[llvm] r226075 - Fix PR22222

[Sanjoy Das]

Hi Hans,

This should go into 3.6 only if r225282 is going into 3.6.

On Thu, Jan 15, 2015 at 10:28 AM, Hans Wennborg <hans at chromium.org> wrote:
> 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