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[GlobalISel] Allow some load/store instructions to be folded in Match Table backend #70830

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[GlobalISel] Allow some load/store instructions to be folded in Match Table backend #70830

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23 changes: 21 additions & 2 deletions llvm/lib/CodeGen/GlobalISel/GIMatchTableExecutor.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -70,6 +70,25 @@ bool GIMatchTableExecutor::isObviouslySafeToFold(MachineInstr &MI,
if (MI.isConvergent() && MI.getParent() != IntoMI.getParent())
return false;

return !MI.mayLoadOrStore() && !MI.mayRaiseFPException() &&
!MI.hasUnmodeledSideEffects() && MI.implicit_operands().empty();
auto IsSafe = [](const MachineInstr &MI) {
return !MI.mayRaiseFPException() && !MI.hasUnmodeledSideEffects() &&
MI.implicit_operands().empty();
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@arsenm arsenm Nov 1, 2023

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Don't understand the implicit operands check. I think this is starting to reproduce MachineInstr::isSafeToMove

};
auto IsSafeNoMem = [IsSafe](const MachineInstr &MI) {
return !MI.mayLoadOrStore() && IsSafe(MI);
};

// If source instruction uses memory, fold if no intermediate
// instructions use it.
if (MI.mayLoadOrStore() && IsSafe(MI) &&
MI.getParent() == IntoMI.getParent()) {
auto IntoIt = IntoMI.getIterator();
auto NextIt = std::next(MI.getIterator());
while (!NextIt.isEnd() && NextIt != IntoIt && IsSafeNoMem(*NextIt))
++NextIt;
if (NextIt == IntoIt)
return true;
}

return IsSafeNoMem(MI);
}