https://gcc.gnu.org/bugzilla/show_bug.cgi?id=102015
Bug ID: 102015 Summary: [missed optimization] Small memory overhead in _Rb_tree_impl (fix would require ABI break) Product: gcc Version: 11.2.1 Status: UNCONFIRMED Severity: normal Priority: P3 Component: c++ Assignee: unassigned at gcc dot gnu.org Reporter: kamkaz at windowslive dot com Target Milestone: --- Current definition of _Rb_tree_key_compare causes size overhead for all std::(multi)set/map-s: template<typename _Key_compare> struct _Rb_tree_key_compare { _Key_compare _M_key_compare; ... }; If it were possible to change the ABI in the future, I think it can be improved by empty-base-optimization for comparators that are not final classes - or by adding [[no_unique_address]] to _M_key_compare.