src/v8/src/lithium-allocator.cc

   1 // Copyright 2012 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/v8.h"
   6
   7 #include "src/hydrogen.h"
   8 #include "src/lithium-inl.h"
   9 #include "src/lithium-allocator-inl.h"
  10 #include "src/string-stream.h"
  11
  12 namespace v8 {
  13 namespace internal {
  14
  15 static inline LifetimePosition Min(LifetimePosition a, LifetimePosition b) {
  16   return a.Value() < b.Value() ? a : b;
  17 }
  18
  19
  20 static inline LifetimePosition Max(LifetimePosition a, LifetimePosition b) {
  21   return a.Value() > b.Value() ? a : b;
  22 }
  23
  24
  25 UsePosition::UsePosition(LifetimePosition pos,
  26                          LOperand* operand,
  27                          LOperand* hint)
  28     : operand_(operand),
  29       hint_(hint),
  30       pos_(pos),
  31       next_(NULL),
  32       requires_reg_(false),
  33       register_beneficial_(true) {
  34   if (operand_ != NULL && operand_->IsUnallocated()) {
  35     LUnallocated* unalloc = LUnallocated::cast(operand_);
  36     requires_reg_ = unalloc->HasRegisterPolicy() ||
  37         unalloc->HasDoubleRegisterPolicy();
  38     register_beneficial_ = !unalloc->HasAnyPolicy();
  39   }
  40   DCHECK(pos_.IsValid());
  41 }
  42
  43
  44 bool UsePosition::HasHint() const {
  45   return hint_ != NULL && !hint_->IsUnallocated();
  46 }
  47
  48
  49 bool UsePosition::RequiresRegister() const {
  50   return requires_reg_;
  51 }
  52
  53
  54 bool UsePosition::RegisterIsBeneficial() const {
  55   return register_beneficial_;
  56 }
  57
  58
  59 void UseInterval::SplitAt(LifetimePosition pos, Zone* zone) {
  60   DCHECK(Contains(pos) && pos.Value() != start().Value());
  61   UseInterval* after = new(zone) UseInterval(pos, end_);
  62   after->next_ = next_;
  63   next_ = after;
  64   end_ = pos;
  65 }
  66
  67
  68 #ifdef DEBUG
  69
  70
  71 void LiveRange::Verify() const {
  72   UsePosition* cur = first_pos_;
  73   while (cur != NULL) {
  74     DCHECK(Start().Value() <= cur->pos().Value() &&
  75            cur->pos().Value() <= End().Value());
  76     cur = cur->next();
  77   }
  78 }
  79
  80
  81 bool LiveRange::HasOverlap(UseInterval* target) const {
  82   UseInterval* current_interval = first_interval_;
  83   while (current_interval != NULL) {
  84     // Intervals overlap if the start of one is contained in the other.
  85     if (current_interval->Contains(target->start()) ||
  86         target->Contains(current_interval->start())) {
  87       return true;
  88     }
  89     current_interval = current_interval->next();
  90   }
  91   return false;
  92 }
  93
  94
  95 #endif
  96
  97
  98 LiveRange::LiveRange(int id, Zone* zone)
  99     : id_(id),
 100       spilled_(false),
 101       kind_(UNALLOCATED_REGISTERS),
 102       assigned_register_(kInvalidAssignment),
 103       last_interval_(NULL),
 104       first_interval_(NULL),
 105       first_pos_(NULL),
 106       parent_(NULL),
 107       next_(NULL),
 108       current_interval_(NULL),
 109       last_processed_use_(NULL),
 110       current_hint_operand_(NULL),
 111       spill_operand_(new(zone) LOperand()),
 112       spill_start_index_(kMaxInt) { }
 113
 114
 115 void LiveRange::set_assigned_register(int reg, Zone* zone) {
 116   DCHECK(!HasRegisterAssigned() && !IsSpilled());
 117   assigned_register_ = reg;
 118   ConvertOperands(zone);
 119 }
 120
 121
 122 void LiveRange::MakeSpilled(Zone* zone) {
 123   DCHECK(!IsSpilled());
 124   DCHECK(TopLevel()->HasAllocatedSpillOperand());
 125   spilled_ = true;
 126   assigned_register_ = kInvalidAssignment;
 127   ConvertOperands(zone);
 128 }
 129
 130
 131 bool LiveRange::HasAllocatedSpillOperand() const {
 132   DCHECK(spill_operand_ != NULL);
 133   return !spill_operand_->IsIgnored();
 134 }
 135
 136
 137 void LiveRange::SetSpillOperand(LOperand* operand) {
 138   DCHECK(!operand->IsUnallocated());
 139   DCHECK(spill_operand_ != NULL);
 140   DCHECK(spill_operand_->IsIgnored());
 141   spill_operand_->ConvertTo(operand->kind(), operand->index());
 142 }
 143
 144
 145 UsePosition* LiveRange::NextUsePosition(LifetimePosition start) {
 146   UsePosition* use_pos = last_processed_use_;
 147   if (use_pos == NULL) use_pos = first_pos();
 148   while (use_pos != NULL && use_pos->pos().Value() < start.Value()) {
 149     use_pos = use_pos->next();
 150   }
 151   last_processed_use_ = use_pos;
 152   return use_pos;
 153 }
 154
 155
 156 UsePosition* LiveRange::NextUsePositionRegisterIsBeneficial(
 157     LifetimePosition start) {
 158   UsePosition* pos = NextUsePosition(start);
 159   while (pos != NULL && !pos->RegisterIsBeneficial()) {
 160     pos = pos->next();
 161   }
 162   return pos;
 163 }
 164
 165
 166 UsePosition* LiveRange::PreviousUsePositionRegisterIsBeneficial(
 167     LifetimePosition start) {
 168   UsePosition* pos = first_pos();
 169   UsePosition* prev = NULL;
 170   while (pos != NULL && pos->pos().Value() < start.Value()) {
 171     if (pos->RegisterIsBeneficial()) prev = pos;
 172     pos = pos->next();
 173   }
 174   return prev;
 175 }
 176
 177
 178 UsePosition* LiveRange::NextRegisterPosition(LifetimePosition start) {
 179   UsePosition* pos = NextUsePosition(start);
 180   while (pos != NULL && !pos->RequiresRegister()) {
 181     pos = pos->next();
 182   }
 183   return pos;
 184 }
 185
 186
 187 bool LiveRange::CanBeSpilled(LifetimePosition pos) {
 188   // We cannot spill a live range that has a use requiring a register
 189   // at the current or the immediate next position.
