[Bug c++/59823] New: conversion operator to const X& causes copy-construction of temporary

[Bug c++/59823] New: conversion operator to const X& causes copy-construction of temporary

[redi at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=59823

            Bug ID: 59823
           Summary: conversion operator to const X& causes
                    copy-construction of temporary
           Product: gcc
           Version: 4.9.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: redi at gcc dot gnu.org

extern "C" int puts(const char*);

struct X
{
  X() { }

  X(const X&) { puts("copy"); }
  X(X&&) { puts("move"); }

  X& operator=(const X&) { puts("copy assign"); return *this; }
  X& operator=(X&&) { puts("move assign"); return *this; }
};

struct wrap
{
  wrap(const X& x) : wrapped(&x) { }

  const X* wrapped;

  operator const X&() const { return *wrapped; }
};

int main()
{
  X x1, x2;
  wrap w(x2);
  x1 = w;
}


When compiled with -std=c++11 the expected output is:

copy assign

but G++ produces:

copy
move assign

It seems that on the last line of main() G++ incorrectly creates a
temporary, doing "x1 = X(w)" instead of "x1 = w"

[Bug c++/59823] [4.7/4.8/4.9 Regression] conversion operator to const X& causes copy-construction of temporary

[redi at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=59823

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
      Known to work|                            |4.6.4
            Summary|conversion operator to      |[4.7/4.8/4.9 Regression]
                   |const X& causes             |conversion operator to
                   |copy-construction of        |const X& causes
                   |temporary                   |copy-construction of
                   |                            |temporary
      Known to fail|                            |4.7.4, 4.8.2, 4.9.0

--- Comment #1 from Jonathan Wakely <redi at gcc dot gnu.org> ---
GCC 4.6 correctly printed "copy assign" so this is a regression.

[Bug c++/59823] [4.7/4.8/4.9 Regression] conversion operator to const X& causes copy-construction of temporary

[jason at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=59823

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |ASSIGNED
   Last reconfirmed|                            |2014-01-27
                 CC|                            |jason at gcc dot gnu.org
           Assignee|unassigned at gcc dot gnu.org      |jason at gcc dot gnu.org
     Ever confirmed|0                           |1

[Bug c++/59823] [4.7/4.8/4.9 Regression] conversion operator to const X& causes copy-construction of temporary

[jason at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=59823

--- Comment #2 from Jason Merrill <jason at gcc dot gnu.org> ---
Author: jason
Date: Tue Jan 28 04:31:39 2014
New Revision: 207170

URL: http://gcc.gnu.org/viewcvs?rev=207170&root=gcc&view=rev
Log:
    PR c++/59823
    Core DR 1138
    * call.c (reference_binding): Pass LOOKUP_NO_TEMP_BIND for
    list-initialization.  A conversion to rvalue ref that involves
    an lvalue-rvalue conversion is bad.
    (convert_like_real): Give helpful error message.

Added:
    trunk/gcc/testsuite/g++.dg/cpp0x/overload3.C
Modified:
    trunk/gcc/cp/ChangeLog
    trunk/gcc/cp/call.c

[Bug c++/59823] [4.7/4.8/4.9 Regression] conversion operator to const X& causes copy-construction of temporary

[jason at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=59823

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|---                         |4.9.0

--- Comment #3 from Jason Merrill <jason at gcc dot gnu.org> ---
Fixed in 4.9.  Will apply to 4.8 later if no problems arise.

[Bug c++/59823] [4.7/4.8 Regression] conversion operator to const X& causes copy-construction of temporary

[jakub at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=59823

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|4.9.0                       |4.9.1

--- Comment #4 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
GCC 4.9.0 has been released

[Bug c++/59823] [4.7/4.8 Regression] conversion operator to const X& causes copy-construction of temporary

[redi at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=59823

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
      Known to work|                            |4.9.0
   Target Milestone|4.9.1                       |4.9.0
      Known to fail|4.9.0                       |

--- Comment #5 from Jonathan Wakely <redi at gcc dot gnu.org> ---
Resetting target milestone, the fix is already in 4.9.0

[Bug c++/59823] [4.8 Regression] conversion operator to const X& causes copy-construction of temporary

[jason at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=59823

--- Comment #6 from Jason Merrill <jason at gcc dot gnu.org> ---
Author: jason
Date: Fri Aug  1 18:33:54 2014
New Revision: 213502

URL: https://gcc.gnu.org/viewcvs?rev=213502&root=gcc&view=rev
Log:
    PR c++/59823
    Core DR 1138
    * call.c (reference_binding): Pass LOOKUP_NO_TEMP_BIND for
    list-initialization.  A conversion to rvalue ref that involves
    an lvalue-rvalue conversion is bad.
    (convert_like_real): Give helpful error message.

Added:
    branches/gcc-4_8-branch/gcc/testsuite/g++.dg/cpp0x/overload3.C
Modified:
    branches/gcc-4_8-branch/gcc/cp/ChangeLog
    branches/gcc-4_8-branch/gcc/cp/call.c

[Bug c++/59823] [4.8 Regression] conversion operator to const X& causes copy-construction of temporary

[jason at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=59823

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|ASSIGNED                    |RESOLVED
         Resolution|---                         |FIXED
   Target Milestone|4.9.0                       |4.8.4

--- Comment #7 from Jason Merrill <jason at gcc dot gnu.org> ---
Fixed for 4.8.4.