[Diffusion] rL246675: [PowerPC] Don't always consider P8Altivec-only masks in LowerVECTOR_SHUFFLE

[Bill Schmidt via llvm-commits]

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Addresses a serious problem on pre-P8 hardware.


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  hfinkel (Author, Auditor)
  3.7-release (Auditor)
  llvm-commits (Auditor)
  tstellarAMD (Auditor)

http://reviews.llvm.org/rL246675