 190   UsePosition* use_pos = NextRegisterPosition(pos);
 191   if (use_pos == NULL) return true;
 192   return
 193       use_pos->pos().Value() > pos.NextInstruction().InstructionEnd().Value();
 194 }
 195
 196
 197 LOperand* LiveRange::CreateAssignedOperand(Zone* zone) {
 198   LOperand* op = NULL;
 199   if (HasRegisterAssigned()) {
 200     DCHECK(!IsSpilled());
 201     switch (Kind()) {
 202       case GENERAL_REGISTERS:
 203         op = LRegister::Create(assigned_register(), zone);
 204         break;
 205       case DOUBLE_REGISTERS:
 206         op = LDoubleRegister::Create(assigned_register(), zone);
 207         break;
 208       default:
 209         UNREACHABLE();
 210     }
 211   } else if (IsSpilled()) {
 212     DCHECK(!HasRegisterAssigned());
 213     op = TopLevel()->GetSpillOperand();
 214     DCHECK(!op->IsUnallocated());
 215   } else {
 216     LUnallocated* unalloc = new(zone) LUnallocated(LUnallocated::NONE);
 217     unalloc->set_virtual_register(id_);
 218     op = unalloc;
 219   }
 220   return op;
 221 }
 222
 223
 224 UseInterval* LiveRange::FirstSearchIntervalForPosition(
 225     LifetimePosition position) const {
 226   if (current_interval_ == NULL) return first_interval_;
 227   if (current_interval_->start().Value() > position.Value()) {
 228     current_interval_ = NULL;
 229     return first_interval_;
 230   }
 231   return current_interval_;
 232 }
 233
 234
 235 void LiveRange::AdvanceLastProcessedMarker(
 236     UseInterval* to_start_of, LifetimePosition but_not_past) const {
 237   if (to_start_of == NULL) return;
 238   if (to_start_of->start().Value() > but_not_past.Value()) return;
 239   LifetimePosition start =
 240       current_interval_ == NULL ? LifetimePosition::Invalid()
 241                                 : current_interval_->start();
 242   if (to_start_of->start().Value() > start.Value()) {
 243     current_interval_ = to_start_of;
 244   }
 245 }
 246
 247
 248 void LiveRange::SplitAt(LifetimePosition position,
 249                         LiveRange* result,
 250                         Zone* zone) {
 251   DCHECK(Start().Value() < position.Value());
 252   DCHECK(result->IsEmpty());
 253   // Find the last interval that ends before the position. If the
 254   // position is contained in one of the intervals in the chain, we
 255   // split that interval and use the first part.
 256   UseInterval* current = FirstSearchIntervalForPosition(position);
 257
 258   // If the split position coincides with the beginning of a use interval
 259   // we need to split use positons in a special way.
 260   bool split_at_start = false;
 261
 262   if (current->start().Value() == position.Value()) {
 263     // When splitting at start we need to locate the previous use interval.
 264     current = first_interval_;
 265   }
 266
 267   while (current != NULL) {
 268     if (current->Contains(position)) {
 269       current->SplitAt(position, zone);
 270       break;
 271     }
 272     UseInterval* next = current->next();
 273     if (next->start().Value() >= position.Value()) {
 274       split_at_start = (next->start().Value() == position.Value());
 275       break;
 276     }
 277     current = next;
 278   }
 279
 280   // Partition original use intervals to the two live ranges.
 281   UseInterval* before = current;
 282   UseInterval* after = before->next();
 283   result->last_interval_ = (last_interval_ == before)
 284       ? after            // Only interval in the range after split.
 285       : last_interval_;  // Last interval of the original range.
 286   result->first_interval_ = after;
 287   last_interval_ = before;
 288
 289   // Find the last use position before the split and the first use
 290   // position after it.
 291   UsePosition* use_after = first_pos_;
 292   UsePosition* use_before = NULL;
 293   if (split_at_start) {
 294     // The split position coincides with the beginning of a use interval (the
 295     // end of a lifetime hole). Use at this position should be attributed to
 296     // the split child because split child owns use interval covering it.
 297     while (use_after != NULL && use_after->pos().Value() < position.Value()) {
 298       use_before = use_after;
 299       use_after = use_after->next();
 300     }
 301   } else {
 302     while (use_after != NULL && use_after->pos().Value() <= position.Value()) {
 303       use_before = use_after;
 304       use_after = use_after->next();
 305     }
 306   }
 307
 308   // Partition original use positions to the two live ranges.
 309   if (use_before != NULL) {
 310     use_before->next_ = NULL;
 311   } else {
 312     first_pos_ = NULL;
 313   }
 314   result->first_pos_ = use_after;
 315
 316   // Discard cached iteration state. It might be pointing
 317   // to the use that no longer belongs to this live range.
 318   last_processed_use_ = NULL;
 319   current_interval_ = NULL;
 320
 321   // Link the new live range in the chain before any of the other
 322   // ranges linked from the range before the split.
 323   result->parent_ = (parent_ == NULL) ? this : parent_;
 324   result->kind_ = result->parent_->kind_;
 325   result->next_ = next_;
 326   next_ = result;
 327
 328 #ifdef DEBUG
 329   Verify();
 330   result->Verify();
 331 #endif
 332 }
 333
 334
 335 // This implements an ordering on live ranges so that they are ordered by their
 336 // start positions.  This is needed for the correctness of the register
 337 // allocation algorithm.  If two live ranges start at the same offset then there
 338 // is a tie breaker based on where the value is first used.  This part of the
 339 // ordering is merely a heuristic.
 340 bool LiveRange::ShouldBeAllocatedBefore(const LiveRange* other) const {
 341   LifetimePosition start = Start();
 342   LifetimePosition other_start = other->Start();
 343   if (start.Value() == other_start.Value()) {
 344     UsePosition* pos = first_pos();
 345     if (pos == NULL) return false;
 346     UsePosition* other_pos = other->first_pos();
 347     if (other_pos == NULL) return true;
 348     return pos->pos().Value() < other_pos->pos().Value();
 349   }
 350   return start.Value() < other_start.Value();
 351 }
 352
 353
 354 void LiveRange::ShortenTo(LifetimePosition start) {
 355   LAllocator::TraceAlloc("Shorten live range %d to [%d\n", id_, start.Value());
 356   DCHECK(first_interval_ != NULL);
 357   DCHECK(first_interval_->start().Value() <= start.Value());
 358   DCHECK(start.Value() < first_interval_->end().Value());
 359   first_interval_->set_start(start);
 360 }
 361
 362
 363 void LiveRange::EnsureInterval(LifetimePosition start,
 364                                LifetimePosition end,
 365                                Zone* zone) {
 366   LAllocator::TraceAlloc("Ensure live range %d in interval [%d %d[\n",
 367                          id_,
 368                          start.Value(),
 369                          end.Value());
 370   LifetimePosition new_end = end;
 371   while (first_interval_ != NULL &&
 372          first_interval_->start().Value() <= end.Value()) {
 373     if (first_interval_->end().Value() > end.Value()) {
 374       new_end = first_interval_->end();
 375     }
 376     first_interval_ = first_interval_->next();
 377   }
 378
 379   UseInterval* new_interval = new(zone) UseInterval(start, new_end);
 380   new_interval->next_ = first_interval_;
 381   first_interval_ = new_interval;
 382   if (new_interval->next() == NULL) {
 383     last_interval_ = new_interval;
 384   }
 385 }
 386
 387
 388 void LiveRange::AddUseInterval(LifetimePosition start,
 389                                LifetimePosition end,
 390                                Zone* zone) {
 391   LAllocator::TraceAlloc("Add to live range %d interval [%d %d[\n",
 392                          id_,
 393                          start.Value(),
 394                          end.Value());
 395   if (first_interval_ == NULL) {
 396     UseInterval* interval = new(zone) UseInterval(start, end);
 397     first_interval_ = interval;
 398     last_interval_ = interval;
 399   } else {
 400     if (end.Value() == first_interval_->start().Value()) {
 401       first_interval_->set_start(start);
 402     } else if (end.Value() < first_interval_->start().Value()) {
 403       UseInterval* interval = new(zone) UseInterval(start, end);
 404       interval->set_next(first_interval_);
 405       first_interval_ = interval;
 406     } else {
 407       // Order of instruction's processing (see ProcessInstructions) guarantees
 408       // that each new use interval either precedes or intersects with
 409       // last added interval.
