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[DAG] Optimize Constant Xor And And Not Operation #161784

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[DAG] Optimize Constant Xor And And Not Operation #161784

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af5dcb5
added optimization and tests
manik-muk Oct 3, 2025
b176fd6
Move constant XOR AND ANDNOT optimization to generic DAG combiner
manik-muk Oct 4, 2025
4a2e546
changed combiner logic to account for infinite loops
manik-muk Oct 4, 2025
7fb0e39
refactored to remove goto
manik-muk Oct 5, 2025
d9c1a75
addressed comments
manik-muk Oct 10, 2025
be724f2
Merge branch 'main' into optimizeConstantXorAndAndNot
manik-muk Oct 10, 2025
6fcb51f
only changed modified lines of code
manik-muk Oct 10, 2025
9022deb
refactored to use sd match
manik-muk Oct 10, 2025
7e6ffa7
addressed comments
manik-muk Oct 13, 2025
de88c96
made use case more generalizable to all similar patterns
manik-muk Oct 15, 2025
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48 changes: 21 additions & 27 deletions llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -1265,37 +1265,31 @@ SDValue DAGCombiner::reassociateOpsCommutative(unsigned Opc, const SDLoc &DL,

// Optimize (Constant XOR a) & b & ~c -> (Constant XOR a) & (b & ~c)
// This allows the andn operation to be done in parallel with the xor
if (Opc == ISD::AND && TLI.hasAndNot(N1)) {
if (Opc == ISD::AND && (TLI.hasAndNot(N1) || TLI.hasAndNot(N0)) &&
sd_match(N1, m_Xor(m_Value(), m_AllOnes()))) {
// Look for pattern: AND(AND(XOR(Constant, a), b), NOT(c))
// Transform to: AND(XOR(Constant, a), AND(b, NOT(c)))

// Check if N1 is NOT(c) - i.e., XOR(c, -1)
if (N1.getOpcode() == ISD::XOR &&
DAG.isConstantIntBuildVectorOrConstantInt(N1.getOperand(1)) &&
isAllOnesConstant(N1.getOperand(1))) {

// Check if one operand of N0 is XOR(Constant, a)
SDValue XorOp, OtherOp;
if (N00.getOpcode() == ISD::XOR) {
XorOp = N00;
OtherOp = N01;
} else if (N01.getOpcode() == ISD::XOR) {
XorOp = N01;
OtherOp = N00;
} else {
return SDValue();
}

// Check if XOR has a constant operand
if (DAG.isConstantIntBuildVectorOrConstantInt(XorOp.getOperand(0)) ||
DAG.isConstantIntBuildVectorOrConstantInt(XorOp.getOperand(1))) {
// Transform: AND(AND(XOR(Constant, a), b), NOT(c))
// To: AND(XOR(Constant, a), AND(b, NOT(c)))
// This allows the andn (b & ~c) to be done in parallel with the xor
SDValue NewAnd = DAG.getNode(ISD::AND, DL, VT, OtherOp, N1);
return DAG.getNode(ISD::AND, DL, VT, XorOp, NewAnd);
}
SDValue XorOp, OtherOp;
APInt XorConst;

// Check which operand of N0 is XOR(Constant, X)
if (sd_match(N00, m_Xor(m_ConstInt(XorConst), m_Value())) &&
!XorConst.isAllOnes()) {
XorOp = N00;
OtherOp = N01;
} else if (sd_match(N01, m_Xor(m_ConstInt(XorConst), m_Value())) &&
!XorConst.isAllOnes()) {
XorOp = N01;
OtherOp = N00;
} else {
return SDValue();
}

// Transform: AND(AND(XOR(Constant, a), b), NOT(c))
// To: AND(XOR(Constant, a), AND(b, NOT(c)))
SDValue NewAnd = DAG.getNode(ISD::AND, DL, VT, OtherOp, N1);
return DAG.getNode(ISD::AND, DL, VT, XorOp, NewAnd);
}
if (Opc == ISD::XOR) {
// (N00 ^ N01) ^ N00 --> N01
Expand Down