[llvm] [SelectionDAG] Lowering usub.sat(a, 1) to a - (a != 0) (PR #170076)

[guan jian via llvm-commits]

rez5427 wrote:

Well, I rebase it, And add freeze, and limit if for scalar, because I saw some regressions on test files.

https://github.com/llvm/llvm-project/pull/170076