[all-commits] [llvm/llvm-project] cca010: Move "auto-init" instructions to the dominator of ...

[serge-sans-paille via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: cca01008cc31a891d0ec70aff2201b25d05d8f1b
      https://github.com/llvm/llvm-project/commit/cca01008cc31a891d0ec70aff2201b25d05d8f1b
  Author: serge-sans-paille <sguelton at mozilla.com>
  Date:   2023-04-03 (Mon, 03 Apr 2023)

  Changed paths:
    A llvm/include/llvm/Transforms/Utils/MoveAutoInit.h
    M llvm/lib/Passes/PassBuilder.cpp
    M llvm/lib/Passes/PassBuilderPipelines.cpp
    M llvm/lib/Passes/PassRegistry.def
    M llvm/lib/Transforms/Utils/CMakeLists.txt
    A llvm/lib/Transforms/Utils/MoveAutoInit.cpp
    M llvm/test/Other/new-pm-defaults.ll
    M llvm/test/Other/new-pm-lto-defaults.ll
    M llvm/test/Other/new-pm-thinlto-postlink-defaults.ll
    M llvm/test/Other/new-pm-thinlto-postlink-pgo-defaults.ll
    M llvm/test/Other/new-pm-thinlto-postlink-samplepgo-defaults.ll
    M llvm/test/Other/new-pm-thinlto-prelink-defaults.ll
    M llvm/test/Other/new-pm-thinlto-prelink-pgo-defaults.ll
    M llvm/test/Other/new-pm-thinlto-prelink-samplepgo-defaults.ll
    A llvm/test/Transforms/MoveAutoInit/branch.ll
    A llvm/test/Transforms/MoveAutoInit/clobber.ll
    A llvm/test/Transforms/MoveAutoInit/fence.ll
    A llvm/test/Transforms/MoveAutoInit/loop.ll
    A llvm/test/Transforms/MoveAutoInit/scalar.ll

  Log Message:
  -----------
  Move "auto-init" instructions to the dominator of their users

As a result of -ftrivial-auto-var-init, clang generates instructions to
set alloca'd memory to a given pattern, right after the allocation site.
In some cases, this (somehow costly) operation could be delayed, leading
to conditional execution in some cases.

This is not an uncommon situation: it happens ~500 times on the cPython
code base, and much more on the LLVM codebase. The benefit greatly
varies on the execution path, but it should not regress on performance.

Differential Revision: https://reviews.llvm.org/D137707