 410       DCHECK(start.Value() < first_interval_->end().Value());
 411       first_interval_->start_ = Min(start, first_interval_->start_);
 412       first_interval_->end_ = Max(end, first_interval_->end_);
 413     }
 414   }
 415 }
 416
 417
 418 void LiveRange::AddUsePosition(LifetimePosition pos,
 419                                LOperand* operand,
 420                                LOperand* hint,
 421                                Zone* zone) {
 422   LAllocator::TraceAlloc("Add to live range %d use position %d\n",
 423                          id_,
 424                          pos.Value());
 425   UsePosition* use_pos = new(zone) UsePosition(pos, operand, hint);
 426   UsePosition* prev_hint = NULL;
 427   UsePosition* prev = NULL;
 428   UsePosition* current = first_pos_;
 429   while (current != NULL && current->pos().Value() < pos.Value()) {
 430     prev_hint = current->HasHint() ? current : prev_hint;
 431     prev = current;
 432     current = current->next();
 433   }
 434
 435   if (prev == NULL) {
 436     use_pos->set_next(first_pos_);
 437     first_pos_ = use_pos;
 438   } else {
 439     use_pos->next_ = prev->next_;
 440     prev->next_ = use_pos;
 441   }
 442
 443   if (prev_hint == NULL && use_pos->HasHint()) {
 444     current_hint_operand_ = hint;
 445   }
 446 }
 447
 448
 449 void LiveRange::ConvertOperands(Zone* zone) {
 450   LOperand* op = CreateAssignedOperand(zone);
 451   UsePosition* use_pos = first_pos();
 452   while (use_pos != NULL) {
 453     DCHECK(Start().Value() <= use_pos->pos().Value() &&
 454            use_pos->pos().Value() <= End().Value());
 455
 456     if (use_pos->HasOperand()) {
 457       DCHECK(op->IsRegister() || op->IsDoubleRegister() ||
 458              !use_pos->RequiresRegister());
 459       use_pos->operand()->ConvertTo(op->kind(), op->index());
 460     }
 461     use_pos = use_pos->next();
 462   }
 463 }
 464
 465
 466 bool LiveRange::CanCover(LifetimePosition position) const {
 467   if (IsEmpty()) return false;
 468   return Start().Value() <= position.Value() &&
 469          position.Value() < End().Value();
 470 }
 471
 472
 473 bool LiveRange::Covers(LifetimePosition position) {
 474   if (!CanCover(position)) return false;
 475   UseInterval* start_search = FirstSearchIntervalForPosition(position);
 476   for (UseInterval* interval = start_search;
 477        interval != NULL;
 478        interval = interval->next()) {
 479     DCHECK(interval->next() == NULL ||
 480            interval->next()->start().Value() >= interval->start().Value());
 481     AdvanceLastProcessedMarker(interval, position);
 482     if (interval->Contains(position)) return true;
 483     if (interval->start().Value() > position.Value()) return false;
 484   }
 485   return false;
 486 }
 487
 488
 489 LifetimePosition LiveRange::FirstIntersection(LiveRange* other) {
 490   UseInterval* b = other->first_interval();
 491   if (b == NULL) return LifetimePosition::Invalid();
 492   LifetimePosition advance_last_processed_up_to = b->start();
 493   UseInterval* a = FirstSearchIntervalForPosition(b->start());
 494   while (a != NULL && b != NULL) {
 495     if (a->start().Value() > other->End().Value()) break;
 496     if (b->start().Value() > End().Value()) break;
 497     LifetimePosition cur_intersection = a->Intersect(b);
 498     if (cur_intersection.IsValid()) {
 499       return cur_intersection;
 500     }
 501     if (a->start().Value() < b->start().Value()) {
 502       a = a->next();
 503       if (a == NULL || a->start().Value() > other->End().Value()) break;
 504       AdvanceLastProcessedMarker(a, advance_last_processed_up_to);
 505     } else {
 506       b = b->next();
 507     }
 508   }
 509   return LifetimePosition::Invalid();
 510 }
 511
 512
 513 LAllocator::LAllocator(int num_values, HGraph* graph)
 514     : zone_(graph->isolate()),
 515       chunk_(NULL),
 516       live_in_sets_(graph->blocks()->length(), zone()),
 517       live_ranges_(num_values * 2, zone()),
 518       fixed_live_ranges_(NULL),
 519       fixed_double_live_ranges_(NULL),
 520       unhandled_live_ranges_(num_values * 2, zone()),
 521       active_live_ranges_(8, zone()),
 522       inactive_live_ranges_(8, zone()),
 523       reusable_slots_(8, zone()),
 524       next_virtual_register_(num_values),
 525       first_artificial_register_(num_values),
 526       mode_(UNALLOCATED_REGISTERS),
 527       num_registers_(-1),
 528       graph_(graph),
 529       has_osr_entry_(false),
 530       allocation_ok_(true) { }
 531
 532
 533 void LAllocator::InitializeLivenessAnalysis() {
 534   // Initialize the live_in sets for each block to NULL.
 535   int block_count = graph_->blocks()->length();
 536   live_in_sets_.Initialize(block_count, zone());
 537   live_in_sets_.AddBlock(NULL, block_count, zone());
 538 }
 539
 540
 541 BitVector* LAllocator::ComputeLiveOut(HBasicBlock* block) {
 542   // Compute live out for the given block, except not including backward
 543   // successor edges.
