Evaluate Profile-Guided Optimization (PGO) and LLVM BOLT

[zamazan4ik]

Hi!

I did a lot of Profile-Guided Optimization (PGO) benchmarks recently on different kinds of software (including many compilers and compiler-like projects like Clang, Rustc, Clangd, clang-tidy, etc.) - all currently available results are located at https://github.com/zamazan4ik/awesome-pgo . According to the tests, PGO usually helps a lot for compiler-like workloads. That's why I think testing PGO would be a good idea for Redpen.

I can suggest to do the following things:

• Evaluate PGO on Redpen
• If it benefits Redpen - add a note to the Redpen documentation about building with PGO. In this case, users and maintainers who build their own Redpen binaries will be aware of PGO as an additional way to optimize the project
• Optimize provided by Redpen project binaries on the CI (like it's already done for other projects like Rustc), if any
• After that, I suggest trying to apply LLVM BOLT as an additional post-PGO step. Rustc already does it on some platforms

For the Rust projects, I suggest PGO optimizing with cargo-pgo.

I understand that the project is in the early stages of development. So just consider the issue just an idea for the possible future improvements.

[estebank]

This is a great idea and I'll keep it in mind. Thank you for taking the time to document it.