detect empty functions

[Florian Weimer]

On 02/06/2014 03:30 PM, Prathamesh Kulkarni wrote:

> I was trying to make -Wunused-parameter not warn, if the function is
> empty (since an empty function would most likely
> be a stub function).
> Does that sound reasonable ?

Yes, why not.  You should add a test case and a changelog entry and post 
it to gcc-patches for review.

>
> +bool
> +is_tree_empty_function (tree fn)
> +{
> +  tree body, kid;
> +
> +  body = DECL_SAVED_TREE (fn);
> +  if (!body)
> +    return false;
> +  kid = TREE_OPERAND (body, 1); // body is bind_expr
> +  gcc_assert (kid);
> +  return TREE_CODE (kid) == STATEMENT_LIST && (STATEMENT_LIST_HEAD
> (kid) == NULL);
> +}

Not sure about the name and how general this is.

>   /* Possibly warn about unused parameters.  */
>   void
>   do_warn_unused_parameter (tree fn)
>   {
>     tree decl;
> -
> +  bool empty_function;
> +
> +  empty_function = is_tree_empty_function (fn);
>     for (decl = DECL_ARGUMENTS (fn);
>          decl; decl = DECL_CHAIN (decl))
>       if (!TREE_USED (decl) && TREE_CODE (decl) == PARM_DECL
>       && DECL_NAME (decl) && !DECL_ARTIFICIAL (decl)
> -    && !TREE_NO_WARNING (decl))
> +    && !TREE_NO_WARNING (decl) && !empty_function)
>         warning (OPT_Wunused_parameter, "unused parameter %q+D", decl);
>   }

You should call the function only if the preceding conditions aren't false.


-- 
Florian Weimer / Red Hat Product Security Team