Evaluate using Profile-Guided Optimization (PGO) for optimizing the compiler

[zamazan4ik]

Hi!

Recently I checked Profile-Guided Optimization (PGO) improvements on multiple projects, including many compilers (like Clang, Rustc, etc.) - the results are here. According to the multiple tests, PGO can help with improving performance in many cases. E.g. there is a PGO benchmark for the Naga compiler - link. Since this, I think PGO integration into the DirectX Shader Compiler would be a good thing to have.

I can suggest the following action points:

• Perform PGO benchmarks on the project. If it shows improvements - add a note to the documentation about possible improvements in the compiler performance with PGO.
• Providing an easier way (e.g. a build option) to build scripts to build the compiler with PGO can be helpful for the end-users and maintainers since they will be able to optimize the compiler according to their workloads.
• Optimize pre-built binaries with PGO. In this case, users will get a PGO-optimized compiler version.

As an integration example into the build scripts, I can recommend starting with Clang instructions - the corresponding CMake scripts are located here

Thank you.

P.S. I didn't find information in the build scripts. Are current release builds optimized with Link-Time Optimization (LTO) on CI?