Merging r246675:

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r246675 | hfinkel | 2015-09-02 12:52:37 -0400 (Wed, 02 Sep 2015) | 9 lines

[PowerPC] Don't always consider P8Altivec-only masks in LowerVECTOR_SHUFFLE

LowerVECTOR_SHUFFLE needs to decide whether to pass a vector shuffle off to the
TableGen-generated matching code, and it does this by testing the same
predicates used by the TableGen files. Unfortunately, when we added new
P8Altivec-only predicates, we started universally testing them in
LowerVECTOR_SHUFFLE, and if then matched when targeting a system prior to a P8,
we'd end up with a selection failure.

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llvm-svn: 252479