, BMI,
          BMI2, LZCNT, FMA, MOVBE, HLE, RDSEED, ADCX, PREFETCHW, AES,
          CLFLUSHOPT, XSAVEC, XSAVES, SGX, AVX512F, AVX512VL, AVX512BW,
          AVX512DQ, AVX512CD, PKU, AVX512VBMI, AVX512IFMA, SHA,
          AVX512VNNI, GFNI, VAES, AVX512VBMI2 , VPCLMULQDQ,
          AVX512BITALG, RDPID and AVX512VPOPCNTDQ instruction set
          support.

     ‘icelake-server’
          Intel Icelake Server CPU with 64-bit extensions, MOVBE, MMX,
          SSE, SSE2, SSE3, SSSE3, SSE4.1, SSE4.2, POPCNT, CX16, SAHF,
          FXSR, AVX, XSAVE, PCLMUL, FSGSBASE, RDRND, F16C, AVX2, BMI,
          BMI2, LZCNT, FMA, MOVBE, HLE, RDSEED, ADCX, PREFETCHW, AES,
          CLFLUSHOPT, XSAVEC, XSAVES, SGX, AVX512F, AVX512VL, AVX512BW,
          AVX512DQ, AVX512CD, PKU, AVX512VBMI, AVX512IFMA, SHA,
          AVX512VNNI, GFNI, VAES, AVX512VBMI2 , VPCLMULQDQ,
          AVX512BITALG, RDPID, AVX512VPOPCNTDQ, PCONFIG, WBNOINVD and
          CLWB instruction set support.

     ‘cascadelake’
          Intel Cascadelake CPU with 64-bit extensions, MOVBE, MMX, SSE,
          SSE2, SSE3, SSSE3, SSE4.1, SSE4.2, POPCNT, CX16, SAHF, FXSR,
          AVX, XSAVE, PCLMUL, FSGSBASE, RDRND, F16C, AVX2, BMI, BMI2,
          LZCNT, FMA, MOVBE, HLE, RDSEED, ADCX, PREFETCHW, AES,
          CLFLUSHOPT, XSAVEC, XSAVES, SGX, AVX512F, CLWB, AVX512VL,
          AVX512BW, AVX512DQ, AVX512CD and AVX512VNNI instruction set
          support.

     ‘cooperlake’
          Intel cooperlake CPU with 64-bit extensions, MOVBE, MMX, SSE,
          SSE2, SSE3, SSSE3, SSE4.1, SSE4.2, POPCNT, CX16, SAHF, FXSR,
          AVX, XSAVE, PCLMUL, FSGSBASE, RDRND, F16C, AVX2, BMI, BMI2,
          LZCNT, FMA, MOVBE, HLE, RDSEED, ADCX, PREFETCHW, AES,
          CLFLUSHOPT, XSAVEC, XSAVES, SGX, AVX512F, CLWB, AVX512VL,
          AVX512BW, AVX512DQ, AVX512CD, AVX512VNNI and AVX512BF16
          instruction set support.

     ‘tigerlake’
          Intel Tigerlake CPU with 64-bit extensions, MOVBE, MMX, SSE,
          SSE2, SSE3, SSSE3, SSE4.1, SSE4.2, POPCNT, CX16, SAHF, FXSR,
          AVX, XSAVE, PCLMUL, FSGSBASE, RDRND, F16C, AVX2, BMI, BMI2,
          LZCNT, FMA, MOVBE, HLE, RDSEED, ADCX, PREFETCHW, AES,
          CLFLUSHOPT, XSAVEC, XSAVES, SGX, AVX512F, AVX512VL, AVX512BW,
          AVX512DQ, AVX512CD PKU, AVX512VBMI, AVX512IFMA, SHA,
          AVX512VNNI, GFNI, VAES, AVX512VBMI2, VPCLMULQDQ, AVX512BITALG,
          RDPID, AVX512VPOPCNTDQ, MOVDIRI, MOVDIR64B, CLWB,
          AVX512VP2INTERSECT and KEYLOCKER instruction set support.

     ‘sapphirerapids’
          Intel sapphirerapids CPU with 64-bit extensions, MOVBE, MMX,
          SSE, SSE2, SSE3, SSSE3, SSE4.1, SSE4.2, POPCNT, CX16, SAHF,
          FXSR, AVX, XSAVE, PCLMUL, FSGSBASE, RDRND, F16C, AVX2, BMI,
          BMI2, LZCNT, FMA, MOVBE, HLE, RDSEED, ADCX, PREFETCHW, AES,
          CLFLUSHOPT, XSAVEC, XSAVES, SGX, AVX512F, AVX512VL, AVX512BW,
          AVX512DQ, AVX512CD, PKU, AVX512VBMI, AVX512IFMA, SHA,
          AVX512VNNI, GFNI, VAES, AVX512VBMI2 VPCLMULQDQ, AVX512BITALG,
          RDPID, AVX512VPOPCNTDQ, PCONFIG, WBNOINVD, CLWB, MOVDIRI,
          MOVDIR64B, AVX512VP2INTERSECT, ENQCMD, CLDEMOTE, PTWRITE,
          WAITPKG, SERIALIZE, TSXLDTRK, UINTR, AMX-BF16, AMX-TILE,
          AMX-INT8, AVX-VNNI, AVX512FP16 and AVX512BF16 instruction set
          support.

     ‘alderlake’
          Intel Alderlake CPU with 64-bit extensions, MOVBE, MMX, SSE,
          SSE2, SSE3, SSSE3, SSE4.1, SSE4.2, POPCNT, AES, PREFETCHW,
          PCLMUL, RDRND, XSAVE, XSAVEC, XSAVES, XSAVEOPT, FSGSBASE,
          PTWRITE, RDPID, SGX, GFNI-SSE, CLWB, MOVDIRI, MOVDIR64B,
          CLDEMOTE, WAITPKG, ADCX, AVX, AVX2, BMI, BMI2, F16C, FMA,
          LZCNT, PCONFIG, PKU, VAES, VPCLMULQDQ, SERIALIZE, HRESET, KL,
          WIDEKL and AVX-VNNI instruction set support.

     ‘rocketlake’
          Intel Rocketlake CPU with 64-bit extensions, MOVBE, MMX, SSE,
          SSE2, SSE3, SSSE3 , SSE4.1, SSE4.2, POPCNT, CX16, SAHF, FXSR,
          AVX, XSAVE, PCLMUL, FSGSBASE, RDRND, F16C, AVX2, BMI, BMI2,
          LZCNT, FMA, MOVBE, HLE, RDSEED, ADCX, PREFETCHW, AES,
          CLFLUSHOPT, XSAVEC, XSAVES, AVX512F, AVX512VL, AVX512BW,
          AVX512DQ, AVX512CD PKU, AVX512VBMI, AVX512IFMA, SHA,
          AVX512VNNI, GFNI, VAES, AVX512VBMI2, VPCLMULQDQ, AVX512BITALG,
          RDPID and AVX512VPOPCNTDQ instruction set support.

     ‘k6’
          AMD K6 CPU with MMX instruction set support.

     ‘k6-2’
     ‘k6-3’
          Improved versions of AMD K6 CPU with MMX and 3DNow!
          instruction set support.

     ‘athlon’
     ‘athlon-tbird’
          AMD Athlon CPU with MMX, 3dNOW!, enhanced 3DNow! and SSE
          prefetch instructions support.

     ‘athlon-4’
     ‘athlon-xp’
     ‘athlon-mp’
          Improved AMD Athlon CPU with MMX, 3DNow!, enhanced 3DNow! and
          full SSE instruction set support.

     ‘k8’
     ‘opteron’
     ‘athlon64’
     ‘athlon-fx’
          Processors based on the AMD K8 core with x86-64 instruction
          set support, including the AMD Opteron, Athlon 64, and Athlon
          64 FX processors.  (This supersets MMX, SSE, SSE2, 3DNow!,
          enhanced 3DNow! and 64-bit instruction set extensions.)

     ‘k8-sse3’
     ‘opteron-sse3’
     ‘athlon64-sse3’
          Improved versions of AMD K8 cores with SSE3 instruction set
          support.

     ‘amdfam10’
     ‘barcelona’
          CPUs based on AMD Family 10h cores with x86-64 instruction set
          support.  (This supersets MMX, SSE, SSE2, SSE3, SSE4A, 3DNow!,
          enhanced 3DNow!, ABM and 64-bit instruction set extensions.)

     ‘bdver1’
          CPUs based on AMD Family 15h cores with x86-64 instruction set
          support.  (This supersets FMA4, AVX, XOP, LWP, AES, PCLMUL,
          CX16, MMX, SSE, SSE2, SSE3, SSE4A, SSSE3, SSE4.1, SSE4.2, ABM
          and 64-bit instruction set extensions.)

     ‘bdver2’
          AMD Family 15h core based CPUs with x86-64 instruction set
          support.  (This supersets BMI, TBM, F16C, FMA, FMA4, AVX, XOP,
          LWP, AES, PCLMUL, CX16, MMX, SSE, SSE2, SSE3, SSE4A, SSSE3,
          SSE4.1, SSE4.2, ABM and 64-bit instruction set extensions.)

     ‘bdver3’
          AMD Family 15h core based CPUs with x86-64 instruction set
          support.  (This supersets BMI, TBM, F16C, FMA, FMA4, FSGSBASE,
          AVX, XOP, LWP, AES, PCLMUL, CX16, MMX, SSE, SSE2, SSE3, SSE4A,
          SSSE3, SSE4.1, SSE4.2, ABM and 64-bit instruction set
          extensions.)

     ‘bdver4’
          AMD Family 15h core based CPUs with x86-64 instruction set
          support.  (This supersets BMI, BMI2, TBM, F16C, FMA, FMA4,
          FSGSBASE, AVX, AVX2, XOP, LWP, AES, PCLMUL, CX16, MOVBE, MMX,
          SSE, SSE2, SSE3, SSE4A, SSSE3, SSE4.1, SSE4.2, ABM and 64-bit
          instruction set extensions.)

     ‘znver1’
          AMD Family 17h core based CPUs with x86-64 instruction set
          support.  (This supersets BMI, BMI2, F16C, FMA, FSGSBASE, AVX,
          AVX2, ADCX, RDSEED, MWAITX, SHA, CLZERO, AES, PCLMUL, CX16,
          MOVBE, MMX, SSE, SSE2, SSE3, SSE4A, SSSE3, SSE4.1, SSE4.2,
          ABM, XSAVEC, XSAVES, CLFLUSHOPT, POPCNT, and 64-bit
          instruction set extensions.)

     ‘znver2’
          AMD Family 17h core based CPUs with x86-64 instruction set
          support.  (This supersets BMI, BMI2, CLWB, F16C, FMA,
          FSGSBASE, AVX, AVX2, ADCX, RDSEED, MWAITX, SHA, CLZERO, AES,
          PCLMUL, CX16, MOVBE, MMX, SSE, SSE2, SSE3, SSE4A, SSSE3,
          SSE4.1, SSE4.2, ABM, XSAVEC, XSAVES, CLFLUSHOPT, POPCNT,
          RDPID, WBNOINVD, and 64-bit instruction set extensions.)

     ‘znver3’
          AMD Family 19h core based CPUs with x86-64 instruction set
          support.  (This supersets BMI, BMI2, CLWB, F16C, FMA,
          FSGSBASE, AVX, AVX2, ADCX, RDSEED, MWAITX, SHA, CLZERO, AES,
          PCLMUL, CX16, MOVBE, MMX, SSE, SSE2, SSE3, SSE4A, SSSE3,
          SSE4.1, SSE4.2, ABM, XSAVEC, XSAVES, CLFLUSHOPT, POPCNT,
          RDPID, WBNOINVD, PKU, VPCLMULQDQ, VAES, and 64-bit instruction
          set extensions.)

     ‘btver1’
          CPUs based on AMD Family 14h cores with x86-64 instruction set
          support.  (This supersets MMX, SSE, SSE2, SSE3, SSSE3, SSE4A,
          CX16, ABM and 64-bit instruction set extensions.)

     ‘btver2’
          CPUs based on AMD Family 16h cores with x86-64 instruction set
          support.  This includes MOVBE, F16C, BMI, AVX, PCLMUL, AES,
          SSE4.2, SSE4.1, CX16, ABM, SSE4A, SSSE3, SSE3, SSE2, SSE, MMX
          and 64-bit instruction set extensions.

     ‘winchip-c6’
          IDT WinChip C6 CPU, dealt in same way as i486 with additional
          MMX instruction set support.

     ‘winchip2’
          IDT WinChip 2 CPU, dealt in same way as i486 with additional
          MMX and 3DNow! instruction set support.

     ‘c3’
          VIA C3 CPU with MMX and 3DNow! instruction set support.  (No
          scheduling is implemented for this chip.)

     ‘c3-2’
          VIA C3-2 (Nehemiah/C5XL) CPU with MMX and SSE instruction set
          support.  (No scheduling is implemented for this chip.)

     ‘c7’
          VIA C7 (Esther) CPU with MMX, SSE, SSE2 and SSE3 instruction
          set support.  (No scheduling is implemented for this chip.)

     ‘samuel-2’
          VIA Eden Samuel 2 CPU with MMX and 3DNow! instruction set
          support.  (No scheduling is implemented for this chip.)

     ‘nehemiah’
          VIA Eden Nehemiah CPU with MMX and SSE instruction set
          support.  (No scheduling is implemented for this chip.)

     ‘esther’
          VIA Eden Esther CPU with MMX, SSE, SSE2 and SSE3 instruction
          set support.  (No scheduling is implemented for this chip.)

     ‘eden-x2’
          VIA Eden X2 CPU with x86-64, MMX, SSE, SSE2 and SSE3
          instruction set support.  (No scheduling is implemented for
          this chip.)

     ‘eden-x4’
          VIA Eden X4 CPU with x86-64, MMX, SSE, SSE2, SSE3, SSSE3,
          SSE4.1, SSE4.2, AVX and AVX2 instruction set support.  (No
          scheduling is implemented for this chip.)

     ‘nano’
          Generic VIA Nano CPU with x86-64, MMX, SSE, SSE2, SSE3 and
          SSSE3 instruction set support.  (No scheduling is implemented
          for this chip.)

     ‘nano-1000’
          VIA Nano 1xxx CPU with x86-64, MMX, SSE, SSE2, SSE3 and SSSE3
          instruction set support.  (No scheduling is implemented for
          this chip.)

     ‘nano-2000’
          VIA Nano 2xxx CPU with x86-64, MMX, SSE, SSE2, SSE3 and SSSE3
          instruction set support.  (No scheduling is implemented for
          this chip.)

     ‘nano-3000’
          VIA Nano 3xxx CPU with x86-64, MMX, SSE, SSE2, SSE3, SSSE3 and
          SSE4.1 instruction set support.  (No scheduling is implemented
          for this chip.)

     ‘nano-x2’
          VIA Nano Dual Core CPU with x86-64, MMX, SSE, SSE2, SSE3,
          SSSE3 and SSE4.1 instruction set support.  (No scheduling is
          implemented for this chip.)

     ‘nano-x4’
          VIA Nano Quad Core CPU with x86-64, MMX, SSE, SSE2, SSE3,
          SSSE3 and SSE4.1 instruction set support.  (No scheduling is
          implemented for this chip.)

     ‘geode’
          AMD Geode embedded processor with MMX and 3DNow! instruction
          set support.

‘-mtune=CPU-TYPE’
     Tune to CPU-TYPE everything applicable about the generated code,
     except for the ABI and the set of available instructions.  While
     picking a specific CPU-TYPE schedules things appropriately for that
     particular chip, the compiler does not generate any code that
     cannot run on the default machine type unless you use a
     ‘-march=CPU-TYPE’ option.  For example, if GCC is configured for
     i686-pc-linux-gnu then ‘-mtune=pentium4’ generates code that is
     tuned for Pentium 4 but still runs on i686 machines.

     The choices for CPU-TYPE are the same as for ‘-march’.  In
     addition, ‘-mtune’ supports 2 extra choices for CPU-TYPE:

     ‘generic’
          Produce code optimized for the most common IA32/AMD64/EM64T
          processors.  If you know the CPU on which your code will run,
          then you should use the corresponding ‘-mtune’ or ‘-march’
          option instead of ‘-mtune=generic’.  But, if you do not know
          exactly what CPU users of your application will have, then you
          should use this option.

          As new processors are deployed in the marketplace, the
          behavior of this option will change.  Therefore, if you
          upgrade to a newer version of GCC, code generation controlled
          by this option will change to reflect the processors that are
          most common at the time that version of GCC is released.

          There is no ‘-march=generic’ option because ‘-march’ indicates
          the instruction set the compiler can use, and there is no
          generic instruction set applicable to all processors.  In
          contrast, ‘-mtune’ indicates the processor (or, in this case,
          collection of processors) for which the code is optimized.

     ‘intel’
          Produce code optimized for the most current Intel processors,
          which are Haswell and Silvermont for this version of GCC. If
          you know the CPU on which your code will run, then you should
          use the corresponding ‘-mtune’ or ‘-march’ option instead of
          ‘-mtune=intel’.  But, if you want your application performs
          better on both Haswell and Silvermont, then you should use
          this option.

          As new Intel processors are deployed in the marketplace, the
          behavior of this option will change.  Therefore, if you
          upgrade to a newer version of GCC, code generation controlled
          by this option will change to reflect the most current Intel
          processors at the time that version of GCC is released.

          There is no ‘-march=intel’ option because ‘-march’ indicates
          the instruction set the compiler can use, and there is no
          common instruction set applicable to all processors.  In
          contrast, ‘-mtune’ indicates the processor (or, in this case,
          collection of processors) for which the code is optimized.

‘-mcpu=CPU-TYPE’
     A deprecated synonym for ‘-mtune’.

‘-mfpmath=UNIT’
     Generate floating-point arithmetic for selected unit UNIT.  The
     choices for UNIT are:

     ‘387’
          Use the standard 387 floating-point coprocessor present on the
          majority of chips and emulated otherwise.  Code compiled with
          this option runs almost everywhere.  The temporary results are
          computed in 80-bit precision instead of the precision
          specified by the type, resulting in slightly different results
          compared to most of other chips.  See ‘-ffloat-store’ for more
          detailed description.

          This is the default choice for non-Darwin x86-32 targets.

     ‘sse’
          Use scalar floating-point instructions present in the SSE
          instruction set.  This instruction set is supported by Pentium
          III and newer chips, and in the AMD line by Athlon-4, Athlon
          XP and Athlon MP chips.  The earlier version of the SSE
          instruction set supports only single-precision arithmetic,
          thus the double and extended-precision arithmetic are still
          done using 387.  A later version, present only in Pentium 4
          and AMD x86-64 chips, supports double-precision arithmetic
          too.

          For the x86-32 compiler, you must use ‘-march=CPU-TYPE’,
          ‘-msse’ or ‘-msse2’ switches to enable SSE extensions and make
          this option effective.  For the x86-64 compiler, these
          extensions are enabled by default.

          The resulting code should be considerably faster in the
          majority of cases and avoid the numerical instability problems
          of 387 code, but may break some existing code that expects
          temporaries to be 80 bits.

          This is the default choice for the x86-64 compiler, Darwin
          x86-32 targets, and the default choice for x86-32 targets with
          the SSE2 instruction set when ‘-ffast-math’ is enabled.

     ‘sse,387’
     ‘sse+387’
     ‘both’
          Attempt to utilize both instruction sets at once.  This
          effectively doubles the amount of available registers, and on
          chips with separate execution units for 387 and SSE the
          execution resources too.  Use this option with care, as it is
          still experimental, because the GCC register allocator does
          not model separate functional units well, resulting in
          unstable performance.

‘-masm=DIALECT’
     Output assembly instructions using selected DIALECT.  Also affects
     which dialect is used for basic ‘asm’ (*note Basic Asm::) and
     extended ‘asm’ (*note Extended Asm::).  Supported choices (in
     dialect order) are ‘att’ or ‘intel’.  The default is ‘att’.  Darwin
     does not support ‘intel’.

‘-mieee-fp’
‘-mno-ieee-fp’
     Control whether or not the compiler uses IEEE floating-point
     comparisons.  These correctly handle the case where the result of a
     comparison is unordered.

‘-m80387’
‘-mhard-float’
     Generate output containing 80387 instructions for floating point.

‘-mno-80387’
‘-msoft-float’
     Generate output containing library calls for floating point.

     *Warning:* the requisite libraries are not part of GCC.  Normally
     the facilities of the machine's usual C compiler are used, but this
     cannot be done directly in cross-compilation.  You must make your
     own arrangements to provide suitable library functions for
     cross-compilation.

     On machines where a function returns floating-point results in the
     80387 register stack, some floating-point opcodes may be emitted
     even if ‘-msoft-float’ is used.

‘-mno-fp-ret-in-387’
     Do not use the FPU registers for return values of functions.

     The usual calling convention has functions return values of types
     ‘float’ and ‘double’ in an FPU register, even if there is no FPU.
     The idea is that the operating system should emulate an FPU.

     The option ‘-mno-fp-ret-in-387’ causes such values to be returned
     in ordinary CPU registers instead.

‘-mno-fancy-math-387’
     Some 387 emulators do not support the ‘sin’, ‘cos’ and ‘sqrt’
     instructions for the 387.  Specify this option to avoid generating
     those instructions.  This option is overridden when ‘-march’
     indicates that the target CPU always has an FPU and so the
     instruction does not need emulation.  These instructions are not
     generated unless you also use the ‘-funsafe-math-optimizations’
     switch.

‘-malign-double’
‘-mno-align-double’
     Control whether GCC aligns ‘double’, ‘long double’, and ‘long long’
     variables on a two-word boundary or a one-word boundary.  Aligning
     ‘double’ variables on a two-word boundary produces code that runs
     somewhat faster on a Pentium at the expense of more memory.

     On x86-64, ‘-malign-double’ is enabled by default.

     *Warning:* if you use the ‘-malign-double’ switch, structures
     containing the above types are aligned differently than the
     published application binary interface specifications for the
     x86-32 and are not binary compatible with structures in code
     compiled without that switch.

‘-m96bit-long-double’
‘-m128bit-long-double’
     These switches control the size of ‘long double’ type.  The x86-32
     application binary interface specifies the size to be 96 bits, so
     ‘-m96bit-long-double’ is the default in 32-bit mode.

     Modern architectures (Pentium and newer) prefer ‘long double’ to be
     aligned to an 8- or 16-byte boundary.  In arrays or structures
     conforming to the ABI, this is not possible.  So specifying
     ‘-m128bit-long-double’ aligns ‘long double’ to a 16-byte boundary
     by padding the ‘long double’ with an additional 32-bit zero.

     In the x86-64 compiler, ‘-m128bit-long-double’ is the default
     choice as its ABI specifies that ‘long double’ is aligned on
     16-byte boundary.

     Notice that neither of these options enable any extra precision
     over the x87 standard of 80 bits for a ‘long double’.

     *Warning:* if you override the default value for your target ABI,
     this changes the size of structures and arrays containing ‘long
     double’ variables, as well as modifying the function calling
     convention for functions taking ‘long double’.  Hence they are not
     binary-compatible with code compiled without that switch.

‘-mlong-double-64’
‘-mlong-double-80’
‘-mlong-double-128’
     These switches control the size of ‘long double’ type.  A size of
     64 bits makes the ‘long double’ type equivalent to the ‘double’
     type.  This is the default for 32-bit Bionic C library.  A size of
     128 bits makes the ‘long double’ type equivalent to the
     ‘__float128’ type.  This is the default for 64-bit Bionic C
     library.

     *Warning:* if you override the default value for your target ABI,
     this changes the size of structures and arrays containing ‘long
     double’ variables, as well as modifying the function calling
     convention for functions taking ‘long double’.  Hence they are not
     binary-compatible with code compiled without that switch.

‘-malign-data=TYPE’
     Control how GCC aligns variables.  Supported values for TYPE are
     ‘compat’ uses increased alignment value compatible uses GCC 4.8 and
     earlier, ‘abi’ uses alignment value as specified by the psABI, and
     ‘cacheline’ uses increased alignment value to match the cache line
     size.  ‘compat’ is the default.

‘-mlarge-data-threshold=THRESHOLD’
     When ‘-mcmodel=medium’ is specified, data objects larger than
     THRESHOLD are placed in the large data section.  This value must be
     the same across all objects linked into the binary, and defaults to
     65535.

‘-mrtd’
     Use a different function-calling convention, in which functions
     that take a fixed number of arguments return with the ‘ret NUM’
     instruction, which pops their arguments while returning.  This
     saves one instruction in the caller since there is no need to pop
     the arguments there.

     You can specify that an individual function is called with this
     calling sequence with the function attribute ‘stdcall’.  You can
     also override the ‘-mrtd’ option by using the function attribute
     ‘cdecl’.  *Note Function Attributes::.

     *Warning:* this calling convention is incompatible with the one
     normally used on Unix, so you cannot use it if you need to call
     libraries compiled with the Unix compiler.

     Also, you must provide function prototypes for all functions that
     take variable numbers of arguments (including ‘printf’); otherwise
     incorrect code is generated for calls to those functions.

     In addition, seriously incorrect code results if you call a
     function with too many arguments.  (Normally, extra arguments are
     harmlessly ignored.)

‘-mregparm=NUM’
     Control how many registers are used to pass integer arguments.  By
     default, no registers are used to pass arguments, and at most 3
     registers can be used.  You can control this behavior for a
     specific function by using the function attribute ‘regparm’.  *Note
     Function Attributes::.

     *Warning:* if you use this switch, and NUM is nonzero, then you
     must build all modules with the same value, including any
     libraries.  This includes the system libraries and startup modules.

‘-msseregparm’
     Use SSE register passing conventions for float and double arguments
     and return values.  You can control this behavior for a specific
     function by using the function attribute ‘sseregparm’.  *Note
     Function Attributes::.

     *Warning:* if you use this switch then you must build all modules
     with the same value, including any libraries.  This includes the
     system libraries and startup modules.

‘-mvect8-ret-in-mem’
     Return 8-byte vectors in memory instead of MMX registers.  This is
     the default on VxWorks to match the ABI of the Sun Studio compilers
     until version 12.  _Only_ use this option if you need to remain
     compatible with existing code produced by those previous compiler
     versions or older versions of GCC.

‘-mpc32’
‘-mpc64’
‘-mpc80’

     Set 80387 floating-point precision to 32, 64 or 80 bits.  When
     ‘-mpc32’ is specified, the significands of results of
     floating-point operations are rounded to 24 bits (single
     precision); ‘-mpc64’ rounds the significands of results of
     floating-point operations to 53 bits (double precision) and
     ‘-mpc80’ rounds the significands of results of floating-point
     operations to 64 bits (extended double precision), which is the
     default.  When this option is used, floating-point operations in
     higher precisions are not available to the programmer without
     setting the FPU control word explicitly.

     Setting the rounding of floating-point operations to less than the
     default 80 bits can speed some programs by 2% or more.  Note that
     some mathematical libraries assume that extended-precision (80-bit)
     floating-point operations are enabled by default; routines in such
     libraries could suffer significant loss of accuracy, typically
     through so-called "catastrophic cancellation", when this option is
     used to set the precision to less than extended precision.

‘-mstackrealign’
     Realign the stack at entry.  On the x86, the ‘-mstackrealign’
     option generates an alternate prologue and epilogue that realigns
     the run-time stack if necessary.  This supports mixing legacy codes
     that keep 4-byte stack alignment with modern codes that keep
     16-byte stack alignment for SSE compatibility.  See also the
     attribute ‘force_align_arg_pointer’, applicable to individual
     functions.

‘-mpreferred-stack-boundary=NUM’
     Attempt to keep the stack boundary aligned to a 2 raised to NUM
     byte boundary.  If ‘-mpreferred-stack-boundary’ is not specified,
     the default is 4 (16 bytes or 128 bits).

     *Warning:* When generating code for the x86-64 architecture with
     SSE extensions disabled, ‘-mpreferred-stack-boundary=3’ can be used
     to keep the stack boundary aligned to 8 byte boundary.  Since
     x86-64 ABI require 16 byte stack alignment, this is ABI
     incompatible and intended to be used in controlled environment
     where stack space is important limitation.  This option leads to
     wrong code when functions compiled with 16 byte stack alignment
     (such as functions from a standard library) are called with
     misaligned stack.  In this case, SSE instructions may lead to
     misaligned memory access traps.  In addition, variable arguments
     are handled incorrectly for 16 byte aligned objects (including x87
     long double and __int128), leading to wrong results.  You must
     build all modules with ‘-mpreferred-stack-boundary=3’, including
     any libraries.  This includes the system libraries and startup
     modules.

‘-mincoming-stack-boundary=NUM’
     Assume the incoming stack is aligned to a 2 raised to NUM byte
     boundary.  If ‘-mincoming-stack-boundary’ is not specified, the one
     specified by ‘-mpreferred-stack-boundary’ is used.

     On Pentium and Pentium Pro, ‘double’ and ‘long double’ values
     should be aligned to an 8-byte boundary (see ‘-malign-double’) or
     suffer significant run time performance penalties.  On Pentium III,
     the Streaming SIMD Extension (SSE) data type ‘__m128’ may not work
     properly if it is not 16-byte aligned.

     To ensure proper alignment of this values on the stack, the stack
     boundary must be as aligned as that required by any value stored on
     the stack.  Further, every function must be generated such that it
     keeps the stack aligned.  Thus calling a function compiled with a
     higher preferred stack boundary from a function compiled with a
     lower preferred stack boundary most likely misaligns the stack.  It
     is recommended that libraries that use callbacks always use the
     default setting.

     This extra alignment does consume extra stack space, and generally
     increases code size.  Code that is sensitive to stack space usage,
     such as embedded systems and operating system kernels, may want to
     reduce the preferred alignment to ‘-mpreferred-stack-boundary=2’.

‘-mmmx’
‘-msse’
‘-msse2’
‘-msse3’
‘-mssse3’
‘-msse4’
‘-msse4a’
‘-msse4.1’
‘-msse4.2’
‘-mavx’
‘-mavx2’
‘-mavx512f’
‘-mavx512pf’
‘-mavx512er’
‘-mavx512cd’
‘-mavx512vl’
‘-mavx512bw’
‘-mavx512dq’
‘-mavx512ifma’
‘-mavx512vbmi’
‘-msha’
‘-maes’
‘-mpclmul’
‘-mclflushopt’
‘-mclwb’
‘-mfsgsbase’
‘-mptwrite’
‘-mrdrnd’
‘-mf16c’
‘-mfma’
‘-mpconfig’
‘-mwbnoinvd’
‘-mfma4’
‘-mprfchw’
‘-mrdpid’
‘-mprefetchwt1’
‘-mrdseed’
‘-msgx’
‘-mxop’
‘-mlwp’
‘-m3dnow’
‘-m3dnowa’
‘-mpopcnt’
‘-mabm’
‘-madx’
‘-mbmi’
‘-mbmi2’
‘-mlzcnt’
‘-mfxsr’
‘-mxsave’
‘-mxsaveopt’
‘-mxsavec’
‘-mxsaves’
‘-mrtm’
‘-mhle’
‘-mtbm’
‘-mmwaitx’
‘-mclzero’
‘-mpku’
‘-mavx512vbmi2’
‘-mavx512bf16’
‘-mavx512fp16’
‘-mgfni’
‘-mvaes’
‘-mwaitpkg’
‘-mvpclmulqdq’
‘-mavx512bitalg’
‘-mmovdiri’
‘-mmovdir64b’
‘-menqcmd’
‘-muintr’
‘-mtsxldtrk’
‘-mavx512vpopcntdq’
‘-mavx512vp2intersect’
‘-mavx5124fmaps’
‘-mavx512vnni’
‘-mavxvnni’
‘-mavx5124vnniw’
‘-mcldemote’
‘-mserialize’
‘-mamx-tile’
‘-mamx-int8’
‘-mamx-bf16’
‘-mhreset’
‘-mkl’
‘-mwidekl’
     These switches enable the use of instructions in the MMX, SSE,
     SSE2, SSE3, SSSE3, SSE4, SSE4A, SSE4.1, SSE4.2, AVX, AVX2, AVX512F,
     AVX512PF, AVX512ER, AVX512CD, AVX512VL, AVX512BW, AVX512DQ,
     AVX512IFMA, AVX512VBMI, SHA, AES, PCLMUL, CLFLUSHOPT, CLWB,
     FSGSBASE, PTWRITE, RDRND, F16C, FMA, PCONFIG, WBNOINVD, FMA4,
     PREFETCHW, RDPID, PREFETCHWT1, RDSEED, SGX, XOP, LWP, 3DNow!,
     enhanced 3DNow!, POPCNT, ABM, ADX, BMI, BMI2, LZCNT, FXSR, XSAVE,
     XSAVEOPT, XSAVEC, XSAVES, RTM, HLE, TBM, MWAITX, CLZERO, PKU,
     AVX512VBMI2, GFNI, VAES, WAITPKG, VPCLMULQDQ, AVX512BITALG,
     MOVDIRI, MOVDIR64B, AVX512BF16, ENQCMD, AVX512VPOPCNTDQ,
     AVX5124FMAPS, AVX512VNNI, AVX5124VNNIW, SERIALIZE, UINTR, HRESET,
     AMXTILE, AMXINT8, AMXBF16, KL, WIDEKL, AVXVNNI, AVX512FP16 or
     CLDEMOTE extended instruction sets.  Each has a corresponding
     ‘-mno-’ option to disable use of these instructions.

     These extensions are also available as built-in functions: see
     *note x86 Built-in Functions::, for details of the functions
     enabled and disabled by these switches.

     To generate SSE/SSE2 instructions automatically from floating-point
     code (as opposed to 387 instructions), see ‘-mfpmath=sse’.

     GCC depresses SSEx instructions when ‘-mavx’ is used.  Instead, it
     generates new AVX instructions or AVX equivalence for all SSEx
     instructions when needed.

     These options enable GCC to use these extended instructions in
     generated code, even without ‘-mfpmath=sse’.  Applications that
     perform run-time CPU detection must compile separate files for each
     supported architecture, using the appropriate flags.  In
     particular, the file containing the CPU detection code should be
     compiled without these options.

‘-mdump-tune-features’
     This option instructs GCC to dump the names of the x86 performance
     tuning features and default settings.  The names can be used in
     ‘-mtune-ctrl=FEATURE-LIST’.

‘-mtune-ctrl=FEATURE-LIST’
     This option is used to do fine grain control of x86 code generation
     features.  FEATURE-LIST is a comma separated list of FEATURE names.
     See also ‘-mdump-tune-features’.  When specified, the FEATURE is
     turned on if it is not preceded with ‘^’, otherwise, it is turned
     off.  ‘-mtune-ctrl=FEATURE-LIST’ is intended to be used by GCC
     developers.  Using it may lead to code paths not covered by testing
     and can potentially result in compiler ICEs or runtime errors.

‘-mno-default’
     This option instructs GCC to turn off all tunable features.  See
     also ‘-mtune-ctrl=FEATURE-LIST’ and ‘-mdump-tune-features’.

‘-mcld’
     This option instructs GCC to emit a ‘cld’ instruction in the
     prologue of functions that use string instructions.  String
     instructions depend on the DF flag to select between autoincrement
     or autodecrement mode.  While the ABI specifies the DF flag to be
     cleared on function entry, some operating systems violate this
     specification by not clearing the DF flag in their exception
     dispatchers.  The exception handler can be invoked with the DF flag
     set, which leads to wrong direction mode when string instructions
     are used.  This option can be enabled by default on 32-bit x86
     targets by configuring GCC with the ‘--enable-cld’ configure
     option.  Generation of ‘cld’ instructions can be suppressed with
     the ‘-mno-cld’ compiler option in this case.

‘-mvzeroupper’
     This option instructs GCC to emit a ‘vzeroupper’ instruction before
     a transfer of control flow out of the function to minimize the AVX
     to SSE transition penalty as well as remove unnecessary ‘zeroupper’
     intrinsics.

‘-mprefer-avx128’
     This option instructs GCC to use 128-bit AVX instructions instead
     of 256-bit AVX instructions in the auto-vectorizer.

‘-mprefer-vector-width=OPT’
     This option instructs GCC to use OPT-bit vector width in
     instructions instead of default on the selected platform.

‘-mmove-max=BITS’
     This option instructs GCC to set the maximum number of bits can be
     moved from memory to memory efficiently to BITS.  The valid BITS
     are 128, 256 and 512.

‘-mstore-max=BITS’
     This option instructs GCC to set the maximum number of bits can be
     stored to memory efficiently to BITS.  The valid BITS are 128, 256
     and 512.

     ‘none’
          No extra limitations applied to GCC other than defined by the
          selected platform.

     ‘128’
          Prefer 128-bit vector width for instructions.

     ‘256’
          Prefer 256-bit vector width for instructions.

     ‘512’
          Prefer 512-bit vector width for instructions.

‘-mcx16’
     This option enables GCC to generate ‘CMPXCHG16B’ instructions in
     64-bit code to implement compare-and-exchange operations on 16-byte
     aligned 128-bit objects.  This is useful for atomic updates of data
     structures exceeding one machine word in size.  The compiler uses
     this instruction to implement *note __sync Builtins::.  However,
     for *note __atomic Builtins:: operating on 128-bit integers, a
     library call is always used.

‘-msahf’
     This option enables generation of ‘SAHF’ instructions in 64-bit
     code.  Early Intel Pentium 4 CPUs with Intel 64 support, prior to
     the introduction of Pentium 4 G1 step in December 2005, lacked the
     ‘LAHF’ and ‘SAHF’ instructions which are supported by AMD64.  These
     are load and store instructions, respectively, for certain status
     flags.  In 64-bit mode, the ‘SAHF’ instruction is used to optimize
     ‘fmod’, ‘drem’, and ‘remainder’ built-in functions; see *note Other
     Builtins:: for details.

‘-mmovbe’
     This option enables use of the ‘movbe’ instruction to implement
     ‘__builtin_bswap32’ and ‘__builtin_bswap64’.

‘-mshstk’
     The ‘-mshstk’ option enables shadow stack built-in functions from
     x86 Control-flow Enforcement Technology (CET).

‘-mcrc32’
     This option enables built-in functions ‘__builtin_ia32_crc32qi’,
     ‘__builtin_ia32_crc32hi’, ‘__builtin_ia32_crc32si’ and
     ‘__builtin_ia32_crc32di’ to generate the ‘crc32’ machine
     instruction.

‘-mmwait’
     This option enables built-in functions ‘__builtin_ia32_monitor’,
     and ‘__builtin_ia32_mwait’ to generate the ‘monitor’ and ‘mwait’
     machine instructions.

‘-mrecip’
     This option enables use of ‘RCPSS’ and ‘RSQRTSS’ instructions (and
     their vectorized variants ‘RCPPS’ and ‘RSQRTPS’) with an additional
     Newton-Raphson step to increase precision instead of ‘DIVSS’ and
     ‘SQRTSS’ (and their vectorized variants) for single-precision
     floating-point arguments.  These instructions are generated only
     when ‘-funsafe-math-optimizations’ is enabled together with
     ‘-ffinite-math-only’ and ‘-fno-trapping-math’.  Note that while the
     throughput of the sequence is higher than the throughput of the
     non-reciprocal instruction, the precision of the sequence can be
     decreased by up to 2 ulp (i.e. the inverse of 1.0 equals
     0.99999994).

     Note that GCC implements ‘1.0f/sqrtf(X)’ in terms of ‘RSQRTSS’ (or
     ‘RSQRTPS’) already with ‘-ffast-math’ (or the above option
     combination), and doesn't need ‘-mrecip’.

     Also note that GCC emits the above sequence with additional
     Newton-Raphson step for vectorized single-float division and
     vectorized ‘sqrtf(X)’ already with ‘-ffast-math’ (or the above
     option combination), and doesn't need ‘-mrecip’.

‘-mrecip=OPT’
     This option controls which reciprocal estimate instructions may be
     used.  OPT is a comma-separated list of options, which may be
     preceded by a ‘!’ to invert the option:

     ‘all’
          Enable all estimate instructions.

     ‘default’
          Enable the default instructions, equivalent to ‘-mrecip’.

     ‘none’
          Disable all estimate instructions, equivalent to ‘-mno-recip’.

     ‘div’
          Enable the approximation for scalar division.

     ‘vec-div’
          Enable the approximation for vectorized division.

     ‘sqrt’
          Enable the approximation for scalar square root.

     ‘vec-sqrt’
          Enable the approximation for vectorized square root.

     So, for example, ‘-mrecip=all,!sqrt’ enables all of the reciprocal
     approximations, except for square root.

‘-mveclibabi=TYPE’
     Specifies the ABI type to use for vectorizing intrinsics using an
     external library.  Supported values for TYPE are ‘svml’ for the
     Intel short vector math library and ‘acml’ for the AMD math core
     library.  To use this option, both ‘-ftree-vectorize’ and
     ‘-funsafe-math-optimizations’ have to be enabled, and an SVML or
     ACML ABI-compatible library must be specified at link time.

     GCC currently emits calls to ‘vmldExp2’, ‘vmldLn2’, ‘vmldLog102’,
     ‘vmldPow2’, ‘vmldTanh2’, ‘vmldTan2’, ‘vmldAtan2’, ‘vmldAtanh2’,
     ‘vmldCbrt2’, ‘vmldSinh2’, ‘vmldSin2’, ‘vmldAsinh2’, ‘vmldAsin2’,
     ‘vmldCosh2’, ‘vmldCos2’, ‘vmldAcosh2’, ‘vmldAcos2’, ‘vmlsExp4’,
     ‘vmlsLn4’, ‘vmlsLog104’, ‘vmlsPow4’, ‘vmlsTanh4’, ‘vmlsTan4’,
     ‘vmlsAtan4’, ‘vmlsAtanh4’, ‘vmlsCbrt4’, ‘vmlsSinh4’, ‘vmlsSin4’,
     ‘vmlsAsinh4’, ‘vmlsAsin4’, ‘vmlsCosh4’, ‘vmlsCos4’, ‘vmlsAcosh4’
     and ‘vmlsAcos4’ for corresponding function type when
     ‘-mveclibabi=svml’ is used, and ‘__vrd2_sin’, ‘__vrd2_cos’,
     ‘__vrd2_exp’, ‘__vrd2_log’, ‘__vrd2_log2’, ‘__vrd2_log10’,
     ‘__vrs4_sinf’, ‘__vrs4_cosf’, ‘__vrs4_expf’, ‘__vrs4_logf’,
     ‘__vrs4_log2f’, ‘__vrs4_log10f’ and ‘__vrs4_powf’ for the
     corresponding function type when ‘-mveclibabi=acml’ is used.

‘-mabi=NAME’
     Generate code for the specified calling convention.  Permissible
     values are ‘sysv’ for the ABI used on GNU/Linux and other systems,
     and ‘ms’ for the Microsoft ABI. The default is to use the Microsoft
     ABI when targeting Microsoft Windows and the SysV ABI on all other
     systems.  You can control this behavior for specific functions by
     using the function attributes ‘ms_abi’ and ‘sysv_abi’.  *Note
     Function Attributes::.

‘-mforce-indirect-call’
     Force all calls to functions to be indirect.  This is useful when
     using Intel Processor Trace where it generates more precise timing
     information for function calls.

‘-mmanual-endbr’
     Insert ENDBR instruction at function entry only via the ‘cf_check’
     function attribute.  This is useful when used with the option
     ‘-fcf-protection=branch’ to control ENDBR insertion at the function
     entry.

‘-mcall-ms2sysv-xlogues’
     Due to differences in 64-bit ABIs, any Microsoft ABI function that
     calls a System V ABI function must consider RSI, RDI and XMM6-15 as
     clobbered.  By default, the code for saving and restoring these
     registers is emitted inline, resulting in fairly lengthy prologues
     and epilogues.  Using ‘-mcall-ms2sysv-xlogues’ emits prologues and
     epilogues that use stubs in the static portion of libgcc to perform
     these saves and restores, thus reducing function size at the cost
     of a few extra instructions.

‘-mtls-dialect=TYPE’
     Generate code to access thread-local storage using the ‘gnu’ or
     ‘gnu2’ conventions.  ‘gnu’ is the conservative default; ‘gnu2’ is
     more efficient, but it may add compile- and run-time requirements
     that cannot be satisfied on all systems.

‘-mpush-args’
‘-mno-push-args’
     Use PUSH operations to store outgoing parameters.  This method is
     shorter and usually equally fast as method using SUB/MOV operations
     and is enabled by default.  In some cases disabling it may improve
     performance because of improved scheduling and reduced
     dependencies.

‘-maccumulate-outgoing-args’
     If enabled, the maximum amount of space required for outgoing
     arguments is computed in the function prologue.  This is faster on
     most modern CPUs because of reduced dependencies, improved
     scheduling and reduced stack usage when the preferred stack
     boundary is not equal to 2.  The drawback is a notable increase in
     code size.  This switch implies ‘-mno-push-args’.

‘-mthreads’
     Support thread-safe exception handling on MinGW. Programs that rely
     on thread-safe exception handling must compile and link all code
     with the ‘-mthreads’ option.  When compiling, ‘-mthreads’ defines
     ‘-D_MT’; when linking, it links in a special thread helper library
     ‘-lmingwthrd’ which cleans up per-thread exception-handling data.

‘-mms-bitfields’
‘-mno-ms-bitfields’

     Enable/disable bit-field layout compatible with the native
     Microsoft Windows compiler.

     If ‘packed’ is used on a structure, or if bit-fields are used, it
     may be that the Microsoft ABI lays out the structure differently
     than the way GCC normally does.  Particularly when moving packed
     data between functions compiled with GCC and the native Microsoft
     compiler (either via function call or as data in a file), it may be
     necessary to access either format.

     This option is enabled by default for Microsoft Windows targets.
     This behavior can also be controlled locally by use of variable or
     type attributes.  For more information, see *note x86 Variable
     Attributes:: and *note x86 Type Attributes::.

     The Microsoft structure layout algorithm is fairly simple with the
     exception of the bit-field packing.  The padding and alignment of
     members of structures and whether a bit-field can straddle a
     storage-unit boundary are determine by these rules:

       1. Structure members are stored sequentially in the order in
          which they are declared: the first member has the lowest
          memory address and the last member the highest.

       2. Every data object has an alignment requirement.  The alignment
          requirement for all data except structures, unions, and arrays
          is either the size of the object or the current packing size
          (specified with either the ‘aligned’ attribute or the ‘pack’
          pragma), whichever is less.  For structures, unions, and
          arrays, the alignment requirement is the largest alignment
          requirement of its members.  Every object is allocated an
          offset so that:

               offset % alignment_requirement == 0

       3. Adjacent bit-fields are packed into the same 1-, 2-, or 4-byte
          allocation unit if the integral types are the same size and if
          the next bit-field fits into the current allocation unit
          without crossing the boundary imposed by the common alignment
          requirements of the bit-fields.

     MSVC interprets zero-length bit-fields in the following ways:

       1. If a zero-length bit-field is inserted between two bit-fields
          that are normally coalesced, the bit-fields are not coalesced.

          For example:

               struct
                {
                  unsigned long bf_1 : 12;
                  unsigned long : 0;
                  unsigned long bf_2 : 12;
                } t1;

          The size of ‘t1’ is 8 bytes with the zero-length bit-field.
          If the zero-length bit-field were removed, ‘t1’'s size would
          be 4 bytes.

       2. If a zero-length bit-field is inserted after a bit-field,
          ‘foo’, and the alignment of the zero-length bit-field is
          greater than the member that follows it, ‘bar’, ‘bar’ is
          aligned as the type of the zero-length bit-field.

          For example:

               struct
                {
                  char foo : 4;
                  short : 0;
                  char bar;
                } t2;

               struct
                {
                  char foo : 4;
                  short : 0;
                  double bar;
                } t3;

          For ‘t2’, ‘bar’ is placed at offset 2, rather than offset 1.
          Accordingly, the size of ‘t2’ is 4.  For ‘t3’, the zero-length
          bit-field does not affect the alignment of ‘bar’ or, as a
          result, the size of the structure.

          Taking this into account, it is important to note the
          following:

            1. If a zero-length bit-field follows a normal bit-field,
               the type of the zero-length bit-field may affect the
               alignment of the structure as whole.  For example, ‘t2’
               has a size of 4 bytes, since the zero-length bit-field
               follows a normal bit-field, and is of type short.

            2. Even if a zero-length bit-field is not followed by a
               normal bit-field, it may still affect the alignment of
               the structure:

                    struct
                     {
                       char foo : 6;
                       long : 0;
                     } t4;

               Here, ‘t4’ takes up 4 bytes.

       3. Zero-length bit-fields following non-bit-field members are
          ignored:

               struct
                {
                  char foo;
                  long : 0;
                  char bar;
                } t5;

          Here, ‘t5’ takes up 2 bytes.

‘-mno-align-stringops’
     Do not align the destination of inlined string operations.  This
     switch reduces code size and improves performance in case the
     destination is already aligned, but GCC doesn't know about it.

‘-minline-all-stringops’
     By default GCC inlines string operations only when the destination
     is known to be aligned to least a 4-byte boundary.  This enables
     more inlining and increases code size, but may improve performance
     of code that depends on fast ‘memcpy’ and ‘memset’ for short
     lengths.  The option enables inline expansion of ‘strlen’ for all
     pointer alignments.

‘-minline-stringops-dynamically’
     For string operations of unknown size, use run-time checks with
     inline code for small blocks and a library call for large blocks.

‘-mstringop-strategy=ALG’
     Override the internal decision heuristic for the particular
     algorithm to use for inlining string operations.  The allowed
     values for ALG are:

     ‘rep_byte’
     ‘rep_4byte’
     ‘rep_8byte’
          Expand using i386 ‘rep’ prefix of the specified size.

     ‘byte_loop’
     ‘loop’
     ‘unrolled_loop’
          Expand into an inline loop.

     ‘libcall’
          Always use a library call.

‘-mmemcpy-strategy=STRATEGY’
     Override the internal decision heuristic to decide if
     ‘__builtin_memcpy’ should be inlined and what inline algorithm to
     use when the expected size of the copy operation is known.
     STRATEGY is a comma-separated list of ALG:MAX_SIZE:DEST_ALIGN
     triplets.  ALG is specified in ‘-mstringop-strategy’, MAX_SIZE
     specifies the max byte size with which inline algorithm ALG is
     allowed.  For the last triplet, the MAX_SIZE must be ‘-1’.  The
     MAX_SIZE of the triplets in the list must be specified in
     increasing order.  The minimal byte size for ALG is ‘0’ for the
     first triplet and ‘MAX_SIZE + 1’ of the preceding range.

‘-mmemset-strategy=STRATEGY’
     The option is similar to ‘-mmemcpy-strategy=’ except that it is to
     control ‘__builtin_memset’ expansion.

‘-momit-leaf-frame-pointer’
     Don't keep the frame pointer in a register for leaf functions.
     This avoids the instructions to save, set up, and restore frame
     pointers and makes an extra register available in leaf functions.
     The option ‘-fomit-leaf-frame-pointer’ removes the frame pointer
     for leaf functions, which might make debugging harder.

‘-mtls-direct-seg-refs’
‘-mno-tls-direct-seg-refs’
     Controls whether TLS variables may be accessed with offsets from
     the TLS segment register (‘%gs’ for 32-bit, ‘%fs’ for 64-bit), or
     whether the thread base pointer must be added.  Whether or not this
     is valid depends on the operating system, and whether it maps the
     segment to cover the entire TLS area.

     For systems that use the GNU C Library, the default is on.

‘-msse2avx’
‘-mno-sse2avx’
     Specify that the assembler should encode SSE instructions with VEX
     prefix.  The option ‘-mavx’ turns this on by default.

‘-mfentry’
‘-mno-fentry’
     If profiling is active (‘-pg’), put the profiling counter call
     before the prologue.  Note: On x86 architectures the attribute
     ‘ms_hook_prologue’ isn't possible at the moment for ‘-mfentry’ and
     ‘-pg’.

‘-mrecord-mcount’
‘-mno-record-mcount’
     If profiling is active (‘-pg’), generate a __mcount_loc section
     that contains pointers to each profiling call.  This is useful for
     automatically patching and out calls.

‘-mnop-mcount’
‘-mno-nop-mcount’
     If profiling is active (‘-pg’), generate the calls to the profiling
     functions as NOPs.  This is useful when they should be patched in
     later dynamically.  This is likely only useful together with
     ‘-mrecord-mcount’.

‘-minstrument-return=TYPE’
     Instrument function exit in -pg -mfentry instrumented functions
     with call to specified function.  This only instruments true
     returns ending with ret, but not sibling calls ending with jump.
     Valid types are NONE to not instrument, CALL to generate a call to
     __return__, or NOP5 to generate a 5 byte nop.

‘-mrecord-return’
‘-mno-record-return’
     Generate a __return_loc section pointing to all return
     instrumentation code.

‘-mfentry-name=NAME’
     Set name of __fentry__ symbol called at function entry for -pg
     -mfentry functions.

‘-mfentry-section=NAME’
     Set name of section to record -mrecord-mcount calls (default
     __mcount_loc).

‘-mskip-rax-setup’
‘-mno-skip-rax-setup’
     When generating code for the x86-64 architecture with SSE
     extensions disabled, ‘-mskip-rax-setup’ can be used to skip setting
     up RAX register when there are no variable arguments passed in
     vector registers.

     *Warning:* Since RAX register is used to avoid unnecessarily saving
     vector registers on stack when passing variable arguments, the
     impacts of this option are callees may waste some stack space,
     misbehave or jump to a random location.  GCC 4.4 or newer don't
     have those issues, regardless the RAX register value.

‘-m8bit-idiv’
‘-mno-8bit-idiv’
     On some processors, like Intel Atom, 8-bit unsigned integer divide
     is much faster than 32-bit/64-bit integer divide.  This option
     generates a run-time check.  If both dividend and divisor are
     within range of 0 to 255, 8-bit unsigned integer divide is used
     instead of 32-bit/64-bit integer divide.

‘-mavx256-split-unaligned-load’
‘-mavx256-split-unaligned-store’
     Split 32-byte AVX unaligned load and store.

‘-mstack-protector-guard=GUARD’
‘-mstack-protector-guard-reg=REG’
‘-mstack-protector-guard-offset=OFFSET’
     Generate stack protection code using canary at GUARD.  Supported
     locations are ‘global’ for global canary or ‘tls’ for per-thread
     canary in the TLS block (the default).  This option has effect only
     when ‘-fstack-protector’ or ‘-fstack-protector-all’ is specified.

     With the latter choice the options
     ‘-mstack-protector-guard-reg=REG’ and
     ‘-mstack-protector-guard-offset=OFFSET’ furthermore specify which
     segment register (‘%fs’ or ‘%gs’) to use as base register for
     reading the canary, and from what offset from that base register.
     The default for those is as specified in the relevant ABI.

‘-mgeneral-regs-only’
     Generate code that uses only the general-purpose registers.  This
     prevents the compiler from using floating-point, vector, mask and
     bound registers.

‘-mrelax-cmpxchg-loop’
     Relax cmpxchg loop by emitting an early load and compare before
     cmpxchg, execute pause if load value is not expected.  This reduces
     excessive cachline bouncing when and works for all atomic logic
     fetch builtins that generates compare and swap loop.

‘-mindirect-branch=CHOICE’
     Convert indirect call and jump with CHOICE.  The default is ‘keep’,
     which keeps indirect call and jump unmodified.  ‘thunk’ converts
     indirect call and jump to call and return thunk.  ‘thunk-inline’
     converts indirect call and jump to inlined call and return thunk.
     ‘thunk-extern’ converts indirect call and jump to external call and
     return thunk provided in a separate object file.  You can control
     this behavior for a specific function by using the function
     attribute ‘indirect_branch’.  *Note Function Attributes::.

     Note that ‘-mcmodel=large’ is incompatible with
     ‘-mindirect-branch=thunk’ and ‘-mindirect-branch=thunk-extern’
     since the thunk function may not be reachable in the large code
     model.

     Note that ‘-mindirect-branch=thunk-extern’ is compatible with
     ‘-fcf-protection=branch’ since the external thunk can be made to
     enable control-flow check.

‘-mfunction-return=CHOICE’
     Convert function return with CHOICE.  The default is ‘keep’, which
     keeps function return unmodified.  ‘thunk’ converts function return
     to call and return thunk.  ‘thunk-inline’ converts function return
     to inlined call and return thunk.  ‘thunk-extern’ converts function
     return to external call and return thunk provided in a separate
     object file.  You can control this behavior for a specific function
     by using the function attribute ‘function_return’.  *Note Function
     Attributes::.

     Note that ‘-mindirect-return=thunk-extern’ is compatible with
     ‘-fcf-protection=branch’ since the external thunk can be made to
     enable control-flow check.

     Note that ‘-mcmodel=large’ is incompatible with
     ‘-mfunction-return=thunk’ and ‘-mfunction-return=thunk-extern’
     since the thunk function may not be reachable in the large code
     model.

‘-mindirect-branch-register’
     Force indirect call and jump via register.

‘-mharden-sls=CHOICE’
     Generate code to mitigate against straight line speculation (SLS)
     with CHOICE.  The default is ‘none’ which disables all SLS
     hardening.  ‘return’ enables SLS hardening for function returns.
     ‘indirect-jmp’ enables SLS hardening for indirect jumps.  ‘all’
     enables all SLS hardening.

‘-mindirect-branch-cs-prefix’
     Add CS prefix to call and jmp to indirect thunk with branch target
     in r8-r15 registers so that the call and jmp instruction length is
     6 bytes to allow them to be replaced with ‘lfence; call *%r8-r15’
     or ‘lfence; jmp *%r8-r15’ at run-time.

 These ‘-m’ switches are supported in addition to the above on x86-64
processors in 64-bit environments.

‘-m32’
‘-m64’
‘-mx32’
‘-m16’
‘-miamcu’
     Generate code for a 16-bit, 32-bit or 64-bit environment.  The
     ‘-m32’ option sets ‘int’, ‘long’, and pointer types to 32 bits, and
     generates code that runs on any i386 system.

     The ‘-m64’ option sets ‘int’ to 32 bits and ‘long’ and pointer
     types to 64 bits, and generates code for the x86-64 architecture.
     For Darwin only the ‘-m64’ option also turns off the ‘-fno-pic’ and
     ‘-mdynamic-no-pic’ options.

     The ‘-mx32’ option sets ‘int’, ‘long’, and pointer types to 32
     bits, and generates code for the x86-64 architecture.

     The ‘-m16’ option is the same as ‘-m32’, except for that it outputs
     the ‘.code16gcc’ assembly directive at the beginning of the
     assembly output so that the binary can run in 16-bit mode.

     The ‘-miamcu’ option generates code which conforms to Intel MCU
     psABI.  It requires the ‘-m32’ option to be turned on.

‘-mno-red-zone’
     Do not use a so-called "red zone" for x86-64 code.  The red zone is
     mandated by the x86-64 ABI; it is a 128-byte area beyond the
     location of the stack pointer that is not modified by signal or
     interrupt handlers and therefore can be used for temporary data
     without adjusting the stack pointer.  The flag ‘-mno-red-zone’
     disables this red zone.

‘-mcmodel=small’
     Generate code for the small code model: the program and its symbols
     must be linked in the lower 2 GB of the address space.  Pointers
     are 64 bits.  Programs can be statically or dynamically linked.
     This is the default code model.

‘-mcmodel=kernel’
     Generate code for the kernel code model.  The kernel runs in the
     negative 2 GB of the address space.  This model has to be used for
     Linux kernel code.

‘-mcmodel=medium’
     Generate code for the medium model: the program is linked in the
     lower 2 GB of the address space.  Small symbols are also placed
     there.  Symbols with sizes larger than ‘-mlarge-data-threshold’ are
     put into large data or BSS sections and can be located above 2GB.
     Programs can be statically or dynamically linked.

‘-mcmodel=large’
     Generate code for the large model.  This model makes no assumptions
     about addresses and sizes of sections.

‘-maddress-mode=long’
     Generate code for long address mode.  This is only supported for
     64-bit and x32 environments.  It is the default address mode for
     64-bit environments.

‘-maddress-mode=short’
     Generate code for short address mode.  This is only supported for
     32-bit and x32 environments.  It is the default address mode for
     32-bit and x32 environments.

‘-mneeded’
‘-mno-needed’
     Emit GNU_PROPERTY_X86_ISA_1_NEEDED GNU property for Linux target to
     indicate the micro-architecture ISA level required to execute the
     binary.

‘-mno-direct-extern-access’
     Without ‘-fpic’ nor ‘-fPIC’, always use the GOT pointer to access
     external symbols.  With ‘-fpic’ or ‘-fPIC’, treat access to
     protected symbols as local symbols.  The default is
     ‘-mdirect-extern-access’.

     *Warning:* shared libraries compiled with
     ‘-mno-direct-extern-access’ and executable compiled with
     ‘-mdirect-extern-access’ may not be binary compatible if protected
     symbols are used in shared libraries and executable.


File: gcc.info,  Node: x86 Windows Options,  Next: Xstormy16 Options,  Prev: x86 Options,  Up: Submodel Options

3.19.61 x86 Windows Options
---------------------------

These additional options are available for Microsoft Windows targets:

‘-mconsole’
     This option specifies that a console application is to be
     generated, by instructing the linker to set the PE header subsystem
     type required for console applications.  This option is available
     for Cygwin and MinGW targets and is enabled by default on those
     targets.

‘-mdll’
     This option is available for Cygwin and MinGW targets.  It
     specifies that a DLL--a dynamic link library--is to be generated,
     enabling the selection of the required runtime startup object and
     entry point.

‘-mnop-fun-dllimport’
     This option is available for Cygwin and MinGW targets.  It
     specifies that the ‘dllimport’ attribute should be ignored.

‘-mthreads’
     This option is available for MinGW targets.  It specifies that
     MinGW-specific thread support is to be used.

‘-municode’
     This option is available for MinGW-w64 targets.  It causes the
     ‘UNICODE’ preprocessor macro to be predefined, and chooses
     Unicode-capable runtime startup code.

‘-mwin32’
     This option is available for Cygwin and MinGW targets.  It
     specifies that the typical Microsoft Windows predefined macros are
     to be set in the pre-processor, but does not influence the choice
     of runtime library/startup code.

‘-mwindows’
     This option is available for Cygwin and MinGW targets.  It
     specifies that a GUI application is to be generated by instructing
     the linker to set the PE header subsystem type appropriately.

‘-fno-set-stack-executable’
     This option is available for MinGW targets.  It specifies that the
     executable flag for the stack used by nested functions isn't set.
     This is necessary for binaries running in kernel mode of Microsoft
     Windows, as there the User32 API, which is used to set executable
     privileges, isn't available.

‘-fwritable-relocated-rdata’
     This option is available for MinGW and Cygwin targets.  It
     specifies that relocated-data in read-only section is put into the
     ‘.data’ section.  This is a necessary for older runtimes not
     supporting modification of ‘.rdata’ sections for pseudo-relocation.

‘-mpe-aligned-commons’
     This option is available for Cygwin and MinGW targets.  It
     specifies that the GNU extension to the PE file format that permits
     the correct alignment of COMMON variables should be used when
     generating code.  It is enabled by default if GCC detects that the
     target assembler found during configuration supports the feature.

 See also under *note x86 Options:: for standard options.


File: gcc.info,  Node: Xstormy16 Options,  Next: Xtensa Options,  Prev: x86 Windows Options,  Up: Submodel Options

3.19.62 Xstormy16 Options
-------------------------

These options are defined for Xstormy16:

‘-msim’
     Choose startup files and linker script suitable for the simulator.


File: gcc.info,  Node: Xtensa Options,  Next: zSeries Options,  Prev: Xstormy16 Options,  Up: Submodel Options

3.19.63 Xtensa Options
----------------------

These options are supported for Xtensa targets:

‘-mconst16’
‘-mno-const16’
     Enable or disable use of ‘CONST16’ instructions for loading
     constant values.  The ‘CONST16’ instruction is currently not a
     standard option from Tensilica.  When enabled, ‘CONST16’
     instructions are always used in place of the standard ‘L32R’
     instructions.  The use of ‘CONST16’ is enabled by default only if
     the ‘L32R’ instruction is not available.

‘-mfused-madd’
‘-mno-fused-madd’
     Enable or disable use of fused multiply/add and multiply/subtract
     instructions in the floating-point option.  This has no effect if
     the floating-point option is not also enabled.  Disabling fused
     multiply/add and multiply/subtract instructions forces the compiler
     to use separate instructions for the multiply and add/subtract
     operations.  This may be desirable in some cases where strict IEEE
     754-compliant results are required: the fused multiply add/subtract
     instructions do not round the intermediate result, thereby
     producing results with _more_ bits of precision than specified by
     the IEEE standard.  Disabling fused multiply add/subtract
     instructions also ensures that the program output is not sensitive
     to the compiler's ability to combine multiply and add/subtract
     operations.

‘-mserialize-volatile’
‘-mno-serialize-volatile’
     When this option is enabled, GCC inserts ‘MEMW’ instructions before
     ‘volatile’ memory references to guarantee sequential consistency.
     The default is ‘-mserialize-volatile’.  Use
     ‘-mno-serialize-volatile’ to omit the ‘MEMW’ instructions.

‘-mforce-no-pic’
     For targets, like GNU/Linux, where all user-mode Xtensa code must
     be position-independent code (PIC), this option disables PIC for
     compiling kernel code.

‘-mtext-section-literals’
‘-mno-text-section-literals’
     These options control the treatment of literal pools.  The default
     is ‘-mno-text-section-literals’, which places literals in a
     separate section in the output file.  This allows the literal pool
     to be placed in a data RAM/ROM, and it also allows the linker to
     combine literal pools from separate object files to remove
     redundant literals and improve code size.  With
     ‘-mtext-section-literals’, the literals are interspersed in the
     text section in order to keep them as close as possible to their
     references.  This may be necessary for large assembly files.
     Literals for each function are placed right before that function.

‘-mauto-litpools’
‘-mno-auto-litpools’
     These options control the treatment of literal pools.  The default
     is ‘-mno-auto-litpools’, which places literals in a separate
     section in the output file unless ‘-mtext-section-literals’ is
     used.  With ‘-mauto-litpools’ the literals are interspersed in the
     text section by the assembler.  Compiler does not produce explicit
     ‘.literal’ directives and loads literals into registers with ‘MOVI’
     instructions instead of ‘L32R’ to let the assembler do relaxation
     and place literals as necessary.  This option allows assembler to
     create several literal pools per function and assemble very big
     functions, which may not be possible with
     ‘-mtext-section-literals’.

‘-mtarget-align’
‘-mno-target-align’
     When this option is enabled, GCC instructs the assembler to
     automatically align instructions to reduce branch penalties at the
     expense of some code density.  The assembler attempts to widen
     density instructions to align branch targets and the instructions
     following call instructions.  If there are not enough preceding
     safe density instructions to align a target, no widening is
     performed.  The default is ‘-mtarget-align’.  These options do not
     affect the treatment of auto-aligned instructions like ‘LOOP’,
     which the assembler always aligns, either by widening density
     instructions or by inserting NOP instructions.

‘-mlongcalls’
‘-mno-longcalls’
     When this option is enabled, GCC instructs the assembler to
     translate direct calls to indirect calls unless it can determine
     that the target of a direct call is in the range allowed by the
     call instruction.  This translation typically occurs for calls to
     functions in other source files.  Specifically, the assembler
     translates a direct ‘CALL’ instruction into an ‘L32R’ followed by a
     ‘CALLX’ instruction.  The default is ‘-mno-longcalls’.  This option
     should be used in programs where the call target can potentially be
     out of range.  This option is implemented in the assembler, not the
     compiler, so the assembly code generated by GCC still shows direct
     call instructions--look at the disassembled object code to see the
     actual instructions.  Note that the assembler uses an indirect call
     for every cross-file call, not just those that really are out of
     range.

‘-mabi=NAME’
     Generate code for the specified ABI.  Permissible values are:
     ‘call0’, ‘windowed’.  Default ABI is chosen by the Xtensa core
     configuration.

‘-mabi=call0’
     When this option is enabled function parameters are passed in
     registers ‘a2’ through ‘a7’, registers ‘a12’ through ‘a15’ are
     caller-saved, and register ‘a15’ may be used as a frame pointer.
     When this version of the ABI is enabled the C preprocessor symbol
     ‘__XTENSA_CALL0_ABI__’ is defined.

‘-mabi=windowed’
     When this option is enabled function parameters are passed in
     registers ‘a10’ through ‘a15’, and called function rotates register
     window by 8 registers on entry so that its arguments are found in
     registers ‘a2’ through ‘a7’.  Register ‘a7’ may be used as a frame
     pointer.  Register window is rotated 8 registers back upon return.
     When this version of the ABI is enabled the C preprocessor symbol
     ‘__XTENSA_WINDOWED_ABI__’ is defined.


File: gcc.info,  Node: zSeries Options,  Prev: Xtensa Options,  Up: Submodel Options

3.19.64 zSeries Options
-----------------------

These are listed under *Note S/390 and zSeries Options::.


File: gcc.info,  Node: Spec Files,  Next: Environment Variables,  Prev: Submodel Options,  Up: Invoking GCC

3.20 Specifying Subprocesses and the Switches to Pass to Them
=============================================================

‘gcc’ is a driver program.  It performs its job by invoking a sequence
of other programs to do the work of compiling, assembling and linking.
GCC interprets its command-line parameters and uses these to deduce
which programs it should invoke, and which command-line options it ought
to place on their command lines.  This behavior is controlled by “spec
strings”.  In most cases there is one spec string for each program that
GCC can invoke, but a few programs have multiple spec strings to control
their behavior.  The spec strings built into GCC can be overridden by
using the ‘-specs=’ command-line switch to specify a spec file.

 “Spec files” are plain-text files that are used to construct spec
strings.  They consist of a sequence of directives separated by blank
lines.  The type of directive is determined by the first non-whitespace
character on the line, which can be one of the following:

‘%COMMAND’
     Issues a COMMAND to the spec file processor.  The commands that can
     appear here are:

     ‘%include <FILE>’
          Search for FILE and insert its text at the current point in
          the specs file.

     ‘%include_noerr <FILE>’
          Just like ‘%include’, but do not generate an error message if
          the include file cannot be found.

     ‘%rename OLD_NAME NEW_NAME’
          Rename the spec string OLD_NAME to NEW_NAME.

‘*[SPEC_NAME]:’
     This tells the compiler to create, override or delete the named
     spec string.  All lines after this directive up to the next
     directive or blank line are considered to be the text for the spec
     string.  If this results in an empty string then the spec is
     deleted.  (Or, if the spec did not exist, then nothing happens.)
     Otherwise, if the spec does not currently exist a new spec is
     created.  If the spec does exist then its contents are overridden
     by the text of this directive, unless the first character of that
     text is the ‘+’ character, in which case the text is appended to
     the spec.

‘[SUFFIX]:’
     Creates a new ‘[SUFFIX] spec’ pair.  All lines after this directive
     and up to the next directive or blank line are considered to make
     up the spec string for the indicated suffix.  When the compiler
     encounters an input file with the named suffix, it processes the
     spec string in order to work out how to compile that file.  For
     example:

          .ZZ:
          z-compile -input %i

     This says that any input file whose name ends in ‘.ZZ’ should be
     passed to the program ‘z-compile’, which should be invoked with the
     command-line switch ‘-input’ and with the result of performing the
     ‘%i’ substitution.  (See below.)

     As an alternative to providing a spec string, the text following a
     suffix directive can be one of the following:

     ‘@LANGUAGE’
          This says that the suffix is an alias for a known LANGUAGE.
          This is similar to using the ‘-x’ command-line switch to GCC
          to specify a language explicitly.  For example:

               .ZZ:
               @c++

          Says that .ZZ files are, in fact, C++ source files.

     ‘#NAME’
          This causes an error messages saying:

               NAME compiler not installed on this system.

     GCC already has an extensive list of suffixes built into it.  This
     directive adds an entry to the end of the list of suffixes, but
     since the list is searched from the end backwards, it is
     effectively possible to override earlier entries using this
     technique.

 GCC has the following spec strings built into it.  Spec files can
override these strings or create their own.  Note that individual
targets can also add their own spec strings to this list.

     asm          Options to pass to the assembler
     asm_final    Options to pass to the assembler post-processor
     cpp          Options to pass to the C preprocessor
     cc1          Options to pass to the C compiler
     cc1plus      Options to pass to the C++ compiler
     endfile      Object files to include at the end of the link
     link         Options to pass to the linker
     lib          Libraries to include on the command line to the linker
     libgcc       Decides which GCC support library to pass to the linker
     linker       Sets the name of the linker
     predefines   Defines to be passed to the C preprocessor
     signed_char  Defines to pass to CPP to say whether char is signed
                  by default
     startfile    Object files to include at the start of the link

 Here is a small example of a spec file:

     %rename lib                 old_lib

     *lib:
     --start-group -lgcc -lc -leval1 --end-group %(old_lib)

 This example renames the spec called ‘lib’ to ‘old_lib’ and then
overrides the previous definition of ‘lib’ with a new one.  The new
definition adds in some extra command-line options before including the
text of the old definition.

 “Spec strings” are a list of command-line options to be passed to their
corresponding program.  In addition, the spec strings can contain
‘%’-prefixed sequences to substitute variable text or to conditionally
insert text into the command line.  Using these constructs it is
possible to generate quite complex command lines.

 Here is a table of all defined ‘%’-sequences for spec strings.  Note
that spaces are not generated automatically around the results of
expanding these sequences.  Therefore you can concatenate them together
or combine them with constant text in a single argument.

‘%%’
     Substitute one ‘%’ into the program name or argument.

‘%"’
     Substitute an empty argument.

‘%i’
     Substitute the name of the input file being processed.

‘%b’
     Substitute the basename for outputs related with the input file
     being processed.  This is often the substring up to (and not
     including) the last period and not including the directory but,
     unless %w is active, it expands to the basename for auxiliary
     outputs, which may be influenced by an explicit output name, and by
     various other options that control how auxiliary outputs are named.

‘%B’
     This is the same as ‘%b’, but include the file suffix (text after
     the last period).  Without %w, it expands to the basename for dump
     outputs.

‘%d’
     Marks the argument containing or following the ‘%d’ as a temporary
     file name, so that that file is deleted if GCC exits successfully.
     Unlike ‘%g’, this contributes no text to the argument.

‘%gSUFFIX’
     Substitute a file name that has suffix SUFFIX and is chosen once
     per compilation, and mark the argument in the same way as ‘%d’.  To
     reduce exposure to denial-of-service attacks, the file name is now
     chosen in a way that is hard to predict even when previously chosen
     file names are known.  For example, ‘%g.s ... %g.o ... %g.s’ might
     turn into ‘ccUVUUAU.s ccXYAXZ12.o ccUVUUAU.s’.  SUFFIX matches the
     regexp ‘[.A-Za-z]*’ or the special string ‘%O’, which is treated
     exactly as if ‘%O’ had been preprocessed.  Previously, ‘%g’ was
     simply substituted with a file name chosen once per compilation,
     without regard to any appended suffix (which was therefore treated
     just like ordinary text), making such attacks more likely to
     succeed.

‘%uSUFFIX’
     Like ‘%g’, but generates a new temporary file name each time it
     appears instead of once per compilation.

‘%USUFFIX’
     Substitutes the last file name generated with ‘%uSUFFIX’,
     generating a new one if there is no such last file name.  In the
     absence of any ‘%uSUFFIX’, this is just like ‘%gSUFFIX’, except
     they don't share the same suffix _space_, so ‘%g.s ... %U.s ...
     %g.s ... %U.s’ involves the generation of two distinct file names,
     one for each ‘%g.s’ and another for each ‘%U.s’.  Previously, ‘%U’
     was simply substituted with a file name chosen for the previous
     ‘%u’, without regard to any appended suffix.

‘%jSUFFIX’
     Substitutes the name of the ‘HOST_BIT_BUCKET’, if any, and if it is
     writable, and if ‘-save-temps’ is not used; otherwise, substitute
     the name of a temporary file, just like ‘%u’.  This temporary file
     is not meant for communication between processes, but rather as a
     junk disposal mechanism.

‘%|SUFFIX’
‘%mSUFFIX’
     Like ‘%g’, except if ‘-pipe’ is in effect.  In that case ‘%|’
     substitutes a single dash and ‘%m’ substitutes nothing at all.
     These are the two most common ways to instruct a program that it
     should read from standard input or write to standard output.  If
     you need something more elaborate you can use an ‘%{pipe:‘X’}’
     construct: see for example ‘gcc/fortran/lang-specs.h’.

‘%.SUFFIX’
     Substitutes .SUFFIX for the suffixes of a matched switch's args
     when it is subsequently output with ‘%*’.  SUFFIX is terminated by
     the next space or %.

‘%w’
     Marks the argument containing or following the ‘%w’ as the
     designated output file of this compilation.  This puts the argument
     into the sequence of arguments that ‘%o’ substitutes.

‘%V’
     Indicates that this compilation produces no output file.

‘%o’
     Substitutes the names of all the output files, with spaces
     automatically placed around them.  You should write spaces around
     the ‘%o’ as well or the results are undefined.  ‘%o’ is for use in
     the specs for running the linker.  Input files whose names have no
     recognized suffix are not compiled at all, but they are included
     among the output files, so they are linked.

‘%O’
     Substitutes the suffix for object files.  Note that this is handled
     specially when it immediately follows ‘%g, %u, or %U’, because of
     the need for those to form complete file names.  The handling is
     such that ‘%O’ is treated exactly as if it had already been
     substituted, except that ‘%g, %u, and %U’ do not currently support
     additional SUFFIX characters following ‘%O’ as they do following,
     for example, ‘.o’.

‘%I’
     Substitute any of ‘-iprefix’ (made from ‘GCC_EXEC_PREFIX’),
     ‘-isysroot’ (made from ‘TARGET_SYSTEM_ROOT’), ‘-isystem’ (made from
     ‘COMPILER_PATH’ and ‘-B’ options) and ‘-imultilib’ as necessary.

‘%s’
     Current argument is the name of a library or startup file of some
     sort.  Search for that file in a standard list of directories and
     substitute the full name found.  The current working directory is
     included in the list of directories scanned.

‘%T’
     Current argument is the name of a linker script.  Search for that
     file in the current list of directories to scan for libraries.  If
     the file is located insert a ‘--script’ option into the command
     line followed by the full path name found.  If the file is not
     found then generate an error message.  Note: the current working
     directory is not searched.

‘%eSTR’
     Print STR as an error message.  STR is terminated by a newline.
     Use this when inconsistent options are detected.

‘%nSTR’
     Print STR as a notice.  STR is terminated by a newline.

‘%(NAME)’
     Substitute the contents of spec string NAME at this point.

‘%x{OPTION}’
     Accumulate an option for ‘%X’.

‘%X’
     Output the accumulated linker options specified by a ‘%x’ spec
     string.

‘%Y’
     Output the accumulated assembler options specified by ‘-Wa’.

‘%Z’
     Output the accumulated preprocessor options specified by ‘-Wp’.

‘%M’
     Output ‘multilib_os_dir’.

‘%R’
     Output the concatenation of ‘target_system_root’ and
     ‘target_sysroot_suffix’.

‘%a’
     Process the ‘asm’ spec.  This is used to compute the switches to be
     passed to the assembler.

‘%A’
     Process the ‘asm_final’ spec.  This is a spec string for passing
     switches to an assembler post-processor, if such a program is
     needed.

‘%l’
     Process the ‘link’ spec.  This is the spec for computing the
     command line passed to the linker.  Typically it makes use of the
     ‘%L %G %S %D and %E’ sequences.

‘%D’
     Dump out a ‘-L’ option for each directory that GCC believes might
     contain startup files.  If the target supports multilibs then the
     current multilib directory is prepended to each of these paths.

‘%L’
     Process the ‘lib’ spec.  This is a spec string for deciding which
     libraries are included on the command line to the linker.

‘%G’
     Process the ‘libgcc’ spec.  This is a spec string for deciding
     which GCC support library is included on the command line to the
     linker.

‘%S’
     Process the ‘startfile’ spec.  This is a spec for deciding which
     object files are the first ones passed to the linker.  Typically
     this might be a file named ‘crt0.o’.

‘%E’
     Process the ‘endfile’ spec.  This is a spec string that specifies
     the last object files that are passed to the linker.

‘%C’
     Process the ‘cpp’ spec.  This is used to construct the arguments to
     be passed to the C preprocessor.

‘%1’
     Process the ‘cc1’ spec.  This is used to construct the options to
     be passed to the actual C compiler (‘cc1’).

‘%2’
     Process the ‘cc1plus’ spec.  This is used to construct the options
     to be passed to the actual C++ compiler (‘cc1plus’).

‘%*’
     Substitute the variable part of a matched option.  See below.  Note
     that each comma in the substituted string is replaced by a single
     space.

‘%<S’
     Remove all occurrences of ‘-S’ from the command line.  Note--this
     command is position dependent.  ‘%’ commands in the spec string
     before this one see ‘-S’, ‘%’ commands in the spec string after
     this one do not.

‘%<S*’
     Similar to ‘%<S’, but match all switches beginning with ‘-S’.

‘%>S’
     Similar to ‘%<S’, but keep ‘-S’ in the GCC command line.

‘%:FUNCTION(ARGS)’
     Call the named function FUNCTION, passing it ARGS.  ARGS is first
     processed as a nested spec string, then split into an argument
     vector in the usual fashion.  The function returns a string which
     is processed as if it had appeared literally as part of the current
     spec.

     The following built-in spec functions are provided:

     ‘getenv’
          The ‘getenv’ spec function takes two arguments: an environment
          variable name and a string.  If the environment variable is
          not defined, a fatal error is issued.  Otherwise, the return
          value is the value of the environment variable concatenated
          with the string.  For example, if ‘TOPDIR’ is defined as
          ‘/path/to/top’, then:

               %:getenv(TOPDIR /include)

          expands to ‘/path/to/top/include’.

     ‘if-exists’
          The ‘if-exists’ spec function takes one argument, an absolute
          pathname to a file.  If the file exists, ‘if-exists’ returns
          the pathname.  Here is a small example of its usage:

               *startfile:
               crt0%O%s %:if-exists(crti%O%s) crtbegin%O%s

     ‘if-exists-else’
          The ‘if-exists-else’ spec function is similar to the
          ‘if-exists’ spec function, except that it takes two arguments.
          The first argument is an absolute pathname to a file.  If the
          file exists, ‘if-exists-else’ returns the pathname.  If it
          does not exist, it returns the second argument.  This way,
          ‘if-exists-else’ can be used to select one file or another,
          based on the existence of the first.  Here is a small example
          of its usage:

               *startfile:
               crt0%O%s %:if-exists(crti%O%s) \
               %:if-exists-else(crtbeginT%O%s crtbegin%O%s)

     ‘if-exists-then-else’
          The ‘if-exists-then-else’ spec function takes at least two
          arguments and an optional third one.  The first argument is an
          absolute pathname to a file.  If the file exists, the function
          returns the second argument.  If the file does not exist, the
          function returns the third argument if there is one, or NULL
          otherwise.  This can be used to expand one text, or optionally
          another, based on the existence of a file.  Here is a small
          example of its usage:

               -l%:if-exists-then-else(%:getenv(VSB_DIR rtnet.h) rtnet net)

     ‘sanitize’
          The ‘sanitize’ spec function takes no arguments.  It returns
          non-NULL if any address, thread or undefined behavior
          sanitizers are active.

               %{%:sanitize(address):-funwind-tables}

     ‘replace-outfile’
          The ‘replace-outfile’ spec function takes two arguments.  It
          looks for the first argument in the outfiles array and
          replaces it with the second argument.  Here is a small example
          of its usage:

               %{fgnu-runtime:%:replace-outfile(-lobjc -lobjc-gnu)}

     ‘remove-outfile’
          The ‘remove-outfile’ spec function takes one argument.  It
          looks for the first argument in the outfiles array and removes
          it.  Here is a small example its usage:

               %:remove-outfile(-lm)

     ‘version-compare’
          The ‘version-compare’ spec function takes four or five
          arguments of the following form:

               <comparison-op> <arg1> [<arg2>] <switch> <result>

          It returns ‘result’ if the comparison evaluates to true, and
          NULL if it doesn't.  The supported ‘comparison-op’ values are:

          ‘>=’
               True if ‘switch’ is a later (or same) version than ‘arg1’

          ‘!>’
               Opposite of ‘>=’

          ‘<’
               True if ‘switch’ is an earlier version than ‘arg1’

          ‘!<’
               Opposite of ‘<’

          ‘><’
               True if ‘switch’ is ‘arg1’ or later, and earlier than
               ‘arg2’

          ‘<>’
               True if ‘switch’ is earlier than ‘arg1’, or is ‘arg2’ or
               later

          If the ‘switch’ is not present at all, the condition is false
          unless the first character of the ‘comparison-op’ is ‘!’.

               %:version-compare(>= 10.3 mmacosx-version-min= -lmx)

          The above example would add ‘-lmx’ if
          ‘-mmacosx-version-min=10.3.9’ was passed.

     ‘include’
          The ‘include’ spec function behaves much like ‘%include’, with
          the advantage that it can be nested inside a spec and thus be
          conditionalized.  It takes one argument, the filename, and
          looks for it in the startfile path.  It always returns NULL.

               %{static-libasan|static:%:include(libsanitizer.spec)%(link_libasan)}

     ‘pass-through-libs’
          The ‘pass-through-libs’ spec function takes any number of
          arguments.  It finds any ‘-l’ options and any non-options
          ending in ‘.a’ (which it assumes are the names of linker input
          library archive files) and returns a result containing all the
          found arguments each prepended by ‘-plugin-opt=-pass-through=’
          and joined by spaces.  This list is intended to be passed to
          the LTO linker plugin.

               %:pass-through-libs(%G %L %G)

     ‘print-asm-header’
          The ‘print-asm-header’ function takes no arguments and simply
          prints a banner like:

               Assembler options
               =================

               Use "-Wa,OPTION" to pass "OPTION" to the assembler.

          It is used to separate compiler options from assembler options
          in the ‘--target-help’ output.

     ‘gt’
          The ‘gt’ spec function takes two or more arguments.  It
          returns ‘""’ (the empty string) if the second-to-last argument
          is greater than the last argument, and NULL otherwise.  The
          following example inserts the ‘link_gomp’ spec if the last
          ‘-ftree-parallelize-loops=’ option given on the command line
          is greater than 1:

               %{%:gt(%{ftree-parallelize-loops=*:%*} 1):%:include(libgomp.spec)%(link_gomp)}

     ‘debug-level-gt’
          The ‘debug-level-gt’ spec function takes one argument and
          returns ‘""’ (the empty string) if ‘debug_info_level’ is
          greater than the specified number, and NULL otherwise.

               %{%:debug-level-gt(0):%{gdwarf*:--gdwarf2}}

‘%{S}’
     Substitutes the ‘-S’ switch, if that switch is given to GCC.  If
     that switch is not specified, this substitutes nothing.  Note that
     the leading dash is omitted when specifying this option, and it is
     automatically inserted if the substitution is performed.  Thus the
     spec string ‘%{foo}’ matches the command-line option ‘-foo’ and
     outputs the command-line option ‘-foo’.

‘%W{S}’
     Like %{‘S’} but mark last argument supplied within as a file to be
     deleted on failure.

‘%@{S}’
     Like %{‘S’} but puts the result into a ‘FILE’ and substitutes
     ‘@FILE’ if an ‘@file’ argument has been supplied.

‘%{S*}’
     Substitutes all the switches specified to GCC whose names start
     with ‘-S’, but which also take an argument.  This is used for
     switches like ‘-o’, ‘-D’, ‘-I’, etc.  GCC considers ‘-o foo’ as
     being one switch whose name starts with ‘o’.  %{o*} substitutes
     this text, including the space.  Thus two arguments are generated.

‘%{S*&T*}’
     Like %{‘S’*}, but preserve order of ‘S’ and ‘T’ options (the order
     of ‘S’ and ‘T’ in the spec is not significant).  There can be any
     number of ampersand-separated variables; for each the wild card is
     optional.  Useful for CPP as ‘%{D*&U*&A*}’.

‘%{S:X}’
     Substitutes ‘X’, if the ‘-S’ switch is given to GCC.

‘%{!S:X}’
     Substitutes ‘X’, if the ‘-S’ switch is _not_ given to GCC.

‘%{S*:X}’
     Substitutes ‘X’ if one or more switches whose names start with ‘-S’
     are specified to GCC.  Normally ‘X’ is substituted only once, no
     matter how many such switches appeared.  However, if ‘%*’ appears
     somewhere in ‘X’, then ‘X’ is substituted once for each matching
     switch, with the ‘%*’ replaced by the part of that switch matching
     the ‘*’.

     If ‘%*’ appears as the last part of a spec sequence then a space is
     added after the end of the last substitution.  If there is more
     text in the sequence, however, then a space is not generated.  This
     allows the ‘%*’ substitution to be used as part of a larger string.
     For example, a spec string like this:

          %{mcu=*:--script=%*/memory.ld}

     when matching an option like ‘-mcu=newchip’ produces:

          --script=newchip/memory.ld

‘%{.S:X}’
     Substitutes ‘X’, if processing a file with suffix ‘S’.

‘%{!.S:X}’
     Substitutes ‘X’, if _not_ processing a file with suffix ‘S’.

‘%{,S:X}’
     Substitutes ‘X’, if processing a file for language ‘S’.

‘%{!,S:X}’
     Substitutes ‘X’, if not processing a file for language ‘S’.

‘%{S|P:X}’
     Substitutes ‘X’ if either ‘-S’ or ‘-P’ is given to GCC.  This may
     be combined with ‘!’, ‘.’, ‘,’, and ‘*’ sequences as well, although
     they have a stronger binding than the ‘|’.  If ‘%*’ appears in ‘X’,
     all of the alternatives must be starred, and only the first
     matching alternative is substituted.

     For example, a spec string like this:

          %{.c:-foo} %{!.c:-bar} %{.c|d:-baz} %{!.c|d:-boggle}

     outputs the following command-line options from the following input
     command-line options:

          fred.c        -foo -baz
          jim.d         -bar -boggle
          -d fred.c     -foo -baz -boggle
          -d jim.d      -bar -baz -boggle

‘%{%:FUNCTION(ARGS):X}’

     Call function named FUNCTION with args ARGS.  If the function
     returns non-NULL, then ‘X’ is substituted, if it returns NULL, it
     isn't substituted.

‘%{S:X; T:Y; :D}’

     If ‘S’ is given to GCC, substitutes ‘X’; else if ‘T’ is given to
     GCC, substitutes ‘Y’; else substitutes ‘D’.  There can be as many
     clauses as you need.  This may be combined with ‘.’, ‘,’, ‘!’, ‘|’,
     and ‘*’ as needed.

 The switch matching text ‘S’ in a ‘%{S}’, ‘%{S:X}’ or similar construct
can use a backslash to ignore the special meaning of the character
following it, thus allowing literal matching of a character that is
otherwise specially treated.  For example, ‘%{std=iso9899\:1999:X}’
substitutes ‘X’ if the ‘-std=iso9899:1999’ option is given.

 The conditional text ‘X’ in a ‘%{S:X}’ or similar construct may contain
other nested ‘%’ constructs or spaces, or even newlines.  They are
processed as usual, as described above.  Trailing white space in ‘X’ is
ignored.  White space may also appear anywhere on the left side of the
colon in these constructs, except between ‘.’ or ‘*’ and the
corresponding word.

 The ‘-O’, ‘-f’, ‘-m’, and ‘-W’ switches are handled specifically in
these constructs.  If another value of ‘-O’ or the negated form of a
‘-f’, ‘-m’, or ‘-W’ switch is found later in the command line, the
earlier switch value is ignored, except with {‘S’*} where ‘S’ is just
one letter, which passes all matching options.

 The character ‘|’ at the beginning of the predicate text is used to
indicate that a command should be piped to the following command, but
only if ‘-pipe’ is specified.

 It is built into GCC which switches take arguments and which do not.
(You might think it would be useful to generalize this to allow each
compiler's spec to say which switches take arguments.  But this cannot
be done in a consistent fashion.  GCC cannot even decide which input
files have been specified without knowing which switches take arguments,
and it must know which input files to compile in order to tell which
compilers to run).

 GCC also knows implicitly that arguments starting in ‘-l’ are to be
treated as compiler output files, and passed to the linker in their
proper position among the other output files.


File: gcc.info,  Node: Environment Variables,  Next: Precompiled Headers,  Prev: Spec Files,  Up: Invoking GCC

3.21 Environment Variables Affecting GCC
========================================

This section describes several environment variables that affect how GCC
operates.  Some of them work by specifying directories or prefixes to
use when searching for various kinds of files.  Some are used to specify
other aspects of the compilation environment.

 Note that you can also specify places to search using options such as
‘-B’, ‘-I’ and ‘-L’ (*note Directory Options::).  These take precedence
over places specified using environment variables, which in turn take
precedence over those specified by the configuration of GCC.  *Note
Controlling the Compilation Driver ‘gcc’: (gccint)Driver.

‘LANG’
‘LC_CTYPE’
‘LC_MESSAGES’
‘LC_ALL’
     These environment variables control the way that GCC uses
     localization information which allows GCC to work with different
     national conventions.  GCC inspects the locale categories
     ‘LC_CTYPE’ and ‘LC_MESSAGES’ if it has been configured to do so.
     These locale categories can be set to any value supported by your
     installation.  A typical value is ‘en_GB.UTF-8’ for English in the
     United Kingdom encoded in UTF-8.

     The ‘LC_CTYPE’ environment variable specifies character
     classification.  GCC uses it to determine the character boundaries
     in a string; this is needed for some multibyte encodings that
     contain quote and escape characters that are otherwise interpreted
     as a string end or escape.

     The ‘LC_MESSAGES’ environment variable specifies the language to
     use in diagnostic messages.

     If the ‘LC_ALL’ environment variable is set, it overrides the value
     of ‘LC_CTYPE’ and ‘LC_MESSAGES’; otherwise, ‘LC_CTYPE’ and
     ‘LC_MESSAGES’ default to the value of the ‘LANG’ environment
     variable.  If none of these variables are set, GCC defaults to
     traditional C English behavior.

‘TMPDIR’
     If ‘TMPDIR’ is set, it specifies the directory to use for temporary
     files.  GCC uses temporary files to hold the output of one stage of
     compilation which is to be used as input to the next stage: for
     example, the output of the preprocessor, which is the input to the
     compiler proper.

‘GCC_COMPARE_DEBUG’
     Setting ‘GCC_COMPARE_DEBUG’ is nearly equivalent to passing
     ‘-fcompare-debug’ to the compiler driver.  See the documentation of
     this option for more details.

‘GCC_EXEC_PREFIX’
     If ‘GCC_EXEC_PREFIX’ is set, it specifies a prefix to use in the
     names of the subprograms executed by the compiler.  No slash is
     added when this prefix is combined with the name of a subprogram,
     but you can specify a prefix that ends with a slash if you wish.

     If ‘GCC_EXEC_PREFIX’ is not set, GCC attempts to figure out an
     appropriate prefix to use based on the pathname it is invoked with.

     If GCC cannot find the subprogram using the specified prefix, it
     tries looking in the usual places for the subprogram.

     The default value of ‘GCC_EXEC_PREFIX’ is ‘PREFIX/lib/gcc/’ where
     PREFIX is the prefix to the installed compiler.  In many cases
     PREFIX is the value of ‘prefix’ when you ran the ‘configure’
     script.

     Other prefixes specified with ‘-B’ take precedence over this
     prefix.

     This prefix is also used for finding files such as ‘crt0.o’ that
     are used for linking.

     In addition, the prefix is used in an unusual way in finding the
     directories to search for header files.  For each of the standard
     directories whose name normally begins with ‘/usr/local/lib/gcc’
     (more precisely, with the value of ‘GCC_INCLUDE_DIR’), GCC tries
     replacing that beginning with the specified prefix to produce an
     alternate directory name.  Thus, with ‘-Bfoo/’, GCC searches
     ‘foo/bar’ just before it searches the standard directory
     ‘/usr/local/lib/bar’.  If a standard directory begins with the
     configured PREFIX then the value of PREFIX is replaced by
     ‘GCC_EXEC_PREFIX’ when looking for header files.

‘COMPILER_PATH’
     The value of ‘COMPILER_PATH’ is a colon-separated list of
     directories, much like ‘PATH’.  GCC tries the directories thus
     specified when searching for subprograms, if it cannot find the
     subprograms using ‘GCC_EXEC_PREFIX’.

‘LIBRARY_PATH’
     The value of ‘LIBRARY_PATH’ is a colon-separated list of
     directories, much like ‘PATH’.  When configured as a native
     compiler, GCC tries the directories thus specified when searching
     for special linker files, if it cannot find them using
     ‘GCC_EXEC_PREFIX’.  Linking using GCC also uses these directories
     when searching for ordinary libraries for the ‘-l’ option (but
     directories specified with ‘-L’ come first).

‘LANG’
     This variable is used to pass locale information to the compiler.
     One way in which this information is used is to determine the
     character set to be used when character literals, string literals
     and comments are parsed in C and C++.  When the compiler is
     configured to allow multibyte characters, the following values for
     ‘LANG’ are recognized:

     ‘C-JIS’
          Recognize JIS characters.
     ‘C-SJIS’
          Recognize SJIS characters.
     ‘C-EUCJP’
          Recognize EUCJP characters.

     If ‘LANG’ is not defined, or if it has some other value, then the
     compiler uses ‘mblen’ and ‘mbtowc’ as defined by the default locale
     to recognize and translate multibyte characters.

‘GCC_EXTRA_DIAGNOSTIC_OUTPUT’
     If ‘GCC_EXTRA_DIAGNOSTIC_OUTPUT’ is set to one of the following
     values, then additional text will be emitted to stderr when fix-it
     hints are emitted.  ‘-fdiagnostics-parseable-fixits’ and
     ‘-fno-diagnostics-parseable-fixits’ take precedence over this
     environment variable.

     ‘fixits-v1’
          Emit parseable fix-it hints, equivalent to
          ‘-fdiagnostics-parseable-fixits’.  In particular, columns are
          expressed as a count of bytes, starting at byte 1 for the
          initial column.

     ‘fixits-v2’
          As ‘fixits-v1’, but columns are expressed as display columns,
          as per ‘-fdiagnostics-column-unit=display’.

Some additional environment variables affect the behavior of the
preprocessor.

‘CPATH’
‘C_INCLUDE_PATH’
‘CPLUS_INCLUDE_PATH’
‘OBJC_INCLUDE_PATH’
     Each variable's value is a list of directories separated by a
     special character, much like ‘PATH’, in which to look for header
     files.  The special character, ‘PATH_SEPARATOR’, is
     target-dependent and determined at GCC build time.  For Microsoft
     Windows-based targets it is a semicolon, and for almost all other
     targets it is a colon.

     ‘CPATH’ specifies a list of directories to be searched as if
     specified with ‘-I’, but after any paths given with ‘-I’ options on
     the command line.  This environment variable is used regardless of
     which language is being preprocessed.

     The remaining environment variables apply only when preprocessing
     the particular language indicated.  Each specifies a list of
     directories to be searched as if specified with ‘-isystem’, but
     after any paths given with ‘-isystem’ options on the command line.

     In all these variables, an empty element instructs the compiler to
     search its current working directory.  Empty elements can appear at
     the beginning or end of a path.  For instance, if the value of
     ‘CPATH’ is ‘:/special/include’, that has the same effect as
     ‘-I. -I/special/include’.

‘DEPENDENCIES_OUTPUT’
     If this variable is set, its value specifies how to output
     dependencies for Make based on the non-system header files
     processed by the compiler.  System header files are ignored in the
     dependency output.

     The value of ‘DEPENDENCIES_OUTPUT’ can be just a file name, in
     which case the Make rules are written to that file, guessing the
     target name from the source file name.  Or the value can have the
     form ‘FILE TARGET’, in which case the rules are written to file
     FILE using TARGET as the target name.

     In other words, this environment variable is equivalent to
     combining the options ‘-MM’ and ‘-MF’ (*note Preprocessor
     Options::), with an optional ‘-MT’ switch too.

‘SUNPRO_DEPENDENCIES’
     This variable is the same as ‘DEPENDENCIES_OUTPUT’ (see above),
     except that system header files are not ignored, so it implies ‘-M’
     rather than ‘-MM’.  However, the dependence on the main input file
     is omitted.  *Note Preprocessor Options::.

‘SOURCE_DATE_EPOCH’
     If this variable is set, its value specifies a UNIX timestamp to be
     used in replacement of the current date and time in the ‘__DATE__’
     and ‘__TIME__’ macros, so that the embedded timestamps become
     reproducible.

     The value of ‘SOURCE_DATE_EPOCH’ must be a UNIX timestamp, defined
     as the number of seconds (excluding leap seconds) since 01 Jan 1970
     00:00:00 represented in ASCII; identical to the output of ‘date
     +%s’ on GNU/Linux and other systems that support the ‘%s’ extension
     in the ‘date’ command.

     The value should be a known timestamp such as the last modification
     time of the source or package and it should be set by the build
     process.


File: gcc.info,  Node: Precompiled Headers,  Next: C++ Modules,  Prev: Environment Variables,  Up: Invoking GCC

3.22 Using Precompiled Headers
==============================

Often large projects have many header files that are included in every
source file.  The time the compiler takes to process these header files
over and over again can account for nearly all of the time required to
build the project.  To make builds faster, GCC allows you to
“precompile” a header file.

 To create a precompiled header file, simply compile it as you would any
other file, if necessary using the ‘-x’ option to make the driver treat
it as a C or C++ header file.  You may want to use a tool like ‘make’ to
keep the precompiled header up-to-date when the headers it contains
change.

 A precompiled header file is searched for when ‘#include’ is seen in
the compilation.  As it searches for the included file (*note Search
Path: (cpp)Search Path.) the compiler looks for a precompiled header in
each directory just before it looks for the include file in that
directory.  The name searched for is the name specified in the
‘#include’ with ‘.gch’ appended.  If the precompiled header file cannot
be used, it is ignored.

 For instance, if you have ‘#include "all.h"’, and you have ‘all.h.gch’
in the same directory as ‘all.h’, then the precompiled header file is
used if possible, and the original header is used otherwise.

 Alternatively, you might decide to put the precompiled header file in a
directory and use ‘-I’ to ensure that directory is searched before (or
instead of) the directory containing the original header.  Then, if you
want to check that the precompiled header file is always used, you can
put a file of the same name as the original header in this directory
containing an ‘#error’ command.

 This also works with ‘-include’.  So yet another way to use precompiled
headers, good for projects not designed with precompiled header files in
mind, is to simply take most of the header files used by a project,
include them from another header file, precompile that header file, and
‘-include’ the precompiled header.  If the header files have guards
against multiple inclusion, they are skipped because they've already
been included (in the precompiled header).

 If you need to precompile the same header file for different languages,
targets, or compiler options, you can instead make a _directory_ named
like ‘all.h.gch’, and put each precompiled header in the directory,
perhaps using ‘-o’.  It doesn't matter what you call the files in the
directory; every precompiled header in the directory is considered.  The
first precompiled header encountered in the directory that is valid for
this compilation is used; they're searched in no particular order.

 There are many other possibilities, limited only by your imagination,
good sense, and the constraints of your build system.

 A precompiled header file can be used only when these conditions apply:

   • Only one precompiled header can be used in a particular
     compilation.

   • A precompiled header cannot be used once the first C token is seen.
     You can have preprocessor directives before a precompiled header;
     you cannot include a precompiled header from inside another header.

   • The precompiled header file must be produced for the same language
     as the current compilation.  You cannot use a C precompiled header
     for a C++ compilation.

   • The precompiled header file must have been produced by the same
     compiler binary as the current compilation is using.

   • Any macros defined before the precompiled header is included must
     either be defined in the same way as when the precompiled header
     was generated, or must not affect the precompiled header, which
     usually means that they don't appear in the precompiled header at
     all.

     The ‘-D’ option is one way to define a macro before a precompiled
     header is included; using a ‘#define’ can also do it.  There are
     also some options that define macros implicitly, like ‘-O’ and
     ‘-Wdeprecated’; the same rule applies to macros defined this way.

   • If debugging information is output when using the precompiled
     header, using ‘-g’ or similar, the same kind of debugging
     information must have been output when building the precompiled
     header.  However, a precompiled header built using ‘-g’ can be used
     in a compilation when no debugging information is being output.

   • The same ‘-m’ options must generally be used when building and
     using the precompiled header.  *Note Submodel Options::, for any
     cases where this rule is relaxed.

   • Each of the following options must be the same when building and
     using the precompiled header:

          -fexceptions

   • Some other command-line options starting with ‘-f’, ‘-p’, or ‘-O’
     must be defined in the same way as when the precompiled header was
     generated.  At present, it's not clear which options are safe to
     change and which are not; the safest choice is to use exactly the
     same options when generating and using the precompiled header.  The
     following are known to be safe:

          -fmessage-length=  -fpreprocessed  -fsched-interblock
          -fsched-spec  -fsched-spec-load  -fsched-spec-load-dangerous
          -fsched-verbose=NUMBER  -fschedule-insns  -fvisibility=
          -pedantic-errors

   • Address space layout randomization (ASLR) can lead to not binary
     identical PCH files.  If you rely on stable PCH file contents
     disable ASLR when generating PCH files.

 For all of these except the last, the compiler automatically ignores
the precompiled header if the conditions aren't met.  If you find an
option combination that doesn't work and doesn't cause the precompiled
header to be ignored, please consider filing a bug report, see *note
Bugs::.

 If you do use differing options when generating and using the
precompiled header, the actual behavior is a mixture of the behavior for
the options.  For instance, if you use ‘-g’ to generate the precompiled
header but not when using it, you may or may not get debugging
information for routines in the precompiled header.


File: gcc.info,  Node: C++ Modules,  Prev: Precompiled Headers,  Up: Invoking GCC

3.23 C++ Modules
================

Modules are a C++20 language feature.  As the name suggests, they
provides a modular compilation system, intending to provide both faster
builds and better library isolation.  The "Merging Modules" paper
<https://wg21.link/p1103>, provides the easiest to read set of changes
to the standard, although it does not capture later changes.

 _G++'s modules support is not complete._  Other than bugs, the known
missing pieces are:

_Private Module Fragment_
     The Private Module Fragment is recognized, but an error is emitted.

_Partition definition visibility rules_
     Entities may be defined in implementation partitions, and those
     definitions are not available outside of the module.  This is not
     implemented, and the definitions are available to extra-module use.

_Textual merging of reachable GM entities_
     Entities may be multiply defined across different header-units.
     These must be de-duplicated, and this is implemented across
     imports, or when an import redefines a textually-defined entity.
     However the reverse is not implemented--textually redefining an
     entity that has been defined in an imported header-unit.  A
     redefinition error is emitted.

_Translation-Unit local referencing rules_
     Papers p1815 (<https://wg21.link/p1815>) and p2003
     (<https://wg21.link/p2003>) add limitations on which entities an
     exported region may reference (for instance, the entities an
     exported template definition may reference).  These are not fully
     implemented.

_Language-linkage module attachment_
     Declarations with explicit language linkage (‘extern "C"’ or
     ‘extern "C++"’) are attached to the global module, even when in the
     purview of a named module.  This is not implemented.  Such
     declarations will be attached to the module, if any, in which they
     are declared.

_Standard Library Header Units_
     The Standard Library is not provided as importable header units.
     If you want to import such units, you must explicitly build them
     first.  If you do not do this with care, you may have multiple
     declarations, which the module machinery must merge--compiler
     resource usage can be affected by how you partition header files
     into header units.

 Modular compilation is _not_ enabled with just the ‘-std=c++20’ option.
You must explicitly enable it with the ‘-fmodules-ts’ option.  It is
independent of the language version selected, although in pre-C++20
versions, it is of course an extension.

 No new source file suffixes are required or supported.  If you wish to
use a non-standard suffix (*note Overall Options::), you also need to
provide a ‘-x c++’ option too.(1)

 Compiling a module interface unit produces an additional output (to the
assembly or object file), called a Compiled Module Interface (CMI). This
encodes the exported declarations of the module.  Importing a module
reads in the CMI. The import graph is a Directed Acyclic Graph (DAG).
You must build imports before the importer.

 Header files may themselves be compiled to header units, which are a
transitional ability aiming at faster compilation.  The
‘-fmodule-header’ option is used to enable this, and implies the
‘-fmodules-ts’ option.  These CMIs are named by the fully resolved
underlying header file, and thus may be a complete pathname containing
subdirectories.  If the header file is found at an absolute pathname,
the CMI location is still relative to a CMI root directory.

 As header files often have no suffix, you commonly have to specify a
‘-x’ option to tell the compiler the source is a header file.  You may
use ‘-x c++-header’, ‘-x c++-user-header’ or ‘-x c++-system-header’.
When used in conjunction with ‘-fmodules-ts’, these all imply an
appropriate ‘-fmodule-header’ option.  The latter two variants use the
user or system include path to search for the file specified.  This
allows you to, for instance, compile standard library header files as
header units, without needing to know exactly where they are installed.
Specifying the language as one of these variants also inhibits output of
the object file, as header files have no associated object file.

 The ‘-fmodule-only’ option disables generation of the associated object
file for compiling a module interface.  Only the CMI is generated.  This
option is implied when using the ‘-fmodule-header’ option.

 The ‘-flang-info-include-translate’ and
‘-flang-info-include-translate-not’ options notes whether include
translation occurs or not.  With no argument, the first will note all
include translation.  The second will note all non-translations of
include files not known to intentionally be textual.  With an argument,
queries about include translation of a header files with that particular
trailing pathname are noted.  You may repeat this form to cover several
different header files.  This option may be helpful in determining
whether include translation is happening--if it is working correctly, it
behaves as if it isn't there at all.

 The ‘-flang-info-module-cmi’ option can be used to determine where the
compiler is reading a CMI from.  Without the option, the compiler is
silent when such a read is successful.  This option has an optional
argument, which will restrict the notification to just the set of named
modules or header units specified.

 The ‘-Winvalid-imported-macros’ option causes all imported macros to be
resolved at the end of compilation.  Without this, imported macros are
only resolved when expanded or (re)defined.  This option detects
conflicting import definitions for all macros.

 For details of the ‘-fmodule-mapper’ family of options, *note C++
Module Mapper::.

* Menu:

* C++ Module Mapper::       Module Mapper
* C++ Module Preprocessing::  Module Preprocessing
* C++ Compiled Module Interface:: Compiled Module Interface

   ---------- Footnotes ----------

   (1) Some users like to distinguish module interface files with a new
suffix, such as naming the source ‘module.cppm’, which involves teaching
all tools about the new suffix.  A different scheme, such as naming
‘module-m.cpp’ would be less invasive.


File: gcc.info,  Node: C++ Module Mapper,  Next: C++ Module Preprocessing,  Up: C++ Modules

3.23.1 Module Mapper
--------------------

A module mapper provides a server or file that the compiler queries to
determine the mapping between module names and CMI files.  It is also
used to build CMIs on demand.  _Mapper functionality is in its infancy
and is intended for experimentation with build system interactions._

 You can specify a mapper with the ‘-fmodule-mapper=VAL’ option or
‘CXX_MODULE_MAPPER’ environment variable.  The value may have one of the
following forms:

‘[HOSTNAME]:PORT[?IDENT]’
     An optional hostname and a numeric port number to connect to.  If
     the hostname is omitted, the loopback address is used.  If the
     hostname corresponds to multiple IPV6 addresses, these are tried in
     turn, until one is successful.  If your host lacks IPv6, this form
     is non-functional.  If you must use IPv4 use
     ‘-fmodule-mapper='|ncat IPV4HOST PORT'’.

‘=SOCKET[?IDENT]’
     A local domain socket.  If your host lacks local domain sockets,
     this form is non-functional.

‘|PROGRAM[?IDENT] [ARGS...]’
     A program to spawn, and communicate with on its stdin/stdout
     streams.  Your PATH environment variable is searched for the
     program.  Arguments are separated by space characters, (it is not
     possible for one of the arguments delivered to the program to
     contain a space).  An exception is if PROGRAM begins with @.  In
     that case PROGRAM (sans @) is looked for in the compiler's internal
     binary directory.  Thus the sample mapper-server can be specified
     with ‘@g++-mapper-server’.

‘<>[?IDENT]’
‘<>INOUT[?IDENT]’
‘<IN>OUT[?IDENT]’
     Named pipes or file descriptors to communicate over.  The first
     form, ‘<>’, communicates over stdin and stdout.  The other forms
     allow you to specify a file descriptor or name a pipe.  A numeric
     value is interpreted as a file descriptor, otherwise named pipe is
     opened.  The second form specifies a bidirectional pipe and the
     last form allows specifying two independent pipes.  Using file
     descriptors directly in this manner is fragile in general, as it
     can require the cooperation of intermediate processes.  In
     particular using stdin & stdout is fraught with danger as other
     compiler options might also cause the compiler to read stdin or
     write stdout, and it can have unfortunate interactions with signal
     delivery from the terminal.

‘FILE[?IDENT]’
     A mapping file consisting of space-separated module-name, filename
     pairs, one per line.  Only the mappings for the direct imports and
     any module export name need be provided.  If other mappings are
     provided, they override those stored in any imported CMI files.  A
     repository root may be specified in the mapping file by using
     ‘$root’ as the module name in the first active line.  Use of this
     option will disable any default module->CMI name mapping.

 As shown, an optional IDENT may suffix the first word of the option,
indicated by a ‘?’ prefix.  The value is used in the initial handshake
with the module server, or to specify a prefix on mapping file lines.
In the server case, the main source file name is used if no IDENT is
specified.  In the file case, all non-blank lines are significant,
unless a value is specified, in which case only lines beginning with
IDENT are significant.  The IDENT must be separated by whitespace from
the module name.  Be aware that ‘<’, ‘>’, ‘?’, and ‘|’ characters are
often significant to the shell, and therefore may need quoting.

 The mapper is connected to or loaded lazily, when the first module
mapping is required.  The networking protocols are only supported on
hosts that provide networking.  If no mapper is specified a default is
provided.

 A project-specific mapper is expected to be provided by the build
system that invokes the compiler.  It is not expected that a
general-purpose server is provided for all compilations.  As such, the
server will know the build configuration, the compiler it invoked, and
the environment (such as working directory) in which that is operating.
As it may parallelize builds, several compilations may connect to the
same socket.

 The default mapper generates CMI files in a ‘gcm.cache’ directory.  CMI
files have a ‘.gcm’ suffix.  The module unit name is used directly to
provide the basename.  Header units construct a relative path using the
underlying header file name.  If the path is already relative, a ‘,’
directory is prepended.  Internal ‘..’ components are translated to
‘,,’.  No attempt is made to canonicalize these filenames beyond that
done by the preprocessor's include search algorithm, as in general it is
ambiguous when symbolic links are present.

 The mapper protocol was published as "A Module Mapper"
<https://wg21.link/p1184>.  The implementation is provided by ‘libcody’,
<https://github.com/urnathan/libcody>, which specifies the canonical
protocol definition.  A proof of concept server implementation embedded
in ‘make’ was described in "Make Me A Module",
<https://wg21.link/p1602>.


File: gcc.info,  Node: C++ Module Preprocessing,  Next: C++ Compiled Module Interface,  Prev: C++ Module Mapper,  Up: C++ Modules

3.23.2 Module Preprocessing
---------------------------

Modules affect preprocessing because of header units and include
translation.  Some uses of the preprocessor as a separate step either do
not produce a correct output, or require CMIs to be available.

 Header units import macros.  These macros can affect later conditional
inclusion, which therefore can cascade to differing import sets.  When
preprocessing, it is necessary to load the CMI. If a header unit is
unavailable, the preprocessor issues a warning and continue (when not
just preprocessing, an error is emitted).  Detecting such imports
requires preprocessor tokenization of the input stream to phase 4 (macro
expansion).

 Include translation converts ‘#include’, ‘#include_next’ and ‘#import’
directives to internal ‘import’ declarations.  Whether a particular
directive is translated is controlled by the module mapper.  Header unit
names are canonicalized during preprocessing.

 Dependency information can be emitted for macro import, extending the
functionality of ‘-MD’ and ‘-MMD’ options.  Detection of import
declarations also requires phase 4 preprocessing, and thus requires full
preprocessing (or compilation).

 The ‘-M’, ‘-MM’ and ‘-E -fdirectives-only’ options halt preprocessing
before phase 4.

 The ‘-save-temps’ option uses ‘-fdirectives-only’ for preprocessing,
and preserve the macro definitions in the preprocessed output.  Usually
you also want to use this option when explicitly preprocessing a
header-unit, or consuming such preprocessed output:

     g++ -fmodules-ts -E -fdirectives-only my-header.hh -o my-header.ii
     g++ -x c++-header -fmodules-ts -fpreprocessed -fdirectives-only my-header.ii


File: gcc.info,  Node: C++ Compiled Module Interface,  Prev: C++ Module Preprocessing,  Up: C++ Modules

3.23.3 Compiled Module Interface
--------------------------------

CMIs are an additional artifact when compiling named module interfaces,
partitions or header units.  These are read when importing.  CMI
contents are implementation-specific, and in GCC's case tied to the
compiler version.  Consider them a rebuildable cache artifact, not a
distributable object.

 When creating an output CMI, any missing directory components are
created in a manner that is safe for concurrent builds creating
multiple, different, CMIs within a common subdirectory tree.

 CMI contents are written to a temporary file, which is then atomically
renamed.  Observers either see old contents (if there is an existing
file), or complete new contents.  They do not observe the CMI during its
creation.  This is unlike object file writing, which may be observed by
an external process.

 CMIs are read in lazily, if the host OS provides ‘mmap’ functionality.
Generally blocks are read when name lookup or template instantiation
occurs.  To inhibit this, the ‘-fno-module-lazy’ option may be used.

 The ‘--param lazy-modules=N’ parameter controls the limit on the number
of concurrently open module files during lazy loading.  Should more
modules be imported, an LRU algorithm is used to determine which files
to close--until that file is needed again.  This limit may be exceeded
with deep module dependency hierarchies.  With large code bases there
may be more imports than the process limit of file descriptors.  By
default, the limit is a few less than the per-process file descriptor
hard limit, if that is determinable.(1)

 GCC CMIs use ELF32 as an architecture-neutral encapsulation mechanism.
You may use ‘readelf’ to inspect them, although section contents are
largely undecipherable.  There is a section named ‘.gnu.c++.README’,
which contains human-readable text.  Other than the first line, each
line consists of ‘TAG: value’ tuples.

     > readelf -p.gnu.c++.README gcm.cache/foo.gcm

     String dump of section '.gnu.c++.README':
       [     0]  GNU C++ primary module interface
       [    21]  compiler: 11.0.0 20201116 (experimental) [c++-modules revision 20201116-0454]
       [    6f]  version: 2020/11/16-04:54
       [    89]  module: foo
       [    95]  source: c_b.ii
       [    a4]  dialect: C++20/coroutines
       [    be]  cwd: /data/users/nathans/modules/obj/x86_64/gcc
       [    ee]  repository: gcm.cache
       [   104]  buildtime: 2020/11/16 15:03:21 UTC
       [   127]  localtime: 2020/11/16 07:03:21 PST
       [   14a]  export: foo:part1 foo-part1.gcm

 Amongst other things, this lists the source that was built, C++ dialect
used and imports of the module.(2)  The timestamp is the same value as
that provided by the ‘__DATE__’ & ‘__TIME__’ macros, and may be
explicitly specified with the environment variable ‘SOURCE_DATE_EPOCH’.
For further details *note Environment Variables::.

 A set of related CMIs may be copied, provided the relative pathnames
are preserved.

 The ‘.gnu.c++.README’ contents do not affect CMI integrity, and it may
be removed or altered.  The section numbering of the sections whose
names do not begin with ‘.gnu.c++.’, or are not the string section is
significant and must not be altered.

   ---------- Footnotes ----------

   (1) Where applicable the soft limit is incremented as needed towards
the hard limit.

   (2) The precise contents of this output may change.


File: gcc.info,  Node: C Implementation,  Next: C++ Implementation,  Prev: Invoking GCC,  Up: Top

4 C Implementation-Defined Behavior
***********************************

A conforming implementation of ISO C is required to document its choice
of behavior in each of the areas that are designated "implementation
defined".  The following lists all such areas, along with the section
numbers from the ISO/IEC 9899:1990, ISO/IEC 9899:1999 and ISO/IEC
9899:2011 standards.  Some areas are only implementation-defined in one
version of the standard.

 Some choices depend on the externally determined ABI for the platform
(including standard character encodings) which GCC follows; these are
listed as "determined by ABI" below.  *Note Binary Compatibility:
Compatibility, and <https://gcc.gnu.org/readings.html>.  Some choices
are documented in the preprocessor manual.  *Note Implementation-defined
behavior: (cpp)Implementation-defined behavior.  Some choices are made
by the library and operating system (or other environment when compiling
for a freestanding environment); refer to their documentation for
details.

* Menu:

* Translation implementation::
* Environment implementation::
* Identifiers implementation::
* Characters implementation::
* Integers implementation::
* Floating point implementation::
* Arrays and pointers implementation::
* Hints implementation::
* Structures unions enumerations and bit-fields implementation::
* Qualifiers implementation::
* Declarators implementation::
* Statements implementation::
* Preprocessing directives implementation::
* Library functions implementation::
* Architecture implementation::
* Locale-specific behavior implementation::


File: gcc.info,  Node: Translation implementation,  Next: Environment implementation,  Up: C Implementation

4.1 Translation
===============

   • ‘How a diagnostic is identified (C90 3.7, C99 and C11 3.10, C90,
     C99 and C11 5.1.1.3).’

     Diagnostics consist of all the output sent to stderr by GCC.

   • ‘Whether each nonempty sequence of white-space characters other
     than new-line is retained or replaced by one space character in
     translation phase 3 (C90, C99 and C11 5.1.1.2).’

     *Note Implementation-defined behavior: (cpp)Implementation-defined
     behavior.


File: gcc.info,  Node: Environment implementation,  Next: Identifiers implementation,  Prev: Translation implementation,  Up: C Implementation

4.2 Environment
===============

The behavior of most of these points are dependent on the implementation
of the C library, and are not defined by GCC itself.

   • ‘The mapping between physical source file multibyte characters and
     the source character set in translation phase 1 (C90, C99 and C11
     5.1.1.2).’

     *Note Implementation-defined behavior: (cpp)Implementation-defined
     behavior.


File: gcc.info,  Node: Identifiers implementation,  Next: Characters implementation,  Prev: Environment implementation,  Up: C Implementation

4.3 Identifiers
===============

   • ‘Which additional multibyte characters may appear in identifiers
     and their correspondence to universal character names (C99 and C11
     6.4.2).’

     *Note Implementation-defined behavior: (cpp)Implementation-defined
     behavior.

   • ‘The number of significant initial characters in an identifier (C90
     6.1.2, C90, C99 and C11 5.2.4.1, C99 and C11 6.4.2).’

     For internal names, all characters are significant.  For external
     names, the number of significant characters are defined by the
     linker; for almost all targets, all characters are significant.

   • ‘Whether case distinctions are significant in an identifier with
     external linkage (C90 6.1.2).’

     This is a property of the linker.  C99 and C11 require that case
     distinctions are always significant in identifiers with external
     linkage and systems without this property are not supported by GCC.


File: gcc.info,  Node: Characters implementation,  Next: Integers implementation,  Prev: Identifiers implementation,  Up: C Implementation

4.4 Characters
==============

   • ‘The number of bits in a byte (C90 3.4, C99 and C11 3.6).’

     Determined by ABI.

   • ‘The values of the members of the execution character set (C90, C99
     and C11 5.2.1).’

     Determined by ABI.

   • ‘The unique value of the member of the execution character set
     produced for each of the standard alphabetic escape sequences (C90,
     C99 and C11 5.2.2).’

     Determined by ABI.

   • ‘The value of a ‘char’ object into which has been stored any
     character other than a member of the basic execution character set
     (C90 6.1.2.5, C99 and C11 6.2.5).’

     Determined by ABI.

   • ‘Which of ‘signed char’ or ‘unsigned char’ has the same range,
     representation, and behavior as "plain" ‘char’ (C90 6.1.2.5, C90
     6.2.1.1, C99 and C11 6.2.5, C99 and C11 6.3.1.1).’

     Determined by ABI.  The options ‘-funsigned-char’ and
     ‘-fsigned-char’ change the default.  *Note Options Controlling C
     Dialect: C Dialect Options.

   • ‘The mapping of members of the source character set (in character
     constants and string literals) to members of the execution
     character set (C90 6.1.3.4, C99 and C11 6.4.4.4, C90, C99 and C11
     5.1.1.2).’

     Determined by ABI.

   • ‘The value of an integer character constant containing more than
     one character or containing a character or escape sequence that
     does not map to a single-byte execution character (C90 6.1.3.4, C99
     and C11 6.4.4.4).’

     *Note Implementation-defined behavior: (cpp)Implementation-defined
     behavior.

   • ‘The value of a wide character constant containing more than one
     multibyte character or a single multibyte character that maps to
     multiple members of the extended execution character set, or
     containing a multibyte character or escape sequence not represented
     in the extended execution character set (C90 6.1.3.4, C99 and C11
     6.4.4.4).’

     *Note Implementation-defined behavior: (cpp)Implementation-defined
     behavior.

   • ‘The current locale used to convert a wide character constant
     consisting of a single multibyte character that maps to a member of
     the extended execution character set into a corresponding wide
     character code (C90 6.1.3.4, C99 and C11 6.4.4.4).’

     *Note Implementation-defined behavior: (cpp)Implementation-defined
     behavior.

   • ‘Whether differently-prefixed wide string literal tokens can be
     concatenated and, if so, the treatment of the resulting multibyte
     character sequence (C11 6.4.5).’

     Such tokens may not be concatenated.

   • ‘The current locale used to convert a wide string literal into
     corresponding wide character codes (C90 6.1.4, C99 and C11 6.4.5).’

     *Note Implementation-defined behavior: (cpp)Implementation-defined
     behavior.

   • ‘The value of a string literal containing a multibyte character or
     escape sequence not represented in the execution character set (C90
     6.1.4, C99 and C11 6.4.5).’

     *Note Implementation-defined behavior: (cpp)Implementation-defined
     behavior.

   • ‘The encoding of any of ‘wchar_t’, ‘char16_t’, and ‘char32_t’ where
     the corresponding standard encoding macro (‘__STDC_ISO_10646__’,
     ‘__STDC_UTF_16__’, or ‘__STDC_UTF_32__’) is not defined (C11
     6.10.8.2).’

     *Note Implementation-defined behavior: (cpp)Implementation-defined
     behavior.  ‘char16_t’ and ‘char32_t’ literals are always encoded in
     UTF-16 and UTF-32 respectively.


File: gcc.info,  Node: Integers implementation,  Next: Floating point implementation,  Prev: Characters implementation,  Up: C Implementation

4.5 Integers
============

   • ‘Any extended integer types that exist in the implementation (C99
     and C11 6.2.5).’

     GCC does not support any extended integer types.

   • ‘Whether signed integer types are represented using sign and
     magnitude, two's complement, or one's complement, and whether the
     extraordinary value is a trap representation or an ordinary value
     (C99 and C11 6.2.6.2).’

     GCC supports only two's complement integer types, and all bit
     patterns are ordinary values.

   • ‘The rank of any extended integer type relative to another extended
     integer type with the same precision (C99 and C11 6.3.1.1).’

     GCC does not support any extended integer types.

   • ‘The result of, or the signal raised by, converting an integer to a
     signed integer type when the value cannot be represented in an
     object of that type (C90 6.2.1.2, C99 and C11 6.3.1.3).’

     For conversion to a type of width N, the value is reduced modulo
     2^N to be within range of the type; no signal is raised.

   • ‘The results of some bitwise operations on signed integers (C90
     6.3, C99 and C11 6.5).’

     Bitwise operators act on the representation of the value including
     both the sign and value bits, where the sign bit is considered
     immediately above the highest-value value bit.  Signed ‘>>’ acts on
     negative numbers by sign extension.

     As an extension to the C language, GCC does not use the latitude
     given in C99 and C11 only to treat certain aspects of signed ‘<<’
     as undefined.  However, ‘-fsanitize=shift’ (and
     ‘-fsanitize=undefined’) will diagnose such cases.  They are also
     diagnosed where constant expressions are required.

   • ‘The sign of the remainder on integer division (C90 6.3.5).’

     GCC always follows the C99 and C11 requirement that the result of
     division is truncated towards zero.


File: gcc.info,  Node: Floating point implementation,  Next: Arrays and pointers implementation,  Prev: Integers implementation,  Up: C Implementation

4.6 Floating Point
==================

   • ‘The accuracy of the floating-point operations and of the library
     functions in ‘<math.h>’ and ‘<complex.h>’ that return
     floating-point results (C90, C99 and C11 5.2.4.2.2).’

     The accuracy is unknown.

   • ‘The rounding behaviors characterized by non-standard values of
     ‘FLT_ROUNDS’ (C90, C99 and C11 5.2.4.2.2).’

     GCC does not use such values.

   • ‘The evaluation methods characterized by non-standard negative
     values of ‘FLT_EVAL_METHOD’ (C99 and C11 5.2.4.2.2).’

     GCC does not use such values.

   • ‘The direction of rounding when an integer is converted to a
     floating-point number that cannot exactly represent the original
     value (C90 6.2.1.3, C99 and C11 6.3.1.4).’

     C99 Annex F is followed.

   • ‘The direction of rounding when a floating-point number is
     converted to a narrower floating-point number (C90 6.2.1.4, C99 and
     C11 6.3.1.5).’

     C99 Annex F is followed.

   • ‘How the nearest representable value or the larger or smaller
     representable value immediately adjacent to the nearest
     representable value is chosen for certain floating constants (C90
     6.1.3.1, C99 and C11 6.4.4.2).’

     C99 Annex F is followed.

   • ‘Whether and how floating expressions are contracted when not
     disallowed by the ‘FP_CONTRACT’ pragma (C99 and C11 6.5).’

     Expressions are currently only contracted if ‘-ffp-contract=fast’,
     ‘-funsafe-math-optimizations’ or ‘-ffast-math’ are used.  This is
     subject to change.

   • ‘The default state for the ‘FENV_ACCESS’ pragma (C99 and C11
     7.6.1).’

     This pragma is not implemented, but the default is to "off" unless
     ‘-frounding-math’ is used in which case it is "on".

   • ‘Additional floating-point exceptions, rounding modes,
     environments, and classifications, and their macro names (C99 and
     C11 7.6, C99 and C11 7.12).’

     This is dependent on the implementation of the C library, and is
     not defined by GCC itself.

   • ‘The default state for the ‘FP_CONTRACT’ pragma (C99 and C11
     7.12.2).’

     This pragma is not implemented.  Expressions are currently only
     contracted if ‘-ffp-contract=fast’, ‘-funsafe-math-optimizations’
     or ‘-ffast-math’ are used.  This is subject to change.

   • ‘Whether the "inexact" floating-point exception can be raised when
     the rounded result actually does equal the mathematical result in
     an IEC 60559 conformant implementation (C99 F.9).’

     This is dependent on the implementation of the C library, and is
     not defined by GCC itself.

   • ‘Whether the "underflow" (and "inexact") floating-point exception
     can be raised when a result is tiny but not inexact in an IEC 60559
     conformant implementation (C99 F.9).’

     This is dependent on the implementation of the C library, and is
     not defined by GCC itself.


File: gcc.info,  Node: Arrays and pointers implementation,  Next: Hints implementation,  Prev: Floating point implementation,  Up: C Implementation

4.7 Arrays and Pointers
=======================

   • ‘The result of converting a pointer to an integer or vice versa
     (C90 6.3.4, C99 and C11 6.3.2.3).’

     A cast from pointer to integer discards most-significant bits if
     the pointer representation is larger than the integer type,
     sign-extends(1) if the pointer representation is smaller than the
     integer type, otherwise the bits are unchanged.

     A cast from integer to pointer discards most-significant bits if
     the pointer representation is smaller than the integer type,
     extends according to the signedness of the integer type if the
     pointer representation is larger than the integer type, otherwise
     the bits are unchanged.

     When casting from pointer to integer and back again, the resulting
     pointer must reference the same object as the original pointer,
     otherwise the behavior is undefined.  That is, one may not use
     integer arithmetic to avoid the undefined behavior of pointer
     arithmetic as proscribed in C99 and C11 6.5.6/8.

   • ‘The size of the result of subtracting two pointers to elements of
     the same array (C90 6.3.6, C99 and C11 6.5.6).’

     The value is as specified in the standard and the type is
     determined by the ABI.

   ---------- Footnotes ----------

   (1) Future versions of GCC may zero-extend, or use a target-defined
‘ptr_extend’ pattern.  Do not rely on sign extension.


File: gcc.info,  Node: Hints implementation,  Next: Structures unions enumerations and bit-fields implementation,  Prev: Arrays and pointers implementation,  Up: C Implementation

4.8 Hints
=========

   • ‘The extent to which suggestions made by using the ‘register’
     storage-class specifier are effective (C90 6.5.1, C99 and C11
     6.7.1).’

     The ‘register’ specifier affects code generation only in these
     ways:

        • When used as part of the register variable extension, see
          *note Explicit Register Variables::.

        • When ‘-O0’ is in use, the compiler allocates distinct stack
          memory for all variables that do not have the ‘register’
          storage-class specifier; if ‘register’ is specified, the
          variable may have a shorter lifespan than the code would
          indicate and may never be placed in memory.

        • On some rare x86 targets, ‘setjmp’ doesn't save the registers
          in all circumstances.  In those cases, GCC doesn't allocate
          any variables in registers unless they are marked ‘register’.

   • ‘The extent to which suggestions made by using the inline function
     specifier are effective (C99 and C11 6.7.4).’

     GCC will not inline any functions if the ‘-fno-inline’ option is
     used or if ‘-O0’ is used.  Otherwise, GCC may still be unable to
     inline a function for many reasons; the ‘-Winline’ option may be
     used to determine if a function has not been inlined and why not.


File: gcc.info,  Node: Structures unions enumerations and bit-fields implementation,  Next: Qualifiers implementation,  Prev: Hints implementation,  Up: C Implementation

4.9 Structures, Unions, Enumerations, and Bit-Fields
====================================================

   • ‘A member of a union object is accessed using a member of a
     different type (C90 6.3.2.3).’

     The relevant bytes of the representation of the object are treated
     as an object of the type used for the access.  *Note
     Type-punning::.  This may be a trap representation.

   • ‘Whether a "plain" ‘int’ bit-field is treated as a ‘signed int’
     bit-field or as an ‘unsigned int’ bit-field (C90 6.5.2, C90
     6.5.2.1, C99 and C11 6.7.2, C99 and C11 6.7.2.1).’

     By default it is treated as ‘signed int’ but this may be changed by
     the ‘-funsigned-bitfields’ option.

   • ‘Allowable bit-field types other than ‘_Bool’, ‘signed int’, and
     ‘unsigned int’ (C99 and C11 6.7.2.1).’

     Other integer types, such as ‘long int’, and enumerated types are
     permitted even in strictly conforming mode.

   • ‘Whether atomic types are permitted for bit-fields (C11 6.7.2.1).’

     Atomic types are not permitted for bit-fields.

   • ‘Whether a bit-field can straddle a storage-unit boundary (C90
     6.5.2.1, C99 and C11 6.7.2.1).’

     Determined by ABI.

   • ‘The order of allocation of bit-fields within a unit (C90 6.5.2.1,
     C99 and C11 6.7.2.1).’

     Determined by ABI.

   • ‘The alignment of non-bit-field members of structures (C90 6.5.2.1,
     C99 and C11 6.7.2.1).’

     Determined by ABI.

   • ‘The integer type compatible with each enumerated type (C90
     6.5.2.2, C99 and C11 6.7.2.2).’

     Normally, the type is ‘unsigned int’ if there are no negative
     values in the enumeration, otherwise ‘int’.  If ‘-fshort-enums’ is
     specified, then if there are negative values it is the first of
     ‘signed char’, ‘short’ and ‘int’ that can represent all the values,
     otherwise it is the first of ‘unsigned char’, ‘unsigned short’ and
     ‘unsigned int’ that can represent all the values.

     On some targets, ‘-fshort-enums’ is the default; this is determined
     by the ABI.


File: gcc.info,  Node: Qualifiers implementation,  Next: Declarators implementation,  Prev: Structures unions enumerations and bit-fields implementation,  Up: C Implementation

4.10 Qualifiers
===============

   • ‘What constitutes an access to an object that has
     volatile-qualified type (C90 6.5.3, C99 and C11 6.7.3).’

     Such an object is normally accessed by pointers and used for
     accessing hardware.  In most expressions, it is intuitively obvious
     what is a read and what is a write.  For example

          volatile int *dst = SOMEVALUE;
          volatile int *src = SOMEOTHERVALUE;
          *dst = *src;

     will cause a read of the volatile object pointed to by SRC and
     store the value into the volatile object pointed to by DST.  There
     is no guarantee that these reads and writes are atomic, especially
     for objects larger than ‘int’.

     However, if the volatile storage is not being modified, and the
     value of the volatile storage is not used, then the situation is
     less obvious.  For example

          volatile int *src = SOMEVALUE;
          *src;

     According to the C standard, such an expression is an rvalue whose
     type is the unqualified version of its original type, i.e. ‘int’.
     Whether GCC interprets this as a read of the volatile object being
     pointed to or only as a request to evaluate the expression for its
     side effects depends on this type.

     If it is a scalar type, or on most targets an aggregate type whose
     only member object is of a scalar type, or a union type whose
     member objects are of scalar types, the expression is interpreted
     by GCC as a read of the volatile object; in the other cases, the
     expression is only evaluated for its side effects.

     When an object of an aggregate type, with the same size and
     alignment as a scalar type ‘S’, is the subject of a volatile access
     by an assignment expression or an atomic function, the access to it
     is performed as if the object's declared type were ‘volatile S’.


File: gcc.info,  Node: Declarators implementation,  Next: Statements implementation,  Prev: Qualifiers implementation,  Up: C Implementation

4.11 Declarators
================

   • ‘The maximum number of declarators that may modify an arithmetic,
     structure or union type (C90 6.5.4).’

     GCC is only limited by available memory.


File: gcc.info,  Node: Statements implementation,  Next: Preprocessing directives implementation,  Prev: Declarators implementation,  Up: C Implementation

4.12 Statements
===============

   • ‘The maximum number of ‘case’ values in a ‘switch’ statement (C90
     6.6.4.2).’

     GCC is only limited by available memory.


File: gcc.info,  Node: Preprocessing directives implementation,  Next: Library functions implementation,  Prev: Statements implementation,  Up: C Implementation

4.13 Preprocessing Directives
=============================

*Note Implementation-defined behavior: (cpp)Implementation-defined
behavior, for details of these aspects of implementation-defined
behavior.

   • ‘The locations within ‘#pragma’ directives where header name
     preprocessing tokens are recognized (C11 6.4, C11 6.4.7).’

   • ‘How sequences in both forms of header names are mapped to headers
     or external source file names (C90 6.1.7, C99 and C11 6.4.7).’

   • ‘Whether the value of a character constant in a constant expression
     that controls conditional inclusion matches the value of the same
     character constant in the execution character set (C90 6.8.1, C99
     and C11 6.10.1).’

   • ‘Whether the value of a single-character character constant in a
     constant expression that controls conditional inclusion may have a
     negative value (C90 6.8.1, C99 and C11 6.10.1).’

   • ‘The places that are searched for an included ‘<>’ delimited
     header, and how the places are specified or the header is
     identified (C90 6.8.2, C99 and C11 6.10.2).’

   • ‘How the named source file is searched for in an included ‘""’
     delimited header (C90 6.8.2, C99 and C11 6.10.2).’

   • ‘The method by which preprocessing tokens (possibly resulting from
     macro expansion) in a ‘#include’ directive are combined into a
     header name (C90 6.8.2, C99 and C11 6.10.2).’

   • ‘The nesting limit for ‘#include’ processing (C90 6.8.2, C99 and
     C11 6.10.2).’

   • ‘Whether the ‘#’ operator inserts a ‘\’ character before the ‘\’
     character that begins a universal character name in a character
     constant or string literal (C99 and C11 6.10.3.2).’

   • ‘The behavior on each recognized non-‘STDC #pragma’ directive (C90
     6.8.6, C99 and C11 6.10.6).’

     *Note Pragmas: (cpp)Pragmas, for details of pragmas accepted by GCC
     on all targets.  *Note Pragmas Accepted by GCC: Pragmas, for
     details of target-specific pragmas.

   • ‘The definitions for ‘__DATE__’ and ‘__TIME__’ when respectively,
     the date and time of translation are not available (C90 6.8.8, C99
     6.10.8, C11 6.10.8.1).’


File: gcc.info,  Node: Library functions implementation,  Next: Architecture implementation,  Prev: Preprocessing directives implementation,  Up: C Implementation

4.14 Library Functions
======================

The behavior of most of these points are dependent on the implementation
of the C library, and are not defined by GCC itself.

   • ‘The null pointer constant to which the macro ‘NULL’ expands (C90
     7.1.6, C99 7.17, C11 7.19).’

     In ‘<stddef.h>’, ‘NULL’ expands to ‘((void *)0)’.  GCC does not
     provide the other headers which define ‘NULL’ and some library
     implementations may use other definitions in those headers.


File: gcc.info,  Node: Architecture implementation,  Next: Locale-specific behavior implementation,  Prev: Library functions implementation,  Up: C Implementation

4.15 Architecture
=================

   • ‘The values or expressions assigned to the macros specified in the
     headers ‘<float.h>’, ‘<limits.h>’, and ‘<stdint.h>’ (C90, C99 and
     C11 5.2.4.2, C99 7.18.2, C99 7.18.3, C11 7.20.2, C11 7.20.3).’

     Determined by ABI.

   • ‘The result of attempting to indirectly access an object with
     automatic or thread storage duration from a thread other than the
     one with which it is associated (C11 6.2.4).’

     Such accesses are supported, subject to the same requirements for
     synchronization for concurrent accesses as for concurrent accesses
     to any object.

   • ‘The number, order, and encoding of bytes in any object (when not
     explicitly specified in this International Standard) (C99 and C11
     6.2.6.1).’

     Determined by ABI.

   • ‘Whether any extended alignments are supported and the contexts in
     which they are supported (C11 6.2.8).’

     Extended alignments up to 2^{28} (bytes) are supported for objects
     of automatic storage duration.  Alignments supported for objects of
     static and thread storage duration are determined by the ABI.

   • ‘Valid alignment values other than those returned by an _Alignof
     expression for fundamental types, if any (C11 6.2.8).’

     Valid alignments are powers of 2 up to and including 2^{28}.

   • ‘The value of the result of the ‘sizeof’ and ‘_Alignof’ operators
     (C90 6.3.3.4, C99 and C11 6.5.3.4).’

     Determined by ABI.


File: gcc.info,  Node: Locale-specific behavior implementation,  Prev: Architecture implementation,  Up: C Implementation

4.16 Locale-Specific Behavior
=============================

The behavior of these points are dependent on the implementation of the
C library, and are not defined by GCC itself.


File: gcc.info,  Node: C++ Implementation,  Next: C Extensions,  Prev: C Implementation,  Up: Top

5 C++ Implementation-Defined Behavior
*************************************

A conforming implementation of ISO C++ is required to document its
choice of behavior in each of the areas that are designated
"implementation defined".  The following lists all such areas, along
with the section numbers from the ISO/IEC 14882:1998 and ISO/IEC
14882:2003 standards.  Some areas are only implementation-defined in one
version of the standard.

 Some choices depend on the externally determined ABI for the platform
(including standard character encodings) which GCC follows; these are
listed as "determined by ABI" below.  *Note Binary Compatibility:
Compatibility, and <https://gcc.gnu.org/readings.html>.  Some choices
are documented in the preprocessor manual.  *Note Implementation-defined
behavior: (cpp)Implementation-defined behavior.  Some choices are
documented in the corresponding document for the C language.  *Note C
Implementation::.  Some choices are made by the library and operating
system (or other environment when compiling for a freestanding
environment); refer to their documentation for details.

* Menu:

* Conditionally-supported behavior::
* Exception handling::


File: gcc.info,  Node: Conditionally-supported behavior,  Next: Exception handling,  Up: C++ Implementation

5.1 Conditionally-Supported Behavior
====================================

‘Each implementation shall include documentation that identifies all
conditionally-supported constructs that it does not support (C++0x
1.4).’

   • ‘Whether an argument of class type with a non-trivial copy
     constructor or destructor can be passed to ... (C++0x 5.2.2).’

     Such argument passing is supported, using the same
     pass-by-invisible-reference approach used for normal function
     arguments of such types.


File: gcc.info,  Node: Exception handling,  Prev: Conditionally-supported behavior,  Up: C++ Implementation

5.2 Exception Handling
======================

   • ‘In the situation where no matching handler is found, it is
     implementation-defined whether or not the stack is unwound before
     std::terminate() is called (C++98 15.5.1).’

     The stack is not unwound before std::terminate is called.

 c Copyright (C) 1988-2022 Free Software Foundation, Inc.


File: gcc.info,  Node: C Extensions,  Next: C++ Extensions,  Prev: C++ Implementation,  Up: Top

6 Extensions to the C Language Family
*************************************

GNU C provides several language features not found in ISO standard C.
(The ‘-pedantic’ option directs GCC to print a warning message if any of
these features is used.)  To test for the availability of these features
in conditional compilation, check for a predefined macro ‘__GNUC__’,
which is always defined under GCC.

 These extensions are available in C and Objective-C.  Most of them are
also available in C++.  *Note Extensions to the C++ Language: C++
Extensions, for extensions that apply _only_ to C++.

 Some features that are in ISO C99 but not C90 or C++ are also, as
extensions, accepted by GCC in C90 mode and in C++.

* Menu:

* Statement Exprs::     Putting statements and declarations inside expressions.
* Local Labels::        Labels local to a block.
* Labels as Values::    Getting pointers to labels, and computed gotos.
* Nested Functions::    Nested function in GNU C.
* Nonlocal Gotos::      Nonlocal gotos.
* Constructing Calls::  Dispatching a call to another function.
* Typeof::              ‘typeof’: referring to the type of an expression.
* Conditionals::        Omitting the middle operand of a ‘?:’ expression.
* __int128::		128-bit integers--‘__int128’.
* Long Long::           Double-word integers--‘long long int’.
* Complex::             Data types for complex numbers.
* Floating Types::      Additional Floating Types.
* Half-Precision::      Half-Precision Floating Point.
* Decimal Float::       Decimal Floating Types.
* Hex Floats::          Hexadecimal floating-point constants.
* Fixed-Point::         Fixed-Point Types.
* Named Address Spaces::Named address spaces.
* Zero Length::         Zero-length arrays.
* Empty Structures::    Structures with no members.
* Variable Length::     Arrays whose length is computed at run time.
* Variadic Macros::     Macros with a variable number of arguments.
* Escaped Newlines::    Slightly looser rules for escaped newlines.
* Subscripting::        Any array can be subscripted, even if not an lvalue.
* Pointer Arith::       Arithmetic on ‘void’-pointers and function pointers.
* Variadic Pointer Args::  Pointer arguments to variadic functions.
* Pointers to Arrays::  Pointers to arrays with qualifiers work as expected.
* Initializers::        Non-constant initializers.
* Compound Literals::   Compound literals give structures, unions
                        or arrays as values.
* Designated Inits::    Labeling elements of initializers.
* Case Ranges::         'case 1 ... 9' and such.
* Cast to Union::       Casting to union type from any member of the union.
* Mixed Labels and Declarations::  Mixing declarations, labels and code.
* Function Attributes:: Declaring that functions have no side effects,
                        or that they can never return.
* Variable Attributes:: Specifying attributes of variables.
* Type Attributes::     Specifying attributes of types.
* Label Attributes::    Specifying attributes on labels.
* Enumerator Attributes:: Specifying attributes on enumerators.
* Statement Attributes:: Specifying attributes on statements.
* Attribute Syntax::    Formal syntax for attributes.
* Function Prototypes:: Prototype declarations and old-style definitions.
* C++ Comments::        C++ comments are recognized.
* Dollar Signs::        Dollar sign is allowed in identifiers.
* Character Escapes::   ‘\e’ stands for the character <ESC>.
* Alignment::           Determining the alignment of a function, type or variable.
* Inline::              Defining inline functions (as fast as macros).
* Volatiles::           What constitutes an access to a volatile object.
* Using Assembly Language with C:: Instructions and extensions for interfacing C with assembler.
* Alternate Keywords::  ‘__const__’, ‘__asm__’, etc., for header files.
* Incomplete Enums::    ‘enum foo;’, with details to follow.
* Function Names::      Printable strings which are the name of the current
                        function.
* Return Address::      Getting the return or frame address of a function.
* Vector Extensions::   Using vector instructions through built-in functions.
* Offsetof::            Special syntax for implementing ‘offsetof’.
* __sync Builtins::     Legacy built-in functions for atomic memory access.
* __atomic Builtins::   Atomic built-in functions with memory model.
* Integer Overflow Builtins:: Built-in functions to perform arithmetics and
                        arithmetic overflow checking.
* x86 specific memory model extensions for transactional memory:: x86 memory models.
* Object Size Checking:: Built-in functions for limited buffer overflow
                        checking.
* Other Builtins::      Other built-in functions.
* Target Builtins::     Built-in functions specific to particular targets.
* Target Format Checks:: Format checks specific to particular targets.
* Pragmas::             Pragmas accepted by GCC.
* Unnamed Fields::      Unnamed struct/union fields within structs/unions.
* Thread-Local::        Per-thread variables.
* Binary constants::    Binary constants using the ‘0b’ prefix.


File: gcc.info,  Node: Statement Exprs,  Next: Local Labels,  Up: C Extensions

6.1 Statements and Declarations in Expressions
==============================================

A compound statement enclosed in parentheses may appear as an expression
in GNU C.  This allows you to use loops, switches, and local variables
within an expression.

 Recall that a compound statement is a sequence of statements surrounded
by braces; in this construct, parentheses go around the braces.  For
example:

     ({ int y = foo (); int z;
        if (y > 0) z = y;
        else z = - y;
        z; })

is a valid (though slightly more complex than necessary) expression for
the absolute value of ‘foo ()’.

 The last thing in the compound statement should be an expression
followed by a semicolon; the value of this subexpression serves as the
value of the entire construct.  (If you use some other kind of statement
last within the braces, the construct has type ‘void’, and thus
effectively no value.)

 This feature is especially useful in making macro definitions "safe"
(so that they evaluate each operand exactly once).  For example, the
"maximum" function is commonly defined as a macro in standard C as
follows:

     #define max(a,b) ((a) > (b) ? (a) : (b))

But this definition computes either A or B twice, with bad results if
the operand has side effects.  In GNU C, if you know the type of the
operands (here taken as ‘int’), you can avoid this problem by defining
the macro as follows:

     #define maxint(a,b) \
       ({int _a = (a), _b = (b); _a > _b ? _a : _b; })

 Note that introducing variable declarations (as we do in ‘maxint’) can
cause variable shadowing, so while this example using the ‘max’ macro
produces correct results:
     int _a = 1, _b = 2, c;
     c = max (_a, _b);
this example using maxint will not:
     int _a = 1, _b = 2, c;
     c = maxint (_a, _b);

 This problem may for instance occur when we use this pattern
recursively, like so:

     #define maxint3(a, b, c) \
       ({int _a = (a), _b = (b), _c = (c); maxint (maxint (_a, _b), _c); })

 Embedded statements are not allowed in constant expressions, such as
the value of an enumeration constant, the width of a bit-field, or the
initial value of a static variable.

 If you don't know the type of the operand, you can still do this, but
you must use ‘typeof’ or ‘__auto_type’ (*note Typeof::).

 In G++, the result value of a statement expression undergoes array and
function pointer decay, and is returned by value to the enclosing
expression.  For instance, if ‘A’ is a class, then

             A a;

             ({a;}).Foo ()

constructs a temporary ‘A’ object to hold the result of the statement
expression, and that is used to invoke ‘Foo’.  Therefore the ‘this’
pointer observed by ‘Foo’ is not the address of ‘a’.

 In a statement expression, any temporaries created within a statement
are destroyed at that statement's end.  This makes statement expressions
inside macros slightly different from function calls.  In the latter
case temporaries introduced during argument evaluation are destroyed at
the end of the statement that includes the function call.  In the
statement expression case they are destroyed during the statement
expression.  For instance,

     #define macro(a)  ({__typeof__(a) b = (a); b + 3; })
     template<typename T> T function(T a) { T b = a; return b + 3; }

     void foo ()
     {
       macro (X ());
       function (X ());
     }

has different places where temporaries are destroyed.  For the ‘macro’
case, the temporary ‘X’ is destroyed just after the initialization of
‘b’.  In the ‘function’ case that temporary is destroyed when the
function returns.

 These considerations mean that it is probably a bad idea to use
statement expressions of this form in header files that are designed to
work with C++.  (Note that some versions of the GNU C Library contained
header files using statement expressions that lead to precisely this
bug.)

 Jumping into a statement expression with ‘goto’ or using a ‘switch’
statement outside the statement expression with a ‘case’ or ‘default’
label inside the statement expression is not permitted.  Jumping into a
statement expression with a computed ‘goto’ (*note Labels as Values::)
has undefined behavior.  Jumping out of a statement expression is
permitted, but if the statement expression is part of a larger
expression then it is unspecified which other subexpressions of that
expression have been evaluated except where the language definition
requires certain subexpressions to be evaluated before or after the
statement expression.  A ‘break’ or ‘continue’ statement inside of a
statement expression used in ‘while’, ‘do’ or ‘for’ loop or ‘switch’
statement condition or ‘for’ statement init or increment expressions
jumps to an outer loop or ‘switch’ statement if any (otherwise it is an
error), rather than to the loop or ‘switch’ statement in whose condition
or init or increment expression it appears.  In any case, as with a
function call, the evaluation of a statement expression is not
interleaved with the evaluation of other parts of the containing
expression.  For example,

       foo (), (({ bar1 (); goto a; 0; }) + bar2 ()), baz();

calls ‘foo’ and ‘bar1’ and does not call ‘baz’ but may or may not call
‘bar2’.  If ‘bar2’ is called, it is called after ‘foo’ and before
‘bar1’.


File: gcc.info,  Node: Local Labels,  Next: Labels as Values,  Prev: Statement Exprs,  Up: C Extensions

6.2 Locally Declared Labels
===========================

GCC allows you to declare “local labels” in any nested block scope.  A
local label is just like an ordinary label, but you can only reference
it (with a ‘goto’ statement, or by taking its address) within the block
in which it is declared.

 A local label declaration looks like this:

     __label__ LABEL;

or

     __label__ LABEL1, LABEL2, /* ... */;

 Local label declarations must come at the beginning of the block,
before any ordinary declarations or statements.

 The label declaration defines the label _name_, but does not define the
label itself.  You must do this in the usual way, with ‘LABEL:’, within
the statements of the statement expression.

 The local label feature is useful for complex macros.  If a macro
contains nested loops, a ‘goto’ can be useful for breaking out of them.
However, an ordinary label whose scope is the whole function cannot be
used: if the macro can be expanded several times in one function, the
label is multiply defined in that function.  A local label avoids this
problem.  For example:

     #define SEARCH(value, array, target)              \
     do {                                              \
       __label__ found;                                \
       typeof (target) _SEARCH_target = (target);      \
       typeof (*(array)) *_SEARCH_array = (array);     \
       int i, j;                                       \
       int value;                                      \
       for (i = 0; i < max; i++)                       \
         for (j = 0; j < max; j++)                     \
           if (_SEARCH_array[i][j] == _SEARCH_target)  \
             { (value) = i; goto found; }              \
       (value) = -1;                                   \
      found:;                                          \
     } while (0)

 This could also be written using a statement expression:

     #define SEARCH(array, target)                     \
     ({                                                \
       __label__ found;                                \
       typeof (target) _SEARCH_target = (target);      \
       typeof (*(array)) *_SEARCH_array = (array);     \
       int i, j;                                       \
       int value;                                      \
       for (i = 0; i < max; i++)                       \
         for (j = 0; j < max; j++)                     \
           if (_SEARCH_array[i][j] == _SEARCH_target)  \
             { value = i; goto found; }                \
       value = -1;                                     \
      found:                                           \
       value;                                          \
     })

 Local label declarations also make the labels they declare visible to
nested functions, if there are any.  *Note Nested Functions::, for
details.


File: gcc.info,  Node: Labels as Values,  Next: Nested Functions,  Prev: Local Labels,  Up: C Extensions

6.3 Labels as Values
====================

You can get the address of a label defined in the current function (or a
containing function) with the unary operator ‘&&’.  The value has type
‘void *’.  This value is a constant and can be used wherever a constant
of that type is valid.  For example:

     void *ptr;
     /* ... */
     ptr = &&foo;

 To use these values, you need to be able to jump to one.  This is done
with the computed goto statement(1), ‘goto *EXP;’.  For example,

     goto *ptr;

Any expression of type ‘void *’ is allowed.

 One way of using these constants is in initializing a static array that
serves as a jump table:

     static void *array[] = { &&foo, &&bar, &&hack };

Then you can select a label with indexing, like this:

     goto *array[i];

Note that this does not check whether the subscript is in bounds--array
indexing in C never does that.

 Such an array of label values serves a purpose much like that of the
‘switch’ statement.  The ‘switch’ statement is cleaner, so use that
rather than an array unless the problem does not fit a ‘switch’
statement very well.

 Another use of label values is in an interpreter for threaded code.
The labels within the interpreter function can be stored in the threaded
code for super-fast dispatching.

 You may not use this mechanism to jump to code in a different function.
If you do that, totally unpredictable things happen.  The best way to
avoid this is to store the label address only in automatic variables and
never pass it as an argument.

 An alternate way to write the above example is

     static const int array[] = { &&foo - &&foo, &&bar - &&foo,
                                  &&hack - &&foo };
     goto *(&&foo + array[i]);

This is more friendly to code living in shared libraries, as it reduces
the number of dynamic relocations that are needed, and by consequence,
allows the data to be read-only.  This alternative with label
differences is not supported for the AVR target, please use the first
approach for AVR programs.

 The ‘&&foo’ expressions for the same label might have different values
if the containing function is inlined or cloned.  If a program relies on
them being always the same, ‘__attribute__((__noinline__,__noclone__))’
should be used to prevent inlining and cloning.  If ‘&&foo’ is used in a
static variable initializer, inlining and cloning is forbidden.

   ---------- Footnotes ----------

   (1) The analogous feature in Fortran is called an assigned goto, but
that name seems inappropriate in C, where one can do more than simply
store label addresses in label variables.


File: gcc.info,  Node: Nested Functions,  Next: Nonlocal Gotos,  Prev: Labels as Values,  Up: C Extensions

6.4 Nested Functions
====================

A “nested function” is a function defined inside another function.
Nested functions are supported as an extension in GNU C, but are not
supported by GNU C++.

 The nested function's name is local to the block where it is defined.
For example, here we define a nested function named ‘square’, and call
it twice:

     foo (double a, double b)
     {
       double square (double z) { return z * z; }

       return square (a) + square (b);
     }

 The nested function can access all the variables of the containing
function that are visible at the point of its definition.  This is
called “lexical scoping”.  For example, here we show a nested function
which uses an inherited variable named ‘offset’:

     bar (int *array, int offset, int size)
     {
       int access (int *array, int index)
         { return array[index + offset]; }
       int i;
       /* ... */
       for (i = 0; i < size; i++)
         /* ... */ access (array, i) /* ... */
     }

 Nested function definitions are permitted within functions in the
places where variable definitions are allowed; that is, in any block,
mixed with the other declarations and statements in the block.

 It is possible to call the nested function from outside the scope of
its name by storing its address or passing the address to another
function:

     hack (int *array, int size)
     {
       void store (int index, int value)
         { array[index] = value; }

       intermediate (store, size);
     }

 Here, the function ‘intermediate’ receives the address of ‘store’ as an
argument.  If ‘intermediate’ calls ‘store’, the arguments given to
‘store’ are used to store into ‘array’.  But this technique works only
so long as the containing function (‘hack’, in this example) does not
exit.

 If you try to call the nested function through its address after the
containing function exits, all hell breaks loose.  If you try to call it
after a containing scope level exits, and if it refers to some of the
variables that are no longer in scope, you may be lucky, but it's not
wise to take the risk.  If, however, the nested function does not refer
to anything that has gone out of scope, you should be safe.

 GCC implements taking the address of a nested function using a
technique called “trampolines”.  This technique was described in
‘Lexical Closures for C++’ (Thomas M. Breuel, USENIX C++ Conference
Proceedings, October 17-21, 1988).

 A nested function can jump to a label inherited from a containing
function, provided the label is explicitly declared in the containing
function (*note Local Labels::).  Such a jump returns instantly to the
containing function, exiting the nested function that did the ‘goto’ and
any intermediate functions as well.  Here is an example:

     bar (int *array, int offset, int size)
     {
       __label__ failure;
       int access (int *array, int index)
         {
           if (index > size)
             goto failure;
           return array[index + offset];
         }
       int i;
       /* ... */
       for (i = 0; i < size; i++)
         /* ... */ access (array, i) /* ... */
       /* ... */
       return 0;

      /* Control comes here from ‘access’
         if it detects an error.  */
      failure:
       return -1;
     }

 A nested function always has no linkage.  Declaring one with ‘extern’
or ‘static’ is erroneous.  If you need to declare the nested function
before its definition, use ‘auto’ (which is otherwise meaningless for
function declarations).

     bar (int *array, int offset, int size)
     {
       __label__ failure;
       auto int access (int *, int);
       /* ... */
       int access (int *array, int index)
         {
           if (index > size)
             goto failure;
           return array[index + offset];
         }
       /* ... */
     }


File: gcc.info,  Node: Nonlocal Gotos,  Next: Constructing Calls,  Prev: Nested Functions,  Up: C Extensions

6.5 Nonlocal Gotos
==================

GCC provides the built-in functions ‘__builtin_setjmp’ and
‘__builtin_longjmp’ which are similar to, but not interchangeable with,
the C library functions ‘setjmp’ and ‘longjmp’.  The built-in versions
are used internally by GCC's libraries to implement exception handling
on some targets.  You should use the standard C library functions
declared in ‘<setjmp.h>’ in user code instead of the builtins.

 The built-in versions of these functions use GCC's normal mechanisms to
save and restore registers using the stack on function entry and exit.
The jump buffer argument BUF holds only the information needed to
restore the stack frame, rather than the entire set of saved register
values.

 An important caveat is that GCC arranges to save and restore only those
registers known to the specific architecture variant being compiled for.
This can make ‘__builtin_setjmp’ and ‘__builtin_longjmp’ more efficient
than their library counterparts in some cases, but it can also cause
incorrect and mysterious behavior when mixing with code that uses the
full register set.

 You should declare the jump buffer argument BUF to the built-in
functions as:

     #include <stdint.h>
     intptr_t BUF[5];

 -- Built-in Function: int __builtin_setjmp (intptr_t *BUF)
     This function saves the current stack context in BUF.
     ‘__builtin_setjmp’ returns 0 when returning directly, and 1 when
     returning from ‘__builtin_longjmp’ using the same BUF.

 -- Built-in Function: void __builtin_longjmp (intptr_t *BUF, int VAL)
     This function restores the stack context in BUF, saved by a
     previous call to ‘__builtin_setjmp’.  After ‘__builtin_longjmp’ is
     finished, the program resumes execution as if the matching
     ‘__builtin_setjmp’ returns the value VAL, which must be 1.

     Because ‘__builtin_longjmp’ depends on the function return
     mechanism to restore the stack context, it cannot be called from
     the same function calling ‘__builtin_setjmp’ to initialize BUF.  It
     can only be called from a function called (directly or indirectly)
     from the function calling ‘__builtin_setjmp’.


File: gcc.info,  Node: Constructing Calls,  Next: Typeof,  Prev: Nonlocal Gotos,  Up: C Extensions

6.6 Constructing Function Calls
===============================

Using the built-in functions described below, you can record the
arguments a function received, and call another function with the same
arguments, without knowing the number or types of the arguments.

 You can also record the return value of that function call, and later
return that value, without knowing what data type the function tried to
return (as long as your caller expects that data type).

 However, these built-in functions may interact badly with some
sophisticated features or other extensions of the language.  It is,
therefore, not recommended to use them outside very simple functions
acting as mere forwarders for their arguments.

 -- Built-in Function: void * __builtin_apply_args ()
     This built-in function returns a pointer to data describing how to
     perform a call with the same arguments as are passed to the current
     function.

     The function saves the arg pointer register, structure value
     address, and all registers that might be used to pass arguments to
     a function into a block of memory allocated on the stack.  Then it
     returns the address of that block.

 -- Built-in Function: void * __builtin_apply (void (*FUNCTION)(), void
          *ARGUMENTS, size_t SIZE)
     This built-in function invokes FUNCTION with a copy of the
     parameters described by ARGUMENTS and SIZE.

     The value of ARGUMENTS should be the value returned by
     ‘__builtin_apply_args’.  The argument SIZE specifies the size of
     the stack argument data, in bytes.

     This function returns a pointer to data describing how to return
     whatever value is returned by FUNCTION.  The data is saved in a
     block of memory allocated on the stack.

     It is not always simple to compute the proper value for SIZE.  The
     value is used by ‘__builtin_apply’ to compute the amount of data
     that should be pushed on the stack and copied from the incoming
     argument area.

 -- Built-in Function: void __builtin_return (void *RESULT)
     This built-in function returns the value described by RESULT from
     the containing function.  You should specify, for RESULT, a value
     returned by ‘__builtin_apply’.

 -- Built-in Function: __builtin_va_arg_pack ()
     This built-in function represents all anonymous arguments of an
     inline function.  It can be used only in inline functions that are
     always inlined, never compiled as a separate function, such as
     those using ‘__attribute__ ((__always_inline__))’ or ‘__attribute__
     ((__gnu_inline__))’ extern inline functions.  It must be only
     passed as last argument to some other function with variable
     arguments.  This is useful for writing small wrapper inlines for
     variable argument functions, when using preprocessor macros is
     undesirable.  For example:
          extern int myprintf (FILE *f, const char *format, ...);
          extern inline __attribute__ ((__gnu_inline__)) int
          myprintf (FILE *f, const char *format, ...)
          {
            int r = fprintf (f, "myprintf: ");
            if (r < 0)
              return r;
            int s = fprintf (f, format, __builtin_va_arg_pack ());
            if (s < 0)
              return s;
            return r + s;
          }

 -- Built-in Function: size_t __builtin_va_arg_pack_len ()
     This built-in function returns the number of anonymous arguments of
     an inline function.  It can be used only in inline functions that
     are always inlined, never compiled as a separate function, such as
     those using ‘__attribute__ ((__always_inline__))’ or ‘__attribute__
     ((__gnu_inline__))’ extern inline functions.  For example following
     does link- or run-time checking of open arguments for optimized
     code:
          #ifdef __OPTIMIZE__
          extern inline __attribute__((__gnu_inline__)) int
          myopen (const char *path, int oflag, ...)
          {
            if (__builtin_va_arg_pack_len () > 1)
              warn_open_too_many_arguments ();

            if (__builtin_constant_p (oflag))
              {
                if ((oflag & O_CREAT) != 0 && __builtin_va_arg_pack_len () < 1)
                  {
                    warn_open_missing_mode ();
                    return __open_2 (path, oflag);
                  }
                return open (path, oflag, __builtin_va_arg_pack ());
              }

            if (__builtin_va_arg_pack_len () < 1)
              return __open_2 (path, oflag);

            return open (path, oflag, __builtin_va_arg_pack ());
          }
          #endif


File: gcc.info,  Node: Typeof,  Next: Conditionals,  Prev: Constructing Calls,  Up: C Extensions

6.7 Referring to a Type with ‘typeof’
=====================================

Another way to refer to the type of an expression is with ‘typeof’.  The
syntax of using of this keyword looks like ‘sizeof’, but the construct
acts semantically like a type name defined with ‘typedef’.

 There are two ways of writing the argument to ‘typeof’: with an
expression or with a type.  Here is an example with an expression:

     typeof (x[0](1))

This assumes that ‘x’ is an array of pointers to functions; the type
described is that of the values of the functions.

 Here is an example with a typename as the argument:

     typeof (int *)

Here the type described is that of pointers to ‘int’.

 If you are writing a header file that must work when included in ISO C
programs, write ‘__typeof__’ instead of ‘typeof’.  *Note Alternate
Keywords::.

 A ‘typeof’ construct can be used anywhere a typedef name can be used.
For example, you can use it in a declaration, in a cast, or inside of
‘sizeof’ or ‘typeof’.

 The operand of ‘typeof’ is evaluated for its side effects if and only
if it is an expression of variably modified type or the name of such a
type.

 ‘typeof’ is often useful in conjunction with statement expressions
(*note Statement Exprs::).  Here is how the two together can be used to
define a safe "maximum" macro which operates on any arithmetic type and
evaluates each of its arguments exactly once:

     #define max(a,b) \
       ({ typeof (a) _a = (a); \
           typeof (b) _b = (b); \
         _a > _b ? _a : _b; })

 The reason for using names that start with underscores for the local
variables is to avoid conflicts with variable names that occur within
the expressions that are substituted for ‘a’ and ‘b’.  Eventually we
hope to design a new form of declaration syntax that allows you to
declare variables whose scopes start only after their initializers; this
will be a more reliable way to prevent such conflicts.

Some more examples of the use of ‘typeof’:

   • This declares ‘y’ with the type of what ‘x’ points to.

          typeof (*x) y;

   • This declares ‘y’ as an array of such values.

          typeof (*x) y[4];

   • This declares ‘y’ as an array of pointers to characters:

          typeof (typeof (char *)[4]) y;

     It is equivalent to the following traditional C declaration:

          char *y[4];

     To see the meaning of the declaration using ‘typeof’, and why it
     might be a useful way to write, rewrite it with these macros:

          #define pointer(T)  typeof(T *)
          #define array(T, N) typeof(T [N])

     Now the declaration can be rewritten this way:

          array (pointer (char), 4) y;

     Thus, ‘array (pointer (char), 4)’ is the type of arrays of 4
     pointers to ‘char’.

 In GNU C, but not GNU C++, you may also declare the type of a variable
as ‘__auto_type’.  In that case, the declaration must declare only one
variable, whose declarator must just be an identifier, the declaration
must be initialized, and the type of the variable is determined by the
initializer; the name of the variable is not in scope until after the
initializer.  (In C++, you should use C++11 ‘auto’ for this purpose.)
Using ‘__auto_type’, the "maximum" macro above could be written as:

     #define max(a,b) \
       ({ __auto_type _a = (a); \
           __auto_type _b = (b); \
         _a > _b ? _a : _b; })

 Using ‘__auto_type’ instead of ‘typeof’ has two advantages:

   • Each argument to the macro appears only once in the expansion of
     the macro.  This prevents the size of the macro expansion growing
     exponentially when calls to such macros are nested inside arguments
     of such macros.

   • If the argument to the macro has variably modified type, it is
     evaluated only once when using ‘__auto_type’, but twice if ‘typeof’
     is used.


File: gcc.info,  Node: Conditionals,  Next: __int128,  Prev: Typeof,  Up: C Extensions

6.8 Conditionals with Omitted Operands
======================================

The middle operand in a conditional expression may be omitted.  Then if
the first operand is nonzero, its value is the value of the conditional
expression.

 Therefore, the expression

     x ? : y

has the value of ‘x’ if that is nonzero; otherwise, the value of ‘y’.

 This example is perfectly equivalent to

     x ? x : y

In this simple case, the ability to omit the middle operand is not
especially useful.  When it becomes useful is when the first operand
does, or may (if it is a macro argument), contain a side effect.  Then
repeating the operand in the middle would perform the side effect twice.
Omitting the middle operand uses the value already computed without the
undesirable effects of recomputing it.


File: gcc.info,  Node: __int128,  Next: Long Long,  Prev: Conditionals,  Up: C Extensions

6.9 128-bit Integers
====================

As an extension the integer scalar type ‘__int128’ is supported for
targets which have an integer mode wide enough to hold 128 bits.  Simply
write ‘__int128’ for a signed 128-bit integer, or ‘unsigned __int128’
for an unsigned 128-bit integer.  There is no support in GCC for
expressing an integer constant of type ‘__int128’ for targets with ‘long
long’ integer less than 128 bits wide.


File: gcc.info,  Node: Long Long,  Next: Complex,  Prev: __int128,  Up: C Extensions

6.10 Double-Word Integers
=========================

ISO C99 and ISO C++11 support data types for integers that are at least
64 bits wide, and as an extension GCC supports them in C90 and C++98
modes.  Simply write ‘long long int’ for a signed integer, or ‘unsigned
long long int’ for an unsigned integer.  To make an integer constant of
type ‘long long int’, add the suffix ‘LL’ to the integer.  To make an
integer constant of type ‘unsigned long long int’, add the suffix ‘ULL’
to the integer.

 You can use these types in arithmetic like any other integer types.
Addition, subtraction, and bitwise boolean operations on these types are
open-coded on all types of machines.  Multiplication is open-coded if
the machine supports a fullword-to-doubleword widening multiply
instruction.  Division and shifts are open-coded only on machines that
provide special support.  The operations that are not open-coded use
special library routines that come with GCC.

 There may be pitfalls when you use ‘long long’ types for function
arguments without function prototypes.  If a function expects type ‘int’
for its argument, and you pass a value of type ‘long long int’,
confusion results because the caller and the subroutine disagree about
the number of bytes for the argument.  Likewise, if the function expects
‘long long int’ and you pass ‘int’.  The best way to avoid such problems
is to use prototypes.


File: gcc.info,  Node: Complex,  Next: Floating Types,  Prev: Long Long,  Up: C Extensions

6.11 Complex Numbers
====================

ISO C99 supports complex floating data types, and as an extension GCC
supports them in C90 mode and in C++.  GCC also supports complex integer
data types which are not part of ISO C99.  You can declare complex types
using the keyword ‘_Complex’.  As an extension, the older GNU keyword
‘__complex__’ is also supported.

 For example, ‘_Complex double x;’ declares ‘x’ as a variable whose real
part and imaginary part are both of type ‘double’.  ‘_Complex short int
y;’ declares ‘y’ to have real and imaginary parts of type ‘short int’;
this is not likely to be useful, but it shows that the set of complex
types is complete.

 To write a constant with a complex data type, use the suffix ‘i’ or ‘j’
(either one; they are equivalent).  For example, ‘2.5fi’ has type
‘_Complex float’ and ‘3i’ has type ‘_Complex int’.  Such a constant
always has a pure imaginary value, but you can form any complex value
you like by adding one to a real constant.  This is a GNU extension; if
you have an ISO C99 conforming C library (such as the GNU C Library),
and want to construct complex constants of floating type, you should
include ‘<complex.h>’ and use the macros ‘I’ or ‘_Complex_I’ instead.

 The ISO C++14 library also defines the ‘i’ suffix, so C++14 code that
includes the ‘<complex>’ header cannot use ‘i’ for the GNU extension.
The ‘j’ suffix still has the GNU meaning.

 GCC can handle both implicit and explicit casts between the ‘_Complex’
types and other ‘_Complex’ types as casting both the real and imaginary
parts to the scalar type.  GCC can handle implicit and explicit casts
from a scalar type to a ‘_Complex’ type and where the imaginary part
will be considered zero.  The C front-end can handle implicit and
explicit casts from a ‘_Complex’ type to a scalar type where the
imaginary part will be ignored.  In C++ code, this cast is considered
illformed and G++ will error out.

 GCC provides a built-in function ‘__builtin_complex’ will can be used
to construct a complex value.

 GCC has a few extensions which can be used to extract the real and the
imaginary part of the complex-valued expression.  Note these expressions
are lvalues if the EXP is an lvalue.  These expressions operands have
the type of a complex type which might get prompoted to a complex type
from a scalar type.  E.g.  ‘__real__ (int)X’ is the same as casting to
‘_Complex int’ before ‘__real__’ is done.

Expression                    Description
--------------------------------------------------------------------------
‘__real__ EXP’                Extract the real part of EXP.
‘__imag__ EXP’                Extract the imaginary part of EXP.

 For values of floating point, you should use the ISO C99 functions,
declared in ‘<complex.h>’ and also provided as built-in functions by
GCC.

Expression                    float          double         long double
---------------------------------------------------------------------------
‘__real__ EXP’                ‘crealf’       ‘creal’        ‘creall’
‘__imag__ EXP’                ‘cimagf’       ‘cimag’        ‘cimagl’

 The operator ‘~’ performs complex conjugation when used on a value with
a complex type.  This is a GNU extension; for values of floating type,
you should use the ISO C99 functions ‘conjf’, ‘conj’ and ‘conjl’,
declared in ‘<complex.h>’ and also provided as built-in functions by
GCC.  Note unlike the ‘__real__’ and ‘__imag__’ operators, this operator
will not do an implicit cast to the complex type because the ‘~’ is
already a normal operator.

 GCC can allocate complex automatic variables in a noncontiguous
fashion; it's even possible for the real part to be in a register while
the imaginary part is on the stack (or vice versa).  Only the DWARF
debug info format can represent this, so use of DWARF is recommended.
If you are using the stabs debug info format, GCC describes a
noncontiguous complex variable as if it were two separate variables of
noncomplex type.  If the variable's actual name is ‘foo’, the two
fictitious variables are named ‘foo$real’ and ‘foo$imag’.  You can
examine and set these two fictitious variables with your debugger.

 -- Built-in Function: TYPE __builtin_complex (REAL, IMAG)

     The built-in function ‘__builtin_complex’ is provided for use in
     implementing the ISO C11 macros ‘CMPLXF’, ‘CMPLX’ and ‘CMPLXL’.
     REAL and IMAG must have the same type, a real binary floating-point
     type, and the result has the corresponding complex type with real
     and imaginary parts REAL and IMAG.  Unlike ‘REAL + I * IMAG’, this
     works even when infinities, NaNs and negative zeros are involved.


File: gcc.info,  Node: Floating Types,  Next: Half-Precision,  Prev: Complex,  Up: C Extensions

6.12 Additional Floating Types
==============================

ISO/IEC TS 18661-3:2015 defines C support for additional floating types
‘_FloatN’ and ‘_FloatNx’, and GCC supports these type names; the set of
types supported depends on the target architecture.  These types are not
supported when compiling C++.  Constants with these types use suffixes
‘fN’ or ‘FN’ and ‘fNx’ or ‘FNx’.  These type names can be used together
with ‘_Complex’ to declare complex types.

 As an extension, GNU C and GNU C++ support additional floating types,
which are not supported by all targets.
   • ‘__float128’ is available on i386, x86_64, IA-64, and hppa HP-UX,
     as well as on PowerPC GNU/Linux targets that enable the vector
     scalar (VSX) instruction set.  ‘__float128’ supports the 128-bit
     floating type.  On i386, x86_64, PowerPC, and IA-64 other than
     HP-UX, ‘__float128’ is an alias for ‘_Float128’.  On hppa and IA-64
     HP-UX, ‘__float128’ is an alias for ‘long double’.

   • ‘__float80’ is available on the i386, x86_64, and IA-64 targets,
     and supports the 80-bit (‘XFmode’) floating type.  It is an alias
     for the type name ‘_Float64x’ on these targets.

   • ‘__ibm128’ is available on PowerPC targets, and provides access to
     the IBM extended double format which is the current format used for
     ‘long double’.  When ‘long double’ transitions to ‘__float128’ on
     PowerPC in the future, ‘__ibm128’ will remain for use in
     conversions between the two types.

 Support for these additional types includes the arithmetic operators:
add, subtract, multiply, divide; unary arithmetic operators; relational
operators; equality operators; and conversions to and from integer and
other floating types.  Use a suffix ‘w’ or ‘W’ in a literal constant of
type ‘__float80’ or type ‘__ibm128’.  Use a suffix ‘q’ or ‘Q’ for
‘_float128’.

 In order to use ‘_Float128’, ‘__float128’, and ‘__ibm128’ on PowerPC
Linux systems, you must use the ‘-mfloat128’ option.  It is expected in
future versions of GCC that ‘_Float128’ and ‘__float128’ will be enabled
automatically.

 The ‘_Float128’ type is supported on all systems where ‘__float128’ is
supported or where ‘long double’ has the IEEE binary128 format.  The
‘_Float64x’ type is supported on all systems where ‘__float128’ is
supported.  The ‘_Float32’ type is supported on all systems supporting
IEEE binary32; the ‘_Float64’ and ‘_Float32x’ types are supported on all
systems supporting IEEE binary64.  The ‘_Float16’ type is supported on
AArch64 systems by default, on ARM systems when the IEEE format for
16-bit floating-point types is selected with ‘-mfp16-format=ieee’ and,
for both C and C++, on x86 systems with SSE2 enabled.  GCC does not
currently support ‘_Float128x’ on any systems.

 On the i386, x86_64, IA-64, and HP-UX targets, you can declare complex
types using the corresponding internal complex type, ‘XCmode’ for
‘__float80’ type and ‘TCmode’ for ‘__float128’ type:

     typedef _Complex float __attribute__((mode(TC))) _Complex128;
     typedef _Complex float __attribute__((mode(XC))) _Complex80;

 On the PowerPC Linux VSX targets, you can declare complex types using
the corresponding internal complex type, ‘KCmode’ for ‘__float128’ type
and ‘ICmode’ for ‘__ibm128’ type:

     typedef _Complex float __attribute__((mode(KC))) _Complex_float128;
     typedef _Complex float __attribute__((mode(IC))) _Complex_ibm128;


File: gcc.info,  Node: Half-Precision,  Next: Decimal Float,  Prev: Floating Types,  Up: C Extensions

6.13 Half-Precision Floating Point
==================================

On ARM and AArch64 targets, GCC supports half-precision (16-bit)
floating point via the ‘__fp16’ type defined in the ARM C Language
Extensions.  On ARM systems, you must enable this type explicitly with
the ‘-mfp16-format’ command-line option in order to use it.  On x86
targets with SSE2 enabled, GCC supports half-precision (16-bit) floating
point via the ‘_Float16’ type.  For C++, x86 provides a builtin type
named ‘_Float16’ which contains same data format as C.

 ARM targets support two incompatible representations for half-precision
floating-point values.  You must choose one of the representations and
use it consistently in your program.

 Specifying ‘-mfp16-format=ieee’ selects the IEEE 754-2008 format.  This
format can represent normalized values in the range of 2^{-14} to 65504.
There are 11 bits of significand precision, approximately 3 decimal
digits.

 Specifying ‘-mfp16-format=alternative’ selects the ARM alternative
format.  This representation is similar to the IEEE format, but does not
support infinities or NaNs.  Instead, the range of exponents is
extended, so that this format can represent normalized values in the
range of 2^{-14} to 131008.

 The GCC port for AArch64 only supports the IEEE 754-2008 format, and
does not require use of the ‘-mfp16-format’ command-line option.

 The ‘__fp16’ type may only be used as an argument to intrinsics defined
in ‘<arm_fp16.h>’, or as a storage format.  For purposes of arithmetic
and other operations, ‘__fp16’ values in C or C++ expressions are
automatically promoted to ‘float’.

 The ARM target provides hardware support for conversions between
‘__fp16’ and ‘float’ values as an extension to VFP and NEON (Advanced
SIMD), and from ARMv8-A provides hardware support for conversions
between ‘__fp16’ and ‘double’ values.  GCC generates code using these
hardware instructions if you compile with options to select an FPU that
provides them; for example, ‘-mfpu=neon-fp16 -mfloat-abi=softfp’, in
addition to the ‘-mfp16-format’ option to select a half-precision
format.

 Language-level support for the ‘__fp16’ data type is independent of
whether GCC generates code using hardware floating-point instructions.
In cases where hardware support is not specified, GCC implements
conversions between ‘__fp16’ and other types as library calls.

 It is recommended that portable code use the ‘_Float16’ type defined by
ISO/IEC TS 18661-3:2015.  *Note Floating Types::.

 On x86 targets with SSE2 enabled, without ‘-mavx512fp16’, all
operations will be emulated by software emulation and the ‘float’
instructions.  The default behavior for ‘FLT_EVAL_METHOD’ is to keep the
intermediate result of the operation as 32-bit precision.  This may lead
to inconsistent behavior between software emulation and AVX512-FP16
instructions.  Using ‘-fexcess-precision=16’ will force round back after
each operation.

 Using ‘-mavx512fp16’ will generate AVX512-FP16 instructions instead of
software emulation.  The default behavior of ‘FLT_EVAL_METHOD’ is to
round after each operation.  The same is true with
‘-fexcess-precision=standard’ and ‘-mfpmath=sse’.  If there is no
‘-mfpmath=sse’, ‘-fexcess-precision=standard’ alone does the same thing
as before, It is useful for code that does not have ‘_Float16’ and runs
on the x87 FPU.


File: gcc.info,  Node: Decimal Float,  Next: Hex Floats,  Prev: Half-Precision,  Up: C Extensions

6.14 Decimal Floating Types
===========================

As an extension, GNU C supports decimal floating types as defined in the
N1312 draft of ISO/IEC WDTR24732.  Support for decimal floating types in
GCC will evolve as the draft technical report changes.  Calling
conventions for any target might also change.  Not all targets support
decimal floating types.

 The decimal floating types are ‘_Decimal32’, ‘_Decimal64’, and
‘_Decimal128’.  They use a radix of ten, unlike the floating types
‘float’, ‘double’, and ‘long double’ whose radix is not specified by the
C standard but is usually two.

 Support for decimal floating types includes the arithmetic operators
add, subtract, multiply, divide; unary arithmetic operators; relational
operators; equality operators; and conversions to and from integer and
other floating types.  Use a suffix ‘df’ or ‘DF’ in a literal constant
of type ‘_Decimal32’, ‘dd’ or ‘DD’ for ‘_Decimal64’, and ‘dl’ or ‘DL’
for ‘_Decimal128’.

 GCC support of decimal float as specified by the draft technical report
is incomplete:

   • When the value of a decimal floating type cannot be represented in
     the integer type to which it is being converted, the result is
     undefined rather than the result value specified by the draft
     technical report.

   • GCC does not provide the C library functionality associated with
     ‘math.h’, ‘fenv.h’, ‘stdio.h’, ‘stdlib.h’, and ‘wchar.h’, which
     must come from a separate C library implementation.  Because of
     this the GNU C compiler does not define macro ‘__STDC_DEC_FP__’ to
     indicate that the implementation conforms to the technical report.

 Types ‘_Decimal32’, ‘_Decimal64’, and ‘_Decimal128’ are supported by
the DWARF debug information format.


File: gcc.info,  Node: Hex Floats,  Next: Fixed-Point,  Prev: Decimal Float,  Up: C Extensions

6.15 Hex Floats
===============

ISO C99 and ISO C++17 support floating-point numbers written not only in
the usual decimal notation, such as ‘1.55e1’, but also numbers such as
‘0x1.fp3’ written in hexadecimal format.  As a GNU extension, GCC
supports this in C90 mode (except in some cases when strictly
conforming) and in C++98, C++11 and C++14 modes.  In that format the
‘0x’ hex introducer and the ‘p’ or ‘P’ exponent field are mandatory.
The exponent is a decimal number that indicates the power of 2 by which
the significant part is multiplied.  Thus ‘0x1.f’ is 1 15/16, ‘p3’
multiplies it by 8, and the value of ‘0x1.fp3’ is the same as ‘1.55e1’.

 Unlike for floating-point numbers in the decimal notation the exponent
is always required in the hexadecimal notation.  Otherwise the compiler
would not be able to resolve the ambiguity of, e.g., ‘0x1.f’.  This
could mean ‘1.0f’ or ‘1.9375’ since ‘f’ is also the extension for
floating-point constants of type ‘float’.


File: gcc.info,  Node: Fixed-Point,  Next: Named Address Spaces,  Prev: Hex Floats,  Up: C Extensions

6.16 Fixed-Point Types
======================

As an extension, GNU C supports fixed-point types as defined in the
N1169 draft of ISO/IEC DTR 18037.  Support for fixed-point types in GCC
will evolve as the draft technical report changes.  Calling conventions
for any target might also change.  Not all targets support fixed-point
types.

 The fixed-point types are ‘short _Fract’, ‘_Fract’, ‘long _Fract’,
‘long long _Fract’, ‘unsigned short _Fract’, ‘unsigned _Fract’,
‘unsigned long _Fract’, ‘unsigned long long _Fract’, ‘_Sat short
_Fract’, ‘_Sat _Fract’, ‘_Sat long _Fract’, ‘_Sat long long _Fract’,
‘_Sat unsigned short _Fract’, ‘_Sat unsigned _Fract’, ‘_Sat unsigned
long _Fract’, ‘_Sat unsigned long long _Fract’, ‘short _Accum’,
‘_Accum’, ‘long _Accum’, ‘long long _Accum’, ‘unsigned short _Accum’,
‘unsigned _Accum’, ‘unsigned long _Accum’, ‘unsigned long long _Accum’,
‘_Sat short _Accum’, ‘_Sat _Accum’, ‘_Sat long _Accum’, ‘_Sat long long
_Accum’, ‘_Sat unsigned short _Accum’, ‘_Sat unsigned _Accum’, ‘_Sat
unsigned long _Accum’, ‘_Sat unsigned long long _Accum’.

 Fixed-point data values contain fractional and optional integral parts.
The format of fixed-point data varies and depends on the target machine.

 Support for fixed-point types includes:
   • prefix and postfix increment and decrement operators (‘++’, ‘--’)
   • unary arithmetic operators (‘+’, ‘-’, ‘!’)
   • binary arithmetic operators (‘+’, ‘-’, ‘*’, ‘/’)
   • binary shift operators (‘<<’, ‘>>’)
   • relational operators (‘<’, ‘<=’, ‘>=’, ‘>’)
   • equality operators (‘==’, ‘!=’)
   • assignment operators (‘+=’, ‘-=’, ‘*=’, ‘/=’, ‘<<=’, ‘>>=’)
   • conversions to and from integer, floating-point, or fixed-point
     types

 Use a suffix in a fixed-point literal constant:
   • ‘hr’ or ‘HR’ for ‘short _Fract’ and ‘_Sat short _Fract’
   • ‘r’ or ‘R’ for ‘_Fract’ and ‘_Sat _Fract’
   • ‘lr’ or ‘LR’ for ‘long _Fract’ and ‘_Sat long _Fract’
   • ‘llr’ or ‘LLR’ for ‘long long _Fract’ and ‘_Sat long long _Fract’
   • ‘uhr’ or ‘UHR’ for ‘unsigned short _Fract’ and ‘_Sat unsigned short
     _Fract’
   • ‘ur’ or ‘UR’ for ‘unsigned _Fract’ and ‘_Sat unsigned _Fract’
   • ‘ulr’ or ‘ULR’ for ‘unsigned long _Fract’ and ‘_Sat unsigned long
     _Fract’
   • ‘ullr’ or ‘ULLR’ for ‘unsigned long long _Fract’ and ‘_Sat unsigned
     long long _Fract’
   • ‘hk’ or ‘HK’ for ‘short _Accum’ and ‘_Sat short _Accum’
   • ‘k’ or ‘K’ for ‘_Accum’ and ‘_Sat _Accum’
   • ‘lk’ or ‘LK’ for ‘long _Accum’ and ‘_Sat long _Accum’
   • ‘llk’ or ‘LLK’ for ‘long long _Accum’ and ‘_Sat long long _Accum’
   • ‘uhk’ or ‘UHK’ for ‘unsigned short _Accum’ and ‘_Sat unsigned short
     _Accum’
   • ‘uk’ or ‘UK’ for ‘unsigned _Accum’ and ‘_Sat unsigned _Accum’
   • ‘ulk’ or ‘ULK’ for ‘unsigned long _Accum’ and ‘_Sat unsigned long
     _Accum’
   • ‘ullk’ or ‘ULLK’ for ‘unsigned long long _Accum’ and ‘_Sat unsigned
     long long _Accum’

 GCC support of fixed-point types as specified by the draft technical
report is incomplete:

   • Pragmas to control overflow and rounding behaviors are not
     implemented.

 Fixed-point types are supported by the DWARF debug information format.


File: gcc.info,  Node: Named Address Spaces,  Next: Zero Length,  Prev: Fixed-Point,  Up: C Extensions

6.17 Named Address Spaces
=========================

As an extension, GNU C supports named address spaces as defined in the
N1275 draft of ISO/IEC DTR 18037.  Support for named address spaces in
GCC will evolve as the draft technical report changes.  Calling
conventions for any target might also change.  At present, only the AVR,
M32C, PRU, RL78, and x86 targets support address spaces other than the
generic address space.

 Address space identifiers may be used exactly like any other C type
qualifier (e.g., ‘const’ or ‘volatile’).  See the N1275 document for
more details.

6.17.1 AVR Named Address Spaces
-------------------------------

On the AVR target, there are several address spaces that can be used in
order to put read-only data into the flash memory and access that data
by means of the special instructions ‘LPM’ or ‘ELPM’ needed to read from
flash.

 Devices belonging to ‘avrtiny’ and ‘avrxmega3’ can access flash memory
by means of ‘LD*’ instructions because the flash memory is mapped into
the RAM address space.  There is _no need_ for language extensions like
‘__flash’ or attribute *note ‘progmem’: AVR Variable Attributes.  The
default linker description files for these devices cater for that
feature and ‘.rodata’ stays in flash: The compiler just generates ‘LD*’
instructions, and the linker script adds core specific offsets to all
‘.rodata’ symbols: ‘0x4000’ in the case of ‘avrtiny’ and ‘0x8000’ in the
case of ‘avrxmega3’.  See *note AVR Options:: for a list of respective
devices.

 For devices not in ‘avrtiny’ or ‘avrxmega3’, any data including
read-only data is located in RAM (the generic address space) because
flash memory is not visible in the RAM address space.  In order to
locate read-only data in flash memory _and_ to generate the right
instructions to access this data without using (inline) assembler code,
special address spaces are needed.

‘__flash’
     The ‘__flash’ qualifier locates data in the ‘.progmem.data’
     section.  Data is read using the ‘LPM’ instruction.  Pointers to
     this address space are 16 bits wide.

‘__flash1’
‘__flash2’
‘__flash3’
‘__flash4’
‘__flash5’
     These are 16-bit address spaces locating data in section
     ‘.progmemN.data’ where N refers to address space ‘__flashN’.  The
     compiler sets the ‘RAMPZ’ segment register appropriately before
     reading data by means of the ‘ELPM’ instruction.

‘__memx’
     This is a 24-bit address space that linearizes flash and RAM: If
     the high bit of the address is set, data is read from RAM using the
     lower two bytes as RAM address.  If the high bit of the address is
     clear, data is read from flash with ‘RAMPZ’ set according to the
     high byte of the address.  *Note ‘__builtin_avr_flash_segment’: AVR
     Built-in Functions.

     Objects in this address space are located in ‘.progmemx.data’.

 Example

     char my_read (const __flash char ** p)
     {
         /* p is a pointer to RAM that points to a pointer to flash.
            The first indirection of p reads that flash pointer
            from RAM and the second indirection reads a char from this
            flash address.  */

         return **p;
     }

     /* Locate array[] in flash memory */
     const __flash int array[] = { 3, 5, 7, 11, 13, 17, 19 };

     int i = 1;

     int main (void)
     {
        /* Return 17 by reading from flash memory */
        return array[array[i]];
     }

For each named address space supported by avr-gcc there is an equally
named but uppercase built-in macro defined.  The purpose is to
facilitate testing if respective address space support is available or
not:

     #ifdef __FLASH
     const __flash int var = 1;

     int read_var (void)
     {
         return var;
     }
     #else
     #include <avr/pgmspace.h> /* From AVR-LibC */

     const int var PROGMEM = 1;

     int read_var (void)
     {
         return (int) pgm_read_word (&var);
     }
     #endif /* __FLASH */

Notice that attribute *note ‘progmem’: AVR Variable Attributes. locates
data in flash but accesses to these data read from generic address
space, i.e. from RAM, so that you need special accessors like
‘pgm_read_byte’ from AVR-LibC (http://nongnu.org/avr-libc/user-manual/)
together with attribute ‘progmem’.

Limitations and caveats

   • Reading across the 64 KiB section boundary of the ‘__flash’ or
     ‘__flashN’ address spaces shows undefined behavior.  The only
     address space that supports reading across the 64 KiB flash segment
     boundaries is ‘__memx’.

   • If you use one of the ‘__flashN’ address spaces you must arrange
     your linker script to locate the ‘.progmemN.data’ sections
     according to your needs.

   • Any data or pointers to the non-generic address spaces must be
     qualified as ‘const’, i.e. as read-only data.  This still applies
     if the data in one of these address spaces like software version
     number or calibration lookup table are intended to be changed after
     load time by, say, a boot loader.  In this case the right
     qualification is ‘const’ ‘volatile’ so that the compiler must not
     optimize away known values or insert them as immediates into
     operands of instructions.

   • The following code initializes a variable ‘pfoo’ located in static
     storage with a 24-bit address:
          extern const __memx char foo;
          const __memx void *pfoo = &foo;

   • On the reduced Tiny devices like ATtiny40, no address spaces are
     supported.  Just use vanilla C / C++ code without overhead as
     outlined above.  Attribute ‘progmem’ is supported but works
     differently, see *note AVR Variable Attributes::.

6.17.2 M32C Named Address Spaces
--------------------------------

On the M32C target, with the R8C and M16C CPU variants, variables
qualified with ‘__far’ are accessed using 32-bit addresses in order to
access memory beyond the first 64 Ki bytes.  If ‘__far’ is used with the
M32CM or M32C CPU variants, it has no effect.

6.17.3 PRU Named Address Spaces
-------------------------------

On the PRU target, variables qualified with ‘__regio_symbol’ are aliases
used to access the special I/O CPU registers.  They must be declared as
‘extern’ because such variables will not be allocated in any data
memory.  They must also be marked as ‘volatile’, and can only be 32-bit
integer types.  The only names those variables can have are ‘__R30’ and
‘__R31’, representing respectively the ‘R30’ and ‘R31’ special I/O CPU
registers.  Hence the following example is the only valid usage of
‘__regio_symbol’:

     extern volatile __regio_symbol uint32_t __R30;
     extern volatile __regio_symbol uint32_t __R31;

6.17.4 RL78 Named Address Spaces
--------------------------------

On the RL78 target, variables qualified with ‘__far’ are accessed with
32-bit pointers (20-bit addresses) rather than the default 16-bit
addresses.  Non-far variables are assumed to appear in the topmost
64 KiB of the address space.

6.17.5 x86 Named Address Spaces
-------------------------------

On the x86 target, variables may be declared as being relative to the
‘%fs’ or ‘%gs’ segments.

‘__seg_fs’
‘__seg_gs’
     The object is accessed with the respective segment override prefix.

     The respective segment base must be set via some method specific to
     the operating system.  Rather than require an expensive system call
     to retrieve the segment base, these address spaces are not
     considered to be subspaces of the generic (flat) address space.
     This means that explicit casts are required to convert pointers
     between these address spaces and the generic address space.  In
     practice the application should cast to ‘uintptr_t’ and apply the
     segment base offset that it installed previously.

     The preprocessor symbols ‘__SEG_FS’ and ‘__SEG_GS’ are defined when
     these address spaces are supported.


File: gcc.info,  Node: Zero Length,  Next: Empty Structures,  Prev: Named Address Spaces,  Up: C Extensions

6.18 Arrays of Length Zero
==========================

Declaring zero-length arrays is allowed in GNU C as an extension.  A
zero-length array can be useful as the last element of a structure that
is really a header for a variable-length object:

     struct line {
       int length;
       char contents[0];
     };

     struct line *thisline = (struct line *)
       malloc (sizeof (struct line) + this_length);
     thisline->length = this_length;

 Although the size of a zero-length array is zero, an array member of
this kind may increase the size of the enclosing type as a result of
tail padding.  The offset of a zero-length array member from the
beginning of the enclosing structure is the same as the offset of an
array with one or more elements of the same type.  The alignment of a
zero-length array is the same as the alignment of its elements.

 Declaring zero-length arrays in other contexts, including as interior
members of structure objects or as non-member objects, is discouraged.
Accessing elements of zero-length arrays declared in such contexts is
undefined and may be diagnosed.

 In the absence of the zero-length array extension, in ISO C90 the
‘contents’ array in the example above would typically be declared to
have a single element.  Unlike a zero-length array which only
contributes to the size of the enclosing structure for the purposes of
alignment, a one-element array always occupies at least as much space as
a single object of the type.  Although using one-element arrays this way
is discouraged, GCC handles accesses to trailing one-element array
members analogously to zero-length arrays.

 The preferred mechanism to declare variable-length types like ‘struct
line’ above is the ISO C99 “flexible array member”, with slightly
different syntax and semantics:

   • Flexible array members are written as ‘contents[]’ without the ‘0’.

   • Flexible array members have incomplete type, and so the ‘sizeof’
     operator may not be applied.  As a quirk of the original
     implementation of zero-length arrays, ‘sizeof’ evaluates to zero.

   • Flexible array members may only appear as the last member of a
     ‘struct’ that is otherwise non-empty.

   • A structure containing a flexible array member, or a union
     containing such a structure (possibly recursively), may not be a
     member of a structure or an element of an array.  (However, these
     uses are permitted by GCC as extensions.)

 Non-empty initialization of zero-length arrays is treated like any case
where there are more initializer elements than the array holds, in that
a suitable warning about "excess elements in array" is given, and the
excess elements (all of them, in this case) are ignored.

 GCC allows static initialization of flexible array members.  This is
equivalent to defining a new structure containing the original structure
followed by an array of sufficient size to contain the data.  E.g. in
the following, ‘f1’ is constructed as if it were declared like ‘f2’.

     struct f1 {
       int x; int y[];
     } f1 = { 1, { 2, 3, 4 } };

     struct f2 {
       struct f1 f1; int data[3];
     } f2 = { { 1 }, { 2, 3, 4 } };

The convenience of this extension is that ‘f1’ has the desired type,
eliminating the need to consistently refer to ‘f2.f1’.

 This has symmetry with normal static arrays, in that an array of
unknown size is also written with ‘[]’.

 Of course, this extension only makes sense if the extra data comes at
the end of a top-level object, as otherwise we would be overwriting data
at subsequent offsets.  To avoid undue complication and confusion with
initialization of deeply nested arrays, we simply disallow any non-empty
initialization except when the structure is the top-level object.  For
example:

     struct foo { int x; int y[]; };
     struct bar { struct foo z; };

     struct foo a = { 1, { 2, 3, 4 } };        // Valid.
     struct bar b = { { 1, { 2, 3, 4 } } };    // Invalid.
     struct bar c = { { 1, { } } };            // Valid.
     struct foo d[1] = { { 1, { 2, 3, 4 } } };  // Invalid.


File: gcc.info,  Node: Empty Structures,  Next: Variable Length,  Prev: Zero Length,  Up: C Extensions

6.19 Structures with No Members
===============================

GCC permits a C structure to have no members:

     struct empty {
     };

 The structure has size zero.  In C++, empty structures are part of the
language.  G++ treats empty structures as if they had a single member of
type ‘char’.


File: gcc.info,  Node: Variable Length,  Next: Variadic Macros,  Prev: Empty Structures,  Up: C Extensions

6.20 Arrays of Variable Length
==============================

Variable-length automatic arrays are allowed in ISO C99, and as an
extension GCC accepts them in C90 mode and in C++.  These arrays are
declared like any other automatic arrays, but with a length that is not
a constant expression.  The storage is allocated at the point of
declaration and deallocated when the block scope containing the
declaration exits.  For example:

     FILE *
     concat_fopen (char *s1, char *s2, char *mode)
     {
       char str[strlen (s1) + strlen (s2) + 1];
       strcpy (str, s1);
       strcat (str, s2);
       return fopen (str, mode);
     }

 Jumping or breaking out of the scope of the array name deallocates the
storage.  Jumping into the scope is not allowed; you get an error
message for it.

 As an extension, GCC accepts variable-length arrays as a member of a
structure or a union.  For example:

     void
     foo (int n)
     {
       struct S { int x[n]; };
     }

 You can use the function ‘alloca’ to get an effect much like
variable-length arrays.  The function ‘alloca’ is available in many
other C implementations (but not in all).  On the other hand,
variable-length arrays are more elegant.

 There are other differences between these two methods.  Space allocated
with ‘alloca’ exists until the containing _function_ returns.  The space
for a variable-length array is deallocated as soon as the array name's
scope ends, unless you also use ‘alloca’ in this scope.

 You can also use variable-length arrays as arguments to functions:

     struct entry
     tester (int len, char data[len][len])
     {
       /* ... */
     }

 The length of an array is computed once when the storage is allocated
and is remembered for the scope of the array in case you access it with
‘sizeof’.

 If you want to pass the array first and the length afterward, you can
use a forward declaration in the parameter list--another GNU extension.

     struct entry
     tester (int len; char data[len][len], int len)
     {
       /* ... */
     }

 The ‘int len’ before the semicolon is a “parameter forward
declaration”, and it serves the purpose of making the name ‘len’ known
when the declaration of ‘data’ is parsed.

 You can write any number of such parameter forward declarations in the
parameter list.  They can be separated by commas or semicolons, but the
last one must end with a semicolon, which is followed by the "real"
parameter declarations.  Each forward declaration must match a "real"
declaration in parameter name and data type.  ISO C99 does not support
parameter forward declarations.


File: gcc.info,  Node: Variadic Macros,  Next: Escaped Newlines,  Prev: Variable Length,  Up: C Extensions

6.21 Macros with a Variable Number of Arguments.
================================================

In the ISO C standard of 1999, a macro can be declared to accept a
variable number of arguments much as a function can.  The syntax for
defining the macro is similar to that of a function.  Here is an
example:

     #define debug(format, ...) fprintf (stderr, format, __VA_ARGS__)

Here ‘...’ is a “variable argument”.  In the invocation of such a macro,
it represents the zero or more tokens until the closing parenthesis that
ends the invocation, including any commas.  This set of tokens replaces
the identifier ‘__VA_ARGS__’ in the macro body wherever it appears.  See
the CPP manual for more information.

 GCC has long supported variadic macros, and used a different syntax
that allowed you to give a name to the variable arguments just like any
other argument.  Here is an example:

     #define debug(format, args...) fprintf (stderr, format, args)

This is in all ways equivalent to the ISO C example above, but arguably
more readable and descriptive.

 GNU CPP has two further variadic macro extensions, and permits them to
be used with either of the above forms of macro definition.

 In standard C, you are not allowed to leave the variable argument out
entirely; but you are allowed to pass an empty argument.  For example,
this invocation is invalid in ISO C, because there is no comma after the
string:

     debug ("A message")

 GNU CPP permits you to completely omit the variable arguments in this
way.  In the above examples, the compiler would complain, though since
the expansion of the macro still has the extra comma after the format
string.

 To help solve this problem, CPP behaves specially for variable
arguments used with the token paste operator, ‘##’.  If instead you
write

     #define debug(format, ...) fprintf (stderr, format, ## __VA_ARGS__)

and if the variable arguments are omitted or empty, the ‘##’ operator
causes the preprocessor to remove the comma before it.  If you do
provide some variable arguments in your macro invocation, GNU CPP does
not complain about the paste operation and instead places the variable
arguments after the comma.  Just like any other pasted macro argument,
these arguments are not macro expanded.


File: gcc.info,  Node: Escaped Newlines,  Next: Subscripting,  Prev: Variadic Macros,  Up: C Extensions

6.22 Slightly Looser Rules for Escaped Newlines
===============================================

The preprocessor treatment of escaped newlines is more relaxed than that
specified by the C90 standard, which requires the newline to immediately
follow a backslash.  GCC's implementation allows whitespace in the form
of spaces, horizontal and vertical tabs, and form feeds between the
backslash and the subsequent newline.  The preprocessor issues a
warning, but treats it as a valid escaped newline and combines the two
lines to form a single logical line.  This works within comments and
tokens, as well as between tokens.  Comments are _not_ treated as
whitespace for the purposes of this relaxation, since they have not yet
been replaced with spaces.


File: gcc.info,  Node: Subscripting,  Next: Pointer Arith,  Prev: Escaped Newlines,  Up: C Extensions

6.23 Non-Lvalue Arrays May Have Subscripts
==========================================

In ISO C99, arrays that are not lvalues still decay to pointers, and may
be subscripted, although they may not be modified or used after the next
sequence point and the unary ‘&’ operator may not be applied to them.
As an extension, GNU C allows such arrays to be subscripted in C90 mode,
though otherwise they do not decay to pointers outside C99 mode.  For
example, this is valid in GNU C though not valid in C90:

     struct foo {int a[4];};

     struct foo f();

     bar (int index)
     {
       return f().a[index];
     }


File: gcc.info,  Node: Pointer Arith,  Next: Variadic Pointer Args,  Prev: Subscripting,  Up: C Extensions

6.24 Arithmetic on ‘void’- and Function-Pointers
================================================

In GNU C, addition and subtraction operations are supported on pointers
to ‘void’ and on pointers to functions.  This is done by treating the
size of a ‘void’ or of a function as 1.

 A consequence of this is that ‘sizeof’ is also allowed on ‘void’ and on
function types, and returns 1.

 The option ‘-Wpointer-arith’ requests a warning if these extensions are
used.


File: gcc.info,  Node: Variadic Pointer Args,  Next: Pointers to Arrays,  Prev: Pointer Arith,  Up: C Extensions

6.25 Pointer Arguments in Variadic Functions
============================================

Standard C requires that pointer types used with ‘va_arg’ in functions
with variable argument lists either must be compatible with that of the
actual argument, or that one type must be a pointer to ‘void’ and the
other a pointer to a character type.  GNU C implements the POSIX XSI
extension that additionally permits the use of ‘va_arg’ with a pointer
type to receive arguments of any other pointer type.

 In particular, in GNU C ‘va_arg (ap, void *)’ can safely be used to
consume an argument of any pointer type.


File: gcc.info,  Node: Pointers to Arrays,  Next: Initializers,  Prev: Variadic Pointer Args,  Up: C Extensions

6.26 Pointers to Arrays with Qualifiers Work as Expected
========================================================

In GNU C, pointers to arrays with qualifiers work similar to pointers to
other qualified types.  For example, a value of type ‘int (*)[5]’ can be
used to initialize a variable of type ‘const int (*)[5]’.  These types
are incompatible in ISO C because the ‘const’ qualifier is formally
attached to the element type of the array and not the array itself.

     extern void
     transpose (int N, int M, double out[M][N], const double in[N][M]);
     double x[3][2];
     double y[2][3];
     ...
     transpose(3, 2, y, x);


File: gcc.info,  Node: Initializers,  Next: Compound Literals,  Prev: Pointers to Arrays,  Up: C Extensions

6.27 Non-Constant Initializers
==============================

As in standard C++ and ISO C99, the elements of an aggregate initializer
for an automatic variable are not required to be constant expressions in
GNU C.  Here is an example of an initializer with run-time varying
elements:

     foo (float f, float g)
     {
       float beat_freqs[2] = { f-g, f+g };
       /* ... */
     }


File: gcc.info,  Node: Compound Literals,  Next: Designated Inits,  Prev: Initializers,  Up: C Extensions

6.28 Compound Literals
======================

A compound literal looks like a cast of a brace-enclosed aggregate
initializer list.  Its value is an object of the type specified in the
cast, containing the elements specified in the initializer.  Unlike the
result of a cast, a compound literal is an lvalue.  ISO C99 and later
support compound literals.  As an extension, GCC supports compound
literals also in C90 mode and in C++, although as explained below, the
C++ semantics are somewhat different.

 Usually, the specified type of a compound literal is a structure.
Assume that ‘struct foo’ and ‘structure’ are declared as shown:

     struct foo {int a; char b[2];} structure;

Here is an example of constructing a ‘struct foo’ with a compound
literal:

     structure = ((struct foo) {x + y, 'a', 0});

This is equivalent to writing the following:

     {
       struct foo temp = {x + y, 'a', 0};
       structure = temp;
     }

 You can also construct an array, though this is dangerous in C++, as
explained below.  If all the elements of the compound literal are (made
up of) simple constant expressions suitable for use in initializers of
objects of static storage duration, then the compound literal can be
coerced to a pointer to its first element and used in such an
initializer, as shown here:

     char **foo = (char *[]) { "x", "y", "z" };

 Compound literals for scalar types and union types are also allowed.
In the following example the variable ‘i’ is initialized to the value
‘2’, the result of incrementing the unnamed object created by the
compound literal.

     int i = ++(int) { 1 };

 As a GNU extension, GCC allows initialization of objects with static
storage duration by compound literals (which is not possible in ISO C99
because the initializer is not a constant).  It is handled as if the
object were initialized only with the brace-enclosed list if the types
of the compound literal and the object match.  The elements of the
compound literal must be constant.  If the object being initialized has
array type of unknown size, the size is determined by the size of the
compound literal.

     static struct foo x = (struct foo) {1, 'a', 'b'};
     static int y[] = (int []) {1, 2, 3};
     static int z[] = (int [3]) {1};

The above lines are equivalent to the following:
     static struct foo x = {1, 'a', 'b'};
     static int y[] = {1, 2, 3};
     static int z[] = {1, 0, 0};

 In C, a compound literal designates an unnamed object with static or
automatic storage duration.  In C++, a compound literal designates a
temporary object that only lives until the end of its full-expression.
As a result, well-defined C code that takes the address of a subobject
of a compound literal can be undefined in C++, so G++ rejects the
conversion of a temporary array to a pointer.  For instance, if the
array compound literal example above appeared inside a function, any
subsequent use of ‘foo’ in C++ would have undefined behavior because the
lifetime of the array ends after the declaration of ‘foo’.

 As an optimization, G++ sometimes gives array compound literals longer
lifetimes: when the array either appears outside a function or has a
‘const’-qualified type.  If ‘foo’ and its initializer had elements of
type ‘char *const’ rather than ‘char *’, or if ‘foo’ were a global
variable, the array would have static storage duration.  But it is
probably safest just to avoid the use of array compound literals in C++
code.


File: gcc.info,  Node: Designated Inits,  Next: Case Ranges,  Prev: Compound Literals,  Up: C Extensions

6.29 Designated Initializers
============================

Standard C90 requires the elements of an initializer to appear in a
fixed order, the same as the order of the elements in the array or
structure being initialized.

 In ISO C99 you can give the elements in any order, specifying the array
indices or structure field names they apply to, and GNU C allows this as
an extension in C90 mode as well.  This extension is not implemented in
GNU C++.

 To specify an array index, write ‘[INDEX] =’ before the element value.
For example,

     int a[6] = { [4] = 29, [2] = 15 };

is equivalent to

     int a[6] = { 0, 0, 15, 0, 29, 0 };

The index values must be constant expressions, even if the array being
initialized is automatic.

 An alternative syntax for this that has been obsolete since GCC 2.5 but
GCC still accepts is to write ‘[INDEX]’ before the element value, with
no ‘=’.

 To initialize a range of elements to the same value, write ‘[FIRST ...
LAST] = VALUE’.  This is a GNU extension.  For example,

     int widths[] = { [0 ... 9] = 1, [10 ... 99] = 2, [100] = 3 };

If the value in it has side effects, the side effects happen only once,
not for each initialized field by the range initializer.

Note that the length of the array is the highest value specified plus
one.

 In a structure initializer, specify the name of a field to initialize
with ‘.FIELDNAME =’ before the element value.  For example, given the
following structure,

     struct point { int x, y; };

the following initialization

     struct point p = { .y = yvalue, .x = xvalue };

is equivalent to

     struct point p = { xvalue, yvalue };

 Another syntax that has the same meaning, obsolete since GCC 2.5, is
‘FIELDNAME:’, as shown here:

     struct point p = { y: yvalue, x: xvalue };

 Omitted fields are implicitly initialized the same as for objects that
have static storage duration.

 The ‘[INDEX]’ or ‘.FIELDNAME’ is known as a “designator”.  You can also
use a designator (or the obsolete colon syntax) when initializing a
union, to specify which element of the union should be used.  For
example,

     union foo { int i; double d; };

     union foo f = { .d = 4 };

converts 4 to a ‘double’ to store it in the union using the second
element.  By contrast, casting 4 to type ‘union foo’ stores it into the
union as the integer ‘i’, since it is an integer.  *Note Cast to
Union::.

