[llvm] [InstCombine] Preserve range information for `Op0 -nsw umin(X, Op0) --> usub.sat(Op0, X)` (PR #170989)

[via llvm-commits]

ParkHanbum wrote:

The reason this conversion is necessary is that during the process of converting operations like `x nsw-umin(x, y)` to `usub.sat`, `nsw`-related information is lost, resulting in missed optimization opportunities.

In my view, by the time it reaches `icmp`, it's likely already been converted to `usub.sat` and the information has been lost, so the possibility of `icmp` handling this appropriately seems low. What do you think? 


https://github.com/llvm/llvm-project/pull/170989