fix hsigmoid_loss (#49549)

python/paddle/fluid/tests/unittests/test_hsigmoid_op.py

@@ -735,6 +735,11 @@ class TestHSigmoidLossAPI(unittest.TestCase):
         x = paddle.to_tensor(np.reshape(x_arr, (10, 0)), dtype='float32')
         label = paddle.to_tensor([], dtype='int64')
         weight = paddle.to_tensor([], dtype='float32')
+        self.assertRaises(ValueError, F.hsigmoid_loss, x, label, 2, weight)
+
+        x = paddle.to_tensor(np.reshape(x_arr, [1, 0, 0, 1]), dtype='float32')
+        label = paddle.to_tensor(np.reshape(x_arr, [1, 1, 0]), dtype='int64')
+        weight = paddle.to_tensor([], dtype='float32')
         self.assertRaises(ValueError, F.hsigmoid_loss, x, label, 0, weight)
         paddle.enable_static()
 

python/paddle/nn/functional/loss.py

@@ -953,6 +953,11 @@ def hsigmoid_loss(
             #  [2.11009121]
             #  [1.92374969]]
     """
+    if num_classes < 2:
+        raise ValueError(
+            'Expected num_classes >= 2 (got {})'.format(num_classes)
+        )
+
     if in_dygraph_mode():
         out, _, _ = _C_ops.hsigmoid_loss(
             input,