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| 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-alias-analysis.h" | |
| 6 #include "src/hydrogen-flow-engine.h" | |
| 7 #include "src/hydrogen-instructions.h" | |
| 8 #include "src/hydrogen-load-elimination.h" | |
| 9 | |
| 10 namespace v8 { | |
| 11 namespace internal { | |
| 12 | |
| 13 #define GLOBAL true | |
| 14 #define TRACE(x) if (FLAG_trace_load_elimination) PrintF x | |
| 15 | |
| 16 static const int kMaxTrackedFields = 16; | |
| 17 static const int kMaxTrackedObjects = 5; | |
| 18 | |
| 19 // An element in the field approximation list. | |
| 20 class HFieldApproximation : public ZoneObject { | |
| 21 public: // Just a data blob. | |
| 22 HValue* object_; | |
| 23 HValue* last_value_; | |
| 24 HFieldApproximation* next_; | |
| 25 | |
| 26 // Recursively copy the entire linked list of field approximations. | |
| 27 HFieldApproximation* Copy(Zone* zone) { | |
| 28 HFieldApproximation* copy = new(zone) HFieldApproximation(); | |
| 29 copy->object_ = this->object_; | |
| 30 copy->last_value_ = this->last_value_; | |
| 31 copy->next_ = this->next_ == NULL ? NULL : this->next_->Copy(zone); | |
| 32 return copy; | |
| 33 } | |
| 34 }; | |
| 35 | |
| 36 | |
| 37 // The main datastructure used during load/store elimination. Each in-object | |
| 38 // field is tracked separately. For each field, store a list of known field | |
| 39 // values for known objects. | |
| 40 class HLoadEliminationTable : public ZoneObject { | |
| 41 public: | |
| 42 HLoadEliminationTable(Zone* zone, HAliasAnalyzer* aliasing) | |
| 43 : zone_(zone), fields_(kMaxTrackedFields, zone), aliasing_(aliasing) { } | |
| 44 | |
| 45 // The main processing of instructions. | |
| 46 HLoadEliminationTable* Process(HInstruction* instr, Zone* zone) { | |
| 47 switch (instr->opcode()) { | |
| 48 case HValue::kLoadNamedField: { | |
| 49 HLoadNamedField* l = HLoadNamedField::cast(instr); | |
| 50 TRACE((" process L%d field %d (o%d)\n", | |
| 51 instr->id(), | |
| 52 FieldOf(l->access()), | |
| 53 l->object()->ActualValue()->id())); | |
| 54 HValue* result = load(l); | |
| 55 if (result != instr && l->CanBeReplacedWith(result)) { | |
| 56 // The load can be replaced with a previous load or a value. | |
| 57 TRACE((" replace L%d -> v%d\n", instr->id(), result->id())); | |
| 58 instr->DeleteAndReplaceWith(result); | |
| 59 } | |
| 60 break; | |
| 61 } | |
| 62 case HValue::kStoreNamedField: { | |
| 63 HStoreNamedField* s = HStoreNamedField::cast(instr); | |
| 64 TRACE((" process S%d field %d (o%d) = v%d\n", | |
| 65 instr->id(), | |
| 66 FieldOf(s->access()), | |
| 67 s->object()->ActualValue()->id(), | |
| 68 s->value()->id())); | |
| 69 HValue* result = store(s); | |
| 70 if (result == NULL) { | |
| 71 // The store is redundant. Remove it. | |
| 72 TRACE((" remove S%d\n", instr->id())); | |
| 73 instr->DeleteAndReplaceWith(NULL); | |
| 74 } | |
| 75 break; | |
| 76 } | |
| 77 case HValue::kTransitionElementsKind: { | |
| 78 HTransitionElementsKind* t = HTransitionElementsKind::cast(instr); | |
| 79 HValue* object = t->object()->ActualValue(); | |
| 80 KillFieldInternal(object, FieldOf(JSArray::kElementsOffset), NULL); | |
| 81 KillFieldInternal(object, FieldOf(JSObject::kMapOffset), NULL); | |
| 82 break; | |
| 83 } | |
| 84 default: { | |
