Evaluate Profile-Guided Optimization (PGO) and LLVM BOLT

[zamazan4ik]

Hi!

Recently I did many Profile-Guided Optimization (PGO) benchmarks on multiple projects (including static analysis tools and compilers like Rustc, Clang, Clangd, Clang Tidy, and many others) - the results are available here. So that's why I think it's worth trying to apply PGO to Qsharp.

I can suggest the following things to do:

• Evaluate PGO's applicability to Qsharp.
• If PGO helps to achieve better performance - add a note to Qsharp's documentation about that. In this case, users and maintainers will be aware of another optimization opportunity for Qsharp.
• Provide PGO integration into the build scripts. It can help users and maintainers easily apply PGO for their own workloads.
• Optimize prebuilt binaries with PGO.

Here are some examples of how PGO is already integrated into other projects' build scripts:

• Rustc: a CI script for the multi-stage build
• GCC:
  • Official docs, section "Building with profile feedback" (even AutoFDO build is supported)
  • A part in a "wonderful" configure script
• Clang: Docs
• Python:
  • CPython: README
  • Pyston: README
• Go: Bash script
• V8: Bazel flag
• ChakraCore: Scripts
• Chromium: Script
• Firefox: Docs
  • Thunderbird has PGO support too
• PHP - Makefile command and old Centminmod scripts
• MySQL: CMake script
• YugabyteDB: GitHub commit
• FoundationDB: Script
• Zstd: Makefile
• Foot: Scripts
• Windows Terminal: GitHub PR
• Pydantic-core: GitHub PR

After PGO, I can suggest evaluating LLVM BOLT as an additional optimization step after PGO.

For the Rust projects, I recommend starting with cargo-pgo.

[swernli]

This does not seem to be relevant to our ongoing work.

[zamazan4ik]

This does not seem to be relevant to our ongoing work.

@swernli Could you please describe a little bit more, why it's not important? I guess the compiler performance could be interesting for the Qsharp users.

Even if the compiler performance isn't the current dev team focus, I still suggest leaving the issue open. So maybe someone from the community will decide to help with the issue and will make a PR with enabling PGO for Qsharp.