 You can combine this technique of naming elements with ordinary C
initialization of successive elements.  Each initializer element that
does not have a designator applies to the next consecutive element of
the array or structure.  For example,

     int a[6] = { [1] = v1, v2, [4] = v4 };

is equivalent to

     int a[6] = { 0, v1, v2, 0, v4, 0 };

 Labeling the elements of an array initializer is especially useful when
the indices are characters or belong to an ‘enum’ type.  For example:

     int whitespace[256]
       = { [' '] = 1, ['\t'] = 1, ['\h'] = 1,
           ['\f'] = 1, ['\n'] = 1, ['\r'] = 1 };

 You can also write a series of ‘.FIELDNAME’ and ‘[INDEX]’ designators
before an ‘=’ to specify a nested subobject to initialize; the list is
taken relative to the subobject corresponding to the closest surrounding
brace pair.  For example, with the ‘struct point’ declaration above:

     struct point ptarray[10] = { [2].y = yv2, [2].x = xv2, [0].x = xv0 };

 If the same field is initialized multiple times, or overlapping fields
of a union are initialized, the value from the last initialization is
used.  When a field of a union is itself a structure, the entire
structure from the last field initialized is used.  If any previous
initializer has side effect, it is unspecified whether the side effect
happens or not.  Currently, GCC discards the side-effecting initializer
expressions and issues a warning.


File: gcc.info,  Node: Case Ranges,  Next: Cast to Union,  Prev: Designated Inits,  Up: C Extensions

6.30 Case Ranges
================

You can specify a range of consecutive values in a single ‘case’ label,
like this:

     case LOW ... HIGH:

This has the same effect as the proper number of individual ‘case’
labels, one for each integer value from LOW to HIGH, inclusive.

 This feature is especially useful for ranges of ASCII character codes:

     case 'A' ... 'Z':

 *Be careful:* Write spaces around the ‘...’, for otherwise it may be
parsed wrong when you use it with integer values.  For example, write
this:

     case 1 ... 5:

rather than this:

     case 1...5:


File: gcc.info,  Node: Cast to Union,  Next: Mixed Labels and Declarations,  Prev: Case Ranges,  Up: C Extensions

6.31 Cast to a Union Type
=========================

A cast to a union type is a C extension not available in C++.  It looks
just like ordinary casts with the constraint that the type specified is
a union type.  You can specify the type either with the ‘union’ keyword
or with a ‘typedef’ name that refers to a union.  The result of a cast
to a union is a temporary rvalue of the union type with a member whose
type matches that of the operand initialized to the value of the
operand.  The effect of a cast to a union is similar to a compound
literal except that it yields an rvalue like standard casts do.  *Note
Compound Literals::.

 Expressions that may be cast to the union type are those whose type
matches at least one of the members of the union.  Thus, given the
following union and variables:

     union foo { int i; double d; };
     int x;
     double y;
     union foo z;

both ‘x’ and ‘y’ can be cast to type ‘union foo’ and the following
assignments
       z = (union foo) x;
       z = (union foo) y;
 are shorthand equivalents of these
       z = (union foo) { .i = x };
       z = (union foo) { .d = y };

 However, ‘(union foo) FLT_MAX;’ is not a valid cast because the union
has no member of type ‘float’.

 Using the cast as the right-hand side of an assignment to a variable of
union type is equivalent to storing in a member of the union with the
same type

     union foo u;
     /* ... */
     u = (union foo) x  ≡  u.i = x
     u = (union foo) y  ≡  u.d = y

 You can also use the union cast as a function argument:

     void hack (union foo);
     /* ... */
     hack ((union foo) x);


File: gcc.info,  Node: Mixed Labels and Declarations,  Next: Function Attributes,  Prev: Cast to Union,  Up: C Extensions

6.32 Mixed Declarations, Labels and Code
========================================

ISO C99 and ISO C++ allow declarations and code to be freely mixed
within compound statements.  ISO C2X allows labels to be placed before
declarations and at the end of a compound statement.  As an extension,
GNU C also allows all this in C90 mode.  For example, you could do:

     int i;
     /* ... */
     i++;
     int j = i + 2;

 Each identifier is visible from where it is declared until the end of
the enclosing block.


File: gcc.info,  Node: Function Attributes,  Next: Variable Attributes,  Prev: Mixed Labels and Declarations,  Up: C Extensions

6.33 Declaring Attributes of Functions
======================================

In GNU C and C++, you can use function attributes to specify certain
function properties that may help the compiler optimize calls or check
code more carefully for correctness.  For example, you can use
attributes to specify that a function never returns (‘noreturn’),
returns a value depending only on the values of its arguments (‘const’),
or has ‘printf’-style arguments (‘format’).

 You can also use attributes to control memory placement, code
generation options or call/return conventions within the function being
annotated.  Many of these attributes are target-specific.  For example,
many targets support attributes for defining interrupt handler
functions, which typically must follow special register usage and return
conventions.  Such attributes are described in the subsection for each
target.  However, a considerable number of attributes are supported by
most, if not all targets.  Those are described in the *note Common
Function Attributes:: section.

 Function attributes are introduced by the ‘__attribute__’ keyword in
the declaration of a function, followed by an attribute specification
enclosed in double parentheses.  You can specify multiple attributes in
a declaration by separating them by commas within the double parentheses
or by immediately following one attribute specification with another.
*Note Attribute Syntax::, for the exact rules on attribute syntax and
placement.  Compatible attribute specifications on distinct declarations
of the same function are merged.  An attribute specification that is not
compatible with attributes already applied to a declaration of the same
function is ignored with a warning.

 Some function attributes take one or more arguments that refer to the
function's parameters by their positions within the function parameter
list.  Such attribute arguments are referred to as “positional
arguments”.  Unless specified otherwise, positional arguments that
specify properties of parameters with pointer types can also specify the
same properties of the implicit C++ ‘this’ argument in non-static member
functions, and of parameters of reference to a pointer type.  For
ordinary functions, position one refers to the first parameter on the
list.  In C++ non-static member functions, position one refers to the
implicit ‘this’ pointer.  The same restrictions and effects apply to
function attributes used with ordinary functions or C++ member
functions.

 GCC also supports attributes on variable declarations (*note Variable
Attributes::), labels (*note Label Attributes::), enumerators (*note
Enumerator Attributes::), statements (*note Statement Attributes::),
types (*note Type Attributes::), and on field declarations (for
‘tainted_args’).

 There is some overlap between the purposes of attributes and pragmas
(*note Pragmas Accepted by GCC: Pragmas.).  It has been found convenient
to use ‘__attribute__’ to achieve a natural attachment of attributes to
their corresponding declarations, whereas ‘#pragma’ is of use for
compatibility with other compilers or constructs that do not naturally
form part of the grammar.

 In addition to the attributes documented here, GCC plugins may provide
their own attributes.

* Menu:

* Common Function Attributes::
* AArch64 Function Attributes::
* AMD GCN Function Attributes::
* ARC Function Attributes::
* ARM Function Attributes::
* AVR Function Attributes::
* Blackfin Function Attributes::
* BPF Function Attributes::
* CR16 Function Attributes::
* C-SKY Function Attributes::
* Epiphany Function Attributes::
* H8/300 Function Attributes::
* IA-64 Function Attributes::
* M32C Function Attributes::
* M32R/D Function Attributes::
* m68k Function Attributes::
* MCORE Function Attributes::
* MeP Function Attributes::
* MicroBlaze Function Attributes::
* Microsoft Windows Function Attributes::
* MIPS Function Attributes::
* MSP430 Function Attributes::
* NDS32 Function Attributes::
* Nios II Function Attributes::
* Nvidia PTX Function Attributes::
* PowerPC Function Attributes::
* RISC-V Function Attributes::
* RL78 Function Attributes::
* RX Function Attributes::
* S/390 Function Attributes::
* SH Function Attributes::
* Symbian OS Function Attributes::
* V850 Function Attributes::
* Visium Function Attributes::
* x86 Function Attributes::
* Xstormy16 Function Attributes::


File: gcc.info,  Node: Common Function Attributes,  Next: AArch64 Function Attributes,  Up: Function Attributes

6.33.1 Common Function Attributes
---------------------------------

The following attributes are supported on most targets.

‘access (ACCESS-MODE, REF-INDEX)’
‘access (ACCESS-MODE, REF-INDEX, SIZE-INDEX)’

     The ‘access’ attribute enables the detection of invalid or unsafe
     accesses by functions to which they apply or their callers, as well
     as write-only accesses to objects that are never read from.  Such
     accesses may be diagnosed by warnings such as
     ‘-Wstringop-overflow’, ‘-Wuninitialized’, ‘-Wunused’, and others.

     The ‘access’ attribute specifies that a function to whose
     by-reference arguments the attribute applies accesses the
     referenced object according to ACCESS-MODE.  The ACCESS-MODE
     argument is required and must be one of four names: ‘read_only’,
     ‘read_write’, ‘write_only’, or ‘none’.  The remaining two are
     positional arguments.

     The required REF-INDEX positional argument denotes a function
     argument of pointer (or in C++, reference) type that is subject to
     the access.  The same pointer argument can be referenced by at most
     one distinct ‘access’ attribute.

     The optional SIZE-INDEX positional argument denotes a function
     argument of integer type that specifies the maximum size of the
     access.  The size is the number of elements of the type referenced
     by REF-INDEX, or the number of bytes when the pointer type is
     ‘void*’.  When no SIZE-INDEX argument is specified, the pointer
     argument must be either null or point to a space that is suitably
     aligned and large for at least one object of the referenced type
     (this implies that a past-the-end pointer is not a valid argument).
     The actual size of the access may be less but it must not be more.

     The ‘read_only’ access mode specifies that the pointer to which it
     applies is used to read the referenced object but not write to it.
     Unless the argument specifying the size of the access denoted by
     SIZE-INDEX is zero, the referenced object must be initialized.  The
     mode implies a stronger guarantee than the ‘const’ qualifier which,
     when cast away from a pointer, does not prevent the pointed-to
     object from being modified.  Examples of the use of the ‘read_only’
     access mode is the argument to the ‘puts’ function, or the second
     and third arguments to the ‘memcpy’ function.

          __attribute__ ((access (read_only, 1))) int puts (const char*);
          __attribute__ ((access (read_only, 2, 3))) void* memcpy (void*, const void*, size_t);

     The ‘read_write’ access mode applies to arguments of pointer types
     without the ‘const’ qualifier.  It specifies that the pointer to
     which it applies is used to both read and write the referenced
     object.  Unless the argument specifying the size of the access
     denoted by SIZE-INDEX is zero, the object referenced by the pointer
     must be initialized.  An example of the use of the ‘read_write’
     access mode is the first argument to the ‘strcat’ function.

          __attribute__ ((access (read_write, 1), access (read_only, 2))) char* strcat (char*, const char*);

     The ‘write_only’ access mode applies to arguments of pointer types
     without the ‘const’ qualifier.  It specifies that the pointer to
     which it applies is used to write to the referenced object but not
     read from it.  The object referenced by the pointer need not be
     initialized.  An example of the use of the ‘write_only’ access mode
     is the first argument to the ‘strcpy’ function, or the first two
     arguments to the ‘fgets’ function.

          __attribute__ ((access (write_only, 1), access (read_only, 2))) char* strcpy (char*, const char*);
          __attribute__ ((access (write_only, 1, 2), access (read_write, 3))) int fgets (char*, int, FILE*);

     The access mode ‘none’ specifies that the pointer to which it
     applies is not used to access the referenced object at all.  Unless
     the pointer is null the pointed-to object must exist and have at
     least the size as denoted by the SIZE-INDEX argument.  When the
     optional SIZE-INDEX argument is omitted for an argument of ‘void*’
     type the actual pointer agument is ignored.  The referenced object
     need not be initialized.  The mode is intended to be used as a
     means to help validate the expected object size, for example in
     functions that call ‘__builtin_object_size’.  *Note Object Size
     Checking::.

     Note that the ‘access’ attribute merely specifies how an object
     referenced by the pointer argument can be accessed; it does not
     imply that an access *will* happen.  Also, the ‘access’ attribute
     does not imply the attribute ‘nonnull’; it may be appropriate to
     add both attributes at the declaration of a function that
     unconditionally manipulates a buffer via a pointer argument.  See
     the ‘nonnull’ attribute for more information and caveats.

‘alias ("TARGET")’
     The ‘alias’ attribute causes the declaration to be emitted as an
     alias for another symbol, which must have been previously declared
     with the same type, and for variables, also the same size and
     alignment.  Declaring an alias with a different type than the
     target is undefined and may be diagnosed.  As an example, the
     following declarations:

          void __f () { /* Do something. */; }
          void f () __attribute__ ((weak, alias ("__f")));

     define ‘f’ to be a weak alias for ‘__f’.  In C++, the mangled name
     for the target must be used.  It is an error if ‘__f’ is not
     defined in the same translation unit.

     This attribute requires assembler and object file support, and may
     not be available on all targets.

‘aligned’
‘aligned (ALIGNMENT)’
     The ‘aligned’ attribute specifies a minimum alignment for the first
     instruction of the function, measured in bytes.  When specified,
     ALIGNMENT must be an integer constant power of 2.  Specifying no
     ALIGNMENT argument implies the ideal alignment for the target.  The
     ‘__alignof__’ operator can be used to determine what that is (*note
     Alignment::).  The attribute has no effect when a definition for
     the function is not provided in the same translation unit.

     The attribute cannot be used to decrease the alignment of a
     function previously declared with a more restrictive alignment;
     only to increase it.  Attempts to do otherwise are diagnosed.  Some
     targets specify a minimum default alignment for functions that is
     greater than 1.  On such targets, specifying a less restrictive
     alignment is silently ignored.  Using the attribute overrides the
     effect of the ‘-falign-functions’ (*note Optimize Options::) option
     for this function.

     Note that the effectiveness of ‘aligned’ attributes may be limited
     by inherent limitations in the system linker and/or object file
     format.  On some systems, the linker is only able to arrange for
     functions to be aligned up to a certain maximum alignment.  (For
     some linkers, the maximum supported alignment may be very very
     small.)  See your linker documentation for further information.

     The ‘aligned’ attribute can also be used for variables and fields
     (*note Variable Attributes::.)

‘alloc_align (POSITION)’
     The ‘alloc_align’ attribute may be applied to a function that
     returns a pointer and takes at least one argument of an integer or
     enumerated type.  It indicates that the returned pointer is aligned
     on a boundary given by the function argument at POSITION.
     Meaningful alignments are powers of 2 greater than one.  GCC uses
     this information to improve pointer alignment analysis.

     The function parameter denoting the allocated alignment is
     specified by one constant integer argument whose number is the
     argument of the attribute.  Argument numbering starts at one.

     For instance,

          void* my_memalign (size_t, size_t) __attribute__ ((alloc_align (1)));

     declares that ‘my_memalign’ returns memory with minimum alignment
     given by parameter 1.

‘alloc_size (POSITION)’
‘alloc_size (POSITION-1, POSITION-2)’
     The ‘alloc_size’ attribute may be applied to a function that
     returns a pointer and takes at least one argument of an integer or
     enumerated type.  It indicates that the returned pointer points to
     memory whose size is given by the function argument at POSITION-1,
     or by the product of the arguments at POSITION-1 and POSITION-2.
     Meaningful sizes are positive values less than ‘PTRDIFF_MAX’.  GCC
     uses this information to improve the results of
     ‘__builtin_object_size’.

     The function parameter(s) denoting the allocated size are specified
     by one or two integer arguments supplied to the attribute.  The
     allocated size is either the value of the single function argument
     specified or the product of the two function arguments specified.
     Argument numbering starts at one for ordinary functions, and at two
     for C++ non-static member functions.

     For instance,

          void* my_calloc (size_t, size_t) __attribute__ ((alloc_size (1, 2)));
          void* my_realloc (void*, size_t) __attribute__ ((alloc_size (2)));

     declares that ‘my_calloc’ returns memory of the size given by the
     product of parameter 1 and 2 and that ‘my_realloc’ returns memory
     of the size given by parameter 2.

‘always_inline’
     Generally, functions are not inlined unless optimization is
     specified.  For functions declared inline, this attribute inlines
     the function independent of any restrictions that otherwise apply
     to inlining.  Failure to inline such a function is diagnosed as an
     error.  Note that if such a function is called indirectly the
     compiler may or may not inline it depending on optimization level
     and a failure to inline an indirect call may or may not be
     diagnosed.

‘artificial’
     This attribute is useful for small inline wrappers that if possible
     should appear during debugging as a unit.  Depending on the debug
     info format it either means marking the function as artificial or
     using the caller location for all instructions within the inlined
     body.

‘assume_aligned (ALIGNMENT)’
‘assume_aligned (ALIGNMENT, OFFSET)’
     The ‘assume_aligned’ attribute may be applied to a function that
     returns a pointer.  It indicates that the returned pointer is
     aligned on a boundary given by ALIGNMENT.  If the attribute has two
     arguments, the second argument is misalignment OFFSET.  Meaningful
     values of ALIGNMENT are powers of 2 greater than one.  Meaningful
     values of OFFSET are greater than zero and less than ALIGNMENT.

     For instance

          void* my_alloc1 (size_t) __attribute__((assume_aligned (16)));
          void* my_alloc2 (size_t) __attribute__((assume_aligned (32, 8)));

     declares that ‘my_alloc1’ returns 16-byte aligned pointers and that
     ‘my_alloc2’ returns a pointer whose value modulo 32 is equal to 8.

‘cold’
     The ‘cold’ attribute on functions is used to inform the compiler
     that the function is unlikely to be executed.  The function is
     optimized for size rather than speed and on many targets it is
     placed into a special subsection of the text section so all cold
     functions appear close together, improving code locality of
     non-cold parts of program.  The paths leading to calls of cold
     functions within code are marked as unlikely by the branch
     prediction mechanism.  It is thus useful to mark functions used to
     handle unlikely conditions, such as ‘perror’, as cold to improve
     optimization of hot functions that do call marked functions in rare
     occasions.

     When profile feedback is available, via ‘-fprofile-use’, cold
     functions are automatically detected and this attribute is ignored.

‘const’
     Calls to functions whose return value is not affected by changes to
     the observable state of the program and that have no observable
     effects on such state other than to return a value may lend
     themselves to optimizations such as common subexpression
     elimination.  Declaring such functions with the ‘const’ attribute
     allows GCC to avoid emitting some calls in repeated invocations of
     the function with the same argument values.

     For example,

          int square (int) __attribute__ ((const));

     tells GCC that subsequent calls to function ‘square’ with the same
     argument value can be replaced by the result of the first call
     regardless of the statements in between.

     The ‘const’ attribute prohibits a function from reading objects
     that affect its return value between successive invocations.
     However, functions declared with the attribute can safely read
     objects that do not change their return value, such as non-volatile
     constants.

     The ‘const’ attribute imposes greater restrictions on a function's
     definition than the similar ‘pure’ attribute.  Declaring the same
     function with both the ‘const’ and the ‘pure’ attribute is
     diagnosed.  Because a const function cannot have any observable
     side effects it does not make sense for it to return ‘void’.
     Declaring such a function is diagnosed.

     Note that a function that has pointer arguments and examines the
     data pointed to must _not_ be declared ‘const’ if the pointed-to
     data might change between successive invocations of the function.
     In general, since a function cannot distinguish data that might
     change from data that cannot, const functions should never take
     pointer or, in C++, reference arguments.  Likewise, a function that
     calls a non-const function usually must not be const itself.

‘constructor’
‘destructor’
‘constructor (PRIORITY)’
‘destructor (PRIORITY)’
     The ‘constructor’ attribute causes the function to be called
     automatically before execution enters ‘main ()’.  Similarly, the
     ‘destructor’ attribute causes the function to be called
     automatically after ‘main ()’ completes or ‘exit ()’ is called.
     Functions with these attributes are useful for initializing data
     that is used implicitly during the execution of the program.

     On some targets the attributes also accept an integer argument to
     specify a priority to control the order in which constructor and
     destructor functions are run.  A constructor with a smaller
     priority number runs before a constructor with a larger priority
     number; the opposite relationship holds for destructors.  Note that
     priorities 0-100 are reserved.  So, if you have a constructor that
     allocates a resource and a destructor that deallocates the same
     resource, both functions typically have the same priority.  The
     priorities for constructor and destructor functions are the same as
     those specified for namespace-scope C++ objects (*note C++
     Attributes::).  However, at present, the order in which
     constructors for C++ objects with static storage duration and
     functions decorated with attribute ‘constructor’ are invoked is
     unspecified.  In mixed declarations, attribute ‘init_priority’ can
     be used to impose a specific ordering.

     Using the argument forms of the ‘constructor’ and ‘destructor’
     attributes on targets where the feature is not supported is
     rejected with an error.

‘copy’
‘copy (FUNCTION)’
     The ‘copy’ attribute applies the set of attributes with which
     FUNCTION has been declared to the declaration of the function to
     which the attribute is applied.  The attribute is designed for
     libraries that define aliases or function resolvers that are
     expected to specify the same set of attributes as their targets.
     The ‘copy’ attribute can be used with functions, variables, or
     types.  However, the kind of symbol to which the attribute is
     applied (either function or variable) must match the kind of symbol
     to which the argument refers.  The ‘copy’ attribute copies only
     syntactic and semantic attributes but not attributes that affect a
     symbol's linkage or visibility such as ‘alias’, ‘visibility’, or
     ‘weak’.  The ‘deprecated’ and ‘target_clones’ attribute are also
     not copied.  *Note Common Type Attributes::.  *Note Common Variable
     Attributes::.

     For example, the STRONGALIAS macro below makes use of the ‘alias’
     and ‘copy’ attributes to define an alias named ALLOC for function
     ALLOCATE declared with attributes ALLOC_SIZE, MALLOC, and NOTHROW.
     Thanks to the ‘__typeof__’ operator the alias has the same type as
     the target function.  As a result of the ‘copy’ attribute the alias
     also shares the same attributes as the target.

          #define StrongAlias(TargetFunc, AliasDecl)  \
            extern __typeof__ (TargetFunc) AliasDecl  \
              __attribute__ ((alias (#TargetFunc), copy (TargetFunc)));

          extern __attribute__ ((alloc_size (1), malloc, nothrow))
            void* allocate (size_t);
          StrongAlias (allocate, alloc);

‘deprecated’
‘deprecated (MSG)’
     The ‘deprecated’ attribute results in a warning if the function is
     used anywhere in the source file.  This is useful when identifying
     functions that are expected to be removed in a future version of a
     program.  The warning also includes the location of the declaration
     of the deprecated function, to enable users to easily find further
     information about why the function is deprecated, or what they
     should do instead.  Note that the warnings only occurs for uses:

          int old_fn () __attribute__ ((deprecated));
          int old_fn ();
          int (*fn_ptr)() = old_fn;

     results in a warning on line 3 but not line 2.  The optional MSG
     argument, which must be a string, is printed in the warning if
     present.

     The ‘deprecated’ attribute can also be used for variables and types
     (*note Variable Attributes::, *note Type Attributes::.)

     The message attached to the attribute is affected by the setting of
     the ‘-fmessage-length’ option.

‘unavailable’
‘unavailable (MSG)’
     The ‘unavailable’ attribute results in an error if the function is
     used anywhere in the source file.  This is useful when identifying
     functions that have been removed from a particular variation of an
     interface.  Other than emitting an error rather than a warning, the
     ‘unavailable’ attribute behaves in the same manner as ‘deprecated’.

     The ‘unavailable’ attribute can also be used for variables and
     types (*note Variable Attributes::, *note Type Attributes::.)

‘error ("MESSAGE")’
‘warning ("MESSAGE")’
     If the ‘error’ or ‘warning’ attribute is used on a function
     declaration and a call to such a function is not eliminated through
     dead code elimination or other optimizations, an error or warning
     (respectively) that includes MESSAGE is diagnosed.  This is useful
     for compile-time checking, especially together with
     ‘__builtin_constant_p’ and inline functions where checking the
     inline function arguments is not possible through ‘extern char
     [(condition) ? 1 : -1];’ tricks.

     While it is possible to leave the function undefined and thus
     invoke a link failure (to define the function with a message in
     ‘.gnu.warning*’ section), when using these attributes the problem
     is diagnosed earlier and with exact location of the call even in
     presence of inline functions or when not emitting debugging
     information.

‘externally_visible’
     This attribute, attached to a global variable or function,
     nullifies the effect of the ‘-fwhole-program’ command-line option,
     so the object remains visible outside the current compilation unit.

     If ‘-fwhole-program’ is used together with ‘-flto’ and ‘gold’ is
     used as the linker plugin, ‘externally_visible’ attributes are
     automatically added to functions (not variable yet due to a current
     ‘gold’ issue) that are accessed outside of LTO objects according to
     resolution file produced by ‘gold’.  For other linkers that cannot
     generate resolution file, explicit ‘externally_visible’ attributes
     are still necessary.

‘flatten’
     Generally, inlining into a function is limited.  For a function
     marked with this attribute, every call inside this function is
     inlined, if possible.  Functions declared with attribute ‘noinline’
     and similar are not inlined.  Whether the function itself is
     considered for inlining depends on its size and the current
     inlining parameters.

‘format (ARCHETYPE, STRING-INDEX, FIRST-TO-CHECK)’
     The ‘format’ attribute specifies that a function takes ‘printf’,
     ‘scanf’, ‘strftime’ or ‘strfmon’ style arguments that should be
     type-checked against a format string.  For example, the
     declaration:

          extern int
          my_printf (void *my_object, const char *my_format, ...)
                __attribute__ ((format (printf, 2, 3)));

     causes the compiler to check the arguments in calls to ‘my_printf’
     for consistency with the ‘printf’ style format string argument
     ‘my_format’.

     The parameter ARCHETYPE determines how the format string is
     interpreted, and should be ‘printf’, ‘scanf’, ‘strftime’,
     ‘gnu_printf’, ‘gnu_scanf’, ‘gnu_strftime’ or ‘strfmon’.  (You can
     also use ‘__printf__’, ‘__scanf__’, ‘__strftime__’ or
     ‘__strfmon__’.)  On MinGW targets, ‘ms_printf’, ‘ms_scanf’, and
     ‘ms_strftime’ are also present.  ARCHETYPE values such as ‘printf’
     refer to the formats accepted by the system's C runtime library,
     while values prefixed with ‘gnu_’ always refer to the formats
     accepted by the GNU C Library.  On Microsoft Windows targets,
     values prefixed with ‘ms_’ refer to the formats accepted by the
     ‘msvcrt.dll’ library.  The parameter STRING-INDEX specifies which
     argument is the format string argument (starting from 1), while
     FIRST-TO-CHECK is the number of the first argument to check against
     the format string.  For functions where the arguments are not
     available to be checked (such as ‘vprintf’), specify the third
     parameter as zero.  In this case the compiler only checks the
     format string for consistency.  For ‘strftime’ formats, the third
     parameter is required to be zero.  Since non-static C++ methods
     have an implicit ‘this’ argument, the arguments of such methods
     should be counted from two, not one, when giving values for
     STRING-INDEX and FIRST-TO-CHECK.

     In the example above, the format string (‘my_format’) is the second
     argument of the function ‘my_print’, and the arguments to check
     start with the third argument, so the correct parameters for the
     format attribute are 2 and 3.

     The ‘format’ attribute allows you to identify your own functions
     that take format strings as arguments, so that GCC can check the
     calls to these functions for errors.  The compiler always (unless
     ‘-ffreestanding’ or ‘-fno-builtin’ is used) checks formats for the
     standard library functions ‘printf’, ‘fprintf’, ‘sprintf’, ‘scanf’,
     ‘fscanf’, ‘sscanf’, ‘strftime’, ‘vprintf’, ‘vfprintf’ and
     ‘vsprintf’ whenever such warnings are requested (using ‘-Wformat’),
     so there is no need to modify the header file ‘stdio.h’.  In C99
     mode, the functions ‘snprintf’, ‘vsnprintf’, ‘vscanf’, ‘vfscanf’
     and ‘vsscanf’ are also checked.  Except in strictly conforming C
     standard modes, the X/Open function ‘strfmon’ is also checked as
     are ‘printf_unlocked’ and ‘fprintf_unlocked’.  *Note Options
     Controlling C Dialect: C Dialect Options.

     For Objective-C dialects, ‘NSString’ (or ‘__NSString__’) is
     recognized in the same context.  Declarations including these
     format attributes are parsed for correct syntax, however the result
     of checking of such format strings is not yet defined, and is not
     carried out by this version of the compiler.

     The target may also provide additional types of format checks.
     *Note Format Checks Specific to Particular Target Machines: Target
     Format Checks.

‘format_arg (STRING-INDEX)’
     The ‘format_arg’ attribute specifies that a function takes one or
     more format strings for a ‘printf’, ‘scanf’, ‘strftime’ or
     ‘strfmon’ style function and modifies it (for example, to translate
     it into another language), so the result can be passed to a
     ‘printf’, ‘scanf’, ‘strftime’ or ‘strfmon’ style function (with the
     remaining arguments to the format function the same as they would
     have been for the unmodified string).  Multiple ‘format_arg’
     attributes may be applied to the same function, each designating a
     distinct parameter as a format string.  For example, the
     declaration:

          extern char *
          my_dgettext (char *my_domain, const char *my_format)
                __attribute__ ((format_arg (2)));

     causes the compiler to check the arguments in calls to a ‘printf’,
     ‘scanf’, ‘strftime’ or ‘strfmon’ type function, whose format string
     argument is a call to the ‘my_dgettext’ function, for consistency
     with the format string argument ‘my_format’.  If the ‘format_arg’
     attribute had not been specified, all the compiler could tell in
     such calls to format functions would be that the format string
     argument is not constant; this would generate a warning when
     ‘-Wformat-nonliteral’ is used, but the calls could not be checked
     without the attribute.

     In calls to a function declared with more than one ‘format_arg’
     attribute, each with a distinct argument value, the corresponding
     actual function arguments are checked against all format strings
     designated by the attributes.  This capability is designed to
     support the GNU ‘ngettext’ family of functions.

     The parameter STRING-INDEX specifies which argument is the format
     string argument (starting from one).  Since non-static C++ methods
     have an implicit ‘this’ argument, the arguments of such methods
     should be counted from two.

     The ‘format_arg’ attribute allows you to identify your own
     functions that modify format strings, so that GCC can check the
     calls to ‘printf’, ‘scanf’, ‘strftime’ or ‘strfmon’ type function
     whose operands are a call to one of your own function.  The
     compiler always treats ‘gettext’, ‘dgettext’, and ‘dcgettext’ in
     this manner except when strict ISO C support is requested by
     ‘-ansi’ or an appropriate ‘-std’ option, or ‘-ffreestanding’ or
     ‘-fno-builtin’ is used.  *Note Options Controlling C Dialect: C
     Dialect Options.

     For Objective-C dialects, the ‘format-arg’ attribute may refer to
     an ‘NSString’ reference for compatibility with the ‘format’
     attribute above.

     The target may also allow additional types in ‘format-arg’
     attributes.  *Note Format Checks Specific to Particular Target
     Machines: Target Format Checks.

‘gnu_inline’
     This attribute should be used with a function that is also declared
     with the ‘inline’ keyword.  It directs GCC to treat the function as
     if it were defined in gnu90 mode even when compiling in C99 or
     gnu99 mode.

     If the function is declared ‘extern’, then this definition of the
     function is used only for inlining.  In no case is the function
     compiled as a standalone function, not even if you take its address
     explicitly.  Such an address becomes an external reference, as if
     you had only declared the function, and had not defined it.  This
     has almost the effect of a macro.  The way to use this is to put a
     function definition in a header file with this attribute, and put
     another copy of the function, without ‘extern’, in a library file.
     The definition in the header file causes most calls to the function
     to be inlined.  If any uses of the function remain, they refer to
     the single copy in the library.  Note that the two definitions of
     the functions need not be precisely the same, although if they do
     not have the same effect your program may behave oddly.

     In C, if the function is neither ‘extern’ nor ‘static’, then the
     function is compiled as a standalone function, as well as being
     inlined where possible.

     This is how GCC traditionally handled functions declared ‘inline’.
     Since ISO C99 specifies a different semantics for ‘inline’, this
     function attribute is provided as a transition measure and as a
     useful feature in its own right.  This attribute is available in
     GCC 4.1.3 and later.  It is available if either of the preprocessor
     macros ‘__GNUC_GNU_INLINE__’ or ‘__GNUC_STDC_INLINE__’ are defined.
     *Note An Inline Function is As Fast As a Macro: Inline.

     In C++, this attribute does not depend on ‘extern’ in any way, but
     it still requires the ‘inline’ keyword to enable its special
     behavior.

‘hot’
     The ‘hot’ attribute on a function is used to inform the compiler
     that the function is a hot spot of the compiled program.  The
     function is optimized more aggressively and on many targets it is
     placed into a special subsection of the text section so all hot
     functions appear close together, improving locality.

     When profile feedback is available, via ‘-fprofile-use’, hot
     functions are automatically detected and this attribute is ignored.

‘ifunc ("RESOLVER")’
     The ‘ifunc’ attribute is used to mark a function as an indirect
     function using the STT_GNU_IFUNC symbol type extension to the ELF
     standard.  This allows the resolution of the symbol value to be
     determined dynamically at load time, and an optimized version of
     the routine to be selected for the particular processor or other
     system characteristics determined then.  To use this attribute,
     first define the implementation functions available, and a resolver
     function that returns a pointer to the selected implementation
     function.  The implementation functions' declarations must match
     the API of the function being implemented.  The resolver should be
     declared to be a function taking no arguments and returning a
     pointer to a function of the same type as the implementation.  For
     example:

          void *my_memcpy (void *dst, const void *src, size_t len)
          {
            ...
            return dst;
          }

          static void * (*resolve_memcpy (void))(void *, const void *, size_t)
          {
            return my_memcpy; // we will just always select this routine
          }

     The exported header file declaring the function the user calls
     would contain:

          extern void *memcpy (void *, const void *, size_t);

     allowing the user to call ‘memcpy’ as a regular function, unaware
     of the actual implementation.  Finally, the indirect function needs
     to be defined in the same translation unit as the resolver
     function:

          void *memcpy (void *, const void *, size_t)
               __attribute__ ((ifunc ("resolve_memcpy")));

     In C++, the ‘ifunc’ attribute takes a string that is the mangled
     name of the resolver function.  A C++ resolver for a non-static
     member function of class ‘C’ should be declared to return a pointer
     to a non-member function taking pointer to ‘C’ as the first
     argument, followed by the same arguments as of the implementation
     function.  G++ checks the signatures of the two functions and
     issues a ‘-Wattribute-alias’ warning for mismatches.  To suppress a
     warning for the necessary cast from a pointer to the implementation
     member function to the type of the corresponding non-member
     function use the ‘-Wno-pmf-conversions’ option.  For example:

          class S
          {
          private:
            int debug_impl (int);
            int optimized_impl (int);

            typedef int Func (S*, int);

            static Func* resolver ();
          public:

            int interface (int);
          };

          int S::debug_impl (int) { /* ... */ }
          int S::optimized_impl (int) { /* ... */ }

          S::Func* S::resolver ()
          {
            int (S::*pimpl) (int)
              = getenv ("DEBUG") ? &S::debug_impl : &S::optimized_impl;

            // Cast triggers -Wno-pmf-conversions.
            return reinterpret_cast<Func*>(pimpl);
          }

          int S::interface (int) __attribute__ ((ifunc ("_ZN1S8resolverEv")));

     Indirect functions cannot be weak.  Binutils version 2.20.1 or
     higher and GNU C Library version 2.11.1 are required to use this
     feature.

‘interrupt’
‘interrupt_handler’
     Many GCC back ends support attributes to indicate that a function
     is an interrupt handler, which tells the compiler to generate
     function entry and exit sequences that differ from those from
     regular functions.  The exact syntax and behavior are
     target-specific; refer to the following subsections for details.

‘leaf’
     Calls to external functions with this attribute must return to the
     current compilation unit only by return or by exception handling.
     In particular, a leaf function is not allowed to invoke callback
     functions passed to it from the current compilation unit, directly
     call functions exported by the unit, or ‘longjmp’ into the unit.
     Leaf functions might still call functions from other compilation
     units and thus they are not necessarily leaf in the sense that they
     contain no function calls at all.

     The attribute is intended for library functions to improve dataflow
     analysis.  The compiler takes the hint that any data not escaping
     the current compilation unit cannot be used or modified by the leaf
     function.  For example, the ‘sin’ function is a leaf function, but
     ‘qsort’ is not.

     Note that leaf functions might indirectly run a signal handler
     defined in the current compilation unit that uses static variables.
     Similarly, when lazy symbol resolution is in effect, leaf functions
     might invoke indirect functions whose resolver function or
     implementation function is defined in the current compilation unit
     and uses static variables.  There is no standard-compliant way to
     write such a signal handler, resolver function, or implementation
     function, and the best that you can do is to remove the ‘leaf’
     attribute or mark all such static variables ‘volatile’.  Lastly,
     for ELF-based systems that support symbol interposition, care
     should be taken that functions defined in the current compilation
     unit do not unexpectedly interpose other symbols based on the
     defined standards mode and defined feature test macros; otherwise
     an inadvertent callback would be added.

     The attribute has no effect on functions defined within the current
     compilation unit.  This is to allow easy merging of multiple
     compilation units into one, for example, by using the link-time
     optimization.  For this reason the attribute is not allowed on
     types to annotate indirect calls.

‘malloc’
‘malloc (DEALLOCATOR)’
‘malloc (DEALLOCATOR, PTR-INDEX)’
     Attribute ‘malloc’ indicates that a function is ‘malloc’-like,
     i.e., that the pointer P returned by the function cannot alias any
     other pointer valid when the function returns, and moreover no
     pointers to valid objects occur in any storage addressed by P.  In
     addition, the GCC predicts that a function with the attribute
     returns non-null in most cases.

     Independently, the form of the attribute with one or two arguments
     associates ‘deallocator’ as a suitable deallocation function for
     pointers returned from the ‘malloc’-like function.  PTR-INDEX
     denotes the positional argument to which when the pointer is passed
     in calls to ‘deallocator’ has the effect of deallocating it.

     Using the attribute with no arguments is designed to improve
     optimization by relying on the aliasing property it implies.
     Functions like ‘malloc’ and ‘calloc’ have this property because
     they return a pointer to uninitialized or zeroed-out, newly
     obtained storage.  However, functions like ‘realloc’ do not have
     this property, as they may return pointers to storage containing
     pointers to existing objects.  Additionally, since all such
     functions are assumed to return null only infrequently, callers can
     be optimized based on that assumption.

     Associating a function with a DEALLOCATOR helps detect calls to
     mismatched allocation and deallocation functions and diagnose them
     under the control of options such as ‘-Wmismatched-dealloc’.  It
     also makes it possible to diagnose attempts to deallocate objects
     that were not allocated dynamically, by ‘-Wfree-nonheap-object’.
     To indicate that an allocation function both satisifies the
     nonaliasing property and has a deallocator associated with it, both
     the plain form of the attribute and the one with the DEALLOCATOR
     argument must be used.  The same function can be both an allocator
     and a deallocator.  Since inlining one of the associated functions
     but not the other could result in apparent mismatches, this form of
     attribute ‘malloc’ is not accepted on inline functions.  For the
     same reason, using the attribute prevents both the allocation and
     deallocation functions from being expanded inline.

     For example, besides stating that the functions return pointers
     that do not alias any others, the following declarations make
     ‘fclose’ a suitable deallocator for pointers returned from all
     functions except ‘popen’, and ‘pclose’ as the only suitable
     deallocator for pointers returned from ‘popen’.  The deallocator
     functions must be declared before they can be referenced in the
     attribute.

          int fclose (FILE*);
          int pclose (FILE*);

          __attribute__ ((malloc, malloc (fclose, 1)))
            FILE* fdopen (int, const char*);
          __attribute__ ((malloc, malloc (fclose, 1)))
            FILE* fopen (const char*, const char*);
          __attribute__ ((malloc, malloc (fclose, 1)))
            FILE* fmemopen(void *, size_t, const char *);
          __attribute__ ((malloc, malloc (pclose, 1)))
            FILE* popen (const char*, const char*);
          __attribute__ ((malloc, malloc (fclose, 1)))
            FILE* tmpfile (void);

     The warnings guarded by ‘-fanalyzer’ respect allocation and
     deallocation pairs marked with the ‘malloc’.  In particular:

        • The analyzer will emit a ‘-Wanalyzer-mismatching-deallocation’
          diagnostic if there is an execution path in which the result
          of an allocation call is passed to a different deallocator.

        • The analyzer will emit a ‘-Wanalyzer-double-free’ diagnostic
          if there is an execution path in which a value is passed more
          than once to a deallocation call.

        • The analyzer will consider the possibility that an allocation
          function could fail and return NULL. It will emit
          ‘-Wanalyzer-possible-null-dereference’ and
          ‘-Wanalyzer-possible-null-argument’ diagnostics if there are
          execution paths in which an unchecked result of an allocation
          call is dereferenced or passed to a function requiring a
          non-null argument.  If the allocator always returns non-null,
          use ‘__attribute__ ((returns_nonnull))’ to suppress these
          warnings.  For example:
               char *xstrdup (const char *)
                 __attribute__((malloc (free), returns_nonnull));

        • The analyzer will emit a ‘-Wanalyzer-use-after-free’
          diagnostic if there is an execution path in which the memory
          passed by pointer to a deallocation call is used after the
          deallocation.

        • The analyzer will emit a ‘-Wanalyzer-malloc-leak’ diagnostic
          if there is an execution path in which the result of an
          allocation call is leaked (without being passed to the
          deallocation function).

        • The analyzer will emit a ‘-Wanalyzer-free-of-non-heap’
          diagnostic if a deallocation function is used on a global or
          on-stack variable.

     The analyzer assumes that deallocators can gracefully handle the
     ‘NULL’ pointer.  If this is not the case, the deallocator can be
     marked with ‘__attribute__((nonnull))’ so that ‘-fanalyzer’ can
     emit a ‘-Wanalyzer-possible-null-argument’ diagnostic for code
     paths in which the deallocator is called with NULL.

‘no_icf’
     This function attribute prevents a functions from being merged with
     another semantically equivalent function.

‘no_instrument_function’
     If any of ‘-finstrument-functions’, ‘-p’, or ‘-pg’ are given,
     profiling function calls are generated at entry and exit of most
     user-compiled functions.  Functions with this attribute are not so
     instrumented.

‘no_profile_instrument_function’
     The ‘no_profile_instrument_function’ attribute on functions is used
     to inform the compiler that it should not process any profile
     feedback based optimization code instrumentation.

‘no_reorder’
     Do not reorder functions or variables marked ‘no_reorder’ against
     each other or top level assembler statements the executable.  The
     actual order in the program will depend on the linker command line.
     Static variables marked like this are also not removed.  This has a
     similar effect as the ‘-fno-toplevel-reorder’ option, but only
     applies to the marked symbols.

‘no_sanitize ("SANITIZE_OPTION")’
     The ‘no_sanitize’ attribute on functions is used to inform the
     compiler that it should not do sanitization of any option mentioned
     in SANITIZE_OPTION.  A list of values acceptable by the
     ‘-fsanitize’ option can be provided.

          void __attribute__ ((no_sanitize ("alignment", "object-size")))
          f () { /* Do something. */; }
          void __attribute__ ((no_sanitize ("alignment,object-size")))
          g () { /* Do something. */; }

‘no_sanitize_address’
‘no_address_safety_analysis’
     The ‘no_sanitize_address’ attribute on functions is used to inform
     the compiler that it should not instrument memory accesses in the
     function when compiling with the ‘-fsanitize=address’ option.  The
     ‘no_address_safety_analysis’ is a deprecated alias of the
     ‘no_sanitize_address’ attribute, new code should use
     ‘no_sanitize_address’.

‘no_sanitize_thread’
     The ‘no_sanitize_thread’ attribute on functions is used to inform
     the compiler that it should not instrument memory accesses in the
     function when compiling with the ‘-fsanitize=thread’ option.

‘no_sanitize_undefined’
     The ‘no_sanitize_undefined’ attribute on functions is used to
     inform the compiler that it should not check for undefined behavior
     in the function when compiling with the ‘-fsanitize=undefined’
     option.

‘no_sanitize_coverage’
     The ‘no_sanitize_coverage’ attribute on functions is used to inform
     the compiler that it should not do coverage-guided fuzzing code
     instrumentation (‘-fsanitize-coverage’).

‘no_split_stack’
     If ‘-fsplit-stack’ is given, functions have a small prologue which
     decides whether to split the stack.  Functions with the
     ‘no_split_stack’ attribute do not have that prologue, and thus may
     run with only a small amount of stack space available.

‘no_stack_limit’
     This attribute locally overrides the ‘-fstack-limit-register’ and
     ‘-fstack-limit-symbol’ command-line options; it has the effect of
     disabling stack limit checking in the function it applies to.

‘noclone’
     This function attribute prevents a function from being considered
     for cloning--a mechanism that produces specialized copies of
     functions and which is (currently) performed by interprocedural
     constant propagation.

‘noinline’
     This function attribute prevents a function from being considered
     for inlining.  If the function does not have side effects, there
     are optimizations other than inlining that cause function calls to
     be optimized away, although the function call is live.  To keep
     such calls from being optimized away, put
          asm ("");

     (*note Extended Asm::) in the called function, to serve as a
     special side effect.

‘noipa’
     Disable interprocedural optimizations between the function with
     this attribute and its callers, as if the body of the function is
     not available when optimizing callers and the callers are
     unavailable when optimizing the body.  This attribute implies
     ‘noinline’, ‘noclone’ and ‘no_icf’ attributes.  However, this
     attribute is not equivalent to a combination of other attributes,
     because its purpose is to suppress existing and future
     optimizations employing interprocedural analysis, including those
     that do not have an attribute suitable for disabling them
     individually.  This attribute is supported mainly for the purpose
     of testing the compiler.

‘nonnull’
‘nonnull (ARG-INDEX, ...)’
     The ‘nonnull’ attribute may be applied to a function that takes at
     least one argument of a pointer type.  It indicates that the
     referenced arguments must be non-null pointers.  For instance, the
     declaration:

          extern void *
          my_memcpy (void *dest, const void *src, size_t len)
                  __attribute__((nonnull (1, 2)));

     informs the compiler that, in calls to ‘my_memcpy’, arguments DEST
     and SRC must be non-null.

     The attribute has an effect both on functions calls and function
     definitions.

     For function calls:
        • If the compiler determines that a null pointer is passed in an
          argument slot marked as non-null, and the ‘-Wnonnull’ option
          is enabled, a warning is issued.  *Note Warning Options::.
        • The ‘-fisolate-erroneous-paths-attribute’ option can be
          specified to have GCC transform calls with null arguments to
          non-null functions into traps.  *Note Optimize Options::.
        • The compiler may also perform optimizations based on the
          knowledge that certain function arguments cannot be null.
          These optimizations can be disabled by the
          ‘-fno-delete-null-pointer-checks’ option.  *Note Optimize
          Options::.

     For function definitions:
        • If the compiler determines that a function parameter that is
          marked with nonnull is compared with null, and
          ‘-Wnonnull-compare’ option is enabled, a warning is issued.
          *Note Warning Options::.
        • The compiler may also perform optimizations based on the
          knowledge that ‘nonnul’ parameters cannot be null.  This can
          currently not be disabled other than by removing the nonnull
          attribute.

     If no ARG-INDEX is given to the ‘nonnull’ attribute, all pointer
     arguments are marked as non-null.  To illustrate, the following
     declaration is equivalent to the previous example:

          extern void *
          my_memcpy (void *dest, const void *src, size_t len)
                  __attribute__((nonnull));

‘noplt’
     The ‘noplt’ attribute is the counterpart to option ‘-fno-plt’.
     Calls to functions marked with this attribute in
     position-independent code do not use the PLT.

          /* Externally defined function foo.  */
          int foo () __attribute__ ((noplt));

          int
          main (/* ... */)
          {
            /* ... */
            foo ();
            /* ... */
          }

     The ‘noplt’ attribute on function ‘foo’ tells the compiler to
     assume that the function ‘foo’ is externally defined and that the
     call to ‘foo’ must avoid the PLT in position-independent code.

     In position-dependent code, a few targets also convert calls to
     functions that are marked to not use the PLT to use the GOT
     instead.

‘noreturn’
     A few standard library functions, such as ‘abort’ and ‘exit’,
     cannot return.  GCC knows this automatically.  Some programs define
     their own functions that never return.  You can declare them
     ‘noreturn’ to tell the compiler this fact.  For example,

          void fatal () __attribute__ ((noreturn));

          void
          fatal (/* ... */)
          {
            /* ... */ /* Print error message. */ /* ... */
            exit (1);
          }

     The ‘noreturn’ keyword tells the compiler to assume that ‘fatal’
     cannot return.  It can then optimize without regard to what would
     happen if ‘fatal’ ever did return.  This makes slightly better
     code.  More importantly, it helps avoid spurious warnings of
     uninitialized variables.

     The ‘noreturn’ keyword does not affect the exceptional path when
     that applies: a ‘noreturn’-marked function may still return to the
     caller by throwing an exception or calling ‘longjmp’.

     In order to preserve backtraces, GCC will never turn calls to
     ‘noreturn’ functions into tail calls.

     Do not assume that registers saved by the calling function are
     restored before calling the ‘noreturn’ function.

     It does not make sense for a ‘noreturn’ function to have a return
     type other than ‘void’.

‘nothrow’
     The ‘nothrow’ attribute is used to inform the compiler that a
     function cannot throw an exception.  For example, most functions in
     the standard C library can be guaranteed not to throw an exception
     with the notable exceptions of ‘qsort’ and ‘bsearch’ that take
     function pointer arguments.

‘optimize (LEVEL, ...)’
‘optimize (STRING, ...)’
     The ‘optimize’ attribute is used to specify that a function is to
     be compiled with different optimization options than specified on
     the command line.  The optimize attribute arguments of a function
     behave behave as if appended to the command-line.

     Valid arguments are constant non-negative integers and strings.
     Each numeric argument specifies an optimization LEVEL.  Each STRING
     argument consists of one or more comma-separated substrings.  Each
     substring that begins with the letter ‘O’ refers to an optimization
     option such as ‘-O0’ or ‘-Os’.  Other substrings are taken as
     suffixes to the ‘-f’ prefix jointly forming the name of an
     optimization option.  *Note Optimize Options::.

     ‘#pragma GCC optimize’ can be used to set optimization options for
     more than one function.  *Note Function Specific Option Pragmas::,
     for details about the pragma.

     Providing multiple strings as arguments separated by commas to
     specify multiple options is equivalent to separating the option
     suffixes with a comma (‘,’) within a single string.  Spaces are not
     permitted within the strings.

     Not every optimization option that starts with the -F prefix
     specified by the attribute necessarily has an effect on the
     function.  The ‘optimize’ attribute should be used for debugging
     purposes only.  It is not suitable in production code.

‘patchable_function_entry’
     In case the target's text segment can be made writable at run time
     by any means, padding the function entry with a number of NOPs can
     be used to provide a universal tool for instrumentation.

     The ‘patchable_function_entry’ function attribute can be used to
     change the number of NOPs to any desired value.  The two-value
     syntax is the same as for the command-line switch
     ‘-fpatchable-function-entry=N,M’, generating N NOPs, with the
     function entry point before the Mth NOP instruction.  M defaults to
     0 if omitted e.g. function entry point is before the first NOP.

     If patchable function entries are enabled globally using the
     command-line option ‘-fpatchable-function-entry=N,M’, then you must
     disable instrumentation on all functions that are part of the
     instrumentation framework with the attribute
     ‘patchable_function_entry (0)’ to prevent recursion.

‘pure’

     Calls to functions that have no observable effects on the state of
     the program other than to return a value may lend themselves to
     optimizations such as common subexpression elimination.  Declaring
     such functions with the ‘pure’ attribute allows GCC to avoid
     emitting some calls in repeated invocations of the function with
     the same argument values.

     The ‘pure’ attribute prohibits a function from modifying the state
     of the program that is observable by means other than inspecting
     the function's return value.  However, functions declared with the
     ‘pure’ attribute can safely read any non-volatile objects, and
     modify the value of objects in a way that does not affect their
     return value or the observable state of the program.

     For example,

          int hash (char *) __attribute__ ((pure));

     tells GCC that subsequent calls to the function ‘hash’ with the
     same string can be replaced by the result of the first call
     provided the state of the program observable by ‘hash’, including
     the contents of the array itself, does not change in between.  Even
     though ‘hash’ takes a non-const pointer argument it must not modify
     the array it points to, or any other object whose value the rest of
     the program may depend on.  However, the caller may safely change
     the contents of the array between successive calls to the function
     (doing so disables the optimization).  The restriction also applies
     to member objects referenced by the ‘this’ pointer in C++
     non-static member functions.

     Some common examples of pure functions are ‘strlen’ or ‘memcmp’.
     Interesting non-pure functions are functions with infinite loops or
     those depending on volatile memory or other system resource, that
     may change between consecutive calls (such as the standard C ‘feof’
     function in a multithreading environment).

     The ‘pure’ attribute imposes similar but looser restrictions on a
     function's definition than the ‘const’ attribute: ‘pure’ allows the
     function to read any non-volatile memory, even if it changes in
     between successive invocations of the function.  Declaring the same
     function with both the ‘pure’ and the ‘const’ attribute is
     diagnosed.  Because a pure function cannot have any observable side
     effects it does not make sense for such a function to return
     ‘void’.  Declaring such a function is diagnosed.

‘returns_nonnull’
     The ‘returns_nonnull’ attribute specifies that the function return
     value should be a non-null pointer.  For instance, the declaration:

          extern void *
          mymalloc (size_t len) __attribute__((returns_nonnull));

     lets the compiler optimize callers based on the knowledge that the
     return value will never be null.

‘returns_twice’
     The ‘returns_twice’ attribute tells the compiler that a function
     may return more than one time.  The compiler ensures that all
     registers are dead before calling such a function and emits a
     warning about the variables that may be clobbered after the second
     return from the function.  Examples of such functions are ‘setjmp’
     and ‘vfork’.  The ‘longjmp’-like counterpart of such function, if
     any, might need to be marked with the ‘noreturn’ attribute.

‘section ("SECTION-NAME")’
     Normally, the compiler places the code it generates in the ‘text’
     section.  Sometimes, however, you need additional sections, or you
     need certain particular functions to appear in special sections.
     The ‘section’ attribute specifies that a function lives in a
     particular section.  For example, the declaration:

          extern void foobar (void) __attribute__ ((section ("bar")));

     puts the function ‘foobar’ in the ‘bar’ section.

     Some file formats do not support arbitrary sections so the
     ‘section’ attribute is not available on all platforms.  If you need
     to map the entire contents of a module to a particular section,
     consider using the facilities of the linker instead.

‘sentinel’
‘sentinel (POSITION)’
     This function attribute indicates that an argument in a call to the
     function is expected to be an explicit ‘NULL’.  The attribute is
     only valid on variadic functions.  By default, the sentinel is
     expected to be the last argument of the function call.  If the
     optional POSITION argument is specified to the attribute, the
     sentinel must be located at POSITION counting backwards from the
     end of the argument list.

          __attribute__ ((sentinel))
          is equivalent to
          __attribute__ ((sentinel(0)))

     The attribute is automatically set with a position of 0 for the
     built-in functions ‘execl’ and ‘execlp’.  The built-in function
     ‘execle’ has the attribute set with a position of 1.

     A valid ‘NULL’ in this context is defined as zero with any object
     pointer type.  If your system defines the ‘NULL’ macro with an
     integer type then you need to add an explicit cast.  During
     installation GCC replaces the system ‘<stddef.h>’ header with a
     copy that redefines NULL appropriately.

     The warnings for missing or incorrect sentinels are enabled with
     ‘-Wformat’.

‘simd’
‘simd("MASK")’
     This attribute enables creation of one or more function versions
     that can process multiple arguments using SIMD instructions from a
     single invocation.  Specifying this attribute allows compiler to
     assume that such versions are available at link time (provided in
     the same or another translation unit).  Generated versions are
     target-dependent and described in the corresponding Vector ABI
     document.  For x86_64 target this document can be found
     here (https://sourceware.org/glibc/wiki/libmvec?action=AttachFile&do=view&target=VectorABI.txt).

     The optional argument MASK may have the value ‘notinbranch’ or
     ‘inbranch’, and instructs the compiler to generate non-masked or
     masked clones correspondingly.  By default, all clones are
     generated.

     If the attribute is specified and ‘#pragma omp declare simd’ is
     present on a declaration and the ‘-fopenmp’ or ‘-fopenmp-simd’
     switch is specified, then the attribute is ignored.

‘stack_protect’
     This attribute adds stack protection code to the function if flags
     ‘-fstack-protector’, ‘-fstack-protector-strong’ or
     ‘-fstack-protector-explicit’ are set.

‘no_stack_protector’
     This attribute prevents stack protection code for the function.

‘target (STRING, ...)’
     Multiple target back ends implement the ‘target’ attribute to
     specify that a function is to be compiled with different target
     options than specified on the command line.  The original target
     command-line options are ignored.  One or more strings can be
     provided as arguments.  Each string consists of one or more
     comma-separated suffixes to the ‘-m’ prefix jointly forming the
     name of a machine-dependent option.  *Note Machine-Dependent
     Options: Submodel Options.

     The ‘target’ attribute can be used for instance to have a function
     compiled with a different ISA (instruction set architecture) than
     the default.  ‘#pragma GCC target’ can be used to specify
     target-specific options for more than one function.  *Note Function
     Specific Option Pragmas::, for details about the pragma.

     For instance, on an x86, you could declare one function with the
     ‘target("sse4.1,arch=core2")’ attribute and another with
     ‘target("sse4a,arch=amdfam10")’.  This is equivalent to compiling
     the first function with ‘-msse4.1’ and ‘-march=core2’ options, and
     the second function with ‘-msse4a’ and ‘-march=amdfam10’ options.
     It is up to you to make sure that a function is only invoked on a
     machine that supports the particular ISA it is compiled for (for
     example by using ‘cpuid’ on x86 to determine what feature bits and
     architecture family are used).

          int core2_func (void) __attribute__ ((__target__ ("arch=core2")));
          int sse3_func (void) __attribute__ ((__target__ ("sse3")));

     Providing multiple strings as arguments separated by commas to
     specify multiple options is equivalent to separating the option
     suffixes with a comma (‘,’) within a single string.  Spaces are not
     permitted within the strings.

     The options supported are specific to each target; refer to *note
     x86 Function Attributes::, *note PowerPC Function Attributes::,
     *note ARM Function Attributes::, *note AArch64 Function
     Attributes::, *note Nios II Function Attributes::, and *note S/390
     Function Attributes:: for details.

‘symver ("NAME2@NODENAME")’
     On ELF targets this attribute creates a symbol version.  The NAME2
     part of the parameter is the actual name of the symbol by which it
     will be externally referenced.  The ‘nodename’ portion should be
     the name of a node specified in the version script supplied to the
     linker when building a shared library.  Versioned symbol must be
     defined and must be exported with default visibility.

          __attribute__ ((__symver__ ("foo@VERS_1"))) int
          foo_v1 (void)
          {
          }

     Will produce a ‘.symver foo_v1, foo@VERS_1’ directive in the
     assembler output.

     One can also define multiple version for a given symbol (starting
     from binutils 2.35).

          __attribute__ ((__symver__ ("foo@VERS_2"), __symver__ ("foo@VERS_3")))
          int symver_foo_v1 (void)
          {
          }

     This example creates a symbol name ‘symver_foo_v1’ which will be
     version ‘VERS_2’ and ‘VERS_3’ of ‘foo’.

     If you have an older release of binutils, then symbol alias needs
     to be used:

          __attribute__ ((__symver__ ("foo@VERS_2")))
          int foo_v1 (void)
          {
            return 0;
          }

          __attribute__ ((__symver__ ("foo@VERS_3")))
          __attribute__ ((alias ("foo_v1")))
          int symver_foo_v1 (void);

     Finally if the parameter is ‘"NAME2@@NODENAME"’ then in addition to
     creating a symbol version (as if ‘"NAME2@NODENAME"’ was used) the
     version will be also used to resolve NAME2 by the linker.

‘tainted_args’
     The ‘tainted_args’ attribute is used to specify that a function is
     called in a way that requires sanitization of its arguments, such
     as a system call in an operating system kernel.  Such a function
     can be considered part of the "attack surface" of the program.  The
     attribute can be used both on function declarations, and on field
     declarations containing function pointers.  In the latter case, any
     function used as an initializer of such a callback field will be
     treated as being called with tainted arguments.

     The analyzer will pay particular attention to such functions when
     both ‘-fanalyzer’ and ‘-fanalyzer-checker=taint’ are supplied,
     potentially issuing warnings guarded by
     ‘-Wanalyzer-tainted-allocation-size’,
     ‘-Wanalyzer-tainted-array-index’, ‘-Wanalyzer-tainted-divisor’,
     ‘-Wanalyzer-tainted-offset’, and ‘-Wanalyzer-tainted-size’.

‘target_clones (OPTIONS)’
     The ‘target_clones’ attribute is used to specify that a function be
     cloned into multiple versions compiled with different target
     options than specified on the command line.  The supported options
     and restrictions are the same as for ‘target’ attribute.

     For instance, on an x86, you could compile a function with
     ‘target_clones("sse4.1,avx")’.  GCC creates two function clones,
     one compiled with ‘-msse4.1’ and another with ‘-mavx’.

     On a PowerPC, you can compile a function with
     ‘target_clones("cpu=power9,default")’.  GCC will create two
     function clones, one compiled with ‘-mcpu=power9’ and another with
     the default options.  GCC must be configured to use GLIBC 2.23 or
     newer in order to use the ‘target_clones’ attribute.

     It also creates a resolver function (see the ‘ifunc’ attribute
     above) that dynamically selects a clone suitable for current
     architecture.  The resolver is created only if there is a usage of
     a function with ‘target_clones’ attribute.

     Note that any subsequent call of a function without ‘target_clone’
     from a ‘target_clone’ caller will not lead to copying (target
     clone) of the called function.  If you want to enforce such
     behaviour, we recommend declaring the calling function with the
     ‘flatten’ attribute?

‘unused’
     This attribute, attached to a function, means that the function is
     meant to be possibly unused.  GCC does not produce a warning for
     this function.

‘used’
     This attribute, attached to a function, means that code must be
     emitted for the function even if it appears that the function is
     not referenced.  This is useful, for example, when the function is
     referenced only in inline assembly.

     When applied to a member function of a C++ class template, the
     attribute also means that the function is instantiated if the class
     itself is instantiated.

‘retain’
     For ELF targets that support the GNU or FreeBSD OSABIs, this
     attribute will save the function from linker garbage collection.
     To support this behavior, functions that have not been placed in
     specific sections (e.g.  by the ‘section’ attribute, or the
     ‘-ffunction-sections’ option), will be placed in new, unique
     sections.

     This additional functionality requires Binutils version 2.36 or
     later.

‘visibility ("VISIBILITY_TYPE")’
     This attribute affects the linkage of the declaration to which it
     is attached.  It can be applied to variables (*note Common Variable
     Attributes::) and types (*note Common Type Attributes::) as well as
     functions.

     There are four supported VISIBILITY_TYPE values: default, hidden,
     protected or internal visibility.

          void __attribute__ ((visibility ("protected")))
          f () { /* Do something. */; }
          int i __attribute__ ((visibility ("hidden")));

     The possible values of VISIBILITY_TYPE correspond to the visibility
     settings in the ELF gABI.

     ‘default’
          Default visibility is the normal case for the object file
          format.  This value is available for the visibility attribute
          to override other options that may change the assumed
          visibility of entities.

          On ELF, default visibility means that the declaration is
          visible to other modules and, in shared libraries, means that
          the declared entity may be overridden.

          On Darwin, default visibility means that the declaration is
          visible to other modules.

          Default visibility corresponds to "external linkage" in the
          language.

     ‘hidden’
          Hidden visibility indicates that the entity declared has a new
          form of linkage, which we call "hidden linkage".  Two
          declarations of an object with hidden linkage refer to the
          same object if they are in the same shared object.

     ‘internal’
          Internal visibility is like hidden visibility, but with
          additional processor specific semantics.  Unless otherwise
          specified by the psABI, GCC defines internal visibility to
          mean that a function is _never_ called from another module.
          Compare this with hidden functions which, while they cannot be
          referenced directly by other modules, can be referenced
          indirectly via function pointers.  By indicating that a
          function cannot be called from outside the module, GCC may for
          instance omit the load of a PIC register since it is known
          that the calling function loaded the correct value.

     ‘protected’
          Protected visibility is like default visibility except that it
          indicates that references within the defining module bind to
          the definition in that module.  That is, the declared entity
          cannot be overridden by another module.

     All visibilities are supported on many, but not all, ELF targets
     (supported when the assembler supports the ‘.visibility’
     pseudo-op).  Default visibility is supported everywhere.  Hidden
     visibility is supported on Darwin targets.

     The visibility attribute should be applied only to declarations
     that would otherwise have external linkage.  The attribute should
     be applied consistently, so that the same entity should not be
     declared with different settings of the attribute.

     In C++, the visibility attribute applies to types as well as
     functions and objects, because in C++ types have linkage.  A class
     must not have greater visibility than its non-static data member
     types and bases, and class members default to the visibility of
     their class.  Also, a declaration without explicit visibility is
     limited to the visibility of its type.

     In C++, you can mark member functions and static member variables
     of a class with the visibility attribute.  This is useful if you
     know a particular method or static member variable should only be
     used from one shared object; then you can mark it hidden while the
     rest of the class has default visibility.  Care must be taken to
     avoid breaking the One Definition Rule; for example, it is usually
     not useful to mark an inline method as hidden without marking the
     whole class as hidden.

     A C++ namespace declaration can also have the visibility attribute.

          namespace nspace1 __attribute__ ((visibility ("protected")))
          { /* Do something. */; }

     This attribute applies only to the particular namespace body, not
     to other definitions of the same namespace; it is equivalent to
     using ‘#pragma GCC visibility’ before and after the namespace
     definition (*note Visibility Pragmas::).

     In C++, if a template argument has limited visibility, this
     restriction is implicitly propagated to the template instantiation.
     Otherwise, template instantiations and specializations default to
     the visibility of their template.

     If both the template and enclosing class have explicit visibility,
     the visibility from the template is used.

‘warn_unused_result’
     The ‘warn_unused_result’ attribute causes a warning to be emitted
     if a caller of the function with this attribute does not use its
     return value.  This is useful for functions where not checking the
     result is either a security problem or always a bug, such as
     ‘realloc’.

          int fn () __attribute__ ((warn_unused_result));
          int foo ()
          {
            if (fn () < 0) return -1;
            fn ();
            return 0;
          }

     results in warning on line 5.

‘weak’
     The ‘weak’ attribute causes a declaration of an external symbol to
     be emitted as a weak symbol rather than a global.  This is
     primarily useful in defining library functions that can be
     overridden in user code, though it can also be used with
     non-function declarations.  The overriding symbol must have the
     same type as the weak symbol.  In addition, if it designates a
     variable it must also have the same size and alignment as the weak
     symbol.  Weak symbols are supported for ELF targets, and also for
     a.out targets when using the GNU assembler and linker.

‘weakref’
‘weakref ("TARGET")’
     The ‘weakref’ attribute marks a declaration as a weak reference.
     Without arguments, it should be accompanied by an ‘alias’ attribute
     naming the target symbol.  Alternatively, TARGET may be given as an
     argument to ‘weakref’ itself, naming the target definition of the
     alias.  The TARGET must have the same type as the declaration.  In
     addition, if it designates a variable it must also have the same
     size and alignment as the declaration.  In either form of the
     declaration ‘weakref’ implicitly marks the declared symbol as
     ‘weak’.  Without a TARGET given as an argument to ‘weakref’ or to
     ‘alias’, ‘weakref’ is equivalent to ‘weak’ (in that case the
     declaration may be ‘extern’).

          /* Given the declaration: */
          extern int y (void);

          /* the following... */
          static int x (void) __attribute__ ((weakref ("y")));

          /* is equivalent to... */
          static int x (void) __attribute__ ((weakref, alias ("y")));

          /* or, alternatively, to... */
          static int x (void) __attribute__ ((weakref));
          static int x (void) __attribute__ ((alias ("y")));

     A weak reference is an alias that does not by itself require a
     definition to be given for the target symbol.  If the target symbol
     is only referenced through weak references, then it becomes a
     ‘weak’ undefined symbol.  If it is directly referenced, however,
     then such strong references prevail, and a definition is required
     for the symbol, not necessarily in the same translation unit.

     The effect is equivalent to moving all references to the alias to a
     separate translation unit, renaming the alias to the aliased
     symbol, declaring it as weak, compiling the two separate
     translation units and performing a link with relocatable output
     (i.e. ‘ld -r’) on them.

     A declaration to which ‘weakref’ is attached and that is associated
     with a named ‘target’ must be ‘static’.

‘zero_call_used_regs ("CHOICE")’

     The ‘zero_call_used_regs’ attribute causes the compiler to zero a
     subset of all call-used registers(1) at function return.  This is
     used to increase program security by either mitigating
     Return-Oriented Programming (ROP) attacks or preventing information
     leakage through registers.

     In order to satisfy users with different security needs and control
     the run-time overhead at the same time, the CHOICE parameter
     provides a flexible way to choose the subset of the call-used
     registers to be zeroed.  The three basic values of CHOICE are:

        • ‘skip’ doesn't zero any call-used registers.

        • ‘used’ only zeros call-used registers that are used in the
          function.  A "used" register is one whose content has been set
          or referenced in the function.

        • ‘all’ zeros all call-used registers.

     In addition to these three basic choices, it is possible to modify
     ‘used’ or ‘all’ as follows:

        • Adding ‘-gpr’ restricts the zeroing to general-purpose
          registers.

        • Adding ‘-arg’ restricts the zeroing to registers that can
          sometimes be used to pass function arguments.  This includes
          all argument registers defined by the platform's calling
          conversion, regardless of whether the function uses those
          registers for function arguments or not.

     The modifiers can be used individually or together.  If they are
     used together, they must appear in the order above.

     The full list of CHOICEs is therefore:

     ‘skip’
          doesn't zero any call-used register.

     ‘used’
          only zeros call-used registers that are used in the function.

     ‘used-gpr’
          only zeros call-used general purpose registers that are used
          in the function.

     ‘used-arg’
          only zeros call-used registers that are used in the function
          and pass arguments.

     ‘used-gpr-arg’
          only zeros call-used general purpose registers that are used
          in the function and pass arguments.

     ‘all’
          zeros all call-used registers.

     ‘all-gpr’
          zeros all call-used general purpose registers.

     ‘all-arg’
          zeros all call-used registers that pass arguments.

     ‘all-gpr-arg’
          zeros all call-used general purpose registers that pass
          arguments.

     Of this list, ‘used-arg’, ‘used-gpr-arg’, ‘all-arg’, and
     ‘all-gpr-arg’ are mainly used for ROP mitigation.

     The default for the attribute is controlled by
     ‘-fzero-call-used-regs’.

   ---------- Footnotes ----------

   (1) A "call-used" register is a register whose contents can be
changed by a function call; therefore, a caller cannot assume that the
register has the same contents on return from the function as it had
before calling the function.  Such registers are also called
"call-clobbered", "caller-saved", or "volatile".


File: gcc.info,  Node: AArch64 Function Attributes,  Next: AMD GCN Function Attributes,  Prev: Common Function Attributes,  Up: Function Attributes

6.33.2 AArch64 Function Attributes
----------------------------------

The following target-specific function attributes are available for the
AArch64 target.  For the most part, these options mirror the behavior of
similar command-line options (*note AArch64 Options::), but on a
per-function basis.

‘general-regs-only’
     Indicates that no floating-point or Advanced SIMD registers should
     be used when generating code for this function.  If the function
     explicitly uses floating-point code, then the compiler gives an
     error.  This is the same behavior as that of the command-line
     option ‘-mgeneral-regs-only’.

‘fix-cortex-a53-835769’
     Indicates that the workaround for the Cortex-A53 erratum 835769
     should be applied to this function.  To explicitly disable the
     workaround for this function specify the negated form:
     ‘no-fix-cortex-a53-835769’.  This corresponds to the behavior of
     the command line options ‘-mfix-cortex-a53-835769’ and
     ‘-mno-fix-cortex-a53-835769’.

‘cmodel=’
     Indicates that code should be generated for a particular code model
     for this function.  The behavior and permissible arguments are the
     same as for the command line option ‘-mcmodel=’.

‘strict-align’
‘no-strict-align’
     ‘strict-align’ indicates that the compiler should not assume that
     unaligned memory references are handled by the system.  To allow
     the compiler to assume that aligned memory references are handled
     by the system, the inverse attribute ‘no-strict-align’ can be
     specified.  The behavior is same as for the command-line option
     ‘-mstrict-align’ and ‘-mno-strict-align’.

‘omit-leaf-frame-pointer’
     Indicates that the frame pointer should be omitted for a leaf
     function call.  To keep the frame pointer, the inverse attribute
     ‘no-omit-leaf-frame-pointer’ can be specified.  These attributes
     have the same behavior as the command-line options
     ‘-momit-leaf-frame-pointer’ and ‘-mno-omit-leaf-frame-pointer’.

‘tls-dialect=’
     Specifies the TLS dialect to use for this function.  The behavior
     and permissible arguments are the same as for the command-line
     option ‘-mtls-dialect=’.

‘arch=’
     Specifies the architecture version and architectural extensions to
     use for this function.  The behavior and permissible arguments are
     the same as for the ‘-march=’ command-line option.

‘tune=’
     Specifies the core for which to tune the performance of this
     function.  The behavior and permissible arguments are the same as
     for the ‘-mtune=’ command-line option.

‘cpu=’
     Specifies the core for which to tune the performance of this
     function and also whose architectural features to use.  The
     behavior and valid arguments are the same as for the ‘-mcpu=’
     command-line option.

‘sign-return-address’
     Select the function scope on which return address signing will be
     applied.  The behavior and permissible arguments are the same as
     for the command-line option ‘-msign-return-address=’.  The default
     value is ‘none’.  This attribute is deprecated.  The
     ‘branch-protection’ attribute should be used instead.

‘branch-protection’
     Select the function scope on which branch protection will be
     applied.  The behavior and permissible arguments are the same as
     for the command-line option ‘-mbranch-protection=’.  The default
     value is ‘none’.

‘outline-atomics’
     Enable or disable calls to out-of-line helpers to implement atomic
     operations.  This corresponds to the behavior of the command line
     options ‘-moutline-atomics’ and ‘-mno-outline-atomics’.

 The above target attributes can be specified as follows:

     __attribute__((target("ATTR-STRING")))
     int
     f (int a)
     {
       return a + 5;
     }

 where ‘ATTR-STRING’ is one of the attribute strings specified above.

 Additionally, the architectural extension string may be specified on
its own.  This can be used to turn on and off particular architectural
extensions without having to specify a particular architecture version
or core.  Example:

     __attribute__((target("+crc+nocrypto")))
     int
     foo (int a)
     {
       return a + 5;
     }

 In this example ‘target("+crc+nocrypto")’ enables the ‘crc’ extension
and disables the ‘crypto’ extension for the function ‘foo’ without
modifying an existing ‘-march=’ or ‘-mcpu’ option.

 Multiple target function attributes can be specified by separating them
with a comma.  For example:
     __attribute__((target("arch=armv8-a+crc+crypto,tune=cortex-a53")))
     int
     foo (int a)
     {
       return a + 5;
     }

 is valid and compiles function ‘foo’ for ARMv8-A with ‘crc’ and
‘crypto’ extensions and tunes it for ‘cortex-a53’.

6.33.2.1 Inlining rules
.......................

Specifying target attributes on individual functions or performing
link-time optimization across translation units compiled with different
target options can affect function inlining rules:

 In particular, a caller function can inline a callee function only if
the architectural features available to the callee are a subset of the
features available to the caller.  For example: A function ‘foo’
compiled with ‘-march=armv8-a+crc’, or tagged with the equivalent
‘arch=armv8-a+crc’ attribute, can inline a function ‘bar’ compiled with
‘-march=armv8-a+nocrc’ because the all the architectural features that
function ‘bar’ requires are available to function ‘foo’.  Conversely,
function ‘bar’ cannot inline function ‘foo’.

 Additionally inlining a function compiled with ‘-mstrict-align’ into a
function compiled without ‘-mstrict-align’ is not allowed.  However,
inlining a function compiled without ‘-mstrict-align’ into a function
compiled with ‘-mstrict-align’ is allowed.

 Note that CPU tuning options and attributes such as the ‘-mcpu=’,
‘-mtune=’ do not inhibit inlining unless the CPU specified by the
‘-mcpu=’ option or the ‘cpu=’ attribute conflicts with the architectural
feature rules specified above.


File: gcc.info,  Node: AMD GCN Function Attributes,  Next: ARC Function Attributes,  Prev: AArch64 Function Attributes,  Up: Function Attributes

6.33.3 AMD GCN Function Attributes
----------------------------------

These function attributes are supported by the AMD GCN back end:

‘amdgpu_hsa_kernel’
     This attribute indicates that the corresponding function should be
     compiled as a kernel function, that is an entry point that can be
     invoked from the host via the HSA runtime library.  By default
     functions are only callable only from other GCN functions.

     This attribute is implicitly applied to any function named ‘main’,
     using default parameters.

     Kernel functions may return an integer value, which will be written
     to a conventional place within the HSA "kernargs" region.

     The attribute parameters configure what values are passed into the
     kernel function by the GPU drivers, via the initial register state.
     Some values are used by the compiler, and therefore forced on.
     Enabling other options may break assumptions in the compiler and/or
     run-time libraries.

     ‘private_segment_buffer’
          Set ‘enable_sgpr_private_segment_buffer’ flag.  Always on
          (required to locate the stack).

     ‘dispatch_ptr’
          Set ‘enable_sgpr_dispatch_ptr’ flag.  Always on (required to
          locate the launch dimensions).

     ‘queue_ptr’
          Set ‘enable_sgpr_queue_ptr’ flag.  Always on (required to
          convert address spaces).

     ‘kernarg_segment_ptr’
          Set ‘enable_sgpr_kernarg_segment_ptr’ flag.  Always on
          (required to locate the kernel arguments, "kernargs").

     ‘dispatch_id’
          Set ‘enable_sgpr_dispatch_id’ flag.

     ‘flat_scratch_init’
          Set ‘enable_sgpr_flat_scratch_init’ flag.

     ‘private_segment_size’
          Set ‘enable_sgpr_private_segment_size’ flag.

     ‘grid_workgroup_count_X’
          Set ‘enable_sgpr_grid_workgroup_count_x’ flag.  Always on
          (required to use OpenACC/OpenMP).

     ‘grid_workgroup_count_Y’
          Set ‘enable_sgpr_grid_workgroup_count_y’ flag.

     ‘grid_workgroup_count_Z’
          Set ‘enable_sgpr_grid_workgroup_count_z’ flag.

     ‘workgroup_id_X’
          Set ‘enable_sgpr_workgroup_id_x’ flag.

     ‘workgroup_id_Y’
          Set ‘enable_sgpr_workgroup_id_y’ flag.

     ‘workgroup_id_Z’
          Set ‘enable_sgpr_workgroup_id_z’ flag.

     ‘workgroup_info’
          Set ‘enable_sgpr_workgroup_info’ flag.

     ‘private_segment_wave_offset’
          Set ‘enable_sgpr_private_segment_wave_byte_offset’ flag.
          Always on (required to locate the stack).

     ‘work_item_id_X’
          Set ‘enable_vgpr_workitem_id’ parameter.  Always on (can't be
          disabled).

     ‘work_item_id_Y’
          Set ‘enable_vgpr_workitem_id’ parameter.  Always on (required
          to enable vectorization.)

     ‘work_item_id_Z’
          Set ‘enable_vgpr_workitem_id’ parameter.  Always on (required
          to use OpenACC/OpenMP).


File: gcc.info,  Node: ARC Function Attributes,  Next: ARM Function Attributes,  Prev: AMD GCN Function Attributes,  Up: Function Attributes

6.33.4 ARC Function Attributes
------------------------------

These function attributes are supported by the ARC back end:

‘interrupt’
     Use this attribute to indicate that the specified function is an
     interrupt handler.  The compiler generates function entry and exit
     sequences suitable for use in an interrupt handler when this
     attribute is present.

     On the ARC, you must specify the kind of interrupt to be handled in
     a parameter to the interrupt attribute like this:

          void f () __attribute__ ((interrupt ("ilink1")));

     Permissible values for this parameter are: ‘ilink1’ and ‘ilink2’
     for ARCv1 architecture, and ‘ilink’ and ‘firq’ for ARCv2
     architecture.

‘long_call’
‘medium_call’
‘short_call’
     These attributes specify how a particular function is called.
     These attributes override the ‘-mlong-calls’ and ‘-mmedium-calls’
     (*note ARC Options::) command-line switches and ‘#pragma
     long_calls’ settings.

     For ARC, a function marked with the ‘long_call’ attribute is always
     called using register-indirect jump-and-link instructions, thereby
     enabling the called function to be placed anywhere within the
     32-bit address space.  A function marked with the ‘medium_call’
     attribute will always be close enough to be called with an
     unconditional branch-and-link instruction, which has a 25-bit
     offset from the call site.  A function marked with the ‘short_call’
     attribute will always be close enough to be called with a
     conditional branch-and-link instruction, which has a 21-bit offset
     from the call site.

‘jli_always’
     Forces a particular function to be called using ‘jli’ instruction.
     The ‘jli’ instruction makes use of a table stored into ‘.jlitab’
     section, which holds the location of the functions which are
     addressed using this instruction.

‘jli_fixed’
     Identical like the above one, but the location of the function in
     the ‘jli’ table is known and given as an attribute parameter.

‘secure_call’
     This attribute allows one to mark secure-code functions that are
     callable from normal mode.  The location of the secure call
     function into the ‘sjli’ table needs to be passed as argument.

‘naked’
     This attribute allows the compiler to construct the requisite
     function declaration, while allowing the body of the function to be
     assembly code.  The specified function will not have
     prologue/epilogue sequences generated by the compiler.  Only basic
     ‘asm’ statements can safely be included in naked functions (*note
     Basic Asm::).  While using extended ‘asm’ or a mixture of basic
     ‘asm’ and C code may appear to work, they cannot be depended upon
     to work reliably and are not supported.


File: gcc.info,  Node: ARM Function Attributes,  Next: AVR Function Attributes,  Prev: ARC Function Attributes,  Up: Function Attributes

6.33.5 ARM Function Attributes
------------------------------

These function attributes are supported for ARM targets:

‘general-regs-only’
     Indicates that no floating-point or Advanced SIMD registers should
     be used when generating code for this function.  If the function
     explicitly uses floating-point code, then the compiler gives an
     error.  This is the same behavior as that of the command-line
     option ‘-mgeneral-regs-only’.

‘interrupt’
     Use this attribute to indicate that the specified function is an
     interrupt handler.  The compiler generates function entry and exit
     sequences suitable for use in an interrupt handler when this
     attribute is present.

     You can specify the kind of interrupt to be handled by adding an
     optional parameter to the interrupt attribute like this:

          void f () __attribute__ ((interrupt ("IRQ")));

     Permissible values for this parameter are: ‘IRQ’, ‘FIQ’, ‘SWI’,
     ‘ABORT’ and ‘UNDEF’.

     On ARMv7-M the interrupt type is ignored, and the attribute means
     the function may be called with a word-aligned stack pointer.

‘isr’
     Use this attribute on ARM to write Interrupt Service Routines.
     This is an alias to the ‘interrupt’ attribute above.

‘long_call’
‘short_call’
     These attributes specify how a particular function is called.
     These attributes override the ‘-mlong-calls’ (*note ARM Options::)
     command-line switch and ‘#pragma long_calls’ settings.  For ARM,
     the ‘long_call’ attribute indicates that the function might be far
     away from the call site and require a different (more expensive)
     calling sequence.  The ‘short_call’ attribute always places the
     offset to the function from the call site into the ‘BL’ instruction
     directly.

‘naked’
     This attribute allows the compiler to construct the requisite
     function declaration, while allowing the body of the function to be
     assembly code.  The specified function will not have
     prologue/epilogue sequences generated by the compiler.  Only basic
     ‘asm’ statements can safely be included in naked functions (*note
     Basic Asm::).  While using extended ‘asm’ or a mixture of basic
     ‘asm’ and C code may appear to work, they cannot be depended upon
     to work reliably and are not supported.

‘pcs’

     The ‘pcs’ attribute can be used to control the calling convention
     used for a function on ARM. The attribute takes an argument that
     specifies the calling convention to use.

     When compiling using the AAPCS ABI (or a variant of it) then valid
     values for the argument are ‘"aapcs"’ and ‘"aapcs-vfp"’.  In order
     to use a variant other than ‘"aapcs"’ then the compiler must be
     permitted to use the appropriate co-processor registers (i.e., the
     VFP registers must be available in order to use ‘"aapcs-vfp"’).
     For example,

          /* Argument passed in r0, and result returned in r0+r1.  */
          double f2d (float) __attribute__((pcs("aapcs")));

     Variadic functions always use the ‘"aapcs"’ calling convention and
     the compiler rejects attempts to specify an alternative.

‘target (OPTIONS)’
     As discussed in *note Common Function Attributes::, this attribute
     allows specification of target-specific compilation options.

     On ARM, the following options are allowed:

     ‘thumb’
          Force code generation in the Thumb (T16/T32) ISA, depending on
          the architecture level.

     ‘arm’
          Force code generation in the ARM (A32) ISA.

          Functions from different modes can be inlined in the caller's
          mode.

     ‘fpu=’
          Specifies the fpu for which to tune the performance of this
          function.  The behavior and permissible arguments are the same
          as for the ‘-mfpu=’ command-line option.

     ‘arch=’
          Specifies the architecture version and architectural
          extensions to use for this function.  The behavior and
          permissible arguments are the same as for the ‘-march=’
          command-line option.

          The above target attributes can be specified as follows:

               __attribute__((target("arch=armv8-a+crc")))
               int
               f (int a)
               {
                 return a + 5;
               }

          Additionally, the architectural extension string may be
          specified on its own.  This can be used to turn on and off
          particular architectural extensions without having to specify
          a particular architecture version or core.  Example:

               __attribute__((target("+crc+nocrypto")))
               int
               foo (int a)
               {
                 return a + 5;
               }

          In this example ‘target("+crc+nocrypto")’ enables the ‘crc’
          extension and disables the ‘crypto’ extension for the function
          ‘foo’ without modifying an existing ‘-march=’ or ‘-mcpu’
          option.


File: gcc.info,  Node: AVR Function Attributes,  Next: Blackfin Function Attributes,  Prev: ARM Function Attributes,  Up: Function Attributes

6.33.6 AVR Function Attributes
------------------------------

These function attributes are supported by the AVR back end:

‘interrupt’
     Use this attribute to indicate that the specified function is an
     interrupt handler.  The compiler generates function entry and exit
     sequences suitable for use in an interrupt handler when this
     attribute is present.

     On the AVR, the hardware globally disables interrupts when an
     interrupt is executed.  The first instruction of an interrupt
     handler declared with this attribute is a ‘SEI’ instruction to
     re-enable interrupts.  See also the ‘signal’ function attribute
     that does not insert a ‘SEI’ instruction.  If both ‘signal’ and
     ‘interrupt’ are specified for the same function, ‘signal’ is
     silently ignored.

‘naked’
     This attribute allows the compiler to construct the requisite
     function declaration, while allowing the body of the function to be
     assembly code.  The specified function will not have
     prologue/epilogue sequences generated by the compiler.  Only basic
     ‘asm’ statements can safely be included in naked functions (*note
     Basic Asm::).  While using extended ‘asm’ or a mixture of basic
     ‘asm’ and C code may appear to work, they cannot be depended upon
     to work reliably and are not supported.

‘no_gccisr’
     Do not use ‘__gcc_isr’ pseudo instructions in a function with the
     ‘interrupt’ or ‘signal’ attribute aka.  interrupt service routine
     (ISR).  Use this attribute if the preamble of the ISR prologue
     should always read
          push  __zero_reg__
          push  __tmp_reg__
          in    __tmp_reg__, __SREG__
          push  __tmp_reg__
          clr   __zero_reg__
     and accordingly for the postamble of the epilogue -- no matter
     whether the mentioned registers are actually used in the ISR or
     not.  Situations where you might want to use this attribute
     include:
        • Code that (effectively) clobbers bits of ‘SREG’ other than the
          ‘I’-flag by writing to the memory location of ‘SREG’.
        • Code that uses inline assembler to jump to a different
          function which expects (parts of) the prologue code as
          outlined above to be present.
     To disable ‘__gcc_isr’ generation for the whole compilation unit,
     there is option ‘-mno-gas-isr-prologues’, *note AVR Options::.

‘OS_main’
‘OS_task’
     On AVR, functions with the ‘OS_main’ or ‘OS_task’ attribute do not
     save/restore any call-saved register in their prologue/epilogue.

     The ‘OS_main’ attribute can be used when there _is guarantee_ that
     interrupts are disabled at the time when the function is entered.
     This saves resources when the stack pointer has to be changed to
     set up a frame for local variables.

     The ‘OS_task’ attribute can be used when there is _no guarantee_
     that interrupts are disabled at that time when the function is
     entered like for, e.g.  task functions in a multi-threading
     operating system.  In that case, changing the stack pointer
     register is guarded by save/clear/restore of the global interrupt
     enable flag.

     The differences to the ‘naked’ function attribute are:
        • ‘naked’ functions do not have a return instruction whereas
          ‘OS_main’ and ‘OS_task’ functions have a ‘RET’ or ‘RETI’
          return instruction.
        • ‘naked’ functions do not set up a frame for local variables or
          a frame pointer whereas ‘OS_main’ and ‘OS_task’ do this as
          needed.

‘signal’
     Use this attribute on the AVR to indicate that the specified
     function is an interrupt handler.  The compiler generates function
     entry and exit sequences suitable for use in an interrupt handler
     when this attribute is present.

     See also the ‘interrupt’ function attribute.

     The AVR hardware globally disables interrupts when an interrupt is
     executed.  Interrupt handler functions defined with the ‘signal’
     attribute do not re-enable interrupts.  It is save to enable
     interrupts in a ‘signal’ handler.  This "save" only applies to the
     code generated by the compiler and not to the IRQ layout of the
     application which is responsibility of the application.

     If both ‘signal’ and ‘interrupt’ are specified for the same
     function, ‘signal’ is silently ignored.


File: gcc.info,  Node: Blackfin Function Attributes,  Next: BPF Function Attributes,  Prev: AVR Function Attributes,  Up: Function Attributes

6.33.7 Blackfin Function Attributes
-----------------------------------

These function attributes are supported by the Blackfin back end:

‘exception_handler’
     Use this attribute on the Blackfin to indicate that the specified
     function is an exception handler.  The compiler generates function
     entry and exit sequences suitable for use in an exception handler
     when this attribute is present.

‘interrupt_handler’
     Use this attribute to indicate that the specified function is an
     interrupt handler.  The compiler generates function entry and exit
     sequences suitable for use in an interrupt handler when this
     attribute is present.

‘kspisusp’
     When used together with ‘interrupt_handler’, ‘exception_handler’ or
     ‘nmi_handler’, code is generated to load the stack pointer from the
     USP register in the function prologue.

‘l1_text’
     This attribute specifies a function to be placed into L1
     Instruction SRAM.  The function is put into a specific section
     named ‘.l1.text’.  With ‘-mfdpic’, function calls with a such
     function as the callee or caller uses inlined PLT.

‘l2’
     This attribute specifies a function to be placed into L2 SRAM. The
     function is put into a specific section named ‘.l2.text’.  With
     ‘-mfdpic’, callers of such functions use an inlined PLT.

‘longcall’
‘shortcall’
     The ‘longcall’ attribute indicates that the function might be far
     away from the call site and require a different (more expensive)
     calling sequence.  The ‘shortcall’ attribute indicates that the
     function is always close enough for the shorter calling sequence to
     be used.  These attributes override the ‘-mlongcall’ switch.

‘nesting’
     Use this attribute together with ‘interrupt_handler’,
     ‘exception_handler’ or ‘nmi_handler’ to indicate that the function
     entry code should enable nested interrupts or exceptions.

‘nmi_handler’
     Use this attribute on the Blackfin to indicate that the specified
     function is an NMI handler.  The compiler generates function entry
     and exit sequences suitable for use in an NMI handler when this
     attribute is present.

‘saveall’
     Use this attribute to indicate that all registers except the stack
     pointer should be saved in the prologue regardless of whether they
     are used or not.


File: gcc.info,  Node: BPF Function Attributes,  Next: CR16 Function Attributes,  Prev: Blackfin Function Attributes,  Up: Function Attributes

6.33.8 BPF Function Attributes
------------------------------

These function attributes are supported by the BPF back end:

‘kernel_helper’
     use this attribute to indicate the specified function declaration
     is a kernel helper.  The helper function is passed as an argument
     to the attribute.  Example:

          int bpf_probe_read (void *dst, int size, const void *unsafe_ptr)
            __attribute__ ((kernel_helper (4)));


File: gcc.info,  Node: CR16 Function Attributes,  Next: C-SKY Function Attributes,  Prev: BPF Function Attributes,  Up: Function Attributes

6.33.9 CR16 Function Attributes
-------------------------------

These function attributes are supported by the CR16 back end:

‘interrupt’
     Use this attribute to indicate that the specified function is an
     interrupt handler.  The compiler generates function entry and exit
     sequences suitable for use in an interrupt handler when this
     attribute is present.


File: gcc.info,  Node: C-SKY Function Attributes,  Next: Epiphany Function Attributes,  Prev: CR16 Function Attributes,  Up: Function Attributes

6.33.10 C-SKY Function Attributes
---------------------------------

These function attributes are supported by the C-SKY back end:

‘interrupt’
‘isr’
     Use these attributes to indicate that the specified function is an
     interrupt handler.  The compiler generates function entry and exit
     sequences suitable for use in an interrupt handler when either of
     these attributes are present.

     Use of these options requires the ‘-mistack’ command-line option to
     enable support for the necessary interrupt stack instructions.
     They are ignored with a warning otherwise.  *Note C-SKY Options::.

‘naked’
     This attribute allows the compiler to construct the requisite
     function declaration, while allowing the body of the function to be
     assembly code.  The specified function will not have
     prologue/epilogue sequences generated by the compiler.  Only basic
     ‘asm’ statements can safely be included in naked functions (*note
     Basic Asm::).  While using extended ‘asm’ or a mixture of basic
     ‘asm’ and C code may appear to work, they cannot be depended upon
     to work reliably and are not supported.


File: gcc.info,  Node: Epiphany Function Attributes,  Next: H8/300 Function Attributes,  Prev: C-SKY Function Attributes,  Up: Function Attributes

6.33.11 Epiphany Function Attributes
------------------------------------

These function attributes are supported by the Epiphany back end:

‘disinterrupt’
     This attribute causes the compiler to emit instructions to disable
     interrupts for the duration of the given function.

‘forwarder_section’
     This attribute modifies the behavior of an interrupt handler.  The
     interrupt handler may be in external memory which cannot be reached
     by a branch instruction, so generate a local memory trampoline to
     transfer control.  The single parameter identifies the section
     where the trampoline is placed.

‘interrupt’
     Use this attribute to indicate that the specified function is an
     interrupt handler.  The compiler generates function entry and exit
     sequences suitable for use in an interrupt handler when this
     attribute is present.  It may also generate a special section with
     code to initialize the interrupt vector table.

     On Epiphany targets one or more optional parameters can be added
     like this:

          void __attribute__ ((interrupt ("dma0, dma1"))) universal_dma_handler ();

     Permissible values for these parameters are: ‘reset’,
     ‘software_exception’, ‘page_miss’, ‘timer0’, ‘timer1’, ‘message’,
     ‘dma0’, ‘dma1’, ‘wand’ and ‘swi’.  Multiple parameters indicate
     that multiple entries in the interrupt vector table should be
     initialized for this function, i.e. for each parameter NAME, a jump
     to the function is emitted in the section ivt_entry_NAME.  The
     parameter(s) may be omitted entirely, in which case no interrupt
     vector table entry is provided.

     Note that interrupts are enabled inside the function unless the
     ‘disinterrupt’ attribute is also specified.

     The following examples are all valid uses of these attributes on
     Epiphany targets:
          void __attribute__ ((interrupt)) universal_handler ();
          void __attribute__ ((interrupt ("dma1"))) dma1_handler ();
          void __attribute__ ((interrupt ("dma0, dma1")))
            universal_dma_handler ();
          void __attribute__ ((interrupt ("timer0"), disinterrupt))
            fast_timer_handler ();
          void __attribute__ ((interrupt ("dma0, dma1"),
                               forwarder_section ("tramp")))
            external_dma_handler ();

‘long_call’
‘short_call’
     These attributes specify how a particular function is called.
     These attributes override the ‘-mlong-calls’ (*note Adapteva
     Epiphany Options::) command-line switch and ‘#pragma long_calls’
     settings.


File: gcc.info,  Node: H8/300 Function Attributes,  Next: IA-64 Function Attributes,  Prev: Epiphany Function Attributes,  Up: Function Attributes

6.33.12 H8/300 Function Attributes
----------------------------------

These function attributes are available for H8/300 targets:

‘function_vector’
     Use this attribute on the H8/300, H8/300H, and H8S to indicate that
     the specified function should be called through the function
     vector.  Calling a function through the function vector reduces
     code size; however, the function vector has a limited size (maximum
     128 entries on the H8/300 and 64 entries on the H8/300H and H8S)
     and shares space with the interrupt vector.

‘interrupt_handler’
     Use this attribute on the H8/300, H8/300H, and H8S to indicate that
     the specified function is an interrupt handler.  The compiler
     generates function entry and exit sequences suitable for use in an
     interrupt handler when this attribute is present.

‘saveall’
     Use this attribute on the H8/300, H8/300H, and H8S to indicate that
     all registers except the stack pointer should be saved in the
     prologue regardless of whether they are used or not.


File: gcc.info,  Node: IA-64 Function Attributes,  Next: M32C Function Attributes,  Prev: H8/300 Function Attributes,  Up: Function Attributes

6.33.13 IA-64 Function Attributes
---------------------------------

These function attributes are supported on IA-64 targets:

‘syscall_linkage’
     This attribute is used to modify the IA-64 calling convention by
     marking all input registers as live at all function exits.  This
     makes it possible to restart a system call after an interrupt
     without having to save/restore the input registers.  This also
     prevents kernel data from leaking into application code.

‘version_id’
     This IA-64 HP-UX attribute, attached to a global variable or
     function, renames a symbol to contain a version string, thus
     allowing for function level versioning.  HP-UX system header files
     may use function level versioning for some system calls.

          extern int foo () __attribute__((version_id ("20040821")));

     Calls to ‘foo’ are mapped to calls to ‘foo{20040821}’.


File: gcc.info,  Node: M32C Function Attributes,  Next: M32R/D Function Attributes,  Prev: IA-64 Function Attributes,  Up: Function Attributes

6.33.14 M32C Function Attributes
--------------------------------

These function attributes are supported by the M32C back end:

‘bank_switch’
     When added to an interrupt handler with the M32C port, causes the
     prologue and epilogue to use bank switching to preserve the
     registers rather than saving them on the stack.

‘fast_interrupt’
     Use this attribute on the M32C port to indicate that the specified
     function is a fast interrupt handler.  This is just like the
     ‘interrupt’ attribute, except that ‘freit’ is used to return
     instead of ‘reit’.

‘function_vector’
     On M16C/M32C targets, the ‘function_vector’ attribute declares a
     special page subroutine call function.  Use of this attribute
     reduces the code size by 2 bytes for each call generated to the
     subroutine.  The argument to the attribute is the vector number
     entry from the special page vector table which contains the 16
     low-order bits of the subroutine's entry address.  Each vector
     table has special page number (18 to 255) that is used in ‘jsrs’
     instructions.  Jump addresses of the routines are generated by
     adding 0x0F0000 (in case of M16C targets) or 0xFF0000 (in case of
     M32C targets), to the 2-byte addresses set in the vector table.
     Therefore you need to ensure that all the special page vector
     routines should get mapped within the address range 0x0F0000 to
     0x0FFFFF (for M16C) and 0xFF0000 to 0xFFFFFF (for M32C).

     In the following example 2 bytes are saved for each call to
     function ‘foo’.

          void foo (void) __attribute__((function_vector(0x18)));
          void foo (void)
          {
          }

          void bar (void)
          {
              foo();
          }

     If functions are defined in one file and are called in another
     file, then be sure to write this declaration in both files.

     This attribute is ignored for R8C target.

‘interrupt’
     Use this attribute to indicate that the specified function is an
     interrupt handler.  The compiler generates function entry and exit
     sequences suitable for use in an interrupt handler when this
     attribute is present.


File: gcc.info,  Node: M32R/D Function Attributes,  Next: m68k Function Attributes,  Prev: M32C Function Attributes,  Up: Function Attributes

6.33.15 M32R/D Function Attributes
----------------------------------

These function attributes are supported by the M32R/D back end:

‘interrupt’
     Use this attribute to indicate that the specified function is an
     interrupt handler.  The compiler generates function entry and exit
     sequences suitable for use in an interrupt handler when this
     attribute is present.

‘model (MODEL-NAME)’

     On the M32R/D, use this attribute to set the addressability of an
     object, and of the code generated for a function.  The identifier
     MODEL-NAME is one of ‘small’, ‘medium’, or ‘large’, representing
     each of the code models.

     Small model objects live in the lower 16MB of memory (so that their
     addresses can be loaded with the ‘ld24’ instruction), and are
     callable with the ‘bl’ instruction.

     Medium model objects may live anywhere in the 32-bit address space
     (the compiler generates ‘seth/add3’ instructions to load their
     addresses), and are callable with the ‘bl’ instruction.

     Large model objects may live anywhere in the 32-bit address space
     (the compiler generates ‘seth/add3’ instructions to load their
     addresses), and may not be reachable with the ‘bl’ instruction (the
     compiler generates the much slower ‘seth/add3/jl’ instruction
     sequence).


File: gcc.info,  Node: m68k Function Attributes,  Next: MCORE Function Attributes,  Prev: M32R/D Function Attributes,  Up: Function Attributes

6.33.16 m68k Function Attributes
--------------------------------

These function attributes are supported by the m68k back end:

‘interrupt’
‘interrupt_handler’
     Use this attribute to indicate that the specified function is an
     interrupt handler.  The compiler generates function entry and exit
     sequences suitable for use in an interrupt handler when this
     attribute is present.  Either name may be used.

‘interrupt_thread’
     Use this attribute on fido, a subarchitecture of the m68k, to
     indicate that the specified function is an interrupt handler that
     is designed to run as a thread.  The compiler omits generate
     prologue/epilogue sequences and replaces the return instruction
     with a ‘sleep’ instruction.  This attribute is available only on
     fido.


File: gcc.info,  Node: MCORE Function Attributes,  Next: MeP Function Attributes,  Prev: m68k Function Attributes,  Up: Function Attributes

6.33.17 MCORE Function Attributes
---------------------------------

These function attributes are supported by the MCORE back end:

‘naked’
     This attribute allows the compiler to construct the requisite
     function declaration, while allowing the body of the function to be
     assembly code.  The specified function will not have
     prologue/epilogue sequences generated by the compiler.  Only basic
     ‘asm’ statements can safely be included in naked functions (*note
     Basic Asm::).  While using extended ‘asm’ or a mixture of basic
     ‘asm’ and C code may appear to work, they cannot be depended upon
     to work reliably and are not supported.


File: gcc.info,  Node: MeP Function Attributes,  Next: MicroBlaze Function Attributes,  Prev: MCORE Function Attributes,  Up: Function Attributes

6.33.18 MeP Function Attributes
-------------------------------

These function attributes are supported by the MeP back end:

‘disinterrupt’
     On MeP targets, this attribute causes the compiler to emit
     instructions to disable interrupts for the duration of the given
     function.

‘interrupt’
     Use this attribute to indicate that the specified function is an
     interrupt handler.  The compiler generates function entry and exit
     sequences suitable for use in an interrupt handler when this
     attribute is present.

‘near’
     This attribute causes the compiler to assume the called function is
     close enough to use the normal calling convention, overriding the
     ‘-mtf’ command-line option.

‘far’
     On MeP targets this causes the compiler to use a calling convention
     that assumes the called function is too far away for the built-in
     addressing modes.

‘vliw’
     The ‘vliw’ attribute tells the compiler to emit instructions in
     VLIW mode instead of core mode.  Note that this attribute is not
     allowed unless a VLIW coprocessor has been configured and enabled
     through command-line options.


File: gcc.info,  Node: MicroBlaze Function Attributes,  Next: Microsoft Windows Function Attributes,  Prev: MeP Function Attributes,  Up: Function Attributes

6.33.19 MicroBlaze Function Attributes
--------------------------------------

These function attributes are supported on MicroBlaze targets:

‘save_volatiles’
     Use this attribute to indicate that the function is an interrupt
     handler.  All volatile registers (in addition to non-volatile
     registers) are saved in the function prologue.  If the function is
     a leaf function, only volatiles used by the function are saved.  A
     normal function return is generated instead of a return from
     interrupt.

‘break_handler’
     Use this attribute to indicate that the specified function is a
     break handler.  The compiler generates function entry and exit
     sequences suitable for use in an break handler when this attribute
     is present.  The return from ‘break_handler’ is done through the
     ‘rtbd’ instead of ‘rtsd’.

          void f () __attribute__ ((break_handler));

‘interrupt_handler’
‘fast_interrupt’
     These attributes indicate that the specified function is an
     interrupt handler.  Use the ‘fast_interrupt’ attribute to indicate
     handlers used in low-latency interrupt mode, and
     ‘interrupt_handler’ for interrupts that do not use low-latency
     handlers.  In both cases, GCC emits appropriate prologue code and
     generates a return from the handler using ‘rtid’ instead of ‘rtsd’.


File: gcc.info,  Node: Microsoft Windows Function Attributes,  Next: MIPS Function Attributes,  Prev: MicroBlaze Function Attributes,  Up: Function Attributes

6.33.20 Microsoft Windows Function Attributes
---------------------------------------------

The following attributes are available on Microsoft Windows and Symbian
OS targets.

‘dllexport’
     On Microsoft Windows targets and Symbian OS targets the ‘dllexport’
     attribute causes the compiler to provide a global pointer to a
     pointer in a DLL, so that it can be referenced with the ‘dllimport’
     attribute.  On Microsoft Windows targets, the pointer name is
     formed by combining ‘_imp__’ and the function or variable name.

     You can use ‘__declspec(dllexport)’ as a synonym for ‘__attribute__
     ((dllexport))’ for compatibility with other compilers.

     On systems that support the ‘visibility’ attribute, this attribute
     also implies "default" visibility.  It is an error to explicitly
     specify any other visibility.

     GCC's default behavior is to emit all inline functions with the
     ‘dllexport’ attribute.  Since this can cause object file-size
     bloat, you can use ‘-fno-keep-inline-dllexport’, which tells GCC to
     ignore the attribute for inlined functions unless the
     ‘-fkeep-inline-functions’ flag is used instead.

     The attribute is ignored for undefined symbols.

     When applied to C++ classes, the attribute marks defined
     non-inlined member functions and static data members as exports.
     Static consts initialized in-class are not marked unless they are
     also defined out-of-class.

     For Microsoft Windows targets there are alternative methods for
     including the symbol in the DLL's export table such as using a
     ‘.def’ file with an ‘EXPORTS’ section or, with GNU ld, using the
     ‘--export-all’ linker flag.

‘dllimport’
     On Microsoft Windows and Symbian OS targets, the ‘dllimport’
     attribute causes the compiler to reference a function or variable
     via a global pointer to a pointer that is set up by the DLL
     exporting the symbol.  The attribute implies ‘extern’.  On
     Microsoft Windows targets, the pointer name is formed by combining
     ‘_imp__’ and the function or variable name.

     You can use ‘__declspec(dllimport)’ as a synonym for ‘__attribute__
     ((dllimport))’ for compatibility with other compilers.

     On systems that support the ‘visibility’ attribute, this attribute
     also implies "default" visibility.  It is an error to explicitly
     specify any other visibility.

     Currently, the attribute is ignored for inlined functions.  If the
     attribute is applied to a symbol _definition_, an error is
     reported.  If a symbol previously declared ‘dllimport’ is later
     defined, the attribute is ignored in subsequent references, and a
     warning is emitted.  The attribute is also overridden by a
     subsequent declaration as ‘dllexport’.

     When applied to C++ classes, the attribute marks non-inlined member
     functions and static data members as imports.  However, the
     attribute is ignored for virtual methods to allow creation of
     vtables using thunks.

     On the SH Symbian OS target the ‘dllimport’ attribute also has
     another affect--it can cause the vtable and run-time type
     information for a class to be exported.  This happens when the
     class has a dllimported constructor or a non-inline, non-pure
     virtual function and, for either of those two conditions, the class
     also has an inline constructor or destructor and has a key function
     that is defined in the current translation unit.

     For Microsoft Windows targets the use of the ‘dllimport’ attribute
     on functions is not necessary, but provides a small performance
     benefit by eliminating a thunk in the DLL.  The use of the
     ‘dllimport’ attribute on imported variables can be avoided by
     passing the ‘--enable-auto-import’ switch to the GNU linker.  As
     with functions, using the attribute for a variable eliminates a
     thunk in the DLL.

     One drawback to using this attribute is that a pointer to a
     _variable_ marked as ‘dllimport’ cannot be used as a constant
     address.  However, a pointer to a _function_ with the ‘dllimport’
     attribute can be used as a constant initializer; in this case, the
     address of a stub function in the import lib is referenced.  On
     Microsoft Windows targets, the attribute can be disabled for
     functions by setting the ‘-mnop-fun-dllimport’ flag.


File: gcc.info,  Node: MIPS Function Attributes,  Next: MSP430 Function Attributes,  Prev: Microsoft Windows Function Attributes,  Up: Function Attributes

6.33.21 MIPS Function Attributes
--------------------------------

These function attributes are supported by the MIPS back end:

‘interrupt’
     Use this attribute to indicate that the specified function is an
     interrupt handler.  The compiler generates function entry and exit
     sequences suitable for use in an interrupt handler when this
     attribute is present.  An optional argument is supported for the
     interrupt attribute which allows the interrupt mode to be
     described.  By default GCC assumes the external interrupt
     controller (EIC) mode is in use, this can be explicitly set using
     ‘eic’.  When interrupts are non-masked then the requested Interrupt
     Priority Level (IPL) is copied to the current IPL which has the
     effect of only enabling higher priority interrupts.  To use
     vectored interrupt mode use the argument
     ‘vector=[sw0|sw1|hw0|hw1|hw2|hw3|hw4|hw5]’, this will change the
     behavior of the non-masked interrupt support and GCC will arrange
     to mask all interrupts from sw0 up to and including the specified
     interrupt vector.

     You can use the following attributes to modify the behavior of an
     interrupt handler:
     ‘use_shadow_register_set’
          Assume that the handler uses a shadow register set, instead of
          the main general-purpose registers.  An optional argument
          ‘intstack’ is supported to indicate that the shadow register
          set contains a valid stack pointer.

     ‘keep_interrupts_masked’
          Keep interrupts masked for the whole function.  Without this
          attribute, GCC tries to reenable interrupts for as much of the
          function as it can.

     ‘use_debug_exception_return’
          Return using the ‘deret’ instruction.  Interrupt handlers that
          don't have this attribute return using ‘eret’ instead.

     You can use any combination of these attributes, as shown below:
          void __attribute__ ((interrupt)) v0 ();
          void __attribute__ ((interrupt, use_shadow_register_set)) v1 ();
          void __attribute__ ((interrupt, keep_interrupts_masked)) v2 ();
          void __attribute__ ((interrupt, use_debug_exception_return)) v3 ();
          void __attribute__ ((interrupt, use_shadow_register_set,
                               keep_interrupts_masked)) v4 ();
          void __attribute__ ((interrupt, use_shadow_register_set,
                               use_debug_exception_return)) v5 ();
          void __attribute__ ((interrupt, keep_interrupts_masked,
                               use_debug_exception_return)) v6 ();
          void __attribute__ ((interrupt, use_shadow_register_set,
                               keep_interrupts_masked,
                               use_debug_exception_return)) v7 ();
          void __attribute__ ((interrupt("eic"))) v8 ();
          void __attribute__ ((interrupt("vector=hw3"))) v9 ();

‘long_call’
‘short_call’
‘near’
‘far’
     These attributes specify how a particular function is called on
     MIPS.  The attributes override the ‘-mlong-calls’ (*note MIPS
     Options::) command-line switch.  The ‘long_call’ and ‘far’
     attributes are synonyms, and cause the compiler to always call the
     function by first loading its address into a register, and then
     using the contents of that register.  The ‘short_call’ and ‘near’
     attributes are synonyms, and have the opposite effect; they specify
     that non-PIC calls should be made using the more efficient ‘jal’
     instruction.

‘mips16’
‘nomips16’

     On MIPS targets, you can use the ‘mips16’ and ‘nomips16’ function
     attributes to locally select or turn off MIPS16 code generation.  A
     function with the ‘mips16’ attribute is emitted as MIPS16 code,
     while MIPS16 code generation is disabled for functions with the
     ‘nomips16’ attribute.  These attributes override the ‘-mips16’ and
     ‘-mno-mips16’ options on the command line (*note MIPS Options::).

     When compiling files containing mixed MIPS16 and non-MIPS16 code,
     the preprocessor symbol ‘__mips16’ reflects the setting on the
     command line, not that within individual functions.  Mixed MIPS16
     and non-MIPS16 code may interact badly with some GCC extensions
     such as ‘__builtin_apply’ (*note Constructing Calls::).

‘micromips, MIPS’
‘nomicromips, MIPS’

     On MIPS targets, you can use the ‘micromips’ and ‘nomicromips’
     function attributes to locally select or turn off microMIPS code
     generation.  A function with the ‘micromips’ attribute is emitted
     as microMIPS code, while microMIPS code generation is disabled for
     functions with the ‘nomicromips’ attribute.  These attributes
     override the ‘-mmicromips’ and ‘-mno-micromips’ options on the
     command line (*note MIPS Options::).

     When compiling files containing mixed microMIPS and non-microMIPS
     code, the preprocessor symbol ‘__mips_micromips’ reflects the
     setting on the command line, not that within individual functions.
     Mixed microMIPS and non-microMIPS code may interact badly with some
     GCC extensions such as ‘__builtin_apply’ (*note Constructing
     Calls::).

‘nocompression’
     On MIPS targets, you can use the ‘nocompression’ function attribute
     to locally turn off MIPS16 and microMIPS code generation.  This
     attribute overrides the ‘-mips16’ and ‘-mmicromips’ options on the
     command line (*note MIPS Options::).


File: gcc.info,  Node: MSP430 Function Attributes,  Next: NDS32 Function Attributes,  Prev: MIPS Function Attributes,  Up: Function Attributes

6.33.22 MSP430 Function Attributes
----------------------------------

These function attributes are supported by the MSP430 back end:

‘critical’
     Critical functions disable interrupts upon entry and restore the
     previous interrupt state upon exit.  Critical functions cannot also
     have the ‘naked’, ‘reentrant’ or ‘interrupt’ attributes.

     The MSP430 hardware ensures that interrupts are disabled on entry
     to ‘interrupt’ functions, and restores the previous interrupt state
     on exit.  The ‘critical’ attribute is therefore redundant on
     ‘interrupt’ functions.

‘interrupt’
     Use this attribute to indicate that the specified function is an
     interrupt handler.  The compiler generates function entry and exit
     sequences suitable for use in an interrupt handler when this
     attribute is present.

     You can provide an argument to the interrupt attribute which
     specifies a name or number.  If the argument is a number it
     indicates the slot in the interrupt vector table (0 - 31) to which
     this handler should be assigned.  If the argument is a name it is
     treated as a symbolic name for the vector slot.  These names should
     match up with appropriate entries in the linker script.  By default
     the names ‘watchdog’ for vector 26, ‘nmi’ for vector 30 and ‘reset’
     for vector 31 are recognized.

‘naked’
     This attribute allows the compiler to construct the requisite
     function declaration, while allowing the body of the function to be
     assembly code.  The specified function will not have
     prologue/epilogue sequences generated by the compiler.  Only basic
     ‘asm’ statements can safely be included in naked functions (*note
     Basic Asm::).  While using extended ‘asm’ or a mixture of basic
     ‘asm’ and C code may appear to work, they cannot be depended upon
     to work reliably and are not supported.

‘reentrant’
     Reentrant functions disable interrupts upon entry and enable them
     upon exit.  Reentrant functions cannot also have the ‘naked’ or
     ‘critical’ attributes.  They can have the ‘interrupt’ attribute.

‘wakeup’
     This attribute only applies to interrupt functions.  It is silently
     ignored if applied to a non-interrupt function.  A wakeup interrupt
     function will rouse the processor from any low-power state that it
     might be in when the function exits.

‘lower’
‘upper’
‘either’
     On the MSP430 target these attributes can be used to specify
     whether the function or variable should be placed into low memory,
     high memory, or the placement should be left to the linker to
     decide.  The attributes are only significant if compiling for the
     MSP430X architecture in the large memory model.

     The attributes work in conjunction with a linker script that has
     been augmented to specify where to place sections with a ‘.lower’
     and a ‘.upper’ prefix.  So, for example, as well as placing the
     ‘.data’ section, the script also specifies the placement of a
     ‘.lower.data’ and a ‘.upper.data’ section.  The intention is that
     ‘lower’ sections are placed into a small but easier to access
     memory region and the upper sections are placed into a larger, but
     slower to access, region.

     The ‘either’ attribute is special.  It tells the linker to place
     the object into the corresponding ‘lower’ section if there is room
     for it.  If there is insufficient room then the object is placed
     into the corresponding ‘upper’ section instead.  Note that the
     placement algorithm is not very sophisticated.  It does not attempt
     to find an optimal packing of the ‘lower’ sections.  It just makes
     one pass over the objects and does the best that it can.  Using the
     ‘-ffunction-sections’ and ‘-fdata-sections’ command-line options
     can help the packing, however, since they produce smaller, easier
     to pack regions.


File: gcc.info,  Node: NDS32 Function Attributes,  Next: Nios II Function Attributes,  Prev: MSP430 Function Attributes,  Up: Function Attributes

6.33.23 NDS32 Function Attributes
---------------------------------

These function attributes are supported by the NDS32 back end:

‘exception’
     Use this attribute on the NDS32 target to indicate that the
     specified function is an exception handler.  The compiler will
     generate corresponding sections for use in an exception handler.

‘interrupt’
     On NDS32 target, this attribute indicates that the specified
     function is an interrupt handler.  The compiler generates
     corresponding sections for use in an interrupt handler.  You can
     use the following attributes to modify the behavior:
     ‘nested’
          This interrupt service routine is interruptible.
     ‘not_nested’
          This interrupt service routine is not interruptible.
     ‘nested_ready’
          This interrupt service routine is interruptible after
          ‘PSW.GIE’ (global interrupt enable) is set.  This allows
          interrupt service routine to finish some short critical code
          before enabling interrupts.
     ‘save_all’
          The system will help save all registers into stack before
          entering interrupt handler.
     ‘partial_save’
          The system will help save caller registers into stack before
          entering interrupt handler.

‘naked’
     This attribute allows the compiler to construct the requisite
     function declaration, while allowing the body of the function to be
     assembly code.  The specified function will not have
     prologue/epilogue sequences generated by the compiler.  Only basic
     ‘asm’ statements can safely be included in naked functions (*note
     Basic Asm::).  While using extended ‘asm’ or a mixture of basic
     ‘asm’ and C code may appear to work, they cannot be depended upon
     to work reliably and are not supported.

‘reset’
     Use this attribute on the NDS32 target to indicate that the
     specified function is a reset handler.  The compiler will generate
     corresponding sections for use in a reset handler.  You can use the
     following attributes to provide extra exception handling:
     ‘nmi’
          Provide a user-defined function to handle NMI exception.
     ‘warm’
          Provide a user-defined function to handle warm reset
          exception.


File: gcc.info,  Node: Nios II Function Attributes,  Next: Nvidia PTX Function Attributes,  Prev: NDS32 Function Attributes,  Up: Function Attributes

6.33.24 Nios II Function Attributes
-----------------------------------

These function attributes are supported by the Nios II back end:

‘target (OPTIONS)’
     As discussed in *note Common Function Attributes::, this attribute
     allows specification of target-specific compilation options.

     When compiling for Nios II, the following options are allowed:

     ‘custom-INSN=N’
     ‘no-custom-INSN’
          Each ‘custom-INSN=N’ attribute locally enables use of a custom
          instruction with encoding N when generating code that uses
          INSN.  Similarly, ‘no-custom-INSN’ locally inhibits use of the
          custom instruction INSN.  These target attributes correspond
          to the ‘-mcustom-INSN=N’ and ‘-mno-custom-INSN’ command-line
          options, and support the same set of INSN keywords.  *Note
          Nios II Options::, for more information.

     ‘custom-fpu-cfg=NAME’
          This attribute corresponds to the ‘-mcustom-fpu-cfg=NAME’
          command-line option, to select a predefined set of custom
          instructions named NAME.  *Note Nios II Options::, for more
          information.


File: gcc.info,  Node: Nvidia PTX Function Attributes,  Next: PowerPC Function Attributes,  Prev: Nios II Function Attributes,  Up: Function Attributes

6.33.25 Nvidia PTX Function Attributes
--------------------------------------

These function attributes are supported by the Nvidia PTX back end:

‘kernel’
     This attribute indicates that the corresponding function should be
     compiled as a kernel function, which can be invoked from the host
     via the CUDA RT library.  By default functions are only callable
     only from other PTX functions.

     Kernel functions must have ‘void’ return type.


File: gcc.info,  Node: PowerPC Function Attributes,  Next: RISC-V Function Attributes,  Prev: Nvidia PTX Function Attributes,  Up: Function Attributes

6.33.26 PowerPC Function Attributes
-----------------------------------

These function attributes are supported by the PowerPC back end:

‘longcall’
‘shortcall’
     The ‘longcall’ attribute indicates that the function might be far
     away from the call site and require a different (more expensive)
     calling sequence.  The ‘shortcall’ attribute indicates that the
     function is always close enough for the shorter calling sequence to
     be used.  These attributes override both the ‘-mlongcall’ switch
     and the ‘#pragma longcall’ setting.

     *Note RS/6000 and PowerPC Options::, for more information on
     whether long calls are necessary.

‘target (OPTIONS)’
     As discussed in *note Common Function Attributes::, this attribute
     allows specification of target-specific compilation options.

     On the PowerPC, the following options are allowed:

     ‘altivec’
     ‘no-altivec’
          Generate code that uses (does not use) AltiVec instructions.
          In 32-bit code, you cannot enable AltiVec instructions unless
          ‘-mabi=altivec’ is used on the command line.

     ‘cmpb’
     ‘no-cmpb’
          Generate code that uses (does not use) the compare bytes
          instruction implemented on the POWER6 processor and other
          processors that support the PowerPC V2.05 architecture.

     ‘dlmzb’
     ‘no-dlmzb’
          Generate code that uses (does not use) the string-search
          ‘dlmzb’ instruction on the IBM 405, 440, 464 and 476
          processors.  This instruction is generated by default when
          targeting those processors.

     ‘fprnd’
     ‘no-fprnd’
          Generate code that uses (does not use) the FP round to integer
          instructions implemented on the POWER5+ processor and other
          processors that support the PowerPC V2.03 architecture.

     ‘hard-dfp’
     ‘no-hard-dfp’
          Generate code that uses (does not use) the decimal
          floating-point instructions implemented on some POWER
          processors.

     ‘isel’
     ‘no-isel’
          Generate code that uses (does not use) ISEL instruction.

     ‘mfcrf’
     ‘no-mfcrf’
          Generate code that uses (does not use) the move from condition
          register field instruction implemented on the POWER4 processor
          and other processors that support the PowerPC V2.01
          architecture.

     ‘mulhw’
     ‘no-mulhw’
          Generate code that uses (does not use) the half-word multiply
          and multiply-accumulate instructions on the IBM 405, 440, 464
          and 476 processors.  These instructions are generated by
          default when targeting those processors.

     ‘multiple’
     ‘no-multiple’
          Generate code that uses (does not use) the load multiple word
          instructions and the store multiple word instructions.

     ‘update’
     ‘no-update’
          Generate code that uses (does not use) the load or store
          instructions that update the base register to the address of
          the calculated memory location.

     ‘popcntb’
     ‘no-popcntb’
          Generate code that uses (does not use) the popcount and
          double-precision FP reciprocal estimate instruction
          implemented on the POWER5 processor and other processors that
          support the PowerPC V2.02 architecture.

     ‘popcntd’
     ‘no-popcntd’
          Generate code that uses (does not use) the popcount
          instruction implemented on the POWER7 processor and other
          processors that support the PowerPC V2.06 architecture.

     ‘powerpc-gfxopt’
     ‘no-powerpc-gfxopt’
          Generate code that uses (does not use) the optional PowerPC
          architecture instructions in the Graphics group, including
          floating-point select.

     ‘powerpc-gpopt’
     ‘no-powerpc-gpopt’
          Generate code that uses (does not use) the optional PowerPC
          architecture instructions in the General Purpose group,
          including floating-point square root.

     ‘recip-precision’
     ‘no-recip-precision’
          Assume (do not assume) that the reciprocal estimate
          instructions provide higher-precision estimates than is
          mandated by the PowerPC ABI.

     ‘string’
     ‘no-string’
          Generate code that uses (does not use) the load string
          instructions and the store string word instructions to save
          multiple registers and do small block moves.

     ‘vsx’
     ‘no-vsx’
          Generate code that uses (does not use) vector/scalar (VSX)
          instructions, and also enable the use of built-in functions
          that allow more direct access to the VSX instruction set.  In
          32-bit code, you cannot enable VSX or AltiVec instructions
          unless ‘-mabi=altivec’ is used on the command line.

     ‘friz’
     ‘no-friz’
          Generate (do not generate) the ‘friz’ instruction when the
          ‘-funsafe-math-optimizations’ option is used to optimize
          rounding a floating-point value to 64-bit integer and back to
          floating point.  The ‘friz’ instruction does not return the
          same value if the floating-point number is too large to fit in
          an integer.

     ‘avoid-indexed-addresses’
     ‘no-avoid-indexed-addresses’
          Generate code that tries to avoid (not avoid) the use of
          indexed load or store instructions.

     ‘paired’
     ‘no-paired’
          Generate code that uses (does not use) the generation of
          PAIRED simd instructions.

     ‘longcall’
     ‘no-longcall’
          Generate code that assumes (does not assume) that all calls
          are far away so that a longer more expensive calling sequence
          is required.

     ‘cpu=CPU’
          Specify the architecture to generate code for when compiling
          the function.  If you select the ‘target("cpu=power7")’
          attribute when generating 32-bit code, VSX and AltiVec
          instructions are not generated unless you use the
          ‘-mabi=altivec’ option on the command line.

     ‘tune=TUNE’
          Specify the architecture to tune for when compiling the
          function.  If you do not specify the ‘target("tune=TUNE")’
          attribute and you do specify the ‘target("cpu=CPU")’
          attribute, compilation tunes for the CPU architecture, and not
          the default tuning specified on the command line.

     On the PowerPC, the inliner does not inline a function that has
     different target options than the caller, unless the callee has a
     subset of the target options of the caller.


File: gcc.info,  Node: RISC-V Function Attributes,  Next: RL78 Function Attributes,  Prev: PowerPC Function Attributes,  Up: Function Attributes

6.33.27 RISC-V Function Attributes
----------------------------------

These function attributes are supported by the RISC-V back end:

‘naked’
     This attribute allows the compiler to construct the requisite
     function declaration, while allowing the body of the function to be
     assembly code.  The specified function will not have
     prologue/epilogue sequences generated by the compiler.  Only basic
     ‘asm’ statements can safely be included in naked functions (*note
     Basic Asm::).  While using extended ‘asm’ or a mixture of basic
     ‘asm’ and C code may appear to work, they cannot be depended upon
     to work reliably and are not supported.

‘interrupt’
     Use this attribute to indicate that the specified function is an
     interrupt handler.  The compiler generates function entry and exit
     sequences suitable for use in an interrupt handler when this
     attribute is present.

     You can specify the kind of interrupt to be handled by adding an
     optional parameter to the interrupt attribute like this:

          void f (void) __attribute__ ((interrupt ("user")));

     Permissible values for this parameter are ‘user’, ‘supervisor’, and
     ‘machine’.  If there is no parameter, then it defaults to
     ‘machine’.


File: gcc.info,  Node: RL78 Function Attributes,  Next: RX Function Attributes,  Prev: RISC-V Function Attributes,  Up: Function Attributes

6.33.28 RL78 Function Attributes
--------------------------------

These function attributes are supported by the RL78 back end:

‘interrupt’
‘brk_interrupt’
     These attributes indicate that the specified function is an
     interrupt handler.  The compiler generates function entry and exit
     sequences suitable for use in an interrupt handler when this
     attribute is present.

     Use ‘brk_interrupt’ instead of ‘interrupt’ for handlers intended to
     be used with the ‘BRK’ opcode (i.e. those that must end with ‘RETB’
     instead of ‘RETI’).

‘naked’
     This attribute allows the compiler to construct the requisite
     function declaration, while allowing the body of the function to be
     assembly code.  The specified function will not have
     prologue/epilogue sequences generated by the compiler.  Only basic
     ‘asm’ statements can safely be included in naked functions (*note
     Basic Asm::).  While using extended ‘asm’ or a mixture of basic
     ‘asm’ and C code may appear to work, they cannot be depended upon
     to work reliably and are not supported.


File: gcc.info,  Node: RX Function Attributes,  Next: S/390 Function Attributes,  Prev: RL78 Function Attributes,  Up: Function Attributes

6.33.29 RX Function Attributes
------------------------------

These function attributes are supported by the RX back end:

‘fast_interrupt’
     Use this attribute on the RX port to indicate that the specified
     function is a fast interrupt handler.  This is just like the
     ‘interrupt’ attribute, except that ‘freit’ is used to return
     instead of ‘reit’.

‘interrupt’
     Use this attribute to indicate that the specified function is an
     interrupt handler.  The compiler generates function entry and exit
     sequences suitable for use in an interrupt handler when this
     attribute is present.

     On RX and RL78 targets, you may specify one or more vector numbers
     as arguments to the attribute, as well as naming an alternate table
     name.  Parameters are handled sequentially, so one handler can be
     assigned to multiple entries in multiple tables.  One may also pass
     the magic string ‘"$default"’ which causes the function to be used
     for any unfilled slots in the current table.

     This example shows a simple assignment of a function to one vector
     in the default table (note that preprocessor macros may be used for
     chip-specific symbolic vector names):
          void __attribute__ ((interrupt (5))) txd1_handler ();

     This example assigns a function to two slots in the default table
     (using preprocessor macros defined elsewhere) and makes it the
     default for the ‘dct’ table:
          void __attribute__ ((interrupt (RXD1_VECT,RXD2_VECT,"dct","$default")))
          	txd1_handler ();

‘naked’
     This attribute allows the compiler to construct the requisite
     function declaration, while allowing the body of the function to be
     assembly code.  The specified function will not have
     prologue/epilogue sequences generated by the compiler.  Only basic
     ‘asm’ statements can safely be included in naked functions (*note
     Basic Asm::).  While using extended ‘asm’ or a mixture of basic
     ‘asm’ and C code may appear to work, they cannot be depended upon
     to work reliably and are not supported.

‘vector’
     This RX attribute is similar to the ‘interrupt’ attribute,
     including its parameters, but does not make the function an
     interrupt-handler type function (i.e. it retains the normal C
     function calling ABI). See the ‘interrupt’ attribute for a
     description of its arguments.


File: gcc.info,  Node: S/390 Function Attributes,  Next: SH Function Attributes,  Prev: RX Function Attributes,  Up: Function Attributes

6.33.30 S/390 Function Attributes
---------------------------------

These function attributes are supported on the S/390:

‘hotpatch (HALFWORDS-BEFORE-FUNCTION-LABEL,HALFWORDS-AFTER-FUNCTION-LABEL)’

     On S/390 System z targets, you can use this function attribute to
     make GCC generate a "hot-patching" function prologue.  If the
     ‘-mhotpatch=’ command-line option is used at the same time, the
     ‘hotpatch’ attribute takes precedence.  The first of the two
     arguments specifies the number of halfwords to be added before the
     function label.  A second argument can be used to specify the
     number of halfwords to be added after the function label.  For both
     arguments the maximum allowed value is 1000000.

     If both arguments are zero, hotpatching is disabled.

‘target (OPTIONS)’
     As discussed in *note Common Function Attributes::, this attribute
     allows specification of target-specific compilation options.

     On S/390, the following options are supported:

     ‘arch=’
     ‘tune=’
     ‘stack-guard=’
     ‘stack-size=’
     ‘branch-cost=’
     ‘warn-framesize=’
     ‘backchain’
     ‘no-backchain’
     ‘hard-dfp’
     ‘no-hard-dfp’
     ‘hard-float’
     ‘soft-float’
     ‘htm’
     ‘no-htm’
     ‘vx’
     ‘no-vx’
     ‘packed-stack’
     ‘no-packed-stack’
     ‘small-exec’
     ‘no-small-exec’
     ‘mvcle’
     ‘no-mvcle’
     ‘warn-dynamicstack’
     ‘no-warn-dynamicstack’

     The options work exactly like the S/390 specific command line
     options (without the prefix ‘-m’) except that they do not change
     any feature macros.  For example,

          target("no-vx")

     does not undefine the ‘__VEC__’ macro.


File: gcc.info,  Node: SH Function Attributes,  Next: Symbian OS Function Attributes,  Prev: S/390 Function Attributes,  Up: Function Attributes

6.33.31 SH Function Attributes
------------------------------

These function attributes are supported on the SH family of processors:

‘function_vector’
     On SH2A targets, this attribute declares a function to be called
     using the TBR relative addressing mode.  The argument to this
     attribute is the entry number of the same function in a vector
     table containing all the TBR relative addressable functions.  For
     correct operation the TBR must be setup accordingly to point to the
     start of the vector table before any functions with this attribute
     are invoked.  Usually a good place to do the initialization is the
     startup routine.  The TBR relative vector table can have at max 256
     function entries.  The jumps to these functions are generated using
     a SH2A specific, non delayed branch instruction JSR/N @(disp8,TBR).
     You must use GAS and GLD from GNU binutils version 2.7 or later for
     this attribute to work correctly.

     In an application, for a function being called once, this attribute
     saves at least 8 bytes of code; and if other successive calls are
     being made to the same function, it saves 2 bytes of code per each
     of these calls.

‘interrupt_handler’
     Use this attribute to indicate that the specified function is an
     interrupt handler.  The compiler generates function entry and exit
     sequences suitable for use in an interrupt handler when this
     attribute is present.

‘nosave_low_regs’
     Use this attribute on SH targets to indicate that an
     ‘interrupt_handler’ function should not save and restore registers
     R0..R7.  This can be used on SH3* and SH4* targets that have a
     second R0..R7 register bank for non-reentrant interrupt handlers.

‘renesas’
     On SH targets this attribute specifies that the function or struct
     follows the Renesas ABI.

‘resbank’
     On the SH2A target, this attribute enables the high-speed register
     saving and restoration using a register bank for
     ‘interrupt_handler’ routines.  Saving to the bank is performed
     automatically after the CPU accepts an interrupt that uses a
     register bank.

     The nineteen 32-bit registers comprising general register R0 to
     R14, control register GBR, and system registers MACH, MACL, and PR
     and the vector table address offset are saved into a register bank.
     Register banks are stacked in first-in last-out (FILO) sequence.
     Restoration from the bank is executed by issuing a RESBANK
     instruction.

‘sp_switch’
     Use this attribute on the SH to indicate an ‘interrupt_handler’
     function should switch to an alternate stack.  It expects a string
     argument that names a global variable holding the address of the
     alternate stack.

          void *alt_stack;
          void f () __attribute__ ((interrupt_handler,
                                    sp_switch ("alt_stack")));

‘trap_exit’
     Use this attribute on the SH for an ‘interrupt_handler’ to return
     using ‘trapa’ instead of ‘rte’.  This attribute expects an integer
     argument specifying the trap number to be used.

‘trapa_handler’
     On SH targets this function attribute is similar to
     ‘interrupt_handler’ but it does not save and restore all registers.


File: gcc.info,  Node: Symbian OS Function Attributes,  Next: V850 Function Attributes,  Prev: SH Function Attributes,  Up: Function Attributes

6.33.32 Symbian OS Function Attributes
--------------------------------------

*Note Microsoft Windows Function Attributes::, for discussion of the
‘dllexport’ and ‘dllimport’ attributes.


File: gcc.info,  Node: V850 Function Attributes,  Next: Visium Function Attributes,  Prev: Symbian OS Function Attributes,  Up: Function Attributes

6.33.33 V850 Function Attributes
--------------------------------

The V850 back end supports these function attributes:

‘interrupt’
‘interrupt_handler’
     Use these attributes to indicate that the specified function is an
     interrupt handler.  The compiler generates function entry and exit
     sequences suitable for use in an interrupt handler when either
     attribute is present.


File: gcc.info,  Node: Visium Function Attributes,  Next: x86 Function Attributes,  Prev: V850 Function Attributes,  Up: Function Attributes

6.33.34 Visium Function Attributes
----------------------------------

These function attributes are supported by the Visium back end:

‘interrupt’
     Use this attribute to indicate that the specified function is an
     interrupt handler.  The compiler generates function entry and exit
     sequences suitable for use in an interrupt handler when this
     attribute is present.


File: gcc.info,  Node: x86 Function Attributes,  Next: Xstormy16 Function Attributes,  Prev: Visium Function Attributes,  Up: Function Attributes

6.33.35 x86 Function Attributes
-------------------------------

These function attributes are supported by the x86 back end:

‘cdecl’
     On the x86-32 targets, the ‘cdecl’ attribute causes the compiler to
     assume that the calling function pops off the stack space used to
     pass arguments.  This is useful to override the effects of the
     ‘-mrtd’ switch.

‘fastcall’
     On x86-32 targets, the ‘fastcall’ attribute causes the compiler to
     pass the first argument (if of integral type) in the register ECX
     and the second argument (if of integral type) in the register EDX.
     Subsequent and other typed arguments are passed on the stack.  The
     called function pops the arguments off the stack.  If the number of
     arguments is variable all arguments are pushed on the stack.

‘thiscall’
     On x86-32 targets, the ‘thiscall’ attribute causes the compiler to
     pass the first argument (if of integral type) in the register ECX.
     Subsequent and other typed arguments are passed on the stack.  The
     called function pops the arguments off the stack.  If the number of
     arguments is variable all arguments are pushed on the stack.  The
     ‘thiscall’ attribute is intended for C++ non-static member
     functions.  As a GCC extension, this calling convention can be used
     for C functions and for static member methods.

‘ms_abi’
‘sysv_abi’

     On 32-bit and 64-bit x86 targets, you can use an ABI attribute to
     indicate which calling convention should be used for a function.
     The ‘ms_abi’ attribute tells the compiler to use the Microsoft ABI,
     while the ‘sysv_abi’ attribute tells the compiler to use the System
     V ELF ABI, which is used on GNU/Linux and other systems.  The
     default is to use the Microsoft ABI when targeting Windows.  On all
     other systems, the default is the System V ELF ABI.

     Note, the ‘ms_abi’ attribute for Microsoft Windows 64-bit targets
     currently requires the ‘-maccumulate-outgoing-args’ option.

‘callee_pop_aggregate_return (NUMBER)’

     On x86-32 targets, you can use this attribute to control how
     aggregates are returned in memory.  If the caller is responsible
     for popping the hidden pointer together with the rest of the
     arguments, specify NUMBER equal to zero.  If callee is responsible
     for popping the hidden pointer, specify NUMBER equal to one.

     The default x86-32 ABI assumes that the callee pops the stack for
     hidden pointer.  However, on x86-32 Microsoft Windows targets, the
     compiler assumes that the caller pops the stack for hidden pointer.

‘ms_hook_prologue’

     On 32-bit and 64-bit x86 targets, you can use this function
     attribute to make GCC generate the "hot-patching" function prologue
     used in Win32 API functions in Microsoft Windows XP Service Pack 2
     and newer.

‘naked’
     This attribute allows the compiler to construct the requisite
     function declaration, while allowing the body of the function to be
     assembly code.  The specified function will not have
     prologue/epilogue sequences generated by the compiler.  Only basic
     ‘asm’ statements can safely be included in naked functions (*note
     Basic Asm::).  While using extended ‘asm’ or a mixture of basic
     ‘asm’ and C code may appear to work, they cannot be depended upon
     to work reliably and are not supported.

‘regparm (NUMBER)’
     On x86-32 targets, the ‘regparm’ attribute causes the compiler to
     pass arguments number one to NUMBER if they are of integral type in
     registers EAX, EDX, and ECX instead of on the stack.  Functions
     that take a variable number of arguments continue to be passed all
     of their arguments on the stack.

     Beware that on some ELF systems this attribute is unsuitable for
     global functions in shared libraries with lazy binding (which is
     the default).  Lazy binding sends the first call via resolving code
     in the loader, which might assume EAX, EDX and ECX can be
     clobbered, as per the standard calling conventions.  Solaris 8 is
     affected by this.  Systems with the GNU C Library version 2.1 or
     higher and FreeBSD are believed to be safe since the loaders there
     save EAX, EDX and ECX. (Lazy binding can be disabled with the
     linker or the loader if desired, to avoid the problem.)

‘sseregparm’
     On x86-32 targets with SSE support, the ‘sseregparm’ attribute
     causes the compiler to pass up to 3 floating-point arguments in SSE
     registers instead of on the stack.  Functions that take a variable
     number of arguments continue to pass all of their floating-point
     arguments on the stack.

‘force_align_arg_pointer’
     On x86 targets, the ‘force_align_arg_pointer’ attribute may be
     applied to individual function definitions, generating an alternate
     prologue and epilogue that realigns the run-time stack if
     necessary.  This supports mixing legacy codes that run with a
     4-byte aligned stack with modern codes that keep a 16-byte stack
     for SSE compatibility.

‘stdcall’
     On x86-32 targets, the ‘stdcall’ attribute causes the compiler to
     assume that the called function pops off the stack space used to
     pass arguments, unless it takes a variable number of arguments.

‘no_caller_saved_registers’
     Use this attribute to indicate that the specified function has no
     caller-saved registers.  That is, all registers are callee-saved.
     For example, this attribute can be used for a function called from
     an interrupt handler.  The compiler generates proper function entry
     and exit sequences to save and restore any modified registers,
     except for the EFLAGS register.  Since GCC doesn't preserve SSE,
     MMX nor x87 states, the GCC option ‘-mgeneral-regs-only’ should be
     used to compile functions with ‘no_caller_saved_registers’
     attribute.

‘interrupt’
     Use this attribute to indicate that the specified function is an
     interrupt handler or an exception handler (depending on parameters
     passed to the function, explained further).  The compiler generates
     function entry and exit sequences suitable for use in an interrupt
     handler when this attribute is present.  The ‘IRET’ instruction,
     instead of the ‘RET’ instruction, is used to return from interrupt
     handlers.  All registers, except for the EFLAGS register which is
     restored by the ‘IRET’ instruction, are preserved by the compiler.
     Since GCC doesn't preserve SSE, MMX nor x87 states, the GCC option
     ‘-mgeneral-regs-only’ should be used to compile interrupt and
     exception handlers.

     Any interruptible-without-stack-switch code must be compiled with
     ‘-mno-red-zone’ since interrupt handlers can and will, because of
     the hardware design, touch the red zone.

     An interrupt handler must be declared with a mandatory pointer
     argument:

          struct interrupt_frame;

          __attribute__ ((interrupt))
          void
          f (struct interrupt_frame *frame)
          {
          }

     and you must define ‘struct interrupt_frame’ as described in the
     processor's manual.

     Exception handlers differ from interrupt handlers because the
     system pushes an error code on the stack.  An exception handler
     declaration is similar to that for an interrupt handler, but with a
     different mandatory function signature.  The compiler arranges to
     pop the error code off the stack before the ‘IRET’ instruction.

          #ifdef __x86_64__
          typedef unsigned long long int uword_t;
          #else
          typedef unsigned int uword_t;
          #endif

          struct interrupt_frame;

          __attribute__ ((interrupt))
          void
          f (struct interrupt_frame *frame, uword_t error_code)
          {
            ...
          }

     Exception handlers should only be used for exceptions that push an
     error code; you should use an interrupt handler in other cases.
     The system will crash if the wrong kind of handler is used.

‘target (OPTIONS)’
     As discussed in *note Common Function Attributes::, this attribute
     allows specification of target-specific compilation options.

     On the x86, the following options are allowed:
     ‘3dnow’
     ‘no-3dnow’
          Enable/disable the generation of the 3DNow! instructions.

     ‘3dnowa’
     ‘no-3dnowa’
          Enable/disable the generation of the enhanced 3DNow!
          instructions.

     ‘abm’
     ‘no-abm’
          Enable/disable the generation of the advanced bit
          instructions.

     ‘adx’
     ‘no-adx’
          Enable/disable the generation of the ADX instructions.

     ‘aes’
     ‘no-aes’
          Enable/disable the generation of the AES instructions.

     ‘avx’
     ‘no-avx’
          Enable/disable the generation of the AVX instructions.

     ‘avx2’
     ‘no-avx2’
          Enable/disable the generation of the AVX2 instructions.

     ‘avx5124fmaps’
     ‘no-avx5124fmaps’
          Enable/disable the generation of the AVX5124FMAPS
          instructions.

     ‘avx5124vnniw’
     ‘no-avx5124vnniw’
          Enable/disable the generation of the AVX5124VNNIW
          instructions.

     ‘avx512bitalg’
     ‘no-avx512bitalg’
          Enable/disable the generation of the AVX512BITALG
          instructions.

     ‘avx512bw’
     ‘no-avx512bw’
          Enable/disable the generation of the AVX512BW instructions.

     ‘avx512cd’
     ‘no-avx512cd’
          Enable/disable the generation of the AVX512CD instructions.

     ‘avx512dq’
     ‘no-avx512dq’
          Enable/disable the generation of the AVX512DQ instructions.

     ‘avx512er’
     ‘no-avx512er’
          Enable/disable the generation of the AVX512ER instructions.

     ‘avx512f’
     ‘no-avx512f’
          Enable/disable the generation of the AVX512F instructions.

     ‘avx512ifma’
     ‘no-avx512ifma’
          Enable/disable the generation of the AVX512IFMA instructions.

     ‘avx512pf’
     ‘no-avx512pf’
          Enable/disable the generation of the AVX512PF instructions.

     ‘avx512vbmi’
     ‘no-avx512vbmi’
          Enable/disable the generation of the AVX512VBMI instructions.

     ‘avx512vbmi2’
     ‘no-avx512vbmi2’
          Enable/disable the generation of the AVX512VBMI2 instructions.

     ‘avx512vl’
     ‘no-avx512vl’
          Enable/disable the generation of the AVX512VL instructions.

     ‘avx512vnni’
     ‘no-avx512vnni’
          Enable/disable the generation of the AVX512VNNI instructions.

     ‘avx512vpopcntdq’
     ‘no-avx512vpopcntdq’
          Enable/disable the generation of the AVX512VPOPCNTDQ
          instructions.

     ‘bmi’
     ‘no-bmi’
          Enable/disable the generation of the BMI instructions.

     ‘bmi2’
     ‘no-bmi2’
          Enable/disable the generation of the BMI2 instructions.

     ‘cldemote’
     ‘no-cldemote’
          Enable/disable the generation of the CLDEMOTE instructions.

     ‘clflushopt’
     ‘no-clflushopt’
          Enable/disable the generation of the CLFLUSHOPT instructions.

     ‘clwb’
     ‘no-clwb’
          Enable/disable the generation of the CLWB instructions.

     ‘clzero’
     ‘no-clzero’
          Enable/disable the generation of the CLZERO instructions.

     ‘crc32’
     ‘no-crc32’
          Enable/disable the generation of the CRC32 instructions.

     ‘cx16’
     ‘no-cx16’
          Enable/disable the generation of the CMPXCHG16B instructions.

     ‘default’
          *Note Function Multiversioning::, where it is used to specify
          the default function version.

     ‘f16c’
     ‘no-f16c’
          Enable/disable the generation of the F16C instructions.

     ‘fma’
     ‘no-fma’
          Enable/disable the generation of the FMA instructions.

     ‘fma4’
     ‘no-fma4’
          Enable/disable the generation of the FMA4 instructions.

     ‘fsgsbase’
     ‘no-fsgsbase’
          Enable/disable the generation of the FSGSBASE instructions.

     ‘fxsr’
     ‘no-fxsr’
          Enable/disable the generation of the FXSR instructions.

     ‘gfni’
     ‘no-gfni’
          Enable/disable the generation of the GFNI instructions.

     ‘hle’
     ‘no-hle’
          Enable/disable the generation of the HLE instruction prefixes.

     ‘lwp’
     ‘no-lwp’
          Enable/disable the generation of the LWP instructions.

     ‘lzcnt’
     ‘no-lzcnt’
          Enable/disable the generation of the LZCNT instructions.

     ‘mmx’
     ‘no-mmx’
          Enable/disable the generation of the MMX instructions.

     ‘movbe’
     ‘no-movbe’
          Enable/disable the generation of the MOVBE instructions.

     ‘movdir64b’
     ‘no-movdir64b’
          Enable/disable the generation of the MOVDIR64B instructions.

     ‘movdiri’
     ‘no-movdiri’
          Enable/disable the generation of the MOVDIRI instructions.

     ‘mwait’
     ‘no-mwait’
          Enable/disable the generation of the MWAIT and MONITOR
          instructions.

     ‘mwaitx’
     ‘no-mwaitx’
          Enable/disable the generation of the MWAITX instructions.

     ‘pclmul’
     ‘no-pclmul’
          Enable/disable the generation of the PCLMUL instructions.

     ‘pconfig’
     ‘no-pconfig’
          Enable/disable the generation of the PCONFIG instructions.

     ‘pku’
     ‘no-pku’
          Enable/disable the generation of the PKU instructions.

     ‘popcnt’
     ‘no-popcnt’
          Enable/disable the generation of the POPCNT instruction.

     ‘prefetchwt1’
     ‘no-prefetchwt1’
          Enable/disable the generation of the PREFETCHWT1 instructions.

     ‘prfchw’
     ‘no-prfchw’
          Enable/disable the generation of the PREFETCHW instruction.

     ‘ptwrite’
     ‘no-ptwrite’
          Enable/disable the generation of the PTWRITE instructions.

     ‘rdpid’
     ‘no-rdpid’
          Enable/disable the generation of the RDPID instructions.

     ‘rdrnd’
     ‘no-rdrnd’
          Enable/disable the generation of the RDRND instructions.

     ‘rdseed’
     ‘no-rdseed’
          Enable/disable the generation of the RDSEED instructions.

     ‘rtm’
     ‘no-rtm’
          Enable/disable the generation of the RTM instructions.

     ‘sahf’
     ‘no-sahf’
          Enable/disable the generation of the SAHF instructions.

     ‘sgx’
     ‘no-sgx’
          Enable/disable the generation of the SGX instructions.

     ‘sha’
     ‘no-sha’
          Enable/disable the generation of the SHA instructions.

     ‘shstk’
     ‘no-shstk’
          Enable/disable the shadow stack built-in functions from CET.

     ‘sse’
     ‘no-sse’
          Enable/disable the generation of the SSE instructions.

     ‘sse2’
     ‘no-sse2’
          Enable/disable the generation of the SSE2 instructions.

     ‘sse3’
     ‘no-sse3’
          Enable/disable the generation of the SSE3 instructions.

     ‘sse4’
     ‘no-sse4’
          Enable/disable the generation of the SSE4 instructions (both
          SSE4.1 and SSE4.2).

     ‘sse4.1’
     ‘no-sse4.1’
          Enable/disable the generation of the SSE4.1 instructions.

     ‘sse4.2’
     ‘no-sse4.2’
          Enable/disable the generation of the SSE4.2 instructions.

     ‘sse4a’
     ‘no-sse4a’
          Enable/disable the generation of the SSE4A instructions.

     ‘ssse3’
     ‘no-ssse3’
          Enable/disable the generation of the SSSE3 instructions.

     ‘tbm’
     ‘no-tbm’
          Enable/disable the generation of the TBM instructions.

     ‘vaes’
     ‘no-vaes’
          Enable/disable the generation of the VAES instructions.

     ‘vpclmulqdq’
     ‘no-vpclmulqdq’
          Enable/disable the generation of the VPCLMULQDQ instructions.

     ‘waitpkg’
     ‘no-waitpkg’
          Enable/disable the generation of the WAITPKG instructions.

     ‘wbnoinvd’
     ‘no-wbnoinvd’
          Enable/disable the generation of the WBNOINVD instructions.

     ‘xop’
     ‘no-xop’
          Enable/disable the generation of the XOP instructions.

     ‘xsave’
     ‘no-xsave’
          Enable/disable the generation of the XSAVE instructions.

     ‘xsavec’
     ‘no-xsavec’
          Enable/disable the generation of the XSAVEC instructions.

     ‘xsaveopt’
     ‘no-xsaveopt’
          Enable/disable the generation of the XSAVEOPT instructions.

     ‘xsaves’
     ‘no-xsaves’
          Enable/disable the generation of the XSAVES instructions.

     ‘amx-tile’
     ‘no-amx-tile’
          Enable/disable the generation of the AMX-TILE instructions.

     ‘amx-int8’
     ‘no-amx-int8’
          Enable/disable the generation of the AMX-INT8 instructions.

     ‘amx-bf16’
     ‘no-amx-bf16’
          Enable/disable the generation of the AMX-BF16 instructions.

     ‘uintr’
     ‘no-uintr’
          Enable/disable the generation of the UINTR instructions.

     ‘hreset’
     ‘no-hreset’
          Enable/disable the generation of the HRESET instruction.

     ‘kl’
     ‘no-kl’
          Enable/disable the generation of the KEYLOCKER instructions.

     ‘widekl’
     ‘no-widekl’
          Enable/disable the generation of the WIDEKL instructions.

     ‘avxvnni’
     ‘no-avxvnni’
          Enable/disable the generation of the AVXVNNI instructions.

     ‘cld’
     ‘no-cld’
          Enable/disable the generation of the CLD before string moves.

     ‘fancy-math-387’
     ‘no-fancy-math-387’
          Enable/disable the generation of the ‘sin’, ‘cos’, and ‘sqrt’
          instructions on the 387 floating-point unit.

     ‘ieee-fp’
     ‘no-ieee-fp’
          Enable/disable the generation of floating point that depends
          on IEEE arithmetic.

     ‘inline-all-stringops’
     ‘no-inline-all-stringops’
          Enable/disable inlining of string operations.

     ‘inline-stringops-dynamically’
     ‘no-inline-stringops-dynamically’
          Enable/disable the generation of the inline code to do small
          string operations and calling the library routines for large
          operations.

     ‘align-stringops’
     ‘no-align-stringops’
          Do/do not align destination of inlined string operations.

     ‘recip’
     ‘no-recip’
          Enable/disable the generation of RCPSS, RCPPS, RSQRTSS and
          RSQRTPS instructions followed an additional Newton-Raphson
          step instead of doing a floating-point division.

     ‘general-regs-only’
          Generate code which uses only the general registers.

     ‘arch=ARCH’
          Specify the architecture to generate code for in compiling the
          function.

     ‘tune=TUNE’
          Specify the architecture to tune for in compiling the
          function.

     ‘fpmath=FPMATH’
          Specify which floating-point unit to use.  You must specify
          the ‘target("fpmath=sse,387")’ option as
          ‘target("fpmath=sse+387")’ because the comma would separate
          different options.

     ‘prefer-vector-width=OPT’
          On x86 targets, the ‘prefer-vector-width’ attribute informs
          the compiler to use OPT-bit vector width in instructions
          instead of the default on the selected platform.

          Valid OPT values are:

          ‘none’
               No extra limitations applied to GCC other than defined by
               the selected platform.

          ‘128’
               Prefer 128-bit vector width for instructions.

          ‘256’
               Prefer 256-bit vector width for instructions.

          ‘512’
               Prefer 512-bit vector width for instructions.

          On the x86, the inliner does not inline a function that has
          different target options than the caller, unless the callee
          has a subset of the target options of the caller.  For example
          a function declared with ‘target("sse3")’ can inline a
          function with ‘target("sse2")’, since ‘-msse3’ implies
          ‘-msse2’.

‘indirect_branch("CHOICE")’
     On x86 targets, the ‘indirect_branch’ attribute causes the compiler
     to convert indirect call and jump with CHOICE.  ‘keep’ keeps
     indirect call and jump unmodified.  ‘thunk’ converts indirect call
     and jump to call and return thunk.  ‘thunk-inline’ converts
     indirect call and jump to inlined call and return thunk.
     ‘thunk-extern’ converts indirect call and jump to external call and
     return thunk provided in a separate object file.

‘function_return("CHOICE")’
     On x86 targets, the ‘function_return’ attribute causes the compiler
     to convert function return with CHOICE.  ‘keep’ keeps function
     return unmodified.  ‘thunk’ converts function return to call and
     return thunk.  ‘thunk-inline’ converts function return to inlined
     call and return thunk.  ‘thunk-extern’ converts function return to
     external call and return thunk provided in a separate object file.

‘nocf_check’
     The ‘nocf_check’ attribute on a function is used to inform the
     compiler that the function's prologue should not be instrumented
     when compiled with the ‘-fcf-protection=branch’ option.  The
     compiler assumes that the function's address is a valid target for
     a control-flow transfer.

     The ‘nocf_check’ attribute on a type of pointer to function is used
     to inform the compiler that a call through the pointer should not
     be instrumented when compiled with the ‘-fcf-protection=branch’
     option.  The compiler assumes that the function's address from the
     pointer is a valid target for a control-flow transfer.  A direct
     function call through a function name is assumed to be a safe call
     thus direct calls are not instrumented by the compiler.

     The ‘nocf_check’ attribute is applied to an object's type.  In case
     of assignment of a function address or a function pointer to
     another pointer, the attribute is not carried over from the
     right-hand object's type; the type of left-hand object stays
     unchanged.  The compiler checks for ‘nocf_check’ attribute mismatch
     and reports a warning in case of mismatch.

          {
          int foo (void) __attribute__(nocf_check);
          void (*foo1)(void) __attribute__(nocf_check);
          void (*foo2)(void);

          /* foo's address is assumed to be valid.  */
          int
          foo (void)

            /* This call site is not checked for control-flow
               validity.  */
            (*foo1)();

            /* A warning is issued about attribute mismatch.  */
            foo1 = foo2;

            /* This call site is still not checked.  */
            (*foo1)();

            /* This call site is checked.  */
            (*foo2)();

            /* A warning is issued about attribute mismatch.  */
            foo2 = foo1;

            /* This call site is still checked.  */
            (*foo2)();

            return 0;
          }

‘cf_check’

     The ‘cf_check’ attribute on a function is used to inform the
     compiler that ENDBR instruction should be placed at the function
     entry when ‘-fcf-protection=branch’ is enabled.

‘indirect_return’

     The ‘indirect_return’ attribute can be applied to a function, as
     well as variable or type of function pointer to inform the compiler
     that the function may return via indirect branch.

‘fentry_name("NAME")’
     On x86 targets, the ‘fentry_name’ attribute sets the function to
     call on function entry when function instrumentation is enabled
     with ‘-pg -mfentry’.  When NAME is nop then a 5 byte nop sequence
     is generated.

‘fentry_section("NAME")’
     On x86 targets, the ‘fentry_section’ attribute sets the name of the
     section to record function entry instrumentation calls in when
     enabled with ‘-pg -mrecord-mcount’

‘nodirect_extern_access’
     This attribute, attached to a global variable or function, is the
     counterpart to option ‘-mno-direct-extern-access’.


File: gcc.info,  Node: Xstormy16 Function Attributes,  Prev: x86 Function Attributes,  Up: Function Attributes

6.33.36 Xstormy16 Function Attributes
-------------------------------------

These function attributes are supported by the Xstormy16 back end:

‘interrupt’
     Use this attribute to indicate that the specified function is an
     interrupt handler.  The compiler generates function entry and exit
     sequences suitable for use in an interrupt handler when this
     attribute is present.


File: gcc.info,  Node: Variable Attributes,  Next: Type Attributes,  Prev: Function Attributes,  Up: C Extensions

6.34 Specifying Attributes of Variables
=======================================

The keyword ‘__attribute__’ allows you to specify special properties of
variables, function parameters, or structure, union, and, in C++, class
members.  This ‘__attribute__’ keyword is followed by an attribute
specification enclosed in double parentheses.  Some attributes are
currently defined generically for variables.  Other attributes are
defined for variables on particular target systems.  Other attributes
are available for functions (*note Function Attributes::), labels (*note
Label Attributes::), enumerators (*note Enumerator Attributes::),
statements (*note Statement Attributes::), and for types (*note Type
Attributes::).  Other front ends might define more attributes (*note
Extensions to the C++ Language: C++ Extensions.).

 *Note Attribute Syntax::, for details of the exact syntax for using
attributes.

* Menu:

* Common Variable Attributes::
* ARC Variable Attributes::
* AVR Variable Attributes::
* Blackfin Variable Attributes::
* H8/300 Variable Attributes::
* IA-64 Variable Attributes::
* M32R/D Variable Attributes::
* MeP Variable Attributes::
* Microsoft Windows Variable Attributes::
* MSP430 Variable Attributes::
* Nvidia PTX Variable Attributes::
* PowerPC Variable Attributes::
* RL78 Variable Attributes::
* V850 Variable Attributes::
* x86 Variable Attributes::
* Xstormy16 Variable Attributes::


File: gcc.info,  Node: Common Variable Attributes,  Next: ARC Variable Attributes,  Up: Variable Attributes

6.34.1 Common Variable Attributes
---------------------------------

The following attributes are supported on most targets.

‘alias ("TARGET")’
     The ‘alias’ variable attribute causes the declaration to be emitted
     as an alias for another symbol known as an “alias target”.  Except
     for top-level qualifiers the alias target must have the same type
     as the alias.  For instance, the following

          int var_target;
          extern int __attribute__ ((alias ("var_target"))) var_alias;

     defines ‘var_alias’ to be an alias for the ‘var_target’ variable.

     It is an error if the alias target is not defined in the same
     translation unit as the alias.

     Note that in the absence of the attribute GCC assumes that distinct
     declarations with external linkage denote distinct objects.  Using
     both the alias and the alias target to access the same object is
     undefined in a translation unit without a declaration of the alias
     with the attribute.

     This attribute requires assembler and object file support, and may
     not be available on all targets.

‘aligned’
‘aligned (ALIGNMENT)’
     The ‘aligned’ attribute specifies a minimum alignment for the
     variable or structure field, measured in bytes.  When specified,
     ALIGNMENT must be an integer constant power of 2.  Specifying no
     ALIGNMENT argument implies the maximum alignment for the target,
     which is often, but by no means always, 8 or 16 bytes.

     For example, the declaration:

          int x __attribute__ ((aligned (16))) = 0;

     causes the compiler to allocate the global variable ‘x’ on a
     16-byte boundary.  On a 68040, this could be used in conjunction
     with an ‘asm’ expression to access the ‘move16’ instruction which
     requires 16-byte aligned operands.

     You can also specify the alignment of structure fields.  For
     example, to create a double-word aligned ‘int’ pair, you could
     write:

          struct foo { int x[2] __attribute__ ((aligned (8))); };

     This is an alternative to creating a union with a ‘double’ member,
     which forces the union to be double-word aligned.

     As in the preceding examples, you can explicitly specify the
     alignment (in bytes) that you wish the compiler to use for a given
     variable or structure field.  Alternatively, you can leave out the
     alignment factor and just ask the compiler to align a variable or
     field to the default alignment for the target architecture you are
     compiling for.  The default alignment is sufficient for all scalar
     types, but may not be enough for all vector types on a target that
     supports vector operations.  The default alignment is fixed for a
     particular target ABI.

     GCC also provides a target specific macro ‘__BIGGEST_ALIGNMENT__’,
     which is the largest alignment ever used for any data type on the
     target machine you are compiling for.  For example, you could
     write:

          short array[3] __attribute__ ((aligned (__BIGGEST_ALIGNMENT__)));

     The compiler automatically sets the alignment for the declared
     variable or field to ‘__BIGGEST_ALIGNMENT__’.  Doing this can often
     make copy operations more efficient, because the compiler can use
     whatever instructions copy the biggest chunks of memory when
     performing copies to or from the variables or fields that you have
     aligned this way.  Note that the value of ‘__BIGGEST_ALIGNMENT__’
     may change depending on command-line options.

     When used on a struct, or struct member, the ‘aligned’ attribute
     can only increase the alignment; in order to decrease it, the
     ‘packed’ attribute must be specified as well.  When used as part of
     a typedef, the ‘aligned’ attribute can both increase and decrease
     alignment, and specifying the ‘packed’ attribute generates a
     warning.

     Note that the effectiveness of ‘aligned’ attributes for static
     variables may be limited by inherent limitations in the system
     linker and/or object file format.  On some systems, the linker is
     only able to arrange for variables to be aligned up to a certain
     maximum alignment.  (For some linkers, the maximum supported
     alignment may be very very small.)  If your linker is only able to
     align variables up to a maximum of 8-byte alignment, then
     specifying ‘aligned(16)’ in an ‘__attribute__’ still only provides
     you with 8-byte alignment.  See your linker documentation for
     further information.

     Stack variables are not affected by linker restrictions; GCC can
     properly align them on any target.

     The ‘aligned’ attribute can also be used for functions (*note
     Common Function Attributes::.)

‘warn_if_not_aligned (ALIGNMENT)’
     This attribute specifies a threshold for the structure field,
     measured in bytes.  If the structure field is aligned below the
     threshold, a warning will be issued.  For example, the declaration:

          struct foo
          {
            int i1;
            int i2;
            unsigned long long x __attribute__ ((warn_if_not_aligned (16)));
          };

     causes the compiler to issue an warning on ‘struct foo’, like
     ‘warning: alignment 8 of 'struct foo' is less than 16’.  The
     compiler also issues a warning, like ‘warning: 'x' offset 8 in
     'struct foo' isn't aligned to 16’, when the structure field has the
     misaligned offset:

          struct __attribute__ ((aligned (16))) foo
          {
            int i1;
            int i2;
            unsigned long long x __attribute__ ((warn_if_not_aligned (16)));
          };

     This warning can be disabled by ‘-Wno-if-not-aligned’.  The
     ‘warn_if_not_aligned’ attribute can also be used for types (*note
     Common Type Attributes::.)

‘alloc_size (POSITION)’
‘alloc_size (POSITION-1, POSITION-2)’
     The ‘alloc_size’ variable attribute may be applied to the
     declaration of a pointer to a function that returns a pointer and
     takes at least one argument of an integer type.  It indicates that
     the returned pointer points to an object whose size is given by the
     function argument at POSITION, or by the product of the arguments
     at POSITION-1 and POSITION-2.  Meaningful sizes are positive values
     less than ‘PTRDIFF_MAX’.  Other sizes are diagnosed when detected.
     GCC uses this information to improve the results of
     ‘__builtin_object_size’.

     For instance, the following declarations

          typedef __attribute__ ((alloc_size (1, 2))) void*
            (*calloc_ptr) (size_t, size_t);
          typedef __attribute__ ((alloc_size (1))) void*
            (*malloc_ptr) (size_t);

     specify that ‘calloc_ptr’ is a pointer of a function that, like the
     standard C function ‘calloc’, returns an object whose size is given
     by the product of arguments 1 and 2, and similarly, that
     ‘malloc_ptr’, like the standard C function ‘malloc’, returns an
     object whose size is given by argument 1 to the function.

‘cleanup (CLEANUP_FUNCTION)’
     The ‘cleanup’ attribute runs a function when the variable goes out
     of scope.  This attribute can only be applied to auto function
     scope variables; it may not be applied to parameters or variables
     with static storage duration.  The function must take one
     parameter, a pointer to a type compatible with the variable.  The
     return value of the function (if any) is ignored.

     If ‘-fexceptions’ is enabled, then CLEANUP_FUNCTION is run during
     the stack unwinding that happens during the processing of the
     exception.  Note that the ‘cleanup’ attribute does not allow the
     exception to be caught, only to perform an action.  It is undefined
     what happens if CLEANUP_FUNCTION does not return normally.

‘common’
‘nocommon’
     The ‘common’ attribute requests GCC to place a variable in "common"
     storage.  The ‘nocommon’ attribute requests the opposite--to
     allocate space for it directly.

     These attributes override the default chosen by the ‘-fno-common’
     and ‘-fcommon’ flags respectively.

‘copy’
‘copy (VARIABLE)’
     The ‘copy’ attribute applies the set of attributes with which
     VARIABLE has been declared to the declaration of the variable to
     which the attribute is applied.  The attribute is designed for
     libraries that define aliases that are expected to specify the same
     set of attributes as the aliased symbols.  The ‘copy’ attribute can
     be used with variables, functions or types.  However, the kind of
     symbol to which the attribute is applied (either varible or
     function) must match the kind of symbol to which the argument
     refers.  The ‘copy’ attribute copies only syntactic and semantic
     attributes but not attributes that affect a symbol's linkage or
     visibility such as ‘alias’, ‘visibility’, or ‘weak’.  The
     ‘deprecated’ attribute is also not copied.  *Note Common Function
     Attributes::.  *Note Common Type Attributes::.

‘deprecated’
‘deprecated (MSG)’
     The ‘deprecated’ attribute results in a warning if the variable is
     used anywhere in the source file.  This is useful when identifying
     variables that are expected to be removed in a future version of a
     program.  The warning also includes the location of the declaration
     of the deprecated variable, to enable users to easily find further
     information about why the variable is deprecated, or what they
     should do instead.  Note that the warning only occurs for uses:

          extern int old_var __attribute__ ((deprecated));
          extern int old_var;
          int new_fn () { return old_var; }

     results in a warning on line 3 but not line 2.  The optional MSG
     argument, which must be a string, is printed in the warning if
     present.

     The ‘deprecated’ attribute can also be used for functions and types
     (*note Common Function Attributes::, *note Common Type
     Attributes::).

     The message attached to the attribute is affected by the setting of
     the ‘-fmessage-length’ option.

‘unavailable’
‘unavailable (MSG)’
     The ‘unavailable’ attribute indicates that the variable so marked
     is not available, if it is used anywhere in the source file.  It
     behaves in the same manner as the ‘deprecated’ attribute except
     that the compiler will emit an error rather than a warning.

     It is expected that items marked as ‘deprecated’ will eventually be
     withdrawn from interfaces, and then become unavailable.  This
     attribute allows for marking them appropriately.

     The ‘unavailable’ attribute can also be used for functions and
     types (*note Common Function Attributes::, *note Common Type
     Attributes::).

‘mode (MODE)’
     This attribute specifies the data type for the
     declaration--whichever type corresponds to the mode MODE.  This in
     effect lets you request an integer or floating-point type according
     to its width.

     *Note (gccint)Machine Modes::, for a list of the possible keywords
     for MODE.  You may also specify a mode of ‘byte’ or ‘__byte__’ to
     indicate the mode corresponding to a one-byte integer, ‘word’ or
     ‘__word__’ for the mode of a one-word integer, and ‘pointer’ or
     ‘__pointer__’ for the mode used to represent pointers.

‘nonstring’
     The ‘nonstring’ variable attribute specifies that an object or
     member declaration with type array of ‘char’, ‘signed char’, or
     ‘unsigned char’, or pointer to such a type is intended to store
     character arrays that do not necessarily contain a terminating
     ‘NUL’.  This is useful in detecting uses of such arrays or pointers
     with functions that expect ‘NUL’-terminated strings, and to avoid
     warnings when such an array or pointer is used as an argument to a
     bounded string manipulation function such as ‘strncpy’.  For
     example, without the attribute, GCC will issue a warning for the
     ‘strncpy’ call below because it may truncate the copy without
     appending the terminating ‘NUL’ character.  Using the attribute
     makes it possible to suppress the warning.  However, when the array
     is declared with the attribute the call to ‘strlen’ is diagnosed
     because when the array doesn't contain a ‘NUL’-terminated string
     the call is undefined.  To copy, compare, of search non-string
     character arrays use the ‘memcpy’, ‘memcmp’, ‘memchr’, and other
     functions that operate on arrays of bytes.  In addition, calling
     ‘strnlen’ and ‘strndup’ with such arrays is safe provided a
     suitable bound is specified, and not diagnosed.

          struct Data
          {
            char name [32] __attribute__ ((nonstring));
          };

          int f (struct Data *pd, const char *s)
          {
            strncpy (pd->name, s, sizeof pd->name);
            ...
            return strlen (pd->name);   // unsafe, gets a warning
          }

‘packed’
     The ‘packed’ attribute specifies that a structure member should
     have the smallest possible alignment--one bit for a bit-field and
     one byte otherwise, unless a larger value is specified with the
     ‘aligned’ attribute.  The attribute does not apply to non-member
     objects.

     For example in the structure below, the member array ‘x’ is packed
     so that it immediately follows ‘a’ with no intervening padding:

          struct foo
          {
            char a;
            int x[2] __attribute__ ((packed));
          };

     _Note:_ The 4.1, 4.2 and 4.3 series of GCC ignore the ‘packed’
     attribute on bit-fields of type ‘char’.  This has been fixed in GCC
     4.4 but the change can lead to differences in the structure layout.
     See the documentation of ‘-Wpacked-bitfield-compat’ for more
     information.

‘section ("SECTION-NAME")’
     Normally, the compiler places the objects it generates in sections
     like ‘data’ and ‘bss’.  Sometimes, however, you need additional
     sections, or you need certain particular variables to appear in
     special sections, for example to map to special hardware.  The
     ‘section’ attribute specifies that a variable (or function) lives
     in a particular section.  For example, this small program uses
     several specific section names:

          struct duart a __attribute__ ((section ("DUART_A"))) = { 0 };
          struct duart b __attribute__ ((section ("DUART_B"))) = { 0 };
          char stack[10000] __attribute__ ((section ("STACK"))) = { 0 };
          int init_data __attribute__ ((section ("INITDATA")));

          main()
          {
            /* Initialize stack pointer */
            init_sp (stack + sizeof (stack));

            /* Initialize initialized data */
            memcpy (&init_data, &data, &edata - &data);

            /* Turn on the serial ports */
            init_duart (&a);
            init_duart (&b);
          }

     Use the ‘section’ attribute with _global_ variables and not _local_
     variables, as shown in the example.

     You may use the ‘section’ attribute with initialized or
     uninitialized global variables but the linker requires each object
     be defined once, with the exception that uninitialized variables
     tentatively go in the ‘common’ (or ‘bss’) section and can be
     multiply "defined".  Using the ‘section’ attribute changes what
     section the variable goes into and may cause the linker to issue an
     error if an uninitialized variable has multiple definitions.  You
     can force a variable to be initialized with the ‘-fno-common’ flag
     or the ‘nocommon’ attribute.

     Some file formats do not support arbitrary sections so the
     ‘section’ attribute is not available on all platforms.  If you need
     to map the entire contents of a module to a particular section,
     consider using the facilities of the linker instead.

‘tls_model ("TLS_MODEL")’
     The ‘tls_model’ attribute sets thread-local storage model (*note
     Thread-Local::) of a particular ‘__thread’ variable, overriding
     ‘-ftls-model=’ command-line switch on a per-variable basis.  The
     TLS_MODEL argument should be one of ‘global-dynamic’,
     ‘local-dynamic’, ‘initial-exec’ or ‘local-exec’.

     Not all targets support this attribute.

‘unused’
     This attribute, attached to a variable or structure field, means
     that the variable or field is meant to be possibly unused.  GCC
     does not produce a warning for this variable or field.

‘used’
     This attribute, attached to a variable with static storage, means
     that the variable must be emitted even if it appears that the
     variable is not referenced.

     When applied to a static data member of a C++ class template, the
     attribute also means that the member is instantiated if the class
     itself is instantiated.

‘retain’
     For ELF targets that support the GNU or FreeBSD OSABIs, this
     attribute will save the variable from linker garbage collection.
     To support this behavior, variables that have not been placed in
     specific sections (e.g.  by the ‘section’ attribute, or the
     ‘-fdata-sections’ option), will be placed in new, unique sections.

     This additional functionality requires Binutils version 2.36 or
     later.

‘uninitialized’
     This attribute, attached to a variable with automatic storage,
     means that the variable should not be automatically initialized by
     the compiler when the option ‘-ftrivial-auto-var-init’ presents.

     With the option ‘-ftrivial-auto-var-init’, all the automatic
     variables that do not have explicit initializers will be
     initialized by the compiler.  These additional compiler
     initializations might incur run-time overhead, sometimes
     dramatically.  This attribute can be used to mark some variables to
     be excluded from such automatical initialization in order to reduce
     runtime overhead.

     This attribute has no effect when the option
     ‘-ftrivial-auto-var-init’ does not present.

‘vector_size (BYTES)’
     This attribute specifies the vector size for the type of the
     declared variable, measured in bytes.  The type to which it applies
     is known as the “base type”.  The BYTES argument must be a positive
     power-of-two multiple of the base type size.  For example, the
     declaration:

          int foo __attribute__ ((vector_size (16)));

     causes the compiler to set the mode for ‘foo’, to be 16 bytes,
     divided into ‘int’ sized units.  Assuming a 32-bit ‘int’, ‘foo’'s
     type is a vector of four units of four bytes each, and the
     corresponding mode of ‘foo’ is ‘V4SI’.  *Note Vector Extensions::,
     for details of manipulating vector variables.

     This attribute is only applicable to integral and floating scalars,
     although arrays, pointers, and function return values are allowed
     in conjunction with this construct.

     Aggregates with this attribute are invalid, even if they are of the
     same size as a corresponding scalar.  For example, the declaration:

          struct S { int a; };
          struct S  __attribute__ ((vector_size (16))) foo;

     is invalid even if the size of the structure is the same as the
     size of the ‘int’.

‘visibility ("VISIBILITY_TYPE")’
     This attribute affects the linkage of the declaration to which it
     is attached.  The ‘visibility’ attribute is described in *note
     Common Function Attributes::.

‘weak’
     The ‘weak’ attribute is described in *note Common Function
     Attributes::.

‘noinit’
     Any data with the ‘noinit’ attribute will not be initialized by the
     C runtime startup code, or the program loader.  Not initializing
     data in this way can reduce program startup times.

     This attribute is specific to ELF targets and relies on the linker
     script to place sections with the ‘.noinit’ prefix in the right
     location.

‘persistent’
     Any data with the ‘persistent’ attribute will not be initialized by
     the C runtime startup code, but will be initialized by the program
     loader.  This enables the value of the variable to ‘persist’
     between processor resets.

     This attribute is specific to ELF targets and relies on the linker
     script to place the sections with the ‘.persistent’ prefix in the
     right location.  Specifically, some type of non-volatile, writeable
     memory is required.

‘objc_nullability (NULLABILITY KIND) (Objective-C and Objective-C++ only)’
     This attribute applies to pointer variables only.  It allows
     marking the pointer with one of four possible values describing the
     conditions under which the pointer might have a ‘nil’ value.  In
     most cases, the attribute is intended to be an internal
     representation for property and method nullability (specified by
     language keywords); it is not recommended to use it directly.

     When NULLABILITY KIND is ‘"unspecified"’ or ‘0’, nothing is known
     about the conditions in which the pointer might be ‘nil’.  Making
     this state specific serves to avoid false positives in diagnostics.

     When NULLABILITY KIND is ‘"nonnull"’ or ‘1’, the pointer has no
     meaning if it is ‘nil’ and thus the compiler is free to emit
     diagnostics if it can be determined that the value will be ‘nil’.

     When NULLABILITY KIND is ‘"nullable"’ or ‘2’, the pointer might be
     ‘nil’ and carry meaning as such.

     When NULLABILITY KIND is ‘"resettable"’ or ‘3’ (used only in the
     context of property attribute lists) this describes the case in
     which a property setter may take the value ‘nil’ (which perhaps
     causes the property to be reset in some manner to a default) but
     for which the property getter will never validly return ‘nil’.


File: gcc.info,  Node: ARC Variable Attributes,  Next: AVR Variable Attributes,  Prev: Common Variable Attributes,  Up: Variable Attributes

6.34.2 ARC Variable Attributes
------------------------------

‘aux’
     The ‘aux’ attribute is used to directly access the ARC's auxiliary
     register space from C. The auxilirary register number is given via
     attribute argument.


File: gcc.info,  Node: AVR Variable Attributes,  Next: Blackfin Variable Attributes,  Prev: ARC Variable Attributes,  Up: Variable Attributes

6.34.3 AVR Variable Attributes
------------------------------

‘progmem’
     The ‘progmem’ attribute is used on the AVR to place read-only data
     in the non-volatile program memory (flash).  The ‘progmem’
     attribute accomplishes this by putting respective variables into a
     section whose name starts with ‘.progmem’.

     This attribute works similar to the ‘section’ attribute but adds
     additional checking.

     •  Ordinary AVR cores with 32 general purpose registers:
          ‘progmem’ affects the location of the data but not how this
          data is accessed.  In order to read data located with the
          ‘progmem’ attribute (inline) assembler must be used.
               /* Use custom macros from AVR-LibC (http://nongnu.org/avr-libc/user-manual/) */
               #include <avr/pgmspace.h>

               /* Locate var in flash memory */
               const int var[2] PROGMEM = { 1, 2 };

               int read_var (int i)
               {
                   /* Access var[] by accessor macro from avr/pgmspace.h */
                   return (int) pgm_read_word (& var[i]);
               }

          AVR is a Harvard architecture processor and data and read-only
          data normally resides in the data memory (RAM).

          See also the *note AVR Named Address Spaces:: section for an
          alternate way to locate and access data in flash memory.

     •  AVR cores with flash memory visible in the RAM address range:
          On such devices, there is no need for attribute ‘progmem’ or
          *note ‘__flash’: AVR Named Address Spaces. qualifier at all.
          Just use standard C / C++.  The compiler will generate ‘LD*’
          instructions.  As flash memory is visible in the RAM address
          range, and the default linker script does _not_ locate
          ‘.rodata’ in RAM, no special features are needed in order not
          to waste RAM for read-only data or to read from flash.  You
          might even get slightly better performance by avoiding
          ‘progmem’ and ‘__flash’.  This applies to devices from
          families ‘avrtiny’ and ‘avrxmega3’, see *note AVR Options::
          for an overview.

     • Reduced AVR Tiny cores like ATtiny40:
          The compiler adds ‘0x4000’ to the addresses of objects and
          declarations in ‘progmem’ and locates the objects in flash
          memory, namely in section ‘.progmem.data’.  The offset is
          needed because the flash memory is visible in the RAM address
          space starting at address ‘0x4000’.

          Data in ‘progmem’ can be accessed by means of ordinary C code,
          no special functions or macros are needed.

               /* var is located in flash memory */
               extern const int var[2] __attribute__((progmem));

               int read_var (int i)
               {
                   return var[i];
               }

          Please notice that on these devices, there is no need for
          ‘progmem’ at all.

‘io’
‘io (ADDR)’
     Variables with the ‘io’ attribute are used to address memory-mapped
     peripherals in the io address range.  If an address is specified,
     the variable is assigned that address, and the value is interpreted
     as an address in the data address space.  Example:

          volatile int porta __attribute__((io (0x22)));

     The address specified in the address in the data address range.

     Otherwise, the variable it is not assigned an address, but the
     compiler will still use in/out instructions where applicable,
     assuming some other module assigns an address in the io address
     range.  Example:

          extern volatile int porta __attribute__((io));

‘io_low’
‘io_low (ADDR)’
     This is like the ‘io’ attribute, but additionally it informs the
     compiler that the object lies in the lower half of the I/O area,
     allowing the use of ‘cbi’, ‘sbi’, ‘sbic’ and ‘sbis’ instructions.

‘address’
‘address (ADDR)’
     Variables with the ‘address’ attribute are used to address
     memory-mapped peripherals that may lie outside the io address
     range.

          volatile int porta __attribute__((address (0x600)));

‘absdata’
     Variables in static storage and with the ‘absdata’ attribute can be
     accessed by the ‘LDS’ and ‘STS’ instructions which take absolute
     addresses.

        • This attribute is only supported for the reduced AVR Tiny core
          like ATtiny40.

        • You must make sure that respective data is located in the
          address range ‘0x40’...‘0xbf’ accessible by ‘LDS’ and ‘STS’.
          One way to achieve this as an appropriate linker description
          file.

        • If the location does not fit the address range of ‘LDS’ and
          ‘STS’, there is currently (Binutils 2.26) just an unspecific
          warning like
               ‘module.cc:(.text+0x1c): warning: internal error: out of
               range error’

     See also the ‘-mabsdata’ *note command-line option: AVR Options.


File: gcc.info,  Node: Blackfin Variable Attributes,  Next: H8/300 Variable Attributes,  Prev: AVR Variable Attributes,  Up: Variable Attributes

6.34.4 Blackfin Variable Attributes
-----------------------------------

Three attributes are currently defined for the Blackfin.

‘l1_data’
‘l1_data_A’
‘l1_data_B’
     Use these attributes on the Blackfin to place the variable into L1
     Data SRAM. Variables with ‘l1_data’ attribute are put into the
     specific section named ‘.l1.data’.  Those with ‘l1_data_A’
     attribute are put into the specific section named ‘.l1.data.A’.
     Those with ‘l1_data_B’ attribute are put into the specific section
     named ‘.l1.data.B’.

‘l2’
     Use this attribute on the Blackfin to place the variable into L2
     SRAM.  Variables with ‘l2’ attribute are put into the specific
     section named ‘.l2.data’.


File: gcc.info,  Node: H8/300 Variable Attributes,  Next: IA-64 Variable Attributes,  Prev: Blackfin Variable Attributes,  Up: Variable Attributes

6.34.5 H8/300 Variable Attributes
---------------------------------

These variable attributes are available for H8/300 targets:

‘eightbit_data’
     Use this attribute on the H8/300, H8/300H, and H8S to indicate that
     the specified variable should be placed into the eight-bit data
     section.  The compiler generates more efficient code for certain
     operations on data in the eight-bit data area.  Note the eight-bit
     data area is limited to 256 bytes of data.

     You must use GAS and GLD from GNU binutils version 2.7 or later for
     this attribute to work correctly.

‘tiny_data’
     Use this attribute on the H8/300H and H8S to indicate that the
     specified variable should be placed into the tiny data section.
     The compiler generates more efficient code for loads and stores on
     data in the tiny data section.  Note the tiny data area is limited
     to slightly under 32KB of data.


File: gcc.info,  Node: IA-64 Variable Attributes,  Next: M32R/D Variable Attributes,  Prev: H8/300 Variable Attributes,  Up: Variable Attributes

6.34.6 IA-64 Variable Attributes
--------------------------------

The IA-64 back end supports the following variable attribute:

‘model (MODEL-NAME)’

     On IA-64, use this attribute to set the addressability of an
     object.  At present, the only supported identifier for MODEL-NAME
     is ‘small’, indicating addressability via "small" (22-bit)
     addresses (so that their addresses can be loaded with the ‘addl’
     instruction).  Caveat: such addressing is by definition not
     position independent and hence this attribute must not be used for
     objects defined by shared libraries.


File: gcc.info,  Node: M32R/D Variable Attributes,  Next: MeP Variable Attributes,  Prev: IA-64 Variable Attributes,  Up: Variable Attributes

6.34.7 M32R/D Variable Attributes
---------------------------------

One attribute is currently defined for the M32R/D.

‘model (MODEL-NAME)’
     Use this attribute on the M32R/D to set the addressability of an
     object.  The identifier MODEL-NAME is one of ‘small’, ‘medium’, or
     ‘large’, representing each of the code models.

     Small model objects live in the lower 16MB of memory (so that their
     addresses can be loaded with the ‘ld24’ instruction).

     Medium and large model objects may live anywhere in the 32-bit
     address space (the compiler generates ‘seth/add3’ instructions to
     load their addresses).


File: gcc.info,  Node: MeP Variable Attributes,  Next: Microsoft Windows Variable Attributes,  Prev: M32R/D Variable Attributes,  Up: Variable Attributes

6.34.8 MeP Variable Attributes
------------------------------

The MeP target has a number of addressing modes and busses.  The ‘near’
space spans the standard memory space's first 16 megabytes (24 bits).
The ‘far’ space spans the entire 32-bit memory space.  The ‘based’ space
is a 128-byte region in the memory space that is addressed relative to
the ‘$tp’ register.  The ‘tiny’ space is a 65536-byte region relative to
the ‘$gp’ register.  In addition to these memory regions, the MeP target
has a separate 16-bit control bus which is specified with ‘cb’
attributes.

‘based’
     Any variable with the ‘based’ attribute is assigned to the ‘.based’
     section, and is accessed with relative to the ‘$tp’ register.

‘tiny’
     Likewise, the ‘tiny’ attribute assigned variables to the ‘.tiny’
     section, relative to the ‘$gp’ register.

‘near’
     Variables with the ‘near’ attribute are assumed to have addresses
     that fit in a 24-bit addressing mode.  This is the default for
     large variables (‘-mtiny=4’ is the default) but this attribute can
     override ‘-mtiny=’ for small variables, or override ‘-ml’.

‘far’
     Variables with the ‘far’ attribute are addressed using a full
     32-bit address.  Since this covers the entire memory space, this
     allows modules to make no assumptions about where variables might
     be stored.

‘io’
‘io (ADDR)’
     Variables with the ‘io’ attribute are used to address memory-mapped
     peripherals.  If an address is specified, the variable is assigned
     that address, else it is not assigned an address (it is assumed
     some other module assigns an address).  Example:

          int timer_count __attribute__((io(0x123)));

‘cb’
‘cb (ADDR)’
     Variables with the ‘cb’ attribute are used to access the control
     bus, using special instructions.  ‘addr’ indicates the control bus
     address.  Example:

          int cpu_clock __attribute__((cb(0x123)));


File: gcc.info,  Node: Microsoft Windows Variable Attributes,  Next: MSP430 Variable Attributes,  Prev: MeP Variable Attributes,  Up: Variable Attributes

6.34.9 Microsoft Windows Variable Attributes
--------------------------------------------

You can use these attributes on Microsoft Windows targets.  *note x86
Variable Attributes:: for additional Windows compatibility attributes
available on all x86 targets.

‘dllimport’
‘dllexport’
     The ‘dllimport’ and ‘dllexport’ attributes are described in *note
     Microsoft Windows Function Attributes::.

‘selectany’
     The ‘selectany’ attribute causes an initialized global variable to
     have link-once semantics.  When multiple definitions of the
     variable are encountered by the linker, the first is selected and
     the remainder are discarded.  Following usage by the Microsoft
     compiler, the linker is told _not_ to warn about size or content
     differences of the multiple definitions.

     Although the primary usage of this attribute is for POD types, the
     attribute can also be applied to global C++ objects that are
     initialized by a constructor.  In this case, the static
     initialization and destruction code for the object is emitted in
     each translation defining the object, but the calls to the
     constructor and destructor are protected by a link-once guard
     variable.

     The ‘selectany’ attribute is only available on Microsoft Windows
     targets.  You can use ‘__declspec (selectany)’ as a synonym for
     ‘__attribute__ ((selectany))’ for compatibility with other
     compilers.

‘shared’
     On Microsoft Windows, in addition to putting variable definitions
     in a named section, the section can also be shared among all
     running copies of an executable or DLL.  For example, this small
     program defines shared data by putting it in a named section
     ‘shared’ and marking the section shareable:

          int foo __attribute__((section ("shared"), shared)) = 0;

          int
          main()
          {
            /* Read and write foo.  All running
               copies see the same value.  */
            return 0;
          }

     You may only use the ‘shared’ attribute along with ‘section’
     attribute with a fully-initialized global definition because of the
     way linkers work.  See ‘section’ attribute for more information.

     The ‘shared’ attribute is only available on Microsoft Windows.


File: gcc.info,  Node: MSP430 Variable Attributes,  Next: Nvidia PTX Variable Attributes,  Prev: Microsoft Windows Variable Attributes,  Up: Variable Attributes

6.34.10 MSP430 Variable Attributes
----------------------------------

‘upper’
‘either’
     These attributes are the same as the MSP430 function attributes of
     the same name (*note MSP430 Function Attributes::).

‘lower’
     This option behaves mostly the same as the MSP430 function
     attribute of the same name (*note MSP430 Function Attributes::),
     but it has some additional functionality.

     If ‘-mdata-region=’{‘upper,either,none’} has been passed, or the
     ‘section’ attribute is applied to a variable, the compiler will
     generate 430X instructions to handle it.  This is because the
     compiler has to assume that the variable could get placed in the
     upper memory region (above address 0xFFFF). Marking the variable
     with the ‘lower’ attribute informs the compiler that the variable
     will be placed in lower memory so it is safe to use 430
     instructions to handle it.

     In the case of the ‘section’ attribute, the section name given will
     be used, and the ‘.lower’ prefix will not be added.


File: gcc.info,  Node: Nvidia PTX Variable Attributes,  Next: PowerPC Variable Attributes,  Prev: MSP430 Variable Attributes,  Up: Variable Attributes

6.34.11 Nvidia PTX Variable Attributes
--------------------------------------

These variable attributes are supported by the Nvidia PTX back end:

‘shared’
     Use this attribute to place a variable in the ‘.shared’ memory
     space.  This memory space is private to each cooperative thread
     array; only threads within one thread block refer to the same
     instance of the variable.  The runtime does not initialize
     variables in this memory space.


File: gcc.info,  Node: PowerPC Variable Attributes,  Next: RL78 Variable Attributes,  Prev: Nvidia PTX Variable Attributes,  Up: Variable Attributes

6.34.12 PowerPC Variable Attributes
-----------------------------------

Three attributes currently are defined for PowerPC configurations:
‘altivec’, ‘ms_struct’ and ‘gcc_struct’.

 For full documentation of the struct attributes please see the
documentation in *note x86 Variable Attributes::.

 For documentation of ‘altivec’ attribute please see the documentation
in *note PowerPC Type Attributes::.


File: gcc.info,  Node: RL78 Variable Attributes,  Next: V850 Variable Attributes,  Prev: PowerPC Variable Attributes,  Up: Variable Attributes

6.34.13 RL78 Variable Attributes
--------------------------------

The RL78 back end supports the ‘saddr’ variable attribute.  This
specifies placement of the corresponding variable in the SADDR area,
which can be accessed more efficiently than the default memory region.


File: gcc.info,  Node: V850 Variable Attributes,  Next: x86 Variable Attributes,  Prev: RL78 Variable Attributes,  Up: Variable Attributes

6.34.14 V850 Variable Attributes
--------------------------------

These variable attributes are supported by the V850 back end:

‘sda’
     Use this attribute to explicitly place a variable in the small data
     area, which can hold up to 64 kilobytes.

‘tda’
     Use this attribute to explicitly place a variable in the tiny data
     area, which can hold up to 256 bytes in total.

‘zda’
     Use this attribute to explicitly place a variable in the first 32
     kilobytes of memory.


File: gcc.info,  Node: x86 Variable Attributes,  Next: Xstormy16 Variable Attributes,  Prev: V850 Variable Attributes,  Up: Variable Attributes

6.34.15 x86 Variable Attributes
-------------------------------

Two attributes are currently defined for x86 configurations: ‘ms_struct’
and ‘gcc_struct’.

‘ms_struct’
‘gcc_struct’

     If ‘packed’ is used on a structure, or if bit-fields are used, it
     may be that the Microsoft ABI lays out the structure differently
     than the way GCC normally does.  Particularly when moving packed
     data between functions compiled with GCC and the native Microsoft
     compiler (either via function call or as data in a file), it may be
     necessary to access either format.

     The ‘ms_struct’ and ‘gcc_struct’ attributes correspond to the
     ‘-mms-bitfields’ and ‘-mno-ms-bitfields’ command-line options,
     respectively; see *note x86 Options::, for details of how structure
     layout is affected.  *Note x86 Type Attributes::, for information
     about the corresponding attributes on types.


File: gcc.info,  Node: Xstormy16 Variable Attributes,  Prev: x86 Variable Attributes,  Up: Variable Attributes

6.34.16 Xstormy16 Variable Attributes
-------------------------------------

One attribute is currently defined for xstormy16 configurations:
‘below100’.

‘below100’

     If a variable has the ‘below100’ attribute (‘BELOW100’ is allowed
     also), GCC places the variable in the first 0x100 bytes of memory
     and use special opcodes to access it.  Such variables are placed in
     either the ‘.bss_below100’ section or the ‘.data_below100’ section.


File: gcc.info,  Node: Type Attributes,  Next: Label Attributes,  Prev: Variable Attributes,  Up: C Extensions

6.35 Specifying Attributes of Types
===================================

The keyword ‘__attribute__’ allows you to specify various special
properties of types.  Some type attributes apply only to structure and
union types, and in C++, also class types, while others can apply to any
type defined via a ‘typedef’ declaration.  Unless otherwise specified,
the same restrictions and effects apply to attributes regardless of
whether a type is a trivial structure or a C++ class with user-defined
constructors, destructors, or a copy assignment.

 Other attributes are defined for functions (*note Function
Attributes::), labels (*note Label Attributes::), enumerators (*note
Enumerator Attributes::), statements (*note Statement Attributes::), and
for variables (*note Variable Attributes::).

 The ‘__attribute__’ keyword is followed by an attribute specification
enclosed in double parentheses.

 You may specify type attributes in an enum, struct or union type
declaration or definition by placing them immediately after the
‘struct’, ‘union’ or ‘enum’ keyword.  You can also place them just past
the closing curly brace of the definition, but this is less preferred
because logically the type should be fully defined at the closing brace.

 You can also include type attributes in a ‘typedef’ declaration.  *Note
Attribute Syntax::, for details of the exact syntax for using
attributes.

* Menu:

* Common Type Attributes::
* ARC Type Attributes::
* ARM Type Attributes::
* BPF Type Attributes::
* MeP Type Attributes::
* PowerPC Type Attributes::
* x86 Type Attributes::


File: gcc.info,  Node: Common Type Attributes,  Next: ARC Type Attributes,  Up: Type Attributes

6.35.1 Common Type Attributes
-----------------------------

The following type attributes are supported on most targets.

‘aligned’
‘aligned (ALIGNMENT)’
     The ‘aligned’ attribute specifies a minimum alignment (in bytes)
     for variables of the specified type.  When specified, ALIGNMENT
     must be a power of 2.  Specifying no ALIGNMENT argument implies the
     maximum alignment for the target, which is often, but by no means
     always, 8 or 16 bytes.  For example, the declarations:

          struct __attribute__ ((aligned (8))) S { short f[3]; };
          typedef int more_aligned_int __attribute__ ((aligned (8)));

     force the compiler to ensure (as far as it can) that each variable
     whose type is ‘struct S’ or ‘more_aligned_int’ is allocated and
     aligned _at least_ on a 8-byte boundary.  On a SPARC, having all
     variables of type ‘struct S’ aligned to 8-byte boundaries allows
     the compiler to use the ‘ldd’ and ‘std’ (doubleword load and store)
     instructions when copying one variable of type ‘struct S’ to
     another, thus improving run-time efficiency.

     Note that the alignment of any given ‘struct’ or ‘union’ type is
     required by the ISO C standard to be at least a perfect multiple of
     the lowest common multiple of the alignments of all of the members
     of the ‘struct’ or ‘union’ in question.  This means that you _can_
     effectively adjust the alignment of a ‘struct’ or ‘union’ type by
     attaching an ‘aligned’ attribute to any one of the members of such
     a type, but the notation illustrated in the example above is a more
     obvious, intuitive, and readable way to request the compiler to
     adjust the alignment of an entire ‘struct’ or ‘union’ type.

     As in the preceding example, you can explicitly specify the
     alignment (in bytes) that you wish the compiler to use for a given
     ‘struct’ or ‘union’ type.  Alternatively, you can leave out the
     alignment factor and just ask the compiler to align a type to the
     maximum useful alignment for the target machine you are compiling
     for.  For example, you could write:

          struct __attribute__ ((aligned)) S { short f[3]; };

     Whenever you leave out the alignment factor in an ‘aligned’
     attribute specification, the compiler automatically sets the
     alignment for the type to the largest alignment that is ever used
     for any data type on the target machine you are compiling for.
     Doing this can often make copy operations more efficient, because
     the compiler can use whatever instructions copy the biggest chunks
     of memory when performing copies to or from the variables that have
     types that you have aligned this way.

     In the example above, if the size of each ‘short’ is 2 bytes, then
     the size of the entire ‘struct S’ type is 6 bytes.  The smallest
     power of two that is greater than or equal to that is 8, so the
     compiler sets the alignment for the entire ‘struct S’ type to 8
     bytes.

     Note that although you can ask the compiler to select a
     time-efficient alignment for a given type and then declare only
     individual stand-alone objects of that type, the compiler's ability
     to select a time-efficient alignment is primarily useful only when
     you plan to create arrays of variables having the relevant
     (efficiently aligned) type.  If you declare or use arrays of
     variables of an efficiently-aligned type, then it is likely that
     your program also does pointer arithmetic (or subscripting, which
     amounts to the same thing) on pointers to the relevant type, and
     the code that the compiler generates for these pointer arithmetic
     operations is often more efficient for efficiently-aligned types
     than for other types.

     Note that the effectiveness of ‘aligned’ attributes may be limited
     by inherent limitations in your linker.  On many systems, the
     linker is only able to arrange for variables to be aligned up to a
     certain maximum alignment.  (For some linkers, the maximum
     supported alignment may be very very small.)  If your linker is
     only able to align variables up to a maximum of 8-byte alignment,
     then specifying ‘aligned (16)’ in an ‘__attribute__’ still only
     provides you with 8-byte alignment.  See your linker documentation
     for further information.

     When used on a struct, or struct member, the ‘aligned’ attribute
     can only increase the alignment; in order to decrease it, the
     ‘packed’ attribute must be specified as well.  When used as part of
     a typedef, the ‘aligned’ attribute can both increase and decrease
     alignment, and specifying the ‘packed’ attribute generates a
     warning.

‘warn_if_not_aligned (ALIGNMENT)’
     This attribute specifies a threshold for the structure field,
     measured in bytes.  If the structure field is aligned below the
     threshold, a warning will be issued.  For example, the declaration:

          typedef unsigned long long __u64
             __attribute__((aligned (4), warn_if_not_aligned (8)));

          struct foo
          {
            int i1;
            int i2;
            __u64 x;
          };

     causes the compiler to issue an warning on ‘struct foo’, like
     ‘warning: alignment 4 of 'struct foo' is less than 8’.  It is used
     to define ‘struct foo’ in such a way that ‘struct foo’ has the same
     layout and the structure field ‘x’ has the same alignment when
     ‘__u64’ is aligned at either 4 or 8 bytes.  Align ‘struct foo’ to 8
     bytes:

          struct __attribute__ ((aligned (8))) foo
          {
            int i1;
            int i2;
            __u64 x;
          };

     silences the warning.  The compiler also issues a warning, like
     ‘warning: 'x' offset 12 in 'struct foo' isn't aligned to 8’, when
     the structure field has the misaligned offset:

          struct __attribute__ ((aligned (8))) foo
          {
            int i1;
            int i2;
            int i3;
            __u64 x;
          };

     This warning can be disabled by ‘-Wno-if-not-aligned’.

‘alloc_size (POSITION)’
‘alloc_size (POSITION-1, POSITION-2)’
     The ‘alloc_size’ type attribute may be applied to the definition of
     a type of a function that returns a pointer and takes at least one
     argument of an integer type.  It indicates that the returned
     pointer points to an object whose size is given by the function
     argument at POSITION-1, or by the product of the arguments at
     POSITION-1 and POSITION-2.  Meaningful sizes are positive values
     less than ‘PTRDIFF_MAX’.  Other sizes are disagnosed when detected.
     GCC uses this information to improve the results of
     ‘__builtin_object_size’.

     For instance, the following declarations

          typedef __attribute__ ((alloc_size (1, 2))) void*
            calloc_type (size_t, size_t);
          typedef __attribute__ ((alloc_size (1))) void*
            malloc_type (size_t);

     specify that ‘calloc_type’ is a type of a function that, like the
     standard C function ‘calloc’, returns an object whose size is given
     by the product of arguments 1 and 2, and that ‘malloc_type’, like
     the standard C function ‘malloc’, returns an object whose size is
     given by argument 1 to the function.

‘copy’
‘copy (EXPRESSION)’
     The ‘copy’ attribute applies the set of attributes with which the
     type of the EXPRESSION has been declared to the declaration of the
     type to which the attribute is applied.  The attribute is designed
     for libraries that define aliases that are expected to specify the
     same set of attributes as the aliased symbols.  The ‘copy’
     attribute can be used with types, variables, or functions.
     However, the kind of symbol to which the attribute is applied
     (either varible or function) must match the kind of symbol to which
     the argument refers.  The ‘copy’ attribute copies only syntactic
     and semantic attributes but not attributes that affect a symbol's
     linkage or visibility such as ‘alias’, ‘visibility’, or ‘weak’.
     The ‘deprecated’ attribute is also not copied.  *Note Common
     Function Attributes::.  *Note Common Variable Attributes::.

     For example, suppose ‘struct A’ below is defined in some third
     party library header to have the alignment requirement ‘N’ and to
     force a warning whenever a variable of the type is not so aligned
     due to attribute ‘packed’.  Specifying the ‘copy’ attribute on the
     definition on the unrelated ‘struct B’ has the effect of copying
     all relevant attributes from the type referenced by the pointer
     expression to ‘struct B’.

          struct __attribute__ ((aligned (N), warn_if_not_aligned (N)))
          A { /* ... */ };
          struct __attribute__ ((copy ( (struct A *)0)) B { /* ... */ };

‘deprecated’
‘deprecated (MSG)’
     The ‘deprecated’ attribute results in a warning if the type is used
     anywhere in the source file.  This is useful when identifying types
     that are expected to be removed in a future version of a program.
     If possible, the warning also includes the location of the
     declaration of the deprecated type, to enable users to easily find
     further information about why the type is deprecated, or what they
     should do instead.  Note that the warnings only occur for uses and
     then only if the type is being applied to an identifier that itself
     is not being declared as deprecated.

          typedef int T1 __attribute__ ((deprecated));
          T1 x;
          typedef T1 T2;
          T2 y;
          typedef T1 T3 __attribute__ ((deprecated));
          T3 z __attribute__ ((deprecated));

     results in a warning on line 2 and 3 but not lines 4, 5, or 6.  No
     warning is issued for line 4 because T2 is not explicitly
     deprecated.  Line 5 has no warning because T3 is explicitly
     deprecated.  Similarly for line 6.  The optional MSG argument,
     which must be a string, is printed in the warning if present.
     Control characters in the string will be replaced with escape
     sequences, and if the ‘-fmessage-length’ option is set to 0 (its
     default value) then any newline characters will be ignored.

     The ‘deprecated’ attribute can also be used for functions and
     variables (*note Function Attributes::, *note Variable
     Attributes::.)

     The message attached to the attribute is affected by the setting of
     the ‘-fmessage-length’ option.

‘unavailable’
‘unavailable (MSG)’
     The ‘unavailable’ attribute behaves in the same manner as the
     ‘deprecated’ one, but emits an error rather than a warning.  It is
     used to indicate that a (perhaps previously ‘deprecated’) type is
     no longer usable.

     The ‘unavailable’ attribute can also be used for functions and
     variables (*note Function Attributes::, *note Variable
     Attributes::.)

‘designated_init’
     This attribute may only be applied to structure types.  It
     indicates that any initialization of an object of this type must
     use designated initializers rather than positional initializers.
     The intent of this attribute is to allow the programmer to indicate
     that a structure's layout may change, and that therefore relying on
     positional initialization will result in future breakage.

     GCC emits warnings based on this attribute by default; use
     ‘-Wno-designated-init’ to suppress them.

‘may_alias’
     Accesses through pointers to types with this attribute are not
     subject to type-based alias analysis, but are instead assumed to be
     able to alias any other type of objects.  In the context of section
     6.5 paragraph 7 of the C99 standard, an lvalue expression
     dereferencing such a pointer is treated like having a character
     type.  See ‘-fstrict-aliasing’ for more information on aliasing
     issues.  This extension exists to support some vector APIs, in
     which pointers to one vector type are permitted to alias pointers
     to a different vector type.

     Note that an object of a type with this attribute does not have any
     special semantics.

     Example of use:

          typedef short __attribute__ ((__may_alias__)) short_a;

          int
          main (void)
          {
            int a = 0x12345678;
            short_a *b = (short_a *) &a;

            b[1] = 0;

            if (a == 0x12345678)
              abort();

            exit(0);
          }

     If you replaced ‘short_a’ with ‘short’ in the variable declaration,
     the above program would abort when compiled with
     ‘-fstrict-aliasing’, which is on by default at ‘-O2’ or above.

‘mode (MODE)’
     This attribute specifies the data type for the
     declaration--whichever type corresponds to the mode MODE.  This in
     effect lets you request an integer or floating-point type according
     to its width.

     *Note (gccint)Machine Modes::, for a list of the possible keywords
     for MODE.  You may also specify a mode of ‘byte’ or ‘__byte__’ to
     indicate the mode corresponding to a one-byte integer, ‘word’ or
     ‘__word__’ for the mode of a one-word integer, and ‘pointer’ or
     ‘__pointer__’ for the mode used to represent pointers.

‘packed’
     This attribute, attached to a ‘struct’, ‘union’, or C++ ‘class’
     type definition, specifies that each of its members (other than
     zero-width bit-fields) is placed to minimize the memory required.
     This is equivalent to specifying the ‘packed’ attribute on each of
     the members.

     When attached to an ‘enum’ definition, the ‘packed’ attribute
     indicates that the smallest integral type should be used.
     Specifying the ‘-fshort-enums’ flag on the command line is
     equivalent to specifying the ‘packed’ attribute on all ‘enum’
     definitions.

     In the following example ‘struct my_packed_struct’'s members are
     packed closely together, but the internal layout of its ‘s’ member
     is not packed--to do that, ‘struct my_unpacked_struct’ needs to be
     packed too.

          struct my_unpacked_struct
           {
              char c;
              int i;
           };

          struct __attribute__ ((__packed__)) my_packed_struct
            {
               char c;
               int  i;
               struct my_unpacked_struct s;
            };

     You may only specify the ‘packed’ attribute on the definition of an
     ‘enum’, ‘struct’, ‘union’, or ‘class’, not on a ‘typedef’ that does
     not also define the enumerated type, structure, union, or class.

‘scalar_storage_order ("ENDIANNESS")’
     When attached to a ‘union’ or a ‘struct’, this attribute sets the
     storage order, aka endianness, of the scalar fields of the type, as
     well as the array fields whose component is scalar.  The supported
     endiannesses are ‘big-endian’ and ‘little-endian’.  The attribute
     has no effects on fields which are themselves a ‘union’, a ‘struct’
     or an array whose component is a ‘union’ or a ‘struct’, and it is
     possible for these fields to have a different scalar storage order
     than the enclosing type.

     Note that neither pointer nor vector fields are considered scalar
     fields in this context, so the attribute has no effects on these
     fields.

     This attribute is supported only for targets that use a uniform
     default scalar storage order (fortunately, most of them), i.e.
     targets that store the scalars either all in big-endian or all in
     little-endian.

     Additional restrictions are enforced for types with the reverse
     scalar storage order with regard to the scalar storage order of the
     target:

        • Taking the address of a scalar field of a ‘union’ or a
          ‘struct’ with reverse scalar storage order is not permitted
          and yields an error.
        • Taking the address of an array field, whose component is
          scalar, of a ‘union’ or a ‘struct’ with reverse scalar storage
          order is permitted but yields a warning, unless
          ‘-Wno-scalar-storage-order’ is specified.
        • Taking the address of a ‘union’ or a ‘struct’ with reverse
          scalar storage order is permitted.

     These restrictions exist because the storage order attribute is
     lost when the address of a scalar or the address of an array with
     scalar component is taken, so storing indirectly through this
     address generally does not work.  The second case is nevertheless
     allowed to be able to perform a block copy from or to the array.

     Moreover, the use of type punning or aliasing to toggle the storage
     order is not supported; that is to say, if a given scalar object
     can be accessed through distinct types that assign a different
     storage order to it, then the behavior is undefined.

‘transparent_union’

     This attribute, attached to a ‘union’ type definition, indicates
     that any function parameter having that union type causes calls to
     that function to be treated in a special way.

     First, the argument corresponding to a transparent union type can
     be of any type in the union; no cast is required.  Also, if the
     union contains a pointer type, the corresponding argument can be a
     null pointer constant or a void pointer expression; and if the
     union contains a void pointer type, the corresponding argument can
     be any pointer expression.  If the union member type is a pointer,
     qualifiers like ‘const’ on the referenced type must be respected,
     just as with normal pointer conversions.

     Second, the argument is passed to the function using the calling
     conventions of the first member of the transparent union, not the
     calling conventions of the union itself.  All members of the union
     must have the same machine representation; this is necessary for
     this argument passing to work properly.

     Transparent unions are designed for library functions that have
     multiple interfaces for compatibility reasons.  For example,
     suppose the ‘wait’ function must accept either a value of type ‘int
     *’ to comply with POSIX, or a value of type ‘union wait *’ to
     comply with the 4.1BSD interface.  If ‘wait’'s parameter were ‘void
     *’, ‘wait’ would accept both kinds of arguments, but it would also
     accept any other pointer type and this would make argument type
     checking less useful.  Instead, ‘<sys/wait.h>’ might define the
     interface as follows:

          typedef union __attribute__ ((__transparent_union__))
            {
              int *__ip;
              union wait *__up;
            } wait_status_ptr_t;

          pid_t wait (wait_status_ptr_t);

     This interface allows either ‘int *’ or ‘union wait *’ arguments to
     be passed, using the ‘int *’ calling convention.  The program can
     call ‘wait’ with arguments of either type:

          int w1 () { int w; return wait (&w); }
          int w2 () { union wait w; return wait (&w); }

     With this interface, ‘wait’'s implementation might look like this:

          pid_t wait (wait_status_ptr_t p)
          {
            return waitpid (-1, p.__ip, 0);
          }

‘unused’
     When attached to a type (including a ‘union’ or a ‘struct’), this
     attribute means that variables of that type are meant to appear
     possibly unused.  GCC does not produce a warning for any variables
     of that type, even if the variable appears to do nothing.  This is
     often the case with lock or thread classes, which are usually
     defined and then not referenced, but contain constructors and
     destructors that have nontrivial bookkeeping functions.

‘vector_size (BYTES)’
     This attribute specifies the vector size for the type, measured in
     bytes.  The type to which it applies is known as the “base type”.
     The BYTES argument must be a positive power-of-two multiple of the
     base type size.  For example, the following declarations:

          typedef __attribute__ ((vector_size (32))) int int_vec32_t ;
          typedef __attribute__ ((vector_size (32))) int* int_vec32_ptr_t;
          typedef __attribute__ ((vector_size (32))) int int_vec32_arr3_t[3];

     define ‘int_vec32_t’ to be a 32-byte vector type composed of ‘int’
     sized units.  With ‘int’ having a size of 4 bytes, the type defines
     a vector of eight units, four bytes each.  The mode of variables of
     type ‘int_vec32_t’ is ‘V8SI’.  ‘int_vec32_ptr_t’ is then defined to
     be a pointer to such a vector type, and ‘int_vec32_arr3_t’ to be an
     array of three such vectors.  *Note Vector Extensions::, for
     details of manipulating objects of vector types.

     This attribute is only applicable to integral and floating scalar
     types.  In function declarations the attribute applies to the
     function return type.

     For example, the following:
          __attribute__ ((vector_size (16))) float get_flt_vec16 (void);
     declares ‘get_flt_vec16’ to be a function returning a 16-byte
     vector with the base type ‘float’.

‘visibility’
     In C++, attribute visibility (*note Function Attributes::) can also
     be applied to class, struct, union and enum types.  Unlike other
     type attributes, the attribute must appear between the initial
     keyword and the name of the type; it cannot appear after the body
     of the type.

     Note that the type visibility is applied to vague linkage entities
     associated with the class (vtable, typeinfo node, etc.).  In
     particular, if a class is thrown as an exception in one shared
     object and caught in another, the class must have default
     visibility.  Otherwise the two shared objects are unable to use the
     same typeinfo node and exception handling will break.

‘objc_root_class (Objective-C and Objective-C++ only)’
     This attribute marks a class as being a root class, and thus allows
     the compiler to elide any warnings about a missing superclass and
     to make additional checks for mandatory methods as needed.

 To specify multiple attributes, separate them by commas within the
double parentheses: for example, ‘__attribute__ ((aligned (16),
packed))’.


