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

[Hans Wennborg via llvm-commits]

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.