[llvm] [RISCV][VLOPT] Look through PHI instructions (PR #132236)

[Michael Maitland via llvm-commits]

michaelmaitland wrote:

> Nice, is there a specific workload you're seeing that motivates this?

We were experimenting with not using vp intrinsics and saw it in x264.

https://github.com/llvm/llvm-project/pull/132236