[X86] Cleanup the LowerMULH code by hoisting some commonalities between the vXi32 and vXi8 handling. NFCI

vXi32 support was recently moved from LowerMUL_LOHI to LowerMULH.

This commit shares the getOperand calls, switches both to use common IsSigned flag, and hoists the NumElems/NumElts variable.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@340720 91177308-0d34-0410-b5e6-96231b3b80d8
1 file changed