[SLSR] use 'match' to simplify code; NFC

This pass could probably be modified slightly to allow
vector splat transforms for practically no cost, but
it only works on scalars for now. So the use of the
newer 'match' API should make no functional difference. 


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@345030 91177308-0d34-0410-b5e6-96231b3b80d8
2 files changed