[llvm] RISCV: Implement isLoadFromStackSlot/isStoreToStackSlot for rvv (PR #120524)

[Philip Reames via llvm-commits]

preames wrote:

> > @preames want to adopt this if you're touching RISCV regalloc?
> 
> Possibly. Let's chat about it when we talk Wednesday. I'm missing a bit of context on motivation, and mechanism.

I talked with @arsenm and I am going to adopt this one.  The motivation here is in optimizing spill/fill placement after initial spilling via the postOptimzation hooks.  Expect to see a patch from me in this area in the next week or so.

https://github.com/llvm/llvm-project/pull/120524