[llvm] [RISCV] Introduce VLOptimizer pass (PR #108640)

[Philip Reames via llvm-commits]

preames wrote:

Hey, awesome!  Really happy to see this making it's way upstream.   As I'm sure you know, I've been slowly expanding tryToReduceVL in RISCVVectorPeephole in this direction.  We should definitely make sure we're sharing as much code as possible.  I think we still need the early peephole (to drive the vmv.v.v conversions), but we should at least share code.

I'm going to take a real look at the code on Monday, but wanted to state initial support!

https://github.com/llvm/llvm-project/pull/108640