IME Rust is more dependent than C++ on these fragile optimizations. I think it is because idiomatic Rust is more abstract, and also because C++ has more advanced specialization features which allows implementing optimizations directly. For example in C++ you can say "if the type is uint8_t then do this instead..." but this is harder in Rust.
You asked for other examples: consider a simple operation over an array, like bitwise not. A C-style for-loop does the obvious thing but idiomatic Rust emits a gazillion one-byte 'not' instructions. This doesn't involve 'unsafe' but it does illustrate that you really do have to babysit Rust to get efficient codegen. https://rust.godbolt.org/z/PjW5vo
(In fairness C++ has its own stupid pitfalls too: https://travisdowns.github.io/blog/2019/11/19/toupper.html)