Merge changes from github.

PiperOrigin-RevId: 194031845

2 files changed, 20 insertions, 3 deletions

diff --git a/tensorflow/contrib/crf/python/kernel_tests/crf_test.py b/tensorflow/contrib/crf/python/kernel_tests/crf_test.py
index 721dc4d080..a5e065b93a 100644
--- a/tensorflow/contrib/crf/python/kernel_tests/crf_test.py
+++ b/tensorflow/contrib/crf/python/kernel_tests/crf_test.py
@@ -281,6 +281,21 @@ class CrfTest(test.TestCase):
         self.assertEqual(list(tf_actual_max_sequence[:sequence_lengths]),
                          expected_max_sequence[:sequence_lengths])
 
+  def testCrfDecodeZeroSeqLength(self):
+    """
+    Test that crf_decode works when sequence_length contains one or more zeros.
+    """
+    with self.test_session() as sess:
+      inputs = constant_op.constant(np.ones([2, 10, 5],
+                                            dtype=np.float32))
+      transition_params = constant_op.constant(np.ones([5, 5],
+                                                       dtype=np.float32))
+      sequence_lengths = constant_op.constant(np.zeros([2],
+                                                       dtype=np.int32))
+      values = crf.crf_decode(inputs, transition_params, sequence_lengths)
+      tags, scores = sess.run(values)
+      self.assertEqual(len(tags.shape), 2)
+      self.assertEqual(len(scores.shape), 1)
 
 if __name__ == "__main__":
   test.main()
diff --git a/tensorflow/contrib/crf/python/ops/crf.py b/tensorflow/contrib/crf/python/ops/crf.py
index 1233c8f251..e37c029ceb 100644
--- a/tensorflow/contrib/crf/python/ops/crf.py
+++ b/tensorflow/contrib/crf/python/ops/crf.py
@@ -479,15 +479,17 @@ def crf_decode(potentials, transition_params, sequence_length):
     initial_state = array_ops.slice(potentials, [0, 0, 0], [-1, 1, -1])
     initial_state = array_ops.squeeze(initial_state, axis=[1])  # [B, O]
     inputs = array_ops.slice(potentials, [0, 1, 0], [-1, -1, -1])  # [B, T-1, O]
+    # sequence length is not allowed to be less than zero
+    sequence_length_less_one = math_ops.maximum(0, sequence_length - 1)
     backpointers, last_score = rnn.dynamic_rnn(  # [B, T - 1, O], [B, O]
         crf_fwd_cell,
         inputs=inputs,
-        sequence_length=sequence_length - 1,
+        sequence_length=sequence_length_less_one,
         initial_state=initial_state,
         time_major=False,
         dtype=dtypes.int32)
     backpointers = gen_array_ops.reverse_sequence(  # [B, T - 1, O]
-        backpointers, sequence_length - 1, seq_dim=1)
+        backpointers, sequence_length_less_one, seq_dim=1)
 
     # Computes backward decoding. Extract tag indices from backpointers.
     crf_bwd_cell = CrfDecodeBackwardRnnCell(num_tags)
@@ -497,7 +499,7 @@ def crf_decode(potentials, transition_params, sequence_length):
     decode_tags, _ = rnn.dynamic_rnn(  # [B, T - 1, 1]
         crf_bwd_cell,
         inputs=backpointers,
-        sequence_length=sequence_length - 1,
+        sequence_length=sequence_length_less_one,
         initial_state=initial_state,
         time_major=False,
         dtype=dtypes.int32)