[dynamo][guards-log] Print nn module guard saved dict versions for debugging

torch/_dynamo/guards.py

@@ -480,7 +480,9 @@ def NN_MODULE(self, guard: Guard):
             )
             return
         name = self.check_fn_manager.add_extra_closure_var("__nn_module_guard", g)
-        self._produce_guard_code(guard, [f"{name}({ref})"])
+        # debug_msg is only for debugging help and goes to kwargs of guard call,
+        # which is ignored.
+        self._produce_guard_code(guard, [f'{name}({ref}, debug_msg="{g}")'])
 
     def FUNCTION_MATCH(self, guard: Guard):
         """things like torch.add and user defined functions"""

torch/csrc/dynamo/guards.cpp

@@ -651,6 +651,23 @@ static PyObject* NNModuleGuard_call(
   Py_RETURN_TRUE;
 }
 
+static PyObject* NNModuleGuard_repr(PyObject* self) {
+  // Prints versions of the module and the attributes.
+  NNModuleGuard* guard = (NNModuleGuard*)self;
+  std::ostringstream oss;
+  oss << "versions(mod=" << guard->dict_version_tag;
+
+  for (size_t index = 0;
+       index < sizeof(module_guard_attrs) / sizeof(module_guard_attrs[0]);
+       index++) {
+    oss << ", " << module_guard_attrs[index] << "="
+        << guard->attr_tags[index].dict_version_tag;
+  }
+
+  oss << ")";
+  return Py_BuildValue("s", oss.str().c_str());
+}
+
 static PyObject* nn_module_guard(PyObject* dummy, PyObject* obj) {
   // Uses a private tags introduced in PEP 509 - ma_version_tag to check if
   // there are any changes in the dict.
@@ -763,6 +780,7 @@ PyObject* torch_c_dynamo_guards_init() {
   NNModuleGuardType.tp_call = NNModuleGuard_call;
   NNModuleGuardType.tp_dealloc = (destructor)NNModuleGuard_dealloc;
   NNModuleGuardType.tp_flags = Py_TPFLAGS_DEFAULT;
+  NNModuleGuardType.tp_repr = NNModuleGuard_repr;
 
   GlobalStateGuardType.tp_name = "torch._C._dynamo.guards.GlobalStateGuard";
   GlobalStateGuardType.tp_basicsize = sizeof(GlobalStateGuard);