[all-commits] [llvm/llvm-project] 03bd51: [OldPM] Pass manager: run SROA after (simple) loop...

[Roman Lebedev via All-commits]

  Branch: refs/heads/master
  Home:   https://github.com/llvm/llvm-project
  Commit: 03bd5198b6f7d9f49d72e6516d813a206f3b6d0d
      https://github.com/llvm/llvm-project/commit/03bd5198b6f7d9f49d72e6516d813a206f3b6d0d
  Author: Roman Lebedev <lebedev.ri at gmail.com>
  Date:   2020-10-04 (Sun, 04 Oct 2020)

  Changed paths:
    M clang/test/CodeGenCXX/union-tbaa2.cpp
    M clang/test/Misc/loop-opt-setup.c
    M llvm/lib/Target/AMDGPU/AMDGPUTargetMachine.cpp
    M llvm/lib/Transforms/IPO/PassManagerBuilder.cpp
    M llvm/test/Other/opt-O2-pipeline.ll
    M llvm/test/Other/opt-O3-pipeline-enable-matrix.ll
    M llvm/test/Other/opt-O3-pipeline.ll
    M llvm/test/Other/opt-Os-pipeline.ll
    M llvm/test/Transforms/PhaseOrdering/X86/SROA-after-loop-unrolling.ll

  Log Message:
  -----------
  [OldPM] Pass manager: run SROA after (simple) loop unrolling

I have stumbled into this pretty accidentally, when rewriting
some spaghetti-like code into something more structured,
which involved using some `std::array<>`s. And to my surprise,
the `alloca`s remained, causing about `+160%` perf regression.

https://llvm-compile-time-tracker.com/compare.php?from=bb6f4d32aac3eecb51909f4facc625219307ee68&to=d563e66f40f9d4d145cb2050e41cb961e2b37785&stat=instructions
suggests that this has geomean compile-time cost of `+0.08%`.

Note that D68593 / cecc0d27ad58c0aed8ef9ed99bbf691e137a0f26
already did this chage for NewPM, but left OldPM in a pessimized state.

This fixes [[ https://bugs.llvm.org/show_bug.cgi?id=40011 | PR40011 ]], [[ https://bugs.llvm.org/show_bug.cgi?id=42794 | PR42794 ]] and probably some other reports.

Reviewed By: nikic, xbolva00

Differential Revision: https://reviews.llvm.org/D87972