[Bug c++/54506] New: Defaulted move constructors and move assignment operators are erroneously defined as deleted

[Bug c++/54506] New: Defaulted move constructors and move assignment operators are erroneously defined as deleted

[tsoae at mail dot ru]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=54506

             Bug #: 54506
           Summary: Defaulted move constructors and move assignment
                    operators are erroneously defined as deleted
    Classification: Unclassified
           Product: gcc
           Version: 4.7.1
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: tsoae@mail.ru


g++ rejects the following well-formed code:

    template <class T>
        struct A
    {
        A() {}

        A(A const volatile &&) = delete;
        A &operator =(A const volatile &&) = delete;

        template <class U>
            A(A<U> &&) {}
        template <class U>
            A &operator =(A<U> &&) { return *this; }
    };

    struct B
    {
        A<int> a;
        B() = default;
        B(B &&) = default;
        B &operator =(B &&) = default;
    };

    int main()
    {
        B b = B();
        b = B();
    }
The compiler says that the defaulted move functions in B are deleted, however
12.8/11 and 12.8/23 do not define such functions as deleted.

[Bug c++/54506] Defaulted move constructors and move assignment operators are erroneously defined as deleted

[redi at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=54506

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |WAITING
   Last reconfirmed|                            |2012-09-07
     Ever Confirmed|0                           |1

--- Comment #1 from Jonathan Wakely <redi at gcc dot gnu.org> 2012-09-07 23:16:29 UTC ---
How are you calling g++? What version are you using? What is the diagnostic you
get?

[Bug c++/54506] Defaulted move constructors and move assignment operators are erroneously defined as deleted

[tsoae at mail dot ru]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=54506

--- Comment #2 from Nikolka <tsoae at mail dot ru> 2012-09-08 12:17:24 UTC ---
(In reply to comment #1)
> How are you calling g++?

/mingw-gcc-4.7.1/bin/g++ test.cpp -std=c++11

> What version are you using?

Target: i686-pc-mingw32
Configured with: ../src/configure --prefix=/c/temp/gcc/dest
--with-gmp=/c/temp/gcc/gmp --with-mpfr=/c/temp/gcc/mpfr
--with-mpc=/c/temp/gcc/mpc --enable-languages=c,c++ --with-arch=i686
--with-tune=generic --disable-libstdcxx-pch --disable-nls --disable-shared
--disable-sjlj-exceptions --disable-win32-registry --enable-checking=release
--enable-lto
Thread model: win32
gcc version 4.7.1 (GCC) 

> What is the diagnostic you get?

test.cpp: In function 'int main()':
test.cpp:25:17: error: use of deleted function 'B::B(B&&)'
test.cpp:19:9: note: 'B::B(B&&)' is implicitly deleted because the default
definition would be ill-formed:
test.cpp:19:9: error: non-static data member 'B::a' does not have a move
constructor or trivial copy constructor
test.cpp:26:15: error: use of deleted function 'B& B::operator=(B&&)'
test.cpp:20:12: note: 'B& B::operator=(B&&)' is implicitly deleted because the
default definition would be ill-formed:
test.cpp:20:12: error: non-static data member 'B::a' does not have a move
assignment operator or trivial copy assignment operator

[Bug c++/54506] Defaulted move constructors and move assignment operators are erroneously defined as deleted

[tsoae at mail dot ru]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=54506

--- Comment #3 from Nikolka <tsoae at mail dot ru> 2012-09-09 20:55:38 UTC ---
g++ v4.7.2 20120908 (prerelease) compiles the original example successfully,
but it fails to compile the following code:

    template <class T>
        struct A
    {
        A() {}

        A(A const volatile &&) = delete;
        A &operator =(A const volatile &&) = delete;

        template <class U>
            A(A<U> &&) {}
        template <class U>
            A &operator =(A<U> &&) { return *this; }
    };

    struct B
    {
        A<int> a;
        B() = default;
    };