File: gcc.info,  Node: ARC Type Attributes,  Next: ARM Type Attributes,  Prev: Common Type Attributes,  Up: Type Attributes

6.35.2 ARC Type Attributes
--------------------------

Declaring objects with ‘uncached’ allows you to exclude data-cache
participation in load and store operations on those objects without
involving the additional semantic implications of ‘volatile’.  The ‘.di’
instruction suffix is used for all loads and stores of data declared
‘uncached’.


File: gcc.info,  Node: ARM Type Attributes,  Next: BPF Type Attributes,  Prev: ARC Type Attributes,  Up: Type Attributes

6.35.3 ARM Type Attributes
--------------------------

On those ARM targets that support ‘dllimport’ (such as Symbian OS), you
can use the ‘notshared’ attribute to indicate that the virtual table and
other similar data for a class should not be exported from a DLL.  For
example:

     class __declspec(notshared) C {
     public:
       __declspec(dllimport) C();
       virtual void f();
     }

     __declspec(dllexport)
     C::C() {}

In this code, ‘C::C’ is exported from the current DLL, but the virtual
table for ‘C’ is not exported.  (You can use ‘__attribute__’ instead of
‘__declspec’ if you prefer, but most Symbian OS code uses ‘__declspec’.)


File: gcc.info,  Node: BPF Type Attributes,  Next: MeP Type Attributes,  Prev: ARM Type Attributes,  Up: Type Attributes

6.35.4 BPF Type Attributes
--------------------------

BPF Compile Once - Run Everywhere (CO-RE) support.  When attached to a
‘struct’ or ‘union’ type definition, indicates that CO-RE relocation
information should be generated for any access to a variable of that
type.  The behavior is equivalent to the programmer manually wrapping
every such access with ‘__builtin_preserve_access_index’.


File: gcc.info,  Node: MeP Type Attributes,  Next: PowerPC Type Attributes,  Prev: BPF Type Attributes,  Up: Type Attributes

6.35.5 MeP Type Attributes
--------------------------

Many of the MeP variable attributes may be applied to types as well.
Specifically, the ‘based’, ‘tiny’, ‘near’, and ‘far’ attributes may be
applied to either.  The ‘io’ and ‘cb’ attributes may not be applied to
types.


File: gcc.info,  Node: PowerPC Type Attributes,  Next: x86 Type Attributes,  Prev: MeP Type Attributes,  Up: Type Attributes

6.35.6 PowerPC Type Attributes
------------------------------

Three attributes currently are defined for PowerPC configurations:
‘altivec’, ‘ms_struct’ and ‘gcc_struct’.

 For full documentation of the ‘ms_struct’ and ‘gcc_struct’ attributes
please see the documentation in *note x86 Type Attributes::.

 The ‘altivec’ attribute allows one to declare AltiVec vector data types
supported by the AltiVec Programming Interface Manual.  The attribute
requires an argument to specify one of three vector types: ‘vector__’,
‘pixel__’ (always followed by unsigned short), and ‘bool__’ (always
followed by unsigned).

     __attribute__((altivec(vector__)))
     __attribute__((altivec(pixel__))) unsigned short
     __attribute__((altivec(bool__))) unsigned

 These attributes mainly are intended to support the ‘__vector’,
‘__pixel’, and ‘__bool’ AltiVec keywords.


File: gcc.info,  Node: x86 Type Attributes,  Prev: PowerPC Type Attributes,  Up: Type Attributes

6.35.7 x86 Type Attributes
--------------------------

Two attributes are currently defined for x86 configurations: ‘ms_struct’
and ‘gcc_struct’.

‘ms_struct’
‘gcc_struct’

     If ‘packed’ is used on a structure, or if bit-fields are used it
     may be that the Microsoft ABI packs them differently than GCC
     normally packs them.  Particularly when moving packed data between
     functions compiled with GCC and the native Microsoft compiler
     (either via function call or as data in a file), it may be
     necessary to access either format.

     The ‘ms_struct’ and ‘gcc_struct’ attributes correspond to the
     ‘-mms-bitfields’ and ‘-mno-ms-bitfields’ command-line options,
     respectively; see *note x86 Options::, for details of how structure
     layout is affected.  *Note x86 Variable Attributes::, for
     information about the corresponding attributes on variables.


File: gcc.info,  Node: Label Attributes,  Next: Enumerator Attributes,  Prev: Type Attributes,  Up: C Extensions

6.36 Label Attributes
=====================

GCC allows attributes to be set on C labels.  *Note Attribute Syntax::,
for details of the exact syntax for using attributes.  Other attributes
are available for functions (*note Function Attributes::), variables
(*note Variable Attributes::), enumerators (*note Enumerator
Attributes::), statements (*note Statement Attributes::), and for types
(*note Type Attributes::).  A label attribute followed by a declaration
appertains to the label and not the declaration.

 This example uses the ‘cold’ label attribute to indicate the
‘ErrorHandling’ branch is unlikely to be taken and that the
‘ErrorHandling’ label is unused:


        asm goto ("some asm" : : : : NoError);

     /* This branch (the fall-through from the asm) is less commonly used */
     ErrorHandling:
        __attribute__((cold, unused)); /* Semi-colon is required here */
        printf("error\n");
        return 0;

     NoError:
        printf("no error\n");
        return 1;

‘unused’
     This feature is intended for program-generated code that may
     contain unused labels, but which is compiled with ‘-Wall’.  It is
     not normally appropriate to use in it human-written code, though it
     could be useful in cases where the code that jumps to the label is
     contained within an ‘#ifdef’ conditional.

‘hot’
     The ‘hot’ attribute on a label is used to inform the compiler that
     the path following the label is more likely than paths that are not
     so annotated.  This attribute is used in cases where
     ‘__builtin_expect’ cannot be used, for instance with computed goto
     or ‘asm goto’.

‘cold’
     The ‘cold’ attribute on labels is used to inform the compiler that
     the path following the label is unlikely to be executed.  This
     attribute is used in cases where ‘__builtin_expect’ cannot be used,
     for instance with computed goto or ‘asm goto’.


File: gcc.info,  Node: Enumerator Attributes,  Next: Statement Attributes,  Prev: Label Attributes,  Up: C Extensions

6.37 Enumerator Attributes
==========================

GCC allows attributes to be set on enumerators.  *Note Attribute
Syntax::, for details of the exact syntax for using attributes.  Other
attributes are available for functions (*note Function Attributes::),
variables (*note Variable Attributes::), labels (*note Label
Attributes::), statements (*note Statement Attributes::), and for types
(*note Type Attributes::).

 This example uses the ‘deprecated’ enumerator attribute to indicate the
‘oldval’ enumerator is deprecated:

     enum E {
       oldval __attribute__((deprecated)),
       newval
     };

     int
     fn (void)
     {
       return oldval;
     }

‘deprecated’
     The ‘deprecated’ attribute results in a warning if the enumerator
     is used anywhere in the source file.  This is useful when
     identifying enumerators that are expected to be removed in a future
     version of a program.  The warning also includes the location of
     the declaration of the deprecated enumerator, to enable users to
     easily find further information about why the enumerator is
     deprecated, or what they should do instead.  Note that the warnings
     only occurs for uses.

‘unavailable’
     The ‘unavailable’ attribute results in an error if the enumerator
     is used anywhere in the source file.  In other respects it behaves
     in the same manner as the ‘deprecated’ attribute.


File: gcc.info,  Node: Statement Attributes,  Next: Attribute Syntax,  Prev: Enumerator Attributes,  Up: C Extensions

6.38 Statement Attributes
=========================

GCC allows attributes to be set on null statements.  *Note Attribute
Syntax::, for details of the exact syntax for using attributes.  Other
attributes are available for functions (*note Function Attributes::),
variables (*note Variable Attributes::), labels (*note Label
Attributes::), enumerators (*note Enumerator Attributes::), and for
types (*note Type Attributes::).

 This example uses the ‘fallthrough’ statement attribute to indicate
that the ‘-Wimplicit-fallthrough’ warning should not be emitted:

     switch (cond)
       {
       case 1:
         bar (1);
         __attribute__((fallthrough));
       case 2:
         ...
       }

‘fallthrough’
     The ‘fallthrough’ attribute with a null statement serves as a
     fallthrough statement.  It hints to the compiler that a statement
     that falls through to another case label, or user-defined label in
     a switch statement is intentional and thus the
     ‘-Wimplicit-fallthrough’ warning must not trigger.  The fallthrough
     attribute may appear at most once in each attribute list, and may
     not be mixed with other attributes.  It can only be used in a
     switch statement (the compiler will issue an error otherwise),
     after a preceding statement and before a logically succeeding case
     label, or user-defined label.


File: gcc.info,  Node: Attribute Syntax,  Next: Function Prototypes,  Prev: Statement Attributes,  Up: C Extensions

6.39 Attribute Syntax
=====================

This section describes the syntax with which ‘__attribute__’ may be
used, and the constructs to which attribute specifiers bind, for the C
language.  Some details may vary for C++ and Objective-C.  Because of
infelicities in the grammar for attributes, some forms described here
may not be successfully parsed in all cases.

 There are some problems with the semantics of attributes in C++.  For
example, there are no manglings for attributes, although they may affect
code generation, so problems may arise when attributed types are used in
conjunction with templates or overloading.  Similarly, ‘typeid’ does not
distinguish between types with different attributes.  Support for
attributes in C++ may be restricted in future to attributes on
declarations only, but not on nested declarators.

 *Note Function Attributes::, for details of the semantics of attributes
applying to functions.  *Note Variable Attributes::, for details of the
semantics of attributes applying to variables.  *Note Type Attributes::,
for details of the semantics of attributes applying to structure, union
and enumerated types.  *Note Label Attributes::, for details of the
semantics of attributes applying to labels.  *Note Enumerator
Attributes::, for details of the semantics of attributes applying to
enumerators.  *Note Statement Attributes::, for details of the semantics
of attributes applying to statements.

 An “attribute specifier” is of the form ‘__attribute__
((ATTRIBUTE-LIST))’.  An “attribute list” is a possibly empty
comma-separated sequence of “attributes”, where each attribute is one of
the following:

   • Empty.  Empty attributes are ignored.

   • An attribute name (which may be an identifier such as ‘unused’, or
     a reserved word such as ‘const’).

   • An attribute name followed by a parenthesized list of parameters
     for the attribute.  These parameters take one of the following
     forms:

        • An identifier.  For example, ‘mode’ attributes use this form.

        • An identifier followed by a comma and a non-empty
          comma-separated list of expressions.  For example, ‘format’
          attributes use this form.

        • A possibly empty comma-separated list of expressions.  For
          example, ‘format_arg’ attributes use this form with the list
          being a single integer constant expression, and ‘alias’
          attributes use this form with the list being a single string
          constant.

 An “attribute specifier list” is a sequence of one or more attribute
specifiers, not separated by any other tokens.

 You may optionally specify attribute names with ‘__’ preceding and
following the name.  This allows you to use them in header files without
being concerned about a possible macro of the same name.  For example,
you may use the attribute name ‘__noreturn__’ instead of ‘noreturn’.

Label Attributes
................

In GNU C, an attribute specifier list may appear after the colon
following a label, other than a ‘case’ or ‘default’ label.  GNU C++ only
permits attributes on labels if the attribute specifier is immediately
followed by a semicolon (i.e., the label applies to an empty statement).
If the semicolon is missing, C++ label attributes are ambiguous, as it
is permissible for a declaration, which could begin with an attribute
list, to be labelled in C++.  Declarations cannot be labelled in C90 or
C99, so the ambiguity does not arise there.

Enumerator Attributes
.....................

In GNU C, an attribute specifier list may appear as part of an
enumerator.  The attribute goes after the enumeration constant, before
‘=’, if present.  The optional attribute in the enumerator appertains to
the enumeration constant.  It is not possible to place the attribute
after the constant expression, if present.

Statement Attributes
....................

In GNU C, an attribute specifier list may appear as part of a null
statement.  The attribute goes before the semicolon.

Type Attributes
...............

An attribute specifier list may appear as part of a ‘struct’, ‘union’ or
‘enum’ specifier.  It may go either immediately after the ‘struct’,
‘union’ or ‘enum’ keyword, or after the closing brace.  The former
syntax is preferred.  Where attribute specifiers follow the closing
brace, they are considered to relate to the structure, union or
enumerated type defined, not to any enclosing declaration the type
specifier appears in, and the type defined is not complete until after
the attribute specifiers.

All other attributes
....................

Otherwise, an attribute specifier appears as part of a declaration,
counting declarations of unnamed parameters and type names, and relates
to that declaration (which may be nested in another declaration, for
example in the case of a parameter declaration), or to a particular
declarator within a declaration.  Where an attribute specifier is
applied to a parameter declared as a function or an array, it should
apply to the function or array rather than the pointer to which the
parameter is implicitly converted, but this is not yet correctly
implemented.

 Any list of specifiers and qualifiers at the start of a declaration may
contain attribute specifiers, whether or not such a list may in that
context contain storage class specifiers.  (Some attributes, however,
are essentially in the nature of storage class specifiers, and only make
sense where storage class specifiers may be used; for example,
‘section’.)  There is one necessary limitation to this syntax: the first
old-style parameter declaration in a function definition cannot begin
with an attribute specifier, because such an attribute applies to the
function instead by syntax described below (which, however, is not yet
implemented in this case).  In some other cases, attribute specifiers
are permitted by this grammar but not yet supported by the compiler.
All attribute specifiers in this place relate to the declaration as a
whole.  In the obsolescent usage where a type of ‘int’ is implied by the
absence of type specifiers, such a list of specifiers and qualifiers may
be an attribute specifier list with no other specifiers or qualifiers.

 At present, the first parameter in a function prototype must have some
type specifier that is not an attribute specifier; this resolves an
ambiguity in the interpretation of ‘void f(int (__attribute__((foo))
x))’, but is subject to change.  At present, if the parentheses of a
function declarator contain only attributes then those attributes are
ignored, rather than yielding an error or warning or implying a single
parameter of type int, but this is subject to change.

 An attribute specifier list may appear immediately before a declarator
(other than the first) in a comma-separated list of declarators in a
declaration of more than one identifier using a single list of
specifiers and qualifiers.  Such attribute specifiers apply only to the
identifier before whose declarator they appear.  For example, in

     __attribute__((noreturn)) void d0 (void),
         __attribute__((format(printf, 1, 2))) d1 (const char *, ...),
          d2 (void);

the ‘noreturn’ attribute applies to all the functions declared; the
‘format’ attribute only applies to ‘d1’.

 An attribute specifier list may appear immediately before the comma,
‘=’ or semicolon terminating the declaration of an identifier other than
a function definition.  Such attribute specifiers apply to the declared
object or function.  Where an assembler name for an object or function
is specified (*note Asm Labels::), the attribute must follow the ‘asm’
specification.

 An attribute specifier list may, in future, be permitted to appear
after the declarator in a function definition (before any old-style
parameter declarations or the function body).

 Attribute specifiers may be mixed with type qualifiers appearing inside
the ‘[]’ of a parameter array declarator, in the C99 construct by which
such qualifiers are applied to the pointer to which the array is
implicitly converted.  Such attribute specifiers apply to the pointer,
not to the array, but at present this is not implemented and they are
ignored.

 An attribute specifier list may appear at the start of a nested
declarator.  At present, there are some limitations in this usage: the
attributes correctly apply to the declarator, but for most individual
attributes the semantics this implies are not implemented.  When
attribute specifiers follow the ‘*’ of a pointer declarator, they may be
mixed with any type qualifiers present.  The following describes the
formal semantics of this syntax.  It makes the most sense if you are
familiar with the formal specification of declarators in the ISO C
standard.

 Consider (as in C99 subclause 6.7.5 paragraph 4) a declaration ‘T D1’,
where ‘T’ contains declaration specifiers that specify a type TYPE (such
as ‘int’) and ‘D1’ is a declarator that contains an identifier IDENT.
The type specified for IDENT for derived declarators whose type does not
include an attribute specifier is as in the ISO C standard.

 If ‘D1’ has the form ‘( ATTRIBUTE-SPECIFIER-LIST D )’, and the
declaration ‘T D’ specifies the type "DERIVED-DECLARATOR-TYPE-LIST TYPE"
for IDENT, then ‘T D1’ specifies the type "DERIVED-DECLARATOR-TYPE-LIST
ATTRIBUTE-SPECIFIER-LIST TYPE" for IDENT.

 If ‘D1’ has the form ‘* TYPE-QUALIFIER-AND-ATTRIBUTE-SPECIFIER-LIST D’,
and the declaration ‘T D’ specifies the type
"DERIVED-DECLARATOR-TYPE-LIST TYPE" for IDENT, then ‘T D1’ specifies the
type "DERIVED-DECLARATOR-TYPE-LIST
TYPE-QUALIFIER-AND-ATTRIBUTE-SPECIFIER-LIST pointer to TYPE" for IDENT.

 For example,

     void (__attribute__((noreturn)) ****f) (void);

specifies the type "pointer to pointer to pointer to pointer to
non-returning function returning ‘void’".  As another example,

     char *__attribute__((aligned(8))) *f;

specifies the type "pointer to 8-byte-aligned pointer to ‘char’".  Note
again that this does not work with most attributes; for example, the
usage of ‘aligned’ and ‘noreturn’ attributes given above is not yet
supported.

 For compatibility with existing code written for compiler versions that
did not implement attributes on nested declarators, some laxity is
allowed in the placing of attributes.  If an attribute that only applies
to types is applied to a declaration, it is treated as applying to the
type of that declaration.  If an attribute that only applies to
declarations is applied to the type of a declaration, it is treated as
applying to that declaration; and, for compatibility with code placing
the attributes immediately before the identifier declared, such an
attribute applied to a function return type is treated as applying to
the function type, and such an attribute applied to an array element
type is treated as applying to the array type.  If an attribute that
only applies to function types is applied to a pointer-to-function type,
it is treated as applying to the pointer target type; if such an
attribute is applied to a function return type that is not a
pointer-to-function type, it is treated as applying to the function
type.


File: gcc.info,  Node: Function Prototypes,  Next: C++ Comments,  Prev: Attribute Syntax,  Up: C Extensions

6.40 Prototypes and Old-Style Function Definitions
==================================================

GNU C extends ISO C to allow a function prototype to override a later
old-style non-prototype definition.  Consider the following example:

     /* Use prototypes unless the compiler is old-fashioned.  */
     #ifdef __STDC__
     #define P(x) x
     #else
     #define P(x) ()
     #endif

     /* Prototype function declaration.  */
     int isroot P((uid_t));

     /* Old-style function definition.  */
     int
     isroot (x)   /* ??? lossage here ??? */
          uid_t x;
     {
       return x == 0;
     }

 Suppose the type ‘uid_t’ happens to be ‘short’.  ISO C does not allow
this example, because subword arguments in old-style non-prototype
definitions are promoted.  Therefore in this example the function
definition's argument is really an ‘int’, which does not match the
prototype argument type of ‘short’.

 This restriction of ISO C makes it hard to write code that is portable
to traditional C compilers, because the programmer does not know whether
the ‘uid_t’ type is ‘short’, ‘int’, or ‘long’.  Therefore, in cases like
these GNU C allows a prototype to override a later old-style definition.
More precisely, in GNU C, a function prototype argument type overrides
the argument type specified by a later old-style definition if the
former type is the same as the latter type before promotion.  Thus in
GNU C the above example is equivalent to the following:

     int isroot (uid_t);

     int
     isroot (uid_t x)
     {
       return x == 0;
     }

GNU C++ does not support old-style function definitions, so this
extension is irrelevant.


File: gcc.info,  Node: C++ Comments,  Next: Dollar Signs,  Prev: Function Prototypes,  Up: C Extensions

6.41 C++ Style Comments
=======================

In GNU C, you may use C++ style comments, which start with ‘//’ and
continue until the end of the line.  Many other C implementations allow
such comments, and they are included in the 1999 C standard.  However,
C++ style comments are not recognized if you specify an ‘-std’ option
specifying a version of ISO C before C99, or ‘-ansi’ (equivalent to
‘-std=c90’).


File: gcc.info,  Node: Dollar Signs,  Next: Character Escapes,  Prev: C++ Comments,  Up: C Extensions

6.42 Dollar Signs in Identifier Names
=====================================

In GNU C, you may normally use dollar signs in identifier names.  This
is because many traditional C implementations allow such identifiers.
However, dollar signs in identifiers are not supported on a few target
machines, typically because the target assembler does not allow them.


File: gcc.info,  Node: Character Escapes,  Next: Alignment,  Prev: Dollar Signs,  Up: C Extensions

6.43 The Character <ESC> in Constants
=====================================

You can use the sequence ‘\e’ in a string or character constant to stand
for the ASCII character <ESC>.


File: gcc.info,  Node: Alignment,  Next: Inline,  Prev: Character Escapes,  Up: C Extensions

6.44 Determining the Alignment of Functions, Types or Variables
===============================================================

The keyword ‘__alignof__’ determines the alignment requirement of a
function, object, or a type, or the minimum alignment usually required
by a type.  Its syntax is just like ‘sizeof’ and C11 ‘_Alignof’.

 For example, if the target machine requires a ‘double’ value to be
aligned on an 8-byte boundary, then ‘__alignof__ (double)’ is 8.  This
is true on many RISC machines.  On more traditional machine designs,
‘__alignof__ (double)’ is 4 or even 2.

 Some machines never actually require alignment; they allow references
to any data type even at an odd address.  For these machines,
‘__alignof__’ reports the smallest alignment that GCC gives the data
type, usually as mandated by the target ABI.

 If the operand of ‘__alignof__’ is an lvalue rather than a type, its
value is the required alignment for its type, taking into account any
minimum alignment specified by attribute ‘aligned’ (*note Common
Variable Attributes::).  For example, after this declaration:

     struct foo { int x; char y; } foo1;

the value of ‘__alignof__ (foo1.y)’ is 1, even though its actual
alignment is probably 2 or 4, the same as ‘__alignof__ (int)’.  It is an
error to ask for the alignment of an incomplete type other than ‘void’.

 If the operand of the ‘__alignof__’ expression is a function, the
expression evaluates to the alignment of the function which may be
specified by attribute ‘aligned’ (*note Common Function Attributes::).


File: gcc.info,  Node: Inline,  Next: Volatiles,  Prev: Alignment,  Up: C Extensions

6.45 An Inline Function is As Fast As a Macro
=============================================

By declaring a function inline, you can direct GCC to make calls to that
function faster.  One way GCC can achieve this is to integrate that
function's code into the code for its callers.  This makes execution
faster by eliminating the function-call overhead; in addition, if any of
the actual argument values are constant, their known values may permit
simplifications at compile time so that not all of the inline function's
code needs to be included.  The effect on code size is less predictable;
object code may be larger or smaller with function inlining, depending
on the particular case.  You can also direct GCC to try to integrate all
"simple enough" functions into their callers with the option
‘-finline-functions’.

 GCC implements three different semantics of declaring a function
inline.  One is available with ‘-std=gnu89’ or ‘-fgnu89-inline’ or when
‘gnu_inline’ attribute is present on all inline declarations, another
when ‘-std=c99’, ‘-std=gnu99’ or an option for a later C version is used
(without ‘-fgnu89-inline’), and the third is used when compiling C++.

 To declare a function inline, use the ‘inline’ keyword in its
declaration, like this:

     static inline int
     inc (int *a)
     {
       return (*a)++;
     }

 If you are writing a header file to be included in ISO C90 programs,
write ‘__inline__’ instead of ‘inline’.  *Note Alternate Keywords::.

 The three types of inlining behave similarly in two important cases:
when the ‘inline’ keyword is used on a ‘static’ function, like the
example above, and when a function is first declared without using the
‘inline’ keyword and then is defined with ‘inline’, like this:

     extern int inc (int *a);
     inline int
     inc (int *a)
     {
       return (*a)++;
     }

 In both of these common cases, the program behaves the same as if you
had not used the ‘inline’ keyword, except for its speed.

 When a function is both inline and ‘static’, if all calls to the
function are integrated into the caller, and the function's address is
never used, then the function's own assembler code is never referenced.
In this case, GCC does not actually output assembler code for the
function, unless you specify the option ‘-fkeep-inline-functions’.  If
there is a nonintegrated call, then the function is compiled to
assembler code as usual.  The function must also be compiled as usual if
the program refers to its address, because that cannot be inlined.

 Note that certain usages in a function definition can make it
unsuitable for inline substitution.  Among these usages are: variadic
functions, use of ‘alloca’, use of computed goto (*note Labels as
Values::), use of nonlocal goto, use of nested functions, use of
‘setjmp’, use of ‘__builtin_longjmp’ and use of ‘__builtin_return’ or
‘__builtin_apply_args’.  Using ‘-Winline’ warns when a function marked
‘inline’ could not be substituted, and gives the reason for the failure.

 As required by ISO C++, GCC considers member functions defined within
the body of a class to be marked inline even if they are not explicitly
declared with the ‘inline’ keyword.  You can override this with
‘-fno-default-inline’; *note Options Controlling C++ Dialect: C++
Dialect Options.

 GCC does not inline any functions when not optimizing unless you
specify the ‘always_inline’ attribute for the function, like this:

     /* Prototype.  */
     inline void foo (const char) __attribute__((always_inline));

 The remainder of this section is specific to GNU C90 inlining.

 When an inline function is not ‘static’, then the compiler must assume
that there may be calls from other source files; since a global symbol
can be defined only once in any program, the function must not be
defined in the other source files, so the calls therein cannot be
integrated.  Therefore, a non-‘static’ inline function is always
compiled on its own in the usual fashion.

 If you specify both ‘inline’ and ‘extern’ in the function definition,
then the definition is used only for inlining.  In no case is the
function compiled on its own, not even if you refer to its address
explicitly.  Such an address becomes an external reference, as if you
had only declared the function, and had not defined it.

 This combination of ‘inline’ and ‘extern’ has almost the effect of a
macro.  The way to use it is to put a function definition in a header
file with these keywords, and put another copy of the definition
(lacking ‘inline’ and ‘extern’) in a library file.  The definition in
the header file causes most calls to the function to be inlined.  If any
uses of the function remain, they refer to the single copy in the
library.


File: gcc.info,  Node: Volatiles,  Next: Using Assembly Language with C,  Prev: Inline,  Up: C Extensions

6.46 When is a Volatile Object Accessed?
========================================

C has the concept of volatile objects.  These are normally accessed by
pointers and used for accessing hardware or inter-thread communication.
The standard encourages compilers to refrain from optimizations
concerning accesses to volatile objects, but leaves it implementation
defined as to what constitutes a volatile access.  The minimum
requirement is that at a sequence point all previous accesses to
volatile objects have stabilized and no subsequent accesses have
occurred.  Thus an implementation is free to reorder and combine
volatile accesses that occur between sequence points, but cannot do so
for accesses across a sequence point.  The use of volatile does not
allow you to violate the restriction on updating objects multiple times
between two sequence points.

 Accesses to non-volatile objects are not ordered with respect to
volatile accesses.  You cannot use a volatile object as a memory barrier
to order a sequence of writes to non-volatile memory.  For instance:

     int *ptr = SOMETHING;
     volatile int vobj;
     *ptr = SOMETHING;
     vobj = 1;

Unless *PTR and VOBJ can be aliased, it is not guaranteed that the write
to *PTR occurs by the time the update of VOBJ happens.  If you need this
guarantee, you must use a stronger memory barrier such as:

     int *ptr = SOMETHING;
     volatile int vobj;
     *ptr = SOMETHING;
     asm volatile ("" : : : "memory");
     vobj = 1;

 A scalar volatile object is read when it is accessed in a void context:

     volatile int *src = SOMEVALUE;
     *src;

 Such expressions are rvalues, and GCC implements this as a read of the
volatile object being pointed to.

 Assignments are also expressions and have an rvalue.  However when
assigning to a scalar volatile, the volatile object is not reread,
regardless of whether the assignment expression's rvalue is used or not.
If the assignment's rvalue is used, the value is that assigned to the
volatile object.  For instance, there is no read of VOBJ in all the
following cases:

     int obj;
     volatile int vobj;
     vobj = SOMETHING;
     obj = vobj = SOMETHING;
     obj ? vobj = ONETHING : vobj = ANOTHERTHING;
     obj = (SOMETHING, vobj = ANOTHERTHING);

 If you need to read the volatile object after an assignment has
occurred, you must use a separate expression with an intervening
sequence point.

 As bit-fields are not individually addressable, volatile bit-fields may
be implicitly read when written to, or when adjacent bit-fields are
accessed.  Bit-field operations may be optimized such that adjacent
bit-fields are only partially accessed, if they straddle a storage unit
boundary.  For these reasons it is unwise to use volatile bit-fields to
access hardware.


File: gcc.info,  Node: Using Assembly Language with C,  Next: Alternate Keywords,  Prev: Volatiles,  Up: C Extensions

6.47 How to Use Inline Assembly Language in C Code
==================================================

The ‘asm’ keyword allows you to embed assembler instructions within C
code.  GCC provides two forms of inline ‘asm’ statements.  A “basic
‘asm’” statement is one with no operands (*note Basic Asm::), while an
“extended ‘asm’” statement (*note Extended Asm::) includes one or more
operands.  The extended form is preferred for mixing C and assembly
language within a function, but to include assembly language at top
level you must use basic ‘asm’.

 You can also use the ‘asm’ keyword to override the assembler name for a
C symbol, or to place a C variable in a specific register.

* Menu:

* Basic Asm::          Inline assembler without operands.
* Extended Asm::       Inline assembler with operands.
* Constraints::        Constraints for ‘asm’ operands
* Asm Labels::         Specifying the assembler name to use for a C symbol.
* Explicit Register Variables::  Defining variables residing in specified
                       registers.
* Size of an asm::     How GCC calculates the size of an ‘asm’ block.


File: gcc.info,  Node: Basic Asm,  Next: Extended Asm,  Up: Using Assembly Language with C

6.47.1 Basic Asm -- Assembler Instructions Without Operands
-----------------------------------------------------------

A basic ‘asm’ statement has the following syntax:

     asm ASM-QUALIFIERS ( ASSEMBLERINSTRUCTIONS )

 For the C language, the ‘asm’ keyword is a GNU extension.  When writing
C code that can be compiled with ‘-ansi’ and the ‘-std’ options that
select C dialects without GNU extensions, use ‘__asm__’ instead of ‘asm’
(*note Alternate Keywords::).  For the C++ language, ‘asm’ is a standard
keyword, but ‘__asm__’ can be used for code compiled with ‘-fno-asm’.

Qualifiers
..........

‘volatile’
     The optional ‘volatile’ qualifier has no effect.  All basic ‘asm’
     blocks are implicitly volatile.

‘inline’
     If you use the ‘inline’ qualifier, then for inlining purposes the
     size of the ‘asm’ statement is taken as the smallest size possible
     (*note Size of an asm::).

Parameters
..........

ASSEMBLERINSTRUCTIONS
     This is a literal string that specifies the assembler code.  The
     string can contain any instructions recognized by the assembler,
     including directives.  GCC does not parse the assembler
     instructions themselves and does not know what they mean or even
     whether they are valid assembler input.

     You may place multiple assembler instructions together in a single
     ‘asm’ string, separated by the characters normally used in assembly
     code for the system.  A combination that works in most places is a
     newline to break the line, plus a tab character (written as
     ‘\n\t’).  Some assemblers allow semicolons as a line separator.
     However, note that some assembler dialects use semicolons to start
     a comment.

Remarks
.......

Using extended ‘asm’ (*note Extended Asm::) typically produces smaller,
safer, and more efficient code, and in most cases it is a better
solution than basic ‘asm’.  However, there are two situations where only
basic ‘asm’ can be used:

   • Extended ‘asm’ statements have to be inside a C function, so to
     write inline assembly language at file scope ("top-level"), outside
     of C functions, you must use basic ‘asm’.  You can use this
     technique to emit assembler directives, define assembly language
     macros that can be invoked elsewhere in the file, or write entire
     functions in assembly language.  Basic ‘asm’ statements outside of
     functions may not use any qualifiers.

   • Functions declared with the ‘naked’ attribute also require basic
     ‘asm’ (*note Function Attributes::).

 Safely accessing C data and calling functions from basic ‘asm’ is more
complex than it may appear.  To access C data, it is better to use
extended ‘asm’.

 Do not expect a sequence of ‘asm’ statements to remain perfectly
consecutive after compilation.  If certain instructions need to remain
consecutive in the output, put them in a single multi-instruction ‘asm’
statement.  Note that GCC's optimizers can move ‘asm’ statements
relative to other code, including across jumps.

 ‘asm’ statements may not perform jumps into other ‘asm’ statements.
GCC does not know about these jumps, and therefore cannot take account
of them when deciding how to optimize.  Jumps from ‘asm’ to C labels are
only supported in extended ‘asm’.

 Under certain circumstances, GCC may duplicate (or remove duplicates
of) your assembly code when optimizing.  This can lead to unexpected
duplicate symbol errors during compilation if your assembly code defines
symbols or labels.

 *Warning:* The C standards do not specify semantics for ‘asm’, making
it a potential source of incompatibilities between compilers.  These
incompatibilities may not produce compiler warnings/errors.

 GCC does not parse basic ‘asm’'s ASSEMBLERINSTRUCTIONS, which means
there is no way to communicate to the compiler what is happening inside
them.  GCC has no visibility of symbols in the ‘asm’ and may discard
them as unreferenced.  It also does not know about side effects of the
assembler code, such as modifications to memory or registers.  Unlike
some compilers, GCC assumes that no changes to general purpose registers
occur.  This assumption may change in a future release.

 To avoid complications from future changes to the semantics and the
compatibility issues between compilers, consider replacing basic ‘asm’
with extended ‘asm’.  See How to convert from basic asm to extended asm
(https://gcc.gnu.org/wiki/ConvertBasicAsmToExtended) for information
about how to perform this conversion.

 The compiler copies the assembler instructions in a basic ‘asm’
verbatim to the assembly language output file, without processing
dialects or any of the ‘%’ operators that are available with extended
‘asm’.  This results in minor differences between basic ‘asm’ strings
and extended ‘asm’ templates.  For example, to refer to registers you
might use ‘%eax’ in basic ‘asm’ and ‘%%eax’ in extended ‘asm’.

 On targets such as x86 that support multiple assembler dialects, all
basic ‘asm’ blocks use the assembler dialect specified by the ‘-masm’
command-line option (*note x86 Options::).  Basic ‘asm’ provides no
mechanism to provide different assembler strings for different dialects.

 For basic ‘asm’ with non-empty assembler string GCC assumes the
assembler block does not change any general purpose registers, but it
may read or write any globally accessible variable.

 Here is an example of basic ‘asm’ for i386:

     /* Note that this code will not compile with -masm=intel */
     #define DebugBreak() asm("int $3")


File: gcc.info,  Node: Extended Asm,  Next: Constraints,  Prev: Basic Asm,  Up: Using Assembly Language with C

6.47.2 Extended Asm - Assembler Instructions with C Expression Operands
-----------------------------------------------------------------------

With extended ‘asm’ you can read and write C variables from assembler
and perform jumps from assembler code to C labels.  Extended ‘asm’
syntax uses colons (‘:’) to delimit the operand parameters after the
assembler template:

     asm ASM-QUALIFIERS ( ASSEMBLERTEMPLATE
                      : OUTPUTOPERANDS
                      [ : INPUTOPERANDS
                      [ : CLOBBERS ] ])

     asm ASM-QUALIFIERS ( ASSEMBLERTEMPLATE
                           : OUTPUTOPERANDS
                           : INPUTOPERANDS
                           : CLOBBERS
                           : GOTOLABELS)
 where in the last form, ASM-QUALIFIERS contains ‘goto’ (and in the
first form, not).

 The ‘asm’ keyword is a GNU extension.  When writing code that can be
compiled with ‘-ansi’ and the various ‘-std’ options, use ‘__asm__’
instead of ‘asm’ (*note Alternate Keywords::).

Qualifiers
..........

‘volatile’
     The typical use of extended ‘asm’ statements is to manipulate input
     values to produce output values.  However, your ‘asm’ statements
     may also produce side effects.  If so, you may need to use the
     ‘volatile’ qualifier to disable certain optimizations.  *Note
     Volatile::.

‘inline’
     If you use the ‘inline’ qualifier, then for inlining purposes the
     size of the ‘asm’ statement is taken as the smallest size possible
     (*note Size of an asm::).

‘goto’
     This qualifier informs the compiler that the ‘asm’ statement may
     perform a jump to one of the labels listed in the GOTOLABELS.
     *Note GotoLabels::.

Parameters
..........

ASSEMBLERTEMPLATE
     This is a literal string that is the template for the assembler
     code.  It is a combination of fixed text and tokens that refer to
     the input, output, and goto parameters.  *Note AssemblerTemplate::.

OUTPUTOPERANDS
     A comma-separated list of the C variables modified by the
     instructions in the ASSEMBLERTEMPLATE.  An empty list is permitted.
     *Note OutputOperands::.

INPUTOPERANDS
     A comma-separated list of C expressions read by the instructions in
     the ASSEMBLERTEMPLATE.  An empty list is permitted.  *Note
     InputOperands::.

CLOBBERS
     A comma-separated list of registers or other values changed by the
     ASSEMBLERTEMPLATE, beyond those listed as outputs.  An empty list
     is permitted.  *Note Clobbers and Scratch Registers::.

GOTOLABELS
     When you are using the ‘goto’ form of ‘asm’, this section contains
     the list of all C labels to which the code in the ASSEMBLERTEMPLATE
     may jump.  *Note GotoLabels::.

     ‘asm’ statements may not perform jumps into other ‘asm’ statements,
     only to the listed GOTOLABELS.  GCC's optimizers do not know about
     other jumps; therefore they cannot take account of them when
     deciding how to optimize.

 The total number of input + output + goto operands is limited to 30.

Remarks
.......

The ‘asm’ statement allows you to include assembly instructions directly
within C code.  This may help you to maximize performance in
time-sensitive code or to access assembly instructions that are not
readily available to C programs.

 Note that extended ‘asm’ statements must be inside a function.  Only
basic ‘asm’ may be outside functions (*note Basic Asm::).  Functions
declared with the ‘naked’ attribute also require basic ‘asm’ (*note
Function Attributes::).

 While the uses of ‘asm’ are many and varied, it may help to think of an
‘asm’ statement as a series of low-level instructions that convert input
parameters to output parameters.  So a simple (if not particularly
useful) example for i386 using ‘asm’ might look like this:

     int src = 1;
     int dst;

     asm ("mov %1, %0\n\t"
         "add $1, %0"
         : "=r" (dst)
         : "r" (src));

     printf("%d\n", dst);

 This code copies ‘src’ to ‘dst’ and add 1 to ‘dst’.

6.47.2.1 Volatile
.................

GCC's optimizers sometimes discard ‘asm’ statements if they determine
there is no need for the output variables.  Also, the optimizers may
move code out of loops if they believe that the code will always return
the same result (i.e. none of its input values change between calls).
Using the ‘volatile’ qualifier disables these optimizations.  ‘asm’
statements that have no output operands and ‘asm goto’ statements, are
implicitly volatile.

 This i386 code demonstrates a case that does not use (or require) the
‘volatile’ qualifier.  If it is performing assertion checking, this code
uses ‘asm’ to perform the validation.  Otherwise, ‘dwRes’ is
unreferenced by any code.  As a result, the optimizers can discard the
‘asm’ statement, which in turn removes the need for the entire ‘DoCheck’
routine.  By omitting the ‘volatile’ qualifier when it isn't needed you
allow the optimizers to produce the most efficient code possible.

     void DoCheck(uint32_t dwSomeValue)
     {
        uint32_t dwRes;

        // Assumes dwSomeValue is not zero.
        asm ("bsfl %1,%0"
          : "=r" (dwRes)
          : "r" (dwSomeValue)
          : "cc");

        assert(dwRes > 3);
     }

 The next example shows a case where the optimizers can recognize that
the input (‘dwSomeValue’) never changes during the execution of the
function and can therefore move the ‘asm’ outside the loop to produce
more efficient code.  Again, using the ‘volatile’ qualifier disables
this type of optimization.

     void do_print(uint32_t dwSomeValue)
     {
        uint32_t dwRes;

        for (uint32_t x=0; x < 5; x++)
        {
           // Assumes dwSomeValue is not zero.
           asm ("bsfl %1,%0"
             : "=r" (dwRes)
             : "r" (dwSomeValue)
             : "cc");

           printf("%u: %u %u\n", x, dwSomeValue, dwRes);
        }
     }

 The following example demonstrates a case where you need to use the
‘volatile’ qualifier.  It uses the x86 ‘rdtsc’ instruction, which reads
the computer's time-stamp counter.  Without the ‘volatile’ qualifier,
the optimizers might assume that the ‘asm’ block will always return the
same value and therefore optimize away the second call.

     uint64_t msr;

     asm volatile ( "rdtsc\n\t"    // Returns the time in EDX:EAX.
             "shl $32, %%rdx\n\t"  // Shift the upper bits left.
             "or %%rdx, %0"        // 'Or' in the lower bits.
             : "=a" (msr)
             :
             : "rdx");

     printf("msr: %llx\n", msr);

     // Do other work...

     // Reprint the timestamp
     asm volatile ( "rdtsc\n\t"    // Returns the time in EDX:EAX.
             "shl $32, %%rdx\n\t"  // Shift the upper bits left.
             "or %%rdx, %0"        // 'Or' in the lower bits.
             : "=a" (msr)
             :
             : "rdx");

     printf("msr: %llx\n", msr);

 GCC's optimizers do not treat this code like the non-volatile code in
the earlier examples.  They do not move it out of loops or omit it on
the assumption that the result from a previous call is still valid.

 Note that the compiler can move even ‘volatile asm’ instructions
relative to other code, including across jump instructions.  For
example, on many targets there is a system register that controls the
rounding mode of floating-point operations.  Setting it with a ‘volatile
asm’ statement, as in the following PowerPC example, does not work
reliably.

     asm volatile("mtfsf 255, %0" : : "f" (fpenv));
     sum = x + y;

 The compiler may move the addition back before the ‘volatile asm’
statement.  To make it work as expected, add an artificial dependency to
the ‘asm’ by referencing a variable in the subsequent code, for example:

     asm volatile ("mtfsf 255,%1" : "=X" (sum) : "f" (fpenv));
     sum = x + y;

 Under certain circumstances, GCC may duplicate (or remove duplicates
of) your assembly code when optimizing.  This can lead to unexpected
duplicate symbol errors during compilation if your ‘asm’ code defines
symbols or labels.  Using ‘%=’ (*note AssemblerTemplate::) may help
resolve this problem.

6.47.2.2 Assembler Template
...........................

An assembler template is a literal string containing assembler
instructions.  The compiler replaces tokens in the template that refer
to inputs, outputs, and goto labels, and then outputs the resulting
string to the assembler.  The string can contain any instructions
recognized by the assembler, including directives.  GCC does not parse
the assembler instructions themselves and does not know what they mean
or even whether they are valid assembler input.  However, it does count
the statements (*note Size of an asm::).

 You may place multiple assembler instructions together in a single
‘asm’ string, separated by the characters normally used in assembly code
for the system.  A combination that works in most places is a newline to
break the line, plus a tab character to move to the instruction field
(written as ‘\n\t’).  Some assemblers allow semicolons as a line
separator.  However, note that some assembler dialects use semicolons to
start a comment.

 Do not expect a sequence of ‘asm’ statements to remain perfectly
consecutive after compilation, even when you are using the ‘volatile’
qualifier.  If certain instructions need to remain consecutive in the
output, put them in a single multi-instruction ‘asm’ statement.

 Accessing data from C programs without using input/output operands
(such as by using global symbols directly from the assembler template)
may not work as expected.  Similarly, calling functions directly from an
assembler template requires a detailed understanding of the target
assembler and ABI.

 Since GCC does not parse the assembler template, it has no visibility
of any symbols it references.  This may result in GCC discarding those
symbols as unreferenced unless they are also listed as input, output, or
goto operands.

Special format strings
......................

In addition to the tokens described by the input, output, and goto
operands, these tokens have special meanings in the assembler template:

‘%%’
     Outputs a single ‘%’ into the assembler code.

‘%=’
     Outputs a number that is unique to each instance of the ‘asm’
     statement in the entire compilation.  This option is useful when
     creating local labels and referring to them multiple times in a
     single template that generates multiple assembler instructions.

‘%{’
‘%|’
‘%}’
     Outputs ‘{’, ‘|’, and ‘}’ characters (respectively) into the
     assembler code.  When unescaped, these characters have special
     meaning to indicate multiple assembler dialects, as described
     below.

Multiple assembler dialects in ‘asm’ templates
..............................................

On targets such as x86, GCC supports multiple assembler dialects.  The
‘-masm’ option controls which dialect GCC uses as its default for inline
assembler.  The target-specific documentation for the ‘-masm’ option
contains the list of supported dialects, as well as the default dialect
if the option is not specified.  This information may be important to
understand, since assembler code that works correctly when compiled
using one dialect will likely fail if compiled using another.  *Note x86
Options::.

 If your code needs to support multiple assembler dialects (for example,
if you are writing public headers that need to support a variety of
compilation options), use constructs of this form:

     { dialect0 | dialect1 | dialect2... }

 This construct outputs ‘dialect0’ when using dialect #0 to compile the
code, ‘dialect1’ for dialect #1, etc.  If there are fewer alternatives
within the braces than the number of dialects the compiler supports, the
construct outputs nothing.

 For example, if an x86 compiler supports two dialects (‘att’, ‘intel’),
an assembler template such as this:

     "bt{l %[Offset],%[Base] | %[Base],%[Offset]}; jc %l2"

is equivalent to one of

     "btl %[Offset],%[Base] ; jc %l2"   /* att dialect */
     "bt %[Base],%[Offset]; jc %l2"     /* intel dialect */

 Using that same compiler, this code:

     "xchg{l}\t{%%}ebx, %1"

corresponds to either

     "xchgl\t%%ebx, %1"                 /* att dialect */
     "xchg\tebx, %1"                    /* intel dialect */

 There is no support for nesting dialect alternatives.

6.47.2.3 Output Operands
........................

An ‘asm’ statement has zero or more output operands indicating the names
of C variables modified by the assembler code.

 In this i386 example, ‘old’ (referred to in the template string as
‘%0’) and ‘*Base’ (as ‘%1’) are outputs and ‘Offset’ (‘%2’) is an input:

     bool old;

     __asm__ ("btsl %2,%1\n\t" // Turn on zero-based bit #Offset in Base.
              "sbb %0,%0"      // Use the CF to calculate old.
        : "=r" (old), "+rm" (*Base)
        : "Ir" (Offset)
        : "cc");

     return old;

 Operands are separated by commas.  Each operand has this format:

     [ [ASMSYMBOLICNAME] ] CONSTRAINT (CVARIABLENAME)

ASMSYMBOLICNAME
     Specifies a symbolic name for the operand.  Reference the name in
     the assembler template by enclosing it in square brackets (i.e.
     ‘%[Value]’).  The scope of the name is the ‘asm’ statement that
     contains the definition.  Any valid C variable name is acceptable,
     including names already defined in the surrounding code.  No two
     operands within the same ‘asm’ statement can use the same symbolic
     name.

     When not using an ASMSYMBOLICNAME, use the (zero-based) position of
     the operand in the list of operands in the assembler template.  For
     example if there are three output operands, use ‘%0’ in the
     template to refer to the first, ‘%1’ for the second, and ‘%2’ for
     the third.

CONSTRAINT
     A string constant specifying constraints on the placement of the
     operand; *Note Constraints::, for details.

     Output constraints must begin with either ‘=’ (a variable
     overwriting an existing value) or ‘+’ (when reading and writing).
     When using ‘=’, do not assume the location contains the existing
     value on entry to the ‘asm’, except when the operand is tied to an
     input; *note Input Operands: InputOperands.

     After the prefix, there must be one or more additional constraints
     (*note Constraints::) that describe where the value resides.
     Common constraints include ‘r’ for register and ‘m’ for memory.
     When you list more than one possible location (for example,
     ‘"=rm"’), the compiler chooses the most efficient one based on the
     current context.  If you list as many alternates as the ‘asm’
     statement allows, you permit the optimizers to produce the best
     possible code.  If you must use a specific register, but your
     Machine Constraints do not provide sufficient control to select the
     specific register you want, local register variables may provide a
     solution (*note Local Register Variables::).

CVARIABLENAME
     Specifies a C lvalue expression to hold the output, typically a
     variable name.  The enclosing parentheses are a required part of
     the syntax.

 When the compiler selects the registers to use to represent the output
operands, it does not use any of the clobbered registers (*note Clobbers
and Scratch Registers::).

 Output operand expressions must be lvalues.  The compiler cannot check
whether the operands have data types that are reasonable for the
instruction being executed.  For output expressions that are not
directly addressable (for example a bit-field), the constraint must
allow a register.  In that case, GCC uses the register as the output of
the ‘asm’, and then stores that register into the output.

 Operands using the ‘+’ constraint modifier count as two operands (that
is, both as input and output) towards the total maximum of 30 operands
per ‘asm’ statement.

 Use the ‘&’ constraint modifier (*note Modifiers::) on all output
operands that must not overlap an input.  Otherwise, GCC may allocate
the output operand in the same register as an unrelated input operand,
on the assumption that the assembler code consumes its inputs before
producing outputs.  This assumption may be false if the assembler code
actually consists of more than one instruction.

 The same problem can occur if one output parameter (A) allows a
register constraint and another output parameter (B) allows a memory
constraint.  The code generated by GCC to access the memory address in B
can contain registers which _might_ be shared by A, and GCC considers
those registers to be inputs to the asm.  As above, GCC assumes that
such input registers are consumed before any outputs are written.  This
assumption may result in incorrect behavior if the ‘asm’ statement
writes to A before using B.  Combining the ‘&’ modifier with the
register constraint on A ensures that modifying A does not affect the
address referenced by B.  Otherwise, the location of B is undefined if A
is modified before using B.

 ‘asm’ supports operand modifiers on operands (for example ‘%k2’ instead
of simply ‘%2’).  Typically these qualifiers are hardware dependent.
The list of supported modifiers for x86 is found at *note x86 Operand
modifiers: x86Operandmodifiers.

 If the C code that follows the ‘asm’ makes no use of any of the output
operands, use ‘volatile’ for the ‘asm’ statement to prevent the
optimizers from discarding the ‘asm’ statement as unneeded (see *note
Volatile::).

 This code makes no use of the optional ASMSYMBOLICNAME.  Therefore it
references the first output operand as ‘%0’ (were there a second, it
would be ‘%1’, etc).  The number of the first input operand is one
greater than that of the last output operand.  In this i386 example,
that makes ‘Mask’ referenced as ‘%1’:

     uint32_t Mask = 1234;
     uint32_t Index;

       asm ("bsfl %1, %0"
          : "=r" (Index)
          : "r" (Mask)
          : "cc");

 That code overwrites the variable ‘Index’ (‘=’), placing the value in a
register (‘r’).  Using the generic ‘r’ constraint instead of a
constraint for a specific register allows the compiler to pick the
register to use, which can result in more efficient code.  This may not
be possible if an assembler instruction requires a specific register.

 The following i386 example uses the ASMSYMBOLICNAME syntax.  It
produces the same result as the code above, but some may consider it
more readable or more maintainable since reordering index numbers is not
necessary when adding or removing operands.  The names ‘aIndex’ and
‘aMask’ are only used in this example to emphasize which names get used
where.  It is acceptable to reuse the names ‘Index’ and ‘Mask’.

     uint32_t Mask = 1234;
     uint32_t Index;

       asm ("bsfl %[aMask], %[aIndex]"
          : [aIndex] "=r" (Index)
          : [aMask] "r" (Mask)
          : "cc");

 Here are some more examples of output operands.

     uint32_t c = 1;
     uint32_t d;
     uint32_t *e = &c;

     asm ("mov %[e], %[d]"
        : [d] "=rm" (d)
        : [e] "rm" (*e));

 Here, ‘d’ may either be in a register or in memory.  Since the compiler
might already have the current value of the ‘uint32_t’ location pointed
to by ‘e’ in a register, you can enable it to choose the best location
for ‘d’ by specifying both constraints.

6.47.2.4 Flag Output Operands
.............................

Some targets have a special register that holds the "flags" for the
result of an operation or comparison.  Normally, the contents of that
register are either unmodifed by the asm, or the ‘asm’ statement is
considered to clobber the contents.

 On some targets, a special form of output operand exists by which
conditions in the flags register may be outputs of the asm.  The set of
conditions supported are target specific, but the general rule is that
the output variable must be a scalar integer, and the value is boolean.
When supported, the target defines the preprocessor symbol
‘__GCC_ASM_FLAG_OUTPUTS__’.

 Because of the special nature of the flag output operands, the
constraint may not include alternatives.

 Most often, the target has only one flags register, and thus is an
implied operand of many instructions.  In this case, the operand should
not be referenced within the assembler template via ‘%0’ etc, as there's
no corresponding text in the assembly language.

ARM
AArch64
     The flag output constraints for the ARM family are of the form
     ‘=@ccCOND’ where COND is one of the standard conditions defined in
     the ARM ARM for ‘ConditionHolds’.

     ‘eq’
          Z flag set, or equal
     ‘ne’
          Z flag clear or not equal
     ‘cs’
     ‘hs’
          C flag set or unsigned greater than equal
     ‘cc’
     ‘lo’
          C flag clear or unsigned less than
     ‘mi’
          N flag set or "minus"
     ‘pl’
          N flag clear or "plus"
     ‘vs’
          V flag set or signed overflow
     ‘vc’
          V flag clear
     ‘hi’
          unsigned greater than
     ‘ls’
          unsigned less than equal
     ‘ge’
          signed greater than equal
     ‘lt’
          signed less than
     ‘gt’
          signed greater than
     ‘le’
          signed less than equal

     The flag output constraints are not supported in thumb1 mode.

x86 family
     The flag output constraints for the x86 family are of the form
     ‘=@ccCOND’ where COND is one of the standard conditions defined in
     the ISA manual for ‘jCC’ or ‘setCC’.

     ‘a’
          "above" or unsigned greater than
     ‘ae’
          "above or equal" or unsigned greater than or equal
     ‘b’
          "below" or unsigned less than
     ‘be’
          "below or equal" or unsigned less than or equal
     ‘c’
          carry flag set
     ‘e’
     ‘z’
          "equal" or zero flag set
     ‘g’
          signed greater than
     ‘ge’
          signed greater than or equal
     ‘l’
          signed less than
     ‘le’
          signed less than or equal
     ‘o’
          overflow flag set
     ‘p’
          parity flag set
     ‘s’
          sign flag set
     ‘na’
     ‘nae’
     ‘nb’
     ‘nbe’
     ‘nc’
     ‘ne’
     ‘ng’
     ‘nge’
     ‘nl’
     ‘nle’
     ‘no’
     ‘np’
     ‘ns’
     ‘nz’
          "not" FLAG, or inverted versions of those above

6.47.2.5 Input Operands
.......................

Input operands make values from C variables and expressions available to
the assembly code.

 Operands are separated by commas.  Each operand has this format:

     [ [ASMSYMBOLICNAME] ] CONSTRAINT (CEXPRESSION)

ASMSYMBOLICNAME
     Specifies a symbolic name for the operand.  Reference the name in
     the assembler template by enclosing it in square brackets (i.e.
     ‘%[Value]’).  The scope of the name is the ‘asm’ statement that
     contains the definition.  Any valid C variable name is acceptable,
     including names already defined in the surrounding code.  No two
     operands within the same ‘asm’ statement can use the same symbolic
     name.

     When not using an ASMSYMBOLICNAME, use the (zero-based) position of
     the operand in the list of operands in the assembler template.  For
     example if there are two output operands and three inputs, use ‘%2’
     in the template to refer to the first input operand, ‘%3’ for the
     second, and ‘%4’ for the third.

CONSTRAINT
     A string constant specifying constraints on the placement of the
     operand; *Note Constraints::, for details.

     Input constraint strings may not begin with either ‘=’ or ‘+’.
     When you list more than one possible location (for example,
     ‘"irm"’), the compiler chooses the most efficient one based on the
     current context.  If you must use a specific register, but your
     Machine Constraints do not provide sufficient control to select the
     specific register you want, local register variables may provide a
     solution (*note Local Register Variables::).

     Input constraints can also be digits (for example, ‘"0"’).  This
     indicates that the specified input must be in the same place as the
     output constraint at the (zero-based) index in the output
     constraint list.  When using ASMSYMBOLICNAME syntax for the output
     operands, you may use these names (enclosed in brackets ‘[]’)
     instead of digits.

CEXPRESSION
     This is the C variable or expression being passed to the ‘asm’
     statement as input.  The enclosing parentheses are a required part
     of the syntax.

 When the compiler selects the registers to use to represent the input
operands, it does not use any of the clobbered registers (*note Clobbers
and Scratch Registers::).

 If there are no output operands but there are input operands, place two
consecutive colons where the output operands would go:

     __asm__ ("some instructions"
        : /* No outputs. */
        : "r" (Offset / 8));

 *Warning:* Do _not_ modify the contents of input-only operands (except
for inputs tied to outputs).  The compiler assumes that on exit from the
‘asm’ statement these operands contain the same values as they had
before executing the statement.  It is _not_ possible to use clobbers to
inform the compiler that the values in these inputs are changing.  One
common work-around is to tie the changing input variable to an output
variable that never gets used.  Note, however, that if the code that
follows the ‘asm’ statement makes no use of any of the output operands,
the GCC optimizers may discard the ‘asm’ statement as unneeded (see
*note Volatile::).

 ‘asm’ supports operand modifiers on operands (for example ‘%k2’ instead
of simply ‘%2’).  Typically these qualifiers are hardware dependent.
The list of supported modifiers for x86 is found at *note x86 Operand
modifiers: x86Operandmodifiers.

 In this example using the fictitious ‘combine’ instruction, the
constraint ‘"0"’ for input operand 1 says that it must occupy the same
location as output operand 0.  Only input operands may use numbers in
constraints, and they must each refer to an output operand.  Only a
number (or the symbolic assembler name) in the constraint can guarantee
that one operand is in the same place as another.  The mere fact that
‘foo’ is the value of both operands is not enough to guarantee that they
are in the same place in the generated assembler code.

     asm ("combine %2, %0"
        : "=r" (foo)
        : "0" (foo), "g" (bar));

 Here is an example using symbolic names.

     asm ("cmoveq %1, %2, %[result]"
        : [result] "=r"(result)
        : "r" (test), "r" (new), "[result]" (old));

6.47.2.6 Clobbers and Scratch Registers
.......................................

While the compiler is aware of changes to entries listed in the output
operands, the inline ‘asm’ code may modify more than just the outputs.
For example, calculations may require additional registers, or the
processor may overwrite a register as a side effect of a particular
assembler instruction.  In order to inform the compiler of these
changes, list them in the clobber list.  Clobber list items are either
register names or the special clobbers (listed below).  Each clobber
list item is a string constant enclosed in double quotes and separated
by commas.

 Clobber descriptions may not in any way overlap with an input or output
operand.  For example, you may not have an operand describing a register
class with one member when listing that register in the clobber list.
Variables declared to live in specific registers (*note Explicit
Register Variables::) and used as ‘asm’ input or output operands must
have no part mentioned in the clobber description.  In particular, there
is no way to specify that input operands get modified without also
specifying them as output operands.

 When the compiler selects which registers to use to represent input and
output operands, it does not use any of the clobbered registers.  As a
result, clobbered registers are available for any use in the assembler
code.

 Another restriction is that the clobber list should not contain the
stack pointer register.  This is because the compiler requires the value
of the stack pointer to be the same after an ‘asm’ statement as it was
on entry to the statement.  However, previous versions of GCC did not
enforce this rule and allowed the stack pointer to appear in the list,
with unclear semantics.  This behavior is deprecated and listing the
stack pointer may become an error in future versions of GCC.

 Here is a realistic example for the VAX showing the use of clobbered
registers:

     asm volatile ("movc3 %0, %1, %2"
                        : /* No outputs. */
                        : "g" (from), "g" (to), "g" (count)
                        : "r0", "r1", "r2", "r3", "r4", "r5", "memory");

 Also, there are two special clobber arguments:

‘"cc"’
     The ‘"cc"’ clobber indicates that the assembler code modifies the
     flags register.  On some machines, GCC represents the condition
     codes as a specific hardware register; ‘"cc"’ serves to name this
     register.  On other machines, condition code handling is different,
     and specifying ‘"cc"’ has no effect.  But it is valid no matter
     what the target.

‘"memory"’
     The ‘"memory"’ clobber tells the compiler that the assembly code
     performs memory reads or writes to items other than those listed in
     the input and output operands (for example, accessing the memory
     pointed to by one of the input parameters).  To ensure memory
     contains correct values, GCC may need to flush specific register
     values to memory before executing the ‘asm’.  Further, the compiler
     does not assume that any values read from memory before an ‘asm’
     remain unchanged after that ‘asm’; it reloads them as needed.
     Using the ‘"memory"’ clobber effectively forms a read/write memory
     barrier for the compiler.

     Note that this clobber does not prevent the _processor_ from doing
     speculative reads past the ‘asm’ statement.  To prevent that, you
     need processor-specific fence instructions.

 Flushing registers to memory has performance implications and may be an
issue for time-sensitive code.  You can provide better information to
GCC to avoid this, as shown in the following examples.  At a minimum,
aliasing rules allow GCC to know what memory _doesn't_ need to be
flushed.

 Here is a fictitious sum of squares instruction, that takes two
pointers to floating point values in memory and produces a floating
point register output.  Notice that ‘x’, and ‘y’ both appear twice in
the ‘asm’ parameters, once to specify memory accessed, and once to
specify a base register used by the ‘asm’.  You won't normally be
wasting a register by doing this as GCC can use the same register for
both purposes.  However, it would be foolish to use both ‘%1’ and ‘%3’
for ‘x’ in this ‘asm’ and expect them to be the same.  In fact, ‘%3’ may
well not be a register.  It might be a symbolic memory reference to the
object pointed to by ‘x’.

     asm ("sumsq %0, %1, %2"
          : "+f" (result)
          : "r" (x), "r" (y), "m" (*x), "m" (*y));

 Here is a fictitious ‘*z++ = *x++ * *y++’ instruction.  Notice that the
‘x’, ‘y’ and ‘z’ pointer registers must be specified as input/output
because the ‘asm’ modifies them.

     asm ("vecmul %0, %1, %2"
          : "+r" (z), "+r" (x), "+r" (y), "=m" (*z)
          : "m" (*x), "m" (*y));

 An x86 example where the string memory argument is of unknown length.

     asm("repne scasb"
         : "=c" (count), "+D" (p)
         : "m" (*(const char (*)[]) p), "0" (-1), "a" (0));

 If you know the above will only be reading a ten byte array then you
could instead use a memory input like: ‘"m" (*(const char (*)[10]) p)’.

 Here is an example of a PowerPC vector scale implemented in assembly,
complete with vector and condition code clobbers, and some initialized
offset registers that are unchanged by the ‘asm’.

     void
     dscal (size_t n, double *x, double alpha)
     {
       asm ("/* lots of asm here */"
            : "+m" (*(double (*)[n]) x), "+&r" (n), "+b" (x)
            : "d" (alpha), "b" (32), "b" (48), "b" (64),
              "b" (80), "b" (96), "b" (112)
            : "cr0",
              "vs32","vs33","vs34","vs35","vs36","vs37","vs38","vs39",
              "vs40","vs41","vs42","vs43","vs44","vs45","vs46","vs47");
     }

 Rather than allocating fixed registers via clobbers to provide scratch
registers for an ‘asm’ statement, an alternative is to define a variable
and make it an early-clobber output as with ‘a2’ and ‘a3’ in the example
below.  This gives the compiler register allocator more freedom.  You
can also define a variable and make it an output tied to an input as
with ‘a0’ and ‘a1’, tied respectively to ‘ap’ and ‘lda’.  Of course,
with tied outputs your ‘asm’ can't use the input value after modifying
the output register since they are one and the same register.  What's
more, if you omit the early-clobber on the output, it is possible that
GCC might allocate the same register to another of the inputs if GCC
could prove they had the same value on entry to the ‘asm’.  This is why
‘a1’ has an early-clobber.  Its tied input, ‘lda’ might conceivably be
known to have the value 16 and without an early-clobber share the same
register as ‘%11’.  On the other hand, ‘ap’ can't be the same as any of
the other inputs, so an early-clobber on ‘a0’ is not needed.  It is also
not desirable in this case.  An early-clobber on ‘a0’ would cause GCC to
allocate a separate register for the ‘"m" (*(const double (*)[]) ap)’
input.  Note that tying an input to an output is the way to set up an
initialized temporary register modified by an ‘asm’ statement.  An input
not tied to an output is assumed by GCC to be unchanged, for example
‘"b" (16)’ below sets up ‘%11’ to 16, and GCC might use that register in
following code if the value 16 happened to be needed.  You can even use
a normal ‘asm’ output for a scratch if all inputs that might share the
same register are consumed before the scratch is used.  The VSX
registers clobbered by the ‘asm’ statement could have used this
technique except for GCC's limit on the number of ‘asm’ parameters.

     static void
     dgemv_kernel_4x4 (long n, const double *ap, long lda,
                       const double *x, double *y, double alpha)
     {
       double *a0;
       double *a1;
       double *a2;
       double *a3;

       __asm__
         (
          /* lots of asm here */
          "#n=%1 ap=%8=%12 lda=%13 x=%7=%10 y=%0=%2 alpha=%9 o16=%11\n"
          "#a0=%3 a1=%4 a2=%5 a3=%6"
          :
            "+m" (*(double (*)[n]) y),
            "+&r" (n),	// 1
            "+b" (y),	// 2
            "=b" (a0),	// 3
            "=&b" (a1),	// 4
            "=&b" (a2),	// 5
            "=&b" (a3)	// 6
          :
            "m" (*(const double (*)[n]) x),
            "m" (*(const double (*)[]) ap),
            "d" (alpha),	// 9
            "r" (x),		// 10
            "b" (16),	// 11
            "3" (ap),	// 12
            "4" (lda)	// 13
          :
            "cr0",
            "vs32","vs33","vs34","vs35","vs36","vs37",
            "vs40","vs41","vs42","vs43","vs44","vs45","vs46","vs47"
          );
     }

6.47.2.7 Goto Labels
....................

‘asm goto’ allows assembly code to jump to one or more C labels.  The
GOTOLABELS section in an ‘asm goto’ statement contains a comma-separated
list of all C labels to which the assembler code may jump.  GCC assumes
that ‘asm’ execution falls through to the next statement (if this is not
the case, consider using the ‘__builtin_unreachable’ intrinsic after the
‘asm’ statement).  Optimization of ‘asm goto’ may be improved by using
the ‘hot’ and ‘cold’ label attributes (*note Label Attributes::).

 If the assembler code does modify anything, use the ‘"memory"’ clobber
to force the optimizers to flush all register values to memory and
reload them if necessary after the ‘asm’ statement.

 Also note that an ‘asm goto’ statement is always implicitly considered
volatile.

 Be careful when you set output operands inside ‘asm goto’ only on some
possible control flow paths.  If you don't set up the output on given
path and never use it on this path, it is okay.  Otherwise, you should
use ‘+’ constraint modifier meaning that the operand is input and output
one.  With this modifier you will have the correct values on all
possible paths from the ‘asm goto’.

 To reference a label in the assembler template, prefix it with ‘%l’
(lowercase ‘L’) followed by its (zero-based) position in GOTOLABELS plus
the number of input and output operands.  Output operand with constraint
modifier ‘+’ is counted as two operands because it is considered as one
output and one input operand.  For example, if the ‘asm’ has three
inputs, one output operand with constraint modifier ‘+’ and one output
operand with constraint modifier ‘=’ and references two labels, refer to
the first label as ‘%l6’ and the second as ‘%l7’).

 Alternately, you can reference labels using the actual C label name
enclosed in brackets.  For example, to reference a label named ‘carry’,
you can use ‘%l[carry]’.  The label must still be listed in the
GOTOLABELS section when using this approach.  It is better to use the
named references for labels as in this case you can avoid counting input
and output operands and special treatment of output operands with
constraint modifier ‘+’.

 Here is an example of ‘asm goto’ for i386:

     asm goto (
         "btl %1, %0\n\t"
         "jc %l2"
         : /* No outputs. */
         : "r" (p1), "r" (p2)
         : "cc"
         : carry);

     return 0;

     carry:
     return 1;

 The following example shows an ‘asm goto’ that uses a memory clobber.

     int frob(int x)
     {
       int y;
       asm goto ("frob %%r5, %1; jc %l[error]; mov (%2), %%r5"
                 : /* No outputs. */
                 : "r"(x), "r"(&y)
                 : "r5", "memory"
                 : error);
       return y;
     error:
       return -1;
     }

 The following example shows an ‘asm goto’ that uses an output.

     int foo(int count)
     {
       asm goto ("dec %0; jb %l[stop]"
                 : "+r" (count)
                 :
                 :
                 : stop);
       return count;
     stop:
       return 0;
     }

 The following artificial example shows an ‘asm goto’ that sets up an
output only on one path inside the ‘asm goto’.  Usage of constraint
modifier ‘=’ instead of ‘+’ would be wrong as ‘factor’ is used on all
paths from the ‘asm goto’.

     int foo(int inp)
     {
       int factor = 0;
       asm goto ("cmp %1, 10; jb %l[lab]; mov 2, %0"
                 : "+r" (factor)
                 : "r" (inp)
                 :
                 : lab);
     lab:
       return inp * factor; /* return 2 * inp or 0 if inp < 10 */
     }

6.47.2.8 x86 Operand Modifiers
..............................

References to input, output, and goto operands in the assembler template
of extended ‘asm’ statements can use modifiers to affect the way the
operands are formatted in the code output to the assembler.  For
example, the following code uses the ‘h’ and ‘b’ modifiers for x86:

     uint16_t  num;
     asm volatile ("xchg %h0, %b0" : "+a" (num) );

These modifiers generate this assembler code:

     xchg %ah, %al

 The rest of this discussion uses the following code for illustrative
purposes.

     int main()
     {
        int iInt = 1;

     top:

        asm volatile goto ("some assembler instructions here"
        : /* No outputs. */
        : "q" (iInt), "X" (sizeof(unsigned char) + 1), "i" (42)
        : /* No clobbers. */
        : top);
     }

 With no modifiers, this is what the output from the operands would be
for the ‘att’ and ‘intel’ dialects of assembler:

Operand   ‘att’  ‘intel’
-----------------------------------
‘%0’      ‘%eax’ ‘eax’
‘%1’      ‘$2’   ‘2’
‘%3’      ‘$.L3’ ‘OFFSET
                 FLAT:.L3’
‘%4’      ‘$8’   ‘8’
‘%5’      ‘%xmm0’‘xmm0’
‘%7’      ‘$0’   ‘0’

 The table below shows the list of supported modifiers and their
effects.

Modifier   Description                                  Operand   ‘att’   ‘intel’
------------------------------------------------------------------------------------
‘A’        Print an absolute memory reference.          ‘%A0’     ‘*%rax’ ‘rax’
‘b’        Print the QImode name of the register.       ‘%b0’     ‘%al’   ‘al’
‘B’        print the opcode suffix of b.                ‘%B0’     ‘b’
‘c’        Require a constant operand and print the     ‘%c1’     ‘2’     ‘2’
           constant expression with no punctuation.
‘d’        print duplicated register operand for AVX    ‘%d5’     ‘%xmm0, ‘xmm0,
           instruction.                                           %xmm0’  xmm0’
‘E’        Print the address in Double Integer          ‘%E1’     ‘%(rax)’‘[rax]’
           (DImode) mode (8 bytes) when the target is
           64-bit.  Otherwise mode is unspecified
           (VOIDmode).
‘g’        Print the V16SFmode name of the register.    ‘%g0’     ‘%zmm0’ ‘zmm0’
‘h’        Print the QImode name for a "high"           ‘%h0’     ‘%ah’   ‘ah’
           register.
‘H’        Add 8 bytes to an offsettable memory         ‘%H0’     ‘8(%rax)’‘8[rax]’
           reference.  Useful when accessing the high
           8 bytes of SSE values.  For a memref in
           (%rax), it generates
‘k’        Print the SImode name of the register.       ‘%k0’     ‘%eax’  ‘eax’
‘l’        Print the label name with no punctuation.    ‘%l3’     ‘.L3’   ‘.L3’
‘L’        print the opcode suffix of l.                ‘%L0’     ‘l’
‘N’        print maskz.                                 ‘%N7’     ‘{z}’   ‘{z}’
‘p’        Print raw symbol name (without               ‘%p2’     ‘42’    ‘42’
           syntax-specific prefixes).
‘P’        If used for a function, print the PLT
           suffix and generate PIC code.  For
           example, emit ‘foo@PLT’ instead of 'foo'
           for the function foo().  If used for a
           constant, drop all syntax-specific
           prefixes and issue the bare constant.  See
           ‘p’ above.
‘q’        Print the DImode name of the register.       ‘%q0’     ‘%rax’  ‘rax’
‘Q’        print the opcode suffix of q.                ‘%Q0’     ‘q’
‘R’        print embedded rounding and sae.             ‘%R4’     ‘{rn-sae},‘,
                                                                  ’       {rn-sae}’
‘r’        print only sae.                              ‘%r4’     ‘{sae}, ‘,
                                                                  ’       {sae}’
‘s’        print a shift double count, followed by      ‘%s1’     ‘$2,    ‘2, ’
           the assemblers argument delimiterprint the             ’
           opcode suffix of s.
‘S’        print the opcode suffix of s.                ‘%S0’     ‘s’
‘t’        print the V8SFmode name of the register.     ‘%t5’     ‘%ymm0’ ‘ymm0’
‘T’        print the opcode suffix of t.                ‘%T0’     ‘t’
‘V’        print naked full integer register name       ‘%V0’     ‘eax’   ‘eax’
           without %.
‘w’        Print the HImode name of the register.       ‘%w0’     ‘%ax’   ‘ax’
‘W’        print the opcode suffix of w.                ‘%W0’     ‘w’
‘x’        print the V4SFmode name of the register.     ‘%x5’     ‘%xmm0’ ‘xmm0’
‘y’        print "st(0)" instead of "st" as a           ‘%y6’     ‘%st(0)’‘st(0)’
           register.
‘z’        Print the opcode suffix for the size of      ‘%z0’     ‘l’
           the current integer operand (one of
           ‘b’/‘w’/‘l’/‘q’).
‘Z’        Like ‘z’, with special suffixes for x87
           instructions.

6.47.2.9 x86 Floating-Point ‘asm’ Operands
..........................................

On x86 targets, there are several rules on the usage of stack-like
registers in the operands of an ‘asm’.  These rules apply only to the
operands that are stack-like registers:

  1. Given a set of input registers that die in an ‘asm’, it is
     necessary to know which are implicitly popped by the ‘asm’, and
     which must be explicitly popped by GCC.

     An input register that is implicitly popped by the ‘asm’ must be
     explicitly clobbered, unless it is constrained to match an output
     operand.

  2. For any input register that is implicitly popped by an ‘asm’, it is
     necessary to know how to adjust the stack to compensate for the
     pop.  If any non-popped input is closer to the top of the reg-stack
     than the implicitly popped register, it would not be possible to
     know what the stack looked like--it's not clear how the rest of the
     stack "slides up".

     All implicitly popped input registers must be closer to the top of
     the reg-stack than any input that is not implicitly popped.

     It is possible that if an input dies in an ‘asm’, the compiler
     might use the input register for an output reload.  Consider this
     example:

          asm ("foo" : "=t" (a) : "f" (b));

     This code says that input ‘b’ is not popped by the ‘asm’, and that
     the ‘asm’ pushes a result onto the reg-stack, i.e., the stack is
     one deeper after the ‘asm’ than it was before.  But, it is possible
     that reload may think that it can use the same register for both
     the input and the output.

     To prevent this from happening, if any input operand uses the ‘f’
     constraint, all output register constraints must use the ‘&’
     early-clobber modifier.

     The example above is correctly written as:

          asm ("foo" : "=&t" (a) : "f" (b));

  3. Some operands need to be in particular places on the stack.  All
     output operands fall in this category--GCC has no other way to know
     which registers the outputs appear in unless you indicate this in
     the constraints.

     Output operands must specifically indicate which register an output
     appears in after an ‘asm’.  ‘=f’ is not allowed: the operand
     constraints must select a class with a single register.

  4. Output operands may not be "inserted" between existing stack
     registers.  Since no 387 opcode uses a read/write operand, all
     output operands are dead before the ‘asm’, and are pushed by the
     ‘asm’.  It makes no sense to push anywhere but the top of the
     reg-stack.

     Output operands must start at the top of the reg-stack: output
     operands may not "skip" a register.

  5. Some ‘asm’ statements may need extra stack space for internal
     calculations.  This can be guaranteed by clobbering stack registers
     unrelated to the inputs and outputs.

 This ‘asm’ takes one input, which is internally popped, and produces
two outputs.

     asm ("fsincos" : "=t" (cos), "=u" (sin) : "0" (inp));

This ‘asm’ takes two inputs, which are popped by the ‘fyl2xp1’ opcode,
and replaces them with one output.  The ‘st(1)’ clobber is necessary for
the compiler to know that ‘fyl2xp1’ pops both inputs.

     asm ("fyl2xp1" : "=t" (result) : "0" (x), "u" (y) : "st(1)");

6.47.2.10 MSP430 Operand Modifiers
..................................

The list below describes the supported modifiers and their effects for
MSP430.

ModifierDescription
--------------------------------------------------------------------------
‘A’     Select low 16-bits of the constant/register/memory operand.
‘B’     Select high 16-bits of the constant/register/memory operand.
‘C’     Select bits 32-47 of the constant/register/memory operand.
‘D’     Select bits 48-63 of the constant/register/memory operand.
‘H’     Equivalent to ‘B’ (for backwards compatibility).
‘I’     Print the inverse (logical ‘NOT’) of the constant value.
‘J’     Print an integer without a ‘#’ prefix.
‘L’     Equivalent to ‘A’ (for backwards compatibility).
‘O’     Offset of the current frame from the top of the stack.
‘Q’     Use the ‘A’ instruction postfix.
‘R’     Inverse of condition code, for unsigned comparisons.
‘W’     Subtract 16 from the constant value.
‘X’     Use the ‘X’ instruction postfix.
‘Y’     Subtract 4 from the constant value.
‘Z’     Subtract 1 from the constant value.
‘b’     Append ‘.B’, ‘.W’ or ‘.A’ to the instruction, depending on the
        mode.
‘d’     Offset 1 byte of a memory reference or constant value.
‘e’     Offset 3 bytes of a memory reference or constant value.
‘f’     Offset 5 bytes of a memory reference or constant value.
‘g’     Offset 7 bytes of a memory reference or constant value.
‘p’     Print the value of 2, raised to the power of the given
        constant.  Used to select the specified bit position.
‘r’     Inverse of condition code, for signed comparisons.
‘x’     Equivialent to ‘X’, but only for pointers.


File: gcc.info,  Node: Constraints,  Next: Asm Labels,  Prev: Extended Asm,  Up: Using Assembly Language with C

6.47.3 Constraints for ‘asm’ Operands
-------------------------------------

Here are specific details on what constraint letters you can use with
‘asm’ operands.  Constraints can say whether an operand may be in a
register, and which kinds of register; whether the operand can be a
memory reference, and which kinds of address; whether the operand may be
an immediate constant, and which possible values it may have.
Constraints can also require two operands to match.  Side-effects aren't
allowed in operands of inline ‘asm’, unless ‘<’ or ‘>’ constraints are
used, because there is no guarantee that the side effects will happen
exactly once in an instruction that can update the addressing register.

* Menu:

* Simple Constraints::  Basic use of constraints.
* Multi-Alternative::   When an insn has two alternative constraint-patterns.
* Modifiers::           More precise control over effects of constraints.
* Machine Constraints:: Special constraints for some particular machines.


File: gcc.info,  Node: Simple Constraints,  Next: Multi-Alternative,  Up: Constraints

6.47.3.1 Simple Constraints
...........................

The simplest kind of constraint is a string full of letters, each of
which describes one kind of operand that is permitted.  Here are the
letters that are allowed:

whitespace
     Whitespace characters are ignored and can be inserted at any
     position except the first.  This enables each alternative for
     different operands to be visually aligned in the machine
     description even if they have different number of constraints and
     modifiers.

‘m’
     A memory operand is allowed, with any kind of address that the
     machine supports in general.  Note that the letter used for the
     general memory constraint can be re-defined by a back end using the
     ‘TARGET_MEM_CONSTRAINT’ macro.

‘o’
     A memory operand is allowed, but only if the address is
     “offsettable”.  This means that adding a small integer (actually,
     the width in bytes of the operand, as determined by its machine
     mode) may be added to the address and the result is also a valid
     memory address.

     For example, an address which is constant is offsettable; so is an
     address that is the sum of a register and a constant (as long as a
     slightly larger constant is also within the range of
     address-offsets supported by the machine); but an autoincrement or
     autodecrement address is not offsettable.  More complicated
     indirect/indexed addresses may or may not be offsettable depending
     on the other addressing modes that the machine supports.

     Note that in an output operand which can be matched by another
     operand, the constraint letter ‘o’ is valid only when accompanied
     by both ‘<’ (if the target machine has predecrement addressing) and
     ‘>’ (if the target machine has preincrement addressing).

‘V’
     A memory operand that is not offsettable.  In other words, anything
     that would fit the ‘m’ constraint but not the ‘o’ constraint.

‘<’
     A memory operand with autodecrement addressing (either predecrement
     or postdecrement) is allowed.  In inline ‘asm’ this constraint is
     only allowed if the operand is used exactly once in an instruction
     that can handle the side effects.  Not using an operand with ‘<’ in
     constraint string in the inline ‘asm’ pattern at all or using it in
     multiple instructions isn't valid, because the side effects
     wouldn't be performed or would be performed more than once.
     Furthermore, on some targets the operand with ‘<’ in constraint
     string must be accompanied by special instruction suffixes like
     ‘%U0’ instruction suffix on PowerPC or ‘%P0’ on IA-64.

‘>’
     A memory operand with autoincrement addressing (either preincrement
     or postincrement) is allowed.  In inline ‘asm’ the same
     restrictions as for ‘<’ apply.

‘r’
     A register operand is allowed provided that it is in a general
     register.

‘i’
     An immediate integer operand (one with constant value) is allowed.
     This includes symbolic constants whose values will be known only at
     assembly time or later.

‘n’
     An immediate integer operand with a known numeric value is allowed.
     Many systems cannot support assembly-time constants for operands
     less than a word wide.  Constraints for these operands should use
     ‘n’ rather than ‘i’.

‘I’, ‘J’, ‘K’, ... ‘P’
     Other letters in the range ‘I’ through ‘P’ may be defined in a
     machine-dependent fashion to permit immediate integer operands with
     explicit integer values in specified ranges.  For example, on the
     68000, ‘I’ is defined to stand for the range of values 1 to 8.
     This is the range permitted as a shift count in the shift
     instructions.

‘E’
     An immediate floating operand (expression code ‘const_double’) is
     allowed, but only if the target floating point format is the same
     as that of the host machine (on which the compiler is running).

‘F’
     An immediate floating operand (expression code ‘const_double’ or
     ‘const_vector’) is allowed.

‘G’, ‘H’
     ‘G’ and ‘H’ may be defined in a machine-dependent fashion to permit
     immediate floating operands in particular ranges of values.

‘s’
     An immediate integer operand whose value is not an explicit integer
     is allowed.

     This might appear strange; if an insn allows a constant operand
     with a value not known at compile time, it certainly must allow any
     known value.  So why use ‘s’ instead of ‘i’?  Sometimes it allows
     better code to be generated.

     For example, on the 68000 in a fullword instruction it is possible
     to use an immediate operand; but if the immediate value is between
     −128 and 127, better code results from loading the value into a
     register and using the register.  This is because the load into the
     register can be done with a ‘moveq’ instruction.  We arrange for
     this to happen by defining the letter ‘K’ to mean "any integer
     outside the range −128 to 127", and then specifying ‘Ks’ in the
     operand constraints.

‘g’
     Any register, memory or immediate integer operand is allowed,
     except for registers that are not general registers.

‘X’
     Any operand whatsoever is allowed.

‘0’, ‘1’, ‘2’, ... ‘9’
     An operand that matches the specified operand number is allowed.
     If a digit is used together with letters within the same
     alternative, the digit should come last.

     This number is allowed to be more than a single digit.  If multiple
     digits are encountered consecutively, they are interpreted as a
     single decimal integer.  There is scant chance for ambiguity, since
     to-date it has never been desirable that ‘10’ be interpreted as
     matching either operand 1 _or_ operand 0.  Should this be desired,
     one can use multiple alternatives instead.

     This is called a “matching constraint” and what it really means is
     that the assembler has only a single operand that fills two roles
     which ‘asm’ distinguishes.  For example, an add instruction uses
     two input operands and an output operand, but on most CISC machines
     an add instruction really has only two operands, one of them an
     input-output operand:

          addl #35,r12

     Matching constraints are used in these circumstances.  More
     precisely, the two operands that match must include one input-only
     operand and one output-only operand.  Moreover, the digit must be a
     smaller number than the number of the operand that uses it in the
     constraint.

‘p’
     An operand that is a valid memory address is allowed.  This is for
     "load address" and "push address" instructions.

     ‘p’ in the constraint must be accompanied by ‘address_operand’ as
     the predicate in the ‘match_operand’.  This predicate interprets
     the mode specified in the ‘match_operand’ as the mode of the memory
     reference for which the address would be valid.

OTHER-LETTERS
     Other letters can be defined in machine-dependent fashion to stand
     for particular classes of registers or other arbitrary operand
     types.  ‘d’, ‘a’ and ‘f’ are defined on the 68000/68020 to stand
     for data, address and floating point registers.


File: gcc.info,  Node: Multi-Alternative,  Next: Modifiers,  Prev: Simple Constraints,  Up: Constraints

6.47.3.2 Multiple Alternative Constraints
.........................................

Sometimes a single instruction has multiple alternative sets of possible
operands.  For example, on the 68000, a logical-or instruction can
combine register or an immediate value into memory, or it can combine
any kind of operand into a register; but it cannot combine one memory
location into another.

 These constraints are represented as multiple alternatives.  An
alternative can be described by a series of letters for each operand.
The overall constraint for an operand is made from the letters for this
operand from the first alternative, a comma, the letters for this
operand from the second alternative, a comma, and so on until the last
alternative.  All operands for a single instruction must have the same
number of alternatives.

 So the first alternative for the 68000's logical-or could be written as
‘"+m" (output) : "ir" (input)’.  The second could be ‘"+r" (output):
"irm" (input)’.  However, the fact that two memory locations cannot be
used in a single instruction prevents simply using ‘"+rm" (output) :
"irm" (input)’.  Using multi-alternatives, this might be written as
‘"+m,r" (output) : "ir,irm" (input)’.  This describes all the available
alternatives to the compiler, allowing it to choose the most efficient
one for the current conditions.

 There is no way within the template to determine which alternative was
chosen.  However you may be able to wrap your ‘asm’ statements with
builtins such as ‘__builtin_constant_p’ to achieve the desired results.


File: gcc.info,  Node: Modifiers,  Next: Machine Constraints,  Prev: Multi-Alternative,  Up: Constraints

6.47.3.3 Constraint Modifier Characters
.......................................

Here are constraint modifier characters.

‘=’
     Means that this operand is written to by this instruction: the
     previous value is discarded and replaced by new data.

‘+’
     Means that this operand is both read and written by the
     instruction.

     When the compiler fixes up the operands to satisfy the constraints,
     it needs to know which operands are read by the instruction and
     which are written by it.  ‘=’ identifies an operand which is only
     written; ‘+’ identifies an operand that is both read and written;
     all other operands are assumed to only be read.

     If you specify ‘=’ or ‘+’ in a constraint, you put it in the first
     character of the constraint string.

‘&’
     Means (in a particular alternative) that this operand is an
     “earlyclobber” operand, which is written before the instruction is
     finished using the input operands.  Therefore, this operand may not
     lie in a register that is read by the instruction or as part of any
     memory address.

     ‘&’ applies only to the alternative in which it is written.  In
     constraints with multiple alternatives, sometimes one alternative
     requires ‘&’ while others do not.  See, for example, the ‘movdf’
     insn of the 68000.

     An operand which is read by the instruction can be tied to an
     earlyclobber operand if its only use as an input occurs before the
     early result is written.  Adding alternatives of this form often
     allows GCC to produce better code when only some of the read
     operands can be affected by the earlyclobber.  See, for example,
     the ‘mulsi3’ insn of the ARM.

     Furthermore, if the “earlyclobber” operand is also a read/write
     operand, then that operand is written only after it's used.

     ‘&’ does not obviate the need to write ‘=’ or ‘+’.  As
     “earlyclobber” operands are always written, a read-only
     “earlyclobber” operand is ill-formed and will be rejected by the
     compiler.

‘%’
     Declares the instruction to be commutative for this operand and the
     following operand.  This means that the compiler may interchange
     the two operands if that is the cheapest way to make all operands
     fit the constraints.  ‘%’ applies to all alternatives and must
     appear as the first character in the constraint.  Only read-only
     operands can use ‘%’.

     GCC can only handle one commutative pair in an asm; if you use
     more, the compiler may fail.  Note that you need not use the
     modifier if the two alternatives are strictly identical; this would
     only waste time in the reload pass.


File: gcc.info,  Node: Machine Constraints,  Prev: Modifiers,  Up: Constraints

6.47.3.4 Constraints for Particular Machines
............................................

Whenever possible, you should use the general-purpose constraint letters
in ‘asm’ arguments, since they will convey meaning more readily to
people reading your code.  Failing that, use the constraint letters that
usually have very similar meanings across architectures.  The most
commonly used constraints are ‘m’ and ‘r’ (for memory and
general-purpose registers respectively; *note Simple Constraints::), and
‘I’, usually the letter indicating the most common immediate-constant
format.

 Each architecture defines additional constraints.  These constraints
are used by the compiler itself for instruction generation, as well as
for ‘asm’ statements; therefore, some of the constraints are not
particularly useful for ‘asm’.  Here is a summary of some of the
machine-dependent constraints available on some particular machines; it
includes both constraints that are useful for ‘asm’ and constraints that
aren't.  The compiler source file mentioned in the table heading for
each architecture is the definitive reference for the meanings of that
architecture's constraints.

_AArch64 family--‘config/aarch64/constraints.md’_
     ‘k’
          The stack pointer register (‘SP’)

     ‘w’
          Floating point register, Advanced SIMD vector register or SVE
          vector register

     ‘x’
          Like ‘w’, but restricted to registers 0 to 15 inclusive.

     ‘y’
          Like ‘w’, but restricted to registers 0 to 7 inclusive.

     ‘Upl’
          One of the low eight SVE predicate registers (‘P0’ to ‘P7’)

     ‘Upa’
          Any of the SVE predicate registers (‘P0’ to ‘P15’)

     ‘I’
          Integer constant that is valid as an immediate operand in an
          ‘ADD’ instruction

     ‘J’
          Integer constant that is valid as an immediate operand in a
          ‘SUB’ instruction (once negated)

     ‘K’
          Integer constant that can be used with a 32-bit logical
          instruction

     ‘L’
          Integer constant that can be used with a 64-bit logical
          instruction

     ‘M’
          Integer constant that is valid as an immediate operand in a
          32-bit ‘MOV’ pseudo instruction.  The ‘MOV’ may be assembled
          to one of several different machine instructions depending on
          the value

     ‘N’
          Integer constant that is valid as an immediate operand in a
          64-bit ‘MOV’ pseudo instruction

     ‘S’
          An absolute symbolic address or a label reference

     ‘Y’
          Floating point constant zero

     ‘Z’
          Integer constant zero

     ‘Ush’
          The high part (bits 12 and upwards) of the pc-relative address
          of a symbol within 4GB of the instruction

     ‘Q’
          A memory address which uses a single base register with no
          offset

     ‘Ump’
          A memory address suitable for a load/store pair instruction in
          SI, DI, SF and DF modes

_AMD GCN --‘config/gcn/constraints.md’_
     ‘I’
          Immediate integer in the range −16 to 64

     ‘J’
          Immediate 16-bit signed integer

     ‘Kf’
          Immediate constant −1

     ‘L’
          Immediate 15-bit unsigned integer

     ‘A’
          Immediate constant that can be inlined in an instruction
          encoding: integer −16..64, or float 0.0, +/−0.5, +/−1.0,
          +/−2.0, +/−4.0, 1.0/(2.0*PI)

     ‘B’
          Immediate 32-bit signed integer that can be attached to an
          instruction encoding

     ‘C’
          Immediate 32-bit integer in range −16..4294967295 (i.e.
          32-bit unsigned integer or ‘A’ constraint)

     ‘DA’
          Immediate 64-bit constant that can be split into two ‘A’
          constants

     ‘DB’
          Immediate 64-bit constant that can be split into two ‘B’
          constants

     ‘U’
          Any ‘unspec’

     ‘Y’
          Any ‘symbol_ref’ or ‘label_ref’

     ‘v’
          VGPR register

     ‘Sg’
          SGPR register

     ‘SD’
          SGPR registers valid for instruction destinations, including
          VCC, M0 and EXEC

     ‘SS’
          SGPR registers valid for instruction sources, including VCC,
          M0, EXEC and SCC

     ‘Sm’
          SGPR registers valid as a source for scalar memory
          instructions (excludes M0 and EXEC)

     ‘Sv’
          SGPR registers valid as a source or destination for vector
          instructions (excludes EXEC)

     ‘ca’
          All condition registers: SCC, VCCZ, EXECZ

     ‘cs’
          Scalar condition register: SCC

     ‘cV’
          Vector condition register: VCC, VCC_LO, VCC_HI

     ‘e’
          EXEC register (EXEC_LO and EXEC_HI)

     ‘RB’
          Memory operand with address space suitable for ‘buffer_*’
          instructions

     ‘RF’
          Memory operand with address space suitable for ‘flat_*’
          instructions

     ‘RS’
          Memory operand with address space suitable for ‘s_*’
          instructions

     ‘RL’
          Memory operand with address space suitable for ‘ds_*’ LDS
          instructions

     ‘RG’
          Memory operand with address space suitable for ‘ds_*’ GDS
          instructions

     ‘RD’
          Memory operand with address space suitable for any ‘ds_*’
          instructions

     ‘RM’
          Memory operand with address space suitable for ‘global_*’
          instructions

_ARC --‘config/arc/constraints.md’_
     ‘q’
          Registers usable in ARCompact 16-bit instructions: ‘r0’-‘r3’,
          ‘r12’-‘r15’.  This constraint can only match when the ‘-mq’
          option is in effect.

     ‘e’
          Registers usable as base-regs of memory addresses in ARCompact
          16-bit memory instructions: ‘r0’-‘r3’, ‘r12’-‘r15’, ‘sp’.
          This constraint can only match when the ‘-mq’ option is in
          effect.
     ‘D’
          ARC FPX (dpfp) 64-bit registers.  ‘D0’, ‘D1’.

     ‘I’
          A signed 12-bit integer constant.

     ‘Cal’
          constant for arithmetic/logical operations.  This might be any
          constant that can be put into a long immediate by the assmbler
          or linker without involving a PIC relocation.

     ‘K’
          A 3-bit unsigned integer constant.

     ‘L’
          A 6-bit unsigned integer constant.

     ‘CnL’
          One's complement of a 6-bit unsigned integer constant.

     ‘CmL’
          Two's complement of a 6-bit unsigned integer constant.

     ‘M’
          A 5-bit unsigned integer constant.

     ‘O’
          A 7-bit unsigned integer constant.

     ‘P’
          A 8-bit unsigned integer constant.

     ‘H’
          Any const_double value.

_ARM family--‘config/arm/constraints.md’_

     ‘h’
          In Thumb state, the core registers ‘r8’-‘r15’.

     ‘k’
          The stack pointer register.

     ‘l’
          In Thumb State the core registers ‘r0’-‘r7’.  In ARM state
          this is an alias for the ‘r’ constraint.

     ‘t’
          VFP floating-point registers ‘s0’-‘s31’.  Used for 32 bit
          values.

     ‘w’
          VFP floating-point registers ‘d0’-‘d31’ and the appropriate
          subset ‘d0’-‘d15’ based on command line options.  Used for 64
          bit values only.  Not valid for Thumb1.

     ‘y’
          The iWMMX co-processor registers.

     ‘z’
          The iWMMX GR registers.

     ‘G’
          The floating-point constant 0.0

     ‘I’
          Integer that is valid as an immediate operand in a data
          processing instruction.  That is, an integer in the range 0 to
          255 rotated by a multiple of 2

     ‘J’
          Integer in the range −4095 to 4095

     ‘K’
          Integer that satisfies constraint ‘I’ when inverted (ones
          complement)

     ‘L’
          Integer that satisfies constraint ‘I’ when negated (twos
          complement)

     ‘M’
          Integer in the range 0 to 32

     ‘Q’
          A memory reference where the exact address is in a single
          register ('‘m’' is preferable for ‘asm’ statements)

     ‘R’
          An item in the constant pool

     ‘S’
          A symbol in the text segment of the current file

     ‘Uv’
          A memory reference suitable for VFP load/store insns
          (reg+constant offset)

     ‘Uy’
          A memory reference suitable for iWMMXt load/store
          instructions.

     ‘Uq’
          A memory reference suitable for the ARMv4 ldrsb instruction.

_AVR family--‘config/avr/constraints.md’_
     ‘l’
          Registers from r0 to r15

     ‘a’
          Registers from r16 to r23

     ‘d’
          Registers from r16 to r31

     ‘w’
          Registers from r24 to r31.  These registers can be used in
          ‘adiw’ command

     ‘e’
          Pointer register (r26-r31)

     ‘b’
          Base pointer register (r28-r31)

     ‘q’
          Stack pointer register (SPH:SPL)

     ‘t’
          Temporary register r0

     ‘x’
          Register pair X (r27:r26)

     ‘y’
          Register pair Y (r29:r28)

     ‘z’
          Register pair Z (r31:r30)

     ‘I’
          Constant greater than −1, less than 64

     ‘J’
          Constant greater than −64, less than 1

     ‘K’
          Constant integer 2

     ‘L’
          Constant integer 0

     ‘M’
          Constant that fits in 8 bits

     ‘N’
          Constant integer −1

     ‘O’
          Constant integer 8, 16, or 24

     ‘P’
          Constant integer 1

     ‘G’
          A floating point constant 0.0

     ‘Q’
          A memory address based on Y or Z pointer with displacement.

_Blackfin family--‘config/bfin/constraints.md’_
     ‘a’
          P register

     ‘d’
          D register

     ‘z’
          A call clobbered P register.

     ‘qN’
          A single register.  If N is in the range 0 to 7, the
          corresponding D register.  If it is ‘A’, then the register P0.

     ‘D’
          Even-numbered D register

     ‘W’
          Odd-numbered D register

     ‘e’
          Accumulator register.

     ‘A’
          Even-numbered accumulator register.

     ‘B’
          Odd-numbered accumulator register.

     ‘b’
          I register

     ‘v’
          B register

     ‘f’
          M register

     ‘c’
          Registers used for circular buffering, i.e. I, B, or L
          registers.

     ‘C’
          The CC register.

     ‘t’
          LT0 or LT1.

     ‘k’
          LC0 or LC1.

     ‘u’
          LB0 or LB1.

     ‘x’
          Any D, P, B, M, I or L register.

     ‘y’
          Additional registers typically used only in prologues and
          epilogues: RETS, RETN, RETI, RETX, RETE, ASTAT, SEQSTAT and
          USP.

     ‘w’
          Any register except accumulators or CC.

     ‘Ksh’
          Signed 16 bit integer (in the range −32768 to 32767)

     ‘Kuh’
          Unsigned 16 bit integer (in the range 0 to 65535)

     ‘Ks7’
          Signed 7 bit integer (in the range −64 to 63)

     ‘Ku7’
          Unsigned 7 bit integer (in the range 0 to 127)

     ‘Ku5’
          Unsigned 5 bit integer (in the range 0 to 31)

     ‘Ks4’
          Signed 4 bit integer (in the range −8 to 7)

     ‘Ks3’
          Signed 3 bit integer (in the range −3 to 4)

     ‘Ku3’
          Unsigned 3 bit integer (in the range 0 to 7)

     ‘PN’
          Constant N, where N is a single-digit constant in the range 0
          to 4.

     ‘PA’
          An integer equal to one of the MACFLAG_XXX constants that is
          suitable for use with either accumulator.

     ‘PB’
          An integer equal to one of the MACFLAG_XXX constants that is
          suitable for use only with accumulator A1.

     ‘M1’
          Constant 255.

     ‘M2’
          Constant 65535.

     ‘J’
          An integer constant with exactly a single bit set.

     ‘L’
          An integer constant with all bits set except exactly one.

     ‘H’

     ‘Q’
          Any SYMBOL_REF.

_CR16 Architecture--‘config/cr16/cr16.h’_

     ‘b’
          Registers from r0 to r14 (registers without stack pointer)

     ‘t’
          Register from r0 to r11 (all 16-bit registers)

     ‘p’
          Register from r12 to r15 (all 32-bit registers)

     ‘I’
          Signed constant that fits in 4 bits

     ‘J’
          Signed constant that fits in 5 bits

     ‘K’
          Signed constant that fits in 6 bits

     ‘L’
          Unsigned constant that fits in 4 bits

     ‘M’
          Signed constant that fits in 32 bits

     ‘N’
          Check for 64 bits wide constants for add/sub instructions

     ‘G’
          Floating point constant that is legal for store immediate

_C-SKY--‘config/csky/constraints.md’_

     ‘a’
          The mini registers r0 - r7.

     ‘b’
          The low registers r0 - r15.

     ‘c’
          C register.

     ‘y’
          HI and LO registers.

     ‘l’
          LO register.

     ‘h’
          HI register.

     ‘v’
          Vector registers.

     ‘z’
          Stack pointer register (SP).

     ‘Q’
          A memory address which uses a base register with a short
          offset or with a index register with its scale.

     ‘W’
          A memory address which uses a base register with a index
          register with its scale.

_Epiphany--‘config/epiphany/constraints.md’_
     ‘U16’
          An unsigned 16-bit constant.

     ‘K’
          An unsigned 5-bit constant.

     ‘L’
          A signed 11-bit constant.

     ‘Cm1’
          A signed 11-bit constant added to −1.  Can only match when the
          ‘-m1reg-REG’ option is active.

     ‘Cl1’
          Left-shift of −1, i.e., a bit mask with a block of leading
          ones, the rest being a block of trailing zeroes.  Can only
          match when the ‘-m1reg-REG’ option is active.

     ‘Cr1’
          Right-shift of −1, i.e., a bit mask with a trailing block of
          ones, the rest being zeroes.  Or to put it another way, one
          less than a power of two.  Can only match when the
          ‘-m1reg-REG’ option is active.

     ‘Cal’
          Constant for arithmetic/logical operations.  This is like ‘i’,
          except that for position independent code, no symbols /
          expressions needing relocations are allowed.

     ‘Csy’
          Symbolic constant for call/jump instruction.

     ‘Rcs’
          The register class usable in short insns.  This is a register
          class constraint, and can thus drive register allocation.
          This constraint won't match unless ‘-mprefer-short-insn-regs’
          is in effect.

     ‘Rsc’
          The the register class of registers that can be used to hold a
          sibcall call address.  I.e., a caller-saved register.

     ‘Rct’
          Core control register class.

     ‘Rgs’
          The register group usable in short insns.  This constraint
          does not use a register class, so that it only passively
          matches suitable registers, and doesn't drive register
          allocation.

     ‘Rra’
          Matches the return address if it can be replaced with the link
          register.

     ‘Rcc’
          Matches the integer condition code register.

     ‘Sra’
          Matches the return address if it is in a stack slot.

     ‘Cfm’
          Matches control register values to switch fp mode, which are
          encapsulated in ‘UNSPEC_FP_MODE’.

_FRV--‘config/frv/frv.h’_
     ‘a’
          Register in the class ‘ACC_REGS’ (‘acc0’ to ‘acc7’).

     ‘b’
          Register in the class ‘EVEN_ACC_REGS’ (‘acc0’ to ‘acc7’).

     ‘c’
          Register in the class ‘CC_REGS’ (‘fcc0’ to ‘fcc3’ and ‘icc0’
          to ‘icc3’).

     ‘d’
          Register in the class ‘GPR_REGS’ (‘gr0’ to ‘gr63’).

     ‘e’
          Register in the class ‘EVEN_REGS’ (‘gr0’ to ‘gr63’).  Odd
          registers are excluded not in the class but through the use of
          a machine mode larger than 4 bytes.

     ‘f’
          Register in the class ‘FPR_REGS’ (‘fr0’ to ‘fr63’).

     ‘h’
          Register in the class ‘FEVEN_REGS’ (‘fr0’ to ‘fr63’).  Odd
          registers are excluded not in the class but through the use of
          a machine mode larger than 4 bytes.

     ‘l’
          Register in the class ‘LR_REG’ (the ‘lr’ register).

     ‘q’
          Register in the class ‘QUAD_REGS’ (‘gr2’ to ‘gr63’).  Register
          numbers not divisible by 4 are excluded not in the class but
          through the use of a machine mode larger than 8 bytes.

     ‘t’
          Register in the class ‘ICC_REGS’ (‘icc0’ to ‘icc3’).

     ‘u’
          Register in the class ‘FCC_REGS’ (‘fcc0’ to ‘fcc3’).

     ‘v’
          Register in the class ‘ICR_REGS’ (‘cc4’ to ‘cc7’).

     ‘w’
          Register in the class ‘FCR_REGS’ (‘cc0’ to ‘cc3’).

     ‘x’
          Register in the class ‘QUAD_FPR_REGS’ (‘fr0’ to ‘fr63’).
          Register numbers not divisible by 4 are excluded not in the
          class but through the use of a machine mode larger than 8
          bytes.

     ‘z’
          Register in the class ‘SPR_REGS’ (‘lcr’ and ‘lr’).

     ‘A’
          Register in the class ‘QUAD_ACC_REGS’ (‘acc0’ to ‘acc7’).

     ‘B’
          Register in the class ‘ACCG_REGS’ (‘accg0’ to ‘accg7’).

     ‘C’
          Register in the class ‘CR_REGS’ (‘cc0’ to ‘cc7’).

     ‘G’
          Floating point constant zero

     ‘I’
          6-bit signed integer constant

     ‘J’
          10-bit signed integer constant

     ‘L’
          16-bit signed integer constant

     ‘M’
          16-bit unsigned integer constant

     ‘N’
          12-bit signed integer constant that is negative--i.e. in the
          range of −2048 to −1

     ‘O’
          Constant zero

     ‘P’
          12-bit signed integer constant that is greater than zero--i.e.
          in the range of 1 to 2047.

_FT32--‘config/ft32/constraints.md’_
     ‘A’
          An absolute address

     ‘B’
          An offset address

     ‘W’
          A register indirect memory operand

     ‘e’
          An offset address.

     ‘f’
          An offset address.

     ‘O’
          The constant zero or one

     ‘I’
          A 16-bit signed constant (−32768 ... 32767)

     ‘w’
          A bitfield mask suitable for bext or bins

     ‘x’
          An inverted bitfield mask suitable for bext or bins

     ‘L’
          A 16-bit unsigned constant, multiple of 4 (0 ... 65532)

     ‘S’
          A 20-bit signed constant (−524288 ... 524287)

     ‘b’
          A constant for a bitfield width (1 ... 16)

     ‘KA’
          A 10-bit signed constant (−512 ... 511)

_Hewlett-Packard PA-RISC--‘config/pa/pa.h’_
     ‘a’
          General register 1

     ‘f’
          Floating point register

     ‘q’
          Shift amount register

     ‘x’
          Floating point register (deprecated)

     ‘y’
          Upper floating point register (32-bit), floating point
          register (64-bit)

     ‘Z’
          Any register

     ‘I’
          Signed 11-bit integer constant

     ‘J’
          Signed 14-bit integer constant

     ‘K’
          Integer constant that can be deposited with a ‘zdepi’
          instruction

     ‘L’
          Signed 5-bit integer constant

     ‘M’
          Integer constant 0

     ‘N’
          Integer constant that can be loaded with a ‘ldil’ instruction

     ‘O’
          Integer constant whose value plus one is a power of 2

     ‘P’
          Integer constant that can be used for ‘and’ operations in
          ‘depi’ and ‘extru’ instructions

     ‘S’
          Integer constant 31

     ‘U’
          Integer constant 63

     ‘G’
          Floating-point constant 0.0

     ‘A’
          A ‘lo_sum’ data-linkage-table memory operand

     ‘Q’
          A memory operand that can be used as the destination operand
          of an integer store instruction

     ‘R’
          A scaled or unscaled indexed memory operand

     ‘T’
          A memory operand for floating-point loads and stores

     ‘W’
          A register indirect memory operand

_Intel IA-64--‘config/ia64/ia64.h’_
     ‘a’
          General register ‘r0’ to ‘r3’ for ‘addl’ instruction

     ‘b’
          Branch register

     ‘c’
          Predicate register (‘c’ as in "conditional")

     ‘d’
          Application register residing in M-unit

     ‘e’
          Application register residing in I-unit

     ‘f’
          Floating-point register

     ‘m’
          Memory operand.  If used together with ‘<’ or ‘>’, the operand
          can have postincrement and postdecrement which require
          printing with ‘%Pn’ on IA-64.

     ‘G’
          Floating-point constant 0.0 or 1.0

     ‘I’
          14-bit signed integer constant

     ‘J’
          22-bit signed integer constant

     ‘K’
          8-bit signed integer constant for logical instructions

     ‘L’
          8-bit adjusted signed integer constant for compare pseudo-ops

     ‘M’
          6-bit unsigned integer constant for shift counts

     ‘N’
          9-bit signed integer constant for load and store
          postincrements

     ‘O’
          The constant zero

     ‘P’
          0 or −1 for ‘dep’ instruction

     ‘Q’
          Non-volatile memory for floating-point loads and stores

     ‘R’
          Integer constant in the range 1 to 4 for ‘shladd’ instruction

     ‘S’
          Memory operand except postincrement and postdecrement.  This
          is now roughly the same as ‘m’ when not used together with ‘<’
          or ‘>’.

_M32C--‘config/m32c/m32c.cc’_
     ‘Rsp’
     ‘Rfb’
     ‘Rsb’
          ‘$sp’, ‘$fb’, ‘$sb’.

     ‘Rcr’
          Any control register, when they're 16 bits wide (nothing if
          control registers are 24 bits wide)

     ‘Rcl’
          Any control register, when they're 24 bits wide.

     ‘R0w’
     ‘R1w’
     ‘R2w’
     ‘R3w’
          $r0, $r1, $r2, $r3.

     ‘R02’
          $r0 or $r2, or $r2r0 for 32 bit values.

     ‘R13’
          $r1 or $r3, or $r3r1 for 32 bit values.

     ‘Rdi’
          A register that can hold a 64 bit value.

     ‘Rhl’
          $r0 or $r1 (registers with addressable high/low bytes)

     ‘R23’
          $r2 or $r3

     ‘Raa’
          Address registers

     ‘Raw’
          Address registers when they're 16 bits wide.

     ‘Ral’
          Address registers when they're 24 bits wide.

     ‘Rqi’
          Registers that can hold QI values.

     ‘Rad’
          Registers that can be used with displacements ($a0, $a1, $sb).

     ‘Rsi’
          Registers that can hold 32 bit values.

     ‘Rhi’
          Registers that can hold 16 bit values.

     ‘Rhc’
          Registers chat can hold 16 bit values, including all control
          registers.

     ‘Rra’
          $r0 through R1, plus $a0 and $a1.

     ‘Rfl’
          The flags register.

     ‘Rmm’
          The memory-based pseudo-registers $mem0 through $mem15.

     ‘Rpi’
          Registers that can hold pointers (16 bit registers for r8c,
          m16c; 24 bit registers for m32cm, m32c).

     ‘Rpa’
          Matches multiple registers in a PARALLEL to form a larger
          register.  Used to match function return values.

     ‘Is3’
          −8 ... 7

     ‘IS1’
          −128 ... 127

     ‘IS2’
          −32768 ... 32767

     ‘IU2’
          0 ... 65535

     ‘In4’
          −8 ... −1 or 1 ... 8

     ‘In5’
          −16 ... −1 or 1 ... 16

     ‘In6’
          −32 ... −1 or 1 ... 32

     ‘IM2’
          −65536 ... −1

     ‘Ilb’
          An 8 bit value with exactly one bit set.

     ‘Ilw’
          A 16 bit value with exactly one bit set.

     ‘Sd’
          The common src/dest memory addressing modes.

     ‘Sa’
          Memory addressed using $a0 or $a1.

     ‘Si’
          Memory addressed with immediate addresses.

     ‘Ss’
          Memory addressed using the stack pointer ($sp).

     ‘Sf’
          Memory addressed using the frame base register ($fb).

     ‘Ss’
          Memory addressed using the small base register ($sb).

     ‘S1’
          $r1h

_LoongArch--‘config/loongarch/constraints.md’_
     ‘f’
          A floating-point register (if available).
     ‘k’
          A memory operand whose address is formed by a base register
          and (optionally scaled) index register.
     ‘l’
          A signed 16-bit constant.
     ‘m’
          A memory operand whose address is formed by a base register
          and offset that is suitable for use in instructions with the
          same addressing mode as ‘st.w’ and ‘ld.w’.
     ‘I’
          A signed 12-bit constant (for arithmetic instructions).
     ‘K’
          An unsigned 12-bit constant (for logic instructions).
     ‘ZB’
          An address that is held in a general-purpose register.  The
          offset is zero.
     ‘ZC’
          A memory operand whose address is formed by a base register
          and offset that is suitable for use in instructions with the
          same addressing mode as ‘ll.w’ and ‘sc.w’.

_MicroBlaze--‘config/microblaze/constraints.md’_
     ‘d’
          A general register (‘r0’ to ‘r31’).

     ‘z’
          A status register (‘rmsr’, ‘$fcc1’ to ‘$fcc7’).

_MIPS--‘config/mips/constraints.md’_
     ‘d’
          A general-purpose register.  This is equivalent to ‘r’ unless
          generating MIPS16 code, in which case the MIPS16 register set
          is used.

     ‘f’
          A floating-point register (if available).

     ‘h’
          Formerly the ‘hi’ register.  This constraint is no longer
          supported.

     ‘l’
          The ‘lo’ register.  Use this register to store values that are
          no bigger than a word.

     ‘x’
          The concatenated ‘hi’ and ‘lo’ registers.  Use this register
          to store doubleword values.

     ‘c’
          A register suitable for use in an indirect jump.  This will
          always be ‘$25’ for ‘-mabicalls’.

     ‘v’
          Register ‘$3’.  Do not use this constraint in new code; it is
          retained only for compatibility with glibc.

     ‘y’
          Equivalent to ‘r’; retained for backwards compatibility.

     ‘z’
          A floating-point condition code register.

     ‘I’
          A signed 16-bit constant (for arithmetic instructions).

     ‘J’
          Integer zero.

     ‘K’
          An unsigned 16-bit constant (for logic instructions).

     ‘L’
          A signed 32-bit constant in which the lower 16 bits are zero.
          Such constants can be loaded using ‘lui’.

     ‘M’
          A constant that cannot be loaded using ‘lui’, ‘addiu’ or
          ‘ori’.

     ‘N’
          A constant in the range −65535 to −1 (inclusive).

     ‘O’
          A signed 15-bit constant.

     ‘P’
          A constant in the range 1 to 65535 (inclusive).

     ‘G’
          Floating-point zero.

     ‘R’
          An address that can be used in a non-macro load or store.

     ‘ZC’
          A memory operand whose address is formed by a base register
          and offset that is suitable for use in instructions with the
          same addressing mode as ‘ll’ and ‘sc’.

     ‘ZD’
          An address suitable for a ‘prefetch’ instruction, or for any
          other instruction with the same addressing mode as ‘prefetch’.

_Motorola 680x0--‘config/m68k/constraints.md’_
     ‘a’
          Address register

     ‘d’
          Data register

     ‘f’
          68881 floating-point register, if available

     ‘I’
          Integer in the range 1 to 8

     ‘J’
          16-bit signed number

     ‘K’
          Signed number whose magnitude is greater than 0x80

     ‘L’
          Integer in the range −8 to −1

     ‘M’
          Signed number whose magnitude is greater than 0x100

     ‘N’
          Range 24 to 31, rotatert:SI 8 to 1 expressed as rotate

     ‘O’
          16 (for rotate using swap)

     ‘P’
          Range 8 to 15, rotatert:HI 8 to 1 expressed as rotate

     ‘R’
          Numbers that mov3q can handle

     ‘G’
          Floating point constant that is not a 68881 constant

     ‘S’
          Operands that satisfy 'm' when -mpcrel is in effect

     ‘T’
          Operands that satisfy 's' when -mpcrel is not in effect

     ‘Q’
          Address register indirect addressing mode

     ‘U’
          Register offset addressing

     ‘W’
          const_call_operand

     ‘Cs’
          symbol_ref or const

     ‘Ci’
          const_int

     ‘C0’
          const_int 0

     ‘Cj’
          Range of signed numbers that don't fit in 16 bits

     ‘Cmvq’
          Integers valid for mvq

     ‘Capsw’
          Integers valid for a moveq followed by a swap

     ‘Cmvz’
          Integers valid for mvz

     ‘Cmvs’
          Integers valid for mvs

     ‘Ap’
          push_operand

     ‘Ac’
          Non-register operands allowed in clr

_Moxie--‘config/moxie/constraints.md’_
     ‘A’
          An absolute address

     ‘B’
          An offset address

     ‘W’
          A register indirect memory operand

     ‘I’
          A constant in the range of 0 to 255.

     ‘N’
          A constant in the range of 0 to −255.

_MSP430-‘config/msp430/constraints.md’_

     ‘R12’
          Register R12.

     ‘R13’
          Register R13.

     ‘K’
          Integer constant 1.

     ‘L’
          Integer constant -1^20..1^19.

     ‘M’
          Integer constant 1-4.

     ‘Ya’
          Memory references which do not require an extended MOVX
          instruction.

     ‘Yl’
          Memory reference, labels only.

     ‘Ys’
          Memory reference, stack only.

_NDS32--‘config/nds32/constraints.md’_
     ‘w’
          LOW register class $r0 to $r7 constraint for V3/V3M ISA.
     ‘l’
          LOW register class $r0 to $r7.
     ‘d’
          MIDDLE register class $r0 to $r11, $r16 to $r19.
     ‘h’
          HIGH register class $r12 to $r14, $r20 to $r31.
     ‘t’
          Temporary assist register $ta (i.e. $r15).
     ‘k’
          Stack register $sp.
     ‘Iu03’
          Unsigned immediate 3-bit value.
     ‘In03’
          Negative immediate 3-bit value in the range of −7-0.
     ‘Iu04’
          Unsigned immediate 4-bit value.
     ‘Is05’
          Signed immediate 5-bit value.
     ‘Iu05’
          Unsigned immediate 5-bit value.
     ‘In05’
          Negative immediate 5-bit value in the range of −31-0.
     ‘Ip05’
          Unsigned immediate 5-bit value for movpi45 instruction with
          range 16-47.
     ‘Iu06’
          Unsigned immediate 6-bit value constraint for addri36.sp
          instruction.
     ‘Iu08’
          Unsigned immediate 8-bit value.
     ‘Iu09’
          Unsigned immediate 9-bit value.
     ‘Is10’
          Signed immediate 10-bit value.
     ‘Is11’
          Signed immediate 11-bit value.
     ‘Is15’
          Signed immediate 15-bit value.
     ‘Iu15’
          Unsigned immediate 15-bit value.
     ‘Ic15’
          A constant which is not in the range of imm15u but ok for bclr
          instruction.
     ‘Ie15’
          A constant which is not in the range of imm15u but ok for bset
          instruction.
     ‘It15’
          A constant which is not in the range of imm15u but ok for btgl
          instruction.
     ‘Ii15’
          A constant whose compliment value is in the range of imm15u
          and ok for bitci instruction.
     ‘Is16’
          Signed immediate 16-bit value.
     ‘Is17’
          Signed immediate 17-bit value.
     ‘Is19’
          Signed immediate 19-bit value.
     ‘Is20’
          Signed immediate 20-bit value.
     ‘Ihig’
          The immediate value that can be simply set high 20-bit.
     ‘Izeb’
          The immediate value 0xff.
     ‘Izeh’
          The immediate value 0xffff.
     ‘Ixls’
          The immediate value 0x01.
     ‘Ix11’
          The immediate value 0x7ff.
     ‘Ibms’
          The immediate value with power of 2.
     ‘Ifex’
          The immediate value with power of 2 minus 1.
     ‘U33’
          Memory constraint for 333 format.
     ‘U45’
          Memory constraint for 45 format.
     ‘U37’
          Memory constraint for 37 format.

_Nios II family--‘config/nios2/constraints.md’_

     ‘I’
          Integer that is valid as an immediate operand in an
          instruction taking a signed 16-bit number.  Range −32768 to
          32767.

     ‘J’
          Integer that is valid as an immediate operand in an
          instruction taking an unsigned 16-bit number.  Range 0 to
          65535.

     ‘K’
          Integer that is valid as an immediate operand in an
          instruction taking only the upper 16-bits of a 32-bit number.
          Range 32-bit numbers with the lower 16-bits being 0.

     ‘L’
          Integer that is valid as an immediate operand for a shift
          instruction.  Range 0 to 31.

     ‘M’
          Integer that is valid as an immediate operand for only the
          value 0.  Can be used in conjunction with the format modifier
          ‘z’ to use ‘r0’ instead of ‘0’ in the assembly output.

     ‘N’
          Integer that is valid as an immediate operand for a custom
          instruction opcode.  Range 0 to 255.

     ‘P’
          An immediate operand for R2 andchi/andci instructions.

     ‘S’
          Matches immediates which are addresses in the small data
          section and therefore can be added to ‘gp’ as a 16-bit
          immediate to re-create their 32-bit value.

     ‘U’
          Matches constants suitable as an operand for the rdprs and
          cache instructions.

     ‘v’
          A memory operand suitable for Nios II R2 load/store exclusive
          instructions.

     ‘w’
          A memory operand suitable for load/store IO and cache
          instructions.

_OpenRISC--‘config/or1k/constraints.md’_
     ‘I’
          Integer that is valid as an immediate operand in an
          instruction taking a signed 16-bit number.  Range −32768 to
          32767.

     ‘K’
          Integer that is valid as an immediate operand in an
          instruction taking an unsigned 16-bit number.  Range 0 to
          65535.

     ‘M’
          Signed 16-bit constant shifted left 16 bits.  (Used with
          ‘l.movhi’)

     ‘O’
          Zero

_PDP-11--‘config/pdp11/constraints.md’_
     ‘a’
          Floating point registers AC0 through AC3.  These can be loaded
          from/to memory with a single instruction.

     ‘d’
          Odd numbered general registers (R1, R3, R5).  These are used
          for 16-bit multiply operations.

     ‘D’
          A memory reference that is encoded within the opcode, but not
          auto-increment or auto-decrement.

     ‘f’
          Any of the floating point registers (AC0 through AC5).

     ‘G’
          Floating point constant 0.

     ‘h’
          Floating point registers AC4 and AC5.  These cannot be loaded
          from/to memory with a single instruction.

     ‘I’
          An integer constant that fits in 16 bits.

     ‘J’
          An integer constant whose low order 16 bits are zero.

     ‘K’
          An integer constant that does not meet the constraints for
          codes ‘I’ or ‘J’.

     ‘L’
          The integer constant 1.

     ‘M’
          The integer constant −1.

     ‘N’
          The integer constant 0.

     ‘O’
          Integer constants 0 through 3; shifts by these amounts are
          handled as multiple single-bit shifts rather than a single
          variable-length shift.

     ‘Q’
          A memory reference which requires an additional word (address
          or offset) after the opcode.

     ‘R’
          A memory reference that is encoded within the opcode.

_PowerPC and IBM RS6000--‘config/rs6000/constraints.md’_
     ‘r’
          A general purpose register (GPR), ‘r0’...‘r31’.

     ‘b’
          A base register.  Like ‘r’, but ‘r0’ is not allowed, so
          ‘r1’...‘r31’.

     ‘f’
          A floating point register (FPR), ‘f0’...‘f31’.

     ‘d’
          A floating point register.  This is the same as ‘f’ nowadays;
          historically ‘f’ was for single-precision and ‘d’ was for
          double-precision floating point.

     ‘v’
          An Altivec vector register (VR), ‘v0’...‘v31’.

     ‘wa’
          A VSX register (VSR), ‘vs0’...‘vs63’.  This is either an FPR
          (‘vs0’...‘vs31’ are ‘f0’...‘f31’) or a VR (‘vs32’...‘vs63’ are
          ‘v0’...‘v31’).

          When using ‘wa’, you should use the ‘%x’ output modifier, so
          that the correct register number is printed.  For example:

               asm ("xvadddp %x0,%x1,%x2"
                    : "=wa" (v1)
                    : "wa" (v2), "wa" (v3));

          You should not use ‘%x’ for ‘v’ operands:

               asm ("xsaddqp %0,%1,%2"
                    : "=v" (v1)
                    : "v" (v2), "v" (v3));

     ‘c’
          The count register, ‘ctr’.

     ‘l’
          The link register, ‘lr’.

     ‘x’
          Condition register field 0, ‘cr0’.

     ‘y’
          Any condition register field, ‘cr0’...‘cr7’.

     ‘I’
          A signed 16-bit constant.

     ‘J’
          An unsigned 16-bit constant shifted left 16 bits (use ‘L’
          instead for ‘SImode’ constants).

     ‘K’
          An unsigned 16-bit constant.

     ‘L’
          A signed 16-bit constant shifted left 16 bits.

     ‘eI’
          A signed 34-bit integer constant if prefixed instructions are
          supported.

     ‘eP’
          A scalar floating point constant or a vector constant that can
          be loaded to a VSX register with one prefixed instruction.

     ‘eQ’
          An IEEE 128-bit constant that can be loaded into a VSX
          register with the ‘lxvkq’ instruction.

     ‘m’
          A memory operand.  Normally, ‘m’ does not allow addresses that
          update the base register.  If the ‘<’ or ‘>’ constraint is
          also used, they are allowed and therefore on PowerPC targets
          in that case it is only safe to use ‘m<>’ in an ‘asm’
          statement if that ‘asm’ statement accesses the operand exactly
          once.  The ‘asm’ statement must also use ‘%U<OPNO>’ as a
          placeholder for the "update" flag in the corresponding load or
          store instruction.  For example:

               asm ("st%U0 %1,%0" : "=m<>" (mem) : "r" (val));

          is correct but:

               asm ("st %1,%0" : "=m<>" (mem) : "r" (val));

          is not.

     ‘Q’
          A memory operand addressed by just a base register.

     ‘Z’
          A memory operand accessed with indexed or indirect addressing.

     ‘a’
          An indexed or indirect address.

_PRU--‘config/pru/constraints.md’_
     ‘I’
          An unsigned 8-bit integer constant.

     ‘J’
          An unsigned 16-bit integer constant.

     ‘L’
          An unsigned 5-bit integer constant (for shift counts).

     ‘T’
          A text segment (program memory) constant label.

     ‘Z’
          Integer constant zero.

_RL78--‘config/rl78/constraints.md’_

     ‘Int3’
          An integer constant in the range 1 ... 7.
     ‘Int8’
          An integer constant in the range 0 ... 255.
     ‘J’
          An integer constant in the range −255 ... 0
     ‘K’
          The integer constant 1.
     ‘L’
          The integer constant -1.
     ‘M’
          The integer constant 0.
     ‘N’
          The integer constant 2.
     ‘O’
          The integer constant -2.
     ‘P’
          An integer constant in the range 1 ... 15.
     ‘Qbi’
          The built-in compare types-eq, ne, gtu, ltu, geu, and leu.
     ‘Qsc’
          The synthetic compare types-gt, lt, ge, and le.
     ‘Wab’
          A memory reference with an absolute address.
     ‘Wbc’
          A memory reference using ‘BC’ as a base register, with an
          optional offset.
     ‘Wca’
          A memory reference using ‘AX’, ‘BC’, ‘DE’, or ‘HL’ for the
          address, for calls.
     ‘Wcv’
          A memory reference using any 16-bit register pair for the
          address, for calls.
     ‘Wd2’
          A memory reference using ‘DE’ as a base register, with an
          optional offset.
     ‘Wde’
          A memory reference using ‘DE’ as a base register, without any
          offset.
     ‘Wfr’
          Any memory reference to an address in the far address space.
     ‘Wh1’
          A memory reference using ‘HL’ as a base register, with an
          optional one-byte offset.
     ‘Whb’
          A memory reference using ‘HL’ as a base register, with ‘B’ or
          ‘C’ as the index register.
     ‘Whl’
          A memory reference using ‘HL’ as a base register, without any
          offset.
     ‘Ws1’
          A memory reference using ‘SP’ as a base register, with an
          optional one-byte offset.
     ‘Y’
          Any memory reference to an address in the near address space.
     ‘A’
          The ‘AX’ register.
     ‘B’
          The ‘BC’ register.
     ‘D’
          The ‘DE’ register.
     ‘R’
          ‘A’ through ‘L’ registers.
     ‘S’
          The ‘SP’ register.
     ‘T’
          The ‘HL’ register.
     ‘Z08W’
          The 16-bit ‘R8’ register.
     ‘Z10W’
          The 16-bit ‘R10’ register.
     ‘Zint’
          The registers reserved for interrupts (‘R24’ to ‘R31’).
     ‘a’
          The ‘A’ register.
     ‘b’
          The ‘B’ register.
     ‘c’
          The ‘C’ register.
     ‘d’
          The ‘D’ register.
     ‘e’
          The ‘E’ register.
     ‘h’
          The ‘H’ register.
     ‘l’
          The ‘L’ register.
     ‘v’
          The virtual registers.
     ‘w’
          The ‘PSW’ register.
     ‘x’
          The ‘X’ register.

_RISC-V--‘config/riscv/constraints.md’_

     ‘f’
          A floating-point register (if available).

     ‘I’
          An I-type 12-bit signed immediate.

     ‘J’
          Integer zero.

     ‘K’
          A 5-bit unsigned immediate for CSR access instructions.

     ‘A’
          An address that is held in a general-purpose register.

     ‘S’
          A constraint that matches an absolute symbolic address.

_RX--‘config/rx/constraints.md’_
     ‘Q’
          An address which does not involve register indirect addressing
          or pre/post increment/decrement addressing.

     ‘Symbol’
          A symbol reference.

     ‘Int08’
          A constant in the range −256 to 255, inclusive.

     ‘Sint08’
          A constant in the range −128 to 127, inclusive.

     ‘Sint16’
          A constant in the range −32768 to 32767, inclusive.

     ‘Sint24’
          A constant in the range −8388608 to 8388607, inclusive.

     ‘Uint04’
          A constant in the range 0 to 15, inclusive.

_S/390 and zSeries--‘config/s390/s390.h’_
     ‘a’
          Address register (general purpose register except r0)

     ‘c’
          Condition code register

     ‘d’
          Data register (arbitrary general purpose register)

     ‘f’
          Floating-point register

     ‘I’
          Unsigned 8-bit constant (0-255)

     ‘J’
          Unsigned 12-bit constant (0-4095)

     ‘K’
          Signed 16-bit constant (−32768-32767)

     ‘L’
          Value appropriate as displacement.
          ‘(0..4095)’
               for short displacement
          ‘(−524288..524287)’
               for long displacement

     ‘M’
          Constant integer with a value of 0x7fffffff.

     ‘N’
          Multiple letter constraint followed by 4 parameter letters.
          ‘0..9:’
               number of the part counting from most to least
               significant
          ‘H,Q:’
               mode of the part
          ‘D,S,H:’
               mode of the containing operand
          ‘0,F:’
               value of the other parts (F--all bits set)
          The constraint matches if the specified part of a constant has
          a value different from its other parts.

     ‘Q’
          Memory reference without index register and with short
          displacement.

     ‘R’
          Memory reference with index register and short displacement.

     ‘S’
          Memory reference without index register but with long
          displacement.

     ‘T’
          Memory reference with index register and long displacement.

     ‘U’
          Pointer with short displacement.

     ‘W’
          Pointer with long displacement.

     ‘Y’
          Shift count operand.

_SPARC--‘config/sparc/sparc.h’_
     ‘f’
          Floating-point register on the SPARC-V8 architecture and lower
          floating-point register on the SPARC-V9 architecture.

     ‘e’
          Floating-point register.  It is equivalent to ‘f’ on the
          SPARC-V8 architecture and contains both lower and upper
          floating-point registers on the SPARC-V9 architecture.

     ‘c’
          Floating-point condition code register.

     ‘d’
          Lower floating-point register.  It is only valid on the
          SPARC-V9 architecture when the Visual Instruction Set is
          available.

     ‘b’
          Floating-point register.  It is only valid on the SPARC-V9
          architecture when the Visual Instruction Set is available.

     ‘h’
          64-bit global or out register for the SPARC-V8+ architecture.

     ‘C’
          The constant all-ones, for floating-point.

     ‘A’
          Signed 5-bit constant

     ‘D’
          A vector constant

     ‘I’
          Signed 13-bit constant

     ‘J’
          Zero

     ‘K’
          32-bit constant with the low 12 bits clear (a constant that
          can be loaded with the ‘sethi’ instruction)

     ‘L’
          A constant in the range supported by ‘movcc’ instructions
          (11-bit signed immediate)

     ‘M’
          A constant in the range supported by ‘movrcc’ instructions
          (10-bit signed immediate)

     ‘N’
          Same as ‘K’, except that it verifies that bits that are not in
          the lower 32-bit range are all zero.  Must be used instead of
          ‘K’ for modes wider than ‘SImode’

     ‘O’
          The constant 4096

     ‘G’
          Floating-point zero

     ‘H’
          Signed 13-bit constant, sign-extended to 32 or 64 bits

     ‘P’
          The constant -1

     ‘Q’
          Floating-point constant whose integral representation can be
          moved into an integer register using a single sethi
          instruction

     ‘R’
          Floating-point constant whose integral representation can be
          moved into an integer register using a single mov instruction

     ‘S’
          Floating-point constant whose integral representation can be
          moved into an integer register using a high/lo_sum instruction
          sequence

     ‘T’
          Memory address aligned to an 8-byte boundary

     ‘U’
          Even register

     ‘W’
          Memory address for ‘e’ constraint registers

     ‘w’
          Memory address with only a base register

     ‘Y’
          Vector zero

_TI C6X family--‘config/c6x/constraints.md’_
     ‘a’
          Register file A (A0-A31).

     ‘b’
          Register file B (B0-B31).

     ‘A’
          Predicate registers in register file A (A0-A2 on C64X and
          higher, A1 and A2 otherwise).

     ‘B’
          Predicate registers in register file B (B0-B2).

     ‘C’
          A call-used register in register file B (B0-B9, B16-B31).

     ‘Da’
          Register file A, excluding predicate registers (A3-A31, plus
          A0 if not C64X or higher).

     ‘Db’
          Register file B, excluding predicate registers (B3-B31).

     ‘Iu4’
          Integer constant in the range 0 ... 15.

     ‘Iu5’
          Integer constant in the range 0 ... 31.

     ‘In5’
          Integer constant in the range −31 ... 0.

     ‘Is5’
          Integer constant in the range −16 ... 15.

     ‘I5x’
          Integer constant that can be the operand of an ADDA or a SUBA
          insn.

     ‘IuB’
          Integer constant in the range 0 ... 65535.

     ‘IsB’
          Integer constant in the range −32768 ... 32767.

     ‘IsC’
          Integer constant in the range -2^{20} ... 2^{20} - 1.

     ‘Jc’
          Integer constant that is a valid mask for the clr instruction.

     ‘Js’
          Integer constant that is a valid mask for the set instruction.

     ‘Q’
          Memory location with A base register.

     ‘R’
          Memory location with B base register.

     ‘Z’
          Register B14 (aka DP).

_TILE-Gx--‘config/tilegx/constraints.md’_
     ‘R00’
     ‘R01’
     ‘R02’
     ‘R03’
     ‘R04’
     ‘R05’
     ‘R06’
     ‘R07’
     ‘R08’
     ‘R09’
     ‘R10’
          Each of these represents a register constraint for an
          individual register, from r0 to r10.

     ‘I’
          Signed 8-bit integer constant.

     ‘J’
          Signed 16-bit integer constant.

     ‘K’
          Unsigned 16-bit integer constant.

     ‘L’
          Integer constant that fits in one signed byte when incremented
          by one (−129 ... 126).

     ‘m’
          Memory operand.  If used together with ‘<’ or ‘>’, the operand
          can have postincrement which requires printing with ‘%In’ and
          ‘%in’ on TILE-Gx.  For example:

               asm ("st_add %I0,%1,%i0" : "=m<>" (*mem) : "r" (val));

     ‘M’
          A bit mask suitable for the BFINS instruction.

     ‘N’
          Integer constant that is a byte tiled out eight times.

     ‘O’
          The integer zero constant.

     ‘P’
          Integer constant that is a sign-extended byte tiled out as
          four shorts.

     ‘Q’
          Integer constant that fits in one signed byte when incremented
          (−129 ... 126), but excluding -1.

     ‘S’
          Integer constant that has all 1 bits consecutive and starting
          at bit 0.

     ‘T’
          A 16-bit fragment of a got, tls, or pc-relative reference.

     ‘U’
          Memory operand except postincrement.  This is roughly the same
          as ‘m’ when not used together with ‘<’ or ‘>’.

     ‘W’
          An 8-element vector constant with identical elements.

     ‘Y’
          A 4-element vector constant with identical elements.

     ‘Z0’
          The integer constant 0xffffffff.

     ‘Z1’
          The integer constant 0xffffffff00000000.

_TILEPro--‘config/tilepro/constraints.md’_
     ‘R00’
     ‘R01’
     ‘R02’
     ‘R03’
     ‘R04’
     ‘R05’
     ‘R06’
     ‘R07’
     ‘R08’
     ‘R09’
     ‘R10’
          Each of these represents a register constraint for an
          individual register, from r0 to r10.

     ‘I’
          Signed 8-bit integer constant.

     ‘J’
          Signed 16-bit integer constant.

     ‘K’
          Nonzero integer constant with low 16 bits zero.

     ‘L’
          Integer constant that fits in one signed byte when incremented
          by one (−129 ... 126).

     ‘m’
          Memory operand.  If used together with ‘<’ or ‘>’, the operand
          can have postincrement which requires printing with ‘%In’ and
          ‘%in’ on TILEPro.  For example:

               asm ("swadd %I0,%1,%i0" : "=m<>" (mem) : "r" (val));

     ‘M’
          A bit mask suitable for the MM instruction.

     ‘N’
          Integer constant that is a byte tiled out four times.

     ‘O’
          The integer zero constant.

     ‘P’
          Integer constant that is a sign-extended byte tiled out as two
          shorts.

     ‘Q’
          Integer constant that fits in one signed byte when incremented
          (−129 ... 126), but excluding -1.

     ‘T’
          A symbolic operand, or a 16-bit fragment of a got, tls, or
          pc-relative reference.

     ‘U’
          Memory operand except postincrement.  This is roughly the same
          as ‘m’ when not used together with ‘<’ or ‘>’.

     ‘W’
          A 4-element vector constant with identical elements.

     ‘Y’
          A 2-element vector constant with identical elements.

_Visium--‘config/visium/constraints.md’_
     ‘b’
          EAM register ‘mdb’

     ‘c’
          EAM register ‘mdc’

     ‘f’
          Floating point register

     ‘l’
          General register, but not ‘r29’, ‘r30’ and ‘r31’

     ‘t’
          Register ‘r1’

     ‘u’
          Register ‘r2’

     ‘v’
          Register ‘r3’

     ‘G’
          Floating-point constant 0.0

     ‘J’
          Integer constant in the range 0 ..  65535 (16-bit immediate)

     ‘K’
          Integer constant in the range 1 ..  31 (5-bit immediate)

     ‘L’
          Integer constant in the range −65535 ..  −1 (16-bit negative
          immediate)

     ‘M’
          Integer constant −1

     ‘O’
          Integer constant 0

     ‘P’
          Integer constant 32

_x86 family--‘config/i386/constraints.md’_
     ‘R’
          Legacy register--the eight integer registers available on all
          i386 processors (‘a’, ‘b’, ‘c’, ‘d’, ‘si’, ‘di’, ‘bp’, ‘sp’).

     ‘q’
          Any register accessible as ‘Rl’.  In 32-bit mode, ‘a’, ‘b’,
          ‘c’, and ‘d’; in 64-bit mode, any integer register.

     ‘Q’
          Any register accessible as ‘Rh’: ‘a’, ‘b’, ‘c’, and ‘d’.

     ‘a’
          The ‘a’ register.

     ‘b’
          The ‘b’ register.

     ‘c’
          The ‘c’ register.

     ‘d’
          The ‘d’ register.

     ‘S’
          The ‘si’ register.

     ‘D’
          The ‘di’ register.

     ‘A’
          The ‘a’ and ‘d’ registers.  This class is used for
          instructions that return double word results in the ‘ax:dx’
          register pair.  Single word values will be allocated either in
          ‘ax’ or ‘dx’.  For example on i386 the following implements
          ‘rdtsc’:

               unsigned long long rdtsc (void)
               {
                 unsigned long long tick;
                 __asm__ __volatile__("rdtsc":"=A"(tick));
                 return tick;
               }

          This is not correct on x86-64 as it would allocate tick in
          either ‘ax’ or ‘dx’.  You have to use the following variant
          instead:

               unsigned long long rdtsc (void)
               {
                 unsigned int tickl, tickh;
                 __asm__ __volatile__("rdtsc":"=a"(tickl),"=d"(tickh));
                 return ((unsigned long long)tickh << 32)|tickl;
               }

     ‘U’
          The call-clobbered integer registers.

     ‘f’
          Any 80387 floating-point (stack) register.

     ‘t’
          Top of 80387 floating-point stack (‘%st(0)’).

     ‘u’
          Second from top of 80387 floating-point stack (‘%st(1)’).

     ‘y’
          Any MMX register.

     ‘x’
          Any SSE register.

     ‘v’
          Any EVEX encodable SSE register (‘%xmm0-%xmm31’).

     ‘Yz’
          First SSE register (‘%xmm0’).

     ‘I’
          Integer constant in the range 0 ... 31, for 32-bit shifts.

     ‘J’
          Integer constant in the range 0 ... 63, for 64-bit shifts.

     ‘K’
          Signed 8-bit integer constant.

     ‘L’
          ‘0xFF’ or ‘0xFFFF’, for andsi as a zero-extending move.

     ‘M’
          0, 1, 2, or 3 (shifts for the ‘lea’ instruction).

     ‘N’
          Unsigned 8-bit integer constant (for ‘in’ and ‘out’
          instructions).

     ‘G’
          Standard 80387 floating point constant.

     ‘C’
          SSE constant zero operand.

     ‘e’
          32-bit signed integer constant, or a symbolic reference known
          to fit that range (for immediate operands in sign-extending
          x86-64 instructions).

     ‘We’
          32-bit signed integer constant, or a symbolic reference known
          to fit that range (for sign-extending conversion operations
          that require non-‘VOIDmode’ immediate operands).

     ‘Wz’
          32-bit unsigned integer constant, or a symbolic reference
          known to fit that range (for zero-extending conversion
          operations that require non-‘VOIDmode’ immediate operands).

     ‘Wd’
          128-bit integer constant where both the high and low 64-bit
          word satisfy the ‘e’ constraint.

     ‘Z’
          32-bit unsigned integer constant, or a symbolic reference
          known to fit that range (for immediate operands in
          zero-extending x86-64 instructions).

     ‘Tv’
          VSIB address operand.

     ‘Ts’
          Address operand without segment register.

_Xstormy16--‘config/stormy16/stormy16.h’_
     ‘a’
          Register r0.

     ‘b’
          Register r1.

     ‘c’
          Register r2.

     ‘d’
          Register r8.

     ‘e’
          Registers r0 through r7.

     ‘t’
          Registers r0 and r1.

     ‘y’
          The carry register.

     ‘z’
          Registers r8 and r9.

     ‘I’
          A constant between 0 and 3 inclusive.

     ‘J’
          A constant that has exactly one bit set.

     ‘K’
          A constant that has exactly one bit clear.

     ‘L’
          A constant between 0 and 255 inclusive.

     ‘M’
          A constant between −255 and 0 inclusive.

     ‘N’
          A constant between −3 and 0 inclusive.

     ‘O’
          A constant between 1 and 4 inclusive.

     ‘P’
          A constant between −4 and −1 inclusive.

     ‘Q’
          A memory reference that is a stack push.

     ‘R’
          A memory reference that is a stack pop.

     ‘S’
          A memory reference that refers to a constant address of known
          value.

     ‘T’
          The register indicated by Rx (not implemented yet).

     ‘U’
          A constant that is not between 2 and 15 inclusive.

     ‘Z’
          The constant 0.

_Xtensa--‘config/xtensa/constraints.md’_
     ‘a’
          General-purpose 32-bit register

     ‘b’
          One-bit boolean register

     ‘A’
          MAC16 40-bit accumulator register

     ‘I’
          Signed 12-bit integer constant, for use in MOVI instructions

     ‘J’
          Signed 8-bit integer constant, for use in ADDI instructions

     ‘K’
          Integer constant valid for BccI instructions

     ‘L’
          Unsigned constant valid for BccUI instructions


File: gcc.info,  Node: Asm Labels,  Next: Explicit Register Variables,  Prev: Constraints,  Up: Using Assembly Language with C

6.47.4 Controlling Names Used in Assembler Code
-----------------------------------------------

You can specify the name to be used in the assembler code for a C
function or variable by writing the ‘asm’ (or ‘__asm__’) keyword after
the declarator.  It is up to you to make sure that the assembler names
you choose do not conflict with any other assembler symbols, or
reference registers.

Assembler names for data:
.........................

This sample shows how to specify the assembler name for data:

     int foo asm ("myfoo") = 2;

This specifies that the name to be used for the variable ‘foo’ in the
assembler code should be ‘myfoo’ rather than the usual ‘_foo’.

 On systems where an underscore is normally prepended to the name of a C
variable, this feature allows you to define names for the linker that do
not start with an underscore.

 GCC does not support using this feature with a non-static local
variable since such variables do not have assembler names.  If you are
trying to put the variable in a particular register, see *note Explicit
Register Variables::.

Assembler names for functions:
..............................

To specify the assembler name for functions, write a declaration for the
function before its definition and put ‘asm’ there, like this:

     int func (int x, int y) asm ("MYFUNC");

     int func (int x, int y)
     {
        /* ... */

This specifies that the name to be used for the function ‘func’ in the
assembler code should be ‘MYFUNC’.


File: gcc.info,  Node: Explicit Register Variables,  Next: Size of an asm,  Prev: Asm Labels,  Up: Using Assembly Language with C

6.47.5 Variables in Specified Registers
---------------------------------------

GNU C allows you to associate specific hardware registers with C
variables.  In almost all cases, allowing the compiler to assign
registers produces the best code.  However under certain unusual
circumstances, more precise control over the variable storage is
required.

 Both global and local variables can be associated with a register.  The
consequences of performing this association are very different between
the two, as explained in the sections below.

* Menu:

* Global Register Variables::   Variables declared at global scope.
* Local Register Variables::    Variables declared within a function.


File: gcc.info,  Node: Global Register Variables,  Next: Local Register Variables,  Up: Explicit Register Variables

6.47.5.1 Defining Global Register Variables
...........................................

You can define a global register variable and associate it with a
specified register like this:

     register int *foo asm ("r12");

Here ‘r12’ is the name of the register that should be used.  Note that
this is the same syntax used for defining local register variables, but
for a global variable the declaration appears outside a function.  The
‘register’ keyword is required, and cannot be combined with ‘static’.
The register name must be a valid register name for the target platform.

 Do not use type qualifiers such as ‘const’ and ‘volatile’, as the
outcome may be contrary to expectations.  In particular, using the
‘volatile’ qualifier does not fully prevent the compiler from optimizing
accesses to the register.

 Registers are a scarce resource on most systems and allowing the
compiler to manage their usage usually results in the best code.
However, under special circumstances it can make sense to reserve some
globally.  For example this may be useful in programs such as
programming language interpreters that have a couple of global variables
that are accessed very often.

 After defining a global register variable, for the current compilation
unit:

   • If the register is a call-saved register, call ABI is affected: the
     register will not be restored in function epilogue sequences after
     the variable has been assigned.  Therefore, functions cannot safely
     return to callers that assume standard ABI.
   • Conversely, if the register is a call-clobbered register, making
     calls to functions that use standard ABI may lose contents of the
     variable.  Such calls may be created by the compiler even if none
     are evident in the original program, for example when libgcc
     functions are used to make up for unavailable instructions.
   • Accesses to the variable may be optimized as usual and the register
     remains available for allocation and use in any computations,
     provided that observable values of the variable are not affected.
   • If the variable is referenced in inline assembly, the type of
     access must be provided to the compiler via constraints (*note
     Constraints::).  Accesses from basic asms are not supported.

 Note that these points _only_ apply to code that is compiled with the
definition.  The behavior of code that is merely linked in (for example
code from libraries) is not affected.

 If you want to recompile source files that do not actually use your
global register variable so they do not use the specified register for
any other purpose, you need not actually add the global register
declaration to their source code.  It suffices to specify the compiler
option ‘-ffixed-REG’ (*note Code Gen Options::) to reserve the register.

Declaring the variable
......................

Global register variables cannot have initial values, because an
executable file has no means to supply initial contents for a register.

 When selecting a register, choose one that is normally saved and
restored by function calls on your machine.  This ensures that code
which is unaware of this reservation (such as library routines) will
restore it before returning.

 On machines with register windows, be sure to choose a global register
that is not affected magically by the function call mechanism.

Using the variable
..................

When calling routines that are not aware of the reservation, be cautious
if those routines call back into code which uses them.  As an example,
if you call the system library version of ‘qsort’, it may clobber your
registers during execution, but (if you have selected appropriate
registers) it will restore them before returning.  However it will _not_
restore them before calling ‘qsort’'s comparison function.  As a result,
global values will not reliably be available to the comparison function
unless the ‘qsort’ function itself is rebuilt.

 Similarly, it is not safe to access the global register variables from
signal handlers or from more than one thread of control.  Unless you
recompile them specially for the task at hand, the system library
routines may temporarily use the register for other things.
Furthermore, since the register is not reserved exclusively for the
variable, accessing it from handlers of asynchronous signals may observe
unrelated temporary values residing in the register.

 On most machines, ‘longjmp’ restores to each global register variable
the value it had at the time of the ‘setjmp’.  On some machines,
however, ‘longjmp’ does not change the value of global register
variables.  To be portable, the function that called ‘setjmp’ should
make other arrangements to save the values of the global register
variables, and to restore them in a ‘longjmp’.  This way, the same thing
happens regardless of what ‘longjmp’ does.


File: gcc.info,  Node: Local Register Variables,  Prev: Global Register Variables,  Up: Explicit Register Variables

6.47.5.2 Specifying Registers for Local Variables
.................................................

You can define a local register variable and associate it with a
specified register like this:

     register int *foo asm ("r12");

Here ‘r12’ is the name of the register that should be used.  Note that
this is the same syntax used for defining global register variables, but
for a local variable the declaration appears within a function.  The
‘register’ keyword is required, and cannot be combined with ‘static’.
The register name must be a valid register name for the target platform.

 Do not use type qualifiers such as ‘const’ and ‘volatile’, as the
outcome may be contrary to expectations.  In particular, when the
‘const’ qualifier is used, the compiler may substitute the variable with
its initializer in ‘asm’ statements, which may cause the corresponding
operand to appear in a different register.

 As with global register variables, it is recommended that you choose a
register that is normally saved and restored by function calls on your
machine, so that calls to library routines will not clobber it.

 The only supported use for this feature is to specify registers for
input and output operands when calling Extended ‘asm’ (*note Extended
Asm::).  This may be necessary if the constraints for a particular
machine don't provide sufficient control to select the desired register.
To force an operand into a register, create a local variable and specify
the register name after the variable's declaration.  Then use the local
variable for the ‘asm’ operand and specify any constraint letter that
matches the register:

     register int *p1 asm ("r0") = ...;
     register int *p2 asm ("r1") = ...;
     register int *result asm ("r0");
     asm ("sysint" : "=r" (result) : "0" (p1), "r" (p2));

 _Warning:_ In the above example, be aware that a register (for example
‘r0’) can be call-clobbered by subsequent code, including function calls
and library calls for arithmetic operators on other variables (for
example the initialization of ‘p2’).  In this case, use temporary
variables for expressions between the register assignments:

     int t1 = ...;
     register int *p1 asm ("r0") = ...;
     register int *p2 asm ("r1") = t1;
     register int *result asm ("r0");
     asm ("sysint" : "=r" (result) : "0" (p1), "r" (p2));

 Defining a register variable does not reserve the register.  Other than
when invoking the Extended ‘asm’, the contents of the specified register
are not guaranteed.  For this reason, the following uses are explicitly
_not_ supported.  If they appear to work, it is only happenstance, and
may stop working as intended due to (seemingly) unrelated changes in
surrounding code, or even minor changes in the optimization of a future
version of gcc:

   • Passing parameters to or from Basic ‘asm’
   • Passing parameters to or from Extended ‘asm’ without using input or
     output operands.
   • Passing parameters to or from routines written in assembler (or
     other languages) using non-standard calling conventions.

 Some developers use Local Register Variables in an attempt to improve
gcc's allocation of registers, especially in large functions.  In this
case the register name is essentially a hint to the register allocator.
While in some instances this can generate better code, improvements are
subject to the whims of the allocator/optimizers.  Since there are no
guarantees that your improvements won't be lost, this usage of Local
Register Variables is discouraged.

 On the MIPS platform, there is related use for local register variables
with slightly different characteristics (*note Defining coprocessor
specifics for MIPS targets: (gccint)MIPS Coprocessors.).


File: gcc.info,  Node: Size of an asm,  Prev: Explicit Register Variables,  Up: Using Assembly Language with C

6.47.6 Size of an ‘asm’
-----------------------

Some targets require that GCC track the size of each instruction used in
order to generate correct code.  Because the final length of the code
produced by an ‘asm’ statement is only known by the assembler, GCC must
make an estimate as to how big it will be.  It does this by counting the
number of instructions in the pattern of the ‘asm’ and multiplying that
by the length of the longest instruction supported by that processor.
(When working out the number of instructions, it assumes that any
occurrence of a newline or of whatever statement separator character is
supported by the assembler -- typically ‘;’ -- indicates the end of an
instruction.)

 Normally, GCC's estimate is adequate to ensure that correct code is
generated, but it is possible to confuse the compiler if you use pseudo
instructions or assembler macros that expand into multiple real
instructions, or if you use assembler directives that expand to more
space in the object file than is needed for a single instruction.  If
this happens then the assembler may produce a diagnostic saying that a
label is unreachable.

 This size is also used for inlining decisions.  If you use ‘asm inline’
instead of just ‘asm’, then for inlining purposes the size of the asm is
taken as the minimum size, ignoring how many instructions GCC thinks it
is.


File: gcc.info,  Node: Alternate Keywords,  Next: Incomplete Enums,  Prev: Using Assembly Language with C,  Up: C Extensions

6.48 Alternate Keywords
=======================

‘-ansi’ and the various ‘-std’ options disable certain keywords.  This
causes trouble when you want to use GNU C extensions, or a
general-purpose header file that should be usable by all programs,
including ISO C programs.  The keywords ‘asm’, ‘typeof’ and ‘inline’ are
not available in programs compiled with ‘-ansi’ or ‘-std’ (although
‘inline’ can be used in a program compiled with ‘-std=c99’ or a later
standard).  The ISO C99 keyword ‘restrict’ is only available when
‘-std=gnu99’ (which will eventually be the default) or ‘-std=c99’ (or
the equivalent ‘-std=iso9899:1999’), or an option for a later standard
version, is used.

 The way to solve these problems is to put ‘__’ at the beginning and end
of each problematical keyword.  For example, use ‘__asm__’ instead of
‘asm’, and ‘__inline__’ instead of ‘inline’.

 Other C compilers won't accept these alternative keywords; if you want
to compile with another compiler, you can define the alternate keywords
as macros to replace them with the customary keywords.  It looks like
this:

     #ifndef __GNUC__
     #define __asm__ asm
     #endif

 ‘-pedantic’ and other options cause warnings for many GNU C extensions.
You can prevent such warnings within one expression by writing
‘__extension__’ before the expression.  ‘__extension__’ has no effect
aside from this.


File: gcc.info,  Node: Incomplete Enums,  Next: Function Names,  Prev: Alternate Keywords,  Up: C Extensions

6.49 Incomplete ‘enum’ Types
============================

You can define an ‘enum’ tag without specifying its possible values.
This results in an incomplete type, much like what you get if you write
‘struct foo’ without describing the elements.  A later declaration that
does specify the possible values completes the type.

 You cannot allocate variables or storage using the type while it is
incomplete.  However, you can work with pointers to that type.

 This extension may not be very useful, but it makes the handling of
‘enum’ more consistent with the way ‘struct’ and ‘union’ are handled.

 This extension is not supported by GNU C++.


File: gcc.info,  Node: Function Names,  Next: Return Address,  Prev: Incomplete Enums,  Up: C Extensions

6.50 Function Names as Strings
==============================

GCC provides three magic constants that hold the name of the current
function as a string.  In C++11 and later modes, all three are treated
as constant expressions and can be used in ‘constexpr’ constexts.  The
first of these constants is ‘__func__’, which is part of the C99
standard:

 The identifier ‘__func__’ is implicitly declared by the translator as
if, immediately following the opening brace of each function definition,
the declaration

     static const char __func__[] = "function-name";

appeared, where function-name is the name of the lexically-enclosing
function.  This name is the unadorned name of the function.  As an
extension, at file (or, in C++, namespace scope), ‘__func__’ evaluates
to the empty string.

 ‘__FUNCTION__’ is another name for ‘__func__’, provided for backward
compatibility with old versions of GCC.

 In C, ‘__PRETTY_FUNCTION__’ is yet another name for ‘__func__’, except
that at file scope (or, in C++, namespace scope), it evaluates to the
string ‘"top level"’.  In addition, in C++, ‘__PRETTY_FUNCTION__’
contains the signature of the function as well as its bare name.  For
example, this program:

     extern "C" int printf (const char *, ...);

     class a {
      public:
       void sub (int i)
         {
           printf ("__FUNCTION__ = %s\n", __FUNCTION__);
           printf ("__PRETTY_FUNCTION__ = %s\n", __PRETTY_FUNCTION__);
         }
     };

     int
     main (void)
     {
       a ax;
       ax.sub (0);
       return 0;
     }

gives this output:

     __FUNCTION__ = sub
     __PRETTY_FUNCTION__ = void a::sub(int)

 These identifiers are variables, not preprocessor macros, and may not
be used to initialize ‘char’ arrays or be concatenated with string
literals.


File: gcc.info,  Node: Return Address,  Next: Vector Extensions,  Prev: Function Names,  Up: C Extensions

6.51 Getting the Return or Frame Address of a Function
======================================================

These functions may be used to get information about the callers of a
function.

 -- Built-in Function: void * __builtin_return_address (unsigned int
          LEVEL)
     This function returns the return address of the current function,
     or of one of its callers.  The LEVEL argument is number of frames
     to scan up the call stack.  A value of ‘0’ yields the return
     address of the current function, a value of ‘1’ yields the return
     address of the caller of the current function, and so forth.  When
     inlining the expected behavior is that the function returns the
     address of the function that is returned to.  To work around this
     behavior use the ‘noinline’ function attribute.

     The LEVEL argument must be a constant integer.

     On some machines it may be impossible to determine the return
     address of any function other than the current one; in such cases,
     or when the top of the stack has been reached, this function
     returns an unspecified value.  In addition,
     ‘__builtin_frame_address’ may be used to determine if the top of
     the stack has been reached.

     Additional post-processing of the returned value may be needed, see
     ‘__builtin_extract_return_addr’.

     The stored representation of the return address in memory may be
     different from the address returned by ‘__builtin_return_address’.
     For example, on AArch64 the stored address may be mangled with
     return address signing whereas the address returned by
     ‘__builtin_return_address’ is not.

     Calling this function with a nonzero argument can have
     unpredictable effects, including crashing the calling program.  As
     a result, calls that are considered unsafe are diagnosed when the
     ‘-Wframe-address’ option is in effect.  Such calls should only be
     made in debugging situations.

     On targets where code addresses are representable as ‘void *’,
          void *addr = __builtin_extract_return_addr (__builtin_return_address (0));
     gives the code address where the current function would return.
     For example, such an address may be used with ‘dladdr’ or other
     interfaces that work with code addresses.

 -- Built-in Function: void * __builtin_extract_return_addr (void *ADDR)
     The address as returned by ‘__builtin_return_address’ may have to
     be fed through this function to get the actual encoded address.
     For example, on the 31-bit S/390 platform the highest bit has to be
     masked out, or on SPARC platforms an offset has to be added for the
     true next instruction to be executed.

     If no fixup is needed, this function simply passes through ADDR.

 -- Built-in Function: void * __builtin_frob_return_addr (void *ADDR)
     This function does the reverse of ‘__builtin_extract_return_addr’.

 -- Built-in Function: void * __builtin_frame_address (unsigned int
          LEVEL)
     This function is similar to ‘__builtin_return_address’, but it
     returns the address of the function frame rather than the return
     address of the function.  Calling ‘__builtin_frame_address’ with a
     value of ‘0’ yields the frame address of the current function, a
     value of ‘1’ yields the frame address of the caller of the current
     function, and so forth.

     The frame is the area on the stack that holds local variables and
     saved registers.  The frame address is normally the address of the
     first word pushed on to the stack by the function.  However, the
     exact definition depends upon the processor and the calling
     convention.  If the processor has a dedicated frame pointer
     register, and the function has a frame, then
     ‘__builtin_frame_address’ returns the value of the frame pointer
     register.

     On some machines it may be impossible to determine the frame
     address of any function other than the current one; in such cases,
     or when the top of the stack has been reached, this function
     returns ‘0’ if the first frame pointer is properly initialized by
     the startup code.

     Calling this function with a nonzero argument can have
     unpredictable effects, including crashing the calling program.  As
     a result, calls that are considered unsafe are diagnosed when the
     ‘-Wframe-address’ option is in effect.  Such calls should only be
     made in debugging situations.


File: gcc.info,  Node: Vector Extensions,  Next: Offsetof,  Prev: Return Address,  Up: C Extensions

6.52 Using Vector Instructions through Built-in Functions
=========================================================

On some targets, the instruction set contains SIMD vector instructions
which operate on multiple values contained in one large register at the
same time.  For example, on the x86 the MMX, 3DNow! and SSE extensions
can be used this way.

 The first step in using these extensions is to provide the necessary
data types.  This should be done using an appropriate ‘typedef’:

     typedef int v4si __attribute__ ((vector_size (16)));

The ‘int’ type specifies the “base type”, while the attribute specifies
the vector size for the variable, measured in bytes.  For example, the
declaration above causes the compiler to set the mode for the ‘v4si’
type to be 16 bytes wide and divided into ‘int’ sized units.  For a
32-bit ‘int’ this means a vector of 4 units of 4 bytes, and the
corresponding mode of ‘foo’ is V4SI.

 The ‘vector_size’ attribute is only applicable to integral and floating
scalars, although arrays, pointers, and function return values are
allowed in conjunction with this construct.  Only sizes that are
positive power-of-two multiples of the base type size are currently
allowed.

 All the basic integer types can be used as base types, both as signed
and as unsigned: ‘char’, ‘short’, ‘int’, ‘long’, ‘long long’.  In
addition, ‘float’ and ‘double’ can be used to build floating-point
vector types.

 Specifying a combination that is not valid for the current architecture
causes GCC to synthesize the instructions using a narrower mode.  For
example, if you specify a variable of type ‘V4SI’ and your architecture
does not allow for this specific SIMD type, GCC produces code that uses
4 ‘SIs’.

 The types defined in this manner can be used with a subset of normal C
operations.  Currently, GCC allows using the following operators on
these types: ‘+, -, *, /, unary minus, ^, |, &, ~, %’.

 The operations behave like C++ ‘valarrays’.  Addition is defined as the
addition of the corresponding elements of the operands.  For example, in
the code below, each of the 4 elements in A is added to the
corresponding 4 elements in B and the resulting vector is stored in C.

     typedef int v4si __attribute__ ((vector_size (16)));

     v4si a, b, c;

     c = a + b;

 Subtraction, multiplication, division, and the logical operations
operate in a similar manner.  Likewise, the result of using the unary
minus or complement operators on a vector type is a vector whose
elements are the negative or complemented values of the corresponding
elements in the operand.

 It is possible to use shifting operators ‘<<’, ‘>>’ on integer-type
vectors.  The operation is defined as following: ‘{a0, a1, ..., an} >>
{b0, b1, ..., bn} == {a0 >> b0, a1 >> b1, ..., an >> bn}’.  Vector
operands must have the same number of elements.

 For convenience, it is allowed to use a binary vector operation where
one operand is a scalar.  In that case the compiler transforms the
scalar operand into a vector where each element is the scalar from the
operation.  The transformation happens only if the scalar could be
safely converted to the vector-element type.  Consider the following
code.

     typedef int v4si __attribute__ ((vector_size (16)));

     v4si a, b, c;
     long l;

     a = b + 1;    /* a = b + {1,1,1,1}; */
     a = 2 * b;    /* a = {2,2,2,2} * b; */

     a = l + a;    /* Error, cannot convert long to int. */

 Vectors can be subscripted as if the vector were an array with the same
number of elements and base type.  Out of bound accesses invoke
undefined behavior at run time.  Warnings for out of bound accesses for
vector subscription can be enabled with ‘-Warray-bounds’.

 Vector comparison is supported with standard comparison operators: ‘==,
!=, <, <=, >, >=’.  Comparison operands can be vector expressions of
integer-type or real-type.  Comparison between integer-type vectors and
real-type vectors are not supported.  The result of the comparison is a
vector of the same width and number of elements as the comparison
operands with a signed integral element type.

 Vectors are compared element-wise producing 0 when comparison is false
and -1 (constant of the appropriate type where all bits are set)
otherwise.  Consider the following example.

     typedef int v4si __attribute__ ((vector_size (16)));

     v4si a = {1,2,3,4};
     v4si b = {3,2,1,4};
     v4si c;

     c = a >  b;     /* The result would be {0, 0,-1, 0}  */
     c = a == b;     /* The result would be {0,-1, 0,-1}  */

 In C++, the ternary operator ‘?:’ is available.  ‘a?b:c’, where ‘b’ and
‘c’ are vectors of the same type and ‘a’ is an integer vector with the
same number of elements of the same size as ‘b’ and ‘c’, computes all
three arguments and creates a vector ‘{a[0]?b[0]:c[0], a[1]?b[1]:c[1],
...}’.  Note that unlike in OpenCL, ‘a’ is thus interpreted as ‘a != 0’
and not ‘a < 0’.  As in the case of binary operations, this syntax is
also accepted when one of ‘b’ or ‘c’ is a scalar that is then
transformed into a vector.  If both ‘b’ and ‘c’ are scalars and the type
of ‘true?b:c’ has the same size as the element type of ‘a’, then ‘b’ and
‘c’ are converted to a vector type whose elements have this type and
with the same number of elements as ‘a’.

 In C++, the logic operators ‘!, &&, ||’ are available for vectors.
‘!v’ is equivalent to ‘v == 0’, ‘a && b’ is equivalent to ‘a!=0 & b!=0’
and ‘a || b’ is equivalent to ‘a!=0 | b!=0’.  For mixed operations
between a scalar ‘s’ and a vector ‘v’, ‘s && v’ is equivalent to
‘s?v!=0:0’ (the evaluation is short-circuit) and ‘v && s’ is equivalent
to ‘v!=0 & (s?-1:0)’.

 Vector shuffling is available using functions ‘__builtin_shuffle (vec,
mask)’ and ‘__builtin_shuffle (vec0, vec1, mask)’.  Both functions
construct a permutation of elements from one or two vectors and return a
vector of the same type as the input vector(s).  The MASK is an integral
vector with the same width (W) and element count (N) as the output
vector.

 The elements of the input vectors are numbered in memory ordering of
VEC0 beginning at 0 and VEC1 beginning at N.  The elements of MASK are
considered modulo N in the single-operand case and modulo 2*N in the
two-operand case.

 Consider the following example,

     typedef int v4si __attribute__ ((vector_size (16)));

     v4si a = {1,2,3,4};
     v4si b = {5,6,7,8};
     v4si mask1 = {0,1,1,3};
     v4si mask2 = {0,4,2,5};
     v4si res;

     res = __builtin_shuffle (a, mask1);       /* res is {1,2,2,4}  */
     res = __builtin_shuffle (a, b, mask2);    /* res is {1,5,3,6}  */

 Note that ‘__builtin_shuffle’ is intentionally semantically compatible
with the OpenCL ‘shuffle’ and ‘shuffle2’ functions.

 You can declare variables and use them in function calls and returns,
as well as in assignments and some casts.  You can specify a vector type
as a return type for a function.  Vector types can also be used as
function arguments.  It is possible to cast from one vector type to
another, provided they are of the same size (in fact, you can also cast
vectors to and from other datatypes of the same size).

 You cannot operate between vectors of different lengths or different
signedness without a cast.

 Vector shuffling is available using the ‘__builtin_shufflevector (vec1,
vec2, index...)’ function.  VEC1 and VEC2 must be expressions with
vector type with a compatible element type.  The result of
‘__builtin_shufflevector’ is a vector with the same element type as VEC1
and VEC2 but that has an element count equal to the number of indices
specified.

 The INDEX arguments are a list of integers that specify the elements
indices of the first two vectors that should be extracted and returned
in a new vector.  These element indices are numbered sequentially
starting with the first vector, continuing into the second vector.  An
index of -1 can be used to indicate that the corresponding element in
the returned vector is a don't care and can be freely chosen to
optimized the generated code sequence performing the shuffle operation.

 Consider the following example,
     typedef int v4si __attribute__ ((vector_size (16)));
     typedef int v8si __attribute__ ((vector_size (32)));

     v8si a = {1,-2,3,-4,5,-6,7,-8};
     v4si b = __builtin_shufflevector (a, a, 0, 2, 4, 6); /* b is {1,3,5,7} */
     v4si c = {-2,-4,-6,-8};
     v8si d = __builtin_shufflevector (c, b, 4, 0, 5, 1, 6, 2, 7, 3); /* d is a */

 Vector conversion is available using the ‘__builtin_convertvector (vec,
vectype)’ function.  VEC must be an expression with integral or floating
vector type and VECTYPE an integral or floating vector type with the
same number of elements.  The result has VECTYPE type and value of a C
cast of every element of VEC to the element type of VECTYPE.

 Consider the following example,
     typedef int v4si __attribute__ ((vector_size (16)));
     typedef float v4sf __attribute__ ((vector_size (16)));
     typedef double v4df __attribute__ ((vector_size (32)));
     typedef unsigned long long v4di __attribute__ ((vector_size (32)));

     v4si a = {1,-2,3,-4};
     v4sf b = {1.5f,-2.5f,3.f,7.f};
     v4di c = {1ULL,5ULL,0ULL,10ULL};
     v4sf d = __builtin_convertvector (a, v4sf); /* d is {1.f,-2.f,3.f,-4.f} */
     /* Equivalent of:
        v4sf d = { (float)a[0], (float)a[1], (float)a[2], (float)a[3] }; */
     v4df e = __builtin_convertvector (a, v4df); /* e is {1.,-2.,3.,-4.} */
     v4df f = __builtin_convertvector (b, v4df); /* f is {1.5,-2.5,3.,7.} */
     v4si g = __builtin_convertvector (f, v4si); /* g is {1,-2,3,7} */
     v4si h = __builtin_convertvector (c, v4si); /* h is {1,5,0,10} */

 Sometimes it is desirable to write code using a mix of generic vector
operations (for clarity) and machine-specific vector intrinsics (to
access vector instructions that are not exposed via generic built-ins).
On x86, intrinsic functions for integer vectors typically use the same
vector type ‘__m128i’ irrespective of how they interpret the vector,
making it necessary to cast their arguments and return values from/to
other vector types.  In C, you can make use of a ‘union’ type:
     #include <immintrin.h>

     typedef unsigned char u8x16 __attribute__ ((vector_size (16)));
     typedef unsigned int  u32x4 __attribute__ ((vector_size (16)));

     typedef union {
             __m128i mm;
             u8x16   u8;
             u32x4   u32;
     } v128;

for variables that can be used with both built-in operators and x86
intrinsics:

     v128 x, y = { 0 };
     memcpy (&x, ptr, sizeof x);
     y.u8  += 0x80;
     x.mm  = _mm_adds_epu8 (x.mm, y.mm);
     x.u32 &= 0xffffff;

     /* Instead of a variable, a compound literal may be used to pass the
        return value of an intrinsic call to a function expecting the union: */
     v128 foo (v128);
     x = foo ((v128) {_mm_adds_epu8 (x.mm, y.mm)});


File: gcc.info,  Node: Offsetof,  Next: __sync Builtins,  Prev: Vector Extensions,  Up: C Extensions

6.53 Support for ‘offsetof’
===========================

GCC implements for both C and C++ a syntactic extension to implement the
‘offsetof’ macro.

     primary:
             "__builtin_offsetof" "(" typename "," offsetof_member_designator ")"

     offsetof_member_designator:
               identifier
             | offsetof_member_designator "." identifier
             | offsetof_member_designator "[" expr "]"

 This extension is sufficient such that

     #define offsetof(TYPE, MEMBER)  __builtin_offsetof (TYPE, MEMBER)

is a suitable definition of the ‘offsetof’ macro.  In C++, TYPE may be
dependent.  In either case, MEMBER may consist of a single identifier,
or a sequence of member accesses and array references.


File: gcc.info,  Node: __sync Builtins,  Next: __atomic Builtins,  Prev: Offsetof,  Up: C Extensions

6.54 Legacy ‘__sync’ Built-in Functions for Atomic Memory Access
================================================================

The following built-in functions are intended to be compatible with
those described in the ‘Intel Itanium Processor-specific Application
Binary Interface’, section 7.4.  As such, they depart from normal GCC
practice by not using the ‘__builtin_’ prefix and also by being
overloaded so that they work on multiple types.

 The definition given in the Intel documentation allows only for the use
of the types ‘int’, ‘long’, ‘long long’ or their unsigned counterparts.
GCC allows any scalar type that is 1, 2, 4 or 8 bytes in size other than
the C type ‘_Bool’ or the C++ type ‘bool’.  Operations on pointer
arguments are performed as if the operands were of the ‘uintptr_t’ type.
That is, they are not scaled by the size of the type to which the
pointer points.

 These functions are implemented in terms of the ‘__atomic’ builtins
(*note __atomic Builtins::).  They should not be used for new code which
should use the ‘__atomic’ builtins instead.

 Not all operations are supported by all target processors.  If a
particular operation cannot be implemented on the target processor, a
warning is generated and a call to an external function is generated.
The external function carries the same name as the built-in version,
with an additional suffix ‘_N’ where N is the size of the data type.

 In most cases, these built-in functions are considered a “full
barrier”.  That is, no memory operand is moved across the operation,
either forward or backward.  Further, instructions are issued as
necessary to prevent the processor from speculating loads across the
operation and from queuing stores after the operation.

 All of the routines are described in the Intel documentation to take
"an optional list of variables protected by the memory barrier".  It's
not clear what is meant by that; it could mean that _only_ the listed
variables are protected, or it could mean a list of additional variables
to be protected.  The list is ignored by GCC which treats it as empty.
GCC interprets an empty list as meaning that all globally accessible
variables should be protected.

‘TYPE __sync_fetch_and_add (TYPE *ptr, TYPE value, ...)’
‘TYPE __sync_fetch_and_sub (TYPE *ptr, TYPE value, ...)’
‘TYPE __sync_fetch_and_or (TYPE *ptr, TYPE value, ...)’
‘TYPE __sync_fetch_and_and (TYPE *ptr, TYPE value, ...)’
‘TYPE __sync_fetch_and_xor (TYPE *ptr, TYPE value, ...)’
‘TYPE __sync_fetch_and_nand (TYPE *ptr, TYPE value, ...)’
     These built-in functions perform the operation suggested by the
     name, and returns the value that had previously been in memory.
     That is, operations on integer operands have the following
     semantics.  Operations on pointer arguments are performed as if the
     operands were of the ‘uintptr_t’ type.  That is, they are not
     scaled by the size of the type to which the pointer points.

          { tmp = *ptr; *ptr OP= value; return tmp; }
          { tmp = *ptr; *ptr = ~(tmp & value); return tmp; }   // nand

     The object pointed to by the first argument must be of integer or
     pointer type.  It must not be a boolean type.

     _Note:_ GCC 4.4 and later implement ‘__sync_fetch_and_nand’ as
     ‘*ptr = ~(tmp & value)’ instead of ‘*ptr = ~tmp & value’.

‘TYPE __sync_add_and_fetch (TYPE *ptr, TYPE value, ...)’
‘TYPE __sync_sub_and_fetch (TYPE *ptr, TYPE value, ...)’
‘TYPE __sync_or_and_fetch (TYPE *ptr, TYPE value, ...)’
‘TYPE __sync_and_and_fetch (TYPE *ptr, TYPE value, ...)’
‘TYPE __sync_xor_and_fetch (TYPE *ptr, TYPE value, ...)’
‘TYPE __sync_nand_and_fetch (TYPE *ptr, TYPE value, ...)’
     These built-in functions perform the operation suggested by the
     name, and return the new value.  That is, operations on integer
     operands have the following semantics.  Operations on pointer
     operands are performed as if the operand's type were ‘uintptr_t’.

          { *ptr OP= value; return *ptr; }
          { *ptr = ~(*ptr & value); return *ptr; }   // nand

     The same constraints on arguments apply as for the corresponding
     ‘__sync_op_and_fetch’ built-in functions.

     _Note:_ GCC 4.4 and later implement ‘__sync_nand_and_fetch’ as
     ‘*ptr = ~(*ptr & value)’ instead of ‘*ptr = ~*ptr & value’.

‘bool __sync_bool_compare_and_swap (TYPE *ptr, TYPE oldval, TYPE newval, ...)’
‘TYPE __sync_val_compare_and_swap (TYPE *ptr, TYPE oldval, TYPE newval, ...)’
     These built-in functions perform an atomic compare and swap.  That
     is, if the current value of ‘*PTR’ is OLDVAL, then write NEWVAL
     into ‘*PTR’.

     The "bool" version returns ‘true’ if the comparison is successful
     and NEWVAL is written.  The "val" version returns the contents of
     ‘*PTR’ before the operation.

‘__sync_synchronize (...)’
     This built-in function issues a full memory barrier.

‘TYPE __sync_lock_test_and_set (TYPE *ptr, TYPE value, ...)’
     This built-in function, as described by Intel, is not a traditional
     test-and-set operation, but rather an atomic exchange operation.
     It writes VALUE into ‘*PTR’, and returns the previous contents of
     ‘*PTR’.

     Many targets have only minimal support for such locks, and do not
     support a full exchange operation.  In this case, a target may
     support reduced functionality here by which the _only_ valid value
     to store is the immediate constant 1.  The exact value actually
     stored in ‘*PTR’ is implementation defined.

     This built-in function is not a full barrier, but rather an
     “acquire barrier”.  This means that references after the operation
     cannot move to (or be speculated to) before the operation, but
     previous memory stores may not be globally visible yet, and
     previous memory loads may not yet be satisfied.

‘void __sync_lock_release (TYPE *ptr, ...)’
     This built-in function releases the lock acquired by
     ‘__sync_lock_test_and_set’.  Normally this means writing the
     constant 0 to ‘*PTR’.

     This built-in function is not a full barrier, but rather a “release
     barrier”.  This means that all previous memory stores are globally
     visible, and all previous memory loads have been satisfied, but
     following memory reads are not prevented from being speculated to
     before the barrier.


File: gcc.info,  Node: __atomic Builtins,  Next: Integer Overflow Builtins,  Prev: __sync Builtins,  Up: C Extensions

6.55 Built-in Functions for Memory Model Aware Atomic Operations
================================================================

The following built-in functions approximately match the requirements
for the C++11 memory model.  They are all identified by being prefixed
with ‘__atomic’ and most are overloaded so that they work with multiple
types.

 These functions are intended to replace the legacy ‘__sync’ builtins.
The main difference is that the memory order that is requested is a
parameter to the functions.  New code should always use the ‘__atomic’
builtins rather than the ‘__sync’ builtins.

 Note that the ‘__atomic’ builtins assume that programs will conform to
the C++11 memory model.  In particular, they assume that programs are
free of data races.  See the C++11 standard for detailed requirements.

 The ‘__atomic’ builtins can be used with any integral scalar or pointer
type that is 1, 2, 4, or 8 bytes in length.  16-byte integral types are
also allowed if ‘__int128’ (*note __int128::) is supported by the
architecture.

 The four non-arithmetic functions (load, store, exchange, and
compare_exchange) all have a generic version as well.  This generic
version works on any data type.  It uses the lock-free built-in function
if the specific data type size makes that possible; otherwise, an
external call is left to be resolved at run time.  This external call is
the same format with the addition of a ‘size_t’ parameter inserted as
the first parameter indicating the size of the object being pointed to.
All objects must be the same size.

 There are 6 different memory orders that can be specified.  These map
to the C++11 memory orders with the same names, see the C++11 standard
or the GCC wiki on atomic synchronization
(https://gcc.gnu.org/wiki/Atomic/GCCMM/AtomicSync) for detailed
definitions.  Individual targets may also support additional memory
orders for use on specific architectures.  Refer to the target
documentation for details of these.

 An atomic operation can both constrain code motion and be mapped to
hardware instructions for synchronization between threads (e.g., a
fence).  To which extent this happens is controlled by the memory
orders, which are listed here in approximately ascending order of
strength.  The description of each memory order is only meant to roughly
illustrate the effects and is not a specification; see the C++11 memory
model for precise semantics.

‘__ATOMIC_RELAXED’
     Implies no inter-thread ordering constraints.
‘__ATOMIC_CONSUME’
     This is currently implemented using the stronger ‘__ATOMIC_ACQUIRE’
     memory order because of a deficiency in C++11's semantics for
     ‘memory_order_consume’.
‘__ATOMIC_ACQUIRE’
     Creates an inter-thread happens-before constraint from the release
     (or stronger) semantic store to this acquire load.  Can prevent
     hoisting of code to before the operation.
‘__ATOMIC_RELEASE’
     Creates an inter-thread happens-before constraint to acquire (or
     stronger) semantic loads that read from this release store.  Can
     prevent sinking of code to after the operation.
‘__ATOMIC_ACQ_REL’
     Combines the effects of both ‘__ATOMIC_ACQUIRE’ and
     ‘__ATOMIC_RELEASE’.
‘__ATOMIC_SEQ_CST’
     Enforces total ordering with all other ‘__ATOMIC_SEQ_CST’
     operations.

 Note that in the C++11 memory model, _fences_ (e.g.,
‘__atomic_thread_fence’) take effect in combination with other atomic
operations on specific memory locations (e.g., atomic loads); operations
on specific memory locations do not necessarily affect other operations
in the same way.

 Target architectures are encouraged to provide their own patterns for
each of the atomic built-in functions.  If no target is provided, the
original non-memory model set of ‘__sync’ atomic built-in functions are
used, along with any required synchronization fences surrounding it in
order to achieve the proper behavior.  Execution in this case is subject
to the same restrictions as those built-in functions.

 If there is no pattern or mechanism to provide a lock-free instruction
sequence, a call is made to an external routine with the same parameters
to be resolved at run time.

 When implementing patterns for these built-in functions, the memory
order parameter can be ignored as long as the pattern implements the
most restrictive ‘__ATOMIC_SEQ_CST’ memory order.  Any of the other
memory orders execute correctly with this memory order but they may not
execute as efficiently as they could with a more appropriate
implementation of the relaxed requirements.

 Note that the C++11 standard allows for the memory order parameter to
be determined at run time rather than at compile time.  These built-in
functions map any run-time value to ‘__ATOMIC_SEQ_CST’ rather than
invoke a runtime library call or inline a switch statement.  This is
standard compliant, safe, and the simplest approach for now.

 The memory order parameter is a signed int, but only the lower 16 bits
are reserved for the memory order.  The remainder of the signed int is
reserved for target use and should be 0.  Use of the predefined atomic
values ensures proper usage.

 -- Built-in Function: TYPE __atomic_load_n (TYPE *ptr, int memorder)
     This built-in function implements an atomic load operation.  It
     returns the contents of ‘*PTR’.

     The valid memory order variants are ‘__ATOMIC_RELAXED’,
     ‘__ATOMIC_SEQ_CST’, ‘__ATOMIC_ACQUIRE’, and ‘__ATOMIC_CONSUME’.

 -- Built-in Function: void __atomic_load (TYPE *ptr, TYPE *ret, int
          memorder)
     This is the generic version of an atomic load.  It returns the
     contents of ‘*PTR’ in ‘*RET’.

 -- Built-in Function: void __atomic_store_n (TYPE *ptr, TYPE val, int
          memorder)
     This built-in function implements an atomic store operation.  It
     writes ‘VAL’ into ‘*PTR’.

     The valid memory order variants are ‘__ATOMIC_RELAXED’,
     ‘__ATOMIC_SEQ_CST’, and ‘__ATOMIC_RELEASE’.

 -- Built-in Function: void __atomic_store (TYPE *ptr, TYPE *val, int
          memorder)
     This is the generic version of an atomic store.  It stores the
     value of ‘*VAL’ into ‘*PTR’.

 -- Built-in Function: TYPE __atomic_exchange_n (TYPE *ptr, TYPE val,
          int memorder)
     This built-in function implements an atomic exchange operation.  It
     writes VAL into ‘*PTR’, and returns the previous contents of
     ‘*PTR’.

     All memory order variants are valid.

 -- Built-in Function: void __atomic_exchange (TYPE *ptr, TYPE *val,
          TYPE *ret, int memorder)
     This is the generic version of an atomic exchange.  It stores the
     contents of ‘*VAL’ into ‘*PTR’.  The original value of ‘*PTR’ is
     copied into ‘*RET’.

 -- Built-in Function: bool __atomic_compare_exchange_n (TYPE *ptr, TYPE
          *expected, TYPE desired, bool weak, int success_memorder, int
          failure_memorder)
     This built-in function implements an atomic compare and exchange
     operation.  This compares the contents of ‘*PTR’ with the contents
     of ‘*EXPECTED’.  If equal, the operation is a _read-modify-write_
     operation that writes DESIRED into ‘*PTR’.  If they are not equal,
     the operation is a _read_ and the current contents of ‘*PTR’ are
     written into ‘*EXPECTED’.  WEAK is ‘true’ for weak
     compare_exchange, which may fail spuriously, and ‘false’ for the
     strong variation, which never fails spuriously.  Many targets only
     offer the strong variation and ignore the parameter.  When in
     doubt, use the strong variation.

     If DESIRED is written into ‘*PTR’ then ‘true’ is returned and
     memory is affected according to the memory order specified by
     SUCCESS_MEMORDER.  There are no restrictions on what memory order
     can be used here.

     Otherwise, ‘false’ is returned and memory is affected according to
     FAILURE_MEMORDER.  This memory order cannot be ‘__ATOMIC_RELEASE’
     nor ‘__ATOMIC_ACQ_REL’.  It also cannot be a stronger order than
     that specified by SUCCESS_MEMORDER.

 -- Built-in Function: bool __atomic_compare_exchange (TYPE *ptr, TYPE
          *expected, TYPE *desired, bool weak, int success_memorder, int
          failure_memorder)
     This built-in function implements the generic version of
     ‘__atomic_compare_exchange’.  The function is virtually identical
     to ‘__atomic_compare_exchange_n’, except the desired value is also
     a pointer.

 -- Built-in Function: TYPE __atomic_add_fetch (TYPE *ptr, TYPE val, int
          memorder)
 -- Built-in Function: TYPE __atomic_sub_fetch (TYPE *ptr, TYPE val, int
          memorder)
 -- Built-in Function: TYPE __atomic_and_fetch (TYPE *ptr, TYPE val, int
          memorder)
 -- Built-in Function: TYPE __atomic_xor_fetch (TYPE *ptr, TYPE val, int
          memorder)
 -- Built-in Function: TYPE __atomic_or_fetch (TYPE *ptr, TYPE val, int
          memorder)
 -- Built-in Function: TYPE __atomic_nand_fetch (TYPE *ptr, TYPE val,
          int memorder)
     These built-in functions perform the operation suggested by the
     name, and return the result of the operation.  Operations on
     pointer arguments are performed as if the operands were of the
     ‘uintptr_t’ type.  That is, they are not scaled by the size of the
     type to which the pointer points.

          { *ptr OP= val; return *ptr; }
          { *ptr = ~(*ptr & val); return *ptr; } // nand

     The object pointed to by the first argument must be of integer or
     pointer type.  It must not be a boolean type.  All memory orders
     are valid.

 -- Built-in Function: TYPE __atomic_fetch_add (TYPE *ptr, TYPE val, int
          memorder)
 -- Built-in Function: TYPE __atomic_fetch_sub (TYPE *ptr, TYPE val, int
          memorder)
 -- Built-in Function: TYPE __atomic_fetch_and (TYPE *ptr, TYPE val, int
          memorder)
 -- Built-in Function: TYPE __atomic_fetch_xor (TYPE *ptr, TYPE val, int
          memorder)
 -- Built-in Function: TYPE __atomic_fetch_or (TYPE *ptr, TYPE val, int
          memorder)
 -- Built-in Function: TYPE __atomic_fetch_nand (TYPE *ptr, TYPE val,
          int memorder)
     These built-in functions perform the operation suggested by the
     name, and return the value that had previously been in ‘*PTR’.
     Operations on pointer arguments are performed as if the operands
     were of the ‘uintptr_t’ type.  That is, they are not scaled by the
     size of the type to which the pointer points.

          { tmp = *ptr; *ptr OP= val; return tmp; }
          { tmp = *ptr; *ptr = ~(*ptr & val); return tmp; } // nand

     The same constraints on arguments apply as for the corresponding
     ‘__atomic_op_fetch’ built-in functions.  All memory orders are
     valid.

 -- Built-in Function: bool __atomic_test_and_set (void *ptr, int
          memorder)

     This built-in function performs an atomic test-and-set operation on
     the byte at ‘*PTR’.  The byte is set to some implementation defined
     nonzero "set" value and the return value is ‘true’ if and only if
     the previous contents were "set".  It should be only used for
     operands of type ‘bool’ or ‘char’.  For other types only part of
     the value may be set.

     All memory orders are valid.

 -- Built-in Function: void __atomic_clear (bool *ptr, int memorder)

     This built-in function performs an atomic clear operation on
     ‘*PTR’.  After the operation, ‘*PTR’ contains 0.  It should be only
     used for operands of type ‘bool’ or ‘char’ and in conjunction with
     ‘__atomic_test_and_set’.  For other types it may only clear
     partially.  If the type is not ‘bool’ prefer using
     ‘__atomic_store’.

     The valid memory order variants are ‘__ATOMIC_RELAXED’,
     ‘__ATOMIC_SEQ_CST’, and ‘__ATOMIC_RELEASE’.

 -- Built-in Function: void __atomic_thread_fence (int memorder)

     This built-in function acts as a synchronization fence between
     threads based on the specified memory order.

     All memory orders are valid.

 -- Built-in Function: void __atomic_signal_fence (int memorder)

     This built-in function acts as a synchronization fence between a
     thread and signal handlers based in the same thread.

     All memory orders are valid.

 -- Built-in Function: bool __atomic_always_lock_free (size_t size, void
          *ptr)

     This built-in function returns ‘true’ if objects of SIZE bytes
     always generate lock-free atomic instructions for the target
     architecture.  SIZE must resolve to a compile-time constant and the
     result also resolves to a compile-time constant.

     PTR is an optional pointer to the object that may be used to
     determine alignment.  A value of 0 indicates typical alignment
     should be used.  The compiler may also ignore this parameter.

          if (__atomic_always_lock_free (sizeof (long long), 0))

 -- Built-in Function: bool __atomic_is_lock_free (size_t size, void
          *ptr)

     This built-in function returns ‘true’ if objects of SIZE bytes
     always generate lock-free atomic instructions for the target
     architecture.  If the built-in function is not known to be
     lock-free, a call is made to a runtime routine named
     ‘__atomic_is_lock_free’.

     PTR is an optional pointer to the object that may be used to
     determine alignment.  A value of 0 indicates typical alignment
     should be used.  The compiler may also ignore this parameter.


File: gcc.info,  Node: Integer Overflow Builtins,  Next: x86 specific memory model extensions for transactional memory,  Prev: __atomic Builtins,  Up: C Extensions

6.56 Built-in Functions to Perform Arithmetic with Overflow Checking
====================================================================

The following built-in functions allow performing simple arithmetic
operations together with checking whether the operations overflowed.

 -- Built-in Function: bool __builtin_add_overflow (TYPE1 a, TYPE2 b,
          TYPE3 *res)
 -- Built-in Function: bool __builtin_sadd_overflow (int a, int b, int
          *res)
 -- Built-in Function: bool __builtin_saddl_overflow (long int a, long
          int b, long int *res)
 -- Built-in Function: bool __builtin_saddll_overflow (long long int a,
          long long int b, long long int *res)
 -- Built-in Function: bool __builtin_uadd_overflow (unsigned int a,
          unsigned int b, unsigned int *res)
 -- Built-in Function: bool __builtin_uaddl_overflow (unsigned long int
          a, unsigned long int b, unsigned long int *res)
 -- Built-in Function: bool __builtin_uaddll_overflow (unsigned long
          long int a, unsigned long long int b, unsigned long long int
          *res)

     These built-in functions promote the first two operands into
     infinite precision signed type and perform addition on those
     promoted operands.  The result is then cast to the type the third
     pointer argument points to and stored there.  If the stored result
     is equal to the infinite precision result, the built-in functions
     return ‘false’, otherwise they return ‘true’.  As the addition is
     performed in infinite signed precision, these built-in functions
     have fully defined behavior for all argument values.

     The first built-in function allows arbitrary integral types for
     operands and the result type must be pointer to some integral type
     other than enumerated or boolean type, the rest of the built-in
     functions have explicit integer types.

     The compiler will attempt to use hardware instructions to implement
     these built-in functions where possible, like conditional jump on
     overflow after addition, conditional jump on carry etc.

 -- Built-in Function: bool __builtin_sub_overflow (TYPE1 a, TYPE2 b,
          TYPE3 *res)
 -- Built-in Function: bool __builtin_ssub_overflow (int a, int b, int
          *res)
 -- Built-in Function: bool __builtin_ssubl_overflow (long int a, long
          int b, long int *res)
 -- Built-in Function: bool __builtin_ssubll_overflow (long long int a,
          long long int b, long long int *res)
 -- Built-in Function: bool __builtin_usub_overflow (unsigned int a,
          unsigned int b, unsigned int *res)
 -- Built-in Function: bool __builtin_usubl_overflow (unsigned long int
          a, unsigned long int b, unsigned long int *res)
 -- Built-in Function: bool __builtin_usubll_overflow (unsigned long
          long int a, unsigned long long int b, unsigned long long int
          *res)

     These built-in functions are similar to the add overflow checking
     built-in functions above, except they perform subtraction, subtract
     the second argument from the first one, instead of addition.

 -- Built-in Function: bool __builtin_mul_overflow (TYPE1 a, TYPE2 b,
          TYPE3 *res)
 -- Built-in Function: bool __builtin_smul_overflow (int a, int b, int
          *res)
 -- Built-in Function: bool __builtin_smull_overflow (long int a, long
          int b, long int *res)
 -- Built-in Function: bool __builtin_smulll_overflow (long long int a,
          long long int b, long long int *res)
 -- Built-in Function: bool __builtin_umul_overflow (unsigned int a,
          unsigned int b, unsigned int *res)
 -- Built-in Function: bool __builtin_umull_overflow (unsigned long int
          a, unsigned long int b, unsigned long int *res)
 -- Built-in Function: bool __builtin_umulll_overflow (unsigned long
          long int a, unsigned long long int b, unsigned long long int
          *res)

     These built-in functions are similar to the add overflow checking
     built-in functions above, except they perform multiplication,
     instead of addition.

 The following built-in functions allow checking if simple arithmetic
operation would overflow.

 -- Built-in Function: bool __builtin_add_overflow_p (TYPE1 a, TYPE2 b,
          TYPE3 c)
 -- Built-in Function: bool __builtin_sub_overflow_p (TYPE1 a, TYPE2 b,
          TYPE3 c)
 -- Built-in Function: bool __builtin_mul_overflow_p (TYPE1 a, TYPE2 b,
          TYPE3 c)

     These built-in functions are similar to ‘__builtin_add_overflow’,
     ‘__builtin_sub_overflow’, or ‘__builtin_mul_overflow’, except that
     they don't store the result of the arithmetic operation anywhere
     and the last argument is not a pointer, but some expression with
     integral type other than enumerated or boolean type.

     The built-in functions promote the first two operands into infinite
     precision signed type and perform addition on those promoted
     operands.  The result is then cast to the type of the third
     argument.  If the cast result is equal to the infinite precision
     result, the built-in functions return ‘false’, otherwise they
     return ‘true’.  The value of the third argument is ignored, just
     the side effects in the third argument are evaluated, and no
     integral argument promotions are performed on the last argument.
     If the third argument is a bit-field, the type used for the result
     cast has the precision and signedness of the given bit-field,
     rather than precision and signedness of the underlying type.

     For example, the following macro can be used to portably check, at
     compile-time, whether or not adding two constant integers will
     overflow, and perform the addition only when it is known to be safe
     and not to trigger a ‘-Woverflow’ warning.

          #define INT_ADD_OVERFLOW_P(a, b) \
             __builtin_add_overflow_p (a, b, (__typeof__ ((a) + (b))) 0)

          enum {
              A = INT_MAX, B = 3,
              C = INT_ADD_OVERFLOW_P (A, B) ? 0 : A + B,
              D = __builtin_add_overflow_p (1, SCHAR_MAX, (signed char) 0)
          };

     The compiler will attempt to use hardware instructions to implement
     these built-in functions where possible, like conditional jump on
     overflow after addition, conditional jump on carry etc.


File: gcc.info,  Node: x86 specific memory model extensions for transactional memory,  Next: Object Size Checking,  Prev: Integer Overflow Builtins,  Up: C Extensions

6.57 x86-Specific Memory Model Extensions for Transactional Memory
==================================================================

The x86 architecture supports additional memory ordering flags to mark
critical sections for hardware lock elision.  These must be specified in
addition to an existing memory order to atomic intrinsics.

‘__ATOMIC_HLE_ACQUIRE’
     Start lock elision on a lock variable.  Memory order must be
     ‘__ATOMIC_ACQUIRE’ or stronger.
‘__ATOMIC_HLE_RELEASE’
     End lock elision on a lock variable.  Memory order must be
     ‘__ATOMIC_RELEASE’ or stronger.

 When a lock acquire fails, it is required for good performance to abort
the transaction quickly.  This can be done with a ‘_mm_pause’.

     #include <immintrin.h> // For _mm_pause

     int lockvar;

     /* Acquire lock with lock elision */
     while (__atomic_exchange_n(&lockvar, 1, __ATOMIC_ACQUIRE|__ATOMIC_HLE_ACQUIRE))
         _mm_pause(); /* Abort failed transaction */
     ...
     /* Free lock with lock elision */
     __atomic_store_n(&lockvar, 0, __ATOMIC_RELEASE|__ATOMIC_HLE_RELEASE);


File: gcc.info,  Node: Object Size Checking,  Next: Other Builtins,  Prev: x86 specific memory model extensions for transactional memory,  Up: C Extensions

6.58 Object Size Checking Built-in Functions
============================================

GCC implements a limited buffer overflow protection mechanism that can
prevent some buffer overflow attacks by determining the sizes of objects
into which data is about to be written and preventing the writes when
the size isn't sufficient.  The built-in functions described below yield
the best results when used together and when optimization is enabled.
For example, to detect object sizes across function boundaries or to
follow pointer assignments through non-trivial control flow they rely on
various optimization passes enabled with ‘-O2’.  However, to a limited
extent, they can be used without optimization as well.

 -- Built-in Function: size_t __builtin_object_size (const void * PTR,
          int TYPE)
     is a built-in construct that returns a constant number of bytes
     from PTR to the end of the object PTR pointer points to (if known
     at compile time).  To determine the sizes of dynamically allocated
     objects the function relies on the allocation functions called to
     obtain the storage to be declared with the ‘alloc_size’ attribute
     (*note Common Function Attributes::).  ‘__builtin_object_size’
     never evaluates its arguments for side effects.  If there are any
     side effects in them, it returns ‘(size_t) -1’ for TYPE 0 or 1 and
     ‘(size_t) 0’ for TYPE 2 or 3.  If there are multiple objects PTR
     can point to and all of them are known at compile time, the
     returned number is the maximum of remaining byte counts in those
     objects if TYPE & 2 is 0 and minimum if nonzero.  If it is not
     possible to determine which objects PTR points to at compile time,
     ‘__builtin_object_size’ should return ‘(size_t) -1’ for TYPE 0 or 1
     and ‘(size_t) 0’ for TYPE 2 or 3.

     TYPE is an integer constant from 0 to 3.  If the least significant
     bit is clear, objects are whole variables, if it is set, a closest
     surrounding subobject is considered the object a pointer points to.
     The second bit determines if maximum or minimum of remaining bytes
     is computed.

          struct V { char buf1[10]; int b; char buf2[10]; } var;
          char *p = &var.buf1[1], *q = &var.b;

          /* Here the object p points to is var.  */
          assert (__builtin_object_size (p, 0) == sizeof (var) - 1);
          /* The subobject p points to is var.buf1.  */
          assert (__builtin_object_size (p, 1) == sizeof (var.buf1) - 1);
          /* The object q points to is var.  */
          assert (__builtin_object_size (q, 0)
                  == (char *) (&var + 1) - (char *) &var.b);
          /* The subobject q points to is var.b.  */
          assert (__builtin_object_size (q, 1) == sizeof (var.b));

 -- Built-in Function: size_t __builtin_dynamic_object_size (const void
          * PTR, int TYPE)
     is similar to ‘__builtin_object_size’ in that it returns a number
     of bytes from PTR to the end of the object PTR pointer points to,
     except that the size returned may not be a constant.  This results
     in successful evaluation of object size estimates in a wider range
     of use cases and can be more precise than ‘__builtin_object_size’,
     but it incurs a performance penalty since it may add a runtime
     overhead on size computation.  Semantics of TYPE as well as return
     values in case it is not possible to determine which objects PTR
     points to at compile time are the same as in the case of
     ‘__builtin_object_size’.

 There are built-in functions added for many common string operation
functions, e.g., for ‘memcpy’ ‘__builtin___memcpy_chk’ built-in is
provided.  This built-in has an additional last argument, which is the
number of bytes remaining in the object the DEST argument points to or
‘(size_t) -1’ if the size is not known.

 The built-in functions are optimized into the normal string functions
like ‘memcpy’ if the last argument is ‘(size_t) -1’ or if it is known at
compile time that the destination object will not be overflowed.  If the
compiler can determine at compile time that the object will always be
overflowed, it issues a warning.

 The intended use can be e.g.

     #undef memcpy
     #define bos0(dest) __builtin_object_size (dest, 0)
     #define memcpy(dest, src, n) \
       __builtin___memcpy_chk (dest, src, n, bos0 (dest))

     char *volatile p;
     char buf[10];
     /* It is unknown what object p points to, so this is optimized
        into plain memcpy - no checking is possible.  */
     memcpy (p, "abcde", n);
     /* Destination is known and length too.  It is known at compile
        time there will be no overflow.  */
     memcpy (&buf[5], "abcde", 5);
     /* Destination is known, but the length is not known at compile time.
        This will result in __memcpy_chk call that can check for overflow
        at run time.  */
     memcpy (&buf[5], "abcde", n);
     /* Destination is known and it is known at compile time there will
        be overflow.  There will be a warning and __memcpy_chk call that
        will abort the program at run time.  */
     memcpy (&buf[6], "abcde", 5);

 Such built-in functions are provided for ‘memcpy’, ‘mempcpy’,
‘memmove’, ‘memset’, ‘strcpy’, ‘stpcpy’, ‘strncpy’, ‘strcat’ and
‘strncat’.

 There are also checking built-in functions for formatted output
functions.
     int __builtin___sprintf_chk (char *s, int flag, size_t os, const char *fmt, ...);
     int __builtin___snprintf_chk (char *s, size_t maxlen, int flag, size_t os,
                                   const char *fmt, ...);
     int __builtin___vsprintf_chk (char *s, int flag, size_t os, const char *fmt,
                                   va_list ap);
     int __builtin___vsnprintf_chk (char *s, size_t maxlen, int flag, size_t os,
                                    const char *fmt, va_list ap);

 The added FLAG argument is passed unchanged to ‘__sprintf_chk’ etc.
functions and can contain implementation specific flags on what
additional security measures the checking function might take, such as
handling ‘%n’ differently.

 The OS argument is the object size S points to, like in the other
built-in functions.  There is a small difference in the behavior though,
if OS is ‘(size_t) -1’, the built-in functions are optimized into the
non-checking functions only if FLAG is 0, otherwise the checking
function is called with OS argument set to ‘(size_t) -1’.

 In addition to this, there are checking built-in functions
‘__builtin___printf_chk’, ‘__builtin___vprintf_chk’,
‘__builtin___fprintf_chk’ and ‘__builtin___vfprintf_chk’.  These have
just one additional argument, FLAG, right before format string FMT.  If
the compiler is able to optimize them to ‘fputc’ etc. functions, it
does, otherwise the checking function is called and the FLAG argument
passed to it.


File: gcc.info,  Node: Other Builtins,  Next: Target Builtins,  Prev: Object Size Checking,  Up: C Extensions

6.59 Other Built-in Functions Provided by GCC
=============================================

GCC provides a large number of built-in functions other than the ones
mentioned above.  Some of these are for internal use in the processing
of exceptions or variable-length argument lists and are not documented
here because they may change from time to time; we do not recommend
general use of these functions.

 The remaining functions are provided for optimization purposes.

 With the exception of built-ins that have library equivalents such as
the standard C library functions discussed below, or that expand to
library calls, GCC built-in functions are always expanded inline and
thus do not have corresponding entry points and their address cannot be
obtained.  Attempting to use them in an expression other than a function
call results in a compile-time error.

 GCC includes built-in versions of many of the functions in the standard
C library.  These functions come in two forms: one whose names start
with the ‘__builtin_’ prefix, and the other without.  Both forms have
the same type (including prototype), the same address (when their
address is taken), and the same meaning as the C library functions even
if you specify the ‘-fno-builtin’ option *note C Dialect Options::).
Many of these functions are only optimized in certain cases; if they are
not optimized in a particular case, a call to the library function is
emitted.

 Outside strict ISO C mode (‘-ansi’, ‘-std=c90’, ‘-std=c99’ or
‘-std=c11’), the functions ‘_exit’, ‘alloca’, ‘bcmp’, ‘bzero’,
‘dcgettext’, ‘dgettext’, ‘dremf’, ‘dreml’, ‘drem’, ‘exp10f’, ‘exp10l’,
‘exp10’, ‘ffsll’, ‘ffsl’, ‘ffs’, ‘fprintf_unlocked’, ‘fputs_unlocked’,
‘gammaf’, ‘gammal’, ‘gamma’, ‘gammaf_r’, ‘gammal_r’, ‘gamma_r’,
‘gettext’, ‘index’, ‘isascii’, ‘j0f’, ‘j0l’, ‘j0’, ‘j1f’, ‘j1l’, ‘j1’,
‘jnf’, ‘jnl’, ‘jn’, ‘lgammaf_r’, ‘lgammal_r’, ‘lgamma_r’, ‘mempcpy’,
‘pow10f’, ‘pow10l’, ‘pow10’, ‘printf_unlocked’, ‘rindex’, ‘roundeven’,
‘roundevenf’, ‘roundevenl’, ‘scalbf’, ‘scalbl’, ‘scalb’, ‘signbit’,
‘signbitf’, ‘signbitl’, ‘signbitd32’, ‘signbitd64’, ‘signbitd128’,
‘significandf’, ‘significandl’, ‘significand’, ‘sincosf’, ‘sincosl’,
‘sincos’, ‘stpcpy’, ‘stpncpy’, ‘strcasecmp’, ‘strdup’, ‘strfmon’,
‘strncasecmp’, ‘strndup’, ‘strnlen’, ‘toascii’, ‘y0f’, ‘y0l’, ‘y0’,
‘y1f’, ‘y1l’, ‘y1’, ‘ynf’, ‘ynl’ and ‘yn’ may be handled as built-in
functions.  All these functions have corresponding versions prefixed
with ‘__builtin_’, which may be used even in strict C90 mode.

 The ISO C99 functions ‘_Exit’, ‘acoshf’, ‘acoshl’, ‘acosh’, ‘asinhf’,
‘asinhl’, ‘asinh’, ‘atanhf’, ‘atanhl’, ‘atanh’, ‘cabsf’, ‘cabsl’,
‘cabs’, ‘cacosf’, ‘cacoshf’, ‘cacoshl’, ‘cacosh’, ‘cacosl’, ‘cacos’,
‘cargf’, ‘cargl’, ‘carg’, ‘casinf’, ‘casinhf’, ‘casinhl’, ‘casinh’,
‘casinl’, ‘casin’, ‘catanf’, ‘catanhf’, ‘catanhl’, ‘catanh’, ‘catanl’,
‘catan’, ‘cbrtf’, ‘cbrtl’, ‘cbrt’, ‘ccosf’, ‘ccoshf’, ‘ccoshl’, ‘ccosh’,
‘ccosl’, ‘ccos’, ‘cexpf’, ‘cexpl’, ‘cexp’, ‘cimagf’, ‘cimagl’, ‘cimag’,
‘clogf’, ‘clogl’, ‘clog’, ‘conjf’, ‘conjl’, ‘conj’, ‘copysignf’,
‘copysignl’, ‘copysign’, ‘cpowf’, ‘cpowl’, ‘cpow’, ‘cprojf’, ‘cprojl’,
‘cproj’, ‘crealf’, ‘creall’, ‘creal’, ‘csinf’, ‘csinhf’, ‘csinhl’,
‘csinh’, ‘csinl’, ‘csin’, ‘csqrtf’, ‘csqrtl’, ‘csqrt’, ‘ctanf’,
‘ctanhf’, ‘ctanhl’, ‘ctanh’, ‘ctanl’, ‘ctan’, ‘erfcf’, ‘erfcl’, ‘erfc’,
‘erff’, ‘erfl’, ‘erf’, ‘exp2f’, ‘exp2l’, ‘exp2’, ‘expm1f’, ‘expm1l’,
‘expm1’, ‘fdimf’, ‘fdiml’, ‘fdim’, ‘fmaf’, ‘fmal’, ‘fmaxf’, ‘fmaxl’,
‘fmax’, ‘fma’, ‘fminf’, ‘fminl’, ‘fmin’, ‘hypotf’, ‘hypotl’, ‘hypot’,
‘ilogbf’, ‘ilogbl’, ‘ilogb’, ‘imaxabs’, ‘isblank’, ‘iswblank’,
‘lgammaf’, ‘lgammal’, ‘lgamma’, ‘llabs’, ‘llrintf’, ‘llrintl’, ‘llrint’,
‘llroundf’, ‘llroundl’, ‘llround’, ‘log1pf’, ‘log1pl’, ‘log1p’, ‘log2f’,
‘log2l’, ‘log2’, ‘logbf’, ‘logbl’, ‘logb’, ‘lrintf’, ‘lrintl’, ‘lrint’,
‘lroundf’, ‘lroundl’, ‘lround’, ‘nearbyintf’, ‘nearbyintl’, ‘nearbyint’,
‘nextafterf’, ‘nextafterl’, ‘nextafter’, ‘nexttowardf’, ‘nexttowardl’,
‘nexttoward’, ‘remainderf’, ‘remainderl’, ‘remainder’, ‘remquof’,
‘remquol’, ‘remquo’, ‘rintf’, ‘rintl’, ‘rint’, ‘roundf’, ‘roundl’,
‘round’, ‘scalblnf’, ‘scalblnl’, ‘scalbln’, ‘scalbnf’, ‘scalbnl’,
‘scalbn’, ‘snprintf’, ‘tgammaf’, ‘tgammal’, ‘tgamma’, ‘truncf’,
‘truncl’, ‘trunc’, ‘vfscanf’, ‘vscanf’, ‘vsnprintf’ and ‘vsscanf’ are
handled as built-in functions except in strict ISO C90 mode (‘-ansi’ or
‘-std=c90’).

 There are also built-in versions of the ISO C99 functions ‘acosf’,
‘acosl’, ‘asinf’, ‘asinl’, ‘atan2f’, ‘atan2l’, ‘atanf’, ‘atanl’,
‘ceilf’, ‘ceill’, ‘cosf’, ‘coshf’, ‘coshl’, ‘cosl’, ‘expf’, ‘expl’,
‘fabsf’, ‘fabsl’, ‘floorf’, ‘floorl’, ‘fmodf’, ‘fmodl’, ‘frexpf’,
‘frexpl’, ‘ldexpf’, ‘ldexpl’, ‘log10f’, ‘log10l’, ‘logf’, ‘logl’,
‘modfl’, ‘modff’, ‘powf’, ‘powl’, ‘sinf’, ‘sinhf’, ‘sinhl’, ‘sinl’,
‘sqrtf’, ‘sqrtl’, ‘tanf’, ‘tanhf’, ‘tanhl’ and ‘tanl’ that are
recognized in any mode since ISO C90 reserves these names for the
purpose to which ISO C99 puts them.  All these functions have
corresponding versions prefixed with ‘__builtin_’.

 There are also built-in functions ‘__builtin_fabsfN’,
‘__builtin_fabsfNx’, ‘__builtin_copysignfN’ and ‘__builtin_copysignfNx’,
corresponding to the TS 18661-3 functions ‘fabsfN’, ‘fabsfNx’,
‘copysignfN’ and ‘copysignfNx’, for supported types ‘_FloatN’ and
‘_FloatNx’.

 There are also GNU extension functions ‘clog10’, ‘clog10f’ and
‘clog10l’ which names are reserved by ISO C99 for future use.  All these
functions have versions prefixed with ‘__builtin_’.

 The ISO C94 functions ‘iswalnum’, ‘iswalpha’, ‘iswcntrl’, ‘iswdigit’,
‘iswgraph’, ‘iswlower’, ‘iswprint’, ‘iswpunct’, ‘iswspace’, ‘iswupper’,
‘iswxdigit’, ‘towlower’ and ‘towupper’ are handled as built-in functions
except in strict ISO C90 mode (‘-ansi’ or ‘-std=c90’).

 The ISO C90 functions ‘abort’, ‘abs’, ‘acos’, ‘asin’, ‘atan2’, ‘atan’,
‘calloc’, ‘ceil’, ‘cosh’, ‘cos’, ‘exit’, ‘exp’, ‘fabs’, ‘floor’, ‘fmod’,
‘fprintf’, ‘fputs’, ‘free’, ‘frexp’, ‘fscanf’, ‘isalnum’, ‘isalpha’,
‘iscntrl’, ‘isdigit’, ‘isgraph’, ‘islower’, ‘isprint’, ‘ispunct’,
‘isspace’, ‘isupper’, ‘isxdigit’, ‘tolower’, ‘toupper’, ‘labs’, ‘ldexp’,
‘log10’, ‘log’, ‘malloc’, ‘memchr’, ‘memcmp’, ‘memcpy’, ‘memset’,
‘modf’, ‘pow’, ‘printf’, ‘putchar’, ‘puts’, ‘realloc’, ‘scanf’, ‘sinh’,
‘sin’, ‘snprintf’, ‘sprintf’, ‘sqrt’, ‘sscanf’, ‘strcat’, ‘strchr’,
‘strcmp’, ‘strcpy’, ‘strcspn’, ‘strlen’, ‘strncat’, ‘strncmp’,
‘strncpy’, ‘strpbrk’, ‘strrchr’, ‘strspn’, ‘strstr’, ‘tanh’, ‘tan’,
‘vfprintf’, ‘vprintf’ and ‘vsprintf’ are all recognized as built-in
functions unless ‘-fno-builtin’ is specified (or ‘-fno-builtin-FUNCTION’
is specified for an individual function).  All of these functions have
corresponding versions prefixed with ‘__builtin_’.

