Update loss.py

python/paddle/nn/functional/loss.py

@@ -1804,8 +1804,15 @@ def cross_entropy(input,
                             "when weight is provided"
                                  .format(input.shape[-1], weight.shape[-1]))
 
-            weight_gather = paddle.gather_nd(
-                weight, label)  #trans weight from class to sample, shape:N
+            valid_label = paddle.where(label == ignore_index,
+                                       paddle.zeros_like(label), label)
+            ignore_weight_mask = paddle.cast((label != ignore_index), input.dtype)
+            if ignore_weight_mask.ndim > 1 and ignore_weight_mask.shape[
+                    -1] == 1:
+                ignore_weight_mask = paddle.squeeze(ignore_weight_mask, -1)
+            weight_gather = paddle.gather_nd(weight, valid_label)
+            weight_gather = paddle.multiply(weight_gather, ignore_weight_mask)
+
             input_shape = list(label.shape)
             weight_gather_reshape = reshape(weight_gather, shape=input_shape)
         out = paddle.multiply(out, weight_gather_reshape, name=weight_name)