 544   BitVector* live_out = new(zone()) BitVector(next_virtual_register_, zone());
 545
 546   // Process all successor blocks.
 547   for (HSuccessorIterator it(block->end()); !it.Done(); it.Advance()) {
 548     // Add values live on entry to the successor. Note the successor's
 549     // live_in will not be computed yet for backwards edges.
 550     HBasicBlock* successor = it.Current();
 551     BitVector* live_in = live_in_sets_[successor->block_id()];
 552     if (live_in != NULL) live_out->Union(*live_in);
 553
 554     // All phi input operands corresponding to this successor edge are live
 555     // out from this block.
 556     int index = successor->PredecessorIndexOf(block);
 557     const ZoneList<HPhi*>* phis = successor->phis();
 558     for (int i = 0; i < phis->length(); ++i) {
 559       HPhi* phi = phis->at(i);
 560       if (!phi->OperandAt(index)->IsConstant()) {
 561         live_out->Add(phi->OperandAt(index)->id());
 562       }
 563     }
 564   }
 565
 566   return live_out;
 567 }
 568
 569
 570 void LAllocator::AddInitialIntervals(HBasicBlock* block,
 571                                      BitVector* live_out) {
 572   // Add an interval that includes the entire block to the live range for
 573   // each live_out value.
 574   LifetimePosition start = LifetimePosition::FromInstructionIndex(
 575       block->first_instruction_index());
 576   LifetimePosition end = LifetimePosition::FromInstructionIndex(
 577       block->last_instruction_index()).NextInstruction();
 578   BitVector::Iterator iterator(live_out);
 579   while (!iterator.Done()) {
 580     int operand_index = iterator.Current();
 581     LiveRange* range = LiveRangeFor(operand_index);
 582     range->AddUseInterval(start, end, zone());
 583     iterator.Advance();
 584   }
 585 }
 586
 587
 588 int LAllocator::FixedDoubleLiveRangeID(int index) {
 589   return -index - 1 - Register::kMaxNumAllocatableRegisters;
 590 }
 591
 592
 593 LOperand* LAllocator::AllocateFixed(LUnallocated* operand,
 594                                     int pos,
 595                                     bool is_tagged) {
 596   TraceAlloc("Allocating fixed reg for op %d\n", operand->virtual_register());
 597   DCHECK(operand->HasFixedPolicy());
 598   if (operand->HasFixedSlotPolicy()) {
 599     operand->ConvertTo(LOperand::STACK_SLOT, operand->fixed_slot_index());
 600   } else if (operand->HasFixedRegisterPolicy()) {
 601     int reg_index = operand->fixed_register_index();
 602     operand->ConvertTo(LOperand::REGISTER, reg_index);
 603   } else if (operand->HasFixedDoubleRegisterPolicy()) {
 604     int reg_index = operand->fixed_register_index();
 605     operand->ConvertTo(LOperand::DOUBLE_REGISTER, reg_index);
 606   } else {
 607     UNREACHABLE();
 608   }
 609   if (is_tagged) {
 610     TraceAlloc("Fixed reg is tagged at %d\n", pos);
 611     LInstruction* instr = InstructionAt(pos);
 612     if (instr->HasPointerMap()) {
 613       instr->pointer_map()->RecordPointer(operand, chunk()->zone());
 614     }
 615   }
 616   return operand;
 617 }
 618
 619
 620 LiveRange* LAllocator::FixedLiveRangeFor(int index) {
 621   DCHECK(index < Register::kMaxNumAllocatableRegisters);
 622   LiveRange* result = fixed_live_ranges_[index];
 623   if (result == NULL) {
 624     result = new(zone()) LiveRange(FixedLiveRangeID(index), chunk()->zone());
 625     DCHECK(result->IsFixed());
 626     result->kind_ = GENERAL_REGISTERS;
 627     SetLiveRangeAssignedRegister(result, index);
 628     fixed_live_ranges_[index] = result;
 629   }
 630   return result;
 631 }
 632
 633
 634 LiveRange* LAllocator::FixedDoubleLiveRangeFor(int index) {
 635   DCHECK(index < DoubleRegister::NumAllocatableRegisters());
 636   LiveRange* result = fixed_double_live_ranges_[index];
 637   if (result == NULL) {
 638     result = new(zone()) LiveRange(FixedDoubleLiveRangeID(index),
 639                                    chunk()->zone());
 640     DCHECK(result->IsFixed());
 641     result->kind_ = DOUBLE_REGISTERS;
 642     SetLiveRangeAssignedRegister(result, index);
 643     fixed_double_live_ranges_[index] = result;
 644   }
 645   return result;
 646 }
 647
 648
 649 LiveRange* LAllocator::LiveRangeFor(int index) {
 650   if (index >= live_ranges_.length()) {
 651     live_ranges_.AddBlock(NULL, index - live_ranges_.length() + 1, zone());
 652   }
 653   LiveRange* result = live_ranges_[index];
 654   if (result == NULL) {
 655     result = new(zone()) LiveRange(index, chunk()->zone());
 656     live_ranges_[index] = result;
 657   }
 658   return result;
 659 }
 660
 661
 662 LGap* LAllocator::GetLastGap(HBasicBlock* block) {
 663   int last_instruction = block->last_instruction_index();
 664   int index = chunk_->NearestGapPos(last_instruction);
 665   return GapAt(index);
 666 }
 667
 668
 669 HPhi* LAllocator::LookupPhi(LOperand* operand) const {
 670   if (!operand->IsUnallocated()) return NULL;
 671   int index = LUnallocated::cast(operand)->virtual_register();
 672   HValue* instr = graph_->LookupValue(index);
 673   if (instr != NULL && instr->IsPhi()) {
 674     return HPhi::cast(instr);
 675   }
 676   return NULL;
 677 }
 678
 679
 680 LiveRange* LAllocator::LiveRangeFor(LOperand* operand) {
 681   if (operand->IsUnallocated()) {
 682     return LiveRangeFor(LUnallocated::cast(operand)->virtual_register());
 683   } else if (operand->IsRegister()) {
 684     return FixedLiveRangeFor(operand->index());
 685   } else if (operand->IsDoubleRegister()) {
 686     return FixedDoubleLiveRangeFor(operand->index());
 687   } else {
 688     return NULL;
 689   }
 690 }
 691
 692
 693 void LAllocator::Define(LifetimePosition position,
 694                         LOperand* operand,
 695                         LOperand* hint) {
 696   LiveRange* range = LiveRangeFor(operand);
 697   if (range == NULL) return;
 698
 699   if (range->IsEmpty() || range->Start().Value() > position.Value()) {
 700     // Can happen if there is a definition without use.
