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-uint32-analysis.h" 6 7 namespace v8 { 8 namespace internal { 9 10 11 static bool IsUnsignedLoad(HLoadKeyed* instr) { 12 switch (instr->elements_kind()) { 13 case EXTERNAL_UINT8_ELEMENTS: 14 case EXTERNAL_UINT16_ELEMENTS: 15 case EXTERNAL_UINT32_ELEMENTS: 16 case EXTERNAL_UINT8_CLAMPED_ELEMENTS: 17 case UINT8_ELEMENTS: 18 case UINT16_ELEMENTS: 19 case UINT32_ELEMENTS: 20 case UINT8_CLAMPED_ELEMENTS: 21 return true; 22 default: 23 return false; 24 } 25 } 26 27 28 static bool IsUint32Operation(HValue* instr) { 29 return instr->IsShr() || 30 (instr->IsLoadKeyed() && IsUnsignedLoad(HLoadKeyed::cast(instr))) || 31 (instr->IsInteger32Constant() && instr->GetInteger32Constant() >= 0); 32 } 33 34 35 bool HUint32AnalysisPhase::IsSafeUint32Use(HValue* val, HValue* use) { 36 // Operations that operate on bits are safe. 37 if (use->IsBitwise() || use->IsShl() || use->IsSar() || use->IsShr()) { 38 return true; 39 } else if (use->IsSimulate()) { 40 // Deoptimization has special support for uint32. 41 return true; 42 } else if (use->IsChange()) { 43 // Conversions have special support for uint32. 44 // This ASSERT guards that the conversion in question is actually 45 // implemented. Do not extend the whitelist without adding 46 // support to LChunkBuilder::DoChange(). 47 ASSERT(HChange::cast(use)->to().IsDouble() || 48 HChange::cast(use)->to().IsSmi() || 49 HChange::cast(use)->to().IsTagged()); 50 return true; 51 } else if (use->IsStoreKeyed()) { 52 HStoreKeyed* store = HStoreKeyed::cast(use); 53 if (store->is_external()) { 54 // Storing a value into an external integer array is a bit level 55 // operation. 56 if (store->value() == val) { 57 // Clamping or a conversion to double should have beed inserted. 58 ASSERT(store->elements_kind() != EXTERNAL_UINT8_CLAMPED_ELEMENTS); 59 ASSERT(store->elements_kind() != EXTERNAL_FLOAT32_ELEMENTS); 60 ASSERT(store->elements_kind() != EXTERNAL_FLOAT64_ELEMENTS); 61 return true; 62 } 63 } 64 } else if (use->IsCompareNumericAndBranch()) { 65 HCompareNumericAndBranch* c = HCompareNumericAndBranch::cast(use); 66 return IsUint32Operation(c->left()) && IsUint32Operation(c->right()); 67 } 68 69 return false; 70 } 71 72 73 // Iterate over all uses and verify that they are uint32 safe: either don't 74 // distinguish between int32 and uint32 due to their bitwise nature or 75 // have special support for uint32 values. 76 // Encountered phis are optimistically treated as safe uint32 uses, 77 // marked with kUint32 flag and collected in the phis_ list. A separate 78 // pass will be performed later by UnmarkUnsafePhis to clear kUint32 from 79 // phis that are not actually uint32-safe (it requires fix point iteration). 80 bool HUint32AnalysisPhase::Uint32UsesAreSafe(HValue* uint32val) { 81 bool collect_phi_uses = false; 82 for (HUseIterator it(uint32val->uses()); !it.Done(); it.Advance()) { 83 HValue* use = it.value(); 84 85 if (use->IsPhi()) { 86 if (!use->CheckFlag(HInstruction::kUint32)) { 87 // There is a phi use of this value from a phi that is not yet 88 // collected in phis_ array. Separate pass is required. 89 collect_phi_uses = true; 90 } 91 92 // Optimistically treat phis as uint32 safe. 93 continue; 94 } 95 96 if (!IsSafeUint32Use(uint32val, use)) { 97 return false; 98 } 99 } 100 101 if (collect_phi_uses) { 102 for (HUseIterator it(uint32val->uses()); !it.Done(); it.Advance()) { 103 HValue* use = it.value(); 104 105 // There is a phi use of this value from a phi that is not yet 106 // collected in phis_ array. Separate pass is required. 107 if (use->IsPhi() && !use->CheckFlag(HInstruction::kUint32)) { 108 use->SetFlag(HInstruction::kUint32); 109 phis_.Add(HPhi::cast(use), zone()); 110 } 111 } 112 } 113 114 return true; 115 } 116 117 118 // Check if all operands to the given phi are marked with kUint32 flag. 119 bool HUint32AnalysisPhase::CheckPhiOperands(HPhi* phi) { 120 if (!phi->CheckFlag(HInstruction::kUint32)) { 121 // This phi is not uint32 safe. No need to check operands. 