[Bug libstdc++/52745] New: GCC4.7 vector uses copy instead of move constructor

["J.W.Rogers+gcc at gmail dot com" <gcc-bugzilla@gcc.gnu.org>]

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