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### 11.7 General principles

A few general principles have been followed when designing the FPC implementation of WPO:

- All information necessary to generate a WPO feedback file for a program is always stored in the ppu files. This means that it is possible to use a generic RTL for WPO (or, in general, any compiled unit). It does mean that the RTL itself will then not be optimised, the compiled program code and its units can be correctly optimised because the compiler knows everything it has to know about all RTL units.
- The generated WPO feedback file is plain text. The idea is that it should be easy to inspect this file by hand, and to add information to it produced by external tools if desired (e.g., profile information).
- The implementation of the WPO subsystem in the compiler is very modular, so it should be easy to plug in additional WPO information providers, or to choose at run time between different information providers for the same kind of information. At the same time, the interaction with the rest of the compiler is kept to a bare minimum to improve maintainability.
- It is possible to generate a WPO feedback file while at the same time using another one as input. In some cases, using this second feedback file as input during a third compilation can further improve the results.

11.7.1 How to use
Step 1: Generate WPO feedback file
Step 2: Use the generated WPO feedback file
11.7.2 Available WPO optimizations
11.7.3 format of the WPO file

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