| Message ID | 20210611214434.GE7706@tucnak |
|---|---|
| State | New |
| Headers | show |
| Series | c++: Don't complain about [[maybe_unused]] on non-static data members | expand |
On Fri, Jun 11, 2021 at 5:44 PM Jakub Jelinek <jakub@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 <jakub@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 > >
--- 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; +};