Make sure Elemwise and Composite prepare_node is called

theano/scalar/basic.py

@@ -3667,9 +3667,10 @@ class Composite(ScalarOp):
     def prepare_node(self, node, storage_map, compute_map, impl):
         if impl == 'py':
             self.init_py_impls()  # self._impls
-        elif impl == 'c':
+        if not getattr(node.tag, 'graph_prepare_node_called', False):
             for n in theano.gof.graph.list_of_nodes(self.inputs, self.outputs):
                 n.op.prepare_node(n, None, None, impl)
+            node.tag.graph_prepare_node_called = True
 
     def output_types(self, input_types):
         if tuple(input_types) != self.inputs_type:

theano/tensor/elemwise.py

@@ -891,6 +891,14 @@ second dimension
             # numpy the first (faster) version leads to segfaults
             if self.ufunc:
                 ufunc = self.ufunc
+            elif not hasattr(node.tag, 'ufunc'):
+                # It happen that make_thunk isn't called, like in
+                # get_scalar_constant_value
+                self.prepare_node(node, None, None, 'py')
+                if self.ufunc:
+                    ufunc = self.ufunc
+                else:
+                    ufunc = node.tag.ufunc
             else:
                 ufunc = node.tag.ufunc