[llvm] [LV] Add support for partial reductions without a binary op (PR #133922)

[Florian Hahn via llvm-commits]

https://github.com/fhahn commented:

Curious if/how this will interact with https://github.com/llvm/llvm-project/pull/136173? 

Would it potentially help to simplify computeCost & co?

https://github.com/llvm/llvm-project/pull/133922