I would argue that data layout is even more important the the data structure you use(see radix sort) which is also something the compiler can't control.

I pretty strongly disagree that with the meta-parent that it's the "compiler's job to speed up your code". It just doesn't have enough context to be able to do it effectively. I would actually prefer a predictable compiler to one that tries to do all sorts of magic tricks that can be perturbed by seemingly trivial code changes.