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[TargetLowering] SimplifyDemandedBits trunc(srl(x, C1)) - early out for out of range C1. NFCI. 

llvm-svn: 356810
This commit is contained in:
Simon Pilgrim 2019-03-22 20:53:49 +00:00
parent b906bba576
commit 94e8f152c1
1 changed files with 18 additions and 18 deletions
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36
llvm/lib/CodeGen/SelectionDAG/TargetLowering.cpp
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@ -1257,29 +1257,29 @@ bool TargetLowering::SimplifyDemandedBits(
// Do not turn (vt1 truncate (vt2 srl)) into (vt1 srl) if vt1 is
// undesirable.
break;
ConstantSDNode *ShAmt = dyn_cast<ConstantSDNode>(Src.getOperand(1));
if (!ShAmt)
auto *ShAmt = dyn_cast<ConstantSDNode>(Src.getOperand(1));
if (!ShAmt || ShAmt->getAPIntValue().uge(BitWidth))
break;
SDValue Shift = Src.getOperand(1);
if (TLO.LegalTypes()) {
uint64_t ShVal = ShAmt->getZExtValue();
uint64_t ShVal = ShAmt->getZExtValue();
if (TLO.LegalTypes())
Shift = TLO.DAG.getConstant(ShVal, dl, getShiftAmountTy(VT, DL));
}
if (ShAmt->getZExtValue() < BitWidth) {
APInt HighBits = APInt::getHighBitsSet(OperandBitWidth,
OperandBitWidth - BitWidth);
HighBits.lshrInPlace(ShAmt->getZExtValue());
HighBits = HighBits.trunc(BitWidth);
APInt HighBits =
APInt::getHighBitsSet(OperandBitWidth, OperandBitWidth - BitWidth);
HighBits.lshrInPlace(ShVal);
HighBits = HighBits.trunc(BitWidth);
if (!(HighBits & DemandedBits)) {
// None of the shifted in bits are needed. Add a truncate of the
// shift input, then shift it.
SDValue NewTrunc =
TLO.DAG.getNode(ISD::TRUNCATE, dl, VT, Src.getOperand(0));
return TLO.CombineTo(
Op, TLO.DAG.getNode(ISD::SRL, dl, VT, NewTrunc, Shift));
}
if (!(HighBits & DemandedBits)) {
// None of the shifted in bits are needed. Add a truncate of the
// shift input, then shift it.
SDValue NewTrunc =
TLO.DAG.getNode(ISD::TRUNCATE, dl, VT, Src.getOperand(0));
return TLO.CombineTo(
Op, TLO.DAG.getNode(ISD::SRL, dl, VT, NewTrunc, Shift));
}
break;
}