Implement C++17 [[maybe_unused]] attribute.

gcc/
	* attribs.c (register_scoped_attributes): Fix logic.
	* attribs.h: Declare register_scoped_attributes.
c-family/
	* c-common.c (handle_unused_attribute): Accept CONST_DECL.
	No longer static.
	* c-common.h: Declare it.
	* c-lex.c (c_common_has_attribute): Add maybe_unused.
cp/
	* tree.c (std_attribute_table): New.
	(init_tree): Register it.

From-SVN: r235414

gcc/ChangeLog

+2016-04-25  Jason Merrill  <jason@redhat.com>
+
+	* attribs.c (register_scoped_attributes): Fix logic.
+	* attribs.h: Declare register_scoped_attributes.
+
 2016-04-25  Bill Schmidt  <wschmidt@linux.vnet.ibm.com>
 
 	* config/rs6000/rs6000-builtin.def: Correct pasto error for

gcc/attribs.c

@@ -130,7 +130,7 @@ register_scoped_attributes (const struct attribute_spec * attributes,
       /* We don't have any namespace NS yet.  Create one.  */
       scoped_attributes sa;
 
-      if (!attributes_table.is_empty ())
+      if (attributes_table.is_empty ())
 	attributes_table.create (64);
 
       memset (&sa, 0, sizeof (sa));

gcc/attribs.h

@@ -38,4 +38,7 @@ extern tree get_attribute_name (const_tree);
 extern void apply_tm_attr (tree, tree);
 extern tree make_attribute (const char *, const char *, tree);
 
+extern struct scoped_attributes* register_scoped_attributes (const struct attribute_spec *,
+							     const char *);
+
 #endif // GCC_ATTRIBS_H

gcc/c-family/ChangeLog

+2016-04-25  Jason Merrill  <jason@redhat.com>
+
+	* c-common.c (handle_unused_attribute): Accept CONST_DECL.
+	No longer static.
+	* c-common.h: Declare it.
+	* c-lex.c (c_common_has_attribute): Add maybe_unused.
+
 2016-04-22  Jason Merrill  <jason@redhat.com>
 
 	* c-cppbuiltin.c (c_cpp_builtins): Fix __cpp_range_based_for.

gcc/c-family/c-common.c

@@ -327,7 +327,6 @@ static tree handle_artificial_attribute (tree *, tree, tree, int, bool *);
 static tree handle_flatten_attribute (tree *, tree, tree, int, bool *);
 static tree handle_error_attribute (tree *, tree, tree, int, bool *);
 static tree handle_used_attribute (tree *, tree, tree, int, bool *);
-static tree handle_unused_attribute (tree *, tree, tree, int, bool *);
 static tree handle_externally_visible_attribute (tree *, tree, tree, int,
 						 bool *);
 static tree handle_no_reorder_attribute (tree *, tree, tree, int,
@@ -7033,7 +7032,7 @@ handle_used_attribute (tree *pnode, tree name, tree ARG_UNUSED (args),
 /* Handle a "unused" attribute; arguments as in
    struct attribute_spec.handler.  */
 
-static tree
+tree
 handle_unused_attribute (tree *node, tree name, tree ARG_UNUSED (args),
 			 int flags, bool *no_add_attrs)
 {
@@ -7044,6 +7043,7 @@ handle_unused_attribute (tree *node, tree name, tree ARG_UNUSED (args),
       if (TREE_CODE (decl) == PARM_DECL
 	  || VAR_OR_FUNCTION_DECL_P (decl)
 	  || TREE_CODE (decl) == LABEL_DECL
+	  || TREE_CODE (decl) == CONST_DECL
 	  || TREE_CODE (decl) == TYPE_DECL)
 	{
 	  TREE_USED (decl) = 1;

gcc/c-family/c-common.h

@@ -790,6 +790,7 @@ extern void check_function_arguments_recurse (void (*)
 					      unsigned HOST_WIDE_INT);
 extern bool check_builtin_function_arguments (tree, int, tree *);
 extern void check_function_format (tree, int, tree *);
+extern tree handle_unused_attribute (tree *, tree, tree, int, bool *);
 extern tree handle_format_attribute (tree *, tree, tree, int, bool *);
 extern tree handle_format_arg_attribute (tree *, tree, tree, int, bool *);
 extern bool attribute_takes_identifier_p (const_tree);

gcc/c-family/c-lex.c

@@ -340,23 +340,26 @@ c_common_has_attribute (cpp_reader *pfile)
 		  attr_name = NULL_TREE;
 		}
 	    }
-	}
-      if (attr_name)
-	{
-	  init_attributes ();
-	  const struct attribute_spec *attr = lookup_attribute_spec (attr_name);
-	  if (attr)
+	  else
 	    {
-	      if (TREE_CODE (attr_name) == TREE_LIST)
-		attr_name = TREE_VALUE (attr_name);
+	      /* Some standard attributes need special handling.  */
 	      if (is_attribute_p ("noreturn", attr_name))
 		result = 200809;
 	      else if (is_attribute_p ("deprecated", attr_name))
 		result = 201309;
-	      else
-		result = 1;
+	      else if (is_attribute_p ("maybe_unused", attr_name))
+		result = 201603;
+	      if (result)
+		attr_name = NULL_TREE;
 	    }
 	}
+      if (attr_name)
+	{
+	  init_attributes ();
+	  const struct attribute_spec *attr = lookup_attribute_spec (attr_name);
+	  if (attr)
+	    result = 1;
+	}
     }
   else
     {

gcc/cp/ChangeLog

+2016-04-25  Jason Merrill  <jason@redhat.com>
+
+	* tree.c (std_attribute_table): New.
+	(init_tree): Register it.
+
 2016-04-22  Jason Merrill  <jason@redhat.com>
 
