[all-commits] [llvm/llvm-project] bdcf04: [LoopIdiom] Don't transform loop into memmove when...

[yurai007 via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: bdcf04246c401aec9bdddf32fabc99fa4834a477
      https://github.com/llvm/llvm-project/commit/bdcf04246c401aec9bdddf32fabc99fa4834a477
  Author: Dawid Jurczak <dawid_jurek at vp.pl>
  Date:   2021-08-25 (Wed, 25 Aug 2021)

  Changed paths:
    M llvm/lib/Transforms/Scalar/LoopIdiomRecognize.cpp
    M llvm/test/Transforms/LoopIdiom/basic.ll

  Log Message:
  -----------
  [LoopIdiom] Don't transform loop into memmove when load from body has more than one use

This change fixes issue found by Markus: https://reviews.llvm.org/rG11338e998df1
Before this patch following code was transformed to memmove:

for (int i = 15; i >= 1; i--) {
  p[i] = p[i-1];
  sum += p[i-1];
}

However load from p[i-1] is used not only by store to p[i] but also by sum computation.
Therefore we cannot emit memmove in loop header.

Differential Revision: https://reviews.llvm.org/D107964