Not only math optimizations are like this. Strict aliasing is a promise to the compiler to not make two pointers of different types point to the same address.

Not only math optimizations are like this. Strict aliasing is a promise to the compiler to not make two pointers of different types point to the same address. You technically make that promise by writing in C (except a narrow set of allowed conversions) but most compilers on standard settings do let you get away with it.