Hmm true, we could have a new 'safe' keyword (or even #pragma) which would switch off 'unsafe' language features (basically the opposite of Rust's 'unsafe' enforce a stricter, more restrictive code style which is easier for the static analyzer to reason about). The majority of even high-performance C/C++ apps only needs to twiddle bits in very small areas of the code. That's still a lot better then trying to rewrite basically all software that has been written in the last 50 years ;)
The correctness invariants of complex C++ programs (such as browsers and JITs) cannot be 'discovered' by static analysis - they must be, at least in part, supplied by the programmer.
C and C++ were not designed to allow programmers to specify such invariants (and have them automatically checked). I am not convinced that introducing them can be done in a clean way.