Even if such thing would be possible to do by a bare a look at the code, which is most certainly not, it's still unclear to me how would you do that in a non-trivial, let's say, 1M LoC codebase. Or how do you make sure that none of your 3rd-party code even holds to that promise? Although noble that is unreachable goal.
UB does not happen because there's few lines of code that do the wrong(TM) kind of obvious thing but it happens because that chunk of code interacts with other parts of the code in ways that you usually cannot conceive without tooling or realistic workloads.
I guess that for that or similar reason, Rust also happens to be working on adding support for UBSAN, ASAN, TSAN and MSAN sanitizers. Unfortunately it has been WIP for almost 7 years: https://github.com/rust-lang/rust/issues/39699
UB does not happen because there's few lines of code that do the wrong(TM) kind of obvious thing but it happens because that chunk of code interacts with other parts of the code in ways that you usually cannot conceive without tooling or realistic workloads.
I guess that for that or similar reason, Rust also happens to be working on adding support for UBSAN, ASAN, TSAN and MSAN sanitizers. Unfortunately it has been WIP for almost 7 years: https://github.com/rust-lang/rust/issues/39699