[Bug c++/47783] New: Warning 'set but not used' [-Wunused-but-set-parameter] incorrectly issued for update through reference wrapper

[Bug c++/47783] New: Warning 'set but not used' [-Wunused-but-set-parameter] incorrectly issued for update through reference wrapper

[dev.lists at jessamine dot co.uk]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=47783

           Summary: Warning 'set but not used'
                    [-Wunused-but-set-parameter] incorrectly issued for
                    update through reference wrapper
           Product: gcc
           Version: 4.6.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: dev.lists@jessamine.co.uk


Compiling the following program with warning options -W -Wall yields
<stdin>: In function ‘void f(ref_wrapper)’:
<stdin>:6:6: warning: parameter ‘ref’ set but not used
[-Wunused-but-set-parameter]

If the reference-to-int is replaced with a pointer-to-int and dereference and
address-of operators are used in the appropriate places the warning does not
occur.

In all cases and at all optimization levels the resulting program returns 7 as
expected.


struct ref_wrapper
{
   int& i;
};

void f( ref_wrapper ref )
{
   ref.i = 7;
}

int main()
{
   int x = 1;
   ref_wrapper xref = {x};
   f(xref);
   return x;
}

[Bug c++/47783] [4.6 Regression] Warning 'set but not used' [-Wunused-but-set-parameter] incorrectly issued for update through reference wrapper

[redi at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=47783

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|                            |diagnostic
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|                            |2011.02.17 14:32:03
            Summary|Warning 'set but not used'  |[4.6 Regression] Warning
                   |[-Wunused-but-set-parameter |'set but not used'
                   |] incorrectly issued for    |[-Wunused-but-set-parameter
                   |update through reference    |] incorrectly issued for
                   |wrapper                     |update through reference
                   |                            |wrapper
     Ever Confirmed|0                           |1

--- Comment #1 from Jonathan Wakely <redi at gcc dot gnu.org> 2011-02-17 14:32:03 UTC ---
confirmed - no warning with 4.4 or 4.5

[Bug c++/47783] [4.6 Regression] Warning 'set but not used' [-Wunused-but-set-parameter] incorrectly issued for update through reference wrapper

[rguenth at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=47783

Richard Guenther <rguenth at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|---                         |4.6.0

[Bug c++/47783] [4.6 Regression] Warning 'set but not used' [-Wunused-but-set-parameter] incorrectly issued for update through reference wrapper

[paolo.carlini at oracle dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=47783

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |jakub at gcc dot gnu.org

--- Comment #2 from Paolo Carlini <paolo.carlini at oracle dot com> 2011-02-17 15:39:13 UTC ---
Let's CC Jakub...

[Bug c++/47783] [4.6 Regression] Warning 'set but not used' [-Wunused-but-set-parameter] incorrectly issued for update through reference wrapper

[jakub at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=47783

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |ASSIGNED
         AssignedTo|unassigned at gcc dot       |jakub at gcc dot gnu.org
                   |gnu.org                     |

--- Comment #3 from Jakub Jelinek <jakub at gcc dot gnu.org> 2011-02-17 17:13:45 UTC ---
Created attachment 23388
  --> http://gcc.gnu.org/bugzilla/attachment.cgi?id=23388
gcc46-pr47783.patch

Untested fix.

[Bug c++/47783] [4.6 Regression] Warning 'set but not used' [-Wunused-but-set-parameter] incorrectly issued for update through reference wrapper

[jakub at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=47783

--- Comment #4 from Jakub Jelinek <jakub at gcc dot gnu.org> 2011-02-17 20:44:16 UTC ---
Author: jakub
Date: Thu Feb 17 20:44:14 2011
New Revision: 170255

URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=170255
Log:
    PR c++/47783
    * cvt.c (convert_from_reference): Call mark_exp_read.

    * g++.dg/warn/Wunused-parm-4.C: New test.

Added:
    trunk/gcc/testsuite/g++.dg/warn/Wunused-parm-4.C
Modified:
    trunk/gcc/cp/ChangeLog
    trunk/gcc/cp/cvt.c
    trunk/gcc/testsuite/ChangeLog

[Bug c++/47783] [4.6 Regression] Warning 'set but not used' [-Wunused-but-set-parameter] incorrectly issued for update through reference wrapper

[jakub at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=47783

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|ASSIGNED                    |RESOLVED
         Resolution|                            |FIXED

--- Comment #5 from Jakub Jelinek <jakub at gcc dot gnu.org> 2011-02-17 20:48:05 UTC ---
Fixed.