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 19 #include "side_effects_analysis.h" 20 21 namespace art { 22 23 static bool IsPhiOf(HInstruction* instruction, HBasicBlock* block) { 24 return instruction->IsPhi() && instruction->GetBlock() == block; 25 } 26 27 /** 28 * Returns whether `instruction` has all its inputs and environment defined 29 * before the loop it is in. 30 */ 31 static bool InputsAreDefinedBeforeLoop(HInstruction* instruction) { 32 DCHECK(instruction->IsInLoop()); 33 HLoopInformation* info = instruction->GetBlock()->GetLoopInformation(); 34 for (const HInstruction* input : instruction->GetInputs()) { 35 HLoopInformation* input_loop = input->GetBlock()->GetLoopInformation(); 36 // We only need to check whether the input is defined in the loop. If it is not 37 // it is defined before the loop. 38 if (input_loop != nullptr && input_loop->IsIn(*info)) { 39 return false; 40 } 41 } 42 43 for (HEnvironment* environment = instruction->GetEnvironment(); 44 environment != nullptr; 45 environment = environment->GetParent()) { 46 for (size_t i = 0, e = environment->Size(); i < e; ++i) { 47 HInstruction* input = environment->GetInstructionAt(i); 48 if (input != nullptr) { 49 HLoopInformation* input_loop = input->GetBlock()->GetLoopInformation(); 50 if (input_loop != nullptr && input_loop->IsIn(*info)) { 51 // We can move an instruction that takes a loop header phi in the environment: 52 // we will just replace that phi with its first input later in `UpdateLoopPhisIn`. 53 bool is_loop_header_phi = IsPhiOf(input, info->GetHeader()); 54 if (!is_loop_header_phi) { 55 return false; 56 } 57 } 58 } 59 } 60 } 61 return true; 62 } 63 64 /** 65 * If `environment` has a loop header phi, we replace it with its first input. 66 */ 67 static void UpdateLoopPhisIn(HEnvironment* environment, HLoopInformation* info) { 68 for (; environment != nullptr; environment = environment->GetParent()) { 69 for (size_t i = 0, e = environment->Size(); i < e; ++i) { 70 HInstruction* input = environment->GetInstructionAt(i); 71 if (input != nullptr && IsPhiOf(input, info->GetHeader())) { 72 environment->RemoveAsUserOfInput(i); 73 HInstruction* incoming = input->InputAt(0); 74 environment->SetRawEnvAt(i, incoming); 75 incoming->AddEnvUseAt(environment, i); 76 } 77 } 78 } 79 } 80 81 void LICM::Run() { 82 DCHECK(side_effects_.HasRun()); 83 84 // Only used during debug. 85 ArenaBitVector* visited = nullptr; 86 if (kIsDebugBuild) { 87 visited = new (graph_->GetArena()) ArenaBitVector(graph_->GetArena(), 88 graph_->GetBlocks().size(), 89 false, 90 kArenaAllocLICM); 91 } 92 93 // Post order visit to visit inner loops before outer loops. 94 for (HBasicBlock* block : graph_->GetPostOrder()) { 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 as long as it is the first visible 124 // instruction (throw or write) in the loop. Note that the first potentially visible 125 // instruction that is not hoisted stops this optimization. Non-throwing instructions, 126 // on the other hand, can still be hoisted. 127 bool found_first_non_hoisted_visible_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_visible_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() || instruction->DoesAnyWrite()) { 146 // If `instruction` can do something visible (throw or write), 147 // we cannot move further instructions that can throw. 148 found_first_non_hoisted_visible_instruction_in_loop = true; 149 } 150 } 151 } 152 } 153 } 154 155 } // namespace art 156