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Change the default FMA codegen to be of 231 form instead of 213 form #25387

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Change the default FMA codegen to be of 231 form instead of 213 form #25387

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13 changes: 2 additions & 11 deletions src/jit/hwintrinsiccodegenxarch.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -2316,24 +2316,15 @@ void CodeGen::genFMAIntrinsic(GenTreeHWIntrinsic* node)
op2Reg = op3->gtRegNum;
op3 = op2;
}
else if (op1->isContained() || op1->isUsedFromSpillTemp())
else
{
// 231 form: op3 = (op2 * op3) + [op1]
// 231 form: o1 = (op2 * op3) + [op1]

ins = (instruction)(ins + 1);
op1Reg = op3->gtRegNum;
op2Reg = op2->gtRegNum;
op3 = op1;
}
else
{
// 213 form: op1 = (op2 * op1) + op3

op1Reg = op1->gtRegNum;
op2Reg = op2->gtRegNum;

isCommutative = !copiesUpperBits;
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@tannergooding tannergooding Jun 25, 2019

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I'm pretty sure we need to keep the isCommutative handling for the cases where the multiplicand and multiplier can be swapped.

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@hanblee hanblee Jun 26, 2019

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I missed that. Thanks.

}

if (isCommutative && (op1Reg != targetReg) && (op2Reg == targetReg))
{
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26 changes: 2 additions & 24 deletions src/jit/lsraxarch.cpp
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Expand Up @@ -2606,38 +2606,16 @@ int LinearScan::BuildHWIntrinsic(GenTreeHWIntrinsic* intrinsicTree)
srcCount += BuildOperandUses(op2);
srcCount += BuildDelayFreeUses(op3);
}
else if (op1->isContained())
else
{
// 231 form: op3 = (op2 * op3) + [op1]
// 231 form: op1 = (op2 * op3) + [op1]

tgtPrefUse = BuildUse(op3);

srcCount += BuildOperandUses(op1);
srcCount += BuildDelayFreeUses(op2);
srcCount += 1;
}
else
{
// 213 form: op1 = (op2 * op1) + op3

if (copiesUpperBits)
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@tannergooding tannergooding Jun 25, 2019

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Similar comment, pretty sure we need to preserve this logic since op1 impacts determinism.

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@CarolEidt CarolEidt Jun 26, 2019

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For clarity as well, I think it makes sense to continue to keep the reg-only case separate, even if it's using the same form as the case above.

{
tgtPrefUse = BuildUse(op1);

srcCount += 1;
srcCount += BuildDelayFreeUses(op2);
}
else
{
// op1 and op2 are commutative, so don't
// set either to be tgtPref or delayFree

srcCount += BuildOperandUses(op1);
srcCount += BuildOperandUses(op2);
}

srcCount += BuildDelayFreeUses(op3);
}

buildUses = false;
break;
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