> The CPU also doesn't care if you use prefixes that aren't valid for a specific instruction, for example a REP on a non-repeatable instruction.

This is one of the reasons why the x86 could be extended so much. PAUSE is just REP NOP, for example. Segment prefixes in front of conditional branches were used as static branch prediction hints (which I believe have returned in some newer Intel CPUs). Useful if you want to make a hint on newer CPUs that is harmless on older CPUs.

Some prefixes have become part of the encoding for certain SIMD instructions, but that is a different case because those prefixes aren't hints.

I wonder whether there are some prefixes that cause (some) CPUs to execute the instruction a lot slower.

The fact sites do evil things with these headers is why I configure Firefox with

  network.http.referer.XOriginTrimmingPolicy

Copy the URL and manually paste it into a new tab, no referrer then.

If you have JavaScript enabled, that is. JWZ at least does the redirect on the server side.

The following is pulled in from `https://soc.me/assets/js/turnBack.js`:

    const undesirables = [
      "news.ycombinator.com/",
      // "reddit.com/", // disable temporaily
      "lobste.rs/"
    ] ;

    if (undesirables.find(site => document.referrer.includes(site))) {
      window.location.replace(document.referrer);
    }

This is an interesting way to prevent the hug of death. I wonder what the author's reasoning is, also would it really be effective?

Wow, I didn't even notice because I have extensions that strip the referrer header. Excellent.

open in new tab

Which clever code can utilize to determine which mode its running in and branch appropriately depending if the inc/dec were executed or not.

Awful compared to what?

I've seen benchmarks that go both ways in terms of a "winner" but in terms of overall variance there seems to be very little. There are some cases where ARM64 or RISCV do better and there are some cases where x86_64 does better. I can't see code density being a relevant factor when picking one ISA over another.

We've got good compilers now anyways.. outside of power consumption.. the ISA wars are dead.