diff options
Diffstat (limited to 'llvm/lib/CodeGen/SelectionDAG/TargetLowering.cpp')
| -rw-r--r-- | llvm/lib/CodeGen/SelectionDAG/TargetLowering.cpp | 31 |
1 files changed, 13 insertions, 18 deletions
diff --git a/llvm/lib/CodeGen/SelectionDAG/TargetLowering.cpp b/llvm/lib/CodeGen/SelectionDAG/TargetLowering.cpp index 2d09b2cc9df..d7286a2789b 100644 --- a/llvm/lib/CodeGen/SelectionDAG/TargetLowering.cpp +++ b/llvm/lib/CodeGen/SelectionDAG/TargetLowering.cpp @@ -6907,24 +6907,19 @@ void TargetLowering::expandSADDSUBO( SDValue Zero = DAG.getConstant(0, dl, LHS.getValueType()); - // LHSSign -> LHS >= 0 - // RHSSign -> RHS >= 0 - // SumSign -> Result >= 0 - // - // Add: - // Overflow -> (LHSSign == RHSSign) && (LHSSign != SumSign) - // Sub: - // Overflow -> (LHSSign != RHSSign) && (LHSSign != SumSign) - SDValue LHSSign = DAG.getSetCC(dl, OType, LHS, Zero, ISD::SETGE); - SDValue RHSSign = DAG.getSetCC(dl, OType, RHS, Zero, ISD::SETGE); - SDValue SignsMatch = DAG.getSetCC(dl, OType, LHSSign, RHSSign, - IsAdd ? ISD::SETEQ : ISD::SETNE); - - SDValue SumSign = DAG.getSetCC(dl, OType, Result, Zero, ISD::SETGE); - SDValue SumSignNE = DAG.getSetCC(dl, OType, LHSSign, SumSign, ISD::SETNE); - - SDValue Cmp = DAG.getNode(ISD::AND, dl, OType, SignsMatch, SumSignNE); - Overflow = DAG.getBoolExtOrTrunc(Cmp, dl, ResultType, ResultType); + // For an addition, the result should be less than one of the operands (LHS) + // if and only if the other operand (RHS) is negative, otherwise there will + // be overflow. + // For a subtraction, the result should be less than one of the operands + // (LHS) if and only if the other operand (RHS) is (non-zero) positive, + // otherwise there will be overflow. + SDValue ResultLowerThanLHS = DAG.getSetCC(dl, OType, Result, LHS, ISD::SETLT); + SDValue ConditionRHS = + DAG.getSetCC(dl, OType, RHS, Zero, IsAdd ? ISD::SETLT : ISD::SETGT); + + Overflow = DAG.getBoolExtOrTrunc( + DAG.getNode(ISD::XOR, dl, OType, ConditionRHS, ResultLowerThanLHS), dl, + ResultType, ResultType); } bool TargetLowering::expandMULO(SDNode *Node, SDValue &Result, |
