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RedundantFlagCalculationElimination: select testz

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this saves uops.

Signed-off-by: Alyssa Rosenzweig <alyssa@rosenzweig.io>
This commit is contained in:
Alyssa Rosenzweig 2024-09-06 11:00:47 -04:00
parent 6e6d640fec
commit 47ac9edd7a
1 changed files with 13 additions and 6 deletions
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19
FEXCore/Source/Interface/IR/Passes/RedundantFlagCalculationElimination.cpp
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@ -523,14 +523,21 @@ bool DeadFlagCalculationEliminination::ProcessBlock(IREmitter* IREmit, IRListVie
} else if (Info.Replacement) {
IROp->Op = Info.Replacement;
}
} else {
FlagsRead &= ~Info.Write;
if (Info.ReplacementNoWrite && CodeNode->GetUses() == 0) {
IROp->Op = Info.ReplacementNoWrite;
}
} else if (Info.ReplacementNoWrite && CodeNode->GetUses() == 0) {
IROp->Op = Info.ReplacementNoWrite;
}
// If we don't care about the sign or carry, we can optimize testnz.
// Carry is inverted between testz and testnz so we check that too. Note
// this flag is outside of the if, since the TestNZ might result from
// optimizing AndWithFlags, and we need to converge locally in a single
// iteration.
if (IROp->Op == OP_TESTNZ && IROp->Size < 4 && !(FlagsRead & (FLAG_N | FLAG_C))) {
IROp->Op = OP_TESTZ;
}
FlagsRead &= ~Info.Write;
// If we eliminated the instruction, we eliminate its read too. This
// check is required to ensure the pass converges locally in a single
// iteration.