[all-commits] [llvm/llvm-project] 503dee: Temporairly revert "[SimplifyCFG][LoopRotate] Simp...

[Roman Lebedev via All-commits]

  Branch: refs/heads/master
  Home:   https://github.com/llvm/llvm-project
  Commit: 503deec2183d466dad64b763bab4e15fd8804239
      https://github.com/llvm/llvm-project/commit/503deec2183d466dad64b763bab4e15fd8804239
  Author: Roman Lebedev <lebedev.ri at gmail.com>
  Date:   2020-08-22 (Sat, 22 Aug 2020)

  Changed paths:
    M llvm/include/llvm/Transforms/Utils/SimplifyCFGOptions.h
    M llvm/lib/Passes/PassBuilder.cpp
    M llvm/lib/Target/AArch64/AArch64TargetMachine.cpp
    M llvm/lib/Target/ARM/ARMTargetMachine.cpp
    M llvm/lib/Target/Hexagon/HexagonTargetMachine.cpp
    M llvm/lib/Transforms/IPO/PassManagerBuilder.cpp
    M llvm/lib/Transforms/Scalar/SimplifyCFGPass.cpp
    M llvm/test/Transforms/PGOProfile/chr.ll
    M llvm/test/Transforms/PhaseOrdering/loop-rotation-vs-common-code-hoisting.ll
    M llvm/test/Transforms/SimplifyCFG/common-code-hoisting.ll

  Log Message:
  -----------
  Temporairly revert "[SimplifyCFG][LoopRotate] SimplifyCFG: disable common instruction hoisting by default, enable late in pipeline"

As disscussed in post-commit review starting with
	https://reviews.llvm.org/D84108#2227365
while this appears to be mostly a win overall, especially code-size-wise,
this appears to shake //certain// code pattens in a way that is extremely
unfavorable for performance (+30% runtime regression)
on certain CPU's (i personally can't reproduce).

So until the behaviour is better understood, and a path forward is mapped,
let's back this out for now.

This reverts commit 1d51dc38d89bd33fb8874e242ab87b265b4dec1c.