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[DAGCombine] Use FoldConstantArithmetic() to perform C2-(A+C1) -> (C2-C1)-A fold
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Authored by lebedev.ri on May 30 2019, 7:13 AM.

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No tests change, and i'm not sure how to test this, but it's better safe than sorry.

LGTM

This revision is now accepted and ready to land.May 30 2019, 11:14 AM

This revision was automatically updated to reflect the committed changes.

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Show First 20 Lines • Show All 2,862 Lines • ▼ Show 20 Lines	SDValue DAGCombiner::visitSUB(SDNode *N) {
if (N0.getOpcode() == ISD::ADD && N0.getOperand(1) == N1)		if (N0.getOpcode() == ISD::ADD && N0.getOperand(1) == N1)
return N0.getOperand(0);		return N0.getOperand(0);

// fold C2-(A+C1) -> (C2-C1)-A		// fold C2-(A+C1) -> (C2-C1)-A
if (N1.getOpcode() == ISD::ADD) {		if (N1.getOpcode() == ISD::ADD) {
SDValue N11 = N1.getOperand(1);		SDValue N11 = N1.getOperand(1);
if (isConstantOrConstantVector(N0, /* NoOpaques */ true) &&		if (isConstantOrConstantVector(N0, /* NoOpaques */ true) &&
isConstantOrConstantVector(N11, /* NoOpaques */ true)) {		isConstantOrConstantVector(N11, /* NoOpaques */ true)) {
SDValue NewC = DAG.getNode(ISD::SUB, DL, VT, N0, N11);		SDValue NewC = DAG.FoldConstantArithmetic(ISD::SUB, DL, VT, N0.getNode(),
		N11.getNode());
		assert(NewC && "Constant folding failed");
return DAG.getNode(ISD::SUB, DL, VT, NewC, N1.getOperand(0));		return DAG.getNode(ISD::SUB, DL, VT, NewC, N1.getOperand(0));
}		}
}		}

// fold ((A+(B+or-C))-B) -> A+or-C		// fold ((A+(B+or-C))-B) -> A+or-C
if (N0.getOpcode() == ISD::ADD &&		if (N0.getOpcode() == ISD::ADD &&
(N0.getOperand(1).getOpcode() == ISD::SUB \|\|		(N0.getOperand(1).getOpcode() == ISD::SUB \|\|
N0.getOperand(1).getOpcode() == ISD::ADD) &&		N0.getOperand(1).getOpcode() == ISD::ADD) &&
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