That’s unfortunately incorrect. That flag does not turn integer overflow into UB, which is what allows the C++ optimizations that assume it cannot happen, and can be used to prove that loops terminate, etc.

That flag changes the behavior of integer overflow from trapping to “modulo 2 arithmetic”.

If you want to change the behavior of integer overflow in Rust to “always assume it cannot happen”, you need to “hack” the compiler AFAIK.

If you believe this is incorrect, provide the flag that proves that (hint: such a flag makes safe Rust unsound and it therefore does not exist).