[llvm-commits] [llvm] r73243 - in /llvm/trunk: lib/Transforms/Scalar/InstructionCombining.cpp test/Transforms/InstCombine/fsub-fsub.ll

[Dale Johannesen]

On Jun 12, 2009, at 12:23 PMPDT, Dan Gohman wrote:

> Author: djg
> Date: Fri Jun 12 14:23:25 2009
> New Revision: 73243
>
> URL: http://llvm.org/viewvc/llvm-project?rev=73243&view=rev
> Log:
> Don't do (x - (y - z)) --> (x + (z - y)) on floating-point types,  
> because
> it may round differently. This fixes PR4374.

Shouldn't we do this if UnsafeFPMath is on?

>
> Added:
>    llvm/trunk/test/Transforms/InstCombine/fsub-fsub.ll
> 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=73243&r1=73242&r2=73243&view=diff
>
> = 
> = 
> = 
> = 
> = 
> = 
> = 
> = 
> ======================================================================
> --- llvm/trunk/lib/Transforms/Scalar/InstructionCombining.cpp  
> (original)
> +++ llvm/trunk/lib/Transforms/Scalar/InstructionCombining.cpp Fri  
> Jun 12 14:23:25 2009
> @@ -2608,21 +2608,6 @@
>       else if (Op1I->getOperand(1) == Op0)         // X-(Y+X) == -Y
>         return BinaryOperator::CreateFNeg(Op1I->getOperand(0),  
> I.getName());
>     }
> -
> -    if (Op1I->hasOneUse()) {
> -      // Replace (x - (y - z)) with (x + (z - y)) if the (y - z)  
> subexpression
> -      // is not used by anyone else...
> -      //
> -      if (Op1I->getOpcode() == Instruction::FSub) {
> -        // Swap the two operands of the subexpr...
> -        Value *IIOp0 = Op1I->getOperand(0), *IIOp1 = Op1I- 
> >getOperand(1);
> -        Op1I->setOperand(0, IIOp1);
> -        Op1I->setOperand(1, IIOp0);
> -
> -        // Create the new top level fadd instruction...
> -        return BinaryOperator::CreateFAdd(Op0, Op1);
> -      }
> -    }
>   }
>
>   return 0;
>
> Added: llvm/trunk/test/Transforms/InstCombine/fsub-fsub.ll
> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/InstCombine/fsub-fsub.ll?rev=73243&view=auto
>
> = 
> = 
> = 
> = 
> = 
> = 
> = 
> = 
> ======================================================================
> --- llvm/trunk/test/Transforms/InstCombine/fsub-fsub.ll (added)
> +++ llvm/trunk/test/Transforms/InstCombine/fsub-fsub.ll Fri Jun 12  
> 14:23:25 2009
> @@ -0,0 +1,8 @@
> +; RUN: llvm-as < %s | opt -instcombine | llvm-dis | grep fsub |  
> count 2
> +; PR4374
> +
> +define float @func(float %a, float %b) nounwind {
> +        %tmp3 = fsub float %a, %b
> +        %tmp4 = fsub float -0.000000e+00, %tmp3
> +        ret float %tmp4
> +}
>
>
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