Symintify embedding_sparse_backward (pytorch#88746)

Pull Request resolved: pytorch#88746
Approved by: https://github.com/ezyang

aten/src/ATen/native/Embedding.cpp

@@ -89,20 +89,20 @@ Tensor embedding_sparse_backward(
     grad = grad.index(c);
   }
 
-  int64_t num_features = grad_.size(-1);
-  auto weight_size = std::array<int64_t, 2>{{ num_weights, num_features }};
+  auto num_features = grad_.sym_size(-1);
+  auto weight_size = std::array<c10::SymInt, 2>{{ num_weights, num_features }};
   auto dense_options = grad.options();
 
   // check if all our grad come from padding_idx
-  if (grad.numel() == 0) {
-    return at::_sparse_coo_tensor_unsafe(at::empty({1, 0}, indices_.options().dtype(kLong)),
-                                         at::empty({0, num_features}, dense_options),
+  if (grad.sym_numel() == 0) {
+    return at::_sparse_coo_tensor_unsafe_symint(at::empty({1, 0}, indices_.options().dtype(kLong)),
+                                         at::empty_symint({c10::SymInt(0), num_features}, dense_options),
                                          weight_size);
   }
 
   auto index = indices.reshape({1, -1});
-  auto values = grad.reshape({-1, num_features});
-  return at::_sparse_coo_tensor_unsafe(index.to(kLong), values, weight_size);
+  auto values = grad.reshape_symint({c10::SymInt(-1), num_features});
+  return at::_sparse_coo_tensor_unsafe_symint(index.to(kLong), values, weight_size);
 }
 
 Tensor embedding_dense_backward_cpu(