Merging r259236:

Merging r259236:
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r259236 | spatel | 2016-01-29 12:21:02 -0800 (Fri, 29 Jan 2016) | 8 lines

[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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git-svn-id: https://llvm.org/svn/llvm-project/llvm/branches/release_38@259245 91177308-0d34-0410-b5e6-96231b3b80d8