Merging r266825:

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r266825 | nhaehnle | 2016-04-19 14:58:22 -0700 (Tue, 19 Apr 2016) | 12 lines

AMDGPU: Guard VOPC instructions against incorrect commute

Summary:
The added testcase, which triggered this, was derived from a shader-db case
via bugpoint. A separate question is why scalar branching wasn't used.

Reviewers: arsenm, tstellarAMD

Subscribers: arsenm, llvm-commits

Differential Revision: http://reviews.llvm.org/D19208

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llvm-svn: 271767