[llvm-commits] [llvm] r49928 - /llvm/trunk/lib/Analysis/ScalarEvolution.cpp

[Chris Lattner]

On Apr 18, 2008, at 2:38 PM, Dale Johannesen wrote:
> URL: http://llvm.org/viewvc/llvm-project?rev=49928&view=rev
> Log:
> Fix a scalar evolution bug.  Reversing everything
> does not work because of 0; 2>0 but -2U is also >0.

Sorry for being late to the party :)

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> ======================================================================
> --- llvm/trunk/lib/Analysis/ScalarEvolution.cpp (original)
> +++ llvm/trunk/lib/Analysis/ScalarEvolution.cpp Fri Apr 18 16:38:31  
> 2008
> @@ -1980,8 +1980,7 @@
>     break;
>   }
>   case ICmpInst::ICMP_UGT: {
> -    SCEVHandle TC = HowManyLessThans(SE.getNegativeSCEV(LHS),
> -                                     SE.getNegativeSCEV(RHS), L,  
> false);
> +    SCEVHandle TC = HowFarToZero(SE.getMinusSCEV(LHS, RHS), L);
>     if (!isa<SCEVCouldNotCompute>(TC)) return TC;
>     break;
>   }

Shouldn't this just be:

   case ICmpInst::ICMP_ULT: {
     SCEVHandle TC = HowManyLessThans(LHS, RHS, L, false);
     if (!isa<SCEVCouldNotCompute>(TC)) return TC;
     break;
   }
   case ICmpInst::ICMP_UGT: {
     SCEVHandle TC = HowManyLessThans(RHS, LHS, L, false);
     if (!isa<SCEVCouldNotCompute>(TC)) return TC;
     break;
   }

x > y  -->  y < x

-Chris