[all-commits] [llvm/llvm-project] bc1fe6: RegisterCoalescer: Fix producing malformed IMPLICI...

[Matt Arsenault via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: bc1fe6fd49b28e52ad289ec2aee6ea5709c3b25c
      https://github.com/llvm/llvm-project/commit/bc1fe6fd49b28e52ad289ec2aee6ea5709c3b25c
  Author: Matt Arsenault <Matthew.Arsenault at amd.com>
  Date:   2023-12-04 (Mon, 04 Dec 2023)

  Changed paths:
    M llvm/lib/CodeGen/RegisterCoalescer.cpp
    A llvm/test/CodeGen/AArch64/coalescer-drop-subreg-to-reg-imm-ops.mir

  Log Message:
  -----------
  RegisterCoalescer: Fix producing malformed IMPLICIT_DEFs (#73784)

If this was coalescing a SUBREG_TO_REG as a copy, the resulting
instruction would be an IMPLICIT_DEF with an unexpected 2 immediate
operands, which need to be dropped. Until recently the verifier did not
catch this error, and an assert would fire if later the broken
IMPLICIT_DEF was rematerialized P

#73758 is related, it changes the failure mode to a verifier error.