[llvm] [LoopVectorizer] Add support for chaining partial reductions (PR #120272)

[Florian Hahn via llvm-commits]

fhahn wrote:

> > Sounds like supporting partial reduction subtractions would be a good extension on its own (and test-able independently), could it be split off?
> 
> Yep. I've pulled it out completely, and will create a new PR for adding sub support.
> 
> Edit; PR for adding subtraction partial reductions: #123636

Ok great thanks! It’s a deft at the moment, any issues?

https://github.com/llvm/llvm-project/pull/120272