[ONNXGraph] delete_orphaned_node_branches utility function (#1694)

* [ONNXGraph] delete_orphaned_nodes utility function

* rename to

* additionally remove appropriate initializers (constants)

---------

Co-authored-by: bogunowicz@arrival.com <bogunowicz@arrival.com>

src/sparseml/exporters/transforms/kv_cache/transforms_base.py

@@ -157,7 +157,6 @@ def swap_nodes_for_input(
         """
 
         graph = ONNXGraph(model)
-        orphaned_nodes = []
         for node in nodes:
             child_node = graph.get_node_children(node)[0]
 
@@ -172,11 +171,7 @@ def swap_nodes_for_input(
                 if input_name_child_node == output_to_replace:
                     graph.update_node_input(child_node, input_name, idx)
 
-            orphaned_nodes.extend(graph.find_orphaned_nodes(node))
-
-        graph.delete_nodes(orphaned_nodes)
-        graph.update()
-        graph.delete_unused_initializers()
+        graph.delete_orphaned_node_branches()
 
         _LOGGER.info(
             f"Successfully swapped {len(nodes)} nodes for input '{input_name}'"

src/sparseml/onnx/utils/graph_editor.py

@@ -328,6 +328,48 @@ def sort_nodes_topologically(self):
         self._model.graph.ClearField("node")
         self._model.graph.node.extend(updated_node_list)
 
+    def get_orphaned_nodes(
+        self,
+        graph_output_ids: Optional[Iterable[str]] = None,
+    ) -> List[NodeProto]:
+        """
+        :param graph_output_ids: iterable of output ids in graph. if not supplied,
+            will be read from the model
+        :return: list of all nodes in the graph that are not inputs to
+            other nodes or outputs of the graph
+        """
+        if graph_output_ids is None:
+            graph_output_ids = {output.name for output in self._model.graph.output}
+
+        orphaned_nodes = []
+        for node in self.nodes:
+            node_is_orphaned = True
+            # iterate over possible output ids, in practice, there is almost
+            # always only 1
+            for out_id in node.output:
+                if out_id in self._input_id_to_nodes or out_id in graph_output_ids:
+                    node_is_orphaned = False
+            if node_is_orphaned:
+                orphaned_nodes.append(node)
+        return orphaned_nodes
+
+    def delete_orphaned_node_branches(self):
+        """
+        Deletes all nodes in the graph that are not inputs to other nodes or outputs of
+        the graph. Additionally deletes all nodes that would become orphaned
+        after the node deletion until the graph contains no orphaned nodes
+        """
+        graph_output_ids = {output.name for output in self._model.graph.output}
+        orphaned_nodes = self.get_orphaned_nodes(graph_output_ids=graph_output_ids)
+
+        while orphaned_nodes:
+            # no need to refresh self, delete nodes should update internal graph edges
+            self.delete_nodes(orphaned_nodes)
+            self.update()
+            self.delete_unused_initializers()
+            # update now orphaned nodes, can only run up to len(nodes) times
+            orphaned_nodes = self.get_orphaned_nodes(graph_output_ids=graph_output_ids)
+
     def _store_node_edges(self, node: NodeProto):
         for output_id in node.output:
             self._output_id_to_node[output_id] = node