There are many things that can help your compiler generate efficient code for you. Some boil down to steering it properly, others require writing your code in a compiler-friendly way.
It's also important to know what you need to do on your critical path and to design it efficiently. For instance, try to avoid virtual dispatch there (unless you can prove it's being devirtualized), and try not to allocate new memory on it. Often, the clever design of code to avoid locking (or at least using lock-free algorithms) is helpful. Generally speaking, everything that can worsen your performance should be kept outside your hot path. Having both your instruction and data caches hot is really going to pay out. Even attributes such as [[likely]] and [[unlikely]] that hint to the compiler which branch it should expect to be executed can sometimes change a lot.
