diff options
Diffstat (limited to 'llvm/lib/CodeGen/SelectionDAG')
| -rw-r--r-- | llvm/lib/CodeGen/SelectionDAG/TargetLowering.cpp | 29 |
1 files changed, 18 insertions, 11 deletions
diff --git a/llvm/lib/CodeGen/SelectionDAG/TargetLowering.cpp b/llvm/lib/CodeGen/SelectionDAG/TargetLowering.cpp index a1f425eeac1..f2c5a63354e 100644 --- a/llvm/lib/CodeGen/SelectionDAG/TargetLowering.cpp +++ b/llvm/lib/CodeGen/SelectionDAG/TargetLowering.cpp @@ -793,19 +793,26 @@ bool TargetLowering::SimplifyDemandedBits(SDValue Op, APInt MsbMask = APInt::getHighBitsSet(BitWidth, 1); // If we only care about the highest bit, don't bother shifting right. - if (MsbMask == DemandedMask) { + if (MsbMask == NewMask) { unsigned ShAmt = ExVT.getScalarType().getSizeInBits(); SDValue InOp = Op.getOperand(0); - - // Compute the correct shift amount type, which must be getShiftAmountTy - // for scalar types after legalization. - EVT ShiftAmtTy = Op.getValueType(); - if (TLO.LegalTypes() && !ShiftAmtTy.isVector()) - ShiftAmtTy = getShiftAmountTy(ShiftAmtTy); - - SDValue ShiftAmt = TLO.DAG.getConstant(BitWidth - ShAmt, ShiftAmtTy); - return TLO.CombineTo(Op, TLO.DAG.getNode(ISD::SHL, dl, - Op.getValueType(), InOp, ShiftAmt)); + unsigned VTBits = Op->getValueType(0).getScalarType().getSizeInBits(); + bool AlreadySignExtended = + TLO.DAG.ComputeNumSignBits(InOp) >= VTBits-ShAmt+1; + // However if the input is already sign extended we expect the sign + // extension to be dropped altogether later and do not simplify. + if (!AlreadySignExtended) { + // Compute the correct shift amount type, which must be getShiftAmountTy + // for scalar types after legalization. + EVT ShiftAmtTy = Op.getValueType(); + if (TLO.LegalTypes() && !ShiftAmtTy.isVector()) + ShiftAmtTy = getShiftAmountTy(ShiftAmtTy); + + SDValue ShiftAmt = TLO.DAG.getConstant(BitWidth - ShAmt, ShiftAmtTy); + return TLO.CombineTo(Op, TLO.DAG.getNode(ISD::SHL, dl, + Op.getValueType(), InOp, + ShiftAmt)); + } } // Sign extension. Compute the demanded bits in the result that are not |
