fix fp16 bug

tools/train.py

@@ -119,9 +119,6 @@ def main(config, device, logger, vdl_writer):
             config['Loss']['ignore_index'] = char_num - 1
 
     model = build_model(config['Architecture'])
-    if config['Global']['distributed']:
-        model = paddle.DataParallel(model)
-
     model = apply_to_static(model, config, logger)
 
     # build loss
@@ -157,10 +154,13 @@ def main(config, device, logger, vdl_writer):
         scaler = paddle.amp.GradScaler(
             init_loss_scaling=scale_loss,
             use_dynamic_loss_scaling=use_dynamic_loss_scaling)
-        model, optimizer = paddle.amp.decorate(models=model, optimizers=optimizer, level='O2', master_weight=True)
+        model, optimizer = paddle.amp.decorate(
+            models=model, optimizers=optimizer, level='O2', master_weight=True)
     else:
         scaler = None
 
+    if config['Global']['distributed']:
+        model = paddle.DataParallel(model)
     # start train
     program.train(config, train_dataloader, valid_dataloader, device, model,
                   loss_class, optimizer, lr_scheduler, post_process_class,