Make sure code_typet is fully constructed

The existence of the parameters and return_type properties may
depend on whether parameters() or return_type() has been called
or not, which can lead to unexpectedly unequal instructions
in goto programs.

Author: peterschrammel

src/util/std_types.h

@@ -760,6 +760,10 @@ class code_typet:public typet
 public:
   code_typet():typet(ID_code)
   {
+    // make sure these properties are always there to avoid problems
+    // with irept comparisons
+    add(ID_parameters);
+    add_type(ID_return_type);
   }
 
   // used to be argumentt -- now uses standard terminology
@@ -858,13 +862,13 @@ class code_typet:public typet
     add(ID_parameters).remove(ID_ellipsis);
   }
 
-  typedef std::vector<parametert> parameterst;
-
   const typet &return_type() const
   {
     return find_type(ID_return_type);
   }
 
+  typedef std::vector<parametert> parameterst;
+
   typet &return_type()
   {
     return add_type(ID_return_type);