Ben Murdoch | 4a90d5f | 2016-03-22 12:00:34 +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/crankshaft/hydrogen-infer-representation.h" |
| 6 | |
| 7 | namespace v8 { |
| 8 | namespace internal { |
| 9 | |
| 10 | void HInferRepresentationPhase::AddToWorklist(HValue* current) { |
| 11 | if (current->representation().IsTagged()) return; |
| 12 | if (!current->CheckFlag(HValue::kFlexibleRepresentation)) return; |
| 13 | if (in_worklist_.Contains(current->id())) return; |
| 14 | worklist_.Add(current, zone()); |
| 15 | in_worklist_.Add(current->id()); |
| 16 | } |
| 17 | |
| 18 | |
| 19 | void HInferRepresentationPhase::Run() { |
| 20 | // (1) Initialize bit vectors and count real uses. Each phi gets a |
| 21 | // bit-vector of length <number of phis>. |
| 22 | const ZoneList<HPhi*>* phi_list = graph()->phi_list(); |
| 23 | int phi_count = phi_list->length(); |
| 24 | ZoneList<BitVector*> connected_phis(phi_count, zone()); |
| 25 | for (int i = 0; i < phi_count; ++i) { |
| 26 | phi_list->at(i)->InitRealUses(i); |
| 27 | BitVector* connected_set = new(zone()) BitVector(phi_count, zone()); |
| 28 | connected_set->Add(i); |
| 29 | connected_phis.Add(connected_set, zone()); |
| 30 | } |
| 31 | |
| 32 | // (2) Do a fixed point iteration to find the set of connected phis. A |
| 33 | // phi is connected to another phi if its value is used either directly or |
| 34 | // indirectly through a transitive closure of the def-use relation. |
| 35 | bool change = true; |
| 36 | while (change) { |
| 37 | change = false; |
| 38 | // We normally have far more "forward edges" than "backward edges", |
| 39 | // so we terminate faster when we walk backwards. |
| 40 | for (int i = phi_count - 1; i >= 0; --i) { |
| 41 | HPhi* phi = phi_list->at(i); |
| 42 | for (HUseIterator it(phi->uses()); !it.Done(); it.Advance()) { |
| 43 | HValue* use = it.value(); |
| 44 | if (use->IsPhi()) { |
| 45 | int id = HPhi::cast(use)->phi_id(); |
| 46 | if (connected_phis[i]->UnionIsChanged(*connected_phis[id])) |
| 47 | change = true; |
| 48 | } |
| 49 | } |
| 50 | } |
| 51 | } |
| 52 | |
| 53 | // Set truncation flags for groups of connected phis. This is a conservative |
| 54 | // approximation; the flag will be properly re-computed after representations |
| 55 | // have been determined. |
| 56 | if (phi_count > 0) { |
| 57 | BitVector done(phi_count, zone()); |
| 58 | for (int i = 0; i < phi_count; ++i) { |
| 59 | if (done.Contains(i)) continue; |
| 60 | |
| 61 | // Check if all uses of all connected phis in this group are truncating. |
| 62 | bool all_uses_everywhere_truncating_int32 = true; |
| 63 | bool all_uses_everywhere_truncating_smi = true; |
| 64 | for (BitVector::Iterator it(connected_phis[i]); |
| 65 | !it.Done(); |
| 66 | it.Advance()) { |
| 67 | int index = it.Current(); |
| 68 | all_uses_everywhere_truncating_int32 &= |
| 69 | phi_list->at(index)->CheckFlag(HInstruction::kTruncatingToInt32); |
| 70 | all_uses_everywhere_truncating_smi &= |
| 71 | phi_list->at(index)->CheckFlag(HInstruction::kTruncatingToSmi); |
| 72 | done.Add(index); |
| 73 | } |
| 74 | |
| 75 | if (!all_uses_everywhere_truncating_int32) { |
| 76 | // Clear truncation flag of this group of connected phis. |
| 77 | for (BitVector::Iterator it(connected_phis[i]); |
