[Bug c/51579] New: GCC should be able report a warning for usage of parameters marked with __attribute__((unused))

[yann at droneaud dot fr]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=51579

             Bug #: 51579
           Summary: GCC should be able report a warning for usage of
                    parameters marked with __attribute__((unused))
    Classification: Unclassified
           Product: gcc
           Version: 4.6.2
            Status: UNCONFIRMED
          Severity: enhancement
          Priority: P3
         Component: c
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: yann@droneaud.fr


I would like to see GCC emit a warning when a parameter marked as unused is in
fact used in the function. The warning option could be something like
-Wunused-parameter-used

For example, the following code doesn't produce any warning.

int foo (int *ptr, int val __attribute__((unused)))
{
   int res;

   res = *ptr + val;

   return res;
}

It would be interesting to have a warning like this:

test.c: In function 'foo':
test.c:5:21: warning: parameter 'val' is used but marked as "unused" in
declaration [-Wunused-parameter-used]

Same thing could apply to function, type and variable specified with
__attribute__((unused))

Additionally, a new attribute "warn_use" could be introduced to enforce the
"unused" attribute, since "unused" attribute is not meant to prevent usage:

- "This attribute, attached to a function, means that the function is meant to
be possibly unused"
- "When attached to a type (including a union or a struct), this attribute
means that variables of that type are meant to appear possibly unused"
- "This attribute, attached to a variable, means that the variable is meant to
be possibly unused"