 GCC provides built-in versions of the ISO C99 floating-point comparison
macros that avoid raising exceptions for unordered operands.  They have
the same names as the standard macros ( ‘isgreater’, ‘isgreaterequal’,
‘isless’, ‘islessequal’, ‘islessgreater’, and ‘isunordered’) , with
‘__builtin_’ prefixed.  We intend for a library implementor to be able
to simply ‘#define’ each standard macro to its built-in equivalent.  In
the same fashion, GCC provides ‘fpclassify’, ‘isfinite’, ‘isinf_sign’,
‘isnormal’ and ‘signbit’ built-ins used with ‘__builtin_’ prefixed.  The
‘isinf’ and ‘isnan’ built-in functions appear both with and without the
‘__builtin_’ prefix.

 GCC provides built-in versions of the ISO C99 floating-point rounding
and exceptions handling functions ‘fegetround’, ‘feclearexcept’ and
‘feraiseexcept’.  They may not be available for all targets, and because
they need close interaction with libc internal values, they may not be
available for all target libcs, but in all cases they will gracefully
fallback to libc calls.  These built-in functions appear both with and
without the ‘__builtin_’ prefix.

 -- Built-in Function: void *__builtin_alloca (size_t size)
     The ‘__builtin_alloca’ function must be called at block scope.  The
     function allocates an object SIZE bytes large on the stack of the
     calling function.  The object is aligned on the default stack
     alignment boundary for the target determined by the
     ‘__BIGGEST_ALIGNMENT__’ macro.  The ‘__builtin_alloca’ function
     returns a pointer to the first byte of the allocated object.  The
     lifetime of the allocated object ends just before the calling
     function returns to its caller.  This is so even when
     ‘__builtin_alloca’ is called within a nested block.

     For example, the following function allocates eight objects of ‘n’
     bytes each on the stack, storing a pointer to each in consecutive
     elements of the array ‘a’.  It then passes the array to function
     ‘g’ which can safely use the storage pointed to by each of the
     array elements.

          void f (unsigned n)
          {
            void *a [8];
            for (int i = 0; i != 8; ++i)
              a [i] = __builtin_alloca (n);

            g (a, n);   // safe
          }

     Since the ‘__builtin_alloca’ function doesn't validate its argument
     it is the responsibility of its caller to make sure the argument
     doesn't cause it to exceed the stack size limit.  The
     ‘__builtin_alloca’ function is provided to make it possible to
     allocate on the stack arrays of bytes with an upper bound that may
     be computed at run time.  Since C99 Variable Length Arrays offer
     similar functionality under a portable, more convenient, and safer
     interface they are recommended instead, in both C99 and C++
     programs where GCC provides them as an extension.  *Note Variable
     Length::, for details.

 -- Built-in Function: void *__builtin_alloca_with_align (size_t size,
          size_t alignment)
     The ‘__builtin_alloca_with_align’ function must be called at block
     scope.  The function allocates an object SIZE bytes large on the
     stack of the calling function.  The allocated object is aligned on
     the boundary specified by the argument ALIGNMENT whose unit is
     given in bits (not bytes).  The SIZE argument must be positive and
     not exceed the stack size limit.  The ALIGNMENT argument must be a
     constant integer expression that evaluates to a power of 2 greater
     than or equal to ‘CHAR_BIT’ and less than some unspecified maximum.
     Invocations with other values are rejected with an error indicating
     the valid bounds.  The function returns a pointer to the first byte
     of the allocated object.  The lifetime of the allocated object ends
     at the end of the block in which the function was called.  The
     allocated storage is released no later than just before the calling
     function returns to its caller, but may be released at the end of
     the block in which the function was called.

     For example, in the following function the call to ‘g’ is unsafe
     because when ‘overalign’ is non-zero, the space allocated by
     ‘__builtin_alloca_with_align’ may have been released at the end of
     the ‘if’ statement in which it was called.

          void f (unsigned n, bool overalign)
          {
            void *p;
            if (overalign)
              p = __builtin_alloca_with_align (n, 64 /* bits */);
            else
              p = __builtin_alloc (n);

            g (p, n);   // unsafe
          }

     Since the ‘__builtin_alloca_with_align’ function doesn't validate
     its SIZE argument it is the responsibility of its caller to make
     sure the argument doesn't cause it to exceed the stack size limit.
     The ‘__builtin_alloca_with_align’ function is provided to make it
     possible to allocate on the stack overaligned arrays of bytes with
     an upper bound that may be computed at run time.  Since C99
     Variable Length Arrays offer the same functionality under a
     portable, more convenient, and safer interface they are recommended
     instead, in both C99 and C++ programs where GCC provides them as an
     extension.  *Note Variable Length::, for details.

 -- Built-in Function: void *__builtin_alloca_with_align_and_max (size_t
          size, size_t alignment, size_t max_size)
     Similar to ‘__builtin_alloca_with_align’ but takes an extra
     argument specifying an upper bound for SIZE in case its value
     cannot be computed at compile time, for use by ‘-fstack-usage’,
     ‘-Wstack-usage’ and ‘-Walloca-larger-than’.  MAX_SIZE must be a
     constant integer expression, it has no effect on code generation
     and no attempt is made to check its compatibility with SIZE.

 -- Built-in Function: bool __builtin_has_attribute (TYPE-OR-EXPRESSION,
          ATTRIBUTE)
     The ‘__builtin_has_attribute’ function evaluates to an integer
     constant expression equal to ‘true’ if the symbol or type
     referenced by the TYPE-OR-EXPRESSION argument has been declared
     with the ATTRIBUTE referenced by the second argument.  For an
     TYPE-OR-EXPRESSION argument that does not reference a symbol, since
     attributes do not apply to expressions the built-in consider the
     type of the argument.  Neither argument is evaluated.  The
     TYPE-OR-EXPRESSION argument is subject to the same restrictions as
     the argument to ‘typeof’ (*note Typeof::).  The ATTRIBUTE argument
     is an attribute name optionally followed by a comma-separated list
     of arguments enclosed in parentheses.  Both forms of attribute
     names--with and without double leading and trailing
     underscores--are recognized.  *Note Attribute Syntax::, for
     details.  When no attribute arguments are specified for an
     attribute that expects one or more arguments the function returns
     ‘true’ if TYPE-OR-EXPRESSION has been declared with the attribute
     regardless of the attribute argument values.  Arguments provided
     for an attribute that expects some are validated and matched up to
     the provided number.  The function returns ‘true’ if all provided
     arguments match.  For example, the first call to the function below
     evaluates to ‘true’ because ‘x’ is declared with the ‘aligned’
     attribute but the second call evaluates to ‘false’ because ‘x’ is
     declared ‘aligned (8)’ and not ‘aligned (4)’.

          __attribute__ ((aligned (8))) int x;
          _Static_assert (__builtin_has_attribute (x, aligned), "aligned");
          _Static_assert (!__builtin_has_attribute (x, aligned (4)), "aligned (4)");

     Due to a limitation the ‘__builtin_has_attribute’ function returns
     ‘false’ for the ‘mode’ attribute even if the type or variable
     referenced by the TYPE-OR-EXPRESSION argument was declared with
     one.  The function is also not supported with labels, and in C with
     enumerators.

     Note that unlike the ‘__has_attribute’ preprocessor operator which
     is suitable for use in ‘#if’ preprocessing directives
     ‘__builtin_has_attribute’ is an intrinsic function that is not
     recognized in such contexts.

 -- Built-in Function: TYPE __builtin_speculation_safe_value (TYPE val,
          TYPE failval)

     This built-in function can be used to help mitigate against unsafe
     speculative execution.  TYPE may be any integral type or any
     pointer type.

       1. If the CPU is not speculatively executing the code, then VAL
          is returned.
       2. If the CPU is executing speculatively then either:
             • The function may cause execution to pause until it is
               known that the code is no-longer being executed
               speculatively (in which case VAL can be returned, as
               above); or
             • The function may use target-dependent speculation
               tracking state to cause FAILVAL to be returned when it is
               known that speculative execution has incorrectly
               predicted a conditional branch operation.

     The second argument, FAILVAL, is optional and defaults to zero if
     omitted.

     GCC defines the preprocessor macro
     ‘__HAVE_BUILTIN_SPECULATION_SAFE_VALUE’ for targets that have been
     updated to support this builtin.

     The built-in function can be used where a variable appears to be
     used in a safe way, but the CPU, due to speculative execution may
     temporarily ignore the bounds checks.  Consider, for example, the
     following function:

          int array[500];
          int f (unsigned untrusted_index)
          {
            if (untrusted_index < 500)
              return array[untrusted_index];
            return 0;
          }

     If the function is called repeatedly with ‘untrusted_index’ less
     than the limit of 500, then a branch predictor will learn that the
     block of code that returns a value stored in ‘array’ will be
     executed.  If the function is subsequently called with an
     out-of-range value it will still try to execute that block of code
     first until the CPU determines that the prediction was incorrect
     (the CPU will unwind any incorrect operations at that point).
     However, depending on how the result of the function is used, it
     might be possible to leave traces in the cache that can reveal what
     was stored at the out-of-bounds location.  The built-in function
     can be used to provide some protection against leaking data in this
     way by changing the code to:

          int array[500];
          int f (unsigned untrusted_index)
          {
            if (untrusted_index < 500)
              return array[__builtin_speculation_safe_value (untrusted_index)];
            return 0;
          }

     The built-in function will either cause execution to stall until
     the conditional branch has been fully resolved, or it may permit
     speculative execution to continue, but using 0 instead of
     ‘untrusted_value’ if that exceeds the limit.

     If accessing any memory location is potentially unsafe when
     speculative execution is incorrect, then the code can be rewritten
     as

          int array[500];
          int f (unsigned untrusted_index)
          {
            if (untrusted_index < 500)
              return *__builtin_speculation_safe_value (&array[untrusted_index], NULL);
            return 0;
          }

     which will cause a ‘NULL’ pointer to be used for the unsafe case.

 -- Built-in Function: int __builtin_types_compatible_p (TYPE1, TYPE2)

     You can use the built-in function ‘__builtin_types_compatible_p’ to
     determine whether two types are the same.

     This built-in function returns 1 if the unqualified versions of the
     types TYPE1 and TYPE2 (which are types, not expressions) are
     compatible, 0 otherwise.  The result of this built-in function can
     be used in integer constant expressions.

     This built-in function ignores top level qualifiers (e.g., ‘const’,
     ‘volatile’).  For example, ‘int’ is equivalent to ‘const int’.

     The type ‘int[]’ and ‘int[5]’ are compatible.  On the other hand,
     ‘int’ and ‘char *’ are not compatible, even if the size of their
     types, on the particular architecture are the same.  Also, the
     amount of pointer indirection is taken into account when
     determining similarity.  Consequently, ‘short *’ is not similar to
     ‘short **’.  Furthermore, two types that are typedefed are
     considered compatible if their underlying types are compatible.

     An ‘enum’ type is not considered to be compatible with another
     ‘enum’ type even if both are compatible with the same integer type;
     this is what the C standard specifies.  For example, ‘enum {foo,
     bar}’ is not similar to ‘enum {hot, dog}’.

     You typically use this function in code whose execution varies
     depending on the arguments' types.  For example:

          #define foo(x)                                                  \
            ({                                                           \
              typeof (x) tmp = (x);                                       \
              if (__builtin_types_compatible_p (typeof (x), long double)) \
                tmp = foo_long_double (tmp);                              \
              else if (__builtin_types_compatible_p (typeof (x), double)) \
                tmp = foo_double (tmp);                                   \
              else if (__builtin_types_compatible_p (typeof (x), float))  \
                tmp = foo_float (tmp);                                    \
              else                                                        \
                abort ();                                                 \
              tmp;                                                        \
            })

     _Note:_ This construct is only available for C.

 -- Built-in Function: TYPE __builtin_call_with_static_chain (CALL_EXP,
          POINTER_EXP)

     The CALL_EXP expression must be a function call, and the
     POINTER_EXP expression must be a pointer.  The POINTER_EXP is
     passed to the function call in the target's static chain location.
     The result of builtin is the result of the function call.

     _Note:_ This builtin is only available for C.  This builtin can be
     used to call Go closures from C.

 -- Built-in Function: TYPE __builtin_choose_expr (CONST_EXP, EXP1,
          EXP2)

     You can use the built-in function ‘__builtin_choose_expr’ to
     evaluate code depending on the value of a constant expression.
     This built-in function returns EXP1 if CONST_EXP, which is an
     integer constant expression, is nonzero.  Otherwise it returns
     EXP2.

     This built-in function is analogous to the ‘? :’ operator in C,
     except that the expression returned has its type unaltered by
     promotion rules.  Also, the built-in function does not evaluate the
     expression that is not chosen.  For example, if CONST_EXP evaluates
     to ‘true’, EXP2 is not evaluated even if it has side effects.

     This built-in function can return an lvalue if the chosen argument
     is an lvalue.

     If EXP1 is returned, the return type is the same as EXP1's type.
     Similarly, if EXP2 is returned, its return type is the same as
     EXP2.

     Example:

          #define foo(x)                                                    \
            __builtin_choose_expr (                                         \
              __builtin_types_compatible_p (typeof (x), double),            \
              foo_double (x),                                               \
              __builtin_choose_expr (                                       \
                __builtin_types_compatible_p (typeof (x), float),           \
                foo_float (x),                                              \
                /* The void expression results in a compile-time error  \
                   when assigning the result to something.  */          \
                (void)0))

     _Note:_ This construct is only available for C.  Furthermore, the
     unused expression (EXP1 or EXP2 depending on the value of
     CONST_EXP) may still generate syntax errors.  This may change in
     future revisions.

 -- Built-in Function: TYPE __builtin_tgmath (FUNCTIONS, ARGUMENTS)

     The built-in function ‘__builtin_tgmath’, available only for C and
     Objective-C, calls a function determined according to the rules of
     ‘<tgmath.h>’ macros.  It is intended to be used in implementations
     of that header, so that expansions of macros from that header only
     expand each of their arguments once, to avoid problems when calls
     to such macros are nested inside the arguments of other calls to
     such macros; in addition, it results in better diagnostics for
     invalid calls to ‘<tgmath.h>’ macros than implementations using
     other GNU C language features.  For example, the ‘pow’ type-generic
     macro might be defined as:

          #define pow(a, b) __builtin_tgmath (powf, pow, powl, \
                                              cpowf, cpow, cpowl, a, b)

     The arguments to ‘__builtin_tgmath’ are at least two pointers to
     functions, followed by the arguments to the type-generic macro
     (which will be passed as arguments to the selected function).  All
     the pointers to functions must be pointers to prototyped functions,
     none of which may have variable arguments, and all of which must
     have the same number of parameters; the number of parameters of the
     first function determines how many arguments to ‘__builtin_tgmath’
     are interpreted as function pointers, and how many as the arguments
     to the called function.

     The types of the specified functions must all be different, but
     related to each other in the same way as a set of functions that
     may be selected between by a macro in ‘<tgmath.h>’.  This means
     that the functions are parameterized by a floating-point type T,
     different for each such function.  The function return types may
     all be the same type, or they may be T for each function, or they
     may be the real type corresponding to T for each function (if some
     of the types T are complex).  Likewise, for each parameter
     position, the type of the parameter in that position may always be
     the same type, or may be T for each function (this case must apply
     for at least one parameter position), or may be the real type
     corresponding to T for each function.

     The standard rules for ‘<tgmath.h>’ macros are used to find a
     common type U from the types of the arguments for parameters whose
     types vary between the functions; complex integer types (a GNU
     extension) are treated like ‘_Complex double’ for this purpose (or
     ‘_Complex _Float64’ if all the function return types are the same
     ‘_FloatN’ or ‘_FloatNx’ type).  If the function return types vary,
     or are all the same integer type, the function called is the one
     for which T is U, and it is an error if there is no such function.
     If the function return types are all the same floating-point type,
     the type-generic macro is taken to be one of those from TS 18661
     that rounds the result to a narrower type; if there is a function
     for which T is U, it is called, and otherwise the first function,
     if any, for which T has at least the range and precision of U is
     called, and it is an error if there is no such function.

 -- Built-in Function: int __builtin_constant_p (EXP)
     You can use the built-in function ‘__builtin_constant_p’ to
     determine if a value is known to be constant at compile time and
     hence that GCC can perform constant-folding on expressions
     involving that value.  The argument of the function is the value to
     test.  The function returns the integer 1 if the argument is known
     to be a compile-time constant and 0 if it is not known to be a
     compile-time constant.  A return of 0 does not indicate that the
     value is _not_ a constant, but merely that GCC cannot prove it is a
     constant with the specified value of the ‘-O’ option.

     You typically use this function in an embedded application where
     memory is a critical resource.  If you have some complex
     calculation, you may want it to be folded if it involves constants,
     but need to call a function if it does not.  For example:

          #define Scale_Value(X)      \
            (__builtin_constant_p (X) \
            ? ((X) * SCALE + OFFSET) : Scale (X))

     You may use this built-in function in either a macro or an inline
     function.  However, if you use it in an inlined function and pass
     an argument of the function as the argument to the built-in, GCC
     never returns 1 when you call the inline function with a string
     constant or compound literal (*note Compound Literals::) and does
     not return 1 when you pass a constant numeric value to the inline
     function unless you specify the ‘-O’ option.

     You may also use ‘__builtin_constant_p’ in initializers for static
     data.  For instance, you can write

          static const int table[] = {
             __builtin_constant_p (EXPRESSION) ? (EXPRESSION) : -1,
             /* ... */
          };

     This is an acceptable initializer even if EXPRESSION is not a
     constant expression, including the case where
     ‘__builtin_constant_p’ returns 1 because EXPRESSION can be folded
     to a constant but EXPRESSION contains operands that are not
     otherwise permitted in a static initializer (for example, ‘0 && foo
     ()’).  GCC must be more conservative about evaluating the built-in
     in this case, because it has no opportunity to perform
     optimization.

 -- Built-in Function: bool __builtin_is_constant_evaluated (void)
     The ‘__builtin_is_constant_evaluated’ function is available only in
     C++.  The built-in is intended to be used by implementations of the
     ‘std::is_constant_evaluated’ C++ function.  Programs should make
     use of the latter function rather than invoking the built-in
     directly.

     The main use case of the built-in is to determine whether a
     ‘constexpr’ function is being called in a ‘constexpr’ context.  A
     call to the function evaluates to a core constant expression with
     the value ‘true’ if and only if it occurs within the evaluation of
     an expression or conversion that is manifestly constant-evaluated
     as defined in the C++ standard.  Manifestly constant-evaluated
     contexts include constant-expressions, the conditions of ‘constexpr
     if’ statements, constraint-expressions, and initializers of
     variables usable in constant expressions.  For more details refer
     to the latest revision of the C++ standard.

 -- Built-in Function: void __builtin_clear_padding (PTR)
     The built-in function ‘__builtin_clear_padding’ function clears
     padding bits inside of the object representation of object pointed
     by PTR, which has to be a pointer.  The value representation of the
     object is not affected.  The type of the object is assumed to be
     the type the pointer points to.  Inside of a union, the only
     cleared bits are bits that are padding bits for all the union
     members.

     This built-in-function is useful if the padding bits of an object
     might have intederminate values and the object representation needs
     to be bitwise compared to some other object, for example for atomic
     operations.

     For C++, PTR argument type should be pointer to trivially-copyable
     type, unless the argument is address of a variable or parameter,
     because otherwise it isn't known if the type isn't just a base
     class whose padding bits are reused or laid out differently in a
     derived class.

 -- Built-in Function: TYPE __builtin_bit_cast (TYPE, ARG)
     The ‘__builtin_bit_cast’ function is available only in C++.  The
     built-in is intended to be used by implementations of the
     ‘std::bit_cast’ C++ template function.  Programs should make use of
     the latter function rather than invoking the built-in directly.

     This built-in function allows reinterpreting the bits of the ARG
     argument as if it had type TYPE.  TYPE and the type of the ARG
     argument need to be trivially copyable types with the same size.
     When manifestly constant-evaluated, it performs extra diagnostics
     required for ‘std::bit_cast’ and returns a constant expression if
     ARG is a constant expression.  For more details refer to the latest
     revision of the C++ standard.

 -- Built-in Function: long __builtin_expect (long EXP, long C)
     You may use ‘__builtin_expect’ to provide the compiler with branch
     prediction information.  In general, you should prefer to use
     actual profile feedback for this (‘-fprofile-arcs’), as programmers
     are notoriously bad at predicting how their programs actually
     perform.  However, there are applications in which this data is
     hard to collect.

     The return value is the value of EXP, which should be an integral
     expression.  The semantics of the built-in are that it is expected
     that EXP == C.  For example:

          if (__builtin_expect (x, 0))
            foo ();

     indicates that we do not expect to call ‘foo’, since we expect ‘x’
     to be zero.  Since you are limited to integral expressions for EXP,
     you should use constructions such as

          if (__builtin_expect (ptr != NULL, 1))
            foo (*ptr);

     when testing pointer or floating-point values.

     For the purposes of branch prediction optimizations, the
     probability that a ‘__builtin_expect’ expression is ‘true’ is
     controlled by GCC's ‘builtin-expect-probability’ parameter, which
     defaults to 90%.

     You can also use ‘__builtin_expect_with_probability’ to explicitly
     assign a probability value to individual expressions.  If the
     built-in is used in a loop construct, the provided probability will
     influence the expected number of iterations made by loop
     optimizations.

 -- Built-in Function: long __builtin_expect_with_probability
     (long EXP, long C, double PROBABILITY)

     This function has the same semantics as ‘__builtin_expect’, but the
     caller provides the expected probability that EXP == C.  The last
     argument, PROBABILITY, is a floating-point value in the range 0.0
     to 1.0, inclusive.  The PROBABILITY argument must be constant
     floating-point expression.

 -- Built-in Function: void __builtin_trap (void)
     This function causes the program to exit abnormally.  GCC
     implements this function by using a target-dependent mechanism
     (such as intentionally executing an illegal instruction) or by
     calling ‘abort’.  The mechanism used may vary from release to
     release so you should not rely on any particular implementation.

 -- Built-in Function: void __builtin_unreachable (void)
     If control flow reaches the point of the ‘__builtin_unreachable’,
     the program is undefined.  It is useful in situations where the
     compiler cannot deduce the unreachability of the code.

     One such case is immediately following an ‘asm’ statement that
     either never terminates, or one that transfers control elsewhere
     and never returns.  In this example, without the
     ‘__builtin_unreachable’, GCC issues a warning that control reaches
     the end of a non-void function.  It also generates code to return
     after the ‘asm’.

          int f (int c, int v)
          {
            if (c)
              {
                return v;
              }
            else
              {
                asm("jmp error_handler");
                __builtin_unreachable ();
              }
          }

     Because the ‘asm’ statement unconditionally transfers control out
     of the function, control never reaches the end of the function
     body.  The ‘__builtin_unreachable’ is in fact unreachable and
     communicates this fact to the compiler.

     Another use for ‘__builtin_unreachable’ is following a call a
     function that never returns but that is not declared
     ‘__attribute__((noreturn))’, as in this example:

          void function_that_never_returns (void);

          int g (int c)
          {
            if (c)
              {
                return 1;
              }
            else
              {
                function_that_never_returns ();
                __builtin_unreachable ();
              }
          }

 -- Built-in Function: TYPE __builtin_assoc_barrier (TYPE EXPR)
     This built-in inhibits re-association of the floating-point
     expression EXPR with expressions consuming the return value of the
     built-in.  The expression EXPR itself can be reordered, and the
     whole expression EXPR can be reordered with operands after the
     barrier.  The barrier is only relevant when ‘-fassociative-math’ is
     active, since otherwise floating-point is not treated as
     associative.

          float x0 = a + b - b;
          float x1 = __builtin_assoc_barrier(a + b) - b;

     means that, with ‘-fassociative-math’, ‘x0’ can be optimized to ‘x0
     = a’ but ‘x1’ cannot.

 -- Built-in Function: void * __builtin_assume_aligned (const void *EXP,
          size_t ALIGN, ...)
     This function returns its first argument, and allows the compiler
     to assume that the returned pointer is at least ALIGN bytes
     aligned.  This built-in can have either two or three arguments, if
     it has three, the third argument should have integer type, and if
     it is nonzero means misalignment offset.  For example:

          void *x = __builtin_assume_aligned (arg, 16);

     means that the compiler can assume ‘x’, set to ‘arg’, is at least
     16-byte aligned, while:

          void *x = __builtin_assume_aligned (arg, 32, 8);

     means that the compiler can assume for ‘x’, set to ‘arg’, that
     ‘(char *) x - 8’ is 32-byte aligned.

 -- Built-in Function: int __builtin_LINE ()
     This function is the equivalent of the preprocessor ‘__LINE__’
     macro and returns a constant integer expression that evaluates to
     the line number of the invocation of the built-in.  When used as a
     C++ default argument for a function F, it returns the line number
     of the call to F.

 -- Built-in Function: const char * __builtin_FUNCTION ()
     This function is the equivalent of the ‘__FUNCTION__’ symbol and
     returns an address constant pointing to the name of the function
     from which the built-in was invoked, or the empty string if the
     invocation is not at function scope.  When used as a C++ default
     argument for a function F, it returns the name of F's caller or the
     empty string if the call was not made at function scope.

 -- Built-in Function: const char * __builtin_FILE ()
     This function is the equivalent of the preprocessor ‘__FILE__’
     macro and returns an address constant pointing to the file name
     containing the invocation of the built-in, or the empty string if
     the invocation is not at function scope.  When used as a C++
     default argument for a function F, it returns the file name of the
     call to F or the empty string if the call was not made at function
     scope.

     For example, in the following, each call to function ‘foo’ will
     print a line similar to ‘"file.c:123: foo: message"’ with the name
     of the file and the line number of the ‘printf’ call, the name of
     the function ‘foo’, followed by the word ‘message’.

          const char*
          function (const char *func = __builtin_FUNCTION ())
          {
            return func;
          }

          void foo (void)
          {
            printf ("%s:%i: %s: message\n", file (), line (), function ());
          }

 -- Built-in Function: void __builtin___clear_cache (void *BEGIN, void
          *END)
     This function is used to flush the processor's instruction cache
     for the region of memory between BEGIN inclusive and END exclusive.
     Some targets require that the instruction cache be flushed, after
     modifying memory containing code, in order to obtain deterministic
     behavior.

     If the target does not require instruction cache flushes,
     ‘__builtin___clear_cache’ has no effect.  Otherwise either
     instructions are emitted in-line to clear the instruction cache or
     a call to the ‘__clear_cache’ function in libgcc is made.

 -- Built-in Function: void __builtin_prefetch (const void *ADDR, ...)
     This function is used to minimize cache-miss latency by moving data
     into a cache before it is accessed.  You can insert calls to
     ‘__builtin_prefetch’ into code for which you know addresses of data
     in memory that is likely to be accessed soon.  If the target
     supports them, data prefetch instructions are generated.  If the
     prefetch is done early enough before the access then the data will
     be in the cache by the time it is accessed.

     The value of ADDR is the address of the memory to prefetch.  There
     are two optional arguments, RW and LOCALITY.  The value of RW is a
     compile-time constant one or zero; one means that the prefetch is
     preparing for a write to the memory address and zero, the default,
     means that the prefetch is preparing for a read.  The value
     LOCALITY must be a compile-time constant integer between zero and
     three.  A value of zero means that the data has no temporal
     locality, so it need not be left in the cache after the access.  A
     value of three means that the data has a high degree of temporal
     locality and should be left in all levels of cache possible.
     Values of one and two mean, respectively, a low or moderate degree
     of temporal locality.  The default is three.

          for (i = 0; i < n; i++)
            {
              a[i] = a[i] + b[i];
              __builtin_prefetch (&a[i+j], 1, 1);
              __builtin_prefetch (&b[i+j], 0, 1);
              /* ... */
            }

     Data prefetch does not generate faults if ADDR is invalid, but the
     address expression itself must be valid.  For example, a prefetch
     of ‘p->next’ does not fault if ‘p->next’ is not a valid address,
     but evaluation faults if ‘p’ is not a valid address.

     If the target does not support data prefetch, the address
     expression is evaluated if it includes side effects but no other
     code is generated and GCC does not issue a warning.

 -- Built-in Functionsize_t: __builtin_object_size (const void * PTR,
          int TYPE)
     Returns the size of an object pointed to by PTR.  *Note Object Size
     Checking::, for a detailed description of the function.

 -- Built-in Function: double __builtin_huge_val (void)
     Returns a positive infinity, if supported by the floating-point
     format, else ‘DBL_MAX’.  This function is suitable for implementing
     the ISO C macro ‘HUGE_VAL’.

 -- Built-in Function: float __builtin_huge_valf (void)
     Similar to ‘__builtin_huge_val’, except the return type is ‘float’.

 -- Built-in Function: long double __builtin_huge_vall (void)
     Similar to ‘__builtin_huge_val’, except the return type is ‘long
     double’.

 -- Built-in Function: _FloatN __builtin_huge_valfN (void)
     Similar to ‘__builtin_huge_val’, except the return type is
     ‘_FloatN’.

 -- Built-in Function: _FloatNx __builtin_huge_valfNx (void)
     Similar to ‘__builtin_huge_val’, except the return type is
     ‘_FloatNx’.

 -- Built-in Function: int __builtin_fpclassify (int, int, int, int,
          int, ...)
     This built-in implements the C99 fpclassify functionality.  The
     first five int arguments should be the target library's notion of
     the possible FP classes and are used for return values.  They must
     be constant values and they must appear in this order: ‘FP_NAN’,
     ‘FP_INFINITE’, ‘FP_NORMAL’, ‘FP_SUBNORMAL’ and ‘FP_ZERO’.  The
     ellipsis is for exactly one floating-point value to classify.  GCC
     treats the last argument as type-generic, which means it does not
     do default promotion from float to double.

 -- Built-in Function: double __builtin_inf (void)
     Similar to ‘__builtin_huge_val’, except a warning is generated if
     the target floating-point format does not support infinities.

 -- Built-in Function: _Decimal32 __builtin_infd32 (void)
     Similar to ‘__builtin_inf’, except the return type is ‘_Decimal32’.

 -- Built-in Function: _Decimal64 __builtin_infd64 (void)
     Similar to ‘__builtin_inf’, except the return type is ‘_Decimal64’.

 -- Built-in Function: _Decimal128 __builtin_infd128 (void)
     Similar to ‘__builtin_inf’, except the return type is
     ‘_Decimal128’.

 -- Built-in Function: float __builtin_inff (void)
     Similar to ‘__builtin_inf’, except the return type is ‘float’.
     This function is suitable for implementing the ISO C99 macro
     ‘INFINITY’.

 -- Built-in Function: long double __builtin_infl (void)
     Similar to ‘__builtin_inf’, except the return type is ‘long
     double’.

 -- Built-in Function: _FloatN __builtin_inffN (void)
     Similar to ‘__builtin_inf’, except the return type is ‘_FloatN’.

 -- Built-in Function: _FloatN __builtin_inffNx (void)
     Similar to ‘__builtin_inf’, except the return type is ‘_FloatNx’.

 -- Built-in Function: int __builtin_isinf_sign (...)
     Similar to ‘isinf’, except the return value is -1 for an argument
     of ‘-Inf’ and 1 for an argument of ‘+Inf’.  Note while the
     parameter list is an ellipsis, this function only accepts exactly
     one floating-point argument.  GCC treats this parameter as
     type-generic, which means it does not do default promotion from
     float to double.

 -- Built-in Function: double __builtin_nan (const char *str)
     This is an implementation of the ISO C99 function ‘nan’.

     Since ISO C99 defines this function in terms of ‘strtod’, which we
     do not implement, a description of the parsing is in order.  The
     string is parsed as by ‘strtol’; that is, the base is recognized by
     leading ‘0’ or ‘0x’ prefixes.  The number parsed is placed in the
     significand such that the least significant bit of the number is at
     the least significant bit of the significand.  The number is
     truncated to fit the significand field provided.  The significand
     is forced to be a quiet NaN.

     This function, if given a string literal all of which would have
     been consumed by ‘strtol’, is evaluated early enough that it is
     considered a compile-time constant.

 -- Built-in Function: _Decimal32 __builtin_nand32 (const char *str)
     Similar to ‘__builtin_nan’, except the return type is ‘_Decimal32’.

 -- Built-in Function: _Decimal64 __builtin_nand64 (const char *str)
     Similar to ‘__builtin_nan’, except the return type is ‘_Decimal64’.

 -- Built-in Function: _Decimal128 __builtin_nand128 (const char *str)
     Similar to ‘__builtin_nan’, except the return type is
     ‘_Decimal128’.

 -- Built-in Function: float __builtin_nanf (const char *str)
     Similar to ‘__builtin_nan’, except the return type is ‘float’.

 -- Built-in Function: long double __builtin_nanl (const char *str)
     Similar to ‘__builtin_nan’, except the return type is ‘long
     double’.

 -- Built-in Function: _FloatN __builtin_nanfN (const char *str)
     Similar to ‘__builtin_nan’, except the return type is ‘_FloatN’.

 -- Built-in Function: _FloatNx __builtin_nanfNx (const char *str)
     Similar to ‘__builtin_nan’, except the return type is ‘_FloatNx’.

 -- Built-in Function: double __builtin_nans (const char *str)
     Similar to ‘__builtin_nan’, except the significand is forced to be
     a signaling NaN.  The ‘nans’ function is proposed by WG14 N965.

 -- Built-in Function: _Decimal32 __builtin_nansd32 (const char *str)
     Similar to ‘__builtin_nans’, except the return type is
     ‘_Decimal32’.

 -- Built-in Function: _Decimal64 __builtin_nansd64 (const char *str)
     Similar to ‘__builtin_nans’, except the return type is
     ‘_Decimal64’.

 -- Built-in Function: _Decimal128 __builtin_nansd128 (const char *str)
     Similar to ‘__builtin_nans’, except the return type is
     ‘_Decimal128’.

 -- Built-in Function: float __builtin_nansf (const char *str)
     Similar to ‘__builtin_nans’, except the return type is ‘float’.

 -- Built-in Function: long double __builtin_nansl (const char *str)
     Similar to ‘__builtin_nans’, except the return type is ‘long
     double’.

 -- Built-in Function: _FloatN __builtin_nansfN (const char *str)
     Similar to ‘__builtin_nans’, except the return type is ‘_FloatN’.

 -- Built-in Function: _FloatNx __builtin_nansfNx (const char *str)
     Similar to ‘__builtin_nans’, except the return type is ‘_FloatNx’.

 -- Built-in Function: int __builtin_ffs (int x)
     Returns one plus the index of the least significant 1-bit of X, or
     if X is zero, returns zero.

 -- Built-in Function: int __builtin_clz (unsigned int x)
     Returns the number of leading 0-bits in X, starting at the most
     significant bit position.  If X is 0, the result is undefined.

 -- Built-in Function: int __builtin_ctz (unsigned int x)
     Returns the number of trailing 0-bits in X, starting at the least
     significant bit position.  If X is 0, the result is undefined.

 -- Built-in Function: int __builtin_clrsb (int x)
     Returns the number of leading redundant sign bits in X, i.e. the
     number of bits following the most significant bit that are
     identical to it.  There are no special cases for 0 or other values.

 -- Built-in Function: int __builtin_popcount (unsigned int x)
     Returns the number of 1-bits in X.

 -- Built-in Function: int __builtin_parity (unsigned int x)
     Returns the parity of X, i.e. the number of 1-bits in X modulo 2.

 -- Built-in Function: int __builtin_ffsl (long)
     Similar to ‘__builtin_ffs’, except the argument type is ‘long’.

 -- Built-in Function: int __builtin_clzl (unsigned long)
     Similar to ‘__builtin_clz’, except the argument type is ‘unsigned
     long’.

 -- Built-in Function: int __builtin_ctzl (unsigned long)
     Similar to ‘__builtin_ctz’, except the argument type is ‘unsigned
     long’.

 -- Built-in Function: int __builtin_clrsbl (long)
     Similar to ‘__builtin_clrsb’, except the argument type is ‘long’.

 -- Built-in Function: int __builtin_popcountl (unsigned long)
     Similar to ‘__builtin_popcount’, except the argument type is
     ‘unsigned long’.

 -- Built-in Function: int __builtin_parityl (unsigned long)
     Similar to ‘__builtin_parity’, except the argument type is
     ‘unsigned long’.

 -- Built-in Function: int __builtin_ffsll (long long)
     Similar to ‘__builtin_ffs’, except the argument type is ‘long
     long’.

 -- Built-in Function: int __builtin_clzll (unsigned long long)
     Similar to ‘__builtin_clz’, except the argument type is ‘unsigned
     long long’.

 -- Built-in Function: int __builtin_ctzll (unsigned long long)
     Similar to ‘__builtin_ctz’, except the argument type is ‘unsigned
     long long’.

 -- Built-in Function: int __builtin_clrsbll (long long)
     Similar to ‘__builtin_clrsb’, except the argument type is ‘long
     long’.

 -- Built-in Function: int __builtin_popcountll (unsigned long long)
     Similar to ‘__builtin_popcount’, except the argument type is
     ‘unsigned long long’.

 -- Built-in Function: int __builtin_parityll (unsigned long long)
     Similar to ‘__builtin_parity’, except the argument type is
     ‘unsigned long long’.

 -- Built-in Function: double __builtin_powi (double, int)
     Returns the first argument raised to the power of the second.
     Unlike the ‘pow’ function no guarantees about precision and
     rounding are made.

 -- Built-in Function: float __builtin_powif (float, int)
     Similar to ‘__builtin_powi’, except the argument and return types
     are ‘float’.

 -- Built-in Function: long double __builtin_powil (long double, int)
     Similar to ‘__builtin_powi’, except the argument and return types
     are ‘long double’.

 -- Built-in Function: uint16_t __builtin_bswap16 (uint16_t x)
     Returns X with the order of the bytes reversed; for example,
     ‘0xaabb’ becomes ‘0xbbaa’.  Byte here always means exactly 8 bits.

 -- Built-in Function: uint32_t __builtin_bswap32 (uint32_t x)
     Similar to ‘__builtin_bswap16’, except the argument and return
     types are 32-bit.

 -- Built-in Function: uint64_t __builtin_bswap64 (uint64_t x)
     Similar to ‘__builtin_bswap32’, except the argument and return
     types are 64-bit.

 -- Built-in Function: uint128_t __builtin_bswap128 (uint128_t x)
     Similar to ‘__builtin_bswap64’, except the argument and return
     types are 128-bit.  Only supported on targets when 128-bit types
     are supported.

 -- Built-in Function: Pmode __builtin_extend_pointer (void * x)
     On targets where the user visible pointer size is smaller than the
     size of an actual hardware address this function returns the
     extended user pointer.  Targets where this is true included ILP32
     mode on x86_64 or Aarch64.  This function is mainly useful when
     writing inline assembly code.

 -- Built-in Function: int __builtin_goacc_parlevel_id (int x)
     Returns the openacc gang, worker or vector id depending on whether
     X is 0, 1 or 2.

 -- Built-in Function: int __builtin_goacc_parlevel_size (int x)
     Returns the openacc gang, worker or vector size depending on
     whether X is 0, 1 or 2.


File: gcc.info,  Node: Target Builtins,  Next: Target Format Checks,  Prev: Other Builtins,  Up: C Extensions

6.60 Built-in Functions Specific to Particular Target Machines
==============================================================

On some target machines, GCC supports many built-in functions specific
to those machines.  Generally these generate calls to specific machine
instructions, but allow the compiler to schedule those calls.

* Menu:

* AArch64 Built-in Functions::
* Alpha Built-in Functions::
* Altera Nios II Built-in Functions::
* ARC Built-in Functions::
* ARC SIMD Built-in Functions::
* ARM iWMMXt Built-in Functions::
* ARM C Language Extensions (ACLE)::
* ARM Floating Point Status and Control Intrinsics::
* ARM ARMv8-M Security Extensions::
* AVR Built-in Functions::
* Blackfin Built-in Functions::
* BPF Built-in Functions::
* FR-V Built-in Functions::
* MIPS DSP Built-in Functions::
* MIPS Paired-Single Support::
* MIPS Loongson Built-in Functions::
* MIPS SIMD Architecture (MSA) Support::
* Other MIPS Built-in Functions::
* MSP430 Built-in Functions::
* NDS32 Built-in Functions::
* picoChip Built-in Functions::
* Basic PowerPC Built-in Functions::
* PowerPC AltiVec/VSX Built-in Functions::
* PowerPC Hardware Transactional Memory Built-in Functions::
* PowerPC Atomic Memory Operation Functions::
* PowerPC Matrix-Multiply Assist Built-in Functions::
* PRU Built-in Functions::
* RISC-V Built-in Functions::
* RX Built-in Functions::
* S/390 System z Built-in Functions::
* SH Built-in Functions::
* SPARC VIS Built-in Functions::
* TI C6X Built-in Functions::
* TILE-Gx Built-in Functions::
* TILEPro Built-in Functions::
* x86 Built-in Functions::
* x86 transactional memory intrinsics::
* x86 control-flow protection intrinsics::


File: gcc.info,  Node: AArch64 Built-in Functions,  Next: Alpha Built-in Functions,  Up: Target Builtins

6.60.1 AArch64 Built-in Functions
---------------------------------

These built-in functions are available for the AArch64 family of
processors.
     unsigned int __builtin_aarch64_get_fpcr ();
     void __builtin_aarch64_set_fpcr (unsigned int);
     unsigned int __builtin_aarch64_get_fpsr ();
     void __builtin_aarch64_set_fpsr (unsigned int);

     unsigned long long __builtin_aarch64_get_fpcr64 ();
     void __builtin_aarch64_set_fpcr64 (unsigned long long);
     unsigned long long __builtin_aarch64_get_fpsr64 ();
     void __builtin_aarch64_set_fpsr64 (unsigned long long);


File: gcc.info,  Node: Alpha Built-in Functions,  Next: Altera Nios II Built-in Functions,  Prev: AArch64 Built-in Functions,  Up: Target Builtins

6.60.2 Alpha Built-in Functions
-------------------------------

These built-in functions are available for the Alpha family of
processors, depending on the command-line switches used.

 The following built-in functions are always available.  They all
generate the machine instruction that is part of the name.

     long __builtin_alpha_implver (void);
     long __builtin_alpha_rpcc (void);
     long __builtin_alpha_amask (long);
     long __builtin_alpha_cmpbge (long, long);
     long __builtin_alpha_extbl (long, long);
     long __builtin_alpha_extwl (long, long);
     long __builtin_alpha_extll (long, long);
     long __builtin_alpha_extql (long, long);
     long __builtin_alpha_extwh (long, long);
     long __builtin_alpha_extlh (long, long);
     long __builtin_alpha_extqh (long, long);
     long __builtin_alpha_insbl (long, long);
     long __builtin_alpha_inswl (long, long);
     long __builtin_alpha_insll (long, long);
     long __builtin_alpha_insql (long, long);
     long __builtin_alpha_inswh (long, long);
     long __builtin_alpha_inslh (long, long);
     long __builtin_alpha_insqh (long, long);
     long __builtin_alpha_mskbl (long, long);
     long __builtin_alpha_mskwl (long, long);
     long __builtin_alpha_mskll (long, long);
     long __builtin_alpha_mskql (long, long);
     long __builtin_alpha_mskwh (long, long);
     long __builtin_alpha_msklh (long, long);
     long __builtin_alpha_mskqh (long, long);
     long __builtin_alpha_umulh (long, long);
     long __builtin_alpha_zap (long, long);
     long __builtin_alpha_zapnot (long, long);

 The following built-in functions are always with ‘-mmax’ or ‘-mcpu=CPU’
where CPU is ‘pca56’ or later.  They all generate the machine
instruction that is part of the name.

     long __builtin_alpha_pklb (long);
     long __builtin_alpha_pkwb (long);
     long __builtin_alpha_unpkbl (long);
     long __builtin_alpha_unpkbw (long);
     long __builtin_alpha_minub8 (long, long);
     long __builtin_alpha_minsb8 (long, long);
     long __builtin_alpha_minuw4 (long, long);
     long __builtin_alpha_minsw4 (long, long);
     long __builtin_alpha_maxub8 (long, long);
     long __builtin_alpha_maxsb8 (long, long);
     long __builtin_alpha_maxuw4 (long, long);
     long __builtin_alpha_maxsw4 (long, long);
     long __builtin_alpha_perr (long, long);

 The following built-in functions are always with ‘-mcix’ or ‘-mcpu=CPU’
where CPU is ‘ev67’ or later.  They all generate the machine instruction
that is part of the name.

     long __builtin_alpha_cttz (long);
     long __builtin_alpha_ctlz (long);
     long __builtin_alpha_ctpop (long);

 The following built-in functions are available on systems that use the
OSF/1 PALcode.  Normally they invoke the ‘rduniq’ and ‘wruniq’ PAL
calls, but when invoked with ‘-mtls-kernel’, they invoke ‘rdval’ and
‘wrval’.

     void *__builtin_thread_pointer (void);
     void __builtin_set_thread_pointer (void *);


File: gcc.info,  Node: Altera Nios II Built-in Functions,  Next: ARC Built-in Functions,  Prev: Alpha Built-in Functions,  Up: Target Builtins

6.60.3 Altera Nios II Built-in Functions
----------------------------------------

These built-in functions are available for the Altera Nios II family of
processors.

 The following built-in functions are always available.  They all
generate the machine instruction that is part of the name.

     int __builtin_ldbio (volatile const void *);
     int __builtin_ldbuio (volatile const void *);
     int __builtin_ldhio (volatile const void *);
     int __builtin_ldhuio (volatile const void *);
     int __builtin_ldwio (volatile const void *);
     void __builtin_stbio (volatile void *, int);
     void __builtin_sthio (volatile void *, int);
     void __builtin_stwio (volatile void *, int);
     void __builtin_sync (void);
     int __builtin_rdctl (int);
     int __builtin_rdprs (int, int);
     void __builtin_wrctl (int, int);
     void __builtin_flushd (volatile void *);
     void __builtin_flushda (volatile void *);
     int __builtin_wrpie (int);
     void __builtin_eni (int);
     int __builtin_ldex (volatile const void *);
     int __builtin_stex (volatile void *, int);
     int __builtin_ldsex (volatile const void *);
     int __builtin_stsex (volatile void *, int);

 The following built-in functions are always available.  They all
generate a Nios II Custom Instruction.  The name of the function
represents the types that the function takes and returns.  The letter
before the ‘n’ is the return type or void if absent.  The ‘n’ represents
the first parameter to all the custom instructions, the custom
instruction number.  The two letters after the ‘n’ represent the up to
two parameters to the function.

 The letters represent the following data types:
‘<no letter>’
     ‘void’ for return type and no parameter for parameter types.

‘i’
     ‘int’ for return type and parameter type

‘f’
     ‘float’ for return type and parameter type

‘p’
     ‘void *’ for return type and parameter type

 And the function names are:
     void __builtin_custom_n (void);
     void __builtin_custom_ni (int);
     void __builtin_custom_nf (float);
     void __builtin_custom_np (void *);
     void __builtin_custom_nii (int, int);
     void __builtin_custom_nif (int, float);
     void __builtin_custom_nip (int, void *);
     void __builtin_custom_nfi (float, int);
     void __builtin_custom_nff (float, float);
     void __builtin_custom_nfp (float, void *);
     void __builtin_custom_npi (void *, int);
     void __builtin_custom_npf (void *, float);
     void __builtin_custom_npp (void *, void *);
     int __builtin_custom_in (void);
     int __builtin_custom_ini (int);
     int __builtin_custom_inf (float);
     int __builtin_custom_inp (void *);
     int __builtin_custom_inii (int, int);
     int __builtin_custom_inif (int, float);
     int __builtin_custom_inip (int, void *);
     int __builtin_custom_infi (float, int);
     int __builtin_custom_inff (float, float);
     int __builtin_custom_infp (float, void *);
     int __builtin_custom_inpi (void *, int);
     int __builtin_custom_inpf (void *, float);
     int __builtin_custom_inpp (void *, void *);
     float __builtin_custom_fn (void);
     float __builtin_custom_fni (int);
     float __builtin_custom_fnf (float);
     float __builtin_custom_fnp (void *);
     float __builtin_custom_fnii (int, int);
     float __builtin_custom_fnif (int, float);
     float __builtin_custom_fnip (int, void *);
     float __builtin_custom_fnfi (float, int);
     float __builtin_custom_fnff (float, float);
     float __builtin_custom_fnfp (float, void *);
     float __builtin_custom_fnpi (void *, int);
     float __builtin_custom_fnpf (void *, float);
     float __builtin_custom_fnpp (void *, void *);
     void * __builtin_custom_pn (void);
     void * __builtin_custom_pni (int);
     void * __builtin_custom_pnf (float);
     void * __builtin_custom_pnp (void *);
     void * __builtin_custom_pnii (int, int);
     void * __builtin_custom_pnif (int, float);
     void * __builtin_custom_pnip (int, void *);
     void * __builtin_custom_pnfi (float, int);
     void * __builtin_custom_pnff (float, float);
     void * __builtin_custom_pnfp (float, void *);
     void * __builtin_custom_pnpi (void *, int);
     void * __builtin_custom_pnpf (void *, float);
     void * __builtin_custom_pnpp (void *, void *);


File: gcc.info,  Node: ARC Built-in Functions,  Next: ARC SIMD Built-in Functions,  Prev: Altera Nios II Built-in Functions,  Up: Target Builtins

6.60.4 ARC Built-in Functions
-----------------------------

The following built-in functions are provided for ARC targets.  The
built-ins generate the corresponding assembly instructions.  In the
examples given below, the generated code often requires an operand or
result to be in a register.  Where necessary further code will be
generated to ensure this is true, but for brevity this is not described
in each case.

 _Note:_ Using a built-in to generate an instruction not supported by a
target may cause problems.  At present the compiler is not guaranteed to
detect such misuse, and as a result an internal compiler error may be
generated.

 -- Built-in Function: int __builtin_arc_aligned (void *VAL, int
          ALIGNVAL)
     Return 1 if VAL is known to have the byte alignment given by
     ALIGNVAL, otherwise return 0.  Note that this is different from
          __alignof__(*(char *)VAL) >= alignval
     because __alignof__ sees only the type of the dereference, whereas
     __builtin_arc_align uses alignment information from the pointer as
     well as from the pointed-to type.  The information available will
     depend on optimization level.

 -- Built-in Function: void __builtin_arc_brk (void)
     Generates
          brk

 -- Built-in Function: unsigned int __builtin_arc_core_read (unsigned
          int REGNO)
     The operand is the number of a register to be read.  Generates:
          mov  DEST, rREGNO
     where the value in DEST will be the result returned from the
     built-in.

 -- Built-in Function: void __builtin_arc_core_write (unsigned int
          REGNO, unsigned int VAL)
     The first operand is the number of a register to be written, the
     second operand is a compile time constant to write into that
     register.  Generates:
          mov  rREGNO, VAL

 -- Built-in Function: int __builtin_arc_divaw (int A, int B)
     Only available if either ‘-mcpu=ARC700’ or ‘-meA’ is set.
     Generates:
          divaw  DEST, A, B
     where the value in DEST will be the result returned from the
     built-in.

 -- Built-in Function: void __builtin_arc_flag (unsigned int A)
     Generates
          flag  A

 -- Built-in Function: unsigned int __builtin_arc_lr (unsigned int AUXR)
     The operand, AUXV, is the address of an auxiliary register and must
     be a compile time constant.  Generates:
          lr  DEST, [AUXR]
     Where the value in DEST will be the result returned from the
     built-in.

 -- Built-in Function: void __builtin_arc_mul64 (int A, int B)
     Only available with ‘-mmul64’.  Generates:
          mul64  A, B

 -- Built-in Function: void __builtin_arc_mulu64 (unsigned int A,
          unsigned int B)
     Only available with ‘-mmul64’.  Generates:
          mulu64  A, B

 -- Built-in Function: void __builtin_arc_nop (void)
     Generates:
          nop

 -- Built-in Function: int __builtin_arc_norm (int SRC)
     Only valid if the ‘norm’ instruction is available through the
     ‘-mnorm’ option or by default with ‘-mcpu=ARC700’.  Generates:
          norm  DEST, SRC
     Where the value in DEST will be the result returned from the
     built-in.

 -- Built-in Function: short int __builtin_arc_normw (short int SRC)
     Only valid if the ‘normw’ instruction is available through the
     ‘-mnorm’ option or by default with ‘-mcpu=ARC700’.  Generates:
          normw  DEST, SRC
     Where the value in DEST will be the result returned from the
     built-in.

 -- Built-in Function: void __builtin_arc_rtie (void)
     Generates:
          rtie

 -- Built-in Function: void __builtin_arc_sleep (int A
     Generates:
          sleep  A

 -- Built-in Function: void __builtin_arc_sr (unsigned int VAL, unsigned
          int AUXR)
     The first argument, VAL, is a compile time constant to be written
     to the register, the second argument, AUXR, is the address of an
     auxiliary register.  Generates:
          sr  VAL, [AUXR]

 -- Built-in Function: int __builtin_arc_swap (int SRC)
     Only valid with ‘-mswap’.  Generates:
          swap  DEST, SRC
     Where the value in DEST will be the result returned from the
     built-in.

 -- Built-in Function: void __builtin_arc_swi (void)
     Generates:
          swi

 -- Built-in Function: void __builtin_arc_sync (void)
     Only available with ‘-mcpu=ARC700’.  Generates:
          sync

 -- Built-in Function: void __builtin_arc_trap_s (unsigned int C)
     Only available with ‘-mcpu=ARC700’.  Generates:
          trap_s  C

 -- Built-in Function: void __builtin_arc_unimp_s (void)
     Only available with ‘-mcpu=ARC700’.  Generates:
          unimp_s

 The instructions generated by the following builtins are not considered
as candidates for scheduling.  They are not moved around by the compiler
during scheduling, and thus can be expected to appear where they are put
in the C code:
     __builtin_arc_brk()
     __builtin_arc_core_read()
     __builtin_arc_core_write()
     __builtin_arc_flag()
     __builtin_arc_lr()
     __builtin_arc_sleep()
     __builtin_arc_sr()
     __builtin_arc_swi()


File: gcc.info,  Node: ARC SIMD Built-in Functions,  Next: ARM iWMMXt Built-in Functions,  Prev: ARC Built-in Functions,  Up: Target Builtins

6.60.5 ARC SIMD Built-in Functions
----------------------------------

SIMD builtins provided by the compiler can be used to generate the
vector instructions.  This section describes the available builtins and
their usage in programs.  With the ‘-msimd’ option, the compiler
provides 128-bit vector types, which can be specified using the
‘vector_size’ attribute.  The header file ‘arc-simd.h’ can be included
to use the following predefined types:
     typedef int __v4si   __attribute__((vector_size(16)));
     typedef short __v8hi __attribute__((vector_size(16)));

 These types can be used to define 128-bit variables.  The built-in
functions listed in the following section can be used on these variables
to generate the vector operations.

 For all builtins, ‘__builtin_arc_SOMEINSN’, the header file
‘arc-simd.h’ also provides equivalent macros called ‘_SOMEINSN’ that can
be used for programming ease and improved readability.  The following
macros for DMA control are also provided:
     #define _setup_dma_in_channel_reg _vdiwr
     #define _setup_dma_out_channel_reg _vdowr

 The following is a complete list of all the SIMD built-ins provided for
ARC, grouped by calling signature.

 The following take two ‘__v8hi’ arguments and return a ‘__v8hi’ result:
     __v8hi __builtin_arc_vaddaw (__v8hi, __v8hi);
     __v8hi __builtin_arc_vaddw (__v8hi, __v8hi);
     __v8hi __builtin_arc_vand (__v8hi, __v8hi);
     __v8hi __builtin_arc_vandaw (__v8hi, __v8hi);
     __v8hi __builtin_arc_vavb (__v8hi, __v8hi);
     __v8hi __builtin_arc_vavrb (__v8hi, __v8hi);
     __v8hi __builtin_arc_vbic (__v8hi, __v8hi);
     __v8hi __builtin_arc_vbicaw (__v8hi, __v8hi);
     __v8hi __builtin_arc_vdifaw (__v8hi, __v8hi);
     __v8hi __builtin_arc_vdifw (__v8hi, __v8hi);
     __v8hi __builtin_arc_veqw (__v8hi, __v8hi);
     __v8hi __builtin_arc_vh264f (__v8hi, __v8hi);
     __v8hi __builtin_arc_vh264ft (__v8hi, __v8hi);
     __v8hi __builtin_arc_vh264fw (__v8hi, __v8hi);
     __v8hi __builtin_arc_vlew (__v8hi, __v8hi);
     __v8hi __builtin_arc_vltw (__v8hi, __v8hi);
     __v8hi __builtin_arc_vmaxaw (__v8hi, __v8hi);
     __v8hi __builtin_arc_vmaxw (__v8hi, __v8hi);
     __v8hi __builtin_arc_vminaw (__v8hi, __v8hi);
     __v8hi __builtin_arc_vminw (__v8hi, __v8hi);
     __v8hi __builtin_arc_vmr1aw (__v8hi, __v8hi);
     __v8hi __builtin_arc_vmr1w (__v8hi, __v8hi);
     __v8hi __builtin_arc_vmr2aw (__v8hi, __v8hi);
     __v8hi __builtin_arc_vmr2w (__v8hi, __v8hi);
     __v8hi __builtin_arc_vmr3aw (__v8hi, __v8hi);
     __v8hi __builtin_arc_vmr3w (__v8hi, __v8hi);
     __v8hi __builtin_arc_vmr4aw (__v8hi, __v8hi);
     __v8hi __builtin_arc_vmr4w (__v8hi, __v8hi);
     __v8hi __builtin_arc_vmr5aw (__v8hi, __v8hi);
     __v8hi __builtin_arc_vmr5w (__v8hi, __v8hi);
     __v8hi __builtin_arc_vmr6aw (__v8hi, __v8hi);
     __v8hi __builtin_arc_vmr6w (__v8hi, __v8hi);
     __v8hi __builtin_arc_vmr7aw (__v8hi, __v8hi);
     __v8hi __builtin_arc_vmr7w (__v8hi, __v8hi);
     __v8hi __builtin_arc_vmrb (__v8hi, __v8hi);
     __v8hi __builtin_arc_vmulaw (__v8hi, __v8hi);
     __v8hi __builtin_arc_vmulfaw (__v8hi, __v8hi);
     __v8hi __builtin_arc_vmulfw (__v8hi, __v8hi);
     __v8hi __builtin_arc_vmulw (__v8hi, __v8hi);
     __v8hi __builtin_arc_vnew (__v8hi, __v8hi);
     __v8hi __builtin_arc_vor (__v8hi, __v8hi);
     __v8hi __builtin_arc_vsubaw (__v8hi, __v8hi);
     __v8hi __builtin_arc_vsubw (__v8hi, __v8hi);
     __v8hi __builtin_arc_vsummw (__v8hi, __v8hi);
     __v8hi __builtin_arc_vvc1f (__v8hi, __v8hi);
     __v8hi __builtin_arc_vvc1ft (__v8hi, __v8hi);
     __v8hi __builtin_arc_vxor (__v8hi, __v8hi);
     __v8hi __builtin_arc_vxoraw (__v8hi, __v8hi);

 The following take one ‘__v8hi’ and one ‘int’ argument and return a
‘__v8hi’ result:

     __v8hi __builtin_arc_vbaddw (__v8hi, int);
     __v8hi __builtin_arc_vbmaxw (__v8hi, int);
     __v8hi __builtin_arc_vbminw (__v8hi, int);
     __v8hi __builtin_arc_vbmulaw (__v8hi, int);
     __v8hi __builtin_arc_vbmulfw (__v8hi, int);
     __v8hi __builtin_arc_vbmulw (__v8hi, int);
     __v8hi __builtin_arc_vbrsubw (__v8hi, int);
     __v8hi __builtin_arc_vbsubw (__v8hi, int);

 The following take one ‘__v8hi’ argument and one ‘int’ argument which
must be a 3-bit compile time constant indicating a register number
I0-I7.  They return a ‘__v8hi’ result.
     __v8hi __builtin_arc_vasrw (__v8hi, const int);
     __v8hi __builtin_arc_vsr8 (__v8hi, const int);
     __v8hi __builtin_arc_vsr8aw (__v8hi, const int);

 The following take one ‘__v8hi’ argument and one ‘int’ argument which
must be a 6-bit compile time constant.  They return a ‘__v8hi’ result.
     __v8hi __builtin_arc_vasrpwbi (__v8hi, const int);
     __v8hi __builtin_arc_vasrrpwbi (__v8hi, const int);
     __v8hi __builtin_arc_vasrrwi (__v8hi, const int);
     __v8hi __builtin_arc_vasrsrwi (__v8hi, const int);
     __v8hi __builtin_arc_vasrwi (__v8hi, const int);
     __v8hi __builtin_arc_vsr8awi (__v8hi, const int);
     __v8hi __builtin_arc_vsr8i (__v8hi, const int);

 The following take one ‘__v8hi’ argument and one ‘int’ argument which
must be a 8-bit compile time constant.  They return a ‘__v8hi’ result.
     __v8hi __builtin_arc_vd6tapf (__v8hi, const int);
     __v8hi __builtin_arc_vmvaw (__v8hi, const int);
     __v8hi __builtin_arc_vmvw (__v8hi, const int);
     __v8hi __builtin_arc_vmvzw (__v8hi, const int);

 The following take two ‘int’ arguments, the second of which which must
be a 8-bit compile time constant.  They return a ‘__v8hi’ result:
     __v8hi __builtin_arc_vmovaw (int, const int);
     __v8hi __builtin_arc_vmovw (int, const int);
     __v8hi __builtin_arc_vmovzw (int, const int);

 The following take a single ‘__v8hi’ argument and return a ‘__v8hi’
result:
     __v8hi __builtin_arc_vabsaw (__v8hi);
     __v8hi __builtin_arc_vabsw (__v8hi);
     __v8hi __builtin_arc_vaddsuw (__v8hi);
     __v8hi __builtin_arc_vexch1 (__v8hi);
     __v8hi __builtin_arc_vexch2 (__v8hi);
     __v8hi __builtin_arc_vexch4 (__v8hi);
     __v8hi __builtin_arc_vsignw (__v8hi);
     __v8hi __builtin_arc_vupbaw (__v8hi);
     __v8hi __builtin_arc_vupbw (__v8hi);
     __v8hi __builtin_arc_vupsbaw (__v8hi);
     __v8hi __builtin_arc_vupsbw (__v8hi);

 The following take two ‘int’ arguments and return no result:
     void __builtin_arc_vdirun (int, int);
     void __builtin_arc_vdorun (int, int);

 The following take two ‘int’ arguments and return no result.  The first
argument must a 3-bit compile time constant indicating one of the
DR0-DR7 DMA setup channels:
     void __builtin_arc_vdiwr (const int, int);
     void __builtin_arc_vdowr (const int, int);

 The following take an ‘int’ argument and return no result:
     void __builtin_arc_vendrec (int);
     void __builtin_arc_vrec (int);
     void __builtin_arc_vrecrun (int);
     void __builtin_arc_vrun (int);

 The following take a ‘__v8hi’ argument and two ‘int’ arguments and
return a ‘__v8hi’ result.  The second argument must be a 3-bit compile
time constants, indicating one the registers I0-I7, and the third
argument must be an 8-bit compile time constant.

 _Note:_ Although the equivalent hardware instructions do not take an
SIMD register as an operand, these builtins overwrite the relevant bits
of the ‘__v8hi’ register provided as the first argument with the value
loaded from the ‘[Ib, u8]’ location in the SDM.

     __v8hi __builtin_arc_vld32 (__v8hi, const int, const int);
     __v8hi __builtin_arc_vld32wh (__v8hi, const int, const int);
     __v8hi __builtin_arc_vld32wl (__v8hi, const int, const int);
     __v8hi __builtin_arc_vld64 (__v8hi, const int, const int);

 The following take two ‘int’ arguments and return a ‘__v8hi’ result.
The first argument must be a 3-bit compile time constants, indicating
one the registers I0-I7, and the second argument must be an 8-bit
compile time constant.

     __v8hi __builtin_arc_vld128 (const int, const int);
     __v8hi __builtin_arc_vld64w (const int, const int);

 The following take a ‘__v8hi’ argument and two ‘int’ arguments and
return no result.  The second argument must be a 3-bit compile time
constants, indicating one the registers I0-I7, and the third argument
must be an 8-bit compile time constant.

     void __builtin_arc_vst128 (__v8hi, const int, const int);
     void __builtin_arc_vst64 (__v8hi, const int, const int);

 The following take a ‘__v8hi’ argument and three ‘int’ arguments and
return no result.  The second argument must be a 3-bit compile-time
constant, identifying the 16-bit sub-register to be stored, the third
argument must be a 3-bit compile time constants, indicating one the
registers I0-I7, and the fourth argument must be an 8-bit compile time
constant.

     void __builtin_arc_vst16_n (__v8hi, const int, const int, const int);
     void __builtin_arc_vst32_n (__v8hi, const int, const int, const int);


File: gcc.info,  Node: ARM iWMMXt Built-in Functions,  Next: ARM C Language Extensions (ACLE),  Prev: ARC SIMD Built-in Functions,  Up: Target Builtins

6.60.6 ARM iWMMXt Built-in Functions
------------------------------------

These built-in functions are available for the ARM family of processors
when the ‘-mcpu=iwmmxt’ switch is used:

     typedef int v2si __attribute__ ((vector_size (8)));
     typedef short v4hi __attribute__ ((vector_size (8)));
     typedef char v8qi __attribute__ ((vector_size (8)));

     int __builtin_arm_getwcgr0 (void);
     void __builtin_arm_setwcgr0 (int);
     int __builtin_arm_getwcgr1 (void);
     void __builtin_arm_setwcgr1 (int);
     int __builtin_arm_getwcgr2 (void);
     void __builtin_arm_setwcgr2 (int);
     int __builtin_arm_getwcgr3 (void);
     void __builtin_arm_setwcgr3 (int);
     int __builtin_arm_textrmsb (v8qi, int);
     int __builtin_arm_textrmsh (v4hi, int);
     int __builtin_arm_textrmsw (v2si, int);
     int __builtin_arm_textrmub (v8qi, int);
     int __builtin_arm_textrmuh (v4hi, int);
     int __builtin_arm_textrmuw (v2si, int);
     v8qi __builtin_arm_tinsrb (v8qi, int, int);
     v4hi __builtin_arm_tinsrh (v4hi, int, int);
     v2si __builtin_arm_tinsrw (v2si, int, int);
     long long __builtin_arm_tmia (long long, int, int);
     long long __builtin_arm_tmiabb (long long, int, int);
     long long __builtin_arm_tmiabt (long long, int, int);
     long long __builtin_arm_tmiaph (long long, int, int);
     long long __builtin_arm_tmiatb (long long, int, int);
     long long __builtin_arm_tmiatt (long long, int, int);
     int __builtin_arm_tmovmskb (v8qi);
     int __builtin_arm_tmovmskh (v4hi);
     int __builtin_arm_tmovmskw (v2si);
     long long __builtin_arm_waccb (v8qi);
     long long __builtin_arm_wacch (v4hi);
     long long __builtin_arm_waccw (v2si);
     v8qi __builtin_arm_waddb (v8qi, v8qi);
     v8qi __builtin_arm_waddbss (v8qi, v8qi);
     v8qi __builtin_arm_waddbus (v8qi, v8qi);
     v4hi __builtin_arm_waddh (v4hi, v4hi);
     v4hi __builtin_arm_waddhss (v4hi, v4hi);
     v4hi __builtin_arm_waddhus (v4hi, v4hi);
     v2si __builtin_arm_waddw (v2si, v2si);
     v2si __builtin_arm_waddwss (v2si, v2si);
     v2si __builtin_arm_waddwus (v2si, v2si);
     v8qi __builtin_arm_walign (v8qi, v8qi, int);
     long long __builtin_arm_wand(long long, long long);
     long long __builtin_arm_wandn (long long, long long);
     v8qi __builtin_arm_wavg2b (v8qi, v8qi);
     v8qi __builtin_arm_wavg2br (v8qi, v8qi);
     v4hi __builtin_arm_wavg2h (v4hi, v4hi);
     v4hi __builtin_arm_wavg2hr (v4hi, v4hi);
     v8qi __builtin_arm_wcmpeqb (v8qi, v8qi);
     v4hi __builtin_arm_wcmpeqh (v4hi, v4hi);
     v2si __builtin_arm_wcmpeqw (v2si, v2si);
     v8qi __builtin_arm_wcmpgtsb (v8qi, v8qi);
     v4hi __builtin_arm_wcmpgtsh (v4hi, v4hi);
     v2si __builtin_arm_wcmpgtsw (v2si, v2si);
     v8qi __builtin_arm_wcmpgtub (v8qi, v8qi);
     v4hi __builtin_arm_wcmpgtuh (v4hi, v4hi);
     v2si __builtin_arm_wcmpgtuw (v2si, v2si);
     long long __builtin_arm_wmacs (long long, v4hi, v4hi);
     long long __builtin_arm_wmacsz (v4hi, v4hi);
     long long __builtin_arm_wmacu (long long, v4hi, v4hi);
     long long __builtin_arm_wmacuz (v4hi, v4hi);
     v4hi __builtin_arm_wmadds (v4hi, v4hi);
     v4hi __builtin_arm_wmaddu (v4hi, v4hi);
     v8qi __builtin_arm_wmaxsb (v8qi, v8qi);
     v4hi __builtin_arm_wmaxsh (v4hi, v4hi);
     v2si __builtin_arm_wmaxsw (v2si, v2si);
     v8qi __builtin_arm_wmaxub (v8qi, v8qi);
     v4hi __builtin_arm_wmaxuh (v4hi, v4hi);
     v2si __builtin_arm_wmaxuw (v2si, v2si);
     v8qi __builtin_arm_wminsb (v8qi, v8qi);
     v4hi __builtin_arm_wminsh (v4hi, v4hi);
     v2si __builtin_arm_wminsw (v2si, v2si);
     v8qi __builtin_arm_wminub (v8qi, v8qi);
     v4hi __builtin_arm_wminuh (v4hi, v4hi);
     v2si __builtin_arm_wminuw (v2si, v2si);
     v4hi __builtin_arm_wmulsm (v4hi, v4hi);
     v4hi __builtin_arm_wmulul (v4hi, v4hi);
     v4hi __builtin_arm_wmulum (v4hi, v4hi);
     long long __builtin_arm_wor (long long, long long);
     v2si __builtin_arm_wpackdss (long long, long long);
     v2si __builtin_arm_wpackdus (long long, long long);
     v8qi __builtin_arm_wpackhss (v4hi, v4hi);
     v8qi __builtin_arm_wpackhus (v4hi, v4hi);
     v4hi __builtin_arm_wpackwss (v2si, v2si);
     v4hi __builtin_arm_wpackwus (v2si, v2si);
     long long __builtin_arm_wrord (long long, long long);
     long long __builtin_arm_wrordi (long long, int);
     v4hi __builtin_arm_wrorh (v4hi, long long);
     v4hi __builtin_arm_wrorhi (v4hi, int);
     v2si __builtin_arm_wrorw (v2si, long long);
     v2si __builtin_arm_wrorwi (v2si, int);
     v2si __builtin_arm_wsadb (v2si, v8qi, v8qi);
     v2si __builtin_arm_wsadbz (v8qi, v8qi);
     v2si __builtin_arm_wsadh (v2si, v4hi, v4hi);
     v2si __builtin_arm_wsadhz (v4hi, v4hi);
     v4hi __builtin_arm_wshufh (v4hi, int);
     long long __builtin_arm_wslld (long long, long long);
     long long __builtin_arm_wslldi (long long, int);
     v4hi __builtin_arm_wsllh (v4hi, long long);
     v4hi __builtin_arm_wsllhi (v4hi, int);
     v2si __builtin_arm_wsllw (v2si, long long);
     v2si __builtin_arm_wsllwi (v2si, int);
     long long __builtin_arm_wsrad (long long, long long);
     long long __builtin_arm_wsradi (long long, int);
     v4hi __builtin_arm_wsrah (v4hi, long long);
     v4hi __builtin_arm_wsrahi (v4hi, int);
     v2si __builtin_arm_wsraw (v2si, long long);
     v2si __builtin_arm_wsrawi (v2si, int);
     long long __builtin_arm_wsrld (long long, long long);
     long long __builtin_arm_wsrldi (long long, int);
     v4hi __builtin_arm_wsrlh (v4hi, long long);
     v4hi __builtin_arm_wsrlhi (v4hi, int);
     v2si __builtin_arm_wsrlw (v2si, long long);
     v2si __builtin_arm_wsrlwi (v2si, int);
     v8qi __builtin_arm_wsubb (v8qi, v8qi);
     v8qi __builtin_arm_wsubbss (v8qi, v8qi);
     v8qi __builtin_arm_wsubbus (v8qi, v8qi);
     v4hi __builtin_arm_wsubh (v4hi, v4hi);
     v4hi __builtin_arm_wsubhss (v4hi, v4hi);
     v4hi __builtin_arm_wsubhus (v4hi, v4hi);
     v2si __builtin_arm_wsubw (v2si, v2si);
     v2si __builtin_arm_wsubwss (v2si, v2si);
     v2si __builtin_arm_wsubwus (v2si, v2si);
     v4hi __builtin_arm_wunpckehsb (v8qi);
     v2si __builtin_arm_wunpckehsh (v4hi);
     long long __builtin_arm_wunpckehsw (v2si);
     v4hi __builtin_arm_wunpckehub (v8qi);
     v2si __builtin_arm_wunpckehuh (v4hi);
     long long __builtin_arm_wunpckehuw (v2si);
     v4hi __builtin_arm_wunpckelsb (v8qi);
     v2si __builtin_arm_wunpckelsh (v4hi);
     long long __builtin_arm_wunpckelsw (v2si);
     v4hi __builtin_arm_wunpckelub (v8qi);
     v2si __builtin_arm_wunpckeluh (v4hi);
     long long __builtin_arm_wunpckeluw (v2si);
     v8qi __builtin_arm_wunpckihb (v8qi, v8qi);
     v4hi __builtin_arm_wunpckihh (v4hi, v4hi);
     v2si __builtin_arm_wunpckihw (v2si, v2si);
     v8qi __builtin_arm_wunpckilb (v8qi, v8qi);
     v4hi __builtin_arm_wunpckilh (v4hi, v4hi);
     v2si __builtin_arm_wunpckilw (v2si, v2si);
     long long __builtin_arm_wxor (long long, long long);
     long long __builtin_arm_wzero ();


File: gcc.info,  Node: ARM C Language Extensions (ACLE),  Next: ARM Floating Point Status and Control Intrinsics,  Prev: ARM iWMMXt Built-in Functions,  Up: Target Builtins

6.60.7 ARM C Language Extensions (ACLE)
---------------------------------------

GCC implements extensions for C as described in the ARM C Language
Extensions (ACLE) specification, which can be found at
<https://developer.arm.com/documentation/ihi0053/latest/>.

 As a part of ACLE, GCC implements extensions for Advanced SIMD as
described in the ARM C Language Extensions Specification.  The complete
list of Advanced SIMD intrinsics can be found at
<https://developer.arm.com/documentation/ihi0073/latest/>.  The built-in
intrinsics for the Advanced SIMD extension are available when NEON is
enabled.

 Currently, ARM and AArch64 back ends do not support ACLE 2.0 fully.
Both back ends support CRC32 intrinsics and the ARM back end supports
the Coprocessor intrinsics, all from ‘arm_acle.h’.  The ARM back end's
16-bit floating-point Advanced SIMD intrinsics currently comply to ACLE
v1.1.  AArch64's back end does not have support for 16-bit floating
point Advanced SIMD intrinsics yet.

 See *note ARM Options:: and *note AArch64 Options:: for more
information on the availability of extensions.


File: gcc.info,  Node: ARM Floating Point Status and Control Intrinsics,  Next: ARM ARMv8-M Security Extensions,  Prev: ARM C Language Extensions (ACLE),  Up: Target Builtins

6.60.8 ARM Floating Point Status and Control Intrinsics
-------------------------------------------------------

These built-in functions are available for the ARM family of processors
with floating-point unit.

     unsigned int __builtin_arm_get_fpscr ();
     void __builtin_arm_set_fpscr (unsigned int);


File: gcc.info,  Node: ARM ARMv8-M Security Extensions,  Next: AVR Built-in Functions,  Prev: ARM Floating Point Status and Control Intrinsics,  Up: Target Builtins

6.60.9 ARM ARMv8-M Security Extensions
--------------------------------------

GCC implements the ARMv8-M Security Extensions as described in the
ARMv8-M Security Extensions: Requirements on Development Tools
Engineering Specification, which can be found at
<https://developer.arm.com/documentation/ecm0359818/latest/>.

 As part of the Security Extensions GCC implements two new function
attributes: ‘cmse_nonsecure_entry’ and ‘cmse_nonsecure_call’.

 As part of the Security Extensions GCC implements the intrinsics below.
FPTR is used here to mean any function pointer type.

     cmse_address_info_t cmse_TT (void *);
     cmse_address_info_t cmse_TT_fptr (FPTR);
     cmse_address_info_t cmse_TTT (void *);
     cmse_address_info_t cmse_TTT_fptr (FPTR);
     cmse_address_info_t cmse_TTA (void *);
     cmse_address_info_t cmse_TTA_fptr (FPTR);
     cmse_address_info_t cmse_TTAT (void *);
     cmse_address_info_t cmse_TTAT_fptr (FPTR);
     void * cmse_check_address_range (void *, size_t, int);
     typeof(p) cmse_nsfptr_create (FPTR p);
     intptr_t cmse_is_nsfptr (FPTR);
     int cmse_nonsecure_caller (void);


File: gcc.info,  Node: AVR Built-in Functions,  Next: Blackfin Built-in Functions,  Prev: ARM ARMv8-M Security Extensions,  Up: Target Builtins

6.60.10 AVR Built-in Functions
------------------------------

For each built-in function for AVR, there is an equally named, uppercase
built-in macro defined.  That way users can easily query if or if not a
specific built-in is implemented or not.  For example, if
‘__builtin_avr_nop’ is available the macro ‘__BUILTIN_AVR_NOP’ is
defined to ‘1’ and undefined otherwise.

‘void __builtin_avr_nop (void)’
‘void __builtin_avr_sei (void)’
‘void __builtin_avr_cli (void)’
‘void __builtin_avr_sleep (void)’
‘void __builtin_avr_wdr (void)’
‘unsigned char __builtin_avr_swap (unsigned char)’
‘unsigned int __builtin_avr_fmul (unsigned char, unsigned char)’
‘int __builtin_avr_fmuls (char, char)’
‘int __builtin_avr_fmulsu (char, unsigned char)’
     These built-in functions map to the respective machine instruction,
     i.e. ‘nop’, ‘sei’, ‘cli’, ‘sleep’, ‘wdr’, ‘swap’, ‘fmul’, ‘fmuls’
     resp.  ‘fmulsu’.  The three ‘fmul*’ built-ins are implemented as
     library call if no hardware multiplier is available.

‘void __builtin_avr_delay_cycles (unsigned long ticks)’
     Delay execution for TICKS cycles.  Note that this built-in does not
     take into account the effect of interrupts that might increase
     delay time.  TICKS must be a compile-time integer constant; delays
     with a variable number of cycles are not supported.

‘char __builtin_avr_flash_segment (const __memx void*)’
     This built-in takes a byte address to the 24-bit *note address
     space: AVR Named Address Spaces. ‘__memx’ and returns the number of
     the flash segment (the 64 KiB chunk) where the address points to.
     Counting starts at ‘0’.  If the address does not point to flash
     memory, return ‘-1’.

‘uint8_t __builtin_avr_insert_bits (uint32_t map, uint8_t bits, uint8_t val)’
     Insert bits from BITS into VAL and return the resulting value.  The
     nibbles of MAP determine how the insertion is performed: Let X be
     the N-th nibble of MAP
       1. If X is ‘0xf’, then the N-th bit of VAL is returned unaltered.

       2. If X is in the range 0...7, then the N-th result bit is set to
          the X-th bit of BITS

       3. If X is in the range 8...‘0xe’, then the N-th result bit is
          undefined.

     One typical use case for this built-in is adjusting input and
     output values to non-contiguous port layouts.  Some examples:

          // same as val, bits is unused
          __builtin_avr_insert_bits (0xffffffff, bits, val);

          // same as bits, val is unused
          __builtin_avr_insert_bits (0x76543210, bits, val);

          // same as rotating bits by 4
          __builtin_avr_insert_bits (0x32107654, bits, 0);

          // high nibble of result is the high nibble of val
          // low nibble of result is the low nibble of bits
          __builtin_avr_insert_bits (0xffff3210, bits, val);

          // reverse the bit order of bits
          __builtin_avr_insert_bits (0x01234567, bits, 0);

‘void __builtin_avr_nops (unsigned count)’
     Insert COUNT ‘NOP’ instructions.  The number of instructions must
     be a compile-time integer constant.

There are many more AVR-specific built-in functions that are used to
implement the ISO/IEC TR 18037 "Embedded C" fixed-point functions of
section 7.18a.6.  You don't need to use these built-ins directly.
Instead, use the declarations as supplied by the ‘stdfix.h’ header with
GNU-C99:

     #include <stdfix.h>

     // Re-interpret the bit representation of unsigned 16-bit
     // integer UVAL as Q-format 0.16 value.
     unsigned fract get_bits (uint_ur_t uval)
     {
         return urbits (uval);
     }


File: gcc.info,  Node: Blackfin Built-in Functions,  Next: BPF Built-in Functions,  Prev: AVR Built-in Functions,  Up: Target Builtins

6.60.11 Blackfin Built-in Functions
-----------------------------------

Currently, there are two Blackfin-specific built-in functions.  These
are used for generating ‘CSYNC’ and ‘SSYNC’ machine insns without using
inline assembly; by using these built-in functions the compiler can
automatically add workarounds for hardware errata involving these
instructions.  These functions are named as follows:

     void __builtin_bfin_csync (void);
     void __builtin_bfin_ssync (void);


File: gcc.info,  Node: BPF Built-in Functions,  Next: FR-V Built-in Functions,  Prev: Blackfin Built-in Functions,  Up: Target Builtins

6.60.12 BPF Built-in Functions
------------------------------

The following built-in functions are available for eBPF targets.

 -- Built-in Function: unsigned long long __builtin_bpf_load_byte
          (unsigned long long OFFSET)
     Load a byte from the ‘struct sk_buff’ packet data pointed by the
     register ‘%r6’ and return it.

 -- Built-in Function: unsigned long long __builtin_bpf_load_half
          (unsigned long long OFFSET)
     Load 16-bits from the ‘struct sk_buff’ packet data pointed by the
     register ‘%r6’ and return it.

 -- Built-in Function: unsigned long long __builtin_bpf_load_word
          (unsigned long long OFFSET)
     Load 32-bits from the ‘struct sk_buff’ packet data pointed by the
     register ‘%r6’ and return it.

 -- Built-in Function: void * __builtin_preserve_access_index (EXPR)
     BPF Compile Once-Run Everywhere (CO-RE) support.  Instruct GCC to
     generate CO-RE relocation records for any accesses to aggregate
     data structures (struct, union, array types) in EXPR.  This builtin
     is otherwise transparent, the return value is whatever EXPR
     evaluates to.  It is also overloaded: EXPR may be of any type (not
     necessarily a pointer), the return type is the same.  Has no effect
     if ‘-mco-re’ is not in effect (either specified or implied).


File: gcc.info,  Node: FR-V Built-in Functions,  Next: MIPS DSP Built-in Functions,  Prev: BPF Built-in Functions,  Up: Target Builtins

6.60.13 FR-V Built-in Functions
-------------------------------

GCC provides many FR-V-specific built-in functions.  In general, these
functions are intended to be compatible with those described by ‘FR-V
Family, Softune C/C++ Compiler Manual (V6), Fujitsu Semiconductor’.  The
two exceptions are ‘__MDUNPACKH’ and ‘__MBTOHE’, the GCC forms of which
pass 128-bit values by pointer rather than by value.

 Most of the functions are named after specific FR-V instructions.  Such
functions are said to be "directly mapped" and are summarized here in
tabular form.

* Menu:

* Argument Types::
* Directly-mapped Integer Functions::
* Directly-mapped Media Functions::
* Raw read/write Functions::
* Other Built-in Functions::


File: gcc.info,  Node: Argument Types,  Next: Directly-mapped Integer Functions,  Up: FR-V Built-in Functions

6.60.13.1 Argument Types
........................

The arguments to the built-in functions can be divided into three
groups: register numbers, compile-time constants and run-time values.
In order to make this classification clear at a glance, the arguments
and return values are given the following pseudo types:

Pseudo type    Real C type            Constant?   Description
----------------------------------------------------------------------------
‘uh’           ‘unsigned short’       No          an unsigned halfword
‘uw1’          ‘unsigned int’         No          an unsigned word
‘sw1’          ‘int’                  No          a signed word
‘uw2’          ‘unsigned long long’   No          an unsigned doubleword
‘sw2’          ‘long long’            No          a signed doubleword
‘const’        ‘int’                  Yes         an integer constant
‘acc’          ‘int’                  Yes         an ACC register number
‘iacc’         ‘int’                  Yes         an IACC register number

 These pseudo types are not defined by GCC, they are simply a notational
convenience used in this manual.

 Arguments of type ‘uh’, ‘uw1’, ‘sw1’, ‘uw2’ and ‘sw2’ are evaluated at
run time.  They correspond to register operands in the underlying FR-V
instructions.

 ‘const’ arguments represent immediate operands in the underlying FR-V
instructions.  They must be compile-time constants.

 ‘acc’ arguments are evaluated at compile time and specify the number of
an accumulator register.  For example, an ‘acc’ argument of 2 selects
the ACC2 register.

 ‘iacc’ arguments are similar to ‘acc’ arguments but specify the number
of an IACC register.  See *note Other Built-in Functions:: for more
details.


File: gcc.info,  Node: Directly-mapped Integer Functions,  Next: Directly-mapped Media Functions,  Prev: Argument Types,  Up: FR-V Built-in Functions

6.60.13.2 Directly-Mapped Integer Functions
...........................................

The functions listed below map directly to FR-V I-type instructions.

Function prototype               Example usage           Assembly output
---------------------------------------------------------------------------
‘sw1 __ADDSS (sw1, sw1)’         ‘C = __ADDSS (A, B)’    ‘ADDSS A,B,C’
‘sw1 __SCAN (sw1, sw1)’          ‘C = __SCAN (A, B)’     ‘SCAN A,B,C’
‘sw1 __SCUTSS (sw1)’             ‘B = __SCUTSS (A)’      ‘SCUTSS A,B’
‘sw1 __SLASS (sw1, sw1)’         ‘C = __SLASS (A, B)’    ‘SLASS A,B,C’
‘void __SMASS (sw1, sw1)’        ‘__SMASS (A, B)’        ‘SMASS A,B’
‘void __SMSSS (sw1, sw1)’        ‘__SMSSS (A, B)’        ‘SMSSS A,B’
‘void __SMU (sw1, sw1)’          ‘__SMU (A, B)’          ‘SMU A,B’
‘sw2 __SMUL (sw1, sw1)’          ‘C = __SMUL (A, B)’     ‘SMUL A,B,C’
‘sw1 __SUBSS (sw1, sw1)’         ‘C = __SUBSS (A, B)’    ‘SUBSS A,B,C’
‘uw2 __UMUL (uw1, uw1)’          ‘C = __UMUL (A, B)’     ‘UMUL A,B,C’


File: gcc.info,  Node: Directly-mapped Media Functions,  Next: Raw read/write Functions,  Prev: Directly-mapped Integer Functions,  Up: FR-V Built-in Functions

6.60.13.3 Directly-Mapped Media Functions
.........................................

The functions listed below map directly to FR-V M-type instructions.

Function prototype               Example usage           Assembly output
---------------------------------------------------------------------------
‘uw1 __MABSHS (sw1)’             ‘B = __MABSHS (A)’      ‘MABSHS A,B’
‘void __MADDACCS (acc, acc)’     ‘__MADDACCS (B, A)’     ‘MADDACCS A,B’
‘sw1 __MADDHSS (sw1, sw1)’       ‘C = __MADDHSS (A,      ‘MADDHSS A,B,C’
                                 B)’
‘uw1 __MADDHUS (uw1, uw1)’       ‘C = __MADDHUS (A,      ‘MADDHUS A,B,C’
                                 B)’
‘uw1 __MAND (uw1, uw1)’          ‘C = __MAND (A, B)’     ‘MAND A,B,C’
‘void __MASACCS (acc, acc)’      ‘__MASACCS (B, A)’      ‘MASACCS A,B’
‘uw1 __MAVEH (uw1, uw1)’         ‘C = __MAVEH (A, B)’    ‘MAVEH A,B,C’
‘uw2 __MBTOH (uw1)’              ‘B = __MBTOH (A)’       ‘MBTOH A,B’
‘void __MBTOHE (uw1 *, uw1)’     ‘__MBTOHE (&B, A)’      ‘MBTOHE A,B’
‘void __MCLRACC (acc)’           ‘__MCLRACC (A)’         ‘MCLRACC A’
‘void __MCLRACCA (void)’         ‘__MCLRACCA ()’         ‘MCLRACCA’
‘uw1 __Mcop1 (uw1, uw1)’         ‘C = __Mcop1 (A, B)’    ‘Mcop1 A,B,C’
‘uw1 __Mcop2 (uw1, uw1)’         ‘C = __Mcop2 (A, B)’    ‘Mcop2 A,B,C’
‘uw1 __MCPLHI (uw2, const)’      ‘C = __MCPLHI (A, B)’   ‘MCPLHI A,#B,C’
‘uw1 __MCPLI (uw2, const)’       ‘C = __MCPLI (A, B)’    ‘MCPLI A,#B,C’
‘void __MCPXIS (acc, sw1,        ‘__MCPXIS (C, A, B)’    ‘MCPXIS A,B,C’
sw1)’
‘void __MCPXIU (acc, uw1,        ‘__MCPXIU (C, A, B)’    ‘MCPXIU A,B,C’
uw1)’
‘void __MCPXRS (acc, sw1,        ‘__MCPXRS (C, A, B)’    ‘MCPXRS A,B,C’
sw1)’
‘void __MCPXRU (acc, uw1,        ‘__MCPXRU (C, A, B)’    ‘MCPXRU A,B,C’
uw1)’
‘uw1 __MCUT (acc, uw1)’          ‘C = __MCUT (A, B)’     ‘MCUT A,B,C’
‘uw1 __MCUTSS (acc, sw1)’        ‘C = __MCUTSS (A, B)’   ‘MCUTSS A,B,C’
‘void __MDADDACCS (acc, acc)’    ‘__MDADDACCS (B, A)’    ‘MDADDACCS A,B’
‘void __MDASACCS (acc, acc)’     ‘__MDASACCS (B, A)’     ‘MDASACCS A,B’
‘uw2 __MDCUTSSI (acc, const)’    ‘C = __MDCUTSSI (A,     ‘MDCUTSSI
                                 B)’                     A,#B,C’
‘uw2 __MDPACKH (uw2, uw2)’       ‘C = __MDPACKH (A,      ‘MDPACKH A,B,C’
                                 B)’
‘uw2 __MDROTLI (uw2, const)’     ‘C = __MDROTLI (A,      ‘MDROTLI
                                 B)’                     A,#B,C’
‘void __MDSUBACCS (acc, acc)’    ‘__MDSUBACCS (B, A)’    ‘MDSUBACCS A,B’
‘void __MDUNPACKH (uw1 *,        ‘__MDUNPACKH (&B, A)’   ‘MDUNPACKH A,B’
uw2)’
‘uw2 __MEXPDHD (uw1, const)’     ‘C = __MEXPDHD (A,      ‘MEXPDHD
                                 B)’                     A,#B,C’
‘uw1 __MEXPDHW (uw1, const)’     ‘C = __MEXPDHW (A,      ‘MEXPDHW
                                 B)’                     A,#B,C’
‘uw1 __MHDSETH (uw1, const)’     ‘C = __MHDSETH (A,      ‘MHDSETH
                                 B)’                     A,#B,C’
‘sw1 __MHDSETS (const)’          ‘B = __MHDSETS (A)’     ‘MHDSETS #A,B’
‘uw1 __MHSETHIH (uw1, const)’    ‘B = __MHSETHIH (B,     ‘MHSETHIH #A,B’
                                 A)’
‘sw1 __MHSETHIS (sw1, const)’    ‘B = __MHSETHIS (B,     ‘MHSETHIS #A,B’
                                 A)’
‘uw1 __MHSETLOH (uw1, const)’    ‘B = __MHSETLOH (B,     ‘MHSETLOH #A,B’
                                 A)’
‘sw1 __MHSETLOS (sw1, const)’    ‘B = __MHSETLOS (B,     ‘MHSETLOS #A,B’
                                 A)’
‘uw1 __MHTOB (uw2)’              ‘B = __MHTOB (A)’       ‘MHTOB A,B’
‘void __MMACHS (acc, sw1,        ‘__MMACHS (C, A, B)’    ‘MMACHS A,B,C’
sw1)’
‘void __MMACHU (acc, uw1,        ‘__MMACHU (C, A, B)’    ‘MMACHU A,B,C’
uw1)’
‘void __MMRDHS (acc, sw1,        ‘__MMRDHS (C, A, B)’    ‘MMRDHS A,B,C’
sw1)’
‘void __MMRDHU (acc, uw1,        ‘__MMRDHU (C, A, B)’    ‘MMRDHU A,B,C’
uw1)’
‘void __MMULHS (acc, sw1,        ‘__MMULHS (C, A, B)’    ‘MMULHS A,B,C’
sw1)’
‘void __MMULHU (acc, uw1,        ‘__MMULHU (C, A, B)’    ‘MMULHU A,B,C’
uw1)’
‘void __MMULXHS (acc, sw1,       ‘__MMULXHS (C, A, B)’   ‘MMULXHS A,B,C’
sw1)’
‘void __MMULXHU (acc, uw1,       ‘__MMULXHU (C, A, B)’   ‘MMULXHU A,B,C’
uw1)’
‘uw1 __MNOT (uw1)’               ‘B = __MNOT (A)’        ‘MNOT A,B’
‘uw1 __MOR (uw1, uw1)’           ‘C = __MOR (A, B)’      ‘MOR A,B,C’
‘uw1 __MPACKH (uh, uh)’          ‘C = __MPACKH (A, B)’   ‘MPACKH A,B,C’
‘sw2 __MQADDHSS (sw2, sw2)’      ‘C = __MQADDHSS (A,     ‘MQADDHSS
                                 B)’                     A,B,C’
‘uw2 __MQADDHUS (uw2, uw2)’      ‘C = __MQADDHUS (A,     ‘MQADDHUS
                                 B)’                     A,B,C’
‘void __MQCPXIS (acc, sw2,       ‘__MQCPXIS (C, A, B)’   ‘MQCPXIS A,B,C’
sw2)’
‘void __MQCPXIU (acc, uw2,       ‘__MQCPXIU (C, A, B)’   ‘MQCPXIU A,B,C’
uw2)’
‘void __MQCPXRS (acc, sw2,       ‘__MQCPXRS (C, A, B)’   ‘MQCPXRS A,B,C’
sw2)’
‘void __MQCPXRU (acc, uw2,       ‘__MQCPXRU (C, A, B)’   ‘MQCPXRU A,B,C’
uw2)’
‘sw2 __MQLCLRHS (sw2, sw2)’      ‘C = __MQLCLRHS (A,     ‘MQLCLRHS
                                 B)’                     A,B,C’
‘sw2 __MQLMTHS (sw2, sw2)’       ‘C = __MQLMTHS (A,      ‘MQLMTHS A,B,C’
                                 B)’
‘void __MQMACHS (acc, sw2,       ‘__MQMACHS (C, A, B)’   ‘MQMACHS A,B,C’
sw2)’
‘void __MQMACHU (acc, uw2,       ‘__MQMACHU (C, A, B)’   ‘MQMACHU A,B,C’
uw2)’
‘void __MQMACXHS (acc, sw2,      ‘__MQMACXHS (C, A,      ‘MQMACXHS
sw2)’                            B)’                     A,B,C’
‘void __MQMULHS (acc, sw2,       ‘__MQMULHS (C, A, B)’   ‘MQMULHS A,B,C’
sw2)’
‘void __MQMULHU (acc, uw2,       ‘__MQMULHU (C, A, B)’   ‘MQMULHU A,B,C’
uw2)’
‘void __MQMULXHS (acc, sw2,      ‘__MQMULXHS (C, A,      ‘MQMULXHS
sw2)’                            B)’                     A,B,C’
‘void __MQMULXHU (acc, uw2,      ‘__MQMULXHU (C, A,      ‘MQMULXHU
uw2)’                            B)’                     A,B,C’
‘sw2 __MQSATHS (sw2, sw2)’       ‘C = __MQSATHS (A,      ‘MQSATHS A,B,C’
                                 B)’
‘uw2 __MQSLLHI (uw2, int)’       ‘C = __MQSLLHI (A,      ‘MQSLLHI A,B,C’
                                 B)’
‘sw2 __MQSRAHI (sw2, int)’       ‘C = __MQSRAHI (A,      ‘MQSRAHI A,B,C’
                                 B)’
‘sw2 __MQSUBHSS (sw2, sw2)’      ‘C = __MQSUBHSS (A,     ‘MQSUBHSS
                                 B)’                     A,B,C’
‘uw2 __MQSUBHUS (uw2, uw2)’      ‘C = __MQSUBHUS (A,     ‘MQSUBHUS
                                 B)’                     A,B,C’
‘void __MQXMACHS (acc, sw2,      ‘__MQXMACHS (C, A,      ‘MQXMACHS
sw2)’                            B)’                     A,B,C’
‘void __MQXMACXHS (acc, sw2,     ‘__MQXMACXHS (C, A,     ‘MQXMACXHS
sw2)’                            B)’                     A,B,C’
‘uw1 __MRDACC (acc)’             ‘B = __MRDACC (A)’      ‘MRDACC A,B’
‘uw1 __MRDACCG (acc)’            ‘B = __MRDACCG (A)’     ‘MRDACCG A,B’
‘uw1 __MROTLI (uw1, const)’      ‘C = __MROTLI (A, B)’   ‘MROTLI A,#B,C’
‘uw1 __MROTRI (uw1, const)’      ‘C = __MROTRI (A, B)’   ‘MROTRI A,#B,C’
‘sw1 __MSATHS (sw1, sw1)’        ‘C = __MSATHS (A, B)’   ‘MSATHS A,B,C’
‘uw1 __MSATHU (uw1, uw1)’        ‘C = __MSATHU (A, B)’   ‘MSATHU A,B,C’
‘uw1 __MSLLHI (uw1, const)’      ‘C = __MSLLHI (A, B)’   ‘MSLLHI A,#B,C’
‘sw1 __MSRAHI (sw1, const)’      ‘C = __MSRAHI (A, B)’   ‘MSRAHI A,#B,C’
‘uw1 __MSRLHI (uw1, const)’      ‘C = __MSRLHI (A, B)’   ‘MSRLHI A,#B,C’
‘void __MSUBACCS (acc, acc)’     ‘__MSUBACCS (B, A)’     ‘MSUBACCS A,B’
‘sw1 __MSUBHSS (sw1, sw1)’       ‘C = __MSUBHSS (A,      ‘MSUBHSS A,B,C’
                                 B)’
‘uw1 __MSUBHUS (uw1, uw1)’       ‘C = __MSUBHUS (A,      ‘MSUBHUS A,B,C’
                                 B)’
‘void __MTRAP (void)’            ‘__MTRAP ()’            ‘MTRAP’
‘uw2 __MUNPACKH (uw1)’           ‘B = __MUNPACKH (A)’    ‘MUNPACKH A,B’
‘uw1 __MWCUT (uw2, uw1)’         ‘C = __MWCUT (A, B)’    ‘MWCUT A,B,C’
‘void __MWTACC (acc, uw1)’       ‘__MWTACC (B, A)’       ‘MWTACC A,B’
‘void __MWTACCG (acc, uw1)’      ‘__MWTACCG (B, A)’      ‘MWTACCG A,B’
‘uw1 __MXOR (uw1, uw1)’          ‘C = __MXOR (A, B)’     ‘MXOR A,B,C’


File: gcc.info,  Node: Raw read/write Functions,  Next: Other Built-in Functions,  Prev: Directly-mapped Media Functions,  Up: FR-V Built-in Functions

6.60.13.4 Raw Read/Write Functions
..................................

This sections describes built-in functions related to read and write
instructions to access memory.  These functions generate ‘membar’
instructions to flush the I/O load and stores where appropriate, as
described in Fujitsu's manual described above.

‘unsigned char __builtin_read8 (void *DATA)’
‘unsigned short __builtin_read16 (void *DATA)’
‘unsigned long __builtin_read32 (void *DATA)’
‘unsigned long long __builtin_read64 (void *DATA)’

‘void __builtin_write8 (void *DATA, unsigned char DATUM)’
‘void __builtin_write16 (void *DATA, unsigned short DATUM)’
‘void __builtin_write32 (void *DATA, unsigned long DATUM)’
‘void __builtin_write64 (void *DATA, unsigned long long DATUM)’


File: gcc.info,  Node: Other Built-in Functions,  Prev: Raw read/write Functions,  Up: FR-V Built-in Functions

6.60.13.5 Other Built-in Functions
..................................

This section describes built-in functions that are not named after a
specific FR-V instruction.

‘sw2 __IACCreadll (iacc REG)’
     Return the full 64-bit value of IACC0.  The REG argument is
     reserved for future expansion and must be 0.

‘sw1 __IACCreadl (iacc REG)’
     Return the value of IACC0H if REG is 0 and IACC0L if REG is 1.
     Other values of REG are rejected as invalid.

‘void __IACCsetll (iacc REG, sw2 X)’
     Set the full 64-bit value of IACC0 to X.  The REG argument is
     reserved for future expansion and must be 0.

‘void __IACCsetl (iacc REG, sw1 X)’
     Set IACC0H to X if REG is 0 and IACC0L to X if REG is 1.  Other
     values of REG are rejected as invalid.

‘void __data_prefetch0 (const void *X)’
     Use the ‘dcpl’ instruction to load the contents of address X into
     the data cache.

‘void __data_prefetch (const void *X)’
     Use the ‘nldub’ instruction to load the contents of address X into
     the data cache.  The instruction is issued in slot I1.


File: gcc.info,  Node: MIPS DSP Built-in Functions,  Next: MIPS Paired-Single Support,  Prev: FR-V Built-in Functions,  Up: Target Builtins

6.60.14 MIPS DSP Built-in Functions
-----------------------------------

The MIPS DSP Application-Specific Extension (ASE) includes new
instructions that are designed to improve the performance of DSP and
media applications.  It provides instructions that operate on packed
8-bit/16-bit integer data, Q7, Q15 and Q31 fractional data.

 GCC supports MIPS DSP operations using both the generic vector
extensions (*note Vector Extensions::) and a collection of MIPS-specific
built-in functions.  Both kinds of support are enabled by the ‘-mdsp’
command-line option.

 Revision 2 of the ASE was introduced in the second half of 2006.  This
revision adds extra instructions to the original ASE, but is otherwise
backwards-compatible with it.  You can select revision 2 using the
command-line option ‘-mdspr2’; this option implies ‘-mdsp’.

 The SCOUNT and POS bits of the DSP control register are global.  The
WRDSP, EXTPDP, EXTPDPV and MTHLIP instructions modify the SCOUNT and POS
bits.  During optimization, the compiler does not delete these
instructions and it does not delete calls to functions containing these
instructions.

 At present, GCC only provides support for operations on 32-bit vectors.
The vector type associated with 8-bit integer data is usually called
‘v4i8’, the vector type associated with Q7 is usually called ‘v4q7’, the
vector type associated with 16-bit integer data is usually called
‘v2i16’, and the vector type associated with Q15 is usually called
‘v2q15’.  They can be defined in C as follows:

     typedef signed char v4i8 __attribute__ ((vector_size(4)));
     typedef signed char v4q7 __attribute__ ((vector_size(4)));
     typedef short v2i16 __attribute__ ((vector_size(4)));
     typedef short v2q15 __attribute__ ((vector_size(4)));

 ‘v4i8’, ‘v4q7’, ‘v2i16’ and ‘v2q15’ values are initialized in the same
way as aggregates.  For example:

     v4i8 a = {1, 2, 3, 4};
     v4i8 b;
     b = (v4i8) {5, 6, 7, 8};

     v2q15 c = {0x0fcb, 0x3a75};
     v2q15 d;
     d = (v2q15) {0.1234 * 0x1.0p15, 0.4567 * 0x1.0p15};

 _Note:_ The CPU's endianness determines the order in which values are
packed.  On little-endian targets, the first value is the least
significant and the last value is the most significant.  The opposite
order applies to big-endian targets.  For example, the code above sets
the lowest byte of ‘a’ to ‘1’ on little-endian targets and ‘4’ on
big-endian targets.

 _Note:_ Q7, Q15 and Q31 values must be initialized with their integer
representation.  As shown in this example, the integer representation of
a Q7 value can be obtained by multiplying the fractional value by
‘0x1.0p7’.  The equivalent for Q15 values is to multiply by ‘0x1.0p15’.
The equivalent for Q31 values is to multiply by ‘0x1.0p31’.

 The table below lists the ‘v4i8’ and ‘v2q15’ operations for which
hardware support exists.  ‘a’ and ‘b’ are ‘v4i8’ values, and ‘c’ and ‘d’
are ‘v2q15’ values.

C code                               MIPS instruction
--------------------------------------------------------------------------
‘a + b’                              ‘addu.qb’
‘c + d’                              ‘addq.ph’
‘a - b’                              ‘subu.qb’
‘c - d’                              ‘subq.ph’

 The table below lists the ‘v2i16’ operation for which hardware support
exists for the DSP ASE REV 2.  ‘e’ and ‘f’ are ‘v2i16’ values.

C code                               MIPS instruction
--------------------------------------------------------------------------
‘e * f’                              ‘mul.ph’

 It is easier to describe the DSP built-in functions if we first define
the following types:

     typedef int q31;
     typedef int i32;
     typedef unsigned int ui32;
     typedef long long a64;

 ‘q31’ and ‘i32’ are actually the same as ‘int’, but we use ‘q31’ to
indicate a Q31 fractional value and ‘i32’ to indicate a 32-bit integer
value.  Similarly, ‘a64’ is the same as ‘long long’, but we use ‘a64’ to
indicate values that are placed in one of the four DSP accumulators
(‘$ac0’, ‘$ac1’, ‘$ac2’ or ‘$ac3’).

 Also, some built-in functions prefer or require immediate numbers as
parameters, because the corresponding DSP instructions accept both
immediate numbers and register operands, or accept immediate numbers
only.  The immediate parameters are listed as follows.

     imm0_3: 0 to 3.
     imm0_7: 0 to 7.
     imm0_15: 0 to 15.
     imm0_31: 0 to 31.
     imm0_63: 0 to 63.
     imm0_255: 0 to 255.
     imm_n32_31: -32 to 31.
     imm_n512_511: -512 to 511.

 The following built-in functions map directly to a particular MIPS DSP
instruction.  Please refer to the architecture specification for details
on what each instruction does.

     v2q15 __builtin_mips_addq_ph (v2q15, v2q15);
     v2q15 __builtin_mips_addq_s_ph (v2q15, v2q15);
     q31 __builtin_mips_addq_s_w (q31, q31);
     v4i8 __builtin_mips_addu_qb (v4i8, v4i8);
     v4i8 __builtin_mips_addu_s_qb (v4i8, v4i8);
     v2q15 __builtin_mips_subq_ph (v2q15, v2q15);
     v2q15 __builtin_mips_subq_s_ph (v2q15, v2q15);
     q31 __builtin_mips_subq_s_w (q31, q31);
     v4i8 __builtin_mips_subu_qb (v4i8, v4i8);
     v4i8 __builtin_mips_subu_s_qb (v4i8, v4i8);
     i32 __builtin_mips_addsc (i32, i32);
     i32 __builtin_mips_addwc (i32, i32);
     i32 __builtin_mips_modsub (i32, i32);
     i32 __builtin_mips_raddu_w_qb (v4i8);
     v2q15 __builtin_mips_absq_s_ph (v2q15);
     q31 __builtin_mips_absq_s_w (q31);
     v4i8 __builtin_mips_precrq_qb_ph (v2q15, v2q15);
     v2q15 __builtin_mips_precrq_ph_w (q31, q31);
     v2q15 __builtin_mips_precrq_rs_ph_w (q31, q31);
     v4i8 __builtin_mips_precrqu_s_qb_ph (v2q15, v2q15);
     q31 __builtin_mips_preceq_w_phl (v2q15);
     q31 __builtin_mips_preceq_w_phr (v2q15);
     v2q15 __builtin_mips_precequ_ph_qbl (v4i8);
     v2q15 __builtin_mips_precequ_ph_qbr (v4i8);
     v2q15 __builtin_mips_precequ_ph_qbla (v4i8);
     v2q15 __builtin_mips_precequ_ph_qbra (v4i8);
     v2q15 __builtin_mips_preceu_ph_qbl (v4i8);
     v2q15 __builtin_mips_preceu_ph_qbr (v4i8);
     v2q15 __builtin_mips_preceu_ph_qbla (v4i8);
     v2q15 __builtin_mips_preceu_ph_qbra (v4i8);
     v4i8 __builtin_mips_shll_qb (v4i8, imm0_7);
     v4i8 __builtin_mips_shll_qb (v4i8, i32);
     v2q15 __builtin_mips_shll_ph (v2q15, imm0_15);
     v2q15 __builtin_mips_shll_ph (v2q15, i32);
     v2q15 __builtin_mips_shll_s_ph (v2q15, imm0_15);
     v2q15 __builtin_mips_shll_s_ph (v2q15, i32);
     q31 __builtin_mips_shll_s_w (q31, imm0_31);
     q31 __builtin_mips_shll_s_w (q31, i32);
     v4i8 __builtin_mips_shrl_qb (v4i8, imm0_7);
     v4i8 __builtin_mips_shrl_qb (v4i8, i32);
     v2q15 __builtin_mips_shra_ph (v2q15, imm0_15);
     v2q15 __builtin_mips_shra_ph (v2q15, i32);
     v2q15 __builtin_mips_shra_r_ph (v2q15, imm0_15);
     v2q15 __builtin_mips_shra_r_ph (v2q15, i32);
     q31 __builtin_mips_shra_r_w (q31, imm0_31);
     q31 __builtin_mips_shra_r_w (q31, i32);
     v2q15 __builtin_mips_muleu_s_ph_qbl (v4i8, v2q15);
     v2q15 __builtin_mips_muleu_s_ph_qbr (v4i8, v2q15);
     v2q15 __builtin_mips_mulq_rs_ph (v2q15, v2q15);
     q31 __builtin_mips_muleq_s_w_phl (v2q15, v2q15);
     q31 __builtin_mips_muleq_s_w_phr (v2q15, v2q15);
     a64 __builtin_mips_dpau_h_qbl (a64, v4i8, v4i8);
     a64 __builtin_mips_dpau_h_qbr (a64, v4i8, v4i8);
     a64 __builtin_mips_dpsu_h_qbl (a64, v4i8, v4i8);
     a64 __builtin_mips_dpsu_h_qbr (a64, v4i8, v4i8);
     a64 __builtin_mips_dpaq_s_w_ph (a64, v2q15, v2q15);
     a64 __builtin_mips_dpaq_sa_l_w (a64, q31, q31);
     a64 __builtin_mips_dpsq_s_w_ph (a64, v2q15, v2q15);
     a64 __builtin_mips_dpsq_sa_l_w (a64, q31, q31);
     a64 __builtin_mips_mulsaq_s_w_ph (a64, v2q15, v2q15);
     a64 __builtin_mips_maq_s_w_phl (a64, v2q15, v2q15);
     a64 __builtin_mips_maq_s_w_phr (a64, v2q15, v2q15);
     a64 __builtin_mips_maq_sa_w_phl (a64, v2q15, v2q15);
     a64 __builtin_mips_maq_sa_w_phr (a64, v2q15, v2q15);
     i32 __builtin_mips_bitrev (i32);
     i32 __builtin_mips_insv (i32, i32);
     v4i8 __builtin_mips_repl_qb (imm0_255);
     v4i8 __builtin_mips_repl_qb (i32);
     v2q15 __builtin_mips_repl_ph (imm_n512_511);
     v2q15 __builtin_mips_repl_ph (i32);
     void __builtin_mips_cmpu_eq_qb (v4i8, v4i8);
     void __builtin_mips_cmpu_lt_qb (v4i8, v4i8);
     void __builtin_mips_cmpu_le_qb (v4i8, v4i8);
     i32 __builtin_mips_cmpgu_eq_qb (v4i8, v4i8);
     i32 __builtin_mips_cmpgu_lt_qb (v4i8, v4i8);
     i32 __builtin_mips_cmpgu_le_qb (v4i8, v4i8);
     void __builtin_mips_cmp_eq_ph (v2q15, v2q15);
     void __builtin_mips_cmp_lt_ph (v2q15, v2q15);
     void __builtin_mips_cmp_le_ph (v2q15, v2q15);
     v4i8 __builtin_mips_pick_qb (v4i8, v4i8);
     v2q15 __builtin_mips_pick_ph (v2q15, v2q15);
     v2q15 __builtin_mips_packrl_ph (v2q15, v2q15);
     i32 __builtin_mips_extr_w (a64, imm0_31);
     i32 __builtin_mips_extr_w (a64, i32);
     i32 __builtin_mips_extr_r_w (a64, imm0_31);
     i32 __builtin_mips_extr_s_h (a64, i32);
     i32 __builtin_mips_extr_rs_w (a64, imm0_31);
     i32 __builtin_mips_extr_rs_w (a64, i32);
     i32 __builtin_mips_extr_s_h (a64, imm0_31);
     i32 __builtin_mips_extr_r_w (a64, i32);
     i32 __builtin_mips_extp (a64, imm0_31);
     i32 __builtin_mips_extp (a64, i32);
     i32 __builtin_mips_extpdp (a64, imm0_31);
     i32 __builtin_mips_extpdp (a64, i32);
     a64 __builtin_mips_shilo (a64, imm_n32_31);
     a64 __builtin_mips_shilo (a64, i32);
     a64 __builtin_mips_mthlip (a64, i32);
     void __builtin_mips_wrdsp (i32, imm0_63);
     i32 __builtin_mips_rddsp (imm0_63);
     i32 __builtin_mips_lbux (void *, i32);
     i32 __builtin_mips_lhx (void *, i32);
     i32 __builtin_mips_lwx (void *, i32);
     a64 __builtin_mips_ldx (void *, i32); /* MIPS64 only */
     i32 __builtin_mips_bposge32 (void);
     a64 __builtin_mips_madd (a64, i32, i32);
     a64 __builtin_mips_maddu (a64, ui32, ui32);
     a64 __builtin_mips_msub (a64, i32, i32);
     a64 __builtin_mips_msubu (a64, ui32, ui32);
     a64 __builtin_mips_mult (i32, i32);
     a64 __builtin_mips_multu (ui32, ui32);

 The following built-in functions map directly to a particular MIPS DSP
REV 2 instruction.  Please refer to the architecture specification for
details on what each instruction does.

     v4q7 __builtin_mips_absq_s_qb (v4q7);
     v2i16 __builtin_mips_addu_ph (v2i16, v2i16);
     v2i16 __builtin_mips_addu_s_ph (v2i16, v2i16);
     v4i8 __builtin_mips_adduh_qb (v4i8, v4i8);
     v4i8 __builtin_mips_adduh_r_qb (v4i8, v4i8);
     i32 __builtin_mips_append (i32, i32, imm0_31);
     i32 __builtin_mips_balign (i32, i32, imm0_3);
     i32 __builtin_mips_cmpgdu_eq_qb (v4i8, v4i8);
     i32 __builtin_mips_cmpgdu_lt_qb (v4i8, v4i8);
     i32 __builtin_mips_cmpgdu_le_qb (v4i8, v4i8);
     a64 __builtin_mips_dpa_w_ph (a64, v2i16, v2i16);
     a64 __builtin_mips_dps_w_ph (a64, v2i16, v2i16);
     v2i16 __builtin_mips_mul_ph (v2i16, v2i16);
     v2i16 __builtin_mips_mul_s_ph (v2i16, v2i16);
     q31 __builtin_mips_mulq_rs_w (q31, q31);
     v2q15 __builtin_mips_mulq_s_ph (v2q15, v2q15);
     q31 __builtin_mips_mulq_s_w (q31, q31);
     a64 __builtin_mips_mulsa_w_ph (a64, v2i16, v2i16);
     v4i8 __builtin_mips_precr_qb_ph (v2i16, v2i16);
     v2i16 __builtin_mips_precr_sra_ph_w (i32, i32, imm0_31);
     v2i16 __builtin_mips_precr_sra_r_ph_w (i32, i32, imm0_31);
     i32 __builtin_mips_prepend (i32, i32, imm0_31);
     v4i8 __builtin_mips_shra_qb (v4i8, imm0_7);
     v4i8 __builtin_mips_shra_r_qb (v4i8, imm0_7);
     v4i8 __builtin_mips_shra_qb (v4i8, i32);
     v4i8 __builtin_mips_shra_r_qb (v4i8, i32);
     v2i16 __builtin_mips_shrl_ph (v2i16, imm0_15);
     v2i16 __builtin_mips_shrl_ph (v2i16, i32);
     v2i16 __builtin_mips_subu_ph (v2i16, v2i16);
     v2i16 __builtin_mips_subu_s_ph (v2i16, v2i16);
     v4i8 __builtin_mips_subuh_qb (v4i8, v4i8);
     v4i8 __builtin_mips_subuh_r_qb (v4i8, v4i8);
     v2q15 __builtin_mips_addqh_ph (v2q15, v2q15);
     v2q15 __builtin_mips_addqh_r_ph (v2q15, v2q15);
     q31 __builtin_mips_addqh_w (q31, q31);
     q31 __builtin_mips_addqh_r_w (q31, q31);
     v2q15 __builtin_mips_subqh_ph (v2q15, v2q15);
     v2q15 __builtin_mips_subqh_r_ph (v2q15, v2q15);
     q31 __builtin_mips_subqh_w (q31, q31);
     q31 __builtin_mips_subqh_r_w (q31, q31);
     a64 __builtin_mips_dpax_w_ph (a64, v2i16, v2i16);
     a64 __builtin_mips_dpsx_w_ph (a64, v2i16, v2i16);
     a64 __builtin_mips_dpaqx_s_w_ph (a64, v2q15, v2q15);
     a64 __builtin_mips_dpaqx_sa_w_ph (a64, v2q15, v2q15);
     a64 __builtin_mips_dpsqx_s_w_ph (a64, v2q15, v2q15);
     a64 __builtin_mips_dpsqx_sa_w_ph (a64, v2q15, v2q15);


File: gcc.info,  Node: MIPS Paired-Single Support,  Next: MIPS Loongson Built-in Functions,  Prev: MIPS DSP Built-in Functions,  Up: Target Builtins

6.60.15 MIPS Paired-Single Support
----------------------------------

The MIPS64 architecture includes a number of instructions that operate
on pairs of single-precision floating-point values.  Each pair is packed
into a 64-bit floating-point register, with one element being designated
the "upper half" and the other being designated the "lower half".

 GCC supports paired-single operations using both the generic vector
extensions (*note Vector Extensions::) and a collection of MIPS-specific
built-in functions.  Both kinds of support are enabled by the
‘-mpaired-single’ command-line option.

 The vector type associated with paired-single values is usually called
‘v2sf’.  It can be defined in C as follows:

     typedef float v2sf __attribute__ ((vector_size (8)));

 ‘v2sf’ values are initialized in the same way as aggregates.  For
example:

     v2sf a = {1.5, 9.1};
     v2sf b;
     float e, f;
     b = (v2sf) {e, f};

 _Note:_ The CPU's endianness determines which value is stored in the
upper half of a register and which value is stored in the lower half.
On little-endian targets, the first value is the lower one and the
second value is the upper one.  The opposite order applies to big-endian
targets.  For example, the code above sets the lower half of ‘a’ to
‘1.5’ on little-endian targets and ‘9.1’ on big-endian targets.


File: gcc.info,  Node: MIPS Loongson Built-in Functions,  Next: MIPS SIMD Architecture (MSA) Support,  Prev: MIPS Paired-Single Support,  Up: Target Builtins

6.60.16 MIPS Loongson Built-in Functions
----------------------------------------

GCC provides intrinsics to access the SIMD instructions provided by the
ST Microelectronics Loongson-2E and -2F processors.  These intrinsics,
available after inclusion of the ‘loongson.h’ header file, operate on
the following 64-bit vector types:

   • ‘uint8x8_t’, a vector of eight unsigned 8-bit integers;
   • ‘uint16x4_t’, a vector of four unsigned 16-bit integers;
   • ‘uint32x2_t’, a vector of two unsigned 32-bit integers;
   • ‘int8x8_t’, a vector of eight signed 8-bit integers;
   • ‘int16x4_t’, a vector of four signed 16-bit integers;
   • ‘int32x2_t’, a vector of two signed 32-bit integers.

 The intrinsics provided are listed below; each is named after the
machine instruction to which it corresponds, with suffixes added as
appropriate to distinguish intrinsics that expand to the same machine
instruction yet have different argument types.  Refer to the
architecture documentation for a description of the functionality of
each instruction.

     int16x4_t packsswh (int32x2_t s, int32x2_t t);
     int8x8_t packsshb (int16x4_t s, int16x4_t t);
     uint8x8_t packushb (uint16x4_t s, uint16x4_t t);
     uint32x2_t paddw_u (uint32x2_t s, uint32x2_t t);
     uint16x4_t paddh_u (uint16x4_t s, uint16x4_t t);
     uint8x8_t paddb_u (uint8x8_t s, uint8x8_t t);
     int32x2_t paddw_s (int32x2_t s, int32x2_t t);
     int16x4_t paddh_s (int16x4_t s, int16x4_t t);
     int8x8_t paddb_s (int8x8_t s, int8x8_t t);
     uint64_t paddd_u (uint64_t s, uint64_t t);
     int64_t paddd_s (int64_t s, int64_t t);
     int16x4_t paddsh (int16x4_t s, int16x4_t t);
     int8x8_t paddsb (int8x8_t s, int8x8_t t);
     uint16x4_t paddush (uint16x4_t s, uint16x4_t t);
     uint8x8_t paddusb (uint8x8_t s, uint8x8_t t);
     uint64_t pandn_ud (uint64_t s, uint64_t t);
     uint32x2_t pandn_uw (uint32x2_t s, uint32x2_t t);
     uint16x4_t pandn_uh (uint16x4_t s, uint16x4_t t);
     uint8x8_t pandn_ub (uint8x8_t s, uint8x8_t t);
     int64_t pandn_sd (int64_t s, int64_t t);
     int32x2_t pandn_sw (int32x2_t s, int32x2_t t);
     int16x4_t pandn_sh (int16x4_t s, int16x4_t t);
     int8x8_t pandn_sb (int8x8_t s, int8x8_t t);
     uint16x4_t pavgh (uint16x4_t s, uint16x4_t t);
     uint8x8_t pavgb (uint8x8_t s, uint8x8_t t);
     uint32x2_t pcmpeqw_u (uint32x2_t s, uint32x2_t t);
     uint16x4_t pcmpeqh_u (uint16x4_t s, uint16x4_t t);
     uint8x8_t pcmpeqb_u (uint8x8_t s, uint8x8_t t);
     int32x2_t pcmpeqw_s (int32x2_t s, int32x2_t t);
     int16x4_t pcmpeqh_s (int16x4_t s, int16x4_t t);
     int8x8_t pcmpeqb_s (int8x8_t s, int8x8_t t);
     uint32x2_t pcmpgtw_u (uint32x2_t s, uint32x2_t t);
     uint16x4_t pcmpgth_u (uint16x4_t s, uint16x4_t t);
     uint8x8_t pcmpgtb_u (uint8x8_t s, uint8x8_t t);
     int32x2_t pcmpgtw_s (int32x2_t s, int32x2_t t);
     int16x4_t pcmpgth_s (int16x4_t s, int16x4_t t);
     int8x8_t pcmpgtb_s (int8x8_t s, int8x8_t t);
     uint16x4_t pextrh_u (uint16x4_t s, int field);
     int16x4_t pextrh_s (int16x4_t s, int field);
     uint16x4_t pinsrh_0_u (uint16x4_t s, uint16x4_t t);
     uint16x4_t pinsrh_1_u (uint16x4_t s, uint16x4_t t);
     uint16x4_t pinsrh_2_u (uint16x4_t s, uint16x4_t t);
     uint16x4_t pinsrh_3_u (uint16x4_t s, uint16x4_t t);
     int16x4_t pinsrh_0_s (int16x4_t s, int16x4_t t);
     int16x4_t pinsrh_1_s (int16x4_t s, int16x4_t t);
     int16x4_t pinsrh_2_s (int16x4_t s, int16x4_t t);
     int16x4_t pinsrh_3_s (int16x4_t s, int16x4_t t);
     int32x2_t pmaddhw (int16x4_t s, int16x4_t t);
     int16x4_t pmaxsh (int16x4_t s, int16x4_t t);
     uint8x8_t pmaxub (uint8x8_t s, uint8x8_t t);
     int16x4_t pminsh (int16x4_t s, int16x4_t t);
     uint8x8_t pminub (uint8x8_t s, uint8x8_t t);
     uint8x8_t pmovmskb_u (uint8x8_t s);
     int8x8_t pmovmskb_s (int8x8_t s);
     uint16x4_t pmulhuh (uint16x4_t s, uint16x4_t t);
     int16x4_t pmulhh (int16x4_t s, int16x4_t t);
     int16x4_t pmullh (int16x4_t s, int16x4_t t);
     int64_t pmuluw (uint32x2_t s, uint32x2_t t);
     uint8x8_t pasubub (uint8x8_t s, uint8x8_t t);
     uint16x4_t biadd (uint8x8_t s);
     uint16x4_t psadbh (uint8x8_t s, uint8x8_t t);
     uint16x4_t pshufh_u (uint16x4_t dest, uint16x4_t s, uint8_t order);
     int16x4_t pshufh_s (int16x4_t dest, int16x4_t s, uint8_t order);
     uint16x4_t psllh_u (uint16x4_t s, uint8_t amount);
     int16x4_t psllh_s (int16x4_t s, uint8_t amount);
     uint32x2_t psllw_u (uint32x2_t s, uint8_t amount);
     int32x2_t psllw_s (int32x2_t s, uint8_t amount);
     uint16x4_t psrlh_u (uint16x4_t s, uint8_t amount);
     int16x4_t psrlh_s (int16x4_t s, uint8_t amount);
     uint32x2_t psrlw_u (uint32x2_t s, uint8_t amount);
     int32x2_t psrlw_s (int32x2_t s, uint8_t amount);
     uint16x4_t psrah_u (uint16x4_t s, uint8_t amount);
     int16x4_t psrah_s (int16x4_t s, uint8_t amount);
     uint32x2_t psraw_u (uint32x2_t s, uint8_t amount);
     int32x2_t psraw_s (int32x2_t s, uint8_t amount);
     uint32x2_t psubw_u (uint32x2_t s, uint32x2_t t);
     uint16x4_t psubh_u (uint16x4_t s, uint16x4_t t);
     uint8x8_t psubb_u (uint8x8_t s, uint8x8_t t);
     int32x2_t psubw_s (int32x2_t s, int32x2_t t);
     int16x4_t psubh_s (int16x4_t s, int16x4_t t);
     int8x8_t psubb_s (int8x8_t s, int8x8_t t);
     uint64_t psubd_u (uint64_t s, uint64_t t);
     int64_t psubd_s (int64_t s, int64_t t);
     int16x4_t psubsh (int16x4_t s, int16x4_t t);
     int8x8_t psubsb (int8x8_t s, int8x8_t t);
     uint16x4_t psubush (uint16x4_t s, uint16x4_t t);
     uint8x8_t psubusb (uint8x8_t s, uint8x8_t t);
     uint32x2_t punpckhwd_u (uint32x2_t s, uint32x2_t t);
     uint16x4_t punpckhhw_u (uint16x4_t s, uint16x4_t t);
     uint8x8_t punpckhbh_u (uint8x8_t s, uint8x8_t t);
     int32x2_t punpckhwd_s (int32x2_t s, int32x2_t t);
     int16x4_t punpckhhw_s (int16x4_t s, int16x4_t t);
     int8x8_t punpckhbh_s (int8x8_t s, int8x8_t t);
     uint32x2_t punpcklwd_u (uint32x2_t s, uint32x2_t t);
     uint16x4_t punpcklhw_u (uint16x4_t s, uint16x4_t t);
     uint8x8_t punpcklbh_u (uint8x8_t s, uint8x8_t t);
     int32x2_t punpcklwd_s (int32x2_t s, int32x2_t t);
     int16x4_t punpcklhw_s (int16x4_t s, int16x4_t t);
     int8x8_t punpcklbh_s (int8x8_t s, int8x8_t t);

* Menu:

* Paired-Single Arithmetic::
* Paired-Single Built-in Functions::
* MIPS-3D Built-in Functions::


File: gcc.info,  Node: Paired-Single Arithmetic,  Next: Paired-Single Built-in Functions,  Up: MIPS Loongson Built-in Functions

6.60.16.1 Paired-Single Arithmetic
..................................

The table below lists the ‘v2sf’ operations for which hardware support
exists.  ‘a’, ‘b’ and ‘c’ are ‘v2sf’ values and ‘x’ is an integral
value.

C code                               MIPS instruction
--------------------------------------------------------------------------
‘a + b’                              ‘add.ps’
‘a - b’                              ‘sub.ps’
‘-a’                                 ‘neg.ps’
‘a * b’                              ‘mul.ps’
‘a * b + c’                          ‘madd.ps’
‘a * b - c’                          ‘msub.ps’
‘-(a * b + c)’                       ‘nmadd.ps’
‘-(a * b - c)’                       ‘nmsub.ps’
‘x ? a : b’                          ‘movn.ps’/‘movz.ps’

 Note that the multiply-accumulate instructions can be disabled using
the command-line option ‘-mno-fused-madd’.


File: gcc.info,  Node: Paired-Single Built-in Functions,  Next: MIPS-3D Built-in Functions,  Prev: Paired-Single Arithmetic,  Up: MIPS Loongson Built-in Functions

6.60.16.2 Paired-Single Built-in Functions
..........................................

The following paired-single functions map directly to a particular MIPS
instruction.  Please refer to the architecture specification for details
on what each instruction does.

‘v2sf __builtin_mips_pll_ps (v2sf, v2sf)’
     Pair lower lower (‘pll.ps’).

‘v2sf __builtin_mips_pul_ps (v2sf, v2sf)’
     Pair upper lower (‘pul.ps’).

‘v2sf __builtin_mips_plu_ps (v2sf, v2sf)’
     Pair lower upper (‘plu.ps’).

‘v2sf __builtin_mips_puu_ps (v2sf, v2sf)’
     Pair upper upper (‘puu.ps’).

‘v2sf __builtin_mips_cvt_ps_s (float, float)’
     Convert pair to paired single (‘cvt.ps.s’).

‘float __builtin_mips_cvt_s_pl (v2sf)’
     Convert pair lower to single (‘cvt.s.pl’).

‘float __builtin_mips_cvt_s_pu (v2sf)’
     Convert pair upper to single (‘cvt.s.pu’).

‘v2sf __builtin_mips_abs_ps (v2sf)’
     Absolute value (‘abs.ps’).

‘v2sf __builtin_mips_alnv_ps (v2sf, v2sf, int)’
     Align variable (‘alnv.ps’).

     _Note:_ The value of the third parameter must be 0 or 4 modulo 8,
     otherwise the result is unpredictable.  Please read the instruction
     description for details.

 The following multi-instruction functions are also available.  In each
case, COND can be any of the 16 floating-point conditions: ‘f’, ‘un’,
‘eq’, ‘ueq’, ‘olt’, ‘ult’, ‘ole’, ‘ule’, ‘sf’, ‘ngle’, ‘seq’, ‘ngl’,
‘lt’, ‘nge’, ‘le’ or ‘ngt’.

‘v2sf __builtin_mips_movt_c_COND_ps (v2sf A, v2sf B, v2sf C, v2sf D)’
‘v2sf __builtin_mips_movf_c_COND_ps (v2sf A, v2sf B, v2sf C, v2sf D)’
     Conditional move based on floating-point comparison (‘c.COND.ps’,
     ‘movt.ps’/‘movf.ps’).

     The ‘movt’ functions return the value X computed by:

          c.COND.ps CC,A,B
          mov.ps X,C
          movt.ps X,D,CC

     The ‘movf’ functions are similar but use ‘movf.ps’ instead of
     ‘movt.ps’.

‘int __builtin_mips_upper_c_COND_ps (v2sf A, v2sf B)’
‘int __builtin_mips_lower_c_COND_ps (v2sf A, v2sf B)’
     Comparison of two paired-single values (‘c.COND.ps’,
     ‘bc1t’/‘bc1f’).

     These functions compare A and B using ‘c.COND.ps’ and return either
     the upper or lower half of the result.  For example:

          v2sf a, b;
          if (__builtin_mips_upper_c_eq_ps (a, b))
            upper_halves_are_equal ();
          else
            upper_halves_are_unequal ();

          if (__builtin_mips_lower_c_eq_ps (a, b))
            lower_halves_are_equal ();
          else
            lower_halves_are_unequal ();


File: gcc.info,  Node: MIPS-3D Built-in Functions,  Prev: Paired-Single Built-in Functions,  Up: MIPS Loongson Built-in Functions

6.60.16.3 MIPS-3D Built-in Functions
....................................

The MIPS-3D Application-Specific Extension (ASE) includes additional
paired-single instructions that are designed to improve the performance
of 3D graphics operations.  Support for these instructions is controlled
by the ‘-mips3d’ command-line option.

 The functions listed below map directly to a particular MIPS-3D
instruction.  Please refer to the architecture specification for more
details on what each instruction does.

‘v2sf __builtin_mips_addr_ps (v2sf, v2sf)’
     Reduction add (‘addr.ps’).

‘v2sf __builtin_mips_mulr_ps (v2sf, v2sf)’
     Reduction multiply (‘mulr.ps’).

‘v2sf __builtin_mips_cvt_pw_ps (v2sf)’
     Convert paired single to paired word (‘cvt.pw.ps’).

‘v2sf __builtin_mips_cvt_ps_pw (v2sf)’
     Convert paired word to paired single (‘cvt.ps.pw’).

‘float __builtin_mips_recip1_s (float)’
‘double __builtin_mips_recip1_d (double)’
‘v2sf __builtin_mips_recip1_ps (v2sf)’
     Reduced-precision reciprocal (sequence step 1) (‘recip1.FMT’).

‘float __builtin_mips_recip2_s (float, float)’
‘double __builtin_mips_recip2_d (double, double)’
‘v2sf __builtin_mips_recip2_ps (v2sf, v2sf)’
     Reduced-precision reciprocal (sequence step 2) (‘recip2.FMT’).

‘float __builtin_mips_rsqrt1_s (float)’
‘double __builtin_mips_rsqrt1_d (double)’
‘v2sf __builtin_mips_rsqrt1_ps (v2sf)’
     Reduced-precision reciprocal square root (sequence step 1)
     (‘rsqrt1.FMT’).

‘float __builtin_mips_rsqrt2_s (float, float)’
‘double __builtin_mips_rsqrt2_d (double, double)’
‘v2sf __builtin_mips_rsqrt2_ps (v2sf, v2sf)’
     Reduced-precision reciprocal square root (sequence step 2)
     (‘rsqrt2.FMT’).

 The following multi-instruction functions are also available.  In each
case, COND can be any of the 16 floating-point conditions: ‘f’, ‘un’,
‘eq’, ‘ueq’, ‘olt’, ‘ult’, ‘ole’, ‘ule’, ‘sf’, ‘ngle’, ‘seq’, ‘ngl’,
‘lt’, ‘nge’, ‘le’ or ‘ngt’.

‘int __builtin_mips_cabs_COND_s (float A, float B)’
‘int __builtin_mips_cabs_COND_d (double A, double B)’
     Absolute comparison of two scalar values (‘cabs.COND.FMT’,
     ‘bc1t’/‘bc1f’).

     These functions compare A and B using ‘cabs.COND.s’ or
     ‘cabs.COND.d’ and return the result as a boolean value.  For
     example:

          float a, b;
          if (__builtin_mips_cabs_eq_s (a, b))
            true ();
          else
            false ();

‘int __builtin_mips_upper_cabs_COND_ps (v2sf A, v2sf B)’
‘int __builtin_mips_lower_cabs_COND_ps (v2sf A, v2sf B)’
     Absolute comparison of two paired-single values (‘cabs.COND.ps’,
     ‘bc1t’/‘bc1f’).

     These functions compare A and B using ‘cabs.COND.ps’ and return
     either the upper or lower half of the result.  For example:

          v2sf a, b;
          if (__builtin_mips_upper_cabs_eq_ps (a, b))
            upper_halves_are_equal ();
          else
            upper_halves_are_unequal ();

          if (__builtin_mips_lower_cabs_eq_ps (a, b))
            lower_halves_are_equal ();
          else
            lower_halves_are_unequal ();

‘v2sf __builtin_mips_movt_cabs_COND_ps (v2sf A, v2sf B, v2sf C, v2sf D)’
‘v2sf __builtin_mips_movf_cabs_COND_ps (v2sf A, v2sf B, v2sf C, v2sf D)’
     Conditional move based on absolute comparison (‘cabs.COND.ps’,
     ‘movt.ps’/‘movf.ps’).

     The ‘movt’ functions return the value X computed by:

          cabs.COND.ps CC,A,B
          mov.ps X,C
          movt.ps X,D,CC

     The ‘movf’ functions are similar but use ‘movf.ps’ instead of
     ‘movt.ps’.

‘int __builtin_mips_any_c_COND_ps (v2sf A, v2sf B)’
‘int __builtin_mips_all_c_COND_ps (v2sf A, v2sf B)’
‘int __builtin_mips_any_cabs_COND_ps (v2sf A, v2sf B)’
‘int __builtin_mips_all_cabs_COND_ps (v2sf A, v2sf B)’
     Comparison of two paired-single values (‘c.COND.ps’/‘cabs.COND.ps’,
     ‘bc1any2t’/‘bc1any2f’).

     These functions compare A and B using ‘c.COND.ps’ or
     ‘cabs.COND.ps’.  The ‘any’ forms return ‘true’ if either result is
     ‘true’ and the ‘all’ forms return ‘true’ if both results are
     ‘true’.  For example:

          v2sf a, b;
          if (__builtin_mips_any_c_eq_ps (a, b))
            one_is_true ();
          else
            both_are_false ();

          if (__builtin_mips_all_c_eq_ps (a, b))
            both_are_true ();
          else
            one_is_false ();

‘int __builtin_mips_any_c_COND_4s (v2sf A, v2sf B, v2sf C, v2sf D)’
‘int __builtin_mips_all_c_COND_4s (v2sf A, v2sf B, v2sf C, v2sf D)’
‘int __builtin_mips_any_cabs_COND_4s (v2sf A, v2sf B, v2sf C, v2sf D)’
‘int __builtin_mips_all_cabs_COND_4s (v2sf A, v2sf B, v2sf C, v2sf D)’
     Comparison of four paired-single values
     (‘c.COND.ps’/‘cabs.COND.ps’, ‘bc1any4t’/‘bc1any4f’).

     These functions use ‘c.COND.ps’ or ‘cabs.COND.ps’ to compare A with
     B and to compare C with D.  The ‘any’ forms return ‘true’ if any of
     the four results are ‘true’ and the ‘all’ forms return ‘true’ if
     all four results are ‘true’.  For example:

          v2sf a, b, c, d;
          if (__builtin_mips_any_c_eq_4s (a, b, c, d))
            some_are_true ();
          else
            all_are_false ();

          if (__builtin_mips_all_c_eq_4s (a, b, c, d))
            all_are_true ();
          else
            some_are_false ();


File: gcc.info,  Node: MIPS SIMD Architecture (MSA) Support,  Next: Other MIPS Built-in Functions,  Prev: MIPS Loongson Built-in Functions,  Up: Target Builtins

6.60.17 MIPS SIMD Architecture (MSA) Support
--------------------------------------------

* Menu:

* MIPS SIMD Architecture Built-in Functions::

GCC provides intrinsics to access the SIMD instructions provided by the
MSA MIPS SIMD Architecture.  The interface is made available by
including ‘<msa.h>’ and using ‘-mmsa -mhard-float -mfp64 -mnan=2008’.
For each ‘__builtin_msa_*’, there is a shortened name of the intrinsic,
‘__msa_*’.

 MSA implements 128-bit wide vector registers, operating on 8-, 16-, 32-
and 64-bit integer, 16- and 32-bit fixed-point, or 32- and 64-bit
floating point data elements.  The following vectors typedefs are
included in ‘msa.h’:
   • ‘v16i8’, a vector of sixteen signed 8-bit integers;
   • ‘v16u8’, a vector of sixteen unsigned 8-bit integers;
   • ‘v8i16’, a vector of eight signed 16-bit integers;
   • ‘v8u16’, a vector of eight unsigned 16-bit integers;
   • ‘v4i32’, a vector of four signed 32-bit integers;
   • ‘v4u32’, a vector of four unsigned 32-bit integers;
   • ‘v2i64’, a vector of two signed 64-bit integers;
   • ‘v2u64’, a vector of two unsigned 64-bit integers;
   • ‘v4f32’, a vector of four 32-bit floats;
   • ‘v2f64’, a vector of two 64-bit doubles.

 Instructions and corresponding built-ins may have additional
restrictions and/or input/output values manipulated:
   • ‘imm0_1’, an integer literal in range 0 to 1;
   • ‘imm0_3’, an integer literal in range 0 to 3;
   • ‘imm0_7’, an integer literal in range 0 to 7;
   • ‘imm0_15’, an integer literal in range 0 to 15;
   • ‘imm0_31’, an integer literal in range 0 to 31;
   • ‘imm0_63’, an integer literal in range 0 to 63;
   • ‘imm0_255’, an integer literal in range 0 to 255;
   • ‘imm_n16_15’, an integer literal in range -16 to 15;
   • ‘imm_n512_511’, an integer literal in range -512 to 511;
   • ‘imm_n1024_1022’, an integer literal in range -512 to 511 left
     shifted by 1 bit, i.e., -1024, -1022, ..., 1020, 1022;
   • ‘imm_n2048_2044’, an integer literal in range -512 to 511 left
     shifted by 2 bits, i.e., -2048, -2044, ..., 2040, 2044;
   • ‘imm_n4096_4088’, an integer literal in range -512 to 511 left
     shifted by 3 bits, i.e., -4096, -4088, ..., 4080, 4088;
   • ‘imm1_4’, an integer literal in range 1 to 4;
   • ‘i32, i64, u32, u64, f32, f64’, defined as follows:

     {
     typedef int i32;
     #if __LONG_MAX__ == __LONG_LONG_MAX__
     typedef long i64;
     #else
     typedef long long i64;
     #endif

     typedef unsigned int u32;
     #if __LONG_MAX__ == __LONG_LONG_MAX__
     typedef unsigned long u64;
     #else
     typedef unsigned long long u64;
     #endif

     typedef double f64;
     typedef float f32;
     }


File: gcc.info,  Node: MIPS SIMD Architecture Built-in Functions,  Up: MIPS SIMD Architecture (MSA) Support

6.60.17.1 MIPS SIMD Architecture Built-in Functions
...................................................

The intrinsics provided are listed below; each is named after the
machine instruction.

     v16i8 __builtin_msa_add_a_b (v16i8, v16i8);
     v8i16 __builtin_msa_add_a_h (v8i16, v8i16);
     v4i32 __builtin_msa_add_a_w (v4i32, v4i32);
     v2i64 __builtin_msa_add_a_d (v2i64, v2i64);

     v16i8 __builtin_msa_adds_a_b (v16i8, v16i8);
     v8i16 __builtin_msa_adds_a_h (v8i16, v8i16);
     v4i32 __builtin_msa_adds_a_w (v4i32, v4i32);
     v2i64 __builtin_msa_adds_a_d (v2i64, v2i64);

     v16i8 __builtin_msa_adds_s_b (v16i8, v16i8);
     v8i16 __builtin_msa_adds_s_h (v8i16, v8i16);
     v4i32 __builtin_msa_adds_s_w (v4i32, v4i32);
     v2i64 __builtin_msa_adds_s_d (v2i64, v2i64);

     v16u8 __builtin_msa_adds_u_b (v16u8, v16u8);
     v8u16 __builtin_msa_adds_u_h (v8u16, v8u16);
     v4u32 __builtin_msa_adds_u_w (v4u32, v4u32);
     v2u64 __builtin_msa_adds_u_d (v2u64, v2u64);

     v16i8 __builtin_msa_addv_b (v16i8, v16i8);
     v8i16 __builtin_msa_addv_h (v8i16, v8i16);
     v4i32 __builtin_msa_addv_w (v4i32, v4i32);
     v2i64 __builtin_msa_addv_d (v2i64, v2i64);

     v16i8 __builtin_msa_addvi_b (v16i8, imm0_31);
     v8i16 __builtin_msa_addvi_h (v8i16, imm0_31);
     v4i32 __builtin_msa_addvi_w (v4i32, imm0_31);
     v2i64 __builtin_msa_addvi_d (v2i64, imm0_31);

     v16u8 __builtin_msa_and_v (v16u8, v16u8);

     v16u8 __builtin_msa_andi_b (v16u8, imm0_255);

     v16i8 __builtin_msa_asub_s_b (v16i8, v16i8);
     v8i16 __builtin_msa_asub_s_h (v8i16, v8i16);
     v4i32 __builtin_msa_asub_s_w (v4i32, v4i32);
     v2i64 __builtin_msa_asub_s_d (v2i64, v2i64);

     v16u8 __builtin_msa_asub_u_b (v16u8, v16u8);
     v8u16 __builtin_msa_asub_u_h (v8u16, v8u16);
     v4u32 __builtin_msa_asub_u_w (v4u32, v4u32);
     v2u64 __builtin_msa_asub_u_d (v2u64, v2u64);

     v16i8 __builtin_msa_ave_s_b (v16i8, v16i8);
     v8i16 __builtin_msa_ave_s_h (v8i16, v8i16);
     v4i32 __builtin_msa_ave_s_w (v4i32, v4i32);
     v2i64 __builtin_msa_ave_s_d (v2i64, v2i64);

     v16u8 __builtin_msa_ave_u_b (v16u8, v16u8);
     v8u16 __builtin_msa_ave_u_h (v8u16, v8u16);
     v4u32 __builtin_msa_ave_u_w (v4u32, v4u32);
     v2u64 __builtin_msa_ave_u_d (v2u64, v2u64);

     v16i8 __builtin_msa_aver_s_b (v16i8, v16i8);
     v8i16 __builtin_msa_aver_s_h (v8i16, v8i16);
     v4i32 __builtin_msa_aver_s_w (v4i32, v4i32);
     v2i64 __builtin_msa_aver_s_d (v2i64, v2i64);

     v16u8 __builtin_msa_aver_u_b (v16u8, v16u8);
     v8u16 __builtin_msa_aver_u_h (v8u16, v8u16);
     v4u32 __builtin_msa_aver_u_w (v4u32, v4u32);
     v2u64 __builtin_msa_aver_u_d (v2u64, v2u64);

     v16u8 __builtin_msa_bclr_b (v16u8, v16u8);
     v8u16 __builtin_msa_bclr_h (v8u16, v8u16);
     v4u32 __builtin_msa_bclr_w (v4u32, v4u32);
     v2u64 __builtin_msa_bclr_d (v2u64, v2u64);

     v16u8 __builtin_msa_bclri_b (v16u8, imm0_7);
     v8u16 __builtin_msa_bclri_h (v8u16, imm0_15);
     v4u32 __builtin_msa_bclri_w (v4u32, imm0_31);
     v2u64 __builtin_msa_bclri_d (v2u64, imm0_63);

     v16u8 __builtin_msa_binsl_b (v16u8, v16u8, v16u8);
     v8u16 __builtin_msa_binsl_h (v8u16, v8u16, v8u16);
     v4u32 __builtin_msa_binsl_w (v4u32, v4u32, v4u32);
     v2u64 __builtin_msa_binsl_d (v2u64, v2u64, v2u64);

     v16u8 __builtin_msa_binsli_b (v16u8, v16u8, imm0_7);
     v8u16 __builtin_msa_binsli_h (v8u16, v8u16, imm0_15);
     v4u32 __builtin_msa_binsli_w (v4u32, v4u32, imm0_31);
     v2u64 __builtin_msa_binsli_d (v2u64, v2u64, imm0_63);

     v16u8 __builtin_msa_binsr_b (v16u8, v16u8, v16u8);
     v8u16 __builtin_msa_binsr_h (v8u16, v8u16, v8u16);
     v4u32 __builtin_msa_binsr_w (v4u32, v4u32, v4u32);
     v2u64 __builtin_msa_binsr_d (v2u64, v2u64, v2u64);

     v16u8 __builtin_msa_binsri_b (v16u8, v16u8, imm0_7);
     v8u16 __builtin_msa_binsri_h (v8u16, v8u16, imm0_15);
     v4u32 __builtin_msa_binsri_w (v4u32, v4u32, imm0_31);
     v2u64 __builtin_msa_binsri_d (v2u64, v2u64, imm0_63);

     v16u8 __builtin_msa_bmnz_v (v16u8, v16u8, v16u8);

     v16u8 __builtin_msa_bmnzi_b (v16u8, v16u8, imm0_255);

     v16u8 __builtin_msa_bmz_v (v16u8, v16u8, v16u8);

     v16u8 __builtin_msa_bmzi_b (v16u8, v16u8, imm0_255);

     v16u8 __builtin_msa_bneg_b (v16u8, v16u8);
     v8u16 __builtin_msa_bneg_h (v8u16, v8u16);
     v4u32 __builtin_msa_bneg_w (v4u32, v4u32);
     v2u64 __builtin_msa_bneg_d (v2u64, v2u64);

     v16u8 __builtin_msa_bnegi_b (v16u8, imm0_7);
     v8u16 __builtin_msa_bnegi_h (v8u16, imm0_15);
     v4u32 __builtin_msa_bnegi_w (v4u32, imm0_31);
     v2u64 __builtin_msa_bnegi_d (v2u64, imm0_63);

     i32 __builtin_msa_bnz_b (v16u8);
     i32 __builtin_msa_bnz_h (v8u16);
     i32 __builtin_msa_bnz_w (v4u32);
     i32 __builtin_msa_bnz_d (v2u64);

     i32 __builtin_msa_bnz_v (v16u8);

     v16u8 __builtin_msa_bsel_v (v16u8, v16u8, v16u8);

     v16u8 __builtin_msa_bseli_b (v16u8, v16u8, imm0_255);

     v16u8 __builtin_msa_bset_b (v16u8, v16u8);
     v8u16 __builtin_msa_bset_h (v8u16, v8u16);
     v4u32 __builtin_msa_bset_w (v4u32, v4u32);
     v2u64 __builtin_msa_bset_d (v2u64, v2u64);

     v16u8 __builtin_msa_bseti_b (v16u8, imm0_7);
     v8u16 __builtin_msa_bseti_h (v8u16, imm0_15);
     v4u32 __builtin_msa_bseti_w (v4u32, imm0_31);
     v2u64 __builtin_msa_bseti_d (v2u64, imm0_63);

     i32 __builtin_msa_bz_b (v16u8);
     i32 __builtin_msa_bz_h (v8u16);
     i32 __builtin_msa_bz_w (v4u32);
     i32 __builtin_msa_bz_d (v2u64);

     i32 __builtin_msa_bz_v (v16u8);

     v16i8 __builtin_msa_ceq_b (v16i8, v16i8);
     v8i16 __builtin_msa_ceq_h (v8i16, v8i16);
     v4i32 __builtin_msa_ceq_w (v4i32, v4i32);
     v2i64 __builtin_msa_ceq_d (v2i64, v2i64);

     v16i8 __builtin_msa_ceqi_b (v16i8, imm_n16_15);
     v8i16 __builtin_msa_ceqi_h (v8i16, imm_n16_15);
     v4i32 __builtin_msa_ceqi_w (v4i32, imm_n16_15);
     v2i64 __builtin_msa_ceqi_d (v2i64, imm_n16_15);

     i32 __builtin_msa_cfcmsa (imm0_31);

     v16i8 __builtin_msa_cle_s_b (v16i8, v16i8);
     v8i16 __builtin_msa_cle_s_h (v8i16, v8i16);
     v4i32 __builtin_msa_cle_s_w (v4i32, v4i32);
     v2i64 __builtin_msa_cle_s_d (v2i64, v2i64);

     v16i8 __builtin_msa_cle_u_b (v16u8, v16u8);
     v8i16 __builtin_msa_cle_u_h (v8u16, v8u16);
     v4i32 __builtin_msa_cle_u_w (v4u32, v4u32);
     v2i64 __builtin_msa_cle_u_d (v2u64, v2u64);

     v16i8 __builtin_msa_clei_s_b (v16i8, imm_n16_15);
     v8i16 __builtin_msa_clei_s_h (v8i16, imm_n16_15);
     v4i32 __builtin_msa_clei_s_w (v4i32, imm_n16_15);
     v2i64 __builtin_msa_clei_s_d (v2i64, imm_n16_15);

     v16i8 __builtin_msa_clei_u_b (v16u8, imm0_31);
     v8i16 __builtin_msa_clei_u_h (v8u16, imm0_31);
     v4i32 __builtin_msa_clei_u_w (v4u32, imm0_31);
     v2i64 __builtin_msa_clei_u_d (v2u64, imm0_31);

     v16i8 __builtin_msa_clt_s_b (v16i8, v16i8);
     v8i16 __builtin_msa_clt_s_h (v8i16, v8i16);
     v4i32 __builtin_msa_clt_s_w (v4i32, v4i32);
     v2i64 __builtin_msa_clt_s_d (v2i64, v2i64);

     v16i8 __builtin_msa_clt_u_b (v16u8, v16u8);
     v8i16 __builtin_msa_clt_u_h (v8u16, v8u16);
     v4i32 __builtin_msa_clt_u_w (v4u32, v4u32);
     v2i64 __builtin_msa_clt_u_d (v2u64, v2u64);

     v16i8 __builtin_msa_clti_s_b (v16i8, imm_n16_15);
     v8i16 __builtin_msa_clti_s_h (v8i16, imm_n16_15);
     v4i32 __builtin_msa_clti_s_w (v4i32, imm_n16_15);
     v2i64 __builtin_msa_clti_s_d (v2i64, imm_n16_15);

     v16i8 __builtin_msa_clti_u_b (v16u8, imm0_31);
     v8i16 __builtin_msa_clti_u_h (v8u16, imm0_31);
     v4i32 __builtin_msa_clti_u_w (v4u32, imm0_31);
     v2i64 __builtin_msa_clti_u_d (v2u64, imm0_31);

     i32 __builtin_msa_copy_s_b (v16i8, imm0_15);
     i32 __builtin_msa_copy_s_h (v8i16, imm0_7);
     i32 __builtin_msa_copy_s_w (v4i32, imm0_3);
     i64 __builtin_msa_copy_s_d (v2i64, imm0_1);

     u32 __builtin_msa_copy_u_b (v16i8, imm0_15);
     u32 __builtin_msa_copy_u_h (v8i16, imm0_7);
     u32 __builtin_msa_copy_u_w (v4i32, imm0_3);
     u64 __builtin_msa_copy_u_d (v2i64, imm0_1);

     void __builtin_msa_ctcmsa (imm0_31, i32);

     v16i8 __builtin_msa_div_s_b (v16i8, v16i8);
     v8i16 __builtin_msa_div_s_h (v8i16, v8i16);
     v4i32 __builtin_msa_div_s_w (v4i32, v4i32);
     v2i64 __builtin_msa_div_s_d (v2i64, v2i64);

     v16u8 __builtin_msa_div_u_b (v16u8, v16u8);
     v8u16 __builtin_msa_div_u_h (v8u16, v8u16);
     v4u32 __builtin_msa_div_u_w (v4u32, v4u32);
     v2u64 __builtin_msa_div_u_d (v2u64, v2u64);

     v8i16 __builtin_msa_dotp_s_h (v16i8, v16i8);
     v4i32 __builtin_msa_dotp_s_w (v8i16, v8i16);
     v2i64 __builtin_msa_dotp_s_d (v4i32, v4i32);

     v8u16 __builtin_msa_dotp_u_h (v16u8, v16u8);
     v4u32 __builtin_msa_dotp_u_w (v8u16, v8u16);
     v2u64 __builtin_msa_dotp_u_d (v4u32, v4u32);

     v8i16 __builtin_msa_dpadd_s_h (v8i16, v16i8, v16i8);
     v4i32 __builtin_msa_dpadd_s_w (v4i32, v8i16, v8i16);
     v2i64 __builtin_msa_dpadd_s_d (v2i64, v4i32, v4i32);

     v8u16 __builtin_msa_dpadd_u_h (v8u16, v16u8, v16u8);
     v4u32 __builtin_msa_dpadd_u_w (v4u32, v8u16, v8u16);
     v2u64 __builtin_msa_dpadd_u_d (v2u64, v4u32, v4u32);

     v8i16 __builtin_msa_dpsub_s_h (v8i16, v16i8, v16i8);
     v4i32 __builtin_msa_dpsub_s_w (v4i32, v8i16, v8i16);
     v2i64 __builtin_msa_dpsub_s_d (v2i64, v4i32, v4i32);

     v8i16 __builtin_msa_dpsub_u_h (v8i16, v16u8, v16u8);
     v4i32 __builtin_msa_dpsub_u_w (v4i32, v8u16, v8u16);
     v2i64 __builtin_msa_dpsub_u_d (v2i64, v4u32, v4u32);

     v4f32 __builtin_msa_fadd_w (v4f32, v4f32);
     v2f64 __builtin_msa_fadd_d (v2f64, v2f64);

     v4i32 __builtin_msa_fcaf_w (v4f32, v4f32);
     v2i64 __builtin_msa_fcaf_d (v2f64, v2f64);

     v4i32 __builtin_msa_fceq_w (v4f32, v4f32);
     v2i64 __builtin_msa_fceq_d (v2f64, v2f64);

     v4i32 __builtin_msa_fclass_w (v4f32);
     v2i64 __builtin_msa_fclass_d (v2f64);

     v4i32 __builtin_msa_fcle_w (v4f32, v4f32);
     v2i64 __builtin_msa_fcle_d (v2f64, v2f64);

     v4i32 __builtin_msa_fclt_w (v4f32, v4f32);
     v2i64 __builtin_msa_fclt_d (v2f64, v2f64);

     v4i32 __builtin_msa_fcne_w (v4f32, v4f32);
     v2i64 __builtin_msa_fcne_d (v2f64, v2f64);

     v4i32 __builtin_msa_fcor_w (v4f32, v4f32);
     v2i64 __builtin_msa_fcor_d (v2f64, v2f64);

     v4i32 __builtin_msa_fcueq_w (v4f32, v4f32);
     v2i64 __builtin_msa_fcueq_d (v2f64, v2f64);

     v4i32 __builtin_msa_fcule_w (v4f32, v4f32);
     v2i64 __builtin_msa_fcule_d (v2f64, v2f64);

     v4i32 __builtin_msa_fcult_w (v4f32, v4f32);
     v2i64 __builtin_msa_fcult_d (v2f64, v2f64);

     v4i32 __builtin_msa_fcun_w (v4f32, v4f32);
     v2i64 __builtin_msa_fcun_d (v2f64, v2f64);

     v4i32 __builtin_msa_fcune_w (v4f32, v4f32);
     v2i64 __builtin_msa_fcune_d (v2f64, v2f64);

     v4f32 __builtin_msa_fdiv_w (v4f32, v4f32);
     v2f64 __builtin_msa_fdiv_d (v2f64, v2f64);

     v8i16 __builtin_msa_fexdo_h (v4f32, v4f32);
     v4f32 __builtin_msa_fexdo_w (v2f64, v2f64);

     v4f32 __builtin_msa_fexp2_w (v4f32, v4i32);
     v2f64 __builtin_msa_fexp2_d (v2f64, v2i64);

     v4f32 __builtin_msa_fexupl_w (v8i16);
     v2f64 __builtin_msa_fexupl_d (v4f32);

     v4f32 __builtin_msa_fexupr_w (v8i16);
     v2f64 __builtin_msa_fexupr_d (v4f32);

     v4f32 __builtin_msa_ffint_s_w (v4i32);
     v2f64 __builtin_msa_ffint_s_d (v2i64);

     v4f32 __builtin_msa_ffint_u_w (v4u32);
     v2f64 __builtin_msa_ffint_u_d (v2u64);

     v4f32 __builtin_msa_ffql_w (v8i16);
     v2f64 __builtin_msa_ffql_d (v4i32);

     v4f32 __builtin_msa_ffqr_w (v8i16);
     v2f64 __builtin_msa_ffqr_d (v4i32);

     v16i8 __builtin_msa_fill_b (i32);
     v8i16 __builtin_msa_fill_h (i32);
     v4i32 __builtin_msa_fill_w (i32);
     v2i64 __builtin_msa_fill_d (i64);

     v4f32 __builtin_msa_flog2_w (v4f32);
     v2f64 __builtin_msa_flog2_d (v2f64);

     v4f32 __builtin_msa_fmadd_w (v4f32, v4f32, v4f32);
     v2f64 __builtin_msa_fmadd_d (v2f64, v2f64, v2f64);

     v4f32 __builtin_msa_fmax_w (v4f32, v4f32);
     v2f64 __builtin_msa_fmax_d (v2f64, v2f64);

     v4f32 __builtin_msa_fmax_a_w (v4f32, v4f32);
     v2f64 __builtin_msa_fmax_a_d (v2f64, v2f64);

     v4f32 __builtin_msa_fmin_w (v4f32, v4f32);
     v2f64 __builtin_msa_fmin_d (v2f64, v2f64);

     v4f32 __builtin_msa_fmin_a_w (v4f32, v4f32);
     v2f64 __builtin_msa_fmin_a_d (v2f64, v2f64);

     v4f32 __builtin_msa_fmsub_w (v4f32, v4f32, v4f32);
     v2f64 __builtin_msa_fmsub_d (v2f64, v2f64, v2f64);

     v4f32 __builtin_msa_fmul_w (v4f32, v4f32);
     v2f64 __builtin_msa_fmul_d (v2f64, v2f64);

     v4f32 __builtin_msa_frint_w (v4f32);
     v2f64 __builtin_msa_frint_d (v2f64);

     v4f32 __builtin_msa_frcp_w (v4f32);
     v2f64 __builtin_msa_frcp_d (v2f64);

     v4f32 __builtin_msa_frsqrt_w (v4f32);
     v2f64 __builtin_msa_frsqrt_d (v2f64);

     v4i32 __builtin_msa_fsaf_w (v4f32, v4f32);
     v2i64 __builtin_msa_fsaf_d (v2f64, v2f64);

     v4i32 __builtin_msa_fseq_w (v4f32, v4f32);
     v2i64 __builtin_msa_fseq_d (v2f64, v2f64);

     v4i32 __builtin_msa_fsle_w (v4f32, v4f32);
     v2i64 __builtin_msa_fsle_d (v2f64, v2f64);

     v4i32 __builtin_msa_fslt_w (v4f32, v4f32);
     v2i64 __builtin_msa_fslt_d (v2f64, v2f64);

     v4i32 __builtin_msa_fsne_w (v4f32, v4f32);
     v2i64 __builtin_msa_fsne_d (v2f64, v2f64);

     v4i32 __builtin_msa_fsor_w (v4f32, v4f32);
     v2i64 __builtin_msa_fsor_d (v2f64, v2f64);

     v4f32 __builtin_msa_fsqrt_w (v4f32);
     v2f64 __builtin_msa_fsqrt_d (v2f64);

     v4f32 __builtin_msa_fsub_w (v4f32, v4f32);
     v2f64 __builtin_msa_fsub_d (v2f64, v2f64);

     v4i32 __builtin_msa_fsueq_w (v4f32, v4f32);
     v2i64 __builtin_msa_fsueq_d (v2f64, v2f64);

     v4i32 __builtin_msa_fsule_w (v4f32, v4f32);
     v2i64 __builtin_msa_fsule_d (v2f64, v2f64);

     v4i32 __builtin_msa_fsult_w (v4f32, v4f32);
     v2i64 __builtin_msa_fsult_d (v2f64, v2f64);

     v4i32 __builtin_msa_fsun_w (v4f32, v4f32);
     v2i64 __builtin_msa_fsun_d (v2f64, v2f64);

     v4i32 __builtin_msa_fsune_w (v4f32, v4f32);
     v2i64 __builtin_msa_fsune_d (v2f64, v2f64);

     v4i32 __builtin_msa_ftint_s_w (v4f32);
     v2i64 __builtin_msa_ftint_s_d (v2f64);

     v4u32 __builtin_msa_ftint_u_w (v4f32);
     v2u64 __builtin_msa_ftint_u_d (v2f64);

     v8i16 __builtin_msa_ftq_h (v4f32, v4f32);
     v4i32 __builtin_msa_ftq_w (v2f64, v2f64);

     v4i32 __builtin_msa_ftrunc_s_w (v4f32);
     v2i64 __builtin_msa_ftrunc_s_d (v2f64);

     v4u32 __builtin_msa_ftrunc_u_w (v4f32);
     v2u64 __builtin_msa_ftrunc_u_d (v2f64);

     v8i16 __builtin_msa_hadd_s_h (v16i8, v16i8);
     v4i32 __builtin_msa_hadd_s_w (v8i16, v8i16);
     v2i64 __builtin_msa_hadd_s_d (v4i32, v4i32);

     v8u16 __builtin_msa_hadd_u_h (v16u8, v16u8);
     v4u32 __builtin_msa_hadd_u_w (v8u16, v8u16);
     v2u64 __builtin_msa_hadd_u_d (v4u32, v4u32);

     v8i16 __builtin_msa_hsub_s_h (v16i8, v16i8);
     v4i32 __builtin_msa_hsub_s_w (v8i16, v8i16);
     v2i64 __builtin_msa_hsub_s_d (v4i32, v4i32);

     v8i16 __builtin_msa_hsub_u_h (v16u8, v16u8);
     v4i32 __builtin_msa_hsub_u_w (v8u16, v8u16);
     v2i64 __builtin_msa_hsub_u_d (v4u32, v4u32);

     v16i8 __builtin_msa_ilvev_b (v16i8, v16i8);
     v8i16 __builtin_msa_ilvev_h (v8i16, v8i16);
     v4i32 __builtin_msa_ilvev_w (v4i32, v4i32);
     v2i64 __builtin_msa_ilvev_d (v2i64, v2i64);

     v16i8 __builtin_msa_ilvl_b (v16i8, v16i8);
     v8i16 __builtin_msa_ilvl_h (v8i16, v8i16);
     v4i32 __builtin_msa_ilvl_w (v4i32, v4i32);
     v2i64 __builtin_msa_ilvl_d (v2i64, v2i64);

     v16i8 __builtin_msa_ilvod_b (v16i8, v16i8);
     v8i16 __builtin_msa_ilvod_h (v8i16, v8i16);
     v4i32 __builtin_msa_ilvod_w (v4i32, v4i32);
     v2i64 __builtin_msa_ilvod_d (v2i64, v2i64);

     v16i8 __builtin_msa_ilvr_b (v16i8, v16i8);
     v8i16 __builtin_msa_ilvr_h (v8i16, v8i16);
     v4i32 __builtin_msa_ilvr_w (v4i32, v4i32);
     v2i64 __builtin_msa_ilvr_d (v2i64, v2i64);

     v16i8 __builtin_msa_insert_b (v16i8, imm0_15, i32);
     v8i16 __builtin_msa_insert_h (v8i16, imm0_7, i32);
     v4i32 __builtin_msa_insert_w (v4i32, imm0_3, i32);
     v2i64 __builtin_msa_insert_d (v2i64, imm0_1, i64);

     v16i8 __builtin_msa_insve_b (v16i8, imm0_15, v16i8);
     v8i16 __builtin_msa_insve_h (v8i16, imm0_7, v8i16);
     v4i32 __builtin_msa_insve_w (v4i32, imm0_3, v4i32);
     v2i64 __builtin_msa_insve_d (v2i64, imm0_1, v2i64);

     v16i8 __builtin_msa_ld_b (const void *, imm_n512_511);
     v8i16 __builtin_msa_ld_h (const void *, imm_n1024_1022);
     v4i32 __builtin_msa_ld_w (const void *, imm_n2048_2044);
     v2i64 __builtin_msa_ld_d (const void *, imm_n4096_4088);

     v16i8 __builtin_msa_ldi_b (imm_n512_511);
     v8i16 __builtin_msa_ldi_h (imm_n512_511);
     v4i32 __builtin_msa_ldi_w (imm_n512_511);
     v2i64 __builtin_msa_ldi_d (imm_n512_511);

     v8i16 __builtin_msa_madd_q_h (v8i16, v8i16, v8i16);
     v4i32 __builtin_msa_madd_q_w (v4i32, v4i32, v4i32);

     v8i16 __builtin_msa_maddr_q_h (v8i16, v8i16, v8i16);
     v4i32 __builtin_msa_maddr_q_w (v4i32, v4i32, v4i32);

     v16i8 __builtin_msa_maddv_b (v16i8, v16i8, v16i8);
     v8i16 __builtin_msa_maddv_h (v8i16, v8i16, v8i16);
     v4i32 __builtin_msa_maddv_w (v4i32, v4i32, v4i32);
     v2i64 __builtin_msa_maddv_d (v2i64, v2i64, v2i64);

     v16i8 __builtin_msa_max_a_b (v16i8, v16i8);
     v8i16 __builtin_msa_max_a_h (v8i16, v8i16);
     v4i32 __builtin_msa_max_a_w (v4i32, v4i32);
     v2i64 __builtin_msa_max_a_d (v2i64, v2i64);

     v16i8 __builtin_msa_max_s_b (v16i8, v16i8);
     v8i16 __builtin_msa_max_s_h (v8i16, v8i16);
     v4i32 __builtin_msa_max_s_w (v4i32, v4i32);
     v2i64 __builtin_msa_max_s_d (v2i64, v2i64);

     v16u8 __builtin_msa_max_u_b (v16u8, v16u8);
     v8u16 __builtin_msa_max_u_h (v8u16, v8u16);
     v4u32 __builtin_msa_max_u_w (v4u32, v4u32);
     v2u64 __builtin_msa_max_u_d (v2u64, v2u64);

     v16i8 __builtin_msa_maxi_s_b (v16i8, imm_n16_15);
     v8i16 __builtin_msa_maxi_s_h (v8i16, imm_n16_15);
     v4i32 __builtin_msa_maxi_s_w (v4i32, imm_n16_15);
     v2i64 __builtin_msa_maxi_s_d (v2i64, imm_n16_15);

     v16u8 __builtin_msa_maxi_u_b (v16u8, imm0_31);
     v8u16 __builtin_msa_maxi_u_h (v8u16, imm0_31);
     v4u32 __builtin_msa_maxi_u_w (v4u32, imm0_31);
     v2u64 __builtin_msa_maxi_u_d (v2u64, imm0_31);

     v16i8 __builtin_msa_min_a_b (v16i8, v16i8);
     v8i16 __builtin_msa_min_a_h (v8i16, v8i16);
     v4i32 __builtin_msa_min_a_w (v4i32, v4i32);
     v2i64 __builtin_msa_min_a_d (v2i64, v2i64);

     v16i8 __builtin_msa_min_s_b (v16i8, v16i8);
     v8i16 __builtin_msa_min_s_h (v8i16, v8i16);
     v4i32 __builtin_msa_min_s_w (v4i32, v4i32);
     v2i64 __builtin_msa_min_s_d (v2i64, v2i64);

     v16u8 __builtin_msa_min_u_b (v16u8, v16u8);
     v8u16 __builtin_msa_min_u_h (v8u16, v8u16);
     v4u32 __builtin_msa_min_u_w (v4u32, v4u32);
     v2u64 __builtin_msa_min_u_d (v2u64, v2u64);

     v16i8 __builtin_msa_mini_s_b (v16i8, imm_n16_15);
     v8i16 __builtin_msa_mini_s_h (v8i16, imm_n16_15);
     v4i32 __builtin_msa_mini_s_w (v4i32, imm_n16_15);
     v2i64 __builtin_msa_mini_s_d (v2i64, imm_n16_15);

     v16u8 __builtin_msa_mini_u_b (v16u8, imm0_31);
     v8u16 __builtin_msa_mini_u_h (v8u16, imm0_31);
     v4u32 __builtin_msa_mini_u_w (v4u32, imm0_31);
     v2u64 __builtin_msa_mini_u_d (v2u64, imm0_31);

     v16i8 __builtin_msa_mod_s_b (v16i8, v16i8);
     v8i16 __builtin_msa_mod_s_h (v8i16, v8i16);
     v4i32 __builtin_msa_mod_s_w (v4i32, v4i32);
     v2i64 __builtin_msa_mod_s_d (v2i64, v2i64);

     v16u8 __builtin_msa_mod_u_b (v16u8, v16u8);
     v8u16 __builtin_msa_mod_u_h (v8u16, v8u16);
     v4u32 __builtin_msa_mod_u_w (v4u32, v4u32);
     v2u64 __builtin_msa_mod_u_d (v2u64, v2u64);

     v16i8 __builtin_msa_move_v (v16i8);

     v8i16 __builtin_msa_msub_q_h (v8i16, v8i16, v8i16);
     v4i32 __builtin_msa_msub_q_w (v4i32, v4i32, v4i32);

     v8i16 __builtin_msa_msubr_q_h (v8i16, v8i16, v8i16);
     v4i32 __builtin_msa_msubr_q_w (v4i32, v4i32, v4i32);

     v16i8 __builtin_msa_msubv_b (v16i8, v16i8, v16i8);
     v8i16 __builtin_msa_msubv_h (v8i16, v8i16, v8i16);
     v4i32 __builtin_msa_msubv_w (v4i32, v4i32, v4i32);
     v2i64 __builtin_msa_msubv_d (v2i64, v2i64, v2i64);

     v8i16 __builtin_msa_mul_q_h (v8i16, v8i16);
     v4i32 __builtin_msa_mul_q_w (v4i32, v4i32);

     v8i16 __builtin_msa_mulr_q_h (v8i16, v8i16);
     v4i32 __builtin_msa_mulr_q_w (v4i32, v4i32);

     v16i8 __builtin_msa_mulv_b (v16i8, v16i8);
     v8i16 __builtin_msa_mulv_h (v8i16, v8i16);
     v4i32 __builtin_msa_mulv_w (v4i32, v4i32);
     v2i64 __builtin_msa_mulv_d (v2i64, v2i64);

     v16i8 __builtin_msa_nloc_b (v16i8);
     v8i16 __builtin_msa_nloc_h (v8i16);
     v4i32 __builtin_msa_nloc_w (v4i32);
     v2i64 __builtin_msa_nloc_d (v2i64);

     v16i8 __builtin_msa_nlzc_b (v16i8);
     v8i16 __builtin_msa_nlzc_h (v8i16);
     v4i32 __builtin_msa_nlzc_w (v4i32);
     v2i64 __builtin_msa_nlzc_d (v2i64);

     v16u8 __builtin_msa_nor_v (v16u8, v16u8);

     v16u8 __builtin_msa_nori_b (v16u8, imm0_255);

     v16u8 __builtin_msa_or_v (v16u8, v16u8);

     v16u8 __builtin_msa_ori_b (v16u8, imm0_255);

     v16i8 __builtin_msa_pckev_b (v16i8, v16i8);
     v8i16 __builtin_msa_pckev_h (v8i16, v8i16);
     v4i32 __builtin_msa_pckev_w (v4i32, v4i32);
     v2i64 __builtin_msa_pckev_d (v2i64, v2i64);

     v16i8 __builtin_msa_pckod_b (v16i8, v16i8);
     v8i16 __builtin_msa_pckod_h (v8i16, v8i16);
     v4i32 __builtin_msa_pckod_w (v4i32, v4i32);
     v2i64 __builtin_msa_pckod_d (v2i64, v2i64);

     v16i8 __builtin_msa_pcnt_b (v16i8);
     v8i16 __builtin_msa_pcnt_h (v8i16);
     v4i32 __builtin_msa_pcnt_w (v4i32);
     v2i64 __builtin_msa_pcnt_d (v2i64);

     v16i8 __builtin_msa_sat_s_b (v16i8, imm0_7);
     v8i16 __builtin_msa_sat_s_h (v8i16, imm0_15);
     v4i32 __builtin_msa_sat_s_w (v4i32, imm0_31);
     v2i64 __builtin_msa_sat_s_d (v2i64, imm0_63);

     v16u8 __builtin_msa_sat_u_b (v16u8, imm0_7);
     v8u16 __builtin_msa_sat_u_h (v8u16, imm0_15);
     v4u32 __builtin_msa_sat_u_w (v4u32, imm0_31);
     v2u64 __builtin_msa_sat_u_d (v2u64, imm0_63);

     v16i8 __builtin_msa_shf_b (v16i8, imm0_255);
     v8i16 __builtin_msa_shf_h (v8i16, imm0_255);
     v4i32 __builtin_msa_shf_w (v4i32, imm0_255);

     v16i8 __builtin_msa_sld_b (v16i8, v16i8, i32);
     v8i16 __builtin_msa_sld_h (v8i16, v8i16, i32);
     v4i32 __builtin_msa_sld_w (v4i32, v4i32, i32);
     v2i64 __builtin_msa_sld_d (v2i64, v2i64, i32);

     v16i8 __builtin_msa_sldi_b (v16i8, v16i8, imm0_15);
     v8i16 __builtin_msa_sldi_h (v8i16, v8i16, imm0_7);
     v4i32 __builtin_msa_sldi_w (v4i32, v4i32, imm0_3);
     v2i64 __builtin_msa_sldi_d (v2i64, v2i64, imm0_1);

     v16i8 __builtin_msa_sll_b (v16i8, v16i8);
     v8i16 __builtin_msa_sll_h (v8i16, v8i16);
     v4i32 __builtin_msa_sll_w (v4i32, v4i32);
     v2i64 __builtin_msa_sll_d (v2i64, v2i64);

     v16i8 __builtin_msa_slli_b (v16i8, imm0_7);
     v8i16 __builtin_msa_slli_h (v8i16, imm0_15);
     v4i32 __builtin_msa_slli_w (v4i32, imm0_31);
     v2i64 __builtin_msa_slli_d (v2i64, imm0_63);

     v16i8 __builtin_msa_splat_b (v16i8, i32);
     v8i16 __builtin_msa_splat_h (v8i16, i32);
     v4i32 __builtin_msa_splat_w (v4i32, i32);
     v2i64 __builtin_msa_splat_d (v2i64, i32);

     v16i8 __builtin_msa_splati_b (v16i8, imm0_15);
     v8i16 __builtin_msa_splati_h (v8i16, imm0_7);
     v4i32 __builtin_msa_splati_w (v4i32, imm0_3);
     v2i64 __builtin_msa_splati_d (v2i64, imm0_1);

     v16i8 __builtin_msa_sra_b (v16i8, v16i8);
     v8i16 __builtin_msa_sra_h (v8i16, v8i16);
     v4i32 __builtin_msa_sra_w (v4i32, v4i32);
     v2i64 __builtin_msa_sra_d (v2i64, v2i64);

     v16i8 __builtin_msa_srai_b (v16i8, imm0_7);
     v8i16 __builtin_msa_srai_h (v8i16, imm0_15);
     v4i32 __builtin_msa_srai_w (v4i32, imm0_31);
     v2i64 __builtin_msa_srai_d (v2i64, imm0_63);

     v16i8 __builtin_msa_srar_b (v16i8, v16i8);
     v8i16 __builtin_msa_srar_h (v8i16, v8i16);
     v4i32 __builtin_msa_srar_w (v4i32, v4i32);
     v2i64 __builtin_msa_srar_d (v2i64, v2i64);

     v16i8 __builtin_msa_srari_b (v16i8, imm0_7);
     v8i16 __builtin_msa_srari_h (v8i16, imm0_15);
     v4i32 __builtin_msa_srari_w (v4i32, imm0_31);
     v2i64 __builtin_msa_srari_d (v2i64, imm0_63);

     v16i8 __builtin_msa_srl_b (v16i8, v16i8);
     v8i16 __builtin_msa_srl_h (v8i16, v8i16);
     v4i32 __builtin_msa_srl_w (v4i32, v4i32);
     v2i64 __builtin_msa_srl_d (v2i64, v2i64);

     v16i8 __builtin_msa_srli_b (v16i8, imm0_7);
     v8i16 __builtin_msa_srli_h (v8i16, imm0_15);
     v4i32 __builtin_msa_srli_w (v4i32, imm0_31);
     v2i64 __builtin_msa_srli_d (v2i64, imm0_63);

     v16i8 __builtin_msa_srlr_b (v16i8, v16i8);
     v8i16 __builtin_msa_srlr_h (v8i16, v8i16);
     v4i32 __builtin_msa_srlr_w (v4i32, v4i32);
     v2i64 __builtin_msa_srlr_d (v2i64, v2i64);

     v16i8 __builtin_msa_srlri_b (v16i8, imm0_7);
     v8i16 __builtin_msa_srlri_h (v8i16, imm0_15);
     v4i32 __builtin_msa_srlri_w (v4i32, imm0_31);
     v2i64 __builtin_msa_srlri_d (v2i64, imm0_63);

     void __builtin_msa_st_b (v16i8, void *, imm_n512_511);
     void __builtin_msa_st_h (v8i16, void *, imm_n1024_1022);
     void __builtin_msa_st_w (v4i32, void *, imm_n2048_2044);
     void __builtin_msa_st_d (v2i64, void *, imm_n4096_4088);

     v16i8 __builtin_msa_subs_s_b (v16i8, v16i8);
     v8i16 __builtin_msa_subs_s_h (v8i16, v8i16);
     v4i32 __builtin_msa_subs_s_w (v4i32, v4i32);
     v2i64 __builtin_msa_subs_s_d (v2i64, v2i64);

     v16u8 __builtin_msa_subs_u_b (v16u8, v16u8);
     v8u16 __builtin_msa_subs_u_h (v8u16, v8u16);
     v4u32 __builtin_msa_subs_u_w (v4u32, v4u32);
     v2u64 __builtin_msa_subs_u_d (v2u64, v2u64);

     v16u8 __builtin_msa_subsus_u_b (v16u8, v16i8);
     v8u16 __builtin_msa_subsus_u_h (v8u16, v8i16);
     v4u32 __builtin_msa_subsus_u_w (v4u32, v4i32);
     v2u64 __builtin_msa_subsus_u_d (v2u64, v2i64);

     v16i8 __builtin_msa_subsuu_s_b (v16u8, v16u8);
     v8i16 __builtin_msa_subsuu_s_h (v8u16, v8u16);
     v4i32 __builtin_msa_subsuu_s_w (v4u32, v4u32);
     v2i64 __builtin_msa_subsuu_s_d (v2u64, v2u64);

     v16i8 __builtin_msa_subv_b (v16i8, v16i8);
     v8i16 __builtin_msa_subv_h (v8i16, v8i16);
     v4i32 __builtin_msa_subv_w (v4i32, v4i32);
     v2i64 __builtin_msa_subv_d (v2i64, v2i64);

     v16i8 __builtin_msa_subvi_b (v16i8, imm0_31);
     v8i16 __builtin_msa_subvi_h (v8i16, imm0_31);
     v4i32 __builtin_msa_subvi_w (v4i32, imm0_31);
     v2i64 __builtin_msa_subvi_d (v2i64, imm0_31);

     v16i8 __builtin_msa_vshf_b (v16i8, v16i8, v16i8);
     v8i16 __builtin_msa_vshf_h (v8i16, v8i16, v8i16);
     v4i32 __builtin_msa_vshf_w (v4i32, v4i32, v4i32);
     v2i64 __builtin_msa_vshf_d (v2i64, v2i64, v2i64);

     v16u8 __builtin_msa_xor_v (v16u8, v16u8);

     v16u8 __builtin_msa_xori_b (v16u8, imm0_255);


File: gcc.info,  Node: Other MIPS Built-in Functions,  Next: MSP430 Built-in Functions,  Prev: MIPS SIMD Architecture (MSA) Support,  Up: Target Builtins

6.60.18 Other MIPS Built-in Functions
-------------------------------------

GCC provides other MIPS-specific built-in functions:

‘void __builtin_mips_cache (int OP, const volatile void *ADDR)’
     Insert a ‘cache’ instruction with operands OP and ADDR.  GCC
     defines the preprocessor macro ‘___GCC_HAVE_BUILTIN_MIPS_CACHE’
     when this function is available.

‘unsigned int __builtin_mips_get_fcsr (void)’
‘void __builtin_mips_set_fcsr (unsigned int VALUE)’
     Get and set the contents of the floating-point control and status
     register (FPU control register 31).  These functions are only
     available in hard-float code but can be called in both MIPS16 and
     non-MIPS16 contexts.

     ‘__builtin_mips_set_fcsr’ can be used to change any bit of the
     register except the condition codes, which GCC assumes are
     preserved.


File: gcc.info,  Node: MSP430 Built-in Functions,  Next: NDS32 Built-in Functions,  Prev: Other MIPS Built-in Functions,  Up: Target Builtins

6.60.19 MSP430 Built-in Functions
---------------------------------

GCC provides a couple of special builtin functions to aid in the writing
of interrupt handlers in C.

‘__bic_SR_register_on_exit (int MASK)’
     This clears the indicated bits in the saved copy of the status
     register currently residing on the stack.  This only works inside
     interrupt handlers and the changes to the status register will only
     take affect once the handler returns.

‘__bis_SR_register_on_exit (int MASK)’
     This sets the indicated bits in the saved copy of the status
     register currently residing on the stack.  This only works inside
     interrupt handlers and the changes to the status register will only
     take affect once the handler returns.

‘__delay_cycles (long long CYCLES)’
     This inserts an instruction sequence that takes exactly CYCLES
     cycles (between 0 and about 17E9) to complete.  The inserted
     sequence may use jumps, loops, or no-ops, and does not interfere
     with any other instructions.  Note that CYCLES must be a
     compile-time constant integer - that is, you must pass a number,
     not a variable that may be optimized to a constant later.  The
     number of cycles delayed by this builtin is exact.


File: gcc.info,  Node: NDS32 Built-in Functions,  Next: picoChip Built-in Functions,  Prev: MSP430 Built-in Functions,  Up: Target Builtins

6.60.20 NDS32 Built-in Functions
--------------------------------

These built-in functions are available for the NDS32 target:

 -- Built-in Function: void __builtin_nds32_isync (int *ADDR)
     Insert an ISYNC instruction into the instruction stream where ADDR
     is an instruction address for serialization.

 -- Built-in Function: void __builtin_nds32_isb (void)
     Insert an ISB instruction into the instruction stream.

 -- Built-in Function: int __builtin_nds32_mfsr (int SR)
     Return the content of a system register which is mapped by SR.

 -- Built-in Function: int __builtin_nds32_mfusr (int USR)
     Return the content of a user space register which is mapped by USR.

 -- Built-in Function: void __builtin_nds32_mtsr (int VALUE, int SR)
     Move the VALUE to a system register which is mapped by SR.

 -- Built-in Function: void __builtin_nds32_mtusr (int VALUE, int USR)
     Move the VALUE to a user space register which is mapped by USR.

 -- Built-in Function: void __builtin_nds32_setgie_en (void)
     Enable global interrupt.

 -- Built-in Function: void __builtin_nds32_setgie_dis (void)
     Disable global interrupt.


File: gcc.info,  Node: picoChip Built-in Functions,  Next: Basic PowerPC Built-in Functions,  Prev: NDS32 Built-in Functions,  Up: Target Builtins

6.60.21 picoChip Built-in Functions
-----------------------------------

GCC provides an interface to selected machine instructions from the
picoChip instruction set.

‘int __builtin_sbc (int VALUE)’
     Sign bit count.  Return the number of consecutive bits in VALUE
     that have the same value as the sign bit.  The result is the number
     of leading sign bits minus one, giving the number of redundant sign
     bits in VALUE.

‘int __builtin_byteswap (int VALUE)’
     Byte swap.  Return the result of swapping the upper and lower bytes
     of VALUE.

‘int __builtin_brev (int VALUE)’
     Bit reversal.  Return the result of reversing the bits in VALUE.
     Bit 15 is swapped with bit 0, bit 14 is swapped with bit 1, and so
     on.

‘int __builtin_adds (int X, int Y)’
     Saturating addition.  Return the result of adding X and Y, storing
     the value 32767 if the result overflows.

‘int __builtin_subs (int X, int Y)’
     Saturating subtraction.  Return the result of subtracting Y from X,
     storing the value −32768 if the result overflows.

‘void __builtin_halt (void)’
     Halt.  The processor stops execution.  This built-in is useful for
     implementing assertions.


File: gcc.info,  Node: Basic PowerPC Built-in Functions,  Next: PowerPC AltiVec/VSX Built-in Functions,  Prev: picoChip Built-in Functions,  Up: Target Builtins

6.60.22 Basic PowerPC Built-in Functions
----------------------------------------

* Menu:

* Basic PowerPC Built-in Functions Available on all Configurations::
* Basic PowerPC Built-in Functions Available on ISA 2.05::
* Basic PowerPC Built-in Functions Available on ISA 2.06::
* Basic PowerPC Built-in Functions Available on ISA 2.07::
* Basic PowerPC Built-in Functions Available on ISA 3.0::
* Basic PowerPC Built-in Functions Available on ISA 3.1::

This section describes PowerPC built-in functions that do not require
the inclusion of any special header files to declare prototypes or
provide macro definitions.  The sections that follow describe additional
PowerPC built-in functions.


File: gcc.info,  Node: Basic PowerPC Built-in Functions Available on all Configurations,  Next: Basic PowerPC Built-in Functions Available on ISA 2.05,  Up: Basic PowerPC Built-in Functions

6.60.22.1 Basic PowerPC Built-in Functions Available on all Configurations
..........................................................................

 -- Built-in Function: void __builtin_cpu_init (void)
     This function is a ‘nop’ on the PowerPC platform and is included
     solely to maintain API compatibility with the x86 builtins.

 -- Built-in Function: int __builtin_cpu_is (const char *CPUNAME)
     This function returns a value of ‘1’ if the run-time CPU is of type
     CPUNAME and returns ‘0’ otherwise

     The ‘__builtin_cpu_is’ function requires GLIBC 2.23 or newer which
     exports the hardware capability bits.  GCC defines the macro
     ‘__BUILTIN_CPU_SUPPORTS__’ if the ‘__builtin_cpu_supports’ built-in
     function is fully supported.

     If GCC was configured to use a GLIBC before 2.23, the built-in
     function ‘__builtin_cpu_is’ always returns a 0 and the compiler
     issues a warning.

     The following CPU names can be detected:

     ‘power10’
          IBM POWER10 Server CPU.
     ‘power9’
          IBM POWER9 Server CPU.
     ‘power8’
          IBM POWER8 Server CPU.
     ‘power7’
          IBM POWER7 Server CPU.
     ‘power6x’
          IBM POWER6 Server CPU (RAW mode).
     ‘power6’
          IBM POWER6 Server CPU (Architected mode).
     ‘power5+’
          IBM POWER5+ Server CPU.
     ‘power5’
          IBM POWER5 Server CPU.
     ‘ppc970’
          IBM 970 Server CPU (ie, Apple G5).
     ‘power4’
          IBM POWER4 Server CPU.
     ‘ppca2’
          IBM A2 64-bit Embedded CPU
     ‘ppc476’
          IBM PowerPC 476FP 32-bit Embedded CPU.
     ‘ppc464’
          IBM PowerPC 464 32-bit Embedded CPU.
     ‘ppc440’
          PowerPC 440 32-bit Embedded CPU.
     ‘ppc405’
          PowerPC 405 32-bit Embedded CPU.
     ‘ppc-cell-be’
          IBM PowerPC Cell Broadband Engine Architecture CPU.

     Here is an example:
          #ifdef __BUILTIN_CPU_SUPPORTS__
            if (__builtin_cpu_is ("power8"))
              {
                 do_power8 (); // POWER8 specific implementation.
              }
            else
          #endif
              {
                 do_generic (); // Generic implementation.
              }

 -- Built-in Function: int __builtin_cpu_supports (const char *FEATURE)
     This function returns a value of ‘1’ if the run-time CPU supports
     the HWCAP feature FEATURE and returns ‘0’ otherwise.

     The ‘__builtin_cpu_supports’ function requires GLIBC 2.23 or newer
     which exports the hardware capability bits.  GCC defines the macro
     ‘__BUILTIN_CPU_SUPPORTS__’ if the ‘__builtin_cpu_supports’ built-in
     function is fully supported.

     If GCC was configured to use a GLIBC before 2.23, the built-in
     function ‘__builtin_cpu_supports’ always returns a 0 and the
     compiler issues a warning.

     The following features can be detected:

     ‘4xxmac’
          4xx CPU has a Multiply Accumulator.
     ‘altivec’
          CPU has a SIMD/Vector Unit.
     ‘arch_2_05’
          CPU supports ISA 2.05 (eg, POWER6)
     ‘arch_2_06’
          CPU supports ISA 2.06 (eg, POWER7)
     ‘arch_2_07’
          CPU supports ISA 2.07 (eg, POWER8)
     ‘arch_3_00’
          CPU supports ISA 3.0 (eg, POWER9)
     ‘arch_3_1’
          CPU supports ISA 3.1 (eg, POWER10)
     ‘archpmu’
          CPU supports the set of compatible performance monitoring
          events.
     ‘booke’
          CPU supports the Embedded ISA category.
     ‘cellbe’
          CPU has a CELL broadband engine.
     ‘darn’
          CPU supports the ‘darn’ (deliver a random number) instruction.
     ‘dfp’
          CPU has a decimal floating point unit.
     ‘dscr’
          CPU supports the data stream control register.
     ‘ebb’
          CPU supports event base branching.
     ‘efpdouble’
          CPU has a SPE double precision floating point unit.
     ‘efpsingle’
          CPU has a SPE single precision floating point unit.
     ‘fpu’
          CPU has a floating point unit.
     ‘htm’
          CPU has hardware transaction memory instructions.
     ‘htm-nosc’
          Kernel aborts hardware transactions when a syscall is made.
     ‘htm-no-suspend’
          CPU supports hardware transaction memory but does not support
          the ‘tsuspend.’ instruction.
     ‘ic_snoop’
          CPU supports icache snooping capabilities.
     ‘ieee128’
          CPU supports 128-bit IEEE binary floating point instructions.
     ‘isel’
          CPU supports the integer select instruction.
     ‘mma’
          CPU supports the matrix-multiply assist instructions.
     ‘mmu’
          CPU has a memory management unit.
     ‘notb’
          CPU does not have a timebase (eg, 601 and 403gx).
     ‘pa6t’
          CPU supports the PA Semi 6T CORE ISA.
     ‘power4’
          CPU supports ISA 2.00 (eg, POWER4)
     ‘power5’
          CPU supports ISA 2.02 (eg, POWER5)
     ‘power5+’
          CPU supports ISA 2.03 (eg, POWER5+)
     ‘power6x’
          CPU supports ISA 2.05 (eg, POWER6) extended opcodes mffgpr and
          mftgpr.
     ‘ppc32’
          CPU supports 32-bit mode execution.
     ‘ppc601’
          CPU supports the old POWER ISA (eg, 601)
     ‘ppc64’
          CPU supports 64-bit mode execution.
     ‘ppcle’
          CPU supports a little-endian mode that uses address swizzling.
     ‘scv’
          Kernel supports system call vectored.
     ‘smt’
          CPU support simultaneous multi-threading.
     ‘spe’
          CPU has a signal processing extension unit.
     ‘tar’
          CPU supports the target address register.
     ‘true_le’
          CPU supports true little-endian mode.
     ‘ucache’
          CPU has unified I/D cache.
     ‘vcrypto’
          CPU supports the vector cryptography instructions.
     ‘vsx’
          CPU supports the vector-scalar extension.

     Here is an example:
          #ifdef __BUILTIN_CPU_SUPPORTS__
            if (__builtin_cpu_supports ("fpu"))
              {
                 asm("fadd %0,%1,%2" : "=d"(dst) : "d"(src1), "d"(src2));
              }
            else
          #endif
              {
                 dst = __fadd (src1, src2); // Software FP addition function.
              }

 The following built-in functions are also available on all PowerPC
processors:
     uint64_t __builtin_ppc_get_timebase ();
     unsigned long __builtin_ppc_mftb ();
     double __builtin_unpack_ibm128 (__ibm128, int);
     __ibm128 __builtin_pack_ibm128 (double, double);
     double __builtin_mffs (void);
     void __builtin_mtfsf (const int, double);
     void __builtin_mtfsb0 (const int);
     void __builtin_mtfsb1 (const int);
     void __builtin_set_fpscr_rn (int);

 The ‘__builtin_ppc_get_timebase’ and ‘__builtin_ppc_mftb’ functions
generate instructions to read the Time Base Register.  The
‘__builtin_ppc_get_timebase’ function may generate multiple instructions
and always returns the 64 bits of the Time Base Register.  The
‘__builtin_ppc_mftb’ function always generates one instruction and
returns the Time Base Register value as an unsigned long, throwing away
the most significant word on 32-bit environments.  The ‘__builtin_mffs’
return the value of the FPSCR register.  Note, ISA 3.0 supports the
‘__builtin_mffsl()’ which permits software to read the control and
non-sticky status bits in the FSPCR without the higher latency
associated with accessing the sticky status bits.  The ‘__builtin_mtfsf’
takes a constant 8-bit integer field mask and a double precision
floating point argument and generates the ‘mtfsf’ (extended mnemonic)
instruction to write new values to selected fields of the FPSCR. The
‘__builtin_mtfsb0’ and ‘__builtin_mtfsb1’ take the bit to change as an
argument.  The valid bit range is between 0 and 31.  The builtins map to
the ‘mtfsb0’ and ‘mtfsb1’ instructions which take the argument and add
32.  Hence these instructions only modify the FPSCR[32:63] bits by
changing the specified bit to a zero or one respectively.  The
‘__builtin_set_fpscr_rn’ builtin allows changing both of the floating
point rounding mode bits.  The argument is a 2-bit value.  The argument
can either be a ‘const int’ or stored in a variable.  The builtin uses
the ISA 3.0 instruction ‘mffscrn’ if available, otherwise it reads the
FPSCR, masks the current rounding mode bits out and OR's in the new
value.


File: gcc.info,  Node: Basic PowerPC Built-in Functions Available on ISA 2.05,  Next: Basic PowerPC Built-in Functions Available on ISA 2.06,  Prev: Basic PowerPC Built-in Functions Available on all Configurations,  Up: Basic PowerPC Built-in Functions

6.60.22.2 Basic PowerPC Built-in Functions Available on ISA 2.05
................................................................

The basic built-in functions described in this section are available on
the PowerPC family of processors starting with ISA 2.05 or later.
Unless specific options are explicitly disabled on the command line,
specifying option ‘-mcpu=power6’ has the effect of enabling the
‘-mpowerpc64’, ‘-mpowerpc-gpopt’, ‘-mpowerpc-gfxopt’, ‘-mmfcrf’,
‘-mpopcntb’, ‘-mfprnd’, ‘-mcmpb’, ‘-mhard-dfp’, and ‘-mrecip-precision’
options.  Specify the ‘-maltivec’ option explicitly in combination with
the above options if desired.

 The following functions require option ‘-mcmpb’.
     unsigned long long __builtin_cmpb (unsigned long long int, unsigned long long int);
     unsigned int __builtin_cmpb (unsigned int, unsigned int);

 The ‘__builtin_cmpb’ function performs a byte-wise compare on the
contents of its two arguments, returning the result of the byte-wise
comparison as the returned value.  For each byte comparison, the
corresponding byte of the return value holds 0xff if the input bytes are
equal and 0 if the input bytes are not equal.  If either of the
arguments to this built-in function is wider than 32 bits, the function
call expands into the form that expects ‘unsigned long long int’
arguments which is only available on 64-bit targets.

 The following built-in functions are available when hardware decimal
floating point (‘-mhard-dfp’) is available:
     void __builtin_set_fpscr_drn(int);
     _Decimal64 __builtin_ddedpd (int, _Decimal64);
     _Decimal128 __builtin_ddedpdq (int, _Decimal128);
     _Decimal64 __builtin_denbcd (int, _Decimal64);
     _Decimal128 __builtin_denbcdq (int, _Decimal128);
     _Decimal64 __builtin_diex (long long, _Decimal64);
     _Decimal128 _builtin_diexq (long long, _Decimal128);
     _Decimal64 __builtin_dscli (_Decimal64, int);
     _Decimal128 __builtin_dscliq (_Decimal128, int);
     _Decimal64 __builtin_dscri (_Decimal64, int);
     _Decimal128 __builtin_dscriq (_Decimal128, int);
     long long __builtin_dxex (_Decimal64);
     long long __builtin_dxexq (_Decimal128);
     _Decimal128 __builtin_pack_dec128 (unsigned long long, unsigned long long);
     unsigned long long __builtin_unpack_dec128 (_Decimal128, int);

     The __builtin_set_fpscr_drn builtin allows changing the three decimal
     floating point rounding mode bits.  The argument is a 3-bit value.  The
     argument can either be a const int or the value can be stored in
     a variable.
     The builtin uses the ISA 3.0 instruction mffscdrn if available.
     Otherwise the builtin reads the FPSCR, masks the current decimal rounding
     mode bits out and OR's in the new value.

 The following functions require ‘-mhard-float’, ‘-mpowerpc-gfxopt’, and
‘-mpopcntb’ options.

     double __builtin_recipdiv (double, double);
     float __builtin_recipdivf (float, float);
     double __builtin_rsqrt (double);
     float __builtin_rsqrtf (float);

 The ‘vec_rsqrt’, ‘__builtin_rsqrt’, and ‘__builtin_rsqrtf’ functions
generate multiple instructions to implement the reciprocal sqrt
functionality using reciprocal sqrt estimate instructions.

 The ‘__builtin_recipdiv’, and ‘__builtin_recipdivf’ functions generate
multiple instructions to implement division using the reciprocal
estimate instructions.

 The following functions require ‘-mhard-float’ and ‘-mmultiple’
options.

 The ‘__builtin_unpack_longdouble’ function takes a ‘long double’
argument and a compile time constant of 0 or 1.  If the constant is 0,
the first ‘double’ within the ‘long double’ is returned, otherwise the
second ‘double’ is returned.  The ‘__builtin_unpack_longdouble’ function
is only available if ‘long double’ uses the IBM extended double
representation.

 The ‘__builtin_pack_longdouble’ function takes two ‘double’ arguments
and returns a ‘long double’ value that combines the two arguments.  The
‘__builtin_pack_longdouble’ function is only available if ‘long double’
uses the IBM extended double representation.

 The ‘__builtin_unpack_ibm128’ function takes a ‘__ibm128’ argument and
a compile time constant of 0 or 1.  If the constant is 0, the first
‘double’ within the ‘__ibm128’ is returned, otherwise the second
‘double’ is returned.

 The ‘__builtin_pack_ibm128’ function takes two ‘double’ arguments and
returns a ‘__ibm128’ value that combines the two arguments.

 Additional built-in functions are available for the 64-bit PowerPC
family of processors, for efficient use of 128-bit floating point
(‘__float128’) values.


File: gcc.info,  Node: Basic PowerPC Built-in Functions Available on ISA 2.06,  Next: Basic PowerPC Built-in Functions Available on ISA 2.07,  Prev: Basic PowerPC Built-in Functions Available on ISA 2.05,  Up: Basic PowerPC Built-in Functions

6.60.22.3 Basic PowerPC Built-in Functions Available on ISA 2.06
................................................................

The basic built-in functions described in this section are available on
the PowerPC family of processors starting with ISA 2.05 or later.
Unless specific options are explicitly disabled on the command line,
specifying option ‘-mcpu=power7’ has the effect of enabling all the same
options as for ‘-mcpu=power6’ in addition to the ‘-maltivec’,
‘-mpopcntd’, and ‘-mvsx’ options.

 The following basic built-in functions require ‘-mpopcntd’:
     unsigned int __builtin_addg6s (unsigned int, unsigned int);
     long long __builtin_bpermd (long long, long long);
     unsigned int __builtin_cbcdtd (unsigned int);
     unsigned int __builtin_cdtbcd (unsigned int);
     long long __builtin_divde (long long, long long);
     unsigned long long __builtin_divdeu (unsigned long long, unsigned long long);
     int __builtin_divwe (int, int);
     unsigned int __builtin_divweu (unsigned int, unsigned int);
     vector __int128 __builtin_pack_vector_int128 (long long, long long);
     void __builtin_rs6000_speculation_barrier (void);
     long long __builtin_unpack_vector_int128 (vector __int128, signed char);

 Of these, the ‘__builtin_divde’ and ‘__builtin_divdeu’ functions
require a 64-bit environment.

 The following basic built-in functions, which are also supported on x86
targets, require ‘-mfloat128’.
     __float128 __builtin_fabsq (__float128);
     __float128 __builtin_copysignq (__float128, __float128);
     __float128 __builtin_infq (void);
     __float128 __builtin_huge_valq (void);
     __float128 __builtin_nanq (void);
     __float128 __builtin_nansq (void);

     __float128 __builtin_sqrtf128 (__float128);
     __float128 __builtin_fmaf128 (__float128, __float128, __float128);


File: gcc.info,  Node: Basic PowerPC Built-in Functions Available on ISA 2.07,  Next: Basic PowerPC Built-in Functions Available on ISA 3.0,  Prev: Basic PowerPC Built-in Functions Available on ISA 2.06,  Up: Basic PowerPC Built-in Functions

6.60.22.4 Basic PowerPC Built-in Functions Available on ISA 2.07
................................................................

The basic built-in functions described in this section are available on
the PowerPC family of processors starting with ISA 2.07 or later.
Unless specific options are explicitly disabled on the command line,
specifying option ‘-mcpu=power8’ has the effect of enabling all the same
options as for ‘-mcpu=power7’ in addition to the ‘-mpower8-fusion’,
‘-mpower8-vector’, ‘-mcrypto’, ‘-mhtm’, ‘-mquad-memory’, and
‘-mquad-memory-atomic’ options.

 This section intentionally empty.


File: gcc.info,  Node: Basic PowerPC Built-in Functions Available on ISA 3.0,  Next: Basic PowerPC Built-in Functions Available on ISA 3.1,  Prev: Basic PowerPC Built-in Functions Available on ISA 2.07,  Up: Basic PowerPC Built-in Functions

6.60.22.5 Basic PowerPC Built-in Functions Available on ISA 3.0
...............................................................

The basic built-in functions described in this section are available on
the PowerPC family of processors starting with ISA 3.0 or later.  Unless
specific options are explicitly disabled on the command line, specifying
option ‘-mcpu=power9’ has the effect of enabling all the same options as
for ‘-mcpu=power8’ in addition to the ‘-misel’ option.

 The following built-in functions are available on Linux 64-bit systems
that use the ISA 3.0 instruction set (‘-mcpu=power9’):

‘__float128 __builtin_addf128_round_to_odd (__float128, __float128)’
     Perform a 128-bit IEEE floating point add using round to odd as the
     rounding mode.

‘__float128 __builtin_subf128_round_to_odd (__float128, __float128)’
     Perform a 128-bit IEEE floating point subtract using round to odd
     as the rounding mode.

‘__float128 __builtin_mulf128_round_to_odd (__float128, __float128)’
     Perform a 128-bit IEEE floating point multiply using round to odd
     as the rounding mode.

‘__float128 __builtin_divf128_round_to_odd (__float128, __float128)’
     Perform a 128-bit IEEE floating point divide using round to odd as
     the rounding mode.

‘__float128 __builtin_sqrtf128_round_to_odd (__float128)’
     Perform a 128-bit IEEE floating point square root using round to
     odd as the rounding mode.

‘__float128 __builtin_fmaf128_round_to_odd (__float128, __float128, __float128)’
     Perform a 128-bit IEEE floating point fused multiply and add
     operation using round to odd as the rounding mode.

‘double __builtin_truncf128_round_to_odd (__float128)’
     Convert a 128-bit IEEE floating point value to ‘double’ using round
     to odd as the rounding mode.

 The following additional built-in functions are also available for the
PowerPC family of processors, starting with ISA 3.0 or later:
     long long __builtin_darn (void);
     long long __builtin_darn_raw (void);
     int __builtin_darn_32 (void);

 The ‘__builtin_darn’ and ‘__builtin_darn_raw’ functions require a
64-bit environment supporting ISA 3.0 or later.  The ‘__builtin_darn’
function provides a 64-bit conditioned random number.  The
‘__builtin_darn_raw’ function provides a 64-bit raw random number.  The
‘__builtin_darn_32’ function provides a 32-bit conditioned random
number.

 The following additional built-in functions are also available for the
PowerPC family of processors, starting with ISA 3.0 or later:

     int __builtin_byte_in_set (unsigned char u, unsigned long long set);
     int __builtin_byte_in_range (unsigned char u, unsigned int range);
     int __builtin_byte_in_either_range (unsigned char u, unsigned int ranges);

     int __builtin_dfp_dtstsfi_lt (unsigned int comparison, _Decimal64 value);
     int __builtin_dfp_dtstsfi_lt (unsigned int comparison, _Decimal128 value);
     int __builtin_dfp_dtstsfi_lt_dd (unsigned int comparison, _Decimal64 value);
     int __builtin_dfp_dtstsfi_lt_td (unsigned int comparison, _Decimal128 value);

     int __builtin_dfp_dtstsfi_gt (unsigned int comparison, _Decimal64 value);
     int __builtin_dfp_dtstsfi_gt (unsigned int comparison, _Decimal128 value);
     int __builtin_dfp_dtstsfi_gt_dd (unsigned int comparison, _Decimal64 value);
     int __builtin_dfp_dtstsfi_gt_td (unsigned int comparison, _Decimal128 value);

     int __builtin_dfp_dtstsfi_eq (unsigned int comparison, _Decimal64 value);
     int __builtin_dfp_dtstsfi_eq (unsigned int comparison, _Decimal128 value);
     int __builtin_dfp_dtstsfi_eq_dd (unsigned int comparison, _Decimal64 value);
     int __builtin_dfp_dtstsfi_eq_td (unsigned int comparison, _Decimal128 value);

     int __builtin_dfp_dtstsfi_ov (unsigned int comparison, _Decimal64 value);
     int __builtin_dfp_dtstsfi_ov (unsigned int comparison, _Decimal128 value);
     int __builtin_dfp_dtstsfi_ov_dd (unsigned int comparison, _Decimal64 value);
     int __builtin_dfp_dtstsfi_ov_td (unsigned int comparison, _Decimal128 value);

     double __builtin_mffsl(void);

 The ‘__builtin_byte_in_set’ function requires a 64-bit environment
supporting ISA 3.0 or later.  This function returns a non-zero value if
and only if its ‘u’ argument exactly equals one of the eight bytes
contained within its 64-bit ‘set’ argument.

 The ‘__builtin_byte_in_range’ and ‘__builtin_byte_in_either_range’
require an environment supporting ISA 3.0 or later.  For these two
functions, the ‘range’ argument is encoded as 4 bytes, organized as
‘hi_1:lo_1:hi_2:lo_2’.  The ‘__builtin_byte_in_range’ function returns a
non-zero value if and only if its ‘u’ argument is within the range
bounded between ‘lo_2’ and ‘hi_2’ inclusive.  The
‘__builtin_byte_in_either_range’ function returns non-zero if and only
if its ‘u’ argument is within either the range bounded between ‘lo_1’
and ‘hi_1’ inclusive or the range bounded between ‘lo_2’ and ‘hi_2’
inclusive.

 The ‘__builtin_dfp_dtstsfi_lt’ function returns a non-zero value if and
only if the number of signficant digits of its ‘value’ argument is less
than its ‘comparison’ argument.  The ‘__builtin_dfp_dtstsfi_lt_dd’ and
‘__builtin_dfp_dtstsfi_lt_td’ functions behave similarly, but require
that the type of the ‘value’ argument be ‘__Decimal64’ and
‘__Decimal128’ respectively.

 The ‘__builtin_dfp_dtstsfi_gt’ function returns a non-zero value if and
only if the number of signficant digits of its ‘value’ argument is
greater than its ‘comparison’ argument.  The
‘__builtin_dfp_dtstsfi_gt_dd’ and ‘__builtin_dfp_dtstsfi_gt_td’
functions behave similarly, but require that the type of the ‘value’
argument be ‘__Decimal64’ and ‘__Decimal128’ respectively.

 The ‘__builtin_dfp_dtstsfi_eq’ function returns a non-zero value if and
only if the number of signficant digits of its ‘value’ argument equals
its ‘comparison’ argument.  The ‘__builtin_dfp_dtstsfi_eq_dd’ and
‘__builtin_dfp_dtstsfi_eq_td’ functions behave similarly, but require
that the type of the ‘value’ argument be ‘__Decimal64’ and
‘__Decimal128’ respectively.

 The ‘__builtin_dfp_dtstsfi_ov’ function returns a non-zero value if and
only if its ‘value’ argument has an undefined number of significant
digits, such as when ‘value’ is an encoding of ‘NaN’.  The
‘__builtin_dfp_dtstsfi_ov_dd’ and ‘__builtin_dfp_dtstsfi_ov_td’
functions behave similarly, but require that the type of the ‘value’
argument be ‘__Decimal64’ and ‘__Decimal128’ respectively.

 The ‘__builtin_mffsl’ uses the ISA 3.0 ‘mffsl’ instruction to read the
FPSCR.  The instruction is a lower latency version of the ‘mffs’
instruction.  If the ‘mffsl’ instruction is not available, then the
builtin uses the older ‘mffs’ instruction to read the FPSCR.


File: gcc.info,  Node: Basic PowerPC Built-in Functions Available on ISA 3.1,  Prev: Basic PowerPC Built-in Functions Available on ISA 3.0,  Up: Basic PowerPC Built-in Functions

6.60.22.6 Basic PowerPC Built-in Functions Available on ISA 3.1
...............................................................

The basic built-in functions described in this section are available on
the PowerPC family of processors starting with ISA 3.1.  Unless specific
options are explicitly disabled on the command line, specifying option
‘-mcpu=power10’ has the effect of enabling all the same options as for
‘-mcpu=power9’.

 The following built-in functions are available on Linux 64-bit systems
that use a future architecture instruction set (‘-mcpu=power10’):

unsigned long long
__builtin_cfuged (unsigned long long, unsigned long long)
 Perform a 64-bit centrifuge operation, as if implemented by the
‘cfuged’ instruction.

unsigned long long
__builtin_cntlzdm (unsigned long long, unsigned long long)
 Perform a 64-bit count leading zeros operation under mask, as if
implemented by the ‘cntlzdm’ instruction.

unsigned long long
__builtin_cnttzdm (unsigned long long, unsigned long long)
 Perform a 64-bit count trailing zeros operation under mask, as if
implemented by the ‘cnttzdm’ instruction.

unsigned long long
__builtin_pdepd (unsigned long long, unsigned long long)
 Perform a 64-bit parallel bits deposit operation, as if implemented by
the ‘pdepd’ instruction.

unsigned long long
__builtin_pextd (unsigned long long, unsigned long long)
 Perform a 64-bit parallel bits extract operation, as if implemented by
the ‘pextd’ instruction.

vector signed __int128 vsx_xl_sext (signed long long, signed char *)

vector signed __int128 vsx_xl_sext (signed long long, signed short *)

vector signed __int128 vsx_xl_sext (signed long long, signed int *)

vector signed __int128 vsx_xl_sext (signed long long, signed long long *)

vector unsigned __int128 vsx_xl_zext (signed long long, unsigned char *)

vector unsigned __int128 vsx_xl_zext (signed long long, unsigned short *)

vector unsigned __int128 vsx_xl_zext (signed long long, unsigned int *)

vector unsigned __int128 vsx_xl_zext (signed long long, unsigned long long *)

 Load (and sign extend) to an __int128 vector, as if implemented by the
ISA 3.1 ‘lxvrbx’, ‘lxvrhx’, ‘lxvrwx’, and ‘lxvrdx’ instructions.

void vec_xst_trunc (vector signed __int128, signed long long, signed char *)

void vec_xst_trunc (vector signed __int128, signed long long, signed short *)

void vec_xst_trunc (vector signed __int128, signed long long, signed int *)

void vec_xst_trunc (vector signed __int128, signed long long, signed long long *)

void vec_xst_trunc (vector unsigned __int128, signed long long, unsigned char *)

void vec_xst_trunc (vector unsigned __int128, signed long long, unsigned short *)

void vec_xst_trunc (vector unsigned __int128, signed long long, unsigned int *)

void vec_xst_trunc (vector unsigned __int128, signed long long, unsigned long long *)

 Truncate and store the rightmost element of a vector, as if implemented
by the ISA 3.1 ‘stxvrbx’, ‘stxvrhx’, ‘stxvrwx’, and ‘stxvrdx’
instructions.


