1/* 2 * Copyright (C) 2015 The Android Open Source Project 3 * 4 * Licensed under the Apache License, Version 2.0 (the "License"); 5 * you may not use this file except in compliance with the License. 6 * You may obtain a copy of the License at 7 * 8 * http://www.apache.org/licenses/LICENSE-2.0 9 * 10 * Unless required by applicable law or agreed to in writing, software 11 * distributed under the License is distributed on an "AS IS" BASIS, 12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 13 * See the License for the specific language governing permissions and 14 * limitations under the License. 15 */ 16 17#include "licm.h" 18#include "side_effects_analysis.h" 19 20namespace art { 21 22static bool IsPhiOf(HInstruction* instruction, HBasicBlock* block) { 23 return instruction->IsPhi() && instruction->GetBlock() == block; 24} 25 26/** 27 * Returns whether `instruction` has all its inputs and environment defined 28 * before the loop it is in. 29 */ 30static bool InputsAreDefinedBeforeLoop(HInstruction* instruction) { 31 DCHECK(instruction->IsInLoop()); 32 HLoopInformation* info = instruction->GetBlock()->GetLoopInformation(); 33 for (HInputIterator it(instruction); !it.Done(); it.Advance()) { 34 HLoopInformation* input_loop = it.Current()->GetBlock()->GetLoopInformation(); 35 // We only need to check whether the input is defined in the loop. If it is not 36 // it is defined before the loop. 37 if (input_loop != nullptr && input_loop->IsIn(*info)) { 38 return false; 39 } 40 } 41 42 for (HEnvironment* environment = instruction->GetEnvironment(); 43 environment != nullptr; 44 environment = environment->GetParent()) { 45 for (size_t i = 0, e = environment->Size(); i < e; ++i) { 46 HInstruction* input = environment->GetInstructionAt(i); 47 if (input != nullptr) { 48 HLoopInformation* input_loop = input->GetBlock()->GetLoopInformation(); 49 if (input_loop != nullptr && input_loop->IsIn(*info)) { 50 // We can move an instruction that takes a loop header phi in the environment: 51 // we will just replace that phi with its first input later in `UpdateLoopPhisIn`. 52 bool is_loop_header_phi = IsPhiOf(input, info->GetHeader()); 53 if (!is_loop_header_phi) { 54 return false; 55 } 56 } 57 } 58 } 59 } 60 return true; 61} 62 63/** 64 * If `environment` has a loop header phi, we replace it with its first input. 65 */ 66static void UpdateLoopPhisIn(HEnvironment* environment, HLoopInformation* info) { 67 for (; environment != nullptr; environment = environment->GetParent()) { 68 for (size_t i = 0, e = environment->Size(); i < e; ++i) { 69 HInstruction* input = environment->GetInstructionAt(i); 70 if (input != nullptr && IsPhiOf(input, info->GetHeader())) { 71 environment->RemoveAsUserOfInput(i); 72 HInstruction* incoming = input->InputAt(0); 73 environment->SetRawEnvAt(i, incoming); 74 incoming->AddEnvUseAt(environment, i); 75 } 76 } 77 } 78} 79 80void LICM::Run() { 81 DCHECK(side_effects_.HasRun()); 82 83 // Only used during debug. 84 ArenaBitVector* visited = nullptr; 85 if (kIsDebugBuild) { 86 visited = new (graph_->GetArena()) ArenaBitVector(graph_->GetArena(), 87 graph_->GetBlocks().size(), 88 false, 89 kArenaAllocLICM); 90 } 91 92 // Post order visit to visit inner loops before outer loops. 93 for (HPostOrderIterator it(*graph_); !it.Done(); it.Advance()) { 94 HBasicBlock* block = it.Current(); 95 if (!block->IsLoopHeader()) { 96 // Only visit the loop when we reach the header. 97 continue; 98 } 99 100 HLoopInformation* loop_info = block->GetLoopInformation(); 101 SideEffects loop_effects = side_effects_.GetLoopEffects(block); 102 HBasicBlock* pre_header = loop_info->GetPreHeader(); 103 104 for (HBlocksInLoopIterator it_loop(*loop_info); !it_loop.Done(); it_loop.Advance()) { 105 HBasicBlock* inner = it_loop.Current(); 106 DCHECK(inner->IsInLoop()); 107 if (inner->GetLoopInformation() != loop_info) { 108 // Thanks to post order visit, inner loops were already visited. 109 DCHECK(visited->IsBitSet(inner->GetBlockId())); 110 continue; 111 } 112 if (kIsDebugBuild) { 113 visited->SetBit(inner->GetBlockId()); 114 } 115 116 if (loop_info->ContainsIrreducibleLoop()) { 117 // We cannot licm in an irreducible loop, or in a natural loop containing an 118 // irreducible loop. 119 continue; 120 } 121 DCHECK(!loop_info->IsIrreducible()); 122 123 // We can move an instruction that can throw only if it is the first 124 // throwing instruction in the loop. Note that the first potentially 125 // throwing instruction encountered that is not hoisted stops this 126 // optimization. Non-throwing instruction can still be hoisted. 127 bool found_first_non_hoisted_throwing_instruction_in_loop = !inner->IsLoopHeader(); 128 for (HInstructionIterator inst_it(inner->GetInstructions()); 129 !inst_it.Done(); 130 inst_it.Advance()) { 131 HInstruction* instruction = inst_it.Current(); 132 if (instruction->CanBeMoved() 133 && (!instruction->CanThrow() || !found_first_non_hoisted_throwing_instruction_in_loop) 134 && !instruction->GetSideEffects().MayDependOn(loop_effects) 135 && InputsAreDefinedBeforeLoop(instruction)) { 136 // We need to update the environment if the instruction has a loop header 137 // phi in it. 138 if (instruction->NeedsEnvironment()) { 139 UpdateLoopPhisIn(instruction->GetEnvironment(), loop_info); 140 } else { 141 DCHECK(!instruction->HasEnvironment()); 142 } 143 instruction->MoveBefore(pre_header->GetLastInstruction()); 144 MaybeRecordStat(MethodCompilationStat::kLoopInvariantMoved); 145 } else if (instruction->CanThrow()) { 146 // If `instruction` can throw, we cannot move further instructions 147 // that can throw as well. 148 found_first_non_hoisted_throwing_instruction_in_loop = true; 149 } 150 } 151 } 152 } 153} 154 155} // namespace art 156