[llvm] [SLP]Add subvector vectorization for non-load nodes (PR #108430)

[Arthur Eubanks via llvm-commits]

aeubanks wrote:

I tried minimizing some more by outlining code and am seeing SLPVectorizer trunc i64 to i8 then zext to i32 when the original code only truncs from i64 to i32, is that something that should happen?

https://github.com/llvm/llvm-project/pull/108430