[Bug c++/57610] New: Result of conversion

[Bug c++/57610] New: Result of conversion

[o_kniemeyer at maxon dot net]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=57610

            Bug ID: 57610
           Summary: Result of conversion
           Product: gcc
           Version: 4.8.1
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: o_kniemeyer at maxon dot net

[Bug c++/57610] Result of conversion

[paolo.carlini at oracle dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=57610

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |RESOLVED
         Resolution|---                         |INVALID

--- Comment #1 from Paolo Carlini <paolo.carlini at oracle dot com> ---
.

[Bug c++/57610] Result of conversion

[o_kniemeyer at maxon dot net]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=57610

--- Comment #2 from Ole Kniemeyer <o_kniemeyer at maxon dot net> ---
Created attachment 30301
  --> http://gcc.gnu.org/bugzilla/attachment.cgi?id=30301&action=edit
cpp file (without any #includes) which shows the bug

[Bug c++/57610] Reference initialized with temporary instead of sub-object of conversion result

[o_kniemeyer at maxon dot net]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=57610

Ole Kniemeyer <o_kniemeyer at maxon dot net> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|RESOLVED                    |UNCONFIRMED
         Resolution|INVALID                     |---

--- Comment #3 from Ole Kniemeyer <o_kniemeyer at maxon dot net> ---
In the example X can be converted to B which is a derived class of A. When an A
reference is initialized with an X object, the result of the X::operator B()
should be used directly for the A reference, but GCC creates a temporary A
object and initializes this by copy-construction from the conversion result.

At least if the classes use virtual functions, this leads to wrong results.

[Bug c++/57610] Reference initialized with temporary instead of sub-object of conversion result

[o_kniemeyer at maxon dot net]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=57610

--- Comment #4 from Ole Kniemeyer <o_kniemeyer at maxon dot net> ---
As I commented in the cpp example, the C++11 standard shows exactly this
example in sections 8.5.3. So this is definitely a bug according to C++11. I
think the GCC behaviour is correct according to older C++11 standards.

[Bug c++/57610] Reference initialized with temporary instead of sub-object of conversion result

[o_kniemeyer at maxon dot net]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=57610

--- Comment #5 from Ole Kniemeyer <o_kniemeyer at maxon dot net> ---
Ops, sorry, of course I meant "... to older C++ standards."

[Bug c++/57610] Reference initialized with temporary instead of sub-object of conversion result

[hstong at ca dot ibm.com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=57610

Hubert Tong <hstong at ca dot ibm.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |hstong at ca dot ibm.com

--- Comment #8 from Hubert Tong <hstong at ca dot ibm.com> ---
Affects the candidate list for direct binding to a result of a conversion.

struct Z { };

struct A {
   operator Z &&() const = delete;  // GCC like this
   operator Z();
};

void zip() {
   Z &&x = A();
}

[Bug c++/57610] Reference initialized with temporary instead of sub-object of conversion result

[kariya_mitsuru at hotmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=57610

Mitsuru Kariya <kariya_mitsuru at hotmail dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |kariya_mitsuru at hotmail dot com

--- Comment #10 from Mitsuru Kariya <kariya_mitsuru at hotmail dot com> ---
Each status of the issues mentioned above is

CWG 1287: DRWP
CWG 1604: DR
CWG 1650: NAD

And, gcc HEAD (5.0.0) does not cause the slicing problem.

cf. 5.0.0 http://melpon.org/wandbox/permlink/xQQq1n98s7blSz8x
cf. 4.9.1 http://melpon.org/wandbox/permlink/l69tDXdptf1WVdAT

Note that these are compiled with the option "-fno-elide-constructors".

(Sorry, I don't know whether this issue should be "RESOLVED FIXED" or not,
however.)

[Bug c++/57610] Reference initialized with temporary instead of sub-object of conversion result

[paolo.carlini at oracle dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=57610

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |paolo.carlini at oracle dot com

--- Comment #11 from Paolo Carlini <paolo.carlini at oracle dot com> ---
I'm looking for somebody willing to *summarize* for me where do we stand on
this. Is GCC already Ok vs the most recent resolutions and we could resolve the
issue (maybe commit a testcase too)? Or ISO work is still pending and the bug
should be suspended, as usual in such cases? Something else? Thanks.

[Bug c++/57610] Reference initialized with temporary instead of sub-object of conversion result

[paolo.carlini at oracle dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=57610

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|paolo.carlini at oracle dot com    |

--- Comment #12 from Paolo Carlini <paolo.carlini at oracle dot com> ---
This is fixed in 5.1. I'm adding a testcase and closing the bug.

[Bug c++/57610] Reference initialized with temporary instead of sub-object of conversion result

[paolo at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=57610

--- Comment #13 from paolo at gcc dot gnu.org <paolo at gcc dot gnu.org> ---
Author: paolo
Date: Thu Apr 30 09:43:39 2015
New Revision: 222615

URL: https://gcc.gnu.org/viewcvs?rev=222615&root=gcc&view=rev
Log:
2015-04-30  Paolo Carlini  <paolo.carlini@oracle.com>

        PR c++/57610
        * g++.dg/init/ref22.C: New.

Added:
    trunk/gcc/testsuite/g++.dg/init/ref22.C
Modified:
    trunk/gcc/testsuite/ChangeLog

[Bug c++/57610] Reference initialized with temporary instead of sub-object of conversion result

[paolo.carlini at oracle dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=57610

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |RESOLVED
         Resolution|---                         |FIXED
   Target Milestone|---                         |5.0

--- Comment #14 from Paolo Carlini <paolo.carlini at oracle dot com> ---
Done.