-
- // 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, dl,
+ ShiftAmtTy);
+ return TLO.CombineTo(Op, TLO.DAG.getNode(ISD::SHL, dl,
+ Op.getValueType(), InOp,
+ ShiftAmt));
+ }