[PATCH] [CodeGen] Combine small-element shuffles of scalar_to_vector in terms of the wider scalar.

[Simon Pilgrim]

In http://reviews.llvm.org/D8885#153311, @ab wrote:

> I'm not sure: I initially dismissed it because it works on multiple scalar inputs, for which it makes sense to do a BUILD_VECTOR directly.  For a single scalar input, I found it more straightforward to shuffle a SCALAR_TO_VECTOR, but I agree it's not very consistent.


If you look at the early versions of the patch on http://reviews.llvm.org/D8516 we did have a version that would create a SCALAR_TO_VECTOR if only the first scalar was defined, but there wasn't a good use case for it so it got dropped. Readding that path should be trivial.


http://reviews.llvm.org/D8885

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