[ModelWrapper] add find_upstream helper function

src/finn/core/modelwrapper.py

@@ -262,6 +262,24 @@ class ModelWrapper:
         except ValueError:
             return None
 
+    def find_upstream(self, tensor_name, finder_fxn):
+        """Follow the producer chain upstream, calling finder_fxn on each upstream
+        node until it returns True or there are no nodes left. Returns the list
+        of nodes visited, or None if finder_fxn did not return True."""
+        visit_list = []
+        current_tensor = tensor_name
+        while True:
+            current_producer = self.find_producer(current_tensor)
+            if current_producer is None:
+                return []
+            else:
+                found = finder_fxn(current_producer)
+                visit_list.append(current_producer)
+                if found:
+                    return visit_list
+                else:
+                    current_tensor = current_producer.input[0]
+
     def find_consumer(self, tensor_name):
         """Finds and returns the node that consumes the tensor with given name.
         Currently only works for linear graphs."""