Ben Murdoch | b8a8cc1 | 2014-11-26 15:28:44 +0000 | [diff] [blame] | 1 | // Copyright 2013 the V8 project authors. All rights reserved. |
| 2 | // Use of this source code is governed by a BSD-style license that can be |
| 3 | // found in the LICENSE file. |
| 4 | |
| 5 | #include "src/hydrogen-dce.h" |
| 6 | #include "src/v8.h" |
| 7 | |
| 8 | namespace v8 { |
| 9 | namespace internal { |
| 10 | |
| 11 | void HDeadCodeEliminationPhase::MarkLive( |
| 12 | HValue* instr, ZoneList<HValue*>* worklist) { |
| 13 | if (instr->CheckFlag(HValue::kIsLive)) return; // Already live. |
| 14 | |
| 15 | if (FLAG_trace_dead_code_elimination) PrintLive(NULL, instr); |
| 16 | |
| 17 | // Transitively mark all inputs of live instructions live. |
| 18 | worklist->Add(instr, zone()); |
| 19 | while (!worklist->is_empty()) { |
| 20 | HValue* instr = worklist->RemoveLast(); |
| 21 | instr->SetFlag(HValue::kIsLive); |
| 22 | for (int i = 0; i < instr->OperandCount(); ++i) { |
| 23 | HValue* input = instr->OperandAt(i); |
| 24 | if (!input->CheckFlag(HValue::kIsLive)) { |
| 25 | input->SetFlag(HValue::kIsLive); |
| 26 | worklist->Add(input, zone()); |
| 27 | if (FLAG_trace_dead_code_elimination) PrintLive(instr, input); |
| 28 | } |
| 29 | } |
| 30 | } |
| 31 | } |
| 32 | |
| 33 | |
| 34 | void HDeadCodeEliminationPhase::PrintLive(HValue* ref, HValue* instr) { |
| 35 | OFStream os(stdout); |
| 36 | os << "[MarkLive "; |
| 37 | if (ref != NULL) { |
| 38 | os << *ref; |
| 39 | } else { |
| 40 | os << "root "; |
| 41 | } |
Emily Bernier | d0a1eb7 | 2015-03-24 16:35:39 -0400 | [diff] [blame] | 42 | os << " -> " << *instr << "]" << std::endl; |
Ben Murdoch | b8a8cc1 | 2014-11-26 15:28:44 +0000 | [diff] [blame] | 43 | } |
| 44 | |
| 45 | |
| 46 | void HDeadCodeEliminationPhase::MarkLiveInstructions() { |
| 47 | ZoneList<HValue*> worklist(10, zone()); |
| 48 | |
| 49 | // Transitively mark all live instructions, starting from roots. |
| 50 | for (int i = 0; i < graph()->blocks()->length(); ++i) { |
| 51 | HBasicBlock* block = graph()->blocks()->at(i); |
| 52 | for (HInstructionIterator it(block); !it.Done(); it.Advance()) { |
| 53 | HInstruction* instr = it.Current(); |
| 54 | if (instr->CannotBeEliminated()) MarkLive(instr, &worklist); |
| 55 | } |
| 56 | for (int j = 0; j < block->phis()->length(); j++) { |
| 57 | HPhi* phi = block->phis()->at(j); |
| 58 | if (phi->CannotBeEliminated()) MarkLive(phi, &worklist); |
| 59 | } |
| 60 | } |
| 61 | |
| 62 | DCHECK(worklist.is_empty()); // Should have processed everything. |
| 63 | } |
| 64 | |
| 65 | |
| 66 | void HDeadCodeEliminationPhase::RemoveDeadInstructions() { |
| 67 | ZoneList<HPhi*> worklist(graph()->blocks()->length(), zone()); |
| 68 | |
| 69 | // Remove any instruction not marked kIsLive. |
| 70 | for (int i = 0; i < graph()->blocks()->length(); ++i) { |
| 71 | HBasicBlock* block = graph()->blocks()->at(i); |
| 72 | for (HInstructionIterator it(block); !it.Done(); it.Advance()) { |
| 73 | HInstruction* instr = it.Current(); |
| 74 | if (!instr->CheckFlag(HValue::kIsLive)) { |
| 75 | // Instruction has not been marked live, so remove it. |
| 76 | instr->DeleteAndReplaceWith(NULL); |
| 77 | } else { |
| 78 | // Clear the liveness flag to leave the graph clean for the next DCE. |
| 79 | instr->ClearFlag(HValue::kIsLive); |
| 80 | } |
| 81 | } |
| 82 | // Collect phis that are dead and remove them in the next pass. |
| 83 | for (int j = 0; j < block->phis()->length(); j++) { |
| 84 | HPhi* phi = block->phis()->at(j); |
| 85 | if (!phi->CheckFlag(HValue::kIsLive)) { |
| 86 | worklist.Add(phi, zone()); |
| 87 | } else { |
| 88 | phi->ClearFlag(HValue::kIsLive); |
| 89 | } |
| 90 | } |
| 91 | } |
| 92 | |
| 93 | // Process phis separately to avoid simultaneously mutating the phi list. |
| 94 | while (!worklist.is_empty()) { |
| 95 | HPhi* phi = worklist.RemoveLast(); |
| 96 | HBasicBlock* block = phi->block(); |
| 97 | phi->DeleteAndReplaceWith(NULL); |
| 98 | if (phi->HasMergedIndex()) { |
| 99 | block->RecordDeletedPhi(phi->merged_index()); |
| 100 | } |
| 101 | } |
| 102 | } |
| 103 | |
| 104 | } } // namespace v8::internal |