Function std::intrinsics::unreachable

pub unsafe extern "rust-intrinsic" fn unreachable() -> !

Unstable (core_intrinsics #0)

: intrinsics are unlikely to ever be stabilized, instead they should be used through stabilized interfaces in the rest of the standard library

Tells LLVM that this point in the code is not reachable, enabling further optimizations.

NB: This is very different from the unreachable!() macro!