| 85 if (instr->CheckChangesFlag(kInobjectFields)) { | |
| 86 TRACE((" kill-all i%d\n", instr->id())); | |
| 87 Kill(); | |
| 88 break; | |
| 89 } | |
| 90 if (instr->CheckChangesFlag(kMaps)) { | |
| 91 TRACE((" kill-maps i%d\n", instr->id())); | |
| 92 KillOffset(JSObject::kMapOffset); | |
| 93 } | |
| 94 if (instr->CheckChangesFlag(kElementsKind)) { | |
| 95 TRACE((" kill-elements-kind i%d\n", instr->id())); | |
| 96 KillOffset(JSObject::kMapOffset); | |
| 97 KillOffset(JSObject::kElementsOffset); | |
| 98 } | |
| 99 if (instr->CheckChangesFlag(kElementsPointer)) { | |
| 100 TRACE((" kill-elements i%d\n", instr->id())); | |
| 101 KillOffset(JSObject::kElementsOffset); | |
| 102 } | |
| 103 if (instr->CheckChangesFlag(kOsrEntries)) { | |
| 104 TRACE((" kill-osr i%d\n", instr->id())); | |
| 105 Kill(); | |
| 106 } | |
| 107 } | |
| 108 // Improvements possible: | |
| 109 // - learn from HCheckMaps for field 0 | |
| 110 // - remove unobservable stores (write-after-write) | |
| 111 // - track cells | |
| 112 // - track globals | |
| 113 // - track roots | |
| 114 } | |
| 115 return this; | |
| 116 } | |
| 117 | |
| 118 // Support for global analysis with HFlowEngine: Merge given state with | |
| 119 // the other incoming state. | |
| 120 static HLoadEliminationTable* Merge(HLoadEliminationTable* succ_state, | |
| 121 HBasicBlock* succ_block, | |
| 122 HLoadEliminationTable* pred_state, | |
| 123 HBasicBlock* pred_block, | |
| 124 Zone* zone) { | |
| 125 DCHECK(pred_state != NULL); | |
| 126 if (succ_state == NULL) { | |
| 127 return pred_state->Copy(succ_block, pred_block, zone); | |
| 128 } else { | |
| 129 return succ_state->Merge(succ_block, pred_state, pred_block, zone); | |
| 130 } | |
| 131 } | |
| 132 | |
| 133 // Support for global analysis with HFlowEngine: Given state merged with all | |
| 134 // the other incoming states, prepare it for use. | |
| 135 static HLoadEliminationTable* Finish(HLoadEliminationTable* state, | |
| 136 HBasicBlock* block, | |
| 137 Zone* zone) { | |
| 138 DCHECK(state != NULL); | |
| 139 return state; | |
| 140 } | |
| 141 | |
| 142 private: | |
| 143 // Copy state to successor block. | |
| 144 HLoadEliminationTable* Copy(HBasicBlock* succ, HBasicBlock* from_block, | |
| 145 Zone* zone) { | |
| 146 HLoadEliminationTable* copy = | |
| 147 new(zone) HLoadEliminationTable(zone, aliasing_); | |
| 148 copy->EnsureFields(fields_.length()); | |
| 149 for (int i = 0; i < fields_.length(); i++) { | |
| 150 copy->fields_[i] = fields_[i] == NULL ? NULL : fields_[i]->Copy(zone); | |
| 151 } | |
| 152 if (FLAG_trace_load_elimination) { | |
| 153 TRACE((" copy-to B%d\n", succ->block_id())); | |
| 154 copy->Print(); | |
| 155 } | |
| 156 return copy; | |
| 157 } | |
| 158 | |
| 159 // Merge this state with the other incoming state. | |
| 160 HLoadEliminationTable* Merge(HBasicBlock* succ, HLoadEliminationTable* that, | |
| 161 HBasicBlock* that_block, Zone* zone) { | |
| 162 if (that->fields_.length() < fields_.length()) { | |
| 163 // Drop fields not in the other table. | |
| 164 fields_.Rewind(that->fields_.length()); | |
| 165 } | |
| 166 for (int i = 0; i < fields_.length(); i++) { | |
| 167 // Merge the field approximations for like fields. | |
| 168 HFieldApproximation* approx = fields_[i]; | |
| 169 HFieldApproximation* prev = NULL; | |
| 170 while (approx != NULL) { | |
