[llvm] r226075 - Fix PR22222

[Hans Wennborg]

Hi Sanjoy,

On Wed, Jan 14, 2015 at 5:46 PM, Sanjoy Das
<sanjoy at playingwithpointers.com> wrote:
> Author: sanjoy
> Date: Wed Jan 14 19:46:09 2015
> New Revision: 226075
>
> URL: http://llvm.org/viewvc/llvm-project?rev=226075&view=rev
> Log:
> Fix PR22222
>
> The bug was introduced in r225282. r225282 assumed that sub X, Y is
> the same as add X, -Y. This is not correct if we are going to upgrade
> the sub to sub nuw. This change fixes the issue by making the
> optimization ignore sub instructions.

Should we merge this to the 3.6 branch?

 - Hans