[all-commits] [llvm/llvm-project] 538a83: RegisterCoalescer: Add undef flags in removePartia...

[Matt Arsenault via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: 538a83e4b9ddaa6cc9e8680fa97b2e33cd03192d
      https://github.com/llvm/llvm-project/commit/538a83e4b9ddaa6cc9e8680fa97b2e33cd03192d
  Author: Matt Arsenault <Matthew.Arsenault at amd.com>
  Date:   2023-12-13 (Wed, 13 Dec 2023)

  Changed paths:
    M llvm/lib/CodeGen/RegisterCoalescer.cpp
    A llvm/test/CodeGen/X86/coalescer-partial-redundancy-clear-dead-flag-undef-copy.mir

  Log Message:
  -----------
  RegisterCoalescer: Add undef flags in removePartialRedundancy (#75152)

If the copy being hoisted was undef, we have the same problems that
eliminateUndefCopy needs to solve. We would effectively be introducing a
new live out implicit_def. We need to add an undef flag to avoid
artificially introducing a live through undef value. Previously, the
verifier would fail due to the dead def inside the loop providing the
live in value for the %1 use.