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llvm / llvm-project / d1b376fd7bf73bca557f3c174d4c129ed4d45ae5
commitd1b376fd7bf73bca557f3c174d4c129ed4d45ae5[log] [tgz]
authorAlexandros Lamprineas <alexandros.lamprineas@arm.com>Mon Aug 07 13:34:48 2023 +0100
committerAlexandros Lamprineas <alexandros.lamprineas@arm.com>Wed Aug 09 10:28:46 2023 +0100
treef5abc9aa8f7b3da0b00ddb1388a575102cb9a5a7
parent7ec88f06d5833dfb4c7029c7645ae6cb89520504 [diff]
[FuncSpec] Rework the discardment logic for unprofitable specializations.

Currently we make an arbitrary comparison between codesize and latency
in order to decide whether to keep a specialization or not. Sometimes
the latency savings are biased in favor of loops because of imprecise
block frequencies, therefore this metric contains a lot of noise. This
patch tries to address the problem as follows:

* Reject specializations whose codesize savings are less than X% of
  the original function size.
* Reject specializations whose latency savings are less than Y% of
  the original function size.
* Reject specializations whose inlining bonus is less than Z% of
  the original function size.

I am not saying this is super precise, but at least X, Y and Z are
configurable, allowing us to tweak the cost model. Moreover, it lets
us prioritize codesize over latency, which is a less noisy metric.

I am also increasing the minimum size a function should have to be
considered a candidate for specialization. Initially the cost of
a function was calculated as

  CodeMetrics::NumInsts * InlineConstants::getInstrCost()

which later in D150464 was altered into CodeMetrics::NumInsts since
the metric is supposed to model TargetTransformInfo::TCK_CodeSize.
However, we omitted adjusting MinFunctionSize in that commit.

Differential Revision: https://reviews.llvm.org/D157123
3 files changed
tree: f5abc9aa8f7b3da0b00ddb1388a575102cb9a5a7
  1. .ci/
  2. .github/
  3. bolt/
  4. clang/
  5. clang-tools-extra/
  6. cmake/
  7. compiler-rt/
  8. cross-project-tests/
  9. flang/
  10. libc/
  11. libclc/
  12. libcxx/
  13. libcxxabi/
  14. libunwind/
  15. lld/
  16. lldb/
  17. llvm/
  18. llvm-libgcc/
  19. mlir/
  20. openmp/
  21. polly/
  22. pstl/
  23. runtimes/
  24. third-party/
  25. utils/
  26. .arcconfig
  27. .arclint
  28. .clang-format
  29. .clang-tidy
  30. .git-blame-ignore-revs
  31. .gitignore
  32. .mailmap
  33. CONTRIBUTING.md
  34. LICENSE.TXT
  35. README.md
  36. SECURITY.md
README.md

The LLVM Compiler Infrastructure

Welcome to the LLVM project!

This repository contains the source code for LLVM, a toolkit for the construction of highly optimized compilers, optimizers, and run-time environments.

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