That’s true but for the most part such optimisations happen very predictably (and are extensively verified when applicable). This isn’t a case of writing some v

That’s true but for the most part such optimisations happen very predictably (and are extensively verified when applicable). This isn’t a case of writing some very abstract code and hoping that the compiler will sort it. Rather, you use abstractions that have been carefully designed and implemented (probably by you) to result in predictable machine code (another comment links to a good example of this by James Turner; the key here is that this example is obviously chosen for illustration purposes, but can be generalised). C++ does not relieve you of the responsibility to understand the abstractions you’re using, but it does make it possible to write such abstractions; for example, writing an iterator over a complex container type that, when used with a range-for loop, compiles down to a single inc/cmp/jne (this is in fact what a range-for loop over a `std::vector` does). Optimisations in C++ (those that are relevant here, anyway) are something that need to be relied on to write efficient code, but they also can be relied on.