Re: C++ PATCH for c++/60364 - noreturn after first decl not diagnosed (v2)

[Marek Polacek <polacek@redhat.com>]

On Mon, Jun 17, 2019 at 09:02:17AM -0600, Martin Sebor wrote:
> > diff --git gcc/cp/tree.c gcc/cp/tree.c
> > index cd021b7f594..bb695e14e73 100644
> > --- gcc/cp/tree.c
> > +++ gcc/cp/tree.c
> > @@ -4453,6 +4453,8 @@ const struct attribute_spec std_attribute_table[] =
> >       handle_likeliness_attribute, attr_cold_hot_exclusions },
> >     { "unlikely", 0, 0, false, false, false, false,
> >       handle_likeliness_attribute, attr_cold_hot_exclusions },
> > +  { "noreturn", 0, 0, true, false, false, false,
> > +    handle_noreturn_attribute, NULL },
>                                   ^^^^
> 
> The GNU attribute is made mutually exclusive with a bunch of other
> attributes (e.g., malloc or warn_unused_result) by setting the last
> member to the array of exclusive attribute.  Does the change preserve
> this relationship some other way?

Oop, no, that is a bug.  I meant to go back to that, but I'd forgotten to add
an XXX comment as I'm wont to, and the testsuite doesn't test that, so it
slipped.  Fixed & new test added.  Thanks for catching it.

Also added a test for the scenario Jakub pointed out in the other mail.

Bootstrapped/regtested on x86_64-linux, ok for trunk?

2019-06-17  Marek Polacek  <polacek@redhat.com>

	PR c++/60364 - noreturn after first decl not diagnosed.
	* attribs.c (get_attribute_namespace): No longer static.
	(decl_attributes): Avoid shadowing.  Preserve the C++11 form for C++11
	attributes.
	(attr_noreturn_exclusions): Make it extern.
	* attribs.h (get_attribute_namespace): Declare.
	* tree-inline.c (function_attribute_inlinable_p): Use
	get_attribute_name.

	* c-attribs.c (handle_noreturn_attribute): No longer static.
	* c-common.h (handle_noreturn_attribute, attr_noreturn_exclusions):
	Declare.
	* c-format.c (check_function_format): Use get_attribute_name.

	* decl.c (duplicate_decls): Give an error when a function is
	declared [[noreturn]] after its first declaration.
	* parser.c (cp_parser_std_attribute): Don't treat C++11 noreturn
	attribute as equivalent to GNU's.
	* tree.c (std_attribute_table): Add noreturn.

	* g++.dg/warn/noreturn-8.C: New test.
	* g++.dg/warn/noreturn-9.C: New test.
	* g++.dg/warn/noreturn-10.C: New test.
	* g++.dg/warn/noreturn-11.C: New test.

diff --git gcc/attribs.c gcc/attribs.c
index 4441922543f..8e540165597 100644
--- gcc/attribs.c
+++ gcc/attribs.c
@@ -340,7 +340,7 @@ lookup_attribute_spec (const_tree name)
    Please read the comments of cxx11_attribute_p to understand the
    format of attributes.  */
 
-static tree
+tree
 get_attribute_namespace (const_tree attr)
 {
   if (cxx11_attribute_p (attr))
@@ -469,7 +469,6 @@ tree
 decl_attributes (tree *node, tree attributes, int flags,
 		 tree last_decl /* = NULL_TREE */)
 {
-  tree a;
   tree returned_attrs = NULL_TREE;
 
   if (TREE_TYPE (*node) == error_mark_node || attributes == error_mark_node)
@@ -548,22 +547,23 @@ decl_attributes (tree *node, tree attributes, int flags,
 
