If that were the case Safari wouldn't perform much better than Chrome on certain benchmarks on Apple ARM based devices. But I think "optimization" is more makin

If that were the case Safari wouldn't perform much better than Chrome on certain benchmarks on Apple ARM based devices. But I think "optimization" is more making commonly used instructions really fast (such as uncontended atomics) and providing custom instruction extensions to accelerate common use cases in hardware (for example, I believe there is an undocumented branch prediction hint capability, whereas afaik for x86 you can only tell your compiler to order branches according to compile-time hints).