[Bug c++/48562] New: Prematurely destroys initializer_list array when using new-expression

[Bug c++/48562] New: Prematurely destroys initializer_list array when using new-expression

[schaub.johannes at googlemail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=48562

           Summary: Prematurely destroys initializer_list array when using
                    new-expression
           Product: gcc
           Version: 4.6.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: schaub.johannes@googlemail.com


The C++0x spec requires that GCC destroys the backing-up array at "delete p",
but GCC appears to destroy it immediately after the first declaration (as
checked by using a class type that has a side-effecting destructor). 

    auto *p= new initializer_list<int>{1, 2, 3}; 
    { auto q(*p); }
    delete p;

[Bug c++/48562] Prematurely destroys initializer_list array when using new-expression

[amonakov at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=48562

Alexander Monakov <amonakov at gcc dot gnu.org> changed:

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

--- Comment #1 from Alexander Monakov <amonakov at gcc dot gnu.org> 2011-04-19 09:20:05 UTC ---
*** Bug 48669 has been marked as a duplicate of this bug. ***

[Bug c++/48562] [C++0x] Prematurely destroys initializer_list array when using new-expression

[paolo.carlini at oracle dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=48562

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |jason at gcc dot gnu.org
            Summary|Prematurely destroys        |[C++0x] Prematurely
                   |initializer_list array when |destroys initializer_list
                   |using new-expression        |array when using
                   |                            |new-expression

--- Comment #2 from Paolo Carlini <paolo.carlini at oracle dot com> 2011-09-23 22:01:23 UTC ---
Is this again PR48370, or should be kept separate?

[Bug c++/48562] [C++0x] warn about uses of initializer_list that will lead to dangling pointers

[jason at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=48562

Jason Merrill <jason at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|                            |diagnostic
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|                            |2011-09-23
            Summary|[C++0x] Prematurely         |[C++0x] warn about uses of
                   |destroys initializer_list   |initializer_list that will
                   |array when using            |lead to dangling pointers
                   |new-expression              |
     Ever Confirmed|0                           |1

--- Comment #3 from Jason Merrill <jason at gcc dot gnu.org> 2011-09-23 22:13:45 UTC ---
This is related to DR 1290.  At Bloomington we decided to clarify that the
lifetime of the array is like a temporary bound to a reference; in this case it
has full-expression lifetime.  We should probably add a warning about "new
initializer_list".

[Bug c++/48562] [C++0x] warn about uses of initializer_list that will lead to dangling pointers

[paolo.carlini at oracle dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=48562

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
         AssignedTo|unassigned at gcc dot       |paolo.carlini at oracle dot
                   |gnu.org                     |com

--- Comment #4 from Paolo Carlini <paolo.carlini at oracle dot com> 2011-09-23 22:23:04 UTC ---
Ah, Ok, thanks. Let's see what I can do.

[Bug c++/48562] [C++0x] warn about uses of initializer_list that will lead to dangling pointers

[paolo.carlini at oracle dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=48562

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |ASSIGNED

[Bug c++/48562] [C++0x] warn about uses of initializer_list that will lead to dangling pointers

[paolo.carlini at oracle dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=48562

--- Comment #5 from Paolo Carlini <paolo.carlini at oracle dot com> 2011-09-25 10:54:07 UTC ---
Johannes, sorry about the dumb question: now I understand the issue decently
well - and after all boils down to adding a warning - but I'm not sure to
understand your code snippet: is it meant to crash at runtime? Trigger valgrind
errors?

[Bug c++/48562] [C++0x] warn about uses of initializer_list that will lead to dangling pointers

[schaub.johannes at googlemail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=48562

--- Comment #6 from Johannes Schaub <schaub.johannes at googlemail dot com> 2011-09-25 14:22:33 UTC ---
(In reply to comment #5)
> Johannes, sorry about the dumb question: now I understand the issue decently
> well - and after all boils down to adding a warning - but I'm not sure to
> understand your code snippet: is it meant to crash at runtime? Trigger valgrind
> errors?

In the C++11 spec, it is said that the lifetime of the backing-up array is the
same as the lifetime of the initializer_list object which was initialized by
the array (not considering the DRs and their resolution that Jason has pointed
to). My code was just meant to test whether GCC obeys those rules.

struct X {
  X(int) { cout << "+"; }
  X(X const&) { cout << "+"; }
  ~X() { cout << "-"; }
};

auto *p = new initalizer_list<X>{1, 2, 3}; // ... not at this
delete p; // C++11 requires "now" at this point ...

(again not considering those DRs that revise these rules). 

I think that a warning against "({...})" would be useful too

    // fine
    initializer_list<int> a{1, 2, 3};

    // this is bad
    initializer_list<int> b({1, 2, 3});

Second one is bad because it will destroy the array after initializing 'b', and
won't lengthen the lifetime (because it will use the copy/move constructor).

[Bug c++/48562] [C++0x] warn about uses of initializer_list that will lead to dangling pointers

[paolo.carlini at oracle dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=48562

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|ASSIGNED                    |NEW
         AssignedTo|paolo.carlini at oracle dot |unassigned at gcc dot
                   |com                         |gnu.org

--- Comment #7 from Paolo Carlini <paolo.carlini at oracle dot com> 2011-09-25 14:39:07 UTC ---
Ok, thanks. At the moment, I'm not really working on this.