I thought that i++ ++i difference is related to the inner data structures of C++ iterators and that when using the former you need to keep 2 states compared to just one for that fraction of execution.
int i = 0;
i++;
(Copying an iterator might be a lot more expensive than just copying an int, and might not be effectively optimized out by the compiler - e.g. if someone builds an iterator that's referenced-counted to an owning object or something)