feat(traced_module): delete value of node when it will not be used by any expr

GitOrigin-RevId: 3fb7350d018ca7e32e7552fc4644eb5f34c59913

imperative/python/megengine/traced_module/traced_module.py

@@ -756,24 +756,32 @@ class InternalGraph:
                 return not end_nodes_set
             return False
 
+        ref_count = lambda n: len(n.users) + (1 if n in self._outputs else 0)
+
         for n, v in zip(self._inputs, inputs):
-            node2value[n] = v
+            if ref_count(n) > 0:
+                node2value[n] = [v, ref_count(n)]
             if n in self._watch_point:
                 self._rst[n].append(v)
             if n in self._end_point and get_all_endnode_val(n, v):
                 return list(endnode2value[i] for i in self._end_point)
 
         for expr in self._exprs:
-            values = expr.interpret(*list(node2value[i] for i in expr.inputs))
+            values = expr.interpret(*list(node2value[i][0] for i in expr.inputs))
+            for n in expr.inputs:
+                node2value[n][1] -= 1
+                if node2value[n][1] == 0:
+                    node2value.pop(n)
             if values is not None:
                 for n, v in zip(expr.outputs, values):
-                    node2value[n] = v
+                    if ref_count(n) > 0:
+                        node2value[n] = [v, ref_count(n)]
                     if n in self._watch_point:
                         self._rst[n] = v
                     if self._end_point and get_all_endnode_val(n, v):
                         return list(endnode2value[i] for i in self._end_point)
 
-        return list(node2value[i] for i in self._outputs)
+        return list(node2value[i][0] for i in self._outputs)
 
     def eval(self, *inputs):
         assert len(inputs) == len(self._inputs) - 1
@@ -1575,6 +1583,7 @@ class TracedModule(Module):
                             for index, inp in enumerate(expr.inputs):
                                 if inp is call_out:
                                     expr.inputs[index] = repl_dict[out]
+                                    repl_dict[out].users.append(expr)
 
                         continue
                     repl_dict[out] = call.outputs[ind]