[all-commits] [llvm/llvm-project] cd4a74: FastISel: Mark implicit physreg defs dead when emi...

[Matt Arsenault via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: cd4a743905b27afafc26915091b29137e9d0c385
      https://github.com/llvm/llvm-project/commit/cd4a743905b27afafc26915091b29137e9d0c385
  Author: Matt Arsenault <Matthew.Arsenault at amd.com>
  Date:   2026-09-30 (Wed, 30 Sep 2026)

  Changed paths:
    M llvm/include/llvm/CodeGen/MachineInstr.h
    M llvm/lib/CodeGen/SelectionDAG/FastISel.cpp
    M llvm/lib/Target/WebAssembly/WebAssemblyFastISel.cpp
    M llvm/lib/Target/X86/X86FastISel.cpp
    M llvm/test/CodeGen/X86/expand-large-fp-optnone.ll
    A llvm/test/CodeGen/X86/fast-isel-dead-implicit-defs.ll
    M llvm/test/CodeGen/X86/fast-isel-sext-dead-eflags.ll

  Log Message:
  -----------
  FastISel: Mark implicit physreg defs dead when emitting instructions (#227598)

fastEmitInst_* callers only use the explicit result, so the implicit
physical register defs of the emitted instruction are unused.
InstrEmitter would mark these as dead, but fast isel would end up
relying on
later dead flag computation in LiveVariables or RegAllocFast.

The X86 with-overflow lowering is the one caller that reads an implicit
def, so handle that separately.

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



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