Optimize performance of amp (#45188)

python/paddle/fluid/dygraph/amp/loss_scaler.py

@@ -278,14 +278,12 @@ class AmpScaler(object):
                 if param._grad_ivar() is not None
             ]
             param_grads_fp16 = [
-                param._grad_ivar() for param in optimizer._parameter_list
-                if (param._grad_ivar() is not None) and (
-                    param._grad_ivar().dtype == core.VarDesc.VarType.FP16)
+                param for param in param_grads
+                if param.dtype == core.VarDesc.VarType.FP16
             ]
             param_grads_fp32 = [
-                param._grad_ivar() for param in optimizer._parameter_list
-                if (param._grad_ivar() is not None) and (
-                    param._grad_ivar().dtype == core.VarDesc.VarType.FP32)
+                param for param in param_grads
+                if param.dtype == core.VarDesc.VarType.FP32
             ]
         if core.is_compiled_with_npu():
             float_status = _C_ops.alloc_float_status()
@@ -309,12 +307,7 @@ class AmpScaler(object):
                                                 param_grads_fp32,
                                                 self._temp_found_inf_fp32)
 
-        if len(param_grads_fp16) and len(param_grads_fp32):
         self._found_inf = self._temp_found_inf_fp16 or self._temp_found_inf_fp32
-        elif len(param_grads_fp16):
-            self._found_inf = self._temp_found_inf_fp16
-        else:
-            self._found_inf = self._temp_found_inf_fp32
 
         optimizer_state["state"] = OptimizerState.UNSCALED