[PIR] Warning once in ir backward (#64696)

Author: SigureMo

python/paddle/autograd/backward_utils.py

@@ -14,8 +14,10 @@
 from __future__ import annotations
 
 import collections
+import logging
 import warnings
 from collections.abc import Sequence
+from functools import lru_cache
 from typing import Any
 
 from paddle import pir
@@ -660,3 +662,8 @@ def get_split_op(value):
         if op.name() == "builtin.split":
             return op
     return None
+
+
+@lru_cache
+def warning_once(message: str):
+    logging.warning(message)

python/paddle/autograd/ir_backward.py

@@ -45,6 +45,7 @@
     return_map_value_list,
     some_in_set,
     update_no_grad_set_by_stopgradient,
+    warning_once,
     while_prune_check,
 )
 from paddle.base.libpaddle.pir import (
@@ -906,7 +907,7 @@ def prepare_backward_prune_set(inputs, outputs):
                 for item in get_real_op_inputs(used_op):
                     outputs_fwd_set.add(item)
         else:
-            logging.warning("input provided by inputs has no use")
+            warning_once("input provided by inputs has no use")
 
     inputs_fwd_set = ValueSet()
     for output in outputs: