[PATCH] [X86][AVX] Fix wrong lowering of VPERM2X128 nodes.

[Michael Kuperstein]

I may be missing something, but I don't see how this helps.
We'll still get a nonsense MaskLO if both Mask[0] and Mask[1] are SM_SentinelUndef, and SM_SentinelUndef happens to be -INT_MAX.
Why not set MaskLO/MaskHI to 0 explicitly if both relevant Mask elements are undef?

(I know this is purely theoretical, if you feel it unnecessarily complicates the code, feel free to ignore.)


http://reviews.llvm.org/D8119

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