[PATCH] [X86][AVX] Add support for shuffle decoding of vperm2f128/vperm2i128 with zero'd lanes

[Simon Pilgrim]

Hi chandlerc, spatel,

The vperm2f128/vperm2i128 shuffle mask decoding was not attempting to deal with shuffles that give zero lanes. This patch fixes this so that the assembly printer can provide shuffle comments.

As this decoder is also used in X86ISelLowering for shuffle combining, I've added an early-out to match existing behaviour. The hope is that we can add zero support in the future, this would allow other ops' decodes (e.g. insertps) to be combined as well.

REPOSITORY
  rL LLVM

http://reviews.llvm.org/D10593

Files:
  lib/Target/X86/Utils/X86ShuffleDecode.cpp
  lib/Target/X86/X86ISelLowering.cpp
  test/CodeGen/X86/avx-vperm2x128.ll

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