1 // Copyright 2013 the V8 project authors. All rights reserved. 2 // Redistribution and use in source and binary forms, with or without 3 // modification, are permitted provided that the following conditions are 4 // met: 5 // 6 // * Redistributions of source code must retain the above copyright 7 // notice, this list of conditions and the following disclaimer. 8 // * Redistributions in binary form must reproduce the above 9 // copyright notice, this list of conditions and the following 10 // disclaimer in the documentation and/or other materials provided 11 // with the distribution. 12 // * Neither the name of Google Inc. nor the names of its 13 // contributors may be used to endorse or promote products derived 14 // from this software without specific prior written permission. 15 // 16 // THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS 17 // "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT 18 // LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR 19 // A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT 20 // OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, 21 // SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT 22 // LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, 23 // DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY 24 // THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT 25 // (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE 26 // OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. 27 28 #include "hydrogen-infer-representation.h" 29 30 namespace v8 { 31 namespace internal { 32 33 void HInferRepresentationPhase::AddToWorklist(HValue* current) { 34 if (current->representation().IsTagged()) return; 35 if (!current->CheckFlag(HValue::kFlexibleRepresentation)) return; 36 if (in_worklist_.Contains(current->id())) return; 37 worklist_.Add(current, zone()); 38 in_worklist_.Add(current->id()); 39 } 40 41 42 void HInferRepresentationPhase::Run() { 43 // (1) Initialize bit vectors and count real uses. Each phi gets a 44 // bit-vector of length <number of phis>. 45 const ZoneList<HPhi*>* phi_list = graph()->phi_list(); 46 int phi_count = phi_list->length(); 47 ZoneList<BitVector*> connected_phis(phi_count, zone()); 48 for (int i = 0; i < phi_count; ++i) { 49 phi_list->at(i)->InitRealUses(i); 50 BitVector* connected_set = new(zone()) BitVector(phi_count, zone()); 51 connected_set->Add(i); 52 connected_phis.Add(connected_set, zone()); 53 } 54 55 // (2) Do a fixed point iteration to find the set of connected phis. A 56 // phi is connected to another phi if its value is used either directly or 57 // indirectly through a transitive closure of the def-use relation. 58 bool change = true; 59 while (change) { 60 change = false; 61 // We normally have far more "forward edges" than "backward edges", 62 // so we terminate faster when we walk backwards. 63 for (int i = phi_count - 1; i >= 0; --i) { 64 HPhi* phi = phi_list->at(i); 65 for (HUseIterator it(phi->uses()); !it.Done(); it.Advance()) { 66 HValue* use = it.value(); 67 if (use->IsPhi()) { 68 int id = HPhi::cast(use)->phi_id(); 69 if (connected_phis[i]->UnionIsChanged(*connected_phis[id])) 70 change = true; 71 } 72 } 73 } 74 } 75 76 // Set truncation flags for groups of connected phis. This is a conservative 77 // approximation; the flag will be properly re-computed after representations 78 // have been determined. 79 if (phi_count > 0) { 80 BitVector done(phi_count, zone()); 81 for (int i = 0; i < phi_count; ++i) { 82 if (done.Contains(i)) continue; 83 84 // Check if all uses of all connected phis in this group are truncating. 85 bool all_uses_everywhere_truncating = true; 86 for (BitVector::Iterator it(connected_phis[i]); 87 !it.Done(); 88 it.Advance()) { 89 int index = it.Current(); 90 all_uses_everywhere_truncating &= 91 phi_list->at(index)->CheckFlag(HInstruction::kTruncatingToInt32); 92 done.Add(index); 93 } 94 if (all_uses_everywhere_truncating) { 95 continue; // Great, nothing to do. 96 } 97 // Clear truncation flag of this group of connected phis. 98 for (BitVector::Iterator it(connected_phis[i]); 99 !it.Done(); 100 it.Advance()) { 101 int index = it.Current(); 102 phi_list->at(index)->ClearFlag(HInstruction::kTruncatingToInt32); 103 } 104 } 105 } 106 107 // Simplify constant phi inputs where possible. 108 // This step uses kTruncatingToInt32 flags of phis. 109 for (int i = 0; i < phi_count; ++i) { 110 phi_list->at(i)->SimplifyConstantInputs(); 111 } 112 113 // Use the phi reachability information from step 2 to 114 // sum up the non-phi use counts of all connected phis. 115 for (int i = 0; i < phi_count; ++i) { 116 HPhi* phi = phi_list->at(i); 117 for (BitVector::Iterator it(connected_phis[i]); 118 !it.Done(); 119 it.Advance()) { 120 int index = it.Current(); 121 HPhi* it_use = phi_list->at(index); 122 if (index != i) phi->AddNonPhiUsesFrom(it_use); // Don't count twice. 123 } 124 } 125 126 // Initialize work list 127 for (int i = 0; i < graph()->blocks()->length(); ++i) { 128 HBasicBlock* block = graph()->blocks()->at(i); 129 const ZoneList<HPhi*>* phis = block->phis(); 130 for (int j = 0; j < phis->length(); ++j) { 131 AddToWorklist(phis->at(j)); 132 } 133 134 for (HInstructionIterator it(block); !it.Done(); it.Advance()) { 135 HInstruction* current = it.Current(); 136 AddToWorklist(current); 137 } 138 } 139 140 // Do a fixed point iteration, trying to improve representations 141 while (!worklist_.is_empty()) { 142 HValue* current = worklist_.RemoveLast(); 143 in_worklist_.Remove(current->id()); 144 current->InferRepresentation(this); 145 } 146 147 // Lastly: any instruction that we don't have representation information 148 // for defaults to Tagged. 149 for (int i = 0; i < graph()->blocks()->length(); ++i) { 150 HBasicBlock* block = graph()->blocks()->at(i); 151 const ZoneList<HPhi*>* phis = block->phis(); 152 for (int j = 0; j < phis->length(); ++j) { 153 HPhi* phi = phis->at(j); 154 if (phi->representation().IsNone()) { 155 phi->ChangeRepresentation(Representation::Tagged()); 156 } 157 } 158 for (HInstructionIterator it(block); !it.Done(); it.Advance()) { 159 HInstruction* current = it.Current(); 160 if (current->representation().IsNone() && 161 current->CheckFlag(HInstruction::kFlexibleRepresentation)) { 162 if (current->CheckFlag(HInstruction::kCannotBeTagged)) { 163 current->ChangeRepresentation(Representation::Double()); 164 } else { 165 current->ChangeRepresentation(Representation::Tagged()); 166 } 167 } 168 } 169 } 170 } 171 172 } } // namespace v8::internal 173