fix save_checkpoint bug with native amp

Author: tgisaturday

train.py

@@ -544,7 +544,7 @@ def main():
                 save_metric = eval_metrics[eval_metric]
                 best_metric, best_epoch = saver.save_checkpoint(
                     model, optimizer, args,
-                    epoch=epoch, model_ema=model_ema, metric=save_metric, use_amp=use_amp)
+                    epoch=epoch, model_ema=model_ema, metric=save_metric, use_amp=has_apex&use_amp)
 
     except KeyboardInterrupt:
         pass
@@ -647,8 +647,9 @@ def train_epoch(
 
         if saver is not None and args.recovery_interval and (
                 last_batch or (batch_idx + 1) % args.recovery_interval == 0):
+            
             saver.save_recovery(
-                model, optimizer, args, epoch, model_ema=model_ema, use_amp=use_amp, batch_idx=batch_idx)
+                model, optimizer, args, epoch, model_ema=model_ema, use_amp=has_apex&use_amp, batch_idx=batch_idx)
 
         if lr_scheduler is not None:
             lr_scheduler.step_update(num_updates=num_updates, metric=losses_m.avg)