diff options
| -rw-r--r-- | lib/Transforms/Scalar/InstructionCombining.cpp | 24 |
1 files changed, 21 insertions, 3 deletions
diff --git a/lib/Transforms/Scalar/InstructionCombining.cpp b/lib/Transforms/Scalar/InstructionCombining.cpp index 3a7d1018c4..2311f1eb5a 100644 --- a/lib/Transforms/Scalar/InstructionCombining.cpp +++ b/lib/Transforms/Scalar/InstructionCombining.cpp @@ -7354,8 +7354,17 @@ Instruction *InstCombiner::visitSelectInst(SelectInst &SI) { if (FCmpInst *FCI = dyn_cast<FCmpInst>(CondVal)) { if (FCI->getOperand(0) == TrueVal && FCI->getOperand(1) == FalseVal) { // Transform (X == Y) ? X : Y -> Y - if (FCI->getPredicate() == FCmpInst::FCMP_OEQ) + if (FCI->getPredicate() == FCmpInst::FCMP_OEQ) { + // This is not safe in general for floating point: + // consider X== -0, Y== +0. + // It becomes safe if either operand is a nonzero constant. + ConstantFP *CFPt, *CFPf; + if (((CFPt = dyn_cast<ConstantFP>(TrueVal)) && + !CFPt->getValueAPF().isZero()) || + ((CFPf = dyn_cast<ConstantFP>(FalseVal)) && + !CFPf->getValueAPF().isZero())) return ReplaceInstUsesWith(SI, FalseVal); + } // Transform (X != Y) ? X : Y -> X if (FCI->getPredicate() == FCmpInst::FCMP_ONE) return ReplaceInstUsesWith(SI, TrueVal); @@ -7363,8 +7372,17 @@ Instruction *InstCombiner::visitSelectInst(SelectInst &SI) { } else if (FCI->getOperand(0) == FalseVal && FCI->getOperand(1) == TrueVal){ // Transform (X == Y) ? Y : X -> X - if (FCI->getPredicate() == FCmpInst::FCMP_OEQ) - return ReplaceInstUsesWith(SI, FalseVal); + if (FCI->getPredicate() == FCmpInst::FCMP_OEQ) { + // This is not safe in general for floating point: + // consider X== -0, Y== +0. + // It becomes safe if either operand is a nonzero constant. + ConstantFP *CFPt, *CFPf; + if (((CFPt = dyn_cast<ConstantFP>(TrueVal)) && + !CFPt->getValueAPF().isZero()) || + ((CFPf = dyn_cast<ConstantFP>(FalseVal)) && + !CFPf->getValueAPF().isZero())) + return ReplaceInstUsesWith(SI, FalseVal); + } // Transform (X != Y) ? Y : X -> Y if (FCI->getPredicate() == FCmpInst::FCMP_ONE) return ReplaceInstUsesWith(SI, TrueVal); |