4 ms·

Ego.

• kevincox 6y ago
  If you are really sure put __builtin_unreachable()
  • pvarangot 6y ago
    I'm pretty sure he didn't have that on most of the platforms he was targeting with his portable C code, it's not even there on some of them now.
    • jstimpfle 6y ago
      what you do is you define a macro in a common header. Like UNREACHABLE().
  • jstimpfle 6y ago
    Shoot I have done that in the past but it seems I actually wanted __builtin_trap().
    • kevincox 6y ago
      Yeah, that footgun should really have a more explicit name. __dear_compiler_i_promise_that_this_statement_is_unreachable_and_you_may_optimize_based_on_my_good_word_upon_penalty_of_undefined_behaviour()
      • derefr 6y ago
        I mean, what other semantics would anyone expect it to have—presuming they think for a moment about why it exists as its own thing in the first place?
        • dodobirdlord 6y ago
          Rust being Rust, the equivalent causes a safe teardown. https://doc.rust-lang.org/std/macro.unreachable.html https://doc.rust-lang.org/std/macro.unreachable.html The UB causing equivalent is of course unsafe. https://doc.rust-lang.org/std/hint/fn.unreachable_unchecked.html https://doc.rust-lang.org/std/hint/fn.unreachable_unchecked....
        • jstimpfle 6y ago
          Ok so what's the answer if you apply the question to __builtin_trap()?
      • saagarjha 6y ago
        Even better, just actually perform undefined behavior on that branch and the compiler will get rid of it.
        • kevincox 6y ago
          This is literally what __builtin_unreachable() does. But it has the added benefit of the compiler understanding the intent so it works well with diagnostics.
          • saagarjha 6y ago
            But that's a builtin, rather than something that's part of the core language :)