Merging r341416:

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r341416 | annat | 2018-09-05 00:12:23 +0200 (Wed, 05 Sep 2018) | 11 lines

[LV] First order recurrence phis should not be treated as uniform

This is fix for PR38786.
First order recurrence phis were incorrectly treated as uniform,
which caused them to be vectorized as uniform instructions.

Patch by Ayal Zaks and Orivej Desh!

Reviewed by: Anna

Differential Revision: https://reviews.llvm.org/D51639
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git-svn-id: https://llvm.org/svn/llvm-project/llvm/branches/release_70@341523 91177308-0d34-0410-b5e6-96231b3b80d8