Getting Started with the LLVM System using Microsoft Visual Studio

- Overview
- Getting Started Quickly (A Summary)
- Requirements
  1. Hardware
  2. Software
- Getting Started with LLVM
  1. Terminology and Notation
  2. The Location of LLVM Object Files
- An Example Using the LLVM Tool Chain
- Common Problems
- Links

Written by: Jeff Cohen

Overview

The Visual Studio port at this time is experimental. It is suitable for use only if you are writing your own compiler front end or otherwise have a need to dynamically generate machine code. The JIT and interpreter are functional, but it is currently not possible to generate assembly code which is then assembled into an executable. You can indirectly create executables by using the C back end.

To emphasize, there is no C/C++ front end currently available. `llvm-gcc` is based on GCC, which cannot be bootstrapped using VC++. Eventually there should be a `llvm-gcc` based on Cygwin or MinGW that is usable. There is also the option of generating bitcode files on Unix and copying them over to Windows. But be aware the odds of linking C++ code compiled with `llvm-gcc` with code compiled with VC++ is essentially zero.

The LLVM test suite cannot be run on the Visual Studio port at this time.

Most of the tools build and work. `bugpoint` does build, but does not work. The other tools 'should' work, but have not been fully tested.

Additional information about the LLVM directory structure and tool chain can be found on the main Getting Started page.

Getting Started Quickly (A Summary)

Here's the short story for getting up and running quickly with LLVM:

1. Read the documentation.
2. Seriously, read the documentation.
3. Remember that you were warned twice about reading the documentation.
4. Get the Source Code
   - With the distributed files:
     1. `cd where-you-want-llvm-to-live`
     2. `gunzip --stdout llvm-version.tar.gz | tar -xvf -` or use WinZip
     3. `cd llvm`
   - With anonymous Subversion access:
     1. `cd where-you-want-llvm-to-live`
     2. `svn co http://llvm.org/svn/llvm-project/llvm-top/trunk llvm-top`
     3. `make checkout MODULE=llvm`
     4. `cd llvm`
5. Use CMake to generate up-to-date project files:
   - This step is currently optional as LLVM does still come with a normal Visual Studio solution file, but it is not always kept up-to-date and will soon be deprecated in favor of the multi-platform generator CMake.
   - If CMake is installed then the most simple way is to just start the CMake GUI, select the directory where you have LLVM extracted to, and the default options should all be fine. The one option you may really want to change, regardless of anything else, might be the CMAKE_INSTALL_PREFIX setting to select a directory to INSTALL to once compiling is complete.
   - If you use CMake to generate the Visual Studio solution and project files, then the Solution will have a few extra options compared to the current included one. The projects may still be built individually, but to build them all do not just select all of them in batch build (as some are meant as configuration projects), but rather select and build just the ALL_BUILD project to build everything, or the INSTALL project, which first builds the ALL_BUILD project, then installs the LLVM headers, libs, and other useful things to the directory set by the CMAKE_INSTALL_PREFIX setting when you first configured CMake.
6. Start Visual Studio
   - If you did not use CMake, then simply double click on the solution file `llvm/win32/llvm.sln`.
   - If you used CMake, then the directory you created the project files, the root directory will have an `llvm.sln` file, just double-click on that to open Visual Studio.
7. Build the LLVM Suite:
   - Simply build the solution.
   - The Fibonacci project is a sample program that uses the JIT. Modify the project's debugging properties to provide a numeric command line argument. The program will print the corresponding fibonacci value.

It is strongly encouraged that you get the latest version from Subversion as changes are continually making the VS support better.

Requirements

Before you begin to use the LLVM system, review the requirements given below. This may save you some trouble by knowing ahead of time what hardware and software you will need.

Hardware

Any system that can adequately run Visual Studio .NET 2005 SP1 is fine. The LLVM source tree and object files, libraries and executables will consume approximately 3GB.

Software

You will need Visual Studio .NET 2005 SP1 or higher. The VS2005 SP1 beta and the normal VS2005 still have bugs that are not completely compatible. VS2003 would work except (at last check) it has a bug with friend classes that you can work-around with some minor code rewriting (and please submit a patch if you do). Earlier versions of Visual Studio do not support the C++ standard well enough and will not work.

You will also need the CMake build system since it generates the project files you will use to build with.

Do not install the LLVM directory tree into a path containing spaces (e.g. C:\Documents and Settings\...) as the configure step will fail.

Getting Started with LLVM

The remainder of this guide is meant to get you up and running with LLVM using Visual Studio and to give you some basic information about the LLVM environment.

Terminology and Notation

Throughout this manual, the following names are used to denote paths specific to the local system and working environment. These are not environment variables you need to set but just strings used in the rest of this document below. In any of the examples below, simply replace each of these names with the appropriate pathname on your local system. All these paths are absolute:

SRC_ROOT

  This is the top level directory of the LLVM source tree.

OBJ_ROOT

  This is the top level directory of the LLVM object tree (i.e. the tree where object files and compiled programs will be placed. It is fixed at SRC_ROOT/win32).

The Location of LLVM Object Files

The object files are placed under `OBJ_ROOT/Debug` for debug builds and `OBJ_ROOT/Release` for release (optimized) builds. These include both executables and libararies that your application can link against.

The files that `configure` would create when building on Unix are created by the `Configure` project and placed in `OBJ_ROOT/llvm`. You application must have OBJ_ROOT in its include search path just before `SRC_ROOT/include`.

An Example Using the LLVM Tool Chain

1. First, create a simple C file, name it 'hello.c':

       #include <stdio.h>
       int main() {
         printf("hello world\n");
         return 0;
       }

2. Next, compile the C file into a LLVM bitcode file:

       % llvm-gcc -c hello.c -emit-llvm -o hello.bc

   This will create the result file `hello.bc` which is the LLVM bitcode that corresponds the the compiled program and the library facilities that it required. You can execute this file directly using `lli` tool, compile it to native assembly with the `llc`, optimize or analyze it further with the `opt` tool, etc.

   Note: while you cannot do this step on Windows, you can do it on a Unix system and transfer `hello.bc` to Windows. Important: transfer as a binary file!

3. Run the program using the just-in-time compiler:

       % lli hello.bc

   Note: this will only work for trivial C programs. Non-trivial programs (and any C++ program) will have dependencies on the GCC runtime that won't be satisfied by the Microsoft runtime libraries.

4. Use the `llvm-dis` utility to take a look at the LLVM assembly code:

       % llvm-dis < hello.bc | more

5. Compile the program to C using the LLC code generator:

       % llc -march=c hello.bc

6. Compile to binary using Microsoft C:

       % cl hello.cbe.c

   Note: this will only work for trivial C programs. Non-trivial programs (and any C++ program) will have dependencies on the GCC runtime that won't be satisfied by the Microsoft runtime libraries.

7. Execute the native code program:

       % hello.cbe.exe

Common Problems

- In Visual C++, if you are linking with the x86 target statically, the linker will remove the x86 target library from your generated executable or shared library because there are no references to it. You can force the linker to include these references by using `"/INCLUDE:_X86TargetMachineModule"` when linking. In the Visual Studio IDE, this can be added in `Project Properties->Linker->Input->Force Symbol References`.

If you are having problems building or using LLVM, or if you have any other general questions about LLVM, please consult the Frequently Asked Questions page.

Links

This document is just an introduction to how to use LLVM to do some simple things... there are many more interesting and complicated things that you can do that aren't documented here (but we'll gladly accept a patch if you want to write something up!). For more information about LLVM, check out:

- LLVM homepage
- LLVM doxygen tree
- Starting a Project that Uses LLVM