File: gcc.info,  Node: PowerPC AltiVec/VSX Built-in Functions,  Next: PowerPC Hardware Transactional Memory Built-in Functions,  Prev: Basic PowerPC Built-in Functions,  Up: Target Builtins

6.60.23 PowerPC AltiVec/VSX Built-in Functions
----------------------------------------------

GCC provides an interface for the PowerPC family of processors to access
the AltiVec operations described in Motorola's AltiVec Programming
Interface Manual.  The interface is made available by including
‘<altivec.h>’ and using ‘-maltivec’ and ‘-mabi=altivec’.  The interface
supports the following vector types.

     vector unsigned char
     vector signed char
     vector bool char

     vector unsigned short
     vector signed short
     vector bool short
     vector pixel

     vector unsigned int
     vector signed int
     vector bool int
     vector float

 GCC's implementation of the high-level language interface available
from C and C++ code differs from Motorola's documentation in several
ways.

   • A vector constant is a list of constant expressions within curly
     braces.

   • A vector initializer requires no cast if the vector constant is of
     the same type as the variable it is initializing.

   • If ‘signed’ or ‘unsigned’ is omitted, the signedness of the vector
     type is the default signedness of the base type.  The default
     varies depending on the operating system, so a portable program
     should always specify the signedness.

   • Compiling with ‘-maltivec’ adds keywords ‘__vector’, ‘vector’,
     ‘__pixel’, ‘pixel’, ‘__bool’ and ‘bool’.  When compiling ISO C, the
     context-sensitive substitution of the keywords ‘vector’, ‘pixel’
     and ‘bool’ is disabled.  To use them, you must include
     ‘<altivec.h>’ instead.

   • GCC allows using a ‘typedef’ name as the type specifier for a
     vector type, but only under the following circumstances:

        • When using ‘__vector’ instead of ‘vector’; for example,

               typedef signed short int16;
               __vector int16 data;

        • When using ‘vector’ in keyword-and-predefine mode; for
          example,

               typedef signed short int16;
               vector int16 data;

          Note that keyword-and-predefine mode is enabled by disabling
          GNU extensions (e.g., by using ‘-std=c11’) and including
          ‘<altivec.h>’.

   • For C, overloaded functions are implemented with macros so the
     following does not work:

            vec_add ((vector signed int){1, 2, 3, 4}, foo);

     Since ‘vec_add’ is a macro, the vector constant in the example is
     treated as four separate arguments.  Wrap the entire argument in
     parentheses for this to work.

 _Note:_ Only the ‘<altivec.h>’ interface is supported.  Internally, GCC
uses built-in functions to achieve the functionality in the
aforementioned header file, but they are not supported and are subject
to change without notice.

 GCC complies with the Power Vector Intrinsic Programming Reference
(PVIPR), which may be found at
<https://openpowerfoundation.org/?resource_lib=power-vector-intrinsic-programming-reference>.
Chapter 4 of this document fully documents the vector API interfaces
that must be provided by compliant compilers.  Programmers should
preferentially use the interfaces described therein.  However,
historically GCC has provided additional interfaces for access to vector
instructions.  These are briefly described below.  Where the PVIPR
provides a portable interface, other functions in GCC that provide the
same capabilities should be considered deprecated.

 The PVIPR documents the following overloaded functions:

‘vec_abs’                ‘vec_absd’               ‘vec_abss’
‘vec_add’                ‘vec_addc’               ‘vec_adde’
‘vec_addec’              ‘vec_adds’               ‘vec_all_eq’
‘vec_all_ge’             ‘vec_all_gt’             ‘vec_all_in’
‘vec_all_le’             ‘vec_all_lt’             ‘vec_all_nan’
‘vec_all_ne’             ‘vec_all_nge’            ‘vec_all_ngt’
‘vec_all_nle’            ‘vec_all_nlt’            ‘vec_all_numeric’
‘vec_and’                ‘vec_andc’               ‘vec_any_eq’
‘vec_any_ge’             ‘vec_any_gt’             ‘vec_any_le’
‘vec_any_lt’             ‘vec_any_nan’            ‘vec_any_ne’
‘vec_any_nge’            ‘vec_any_ngt’            ‘vec_any_nle’
‘vec_any_nlt’            ‘vec_any_numeric’        ‘vec_any_out’
‘vec_avg’                ‘vec_bperm’              ‘vec_ceil’
‘vec_cipher_be’          ‘vec_cipherlast_be’      ‘vec_cmpb’
‘vec_cmpeq’              ‘vec_cmpge’              ‘vec_cmpgt’
‘vec_cmple’              ‘vec_cmplt’              ‘vec_cmpne’
‘vec_cmpnez’             ‘vec_cntlz’              ‘vec_cntlz_lsbb’
‘vec_cnttz’              ‘vec_cnttz_lsbb’         ‘vec_cpsgn’
‘vec_ctf’                ‘vec_cts’                ‘vec_ctu’
‘vec_div’                ‘vec_double’             ‘vec_doublee’
‘vec_doubleh’            ‘vec_doublel’            ‘vec_doubleo’
‘vec_eqv’                ‘vec_expte’              ‘vec_extract’
‘vec_extract_exp’        ‘vec_extract_fp32_from_shorth’‘vec_extract_fp32_from_shortl’
‘vec_extract_sig’        ‘vec_extract_4b’         ‘vec_first_match_index’
‘vec_first_match_or_eos_index’‘vec_first_mismatch_index’‘vec_first_mismatch_or_eos_index’
‘vec_float’              ‘vec_float2’             ‘vec_floate’
‘vec_floato’             ‘vec_floor’              ‘vec_gb’
‘vec_insert’             ‘vec_insert_exp’         ‘vec_insert4b’
‘vec_ld’                 ‘vec_lde’                ‘vec_ldl’
‘vec_loge’               ‘vec_madd’               ‘vec_madds’
‘vec_max’                ‘vec_mergee’             ‘vec_mergeh’
‘vec_mergel’             ‘vec_mergeo’             ‘vec_mfvscr’
‘vec_min’                ‘vec_mradds’             ‘vec_msub’
‘vec_msum’               ‘vec_msums’              ‘vec_mtvscr’
‘vec_mul’                ‘vec_mule’               ‘vec_mulo’
‘vec_nabs’               ‘vec_nand’               ‘vec_ncipher_be’
‘vec_ncipherlast_be’     ‘vec_nearbyint’          ‘vec_neg’
‘vec_nmadd’              ‘vec_nmsub’              ‘vec_nor’
‘vec_or’                 ‘vec_orc’                ‘vec_pack’
‘vec_pack_to_short_fp32’ ‘vec_packpx’             ‘vec_packs’
‘vec_packsu’             ‘vec_parity_lsbb’        ‘vec_perm’
‘vec_permxor’            ‘vec_pmsum_be’           ‘vec_popcnt’
‘vec_re’                 ‘vec_recipdiv’           ‘vec_revb’
‘vec_reve’               ‘vec_rint’               ‘vec_rl’
‘vec_rlmi’               ‘vec_rlnm’               ‘vec_round’
‘vec_rsqrt’              ‘vec_rsqrte’             ‘vec_sbox_be’
‘vec_sel’                ‘vec_shasigma_be’        ‘vec_signed’
‘vec_signed2’            ‘vec_signede’            ‘vec_signedo’
‘vec_sl’                 ‘vec_sld’                ‘vec_sldw’
‘vec_sll’                ‘vec_slo’                ‘vec_slv’
‘vec_splat’              ‘vec_splat_s8’           ‘vec_splat_s16’
‘vec_splat_s32’          ‘vec_splat_u8’           ‘vec_splat_u16’
‘vec_splat_u32’          ‘vec_splats’             ‘vec_sqrt’
‘vec_sr’                 ‘vec_sra’                ‘vec_srl’
‘vec_sro’                ‘vec_srv’                ‘vec_st’
‘vec_ste’                ‘vec_stl’                ‘vec_sub’
‘vec_subc’               ‘vec_sube’               ‘vec_subec’
‘vec_subs’               ‘vec_sum2s’              ‘vec_sum4s’
‘vec_sums’               ‘vec_test_data_class’    ‘vec_trunc’
‘vec_unpackh’            ‘vec_unpackl’            ‘vec_unsigned’
‘vec_unsigned2’          ‘vec_unsignede’          ‘vec_unsignedo’
‘vec_xl’                 ‘vec_xl_be’              ‘vec_xl_len’
‘vec_xl_len_r’           ‘vec_xor’                ‘vec_xst’
‘vec_xst_be’             ‘vec_xst_len’            ‘vec_xst_len_r’
                                                  

* Menu:

* PowerPC AltiVec Built-in Functions on ISA 2.05::
* PowerPC AltiVec Built-in Functions Available on ISA 2.06::
* PowerPC AltiVec Built-in Functions Available on ISA 2.07::
* PowerPC AltiVec Built-in Functions Available on ISA 3.0::
* PowerPC AltiVec Built-in Functions Available on ISA 3.1::


File: gcc.info,  Node: PowerPC AltiVec Built-in Functions on ISA 2.05,  Next: PowerPC AltiVec Built-in Functions Available on ISA 2.06,  Up: PowerPC AltiVec/VSX Built-in Functions

6.60.23.1 PowerPC AltiVec Built-in Functions on ISA 2.05
........................................................

The following interfaces are supported for the generic and specific
AltiVec operations and the AltiVec predicates.  In cases where there is
a direct mapping between generic and specific operations, only the
generic names are shown here, although the specific operations can also
be used.

 Arguments that are documented as ‘const int’ require literal integral
values within the range required for that operation.

 Only functions excluded from the PVIPR are listed here.

     void vec_dss (const int);

     void vec_dssall (void);

     void vec_dst (const vector unsigned char *, int, const int);
     void vec_dst (const vector signed char *, int, const int);
     void vec_dst (const vector bool char *, int, const int);
     void vec_dst (const vector unsigned short *, int, const int);
     void vec_dst (const vector signed short *, int, const int);
     void vec_dst (const vector bool short *, int, const int);
     void vec_dst (const vector pixel *, int, const int);
     void vec_dst (const vector unsigned int *, int, const int);
     void vec_dst (const vector signed int *, int, const int);
     void vec_dst (const vector bool int *, int, const int);
     void vec_dst (const vector float *, int, const int);
     void vec_dst (const unsigned char *, int, const int);
     void vec_dst (const signed char *, int, const int);
     void vec_dst (const unsigned short *, int, const int);
     void vec_dst (const short *, int, const int);
     void vec_dst (const unsigned int *, int, const int);
     void vec_dst (const int *, int, const int);
     void vec_dst (const float *, int, const int);

     void vec_dstst (const vector unsigned char *, int, const int);
     void vec_dstst (const vector signed char *, int, const int);
     void vec_dstst (const vector bool char *, int, const int);
     void vec_dstst (const vector unsigned short *, int, const int);
     void vec_dstst (const vector signed short *, int, const int);
     void vec_dstst (const vector bool short *, int, const int);
     void vec_dstst (const vector pixel *, int, const int);
     void vec_dstst (const vector unsigned int *, int, const int);
     void vec_dstst (const vector signed int *, int, const int);
     void vec_dstst (const vector bool int *, int, const int);
     void vec_dstst (const vector float *, int, const int);
     void vec_dstst (const unsigned char *, int, const int);
     void vec_dstst (const signed char *, int, const int);
     void vec_dstst (const unsigned short *, int, const int);
     void vec_dstst (const short *, int, const int);
     void vec_dstst (const unsigned int *, int, const int);
     void vec_dstst (const int *, int, const int);
     void vec_dstst (const unsigned long *, int, const int);
     void vec_dstst (const long *, int, const int);
     void vec_dstst (const float *, int, const int);

     void vec_dststt (const vector unsigned char *, int, const int);
     void vec_dststt (const vector signed char *, int, const int);
     void vec_dststt (const vector bool char *, int, const int);
     void vec_dststt (const vector unsigned short *, int, const int);
     void vec_dststt (const vector signed short *, int, const int);
     void vec_dststt (const vector bool short *, int, const int);
     void vec_dststt (const vector pixel *, int, const int);
     void vec_dststt (const vector unsigned int *, int, const int);
     void vec_dststt (const vector signed int *, int, const int);
     void vec_dststt (const vector bool int *, int, const int);
     void vec_dststt (const vector float *, int, const int);
     void vec_dststt (const unsigned char *, int, const int);
     void vec_dststt (const signed char *, int, const int);
     void vec_dststt (const unsigned short *, int, const int);
     void vec_dststt (const short *, int, const int);
     void vec_dststt (const unsigned int *, int, const int);
     void vec_dststt (const int *, int, const int);
     void vec_dststt (const float *, int, const int);

     void vec_dstt (const vector unsigned char *, int, const int);
     void vec_dstt (const vector signed char *, int, const int);
     void vec_dstt (const vector bool char *, int, const int);
     void vec_dstt (const vector unsigned short *, int, const int);
     void vec_dstt (const vector signed short *, int, const int);
     void vec_dstt (const vector bool short *, int, const int);
     void vec_dstt (const vector pixel *, int, const int);
     void vec_dstt (const vector unsigned int *, int, const int);
     void vec_dstt (const vector signed int *, int, const int);
     void vec_dstt (const vector bool int *, int, const int);
     void vec_dstt (const vector float *, int, const int);
     void vec_dstt (const unsigned char *, int, const int);
     void vec_dstt (const signed char *, int, const int);
     void vec_dstt (const unsigned short *, int, const int);
     void vec_dstt (const short *, int, const int);
     void vec_dstt (const unsigned int *, int, const int);
     void vec_dstt (const int *, int, const int);
     void vec_dstt (const float *, int, const int);

     vector signed char vec_lvebx (int, char *);
     vector unsigned char vec_lvebx (int, unsigned char *);

     vector signed short vec_lvehx (int, short *);
     vector unsigned short vec_lvehx (int, unsigned short *);

     vector float vec_lvewx (int, float *);
     vector signed int vec_lvewx (int, int *);
     vector unsigned int vec_lvewx (int, unsigned int *);

     vector unsigned char vec_lvsl (int, const unsigned char *);
     vector unsigned char vec_lvsl (int, const signed char *);
     vector unsigned char vec_lvsl (int, const unsigned short *);
     vector unsigned char vec_lvsl (int, const short *);
     vector unsigned char vec_lvsl (int, const unsigned int *);
     vector unsigned char vec_lvsl (int, const int *);
     vector unsigned char vec_lvsl (int, const float *);

     vector unsigned char vec_lvsr (int, const unsigned char *);
     vector unsigned char vec_lvsr (int, const signed char *);
     vector unsigned char vec_lvsr (int, const unsigned short *);
     vector unsigned char vec_lvsr (int, const short *);
     vector unsigned char vec_lvsr (int, const unsigned int *);
     vector unsigned char vec_lvsr (int, const int *);
     vector unsigned char vec_lvsr (int, const float *);

     void vec_stvebx (vector signed char, int, signed char *);
     void vec_stvebx (vector unsigned char, int, unsigned char *);
     void vec_stvebx (vector bool char, int, signed char *);
     void vec_stvebx (vector bool char, int, unsigned char *);

     void vec_stvehx (vector signed short, int, short *);
     void vec_stvehx (vector unsigned short, int, unsigned short *);
     void vec_stvehx (vector bool short, int, short *);
     void vec_stvehx (vector bool short, int, unsigned short *);

     void vec_stvewx (vector float, int, float *);
     void vec_stvewx (vector signed int, int, int *);
     void vec_stvewx (vector unsigned int, int, unsigned int *);
     void vec_stvewx (vector bool int, int, int *);
     void vec_stvewx (vector bool int, int, unsigned int *);

     vector float vec_vaddfp (vector float, vector float);

     vector signed char vec_vaddsbs (vector bool char, vector signed char);
     vector signed char vec_vaddsbs (vector signed char, vector bool char);
     vector signed char vec_vaddsbs (vector signed char, vector signed char);

     vector signed short vec_vaddshs (vector bool short, vector signed short);
     vector signed short vec_vaddshs (vector signed short, vector bool short);
     vector signed short vec_vaddshs (vector signed short, vector signed short);

     vector signed int vec_vaddsws (vector bool int, vector signed int);
     vector signed int vec_vaddsws (vector signed int, vector bool int);
     vector signed int vec_vaddsws (vector signed int, vector signed int);

     vector signed char vec_vaddubm (vector bool char, vector signed char);
     vector signed char vec_vaddubm (vector signed char, vector bool char);
     vector signed char vec_vaddubm (vector signed char, vector signed char);
     vector unsigned char vec_vaddubm (vector bool char, vector unsigned char);
     vector unsigned char vec_vaddubm (vector unsigned char, vector bool char);
     vector unsigned char vec_vaddubm (vector unsigned char, vector unsigned char);

     vector unsigned char vec_vaddubs (vector bool char, vector unsigned char);
     vector unsigned char vec_vaddubs (vector unsigned char, vector bool char);
     vector unsigned char vec_vaddubs (vector unsigned char, vector unsigned char);

     vector signed short vec_vadduhm (vector bool short, vector signed short);
     vector signed short vec_vadduhm (vector signed short, vector bool short);
     vector signed short vec_vadduhm (vector signed short, vector signed short);
     vector unsigned short vec_vadduhm (vector bool short, vector unsigned short);
     vector unsigned short vec_vadduhm (vector unsigned short, vector bool short);
     vector unsigned short vec_vadduhm (vector unsigned short, vector unsigned short);

     vector unsigned short vec_vadduhs (vector bool short, vector unsigned short);
     vector unsigned short vec_vadduhs (vector unsigned short, vector bool short);
     vector unsigned short vec_vadduhs (vector unsigned short, vector unsigned short);

     vector signed int vec_vadduwm (vector bool int, vector signed int);
     vector signed int vec_vadduwm (vector signed int, vector bool int);
     vector signed int vec_vadduwm (vector signed int, vector signed int);
     vector unsigned int vec_vadduwm (vector bool int, vector unsigned int);
     vector unsigned int vec_vadduwm (vector unsigned int, vector bool int);
     vector unsigned int vec_vadduwm (vector unsigned int, vector unsigned int);

     vector unsigned int vec_vadduws (vector bool int, vector unsigned int);
     vector unsigned int vec_vadduws (vector unsigned int, vector bool int);
     vector unsigned int vec_vadduws (vector unsigned int, vector unsigned int);

     vector signed char vec_vavgsb (vector signed char, vector signed char);

     vector signed short vec_vavgsh (vector signed short, vector signed short);

     vector signed int vec_vavgsw (vector signed int, vector signed int);

     vector unsigned char vec_vavgub (vector unsigned char, vector unsigned char);

     vector unsigned short vec_vavguh (vector unsigned short, vector unsigned short);

     vector unsigned int vec_vavguw (vector unsigned int, vector unsigned int);

     vector float vec_vcfsx (vector signed int, const int);

     vector float vec_vcfux (vector unsigned int, const int);

     vector bool int vec_vcmpeqfp (vector float, vector float);

     vector bool char vec_vcmpequb (vector signed char, vector signed char);
     vector bool char vec_vcmpequb (vector unsigned char, vector unsigned char);

     vector bool short vec_vcmpequh (vector signed short, vector signed short);
     vector bool short vec_vcmpequh (vector unsigned short, vector unsigned short);

     vector bool int vec_vcmpequw (vector signed int, vector signed int);
     vector bool int vec_vcmpequw (vector unsigned int, vector unsigned int);

     vector bool int vec_vcmpgtfp (vector float, vector float);

     vector bool char vec_vcmpgtsb (vector signed char, vector signed char);

     vector bool short vec_vcmpgtsh (vector signed short, vector signed short);

     vector bool int vec_vcmpgtsw (vector signed int, vector signed int);

     vector bool char vec_vcmpgtub (vector unsigned char, vector unsigned char);

     vector bool short vec_vcmpgtuh (vector unsigned short, vector unsigned short);

     vector bool int vec_vcmpgtuw (vector unsigned int, vector unsigned int);

     vector float vec_vmaxfp (vector float, vector float);

     vector signed char vec_vmaxsb (vector bool char, vector signed char);
     vector signed char vec_vmaxsb (vector signed char, vector bool char);
     vector signed char vec_vmaxsb (vector signed char, vector signed char);

     vector signed short vec_vmaxsh (vector bool short, vector signed short);
     vector signed short vec_vmaxsh (vector signed short, vector bool short);
     vector signed short vec_vmaxsh (vector signed short, vector signed short);

     vector signed int vec_vmaxsw (vector bool int, vector signed int);
     vector signed int vec_vmaxsw (vector signed int, vector bool int);
     vector signed int vec_vmaxsw (vector signed int, vector signed int);

     vector unsigned char vec_vmaxub (vector bool char, vector unsigned char);
     vector unsigned char vec_vmaxub (vector unsigned char, vector bool char);
     vector unsigned char vec_vmaxub (vector unsigned char, vector unsigned char);

     vector unsigned short vec_vmaxuh (vector bool short, vector unsigned short);
     vector unsigned short vec_vmaxuh (vector unsigned short, vector bool short);
     vector unsigned short vec_vmaxuh (vector unsigned short, vector unsigned short);

     vector unsigned int vec_vmaxuw (vector bool int, vector unsigned int);
     vector unsigned int vec_vmaxuw (vector unsigned int, vector bool int);
     vector unsigned int vec_vmaxuw (vector unsigned int, vector unsigned int);

     vector float vec_vminfp (vector float, vector float);

     vector signed char vec_vminsb (vector bool char, vector signed char);
     vector signed char vec_vminsb (vector signed char, vector bool char);
     vector signed char vec_vminsb (vector signed char, vector signed char);

     vector signed short vec_vminsh (vector bool short, vector signed short);
     vector signed short vec_vminsh (vector signed short, vector bool short);
     vector signed short vec_vminsh (vector signed short, vector signed short);

     vector signed int vec_vminsw (vector bool int, vector signed int);
     vector signed int vec_vminsw (vector signed int, vector bool int);
     vector signed int vec_vminsw (vector signed int, vector signed int);

     vector unsigned char vec_vminub (vector bool char, vector unsigned char);
     vector unsigned char vec_vminub (vector unsigned char, vector bool char);
     vector unsigned char vec_vminub (vector unsigned char, vector unsigned char);

     vector unsigned short vec_vminuh (vector bool short, vector unsigned short);
     vector unsigned short vec_vminuh (vector unsigned short, vector bool short);
     vector unsigned short vec_vminuh (vector unsigned short, vector unsigned short);

     vector unsigned int vec_vminuw (vector bool int, vector unsigned int);
     vector unsigned int vec_vminuw (vector unsigned int, vector bool int);
     vector unsigned int vec_vminuw (vector unsigned int, vector unsigned int);

     vector bool char vec_vmrghb (vector bool char, vector bool char);
     vector signed char vec_vmrghb (vector signed char, vector signed char);
     vector unsigned char vec_vmrghb (vector unsigned char, vector unsigned char);

     vector bool short vec_vmrghh (vector bool short, vector bool short);
     vector signed short vec_vmrghh (vector signed short, vector signed short);
     vector unsigned short vec_vmrghh (vector unsigned short, vector unsigned short);
     vector pixel vec_vmrghh (vector pixel, vector pixel);

     vector float vec_vmrghw (vector float, vector float);
     vector bool int vec_vmrghw (vector bool int, vector bool int);
     vector signed int vec_vmrghw (vector signed int, vector signed int);
     vector unsigned int vec_vmrghw (vector unsigned int, vector unsigned int);

     vector bool char vec_vmrglb (vector bool char, vector bool char);
     vector signed char vec_vmrglb (vector signed char, vector signed char);
     vector unsigned char vec_vmrglb (vector unsigned char, vector unsigned char);

     vector bool short vec_vmrglh (vector bool short, vector bool short);
     vector signed short vec_vmrglh (vector signed short, vector signed short);
     vector unsigned short vec_vmrglh (vector unsigned short, vector unsigned short);
     vector pixel vec_vmrglh (vector pixel, vector pixel);

     vector float vec_vmrglw (vector float, vector float);
     vector signed int vec_vmrglw (vector signed int, vector signed int);
     vector unsigned int vec_vmrglw (vector unsigned int, vector unsigned int);
     vector bool int vec_vmrglw (vector bool int, vector bool int);

     vector signed int vec_vmsummbm (vector signed char, vector unsigned char,
                                     vector signed int);

     vector signed int vec_vmsumshm (vector signed short, vector signed short,
                                     vector signed int);

     vector signed int vec_vmsumshs (vector signed short, vector signed short,
                                     vector signed int);

     vector unsigned int vec_vmsumubm (vector unsigned char, vector unsigned char,
                                       vector unsigned int);

     vector unsigned int vec_vmsumuhm (vector unsigned short, vector unsigned short,
                                       vector unsigned int);

     vector unsigned int vec_vmsumuhs (vector unsigned short, vector unsigned short,
                                       vector unsigned int);

     vector signed short vec_vmulesb (vector signed char, vector signed char);

     vector signed int vec_vmulesh (vector signed short, vector signed short);

     vector unsigned short vec_vmuleub (vector unsigned char, vector unsigned char);

     vector unsigned int vec_vmuleuh (vector unsigned short, vector unsigned short);

     vector signed short vec_vmulosb (vector signed char, vector signed char);

     vector signed int vec_vmulosh (vector signed short, vector signed short);

     vector unsigned short vec_vmuloub (vector unsigned char, vector unsigned char);

     vector unsigned int vec_vmulouh (vector unsigned short, vector unsigned short);

     vector signed char vec_vpkshss (vector signed short, vector signed short);

     vector unsigned char vec_vpkshus (vector signed short, vector signed short);

     vector signed short vec_vpkswss (vector signed int, vector signed int);

     vector unsigned short vec_vpkswus (vector signed int, vector signed int);

     vector bool char vec_vpkuhum (vector bool short, vector bool short);
     vector signed char vec_vpkuhum (vector signed short, vector signed short);
     vector unsigned char vec_vpkuhum (vector unsigned short, vector unsigned short);

     vector unsigned char vec_vpkuhus (vector unsigned short, vector unsigned short);

     vector bool short vec_vpkuwum (vector bool int, vector bool int);
     vector signed short vec_vpkuwum (vector signed int, vector signed int);
     vector unsigned short vec_vpkuwum (vector unsigned int, vector unsigned int);

     vector unsigned short vec_vpkuwus (vector unsigned int, vector unsigned int);

     vector signed char vec_vrlb (vector signed char, vector unsigned char);
     vector unsigned char vec_vrlb (vector unsigned char, vector unsigned char);

     vector signed short vec_vrlh (vector signed short, vector unsigned short);
     vector unsigned short vec_vrlh (vector unsigned short, vector unsigned short);

     vector signed int vec_vrlw (vector signed int, vector unsigned int);
     vector unsigned int vec_vrlw (vector unsigned int, vector unsigned int);

     vector signed char vec_vslb (vector signed char, vector unsigned char);
     vector unsigned char vec_vslb (vector unsigned char, vector unsigned char);

     vector signed short vec_vslh (vector signed short, vector unsigned short);
     vector unsigned short vec_vslh (vector unsigned short, vector unsigned short);

     vector signed int vec_vslw (vector signed int, vector unsigned int);
     vector unsigned int vec_vslw (vector unsigned int, vector unsigned int);

     vector signed char vec_vspltb (vector signed char, const int);
     vector unsigned char vec_vspltb (vector unsigned char, const int);
     vector bool char vec_vspltb (vector bool char, const int);

     vector bool short vec_vsplth (vector bool short, const int);
     vector signed short vec_vsplth (vector signed short, const int);
     vector unsigned short vec_vsplth (vector unsigned short, const int);
     vector pixel vec_vsplth (vector pixel, const int);

     vector float vec_vspltw (vector float, const int);
     vector signed int vec_vspltw (vector signed int, const int);
     vector unsigned int vec_vspltw (vector unsigned int, const int);
     vector bool int vec_vspltw (vector bool int, const int);

     vector signed char vec_vsrab (vector signed char, vector unsigned char);
     vector unsigned char vec_vsrab (vector unsigned char, vector unsigned char);

     vector signed short vec_vsrah (vector signed short, vector unsigned short);
     vector unsigned short vec_vsrah (vector unsigned short, vector unsigned short);

     vector signed int vec_vsraw (vector signed int, vector unsigned int);
     vector unsigned int vec_vsraw (vector unsigned int, vector unsigned int);

     vector signed char vec_vsrb (vector signed char, vector unsigned char);
     vector unsigned char vec_vsrb (vector unsigned char, vector unsigned char);

     vector signed short vec_vsrh (vector signed short, vector unsigned short);
     vector unsigned short vec_vsrh (vector unsigned short, vector unsigned short);

     vector signed int vec_vsrw (vector signed int, vector unsigned int);
     vector unsigned int vec_vsrw (vector unsigned int, vector unsigned int);

     vector float vec_vsubfp (vector float, vector float);

     vector signed char vec_vsubsbs (vector bool char, vector signed char);
     vector signed char vec_vsubsbs (vector signed char, vector bool char);
     vector signed char vec_vsubsbs (vector signed char, vector signed char);

     vector signed short vec_vsubshs (vector bool short, vector signed short);
     vector signed short vec_vsubshs (vector signed short, vector bool short);
     vector signed short vec_vsubshs (vector signed short, vector signed short);

     vector signed int vec_vsubsws (vector bool int, vector signed int);
     vector signed int vec_vsubsws (vector signed int, vector bool int);
     vector signed int vec_vsubsws (vector signed int, vector signed int);

     vector signed char vec_vsububm (vector bool char, vector signed char);
     vector signed char vec_vsububm (vector signed char, vector bool char);
     vector signed char vec_vsububm (vector signed char, vector signed char);
     vector unsigned char vec_vsububm (vector bool char, vector unsigned char);
     vector unsigned char vec_vsububm (vector unsigned char, vector bool char);
     vector unsigned char vec_vsububm (vector unsigned char, vector unsigned char);

     vector unsigned char vec_vsububs (vector bool char, vector unsigned char);
     vector unsigned char vec_vsububs (vector unsigned char, vector bool char);
     vector unsigned char vec_vsububs (vector unsigned char, vector unsigned char);

     vector signed short vec_vsubuhm (vector bool short, vector signed short);
     vector signed short vec_vsubuhm (vector signed short, vector bool short);
     vector signed short vec_vsubuhm (vector signed short, vector signed short);
     vector unsigned short vec_vsubuhm (vector bool short, vector unsigned short);
     vector unsigned short vec_vsubuhm (vector unsigned short, vector bool short);
     vector unsigned short vec_vsubuhm (vector unsigned short, vector unsigned short);

     vector unsigned short vec_vsubuhs (vector bool short, vector unsigned short);
     vector unsigned short vec_vsubuhs (vector unsigned short, vector bool short);
     vector unsigned short vec_vsubuhs (vector unsigned short, vector unsigned short);

     vector signed int vec_vsubuwm (vector bool int, vector signed int);
     vector signed int vec_vsubuwm (vector signed int, vector bool int);
     vector signed int vec_vsubuwm (vector signed int, vector signed int);
     vector unsigned int vec_vsubuwm (vector bool int, vector unsigned int);
     vector unsigned int vec_vsubuwm (vector unsigned int, vector bool int);
     vector unsigned int vec_vsubuwm (vector unsigned int, vector unsigned int);

     vector unsigned int vec_vsubuws (vector bool int, vector unsigned int);
     vector unsigned int vec_vsubuws (vector unsigned int, vector bool int);
     vector unsigned int vec_vsubuws (vector unsigned int, vector unsigned int);

     vector signed int vec_vsum4sbs (vector signed char, vector signed int);

     vector signed int vec_vsum4shs (vector signed short, vector signed int);

     vector unsigned int vec_vsum4ubs (vector unsigned char, vector unsigned int);

     vector unsigned int vec_vupkhpx (vector pixel);

     vector bool short vec_vupkhsb (vector bool char);
     vector signed short vec_vupkhsb (vector signed char);

     vector bool int vec_vupkhsh (vector bool short);
     vector signed int vec_vupkhsh (vector signed short);

     vector unsigned int vec_vupklpx (vector pixel);

     vector bool short vec_vupklsb (vector bool char);
     vector signed short vec_vupklsb (vector signed char);

     vector bool int vec_vupklsh (vector bool short);
     vector signed int vec_vupklsh (vector signed short);


File: gcc.info,  Node: PowerPC AltiVec Built-in Functions Available on ISA 2.06,  Next: PowerPC AltiVec Built-in Functions Available on ISA 2.07,  Prev: PowerPC AltiVec Built-in Functions on ISA 2.05,  Up: PowerPC AltiVec/VSX Built-in Functions

6.60.23.2 PowerPC AltiVec Built-in Functions Available on ISA 2.06
..................................................................

The AltiVec built-in functions described in this section are available
on the PowerPC family of processors starting with ISA 2.06 or later.
These are normally enabled by adding ‘-mvsx’ to the command line.

 When ‘-mvsx’ is used, the following additional vector types are
implemented.

     vector unsigned __int128
     vector signed __int128
     vector unsigned long long int
     vector signed long long int
     vector double

 The long long types are only implemented for 64-bit code generation.

 Only functions excluded from the PVIPR are listed here.

     void vec_dst (const unsigned long *, int, const int);
     void vec_dst (const long *, int, const int);

     void vec_dststt (const unsigned long *, int, const int);
     void vec_dststt (const long *, int, const int);

     void vec_dstt (const unsigned long *, int, const int);
     void vec_dstt (const long *, int, const int);

     vector unsigned char vec_lvsl (int, const unsigned long *);
     vector unsigned char vec_lvsl (int, const long *);

     vector unsigned char vec_lvsr (int, const unsigned long *);
     vector unsigned char vec_lvsr (int, const long *);

     vector unsigned char vec_lvsl (int, const double *);
     vector unsigned char vec_lvsr (int, const double *);

     vector double vec_vsx_ld (int, const vector double *);
     vector double vec_vsx_ld (int, const double *);
     vector float vec_vsx_ld (int, const vector float *);
     vector float vec_vsx_ld (int, const float *);
     vector bool int vec_vsx_ld (int, const vector bool int *);
     vector signed int vec_vsx_ld (int, const vector signed int *);
     vector signed int vec_vsx_ld (int, const int *);
     vector signed int vec_vsx_ld (int, const long *);
     vector unsigned int vec_vsx_ld (int, const vector unsigned int *);
     vector unsigned int vec_vsx_ld (int, const unsigned int *);
     vector unsigned int vec_vsx_ld (int, const unsigned long *);
     vector bool short vec_vsx_ld (int, const vector bool short *);
     vector pixel vec_vsx_ld (int, const vector pixel *);
     vector signed short vec_vsx_ld (int, const vector signed short *);
     vector signed short vec_vsx_ld (int, const short *);
     vector unsigned short vec_vsx_ld (int, const vector unsigned short *);
     vector unsigned short vec_vsx_ld (int, const unsigned short *);
     vector bool char vec_vsx_ld (int, const vector bool char *);
     vector signed char vec_vsx_ld (int, const vector signed char *);
     vector signed char vec_vsx_ld (int, const signed char *);
     vector unsigned char vec_vsx_ld (int, const vector unsigned char *);
     vector unsigned char vec_vsx_ld (int, const unsigned char *);

     void vec_vsx_st (vector double, int, vector double *);
     void vec_vsx_st (vector double, int, double *);
     void vec_vsx_st (vector float, int, vector float *);
     void vec_vsx_st (vector float, int, float *);
     void vec_vsx_st (vector signed int, int, vector signed int *);
     void vec_vsx_st (vector signed int, int, int *);
     void vec_vsx_st (vector unsigned int, int, vector unsigned int *);
     void vec_vsx_st (vector unsigned int, int, unsigned int *);
     void vec_vsx_st (vector bool int, int, vector bool int *);
     void vec_vsx_st (vector bool int, int, unsigned int *);
     void vec_vsx_st (vector bool int, int, int *);
     void vec_vsx_st (vector signed short, int, vector signed short *);
     void vec_vsx_st (vector signed short, int, short *);
     void vec_vsx_st (vector unsigned short, int, vector unsigned short *);
     void vec_vsx_st (vector unsigned short, int, unsigned short *);
     void vec_vsx_st (vector bool short, int, vector bool short *);
     void vec_vsx_st (vector bool short, int, unsigned short *);
     void vec_vsx_st (vector pixel, int, vector pixel *);
     void vec_vsx_st (vector pixel, int, unsigned short *);
     void vec_vsx_st (vector pixel, int, short *);
     void vec_vsx_st (vector bool short, int, short *);
     void vec_vsx_st (vector signed char, int, vector signed char *);
     void vec_vsx_st (vector signed char, int, signed char *);
     void vec_vsx_st (vector unsigned char, int, vector unsigned char *);
     void vec_vsx_st (vector unsigned char, int, unsigned char *);
     void vec_vsx_st (vector bool char, int, vector bool char *);
     void vec_vsx_st (vector bool char, int, unsigned char *);
     void vec_vsx_st (vector bool char, int, signed char *);

     vector double vec_xxpermdi (vector double, vector double, const int);
     vector float vec_xxpermdi (vector float, vector float, const int);
     vector long long vec_xxpermdi (vector long long, vector long long, const int);
     vector unsigned long long vec_xxpermdi (vector unsigned long long,
                                             vector unsigned long long, const int);
     vector int vec_xxpermdi (vector int, vector int, const int);
     vector unsigned int vec_xxpermdi (vector unsigned int,
                                       vector unsigned int, const int);
     vector short vec_xxpermdi (vector short, vector short, const int);
     vector unsigned short vec_xxpermdi (vector unsigned short,
                                         vector unsigned short, const int);
     vector signed char vec_xxpermdi (vector signed char, vector signed char,
                                      const int);
     vector unsigned char vec_xxpermdi (vector unsigned char,
                                        vector unsigned char, const int);

     vector double vec_xxsldi (vector double, vector double, int);
     vector float vec_xxsldi (vector float, vector float, int);
     vector long long vec_xxsldi (vector long long, vector long long, int);
     vector unsigned long long vec_xxsldi (vector unsigned long long,
                                           vector unsigned long long, int);
     vector int vec_xxsldi (vector int, vector int, int);
     vector unsigned int vec_xxsldi (vector unsigned int, vector unsigned int, int);
     vector short vec_xxsldi (vector short, vector short, int);
     vector unsigned short vec_xxsldi (vector unsigned short,
                                       vector unsigned short, int);
     vector signed char vec_xxsldi (vector signed char, vector signed char, int);
     vector unsigned char vec_xxsldi (vector unsigned char,
                                      vector unsigned char, int);

 Note that the ‘vec_ld’ and ‘vec_st’ built-in functions always generate
the AltiVec ‘LVX’ and ‘STVX’ instructions even if the VSX instruction
set is available.  The ‘vec_vsx_ld’ and ‘vec_vsx_st’ built-in functions
always generate the VSX ‘LXVD2X’, ‘LXVW4X’, ‘STXVD2X’, and ‘STXVW4X’
instructions.


File: gcc.info,  Node: PowerPC AltiVec Built-in Functions Available on ISA 2.07,  Next: PowerPC AltiVec Built-in Functions Available on ISA 3.0,  Prev: PowerPC AltiVec Built-in Functions Available on ISA 2.06,  Up: PowerPC AltiVec/VSX Built-in Functions

6.60.23.3 PowerPC AltiVec Built-in Functions Available on ISA 2.07
..................................................................

If the ISA 2.07 additions to the vector/scalar (power8-vector)
instruction set are available, the following additional functions are
available for both 32-bit and 64-bit targets.  For 64-bit targets, you
can use VECTOR LONG instead of VECTOR LONG LONG, VECTOR BOOL LONG
instead of VECTOR BOOL LONG LONG, and VECTOR UNSIGNED LONG instead of
VECTOR UNSIGNED LONG LONG.

 Only functions excluded from the PVIPR are listed here.

     vector long long vec_vaddudm (vector long long, vector long long);
     vector long long vec_vaddudm (vector bool long long, vector long long);
     vector long long vec_vaddudm (vector long long, vector bool long long);
     vector unsigned long long vec_vaddudm (vector unsigned long long,
                                            vector unsigned long long);
     vector unsigned long long vec_vaddudm (vector bool unsigned long long,
                                            vector unsigned long long);
     vector unsigned long long vec_vaddudm (vector unsigned long long,
                                            vector bool unsigned long long);

     vector long long vec_vclz (vector long long);
     vector unsigned long long vec_vclz (vector unsigned long long);
     vector int vec_vclz (vector int);
     vector unsigned int vec_vclz (vector int);
     vector short vec_vclz (vector short);
     vector unsigned short vec_vclz (vector unsigned short);
     vector signed char vec_vclz (vector signed char);
     vector unsigned char vec_vclz (vector unsigned char);

     vector signed char vec_vclzb (vector signed char);
     vector unsigned char vec_vclzb (vector unsigned char);

     vector long long vec_vclzd (vector long long);
     vector unsigned long long vec_vclzd (vector unsigned long long);

     vector short vec_vclzh (vector short);
     vector unsigned short vec_vclzh (vector unsigned short);

     vector int vec_vclzw (vector int);
     vector unsigned int vec_vclzw (vector int);

     vector signed char vec_vgbbd (vector signed char);
     vector unsigned char vec_vgbbd (vector unsigned char);

     vector long long vec_vmaxsd (vector long long, vector long long);

     vector unsigned long long vec_vmaxud (vector unsigned long long,
                                           unsigned vector long long);

     vector long long vec_vminsd (vector long long, vector long long);

     vector unsigned long long vec_vminud (vector long long, vector long long);

     vector int vec_vpksdss (vector long long, vector long long);
     vector unsigned int vec_vpksdss (vector long long, vector long long);

     vector unsigned int vec_vpkudus (vector unsigned long long,
                                      vector unsigned long long);

     vector int vec_vpkudum (vector long long, vector long long);
     vector unsigned int vec_vpkudum (vector unsigned long long,
                                      vector unsigned long long);
     vector bool int vec_vpkudum (vector bool long long, vector bool long long);

     vector long long vec_vpopcnt (vector long long);
     vector unsigned long long vec_vpopcnt (vector unsigned long long);
     vector int vec_vpopcnt (vector int);
     vector unsigned int vec_vpopcnt (vector int);
     vector short vec_vpopcnt (vector short);
     vector unsigned short vec_vpopcnt (vector unsigned short);
     vector signed char vec_vpopcnt (vector signed char);
     vector unsigned char vec_vpopcnt (vector unsigned char);

     vector signed char vec_vpopcntb (vector signed char);
     vector unsigned char vec_vpopcntb (vector unsigned char);

     vector long long vec_vpopcntd (vector long long);
     vector unsigned long long vec_vpopcntd (vector unsigned long long);

     vector short vec_vpopcnth (vector short);
     vector unsigned short vec_vpopcnth (vector unsigned short);

     vector int vec_vpopcntw (vector int);
     vector unsigned int vec_vpopcntw (vector int);

     vector long long vec_vrld (vector long long, vector unsigned long long);
     vector unsigned long long vec_vrld (vector unsigned long long,
                                         vector unsigned long long);

     vector long long vec_vsld (vector long long, vector unsigned long long);
     vector long long vec_vsld (vector unsigned long long,
                                vector unsigned long long);

     vector long long vec_vsrad (vector long long, vector unsigned long long);
     vector unsigned long long vec_vsrad (vector unsigned long long,
                                          vector unsigned long long);

     vector long long vec_vsrd (vector long long, vector unsigned long long);
     vector unsigned long long char vec_vsrd (vector unsigned long long,
                                              vector unsigned long long);

     vector long long vec_vsubudm (vector long long, vector long long);
     vector long long vec_vsubudm (vector bool long long, vector long long);
     vector long long vec_vsubudm (vector long long, vector bool long long);
     vector unsigned long long vec_vsubudm (vector unsigned long long,
                                            vector unsigned long long);
     vector unsigned long long vec_vsubudm (vector bool long long,
                                            vector unsigned long long);
     vector unsigned long long vec_vsubudm (vector unsigned long long,
                                            vector bool long long);

     vector long long vec_vupkhsw (vector int);
     vector unsigned long long vec_vupkhsw (vector unsigned int);

     vector long long vec_vupklsw (vector int);
     vector unsigned long long vec_vupklsw (vector int);

 If the ISA 2.07 additions to the vector/scalar (power8-vector)
instruction set are available, the following additional functions are
available for 64-bit targets.  New vector types (VECTOR __INT128 and
VECTOR __UINT128) are available to hold the __INT128 and __UINT128 types
to use these builtins.

 The normal vector extract, and set operations work on VECTOR __INT128
and VECTOR __UINT128 types, but the index value must be 0.

 Only functions excluded from the PVIPR are listed here.

     vector __int128 vec_vaddcuq (vector __int128, vector __int128);
     vector __uint128 vec_vaddcuq (vector __uint128, vector __uint128);

     vector __int128 vec_vadduqm (vector __int128, vector __int128);
     vector __uint128 vec_vadduqm (vector __uint128, vector __uint128);

     vector __int128 vec_vaddecuq (vector __int128, vector __int128,
                                     vector __int128);
     vector __uint128 vec_vaddecuq (vector __uint128, vector __uint128,
                                      vector __uint128);

     vector __int128 vec_vaddeuqm (vector __int128, vector __int128,
                                     vector __int128);
     vector __uint128 vec_vaddeuqm (vector __uint128, vector __uint128,
                                      vector __uint128);

     vector __int128 vec_vsubecuq (vector __int128, vector __int128,
                                     vector __int128);
     vector __uint128 vec_vsubecuq (vector __uint128, vector __uint128,
                                      vector __uint128);

     vector __int128 vec_vsubeuqm (vector __int128, vector __int128,
                                     vector __int128);
     vector __uint128 vec_vsubeuqm (vector __uint128, vector __uint128,
                                      vector __uint128);

     vector __int128 vec_vsubcuq (vector __int128, vector __int128);
     vector __uint128 vec_vsubcuq (vector __uint128, vector __uint128);

     __int128 vec_vsubuqm (__int128, __int128);
     __uint128 vec_vsubuqm (__uint128, __uint128);

     vector __int128 __builtin_bcdadd (vector __int128, vector __int128, const int);
     vector unsigned char __builtin_bcdadd (vector unsigned char, vector unsigned char,
                                            const int);
     int __builtin_bcdadd_lt (vector __int128, vector __int128, const int);
     int __builtin_bcdadd_lt (vector unsigned char, vector unsigned char, const int);
     int __builtin_bcdadd_eq (vector __int128, vector __int128, const int);
     int __builtin_bcdadd_eq (vector unsigned char, vector unsigned char, const int);
     int __builtin_bcdadd_gt (vector __int128, vector __int128, const int);
     int __builtin_bcdadd_gt (vector unsigned char, vector unsigned char, const int);
     int __builtin_bcdadd_ov (vector __int128, vector __int128, const int);
     int __builtin_bcdadd_ov (vector unsigned char, vector unsigned char, const int);

     vector __int128 __builtin_bcdsub (vector __int128, vector __int128, const int);
     vector unsigned char __builtin_bcdsub (vector unsigned char, vector unsigned char,
                                            const int);
     int __builtin_bcdsub_lt (vector __int128, vector __int128, const int);
     int __builtin_bcdsub_lt (vector unsigned char, vector unsigned char, const int);
     int __builtin_bcdsub_eq (vector __int128, vector __int128, const int);
     int __builtin_bcdsub_eq (vector unsigned char, vector unsigned char, const int);
     int __builtin_bcdsub_gt (vector __int128, vector __int128, const int);
     int __builtin_bcdsub_gt (vector unsigned char, vector unsigned char, const int);
     int __builtin_bcdsub_ov (vector __int128, vector __int128, const int);
     int __builtin_bcdsub_ov (vector unsigned char, vector unsigned char, const int);


File: gcc.info,  Node: PowerPC AltiVec Built-in Functions Available on ISA 3.0,  Next: PowerPC AltiVec Built-in Functions Available on ISA 3.1,  Prev: PowerPC AltiVec Built-in Functions Available on ISA 2.07,  Up: PowerPC AltiVec/VSX Built-in Functions

6.60.23.4 PowerPC AltiVec Built-in Functions Available on ISA 3.0
.................................................................

The following additional built-in functions are also available for the
PowerPC family of processors, starting with ISA 3.0 (‘-mcpu=power9’) or
later.

 Only instructions excluded from the PVIPR are listed here.

     unsigned int scalar_extract_exp (double source);
     unsigned long long int scalar_extract_exp (__ieee128 source);

     unsigned long long int scalar_extract_sig (double source);
     unsigned __int128 scalar_extract_sig (__ieee128 source);

     double scalar_insert_exp (unsigned long long int significand,
                               unsigned long long int exponent);
     double scalar_insert_exp (double significand, unsigned long long int exponent);

     ieee_128 scalar_insert_exp (unsigned __int128 significand,
                                 unsigned long long int exponent);
     ieee_128 scalar_insert_exp (ieee_128 significand, unsigned long long int exponent);

     int scalar_cmp_exp_gt (double arg1, double arg2);
     int scalar_cmp_exp_lt (double arg1, double arg2);
     int scalar_cmp_exp_eq (double arg1, double arg2);
     int scalar_cmp_exp_unordered (double arg1, double arg2);

     bool scalar_test_data_class (float source, const int condition);
     bool scalar_test_data_class (double source, const int condition);
     bool scalar_test_data_class (__ieee128 source, const int condition);

     bool scalar_test_neg (float source);
     bool scalar_test_neg (double source);
     bool scalar_test_neg (__ieee128 source);

 The ‘scalar_extract_exp’ and ‘scalar_extract_sig’ functions require a
64-bit environment supporting ISA 3.0 or later.  The
‘scalar_extract_exp’ and ‘scalar_extract_sig’ built-in functions return
the significand and the biased exponent value respectively of their
‘source’ arguments.  When supplied with a 64-bit ‘source’ argument, the
result returned by ‘scalar_extract_sig’ has the ‘0x0010000000000000’ bit
set if the function's ‘source’ argument is in normalized form.
Otherwise, this bit is set to 0.  When supplied with a 128-bit ‘source’
argument, the ‘0x00010000000000000000000000000000’ bit of the result is
treated similarly.  Note that the sign of the significand is not
represented in the result returned from the ‘scalar_extract_sig’
function.  Use the ‘scalar_test_neg’ function to test the sign of its
‘double’ argument.

 The ‘scalar_insert_exp’ functions require a 64-bit environment
supporting ISA 3.0 or later.  When supplied with a 64-bit first
argument, the ‘scalar_insert_exp’ built-in function returns a
double-precision floating point value that is constructed by assembling
the values of its ‘significand’ and ‘exponent’ arguments.  The sign of
the result is copied from the most significant bit of the ‘significand’
argument.  The significand and exponent components of the result are
composed of the least significant 11 bits of the ‘exponent’ argument and
the least significant 52 bits of the ‘significand’ argument
respectively.

 When supplied with a 128-bit first argument, the ‘scalar_insert_exp’
built-in function returns a quad-precision ieee floating point value.
The sign bit of the result is copied from the most significant bit of
the ‘significand’ argument.  The significand and exponent components of
the result are composed of the least significant 15 bits of the
‘exponent’ argument and the least significant 112 bits of the
‘significand’ argument respectively.

 The ‘scalar_cmp_exp_gt’, ‘scalar_cmp_exp_lt’, ‘scalar_cmp_exp_eq’, and
‘scalar_cmp_exp_unordered’ built-in functions return a non-zero value if
‘arg1’ is greater than, less than, equal to, or not comparable to ‘arg2’
respectively.  The arguments are not comparable if one or the other
equals NaN (not a number).

 The ‘scalar_test_data_class’ built-in function returns 1 if any of the
condition tests enabled by the value of the ‘condition’ variable are
true, and 0 otherwise.  The ‘condition’ argument must be a compile-time
constant integer with value not exceeding 127.  The ‘condition’ argument
is encoded as a bitmask with each bit enabling the testing of a
different condition, as characterized by the following:
     0x40    Test for NaN
     0x20    Test for +Infinity
     0x10    Test for -Infinity
     0x08    Test for +Zero
     0x04    Test for -Zero
     0x02    Test for +Denormal
     0x01    Test for -Denormal

 The ‘scalar_test_neg’ built-in function returns 1 if its ‘source’
argument holds a negative value, 0 otherwise.

 The following built-in functions are also available for the PowerPC
family of processors, starting with ISA 3.0 or later (‘-mcpu=power9’).
These string functions are described separately in order to group the
descriptions closer to the function prototypes.

 Only functions excluded from the PVIPR are listed here.

     int vec_all_nez (vector signed char, vector signed char);
     int vec_all_nez (vector unsigned char, vector unsigned char);
     int vec_all_nez (vector signed short, vector signed short);
     int vec_all_nez (vector unsigned short, vector unsigned short);
     int vec_all_nez (vector signed int, vector signed int);
     int vec_all_nez (vector unsigned int, vector unsigned int);

     int vec_any_eqz (vector signed char, vector signed char);
     int vec_any_eqz (vector unsigned char, vector unsigned char);
     int vec_any_eqz (vector signed short, vector signed short);
     int vec_any_eqz (vector unsigned short, vector unsigned short);
     int vec_any_eqz (vector signed int, vector signed int);
     int vec_any_eqz (vector unsigned int, vector unsigned int);

     signed char vec_xlx (unsigned int index, vector signed char data);
     unsigned char vec_xlx (unsigned int index, vector unsigned char data);
     signed short vec_xlx (unsigned int index, vector signed short data);
     unsigned short vec_xlx (unsigned int index, vector unsigned short data);
     signed int vec_xlx (unsigned int index, vector signed int data);
     unsigned int vec_xlx (unsigned int index, vector unsigned int data);
     float vec_xlx (unsigned int index, vector float data);

     signed char vec_xrx (unsigned int index, vector signed char data);
     unsigned char vec_xrx (unsigned int index, vector unsigned char data);
     signed short vec_xrx (unsigned int index, vector signed short data);
     unsigned short vec_xrx (unsigned int index, vector unsigned short data);
     signed int vec_xrx (unsigned int index, vector signed int data);
     unsigned int vec_xrx (unsigned int index, vector unsigned int data);
     float vec_xrx (unsigned int index, vector float data);

 The ‘vec_all_nez’, ‘vec_any_eqz’, and ‘vec_cmpnez’ perform pairwise
comparisons between the elements at the same positions within their two
vector arguments.  The ‘vec_all_nez’ function returns a non-zero value
if and only if all pairwise comparisons are not equal and no element of
either vector argument contains a zero.  The ‘vec_any_eqz’ function
returns a non-zero value if and only if at least one pairwise comparison
is equal or if at least one element of either vector argument contains a
zero.  The ‘vec_cmpnez’ function returns a vector of the same type as
its two arguments, within which each element consists of all ones to
denote that either the corresponding elements of the incoming arguments
are not equal or that at least one of the corresponding elements
contains zero.  Otherwise, the element of the returned vector contains
all zeros.

 The ‘vec_xlx’ and ‘vec_xrx’ functions extract the single element
selected by the ‘index’ argument from the vector represented by the
‘data’ argument.  The ‘index’ argument always specifies a byte offset,
regardless of the size of the vector element.  With ‘vec_xlx’, ‘index’
is the offset of the first byte of the element to be extracted.  With
‘vec_xrx’, ‘index’ represents the last byte of the element to be
extracted, measured from the right end of the vector.  In other words,
the last byte of the element to be extracted is found at position ‘(15 -
index)’.  There is no requirement that ‘index’ be a multiple of the
vector element size.  However, if the size of the vector element added
to ‘index’ is greater than 15, the content of the returned value is
undefined.

 The following functions are also available if the ISA 3.0 instruction
set additions (‘-mcpu=power9’) are available.

 Only functions excluded from the PVIPR are listed here.

     vector long long vec_vctz (vector long long);
     vector unsigned long long vec_vctz (vector unsigned long long);
     vector int vec_vctz (vector int);
     vector unsigned int vec_vctz (vector int);
     vector short vec_vctz (vector short);
     vector unsigned short vec_vctz (vector unsigned short);
     vector signed char vec_vctz (vector signed char);
     vector unsigned char vec_vctz (vector unsigned char);

     vector signed char vec_vctzb (vector signed char);
     vector unsigned char vec_vctzb (vector unsigned char);

     vector long long vec_vctzd (vector long long);
     vector unsigned long long vec_vctzd (vector unsigned long long);

     vector short vec_vctzh (vector short);
     vector unsigned short vec_vctzh (vector unsigned short);

     vector int vec_vctzw (vector int);
     vector unsigned int vec_vctzw (vector int);

     vector int vec_vprtyb (vector int);
     vector unsigned int vec_vprtyb (vector unsigned int);
     vector long long vec_vprtyb (vector long long);
     vector unsigned long long vec_vprtyb (vector unsigned long long);

     vector int vec_vprtybw (vector int);
     vector unsigned int vec_vprtybw (vector unsigned int);

     vector long long vec_vprtybd (vector long long);
     vector unsigned long long vec_vprtybd (vector unsigned long long);

 On 64-bit targets, if the ISA 3.0 additions (‘-mcpu=power9’) are
available:

     vector long vec_vprtyb (vector long);
     vector unsigned long vec_vprtyb (vector unsigned long);
     vector __int128 vec_vprtyb (vector __int128);
     vector __uint128 vec_vprtyb (vector __uint128);

     vector long vec_vprtybd (vector long);
     vector unsigned long vec_vprtybd (vector unsigned long);

     vector __int128 vec_vprtybq (vector __int128);
     vector __uint128 vec_vprtybd (vector __uint128);

 The following built-in functions are available for the PowerPC family
of processors, starting with ISA 3.0 or later (‘-mcpu=power9’).

 Only functions excluded from the PVIPR are listed here.

     __vector unsigned char
     vec_absdb (__vector unsigned char arg1, __vector unsigned char arg2);
     __vector unsigned short
     vec_absdh (__vector unsigned short arg1, __vector unsigned short arg2);
     __vector unsigned int
     vec_absdw (__vector unsigned int arg1, __vector unsigned int arg2);

 The ‘vec_absd’, ‘vec_absdb’, ‘vec_absdh’, and ‘vec_absdw’ built-in
functions each computes the absolute differences of the pairs of vector
elements supplied in its two vector arguments, placing the absolute
differences into the corresponding elements of the vector result.

 The following built-in functions are available for the PowerPC family
of processors, starting with ISA 3.0 or later (‘-mcpu=power9’):
     vector unsigned int vec_vrlnm (vector unsigned int, vector unsigned int);
     vector unsigned long long vec_vrlnm (vector unsigned long long,
                                          vector unsigned long long);

 The result of ‘vec_vrlnm’ is obtained by rotating each element of the
first argument vector left and ANDing it with a mask.  The second
argument vector contains the mask beginning in bits 11:15, the mask end
in bits 19:23, and the shift count in bits 27:31, of each element.

 If the cryptographic instructions are enabled (‘-mcrypto’ or
‘-mcpu=power8’), the following builtins are enabled.

 Only functions excluded from the PVIPR are listed here.

     vector unsigned long long __builtin_crypto_vsbox (vector unsigned long long);

     vector unsigned long long __builtin_crypto_vcipher (vector unsigned long long,
                                                         vector unsigned long long);

     vector unsigned long long __builtin_crypto_vcipherlast
                                          (vector unsigned long long,
                                           vector unsigned long long);

     vector unsigned long long __builtin_crypto_vncipher (vector unsigned long long,
                                                          vector unsigned long long);

     vector unsigned long long __builtin_crypto_vncipherlast (vector unsigned long long,
                                                              vector unsigned long long);

     vector unsigned char __builtin_crypto_vpermxor (vector unsigned char,
                                                     vector unsigned char,
                                                     vector unsigned char);

     vector unsigned short __builtin_crypto_vpermxor (vector unsigned short,
                                                      vector unsigned short,
                                                      vector unsigned short);

     vector unsigned int __builtin_crypto_vpermxor (vector unsigned int,
                                                    vector unsigned int,
                                                    vector unsigned int);

     vector unsigned long long __builtin_crypto_vpermxor (vector unsigned long long,
                                                          vector unsigned long long,
                                                          vector unsigned long long);

     vector unsigned char __builtin_crypto_vpmsumb (vector unsigned char,
                                                    vector unsigned char);

     vector unsigned short __builtin_crypto_vpmsumh (vector unsigned short,
                                                     vector unsigned short);

     vector unsigned int __builtin_crypto_vpmsumw (vector unsigned int,
                                                   vector unsigned int);

     vector unsigned long long __builtin_crypto_vpmsumd (vector unsigned long long,
                                                         vector unsigned long long);

     vector unsigned long long __builtin_crypto_vshasigmad (vector unsigned long long,
                                                            int, int);

     vector unsigned int __builtin_crypto_vshasigmaw (vector unsigned int, int, int);

 The second argument to __BUILTIN_CRYPTO_VSHASIGMAD and
__BUILTIN_CRYPTO_VSHASIGMAW must be a constant integer that is 0 or 1.
The third argument to these built-in functions must be a constant
integer in the range of 0 to 15.

 The following sign extension builtins are provided:

     vector signed int vec_signexti (vector signed char a);
     vector signed long long vec_signextll (vector signed char a);
     vector signed int vec_signexti (vector signed short a);
     vector signed long long vec_signextll (vector signed short a);
     vector signed long long vec_signextll (vector signed int a);
     vector signed long long vec_signextq (vector signed long long a);

 Each element of the result is produced by sign-extending the element of
the input vector that would fall in the least significant portion of the
result element.  For example, a sign-extension of a vector signed char
to a vector signed long long will sign extend the rightmost byte of each
doubleword.


File: gcc.info,  Node: PowerPC AltiVec Built-in Functions Available on ISA 3.1,  Prev: PowerPC AltiVec Built-in Functions Available on ISA 3.0,  Up: PowerPC AltiVec/VSX Built-in Functions

6.60.23.5 PowerPC AltiVec Built-in Functions Available on ISA 3.1
.................................................................

The following additional built-in functions are also available for the
PowerPC family of processors, starting with ISA 3.1 (‘-mcpu=power10’):

vector unsigned long long int
vec_cfuge (vector unsigned long long int, vector unsigned long long int);
 Perform a vector centrifuge operation, as if implemented by the
‘vcfuged’ instruction.

vector unsigned long long int
vec_cntlzm (vector unsigned long long int, vector unsigned long long int);
 Perform a vector count leading zeros under bit mask operation, as if
implemented by the ‘vclzdm’ instruction.

vector unsigned long long int
vec_cnttzm (vector unsigned long long int, vector unsigned long long int);
 Perform a vector count trailing zeros under bit mask operation, as if
implemented by the ‘vctzdm’ instruction.

vector signed char
vec_clrl (vector signed char a, unsigned int n);
vector unsigned char
vec_clrl (vector unsigned char a, unsigned int n);
 Clear the left-most ‘(16 - n)’ bytes of vector argument ‘a’, as if
implemented by the ‘vclrlb’ instruction on a big-endian target and by
the ‘vclrrb’ instruction on a little-endian target.  A value of ‘n’ that
is greater than 16 is treated as if it equaled 16.

vector signed char
vec_clrr (vector signed char a, unsigned int n);
vector unsigned char
vec_clrr (vector unsigned char a, unsigned int n);
 Clear the right-most ‘(16 - n)’ bytes of vector argument ‘a’, as if
implemented by the ‘vclrrb’ instruction on a big-endian target and by
the ‘vclrlb’ instruction on a little-endian target.  A value of ‘n’ that
is greater than 16 is treated as if it equaled 16.

vector unsigned long long int
vec_gnb (vector unsigned __int128, const unsigned char);
 Perform a 128-bit vector gather operation, as if implemented by the
‘vgnb’ instruction.  The second argument must be a literal integer value
between 2 and 7 inclusive.

 Vector Extract

vector unsigned long long int
vec_extractl (vector unsigned char, vector unsigned char, unsigned int);
vector unsigned long long int
vec_extractl (vector unsigned short, vector unsigned short, unsigned int);
vector unsigned long long int
vec_extractl (vector unsigned int, vector unsigned int, unsigned int);
vector unsigned long long int
vec_extractl (vector unsigned long long, vector unsigned long long, unsigned int);
 Extract an element from two concatenated vectors starting at the given
byte index in natural-endian order, and place it zero-extended in
doubleword 1 of the result according to natural element order.  If the
byte index is out of range for the data type, the intrinsic will be
rejected.  For little-endian, this output will match the placement by
the hardware instruction, i.e., dword[0] in RTL notation.  For
big-endian, an additional instruction is needed to move it from the
"left" doubleword to the "right" one.  For little-endian, semantics
matching the ‘vextdubvrx’, ‘vextduhvrx’, ‘vextduwvrx’ instruction will
be generated, while for big-endian, semantics matching the ‘vextdubvlx’,
‘vextduhvlx’, ‘vextduwvlx’ instructions will be generated.  Note that
some fairly anomalous results can be generated if the byte index is not
aligned on an element boundary for the element being extracted.  This is
a limitation of the bi-endian vector programming model is consistent
with the limitation on ‘vec_perm’.

vector unsigned long long int
vec_extracth (vector unsigned char, vector unsigned char, unsigned int);
vector unsigned long long int
vec_extracth (vector unsigned short, vector unsigned short,
     unsigned int);
vector unsigned long long int
vec_extracth (vector unsigned int, vector unsigned int, unsigned int);
vector unsigned long long int
vec_extracth (vector unsigned long long, vector unsigned long long,
     unsigned int);
 Extract an element from two concatenated vectors starting at the given
byte index.  The index is based on big endian order for a little endian
system.  Similarly, the index is based on little endian order for a big
endian system.  The extraced elements are zero-extended and put in
doubleword 1 according to natural element order.  If the byte index is
out of range for the data type, the intrinsic will be rejected.  For
little-endian, this output will match the placement by the hardware
instruction (vextdubvrx, vextduhvrx, vextduwvrx, vextddvrx) i.e.,
dword[0] in RTL notation.  For big-endian, an additional instruction is
needed to move it from the "left" doubleword to the "right" one.  For
little-endian, semantics matching the ‘vextdubvlx’, ‘vextduhvlx’,
‘vextduwvlx’ instructions will be generated, while for big-endian,
semantics matching the ‘vextdubvrx’, ‘vextduhvrx’, ‘vextduwvrx’
instructions will be generated.  Note that some fairly anomalous results
can be generated if the byte index is not aligned on the element
boundary for the element being extracted.  This is a limitation of the
bi-endian vector programming model consistent with the limitation on
‘vec_perm’.
vector unsigned long long int
vec_pdep (vector unsigned long long int, vector unsigned long long int);
 Perform a vector parallel bits deposit operation, as if implemented by
the ‘vpdepd’ instruction.

 Vector Insert

vector unsigned char
vec_insertl (unsigned char, vector unsigned char, unsigned int);
vector unsigned short
vec_insertl (unsigned short, vector unsigned short, unsigned int);
vector unsigned int
vec_insertl (unsigned int, vector unsigned int, unsigned int);
vector unsigned long long
vec_insertl (unsigned long long, vector unsigned long long,
     unsigned int);
vector unsigned char
vec_insertl (vector unsigned char, vector unsigned char, unsigned int;
vector unsigned short
vec_insertl (vector unsigned short, vector unsigned short,
     unsigned int);
vector unsigned int
vec_insertl (vector unsigned int, vector unsigned int, unsigned int);

 Let src be the first argument, when the first argument is a scalar, or
the rightmost element of the left doubleword of the first argument, when
the first argument is a vector.  Insert the source into the destination
at the position given by the third argument, using natural element order
in the second argument.  The rest of the second argument is unchanged.
If the byte index is greater than 14 for halfwords, greater than 12 for
words, or greater than 8 for doublewords the result is undefined.  For
little-endian, the generated code will be semantically equivalent to
‘vins[bhwd]rx’ instructions.  Similarly for big-endian it will be
semantically equivalent to ‘vins[bhwd]lx’.  Note that some fairly
anomalous results can be generated if the byte index is not aligned on
an element boundary for the type of element being inserted.

vector unsigned char
vec_inserth (unsigned char, vector unsigned char, unsigned int);
vector unsigned short
vec_inserth (unsigned short, vector unsigned short, unsigned int);
vector unsigned int
vec_inserth (unsigned int, vector unsigned int, unsigned int);
vector unsigned long long
vec_inserth (unsigned long long, vector unsigned long long,
     unsigned int);
vector unsigned char
vec_inserth (vector unsigned char, vector unsigned char, unsigned int);
vector unsigned short
vec_inserth (vector unsigned short, vector unsigned short,
     unsigned int);
vector unsigned int
vec_inserth (vector unsigned int, vector unsigned int, unsigned int);

 Let src be the first argument, when the first argument is a scalar, or
the rightmost element of the first argument, when the first argument is
a vector.  Insert src into the second argument at the position
identified by the third argument, using opposite element order in the
second argument, and leaving the rest of the second argument unchanged.
If the byte index is greater than 14 for halfwords, 12 for words, or 8
for doublewords, the intrinsic will be rejected.  Note that the
underlying hardware instruction uses the same register for the second
argument and the result.  For little-endian, the code generation will be
semantically equivalent to ‘vins[bhwd]lx’, while for big-endian it will
be semantically equivalent to ‘vins[bhwd]rx’.  Note that some fairly
anomalous results can be generated if the byte index is not aligned on
an element boundary for the sort of element being inserted.

 Vector Replace Element
vector signed int vec_replace_elt (vector signed int, signed int,
     const int);
vector unsigned int vec_replace_elt (vector unsigned int,
     unsigned int, const int);
vector float vec_replace_elt (vector float, float, const int);
vector signed long long vec_replace_elt (vector signed long long,
     signed long long, const int);
vector unsigned long long vec_replace_elt (vector unsigned long long,
     unsigned long long, const int);
vector double rec_replace_elt (vector double, double, const int);
 The third argument (constrained to [0,3]) identifies the natural-endian
element number of the first argument that will be replaced by the second
argument to produce the result.  The other elements of the first
argument will remain unchanged in the result.

 If it's desirable to insert a word at an unaligned position, use
vec_replace_unaligned instead.

 Vector Replace Unaligned
vector unsigned char vec_replace_unaligned (vector unsigned char,
     signed int, const int);
vector unsigned char vec_replace_unaligned (vector unsigned char,
     unsigned int, const int);
vector unsigned char vec_replace_unaligned (vector unsigned char,
     float, const int);
vector unsigned char vec_replace_unaligned (vector unsigned char,
     signed long long, const int);
vector unsigned char vec_replace_unaligned (vector unsigned char,
     unsigned long long, const int);
vector unsigned char vec_replace_unaligned (vector unsigned char,
     double, const int);

 The second argument replaces a portion of the first argument to produce
the result, with the rest of the first argument unchanged in the result.
The third argument identifies the byte index (using left-to-right, or
big-endian order) where the high-order byte of the second argument will
be placed, with the remaining bytes of the second argument placed
naturally "to the right" of the high-order byte.

 The programmer is responsible for understanding the endianness issues
involved with the first argument and the result.

 Vector Shift Left Double Bit Immediate
vector signed char vec_sldb (vector signed char, vector signed char,
     const unsigned int);
vector unsigned char vec_sldb (vector unsigned char,
     vector unsigned char, const unsigned int);
vector signed short vec_sldb (vector signed short, vector signed short,
     const unsigned int);
vector unsigned short vec_sldb (vector unsigned short,
     vector unsigned short, const unsigned int);
vector signed int vec_sldb (vector signed int, vector signed int,
     const unsigned int);
vector unsigned int vec_sldb (vector unsigned int, vector unsigned int,
     const unsigned int);
vector signed long long vec_sldb (vector signed long long,
     vector signed long long, const unsigned int);
vector unsigned long long vec_sldb (vector unsigned long long,
     vector unsigned long long, const unsigned int);

 Shift the combined input vectors left by the amount specified by the
low-order three bits of the third argument, and return the leftmost
remaining 128 bits.  Code using this instruction must be endian-aware.

 Vector Shift Right Double Bit Immediate

vector signed char vec_srdb (vector signed char, vector signed char,
     const unsigned int);
vector unsigned char vec_srdb (vector unsigned char, vector unsigned char,
     const unsigned int);
vector signed short vec_srdb (vector signed short, vector signed short,
     const unsigned int);
vector unsigned short vec_srdb (vector unsigned short, vector unsigned short,
     const unsigned int);
vector signed int vec_srdb (vector signed int, vector signed int,
     const unsigned int);
vector unsigned int vec_srdb (vector unsigned int, vector unsigned int,
     const unsigned int);
vector signed long long vec_srdb (vector signed long long,
     vector signed long long, const unsigned int);
vector unsigned long long vec_srdb (vector unsigned long long,
     vector unsigned long long, const unsigned int);

 Shift the combined input vectors right by the amount specified by the
low-order three bits of the third argument, and return the remaining 128
bits.  Code using this built-in must be endian-aware.

 Vector Splat

vector signed int vec_splati (const signed int);
vector float vec_splati (const float);

 Splat a 32-bit immediate into a vector of words.

vector double vec_splatid (const float);

 Convert a single precision floating-point value to double-precision and
splat the result to a vector of double-precision floats.

vector signed int vec_splati_ins (vector signed int,
     const unsigned int, const signed int);
vector unsigned int vec_splati_ins (vector unsigned int,
     const unsigned int, const unsigned int);
vector float vec_splati_ins (vector float, const unsigned int,
     const float);

 Argument 2 must be either 0 or 1.  Splat the value of argument 3 into
the word identified by argument 2 of each doubleword of argument 1 and
return the result.  The other words of argument 1 are unchanged.

 Vector Blend Variable

vector signed char vec_blendv (vector signed char, vector signed char,
     vector unsigned char);
vector unsigned char vec_blendv (vector unsigned char,
     vector unsigned char, vector unsigned char);
vector signed short vec_blendv (vector signed short,
     vector signed short, vector unsigned short);
vector unsigned short vec_blendv (vector unsigned short,
     vector unsigned short, vector unsigned short);
vector signed int vec_blendv (vector signed int, vector signed int,
     vector unsigned int);
vector unsigned int vec_blendv (vector unsigned int,
     vector unsigned int, vector unsigned int);
vector signed long long vec_blendv (vector signed long long,
     vector signed long long, vector unsigned long long);
vector unsigned long long vec_blendv (vector unsigned long long,
     vector unsigned long long, vector unsigned long long);
vector float vec_blendv (vector float, vector float,
     vector unsigned int);
vector double vec_blendv (vector double, vector double,
     vector unsigned long long);

 Blend the first and second argument vectors according to the sign bits
of the corresponding elements of the third argument vector.  This is
similar to the ‘vsel’ and ‘xxsel’ instructions but for bigger elements.

 Vector Permute Extended

vector signed char vec_permx (vector signed char, vector signed char,
     vector unsigned char, const int);
vector unsigned char vec_permx (vector unsigned char,
     vector unsigned char, vector unsigned char, const int);
vector signed short vec_permx (vector signed short,
     vector signed short, vector unsigned char, const int);
vector unsigned short vec_permx (vector unsigned short,
     vector unsigned short, vector unsigned char, const int);
vector signed int vec_permx (vector signed int, vector signed int,
     vector unsigned char, const int);
vector unsigned int vec_permx (vector unsigned int,
     vector unsigned int, vector unsigned char, const int);
vector signed long long vec_permx (vector signed long long,
     vector signed long long, vector unsigned char, const int);
vector unsigned long long vec_permx (vector unsigned long long,
     vector unsigned long long, vector unsigned char, const int);
vector float (vector float, vector float, vector unsigned char,
     const int);
vector double (vector double, vector double, vector unsigned char,
     const int);

 Perform a partial permute of the first two arguments, which form a
32-byte section of an emulated vector up to 256 bytes wide, using the
partial permute control vector in the third argument.  The fourth
argument (constrained to values of 0-7) identifies which 32-byte section
of the emulated vector is contained in the first two arguments.

vector unsigned long long int
vec_pext (vector unsigned long long int, vector unsigned long long int);
 Perform a vector parallel bit extract operation, as if implemented by
the ‘vpextd’ instruction.

vector unsigned char vec_stril (vector unsigned char);
vector signed char vec_stril (vector signed char);
vector unsigned short vec_stril (vector unsigned short);
vector signed short vec_stril (vector signed short);
 Isolate the left-most non-zero elements of the incoming vector
argument, replacing all elements to the right of the left-most zero
element found within the argument with zero.  The typical implementation
uses the ‘vstribl’ or ‘vstrihl’ instruction on big-endian targets and
uses the ‘vstribr’ or ‘vstrihr’ instruction on little-endian targets.

int vec_stril_p (vector unsigned char);
int vec_stril_p (vector signed char);
int short vec_stril_p (vector unsigned short);
int vec_stril_p (vector signed short);
 Return a non-zero value if and only if the argument contains a zero
element.  The typical implementation uses the ‘vstribl.’ or ‘vstrihl.’
instruction on big-endian targets and uses the ‘vstribr.’ or ‘vstrihr.’
instruction on little-endian targets.  Choose this built-in to check for
presence of zero element if the same argument is also passed to
‘vec_stril’.

vector unsigned char vec_strir (vector unsigned char);
vector signed char vec_strir (vector signed char);
vector unsigned short vec_strir (vector unsigned short);
vector signed short vec_strir (vector signed short);
 Isolate the right-most non-zero elements of the incoming vector
argument, replacing all elements to the left of the right-most zero
element found within the argument with zero.  The typical implementation
uses the ‘vstribr’ or ‘vstrihr’ instruction on big-endian targets and
uses the ‘vstribl’ or ‘vstrihl’ instruction on little-endian targets.

int vec_strir_p (vector unsigned char);
int vec_strir_p (vector signed char);
int short vec_strir_p (vector unsigned short);
int vec_strir_p (vector signed short);
 Return a non-zero value if and only if the argument contains a zero
element.  The typical implementation uses the ‘vstribr.’ or ‘vstrihr.’
instruction on big-endian targets and uses the ‘vstribl.’ or ‘vstrihl.’
instruction on little-endian targets.  Choose this built-in to check for
presence of zero element if the same argument is also passed to
‘vec_strir’.

vector unsigned char
vec_ternarylogic (vector unsigned char, vector unsigned char,
                 vector unsigned char, const unsigned int);
vector unsigned short
vec_ternarylogic (vector unsigned short, vector unsigned short,
                 vector unsigned short, const unsigned int);
vector unsigned int
vec_ternarylogic (vector unsigned int, vector unsigned int,
                 vector unsigned int, const unsigned int);
vector unsigned long long int
vec_ternarylogic (vector unsigned long long int, vector unsigned long long int,
                 vector unsigned long long int, const unsigned int);
vector unsigned __int128
vec_ternarylogic (vector unsigned __int128, vector unsigned __int128,
                 vector unsigned __int128, const unsigned int);
 Perform a 128-bit vector evaluate operation, as if implemented by the
‘xxeval’ instruction.  The fourth argument must be a literal integer
value between 0 and 255 inclusive.

vector unsigned char vec_genpcvm (vector unsigned char, const int);
vector unsigned short vec_genpcvm (vector unsigned short, const int);
vector unsigned int vec_genpcvm (vector unsigned int, const int);
vector unsigned int vec_genpcvm (vector unsigned long long int,
                                              const int);

 Vector Integer Multiply/Divide/Modulo

vector signed int
vec_mulh (vector signed int a, vector signed int b);
vector unsigned int
vec_mulh (vector unsigned int a, vector unsigned int b);

 For each integer value ‘i’ from 0 to 3, do the following.  The integer
value in word element ‘i’ of a is multiplied by the integer value in
word element ‘i’ of b.  The high-order 32 bits of the 64-bit product are
placed into word element ‘i’ of the vector returned.

vector signed long long
vec_mulh (vector signed long long a, vector signed long long b);
vector unsigned long long
vec_mulh (vector unsigned long long a, vector unsigned long long b);

 For each integer value ‘i’ from 0 to 1, do the following.  The integer
value in doubleword element ‘i’ of a is multiplied by the integer value
in doubleword element ‘i’ of b.  The high-order 64 bits of the 128-bit
product are placed into doubleword element ‘i’ of the vector returned.

vector unsigned long long
vec_mul (vector unsigned long long a, vector unsigned long long b);
vector signed long long
vec_mul (vector signed long long a, vector signed long long b);

 For each integer value ‘i’ from 0 to 1, do the following.  The integer
value in doubleword element ‘i’ of a is multiplied by the integer value
in doubleword element ‘i’ of b.  The low-order 64 bits of the 128-bit
product are placed into doubleword element ‘i’ of the vector returned.

vector signed int
vec_div (vector signed int a, vector signed int b);
vector unsigned int
vec_div (vector unsigned int a, vector unsigned int b);

 For each integer value ‘i’ from 0 to 3, do the following.  The integer
in word element ‘i’ of a is divided by the integer in word element ‘i’
of b.  The unique integer quotient is placed into the word element ‘i’
of the vector returned.  If an attempt is made to perform any of the
divisions <anything> ÷ 0 then the quotient is undefined.

vector signed long long
vec_div (vector signed long long a, vector signed long long b);
vector unsigned long long
vec_div (vector unsigned long long a, vector unsigned long long b);

 For each integer value ‘i’ from 0 to 1, do the following.  The integer
in doubleword element ‘i’ of a is divided by the integer in doubleword
element ‘i’ of b.  The unique integer quotient is placed into the
doubleword element ‘i’ of the vector returned.  If an attempt is made to
perform any of the divisions 0x8000_0000_0000_0000 ÷ -1 or <anything> ÷
0 then the quotient is undefined.

vector signed int
vec_dive (vector signed int a, vector signed int b);
vector unsigned int
vec_dive (vector unsigned int a, vector unsigned int b);

 For each integer value ‘i’ from 0 to 3, do the following.  The integer
in word element ‘i’ of a is shifted left by 32 bits, then divided by the
integer in word element ‘i’ of b.  The unique integer quotient is placed
into the word element ‘i’ of the vector returned.  If the quotient
cannot be represented in 32 bits, or if an attempt is made to perform
any of the divisions <anything> ÷ 0 then the quotient is undefined.

vector signed long long
vec_dive (vector signed long long a, vector signed long long b);
vector unsigned long long
vec_dive (vector unsigned long long a, vector unsigned long long b);

 For each integer value ‘i’ from 0 to 1, do the following.  The integer
in doubleword element ‘i’ of a is shifted left by 64 bits, then divided
by the integer in doubleword element ‘i’ of b.  The unique integer
quotient is placed into the doubleword element ‘i’ of the vector
returned.  If the quotient cannot be represented in 64 bits, or if an
attempt is made to perform <anything> ÷ 0 then the quotient is
undefined.

vector signed int
vec_mod (vector signed int a, vector signed int b);
vector unsigned int
vec_mod (vector unsigned int a, vector unsigned int b);

 For each integer value ‘i’ from 0 to 3, do the following.  The integer
in word element ‘i’ of a is divided by the integer in word element ‘i’
of b.  The unique integer remainder is placed into the word element ‘i’
of the vector returned.  If an attempt is made to perform any of the
divisions 0x8000_0000 ÷ -1 or <anything> ÷ 0 then the remainder is
undefined.

vector signed long long
vec_mod (vector signed long long a, vector signed long long b);
vector unsigned long long
vec_mod (vector unsigned long long a, vector unsigned long long b);

 For each integer value ‘i’ from 0 to 1, do the following.  The integer
in doubleword element ‘i’ of a is divided by the integer in doubleword
element ‘i’ of b.  The unique integer remainder is placed into the
doubleword element ‘i’ of the vector returned.  If an attempt is made to
perform <anything> ÷ 0 then the remainder is undefined.

 Generate PCV from specified Mask size, as if implemented by the
‘xxgenpcvbm’, ‘xxgenpcvhm’, ‘xxgenpcvwm’ instructions, where immediate
value is either 0, 1, 2 or 3.

vector unsigned __int128 vec_rl (vector unsigned __int128 A,
                                              vector unsigned __int128 B);
vector signed __int128 vec_rl (vector signed __int128 A,
                                            vector unsigned __int128 B);

 Result value: Each element of R is obtained by rotating the
corresponding element of A left by the number of bits specified by the
corresponding element of B.

vector unsigned __int128 vec_rlmi (vector unsigned __int128,
                                                vector unsigned __int128,
                                                vector unsigned __int128);
vector signed __int128 vec_rlmi (vector signed __int128,
                                              vector signed __int128,
                                              vector unsigned __int128);

 Returns the result of rotating the first input and inserting it under
mask into the second input.  The first bit in the mask, the last bit in
the mask are obtained from the two 7-bit fields bits [108:115] and bits
[117:123] respectively of the second input.  The shift is obtained from
the third input in the 7-bit field [125:131] where all bits counted from
zero at the left.

vector unsigned __int128 vec_rlnm (vector unsigned __int128,
                                                vector unsigned __int128,
                                                vector unsigned __int128);
vector signed __int128 vec_rlnm (vector signed __int128,
                                              vector unsigned __int128,
                                              vector unsigned __int128);

 Returns the result of rotating the first input and ANDing it with a
mask.  The first bit in the mask and the last bit in the mask are
obtained from the two 7-bit fields bits [117:123] and bits [125:131]
respectively of the second input.  The shift is obtained from the third
input in the 7-bit field bits [125:131] where all bits counted from zero
at the left.

vector unsigned __int128 vec_sl(vector unsigned __int128 A, vector unsigned __int128 B);
vector signed __int128 vec_sl(vector signed __int128 A, vector unsigned __int128 B);

 Result value: Each element of R is obtained by shifting the
corresponding element of A left by the number of bits specified by the
corresponding element of B.

vector unsigned __int128 vec_sr(vector unsigned __int128 A, vector unsigned __int128 B);
vector signed __int128 vec_sr(vector signed __int128 A, vector unsigned __int128 B);

 Result value: Each element of R is obtained by shifting the
corresponding element of A right by the number of bits specified by the
corresponding element of B.

vector unsigned __int128 vec_sra(vector unsigned __int128 A, vector unsigned __int128 B);
vector signed __int128 vec_sra(vector signed __int128 A, vector unsigned __int128 B);

 Result value: Each element of R is obtained by arithmetic shifting the
corresponding element of A right by the number of bits specified by the
corresponding element of B.

vector unsigned __int128 vec_mule (vector unsigned long long,
                                                vector unsigned long long);
vector signed __int128 vec_mule (vector signed long long,
                                              vector signed long long);

 Returns a vector containing a 128-bit integer result of multiplying the
even doubleword elements of the two inputs.

vector unsigned __int128 vec_mulo (vector unsigned long long,
                                                vector unsigned long long);
vector signed __int128 vec_mulo (vector signed long long,
                                              vector signed long long);

 Returns a vector containing a 128-bit integer result of multiplying the
odd doubleword elements of the two inputs.

vector unsigned __int128 vec_div (vector unsigned __int128,
                                               vector unsigned __int128);
vector signed __int128 vec_div (vector signed __int128,
                                             vector signed __int128);

 Returns the result of dividing the first operand by the second operand.
An attempt to divide any value by zero or to divide the most negative
signed 128-bit integer by negative one results in an undefined value.

vector unsigned __int128 vec_dive (vector unsigned __int128,
                                                vector unsigned __int128);
vector signed __int128 vec_dive (vector signed __int128,
                                              vector signed __int128);

 The result is produced by shifting the first input left by 128 bits and
dividing by the second.  If an attempt is made to divide by zero or the
result is larger than 128 bits, the result is undefined.

vector unsigned __int128 vec_mod (vector unsigned __int128,
                                               vector unsigned __int128);
vector signed __int128 vec_mod (vector signed __int128,
                                             vector signed __int128);

 The result is the modulo result of dividing the first input by the
second input.

 The following builtins perform 128-bit vector comparisons.  The
‘vec_all_xx’, ‘vec_any_xx’, and ‘vec_cmpxx’, where ‘xx’ is one of the
operations ‘eq, ne, gt, lt, ge, le’ perform pairwise comparisons between
the elements at the same positions within their two vector arguments.
The ‘vec_all_xx’function returns a non-zero value if and only if all
pairwise comparisons are true.  The ‘vec_any_xx’ function returns a
non-zero value if and only if at least one pairwise comparison is true.
The ‘vec_cmpxx’function returns a vector of the same type as its two
arguments, within which each element consists of all ones to denote that
specified logical comparison of the corresponding elements was true.
Otherwise, the element of the returned vector contains all zeros.

     vector bool __int128 vec_cmpeq (vector signed __int128, vector signed __int128);
     vector bool __int128 vec_cmpeq (vector unsigned __int128, vector unsigned __int128);
     vector bool __int128 vec_cmpne (vector signed __int128, vector signed __int128);
     vector bool __int128 vec_cmpne (vector unsigned __int128, vector unsigned __int128);
     vector bool __int128 vec_cmpgt (vector signed __int128, vector signed __int128);
     vector bool __int128 vec_cmpgt (vector unsigned __int128, vector unsigned __int128);
     vector bool __int128 vec_cmplt (vector signed __int128, vector signed __int128);
     vector bool __int128 vec_cmplt (vector unsigned __int128, vector unsigned __int128);
     vector bool __int128 vec_cmpge (vector signed __int128, vector signed __int128);
     vector bool __int128 vec_cmpge (vector unsigned __int128, vector unsigned __int128);
     vector bool __int128 vec_cmple (vector signed __int128, vector signed __int128);
     vector bool __int128 vec_cmple (vector unsigned __int128, vector unsigned __int128);

     int vec_all_eq (vector signed __int128, vector signed __int128);
     int vec_all_eq (vector unsigned __int128, vector unsigned __int128);
     int vec_all_ne (vector signed __int128, vector signed __int128);
     int vec_all_ne (vector unsigned __int128, vector unsigned __int128);
     int vec_all_gt (vector signed __int128, vector signed __int128);
     int vec_all_gt (vector unsigned __int128, vector unsigned __int128);
     int vec_all_lt (vector signed __int128, vector signed __int128);
     int vec_all_lt (vector unsigned __int128, vector unsigned __int128);
     int vec_all_ge (vector signed __int128, vector signed __int128);
     int vec_all_ge (vector unsigned __int128, vector unsigned __int128);
     int vec_all_le (vector signed __int128, vector signed __int128);
     int vec_all_le (vector unsigned __int128, vector unsigned __int128);

     int vec_any_eq (vector signed __int128, vector signed __int128);
     int vec_any_eq (vector unsigned __int128, vector unsigned __int128);
     int vec_any_ne (vector signed __int128, vector signed __int128);
     int vec_any_ne (vector unsigned __int128, vector unsigned __int128);
     int vec_any_gt (vector signed __int128, vector signed __int128);
     int vec_any_gt (vector unsigned __int128, vector unsigned __int128);
     int vec_any_lt (vector signed __int128, vector signed __int128);
     int vec_any_lt (vector unsigned __int128, vector unsigned __int128);
     int vec_any_ge (vector signed __int128, vector signed __int128);
     int vec_any_ge (vector unsigned __int128, vector unsigned __int128);
     int vec_any_le (vector signed __int128, vector signed __int128);
     int vec_any_le (vector unsigned __int128, vector unsigned __int128);


File: gcc.info,  Node: PowerPC Hardware Transactional Memory Built-in Functions,  Next: PowerPC Atomic Memory Operation Functions,  Prev: PowerPC AltiVec/VSX Built-in Functions,  Up: Target Builtins

6.60.24 PowerPC Hardware Transactional Memory Built-in Functions
----------------------------------------------------------------

GCC provides two interfaces for accessing the Hardware Transactional
Memory (HTM) instructions available on some of the PowerPC family of
processors (eg, POWER8).  The two interfaces come in a low level
interface, consisting of built-in functions specific to PowerPC and a
higher level interface consisting of inline functions that are common
between PowerPC and S/390.

6.60.24.1 PowerPC HTM Low Level Built-in Functions
..................................................

The following low level built-in functions are available with ‘-mhtm’ or
‘-mcpu=CPU’ where CPU is 'power8' or later.  They all generate the
machine instruction that is part of the name.

 The HTM builtins (with the exception of ‘__builtin_tbegin’) return the
full 4-bit condition register value set by their associated hardware
instruction.  The header file ‘htmintrin.h’ defines some macros that can
be used to decipher the return value.  The ‘__builtin_tbegin’ builtin
returns a simple ‘true’ or ‘false’ value depending on whether a
transaction was successfully started or not.  The arguments of the
builtins match exactly the type and order of the associated hardware
instruction's operands, except for the ‘__builtin_tcheck’ builtin, which
does not take any input arguments.  Refer to the ISA manual for a
description of each instruction's operands.

     unsigned int __builtin_tbegin (unsigned int);
     unsigned int __builtin_tend (unsigned int);

     unsigned int __builtin_tabort (unsigned int);
     unsigned int __builtin_tabortdc (unsigned int, unsigned int, unsigned int);
     unsigned int __builtin_tabortdci (unsigned int, unsigned int, int);
     unsigned int __builtin_tabortwc (unsigned int, unsigned int, unsigned int);
     unsigned int __builtin_tabortwci (unsigned int, unsigned int, int);

     unsigned int __builtin_tcheck (void);
     unsigned int __builtin_treclaim (unsigned int);
     unsigned int __builtin_trechkpt (void);
     unsigned int __builtin_tsr (unsigned int);

 In addition to the above HTM built-ins, we have added built-ins for
some common extended mnemonics of the HTM instructions:

     unsigned int __builtin_tendall (void);
     unsigned int __builtin_tresume (void);
     unsigned int __builtin_tsuspend (void);

 Note that the semantics of the above HTM builtins are required to mimic
the locking semantics used for critical sections.  Builtins that are
used to create a new transaction or restart a suspended transaction must
have lock acquisition like semantics while those builtins that end or
suspend a transaction must have lock release like semantics.
Specifically, this must mimic lock semantics as specified by C++11, for
example: Lock acquisition is as-if an execution of
__atomic_exchange_n(&globallock,1,__ATOMIC_ACQUIRE) that returns 0, and
lock release is as-if an execution of
__atomic_store(&globallock,0,__ATOMIC_RELEASE), with globallock being an
implicit implementation-defined lock used for all transactions.  The HTM
instructions associated with with the builtins inherently provide the
correct acquisition and release hardware barriers required.  However,
the compiler must also be prohibited from moving loads and stores across
the builtins in a way that would violate their semantics.  This has been
accomplished by adding memory barriers to the associated HTM
instructions (which is a conservative approach to provide acquire and
release semantics).  Earlier versions of the compiler did not treat the
HTM instructions as memory barriers.  A ‘__TM_FENCE__’ macro has been
added, which can be used to determine whether the current compiler
treats HTM instructions as memory barriers or not.  This allows the user
to explicitly add memory barriers to their code when using an older
version of the compiler.

 The following set of built-in functions are available to gain access to
the HTM specific special purpose registers.

     unsigned long __builtin_get_texasr (void);
     unsigned long __builtin_get_texasru (void);
     unsigned long __builtin_get_tfhar (void);
     unsigned long __builtin_get_tfiar (void);

     void __builtin_set_texasr (unsigned long);
     void __builtin_set_texasru (unsigned long);
     void __builtin_set_tfhar (unsigned long);
     void __builtin_set_tfiar (unsigned long);

 Example usage of these low level built-in functions may look like:

     #include <htmintrin.h>

     int num_retries = 10;

     while (1)
       {
         if (__builtin_tbegin (0))
           {
             /* Transaction State Initiated.  */
             if (is_locked (lock))
               __builtin_tabort (0);
             ... transaction code...
             __builtin_tend (0);
             break;
           }
         else
           {
             /* Transaction State Failed.  Use locks if the transaction
                failure is "persistent" or we've tried too many times.  */
             if (num_retries-- <= 0
                 || _TEXASRU_FAILURE_PERSISTENT (__builtin_get_texasru ()))
               {
                 acquire_lock (lock);
                 ... non transactional fallback path...
                 release_lock (lock);
                 break;
               }
           }
       }

 One final built-in function has been added that returns the value of
the 2-bit Transaction State field of the Machine Status Register (MSR)
as stored in ‘CR0’.

     unsigned long __builtin_ttest (void)

 This built-in can be used to determine the current transaction state
using the following code example:

     #include <htmintrin.h>

     unsigned char tx_state = _HTM_STATE (__builtin_ttest ());

     if (tx_state == _HTM_TRANSACTIONAL)
       {
         /* Code to use in transactional state.  */
       }
     else if (tx_state == _HTM_NONTRANSACTIONAL)
       {
         /* Code to use in non-transactional state.  */
       }
     else if (tx_state == _HTM_SUSPENDED)
       {
         /* Code to use in transaction suspended state.  */
       }

6.60.24.2 PowerPC HTM High Level Inline Functions
.................................................

The following high level HTM interface is made available by including
‘<htmxlintrin.h>’ and using ‘-mhtm’ or ‘-mcpu=CPU’ where CPU is 'power8'
or later.  This interface is common between PowerPC and S/390, allowing
users to write one HTM source implementation that can be compiled and
executed on either system.

     long __TM_simple_begin (void);
     long __TM_begin (void* const TM_buff);
     long __TM_end (void);
     void __TM_abort (void);
     void __TM_named_abort (unsigned char const code);
     void __TM_resume (void);
     void __TM_suspend (void);

     long __TM_is_user_abort (void* const TM_buff);
     long __TM_is_named_user_abort (void* const TM_buff, unsigned char *code);
     long __TM_is_illegal (void* const TM_buff);
     long __TM_is_footprint_exceeded (void* const TM_buff);
     long __TM_nesting_depth (void* const TM_buff);
     long __TM_is_nested_too_deep(void* const TM_buff);
     long __TM_is_conflict(void* const TM_buff);
     long __TM_is_failure_persistent(void* const TM_buff);
     long __TM_failure_address(void* const TM_buff);
     long long __TM_failure_code(void* const TM_buff);

 Using these common set of HTM inline functions, we can create a more
portable version of the HTM example in the previous section that will
work on either PowerPC or S/390:

     #include <htmxlintrin.h>

     int num_retries = 10;
     TM_buff_type TM_buff;

     while (1)
       {
         if (__TM_begin (TM_buff) == _HTM_TBEGIN_STARTED)
           {
             /* Transaction State Initiated.  */
             if (is_locked (lock))
               __TM_abort ();
             ... transaction code...
             __TM_end ();
             break;
           }
         else
           {
             /* Transaction State Failed.  Use locks if the transaction
                failure is "persistent" or we've tried too many times.  */
             if (num_retries-- <= 0
                 || __TM_is_failure_persistent (TM_buff))
               {
                 acquire_lock (lock);
                 ... non transactional fallback path...
                 release_lock (lock);
                 break;
               }
           }
       }


File: gcc.info,  Node: PowerPC Atomic Memory Operation Functions,  Next: PowerPC Matrix-Multiply Assist Built-in Functions,  Prev: PowerPC Hardware Transactional Memory Built-in Functions,  Up: Target Builtins

6.60.25 PowerPC Atomic Memory Operation Functions
-------------------------------------------------

ISA 3.0 of the PowerPC added new atomic memory operation (amo)
instructions.  GCC provides support for these instructions in 64-bit
environments.  All of the functions are declared in the include file
‘amo.h’.

 The functions supported are:

     #include <amo.h>

     uint32_t amo_lwat_add (uint32_t *, uint32_t);
     uint32_t amo_lwat_xor (uint32_t *, uint32_t);
     uint32_t amo_lwat_ior (uint32_t *, uint32_t);
     uint32_t amo_lwat_and (uint32_t *, uint32_t);
     uint32_t amo_lwat_umax (uint32_t *, uint32_t);
     uint32_t amo_lwat_umin (uint32_t *, uint32_t);
     uint32_t amo_lwat_swap (uint32_t *, uint32_t);

     int32_t amo_lwat_sadd (int32_t *, int32_t);
     int32_t amo_lwat_smax (int32_t *, int32_t);
     int32_t amo_lwat_smin (int32_t *, int32_t);
     int32_t amo_lwat_sswap (int32_t *, int32_t);

     uint64_t amo_ldat_add (uint64_t *, uint64_t);
     uint64_t amo_ldat_xor (uint64_t *, uint64_t);
     uint64_t amo_ldat_ior (uint64_t *, uint64_t);
     uint64_t amo_ldat_and (uint64_t *, uint64_t);
     uint64_t amo_ldat_umax (uint64_t *, uint64_t);
     uint64_t amo_ldat_umin (uint64_t *, uint64_t);
     uint64_t amo_ldat_swap (uint64_t *, uint64_t);

     int64_t amo_ldat_sadd (int64_t *, int64_t);
     int64_t amo_ldat_smax (int64_t *, int64_t);
     int64_t amo_ldat_smin (int64_t *, int64_t);
     int64_t amo_ldat_sswap (int64_t *, int64_t);

     void amo_stwat_add (uint32_t *, uint32_t);
     void amo_stwat_xor (uint32_t *, uint32_t);
     void amo_stwat_ior (uint32_t *, uint32_t);
     void amo_stwat_and (uint32_t *, uint32_t);
     void amo_stwat_umax (uint32_t *, uint32_t);
     void amo_stwat_umin (uint32_t *, uint32_t);

     void amo_stwat_sadd (int32_t *, int32_t);
     void amo_stwat_smax (int32_t *, int32_t);
     void amo_stwat_smin (int32_t *, int32_t);

     void amo_stdat_add (uint64_t *, uint64_t);
     void amo_stdat_xor (uint64_t *, uint64_t);
     void amo_stdat_ior (uint64_t *, uint64_t);
     void amo_stdat_and (uint64_t *, uint64_t);
     void amo_stdat_umax (uint64_t *, uint64_t);
     void amo_stdat_umin (uint64_t *, uint64_t);

     void amo_stdat_sadd (int64_t *, int64_t);
     void amo_stdat_smax (int64_t *, int64_t);
     void amo_stdat_smin (int64_t *, int64_t);


File: gcc.info,  Node: PowerPC Matrix-Multiply Assist Built-in Functions,  Next: PRU Built-in Functions,  Prev: PowerPC Atomic Memory Operation Functions,  Up: Target Builtins

6.60.26 PowerPC Matrix-Multiply Assist Built-in Functions
---------------------------------------------------------

ISA 3.1 of the PowerPC added new Matrix-Multiply Assist (MMA)
instructions.  GCC provides support for these instructions through the
following built-in functions which are enabled with the ‘-mmma’ option.
The vec_t type below is defined to be a normal vector unsigned char
type.  The uint2, uint4 and uint8 parameters are 2-bit, 4-bit and 8-bit
unsigned integer constants respectively.  The compiler will verify that
they are constants and that their values are within range.

 The built-in functions supported are:

     void __builtin_mma_xvi4ger8 (__vector_quad *, vec_t, vec_t);
     void __builtin_mma_xvi8ger4 (__vector_quad *, vec_t, vec_t);
     void __builtin_mma_xvi16ger2 (__vector_quad *, vec_t, vec_t);
     void __builtin_mma_xvi16ger2s (__vector_quad *, vec_t, vec_t);
     void __builtin_mma_xvf16ger2 (__vector_quad *, vec_t, vec_t);
     void __builtin_mma_xvbf16ger2 (__vector_quad *, vec_t, vec_t);
     void __builtin_mma_xvf32ger (__vector_quad *, vec_t, vec_t);

     void __builtin_mma_xvi4ger8pp (__vector_quad *, vec_t, vec_t);
     void __builtin_mma_xvi8ger4pp (__vector_quad *, vec_t, vec_t);
     void __builtin_mma_xvi8ger4spp(__vector_quad *, vec_t, vec_t);
     void __builtin_mma_xvi16ger2pp (__vector_quad *, vec_t, vec_t);
     void __builtin_mma_xvi16ger2spp (__vector_quad *, vec_t, vec_t);
     void __builtin_mma_xvf16ger2pp (__vector_quad *, vec_t, vec_t);
     void __builtin_mma_xvf16ger2pn (__vector_quad *, vec_t, vec_t);
     void __builtin_mma_xvf16ger2np (__vector_quad *, vec_t, vec_t);
     void __builtin_mma_xvf16ger2nn (__vector_quad *, vec_t, vec_t);
     void __builtin_mma_xvbf16ger2pp (__vector_quad *, vec_t, vec_t);
     void __builtin_mma_xvbf16ger2pn (__vector_quad *, vec_t, vec_t);
     void __builtin_mma_xvbf16ger2np (__vector_quad *, vec_t, vec_t);
     void __builtin_mma_xvbf16ger2nn (__vector_quad *, vec_t, vec_t);
     void __builtin_mma_xvf32gerpp (__vector_quad *, vec_t, vec_t);
     void __builtin_mma_xvf32gerpn (__vector_quad *, vec_t, vec_t);
     void __builtin_mma_xvf32gernp (__vector_quad *, vec_t, vec_t);
     void __builtin_mma_xvf32gernn (__vector_quad *, vec_t, vec_t);

     void __builtin_mma_pmxvi4ger8 (__vector_quad *, vec_t, vec_t, uint4, uint4, uint8);
     void __builtin_mma_pmxvi4ger8pp (__vector_quad *, vec_t, vec_t, uint4, uint4, uint8);

     void __builtin_mma_pmxvi8ger4 (__vector_quad *, vec_t, vec_t, uint4, uint4, uint4);
     void __builtin_mma_pmxvi8ger4pp (__vector_quad *, vec_t, vec_t, uint4, uint4, uint4);
     void __builtin_mma_pmxvi8ger4spp(__vector_quad *, vec_t, vec_t, uint4, uint4, uint4);

     void __builtin_mma_pmxvi16ger2 (__vector_quad *, vec_t, vec_t, uint4, uint4, uint2);
     void __builtin_mma_pmxvi16ger2s (__vector_quad *, vec_t, vec_t, uint4, uint4, uint2);
     void __builtin_mma_pmxvf16ger2 (__vector_quad *, vec_t, vec_t, uint4, uint4, uint2);
     void __builtin_mma_pmxvbf16ger2 (__vector_quad *, vec_t, vec_t, uint4, uint4, uint2);

     void __builtin_mma_pmxvi16ger2pp (__vector_quad *, vec_t, vec_t, uint4, uint4, uint2);
     void __builtin_mma_pmxvi16ger2spp (__vector_quad *, vec_t, vec_t, uint4, uint4, uint2);
     void __builtin_mma_pmxvf16ger2pp (__vector_quad *, vec_t, vec_t, uint4, uint4, uint2);
     void __builtin_mma_pmxvf16ger2pn (__vector_quad *, vec_t, vec_t, uint4, uint4, uint2);
     void __builtin_mma_pmxvf16ger2np (__vector_quad *, vec_t, vec_t, uint4, uint4, uint2);
     void __builtin_mma_pmxvf16ger2nn (__vector_quad *, vec_t, vec_t, uint4, uint4, uint2);
     void __builtin_mma_pmxvbf16ger2pp (__vector_quad *, vec_t, vec_t, uint4, uint4, uint2);
     void __builtin_mma_pmxvbf16ger2pn (__vector_quad *, vec_t, vec_t, uint4, uint4, uint2);
     void __builtin_mma_pmxvbf16ger2np (__vector_quad *, vec_t, vec_t, uint4, uint4, uint2);
     void __builtin_mma_pmxvbf16ger2nn (__vector_quad *, vec_t, vec_t, uint4, uint4, uint2);

     void __builtin_mma_pmxvf32ger (__vector_quad *, vec_t, vec_t, uint4, uint4);
     void __builtin_mma_pmxvf32gerpp (__vector_quad *, vec_t, vec_t, uint4, uint4);
     void __builtin_mma_pmxvf32gerpn (__vector_quad *, vec_t, vec_t, uint4, uint4);
     void __builtin_mma_pmxvf32gernp (__vector_quad *, vec_t, vec_t, uint4, uint4);
     void __builtin_mma_pmxvf32gernn (__vector_quad *, vec_t, vec_t, uint4, uint4);

     void __builtin_mma_xvf64ger (__vector_quad *, __vector_pair, vec_t);
     void __builtin_mma_xvf64gerpp (__vector_quad *, __vector_pair, vec_t);
     void __builtin_mma_xvf64gerpn (__vector_quad *, __vector_pair, vec_t);
     void __builtin_mma_xvf64gernp (__vector_quad *, __vector_pair, vec_t);
     void __builtin_mma_xvf64gernn (__vector_quad *, __vector_pair, vec_t);

     void __builtin_mma_pmxvf64ger (__vector_quad *, __vector_pair, vec_t, uint4, uint2);
     void __builtin_mma_pmxvf64gerpp (__vector_quad *, __vector_pair, vec_t, uint4, uint2);
     void __builtin_mma_pmxvf64gerpn (__vector_quad *, __vector_pair, vec_t, uint4, uint2);
     void __builtin_mma_pmxvf64gernp (__vector_quad *, __vector_pair, vec_t, uint4, uint2);
     void __builtin_mma_pmxvf64gernn (__vector_quad *, __vector_pair, vec_t, uint4, uint2);

     void __builtin_mma_xxmtacc (__vector_quad *);
     void __builtin_mma_xxmfacc (__vector_quad *);
     void __builtin_mma_xxsetaccz (__vector_quad *);

     void __builtin_mma_build_acc (__vector_quad *, vec_t, vec_t, vec_t, vec_t);
     void __builtin_mma_disassemble_acc (void *, __vector_quad *);

     void __builtin_vsx_build_pair (__vector_pair *, vec_t, vec_t);
     void __builtin_vsx_disassemble_pair (void *, __vector_pair *);

     vec_t __builtin_vsx_xvcvspbf16 (vec_t);
     vec_t __builtin_vsx_xvcvbf16spn (vec_t);

     __vector_pair __builtin_vsx_lxvp (size_t, __vector_pair *);
     void __builtin_vsx_stxvp (__vector_pair, size_t, __vector_pair *);


File: gcc.info,  Node: PRU Built-in Functions,  Next: RISC-V Built-in Functions,  Prev: PowerPC Matrix-Multiply Assist Built-in Functions,  Up: Target Builtins

6.60.27 PRU Built-in Functions
------------------------------

GCC provides a couple of special builtin functions to aid in utilizing
special PRU instructions.

 The built-in functions supported are:

‘__delay_cycles (long long CYCLES)’
     This inserts an instruction sequence that takes exactly CYCLES
     cycles (between 0 and 0xffffffff) to complete.  The inserted
     sequence may use jumps, loops, or no-ops, and does not interfere
     with any other instructions.  Note that CYCLES must be a
     compile-time constant integer - that is, you must pass a number,
     not a variable that may be optimized to a constant later.  The
     number of cycles delayed by this builtin is exact.

‘__halt (void)’
     This inserts a HALT instruction to stop processor execution.

‘unsigned int __lmbd (unsigned int WORDVAL, unsigned int BITVAL)’
     This inserts LMBD instruction to calculate the left-most bit with
     value BITVAL in value WORDVAL.  Only the least significant bit of
     BITVAL is taken into account.


File: gcc.info,  Node: RISC-V Built-in Functions,  Next: RX Built-in Functions,  Prev: PRU Built-in Functions,  Up: Target Builtins

6.60.28 RISC-V Built-in Functions
---------------------------------

These built-in functions are available for the RISC-V family of
processors.

 -- Built-in Function: void * __builtin_thread_pointer (void)
     Returns the value that is currently set in the ‘tp’ register.


File: gcc.info,  Node: RX Built-in Functions,  Next: S/390 System z Built-in Functions,  Prev: RISC-V Built-in Functions,  Up: Target Builtins

6.60.29 RX Built-in Functions
-----------------------------

GCC supports some of the RX instructions which cannot be expressed in
the C programming language via the use of built-in functions.  The
following functions are supported:

 -- Built-in Function: void __builtin_rx_brk (void)
     Generates the ‘brk’ machine instruction.

 -- Built-in Function: void __builtin_rx_clrpsw (int)
     Generates the ‘clrpsw’ machine instruction to clear the specified
     bit in the processor status word.

 -- Built-in Function: void __builtin_rx_int (int)
     Generates the ‘int’ machine instruction to generate an interrupt
     with the specified value.

 -- Built-in Function: void __builtin_rx_machi (int, int)
     Generates the ‘machi’ machine instruction to add the result of
     multiplying the top 16 bits of the two arguments into the
     accumulator.

 -- Built-in Function: void __builtin_rx_maclo (int, int)
     Generates the ‘maclo’ machine instruction to add the result of
     multiplying the bottom 16 bits of the two arguments into the
     accumulator.

 -- Built-in Function: void __builtin_rx_mulhi (int, int)
     Generates the ‘mulhi’ machine instruction to place the result of
     multiplying the top 16 bits of the two arguments into the
     accumulator.

 -- Built-in Function: void __builtin_rx_mullo (int, int)
     Generates the ‘mullo’ machine instruction to place the result of
     multiplying the bottom 16 bits of the two arguments into the
     accumulator.

 -- Built-in Function: int __builtin_rx_mvfachi (void)
     Generates the ‘mvfachi’ machine instruction to read the top 32 bits
     of the accumulator.

 -- Built-in Function: int __builtin_rx_mvfacmi (void)
     Generates the ‘mvfacmi’ machine instruction to read the middle 32
     bits of the accumulator.

 -- Built-in Function: int __builtin_rx_mvfc (int)
     Generates the ‘mvfc’ machine instruction which reads the control
     register specified in its argument and returns its value.

 -- Built-in Function: void __builtin_rx_mvtachi (int)
     Generates the ‘mvtachi’ machine instruction to set the top 32 bits
     of the accumulator.

 -- Built-in Function: void __builtin_rx_mvtaclo (int)
     Generates the ‘mvtaclo’ machine instruction to set the bottom 32
     bits of the accumulator.

 -- Built-in Function: void __builtin_rx_mvtc (int reg, int val)
     Generates the ‘mvtc’ machine instruction which sets control
     register number ‘reg’ to ‘val’.

 -- Built-in Function: void __builtin_rx_mvtipl (int)
     Generates the ‘mvtipl’ machine instruction set the interrupt
     priority level.

 -- Built-in Function: void __builtin_rx_racw (int)
     Generates the ‘racw’ machine instruction to round the accumulator
     according to the specified mode.

 -- Built-in Function: int __builtin_rx_revw (int)
     Generates the ‘revw’ machine instruction which swaps the bytes in
     the argument so that bits 0-7 now occupy bits 8-15 and vice versa,
     and also bits 16-23 occupy bits 24-31 and vice versa.

 -- Built-in Function: void __builtin_rx_rmpa (void)
     Generates the ‘rmpa’ machine instruction which initiates a repeated
     multiply and accumulate sequence.

 -- Built-in Function: void __builtin_rx_round (float)
     Generates the ‘round’ machine instruction which returns the
     floating-point argument rounded according to the current rounding
     mode set in the floating-point status word register.

 -- Built-in Function: int __builtin_rx_sat (int)
     Generates the ‘sat’ machine instruction which returns the saturated
     value of the argument.

 -- Built-in Function: void __builtin_rx_setpsw (int)
     Generates the ‘setpsw’ machine instruction to set the specified bit
     in the processor status word.

 -- Built-in Function: void __builtin_rx_wait (void)
     Generates the ‘wait’ machine instruction.


File: gcc.info,  Node: S/390 System z Built-in Functions,  Next: SH Built-in Functions,  Prev: RX Built-in Functions,  Up: Target Builtins

6.60.30 S/390 System z Built-in Functions
-----------------------------------------

 -- Built-in Function: int __builtin_tbegin (void*)
     Generates the ‘tbegin’ machine instruction starting a
     non-constrained hardware transaction.  If the parameter is non-NULL
     the memory area is used to store the transaction diagnostic buffer
     and will be passed as first operand to ‘tbegin’.  This buffer can
     be defined using the ‘struct __htm_tdb’ C struct defined in
     ‘htmintrin.h’ and must reside on a double-word boundary.  The
     second tbegin operand is set to ‘0xff0c’.  This enables
     save/restore of all GPRs and disables aborts for FPR and AR
     manipulations inside the transaction body.  The condition code set
     by the tbegin instruction is returned as integer value.  The tbegin
     instruction by definition overwrites the content of all FPRs.  The
     compiler will generate code which saves and restores the FPRs.  For
     soft-float code it is recommended to used the ‘*_nofloat’ variant.
     In order to prevent a TDB from being written it is required to pass
     a constant zero value as parameter.  Passing a zero value through a
     variable is not sufficient.  Although modifications of access
     registers inside the transaction will not trigger an transaction
     abort it is not supported to actually modify them.  Access
     registers do not get saved when entering a transaction.  They will
     have undefined state when reaching the abort code.

 Macros for the possible return codes of tbegin are defined in the
‘htmintrin.h’ header file:

‘_HTM_TBEGIN_STARTED’
     ‘tbegin’ has been executed as part of normal processing.  The
     transaction body is supposed to be executed.
‘_HTM_TBEGIN_INDETERMINATE’
     The transaction was aborted due to an indeterminate condition which
     might be persistent.
‘_HTM_TBEGIN_TRANSIENT’
     The transaction aborted due to a transient failure.  The
     transaction should be re-executed in that case.
‘_HTM_TBEGIN_PERSISTENT’
     The transaction aborted due to a persistent failure.  Re-execution
     under same circumstances will not be productive.

 -- Macro: _HTM_FIRST_USER_ABORT_CODE
     The ‘_HTM_FIRST_USER_ABORT_CODE’ defined in ‘htmintrin.h’ specifies
     the first abort code which can be used for ‘__builtin_tabort’.
     Values below this threshold are reserved for machine use.

 -- Data type: struct __htm_tdb
     The ‘struct __htm_tdb’ defined in ‘htmintrin.h’ describes the
     structure of the transaction diagnostic block as specified in the
     Principles of Operation manual chapter 5-91.

 -- Built-in Function: int __builtin_tbegin_nofloat (void*)
     Same as ‘__builtin_tbegin’ but without FPR saves and restores.
     Using this variant in code making use of FPRs will leave the FPRs
     in undefined state when entering the transaction abort handler
     code.

 -- Built-in Function: int __builtin_tbegin_retry (void*, int)
     In addition to ‘__builtin_tbegin’ a loop for transient failures is
     generated.  If tbegin returns a condition code of 2 the transaction
     will be retried as often as specified in the second argument.  The
     perform processor assist instruction is used to tell the CPU about
     the number of fails so far.

 -- Built-in Function: int __builtin_tbegin_retry_nofloat (void*, int)
     Same as ‘__builtin_tbegin_retry’ but without FPR saves and
     restores.  Using this variant in code making use of FPRs will leave
     the FPRs in undefined state when entering the transaction abort
     handler code.

 -- Built-in Function: void __builtin_tbeginc (void)
     Generates the ‘tbeginc’ machine instruction starting a constrained
     hardware transaction.  The second operand is set to ‘0xff08’.

 -- Built-in Function: int __builtin_tend (void)
     Generates the ‘tend’ machine instruction finishing a transaction
     and making the changes visible to other threads.  The condition
     code generated by tend is returned as integer value.

 -- Built-in Function: void __builtin_tabort (int)
     Generates the ‘tabort’ machine instruction with the specified abort
     code.  Abort codes from 0 through 255 are reserved and will result
     in an error message.

 -- Built-in Function: void __builtin_tx_assist (int)
     Generates the ‘ppa rX,rY,1’ machine instruction.  Where the integer
     parameter is loaded into rX and a value of zero is loaded into rY.
     The integer parameter specifies the number of times the transaction
     repeatedly aborted.

 -- Built-in Function: int __builtin_tx_nesting_depth (void)
     Generates the ‘etnd’ machine instruction.  The current nesting
     depth is returned as integer value.  For a nesting depth of 0 the
     code is not executed as part of an transaction.

 -- Built-in Function: void __builtin_non_tx_store (uint64_t *,
          uint64_t)

     Generates the ‘ntstg’ machine instruction.  The second argument is
     written to the first arguments location.  The store operation will
     not be rolled-back in case of an transaction abort.


File: gcc.info,  Node: SH Built-in Functions,  Next: SPARC VIS Built-in Functions,  Prev: S/390 System z Built-in Functions,  Up: Target Builtins

6.60.31 SH Built-in Functions
-----------------------------

The following built-in functions are supported on the SH1, SH2, SH3 and
SH4 families of processors:

 -- Built-in Function: void __builtin_set_thread_pointer (void *PTR)
     Sets the ‘GBR’ register to the specified value PTR.  This is
     usually used by system code that manages threads and execution
     contexts.  The compiler normally does not generate code that
     modifies the contents of ‘GBR’ and thus the value is preserved
     across function calls.  Changing the ‘GBR’ value in user code must
     be done with caution, since the compiler might use ‘GBR’ in order
     to access thread local variables.

 -- Built-in Function: void * __builtin_thread_pointer (void)
     Returns the value that is currently set in the ‘GBR’ register.
     Memory loads and stores that use the thread pointer as a base
     address are turned into ‘GBR’ based displacement loads and stores,
     if possible.  For example:
          struct my_tcb
          {
             int a, b, c, d, e;
          };

          int get_tcb_value (void)
          {
            // Generate ‘mov.l @(8,gbr),r0’ instruction
            return ((my_tcb*)__builtin_thread_pointer ())->c;
          }

 -- Built-in Function: unsigned int __builtin_sh_get_fpscr (void)
     Returns the value that is currently set in the ‘FPSCR’ register.

 -- Built-in Function: void __builtin_sh_set_fpscr (unsigned int VAL)
     Sets the ‘FPSCR’ register to the specified value VAL, while
     preserving the current values of the FR, SZ and PR bits.


File: gcc.info,  Node: SPARC VIS Built-in Functions,  Next: TI C6X Built-in Functions,  Prev: SH Built-in Functions,  Up: Target Builtins

6.60.32 SPARC VIS Built-in Functions
------------------------------------

GCC supports SIMD operations on the SPARC using both the generic vector
extensions (*note Vector Extensions::) as well as built-in functions for
the SPARC Visual Instruction Set (VIS). When you use the ‘-mvis’ switch,
the VIS extension is exposed as the following built-in functions:

     typedef int v1si __attribute__ ((vector_size (4)));
     typedef int v2si __attribute__ ((vector_size (8)));
     typedef short v4hi __attribute__ ((vector_size (8)));
     typedef short v2hi __attribute__ ((vector_size (4)));
     typedef unsigned char v8qi __attribute__ ((vector_size (8)));
     typedef unsigned char v4qi __attribute__ ((vector_size (4)));

     void __builtin_vis_write_gsr (int64_t);
     int64_t __builtin_vis_read_gsr (void);

     void * __builtin_vis_alignaddr (void *, long);
     void * __builtin_vis_alignaddrl (void *, long);
     int64_t __builtin_vis_faligndatadi (int64_t, int64_t);
     v2si __builtin_vis_faligndatav2si (v2si, v2si);
     v4hi __builtin_vis_faligndatav4hi (v4si, v4si);
     v8qi __builtin_vis_faligndatav8qi (v8qi, v8qi);

     v4hi __builtin_vis_fexpand (v4qi);

     v4hi __builtin_vis_fmul8x16 (v4qi, v4hi);
     v4hi __builtin_vis_fmul8x16au (v4qi, v2hi);
     v4hi __builtin_vis_fmul8x16al (v4qi, v2hi);
     v4hi __builtin_vis_fmul8sux16 (v8qi, v4hi);
     v4hi __builtin_vis_fmul8ulx16 (v8qi, v4hi);
     v2si __builtin_vis_fmuld8sux16 (v4qi, v2hi);
     v2si __builtin_vis_fmuld8ulx16 (v4qi, v2hi);

     v4qi __builtin_vis_fpack16 (v4hi);
     v8qi __builtin_vis_fpack32 (v2si, v8qi);
     v2hi __builtin_vis_fpackfix (v2si);
     v8qi __builtin_vis_fpmerge (v4qi, v4qi);

     int64_t __builtin_vis_pdist (v8qi, v8qi, int64_t);

     long __builtin_vis_edge8 (void *, void *);
     long __builtin_vis_edge8l (void *, void *);
     long __builtin_vis_edge16 (void *, void *);
     long __builtin_vis_edge16l (void *, void *);
     long __builtin_vis_edge32 (void *, void *);
     long __builtin_vis_edge32l (void *, void *);

     long __builtin_vis_fcmple16 (v4hi, v4hi);
     long __builtin_vis_fcmple32 (v2si, v2si);
     long __builtin_vis_fcmpne16 (v4hi, v4hi);
     long __builtin_vis_fcmpne32 (v2si, v2si);
     long __builtin_vis_fcmpgt16 (v4hi, v4hi);
     long __builtin_vis_fcmpgt32 (v2si, v2si);
     long __builtin_vis_fcmpeq16 (v4hi, v4hi);
     long __builtin_vis_fcmpeq32 (v2si, v2si);

     v4hi __builtin_vis_fpadd16 (v4hi, v4hi);
     v2hi __builtin_vis_fpadd16s (v2hi, v2hi);
     v2si __builtin_vis_fpadd32 (v2si, v2si);
     v1si __builtin_vis_fpadd32s (v1si, v1si);
     v4hi __builtin_vis_fpsub16 (v4hi, v4hi);
     v2hi __builtin_vis_fpsub16s (v2hi, v2hi);
     v2si __builtin_vis_fpsub32 (v2si, v2si);
     v1si __builtin_vis_fpsub32s (v1si, v1si);

     long __builtin_vis_array8 (long, long);
     long __builtin_vis_array16 (long, long);
     long __builtin_vis_array32 (long, long);

 When you use the ‘-mvis2’ switch, the VIS version 2.0 built-in
functions also become available:

     long __builtin_vis_bmask (long, long);
     int64_t __builtin_vis_bshuffledi (int64_t, int64_t);
     v2si __builtin_vis_bshufflev2si (v2si, v2si);
     v4hi __builtin_vis_bshufflev2si (v4hi, v4hi);
     v8qi __builtin_vis_bshufflev2si (v8qi, v8qi);

     long __builtin_vis_edge8n (void *, void *);
     long __builtin_vis_edge8ln (void *, void *);
     long __builtin_vis_edge16n (void *, void *);
     long __builtin_vis_edge16ln (void *, void *);
     long __builtin_vis_edge32n (void *, void *);
     long __builtin_vis_edge32ln (void *, void *);

 When you use the ‘-mvis3’ switch, the VIS version 3.0 built-in
functions also become available:

     void __builtin_vis_cmask8 (long);
     void __builtin_vis_cmask16 (long);
     void __builtin_vis_cmask32 (long);

     v4hi __builtin_vis_fchksm16 (v4hi, v4hi);

     v4hi __builtin_vis_fsll16 (v4hi, v4hi);
     v4hi __builtin_vis_fslas16 (v4hi, v4hi);
     v4hi __builtin_vis_fsrl16 (v4hi, v4hi);
     v4hi __builtin_vis_fsra16 (v4hi, v4hi);
     v2si __builtin_vis_fsll16 (v2si, v2si);
     v2si __builtin_vis_fslas16 (v2si, v2si);
     v2si __builtin_vis_fsrl16 (v2si, v2si);
     v2si __builtin_vis_fsra16 (v2si, v2si);

     long __builtin_vis_pdistn (v8qi, v8qi);

     v4hi __builtin_vis_fmean16 (v4hi, v4hi);

     int64_t __builtin_vis_fpadd64 (int64_t, int64_t);
     int64_t __builtin_vis_fpsub64 (int64_t, int64_t);

     v4hi __builtin_vis_fpadds16 (v4hi, v4hi);
     v2hi __builtin_vis_fpadds16s (v2hi, v2hi);
     v4hi __builtin_vis_fpsubs16 (v4hi, v4hi);
     v2hi __builtin_vis_fpsubs16s (v2hi, v2hi);
     v2si __builtin_vis_fpadds32 (v2si, v2si);
     v1si __builtin_vis_fpadds32s (v1si, v1si);
     v2si __builtin_vis_fpsubs32 (v2si, v2si);
     v1si __builtin_vis_fpsubs32s (v1si, v1si);

     long __builtin_vis_fucmple8 (v8qi, v8qi);
     long __builtin_vis_fucmpne8 (v8qi, v8qi);
     long __builtin_vis_fucmpgt8 (v8qi, v8qi);
     long __builtin_vis_fucmpeq8 (v8qi, v8qi);

     float __builtin_vis_fhadds (float, float);
     double __builtin_vis_fhaddd (double, double);
     float __builtin_vis_fhsubs (float, float);
     double __builtin_vis_fhsubd (double, double);
     float __builtin_vis_fnhadds (float, float);
     double __builtin_vis_fnhaddd (double, double);

     int64_t __builtin_vis_umulxhi (int64_t, int64_t);
     int64_t __builtin_vis_xmulx (int64_t, int64_t);
     int64_t __builtin_vis_xmulxhi (int64_t, int64_t);

 When you use the ‘-mvis4’ switch, the VIS version 4.0 built-in
functions also become available:

     v8qi __builtin_vis_fpadd8 (v8qi, v8qi);
     v8qi __builtin_vis_fpadds8 (v8qi, v8qi);
     v8qi __builtin_vis_fpaddus8 (v8qi, v8qi);
     v4hi __builtin_vis_fpaddus16 (v4hi, v4hi);

     v8qi __builtin_vis_fpsub8 (v8qi, v8qi);
     v8qi __builtin_vis_fpsubs8 (v8qi, v8qi);
     v8qi __builtin_vis_fpsubus8 (v8qi, v8qi);
     v4hi __builtin_vis_fpsubus16 (v4hi, v4hi);

     long __builtin_vis_fpcmple8 (v8qi, v8qi);
     long __builtin_vis_fpcmpgt8 (v8qi, v8qi);
     long __builtin_vis_fpcmpule16 (v4hi, v4hi);
     long __builtin_vis_fpcmpugt16 (v4hi, v4hi);
     long __builtin_vis_fpcmpule32 (v2si, v2si);
     long __builtin_vis_fpcmpugt32 (v2si, v2si);

     v8qi __builtin_vis_fpmax8 (v8qi, v8qi);
     v4hi __builtin_vis_fpmax16 (v4hi, v4hi);
     v2si __builtin_vis_fpmax32 (v2si, v2si);

     v8qi __builtin_vis_fpmaxu8 (v8qi, v8qi);
     v4hi __builtin_vis_fpmaxu16 (v4hi, v4hi);
     v2si __builtin_vis_fpmaxu32 (v2si, v2si);

     v8qi __builtin_vis_fpmin8 (v8qi, v8qi);
     v4hi __builtin_vis_fpmin16 (v4hi, v4hi);
     v2si __builtin_vis_fpmin32 (v2si, v2si);

     v8qi __builtin_vis_fpminu8 (v8qi, v8qi);
     v4hi __builtin_vis_fpminu16 (v4hi, v4hi);
     v2si __builtin_vis_fpminu32 (v2si, v2si);

 When you use the ‘-mvis4b’ switch, the VIS version 4.0B built-in
functions also become available:

     v8qi __builtin_vis_dictunpack8 (double, int);
     v4hi __builtin_vis_dictunpack16 (double, int);
     v2si __builtin_vis_dictunpack32 (double, int);

     long __builtin_vis_fpcmple8shl (v8qi, v8qi, int);
     long __builtin_vis_fpcmpgt8shl (v8qi, v8qi, int);
     long __builtin_vis_fpcmpeq8shl (v8qi, v8qi, int);
     long __builtin_vis_fpcmpne8shl (v8qi, v8qi, int);

     long __builtin_vis_fpcmple16shl (v4hi, v4hi, int);
     long __builtin_vis_fpcmpgt16shl (v4hi, v4hi, int);
     long __builtin_vis_fpcmpeq16shl (v4hi, v4hi, int);
     long __builtin_vis_fpcmpne16shl (v4hi, v4hi, int);

     long __builtin_vis_fpcmple32shl (v2si, v2si, int);
     long __builtin_vis_fpcmpgt32shl (v2si, v2si, int);
     long __builtin_vis_fpcmpeq32shl (v2si, v2si, int);
     long __builtin_vis_fpcmpne32shl (v2si, v2si, int);

     long __builtin_vis_fpcmpule8shl (v8qi, v8qi, int);
     long __builtin_vis_fpcmpugt8shl (v8qi, v8qi, int);
     long __builtin_vis_fpcmpule16shl (v4hi, v4hi, int);
     long __builtin_vis_fpcmpugt16shl (v4hi, v4hi, int);
     long __builtin_vis_fpcmpule32shl (v2si, v2si, int);
     long __builtin_vis_fpcmpugt32shl (v2si, v2si, int);

     long __builtin_vis_fpcmpde8shl (v8qi, v8qi, int);
     long __builtin_vis_fpcmpde16shl (v4hi, v4hi, int);
     long __builtin_vis_fpcmpde32shl (v2si, v2si, int);

     long __builtin_vis_fpcmpur8shl (v8qi, v8qi, int);
     long __builtin_vis_fpcmpur16shl (v4hi, v4hi, int);
     long __builtin_vis_fpcmpur32shl (v2si, v2si, int);


File: gcc.info,  Node: TI C6X Built-in Functions,  Next: TILE-Gx Built-in Functions,  Prev: SPARC VIS Built-in Functions,  Up: Target Builtins

6.60.33 TI C6X Built-in Functions
---------------------------------

GCC provides intrinsics to access certain instructions of the TI C6X
processors.  These intrinsics, listed below, are available after
inclusion of the ‘c6x_intrinsics.h’ header file.  They map directly to
C6X instructions.

     int _sadd (int, int);
     int _ssub (int, int);
     int _sadd2 (int, int);
     int _ssub2 (int, int);
     long long _mpy2 (int, int);
     long long _smpy2 (int, int);
     int _add4 (int, int);
     int _sub4 (int, int);
     int _saddu4 (int, int);

     int _smpy (int, int);
     int _smpyh (int, int);
     int _smpyhl (int, int);
     int _smpylh (int, int);

     int _sshl (int, int);
     int _subc (int, int);

     int _avg2 (int, int);
     int _avgu4 (int, int);

     int _clrr (int, int);
     int _extr (int, int);
     int _extru (int, int);
     int _abs (int);
     int _abs2 (int);


File: gcc.info,  Node: TILE-Gx Built-in Functions,  Next: TILEPro Built-in Functions,  Prev: TI C6X Built-in Functions,  Up: Target Builtins

6.60.34 TILE-Gx Built-in Functions
----------------------------------

GCC provides intrinsics to access every instruction of the TILE-Gx
processor.  The intrinsics are of the form:


     unsigned long long __insn_OP (...)

 Where OP is the name of the instruction.  Refer to the ISA manual for
the complete list of instructions.

 GCC also provides intrinsics to directly access the network registers.
The intrinsics are:

     unsigned long long __tile_idn0_receive (void);
     unsigned long long __tile_idn1_receive (void);
     unsigned long long __tile_udn0_receive (void);
     unsigned long long __tile_udn1_receive (void);
     unsigned long long __tile_udn2_receive (void);
     unsigned long long __tile_udn3_receive (void);
     void __tile_idn_send (unsigned long long);
     void __tile_udn_send (unsigned long long);

 The intrinsic ‘void __tile_network_barrier (void)’ is used to guarantee
that no network operations before it are reordered with those after it.


File: gcc.info,  Node: TILEPro Built-in Functions,  Next: x86 Built-in Functions,  Prev: TILE-Gx Built-in Functions,  Up: Target Builtins

6.60.35 TILEPro Built-in Functions
----------------------------------

GCC provides intrinsics to access every instruction of the TILEPro
processor.  The intrinsics are of the form:


     unsigned __insn_OP (...)

where OP is the name of the instruction.  Refer to the ISA manual for
the complete list of instructions.

 GCC also provides intrinsics to directly access the network registers.
The intrinsics are:

     unsigned __tile_idn0_receive (void);
     unsigned __tile_idn1_receive (void);
     unsigned __tile_sn_receive (void);
     unsigned __tile_udn0_receive (void);
     unsigned __tile_udn1_receive (void);
     unsigned __tile_udn2_receive (void);
     unsigned __tile_udn3_receive (void);
     void __tile_idn_send (unsigned);
     void __tile_sn_send (unsigned);
     void __tile_udn_send (unsigned);

 The intrinsic ‘void __tile_network_barrier (void)’ is used to guarantee
that no network operations before it are reordered with those after it.


File: gcc.info,  Node: x86 Built-in Functions,  Next: x86 transactional memory intrinsics,  Prev: TILEPro Built-in Functions,  Up: Target Builtins

6.60.36 x86 Built-in Functions
------------------------------

These built-in functions are available for the x86-32 and x86-64 family
of computers, depending on the command-line switches used.

 If you specify command-line switches such as ‘-msse’, the compiler
could use the extended instruction sets even if the built-ins are not
used explicitly in the program.  For this reason, applications that
perform run-time CPU detection must compile separate files for each
supported architecture, using the appropriate flags.  In particular, the
file containing the CPU detection code should be compiled without these
options.

 The following machine modes are available for use with MMX built-in
functions (*note Vector Extensions::): ‘V2SI’ for a vector of two 32-bit
integers, ‘V4HI’ for a vector of four 16-bit integers, and ‘V8QI’ for a
vector of eight 8-bit integers.  Some of the built-in functions operate
on MMX registers as a whole 64-bit entity, these use ‘V1DI’ as their
mode.

 If 3DNow! extensions are enabled, ‘V2SF’ is used as a mode for a vector
of two 32-bit floating-point values.

 If SSE extensions are enabled, ‘V4SF’ is used for a vector of four
32-bit floating-point values.  Some instructions use a vector of four
32-bit integers, these use ‘V4SI’.  Finally, some instructions operate
on an entire vector register, interpreting it as a 128-bit integer,
these use mode ‘TI’.

 The x86-32 and x86-64 family of processors use additional built-in
functions for efficient use of ‘TF’ (‘__float128’) 128-bit floating
point and ‘TC’ 128-bit complex floating-point values.

 The following floating-point built-in functions are always available.
All of them implement the function that is part of the name.

     __float128 __builtin_fabsq (__float128)
     __float128 __builtin_copysignq (__float128, __float128)

 The following built-in functions are always available.

‘__float128 __builtin_infq (void)’
     Similar to ‘__builtin_inf’, except the return type is ‘__float128’.

‘__float128 __builtin_huge_valq (void)’
     Similar to ‘__builtin_huge_val’, except the return type is
     ‘__float128’.

‘__float128 __builtin_nanq (void)’
     Similar to ‘__builtin_nan’, except the return type is ‘__float128’.

‘__float128 __builtin_nansq (void)’
     Similar to ‘__builtin_nans’, except the return type is
     ‘__float128’.

 The following built-in function is always available.

‘void __builtin_ia32_pause (void)’
     Generates the ‘pause’ machine instruction with a compiler memory
     barrier.

 The following built-in functions are always available and can be used
to check the target platform type.

 -- Built-in Function: void __builtin_cpu_init (void)
     This function runs the CPU detection code to check the type of CPU
     and the features supported.  This built-in function needs to be
     invoked along with the built-in functions to check CPU type and
     features, ‘__builtin_cpu_is’ and ‘__builtin_cpu_supports’, only
     when used in a function that is executed before any constructors
     are called.  The CPU detection code is automatically executed in a
     very high priority constructor.

     For example, this function has to be used in ‘ifunc’ resolvers that
     check for CPU type using the built-in functions ‘__builtin_cpu_is’
     and ‘__builtin_cpu_supports’, or in constructors on targets that
     don't support constructor priority.

          static void (*resolve_memcpy (void)) (void)
          {
            // ifunc resolvers fire before constructors, explicitly call the init
            // function.
            __builtin_cpu_init ();
            if (__builtin_cpu_supports ("ssse3"))
              return ssse3_memcpy; // super fast memcpy with ssse3 instructions.
            else
              return default_memcpy;
          }

          void *memcpy (void *, const void *, size_t)
               __attribute__ ((ifunc ("resolve_memcpy")));

 -- Built-in Function: int __builtin_cpu_is (const char *CPUNAME)
     This function returns a positive integer if the run-time CPU is of
     type CPUNAME and returns ‘0’ otherwise.  The following CPU names
     can be detected:

     ‘amd’
          AMD CPU.

     ‘intel’
          Intel CPU.

     ‘atom’
          Intel Atom CPU.

     ‘slm’
          Intel Silvermont CPU.

     ‘core2’
          Intel Core 2 CPU.

     ‘corei7’
          Intel Core i7 CPU.

     ‘nehalem’
          Intel Core i7 Nehalem CPU.

     ‘westmere’
          Intel Core i7 Westmere CPU.

     ‘sandybridge’
          Intel Core i7 Sandy Bridge CPU.

     ‘ivybridge’
          Intel Core i7 Ivy Bridge CPU.

     ‘haswell’
          Intel Core i7 Haswell CPU.

     ‘broadwell’
          Intel Core i7 Broadwell CPU.

     ‘skylake’
          Intel Core i7 Skylake CPU.

     ‘skylake-avx512’
          Intel Core i7 Skylake AVX512 CPU.

     ‘cannonlake’
          Intel Core i7 Cannon Lake CPU.

     ‘icelake-client’
          Intel Core i7 Ice Lake Client CPU.

     ‘icelake-server’
          Intel Core i7 Ice Lake Server CPU.

     ‘cascadelake’
          Intel Core i7 Cascadelake CPU.

     ‘tigerlake’
          Intel Core i7 Tigerlake CPU.

     ‘cooperlake’
          Intel Core i7 Cooperlake CPU.

     ‘sapphirerapids’
          Intel Core i7 sapphirerapids CPU.

     ‘alderlake’
          Intel Core i7 Alderlake CPU.

     ‘rocketlake’
          Intel Core i7 Rocketlake CPU.

     ‘bonnell’
          Intel Atom Bonnell CPU.

     ‘silvermont’
          Intel Atom Silvermont CPU.

     ‘goldmont’
          Intel Atom Goldmont CPU.

     ‘goldmont-plus’
          Intel Atom Goldmont Plus CPU.

     ‘tremont’
          Intel Atom Tremont CPU.

     ‘knl’
          Intel Knights Landing CPU.

     ‘knm’
          Intel Knights Mill CPU.

     ‘amdfam10h’
          AMD Family 10h CPU.

     ‘barcelona’
          AMD Family 10h Barcelona CPU.

     ‘shanghai’
          AMD Family 10h Shanghai CPU.

     ‘istanbul’
          AMD Family 10h Istanbul CPU.

     ‘btver1’
          AMD Family 14h CPU.

     ‘amdfam15h’
          AMD Family 15h CPU.

     ‘bdver1’
          AMD Family 15h Bulldozer version 1.

     ‘bdver2’
          AMD Family 15h Bulldozer version 2.

     ‘bdver3’
          AMD Family 15h Bulldozer version 3.

     ‘bdver4’
          AMD Family 15h Bulldozer version 4.

     ‘btver2’
          AMD Family 16h CPU.

     ‘amdfam17h’
          AMD Family 17h CPU.

     ‘znver1’
          AMD Family 17h Zen version 1.

     ‘znver2’
          AMD Family 17h Zen version 2.

     ‘amdfam19h’
          AMD Family 19h CPU.

     ‘znver3’
          AMD Family 19h Zen version 3.

     ‘x86-64’
          Baseline x86-64 microarchitecture level (as defined in x86-64
          psABI).

     ‘x86-64-v2’
          x86-64-v2 microarchitecture level.

     ‘x86-64-v3’
          x86-64-v3 microarchitecture level.

     ‘x86-64-v4’
          x86-64-v4 microarchitecture level.

     Here is an example:
          if (__builtin_cpu_is ("corei7"))
            {
               do_corei7 (); // Core i7 specific implementation.
            }
          else
            {
               do_generic (); // Generic implementation.
            }

 -- Built-in Function: int __builtin_cpu_supports (const char *FEATURE)
     This function returns a positive integer if the run-time CPU
     supports FEATURE and returns ‘0’ otherwise.  The following features
     can be detected:

     ‘cmov’
          CMOV instruction.
     ‘mmx’
          MMX instructions.
     ‘popcnt’
          POPCNT instruction.
     ‘sse’
          SSE instructions.
     ‘sse2’
          SSE2 instructions.
     ‘sse3’
          SSE3 instructions.
     ‘ssse3’
          SSSE3 instructions.
     ‘sse4.1’
          SSE4.1 instructions.
     ‘sse4.2’
          SSE4.2 instructions.
     ‘avx’
          AVX instructions.
     ‘avx2’
          AVX2 instructions.
     ‘sse4a’
          SSE4A instructions.
     ‘fma4’
          FMA4 instructions.
     ‘xop’
          XOP instructions.
     ‘fma’
          FMA instructions.
     ‘avx512f’
          AVX512F instructions.
     ‘bmi’
          BMI instructions.
     ‘bmi2’
          BMI2 instructions.
     ‘aes’
          AES instructions.
     ‘pclmul’
          PCLMUL instructions.
     ‘avx512vl’
          AVX512VL instructions.
     ‘avx512bw’
          AVX512BW instructions.
     ‘avx512dq’
          AVX512DQ instructions.
     ‘avx512cd’
          AVX512CD instructions.
     ‘avx512er’
          AVX512ER instructions.
     ‘avx512pf’
          AVX512PF instructions.
     ‘avx512vbmi’
          AVX512VBMI instructions.
     ‘avx512ifma’
          AVX512IFMA instructions.
     ‘avx5124vnniw’
          AVX5124VNNIW instructions.
     ‘avx5124fmaps’
          AVX5124FMAPS instructions.
     ‘avx512vpopcntdq’
          AVX512VPOPCNTDQ instructions.
     ‘avx512vbmi2’
          AVX512VBMI2 instructions.
     ‘gfni’
          GFNI instructions.
     ‘vpclmulqdq’
          VPCLMULQDQ instructions.
     ‘avx512vnni’
          AVX512VNNI instructions.
     ‘avx512bitalg’
          AVX512BITALG instructions.

     Here is an example:
          if (__builtin_cpu_supports ("popcnt"))
            {
               asm("popcnt %1,%0" : "=r"(count) : "rm"(n) : "cc");
            }
          else
            {
               count = generic_countbits (n); //generic implementation.
            }

 The following built-in functions are made available by ‘-mmmx’.  All of
them generate the machine instruction that is part of the name.

     v8qi __builtin_ia32_paddb (v8qi, v8qi);
     v4hi __builtin_ia32_paddw (v4hi, v4hi);
     v2si __builtin_ia32_paddd (v2si, v2si);
     v8qi __builtin_ia32_psubb (v8qi, v8qi);
     v4hi __builtin_ia32_psubw (v4hi, v4hi);
     v2si __builtin_ia32_psubd (v2si, v2si);
     v8qi __builtin_ia32_paddsb (v8qi, v8qi);
     v4hi __builtin_ia32_paddsw (v4hi, v4hi);
     v8qi __builtin_ia32_psubsb (v8qi, v8qi);
     v4hi __builtin_ia32_psubsw (v4hi, v4hi);
     v8qi __builtin_ia32_paddusb (v8qi, v8qi);
     v4hi __builtin_ia32_paddusw (v4hi, v4hi);
     v8qi __builtin_ia32_psubusb (v8qi, v8qi);
     v4hi __builtin_ia32_psubusw (v4hi, v4hi);
     v4hi __builtin_ia32_pmullw (v4hi, v4hi);
     v4hi __builtin_ia32_pmulhw (v4hi, v4hi);
     di __builtin_ia32_pand (di, di);
     di __builtin_ia32_pandn (di,di);
     di __builtin_ia32_por (di, di);
     di __builtin_ia32_pxor (di, di);
     v8qi __builtin_ia32_pcmpeqb (v8qi, v8qi);
     v4hi __builtin_ia32_pcmpeqw (v4hi, v4hi);
     v2si __builtin_ia32_pcmpeqd (v2si, v2si);
     v8qi __builtin_ia32_pcmpgtb (v8qi, v8qi);
     v4hi __builtin_ia32_pcmpgtw (v4hi, v4hi);
     v2si __builtin_ia32_pcmpgtd (v2si, v2si);
     v8qi __builtin_ia32_punpckhbw (v8qi, v8qi);
     v4hi __builtin_ia32_punpckhwd (v4hi, v4hi);
     v2si __builtin_ia32_punpckhdq (v2si, v2si);
     v8qi __builtin_ia32_punpcklbw (v8qi, v8qi);
     v4hi __builtin_ia32_punpcklwd (v4hi, v4hi);
     v2si __builtin_ia32_punpckldq (v2si, v2si);
     v8qi __builtin_ia32_packsswb (v4hi, v4hi);
     v4hi __builtin_ia32_packssdw (v2si, v2si);
     v8qi __builtin_ia32_packuswb (v4hi, v4hi);

     v4hi __builtin_ia32_psllw (v4hi, v4hi);
     v2si __builtin_ia32_pslld (v2si, v2si);
     v1di __builtin_ia32_psllq (v1di, v1di);
     v4hi __builtin_ia32_psrlw (v4hi, v4hi);
     v2si __builtin_ia32_psrld (v2si, v2si);
     v1di __builtin_ia32_psrlq (v1di, v1di);
     v4hi __builtin_ia32_psraw (v4hi, v4hi);
     v2si __builtin_ia32_psrad (v2si, v2si);
     v4hi __builtin_ia32_psllwi (v4hi, int);
     v2si __builtin_ia32_pslldi (v2si, int);
     v1di __builtin_ia32_psllqi (v1di, int);
     v4hi __builtin_ia32_psrlwi (v4hi, int);
     v2si __builtin_ia32_psrldi (v2si, int);
     v1di __builtin_ia32_psrlqi (v1di, int);
     v4hi __builtin_ia32_psrawi (v4hi, int);
     v2si __builtin_ia32_psradi (v2si, int);

 The following built-in functions are made available either with
‘-msse’, or with ‘-m3dnowa’.  All of them generate the machine
instruction that is part of the name.

     v4hi __builtin_ia32_pmulhuw (v4hi, v4hi);
     v8qi __builtin_ia32_pavgb (v8qi, v8qi);
     v4hi __builtin_ia32_pavgw (v4hi, v4hi);
     v1di __builtin_ia32_psadbw (v8qi, v8qi);
     v8qi __builtin_ia32_pmaxub (v8qi, v8qi);
     v4hi __builtin_ia32_pmaxsw (v4hi, v4hi);
     v8qi __builtin_ia32_pminub (v8qi, v8qi);
     v4hi __builtin_ia32_pminsw (v4hi, v4hi);
     int __builtin_ia32_pmovmskb (v8qi);
     void __builtin_ia32_maskmovq (v8qi, v8qi, char *);
     void __builtin_ia32_movntq (di *, di);
     void __builtin_ia32_sfence (void);

 The following built-in functions are available when ‘-msse’ is used.
All of them generate the machine instruction that is part of the name.

     int __builtin_ia32_comieq (v4sf, v4sf);
     int __builtin_ia32_comineq (v4sf, v4sf);
     int __builtin_ia32_comilt (v4sf, v4sf);
     int __builtin_ia32_comile (v4sf, v4sf);
     int __builtin_ia32_comigt (v4sf, v4sf);
     int __builtin_ia32_comige (v4sf, v4sf);
     int __builtin_ia32_ucomieq (v4sf, v4sf);
     int __builtin_ia32_ucomineq (v4sf, v4sf);
     int __builtin_ia32_ucomilt (v4sf, v4sf);
     int __builtin_ia32_ucomile (v4sf, v4sf);
     int __builtin_ia32_ucomigt (v4sf, v4sf);
     int __builtin_ia32_ucomige (v4sf, v4sf);
     v4sf __builtin_ia32_addps (v4sf, v4sf);
     v4sf __builtin_ia32_subps (v4sf, v4sf);
     v4sf __builtin_ia32_mulps (v4sf, v4sf);
     v4sf __builtin_ia32_divps (v4sf, v4sf);
     v4sf __builtin_ia32_addss (v4sf, v4sf);
     v4sf __builtin_ia32_subss (v4sf, v4sf);
     v4sf __builtin_ia32_mulss (v4sf, v4sf);
     v4sf __builtin_ia32_divss (v4sf, v4sf);
     v4sf __builtin_ia32_cmpeqps (v4sf, v4sf);
     v4sf __builtin_ia32_cmpltps (v4sf, v4sf);
     v4sf __builtin_ia32_cmpleps (v4sf, v4sf);
     v4sf __builtin_ia32_cmpgtps (v4sf, v4sf);
     v4sf __builtin_ia32_cmpgeps (v4sf, v4sf);
     v4sf __builtin_ia32_cmpunordps (v4sf, v4sf);
     v4sf __builtin_ia32_cmpneqps (v4sf, v4sf);
     v4sf __builtin_ia32_cmpnltps (v4sf, v4sf);
     v4sf __builtin_ia32_cmpnleps (v4sf, v4sf);
     v4sf __builtin_ia32_cmpngtps (v4sf, v4sf);
     v4sf __builtin_ia32_cmpngeps (v4sf, v4sf);
     v4sf __builtin_ia32_cmpordps (v4sf, v4sf);
     v4sf __builtin_ia32_cmpeqss (v4sf, v4sf);
     v4sf __builtin_ia32_cmpltss (v4sf, v4sf);
     v4sf __builtin_ia32_cmpless (v4sf, v4sf);
     v4sf __builtin_ia32_cmpunordss (v4sf, v4sf);
     v4sf __builtin_ia32_cmpneqss (v4sf, v4sf);
     v4sf __builtin_ia32_cmpnltss (v4sf, v4sf);
     v4sf __builtin_ia32_cmpnless (v4sf, v4sf);
     v4sf __builtin_ia32_cmpordss (v4sf, v4sf);
     v4sf __builtin_ia32_maxps (v4sf, v4sf);
     v4sf __builtin_ia32_maxss (v4sf, v4sf);
     v4sf __builtin_ia32_minps (v4sf, v4sf);
     v4sf __builtin_ia32_minss (v4sf, v4sf);
     v4sf __builtin_ia32_andps (v4sf, v4sf);
     v4sf __builtin_ia32_andnps (v4sf, v4sf);
     v4sf __builtin_ia32_orps (v4sf, v4sf);
     v4sf __builtin_ia32_xorps (v4sf, v4sf);
     v4sf __builtin_ia32_movss (v4sf, v4sf);
     v4sf __builtin_ia32_movhlps (v4sf, v4sf);
     v4sf __builtin_ia32_movlhps (v4sf, v4sf);
     v4sf __builtin_ia32_unpckhps (v4sf, v4sf);
     v4sf __builtin_ia32_unpcklps (v4sf, v4sf);
     v4sf __builtin_ia32_cvtpi2ps (v4sf, v2si);
     v4sf __builtin_ia32_cvtsi2ss (v4sf, int);
     v2si __builtin_ia32_cvtps2pi (v4sf);
     int __builtin_ia32_cvtss2si (v4sf);
     v2si __builtin_ia32_cvttps2pi (v4sf);
     int __builtin_ia32_cvttss2si (v4sf);
     v4sf __builtin_ia32_rcpps (v4sf);
     v4sf __builtin_ia32_rsqrtps (v4sf);
     v4sf __builtin_ia32_sqrtps (v4sf);
     v4sf __builtin_ia32_rcpss (v4sf);
     v4sf __builtin_ia32_rsqrtss (v4sf);
     v4sf __builtin_ia32_sqrtss (v4sf);
     v4sf __builtin_ia32_shufps (v4sf, v4sf, int);
     void __builtin_ia32_movntps (float *, v4sf);
     int __builtin_ia32_movmskps (v4sf);

 The following built-in functions are available when ‘-msse’ is used.

‘v4sf __builtin_ia32_loadups (float *)’
     Generates the ‘movups’ machine instruction as a load from memory.
‘void __builtin_ia32_storeups (float *, v4sf)’
     Generates the ‘movups’ machine instruction as a store to memory.
‘v4sf __builtin_ia32_loadss (float *)’
     Generates the ‘movss’ machine instruction as a load from memory.
‘v4sf __builtin_ia32_loadhps (v4sf, const v2sf *)’
     Generates the ‘movhps’ machine instruction as a load from memory.
‘v4sf __builtin_ia32_loadlps (v4sf, const v2sf *)’
     Generates the ‘movlps’ machine instruction as a load from memory
‘void __builtin_ia32_storehps (v2sf *, v4sf)’
     Generates the ‘movhps’ machine instruction as a store to memory.
‘void __builtin_ia32_storelps (v2sf *, v4sf)’
     Generates the ‘movlps’ machine instruction as a store to memory.

 The following built-in functions are available when ‘-msse2’ is used.
All of them generate the machine instruction that is part of the name.

     int __builtin_ia32_comisdeq (v2df, v2df);
     int __builtin_ia32_comisdlt (v2df, v2df);
     int __builtin_ia32_comisdle (v2df, v2df);
     int __builtin_ia32_comisdgt (v2df, v2df);
     int __builtin_ia32_comisdge (v2df, v2df);
     int __builtin_ia32_comisdneq (v2df, v2df);
     int __builtin_ia32_ucomisdeq (v2df, v2df);
     int __builtin_ia32_ucomisdlt (v2df, v2df);
     int __builtin_ia32_ucomisdle (v2df, v2df);
     int __builtin_ia32_ucomisdgt (v2df, v2df);
     int __builtin_ia32_ucomisdge (v2df, v2df);
     int __builtin_ia32_ucomisdneq (v2df, v2df);
     v2df __builtin_ia32_cmpeqpd (v2df, v2df);
     v2df __builtin_ia32_cmpltpd (v2df, v2df);
     v2df __builtin_ia32_cmplepd (v2df, v2df);
     v2df __builtin_ia32_cmpgtpd (v2df, v2df);
     v2df __builtin_ia32_cmpgepd (v2df, v2df);
     v2df __builtin_ia32_cmpunordpd (v2df, v2df);
     v2df __builtin_ia32_cmpneqpd (v2df, v2df);
     v2df __builtin_ia32_cmpnltpd (v2df, v2df);
     v2df __builtin_ia32_cmpnlepd (v2df, v2df);
     v2df __builtin_ia32_cmpngtpd (v2df, v2df);
     v2df __builtin_ia32_cmpngepd (v2df, v2df);
     v2df __builtin_ia32_cmpordpd (v2df, v2df);
     v2df __builtin_ia32_cmpeqsd (v2df, v2df);
     v2df __builtin_ia32_cmpltsd (v2df, v2df);
     v2df __builtin_ia32_cmplesd (v2df, v2df);
     v2df __builtin_ia32_cmpunordsd (v2df, v2df);
     v2df __builtin_ia32_cmpneqsd (v2df, v2df);
     v2df __builtin_ia32_cmpnltsd (v2df, v2df);
     v2df __builtin_ia32_cmpnlesd (v2df, v2df);
     v2df __builtin_ia32_cmpordsd (v2df, v2df);
     v2di __builtin_ia32_paddq (v2di, v2di);
     v2di __builtin_ia32_psubq (v2di, v2di);
     v2df __builtin_ia32_addpd (v2df, v2df);
     v2df __builtin_ia32_subpd (v2df, v2df);
     v2df __builtin_ia32_mulpd (v2df, v2df);
     v2df __builtin_ia32_divpd (v2df, v2df);
     v2df __builtin_ia32_addsd (v2df, v2df);
     v2df __builtin_ia32_subsd (v2df, v2df);
     v2df __builtin_ia32_mulsd (v2df, v2df);
     v2df __builtin_ia32_divsd (v2df, v2df);
     v2df __builtin_ia32_minpd (v2df, v2df);
     v2df __builtin_ia32_maxpd (v2df, v2df);
     v2df __builtin_ia32_minsd (v2df, v2df);
     v2df __builtin_ia32_maxsd (v2df, v2df);
     v2df __builtin_ia32_andpd (v2df, v2df);
     v2df __builtin_ia32_andnpd (v2df, v2df);
     v2df __builtin_ia32_orpd (v2df, v2df);
     v2df __builtin_ia32_xorpd (v2df, v2df);
     v2df __builtin_ia32_movsd (v2df, v2df);
     v2df __builtin_ia32_unpckhpd (v2df, v2df);
     v2df __builtin_ia32_unpcklpd (v2df, v2df);
     v16qi __builtin_ia32_paddb128 (v16qi, v16qi);
     v8hi __builtin_ia32_paddw128 (v8hi, v8hi);
     v4si __builtin_ia32_paddd128 (v4si, v4si);
     v2di __builtin_ia32_paddq128 (v2di, v2di);
     v16qi __builtin_ia32_psubb128 (v16qi, v16qi);
     v8hi __builtin_ia32_psubw128 (v8hi, v8hi);
     v4si __builtin_ia32_psubd128 (v4si, v4si);
     v2di __builtin_ia32_psubq128 (v2di, v2di);
     v8hi __builtin_ia32_pmullw128 (v8hi, v8hi);
     v8hi __builtin_ia32_pmulhw128 (v8hi, v8hi);
     v2di __builtin_ia32_pand128 (v2di, v2di);
     v2di __builtin_ia32_pandn128 (v2di, v2di);
     v2di __builtin_ia32_por128 (v2di, v2di);
     v2di __builtin_ia32_pxor128 (v2di, v2di);
     v16qi __builtin_ia32_pavgb128 (v16qi, v16qi);
     v8hi __builtin_ia32_pavgw128 (v8hi, v8hi);
     v16qi __builtin_ia32_pcmpeqb128 (v16qi, v16qi);
     v8hi __builtin_ia32_pcmpeqw128 (v8hi, v8hi);
     v4si __builtin_ia32_pcmpeqd128 (v4si, v4si);
     v16qi __builtin_ia32_pcmpgtb128 (v16qi, v16qi);
     v8hi __builtin_ia32_pcmpgtw128 (v8hi, v8hi);
     v4si __builtin_ia32_pcmpgtd128 (v4si, v4si);
     v16qi __builtin_ia32_pmaxub128 (v16qi, v16qi);
     v8hi __builtin_ia32_pmaxsw128 (v8hi, v8hi);
     v16qi __builtin_ia32_pminub128 (v16qi, v16qi);
     v8hi __builtin_ia32_pminsw128 (v8hi, v8hi);
     v16qi __builtin_ia32_punpckhbw128 (v16qi, v16qi);
     v8hi __builtin_ia32_punpckhwd128 (v8hi, v8hi);
     v4si __builtin_ia32_punpckhdq128 (v4si, v4si);
     v2di __builtin_ia32_punpckhqdq128 (v2di, v2di);
     v16qi __builtin_ia32_punpcklbw128 (v16qi, v16qi);
     v8hi __builtin_ia32_punpcklwd128 (v8hi, v8hi);
     v4si __builtin_ia32_punpckldq128 (v4si, v4si);
     v2di __builtin_ia32_punpcklqdq128 (v2di, v2di);
     v16qi __builtin_ia32_packsswb128 (v8hi, v8hi);
     v8hi __builtin_ia32_packssdw128 (v4si, v4si);
     v16qi __builtin_ia32_packuswb128 (v8hi, v8hi);
     v8hi __builtin_ia32_pmulhuw128 (v8hi, v8hi);
     void __builtin_ia32_maskmovdqu (v16qi, v16qi);
     v2df __builtin_ia32_loadupd (double *);
     void __builtin_ia32_storeupd (double *, v2df);
     v2df __builtin_ia32_loadhpd (v2df, double const *);
     v2df __builtin_ia32_loadlpd (v2df, double const *);
     int __builtin_ia32_movmskpd (v2df);
     int __builtin_ia32_pmovmskb128 (v16qi);
     void __builtin_ia32_movnti (int *, int);
     void __builtin_ia32_movnti64 (long long int *, long long int);
     void __builtin_ia32_movntpd (double *, v2df);
     void __builtin_ia32_movntdq (v2df *, v2df);
     v4si __builtin_ia32_pshufd (v4si, int);
     v8hi __builtin_ia32_pshuflw (v8hi, int);
     v8hi __builtin_ia32_pshufhw (v8hi, int);
     v2di __builtin_ia32_psadbw128 (v16qi, v16qi);
     v2df __builtin_ia32_sqrtpd (v2df);
     v2df __builtin_ia32_sqrtsd (v2df);
     v2df __builtin_ia32_shufpd (v2df, v2df, int);
     v2df __builtin_ia32_cvtdq2pd (v4si);
     v4sf __builtin_ia32_cvtdq2ps (v4si);
     v4si __builtin_ia32_cvtpd2dq (v2df);
     v2si __builtin_ia32_cvtpd2pi (v2df);
     v4sf __builtin_ia32_cvtpd2ps (v2df);
     v4si __builtin_ia32_cvttpd2dq (v2df);
     v2si __builtin_ia32_cvttpd2pi (v2df);
     v2df __builtin_ia32_cvtpi2pd (v2si);
     int __builtin_ia32_cvtsd2si (v2df);
     int __builtin_ia32_cvttsd2si (v2df);
     long long __builtin_ia32_cvtsd2si64 (v2df);
     long long __builtin_ia32_cvttsd2si64 (v2df);
     v4si __builtin_ia32_cvtps2dq (v4sf);
     v2df __builtin_ia32_cvtps2pd (v4sf);
     v4si __builtin_ia32_cvttps2dq (v4sf);
     v2df __builtin_ia32_cvtsi2sd (v2df, int);
     v2df __builtin_ia32_cvtsi642sd (v2df, long long);
     v4sf __builtin_ia32_cvtsd2ss (v4sf, v2df);
     v2df __builtin_ia32_cvtss2sd (v2df, v4sf);
     void __builtin_ia32_clflush (const void *);
     void __builtin_ia32_lfence (void);
     void __builtin_ia32_mfence (void);
     v16qi __builtin_ia32_loaddqu (const char *);
     void __builtin_ia32_storedqu (char *, v16qi);
     v1di __builtin_ia32_pmuludq (v2si, v2si);
     v2di __builtin_ia32_pmuludq128 (v4si, v4si);
     v8hi __builtin_ia32_psllw128 (v8hi, v8hi);
     v4si __builtin_ia32_pslld128 (v4si, v4si);
     v2di __builtin_ia32_psllq128 (v2di, v2di);
     v8hi __builtin_ia32_psrlw128 (v8hi, v8hi);
     v4si __builtin_ia32_psrld128 (v4si, v4si);
     v2di __builtin_ia32_psrlq128 (v2di, v2di);
     v8hi __builtin_ia32_psraw128 (v8hi, v8hi);
     v4si __builtin_ia32_psrad128 (v4si, v4si);
     v2di __builtin_ia32_pslldqi128 (v2di, int);
     v8hi __builtin_ia32_psllwi128 (v8hi, int);
     v4si __builtin_ia32_pslldi128 (v4si, int);
     v2di __builtin_ia32_psllqi128 (v2di, int);
     v2di __builtin_ia32_psrldqi128 (v2di, int);
     v8hi __builtin_ia32_psrlwi128 (v8hi, int);
     v4si __builtin_ia32_psrldi128 (v4si, int);
     v2di __builtin_ia32_psrlqi128 (v2di, int);
     v8hi __builtin_ia32_psrawi128 (v8hi, int);
     v4si __builtin_ia32_psradi128 (v4si, int);
     v4si __builtin_ia32_pmaddwd128 (v8hi, v8hi);
     v2di __builtin_ia32_movq128 (v2di);

 The following built-in functions are available when ‘-msse3’ is used.
All of them generate the machine instruction that is part of the name.

     v2df __builtin_ia32_addsubpd (v2df, v2df);
     v4sf __builtin_ia32_addsubps (v4sf, v4sf);
     v2df __builtin_ia32_haddpd (v2df, v2df);
     v4sf __builtin_ia32_haddps (v4sf, v4sf);
     v2df __builtin_ia32_hsubpd (v2df, v2df);
     v4sf __builtin_ia32_hsubps (v4sf, v4sf);
     v16qi __builtin_ia32_lddqu (char const *);
     void __builtin_ia32_monitor (void *, unsigned int, unsigned int);
     v4sf __builtin_ia32_movshdup (v4sf);
     v4sf __builtin_ia32_movsldup (v4sf);
     void __builtin_ia32_mwait (unsigned int, unsigned int);

 The following built-in functions are available when ‘-mssse3’ is used.
All of them generate the machine instruction that is part of the name.

     v2si __builtin_ia32_phaddd (v2si, v2si);
     v4hi __builtin_ia32_phaddw (v4hi, v4hi);
     v4hi __builtin_ia32_phaddsw (v4hi, v4hi);
     v2si __builtin_ia32_phsubd (v2si, v2si);
     v4hi __builtin_ia32_phsubw (v4hi, v4hi);
     v4hi __builtin_ia32_phsubsw (v4hi, v4hi);
     v4hi __builtin_ia32_pmaddubsw (v8qi, v8qi);
     v4hi __builtin_ia32_pmulhrsw (v4hi, v4hi);
     v8qi __builtin_ia32_pshufb (v8qi, v8qi);
     v8qi __builtin_ia32_psignb (v8qi, v8qi);
     v2si __builtin_ia32_psignd (v2si, v2si);
     v4hi __builtin_ia32_psignw (v4hi, v4hi);
     v1di __builtin_ia32_palignr (v1di, v1di, int);
     v8qi __builtin_ia32_pabsb (v8qi);
     v2si __builtin_ia32_pabsd (v2si);
     v4hi __builtin_ia32_pabsw (v4hi);

 The following built-in functions are available when ‘-mssse3’ is used.
All of them generate the machine instruction that is part of the name.

     v4si __builtin_ia32_phaddd128 (v4si, v4si);
     v8hi __builtin_ia32_phaddw128 (v8hi, v8hi);
     v8hi __builtin_ia32_phaddsw128 (v8hi, v8hi);
     v4si __builtin_ia32_phsubd128 (v4si, v4si);
     v8hi __builtin_ia32_phsubw128 (v8hi, v8hi);
     v8hi __builtin_ia32_phsubsw128 (v8hi, v8hi);
     v8hi __builtin_ia32_pmaddubsw128 (v16qi, v16qi);
     v8hi __builtin_ia32_pmulhrsw128 (v8hi, v8hi);
     v16qi __builtin_ia32_pshufb128 (v16qi, v16qi);
     v16qi __builtin_ia32_psignb128 (v16qi, v16qi);
     v4si __builtin_ia32_psignd128 (v4si, v4si);
     v8hi __builtin_ia32_psignw128 (v8hi, v8hi);
     v2di __builtin_ia32_palignr128 (v2di, v2di, int);
     v16qi __builtin_ia32_pabsb128 (v16qi);
     v4si __builtin_ia32_pabsd128 (v4si);
     v8hi __builtin_ia32_pabsw128 (v8hi);

 The following built-in functions are available when ‘-msse4.1’ is used.
All of them generate the machine instruction that is part of the name.

     v2df __builtin_ia32_blendpd (v2df, v2df, const int);
     v4sf __builtin_ia32_blendps (v4sf, v4sf, const int);
     v2df __builtin_ia32_blendvpd (v2df, v2df, v2df);
     v4sf __builtin_ia32_blendvps (v4sf, v4sf, v4sf);
     v2df __builtin_ia32_dppd (v2df, v2df, const int);
     v4sf __builtin_ia32_dpps (v4sf, v4sf, const int);
     v4sf __builtin_ia32_insertps128 (v4sf, v4sf, const int);
     v2di __builtin_ia32_movntdqa (v2di *);
     v16qi __builtin_ia32_mpsadbw128 (v16qi, v16qi, const int);
     v8hi __builtin_ia32_packusdw128 (v4si, v4si);
     v16qi __builtin_ia32_pblendvb128 (v16qi, v16qi, v16qi);
     v8hi __builtin_ia32_pblendw128 (v8hi, v8hi, const int);
     v2di __builtin_ia32_pcmpeqq (v2di, v2di);
     v8hi __builtin_ia32_phminposuw128 (v8hi);
     v16qi __builtin_ia32_pmaxsb128 (v16qi, v16qi);
     v4si __builtin_ia32_pmaxsd128 (v4si, v4si);
     v4si __builtin_ia32_pmaxud128 (v4si, v4si);
     v8hi __builtin_ia32_pmaxuw128 (v8hi, v8hi);
     v16qi __builtin_ia32_pminsb128 (v16qi, v16qi);
     v4si __builtin_ia32_pminsd128 (v4si, v4si);
     v4si __builtin_ia32_pminud128 (v4si, v4si);
     v8hi __builtin_ia32_pminuw128 (v8hi, v8hi);
     v4si __builtin_ia32_pmovsxbd128 (v16qi);
     v2di __builtin_ia32_pmovsxbq128 (v16qi);
     v8hi __builtin_ia32_pmovsxbw128 (v16qi);
     v2di __builtin_ia32_pmovsxdq128 (v4si);
     v4si __builtin_ia32_pmovsxwd128 (v8hi);
     v2di __builtin_ia32_pmovsxwq128 (v8hi);
     v4si __builtin_ia32_pmovzxbd128 (v16qi);
     v2di __builtin_ia32_pmovzxbq128 (v16qi);
     v8hi __builtin_ia32_pmovzxbw128 (v16qi);
     v2di __builtin_ia32_pmovzxdq128 (v4si);
     v4si __builtin_ia32_pmovzxwd128 (v8hi);
     v2di __builtin_ia32_pmovzxwq128 (v8hi);
     v2di __builtin_ia32_pmuldq128 (v4si, v4si);
     v4si __builtin_ia32_pmulld128 (v4si, v4si);
     int __builtin_ia32_ptestc128 (v2di, v2di);
     int __builtin_ia32_ptestnzc128 (v2di, v2di);
     int __builtin_ia32_ptestz128 (v2di, v2di);
     v2df __builtin_ia32_roundpd (v2df, const int);
     v4sf __builtin_ia32_roundps (v4sf, const int);
     v2df __builtin_ia32_roundsd (v2df, v2df, const int);
     v4sf __builtin_ia32_roundss (v4sf, v4sf, const int);

 The following built-in functions are available when ‘-msse4.1’ is used.

‘v4sf __builtin_ia32_vec_set_v4sf (v4sf, float, const int)’
     Generates the ‘insertps’ machine instruction.
‘int __builtin_ia32_vec_ext_v16qi (v16qi, const int)’
     Generates the ‘pextrb’ machine instruction.
‘v16qi __builtin_ia32_vec_set_v16qi (v16qi, int, const int)’
     Generates the ‘pinsrb’ machine instruction.
‘v4si __builtin_ia32_vec_set_v4si (v4si, int, const int)’
     Generates the ‘pinsrd’ machine instruction.
‘v2di __builtin_ia32_vec_set_v2di (v2di, long long, const int)’
     Generates the ‘pinsrq’ machine instruction in 64bit mode.

 The following built-in functions are changed to generate new SSE4.1
instructions when ‘-msse4.1’ is used.

‘float __builtin_ia32_vec_ext_v4sf (v4sf, const int)’
     Generates the ‘extractps’ machine instruction.
‘int __builtin_ia32_vec_ext_v4si (v4si, const int)’
     Generates the ‘pextrd’ machine instruction.
‘long long __builtin_ia32_vec_ext_v2di (v2di, const int)’
     Generates the ‘pextrq’ machine instruction in 64bit mode.

 The following built-in functions are available when ‘-msse4.2’ is used.
All of them generate the machine instruction that is part of the name.

     v16qi __builtin_ia32_pcmpestrm128 (v16qi, int, v16qi, int, const int);
     int __builtin_ia32_pcmpestri128 (v16qi, int, v16qi, int, const int);
     int __builtin_ia32_pcmpestria128 (v16qi, int, v16qi, int, const int);
     int __builtin_ia32_pcmpestric128 (v16qi, int, v16qi, int, const int);
     int __builtin_ia32_pcmpestrio128 (v16qi, int, v16qi, int, const int);
     int __builtin_ia32_pcmpestris128 (v16qi, int, v16qi, int, const int);
     int __builtin_ia32_pcmpestriz128 (v16qi, int, v16qi, int, const int);
     v16qi __builtin_ia32_pcmpistrm128 (v16qi, v16qi, const int);
     int __builtin_ia32_pcmpistri128 (v16qi, v16qi, const int);
     int __builtin_ia32_pcmpistria128 (v16qi, v16qi, const int);
     int __builtin_ia32_pcmpistric128 (v16qi, v16qi, const int);
     int __builtin_ia32_pcmpistrio128 (v16qi, v16qi, const int);
     int __builtin_ia32_pcmpistris128 (v16qi, v16qi, const int);
     int __builtin_ia32_pcmpistriz128 (v16qi, v16qi, const int);
     v2di __builtin_ia32_pcmpgtq (v2di, v2di);

 The following built-in functions are available when ‘-msse4.2’ is used.

‘unsigned int __builtin_ia32_crc32qi (unsigned int, unsigned char)’
     Generates the ‘crc32b’ machine instruction.
‘unsigned int __builtin_ia32_crc32hi (unsigned int, unsigned short)’
     Generates the ‘crc32w’ machine instruction.
‘unsigned int __builtin_ia32_crc32si (unsigned int, unsigned int)’
     Generates the ‘crc32l’ machine instruction.
‘unsigned long long __builtin_ia32_crc32di (unsigned long long, unsigned long long)’
     Generates the ‘crc32q’ machine instruction.

 The following built-in functions are changed to generate new SSE4.2
instructions when ‘-msse4.2’ is used.

‘int __builtin_popcount (unsigned int)’
     Generates the ‘popcntl’ machine instruction.
‘int __builtin_popcountl (unsigned long)’
     Generates the ‘popcntl’ or ‘popcntq’ machine instruction, depending
     on the size of ‘unsigned long’.
‘int __builtin_popcountll (unsigned long long)’
     Generates the ‘popcntq’ machine instruction.

 The following built-in functions are available when ‘-mavx’ is used.
All of them generate the machine instruction that is part of the name.

     v4df __builtin_ia32_addpd256 (v4df,v4df);
     v8sf __builtin_ia32_addps256 (v8sf,v8sf);
     v4df __builtin_ia32_addsubpd256 (v4df,v4df);
     v8sf __builtin_ia32_addsubps256 (v8sf,v8sf);
     v4df __builtin_ia32_andnpd256 (v4df,v4df);
     v8sf __builtin_ia32_andnps256 (v8sf,v8sf);
     v4df __builtin_ia32_andpd256 (v4df,v4df);
     v8sf __builtin_ia32_andps256 (v8sf,v8sf);
     v4df __builtin_ia32_blendpd256 (v4df,v4df,int);
     v8sf __builtin_ia32_blendps256 (v8sf,v8sf,int);
     v4df __builtin_ia32_blendvpd256 (v4df,v4df,v4df);
     v8sf __builtin_ia32_blendvps256 (v8sf,v8sf,v8sf);
     v2df __builtin_ia32_cmppd (v2df,v2df,int);
     v4df __builtin_ia32_cmppd256 (v4df,v4df,int);
     v4sf __builtin_ia32_cmpps (v4sf,v4sf,int);
     v8sf __builtin_ia32_cmpps256 (v8sf,v8sf,int);
     v2df __builtin_ia32_cmpsd (v2df,v2df,int);
     v4sf __builtin_ia32_cmpss (v4sf,v4sf,int);
     v4df __builtin_ia32_cvtdq2pd256 (v4si);
     v8sf __builtin_ia32_cvtdq2ps256 (v8si);
     v4si __builtin_ia32_cvtpd2dq256 (v4df);
     v4sf __builtin_ia32_cvtpd2ps256 (v4df);
     v8si __builtin_ia32_cvtps2dq256 (v8sf);
     v4df __builtin_ia32_cvtps2pd256 (v4sf);
     v4si __builtin_ia32_cvttpd2dq256 (v4df);
     v8si __builtin_ia32_cvttps2dq256 (v8sf);
     v4df __builtin_ia32_divpd256 (v4df,v4df);
     v8sf __builtin_ia32_divps256 (v8sf,v8sf);
     v8sf __builtin_ia32_dpps256 (v8sf,v8sf,int);
     v4df __builtin_ia32_haddpd256 (v4df,v4df);
     v8sf __builtin_ia32_haddps256 (v8sf,v8sf);
     v4df __builtin_ia32_hsubpd256 (v4df,v4df);
     v8sf __builtin_ia32_hsubps256 (v8sf,v8sf);
     v32qi __builtin_ia32_lddqu256 (pcchar);
     v32qi __builtin_ia32_loaddqu256 (pcchar);
     v4df __builtin_ia32_loadupd256 (pcdouble);
     v8sf __builtin_ia32_loadups256 (pcfloat);
     v2df __builtin_ia32_maskloadpd (pcv2df,v2df);
     v4df __builtin_ia32_maskloadpd256 (pcv4df,v4df);
     v4sf __builtin_ia32_maskloadps (pcv4sf,v4sf);
     v8sf __builtin_ia32_maskloadps256 (pcv8sf,v8sf);
     void __builtin_ia32_maskstorepd (pv2df,v2df,v2df);
     void __builtin_ia32_maskstorepd256 (pv4df,v4df,v4df);
     void __builtin_ia32_maskstoreps (pv4sf,v4sf,v4sf);
     void __builtin_ia32_maskstoreps256 (pv8sf,v8sf,v8sf);
     v4df __builtin_ia32_maxpd256 (v4df,v4df);
     v8sf __builtin_ia32_maxps256 (v8sf,v8sf);
     v4df __builtin_ia32_minpd256 (v4df,v4df);
     v8sf __builtin_ia32_minps256 (v8sf,v8sf);
     v4df __builtin_ia32_movddup256 (v4df);
     int __builtin_ia32_movmskpd256 (v4df);
     int __builtin_ia32_movmskps256 (v8sf);
     v8sf __builtin_ia32_movshdup256 (v8sf);
     v8sf __builtin_ia32_movsldup256 (v8sf);
     v4df __builtin_ia32_mulpd256 (v4df,v4df);
     v8sf __builtin_ia32_mulps256 (v8sf,v8sf);
     v4df __builtin_ia32_orpd256 (v4df,v4df);
     v8sf __builtin_ia32_orps256 (v8sf,v8sf);
     v2df __builtin_ia32_pd_pd256 (v4df);
     v4df __builtin_ia32_pd256_pd (v2df);
     v4sf __builtin_ia32_ps_ps256 (v8sf);
     v8sf __builtin_ia32_ps256_ps (v4sf);
     int __builtin_ia32_ptestc256 (v4di,v4di,ptest);
     int __builtin_ia32_ptestnzc256 (v4di,v4di,ptest);
     int __builtin_ia32_ptestz256 (v4di,v4di,ptest);
     v8sf __builtin_ia32_rcpps256 (v8sf);
     v4df __builtin_ia32_roundpd256 (v4df,int);
     v8sf __builtin_ia32_roundps256 (v8sf,int);
     v8sf __builtin_ia32_rsqrtps_nr256 (v8sf);
     v8sf __builtin_ia32_rsqrtps256 (v8sf);
     v4df __builtin_ia32_shufpd256 (v4df,v4df,int);
     v8sf __builtin_ia32_shufps256 (v8sf,v8sf,int);
     v4si __builtin_ia32_si_si256 (v8si);
     v8si __builtin_ia32_si256_si (v4si);
     v4df __builtin_ia32_sqrtpd256 (v4df);
     v8sf __builtin_ia32_sqrtps_nr256 (v8sf);
     v8sf __builtin_ia32_sqrtps256 (v8sf);
     void __builtin_ia32_storedqu256 (pchar,v32qi);
     void __builtin_ia32_storeupd256 (pdouble,v4df);
     void __builtin_ia32_storeups256 (pfloat,v8sf);
     v4df __builtin_ia32_subpd256 (v4df,v4df);
     v8sf __builtin_ia32_subps256 (v8sf,v8sf);
     v4df __builtin_ia32_unpckhpd256 (v4df,v4df);
     v8sf __builtin_ia32_unpckhps256 (v8sf,v8sf);
     v4df __builtin_ia32_unpcklpd256 (v4df,v4df);
     v8sf __builtin_ia32_unpcklps256 (v8sf,v8sf);
     v4df __builtin_ia32_vbroadcastf128_pd256 (pcv2df);
     v8sf __builtin_ia32_vbroadcastf128_ps256 (pcv4sf);
     v4df __builtin_ia32_vbroadcastsd256 (pcdouble);
     v4sf __builtin_ia32_vbroadcastss (pcfloat);
     v8sf __builtin_ia32_vbroadcastss256 (pcfloat);
     v2df __builtin_ia32_vextractf128_pd256 (v4df,int);
     v4sf __builtin_ia32_vextractf128_ps256 (v8sf,int);
     v4si __builtin_ia32_vextractf128_si256 (v8si,int);
     v4df __builtin_ia32_vinsertf128_pd256 (v4df,v2df,int);
     v8sf __builtin_ia32_vinsertf128_ps256 (v8sf,v4sf,int);
     v8si __builtin_ia32_vinsertf128_si256 (v8si,v4si,int);
     v4df __builtin_ia32_vperm2f128_pd256 (v4df,v4df,int);
     v8sf __builtin_ia32_vperm2f128_ps256 (v8sf,v8sf,int);
     v8si __builtin_ia32_vperm2f128_si256 (v8si,v8si,int);
     v2df __builtin_ia32_vpermil2pd (v2df,v2df,v2di,int);
     v4df __builtin_ia32_vpermil2pd256 (v4df,v4df,v4di,int);
     v4sf __builtin_ia32_vpermil2ps (v4sf,v4sf,v4si,int);
     v8sf __builtin_ia32_vpermil2ps256 (v8sf,v8sf,v8si,int);
     v2df __builtin_ia32_vpermilpd (v2df,int);
     v4df __builtin_ia32_vpermilpd256 (v4df,int);
     v4sf __builtin_ia32_vpermilps (v4sf,int);
     v8sf __builtin_ia32_vpermilps256 (v8sf,int);
     v2df __builtin_ia32_vpermilvarpd (v2df,v2di);
     v4df __builtin_ia32_vpermilvarpd256 (v4df,v4di);
     v4sf __builtin_ia32_vpermilvarps (v4sf,v4si);
     v8sf __builtin_ia32_vpermilvarps256 (v8sf,v8si);
     int __builtin_ia32_vtestcpd (v2df,v2df,ptest);
     int __builtin_ia32_vtestcpd256 (v4df,v4df,ptest);
     int __builtin_ia32_vtestcps (v4sf,v4sf,ptest);
     int __builtin_ia32_vtestcps256 (v8sf,v8sf,ptest);
     int __builtin_ia32_vtestnzcpd (v2df,v2df,ptest);
     int __builtin_ia32_vtestnzcpd256 (v4df,v4df,ptest);
     int __builtin_ia32_vtestnzcps (v4sf,v4sf,ptest);
     int __builtin_ia32_vtestnzcps256 (v8sf,v8sf,ptest);
     int __builtin_ia32_vtestzpd (v2df,v2df,ptest);
     int __builtin_ia32_vtestzpd256 (v4df,v4df,ptest);
     int __builtin_ia32_vtestzps (v4sf,v4sf,ptest);
     int __builtin_ia32_vtestzps256 (v8sf,v8sf,ptest);
     void __builtin_ia32_vzeroall (void);
     void __builtin_ia32_vzeroupper (void);
     v4df __builtin_ia32_xorpd256 (v4df,v4df);
     v8sf __builtin_ia32_xorps256 (v8sf,v8sf);

 The following built-in functions are available when ‘-mavx2’ is used.
All of them generate the machine instruction that is part of the name.

     v32qi __builtin_ia32_mpsadbw256 (v32qi,v32qi,int);
     v32qi __builtin_ia32_pabsb256 (v32qi);
     v16hi __builtin_ia32_pabsw256 (v16hi);
     v8si __builtin_ia32_pabsd256 (v8si);
     v16hi __builtin_ia32_packssdw256 (v8si,v8si);
     v32qi __builtin_ia32_packsswb256 (v16hi,v16hi);
     v16hi __builtin_ia32_packusdw256 (v8si,v8si);
     v32qi __builtin_ia32_packuswb256 (v16hi,v16hi);
     v32qi __builtin_ia32_paddb256 (v32qi,v32qi);
     v16hi __builtin_ia32_paddw256 (v16hi,v16hi);
     v8si __builtin_ia32_paddd256 (v8si,v8si);
     v4di __builtin_ia32_paddq256 (v4di,v4di);
     v32qi __builtin_ia32_paddsb256 (v32qi,v32qi);
     v16hi __builtin_ia32_paddsw256 (v16hi,v16hi);
     v32qi __builtin_ia32_paddusb256 (v32qi,v32qi);
     v16hi __builtin_ia32_paddusw256 (v16hi,v16hi);
     v4di __builtin_ia32_palignr256 (v4di,v4di,int);
     v4di __builtin_ia32_andsi256 (v4di,v4di);
     v4di __builtin_ia32_andnotsi256 (v4di,v4di);
     v32qi __builtin_ia32_pavgb256 (v32qi,v32qi);
     v16hi __builtin_ia32_pavgw256 (v16hi,v16hi);
     v32qi __builtin_ia32_pblendvb256 (v32qi,v32qi,v32qi);
     v16hi __builtin_ia32_pblendw256 (v16hi,v16hi,int);
     v32qi __builtin_ia32_pcmpeqb256 (v32qi,v32qi);
     v16hi __builtin_ia32_pcmpeqw256 (v16hi,v16hi);
     v8si __builtin_ia32_pcmpeqd256 (c8si,v8si);
     v4di __builtin_ia32_pcmpeqq256 (v4di,v4di);
     v32qi __builtin_ia32_pcmpgtb256 (v32qi,v32qi);
     v16hi __builtin_ia32_pcmpgtw256 (16hi,v16hi);
     v8si __builtin_ia32_pcmpgtd256 (v8si,v8si);
     v4di __builtin_ia32_pcmpgtq256 (v4di,v4di);
     v16hi __builtin_ia32_phaddw256 (v16hi,v16hi);
     v8si __builtin_ia32_phaddd256 (v8si,v8si);
     v16hi __builtin_ia32_phaddsw256 (v16hi,v16hi);
     v16hi __builtin_ia32_phsubw256 (v16hi,v16hi);
     v8si __builtin_ia32_phsubd256 (v8si,v8si);
     v16hi __builtin_ia32_phsubsw256 (v16hi,v16hi);
     v32qi __builtin_ia32_pmaddubsw256 (v32qi,v32qi);
     v16hi __builtin_ia32_pmaddwd256 (v16hi,v16hi);
     v32qi __builtin_ia32_pmaxsb256 (v32qi,v32qi);
     v16hi __builtin_ia32_pmaxsw256 (v16hi,v16hi);
     v8si __builtin_ia32_pmaxsd256 (v8si,v8si);
     v32qi __builtin_ia32_pmaxub256 (v32qi,v32qi);
     v16hi __builtin_ia32_pmaxuw256 (v16hi,v16hi);
     v8si __builtin_ia32_pmaxud256 (v8si,v8si);
     v32qi __builtin_ia32_pminsb256 (v32qi,v32qi);
     v16hi __builtin_ia32_pminsw256 (v16hi,v16hi);
     v8si __builtin_ia32_pminsd256 (v8si,v8si);
     v32qi __builtin_ia32_pminub256 (v32qi,v32qi);
     v16hi __builtin_ia32_pminuw256 (v16hi,v16hi);
     v8si __builtin_ia32_pminud256 (v8si,v8si);
     int __builtin_ia32_pmovmskb256 (v32qi);
     v16hi __builtin_ia32_pmovsxbw256 (v16qi);
     v8si __builtin_ia32_pmovsxbd256 (v16qi);
     v4di __builtin_ia32_pmovsxbq256 (v16qi);
     v8si __builtin_ia32_pmovsxwd256 (v8hi);
     v4di __builtin_ia32_pmovsxwq256 (v8hi);
     v4di __builtin_ia32_pmovsxdq256 (v4si);
     v16hi __builtin_ia32_pmovzxbw256 (v16qi);
     v8si __builtin_ia32_pmovzxbd256 (v16qi);
     v4di __builtin_ia32_pmovzxbq256 (v16qi);
     v8si __builtin_ia32_pmovzxwd256 (v8hi);
     v4di __builtin_ia32_pmovzxwq256 (v8hi);
     v4di __builtin_ia32_pmovzxdq256 (v4si);
     v4di __builtin_ia32_pmuldq256 (v8si,v8si);
     v16hi __builtin_ia32_pmulhrsw256 (v16hi, v16hi);
     v16hi __builtin_ia32_pmulhuw256 (v16hi,v16hi);
     v16hi __builtin_ia32_pmulhw256 (v16hi,v16hi);
     v16hi __builtin_ia32_pmullw256 (v16hi,v16hi);
     v8si __builtin_ia32_pmulld256 (v8si,v8si);
     v4di __builtin_ia32_pmuludq256 (v8si,v8si);
     v4di __builtin_ia32_por256 (v4di,v4di);
     v16hi __builtin_ia32_psadbw256 (v32qi,v32qi);
     v32qi __builtin_ia32_pshufb256 (v32qi,v32qi);
     v8si __builtin_ia32_pshufd256 (v8si,int);
     v16hi __builtin_ia32_pshufhw256 (v16hi,int);
     v16hi __builtin_ia32_pshuflw256 (v16hi,int);
     v32qi __builtin_ia32_psignb256 (v32qi,v32qi);
     v16hi __builtin_ia32_psignw256 (v16hi,v16hi);
     v8si __builtin_ia32_psignd256 (v8si,v8si);
     v4di __builtin_ia32_pslldqi256 (v4di,int);
     v16hi __builtin_ia32_psllwi256 (16hi,int);
     v16hi __builtin_ia32_psllw256(v16hi,v8hi);
     v8si __builtin_ia32_pslldi256 (v8si,int);
     v8si __builtin_ia32_pslld256(v8si,v4si);
     v4di __builtin_ia32_psllqi256 (v4di,int);
     v4di __builtin_ia32_psllq256(v4di,v2di);
     v16hi __builtin_ia32_psrawi256 (v16hi,int);
     v16hi __builtin_ia32_psraw256 (v16hi,v8hi);
     v8si __builtin_ia32_psradi256 (v8si,int);
     v8si __builtin_ia32_psrad256 (v8si,v4si);
     v4di __builtin_ia32_psrldqi256 (v4di, int);
     v16hi __builtin_ia32_psrlwi256 (v16hi,int);
     v16hi __builtin_ia32_psrlw256 (v16hi,v8hi);
     v8si __builtin_ia32_psrldi256 (v8si,int);
     v8si __builtin_ia32_psrld256 (v8si,v4si);
     v4di __builtin_ia32_psrlqi256 (v4di,int);
     v4di __builtin_ia32_psrlq256(v4di,v2di);
     v32qi __builtin_ia32_psubb256 (v32qi,v32qi);
     v32hi __builtin_ia32_psubw256 (v16hi,v16hi);
     v8si __builtin_ia32_psubd256 (v8si,v8si);
     v4di __builtin_ia32_psubq256 (v4di,v4di);
     v32qi __builtin_ia32_psubsb256 (v32qi,v32qi);
     v16hi __builtin_ia32_psubsw256 (v16hi,v16hi);
     v32qi __builtin_ia32_psubusb256 (v32qi,v32qi);
     v16hi __builtin_ia32_psubusw256 (v16hi,v16hi);
     v32qi __builtin_ia32_punpckhbw256 (v32qi,v32qi);
     v16hi __builtin_ia32_punpckhwd256 (v16hi,v16hi);
     v8si __builtin_ia32_punpckhdq256 (v8si,v8si);
     v4di __builtin_ia32_punpckhqdq256 (v4di,v4di);
     v32qi __builtin_ia32_punpcklbw256 (v32qi,v32qi);
     v16hi __builtin_ia32_punpcklwd256 (v16hi,v16hi);
     v8si __builtin_ia32_punpckldq256 (v8si,v8si);
     v4di __builtin_ia32_punpcklqdq256 (v4di,v4di);
     v4di __builtin_ia32_pxor256 (v4di,v4di);
     v4di __builtin_ia32_movntdqa256 (pv4di);
     v4sf __builtin_ia32_vbroadcastss_ps (v4sf);
     v8sf __builtin_ia32_vbroadcastss_ps256 (v4sf);
     v4df __builtin_ia32_vbroadcastsd_pd256 (v2df);
     v4di __builtin_ia32_vbroadcastsi256 (v2di);
     v4si __builtin_ia32_pblendd128 (v4si,v4si);
     v8si __builtin_ia32_pblendd256 (v8si,v8si);
     v32qi __builtin_ia32_pbroadcastb256 (v16qi);
     v16hi __builtin_ia32_pbroadcastw256 (v8hi);
     v8si __builtin_ia32_pbroadcastd256 (v4si);
     v4di __builtin_ia32_pbroadcastq256 (v2di);
     v16qi __builtin_ia32_pbroadcastb128 (v16qi);
     v8hi __builtin_ia32_pbroadcastw128 (v8hi);
     v4si __builtin_ia32_pbroadcastd128 (v4si);
     v2di __builtin_ia32_pbroadcastq128 (v2di);
     v8si __builtin_ia32_permvarsi256 (v8si,v8si);
     v4df __builtin_ia32_permdf256 (v4df,int);
     v8sf __builtin_ia32_permvarsf256 (v8sf,v8sf);
     v4di __builtin_ia32_permdi256 (v4di,int);
     v4di __builtin_ia32_permti256 (v4di,v4di,int);
     v4di __builtin_ia32_extract128i256 (v4di,int);
     v4di __builtin_ia32_insert128i256 (v4di,v2di,int);
     v8si __builtin_ia32_maskloadd256 (pcv8si,v8si);
     v4di __builtin_ia32_maskloadq256 (pcv4di,v4di);
     v4si __builtin_ia32_maskloadd (pcv4si,v4si);
     v2di __builtin_ia32_maskloadq (pcv2di,v2di);
     void __builtin_ia32_maskstored256 (pv8si,v8si,v8si);
     void __builtin_ia32_maskstoreq256 (pv4di,v4di,v4di);
     void __builtin_ia32_maskstored (pv4si,v4si,v4si);
     void __builtin_ia32_maskstoreq (pv2di,v2di,v2di);
     v8si __builtin_ia32_psllv8si (v8si,v8si);
     v4si __builtin_ia32_psllv4si (v4si,v4si);
     v4di __builtin_ia32_psllv4di (v4di,v4di);
     v2di __builtin_ia32_psllv2di (v2di,v2di);
     v8si __builtin_ia32_psrav8si (v8si,v8si);
     v4si __builtin_ia32_psrav4si (v4si,v4si);
     v8si __builtin_ia32_psrlv8si (v8si,v8si);
     v4si __builtin_ia32_psrlv4si (v4si,v4si);
     v4di __builtin_ia32_psrlv4di (v4di,v4di);
     v2di __builtin_ia32_psrlv2di (v2di,v2di);
     v2df __builtin_ia32_gathersiv2df (v2df, pcdouble,v4si,v2df,int);
     v4df __builtin_ia32_gathersiv4df (v4df, pcdouble,v4si,v4df,int);
     v2df __builtin_ia32_gatherdiv2df (v2df, pcdouble,v2di,v2df,int);
     v4df __builtin_ia32_gatherdiv4df (v4df, pcdouble,v4di,v4df,int);
     v4sf __builtin_ia32_gathersiv4sf (v4sf, pcfloat,v4si,v4sf,int);
     v8sf __builtin_ia32_gathersiv8sf (v8sf, pcfloat,v8si,v8sf,int);
     v4sf __builtin_ia32_gatherdiv4sf (v4sf, pcfloat,v2di,v4sf,int);
     v4sf __builtin_ia32_gatherdiv4sf256 (v4sf, pcfloat,v4di,v4sf,int);
     v2di __builtin_ia32_gathersiv2di (v2di, pcint64,v4si,v2di,int);
     v4di __builtin_ia32_gathersiv4di (v4di, pcint64,v4si,v4di,int);
     v2di __builtin_ia32_gatherdiv2di (v2di, pcint64,v2di,v2di,int);
     v4di __builtin_ia32_gatherdiv4di (v4di, pcint64,v4di,v4di,int);
     v4si __builtin_ia32_gathersiv4si (v4si, pcint,v4si,v4si,int);
     v8si __builtin_ia32_gathersiv8si (v8si, pcint,v8si,v8si,int);
     v4si __builtin_ia32_gatherdiv4si (v4si, pcint,v2di,v4si,int);
     v4si __builtin_ia32_gatherdiv4si256 (v4si, pcint,v4di,v4si,int);

 The following built-in functions are available when ‘-maes’ is used.
All of them generate the machine instruction that is part of the name.

     v2di __builtin_ia32_aesenc128 (v2di, v2di);
     v2di __builtin_ia32_aesenclast128 (v2di, v2di);
     v2di __builtin_ia32_aesdec128 (v2di, v2di);
     v2di __builtin_ia32_aesdeclast128 (v2di, v2di);
     v2di __builtin_ia32_aeskeygenassist128 (v2di, const int);
     v2di __builtin_ia32_aesimc128 (v2di);

 The following built-in function is available when ‘-mpclmul’ is used.

‘v2di __builtin_ia32_pclmulqdq128 (v2di, v2di, const int)’
     Generates the ‘pclmulqdq’ machine instruction.

 The following built-in function is available when ‘-mfsgsbase’ is used.
All of them generate the machine instruction that is part of the name.

     unsigned int __builtin_ia32_rdfsbase32 (void);
     unsigned long long __builtin_ia32_rdfsbase64 (void);
     unsigned int __builtin_ia32_rdgsbase32 (void);
     unsigned long long __builtin_ia32_rdgsbase64 (void);
     void _writefsbase_u32 (unsigned int);
     void _writefsbase_u64 (unsigned long long);
     void _writegsbase_u32 (unsigned int);
     void _writegsbase_u64 (unsigned long long);

 The following built-in function is available when ‘-mrdrnd’ is used.
All of them generate the machine instruction that is part of the name.

     unsigned int __builtin_ia32_rdrand16_step (unsigned short *);
     unsigned int __builtin_ia32_rdrand32_step (unsigned int *);
     unsigned int __builtin_ia32_rdrand64_step (unsigned long long *);

 The following built-in function is available when ‘-mptwrite’ is used.
All of them generate the machine instruction that is part of the name.

     void __builtin_ia32_ptwrite32 (unsigned);
     void __builtin_ia32_ptwrite64 (unsigned long long);

 The following built-in functions are available when ‘-msse4a’ is used.
All of them generate the machine instruction that is part of the name.

     void __builtin_ia32_movntsd (double *, v2df);
     void __builtin_ia32_movntss (float *, v4sf);
     v2di __builtin_ia32_extrq  (v2di, v16qi);
     v2di __builtin_ia32_extrqi (v2di, const unsigned int, const unsigned int);
     v2di __builtin_ia32_insertq (v2di, v2di);
     v2di __builtin_ia32_insertqi (v2di, v2di, const unsigned int, const unsigned int);

 The following built-in functions are available when ‘-mxop’ is used.
     v2df __builtin_ia32_vfrczpd (v2df);
     v4sf __builtin_ia32_vfrczps (v4sf);
     v2df __builtin_ia32_vfrczsd (v2df);
     v4sf __builtin_ia32_vfrczss (v4sf);
     v4df __builtin_ia32_vfrczpd256 (v4df);
     v8sf __builtin_ia32_vfrczps256 (v8sf);
     v2di __builtin_ia32_vpcmov (v2di, v2di, v2di);
     v2di __builtin_ia32_vpcmov_v2di (v2di, v2di, v2di);
     v4si __builtin_ia32_vpcmov_v4si (v4si, v4si, v4si);
     v8hi __builtin_ia32_vpcmov_v8hi (v8hi, v8hi, v8hi);
     v16qi __builtin_ia32_vpcmov_v16qi (v16qi, v16qi, v16qi);
     v2df __builtin_ia32_vpcmov_v2df (v2df, v2df, v2df);
     v4sf __builtin_ia32_vpcmov_v4sf (v4sf, v4sf, v4sf);
     v4di __builtin_ia32_vpcmov_v4di256 (v4di, v4di, v4di);
     v8si __builtin_ia32_vpcmov_v8si256 (v8si, v8si, v8si);
     v16hi __builtin_ia32_vpcmov_v16hi256 (v16hi, v16hi, v16hi);
     v32qi __builtin_ia32_vpcmov_v32qi256 (v32qi, v32qi, v32qi);
     v4df __builtin_ia32_vpcmov_v4df256 (v4df, v4df, v4df);
     v8sf __builtin_ia32_vpcmov_v8sf256 (v8sf, v8sf, v8sf);
     v16qi __builtin_ia32_vpcomeqb (v16qi, v16qi);
     v8hi __builtin_ia32_vpcomeqw (v8hi, v8hi);
     v4si __builtin_ia32_vpcomeqd (v4si, v4si);
     v2di __builtin_ia32_vpcomeqq (v2di, v2di);
     v16qi __builtin_ia32_vpcomequb (v16qi, v16qi);
     v4si __builtin_ia32_vpcomequd (v4si, v4si);
     v2di __builtin_ia32_vpcomequq (v2di, v2di);
     v8hi __builtin_ia32_vpcomequw (v8hi, v8hi);
     v8hi __builtin_ia32_vpcomeqw (v8hi, v8hi);
     v16qi __builtin_ia32_vpcomfalseb (v16qi, v16qi);
     v4si __builtin_ia32_vpcomfalsed (v4si, v4si);
     v2di __builtin_ia32_vpcomfalseq (v2di, v2di);
     v16qi __builtin_ia32_vpcomfalseub (v16qi, v16qi);
     v4si __builtin_ia32_vpcomfalseud (v4si, v4si);
     v2di __builtin_ia32_vpcomfalseuq (v2di, v2di);
     v8hi __builtin_ia32_vpcomfalseuw (v8hi, v8hi);
     v8hi __builtin_ia32_vpcomfalsew (v8hi, v8hi);
     v16qi __builtin_ia32_vpcomgeb (v16qi, v16qi);
     v4si __builtin_ia32_vpcomged (v4si, v4si);
     v2di __builtin_ia32_vpcomgeq (v2di, v2di);
     v16qi __builtin_ia32_vpcomgeub (v16qi, v16qi);
     v4si __builtin_ia32_vpcomgeud (v4si, v4si);
     v2di __builtin_ia32_vpcomgeuq (v2di, v2di);
     v8hi __builtin_ia32_vpcomgeuw (v8hi, v8hi);
     v8hi __builtin_ia32_vpcomgew (v8hi, v8hi);
     v16qi __builtin_ia32_vpcomgtb (v16qi, v16qi);
     v4si __builtin_ia32_vpcomgtd (v4si, v4si);
     v2di __builtin_ia32_vpcomgtq (v2di, v2di);
     v16qi __builtin_ia32_vpcomgtub (v16qi, v16qi);
     v4si __builtin_ia32_vpcomgtud (v4si, v4si);
     v2di __builtin_ia32_vpcomgtuq (v2di, v2di);
     v8hi __builtin_ia32_vpcomgtuw (v8hi, v8hi);
     v8hi __builtin_ia32_vpcomgtw (v8hi, v8hi);
     v16qi __builtin_ia32_vpcomleb (v16qi, v16qi);
     v4si __builtin_ia32_vpcomled (v4si, v4si);
     v2di __builtin_ia32_vpcomleq (v2di, v2di);
     v16qi __builtin_ia32_vpcomleub (v16qi, v16qi);
     v4si __builtin_ia32_vpcomleud (v4si, v4si);
     v2di __builtin_ia32_vpcomleuq (v2di, v2di);
     v8hi __builtin_ia32_vpcomleuw (v8hi, v8hi);
     v8hi __builtin_ia32_vpcomlew (v8hi, v8hi);
     v16qi __builtin_ia32_vpcomltb (v16qi, v16qi);
     v4si __builtin_ia32_vpcomltd (v4si, v4si);
     v2di __builtin_ia32_vpcomltq (v2di, v2di);
     v16qi __builtin_ia32_vpcomltub (v16qi, v16qi);
     v4si __builtin_ia32_vpcomltud (v4si, v4si);
     v2di __builtin_ia32_vpcomltuq (v2di, v2di);
     v8hi __builtin_ia32_vpcomltuw (v8hi, v8hi);
     v8hi __builtin_ia32_vpcomltw (v8hi, v8hi);
     v16qi __builtin_ia32_vpcomneb (v16qi, v16qi);
     v4si __builtin_ia32_vpcomned (v4si, v4si);
     v2di __builtin_ia32_vpcomneq (v2di, v2di);
     v16qi __builtin_ia32_vpcomneub (v16qi, v16qi);
     v4si __builtin_ia32_vpcomneud (v4si, v4si);
     v2di __builtin_ia32_vpcomneuq (v2di, v2di);
     v8hi __builtin_ia32_vpcomneuw (v8hi, v8hi);
     v8hi __builtin_ia32_vpcomnew (v8hi, v8hi);
     v16qi __builtin_ia32_vpcomtrueb (v16qi, v16qi);
     v4si __builtin_ia32_vpcomtrued (v4si, v4si);
     v2di __builtin_ia32_vpcomtrueq (v2di, v2di);
     v16qi __builtin_ia32_vpcomtrueub (v16qi, v16qi);
     v4si __builtin_ia32_vpcomtrueud (v4si, v4si);
     v2di __builtin_ia32_vpcomtrueuq (v2di, v2di);
     v8hi __builtin_ia32_vpcomtrueuw (v8hi, v8hi);
     v8hi __builtin_ia32_vpcomtruew (v8hi, v8hi);
     v4si __builtin_ia32_vphaddbd (v16qi);
     v2di __builtin_ia32_vphaddbq (v16qi);
     v8hi __builtin_ia32_vphaddbw (v16qi);
     v2di __builtin_ia32_vphadddq (v4si);
     v4si __builtin_ia32_vphaddubd (v16qi);
     v2di __builtin_ia32_vphaddubq (v16qi);
     v8hi __builtin_ia32_vphaddubw (v16qi);
     v2di __builtin_ia32_vphaddudq (v4si);
     v4si __builtin_ia32_vphadduwd (v8hi);
     v2di __builtin_ia32_vphadduwq (v8hi);
     v4si __builtin_ia32_vphaddwd (v8hi);
     v2di __builtin_ia32_vphaddwq (v8hi);
     v8hi __builtin_ia32_vphsubbw (v16qi);
     v2di __builtin_ia32_vphsubdq (v4si);
     v4si __builtin_ia32_vphsubwd (v8hi);
     v4si __builtin_ia32_vpmacsdd (v4si, v4si, v4si);
     v2di __builtin_ia32_vpmacsdqh (v4si, v4si, v2di);
     v2di __builtin_ia32_vpmacsdql (v4si, v4si, v2di);
     v4si __builtin_ia32_vpmacssdd (v4si, v4si, v4si);
     v2di __builtin_ia32_vpmacssdqh (v4si, v4si, v2di);
     v2di __builtin_ia32_vpmacssdql (v4si, v4si, v2di);
     v4si __builtin_ia32_vpmacsswd (v8hi, v8hi, v4si);
     v8hi __builtin_ia32_vpmacssww (v8hi, v8hi, v8hi);
     v4si __builtin_ia32_vpmacswd (v8hi, v8hi, v4si);
     v8hi __builtin_ia32_vpmacsww (v8hi, v8hi, v8hi);
     v4si __builtin_ia32_vpmadcsswd (v8hi, v8hi, v4si);
     v4si __builtin_ia32_vpmadcswd (v8hi, v8hi, v4si);
     v16qi __builtin_ia32_vpperm (v16qi, v16qi, v16qi);
     v16qi __builtin_ia32_vprotb (v16qi, v16qi);
     v4si __builtin_ia32_vprotd (v4si, v4si);
     v2di __builtin_ia32_vprotq (v2di, v2di);
     v8hi __builtin_ia32_vprotw (v8hi, v8hi);
     v16qi __builtin_ia32_vpshab (v16qi, v16qi);
     v4si __builtin_ia32_vpshad (v4si, v4si);
     v2di __builtin_ia32_vpshaq (v2di, v2di);
     v8hi __builtin_ia32_vpshaw (v8hi, v8hi);
     v16qi __builtin_ia32_vpshlb (v16qi, v16qi);
     v4si __builtin_ia32_vpshld (v4si, v4si);
     v2di __builtin_ia32_vpshlq (v2di, v2di);
     v8hi __builtin_ia32_vpshlw (v8hi, v8hi);

 The following built-in functions are available when ‘-mfma4’ is used.
All of them generate the machine instruction that is part of the name.

     v2df __builtin_ia32_vfmaddpd (v2df, v2df, v2df);
     v4sf __builtin_ia32_vfmaddps (v4sf, v4sf, v4sf);
     v2df __builtin_ia32_vfmaddsd (v2df, v2df, v2df);
     v4sf __builtin_ia32_vfmaddss (v4sf, v4sf, v4sf);
     v2df __builtin_ia32_vfmsubpd (v2df, v2df, v2df);
     v4sf __builtin_ia32_vfmsubps (v4sf, v4sf, v4sf);
     v2df __builtin_ia32_vfmsubsd (v2df, v2df, v2df);
     v4sf __builtin_ia32_vfmsubss (v4sf, v4sf, v4sf);
     v2df __builtin_ia32_vfnmaddpd (v2df, v2df, v2df);
     v4sf __builtin_ia32_vfnmaddps (v4sf, v4sf, v4sf);
     v2df __builtin_ia32_vfnmaddsd (v2df, v2df, v2df);
     v4sf __builtin_ia32_vfnmaddss (v4sf, v4sf, v4sf);
     v2df __builtin_ia32_vfnmsubpd (v2df, v2df, v2df);
     v4sf __builtin_ia32_vfnmsubps (v4sf, v4sf, v4sf);
     v2df __builtin_ia32_vfnmsubsd (v2df, v2df, v2df);
     v4sf __builtin_ia32_vfnmsubss (v4sf, v4sf, v4sf);
     v2df __builtin_ia32_vfmaddsubpd  (v2df, v2df, v2df);
     v4sf __builtin_ia32_vfmaddsubps  (v4sf, v4sf, v4sf);
     v2df __builtin_ia32_vfmsubaddpd  (v2df, v2df, v2df);
     v4sf __builtin_ia32_vfmsubaddps  (v4sf, v4sf, v4sf);
     v4df __builtin_ia32_vfmaddpd256 (v4df, v4df, v4df);
     v8sf __builtin_ia32_vfmaddps256 (v8sf, v8sf, v8sf);
     v4df __builtin_ia32_vfmsubpd256 (v4df, v4df, v4df);
     v8sf __builtin_ia32_vfmsubps256 (v8sf, v8sf, v8sf);
     v4df __builtin_ia32_vfnmaddpd256 (v4df, v4df, v4df);
     v8sf __builtin_ia32_vfnmaddps256 (v8sf, v8sf, v8sf);
     v4df __builtin_ia32_vfnmsubpd256 (v4df, v4df, v4df);
     v8sf __builtin_ia32_vfnmsubps256 (v8sf, v8sf, v8sf);
     v4df __builtin_ia32_vfmaddsubpd256 (v4df, v4df, v4df);
     v8sf __builtin_ia32_vfmaddsubps256 (v8sf, v8sf, v8sf);
     v4df __builtin_ia32_vfmsubaddpd256 (v4df, v4df, v4df);
     v8sf __builtin_ia32_vfmsubaddps256 (v8sf, v8sf, v8sf);

 The following built-in functions are available when ‘-mlwp’ is used.

     void __builtin_ia32_llwpcb16 (void *);
     void __builtin_ia32_llwpcb32 (void *);
     void __builtin_ia32_llwpcb64 (void *);
     void * __builtin_ia32_llwpcb16 (void);
     void * __builtin_ia32_llwpcb32 (void);
     void * __builtin_ia32_llwpcb64 (void);
     void __builtin_ia32_lwpval16 (unsigned short, unsigned int, unsigned short);
     void __builtin_ia32_lwpval32 (unsigned int, unsigned int, unsigned int);
     void __builtin_ia32_lwpval64 (unsigned __int64, unsigned int, unsigned int);
     unsigned char __builtin_ia32_lwpins16 (unsigned short, unsigned int, unsigned short);
     unsigned char __builtin_ia32_lwpins32 (unsigned int, unsigned int, unsigned int);
     unsigned char __builtin_ia32_lwpins64 (unsigned __int64, unsigned int, unsigned int);

 The following built-in functions are available when ‘-mbmi’ is used.
All of them generate the machine instruction that is part of the name.
     unsigned int __builtin_ia32_bextr_u32(unsigned int, unsigned int);
     unsigned long long __builtin_ia32_bextr_u64 (unsigned long long, unsigned long long);

 The following built-in functions are available when ‘-mbmi2’ is used.
All of them generate the machine instruction that is part of the name.
     unsigned int _bzhi_u32 (unsigned int, unsigned int);
     unsigned int _pdep_u32 (unsigned int, unsigned int);
     unsigned int _pext_u32 (unsigned int, unsigned int);
     unsigned long long _bzhi_u64 (unsigned long long, unsigned long long);
     unsigned long long _pdep_u64 (unsigned long long, unsigned long long);
     unsigned long long _pext_u64 (unsigned long long, unsigned long long);

 The following built-in functions are available when ‘-mlzcnt’ is used.
All of them generate the machine instruction that is part of the name.
     unsigned short __builtin_ia32_lzcnt_u16(unsigned short);
     unsigned int __builtin_ia32_lzcnt_u32(unsigned int);
     unsigned long long __builtin_ia32_lzcnt_u64 (unsigned long long);

 The following built-in functions are available when ‘-mfxsr’ is used.
All of them generate the machine instruction that is part of the name.
     void __builtin_ia32_fxsave (void *);
     void __builtin_ia32_fxrstor (void *);
     void __builtin_ia32_fxsave64 (void *);
     void __builtin_ia32_fxrstor64 (void *);

 The following built-in functions are available when ‘-mxsave’ is used.
All of them generate the machine instruction that is part of the name.
     void __builtin_ia32_xsave (void *, long long);
     void __builtin_ia32_xrstor (void *, long long);
     void __builtin_ia32_xsave64 (void *, long long);
     void __builtin_ia32_xrstor64 (void *, long long);

 The following built-in functions are available when ‘-mxsaveopt’ is
used.  All of them generate the machine instruction that is part of the
name.
     void __builtin_ia32_xsaveopt (void *, long long);
     void __builtin_ia32_xsaveopt64 (void *, long long);

 The following built-in functions are available when ‘-mtbm’ is used.
Both of them generate the immediate form of the bextr machine
instruction.
     unsigned int __builtin_ia32_bextri_u32 (unsigned int,
                                             const unsigned int);
     unsigned long long __builtin_ia32_bextri_u64 (unsigned long long,
                                                   const unsigned long long);

 The following built-in functions are available when ‘-m3dnow’ is used.
All of them generate the machine instruction that is part of the name.

     void __builtin_ia32_femms (void);
     v8qi __builtin_ia32_pavgusb (v8qi, v8qi);
     v2si __builtin_ia32_pf2id (v2sf);
     v2sf __builtin_ia32_pfacc (v2sf, v2sf);
     v2sf __builtin_ia32_pfadd (v2sf, v2sf);
     v2si __builtin_ia32_pfcmpeq (v2sf, v2sf);
     v2si __builtin_ia32_pfcmpge (v2sf, v2sf);
     v2si __builtin_ia32_pfcmpgt (v2sf, v2sf);
     v2sf __builtin_ia32_pfmax (v2sf, v2sf);
     v2sf __builtin_ia32_pfmin (v2sf, v2sf);
     v2sf __builtin_ia32_pfmul (v2sf, v2sf);
     v2sf __builtin_ia32_pfrcp (v2sf);
     v2sf __builtin_ia32_pfrcpit1 (v2sf, v2sf);
     v2sf __builtin_ia32_pfrcpit2 (v2sf, v2sf);
     v2sf __builtin_ia32_pfrsqrt (v2sf);
     v2sf __builtin_ia32_pfsub (v2sf, v2sf);
     v2sf __builtin_ia32_pfsubr (v2sf, v2sf);
     v2sf __builtin_ia32_pi2fd (v2si);
     v4hi __builtin_ia32_pmulhrw (v4hi, v4hi);

 The following built-in functions are available when ‘-m3dnowa’ is used.
All of them generate the machine instruction that is part of the name.

     v2si __builtin_ia32_pf2iw (v2sf);
     v2sf __builtin_ia32_pfnacc (v2sf, v2sf);
     v2sf __builtin_ia32_pfpnacc (v2sf, v2sf);
     v2sf __builtin_ia32_pi2fw (v2si);
     v2sf __builtin_ia32_pswapdsf (v2sf);
     v2si __builtin_ia32_pswapdsi (v2si);

 The following built-in functions are available when ‘-mrtm’ is used
They are used for restricted transactional memory.  These are the
internal low level functions.  Normally the functions in *note x86
transactional memory intrinsics:: should be used instead.

     int __builtin_ia32_xbegin ();
     void __builtin_ia32_xend ();
     void __builtin_ia32_xabort (status);
     int __builtin_ia32_xtest ();

 The following built-in functions are available when ‘-mmwaitx’ is used.
All of them generate the machine instruction that is part of the name.
     void __builtin_ia32_monitorx (void *, unsigned int, unsigned int);
     void __builtin_ia32_mwaitx (unsigned int, unsigned int, unsigned int);

 The following built-in functions are available when ‘-mclzero’ is used.
All of them generate the machine instruction that is part of the name.
     void __builtin_i32_clzero (void *);

 The following built-in functions are available when ‘-mpku’ is used.
They generate reads and writes to PKRU.
     void __builtin_ia32_wrpkru (unsigned int);
     unsigned int __builtin_ia32_rdpkru ();

 The following built-in functions are available when ‘-mshstk’ option is
used.  They support shadow stack machine instructions from Intel
Control-flow Enforcement Technology (CET). Each built-in function
generates the machine instruction that is part of the function's name.
These are the internal low-level functions.  Normally the functions in
*note x86 control-flow protection intrinsics:: should be used instead.

     unsigned int __builtin_ia32_rdsspd (void);
     unsigned long long __builtin_ia32_rdsspq (void);
     void __builtin_ia32_incsspd (unsigned int);
     void __builtin_ia32_incsspq (unsigned long long);
     void __builtin_ia32_saveprevssp(void);
     void __builtin_ia32_rstorssp(void *);
     void __builtin_ia32_wrssd(unsigned int, void *);
     void __builtin_ia32_wrssq(unsigned long long, void *);
     void __builtin_ia32_wrussd(unsigned int, void *);
     void __builtin_ia32_wrussq(unsigned long long, void *);
     void __builtin_ia32_setssbsy(void);
     void __builtin_ia32_clrssbsy(void *);


File: gcc.info,  Node: x86 transactional memory intrinsics,  Next: x86 control-flow protection intrinsics,  Prev: x86 Built-in Functions,  Up: Target Builtins

6.60.37 x86 Transactional Memory Intrinsics
-------------------------------------------

These hardware transactional memory intrinsics for x86 allow you to use
memory transactions with RTM (Restricted Transactional Memory).  This
support is enabled with the ‘-mrtm’ option.  For using HLE (Hardware
Lock Elision) see *note x86 specific memory model extensions for
transactional memory:: instead.

