fix shared param grad_add op_device is null (#33875)

python/paddle/fluid/backward.py

@@ -462,6 +462,7 @@ def _addup_repetitive_outputs_(op_descs, block_idx):
     var_rename_count = collections.defaultdict(int)
     renamed_vars = collections.defaultdict(list)
     renamed_var_start_idx = collections.defaultdict(list)
+    var_device = collections.defaultdict(str)
     for idx, op_desc in enumerate(op_descs):
         op_device_attr_name = core.op_proto_and_checker_maker.kOpDeviceAttrName(
         )
@@ -528,16 +529,19 @@ def _addup_repetitive_outputs_(op_descs, block_idx):
                     arg_names[arg_idx] = new_name
                     op_desc.set_output(param_name, arg_names)
                     renamed_vars[var_name].append(new_name)
+                    # record the latest device, for shared param
+                    var_device[var_name] = op_device
 
     for var_name, inputs in six.iteritems(renamed_vars):
         if len(renamed_vars[var_name]) > 1:
             if len(renamed_vars[var_name]) > _MAX_ADD_NUM_:
-                _accumulate_gradients_by_sum_op_(var_name, renamed_vars,
-                                                 pending_sum_ops, len(op_descs))
+                _accumulate_gradients_by_sum_op_(
+                    var_name, renamed_vars, pending_sum_ops,
+                    len(op_descs), var_device[var_name])
             else:
-                _accumulate_gradients_by_add_ops_(var_name, renamed_vars,
-                                                  pending_sum_ops,
-                                                  len(op_descs))
+                _accumulate_gradients_by_add_ops_(
+                    var_name, renamed_vars, pending_sum_ops,
+                    len(op_descs), var_device[var_name])
 
     # sum_op descs are sorted according to their insert position
     for key, value in collections.OrderedDict(