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

[David Majnemer via llvm-commits]

LGTM

On Fri, Jan 29, 2016 at 1:03 PM, Hans Wennborg <hans at chromium.org> wrote:

> (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.
>
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