This.

I agree that you will probably just end up writing ASM but it was a trivial example, there are non-trivial examples involving jump tables and unrolling loops etc.

Effectively weird optimisations that rely on the virtual machine the compiler is building for vs reality, there's just more abstractions with rust than with C++ by the virtue of the safety mechanism, it's just plain not possible to have the one without the other.

The hardware can do legal things that rust cannot allow or can allow but you need to write extremely convoluted code, C/C++ is closer to the metal in that regard.

Don't get me wrong I am all for the right abstractions, it allows insane optimisations that humans couldn't dream of, but there is a flip side.