[Bug c++/63437] New: [4.9/5 regression][C++14] Parenthesized "movable but not copyable" object doesn't compile in return statement

[Bug c++/63437] New: [4.9/5 regression][C++14] Parenthesized "movable but not copyable" object doesn't compile in return statement

[flast at flast dot jp]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=63437

            Bug ID: 63437
           Summary: [4.9/5 regression][C++14] Parenthesized "movable but
                    not copyable" object doesn't compile in return
                    statement
           Product: gcc
           Version: 4.9.2
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: flast at flast dot jp

After GCC 4.9, parenthesized "movable but not copyable" object doesn't compile
in return statement under C++14 mode (C++11 mode does compile).
I'm not sure that the behavior was changed in C++14 spec; Clang seems compile
under both of C++11/14 mode.

example:
----
struct X // movable but not copyable
{
    X() = default;
    X(X &&) = default;

    X(const X &) = delete;
};

X non_parenthesized()
{
    X x;
    return x; // works
}

X parenthesized()
{
    X x;
    return (x); // error: use of deleted function 'X::X(const X&)'
}
----

Online compiler results:
- GCC 4.8.2
 - C++11 http://melpon.org/wandbox/permlink/lRR60fvDgKfqd0UZ
 - C++14 http://melpon.org/wandbox/permlink/BAdrBmEG3euQLnqv

- GCC 4.9.1
 - C++11 http://melpon.org/wandbox/permlink/XllfUNu0VV0mnYsu
 - C++14 http://melpon.org/wandbox/permlink/qm67F6vODyADgKvQ (fail)

- GCC 5.0 20141001
 - C++11 http://melpon.org/wandbox/permlink/21bPbcuXB7S87DUG
 - C++14 http://melpon.org/wandbox/permlink/da8AeqX7HrS17T2n (fail)

- Clang 3.5.0
 - C++11 http://melpon.org/wandbox/permlink/VqgnlKRTOBHd5IDt
 - C++14 http://melpon.org/wandbox/permlink/tAkgLiaD50nOMtEz

[Bug c++/63437] [4.9/5 regression][C++14] Parenthesized "movable but not copyable" object doesn't compile in return statement

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=63437

--- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
in C++14 (a) means the same as static_cast<typeof(a) &>(a).

So it is a reference at this point which means const & is better than &&.

Or at least that is how I understand this.  Does clang implement the C++11 ()
rule correctly?

[Bug c++/63437] [4.9/5 regression][C++14] Parenthesized "movable but not copyable" object doesn't compile in return statement

[flast at flast dot jp]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=63437

--- Comment #2 from Kohei Takahashi <flast at flast dot jp> ---
(In reply to Andrew Pinski from comment #1)
> in C++14 (a) means the same as static_cast<typeof(a) &>(a).
> 
> So it is a reference at this point which means const & is better than &&.
> 
> Or at least that is how I understand this.  Does clang implement the C++11
> () rule correctly?

n3376 12.8 [class.copy] paragraph 32 says:

    When the criteria for elision of a copy operation are met or would be met
save for the fact that the source
    object is a function parameter, and the object to be copied is designated
by an lvalue, overload resolution to
    select the constructor for the copy is first performed as if the object
were designated by an rvalue.

And latest draft says more clearly.
https://github.com/cplusplus/draft/blob/master/source/special.tex#L3021-L3062

Therefore, I think move should be performed even if parenthesized.

[Bug c++/63437] [4.9/5 regression][C++14] Parenthesized "movable but not copyable" object doesn't compile in return statement

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=63437

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|                            |2014-10-02
     Ever confirmed|0                           |1

--- Comment #3 from Jonathan Wakely <redi at gcc dot gnu.org> ---
Yes, the new wording is clear that parenthesized names are OK.

[Bug c++/63437] [4.9/5 regression][C++14] Parenthesized "movable but not copyable" object doesn't compile in return statement

[jason at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=63437

--- Comment #4 from Jason Merrill <jason at gcc dot gnu.org> ---
Author: jason
Date: Thu Oct  9 18:05:17 2014
New Revision: 216042

URL: https://gcc.gnu.org/viewcvs?rev=216042&root=gcc&view=rev
Log:
    PR c++/63437
    * cp-tree.h (REF_PARENTHESIZED_P): Also allow INDIRECT_REF.
    * semantics.c (force_paren_expr): And set it.
    * typeck.c (check_return_expr): And handle it.

Added:
    trunk/gcc/testsuite/g++.dg/cpp1y/paren1.C
Modified:
    trunk/gcc/cp/ChangeLog
    trunk/gcc/cp/cp-tree.h
    trunk/gcc/cp/semantics.c
    trunk/gcc/cp/typeck.c

[Bug c++/63437] [4.9/5 regression][C++14] Parenthesized "movable but not copyable" object doesn't compile in return statement

[jason at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=63437

--- Comment #5 from Jason Merrill <jason at gcc dot gnu.org> ---
Author: jason
Date: Fri Oct 10 20:35:18 2014
New Revision: 216106

URL: https://gcc.gnu.org/viewcvs?rev=216106&root=gcc&view=rev
Log:
    PR c++/63437
    * cp-tree.h (REF_PARENTHESIZED_P): Also allow INDIRECT_REF.
    * semantics.c (force_paren_expr): And set it.
    * typeck.c (check_return_expr): And handle it.

Added:
    branches/gcc-4_9-branch/gcc/testsuite/g++.dg/cpp1y/paren1.C
Modified:
    branches/gcc-4_9-branch/gcc/cp/ChangeLog
    branches/gcc-4_9-branch/gcc/cp/cp-tree.h
    branches/gcc-4_9-branch/gcc/cp/semantics.c
    branches/gcc-4_9-branch/gcc/cp/typeck.c

[Bug c++/63437] [4.9/5 regression][C++14] Parenthesized "movable but not copyable" object doesn't compile in return statement

[jason at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=63437

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
                 CC|                            |jason at gcc dot gnu.org
         Resolution|---                         |FIXED
           Assignee|unassigned at gcc dot gnu.org      |jason at gcc dot gnu.org
   Target Milestone|---                         |4.9.2

--- Comment #6 from Jason Merrill <jason at gcc dot gnu.org> ---
Fixed.