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From: "kamkaz at windowslive dot com" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug c++/102015] New: [missed optimization] Small memory overhead in _Rb_tree_impl (fix would require ABI break)
Date: Sun, 22 Aug 2021 17:36:46 +0000	[thread overview]
Message-ID: <bug-102015-4@http.gcc.gnu.org/bugzilla/> (raw)

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.

             reply	other threads:[~2021-08-22 17:36 UTC|newest]

Thread overview: 6+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-08-22 17:36 kamkaz at windowslive dot com [this message]
2021-08-22 19:17 ` [Bug libstdc++/102015] " pinskia at gcc dot gnu.org
2021-08-22 21:08 ` kamkaz at windowslive dot com
2021-08-23  9:45 ` redi at gcc dot gnu.org
2021-08-31 18:27 ` redi at gcc dot gnu.org
2021-08-31 18:28 ` redi at gcc dot gnu.org

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