re PR c++/65936 (ICE: canonical types differ for identical types)

	cp/
	PR c++/65936
	* pt.c (lookup_template_class_1): Copy may_alias attribute too.

	testsuite/
	PR c++/65936
	* g++.dg/template/pr65936.C: New.

From-SVN: r223613

gcc/cp/ChangeLog

+2015-05-23  Nathan Sidwell  <nathan@acm.org>
+
+	PR c++/65936
+	* pt.c (lookup_template_class_1): Copy may_alias attribute too.
+
 2015-05-22  Jim Wilson  <jim.wilson@linaro.org>
 
 	* Make-lang.in (check_g++_parallelize): Update comment.

gcc/cp/pt.c

@@ -7905,15 +7905,22 @@ lookup_template_class_1 (tree d1, tree arglist, tree in_decl, tree context,
       if (OVERLOAD_TYPE_P (t)
 	  && !DECL_ALIAS_TEMPLATE_P (gen_tmpl))
 	{
-	  if (tree attributes
-	      = lookup_attribute ("abi_tag", TYPE_ATTRIBUTES (template_type)))
+	  static const char *tags[] = {"abi_tag", "may_alias"};
+
+	  for (unsigned ix = 0; ix != 2; ix++)
 	    {
-	      if (!TREE_CHAIN (attributes))
+	      tree attributes
+		= lookup_attribute (tags[ix], TYPE_ATTRIBUTES (template_type));
+
+	      if (!attributes)
+		;
+	      else if (!TREE_CHAIN (attributes) && !TYPE_ATTRIBUTES (t))
 		TYPE_ATTRIBUTES (t) = attributes;
 	      else
 		TYPE_ATTRIBUTES (t)
-		  = build_tree_list (TREE_PURPOSE (attributes),
-				     TREE_VALUE (attributes));
+		  = tree_cons (TREE_PURPOSE (attributes),
+			       TREE_VALUE (attributes),
+			       TYPE_ATTRIBUTES (t));
 	    }
 	}
 

gcc/testsuite/ChangeLog

+2015-05-23  Nathan Sidwell  <nathan@acm.org>
+
+	PR c++/65936
+	* g++.dg/template/pr65936.C: New.
+
 2015-05-22  Marc Glisse  <marc.glisse@inria.fr>
 
 	PR tree-optimization/63387

gcc/testsuite/g++.dg/template/pr65936.C

+// checking ICE in canonical typing
+
+class A;
+
+template <typename> struct B
+{
+  typedef A type;
+};
+
+template <class T> class C
+  : public B<T>::type
+{
+} __attribute__ ((__may_alias__));
+
+class A
+{
+  operator const C<int> &()
+  {
+    return *static_cast<const C<int> *> (this);
+  }
+};