make auto-registry layers supporting specified output

python/paddle/v2/fluid/registry.py

@@ -167,13 +167,18 @@ def register_layer(op_type):
             inputs[ipt.name] = val
 
         outputs = dict()
-        out = helper.create_tmp_variable(dtype=dtype)
-        outputs[o_name] = [out]
+        out = kwargs.pop(_convert_(o_name), [])
+        if out:
+            out_var = out[0] if (isinstance(out, list) or
+                                 isinstance(out, tuple)) else out
+        else:
+            out_var = helper.create_tmp_variable(dtype=dtype)
+        outputs[o_name] = [out_var]
         for name in intermediate_output_names:
             outputs[name] = [helper.create_tmp_variable(dtype=dtype)]
         helper.append_op(
             type=op_type, inputs=inputs, outputs=outputs, attrs=kwargs)
-        return helper.append_activation(out)
+        return helper.append_activation(out_var)
 
     func.__name__ = op_type
     func.__doc__ = _generate_doc_string_(op_proto)