fix reader of print_flops (#4959)

ppdet/engine/trainer.py

@@ -370,7 +370,9 @@ class Trainer(object):
         self.status['training_staus'] = stats.TrainingStats(self.cfg.log_iter)
 
         if self.cfg.get('print_flops', False):
-            self._flops(self.loader)
+            flops_loader = create('{}Reader'.format(self.mode.capitalize()))(
+                self.dataset, self.cfg.worker_num)
+            self._flops(flops_loader)
         profiler_options = self.cfg.get('profiler_options', None)
 
         self._compose_callback.on_train_begin(self.status)
@@ -469,7 +471,9 @@ class Trainer(object):
         self.status['mode'] = 'eval'
         self.model.eval()
         if self.cfg.get('print_flops', False):
-            self._flops(loader)
+            flops_loader = create('{}Reader'.format(self.mode.capitalize()))(
+                self.dataset, self.cfg.worker_num, self._eval_batch_sampler)
+            self._flops(flops_loader)
         for step_id, data in enumerate(loader):
             self.status['step_id'] = step_id
             self._compose_callback.on_step_begin(self.status)
@@ -520,7 +524,8 @@ class Trainer(object):
         self.status['mode'] = 'test'
         self.model.eval()
         if self.cfg.get('print_flops', False):
-            self._flops(loader)
+            flops_loader = create('TestReader')(self.dataset, 0)
+            self._flops(flops_loader)
         results = []
         for step_id, data in enumerate(loader):
             self.status['step_id'] = step_id