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

[David Sherwood via llvm-commits]

david-arm wrote:

> > Curious if/how this will interact with #136173?
> > Would it potentially help to simplify computeCost & co?
> 
> I think we'll want to turn a partial reduction without a bin op into a `VPExtendedReductionRecipe` and then expand it back to a partial reduction.

@fhahn @SamTebbs33 Do you think that https://github.com/llvm/llvm-project/pull/136173 is likely to land soon? Ideally I'd like to progress this patch within the next few weeks. It looks like #136173 also depends upon #113903, which looks like it might still take some time.

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