Merging r276181:

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r276181 | majnemer | 2016-07-20 14:05:01 -0700 (Wed, 20 Jul 2016) | 6 lines

[GVNHoist] Don't hoist PHI nodes

We hoisted PHIs without respecting their special insertion point in the
block, leading to verfier errors.

This fixes PR28626.
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llvm-svn: 276418