Today I found, that on aarch64, the std::hint::spin_loop translates to ISB SY. This instruction invalidates instruction caches, essentially throwing away all prefetched instructions, so that CPU has to redo the prefetch.
Question: does that mean, that this hint is undesirable when doing spin locks that one expects to succeed on the first try (e.g. when performing optimistic concurrency control)?
@jonh oh, right, I'm a dummy, I got so confused by the other answer to my SO question that I've forgotten that you wouldn't even get to that instruction in that case.