 A memory transaction commits all changes to memory in an atomic way, as
visible to other threads.  If the transaction fails it is rolled back
and all side effects discarded.

 Generally there is no guarantee that a memory transaction ever succeeds
and suitable fallback code always needs to be supplied.

 -- RTM Function: unsigned _xbegin ()
     Start a RTM (Restricted Transactional Memory) transaction.  Returns
     ‘_XBEGIN_STARTED’ when the transaction started successfully (note
     this is not 0, so the constant has to be explicitly tested).

     If the transaction aborts, all side effects are undone and an abort
     code encoded as a bit mask is returned.  The following macros are
     defined:

     ‘_XABORT_EXPLICIT’
          Transaction was explicitly aborted with ‘_xabort’.  The
          parameter passed to ‘_xabort’ is available with
          ‘_XABORT_CODE(status)’.
     ‘_XABORT_RETRY’
          Transaction retry is possible.
     ‘_XABORT_CONFLICT’
          Transaction abort due to a memory conflict with another
          thread.
     ‘_XABORT_CAPACITY’
          Transaction abort due to the transaction using too much
          memory.
     ‘_XABORT_DEBUG’
          Transaction abort due to a debug trap.
     ‘_XABORT_NESTED’
          Transaction abort in an inner nested transaction.

     There is no guarantee any transaction ever succeeds, so there
     always needs to be a valid fallback path.

 -- RTM Function: void _xend ()
     Commit the current transaction.  When no transaction is active this
     faults.  All memory side effects of the transaction become visible
     to other threads in an atomic manner.

 -- RTM Function: int _xtest ()
     Return a nonzero value if a transaction is currently active,
     otherwise 0.

 -- RTM Function: void _xabort (status)
     Abort the current transaction.  When no transaction is active this
     is a no-op.  The STATUS is an 8-bit constant; its value is encoded
     in the return value from ‘_xbegin’.

 Here is an example showing handling for ‘_XABORT_RETRY’ and a fallback
path for other failures:

     #include <immintrin.h>

     int n_tries, max_tries;
     unsigned status = _XABORT_EXPLICIT;
     ...

     for (n_tries = 0; n_tries < max_tries; n_tries++)
       {
         status = _xbegin ();
         if (status == _XBEGIN_STARTED || !(status & _XABORT_RETRY))
           break;
       }
     if (status == _XBEGIN_STARTED)
       {
         ... transaction code...
         _xend ();
       }
     else
       {
         ... non-transactional fallback path...
       }

Note that, in most cases, the transactional and non-transactional code
must synchronize together to ensure consistency.


File: gcc.info,  Node: x86 control-flow protection intrinsics,  Prev: x86 transactional memory intrinsics,  Up: Target Builtins

6.60.38 x86 Control-Flow Protection Intrinsics
----------------------------------------------

 -- CET Function: ret_type _get_ssp (void)
     Get the current value of shadow stack pointer if shadow stack
     support from Intel CET is enabled in the hardware or ‘0’ otherwise.
     The ‘ret_type’ is ‘unsigned long long’ for 64-bit targets and
     ‘unsigned int’ for 32-bit targets.

 -- CET Function: void _inc_ssp (unsigned int)
     Increment the current shadow stack pointer by the size specified by
     the function argument.  The argument is masked to a byte value for
     security reasons, so to increment by more than 255 bytes you must
     call the function multiple times.

 The shadow stack unwind code looks like:

     #include <immintrin.h>

     /* Unwind the shadow stack for EH.  */
     #define _Unwind_Frames_Extra(x)       \
       do                                  \
         {                                \
           _Unwind_Word ssp = _get_ssp (); \
           if (ssp != 0)                   \
             {                            \
               _Unwind_Word tmp = (x);     \
               while (tmp > 255)           \
                 {                        \
                   _inc_ssp (tmp);         \
                   tmp -= 255;             \
                 }                        \
               _inc_ssp (tmp);             \
             }                            \
         }                                \
         while (0)

This code runs unconditionally on all 64-bit processors.  For 32-bit
processors the code runs on those that support multi-byte NOP
instructions.


File: gcc.info,  Node: Target Format Checks,  Next: Pragmas,  Prev: Target Builtins,  Up: C Extensions

6.61 Format Checks Specific to Particular Target Machines
=========================================================

For some target machines, GCC supports additional options to the format
attribute (*note Declaring Attributes of Functions: Function
Attributes.).

* Menu:

* Solaris Format Checks::
* Darwin Format Checks::


File: gcc.info,  Node: Solaris Format Checks,  Next: Darwin Format Checks,  Up: Target Format Checks

6.61.1 Solaris Format Checks
----------------------------

Solaris targets support the ‘cmn_err’ (or ‘__cmn_err__’) format check.
‘cmn_err’ accepts a subset of the standard ‘printf’ conversions, and the
two-argument ‘%b’ conversion for displaying bit-fields.  See the Solaris
man page for ‘cmn_err’ for more information.


File: gcc.info,  Node: Darwin Format Checks,  Prev: Solaris Format Checks,  Up: Target Format Checks

6.61.2 Darwin Format Checks
---------------------------

In addition to the full set of format archetypes (attribute format style
arguments such as ‘printf’, ‘scanf’, ‘strftime’, and ‘strfmon’), Darwin
targets also support the ‘CFString’ (or ‘__CFString__’) archetype in the
‘format’ attribute.  Declarations with this archetype are parsed for
correct syntax and argument types.  However, parsing of the format
string itself and validating arguments against it in calls to such
functions is currently not performed.

 Additionally, ‘CFStringRefs’ (defined by the ‘CoreFoundation’ headers)
may also be used as format arguments.  Note that the relevant headers
are only likely to be available on Darwin (OSX) installations.  On such
installations, the XCode and system documentation provide descriptions
of ‘CFString’, ‘CFStringRefs’ and associated functions.


File: gcc.info,  Node: Pragmas,  Next: Unnamed Fields,  Prev: Target Format Checks,  Up: C Extensions

6.62 Pragmas Accepted by GCC
============================

GCC supports several types of pragmas, primarily in order to compile
code originally written for other compilers.  Note that in general we do
not recommend the use of pragmas; *Note Function Attributes::, for
further explanation.

 The GNU C preprocessor recognizes several pragmas in addition to the
compiler pragmas documented here.  Refer to the CPP manual for more
information.

* Menu:

* AArch64 Pragmas::
* ARM Pragmas::
* M32C Pragmas::
* MeP Pragmas::
* PRU Pragmas::
* RS/6000 and PowerPC Pragmas::
* S/390 Pragmas::
* Darwin Pragmas::
* Solaris Pragmas::
* Symbol-Renaming Pragmas::
* Structure-Layout Pragmas::
* Weak Pragmas::
* Diagnostic Pragmas::
* Visibility Pragmas::
* Push/Pop Macro Pragmas::
* Function Specific Option Pragmas::
* Loop-Specific Pragmas::


File: gcc.info,  Node: AArch64 Pragmas,  Next: ARM Pragmas,  Up: Pragmas

6.62.1 AArch64 Pragmas
----------------------

The pragmas defined by the AArch64 target correspond to the AArch64
target function attributes.  They can be specified as below:
     #pragma GCC target("string")

 where ‘STRING’ can be any string accepted as an AArch64 target
attribute.  *Note AArch64 Function Attributes::, for more details on the
permissible values of ‘string’.


File: gcc.info,  Node: ARM Pragmas,  Next: M32C Pragmas,  Prev: AArch64 Pragmas,  Up: Pragmas

6.62.2 ARM Pragmas
------------------

The ARM target defines pragmas for controlling the default addition of
‘long_call’ and ‘short_call’ attributes to functions.  *Note Function
Attributes::, for information about the effects of these attributes.

‘long_calls’
     Set all subsequent functions to have the ‘long_call’ attribute.

‘no_long_calls’
     Set all subsequent functions to have the ‘short_call’ attribute.

‘long_calls_off’
     Do not affect the ‘long_call’ or ‘short_call’ attributes of
     subsequent functions.


File: gcc.info,  Node: M32C Pragmas,  Next: MeP Pragmas,  Prev: ARM Pragmas,  Up: Pragmas

6.62.3 M32C Pragmas
-------------------

‘GCC memregs NUMBER’
     Overrides the command-line option ‘-memregs=’ for the current file.
     Use with care!  This pragma must be before any function in the
     file, and mixing different memregs values in different objects may
     make them incompatible.  This pragma is useful when a
     performance-critical function uses a memreg for temporary values,
     as it may allow you to reduce the number of memregs used.

‘ADDRESS NAME ADDRESS’
     For any declared symbols matching NAME, this does three things to
     that symbol: it forces the symbol to be located at the given
     address (a number), it forces the symbol to be volatile, and it
     changes the symbol's scope to be static.  This pragma exists for
     compatibility with other compilers, but note that the common
     ‘1234H’ numeric syntax is not supported (use ‘0x1234’ instead).
     Example:

          #pragma ADDRESS port3 0x103
          char port3;


File: gcc.info,  Node: MeP Pragmas,  Next: PRU Pragmas,  Prev: M32C Pragmas,  Up: Pragmas

6.62.4 MeP Pragmas
------------------

‘custom io_volatile (on|off)’
     Overrides the command-line option ‘-mio-volatile’ for the current
     file.  Note that for compatibility with future GCC releases, this
     option should only be used once before any ‘io’ variables in each
     file.

‘GCC coprocessor available REGISTERS’
     Specifies which coprocessor registers are available to the register
     allocator.  REGISTERS may be a single register, register range
     separated by ellipses, or comma-separated list of those.  Example:

          #pragma GCC coprocessor available $c0...$c10, $c28

‘GCC coprocessor call_saved REGISTERS’
     Specifies which coprocessor registers are to be saved and restored
     by any function using them.  REGISTERS may be a single register,
     register range separated by ellipses, or comma-separated list of
     those.  Example:

          #pragma GCC coprocessor call_saved $c4...$c6, $c31

‘GCC coprocessor subclass '(A|B|C|D)' = REGISTERS’
     Creates and defines a register class.  These register classes can
     be used by inline ‘asm’ constructs.  REGISTERS may be a single
     register, register range separated by ellipses, or comma-separated
     list of those.  Example:

          #pragma GCC coprocessor subclass 'B' = $c2, $c4, $c6

          asm ("cpfoo %0" : "=B" (x));

‘GCC disinterrupt NAME , NAME ...’
     For the named functions, the compiler adds code to disable
     interrupts for the duration of those functions.  If any functions
     so named are not encountered in the source, a warning is emitted
     that the pragma is not used.  Examples:

          #pragma disinterrupt foo
          #pragma disinterrupt bar, grill
          int foo () { ... }

‘GCC call NAME , NAME ...’
     For the named functions, the compiler always uses a
     register-indirect call model when calling the named functions.
     Examples:

          extern int foo ();
          #pragma call foo


File: gcc.info,  Node: PRU Pragmas,  Next: RS/6000 and PowerPC Pragmas,  Prev: MeP Pragmas,  Up: Pragmas

6.62.5 PRU Pragmas
------------------

‘ctable_entry INDEX CONSTANT_ADDRESS’
     Specifies that the PRU CTABLE entry given by INDEX has the value
     CONSTANT_ADDRESS.  This enables GCC to emit LBCO/SBCO instructions
     when the load/store address is known and can be addressed with some
     CTABLE entry.  For example:

          /* will compile to "sbco Rx, 2, 0x10, 4" */
          #pragma ctable_entry 2 0x4802a000
          *(unsigned int *)0x4802a010 = val;


File: gcc.info,  Node: RS/6000 and PowerPC Pragmas,  Next: S/390 Pragmas,  Prev: PRU Pragmas,  Up: Pragmas

6.62.6 RS/6000 and PowerPC Pragmas
----------------------------------

The RS/6000 and PowerPC targets define one pragma for controlling
whether or not the ‘longcall’ attribute is added to function
declarations by default.  This pragma overrides the ‘-mlongcall’ option,
but not the ‘longcall’ and ‘shortcall’ attributes.  *Note RS/6000 and
PowerPC Options::, for more information about when long calls are and
are not necessary.

‘longcall (1)’
     Apply the ‘longcall’ attribute to all subsequent function
     declarations.

‘longcall (0)’
     Do not apply the ‘longcall’ attribute to subsequent function
     declarations.


File: gcc.info,  Node: S/390 Pragmas,  Next: Darwin Pragmas,  Prev: RS/6000 and PowerPC Pragmas,  Up: Pragmas

6.62.7 S/390 Pragmas
--------------------

The pragmas defined by the S/390 target correspond to the S/390 target
function attributes and some the additional options:

‘zvector’
‘no-zvector’

 Note that options of the pragma, unlike options of the target
attribute, do change the value of preprocessor macros like ‘__VEC__’.
They can be specified as below:

     #pragma GCC target("string[,string]...")
     #pragma GCC target("string"[,"string"]...)


File: gcc.info,  Node: Darwin Pragmas,  Next: Solaris Pragmas,  Prev: S/390 Pragmas,  Up: Pragmas

6.62.8 Darwin Pragmas
---------------------

The following pragmas are available for all architectures running the
Darwin operating system.  These are useful for compatibility with other
Mac OS compilers.

‘mark TOKENS...’
     This pragma is accepted, but has no effect.

‘options align=ALIGNMENT’
     This pragma sets the alignment of fields in structures.  The values
     of ALIGNMENT may be ‘mac68k’, to emulate m68k alignment, or
     ‘power’, to emulate PowerPC alignment.  Uses of this pragma nest
     properly; to restore the previous setting, use ‘reset’ for the
     ALIGNMENT.

‘segment TOKENS...’
     This pragma is accepted, but has no effect.

‘unused (VAR [, VAR]...)’
     This pragma declares variables to be possibly unused.  GCC does not
     produce warnings for the listed variables.  The effect is similar
     to that of the ‘unused’ attribute, except that this pragma may
     appear anywhere within the variables' scopes.


File: gcc.info,  Node: Solaris Pragmas,  Next: Symbol-Renaming Pragmas,  Prev: Darwin Pragmas,  Up: Pragmas

6.62.9 Solaris Pragmas
----------------------

The Solaris target supports ‘#pragma redefine_extname’ (*note
Symbol-Renaming Pragmas::).  It also supports additional ‘#pragma’
directives for compatibility with the system compiler.

‘align ALIGNMENT (VARIABLE [, VARIABLE]...)’

     Increase the minimum alignment of each VARIABLE to ALIGNMENT.  This
     is the same as GCC's ‘aligned’ attribute *note Variable
     Attributes::).  Macro expansion occurs on the arguments to this
     pragma when compiling C and Objective-C.  It does not currently
     occur when compiling C++, but this is a bug which may be fixed in a
     future release.

‘fini (FUNCTION [, FUNCTION]...)’

     This pragma causes each listed FUNCTION to be called after main, or
     during shared module unloading, by adding a call to the ‘.fini’
     section.

‘init (FUNCTION [, FUNCTION]...)’

     This pragma causes each listed FUNCTION to be called during
     initialization (before ‘main’) or during shared module loading, by
     adding a call to the ‘.init’ section.


File: gcc.info,  Node: Symbol-Renaming Pragmas,  Next: Structure-Layout Pragmas,  Prev: Solaris Pragmas,  Up: Pragmas

6.62.10 Symbol-Renaming Pragmas
-------------------------------

GCC supports a ‘#pragma’ directive that changes the name used in
assembly for a given declaration.  While this pragma is supported on all
platforms, it is intended primarily to provide compatibility with the
Solaris system headers.  This effect can also be achieved using the asm
labels extension (*note Asm Labels::).

‘redefine_extname OLDNAME NEWNAME’

     This pragma gives the C function OLDNAME the assembly symbol
     NEWNAME.  The preprocessor macro ‘__PRAGMA_REDEFINE_EXTNAME’ is
     defined if this pragma is available (currently on all platforms).

 This pragma and the ‘asm’ labels extension interact in a complicated
manner.  Here are some corner cases you may want to be aware of:

  1. This pragma silently applies only to declarations with external
     linkage.  The ‘asm’ label feature does not have this restriction.

  2. In C++, this pragma silently applies only to declarations with "C"
     linkage.  Again, ‘asm’ labels do not have this restriction.

  3. If either of the ways of changing the assembly name of a
     declaration are applied to a declaration whose assembly name has
     already been determined (either by a previous use of one of these
     features, or because the compiler needed the assembly name in order
     to generate code), and the new name is different, a warning issues
     and the name does not change.

  4. The OLDNAME used by ‘#pragma redefine_extname’ is always the
     C-language name.


File: gcc.info,  Node: Structure-Layout Pragmas,  Next: Weak Pragmas,  Prev: Symbol-Renaming Pragmas,  Up: Pragmas

6.62.11 Structure-Layout Pragmas
--------------------------------

For compatibility with Microsoft Windows compilers, GCC supports a set
of ‘#pragma’ directives that change the maximum alignment of members of
structures (other than zero-width bit-fields), unions, and classes
subsequently defined.  The N value below always is required to be a
small power of two and specifies the new alignment in bytes.

  1. ‘#pragma pack(N)’ simply sets the new alignment.
  2. ‘#pragma pack()’ sets the alignment to the one that was in effect
     when compilation started (see also command-line option
     ‘-fpack-struct[=N]’ *note Code Gen Options::).
  3. ‘#pragma pack(push[,N])’ pushes the current alignment setting on an
     internal stack and then optionally sets the new alignment.
  4. ‘#pragma pack(pop)’ restores the alignment setting to the one saved
     at the top of the internal stack (and removes that stack entry).
     Note that ‘#pragma pack([N])’ does not influence this internal
     stack; thus it is possible to have ‘#pragma pack(push)’ followed by
     multiple ‘#pragma pack(N)’ instances and finalized by a single
     ‘#pragma pack(pop)’.

 Some targets, e.g. x86 and PowerPC, support the ‘#pragma ms_struct’
directive which lays out structures and unions subsequently defined as
the documented ‘__attribute__ ((ms_struct))’.

  1. ‘#pragma ms_struct on’ turns on the Microsoft layout.
  2. ‘#pragma ms_struct off’ turns off the Microsoft layout.
  3. ‘#pragma ms_struct reset’ goes back to the default layout.

 Most targets also support the ‘#pragma scalar_storage_order’ directive
which lays out structures and unions subsequently defined as the
documented ‘__attribute__ ((scalar_storage_order))’.

  1. ‘#pragma scalar_storage_order big-endian’ sets the storage order of
     the scalar fields to big-endian.
  2. ‘#pragma scalar_storage_order little-endian’ sets the storage order
     of the scalar fields to little-endian.
  3. ‘#pragma scalar_storage_order default’ goes back to the endianness
     that was in effect when compilation started (see also command-line
     option ‘-fsso-struct=ENDIANNESS’ *note C Dialect Options::).


File: gcc.info,  Node: Weak Pragmas,  Next: Diagnostic Pragmas,  Prev: Structure-Layout Pragmas,  Up: Pragmas

6.62.12 Weak Pragmas
--------------------

For compatibility with SVR4, GCC supports a set of ‘#pragma’ directives
for declaring symbols to be weak, and defining weak aliases.

‘#pragma weak SYMBOL’
     This pragma declares SYMBOL to be weak, as if the declaration had
     the attribute of the same name.  The pragma may appear before or
     after the declaration of SYMBOL.  It is not an error for SYMBOL to
     never be defined at all.

‘#pragma weak SYMBOL1 = SYMBOL2’
     This pragma declares SYMBOL1 to be a weak alias of SYMBOL2.  It is
     an error if SYMBOL2 is not defined in the current translation unit.


File: gcc.info,  Node: Diagnostic Pragmas,  Next: Visibility Pragmas,  Prev: Weak Pragmas,  Up: Pragmas

6.62.13 Diagnostic Pragmas
--------------------------

GCC allows the user to selectively enable or disable certain types of
diagnostics, and change the kind of the diagnostic.  For example, a
project's policy might require that all sources compile with ‘-Werror’
but certain files might have exceptions allowing specific types of
warnings.  Or, a project might selectively enable diagnostics and treat
them as errors depending on which preprocessor macros are defined.

‘#pragma GCC diagnostic KIND OPTION’

     Modifies the disposition of a diagnostic.  Note that not all
     diagnostics are modifiable; at the moment only warnings (normally
     controlled by ‘-W...’) can be controlled, and not all of them.  Use
     ‘-fdiagnostics-show-option’ to determine which diagnostics are
     controllable and which option controls them.

     KIND is ‘error’ to treat this diagnostic as an error, ‘warning’ to
     treat it like a warning (even if ‘-Werror’ is in effect), or
     ‘ignored’ if the diagnostic is to be ignored.  OPTION is a double
     quoted string that matches the command-line option.

          #pragma GCC diagnostic warning "-Wformat"
          #pragma GCC diagnostic error "-Wformat"
          #pragma GCC diagnostic ignored "-Wformat"

     Note that these pragmas override any command-line options.  GCC
     keeps track of the location of each pragma, and issues diagnostics
     according to the state as of that point in the source file.  Thus,
     pragmas occurring after a line do not affect diagnostics caused by
     that line.

‘#pragma GCC diagnostic push’
‘#pragma GCC diagnostic pop’

     Causes GCC to remember the state of the diagnostics as of each
     ‘push’, and restore to that point at each ‘pop’.  If a ‘pop’ has no
     matching ‘push’, the command-line options are restored.

          #pragma GCC diagnostic error "-Wuninitialized"
            foo(a);                       /* error is given for this one */
          #pragma GCC diagnostic push
          #pragma GCC diagnostic ignored "-Wuninitialized"
            foo(b);                       /* no diagnostic for this one */
          #pragma GCC diagnostic pop
            foo(c);                       /* error is given for this one */
          #pragma GCC diagnostic pop
            foo(d);                       /* depends on command-line options */

‘#pragma GCC diagnostic ignored_attributes’

     Similarly to ‘-Wno-attributes=’, this pragma allows users to
     suppress warnings about unknown scoped attributes (in C++11 and
     C2X).  For example, ‘#pragma GCC diagnostic ignored_attributes
     "vendor::attr"’ disables warning about the following declaration:

          [[vendor::attr]] void f();

     whereas ‘#pragma GCC diagnostic ignored_attributes "vendor::"’
     prevents warning about both of these declarations:

          [[vendor::safe]] void f();
          [[vendor::unsafe]] void f2();

 GCC also offers a simple mechanism for printing messages during
compilation.

‘#pragma message STRING’

     Prints STRING as a compiler message on compilation.  The message is
     informational only, and is neither a compilation warning nor an
     error.  Newlines can be included in the string by using the ‘\n’
     escape sequence.

          #pragma message "Compiling " __FILE__ "..."

     STRING may be parenthesized, and is printed with location
     information.  For example,

          #define DO_PRAGMA(x) _Pragma (#x)
          #define TODO(x) DO_PRAGMA(message ("TODO - " #x))

          TODO(Remember to fix this)

     prints ‘/tmp/file.c:4: note: #pragma message: TODO - Remember to
     fix this’.

‘#pragma GCC error MESSAGE’
     Generates an error message.  This pragma _is_ considered to
     indicate an error in the compilation, and it will be treated as
     such.

     Newlines can be included in the string by using the ‘\n’ escape
     sequence.  They will be displayed as newlines even if the
     ‘-fmessage-length’ option is set to zero.

     The error is only generated if the pragma is present in the code
     after pre-processing has been completed.  It does not matter
     however if the code containing the pragma is unreachable:

          #if 0
          #pragma GCC error "this error is not seen"
          #endif
          void foo (void)
          {
            return;
          #pragma GCC error "this error is seen"
          }

‘#pragma GCC warning MESSAGE’
     This is just like ‘pragma GCC error’ except that a warning message
     is issued instead of an error message.  Unless ‘-Werror’ is in
     effect, in which case this pragma will generate an error as well.


File: gcc.info,  Node: Visibility Pragmas,  Next: Push/Pop Macro Pragmas,  Prev: Diagnostic Pragmas,  Up: Pragmas

6.62.14 Visibility Pragmas
--------------------------

‘#pragma GCC visibility push(VISIBILITY)’
‘#pragma GCC visibility pop’

     This pragma allows the user to set the visibility for multiple
     declarations without having to give each a visibility attribute
     (*note Function Attributes::).

     In C++, ‘#pragma GCC visibility’ affects only namespace-scope
     declarations.  Class members and template specializations are not
     affected; if you want to override the visibility for a particular
     member or instantiation, you must use an attribute.


File: gcc.info,  Node: Push/Pop Macro Pragmas,  Next: Function Specific Option Pragmas,  Prev: Visibility Pragmas,  Up: Pragmas

6.62.15 Push/Pop Macro Pragmas
------------------------------

For compatibility with Microsoft Windows compilers, GCC supports
‘#pragma push_macro("MACRO_NAME")’ and ‘#pragma
pop_macro("MACRO_NAME")’.

‘#pragma push_macro("MACRO_NAME")’
     This pragma saves the value of the macro named as MACRO_NAME to the
     top of the stack for this macro.

‘#pragma pop_macro("MACRO_NAME")’
     This pragma sets the value of the macro named as MACRO_NAME to the
     value on top of the stack for this macro.  If the stack for
     MACRO_NAME is empty, the value of the macro remains unchanged.

 For example:

     #define X  1
     #pragma push_macro("X")
     #undef X
     #define X -1
     #pragma pop_macro("X")
     int x [X];

In this example, the definition of X as 1 is saved by ‘#pragma
push_macro’ and restored by ‘#pragma pop_macro’.


File: gcc.info,  Node: Function Specific Option Pragmas,  Next: Loop-Specific Pragmas,  Prev: Push/Pop Macro Pragmas,  Up: Pragmas

6.62.16 Function Specific Option Pragmas
----------------------------------------

‘#pragma GCC target (STRING, ...)’

     This pragma allows you to set target-specific options for functions
     defined later in the source file.  One or more strings can be
     specified.  Each function that is defined after this point is
     treated as if it had been declared with one ‘target(’STRING‘)’
     attribute for each STRING argument.  The parentheses around the
     strings in the pragma are optional.  *Note Function Attributes::,
     for more information about the ‘target’ attribute and the attribute
     syntax.

     The ‘#pragma GCC target’ pragma is presently implemented for x86,
     ARM, AArch64, PowerPC, S/390, and Nios II targets only.

‘#pragma GCC optimize (STRING, ...)’

     This pragma allows you to set global optimization options for
     functions defined later in the source file.  One or more strings
     can be specified.  Each function that is defined after this point
     is treated as if it had been declared with one ‘optimize(’STRING‘)’
     attribute for each STRING argument.  The parentheses around the
     strings in the pragma are optional.  *Note Function Attributes::,
     for more information about the ‘optimize’ attribute and the
     attribute syntax.

‘#pragma GCC push_options’
‘#pragma GCC pop_options’

     These pragmas maintain a stack of the current target and
     optimization options.  It is intended for include files where you
     temporarily want to switch to using a different ‘#pragma GCC
     target’ or ‘#pragma GCC optimize’ and then to pop back to the
     previous options.

‘#pragma GCC reset_options’

     This pragma clears the current ‘#pragma GCC target’ and ‘#pragma
     GCC optimize’ to use the default switches as specified on the
     command line.


File: gcc.info,  Node: Loop-Specific Pragmas,  Prev: Function Specific Option Pragmas,  Up: Pragmas

6.62.17 Loop-Specific Pragmas
-----------------------------

‘#pragma GCC ivdep’

     With this pragma, the programmer asserts that there are no
     loop-carried dependencies which would prevent consecutive
     iterations of the following loop from executing concurrently with
     SIMD (single instruction multiple data) instructions.

     For example, the compiler can only unconditionally vectorize the
     following loop with the pragma:

          void foo (int n, int *a, int *b, int *c)
          {
            int i, j;
          #pragma GCC ivdep
            for (i = 0; i < n; ++i)
              a[i] = b[i] + c[i];
          }

     In this example, using the ‘restrict’ qualifier had the same
     effect.  In the following example, that would not be possible.
     Assume k < -m or k >= m.  Only with the pragma, the compiler knows
     that it can unconditionally vectorize the following loop:

          void ignore_vec_dep (int *a, int k, int c, int m)
          {
          #pragma GCC ivdep
            for (int i = 0; i < m; i++)
              a[i] = a[i + k] * c;
          }

‘#pragma GCC unroll N’

     You can use this pragma to control how many times a loop should be
     unrolled.  It must be placed immediately before a ‘for’, ‘while’ or
     ‘do’ loop or a ‘#pragma GCC ivdep’, and applies only to the loop
     that follows.  N is an integer constant expression specifying the
     unrolling factor.  The values of 0 and 1 block any unrolling of the
     loop.


File: gcc.info,  Node: Unnamed Fields,  Next: Thread-Local,  Prev: Pragmas,  Up: C Extensions

6.63 Unnamed Structure and Union Fields
=======================================

As permitted by ISO C11 and for compatibility with other compilers, GCC
allows you to define a structure or union that contains, as fields,
structures and unions without names.  For example:

     struct {
       int a;
       union {
         int b;
         float c;
       };
       int d;
     } foo;

In this example, you are able to access members of the unnamed union
with code like ‘foo.b’.  Note that only unnamed structs and unions are
allowed, you may not have, for example, an unnamed ‘int’.

 You must never create such structures that cause ambiguous field
definitions.  For example, in this structure:

     struct {
       int a;
       struct {
         int a;
       };
     } foo;

it is ambiguous which ‘a’ is being referred to with ‘foo.a’.  The
compiler gives errors for such constructs.

 Unless ‘-fms-extensions’ is used, the unnamed field must be a structure
or union definition without a tag (for example, ‘struct { int a; };’).
If ‘-fms-extensions’ is used, the field may also be a definition with a
tag such as ‘struct foo { int a; };’, a reference to a previously
defined structure or union such as ‘struct foo;’, or a reference to a
‘typedef’ name for a previously defined structure or union type.

 The option ‘-fplan9-extensions’ enables ‘-fms-extensions’ as well as
two other extensions.  First, a pointer to a structure is automatically
converted to a pointer to an anonymous field for assignments and
function calls.  For example:

     struct s1 { int a; };
     struct s2 { struct s1; };
     extern void f1 (struct s1 *);
     void f2 (struct s2 *p) { f1 (p); }

In the call to ‘f1’ inside ‘f2’, the pointer ‘p’ is converted into a
pointer to the anonymous field.

 Second, when the type of an anonymous field is a ‘typedef’ for a
‘struct’ or ‘union’, code may refer to the field using the name of the
‘typedef’.

     typedef struct { int a; } s1;
     struct s2 { s1; };
     s1 f1 (struct s2 *p) { return p->s1; }

 These usages are only permitted when they are not ambiguous.


File: gcc.info,  Node: Thread-Local,  Next: Binary constants,  Prev: Unnamed Fields,  Up: C Extensions

6.64 Thread-Local Storage
=========================

Thread-local storage (TLS) is a mechanism by which variables are
allocated such that there is one instance of the variable per extant
thread.  The runtime model GCC uses to implement this originates in the
IA-64 processor-specific ABI, but has since been migrated to other
processors as well.  It requires significant support from the linker
(‘ld’), dynamic linker (‘ld.so’), and system libraries (‘libc.so’ and
‘libpthread.so’), so it is not available everywhere.

 At the user level, the extension is visible with a new storage class
keyword: ‘__thread’.  For example:

     __thread int i;
     extern __thread struct state s;
     static __thread char *p;

 The ‘__thread’ specifier may be used alone, with the ‘extern’ or
‘static’ specifiers, but with no other storage class specifier.  When
used with ‘extern’ or ‘static’, ‘__thread’ must appear immediately after
the other storage class specifier.

 The ‘__thread’ specifier may be applied to any global, file-scoped
static, function-scoped static, or static data member of a class.  It
may not be applied to block-scoped automatic or non-static data member.

 When the address-of operator is applied to a thread-local variable, it
is evaluated at run time and returns the address of the current thread's
instance of that variable.  An address so obtained may be used by any
thread.  When a thread terminates, any pointers to thread-local
variables in that thread become invalid.

 No static initialization may refer to the address of a thread-local
variable.

 In C++, if an initializer is present for a thread-local variable, it
must be a CONSTANT-EXPRESSION, as defined in 5.19.2 of the ANSI/ISO C++
standard.

 See ELF Handling For Thread-Local Storage
(https://www.akkadia.org/drepper/tls.pdf) for a detailed explanation of
the four thread-local storage addressing models, and how the runtime is
expected to function.

* Menu:

* C99 Thread-Local Edits::
* C++98 Thread-Local Edits::


File: gcc.info,  Node: C99 Thread-Local Edits,  Next: C++98 Thread-Local Edits,  Up: Thread-Local

6.64.1 ISO/IEC 9899:1999 Edits for Thread-Local Storage
-------------------------------------------------------

The following are a set of changes to ISO/IEC 9899:1999 (aka C99) that
document the exact semantics of the language extension.

   • ‘5.1.2 Execution environments’

     Add new text after paragraph 1

          Within either execution environment, a “thread” is a flow of
          control within a program.  It is implementation defined
          whether or not there may be more than one thread associated
          with a program.  It is implementation defined how threads
          beyond the first are created, the name and type of the
          function called at thread startup, and how threads may be
          terminated.  However, objects with thread storage duration
          shall be initialized before thread startup.

   • ‘6.2.4 Storage durations of objects’

     Add new text before paragraph 3

          An object whose identifier is declared with the storage-class
          specifier ‘__thread’ has “thread storage duration”.  Its
          lifetime is the entire execution of the thread, and its stored
          value is initialized only once, prior to thread startup.

   • ‘6.4.1 Keywords’

     Add ‘__thread’.

   • ‘6.7.1 Storage-class specifiers’

     Add ‘__thread’ to the list of storage class specifiers in paragraph
     1.

     Change paragraph 2 to

          With the exception of ‘__thread’, at most one storage-class
          specifier may be given [...].  The ‘__thread’ specifier may be
          used alone, or immediately following ‘extern’ or ‘static’.

     Add new text after paragraph 6

          The declaration of an identifier for a variable that has block
          scope that specifies ‘__thread’ shall also specify either
          ‘extern’ or ‘static’.

          The ‘__thread’ specifier shall be used only with variables.


File: gcc.info,  Node: C++98 Thread-Local Edits,  Prev: C99 Thread-Local Edits,  Up: Thread-Local

6.64.2 ISO/IEC 14882:1998 Edits for Thread-Local Storage
--------------------------------------------------------

The following are a set of changes to ISO/IEC 14882:1998 (aka C++98)
that document the exact semantics of the language extension.

   • [intro.execution]

     New text after paragraph 4

          A “thread” is a flow of control within the abstract machine.
          It is implementation defined whether or not there may be more
          than one thread.

     New text after paragraph 7

          It is unspecified whether additional action must be taken to
          ensure when and whether side effects are visible to other
          threads.

   • [lex.key]

     Add ‘__thread’.

   • [basic.start.main]

     Add after paragraph 5

          The thread that begins execution at the ‘main’ function is
          called the “main thread”.  It is implementation defined how
          functions beginning threads other than the main thread are
          designated or typed.  A function so designated, as well as the
          ‘main’ function, is called a “thread startup function”.  It is
          implementation defined what happens if a thread startup
          function returns.  It is implementation defined what happens
          to other threads when any thread calls ‘exit’.

   • [basic.start.init]

     Add after paragraph 4

          The storage for an object of thread storage duration shall be
          statically initialized before the first statement of the
          thread startup function.  An object of thread storage duration
          shall not require dynamic initialization.

   • [basic.start.term]

     Add after paragraph 3

          The type of an object with thread storage duration shall not
          have a non-trivial destructor, nor shall it be an array type
          whose elements (directly or indirectly) have non-trivial
          destructors.

   • [basic.stc]

     Add "thread storage duration" to the list in paragraph 1.

     Change paragraph 2

          Thread, static, and automatic storage durations are associated
          with objects introduced by declarations [...].

     Add ‘__thread’ to the list of specifiers in paragraph 3.

   • [basic.stc.thread]

     New section before [basic.stc.static]

          The keyword ‘__thread’ applied to a non-local object gives the
          object thread storage duration.

          A local variable or class data member declared both ‘static’
          and ‘__thread’ gives the variable or member thread storage
          duration.

   • [basic.stc.static]

     Change paragraph 1

          All objects that have neither thread storage duration, dynamic
          storage duration nor are local [...].

   • [dcl.stc]

     Add ‘__thread’ to the list in paragraph 1.

     Change paragraph 1

          With the exception of ‘__thread’, at most one
          STORAGE-CLASS-SPECIFIER shall appear in a given
          DECL-SPECIFIER-SEQ.  The ‘__thread’ specifier may be used
          alone, or immediately following the ‘extern’ or ‘static’
          specifiers.  [...]

     Add after paragraph 5

          The ‘__thread’ specifier can be applied only to the names of
          objects and to anonymous unions.

   • [class.mem]

     Add after paragraph 6

          Non-‘static’ members shall not be ‘__thread’.


File: gcc.info,  Node: Binary constants,  Prev: Thread-Local,  Up: C Extensions

6.65 Binary Constants using the ‘0b’ Prefix
===========================================

Integer constants can be written as binary constants, consisting of a
sequence of ‘0’ and ‘1’ digits, prefixed by ‘0b’ or ‘0B’.  This is
particularly useful in environments that operate a lot on the bit level
(like microcontrollers).

 The following statements are identical:

     i =       42;
     i =     0x2a;
     i =      052;
     i = 0b101010;

 The type of these constants follows the same rules as for octal or
hexadecimal integer constants, so suffixes like ‘L’ or ‘UL’ can be
applied.


File: gcc.info,  Node: C++ Extensions,  Next: Objective-C,  Prev: C Extensions,  Up: Top

7 Extensions to the C++ Language
********************************

The GNU compiler provides these extensions to the C++ language (and you
can also use most of the C language extensions in your C++ programs).
If you want to write code that checks whether these features are
available, you can test for the GNU compiler the same way as for C
programs: check for a predefined macro ‘__GNUC__’.  You can also use
‘__GNUG__’ to test specifically for GNU C++ (*note Predefined Macros:
(cpp)Common Predefined Macros.).

* Menu:

* C++ Volatiles::       What constitutes an access to a volatile object.
* Restricted Pointers:: C99 restricted pointers and references.
* Vague Linkage::       Where G++ puts inlines, vtables and such.
* C++ Interface::       You can use a single C++ header file for both
                        declarations and definitions.
* Template Instantiation:: Methods for ensuring that exactly one copy of
                        each needed template instantiation is emitted.
* Bound member functions:: You can extract a function pointer to the
                        method denoted by a ‘->*’ or ‘.*’ expression.
* C++ Attributes::      Variable, function, and type attributes for C++ only.
* Function Multiversioning::   Declaring multiple function versions.
* Type Traits::         Compiler support for type traits.
* C++ Concepts::        Improved support for generic programming.
* Deprecated Features:: Things will disappear from G++.
* Backwards Compatibility:: Compatibilities with earlier definitions of C++.


File: gcc.info,  Node: C++ Volatiles,  Next: Restricted Pointers,  Up: C++ Extensions

7.1 When is a Volatile C++ Object Accessed?
===========================================

The C++ standard differs from the C standard in its treatment of
volatile objects.  It fails to specify what constitutes a volatile
access, except to say that C++ should behave in a similar manner to C
with respect to volatiles, where possible.  However, the different
lvalueness of expressions between C and C++ complicate the behavior.
G++ behaves the same as GCC for volatile access, *Note Volatiles: C
Extensions, for a description of GCC's behavior.

 The C and C++ language specifications differ when an object is accessed
in a void context:

     volatile int *src = SOMEVALUE;
     *src;

 The C++ standard specifies that such expressions do not undergo lvalue
to rvalue conversion, and that the type of the dereferenced object may
be incomplete.  The C++ standard does not specify explicitly that it is
lvalue to rvalue conversion that is responsible for causing an access.
There is reason to believe that it is, because otherwise certain simple
expressions become undefined.  However, because it would surprise most
programmers, G++ treats dereferencing a pointer to volatile object of
complete type as GCC would do for an equivalent type in C.  When the
object has incomplete type, G++ issues a warning; if you wish to force
an error, you must force a conversion to rvalue with, for instance, a
static cast.

 When using a reference to volatile, G++ does not treat equivalent
expressions as accesses to volatiles, but instead issues a warning that
no volatile is accessed.  The rationale for this is that otherwise it
becomes difficult to determine where volatile access occur, and not
possible to ignore the return value from functions returning volatile
references.  Again, if you wish to force a read, cast the reference to
an rvalue.

 G++ implements the same behavior as GCC does when assigning to a
volatile object--there is no reread of the assigned-to object, the
assigned rvalue is reused.  Note that in C++ assignment expressions are
lvalues, and if used as an lvalue, the volatile object is referred to.
For instance, VREF refers to VOBJ, as expected, in the following
example:

     volatile int vobj;
     volatile int &vref = vobj = SOMETHING;


File: gcc.info,  Node: Restricted Pointers,  Next: Vague Linkage,  Prev: C++ Volatiles,  Up: C++ Extensions

7.2 Restricting Pointer Aliasing
================================

As with the C front end, G++ understands the C99 feature of restricted
pointers, specified with the ‘__restrict__’, or ‘__restrict’ type
qualifier.  Because you cannot compile C++ by specifying the ‘-std=c99’
language flag, ‘restrict’ is not a keyword in C++.

 In addition to allowing restricted pointers, you can specify restricted
references, which indicate that the reference is not aliased in the
local context.

     void fn (int *__restrict__ rptr, int &__restrict__ rref)
     {
       /* ... */
     }

In the body of ‘fn’, RPTR points to an unaliased integer and RREF refers
to a (different) unaliased integer.

 You may also specify whether a member function's THIS pointer is
unaliased by using ‘__restrict__’ as a member function qualifier.

     void T::fn () __restrict__
     {
       /* ... */
     }

Within the body of ‘T::fn’, THIS has the effective definition ‘T
*__restrict__ const this’.  Notice that the interpretation of a
‘__restrict__’ member function qualifier is different to that of ‘const’
or ‘volatile’ qualifier, in that it is applied to the pointer rather
than the object.  This is consistent with other compilers that implement
restricted pointers.

 As with all outermost parameter qualifiers, ‘__restrict__’ is ignored
in function definition matching.  This means you only need to specify
‘__restrict__’ in a function definition, rather than in a function
prototype as well.


File: gcc.info,  Node: Vague Linkage,  Next: C++ Interface,  Prev: Restricted Pointers,  Up: C++ Extensions

7.3 Vague Linkage
=================

There are several constructs in C++ that require space in the object
file but are not clearly tied to a single translation unit.  We say that
these constructs have "vague linkage".  Typically such constructs are
emitted wherever they are needed, though sometimes we can be more
clever.

Inline Functions
     Inline functions are typically defined in a header file which can
     be included in many different compilations.  Hopefully they can
     usually be inlined, but sometimes an out-of-line copy is necessary,
     if the address of the function is taken or if inlining fails.  In
     general, we emit an out-of-line copy in all translation units where
     one is needed.  As an exception, we only emit inline virtual
     functions with the vtable, since it always requires a copy.

     Local static variables and string constants used in an inline
     function are also considered to have vague linkage, since they must
     be shared between all inlined and out-of-line instances of the
     function.

VTables
     C++ virtual functions are implemented in most compilers using a
     lookup table, known as a vtable.  The vtable contains pointers to
     the virtual functions provided by a class, and each object of the
     class contains a pointer to its vtable (or vtables, in some
     multiple-inheritance situations).  If the class declares any
     non-inline, non-pure virtual functions, the first one is chosen as
     the "key method" for the class, and the vtable is only emitted in
     the translation unit where the key method is defined.

     _Note:_ If the chosen key method is later defined as inline, the
     vtable is still emitted in every translation unit that defines it.
     Make sure that any inline virtuals are declared inline in the class
     body, even if they are not defined there.

‘type_info’ objects
     C++ requires information about types to be written out in order to
     implement ‘dynamic_cast’, ‘typeid’ and exception handling.  For
     polymorphic classes (classes with virtual functions), the
     ‘type_info’ object is written out along with the vtable so that
     ‘dynamic_cast’ can determine the dynamic type of a class object at
     run time.  For all other types, we write out the ‘type_info’ object
     when it is used: when applying ‘typeid’ to an expression, throwing
     an object, or referring to a type in a catch clause or exception
     specification.

Template Instantiations
     Most everything in this section also applies to template
     instantiations, but there are other options as well.  *Note Where's
     the Template?: Template Instantiation.

 When used with GNU ld version 2.8 or later on an ELF system such as
GNU/Linux or Solaris 2, or on Microsoft Windows, duplicate copies of
these constructs will be discarded at link time.  This is known as
COMDAT support.

 On targets that don't support COMDAT, but do support weak symbols, GCC
uses them.  This way one copy overrides all the others, but the unused
copies still take up space in the executable.

 For targets that do not support either COMDAT or weak symbols, most
entities with vague linkage are emitted as local symbols to avoid
duplicate definition errors from the linker.  This does not happen for
local statics in inlines, however, as having multiple copies almost
certainly breaks things.

 *Note Declarations and Definitions in One Header: C++ Interface, for
another way to control placement of these constructs.


File: gcc.info,  Node: C++ Interface,  Next: Template Instantiation,  Prev: Vague Linkage,  Up: C++ Extensions

7.4 C++ Interface and Implementation Pragmas
============================================

‘#pragma interface’ and ‘#pragma implementation’ provide the user with a
way of explicitly directing the compiler to emit entities with vague
linkage (and debugging information) in a particular translation unit.

 _Note:_ These ‘#pragma’s have been superceded as of GCC 2.7.2 by COMDAT
support and the "key method" heuristic mentioned in *note Vague
Linkage::.  Using them can actually cause your program to grow due to
unnecessary out-of-line copies of inline functions.

‘#pragma interface’
‘#pragma interface "SUBDIR/OBJECTS.h"’
     Use this directive in _header files_ that define object classes, to
     save space in most of the object files that use those classes.
     Normally, local copies of certain information (backup copies of
     inline member functions, debugging information, and the internal
     tables that implement virtual functions) must be kept in each
     object file that includes class definitions.  You can use this
     pragma to avoid such duplication.  When a header file containing
     ‘#pragma interface’ is included in a compilation, this auxiliary
     information is not generated (unless the main input source file
     itself uses ‘#pragma implementation’).  Instead, the object files
     contain references to be resolved at link time.

     The second form of this directive is useful for the case where you
     have multiple headers with the same name in different directories.
     If you use this form, you must specify the same string to ‘#pragma
     implementation’.

‘#pragma implementation’
‘#pragma implementation "OBJECTS.h"’
     Use this pragma in a _main input file_, when you want full output
     from included header files to be generated (and made globally
     visible).  The included header file, in turn, should use ‘#pragma
     interface’.  Backup copies of inline member functions, debugging
     information, and the internal tables used to implement virtual
     functions are all generated in implementation files.

     If you use ‘#pragma implementation’ with no argument, it applies to
     an include file with the same basename(1) as your source file.  For
     example, in ‘allclass.cc’, giving just ‘#pragma implementation’ by
     itself is equivalent to ‘#pragma implementation "allclass.h"’.

     Use the string argument if you want a single implementation file to
     include code from multiple header files.  (You must also use
     ‘#include’ to include the header file; ‘#pragma implementation’
     only specifies how to use the file--it doesn't actually include
     it.)

     There is no way to split up the contents of a single header file
     into multiple implementation files.

 ‘#pragma implementation’ and ‘#pragma interface’ also have an effect on
function inlining.

 If you define a class in a header file marked with ‘#pragma interface’,
the effect on an inline function defined in that class is similar to an
explicit ‘extern’ declaration--the compiler emits no code at all to
define an independent version of the function.  Its definition is used
only for inlining with its callers.

 Conversely, when you include the same header file in a main source file
that declares it as ‘#pragma implementation’, the compiler emits code
for the function itself; this defines a version of the function that can
be found via pointers (or by callers compiled without inlining).  If all
calls to the function can be inlined, you can avoid emitting the
function by compiling with ‘-fno-implement-inlines’.  If any calls are
not inlined, you will get linker errors.

   ---------- Footnotes ----------

   (1) A file's “basename” is the name stripped of all leading path
information and of trailing suffixes, such as ‘.h’ or ‘.C’ or ‘.cc’.


File: gcc.info,  Node: Template Instantiation,  Next: Bound member functions,  Prev: C++ Interface,  Up: C++ Extensions

7.5 Where's the Template?
=========================

C++ templates were the first language feature to require more
intelligence from the environment than was traditionally found on a UNIX
system.  Somehow the compiler and linker have to make sure that each
template instance occurs exactly once in the executable if it is needed,
and not at all otherwise.  There are two basic approaches to this
problem, which are referred to as the Borland model and the Cfront
model.

Borland model
     Borland C++ solved the template instantiation problem by adding the
     code equivalent of common blocks to their linker; the compiler
     emits template instances in each translation unit that uses them,
     and the linker collapses them together.  The advantage of this
     model is that the linker only has to consider the object files
     themselves; there is no external complexity to worry about.  The
     disadvantage is that compilation time is increased because the
     template code is being compiled repeatedly.  Code written for this
     model tends to include definitions of all templates in the header
     file, since they must be seen to be instantiated.

Cfront model
     The AT&T C++ translator, Cfront, solved the template instantiation
     problem by creating the notion of a template repository, an
     automatically maintained place where template instances are stored.
     A more modern version of the repository works as follows: As
     individual object files are built, the compiler places any template
     definitions and instantiations encountered in the repository.  At
     link time, the link wrapper adds in the objects in the repository
     and compiles any needed instances that were not previously emitted.
     The advantages of this model are more optimal compilation speed and
     the ability to use the system linker; to implement the Borland
     model a compiler vendor also needs to replace the linker.  The
     disadvantages are vastly increased complexity, and thus potential
     for error; for some code this can be just as transparent, but in
     practice it can been very difficult to build multiple programs in
     one directory and one program in multiple directories.  Code
     written for this model tends to separate definitions of non-inline
     member templates into a separate file, which should be compiled
     separately.

 G++ implements the Borland model on targets where the linker supports
it, including ELF targets (such as GNU/Linux), Mac OS X and Microsoft
Windows.  Otherwise G++ implements neither automatic model.

 You have the following options for dealing with template
instantiations:

  1. Do nothing.  Code written for the Borland model works fine, but
     each translation unit contains instances of each of the templates
     it uses.  The duplicate instances will be discarded by the linker,
     but in a large program, this can lead to an unacceptable amount of
     code duplication in object files or shared libraries.

     Duplicate instances of a template can be avoided by defining an
     explicit instantiation in one object file, and preventing the
     compiler from doing implicit instantiations in any other object
     files by using an explicit instantiation declaration, using the
     ‘extern template’ syntax:

          extern template int max (int, int);

     This syntax is defined in the C++ 2011 standard, but has been
     supported by G++ and other compilers since well before 2011.

     Explicit instantiations can be used for the largest or most
     frequently duplicated instances, without having to know exactly
     which other instances are used in the rest of the program.  You can
     scatter the explicit instantiations throughout your program,
     perhaps putting them in the translation units where the instances
     are used or the translation units that define the templates
     themselves; you can put all of the explicit instantiations you need
     into one big file; or you can create small files like

          #include "Foo.h"
          #include "Foo.cc"

          template class Foo<int>;
          template ostream& operator <<
                          (ostream&, const Foo<int>&);

     for each of the instances you need, and create a template
     instantiation library from those.

     This is the simplest option, but also offers flexibility and
     fine-grained control when necessary.  It is also the most portable
     alternative and programs using this approach will work with most
     modern compilers.

  2. Compile your code with ‘-fno-implicit-templates’ to disable the
     implicit generation of template instances, and explicitly
     instantiate all the ones you use.  This approach requires more
     knowledge of exactly which instances you need than do the others,
     but it's less mysterious and allows greater control if you want to
     ensure that only the intended instances are used.

     If you are using Cfront-model code, you can probably get away with
     not using ‘-fno-implicit-templates’ when compiling files that don't
     ‘#include’ the member template definitions.

     If you use one big file to do the instantiations, you may want to
     compile it without ‘-fno-implicit-templates’ so you get all of the
     instances required by your explicit instantiations (but not by any
     other files) without having to specify them as well.

     In addition to forward declaration of explicit instantiations (with
     ‘extern’), G++ has extended the template instantiation syntax to
     support instantiation of the compiler support data for a template
     class (i.e. the vtable) without instantiating any of its members
     (with ‘inline’), and instantiation of only the static data members
     of a template class, without the support data or member functions
     (with ‘static’):

          inline template class Foo<int>;
          static template class Foo<int>;


File: gcc.info,  Node: Bound member functions,  Next: C++ Attributes,  Prev: Template Instantiation,  Up: C++ Extensions

7.6 Extracting the Function Pointer from a Bound Pointer to Member Function
===========================================================================

In C++, pointer to member functions (PMFs) are implemented using a wide
pointer of sorts to handle all the possible call mechanisms; the PMF
needs to store information about how to adjust the ‘this’ pointer, and
if the function pointed to is virtual, where to find the vtable, and
where in the vtable to look for the member function.  If you are using
PMFs in an inner loop, you should really reconsider that decision.  If
that is not an option, you can extract the pointer to the function that
would be called for a given object/PMF pair and call it directly inside
the inner loop, to save a bit of time.

 Note that you still pay the penalty for the call through a function
pointer; on most modern architectures, such a call defeats the branch
prediction features of the CPU.  This is also true of normal virtual
function calls.

 The syntax for this extension is

     extern A a;
     extern int (A::*fp)();
     typedef int (*fptr)(A *);

     fptr p = (fptr)(a.*fp);

 For PMF constants (i.e. expressions of the form ‘&Klasse::Member’), no
object is needed to obtain the address of the function.  They can be
converted to function pointers directly:

     fptr p1 = (fptr)(&A::foo);

 You must specify ‘-Wno-pmf-conversions’ to use this extension.


File: gcc.info,  Node: C++ Attributes,  Next: Function Multiversioning,  Prev: Bound member functions,  Up: C++ Extensions

7.7 C++-Specific Variable, Function, and Type Attributes
========================================================

Some attributes only make sense for C++ programs.

‘abi_tag ("TAG", ...)’
     The ‘abi_tag’ attribute can be applied to a function, variable, or
     class declaration.  It modifies the mangled name of the entity to
     incorporate the tag name, in order to distinguish the function or
     class from an earlier version with a different ABI; perhaps the
     class has changed size, or the function has a different return type
     that is not encoded in the mangled name.

     The attribute can also be applied to an inline namespace, but does
     not affect the mangled name of the namespace; in this case it is
     only used for ‘-Wabi-tag’ warnings and automatic tagging of
     functions and variables.  Tagging inline namespaces is generally
     preferable to tagging individual declarations, but the latter is
     sometimes necessary, such as when only certain members of a class
     need to be tagged.

     The argument can be a list of strings of arbitrary length.  The
     strings are sorted on output, so the order of the list is
     unimportant.

     A redeclaration of an entity must not add new ABI tags, since doing
     so would change the mangled name.

     The ABI tags apply to a name, so all instantiations and
     specializations of a template have the same tags.  The attribute
     will be ignored if applied to an explicit specialization or
     instantiation.

     The ‘-Wabi-tag’ flag enables a warning about a class which does not
     have all the ABI tags used by its subobjects and virtual functions;
     for users with code that needs to coexist with an earlier ABI,
     using this option can help to find all affected types that need to
     be tagged.

     When a type involving an ABI tag is used as the type of a variable
     or return type of a function where that tag is not already present
     in the signature of the function, the tag is automatically applied
     to the variable or function.  ‘-Wabi-tag’ also warns about this
     situation; this warning can be avoided by explicitly tagging the
     variable or function or moving it into a tagged inline namespace.

‘init_priority (PRIORITY)’

     In Standard C++, objects defined at namespace scope are guaranteed
     to be initialized in an order in strict accordance with that of
     their definitions _in a given translation unit_.  No guarantee is
     made for initializations across translation units.  However, GNU
     C++ allows users to control the order of initialization of objects
     defined at namespace scope with the ‘init_priority’ attribute by
     specifying a relative PRIORITY, a constant integral expression
     currently bounded between 101 and 65535 inclusive.  Lower numbers
     indicate a higher priority.

     In the following example, ‘A’ would normally be created before ‘B’,
     but the ‘init_priority’ attribute reverses that order:

          Some_Class  A  __attribute__ ((init_priority (2000)));
          Some_Class  B  __attribute__ ((init_priority (543)));

     Note that the particular values of PRIORITY do not matter; only
     their relative ordering.

‘warn_unused’

     For C++ types with non-trivial constructors and/or destructors it
     is impossible for the compiler to determine whether a variable of
     this type is truly unused if it is not referenced.  This type
     attribute informs the compiler that variables of this type should
     be warned about if they appear to be unused, just like variables of
     fundamental types.

     This attribute is appropriate for types which just represent a
     value, such as ‘std::string’; it is not appropriate for types which
     control a resource, such as ‘std::lock_guard’.

     This attribute is also accepted in C, but it is unnecessary because
     C does not have constructors or destructors.


File: gcc.info,  Node: Function Multiversioning,  Next: Type Traits,  Prev: C++ Attributes,  Up: C++ Extensions

7.8 Function Multiversioning
============================

With the GNU C++ front end, for x86 targets, you may specify multiple
versions of a function, where each function is specialized for a
specific target feature.  At runtime, the appropriate version of the
function is automatically executed depending on the characteristics of
the execution platform.  Here is an example.

     __attribute__ ((target ("default")))
     int foo ()
     {
       // The default version of foo.
       return 0;
     }

     __attribute__ ((target ("sse4.2")))
     int foo ()
     {
       // foo version for SSE4.2
       return 1;
     }

     __attribute__ ((target ("arch=atom")))
     int foo ()
     {
       // foo version for the Intel ATOM processor
       return 2;
     }

     __attribute__ ((target ("arch=amdfam10")))
     int foo ()
     {
       // foo version for the AMD Family 0x10 processors.
       return 3;
     }

     int main ()
     {
       int (*p)() = &foo;
       assert ((*p) () == foo ());
       return 0;
     }

 In the above example, four versions of function foo are created.  The
first version of foo with the target attribute "default" is the default
version.  This version gets executed when no other target specific
version qualifies for execution on a particular platform.  A new version
of foo is created by using the same function signature but with a
different target string.  Function foo is called or a pointer to it is
taken just like a regular function.  GCC takes care of doing the
dispatching to call the right version at runtime.  Refer to the GCC wiki
on Function Multiversioning
(https://gcc.gnu.org/wiki/FunctionMultiVersioning) for more details.


File: gcc.info,  Node: Type Traits,  Next: C++ Concepts,  Prev: Function Multiversioning,  Up: C++ Extensions

7.9 Type Traits
===============

The C++ front end implements syntactic extensions that allow
compile-time determination of various characteristics of a type (or of a
pair of types).

‘__has_nothrow_assign (type)’
     If ‘type’ is ‘const’-qualified or is a reference type then the
     trait is ‘false’.  Otherwise if ‘__has_trivial_assign (type)’ is
     ‘true’ then the trait is ‘true’, else if ‘type’ is a cv-qualified
     class or union type with copy assignment operators that are known
     not to throw an exception then the trait is ‘true’, else it is
     ‘false’.  Requires: ‘type’ shall be a complete type, (possibly
     cv-qualified) ‘void’, or an array of unknown bound.

‘__has_nothrow_copy (type)’
     If ‘__has_trivial_copy (type)’ is ‘true’ then the trait is ‘true’,
     else if ‘type’ is a cv-qualified class or union type with copy
     constructors that are known not to throw an exception then the
     trait is ‘true’, else it is ‘false’.  Requires: ‘type’ shall be a
     complete type, (possibly cv-qualified) ‘void’, or an array of
     unknown bound.

‘__has_nothrow_constructor (type)’
     If ‘__has_trivial_constructor (type)’ is ‘true’ then the trait is
     ‘true’, else if ‘type’ is a cv class or union type (or array
     thereof) with a default constructor that is known not to throw an
     exception then the trait is ‘true’, else it is ‘false’.  Requires:
     ‘type’ shall be a complete type, (possibly cv-qualified) ‘void’, or
     an array of unknown bound.

‘__has_trivial_assign (type)’
     If ‘type’ is ‘const’- qualified or is a reference type then the
     trait is ‘false’.  Otherwise if ‘__is_trivial (type)’ is ‘true’
     then the trait is ‘true’, else if ‘type’ is a cv-qualified class or
     union type with a trivial copy assignment ([class.copy]) then the
     trait is ‘true’, else it is ‘false’.  Requires: ‘type’ shall be a
     complete type, (possibly cv-qualified) ‘void’, or an array of
     unknown bound.

‘__has_trivial_copy (type)’
     If ‘__is_trivial (type)’ is ‘true’ or ‘type’ is a reference type
     then the trait is ‘true’, else if ‘type’ is a cv class or union
     type with a trivial copy constructor ([class.copy]) then the trait
     is ‘true’, else it is ‘false’.  Requires: ‘type’ shall be a
     complete type, (possibly cv-qualified) ‘void’, or an array of
     unknown bound.

‘__has_trivial_constructor (type)’
     If ‘__is_trivial (type)’ is ‘true’ then the trait is ‘true’, else
     if ‘type’ is a cv-qualified class or union type (or array thereof)
     with a trivial default constructor ([class.ctor]) then the trait is
     ‘true’, else it is ‘false’.  Requires: ‘type’ shall be a complete
     type, (possibly cv-qualified) ‘void’, or an array of unknown bound.

‘__has_trivial_destructor (type)’
     If ‘__is_trivial (type)’ is ‘true’ or ‘type’ is a reference type
     then the trait is ‘true’, else if ‘type’ is a cv class or union
     type (or array thereof) with a trivial destructor ([class.dtor])
     then the trait is ‘true’, else it is ‘false’.  Requires: ‘type’
     shall be a complete type, (possibly cv-qualified) ‘void’, or an
     array of unknown bound.

‘__has_virtual_destructor (type)’
     If ‘type’ is a class type with a virtual destructor ([class.dtor])
     then the trait is ‘true’, else it is ‘false’.  Requires: ‘type’
     shall be a complete type, (possibly cv-qualified) ‘void’, or an
     array of unknown bound.

‘__is_abstract (type)’
     If ‘type’ is an abstract class ([class.abstract]) then the trait is
     ‘true’, else it is ‘false’.  Requires: ‘type’ shall be a complete
     type, (possibly cv-qualified) ‘void’, or an array of unknown bound.

‘__is_base_of (base_type, derived_type)’
     If ‘base_type’ is a base class of ‘derived_type’ ([class.derived])
     then the trait is ‘true’, otherwise it is ‘false’.  Top-level
     cv-qualifications of ‘base_type’ and ‘derived_type’ are ignored.
     For the purposes of this trait, a class type is considered is own
     base.  Requires: if ‘__is_class (base_type)’ and ‘__is_class
     (derived_type)’ are ‘true’ and ‘base_type’ and ‘derived_type’ are
     not the same type (disregarding cv-qualifiers), ‘derived_type’
     shall be a complete type.  A diagnostic is produced if this
     requirement is not met.

‘__is_class (type)’
     If ‘type’ is a cv-qualified class type, and not a union type
     ([basic.compound]) the trait is ‘true’, else it is ‘false’.

‘__is_empty (type)’
     If ‘__is_class (type)’ is ‘false’ then the trait is ‘false’.
     Otherwise ‘type’ is considered empty if and only if: ‘type’ has no
     non-static data members, or all non-static data members, if any,
     are bit-fields of length 0, and ‘type’ has no virtual members, and
     ‘type’ has no virtual base classes, and ‘type’ has no base classes
     ‘base_type’ for which ‘__is_empty (base_type)’ is ‘false’.
     Requires: ‘type’ shall be a complete type, (possibly cv-qualified)
     ‘void’, or an array of unknown bound.

‘__is_enum (type)’
     If ‘type’ is a cv enumeration type ([basic.compound]) the trait is
     ‘true’, else it is ‘false’.

‘__is_literal_type (type)’
     If ‘type’ is a literal type ([basic.types]) the trait is ‘true’,
     else it is ‘false’.  Requires: ‘type’ shall be a complete type,
     (possibly cv-qualified) ‘void’, or an array of unknown bound.

‘__is_pod (type)’
     If ‘type’ is a cv POD type ([basic.types]) then the trait is
     ‘true’, else it is ‘false’.  Requires: ‘type’ shall be a complete
     type, (possibly cv-qualified) ‘void’, or an array of unknown bound.

‘__is_polymorphic (type)’
     If ‘type’ is a polymorphic class ([class.virtual]) then the trait
     is ‘true’, else it is ‘false’.  Requires: ‘type’ shall be a
     complete type, (possibly cv-qualified) ‘void’, or an array of
     unknown bound.

‘__is_standard_layout (type)’
     If ‘type’ is a standard-layout type ([basic.types]) the trait is
     ‘true’, else it is ‘false’.  Requires: ‘type’ shall be a complete
     type, (possibly cv-qualified) ‘void’, or an array of unknown bound.

‘__is_trivial (type)’
     If ‘type’ is a trivial type ([basic.types]) the trait is ‘true’,
     else it is ‘false’.  Requires: ‘type’ shall be a complete type,
     (possibly cv-qualified) ‘void’, or an array of unknown bound.

‘__is_union (type)’
     If ‘type’ is a cv union type ([basic.compound]) the trait is
     ‘true’, else it is ‘false’.

‘__underlying_type (type)’
     The underlying type of ‘type’.  Requires: ‘type’ shall be an
     enumeration type ([dcl.enum]).

‘__integer_pack (length)’
     When used as the pattern of a pack expansion within a template
     definition, expands to a template argument pack containing integers
     from ‘0’ to ‘length-1’.  This is provided for efficient
     implementation of ‘std::make_integer_sequence’.


File: gcc.info,  Node: C++ Concepts,  Next: Deprecated Features,  Prev: Type Traits,  Up: C++ Extensions

7.10 C++ Concepts
=================

C++ concepts provide much-improved support for generic programming.  In
particular, they allow the specification of constraints on template
arguments.  The constraints are used to extend the usual overloading and
partial specialization capabilities of the language, allowing generic
data structures and algorithms to be "refined" based on their properties
rather than their type names.

 The following keywords are reserved for concepts.

‘assumes’
     States an expression as an assumption, and if possible, verifies
     that the assumption is valid.  For example, ‘assume(n > 0)’.

‘axiom’
     Introduces an axiom definition.  Axioms introduce requirements on
     values.

‘forall’
     Introduces a universally quantified object in an axiom.  For
     example, ‘forall (int n) n + 0 == n’).

‘concept’
     Introduces a concept definition.  Concepts are sets of syntactic
     and semantic requirements on types and their values.

‘requires’
     Introduces constraints on template arguments or requirements for a
     member function of a class template.

 The front end also exposes a number of internal mechanism that can be
used to simplify the writing of type traits.  Note that some of these
traits are likely to be removed in the future.

‘__is_same (type1, type2)’
     A binary type trait: ‘true’ whenever the type arguments are the
     same.


File: gcc.info,  Node: Deprecated Features,  Next: Backwards Compatibility,  Prev: C++ Concepts,  Up: C++ Extensions

7.11 Deprecated Features
========================

In the past, the GNU C++ compiler was extended to experiment with new
features, at a time when the C++ language was still evolving.  Now that
the C++ standard is complete, some of those features are superseded by
superior alternatives.  Using the old features might cause a warning in
some cases that the feature will be dropped in the future.  In other
cases, the feature might be gone already.

 G++ allows a virtual function returning ‘void *’ to be overridden by
one returning a different pointer type.  This extension to the covariant
return type rules is now deprecated and will be removed from a future
version.

 The use of default arguments in function pointers, function typedefs
and other places where they are not permitted by the standard is
deprecated and will be removed from a future version of G++.

 G++ allows floating-point literals to appear in integral constant
expressions, e.g. ‘ enum E { e = int(2.2 * 3.7) } ’ This extension is
deprecated and will be removed from a future version.

 G++ allows static data members of const floating-point type to be
declared with an initializer in a class definition.  The standard only
allows initializers for static members of const integral types and const
enumeration types so this extension has been deprecated and will be
removed from a future version.

 G++ allows attributes to follow a parenthesized direct initializer,
e.g. ‘ int f (0) __attribute__ ((something)); ’ This extension has been
ignored since G++ 3.3 and is deprecated.

 G++ allows anonymous structs and unions to have members that are not
public non-static data members (i.e. fields).  These extensions are
deprecated.


File: gcc.info,  Node: Backwards Compatibility,  Prev: Deprecated Features,  Up: C++ Extensions

7.12 Backwards Compatibility
============================

Now that there is a definitive ISO standard C++, G++ has a specification
to adhere to.  The C++ language evolved over time, and features that
used to be acceptable in previous drafts of the standard, such as the
ARM [Annotated C++ Reference Manual], are no longer accepted.  In order
to allow compilation of C++ written to such drafts, G++ contains some
backwards compatibilities.  _All such backwards compatibility features
are liable to disappear in future versions of G++._  They should be
considered deprecated.  *Note Deprecated Features::.

‘Implicit C language’
     Old C system header files did not contain an ‘extern "C" {...}’
     scope to set the language.  On such systems, all system header
     files are implicitly scoped inside a C language scope.  Such
     headers must correctly prototype function argument types, there is
     no leeway for ‘()’ to indicate an unspecified set of arguments.


File: gcc.info,  Node: Objective-C,  Next: Compatibility,  Prev: C++ Extensions,  Up: Top

8 GNU Objective-C Features
**************************

This document is meant to describe some of the GNU Objective-C features.
It is not intended to teach you Objective-C. There are several resources
on the Internet that present the language.

* Menu:

* GNU Objective-C runtime API::
* Executing code before main::
* Type encoding::
* Garbage Collection::
* Constant string objects::
* compatibility_alias::
* Exceptions::
* Synchronization::
* Fast enumeration::
* Messaging with the GNU Objective-C runtime::


File: gcc.info,  Node: GNU Objective-C runtime API,  Next: Executing code before main,  Up: Objective-C

8.1 GNU Objective-C Runtime API
===============================

This section is specific for the GNU Objective-C runtime.  If you are
using a different runtime, you can skip it.

 The GNU Objective-C runtime provides an API that allows you to interact
with the Objective-C runtime system, querying the live runtime
structures and even manipulating them.  This allows you for example to
inspect and navigate classes, methods and protocols; to define new
classes or new methods, and even to modify existing classes or
protocols.

 If you are using a "Foundation" library such as GNUstep-Base, this
library will provide you with a rich set of functionality to do most of
the inspection tasks, and you probably will only need direct access to
the GNU Objective-C runtime API to define new classes or methods.

* Menu:

* Modern GNU Objective-C runtime API::
* Traditional GNU Objective-C runtime API::


File: gcc.info,  Node: Modern GNU Objective-C runtime API,  Next: Traditional GNU Objective-C runtime API,  Up: GNU Objective-C runtime API

8.1.1 Modern GNU Objective-C Runtime API
----------------------------------------

The GNU Objective-C runtime provides an API which is similar to the one
provided by the "Objective-C 2.0" Apple/NeXT Objective-C runtime.  The
API is documented in the public header files of the GNU Objective-C
runtime:

   • ‘objc/objc.h’: this is the basic Objective-C header file, defining
     the basic Objective-C types such as ‘id’, ‘Class’ and ‘BOOL’.  You
     have to include this header to do almost anything with Objective-C.

   • ‘objc/runtime.h’: this header declares most of the public runtime
     API functions allowing you to inspect and manipulate the
     Objective-C runtime data structures.  These functions are fairly
     standardized across Objective-C runtimes and are almost identical
     to the Apple/NeXT Objective-C runtime ones.  It does not declare
     functions in some specialized areas (constructing and forwarding
     message invocations, threading) which are in the other headers
     below.  You have to include ‘objc/objc.h’ and ‘objc/runtime.h’ to
     use any of the functions, such as ‘class_getName()’, declared in
     ‘objc/runtime.h’.

   • ‘objc/message.h’: this header declares public functions used to
     construct, deconstruct and forward message invocations.  Because
     messaging is done in quite a different way on different runtimes,
     functions in this header are specific to the GNU Objective-C
     runtime implementation.

   • ‘objc/objc-exception.h’: this header declares some public functions
     related to Objective-C exceptions.  For example functions in this
     header allow you to throw an Objective-C exception from plain C/C++
     code.

   • ‘objc/objc-sync.h’: this header declares some public functions
     related to the Objective-C ‘@synchronized()’ syntax, allowing you
     to emulate an Objective-C ‘@synchronized()’ block in plain C/C++
     code.

   • ‘objc/thr.h’: this header declares a public runtime API threading
     layer that is only provided by the GNU Objective-C runtime.  It
     declares functions such as ‘objc_mutex_lock()’, which provide a
     platform-independent set of threading functions.

 The header files contain detailed documentation for each function in
the GNU Objective-C runtime API.


File: gcc.info,  Node: Traditional GNU Objective-C runtime API,  Prev: Modern GNU Objective-C runtime API,  Up: GNU Objective-C runtime API

8.1.2 Traditional GNU Objective-C Runtime API
---------------------------------------------

The GNU Objective-C runtime used to provide a different API, which we
call the "traditional" GNU Objective-C runtime API. Functions belonging
to this API are easy to recognize because they use a different naming
convention, such as ‘class_get_super_class()’ (traditional API) instead
of ‘class_getSuperclass()’ (modern API). Software using this API
includes the file ‘objc/objc-api.h’ where it is declared.

 Starting with GCC 4.7.0, the traditional GNU runtime API is no longer
available.


File: gcc.info,  Node: Executing code before main,  Next: Type encoding,  Prev: GNU Objective-C runtime API,  Up: Objective-C

8.2 ‘+load’: Executing Code before ‘main’
=========================================

This section is specific for the GNU Objective-C runtime.  If you are
using a different runtime, you can skip it.

 The GNU Objective-C runtime provides a way that allows you to execute
code before the execution of the program enters the ‘main’ function.
The code is executed on a per-class and a per-category basis, through a
special class method ‘+load’.

 This facility is very useful if you want to initialize global variables
which can be accessed by the program directly, without sending a message
to the class first.  The usual way to initialize global variables, in
the ‘+initialize’ method, might not be useful because ‘+initialize’ is
only called when the first message is sent to a class object, which in
some cases could be too late.

 Suppose for example you have a ‘FileStream’ class that declares
‘Stdin’, ‘Stdout’ and ‘Stderr’ as global variables, like below:


     FileStream *Stdin = nil;
     FileStream *Stdout = nil;
     FileStream *Stderr = nil;

     @implementation FileStream

     + (void)initialize
     {
         Stdin = [[FileStream new] initWithFd:0];
         Stdout = [[FileStream new] initWithFd:1];
         Stderr = [[FileStream new] initWithFd:2];
     }

     /* Other methods here */
     @end

 In this example, the initialization of ‘Stdin’, ‘Stdout’ and ‘Stderr’
in ‘+initialize’ occurs too late.  The programmer can send a message to
one of these objects before the variables are actually initialized, thus
sending messages to the ‘nil’ object.  The ‘+initialize’ method which
actually initializes the global variables is not invoked until the first
message is sent to the class object.  The solution would require these
variables to be initialized just before entering ‘main’.

 The correct solution of the above problem is to use the ‘+load’ method
instead of ‘+initialize’:


     @implementation FileStream

     + (void)load
     {
         Stdin = [[FileStream new] initWithFd:0];
         Stdout = [[FileStream new] initWithFd:1];
         Stderr = [[FileStream new] initWithFd:2];
     }

     /* Other methods here */
     @end

 The ‘+load’ is a method that is not overridden by categories.  If a
class and a category of it both implement ‘+load’, both methods are
invoked.  This allows some additional initializations to be performed in
a category.

 This mechanism is not intended to be a replacement for ‘+initialize’.
You should be aware of its limitations when you decide to use it instead
of ‘+initialize’.

* Menu:

* What you can and what you cannot do in +load::


File: gcc.info,  Node: What you can and what you cannot do in +load,  Up: Executing code before main

8.2.1 What You Can and Cannot Do in ‘+load’
-------------------------------------------

‘+load’ is to be used only as a last resort.  Because it is executed
very early, most of the Objective-C runtime machinery will not be ready
when ‘+load’ is executed; hence ‘+load’ works best for executing C code
that is independent on the Objective-C runtime.

 The ‘+load’ implementation in the GNU runtime guarantees you the
following things:

   • you can write whatever C code you like;

   • you can allocate and send messages to objects whose class is
     implemented in the same file;

   • the ‘+load’ implementation of all super classes of a class are
     executed before the ‘+load’ of that class is executed;

   • the ‘+load’ implementation of a class is executed before the
     ‘+load’ implementation of any category.

 In particular, the following things, even if they can work in a
particular case, are not guaranteed:

   • allocation of or sending messages to arbitrary objects;

   • allocation of or sending messages to objects whose classes have a
     category implemented in the same file;

   • sending messages to Objective-C constant strings (‘@"this is a
     constant string"’);

 You should make no assumptions about receiving ‘+load’ in sibling
classes when you write ‘+load’ of a class.  The order in which sibling
classes receive ‘+load’ is not guaranteed.

 The order in which ‘+load’ and ‘+initialize’ are called could be
problematic if this matters.  If you don't allocate objects inside
‘+load’, it is guaranteed that ‘+load’ is called before ‘+initialize’.
If you create an object inside ‘+load’ the ‘+initialize’ method of
object's class is invoked even if ‘+load’ was not invoked.  Note if you
explicitly call ‘+load’ on a class, ‘+initialize’ will be called first.
To avoid possible problems try to implement only one of these methods.

 The ‘+load’ method is also invoked when a bundle is dynamically loaded
into your running program.  This happens automatically without any
intervening operation from you.  When you write bundles and you need to
write ‘+load’ you can safely create and send messages to objects whose
classes already exist in the running program.  The same restrictions as
above apply to classes defined in bundle.


File: gcc.info,  Node: Type encoding,  Next: Garbage Collection,  Prev: Executing code before main,  Up: Objective-C

8.3 Type Encoding
=================

This is an advanced section.  Type encodings are used extensively by the
compiler and by the runtime, but you generally do not need to know about
them to use Objective-C.

 The Objective-C compiler generates type encodings for all the types.
These type encodings are used at runtime to find out information about
selectors and methods and about objects and classes.

 The types are encoded in the following way:

‘_Bool’            ‘B’
‘char’             ‘c’
‘unsigned char’    ‘C’
‘short’            ‘s’
‘unsigned short’   ‘S’
‘int’              ‘i’
‘unsigned int’     ‘I’
‘long’             ‘l’
‘unsigned long’    ‘L’
‘long long’        ‘q’
‘unsigned long     ‘Q’
long’
‘float’            ‘f’
‘double’           ‘d’
‘long double’      ‘D’
‘void’             ‘v’
‘id’               ‘@’
‘Class’            ‘#’
‘SEL’              ‘:’
‘char*’            ‘*’
‘enum’             an ‘enum’ is encoded exactly as the integer type
                   that the compiler uses for it, which depends on the
                   enumeration values.  Often the compiler users
                   ‘unsigned int’, which is then encoded as ‘I’.
unknown type       ‘?’
Complex types      ‘j’ followed by the inner type.  For example
                   ‘_Complex double’ is encoded as "jd".
bit-fields         ‘b’ followed by the starting position of the
                   bit-field, the type of the bit-field and the size of
                   the bit-field (the bit-fields encoding was changed
                   from the NeXT's compiler encoding, see below)

 The encoding of bit-fields has changed to allow bit-fields to be
properly handled by the runtime functions that compute sizes and
alignments of types that contain bit-fields.  The previous encoding
contained only the size of the bit-field.  Using only this information
it is not possible to reliably compute the size occupied by the
bit-field.  This is very important in the presence of the Boehm's
garbage collector because the objects are allocated using the typed
memory facility available in this collector.  The typed memory
allocation requires information about where the pointers are located
inside the object.

 The position in the bit-field is the position, counting in bits, of the
bit closest to the beginning of the structure.

 The non-atomic types are encoded as follows:

pointers       ‘^’ followed by the pointed type.
arrays         ‘[’ followed by the number of elements in the array
               followed by the type of the elements followed by ‘]’
structures     ‘{’ followed by the name of the structure (or ‘?’ if the
               structure is unnamed), the ‘=’ sign, the type of the
               members and by ‘}’
unions         ‘(’ followed by the name of the structure (or ‘?’ if the
               union is unnamed), the ‘=’ sign, the type of the members
               followed by ‘)’
vectors        ‘![’ followed by the vector_size (the number of bytes
               composing the vector) followed by a comma, followed by
               the alignment (in bytes) of the vector, followed by the
               type of the elements followed by ‘]’

 Here are some types and their encodings, as they are generated by the
compiler on an i386 machine:


Objective-C type                            Compiler encoding
--------------------------------------------------------------------------
     int a[10];                             ‘[10i]’
     struct {                               ‘{?=i[3f]b128i3b131i2c}’
       int i;
       float f[3];
       int a:3;
       int b:2;
       char c;
     }
     int a __attribute__ ((vector_size (16)));‘![16,16i]’ (alignment
                                            depends on the machine)


 In addition to the types the compiler also encodes the type specifiers.
The table below describes the encoding of the current Objective-C type
specifiers:


Specifier          Encoding
--------------------------------------------------------------------------
‘const’            ‘r’
‘in’               ‘n’
‘inout’            ‘N’
‘out’              ‘o’
‘bycopy’           ‘O’
‘byref’            ‘R’
‘oneway’           ‘V’


 The type specifiers are encoded just before the type.  Unlike types
however, the type specifiers are only encoded when they appear in method
argument types.

 Note how ‘const’ interacts with pointers:


Objective-C type   Compiler encoding
--------------------------------------------------------------------------
     const int     ‘ri’
     const int*    ‘^ri’
     int *const    ‘r^i’


 ‘const int*’ is a pointer to a ‘const int’, and so is encoded as ‘^ri’.
‘int* const’, instead, is a ‘const’ pointer to an ‘int’, and so is
encoded as ‘r^i’.

 Finally, there is a complication when encoding ‘const char *’ versus
‘char * const’.  Because ‘char *’ is encoded as ‘*’ and not as ‘^c’,
there is no way to express the fact that ‘r’ applies to the pointer or
to the pointee.

 Hence, it is assumed as a convention that ‘r*’ means ‘const char *’
(since it is what is most often meant), and there is no way to encode
‘char *const’.  ‘char *const’ would simply be encoded as ‘*’, and the
‘const’ is lost.

* Menu:

* Legacy type encoding::
* @encode::
* Method signatures::


File: gcc.info,  Node: Legacy type encoding,  Next: @encode,  Up: Type encoding

8.3.1 Legacy Type Encoding
--------------------------

Unfortunately, historically GCC used to have a number of bugs in its
encoding code.  The NeXT runtime expects GCC to emit type encodings in
this historical format (compatible with GCC-3.3), so when using the NeXT
runtime, GCC will introduce on purpose a number of incorrect encodings:

   • the read-only qualifier of the pointee gets emitted before the '^'.
     The read-only qualifier of the pointer itself gets ignored, unless
     it is a typedef.  Also, the 'r' is only emitted for the outermost
     type.

   • 32-bit longs are encoded as 'l' or 'L', but not always.  For
     typedefs, the compiler uses 'i' or 'I' instead if encoding a struct
     field or a pointer.

   • ‘enum’s are always encoded as 'i' (int) even if they are actually
     unsigned or long.

 In addition to that, the NeXT runtime uses a different encoding for
bitfields.  It encodes them as ‘b’ followed by the size, without a bit
offset or the underlying field type.


File: gcc.info,  Node: @encode,  Next: Method signatures,  Prev: Legacy type encoding,  Up: Type encoding

8.3.2 ‘@encode’
---------------

GNU Objective-C supports the ‘@encode’ syntax that allows you to create
a type encoding from a C/Objective-C type.  For example, ‘@encode(int)’
is compiled by the compiler into ‘"i"’.

 ‘@encode’ does not support type qualifiers other than ‘const’.  For
example, ‘@encode(const char*)’ is valid and is compiled into ‘"r*"’,
while ‘@encode(bycopy char *)’ is invalid and will cause a compilation
error.


File: gcc.info,  Node: Method signatures,  Prev: @encode,  Up: Type encoding

8.3.3 Method Signatures
-----------------------

This section documents the encoding of method types, which is rarely
needed to use Objective-C. You should skip it at a first reading; the
runtime provides functions that will work on methods and can walk
through the list of parameters and interpret them for you.  These
functions are part of the public "API" and are the preferred way to
interact with method signatures from user code.

 But if you need to debug a problem with method signatures and need to
know how they are implemented (i.e., the "ABI"), read on.

 Methods have their "signature" encoded and made available to the
runtime.  The "signature" encodes all the information required to
dynamically build invocations of the method at runtime: return type and
arguments.

 The "signature" is a null-terminated string, composed of the following:

   • The return type, including type qualifiers.  For example, a method
     returning ‘int’ would have ‘i’ here.

   • The total size (in bytes) required to pass all the parameters.
     This includes the two hidden parameters (the object ‘self’ and the
     method selector ‘_cmd’).

   • Each argument, with the type encoding, followed by the offset (in
     bytes) of the argument in the list of parameters.

 For example, a method with no arguments and returning ‘int’ would have
the signature ‘i8@0:4’ if the size of a pointer is 4.  The signature is
interpreted as follows: the ‘i’ is the return type (an ‘int’), the ‘8’
is the total size of the parameters in bytes (two pointers each of size
4), the ‘@0’ is the first parameter (an object at byte offset ‘0’) and
‘:4’ is the second parameter (a ‘SEL’ at byte offset ‘4’).

 You can easily find more examples by running the "strings" program on
an Objective-C object file compiled by GCC. You'll see a lot of strings
that look very much like ‘i8@0:4’.  They are signatures of Objective-C
methods.


File: gcc.info,  Node: Garbage Collection,  Next: Constant string objects,  Prev: Type encoding,  Up: Objective-C

8.4 Garbage Collection
======================

This section is specific for the GNU Objective-C runtime.  If you are
using a different runtime, you can skip it.

 Support for garbage collection with the GNU runtime has been added by
using a powerful conservative garbage collector, known as the
Boehm-Demers-Weiser conservative garbage collector.

 To enable the support for it you have to configure the compiler using
an additional argument, ‘--enable-objc-gc’.  This will build the
boehm-gc library, and build an additional runtime library which has
several enhancements to support the garbage collector.  The new library
has a new name, ‘libobjc_gc.a’ to not conflict with the
non-garbage-collected library.

 When the garbage collector is used, the objects are allocated using the
so-called typed memory allocation mechanism available in the
Boehm-Demers-Weiser collector.  This mode requires precise information
on where pointers are located inside objects.  This information is
computed once per class, immediately after the class has been
initialized.

 There is a new runtime function ‘class_ivar_set_gcinvisible()’ which
can be used to declare a so-called “weak pointer” reference.  Such a
pointer is basically hidden for the garbage collector; this can be
useful in certain situations, especially when you want to keep track of
the allocated objects, yet allow them to be collected.  This kind of
pointers can only be members of objects, you cannot declare a global
pointer as a weak reference.  Every type which is a pointer type can be
declared a weak pointer, including ‘id’, ‘Class’ and ‘SEL’.

 Here is an example of how to use this feature.  Suppose you want to
implement a class whose instances hold a weak pointer reference; the
following class does this:


     @interface WeakPointer : Object
     {
         const void* weakPointer;
     }

     - initWithPointer:(const void*)p;
     - (const void*)weakPointer;
     @end


     @implementation WeakPointer

     + (void)initialize
     {
       if (self == objc_lookUpClass ("WeakPointer"))
         class_ivar_set_gcinvisible (self, "weakPointer", YES);
     }

     - initWithPointer:(const void*)p
     {
       weakPointer = p;
       return self;
     }

     - (const void*)weakPointer
     {
       return weakPointer;
     }

     @end

 Weak pointers are supported through a new type character specifier
represented by the ‘!’ character.  The ‘class_ivar_set_gcinvisible()’
function adds or removes this specifier to the string type description
of the instance variable named as argument.


File: gcc.info,  Node: Constant string objects,  Next: compatibility_alias,  Prev: Garbage Collection,  Up: Objective-C

8.5 Constant String Objects
===========================

GNU Objective-C provides constant string objects that are generated
directly by the compiler.  You declare a constant string object by
prefixing a C constant string with the character ‘@’:

       id myString = @"this is a constant string object";

 The constant string objects are by default instances of the
‘NXConstantString’ class which is provided by the GNU Objective-C
runtime.  To get the definition of this class you must include the
‘objc/NXConstStr.h’ header file.

 User defined libraries may want to implement their own constant string
class.  To be able to support them, the GNU Objective-C compiler
provides a new command line options
‘-fconstant-string-class=CLASS-NAME’.  The provided class should adhere
to a strict structure, the same as ‘NXConstantString’'s structure:


     @interface MyConstantStringClass
     {
       Class isa;
       char *c_string;
       unsigned int len;
     }
     @end

 ‘NXConstantString’ inherits from ‘Object’; user class libraries may
choose to inherit the customized constant string class from a different
class than ‘Object’.  There is no requirement in the methods the
constant string class has to implement, but the final ivar layout of the
class must be the compatible with the given structure.

 When the compiler creates the statically allocated constant string
object, the ‘c_string’ field will be filled by the compiler with the
string; the ‘length’ field will be filled by the compiler with the
string length; the ‘isa’ pointer will be filled with ‘NULL’ by the
compiler, and it will later be fixed up automatically at runtime by the
GNU Objective-C runtime library to point to the class which was set by
the ‘-fconstant-string-class’ option when the object file is loaded (if
you wonder how it works behind the scenes, the name of the class to use,
and the list of static objects to fixup, are stored by the compiler in
the object file in a place where the GNU runtime library will find them
at runtime).

 As a result, when a file is compiled with the ‘-fconstant-string-class’
option, all the constant string objects will be instances of the class
specified as argument to this option.  It is possible to have multiple
compilation units referring to different constant string classes,
neither the compiler nor the linker impose any restrictions in doing
this.


File: gcc.info,  Node: compatibility_alias,  Next: Exceptions,  Prev: Constant string objects,  Up: Objective-C

8.6 ‘compatibility_alias’
=========================

The keyword ‘@compatibility_alias’ allows you to define a class name as
equivalent to another class name.  For example:

     @compatibility_alias WOApplication GSWApplication;

 tells the compiler that each time it encounters ‘WOApplication’ as a
class name, it should replace it with ‘GSWApplication’ (that is,
‘WOApplication’ is just an alias for ‘GSWApplication’).

 There are some constraints on how this can be used--

   • ‘WOApplication’ (the alias) must not be an existing class;

   • ‘GSWApplication’ (the real class) must be an existing class.


File: gcc.info,  Node: Exceptions,  Next: Synchronization,  Prev: compatibility_alias,  Up: Objective-C

8.7 Exceptions
==============

GNU Objective-C provides exception support built into the language, as
in the following example:

       @try {
         ...
            @throw expr;
         ...
       }
       @catch (AnObjCClass *exc) {
         ...
           @throw expr;
         ...
           @throw;
         ...
       }
       @catch (AnotherClass *exc) {
         ...
       }
       @catch (id allOthers) {
         ...
       }
       @finally {
         ...
           @throw expr;
         ...
       }

 The ‘@throw’ statement may appear anywhere in an Objective-C or
Objective-C++ program; when used inside of a ‘@catch’ block, the
‘@throw’ may appear without an argument (as shown above), in which case
the object caught by the ‘@catch’ will be rethrown.

 Note that only (pointers to) Objective-C objects may be thrown and
caught using this scheme.  When an object is thrown, it will be caught
by the nearest ‘@catch’ clause capable of handling objects of that type,
analogously to how ‘catch’ blocks work in C++ and Java.  A ‘@catch(id
...)’ clause (as shown above) may also be provided to catch any and all
Objective-C exceptions not caught by previous ‘@catch’ clauses (if any).

 The ‘@finally’ clause, if present, will be executed upon exit from the
immediately preceding ‘@try ... @catch’ section.  This will happen
regardless of whether any exceptions are thrown, caught or rethrown
inside the ‘@try ... @catch’ section, analogously to the behavior of the
‘finally’ clause in Java.

 There are several caveats to using the new exception mechanism:

   • The ‘-fobjc-exceptions’ command line option must be used when
     compiling Objective-C files that use exceptions.

   • With the GNU runtime, exceptions are always implemented as "native"
     exceptions and it is recommended that the ‘-fexceptions’ and
     ‘-shared-libgcc’ options are used when linking.

   • With the NeXT runtime, although currently designed to be binary
     compatible with ‘NS_HANDLER’-style idioms provided by the
     ‘NSException’ class, the new exceptions can only be used on Mac OS
     X 10.3 (Panther) and later systems, due to additional functionality
     needed in the NeXT Objective-C runtime.

   • As mentioned above, the new exceptions do not support handling
     types other than Objective-C objects.  Furthermore, when used from
     Objective-C++, the Objective-C exception model does not
     interoperate with C++ exceptions at this time.  This means you
     cannot ‘@throw’ an exception from Objective-C and ‘catch’ it in
     C++, or vice versa (i.e., ‘throw ... @catch’).


File: gcc.info,  Node: Synchronization,  Next: Fast enumeration,  Prev: Exceptions,  Up: Objective-C

8.8 Synchronization
===================

GNU Objective-C provides support for synchronized blocks:

       @synchronized (ObjCClass *guard) {
         ...
       }

 Upon entering the ‘@synchronized’ block, a thread of execution shall
first check whether a lock has been placed on the corresponding ‘guard’
object by another thread.  If it has, the current thread shall wait
until the other thread relinquishes its lock.  Once ‘guard’ becomes
available, the current thread will place its own lock on it, execute the
code contained in the ‘@synchronized’ block, and finally relinquish the
lock (thereby making ‘guard’ available to other threads).

 Unlike Java, Objective-C does not allow for entire methods to be marked
‘@synchronized’.  Note that throwing exceptions out of ‘@synchronized’
blocks is allowed, and will cause the guarding object to be unlocked
properly.

 Because of the interactions between synchronization and exception
handling, you can only use ‘@synchronized’ when compiling with
exceptions enabled, that is with the command line option
‘-fobjc-exceptions’.


File: gcc.info,  Node: Fast enumeration,  Next: Messaging with the GNU Objective-C runtime,  Prev: Synchronization,  Up: Objective-C

8.9 Fast Enumeration
====================

* Menu:

* Using fast enumeration::
* c99-like fast enumeration syntax::
* Fast enumeration details::
* Fast enumeration protocol::


File: gcc.info,  Node: Using fast enumeration,  Next: c99-like fast enumeration syntax,  Up: Fast enumeration

8.9.1 Using Fast Enumeration
----------------------------

GNU Objective-C provides support for the fast enumeration syntax:

       id array = ...;
       id object;

       for (object in array)
       {
         /* Do something with 'object' */
       }

 ‘array’ needs to be an Objective-C object (usually a collection object,
for example an array, a dictionary or a set) which implements the "Fast
Enumeration Protocol" (see below).  If you are using a Foundation
library such as GNUstep Base or Apple Cocoa Foundation, all collection
objects in the library implement this protocol and can be used in this
way.

 The code above would iterate over all objects in ‘array’.  For each of
them, it assigns it to ‘object’, then executes the ‘Do something with
'object'’ statements.

 Here is a fully worked-out example using a Foundation library (which
provides the implementation of ‘NSArray’, ‘NSString’ and ‘NSLog’):

       NSArray *array = [NSArray arrayWithObjects: @"1", @"2", @"3", nil];
       NSString *object;

       for (object in array)
         NSLog (@"Iterating over %@", object);


File: gcc.info,  Node: c99-like fast enumeration syntax,  Next: Fast enumeration details,  Prev: Using fast enumeration,  Up: Fast enumeration

8.9.2 C99-Like Fast Enumeration Syntax
--------------------------------------

A c99-like declaration syntax is also allowed:

       id array = ...;

       for (id object in array)
       {
         /* Do something with 'object'  */
       }

 this is completely equivalent to:

       id array = ...;

       {
         id object;
         for (object in array)
         {
           /* Do something with 'object'  */
         }
       }

 but can save some typing.

 Note that the option ‘-std=c99’ is not required to allow this syntax in
Objective-C.


File: gcc.info,  Node: Fast enumeration details,  Next: Fast enumeration protocol,  Prev: c99-like fast enumeration syntax,  Up: Fast enumeration

8.9.3 Fast Enumeration Details
------------------------------

Here is a more technical description with the gory details.  Consider
the code

       for (OBJECT EXPRESSION in COLLECTION EXPRESSION)
       {
         STATEMENTS
       }

 here is what happens when you run it:

   • ‘COLLECTION EXPRESSION’ is evaluated exactly once and the result is
     used as the collection object to iterate over.  This means it is
     safe to write code such as ‘for (object in [NSDictionary
     keyEnumerator]) ...’.

   • the iteration is implemented by the compiler by repeatedly getting
     batches of objects from the collection object using the fast
     enumeration protocol (see below), then iterating over all objects
     in the batch.  This is faster than a normal enumeration where
     objects are retrieved one by one (hence the name "fast
     enumeration").

   • if there are no objects in the collection, then ‘OBJECT EXPRESSION’
     is set to ‘nil’ and the loop immediately terminates.

   • if there are objects in the collection, then for each object in the
     collection (in the order they are returned) ‘OBJECT EXPRESSION’ is
     set to the object, then ‘STATEMENTS’ are executed.

   • ‘STATEMENTS’ can contain ‘break’ and ‘continue’ commands, which
     will abort the iteration or skip to the next loop iteration as
     expected.

   • when the iteration ends because there are no more objects to
     iterate over, ‘OBJECT EXPRESSION’ is set to ‘nil’.  This allows you
     to determine whether the iteration finished because a ‘break’
     command was used (in which case ‘OBJECT EXPRESSION’ will remain set
     to the last object that was iterated over) or because it iterated
     over all the objects (in which case ‘OBJECT EXPRESSION’ will be set
     to ‘nil’).

   • ‘STATEMENTS’ must not make any changes to the collection object; if
     they do, it is a hard error and the fast enumeration terminates by
     invoking ‘objc_enumerationMutation’, a runtime function that
     normally aborts the program but which can be customized by
     Foundation libraries via ‘objc_set_mutation_handler’ to do
     something different, such as raising an exception.


File: gcc.info,  Node: Fast enumeration protocol,  Prev: Fast enumeration details,  Up: Fast enumeration

8.9.4 Fast Enumeration Protocol
-------------------------------

If you want your own collection object to be usable with fast
enumeration, you need to have it implement the method

     - (unsigned long) countByEnumeratingWithState: (NSFastEnumerationState *)state
                                           objects: (id *)objects
                                             count: (unsigned long)len;

 where ‘NSFastEnumerationState’ must be defined in your code as follows:

     typedef struct
     {
       unsigned long state;
       id            *itemsPtr;
       unsigned long *mutationsPtr;
       unsigned long extra[5];
     } NSFastEnumerationState;

 If no ‘NSFastEnumerationState’ is defined in your code, the compiler
will automatically replace ‘NSFastEnumerationState *’ with ‘struct
__objcFastEnumerationState *’, where that type is silently defined by
the compiler in an identical way.  This can be confusing and we
recommend that you define ‘NSFastEnumerationState’ (as shown above)
instead.

 The method is called repeatedly during a fast enumeration to retrieve
batches of objects.  Each invocation of the method should retrieve the
next batch of objects.

 The return value of the method is the number of objects in the current
batch; this should not exceed ‘len’, which is the maximum size of a
batch as requested by the caller.  The batch itself is returned in the
‘itemsPtr’ field of the ‘NSFastEnumerationState’ struct.

 To help with returning the objects, the ‘objects’ array is a C array
preallocated by the caller (on the stack) of size ‘len’.  In many cases
you can put the objects you want to return in that ‘objects’ array, then
do ‘itemsPtr = objects’.  But you don't have to; if your collection
already has the objects to return in some form of C array, it could
return them from there instead.

 The ‘state’ and ‘extra’ fields of the ‘NSFastEnumerationState’
structure allows your collection object to keep track of the state of
the enumeration.  In a simple array implementation, ‘state’ may keep
track of the index of the last object that was returned, and ‘extra’ may
be unused.

 The ‘mutationsPtr’ field of the ‘NSFastEnumerationState’ is used to
keep track of mutations.  It should point to a number; before working on
each object, the fast enumeration loop will check that this number has
not changed.  If it has, a mutation has happened and the fast
enumeration will abort.  So, ‘mutationsPtr’ could be set to point to
some sort of version number of your collection, which is increased by
one every time there is a change (for example when an object is added or
removed).  Or, if you are content with less strict mutation checks, it
could point to the number of objects in your collection or some other
value that can be checked to perform an approximate check that the
collection has not been mutated.

 Finally, note how we declared the ‘len’ argument and the return value
to be of type ‘unsigned long’.  They could also be declared to be of
type ‘unsigned int’ and everything would still work.


File: gcc.info,  Node: Messaging with the GNU Objective-C runtime,  Prev: Fast enumeration,  Up: Objective-C

8.10 Messaging with the GNU Objective-C Runtime
===============================================

This section is specific for the GNU Objective-C runtime.  If you are
using a different runtime, you can skip it.

 The implementation of messaging in the GNU Objective-C runtime is
designed to be portable, and so is based on standard C.

 Sending a message in the GNU Objective-C runtime is composed of two
separate steps.  First, there is a call to the lookup function,
‘objc_msg_lookup ()’ (or, in the case of messages to super,
‘objc_msg_lookup_super ()’).  This runtime function takes as argument
the receiver and the selector of the method to be called; it returns the
‘IMP’, that is a pointer to the function implementing the method.  The
second step of method invocation consists of casting this pointer
function to the appropriate function pointer type, and calling the
function pointed to it with the right arguments.

 For example, when the compiler encounters a method invocation such as
‘[object init]’, it compiles it into a call to ‘objc_msg_lookup (object,
@selector(init))’ followed by a cast of the returned value to the
appropriate function pointer type, and then it calls it.

* Menu:

* Dynamically registering methods::
* Forwarding hook::


File: gcc.info,  Node: Dynamically registering methods,  Next: Forwarding hook,  Up: Messaging with the GNU Objective-C runtime

8.10.1 Dynamically Registering Methods
--------------------------------------

If ‘objc_msg_lookup()’ does not find a suitable method implementation,
because the receiver does not implement the required method, it tries to
see if the class can dynamically register the method.

 To do so, the runtime checks if the class of the receiver implements
the method

     + (BOOL) resolveInstanceMethod: (SEL)selector;

 in the case of an instance method, or

     + (BOOL) resolveClassMethod: (SEL)selector;

 in the case of a class method.  If the class implements it, the runtime
invokes it, passing as argument the selector of the original method, and
if it returns ‘YES’, the runtime tries the lookup again, which could now
succeed if a matching method was added dynamically by
‘+resolveInstanceMethod:’ or ‘+resolveClassMethod:’.

 This allows classes to dynamically register methods (by adding them to
the class using ‘class_addMethod’) when they are first called.  To do
so, a class should implement ‘+resolveInstanceMethod:’ (or, depending on
the case, ‘+resolveClassMethod:’) and have it recognize the selectors of
methods that can be registered dynamically at runtime, register them,
and return ‘YES’.  It should return ‘NO’ for methods that it does not
dynamically registered at runtime.

 If ‘+resolveInstanceMethod:’ (or ‘+resolveClassMethod:’) is not
implemented or returns ‘NO’, the runtime then tries the forwarding hook.

 Support for ‘+resolveInstanceMethod:’ and ‘resolveClassMethod:’ was
added to the GNU Objective-C runtime in GCC version 4.6.


File: gcc.info,  Node: Forwarding hook,  Prev: Dynamically registering methods,  Up: Messaging with the GNU Objective-C runtime

8.10.2 Forwarding Hook
----------------------

The GNU Objective-C runtime provides a hook, called
‘__objc_msg_forward2’, which is called by ‘objc_msg_lookup()’ when it
cannot find a method implementation in the runtime tables and after
calling ‘+resolveInstanceMethod:’ and ‘+resolveClassMethod:’ has been
attempted and did not succeed in dynamically registering the method.

 To configure the hook, you set the global variable
‘__objc_msg_forward2’ to a function with the same argument and return
types of ‘objc_msg_lookup()’.  When ‘objc_msg_lookup()’ cannot find a
method implementation, it invokes the hook function you provided to get
a method implementation to return.  So, in practice
‘__objc_msg_forward2’ allows you to extend ‘objc_msg_lookup()’ by adding
some custom code that is called to do a further lookup when no standard
method implementation can be found using the normal lookup.

 This hook is generally reserved for "Foundation" libraries such as
GNUstep Base, which use it to implement their high-level method
forwarding API, typically based around the ‘forwardInvocation:’ method.
So, unless you are implementing your own "Foundation" library, you
should not set this hook.

 In a typical forwarding implementation, the ‘__objc_msg_forward2’ hook
function determines the argument and return type of the method that is
being looked up, and then creates a function that takes these arguments
and has that return type, and returns it to the caller.  Creating this
function is non-trivial and is typically performed using a dedicated
library such as ‘libffi’.

 The forwarding method implementation thus created is returned by
‘objc_msg_lookup()’ and is executed as if it was a normal method
implementation.  When the forwarding method implementation is called, it
is usually expected to pack all arguments into some sort of object
(typically, an ‘NSInvocation’ in a "Foundation" library), and hand it
over to the programmer (‘forwardInvocation:’) who is then allowed to
manipulate the method invocation using a high-level API provided by the
"Foundation" library.  For example, the programmer may want to examine
the method invocation arguments and name and potentially change them
before forwarding the method invocation to one or more local objects
(‘performInvocation:’) or even to remote objects (by using Distributed
Objects or some other mechanism).  When all this completes, the return
value is passed back and must be returned correctly to the original
caller.

 Note that the GNU Objective-C runtime currently provides no support for
method forwarding or method invocations other than the
‘__objc_msg_forward2’ hook.

 If the forwarding hook does not exist or returns ‘NULL’, the runtime
currently attempts forwarding using an older, deprecated API, and if
that fails, it aborts the program.  In future versions of the GNU
Objective-C runtime, the runtime will immediately abort.


File: gcc.info,  Node: Compatibility,  Next: Gcov,  Prev: Objective-C,  Up: Top

9 Binary Compatibility
**********************

Binary compatibility encompasses several related concepts:

“application binary interface (ABI)”
     The set of runtime conventions followed by all of the tools that
     deal with binary representations of a program, including compilers,
     assemblers, linkers, and language runtime support.  Some ABIs are
     formal with a written specification, possibly designed by multiple
     interested parties.  Others are simply the way things are actually
     done by a particular set of tools.

“ABI conformance”
     A compiler conforms to an ABI if it generates code that follows all
     of the specifications enumerated by that ABI.  A library conforms
     to an ABI if it is implemented according to that ABI.  An
     application conforms to an ABI if it is built using tools that
     conform to that ABI and does not contain source code that
     specifically changes behavior specified by the ABI.

“calling conventions”
     Calling conventions are a subset of an ABI that specify of how
     arguments are passed and function results are returned.

“interoperability”
     Different sets of tools are interoperable if they generate files
     that can be used in the same program.  The set of tools includes
     compilers, assemblers, linkers, libraries, header files, startup
     files, and debuggers.  Binaries produced by different sets of tools
     are not interoperable unless they implement the same ABI.  This
     applies to different versions of the same tools as well as tools
     from different vendors.

“intercallability”
     Whether a function in a binary built by one set of tools can call a
     function in a binary built by a different set of tools is a subset
     of interoperability.

“implementation-defined features”
     Language standards include lists of implementation-defined features
     whose behavior can vary from one implementation to another.  Some
     of these features are normally covered by a platform's ABI and
     others are not.  The features that are not covered by an ABI
     generally affect how a program behaves, but not intercallability.

“compatibility”
     Conformance to the same ABI and the same behavior of
     implementation-defined features are both relevant for
     compatibility.

 The application binary interface implemented by a C or C++ compiler
affects code generation and runtime support for:

   • size and alignment of data types
   • layout of structured types
   • calling conventions
   • register usage conventions
   • interfaces for runtime arithmetic support
   • object file formats

 In addition, the application binary interface implemented by a C++
compiler affects code generation and runtime support for:
   • name mangling
   • exception handling
   • invoking constructors and destructors
   • layout, alignment, and padding of classes
   • layout and alignment of virtual tables

 Some GCC compilation options cause the compiler to generate code that
does not conform to the platform's default ABI.  Other options cause
different program behavior for implementation-defined features that are
not covered by an ABI.  These options are provided for consistency with
other compilers that do not follow the platform's default ABI or the
usual behavior of implementation-defined features for the platform.  Be
very careful about using such options.

 Most platforms have a well-defined ABI that covers C code, but ABIs
that cover C++ functionality are not yet common.

 Starting with GCC 3.2, GCC binary conventions for C++ are based on a
written, vendor-neutral C++ ABI that was designed to be specific to
64-bit Itanium but also includes generic specifications that apply to
any platform.  This C++ ABI is also implemented by other compiler
vendors on some platforms, notably GNU/Linux and BSD systems.  We have
tried hard to provide a stable ABI that will be compatible with future
GCC releases, but it is possible that we will encounter problems that
make this difficult.  Such problems could include different
interpretations of the C++ ABI by different vendors, bugs in the ABI, or
bugs in the implementation of the ABI in different compilers.  GCC's
‘-Wabi’ switch warns when G++ generates code that is probably not
compatible with the C++ ABI.

 The C++ library used with a C++ compiler includes the Standard C++
Library, with functionality defined in the C++ Standard, plus language
runtime support.  The runtime support is included in a C++ ABI, but
there is no formal ABI for the Standard C++ Library.  Two
implementations of that library are interoperable if one follows the
de-facto ABI of the other and if they are both built with the same
compiler, or with compilers that conform to the same ABI for C++
compiler and runtime support.

 When G++ and another C++ compiler conform to the same C++ ABI, but the
implementations of the Standard C++ Library that they normally use do
not follow the same ABI for the Standard C++ Library, object files built
with those compilers can be used in the same program only if they use
the same C++ library.  This requires specifying the location of the C++
library header files when invoking the compiler whose usual library is
not being used.  The location of GCC's C++ header files depends on how
the GCC build was configured, but can be seen by using the G++ ‘-v’
option.  With default configuration options for G++ 3.3 the compile line
for a different C++ compiler needs to include

         -IGCC_INSTALL_DIRECTORY/include/c++/3.3

 Similarly, compiling code with G++ that must use a C++ library other
than the GNU C++ library requires specifying the location of the header
files for that other library.

 The most straightforward way to link a program to use a particular C++
library is to use a C++ driver that specifies that C++ library by
default.  The ‘g++’ driver, for example, tells the linker where to find
GCC's C++ library (‘libstdc++’) plus the other libraries and startup
files it needs, in the proper order.

 If a program must use a different C++ library and it's not possible to
do the final link using a C++ driver that uses that library by default,
it is necessary to tell ‘g++’ the location and name of that library.  It
might also be necessary to specify different startup files and other
runtime support libraries, and to suppress the use of GCC's support
libraries with one or more of the options ‘-nostdlib’, ‘-nostartfiles’,
and ‘-nodefaultlibs’.


File: gcc.info,  Node: Gcov,  Next: Gcov-tool,  Prev: Compatibility,  Up: Top

10 ‘gcov’--a Test Coverage Program
**********************************

‘gcov’ is a tool you can use in conjunction with GCC to test code
coverage in your programs.

* Menu:

* Gcov Intro::                  Introduction to gcov.
* Invoking Gcov::               How to use gcov.
* Gcov and Optimization::       Using gcov with GCC optimization.
* Gcov Data Files::             The files used by gcov.
* Cross-profiling::             Data file relocation.


File: gcc.info,  Node: Gcov Intro,  Next: Invoking Gcov,  Up: Gcov

10.1 Introduction to ‘gcov’
===========================

‘gcov’ is a test coverage program.  Use it in concert with GCC to
analyze your programs to help create more efficient, faster running code
and to discover untested parts of your program.  You can use ‘gcov’ as a
profiling tool to help discover where your optimization efforts will
best affect your code.  You can also use ‘gcov’ along with the other
profiling tool, ‘gprof’, to assess which parts of your code use the
greatest amount of computing time.

 Profiling tools help you analyze your code's performance.  Using a
profiler such as ‘gcov’ or ‘gprof’, you can find out some basic
performance statistics, such as:

   • how often each line of code executes

   • what lines of code are actually executed

   • how much computing time each section of code uses

 Once you know these things about how your code works when compiled, you
can look at each module to see which modules should be optimized.
‘gcov’ helps you determine where to work on optimization.

 Software developers also use coverage testing in concert with
testsuites, to make sure software is actually good enough for a release.
Testsuites can verify that a program works as expected; a coverage
program tests to see how much of the program is exercised by the
testsuite.  Developers can then determine what kinds of test cases need
to be added to the testsuites to create both better testing and a better
final product.

 You should compile your code without optimization if you plan to use
‘gcov’ because the optimization, by combining some lines of code into
one function, may not give you as much information as you need to look
for 'hot spots' where the code is using a great deal of computer time.
Likewise, because ‘gcov’ accumulates statistics by line (at the lowest
resolution), it works best with a programming style that places only one
statement on each line.  If you use complicated macros that expand to
loops or to other control structures, the statistics are less
helpful--they only report on the line where the macro call appears.  If
your complex macros behave like functions, you can replace them with
inline functions to solve this problem.

 ‘gcov’ creates a logfile called ‘SOURCEFILE.gcov’ which indicates how
many times each line of a source file ‘SOURCEFILE.c’ has executed.  You
can use these logfiles along with ‘gprof’ to aid in fine-tuning the
performance of your programs.  ‘gprof’ gives timing information you can
use along with the information you get from ‘gcov’.

 ‘gcov’ works only on code compiled with GCC.  It is not compatible with
any other profiling or test coverage mechanism.


File: gcc.info,  Node: Invoking Gcov,  Next: Gcov and Optimization,  Prev: Gcov Intro,  Up: Gcov

10.2 Invoking ‘gcov’
====================

     gcov [OPTIONS] FILES

 ‘gcov’ accepts the following options:

‘-a’
‘--all-blocks’
     Write individual execution counts for every basic block.  Normally
     gcov outputs execution counts only for the main blocks of a line.
     With this option you can determine if blocks within a single line
     are not being executed.

‘-b’
‘--branch-probabilities’
     Write branch frequencies to the output file, and write branch
     summary info to the standard output.  This option allows you to see
     how often each branch in your program was taken.  Unconditional
     branches will not be shown, unless the ‘-u’ option is given.

‘-c’
‘--branch-counts’
     Write branch frequencies as the number of branches taken, rather
     than the percentage of branches taken.

‘-d’
‘--display-progress’
     Display the progress on the standard output.

‘-f’
‘--function-summaries’
     Output summaries for each function in addition to the file level
     summary.

‘-h’
‘--help’
     Display help about using ‘gcov’ (on the standard output), and exit
     without doing any further processing.

‘-j’
‘--json-format’
     Output gcov file in an easy-to-parse JSON intermediate format which
     does not require source code for generation.  The JSON file is
     compressed with gzip compression algorithm and the files have
     ‘.gcov.json.gz’ extension.

     Structure of the JSON is following:

          {
            "current_working_directory": "foo/bar",
            "data_file": "a.out",
            "format_version": "1",
            "gcc_version": "11.1.1 20210510"
            "files": ["$file"]
          }

     Fields of the root element have following semantics:

        • CURRENT_WORKING_DIRECTORY: working directory where a
          compilation unit was compiled

        • DATA_FILE: name of the data file (GCDA)

        • FORMAT_VERSION: semantic version of the format

        • GCC_VERSION: version of the GCC compiler

     Each FILE has the following form:

          {
            "file": "a.c",
            "functions": ["$function"],
            "lines": ["$line"]
          }

     Fields of the FILE element have following semantics:

        • FILE_NAME: name of the source file

     Each FUNCTION has the following form:

          {
            "blocks": 2,
            "blocks_executed": 2,
            "demangled_name": "foo",
            "end_column": 1,
            "end_line": 4,
            "execution_count": 1,
            "name": "foo",
            "start_column": 5,
            "start_line": 1
          }

     Fields of the FUNCTION element have following semantics:

        • BLOCKS: number of blocks that are in the function

        • BLOCKS_EXECUTED: number of executed blocks of the function

        • DEMANGLED_NAME: demangled name of the function

        • END_COLUMN: column in the source file where the function ends

        • END_LINE: line in the source file where the function ends

        • EXECUTION_COUNT: number of executions of the function

        • NAME: name of the function

        • START_COLUMN: column in the source file where the function
          begins

        • START_LINE: line in the source file where the function begins

     Note that line numbers and column numbers number from 1.  In the
     current implementation, START_LINE and START_COLUMN do not include
     any template parameters and the leading return type but that this
     is likely to be fixed in the future.

     Each LINE has the following form:

          {
            "branches": ["$branch"],
            "count": 2,
            "line_number": 15,
            "unexecuted_block": false,
            "function_name": "foo",
          }

     Branches are present only with -B option.  Fields of the LINE
     element have following semantics:

        • COUNT: number of executions of the line

        • LINE_NUMBER: line number

        • UNEXECUTED_BLOCK: flag whether the line contains an unexecuted
          block (not all statements on the line are executed)

        • FUNCTION_NAME: a name of a function this LINE belongs to (for
          a line with an inlined statements can be not set)

     Each BRANCH has the following form:

          {
            "count": 11,
            "fallthrough": true,
            "throw": false
          }

     Fields of the BRANCH element have following semantics:

        • COUNT: number of executions of the branch

        • FALLTHROUGH: true when the branch is a fall through branch

        • THROW: true when the branch is an exceptional branch

‘-H’
‘--human-readable’
     Write counts in human readable format (like 24.6k).

‘-k’
‘--use-colors’

     Use colors for lines of code that have zero coverage.  We use red
     color for non-exceptional lines and cyan for exceptional.  Same
     colors are used for basic blocks with ‘-a’ option.

‘-l’
‘--long-file-names’
     Create long file names for included source files.  For example, if
     the header file ‘x.h’ contains code, and was included in the file
     ‘a.c’, then running ‘gcov’ on the file ‘a.c’ will produce an output
     file called ‘a.c##x.h.gcov’ instead of ‘x.h.gcov’.  This can be
     useful if ‘x.h’ is included in multiple source files and you want
     to see the individual contributions.  If you use the ‘-p’ option,
     both the including and included file names will be complete path
     names.

‘-m’
‘--demangled-names’
     Display demangled function names in output.  The default is to show
     mangled function names.

‘-n’
‘--no-output’
     Do not create the ‘gcov’ output file.

‘-o DIRECTORY|FILE’
‘--object-directory DIRECTORY’
‘--object-file FILE’
     Specify either the directory containing the gcov data files, or the
     object path name.  The ‘.gcno’, and ‘.gcda’ data files are searched
     for using this option.  If a directory is specified, the data files
     are in that directory and named after the input file name, without
     its extension.  If a file is specified here, the data files are
     named after that file, without its extension.

‘-p’
‘--preserve-paths’
     Preserve complete path information in the names of generated
     ‘.gcov’ files.  Without this option, just the filename component is
     used.  With this option, all directories are used, with ‘/’
     characters translated to ‘#’ characters, ‘.’ directory components
     removed and unremoveable ‘..’ components renamed to ‘^’.  This is
     useful if sourcefiles are in several different directories.

‘-q’
‘--use-hotness-colors’

     Emit perf-like colored output for hot lines.  Legend of the color
     scale is printed at the very beginning of the output file.

‘-r’
‘--relative-only’
     Only output information about source files with a relative pathname
     (after source prefix elision).  Absolute paths are usually system
     header files and coverage of any inline functions therein is
     normally uninteresting.

‘-s DIRECTORY’
‘--source-prefix DIRECTORY’
     A prefix for source file names to remove when generating the output
     coverage files.  This option is useful when building in a separate
     directory, and the pathname to the source directory is not wanted
     when determining the output file names.  Note that this prefix
     detection is applied before determining whether the source file is
     absolute.

‘-t’
‘--stdout’
     Output to standard output instead of output files.

‘-u’
‘--unconditional-branches’
     When branch probabilities are given, include those of unconditional
     branches.  Unconditional branches are normally not interesting.

‘-v’
‘--version’
     Display the ‘gcov’ version number (on the standard output), and
     exit without doing any further processing.

‘-w’
‘--verbose’
     Print verbose informations related to basic blocks and arcs.

‘-x’
‘--hash-filenames’
     When using -PRESERVE-PATHS, gcov uses the full pathname of the
     source files to create an output filename.  This can lead to long
     filenames that can overflow filesystem limits.  This option creates
     names of the form ‘SOURCE-FILE##MD5.gcov’, where the SOURCE-FILE
     component is the final filename part and the MD5 component is
     calculated from the full mangled name that would have been used
     otherwise.  The option is an alternative to the -PRESERVE-PATHS on
     systems which have a filesystem limit.

 ‘gcov’ should be run with the current directory the same as that when
you invoked the compiler.  Otherwise it will not be able to locate the
source files.  ‘gcov’ produces files called ‘MANGLEDNAME.gcov’ in the
current directory.  These contain the coverage information of the source
file they correspond to.  One ‘.gcov’ file is produced for each source
(or header) file containing code, which was compiled to produce the data
files.  The MANGLEDNAME part of the output file name is usually simply
the source file name, but can be something more complicated if the ‘-l’
or ‘-p’ options are given.  Refer to those options for details.

 If you invoke ‘gcov’ with multiple input files, the contributions from
each input file are summed.  Typically you would invoke it with the same
list of files as the final link of your executable.

 The ‘.gcov’ files contain the ‘:’ separated fields along with program
source code.  The format is

     EXECUTION_COUNT:LINE_NUMBER:SOURCE LINE TEXT

 Additional block information may succeed each line, when requested by
command line option.  The EXECUTION_COUNT is ‘-’ for lines containing no
code.  Unexecuted lines are marked ‘#####’ or ‘=====’, depending on
whether they are reachable by non-exceptional paths or only exceptional
paths such as C++ exception handlers, respectively.  Given the ‘-a’
option, unexecuted blocks are marked ‘$$$$$’ or ‘%%%%%’, depending on
whether a basic block is reachable via non-exceptional or exceptional
paths.  Executed basic blocks having a statement with zero
EXECUTION_COUNT end with ‘*’ character and are colored with magenta
color with the ‘-k’ option.  This functionality is not supported in Ada.

 Note that GCC can completely remove the bodies of functions that are
not needed - for instance if they are inlined everywhere.  Such
functions are marked with ‘-’, which can be confusing.  Use the
‘-fkeep-inline-functions’ and ‘-fkeep-static-functions’ options to
retain these functions and allow gcov to properly show their
EXECUTION_COUNT.

 Some lines of information at the start have LINE_NUMBER of zero.  These
preamble lines are of the form

     -:0:TAG:VALUE

 The ordering and number of these preamble lines will be augmented as
‘gcov’ development progresses -- do not rely on them remaining
unchanged.  Use TAG to locate a particular preamble line.

 The additional block information is of the form

     TAG INFORMATION

 The INFORMATION is human readable, but designed to be simple enough for
machine parsing too.

 When printing percentages, 0% and 100% are only printed when the values
are _exactly_ 0% and 100% respectively.  Other values which would
conventionally be rounded to 0% or 100% are instead printed as the
nearest non-boundary value.

 When using ‘gcov’, you must first compile your program with a special
GCC option ‘--coverage’.  This tells the compiler to generate additional
information needed by gcov (basically a flow graph of the program) and
also includes additional code in the object files for generating the
extra profiling information needed by gcov.  These additional files are
placed in the directory where the object file is located.

 Running the program will cause profile output to be generated.  For
each source file compiled with ‘-fprofile-arcs’, an accompanying ‘.gcda’
file will be placed in the object file directory.

 Running ‘gcov’ with your program's source file names as arguments will
now produce a listing of the code along with frequency of execution for
each line.  For example, if your program is called ‘tmp.cpp’, this is
what you see when you use the basic ‘gcov’ facility:

     $ g++ --coverage tmp.cpp -c
     $ g++ --coverage tmp.o
     $ a.out
     $ gcov tmp.cpp -m
     File 'tmp.cpp'
     Lines executed:92.86% of 14
     Creating 'tmp.cpp.gcov'

 The file ‘tmp.cpp.gcov’ contains output from ‘gcov’.  Here is a sample:

             -:    0:Source:tmp.cpp
             -:    0:Working directory:/home/gcc/testcase
             -:    0:Graph:tmp.gcno
             -:    0:Data:tmp.gcda
             -:    0:Runs:1
             -:    0:Programs:1
             -:    1:#include <stdio.h>
             -:    2:
             -:    3:template<class T>
             -:    4:class Foo
             -:    5:{
             -:    6:  public:
            1*:    7:  Foo(): b (1000) {}
     ------------------
     Foo<char>::Foo():
         #####:    7:  Foo(): b (1000) {}
     ------------------
     Foo<int>::Foo():
             1:    7:  Foo(): b (1000) {}
     ------------------
            2*:    8:  void inc () { b++; }
     ------------------
     Foo<char>::inc():
         #####:    8:  void inc () { b++; }
     ------------------
     Foo<int>::inc():
             2:    8:  void inc () { b++; }
     ------------------
             -:    9:
             -:   10:  private:
             -:   11:  int b;
             -:   12:};
             -:   13:
             -:   14:template class Foo<int>;
             -:   15:template class Foo<char>;
             -:   16:
             -:   17:int
             1:   18:main (void)
             -:   19:{
             -:   20:  int i, total;
             1:   21:  Foo<int> counter;
             -:   22:
             1:   23:  counter.inc();
             1:   24:  counter.inc();
             1:   25:  total = 0;
             -:   26:
            11:   27:  for (i = 0; i < 10; i++)
            10:   28:    total += i;
             -:   29:
            1*:   30:  int v = total > 100 ? 1 : 2;
             -:   31:
             1:   32:  if (total != 45)
         #####:   33:    printf ("Failure\n");
             -:   34:  else
             1:   35:    printf ("Success\n");
             1:   36:  return 0;
             -:   37:}

 Note that line 7 is shown in the report multiple times.  First
occurrence presents total number of execution of the line and the next
two belong to instances of class Foo constructors.  As you can also see,
line 30 contains some unexecuted basic blocks and thus execution count
has asterisk symbol.

 When you use the ‘-a’ option, you will get individual block counts, and
the output looks like this:

             -:    0:Source:tmp.cpp
             -:    0:Working directory:/home/gcc/testcase
             -:    0:Graph:tmp.gcno
             -:    0:Data:tmp.gcda
             -:    0:Runs:1
             -:    0:Programs:1
             -:    1:#include <stdio.h>
             -:    2:
             -:    3:template<class T>
             -:    4:class Foo
             -:    5:{
             -:    6:  public:
            1*:    7:  Foo(): b (1000) {}
     ------------------
     Foo<char>::Foo():
         #####:    7:  Foo(): b (1000) {}
     ------------------
     Foo<int>::Foo():
             1:    7:  Foo(): b (1000) {}
     ------------------
            2*:    8:  void inc () { b++; }
     ------------------
     Foo<char>::inc():
         #####:    8:  void inc () { b++; }
     ------------------
     Foo<int>::inc():
             2:    8:  void inc () { b++; }
     ------------------
             -:    9:
             -:   10:  private:
             -:   11:  int b;
             -:   12:};
             -:   13:
             -:   14:template class Foo<int>;
             -:   15:template class Foo<char>;
             -:   16:
             -:   17:int
             1:   18:main (void)
             -:   19:{
             -:   20:  int i, total;
             1:   21:  Foo<int> counter;
             1:   21-block  0
             -:   22:
             1:   23:  counter.inc();
             1:   23-block  0
             1:   24:  counter.inc();
             1:   24-block  0
             1:   25:  total = 0;
             -:   26:
            11:   27:  for (i = 0; i < 10; i++)
             1:   27-block  0
            11:   27-block  1
            10:   28:    total += i;
            10:   28-block  0
             -:   29:
            1*:   30:  int v = total > 100 ? 1 : 2;
             1:   30-block  0
         %%%%%:   30-block  1
             1:   30-block  2
             -:   31:
             1:   32:  if (total != 45)
             1:   32-block  0
         #####:   33:    printf ("Failure\n");
         %%%%%:   33-block  0
             -:   34:  else
             1:   35:    printf ("Success\n");
             1:   35-block  0
             1:   36:  return 0;
             1:   36-block  0
             -:   37:}

 In this mode, each basic block is only shown on one line - the last
line of the block.  A multi-line block will only contribute to the
execution count of that last line, and other lines will not be shown to
contain code, unless previous blocks end on those lines.  The total
execution count of a line is shown and subsequent lines show the
execution counts for individual blocks that end on that line.  After
each block, the branch and call counts of the block will be shown, if
the ‘-b’ option is given.

 Because of the way GCC instruments calls, a call count can be shown
after a line with no individual blocks.  As you can see, line 33
contains a basic block that was not executed.

 When you use the ‘-b’ option, your output looks like this:

             -:    0:Source:tmp.cpp
             -:    0:Working directory:/home/gcc/testcase
             -:    0:Graph:tmp.gcno
             -:    0:Data:tmp.gcda
             -:    0:Runs:1
             -:    0:Programs:1
             -:    1:#include <stdio.h>
             -:    2:
             -:    3:template<class T>
             -:    4:class Foo
             -:    5:{
             -:    6:  public:
            1*:    7:  Foo(): b (1000) {}
     ------------------
     Foo<char>::Foo():
     function Foo<char>::Foo() called 0 returned 0% blocks executed 0%
         #####:    7:  Foo(): b (1000) {}
     ------------------
     Foo<int>::Foo():
     function Foo<int>::Foo() called 1 returned 100% blocks executed 100%
             1:    7:  Foo(): b (1000) {}
     ------------------
            2*:    8:  void inc () { b++; }
     ------------------
     Foo<char>::inc():
     function Foo<char>::inc() called 0 returned 0% blocks executed 0%
         #####:    8:  void inc () { b++; }
     ------------------
     Foo<int>::inc():
     function Foo<int>::inc() called 2 returned 100% blocks executed 100%
             2:    8:  void inc () { b++; }
     ------------------
             -:    9:
             -:   10:  private:
             -:   11:  int b;
             -:   12:};
             -:   13:
             -:   14:template class Foo<int>;
             -:   15:template class Foo<char>;
             -:   16:
             -:   17:int
     function main called 1 returned 100% blocks executed 81%
             1:   18:main (void)
             -:   19:{
             -:   20:  int i, total;
             1:   21:  Foo<int> counter;
     call    0 returned 100%
     branch  1 taken 100% (fallthrough)
     branch  2 taken 0% (throw)
             -:   22:
             1:   23:  counter.inc();
     call    0 returned 100%
     branch  1 taken 100% (fallthrough)
     branch  2 taken 0% (throw)
             1:   24:  counter.inc();
     call    0 returned 100%
     branch  1 taken 100% (fallthrough)
     branch  2 taken 0% (throw)
             1:   25:  total = 0;
             -:   26:
            11:   27:  for (i = 0; i < 10; i++)
     branch  0 taken 91% (fallthrough)
     branch  1 taken 9%
            10:   28:    total += i;
             -:   29:
            1*:   30:  int v = total > 100 ? 1 : 2;
     branch  0 taken 0% (fallthrough)
     branch  1 taken 100%
             -:   31:
             1:   32:  if (total != 45)
     branch  0 taken 0% (fallthrough)
     branch  1 taken 100%
         #####:   33:    printf ("Failure\n");
     call    0 never executed
     branch  1 never executed
     branch  2 never executed
             -:   34:  else
             1:   35:    printf ("Success\n");
     call    0 returned 100%
     branch  1 taken 100% (fallthrough)
     branch  2 taken 0% (throw)
             1:   36:  return 0;
             -:   37:}

 For each function, a line is printed showing how many times the
function is called, how many times it returns and what percentage of the
function's blocks were executed.

 For each basic block, a line is printed after the last line of the
basic block describing the branch or call that ends the basic block.
There can be multiple branches and calls listed for a single source line
if there are multiple basic blocks that end on that line.  In this case,
the branches and calls are each given a number.  There is no simple way
to map these branches and calls back to source constructs.  In general,
though, the lowest numbered branch or call will correspond to the
leftmost construct on the source line.

 For a branch, if it was executed at least once, then a percentage
indicating the number of times the branch was taken divided by the
number of times the branch was executed will be printed.  Otherwise, the
message "never executed" is printed.

 For a call, if it was executed at least once, then a percentage
indicating the number of times the call returned divided by the number
of times the call was executed will be printed.  This will usually be
100%, but may be less for functions that call ‘exit’ or ‘longjmp’, and
thus may not return every time they are called.

 The execution counts are cumulative.  If the example program were
executed again without removing the ‘.gcda’ file, the count for the
number of times each line in the source was executed would be added to
the results of the previous run(s).  This is potentially useful in
several ways.  For example, it could be used to accumulate data over a
number of program runs as part of a test verification suite, or to
provide more accurate long-term information over a large number of
program runs.

 The data in the ‘.gcda’ files is saved immediately before the program
exits.  For each source file compiled with ‘-fprofile-arcs’, the
profiling code first attempts to read in an existing ‘.gcda’ file; if
the file doesn't match the executable (differing number of basic block
counts) it will ignore the contents of the file.  It then adds in the
new execution counts and finally writes the data to the file.


File: gcc.info,  Node: Gcov and Optimization,  Next: Gcov Data Files,  Prev: Invoking Gcov,  Up: Gcov

10.3 Using ‘gcov’ with GCC Optimization
=======================================

If you plan to use ‘gcov’ to help optimize your code, you must first
compile your program with a special GCC option ‘--coverage’.  Aside from
that, you can use any other GCC options; but if you want to prove that
every single line in your program was executed, you should not compile
with optimization at the same time.  On some machines the optimizer can
eliminate some simple code lines by combining them with other lines.
For example, code like this:

     if (a != b)
       c = 1;
     else
       c = 0;

can be compiled into one instruction on some machines.  In this case,
there is no way for ‘gcov’ to calculate separate execution counts for
each line because there isn't separate code for each line.  Hence the
‘gcov’ output looks like this if you compiled the program with
optimization:

           100:   12:if (a != b)
           100:   13:  c = 1;
           100:   14:else
           100:   15:  c = 0;

 The output shows that this block of code, combined by optimization,
executed 100 times.  In one sense this result is correct, because there
was only one instruction representing all four of these lines.  However,
the output does not indicate how many times the result was 0 and how
many times the result was 1.

 Inlineable functions can create unexpected line counts.  Line counts
are shown for the source code of the inlineable function, but what is
shown depends on where the function is inlined, or if it is not inlined
at all.

 If the function is not inlined, the compiler must emit an out of line
copy of the function, in any object file that needs it.  If ‘fileA.o’
and ‘fileB.o’ both contain out of line bodies of a particular inlineable
function, they will also both contain coverage counts for that function.
When ‘fileA.o’ and ‘fileB.o’ are linked together, the linker will, on
many systems, select one of those out of line bodies for all calls to
that function, and remove or ignore the other.  Unfortunately, it will
not remove the coverage counters for the unused function body.  Hence
when instrumented, all but one use of that function will show zero
counts.

 If the function is inlined in several places, the block structure in
each location might not be the same.  For instance, a condition might
now be calculable at compile time in some instances.  Because the
coverage of all the uses of the inline function will be shown for the
same source lines, the line counts themselves might seem inconsistent.

 Long-running applications can use the ‘__gcov_reset’ and ‘__gcov_dump’
facilities to restrict profile collection to the program region of
interest.  Calling ‘__gcov_reset(void)’ will clear all run-time profile
counters to zero, and calling ‘__gcov_dump(void)’ will cause the profile
information collected at that point to be dumped to ‘.gcda’ output
files.  Instrumented applications use a static destructor with priority
99 to invoke the ‘__gcov_dump’ function.  Thus ‘__gcov_dump’ is executed
after all user defined static destructors, as well as handlers
registered with ‘atexit’.

 If an executable loads a dynamic shared object via dlopen
functionality, ‘-Wl,--dynamic-list-data’ is needed to dump all profile
data.

 Profiling run-time library reports various errors related to profile
manipulation and profile saving.  Errors are printed into standard error
output or ‘GCOV_ERROR_FILE’ file, if environment variable is used.  In
order to terminate immediately after an errors occurs set
‘GCOV_EXIT_AT_ERROR’ environment variable.  That can help users to find
profile clashing which leads to a misleading profile.


File: gcc.info,  Node: Gcov Data Files,  Next: Cross-profiling,  Prev: Gcov and Optimization,  Up: Gcov

10.4 Brief Description of ‘gcov’ Data Files
===========================================

‘gcov’ uses two files for profiling.  The names of these files are
derived from the original _object_ file by substituting the file suffix
with either ‘.gcno’, or ‘.gcda’.  The files contain coverage and profile
data stored in a platform-independent format.  The ‘.gcno’ files are
placed in the same directory as the object file.  By default, the
‘.gcda’ files are also stored in the same directory as the object file,
but the GCC ‘-fprofile-dir’ option may be used to store the ‘.gcda’
files in a separate directory.

 The ‘.gcno’ notes file is generated when the source file is compiled
with the GCC ‘-ftest-coverage’ option.  It contains information to
reconstruct the basic block graphs and assign source line numbers to
blocks.

 The ‘.gcda’ count data file is generated when a program containing
object files built with the GCC ‘-fprofile-arcs’ option is executed.  A
separate ‘.gcda’ file is created for each object file compiled with this
option.  It contains arc transition counts, value profile counts, and
some summary information.

 It is not recommended to access the coverage files directly.  Consumers
should use the intermediate format that is provided by ‘gcov’ tool via
‘--json-format’ option.


File: gcc.info,  Node: Cross-profiling,  Prev: Gcov Data Files,  Up: Gcov

10.5 Data File Relocation to Support Cross-Profiling
====================================================

Running the program will cause profile output to be generated.  For each
source file compiled with ‘-fprofile-arcs’, an accompanying ‘.gcda’ file
will be placed in the object file directory.  That implicitly requires
running the program on the same system as it was built or having the
same absolute directory structure on the target system.  The program
will try to create the needed directory structure, if it is not already
present.

 To support cross-profiling, a program compiled with ‘-fprofile-arcs’
can relocate the data files based on two environment variables:

   • GCOV_PREFIX contains the prefix to add to the absolute paths in the
     object file.  Prefix can be absolute, or relative.  The default is
     no prefix.

   • GCOV_PREFIX_STRIP indicates the how many initial directory names to
     strip off the hardwired absolute paths.  Default value is 0.

     _Note:_ If GCOV_PREFIX_STRIP is set without GCOV_PREFIX is
     undefined, then a relative path is made out of the hardwired
     absolute paths.

 For example, if the object file ‘/user/build/foo.o’ was built with
‘-fprofile-arcs’, the final executable will try to create the data file
‘/user/build/foo.gcda’ when running on the target system.  This will
fail if the corresponding directory does not exist and it is unable to
create it.  This can be overcome by, for example, setting the
environment as ‘GCOV_PREFIX=/target/run’ and ‘GCOV_PREFIX_STRIP=1’.
Such a setting will name the data file ‘/target/run/build/foo.gcda’.

 You must move the data files to the expected directory tree in order to
use them for profile directed optimizations (‘-fprofile-use’), or to use
the ‘gcov’ tool.


File: gcc.info,  Node: Gcov-tool,  Next: Gcov-dump,  Prev: Gcov,  Up: Top

11 ‘gcov-tool’--an Offline Gcda Profile Processing Tool
*******************************************************

‘gcov-tool’ is a tool you can use in conjunction with GCC to manipulate
or process gcda profile files offline.

* Menu:

* Gcov-tool Intro::             Introduction to gcov-tool.
* Invoking Gcov-tool::          How to use gcov-tool.


File: gcc.info,  Node: Gcov-tool Intro,  Next: Invoking Gcov-tool,  Up: Gcov-tool

11.1 Introduction to ‘gcov-tool’
================================

‘gcov-tool’ is an offline tool to process gcc's gcda profile files.

 Current gcov-tool supports the following functionalities:

   • merge two sets of profiles with weights.

   • read one set of profile and rewrite profile contents.  One can
     scale or normalize the count values.

 Examples of the use cases for this tool are:
   • Collect the profiles for different set of inputs, and use this tool
     to merge them.  One can specify the weight to factor in the
     relative importance of each input.

   • Rewrite the profile after removing a subset of the gcda files,
     while maintaining the consistency of the summary and the histogram.

   • It can also be used to debug or libgcov code as the tools shares
     the majority code as the runtime library.

 Note that for the merging operation, this profile generated offline may
contain slight different values from the online merged profile.  Here
are a list of typical differences:

   • histogram difference: This offline tool recomputes the histogram
     after merging the counters.  The resulting histogram, therefore, is
     precise.  The online merging does not have this capability - the
     histogram is merged from two histograms and the result is an
     approximation.

   • summary checksum difference: Summary checksum uses a CRC32
     operation.  The value depends on the link list order of gcov-info
     objects.  This order is different in gcov-tool from that in the
     online merge.  It's expected to have different summary checksums.
     It does not really matter as the compiler does not use this
     checksum anywhere.

   • value profile counter values difference: Some counter values for
     value profile are runtime dependent, like heap addresses.  It's
     normal to see some difference in these kind of counters.


File: gcc.info,  Node: Invoking Gcov-tool,  Prev: Gcov-tool Intro,  Up: Gcov-tool

11.2 Invoking ‘gcov-tool’
=========================

     gcov-tool [GLOBAL-OPTIONS] SUB_COMMAND [SUB_COMMAND-OPTIONS] PROFILE_DIR

 ‘gcov-tool’ accepts the following options:

‘-h’
‘--help’
     Display help about using ‘gcov-tool’ (on the standard output), and
     exit without doing any further processing.

‘-v’
‘--version’
     Display the ‘gcov-tool’ version number (on the standard output),
     and exit without doing any further processing.

‘merge’
     Merge two profile directories.

     ‘-o DIRECTORY’
     ‘--output DIRECTORY’
          Set the output profile directory.  Default output directory
          name is MERGED_PROFILE.

     ‘-v’
     ‘--verbose’
          Set the verbose mode.

     ‘-w W1,W2’
     ‘--weight W1,W2’
          Set the merge weights of the DIRECTORY1 and DIRECTORY2,
          respectively.  The default weights are 1 for both.

‘rewrite’
     Read the specified profile directory and rewrite to a new
     directory.

     ‘-n LONG_LONG_VALUE’
     ‘--normalize <long_long_value>’
          Normalize the profile.  The specified value is the max counter
          value in the new profile.

     ‘-o DIRECTORY’
     ‘--output DIRECTORY’
          Set the output profile directory.  Default output name is
          REWRITE_PROFILE.

     ‘-s FLOAT_OR_SIMPLE-FRAC_VALUE’
     ‘--scale FLOAT_OR_SIMPLE-FRAC_VALUE’
          Scale the profile counters.  The specified value can be in
          floating point value, or simple fraction value form, such 1,
          2, 2/3, and 5/3.

     ‘-v’
     ‘--verbose’
          Set the verbose mode.

‘overlap’
     Compute the overlap score between the two specified profile
     directories.  The overlap score is computed based on the arc
     profiles.  It is defined as the sum of min (p1_counter[i] /
     p1_sum_all, p2_counter[i] / p2_sum_all), for all arc counter i,
     where p1_counter[i] and p2_counter[i] are two matched counters and
     p1_sum_all and p2_sum_all are the sum of counter values in profile
     1 and profile 2, respectively.

     ‘-f’
     ‘--function’
          Print function level overlap score.

     ‘-F’
     ‘--fullname’
          Print full gcda filename.

     ‘-h’
     ‘--hotonly’
          Only print info for hot objects/functions.

     ‘-o’
     ‘--object’
          Print object level overlap score.

     ‘-t FLOAT’
     ‘--hot_threshold <float>’
          Set the threshold for hot counter value.

     ‘-v’
     ‘--verbose’
          Set the verbose mode.


File: gcc.info,  Node: Gcov-dump,  Next: lto-dump,  Prev: Gcov-tool,  Up: Top

12 ‘gcov-dump’--an Offline Gcda and Gcno Profile Dump Tool
**********************************************************

* Menu:

* Gcov-dump Intro::             Introduction to gcov-dump.
* Invoking Gcov-dump::          How to use gcov-dump.


File: gcc.info,  Node: Gcov-dump Intro,  Next: Invoking Gcov-dump,  Up: Gcov-dump

12.1 Introduction to ‘gcov-dump’
================================

‘gcov-dump’ is a tool you can use in conjunction with GCC to dump
content of gcda and gcno profile files offline.


File: gcc.info,  Node: Invoking Gcov-dump,  Prev: Gcov-dump Intro,  Up: Gcov-dump

12.2 Invoking ‘gcov-dump’
=========================

     Usage: gcov-dump [OPTION] ... GCOVFILES

 ‘gcov-dump’ accepts the following options:

‘-h’
‘--help’
     Display help about using ‘gcov-dump’ (on the standard output), and
     exit without doing any further processing.

‘-l’
‘--long’
     Dump content of records.

‘-p’
‘--positions’
     Dump positions of records.

‘-r’
‘--raw’
     Print content records in raw format.

‘-v’
‘--version’
     Display the ‘gcov-dump’ version number (on the standard output),
     and exit without doing any further processing.


File: gcc.info,  Node: lto-dump,  Next: Trouble,  Prev: Gcov-dump,  Up: Top

13 ‘lto-dump’--Tool for dumping LTO object files.
*************************************************

* Menu:

* lto-dump Intro::             Introduction to lto-dump.
* Invoking lto-dump::          How to use lto-dump.


File: gcc.info,  Node: lto-dump Intro,  Next: Invoking lto-dump,  Up: lto-dump

13.1 Introduction to ‘lto-dump’
===============================

‘lto-dump’ is a tool you can use in conjunction with GCC to dump link
time optimization object files.


File: gcc.info,  Node: Invoking lto-dump,  Prev: lto-dump Intro,  Up: lto-dump

13.2 Invoking ‘lto-dump’
========================

     Usage: lto-dump [OPTION] ... OBJFILES

 ‘lto-dump’ accepts the following options:

‘-list’
     Dumps list of details of functions and variables.

‘-demangle’
     Dump the demangled output.

‘-defined-only’
     Dump only the defined symbols.

‘-print-value’
     Dump initial values of the variables.

‘-name-sort’
     Sort the symbols alphabetically.

‘-size-sort’
     Sort the symbols according to size.

‘-reverse-sort’
     Dump the symbols in reverse order.

‘-no-sort’
     Dump the symbols in order of occurrence.

‘-symbol=’
     Dump the details of specific symbol.

‘-objects’
     Dump the details of LTO objects.

‘-type-stats’
     Dump the statistics of tree types.

‘-tree-stats’
     Dump the statistics of trees.

‘-gimple-stats’
     Dump the statistics of gimple statements.

‘-dump-level=’
     For deciding the optimization level of body.

‘-dump-body=’
     Dump the specific gimple body.

‘-help’
     Display the dump tool help.


File: gcc.info,  Node: Trouble,  Next: Bugs,  Prev: lto-dump,  Up: Top

14 Known Causes of Trouble with GCC
***********************************

This section describes known problems that affect users of GCC.  Most of
these are not GCC bugs per se--if they were, we would fix them.  But the
result for a user may be like the result of a bug.

 Some of these problems are due to bugs in other software, some are
missing features that are too much work to add, and some are places
where people's opinions differ as to what is best.

* Menu:

* Actual Bugs::         Bugs we will fix later.
* Interoperation::      Problems using GCC with other compilers,
                        and with certain linkers, assemblers and debuggers.
* Incompatibilities::   GCC is incompatible with traditional C.
* Fixed Headers::       GCC uses corrected versions of system header files.
                        This is necessary, but doesn't always work smoothly.
* Standard Libraries::  GCC uses the system C library, which might not be
                        compliant with the ISO C standard.
* Disappointments::     Regrettable things we cannot change, but not quite bugs.
* C++ Misunderstandings:: Common misunderstandings with GNU C++.
* Non-bugs::            Things we think are right, but some others disagree.
* Warnings and Errors:: Which problems in your code get warnings,
                        and which get errors.


File: gcc.info,  Node: Actual Bugs,  Next: Interoperation,  Up: Trouble

14.1 Actual Bugs We Haven't Fixed Yet
=====================================

   • The ‘fixincludes’ script interacts badly with automounters; if the
     directory of system header files is automounted, it tends to be
     unmounted while ‘fixincludes’ is running.  This would seem to be a
     bug in the automounter.  We don't know any good way to work around
     it.


File: gcc.info,  Node: Interoperation,  Next: Incompatibilities,  Prev: Actual Bugs,  Up: Trouble

14.2 Interoperation
===================

This section lists various difficulties encountered in using GCC
together with other compilers or with the assemblers, linkers, libraries
and debuggers on certain systems.

   • On many platforms, GCC supports a different ABI for C++ than do
     other compilers, so the object files compiled by GCC cannot be used
     with object files generated by another C++ compiler.

     An area where the difference is most apparent is name mangling.
     The use of different name mangling is intentional, to protect you
     from more subtle problems.  Compilers differ as to many internal
     details of C++ implementation, including: how class instances are
     laid out, how multiple inheritance is implemented, and how virtual
     function calls are handled.  If the name encoding were made the
     same, your programs would link against libraries provided from
     other compilers--but the programs would then crash when run.
     Incompatible libraries are then detected at link time, rather than
     at run time.

   • On some BSD systems, including some versions of Ultrix, use of
     profiling causes static variable destructors (currently used only
     in C++) not to be run.

   • On a SPARC, GCC aligns all values of type ‘double’ on an 8-byte
     boundary, and it expects every ‘double’ to be so aligned.  The Sun
     compiler usually gives ‘double’ values 8-byte alignment, with one
     exception: function arguments of type ‘double’ may not be aligned.

     As a result, if a function compiled with Sun CC takes the address
     of an argument of type ‘double’ and passes this pointer of type
     ‘double *’ to a function compiled with GCC, dereferencing the
     pointer may cause a fatal signal.

     One way to solve this problem is to compile your entire program
     with GCC.  Another solution is to modify the function that is
     compiled with Sun CC to copy the argument into a local variable;
     local variables are always properly aligned.  A third solution is
     to modify the function that uses the pointer to dereference it via
     the following function ‘access_double’ instead of directly with
     ‘*’:

          inline double
          access_double (double *unaligned_ptr)
          {
            union d2i { double d; int i[2]; };

            union d2i *p = (union d2i *) unaligned_ptr;
            union d2i u;

            u.i[0] = p->i[0];
            u.i[1] = p->i[1];

            return u.d;
          }

     Storing into the pointer can be done likewise with the same union.

   • On Solaris, the ‘malloc’ function in the ‘libmalloc.a’ library may
     allocate memory that is only 4 byte aligned.  Since GCC on the
     SPARC assumes that doubles are 8 byte aligned, this may result in a
     fatal signal if doubles are stored in memory allocated by the
     ‘libmalloc.a’ library.

     The solution is to not use the ‘libmalloc.a’ library.  Use instead
     ‘malloc’ and related functions from ‘libc.a’; they do not have this
     problem.

   • On the HP PA machine, ADB sometimes fails to work on functions
     compiled with GCC.  Specifically, it fails to work on functions
     that use ‘alloca’ or variable-size arrays.  This is because GCC
     doesn't generate HP-UX unwind descriptors for such functions.  It
     may even be impossible to generate them.

   • Debugging (‘-g’) is not supported on the HP PA machine, unless you
     use the preliminary GNU tools.

   • Taking the address of a label may generate errors from the HP-UX PA
     assembler.  GAS for the PA does not have this problem.

   • Using floating point parameters for indirect calls to static
     functions will not work when using the HP assembler.  There simply
     is no way for GCC to specify what registers hold arguments for
     static functions when using the HP assembler.  GAS for the PA does
     not have this problem.

   • In extremely rare cases involving some very large functions you may
     receive errors from the HP linker complaining about an out of
     bounds unconditional branch offset.  This used to occur more often
     in previous versions of GCC, but is now exceptionally rare.  If you
     should run into it, you can work around by making your function
     smaller.

   • GCC compiled code sometimes emits warnings from the HP-UX assembler
     of the form:

          (warning) Use of GR3 when
            frame >= 8192 may cause conflict.

     These warnings are harmless and can be safely ignored.

   • In extremely rare cases involving some very large functions you may
     receive errors from the AIX Assembler complaining about a
     displacement that is too large.  If you should run into it, you can
     work around by making your function smaller.

   • The ‘libstdc++.a’ library in GCC relies on the SVR4 dynamic linker
     semantics which merges global symbols between libraries and
     applications, especially necessary for C++ streams functionality.
     This is not the default behavior of AIX shared libraries and
     dynamic linking.  ‘libstdc++.a’ is built on AIX with
     "runtime-linking" enabled so that symbol merging can occur.  To
     utilize this feature, the application linked with ‘libstdc++.a’
     must include the ‘-Wl,-brtl’ flag on the link line.  G++ cannot
     impose this because this option may interfere with the semantics of
     the user program and users may not always use ‘g++’ to link his or
     her application.  Applications are not required to use the
     ‘-Wl,-brtl’ flag on the link line--the rest of the ‘libstdc++.a’
     library which is not dependent on the symbol merging semantics will
     continue to function correctly.

   • An application can interpose its own definition of functions for
     functions invoked by ‘libstdc++.a’ with "runtime-linking" enabled
     on AIX.  To accomplish this the application must be linked with
     "runtime-linking" option and the functions explicitly must be
     exported by the application (‘-Wl,-brtl,-bE:exportfile’).

   • AIX on the RS/6000 provides support (NLS) for environments outside
     of the United States.  Compilers and assemblers use NLS to support
     locale-specific representations of various objects including
     floating-point numbers (‘.’ vs ‘,’ for separating decimal
     fractions).  There have been problems reported where the library
     linked with GCC does not produce the same floating-point formats
     that the assembler accepts.  If you have this problem, set the
     ‘LANG’ environment variable to ‘C’ or ‘En_US’.

   • Even if you specify ‘-fdollars-in-identifiers’, you cannot
     successfully use ‘$’ in identifiers on the RS/6000 due to a
     restriction in the IBM assembler.  GAS supports these identifiers.


File: gcc.info,  Node: Incompatibilities,  Next: Fixed Headers,  Prev: Interoperation,  Up: Trouble

14.3 Incompatibilities of GCC
=============================

There are several noteworthy incompatibilities between GNU C and K&R
(non-ISO) versions of C.

   • GCC normally makes string constants read-only.  If several
     identical-looking string constants are used, GCC stores only one
     copy of the string.

     One consequence is that you cannot call ‘mktemp’ with a string
     constant argument.  The function ‘mktemp’ always alters the string
     its argument points to.

     Another consequence is that ‘sscanf’ does not work on some very old
     systems when passed a string constant as its format control string
     or input.  This is because ‘sscanf’ incorrectly tries to write into
     the string constant.  Likewise ‘fscanf’ and ‘scanf’.

     The solution to these problems is to change the program to use
     ‘char’-array variables with initialization strings for these
     purposes instead of string constants.

   • ‘-2147483648’ is positive.

     This is because 2147483648 cannot fit in the type ‘int’, so
     (following the ISO C rules) its data type is ‘unsigned long int’.
     Negating this value yields 2147483648 again.

   • GCC does not substitute macro arguments when they appear inside of
     string constants.  For example, the following macro in GCC

          #define foo(a) "a"

     will produce output ‘"a"’ regardless of what the argument A is.

   • When you use ‘setjmp’ and ‘longjmp’, the only automatic variables
     guaranteed to remain valid are those declared ‘volatile’.  This is
     a consequence of automatic register allocation.  Consider this
     function:

          jmp_buf j;

          foo ()
          {
            int a, b;

            a = fun1 ();
            if (setjmp (j))
              return a;

            a = fun2 ();
            /* ‘longjmp (j)’ may occur in ‘fun3’. */
            return a + fun3 ();
          }

     Here ‘a’ may or may not be restored to its first value when the
     ‘longjmp’ occurs.  If ‘a’ is allocated in a register, then its
     first value is restored; otherwise, it keeps the last value stored
     in it.

     If you use the ‘-W’ option with the ‘-O’ option, you will get a
     warning when GCC thinks such a problem might be possible.

   • Programs that use preprocessing directives in the middle of macro
     arguments do not work with GCC.  For example, a program like this
     will not work:

          foobar (
          #define luser
                  hack)

     ISO C does not permit such a construct.

   • K&R compilers allow comments to cross over an inclusion boundary
     (i.e. started in an include file and ended in the including file).

   • Declarations of external variables and functions within a block
     apply only to the block containing the declaration.  In other
     words, they have the same scope as any other declaration in the
     same place.

     In some other C compilers, an ‘extern’ declaration affects all the
     rest of the file even if it happens within a block.

   • In traditional C, you can combine ‘long’, etc., with a typedef
     name, as shown here:

          typedef int foo;
          typedef long foo bar;

     In ISO C, this is not allowed: ‘long’ and other type modifiers
     require an explicit ‘int’.

   • PCC allows typedef names to be used as function parameters.

   • Traditional C allows the following erroneous pair of declarations
     to appear together in a given scope:

          typedef int foo;
          typedef foo foo;

   • GCC treats all characters of identifiers as significant.  According
     to K&R-1 (2.2), "No more than the first eight characters are
     significant, although more may be used.".  Also according to K&R-1
     (2.2), "An identifier is a sequence of letters and digits; the
     first character must be a letter.  The underscore _ counts as a
     letter.", but GCC also allows dollar signs in identifiers.

   • PCC allows whitespace in the middle of compound assignment
     operators such as ‘+=’.  GCC, following the ISO standard, does not
     allow this.

   • GCC complains about unterminated character constants inside of
     preprocessing conditionals that fail.  Some programs have English
     comments enclosed in conditionals that are guaranteed to fail; if
     these comments contain apostrophes, GCC will probably report an
     error.  For example, this code would produce an error:

          #if 0
          You can't expect this to work.
          #endif

     The best solution to such a problem is to put the text into an
     actual C comment delimited by ‘/*...*/’.

   • Many user programs contain the declaration ‘long time ();’.  In the
     past, the system header files on many systems did not actually
     declare ‘time’, so it did not matter what type your program
     declared it to return.  But in systems with ISO C headers, ‘time’
     is declared to return ‘time_t’, and if that is not the same as
     ‘long’, then ‘long time ();’ is erroneous.

     The solution is to change your program to use appropriate system
     headers (‘<time.h>’ on systems with ISO C headers) and not to
     declare ‘time’ if the system header files declare it, or failing
     that to use ‘time_t’ as the return type of ‘time’.

   • When compiling functions that return ‘float’, PCC converts it to a
     double.  GCC actually returns a ‘float’.  If you are concerned with
     PCC compatibility, you should declare your functions to return
     ‘double’; you might as well say what you mean.

   • When compiling functions that return structures or unions, GCC
     output code normally uses a method different from that used on most
     versions of Unix.  As a result, code compiled with GCC cannot call
     a structure-returning function compiled with PCC, and vice versa.

     The method used by GCC is as follows: a structure or union which is
     1, 2, 4 or 8 bytes long is returned like a scalar.  A structure or
     union with any other size is stored into an address supplied by the
     caller (usually in a special, fixed register, but on some machines
     it is passed on the stack).  The target hook
     ‘TARGET_STRUCT_VALUE_RTX’ tells GCC where to pass this address.

     By contrast, PCC on most target machines returns structures and
     unions of any size by copying the data into an area of static
     storage, and then returning the address of that storage as if it
     were a pointer value.  The caller must copy the data from that
     memory area to the place where the value is wanted.  GCC does not
     use this method because it is slower and nonreentrant.

     On some newer machines, PCC uses a reentrant convention for all
     structure and union returning.  GCC on most of these machines uses
     a compatible convention when returning structures and unions in
     memory, but still returns small structures and unions in registers.

     You can tell GCC to use a compatible convention for all structure
     and union returning with the option ‘-fpcc-struct-return’.

   • GCC complains about program fragments such as ‘0x74ae-0x4000’ which
     appear to be two hexadecimal constants separated by the minus
     operator.  Actually, this string is a single “preprocessing token”.
     Each such token must correspond to one token in C.  Since this does
     not, GCC prints an error message.  Although it may appear obvious
     that what is meant is an operator and two values, the ISO C
     standard specifically requires that this be treated as erroneous.

     A “preprocessing token” is a “preprocessing number” if it begins
     with a digit and is followed by letters, underscores, digits,
     periods and ‘e+’, ‘e-’, ‘E+’, ‘E-’, ‘p+’, ‘p-’, ‘P+’, or ‘P-’
     character sequences.  (In strict C90 mode, the sequences ‘p+’,
     ‘p-’, ‘P+’ and ‘P-’ cannot appear in preprocessing numbers.)

     To make the above program fragment valid, place whitespace in front
     of the minus sign.  This whitespace will end the preprocessing
     number.


File: gcc.info,  Node: Fixed Headers,  Next: Standard Libraries,  Prev: Incompatibilities,  Up: Trouble

14.4 Fixed Header Files
=======================

GCC needs to install corrected versions of some system header files.
This is because most target systems have some header files that won't
work with GCC unless they are changed.  Some have bugs, some are
incompatible with ISO C, and some depend on special features of other
compilers.

 Installing GCC automatically creates and installs the fixed header
files, by running a program called ‘fixincludes’.  Normally, you don't
need to pay attention to this.  But there are cases where it doesn't do
the right thing automatically.

   • If you update the system's header files, such as by installing a
     new system version, the fixed header files of GCC are not
     automatically updated.  They can be updated using the ‘mkheaders’
     script installed in ‘LIBEXECDIR/gcc/TARGET/VERSION/install-tools/’.

   • On some systems, header file directories contain machine-specific
     symbolic links in certain places.  This makes it possible to share
     most of the header files among hosts running the same version of
     the system on different machine models.

     The programs that fix the header files do not understand this
     special way of using symbolic links; therefore, the directory of
     fixed header files is good only for the machine model used to build
     it.

     It is possible to make separate sets of fixed header files for the
     different machine models, and arrange a structure of symbolic links
     so as to use the proper set, but you'll have to do this by hand.


File: gcc.info,  Node: Standard Libraries,  Next: Disappointments,  Prev: Fixed Headers,  Up: Trouble

14.5 Standard Libraries
=======================

GCC by itself attempts to be a conforming freestanding implementation.
*Note Language Standards Supported by GCC: Standards, for details of
what this means.  Beyond the library facilities required of such an
implementation, the rest of the C library is supplied by the vendor of
the operating system.  If that C library doesn't conform to the C
standards, then your programs might get warnings (especially when using
‘-Wall’) that you don't expect.

 For example, the ‘sprintf’ function on SunOS 4.1.3 returns ‘char *’
while the C standard says that ‘sprintf’ returns an ‘int’.  The
‘fixincludes’ program could make the prototype for this function match
the Standard, but that would be wrong, since the function will still
return ‘char *’.

 If you need a Standard compliant library, then you need to find one, as
GCC does not provide one.  The GNU C library (called ‘glibc’) provides
ISO C, POSIX, BSD, SystemV and X/Open compatibility for GNU/Linux and
HURD-based GNU systems; no recent version of it supports other systems,
though some very old versions did.  Version 2.2 of the GNU C library
includes nearly complete C99 support.  You could also ask your operating
system vendor if newer libraries are available.


File: gcc.info,  Node: Disappointments,  Next: C++ Misunderstandings,  Prev: Standard Libraries,  Up: Trouble

14.6 Disappointments and Misunderstandings
==========================================

These problems are perhaps regrettable, but we don't know any practical
way around them.

   • Certain local variables aren't recognized by debuggers when you
     compile with optimization.

     This occurs because sometimes GCC optimizes the variable out of
     existence.  There is no way to tell the debugger how to compute the
     value such a variable "would have had", and it is not clear that
     would be desirable anyway.  So GCC simply does not mention the
     eliminated variable when it writes debugging information.

     You have to expect a certain amount of disagreement between the
     executable and your source code, when you use optimization.

   • Users often think it is a bug when GCC reports an error for code
     like this:

          int foo (struct mumble *);

          struct mumble { ... };

          int foo (struct mumble *x)
          { ... }

     This code really is erroneous, because the scope of ‘struct mumble’
     in the prototype is limited to the argument list containing it.  It
     does not refer to the ‘struct mumble’ defined with file scope
     immediately below--they are two unrelated types with similar names
     in different scopes.

     But in the definition of ‘foo’, the file-scope type is used because
     that is available to be inherited.  Thus, the definition and the
     prototype do not match, and you get an error.

     This behavior may seem silly, but it's what the ISO standard
     specifies.  It is easy enough for you to make your code work by
     moving the definition of ‘struct mumble’ above the prototype.  It's
     not worth being incompatible with ISO C just to avoid an error for
     the example shown above.

   • Accesses to bit-fields even in volatile objects works by accessing
     larger objects, such as a byte or a word.  You cannot rely on what
     size of object is accessed in order to read or write the bit-field;
     it may even vary for a given bit-field according to the precise
     usage.

     If you care about controlling the amount of memory that is
     accessed, use volatile but do not use bit-fields.

   • GCC comes with shell scripts to fix certain known problems in
     system header files.  They install corrected copies of various
     header files in a special directory where only GCC will normally
     look for them.  The scripts adapt to various systems by searching
     all the system header files for the problem cases that we know
     about.

     If new system header files are installed, nothing automatically
     arranges to update the corrected header files.  They can be updated
     using the ‘mkheaders’ script installed in
     ‘LIBEXECDIR/gcc/TARGET/VERSION/install-tools/’.

   • On 68000 and x86 systems, for instance, you can get paradoxical
     results if you test the precise values of floating point numbers.
     For example, you can find that a floating point value which is not
     a NaN is not equal to itself.  This results from the fact that the
     floating point registers hold a few more bits of precision than fit
     in a ‘double’ in memory.  Compiled code moves values between memory
     and floating point registers at its convenience, and moving them
     into memory truncates them.

     You can partially avoid this problem by using the ‘-ffloat-store’
     option (*note Optimize Options::).

   • On AIX and other platforms without weak symbol support, templates
     need to be instantiated explicitly and symbols for static members
     of templates will not be generated.

   • On AIX, GCC scans object files and library archives for static
     constructors and destructors when linking an application before the
     linker prunes unreferenced symbols.  This is necessary to prevent
     the AIX linker from mistakenly assuming that static constructor or
     destructor are unused and removing them before the scanning can
     occur.  All static constructors and destructors found will be
     referenced even though the modules in which they occur may not be
     used by the program.  This may lead to both increased executable
     size and unexpected symbol references.


File: gcc.info,  Node: C++ Misunderstandings,  Next: Non-bugs,  Prev: Disappointments,  Up: Trouble

14.7 Common Misunderstandings with GNU C++
==========================================

C++ is a complex language and an evolving one, and its standard
definition (the ISO C++ standard) was only recently completed.  As a
result, your C++ compiler may occasionally surprise you, even when its
behavior is correct.  This section discusses some areas that frequently
give rise to questions of this sort.

* Menu:

* Static Definitions::  Static member declarations are not definitions
* Name lookup::         Name lookup, templates, and accessing members of base classes
* Temporaries::         Temporaries may vanish before you expect
* Copy Assignment::     Copy Assignment operators copy virtual bases twice


File: gcc.info,  Node: Static Definitions,  Next: Name lookup,  Up: C++ Misunderstandings

14.7.1 Declare _and_ Define Static Members
------------------------------------------

When a class has static data members, it is not enough to _declare_ the
static member; you must also _define_ it.  For example:

     class Foo
     {
       ...
       void method();
       static int bar;
     };

 This declaration only establishes that the class ‘Foo’ has an ‘int’
named ‘Foo::bar’, and a member function named ‘Foo::method’.  But you
still need to define _both_ ‘method’ and ‘bar’ elsewhere.  According to
the ISO standard, you must supply an initializer in one (and only one)
source file, such as:

     int Foo::bar = 0;

 Other C++ compilers may not correctly implement the standard behavior.
As a result, when you switch to ‘g++’ from one of these compilers, you
may discover that a program that appeared to work correctly in fact does
not conform to the standard: ‘g++’ reports as undefined symbols any
static data members that lack definitions.


File: gcc.info,  Node: Name lookup,  Next: Temporaries,  Prev: Static Definitions,  Up: C++ Misunderstandings

14.7.2 Name Lookup, Templates, and Accessing Members of Base Classes
--------------------------------------------------------------------

The C++ standard prescribes that all names that are not dependent on
template parameters are bound to their present definitions when parsing
a template function or class.(1)  Only names that are dependent are
looked up at the point of instantiation.  For example, consider

       void foo(double);

       struct A {
         template <typename T>
         void f () {
           foo (1);        // 1
           int i = N;      // 2
           T t;
           t.bar();        // 3
           foo (t);        // 4
         }

         static const int N;
       };

 Here, the names ‘foo’ and ‘N’ appear in a context that does not depend
on the type of ‘T’.  The compiler will thus require that they are
defined in the context of use in the template, not only before the point
of instantiation, and will here use ‘::foo(double)’ and ‘A::N’,
respectively.  In particular, it will convert the integer value to a
‘double’ when passing it to ‘::foo(double)’.

 Conversely, ‘bar’ and the call to ‘foo’ in the fourth marked line are
used in contexts that do depend on the type of ‘T’, so they are only
looked up at the point of instantiation, and you can provide
declarations for them after declaring the template, but before
instantiating it.  In particular, if you instantiate ‘A::f<int>’, the
last line will call an overloaded ‘::foo(int)’ if one was provided, even
if after the declaration of ‘struct A’.

 This distinction between lookup of dependent and non-dependent names is
called two-stage (or dependent) name lookup.  G++ implements it since
version 3.4.

 Two-stage name lookup sometimes leads to situations with behavior
different from non-template codes.  The most common is probably this:

       template <typename T> struct Base {
         int i;
       };

       template <typename T> struct Derived : public Base<T> {
         int get_i() { return i; }
       };

 In ‘get_i()’, ‘i’ is not used in a dependent context, so the compiler
will look for a name declared at the enclosing namespace scope (which is
the global scope here).  It will not look into the base class, since
that is dependent and you may declare specializations of ‘Base’ even
after declaring ‘Derived’, so the compiler cannot really know what ‘i’
would refer to.  If there is no global variable ‘i’, then you will get
an error message.

 In order to make it clear that you want the member of the base class,
you need to defer lookup until instantiation time, at which the base
class is known.  For this, you need to access ‘i’ in a dependent
context, by either using ‘this->i’ (remember that ‘this’ is of type
‘Derived<T>*’, so is obviously dependent), or using ‘Base<T>::i’.
Alternatively, ‘Base<T>::i’ might be brought into scope by a
‘using’-declaration.

 Another, similar example involves calling member functions of a base
class:

       template <typename T> struct Base {
           int f();
       };

       template <typename T> struct Derived : Base<T> {
           int g() { return f(); };
       };

 Again, the call to ‘f()’ is not dependent on template arguments (there
are no arguments that depend on the type ‘T’, and it is also not
otherwise specified that the call should be in a dependent context).
Thus a global declaration of such a function must be available, since
the one in the base class is not visible until instantiation time.  The
compiler will consequently produce the following error message:

       x.cc: In member function `int Derived<T>::g()':
       x.cc:6: error: there are no arguments to `f' that depend on a template
          parameter, so a declaration of `f' must be available
       x.cc:6: error: (if you use `-fpermissive', G++ will accept your code, but
          allowing the use of an undeclared name is deprecated)

 To make the code valid either use ‘this->f()’, or ‘Base<T>::f()’.
Using the ‘-fpermissive’ flag will also let the compiler accept the
code, by marking all function calls for which no declaration is visible
at the time of definition of the template for later lookup at
instantiation time, as if it were a dependent call.  We do not recommend
using ‘-fpermissive’ to work around invalid code, and it will also only
catch cases where functions in base classes are called, not where
variables in base classes are used (as in the example above).

 Note that some compilers (including G++ versions prior to 3.4) get
these examples wrong and accept above code without an error.  Those
compilers do not implement two-stage name lookup correctly.

   ---------- Footnotes ----------

   (1) The C++ standard just uses the term "dependent" for names that
depend on the type or value of template parameters.  This shorter term
will also be used in the rest of this section.


File: gcc.info,  Node: Temporaries,  Next: Copy Assignment,  Prev: Name lookup,  Up: C++ Misunderstandings

14.7.3 Temporaries May Vanish Before You Expect
-----------------------------------------------

It is dangerous to use pointers or references to _portions_ of a
temporary object.  The compiler may very well delete the object before
you expect it to, leaving a pointer to garbage.  The most common place
where this problem crops up is in classes like string classes,
especially ones that define a conversion function to type ‘char *’ or
‘const char *’--which is one reason why the standard ‘string’ class
requires you to call the ‘c_str’ member function.  However, any class
that returns a pointer to some internal structure is potentially subject
to this problem.

 For example, a program may use a function ‘strfunc’ that returns
‘string’ objects, and another function ‘charfunc’ that operates on
pointers to ‘char’:

     string strfunc ();
     void charfunc (const char *);

     void
     f ()
     {
       const char *p = strfunc().c_str();
       ...
       charfunc (p);
       ...
       charfunc (p);
     }

In this situation, it may seem reasonable to save a pointer to the C
string returned by the ‘c_str’ member function and use that rather than
call ‘c_str’ repeatedly.  However, the temporary string created by the
call to ‘strfunc’ is destroyed after ‘p’ is initialized, at which point
‘p’ is left pointing to freed memory.

 Code like this may run successfully under some other compilers,
particularly obsolete cfront-based compilers that delete temporaries
along with normal local variables.  However, the GNU C++ behavior is
standard-conforming, so if your program depends on late destruction of
temporaries it is not portable.

 The safe way to write such code is to give the temporary a name, which
forces it to remain until the end of the scope of the name.  For
example:

     const string& tmp = strfunc ();
     charfunc (tmp.c_str ());


File: gcc.info,  Node: Copy Assignment,  Prev: Temporaries,  Up: C++ Misunderstandings

14.7.4 Implicit Copy-Assignment for Virtual Bases
-------------------------------------------------

When a base class is virtual, only one subobject of the base class
belongs to each full object.  Also, the constructors and destructors are
invoked only once, and called from the most-derived class.  However,
such objects behave unspecified when being assigned.  For example:

     struct Base{
       char *name;
       Base(const char *n) : name(strdup(n)){}
       Base& operator= (const Base& other){
        free (name);
        name = strdup (other.name);
        return *this;
       }
     };

     struct A:virtual Base{
       int val;
       A():Base("A"){}
     };

     struct B:virtual Base{
       int bval;
       B():Base("B"){}
     };

     struct Derived:public A, public B{
       Derived():Base("Derived"){}
     };

     void func(Derived &d1, Derived &d2)
     {
       d1 = d2;
     }

 The C++ standard specifies that ‘Base::Base’ is only called once when
constructing or copy-constructing a Derived object.  It is unspecified
whether ‘Base::operator=’ is called more than once when the implicit
copy-assignment for Derived objects is invoked (as it is inside ‘func’
in the example).

 G++ implements the "intuitive" algorithm for copy-assignment: assign
all direct bases, then assign all members.  In that algorithm, the
virtual base subobject can be encountered more than once.  In the
example, copying proceeds in the following order: ‘name’ (via ‘strdup’),
‘val’, ‘name’ again, and ‘bval’.

 If application code relies on copy-assignment, a user-defined
copy-assignment operator removes any uncertainties.  With such an
operator, the application can define whether and how the virtual base
subobject is assigned.


File: gcc.info,  Node: Non-bugs,  Next: Warnings and Errors,  Prev: C++ Misunderstandings,  Up: Trouble

14.8 Certain Changes We Don't Want to Make
==========================================

This section lists changes that people frequently request, but which we
do not make because we think GCC is better without them.

   • Checking the number and type of arguments to a function which has
     an old-fashioned definition and no prototype.

     Such a feature would work only occasionally--only for calls that
     appear in the same file as the called function, following the
     definition.  The only way to check all calls reliably is to add a
     prototype for the function.  But adding a prototype eliminates the
     motivation for this feature.  So the feature is not worthwhile.

   • Warning about using an expression whose type is signed as a shift
     count.

     Shift count operands are probably signed more often than unsigned.
     Warning about this would cause far more annoyance than good.

   • Warning about assigning a signed value to an unsigned variable.

     Such assignments must be very common; warning about them would
     cause more annoyance than good.

   • Warning when a non-void function value is ignored.

     C contains many standard functions that return a value that most
     programs choose to ignore.  One obvious example is ‘printf’.
     Warning about this practice only leads the defensive programmer to
     clutter programs with dozens of casts to ‘void’.  Such casts are
     required so frequently that they become visual noise.  Writing
     those casts becomes so automatic that they no longer convey useful
     information about the intentions of the programmer.  For functions
     where the return value should never be ignored, use the
     ‘warn_unused_result’ function attribute (*note Function
     Attributes::).

   • Making ‘-fshort-enums’ the default.

     This would cause storage layout to be incompatible with most other
     C compilers.  And it doesn't seem very important, given that you
     can get the same result in other ways.  The case where it matters
     most is when the enumeration-valued object is inside a structure,
     and in that case you can specify a field width explicitly.

   • Making bit-fields unsigned by default on particular machines where
     "the ABI standard" says to do so.

     The ISO C standard leaves it up to the implementation whether a
     bit-field declared plain ‘int’ is signed or not.  This in effect
     creates two alternative dialects of C.

     The GNU C compiler supports both dialects; you can specify the
     signed dialect with ‘-fsigned-bitfields’ and the unsigned dialect
     with ‘-funsigned-bitfields’.  However, this leaves open the
     question of which dialect to use by default.

     Currently, the preferred dialect makes plain bit-fields signed,
     because this is simplest.  Since ‘int’ is the same as ‘signed int’
     in every other context, it is cleanest for them to be the same in
     bit-fields as well.

     Some computer manufacturers have published Application Binary
     Interface standards which specify that plain bit-fields should be
     unsigned.  It is a mistake, however, to say anything about this
     issue in an ABI.  This is because the handling of plain bit-fields
     distinguishes two dialects of C.  Both dialects are meaningful on
     every type of machine.  Whether a particular object file was
     compiled using signed bit-fields or unsigned is of no concern to
     other object files, even if they access the same bit-fields in the
     same data structures.

     A given program is written in one or the other of these two
     dialects.  The program stands a chance to work on most any machine
     if it is compiled with the proper dialect.  It is unlikely to work
     at all if compiled with the wrong dialect.

     Many users appreciate the GNU C compiler because it provides an
     environment that is uniform across machines.  These users would be
     inconvenienced if the compiler treated plain bit-fields differently
     on certain machines.

     Occasionally users write programs intended only for a particular
     machine type.  On these occasions, the users would benefit if the
     GNU C compiler were to support by default the same dialect as the
     other compilers on that machine.  But such applications are rare.
     And users writing a program to run on more than one type of machine
     cannot possibly benefit from this kind of compatibility.

     This is why GCC does and will treat plain bit-fields in the same
     fashion on all types of machines (by default).

     There are some arguments for making bit-fields unsigned by default
     on all machines.  If, for example, this becomes a universal de
     facto standard, it would make sense for GCC to go along with it.
     This is something to be considered in the future.

     (Of course, users strongly concerned about portability should
     indicate explicitly in each bit-field whether it is signed or not.
     In this way, they write programs which have the same meaning in
     both C dialects.)

   • Undefining ‘__STDC__’ when ‘-ansi’ is not used.

     Currently, GCC defines ‘__STDC__’ unconditionally.  This provides
     good results in practice.

     Programmers normally use conditionals on ‘__STDC__’ to ask whether
     it is safe to use certain features of ISO C, such as function
     prototypes or ISO token concatenation.  Since plain ‘gcc’ supports
     all the features of ISO C, the correct answer to these questions is
     "yes".

     Some users try to use ‘__STDC__’ to check for the availability of
     certain library facilities.  This is actually incorrect usage in an
     ISO C program, because the ISO C standard says that a conforming
     freestanding implementation should define ‘__STDC__’ even though it
     does not have the library facilities.  ‘gcc -ansi -pedantic’ is a
     conforming freestanding implementation, and it is therefore
     required to define ‘__STDC__’, even though it does not come with an
     ISO C library.

     Sometimes people say that defining ‘__STDC__’ in a compiler that
     does not completely conform to the ISO C standard somehow violates
     the standard.  This is illogical.  The standard is a standard for
     compilers that claim to support ISO C, such as ‘gcc -ansi’--not for
     other compilers such as plain ‘gcc’.  Whatever the ISO C standard
     says is relevant to the design of plain ‘gcc’ without ‘-ansi’ only
     for pragmatic reasons, not as a requirement.

     GCC normally defines ‘__STDC__’ to be 1, and in addition defines
     ‘__STRICT_ANSI__’ if you specify the ‘-ansi’ option, or a ‘-std’
     option for strict conformance to some version of ISO C.  On some
     hosts, system include files use a different convention, where
     ‘__STDC__’ is normally 0, but is 1 if the user specifies strict
     conformance to the C Standard.  GCC follows the host convention
     when processing system include files, but when processing user
     files it follows the usual GNU C convention.

   • Undefining ‘__STDC__’ in C++.

     Programs written to compile with C++-to-C translators get the value
     of ‘__STDC__’ that goes with the C compiler that is subsequently
     used.  These programs must test ‘__STDC__’ to determine what kind
     of C preprocessor that compiler uses: whether they should
     concatenate tokens in the ISO C fashion or in the traditional
     fashion.

     These programs work properly with GNU C++ if ‘__STDC__’ is defined.
     They would not work otherwise.

     In addition, many header files are written to provide prototypes in
     ISO C but not in traditional C.  Many of these header files can
     work without change in C++ provided ‘__STDC__’ is defined.  If
     ‘__STDC__’ is not defined, they will all fail, and will all need to
     be changed to test explicitly for C++ as well.

   • Deleting "empty" loops.

     Historically, GCC has not deleted "empty" loops under the
     assumption that the most likely reason you would put one in a
     program is to have a delay, so deleting them will not make real
     programs run any faster.

     However, the rationale here is that optimization of a nonempty loop
     cannot produce an empty one.  This held for carefully written C
     compiled with less powerful optimizers but is not always the case
     for carefully written C++ or with more powerful optimizers.  Thus
     GCC will remove operations from loops whenever it can determine
     those operations are not externally visible (apart from the time
     taken to execute them, of course).  In case the loop can be proved
     to be finite, GCC will also remove the loop itself.

     Be aware of this when performing timing tests, for instance the
     following loop can be completely removed, provided
     ‘some_expression’ can provably not change any global state.

          {
             int sum = 0;
             int ix;

             for (ix = 0; ix != 10000; ix++)
                sum += some_expression;
          }

     Even though ‘sum’ is accumulated in the loop, no use is made of
     that summation, so the accumulation can be removed.

   • Making side effects happen in the same order as in some other
     compiler.

     It is never safe to depend on the order of evaluation of side
     effects.  For example, a function call like this may very well
     behave differently from one compiler to another:

          void func (int, int);

          int i = 2;
          func (i++, i++);

     There is no guarantee (in either the C or the C++ standard language
     definitions) that the increments will be evaluated in any
     particular order.  Either increment might happen first.  ‘func’
     might get the arguments ‘2, 3’, or it might get ‘3, 2’, or even ‘2,
     2’.

   • Making certain warnings into errors by default.

     Some ISO C testsuites report failure when the compiler does not
     produce an error message for a certain program.

     ISO C requires a "diagnostic" message for certain kinds of invalid
     programs, but a warning is defined by GCC to count as a diagnostic.
     If GCC produces a warning but not an error, that is correct ISO C
     support.  If testsuites call this "failure", they should be run
     with the GCC option ‘-pedantic-errors’, which will turn these
     warnings into errors.


File: gcc.info,  Node: Warnings and Errors,  Prev: Non-bugs,  Up: Trouble

14.9 Warning Messages and Error Messages
========================================

The GNU compiler can produce two kinds of diagnostics: errors and
warnings.  Each kind has a different purpose:

     “Errors” report problems that make it impossible to compile your
     program.  GCC reports errors with the source file name and line
     number where the problem is apparent.

     “Warnings” report other unusual conditions in your code that _may_
     indicate a problem, although compilation can (and does) proceed.
     Warning messages also report the source file name and line number,
     but include the text ‘warning:’ to distinguish them from error
     messages.

 Warnings may indicate danger points where you should check to make sure
that your program really does what you intend; or the use of obsolete
features; or the use of nonstandard features of GNU C or C++.  Many
warnings are issued only if you ask for them, with one of the ‘-W’
options (for instance, ‘-Wall’ requests a variety of useful warnings).

 GCC always tries to compile your program if possible; it never
gratuitously rejects a program whose meaning is clear merely because
(for instance) it fails to conform to a standard.  In some cases,
however, the C and C++ standards specify that certain extensions are
forbidden, and a diagnostic _must_ be issued by a conforming compiler.
The ‘-pedantic’ option tells GCC to issue warnings in such cases;
‘-pedantic-errors’ says to make them errors instead.  This does not mean
that _all_ non-ISO constructs get warnings or errors.

 *Note Options to Request or Suppress Warnings: Warning Options, for
more detail on these and related command-line options.


File: gcc.info,  Node: Bugs,  Next: Service,  Prev: Trouble,  Up: Top

15 Reporting Bugs
*****************

Your bug reports play an essential role in making GCC reliable.

 When you encounter a problem, the first thing to do is to see if it is
already known.  *Note Trouble::.  If it isn't known, then you should
report the problem.

* Menu:

* Criteria:  Bug Criteria.   Have you really found a bug?
* Reporting: Bug Reporting.  How to report a bug effectively.


File: gcc.info,  Node: Bug Criteria,  Next: Bug Reporting,  Up: Bugs

15.1 Have You Found a Bug?
==========================

If you are not sure whether you have found a bug, here are some
guidelines:

   • If the compiler gets a fatal signal, for any input whatever, that
     is a compiler bug.  Reliable compilers never crash.

   • If the compiler produces invalid assembly code, for any input
     whatever (except an ‘asm’ statement), that is a compiler bug,
     unless the compiler reports errors (not just warnings) which would
     ordinarily prevent the assembler from being run.

   • If the compiler produces valid assembly code that does not
     correctly execute the input source code, that is a compiler bug.

     However, you must double-check to make sure, because you may have a
     program whose behavior is undefined, which happened by chance to
     give the desired results with another C or C++ compiler.

     For example, in many nonoptimizing compilers, you can write ‘x;’ at
     the end of a function instead of ‘return x;’, with the same
     results.  But the value of the function is undefined if ‘return’ is
     omitted; it is not a bug when GCC produces different results.

     Problems often result from expressions with two increment
     operators, as in ‘f (*p++, *p++)’.  Your previous compiler might
     have interpreted that expression the way you intended; GCC might
     interpret it another way.  Neither compiler is wrong.  The bug is
     in your code.

     After you have localized the error to a single source line, it
     should be easy to check for these things.  If your program is
     correct and well defined, you have found a compiler bug.

   • If the compiler produces an error message for valid input, that is
     a compiler bug.

   • If the compiler does not produce an error message for invalid
     input, that is a compiler bug.  However, you should note that your
     idea of "invalid input" might be someone else's idea of "an
     extension" or "support for traditional practice".

   • If you are an experienced user of one of the languages GCC
     supports, your suggestions for improvement of GCC are welcome in
     any case.


File: gcc.info,  Node: Bug Reporting,  Prev: Bug Criteria,  Up: Bugs

15.2 How and Where to Report Bugs
=================================

Bugs should be reported to the bug database at
<https://gcc.gnu.org/bugs/>.


File: gcc.info,  Node: Service,  Next: Contributing,  Prev: Bugs,  Up: Top

16 How To Get Help with GCC
***************************

If you need help installing, using or changing GCC, there are two ways
to find it:

   • Send a message to a suitable network mailing list.  First try
     <gcc-help@gcc.gnu.org> (for help installing or using GCC), and if
     that brings no response, try <gcc@gcc.gnu.org>.  For help changing
     GCC, ask <gcc@gcc.gnu.org>.  If you think you have found a bug in
     GCC, please report it following the instructions at *note Bug
     Reporting::.

   • Look in the service directory for someone who might help you for a
     fee.  The service directory is found at
     <https://www.fsf.org/resources/service>.

 For further information, see <https://gcc.gnu.org/faq.html#support>.


File: gcc.info,  Node: Contributing,  Next: Funding,  Prev: Service,  Up: Top

17 Contributing to GCC Development
**********************************

If you would like to help pretest GCC releases to assure they work well,
current development sources are available via Git (see
<https://gcc.gnu.org/git.html>).  Source and binary snapshots are also
available for FTP; see <https://gcc.gnu.org/snapshots.html>.

 If you would like to work on improvements to GCC, please read the
advice at these URLs:

     <https://gcc.gnu.org/contribute.html>
     <https://gcc.gnu.org/contributewhy.html>

for information on how to make useful contributions and avoid
duplication of effort.  Suggested projects are listed at
<https://gcc.gnu.org/projects/>.


File: gcc.info,  Node: Funding,  Next: GNU Project,  Prev: Contributing,  Up: Top

Funding Free Software
*********************

If you want to have more free software a few years from now, it makes
sense for you to help encourage people to contribute funds for its
development.  The most effective approach known is to encourage
commercial redistributors to donate.

 Users of free software systems can boost the pace of development by
encouraging for-a-fee distributors to donate part of their selling price
to free software developers--the Free Software Foundation, and others.

 The way to convince distributors to do this is to demand it and expect
it from them.  So when you compare distributors, judge them partly by
how much they give to free software development.  Show distributors they
must compete to be the one who gives the most.

 To make this approach work, you must insist on numbers that you can
compare, such as, "We will donate ten dollars to the Frobnitz project
for each disk sold."  Don't be satisfied with a vague promise, such as
"A portion of the profits are donated," since it doesn't give a basis
for comparison.

 Even a precise fraction "of the profits from this disk" is not very
meaningful, since creative accounting and unrelated business decisions
can greatly alter what fraction of the sales price counts as profit.  If
the price you pay is $50, ten percent of the profit is probably less
than a dollar; it might be a few cents, or nothing at all.

 Some redistributors do development work themselves.  This is useful
too; but to keep everyone honest, you need to inquire how much they do,
and what kind.  Some kinds of development make much more long-term
difference than others.  For example, maintaining a separate version of
a program contributes very little; maintaining the standard version of a
program for the whole community contributes much.  Easy new ports
contribute little, since someone else would surely do them; difficult
ports such as adding a new CPU to the GNU Compiler Collection contribute
more; major new features or packages contribute the most.

 By establishing the idea that supporting further development is "the
proper thing to do" when distributing free software for a fee, we can
assure a steady flow of resources into making more free software.

     Copyright © 1994 Free Software Foundation, Inc.
     Verbatim copying and redistribution of this section is permitted
     without royalty; alteration is not permitted.


File: gcc.info,  Node: GNU Project,  Next: Copying,  Prev: Funding,  Up: Top

The GNU Project and GNU/Linux
*****************************

The GNU Project was launched in 1984 to develop a complete Unix-like
operating system which is free software: the GNU system.  (GNU is a
recursive acronym for "GNU's Not Unix"; it is pronounced "guh-NEW".)
Variants of the GNU operating system, which use the kernel Linux, are
now widely used; though these systems are often referred to as "Linux",
they are more accurately called GNU/Linux systems.

 For more information, see:
     <https://www.gnu.org/>
     <https://www.gnu.org/gnu/linux-and-gnu.html>


File: gcc.info,  Node: Copying,  Next: GNU Free Documentation License,  Prev: GNU Project,  Up: Top

GNU General Public License
**************************

                        Version 3, 29 June 2007

     Copyright © 2007 Free Software Foundation, Inc. <https://fsf.org/>

     Everyone is permitted to copy and distribute verbatim copies of this
     license document, but changing it is not allowed.

Preamble
========

The GNU General Public License is a free, copyleft license for software
and other kinds of works.

 The licenses for most software and other practical works are designed
to take away your freedom to share and change the works.  By contrast,
the GNU General Public License is intended to guarantee your freedom to
share and change all versions of a program-to make sure it remains free
software for all its users.  We, the Free Software Foundation, use the
GNU General Public License for most of our software; it applies also to
any other work released this way by its authors.  You can apply it to
your programs, too.

 When we speak of free software, we are referring to freedom, not price.
Our General Public Licenses are designed to make sure that you have the
freedom to distribute copies of free software (and charge for them if
you wish), that you receive source code or can get it if you want it,
that you can change the software or use pieces of it in new free
programs, and that you know you can do these things.

 To protect your rights, we need to prevent others from denying you
these rights or asking you to surrender the rights.  Therefore, you have
certain responsibilities if you distribute copies of the software, or if
you modify it: responsibilities to respect the freedom of others.

 For example, if you distribute copies of such a program, whether gratis
or for a fee, you must pass on to the recipients the same freedoms that
you received.  You must make sure that they, too, receive or can get the
source code.  And you must show them these terms so they know their
rights.

 Developers that use the GNU GPL protect your rights with two steps: (1)
assert copyright on the software, and (2) offer you this License giving
you legal permission to copy, distribute and/or modify it.

 For the developers' and authors' protection, the GPL clearly explains
that there is no warranty for this free software.  For both users' and
authors' sake, the GPL requires that modified versions be marked as
changed, so that their problems will not be attributed erroneously to
authors of previous versions.

 Some devices are designed to deny users access to install or run
modified versions of the software inside them, although the manufacturer
can do so.  This is fundamentally incompatible with the aim of
protecting users' freedom to change the software.  The systematic
pattern of such abuse occurs in the area of products for individuals to
use, which is precisely where it is most unacceptable.  Therefore, we
have designed this version of the GPL to prohibit the practice for those
products.  If such problems arise substantially in other domains, we
stand ready to extend this provision to those domains in future versions
of the GPL, as needed to protect the freedom of users.

 Finally, every program is threatened constantly by software patents.
States should not allow patents to restrict development and use of
software on general-purpose computers, but in those that do, we wish to
avoid the special danger that patents applied to a free program could
make it effectively proprietary.  To prevent this, the GPL assures that
patents cannot be used to render the program non-free.

 The precise terms and conditions for copying, distribution and
modification follow.

TERMS AND CONDITIONS
====================

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     could give under the previous paragraph, plus a right to possession
     of the Corresponding Source of the work from the predecessor in
     interest, if the predecessor has it or can get it with reasonable
     efforts.

     You may not impose any further restrictions on the exercise of the
     rights granted or affirmed under this License.  For example, you
     may not impose a license fee, royalty, or other charge for exercise
     of rights granted under this License, and you may not initiate
     litigation (including a cross-claim or counterclaim in a lawsuit)
     alleging that any patent claim is infringed by making, using,
     selling, offering for sale, or importing the Program or any portion
     of it.

  11. Patents.

     A "contributor" is a copyright holder who authorizes use under this
     License of the Program or a work on which the Program is based.
     The work thus licensed is called the contributor's "contributor
     version".

     A contributor's "essential patent claims" are all patent claims
     owned or controlled by the contributor, whether already acquired or
     hereafter acquired, that would be infringed by some manner,
     permitted by this License, of making, using, or selling its
     contributor version, but do not include claims that would be
     infringed only as a consequence of further modification of the
     contributor version.  For purposes of this definition, "control"
     includes the right to grant patent sublicenses in a manner
     consistent with the requirements of this License.

     Each contributor grants you a non-exclusive, worldwide,
     royalty-free patent license under the contributor's essential
     patent claims, to make, use, sell, offer for sale, import and
     otherwise run, modify and propagate the contents of its contributor
     version.

     In the following three paragraphs, a "patent license" is any
     express agreement or commitment, however denominated, not to
     enforce a patent (such as an express permission to practice a
     patent or covenant not to sue for patent infringement).  To "grant"
     such a patent license to a party means to make such an agreement or
     commitment not to enforce a patent against the party.

     If you convey a covered work, knowingly relying on a patent
     license, and the Corresponding Source of the work is not available
     for anyone to copy, free of charge and under the terms of this
     License, through a publicly available network server or other
     readily accessible means, then you must either (1) cause the
     Corresponding Source to be so available, or (2) arrange to deprive
     yourself of the benefit of the patent license for this particular
     work, or (3) arrange, in a manner consistent with the requirements
     of this License, to extend the patent license to downstream
     recipients.  "Knowingly relying" means you have actual knowledge
     that, but for the patent license, your conveying the covered work
     in a country, or your recipient's use of the covered work in a
     country, would infringe one or more identifiable patents in that
     country that you have reason to believe are valid.

     If, pursuant to or in connection with a single transaction or
     arrangement, you convey, or propagate by procuring conveyance of, a
     covered work, and grant a patent license to some of the parties
     receiving the covered work authorizing them to use, propagate,
     modify or convey a specific copy of the covered work, then the
     patent license you grant is automatically extended to all
     recipients of the covered work and works based on it.

     A patent license is "discriminatory" if it does not include within
     the scope of its coverage, prohibits the exercise of, or is
     conditioned on the non-exercise of one or more of the rights that
     are specifically granted under this License.  You may not convey a
     covered work if you are a party to an arrangement with a third
     party that is in the business of distributing software, under which
     you make payment to the third party based on the extent of your
     activity of conveying the work, and under which the third party
     grants, to any of the parties who would receive the covered work
     from you, a discriminatory patent license (a) in connection with
     copies of the covered work conveyed by you (or copies made from
     those copies), or (b) primarily for and in connection with specific
     products or compilations that contain the covered work, unless you
     entered into that arrangement, or that patent license was granted,
     prior to 28 March 2007.

     Nothing in this License shall be construed as excluding or limiting
     any implied license or other defenses to infringement that may
     otherwise be available to you under applicable patent law.

  12. No Surrender of Others' Freedom.

     If conditions are imposed on you (whether by court order, agreement
     or otherwise) that contradict the conditions of this License, they
     do not excuse you from the conditions of this License.  If you
     cannot convey a covered work so as to satisfy simultaneously your
     obligations under this License and any other pertinent obligations,
     then as a consequence you may not convey it at all.  For example,
     if you agree to terms that obligate you to collect a royalty for
     further conveying from those to whom you convey the Program, the
     only way you could satisfy both those terms and this License would
     be to refrain entirely from conveying the Program.

  13. Use with the GNU Affero General Public License.

     Notwithstanding any other provision of this License, you have
     permission to link or combine any covered work with a work licensed
     under version 3 of the GNU Affero General Public License into a
     single combined work, and to convey the resulting work.  The terms
     of this License will continue to apply to the part which is the
     covered work, but the special requirements of the GNU Affero
     General Public License, section 13, concerning interaction through
     a network will apply to the combination as such.

  14. Revised Versions of this License.

     The Free Software Foundation may publish revised and/or new
     versions of the GNU General Public License from time to time.  Such
     new versions will be similar in spirit to the present version, but
     may differ in detail to address new problems or concerns.

     Each version is given a distinguishing version number.  If the
     Program specifies that a certain numbered version of the GNU
     General Public License "or any later version" applies to it, you
     have the option of following the terms and conditions either of
     that numbered version or of any later version published by the Free
     Software Foundation.  If the Program does not specify a version
     number of the GNU General Public License, you may choose any
     version ever published by the Free Software Foundation.

     If the Program specifies that a proxy can decide which future
     versions of the GNU General Public License can be used, that
     proxy's public statement of acceptance of a version permanently
     authorizes you to choose that version for the Program.

     Later license versions may give you additional or different
     permissions.  However, no additional obligations are imposed on any
     author or copyright holder as a result of your choosing to follow a
     later version.

  15. Disclaimer of Warranty.

     THERE IS NO WARRANTY FOR THE PROGRAM, TO THE EXTENT PERMITTED BY
     APPLICABLE LAW. EXCEPT WHEN OTHERWISE STATED IN WRITING THE
     COPYRIGHT HOLDERS AND/OR OTHER PARTIES PROVIDE THE PROGRAM "AS IS"
     WITHOUT WARRANTY OF ANY KIND, EITHER EXPRESSED OR IMPLIED,
     INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF
     MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. THE ENTIRE
     RISK AS TO THE QUALITY AND PERFORMANCE OF THE PROGRAM IS WITH YOU.
     SHOULD THE PROGRAM PROVE DEFECTIVE, YOU ASSUME THE COST OF ALL
     NECESSARY SERVICING, REPAIR OR CORRECTION.

  16. Limitation of Liability.

     IN NO EVENT UNLESS REQUIRED BY APPLICABLE LAW OR AGREED TO IN
     WRITING WILL ANY COPYRIGHT HOLDER, OR ANY OTHER PARTY WHO MODIFIES
     AND/OR CONVEYS THE PROGRAM AS PERMITTED ABOVE, BE LIABLE TO YOU FOR
     DAMAGES, INCLUDING ANY GENERAL, SPECIAL, INCIDENTAL OR
     CONSEQUENTIAL DAMAGES ARISING OUT OF THE USE OR INABILITY TO USE
     THE PROGRAM (INCLUDING BUT NOT LIMITED TO LOSS OF DATA OR DATA
     BEING RENDERED INACCURATE OR LOSSES SUSTAINED BY YOU OR THIRD
     PARTIES OR A FAILURE OF THE PROGRAM TO OPERATE WITH ANY OTHER
     PROGRAMS), EVEN IF SUCH HOLDER OR OTHER PARTY HAS BEEN ADVISED OF
     THE POSSIBILITY OF SUCH DAMAGES.

  17. Interpretation of Sections 15 and 16.

     If the disclaimer of warranty and limitation of liability provided
     above cannot be given local legal effect according to their terms,
     reviewing courts shall apply local law that most closely
     approximates an absolute waiver of all civil liability in
     connection with the Program, unless a warranty or assumption of
     liability accompanies a copy of the Program in return for a fee.

END OF TERMS AND CONDITIONS
===========================

How to Apply These Terms to Your New Programs
=============================================

If you develop a new program, and you want it to be of the greatest
possible use to the public, the best way to achieve this is to make it
free software which everyone can redistribute and change under these
terms.

 To do so, attach the following notices to the program.  It is safest to
attach them to the start of each source file to most effectively state
the exclusion of warranty; and each file should have at least the
"copyright" line and a pointer to where the full notice is found.

     ONE LINE TO GIVE THE PROGRAM'S NAME AND A BRIEF IDEA OF WHAT IT DOES.
     Copyright (C) YEAR NAME OF AUTHOR

     This program is free software: you can redistribute it and/or modify
     it under the terms of the GNU General Public License as published by
     the Free Software Foundation, either version 3 of the License, or (at
     your option) any later version.

     This program is distributed in the hope that it will be useful, but
     WITHOUT ANY WARRANTY; without even the implied warranty of
     MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
     General Public License for more details.

     You should have received a copy of the GNU General Public License
     along with this program.  If not, see <https://www.gnu.org/licenses/>.

 Also add information on how to contact you by electronic and paper
mail.

 If the program does terminal interaction, make it output a short notice
like this when it starts in an interactive mode:

     PROGRAM Copyright (C) YEAR NAME OF AUTHOR
     This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’.
     This is free software, and you are welcome to redistribute it
     under certain conditions; type ‘show c’ for details.

 The hypothetical commands ‘show w’ and ‘show c’ should show the
appropriate parts of the General Public License.  Of course, your
program's commands might be different; for a GUI interface, you would
use an "about box".

 You should also get your employer (if you work as a programmer) or
school, if any, to sign a "copyright disclaimer" for the program, if
necessary.  For more information on this, and how to apply and follow
the GNU GPL, see <https://www.gnu.org/licenses/>.

 The GNU General Public License does not permit incorporating your
program into proprietary programs.  If your program is a subroutine
library, you may consider it more useful to permit linking proprietary
applications with the library.  If this is what you want to do, use the
GNU Lesser General Public License instead of this License.  But first,
please read <https://www.gnu.org/licenses/why-not-lgpl.html>.


File: gcc.info,  Node: GNU Free Documentation License,  Next: Contributors,  Prev: Copying,  Up: Top

GNU Free Documentation License
******************************

                     Version 1.3, 3 November 2008

     Copyright © 2000, 2001, 2002, 2007, 2008 Free Software Foundation, Inc.
     <https://fsf.org/>

     Everyone is permitted to copy and distribute verbatim copies
     of this license document, but changing it is not allowed.

  0. PREAMBLE

     The purpose of this License is to make a manual, textbook, or other
     functional and useful document “free” in the sense of freedom: to
     assure everyone the effective freedom to copy and redistribute it,
     with or without modifying it, either commercially or
     noncommercially.  Secondarily, this License preserves for the
     author and publisher a way to get credit for their work, while not
     being considered responsible for modifications made by others.

     This License is a kind of "copyleft", which means that derivative
     works of the document must themselves be free in the same sense.
     It complements the GNU General Public License, which is a copyleft
     license designed for free software.

     We have designed this License in order to use it for manuals for
     free software, because free software needs free documentation: a
     free program should come with manuals providing the same freedoms
     that the software does.  But this License is not limited to
     software manuals; it can be used for any textual work, regardless
     of subject matter or whether it is published as a printed book.  We
     recommend this License principally for works whose purpose is
     instruction or reference.

  1. APPLICABILITY AND DEFINITIONS

     This License applies to any manual or other work, in any medium,
     that contains a notice placed by the copyright holder saying it can
     be distributed under the terms of this License.  Such a notice
     grants a world-wide, royalty-free license, unlimited in duration,
     to use that work under the conditions stated herein.  The
     "Document", below, refers to any such manual or work.  Any member
     of the public is a licensee, and is addressed as "you".  You accept
     the license if you copy, modify or distribute the work in a way
     requiring permission under copyright law.

     A "Modified Version" of the Document means any work containing the
     Document or a portion of it, either copied verbatim, or with
     modifications and/or translated into another language.

     A "Secondary Section" is a named appendix or a front-matter section
     of the Document that deals exclusively with the relationship of the
     publishers or authors of the Document to the Document's overall
     subject (or to related matters) and contains nothing that could
     fall directly within that overall subject.  (Thus, if the Document
     is in part a textbook of mathematics, a Secondary Section may not
     explain any mathematics.)  The relationship could be a matter of
     historical connection with the subject or with related matters, or
     of legal, commercial, philosophical, ethical or political position
     regarding them.

     The "Invariant Sections" are certain Secondary Sections whose
     titles are designated, as being those of Invariant Sections, in the
     notice that says that the Document is released under this License.
     If a section does not fit the above definition of Secondary then it
     is not allowed to be designated as Invariant.  The Document may
     contain zero Invariant Sections.  If the Document does not identify
     any Invariant Sections then there are none.

     The "Cover Texts" are certain short passages of text that are
     listed, as Front-Cover Texts or Back-Cover Texts, in the notice
     that says that the Document is released under this License.  A
     Front-Cover Text may be at most 5 words, and a Back-Cover Text may
     be at most 25 words.

     A "Transparent" copy of the Document means a machine-readable copy,
     represented in a format whose specification is available to the
     general public, that is suitable for revising the document
     straightforwardly with generic text editors or (for images composed
     of pixels) generic paint programs or (for drawings) some widely
     available drawing editor, and that is suitable for input to text
     formatters or for automatic translation to a variety of formats
     suitable for input to text formatters.  A copy made in an otherwise
     Transparent file format whose markup, or absence of markup, has
     been arranged to thwart or discourage subsequent modification by
     readers is not Transparent.  An image format is not Transparent if
     used for any substantial amount of text.  A copy that is not
     "Transparent" is called "Opaque".

     Examples of suitable formats for Transparent copies include plain
     ASCII without markup, Texinfo input format, LaTeX input format,
     SGML or XML using a publicly available DTD, and standard-conforming
     simple HTML, PostScript or PDF designed for human modification.
     Examples of transparent image formats include PNG, XCF and JPG.
     Opaque formats include proprietary formats that can be read and
     edited only by proprietary word processors, SGML or XML for which
     the DTD and/or processing tools are not generally available, and
     the machine-generated HTML, PostScript or PDF produced by some word
     processors for output purposes only.

     The "Title Page" means, for a printed book, the title page itself,
     plus such following pages as are needed to hold, legibly, the
     material this License requires to appear in the title page.  For
     works in formats which do not have any title page as such, "Title
     Page" means the text near the most prominent appearance of the
     work's title, preceding the beginning of the body of the text.

     The "publisher" means any person or entity that distributes copies
     of the Document to the public.

     A section "Entitled XYZ" means a named subunit of the Document
     whose title either is precisely XYZ or contains XYZ in parentheses
     following text that translates XYZ in another language.  (Here XYZ
     stands for a specific section name mentioned below, such as
     "Acknowledgements", "Dedications", "Endorsements", or "History".)
     To "Preserve the Title" of such a section when you modify the
     Document means that it remains a section "Entitled XYZ" according
     to this definition.

     The Document may include Warranty Disclaimers next to the notice
     which states that this License applies to the Document.  These
     Warranty Disclaimers are considered to be included by reference in
     this License, but only as regards disclaiming warranties: any other
     implication that these Warranty Disclaimers may have is void and
     has no effect on the meaning of this License.

  2. VERBATIM COPYING

     You may copy and distribute the Document in any medium, either
     commercially or noncommercially, provided that this License, the
     copyright notices, and the license notice saying this License
     applies to the Document are reproduced in all copies, and that you
     add no other conditions whatsoever to those of this License.  You
     may not use technical measures to obstruct or control the reading
     or further copying of the copies you make or distribute.  However,
     you may accept compensation in exchange for copies.  If you
     distribute a large enough number of copies you must also follow the
     conditions in section 3.

     You may also lend copies, under the same conditions stated above,
     and you may publicly display copies.

  3. COPYING IN QUANTITY

     If you publish printed copies (or copies in media that commonly
     have printed covers) of the Document, numbering more than 100, and
     the Document's license notice requires Cover Texts, you must
     enclose the copies in covers that carry, clearly and legibly, all
     these Cover Texts: Front-Cover Texts on the front cover, and
     Back-Cover Texts on the back cover.  Both covers must also clearly
     and legibly identify you as the publisher of these copies.  The
     front cover must present the full title with all words of the title
     equally prominent and visible.  You may add other material on the
     covers in addition.  Copying with changes limited to the covers, as
     long as they preserve the title of the Document and satisfy these
     conditions, can be treated as verbatim copying in other respects.

     If the required texts for either cover are too voluminous to fit
     legibly, you should put the first ones listed (as many as fit
     reasonably) on the actual cover, and continue the rest onto
     adjacent pages.

