From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <gcc-bugs-return-387324-listarch-gcc-bugs=gcc.gnu.org@gcc.gnu.org>
Received: (qmail 10050 invoked by alias); 27 Mar 2012 22:44:32 -0000
Received: (qmail 10032 invoked by uid 22791); 27 Mar 2012 22:44:31 -0000
X-SWARE-Spam-Status: No, hits=-2.8 required=5.0	tests=ALL_TRUSTED,AWL,BAYES_00,TW_RG
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; Tue, 27 Mar 2012 22:43:48 +0000
From: "J.W.Rogers+gcc at gmail dot com" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug libstdc++/52745] New: GCC4.7 vector uses copy instead of move constructor
Date: Tue, 27 Mar 2012 23:06:00 -0000
X-Bugzilla-Reason: CC
X-Bugzilla-Type: new
X-Bugzilla-Watch-Reason: None
X-Bugzilla-Product: gcc
X-Bugzilla-Component: libstdc++
X-Bugzilla-Keywords:
X-Bugzilla-Severity: normal
X-Bugzilla-Who: J.W.Rogers+gcc at gmail dot com
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:
Message-ID: <bug-52745-4@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: 2012-03/txt/msg02377.txt.bz2

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=52745

             Bug #: 52745
           Summary: GCC4.7 vector uses copy instead of move constructor
    Classification: Unclassified
           Product: gcc
           Version: 4.7.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: libstdc++
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: J.W.Rogers+gcc@gmail.com


Using GCC 4.7.0, vector seems to prefer copy rather than move when resizing.

The following program produces different (and I think incorrect) results under
GCC 4.7.0 vs GCC 4.6.1

#include <iostream>
#include <vector>

struct Stuff
{
    Stuff( ) { }
    Stuff( Stuff&& o ) { std::cout << "Move" << std::endl; }
    Stuff( const Stuff& o ) { std::cout << "Copy" << std::endl; }
};


int main( const int argc, const char** argv )
{

    std::vector< Stuff > stuff;
    std::cout << "1" << std::endl;
    stuff.push_back( Stuff() );
    std::cout << "2" << std::endl;
    stuff.push_back( Stuff() );
    std::cout << "3" << std::endl;
    stuff.push_back( Stuff() );
}

Here is the output under GCC 4.6.1

jonathan@grindserv:~$ g++-4.6.1 -std=c++0x test.cpp
jonathan@grindserv:~$ ./a.out
1
Move
2
Move
Move
3
Move
Move
Move


Here is the output under GCC 4.7.0

jonathan@grindserv:~$ g++-4.7.0 -std=c++0x test.cpp
jonathan@grindserv:~$ ./a.out
1
Move
2
Move
Copy
3
Move
Copy
Copy