How to speed up this simple code? Multithreading, simd, inbounds

Excuse me, I need ask more about that. LLVM is able to recognize mathematical code, that have known formula and just use this formula? I’m ignorant in the world of compilers and after my C and C++ expirience, this looks unbelivebly good, so its hard to belive. To be sure, do I understand this correctly?

I don’t mean that compilers of C and C++ are bad, I just never noticing them doing something that. Maybe I just don’t look very cearfully.