On Fri, Jun 11, 2021 at 5:44 PM Jakub Jelinek <ja...@redhat.com> wrote:
> On Fri, Jun 11, 2021 at 10:35:58PM +0200, Jakub Jelinek wrote:
> > > But I also agree that GCC shouldn't warn here.
> >
> > We could do that by using a wrapper around handle_unused_attribute
> > for the maybe_unused attribute, that way warn on unused attribute on
> > FIELD_DECLs, but not for maybe_unused (until we actually implement some
> > warning that uses it).
>
> Here it is in patch form.
> Ok for trunk if it passes bootstrap/regtest?
>
In r12-1405 I changed both warnings to be accepted on FIELD_DECL. I don't
think we need to warn about the GNU attribute, either; an attribute meaning
"don't warn about this being unused" is vacuously satisfied if we don't
warn about any unused fields, we might as well do the normal thing.
> 2021-06-11 Jakub Jelinek <ja...@redhat.com>
>
> * tree.c (handle_maybe_unused_attribute): New function.
> (std_attribute_table): Use it as handler for maybe_unused
> attribute.
>
> * g++.dg/cpp1z/maybe_unused2.C: New test.
>
> --- gcc/cp/tree.c.jj 2021-05-28 11:03:19.490884332 +0200
> +++ gcc/cp/tree.c 2021-06-11 23:41:36.503413441 +0200
> @@ -4872,6 +4872,23 @@ handle_likeliness_attribute (tree *node,
> return error_mark_node;
> }
>
> +/* The C++17 [[maybe_unused]] attribute maps to GNU unused attribute,
> + except that we don't want -Wattributes to warn for [[maybe_unused]]
> + on non-static data members. */
> +
> +static tree
> +handle_maybe_unused_attribute (tree *node, tree name, tree args,
> + int flags, bool *no_add_attrs)
> +{
> + if (TREE_CODE (*node) == FIELD_DECL)
> + {
> + *no_add_attrs = true;
> + return NULL_TREE;
> + }
> + else
> + return handle_unused_attribute (node, name, args, flags,
> no_add_attrs);
> +}
> +
> /* Table of valid C++ attributes. */
> const struct attribute_spec cxx_attribute_table[] =
> {
> @@ -4890,7 +4907,7 @@ const struct attribute_spec std_attribut
> /* { name, min_len, max_len, decl_req, type_req, fn_type_req,
> affects_type_identity, handler, exclude } */
> { "maybe_unused", 0, 0, false, false, false, false,
> - handle_unused_attribute, NULL },
> + handle_maybe_unused_attribute, NULL },
> { "nodiscard", 0, 1, false, false, false, false,
> handle_nodiscard_attribute, NULL },
> { "no_unique_address", 0, 0, true, false, false, false,
> --- gcc/testsuite/g++.dg/cpp1z/maybe_unused2.C.jj 2021-06-11
> 23:40:51.742027943 +0200
> +++ gcc/testsuite/g++.dg/cpp1z/maybe_unused2.C 2021-06-11
> 23:40:47.642084225 +0200
> @@ -0,0 +1,7 @@
> +// { dg-do compile { target c++11 } }
> +// { dg-options "-Wunused -Wextra" }
> +
> +struct [[maybe_unused]] A {
> + [[maybe_unused]] static int i;
> + [[maybe_unused]] int a;
> +};
>
>
> Jakub
>
>
