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+/* Copyright 2017 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.
+==============================================================================*/
+#ifndef TENSORFLOW_COMPILER_XLA_SERVICE_FUSION_QUEUE_H_
+#define TENSORFLOW_COMPILER_XLA_SERVICE_FUSION_QUEUE_H_
+
+#include <utility>
+
+#include "tensorflow/compiler/xla/service/hlo_instruction.h"
+
+namespace xla {
+
+// A queue interface that allows implementations to choose fusion candidates in
+// custom order.
+class FusionQueue {
+ public:
+  FusionQueue() = default;
+  virtual ~FusionQueue() = default;
+
+  // Dequeues the next fusion candidates: a consumer and the list of producers
+  // as operand indices.
+  virtual std::pair<HloInstruction*, std::vector<int64>>
+  DequeueNextInstructionAndOperandsToFuseInOrder() = 0;
+
+  // A callback passed to the queue implementation right before the producer is
+  // fused into the consumer.
+  virtual void PreFusion(HloInstruction* producer, HloInstruction* consumer) {}
+
+  // A callback passed to the queue implementation right after the fusion is
+  // created. Note that original_producer could have been destroyed.
+  virtual void OnFusingInstruction(HloInstruction* fusion,
+                                   HloInstruction* original_producer,
+                                   HloInstruction* original_consumer) {}
+
+  // A callback passed to the queue implementation to notify the removal of an
+  // instruction.
+  virtual void RemoveInstruction(HloInstruction* instruction) = 0;
+};
+
+}  // namespace xla
+
+#endif  // TENSORFLOW_COMPILER_XLA_SERVICE_FUSION_QUEUE_H_