While I agree with your essential point about #1, I think we agree for different reasons.

UBSan is a set of run-time checks and has low compile-time cost. The example function you give, f, would be complained about if you passed it INT_MAX, but that complaint would come at run-time and it would never be triggered if you never passed it INT_MAX.

I also agree that it is not possible to enforce non-INT_MAX limits, like x < 10.