If I can autoport my C++ to Rust, and the port is confirmed identical, and the Rust is confirmed safe, can't I use that to reason about the safety of my C++? Is safe C++ just a matter of proving it has a safe Rust equivalent?
It depends on what “confirmed identical” means. Most compilers (or translators as you like) only guarantee that the output program represents a subset of the behaviors of the input program so it could be that subset is the “safe as in Rust” subset.
> our reference-counted translation model, where every variable is pessimistically wrapped inside a Rc<RefCell<T>> type, checks that would usually execute at compile-time are shifted to run time, degrading performance.
> our reference-counted translation model, where every variable is pessimistically wrapped inside a Rc<RefCell<T>> type, checks that would usually execute at compile-time are shifted to run time, degrading performance.