[X86] Legalize v32i1 without BWI via splitting to v16i1 rather than the...

[X86] Legalize v32i1 without BWI via splitting to v16i1 rather than the default of promoting to v32i8.

Summary:
For the most part its better to keep v32i1 as a mask type of a narrower width than trying to promote it to a ymm register.

I had to add some overrides to the methods that get the types for the calling convention so that we still use v32i8 for argument/return purposes.

There are still some regressions in here. I definitely saw some around shuffles. I think we probably should move vXi1 shuffle from lowering to a DAG combine where I think the extend and truncate we have to emit would be better combined.

I think we also need a DAG combine to remove trunc from (extract_vector_elt (trunc))

Overall this removes something like 13000 CHECK lines from lit tests.

Reviewers: zvi, RKSimon, delena, spatel

Reviewed By: RKSimon

Subscribers: llvm-commits

Differential Revision: https://reviews.llvm.org/D42031

llvm-svn: 323201