detect empty functions

[Prathamesh Kulkarni]

On Thu, Feb 6, 2014 at 7:48 PM, Florian Weimer <fweimer@redhat.com> wrote:
> On 02/06/2014 03:15 PM, Prathamesh Kulkarni wrote:
>>
>> On Thu, Feb 6, 2014 at 5:34 PM, Florian Weimer <fweimer@redhat.com> wrote:
>>>
>>> On 02/05/2014 03:30 PM, Prathamesh Kulkarni wrote:
>>>>
>>>>
>>>> I wanted to ask, is there a way to detect if a function has empty body
>>>> using GCC API ?
>>>
>>>
>>>
>>> Yes, you can write a plug-in and iterate over all the basic blocks in a
>>> function and check if they are empty.
>
>
>> I was looking for a way to detect empty function at GENERIC level.
>> Is the following correct way to do it ?
>
>
> I expect it's not fully reliable because the parser will remove some
> constructs and add others.  It depends on what you're trying to achieve.
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 ?

+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);
+}
+
 /* 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);
 }

>
>
> --
> Florian Weimer / Red Hat Product Security Team