String Tensor SplitToSequence fix (#19942)

Author: Craigacp

onnxruntime/core/providers/cpu/sequence/sequence_ops.cc

@@ -453,7 +453,7 @@ Status SplitToSequence::ComputeImpl(OpKernelContext& context, const Tensor& inpu
   int num_remaining_splits = 0;
   InlinedVector<int64_t> split_sizes;
   const bool is_string_type = input.IsDataTypeString();
-  const size_t element_size = (is_string_type) ? 0U : input.DataType()->Size();
+  const size_t element_size = input.DataType()->Size();
 
   // figure out split_scalar or split_sizes
   if (p_split_input) {

onnxruntime/test/providers/cpu/sequence/sequence_ops_test.cc

@@ -442,6 +442,19 @@ TEST(SequenceOpsTest, SplitToSequence_PositiveAxisScalarSplit) {
   test.Run();
 }
 
+TEST(SequenceOpsTest, SplitToSequence_StringSplit) {
+  OpTester test("SplitToSequence", 11);
+  test.AddInput<std::string>("input", {3}, std::vector<std::string>({"Test string", "Another string", "A third and much longer string"}));
+  int64_t axis = 0;
+  test.AddAttribute("axis", axis);
+  SeqTensors<std::string> output;
+  output.AddTensor({1}, {"Test string"});
+  output.AddTensor({1}, {"Another string"});
+  output.AddTensor({1}, {"A third and much longer string"});
+  test.AddSeqOutput("S2", output);
+  test.Run();
+}
+
 TEST(SequenceOpsTest, SplitToSequence_DefaultAxis0UnevenSplitFloat) {
   OpTester test("SplitToSequence", 11);
   test.AddInput<float>("input", {5, 2}, GetConsecutiveVector<float>(1.f, 10));