[hajile]

This isn't strictly true. Apple has other co-processors and some custom instructions (eg, matrix instructions). If you use their compiler and code, they can offload some calls to these while if you used another compiler and different libraries, these co-processors will be completely unused in all cases.

[astrange]

Using clang won't get you any of those things. Autovectorization is mostly mythical.

Calling into a system BLAS library might, but most benchmarks wouldn't do that.