| 171 // TODO(titzer): Merging is O(N * M); sort? | |
| 172 HFieldApproximation* other = that->Find(approx->object_, i); | |
| 173 if (other == NULL || !Equal(approx->last_value_, other->last_value_)) { | |
| 174 // Kill an entry that doesn't agree with the other value. | |
| 175 if (prev != NULL) { | |
| 176 prev->next_ = approx->next_; | |
| 177 } else { | |
| 178 fields_[i] = approx->next_; | |
| 179 } | |
| 180 approx = approx->next_; | |
| 181 continue; | |
| 182 } | |
| 183 prev = approx; | |
| 184 approx = approx->next_; | |
| 185 } | |
| 186 } | |
| 187 if (FLAG_trace_load_elimination) { | |
| 188 TRACE((" merge-to B%d\n", succ->block_id())); | |
| 189 Print(); | |
| 190 } | |
| 191 return this; | |
| 192 } | |
| 193 | |
| 194 friend class HLoadEliminationEffects; // Calls Kill() and others. | |
| 195 friend class HLoadEliminationPhase; | |
| 196 | |
| 197 private: | |
| 198 // Process a load instruction, updating internal table state. If a previous | |
| 199 // load or store for this object and field exists, return the new value with | |
| 200 // which the load should be replaced. Otherwise, return {instr}. | |
| 201 HValue* load(HLoadNamedField* instr) { | |
| 202 // There must be no loads from non observable in-object properties. | |
| 203 DCHECK(!instr->access().IsInobject() || | |
| 204 instr->access().existing_inobject_property()); | |
| 205 | |
| 206 int field = FieldOf(instr->access()); | |
| 207 if (field < 0) return instr; | |
| 208 | |
| 209 HValue* object = instr->object()->ActualValue(); | |
| 210 HFieldApproximation* approx = FindOrCreate(object, field); | |
| 211 | |
| 212 if (approx->last_value_ == NULL) { | |
| 213 // Load is not redundant. Fill out a new entry. | |
| 214 approx->last_value_ = instr; | |
| 215 return instr; | |
| 216 } else if (approx->last_value_->block()->EqualToOrDominates( | |
| 217 instr->block())) { | |
| 218 // Eliminate the load. Reuse previously stored value or load instruction. | |
| 219 return approx->last_value_; | |
| 220 } else { | |
| 221 return instr; | |
| 222 } | |
| 223 } | |
| 224 | |
| 225 // Process a store instruction, updating internal table state. If a previous | |
| 226 // store to the same object and field makes this store redundant (e.g. because | |
| 227 // the stored values are the same), return NULL indicating that this store | |
| 228 // instruction is redundant. Otherwise, return {instr}. | |
| 229 HValue* store(HStoreNamedField* instr) { | |
| 230 if (instr->access().IsInobject() && | |
| 231 !instr->access().existing_inobject_property()) { | |
| 232 TRACE((" skipping non existing property initialization store\n")); | |
| 233 return instr; | |
| 234 } | |
| 235 | |
| 236 int field = FieldOf(instr->access()); | |
| 237 if (field < 0) return KillIfMisaligned(instr); | |
| 238 | |
| 239 HValue* object = instr->object()->ActualValue(); | |
| 240 HValue* value = instr->value(); | |
| 241 | |
| 242 if (instr->has_transition()) { | |
| 243 // A transition introduces a new field and alters the map of the object. | |
| 244 // Since the field in the object is new, it cannot alias existing entries. | |
| 245 // TODO(titzer): introduce a constant for the new map and remember it. | |
| 246 KillFieldInternal(object, FieldOf(JSObject::kMapOffset), NULL); | |
| 247 } else { | |
| 248 // Kill non-equivalent may-alias entries. | |
