commit 7da5a68ba55cd49c46ff9ac547df59248bd90f7d
Author: Jason Merrill <jason@redhat.com>
Date:   Wed Apr 29 16:04:08 2015 -0400

    	PR c++/50800
    	* tree.c (apply_identity_attributes): Fix handling of classes.

diff --git a/gcc/cp/tree.c b/gcc/cp/tree.c
index d00f0d7..ec9be8c 100644
--- a/gcc/cp/tree.c
+++ b/gcc/cp/tree.c
@@ -1187,6 +1187,13 @@ apply_identity_attributes (tree result, tree attribs, bool *remove_attributes)
   tree new_attribs = NULL_TREE;
   tree *p = &new_attribs;
 
+  if (OVERLOAD_TYPE_P (result))
+    {
+      /* On classes and enums all attributes are ingrained.  */
+      gcc_assert (attribs == TYPE_ATTRIBUTES (result));
+      return result;
+    }
+
   for (tree a = attribs; a; a = TREE_CHAIN (a))
     {
       const attribute_spec *as
diff --git a/gcc/testsuite/g++.dg/cpp0x/alignas3.C b/gcc/testsuite/g++.dg/cpp0x/alignas3.C
new file mode 100644
index 0000000..aa62e5a
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp0x/alignas3.C
@@ -0,0 +1,20 @@
+// PR c++/50800
+// { dg-do compile { target c++11 } }
+
+template <typename> struct A;
+template <typename _Up> struct A<_Up *> { typedef _Up type; };
+template <typename T> struct B { typedef typename A<T>::type type; };
+template <typename> struct C;
+template <typename From> struct C<const From> {
+  typedef typename B<From>::type SimpleType;
+};
+template <class> struct D { typedef int ret_type; };
+template <class From> struct F {
+  typedef typename D<typename C<From>::SimpleType>::ret_type ret_type;
+};
+template <class, class Y> typename F<Y>::ret_type cast(Y &);
+class CompoundStmt;
+class alignas(8) Stmt {
+  Stmt *Children[1];
+  CompoundStmt *getBlock() const { cast<CompoundStmt>(Children[0]); }
+};