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[TII][X86] Do not schedule frame-setup/frame-destory instructions #96611

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Merged
merged 2 commits into from
Jun 26, 2024
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[TII][X86] Do not schedule frame-setup/frame-destory instructions #96611

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[TII] Do not schedule frame-setup/frame-destory instructions
HaohaiWen Jun 25, 2024
460e715
Limit to X86 only
HaohaiWen Jun 26, 2024
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5 changes: 5 additions & 0 deletions llvm/lib/Target/X86/X86InstrInfo.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -8832,6 +8832,11 @@ bool X86InstrInfo::isSchedulingBoundary(const MachineInstr &MI,
Opcode == X86::PLDTILECFGV)
return true;

// Frame setup and destory can't be scheduled around.
if (MI.getFlag(MachineInstr::FrameSetup) ||
MI.getFlag(MachineInstr::FrameDestroy))
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Should we put it in TargetInstrInfo::isSchedulingBoundary?

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Lots of arm tests would fail.

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If arm accepts scheduling with frame setup and destory, why can't for X86?

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Failed arm tests: https://buildkite.com/llvm-project/github-pull-requests/builds/75530#01904eb7-13d0-451e-b1da-bcb86cd44b60

.seh_savexmm %xmm15, 544
.seh_endprologue

For X86, most of frame-setup instruction is related to SEH exception restore.
Changing part of its order does not matter. e.g. two independent register save instructions.
Part of them does matter. e.g. .seh_pushreg, moving .seh_endprologue which may affect prologue size.

Anyway, rescheduling frame-setup instruction does not look like profitable for X86.

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I can't see the reason from the log, but I'm good with this change as long as no performance regression for X86.

return true;

return TargetInstrInfo::isSchedulingBoundary(MI, MBB, MF);
}

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