| 249 KillFieldInternal(object, field, value); | |
| 250 } | |
| 251 HFieldApproximation* approx = FindOrCreate(object, field); | |
| 252 | |
| 253 if (Equal(approx->last_value_, value)) { | |
| 254 // The store is redundant because the field already has this value. | |
| 255 return NULL; | |
| 256 } else { | |
| 257 // The store is not redundant. Update the entry. | |
| 258 approx->last_value_ = value; | |
| 259 return instr; | |
| 260 } | |
| 261 } | |
| 262 | |
| 263 // Kill everything in this table. | |
| 264 void Kill() { | |
| 265 fields_.Rewind(0); | |
| 266 } | |
| 267 | |
| 268 // Kill all entries matching the given offset. | |
| 269 void KillOffset(int offset) { | |
| 270 int field = FieldOf(offset); | |
| 271 if (field >= 0 && field < fields_.length()) { | |
| 272 fields_[field] = NULL; | |
| 273 } | |
| 274 } | |
| 275 | |
| 276 // Kill all entries aliasing the given store. | |
| 277 void KillStore(HStoreNamedField* s) { | |
| 278 int field = FieldOf(s->access()); | |
| 279 if (field >= 0) { | |
| 280 KillFieldInternal(s->object()->ActualValue(), field, s->value()); | |
| 281 } else { | |
| 282 KillIfMisaligned(s); | |
| 283 } | |
| 284 } | |
| 285 | |
| 286 // Kill multiple entries in the case of a misaligned store. | |
| 287 HValue* KillIfMisaligned(HStoreNamedField* instr) { | |
| 288 HObjectAccess access = instr->access(); | |
| 289 if (access.IsInobject()) { | |
| 290 int offset = access.offset(); | |
| 291 if ((offset % kPointerSize) != 0) { | |
| 292 // Kill the field containing the first word of the access. | |
| 293 HValue* object = instr->object()->ActualValue(); | |
| 294 int field = offset / kPointerSize; | |
| 295 KillFieldInternal(object, field, NULL); | |
| 296 | |
| 297 // Kill the next field in case of overlap. | |
| 298 int size = access.representation().size(); | |
| 299 int next_field = (offset + size - 1) / kPointerSize; | |
| 300 if (next_field != field) KillFieldInternal(object, next_field, NULL); | |
| 301 } | |
| 302 } | |
| 303 return instr; | |
| 304 } | |
| 305 | |
| 306 // Find an entry for the given object and field pair. | |
| 307 HFieldApproximation* Find(HValue* object, int field) { | |
| 308 // Search for a field approximation for this object. | |
| 309 HFieldApproximation* approx = fields_[field]; | |
| 310 while (approx != NULL) { | |
| 311 if (aliasing_->MustAlias(object, approx->object_)) return approx; | |
| 312 approx = approx->next_; | |
| 313 } | |
| 314 return NULL; | |
| 315 } | |
| 316 | |
| 317 // Find or create an entry for the given object and field pair. | |
| 318 HFieldApproximation* FindOrCreate(HValue* object, int field) { | |
| 319 EnsureFields(field + 1); | |
| 320 | |
| 321 // Search for a field approximation for this object. | |
| 322 HFieldApproximation* approx = fields_[field]; | |
| 323 int count = 0; | |
| 324 while (approx != NULL) { | |
| 325 if (aliasing_->MustAlias(object, approx->object_)) return approx; | |
| 326 count++; | |
| 327 approx = approx->next_; | |
| 328 } | |
| 329 | |
| 330 if (count >= kMaxTrackedObjects) { | |
| 331 // Pull the last entry off the end and repurpose it for this object. | |
| 332 approx = ReuseLastApproximation(field); | |
| 333 } else { | |
| 334 // Allocate a new entry. | |
| 335 approx = new(zone_) HFieldApproximation(); | |
| 336 } | |
| 337 | |