   /* Note that attributes on the same declaration are not necessarily
      in the same order as in the source.  */
-  for (a = attributes; a; a = TREE_CHAIN (a))
+  for (tree attr = attributes; attr; attr = TREE_CHAIN (attr))
     {
-      tree ns = get_attribute_namespace (a);
-      tree name = get_attribute_name (a);
-      tree args = TREE_VALUE (a);
+      tree ns = get_attribute_namespace (attr);
+      tree name = get_attribute_name (attr);
+      tree args = TREE_VALUE (attr);
       tree *anode = node;
       const struct attribute_spec *spec
 	= lookup_scoped_attribute_spec (ns, name);
       int fn_ptr_quals = 0;
       tree fn_ptr_tmp = NULL_TREE;
+      const bool cxx11_attr_p = cxx11_attribute_p (attr);
 
       if (spec == NULL)
 	{
 	  if (!(flags & (int) ATTR_FLAG_BUILT_IN))
 	    {
-	      if (ns == NULL_TREE || !cxx11_attribute_p (a))
+	      if (ns == NULL_TREE || !cxx11_attr_p)
 		warning (OPT_Wattributes, "%qE attribute directive ignored",
 			 name);
 	      else
@@ -584,7 +584,7 @@ decl_attributes (tree *node, tree attributes, int flags,
       gcc_assert (is_attribute_p (spec->name, name));
 
       if (TYPE_P (*node)
-	  && cxx11_attribute_p (a)
+	  && cxx11_attr_p
 	  && !(flags & ATTR_FLAG_TYPE_IN_PLACE))
 	{
 	  /* This is a c++11 attribute that appertains to a
@@ -707,8 +707,7 @@ decl_attributes (tree *node, tree attributes, int flags,
 
       if (spec->handler != NULL)
 	{
-	  int cxx11_flag =
-	    cxx11_attribute_p (a) ? ATTR_FLAG_CXX11 : 0;
+	  int cxx11_flag = (cxx11_attr_p ? ATTR_FLAG_CXX11 : 0);
 
 	  /* Pass in an array of the current declaration followed
 	     by the last pushed/merged declaration if  one exists.
@@ -756,17 +755,23 @@ decl_attributes (tree *node, tree attributes, int flags,
 	  if (a == NULL_TREE)
 	    {
 	      /* This attribute isn't already in the list.  */
+	      tree r;
+	      /* Preserve the C++11 form.  */
+	      if (cxx11_attr_p)
+		r = tree_cons (build_tree_list (ns, name), args, old_attrs);
+	      else
+		r = tree_cons (name, args, old_attrs);
+
 	      if (DECL_P (*anode))
-		DECL_ATTRIBUTES (*anode) = tree_cons (name, args, old_attrs);
+		DECL_ATTRIBUTES (*anode) = r;
 	      else if (flags & (int) ATTR_FLAG_TYPE_IN_PLACE)
 		{
-		  TYPE_ATTRIBUTES (*anode) = tree_cons (name, args, old_attrs);
+		  TYPE_ATTRIBUTES (*anode) = r;
 		  /* If this is the main variant, also push the attributes
 		     out to the other variants.  */
 		  if (*anode == TYPE_MAIN_VARIANT (*anode))
 		    {
-		      tree variant;
-		      for (variant = *anode; variant;
+		      for (tree variant = *anode; variant;
 			   variant = TYPE_NEXT_VARIANT (variant))
 			{
 			  if (TYPE_ATTRIBUTES (variant) == old_attrs)
@@ -780,9 +785,7 @@ decl_attributes (tree *node, tree attributes, int flags,
 		    }
 		}
 	      else
-		*anode = build_type_attribute_variant (*anode,
-						       tree_cons (name, args,
-								  old_attrs));
+		*anode = build_type_attribute_variant (*anode, r);
 	    }
 	}
 
diff --git gcc/attribs.h gcc/attribs.h
index 83ecbbbeec9..23a7321e04a 100644
--- gcc/attribs.h
+++ gcc/attribs.h
@@ -35,6 +35,7 @@ extern tree decl_attributes (tree *, tree, int, tree = NULL_TREE);
 
 extern bool cxx11_attribute_p (const_tree);
 extern tree get_attribute_name (const_tree);
+extern tree get_attribute_namespace (const_tree);
 extern void apply_tm_attr (tree, tree);
 extern tree make_attribute (const char *, const char *, tree);
 