 701     range->AddUseInterval(position, position.NextInstruction(), zone());
 702     range->AddUsePosition(position.NextInstruction(), NULL, NULL, zone());
 703   } else {
 704     range->ShortenTo(position);
 705   }
 706
 707   if (operand->IsUnallocated()) {
 708     LUnallocated* unalloc_operand = LUnallocated::cast(operand);
 709     range->AddUsePosition(position, unalloc_operand, hint, zone());
 710   }
 711 }
 712
 713
 714 void LAllocator::Use(LifetimePosition block_start,
 715                      LifetimePosition position,
 716                      LOperand* operand,
 717                      LOperand* hint) {
 718   LiveRange* range = LiveRangeFor(operand);
 719   if (range == NULL) return;
 720   if (operand->IsUnallocated()) {
 721     LUnallocated* unalloc_operand = LUnallocated::cast(operand);
 722     range->AddUsePosition(position, unalloc_operand, hint, zone());
 723   }
 724   range->AddUseInterval(block_start, position, zone());
 725 }
 726
 727
 728 void LAllocator::AddConstraintsGapMove(int index,
 729                                        LOperand* from,
 730                                        LOperand* to) {
 731   LGap* gap = GapAt(index);
 732   LParallelMove* move = gap->GetOrCreateParallelMove(LGap::START,
 733                                                      chunk()->zone());
 734   if (from->IsUnallocated()) {
 735     const ZoneList<LMoveOperands>* move_operands = move->move_operands();
 736     for (int i = 0; i < move_operands->length(); ++i) {
 737       LMoveOperands cur = move_operands->at(i);
 738       LOperand* cur_to = cur.destination();
 739       if (cur_to->IsUnallocated()) {
 740         if (LUnallocated::cast(cur_to)->virtual_register() ==
 741             LUnallocated::cast(from)->virtual_register()) {
 742           move->AddMove(cur.source(), to, chunk()->zone());
 743           return;
 744         }
 745       }
 746     }
 747   }
 748   move->AddMove(from, to, chunk()->zone());
 749 }
 750
 751
 752 void LAllocator::MeetRegisterConstraints(HBasicBlock* block) {
 753   int start = block->first_instruction_index();
 754   int end = block->last_instruction_index();
 755   if (start == -1) return;
 756   for (int i = start; i <= end; ++i) {
 757     if (IsGapAt(i)) {
 758       LInstruction* instr = NULL;
 759       LInstruction* prev_instr = NULL;
 760       if (i < end) instr = InstructionAt(i + 1);
 761       if (i > start) prev_instr = InstructionAt(i - 1);
 762       MeetConstraintsBetween(prev_instr, instr, i);
 763       if (!AllocationOk()) return;
 764     }
 765   }
 766 }
 767
 768
 769 void LAllocator::MeetConstraintsBetween(LInstruction* first,
 770                                         LInstruction* second,
 771                                         int gap_index) {
 772   // Handle fixed temporaries.
 773   if (first != NULL) {
 774     for (TempIterator it(first); !it.Done(); it.Advance()) {
 775       LUnallocated* temp = LUnallocated::cast(it.Current());
 776       if (temp->HasFixedPolicy()) {
 777         AllocateFixed(temp, gap_index - 1, false);
 778       }
 779     }
 780   }
 781
 782   // Handle fixed output operand.
 783   if (first != NULL && first->Output() != NULL) {
 784     LUnallocated* first_output = LUnallocated::cast(first->Output());
 785     LiveRange* range = LiveRangeFor(first_output->virtual_register());
 786     bool assigned = false;
 787     if (first_output->HasFixedPolicy()) {
 788       LUnallocated* output_copy = first_output->CopyUnconstrained(
 789           chunk()->zone());
 790       bool is_tagged = HasTaggedValue(first_output->virtual_register());
 791       AllocateFixed(first_output, gap_index, is_tagged);
 792
 793       // This value is produced on the stack, we never need to spill it.
 794       if (first_output->IsStackSlot()) {
 795         range->SetSpillOperand(first_output);
 796         range->SetSpillStartIndex(gap_index - 1);
 797         assigned = true;
 798       }
 799       chunk_->AddGapMove(gap_index, first_output, output_copy);
 800     }
 801
 802     if (!assigned) {
 803       range->SetSpillStartIndex(gap_index);
 804
 805       // This move to spill operand is not a real use. Liveness analysis
 806       // and splitting of live ranges do not account for it.
 807       // Thus it should be inserted to a lifetime position corresponding to
 808       // the instruction end.
 809       LGap* gap = GapAt(gap_index);
 810       LParallelMove* move = gap->GetOrCreateParallelMove(LGap::BEFORE,
 811                                                          chunk()->zone());
 812       move->AddMove(first_output, range->GetSpillOperand(),
 813                     chunk()->zone());
 814     }
 815   }
 816
 817   // Handle fixed input operands of second instruction.
 818   if (second != NULL) {
 819     for (UseIterator it(second); !it.Done(); it.Advance()) {
 820       LUnallocated* cur_input = LUnallocated::cast(it.Current());
 821       if (cur_input->HasFixedPolicy()) {
 822         LUnallocated* input_copy = cur_input->CopyUnconstrained(
 823             chunk()->zone());
 824         bool is_tagged = HasTaggedValue(cur_input->virtual_register());
 825         AllocateFixed(cur_input, gap_index + 1, is_tagged);
 826         AddConstraintsGapMove(gap_index, input_copy, cur_input);
 827       } else if (cur_input->HasWritableRegisterPolicy()) {
 828         // The live range of writable input registers always goes until the end
 829         // of the instruction.
 830         DCHECK(!cur_input->IsUsedAtStart());
 831
 832         LUnallocated* input_copy = cur_input->CopyUnconstrained(
 833             chunk()->zone());
 834         int vreg = GetVirtualRegister();
 835         if (!AllocationOk()) return;
 836         cur_input->set_virtual_register(vreg);
 837
 838         if (RequiredRegisterKind(input_copy->virtual_register()) ==
 839             DOUBLE_REGISTERS) {
 840           double_artificial_registers_.Add(
 841               cur_input->virtual_register() - first_artificial_register_,
 842               zone());
 843         }
 844
 845         AddConstraintsGapMove(gap_index, input_copy, cur_input);
 846       }
 847     }
 848   }
 849
 850   // Handle "output same as input" for second instruction.
