Enable 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. For Clang PGO results are even described in the official documentation (20% improvements) - https://llvm.org/docs/HowToBuildWithPGO.html . I think it could be a good idea to enable PGO at least for Clang dependency in Xeus repl.

I can suggest the following things to do:

• Enable PGO at least for the Clang dependency.
• Document enabling PGO somewhere in the Documentation (possibly in the README file)

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. Building with LLVM BOLT is already supported by Clang too in the upstream.

[vgvassilev]

Hi @zamazan4ik. Thanks for the remarks, I agree with them. Currently we do not have the bandwidth to pursue them but patches are welcome!