Is there an equivalent of assert in metal? I'm looking for a way to abnormally halt a shader and indicate it ought to be debugged. assert itself is defined ((void) 0), so that won't work. __builtin_trap() will halt execution, but there's no indication the shader was trapped other than lack of side effects of it completing. I'm wondering if there is some "other" way to trap, like emitting an invalid instruction into the shader, or doing something the metal API validator will flag as illegal.

I am implementing asset pipelines for a metal app and am deciding between the new Metal IO support and more traditional approaches like dispatch_io. Does the MTLCommandQueue use GCD as its backend, or how do the approaches compare?