[all-commits] [llvm/llvm-project] ef991e: FastISel: Assert the emitted instruction defines t...

[Matt Arsenault via All-commits]

  Branch: refs/heads/users/arsenm/fast-isel/no-zero-def-fallback
  Home:   https://github.com/llvm/llvm-project
  Commit: ef991e5b84ba579d4a8afdc87d8e48e87e4b83b6
      https://github.com/llvm/llvm-project/commit/ef991e5b84ba579d4a8afdc87d8e48e87e4b83b6
  Author: Matt Arsenault <Matthew.Arsenault at amd.com>
  Date:   2026-09-25 (Fri, 25 Sep 2026)

  Changed paths:
    M llvm/lib/CodeGen/SelectionDAG/FastISel.cpp

  Log Message:
  -----------
  FastISel: Assert the emitted instruction defines the result

The fallback path copied the result out of implicit_defs()[0], assuming
the first implicit physical register def is the result. That is an X86
assumption about MUL/IMUL, and it is unreachable for all but
fastEmitInst_r: FastISelEmitter skips any instruction whose first
operand is not an output register, so every opcode reaching these
helpers from generated code has an explicit def.

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



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