[tflite] Validate segment ids for segment_sum.

Segment identifiers in segment_sum should be in a 1-D tensor of same size as the first dimension of the input. The values of the tensor should be integers from {0, 1, 2, ... k-1}, where k is the first dimension of the input. The segment identifiers must not contain jumps and must be increasing.

See https://www.tensorflow.org/api_docs/python/tf/math#Segmentation as the source for these constraints.

PiperOrigin-RevId: 332510942
Change-Id: I898beaba00642c918bcd4b4d4ce893ebb190d869

tensorflow/lite/kernels/segment_sum.cc

@@ -34,11 +34,24 @@ TfLiteStatus ResizeOutputTensor(TfLiteContext* context,
                                 const TfLiteTensor* data,
                                 const TfLiteTensor* segment_ids,
                                 TfLiteTensor* output) {
-  int max_index = -1;
+  // Segment ids should be of same cardinality as first input dimension and they
+  // should be increasing by at most 1, from 0 (e.g., [0, 0, 1, 2, 3] is valid)
   const int segment_id_size = segment_ids->dims->data[0];
-  if (segment_id_size > 0) {
-    max_index = segment_ids->data.i32[segment_id_size - 1];
+  TF_LITE_ENSURE_EQ(context, segment_id_size, data->dims->data[0]);
+  int previous_segment_id = -1;
+  for (int i = 0; i < segment_id_size; i++) {
+    const int current_segment_id = GetTensorData<int32_t>(segment_ids)[i];
+    if (i == 0) {
+      TF_LITE_ENSURE_EQ(context, current_segment_id, 0);
+    } else {
+      int delta = current_segment_id - previous_segment_id;
+      TF_LITE_ENSURE(context, delta == 0 || delta == 1);
+    }
+    previous_segment_id = current_segment_id;
   }
+
+  const int max_index = previous_segment_id;
+
   const int data_rank = NumDimensions(data);
   TfLiteIntArray* output_shape = TfLiteIntArrayCreate(NumDimensions(data));
   output_shape->data[0] = max_index + 1;

tensorflow/lite/kernels/segment_sum_test.cc

@@ -110,5 +110,37 @@ TEST(SegmentSumOpModelTest, Float32Test_ThreeDimensions) {
   EXPECT_THAT(model.GetOutputShape(), ElementsAreArray({2, 2, 1}));
 }
 
+TEST(SegmentSumOpModelTest, TestFailIfSegmentsAreNotSorted) {
+  SegmentSumOpModel<int32_t> model({TensorType_INT32, {3, 2}},
+                                   {TensorType_INT32, {3}});
+  model.PopulateTensor<int32_t>(model.data(), {1, 2, 3, 4, 5, 6});
+  model.PopulateTensor<int32_t>(model.segment_ids(), {0, 3, 1});
+  ASSERT_EQ(model.InvokeUnchecked(), kTfLiteError);
+}
+
+TEST(SegmentSumOpModelTest, TestFailIfSegmentsAreNotConsecutive) {
+  SegmentSumOpModel<int32_t> model({TensorType_INT32, {3, 2}},
+                                   {TensorType_INT32, {3}});
+  model.PopulateTensor<int32_t>(model.data(), {1, 2, 3, 4, 5, 6});
+  model.PopulateTensor<int32_t>(model.segment_ids(), {0, 3, 5});
+  ASSERT_EQ(model.InvokeUnchecked(), kTfLiteError);
+}
+
+TEST(SegmentSumOpModelTest, TestFailIfSegmentsAreNegative) {
+  SegmentSumOpModel<int32_t> model({TensorType_INT32, {3, 2}},
+                                   {TensorType_INT32, {3}});
+  model.PopulateTensor<int32_t>(model.data(), {1, 2, 3, 4, 5, 6});
+  model.PopulateTensor<int32_t>(model.segment_ids(), {-1, 0, 1});
+  ASSERT_EQ(model.InvokeUnchecked(), kTfLiteError);
+}
+
+TEST(SegmentSumOpModelTest, TestFailIfSegmentsAreNotTheRightCardinality) {
+  SegmentSumOpModel<int32_t> model({TensorType_INT32, {3, 2}},
+                                   {TensorType_INT32, {2}});
+  model.PopulateTensor<int32_t>(model.data(), {1, 2, 3, 4, 5, 6});
+  model.PopulateTensor<int32_t>(model.segment_ids(), {0, 1});
+  ASSERT_EQ(model.InvokeUnchecked(), kTfLiteError);
+}
+
 }  // namespace
 }  // namespace tflite