Having the actual const_iterator::operator++() as an out-of-line member function means that the implicit this pointer forces the object onto the stack (registers don't have addresses that could be passed). Since const_iterator is now merely a thinly-disguised pointer, that would cause terrible codegen. So, apply a technique originally developed for QStringView and make the operator an inline function that re-sets the member dirEntry using a call to a QDirListing static function that takes and returns by value. Passing by value enables passing in registers, which means the iterator object can now be a register value and doesn't require spilling to the stack to call the function. Found in API-review. Pick-to: 6.8 Change-Id: I9f4d5be5b72249b368ef3dea9d857178ca7e16aa Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>