Hints to compiler that affects how code should be emitted or optimized. Hints may be compile time or runtime.
An identity function that hints to the compiler to be maximally pessimistic about what
black_box could do.
Emits a machine instruction to signal the processor that it is running in a busy-wait spin-loop (“spin lock”).
Informs the compiler that this point in the code is not reachable, enabling further optimizations.