 851   if (second != NULL && second->Output() != NULL) {
 852     LUnallocated* second_output = LUnallocated::cast(second->Output());
 853     if (second_output->HasSameAsInputPolicy()) {
 854       LUnallocated* cur_input = LUnallocated::cast(second->FirstInput());
 855       int output_vreg = second_output->virtual_register();
 856       int input_vreg = cur_input->virtual_register();
 857
 858       LUnallocated* input_copy = cur_input->CopyUnconstrained(
 859           chunk()->zone());
 860       cur_input->set_virtual_register(second_output->virtual_register());
 861       AddConstraintsGapMove(gap_index, input_copy, cur_input);
 862
 863       if (HasTaggedValue(input_vreg) && !HasTaggedValue(output_vreg)) {
 864         int index = gap_index + 1;
 865         LInstruction* instr = InstructionAt(index);
 866         if (instr->HasPointerMap()) {
 867           instr->pointer_map()->RecordPointer(input_copy, chunk()->zone());
 868         }
 869       } else if (!HasTaggedValue(input_vreg) && HasTaggedValue(output_vreg)) {
 870         // The input is assumed to immediately have a tagged representation,
 871         // before the pointer map can be used. I.e. the pointer map at the
 872         // instruction will include the output operand (whose value at the
 873         // beginning of the instruction is equal to the input operand). If
 874         // this is not desired, then the pointer map at this instruction needs
 875         // to be adjusted manually.
 876       }
 877     }
 878   }
 879 }
 880
 881
 882 void LAllocator::ProcessInstructions(HBasicBlock* block, BitVector* live) {
 883   int block_start = block->first_instruction_index();
 884   int index = block->last_instruction_index();
 885
 886   LifetimePosition block_start_position =
 887       LifetimePosition::FromInstructionIndex(block_start);
 888
 889   while (index >= block_start) {
 890     LifetimePosition curr_position =
 891         LifetimePosition::FromInstructionIndex(index);
 892
 893     if (IsGapAt(index)) {
 894       // We have a gap at this position.
 895       LGap* gap = GapAt(index);
 896       LParallelMove* move = gap->GetOrCreateParallelMove(LGap::START,
 897                                                          chunk()->zone());
 898       const ZoneList<LMoveOperands>* move_operands = move->move_operands();
 899       for (int i = 0; i < move_operands->length(); ++i) {
 900         LMoveOperands* cur = &move_operands->at(i);
 901         if (cur->IsIgnored()) continue;
 902         LOperand* from = cur->source();
 903         LOperand* to = cur->destination();
 904         HPhi* phi = LookupPhi(to);
 905         LOperand* hint = to;
 906         if (phi != NULL) {
 907           // This is a phi resolving move.
 908           if (!phi->block()->IsLoopHeader()) {
 909             hint = LiveRangeFor(phi->id())->current_hint_operand();
 910           }
 911         } else {
 912           if (to->IsUnallocated()) {
 913             if (live->Contains(LUnallocated::cast(to)->virtual_register())) {
 914               Define(curr_position, to, from);
 915               live->Remove(LUnallocated::cast(to)->virtual_register());
 916             } else {
 917               cur->Eliminate();
 918               continue;
 919             }
 920           } else {
 921             Define(curr_position, to, from);
 922           }
 923         }
 924         Use(block_start_position, curr_position, from, hint);
 925         if (from->IsUnallocated()) {
 926           live->Add(LUnallocated::cast(from)->virtual_register());
 927         }
 928       }
 929     } else {
 930       DCHECK(!IsGapAt(index));
 931       LInstruction* instr = InstructionAt(index);
 932
 933       if (instr != NULL) {
 934         LOperand* output = instr->Output();
 935         if (output != NULL) {
 936           if (output->IsUnallocated()) {
 937             live->Remove(LUnallocated::cast(output)->virtual_register());
 938           }
 939           Define(curr_position, output, NULL);
 940         }
 941
 942         if (instr->ClobbersRegisters()) {
 943           for (int i = 0; i < Register::kMaxNumAllocatableRegisters; ++i) {
 944             if (output == NULL || !output->IsRegister() ||
 945                 output->index() != i) {
 946               LiveRange* range = FixedLiveRangeFor(i);
 947               range->AddUseInterval(curr_position,
 948                                     curr_position.InstructionEnd(),
 949                                     zone());
 950             }
 951           }
 952         }
 953
 954         if (instr->ClobbersDoubleRegisters(isolate())) {
 955           for (int i = 0; i < DoubleRegister::NumAllocatableRegisters(); ++i) {
 956             if (output == NULL || !output->IsDoubleRegister() ||
 957                 output->index() != i) {
 958               LiveRange* range = FixedDoubleLiveRangeFor(i);
 959               range->AddUseInterval(curr_position,
 960                                     curr_position.InstructionEnd(),
 961                                     zone());
 962             }
 963           }
 964         }
 965
 966         for (UseIterator it(instr); !it.Done(); it.Advance()) {
 967           LOperand* input = it.Current();
 968
 969           LifetimePosition use_pos;
 970           if (input->IsUnallocated() &&
 971               LUnallocated::cast(input)->IsUsedAtStart()) {
 972             use_pos = curr_position;
 973           } else {
 974             use_pos = curr_position.InstructionEnd();
 975           }
 976
 977           Use(block_start_position, use_pos, input, NULL);
 978           if (input->IsUnallocated()) {
 979             live->Add(LUnallocated::cast(input)->virtual_register());
 980           }
 981         }
 982
 983         for (TempIterator it(instr); !it.Done(); it.Advance()) {
 984           LOperand* temp = it.Current();
 985           if (instr->ClobbersTemps()) {
 986             if (temp->IsRegister()) continue;
 987             if (temp->IsUnallocated()) {
 988               LUnallocated* temp_unalloc = LUnallocated::cast(temp);
 989               if (temp_unalloc->HasFixedPolicy()) {
 990                 continue;
 991               }
 992             }
 993           }
 994           Use(block_start_position, curr_position.InstructionEnd(), temp, NULL);
 995           Define(curr_position, temp, NULL);
 996
 997           if (temp->IsUnallocated()) {
 998             LUnallocated* temp_unalloc = LUnallocated::cast(temp);
 999             if (temp_unalloc->HasDoubleRegisterPolicy()) {
1000               double_artificial_registers_.Add(
1001                   temp_unalloc->virtual_register() - first_artificial_register_,
1002                   zone());
1003             }
1004           }
1005         }
1006       }
1007     }
1008
1009     index = index - 1;
1010   }
1011 }
1012
1013
1014 void LAllocator::ResolvePhis(HBasicBlock* block) {
1015   const ZoneList<HPhi*>* phis = block->phis();
1016   for (int i = 0; i < phis->length(); ++i) {
1017     HPhi* phi = phis->at(i);
1018     LUnallocated* phi_operand =
1019         new(chunk()->zone()) LUnallocated(LUnallocated::NONE);
1020     phi_operand->set_virtual_register(phi->id());
1021     for (int j = 0; j < phi->OperandCount(); ++j) {
1022       HValue* op = phi->OperandAt(j);
1023       LOperand* operand = NULL;
1024       if (op->IsConstant() && op->EmitAtUses()) {
1025         HConstant* constant = HConstant::cast(op);
1026         operand = chunk_->DefineConstantOperand(constant);
1027       } else {
1028         DCHECK(!op->EmitAtUses());
1029         LUnallocated* unalloc =
1030             new(chunk()->zone()) LUnallocated(LUnallocated::ANY);
1031         unalloc->set_virtual_register(op->id());
1032         operand = unalloc;
1033       }
1034       HBasicBlock* cur_block = block->predecessors()->at(j);
1035       // The gap move must be added without any special processing as in
1036       // the AddConstraintsGapMove.
