[llvm] [RISCV] Improve loop by extract reduction instruction (PR #179215)

[Florian Hahn via llvm-commits]

https://github.com/fhahn commented:

I don't think here is anything RISCV specific about this pattch. I think it would be preferable if it would just run after the vectorizers generally?

https://github.com/llvm/llvm-project/pull/179215