[mvuksano]

I think it's worth pointing out that the reason why these two examples execute at different speed is due to how compiler translated code AND because CPU was able to parallelize work. Compilers take knowledge about target platform (e.g. instruction set) and code and translate it into executable code. Compiler CAN (but doesn't have to) rewrite code only if it ALWAYS produces the same result as input code.

I feel like last 110-15 years (majority of) people have stopped thinking about specific CPU and only think about ISA. That works for a lot of workloads but in recent years I have observed that there is more and more interest in how specific CPU can execute code as efficiently as possible.

If you're interested in the kind of optimizations performed in the example you should check out polyhedral compilation (https://polyhedral.info/) and halide (https://halide-lang.org/). Both can be used to speed up certain workloads significantly.