Fixing compilation of graphs with only one host_from_gpu OP

theano/gpuarray/opt.py

@@ -389,17 +389,18 @@ class GraphToGPU(NavigatorOptimizer):
             if new_o.type != o.type:
                 assert isinstance(o.type, tensor.TensorType)
                 assert isinstance(new_o.type, GpuArrayType)
-                assert new_o.owner
+
                 # This condition is needed in the case one input is an
                 # output of the graph. Without this, it would
                 # introduce cycle as we don't replace correctly that
                 # case. It would also add extra transfer to/from the
                 # gpu.
-                if (isinstance(new_o.owner.op, GpuFromHost) and
+                if (new_o.owner and
+                        isinstance(new_o.owner.op, GpuFromHost) and
                         new_o.owner.inputs[0].type == o.type):
                     new_o = new_o.owner.inputs[0]
                 else:
-                    new_o = host_from_gpu(new_o)
+                    new_o = safe_to_cpu(new_o)
             new_nodes.append(new_o)
         fgraph.replace_all_validate(zip(fgraph.outputs, new_nodes),
                                     reason=self.__class__.__name__)