support t attr in onnx (#1300)

nnvm/python/nnvm/frontend/onnx.py

@@ -571,6 +571,13 @@ class GraphProto(object):
             op_name = node.op_type
             attr = self._parse_attr(node.attribute)
             inputs = [self._nodes[self._renames.get(i, i)] for i in node.input]
+            if op_name == "Constant":
+                t_proto = self._parse_attr(node.attribute)["value"]
+                self._num_param += 1
+                self._params[node.output[0]] = self._parse_array(t_proto)
+                self._nodes[node.output[0]] = _sym.Variable(name=node.output[0],
+                                                            shape=list(t_proto.dims))
+            else:
                 op = self._convert_operator(op_name, inputs, attr, opset)
                 node_output = self._fix_outputs(op_name, node.output)
                 assert len(node_output) == len(op.list_output_names()), (
@@ -615,11 +622,18 @@ class GraphProto(object):
                 if list(getattr(a, f)):
                     assert a.name not in attrs, "Only one type of attr is allowed"
                     attrs[a.name] = tuple(getattr(a, f))
-            for f in ['t', 'g']:
+            for f in ['t']:
+                if a.HasField(f):
+                    attrs[a.name] = getattr(a, f)
+            for f in ['tensors']:
+                if list(getattr(a, f)):
+                    assert a.name not in attrs, "Only one type of attr is allowed"
+                    attrs[a.name] = tuple(getattr(a, f))
+            for f in ['g']:
                 if a.HasField(f):
                     raise NotImplementedError(
                         "Filed {} is not supported in nnvm.".format(f))
-            for f in ['tensors', 'graphs']:
+            for f in ['graphs']:
                 if list(getattr(a, f)):
                     raise NotImplementedError(
                         "Filed {} is not supported in nnvm.".format(f))