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[TargetLowering] Add BuildSDIVPattern helper to BuildExactSDIV (NFCI). 

As requested in D50392, pull the magic constant calculations out into a helper function.

llvm-svn: 339346
This commit is contained in:
Simon Pilgrim 2018-08-09 13:56:04 +00:00
parent bdd8493f2b
commit a9f95429d9
1 changed files with 23 additions and 14 deletions
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37
llvm/lib/CodeGen/SelectionDAG/TargetLowering.cpp
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@ -3440,34 +3440,43 @@ static SDValue BuildExactSDIV(const TargetLowering &TLI, SDNode *N,
EVT VT = N->getValueType(0);
EVT ShVT = TLI.getShiftAmountTy(VT, DAG.getDataLayout());
auto BuildSDIVPattern = [](APInt Divisor, unsigned &Shift, APInt &Factor) {
bool UseSRA = false;
Shift = Divisor.countTrailingZeros();
if (Shift) {
Divisor.ashrInPlace(Shift);
UseSRA = true;
}
// Calculate the multiplicative inverse, using Newton's method.
APInt t;
Factor = Divisor;
while ((t = Divisor * Factor) != 1)
Factor *= APInt(Divisor.getBitWidth(), 2) - t;
return UseSRA;
};
ConstantSDNode *C = isConstOrConstSplat(Op1);
if (!C || C->isNullValue())
return SDValue();
APInt d = C->getAPIntValue();
assert(d != 0 && "Division by zero!");
APInt FactorVal;
unsigned ShiftVal;
bool UseSRA = BuildSDIVPattern(C->getAPIntValue(), ShiftVal, FactorVal);
SDValue Shift = DAG.getConstant(ShiftVal, dl, ShVT);
SDValue Factor = DAG.getConstant(FactorVal, dl, VT);
SDValue Res = Op0;
// Shift the value upfront if it is even, so the LSB is one.
unsigned ShAmt = d.countTrailingZeros();
if (ShAmt) {
if (UseSRA) {
// TODO: For UDIV use SRL instead of SRA.
SDValue Amt = DAG.getConstant(ShAmt, dl, ShVT);
SDNodeFlags Flags;
Flags.setExact(true);
Res = DAG.getNode(ISD::SRA, dl, VT, Res, Amt, Flags);
Res = DAG.getNode(ISD::SRA, dl, VT, Res, Shift, Flags);
Created.push_back(Res.getNode());
d.ashrInPlace(ShAmt);
}
// Calculate the multiplicative inverse, using Newton's method.
APInt t, xn = d;
while ((t = d*xn) != 1)
xn *= APInt(d.getBitWidth(), 2) - t;
SDValue Mul = DAG.getConstant(xn, dl, VT);
return DAG.getNode(ISD::MUL, dl, VT, Res, Mul);
return DAG.getNode(ISD::MUL, dl, VT, Res, Factor);
}
SDValue TargetLowering::BuildSDIVPow2(SDNode *N, const APInt &Divisor,