    int main()
    {
        B b = B();
        b = B();
    }

Target: i686-pc-linux-gnu
Configured with: ../configure --prefix=../target --enable-languages=c,c++
Thread model: posix
gcc version 4.7.2 20120908 (prerelease) (GCC) 
COLLECT_GCC_OPTIONS='-v' '-std=c++11' '-shared-libgcc' '-mtune=generic'
'-march=pentiumpro'
 ../target/libexec/gcc/i686-pc-linux-gnu/4.7.2/cc1plus -quiet -v -D_GNU_SOURCE
test.cpp -quiet -dumpbase test.cpp -mtune=generic -march=pentiumpro -auxbase
test -std=c++11 -version -o /tmp/cc0973J0.s
GNU C++ (GCC) version 4.7.2 20120908 (prerelease) (i686-pc-linux-gnu)
    compiled by GNU C version 4.7.2 20120908 (prerelease), GMP version 5.0.2,
MPFR version 3.1.0, MPC version 0.8.2

test.cpp: In function ‘int main()’:
test.cpp:23:17: error: use of deleted function ‘B::B(const B&)’
test.cpp:15:12: note: ‘B::B(const B&)’ is implicitly deleted because the
default definition would be ill-formed:
test.cpp:15:12: error: use of deleted function ‘constexpr A<int>::A(const
A<int>&)’
test.cpp:2:16: note: ‘constexpr A<int>::A(const A<int>&)’ is implicitly
declared as deleted because ‘A<int>’ declares a move constructor or move
assignment operator
test.cpp:24:15: error: use of deleted function ‘B& B::operator=(const B&)’
test.cpp:15:12: note: ‘B& B::operator=(const B&)’ is implicitly deleted because
the default definition would be ill-formed:
test.cpp:15:12: error: use of deleted function ‘A<int>& A<int>::operator=(const
A<int>&)’
test.cpp:2:16: note: ‘A<int>& A<int>::operator=(const A<int>&)’ is implicitly
declared as deleted because ‘A<int>’ declares a move constructor or move
assignment operator

[Bug c++/54506] Defaulted move constructors and move assignment operators are erroneously defined as deleted

[redi at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=54506

--- Comment #4 from Jonathan Wakely <redi at gcc dot gnu.org> 2012-09-09 21:36:40 UTC ---
The example can be simplified to 

    struct A
    {
        A() {}

        A(A &&) = delete;
        A &operator =(A &&) = delete;
    };

    struct B
    {
        A a;
        B() = default;
    };

    int main()
    {
        B b = B();
        b = B();
    }

I think this is ill-formed, so G++ is right to reject it.

struct A cannot be moved because its move operations are deleted, and cannot be
copied because the implicit-declared copy operations are defined as deleted,
see [class.copy]/7.  Therefore struct B cannot be moved or copied either.

[Bug c++/54506] Defaulted move constructors and move assignment operators are erroneously defined as deleted

[tsoae at mail dot ru]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=54506

--- Comment #5 from Nikolka <tsoae at mail dot ru> 2012-09-09 22:42:03 UTC ---
(In reply to comment #4)

These examples aren't similar. An implicitly defined move constructor performs
direct-initialization of non-static data members with the corresponding members
of the argument, which is interpreted as xvalue (12.8/15). In every such a
direct-initialization all constructors are considered (13.3.1.3), including
constructor templates. Template argument for the parameter U can be deduced as
int, and the produced specialization of the constructor template will have
better match than both copy and move constructors.

Similarly for assignment operators.

> struct A cannot be moved because its move operations are deleted

This is not so in my example, and g++ correctly handles the following case:

    template <class T>
        struct A
    {
        A() {}

        A(A const volatile &&) = delete;
        A &operator =(A const volatile &&) = delete;

        template <class U>
            A(A<U> &&) {}
        template <class U>
            A &operator =(A<U> &&) { return *this; }
    };

    int main()
    {
        A<int> a = A<int>(); // OK
        a = A<int>(); // OK
    }

[Bug c++/54506] Defaulted move constructors and move assignment operators are erroneously defined as deleted

[redi at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=54506

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

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

--- Comment #6 from Jonathan Wakely <redi at gcc dot gnu.org> 2012-09-09 22:59:01 UTC ---
(In reply to comment #5)
> These examples aren't similar.

You're right I reduced it too far, sorry.

I'll confirm this then and CC Jason to look at it.

[Bug c++/54506] Defaulted move constructors and move assignment operators are erroneously defined as deleted

[jason at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=54506

--- Comment #7 from Jason Merrill <jason at gcc dot gnu.org> 2012-09-10 02:09:26 UTC ---
(In reply to comment #3)
> g++ v4.7.2 20120908 (prerelease) compiles the original example successfully,
> but it fails to compile the following code:

G++ is following the proposed resolution of DR 1402 here; A<int> does not have
a move constructor and it is not trivially copyable, so the B move constructor
is not implicitly declared.  This seems like a flaw in the 1402 drafting; the
template constructor should count.

