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Evaluate using Profile-Guided Optimization (PGO) and Post-Link Optimization (PLO) for C++ part and LLVM #1526

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@zamazan4ik

Is your feature request related to a problem? Please describe.
Not a problem. It's an idea of how to improve Clasp performance.

Describe the solution you'd like

Recently I checked Profile-Guided Optimization (PGO) and Post-Link Optimization (PLO) improvements on multiple projects. The results are available here. According to the tests, these optimizations can help with achieving better performance in many compilers and compiler-like things: Clang, GCC, Rustc, CPython, etc. Since this, I think trying to optimize the Clasp compiler with PGO and PLO would be a good idea. It could work since LLVM itself and Clasp's C++ part are PGO-optimizable (C++ compilers support PGO very well).

I can suggest the following action points:

  • Perform PGO benchmarks on Clasp. If it shows improvements - add a note to the documentation about possible improvements in 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 Clasp tooling according to their workloads.
  • Optimize pre-built Clasp binaries (if any)

Additional context

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.

Examples of how PGO optimization is integrated into other projects:

I have some examples of how PGO information looks in the documentation:

Regarding LLVM BOLT integration, I have the following examples:

I hope these ideas could be interesting for someone from the Clasp community. Even if right now possibly investing resources into this would be too early for Clasp - it could be a good idea for future improvements.

By the way, if Clasp implements an Ahead-of-Time (AoT) compilation model for Common Lisp, maybe would be a good idea to integrate into the Clasp compiler building Common Lisp code with PGO? Since Clasp is a LLVM-based compiler, you can try to reuse the existing PGO infrastructure from LLVM. As a reference, you can use the Clang compiler and its IR PGO mode (-fprofile-generate/-fprofile-use flags). If you agree with an idea - we can create a separate issue for it.

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