diff --git gcc/c-family/c-attribs.c gcc/c-family/c-attribs.c
index 7a8d3935d79..48819e74e5b 100644
--- gcc/c-family/c-attribs.c
+++ gcc/c-family/c-attribs.c
@@ -49,7 +49,6 @@ along with GCC; see the file COPYING3.  If not see
 static tree handle_packed_attribute (tree *, tree, tree, int, bool *);
 static tree handle_nocommon_attribute (tree *, tree, tree, int, bool *);
 static tree handle_common_attribute (tree *, tree, tree, int, bool *);
-static tree handle_noreturn_attribute (tree *, tree, tree, int, bool *);
 static tree handle_hot_attribute (tree *, tree, tree, int, bool *);
 static tree handle_cold_attribute (tree *, tree, tree, int, bool *);
 static tree handle_no_sanitize_attribute (tree *, tree, tree, int, bool *);
@@ -190,7 +189,7 @@ static const struct attribute_spec::exclusions attr_noinline_exclusions[] =
   ATTR_EXCL (NULL, false, false, false),
 };
 
-static const struct attribute_spec::exclusions attr_noreturn_exclusions[] =
+extern const struct attribute_spec::exclusions attr_noreturn_exclusions[] =
 {
   ATTR_EXCL ("alloc_align", true, true, true),
   ATTR_EXCL ("alloc_size", true, true, true),
@@ -779,7 +778,7 @@ handle_common_attribute (tree *node, tree name, tree ARG_UNUSED (args),
 /* Handle a "noreturn" attribute; arguments as in
    struct attribute_spec.handler.  */
 
-static tree
+tree
 handle_noreturn_attribute (tree *node, tree name, tree ARG_UNUSED (args),
 			   int ARG_UNUSED (flags), bool *no_add_attrs)
 {
diff --git gcc/c-family/c-common.h gcc/c-family/c-common.h
index 1cf2cae6395..5ac6e5eacf9 100644
--- gcc/c-family/c-common.h
+++ gcc/c-family/c-common.h
@@ -1344,6 +1344,8 @@ extern int tm_attr_to_mask (tree);
 extern tree tm_mask_to_attr (int);
 extern tree find_tm_attribute (tree);
 extern const struct attribute_spec::exclusions attr_cold_hot_exclusions[];
+extern const struct attribute_spec::exclusions attr_noreturn_exclusions[];
+extern tree handle_noreturn_attribute (tree *, tree, tree, int, bool *);
 
 /* In c-format.c.  */
 extern bool valid_format_string_type_p (tree);
diff --git gcc/c-family/c-format.c gcc/c-family/c-format.c
index b10599f9982..bd9d5aeda4e 100644
--- gcc/c-family/c-format.c
+++ gcc/c-family/c-format.c
@@ -1110,7 +1110,7 @@ check_function_format (const_tree fntype, tree attrs, int nargs,
   /* See if this function has any format attributes.  */
   for (a = attrs; a; a = TREE_CHAIN (a))
     {
-      if (is_attribute_p ("format", TREE_PURPOSE (a)))
+      if (is_attribute_p ("format", get_attribute_name (a)))
 	{
 	  /* Yup; check it.  */
 	  function_format_info info;
diff --git gcc/cp/decl.c gcc/cp/decl.c
index 0a3ef452536..85f96f73739 100644
--- gcc/cp/decl.c
+++ gcc/cp/decl.c
@@ -1922,10 +1922,29 @@ duplicate_decls (tree newdecl, tree olddecl, bool newdecl_is_friend)
 
   if (TREE_CODE (newdecl) == FUNCTION_DECL)
     {
-      if (merge_attr && diagnose_mismatched_attributes (olddecl, newdecl))
-	inform (olddecl_loc, DECL_INITIAL (olddecl)
-		? G_("previous definition of %qD here")
-		: G_("previous declaration of %qD here"), olddecl);
+      if (merge_attr)
+	{
+	  if (diagnose_mismatched_attributes (olddecl, newdecl))
+	    inform (olddecl_loc, DECL_INITIAL (olddecl)
+		    ? G_("previous definition of %qD here")
+		    : G_("previous declaration of %qD here"), olddecl);
+
+	  /* [dcl.attr.noreturn]: The first declaration of a function shall
+	     specify the noreturn attribute if any declaration of that function
+	     specifies the noreturn attribute.  */
+	  tree a;
+	  if (TREE_THIS_VOLATILE (newdecl)
+	      && !TREE_THIS_VOLATILE (olddecl)
+	      /* This applies to [[noreturn]] only, not its GNU variants.  */
+	      && (a = lookup_attribute ("noreturn", DECL_ATTRIBUTES (newdecl)))
+	      && cxx11_attribute_p (a)
+	      && get_attribute_namespace (a) == NULL_TREE)
+	    {
+	      error_at (newdecl_loc, "function %qD declared %<[[noreturn]]%> "
+			"but its first declaration was not", newdecl);
+	      inform (olddecl_loc, "previous declaration of %qD", olddecl);
+	    }
+	}
 
