[llvm] r259236 - [InstCombine] avoid an insertelement transformation that induces the opposite extractelement fold (PR26354)

[Hans Wennborg via llvm-commits]

(actually cc'ing David this time)

On Fri, Jan 29, 2016 at 1:02 PM, Hans Wennborg <hans at chromium.org> wrote:
> David, OK to merge to 3.8?

^^

>
> On Fri, Jan 29, 2016 at 12:21 PM, Sanjay Patel via llvm-commits
> <llvm-commits at lists.llvm.org> wrote:
>> Author: spatel
>> Date: Fri Jan 29 14:21:02 2016
>> New Revision: 259236
>>
>> URL: http://llvm.org/viewvc/llvm-project?rev=259236&view=rev
>> Log:
>> [InstCombine] avoid an insertelement transformation that induces the opposite extractelement fold (PR26354)
>>
>> We would infinite loop because we created a shufflevector that was wider than
>> needed and then failed to combine that with the insertelement. When subsequently
>> visiting the extractelement from that shuffle, we see that it's unnecessary,
>> delete it, and trigger another visit to the insertelement.