[PATCH] D48032: [RegisterCoalescer] Avoid erasing copy that breaks subranges

[Tim Renouf via Phabricator via llvm-commits]

tpr updated this revision to Diff 150995.
tpr added a comment.

V2: This is a revised fix. Still not the proper fix, but at least it
doesn't stop a copy being erased.

Also tidied the test as suggested.

Here's the new commit message, as I don't think phabricator updates the
summary box:

  [RegisterCoalescer] Recalculate subranges in some cases
  
  Summary:
  I found a case where erasing a copy in coalescing causes a subrange to
  be modified incorrectly.
  
  It looks like it would be quite a large change to fix this properly,
  such that subranges are updated correctly when a subreg is dead in and
  live out of a copy being erased.
  
  So for now, in the case causing my problem, it now just recalculates
  the whole live interval after the coalesce.


Repository:
  rL LLVM

https://reviews.llvm.org/D48032

Files:
  lib/CodeGen/RegisterCoalescer.cpp
  lib/CodeGen/RegisterCoalescer.h
  test/CodeGen/AMDGPU/coalescing-with-subregs-in-loop-bug.mir

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