| 78 | !it.Done(); |
| 79 | it.Advance()) { |
| 80 | int index = it.Current(); |
| 81 | phi_list->at(index)->ClearFlag(HInstruction::kTruncatingToInt32); |
| 82 | } |
| 83 | } |
| 84 | if (!all_uses_everywhere_truncating_smi) { |
| 85 | // Clear truncation flag of this group of connected phis. |
| 86 | for (BitVector::Iterator it(connected_phis[i]); |
| 87 | !it.Done(); |
| 88 | it.Advance()) { |
| 89 | int index = it.Current(); |
| 90 | phi_list->at(index)->ClearFlag(HInstruction::kTruncatingToSmi); |
| 91 | } |
| 92 | } |
| 93 | } |
| 94 | } |
| 95 | |
| 96 | // Simplify constant phi inputs where possible. |
| 97 | // This step uses kTruncatingToInt32 flags of phis. |
| 98 | for (int i = 0; i < phi_count; ++i) { |
| 99 | phi_list->at(i)->SimplifyConstantInputs(); |
| 100 | } |
| 101 | |
| 102 | // Use the phi reachability information from step 2 to |
| 103 | // sum up the non-phi use counts of all connected phis. |
| 104 | for (int i = 0; i < phi_count; ++i) { |
| 105 | HPhi* phi = phi_list->at(i); |
| 106 | for (BitVector::Iterator it(connected_phis[i]); |
| 107 | !it.Done(); |
| 108 | it.Advance()) { |
| 109 | int index = it.Current(); |
| 110 | HPhi* it_use = phi_list->at(index); |
| 111 | if (index != i) phi->AddNonPhiUsesFrom(it_use); // Don't count twice. |
| 112 | } |
| 113 | } |
| 114 | |
| 115 | // Initialize work list |
| 116 | for (int i = 0; i < graph()->blocks()->length(); ++i) { |
| 117 | HBasicBlock* block = graph()->blocks()->at(i); |
| 118 | const ZoneList<HPhi*>* phis = block->phis(); |
| 119 | for (int j = 0; j < phis->length(); ++j) { |
| 120 | AddToWorklist(phis->at(j)); |
| 121 | } |
| 122 | |
| 123 | for (HInstructionIterator it(block); !it.Done(); it.Advance()) { |
| 124 | HInstruction* current = it.Current(); |
| 125 | AddToWorklist(current); |
| 126 | } |
| 127 | } |
| 128 | |
| 129 | // Do a fixed point iteration, trying to improve representations |
| 130 | while (!worklist_.is_empty()) { |
| 131 | HValue* current = worklist_.RemoveLast(); |
| 132 | current->InferRepresentation(this); |
| 133 | in_worklist_.Remove(current->id()); |
| 134 | } |
| 135 | |
| 136 | // Lastly: any instruction that we don't have representation information |
| 137 | // for defaults to Tagged. |
| 138 | for (int i = 0; i < graph()->blocks()->length(); ++i) { |
| 139 | HBasicBlock* block = graph()->blocks()->at(i); |
| 140 | const ZoneList<HPhi*>* phis = block->phis(); |
| 141 | for (int j = 0; j < phis->length(); ++j) { |
| 142 | HPhi* phi = phis->at(j); |
| 143 | if (phi->representation().IsNone()) { |
| 144 | phi->ChangeRepresentation(Representation::Tagged()); |
| 145 | } |
| 146 | } |
| 147 | for (HInstructionIterator it(block); !it.Done(); it.Advance()) { |
| 148 | HInstruction* current = it.Current(); |
| 149 | if (current->representation().IsNone() && |
| 150 | current->CheckFlag(HInstruction::kFlexibleRepresentation)) { |
| 151 | if (current->CheckFlag(HInstruction::kCannotBeTagged)) { |
| 152 | current->ChangeRepresentation(Representation::Double()); |
| 153 | } else { |
| 154 | current->ChangeRepresentation(Representation::Tagged()); |
| 155 | } |
| 156 | } |
| 157 | } |
| 158 | } |
| 159 | } |
| 160 | |
| 161 | } // namespace internal |
| 162 | } // namespace v8 |