Nicolas Geoffray | 804d093 | 2014-05-02 08:46:00 +0100 | [diff] [blame^] | 1 | /* |
| 2 | * Copyright (C) 2014 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 "ssa_liveness_analysis.h" |
| 18 | #include "nodes.h" |
| 19 | |
| 20 | namespace art { |
| 21 | |
| 22 | void SsaLivenessAnalysis::Analyze() { |
| 23 | NumberInstructions(); |
| 24 | ComputeSets(); |
| 25 | } |
| 26 | |
| 27 | void SsaLivenessAnalysis::NumberInstructions() { |
| 28 | int ssa_index = 0; |
| 29 | for (HReversePostOrderIterator it(graph_); !it.Done(); it.Advance()) { |
| 30 | HBasicBlock* block = it.Current(); |
| 31 | |
| 32 | for (HInstructionIterator it(*block->GetPhis()); !it.Done(); it.Advance()) { |
| 33 | HInstruction* current = it.Current(); |
| 34 | if (current->HasUses()) { |
| 35 | current->SetSsaIndex(ssa_index++); |
| 36 | } |
| 37 | } |
| 38 | |
| 39 | for (HInstructionIterator it(*block->GetInstructions()); !it.Done(); it.Advance()) { |
| 40 | HInstruction* current = it.Current(); |
| 41 | if (current->HasUses()) { |
| 42 | current->SetSsaIndex(ssa_index++); |
| 43 | } |
| 44 | } |
| 45 | } |
| 46 | number_of_ssa_values_ = ssa_index; |
| 47 | } |
| 48 | |
| 49 | void SsaLivenessAnalysis::ComputeSets() { |
| 50 | for (HReversePostOrderIterator it(graph_); !it.Done(); it.Advance()) { |
| 51 | HBasicBlock* block = it.Current(); |
| 52 | block_infos_.Put( |
| 53 | block->GetBlockId(), |
| 54 | new (graph_.GetArena()) BlockInfo(graph_.GetArena(), *block, number_of_ssa_values_)); |
| 55 | } |
| 56 | |
| 57 | // Compute the initial live_in, live_out, and kill sets. This method does not handle |
| 58 | // backward branches, therefore live_in and live_out sets are not yet correct. |
| 59 | ComputeInitialSets(); |
| 60 | |
| 61 | // Do a fixed point calculation to take into account backward branches, |
| 62 | // that will update live_in of loop headers, and therefore live_out and live_in |
| 63 | // of blocks in the loop. |
| 64 | ComputeLiveInAndLiveOutSets(); |
| 65 | } |
| 66 | |
| 67 | void SsaLivenessAnalysis::ComputeInitialSets() { |
| 68 | // Do a post orderr visit, adding inputs of instructions live in the block where |
| 69 | // that instruction is defined, and killing instructions that are being visited. |
| 70 | for (HPostOrderIterator it(graph_); !it.Done(); it.Advance()) { |
| 71 | HBasicBlock* block = it.Current(); |
| 72 | |
| 73 | BitVector* kill = GetKillSet(*block); |
| 74 | BitVector* live_in = GetLiveInSet(*block); |
| 75 | |
| 76 | for (HBackwardInstructionIterator it(*block->GetInstructions()); !it.Done(); it.Advance()) { |
| 77 | HInstruction* current = it.Current(); |
| 78 | if (current->HasSsaIndex()) { |
| 79 | kill->SetBit(current->GetSsaIndex()); |
| 80 | live_in->ClearBit(current->GetSsaIndex()); |
| 81 | } |
| 82 | |
| 83 | // All inputs of an instruction must be live. |
| 84 | for (size_t i = 0, e = current->InputCount(); i < e; ++i) { |
| 85 | DCHECK(current->InputAt(i)->HasSsaIndex()); |
| 86 | live_in->SetBit(current->InputAt(i)->GetSsaIndex()); |
| 87 | } |
| 88 | |
| 89 | if (current->HasEnvironment()) { |
| 90 | // All instructions in the environment must be live. |
| 91 | GrowableArray<HInstruction*>* environment = current->GetEnvironment()->GetVRegs(); |
