re PR c++/38908 (Unexplained "'<anonymous>' is used uninitialized in this function" warning in cc1plus -m64)

PR c++/38908
        * class.c (is_really_empty_class): New fn.
        * cp-tree.h: Declare it.
        * cp-objcp-common.c (cp_expr_size): Use it.

From-SVN: r144643

gcc/cp/ChangeLog

@@ -1,5 +1,10 @@
 2009-03-04  Jason Merrill  <jason@redhat.com>
 
+	PR c++/38908
+	* class.c (is_really_empty_class): New fn.
+	* cp-tree.h: Declare it.
+	* cp-objcp-common.c (cp_expr_size): Use it.
+
 	PR c++/13549
 	* semantics.c (perform_koenig_lookup): Handle TEMPLATE_ID_EXPR.
 	* parser.c (cp_parser_postfix_expression): Call it for 

gcc/cp/class.c

@@ -6461,7 +6461,7 @@ is_empty_class (tree type)
   if (type == error_mark_node)
     return 0;
 
-  if (! MAYBE_CLASS_TYPE_P (type))
+  if (! CLASS_TYPE_P (type))
     return 0;
 
   /* In G++ 3.2, whether or not a class was empty was determined by
@@ -6501,6 +6501,37 @@ contains_empty_class_p (tree type)
   return false;
 }
 
+/* Returns true if TYPE contains no actual data, just various
+   possible combinations of empty classes.  */
+
+bool
+is_really_empty_class (tree type)
+{
+  if (is_empty_class (type))
+    return true;
+  if (CLASS_TYPE_P (type))
+    {
+      tree field;
+      tree binfo;
+      tree base_binfo;
+      int i;
+
+      for (binfo = TYPE_BINFO (type), i = 0;
+	   BINFO_BASE_ITERATE (binfo, i, base_binfo); ++i)
+	if (!is_really_empty_class (BINFO_TYPE (base_binfo)))
+	  return false;
+      for (field = TYPE_FIELDS (type); field; field = TREE_CHAIN (field))
+	if (TREE_CODE (field) == FIELD_DECL
+	    && !DECL_ARTIFICIAL (field)
+	    && !is_really_empty_class (TREE_TYPE (field)))
+	  return false;
+      return true;
+    }
+  else if (TREE_CODE (type) == ARRAY_TYPE)
+    return is_really_empty_class (TREE_TYPE (type));
+  return false;
+}
+
 /* Note that NAME was looked up while the current class was being
    defined and that the result of that lookup was DECL.  */
 

gcc/cp/cp-objcp-common.c

@@ -101,7 +101,7 @@ cp_expr_size (const_tree exp)
 	     constructed, this is a valid transformation.  */
 	  || CP_AGGREGATE_TYPE_P (type))
 	/* This would be wrong for a type with virtual bases.  */
-	return (is_empty_class (type)
+	return (is_really_empty_class (type)
 		? size_zero_node
 		: CLASSTYPE_SIZE_UNIT (type));
       else

gcc/cp/cp-tree.h

@@ -4240,6 +4240,7 @@ extern void finish_struct_1			(tree);
 extern int resolves_to_fixed_type_p		(tree, int *);
 extern void init_class_processing		(void);
 extern int is_empty_class			(tree);
+extern bool is_really_empty_class		(tree);
 extern void pushclass				(tree);
 extern void popclass				(void);
 extern void push_nested_class			(tree);

gcc/testsuite/ChangeLog

@@ -1,3 +1,8 @@
+2009-03-05  Jason Merrill  <jason@redhat.com>
+
+	PR c++/38908
+	* g++.dg/warn/Wuninitialized-3.C: New test.
+
 2009-03-05  Jakub Jelinek  <jakub@redhat.com>
 
 	PR debug/39379

gcc/testsuite/g++.dg/warn/Wuninitialized-3.C

@@ -0,0 +1,17 @@
+// PR C++/38908
+// { dg-options "-Wuninitialized -O" }
+
+struct empty {};
+
+struct dfs_visitor {
+    dfs_visitor() { }
+    empty m_vis;
+};
+
+void bar(const dfs_visitor&);
+void foo(void)
+{
+  dfs_visitor vis;
+  dfs_visitor vis2 = vis;
+  bar (vis2);
+}