[X86][SSE] Lower vXi8 general shifts to SSE shifts directly. NFCI.

Most of these shifts are extended to vXi16 so we don't gain anything from forcing another round of generic shift lowering - we know these extended cases are legal constant splat shifts.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@340307 91177308-0d34-0410-b5e6-96231b3b80d8
1 file changed