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[TargetLowering] Refactor BuildSDIV in preparation for D50765. NFCI.

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Pull out magic factor calculators into a helper function, use 0/+1/-1 multiplication factor to (optionally) add/sub the numerator.

llvm-svn: 339898
This commit is contained in:
Simon Pilgrim 2018-08-16 16:54:06 +00:00
parent 67273784b1
commit 61f0571008
1 changed files with 37 additions and 25 deletions
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62
lib/CodeGen/SelectionDAG/TargetLowering.cpp
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@ -3522,6 +3522,23 @@ SDValue TargetLowering::BuildSDIV(SDNode *N, SelectionDAG &DAG,
if (N->getFlags().hasExact())
return BuildExactSDIV(*this, N, dl, DAG, Created);
auto BuildSDIVPattern = [&](const APInt &Divisor, SDValue &MagicFactor,
SDValue &Factor, SDValue &Shift) {
APInt::ms magics = Divisor.magic();
int NumeratorFactor = 0;
// If d > 0 and m < 0, add the numerator.
if (Divisor.isStrictlyPositive() && magics.m.isNegative())
NumeratorFactor = 1;
// If d < 0 and m > 0, subtract the numerator.
else if (Divisor.isNegative() && magics.m.isStrictlyPositive())
NumeratorFactor = -1;
MagicFactor = DAG.getConstant(magics.m, dl, VT);
Factor = DAG.getConstant(NumeratorFactor, dl, VT);
Shift = DAG.getConstant(magics.s, dl, ShVT);
};
SDValue N0 = N->getOperand(0);
SDValue N1 = N->getOperand(1);
@ -3529,41 +3546,36 @@ SDValue TargetLowering::BuildSDIV(SDNode *N, SelectionDAG &DAG,
ConstantSDNode *C = isConstOrConstSplat(N1);
if (!C || C->isNullValue())
return SDValue();
const APInt &Divisor = C->getAPIntValue();
APInt::ms magics = Divisor.magic();
// Collect the shifts/magic values.
SDValue MagicFactor, Factor, Shift;
BuildSDIVPattern(C->getAPIntValue(), MagicFactor, Factor, Shift);
// Multiply the numerator (operand 0) by the magic value
// FIXME: We should support doing a MUL in a wider type
SDValue Q;
if (IsAfterLegalization ? isOperationLegal(ISD::MULHS, VT)
: isOperationLegalOrCustom(ISD::MULHS, VT))
Q = DAG.getNode(ISD::MULHS, dl, VT, N0, DAG.getConstant(magics.m, dl, VT));
Q = DAG.getNode(ISD::MULHS, dl, VT, N0, MagicFactor);
else if (IsAfterLegalization ? isOperationLegal(ISD::SMUL_LOHI, VT)
: isOperationLegalOrCustom(ISD::SMUL_LOHI, VT))
Q = SDValue(DAG.getNode(ISD::SMUL_LOHI, dl, DAG.getVTList(VT, VT), N0,
DAG.getConstant(magics.m, dl, VT))
.getNode(), 1);
else
return SDValue(); // No mulhs or equvialent
: isOperationLegalOrCustom(ISD::SMUL_LOHI, VT)) {
SDValue LoHi =
DAG.getNode(ISD::SMUL_LOHI, dl, DAG.getVTList(VT, VT), N0, MagicFactor);
Q = SDValue(LoHi.getNode(), 1);
} else
return SDValue(); // No mulhs or equivalent
Created.push_back(Q.getNode());
// (Optionally) Add/subtract the numerator using Factor.
Factor = DAG.getNode(ISD::MUL, dl, VT, N0, Factor);
Created.push_back(Factor.getNode());
Q = DAG.getNode(ISD::ADD, dl, VT, Q, Factor);
Created.push_back(Q.getNode());
// Shift right algebraic by shift value.
Q = DAG.getNode(ISD::SRA, dl, VT, Q, Shift);
Created.push_back(Q.getNode());
// If d > 0 and m < 0, add the numerator
if (Divisor.isStrictlyPositive() && magics.m.isNegative()) {
Q = DAG.getNode(ISD::ADD, dl, VT, Q, N0);
Created.push_back(Q.getNode());
}
// If d < 0 and m > 0, subtract the numerator.
if (Divisor.isNegative() && magics.m.isStrictlyPositive()) {
Q = DAG.getNode(ISD::SUB, dl, VT, Q, N0);
Created.push_back(Q.getNode());
}
// Shift right algebraic if shift value is nonzero
if (magics.s > 0) {
Q = DAG.getNode(ISD::SRA, dl, VT, Q, DAG.getConstant(magics.s, dl, ShVT));
Created.push_back(Q.getNode());
}
// Extract the sign bit and add it to the quotient
SDValue T =
DAG.getNode(ISD::SRL, dl, VT, Q, DAG.getConstant(EltBits - 1, dl, ShVT));