[all-commits] [llvm/llvm-project] 8b0df8: [LoopRotate] Get and update MSSA only if available...

[Alina Sbirlea via All-commits]

  Branch: refs/heads/release/10.x
  Home:   https://github.com/llvm/llvm-project
  Commit: 8b0df8e1ed6842095388fce08a0a5f761cd905ed
      https://github.com/llvm/llvm-project/commit/8b0df8e1ed6842095388fce08a0a5f761cd905ed
  Author: Alina Sbirlea <asbirlea at google.com>
  Date:   2020-02-26 (Wed, 26 Feb 2020)

  Changed paths:
    M llvm/lib/Transforms/Scalar/LoopRotation.cpp
    M llvm/test/Other/opt-O2-pipeline.ll
    M llvm/test/Other/opt-O3-pipeline.ll
    M llvm/test/Other/opt-Os-pipeline.ll
    M llvm/test/Other/pass-pipelines.ll

  Log Message:
  -----------
  [LoopRotate] Get and update MSSA only if available in legacy pass manager.

Summary:
Potential fix for: https://bugs.llvm.org/show_bug.cgi?id=44889 and https://bugs.llvm.org/show_bug.cgi?id=44408

In the legacy pass manager, loop rotate need not compute MemorySSA when not being in the same loop pass manager with other loop passes.
There isn't currently a way to differentiate between the two cases, so this attempts to limit the usage in LoopRotate to only update MemorySSA when the analysis is already available.
The side-effect of this is that it will split the Loop pipeline.

This issue does not apply to the new pass manager, where we have a flag specifying if all loop passes in that loop pass manager preserve MemorySSA.

Reviewers: dmgreen, fedor.sergeev, nikic

Subscribers: Prazek, hiraditya, george.burgess.iv, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D74574

(cherry picked from commit 1326a5a4cfe004181f2ec8231d84ecda2b93cb25)