[PATCH] [X86][SSE] Generalised unpackl/unpckh shuffle matching

[Chandler Carruth]

I really disagree with the direction of this commit. I'm sorry I've not replied more promptly, but I would like us to go back and look at *why* we cannot canonicalize this problem away, and if we cannot, making isShuffleMaskEquivalent do the commuting itself. I have an idea of how to implement the latter, but I really don't understand what is breaking canonicalizing yet.

I'm probably just being dense (sorry), I do believe there may be a fundamental problem here, but I'm not seeing it yet. undef lanes *never* impact what is canonical in either direction. Is there some opposing canonicalization rules that we have  pick between, and that forces some cases to be canonicalized the wrong way?


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http://reviews.llvm.org/D7564

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