Module hint

Hints to compiler that affects how code should be emitted or optimized.

Hints may be compile time or runtime.

Functions

assert_unchecked^⚠

Makes a soundness promise to the compiler that cond holds.

black_box

An identity function that hints to the compiler to be maximally pessimistic about what black_box could do.

spin_loop

Emits a machine instruction to signal the processor that it is running in a busy-wait spin-loop (“spin lock”).

unreachable_unchecked^⚠

Informs the compiler that the site which is calling this function is not reachable, possibly enabling further optimizations.

cold_pathExperimental

Hints to the compiler that given path is cold, i.e., unlikely to be taken. The compiler may choose to optimize paths that are not cold at the expense of paths that are cold.

likelyExperimental

Hints to the compiler that a branch condition is likely to be true. Returns the value passed to it.

must_useExperimental

An identity function that causes an unused_must_use warning to be triggered if the given value is not used (returned, stored in a variable, etc) by the caller.

unlikelyExperimental

Hints to the compiler that a branch condition is unlikely to be true. Returns the value passed to it.