 	* parser.c (cp_parser_perform_range_for_lookup): Decay the array.

gcc/cp/tree.c

@@ -3548,6 +3548,16 @@ const struct attribute_spec cxx_attribute_table[] =
   { NULL,	      0, 0, false, false, false, NULL, false }
 };
 
+/* Table of C++ standard attributes.  */
+const struct attribute_spec std_attribute_table[] =
+{
+  /* { name, min_len, max_len, decl_req, type_req, fn_type_req, handler,
+       affects_type_identity } */
+  { "maybe_unused", 0, 0, false, false, false,
+    handle_unused_attribute, false },
+  { NULL,	      0, 0, false, false, false, NULL, false }
+};
+
 /* Handle a "java_interface" attribute; arguments as in
    struct attribute_spec.handler.  */
 static tree
@@ -4026,6 +4036,7 @@ void
 init_tree (void)
 {
   list_hash_table = hash_table<list_hasher>::create_ggc (61);
+  register_scoped_attributes (std_attribute_table, NULL);
 }
 
 /* Returns the kind of special function that DECL (a FUNCTION_DECL)

gcc/testsuite/c-c++-common/attributes-enum-2.c

@@ -6,7 +6,7 @@ enum E {
   A __attribute__((foo)),	/* { dg-warning "ignored" } */
   B __attribute__((cold)),	/* { dg-warning "ignored" } */
   C __attribute__((const)),	/* { dg-warning "ignored" } */
-  D __attribute__((unused)),	/* { dg-warning "ignored" } */
+  D __attribute__((unused)),
   E __attribute__((flatten)),	/* { dg-warning "ignored" } */
   F __attribute__((tm)),	/* { dg-warning "ignored" } */
   G __attribute__((common)),	/* { dg-warning "ignored" } */

gcc/testsuite/c-c++-common/cpp/pr63831-1.c

@@ -17,10 +17,10 @@ T3 t3;
 T4 t4;
 T5 t5;
 #ifdef __cplusplus
-typedef char T6[__has_attribute (gnu::__noreturn__) == 200809 ? 1 : -1];
+typedef char T6[__has_attribute (gnu::__noreturn__) ? 1 : -1];
 typedef char T7[__has_attribute (gnu::alloc_size) == 1 ? 1 : -1];
 typedef char T8[__has_attribute (gnu::non_existent_attribuuuute) == 0 ? 1 : -1];
-#if __has_attribute (gnu::noreturn) == 200809
+#if __has_attribute (gnu::noreturn)
 typedef char T9;
 #endif
 #define d2 gnu::deprecated
@@ -47,10 +47,10 @@ T13 t13;
 T14 t14;
 T15 t15;
 #ifdef __cplusplus
-typedef char T16[__has_cpp_attribute (gnu::__noreturn__) == 200809 ? 1 : -1];
+typedef char T16[__has_cpp_attribute (gnu::__noreturn__) ? 1 : -1];
 typedef char T17[__has_cpp_attribute (gnu::alloc_size) == 1 ? 1 : -1];
 typedef char T18[__has_cpp_attribute (gnu::non_existent_attribuuuute) == 0 ? 1 : -1];
-#if __has_cpp_attribute (gnu::noreturn) == 200809
+#if __has_cpp_attribute (gnu::noreturn)
 typedef char T19;
 #endif
 #define d2 gnu::deprecated

gcc/testsuite/g++.dg/cpp1z/feat-cxx1z.C

@@ -343,3 +343,13 @@
 #elif __cpp_hex_float != 201603
 #  error "__cpp_hex_float != 201603"
 #endif
+
+#ifdef __has_cpp_attribute
+#  if ! __has_cpp_attribute(maybe_unused)
+#    error "__has_cpp_attribute(maybe_unused)"
+#  elif __has_cpp_attribute(maybe_unused) != 201603
+#    error "__has_cpp_attribute(maybe_unused) != 201603"
+#  endif
+#else
+#  error "__has_cpp_attribute"
+#endif

gcc/testsuite/g++.dg/cpp1z/maybe_unused1.C

+// { dg-do compile { target c++11 } }
+// { dg-options "-Wunused -Wextra" }
+
+[[maybe_unused]] static void f() { }
+
+enum [[maybe_unused]] E {
+  e [[maybe_unused]]
+};
+
+struct [[maybe_unused]] A {
+  [[maybe_unused]] static int i;
+};
+
+void g([[maybe_unused]] int i) {
+  [[maybe_unused]] typedef int T;
+  [[maybe_unused]] int j;
+}