Evaluate using Profile-Guided Optimization (PGO) and Post-Link Optimization (PLO) on ctags

[zamazan4ik]

Hi!

Recently I checked Profile-Guided Optimization (PGO) improvements on multiple projects. The results are available here. I also have several examples of applying PGO to the software like ctags:

• LLVM-based tooling (like Clangd): link
• Clangd benchmarks with PGO from Jetbrains: JetBrains blog
• Rust Analyzer: GitHub comment

That's why I think trying to optimize ctags with PGO can be a good idea.

I can suggest the following action points:

• Perform PGO benchmarks on ctags. And if it shows improvements - add a note to the documentation about possible improvements in ctags performance with PGO.
• Providing an easier way (e.g. an additional build option) to build scripts with PGO can be helpful for the end-users and maintainers since they will be able to optimize ctags according to their workloads.
• Optimize pre-built binaries (if it's possible to prepare a good training workload)

Testing Post-Link Optimization techniques (like LLVM BOLT) would be interesting too (Clang and Rustc already use BOLT as an addition to PGO) but I recommend starting from the usual PGO.

Here are some examples of how PGO optimization is integrated in other projects:

• 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
• file.d: GitHub PR
• OceanBase: CMake flag

[masatake]

Thank you for this input.