Hints to compiler that affects how code should be emitted or optimized. Hints may be compile time or runtime.
An identity function that causes an
unused_must_usewarning to be triggered if the given value is not used (returned, stored in a variable, etc) by the caller.
An identity function that hints to the compiler to be maximally pessimistic about what
Emits a machine instruction to signal the processor that it is running in a busy-wait spin-loop (“spin lock”).
Informs the compiler that the site which is calling this function is not reachable, possibly enabling further optimizations.