[Bug c++/8045] Missing "unused variable" warning

[Bug c++/8045] Missing "unused variable" warning

[flameeyes at gentoo dot org]

------- Comment #4 from flameeyes at gentoo dot org  2008-05-11 16:31 -------
I think this applies to 4.3 as well, as the following code does only warn in
the second function:

#include <stdlib.h>
#include <string.h>

char* oldstyle(const char *foo) {
  size_t foolen;

  if ( foo == NULL )
    return NULL;

  foolen = strlen(foo);

  return strdup(foo);
}

char* newstyle(const char *foo) {
  if ( foo == NULL )
    return NULL;

  const size_t foolen = strlen(foo);

  return strdup(foo);
}

And I could really make use of such a warning in xine-lib's code :)


-- 

flameeyes at gentoo dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |flameeyes at gentoo dot org


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=8045

[Bug c++/8045] Missing "unused variable" warning

[manu at gcc dot gnu dot org]

------- Comment #5 from manu at gcc dot gnu dot org  2009-07-08 22:08 -------
Are there some cases where a declaration such T x = y can be considered an use
of 'x' by itself?

The following patch warns for this, but it also produces warnings for some
testcases in the testsuite.

Index: gcc/cp/init.c
===================================================================
--- gcc/cp/init.c       (revision 149319)
+++ gcc/cp/init.c       (working copy)
@@ -1261,11 +1261,11 @@ build_aggr_init (tree exp, tree init, in
       if (init)
        TREE_TYPE (init) = itype;
       return stmt_expr;
     }

-  if (TREE_CODE (exp) == VAR_DECL || TREE_CODE (exp) == PARM_DECL)
+  if (TREE_CODE (exp) == PARM_DECL)
     /* Just know that we've seen something for this node.  */
     TREE_USED (exp) = 1;

   is_global = begin_init_stmts (&stmt_expr, &compound_stmt);
   destroy_temps = stmts_are_full_exprs_p ();


-- 

manu at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
      Known to fail|                            |4.4.0
   Last reconfirmed|2005-12-11 23:03:44         |2009-07-08 22:08:57
               date|                            |


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=8045

[Bug c++/8045] Missing "unused variable" warning

[gerald at pfeifer dot com]

------- Comment #6 from gerald at pfeifer dot com  2010-05-01 16:39 -------
(In reply to comment #0)
> Consider the following code snippet: 
> bash-2.05$ cat foo.cc
> struct X { int y; };
> 
> void foo() {
>   X c;
>   X tmp2;
>   X d = tmp2;
> }
> 
> Both c and d are unused.  However, we only get an 'unused variable' warning from c.

A current (2010-04-26) snapshot of GCC 4.6 detects both cases:

  y.c: In function 'foo':
  y.c:5:5: warning: unused variable 'd' [-Wunused-variable]
  y.c:3:5: warning: unused variable 'c' [-Wunused-variable]


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=8045

[Bug c++/8045] Missing "unused variable" warning

[gerald at pfeifer dot com]

------- Comment #7 from gerald at pfeifer dot com  2010-05-01 16:47 -------
(In reply to comment #4)
> I think this applies to 4.3 as well, as the following code does only warn in
> the second function:

The current snapshot mentioned above now warns as follows:

y.c: In function 'oldstyle':
y.c:5:10: warning: variable 'foolen' set but not used
[-Wunused-but-set-variable]
y.c: In function 'newstyle':
y.c:19:16: warning: unused variable 'foolen' [-Wunused-variable]

In other words, it catches both cases.

Based on this comment, and the previous, which has the original testcase
covered, I am marking this report as FIXED based on the good work Jakub
has done.


-- 

gerald at pfeifer dot com changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |gerald at pfeifer dot com,
                   |                            |jakub at redhat dot com
             Status|NEW                         |RESOLVED
         Resolution|                            |FIXED


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=8045

[Bug c++/8045] Missing "unused variable" warning

[yotamm at mellanox dot co dot il]

------- Additional Comments From yotamm at mellanox dot co dot il  2003-12-23 10:00 -------
Here is an example. It also shows lack of out-of-array-access warning.

mtls47:62> cat bugunused.cpp
class C {
 public:
    int  d(int i) const { return _d[2]; }
    int  _d[2];
};

C c;

int  cd() {
   return c.d(13);
}
mtls47:63> g++ -v
Reading specs from /usr/lib/gcc-lib/i686-pc-linux-gnu/3.2.3/specs
Configured with: /var/tmp/portage/gcc-3.2.3-r2/work/gcc-3.2.3/configure
--prefix=/usr --bindir=/usr/i686-pc-linux-gnu/gcc-bin/3.2
--includedir=/usr/lib/gcc-lib/i686-pc-linux-gnu/3.2.3/include
--datadir=/usr/share/gcc-data/i686-pc-linux-gnu/3.2
--mandir=/usr/share/gcc-data/i686-pc-linux-gnu/3.2/man
--infodir=/usr/share/gcc-data/i686-pc-linux-gnu/3.2/info --enable-shared
--host=i686-pc-linux-gnu --target=i686-pc-linux-gnu --with-system-zlib
--enable-languages=c,c++,f77,objc,java --enable-threads=posix --enable-long-long
--disable-checking --enable-cstdio=stdio --enable-clocale=generic
--enable-__cxa_atexit --enable-version-specific-runtime-libs
--with-gxx-include-dir=/usr/lib/gcc-lib/i686-pc-linux-gnu/3.2.3/include/g++-v3
--with-local-prefix=/usr/local --enable-shared --enable-nls
--without-included-gettext
Thread model: posix
gcc version 3.2.3 20030422 (Gentoo Linux 1.4 3.2.3-r2, propolice)
mtls47:64> g++ -c -Wall -Wunused bugunused.cpp
mtls47:65> echo $?
0
mtls47:66> 

-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=8045

[Bug c++/8045] Missing "unused variable" warning

[pinskia at gcc dot gnu dot org]

------- Additional Comments From pinskia at gcc dot gnu dot org  2003-11-16 02:32 -------
The problem is that the front-end is gerenting code like this (see how the copy for d is after d is 
declared:
{
   {
      struct X c
       struct X tmp2
       struct X d
      ({
         (void)(d = tmp2);
      });
   }
}

-- 
           What    |Removed                     |Added
----------------------------------------------------------------------------
   Last reconfirmed|2003-08-02 17:37:55         |2003-11-16 02:32:29
               date|                            |


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=8045