1037       chunk_->AddGapMove(cur_block->last_instruction_index() - 1,
1038                          operand,
1039                          phi_operand);
1040
1041       // We are going to insert a move before the branch instruction.
1042       // Some branch instructions (e.g. loops' back edges)
1043       // can potentially cause a GC so they have a pointer map.
1044       // By inserting a move we essentially create a copy of a
1045       // value which is invisible to PopulatePointerMaps(), because we store
1046       // it into a location different from the operand of a live range
1047       // covering a branch instruction.
1048       // Thus we need to manually record a pointer.
1049       LInstruction* branch =
1050           InstructionAt(cur_block->last_instruction_index());
1051       if (branch->HasPointerMap()) {
1052         if (phi->representation().IsTagged() && !phi->type().IsSmi()) {
1053           branch->pointer_map()->RecordPointer(phi_operand, chunk()->zone());
1054         } else if (!phi->representation().IsDouble()) {
1055           branch->pointer_map()->RecordUntagged(phi_operand, chunk()->zone());
1056         }
1057       }
1058     }
1059
1060     LiveRange* live_range = LiveRangeFor(phi->id());
1061     LLabel* label = chunk_->GetLabel(phi->block()->block_id());
1062     label->GetOrCreateParallelMove(LGap::START, chunk()->zone())->
1063         AddMove(phi_operand, live_range->GetSpillOperand(), chunk()->zone());
1064     live_range->SetSpillStartIndex(phi->block()->first_instruction_index());
1065   }
1066 }
1067
1068
1069 bool LAllocator::Allocate(LChunk* chunk) {
1070   DCHECK(chunk_ == NULL);
1071   chunk_ = static_cast<LPlatformChunk*>(chunk);
1072   assigned_registers_ =
1073       new(chunk->zone()) BitVector(Register::NumAllocatableRegisters(),
1074                                    chunk->zone());
1075   assigned_double_registers_ =
1076       new(chunk->zone()) BitVector(DoubleRegister::NumAllocatableRegisters(),
1077                                    chunk->zone());
1078   MeetRegisterConstraints();
1079   if (!AllocationOk()) return false;
1080   ResolvePhis();
1081   BuildLiveRanges();
1082   AllocateGeneralRegisters();
1083   if (!AllocationOk()) return false;
1084   AllocateDoubleRegisters();
1085   if (!AllocationOk()) return false;
1086   PopulatePointerMaps();
1087   ConnectRanges();
1088   ResolveControlFlow();
1089   return true;
1090 }
1091
1092
1093 void LAllocator::MeetRegisterConstraints() {
1094   LAllocatorPhase phase("L_Register constraints", this);
1095   const ZoneList<HBasicBlock*>* blocks = graph_->blocks();
1096   for (int i = 0; i < blocks->length(); ++i) {
1097     HBasicBlock* block = blocks->at(i);
1098     MeetRegisterConstraints(block);
1099     if (!AllocationOk()) return;
1100   }
1101 }
1102
1103
1104 void LAllocator::ResolvePhis() {
1105   LAllocatorPhase phase("L_Resolve phis", this);
1106
1107   // Process the blocks in reverse order.
1108   const ZoneList<HBasicBlock*>* blocks = graph_->blocks();
1109   for (int block_id = blocks->length() - 1; block_id >= 0; --block_id) {
1110     HBasicBlock* block = blocks->at(block_id);
1111     ResolvePhis(block);
1112   }
1113 }
1114
1115
1116 void LAllocator::ResolveControlFlow(LiveRange* range,
1117                                     HBasicBlock* block,
1118                                     HBasicBlock* pred) {
1119   LifetimePosition pred_end =
1120       LifetimePosition::FromInstructionIndex(pred->last_instruction_index());
1121   LifetimePosition cur_start =
1122       LifetimePosition::FromInstructionIndex(block->first_instruction_index());
1123   LiveRange* pred_cover = NULL;
1124   LiveRange* cur_cover = NULL;
1125   LiveRange* cur_range = range;
1126   while (cur_range != NULL && (cur_cover == NULL || pred_cover == NULL)) {
1127     if (cur_range->CanCover(cur_start)) {
1128       DCHECK(cur_cover == NULL);
1129       cur_cover = cur_range;
1130     }
1131     if (cur_range->CanCover(pred_end)) {
1132       DCHECK(pred_cover == NULL);
1133       pred_cover = cur_range;
1134     }
1135     cur_range = cur_range->next();
1136   }
1137
1138   if (cur_cover->IsSpilled()) return;
1139   DCHECK(pred_cover != NULL && cur_cover != NULL);
1140   if (pred_cover != cur_cover) {
1141     LOperand* pred_op = pred_cover->CreateAssignedOperand(chunk()->zone());
1142     LOperand* cur_op = cur_cover->CreateAssignedOperand(chunk()->zone());
1143     if (!pred_op->Equals(cur_op)) {
1144       LGap* gap = NULL;
1145       if (block->predecessors()->length() == 1) {
1146         gap = GapAt(block->first_instruction_index());
1147       } else {
1148         DCHECK(pred->end()->SecondSuccessor() == NULL);
1149         gap = GetLastGap(pred);
1150
1151         // We are going to insert a move before the branch instruction.
1152         // Some branch instructions (e.g. loops' back edges)
1153         // can potentially cause a GC so they have a pointer map.
1154         // By inserting a move we essentially create a copy of a
1155         // value which is invisible to PopulatePointerMaps(), because we store
1156         // it into a location different from the operand of a live range
1157         // covering a branch instruction.
1158         // Thus we need to manually record a pointer.
