Evaluate using Profile-Guided Optimization (PGO) and LLVM BOLT

[zamazan4ik]

Hi!

Recently I checked Profile-Guided Optimization (PGO) improvements on multiple projects. The results are here. E.g. PGO results for LLVM-related tooling are here. According to the tests, PGO usually helps with the compiler and compiler-like workloads (like static analysis) - e.g. Clang gets +20% compilation speed with PGO, CPython achieves +10% in pybench. So I think optimizing Quirrel tooling (like VM, compiler and the static analyzer) with PGO would be a good idea at least to try.

I can suggest the following action points:

• Perform PGO benchmarks on the Quirrel tooling. If it shows improvements - add a note about possible improvements in Quirrel's performance with PGO.
• Providing an easier way (e.g. a build option) to build scripts with PGO can be helpful for the end-users and maintainers since they will be able to optimize the Quirrel tools according to their own workloads.
• Optimize pre-built binaries with PGO

Testing Post-Link Optimization techniques (like LLVM BOLT) would be interesting too (CPython, 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:

• ISPC: CMake scipts
• 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
• NodeJS: Configure script

The same issue was created for daScript since these two projects can have different lifecycles, priorities, and PGO can be tested and integrated into them independently.