Fixes two issue in SimplifyDemandedBits of sext_in_reg:
1) We should not try to simplify if the sext has multiple uses
2) There is no need to simplify is the source value is already sign-extended.
Patch by Gil Rapaport <gil.rapaport@intel.com>
Differential Revision: http://reviews.llvm.org/D6949
llvm-svn: 229659
diff --git a/llvm/lib/CodeGen/SelectionDAG/TargetLowering.cpp b/llvm/lib/CodeGen/SelectionDAG/TargetLowering.cpp
index a1f425e..f2c5a63 100644
--- a/llvm/lib/CodeGen/SelectionDAG/TargetLowering.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/TargetLowering.cpp
@@ -793,19 +793,26 @@
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);
+ 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);
- // 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));
+ 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