The optimizing C compilers used in automotive, medical, aerospace and rail are being "qualified" for use by large test code batteries and essentially "old age" and "widespread use with small problems".
There have been cases of compiler and MCU bugs, because the approach above is NOT mathematical correctness proof.
The same can soon be said about the Rust compiler.
Also, functional safety requires very extensive test efforts including unit tests for each subroutine, which would most likely expose compiler bugs.
In the end, there is no absolute safety, but only a "best effort, according to state of the art".