Fix

Author: co63oc

python/paddle/nn/functional/loss.py

@@ -3067,6 +3067,11 @@ def cross_entropy(
             #   so, reduce_sum all directly is ok
             return _C_ops.sum(out, [], None, False)
         elif reduction == "mean":
+            # when reduction is mean, use paddle.nan
+            if input.size == 0:
+                mask = paddle.full(out.shape, paddle.bool)
+                paddle.masked_fill_(out, mask, paddle.nan)
+
             # 1. if weight==none,
             #     numerator: reduce_sum all loss directly is ok causeof base_softmax_with_cross_entropy's inner logic
             #     denominator: count sample num with class_index!=ignore_index

test/legacy_test/test_cross_entropy_op.py

@@ -468,5 +468,34 @@ def test_input_dims():
             self.assertRaises(ValueError, test_input_dims)
 
 
+class TestCrossEntropyOp_ZeroSize(TestCrossEntropyOp):
+    def setUp(self):
+        self.op_type = "cross_entropy"
+        self.python_api = api_wrapper
+        self.soft_label = False
+        self.ignore_index = -100
+        self.dtype = np.float64
+        # 0-size
+        self.batch_size = 0
+        self.class_num = 10
+
+        self.init_dtype_type()
+        self.init_attr_type()
+        self.init_bs_class_num()
+        self.init_x()
+        self.init_label()
+        self.get_cross_entropy()
+
+        self.inputs = {"X": self.x, "Label": self.label}
+        self.outputs = {"Y": self.cross_entropy}
+        self.attrs = {
+            "soft_label": self.soft_label,
+            "ignore_index": self.ignore_index,
+        }
+
+    def get_cross_entropy(self):
+        self.cross_entropy = np.random.random([0, 1]).astype(np.float64)
+
+
 if __name__ == "__main__":
     unittest.main()