[all-commits] [llvm/llvm-project] d82b35: [CodeGen] Ensure `undef` propagation when an undef...

[Ryan Buchner via All-commits]

  Branch: refs/heads/release/23.x
  Home:   https://github.com/llvm/llvm-project
  Commit: d82b356e26bf6fc175b01b949fd3982084b1c572
      https://github.com/llvm/llvm-project/commit/d82b356e26bf6fc175b01b949fd3982084b1c572
  Author: Ryan Buchner <rbuchner at qti.qualcomm.com>
  Date:   2026-07-29 (Wed, 29 Jul 2026)

  Changed paths:
    M llvm/lib/CodeGen/RegisterCoalescer.cpp
    A llvm/test/CodeGen/ARM/coalesce-copy-undef.ll
    A llvm/test/CodeGen/ARM/coalesce-copy-undef.mir

  Log Message:
  -----------
  [CodeGen] Ensure `undef` propagation when an undef copy is eliminated if used as a subregister def (#204039)

If we eliminate an `undef` copy and there is a use of the copy that
`isDef` on just a sub-register, mark it as `undef`.

Fixes #204036.

(cherry picked from commit c85d1c54c5fba6344b117e369328a4b9b5a1386b)



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