commit 724a66ba837560ba233b00cddf5d5d93ec5888f4
Author: Jason Merrill <jason@redhat.com>
Date:   Thu Apr 16 13:57:11 2015 -0400

    	PR c++/50800
    gcc/
    	* tree.c (build_reference_type_for_mode): Don't pass can_alias_all
    	down when building TYPE_CANONICAL.
    	(build_pointer_type_for_mode): Likewise.
    gcc/cp/
    	* typeck.c (structural_comptypes): Don't check TYPE_REF_CAN_ALIAS_ALL.

diff --git a/gcc/cp/typeck.c b/gcc/cp/typeck.c
index e9d4cae..7646225 100644
--- a/gcc/cp/typeck.c
+++ b/gcc/cp/typeck.c
@@ -1310,7 +1310,6 @@ structural_comptypes (tree t1, tree t2, int strict)
 
     case POINTER_TYPE:
       if (TYPE_MODE (t1) != TYPE_MODE (t2)
-	  || TYPE_REF_CAN_ALIAS_ALL (t1) != TYPE_REF_CAN_ALIAS_ALL (t2)
 	  || !same_type_p (TREE_TYPE (t1), TREE_TYPE (t2)))
 	return false;
       break;
diff --git a/gcc/testsuite/g++.dg/ext/alias-canon2.C b/gcc/testsuite/g++.dg/ext/alias-canon2.C
index 4833db8..3806cb4 100644
--- a/gcc/testsuite/g++.dg/ext/alias-canon2.C
+++ b/gcc/testsuite/g++.dg/ext/alias-canon2.C
@@ -31,6 +31,3 @@ out_long (ui64 longVal)
         }
     }
 }
-
-void f(ui32 *) { }
-void f(ui32a *) { }
diff --git a/gcc/testsuite/g++.dg/ext/attrib50.C b/gcc/testsuite/g++.dg/ext/attrib50.C
new file mode 100644
index 0000000..a46c9f7
--- /dev/null
+++ b/gcc/testsuite/g++.dg/ext/attrib50.C
@@ -0,0 +1,11 @@
+// PR c++/50800
+
+template <typename T> struct B;
+template <typename T> struct B<T &> {
+  typedef T type;
+};
+struct A {
+  typedef int TA __attribute__((__may_alias__));
+};
+void d() { B<int &> b; }
+int main() { B<A::TA &> b; }
diff --git a/gcc/tree.c b/gcc/tree.c
index 151e3e2..43c4a36 100644
--- a/gcc/tree.c
+++ b/gcc/tree.c
@@ -7704,7 +7704,7 @@ build_pointer_type_for_mode (tree to_type, machine_mode mode,
   else if (TYPE_CANONICAL (to_type) != to_type)
     TYPE_CANONICAL (t)
       = build_pointer_type_for_mode (TYPE_CANONICAL (to_type),
-				     mode, can_alias_all);
+				     mode, false);
 
   /* Lay out the type.  This function has many callers that are concerned
      with expression-construction, and this simplifies them all.  */
@@ -7771,7 +7771,7 @@ build_reference_type_for_mode (tree to_type, machine_mode mode,
   else if (TYPE_CANONICAL (to_type) != to_type)
     TYPE_CANONICAL (t)
       = build_reference_type_for_mode (TYPE_CANONICAL (to_type),
-				       mode, can_alias_all);
+				       mode, false);
 
   layout_type (t);