decltype(bit field type) is the underlying subtype

Author: tautschnig

regression/cpp/Bit_fields1/test.desc

@@ -1,4 +1,4 @@
-KNOWNBUG
+CORE
 main.cpp
 -std=c++11
 ^EXIT=0$

src/cpp/cpp_typecheck_type.cpp

@@ -238,7 +238,11 @@ void cpp_typecheckt::typecheck_type(typet &type)
   {
     exprt e=static_cast<const exprt &>(type.find(ID_expr_arg));
     typecheck_expr(e);
-    type=e.type();
+
+    if(e.type().id() == ID_c_bit_field)
+      type = e.type().subtype();
+    else
+      type = e.type();
   }
   else if(type.id()==ID_unassigned)
   {