fix quant export model (#3655)

ppdet/engine/trainer.py

@@ -558,8 +558,7 @@ class Trainer(object):
                     shape=[None, 3, 192, 64], name='crops')
             })
 
-        # dy2st and save model
-        if 'slim' not in self.cfg or self.cfg['slim_type'] != 'QAT':
+
         static_model = paddle.jit.to_static(
                 self.model, input_spec=input_spec)
         # NOTE: dy2st do not pruned program, but jit.save will prune program
@@ -567,16 +566,19 @@ class Trainer(object):
         pruned_input_spec = self._prune_input_spec(
                 input_spec, static_model.forward.main_program,
                 static_model.forward.outputs)
+
+        # dy2st and save model
+        if 'slim' not in self.cfg or self.cfg['slim_type'] != 'QAT':
             paddle.jit.save(
                 static_model,
                 os.path.join(save_dir, 'model'),
                 input_spec=pruned_input_spec)
-            logger.info("Export model and saved in {}".format(save_dir))
         else:
             self.cfg.slim.save_quantized_model(
                 self.model,
                 os.path.join(save_dir, 'model'),
-                input_spec=input_spec)
+                input_spec=pruned_input_spec)
+        logger.info("Export model and saved in {}".format(save_dir))
 
     def _prune_input_spec(self, input_spec, program, targets):
         # try to prune static program to figure out pruned input spec