     If you publish or distribute Opaque copies of the Document
     numbering more than 100, you must either include a machine-readable
     Transparent copy along with each Opaque copy, or state in or with
     each Opaque copy a computer-network location from which the general
     network-using public has access to download using public-standard
     network protocols a complete Transparent copy of the Document, free
     of added material.  If you use the latter option, you must take
     reasonably prudent steps, when you begin distribution of Opaque
     copies in quantity, to ensure that this Transparent copy will
     remain thus accessible at the stated location until at least one
     year after the last time you distribute an Opaque copy (directly or
     through your agents or retailers) of that edition to the public.

     It is requested, but not required, that you contact the authors of
     the Document well before redistributing any large number of copies,
     to give them a chance to provide you with an updated version of the
     Document.

  4. MODIFICATIONS

     You may copy and distribute a Modified Version of the Document
     under the conditions of sections 2 and 3 above, provided that you
     release the Modified Version under precisely this License, with the
     Modified Version filling the role of the Document, thus licensing
     distribution and modification of the Modified Version to whoever
     possesses a copy of it.  In addition, you must do these things in
     the Modified Version:

       A. Use in the Title Page (and on the covers, if any) a title
          distinct from that of the Document, and from those of previous
          versions (which should, if there were any, be listed in the
          History section of the Document).  You may use the same title
          as a previous version if the original publisher of that
          version gives permission.

       B. List on the Title Page, as authors, one or more persons or
          entities responsible for authorship of the modifications in
          the Modified Version, together with at least five of the
          principal authors of the Document (all of its principal
          authors, if it has fewer than five), unless they release you
          from this requirement.

       C. State on the Title page the name of the publisher of the
          Modified Version, as the publisher.

       D. Preserve all the copyright notices of the Document.

       E. Add an appropriate copyright notice for your modifications
          adjacent to the other copyright notices.

       F. Include, immediately after the copyright notices, a license
          notice giving the public permission to use the Modified
          Version under the terms of this License, in the form shown in
          the Addendum below.

       G. Preserve in that license notice the full lists of Invariant
          Sections and required Cover Texts given in the Document's
          license notice.

       H. Include an unaltered copy of this License.

       I. Preserve the section Entitled "History", Preserve its Title,
          and add to it an item stating at least the title, year, new
          authors, and publisher of the Modified Version as given on the
          Title Page.  If there is no section Entitled "History" in the
          Document, create one stating the title, year, authors, and
          publisher of the Document as given on its Title Page, then add
          an item describing the Modified Version as stated in the
          previous sentence.

       J. Preserve the network location, if any, given in the Document
          for public access to a Transparent copy of the Document, and
          likewise the network locations given in the Document for
          previous versions it was based on.  These may be placed in the
          "History" section.  You may omit a network location for a work
          that was published at least four years before the Document
          itself, or if the original publisher of the version it refers
          to gives permission.

       K. For any section Entitled "Acknowledgements" or "Dedications",
          Preserve the Title of the section, and preserve in the section
          all the substance and tone of each of the contributor
          acknowledgements and/or dedications given therein.

       L. Preserve all the Invariant Sections of the Document, unaltered
          in their text and in their titles.  Section numbers or the
          equivalent are not considered part of the section titles.

       M. Delete any section Entitled "Endorsements".  Such a section
          may not be included in the Modified Version.

       N. Do not retitle any existing section to be Entitled
          "Endorsements" or to conflict in title with any Invariant
          Section.

       O. Preserve any Warranty Disclaimers.

     If the Modified Version includes new front-matter sections or
     appendices that qualify as Secondary Sections and contain no
     material copied from the Document, you may at your option designate
     some or all of these sections as invariant.  To do this, add their
     titles to the list of Invariant Sections in the Modified Version's
     license notice.  These titles must be distinct from any other
     section titles.

     You may add a section Entitled "Endorsements", provided it contains
     nothing but endorsements of your Modified Version by various
     parties--for example, statements of peer review or that the text
     has been approved by an organization as the authoritative
     definition of a standard.

     You may add a passage of up to five words as a Front-Cover Text,
     and a passage of up to 25 words as a Back-Cover Text, to the end of
     the list of Cover Texts in the Modified Version.  Only one passage
     of Front-Cover Text and one of Back-Cover Text may be added by (or
     through arrangements made by) any one entity.  If the Document
     already includes a cover text for the same cover, previously added
     by you or by arrangement made by the same entity you are acting on
     behalf of, you may not add another; but you may replace the old
     one, on explicit permission from the previous publisher that added
     the old one.

     The author(s) and publisher(s) of the Document do not by this
     License give permission to use their names for publicity for or to
     assert or imply endorsement of any Modified Version.

  5. COMBINING DOCUMENTS

     You may combine the Document with other documents released under
     this License, under the terms defined in section 4 above for
     modified versions, provided that you include in the combination all
     of the Invariant Sections of all of the original documents,
     unmodified, and list them all as Invariant Sections of your
     combined work in its license notice, and that you preserve all
     their Warranty Disclaimers.

     The combined work need only contain one copy of this License, and
     multiple identical Invariant Sections may be replaced with a single
     copy.  If there are multiple Invariant Sections with the same name
     but different contents, make the title of each such section unique
     by adding at the end of it, in parentheses, the name of the
     original author or publisher of that section if known, or else a
     unique number.  Make the same adjustment to the section titles in
     the list of Invariant Sections in the license notice of the
     combined work.

     In the combination, you must combine any sections Entitled
     "History" in the various original documents, forming one section
     Entitled "History"; likewise combine any sections Entitled
     "Acknowledgements", and any sections Entitled "Dedications".  You
     must delete all sections Entitled "Endorsements."

  6. COLLECTIONS OF DOCUMENTS

     You may make a collection consisting of the Document and other
     documents released under this License, and replace the individual
     copies of this License in the various documents with a single copy
     that is included in the collection, provided that you follow the
     rules of this License for verbatim copying of each of the documents
     in all other respects.

     You may extract a single document from such a collection, and
     distribute it individually under this License, provided you insert
     a copy of this License into the extracted document, and follow this
     License in all other respects regarding verbatim copying of that
     document.

  7. AGGREGATION WITH INDEPENDENT WORKS

     A compilation of the Document or its derivatives with other
     separate and independent documents or works, in or on a volume of a
     storage or distribution medium, is called an "aggregate" if the
     copyright resulting from the compilation is not used to limit the
     legal rights of the compilation's users beyond what the individual
     works permit.  When the Document is included in an aggregate, this
     License does not apply to the other works in the aggregate which
     are not themselves derivative works of the Document.

     If the Cover Text requirement of section 3 is applicable to these
     copies of the Document, then if the Document is less than one half
     of the entire aggregate, the Document's Cover Texts may be placed
     on covers that bracket the Document within the aggregate, or the
     electronic equivalent of covers if the Document is in electronic
     form.  Otherwise they must appear on printed covers that bracket
     the whole aggregate.

  8. TRANSLATION

     Translation is considered a kind of modification, so you may
     distribute translations of the Document under the terms of section
     4.  Replacing Invariant Sections with translations requires special
     permission from their copyright holders, but you may include
     translations of some or all Invariant Sections in addition to the
     original versions of these Invariant Sections.  You may include a
     translation of this License, and all the license notices in the
     Document, and any Warranty Disclaimers, provided that you also
     include the original English version of this License and the
     original versions of those notices and disclaimers.  In case of a
     disagreement between the translation and the original version of
     this License or a notice or disclaimer, the original version will
     prevail.

     If a section in the Document is Entitled "Acknowledgements",
     "Dedications", or "History", the requirement (section 4) to
     Preserve its Title (section 1) will typically require changing the
     actual title.

  9. TERMINATION

     You may not copy, modify, sublicense, or distribute the Document
     except as expressly provided under this License.  Any attempt
     otherwise to copy, modify, sublicense, or distribute it is void,
     and will automatically terminate your rights under this License.

     However, if you cease all violation of this License, then your
     license from a particular copyright holder is reinstated (a)
     provisionally, unless and until the copyright holder explicitly and
     finally terminates your license, and (b) permanently, if the
     copyright holder fails to notify you of the violation by some
     reasonable means prior to 60 days after the cessation.

     Moreover, your license from a particular copyright holder is
     reinstated permanently if the copyright holder notifies you of the
     violation by some reasonable means, this is the first time you have
     received notice of violation of this License (for any work) from
     that copyright holder, and you cure the violation prior to 30 days
     after your receipt of the notice.

     Termination of your rights under this section does not terminate
     the licenses of parties who have received copies or rights from you
     under this License.  If your rights have been terminated and not
     permanently reinstated, receipt of a copy of some or all of the
     same material does not give you any rights to use it.

  10. FUTURE REVISIONS OF THIS LICENSE

     The Free Software Foundation may publish new, revised versions of
     the GNU Free Documentation License from time to time.  Such new
     versions will be similar in spirit to the present version, but may
     differ in detail to address new problems or concerns.  See
     <https://www.gnu.org/copyleft/>.

     Each version of the License is given a distinguishing version
     number.  If the Document specifies that a particular numbered
     version of this License "or any later version" applies to it, you
     have the option of following the terms and conditions either of
     that specified version or of any later version that has been
     published (not as a draft) by the Free Software Foundation.  If the
     Document does not specify a version number of this License, you may
     choose any version ever published (not as a draft) by the Free
     Software Foundation.  If the Document specifies that a proxy can
     decide which future versions of this License can be used, that
     proxy's public statement of acceptance of a version permanently
     authorizes you to choose that version for the Document.

  11. RELICENSING

     "Massive Multiauthor Collaboration Site" (or "MMC Site") means any
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File: gcc.info,  Node: Contributors,  Next: Option Index,  Prev: GNU Free Documentation License,  Up: Top

Contributors to GCC
*******************

The GCC project would like to thank its many contributors.  Without them
the project would not have been nearly as successful as it has been.
Any omissions in this list are accidental.  Feel free to contact
<law@redhat.com> or <gerald@pfeifer.com> if you have been left out or
some of your contributions are not listed.  Please keep this list in
alphabetical order.

   • Analog Devices helped implement the support for complex data types
     and iterators.

   • John David Anglin for threading-related fixes and improvements to
     libstdc++-v3, and the HP-UX port.

   • James van Artsdalen wrote the code that makes efficient use of the
     Intel 80387 register stack.

   • Abramo and Roberto Bagnara for the SysV68 Motorola 3300 Delta
     Series port.

   • Alasdair Baird for various bug fixes.

   • Giovanni Bajo for analyzing lots of complicated C++ problem
     reports.

   • Peter Barada for his work to improve code generation for new
     ColdFire cores.

   • Gerald Baumgartner added the signature extension to the C++ front
     end.

   • Godmar Back for his Java improvements and encouragement.

   • Scott Bambrough for help porting the Java compiler.

   • Wolfgang Bangerth for processing tons of bug reports.

   • Jon Beniston for his Microsoft Windows port of Java and port to
     Lattice Mico32.

   • Daniel Berlin for better DWARF 2 support, faster/better
     optimizations, improved alias analysis, plus migrating GCC to
     Bugzilla.

   • Geoff Berry for his Java object serialization work and various
     patches.

   • David Binderman tests weekly snapshots of GCC trunk against Fedora
     Rawhide for several architectures.

   • Laurynas Biveinis for memory management work and DJGPP port fixes.

   • Uros Bizjak for the implementation of x87 math built-in functions
     and for various middle end and i386 back end improvements and bug
     fixes.

   • Eric Blake for helping to make GCJ and libgcj conform to the
     specifications.

   • Janne Blomqvist for contributions to GNU Fortran.

   • Hans-J. Boehm for his garbage collector, IA-64 libffi port, and
     other Java work.

   • Segher Boessenkool for helping maintain the PowerPC port and the
     instruction combiner plus various contributions to the middle end.

   • Neil Booth for work on cpplib, lang hooks, debug hooks and other
     miscellaneous clean-ups.

   • Steven Bosscher for integrating the GNU Fortran front end into GCC
     and for contributing to the tree-ssa branch.

   • Eric Botcazou for fixing middle- and backend bugs left and right.

   • Per Bothner for his direction via the steering committee and
     various improvements to the infrastructure for supporting new
     languages.  Chill front end implementation.  Initial
     implementations of cpplib, fix-header, config.guess, libio, and
     past C++ library (libg++) maintainer.  Dreaming up, designing and
     implementing much of GCJ.

   • Devon Bowen helped port GCC to the Tahoe.

   • Don Bowman for mips-vxworks contributions.

   • James Bowman for the FT32 port.

   • Dave Brolley for work on cpplib and Chill.

   • Paul Brook for work on the ARM architecture and maintaining GNU
     Fortran.

   • Robert Brown implemented the support for Encore 32000 systems.

   • Christian Bruel for improvements to local store elimination.

   • Herman A.J. ten Brugge for various fixes.

   • Joerg Brunsmann for Java compiler hacking and help with the GCJ
     FAQ.

   • Joe Buck for his direction via the steering committee from its
     creation to 2013.

   • Iain Buclaw for the D frontend.

   • Craig Burley for leadership of the G77 Fortran effort.

   • Tobias Burnus for contributions to GNU Fortran.

   • Stephan Buys for contributing Doxygen notes for libstdc++.

   • Paolo Carlini for libstdc++ work: lots of efficiency improvements
     to the C++ strings, streambufs and formatted I/O, hard detective
     work on the frustrating localization issues, and keeping up with
     the problem reports.

   • John Carr for his alias work, SPARC hacking, infrastructure
     improvements, previous contributions to the steering committee,
     loop optimizations, etc.

   • Stephane Carrez for 68HC11 and 68HC12 ports.

   • Steve Chamberlain for support for the Renesas SH and H8 processors
     and the PicoJava processor, and for GCJ config fixes.

   • Glenn Chambers for help with the GCJ FAQ.

   • John-Marc Chandonia for various libgcj patches.

   • Denis Chertykov for contributing and maintaining the AVR port, the
     first GCC port for an 8-bit architecture.

   • Kito Cheng for his work on the RISC-V port, including bringing up
     the test suite and maintenance.

   • Scott Christley for his Objective-C contributions.

   • Eric Christopher for his Java porting help and clean-ups.

   • Branko Cibej for more warning contributions.

   • The GNU Classpath project for all of their merged runtime code.

   • Nick Clifton for arm, mcore, fr30, v850, m32r, msp430 rx work,
     ‘--help’, and other random hacking.

   • Michael Cook for libstdc++ cleanup patches to reduce warnings.

   • R. Kelley Cook for making GCC buildable from a read-only directory
     as well as other miscellaneous build process and documentation
     clean-ups.

   • Ralf Corsepius for SH testing and minor bug fixing.

   • François-Xavier Coudert for contributions to GNU Fortran.

   • Stan Cox for care and feeding of the x86 port and lots of behind
     the scenes hacking.

   • Alex Crain provided changes for the 3b1.

   • Ian Dall for major improvements to the NS32k port.

   • Paul Dale for his work to add uClinux platform support to the m68k
     backend.

   • Palmer Dabbelt for his work maintaining the RISC-V port.

   • Dario Dariol contributed the four varieties of sample programs that
     print a copy of their source.

   • Russell Davidson for fstream and stringstream fixes in libstdc++.

   • Bud Davis for work on the G77 and GNU Fortran compilers.

   • Mo DeJong for GCJ and libgcj bug fixes.

   • Jerry DeLisle for contributions to GNU Fortran.

   • DJ Delorie for the DJGPP port, build and libiberty maintenance,
     various bug fixes, and the M32C, MeP, MSP430, and RL78 ports.

   • Arnaud Desitter for helping to debug GNU Fortran.

   • Gabriel Dos Reis for contributions to G++, contributions and
     maintenance of GCC diagnostics infrastructure, libstdc++-v3,
     including ‘valarray<>’, ‘complex<>’, maintaining the numerics
     library (including that pesky ‘<limits>’ :-) and keeping up-to-date
     anything to do with numbers.

   • Ulrich Drepper for his work on glibc, testing of GCC using glibc,
     ISO C99 support, CFG dumping support, etc., plus support of the C++
     runtime libraries including for all kinds of C interface issues,
     contributing and maintaining ‘complex<>’, sanity checking and
     disbursement, configuration architecture, libio maintenance, and
     early math work.

   • François Dumont for his work on libstdc++-v3, especially
     maintaining and improving ‘debug-mode’ and associative and
     unordered containers.

   • Zdenek Dvorak for a new loop unroller and various fixes.

   • Michael Eager for his work on the Xilinx MicroBlaze port.

   • Richard Earnshaw for his ongoing work with the ARM.

   • David Edelsohn for his direction via the steering committee,
     ongoing work with the RS6000/PowerPC port, help cleaning up Haifa
     loop changes, doing the entire AIX port of libstdc++ with his bare
     hands, and for ensuring GCC properly keeps working on AIX.

   • Kevin Ediger for the floating point formatting of num_put::do_put
     in libstdc++.

   • Phil Edwards for libstdc++ work including configuration hackery,
     documentation maintainer, chief breaker of the web pages, the
     occasional iostream bug fix, and work on shared library symbol
     versioning.

   • Paul Eggert for random hacking all over GCC.

   • Mark Elbrecht for various DJGPP improvements, and for libstdc++
     configuration support for locales and fstream-related fixes.

   • Vadim Egorov for libstdc++ fixes in strings, streambufs, and
     iostreams.

   • Christian Ehrhardt for dealing with bug reports.

   • Ben Elliston for his work to move the Objective-C runtime into its
     own subdirectory and for his work on autoconf.

   • Revital Eres for work on the PowerPC 750CL port.

   • Marc Espie for OpenBSD support.

   • Doug Evans for much of the global optimization framework, arc,
     m32r, and SPARC work.

   • Christopher Faylor for his work on the Cygwin port and for caring
     and feeding the gcc.gnu.org box and saving its users tons of spam.

   • Fred Fish for BeOS support and Ada fixes.

   • Ivan Fontes Garcia for the Portuguese translation of the GCJ FAQ.

   • Peter Gerwinski for various bug fixes and the Pascal front end.

   • Kaveh R. Ghazi for his direction via the steering committee,
     amazing work to make ‘-W -Wall -W* -Werror’ useful, and testing GCC
     on a plethora of platforms.  Kaveh extends his gratitude to the
     CAIP Center at Rutgers University for providing him with computing
     resources to work on Free Software from the late 1980s to 2010.

   • John Gilmore for a donation to the FSF earmarked improving GNU
     Java.

   • Judy Goldberg for c++ contributions.

   • Torbjorn Granlund for various fixes and the c-torture testsuite,
     multiply- and divide-by-constant optimization, improved long long
     support, improved leaf function register allocation, and his
     direction via the steering committee.

   • Jonny Grant for improvements to ‘collect2's’ ‘--help’
     documentation.

   • Anthony Green for his ‘-Os’ contributions, the moxie port, and Java
     front end work.

   • Stu Grossman for gdb hacking, allowing GCJ developers to debug Java
     code.

   • Michael K. Gschwind contributed the port to the PDP-11.

   • Richard Biener for his ongoing middle-end contributions and bug
     fixes and for release management.

   • Ron Guilmette implemented the ‘protoize’ and ‘unprotoize’ tools,
     the support for DWARF 1 symbolic debugging information, and much of
     the support for System V Release 4.  He has also worked heavily on
     the Intel 386 and 860 support.

   • Sumanth Gundapaneni for contributing the CR16 port.

   • Mostafa Hagog for Swing Modulo Scheduling (SMS) and post reload
     GCSE.

   • Bruno Haible for improvements in the runtime overhead for EH, new
     warnings and assorted bug fixes.

   • Andrew Haley for his amazing Java compiler and library efforts.

   • Chris Hanson assisted in making GCC work on HP-UX for the 9000
     series 300.

   • Michael Hayes for various thankless work he's done trying to get
     the c30/c40 ports functional.  Lots of loop and unroll improvements
     and fixes.

   • Dara Hazeghi for wading through myriads of target-specific bug
     reports.

   • Kate Hedstrom for staking the G77 folks with an initial testsuite.

   • Richard Henderson for his ongoing SPARC, alpha, ia32, and ia64
     work, loop opts, and generally fixing lots of old problems we've
     ignored for years, flow rewrite and lots of further stuff,
     including reviewing tons of patches.

   • Aldy Hernandez for working on the PowerPC port, SIMD support, and
     various fixes.

   • Nobuyuki Hikichi of Software Research Associates, Tokyo,
     contributed the support for the Sony NEWS machine.

   • Kazu Hirata for caring and feeding the Renesas H8/300 port and
     various fixes.

   • Katherine Holcomb for work on GNU Fortran.

   • Manfred Hollstein for his ongoing work to keep the m88k alive, lots
     of testing and bug fixing, particularly of GCC configury code.

   • Steve Holmgren for MachTen patches.

   • Mat Hostetter for work on the TILE-Gx and TILEPro ports.

   • Jan Hubicka for his x86 port improvements.

   • Falk Hueffner for working on C and optimization bug reports.

   • Bernardo Innocenti for his m68k work, including merging of ColdFire
     improvements and uClinux support.

   • Christian Iseli for various bug fixes.

   • Kamil Iskra for general m68k hacking.

   • Lee Iverson for random fixes and MIPS testing.

   • Balaji V. Iyer for Cilk+ development and merging.

   • Andreas Jaeger for testing and benchmarking of GCC and various bug
     fixes.

   • Martin Jambor for his work on inter-procedural optimizations, the
     switch conversion pass, and scalar replacement of aggregates.

   • Jakub Jelinek for his SPARC work and sibling call optimizations as
     well as lots of bug fixes and test cases, and for improving the
     Java build system.

   • Janis Johnson for ia64 testing and fixes, her quality improvement
     sidetracks, and web page maintenance.

   • Kean Johnston for SCO OpenServer support and various fixes.

   • Tim Josling for the sample language treelang based originally on
     Richard Kenner's "toy" language.

   • Nicolai Josuttis for additional libstdc++ documentation.

   • Klaus Kaempf for his ongoing work to make alpha-vms a viable
     target.

   • Steven G. Kargl for work on GNU Fortran.

   • David Kashtan of SRI adapted GCC to VMS.

   • Ryszard Kabatek for many, many libstdc++ bug fixes and
     optimizations of strings, especially member functions, and for
     auto_ptr fixes.

   • Geoffrey Keating for his ongoing work to make the PPC work for
     GNU/Linux and his automatic regression tester.

   • Brendan Kehoe for his ongoing work with G++ and for a lot of early
     work in just about every part of libstdc++.

   • Oliver M. Kellogg of Deutsche Aerospace contributed the port to the
     MIL-STD-1750A.

   • Richard Kenner of the New York University Ultracomputer Research
     Laboratory wrote the machine descriptions for the AMD 29000, the
     DEC Alpha, the IBM RT PC, and the IBM RS/6000 as well as the
     support for instruction attributes.  He also made changes to better
     support RISC processors including changes to common subexpression
     elimination, strength reduction, function calling sequence
     handling, and condition code support, in addition to generalizing
     the code for frame pointer elimination and delay slot scheduling.
     Richard Kenner was also the head maintainer of GCC for several
     years.

   • Mumit Khan for various contributions to the Cygwin and Mingw32
     ports and maintaining binary releases for Microsoft Windows hosts,
     and for massive libstdc++ porting work to Cygwin/Mingw32.

   • Robin Kirkham for cpu32 support.

   • Mark Klein for PA improvements.

   • Thomas Koenig for various bug fixes.

   • Bruce Korb for the new and improved fixincludes code.

   • Benjamin Kosnik for his G++ work and for leading the libstdc++-v3
     effort.

   • Maxim Kuvyrkov for contributions to the instruction scheduler, the
     Android and m68k/Coldfire ports, and optimizations.

   • Charles LaBrec contributed the support for the Integrated Solutions
     68020 system.

   • Asher Langton and Mike Kumbera for contributing Cray pointer
     support to GNU Fortran, and for other GNU Fortran improvements.

   • Jeff Law for his direction via the steering committee, coordinating
     the entire egcs project and GCC 2.95, rolling out snapshots and
     releases, handling merges from GCC2, reviewing tons of patches that
     might have fallen through the cracks else, and random but extensive
     hacking.

   • Walter Lee for work on the TILE-Gx and TILEPro ports.

   • Marc Lehmann for his direction via the steering committee and
     helping with analysis and improvements of x86 performance.

   • Victor Leikehman for work on GNU Fortran.

   • Ted Lemon wrote parts of the RTL reader and printer.

   • Kriang Lerdsuwanakij for C++ improvements including template as
     template parameter support, and many C++ fixes.

   • Warren Levy for tremendous work on libgcj (Java Runtime Library)
     and random work on the Java front end.

   • Alain Lichnewsky ported GCC to the MIPS CPU.

   • Oskar Liljeblad for hacking on AWT and his many Java bug reports
     and patches.

   • Robert Lipe for OpenServer support, new testsuites, testing, etc.

   • Chen Liqin for various S+core related fixes/improvement, and for
     maintaining the S+core port.

   • Martin Liska for his work on identical code folding, the
     sanitizers, HSA, general bug fixing and for running automated
     regression testing of GCC and reporting numerous bugs.

   • Weiwen Liu for testing and various bug fixes.

   • Manuel López-Ibáñez for improving ‘-Wconversion’ and many other
     diagnostics fixes and improvements.

   • Dave Love for his ongoing work with the Fortran front end and
     runtime libraries.

   • Martin von Löwis for internal consistency checking infrastructure,
     various C++ improvements including namespace support, and tons of
     assistance with libstdc++/compiler merges.

   • H.J. Lu for his previous contributions to the steering committee,
     many x86 bug reports, prototype patches, and keeping the GNU/Linux
     ports working.

   • Greg McGary for random fixes and (someday) bounded pointers.

   • Andrew MacLeod for his ongoing work in building a real EH system,
     various code generation improvements, work on the global optimizer,
     etc.

   • Vladimir Makarov for hacking some ugly i960 problems, PowerPC
     hacking improvements to compile-time performance, overall knowledge
     and direction in the area of instruction scheduling, design and
     implementation of the automaton based instruction scheduler and
     design and implementation of the integrated and local register
     allocators.

   • David Malcolm for his work on improving GCC diagnostics, JIT,
     self-tests and unit testing.

   • Bob Manson for his behind the scenes work on dejagnu.

   • John Marino for contributing the DragonFly BSD port.

   • Philip Martin for lots of libstdc++ string and vector iterator
     fixes and improvements, and string clean up and testsuites.

   • Michael Matz for his work on dominance tree discovery, the x86-64
     port, link-time optimization framework and general optimization
     improvements.

   • All of the Mauve project contributors for Java test code.

   • Bryce McKinlay for numerous GCJ and libgcj fixes and improvements.

   • Adam Megacz for his work on the Microsoft Windows port of GCJ.

   • Michael Meissner for LRS framework, ia32, m32r, v850, m88k, MIPS,
     powerpc, haifa, ECOFF debug support, and other assorted hacking.

   • Jason Merrill for his direction via the steering committee and
     leading the G++ effort.

   • Martin Michlmayr for testing GCC on several architectures using the
     entire Debian archive.

   • David Miller for his direction via the steering committee, lots of
     SPARC work, improvements in jump.cc and interfacing with the Linux
     kernel developers.

   • Gary Miller ported GCC to Charles River Data Systems machines.

   • Alfred Minarik for libstdc++ string and ios bug fixes, and turning
     the entire libstdc++ testsuite namespace-compatible.

   • Mark Mitchell for his direction via the steering committee,
     mountains of C++ work, load/store hoisting out of loops, alias
     analysis improvements, ISO C ‘restrict’ support, and serving as
     release manager from 2000 to 2011.

   • Alan Modra for various GNU/Linux bits and testing.

   • Toon Moene for his direction via the steering committee, Fortran
     maintenance, and his ongoing work to make us make Fortran run fast.

   • Jason Molenda for major help in the care and feeding of all the
     services on the gcc.gnu.org (formerly egcs.cygnus.com)
     machine--mail, web services, ftp services, etc etc.  Doing all this
     work on scrap paper and the backs of envelopes would have been...
     difficult.

   • Catherine Moore for fixing various ugly problems we have sent her
     way, including the haifa bug which was killing the Alpha & PowerPC
     Linux kernels.

   • Mike Moreton for his various Java patches.

   • David Mosberger-Tang for various Alpha improvements, and for the
     initial IA-64 port.

   • Stephen Moshier contributed the floating point emulator that
     assists in cross-compilation and permits support for floating point
     numbers wider than 64 bits and for ISO C99 support.

   • Bill Moyer for his behind the scenes work on various issues.

   • Philippe De Muyter for his work on the m68k port.

   • Joseph S. Myers for his work on the PDP-11 port, format checking
     and ISO C99 support, and continuous emphasis on (and contributions
     to) documentation.

   • Nathan Myers for his work on libstdc++-v3: architecture and
     authorship through the first three snapshots, including
     implementation of locale infrastructure, string, shadow C headers,
     and the initial project documentation (DESIGN, CHECKLIST, and so
     forth).  Later, more work on MT-safe string and shadow headers.

   • Felix Natter for documentation on porting libstdc++.

   • Nathanael Nerode for cleaning up the configuration/build process.

   • NeXT, Inc. donated the front end that supports the Objective-C
     language.

   • Hans-Peter Nilsson for the CRIS and MMIX ports, improvements to the
     search engine setup, various documentation fixes and other small
     fixes.

   • Geoff Noer for his work on getting cygwin native builds working.

   • Vegard Nossum for running automated regression testing of GCC and
     reporting numerous bugs.

   • Diego Novillo for his work on Tree SSA, OpenMP, SPEC performance
     tracking web pages, GIMPLE tuples, and assorted fixes.

   • David O'Brien for the FreeBSD/alpha, FreeBSD/AMD x86-64,
     FreeBSD/ARM, FreeBSD/PowerPC, and FreeBSD/SPARC64 ports and related
     infrastructure improvements.

   • Alexandre Oliva for various build infrastructure improvements,
     scripts and amazing testing work, including keeping libtool issues
     sane and happy.

   • Stefan Olsson for work on mt_alloc.

   • Melissa O'Neill for various NeXT fixes.

   • Rainer Orth for random MIPS work, including improvements to GCC's
     o32 ABI support, improvements to dejagnu's MIPS support, Java
     configuration clean-ups and porting work, and maintaining the IRIX,
     Solaris 2, and Tru64 UNIX ports.

   • Steven Pemberton for his contribution of ‘enquire’ which allowed
     GCC to determine various properties of the floating point unit and
     generate ‘float.h’ in older versions of GCC.

   • Hartmut Penner for work on the s390 port.

   • Paul Petersen wrote the machine description for the Alliant FX/8.

   • Alexandre Petit-Bianco for implementing much of the Java compiler
     and continued Java maintainership.

   • Matthias Pfaller for major improvements to the NS32k port.

   • Gerald Pfeifer for his direction via the steering committee,
     pointing out lots of problems we need to solve, maintenance of the
     web pages, and taking care of documentation maintenance in general.

   • Marek Polacek for his work on the C front end, the sanitizers and
     general bug fixing.

   • Andrew Pinski for processing bug reports by the dozen.

   • Ovidiu Predescu for his work on the Objective-C front end and
     runtime libraries.

   • Jerry Quinn for major performance improvements in C++ formatted
     I/O.

   • Ken Raeburn for various improvements to checker, MIPS ports and
     various cleanups in the compiler.

   • Rolf W. Rasmussen for hacking on AWT.

   • David Reese of Sun Microsystems contributed to the Solaris on
     PowerPC port.

   • John Regehr for running automated regression testing of GCC and
     reporting numerous bugs.

   • Volker Reichelt for running automated regression testing of GCC and
     reporting numerous bugs and for keeping up with the problem
     reports.

   • Joern Rennecke for maintaining the sh port, loop, regmove & reload
     hacking and developing and maintaining the Epiphany port.

   • Loren J. Rittle for improvements to libstdc++-v3 including the
     FreeBSD port, threading fixes, thread-related configury changes,
     critical threading documentation, and solutions to really tricky
     I/O problems, as well as keeping GCC properly working on FreeBSD
     and continuous testing.

   • Craig Rodrigues for processing tons of bug reports.

   • Ola Rönnerup for work on mt_alloc.

   • Gavin Romig-Koch for lots of behind the scenes MIPS work.

   • David Ronis inspired and encouraged Craig to rewrite the G77
     documentation in texinfo format by contributing a first pass at a
     translation of the old ‘g77-0.5.16/f/DOC’ file.

   • Ken Rose for fixes to GCC's delay slot filling code.

   • Ira Rosen for her contributions to the auto-vectorizer.

   • Paul Rubin wrote most of the preprocessor.

   • Pétur Runólfsson for major performance improvements in C++
     formatted I/O and large file support in C++ filebuf.

   • Chip Salzenberg for libstdc++ patches and improvements to locales,
     traits, Makefiles, libio, libtool hackery, and "long long" support.

   • Juha Sarlin for improvements to the H8 code generator.

   • Greg Satz assisted in making GCC work on HP-UX for the 9000 series
     300.

   • Roger Sayle for improvements to constant folding and GCC's RTL
     optimizers as well as for fixing numerous bugs.

   • Bradley Schatz for his work on the GCJ FAQ.

   • Peter Schauer wrote the code to allow debugging to work on the
     Alpha.

   • William Schelter did most of the work on the Intel 80386 support.

   • Tobias Schlüter for work on GNU Fortran.

   • Bernd Schmidt for various code generation improvements and major
     work in the reload pass, serving as release manager for GCC 2.95.3,
     and work on the Blackfin and C6X ports.

   • Peter Schmid for constant testing of libstdc++--especially
     application testing, going above and beyond what was requested for
     the release criteria--and libstdc++ header file tweaks.

   • Jason Schroeder for jcf-dump patches.

   • Andreas Schwab for his work on the m68k port.

   • Lars Segerlund for work on GNU Fortran.

   • Dodji Seketeli for numerous C++ bug fixes and debug info
     improvements.

   • Tim Shen for major work on ‘<regex>’.

   • Joel Sherrill for his direction via the steering committee, RTEMS
     contributions and RTEMS testing.

   • Nathan Sidwell for many C++ fixes/improvements.

   • Jeffrey Siegal for helping RMS with the original design of GCC,
     some code which handles the parse tree and RTL data structures,
     constant folding and help with the original VAX & m68k ports.

   • Kenny Simpson for prompting libstdc++ fixes due to defect reports
     from the LWG (thereby keeping GCC in line with updates from the
     ISO).

   • Franz Sirl for his ongoing work with making the PPC port stable for
     GNU/Linux.

   • Andrey Slepuhin for assorted AIX hacking.

   • Trevor Smigiel for contributing the SPU port.

   • Christopher Smith did the port for Convex machines.

   • Danny Smith for his major efforts on the Mingw (and Cygwin) ports.
     Retired from GCC maintainership August 2010, having mentored two
     new maintainers into the role.

   • Randy Smith finished the Sun FPA support.

   • Ed Smith-Rowland for his continuous work on libstdc++-v3, special
     functions, ‘<random>’, and various improvements to C++11 features.

   • Scott Snyder for queue, iterator, istream, and string fixes and
     libstdc++ testsuite entries.  Also for providing the patch to G77
     to add rudimentary support for ‘INTEGER*1’, ‘INTEGER*2’, and
     ‘LOGICAL*1’.

   • Zdenek Sojka for running automated regression testing of GCC and
     reporting numerous bugs.

   • Arseny Solokha for running automated regression testing of GCC and
     reporting numerous bugs.

   • Jayant Sonar for contributing the CR16 port.

   • Brad Spencer for contributions to the GLIBCPP_FORCE_NEW technique.

   • Richard Stallman, for writing the original GCC and launching the
     GNU project.

   • Jan Stein of the Chalmers Computer Society provided support for
     Genix, as well as part of the 32000 machine description.

   • Gerhard Steinmetz for running automated regression testing of GCC
     and reporting numerous bugs.

   • Nigel Stephens for various mips16 related fixes/improvements.

   • Jonathan Stone wrote the machine description for the Pyramid
     computer.

   • Graham Stott for various infrastructure improvements.

   • John Stracke for his Java HTTP protocol fixes.

   • Mike Stump for his Elxsi port, G++ contributions over the years and
     more recently his vxworks contributions

   • Jeff Sturm for Java porting help, bug fixes, and encouragement.

   • Zhendong Su for running automated regression testing of GCC and
     reporting numerous bugs.

   • Chengnian Sun for running automated regression testing of GCC and
     reporting numerous bugs.

   • Shigeya Suzuki for this fixes for the bsdi platforms.

   • Ian Lance Taylor for the Go frontend, the initial mips16 and mips64
     support, general configury hacking, fixincludes, etc.

   • Holger Teutsch provided the support for the Clipper CPU.

   • Gary Thomas for his ongoing work to make the PPC work for
     GNU/Linux.

   • Paul Thomas for contributions to GNU Fortran.

   • Philipp Thomas for random bug fixes throughout the compiler

   • Jason Thorpe for thread support in libstdc++ on NetBSD.

   • Kresten Krab Thorup wrote the run time support for the Objective-C
     language and the fantastic Java bytecode interpreter.

   • Michael Tiemann for random bug fixes, the first instruction
     scheduler, initial C++ support, function integration, NS32k, SPARC
     and M88k machine description work, delay slot scheduling.

   • Andreas Tobler for his work porting libgcj to Darwin.

   • Teemu Torma for thread safe exception handling support.

   • Leonard Tower wrote parts of the parser, RTL generator, and RTL
     definitions, and of the VAX machine description.

   • Daniel Towner and Hariharan Sandanagobalane contributed and
     maintain the picoChip port.

   • Tom Tromey for internationalization support and for his many Java
     contributions and libgcj maintainership.

   • Lassi Tuura for improvements to config.guess to determine HP
     processor types.

   • Petter Urkedal for libstdc++ CXXFLAGS, math, and algorithms fixes.

   • Andy Vaught for the design and initial implementation of the GNU
     Fortran front end.

   • Brent Verner for work with the libstdc++ cshadow files and their
     associated configure steps.

   • Todd Vierling for contributions for NetBSD ports.

   • Andrew Waterman for contributing the RISC-V port, as well as
     maintaining it.

   • Jonathan Wakely for contributing libstdc++ Doxygen notes and XHTML
     guidance and maintaining libstdc++.

   • Dean Wakerley for converting the install documentation from HTML to
     texinfo in time for GCC 3.0.

   • Krister Walfridsson for random bug fixes.

   • Feng Wang for contributions to GNU Fortran.

   • Stephen M. Webb for time and effort on making libstdc++ shadow
     files work with the tricky Solaris 8+ headers, and for pushing the
     build-time header tree.  Also, for starting and driving the
     ‘<regex>’ effort.

   • John Wehle for various improvements for the x86 code generator,
     related infrastructure improvements to help x86 code generation,
     value range propagation and other work, WE32k port.

   • Ulrich Weigand for work on the s390 port.

   • Janus Weil for contributions to GNU Fortran.

   • Zack Weinberg for major work on cpplib and various other bug fixes.

   • Matt Welsh for help with Linux Threads support in GCJ.

   • Urban Widmark for help fixing java.io.

   • Mark Wielaard for new Java library code and his work integrating
     with Classpath.

   • Dale Wiles helped port GCC to the Tahoe.

   • Bob Wilson from Tensilica, Inc. for the Xtensa port.

   • Jim Wilson for his direction via the steering committee, tackling
     hard problems in various places that nobody else wanted to work on,
     strength reduction and other loop optimizations.

   • Paul Woegerer and Tal Agmon for the CRX port.

   • Carlo Wood for various fixes.

   • Tom Wood for work on the m88k port.

   • Chung-Ju Wu for his work on the Andes NDS32 port.

   • Canqun Yang for work on GNU Fortran.

   • Masanobu Yuhara of Fujitsu Laboratories implemented the machine
     description for the Tron architecture (specifically, the Gmicro).

   • Kevin Zachmann helped port GCC to the Tahoe.

   • Ayal Zaks for Swing Modulo Scheduling (SMS).

   • Qirun Zhang for running automated regression testing of GCC and
     reporting numerous bugs.

   • Xiaoqiang Zhang for work on GNU Fortran.

   • Gilles Zunino for help porting Java to Irix.

 The following people are recognized for their contributions to GNAT,
the Ada front end of GCC:
   • Bernard Banner

   • Romain Berrendonner

   • Geert Bosch

   • Emmanuel Briot

   • Joel Brobecker

   • Ben Brosgol

   • Vincent Celier

   • Arnaud Charlet

   • Chien Chieng

   • Cyrille Comar

   • Cyrille Crozes

   • Robert Dewar

   • Gary Dismukes

   • Robert Duff

   • Ed Falis

   • Ramon Fernandez

   • Sam Figueroa

   • Vasiliy Fofanov

   • Michael Friess

   • Franco Gasperoni

   • Ted Giering

   • Matthew Gingell

   • Laurent Guerby

   • Jerome Guitton

   • Olivier Hainque

   • Jerome Hugues

   • Hristian Kirtchev

   • Jerome Lambourg

   • Bruno Leclerc

   • Albert Lee

   • Sean McNeil

   • Javier Miranda

   • Laurent Nana

   • Pascal Obry

   • Dong-Ik Oh

   • Laurent Pautet

   • Brett Porter

   • Thomas Quinot

   • Nicolas Roche

   • Pat Rogers

   • Jose Ruiz

   • Douglas Rupp

   • Sergey Rybin

   • Gail Schenker

   • Ed Schonberg

   • Nicolas Setton

   • Samuel Tardieu

 The following people are recognized for their contributions of new
features, bug reports, testing and integration of classpath/libgcj for
GCC version 4.1:
   • Lillian Angel for ‘JTree’ implementation and lots Free Swing
     additions and bug fixes.

   • Wolfgang Baer for ‘GapContent’ bug fixes.

   • Anthony Balkissoon for ‘JList’, Free Swing 1.5 updates and mouse
     event fixes, lots of Free Swing work including ‘JTable’ editing.

   • Stuart Ballard for RMI constant fixes.

   • Goffredo Baroncelli for ‘HTTPURLConnection’ fixes.

   • Gary Benson for ‘MessageFormat’ fixes.

   • Daniel Bonniot for ‘Serialization’ fixes.

   • Chris Burdess for lots of gnu.xml and http protocol fixes, ‘StAX’
     and ‘DOM xml:id’ support.

   • Ka-Hing Cheung for ‘TreePath’ and ‘TreeSelection’ fixes.

   • Archie Cobbs for build fixes, VM interface updates,
     ‘URLClassLoader’ updates.

   • Kelley Cook for build fixes.

   • Martin Cordova for Suggestions for better ‘SocketTimeoutException’.

   • David Daney for ‘BitSet’ bug fixes, ‘HttpURLConnection’ rewrite and
     improvements.

   • Thomas Fitzsimmons for lots of upgrades to the gtk+ AWT and Cairo
     2D support.  Lots of imageio framework additions, lots of AWT and
     Free Swing bug fixes.

   • Jeroen Frijters for ‘ClassLoader’ and nio cleanups, serialization
     fixes, better ‘Proxy’ support, bug fixes and IKVM integration.

   • Santiago Gala for ‘AccessControlContext’ fixes.

   • Nicolas Geoffray for ‘VMClassLoader’ and ‘AccessController’
     improvements.

   • David Gilbert for ‘basic’ and ‘metal’ icon and plaf support and
     lots of documenting, Lots of Free Swing and metal theme additions.
     ‘MetalIconFactory’ implementation.

   • Anthony Green for ‘MIDI’ framework, ‘ALSA’ and ‘DSSI’ providers.

   • Andrew Haley for ‘Serialization’ and ‘URLClassLoader’ fixes, gcj
     build speedups.

   • Kim Ho for ‘JFileChooser’ implementation.

   • Andrew John Hughes for ‘Locale’ and net fixes, URI RFC2986 updates,
     ‘Serialization’ fixes, ‘Properties’ XML support and generic branch
     work, VMIntegration guide update.

   • Bastiaan Huisman for ‘TimeZone’ bug fixing.

   • Andreas Jaeger for mprec updates.

   • Paul Jenner for better ‘-Werror’ support.

   • Ito Kazumitsu for ‘NetworkInterface’ implementation and updates.

   • Roman Kennke for ‘BoxLayout’, ‘GrayFilter’ and ‘SplitPane’, plus
     bug fixes all over.  Lots of Free Swing work including styled text.

   • Simon Kitching for ‘String’ cleanups and optimization suggestions.

   • Michael Koch for configuration fixes, ‘Locale’ updates, bug and
     build fixes.

   • Guilhem Lavaux for configuration, thread and channel fixes and
     Kaffe integration.  JCL native ‘Pointer’ updates.  Logger bug
     fixes.

   • David Lichteblau for JCL support library global/local reference
     cleanups.

   • Aaron Luchko for JDWP updates and documentation fixes.

   • Ziga Mahkovec for ‘Graphics2D’ upgraded to Cairo 0.5 and new regex
     features.

   • Sven de Marothy for BMP imageio support, CSS and ‘TextLayout’
     fixes.  ‘GtkImage’ rewrite, 2D, awt, free swing and date/time fixes
     and implementing the Qt4 peers.

   • Casey Marshall for crypto algorithm fixes, ‘FileChannel’ lock,
     ‘SystemLogger’ and ‘FileHandler’ rotate implementations, NIO
     ‘FileChannel.map’ support, security and policy updates.

   • Bryce McKinlay for RMI work.

   • Audrius Meskauskas for lots of Free Corba, RMI and HTML work plus
     testing and documenting.

   • Kalle Olavi Niemitalo for build fixes.

   • Rainer Orth for build fixes.

   • Andrew Overholt for ‘File’ locking fixes.

   • Ingo Proetel for ‘Image’, ‘Logger’ and ‘URLClassLoader’ updates.

   • Olga Rodimina for ‘MenuSelectionManager’ implementation.

   • Jan Roehrich for ‘BasicTreeUI’ and ‘JTree’ fixes.

   • Julian Scheid for documentation updates and gjdoc support.

   • Christian Schlichtherle for zip fixes and cleanups.

   • Robert Schuster for documentation updates and beans fixes,
     ‘TreeNode’ enumerations and ‘ActionCommand’ and various fixes, XML
     and URL, AWT and Free Swing bug fixes.

   • Keith Seitz for lots of JDWP work.

   • Christian Thalinger for 64-bit cleanups, Configuration and VM
     interface fixes and ‘CACAO’ integration, ‘fdlibm’ updates.

   • Gael Thomas for ‘VMClassLoader’ boot packages support suggestions.

   • Andreas Tobler for Darwin and Solaris testing and fixing, ‘Qt4’
     support for Darwin/OS X, ‘Graphics2D’ support, ‘gtk+’ updates.

   • Dalibor Topic for better ‘DEBUG’ support, build cleanups and Kaffe
     integration.  ‘Qt4’ build infrastructure, ‘SHA1PRNG’ and
     ‘GdkPixbugDecoder’ updates.

   • Tom Tromey for Eclipse integration, generics work, lots of bug
     fixes and gcj integration including coordinating The Big Merge.

   • Mark Wielaard for bug fixes, packaging and release management,
     ‘Clipboard’ implementation, system call interrupts and network
     timeouts and ‘GdkPixpufDecoder’ fixes.

 In addition to the above, all of which also contributed time and energy
in testing GCC, we would like to thank the following for their
contributions to testing:

   • Michael Abd-El-Malek

   • Thomas Arend

   • Bonzo Armstrong

   • Steven Ashe

   • Chris Baldwin

   • David Billinghurst

   • Jim Blandy

   • Stephane Bortzmeyer

   • Horst von Brand

   • Frank Braun

   • Rodney Brown

   • Sidney Cadot

   • Bradford Castalia

   • Robert Clark

   • Jonathan Corbet

   • Ralph Doncaster

   • Richard Emberson

   • Levente Farkas

   • Graham Fawcett

   • Mark Fernyhough

   • Robert A. French

   • Jörgen Freyh

   • Mark K. Gardner

   • Charles-Antoine Gauthier

   • Yung Shing Gene

   • David Gilbert

   • Simon Gornall

   • Fred Gray

   • John Griffin

   • Patrik Hagglund

   • Phil Hargett

   • Amancio Hasty

   • Takafumi Hayashi

   • Bryan W. Headley

   • Kevin B. Hendricks

   • Joep Jansen

   • Christian Joensson

   • Michel Kern

   • David Kidd

   • Tobias Kuipers

   • Anand Krishnaswamy

   • A. O. V. Le Blanc

   • llewelly

   • Damon Love

   • Brad Lucier

   • Matthias Klose

   • Martin Knoblauch

   • Rick Lutowski

   • Jesse Macnish

   • Stefan Morrell

   • Anon A. Mous

   • Matthias Mueller

   • Pekka Nikander

   • Rick Niles

   • Jon Olson

   • Magnus Persson

   • Chris Pollard

   • Richard Polton

   • Derk Reefman

   • David Rees

   • Paul Reilly

   • Tom Reilly

   • Torsten Rueger

   • Danny Sadinoff

   • Marc Schifer

   • Erik Schnetter

   • Wayne K. Schroll

   • David Schuler

   • Vin Shelton

   • Tim Souder

   • Adam Sulmicki

   • Bill Thorson

   • George Talbot

   • Pedro A. M. Vazquez

   • Gregory Warnes

   • Ian Watson

   • David E. Young

   • And many others

 And finally we'd like to thank everyone who uses the compiler, provides
feedback and generally reminds us why we're doing this work in the first
place.


File: gcc.info,  Node: Option Index,  Next: Keyword Index,  Prev: Contributors,  Up: Top

Option Index
************

GCC's command line options are indexed here without any initial ‘-’ or
‘--’.  Where an option has both positive and negative forms (such as
‘-fOPTION’ and ‘-fno-OPTION’), relevant entries in the manual are
indexed under the most appropriate form; it may sometimes be useful to
look up both forms.

[index]
* Menu:

* -march:                                LoongArch Options.  (line    9)
* -mbranch-cost:                         LoongArch Options.  (line   80)
* -mcheck-zero-division:                 LoongArch Options.  (line   84)
* -mcond-move-float:                     LoongArch Options.  (line   95)
* -mcond-move-int:                       LoongArch Options.  (line   90)
* -mdouble-float:                        LoongArch Options.  (line   75)
* -mmax-inline-memcpy-size:              LoongArch Options.  (line  118)
* -mmemcpy:                              LoongArch Options.  (line  100)
* -msingle-float:                        LoongArch Options.  (line   70)
* -msmall-data-limit:                    LoongArch Options.  (line  114)
* -mstrict-align:                        LoongArch Options.  (line  109)
* ###:                                   Overall Options.    (line  472)
* 80387:                                 x86 Options.        (line  593)
* A:                                     Preprocessor Options.
                                                             (line  335)
* all_load:                              Darwin Options.     (line  110)
* allowable_client:                      Darwin Options.     (line  196)
* analyzer:                              Static Analyzer Options.
                                                             (line    7)
* ansi:                                  Standards.          (line   13)
* ansi <1>:                              C Dialect Options.  (line   11)
* ansi <2>:                              Other Builtins.     (line   31)
* ansi <3>:                              Non-bugs.           (line  107)
* arch_errors_fatal:                     Darwin Options.     (line  114)
* aux-info:                              C Dialect Options.  (line  202)
* B:                                     Directory Options.  (line  122)
* Bdynamic:                              VxWorks Options.    (line   22)
* bind_at_load:                          Darwin Options.     (line  118)
* block-ops-unaligned-vsx:               RS/6000 and PowerPC Options.
                                                             (line  959)
* Bstatic:                               VxWorks Options.    (line   22)
* bundle:                                Darwin Options.     (line  123)
* bundle_loader:                         Darwin Options.     (line  127)
* c:                                     Overall Options.    (line  165)
* C:                                     Preprocessor Options.
                                                             (line  344)
* c <1>:                                 Link Options.       (line   20)
* CC:                                    Preprocessor Options.
                                                             (line  356)
* client_name:                           Darwin Options.     (line  196)
* compatibility_version:                 Darwin Options.     (line  196)
* coverage:                              Instrumentation Options.
                                                             (line   56)
* current_version:                       Darwin Options.     (line  196)
* D:                                     Preprocessor Options.
                                                             (line   19)
* d:                                     Preprocessor Options.
                                                             (line  410)
* d <1>:                                 Developer Options.  (line   52)
* da:                                    Developer Options.  (line  246)
* dA:                                    Developer Options.  (line  249)
* dD:                                    Preprocessor Options.
                                                             (line  434)
* dD <1>:                                Developer Options.  (line  253)
* dead_strip:                            Darwin Options.     (line  196)
* dependency-file:                       Darwin Options.     (line  196)
* dH:                                    Developer Options.  (line  257)
* dI:                                    Preprocessor Options.
                                                             (line  444)
* dM:                                    Preprocessor Options.
                                                             (line  419)
* dN:                                    Preprocessor Options.
                                                             (line  440)
* dp:                                    Developer Options.  (line  260)
* dP:                                    Developer Options.  (line  265)
* dU:                                    Preprocessor Options.
                                                             (line  448)
* dump-analyzer-exploded-nodes:          Static Analyzer Options.
                                                             (line  439)
* dump-analyzer-exploded-nodes-2:        Static Analyzer Options.
                                                             (line  443)
* dump-analyzer-exploded-nodes-3:        Static Analyzer Options.
                                                             (line  447)
* dump-analyzer-feasibility:             Static Analyzer Options.
                                                             (line  456)
* dumpbase:                              Overall Options.    (line  252)
* dumpbase-ext:                          Overall Options.    (line  325)
* dumpdir:                               Overall Options.    (line  353)
* dumpfullversion:                       Developer Options.  (line 1013)
* dumpmachine:                           Developer Options.  (line 1001)
* dumpspecs:                             Developer Options.  (line 1018)
* dumpversion:                           Developer Options.  (line 1005)
* dx:                                    Developer Options.  (line  269)
* dylib_file:                            Darwin Options.     (line  196)
* dylinker_install_name:                 Darwin Options.     (line  196)
* dynamic:                               Darwin Options.     (line  196)
* dynamiclib:                            Darwin Options.     (line  131)
* E:                                     Overall Options.    (line  186)
* E <1>:                                 Link Options.       (line   20)
* e:                                     Link Options.       (line  172)
* EB:                                    ARC Options.        (line  588)
* EB <1>:                                C-SKY Options.      (line   29)
* EB <2>:                                MIPS Options.       (line    7)
* EL:                                    ARC Options.        (line  595)
* EL <1>:                                C-SKY Options.      (line   31)
* EL <2>:                                MIPS Options.       (line   10)
* entry:                                 Link Options.       (line  172)
* exported_symbols_list:                 Darwin Options.     (line  196)
* F:                                     Darwin Options.     (line   31)
* fabi-compat-version:                   C++ Dialect Options.
                                                             (line   92)
* fabi-version:                          C++ Dialect Options.
                                                             (line   24)
* faccess-control:                       C++ Dialect Options.
                                                             (line  108)
* fada-spec-parent:                      Overall Options.    (line  655)
* faggressive-loop-optimizations:        Optimize Options.   (line  554)
* falign-functions:                      Optimize Options.   (line 1734)
* falign-jumps:                          Optimize Options.   (line 1816)
* falign-labels:                         Optimize Options.   (line 1775)
* falign-loops:                          Optimize Options.   (line 1795)
* faligned-new:                          C++ Dialect Options.
                                                             (line  112)
* fallow-parameterless-variadic-functions: C Dialect Options.
                                                             (line  218)
* fallow-store-data-races:               Optimize Options.   (line 1836)
* fanalyzer:                             Static Analyzer Options.
                                                             (line    7)
* fanalyzer-call-summaries:              Static Analyzer Options.
                                                             (line  295)
* fanalyzer-checker:                     Static Analyzer Options.
                                                             (line  304)
* fanalyzer-feasibility:                 Static Analyzer Options.
                                                             (line  330)
* fanalyzer-fine-grained:                Static Analyzer Options.
                                                             (line  340)
* fanalyzer-show-duplicate-count:        Static Analyzer Options.
                                                             (line  350)
* fanalyzer-state-merge:                 Static Analyzer Options.
                                                             (line  357)
* fanalyzer-state-purge:                 Static Analyzer Options.
                                                             (line  365)
* fanalyzer-transitivity:                Static Analyzer Options.
                                                             (line  376)
* fasan-shadow-offset:                   Instrumentation Options.
                                                             (line  619)
* fasm:                                  C Dialect Options.  (line  225)
* fassociative-math:                     Optimize Options.   (line 2373)
* fasynchronous-unwind-tables:           Code Gen Options.   (line  158)
* fauto-inc-dec:                         Optimize Options.   (line  576)
* fauto-profile:                         Optimize Options.   (line 2248)
* fbit-tests:                            Code Gen Options.   (line  424)
* fbranch-count-reg:                     Optimize Options.   (line  428)
* fbranch-probabilities:                 Optimize Options.   (line 2519)
* fbuiltin:                              C Dialect Options.  (line  239)
* fcall-saved:                           Code Gen Options.   (line  454)
* fcall-used:                            Code Gen Options.   (line  440)
* fcaller-saves:                         Optimize Options.   (line  934)
* fcallgraph-info:                       Developer Options.  (line   34)
* fcf-protection:                        Instrumentation Options.
                                                             (line  692)
* fchar8_t:                              C++ Dialect Options.
                                                             (line  122)
* fcheck-new:                            C++ Dialect Options.
                                                             (line  165)
* fchecking:                             Developer Options.  (line  715)
* fcode-hoisting:                        Optimize Options.   (line  975)
* fcombine-stack-adjustments:            Optimize Options.   (line  946)
* fcommon:                               Code Gen Options.   (line  233)
* fcommon <1>:                           Common Variable Attributes.
                                                             (line  176)
* fcompare-debug:                        Developer Options.  (line  787)
* fcompare-debug-second:                 Developer Options.  (line  813)
* fcompare-elim:                         Optimize Options.   (line 2178)
* fconcepts:                             C++ Dialect Options.
                                                             (line  176)
* fconcepts-ts:                          C++ Dialect Options.
                                                             (line  176)
* fcond-mismatch:                        C Dialect Options.  (line  273)
* fconserve-stack:                       Optimize Options.   (line  965)
* fconstant-string-class:                Objective-C and Objective-C++ Dialect Options.
                                                             (line   30)
* fconstexpr-cache-depth:                C++ Dialect Options.
                                                             (line  192)
* fconstexpr-depth:                      C++ Dialect Options.
                                                             (line  186)
* fconstexpr-fp-except:                  C++ Dialect Options.
                                                             (line  202)
* fconstexpr-loop-limit:                 C++ Dialect Options.
                                                             (line  213)
* fconstexpr-ops-limit:                  C++ Dialect Options.
                                                             (line  218)
* fcoroutines:                           C++ Dialect Options.
                                                             (line  227)
* fcprop-registers:                      Optimize Options.   (line 2190)
* fcrossjumping:                         Optimize Options.   (line  569)
* fcse-follow-jumps:                     Optimize Options.   (line  488)
* fcse-skip-blocks:                      Optimize Options.   (line  497)
* fcx-fortran-rules:                     Optimize Options.   (line 2506)
* fcx-limited-range:                     Optimize Options.   (line 2494)
* fdata-sections:                        Optimize Options.   (line 2666)
* fdbg-cnt:                              Developer Options.  (line  923)
* fdbg-cnt-list:                         Developer Options.  (line  920)
* fdce:                                  Optimize Options.   (line  582)
* fdebug-cpp:                            Preprocessor Options.
                                                             (line  455)
* fdebug-prefix-map:                     Debugging Options.  (line  173)
* fdebug-types-section:                  Debugging Options.  (line  235)
* fdeclone-ctor-dtor:                    Optimize Options.   (line  605)
* fdefer-pop:                            Optimize Options.   (line  229)
* fdelayed-branch:                       Optimize Options.   (line  758)
* fdelete-dead-exceptions:               Code Gen Options.   (line  141)
* fdelete-null-pointer-checks:           Optimize Options.   (line  616)
* fdevirtualize:                         Optimize Options.   (line  637)
* fdevirtualize-at-ltrans:               Optimize Options.   (line  654)
* fdevirtualize-speculatively:           Optimize Options.   (line  644)
* fdiagnostics-color:                    Diagnostic Message Formatting Options.
                                                             (line   55)
* fdiagnostics-column-origin:            Diagnostic Message Formatting Options.
                                                             (line  431)
* fdiagnostics-column-unit:              Diagnostic Message Formatting Options.
                                                             (line  412)
* fdiagnostics-escape-format:            Diagnostic Message Formatting Options.
                                                             (line  438)
* fdiagnostics-format:                   Diagnostic Message Formatting Options.
                                                             (line  468)
* fdiagnostics-generate-patch:           Diagnostic Message Formatting Options.
                                                             (line  255)
* fdiagnostics-minimum-margin-width:     Diagnostic Message Formatting Options.
                                                             (line  224)
* fdiagnostics-parseable-fixits:         Diagnostic Message Formatting Options.
                                                             (line  228)
* fdiagnostics-path-format:              Diagnostic Message Formatting Options.
                                                             (line  304)
* fdiagnostics-show-caret:               Diagnostic Message Formatting Options.
                                                             (line  188)
* fdiagnostics-show-cwe:                 Diagnostic Message Formatting Options.
                                                             (line  210)
* fdiagnostics-show-labels:              Diagnostic Message Formatting Options.
                                                             (line  197)
* fdiagnostics-show-line-numbers:        Diagnostic Message Formatting Options.
                                                             (line  219)
* fdiagnostics-show-location:            Diagnostic Message Formatting Options.
                                                             (line   40)
* fdiagnostics-show-option:              Diagnostic Message Formatting Options.
                                                             (line  182)
* fdiagnostics-show-path-depths:         Diagnostic Message Formatting Options.
                                                             (line  395)
* fdiagnostics-show-template-tree:       Diagnostic Message Formatting Options.
                                                             (line  272)
* fdiagnostics-urls:                     Diagnostic Message Formatting Options.
                                                             (line  144)
* fdirectives-only:                      Preprocessor Options.
                                                             (line  205)
* fdisable-:                             Developer Options.  (line  647)
* fdollars-in-identifiers:               Preprocessor Options.
                                                             (line  226)
* fdollars-in-identifiers <1>:           Interoperation.     (line  141)
* fdpic:                                 SH Options.         (line  388)
* fdse:                                  Optimize Options.   (line  586)
* fdump-ada-spec:                        Overall Options.    (line  650)
* fdump-analyzer:                        Static Analyzer Options.
                                                             (line  421)
* fdump-analyzer-callgraph:              Static Analyzer Options.
                                                             (line  430)
* fdump-analyzer-exploded-graph:         Static Analyzer Options.
                                                             (line  434)
* fdump-analyzer-exploded-paths:         Static Analyzer Options.
                                                             (line  452)
* fdump-analyzer-json:                   Static Analyzer Options.
                                                             (line  462)
* fdump-analyzer-state-purge:            Static Analyzer Options.
                                                             (line  466)
* fdump-analyzer-stderr:                 Static Analyzer Options.
                                                             (line  426)
* fdump-analyzer-supergraph:             Static Analyzer Options.
                                                             (line  472)
* fdump-analyzer-untracked:              Static Analyzer Options.
                                                             (line  480)
* fdump-debug:                           Developer Options.  (line  273)
* fdump-earlydebug:                      Developer Options.  (line  277)
* fdump-final-insns:                     Developer Options.  (line  781)
* fdump-go-spec:                         Overall Options.    (line  659)
* fdump-ipa:                             Developer Options.  (line  303)
* fdump-lang:                            Developer Options.  (line  332)
* fdump-lang <1>:                        Developer Options.  (line  339)
* fdump-lang-all:                        Developer Options.  (line  339)
* fdump-noaddr:                          Developer Options.  (line  281)
* fdump-passes:                          Developer Options.  (line  364)
* fdump-rtl-alignments:                  Developer Options.  (line   65)
* fdump-rtl-all:                         Developer Options.  (line  246)
* fdump-rtl-asmcons:                     Developer Options.  (line   68)
* fdump-rtl-auto_inc_dec:                Developer Options.  (line   72)
* fdump-rtl-barriers:                    Developer Options.  (line   76)
* fdump-rtl-bbpart:                      Developer Options.  (line   79)
* fdump-rtl-bbro:                        Developer Options.  (line   82)
* fdump-rtl-btl2:                        Developer Options.  (line   86)
* fdump-rtl-btl2 <1>:                    Developer Options.  (line   86)
* fdump-rtl-bypass:                      Developer Options.  (line   90)
* fdump-rtl-ce1:                         Developer Options.  (line  101)
* fdump-rtl-ce2:                         Developer Options.  (line  101)
* fdump-rtl-ce3:                         Developer Options.  (line  101)
* fdump-rtl-combine:                     Developer Options.  (line   93)
* fdump-rtl-compgotos:                   Developer Options.  (line   96)
* fdump-rtl-cprop_hardreg:               Developer Options.  (line  105)
* fdump-rtl-csa:                         Developer Options.  (line  108)
* fdump-rtl-cse1:                        Developer Options.  (line  112)
* fdump-rtl-cse2:                        Developer Options.  (line  112)
* fdump-rtl-dbr:                         Developer Options.  (line  119)
* fdump-rtl-dce:                         Developer Options.  (line  116)
* fdump-rtl-dce1:                        Developer Options.  (line  123)
* fdump-rtl-dce2:                        Developer Options.  (line  123)
* fdump-rtl-dfinish:                     Developer Options.  (line  242)
* fdump-rtl-dfinit:                      Developer Options.  (line  242)
* fdump-rtl-eh:                          Developer Options.  (line  127)
* fdump-rtl-eh_ranges:                   Developer Options.  (line  130)
* fdump-rtl-expand:                      Developer Options.  (line  133)
* fdump-rtl-fwprop1:                     Developer Options.  (line  137)
* fdump-rtl-fwprop2:                     Developer Options.  (line  137)
* fdump-rtl-gcse1:                       Developer Options.  (line  142)
* fdump-rtl-gcse2:                       Developer Options.  (line  142)
* fdump-rtl-init-regs:                   Developer Options.  (line  146)
* fdump-rtl-initvals:                    Developer Options.  (line  149)
* fdump-rtl-into_cfglayout:              Developer Options.  (line  152)
* fdump-rtl-ira:                         Developer Options.  (line  155)
* fdump-rtl-jump:                        Developer Options.  (line  158)
* fdump-rtl-loop2:                       Developer Options.  (line  161)
* fdump-rtl-mach:                        Developer Options.  (line  165)
* fdump-rtl-mode_sw:                     Developer Options.  (line  169)
* fdump-rtl-outof_cfglayout:             Developer Options.  (line  175)
* fdump-rtl-PASS:                        Developer Options.  (line   52)
* fdump-rtl-peephole2:                   Developer Options.  (line  178)
* fdump-rtl-postreload:                  Developer Options.  (line  181)
* fdump-rtl-pro_and_epilogue:            Developer Options.  (line  184)
* fdump-rtl-ree:                         Developer Options.  (line  192)
* fdump-rtl-regclass:                    Developer Options.  (line  242)
* fdump-rtl-rnreg:                       Developer Options.  (line  172)
* fdump-rtl-sched1:                      Developer Options.  (line  188)
* fdump-rtl-sched2:                      Developer Options.  (line  188)
* fdump-rtl-seqabstr:                    Developer Options.  (line  195)
* fdump-rtl-shorten:                     Developer Options.  (line  198)
* fdump-rtl-sibling:                     Developer Options.  (line  201)
* fdump-rtl-sms:                         Developer Options.  (line  212)
* fdump-rtl-split1:                      Developer Options.  (line  208)
* fdump-rtl-split2:                      Developer Options.  (line  208)
* fdump-rtl-split3:                      Developer Options.  (line  208)
* fdump-rtl-split4:                      Developer Options.  (line  208)
* fdump-rtl-split5:                      Developer Options.  (line  208)
* fdump-rtl-stack:                       Developer Options.  (line  216)
* fdump-rtl-subreg1:                     Developer Options.  (line  222)
* fdump-rtl-subreg2:                     Developer Options.  (line  222)
* fdump-rtl-subregs_of_mode_finish:      Developer Options.  (line  242)
* fdump-rtl-subregs_of_mode_init:        Developer Options.  (line  242)
* fdump-rtl-unshare:                     Developer Options.  (line  226)
* fdump-rtl-vartrack:                    Developer Options.  (line  229)
* fdump-rtl-vregs:                       Developer Options.  (line  232)
* fdump-rtl-web:                         Developer Options.  (line  235)
* fdump-statistics:                      Developer Options.  (line  368)
* fdump-tree:                            Developer Options.  (line  381)
* fdump-tree-all:                        Developer Options.  (line  381)
* fdump-unnumbered:                      Developer Options.  (line  291)
* fdump-unnumbered-links:                Developer Options.  (line  297)
* fdwarf2-cfi-asm:                       Debugging Options.  (line  440)
* fearly-inlining:                       Optimize Options.   (line  328)
* felide-constructors:                   C++ Dialect Options.
                                                             (line  230)
* felide-type:                           Diagnostic Message Formatting Options.
                                                             (line  292)
* feliminate-unused-debug-symbols:       Debugging Options.  (line  153)
* feliminate-unused-debug-types:         Debugging Options.  (line  444)
* femit-class-debug-always:              Debugging Options.  (line  158)
* femit-struct-debug-baseonly:           Debugging Options.  (line  371)
* femit-struct-debug-detailed:           Debugging Options.  (line  398)
* femit-struct-debug-reduced:            Debugging Options.  (line  384)
* fenable-:                              Developer Options.  (line  647)
* fenforce-eh-specs:                     C++ Dialect Options.
                                                             (line  241)
* fexceptions:                           Code Gen Options.   (line  118)
* fexcess-precision:                     Optimize Options.   (line 2299)
* fexec-charset:                         Preprocessor Options.
                                                             (line  273)
* fexpensive-optimizations:              Optimize Options.   (line  661)
* fext-numeric-literals:                 C++ Dialect Options.
                                                             (line  546)
* fextended-identifiers:                 Preprocessor Options.
                                                             (line  229)
* fextern-tls-init:                      C++ Dialect Options.
                                                             (line  251)
* ffast-math:                            Optimize Options.   (line 2323)
* ffat-lto-objects:                      Optimize Options.   (line 2155)
* ffile-prefix-map:                      Overall Options.    (line  630)
* ffinite-loops:                         Optimize Options.   (line 1222)
* ffinite-math-only:                     Optimize Options.   (line 2400)
* ffix-and-continue:                     Darwin Options.     (line  104)
* ffixed:                                Code Gen Options.   (line  428)
* ffloat-store:                          Optimize Options.   (line 2285)
* ffloat-store <1>:                      Disappointments.    (line   77)
* ffold-simple-inlines:                  C++ Dialect Options.
                                                             (line  272)
* fforward-propagate:                    Optimize Options.   (line  236)
* ffp-contract:                          Optimize Options.   (line  245)
* ffp-int-builtin-inexact:               Optimize Options.   (line 2472)
* ffreestanding:                         Standards.          (line   99)
* ffreestanding <1>:                     C Dialect Options.  (line  278)
* ffreestanding <2>:                     Warning Options.    (line  432)
* ffreestanding <3>:                     Common Function Attributes.
                                                             (line  451)
* ffunction-cse:                         Optimize Options.   (line  442)
* ffunction-sections:                    Optimize Options.   (line 2666)
* fgcse:                                 Optimize Options.   (line  511)
* fgcse-after-reload:                    Optimize Options.   (line  547)
* fgcse-las:                             Optimize Options.   (line  540)
* fgcse-lm:                              Optimize Options.   (line  522)
* fgcse-sm:                              Optimize Options.   (line  531)
* fgimple:                               C Dialect Options.  (line  289)
* fgnu-keywords:                         C++ Dialect Options.
                                                             (line  279)
* fgnu-runtime:                          Objective-C and Objective-C++ Dialect Options.
                                                             (line   39)
* fgnu-tm:                               C Dialect Options.  (line  295)
* fgnu-unique:                           Code Gen Options.   (line  164)
* fgnu89-inline:                         C Dialect Options.  (line  310)
* fgraphite-identity:                    Optimize Options.   (line 1264)
* fguess-branch-probability:             Optimize Options.   (line 1605)
* fharden-compares:                      Instrumentation Options.
                                                             (line  725)
* fharden-conditional-branches:          Instrumentation Options.
                                                             (line  734)
* fhoist-adjacent-loads:                 Optimize Options.   (line 1005)
* fhosted:                               C Dialect Options.  (line  327)
* fident:                                Code Gen Options.   (line  254)
* fif-conversion:                        Optimize Options.   (line  590)
* fif-conversion2:                       Optimize Options.   (line  599)
* fiji:                                  AMD GCN Options.    (line   13)
* filelist:                              Darwin Options.     (line  196)
* fimplement-inlines:                    C++ Dialect Options.
                                                             (line  305)
* fimplicit-constexpr:                   C++ Dialect Options.
                                                             (line  285)
* fimplicit-inline-templates:            C++ Dialect Options.
                                                             (line  299)
* fimplicit-templates:                   C++ Dialect Options.
                                                             (line  291)
* findirect-data:                        Darwin Options.     (line  104)
* findirect-inlining:                    Optimize Options.   (line  300)
* finhibit-size-directive:               Code Gen Options.   (line  257)
* finline:                               Optimize Options.   (line  283)
* finline-functions:                     Optimize Options.   (line  308)
* finline-functions-called-once:         Optimize Options.   (line  320)
* finline-limit:                         Optimize Options.   (line  344)
* finline-small-functions:               Optimize Options.   (line  291)
* finput-charset:                        Preprocessor Options.
                                                             (line  286)
* finstrument-functions:                 Instrumentation Options.
                                                             (line  911)
* finstrument-functions <1>:             Common Function Attributes.
                                                             (line  814)
* finstrument-functions-exclude-file-list: Instrumentation Options.
                                                             (line  947)
* finstrument-functions-exclude-function-list: Instrumentation Options.
                                                             (line  968)
* fipa-bit-cp:                           Optimize Options.   (line 1072)
* fipa-cp:                               Optimize Options.   (line 1053)
* fipa-cp-clone:                         Optimize Options.   (line 1062)
* fipa-icf:                              Optimize Options.   (line 1082)
* fipa-modref:                           Optimize Options.   (line 1046)
* fipa-profile:                          Optimize Options.   (line 1038)
* fipa-pta:                              Optimize Options.   (line 1032)
* fipa-pure-const:                       Optimize Options.   (line 1016)
* fipa-ra:                               Optimize Options.   (line  952)
* fipa-reference:                        Optimize Options.   (line 1020)
* fipa-reference-addressable:            Optimize Options.   (line 1024)
* fipa-sra:                              Optimize Options.   (line  337)
* fipa-stack-alignment:                  Optimize Options.   (line 1028)
* fipa-strict-aliasing:                  Optimize Options.   (line 1721)
* fipa-vrp:                              Optimize Options.   (line 1077)
* fira-algorithm:                        Optimize Options.   (line  695)
* fira-hoist-pressure:                   Optimize Options.   (line  724)
* fira-loop-pressure:                    Optimize Options.   (line  731)
* fira-region:                           Optimize Options.   (line  703)
* fira-share-save-slots:                 Optimize Options.   (line  739)
* fira-share-spill-slots:                Optimize Options.   (line  745)
* fira-verbose:                          Developer Options.  (line  850)
* fisolate-erroneous-paths-attribute:    Optimize Options.   (line 1164)
* fisolate-erroneous-paths-dereference:  Optimize Options.   (line 1156)
* fivar-visibility:                      Objective-C and Objective-C++ Dialect Options.
                                                             (line  161)
* fivopts:                               Optimize Options.   (line 1389)
* fjump-tables:                          Code Gen Options.   (line  416)
* fkeep-inline-dllexport:                Optimize Options.   (line  369)
* fkeep-inline-functions:                Optimize Options.   (line  375)
* fkeep-inline-functions <1>:            Inline.             (line   51)
* fkeep-static-consts:                   Optimize Options.   (line  386)
* fkeep-static-functions:                Optimize Options.   (line  382)
* flang-info-include-translate:          C++ Dialect Options.
                                                             (line  562)
* flang-info-include-translate-not:      C++ Dialect Options.
                                                             (line  562)
* flang-info-module-cmi:                 C++ Dialect Options.
                                                             (line  571)
* flarge-source-files:                   Preprocessor Options.
                                                             (line  495)
* flat_namespace:                        Darwin Options.     (line  196)
* flax-vector-conversions:               C Dialect Options.  (line  335)
* fleading-underscore:                   Code Gen Options.   (line  484)
* flifetime-dse:                         Optimize Options.   (line  675)
* flinker-output:                        Link Options.       (line   25)
* flive-patching:                        Optimize Options.   (line 1096)
* flive-range-shrinkage:                 Optimize Options.   (line  690)
* flocal-ivars:                          Objective-C and Objective-C++ Dialect Options.
                                                             (line  152)
* floop-block:                           Optimize Options.   (line 1258)
* floop-interchange:                     Optimize Options.   (line 1342)
* floop-nest-optimize:                   Optimize Options.   (line 1272)
* floop-parallelize-all:                 Optimize Options.   (line 1278)
* floop-strip-mine:                      Optimize Options.   (line 1258)
* floop-unroll-and-jam:                  Optimize Options.   (line 1359)
* flra-remat:                            Optimize Options.   (line  751)
* flto:                                  Optimize Options.   (line 1894)
* flto-compression-level:                Optimize Options.   (line 2126)
* flto-partition:                        Optimize Options.   (line 2112)
* flto-report:                           Developer Options.  (line  856)
* flto-report-wpa:                       Developer Options.  (line  864)
* fmacro-prefix-map:                     Preprocessor Options.
                                                             (line  264)
* fmath-errno:                           Optimize Options.   (line 2337)
* fmax-errors:                           Warning Options.    (line   18)
* fmax-include-depth:                    Preprocessor Options.
                                                             (line  238)
* fmem-report:                           Developer Options.  (line  868)
* fmem-report-wpa:                       Developer Options.  (line  872)
* fmerge-all-constants:                  Optimize Options.   (line  405)
* fmerge-constants:                      Optimize Options.   (line  395)
* fmerge-debug-strings:                  Debugging Options.  (line  166)
* fmessage-length:                       Diagnostic Message Formatting Options.
                                                             (line   14)
* fmodule-header:                        C++ Dialect Options.
                                                             (line  319)
* fmodule-implicit-inline:               C++ Dialect Options.
                                                             (line  322)
* fmodule-lazy:                          C++ Dialect Options.
                                                             (line  332)
* fmodule-mapper:                        C++ Dialect Options.
                                                             (line  340)
* fmodule-only:                          C++ Dialect Options.
                                                             (line  345)
* fmodules-ts:                           C++ Dialect Options.
                                                             (line  311)
* fmodulo-sched:                         Optimize Options.   (line  416)
* fmodulo-sched-allow-regmoves:          Optimize Options.   (line  421)
* fmove-loop-invariants:                 Optimize Options.   (line 2618)
* fmove-loop-stores:                     Optimize Options.   (line 2622)
* fms-extensions:                        C Dialect Options.  (line  340)
* fms-extensions <1>:                    C++ Dialect Options.
                                                             (line  349)
* fms-extensions <2>:                    Unnamed Fields.     (line   36)
* fnew-inheriting-ctors:                 C++ Dialect Options.
                                                             (line  354)
* fnew-ttp-matching:                     C++ Dialect Options.
                                                             (line  360)
* fnext-runtime:                         Objective-C and Objective-C++ Dialect Options.
                                                             (line   43)
* fnil-receivers:                        Objective-C and Objective-C++ Dialect Options.
                                                             (line   49)
* fno-access-control:                    C++ Dialect Options.
                                                             (line  108)
* fno-allocation-dce:                    Optimize Options.   (line 1833)
* fno-analyzer:                          Static Analyzer Options.
                                                             (line    7)
* fno-analyzer-call-summaries:           Static Analyzer Options.
                                                             (line  295)
* fno-analyzer-feasibility:              Static Analyzer Options.
                                                             (line  330)
* fno-analyzer-fine-grained:             Static Analyzer Options.
                                                             (line  340)
* fno-analyzer-show-duplicate-count:     Static Analyzer Options.
                                                             (line  350)
* fno-analyzer-state-merge:              Static Analyzer Options.
                                                             (line  357)
* fno-analyzer-state-purge:              Static Analyzer Options.
                                                             (line  365)
* fno-analyzer-transitivity:             Static Analyzer Options.
                                                             (line  376)
* fno-asm:                               C Dialect Options.  (line  225)
* fno-bit-tests:                         Code Gen Options.   (line  424)
* fno-branch-count-reg:                  Optimize Options.   (line  428)
* fno-builtin:                           C Dialect Options.  (line  239)
* fno-builtin <1>:                       Warning Options.    (line  432)
* fno-builtin <2>:                       Common Function Attributes.
                                                             (line  451)
* fno-builtin <3>:                       Other Builtins.     (line   21)
* fno-canonical-system-headers:          Preprocessor Options.
                                                             (line  234)
* fno-char8_t:                           C++ Dialect Options.
                                                             (line  122)
* fno-checking:                          Developer Options.  (line  715)
* fno-common:                            Code Gen Options.   (line  233)
* fno-common <1>:                        Common Variable Attributes.
                                                             (line  176)
* fno-compare-debug:                     Developer Options.  (line  787)
* fno-debug-types-section:               Debugging Options.  (line  235)
* fno-default-inline:                    Inline.             (line   68)
* fno-defer-pop:                         Optimize Options.   (line  229)
* fno-diagnostics-show-caret:            Diagnostic Message Formatting Options.
                                                             (line  188)
* fno-diagnostics-show-cwe:              Diagnostic Message Formatting Options.
                                                             (line  210)
* fno-diagnostics-show-labels:           Diagnostic Message Formatting Options.
                                                             (line  197)
* fno-diagnostics-show-line-numbers:     Diagnostic Message Formatting Options.
                                                             (line  219)
* fno-diagnostics-show-option:           Diagnostic Message Formatting Options.
                                                             (line  182)
* fno-dwarf2-cfi-asm:                    Debugging Options.  (line  440)
* fno-elide-constructors:                C++ Dialect Options.
                                                             (line  230)
* fno-elide-type:                        Diagnostic Message Formatting Options.
                                                             (line  292)
* fno-eliminate-unused-debug-symbols:    Debugging Options.  (line  153)
* fno-eliminate-unused-debug-types:      Debugging Options.  (line  444)
* fno-enforce-eh-specs:                  C++ Dialect Options.
                                                             (line  241)
* fno-ext-numeric-literals:              C++ Dialect Options.
                                                             (line  546)
* fno-extern-tls-init:                   C++ Dialect Options.
                                                             (line  251)
* fno-finite-loops:                      Optimize Options.   (line 1222)
* fno-fold-simple-inlines:               C++ Dialect Options.
                                                             (line  272)
* fno-fp-int-builtin-inexact:            Optimize Options.   (line 2472)
* fno-function-cse:                      Optimize Options.   (line  442)
* fno-gnu-keywords:                      C++ Dialect Options.
                                                             (line  279)
* fno-gnu-unique:                        Code Gen Options.   (line  164)
* fno-guess-branch-probability:          Optimize Options.   (line 1605)
* fno-ident:                             Code Gen Options.   (line  254)
* fno-implement-inlines:                 C++ Dialect Options.
                                                             (line  305)
* fno-implement-inlines <1>:             C++ Interface.      (line   66)
* fno-implicit-inline-templates:         C++ Dialect Options.
                                                             (line  299)
* fno-implicit-templates:                C++ Dialect Options.
                                                             (line  291)
* fno-implicit-templates <1>:            Template Instantiation.
                                                             (line   94)
* fno-inline:                            Optimize Options.   (line  283)
* fno-ira-share-save-slots:              Optimize Options.   (line  739)
* fno-ira-share-spill-slots:             Optimize Options.   (line  745)
* fno-jump-tables:                       Code Gen Options.   (line  416)
* fno-keep-inline-dllexport:             Optimize Options.   (line  369)
* fno-lifetime-dse:                      Optimize Options.   (line  675)
* fno-local-ivars:                       Objective-C and Objective-C++ Dialect Options.
                                                             (line  152)
* fno-math-errno:                        Optimize Options.   (line 2337)
* fno-merge-debug-strings:               Debugging Options.  (line  166)
* fno-module-lazy:                       C++ Dialect Options.
                                                             (line  332)
* fno-modules-ts:                        C++ Dialect Options.
                                                             (line  311)
* fno-nil-receivers:                     Objective-C and Objective-C++ Dialect Options.
                                                             (line   49)
* fno-nonansi-builtins:                  C++ Dialect Options.
                                                             (line  367)
* fno-operator-names:                    C++ Dialect Options.
                                                             (line  383)
* fno-optional-diags:                    C++ Dialect Options.
                                                             (line  387)
* fno-peephole:                          Optimize Options.   (line 1596)
* fno-peephole2:                         Optimize Options.   (line 1596)
* fno-plt:                               Code Gen Options.   (line  398)
* fno-pretty-templates:                  C++ Dialect Options.
                                                             (line  397)
* fno-printf-return-value:               Optimize Options.   (line 1573)
* fno-rtti:                              C++ Dialect Options.
                                                             (line  409)
* fno-sanitize-recover:                  Instrumentation Options.
                                                             (line  628)
* fno-sanitize=all:                      Instrumentation Options.
                                                             (line  613)
* fno-sched-interblock:                  Optimize Options.   (line  784)
* fno-sched-spec:                        Optimize Options.   (line  789)
* fno-set-stack-executable:              x86 Windows Options.
                                                             (line   46)
* fno-show-column:                       Diagnostic Message Formatting Options.
                                                             (line  407)
* fno-signed-bitfields:                  C Dialect Options.  (line  449)
* fno-signed-zeros:                      Optimize Options.   (line 2412)
* fno-stack-limit:                       Instrumentation Options.
                                                             (line  823)
* fno-threadsafe-statics:                C++ Dialect Options.
                                                             (line  464)
* fno-toplevel-reorder:                  Optimize Options.   (line 1859)
* fno-trapping-math:                     Optimize Options.   (line 2422)
* fno-unsigned-bitfields:                C Dialect Options.  (line  449)
* fno-use-cxa-get-exception-ptr:         C++ Dialect Options.
                                                             (line  477)
* fno-var-tracking-assignments:          Debugging Options.  (line  193)
* fno-var-tracking-assignments-toggle:   Developer Options.  (line  834)
* fno-weak:                              C++ Dialect Options.
                                                             (line  539)
* fno-working-directory:                 Preprocessor Options.
                                                             (line  321)
* fno-writable-relocated-rdata:          x86 Windows Options.
                                                             (line   53)
* fno-zero-initialized-in-bss:           Optimize Options.   (line  453)
* fnon-call-exceptions:                  Code Gen Options.   (line  132)
* fnonansi-builtins:                     C++ Dialect Options.
                                                             (line  367)
* fnothrow-opt:                          C++ Dialect Options.
                                                             (line  372)
* fobjc-abi-version:                     Objective-C and Objective-C++ Dialect Options.
                                                             (line   56)
* fobjc-call-cxx-cdtors:                 Objective-C and Objective-C++ Dialect Options.
                                                             (line   67)
* fobjc-direct-dispatch:                 Objective-C and Objective-C++ Dialect Options.
                                                             (line   92)
* fobjc-exceptions:                      Objective-C and Objective-C++ Dialect Options.
                                                             (line   96)
* fobjc-gc:                              Objective-C and Objective-C++ Dialect Options.
                                                             (line  104)
* fobjc-nilcheck:                        Objective-C and Objective-C++ Dialect Options.
                                                             (line  110)
* fobjc-std:                             Objective-C and Objective-C++ Dialect Options.
                                                             (line  119)
* foffload:                              C Dialect Options.  (line  360)
* foffload-options:                      C Dialect Options.  (line  373)
* fomit-frame-pointer:                   Optimize Options.   (line  256)
* fopenacc:                              C Dialect Options.  (line  388)
* fopenacc-dim:                          C Dialect Options.  (line  396)
* fopenmp:                               C Dialect Options.  (line  402)
* fopenmp-simd:                          C Dialect Options.  (line  410)
* foperator-names:                       C++ Dialect Options.
                                                             (line  383)
* fopt-info:                             Developer Options.  (line  487)
* foptimize-sibling-calls:               Optimize Options.   (line  271)
* foptimize-strlen:                      Optimize Options.   (line  276)
* foptional-diags:                       C++ Dialect Options.
                                                             (line  387)
* force_cpusubtype_ALL:                  Darwin Options.     (line  135)
* force_flat_namespace:                  Darwin Options.     (line  196)
* fpack-struct:                          Code Gen Options.   (line  471)
* fpartial-inlining:                     Optimize Options.   (line 1548)
* fpatchable-function-entry:             Instrumentation Options.
                                                             (line  980)
* fpcc-struct-return:                    Code Gen Options.   (line  177)
* fpcc-struct-return <1>:                Incompatibilities.  (line  170)
* fpch-deps:                             Preprocessor Options.
                                                             (line  296)
* fpch-preprocess:                       Preprocessor Options.
                                                             (line  304)
* fpeel-loops:                           Optimize Options.   (line 2610)
* fpeephole:                             Optimize Options.   (line 1596)
* fpeephole2:                            Optimize Options.   (line 1596)
* fpermissive:                           C++ Dialect Options.
                                                             (line  392)
* fpermitted-flt-eval-methods:           C Dialect Options.  (line  414)
* fpermitted-flt-eval-methods=c11:       C Dialect Options.  (line  414)
* fpermitted-flt-eval-methods=ts-18661-3: C Dialect Options. (line  414)
* fpic:                                  Code Gen Options.   (line  355)
* fPIC:                                  Code Gen Options.   (line  376)
* fpie:                                  Code Gen Options.   (line  389)
* fPIE:                                  Code Gen Options.   (line  389)
* fplan9-extensions:                     C Dialect Options.  (line  436)
* fplan9-extensions <1>:                 Unnamed Fields.     (line   43)
* fplt:                                  Code Gen Options.   (line  398)
* fplugin:                               Overall Options.    (line  639)
* fplugin-arg:                           Overall Options.    (line  646)
* fpost-ipa-mem-report:                  Developer Options.  (line  877)
* fpre-ipa-mem-report:                   Developer Options.  (line  876)
* fpredictive-commoning:                 Optimize Options.   (line 1555)
* fprefetch-loop-arrays:                 Optimize Options.   (line 1563)
* fpreprocessed:                         Preprocessor Options.
                                                             (line  192)
* fpretty-templates:                     C++ Dialect Options.
                                                             (line  397)
* fprintf-return-value:                  Optimize Options.   (line 1573)
* fprofile-abs-path:                     Instrumentation Options.
                                                             (line  116)
* fprofile-arcs:                         Instrumentation Options.
                                                             (line   30)
* fprofile-arcs <1>:                     Other Builtins.     (line  596)
* fprofile-correction:                   Optimize Options.   (line 2197)
* fprofile-dir:                          Instrumentation Options.
                                                             (line  122)
* fprofile-exclude-files:                Instrumentation Options.
                                                             (line  299)
* fprofile-filter-files:                 Instrumentation Options.
                                                             (line  291)
* fprofile-generate:                     Instrumentation Options.
                                                             (line  148)
* fprofile-info-section:                 Instrumentation Options.
                                                             (line  166)
* fprofile-note:                         Instrumentation Options.
                                                             (line  248)
* fprofile-partial-training:             Optimize Options.   (line 2206)
* fprofile-prefix-map:                   Instrumentation Options.
                                                             (line  269)
* fprofile-prefix-path:                  Instrumentation Options.
                                                             (line  254)
* fprofile-reorder-functions:            Optimize Options.   (line 2550)
* fprofile-report:                       Developer Options.  (line  881)
* fprofile-reproducible:                 Instrumentation Options.
                                                             (line  308)
* fprofile-update:                       Instrumentation Options.
                                                             (line  274)
* fprofile-use:                          Optimize Options.   (line 2220)
* fprofile-values:                       Optimize Options.   (line 2540)
* fpu:                                   RX Options.         (line   17)
* frandom-seed:                          Developer Options.  (line  720)
* freciprocal-math:                      Optimize Options.   (line 2390)
* frecord-gcc-switches:                  Code Gen Options.   (line  343)
* free:                                  Optimize Options.   (line  667)
* freg-struct-return:                    Code Gen Options.   (line  195)
* frename-registers:                     Optimize Options.   (line 2569)
* freorder-blocks:                       Optimize Options.   (line 1626)
* freorder-blocks-algorithm:             Optimize Options.   (line 1632)
* freorder-blocks-and-partition:         Optimize Options.   (line 1643)
* freorder-functions:                    Optimize Options.   (line 1660)
* freplace-objc-classes:                 Objective-C and Objective-C++ Dialect Options.
                                                             (line  130)
* freport-bug:                           Developer Options.  (line  287)
* frerun-cse-after-loop:                 Optimize Options.   (line  505)
* freschedule-modulo-scheduled-loops:    Optimize Options.   (line  883)
* frounding-math:                        Optimize Options.   (line 2437)
* frtti:                                 C++ Dialect Options.
                                                             (line  409)
* fsanitize-address-use-after-scope:     Instrumentation Options.
                                                             (line  664)
* fsanitize-coverage=trace-cmp:          Instrumentation Options.
                                                             (line  679)
* fsanitize-coverage=trace-pc:           Instrumentation Options.
                                                             (line  675)
* fsanitize-recover:                     Instrumentation Options.
                                                             (line  628)
* fsanitize-sections:                    Instrumentation Options.
                                                             (line  624)
* fsanitize-undefined-trap-on-error:     Instrumentation Options.
                                                             (line  668)
* fsanitize=address:                     Instrumentation Options.
                                                             (line  336)
* fsanitize=alignment:                   Instrumentation Options.
                                                             (line  539)
* fsanitize=bool:                        Instrumentation Options.
                                                             (line  577)
* fsanitize=bounds:                      Instrumentation Options.
                                                             (line  526)
* fsanitize=bounds-strict:               Instrumentation Options.
                                                             (line  532)
* fsanitize=builtin:                     Instrumentation Options.
                                                             (line  601)
* fsanitize=enum:                        Instrumentation Options.
                                                             (line  582)
* fsanitize=float-cast-overflow:         Instrumentation Options.
                                                             (line  557)
* fsanitize=float-divide-by-zero:        Instrumentation Options.
                                                             (line  551)
* fsanitize=hwaddress:                   Instrumentation Options.
                                                             (line  356)
* fsanitize=integer-divide-by-zero:      Instrumentation Options.
                                                             (line  489)
* fsanitize=kernel-address:              Instrumentation Options.
                                                             (line  352)
* fsanitize=kernel-hwaddress:            Instrumentation Options.
                                                             (line  370)
* fsanitize=leak:                        Instrumentation Options.
                                                             (line  451)
* fsanitize=nonnull-attribute:           Instrumentation Options.
                                                             (line  565)
* fsanitize=null:                        Instrumentation Options.
                                                             (line  502)
* fsanitize=object-size:                 Instrumentation Options.
                                                             (line  546)
* fsanitize=pointer-compare:             Instrumentation Options.
                                                             (line  386)
* fsanitize=pointer-overflow:            Instrumentation Options.
                                                             (line  595)
* fsanitize=pointer-subtract:            Instrumentation Options.
                                                             (line  396)
* fsanitize=return:                      Instrumentation Options.
                                                             (line  510)
* fsanitize=returns-nonnull-attribute:   Instrumentation Options.
                                                             (line  571)
* fsanitize=shadow-call-stack:           Instrumentation Options.
                                                             (line  406)
* fsanitize=shift:                       Instrumentation Options.
                                                             (line  469)
* fsanitize=shift-base:                  Instrumentation Options.
                                                             (line  482)
* fsanitize=shift-exponent:              Instrumentation Options.
                                                             (line  477)
* fsanitize=signed-integer-overflow:     Instrumentation Options.
                                                             (line  516)
* fsanitize=thread:                      Instrumentation Options.
                                                             (line  437)
* fsanitize=undefined:                   Instrumentation Options.
                                                             (line  461)
* fsanitize=unreachable:                 Instrumentation Options.
                                                             (line  492)
* fsanitize=vla-bound:                   Instrumentation Options.
                                                             (line  498)
* fsanitize=vptr:                        Instrumentation Options.
                                                             (line  588)
* fsave-optimization-record:             Developer Options.  (line  593)
* fsched-critical-path-heuristic:        Optimize Options.   (line  849)
* fsched-dep-count-heuristic:            Optimize Options.   (line  876)
* fsched-group-heuristic:                Optimize Options.   (line  843)
* fsched-interblock:                     Optimize Options.   (line  784)
* fsched-last-insn-heuristic:            Optimize Options.   (line  869)
* fsched-pressure:                       Optimize Options.   (line  794)
* fsched-rank-heuristic:                 Optimize Options.   (line  862)
* fsched-spec:                           Optimize Options.   (line  789)
* fsched-spec-insn-heuristic:            Optimize Options.   (line  855)
* fsched-spec-load:                      Optimize Options.   (line  803)
* fsched-spec-load-dangerous:            Optimize Options.   (line  808)
* fsched-stalled-insns:                  Optimize Options.   (line  814)
* fsched-stalled-insns-dep:              Optimize Options.   (line  824)
* fsched-verbose:                        Developer Options.  (line  633)
* fsched2-use-superblocks:               Optimize Options.   (line  833)
* fschedule-fusion:                      Optimize Options.   (line 2579)
* fschedule-insns:                       Optimize Options.   (line  765)
* fschedule-insns2:                      Optimize Options.   (line  775)
* fsection-anchors:                      Optimize Options.   (line 2699)
* fsel-sched-pipelining:                 Optimize Options.   (line  896)
* fsel-sched-pipelining-outer-loops:     Optimize Options.   (line  901)
* fselective-scheduling:                 Optimize Options.   (line  888)
* fselective-scheduling2:                Optimize Options.   (line  892)
* fsemantic-interposition:               Optimize Options.   (line  906)
* fset-stack-executable:                 x86 Windows Options.
                                                             (line   46)
* fshort-enums:                          Code Gen Options.   (line  213)
* fshort-enums <1>:                      Structures unions enumerations and bit-fields implementation.
                                                             (line   48)
* fshort-enums <2>:                      Common Type Attributes.
                                                             (line  299)
* fshort-enums <3>:                      Non-bugs.           (line   42)
* fshort-wchar:                          Code Gen Options.   (line  223)
* fshow-column:                          Diagnostic Message Formatting Options.
                                                             (line  407)
* fshrink-wrap:                          Optimize Options.   (line  923)
* fshrink-wrap-separate:                 Optimize Options.   (line  928)
* fsignaling-nans:                       Optimize Options.   (line 2457)
* fsigned-bitfields:                     C Dialect Options.  (line  449)
* fsigned-bitfields <1>:                 Non-bugs.           (line   57)
* fsigned-char:                          C Dialect Options.  (line  455)
* fsigned-char <1>:                      Characters implementation.
                                                             (line   31)
* fsigned-zeros:                         Optimize Options.   (line 2412)
* fsimd-cost-model:                      Optimize Options.   (line 1505)
* fsingle-precision-constant:            Optimize Options.   (line 2490)
* fsized-deallocation:                   C++ Dialect Options.
                                                             (line  424)
* fsplit-ivs-in-unroller:                Optimize Options.   (line 1526)
* fsplit-loops:                          Optimize Options.   (line 2630)
* fsplit-paths:                          Optimize Options.   (line 1521)
* fsplit-stack:                          Instrumentation Options.
                                                             (line  840)
* fsplit-stack <1>:                      Common Function Attributes.
                                                             (line  869)
* fsplit-wide-types:                     Optimize Options.   (line  474)
* fsplit-wide-types-early:               Optimize Options.   (line  482)
* fssa-backprop:                         Optimize Options.   (line 1188)
* fssa-phiopt:                           Optimize Options.   (line 1194)
* fsso-struct:                           C Dialect Options.  (line  480)
* fstack_reuse:                          Code Gen Options.   (line   15)
* fstack-check:                          Instrumentation Options.
                                                             (line  766)
* fstack-clash-protection:               Instrumentation Options.
                                                             (line  808)
* fstack-limit-register:                 Instrumentation Options.
                                                             (line  823)
* fstack-limit-symbol:                   Instrumentation Options.
                                                             (line  823)
* fstack-protector:                      Instrumentation Options.
                                                             (line  741)
* fstack-protector-all:                  Instrumentation Options.
                                                             (line  752)
* fstack-protector-explicit:             Instrumentation Options.
                                                             (line  762)
* fstack-protector-strong:               Instrumentation Options.
                                                             (line  755)
* fstack-usage:                          Developer Options.  (line  885)
* fstats:                                Developer Options.  (line  914)
* fstdarg-opt:                           Optimize Options.   (line 2695)
* fstore-merging:                        Optimize Options.   (line 1413)
* fstrict-aliasing:                      Optimize Options.   (line 1675)
* fstrict-enums:                         C++ Dialect Options.
                                                             (line  434)
* fstrict-overflow:                      Code Gen Options.   (line  114)
* fstrict-volatile-bitfields:            Code Gen Options.   (line  599)
* fstrong-eval-order:                    C++ Dialect Options.
                                                             (line  443)
* fsync-libcalls:                        Code Gen Options.   (line  631)
* fsyntax-only:                          Warning Options.    (line   14)
* ftabstop:                              Preprocessor Options.
                                                             (line  241)
* ftemplate-backtrace-limit:             C++ Dialect Options.
                                                             (line  451)
* ftemplate-depth:                       C++ Dialect Options.
                                                             (line  455)
* ftest-coverage:                        Instrumentation Options.
                                                             (line  107)
* fthread-jumps:                         Optimize Options.   (line  465)
* fthreadsafe-statics:                   C++ Dialect Options.
                                                             (line  464)
* ftime-report:                          Developer Options.  (line  842)
* ftime-report-details:                  Developer Options.  (line  846)
* ftls-model:                            Code Gen Options.   (line  495)
* ftoplevel-reorder:                     Optimize Options.   (line 1859)
* ftracer:                               Optimize Options.   (line 2587)
* ftrack-macro-expansion:                Preprocessor Options.
                                                             (line  247)
* ftrampolines:                          Code Gen Options.   (line  506)
* ftrapping-math:                        Optimize Options.   (line 2422)
* ftrapv:                                Code Gen Options.   (line   90)
* ftree-bit-ccp:                         Optimize Options.   (line 1176)
* ftree-builtin-call-dce:                Optimize Options.   (line 1216)
* ftree-ccp:                             Optimize Options.   (line 1183)
* ftree-ch:                              Optimize Options.   (line 1245)
* ftree-coalesce-vars:                   Optimize Options.   (line 1284)
* ftree-copy-prop:                       Optimize Options.   (line 1011)
* ftree-dce:                             Optimize Options.   (line 1212)
* ftree-dominator-opts:                  Optimize Options.   (line 1231)
* ftree-dse:                             Optimize Options.   (line 1238)
* ftree-forwprop:                        Optimize Options.   (line  990)
* ftree-fre:                             Optimize Options.   (line  994)
* ftree-loop-distribute-patterns:        Optimize Options.   (line 1320)
* ftree-loop-distribution:               Optimize Options.   (line 1301)
* ftree-loop-if-convert:                 Optimize Options.   (line 1294)
* ftree-loop-im:                         Optimize Options.   (line 1365)
* ftree-loop-ivcanon:                    Optimize Options.   (line 1374)
* ftree-loop-linear:                     Optimize Options.   (line 1258)
* ftree-loop-optimize:                   Optimize Options.   (line 1252)
* ftree-loop-vectorize:                  Optimize Options.   (line 1439)
* ftree-parallelize-loops:               Optimize Options.   (line 1394)
* ftree-partial-pre:                     Optimize Options.   (line  986)
* ftree-phiprop:                         Optimize Options.   (line 1001)
* ftree-pre:                             Optimize Options.   (line  982)
* ftree-pta:                             Optimize Options.   (line 1403)
* ftree-reassoc:                         Optimize Options.   (line  971)
* ftree-scev-cprop:                      Optimize Options.   (line 1380)
* ftree-sink:                            Optimize Options.   (line 1172)
* ftree-slp-vectorize:                   Optimize Options.   (line 1444)
* ftree-slsr:                            Optimize Options.   (line 1428)
* ftree-sra:                             Optimize Options.   (line 1407)
* ftree-switch-conversion:               Optimize Options.   (line 1199)
* ftree-tail-merge:                      Optimize Options.   (line 1204)
* ftree-ter:                             Optimize Options.   (line 1420)
* ftree-vectorize:                       Optimize Options.   (line 1434)
* ftree-vrp:                             Optimize Options.   (line 1512)
* ftrivial-auto-var-init:                Optimize Options.   (line 1449)
* funconstrained-commons:                Optimize Options.   (line  563)
* funit-at-a-time:                       Optimize Options.   (line 1852)
* funroll-all-loops:                     Optimize Options.   (line 2604)
* funroll-loops:                         Optimize Options.   (line 2594)
* funsafe-math-optimizations:            Optimize Options.   (line 2355)
* funsigned-bitfields:                   C Dialect Options.  (line  449)
* funsigned-bitfields <1>:               Structures unions enumerations and bit-fields implementation.
                                                             (line   17)
* funsigned-bitfields <2>:               Non-bugs.           (line   57)
* funsigned-char:                        C Dialect Options.  (line  462)
* funsigned-char <1>:                    Characters implementation.
                                                             (line   31)
* funswitch-loops:                       Optimize Options.   (line 2636)
* funwind-tables:                        Code Gen Options.   (line  151)
* fuse-cxa-atexit:                       C++ Dialect Options.
                                                             (line  470)
* fuse-cxa-get-exception-ptr:            C++ Dialect Options.
                                                             (line  477)
* fuse-ld=bfd:                           Link Options.       (line   74)
* fuse-ld=gold:                          Link Options.       (line   77)
* fuse-ld=lld:                           Link Options.       (line   80)
* fuse-ld=mold:                          Link Options.       (line   83)
* fuse-linker-plugin:                    Optimize Options.   (line 2137)
* fvar-tracking:                         Debugging Options.  (line  183)
* fvar-tracking-assignments:             Debugging Options.  (line  193)
* fvar-tracking-assignments-toggle:      Developer Options.  (line  834)
* fvariable-expansion-in-unroller:       Optimize Options.   (line 1540)
* fvect-cost-model:                      Optimize Options.   (line 1484)
* fverbose-asm:                          Code Gen Options.   (line  264)
* fversion-loops-for-strides:            Optimize Options.   (line 2643)
* fvisibility:                           Code Gen Options.   (line  535)
* fvisibility-inlines-hidden:            C++ Dialect Options.
                                                             (line  482)
* fvisibility-ms-compat:                 C++ Dialect Options.
                                                             (line  510)
* fvpt:                                  Optimize Options.   (line 2557)
* fvtable-verify:                        Instrumentation Options.
                                                             (line  858)
* fvtv-counts:                           Instrumentation Options.
                                                             (line  894)
* fvtv-debug:                            Instrumentation Options.
                                                             (line  881)
* fweak:                                 C++ Dialect Options.
                                                             (line  539)
* fweb:                                  Optimize Options.   (line 1872)
* fwhole-program:                        Optimize Options.   (line 1883)
* fwide-exec-charset:                    Preprocessor Options.
                                                             (line  278)
* fworking-directory:                    Preprocessor Options.
                                                             (line  321)
* fwrapv:                                Code Gen Options.   (line   98)
* fwrapv-pointer:                        Code Gen Options.   (line  108)
* fwritable-relocated-rdata:             x86 Windows Options.
                                                             (line   53)
* fzero-call-used-regs:                  Optimize Options.   (line 2723)
* fzero-initialized-in-bss:              Optimize Options.   (line  453)
* fzero-link:                            Objective-C and Objective-C++ Dialect Options.
                                                             (line  140)
* g:                                     Debugging Options.  (line   28)
* G:                                     ARC Options.        (line  414)
* G <1>:                                 M32R/D Options.     (line   57)
* G <2>:                                 MIPS Options.       (line  460)
* G <3>:                                 Nios II Options.    (line    9)
* G <4>:                                 RS/6000 and PowerPC Options.
                                                             (line  714)
* G <5>:                                 System V Options.   (line   10)
* gas-loc-support:                       Debugging Options.  (line  264)
* gas-locview-support:                   Debugging Options.  (line  280)
* gbtf:                                  Debugging Options.  (line   67)
* gcolumn-info:                          Debugging Options.  (line  292)
* gctf:                                  Debugging Options.  (line   75)
* gdescribe-dies:                        Debugging Options.  (line  222)
* gdwarf:                                Debugging Options.  (line   48)
* gdwarf32:                              Debugging Options.  (line  212)
* gdwarf64:                              Debugging Options.  (line  212)
* gen-decls:                             Objective-C and Objective-C++ Dialect Options.
                                                             (line  166)
* gfull:                                 Darwin Options.     (line   69)
* ggdb:                                  Debugging Options.  (line   41)
* ggnu-pubnames:                         Debugging Options.  (line  230)
* ginline-points:                        Debugging Options.  (line  351)
* ginternal-reset-location-views:        Debugging Options.  (line  340)
* gno-as-loc-support:                    Debugging Options.  (line  276)
* gno-column-info:                       Debugging Options.  (line  292)
* gno-inline-points:                     Debugging Options.  (line  351)
* gno-internal-reset-location-views:     Debugging Options.  (line  340)
* gno-record-gcc-switches:               Debugging Options.  (line  245)
* gno-statement-frontiers:               Debugging Options.  (line  297)
* gno-strict-dwarf:                      Debugging Options.  (line  260)
* gno-variable-location-views:           Debugging Options.  (line  308)
* gpubnames:                             Debugging Options.  (line  227)
* grecord-gcc-switches:                  Debugging Options.  (line  245)
* gsplit-dwarf:                          Debugging Options.  (line  204)
* gstabs:                                Debugging Options.  (line   95)
* gstabs+:                               Debugging Options.  (line  103)
* gstatement-frontiers:                  Debugging Options.  (line  297)
* gstrict-dwarf:                         Debugging Options.  (line  254)
* gtoggle:                               Developer Options.  (line  826)
* gused:                                 Darwin Options.     (line   64)
* gvariable-location-views:              Debugging Options.  (line  308)
* gvariable-location-views=incompat5:    Debugging Options.  (line  308)
* gvms:                                  Debugging Options.  (line  122)
* gxcoff:                                Debugging Options.  (line  109)
* gxcoff+:                               Debugging Options.  (line  114)
* gz:                                    Debugging Options.  (line  360)
* H:                                     Preprocessor Options.
                                                             (line  403)
* headerpad_max_install_names:           Darwin Options.     (line  196)
* help:                                  Overall Options.    (line  478)
* I:                                     Directory Options.  (line   13)
* I-:                                    Directory Options.  (line   65)
* idirafter:                             Directory Options.  (line   13)
* iframework:                            Darwin Options.     (line   57)
* imacros:                               Preprocessor Options.
                                                             (line   57)
* image_base:                            Darwin Options.     (line  196)
* imultilib:                             Directory Options.  (line   98)
* include:                               Preprocessor Options.
                                                             (line   46)
* init:                                  Darwin Options.     (line  196)
* install_name:                          Darwin Options.     (line  196)
* iplugindir=:                           Directory Options.  (line  113)
* iprefix:                               Directory Options.  (line   80)
* iquote:                                Directory Options.  (line   13)
* isysroot:                              Directory Options.  (line   92)
* isystem:                               Directory Options.  (line   13)
* iwithprefix:                           Directory Options.  (line   86)
* iwithprefixbefore:                     Directory Options.  (line   86)
* keep_private_externs:                  Darwin Options.     (line  196)
* l:                                     Link Options.       (line   87)
* L:                                     Directory Options.  (line  118)
* lobjc:                                 Link Options.       (line  113)
* M:                                     Preprocessor Options.
                                                             (line   77)
* m:                                     RS/6000 and PowerPC Options.
                                                             (line  521)
* m1:                                    SH Options.         (line    9)
* m10:                                   PDP-11 Options.     (line   29)
* m128bit-long-double:                   x86 Options.        (line  645)
* m16:                                   x86 Options.        (line 1532)
* m16-bit:                               CRIS Options.       (line   62)
* m16-bit <1>:                           NDS32 Options.      (line   51)
* m1reg-:                                Adapteva Epiphany Options.
                                                             (line  131)
* m2:                                    SH Options.         (line   12)
* m210:                                  MCore Options.      (line   43)
* m2a:                                   SH Options.         (line   30)
* m2a-nofpu:                             SH Options.         (line   18)
* m2a-single:                            SH Options.         (line   26)
* m2a-single-only:                       SH Options.         (line   22)
* m3:                                    SH Options.         (line   34)
* m31:                                   S/390 and zSeries Options.
                                                             (line   86)
* m32:                                   RS/6000 and PowerPC Options.
                                                             (line  245)
* m32 <1>:                               SPARC Options.      (line  315)
* m32 <2>:                               TILE-Gx Options.    (line   23)
* m32 <3>:                               TILEPro Options.    (line   13)
* m32 <4>:                               x86 Options.        (line 1532)
* m32-bit:                               CRIS Options.       (line   62)
* m32bit-doubles:                        RL78 Options.       (line   73)
* m32bit-doubles <1>:                    RX Options.         (line   10)
* m32r:                                  M32R/D Options.     (line   15)
* m32r2:                                 M32R/D Options.     (line    9)
* m32rx:                                 M32R/D Options.     (line   12)
* m340:                                  MCore Options.      (line   43)
* m3dnow:                                x86 Options.        (line  868)
* m3dnowa:                               x86 Options.        (line  869)
* m3e:                                   SH Options.         (line   37)
* m4:                                    SH Options.         (line   51)
* m4-100:                                SH Options.         (line   54)
* m4-100-nofpu:                          SH Options.         (line   57)
* m4-100-single:                         SH Options.         (line   61)
* m4-100-single-only:                    SH Options.         (line   65)
* m4-200:                                SH Options.         (line   69)
* m4-200-nofpu:                          SH Options.         (line   72)
* m4-200-single:                         SH Options.         (line   76)
* m4-200-single-only:                    SH Options.         (line   80)
* m4-300:                                SH Options.         (line   84)
* m4-300-nofpu:                          SH Options.         (line   87)
* m4-300-single:                         SH Options.         (line   91)
* m4-300-single-only:                    SH Options.         (line   95)
* m4-340:                                SH Options.         (line   99)
* m4-500:                                SH Options.         (line  102)
* m4-nofpu:                              SH Options.         (line   40)
* m4-single:                             SH Options.         (line   47)
* m4-single-only:                        SH Options.         (line   43)
* m40:                                   PDP-11 Options.     (line   23)
* m45:                                   PDP-11 Options.     (line   26)
* m4a:                                   SH Options.         (line  118)
* m4a-nofpu:                             SH Options.         (line  106)
* m4a-single:                            SH Options.         (line  114)
* m4a-single-only:                       SH Options.         (line  110)
* m4al:                                  SH Options.         (line  121)
* m4byte-functions:                      MCore Options.      (line   27)
* m5200:                                 M680x0 Options.     (line  145)
* m5206e:                                M680x0 Options.     (line  154)
* m528x:                                 M680x0 Options.     (line  158)
* m5307:                                 M680x0 Options.     (line  162)
* m5407:                                 M680x0 Options.     (line  166)
* m64:                                   Nvidia PTX Options. (line    9)
* m64 <1>:                               RS/6000 and PowerPC Options.
                                                             (line  245)
* m64 <2>:                               S/390 and zSeries Options.
                                                             (line   86)
* m64 <3>:                               SPARC Options.      (line  315)
* m64 <4>:                               TILE-Gx Options.    (line   23)
* m64 <5>:                               x86 Options.        (line 1532)
* m64bit-doubles:                        RL78 Options.       (line   73)
* m64bit-doubles <1>:                    RX Options.         (line   10)
* m68000:                                M680x0 Options.     (line   94)
* m68010:                                M680x0 Options.     (line  102)
* m68020:                                M680x0 Options.     (line  108)
* m68020-40:                             M680x0 Options.     (line  176)
* m68020-60:                             M680x0 Options.     (line  185)
* m68030:                                M680x0 Options.     (line  113)
* m68040:                                M680x0 Options.     (line  118)
* m68060:                                M680x0 Options.     (line  127)
* m68881:                                M680x0 Options.     (line  195)
* m8-bit:                                CRIS Options.       (line   62)
* m8bit-idiv:                            x86 Options.        (line 1434)
* m8byte-align:                          V850 Options.       (line  170)
* m96bit-long-double:                    x86 Options.        (line  645)
* mA6:                                   ARC Options.        (line   23)
* mA7:                                   ARC Options.        (line   30)
* mabi:                                  AArch64 Options.    (line    9)
* mabi <1>:                              ARM Options.        (line    9)
* mabi <2>:                              LoongArch Options.  (line   36)
* mabi <3>:                              PRU Options.        (line   28)
* mabi <4>:                              RISC-V Options.     (line   17)
* mabi <5>:                              RS/6000 and PowerPC Options.
                                                             (line  552)
* mabi <6>:                              x86 Options.        (line 1127)
* mabi <7>:                              Xtensa Options.     (line  103)
* mabi=32:                               MIPS Options.       (line  156)
* mabi=64:                               MIPS Options.       (line  156)
* mabi=call0:                            Xtensa Options.     (line  108)
* mabi=eabi:                             MIPS Options.       (line  156)
* mabi=elfv1:                            RS/6000 and PowerPC Options.
                                                             (line  574)
* mabi=elfv2:                            RS/6000 and PowerPC Options.
                                                             (line  580)
* mabi=gnu:                              MMIX Options.       (line   20)
* mabi=ibmlongdouble:                    RS/6000 and PowerPC Options.
                                                             (line  558)
* mabi=ieeelongdouble:                   RS/6000 and PowerPC Options.
                                                             (line  566)
* mabi=mmixware:                         MMIX Options.       (line   20)
* mabi=n32:                              MIPS Options.       (line  156)
* mabi=o64:                              MIPS Options.       (line  156)
* mabi=windowed:                         Xtensa Options.     (line  115)
* mabicalls:                             MIPS Options.       (line  192)
* mabm:                                  x86 Options.        (line  871)
* mabort-on-noreturn:                    ARM Options.        (line  752)
* mabs=2008:                             MIPS Options.       (line  300)
* mabs=legacy:                           MIPS Options.       (line  300)
* mabsdata:                              AVR Options.        (line  162)
* mabsdiff:                              MeP Options.        (line    7)
* mac0:                                  PDP-11 Options.     (line   16)
* macc-4:                                FRV Options.        (line  139)
* macc-8:                                FRV Options.        (line  143)
* maccumulate-args:                      AVR Options.        (line  169)
* maccumulate-outgoing-args:             SH Options.         (line  314)
* maccumulate-outgoing-args <1>:         x86 Options.        (line 1171)
* maddress-mode=long:                    x86 Options.        (line 1582)
* maddress-mode=short:                   x86 Options.        (line 1587)
* mads:                                  RS/6000 and PowerPC Options.
                                                             (line  614)
* madx:                                  x86 Options.        (line  872)
* maes:                                  x86 Options.        (line  849)
* maix-struct-return:                    RS/6000 and PowerPC Options.
                                                             (line  545)
* maix32:                                RS/6000 and PowerPC Options.
                                                             (line  283)
* maix64:                                RS/6000 and PowerPC Options.
                                                             (line  283)
* malign-300:                            H8/300 Options.     (line   41)
* malign-call:                           ARC Options.        (line  433)
* malign-data:                           RISC-V Options.     (line  168)
* malign-data <1>:                       x86 Options.        (line  685)
* malign-double:                         x86 Options.        (line  630)
* malign-int:                            M680x0 Options.     (line  262)
* malign-labels:                         FRV Options.        (line  128)
* malign-loops:                          M32R/D Options.     (line   73)
* malign-natural:                        RS/6000 and PowerPC Options.
                                                             (line  321)
* malign-power:                          RS/6000 and PowerPC Options.
                                                             (line  321)
* malign-stringops:                      x86 Options.        (line 1307)
* mall-opts:                             MeP Options.        (line   11)
* malloc-cc:                             FRV Options.        (line   31)
* mallow-string-insns:                   RX Options.         (line  150)
* mallregs:                              RL78 Options.       (line   66)
* maltivec:                              RS/6000 and PowerPC Options.
                                                             (line  137)
* malu32:                                eBPF Options.       (line   35)
* mam33:                                 MN10300 Options.    (line   17)
* mam33-2:                               MN10300 Options.    (line   24)
* mam34:                                 MN10300 Options.    (line   27)
* mamx-bf16:                             x86 Options.        (line  910)
* mamx-int8:                             x86 Options.        (line  909)
* mamx-tile:                             x86 Options.        (line  908)
* manchor:                               C-SKY Options.      (line  126)
* mandroid:                              GNU/Linux Options.  (line   26)
* mannotate-align:                       ARC Options.        (line  382)
* mapcs:                                 ARM Options.        (line   21)
* mapcs-frame:                           ARM Options.        (line   13)
* mapp-regs:                             SPARC Options.      (line   10)
* mapp-regs <1>:                         V850 Options.       (line  181)
* mARC600:                               ARC Options.        (line   23)
* mARC601:                               ARC Options.        (line   27)
* mARC700:                               ARC Options.        (line   30)
* march:                                 AArch64 Options.    (line  150)
* march <1>:                             AMD GCN Options.    (line    9)
* march <2>:                             ARM Options.        (line   80)
* march <3>:                             C6X Options.        (line    7)
* march <4>:                             CRIS Options.       (line   10)
* march <5>:                             HPPA Options.       (line    9)
* march <6>:                             HPPA Options.       (line  162)
* march <7>:                             M680x0 Options.     (line   12)
* march <8>:                             MIPS Options.       (line   14)
* march <9>:                             NDS32 Options.      (line   64)
* march <10>:                            Nios II Options.    (line   94)
* march <11>:                            Nvidia PTX Options. (line   13)
* march <12>:                            Nvidia PTX Options. (line   25)
* march <13>:                            RISC-V Options.     (line   67)
* march <14>:                            S/390 and zSeries Options.
                                                             (line  148)
* march <15>:                            x86 Options.        (line    9)
* march=:                                C-SKY Options.      (line    9)
* marclinux:                             ARC Options.        (line  388)
* marclinux_prof:                        ARC Options.        (line  394)
* margonaut:                             ARC Options.        (line  584)
* marm:                                  ARM Options.        (line  824)
* mas100-syntax:                         RX Options.         (line   76)
* masm-hex:                              MSP430 Options.     (line    9)
* masm-syntax-unified:                   ARM Options.        (line  932)
* masm=DIALECT:                          x86 Options.        (line  579)
* matomic:                               ARC Options.        (line  155)
* matomic-model=MODEL:                   SH Options.         (line  193)
* mauto-litpools:                        Xtensa Options.     (line   60)
* mauto-modify-reg:                      ARC Options.        (line  436)
* mauto-pic:                             IA-64 Options.      (line   50)
* maverage:                              MeP Options.        (line   16)
* mavoid-indexed-addresses:              RS/6000 and PowerPC Options.
                                                             (line  360)
* mavx:                                  x86 Options.        (line  837)
* mavx2:                                 x86 Options.        (line  838)
* mavx256-split-unaligned-load:          x86 Options.        (line 1442)
* mavx256-split-unaligned-store:         x86 Options.        (line 1442)
* mavx5124fmaps:                         x86 Options.        (line  902)
* mavx5124vnniw:                         x86 Options.        (line  905)
* mavx512bf16:                           x86 Options.        (line  888)
* mavx512bitalg:                         x86 Options.        (line  894)
* mavx512bw:                             x86 Options.        (line  844)
* mavx512cd:                             x86 Options.        (line  842)
* mavx512dq:                             x86 Options.        (line  845)
* mavx512er:                             x86 Options.        (line  841)
* mavx512f:                              x86 Options.        (line  839)
* mavx512fp16:                           x86 Options.        (line  889)
* mavx512ifma:                           x86 Options.        (line  846)
* mavx512pf:                             x86 Options.        (line  840)
* mavx512vbmi:                           x86 Options.        (line  847)
* mavx512vbmi2:                          x86 Options.        (line  887)
* mavx512vl:                             x86 Options.        (line  843)
* mavx512vnni:                           x86 Options.        (line  903)
* mavx512vp2intersect:                   x86 Options.        (line  901)
* mavx512vpopcntdq:                      x86 Options.        (line  900)
* mavxvnni:                              x86 Options.        (line  904)
* max-vect-align:                        Adapteva Epiphany Options.
                                                             (line  119)
* mb:                                    SH Options.         (line  126)
* mbackchain:                            S/390 and zSeries Options.
                                                             (line   35)
* mbarrel_shifter:                       ARC Options.        (line  601)
* mbarrel-shift-enabled:                 LM32 Options.       (line    9)
* mbarrel-shifter:                       ARC Options.        (line   10)
* mbase-addresses:                       MMIX Options.       (line   53)
* mbased=:                               MeP Options.        (line   20)
* mbbit-peephole:                        ARC Options.        (line  439)
* mbe8:                                  ARM Options.        (line   72)
* mbig:                                  RS/6000 and PowerPC Options.
                                                             (line  440)
* mbig-endian:                           AArch64 Options.    (line   20)
* mbig-endian <1>:                       ARC Options.        (line  587)
* mbig-endian <2>:                       ARM Options.        (line   67)
* mbig-endian <3>:                       C6X Options.        (line   13)
* mbig-endian <4>:                       C-SKY Options.      (line   28)
* mbig-endian <5>:                       eBPF Options.       (line   22)
* mbig-endian <6>:                       IA-64 Options.      (line    9)
* mbig-endian <7>:                       MCore Options.      (line   39)
* mbig-endian <8>:                       MicroBlaze Options. (line   56)
* mbig-endian <9>:                       NDS32 Options.      (line    9)
* mbig-endian <10>:                      RISC-V Options.     (line  174)
* mbig-endian <11>:                      RS/6000 and PowerPC Options.
                                                             (line  440)
* mbig-endian <12>:                      TILE-Gx Options.    (line   29)
* mbig-endian-data:                      RX Options.         (line   42)
* mbig-switch:                           V850 Options.       (line  176)
* mbigtable:                             SH Options.         (line  141)
* mbionic:                               GNU/Linux Options.  (line   22)
* mbit-align:                            RS/6000 and PowerPC Options.
                                                             (line  392)
* mbit-ops:                              CR16 Options.       (line   25)
* mbitfield:                             M680x0 Options.     (line  232)
* mbitops:                               MeP Options.        (line   26)
* mbitops <1>:                           SH Options.         (line  145)
* mblock-compare-inline-limit:           RS/6000 and PowerPC Options.
                                                             (line  694)
* mblock-compare-inline-loop-limit:      RS/6000 and PowerPC Options.
                                                             (line  700)
* mblock-move-inline-limit:              RS/6000 and PowerPC Options.
                                                             (line  688)
* mbmi:                                  x86 Options.        (line  873)
* mbmi2:                                 x86 Options.        (line  874)
* mboard:                                OpenRISC Options.   (line    9)
* mbranch-cost:                          Adapteva Epiphany Options.
                                                             (line   18)
* mbranch-cost <1>:                      AVR Options.        (line  184)
* mbranch-cost <2>:                      MIPS Options.       (line  791)
* mbranch-cost <3>:                      RISC-V Options.     (line    9)
* mbranch-cost=:                         C-SKY Options.      (line  159)
* mbranch-cost=NUM:                      SH Options.         (line  334)
* mbranch-cost=NUMBER:                   M32R/D Options.     (line   82)
* mbranch-index:                         ARC Options.        (line  329)
* mbranch-likely:                        MIPS Options.       (line  798)
* mbranch-predict:                       MMIX Options.       (line   48)
* mbranch-protection:                    AArch64 Options.    (line  288)
* mbss-plt:                              RS/6000 and PowerPC Options.
                                                             (line  161)
* mbuild-constants:                      DEC Alpha Options.  (line  141)
* mbwx:                                  DEC Alpha Options.  (line  163)
* mbypass-cache:                         Nios II Options.    (line  103)
* mc=:                                   MeP Options.        (line   31)
* mc68000:                               M680x0 Options.     (line   94)
* mc68020:                               M680x0 Options.     (line  108)
* mcache:                                C-SKY Options.      (line   93)
* mcache-block-size:                     NDS32 Options.      (line   60)
* mcache-volatile:                       Nios II Options.    (line  109)
* mcall-eabi:                            RS/6000 and PowerPC Options.
                                                             (line  515)
* mcall-freebsd:                         RS/6000 and PowerPC Options.
                                                             (line  529)
* mcall-linux:                           RS/6000 and PowerPC Options.
                                                             (line  525)
* mcall-ms2sysv-xlogues:                 x86 Options.        (line 1147)
* mcall-netbsd:                          RS/6000 and PowerPC Options.
                                                             (line  533)
* mcall-netbsd <1>:                      RS/6000 and PowerPC Options.
                                                             (line  537)
* mcall-prologues:                       AVR Options.        (line  189)
* mcall-sysv:                            RS/6000 and PowerPC Options.
                                                             (line  507)
* mcall-sysv-eabi:                       RS/6000 and PowerPC Options.
                                                             (line  515)
* mcall-sysv-noeabi:                     RS/6000 and PowerPC Options.
                                                             (line  518)
* mcallee-super-interworking:            ARM Options.        (line  853)
* mcaller-copies:                        HPPA Options.       (line   23)
* mcaller-super-interworking:            ARM Options.        (line  860)
* mcallgraph-data:                       MCore Options.      (line   31)
* mcase-vector-pcrel:                    ARC Options.        (line  448)
* mcbcond:                               SPARC Options.      (line  260)
* mcbranch-force-delay-slot:             SH Options.         (line  349)
* mcc-init:                              CRIS Options.       (line   40)
* mccrt:                                 C-SKY Options.      (line  155)
* mcfv4e:                                M680x0 Options.     (line  170)
* mcheck-zero-division:                  MIPS Options.       (line  570)
* mcix:                                  DEC Alpha Options.  (line  163)
* mcld:                                  x86 Options.        (line  965)
* mcldemote:                             x86 Options.        (line  906)
* mclear-hwcap:                          Solaris 2 Options.  (line    9)
* mclflushopt:                           x86 Options.        (line  851)
* mclip:                                 MeP Options.        (line   35)
* mclwb:                                 x86 Options.        (line  852)
* mclzero:                               x86 Options.        (line  885)
* mcmodel:                               NDS32 Options.      (line   67)
* mcmodel <1>:                           SPARC Options.      (line  320)
* mcmodel=kernel:                        x86 Options.        (line 1566)
* mcmodel=large:                         AArch64 Options.    (line   45)
* mcmodel=large <1>:                     OpenRISC Options.   (line   77)
* mcmodel=large <2>:                     RS/6000 and PowerPC Options.
                                                             (line  131)
* mcmodel=large <3>:                     TILE-Gx Options.    (line   14)
* mcmodel=large <4>:                     x86 Options.        (line 1578)
* mcmodel=medany:                        RISC-V Options.     (line  142)
* mcmodel=medium:                        RS/6000 and PowerPC Options.
                                                             (line  126)
* mcmodel=medium <1>:                    x86 Options.        (line 1571)
* mcmodel=medlow:                        RISC-V Options.     (line  135)
* mcmodel=small:                         AArch64 Options.    (line   39)
* mcmodel=small <1>:                     OpenRISC Options.   (line   73)
* mcmodel=small <2>:                     RS/6000 and PowerPC Options.
                                                             (line  122)
* mcmodel=small <3>:                     TILE-Gx Options.    (line    9)
* mcmodel=small <4>:                     x86 Options.        (line 1560)
* mcmodel=tiny:                          AArch64 Options.    (line   34)
* mcmov:                                 NDS32 Options.      (line   21)
* mcmov <1>:                             OpenRISC Options.   (line   45)
* mcmove:                                Adapteva Epiphany Options.
                                                             (line   23)
* mcmpb:                                 RS/6000 and PowerPC Options.
                                                             (line   25)
* mcmse:                                 ARM Options.        (line  961)
* mco-re:                                eBPF Options.       (line   56)
* mcode-density:                         ARC Options.        (line  163)
* mcode-density-frame:                   ARC Options.        (line  509)
* mcode-readable:                        MIPS Options.       (line  530)
* mcode-region:                          MSP430 Options.     (line  150)
* mcompact-branches=always:              MIPS Options.       (line  810)
* mcompact-branches=never:               MIPS Options.       (line  810)
* mcompact-branches=optimal:             MIPS Options.       (line  810)
* mcompact-casesi:                       ARC Options.        (line  452)
* mcompat-align-parm:                    RS/6000 and PowerPC Options.
                                                             (line  899)
* mcompress:                             FT32 Options.       (line   26)
* mcond-exec:                            FRV Options.        (line  187)
* mcond-move:                            FRV Options.        (line  159)
* mconfig=:                              MeP Options.        (line   39)
* mconsole:                              x86 Windows Options.
                                                             (line    9)
* mconst-align:                          CRIS Options.       (line   53)
* mconst16:                              Xtensa Options.     (line   10)
* mconstant-gp:                          IA-64 Options.      (line   46)
* mconstpool:                            C-SKY Options.      (line  143)
* mcop:                                  MeP Options.        (line   48)
* mcop32:                                MeP Options.        (line   53)
* mcop64:                                MeP Options.        (line   56)
* mcorea:                                Blackfin Options.   (line  154)
* mcoreb:                                Blackfin Options.   (line  161)
* mcp:                                   C-SKY Options.      (line   90)
* mcpu:                                  AArch64 Options.    (line  235)
* mcpu <1>:                              ARC Options.        (line   18)
* mcpu <2>:                              ARM Options.        (line  622)
* mcpu <3>:                              CRIS Options.       (line   10)
* mcpu <4>:                              DEC Alpha Options.  (line  215)
* mcpu <5>:                              eBPF Options.       (line   38)
* mcpu <6>:                              FRV Options.        (line  258)
* mcpu <7>:                              M680x0 Options.     (line   28)
* mcpu <8>:                              picoChip Options.   (line    9)
* mcpu <9>:                              RISC-V Options.     (line   78)
* mcpu <10>:                             RL78 Options.       (line   32)
* mcpu <11>:                             RS/6000 and PowerPC Options.
                                                             (line   62)
* mcpu <12>:                             RX Options.         (line   30)
* mcpu <13>:                             SPARC Options.      (line  115)
* mcpu <14>:                             TILE-Gx Options.    (line   18)
* mcpu <15>:                             TILEPro Options.    (line    9)
* mcpu <16>:                             Visium Options.     (line   33)
* mcpu <17>:                             x86 Options.        (line  525)
* mcpu=:                                 Blackfin Options.   (line    7)
* mcpu= <1>:                             C-SKY Options.      (line   14)
* mcpu= <2>:                             M32C Options.       (line    7)
* mcpu= <3>:                             MicroBlaze Options. (line   20)
* mcpu= <4>:                             MSP430 Options.     (line   72)
* mcpu32:                                M680x0 Options.     (line  136)
* mcr16c:                                CR16 Options.       (line   14)
* mcr16cplus:                            CR16 Options.       (line   14)
* mcrc:                                  MIPS Options.       (line  416)
* mcrc32:                                x86 Options.        (line 1043)
* mcrypto:                               RS/6000 and PowerPC Options.
                                                             (line  178)
* mcsync-anomaly:                        Blackfin Options.   (line   57)
* mcsync-anomaly <1>:                    Blackfin Options.   (line   63)
* mctor-dtor:                            NDS32 Options.      (line   81)
* mcustom-fpu-cfg:                       Nios II Options.    (line  259)
* mcustom-INSN:                          Nios II Options.    (line  139)
* mcx16:                                 x86 Options.        (line 1016)
* MD:                                    Preprocessor Options.
                                                             (line  172)
* mdalign:                               SH Options.         (line  132)
* mdata-align:                           CRIS Options.       (line   53)
* mdata-model:                           CR16 Options.       (line   28)
* mdata-region:                          MSP430 Options.     (line  150)
* mdc:                                   MeP Options.        (line   62)
* mdebug:                                M32R/D Options.     (line   69)
* mdebug <1>:                            S/390 and zSeries Options.
                                                             (line  144)
* mdebug <2>:                            Visium Options.     (line    7)
* mdebug-main=PREFIX:                    VMS Options.        (line   13)
* mdec-asm:                              PDP-11 Options.     (line   46)
* mdirect-extern-access:                 x86 Options.        (line 1598)
* mdisable-callt:                        V850 Options.       (line   92)
* mdisable-fpregs:                       HPPA Options.       (line   34)
* mdisable-indexing:                     HPPA Options.       (line   40)
* mdiv:                                  C-SKY Options.      (line  109)
* mdiv <1>:                              M680x0 Options.     (line  207)
* mdiv <2>:                              MCore Options.      (line   15)
* mdiv <3>:                              MeP Options.        (line   65)
* mdiv <4>:                              RISC-V Options.     (line   49)
* mdiv-rem:                              ARC Options.        (line  160)
* mdiv=STRATEGY:                         SH Options.         (line  284)
* mdivide-breaks:                        MIPS Options.       (line  576)
* mdivide-enabled:                       LM32 Options.       (line   12)
* mdivide-traps:                         MIPS Options.       (line  576)
* mdivsi3_libfunc=NAME:                  SH Options.         (line  320)
* mdll:                                  x86 Windows Options.
                                                             (line   16)
* mdlmzb:                                RS/6000 and PowerPC Options.
                                                             (line  385)
* mdmx:                                  MIPS Options.       (line  376)
* mdouble:                               AVR Options.        (line  194)
* mdouble <1>:                           FRV Options.        (line   48)
* mdouble-float:                         C-SKY Options.      (line   58)
* mdouble-float <1>:                     MIPS Options.       (line  288)
* mdouble-float <2>:                     OpenRISC Options.   (line   33)
* mdpfp:                                 ARC Options.        (line   99)
* mdpfp_compact:                         ARC Options.        (line  604)
* mdpfp_fast:                            ARC Options.        (line  607)
* mdpfp-compact:                         ARC Options.        (line  100)
* mdpfp-fast:                            ARC Options.        (line  104)
* mdsp:                                  C-SKY Options.      (line  102)
* mdsp <1>:                              MIPS Options.       (line  353)
* mdsp_packa:                            ARC Options.        (line  610)
* mdsp-packa:                            ARC Options.        (line  335)
* mdspr2:                                MIPS Options.       (line  359)
* mdump-tune-features:                   x86 Options.        (line  947)
* mdvbf:                                 ARC Options.        (line  340)
* mdwarf2-asm:                           IA-64 Options.      (line   94)
* mdword:                                FRV Options.        (line   40)
* mdword <1>:                            FRV Options.        (line   44)
* mdynamic-no-pic:                       RS/6000 and PowerPC Options.
                                                             (line  445)
* mea:                                   ARC Options.        (line  112)
* mEA:                                   ARC Options.        (line  613)
* meabi:                                 RS/6000 and PowerPC Options.
                                                             (line  633)
* mearly-cbranchsi:                      ARC Options.        (line  474)
* mearly-stop-bits:                      IA-64 Options.      (line  100)
* meb:                                   MeP Options.        (line   68)
* meb <1>:                               Moxie Options.      (line    7)
* meb <2>:                               Nios II Options.    (line   90)
* meb <3>:                               Score Options.      (line    9)
* medsp:                                 C-SKY Options.      (line  103)
* mel:                                   MeP Options.        (line   71)
* mel <1>:                               Moxie Options.      (line   11)
* mel <2>:                               Nios II Options.    (line   90)
* mel <3>:                               Score Options.      (line   12)
* melf:                                  CRIS Options.       (line   78)
* melf <1>:                              MMIX Options.       (line   43)
* melrw:                                 C-SKY Options.      (line   76)
* memb:                                  RS/6000 and PowerPC Options.
                                                             (line  628)
* membedded-data:                        MIPS Options.       (line  517)
* memregs=:                              M32C Options.       (line   21)
* menqcmd:                               x86 Options.        (line  897)
* mep:                                   V850 Options.       (line   16)
* mepsilon:                              MMIX Options.       (line   15)
* mesa:                                  S/390 and zSeries Options.
                                                             (line   94)
* metrax100:                             CRIS Options.       (line   25)
* metrax4:                               CRIS Options.       (line   25)
* meva:                                  MIPS Options.       (line  403)
* mexpand-adddi:                         ARC Options.        (line  477)
* mexplicit-relocs:                      DEC Alpha Options.  (line  176)
* mexplicit-relocs <1>:                  MIPS Options.       (line  561)
* mexr:                                  H8/300 Options.     (line   28)
* mexr <1>:                              H8/300 Options.     (line   33)
* mext-perf:                             NDS32 Options.      (line   27)
* mext-perf2:                            NDS32 Options.      (line   33)
* mext-string:                           NDS32 Options.      (line   39)
* mextern-sdata:                         MIPS Options.       (line  480)
* MF:                                    Preprocessor Options.
                                                             (line  111)
* mf16c:                                 x86 Options.        (line  856)
* mfancy-math-387:                       x86 Options.        (line  620)
* mfast-fp:                              Blackfin Options.   (line  130)
* mfast-indirect-calls:                  HPPA Options.       (line   52)
* mfast-sw-div:                          Nios II Options.    (line  115)
* mfaster-structs:                       SPARC Options.      (line   91)
* mfdiv:                                 RISC-V Options.     (line   42)
* mfdivdu:                               C-SKY Options.      (line   64)
* mfdpic:                                ARM Options.        (line  984)
* mfdpic <1>:                            FRV Options.        (line   72)
* mfentry:                               x86 Options.        (line 1381)
* mfentry-name:                          x86 Options.        (line 1412)
* mfentry-section:                       x86 Options.        (line 1416)
* mfix:                                  DEC Alpha Options.  (line  163)
* mfix-24k:                              MIPS Options.       (line  647)
* mfix-and-continue:                     Darwin Options.     (line  104)
* mfix-at697f:                           SPARC Options.      (line  294)
* mfix-cmse-cve-2021-35465:              ARM Options.        (line  967)
* mfix-cortex-a53-835769:                AArch64 Options.    (line   90)
* mfix-cortex-a53-843419:                AArch64 Options.    (line   97)
* mfix-cortex-m3-ldrd:                   ARM Options.        (line  894)
* mfix-gr712rc:                          SPARC Options.      (line  307)
* mfix-r10000:                           MIPS Options.       (line  669)
* mfix-r4000:                            MIPS Options.       (line  653)
* mfix-r4400:                            MIPS Options.       (line  663)
* mfix-r5900:                            MIPS Options.       (line  680)
* mfix-rm7000:                           MIPS Options.       (line  690)
* mfix-sb1:                              MIPS Options.       (line  715)
* mfix-ut699:                            SPARC Options.      (line  299)
* mfix-ut700:                            SPARC Options.      (line  303)
* mfix-vr4120:                           MIPS Options.       (line  695)
* mfix-vr4130:                           MIPS Options.       (line  708)
* mfixed-cc:                             FRV Options.        (line   35)
* mfixed-range:                          HPPA Options.       (line   59)
* mfixed-range <1>:                      IA-64 Options.      (line  105)
* mfixed-range <2>:                      SH Options.         (line  327)
* mflat:                                 SPARC Options.      (line   22)
* mflip-mips16:                          MIPS Options.       (line  128)
* mflip-thumb:                           ARM Options.        (line  836)
* mfloat-abi:                            ARM Options.        (line   41)
* mfloat-abi <1>:                        C-SKY Options.      (line   35)
* mfloat-ieee:                           DEC Alpha Options.  (line  171)
* mfloat-vax:                            DEC Alpha Options.  (line  171)
* mfloat128:                             RS/6000 and PowerPC Options.
                                                             (line  215)
* mfloat128-hardware:                    RS/6000 and PowerPC Options.
                                                             (line  236)
* mflush-func:                           MIPS Options.       (line  782)
* mflush-func=NAME:                      M32R/D Options.     (line   93)
* mflush-trap=NUMBER:                    M32R/D Options.     (line   86)
* mfma:                                  x86 Options.        (line  857)
* mfma4:                                 x86 Options.        (line  860)
* mfmaf:                                 SPARC Options.      (line  267)
* mfmovd:                                SH Options.         (line  148)
* mforce-indirect-call:                  x86 Options.        (line 1136)
* mforce-no-pic:                         Xtensa Options.     (line   41)
* mfp-exceptions:                        MIPS Options.       (line  830)
* mfp-mode:                              Adapteva Epiphany Options.
                                                             (line   71)
* mfp-reg:                               DEC Alpha Options.  (line   25)
* mfp-ret-in-387:                        x86 Options.        (line  610)
* mfp-rounding-mode:                     DEC Alpha Options.  (line   85)
* mfp-trap-mode:                         DEC Alpha Options.  (line   63)
* mfp16-format:                          ARM Options.        (line  730)
* mfp32:                                 MIPS Options.       (line  258)
* mfp64:                                 MIPS Options.       (line  261)
* mfpmath:                               Optimize Options.   (line 2316)
* mfpmath <1>:                           x86 Options.        (line  528)
* mfpr-32:                               FRV Options.        (line   15)
* mfpr-64:                               FRV Options.        (line   19)
* mfprnd:                                RS/6000 and PowerPC Options.
                                                             (line   25)
* mfpu:                                  ARC Options.        (line  231)
* mfpu <1>:                              ARM Options.        (line  702)
* mfpu <2>:                              LoongArch Options.  (line   54)
* mfpu <3>:                              PDP-11 Options.     (line    9)
* mfpu <4>:                              SPARC Options.      (line   34)
* mfpu <5>:                              Visium Options.     (line   19)
* mfpu=:                                 C-SKY Options.      (line   69)
* mfpxx:                                 MIPS Options.       (line  264)
* mfract-convert-truncate:               AVR Options.        (line  284)
* mframe-header-opt:                     MIPS Options.       (line  891)
* mfriz:                                 RS/6000 and PowerPC Options.
                                                             (line  870)
* mfsca:                                 SH Options.         (line  365)
* mfsgsbase:                             x86 Options.        (line  853)
* mfsmuld:                               SPARC Options.      (line  274)
* mfsrra:                                SH Options.         (line  374)
* mft32b:                                FT32 Options.       (line   23)
* mfull-regs:                            NDS32 Options.      (line   18)
* mfull-toc:                             RS/6000 and PowerPC Options.
                                                             (line  256)
* mfunction-return:                      x86 Options.        (line 1490)
* mfused-madd:                           IA-64 Options.      (line   88)
* mfused-madd <1>:                       MIPS Options.       (line  630)
* mfused-madd <2>:                       RS/6000 and PowerPC Options.
                                                             (line  369)
* mfused-madd <3>:                       S/390 and zSeries Options.
                                                             (line  183)
* mfused-madd <4>:                       SH Options.         (line  356)
* mfused-madd <5>:                       Xtensa Options.     (line   19)
* mfxsr:                                 x86 Options.        (line  876)
* MG:                                    Preprocessor Options.
                                                             (line  122)
* mg:                                    VAX Options.        (line   17)
* mg10:                                  RL78 Options.       (line   62)
* mg13:                                  RL78 Options.       (line   62)
* mg14:                                  RL78 Options.       (line   62)
* mgas:                                  HPPA Options.       (line   75)
* mgas-isr-prologues:                    AVR Options.        (line  202)
* mgcc-abi:                              V850 Options.       (line  148)
* mgeneral-regs-only:                    AArch64 Options.    (line   24)
* mgeneral-regs-only <1>:                ARM Options.        (line   57)
* mgeneral-regs-only <2>:                x86 Options.        (line 1460)
* mgfni:                                 x86 Options.        (line  890)
* mghs:                                  V850 Options.       (line  127)
* mginv:                                 MIPS Options.       (line  421)
* mglibc:                                GNU/Linux Options.  (line    9)
* mgnu:                                  VAX Options.        (line   13)
* mgnu-as:                               IA-64 Options.      (line   18)
* mgnu-asm:                              PDP-11 Options.     (line   49)
* mgnu-attribute:                        RS/6000 and PowerPC Options.
                                                             (line  587)
* mgnu-ld:                               HPPA Options.       (line  111)
* mgnu-ld <1>:                           IA-64 Options.      (line   23)
* mgomp:                                 Nvidia PTX Options. (line   76)
* mgp32:                                 MIPS Options.       (line  252)
* mgp64:                                 MIPS Options.       (line  255)
* mgpopt:                                MIPS Options.       (line  502)
* mgpopt <1>:                            Nios II Options.    (line   16)
* mgpr-32:                               FRV Options.        (line    7)
* mgpr-64:                               FRV Options.        (line   11)
* mgprel-ro:                             FRV Options.        (line   99)
* mgprel-sec:                            Nios II Options.    (line   65)
* mh:                                    H8/300 Options.     (line   14)
* mhal:                                  Nios II Options.    (line  332)
* mhalf-reg-file:                        Adapteva Epiphany Options.
                                                             (line    9)
* mhard-dfp:                             RS/6000 and PowerPC Options.
                                                             (line   25)
* mhard-dfp <1>:                         S/390 and zSeries Options.
                                                             (line   20)
* mhard-div:                             OpenRISC Options.   (line   19)
* mhard-float:                           C-SKY Options.      (line   51)
* mhard-float <1>:                       FRV Options.        (line   23)
* mhard-float <2>:                       M680x0 Options.     (line  195)
* mhard-float <3>:                       MicroBlaze Options. (line   10)
* mhard-float <4>:                       MIPS Options.       (line  267)
* mhard-float <5>:                       OpenRISC Options.   (line   29)
* mhard-float <6>:                       RS/6000 and PowerPC Options.
                                                             (line  333)
* mhard-float <7>:                       S/390 and zSeries Options.
                                                             (line   11)
* mhard-float <8>:                       SPARC Options.      (line   34)
* mhard-float <9>:                       V850 Options.       (line  113)
* mhard-float <10>:                      Visium Options.     (line   19)
* mhard-float <11>:                      x86 Options.        (line  593)
* mhard-mul:                             OpenRISC Options.   (line   24)
* mhard-quad-float:                      SPARC Options.      (line   55)
* mharden-sls:                           AArch64 Options.    (line  301)
* mharden-sls <1>:                       x86 Options.        (line 1512)
* mhardlit:                              MCore Options.      (line   10)
* mhigh-registers:                       C-SKY Options.      (line  120)
* mhle:                                  x86 Options.        (line  882)
* mhotpatch:                             S/390 and zSeries Options.
                                                             (line  218)
* mhp-ld:                                HPPA Options.       (line  123)
* mhreset:                               x86 Options.        (line  911)
* mhtm:                                  RS/6000 and PowerPC Options.
                                                             (line  184)
* mhtm <1>:                              S/390 and zSeries Options.
                                                             (line  104)
* mhw-div:                               Nios II Options.    (line  124)
* mhw-mul:                               Nios II Options.    (line  124)
* mhw-mulx:                              Nios II Options.    (line  124)
* mhwmult=:                              MSP430 Options.     (line   93)
* miamcu:                                x86 Options.        (line 1532)
* micplb:                                Blackfin Options.   (line  175)
* mid-shared-library:                    Blackfin Options.   (line   78)
* mid-shared-library <1>:                Blackfin Options.   (line   85)
* mieee:                                 DEC Alpha Options.  (line   39)
* mieee <1>:                             SH Options.         (line  165)
* mieee-conformant:                      DEC Alpha Options.  (line  134)
* mieee-fp:                              x86 Options.        (line  587)
* mieee-with-inexact:                    DEC Alpha Options.  (line   52)
* milp32:                                IA-64 Options.      (line  121)
* mimadd:                                MIPS Options.       (line  623)
* mimpure-text:                          Solaris 2 Options.  (line   15)
* mincoming-stack-boundary:              x86 Options.        (line  803)
* mindexed-loads:                        ARC Options.        (line  481)
* mindirect-branch:                      x86 Options.        (line 1471)
* mindirect-branch-cs-prefix:            x86 Options.        (line 1519)
* mindirect-branch-register:             x86 Options.        (line 1509)
* minline-all-stringops:                 x86 Options.        (line 1312)
* minline-float-divide-max-throughput:   IA-64 Options.      (line   58)
* minline-float-divide-min-latency:      IA-64 Options.      (line   54)
* minline-ic_invalidate:                 SH Options.         (line  174)
* minline-int-divide:                    IA-64 Options.      (line   73)
* minline-int-divide-max-throughput:     IA-64 Options.      (line   69)
* minline-int-divide-min-latency:        IA-64 Options.      (line   65)
* minline-plt:                           Blackfin Options.   (line  135)
* minline-plt <1>:                       FRV Options.        (line   81)
* minline-sqrt-max-throughput:           IA-64 Options.      (line   80)
* minline-sqrt-min-latency:              IA-64 Options.      (line   76)
* minline-stringops-dynamically:         x86 Options.        (line 1320)
* minrt:                                 MSP430 Options.     (line  115)
* minrt <1>:                             PRU Options.        (line    9)
* minsert-sched-nops:                    RS/6000 and PowerPC Options.
                                                             (line  485)
* minstrument-return:                    x86 Options.        (line 1400)
* mint-register:                         RX Options.         (line  100)
* mint16:                                PDP-11 Options.     (line   33)
* mint32:                                CR16 Options.       (line   22)
* mint32 <1>:                            H8/300 Options.     (line   38)
* mint32 <2>:                            PDP-11 Options.     (line   37)
* mint8:                                 AVR Options.        (line  211)
* minterlink-compressed:                 MIPS Options.       (line  135)
* minterlink-mips16:                     MIPS Options.       (line  147)
* mio-volatile:                          MeP Options.        (line   74)
* mips1:                                 MIPS Options.       (line   80)
* mips16:                                MIPS Options.       (line  120)
* mips2:                                 MIPS Options.       (line   83)
* mips3:                                 MIPS Options.       (line   86)
* mips32:                                MIPS Options.       (line   92)
* mips32r3:                              MIPS Options.       (line   95)
* mips32r5:                              MIPS Options.       (line   98)
* mips32r6:                              MIPS Options.       (line  101)
* mips3d:                                MIPS Options.       (line  382)
* mips4:                                 MIPS Options.       (line   89)
* mips64:                                MIPS Options.       (line  104)
* mips64r2:                              MIPS Options.       (line  107)
* mips64r3:                              MIPS Options.       (line  110)
* mips64r5:                              MIPS Options.       (line  113)
* mips64r6:                              MIPS Options.       (line  116)
* mirq-ctrl-saved:                       ARC Options.        (line  296)
* misa:                                  Nvidia PTX Options. (line   22)
* misa-spec:                             RISC-V Options.     (line   54)
* misel:                                 RS/6000 and PowerPC Options.
                                                             (line  167)
* misize:                                ARC Options.        (line  379)
* misize <1>:                            SH Options.         (line  186)
* misr-vector-size:                      NDS32 Options.      (line   57)
* missue-rate=NUMBER:                    M32R/D Options.     (line   79)
* mistack:                               C-SKY Options.      (line   81)
* mivc2:                                 MeP Options.        (line   59)
* mjli-always:                           ARC Options.        (line   14)
* mjmp32:                                eBPF Options.       (line   32)
* mjmpext:                               eBPF Options.       (line   28)
* mjsr:                                  RX Options.         (line  169)
* mjump-in-delay:                        HPPA Options.       (line   30)
* mkernel:                               Darwin Options.     (line   82)
* mkernel <1>:                           eBPF Options.       (line   13)
* mkl:                                   x86 Options.        (line  912)
* mknuthdiv:                             MMIX Options.       (line   32)
* ml:                                    MeP Options.        (line   78)
* ml <1>:                                SH Options.         (line  129)
* mlarge:                                MSP430 Options.     (line   82)
* mlarge-data:                           DEC Alpha Options.  (line  187)
* mlarge-data-threshold:                 x86 Options.        (line  692)
* mlarge-text:                           DEC Alpha Options.  (line  205)
* mleadz:                                MeP Options.        (line   81)
* mleaf-id-shared-library:               Blackfin Options.   (line   89)
* mleaf-id-shared-library <1>:           Blackfin Options.   (line   95)
* mlibfuncs:                             MMIX Options.       (line   10)
* mlibrary-pic:                          FRV Options.        (line  135)
* mlinked-fp:                            FRV Options.        (line  116)
* mlinker-opt:                           HPPA Options.       (line   85)
* mlittle:                               RS/6000 and PowerPC Options.
                                                             (line  434)
* mlittle-endian:                        AArch64 Options.    (line   30)
* mlittle-endian <1>:                    ARC Options.        (line  594)
* mlittle-endian <2>:                    ARM Options.        (line   63)
* mlittle-endian <3>:                    C6X Options.        (line   16)
* mlittle-endian <4>:                    C-SKY Options.      (line   30)
* mlittle-endian <5>:                    eBPF Options.       (line   25)
* mlittle-endian <6>:                    IA-64 Options.      (line   13)
* mlittle-endian <7>:                    MCore Options.      (line   39)
* mlittle-endian <8>:                    MicroBlaze Options. (line   59)
* mlittle-endian <9>:                    NDS32 Options.      (line   12)
* mlittle-endian <10>:                   RISC-V Options.     (line  178)
* mlittle-endian <11>:                   RS/6000 and PowerPC Options.
                                                             (line  434)
* mlittle-endian <12>:                   TILE-Gx Options.    (line   29)
* mlittle-endian-data:                   RX Options.         (line   42)
* mliw:                                  MN10300 Options.    (line   54)
* mll64:                                 ARC Options.        (line  167)
* mllsc:                                 MIPS Options.       (line  339)
* mload-store-pairs:                     MIPS Options.       (line  590)
* mlocal-sdata:                          MIPS Options.       (line  468)
* mlock:                                 ARC Options.        (line  345)
* mlong-calls:                           Adapteva Epiphany Options.
                                                             (line   55)
* mlong-calls <1>:                       ARC Options.        (line  402)
* mlong-calls <2>:                       ARM Options.        (line  757)
* mlong-calls <3>:                       Blackfin Options.   (line  118)
* mlong-calls <4>:                       FRV Options.        (line  122)
* mlong-calls <5>:                       HPPA Options.       (line  136)
* mlong-calls <6>:                       MIPS Options.       (line  609)
* mlong-calls <7>:                       V850 Options.       (line   10)
* mlong-double:                          AVR Options.        (line  194)
* mlong-double-128:                      S/390 and zSeries Options.
                                                             (line   29)
* mlong-double-128 <1>:                  x86 Options.        (line  671)
* mlong-double-64:                       S/390 and zSeries Options.
                                                             (line   29)
* mlong-double-64 <1>:                   x86 Options.        (line  671)
* mlong-double-80:                       x86 Options.        (line  671)
* mlong-jump-table-offsets:              M680x0 Options.     (line  340)
* mlong-jumps:                           V850 Options.       (line  108)
* mlong-load-store:                      HPPA Options.       (line   66)
* mlong32:                               MIPS Options.       (line  443)
* mlong64:                               MIPS Options.       (line  438)
* mlongcall:                             RS/6000 and PowerPC Options.
                                                             (line  728)
* mlongcalls:                            Xtensa Options.     (line   87)
* mloongson-ext:                         MIPS Options.       (line  430)
* mloongson-ext2:                        MIPS Options.       (line  434)
* mloongson-mmi:                         MIPS Options.       (line  425)
* mloop:                                 PRU Options.        (line   25)
* mloop <1>:                             V850 Options.       (line  121)
* mlow-precision-div:                    AArch64 Options.    (line  120)
* mlow-precision-recip-sqrt:             AArch64 Options.    (line  103)
* mlow-precision-sqrt:                   AArch64 Options.    (line  111)
* mlow64k:                               Blackfin Options.   (line   67)
* mlp64:                                 IA-64 Options.      (line  121)
* mlpc-width:                            ARC Options.        (line  313)
* mlra:                                  ARC Options.        (line  486)
* mlra <1>:                              FT32 Options.       (line   16)
* mlra <2>:                              PDP-11 Options.     (line   52)
* mlra <3>:                              SPARC Options.      (line  111)
* mlra <4>:                              VAX Options.        (line   22)
* mlra-priority-compact:                 ARC Options.        (line  494)
* mlra-priority-noncompact:              ARC Options.        (line  497)
* mlra-priority-none:                    ARC Options.        (line  491)
* mlwp:                                  x86 Options.        (line  867)
* mlxc1-sxc1:                            MIPS Options.       (line  901)
* mlzcnt:                                x86 Options.        (line  875)
* MM:                                    Preprocessor Options.
                                                             (line  102)
* mm:                                    MeP Options.        (line   84)
* mmac:                                  CR16 Options.       (line    9)
* mmac <1>:                              Score Options.      (line   21)
* mmac_24:                               ARC Options.        (line  616)
* mmac_d16:                              ARC Options.        (line  619)
* mmac-24:                               ARC Options.        (line  354)
* mmac-d16:                              ARC Options.        (line  350)
* mmad:                                  MIPS Options.       (line  618)
* mmadd4:                                MIPS Options.       (line  906)
* mmain-is-OS_task:                      AVR Options.        (line  217)
* mmainkernel:                           Nvidia PTX Options. (line   41)
* mmalloc64:                             VMS Options.        (line   17)
* mmanual-endbr:                         x86 Options.        (line 1141)
* mmax:                                  DEC Alpha Options.  (line  163)
* mmax-constant-size:                    RX Options.         (line   82)
* mmax-inline-shift=:                    MSP430 Options.     (line  134)
* mmax-stack-frame:                      CRIS Options.       (line   21)
* mmcount-ra-address:                    MIPS Options.       (line  878)
* mmcu:                                  AVR Options.        (line    9)
* mmcu <1>:                              MIPS Options.       (line  399)
* mmcu <2>:                              PRU Options.        (line   17)
* mmcu=:                                 MSP430 Options.     (line   14)
* MMD:                                   Preprocessor Options.
                                                             (line  188)
* mmedia:                                FRV Options.        (line   56)
* mmedium-calls:                         ARC Options.        (line  406)
* mmemcpy:                               MicroBlaze Options. (line   13)
* mmemcpy <1>:                           MIPS Options.       (line  603)
* mmemcpy-strategy=STRATEGY:             x86 Options.        (line 1342)
* mmemory-latency:                       DEC Alpha Options.  (line  268)
* mmemory-model:                         SPARC Options.      (line  348)
* mmemset-strategy=STRATEGY:             x86 Options.        (line 1354)
* mmfcrf:                                RS/6000 and PowerPC Options.
                                                             (line   25)
* mmicromips:                            MIPS Options.       (line  387)
* mmillicode:                            ARC Options.        (line  500)
* mminimal-toc:                          RS/6000 and PowerPC Options.
                                                             (line  256)
* mminmax:                               MeP Options.        (line   87)
* mmixed-code:                           ARC Options.        (line  514)
* mmma:                                  RS/6000 and PowerPC Options.
                                                             (line  944)
* mmmx:                                  x86 Options.        (line  828)
* mmodel=large:                          M32R/D Options.     (line   33)
* mmodel=medium:                         M32R/D Options.     (line   27)
* mmodel=small:                          M32R/D Options.     (line   18)
* mmovbe:                                x86 Options.        (line 1035)
* mmovdir64b:                            x86 Options.        (line  896)
* mmovdiri:                              x86 Options.        (line  895)
* mmove-max:                             x86 Options.        (line  993)
* mmp:                                   C-SKY Options.      (line   87)
* mmpy:                                  ARC Options.        (line  117)
* mmpy-option:                           ARC Options.        (line  173)
* mms-bitfields:                         x86 Options.        (line 1187)
* mmt:                                   MIPS Options.       (line  395)
* mmul:                                  RL78 Options.       (line   15)
* mmul-bug-workaround:                   CRIS Options.       (line   30)
* mmul.x:                                Moxie Options.      (line   14)
* mmul32x16:                             ARC Options.        (line  121)
* mmul64:                                ARC Options.        (line  124)
* mmuladd:                               FRV Options.        (line   64)
* mmulhw:                                RS/6000 and PowerPC Options.
                                                             (line  378)
* mmult:                                 MeP Options.        (line   90)
* mmult-bug:                             MN10300 Options.    (line    9)
* mmultcost:                             ARC Options.        (line  574)
* mmulti-cond-exec:                      FRV Options.        (line  215)
* mmulticore:                            Blackfin Options.   (line  139)
* mmultiple:                             RS/6000 and PowerPC Options.
                                                             (line  339)
* mmultiple-stld:                        C-SKY Options.      (line  137)
* mmusl:                                 GNU/Linux Options.  (line   18)
* mmvcle:                                S/390 and zSeries Options.
                                                             (line  138)
* mmvme:                                 RS/6000 and PowerPC Options.
                                                             (line  609)
* mmwait:                                x86 Options.        (line 1049)
* mmwaitx:                               x86 Options.        (line  884)
* mn:                                    H8/300 Options.     (line   20)
* mn-flash:                              AVR Options.        (line  222)
* mnan=2008:                             MIPS Options.       (line  320)
* mnan=legacy:                           MIPS Options.       (line  320)
* mneeded:                               x86 Options.        (line 1593)
* mneon-for-64bits:                      ARM Options.        (line  923)
* mnested-cond-exec:                     FRV Options.        (line  230)
* mnewlib:                               OpenRISC Options.   (line   13)
* mnhwloop:                              Score Options.      (line   15)
* mno-16-bit:                            NDS32 Options.      (line   54)
* mno-4byte-functions:                   MCore Options.      (line   27)
* mno-8byte-align:                       V850 Options.       (line  170)
* mno-abicalls:                          MIPS Options.       (line  192)
* mno-ac0:                               PDP-11 Options.     (line   20)
* mno-align-double:                      x86 Options.        (line  630)
* mno-align-int:                         M680x0 Options.     (line  262)
* mno-align-loops:                       M32R/D Options.     (line   76)
* mno-align-stringops:                   x86 Options.        (line 1307)
* mno-allow-string-insns:                RX Options.         (line  150)
* mno-altivec:                           RS/6000 and PowerPC Options.
                                                             (line  137)
* mno-am33:                              MN10300 Options.    (line   20)
* mno-app-regs:                          SPARC Options.      (line   10)
* mno-app-regs <1>:                      V850 Options.       (line  185)
* mno-as100-syntax:                      RX Options.         (line   76)
* mno-auto-litpools:                     Xtensa Options.     (line   60)
* mno-avoid-indexed-addresses:           RS/6000 and PowerPC Options.
                                                             (line  360)
* mno-backchain:                         S/390 and zSeries Options.
                                                             (line   35)
* mno-base-addresses:                    MMIX Options.       (line   53)
* mno-bit-align:                         RS/6000 and PowerPC Options.
                                                             (line  392)
* mno-bitfield:                          M680x0 Options.     (line  228)
* mno-branch-likely:                     MIPS Options.       (line  798)
* mno-branch-predict:                    MMIX Options.       (line   48)
* mno-brcc:                              ARC Options.        (line  442)
* mno-bwx:                               DEC Alpha Options.  (line  163)
* mno-bypass-cache:                      Nios II Options.    (line  103)
* mno-cache-volatile:                    Nios II Options.    (line  109)
* mno-call-ms2sysv-xlogues:              x86 Options.        (line 1147)
* mno-callgraph-data:                    MCore Options.      (line   31)
* mno-cbcond:                            SPARC Options.      (line  260)
* mno-check-zero-division:               MIPS Options.       (line  570)
* mno-cix:                               DEC Alpha Options.  (line  163)
* mno-clearbss:                          MicroBlaze Options. (line   16)
* mno-cmov:                              NDS32 Options.      (line   24)
* mno-cmpb:                              RS/6000 and PowerPC Options.
                                                             (line   25)
* mno-co-re:                             eBPF Options.       (line   60)
* mno-cond-exec:                         ARC Options.        (line  456)
* mno-cond-exec <1>:                     FRV Options.        (line  194)
* mno-cond-move:                         FRV Options.        (line  166)
* mno-const-align:                       CRIS Options.       (line   53)
* mno-const16:                           Xtensa Options.     (line   10)
* mno-crc:                               MIPS Options.       (line  416)
* mno-crt0:                              MN10300 Options.    (line   43)
* mno-crt0 <1>:                          Moxie Options.      (line   18)
* mno-crypto:                            RS/6000 and PowerPC Options.
                                                             (line  178)
* mno-csync-anomaly:                     Blackfin Options.   (line   63)
* mno-custom-INSN:                       Nios II Options.    (line  139)
* mno-data-align:                        CRIS Options.       (line   53)
* mno-debug:                             S/390 and zSeries Options.
                                                             (line  144)
* mno-default:                           x86 Options.        (line  961)
* mno-direct-extern-access:              x86 Options.        (line 1598)
* mno-direct-extern-access <1>:          x86 Function Attributes.
                                                             (line  712)
* mno-disable-callt:                     V850 Options.       (line   92)
* mno-div:                               M680x0 Options.     (line  207)
* mno-div <1>:                           MCore Options.      (line   15)
* mno-dlmzb:                             RS/6000 and PowerPC Options.
                                                             (line  385)
* mno-double:                            FRV Options.        (line   52)
* mno-dpfp-lrsr:                         ARC Options.        (line  108)
* mno-dsp:                               MIPS Options.       (line  353)
* mno-dspr2:                             MIPS Options.       (line  359)
* mno-dwarf2-asm:                        IA-64 Options.      (line   94)
* mno-dword:                             FRV Options.        (line   44)
* mno-eabi:                              RS/6000 and PowerPC Options.
                                                             (line  633)
* mno-early-stop-bits:                   IA-64 Options.      (line  100)
* mno-eflags:                            FRV Options.        (line  155)
* mno-embedded-data:                     MIPS Options.       (line  517)
* mno-ep:                                V850 Options.       (line   16)
* mno-epsilon:                           MMIX Options.       (line   15)
* mno-eva:                               MIPS Options.       (line  403)
* mno-explicit-relocs:                   DEC Alpha Options.  (line  176)
* mno-explicit-relocs <1>:               MIPS Options.       (line  561)
* mno-exr:                               H8/300 Options.     (line   33)
* mno-ext-perf:                          NDS32 Options.      (line   30)
* mno-ext-perf2:                         NDS32 Options.      (line   36)
* mno-ext-string:                        NDS32 Options.      (line   42)
* mno-extern-sdata:                      MIPS Options.       (line  480)
* mno-fancy-math-387:                    x86 Options.        (line  620)
* mno-fast-sw-div:                       Nios II Options.    (line  115)
* mno-faster-structs:                    SPARC Options.      (line   91)
* mno-fdpic:                             ARM Options.        (line  984)
* mno-fix:                               DEC Alpha Options.  (line  163)
* mno-fix-24k:                           MIPS Options.       (line  647)
* mno-fix-cortex-a53-835769:             AArch64 Options.    (line   90)
* mno-fix-cortex-a53-843419:             AArch64 Options.    (line   97)
* mno-fix-r10000:                        MIPS Options.       (line  669)
* mno-fix-r4000:                         MIPS Options.       (line  653)
* mno-fix-r4400:                         MIPS Options.       (line  663)
* mno-flat:                              SPARC Options.      (line   22)
* mno-float:                             MIPS Options.       (line  274)
* mno-float128:                          RS/6000 and PowerPC Options.
                                                             (line  215)
* mno-float128-hardware:                 RS/6000 and PowerPC Options.
                                                             (line  236)
* mno-flush-func:                        M32R/D Options.     (line   98)
* mno-flush-trap:                        M32R/D Options.     (line   90)
* mno-fmaf:                              SPARC Options.      (line  267)
* mno-fp-in-toc:                         RS/6000 and PowerPC Options.
                                                             (line  256)
* mno-fp-regs:                           DEC Alpha Options.  (line   25)
* mno-fp-ret-in-387:                     x86 Options.        (line  610)
* mno-fprnd:                             RS/6000 and PowerPC Options.
                                                             (line   25)
* mno-fpu:                               SPARC Options.      (line   39)
* mno-fpu <1>:                           Visium Options.     (line   24)
* mno-fsca:                              SH Options.         (line  365)
* mno-fsmuld:                            SPARC Options.      (line  274)
* mno-fsrra:                             SH Options.         (line  374)
* mno-fused-madd:                        IA-64 Options.      (line   88)
* mno-fused-madd <1>:                    MIPS Options.       (line  630)
* mno-fused-madd <2>:                    RS/6000 and PowerPC Options.
                                                             (line  369)
* mno-fused-madd <3>:                    S/390 and zSeries Options.
                                                             (line  183)
* mno-fused-madd <4>:                    SH Options.         (line  356)
* mno-fused-madd <5>:                    Xtensa Options.     (line   19)
* mno-ginv:                              MIPS Options.       (line  421)
* mno-gnu-as:                            IA-64 Options.      (line   18)
* mno-gnu-attribute:                     RS/6000 and PowerPC Options.
                                                             (line  587)
* mno-gnu-ld:                            IA-64 Options.      (line   23)
* mno-gpopt:                             MIPS Options.       (line  502)
* mno-gpopt <1>:                         Nios II Options.    (line   16)
* mno-hard-dfp:                          RS/6000 and PowerPC Options.
                                                             (line   25)
* mno-hard-dfp <1>:                      S/390 and zSeries Options.
                                                             (line   20)
* mno-hardlit:                           MCore Options.      (line   10)
* mno-htm:                               RS/6000 and PowerPC Options.
                                                             (line  184)
* mno-htm <1>:                           S/390 and zSeries Options.
                                                             (line  104)
* mno-hw-div:                            Nios II Options.    (line  124)
* mno-hw-mul:                            Nios II Options.    (line  124)
* mno-hw-mulx:                           Nios II Options.    (line  124)
* mno-id-shared-library:                 Blackfin Options.   (line   85)
* mno-ieee:                              SH Options.         (line  165)
* mno-ieee-fp:                           x86 Options.        (line  587)
* mno-imadd:                             MIPS Options.       (line  623)
* mno-inline-float-divide:               IA-64 Options.      (line   62)
* mno-inline-int-divide:                 IA-64 Options.      (line   73)
* mno-inline-sqrt:                       IA-64 Options.      (line   84)
* mno-int16:                             PDP-11 Options.     (line   37)
* mno-int32:                             PDP-11 Options.     (line   33)
* mno-interlink-compressed:              MIPS Options.       (line  135)
* mno-interlink-mips16:                  MIPS Options.       (line  147)
* mno-interrupts:                        AVR Options.        (line  225)
* mno-isel:                              RS/6000 and PowerPC Options.
                                                             (line  167)
* mno-jsr:                               RX Options.         (line  169)
* mno-knuthdiv:                          MMIX Options.       (line   32)
* mno-leaf-id-shared-library:            Blackfin Options.   (line   95)
* mno-libfuncs:                          MMIX Options.       (line   10)
* mno-liw:                               MN10300 Options.    (line   59)
* mno-llsc:                              MIPS Options.       (line  339)
* mno-load-store-pairs:                  MIPS Options.       (line  590)
* mno-local-sdata:                       MIPS Options.       (line  468)
* mno-long-calls:                        ARM Options.        (line  757)
* mno-long-calls <1>:                    Blackfin Options.   (line  118)
* mno-long-calls <2>:                    HPPA Options.       (line  136)
* mno-long-calls <3>:                    MIPS Options.       (line  609)
* mno-long-calls <4>:                    V850 Options.       (line   10)
* mno-long-jumps:                        V850 Options.       (line  108)
* mno-longcall:                          RS/6000 and PowerPC Options.
                                                             (line  728)
* mno-longcalls:                         Xtensa Options.     (line   87)
* mno-loongson-ext:                      MIPS Options.       (line  430)
* mno-loongson-ext2:                     MIPS Options.       (line  434)
* mno-loongson-mmi:                      MIPS Options.       (line  425)
* mno-low-precision-div:                 AArch64 Options.    (line  120)
* mno-low-precision-recip-sqrt:          AArch64 Options.    (line  103)
* mno-low-precision-sqrt:                AArch64 Options.    (line  111)
* mno-low64k:                            Blackfin Options.   (line   71)
* mno-lra:                               SPARC Options.      (line  111)
* mno-lra <1>:                           VAX Options.        (line   22)
* mno-lsim:                              FR30 Options.       (line   14)
* mno-lsim <1>:                          MCore Options.      (line   46)
* mno-mad:                               MIPS Options.       (line  618)
* mno-max:                               DEC Alpha Options.  (line  163)
* mno-mcount-ra-address:                 MIPS Options.       (line  878)
* mno-mcu:                               MIPS Options.       (line  399)
* mno-mdmx:                              MIPS Options.       (line  376)
* mno-media:                             FRV Options.        (line   60)
* mno-memcpy:                            MIPS Options.       (line  603)
* mno-mfcrf:                             RS/6000 and PowerPC Options.
                                                             (line   25)
* mno-mips16:                            MIPS Options.       (line  120)
* mno-mips3d:                            MIPS Options.       (line  382)
* mno-mma:                               RS/6000 and PowerPC Options.
                                                             (line  944)
* mno-mmicromips:                        MIPS Options.       (line  387)
* Mno-modules:                           Preprocessor Options.
                                                             (line  132)
* mno-mpy:                               ARC Options.        (line  117)
* mno-ms-bitfields:                      x86 Options.        (line 1187)
* mno-mt:                                MIPS Options.       (line  395)
* mno-mul-bug-workaround:                CRIS Options.       (line   30)
* mno-muladd:                            FRV Options.        (line   68)
* mno-mulhw:                             RS/6000 and PowerPC Options.
                                                             (line  378)
* mno-mult-bug:                          MN10300 Options.    (line   13)
* mno-multi-cond-exec:                   FRV Options.        (line  223)
* mno-multiple:                          RS/6000 and PowerPC Options.
                                                             (line  339)
* mno-mvcle:                             S/390 and zSeries Options.
                                                             (line  138)
* mno-nested-cond-exec:                  FRV Options.        (line  237)
* mno-odd-spreg:                         MIPS Options.       (line  293)
* mno-omit-leaf-frame-pointer:           AArch64 Options.    (line   58)
* mno-optimize-membar:                   FRV Options.        (line  249)
* mno-opts:                              MeP Options.        (line   93)
* mno-pack:                              FRV Options.        (line  151)
* mno-packed-stack:                      S/390 and zSeries Options.
                                                             (line   54)
* mno-paired-single:                     MIPS Options.       (line  370)
* mno-pc-relative-literal-loads:         AArch64 Options.    (line  274)
* mno-pcrel:                             RS/6000 and PowerPC Options.
                                                             (line  932)
* mno-pic:                               IA-64 Options.      (line   26)
* mno-pid:                               RX Options.         (line  117)
* mno-plt:                               MIPS Options.       (line  219)
* mno-pltseq:                            RS/6000 and PowerPC Options.
                                                             (line  765)
* mno-popc:                              SPARC Options.      (line  281)
* mno-popcntb:                           RS/6000 and PowerPC Options.
                                                             (line   25)
* mno-popcntd:                           RS/6000 and PowerPC Options.
                                                             (line   25)
* mno-postinc:                           Adapteva Epiphany Options.
                                                             (line  109)
* mno-postmodify:                        Adapteva Epiphany Options.
                                                             (line  109)
* mno-power8-fusion:                     RS/6000 and PowerPC Options.
                                                             (line  190)
* mno-power8-vector:                     RS/6000 and PowerPC Options.
                                                             (line  196)
* mno-powerpc-gfxopt:                    RS/6000 and PowerPC Options.
                                                             (line   25)
* mno-powerpc-gpopt:                     RS/6000 and PowerPC Options.
                                                             (line   25)
* mno-powerpc64:                         RS/6000 and PowerPC Options.
                                                             (line   25)
* mno-prefixed:                          RS/6000 and PowerPC Options.
                                                             (line  938)
* mno-privileged:                        RS/6000 and PowerPC Options.
                                                             (line  955)
* mno-prolog-function:                   V850 Options.       (line   23)
* mno-prologue-epilogue:                 CRIS Options.       (line   69)
* mno-prototype:                         RS/6000 and PowerPC Options.
                                                             (line  593)
* mno-push-args:                         x86 Options.        (line 1164)
* mno-quad-memory:                       RS/6000 and PowerPC Options.
                                                             (line  203)
* mno-quad-memory-atomic:                RS/6000 and PowerPC Options.
                                                             (line  209)
* mno-readonly-in-sdata:                 RS/6000 and PowerPC Options.
                                                             (line  684)
* mno-red-zone:                          x86 Options.        (line 1552)
* mno-register-names:                    IA-64 Options.      (line   37)
* mno-regnames:                          RS/6000 and PowerPC Options.
                                                             (line  722)
* mno-relax:                             PRU Options.        (line   21)
* mno-relax <1>:                         V850 Options.       (line  103)
* mno-relax-immediate:                   MCore Options.      (line   19)
* mno-relocatable:                       RS/6000 and PowerPC Options.
                                                             (line  408)
* mno-relocatable-lib:                   RS/6000 and PowerPC Options.
                                                             (line  419)
* mno-renesas:                           SH Options.         (line  155)
* mno-rop-protect:                       RS/6000 and PowerPC Options.
                                                             (line  949)
* mno-round-nearest:                     Adapteva Epiphany Options.
                                                             (line   51)
* mno-save-mduc-in-interrupts:           RL78 Options.       (line   79)
* mno-scc:                               FRV Options.        (line  180)
* mno-sched-ar-data-spec:                IA-64 Options.      (line  135)
* mno-sched-ar-in-data-spec:             IA-64 Options.      (line  157)
* mno-sched-br-data-spec:                IA-64 Options.      (line  128)
* mno-sched-br-in-data-spec:             IA-64 Options.      (line  150)
* mno-sched-control-spec:                IA-64 Options.      (line  142)
* mno-sched-count-spec-in-critical-path: IA-64 Options.      (line  185)
* mno-sched-in-control-spec:             IA-64 Options.      (line  164)
* mno-sched-prefer-non-control-spec-insns: IA-64 Options.    (line  178)
* mno-sched-prefer-non-data-spec-insns:  IA-64 Options.      (line  171)
* mno-sched-prolog:                      ARM Options.        (line   32)
* mno-sdata:                             ARC Options.        (line  420)
* mno-sdata <1>:                         IA-64 Options.      (line   42)
* mno-sdata <2>:                         RS/6000 and PowerPC Options.
                                                             (line  679)
* mno-sep-data:                          Blackfin Options.   (line  113)
* mno-serialize-volatile:                Xtensa Options.     (line   35)
* mno-setlb:                             MN10300 Options.    (line   69)
* mno-short:                             M680x0 Options.     (line  223)
* mno-side-effects:                      CRIS Options.       (line   44)
* mno-sim:                               RX Options.         (line   71)
* mno-single-exit:                       MMIX Options.       (line   65)
* mno-slow-bytes:                        MCore Options.      (line   35)
* mno-small-exec:                        S/390 and zSeries Options.
                                                             (line   79)
* mno-smartmips:                         MIPS Options.       (line  366)
* mno-soft-cmpsf:                        Adapteva Epiphany Options.
                                                             (line   29)
* mno-soft-float:                        DEC Alpha Options.  (line   10)
* mno-space-regs:                        HPPA Options.       (line   45)
* mno-specld-anomaly:                    Blackfin Options.   (line   53)
* mno-split-addresses:                   MIPS Options.       (line  555)
* mno-split-lohi:                        Adapteva Epiphany Options.
                                                             (line  109)
* mno-stack-align:                       CRIS Options.       (line   53)
* mno-stack-bias:                        SPARC Options.      (line  372)
* mno-std-struct-return:                 SPARC Options.      (line  102)
* mno-strict-align:                      AArch64 Options.    (line   52)
* mno-strict-align <1>:                  M680x0 Options.     (line  281)
* mno-strict-align <2>:                  RS/6000 and PowerPC Options.
                                                             (line  403)
* mno-subxc:                             SPARC Options.      (line  288)
* mno-sum-in-toc:                        RS/6000 and PowerPC Options.
                                                             (line  256)
* mno-sym32:                             MIPS Options.       (line  453)
* mno-target-align:                      Xtensa Options.     (line   74)
* mno-text-section-literals:             Xtensa Options.     (line   47)
* mno-tls-markers:                       RS/6000 and PowerPC Options.
                                                             (line  777)
* mno-toc:                               RS/6000 and PowerPC Options.
                                                             (line  428)
* mno-toplevel-symbols:                  MMIX Options.       (line   39)
* mno-tpf-trace:                         S/390 and zSeries Options.
                                                             (line  169)
* mno-tpf-trace-skip:                    S/390 and zSeries Options.
                                                             (line  175)
* mno-unaligned-access:                  ARM Options.        (line  910)
* mno-unaligned-access <1>:              MIPS Options.       (line  597)
* mno-unaligned-doubles:                 SPARC Options.      (line   73)
* mno-uninit-const-in-rodata:            MIPS Options.       (line  525)
* mno-update:                            RS/6000 and PowerPC Options.
                                                             (line  350)
* mno-user-mode:                         SPARC Options.      (line   85)
* mno-usermode:                          SH Options.         (line  274)
* mno-v3push:                            NDS32 Options.      (line   48)
* mno-v8plus:                            SPARC Options.      (line  214)
* mno-vect-double:                       Adapteva Epiphany Options.
                                                             (line  115)
* mno-virt:                              MIPS Options.       (line  407)
* mno-vis:                               SPARC Options.      (line  221)
* mno-vis2:                              SPARC Options.      (line  227)
* mno-vis3:                              SPARC Options.      (line  235)
* mno-vis4:                              SPARC Options.      (line  243)
* mno-vis4b:                             SPARC Options.      (line  251)
* mno-vliw-branch:                       FRV Options.        (line  208)
* mno-volatile-asm-stop:                 IA-64 Options.      (line   32)
* mno-volatile-cache:                    ARC Options.        (line  429)
* mno-vrsave:                            RS/6000 and PowerPC Options.
                                                             (line  153)
* mno-vsx:                               RS/6000 and PowerPC Options.
                                                             (line  172)
* mno-vx:                                S/390 and zSeries Options.
                                                             (line  112)
* mno-warn-devices-csv:                  MSP430 Options.     (line  168)
* mno-warn-mcu:                          MSP430 Options.     (line   65)
* mno-warn-multiple-fast-interrupts:     RX Options.         (line  143)
* mno-wide-bitfields:                    MCore Options.      (line   23)
* mno-xgot:                              M680x0 Options.     (line  313)
* mno-xgot <1>:                          MIPS Options.       (line  229)
* mno-xl-compat:                         RS/6000 and PowerPC Options.
                                                             (line  291)
* mno-xpa:                               MIPS Options.       (line  411)
* mno-zdcbranch:                         SH Options.         (line  341)
* mno-zero-extend:                       MMIX Options.       (line   26)
* mno-zvector:                           S/390 and zSeries Options.
                                                             (line  123)
* mnobitfield:                           M680x0 Options.     (line  228)
* mnodiv:                                FT32 Options.       (line   20)
* mnomacsave:                            SH Options.         (line  160)
* mnop-fun-dllimport:                    x86 Windows Options.
                                                             (line   22)
* mnop-mcount:                           x86 Options.        (line 1394)
* mnopm:                                 FT32 Options.       (line   29)
* mnops:                                 Adapteva Epiphany Options.
                                                             (line   26)
* mnorm:                                 ARC Options.        (line  128)
* modd-spreg:                            MIPS Options.       (line  293)
* momit-leaf-frame-pointer:              AArch64 Options.    (line   58)
* momit-leaf-frame-pointer <1>:          Blackfin Options.   (line   43)
* momit-leaf-frame-pointer <2>:          x86 Options.        (line 1358)
* mone-byte-bool:                        Darwin Options.     (line   90)
* moptimize:                             Nvidia PTX Options. (line   45)
* moptimize-membar:                      FRV Options.        (line  244)
* moptimize-membar <1>:                  FRV Options.        (line  249)
* moverride:                             AArch64 Options.    (line  261)
* MP:                                    Preprocessor Options.
                                                             (line  135)
* mpa-risc-1-0:                          HPPA Options.       (line   19)
* mpa-risc-1-1:                          HPPA Options.       (line   19)
* mpa-risc-2-0:                          HPPA Options.       (line   19)
* mpack:                                 FRV Options.        (line  147)
* mpacked-stack:                         S/390 and zSeries Options.
                                                             (line   54)
* mpadstruct:                            SH Options.         (line  189)
* mpaired-single:                        MIPS Options.       (line  370)
* mpc-relative-literal-loads:            AArch64 Options.    (line  274)
* mpc32:                                 x86 Options.        (line  752)
* mpc64:                                 x86 Options.        (line  752)
* mpc80:                                 x86 Options.        (line  752)
* mpclmul:                               x86 Options.        (line  850)
* mpconfig:                              x86 Options.        (line  858)
* mpcrel:                                M680x0 Options.     (line  273)
* mpcrel <1>:                            RS/6000 and PowerPC Options.
                                                             (line  932)
* mpdebug:                               CRIS Options.       (line   34)
* mpe:                                   RS/6000 and PowerPC Options.
                                                             (line  310)
* mpe-aligned-commons:                   x86 Windows Options.
                                                             (line   59)
* mpic-data-is-text-relative:            ARM Options.        (line  794)
* mpic-data-is-text-relative <1>:        MicroBlaze Options. (line   92)
* mpic-register:                         ARM Options.        (line  787)
* mpid:                                  RX Options.         (line  117)
* mpku:                                  x86 Options.        (line  886)
* mplt:                                  MIPS Options.       (line  219)
* mpltseq:                               RS/6000 and PowerPC Options.
                                                             (line  765)
* mpointer-size=SIZE:                    VMS Options.        (line   20)
* mpointers-to-nested-functions:         RS/6000 and PowerPC Options.
                                                             (line  878)
* mpoke-function-name:                   ARM Options.        (line  802)
* mpopc:                                 SPARC Options.      (line  281)
* mpopcnt:                               x86 Options.        (line  870)
* mpopcntb:                              RS/6000 and PowerPC Options.
                                                             (line   25)
* mpopcntd:                              RS/6000 and PowerPC Options.
                                                             (line   25)
* mportable-runtime:                     HPPA Options.       (line   71)
* mpostinc:                              Adapteva Epiphany Options.
                                                             (line  109)
* mpostmodify:                           Adapteva Epiphany Options.
                                                             (line  109)
* mpower8-fusion:                        RS/6000 and PowerPC Options.
                                                             (line  190)
* mpower8-vector:                        RS/6000 and PowerPC Options.
                                                             (line  196)
* mpowerpc-gfxopt:                       RS/6000 and PowerPC Options.
                                                             (line   25)
* mpowerpc-gpopt:                        RS/6000 and PowerPC Options.
                                                             (line   25)
* mpowerpc64:                            RS/6000 and PowerPC Options.
                                                             (line   25)
* mprefer-avx128:                        x86 Options.        (line  985)
* mprefer-short-insn-regs:               Adapteva Epiphany Options.
                                                             (line   13)
* mprefer-vector-width:                  x86 Options.        (line  989)
* mprefergot:                            SH Options.         (line  268)
* mpreferred-stack-boundary:             RISC-V Options.     (line  101)
* mpreferred-stack-boundary <1>:         x86 Options.        (line  782)
* mprefetchwt1:                          x86 Options.        (line  863)
* mprefixed:                             RS/6000 and PowerPC Options.
                                                             (line  938)
* mpretend-cmove:                        SH Options.         (line  383)
* mprfchw:                               x86 Options.        (line  861)
* mprint-tune-info:                      ARM Options.        (line  944)
* mprioritize-restricted-insns:          RS/6000 and PowerPC Options.
                                                             (line  457)
* mprivileged:                           RS/6000 and PowerPC Options.
                                                             (line  955)
* mprolog-function:                      V850 Options.       (line   23)
* mprologue-epilogue:                    CRIS Options.       (line   69)
* mprototype:                            RS/6000 and PowerPC Options.
                                                             (line  593)
* mptwrite:                              x86 Options.        (line  854)
* mptx:                                  Nvidia PTX Options. (line   30)
* mpure-code:                            ARM Options.        (line  954)
* mpush-args:                            x86 Options.        (line 1164)
* mpushpop:                              C-SKY Options.      (line  130)
* MQ:                                    Preprocessor Options.
                                                             (line  162)
* mq-class:                              ARC Options.        (line  517)
* mquad-memory:                          RS/6000 and PowerPC Options.
                                                             (line  203)
* mquad-memory-atomic:                   RS/6000 and PowerPC Options.
                                                             (line  209)
* mr0rel-sec:                            Nios II Options.    (line   76)
* mr10k-cache-barrier:                   MIPS Options.       (line  720)
* mRcq:                                  ARC Options.        (line  521)
* mRcw:                                  ARC Options.        (line  525)
* mrdpid:                                x86 Options.        (line  862)
* mrdrnd:                                x86 Options.        (line  855)
* mrdseed:                               x86 Options.        (line  864)
* mreadonly-in-sdata:                    RS/6000 and PowerPC Options.
                                                             (line  684)
* mrecip:                                RS/6000 and PowerPC Options.
                                                             (line  785)
* mrecip <1>:                            x86 Options.        (line 1054)
* mrecip-precision:                      RS/6000 and PowerPC Options.
                                                             (line  842)
* mrecip=opt:                            RS/6000 and PowerPC Options.
                                                             (line  798)
* mrecip=opt <1>:                        x86 Options.        (line 1076)
* mrecord-mcount:                        x86 Options.        (line 1388)
* mrecord-return:                        x86 Options.        (line 1408)
* mred-zone:                             x86 Options.        (line 1552)
* mreduced-regs:                         NDS32 Options.      (line   15)
* mregister-names:                       IA-64 Options.      (line   37)
* mregnames:                             RS/6000 and PowerPC Options.
                                                             (line  722)
* mregparm:                              x86 Options.        (line  722)
* mrelax:                                AVR Options.        (line  229)
* mrelax <1>:                            H8/300 Options.     (line    9)
* mrelax <2>:                            MN10300 Options.    (line   46)
* mrelax <3>:                            MSP430 Options.     (line   88)
* mrelax <4>:                            NDS32 Options.      (line   84)
* mrelax <5>:                            RX Options.         (line   95)
* mrelax <6>:                            SH Options.         (line  137)
* mrelax <7>:                            V850 Options.       (line  103)
* mrelax-cmpxchg-loop:                   x86 Options.        (line 1465)
* mrelax-immediate:                      MCore Options.      (line   19)
* mrelax-pic-calls:                      MIPS Options.       (line  865)
* mrelocatable:                          RS/6000 and PowerPC Options.
                                                             (line  408)
* mrelocatable-lib:                      RS/6000 and PowerPC Options.
                                                             (line  419)
* mrenesas:                              SH Options.         (line  152)
* mrepeat:                               MeP Options.        (line   96)
* mrestrict-it:                          ARM Options.        (line  938)
* mreturn-pointer-on-d0:                 MN10300 Options.    (line   36)
* mrf16:                                 ARC Options.        (line  324)
* mrgf-banked-regs:                      ARC Options.        (line  304)
* mrh850-abi:                            V850 Options.       (line  127)
* mrl78:                                 RL78 Options.       (line   62)
* mrmw:                                  AVR Options.        (line  243)
* mrop-protect:                          RS/6000 and PowerPC Options.
                                                             (line  949)
* mror:                                  OpenRISC Options.   (line   49)
* mrori:                                 OpenRISC Options.   (line   54)
* mround-nearest:                        Adapteva Epiphany Options.
                                                             (line   51)
* mrtd:                                  M680x0 Options.     (line  237)
* mrtd <1>:                              x86 Options.        (line  698)
* mrtd <2>:                              x86 Function Attributes.
                                                             (line    9)
* mrtm:                                  x86 Options.        (line  881)
* mrtp:                                  VxWorks Options.    (line   11)
* mrtsc:                                 ARC Options.        (line  358)
* ms:                                    H8/300 Options.     (line   17)
* ms <1>:                                MeP Options.        (line  100)
* ms2600:                                H8/300 Options.     (line   24)
* msahf:                                 x86 Options.        (line 1025)
* msatur:                                MeP Options.        (line  105)
* msave-acc-in-interrupts:               RX Options.         (line  109)
* msave-mduc-in-interrupts:              RL78 Options.       (line   79)
* msave-restore:                         RISC-V Options.     (line  115)
* msave-toc-indirect:                    RS/6000 and PowerPC Options.
                                                             (line  890)
* mscc:                                  FRV Options.        (line  173)
* msched-ar-data-spec:                   IA-64 Options.      (line  135)
* msched-ar-in-data-spec:                IA-64 Options.      (line  157)
* msched-br-data-spec:                   IA-64 Options.      (line  128)
* msched-br-in-data-spec:                IA-64 Options.      (line  150)
* msched-control-spec:                   IA-64 Options.      (line  142)
* msched-costly-dep:                     RS/6000 and PowerPC Options.
                                                             (line  464)
* msched-count-spec-in-critical-path:    IA-64 Options.      (line  185)
* msched-fp-mem-deps-zero-cost:          IA-64 Options.      (line  202)
* msched-in-control-spec:                IA-64 Options.      (line  164)
* msched-max-memory-insns:               IA-64 Options.      (line  211)
* msched-max-memory-insns-hard-limit:    IA-64 Options.      (line  217)
* msched-prefer-non-control-spec-insns:  IA-64 Options.      (line  178)
* msched-prefer-non-data-spec-insns:     IA-64 Options.      (line  171)
* msched-prolog:                         ARM Options.        (line   32)
* msched-prolog <1>:                     C-SKY Options.      (line  164)
* msched-spec-ldc:                       IA-64 Options.      (line  191)
* msched-spec-ldc <1>:                   IA-64 Options.      (line  194)
* msched-stop-bits-after-every-cycle:    IA-64 Options.      (line  198)
* mschedule:                             HPPA Options.       (line   78)
* mscore5:                               Score Options.      (line   25)
* mscore5u:                              Score Options.      (line   28)
* mscore7:                               Score Options.      (line   31)
* mscore7d:                              Score Options.      (line   35)
* msda:                                  V850 Options.       (line   40)
* msdata:                                ARC Options.        (line  420)
* msdata <1>:                            IA-64 Options.      (line   42)
* msdata <2>:                            RS/6000 and PowerPC Options.
                                                             (line  666)
* msdata=all:                            C6X Options.        (line   30)
* msdata=data:                           RS/6000 and PowerPC Options.
                                                             (line  671)
* msdata=default:                        C6X Options.        (line   22)
* msdata=default <1>:                    RS/6000 and PowerPC Options.
                                                             (line  666)
* msdata=eabi:                           RS/6000 and PowerPC Options.
                                                             (line  647)
* msdata=none:                           C6X Options.        (line   35)
* msdata=none <1>:                       M32R/D Options.     (line   40)
* msdata=none <2>:                       RS/6000 and PowerPC Options.
                                                             (line  679)
* msdata=sdata:                          M32R/D Options.     (line   49)
* msdata=sysv:                           RS/6000 and PowerPC Options.
                                                             (line  657)
* msdata=use:                            M32R/D Options.     (line   53)
* msdram:                                Blackfin Options.   (line  169)
* msdram <1>:                            MeP Options.        (line  110)
* msecure-plt:                           RS/6000 and PowerPC Options.
                                                             (line  156)
* msecurity:                             C-SKY Options.      (line   96)
* msel-sched-dont-check-control-spec:    IA-64 Options.      (line  207)
* msep-data:                             Blackfin Options.   (line  107)
* msep-data <1>:                         Blackfin Options.   (line  113)
* mserialize:                            x86 Options.        (line  907)
* mserialize-volatile:                   Xtensa Options.     (line   35)
* msetlb:                                MN10300 Options.    (line   64)
* msext:                                 OpenRISC Options.   (line   59)
* msfimm:                                OpenRISC Options.   (line   63)
* msgx:                                  x86 Options.        (line  865)
* msha:                                  x86 Options.        (line  848)
* mshared-library-id:                    Blackfin Options.   (line  100)
* mshftimm:                              OpenRISC Options.   (line   68)
* mshort:                                M680x0 Options.     (line  217)
* mshort-calls:                          AVR Options.        (line  247)
* mshorten-memrefs:                      RISC-V Options.     (line  121)
* mshstk:                                x86 Options.        (line 1039)
* mside-effects:                         CRIS Options.       (line   44)
* msign-extend-enabled:                  LM32 Options.       (line   18)
* msign-return-address:                  AArch64 Options.    (line  280)
* msilicon-errata:                       MSP430 Options.     (line  159)
* msilicon-errata-warn:                  MSP430 Options.     (line  163)
* msim:                                  Blackfin Options.   (line   36)
* msim <1>:                              C6X Options.        (line   19)
* msim <2>:                              CR16 Options.       (line   18)
* msim <3>:                              C-SKY Options.      (line  170)
* msim <4>:                              FT32 Options.       (line    9)
* msim <5>:                              M32C Options.       (line   13)
* msim <6>:                              MeP Options.        (line  114)
* msim <7>:                              MSP430 Options.     (line   77)
* msim <8>:                              RL78 Options.       (line    7)
* msim <9>:                              RS/6000 and PowerPC Options.
                                                             (line  603)
* msim <10>:                             RX Options.         (line   71)
* msim <11>:                             Visium Options.     (line   13)
* msim <12>:                             Xstormy16 Options.  (line    9)
* msimd:                                 ARC Options.        (line  141)
* msimnovec:                             MeP Options.        (line  117)
* msingle-exit:                          MMIX Options.       (line   65)
* msingle-float:                         MIPS Options.       (line  284)
* msingle-pic-base:                      ARM Options.        (line  781)
* msingle-pic-base <1>:                  RS/6000 and PowerPC Options.
                                                             (line  451)
* msio:                                  HPPA Options.       (line  105)
* msize-level:                           ARC Options.        (line  529)
* mskip-rax-setup:                       x86 Options.        (line 1421)
* mslow-bytes:                           MCore Options.      (line   35)
* mslow-flash-data:                      ARM Options.        (line  926)
* msmall:                                MSP430 Options.     (line   85)
* msmall-data:                           DEC Alpha Options.  (line  187)
* msmall-data-limit:                     RISC-V Options.     (line  110)
* msmall-data-limit <1>:                 RX Options.         (line   47)
* msmall-divides:                        MicroBlaze Options. (line   38)
* msmall-exec:                           S/390 and zSeries Options.
                                                             (line   79)
* msmall-model:                          FR30 Options.       (line    9)
* msmall-text:                           DEC Alpha Options.  (line  205)
* msmall16:                              Adapteva Epiphany Options.
                                                             (line   66)
* msmallc:                               Nios II Options.    (line  338)
* msmart:                                C-SKY Options.      (line  113)
* msmartmips:                            MIPS Options.       (line  366)
* msoft-cmpsf:                           Adapteva Epiphany Options.
                                                             (line   29)
* msoft-div:                             OpenRISC Options.   (line   19)
* msoft-float:                           ARC Options.        (line  145)
* msoft-float <1>:                       C-SKY Options.      (line   52)
* msoft-float <2>:                       DEC Alpha Options.  (line   10)
* msoft-float <3>:                       FRV Options.        (line   27)
* msoft-float <4>:                       HPPA Options.       (line   91)
* msoft-float <5>:                       LoongArch Options.  (line   66)
* msoft-float <6>:                       M680x0 Options.     (line  201)
* msoft-float <7>:                       MicroBlaze Options. (line    7)
* msoft-float <8>:                       MIPS Options.       (line  270)
* msoft-float <9>:                       OpenRISC Options.   (line   29)
* msoft-float <10>:                      PDP-11 Options.     (line   13)
* msoft-float <11>:                      RS/6000 and PowerPC Options.
                                                             (line  333)
* msoft-float <12>:                      S/390 and zSeries Options.
                                                             (line   11)
* msoft-float <13>:                      SPARC Options.      (line   39)
* msoft-float <14>:                      V850 Options.       (line  113)
* msoft-float <15>:                      Visium Options.     (line   24)
* msoft-float <16>:                      x86 Options.        (line  597)
* msoft-mul:                             OpenRISC Options.   (line   24)
* msoft-quad-float:                      SPARC Options.      (line   59)
* msoft-stack:                           Nvidia PTX Options. (line   49)
* msp8:                                  AVR Options.        (line  254)
* mspace:                                V850 Options.       (line   30)
* mspace-regs:                           HPPA Options.       (line   45)
* mspecld-anomaly:                       Blackfin Options.   (line   48)
* mspecld-anomaly <1>:                   Blackfin Options.   (line   53)
* mspfp:                                 ARC Options.        (line  132)
* mspfp_compact:                         ARC Options.        (line  622)
* mspfp_fast:                            ARC Options.        (line  625)
* mspfp-compact:                         ARC Options.        (line  133)
* mspfp-fast:                            ARC Options.        (line  137)
* msplit:                                PDP-11 Options.     (line   40)
* msplit-addresses:                      MIPS Options.       (line  555)
* msplit-lohi:                           Adapteva Epiphany Options.
                                                             (line  109)
* msplit-vecmove-early:                  Adapteva Epiphany Options.
                                                             (line  126)
* msram-ecc:                             AMD GCN Options.    (line   25)
* msse:                                  x86 Options.        (line  829)
* msse2:                                 x86 Options.        (line  830)
* msse2avx:                              x86 Options.        (line 1376)
* msse3:                                 x86 Options.        (line  831)
* msse4:                                 x86 Options.        (line  833)
* msse4.1:                               x86 Options.        (line  835)
* msse4.2:                               x86 Options.        (line  836)
* msse4a:                                x86 Options.        (line  834)
* msseregparm:                           x86 Options.        (line  733)
* mssse3:                                x86 Options.        (line  832)
* mstack-align:                          CRIS Options.       (line   53)
* mstack-bias:                           SPARC Options.      (line  372)
* mstack-check-l1:                       Blackfin Options.   (line   74)
* mstack-guard:                          S/390 and zSeries Options.
                                                             (line  202)
* mstack-increment:                      MCore Options.      (line   50)
* mstack-offset:                         Adapteva Epiphany Options.
                                                             (line   37)
* mstack-protector-guard:                AArch64 Options.    (line   64)
* mstack-protector-guard <1>:            ARM Options.        (line  976)
* mstack-protector-guard <2>:            RISC-V Options.     (line  185)
* mstack-protector-guard <3>:            RS/6000 and PowerPC Options.
                                                             (line  916)
* mstack-protector-guard <4>:            x86 Options.        (line 1447)
* mstack-protector-guard-offset:         AArch64 Options.    (line   64)
* mstack-protector-guard-offset <1>:     ARM Options.        (line  976)
* mstack-protector-guard-offset <2>:     RISC-V Options.     (line  185)
* mstack-protector-guard-offset <3>:     RS/6000 and PowerPC Options.
                                                             (line  916)
* mstack-protector-guard-offset <4>:     x86 Options.        (line 1447)
* mstack-protector-guard-reg:            AArch64 Options.    (line   64)
* mstack-protector-guard-reg <1>:        RISC-V Options.     (line  185)
* mstack-protector-guard-reg <2>:        RS/6000 and PowerPC Options.
                                                             (line  916)
* mstack-protector-guard-reg <3>:        x86 Options.        (line 1447)
* mstack-protector-guard-symbol:         RS/6000 and PowerPC Options.
                                                             (line  916)
* mstack-size:                           AMD GCN Options.    (line   31)
* mstack-size <1>:                       C-SKY Options.      (line  150)
* mstack-size <2>:                       S/390 and zSeries Options.
                                                             (line  202)
* mstackrealign:                         x86 Options.        (line  773)
* mstd-struct-return:                    SPARC Options.      (line  102)
* mstore-max:                            x86 Options.        (line  998)
* mstrict-align:                         AArch64 Options.    (line   52)
* mstrict-align <1>:                     M680x0 Options.     (line  281)
* mstrict-align <2>:                     RISC-V Options.     (line  130)
* mstrict-align <3>:                     RS/6000 and PowerPC Options.
                                                             (line  403)
* mstrict-X:                             AVR Options.        (line  267)
* mstring-compare-inline-limit:          RS/6000 and PowerPC Options.
                                                             (line  708)
* mstringop-strategy=ALG:                x86 Options.        (line 1324)
* mstructure-size-boundary:              ARM Options.        (line  736)
* msubxc:                                SPARC Options.      (line  288)
* msv-mode:                              Visium Options.     (line   52)
* msve-vector-bits:                      AArch64 Options.    (line  309)
* msvr4-struct-return:                   RS/6000 and PowerPC Options.
                                                             (line  548)
* mswap:                                 ARC Options.        (line  152)
* mswape:                                ARC Options.        (line  363)
* msym32:                                MIPS Options.       (line  453)
* msynci:                                MIPS Options.       (line  851)
* msys-crt0:                             Nios II Options.    (line  342)
* msys-lib:                              Nios II Options.    (line  346)
* MT:                                    Preprocessor Options.
                                                             (line  147)
* mtarget-align:                         Xtensa Options.     (line   74)
* mtas:                                  SH Options.         (line  259)
* mtbm:                                  x86 Options.        (line  883)
* mtda:                                  V850 Options.       (line   34)
* mtelephony:                            ARC Options.        (line  368)
* mtext-section-literals:                Xtensa Options.     (line   47)
* mtf:                                   MeP Options.        (line  121)
* mthreads:                              x86 Options.        (line 1179)
* mthreads <1>:                          x86 Windows Options.
                                                             (line   26)
* mthumb:                                ARM Options.        (line  824)
* mthumb-interwork:                      ARM Options.        (line   24)
* mtiny-printf:                          MSP430 Options.     (line  122)
* mtiny-stack:                           AVR Options.        (line  281)
* mtiny=:                                MeP Options.        (line  125)
* mTLS:                                  FRV Options.        (line   90)
* mtls:                                  FRV Options.        (line   94)
* mtls-dialect:                          ARM Options.        (line  876)
* mtls-dialect <1>:                      x86 Options.        (line 1157)
* mtls-dialect=desc:                     AArch64 Options.    (line   77)
* mtls-dialect=traditional:              AArch64 Options.    (line   81)
* mtls-direct-seg-refs:                  x86 Options.        (line 1366)
* mtls-markers:                          RS/6000 and PowerPC Options.
                                                             (line  777)
* mtls-size:                             AArch64 Options.    (line   85)
* mtls-size <1>:                         IA-64 Options.      (line  112)
* mtoc:                                  RS/6000 and PowerPC Options.
                                                             (line  428)
* mtomcat-stats:                         FRV Options.        (line  254)
* mtoplevel-symbols:                     MMIX Options.       (line   39)
* mtp:                                   ARM Options.        (line  868)
* mtp-regno:                             ARC Options.        (line  170)
* mtpcs-frame:                           ARM Options.        (line  841)
* mtpcs-leaf-frame:                      ARM Options.        (line  847)
* mtpf-trace:                            S/390 and zSeries Options.
                                                             (line  169)
* mtpf-trace-skip:                       S/390 and zSeries Options.
                                                             (line  175)
* mtraceback:                            RS/6000 and PowerPC Options.
                                                             (line  541)
* mtrap-precision:                       DEC Alpha Options.  (line  109)
* mtrust:                                C-SKY Options.      (line   99)
* mtsxldtrk:                             x86 Options.        (line  899)
* mtune:                                 AArch64 Options.    (line  189)
* mtune <1>:                             AMD GCN Options.    (line   10)
* mtune <2>:                             ARC Options.        (line  550)
* mtune <3>:                             ARC Options.        (line  628)
* mtune <4>:                             ARM Options.        (line  571)
* mtune <5>:                             CRIS Options.       (line   15)
* mtune <6>:                             DEC Alpha Options.  (line  259)
* mtune <7>:                             IA-64 Options.      (line  116)
* mtune <8>:                             LoongArch Options.  (line   32)
* mtune <9>:                             M680x0 Options.     (line   69)
* mtune <10>:                            MIPS Options.       (line   66)
* mtune <11>:                            MN10300 Options.    (line   30)
* mtune <12>:                            RISC-V Options.     (line   86)
* mtune <13>:                            RS/6000 and PowerPC Options.
                                                             (line  114)
* mtune <14>:                            S/390 and zSeries Options.
                                                             (line  162)
* mtune <15>:                            SPARC Options.      (line  199)
* mtune <16>:                            Visium Options.     (line   47)
* mtune <17>:                            x86 Options.        (line  471)
* mtune-ctrl=FEATURE-LIST:               x86 Options.        (line  952)
* muclibc:                               GNU/Linux Options.  (line   14)
* muintr:                                x86 Options.        (line  898)
* muls:                                  Score Options.      (line   18)
* multcost:                              ARC Options.        (line  633)
* multcost=NUMBER:                       SH Options.         (line  281)
* multi_module:                          Darwin Options.     (line  196)
* multilib-library-pic:                  FRV Options.        (line  110)
* multiply_defined:                      Darwin Options.     (line  196)
* multiply_defined_unused:               Darwin Options.     (line  196)
* multiply-enabled:                      LM32 Options.       (line   15)
* munalign-prob-threshold:               ARC Options.        (line  578)
* munaligned-access:                     ARM Options.        (line  910)
* munaligned-access <1>:                 MIPS Options.       (line  597)
* munaligned-doubles:                    SPARC Options.      (line   73)
* municode:                              x86 Windows Options.
                                                             (line   30)
* muniform-simt:                         Nvidia PTX Options. (line   61)
* muninit-const-in-rodata:               MIPS Options.       (line  525)
* munix:                                 VAX Options.        (line    9)
* munix-asm:                             PDP-11 Options.     (line   43)
* munordered-float:                      OpenRISC Options.   (line   39)
* mupdate:                               RS/6000 and PowerPC Options.
                                                             (line  350)
* muser-enabled:                         LM32 Options.       (line   21)
* muser-mode:                            SPARC Options.      (line   85)
* muser-mode <1>:                        Visium Options.     (line   57)
* musermode:                             SH Options.         (line  274)
* mv3push:                               NDS32 Options.      (line   45)
* mv850:                                 V850 Options.       (line   49)
* mv850e:                                V850 Options.       (line   79)
* mv850e1:                               V850 Options.       (line   70)
* mv850e2:                               V850 Options.       (line   66)
* mv850e2v3:                             V850 Options.       (line   61)
* mv850e2v4:                             V850 Options.       (line   57)
* mv850e3v5:                             V850 Options.       (line   52)
* mv850es:                               V850 Options.       (line   75)
* mv8plus:                               SPARC Options.      (line  214)
* mvaes:                                 x86 Options.        (line  891)
* mvdsp:                                 C-SKY Options.      (line  104)
* mveclibabi:                            RS/6000 and PowerPC Options.
                                                             (line  851)
* mveclibabi <1>:                        x86 Options.        (line 1105)
* mvect-double:                          Adapteva Epiphany Options.
                                                             (line  115)
* mvect8-ret-in-mem:                     x86 Options.        (line  743)
* mverbose-cost-dump:                    AArch64 Options.    (line  269)
* mverbose-cost-dump <1>:                ARM Options.        (line  950)
* mvirt:                                 MIPS Options.       (line  407)
* mvis:                                  SPARC Options.      (line  221)
* mvis2:                                 SPARC Options.      (line  227)
* mvis3:                                 SPARC Options.      (line  235)
* mvis4:                                 SPARC Options.      (line  243)
* mvis4b:                                SPARC Options.      (line  251)
* mvliw-branch:                          FRV Options.        (line  201)
* mvms-return-codes:                     VMS Options.        (line    9)
* mvolatile-asm-stop:                    IA-64 Options.      (line   32)
* mvolatile-cache:                       ARC Options.        (line  425)
* mvolatile-cache <1>:                   ARC Options.        (line  429)
* mvpclmulqdq:                           x86 Options.        (line  893)
* mvr4130-align:                         MIPS Options.       (line  840)
* mvrsave:                               RS/6000 and PowerPC Options.
                                                             (line  153)
* mvsx:                                  RS/6000 and PowerPC Options.
                                                             (line  172)
* mvx:                                   S/390 and zSeries Options.
                                                             (line  112)
* mvxworks:                              RS/6000 and PowerPC Options.
                                                             (line  624)
* mvzeroupper:                           x86 Options.        (line  979)
* mwaitpkg:                              x86 Options.        (line  892)
* mwarn-devices-csv:                     MSP430 Options.     (line  168)
* mwarn-dynamicstack:                    S/390 and zSeries Options.
                                                             (line  196)
* mwarn-framesize:                       S/390 and zSeries Options.
                                                             (line  188)
* mwarn-mcu:                             MSP430 Options.     (line   65)
* mwarn-multiple-fast-interrupts:        RX Options.         (line  143)
* mwbnoinvd:                             x86 Options.        (line  859)
* mwide-bitfields:                       MCore Options.      (line   23)
* mwidekl:                               x86 Options.        (line  913)
* mwin32:                                x86 Windows Options.
                                                             (line   35)
* mwindows:                              x86 Windows Options.
                                                             (line   41)
* mword-relocations:                     ARM Options.        (line  887)
* mx32:                                  x86 Options.        (line 1532)
* mxgot:                                 M680x0 Options.     (line  313)
* mxgot <1>:                             MIPS Options.       (line  229)
* mxl-barrel-shift:                      MicroBlaze Options. (line   32)
* mxl-compat:                            RS/6000 and PowerPC Options.
                                                             (line  291)
* mxl-float-convert:                     MicroBlaze Options. (line   50)
* mxl-float-sqrt:                        MicroBlaze Options. (line   53)
* mxl-gp-opt:                            MicroBlaze Options. (line   44)
* mxl-multiply-high:                     MicroBlaze Options. (line   47)
* mxl-pattern-compare:                   MicroBlaze Options. (line   35)
* mxl-reorder:                           MicroBlaze Options. (line   62)
* mxl-soft-div:                          MicroBlaze Options. (line   29)
* mxl-soft-mul:                          MicroBlaze Options. (line   26)
* mxl-stack-check:                       MicroBlaze Options. (line   41)
* mxnack:                                AMD GCN Options.    (line   38)
* mxop:                                  x86 Options.        (line  866)
* mxpa:                                  MIPS Options.       (line  411)
* mxsave:                                x86 Options.        (line  877)
* mxsavec:                               x86 Options.        (line  879)
* mxsaveopt:                             x86 Options.        (line  878)
* mxsaves:                               x86 Options.        (line  880)
* mxy:                                   ARC Options.        (line  373)
* myellowknife:                          RS/6000 and PowerPC Options.
                                                             (line  619)
* mzarch:                                S/390 and zSeries Options.
                                                             (line   94)
* mzda:                                  V850 Options.       (line   45)
* mzdcbranch:                            SH Options.         (line  341)
* mzero-extend:                          MMIX Options.       (line   26)
* mzvector:                              S/390 and zSeries Options.
                                                             (line  123)
* no_dead_strip_inits_and_terms:         Darwin Options.     (line  196)
* no-80387:                              x86 Options.        (line  597)
* no-block-ops-unaligned-vsx:            RS/6000 and PowerPC Options.
                                                             (line  959)
* no-canonical-prefixes:                 Directory Options.  (line  164)
* no-integrated-cpp:                     Preprocessor Options.
                                                             (line  483)
* no-pie:                                Link Options.       (line  184)
* no-sysroot-suffix:                     Directory Options.  (line  183)
* noall_load:                            Darwin Options.     (line  196)
* nocpp:                                 MIPS Options.       (line  642)
* nodefaultlibs:                         Link Options.       (line  122)
* nodevicelib:                           AVR Options.        (line  288)
* nodevicespecs:                         AVR Options.        (line  291)
* nofixprebinding:                       Darwin Options.     (line  196)
* nofpu:                                 RX Options.         (line   17)
* nolibc:                                Link Options.       (line  134)
* nolibdld:                              HPPA Options.       (line  188)
* nomultidefs:                           Darwin Options.     (line  196)
* non-static:                            VxWorks Options.    (line   16)
* noprebind:                             Darwin Options.     (line  196)
* noseglinkedit:                         Darwin Options.     (line  196)
* nostartfiles:                          Link Options.       (line  117)
* nostdinc:                              Directory Options.  (line  102)
* nostdinc++:                            C++ Dialect Options.
                                                             (line  555)
* nostdinc++ <1>:                        Directory Options.  (line  108)
* nostdlib:                              Link Options.       (line  146)
* o:                                     Overall Options.    (line  193)
* O:                                     Optimize Options.   (line   39)
* O0:                                    Optimize Options.   (line  166)
* O1:                                    Optimize Options.   (line   39)
* O2:                                    Optimize Options.   (line   97)
* O3:                                    Optimize Options.   (line  148)
* Ofast:                                 Optimize Options.   (line  182)
* Og:                                    Optimize Options.   (line  190)
* Os:                                    Optimize Options.   (line  170)
* Oz:                                    Optimize Options.   (line  209)
* p:                                     Instrumentation Options.
                                                             (line   20)
* P:                                     Preprocessor Options.
                                                             (line  368)
* p <1>:                                 Common Function Attributes.
                                                             (line  814)
* pagezero_size:                         Darwin Options.     (line  196)
* param:                                 Optimize Options.   (line 2736)
* pass-exit-codes:                       Overall Options.    (line  597)
* pedantic:                              Standards.          (line   13)
* pedantic <1>:                          Warning Options.    (line   88)
* pedantic <2>:                          C Extensions.       (line    6)
* pedantic <3>:                          Alternate Keywords. (line   30)
* pedantic <4>:                          Warnings and Errors.
                                                             (line   25)
* pedantic-errors:                       Standards.          (line   13)
* pedantic-errors <1>:                   Warning Options.    (line  131)
* pedantic-errors <2>:                   Non-bugs.           (line  216)
* pedantic-errors <3>:                   Warnings and Errors.
                                                             (line   25)
* pg:                                    Instrumentation Options.
                                                             (line   20)
* pg <1>:                                Common Function Attributes.
                                                             (line  814)
* pie:                                   Link Options.       (line  178)
* pipe:                                  Overall Options.    (line  605)
* plt:                                   RISC-V Options.     (line   13)
* prebind:                               Darwin Options.     (line  196)
* prebind_all_twolevel_modules:          Darwin Options.     (line  196)
* print-file-name:                       Developer Options.  (line  934)
* print-libgcc-file-name:                Developer Options.  (line  968)
* print-multi-directory:                 Developer Options.  (line  940)
* print-multi-lib:                       Developer Options.  (line  945)
* print-multi-os-directory:              Developer Options.  (line  952)
* print-multiarch:                       Developer Options.  (line  961)
* print-objc-runtime-info:               Objective-C and Objective-C++ Dialect Options.
                                                             (line  227)
* print-prog-name:                       Developer Options.  (line  965)
* print-search-dirs:                     Developer Options.  (line  976)
* print-sysroot:                         Developer Options.  (line  989)
* print-sysroot-headers-suffix:          Developer Options.  (line  996)
* private_bundle:                        Darwin Options.     (line  196)
* pthread:                               Preprocessor Options.
                                                             (line   70)
* pthread <1>:                           Link Options.       (line  195)
* pthreads:                              Solaris 2 Options.  (line   30)
* Q:                                     Developer Options.  (line  838)
* Qn:                                    System V Options.   (line   18)
* Qy:                                    System V Options.   (line   14)
* r:                                     Link Options.       (line  202)
* rdynamic:                              Link Options.       (line  206)
* read_only_relocs:                      Darwin Options.     (line  196)
* remap:                                 Preprocessor Options.
                                                             (line  399)
* S:                                     Overall Options.    (line  176)
* S <1>:                                 Link Options.       (line   20)
* s:                                     Link Options.       (line  213)
* save-temps:                            Developer Options.  (line  734)
* save-temps=cwd:                        Developer Options.  (line  745)
* save-temps=obj:                        Developer Options.  (line  748)
* sectalign:                             Darwin Options.     (line  196)
* sectcreate:                            Darwin Options.     (line  196)
* sectobjectsymbols:                     Darwin Options.     (line  196)
* sectobjectsymbols <1>:                 Darwin Options.     (line  196)
* sectorder:                             Darwin Options.     (line  196)
* seg_addr_table:                        Darwin Options.     (line  196)
* seg_addr_table_filename:               Darwin Options.     (line  196)
* seg1addr:                              Darwin Options.     (line  196)
* segaddr:                               Darwin Options.     (line  196)
* seglinkedit:                           Darwin Options.     (line  196)
* segprot:                               Darwin Options.     (line  196)
* segs_read_only_addr:                   Darwin Options.     (line  196)
* segs_read_only_addr <1>:               Darwin Options.     (line  196)
* segs_read_write_addr:                  Darwin Options.     (line  196)
* segs_read_write_addr <1>:              Darwin Options.     (line  196)
* shared:                                Link Options.       (line  222)
* shared-libgcc:                         Link Options.       (line  230)
* short-calls:                           Adapteva Epiphany Options.
                                                             (line   61)
* sim:                                   CRIS Options.       (line   81)
* sim2:                                  CRIS Options.       (line   86)
* single_module:                         Darwin Options.     (line  196)
* specs:                                 Overall Options.    (line  611)
* static:                                Link Options.       (line  217)
* static <1>:                            Darwin Options.     (line  196)
* static <2>:                            HPPA Options.       (line  192)
* static-libasan:                        Link Options.       (line  264)
* static-libgcc:                         Link Options.       (line  230)
* static-liblsan:                        Link Options.       (line  280)
* static-libstdc++:                      Link Options.       (line  297)
* static-libtsan:                        Link Options.       (line  272)
* static-libubsan:                       Link Options.       (line  288)
* static-pie:                            Link Options.       (line  187)
* std:                                   Standards.          (line   13)
* std <1>:                               C Dialect Options.  (line   46)
* std <2>:                               Other Builtins.     (line   31)
* std <3>:                               Non-bugs.           (line  107)
* stdlib:                                C++ Dialect Options.
                                                             (line  578)
* sub_library:                           Darwin Options.     (line  196)
* sub_umbrella:                          Darwin Options.     (line  196)
* symbolic:                              Link Options.       (line  308)
* sysroot:                               Directory Options.  (line  168)
* T:                                     Link Options.       (line  314)
* target-help:                           Overall Options.    (line  487)
* threads:                               HPPA Options.       (line  205)
* time:                                  Developer Options.  (line  754)
* tno-android-cc:                        GNU/Linux Options.  (line   36)
* tno-android-ld:                        GNU/Linux Options.  (line   40)
* traditional:                           Preprocessor Options.
                                                             (line  375)
* traditional <1>:                       Incompatibilities.  (line    6)
* traditional-cpp:                       Preprocessor Options.
                                                             (line  375)
* trigraphs:                             Preprocessor Options.
                                                             (line  385)
* twolevel_namespace:                    Darwin Options.     (line  196)
* U:                                     Preprocessor Options.
                                                             (line   42)
* u:                                     Link Options.       (line  346)
* umbrella:                              Darwin Options.     (line  196)
* undef:                                 Preprocessor Options.
                                                             (line   66)
* undefined:                             Darwin Options.     (line  196)
* unexported_symbols_list:               Darwin Options.     (line  196)
* v:                                     Overall Options.    (line  466)
* version:                               Overall Options.    (line  594)
* w:                                     Warning Options.    (line   25)
* W:                                     Warning Options.    (line  222)
* W <1>:                                 Warning Options.    (line 2948)
* W <2>:                                 Warning Options.    (line 3105)
* W <3>:                                 Incompatibilities.  (line   64)
* Wa:                                    Assembler Options.  (line    9)
* Wabi:                                  Warning Options.    (line  267)
* Wabi-tag:                              C++ Dialect Options.
                                                             (line  590)
* Wabsolute-value:                       Warning Options.    (line 2352)
* Waddr-space-convert:                   AVR Options.        (line  306)
* Waddress:                              Warning Options.    (line 2781)
* Waddress-of-packed-member:             Warning Options.    (line 2815)
* Waggregate-return:                     Warning Options.    (line 2843)
* Waggressive-loop-optimizations:        Warning Options.    (line 2848)
* Waligned-new:                          C++ Dialect Options.
                                                             (line 1180)
* Wall:                                  Warning Options.    (line  140)
* Wall <1>:                              Standard Libraries. (line    6)
* Walloc-size-larger-than=:              Warning Options.    (line 1715)
* Walloc-zero:                           Warning Options.    (line 1705)
* Walloca:                               Warning Options.    (line 1730)
* Walloca-larger-than=:                  Warning Options.    (line 1733)
* Wanalyzer-double-fclose:               Static Analyzer Options.
                                                             (line   51)
* Wanalyzer-double-free:                 Static Analyzer Options.
                                                             (line   58)
* Wanalyzer-exposure-through-output-file: Static Analyzer Options.
                                                             (line   66)
* Wanalyzer-file-leak:                   Static Analyzer Options.
                                                             (line   74)
* Wanalyzer-free-of-non-heap:            Static Analyzer Options.
                                                             (line   81)
* Wanalyzer-malloc-leak:                 Static Analyzer Options.
                                                             (line   89)
* Wanalyzer-mismatching-deallocation:    Static Analyzer Options.
                                                             (line   97)
* Wanalyzer-null-argument:               Static Analyzer Options.
                                                             (line  123)
* Wanalyzer-null-dereference:            Static Analyzer Options.
                                                             (line  131)
* Wanalyzer-possible-null-argument:      Static Analyzer Options.
                                                             (line  108)
* Wanalyzer-possible-null-dereference:   Static Analyzer Options.
                                                             (line  116)
* Wanalyzer-shift-count-negative:        Static Analyzer Options.
                                                             (line  138)
* Wanalyzer-shift-count-overflow:        Static Analyzer Options.
                                                             (line  150)
* Wanalyzer-stale-setjmp-buffer:         Static Analyzer Options.
                                                             (line  163)
* Wanalyzer-tainted-allocation-size:     Static Analyzer Options.
                                                             (line  177)
* Wanalyzer-tainted-array-index:         Static Analyzer Options.
                                                             (line  191)
* Wanalyzer-tainted-divisor:             Static Analyzer Options.
                                                             (line  204)
* Wanalyzer-tainted-offset:              Static Analyzer Options.
                                                             (line  214)
* Wanalyzer-tainted-size:                Static Analyzer Options.
                                                             (line  227)
* Wanalyzer-too-complex:                 Static Analyzer Options.
                                                             (line   41)
* Wanalyzer-unsafe-call-within-signal-handler: Static Analyzer Options.
                                                             (line  237)
* Wanalyzer-use-after-free:              Static Analyzer Options.
                                                             (line  245)
* Wanalyzer-use-of-pointer-in-stale-stack-frame: Static Analyzer Options.
                                                             (line  253)
* Wanalyzer-use-of-uninitialized-value:  Static Analyzer Options.
                                                             (line  280)
* Wanalyzer-write-to-const:              Static Analyzer Options.
                                                             (line  260)
* Wanalyzer-write-to-string-literal:     Static Analyzer Options.
                                                             (line  270)
* Warith-conversion:                     Warning Options.    (line 1798)
* Warray-bounds:                         Warning Options.    (line 1811)
* Warray-compare:                        Warning Options.    (line 1830)
* Wassign-intercept:                     Objective-C and Objective-C++ Dialect Options.
                                                             (line  170)
* Wattribute-alias:                      Warning Options.    (line 1886)
* Wattribute-warning:                    Warning Options.    (line 3072)
* Wattributes:                           Warning Options.    (line 2853)
* Wbad-function-cast:                    Warning Options.    (line 2421)
* Wbidi-chars:                           Warning Options.    (line 1918)
* Wbidi-chars=:                          Warning Options.    (line 1918)
* Wbool-compare:                         Warning Options.    (line 1940)
* Wbool-operation:                       Warning Options.    (line 1949)
* Wbuiltin-declaration-mismatch:         Warning Options.    (line 2875)
* Wbuiltin-macro-redefined:              Warning Options.    (line 2896)
* Wc++-compat:                           Warning Options.    (line 2449)
* Wc++11-compat:                         Warning Options.    (line 2454)
* Wc++11-extensions:                     Warning Options.    (line 2472)
* Wc++14-compat:                         Warning Options.    (line 2460)
* Wc++14-extensions:                     Warning Options.    (line 2477)
* Wc++17-compat:                         Warning Options.    (line 2464)
* Wc++17-extensions:                     Warning Options.    (line 2482)
* Wc++20-compat:                         Warning Options.    (line 2468)
* Wc++20-extensions:                     Warning Options.    (line 2487)
* Wc++23-extensions:                     Warning Options.    (line 2492)
* Wc11-c2x-compat:                       Warning Options.    (line 2441)
* Wc90-c99-compat:                       Warning Options.    (line 2426)
* Wc99-c11-compat:                       Warning Options.    (line 2433)
* Wcast-align:                           Warning Options.    (line 2513)
* Wcast-align=strict:                    Warning Options.    (line 2519)
* Wcast-function-type:                   Warning Options.    (line 2524)
* Wcast-qual:                            Warning Options.    (line 2497)
* Wcatch-value:                          C++ Dialect Options.
                                                             (line 1227)
* Wchar-subscripts:                      Warning Options.    (line  377)
* Wclass-conversion:                     C++ Dialect Options.
                                                             (line 1158)
* Wclass-memaccess:                      C++ Dialect Options.
                                                             (line  785)
* Wclobbered:                            Warning Options.    (line 2550)
* Wcomma-subscript:                      C++ Dialect Options.
                                                             (line  595)
* Wcomment:                              Warning Options.    (line 2363)
* Wcomments:                             Warning Options.    (line 2363)
* Wconditionally-supported:              C++ Dialect Options.
                                                             (line 1235)
* Wconversion:                           Warning Options.    (line 2554)
* Wconversion-null:                      C++ Dialect Options.
                                                             (line 1369)
* Wcoverage-invalid-line-number:         Warning Options.    (line  396)
* Wcoverage-mismatch:                    Warning Options.    (line  382)
* Wcpp:                                  Warning Options.    (line  406)
* Wctad-maybe-unsupported:               C++ Dialect Options.
                                                             (line  616)
* Wctor-dtor-privacy:                    C++ Dialect Options.
                                                             (line  632)
* Wdangling-else:                        Warning Options.    (line 2575)
* Wdangling-pointer:                     Warning Options.    (line 2610)
* Wdate-time:                            Warning Options.    (line 2657)
* Wdeclaration-after-statement:          Warning Options.    (line 2169)
* Wdelete-incomplete:                    C++ Dialect Options.
                                                             (line 1238)
* Wdelete-non-virtual-dtor:              C++ Dialect Options.
                                                             (line  639)
* Wdeprecated:                           Warning Options.    (line 3079)
* Wdeprecated-copy:                      C++ Dialect Options.
                                                             (line  646)
* Wdeprecated-declarations:              Warning Options.    (line 3083)
* Wdeprecated-enum-enum-conversion:      C++ Dialect Options.
                                                             (line  654)
* Wdeprecated-enum-float-conversion:     C++ Dialect Options.
                                                             (line  668)
* Wdesignated-init:                      Warning Options.    (line 3409)
* Wdisabled-optimization:                Warning Options.    (line 3360)
* Wdiscarded-array-qualifiers:           Warning Options.    (line 1988)
* Wdiscarded-qualifiers:                 Warning Options.    (line 1982)
* Wdiv-by-zero:                          Warning Options.    (line 2029)
* Wdouble-promotion:                     Warning Options.    (line  409)
* Wduplicate-decl-specifier:             Warning Options.    (line  427)
* Wduplicated-branches:                  Warning Options.    (line 1959)
* Wduplicated-cond:                      Warning Options.    (line 1970)
* weak_reference_mismatches:             Darwin Options.     (line  196)
* Weffc++:                               C++ Dialect Options.
                                                             (line  951)
* Wempty-body:                           Warning Options.    (line 2662)
* Wendif-labels:                         Warning Options.    (line 2407)
* Wendif-labels <1>:                     Warning Options.    (line 2666)
* Wenum-compare:                         Warning Options.    (line 2669)
* Wenum-conversion:                      Warning Options.    (line 2675)
* Werror:                                Warning Options.    (line   28)
* Werror=:                               Warning Options.    (line   31)
* Wexceptions:                           C++ Dialect Options.
                                                             (line  979)
* Wexpansion-to-defined:                 Warning Options.    (line 2382)
* Wextra:                                Warning Options.    (line  222)
* Wextra <1>:                            Warning Options.    (line 2948)
* Wextra <2>:                            Warning Options.    (line 3105)
* Wextra-semi:                           C++ Dialect Options.
                                                             (line 1243)
* Wfatal-errors:                         Warning Options.    (line   48)
* Wfloat-conversion:                     Warning Options.    (line 2703)
* Wfloat-equal:                          Warning Options.    (line 2069)
* Wformat:                               Warning Options.    (line  432)
* Wformat <1>:                           Warning Options.    (line  457)
* Wformat <2>:                           Warning Options.    (line 1676)
* Wformat <3>:                           Common Function Attributes.
                                                             (line  411)
* Wformat-contains-nul:                  Warning Options.    (line  471)
* Wformat-extra-args:                    Warning Options.    (line  475)
* Wformat-nonliteral:                    Warning Options.    (line  568)
* Wformat-nonliteral <1>:                Common Function Attributes.
                                                             (line  476)
* Wformat-overflow:                      Warning Options.    (line  489)
* Wformat-overflow <1>:                  Warning Options.    (line  500)
* Wformat-security:                      Warning Options.    (line  573)
* Wformat-signedness:                    Warning Options.    (line  584)
* Wformat-truncation:                    Warning Options.    (line  589)
* Wformat-truncation <1>:                Warning Options.    (line  601)
* Wformat-y2k:                           Warning Options.    (line  612)
* Wformat-zero-length:                   Warning Options.    (line  564)
* Wformat=:                              Warning Options.    (line  432)
* Wformat=1:                             Warning Options.    (line  457)
* Wformat=2:                             Warning Options.    (line  466)
* Wframe-address:                        Warning Options.    (line 1976)
* Wframe-larger-than=:                   Warning Options.    (line 2243)
* Wfree-nonheap-object:                  Warning Options.    (line 2260)
* whatsloaded:                           Darwin Options.     (line  196)
* whyload:                               Darwin Options.     (line  196)
* Wif-not-aligned:                       Warning Options.    (line  791)
* Wignored-attributes:                   Warning Options.    (line  806)
* Wignored-qualifiers:                   Warning Options.    (line  795)
* Wimplicit:                             Warning Options.    (line  669)
* Wimplicit-fallthrough:                 Warning Options.    (line  673)
* Wimplicit-fallthrough=:                Warning Options.    (line  678)
* Wimplicit-function-declaration:        Warning Options.    (line  663)
* Wimplicit-int:                         Warning Options.    (line  658)
* Winaccessible-base:                    C++ Dialect Options.
                                                             (line 1247)
* Wincompatible-pointer-types:           Warning Options.    (line 1994)
* Winfinite-recursion:                   Warning Options.    (line  637)
* Winherited-variadic-ctor:              C++ Dialect Options.
                                                             (line 1258)
* Winit-list-lifetime:                   C++ Dialect Options.
                                                             (line  682)
* Winit-self:                            Warning Options.    (line  643)
* Winline:                               Warning Options.    (line 3198)
* Winline <1>:                           Inline.             (line   60)
* Wint-conversion:                       Warning Options.    (line 2000)
* Wint-in-bool-context:                  Warning Options.    (line 3246)
* Wint-to-pointer-cast:                  Warning Options.    (line 3254)
* Winterference-size:                    Warning Options.    (line 3211)
* Winvalid-imported-macros:              C++ Dialect Options.
                                                             (line  717)
* Winvalid-memory-model:                 Warning Options.    (line 1320)
* Winvalid-offsetof:                     C++ Dialect Options.
                                                             (line 1263)
* Winvalid-pch:                          Warning Options.    (line 3263)
* Wjump-misses-init:                     Warning Options.    (line 2680)
* Wl:                                    Link Options.       (line  338)
* Wlarger-than-BYTE-SIZE:                Warning Options.    (line 2228)
* Wlarger-than=:                         Warning Options.    (line 2228)
* Wliteral-suffix:                       C++ Dialect Options.
                                                             (line  723)
* Wlogical-not-parentheses:              Warning Options.    (line 2828)
* Wlogical-op:                           Warning Options.    (line 2820)
* Wlong-long:                            Warning Options.    (line 3267)
* Wlto-type-mismatch:                    Warning Options.    (line 3403)
* Wmain:                                 Warning Options.    (line  813)
* Wmaybe-uninitialized:                  Warning Options.    (line 1337)
* Wmemset-elt-size:                      Warning Options.    (line 2762)
* Wmemset-transposed-args:               Warning Options.    (line 2770)
* Wmisleading-indentation:               Warning Options.    (line  820)
* Wmismatched-dealloc:                   Warning Options.    (line  930)
* Wmismatched-new-delete:                C++ Dialect Options.
                                                             (line 1042)
* Wmismatched-tags:                      C++ Dialect Options.
                                                             (line 1073)
* Wmissing-attributes:                   Warning Options.    (line  854)
* Wmissing-braces:                       Warning Options.    (line  898)
* Wmissing-declarations:                 Warning Options.    (line 2938)
* Wmissing-field-initializers:           Warning Options.    (line 2948)
* Wmissing-format-attribute:             Warning Options.    (line 1676)
* Wmissing-include-dirs:                 Warning Options.    (line  908)
* Wmissing-noreturn:                     Warning Options.    (line 1662)
* Wmissing-parameter-type:               Warning Options.    (line 2920)
* Wmissing-profile:                      Warning Options.    (line  914)
* Wmissing-prototypes:                   Warning Options.    (line 2928)
* Wmissing-requires:                     Warning Options.    (line 2978)
* Wmissing-template-keyword:             Warning Options.    (line 2995)
* Wmisspelled-isr:                       AVR Options.        (line  311)
* Wmultichar:                            Warning Options.    (line 3023)
* Wmultiple-inheritance:                 C++ Dialect Options.
                                                             (line 1098)
* Wmultistatement-macros:                Warning Options.    (line  961)
* Wnamespaces:                           C++ Dialect Options.
                                                             (line 1121)
* Wnarrowing:                            C++ Dialect Options.
                                                             (line  749)
* Wnested-externs:                       Warning Options.    (line 3195)
* Wno-abi:                               Warning Options.    (line  267)
* Wno-absolute-value:                    Warning Options.    (line 2352)
* Wno-addr-space-convert:                AVR Options.        (line  306)
* Wno-address:                           Warning Options.    (line 2781)
* Wno-address-of-packed-member:          Warning Options.    (line 2815)
* Wno-aggregate-return:                  Warning Options.    (line 2843)
* Wno-aggressive-loop-optimizations:     Warning Options.    (line 2848)
* Wno-aligned-new:                       C++ Dialect Options.
                                                             (line 1180)
* Wno-all:                               Warning Options.    (line  140)
* Wno-alloc-size-larger-than:            Warning Options.    (line 1715)
* Wno-alloc-size-larger-than <1>:        Warning Options.    (line 1726)
* Wno-alloc-zero:                        Warning Options.    (line 1705)
* Wno-alloca:                            Warning Options.    (line 1730)
* Wno-alloca-larger-than:                Warning Options.    (line 1733)
* Wno-alloca-larger-than <1>:            Warning Options.    (line 1794)
* Wno-analyzer-double-fclose:            Static Analyzer Options.
                                                             (line   51)
* Wno-analyzer-double-free:              Static Analyzer Options.
                                                             (line   58)
* Wno-analyzer-exposure-through-output-file: Static Analyzer Options.
                                                             (line   66)
* Wno-analyzer-file-leak:                Static Analyzer Options.
                                                             (line   74)
* Wno-analyzer-free-of-non-heap:         Static Analyzer Options.
                                                             (line   81)
* Wno-analyzer-malloc-leak:              Static Analyzer Options.
                                                             (line   89)
* Wno-analyzer-mismatching-deallocation: Static Analyzer Options.
                                                             (line   97)
* Wno-analyzer-null-argument:            Static Analyzer Options.
                                                             (line  123)
* Wno-analyzer-null-dereference:         Static Analyzer Options.
                                                             (line  131)
* Wno-analyzer-possible-null-argument:   Static Analyzer Options.
                                                             (line  108)
* Wno-analyzer-possible-null-dereference: Static Analyzer Options.
                                                             (line  116)
* Wno-analyzer-shift-count-negative:     Static Analyzer Options.
                                                             (line  138)
* Wno-analyzer-shift-count-overflow:     Static Analyzer Options.
                                                             (line  150)
* Wno-analyzer-stale-setjmp-buffer:      Static Analyzer Options.
                                                             (line  163)
* Wno-analyzer-tainted-allocation-size:  Static Analyzer Options.
                                                             (line  177)
* Wno-analyzer-tainted-array-index:      Static Analyzer Options.
                                                             (line  191)
* Wno-analyzer-tainted-divisor:          Static Analyzer Options.
                                                             (line  204)
* Wno-analyzer-tainted-offset:           Static Analyzer Options.
                                                             (line  214)
* Wno-analyzer-tainted-size:             Static Analyzer Options.
                                                             (line  227)
* Wno-analyzer-too-complex:              Static Analyzer Options.
                                                             (line   41)
* Wno-analyzer-unsafe-call-within-signal-handler: Static Analyzer Options.
                                                             (line  237)
* Wno-analyzer-use-after-free:           Static Analyzer Options.
                                                             (line  245)
* Wno-analyzer-use-of-pointer-in-stale-stack-frame: Static Analyzer Options.
                                                             (line  253)
* Wno-analyzer-use-of-uninitialized-value: Static Analyzer Options.
                                                             (line  280)
* Wno-analyzer-write-to-const:           Static Analyzer Options.
                                                             (line  260)
* Wno-analyzer-write-to-string-literal:  Static Analyzer Options.
                                                             (line  270)
* Wno-arith-conversion:                  Warning Options.    (line 1798)
* Wno-array-bounds:                      Warning Options.    (line 1811)
* Wno-array-compare:                     Warning Options.    (line 1830)
* Wno-array-parameter:                   Warning Options.    (line 1842)
* Wno-assign-intercept:                  Objective-C and Objective-C++ Dialect Options.
                                                             (line  170)
* Wno-attribute-alias:                   Warning Options.    (line 1886)
* Wno-attribute-warning:                 Warning Options.    (line 3072)
* Wno-attributes:                        Warning Options.    (line 2853)
* Wno-bad-function-cast:                 Warning Options.    (line 2421)
* Wno-bidi-chars:                        Warning Options.    (line 1918)
* Wno-bool-compare:                      Warning Options.    (line 1940)
* Wno-bool-operation:                    Warning Options.    (line 1949)
* Wno-builtin-declaration-mismatch:      Warning Options.    (line 2875)
* Wno-builtin-macro-redefined:           Warning Options.    (line 2896)
* Wno-c++-compat:                        Warning Options.    (line 2449)
* Wno-c++11-compat:                      Warning Options.    (line 2454)
* Wno-c++11-extensions:                  Warning Options.    (line 2472)
* Wno-c++14-compat:                      Warning Options.    (line 2460)
* Wno-c++14-extensions:                  Warning Options.    (line 2477)
* Wno-c++17-compat:                      Warning Options.    (line 2464)
* Wno-c++17-extensions:                  Warning Options.    (line 2482)
* Wno-c++20-compat:                      Warning Options.    (line 2468)
* Wno-c++20-extensions:                  Warning Options.    (line 2487)
* Wno-c++23-extensions:                  Warning Options.    (line 2492)
* Wno-c11-c2x-compat:                    Warning Options.    (line 2441)
* Wno-c90-c99-compat:                    Warning Options.    (line 2426)
* Wno-c99-c11-compat:                    Warning Options.    (line 2433)
* Wno-cast-align:                        Warning Options.    (line 2513)
* Wno-cast-function-type:                Warning Options.    (line 2524)
* Wno-cast-qual:                         Warning Options.    (line 2497)
* Wno-catch-value:                       C++ Dialect Options.
                                                             (line 1227)
* Wno-char-subscripts:                   Warning Options.    (line  377)
* Wno-class-conversion:                  C++ Dialect Options.
                                                             (line 1158)
* Wno-class-memaccess:                   C++ Dialect Options.
                                                             (line  785)
* Wno-clobbered:                         Warning Options.    (line 2550)
* Wno-comma-subscript:                   C++ Dialect Options.
                                                             (line  595)
* Wno-conditionally-supported:           C++ Dialect Options.
                                                             (line 1235)
* Wno-conversion:                        Warning Options.    (line 2554)
* Wno-conversion-null:                   C++ Dialect Options.
                                                             (line 1369)
* Wno-coverage-invalid-line-number:      Warning Options.    (line  396)
* Wno-coverage-mismatch:                 Warning Options.    (line  382)
* Wno-cpp:                               Warning Options.    (line  406)
* Wno-ctad-maybe-unsupported:            C++ Dialect Options.
                                                             (line  616)
* Wno-ctor-dtor-privacy:                 C++ Dialect Options.
                                                             (line  632)
* Wno-dangling-else:                     Warning Options.    (line 2575)
* Wno-dangling-pointer:                  Warning Options.    (line 2610)
* Wno-date-time:                         Warning Options.    (line 2657)
* Wno-declaration-after-statement:       Warning Options.    (line 2169)
* Wno-delete-incomplete:                 C++ Dialect Options.
                                                             (line 1238)
* Wno-delete-non-virtual-dtor:           C++ Dialect Options.
                                                             (line  639)
* Wno-deprecated:                        Warning Options.    (line 3079)
* Wno-deprecated-copy:                   C++ Dialect Options.
                                                             (line  646)
* Wno-deprecated-declarations:           Warning Options.    (line 3083)
* Wno-deprecated-enum-enum-conversion:   C++ Dialect Options.
                                                             (line  654)
* Wno-deprecated-enum-float-conversion:  C++ Dialect Options.
                                                             (line  668)
* Wno-designated-init:                   Warning Options.    (line 3409)
* Wno-disabled-optimization:             Warning Options.    (line 3360)
* Wno-discarded-array-qualifiers:        Warning Options.    (line 1988)
* Wno-discarded-qualifiers:              Warning Options.    (line 1982)
* Wno-div-by-zero:                       Warning Options.    (line 2029)
* Wno-double-promotion:                  Warning Options.    (line  409)
* Wno-duplicate-decl-specifier:          Warning Options.    (line  427)
* Wno-duplicated-branches:               Warning Options.    (line 1959)
* Wno-duplicated-cond:                   Warning Options.    (line 1970)
* Wno-effc++:                            C++ Dialect Options.
                                                             (line  951)
* Wno-empty-body:                        Warning Options.    (line 2662)
* Wno-endif-labels:                      Warning Options.    (line 2407)
* Wno-endif-labels <1>:                  Warning Options.    (line 2666)
* Wno-enum-compare:                      Warning Options.    (line 2669)
* Wno-enum-conversion:                   Warning Options.    (line 2675)
* Wno-error:                             Warning Options.    (line   28)
* Wno-error=:                            Warning Options.    (line   31)
* Wno-exceptions:                        C++ Dialect Options.
                                                             (line  979)
* Wno-extra:                             Warning Options.    (line  222)
* Wno-extra <1>:                         Warning Options.    (line 2948)
* Wno-extra <2>:                         Warning Options.    (line 3105)
* Wno-extra-semi:                        C++ Dialect Options.
                                                             (line 1243)
* Wno-fatal-errors:                      Warning Options.    (line   48)
* Wno-float-conversion:                  Warning Options.    (line 2703)
* Wno-float-equal:                       Warning Options.    (line 2069)
* Wno-format:                            Warning Options.    (line  432)
* Wno-format <1>:                        Warning Options.    (line 1676)
* Wno-format-contains-nul:               Warning Options.    (line  471)
* Wno-format-extra-args:                 Warning Options.    (line  475)
* Wno-format-nonliteral:                 Warning Options.    (line  568)
* Wno-format-overflow:                   Warning Options.    (line  489)
* Wno-format-overflow <1>:               Warning Options.    (line  500)
* Wno-format-security:                   Warning Options.    (line  573)
* Wno-format-signedness:                 Warning Options.    (line  584)
* Wno-format-truncation:                 Warning Options.    (line  589)
* Wno-format-truncation <1>:             Warning Options.    (line  601)
* Wno-format-y2k:                        Warning Options.    (line  612)
* Wno-format-zero-length:                Warning Options.    (line  564)
* Wno-frame-address:                     Warning Options.    (line 1976)
* Wno-frame-larger-than:                 Warning Options.    (line 2243)
* Wno-frame-larger-than <1>:             Warning Options.    (line 2256)
* Wno-free-nonheap-object:               Warning Options.    (line 2260)
* Wno-if-not-aligned:                    Warning Options.    (line  791)
* Wno-ignored-attributes:                Warning Options.    (line  806)
* Wno-ignored-qualifiers:                Warning Options.    (line  795)
* Wno-implicit:                          Warning Options.    (line  669)
* Wno-implicit-fallthrough:              Warning Options.    (line  673)
* Wno-implicit-function-declaration:     Warning Options.    (line  663)
* Wno-implicit-int:                      Warning Options.    (line  658)
* Wno-inaccessible-base:                 C++ Dialect Options.
                                                             (line 1247)
* Wno-incompatible-pointer-types:        Warning Options.    (line 1994)
* Wno-infinite-recursion:                Warning Options.    (line  637)
* Wno-inherited-variadic-ctor:           C++ Dialect Options.
                                                             (line 1258)
* Wno-init-list-lifetime:                C++ Dialect Options.
                                                             (line  682)
* Wno-init-self:                         Warning Options.    (line  643)
* Wno-inline:                            Warning Options.    (line 3198)
* Wno-int-conversion:                    Warning Options.    (line 2000)
* Wno-int-in-bool-context:               Warning Options.    (line 3246)
* Wno-int-to-pointer-cast:               Warning Options.    (line 3254)
* Wno-invalid-imported-macros:           C++ Dialect Options.
                                                             (line  717)
* Wno-invalid-memory-model:              Warning Options.    (line 1320)
* Wno-invalid-offsetof:                  C++ Dialect Options.
                                                             (line 1263)
* Wno-invalid-pch:                       Warning Options.    (line 3263)
* Wno-jump-misses-init:                  Warning Options.    (line 2680)
* Wno-larger-than:                       Warning Options.    (line 2239)
* Wno-literal-suffix:                    C++ Dialect Options.
                                                             (line  723)
* Wno-logical-not-parentheses:           Warning Options.    (line 2828)
* Wno-logical-op:                        Warning Options.    (line 2820)
* Wno-long-long:                         Warning Options.    (line 3267)
* Wno-lto-type-mismatch:                 Warning Options.    (line 3403)
* Wno-main:                              Warning Options.    (line  813)
* Wno-maybe-uninitialized:               Warning Options.    (line 1337)
* Wno-memset-elt-size:                   Warning Options.    (line 2762)
* Wno-memset-transposed-args:            Warning Options.    (line 2770)
* Wno-misleading-indentation:            Warning Options.    (line  820)
* Wno-mismatched-dealloc:                Warning Options.    (line  930)
* Wno-mismatched-new-delete:             C++ Dialect Options.
                                                             (line 1042)
* Wno-mismatched-tags:                   C++ Dialect Options.
                                                             (line 1073)
* Wno-missing-attributes:                Warning Options.    (line  854)
* Wno-missing-braces:                    Warning Options.    (line  898)
* Wno-missing-declarations:              Warning Options.    (line 2938)
* Wno-missing-field-initializers:        Warning Options.    (line 2948)
* Wno-missing-format-attribute:          Warning Options.    (line 1676)
* Wno-missing-include-dirs:              Warning Options.    (line  908)
* Wno-missing-noreturn:                  Warning Options.    (line 1662)
* Wno-missing-parameter-type:            Warning Options.    (line 2920)
* Wno-missing-profile:                   Warning Options.    (line  914)
* Wno-missing-prototypes:                Warning Options.    (line 2928)
* Wno-missing-requires:                  Warning Options.    (line 2978)
* Wno-missing-template-keyword:          Warning Options.    (line 2995)
* Wno-misspelled-isr:                    AVR Options.        (line  311)
* Wno-multichar:                         Warning Options.    (line 3023)
* Wno-multiple-inheritance:              C++ Dialect Options.
                                                             (line 1098)
* Wno-multistatement-macros:             Warning Options.    (line  961)
* Wno-namespaces:                        C++ Dialect Options.
                                                             (line 1121)
* Wno-narrowing:                         C++ Dialect Options.
                                                             (line  749)
* Wno-nested-externs:                    Warning Options.    (line 3195)
* Wno-noexcept:                          C++ Dialect Options.
                                                             (line  765)
* Wno-noexcept-type:                     C++ Dialect Options.
                                                             (line  771)
* Wno-non-template-friend:               C++ Dialect Options.
                                                             (line  991)
* Wno-non-virtual-dtor:                  C++ Dialect Options.
                                                             (line  805)
* Wno-nonnull:                           Warning Options.    (line  616)
* Wno-nonnull-compare:                   Warning Options.    (line  623)
* Wno-normalized:                        Warning Options.    (line 3029)
* Wno-null-dereference:                  Warning Options.    (line  630)
* Wno-odr:                               Warning Options.    (line 3092)
* Wno-old-style-cast:                    C++ Dialect Options.
                                                             (line 1000)
* Wno-old-style-declaration:             Warning Options.    (line 2907)
* Wno-old-style-definition:              Warning Options.    (line 2913)
* Wno-openacc-parallelism:               Warning Options.    (line 3096)
* Wno-openmp-simd:                       Warning Options.    (line 3100)
* Wno-overflow:                          Warning Options.    (line 3089)
* Wno-overlength-strings:                Warning Options.    (line 3380)
* Wno-overloaded-virtual:                C++ Dialect Options.
                                                             (line 1006)
* Wno-override-init:                     Warning Options.    (line 3105)
* Wno-override-init-side-effects:        Warning Options.    (line 3113)
* Wno-packed:                            Warning Options.    (line 3118)
* Wno-packed-bitfield-compat:            Warning Options.    (line 3135)
* Wno-packed-not-aligned:                Warning Options.    (line 3152)
* Wno-padded:                            Warning Options.    (line 3165)
* Wno-parentheses:                       Warning Options.    (line  981)
* Wno-pedantic:                          Warning Options.    (line   88)
* Wno-pedantic-ms-format:                Warning Options.    (line 2311)
* Wno-pessimizing-move:                  C++ Dialect Options.
                                                             (line  834)
* Wno-placement-new:                     C++ Dialect Options.
                                                             (line 1191)
* Wno-pmf-conversions:                   C++ Dialect Options.
                                                             (line 1025)
* Wno-pmf-conversions <1>:               Bound member functions.
                                                             (line   35)
* Wno-pointer-arith:                     Warning Options.    (line 2317)
* Wno-pointer-compare:                   Warning Options.    (line 2324)
* Wno-pointer-sign:                      Warning Options.    (line 3369)
* Wno-pointer-to-int-cast:               Warning Options.    (line 3259)
* Wno-pragmas:                           Warning Options.    (line 1397)
* Wno-prio-ctor-dtor:                    Warning Options.    (line 1402)
* Wno-property-assign-default:           Objective-C and Objective-C++ Dialect Options.
                                                             (line  174)
* Wno-protocol:                          Objective-C and Objective-C++ Dialect Options.
                                                             (line  178)
* Wno-range-loop-construct:              C++ Dialect Options.
                                                             (line  895)
* Wno-redundant-decls:                   Warning Options.    (line 3172)
* Wno-redundant-move:                    C++ Dialect Options.
                                                             (line  856)
* Wno-redundant-tags:                    C++ Dialect Options.
                                                             (line  924)
* Wno-register:                          C++ Dialect Options.
                                                             (line  813)
* Wno-reorder:                           C++ Dialect Options.
                                                             (line  820)
* Wno-restrict:                          Warning Options.    (line 3176)
* Wno-return-local-addr:                 Warning Options.    (line 1061)
* Wno-return-type:                       Warning Options.    (line 1065)
* Wno-scalar-storage-order:              Warning Options.    (line 2709)
* Wno-selector:                          Objective-C and Objective-C++ Dialect Options.
                                                             (line  195)
* Wno-sequence-point:                    Warning Options.    (line 1008)
* Wno-shadow:                            Warning Options.    (line 2175)
* Wno-shadow-ivar:                       Warning Options.    (line 2186)
* Wno-shift-count-negative:              Warning Options.    (line 1086)
* Wno-shift-count-overflow:              Warning Options.    (line 1090)
* Wno-shift-negative-value:              Warning Options.    (line 1094)
* Wno-shift-overflow:                    Warning Options.    (line 1099)
* Wno-sign-compare:                      Warning Options.    (line 2691)
* Wno-sign-conversion:                   Warning Options.    (line 2697)
* Wno-sign-promo:                        C++ Dialect Options.
                                                             (line 1029)
* Wno-sized-deallocation:                C++ Dialect Options.
                                                             (line 1275)
* Wno-sizeof-array-argument:             Warning Options.    (line 2757)
* Wno-sizeof-array-div:                  Warning Options.    (line 2713)
* Wno-sizeof-pointer-div:                Warning Options.    (line 2727)
* Wno-sizeof-pointer-memaccess:          Warning Options.    (line 2735)
* Wno-stack-protector:                   Warning Options.    (line 3375)
* Wno-stack-usage:                       Warning Options.    (line 2277)
* Wno-stack-usage <1>:                   Warning Options.    (line 2301)
* Wno-strict-aliasing:                   Warning Options.    (line 1410)
* Wno-strict-null-sentinel:              C++ Dialect Options.
                                                             (line  984)
* Wno-strict-overflow:                   Warning Options.    (line 1449)
* Wno-strict-prototypes:                 Warning Options.    (line 2901)
* Wno-strict-selector-match:             Objective-C and Objective-C++ Dialect Options.
                                                             (line  207)
* Wno-string-compare:                    Warning Options.    (line 1497)
* Wno-stringop-overflow:                 Warning Options.    (line 1519)
* Wno-stringop-overflow <1>:             Warning Options.    (line 1558)
* Wno-stringop-overread:                 Warning Options.    (line 1596)
* Wno-stringop-truncation:               Warning Options.    (line 1603)
* Wno-subobject-linkage:                 C++ Dialect Options.
                                                             (line  938)
* Wno-suggest-attribute=:                Warning Options.    (line 1654)
* Wno-suggest-attribute=cold:            Warning Options.    (line 1697)
* Wno-suggest-attribute=const:           Warning Options.    (line 1662)
* Wno-suggest-attribute=format:          Warning Options.    (line 1676)
* Wno-suggest-attribute=malloc:          Warning Options.    (line 1662)
* Wno-suggest-attribute=noreturn:        Warning Options.    (line 1662)
* Wno-suggest-attribute=pure:            Warning Options.    (line 1662)
* Wno-suggest-final-methods:             C++ Dialect Options.
                                                             (line 1295)
* Wno-suggest-final-types:               C++ Dialect Options.
                                                             (line 1286)
* Wno-suggest-override:                  C++ Dialect Options.
                                                             (line 1305)
* Wno-switch:                            Warning Options.    (line 1115)
* Wno-switch-bool:                       Warning Options.    (line 1135)
* Wno-switch-default:                    Warning Options.    (line 1123)
* Wno-switch-enum:                       Warning Options.    (line 1126)
* Wno-switch-outside-range:              Warning Options.    (line 1146)
* Wno-switch-unreachable:                Warning Options.    (line 1151)
* Wno-sync-nand:                         Warning Options.    (line 1175)
* Wno-system-headers:                    Warning Options.    (line 2034)
* Wno-tautological-compare:              Warning Options.    (line 2045)
* Wno-templates:                         C++ Dialect Options.
                                                             (line 1035)
* Wno-terminate:                         C++ Dialect Options.
                                                             (line 1128)
* Wno-traditional:                       Warning Options.    (line 2084)
* Wno-traditional-conversion:            Warning Options.    (line 2161)
* Wno-trampolines:                       Warning Options.    (line 2059)
* Wno-trivial-auto-var-init:             Warning Options.    (line 1180)
* Wno-tsan:                              Warning Options.    (line 2337)
* Wno-type-limits:                       Warning Options.    (line 2345)
* Wno-undeclared-selector:               Objective-C and Objective-C++ Dialect Options.
                                                             (line  215)
* Wno-undef:                             Warning Options.    (line 2378)
* Wno-uninitialized:                     Warning Options.    (line 1282)
* Wno-unknown-pragmas:                   Warning Options.    (line 1390)
* Wno-unsafe-loop-optimizations:         Warning Options.    (line 2305)
* Wno-unsuffixed-float-constants:        Warning Options.    (line 3395)
* Wno-unused:                            Warning Options.    (line 1275)
* Wno-unused-but-set-parameter:          Warning Options.    (line 1186)
* Wno-unused-but-set-variable:           Warning Options.    (line 1195)
* Wno-unused-const-variable:             Warning Options.    (line 1242)
* Wno-unused-function:                   Warning Options.    (line 1205)
* Wno-unused-label:                      Warning Options.    (line 1210)
* Wno-unused-local-typedefs:             Warning Options.    (line 1217)
* Wno-unused-parameter:                  Warning Options.    (line 1221)
* Wno-unused-result:                     Warning Options.    (line 1228)
* Wno-unused-value:                      Warning Options.    (line 1265)
* Wno-unused-variable:                   Warning Options.    (line 1233)
* Wno-use-after-free:                    C++ Dialect Options.
                                                             (line 1310)
* Wno-useless-cast:                      C++ Dialect Options.
                                                             (line 1366)
* Wno-varargs:                           Warning Options.    (line 3278)
* Wno-variadic-macros:                   Warning Options.    (line 3272)
* Wno-vector-operation-performance:      Warning Options.    (line 3283)
* Wno-vexing-parse:                      C++ Dialect Options.
                                                             (line 1132)
* Wno-virtual-inheritance:               C++ Dialect Options.
                                                             (line 1105)
* Wno-virtual-move-assign:               C++ Dialect Options.
                                                             (line 1112)
* Wno-vla:                               Warning Options.    (line 3293)
* Wno-vla-larger-than:                   Warning Options.    (line 3297)
* Wno-vla-larger-than <1>:               Warning Options.    (line 3314)
* Wno-vla-parameter:                     Warning Options.    (line 3318)
* Wno-volatile:                          C++ Dialect Options.
                                                             (line 1163)
* Wno-volatile-register-var:             Warning Options.    (line 3354)
* Wno-write-strings:                     Warning Options.    (line 2537)
* Wno-zero-as-null-pointer-constant:     C++ Dialect Options.
                                                             (line 1176)
* Wnoexcept:                             C++ Dialect Options.
                                                             (line  765)
* Wnoexcept-type:                        C++ Dialect Options.
                                                             (line  771)
* Wnon-template-friend:                  C++ Dialect Options.
                                                             (line  991)
* Wnon-virtual-dtor:                     C++ Dialect Options.
                                                             (line  805)
* Wnonnull:                              Warning Options.    (line  616)
* Wnonnull-compare:                      Warning Options.    (line  623)
* Wnormalized:                           Warning Options.    (line 3029)
* Wnormalized=:                          Warning Options.    (line 3029)
* Wnull-dereference:                     Warning Options.    (line  630)
* Wobjc-root-class:                      Objective-C and Objective-C++ Dialect Options.
                                                             (line  188)
* Wodr:                                  Warning Options.    (line 3092)
* Wold-style-cast:                       C++ Dialect Options.
                                                             (line 1000)
* Wold-style-declaration:                Warning Options.    (line 2907)
* Wold-style-definition:                 Warning Options.    (line 2913)
* Wopenacc-parallelism:                  Warning Options.    (line 3096)
* Wopenmp-simd:                          Warning Options.    (line 3100)
* Woverflow:                             Warning Options.    (line 3089)
* Woverlength-strings:                   Warning Options.    (line 3380)
* Woverloaded-virtual:                   C++ Dialect Options.
                                                             (line 1006)
* Woverride-init:                        Warning Options.    (line 3105)
* Woverride-init-side-effects:           Warning Options.    (line 3113)
* Wp:                                    Preprocessor Options.
                                                             (line  463)
* Wpacked:                               Warning Options.    (line 3118)
* Wpacked-bitfield-compat:               Warning Options.    (line 3135)
* Wpacked-not-aligned:                   Warning Options.    (line 3152)
* Wpadded:                               Warning Options.    (line 3165)
* Wparentheses:                          Warning Options.    (line  981)
* Wpedantic:                             Warning Options.    (line   88)
* Wpedantic-ms-format:                   Warning Options.    (line 2311)
* Wpessimizing-move:                     C++ Dialect Options.
                                                             (line  834)
* Wplacement-new:                        C++ Dialect Options.
                                                             (line 1191)
* Wpmf-conversions:                      C++ Dialect Options.
                                                             (line 1025)
* Wpointer-arith:                        Warning Options.    (line 2317)
* Wpointer-arith <1>:                    Pointer Arith.      (line   13)
* Wpointer-compare:                      Warning Options.    (line 2324)
* Wpointer-sign:                         Warning Options.    (line 3369)
* Wpointer-to-int-cast:                  Warning Options.    (line 3259)
* Wpragmas:                              Warning Options.    (line 1397)
* Wprio-ctor-dtor:                       Warning Options.    (line 1402)
* Wproperty-assign-default:              Objective-C and Objective-C++ Dialect Options.
                                                             (line  174)
* Wprotocol:                             Objective-C and Objective-C++ Dialect Options.
                                                             (line  178)
* Wrange-loop-construct:                 C++ Dialect Options.
                                                             (line  895)
* wrapper:                               Overall Options.    (line  620)
* Wredundant-decls:                      Warning Options.    (line 3172)
* Wredundant-move:                       C++ Dialect Options.
                                                             (line  856)
* Wredundant-tags:                       C++ Dialect Options.
                                                             (line  924)
* Wregister:                             C++ Dialect Options.
                                                             (line  813)
* Wreorder:                              C++ Dialect Options.
                                                             (line  820)
* Wrestrict:                             Warning Options.    (line 3176)
* Wreturn-local-addr:                    Warning Options.    (line 1061)
* Wreturn-type:                          Warning Options.    (line 1065)
* Wscalar-storage-order:                 Warning Options.    (line 2709)
* Wselector:                             Objective-C and Objective-C++ Dialect Options.
                                                             (line  195)
* Wsequence-point:                       Warning Options.    (line 1008)
* Wshadow:                               Warning Options.    (line 2175)
* Wshadow-ivar:                          Warning Options.    (line 2186)
* Wshadow=compatible-local:              Warning Options.    (line 2197)
* Wshadow=global:                        Warning Options.    (line 2190)
* Wshadow=local:                         Warning Options.    (line 2193)
* Wshift-count-negative:                 Warning Options.    (line 1086)
* Wshift-count-overflow:                 Warning Options.    (line 1090)
* Wshift-negative-value:                 Warning Options.    (line 1094)
* Wshift-overflow:                       Warning Options.    (line 1099)
* Wsign-compare:                         Warning Options.    (line 2691)
* Wsign-conversion:                      Warning Options.    (line 2697)
* Wsign-promo:                           C++ Dialect Options.
                                                             (line 1029)
* Wsized-deallocation:                   C++ Dialect Options.
                                                             (line 1275)
* Wsizeof-array-argument:                Warning Options.    (line 2757)
* Wsizeof-array-div:                     Warning Options.    (line 2713)
* Wsizeof-pointer-div:                   Warning Options.    (line 2727)
* Wsizeof-pointer-memaccess:             Warning Options.    (line 2735)
* Wstack-protector:                      Warning Options.    (line 3375)
* Wstack-usage:                          Warning Options.    (line 2277)
* Wstrict-aliasing:                      Warning Options.    (line 1410)
* Wstrict-aliasing=n:                    Warning Options.    (line 1417)
* Wstrict-null-sentinel:                 C++ Dialect Options.
                                                             (line  984)
* Wstrict-overflow:                      Warning Options.    (line 1449)
* Wstrict-prototypes:                    Warning Options.    (line 2901)
* Wstrict-selector-match:                Objective-C and Objective-C++ Dialect Options.
                                                             (line  207)
* Wstring-compare:                       Warning Options.    (line 1497)
* Wstringop-overflow:                    Warning Options.    (line 1519)
* Wstringop-overflow <1>:                Warning Options.    (line 1558)
* Wstringop-overread:                    Warning Options.    (line 1596)
* Wstringop-truncation:                  Warning Options.    (line 1603)
* Wsubobject-linkage:                    C++ Dialect Options.
                                                             (line  938)
* Wsuggest-attribute=:                   Warning Options.    (line 1654)
* Wsuggest-attribute=cold:               Warning Options.    (line 1697)
* Wsuggest-attribute=const:              Warning Options.    (line 1662)
* Wsuggest-attribute=format:             Warning Options.    (line 1676)
* Wsuggest-attribute=malloc:             Warning Options.    (line 1662)
* Wsuggest-attribute=noreturn:           Warning Options.    (line 1662)
* Wsuggest-attribute=pure:               Warning Options.    (line 1662)
* Wsuggest-final-methods:                C++ Dialect Options.
                                                             (line 1295)
* Wsuggest-final-types:                  C++ Dialect Options.
                                                             (line 1286)
* Wsuggest-override:                     C++ Dialect Options.
                                                             (line 1305)
* Wswitch:                               Warning Options.    (line 1115)
* Wswitch-bool:                          Warning Options.    (line 1135)
* Wswitch-default:                       Warning Options.    (line 1123)
* Wswitch-enum:                          Warning Options.    (line 1126)
* Wswitch-outside-range:                 Warning Options.    (line 1146)
* Wswitch-unreachable:                   Warning Options.    (line 1151)
* Wsync-nand:                            Warning Options.    (line 1175)
* Wsystem-headers:                       Warning Options.    (line 2034)
* Wtautological-compare:                 Warning Options.    (line 2045)
* Wtemplates:                            C++ Dialect Options.
                                                             (line 1035)
* Wterminate:                            C++ Dialect Options.
                                                             (line 1128)
* Wtraditional:                          Warning Options.    (line 2084)
* Wtraditional-conversion:               Warning Options.    (line 2161)
* Wtrampolines:                          Warning Options.    (line 2059)
* Wtrigraphs:                            Warning Options.    (line 2368)
* Wtrivial-auto-var-init:                Warning Options.    (line 1180)
* Wtsan:                                 Warning Options.    (line 2337)
* Wtype-limits:                          Warning Options.    (line 2345)
* Wundeclared-selector:                  Objective-C and Objective-C++ Dialect Options.
                                                             (line  215)
* Wundef:                                Warning Options.    (line 2378)
* Wuninitialized:                        Warning Options.    (line 1282)
* Wunknown-pragmas:                      Warning Options.    (line 1390)
* Wunsafe-loop-optimizations:            Warning Options.    (line 2305)
* Wunsuffixed-float-constants:           Warning Options.    (line 3395)
* Wunused:                               Warning Options.    (line 1275)
* Wunused-but-set-parameter:             Warning Options.    (line 1186)
* Wunused-but-set-variable:              Warning Options.    (line 1195)
* Wunused-const-variable:                Warning Options.    (line 1242)
* Wunused-function:                      Warning Options.    (line 1205)
* Wunused-label:                         Warning Options.    (line 1210)
* Wunused-local-typedefs:                Warning Options.    (line 1217)
* Wunused-macros:                        Warning Options.    (line 2388)
* Wunused-parameter:                     Warning Options.    (line 1221)
* Wunused-result:                        Warning Options.    (line 1228)
* Wunused-value:                         Warning Options.    (line 1265)
* Wunused-variable:                      Warning Options.    (line 1233)
* Wuse-after-free:                       C++ Dialect Options.
                                                             (line 1310)
* Wuseless-cast:                         C++ Dialect Options.
                                                             (line 1366)
* Wvarargs:                              Warning Options.    (line 3278)
* Wvariadic-macros:                      Warning Options.    (line 3272)
* Wvector-operation-performance:         Warning Options.    (line 3283)
* Wvexing-parse:                         C++ Dialect Options.
                                                             (line 1132)
* Wvirtual-inheritance:                  C++ Dialect Options.
                                                             (line 1105)
* Wvirtual-move-assign:                  C++ Dialect Options.
                                                             (line 1112)
* Wvla:                                  Warning Options.    (line 3293)
* Wvla-larger-than=:                     Warning Options.    (line 3297)
* Wvolatile:                             C++ Dialect Options.
                                                             (line 1163)
* Wvolatile-register-var:                Warning Options.    (line 3354)
* Wwrite-strings:                        Warning Options.    (line 2537)
* Wzero-as-null-pointer-constant:        C++ Dialect Options.
                                                             (line 1176)
* Wzero-length-bounds:                   Warning Options.    (line 2006)
* Wzero-length-bounds <1>:               Warning Options.    (line 2006)
* x:                                     Overall Options.    (line  135)
* Xassembler:                            Assembler Options.  (line   13)
* Xbind-lazy:                            VxWorks Options.    (line   26)
* Xbind-now:                             VxWorks Options.    (line   30)
* Xlinker:                               Link Options.       (line  320)
* Xpreprocessor:                         Preprocessor Options.
                                                             (line  474)
* Ym:                                    System V Options.   (line   26)
* YP:                                    System V Options.   (line   22)
* z:                                     Link Options.       (line  351)


