[ARM] Permit auto-vectorization using MVE
With enough codegen complete, we can now correctly report the number and size
of vector registers for MVE, allowing auto vectorisation. This also allows FP
auto-vectorization for MVE without -Ofast/-ffast-math, due to support for IEEE
FP arithmetic and parity between scalar and vector FP behaviour.
Patch by David Sherwood.
Differential Revision: https://reviews.llvm.org/D63728
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@368529 91177308-0d34-0410-b5e6-96231b3b80d8