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

[zamazan4ik]

Hi!

Recently I did many Profile-Guided Optimization (PGO) benchmarks on multiple projects (including static analysis tools and compilers like CPython, Rustc, Clang, Clangd, Clang Tidy, and many others) - the results are available here. Trying to enable PGO to the Numbat tooling could be a good thing to try.

I can suggest the following things to do:

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

Some PGO documentation examples in various projects:

• ClickHouse: https://clickhouse.com/docs/en/operations/optimizing-performance/profile-guided-optimization
• Databend: https://databend.rs/doc/contributing/pgo
• Vector: https://vector.dev/docs/administration/tuning/pgo/
• Nebula: https://docs.nebula-graph.io/3.5.0/8.service-tuning/enable_autofdo_for_nebulagraph/
• GCC: Official docs, section "Building with profile feedback" (even AutoFDO build is supported)
• Clang:
  • https://llvm.org/docs/HowToBuildWithPGO.html
  • https://llvm.org/docs/AdvancedBuilds.html
• tsv-utils: https://github.com/eBay/tsv-utils/blob/master/docs/BuildingWithLTO.md

After PGO, I can suggest evaluating LLVM BOLT as an additional optimization step after PGO - Post Link Optimization (PLO). This optimization technique is already integrated into the Clang, CPython, and Rustc build scripts. But I suggest starting with PGO - it's a more stable optimization than PLO in the general case.

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

[sharkdp]

You seem to post this in many different repositories, so I have to assume that you are following some agenda here that is not necessarily aligned with the project goals.

We currently don't have a performance problem in Numbat. If we do, and run out of more basic things to do, we can look in to PGO — of course.