[llvm] [RISCV] and x (sub -1, y) -> andn x y (PR #129253)

[Gábor Spaits via llvm-commits]

spaits wrote:

> Isn't sub -1, x canonicalized to xor x, -1?

Furthermore, if the InstCombiner sees the `xor` version it will replace it with `sub`. See https://godbolt.org/z/4ffxhPbz6
Maybe we shall make it back to sub in SelDAG?

https://github.com/llvm/llvm-project/pull/129253