I've never written native code for an apple device, but have some low-level experience on other things; my guess would be that idiomatic swift contains safety c

I've never written native code for an apple device, but have some low-level experience on other things; my guess would be that idiomatic swift contains safety checks, i.e. predictable branches, but branches nevertheless - and that simpler cores with poor or no branch prediction suffer much more heavily than "smarter" cores from that kind of code. At the end of the day, if all you're doing is basic adding/multiplying, you just don't need a fancy core (and hence: GPGPU, right?) So this microbenchmark result isn't very surprising, although it's nice to see the principles in action.