Support label_smoothing for cross_entropy in nestedtensor (#452)

Summary:
Pull Request resolved: #452

Adds awareness of the new `label_smoothing` functionality in `cross_entropy` added in pytorch/pytorch#63122 to nestedtensor's implementation.

Fixes broken test: `test.test_nested_tensor_functional.TestFunctional`.

Reviewed By: cpuhrsch

Differential Revision: D30730728

fbshipit-source-id: 04f146d6de7f764f165059e4b5654d7f39142e38

Author: jbschlosser

nestedtensor/csrc/python_functions.cpp

@@ -17,7 +17,8 @@ at::Tensor cross_entropy(
     c10::optional<bool>& size_average, // TODO: use
     c10::optional<int64_t>& ignore_index,
     c10::optional<bool>& reduce, // TODO: use
-    c10::optional<std::string>& reduction) {
+    c10::optional<std::string>& reduction,
+    c10::optional<double> label_smoothing) {
   F::CrossEntropyFuncOptions::reduction_t redct;
   if (reduction.value() == "mean" || reduction.value() == "none") {
     redct = torch::kMean;
@@ -32,6 +33,9 @@ at::Tensor cross_entropy(
   if (ignore_index.has_value()) {
     options = options.ignore_index(ignore_index.value());
   }
+  if (label_smoothing.has_value()) {
+    options = options.label_smoothing(label_smoothing.value());
+  }
 
   return map_nested_tensor(
       [&, options](at::Tensor input_tensor, at::Tensor target_tensor) {
@@ -244,23 +248,26 @@ void add_functions(pybind11::module m) {
          c10::optional<bool> size_average, // TODO: use
          c10::optional<int64_t> ignore_index,
          c10::optional<bool> reduce, // TODO: use
-         c10::optional<std::string> reduction) {
+         c10::optional<std::string> reduction,
+         c10::optional<double> label_smoothing) {
         return cross_entropy(
             input,
             target,
             weight,
             size_average,
             ignore_index,
             reduce,
-            reduction);
+            reduction,
+            label_smoothing);
       },
       py::arg("input"),
       py::arg("target"),
       py::arg("weight") = nullptr,
       py::arg("size_average") = true,
       py::arg("ignore_index") = -100,
       py::arg("reduce") = true,
-      py::arg("reduction") = "mean");
+      py::arg("reduction") = "mean",
+      py::arg("label_smoothing") = 0.0);
 }
 } // namespace nested_tensor
 } // namespace torch