1 /* Copyright 2017 The TensorFlow Authors. All Rights Reserved. 2 3 Licensed under the Apache License, Version 2.0 (the "License"); 4 you may not use this file except in compliance with the License. 5 You may obtain a copy of the License at 6 7 http://www.apache.org/licenses/LICENSE-2.0 8 9 Unless required by applicable law or agreed to in writing, software 10 distributed under the License is distributed on an "AS IS" BASIS, 11 WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 12 See the License for the specific language governing permissions and 13 limitations under the License. 14 ==============================================================================*/ 15 16 #ifndef TENSORFLOW_COMPILER_XLA_SERVICE_WHILE_LOOP_SIMPLIFIER_H_ 17 #define TENSORFLOW_COMPILER_XLA_SERVICE_WHILE_LOOP_SIMPLIFIER_H_ 18 19 #include "tensorflow/compiler/xla/service/hlo_module.h" 20 #include "tensorflow/compiler/xla/service/hlo_pass_interface.h" 21 #include "tensorflow/compiler/xla/statusor.h" 22 23 namespace xla { 24 25 // HLO pass that makes the following transformations on while loops: 26 // 27 // - A while loop with static trip count of 0 is deleted. 28 // 29 // - A while loop with static trip count of 1 is replaced by its body (sans 30 // loop). 31 // 32 // - Elements of a while loop's tuple that the loop doesn't use are removed 33 // from the tuple. 34 // 35 // - If the while loop's parameter is a nested tuple, it's flattened to a 36 // single-level tuple. This is good because it usually reduces the number of 37 // kTuple instructions, but also because it unlocks additional optimizations 38 // (e.g. removing unused loop parameters). 39 // 40 // Flattening nested while loop tuples adds a whole mess of likely unnecessary 41 // kGetTupleElement and kTuple operations to the graph. We expect that tuple 42 // simplifier will be run afterwards. 43 // 44 class WhileLoopSimplifier : public HloModulePass { 45 public: ~WhileLoopSimplifier()46 ~WhileLoopSimplifier() override {} name()47 absl::string_view name() const override { return "simplify-while-loops"; } 48 StatusOr<bool> Run(HloModule* module) override; 49 }; 50 51 } // namespace xla 52 53 #endif // TENSORFLOW_COMPILER_XLA_SERVICE_WHILE_LOOP_SIMPLIFIER_H_ 54