       /* Now that functions must hold information normally held
 	 by field decls, there is extra work to do so that
diff --git gcc/cp/parser.c gcc/cp/parser.c
index 8f5ae84670a..996e54235fd 100644
--- gcc/cp/parser.c
+++ gcc/cp/parser.c
@@ -26121,11 +26121,11 @@ cp_parser_std_attribute (cp_parser *parser, tree attr_ns)
       attr_id = canonicalize_attr_name (attr_id);
       attribute = build_tree_list (build_tree_list (NULL_TREE, attr_id),
 				   NULL_TREE);
-      /* C++11 noreturn attribute is equivalent to GNU's.  */
-      if (is_attribute_p ("noreturn", attr_id))
-	TREE_PURPOSE (TREE_PURPOSE (attribute)) = gnu_identifier;
+      /* We used to treat C++11 noreturn attribute as equivalent to GNU's,
+	 but no longer: we have to be able to tell [[noreturn]] and
+	 __attribute__((noreturn)) apart.  */
       /* C++14 deprecated attribute is equivalent to GNU's.  */
-      else if (is_attribute_p ("deprecated", attr_id))
+      if (is_attribute_p ("deprecated", attr_id))
 	TREE_PURPOSE (TREE_PURPOSE (attribute)) = gnu_identifier;
       /* C++17 fallthrough attribute is equivalent to GNU's.  */
       else if (is_attribute_p ("fallthrough", attr_id))
diff --git gcc/cp/tree.c gcc/cp/tree.c
index cd021b7f594..978aea56193 100644
--- gcc/cp/tree.c
+++ gcc/cp/tree.c
@@ -4453,6 +4453,8 @@ const struct attribute_spec std_attribute_table[] =
     handle_likeliness_attribute, attr_cold_hot_exclusions },
   { "unlikely", 0, 0, false, false, false, false,
     handle_likeliness_attribute, attr_cold_hot_exclusions },
+  { "noreturn", 0, 0, true, false, false, false,
+    handle_noreturn_attribute, attr_noreturn_exclusions },
   { NULL, 0, 0, false, false, false, false, NULL, NULL }
 };
 
