Use the right mechanism to change the CDataType Constant signature

theano/gof/cc.py

@@ -1198,14 +1198,7 @@ class CLinker(link.Linker):
             # It is important that a variable (i)
             # yield a 'position' that reflects its role in code_gen()
             if isinstance(i, graph.Constant):  # orphans
-                if isinstance(i.type, theano.gof.type.CDataType):
-                    # The Op can't access the data, so it can't change
-                    # the code depending of it. So there is no need to
-                    # put it in the signature. Also, under pytyon 2,
-                    # PyCObject aren't pickable. So this putting it in
-                    # the key would disable the cache for this module.
-                    isig = "PyCObject"
-                elif id(i) not in constant_ids:
+                if id(i) not in constant_ids:
                     isig = (i.signature(), topological_pos, i_idx)
                     # If the Theano constant provides a strong hash
                     # (no collision for transpose, 2, 1, 0, -1, -2,

theano/gof/type.py

@@ -595,3 +595,14 @@ if (py_%(name)s == NULL) { %(freefunc)s(%(name)s); }
 
     def __str__(self):
         return "%s{%s}" % (self.__class__.__name__, self.ctype)
+
+
+class CDataTypeConstant(graph.Constant):
+    def signature(self):
+        # The Op.c_code* methoss can't access the data, so it can't
+        # change the code depending of it. So there is no need to put
+        # it in the signature. Also, under Python 2, PyCObject aren't
+        # pickable. So using the PyCObject in the signature would
+        # disable the c code cache for op that have it as an input.
+        return (self.type,)
+CDataType.Constant = CDataTypeConstant