[PATCH] Scalarize select vector arguments when extracted

[Nadav Rotem]

Hi Matt, 

I am sorry I missed your first email. Thanks for working on this. 

> When the elements are extracted from a select, do the select on the extracted scalars from the input.
> 

I am not sure that this is always profitable or that it should be done in InstCombine. It is hard to know at IR-level (during inst-combine) if it is better to extract twice and perform a single select or if it is better to perform an vector select and extract once. I think that this kind of decision should be made in SelectionDAG. 

> With this, the vectorizer still isn't able to put a vector select back together. It is skipped because some of the insertelements are before the last select being vectorized.
> 

I assume that you mean the SLP-vectorizer.  What is the problem ? Do you have a test case ? I’d be happy to take a look.

> Also fixes some missing CHECK-LABELs in the test that changed, but those are separate.
> 

Can you commit the label fixes as a separate patch ?

Thanks,
Nadav