[llvm] [RISCV] Optimize pattern `(setcc (selectLT (vfirst_vl ...) , 0, EVL, ...), EVL)` (PR #90538)

[Min-Yih Hsu via llvm-commits]

mshockwave wrote:

I have limited the scope of this optimization to handle only the pattern associated with `RISCVISD::VFIRST_VL`.

https://github.com/llvm/llvm-project/pull/90538