From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <gcc-bugs-return-381041-listarch-gcc-bugs=gcc.gnu.org@gcc.gnu.org>
Received: (qmail 30828 invoked by alias); 23 Jan 2012 23:19:04 -0000
Received: (qmail 30819 invoked by uid 22791); 23 Jan 2012 23:19:03 -0000
X-SWARE-Spam-Status: No, hits=-2.9 required=5.0	tests=ALL_TRUSTED,AWL,BAYES_00
X-Spam-Check-By: sourceware.org
Received: from localhost (HELO gcc.gnu.org) (127.0.0.1)    by sourceware.org (qpsmtpd/0.43rc1) with ESMTP; Mon, 23 Jan 2012 23:18:50 +0000
From: "marc.glisse at normalesup dot org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug libstdc++/51965] Redundant move constructions in heap algorithms
Date: Mon, 23 Jan 2012 23:46:00 -0000
X-Bugzilla-Reason: CC
X-Bugzilla-Type: changed
X-Bugzilla-Watch-Reason: None
X-Bugzilla-Product: gcc
X-Bugzilla-Component: libstdc++
X-Bugzilla-Keywords:
X-Bugzilla-Severity: enhancement
X-Bugzilla-Who: marc.glisse at normalesup dot org
X-Bugzilla-Status: UNCONFIRMED
X-Bugzilla-Priority: P3
X-Bugzilla-Assigned-To: unassigned at gcc dot gnu.org
X-Bugzilla-Target-Milestone: ---
X-Bugzilla-Changed-Fields: CC
Message-ID: <bug-51965-4-XjXcwxRnvm@http.gcc.gnu.org/bugzilla/>
In-Reply-To: <bug-51965-4@http.gcc.gnu.org/bugzilla/>
References: <bug-51965-4@http.gcc.gnu.org/bugzilla/>
X-Bugzilla-URL: http://gcc.gnu.org/bugzilla/
Auto-Submitted: auto-generated
Content-Type: text/plain; charset="UTF-8"
MIME-Version: 1.0
Mailing-List: contact gcc-bugs-help@gcc.gnu.org; run by ezmlm
Precedence: bulk
List-Id: <gcc-bugs.gcc.gnu.org>
List-Archive: <http://gcc.gnu.org/ml/gcc-bugs/>
List-Post: <mailto:gcc-bugs@gcc.gnu.org>
List-Help: <mailto:gcc-bugs-help@gcc.gnu.org>
Sender: gcc-bugs-owner@gcc.gnu.org
X-SW-Source: 2012-01/txt/msg02716.txt.bz2

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=51965

Marc Glisse <marc.glisse at normalesup dot org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |marc.glisse at normalesup
                   |                            |dot org

--- Comment #5 from Marc Glisse <marc.glisse at normalesup dot org> 2012-01-23 23:18:20 UTC ---
(The split into push_heap and __push_heap is just so the first part can be
inlined without the second, right?)

A more direct adaptation of the old code to rvalue references would be:

      std::__push_heap(__first, _DistanceType((__last - __first) - 1),
                       _DistanceType(0), _ValueType(_GLIBCXX_MOVE(*(__last -
1))));

Without the named temporary value, the compiler can perform copy elision.
Aliaksandr's patch looks like a different way to achieve the same goal.

Note that the current code thus seems to have a performance regression in C++03
compared to before the introduction of moves.