File: gcc.info,  Node: Keyword Index,  Prev: Option Index,  Up: Top

Keyword Index
*************

[index]
* Menu:

* _ in variables in macros:              Typeof.             (line   46)
* __atomic_add_fetch:                    __atomic Builtins.  (line  177)
* __atomic_always_lock_free:             __atomic Builtins.  (line  265)
* __atomic_and_fetch:                    __atomic Builtins.  (line  181)
* __atomic_clear:                        __atomic Builtins.  (line  239)
* __atomic_compare_exchange:             __atomic Builtins.  (line  169)
* __atomic_compare_exchange_n:           __atomic Builtins.  (line  145)
* __atomic_exchange:                     __atomic Builtins.  (line  139)
* __atomic_exchange_n:                   __atomic Builtins.  (line  131)
* __atomic_fetch_add:                    __atomic Builtins.  (line  202)
* __atomic_fetch_and:                    __atomic Builtins.  (line  206)
* __atomic_fetch_nand:                   __atomic Builtins.  (line  212)
* __atomic_fetch_or:                     __atomic Builtins.  (line  210)
* __atomic_fetch_sub:                    __atomic Builtins.  (line  204)
* __atomic_fetch_xor:                    __atomic Builtins.  (line  208)
* __atomic_is_lock_free:                 __atomic Builtins.  (line  279)
* __atomic_load:                         __atomic Builtins.  (line  113)
* __atomic_load_n:                       __atomic Builtins.  (line  106)
* __atomic_nand_fetch:                   __atomic Builtins.  (line  187)
* __atomic_or_fetch:                     __atomic Builtins.  (line  185)
* __atomic_signal_fence:                 __atomic Builtins.  (line  258)
* __atomic_store:                        __atomic Builtins.  (line  126)
* __atomic_store_n:                      __atomic Builtins.  (line  118)
* __atomic_sub_fetch:                    __atomic Builtins.  (line  179)
* __atomic_test_and_set:                 __atomic Builtins.  (line  227)
* __atomic_thread_fence:                 __atomic Builtins.  (line  251)
* __atomic_xor_fetch:                    __atomic Builtins.  (line  183)
* __builtin___clear_cache:               Other Builtins.     (line  768)
* __builtin___fprintf_chk:               Object Size Checking.
                                                             (line    6)
* __builtin___memcpy_chk:                Object Size Checking.
                                                             (line    6)
* __builtin___memmove_chk:               Object Size Checking.
                                                             (line    6)
* __builtin___mempcpy_chk:               Object Size Checking.
                                                             (line    6)
* __builtin___memset_chk:                Object Size Checking.
                                                             (line    6)
* __builtin___printf_chk:                Object Size Checking.
                                                             (line    6)
* __builtin___snprintf_chk:              Object Size Checking.
                                                             (line    6)
* __builtin___sprintf_chk:               Object Size Checking.
                                                             (line    6)
* __builtin___stpcpy_chk:                Object Size Checking.
                                                             (line    6)
* __builtin___strcat_chk:                Object Size Checking.
                                                             (line    6)
* __builtin___strcpy_chk:                Object Size Checking.
                                                             (line    6)
* __builtin___strncat_chk:               Object Size Checking.
                                                             (line    6)
* __builtin___strncpy_chk:               Object Size Checking.
                                                             (line    6)
* __builtin___vfprintf_chk:              Object Size Checking.
                                                             (line    6)
* __builtin___vprintf_chk:               Object Size Checking.
                                                             (line    6)
* __builtin___vsnprintf_chk:             Object Size Checking.
                                                             (line    6)
* __builtin___vsprintf_chk:              Object Size Checking.
                                                             (line    6)
* __builtin_add_overflow:                Integer Overflow Builtins.
                                                             (line    9)
* __builtin_add_overflow_p:              Integer Overflow Builtins.
                                                             (line   86)
* __builtin_addf128_round_to_odd:        Basic PowerPC Built-in Functions Available on ISA 3.0.
                                                             (line   17)
* __builtin_alloca:                      Other Builtins.     (line    6)
* __builtin_alloca_with_align:           Other Builtins.     (line    6)
* __builtin_alloca_with_align_and_max:   Other Builtins.     (line    6)
* __builtin_apply:                       Constructing Calls. (line   29)
* __builtin_apply_args:                  Constructing Calls. (line   19)
* __builtin_arc_aligned:                 ARC Built-in Functions.
                                                             (line   18)
* __builtin_arc_brk:                     ARC Built-in Functions.
                                                             (line   28)
* __builtin_arc_core_read:               ARC Built-in Functions.
                                                             (line   32)
* __builtin_arc_core_write:              ARC Built-in Functions.
                                                             (line   39)
* __builtin_arc_divaw:                   ARC Built-in Functions.
                                                             (line   46)
* __builtin_arc_flag:                    ARC Built-in Functions.
                                                             (line   53)
* __builtin_arc_lr:                      ARC Built-in Functions.
                                                             (line   57)
* __builtin_arc_mul64:                   ARC Built-in Functions.
                                                             (line   64)
* __builtin_arc_mulu64:                  ARC Built-in Functions.
                                                             (line   68)
* __builtin_arc_nop:                     ARC Built-in Functions.
                                                             (line   73)
* __builtin_arc_norm:                    ARC Built-in Functions.
                                                             (line   77)
* __builtin_arc_normw:                   ARC Built-in Functions.
                                                             (line   84)
* __builtin_arc_rtie:                    ARC Built-in Functions.
                                                             (line   91)
* __builtin_arc_sleep:                   ARC Built-in Functions.
                                                             (line   95)
* __builtin_arc_sr:                      ARC Built-in Functions.
                                                             (line   99)
* __builtin_arc_swap:                    ARC Built-in Functions.
                                                             (line  106)
* __builtin_arc_swi:                     ARC Built-in Functions.
                                                             (line  112)
* __builtin_arc_sync:                    ARC Built-in Functions.
                                                             (line  116)
* __builtin_arc_trap_s:                  ARC Built-in Functions.
                                                             (line  120)
* __builtin_arc_unimp_s:                 ARC Built-in Functions.
                                                             (line  124)
* __builtin_assoc_barrier:               Other Builtins.     (line  695)
* __builtin_assume_aligned:              Other Builtins.     (line  710)
* __builtin_bit_cast:                    Other Builtins.     (line  581)
* __builtin_bswap128:                    Other Builtins.     (line 1055)
* __builtin_bswap16:                     Other Builtins.     (line 1043)
* __builtin_bswap32:                     Other Builtins.     (line 1047)
* __builtin_bswap64:                     Other Builtins.     (line 1051)
* __builtin_call_with_static_chain:      Other Builtins.     (line    6)
* __builtin_call_with_static_chain <1>:  Other Builtins.     (line  393)
* __builtin_cfuged:                      Basic PowerPC Built-in Functions Available on ISA 3.1.
                                                             (line   18)
* __builtin_choose_expr:                 Other Builtins.     (line  404)
* __builtin_clear_padding:               Other Builtins.     (line  561)
* __builtin_clrsb:                       Other Builtins.     (line  973)
* __builtin_clrsbl:                      Other Builtins.     (line  995)
* __builtin_clrsbll:                     Other Builtins.     (line 1018)
* __builtin_clz:                         Other Builtins.     (line  965)
* __builtin_clzl:                        Other Builtins.     (line  987)
* __builtin_clzll:                       Other Builtins.     (line 1010)
* __builtin_cntlzdm:                     Basic PowerPC Built-in Functions Available on ISA 3.1.
                                                             (line   23)
* __builtin_cnttzdm:                     Basic PowerPC Built-in Functions Available on ISA 3.1.
                                                             (line   28)
* __builtin_complex:                     Complex.            (line   82)
* __builtin_constant_p:                  Other Builtins.     (line  498)
* __builtin_convertvector:               Vector Extensions.  (line  189)
* __builtin_cpu_init:                    Basic PowerPC Built-in Functions Available on all Configurations.
                                                             (line    6)
* __builtin_cpu_init <1>:                x86 Built-in Functions.
                                                             (line   68)
* __builtin_cpu_is:                      Basic PowerPC Built-in Functions Available on all Configurations.
                                                             (line   10)
* __builtin_cpu_is <1>:                  x86 Built-in Functions.
                                                             (line   96)
* __builtin_cpu_supports:                Basic PowerPC Built-in Functions Available on all Configurations.
                                                             (line   70)
* __builtin_cpu_supports <1>:            x86 Built-in Functions.
                                                             (line  262)
* __builtin_ctz:                         Other Builtins.     (line  969)
* __builtin_ctzl:                        Other Builtins.     (line  991)
* __builtin_ctzll:                       Other Builtins.     (line 1014)
* __builtin_divf128_round_to_odd:        Basic PowerPC Built-in Functions Available on ISA 3.0.
                                                             (line   29)
* __builtin_dynamic_object_size:         Object Size Checking.
                                                             (line    6)
* __builtin_dynamic_object_size <1>:     Object Size Checking.
                                                             (line   53)
* __builtin_expect:                      Other Builtins.     (line  595)
* __builtin_expect_with_probability:     Other Builtins.     (line  630)
* __builtin_extend_pointer:              Other Builtins.     (line    6)
* __builtin_extend_pointer <1>:          Other Builtins.     (line 1060)
* __builtin_extract_return_addr:         Return Address.     (line   50)
* __builtin_ffs:                         Other Builtins.     (line  961)
* __builtin_ffsl:                        Other Builtins.     (line  984)
* __builtin_ffsll:                       Other Builtins.     (line 1006)
* __builtin_FILE:                        Other Builtins.     (line  743)
* __builtin_fmaf128_round_to_odd:        Basic PowerPC Built-in Functions Available on ISA 3.0.
                                                             (line   37)
* __builtin_fpclassify:                  Other Builtins.     (line    6)
* __builtin_fpclassify <1>:              Other Builtins.     (line  845)
* __builtin_frame_address:               Return Address.     (line   62)
* __builtin_frob_return_addr:            Return Address.     (line   59)
* __builtin_FUNCTION:                    Other Builtins.     (line  735)
* __builtin_goacc_parlevel_id:           Other Builtins.     (line 1067)
* __builtin_goacc_parlevel_size:         Other Builtins.     (line 1071)
* __builtin_has_attribute:               Other Builtins.     (line    6)
* __builtin_has_attribute <1>:           Other Builtins.     (line  228)
* __builtin_huge_val:                    Other Builtins.     (line  825)
* __builtin_huge_valf:                   Other Builtins.     (line  830)
* __builtin_huge_valfN:                  Other Builtins.     (line  837)
* __builtin_huge_valfNx:                 Other Builtins.     (line  841)
* __builtin_huge_vall:                   Other Builtins.     (line  833)
* __builtin_huge_valq:                   x86 Built-in Functions.
                                                             (line   50)
* __builtin_inf:                         Other Builtins.     (line  856)
* __builtin_infd128:                     Other Builtins.     (line  866)
* __builtin_infd32:                      Other Builtins.     (line  860)
* __builtin_infd64:                      Other Builtins.     (line  863)
* __builtin_inff:                        Other Builtins.     (line  870)
* __builtin_inffN:                       Other Builtins.     (line  879)
* __builtin_inffNx:                      Other Builtins.     (line  882)
* __builtin_infl:                        Other Builtins.     (line  875)
* __builtin_infq:                        x86 Built-in Functions.
                                                             (line   47)
* __builtin_is_constant_evaluated:       Other Builtins.     (line  543)
* __builtin_isfinite:                    Other Builtins.     (line    6)
* __builtin_isgreater:                   Other Builtins.     (line    6)
* __builtin_isgreaterequal:              Other Builtins.     (line    6)
* __builtin_isinf_sign:                  Other Builtins.     (line    6)
* __builtin_isinf_sign <1>:              Other Builtins.     (line  885)
* __builtin_isless:                      Other Builtins.     (line    6)
* __builtin_islessequal:                 Other Builtins.     (line    6)
* __builtin_islessgreater:               Other Builtins.     (line    6)
* __builtin_isnormal:                    Other Builtins.     (line    6)
* __builtin_isunordered:                 Other Builtins.     (line    6)
* __builtin_LINE:                        Other Builtins.     (line  728)
* __builtin_longjmp:                     Nonlocal Gotos.     (line   37)
* __builtin_mul_overflow:                Integer Overflow Builtins.
                                                             (line   63)
* __builtin_mul_overflow_p:              Integer Overflow Builtins.
                                                             (line   90)
* __builtin_mulf128_round_to_odd:        Basic PowerPC Built-in Functions Available on ISA 3.0.
                                                             (line   25)
* __builtin_nan:                         Other Builtins.     (line  893)
* __builtin_nand128:                     Other Builtins.     (line  915)
* __builtin_nand32:                      Other Builtins.     (line  909)
* __builtin_nand64:                      Other Builtins.     (line  912)
* __builtin_nanf:                        Other Builtins.     (line  919)
* __builtin_nanfN:                       Other Builtins.     (line  926)
* __builtin_nanfNx:                      Other Builtins.     (line  929)
* __builtin_nanl:                        Other Builtins.     (line  922)
* __builtin_nanq:                        x86 Built-in Functions.
                                                             (line   54)
* __builtin_nans:                        Other Builtins.     (line  932)
* __builtin_nansd128:                    Other Builtins.     (line  944)
* __builtin_nansd32:                     Other Builtins.     (line  936)
* __builtin_nansd64:                     Other Builtins.     (line  940)
* __builtin_nansf:                       Other Builtins.     (line  948)
* __builtin_nansfN:                      Other Builtins.     (line  955)
* __builtin_nansfNx:                     Other Builtins.     (line  958)
* __builtin_nansl:                       Other Builtins.     (line  951)
* __builtin_nansq:                       x86 Built-in Functions.
                                                             (line   57)
* __builtin_nds32_isb:                   NDS32 Built-in Functions.
                                                             (line   12)
* __builtin_nds32_isync:                 NDS32 Built-in Functions.
                                                             (line    8)
* __builtin_nds32_mfsr:                  NDS32 Built-in Functions.
                                                             (line   15)
* __builtin_nds32_mfusr:                 NDS32 Built-in Functions.
                                                             (line   18)
* __builtin_nds32_mtsr:                  NDS32 Built-in Functions.
                                                             (line   21)
* __builtin_nds32_mtusr:                 NDS32 Built-in Functions.
                                                             (line   24)
* __builtin_nds32_setgie_dis:            NDS32 Built-in Functions.
                                                             (line   30)
* __builtin_nds32_setgie_en:             NDS32 Built-in Functions.
                                                             (line   27)
* __builtin_non_tx_store:                S/390 System z Built-in Functions.
                                                             (line   98)
* __builtin_object_size:                 Object Size Checking.
                                                             (line    6)
* __builtin_object_size <1>:             Object Size Checking.
                                                             (line   16)
* __builtin_object_size <2>:             Other Builtins.     (line    6)
* __builtin_offsetof:                    Offsetof.           (line    6)
* __builtin_parity:                      Other Builtins.     (line  981)
* __builtin_parityl:                     Other Builtins.     (line 1002)
* __builtin_parityll:                    Other Builtins.     (line 1026)
* __builtin_pdepd:                       Basic PowerPC Built-in Functions Available on ISA 3.1.
                                                             (line   33)
* __builtin_pextd:                       Basic PowerPC Built-in Functions Available on ISA 3.1.
                                                             (line   38)
* __builtin_popcount:                    Other Builtins.     (line  978)
* __builtin_popcountl:                   Other Builtins.     (line  998)
* __builtin_popcountll:                  Other Builtins.     (line 1022)
* __builtin_powi:                        Other Builtins.     (line    6)
* __builtin_powi <1>:                    Other Builtins.     (line 1030)
* __builtin_powif:                       Other Builtins.     (line    6)
* __builtin_powif <1>:                   Other Builtins.     (line 1035)
* __builtin_powil:                       Other Builtins.     (line    6)
* __builtin_powil <1>:                   Other Builtins.     (line 1039)
* __builtin_prefetch:                    Other Builtins.     (line  781)
* __builtin_return:                      Constructing Calls. (line   47)
* __builtin_return_address:              Return Address.     (line    9)
* __builtin_rx_brk:                      RX Built-in Functions.
                                                             (line   10)
* __builtin_rx_clrpsw:                   RX Built-in Functions.
                                                             (line   13)
* __builtin_rx_int:                      RX Built-in Functions.
                                                             (line   17)
* __builtin_rx_machi:                    RX Built-in Functions.
                                                             (line   21)
* __builtin_rx_maclo:                    RX Built-in Functions.
                                                             (line   26)
* __builtin_rx_mulhi:                    RX Built-in Functions.
                                                             (line   31)
* __builtin_rx_mullo:                    RX Built-in Functions.
                                                             (line   36)
* __builtin_rx_mvfachi:                  RX Built-in Functions.
                                                             (line   41)
* __builtin_rx_mvfacmi:                  RX Built-in Functions.
                                                             (line   45)
* __builtin_rx_mvfc:                     RX Built-in Functions.
                                                             (line   49)
* __builtin_rx_mvtachi:                  RX Built-in Functions.
                                                             (line   53)
* __builtin_rx_mvtaclo:                  RX Built-in Functions.
                                                             (line   57)
* __builtin_rx_mvtc:                     RX Built-in Functions.
                                                             (line   61)
* __builtin_rx_mvtipl:                   RX Built-in Functions.
                                                             (line   65)
* __builtin_rx_racw:                     RX Built-in Functions.
                                                             (line   69)
* __builtin_rx_revw:                     RX Built-in Functions.
                                                             (line   73)
* __builtin_rx_rmpa:                     RX Built-in Functions.
                                                             (line   78)
* __builtin_rx_round:                    RX Built-in Functions.
                                                             (line   82)
* __builtin_rx_sat:                      RX Built-in Functions.
                                                             (line   87)
* __builtin_rx_setpsw:                   RX Built-in Functions.
                                                             (line   91)
* __builtin_rx_wait:                     RX Built-in Functions.
                                                             (line   95)
* __builtin_sadd_overflow:               Integer Overflow Builtins.
                                                             (line   11)
* __builtin_saddl_overflow:              Integer Overflow Builtins.
                                                             (line   13)
* __builtin_saddll_overflow:             Integer Overflow Builtins.
                                                             (line   15)
* __builtin_set_thread_pointer:          SH Built-in Functions.
                                                             (line    9)
* __builtin_setjmp:                      Nonlocal Gotos.     (line   32)
* __builtin_sh_get_fpscr:                SH Built-in Functions.
                                                             (line   34)
* __builtin_sh_set_fpscr:                SH Built-in Functions.
                                                             (line   37)
* __builtin_shuffle:                     Vector Extensions.  (line  127)
* __builtin_shufflevector:               Vector Extensions.  (line  165)
* __builtin_smul_overflow:               Integer Overflow Builtins.
                                                             (line   65)
* __builtin_smull_overflow:              Integer Overflow Builtins.
                                                             (line   67)
* __builtin_smulll_overflow:             Integer Overflow Builtins.
                                                             (line   69)
* __builtin_speculation_safe_value:      Other Builtins.     (line    6)
* __builtin_speculation_safe_value <1>:  Other Builtins.     (line  269)
* __builtin_sqrtf128_round_to_odd:       Basic PowerPC Built-in Functions Available on ISA 3.0.
                                                             (line   33)
* __builtin_ssub_overflow:               Integer Overflow Builtins.
                                                             (line   45)
* __builtin_ssubl_overflow:              Integer Overflow Builtins.
                                                             (line   47)
* __builtin_ssubll_overflow:             Integer Overflow Builtins.
                                                             (line   49)
* __builtin_sub_overflow:                Integer Overflow Builtins.
                                                             (line   43)
* __builtin_sub_overflow_p:              Integer Overflow Builtins.
                                                             (line   88)
* __builtin_subf128_round_to_odd:        Basic PowerPC Built-in Functions Available on ISA 3.0.
                                                             (line   21)
* __builtin_tabort:                      S/390 System z Built-in Functions.
                                                             (line   82)
* __builtin_tbegin:                      S/390 System z Built-in Functions.
                                                             (line    6)
* __builtin_tbegin_nofloat:              S/390 System z Built-in Functions.
                                                             (line   54)
* __builtin_tbegin_retry:                S/390 System z Built-in Functions.
                                                             (line   60)
* __builtin_tbegin_retry_nofloat:        S/390 System z Built-in Functions.
                                                             (line   67)
* __builtin_tbeginc:                     S/390 System z Built-in Functions.
                                                             (line   73)
* __builtin_tend:                        S/390 System z Built-in Functions.
                                                             (line   77)
* __builtin_tgmath:                      Other Builtins.     (line  444)
* __builtin_thread_pointer:              RISC-V Built-in Functions.
                                                             (line    9)
* __builtin_thread_pointer <1>:          SH Built-in Functions.
                                                             (line   18)
* __builtin_trap:                        Other Builtins.     (line  639)
* __builtin_truncf128_round_to_odd:      Basic PowerPC Built-in Functions Available on ISA 3.0.
                                                             (line   41)
* __builtin_tx_assist:                   S/390 System z Built-in Functions.
                                                             (line   87)
* __builtin_tx_nesting_depth:            S/390 System z Built-in Functions.
                                                             (line   93)
* __builtin_types_compatible_p:          Other Builtins.     (line  348)
* __builtin_uadd_overflow:               Integer Overflow Builtins.
                                                             (line   17)
* __builtin_uaddl_overflow:              Integer Overflow Builtins.
                                                             (line   19)
* __builtin_uaddll_overflow:             Integer Overflow Builtins.
                                                             (line   21)
* __builtin_umul_overflow:               Integer Overflow Builtins.
                                                             (line   71)
* __builtin_umull_overflow:              Integer Overflow Builtins.
                                                             (line   73)
* __builtin_umulll_overflow:             Integer Overflow Builtins.
                                                             (line   75)
* __builtin_unreachable:                 Other Builtins.     (line  646)
* __builtin_usub_overflow:               Integer Overflow Builtins.
                                                             (line   51)
* __builtin_usubl_overflow:              Integer Overflow Builtins.
                                                             (line   53)
* __builtin_usubll_overflow:             Integer Overflow Builtins.
                                                             (line   55)
* __builtin_va_arg_pack:                 Constructing Calls. (line   52)
* __builtin_va_arg_pack_len:             Constructing Calls. (line   75)
* __complex__ keyword:                   Complex.            (line    6)
* __declspec(dllexport):                 Microsoft Windows Function Attributes.
                                                             (line   10)
* __declspec(dllimport):                 Microsoft Windows Function Attributes.
                                                             (line   42)
* __extension__:                         Alternate Keywords. (line   30)
* __far M32C Named Address Spaces:       Named Address Spaces.
                                                             (line  153)
* __far RL78 Named Address Spaces:       Named Address Spaces.
                                                             (line  176)
* __flash AVR Named Address Spaces:      Named Address Spaces.
                                                             (line   44)
* __flash1 AVR Named Address Spaces:     Named Address Spaces.
                                                             (line   53)
* __flash2 AVR Named Address Spaces:     Named Address Spaces.
                                                             (line   53)
* __flash3 AVR Named Address Spaces:     Named Address Spaces.
                                                             (line   53)
* __flash4 AVR Named Address Spaces:     Named Address Spaces.
                                                             (line   53)
* __flash5 AVR Named Address Spaces:     Named Address Spaces.
                                                             (line   53)
* __float128 data type:                  Floating Types.     (line    6)
* __Float16 data type:                   Half-Precision.     (line    6)
* __float80 data type:                   Floating Types.     (line    6)
* __fp16 data type:                      Half-Precision.     (line    6)
* __func__ identifier:                   Function Names.     (line    6)
* __FUNCTION__ identifier:               Function Names.     (line    6)
* __ibm128 data type:                    Floating Types.     (line    6)
* __imag__ keyword:                      Complex.            (line   43)
* __int128 data types:                   __int128.           (line    6)
* __memx AVR Named Address Spaces:       Named Address Spaces.
                                                             (line   59)
* __PRETTY_FUNCTION__ identifier:        Function Names.     (line    6)
* __real__ keyword:                      Complex.            (line   43)
* __regio_symbol PRU Named Address Spaces: Named Address Spaces.
                                                             (line  161)
* __seg_fs x86 named address space:      Named Address Spaces.
                                                             (line  189)
* __seg_gs x86 named address space:      Named Address Spaces.
                                                             (line  189)
* __STDC_HOSTED__:                       Standards.          (line   13)
* __sync_add_and_fetch:                  __sync Builtins.    (line   72)
* __sync_and_and_fetch:                  __sync Builtins.    (line   72)
* __sync_bool_compare_and_swap:          __sync Builtins.    (line   88)
* __sync_fetch_and_add:                  __sync Builtins.    (line   50)
* __sync_fetch_and_and:                  __sync Builtins.    (line   50)
* __sync_fetch_and_nand:                 __sync Builtins.    (line   50)
* __sync_fetch_and_or:                   __sync Builtins.    (line   50)
* __sync_fetch_and_sub:                  __sync Builtins.    (line   50)
* __sync_fetch_and_xor:                  __sync Builtins.    (line   50)
* __sync_lock_release:                   __sync Builtins.    (line  118)
* __sync_lock_test_and_set:              __sync Builtins.    (line  100)
* __sync_nand_and_fetch:                 __sync Builtins.    (line   72)
* __sync_or_and_fetch:                   __sync Builtins.    (line   72)
* __sync_sub_and_fetch:                  __sync Builtins.    (line   72)
* __sync_synchronize:                    __sync Builtins.    (line   97)
* __sync_val_compare_and_swap:           __sync Builtins.    (line   88)
* __sync_xor_and_fetch:                  __sync Builtins.    (line   72)
* __thread:                              Thread-Local.       (line    6)
* _Accum data type:                      Fixed-Point.        (line    6)
* _Complex keyword:                      Complex.            (line    6)
* _Decimal128 data type:                 Decimal Float.      (line    6)
* _Decimal32 data type:                  Decimal Float.      (line    6)
* _Decimal64 data type:                  Decimal Float.      (line    6)
* _Exit:                                 Other Builtins.     (line    6)
* _exit:                                 Other Builtins.     (line    6)
* _FloatN data types:                    Floating Types.     (line    6)
* _FloatNx data types:                   Floating Types.     (line    6)
* _Fract data type:                      Fixed-Point.        (line    6)
* _get_ssp:                              x86 control-flow protection intrinsics.
                                                             (line    6)
* _HTM_FIRST_USER_ABORT_CODE:            S/390 System z Built-in Functions.
                                                             (line   44)
* _inc_ssp:                              x86 control-flow protection intrinsics.
                                                             (line   12)
* _Sat data type:                        Fixed-Point.        (line    6)
* _xabort:                               x86 transactional memory intrinsics.
                                                             (line   57)
* _xbegin:                               x86 transactional memory intrinsics.
                                                             (line   19)
* _xend:                                 x86 transactional memory intrinsics.
                                                             (line   48)
* _xtest:                                x86 transactional memory intrinsics.
                                                             (line   53)
* -lgcc, use with -nodefaultlibs:        Link Options.       (line  157)
* -lgcc, use with -nostdlib:             Link Options.       (line  157)
* -march feature modifiers:              AArch64 Options.    (line  331)
* -mcpu feature modifiers:               AArch64 Options.    (line  331)
* -nodefaultlibs and unresolved references: Link Options.    (line  157)
* -nostdlib and unresolved references:   Link Options.       (line  157)
* ?: extensions:                         Conditionals.       (line    6)
* ?: side effect:                        Conditionals.       (line   20)
* .sdata/.sdata2 references (PowerPC):   RS/6000 and PowerPC Options.
                                                             (line  714)
* ':                                     Incompatibilities.  (line  116)
* (const:                                Other Builtins.     (line  820)
* *:                                     BPF Built-in Functions.
                                                             (line   23)
* *__builtin_alloca:                     Other Builtins.     (line  137)
* *__builtin_alloca_with_align:          Other Builtins.     (line  174)
* *__builtin_alloca_with_align_and_max:  Other Builtins.     (line  219)
* //:                                    C++ Comments.       (line    6)
* & in constraint:                       Modifiers.          (line   25)
* #pragma:                               Pragmas.            (line    6)
* #pragma implementation:                C++ Interface.      (line   36)
* #pragma implementation, implied:       C++ Interface.      (line   43)
* #pragma interface:                     C++ Interface.      (line   17)
* % in constraint:                       Modifiers.          (line   52)
* %include:                              Spec Files.         (line   26)
* %include_noerr:                        Spec Files.         (line   30)
* %rename:                               Spec Files.         (line   34)
* + in constraint:                       Modifiers.          (line   12)
* < in constraint:                       Simple Constraints. (line   47)
* = in constraint:                       Modifiers.          (line    8)
* > in constraint:                       Simple Constraints. (line   59)
* $:                                     Dollar Signs.       (line    6)
* 0 in constraint:                       Simple Constraints. (line  125)
* AArch64 Options:                       AArch64 Options.    (line    6)
* ABI:                                   Compatibility.      (line    6)
* abi_tag function attribute:            C++ Attributes.     (line    9)
* abi_tag type attribute:                C++ Attributes.     (line    9)
* abi_tag variable attribute:            C++ Attributes.     (line    9)
* abort:                                 Other Builtins.     (line    6)
* abs:                                   Other Builtins.     (line    6)
* absdata variable attribute, AVR:       AVR Variable Attributes.
                                                             (line  104)
* accessing volatiles:                   Volatiles.          (line    6)
* accessing volatiles <1>:               C++ Volatiles.      (line    6)
* acos:                                  Other Builtins.     (line    6)
* acosf:                                 Other Builtins.     (line    6)
* acosh:                                 Other Builtins.     (line    6)
* acoshf:                                Other Builtins.     (line    6)
* acoshl:                                Other Builtins.     (line    6)
* acosl:                                 Other Builtins.     (line    6)
* Ada:                                   G++ and GCC.        (line    6)
* Ada <1>:                               G++ and GCC.        (line   29)
* additional floating types:             Floating Types.     (line    6)
* address constraints:                   Simple Constraints. (line  152)
* address of a label:                    Labels as Values.   (line    6)
* address variable attribute, AVR:       AVR Variable Attributes.
                                                             (line   97)
* address_operand:                       Simple Constraints. (line  156)
* alias function attribute:              Common Function Attributes.
                                                             (line   93)
* alias variable attribute:              Common Variable Attributes.
                                                             (line    9)
* aligned function attribute:            Common Function Attributes.
                                                             (line  112)
* aligned type attribute:                Common Type Attributes.
                                                             (line    8)
* aligned variable attribute:            Common Variable Attributes.
                                                             (line   31)
* alignment:                             Alignment.          (line    6)
* alloc_align function attribute:        Common Function Attributes.
                                                             (line  140)
* alloc_size function attribute:         Common Function Attributes.
                                                             (line  160)
* alloc_size type attribute:             Common Type Attributes.
                                                             (line  136)
* alloc_size variable attribute:         Common Variable Attributes.
                                                             (line  137)
* alloca:                                Other Builtins.     (line    6)
* alloca vs variable-length arrays:      Variable Length.    (line   35)
* Allow nesting in an interrupt handler on the Blackfin processor: Blackfin Function Attributes.
                                                             (line   45)
* Altera Nios II options:                Nios II Options.    (line    6)
* alternate keywords:                    Alternate Keywords. (line    6)
* altivec type attribute, PowerPC:       PowerPC Type Attributes.
                                                             (line   12)
* altivec variable attribute, PowerPC:   PowerPC Variable Attributes.
                                                             (line   12)
* always_inline function attribute:      Common Function Attributes.
                                                             (line  186)
* AMD GCN Options:                       AMD GCN Options.    (line    6)
* AMD1:                                  Standards.          (line   13)
* amdgpu_hsa_kernel function attribute, AMD GCN: AMD GCN Function Attributes.
                                                             (line    9)
* ANSI C:                                Standards.          (line   13)
* ANSI C standard:                       Standards.          (line   13)
* ANSI C89:                              Standards.          (line   13)
* ANSI support:                          C Dialect Options.  (line   10)
* ANSI X3.159-1989:                      Standards.          (line   13)
* apostrophes:                           Incompatibilities.  (line  116)
* application binary interface:          Compatibility.      (line    6)
* ARC options:                           ARC Options.        (line    6)
* arch= function attribute, AArch64:     AArch64 Function Attributes.
                                                             (line   53)
* arch= function attribute, ARM:         ARM Function Attributes.
                                                             (line   98)
* ARM [Annotated C++ Reference Manual]:  Backwards Compatibility.
                                                             (line    6)
* ARM options:                           ARM Options.        (line    6)
* arrays of length zero:                 Zero Length.        (line    6)
* arrays of variable length:             Variable Length.    (line    6)
* arrays, non-lvalue:                    Subscripting.       (line    6)
* artificial function attribute:         Common Function Attributes.
                                                             (line  196)
* asin:                                  Other Builtins.     (line    6)
* asinf:                                 Other Builtins.     (line    6)
* asinh:                                 Other Builtins.     (line    6)
* asinhf:                                Other Builtins.     (line    6)
* asinhl:                                Other Builtins.     (line    6)
* asinl:                                 Other Builtins.     (line    6)
* asm assembler template:                Extended Asm.       (line  226)
* asm clobbers:                          Extended Asm.       (line  693)
* asm constraints:                       Constraints.        (line    6)
* asm expressions:                       Extended Asm.       (line  598)
* asm flag output operands:              Extended Asm.       (line  488)
* asm goto labels:                       Extended Asm.       (line  880)
* asm inline:                            Size of an asm.     (line   25)
* asm input operands:                    Extended Asm.       (line  598)
* asm keyword:                           Using Assembly Language with C.
                                                             (line    6)
* asm output operands:                   Extended Asm.       (line  329)
* asm scratch registers:                 Extended Asm.       (line  693)
* asm volatile:                          Extended Asm.       (line  116)
* assembler names for identifiers:       Asm Labels.         (line    6)
* assembly code, invalid:                Bug Criteria.       (line   12)
* assembly language in C:                Using Assembly Language with C.
                                                             (line    6)
* assembly language in C, basic:         Basic Asm.          (line    6)
* assembly language in C, extended:      Extended Asm.       (line    6)
* assume_aligned function attribute:     Common Function Attributes.
                                                             (line  204)
* atan:                                  Other Builtins.     (line    6)
* atan2:                                 Other Builtins.     (line    6)
* atan2f:                                Other Builtins.     (line    6)
* atan2l:                                Other Builtins.     (line    6)
* atanf:                                 Other Builtins.     (line    6)
* atanh:                                 Other Builtins.     (line    6)
* atanhf:                                Other Builtins.     (line    6)
* atanhl:                                Other Builtins.     (line    6)
* atanl:                                 Other Builtins.     (line    6)
* attribute of types:                    Type Attributes.    (line    6)
* attribute of variables:                Variable Attributes.
                                                             (line    6)
* attribute syntax:                      Attribute Syntax.   (line    6)
* autoincrement/decrement addressing:    Simple Constraints. (line   30)
* automatic inline for C++ member fns:   Inline.             (line   68)
* aux variable attribute, ARC:           ARC Variable Attributes.
                                                             (line    7)
* AVR Options:                           AVR Options.        (line    6)
* Backwards Compatibility:               Backwards Compatibility.
                                                             (line    6)
* bank_switch function attribute, M32C:  M32C Function Attributes.
                                                             (line    9)
* base class members:                    Name lookup.        (line    6)
* based type attribute, MeP:             MeP Type Attributes.
                                                             (line    6)
* based variable attribute, MeP:         MeP Variable Attributes.
                                                             (line   16)
* basic asm:                             Basic Asm.          (line    6)
* bcmp:                                  Other Builtins.     (line    6)
* below100 variable attribute, Xstormy16: Xstormy16 Variable Attributes.
                                                             (line   10)
* binary compatibility:                  Compatibility.      (line    6)
* Binary constants using the 0b prefix:  Binary constants.   (line    6)
* Blackfin Options:                      Blackfin Options.   (line    6)
* bound pointer to member function:      Bound member functions.
                                                             (line    6)
* branch-protection function attribute, AArch64: AArch64 Function Attributes.
                                                             (line   76)
* break handler functions:               MicroBlaze Function Attributes.
                                                             (line   17)
* break_handler function attribute, MicroBlaze: MicroBlaze Function Attributes.
                                                             (line   17)
* brk_interrupt function attribute, RL78: RL78 Function Attributes.
                                                             (line   10)
* bug criteria:                          Bug Criteria.       (line    6)
* bugs:                                  Bugs.               (line    6)
* bugs, known:                           Trouble.            (line    6)
* built-in functions:                    C Dialect Options.  (line  239)
* built-in functions <1>:                Other Builtins.     (line    6)
* bzero:                                 Other Builtins.     (line    6)
* C compilation options:                 Invoking GCC.       (line   18)
* C intermediate output, nonexistent:    G++ and GCC.        (line   34)
* C language extensions:                 C Extensions.       (line    6)
* C language, traditional:               Preprocessor Options.
                                                             (line  373)
* C standard:                            Standards.          (line   13)
* C standards:                           Standards.          (line   13)
* C_INCLUDE_PATH:                        Environment Variables.
                                                             (line  145)
* C-SKY Options:                         C-SKY Options.      (line    6)
* c++:                                   Invoking G++.       (line   14)
* C++:                                   G++ and GCC.        (line   29)
* C++ comments:                          C++ Comments.       (line    6)
* C++ Compiled Module Interface:         C++ Compiled Module Interface.
                                                             (line    6)
* C++ interface and implementation headers: C++ Interface.   (line    6)
* C++ language extensions:               C++ Extensions.     (line    6)
* C++ member fns, automatically inline:  Inline.             (line   68)
* C++ misunderstandings:                 C++ Misunderstandings.
                                                             (line    6)
* C++ Module Mapper:                     C++ Module Mapper.  (line    6)
* C++ Module Preprocessing:              C++ Module Preprocessing.
                                                             (line    6)
* C++ options, command-line:             C++ Dialect Options.
                                                             (line    6)
* C++ pragmas, effect on inlining:       C++ Interface.      (line   57)
* C++ source file suffixes:              Invoking G++.       (line    6)
* C++ static data, declaring and defining: Static Definitions.
                                                             (line    6)
* C11:                                   Standards.          (line   13)
* C17:                                   Standards.          (line   13)
* C1X:                                   Standards.          (line   13)
* C2X:                                   Standards.          (line   13)
* C6X Options:                           C6X Options.        (line    6)
* C89:                                   Standards.          (line   13)
* C90:                                   Standards.          (line   13)
* C94:                                   Standards.          (line   13)
* C95:                                   Standards.          (line   13)
* C99:                                   Standards.          (line   13)
* C9X:                                   Standards.          (line   13)
* cabs:                                  Other Builtins.     (line    6)
* cabsf:                                 Other Builtins.     (line    6)
* cabsl:                                 Other Builtins.     (line    6)
* cacos:                                 Other Builtins.     (line    6)
* cacosf:                                Other Builtins.     (line    6)
* cacosh:                                Other Builtins.     (line    6)
* cacoshf:                               Other Builtins.     (line    6)
* cacoshl:                               Other Builtins.     (line    6)
* cacosl:                                Other Builtins.     (line    6)
* callee_pop_aggregate_return function attribute, x86: x86 Function Attributes.
                                                             (line   47)
* calling functions through the function vector on SH2A: SH Function Attributes.
                                                             (line    9)
* calloc:                                Other Builtins.     (line    6)
* carg:                                  Other Builtins.     (line    6)
* cargf:                                 Other Builtins.     (line    6)
* cargl:                                 Other Builtins.     (line    6)
* case labels in initializers:           Designated Inits.   (line    6)
* case ranges:                           Case Ranges.        (line    6)
* casin:                                 Other Builtins.     (line    6)
* casinf:                                Other Builtins.     (line    6)
* casinh:                                Other Builtins.     (line    6)
* casinhf:                               Other Builtins.     (line    6)
* casinhl:                               Other Builtins.     (line    6)
* casinl:                                Other Builtins.     (line    6)
* cast to a union:                       Cast to Union.      (line    6)
* catan:                                 Other Builtins.     (line    6)
* catanf:                                Other Builtins.     (line    6)
* catanh:                                Other Builtins.     (line    6)
* catanhf:                               Other Builtins.     (line    6)
* catanhl:                               Other Builtins.     (line    6)
* catanl:                                Other Builtins.     (line    6)
* cb variable attribute, MeP:            MeP Variable Attributes.
                                                             (line   46)
* cbrt:                                  Other Builtins.     (line    6)
* cbrtf:                                 Other Builtins.     (line    6)
* cbrtl:                                 Other Builtins.     (line    6)
* ccos:                                  Other Builtins.     (line    6)
* ccosf:                                 Other Builtins.     (line    6)
* ccosh:                                 Other Builtins.     (line    6)
* ccoshf:                                Other Builtins.     (line    6)
* ccoshl:                                Other Builtins.     (line    6)
* ccosl:                                 Other Builtins.     (line    6)
* cdecl function attribute, x86-32:      x86 Function Attributes.
                                                             (line    9)
* ceil:                                  Other Builtins.     (line    6)
* ceilf:                                 Other Builtins.     (line    6)
* ceill:                                 Other Builtins.     (line    6)
* cexp:                                  Other Builtins.     (line    6)
* cexpf:                                 Other Builtins.     (line    6)
* cexpl:                                 Other Builtins.     (line    6)
* cf_check function attribute, x86:      x86 Function Attributes.
                                                             (line  689)
* character set, execution:              Preprocessor Options.
                                                             (line  273)
* character set, input:                  Preprocessor Options.
                                                             (line  286)
* character set, input normalization:    Warning Options.    (line 3029)
* character set, wide execution:         Preprocessor Options.
                                                             (line  278)
* cimag:                                 Other Builtins.     (line    6)
* cimagf:                                Other Builtins.     (line    6)
* cimagl:                                Other Builtins.     (line    6)
* cleanup variable attribute:            Common Variable Attributes.
                                                             (line  161)
* clog:                                  Other Builtins.     (line    6)
* clog10:                                Other Builtins.     (line    6)
* clog10f:                               Other Builtins.     (line    6)
* clog10l:                               Other Builtins.     (line    6)
* clogf:                                 Other Builtins.     (line    6)
* clogl:                                 Other Builtins.     (line    6)
* cmodel= function attribute, AArch64:   AArch64 Function Attributes.
                                                             (line   27)
* COBOL:                                 G++ and GCC.        (line   23)
* code generation conventions:           Code Gen Options.   (line    6)
* code, mixed with declarations:         Mixed Labels and Declarations.
                                                             (line    6)
* cold function attribute:               Common Function Attributes.
                                                             (line  220)
* cold label attribute:                  Label Attributes.   (line   46)
* command options:                       Invoking GCC.       (line    6)
* comments, C++ style:                   C++ Comments.       (line    6)
* common variable attribute:             Common Variable Attributes.
                                                             (line  176)
* comparison of signed and unsigned values, warning: Warning Options.
                                                             (line 2691)
* compilation statistics:                Developer Options.  (line    6)
* compiler bugs, reporting:              Bug Reporting.      (line    6)
* compiler compared to C++ preprocessor: G++ and GCC.        (line   34)
* compiler options, C++:                 C++ Dialect Options.
                                                             (line    6)
* compiler options, Objective-C and Objective-C++: Objective-C and Objective-C++ Dialect Options.
                                                             (line    6)
* compiler version, specifying:          Invoking GCC.       (line   24)
* COMPILER_PATH:                         Environment Variables.
                                                             (line   91)
* complex conjugation:                   Complex.            (line   64)
* complex numbers:                       Complex.            (line    6)
* compound literals:                     Compound Literals.  (line    6)
* computed gotos:                        Labels as Values.   (line    6)
* conditional expressions, extensions:   Conditionals.       (line    6)
* conflicting types:                     Disappointments.    (line   21)
* conj:                                  Other Builtins.     (line    6)
* conjf:                                 Other Builtins.     (line    6)
* conjl:                                 Other Builtins.     (line    6)
* const applied to function:             Function Attributes.
                                                             (line    6)
* const function attribute:              Common Function Attributes.
                                                             (line  236)
* const qualifier:                       Pointers to Arrays. (line    6)
* constants in constraints:              Simple Constraints. (line   68)
* constraint modifier characters:        Modifiers.          (line    6)
* constraint, matching:                  Simple Constraints. (line  137)
* constraints, asm:                      Constraints.        (line    6)
* constraints, machine specific:         Machine Constraints.
                                                             (line    6)
* constructing calls:                    Constructing Calls. (line    6)
* constructor expressions:               Compound Literals.  (line    6)
* constructor function attribute:        Common Function Attributes.
                                                             (line  277)
* contributors:                          Contributors.       (line    6)
* copy function attribute:               Common Function Attributes.
                                                             (line  306)
* copy type attribute:                   Common Type Attributes.
                                                             (line  161)
* copy variable attribute:               Common Variable Attributes.
                                                             (line  185)
* copysign:                              Other Builtins.     (line    6)
* copysignf:                             Other Builtins.     (line    6)
* copysignl:                             Other Builtins.     (line    6)
* core dump:                             Bug Criteria.       (line    9)
* cos:                                   Other Builtins.     (line    6)
* cosf:                                  Other Builtins.     (line    6)
* cosh:                                  Other Builtins.     (line    6)
* coshf:                                 Other Builtins.     (line    6)
* coshl:                                 Other Builtins.     (line    6)
* cosl:                                  Other Builtins.     (line    6)
* CPATH:                                 Environment Variables.
                                                             (line  144)
* CPLUS_INCLUDE_PATH:                    Environment Variables.
                                                             (line  146)
* cpow:                                  Other Builtins.     (line    6)
* cpowf:                                 Other Builtins.     (line    6)
* cpowl:                                 Other Builtins.     (line    6)
* cproj:                                 Other Builtins.     (line    6)
* cprojf:                                Other Builtins.     (line    6)
* cprojl:                                Other Builtins.     (line    6)
* cpu= function attribute, AArch64:      AArch64 Function Attributes.
                                                             (line   63)
* CR16 Options:                          CR16 Options.       (line    6)
* creal:                                 Other Builtins.     (line    6)
* crealf:                                Other Builtins.     (line    6)
* creall:                                Other Builtins.     (line    6)
* CRIS Options:                          CRIS Options.       (line    6)
* critical function attribute, MSP430:   MSP430 Function Attributes.
                                                             (line    9)
* cross compiling:                       Invoking GCC.       (line   24)
* csin:                                  Other Builtins.     (line    6)
* csinf:                                 Other Builtins.     (line    6)
* csinh:                                 Other Builtins.     (line    6)
* csinhf:                                Other Builtins.     (line    6)
* csinhl:                                Other Builtins.     (line    6)
* csinl:                                 Other Builtins.     (line    6)
* csqrt:                                 Other Builtins.     (line    6)
* csqrtf:                                Other Builtins.     (line    6)
* csqrtl:                                Other Builtins.     (line    6)
* ctan:                                  Other Builtins.     (line    6)
* ctanf:                                 Other Builtins.     (line    6)
* ctanh:                                 Other Builtins.     (line    6)
* ctanhf:                                Other Builtins.     (line    6)
* ctanhl:                                Other Builtins.     (line    6)
* ctanl:                                 Other Builtins.     (line    6)
* CXX_MODULE_MAPPER environment variable: C++ Dialect Options.
                                                             (line  340)
* D:                                     G++ and GCC.        (line    6)
* Darwin options:                        Darwin Options.     (line    6)
* dcgettext:                             Other Builtins.     (line    6)
* dd integer suffix:                     Decimal Float.      (line    6)
* DD integer suffix:                     Decimal Float.      (line    6)
* deallocating variable length arrays:   Variable Length.    (line   22)
* debug dump options:                    Developer Options.  (line    6)
* debugging GCC:                         Developer Options.  (line    6)
* debugging information options:         Debugging Options.  (line    6)
* decimal floating types:                Decimal Float.      (line    6)
* declaration scope:                     Incompatibilities.  (line   80)
* declarations inside expressions:       Statement Exprs.    (line    6)
* declarations, mixed with code:         Mixed Labels and Declarations.
                                                             (line    6)
* declaring attributes of functions:     Function Attributes.
                                                             (line    6)
* declaring static data in C++:          Static Definitions. (line    6)
* defining static data in C++:           Static Definitions. (line    6)
* dependencies for make as output:       Environment Variables.
                                                             (line  172)
* dependencies for make as output <1>:   Environment Variables.
                                                             (line  188)
* DEPENDENCIES_OUTPUT:                   Environment Variables.
                                                             (line  171)
* dependencies, make:                    Preprocessor Options.
                                                             (line   77)
* dependent name lookup:                 Name lookup.        (line    6)
* deprecated enumerator attribute:       Enumerator Attributes.
                                                             (line   28)
* deprecated function attribute:         Common Function Attributes.
                                                             (line  338)
* deprecated type attribute:             Common Type Attributes.
                                                             (line  189)
* deprecated variable attribute:         Common Variable Attributes.
                                                             (line  201)
* designated initializers:               Designated Inits.   (line    6)
* designated_init type attribute:        Common Type Attributes.
                                                             (line  234)
* designator lists:                      Designated Inits.   (line   96)
* designators:                           Designated Inits.   (line   64)
* destructor function attribute:         Common Function Attributes.
                                                             (line  277)
* developer options:                     Developer Options.  (line    6)
* df integer suffix:                     Decimal Float.      (line    6)
* DF integer suffix:                     Decimal Float.      (line    6)
* dgettext:                              Other Builtins.     (line    6)
* diagnostic messages:                   Diagnostic Message Formatting Options.
                                                             (line    6)
* dialect options:                       C Dialect Options.  (line    6)
* diff-delete GCC_COLORS capability:     Diagnostic Message Formatting Options.
                                                             (line  134)
* diff-filename GCC_COLORS capability:   Diagnostic Message Formatting Options.
                                                             (line  127)
* diff-hunk GCC_COLORS capability:       Diagnostic Message Formatting Options.
                                                             (line  130)
* diff-insert GCC_COLORS capability:     Diagnostic Message Formatting Options.
                                                             (line  137)
* digits in constraint:                  Simple Constraints. (line  125)
* directory options:                     Directory Options.  (line    6)
* disinterrupt function attribute, Epiphany: Epiphany Function Attributes.
                                                             (line    9)
* disinterrupt function attribute, MeP:  MeP Function Attributes.
                                                             (line    9)
* dl integer suffix:                     Decimal Float.      (line    6)
* DL integer suffix:                     Decimal Float.      (line    6)
* dllexport function attribute:          Microsoft Windows Function Attributes.
                                                             (line   10)
* dllexport variable attribute:          Microsoft Windows Variable Attributes.
                                                             (line   12)
* dllimport function attribute:          Microsoft Windows Function Attributes.
                                                             (line   42)
* dllimport variable attribute:          Microsoft Windows Variable Attributes.
                                                             (line   12)
* dollar signs in identifier names:      Dollar Signs.       (line    6)
* double-word arithmetic:                Long Long.          (line    6)
* downward funargs:                      Nested Functions.   (line    6)
* drem:                                  Other Builtins.     (line    6)
* dremf:                                 Other Builtins.     (line    6)
* dreml:                                 Other Builtins.     (line    6)
* dump options:                          Developer Options.  (line    6)
* E in constraint:                       Simple Constraints. (line   87)
* earlyclobber operand:                  Modifiers.          (line   25)
* eBPF Options:                          eBPF Options.       (line    6)
* eight-bit data on the H8/300, H8/300H, and H8S: H8/300 Variable Attributes.
                                                             (line    9)
* eightbit_data variable attribute, H8/300: H8/300 Variable Attributes.
                                                             (line    9)
* EIND:                                  AVR Options.        (line  317)
* either function attribute, MSP430:     MSP430 Function Attributes.
                                                             (line   57)
* either variable attribute, MSP430:     MSP430 Variable Attributes.
                                                             (line    8)
* empty structures:                      Empty Structures.   (line    6)
* Enumerator Attributes:                 Enumerator Attributes.
                                                             (line    6)
* environment variables:                 Environment Variables.
                                                             (line    6)
* erf:                                   Other Builtins.     (line    6)
* erfc:                                  Other Builtins.     (line    6)
* erfcf:                                 Other Builtins.     (line    6)
* erfcl:                                 Other Builtins.     (line    6)
* erff:                                  Other Builtins.     (line    6)
* erfl:                                  Other Builtins.     (line    6)
* error function attribute:              Common Function Attributes.
                                                             (line  373)
* error GCC_COLORS capability:           Diagnostic Message Formatting Options.
                                                             (line   92)
* error messages:                        Warnings and Errors.
                                                             (line    6)
* escaped newlines:                      Escaped Newlines.   (line    6)
* exception function attribute:          NDS32 Function Attributes.
                                                             (line    9)
* exception handler functions, Blackfin: Blackfin Function Attributes.
                                                             (line    9)
* exception handler functions, NDS32:    NDS32 Function Attributes.
                                                             (line    9)
* exception_handler function attribute:  Blackfin Function Attributes.
                                                             (line    9)
* exit:                                  Other Builtins.     (line    6)
* exp:                                   Other Builtins.     (line    6)
* exp10:                                 Other Builtins.     (line    6)
* exp10f:                                Other Builtins.     (line    6)
* exp10l:                                Other Builtins.     (line    6)
* exp2:                                  Other Builtins.     (line    6)
* exp2f:                                 Other Builtins.     (line    6)
* exp2l:                                 Other Builtins.     (line    6)
* expf:                                  Other Builtins.     (line    6)
* expl:                                  Other Builtins.     (line    6)
* explicit register variables:           Explicit Register Variables.
                                                             (line    6)
* expm1:                                 Other Builtins.     (line    6)
* expm1f:                                Other Builtins.     (line    6)
* expm1l:                                Other Builtins.     (line    6)
* expressions containing statements:     Statement Exprs.    (line    6)
* expressions, constructor:              Compound Literals.  (line    6)
* extended asm:                          Extended Asm.       (line    6)
* extensible constraints:                Simple Constraints. (line  161)
* extensions, ?::                        Conditionals.       (line    6)
* extensions, C language:                C Extensions.       (line    6)
* extensions, C++ language:              C++ Extensions.     (line    6)
* external declaration scope:            Incompatibilities.  (line   80)
* externally_visible function attribute: Common Function Attributes.
                                                             (line  390)
* extra NOP instructions at the function entry point: Common Function Attributes.
                                                             (line 1052)
* F in constraint:                       Simple Constraints. (line   92)
* fabs:                                  Other Builtins.     (line    6)
* fabsf:                                 Other Builtins.     (line    6)
* fabsl:                                 Other Builtins.     (line    6)
* fallthrough statement attribute:       Statement Attributes.
                                                             (line   26)
* far function attribute, MeP:           MeP Function Attributes.
                                                             (line   25)
* far function attribute, MIPS:          MIPS Function Attributes.
                                                             (line   63)
* far type attribute, MeP:               MeP Type Attributes.
                                                             (line    6)
* far variable attribute, MeP:           MeP Variable Attributes.
                                                             (line   30)
* fast_interrupt function attribute, M32C: M32C Function Attributes.
                                                             (line   14)
* fast_interrupt function attribute, MicroBlaze: MicroBlaze Function Attributes.
                                                             (line   27)
* fast_interrupt function attribute, RX: RX Function Attributes.
                                                             (line    9)
* fastcall function attribute, x86-32:   x86 Function Attributes.
                                                             (line   15)
* fatal signal:                          Bug Criteria.       (line    9)
* fdim:                                  Other Builtins.     (line    6)
* fdimf:                                 Other Builtins.     (line    6)
* fdiml:                                 Other Builtins.     (line    6)
* FDL, GNU Free Documentation License:   GNU Free Documentation License.
                                                             (line    6)
* fentry_name function attribute, x86:   x86 Function Attributes.
                                                             (line  701)
* fentry_section function attribute, x86: x86 Function Attributes.
                                                             (line  707)
* ffs:                                   Other Builtins.     (line    6)
* file name suffix:                      Overall Options.    (line   14)
* file names:                            Link Options.       (line   10)
* fix-cortex-a53-835769 function attribute, AArch64: AArch64 Function Attributes.
                                                             (line   19)
* fixed-point types:                     Fixed-Point.        (line    6)
* fixit-delete GCC_COLORS capability:    Diagnostic Message Formatting Options.
                                                             (line  124)
* fixit-insert GCC_COLORS capability:    Diagnostic Message Formatting Options.
                                                             (line  120)
* flatten function attribute:            Common Function Attributes.
                                                             (line  403)
* flexible array members:                Zero Length.        (line    6)
* float as function value type:          Incompatibilities.  (line  141)
* floating point precision:              Disappointments.    (line   68)
* floating-point precision:              Optimize Options.   (line 2289)
* floor:                                 Other Builtins.     (line    6)
* floorf:                                Other Builtins.     (line    6)
* floorl:                                Other Builtins.     (line    6)
* fma:                                   Other Builtins.     (line    6)
* fmaf:                                  Other Builtins.     (line    6)
* fmal:                                  Other Builtins.     (line    6)
* fmax:                                  Other Builtins.     (line    6)
* fmaxf:                                 Other Builtins.     (line    6)
* fmaxl:                                 Other Builtins.     (line    6)
* fmin:                                  Other Builtins.     (line    6)
* fminf:                                 Other Builtins.     (line    6)
* fminl:                                 Other Builtins.     (line    6)
* fmod:                                  Other Builtins.     (line    6)
* fmodf:                                 Other Builtins.     (line    6)
* fmodl:                                 Other Builtins.     (line    6)
* force_align_arg_pointer function attribute, x86: x86 Function Attributes.
                                                             (line  100)
* format function attribute:             Common Function Attributes.
                                                             (line  411)
* format_arg function attribute:         Common Function Attributes.
                                                             (line  476)
* Fortran:                               G++ and GCC.        (line    6)
* forwarder_section function attribute, Epiphany: Epiphany Function Attributes.
                                                             (line   13)
* forwarding calls:                      Constructing Calls. (line    6)
* fprintf:                               Other Builtins.     (line    6)
* fprintf_unlocked:                      Other Builtins.     (line    6)
* fputs:                                 Other Builtins.     (line    6)
* fputs_unlocked:                        Other Builtins.     (line    6)
* FR30 Options:                          FR30 Options.       (line    6)
* free:                                  Other Builtins.     (line    6)
* freestanding environment:              Standards.          (line   13)
* freestanding implementation:           Standards.          (line   13)
* frexp:                                 Other Builtins.     (line    6)
* frexpf:                                Other Builtins.     (line    6)
* frexpl:                                Other Builtins.     (line    6)
* FRV Options:                           FRV Options.        (line    6)
* fscanf:                                Other Builtins.     (line    6)
* fscanf, and constant strings:          Incompatibilities.  (line   17)
* FT32 Options:                          FT32 Options.       (line    6)
* function addressability on the M32R/D: M32R/D Function Attributes.
                                                             (line   15)
* function attributes:                   Function Attributes.
                                                             (line    6)
* function pointers, arithmetic:         Pointer Arith.      (line    6)
* function prototype declarations:       Function Prototypes.
                                                             (line    6)
* function versions:                     Function Multiversioning.
                                                             (line    6)
* function_return function attribute, x86: x86 Function Attributes.
                                                             (line  628)
* function_vector function attribute, H8/300: H8/300 Function Attributes.
                                                             (line    9)
* function_vector function attribute, M16C/M32C: M32C Function Attributes.
                                                             (line   20)
* function_vector function attribute, SH: SH Function Attributes.
                                                             (line    9)
* function, size of pointer to:          Pointer Arith.      (line    6)
* functions in arbitrary sections:       Common Function Attributes.
                                                             (line 1136)
* functions that are dynamically resolved: Common Function Attributes.
                                                             (line  577)
* functions that are passed arguments in registers on x86-32: x86 Function Attributes.
                                                             (line   76)
* functions that behave like malloc:     Common Function Attributes.
                                                             (line  706)
* functions that have no side effects:   Common Function Attributes.
                                                             (line  236)
* functions that have no side effects <1>: Common Function Attributes.
                                                             (line 1070)
* functions that never return:           Common Function Attributes.
                                                             (line  982)
* functions that pop the argument stack on x86-32: x86 Function Attributes.
                                                             (line    9)
* functions that pop the argument stack on x86-32 <1>: x86 Function Attributes.
                                                             (line   15)
* functions that pop the argument stack on x86-32 <2>: x86 Function Attributes.
                                                             (line   23)
* functions that pop the argument stack on x86-32 <3>: x86 Function Attributes.
                                                             (line  108)
* functions that return more than once:  Common Function Attributes.
                                                             (line 1127)
* functions with non-null pointer arguments: Common Function Attributes.
                                                             (line  911)
* functions with printf, scanf, strftime or strfmon style arguments: Common Function Attributes.
                                                             (line  411)
* G in constraint:                       Simple Constraints. (line   96)
* g in constraint:                       Simple Constraints. (line  118)
* g++:                                   Invoking G++.       (line   14)
* G++:                                   G++ and GCC.        (line   29)
* gamma:                                 Other Builtins.     (line    6)
* gamma_r:                               Other Builtins.     (line    6)
* gammaf:                                Other Builtins.     (line    6)
* gammaf_r:                              Other Builtins.     (line    6)
* gammal:                                Other Builtins.     (line    6)
* gammal_r:                              Other Builtins.     (line    6)
* GCC:                                   G++ and GCC.        (line    6)
* GCC command options:                   Invoking GCC.       (line    6)
* GCC_COLORS environment variable:       Diagnostic Message Formatting Options.
                                                             (line   55)
* GCC_COMPARE_DEBUG:                     Environment Variables.
                                                             (line   52)
* GCC_EXEC_PREFIX:                       Environment Variables.
                                                             (line   57)
* GCC_EXTRA_DIAGNOSTIC_OUTPUT:           Environment Variables.
                                                             (line  125)
* gcc_struct type attribute, PowerPC:    PowerPC Type Attributes.
                                                             (line    9)
* gcc_struct type attribute, x86:        x86 Type Attributes.
                                                             (line   11)
* gcc_struct variable attribute, PowerPC: PowerPC Variable Attributes.
                                                             (line    9)
* gcc_struct variable attribute, x86:    x86 Variable Attributes.
                                                             (line   11)
* GCC_URLS environment variable:         Diagnostic Message Formatting Options.
                                                             (line  144)
* gcov:                                  Instrumentation Options.
                                                             (line   55)
* general-regs-only function attribute, AArch64: AArch64 Function Attributes.
                                                             (line   12)
* general-regs-only function attribute, ARM: ARM Function Attributes.
                                                             (line    9)
* gettext:                               Other Builtins.     (line    6)
* global offset table:                   Code Gen Options.   (line  355)
* global register after longjmp:         Global Register Variables.
                                                             (line   92)
* global register variables:             Global Register Variables.
                                                             (line    6)
* GNAT:                                  G++ and GCC.        (line   29)
* GNU C Compiler:                        G++ and GCC.        (line    6)
* GNU Compiler Collection:               G++ and GCC.        (line    6)
* gnu_inline function attribute:         Common Function Attributes.
                                                             (line  531)
* Go:                                    G++ and GCC.        (line    6)
* goto with computed label:              Labels as Values.   (line    6)
* gprof:                                 Instrumentation Options.
                                                             (line   18)
* grouping options:                      Invoking GCC.       (line   31)
* H in constraint:                       Simple Constraints. (line   96)
* half-precision floating point:         Half-Precision.     (line    6)
* hardware models and configurations, specifying: Submodel Options.
                                                             (line    6)
* hex floats:                            Hex Floats.         (line    6)
* highlight, color:                      Diagnostic Message Formatting Options.
                                                             (line   55)
* hk fixed-suffix:                       Fixed-Point.        (line    6)
* HK fixed-suffix:                       Fixed-Point.        (line    6)
* hosted environment:                    Standards.          (line   13)
* hosted environment <1>:                C Dialect Options.  (line  278)
* hosted environment <2>:                C Dialect Options.  (line  327)
* hosted implementation:                 Standards.          (line   13)
* hot function attribute:                Common Function Attributes.
                                                             (line  567)
* hot label attribute:                   Label Attributes.   (line   39)
* hotpatch function attribute, S/390:    S/390 Function Attributes.
                                                             (line    9)
* HPPA Options:                          HPPA Options.       (line    6)
* hr fixed-suffix:                       Fixed-Point.        (line    6)
* HR fixed-suffix:                       Fixed-Point.        (line    6)
* hypot:                                 Other Builtins.     (line    6)
* hypotf:                                Other Builtins.     (line    6)
* hypotl:                                Other Builtins.     (line    6)
* i in constraint:                       Simple Constraints. (line   68)
* I in constraint:                       Simple Constraints. (line   79)
* IA-64 Options:                         IA-64 Options.      (line    6)
* IBM RS/6000 and PowerPC Options:       RS/6000 and PowerPC Options.
                                                             (line    6)
* identifier names, dollar signs in:     Dollar Signs.       (line    6)
* identifiers, names in assembler code:  Asm Labels.         (line    6)
* ifunc function attribute:              Common Function Attributes.
                                                             (line  577)
* ilogb:                                 Other Builtins.     (line    6)
* ilogbf:                                Other Builtins.     (line    6)
* ilogbl:                                Other Builtins.     (line    6)
* imaxabs:                               Other Builtins.     (line    6)
* implementation-defined behavior, C language: C Implementation.
                                                             (line    6)
* implementation-defined behavior, C++ language: C++ Implementation.
                                                             (line    6)
* implied #pragma implementation:        C++ Interface.      (line   43)
* incompatibilities of GCC:              Incompatibilities.  (line    6)
* increment operators:                   Bug Criteria.       (line   17)
* index:                                 Other Builtins.     (line    6)
* indirect calls, ARC:                   ARC Function Attributes.
                                                             (line   26)
* indirect calls, ARM:                   ARM Function Attributes.
                                                             (line   38)
* indirect calls, Blackfin:              Blackfin Function Attributes.
                                                             (line   38)
* indirect calls, Epiphany:              Epiphany Function Attributes.
                                                             (line   57)
* indirect calls, MIPS:                  MIPS Function Attributes.
                                                             (line   63)
* indirect calls, PowerPC:               PowerPC Function Attributes.
                                                             (line   10)
* indirect functions:                    Common Function Attributes.
                                                             (line  577)
* indirect_branch function attribute, x86: x86 Function Attributes.
                                                             (line  619)
* indirect_return function attribute, x86: x86 Function Attributes.
                                                             (line  695)
* init_priority variable attribute:      C++ Attributes.     (line   50)
* initializations in expressions:        Compound Literals.  (line    6)
* initializers with labeled elements:    Designated Inits.   (line    6)
* initializers, non-constant:            Initializers.       (line    6)
* inline assembly language:              Using Assembly Language with C.
                                                             (line    6)
* inline automatic for C++ member fns:   Inline.             (line   68)
* inline functions:                      Inline.             (line    6)
* inline functions, omission of:         Inline.             (line   51)
* inlining and C++ pragmas:              C++ Interface.      (line   57)
* installation trouble:                  Trouble.            (line    6)
* instrumentation options:               Instrumentation Options.
                                                             (line    6)
* integrating function code:             Inline.             (line    6)
* interface and implementation headers, C++: C++ Interface.  (line    6)
* intermediate C version, nonexistent:   G++ and GCC.        (line   34)
* interrupt function attribute, ARC:     ARC Function Attributes.
                                                             (line    9)
* interrupt function attribute, ARM:     ARM Function Attributes.
                                                             (line   16)
* interrupt function attribute, AVR:     AVR Function Attributes.
                                                             (line    9)
* interrupt function attribute, C-SKY:   C-SKY Function Attributes.
                                                             (line   10)
* interrupt function attribute, CR16:    CR16 Function Attributes.
                                                             (line    9)
* interrupt function attribute, Epiphany: Epiphany Function Attributes.
                                                             (line   20)
* interrupt function attribute, M32C:    M32C Function Attributes.
                                                             (line   53)
* interrupt function attribute, M32R/D:  M32R/D Function Attributes.
                                                             (line    9)
* interrupt function attribute, m68k:    m68k Function Attributes.
                                                             (line   10)
* interrupt function attribute, MeP:     MeP Function Attributes.
                                                             (line   14)
* interrupt function attribute, MIPS:    MIPS Function Attributes.
                                                             (line    9)
* interrupt function attribute, MSP430:  MSP430 Function Attributes.
                                                             (line   19)
* interrupt function attribute, NDS32:   NDS32 Function Attributes.
                                                             (line   14)
* interrupt function attribute, RISC-V:  RISC-V Function Attributes.
                                                             (line   19)
* interrupt function attribute, RL78:    RL78 Function Attributes.
                                                             (line   10)
* interrupt function attribute, RX:      RX Function Attributes.
                                                             (line   15)
* interrupt function attribute, V850:    V850 Function Attributes.
                                                             (line   10)
* interrupt function attribute, Visium:  Visium Function Attributes.
                                                             (line    9)
* interrupt function attribute, x86:     x86 Function Attributes.
                                                             (line  124)
* interrupt function attribute, Xstormy16: Xstormy16 Function Attributes.
                                                             (line    9)
* interrupt_handler function attribute, Blackfin: Blackfin Function Attributes.
                                                             (line   15)
* interrupt_handler function attribute, H8/300: H8/300 Function Attributes.
                                                             (line   17)
* interrupt_handler function attribute, m68k: m68k Function Attributes.
                                                             (line   10)
* interrupt_handler function attribute, MicroBlaze: MicroBlaze Function Attributes.
                                                             (line   27)
* interrupt_handler function attribute, SH: SH Function Attributes.
                                                             (line   28)
* interrupt_handler function attribute, V850: V850 Function Attributes.
                                                             (line   10)
* interrupt_thread function attribute, fido: m68k Function Attributes.
                                                             (line   16)
* introduction:                          Top.                (line    6)
* invalid assembly code:                 Bug Criteria.       (line   12)
* invalid input:                         Bug Criteria.       (line   42)
* invoking g++:                          Invoking G++.       (line   22)
* io variable attribute, AVR:            AVR Variable Attributes.
                                                             (line   73)
* io variable attribute, MeP:            MeP Variable Attributes.
                                                             (line   36)
* io_low variable attribute, AVR:        AVR Variable Attributes.
                                                             (line   91)
* isalnum:                               Other Builtins.     (line    6)
* isalpha:                               Other Builtins.     (line    6)
* isascii:                               Other Builtins.     (line    6)
* isblank:                               Other Builtins.     (line    6)
* iscntrl:                               Other Builtins.     (line    6)
* isdigit:                               Other Builtins.     (line    6)
* isgraph:                               Other Builtins.     (line    6)
* islower:                               Other Builtins.     (line    6)
* ISO 9899:                              Standards.          (line   13)
* ISO C:                                 Standards.          (line   13)
* ISO C standard:                        Standards.          (line   13)
* ISO C11:                               Standards.          (line   13)
* ISO C17:                               Standards.          (line   13)
* ISO C1X:                               Standards.          (line   13)
* ISO C2X:                               Standards.          (line   13)
* ISO C90:                               Standards.          (line   13)
* ISO C94:                               Standards.          (line   13)
* ISO C95:                               Standards.          (line   13)
* ISO C99:                               Standards.          (line   13)
* ISO C9X:                               Standards.          (line   13)
* ISO support:                           C Dialect Options.  (line   10)
* ISO/IEC 9899:                          Standards.          (line   13)
* isprint:                               Other Builtins.     (line    6)
* ispunct:                               Other Builtins.     (line    6)
* isr function attribute, ARM:           ARM Function Attributes.
                                                             (line   33)
* isr function attribute, C-SKY:         C-SKY Function Attributes.
                                                             (line   10)
* isspace:                               Other Builtins.     (line    6)
* isupper:                               Other Builtins.     (line    6)
* iswalnum:                              Other Builtins.     (line    6)
* iswalpha:                              Other Builtins.     (line    6)
* iswblank:                              Other Builtins.     (line    6)
* iswcntrl:                              Other Builtins.     (line    6)
* iswdigit:                              Other Builtins.     (line    6)
* iswgraph:                              Other Builtins.     (line    6)
* iswlower:                              Other Builtins.     (line    6)
* iswprint:                              Other Builtins.     (line    6)
* iswpunct:                              Other Builtins.     (line    6)
* iswspace:                              Other Builtins.     (line    6)
* iswupper:                              Other Builtins.     (line    6)
* iswxdigit:                             Other Builtins.     (line    6)
* isxdigit:                              Other Builtins.     (line    6)
* j0:                                    Other Builtins.     (line    6)
* j0f:                                   Other Builtins.     (line    6)
* j0l:                                   Other Builtins.     (line    6)
* j1:                                    Other Builtins.     (line    6)
* j1f:                                   Other Builtins.     (line    6)
* j1l:                                   Other Builtins.     (line    6)
* jli_always function attribute, ARC:    ARC Function Attributes.
                                                             (line   43)
* jli_fixed function attribute, ARC:     ARC Function Attributes.
                                                             (line   49)
* jn:                                    Other Builtins.     (line    6)
* jnf:                                   Other Builtins.     (line    6)
* jnl:                                   Other Builtins.     (line    6)
* k fixed-suffix:                        Fixed-Point.        (line    6)
* K fixed-suffix:                        Fixed-Point.        (line    6)
* keep_interrupts_masked function attribute, MIPS: MIPS Function Attributes.
                                                             (line   34)
* kernel attribute, Nvidia PTX:          Nvidia PTX Function Attributes.
                                                             (line    9)
* kernel helper, function attribute, BPF: BPF Function Attributes.
                                                             (line    9)
* keywords, alternate:                   Alternate Keywords. (line    6)
* known causes of trouble:               Trouble.            (line    6)
* kspisusp function attribute, Blackfin: Blackfin Function Attributes.
                                                             (line   21)
* l1_data variable attribute, Blackfin:  Blackfin Variable Attributes.
                                                             (line   11)
* l1_data_A variable attribute, Blackfin: Blackfin Variable Attributes.
                                                             (line   11)
* l1_data_B variable attribute, Blackfin: Blackfin Variable Attributes.
                                                             (line   11)
* l1_text function attribute, Blackfin:  Blackfin Function Attributes.
                                                             (line   26)
* l2 function attribute, Blackfin:       Blackfin Function Attributes.
                                                             (line   32)
* l2 variable attribute, Blackfin:       Blackfin Variable Attributes.
                                                             (line   19)
* Label Attributes:                      Label Attributes.   (line    6)
* labeled elements in initializers:      Designated Inits.   (line    6)
* labels as values:                      Labels as Values.   (line    6)
* labs:                                  Other Builtins.     (line    6)
* LANG:                                  Environment Variables.
                                                             (line   21)
* LANG <1>:                              Environment Variables.
                                                             (line  106)
* language dialect options:              C Dialect Options.  (line    6)
* LC_ALL:                                Environment Variables.
                                                             (line   21)
* LC_CTYPE:                              Environment Variables.
                                                             (line   21)
* LC_MESSAGES:                           Environment Variables.
                                                             (line   21)
* ldexp:                                 Other Builtins.     (line    6)
* ldexpf:                                Other Builtins.     (line    6)
* ldexpl:                                Other Builtins.     (line    6)
* leaf function attribute:               Common Function Attributes.
                                                             (line  667)
* length-zero arrays:                    Zero Length.        (line    6)
* lgamma:                                Other Builtins.     (line    6)
* lgamma_r:                              Other Builtins.     (line    6)
* lgammaf:                               Other Builtins.     (line    6)
* lgammaf_r:                             Other Builtins.     (line    6)
* lgammal:                               Other Builtins.     (line    6)
* lgammal_r:                             Other Builtins.     (line    6)
* Libraries:                             Link Options.       (line   85)
* LIBRARY_PATH:                          Environment Variables.
                                                             (line   97)
* link options:                          Link Options.       (line    6)
* linker script:                         Link Options.       (line  314)
* lk fixed-suffix:                       Fixed-Point.        (line    6)
* LK fixed-suffix:                       Fixed-Point.        (line    6)
* LL integer suffix:                     Long Long.          (line    6)
* llabs:                                 Other Builtins.     (line    6)
* llk fixed-suffix:                      Fixed-Point.        (line    6)
* LLK fixed-suffix:                      Fixed-Point.        (line    6)
* llr fixed-suffix:                      Fixed-Point.        (line    6)
* LLR fixed-suffix:                      Fixed-Point.        (line    6)
* llrint:                                Other Builtins.     (line    6)
* llrintf:                               Other Builtins.     (line    6)
* llrintl:                               Other Builtins.     (line    6)
* llround:                               Other Builtins.     (line    6)
* llroundf:                              Other Builtins.     (line    6)
* llroundl:                              Other Builtins.     (line    6)
* LM32 options:                          LM32 Options.       (line    6)
* load address instruction:              Simple Constraints. (line  152)
* local labels:                          Local Labels.       (line    6)
* local variables in macros:             Typeof.             (line   46)
* local variables, specifying registers: Local Register Variables.
                                                             (line    6)
* locale:                                Environment Variables.
                                                             (line   21)
* locale definition:                     Environment Variables.
                                                             (line  106)
* locus GCC_COLORS capability:           Diagnostic Message Formatting Options.
                                                             (line  113)
* log:                                   Other Builtins.     (line    6)
* log10:                                 Other Builtins.     (line    6)
* log10f:                                Other Builtins.     (line    6)
* log10l:                                Other Builtins.     (line    6)
* log1p:                                 Other Builtins.     (line    6)
* log1pf:                                Other Builtins.     (line    6)
* log1pl:                                Other Builtins.     (line    6)
* log2:                                  Other Builtins.     (line    6)
* log2f:                                 Other Builtins.     (line    6)
* log2l:                                 Other Builtins.     (line    6)
* logb:                                  Other Builtins.     (line    6)
* logbf:                                 Other Builtins.     (line    6)
* logbl:                                 Other Builtins.     (line    6)
* logf:                                  Other Builtins.     (line    6)
* logl:                                  Other Builtins.     (line    6)
* long:                                  BPF Built-in Functions.
                                                             (line    8)
* long <1>:                              BPF Built-in Functions.
                                                             (line   13)
* long <2>:                              BPF Built-in Functions.
                                                             (line   18)
* long long data types:                  Long Long.          (line    6)
* long_call function attribute, ARC:     ARC Function Attributes.
                                                             (line   26)
* long_call function attribute, ARM:     ARM Function Attributes.
                                                             (line   38)
* long_call function attribute, Epiphany: Epiphany Function Attributes.
                                                             (line   57)
* long_call function attribute, MIPS:    MIPS Function Attributes.
                                                             (line   63)
* longcall function attribute, Blackfin: Blackfin Function Attributes.
                                                             (line   38)
* longcall function attribute, PowerPC:  PowerPC Function Attributes.
                                                             (line   10)
* longjmp:                               Global Register Variables.
                                                             (line   92)
* longjmp incompatibilities:             Incompatibilities.  (line   39)
* longjmp warnings:                      Warning Options.    (line 1375)
* LoongArch Options:                     LoongArch Options.  (line    6)
* lower function attribute, MSP430:      MSP430 Function Attributes.
                                                             (line   57)
* lower variable attribute, MSP430:      MSP430 Variable Attributes.
                                                             (line   12)
* lr fixed-suffix:                       Fixed-Point.        (line    6)
* LR fixed-suffix:                       Fixed-Point.        (line    6)
* lrint:                                 Other Builtins.     (line    6)
* lrintf:                                Other Builtins.     (line    6)
* lrintl:                                Other Builtins.     (line    6)
* lround:                                Other Builtins.     (line    6)
* lroundf:                               Other Builtins.     (line    6)
* lroundl:                               Other Builtins.     (line    6)
* m in constraint:                       Simple Constraints. (line   17)
* M32C options:                          M32C Options.       (line    6)
* M32R/D options:                        M32R/D Options.     (line    6)
* M680x0 options:                        M680x0 Options.     (line    6)
* machine specific constraints:          Machine Constraints.
                                                             (line    6)
* machine-dependent options:             Submodel Options.   (line    6)
* macro with variable arguments:         Variadic Macros.    (line    6)
* macros, inline alternative:            Inline.             (line    6)
* macros, local labels:                  Local Labels.       (line    6)
* macros, local variables in:            Typeof.             (line   46)
* macros, statements in expressions:     Statement Exprs.    (line    6)
* macros, types of arguments:            Typeof.             (line    6)
* make:                                  Preprocessor Options.
                                                             (line   77)
* malloc:                                Other Builtins.     (line    6)
* malloc function attribute:             Common Function Attributes.
                                                             (line  706)
* matching constraint:                   Simple Constraints. (line  137)
* may_alias type attribute:              Common Type Attributes.
                                                             (line  245)
* MCore options:                         MCore Options.      (line    6)
* medium_call function attribute, ARC:   ARC Function Attributes.
                                                             (line   26)
* member fns, automatically inline:      Inline.             (line   68)
* memchr:                                Other Builtins.     (line    6)
* memcmp:                                Other Builtins.     (line    6)
* memcpy:                                Other Builtins.     (line    6)
* memory references in constraints:      Simple Constraints. (line   17)
* mempcpy:                               Other Builtins.     (line    6)
* memset:                                Other Builtins.     (line    6)
* MeP options:                           MeP Options.        (line    6)
* Mercury:                               G++ and GCC.        (line   23)
* message formatting:                    Diagnostic Message Formatting Options.
                                                             (line    6)
* messages, warning:                     Warning Options.    (line    6)
* messages, warning and error:           Warnings and Errors.
                                                             (line    6)
* MicroBlaze Options:                    MicroBlaze Options. (line    6)
* micromips function attribute:          MIPS Function Attributes.
                                                             (line   91)
* middle-operands, omitted:              Conditionals.       (line    6)
* MIPS options:                          MIPS Options.       (line    6)
* mips16 function attribute, MIPS:       MIPS Function Attributes.
                                                             (line   75)
* misunderstandings in C++:              C++ Misunderstandings.
                                                             (line    6)
* mixed declarations and code:           Mixed Labels and Declarations.
                                                             (line    6)
* mixing assembly language and C:        Using Assembly Language with C.
                                                             (line    6)
* mktemp, and constant strings:          Incompatibilities.  (line   13)
* MMIX Options:                          MMIX Options.       (line    6)
* MN10300 options:                       MN10300 Options.    (line    6)
* mode type attribute:                   Common Type Attributes.
                                                             (line  281)
* mode variable attribute:               Common Variable Attributes.
                                                             (line  240)
* model function attribute, M32R/D:      M32R/D Function Attributes.
                                                             (line   15)
* model variable attribute, IA-64:       IA-64 Variable Attributes.
                                                             (line    9)
* model-name variable attribute, M32R/D: M32R/D Variable Attributes.
                                                             (line    9)
* modf:                                  Other Builtins.     (line    6)
* modff:                                 Other Builtins.     (line    6)
* modfl:                                 Other Builtins.     (line    6)
* modifiers in constraints:              Modifiers.          (line    6)
* Moxie Options:                         Moxie Options.      (line    6)
* ms_abi function attribute, x86:        x86 Function Attributes.
                                                             (line   34)
* ms_hook_prologue function attribute, x86: x86 Function Attributes.
                                                             (line   59)
* ms_struct type attribute, PowerPC:     PowerPC Type Attributes.
                                                             (line    9)
* ms_struct type attribute, x86:         x86 Type Attributes.
                                                             (line   11)
* ms_struct variable attribute, PowerPC: PowerPC Variable Attributes.
                                                             (line    9)
* ms_struct variable attribute, x86:     x86 Variable Attributes.
                                                             (line   11)
* MSP430 Options:                        MSP430 Options.     (line    6)
* multiple alternative constraints:      Multi-Alternative.  (line    6)
* multiprecision arithmetic:             Long Long.          (line    6)
* n in constraint:                       Simple Constraints. (line   73)
* naked function attribute, ARC:         ARC Function Attributes.
                                                             (line   58)
* naked function attribute, ARM:         ARM Function Attributes.
                                                             (line   48)
* naked function attribute, AVR:         AVR Function Attributes.
                                                             (line   23)
* naked function attribute, C-SKY:       C-SKY Function Attributes.
                                                             (line   20)
* naked function attribute, MCORE:       MCORE Function Attributes.
                                                             (line    9)
* naked function attribute, MSP430:      MSP430 Function Attributes.
                                                             (line   34)
* naked function attribute, NDS32:       NDS32 Function Attributes.
                                                             (line   35)
* naked function attribute, RISC-V:      RISC-V Function Attributes.
                                                             (line    9)
* naked function attribute, RL78:        RL78 Function Attributes.
                                                             (line   20)
* naked function attribute, RX:          RX Function Attributes.
                                                             (line   39)
* naked function attribute, x86:         x86 Function Attributes.
                                                             (line   66)
* Named Address Spaces:                  Named Address Spaces.
                                                             (line    6)
* names used in assembler code:          Asm Labels.         (line    6)
* naming convention, implementation headers: C++ Interface.  (line   43)
* NDS32 Options:                         NDS32 Options.      (line    6)
* near function attribute, MeP:          MeP Function Attributes.
                                                             (line   20)
* near function attribute, MIPS:         MIPS Function Attributes.
                                                             (line   63)
* near type attribute, MeP:              MeP Type Attributes.
                                                             (line    6)
* near variable attribute, MeP:          MeP Variable Attributes.
                                                             (line   24)
* nearbyint:                             Other Builtins.     (line    6)
* nearbyintf:                            Other Builtins.     (line    6)
* nearbyintl:                            Other Builtins.     (line    6)
* nested function attribute, NDS32:      NDS32 Function Attributes.
                                                             (line   19)
* nested functions:                      Nested Functions.   (line    6)
* nested_ready function attribute, NDS32: NDS32 Function Attributes.
                                                             (line   23)
* nesting function attribute, Blackfin:  Blackfin Function Attributes.
                                                             (line   45)
* newlines (escaped):                    Escaped Newlines.   (line    6)
* nextafter:                             Other Builtins.     (line    6)
* nextafterf:                            Other Builtins.     (line    6)
* nextafterl:                            Other Builtins.     (line    6)
* nexttoward:                            Other Builtins.     (line    6)
* nexttowardf:                           Other Builtins.     (line    6)
* nexttowardl:                           Other Builtins.     (line    6)
* NFC:                                   Warning Options.    (line 3029)
* NFKC:                                  Warning Options.    (line 3029)
* Nios II options:                       Nios II Options.    (line    6)
* nmi function attribute, NDS32:         NDS32 Function Attributes.
                                                             (line   50)
* NMI handler functions on the Blackfin processor: Blackfin Function Attributes.
                                                             (line   50)
* nmi_handler function attribute, Blackfin: Blackfin Function Attributes.
                                                             (line   50)
* no_caller_saved_registers function attribute, x86: x86 Function Attributes.
                                                             (line  113)
* no_gccisr function attribute, AVR:     AVR Function Attributes.
                                                             (line   33)
* no_icf function attribute:             Common Function Attributes.
                                                             (line  810)
* no_instrument_function function attribute: Common Function Attributes.
                                                             (line  814)
* no_profile_instrument_function function attribute: Common Function Attributes.
                                                             (line  820)
* no_reorder function attribute:         Common Function Attributes.
                                                             (line  825)
* no_sanitize function attribute:        Common Function Attributes.
                                                             (line  833)
* no_sanitize_address function attribute: Common Function Attributes.
                                                             (line  845)
* no_sanitize_coverage function attribute: Common Function Attributes.
                                                             (line  864)
* no_sanitize_thread function attribute: Common Function Attributes.
                                                             (line  853)
* no_sanitize_undefined function attribute: Common Function Attributes.
                                                             (line  858)
* no_split_stack function attribute:     Common Function Attributes.
                                                             (line  869)
* no_stack_limit function attribute:     Common Function Attributes.
                                                             (line  875)
* no_stack_protector function attribute: Common Function Attributes.
                                                             (line 1204)
* nocf_check function attribute:         x86 Function Attributes.
                                                             (line  636)
* noclone function attribute:            Common Function Attributes.
                                                             (line  880)
* nocommon variable attribute:           Common Variable Attributes.
                                                             (line  176)
* nocompression function attribute, MIPS: MIPS Function Attributes.
                                                             (line  108)
* nodirect_extern_access function attribute: x86 Function Attributes.
                                                             (line  712)
* noinit variable attribute:             Common Variable Attributes.
                                                             (line  438)
* noinline function attribute:           Common Function Attributes.
                                                             (line  886)
* noipa function attribute:              Common Function Attributes.
                                                             (line  897)
* nomicromips function attribute:        MIPS Function Attributes.
                                                             (line   91)
* nomips16 function attribute, MIPS:     MIPS Function Attributes.
                                                             (line   75)
* non-constant initializers:             Initializers.       (line    6)
* non-static inline function:            Inline.             (line   82)
* nonlocal gotos:                        Nonlocal Gotos.     (line    6)
* nonnull function attribute:            Common Function Attributes.
                                                             (line  911)
* nonstring variable attribute:          Common Variable Attributes.
                                                             (line  252)
* noplt function attribute:              Common Function Attributes.
                                                             (line  958)
* noreturn function attribute:           Common Function Attributes.
                                                             (line  982)
* nosave_low_regs function attribute, SH: SH Function Attributes.
                                                             (line   34)
* not_nested function attribute, NDS32:  NDS32 Function Attributes.
                                                             (line   21)
* note GCC_COLORS capability:            Diagnostic Message Formatting Options.
                                                             (line   98)
* nothrow function attribute:            Common Function Attributes.
                                                             (line 1016)
* notshared type attribute, ARM:         ARM Type Attributes.
                                                             (line    6)
* Nvidia PTX options:                    Nvidia PTX Options. (line    6)
* nvptx options:                         Nvidia PTX Options. (line    6)
* o in constraint:                       Simple Constraints. (line   23)
* OBJC_INCLUDE_PATH:                     Environment Variables.
                                                             (line  147)
* objc_nullability variable attribute:   Common Variable Attributes.
                                                             (line  458)
* objc_root_class type attribute:        Common Type Attributes.
                                                             (line  475)
* Objective-C:                           G++ and GCC.        (line    6)
* Objective-C <1>:                       Standards.          (line  197)
* Objective-C and Objective-C++ options, command-line: Objective-C and Objective-C++ Dialect Options.
                                                             (line    6)
* Objective-C++:                         G++ and GCC.        (line    6)
* Objective-C++ <1>:                     Standards.          (line  197)
* Offloading options:                    C Dialect Options.  (line  373)
* Offloading targets:                    C Dialect Options.  (line  360)
* offsettable address:                   Simple Constraints. (line   23)
* old-style function definitions:        Function Prototypes.
                                                             (line    6)
* omit-leaf-frame-pointer function attribute, AArch64: AArch64 Function Attributes.
                                                             (line   41)
* omitted middle-operands:               Conditionals.       (line    6)
* open coding:                           Inline.             (line    6)
* OpenACC accelerator programming:       C Dialect Options.  (line  388)
* OpenACC accelerator programming <1>:   C Dialect Options.  (line  396)
* OpenACC accelerator programming <2>:   Warning Options.    (line 3096)
* OpenACC offloading options:            C Dialect Options.  (line  373)
* OpenACC offloading targets:            C Dialect Options.  (line  360)
* OpenMP offloading options:             C Dialect Options.  (line  373)
* OpenMP offloading targets:             C Dialect Options.  (line  360)
* OpenMP parallel:                       C Dialect Options.  (line  402)
* OpenMP SIMD:                           C Dialect Options.  (line  410)
* OpenRISC Options:                      OpenRISC Options.   (line    6)
* operand constraints, asm:              Constraints.        (line    6)
* optimize function attribute:           Common Function Attributes.
                                                             (line 1024)
* optimize options:                      Optimize Options.   (line    6)
* options to control diagnostics formatting: Diagnostic Message Formatting Options.
                                                             (line    6)
* options to control warnings:           Warning Options.    (line    6)
* options, C++:                          C++ Dialect Options.
                                                             (line    6)
* options, code generation:              Code Gen Options.   (line    6)
* options, debugging:                    Debugging Options.  (line    6)
* options, dialect:                      C Dialect Options.  (line    6)
* options, directory search:             Directory Options.  (line    6)
* options, GCC command:                  Invoking GCC.       (line    6)
* options, grouping:                     Invoking GCC.       (line   31)
* options, linking:                      Link Options.       (line    6)
* options, Objective-C and Objective-C++: Objective-C and Objective-C++ Dialect Options.
                                                             (line    6)
* options, optimization:                 Optimize Options.   (line    6)
* options, order:                        Invoking GCC.       (line   35)
* options, preprocessor:                 Preprocessor Options.
                                                             (line    6)
* options, profiling:                    Instrumentation Options.
                                                             (line    6)
* options, program instrumentation:      Instrumentation Options.
                                                             (line    6)
* options, run-time error checking:      Instrumentation Options.
                                                             (line    6)
* order of evaluation, side effects:     Non-bugs.           (line  196)
* order of options:                      Invoking GCC.       (line   35)
* OS_main function attribute, AVR:       AVR Function Attributes.
                                                             (line   56)
* OS_task function attribute, AVR:       AVR Function Attributes.
                                                             (line   56)
* other register constraints:            Simple Constraints. (line  161)
* outline-atomics function attribute, AArch64: AArch64 Function Attributes.
                                                             (line   82)
* output file option:                    Overall Options.    (line  192)
* overloaded virtual function, warning:  C++ Dialect Options.
                                                             (line 1006)
* p in constraint:                       Simple Constraints. (line  152)
* packed type attribute:                 Common Type Attributes.
                                                             (line  293)
* packed variable attribute:             Common Variable Attributes.
                                                             (line  285)
* parameter forward declaration:         Variable Length.    (line   66)
* partial_save function attribute, NDS32: NDS32 Function Attributes.
                                                             (line   31)
* patchable_function_entry function attribute: Common Function Attributes.
                                                             (line 1052)
* path GCC_COLORS capability:            Diagnostic Message Formatting Options.
                                                             (line  101)
* pcs function attribute, ARM:           ARM Function Attributes.
                                                             (line   58)
* PDP-11 Options:                        PDP-11 Options.     (line    6)
* persistent variable attribute:         Common Variable Attributes.
                                                             (line  447)
* PIC:                                   Code Gen Options.   (line  355)
* picoChip options:                      picoChip Options.   (line    6)
* pmf:                                   Bound member functions.
                                                             (line    6)
* pointer arguments:                     Common Function Attributes.
                                                             (line  265)
* pointer arguments in variadic functions: Variadic Pointer Args.
                                                             (line    6)
* pointer to member function:            Bound member functions.
                                                             (line    6)
* pointers to arrays:                    Pointers to Arrays. (line    6)
* portions of temporary objects, pointers to: Temporaries.   (line    6)
* pow:                                   Other Builtins.     (line    6)
* pow10:                                 Other Builtins.     (line    6)
* pow10f:                                Other Builtins.     (line    6)
* pow10l:                                Other Builtins.     (line    6)
* PowerPC options:                       PowerPC Options.    (line    6)
* powf:                                  Other Builtins.     (line    6)
* powl:                                  Other Builtins.     (line    6)
* pragma GCC ivdep:                      Loop-Specific Pragmas.
                                                             (line    7)
* pragma GCC optimize:                   Function Specific Option Pragmas.
                                                             (line   21)
* pragma GCC pop_options:                Function Specific Option Pragmas.
                                                             (line   33)
* pragma GCC push_options:               Function Specific Option Pragmas.
                                                             (line   33)
* pragma GCC reset_options:              Function Specific Option Pragmas.
                                                             (line   41)
* pragma GCC target:                     Function Specific Option Pragmas.
                                                             (line    7)
* pragma GCC unroll N:                   Loop-Specific Pragmas.
                                                             (line   37)
* pragma, address:                       M32C Pragmas.       (line   15)
* pragma, align:                         Solaris Pragmas.    (line   11)
* pragma, call:                          MeP Pragmas.        (line   48)
* pragma, coprocessor available:         MeP Pragmas.        (line   13)
* pragma, coprocessor call_saved:        MeP Pragmas.        (line   20)
* pragma, coprocessor subclass:          MeP Pragmas.        (line   28)
* pragma, ctable_entry:                  PRU Pragmas.        (line    7)
* pragma, custom io_volatile:            MeP Pragmas.        (line    7)
* pragma, diagnostic:                    Diagnostic Pragmas. (line   14)
* pragma, diagnostic <1>:                Diagnostic Pragmas. (line   72)
* pragma, diagnostic <2>:                Diagnostic Pragmas. (line   92)
* pragma, diagnostic <3>:                Diagnostic Pragmas. (line  114)
* pragma, disinterrupt:                  MeP Pragmas.        (line   38)
* pragma, fini:                          Solaris Pragmas.    (line   20)
* pragma, init:                          Solaris Pragmas.    (line   26)
* pragma, long_calls:                    ARM Pragmas.        (line   11)
* pragma, long_calls_off:                ARM Pragmas.        (line   17)
* pragma, longcall:                      RS/6000 and PowerPC Pragmas.
                                                             (line   14)
* pragma, mark:                          Darwin Pragmas.     (line   11)
* pragma, memregs:                       M32C Pragmas.       (line    7)
* pragma, no_long_calls:                 ARM Pragmas.        (line   14)
* pragma, options align:                 Darwin Pragmas.     (line   14)
* pragma, pop_macro:                     Push/Pop Macro Pragmas.
                                                             (line   15)
* pragma, push_macro:                    Push/Pop Macro Pragmas.
                                                             (line   11)
* pragma, redefine_extname:              Symbol-Renaming Pragmas.
                                                             (line   13)
* pragma, segment:                       Darwin Pragmas.     (line   21)
* pragma, unused:                        Darwin Pragmas.     (line   24)
* pragma, visibility:                    Visibility Pragmas. (line    8)
* pragma, weak:                          Weak Pragmas.       (line   10)
* pragmas:                               Pragmas.            (line    6)
* pragmas in C++, effect on inlining:    C++ Interface.      (line   57)
* pragmas, interface and implementation: C++ Interface.      (line    6)
* pragmas, warning of unknown:           Warning Options.    (line 1390)
* precompiled headers:                   Precompiled Headers.
                                                             (line    6)
* prefer-vector-width function attribute, x86: x86 Function Attributes.
                                                             (line  592)
* preprocessing numbers:                 Incompatibilities.  (line  173)
* preprocessing tokens:                  Incompatibilities.  (line  173)
* preprocessor options:                  Preprocessor Options.
                                                             (line    6)
* preserve_access_index type attribute, BPF: BPF Type Attributes.
                                                             (line    6)
* printf:                                Other Builtins.     (line    6)
* printf_unlocked:                       Other Builtins.     (line    6)
* prof:                                  Instrumentation Options.
                                                             (line   18)
* profiling options:                     Instrumentation Options.
                                                             (line    6)
* progmem variable attribute, AVR:       AVR Variable Attributes.
                                                             (line    7)
* program instrumentation options:       Instrumentation Options.
                                                             (line    6)
* promotion of formal parameters:        Function Prototypes.
                                                             (line    6)
* PRU Options:                           PRU Options.        (line    6)
* pure function attribute:               Common Function Attributes.
                                                             (line 1070)
* push address instruction:              Simple Constraints. (line  152)
* putchar:                               Other Builtins.     (line    6)
* puts:                                  Other Builtins.     (line    6)
* q floating point suffix:               Floating Types.     (line    6)
* Q floating point suffix:               Floating Types.     (line    6)
* qsort, and global register variables:  Global Register Variables.
                                                             (line   75)
* quote GCC_COLORS capability:           Diagnostic Message Formatting Options.
                                                             (line  117)
* r fixed-suffix:                        Fixed-Point.        (line    6)
* R fixed-suffix:                        Fixed-Point.        (line    6)
* r in constraint:                       Simple Constraints. (line   64)
* RAMPD:                                 AVR Options.        (line  428)
* RAMPX:                                 AVR Options.        (line  428)
* RAMPY:                                 AVR Options.        (line  428)
* RAMPZ:                                 AVR Options.        (line  428)
* range1 GCC_COLORS capability:          Diagnostic Message Formatting Options.
                                                             (line  107)
* range2 GCC_COLORS capability:          Diagnostic Message Formatting Options.
                                                             (line  110)
* ranges in case statements:             Case Ranges.        (line    6)
* read-only strings:                     Incompatibilities.  (line    9)
* realloc:                               Other Builtins.     (line    6)
* reentrant function attribute, MSP430:  MSP430 Function Attributes.
                                                             (line   44)
* register variable after longjmp:       Global Register Variables.
                                                             (line   92)
* registers for local variables:         Local Register Variables.
                                                             (line    6)
* registers in constraints:              Simple Constraints. (line   64)
* registers, global allocation:          Global Register Variables.
                                                             (line    6)
* registers, global variables in:        Global Register Variables.
                                                             (line    6)
* regparm function attribute, x86:       x86 Function Attributes.
                                                             (line   76)
* relocation truncated to fit (ColdFire): M680x0 Options.    (line  323)
* relocation truncated to fit (MIPS):    MIPS Options.       (line  237)
* remainder:                             Other Builtins.     (line    6)
* remainderf:                            Other Builtins.     (line    6)
* remainderl:                            Other Builtins.     (line    6)
* remquo:                                Other Builtins.     (line    6)
* remquof:                               Other Builtins.     (line    6)
* remquol:                               Other Builtins.     (line    6)
* renesas function attribute, SH:        SH Function Attributes.
                                                             (line   40)
* reordering, warning:                   C++ Dialect Options.
                                                             (line  820)
* reporting bugs:                        Bugs.               (line    6)
* resbank function attribute, SH:        SH Function Attributes.
                                                             (line   44)
* reset function attribute, NDS32:       NDS32 Function Attributes.
                                                             (line   45)
* reset handler functions:               NDS32 Function Attributes.
                                                             (line   45)
* rest argument (in macro):              Variadic Macros.    (line    6)
* restricted pointers:                   Restricted Pointers.
                                                             (line    6)
* restricted references:                 Restricted Pointers.
                                                             (line    6)
* restricted this pointer:               Restricted Pointers.
                                                             (line    6)
* retain function attribute:             Common Function Attributes.
                                                             (line 1350)
* retain variable attribute:             Common Variable Attributes.
                                                             (line  375)
* returns_nonnull function attribute:    Common Function Attributes.
                                                             (line 1117)
* returns_twice function attribute:      Common Function Attributes.
                                                             (line 1127)
* rindex:                                Other Builtins.     (line    6)
* rint:                                  Other Builtins.     (line    6)
* rintf:                                 Other Builtins.     (line    6)
* rintl:                                 Other Builtins.     (line    6)
* RISC-V Options:                        RISC-V Options.     (line    6)
* RL78 Options:                          RL78 Options.       (line    6)
* round:                                 Other Builtins.     (line    6)
* roundf:                                Other Builtins.     (line    6)
* roundl:                                Other Builtins.     (line    6)
* RS/6000 and PowerPC Options:           RS/6000 and PowerPC Options.
                                                             (line    6)
* RTTI:                                  Vague Linkage.      (line   42)
* run-time error checking options:       Instrumentation Options.
                                                             (line    6)
* run-time options:                      Code Gen Options.   (line    6)
* RX Options:                            RX Options.         (line    6)
* s in constraint:                       Simple Constraints. (line  100)
* S/390 and zSeries Options:             S/390 and zSeries Options.
                                                             (line    6)
* saddr variable attribute, RL78:        RL78 Variable Attributes.
                                                             (line    6)
* save all registers on the Blackfin:    Blackfin Function Attributes.
                                                             (line   56)
* save all registers on the H8/300, H8/300H, and H8S: H8/300 Function Attributes.
                                                             (line   23)
* save_all function attribute, NDS32:    NDS32 Function Attributes.
                                                             (line   28)
* save_volatiles function attribute, MicroBlaze: MicroBlaze Function Attributes.
                                                             (line    9)
* saveall function attribute, Blackfin:  Blackfin Function Attributes.
                                                             (line   56)
* saveall function attribute, H8/300:    H8/300 Function Attributes.
                                                             (line   23)
* scalar_storage_order type attribute:   Common Type Attributes.
                                                             (line  328)
* scalb:                                 Other Builtins.     (line    6)
* scalbf:                                Other Builtins.     (line    6)
* scalbl:                                Other Builtins.     (line    6)
* scalbln:                               Other Builtins.     (line    6)
* scalblnf:                              Other Builtins.     (line    6)
* scalblnf <1>:                          Other Builtins.     (line    6)
* scalbn:                                Other Builtins.     (line    6)
* scalbnf:                               Other Builtins.     (line    6)
* scanf, and constant strings:           Incompatibilities.  (line   17)
* scanfnl:                               Other Builtins.     (line    6)
* scope of a variable length array:      Variable Length.    (line   22)
* scope of declaration:                  Disappointments.    (line   21)
* scope of external declarations:        Incompatibilities.  (line   80)
* Score Options:                         Score Options.      (line    6)
* sda variable attribute, V850:          V850 Variable Attributes.
                                                             (line    9)
* search path:                           Directory Options.  (line    6)
* section function attribute:            Common Function Attributes.
                                                             (line 1136)
* section variable attribute:            Common Variable Attributes.
                                                             (line  307)
* secure_call function attribute, ARC:   ARC Function Attributes.
                                                             (line   53)
* selectany variable attribute:          Microsoft Windows Variable Attributes.
                                                             (line   16)
* sentinel function attribute:           Common Function Attributes.
                                                             (line 1153)
* setjmp:                                Global Register Variables.
                                                             (line   92)
* setjmp incompatibilities:              Incompatibilities.  (line   39)
* shared attribute, Nvidia PTX:          Nvidia PTX Variable Attributes.
                                                             (line    9)
* shared strings:                        Incompatibilities.  (line    9)
* shared variable attribute:             Microsoft Windows Variable Attributes.
                                                             (line   37)
* short_call function attribute, ARC:    ARC Function Attributes.
                                                             (line   26)
* short_call function attribute, ARM:    ARM Function Attributes.
                                                             (line   38)
* short_call function attribute, Epiphany: Epiphany Function Attributes.
                                                             (line   57)
* short_call function attribute, MIPS:   MIPS Function Attributes.
                                                             (line   63)
* shortcall function attribute, Blackfin: Blackfin Function Attributes.
                                                             (line   38)
* shortcall function attribute, PowerPC: PowerPC Function Attributes.
                                                             (line   10)
* side effect in ?::                     Conditionals.       (line   20)
* side effects, macro argument:          Statement Exprs.    (line   35)
* side effects, order of evaluation:     Non-bugs.           (line  196)
* sign-return-address function attribute, AArch64: AArch64 Function Attributes.
                                                             (line   69)
* signal function attribute, AVR:        AVR Function Attributes.
                                                             (line   80)
* signbit:                               Other Builtins.     (line    6)
* signbitd128:                           Other Builtins.     (line    6)
* signbitd32:                            Other Builtins.     (line    6)
* signbitd64:                            Other Builtins.     (line    6)
* signbitf:                              Other Builtins.     (line    6)
* signbitl:                              Other Builtins.     (line    6)
* signed and unsigned values, comparison warning: Warning Options.
                                                             (line 2691)
* significand:                           Other Builtins.     (line    6)
* significandf:                          Other Builtins.     (line    6)
* significandl:                          Other Builtins.     (line    6)
* SIMD:                                  C Dialect Options.  (line  410)
* simd function attribute:               Common Function Attributes.
                                                             (line 1180)
* simple constraints:                    Simple Constraints. (line    6)
* sin:                                   Other Builtins.     (line    6)
* sincos:                                Other Builtins.     (line    6)
* sincosf:                               Other Builtins.     (line    6)
* sincosl:                               Other Builtins.     (line    6)
* sinf:                                  Other Builtins.     (line    6)
* sinh:                                  Other Builtins.     (line    6)
* sinhf:                                 Other Builtins.     (line    6)
* sinhl:                                 Other Builtins.     (line    6)
* sinl:                                  Other Builtins.     (line    6)
* sizeof:                                Typeof.             (line    6)
* smaller data references:               M32R/D Options.     (line   57)
* smaller data references <1>:           Nios II Options.    (line    9)
* smaller data references (PowerPC):     RS/6000 and PowerPC Options.
                                                             (line  714)
* snprintf:                              Other Builtins.     (line    6)
* Solaris 2 options:                     Solaris 2 Options.  (line    6)
* SOURCE_DATE_EPOCH:                     Environment Variables.
                                                             (line  193)
* sp_switch function attribute, SH:      SH Function Attributes.
                                                             (line   58)
* SPARC options:                         SPARC Options.      (line    6)
* Spec Files:                            Spec Files.         (line    6)
* specified registers:                   Explicit Register Variables.
                                                             (line    6)
* specifying compiler version and target machine: Invoking GCC.
                                                             (line   24)
* specifying hardware config:            Submodel Options.   (line    6)
* specifying machine version:            Invoking GCC.       (line   24)
* specifying registers for local variables: Local Register Variables.
                                                             (line    6)
* speed of compilation:                  Precompiled Headers.
                                                             (line    6)
* speed of compilation <1>:              C++ Modules.        (line    6)
* sprintf:                               Other Builtins.     (line    6)
* sqrt:                                  Other Builtins.     (line    6)
* sqrtf:                                 Other Builtins.     (line    6)
* sqrtl:                                 Other Builtins.     (line    6)
* sscanf:                                Other Builtins.     (line    6)
* sscanf, and constant strings:          Incompatibilities.  (line   17)
* sseregparm function attribute, x86:    x86 Function Attributes.
                                                             (line   93)
* stack_protect function attribute:      Common Function Attributes.
                                                             (line 1199)
* Statement Attributes:                  Statement Attributes.
                                                             (line    6)
* statements inside expressions:         Statement Exprs.    (line    6)
* static data in C++, declaring and defining: Static Definitions.
                                                             (line    6)
* stdcall function attribute, x86-32:    x86 Function Attributes.
                                                             (line  108)
* stpcpy:                                Other Builtins.     (line    6)
* stpncpy:                               Other Builtins.     (line    6)
* strcasecmp:                            Other Builtins.     (line    6)
* strcat:                                Other Builtins.     (line    6)
* strchr:                                Other Builtins.     (line    6)
* strcmp:                                Other Builtins.     (line    6)
* strcpy:                                Other Builtins.     (line    6)
* strcspn:                               Other Builtins.     (line    6)
* strdup:                                Other Builtins.     (line    6)
* strfmon:                               Other Builtins.     (line    6)
* strftime:                              Other Builtins.     (line    6)
* strict-align function attribute, AArch64: AArch64 Function Attributes.
                                                             (line   33)
* string constants:                      Incompatibilities.  (line    9)
* strlen:                                Other Builtins.     (line    6)
* strncasecmp:                           Other Builtins.     (line    6)
* strncat:                               Other Builtins.     (line    6)
* strncmp:                               Other Builtins.     (line    6)
* strncpy:                               Other Builtins.     (line    6)
* strndup:                               Other Builtins.     (line    6)
* strnlen:                               Other Builtins.     (line    6)
* strpbrk:                               Other Builtins.     (line    6)
* strrchr:                               Other Builtins.     (line    6)
* strspn:                                Other Builtins.     (line    6)
* strstr:                                Other Builtins.     (line    6)
* struct:                                Unnamed Fields.     (line    6)
* struct __htm_tdb:                      S/390 System z Built-in Functions.
                                                             (line   49)
* structures:                            Incompatibilities.  (line  146)
* structures, constructor expression:    Compound Literals.  (line    6)
* submodel options:                      Submodel Options.   (line    6)
* subscripting:                          Subscripting.       (line    6)
* subscripting and function values:      Subscripting.       (line    6)
* suffixes for C++ source:               Invoking G++.       (line    6)
* SUNPRO_DEPENDENCIES:                   Environment Variables.
                                                             (line  187)
* suppressing warnings:                  Warning Options.    (line    6)
* surprises in C++:                      C++ Misunderstandings.
                                                             (line    6)
* symver function attribute:             Common Function Attributes.
                                                             (line 1247)
* syntax checking:                       Warning Options.    (line   13)
* syscall_linkage function attribute, IA-64: IA-64 Function Attributes.
                                                             (line    9)
* system headers, warnings from:         Warning Options.    (line 2034)
* sysv_abi function attribute, x86:      x86 Function Attributes.
                                                             (line   34)
* tainted_args function attribute:       Common Function Attributes.
                                                             (line 1291)
* tan:                                   Other Builtins.     (line    6)
* tanf:                                  Other Builtins.     (line    6)
* tanh:                                  Other Builtins.     (line    6)
* tanhf:                                 Other Builtins.     (line    6)
* tanhl:                                 Other Builtins.     (line    6)
* tanl:                                  Other Builtins.     (line    6)
* target function attribute:             Common Function Attributes.
                                                             (line 1207)
* target function attribute <1>:         ARM Function Attributes.
                                                             (line   77)
* target function attribute <2>:         Nios II Function Attributes.
                                                             (line    9)
* target function attribute <3>:         PowerPC Function Attributes.
                                                             (line   21)
* target function attribute <4>:         S/390 Function Attributes.
                                                             (line   22)
* target function attribute <5>:         x86 Function Attributes.
                                                             (line  180)
* target machine, specifying:            Invoking GCC.       (line   24)
* target_clones function attribute:      Common Function Attributes.
                                                             (line 1308)
* target-dependent options:              Submodel Options.   (line    6)
* target("3dnow") function attribute, x86: x86 Function Attributes.
                                                             (line  186)
* target("3dnowa") function attribute, x86: x86 Function Attributes.
                                                             (line  190)
* target("abm") function attribute, x86: x86 Function Attributes.
                                                             (line  195)
* target("adx") function attribute, x86: x86 Function Attributes.
                                                             (line  200)
* target("aes") function attribute, x86: x86 Function Attributes.
                                                             (line  204)
* target("align-stringops") function attribute, x86: x86 Function Attributes.
                                                             (line  566)
* target("altivec") function attribute, PowerPC: PowerPC Function Attributes.
                                                             (line   28)
* target("amx-bf16") function attribute, x86: x86 Function Attributes.
                                                             (line  518)
* target("amx-int8") function attribute, x86: x86 Function Attributes.
                                                             (line  514)
* target("amx-tile") function attribute, x86: x86 Function Attributes.
                                                             (line  510)
* target("arch=ARCH") function attribute, x86: x86 Function Attributes.
                                                             (line  578)
* target("arm") function attribute, ARM: ARM Function Attributes.
                                                             (line   87)
* target("avoid-indexed-addresses") function attribute, PowerPC: PowerPC Function Attributes.
                                                             (line  142)
* target("avx") function attribute, x86: x86 Function Attributes.
                                                             (line  208)
* target("avx2") function attribute, x86: x86 Function Attributes.
                                                             (line  212)
* target("avx5124fmaps") function attribute, x86: x86 Function Attributes.
                                                             (line  216)
* target("avx5124vnniw") function attribute, x86: x86 Function Attributes.
                                                             (line  221)
* target("avx512bitalg") function attribute, x86: x86 Function Attributes.
                                                             (line  226)
* target("avx512bw") function attribute, x86: x86 Function Attributes.
                                                             (line  231)
* target("avx512cd") function attribute, x86: x86 Function Attributes.
                                                             (line  235)
* target("avx512dq") function attribute, x86: x86 Function Attributes.
                                                             (line  239)
* target("avx512er") function attribute, x86: x86 Function Attributes.
                                                             (line  243)
* target("avx512f") function attribute, x86: x86 Function Attributes.
                                                             (line  247)
* target("avx512ifma") function attribute, x86: x86 Function Attributes.
                                                             (line  251)
* target("avx512pf") function attribute, x86: x86 Function Attributes.
                                                             (line  255)
* target("avx512vbmi") function attribute, x86: x86 Function Attributes.
                                                             (line  259)
* target("avx512vbmi2") function attribute, x86: x86 Function Attributes.
                                                             (line  263)
* target("avx512vl") function attribute, x86: x86 Function Attributes.
                                                             (line  267)
* target("avx512vnni") function attribute, x86: x86 Function Attributes.
                                                             (line  271)
* target("avx512vpopcntdq") function attribute, x86: x86 Function Attributes.
                                                             (line  275)
* target("avxvnni") function attribute, x86: x86 Function Attributes.
                                                             (line  538)
* target("bmi") function attribute, x86: x86 Function Attributes.
                                                             (line  280)
* target("bmi2") function attribute, x86: x86 Function Attributes.
                                                             (line  284)
* target("cld") function attribute, x86: x86 Function Attributes.
                                                             (line  542)
* target("cldemote") function attribute, x86: x86 Function Attributes.
                                                             (line  288)
* target("clflushopt") function attribute, x86: x86 Function Attributes.
                                                             (line  292)
* target("clwb") function attribute, x86: x86 Function Attributes.
                                                             (line  296)
* target("clzero") function attribute, x86: x86 Function Attributes.
                                                             (line  300)
* target("cmpb") function attribute, PowerPC: PowerPC Function Attributes.
                                                             (line   34)
* target("cpu=CPU") function attribute, PowerPC: PowerPC Function Attributes.
                                                             (line  157)
* target("crc32") function attribute, x86: x86 Function Attributes.
                                                             (line  304)
* target("custom-fpu-cfg=NAME") function attribute, Nios II: Nios II Function Attributes.
                                                             (line   25)
* target("custom-INSN=N") function attribute, Nios II: Nios II Function Attributes.
                                                             (line   16)
* target("cx16") function attribute, x86: x86 Function Attributes.
                                                             (line  308)
* target("default") function attribute, x86: x86 Function Attributes.
                                                             (line  311)
* target("dlmzb") function attribute, PowerPC: PowerPC Function Attributes.
                                                             (line   40)
* target("f16c") function attribute, x86: x86 Function Attributes.
                                                             (line  316)
* target("fancy-math-387") function attribute, x86: x86 Function Attributes.
                                                             (line  546)
* target("fma") function attribute, x86: x86 Function Attributes.
                                                             (line  320)
* target("fma4") function attribute, x86: x86 Function Attributes.
                                                             (line  324)
* target("fpmath=FPMATH") function attribute, x86: x86 Function Attributes.
                                                             (line  586)
* target("fprnd") function attribute, PowerPC: PowerPC Function Attributes.
                                                             (line   47)
* target("fpu=") function attribute, ARM: ARM Function Attributes.
                                                             (line   93)
* target("friz") function attribute, PowerPC: PowerPC Function Attributes.
                                                             (line  133)
* target("fsgsbase") function attribute, x86: x86 Function Attributes.
                                                             (line  328)
* target("fxsr") function attribute, x86: x86 Function Attributes.
                                                             (line  332)
* target("general-regs-only") function attribute, x86: x86 Function Attributes.
                                                             (line  575)
* target("gfni") function attribute, x86: x86 Function Attributes.
                                                             (line  336)
* target("hard-dfp") function attribute, PowerPC: PowerPC Function Attributes.
                                                             (line   53)
* target("hle") function attribute, x86: x86 Function Attributes.
                                                             (line  340)
* target("hreset") function attribute, x86: x86 Function Attributes.
                                                             (line  526)
* target("ieee-fp") function attribute, x86: x86 Function Attributes.
                                                             (line  551)
* target("inline-all-stringops") function attribute, x86: x86 Function Attributes.
                                                             (line  556)
* target("inline-stringops-dynamically") function attribute, x86: x86 Function Attributes.
                                                             (line  560)
* target("isel") function attribute, PowerPC: PowerPC Function Attributes.
                                                             (line   59)
* target("kl") function attribute, x86:  x86 Function Attributes.
                                                             (line  530)
* target("longcall") function attribute, PowerPC: PowerPC Function Attributes.
                                                             (line  152)
* target("lwp") function attribute, x86: x86 Function Attributes.
                                                             (line  344)
* target("lzcnt") function attribute, x86: x86 Function Attributes.
                                                             (line  348)
* target("mfcrf") function attribute, PowerPC: PowerPC Function Attributes.
                                                             (line   63)
* target("mmx") function attribute, x86: x86 Function Attributes.
                                                             (line  352)
* target("movbe") function attribute, x86: x86 Function Attributes.
                                                             (line  356)
* target("movdir64b") function attribute, x86: x86 Function Attributes.
                                                             (line  360)
* target("movdiri") function attribute, x86: x86 Function Attributes.
                                                             (line  364)
* target("mulhw") function attribute, PowerPC: PowerPC Function Attributes.
                                                             (line   70)
* target("multiple") function attribute, PowerPC: PowerPC Function Attributes.
                                                             (line   77)
* target("mwait") function attribute, x86: x86 Function Attributes.
                                                             (line  368)
* target("mwaitx") function attribute, x86: x86 Function Attributes.
                                                             (line  373)
* target("no-custom-INSN") function attribute, Nios II: Nios II Function Attributes.
                                                             (line   16)
* target("paired") function attribute, PowerPC: PowerPC Function Attributes.
                                                             (line  147)
* target("pclmul") function attribute, x86: x86 Function Attributes.
                                                             (line  377)
* target("pconfig") function attribute, x86: x86 Function Attributes.
                                                             (line  381)
* target("pku") function attribute, x86: x86 Function Attributes.
                                                             (line  385)
* target("popcnt") function attribute, x86: x86 Function Attributes.
                                                             (line  389)
* target("popcntb") function attribute, PowerPC: PowerPC Function Attributes.
                                                             (line   88)
* target("popcntd") function attribute, PowerPC: PowerPC Function Attributes.
                                                             (line   95)
* target("powerpc-gfxopt") function attribute, PowerPC: PowerPC Function Attributes.
                                                             (line  101)
* target("powerpc-gpopt") function attribute, PowerPC: PowerPC Function Attributes.
                                                             (line  107)
* target("prefetchwt1") function attribute, x86: x86 Function Attributes.
                                                             (line  393)
* target("prfchw") function attribute, x86: x86 Function Attributes.
                                                             (line  397)
* target("ptwrite") function attribute, x86: x86 Function Attributes.
                                                             (line  401)
* target("rdpid") function attribute, x86: x86 Function Attributes.
                                                             (line  405)
* target("rdrnd") function attribute, x86: x86 Function Attributes.
                                                             (line  409)
* target("rdseed") function attribute, x86: x86 Function Attributes.
                                                             (line  413)
* target("recip-precision") function attribute, PowerPC: PowerPC Function Attributes.
                                                             (line  113)
* target("recip") function attribute, x86: x86 Function Attributes.
                                                             (line  570)
* target("rtm") function attribute, x86: x86 Function Attributes.
                                                             (line  417)
* target("sahf") function attribute, x86: x86 Function Attributes.
                                                             (line  421)
* target("sgx") function attribute, x86: x86 Function Attributes.
                                                             (line  425)
* target("sha") function attribute, x86: x86 Function Attributes.
                                                             (line  429)
* target("shstk") function attribute, x86: x86 Function Attributes.
                                                             (line  433)
* target("sse") function attribute, x86: x86 Function Attributes.
                                                             (line  437)
* target("sse2") function attribute, x86: x86 Function Attributes.
                                                             (line  441)
* target("sse3") function attribute, x86: x86 Function Attributes.
                                                             (line  445)
* target("sse4.1") function attribute, x86: x86 Function Attributes.
                                                             (line  454)
* target("sse4.2") function attribute, x86: x86 Function Attributes.
                                                             (line  458)
* target("sse4") function attribute, x86: x86 Function Attributes.
                                                             (line  449)
* target("sse4a") function attribute, x86: x86 Function Attributes.
                                                             (line  462)
* target("ssse3") function attribute, x86: x86 Function Attributes.
                                                             (line  466)
* target("string") function attribute, PowerPC: PowerPC Function Attributes.
                                                             (line  119)
* target("tbm") function attribute, x86: x86 Function Attributes.
                                                             (line  470)
* target("thumb") function attribute, ARM: ARM Function Attributes.
                                                             (line   83)
* target("tune=TUNE") function attribute, PowerPC: PowerPC Function Attributes.
                                                             (line  164)
* target("tune=TUNE") function attribute, x86: x86 Function Attributes.
                                                             (line  582)
* target("uintr") function attribute, x86: x86 Function Attributes.
                                                             (line  522)
* target("update") function attribute, PowerPC: PowerPC Function Attributes.
                                                             (line   82)
* target("vaes") function attribute, x86: x86 Function Attributes.
                                                             (line  474)
* target("vpclmulqdq") function attribute, x86: x86 Function Attributes.
                                                             (line  478)
* target("vsx") function attribute, PowerPC: PowerPC Function Attributes.
                                                             (line  125)
* target("waitpkg") function attribute, x86: x86 Function Attributes.
                                                             (line  482)
* target("wbnoinvd") function attribute, x86: x86 Function Attributes.
                                                             (line  486)
* target("widekl") function attribute, x86: x86 Function Attributes.
                                                             (line  534)
* target("xop") function attribute, x86: x86 Function Attributes.
                                                             (line  490)
* target("xsave") function attribute, x86: x86 Function Attributes.
                                                             (line  494)
* target("xsavec") function attribute, x86: x86 Function Attributes.
                                                             (line  498)
* target("xsaveopt") function attribute, x86: x86 Function Attributes.
                                                             (line  502)
* target("xsaves") function attribute, x86: x86 Function Attributes.
                                                             (line  506)
* TC1:                                   Standards.          (line   13)
* TC2:                                   Standards.          (line   13)
* TC3:                                   Standards.          (line   13)
* tda variable attribute, V850:          V850 Variable Attributes.
                                                             (line   13)
* Technical Corrigenda:                  Standards.          (line   13)
* Technical Corrigendum 1:               Standards.          (line   13)
* Technical Corrigendum 2:               Standards.          (line   13)
* Technical Corrigendum 3:               Standards.          (line   13)
* template instantiation:                Template Instantiation.
                                                             (line    6)
* temporaries, lifetime of:              Temporaries.        (line    6)
* tentative definitions:                 Code Gen Options.   (line  233)
* TERM_URLS environment variable:        Diagnostic Message Formatting Options.
                                                             (line  144)
* tgamma:                                Other Builtins.     (line    6)
* tgammaf:                               Other Builtins.     (line    6)
* tgammal:                               Other Builtins.     (line    6)
* thiscall function attribute, x86-32:   x86 Function Attributes.
                                                             (line   23)
* Thread-Local Storage:                  Thread-Local.       (line    6)
* thunks:                                Nested Functions.   (line    6)
* TILE-Gx options:                       TILE-Gx Options.    (line    6)
* TILEPro options:                       TILEPro Options.    (line    6)
* tiny data section on the H8/300H and H8S: H8/300 Variable Attributes.
                                                             (line   19)
* tiny type attribute, MeP:              MeP Type Attributes.
                                                             (line    6)
* tiny variable attribute, MeP:          MeP Variable Attributes.
                                                             (line   20)
* tiny_data variable attribute, H8/300:  H8/300 Variable Attributes.
                                                             (line   19)
* TLS:                                   Thread-Local.       (line    6)
* tls_model variable attribute:          Common Variable Attributes.
                                                             (line  352)
* tls-dialect= function attribute, AArch64: AArch64 Function Attributes.
                                                             (line   48)
* TMPDIR:                                Environment Variables.
                                                             (line   45)
* toascii:                               Other Builtins.     (line    6)
* tolower:                               Other Builtins.     (line    6)
* toupper:                               Other Builtins.     (line    6)
* towlower:                              Other Builtins.     (line    6)
* towupper:                              Other Builtins.     (line    6)
* traditional C language:                Preprocessor Options.
                                                             (line  373)
* transparent_union type attribute:      Common Type Attributes.
                                                             (line  372)
* trap_exit function attribute, SH:      SH Function Attributes.
                                                             (line   68)
* trapa_handler function attribute, SH:  SH Function Attributes.
                                                             (line   73)
* trunc:                                 Other Builtins.     (line    6)
* truncf:                                Other Builtins.     (line    6)
* truncl:                                Other Builtins.     (line    6)
* tune= function attribute, AArch64:     AArch64 Function Attributes.
                                                             (line   58)
* two-stage name lookup:                 Name lookup.        (line    6)
* type alignment:                        Alignment.          (line    6)
* type attributes:                       Type Attributes.    (line    6)
* type_info:                             Vague Linkage.      (line   42)
* type-diff GCC_COLORS capability:       Diagnostic Message Formatting Options.
                                                             (line  140)
* typedef names as function parameters:  Incompatibilities.  (line   97)
* typeof:                                Typeof.             (line    6)
* uhk fixed-suffix:                      Fixed-Point.        (line    6)
* UHK fixed-suffix:                      Fixed-Point.        (line    6)
* uhr fixed-suffix:                      Fixed-Point.        (line    6)
* UHR fixed-suffix:                      Fixed-Point.        (line    6)
* uk fixed-suffix:                       Fixed-Point.        (line    6)
* UK fixed-suffix:                       Fixed-Point.        (line    6)
* ulk fixed-suffix:                      Fixed-Point.        (line    6)
* ULK fixed-suffix:                      Fixed-Point.        (line    6)
* ULL integer suffix:                    Long Long.          (line    6)
* ullk fixed-suffix:                     Fixed-Point.        (line    6)
* ULLK fixed-suffix:                     Fixed-Point.        (line    6)
* ullr fixed-suffix:                     Fixed-Point.        (line    6)
* ULLR fixed-suffix:                     Fixed-Point.        (line    6)
* ulr fixed-suffix:                      Fixed-Point.        (line    6)
* ULR fixed-suffix:                      Fixed-Point.        (line    6)
* unavailable enumerator attribute:      Enumerator Attributes.
                                                             (line   38)
* unavailable function attribute:        Common Function Attributes.
                                                             (line  362)
* unavailable type attribute:            Common Type Attributes.
                                                             (line  224)
* unavailable variable attribute:        Common Variable Attributes.
                                                             (line  226)
* uncached type attribute, ARC:          ARC Type Attributes.
                                                             (line    6)
* undefined behavior:                    Bug Criteria.       (line   17)
* undefined function value:              Bug Criteria.       (line   17)
* underscores in variables in macros:    Typeof.             (line   46)
* uninitialized variable attribute:      Common Variable Attributes.
                                                             (line  385)
* union:                                 Unnamed Fields.     (line    6)
* union, casting to a:                   Cast to Union.      (line    6)
* unions:                                Incompatibilities.  (line  146)
* unknown pragmas, warning:              Warning Options.    (line 1390)
* unresolved references and -nodefaultlibs: Link Options.    (line  157)
* unresolved references and -nostdlib:   Link Options.       (line  157)
* unused function attribute:             Common Function Attributes.
                                                             (line 1335)
* unused label attribute:                Label Attributes.   (line   32)
* unused type attribute:                 Common Type Attributes.
                                                             (line  425)
* unused variable attribute:             Common Variable Attributes.
                                                             (line  361)
* upper function attribute, MSP430:      MSP430 Function Attributes.
                                                             (line   57)
* upper variable attribute, MSP430:      MSP430 Variable Attributes.
                                                             (line    8)
* ur fixed-suffix:                       Fixed-Point.        (line    6)
* UR fixed-suffix:                       Fixed-Point.        (line    6)
* urls:                                  Diagnostic Message Formatting Options.
                                                             (line  144)
* use_debug_exception_return function attribute, MIPS: MIPS Function Attributes.
                                                             (line   39)
* use_shadow_register_set function attribute, MIPS: MIPS Function Attributes.
                                                             (line   28)
* used function attribute:               Common Function Attributes.
                                                             (line 1340)
* used variable attribute:               Common Variable Attributes.
                                                             (line  366)
* User stack pointer in interrupts on the Blackfin: Blackfin Function Attributes.
                                                             (line   21)
* V in constraint:                       Simple Constraints. (line   43)
* V850 Options:                          V850 Options.       (line    6)
* vague linkage:                         Vague Linkage.      (line    6)
* value after longjmp:                   Global Register Variables.
                                                             (line   92)
* variable addressability on the M32R/D: M32R/D Variable Attributes.
                                                             (line    9)
* variable alignment:                    Alignment.          (line    6)
* variable attributes:                   Variable Attributes.
                                                             (line    6)
* variable number of arguments:          Variadic Macros.    (line    6)
* variable-length array in a structure:  Variable Length.    (line   26)
* variable-length array scope:           Variable Length.    (line   22)
* variable-length arrays:                Variable Length.    (line    6)
* variables in specified registers:      Explicit Register Variables.
                                                             (line    6)
* variables, local, in macros:           Typeof.             (line   46)
* variadic functions, pointer arguments: Variadic Pointer Args.
                                                             (line    6)
* variadic macros:                       Variadic Macros.    (line    6)
* VAX options:                           VAX Options.        (line    6)
* vec_blendv:                            PowerPC AltiVec Built-in Functions Available on ISA 3.1.
                                                             (line  308)
* vec_cfuge:                             PowerPC AltiVec Built-in Functions Available on ISA 3.1.
                                                             (line   12)
* vec_clrl:                              PowerPC AltiVec Built-in Functions Available on ISA 3.1.
                                                             (line   31)
* vec_clrr:                              PowerPC AltiVec Built-in Functions Available on ISA 3.1.
                                                             (line   40)
* vec_cntlzm:                            PowerPC AltiVec Built-in Functions Available on ISA 3.1.
                                                             (line   17)
* vec_cnttzm:                            PowerPC AltiVec Built-in Functions Available on ISA 3.1.
                                                             (line   22)
* vec_extracth:                          PowerPC AltiVec Built-in Functions Available on ISA 3.1.
                                                             (line  101)
* vec_extractl:                          PowerPC AltiVec Built-in Functions Available on ISA 3.1.
                                                             (line   72)
* vec_genpcvm:                           PowerPC AltiVec Built-in Functions Available on ISA 3.1.
                                                             (line  514)
* vec_gnb:                               PowerPC AltiVec Built-in Functions Available on ISA 3.1.
                                                             (line   46)
* vec_inserth:                           PowerPC AltiVec Built-in Functions Available on ISA 3.1.
                                                             (line  168)
* vec_insertl:                           PowerPC AltiVec Built-in Functions Available on ISA 3.1.
                                                             (line  137)
* vec_pdep:                              PowerPC AltiVec Built-in Functions Available on ISA 3.1.
                                                             (line  105)
* vec_permx:                             PowerPC AltiVec Built-in Functions Available on ISA 3.1.
                                                             (line  335)
* vec_pext:                              PowerPC AltiVec Built-in Functions Available on ISA 3.1.
                                                             (line  340)
* vec_replace_element:                   PowerPC AltiVec Built-in Functions Available on ISA 3.1.
                                                             (line  189)
* vec_replace_unaligned:                 PowerPC AltiVec Built-in Functions Available on ISA 3.1.
                                                             (line  211)
* vec_sldb:                              PowerPC AltiVec Built-in Functions Available on ISA 3.1.
                                                             (line  235)
* vec_splati:                            PowerPC AltiVec Built-in Functions Available on ISA 3.1.
                                                             (line  265)
* vec_splati_ins:                        PowerPC AltiVec Built-in Functions Available on ISA 3.1.
                                                             (line  281)
* vec_splatid:                           PowerPC AltiVec Built-in Functions Available on ISA 3.1.
                                                             (line  270)
* vec_srdb:                              PowerPC AltiVec Built-in Functions Available on ISA 3.1.
                                                             (line  258)
* vec_stril:                             PowerPC AltiVec Built-in Functions Available on ISA 3.1.
                                                             (line  350)
* vec_stril_p:                           PowerPC AltiVec Built-in Functions Available on ISA 3.1.
                                                             (line  361)
* vec_strir:                             PowerPC AltiVec Built-in Functions Available on ISA 3.1.
                                                             (line  371)
* vec_strir_p:                           PowerPC AltiVec Built-in Functions Available on ISA 3.1.
                                                             (line  382)
* vec_ternarylogic:                      PowerPC AltiVec Built-in Functions Available on ISA 3.1.
                                                             (line  401)
* vec_xst_trunc:                         Basic PowerPC Built-in Functions Available on ISA 3.1.
                                                             (line   77)
* vector function attribute, RX:         RX Function Attributes.
                                                             (line   49)
* vector types, using with x86 intrinsics: Vector Extensions.
                                                             (line  212)
* vector_size type attribute:            Common Type Attributes.
                                                             (line  434)
* vector_size variable attribute:        Common Variable Attributes.
                                                             (line  401)
* version_id function attribute, IA-64:  IA-64 Function Attributes.
                                                             (line   16)
* vfprintf:                              Other Builtins.     (line    6)
* vfscanf:                               Other Builtins.     (line    6)
* visibility function attribute:         Common Function Attributes.
                                                             (line 1361)
* visibility type attribute:             Common Type Attributes.
                                                             (line  461)
* visibility variable attribute:         Common Variable Attributes.
                                                             (line  429)
* Visium options:                        Visium Options.     (line    6)
* VLAs:                                  Variable Length.    (line    6)
* vliw function attribute, MeP:          MeP Function Attributes.
                                                             (line   30)
* void pointers, arithmetic:             Pointer Arith.      (line    6)
* void, size of pointer to:              Pointer Arith.      (line    6)
* volatile access:                       Volatiles.          (line    6)
* volatile access <1>:                   C++ Volatiles.      (line    6)
* volatile applied to function:          Function Attributes.
                                                             (line    6)
* volatile asm:                          Extended Asm.       (line  116)
* volatile read:                         Volatiles.          (line    6)
* volatile read <1>:                     C++ Volatiles.      (line    6)
* volatile write:                        Volatiles.          (line    6)
* volatile write <1>:                    C++ Volatiles.      (line    6)
* vprintf:                               Other Builtins.     (line    6)
* vscanf:                                Other Builtins.     (line    6)
* vsnprintf:                             Other Builtins.     (line    6)
* vsprintf:                              Other Builtins.     (line    6)
* vsscanf:                               Other Builtins.     (line    6)
* vsx_xl_sext:                           Basic PowerPC Built-in Functions Available on ISA 3.1.
                                                             (line   57)
* vsx_xl_zext:                           Basic PowerPC Built-in Functions Available on ISA 3.1.
                                                             (line   57)
* vtable:                                Vague Linkage.      (line   27)
* VxWorks Options:                       VxWorks Options.    (line    6)
* w floating point suffix:               Floating Types.     (line    6)
* W floating point suffix:               Floating Types.     (line    6)
* wakeup function attribute, MSP430:     MSP430 Function Attributes.
                                                             (line   49)
* warm function attribute, NDS32:        NDS32 Function Attributes.
                                                             (line   52)
* warn_if_not_aligned type attribute:    Common Type Attributes.
                                                             (line   91)
* warn_if_not_aligned variable attribute: Common Variable Attributes.
                                                             (line  106)
* warn_unused type attribute:            C++ Attributes.     (line   71)
* warn_unused_result function attribute: Common Function Attributes.
                                                             (line 1461)
* warning for comparison of signed and unsigned values: Warning Options.
                                                             (line 2691)
* warning for overloaded virtual function: C++ Dialect Options.
                                                             (line 1006)
* warning for reordering of member initializers: C++ Dialect Options.
                                                             (line  820)
* warning for unknown pragmas:           Warning Options.    (line 1390)
* warning function attribute:            Common Function Attributes.
                                                             (line  373)
* warning GCC_COLORS capability:         Diagnostic Message Formatting Options.
                                                             (line   95)
* warning messages:                      Warning Options.    (line    6)
* warnings from system headers:          Warning Options.    (line 2034)
* warnings vs errors:                    Warnings and Errors.
                                                             (line    6)
* weak function attribute:               Common Function Attributes.
                                                             (line 1478)
* weak variable attribute:               Common Variable Attributes.
                                                             (line  434)
* weakref function attribute:            Common Function Attributes.
                                                             (line 1490)
* whitespace:                            Incompatibilities.  (line  112)
* Windows Options for x86:               x86 Windows Options.
                                                             (line    6)
* X in constraint:                       Simple Constraints. (line  122)
* X3.159-1989:                           Standards.          (line   13)
* x86 named address spaces:              Named Address Spaces.
                                                             (line  184)
* x86 Options:                           x86 Options.        (line    6)
* x86 Windows Options:                   x86 Windows Options.
                                                             (line    6)
* Xstormy16 Options:                     Xstormy16 Options.  (line    6)
* Xtensa Options:                        Xtensa Options.     (line    6)
* y0:                                    Other Builtins.     (line    6)
* y0f:                                   Other Builtins.     (line    6)
* y0l:                                   Other Builtins.     (line    6)
* y1:                                    Other Builtins.     (line    6)
* y1f:                                   Other Builtins.     (line    6)
* y1l:                                   Other Builtins.     (line    6)
* yn:                                    Other Builtins.     (line    6)
* ynf:                                   Other Builtins.     (line    6)
* ynl:                                   Other Builtins.     (line    6)
* zda variable attribute, V850:          V850 Variable Attributes.
                                                             (line   17)
* zero_call_used_regs function attribute: Common Function Attributes.
                                                             (line 1532)
* zero-length arrays:                    Zero Length.        (line    6)
* zero-size structures:                  Empty Structures.   (line    6)
* zSeries options:                       zSeries Options.    (line    6)


Tag Table:
Node: Top2149
Node: G++ and GCC4139
Node: Standards6197
Node: Invoking GCC20226
Node: Option Summary25557
Node: Overall Options84491
Node: Invoking G++113141
Node: C Dialect Options114752
Node: C++ Dialect Options136815
Node: Objective-C and Objective-C++ Dialect Options200978
Node: Diagnostic Message Formatting Options213025
Node: Warning Options244307
Ref: Wtrigraphs352827
Node: Static Analyzer Options399665
Node: Debugging Options420561
Node: Optimize Options442410
Ref: Type-punning517532
Node: Instrumentation Options640981
Node: Preprocessor Options690489
Ref: dashMF695516
Ref: fdollars-in-identifiers700446
Node: Assembler Options714067
Node: Link Options714770
Ref: Link Options-Footnote-1732434
Node: Directory Options732778
Node: Code Gen Options741621
Node: Developer Options771219
Node: Submodel Options814197
Node: AArch64 Options816033
Ref: aarch64-feature-modifiers832508
Node: Adapteva Epiphany Options838333
Node: AMD GCN Options844479
Node: ARC Options846090
Node: ARM Options868047
Node: AVR Options912286
Node: Blackfin Options941192
Node: C6X Options949460
Node: CRIS Options951103
Node: CR16 Options954449
Node: C-SKY Options955421
Node: Darwin Options961712
Node: DEC Alpha Options969701
Node: eBPF Options981757
Node: FR30 Options984323
Node: FT32 Options984895
Node: FRV Options985865
Node: GNU/Linux Options992973
Node: H8/300 Options994458
Node: HPPA Options995986
Node: IA-64 Options1005922
Node: LM32 Options1014382
Node: LoongArch Options1014934
Node: M32C Options1021492
Node: M32R/D Options1022798
Node: M680x0 Options1026503
Node: MCore Options1041718
Node: MeP Options1043312
Node: MicroBlaze Options1047552
Node: MIPS Options1050781
Node: MMIX Options1089664
Node: MN10300 Options1092253
Node: Moxie Options1094912
Node: MSP430 Options1095423
Node: NDS32 Options1103492
Node: Nios II Options1105762
Node: Nvidia PTX Options1119594
Node: OpenRISC Options1123266
Node: PDP-11 Options1126172
Node: picoChip Options1127493
Node: PowerPC Options1129671
Node: PRU Options1129891
Node: RISC-V Options1132156
Node: RL78 Options1140963
Node: RS/6000 and PowerPC Options1144910
Node: RX Options1188607
Node: S/390 and zSeries Options1197565
Node: Score Options1208885
Node: SH Options1209774
Node: Solaris 2 Options1225506
Node: SPARC Options1226796
Node: System V Options1243234
Node: TILE-Gx Options1244102
Node: TILEPro Options1245156
Node: V850 Options1245676
Node: VAX Options1252711
Node: Visium Options1253431
Node: VMS Options1255819
Node: VxWorks Options1256683
Node: x86 Options1257879
Node: x86 Windows Options1328959
Node: Xstormy16 Options1331821
Node: Xtensa Options1332119
Node: zSeries Options1338487
Node: Spec Files1338683
Node: Environment Variables1366054
Node: Precompiled Headers1375875
Node: C++ Modules1382208
Ref: C++ Modules-Footnote-11388283
Node: C++ Module Mapper1388544
Node: C++ Module Preprocessing1393797
Node: C++ Compiled Module Interface1395670
Ref: C++ Compiled Module Interface-Footnote-11399098
Ref: C++ Compiled Module Interface-Footnote-21399187
Node: C Implementation1399243
Node: Translation implementation1400934
Node: Environment implementation1401537
Node: Identifiers implementation1402097
Node: Characters implementation1403201
Node: Integers implementation1406985
Node: Floating point implementation1409086
Node: Arrays and pointers implementation1412277
Ref: Arrays and pointers implementation-Footnote-11413749
Node: Hints implementation1413879
Node: Structures unions enumerations and bit-fields implementation1415432
Node: Qualifiers implementation1417780
Node: Declarators implementation1419863
Node: Statements implementation1420210
Node: Preprocessing directives implementation1420550
Node: Library functions implementation1422981
Node: Architecture implementation1423656
Node: Locale-specific behavior implementation1425357
Node: C++ Implementation1425662
Node: Conditionally-supported behavior1426946
Node: Exception handling1427573
Node: C Extensions1428046
Node: Statement Exprs1433321
Node: Local Labels1438845
Node: Labels as Values1441834
Ref: Labels as Values-Footnote-11444401
Node: Nested Functions1444586
Node: Nonlocal Gotos1448612
Node: Constructing Calls1450938
Node: Typeof1455681
Node: Conditionals1459744
Node: __int1281460641
Node: Long Long1461186
Node: Complex1462721
Node: Floating Types1467690
Node: Half-Precision1471429
Node: Decimal Float1475021
Node: Hex Floats1476975
Node: Fixed-Point1478105
Node: Named Address Spaces1481889
Ref: AVR Named Address Spaces1482583
Node: Zero Length1490143
Node: Empty Structures1494384
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Node: Variadic Macros1497548
Node: Escaped Newlines1499946
Node: Subscripting1500807
Node: Pointer Arith1501536
Node: Variadic Pointer Args1502137
Node: Pointers to Arrays1502878
Node: Initializers1503643
Node: Compound Literals1504144
Node: Designated Inits1507759
Node: Case Ranges1511751
Node: Cast to Union1512444
Node: Mixed Labels and Declarations1514208
Node: Function Attributes1514845
Node: Common Function Attributes1519400
Ref: Common Function Attributes-Footnote-11598521
Node: AArch64 Function Attributes1598838
Node: AMD GCN Function Attributes1605288
Node: ARC Function Attributes1608493
Node: ARM Function Attributes1611534
Node: AVR Function Attributes1616837
Node: Blackfin Function Attributes1621549
Node: BPF Function Attributes1624138
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Node: C-SKY Function Attributes1625253
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Node: IA-64 Function Attributes1630617
Node: M32C Function Attributes1631675
Node: M32R/D Function Attributes1634053
Node: m68k Function Attributes1635575
Node: MCORE Function Attributes1636535
Node: MeP Function Attributes1637362
Node: MicroBlaze Function Attributes1638691
Node: Microsoft Windows Function Attributes1640242
Node: MIPS Function Attributes1644927
Node: MSP430 Function Attributes1650717
Node: NDS32 Function Attributes1654936
Node: Nios II Function Attributes1657420
Node: Nvidia PTX Function Attributes1658753
Node: PowerPC Function Attributes1659376
Node: RISC-V Function Attributes1666394
Node: RL78 Function Attributes1667846
Node: RX Function Attributes1669129
Node: S/390 Function Attributes1671732
Node: SH Function Attributes1673680
Node: Symbian OS Function Attributes1677168
Node: V850 Function Attributes1677512
Node: Visium Function Attributes1678065
Node: x86 Function Attributes1678597
Node: Xstormy16 Function Attributes1703664
Node: Variable Attributes1704175
Node: Common Variable Attributes1705716
Node: ARC Variable Attributes1728287
Node: AVR Variable Attributes1728677
Node: Blackfin Variable Attributes1734036
Node: H8/300 Variable Attributes1734943
Node: IA-64 Variable Attributes1736024
Node: M32R/D Variable Attributes1736787
Node: MeP Variable Attributes1737594
Node: Microsoft Windows Variable Attributes1739803
Node: MSP430 Variable Attributes1742316
Node: Nvidia PTX Variable Attributes1743566
Node: PowerPC Variable Attributes1744191
Node: RL78 Variable Attributes1744764
Node: V850 Variable Attributes1745187
Node: x86 Variable Attributes1745832
Node: Xstormy16 Variable Attributes1746924
Node: Type Attributes1747518
Node: Common Type Attributes1749234
Node: ARC Type Attributes1772237
Node: ARM Type Attributes1772725
Node: BPF Type Attributes1773535
Node: MeP Type Attributes1774064
Node: PowerPC Type Attributes1774490
Node: x86 Type Attributes1775527
Node: Label Attributes1776555
Node: Enumerator Attributes1778638
Node: Statement Attributes1780198
Node: Attribute Syntax1781701
Node: Function Prototypes1793175
Node: C++ Comments1794987
Node: Dollar Signs1795522
Node: Character Escapes1795987
Node: Alignment1796275
Node: Inline1797984
Node: Volatiles1802941
Node: Using Assembly Language with C1805840
Node: Basic Asm1807117
Node: Extended Asm1812956
Ref: Volatile1817202
Ref: AssemblerTemplate1821407
Ref: OutputOperands1825735
Ref: FlagOutputOperands1832898
Ref: InputOperands1836053
Ref: Clobbers and Scratch Registers1840405
Ref: GotoLabels1849258
Ref: x86Operandmodifiers1853017
Ref: x86floatingpointasmoperands1858397
Ref: msp430Operandmodifiers1861818
Node: Constraints1863608
Node: Simple Constraints1864734
Node: Multi-Alternative1872308
Node: Modifiers1874007
Node: Machine Constraints1876890
Node: Asm Labels1939119
Node: Explicit Register Variables1940771
Ref: Explicit Reg Vars1940985
Node: Global Register Variables1941594
Ref: Global Reg Vars1941802
Node: Local Register Variables1946656
Ref: Local Reg Vars1946876
Node: Size of an asm1950566
Node: Alternate Keywords1952068
Node: Incomplete Enums1953657
Node: Function Names1954438
Node: Return Address1956386
Node: Vector Extensions1961049
Node: Offsetof1972300
Node: __sync Builtins1973145
Node: __atomic Builtins1979788
Node: Integer Overflow Builtins1993613
Node: x86 specific memory model extensions for transactional memory2000128
Node: Object Size Checking2001414
Node: Other Builtins2008566
Node: Target Builtins2063869
Node: AArch64 Built-in Functions2065644
Node: Alpha Built-in Functions2066340
Node: Altera Nios II Built-in Functions2069478
Node: ARC Built-in Functions2073961
Node: ARC SIMD Built-in Functions2079229
Node: ARM iWMMXt Built-in Functions2088379
Node: ARM C Language Extensions (ACLE)2095519
Node: ARM Floating Point Status and Control Intrinsics2096800
Node: ARM ARMv8-M Security Extensions2097287
Node: AVR Built-in Functions2098587
Node: Blackfin Built-in Functions2102485
Node: BPF Built-in Functions2103113
Node: FR-V Built-in Functions2104600
Node: Argument Types2105475
Node: Directly-mapped Integer Functions2107410
Node: Directly-mapped Media Functions2108690
Node: Raw read/write Functions2118028
Node: Other Built-in Functions2118972
Node: MIPS DSP Built-in Functions2120190
Node: MIPS Paired-Single Support2133149
Node: MIPS Loongson Built-in Functions2134672
Node: Paired-Single Arithmetic2141234
Node: Paired-Single Built-in Functions2142361
Node: MIPS-3D Built-in Functions2145224
Node: MIPS SIMD Architecture (MSA) Support2150998
Node: MIPS SIMD Architecture Built-in Functions2154002
Node: Other MIPS Built-in Functions2180856
Node: MSP430 Built-in Functions2181889
Node: NDS32 Built-in Functions2183302
Node: picoChip Built-in Functions2184595
Node: Basic PowerPC Built-in Functions2185970
Node: Basic PowerPC Built-in Functions Available on all Configurations2186828
Node: Basic PowerPC Built-in Functions Available on ISA 2.052195694
Node: Basic PowerPC Built-in Functions Available on ISA 2.062200712
Node: Basic PowerPC Built-in Functions Available on ISA 2.072202828
Node: Basic PowerPC Built-in Functions Available on ISA 3.02203714
Node: Basic PowerPC Built-in Functions Available on ISA 3.12210981
Node: PowerPC AltiVec/VSX Built-in Functions2214210
Node: PowerPC AltiVec Built-in Functions on ISA 2.052223159
Node: PowerPC AltiVec Built-in Functions Available on ISA 2.062248563
Node: PowerPC AltiVec Built-in Functions Available on ISA 2.072255677
Node: PowerPC AltiVec Built-in Functions Available on ISA 3.02265487
Node: PowerPC AltiVec Built-in Functions Available on ISA 3.12281482
Node: PowerPC Hardware Transactional Memory Built-in Functions2315178
Node: PowerPC Atomic Memory Operation Functions2323780
Node: PowerPC Matrix-Multiply Assist Built-in Functions2326347
Node: PRU Built-in Functions2332476
Node: RISC-V Built-in Functions2333676
Node: RX Built-in Functions2334091
Node: S/390 System z Built-in Functions2338185
Node: SH Built-in Functions2343523
Node: SPARC VIS Built-in Functions2345286
Node: TI C6X Built-in Functions2353837
Node: TILE-Gx Built-in Functions2354892
Node: TILEPro Built-in Functions2356020
Node: x86 Built-in Functions2357131
Node: x86 transactional memory intrinsics2423257
Node: x86 control-flow protection intrinsics2426576
Node: Target Format Checks2428363
Node: Solaris Format Checks2428795
Node: Darwin Format Checks2429245
Node: Pragmas2430252
Node: AArch64 Pragmas2431193
Node: ARM Pragmas2431658
Node: M32C Pragmas2432321
Node: MeP Pragmas2433413
Node: PRU Pragmas2435501
Node: RS/6000 and PowerPC Pragmas2436083
Node: S/390 Pragmas2436855
Node: Darwin Pragmas2437433
Node: Solaris Pragmas2438518
Node: Symbol-Renaming Pragmas2439718
Node: Structure-Layout Pragmas2441383
Node: Weak Pragmas2443747
Node: Diagnostic Pragmas2444494
Node: Visibility Pragmas2449354
Node: Push/Pop Macro Pragmas2450051
Node: Function Specific Option Pragmas2451048
Node: Loop-Specific Pragmas2453078
Node: Unnamed Fields2454706
Node: Thread-Local2456979
Node: C99 Thread-Local Edits2459133
Node: C++98 Thread-Local Edits2461207
Node: Binary constants2464748
Node: C++ Extensions2465447
Node: C++ Volatiles2467093
Node: Restricted Pointers2469441
Node: Vague Linkage2471084
Node: C++ Interface2474735
Ref: C++ Interface-Footnote-12478624
Node: Template Instantiation2478778
Node: Bound member functions2484901
Node: C++ Attributes2486445
Node: Function Multiversioning2490569
Node: Type Traits2492377
Node: C++ Concepts2499984
Node: Deprecated Features2501526
Node: Backwards Compatibility2503363
Node: Objective-C2504447
Node: GNU Objective-C runtime API2505054
Node: Modern GNU Objective-C runtime API2506061
Node: Traditional GNU Objective-C runtime API2508573
Node: Executing code before main2509312
Node: What you can and what you cannot do in +load2512146
Node: Type encoding2514630
Node: Legacy type encoding2520392
Node: @encode2521496
Node: Method signatures2522077
Node: Garbage Collection2524135
Node: Constant string objects2526860
Node: compatibility_alias2529424
Node: Exceptions2530185
Node: Synchronization2532983
Node: Fast enumeration2534203
Node: Using fast enumeration2534515
Node: c99-like fast enumeration syntax2535754
Node: Fast enumeration details2536461
Node: Fast enumeration protocol2538887
Node: Messaging with the GNU Objective-C runtime2542131
Node: Dynamically registering methods2543523
Node: Forwarding hook2545270
Node: Compatibility2548382
Node: Gcov2555020
Node: Gcov Intro2555563
Node: Invoking Gcov2558355
Node: Gcov and Optimization2581566
Node: Gcov Data Files2585399
Node: Cross-profiling2586868
Node: Gcov-tool2588770
Node: Gcov-tool Intro2589203
Node: Invoking Gcov-tool2591197
Node: Gcov-dump2593923
Node: Gcov-dump Intro2594250
Node: Invoking Gcov-dump2594525
Node: lto-dump2595238
Node: lto-dump Intro2595541
Node: Invoking lto-dump2595799
Node: Trouble2596967
Node: Actual Bugs2598384
Node: Interoperation2598841
Node: Incompatibilities2605890
Node: Fixed Headers2614308
Node: Standard Libraries2615982
Node: Disappointments2617386
Node: C++ Misunderstandings2621791
Node: Static Definitions2622602
Node: Name lookup2623687
Ref: Name lookup-Footnote-12628596
Node: Temporaries2628785
Node: Copy Assignment2630813
Node: Non-bugs2632680
Node: Warnings and Errors2643372
Node: Bugs2645162
Node: Bug Criteria2645629
Node: Bug Reporting2647871
Node: Service2648089
Node: Contributing2648914
Node: Funding2649660
Node: GNU Project2652149
Node: Copying2652797
Node: GNU Free Documentation License2690323
Node: Contributors2715446
Node: Option Index2757778
Node: Keyword Index3056893

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