| 92 | for (size_t i = 0, e = environment->Size(); i < e; ++i) { |
| 93 | HInstruction* instruction = environment->Get(i); |
| 94 | if (instruction != nullptr) { |
| 95 | DCHECK(instruction->HasSsaIndex()); |
| 96 | live_in->SetBit(instruction->GetSsaIndex()); |
| 97 | } |
| 98 | } |
| 99 | } |
| 100 | } |
| 101 | |
| 102 | for (HInstructionIterator it(*block->GetPhis()); !it.Done(); it.Advance()) { |
| 103 | HInstruction* current = it.Current(); |
| 104 | if (current->HasSsaIndex()) { |
| 105 | kill->SetBit(current->GetSsaIndex()); |
| 106 | live_in->ClearBit(current->GetSsaIndex()); |
| 107 | } |
| 108 | |
| 109 | // Mark a phi input live_in for its corresponding predecessor. |
| 110 | for (size_t i = 0, e = current->InputCount(); i < e; ++i) { |
| 111 | HInstruction* input = current->InputAt(i); |
| 112 | |
| 113 | HBasicBlock* predecessor = block->GetPredecessors()->Get(i); |
| 114 | size_t ssa_index = input->GetSsaIndex(); |
| 115 | BitVector* predecessor_kill = GetKillSet(*predecessor); |
| 116 | BitVector* predecessor_live_in = GetLiveInSet(*predecessor); |
| 117 | |
| 118 | // Phi inputs from a back edge have already been visited. If the back edge |
| 119 | // block defines that input, we should not add it to its live_in. |
| 120 | if (!predecessor_kill->IsBitSet(ssa_index)) { |
| 121 | predecessor_live_in->SetBit(ssa_index); |
| 122 | } |
| 123 | } |
| 124 | } |
| 125 | } |
| 126 | } |
| 127 | |
| 128 | void SsaLivenessAnalysis::ComputeLiveInAndLiveOutSets() { |
| 129 | bool changed; |
| 130 | do { |
| 131 | changed = false; |
| 132 | |
| 133 | for (HPostOrderIterator it(graph_); !it.Done(); it.Advance()) { |
| 134 | const HBasicBlock& block = *it.Current(); |
| 135 | |
| 136 | // The live_in set depends on the kill set (which does not |
| 137 | // change in this loop), and the live_out set. If the live_out |
| 138 | // set does not change, there is no need to update the live_in set. |
| 139 | if (UpdateLiveOut(block) && UpdateLiveIn(block)) { |
| 140 | changed = true; |
| 141 | } |
| 142 | } |
| 143 | } while (changed); |
| 144 | } |
| 145 | |
| 146 | bool SsaLivenessAnalysis::UpdateLiveOut(const HBasicBlock& block) { |
| 147 | BitVector* live_out = GetLiveOutSet(block); |
| 148 | bool changed = false; |
| 149 | // The live_out set of a block is the union of live_in sets of its successors. |
| 150 | for (size_t i = 0, e = block.GetSuccessors()->Size(); i < e; ++i) { |
| 151 | HBasicBlock* successor = block.GetSuccessors()->Get(i); |
| 152 | if (live_out->Union(GetLiveInSet(*successor))) { |
| 153 | changed = true; |
| 154 | } |
| 155 | } |
| 156 | return changed; |
| 157 | } |
| 158 | |
| 159 | |
| 160 | bool SsaLivenessAnalysis::UpdateLiveIn(const HBasicBlock& block) { |
| 161 | BitVector* live_out = GetLiveOutSet(block); |
| 162 | BitVector* kill = GetKillSet(block); |
| 163 | BitVector* live_in = GetLiveInSet(block); |
| 164 | // If live_out is updated (because of backward branches), we need to make |
| 165 | // sure instructions in live_out are also in live_in, unless they are killed |
| 166 | // by this block. |
| 167 | return live_in->UnionIfNotIn(live_out, kill); |
| 168 | } |
| 169 | |
| 170 | } // namespace art |