diff --git gcc/testsuite/g++.dg/warn/noreturn-10.C gcc/testsuite/g++.dg/warn/noreturn-10.C
new file mode 100644
index 00000000000..6f7df48bf18
--- /dev/null
+++ gcc/testsuite/g++.dg/warn/noreturn-10.C
@@ -0,0 +1,10 @@
+// PR c++/60364
+// { dg-do compile { target c++11 } }
+
+void* fn1 [[gnu::returns_twice, noreturn]] (); // { dg-warning "ignoring attribute 'noreturn' because it conflicts with attribute 'returns_twice'" }
+void* fn2 [[gnu::alloc_align(1), noreturn]] (int); // { dg-warning "ignoring attribute 'noreturn' because it conflicts with attribute 'alloc_align'" }
+void* fn3 [[gnu::alloc_size(1), noreturn]] (int); // { dg-warning "ignoring attribute 'noreturn' because it conflicts with attribute 'alloc_size'" }
+void* fn4 [[gnu::const, noreturn]] (); // { dg-warning "ignoring attribute 'noreturn' because it conflicts with attribute 'const'" }
+void* fn5 [[gnu::malloc, noreturn]] (int); // { dg-warning "ignoring attribute 'noreturn' because it conflicts with attribute 'malloc'" }
+void* fn6 [[gnu::pure, noreturn]] (); // { dg-warning "ignoring attribute 'noreturn' because it conflicts with attribute 'pure'" }
+void* fn7 [[gnu::warn_unused_result, noreturn]] (); // { dg-warning "ignoring attribute 'noreturn' because it conflicts with attribute 'warn_unused_result'" }
diff --git gcc/testsuite/g++.dg/warn/noreturn-11.C gcc/testsuite/g++.dg/warn/noreturn-11.C
new file mode 100644
index 00000000000..e0265eba701
--- /dev/null
+++ gcc/testsuite/g++.dg/warn/noreturn-11.C
@@ -0,0 +1,25 @@
+// PR c++/60364
+// { dg-do compile { target c++11 } }
+
+void f1 ();
+void f1 [[gnu::noreturn]] ();
+void f1 [[noreturn]] ();
+
+void f2 ();
+__attribute__((noreturn)) void f2 ();
+void f2 [[noreturn]] ();
+
+void f3 ();
+void f3 [[gnu::noreturn]] ();
+void f3 ();
+void f3 [[noreturn]] ();
+
+void f4 ();
+void f4 ();
+void f4 ();
+void f4 [[noreturn]] (); // { dg-error "declared '\\\[\\\[noreturn\\\]\\\]' but its first declaration was not" }
+
+void f5 [[noreturn]] ();
+void f5 ();
+void f5 ();
+void f5 [[noreturn]] ();
diff --git gcc/testsuite/g++.dg/warn/noreturn-8.C gcc/testsuite/g++.dg/warn/noreturn-8.C
new file mode 100644
index 00000000000..d465468decb
--- /dev/null
+++ gcc/testsuite/g++.dg/warn/noreturn-8.C
@@ -0,0 +1,21 @@
+// PR c++/60364
+// { dg-do compile { target c++11 } }
+// { dg-options "-Wpedantic" }
+
+void f (); // { dg-message "previous declaration" }
+void f [[noreturn]] (); // { dg-error "declared '\\\[\\\[noreturn\\\]\\\]' but its first declaration was not" }
+
+void f2 ();
+void f2 [[gnu::noreturn]] ();
+
+void f3 ();
+__attribute__((noreturn)) void f3 ();
+
+void f4 () { __builtin_abort (); } // { dg-message "previous declaration" }
+void f4 [[noreturn]] (); // { dg-error "declared '\\\[\\\[noreturn\\\]\\\]' but its first declaration was not" }
+
+void f5 () { __builtin_abort (); }
+void f5 [[gnu::noreturn]] ();
+
+void f6 () { __builtin_abort (); }
+__attribute__((noreturn)) void f6 ();
diff --git gcc/testsuite/g++.dg/warn/noreturn-9.C gcc/testsuite/g++.dg/warn/noreturn-9.C
new file mode 100644
index 00000000000..f7ede57aab0
--- /dev/null
+++ gcc/testsuite/g++.dg/warn/noreturn-9.C
@@ -0,0 +1,21 @@
+// PR c++/60364
+// { dg-do compile { target c++11 } }
+// { dg-options "-Wpedantic" }
+
+void f1 [[gnu::noreturn]] ();
+void f1 [[noreturn]] ();
+
+void f2 [[noreturn]] ();
+void f2 [[gnu::noreturn]] ();
+
+__attribute__((noreturn)) void f3 ();
+void f3 [[noreturn]] ();
+
+void f4 [[noreturn]] ();
+__attribute__((noreturn)) void f4 ();
+
+__attribute__((noreturn)) void f5 ();
+void f5 [[gnu::noreturn]] ();
+
+void f6 [[gnu::noreturn]] ();
+__attribute__((noreturn)) void f6 ();
diff --git gcc/tree-inline.c gcc/tree-inline.c
index 52f45a73b1d..2de5e22f10f 100644
--- gcc/tree-inline.c
+++ gcc/tree-inline.c
@@ -3899,7 +3899,7 @@ function_attribute_inlinable_p (const_tree fndecl)
 
       for (a = DECL_ATTRIBUTES (fndecl); a; a = TREE_CHAIN (a))
 	{
-	  const_tree name = TREE_PURPOSE (a);
+	  const_tree name = get_attribute_name (a);
 	  int i;
 
 	  for (i = 0; targetm.attribute_table[i].name != NULL; i++)