[llvm] [VP][RISCV] Introduce vp.splat and RISC-V. (PR #98731)

[Yeting Kuo via llvm-commits]

yetingk wrote:

> It would be quite nice to see how this is expected to help codegen where we currently use regular spats. I assume it will likely reduce `vsetvli`s? Is there a plan to introduce it to the vectorizer?

The main reason of this patch is for codegen and codegen prepare optimization. But I am sure the patch could be benefit to VLA vectorizer.


https://github.com/llvm/llvm-project/pull/98731