[Bug c++/51138] New: [C++0x] [4.6 Regression] Uninitialized list elements

[Bug c++/51138] New: [C++0x] [4.6 Regression] Uninitialized list elements

[reichelt at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=51138

             Bug #: 51138
           Summary: [C++0x] [4.6 Regression] Uninitialized list elements
    Classification: Unclassified
           Product: gcc
           Version: 4.6.2
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: reichelt@gcc.gnu.org


The following code snippet does not work as expected when compiled with
"-std=c++0x" even at "-O0" - it returns 42 instead of 0 (on i686-pc-linux-gnu).

===========================================
#include<list>

int main()
{
  {
    const std::list<int> a(100, 42);
  }

  const std::list<int> b(1);
  return b.back();
}
===========================================

The bug only happens with GCC 4.6.x, trunk seems to be unaffected.

[Bug c++/51138] [C++0x] [4.6 Regression] Uninitialized list elements

[reichelt at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=51138

Volker Reichelt <reichelt at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|                            |wrong-code
   Target Milestone|---                         |4.6.3

[Bug c++/51138] [C++0x] [4.6 Regression] Uninitialized list elements

[redi at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=51138

Jonathan Wakely <redi at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|                            |2011-11-15
     Ever Confirmed|0                           |1

--- Comment #1 from Jonathan Wakely <redi at gcc dot gnu.org> 2011-11-15 10:08:44 UTC ---
Confirmed.

With -std=c++0x the constructor calls this with an empty parameter pack:

      template<typename... _Args>
        void
        emplace_back(_Args&&... __args)
        { this->_M_insert(end(), std::forward<_Args>(__args)...); }

which calls allocator::construct with an empty pack:

        _M_get_Node_allocator().construct(__p,
                                          std::forward<_Args>(__args)...);

which does

      template<typename... _Args>
        void
        construct(pointer __p, _Args&&... __args)
        { ::new((void *)__p) _Tp(std::forward<_Args>(__args)...); }

[Bug c++/51138] [C++0x] [4.6 Regression] Uninitialized list elements

[paolo.carlini at oracle dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=51138

Paolo Carlini <paolo.carlini at oracle dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |hjl.tools at gmail dot com

--- Comment #2 from Paolo Carlini <paolo.carlini at oracle dot com> 2011-11-15 10:56:16 UTC ---
Maybe we can save time by asking HJ to find the patch which fixed it in
mainline...

[Bug c++/51138] [C++0x] [4.6 Regression] Uninitialized list elements

[hjl.tools at gmail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=51138

--- Comment #3 from H.J. Lu <hjl.tools at gmail dot com> 2011-11-15 18:36:09 UTC ---
It is fixed by revision 175640:

http://gcc.gnu.org/ml/gcc-cvs/2011-06/msg01131.html

[Bug c++/51138] [C++0x] [4.6 Regression] Uninitialized list elements

[paolo.carlini at oracle dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=51138

Paolo Carlini <paolo.carlini at oracle dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |jason at gcc dot gnu.org

--- Comment #4 from Paolo Carlini <paolo.carlini at oracle dot com> 2011-11-15 19:08:43 UTC ---
Ah nice, very small, thanks. But I have no idea whether the patch has
dependencies. Jason?

[Bug c++/51138] [C++0x] [4.6 Regression] Uninitialized list elements

[jason at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=51138

--- Comment #5 from Jason Merrill <jason at gcc dot gnu.org> 2011-11-15 20:58:12 UTC ---
Backporting that patch doesn't fix the testcase in 4.6.

[Bug c++/51138] [C++0x] [4.6 Regression] Uninitialized list elements

[jakub at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=51138

Jakub Jelinek <jakub at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|4.6.3                       |4.6.4

--- Comment #6 from Jakub Jelinek <jakub at gcc dot gnu.org> 2012-03-01 14:38:52 UTC ---
GCC 4.6.3 is being released.

[Bug c++/51138] [C++0x] [4.6 Regression] Uninitialized list elements

[paolo.carlini at oracle dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=51138

Paolo Carlini <paolo.carlini at oracle dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
         Resolution|                            |WONTFIX

--- Comment #7 from Paolo Carlini <paolo.carlini at oracle dot com> 2012-04-25 01:44:23 UTC ---
At this point, I don't think the issue will be fixed in 4.6.x.