[Bug c/25955] New: regression: value computed not used warning with cast return value

[Bug c/25955] New: regression: value computed not used warning with cast return value

[mike at codeweavers dot com]

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bash-3.00$ cat z1.c 
int foo(void);
void bar(void) { (unsigned int)foo(); }
bash-3.00$ vi z1.c 
bash-3.00$ /usr/local/gcc-4.1-branch/bin/gcc -c z1.c -Wall -O2
z1.c: In function ‘bar’:
z1.c:1: warning: value computed is not used

bash-3.00$ /usr/local/gcc-4.1-branch/bin/gcc -v
Using built-in specs.
Target: i686-pc-linux-gnu
Configured with: ../gcc/configure --prefix=/usr/local/gcc-4.1-branch
--with-gnu-ld=/usr/local/binutils-2.16.1/bin/ld
--with-gnu-as=/usr/local/binutils-2.16.1/bin/as
Thread model: posix
gcc version 4.1.0 20060118 (prerelease)

Background:

Wine's windowsx.h defines:

#define ListBox_SetCurSel(hwndCtl, index) \
        ((int)SendMessage((hwndCtl), LB_SETCURSEL, (WPARAM)(int)(index), 0L))

Using this macro will give a warning in the gcc 4.1 branch, but not with gcc
4.0.2.  Though the warning is technically correct, it doesn't really make much
sense, and I can't think of a real problem it's going to catch.


-- 
           Summary: regression: value computed not used warning with cast
                    return value
           Product: gcc
           Version: 4.1.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: mike at codeweavers dot com
 GCC build triplet: i686-pc-linux-gnu
  GCC host triplet: i486-slackware-linux
GCC target triplet: i686-pc-linux-gnu


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=25955

[Bug c/25955] [4.1/4.2 Regression] value computed not used warning with cast return value

[rguenth at gcc dot gnu dot org]

------- Comment #1 from rguenth at gcc dot gnu dot org  2006-01-25 10:44 -------
Confirmed.  I wouldn't say the cast is an extra computation here - and we don't
warn without it.


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rguenth at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
     Ever Confirmed|0                           |1
  GCC build triplet|i686-pc-linux-gnu           |
   GCC host triplet|i486-slackware-linux        |
 GCC target triplet|i686-pc-linux-gnu           |
           Keywords|                            |diagnostic
      Known to fail|                            |4.1.0 4.2.0
      Known to work|                            |4.0.2
   Last reconfirmed|0000-00-00 00:00:00         |2006-01-25 10:44:51
               date|                            |
            Summary|regression: value computed  |[4.1/4.2 Regression] value
                   |not used warning with cast  |computed not used warning
                   |return value                |with cast return value


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=25955

[Bug c/25955] [4.1/4.2 Regression] value computed not used warning with cast return value

[pinskia at gcc dot gnu dot org]

------- Comment #2 from pinskia at gcc dot gnu dot org  2006-01-25 13:06 -------
Actually we want to warn see PR 24900.

*** This bug has been marked as a duplicate of 24900 ***


-- 

pinskia at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
         Resolution|                            |DUPLICATE


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=25955