pub fn black_box<T>(dummy: T) -> T
NOTE: We don't have a proper black box in stable Rust. This is a workaround implementation, that may have a too big performance overhead, depending on operation, or it may fail to properly avoid having code optimized out. It is good enough that it is used by default.
A function that is opaque to the optimizer, to allow benchmarks to pretend to use outputs to assist in avoiding dead-code elimination.