122 return false; 123 } 124 125 for (int j = 0; j < phi->OperandCount(); j++) { 126 HValue* operand = phi->OperandAt(j); 127 if (!operand->CheckFlag(HInstruction::kUint32)) { 128 // Lazily mark constants that fit into uint32 range with kUint32 flag. 129 if (operand->IsInteger32Constant() && 130 operand->GetInteger32Constant() >= 0) { 131 operand->SetFlag(HInstruction::kUint32); 132 continue; 133 } 134 135 // This phi is not safe, some operands are not uint32 values. 136 return false; 137 } 138 } 139 140 return true; 141 } 142 143 144 // Remove kUint32 flag from the phi itself and its operands. If any operand 145 // was a phi marked with kUint32 place it into a worklist for 146 // transitive clearing of kUint32 flag. 147 void HUint32AnalysisPhase::UnmarkPhi(HPhi* phi, ZoneList<HPhi*>* worklist) { 148 phi->ClearFlag(HInstruction::kUint32); 149 for (int j = 0; j < phi->OperandCount(); j++) { 150 HValue* operand = phi->OperandAt(j); 151 if (operand->CheckFlag(HInstruction::kUint32)) { 152 operand->ClearFlag(HInstruction::kUint32); 153 if (operand->IsPhi()) { 154 worklist->Add(HPhi::cast(operand), zone()); 155 } 156 } 157 } 158 } 159 160 161 void HUint32AnalysisPhase::UnmarkUnsafePhis() { 162 // No phis were collected. Nothing to do. 163 if (phis_.length() == 0) return; 164 165 // Worklist used to transitively clear kUint32 from phis that 166 // are used as arguments to other phis. 167 ZoneList<HPhi*> worklist(phis_.length(), zone()); 168 169 // Phi can be used as a uint32 value if and only if 170 // all its operands are uint32 values and all its 171 // uses are uint32 safe. 172 173 // Iterate over collected phis and unmark those that 174 // are unsafe. When unmarking phi unmark its operands 175 // and add it to the worklist if it is a phi as well. 176 // Phis that are still marked as safe are shifted down 177 // so that all safe phis form a prefix of the phis_ array. 178 int phi_count = 0; 179 for (int i = 0; i < phis_.length(); i++) { 180 HPhi* phi = phis_[i]; 181 182 if (CheckPhiOperands(phi) && Uint32UsesAreSafe(phi)) { 183 phis_[phi_count++] = phi; 184 } else { 185 UnmarkPhi(phi, &worklist); 186 } 187 } 188 189 // Now phis array contains only those phis that have safe 190 // non-phi uses. Start transitively clearing kUint32 flag 191 // from phi operands of discovered non-safe phis until 192 // only safe phis are left. 193 while (!worklist.is_empty()) { 194 while (!worklist.is_empty()) { 195 HPhi* phi = worklist.RemoveLast(); 196 UnmarkPhi(phi, &worklist); 197 } 198 199 // Check if any operands to safe phis were unmarked 200 // turning a safe phi into unsafe. The same value 201 // can flow into several phis. 202 int new_phi_count = 0; 203 for (int i = 0; i < phi_count; i++) { 204 HPhi* phi = phis_[i]; 205 206 if (CheckPhiOperands(phi)) { 207 phis_[new_phi_count++] = phi; 208 } else { 209 UnmarkPhi(phi, &worklist); 210 } 211 } 212 phi_count = new_phi_count; 213 } 214 } 215 216 217 void HUint32AnalysisPhase::Run() { 218 if (!graph()->has_uint32_instructions()) return; 219 220 ZoneList<HInstruction*>* uint32_instructions = graph()->uint32_instructions(); 221 for (int i = 0; i < uint32_instructions->length(); ++i) { 222 // Analyze instruction and mark it with kUint32 if all 223 // its uses are uint32 safe. 224 HInstruction* current = uint32_instructions->at(i); 225 if (current->IsLinked() && 226 current->representation().IsInteger32() && 227 Uint32UsesAreSafe(current)) { 228 current->SetFlag(HInstruction::kUint32); 229 } 230 } 231 232 // Some phis might have been optimistically marked with kUint32 flag. 233 // Remove this flag from those phis that are unsafe and propagate 234 // this information transitively potentially clearing kUint32 flag 235 // from some non-phi operations that are used as operands to unsafe phis. 236 UnmarkUnsafePhis(); 237 } 238 239 240 } } // namespace v8::internal 241
