[PATCH] D127516: RegisterCoalescer: Fix verifier error when merging copy of undef

[Matt Arsenault via Phabricator via llvm-commits]

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There's no real read of the register, so the copy introduced a new
live value. Make sure we introduce a replacement implicit_def instead
of just erasing the copy.

      

Found from llvm-reduce since it tries to set undef on everything.


https://reviews.llvm.org/D127516

Files:
  llvm/lib/CodeGen/RegisterCoalescer.cpp
  llvm/test/CodeGen/AMDGPU/coalesce-liveout-undef-copy.mir

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