| 338 // Insert the entry at the head of the list. | |
| 339 approx->object_ = object; | |
| 340 approx->last_value_ = NULL; | |
| 341 approx->next_ = fields_[field]; | |
| 342 fields_[field] = approx; | |
| 343 | |
| 344 return approx; | |
| 345 } | |
| 346 | |
| 347 // Kill all entries for a given field that _may_ alias the given object | |
| 348 // and do _not_ have the given value. | |
| 349 void KillFieldInternal(HValue* object, int field, HValue* value) { | |
| 350 if (field >= fields_.length()) return; // Nothing to do. | |
| 351 | |
| 352 HFieldApproximation* approx = fields_[field]; | |
| 353 HFieldApproximation* prev = NULL; | |
| 354 while (approx != NULL) { | |
| 355 if (aliasing_->MayAlias(object, approx->object_)) { | |
| 356 if (!Equal(approx->last_value_, value)) { | |
| 357 // Kill an aliasing entry that doesn't agree on the value. | |
| 358 if (prev != NULL) { | |
| 359 prev->next_ = approx->next_; | |
| 360 } else { | |
| 361 fields_[field] = approx->next_; | |
| 362 } | |
| 363 approx = approx->next_; | |
| 364 continue; | |
| 365 } | |
| 366 } | |
| 367 prev = approx; | |
| 368 approx = approx->next_; | |
| 369 } | |
| 370 } | |
| 371 | |
| 372 bool Equal(HValue* a, HValue* b) { | |
| 373 if (a == b) return true; | |
| 374 if (a != NULL && b != NULL && a->CheckFlag(HValue::kUseGVN)) { | |
| 375 return a->Equals(b); | |
| 376 } | |
| 377 return false; | |
| 378 } | |
| 379 | |
| 380 // Remove the last approximation for a field so that it can be reused. | |
| 381 // We reuse the last entry because it was the first inserted and is thus | |
| 382 // farthest away from the current instruction. | |
| 383 HFieldApproximation* ReuseLastApproximation(int field) { | |
| 384 HFieldApproximation* approx = fields_[field]; | |
| 385 DCHECK(approx != NULL); | |
| 386 | |
| 387 HFieldApproximation* prev = NULL; | |
| 388 while (approx->next_ != NULL) { | |
| 389 prev = approx; | |
| 390 approx = approx->next_; | |
| 391 } | |
| 392 if (prev != NULL) prev->next_ = NULL; | |
| 393 return approx; | |
| 394 } | |
| 395 | |
| 396 // Compute the field index for the given object access; -1 if not tracked. | |
| 397 int FieldOf(HObjectAccess access) { | |
| 398 return access.IsInobject() ? FieldOf(access.offset()) : -1; | |
| 399 } | |
| 400 | |
| 401 // Compute the field index for the given in-object offset; -1 if not tracked. | |
| 402 int FieldOf(int offset) { | |
| 403 if (offset >= kMaxTrackedFields * kPointerSize) return -1; | |
| 404 // TODO(titzer): track misaligned loads in a separate list? | |
| 405 if ((offset % kPointerSize) != 0) return -1; // Ignore misaligned accesses. | |
| 406 return offset / kPointerSize; | |
| 407 } | |
| 408 | |
| 409 // Ensure internal storage for the given number of fields. | |
| 410 void EnsureFields(int num_fields) { | |
| 411 if (fields_.length() < num_fields) { | |
| 412 fields_.AddBlock(NULL, num_fields - fields_.length(), zone_); | |
| 413 } | |
| 414 } | |
| 415 | |
| 416 // Print this table to stdout. | |
| 417 void Print() { | |
| 418 for (int i = 0; i < fields_.length(); i++) { | |
| 419 PrintF(" field %d: ", i); | |
| 420 for (HFieldApproximation* a = fields_[i]; a != NULL; a = a->next_) { | |
| 421 PrintF("[o%d =", a->object_->id()); | |
| 422 if (a->last_value_ != NULL) PrintF(" v%d", a->last_value_->id()); | |
| 423 PrintF("] "); | |
| 424 } | |
