re PR c++/68049 (template instantiation involving may_alias defines symbol twice)

	PR c++/68049
	* tree.c (strip_typedefs): Use DECL_ORIGINAL_TYPE.

From-SVN: r233715

gcc/cp/ChangeLog

+2016-02-25  Jason Merrill  <jason@redhat.com>
+
+	PR c++/68049
+	* tree.c (strip_typedefs): Use DECL_ORIGINAL_TYPE.
+
 2016-02-25  Patrick Palka  <ppalka@gcc.gnu.org>
 
 	PR c++/69736

gcc/cp/tree.c

@@ -1447,7 +1447,15 @@ strip_typedefs (tree t, bool *remove_attributes)
     }
 
   if (!result)
-      result = TYPE_MAIN_VARIANT (t);
+    {
+      if (typedef_variant_p (t))
+	/* Explicitly get the underlying type, as TYPE_MAIN_VARIANT doesn't
+	   strip typedefs with attributes.  */
+	result = TYPE_MAIN_VARIANT (DECL_ORIGINAL_TYPE (TYPE_NAME (t)));
+      else
+	result = TYPE_MAIN_VARIANT (t);
+    }
+  gcc_assert (!typedef_variant_p (result));
   if (TYPE_USER_ALIGN (t) != TYPE_USER_ALIGN (result)
       || TYPE_ALIGN (t) != TYPE_ALIGN (result))
     {

gcc/testsuite/g++.dg/ext/attribute-may-alias-3.C

+// PR c++/68049
+// { dg-do compile { target c++11 } }
+
+template <typename T> struct Bar
+{
+    using type = T;
+};
+template <typename T> struct Foo
+{
+    typedef typename Bar<T>::type alias_type [[gnu::may_alias]];
+
+    alias_type operator()() { return {}; }
+};
+
+template <typename T> void print(T) {}
+
+int main()
+{
+    print(Foo<int>()());
+    print(0);
+    return 0;
+}