[Bug c++/52427] New: problem with default copy constructor and -O

[Bug c++/52427] New: problem with default copy constructor and -O

[architectbum at hotmail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=52427

             Bug #: 52427
           Summary: problem with default copy constructor and -O
    Classification: Unclassified
           Product: gcc
           Version: 4.6.2
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: architectbum@hotmail.com


Created attachment 26777
  --> http://gcc.gnu.org/bugzilla/attachment.cgi?id=26777
program with unexpected output

The attached program prints
> 181
> 181
as expected when compiled with "g++-4.6.2 --std=c++0x -o bin/main src/main.cc"
(or g++-4.5.3)
but
> 121
> 181
with any -O option, and even
> 17
> 181
with 4.5.3 with -O.

Replacing the default copy constructor of foo_iterator with a user-defined
constructor that should do the same thing (as in comment in source) fixes the
problem, as does compiling with -fno-elide-constructors. Also, as the testcase
shows, the problem arises with 
> sum += *fi++;
but not with
> sum += *fi;
> ++fi;
even though the postfix increment is defined in the usual way; therefore, the
problem seems to lie in the temporary produced by operator++(int).

A GDB session suggested that the optimized-away default copy constructor may be
setting k to 0; that is, k=0 when operator*() is called on the temporary at
'*fi++'; this is consistent with the output. (And moving the "dereference"
inside operator++(int) so that it returns ulong does the same thing.)

[Bug c++/52427] [C++11] problem with defaulted copy constructor and -O

[redi at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=52427

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|                            |wrong-code
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|                            |2012-02-29
            Summary|problem with defaulted copy |[C++11] problem with
                   |constructor and -O          |defaulted copy constructor
                   |                            |and -O
     Ever Confirmed|0                           |1
      Known to fail|                            |4.5.2, 4.6.2, 4.7.0

--- Comment #1 from Jonathan Wakely <redi at gcc dot gnu.org> 2012-02-29 14:38:47 UTC ---
It gets the wrong value on the 17th iteration, when check_advance() is called,
so you can make it fail sooner by change s/16/3/ in hex_iterator::operator++
and the initializer for pre_foo

[Bug c++/52427] [C++11] problem with defaulted copy constructor and -O

[paolo.carlini at oracle dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=52427

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
      Known to work|                            |4.7.2, 4.8.0, 4.9.0
         Resolution|---                         |FIXED
   Target Milestone|---                         |4.7.2

--- Comment #2 from Paolo Carlini <paolo.carlini at oracle dot com> ---
This is fixed. If you can still see something wrong please re-open, thanks.