fix fetch op rename_input bug in QAT export model (#38012)

python/paddle/fluid/contrib/slim/quantization/imperative/qat.py

@@ -484,7 +484,7 @@ class ImperativeQuantizeOutputs(object):
                 model_filename=model_filename,
                 params_filename=params_filename))
 
-        self._gather_scales(infer_program, scope)
+        self._gather_scales(infer_program, scope, fetch_targets)
 
         self._set_skip_quant_attr(infer_program)
 
@@ -520,10 +520,10 @@ class ImperativeQuantizeOutputs(object):
 
         return flag
 
-    def _gather_scales(self, program, scope):
+    def _gather_scales(self, program, scope, fetch_targets):
         """
         Get all scales from fake ops, save them into the corresponding ops
-        and delete all moving_average_abs_max_scale ops. 
+        and delete all moving_average_abs_max_scale ops.
         """
 
         def _gather_input_scale():
@@ -580,6 +580,11 @@ class ImperativeQuantizeOutputs(object):
 
                 for next_op in next_ops:
                     next_op._rename_input(out_var_name, in_var_name)
+                    # If next_op is `fetch` and out_var_name in fetch_targets,
+                    # fetch_targets must update to in_var_name when rename input.
+                    for i in range(len(fetch_targets)):
+                        if fetch_targets[i].name == out_var_name:
+                            fetch_targets[i] = block.var(in_var_name)
 
         _gather_input_scale()
         _gather_output_scale()