Force nodes without inputs at the start of the pseudo-topological sort in lift_to_graph
diff --git a/tensorflow/python/eager/lift_to_graph.py b/tensorflow/python/eager/lift_to_graph.py
index 4874024..5e8be44 100644
--- a/tensorflow/python/eager/lift_to_graph.py
+++ b/tensorflow/python/eager/lift_to_graph.py
@@ -287,6 +287,13 @@
# we'll do ugly post-hoc mutations instead.
ops_to_visit.append(next(iter(unvisited_ops)))
+ # When the topological sort fails due to loops, it can result in exceptions
+ # later when copying a node which inputs haven't been copied yet. We can
+ # improve that pseudo-topological order slightly by putting the ops without
+ # inputs, such as constants, at the start of the topological order (i.e at
+ # the end of ops_to_copy).
+ ops_to_copy.sort(key=(lambda op: len(op_selector.graph_inputs(op)) == 0))
+
# When lifting from one FuncGraph to another, we will need to capture the
# relevant tensors as well.
captures = []
