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

[Luke Lau via llvm-commits]

lukel97 wrote:

Are the vector loops that this optimizes generated by the loop vectorizer? It looks like this is essentially converting an in-loop reduction to an out-of-loop reduction, but my understanding was that we did in-loop reductions by default anyway?

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