[llvm] [RISCV] Fold (X & -4096) == 0 -> (X >> 12) == 0 (PR #154233)

[Piotr Fusik via llvm-commits]

pfusik wrote:

I think BSETI+SLTU would be even better if we can hoist BSETI (or LI 1 + SLLI) before the loop or have this single-bit constant already available?

https://github.com/llvm/llvm-project/pull/154233