Frontend překladače jazyka C s podporou pragmat

This software is a significant extension of the clang LLVM frontend with pragma support.

Pragmas can be used to give additional information to the compiler.

There was no such support in LLVM before and because of support for following task, it was necessary to significanly modify the existing clang frontend and add required functionality.

Usage of pragmas is mainly in following compiler optimizaitons:

- alias analysis

  - mark block of code where pointers cannot alias

- vectorization

  - e.g. to specify that the programmer want to use SIMD insturctions regardless on price or other 

  - or ignore dependencies between loop iterations

  - + to add other information

- marking of specialozed instructions

  - it is possible to select pieces of source code that should be executed directly in hardware

To keep the pragmas in the source code are special annotations used, the advantage is that compared to debug information, that annotations are kjept even after agressive optimizations.