AVX512: Add extract_subvector patterns v8i1->v4i1 , v4i1->v2i1.

Differential Revision: http://reviews.llvm.org/D17953

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@262929 91177308-0d34-0410-b5e6-96231b3b80d8
2 files changed