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.
Change-Id: I9f4d5be5b72249b368ef3dea9d857178ca7e16aa
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>
(cherry picked from commit aec8398d71d351e956683a695af51317fe65097e)
Reviewed-by: Qt Cherry-pick Bot <cherrypick_bot@qt-project.org>
892012e5d9