Module hint 

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

Hints may be compile time or runtime.

Enums

LocalityExperimental

The expected temporal locality of a memory prefetch operation.

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.

select_unpredictable

Returns either true_val or false_val depending on the value of condition, with a hint to the compiler that condition is unlikely to be correctly predicted by a CPU’s branch predictor.

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.

prefetch_readExperimental

Prefetch the cache line containing ptr for a future read.

prefetch_read_instructionExperimental

Prefetch the cache line containing ptr into the instruction cache for a future read.

prefetch_read_non_temporalExperimental

Prefetch the cache line containing ptr for a single future read, but attempt to avoid polluting the cache.

prefetch_writeExperimental

Prefetch the cache line containing ptr for a future write.

prefetch_write_non_temporalExperimental

Prefetch the cache line containing ptr for a single future write, but attempt to avoid polluting the cache.

unlikelyExperimental

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