No, compilers (correctly) prefer correctness over speed, so they can optimise “obvious” things, but they cannot account for domain knowledge or inefficiencies f

No, compilers (correctly) prefer correctness over speed, so they can optimise “obvious” things, but they cannot account for domain knowledge or inefficiencies further apart, or that “might” alter some global state, so they can only make optimisations where they can be very sure there’s no side effects, because they have to err on the side of caution. They will only give you micro optimisations which could cumulatively speed up sometimes but the burden of wholistic program efficiency is still very much on the programmer. If you’re emptying the swimming pool using only a glass, the compiler will optimise the glass size, and your arm movements, but it won’t optimise “if you’re emptying the correct pool” or “if you should be using a pump instead” - a correct answer to the latter two could be 100,000 times more efficient than the earlier two, which a compiler could answer.