1 files changed, 91 insertions, 0 deletions
diff --git a/tensorflow/core/grappler/optimizers/data/noop_elimination.cc b/tensorflow/core/grappler/optimizers/data/noop_elimination.cc
new file mode 100644
index 0000000000..55d57b3b97
--- /dev/null
+++ b/tensorflow/core/grappler/optimizers/data/noop_elimination.cc
@@ -0,0 +1,91 @@
+/* Copyright 2018 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.
+==============================================================================*/
+
+#include "tensorflow/core/grappler/optimizers/data/noop_elimination.h"
+
+#include "tensorflow/core/framework/attr_value.pb.h"
+#include "tensorflow/core/framework/node_def.pb.h"
+#include "tensorflow/core/grappler/clusters/cluster.h"
+#include "tensorflow/core/grappler/grappler_item.h"
+#include "tensorflow/core/grappler/mutable_graph_view.h"
+#include "tensorflow/core/grappler/op_types.h"
+#include "tensorflow/core/grappler/optimizers/custom_graph_optimizer_registry.h"
+#include "tensorflow/core/grappler/optimizers/data/graph_utils.h"
+#include "tensorflow/core/grappler/utils.h"
+#include "tensorflow/core/platform/protobuf.h"
+
+namespace tensorflow {
+namespace grappler {
+namespace {
+
+bool IsTakeAll(const NodeDef& take_node, const GraphView& graph) {
+  if (take_node.op() != "TakeDataset") return false;
+
+  const NodeDef& count_node = *graph.GetNode(take_node.input(1));
+  // We are looking only for 'take' with negative count.
+  return count_node.attr().at("value").tensor().int64_val(0) < 0;
+}
+
+bool IsSkipNone(const NodeDef& skip_node, const GraphView& graph) {
+  if (skip_node.op() != "SkipDataset") return false;
+
+  const NodeDef& count_node = *graph.GetNode(skip_node.input(1));
+  // We are looking only for skip(0) nodes.
+  return count_node.attr().at("value").tensor().int64_val(0) == 0;
+}
+
+bool IsRepeatOne(const NodeDef& repeat_node, const GraphView& graph) {
+  if (repeat_node.op() != "RepeatDataset") return false;
+
+  const NodeDef& count_node = *graph.GetNode(repeat_node.input(1));
+  // We are looking only for repeat(1) nodes.
+  return count_node.attr().at("value").tensor().int64_val(0) == 1;
+}
+
+bool IsNoOp(const NodeDef& node, const GraphView& graph) {
+  return IsTakeAll(node, graph) || IsSkipNone(node, graph) ||
+         IsRepeatOne(node, graph);
+}
+
+}  // namespace
+
+Status NoOpElimination::Optimize(Cluster* cluster, const GrapplerItem& item,
+                                 GraphDef* output) {
+  *output = item.graph;
+  MutableGraphView graph(output);
+  std::set<string> nodes_to_delete;
+  for (const NodeDef& node : item.graph.node()) {
+    if (!IsNoOp(node, graph)) continue;
+
+    GraphView::InputPort input_port = graph.GetInputPort(node.name(), 0);
+    NodeDef* const parent = graph.GetRegularFanin(input_port).node;
+    graph.ReplaceInput(node, *parent);
+
+    nodes_to_delete.insert(node.name());
+  }
+
+  graph.DeleteNodes(nodes_to_delete);
+  return Status::OK();
+}
+
+void NoOpElimination::Feedback(Cluster* cluster, const GrapplerItem& item,
+                               const GraphDef& optimize_output, double result) {
+  // no-op
+}
+
+REGISTER_GRAPH_OPTIMIZER_AS(NoOpElimination, "noop_elimination");
+
+}  // end namespace grappler
+}  // end namespace tensorflow