[llvm-commits] [llvm] r40595 - in /llvm/trunk: lib/Transforms/Scalar/GVN.cpp test/Transforms/GVN/2007-07-30-PredIDom.ll

[Chris Lattner]

On Jul 30, 2007, at 9:57 AM, Owen Anderson wrote:

> Author: resistor
> Date: Mon Jul 30 11:57:08 2007
> New Revision: 40595
>
> URL: http://llvm.org/viewvc/llvm-project?rev=40595&view=rev
> Log:
> Fix a bug caused by indiscriminantly asking for the dominators of a  
> predecessor.
> ====================================================================== 
> ========
> --- llvm/trunk/lib/Transforms/Scalar/GVN.cpp (original)
> +++ llvm/trunk/lib/Transforms/Scalar/GVN.cpp Mon Jul 30 11:57:08 2007
> @@ -723,7 +723,8 @@
>      return V = GetValueForBlock(IDom->getBlock(), orig, Phis);
>    }
>
> -
> +  if (std::distance(pred_begin(BB), pred_end(BB)) == 1)
> +    return V = GetValueForBlock(IDom->getBlock(), orig, Phis);
>

FYI, the if condition is O(n) in the number of predecessors, instead  
of constant time.  Instead of using std::distance, just use BB- 
 >getSinglePredecessor() which is constant time.

-Chris