| 425 PrintF("\n"); | |
| 426 } | |
| 427 } | |
| 428 | |
| 429 Zone* zone_; | |
| 430 ZoneList<HFieldApproximation*> fields_; | |
| 431 HAliasAnalyzer* aliasing_; | |
| 432 }; | |
| 433 | |
| 434 | |
| 435 // Support for HFlowEngine: collect store effects within loops. | |
| 436 class HLoadEliminationEffects : public ZoneObject { | |
| 437 public: | |
| 438 explicit HLoadEliminationEffects(Zone* zone) | |
| 439 : zone_(zone), stores_(5, zone) { } | |
| 440 | |
| 441 inline bool Disabled() { | |
| 442 return false; // Effects are _not_ disabled. | |
| 443 } | |
| 444 | |
| 445 // Process a possibly side-effecting instruction. | |
| 446 void Process(HInstruction* instr, Zone* zone) { | |
| 447 if (instr->IsStoreNamedField()) { | |
| 448 stores_.Add(HStoreNamedField::cast(instr), zone_); | |
| 449 } else { | |
| 450 flags_.Add(instr->ChangesFlags()); | |
| 451 } | |
| 452 } | |
| 453 | |
| 454 // Apply these effects to the given load elimination table. | |
| 455 void Apply(HLoadEliminationTable* table) { | |
| 456 // Loads must not be hoisted past the OSR entry, therefore we kill | |
| 457 // everything if we see an OSR entry. | |
| 458 if (flags_.Contains(kInobjectFields) || flags_.Contains(kOsrEntries)) { | |
| 459 table->Kill(); | |
| 460 return; | |
| 461 } | |
| 462 if (flags_.Contains(kElementsKind) || flags_.Contains(kMaps)) { | |
| 463 table->KillOffset(JSObject::kMapOffset); | |
| 464 } | |
| 465 if (flags_.Contains(kElementsKind) || flags_.Contains(kElementsPointer)) { | |
| 466 table->KillOffset(JSObject::kElementsOffset); | |
| 467 } | |
| 468 | |
| 469 // Kill non-agreeing fields for each store contained in these effects. | |
| 470 for (int i = 0; i < stores_.length(); i++) { | |
| 471 table->KillStore(stores_[i]); | |
| 472 } | |
| 473 } | |
| 474 | |
| 475 // Union these effects with the other effects. | |
| 476 void Union(HLoadEliminationEffects* that, Zone* zone) { | |
| 477 flags_.Add(that->flags_); | |
| 478 for (int i = 0; i < that->stores_.length(); i++) { | |
| 479 stores_.Add(that->stores_[i], zone); | |
| 480 } | |
| 481 } | |
| 482 | |
| 483 private: | |
| 484 Zone* zone_; | |
| 485 GVNFlagSet flags_; | |
| 486 ZoneList<HStoreNamedField*> stores_; | |
| 487 }; | |
| 488 | |
| 489 | |
| 490 // The main routine of the analysis phase. Use the HFlowEngine for either a | |
| 491 // local or a global analysis. | |
| 492 void HLoadEliminationPhase::Run() { | |
| 493 HFlowEngine<HLoadEliminationTable, HLoadEliminationEffects> | |
| 494 engine(graph(), zone()); | |
| 495 HAliasAnalyzer aliasing; | |
| 496 HLoadEliminationTable* table = | |
| 497 new(zone()) HLoadEliminationTable(zone(), &aliasing); | |
| 498 | |
| 499 if (GLOBAL) { | |
| 500 // Perform a global analysis. | |
| 501 engine.AnalyzeDominatedBlocks(graph()->blocks()->at(0), table); | |
| 502 } else { | |
| 503 // Perform only local analysis. | |
| 504 for (int i = 0; i < graph()->blocks()->length(); i++) { | |
| 505 table->Kill(); | |
| 506 engine.AnalyzeOneBlock(graph()->blocks()->at(i), table); | |
| 507 } | |
| 508 } | |
| 509 } | |
| 510 | |
| 511 } // namespace internal | |
| 512 } // namespace v8 | |
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Chromium Code Reviews
Issue 1405363003:
Move Hydrogen and Lithium to src/crankshaft/ (Closed)
Base URL: https://chromium.googlesource.com/v8/v8.git@master