[all-commits] [llvm/llvm-project] cf8ce5: RegAllocFast: Mark unspilled implicit_def physreg ...

[Matt Arsenault via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: cf8ce56a1f39f9a771d03aeedd9d89475e72a659
      https://github.com/llvm/llvm-project/commit/cf8ce56a1f39f9a771d03aeedd9d89475e72a659
  Author: Matt Arsenault <Matthew.Arsenault at amd.com>
  Date:   2026-09-25 (Fri, 25 Sep 2026)

  Changed paths:
    M llvm/lib/CodeGen/RegAllocFast.cpp
    A llvm/test/CodeGen/X86/regallocfast-implicit-def-live-out.mir

  Log Message:
  -----------
  RegAllocFast: Mark unspilled implicit_def physreg defs dead (#226295)

When a virtual register defined by an IMPLICIT_DEF is live out of the
block, or reloaded below, defineVirtReg deliberately skips the spill.
If there is also no use of the value in the block, the resulting physreg
def has no reader at all, but was left without a dead flag.

This avoids some unnecessary churn between regalloc runs on AMDGPU.
Since RA runs multiple times, missed dead flags in the first RA run get
re-inferred by the later runs which this avoids.

Co-authored-by: Claude Opus 5 <noreply at anthropic.com>



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