[all-commits] [llvm/llvm-project] 396d18: [InstCombine] replace shuffle's insertelement oper...

[RotateRight via All-commits]

  Branch: refs/heads/master
  Home:   https://github.com/llvm/llvm-project
  Commit: 396d18aeb6cb4409ed71ff4c331748ce1c530f33
      https://github.com/llvm/llvm-project/commit/396d18aeb6cb4409ed71ff4c331748ce1c530f33
  Author: Sanjay Patel <spatel at rotateright.com>
  Date:   2019-12-10 (Tue, 10 Dec 2019)

  Changed paths:
    M llvm/lib/Transforms/InstCombine/InstCombineVectorOps.cpp
    M llvm/test/Transforms/InstCombine/insert-extract-shuffle.ll

  Log Message:
  -----------
  [InstCombine] replace shuffle's insertelement operand if inserted scalar is not demanded

This pattern is noted as a regression from:
D70246
...where we removed an over-aggressive shuffle simplification.

SimplifyDemandedVectorElts fails to catch this case when the insert has multiple uses,
so I'm proposing to pattern match the minimal sequence directly. This fold does not
conflict with any of our current shuffle undef/poison semantics.

Differential Revision: https://reviews.llvm.org/D71220