SDValue LanaiTargetLowering::LowerSRL_PARTS(SDValue Op,
SelectionDAG &DAG) const {
MVT VT = Op.getSimpleValueType();
unsigned VTBits = VT.getSizeInBits();
SDLoc dl(Op);
SDValue ShOpLo = Op.getOperand(0);
SDValue ShOpHi = Op.getOperand(1);
SDValue ShAmt = Op.getOperand(2);
// Performs the following for a >> b:
// unsigned r_high = a_high >> b;
// r_high = (32 - b <= 0) ? 0 : r_high;
//
// unsigned r_low = a_low >> b;
// r_low = (32 - b <= 0) ? r_high : r_low;
// r_low = (b == 0) ? r_low : r_low | (a_high << (32 - b));
// return (unsigned long long)r_high << 32 | r_low;
// Note: This takes advantage of Lanai's shift behavior to avoid needing to
// mask the shift amount.
SDValue Zero = DAG.getConstant(0, dl, MVT::i32);
SDValue NegatedPlus32 = DAG.getNode(
ISD::SUB, dl, MVT::i32, DAG.getConstant(VTBits, dl, MVT::i32), ShAmt);
SDValue SetCC = DAG.getSetCC(dl, MVT::i32, NegatedPlus32, Zero, ISD::SETLE);
SDValue Hi = DAG.getNode(ISD::SRL, dl, MVT::i32, ShOpHi, ShAmt);
Hi = DAG.getSelect(dl, MVT::i32, SetCC, Zero, Hi);
SDValue Lo = DAG.getNode(ISD::SRL, dl, MVT::i32, ShOpLo, ShAmt);
Lo = DAG.getSelect(dl, MVT::i32, SetCC, Hi, Lo);
SDValue CarryBits =
DAG.getNode(ISD::SHL, dl, MVT::i32, ShOpHi, NegatedPlus32);
SDValue ShiftIsZero = DAG.getSetCC(dl, MVT::i32, ShAmt, Zero, ISD::SETEQ);
Lo = DAG.getSelect(dl, MVT::i32, ShiftIsZero, Lo,
DAG.getNode(ISD::OR, dl, MVT::i32, Lo, CarryBits));
SDValue Ops[2] = {Lo, Hi};
return DAG.getMergeValues(Ops, dl);
}
