[C PATCH] Fix -Wunused-function (PR debug/66869)

[Richard Biener]

On Mon, Jan 25, 2016 at 9:38 PM, Jakub Jelinek <jakub@redhat.com> wrote:
> Hi!
>
> The early-debug changes moved warnings about unused functions into cgraph.
> The problem is that if we have just unused declarations, they aren't
> sometimes even registered with cgraph and therefore we no longer warn.
>
> Here is an attempt to register those with cgraph anyway to get the warning,
> for C FE only (no idea where to do that in C++ FE).  Or anyone has better
> suggestions what to do?
>
> Bootstrapped/regtested on x86_64-linux and i686-linux.
>
> 2016-01-25  Jakub Jelinek  <jakub@redhat.com>
>
>         PR debug/66869
>         * c-decl.c (c_write_global_declarations_1): For warn_unused_function,
>         ensure creation of cgraph node even if there is no definition.
>
>         * gcc.dg/pr66869.c: New test.
>
> --- gcc/c/c-decl.c.jj   2016-01-21 00:41:47.000000000 +0100
> +++ gcc/c/c-decl.c      2016-01-25 16:36:31.973504082 +0100
> @@ -10741,11 +10741,19 @@ c_write_global_declarations_1 (tree glob
>        if (TREE_CODE (decl) == FUNCTION_DECL
>           && DECL_INITIAL (decl) == 0
>           && DECL_EXTERNAL (decl)
> -         && !TREE_PUBLIC (decl)
> -         && C_DECL_USED (decl))
> +         && !TREE_PUBLIC (decl))
>         {
> -         pedwarn (input_location, 0, "%q+F used but never defined", decl);
> -         TREE_NO_WARNING (decl) = 1;
> +         if (C_DECL_USED (decl))
> +           {
> +             pedwarn (input_location, 0, "%q+F used but never defined", decl);
> +             TREE_NO_WARNING (decl) = 1;
> +           }
> +         /* For -Wunused-function push the unused statics into cgraph,
> +            so that check_global_declaration emits the warning.  */
> +         else if (warn_unused_function
> +                  && ! DECL_ARTIFICIAL (decl)
> +                  && ! TREE_NO_WARNING (decl))
> +           cgraph_node::get_create (decl);

Err, so why not warn here directly?

Richard.

>         }
>
>        wrapup_global_declaration_1 (decl);
> --- gcc/testsuite/gcc.dg/pr66869.c.jj   2016-01-25 16:38:39.037758657 +0100
> +++ gcc/testsuite/gcc.dg/pr66869.c      2016-01-25 16:39:42.346888954 +0100
> @@ -0,0 +1,6 @@
> +/* PR debug/66869 */
> +/* { dg-do compile } */
> +/* { dg-options "-Wunused-function" } */
> +
> +static void test (void); /* { dg-warning "'test' declared 'static' but never defined" } */
> +int i;
>
>         Jakub