[all-commits] [llvm/llvm-project] 4d866f: SystemZ: Mark unread CC defs dead at build time

[Matt Arsenault via All-commits]

  Branch: refs/heads/users/arsenm/systemz/custom-inserter-dead-cc
  Home:   https://github.com/llvm/llvm-project
  Commit: 4d866ffecc7bb32ba3ad1dfcd9d51cf3291a1b49
      https://github.com/llvm/llvm-project/commit/4d866ffecc7bb32ba3ad1dfcd9d51cf3291a1b49
  Author: Matt Arsenault <Matthew.Arsenault at amd.com>
  Date:   2026-09-25 (Fri, 25 Sep 2026)

  Changed paths:
    M llvm/lib/Target/SystemZ/SystemZFrameLowering.cpp
    M llvm/lib/Target/SystemZ/SystemZISelLowering.cpp
    M llvm/test/CodeGen/SystemZ/atomicrmw-fadd-04.ll
    M llvm/test/CodeGen/SystemZ/cmpxchg-01.ll
    M llvm/test/CodeGen/SystemZ/cmpxchg-02.ll
    A llvm/test/CodeGen/SystemZ/dead-cc-defs.ll

  Log Message:
  -----------
  SystemZ: Mark unread CC defs dead at build time

The custom inserters for the subword atomic pseudos and for probed
allocas, plus the inline stack probe emitted by frame lowering, build
instructions whose CC def is never read. Set the dead flags.

Marking the RISBG32 in the subword cmpxchg loop dead lets MachineSink
move it out of the compare block and into the store block, so it is
skipped when the comparison fails.

Co-Authored-By: Claude Opus 5 <noreply at anthropic.com>



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