[Bug c++/54506] Defaulted move constructors and move assignment operators are erroneously defined as deleted

[tsoae at mail dot ru]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=54506

--- Comment #8 from Nikolka <tsoae at mail dot ru> 2012-09-10 06:26:02 UTC ---
(In reply to comment #7)
> (In reply to comment #3)
> > g++ v4.7.2 20120908 (prerelease) compiles the original example successfully,
> > but it fails to compile the following code:
> 
> G++ is following the proposed resolution of DR 1402 here; A<int> does not have
> a move constructor

A<int> does have a move constructor, which is instantiated from

    A(A const volatile &&) = delete;

See 12.8/3:

    A non-template constructor for class X is a move constructor if its first
parameter is of type X&&, const X&&, volatile X&&, or const volatile X&&, and
either there are no other parameters or else all other parameters have default
arguments

[Bug c++/54506] Defaulted move constructors and move assignment operators are erroneously defined as deleted

[jason at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=54506

--- Comment #9 from Jason Merrill <jason at gcc dot gnu.org> 2012-09-10 14:08:36 UTC ---
Author: jason
Date: Mon Sep 10 14:08:32 2012
New Revision: 191140

URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=191140
Log:
    PR c++/54506
    * decl.c (move_signature_fn_p): Split out from move_fn_p.
    * method.c (process_subob_fn): Use it.
    * cp-tree.h: Declare it.

Added:
    trunk/gcc/testsuite/g++.dg/cpp0x/implicit14.C
Modified:
    trunk/gcc/cp/ChangeLog
    trunk/gcc/cp/cp-tree.h
    trunk/gcc/cp/decl.c
    trunk/gcc/cp/method.c
    trunk/gcc/testsuite/ChangeLog

[Bug c++/54506] Defaulted move constructors and move assignment operators are erroneously defined as deleted

[jason at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=54506

--- Comment #10 from Jason Merrill <jason at gcc dot gnu.org> 2012-09-10 14:24:27 UTC ---
Author: jason
Date: Mon Sep 10 14:24:19 2012
New Revision: 191146

URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=191146
Log:
    PR c++/54506
    * decl.c (move_signature_fn_p): Split out from move_fn_p.
    * method.c (process_subob_fn): Use it.
    * cp-tree.h: Declare it.

Added:
    branches/gcc-4_7-branch/gcc/testsuite/g++.dg/cpp0x/implicit14.C
Modified:
    branches/gcc-4_7-branch/gcc/cp/ChangeLog
    branches/gcc-4_7-branch/gcc/cp/cp-tree.h
    branches/gcc-4_7-branch/gcc/cp/decl.c
    branches/gcc-4_7-branch/gcc/cp/method.c
    branches/gcc-4_7-branch/gcc/testsuite/ChangeLog

[Bug c++/54506] Defaulted move constructors and move assignment operators are erroneously defined as deleted

[jason at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=54506

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
         Resolution|                            |FIXED
   Target Milestone|---                         |4.7.2

--- Comment #10 from Jason Merrill <jason at gcc dot gnu.org> 2012-09-10 14:24:27 UTC ---
Author: jason
Date: Mon Sep 10 14:24:19 2012
New Revision: 191146

URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=191146
Log:
    PR c++/54506
    * decl.c (move_signature_fn_p): Split out from move_fn_p.
    * method.c (process_subob_fn): Use it.
    * cp-tree.h: Declare it.

Added:
    branches/gcc-4_7-branch/gcc/testsuite/g++.dg/cpp0x/implicit14.C
Modified:
    branches/gcc-4_7-branch/gcc/cp/ChangeLog
    branches/gcc-4_7-branch/gcc/cp/cp-tree.h
    branches/gcc-4_7-branch/gcc/cp/decl.c
    branches/gcc-4_7-branch/gcc/cp/method.c
    branches/gcc-4_7-branch/gcc/testsuite/ChangeLog

--- Comment #11 from Jason Merrill <jason at gcc dot gnu.org> 2012-09-10 14:25:49 UTC ---
Fixed for 4.7.2.