[X86][AVX512BW] AVX512BW can sign-extend v32i8 to v32i16 for simpler v32i8 multiplies.

Only pre-AVX512BW targets need to split v32i8 vectors.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@264509 91177308-0d34-0410-b5e6-96231b3b80d8
2 files changed