ENH: add Relu6GradGrad (#13268)

* ENH: add Relu6GradGrad

* TST: add test case

* CLN: import nn_grad

* TST: add init value

tensorflow/python/BUILD

@@ -4201,6 +4201,19 @@ cuda_py_test(
     main = "client/session_benchmark.py",
 )
 
+cuda_py_test(
+    name = "nn_grad_test",
+    size = "small",
+    srcs = ["ops/nn_grad_test.py"],
+    additional_deps = [
+        ":client_testlib",
+        ":framework_for_generated_wrappers",
+        ":nn_grad",
+        ":nn_ops",
+        "//third_party/py/numpy",
+    ],
+)
+
 py_library(
     name = "tf_item",
     srcs = [

tensorflow/python/ops/nn_grad.py

@@ -352,6 +352,13 @@ def _Relu6Grad(op, grad):
   return gen_nn_ops._relu6_grad(grad, op.outputs[0])  # pylint: disable=protected-access
 
 
+@ops.RegisterGradient("Relu6Grad")
+def _Relu6GradGrad(op, grad):
+  x = op.inputs[1]
+  return (gen_nn_ops._relu6_grad(grad, x), array_ops.zeros(
+      shape=array_ops.shape(x), dtype=x.dtype))
+
+
 @ops.RegisterGradient("Elu")
 def _EluGrad(op, grad):
   return gen_nn_ops._elu_grad(grad, op.outputs[0])

tensorflow/python/ops/nn_grad_test.py

@@ -0,0 +1,48 @@
+# Copyright 2016 The TensorFlow Authors. All Rights Reserved.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+# ==============================================================================
+"""Tests for Python ops defined in nn_grad.py."""
+
+from __future__ import absolute_import
+from __future__ import division
+from __future__ import print_function
+
+import numpy as np
+
+from tensorflow.python.framework import constant_op
+from tensorflow.python.framework import dtypes
+from tensorflow.python.ops import gradient_checker
+from tensorflow.python.ops import gradients_impl
+from tensorflow.python.ops import nn_grad
+from tensorflow.python.ops import nn_ops
+from tensorflow.python.platform import test
+
+
+class Relu6OpTest(test.TestCase):
+  def testRelu6GradGrad(self):
+    inputs = constant_op.constant([[-2, -1, 1, 3], [5, 7, 8, 9]],
+                                  dtype=dtypes.float32)
+    x_init_value = np.array([[-3.5, -1.5, 2, 4], [4.5, 7.5, 8.5, 11]])
+    r = nn_ops.relu6(inputs)
+    r_g = gradients_impl.gradients(r, inputs)[0]
+    with self.test_session():
+      error = gradient_checker.compute_gradient_error(
+        inputs, inputs.get_shape().as_list(),
+        r_g, r_g.get_shape().as_list(),
+        x_init_value=x_init_value)
+      self.assertLess(error, 1e-4)
+
+
+if __name__ == "__main__":
+  test.main()