[llvm-commits] [llvm] r42582 - /llvm/trunk/lib/Transforms/Scalar/InstructionCombining.cpp

[Chris Lattner]

> URL: http://llvm.org/viewvc/llvm-project?rev=42582&view=rev
> Log:
> Tone down an overzealous optimization.

Nice catch!

-Chris

>
> Modified:
>     llvm/trunk/lib/Transforms/Scalar/InstructionCombining.cpp
>
> Modified: llvm/trunk/lib/Transforms/Scalar/InstructionCombining.cpp
> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/ 
> Scalar/InstructionCombining.cpp?rev=42582&r1=42581&r2=42582&view=diff
>
> ====================================================================== 
> ========
> --- llvm/trunk/lib/Transforms/Scalar/InstructionCombining.cpp  
> (original)
> +++ llvm/trunk/lib/Transforms/Scalar/InstructionCombining.cpp Wed  
> Oct  3 12:45:27 2007
> @@ -7354,8 +7354,17 @@
>    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 @@
>
>      } 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);
>
>
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