[llvm] [LoopVectorizer] Add support for partial reductions (PR #92418)

[Graham Hunter via llvm-commits]

https://github.com/huntergr-arm commented:

Looking nicer, I see what you mean about not having the VFs available when determining support. Maybe a TTI query with a VF of 0 is a query for support of any partial reduction matching those types/extensions, then once the MaxVF for the loop has been determined we can request the cost for those specific VFs.

https://github.com/llvm/llvm-project/pull/92418