1 /* Copyright 2022 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_REDUCE_DECOMPOSER_H_ 17 #define TENSORFLOW_COMPILER_XLA_SERVICE_REDUCE_DECOMPOSER_H_ 18 19 #include <functional> 20 21 #include "tensorflow/compiler/xla/service/hlo_pass_interface.h" 22 23 namespace xla { 24 25 // For each reduction R(I), ensures the postcondition: 26 // 27 // !custom_layout_allowed(R) 28 // => 29 // layout(R) == layout(I) # modulo removed dimensions 30 // 31 // To achieve that, decomposes layout-mutating reductions which do not satisfy 32 // `custom_layout_allowed` into a reduction and a copy. 33 // 34 // For a singular reduction: 35 // 36 // -> reduce -> 37 // 38 // Gets turned into: 39 // 40 // -> reduce -> copy -> 41 // 42 // For a variadic recuction, the layout assignment guarantees that the layout 43 // is the same for all outputs. This pass will transpose the variadic reduction 44 // inputs which have different physical layout to the first operand. 45 // 46 // A{L} \ 47 // B{L} -> reduce{L'} -> 48 // C{L} / 49 // 50 // Get turned into: 51 // 52 // A{L} \ / GTE(1) -> copy{L'} \ 53 // B{L} -> reduce{E(L)} --- GTE(2) -> copy{L'} - Tuple{L'} 54 // C{L} / \ GTE(3) -> copy{L'} / 55 // 56 // Where E(L) is expected layout of a reduction (original layout with reduce 57 // dimensions dropped). 58 // 59 // PRECONDITION: 60 // In variadic reduction, all outputs have the same layout 61 // (enforced by layout assignment). 62 class ReduceDecomposer : public HloModulePass { 63 public: 64 explicit ReduceDecomposer(HloPredicate custom_layout_allowed = nullptr) custom_layout_allowed_(custom_layout_allowed)65 : custom_layout_allowed_(custom_layout_allowed) {} 66 name()67 absl::string_view name() const override { return "reduce-decomposer"; } 68 69 using HloPassInterface::Run; 70 StatusOr<bool> Run( 71 HloModule* module, 72 const absl::flat_hash_set<absl::string_view>& execution_threads) override; 73 74 private: 75 HloPredicate custom_layout_allowed_; 76 }; 77 78 } // namespace xla 79 80 #endif // TENSORFLOW_COMPILER_XLA_SERVICE_REDUCE_DECOMPOSER_H_ 81