strict aliasing rule

The C++ rule that a pointer to one type may be assumed not to point at an object of an unrelated type, which lets the optimizer keep values in registers.

The strict aliasing rule ([basic.lval]) makes accessing an object through a glvalue of an unrelated type undefined behaviour, so the optimizer may assume an int* and a float* never refer to the same storage.

Examples

Reading a float's bits through an int* is undefined; std::bit_cast<std::uint32_t>(f) or std::memcpy is the defined way.