[all-commits] [llvm/llvm-project] 1b3932: [CodeGen] Fix MachineInstr::isSafeToMove handling ...

[Eli Friedman via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: 1b39328d7440aa7a94af4083257ef1c2f9394887
      https://github.com/llvm/llvm-project/commit/1b39328d7440aa7a94af4083257ef1c2f9394887
  Author: Eli Friedman <efriedma at quicinc.com>
  Date:   2025-02-25 (Tue, 25 Feb 2025)

  Changed paths:
    M llvm/lib/CodeGen/MachineInstr.cpp
    A llvm/test/CodeGen/AArch64/inline-asm-speculation.ll
    M llvm/test/CodeGen/AMDGPU/convergent-inlineasm.ll
    M llvm/test/CodeGen/AMDGPU/early-if-convert.ll
    M llvm/test/CodeGen/AMDGPU/sdwa-peephole.ll
    M llvm/test/CodeGen/ARM/arm-shrink-wrapping.ll
    M llvm/test/CodeGen/X86/x86-shrink-wrapping.ll
    M llvm/test/CodeGen/X86/x86-win64-shrink-wrapping.ll

  Log Message:
  -----------
  [CodeGen] Fix MachineInstr::isSafeToMove handling of inline asm. (#126807)

Even if an inline asm doesn't have memory effects, we can't assume it's
safe to speculate: it could trap, or cause undefined behavior. At the
LLVM IR level, this is handled correctly: we don't speculate inline asm
(unless it's marked "speculatable", but I don't think anyone does that).
Codegen also needs to respect this restriction.

This change stops Early If Conversion and similar passes from
speculating an INLINEASM MachineInstr.

Some uses of isSafeToMove probably could be switched to a different API:
isSafeToMove assumes you're hoisting, but we could handle some forms of
sinking more aggressively. But I'll leave that for a followup, if it
turns out to be relevant.

See also discussion on gcc bugtracker
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=102150 .



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