1159         LInstruction* branch = InstructionAt(pred->last_instruction_index());
1160         if (branch->HasPointerMap()) {
1161           if (HasTaggedValue(range->id())) {
1162             branch->pointer_map()->RecordPointer(cur_op, chunk()->zone());
1163           } else if (!cur_op->IsDoubleStackSlot() &&
1164                      !cur_op->IsDoubleRegister()) {
1165             branch->pointer_map()->RemovePointer(cur_op);
1166           }
1167         }
1168       }
1169       gap->GetOrCreateParallelMove(
1170           LGap::START, chunk()->zone())->AddMove(pred_op, cur_op,
1171                                                  chunk()->zone());
1172     }
1173   }
1174 }
1175
1176
1177 LParallelMove* LAllocator::GetConnectingParallelMove(LifetimePosition pos) {
1178   int index = pos.InstructionIndex();
1179   if (IsGapAt(index)) {
1180     LGap* gap = GapAt(index);
1181     return gap->GetOrCreateParallelMove(
1182         pos.IsInstructionStart() ? LGap::START : LGap::END, chunk()->zone());
1183   }
1184   int gap_pos = pos.IsInstructionStart() ? (index - 1) : (index + 1);
1185   return GapAt(gap_pos)->GetOrCreateParallelMove(
1186       (gap_pos < index) ? LGap::AFTER : LGap::BEFORE, chunk()->zone());
1187 }
1188
1189
1190 HBasicBlock* LAllocator::GetBlock(LifetimePosition pos) {
1191   LGap* gap = GapAt(chunk_->NearestGapPos(pos.InstructionIndex()));
1192   return gap->block();
1193 }
1194
1195
1196 void LAllocator::ConnectRanges() {
1197   LAllocatorPhase phase("L_Connect ranges", this);
1198   for (int i = 0; i < live_ranges()->length(); ++i) {
1199     LiveRange* first_range = live_ranges()->at(i);
1200     if (first_range == NULL || first_range->parent() != NULL) continue;
1201
1202     LiveRange* second_range = first_range->next();
1203     while (second_range != NULL) {
1204       LifetimePosition pos = second_range->Start();
1205
1206       if (!second_range->IsSpilled()) {
1207         // Add gap move if the two live ranges touch and there is no block
1208         // boundary.
1209         if (first_range->End().Value() == pos.Value()) {
1210           bool should_insert = true;
1211           if (IsBlockBoundary(pos)) {
1212             should_insert = CanEagerlyResolveControlFlow(GetBlock(pos));
1213           }
1214           if (should_insert) {
1215             LParallelMove* move = GetConnectingParallelMove(pos);
1216             LOperand* prev_operand = first_range->CreateAssignedOperand(
1217                 chunk()->zone());
1218             LOperand* cur_operand = second_range->CreateAssignedOperand(
1219                 chunk()->zone());
1220             move->AddMove(prev_operand, cur_operand,
1221                           chunk()->zone());
1222           }
1223         }
1224       }
1225
1226       first_range = second_range;
1227       second_range = second_range->next();
1228     }
1229   }
1230 }
1231
1232
1233 bool LAllocator::CanEagerlyResolveControlFlow(HBasicBlock* block) const {
1234   if (block->predecessors()->length() != 1) return false;
1235   return block->predecessors()->first()->block_id() == block->block_id() - 1;
1236 }
1237
1238
1239 void LAllocator::ResolveControlFlow() {
1240   LAllocatorPhase phase("L_Resolve control flow", this);
1241   const ZoneList<HBasicBlock*>* blocks = graph_->blocks();
1242   for (int block_id = 1; block_id < blocks->length(); ++block_id) {
1243     HBasicBlock* block = blocks->at(block_id);
1244     if (CanEagerlyResolveControlFlow(block)) continue;
1245     BitVector* live = live_in_sets_[block->block_id()];
1246     BitVector::Iterator iterator(live);
1247     while (!iterator.Done()) {
1248       int operand_index = iterator.Current();
1249       for (int i = 0; i < block->predecessors()->length(); ++i) {
1250         HBasicBlock* cur = block->predecessors()->at(i);
1251         LiveRange* cur_range = LiveRangeFor(operand_index);
1252         ResolveControlFlow(cur_range, block, cur);
1253       }
1254       iterator.Advance();
1255     }
1256   }
1257 }
1258
1259
1260 void LAllocator::BuildLiveRanges() {
1261   LAllocatorPhase phase("L_Build live ranges", this);
1262   InitializeLivenessAnalysis();
1263   // Process the blocks in reverse order.
1264   const ZoneList<HBasicBlock*>* blocks = graph_->blocks();
1265   for (int block_id = blocks->length() - 1; block_id >= 0; --block_id) {
1266     HBasicBlock* block = blocks->at(block_id);
1267     BitVector* live = ComputeLiveOut(block);
1268     // Initially consider all live_out values live for the entire block. We
1269     // will shorten these intervals if necessary.
1270     AddInitialIntervals(block, live);
1271
1272     // Process the instructions in reverse order, generating and killing
1273     // live values.
1274     ProcessInstructions(block, live);
1275     // All phi output operands are killed by this block.
1276     const ZoneList<HPhi*>* phis = block->phis();
1277     for (int i = 0; i < phis->length(); ++i) {
1278       // The live range interval already ends at the first instruction of the
1279       // block.
1280       HPhi* phi = phis->at(i);
1281       live->Remove(phi->id());
1282
1283       LOperand* hint = NULL;
1284       LOperand* phi_operand = NULL;
1285       LGap* gap = GetLastGap(phi->block()->predecessors()->at(0));
1286       LParallelMove* move = gap->GetOrCreateParallelMove(LGap::START,
1287                                                          chunk()->zone());
1288       for (int j = 0; j < move->move_operands()->length(); ++j) {
1289         LOperand* to = move->move_operands()->at(j).destination();
1290         if (to->IsUnallocated() &&
1291             LUnallocated::cast(to)->virtual_register() == phi->id()) {
1292           hint = move->move_operands()->at(j).source();
1293           phi_operand = to;
1294           break;
1295         }
1296       }
1297       DCHECK(hint != NULL);
1298
1299       LifetimePosition block_start = LifetimePosition::FromInstructionIndex(
1300               block->first_instruction_index());
1301       Define(block_start, phi_operand, hint);
1302     }
1303
1304     // Now live is live_in for this block except not including values live
1305     // out on backward successor edges.
1306     live_in_sets_[block_id] = live;
1307
1308     // If this block is a loop header go back and patch up the necessary
1309     // predecessor blocks.
1310     if (block->IsLoopHeader()) {
1311       // TODO(kmillikin): Need to be able to get the last block of the loop
1312       // in the loop information. Add a live range stretching from the first
1313       // loop instruction to the last for each value live on entry to the
1314       // header.
1315       HBasicBlock* back_edge = block->loop_information()->GetLastBackEdge();
1316       BitVector::Iterator iterator(live);
1317       LifetimePosition start = LifetimePosition::FromInstructionIndex(
1318           block->first_instruction_index());
1319       LifetimePosition end = LifetimePosition::FromInstructionIndex(
1320           back_edge->last_instruction_index()).NextInstruction();
1321       while (!iterator.Done()) {
1322         int operand_index = iterator.Current();
1323         LiveRange* range = LiveRangeFor(operand_index);
1324         range->EnsureInterval(start, end, zone());
1325         iterator.Advance();
1326       }
1327
1328       for (int i = block->block_id() + 1; i <= back_edge->block_id(); ++i) {
1329         live_in_sets_[i]->Union(*live);
1330       }
1331     }
1332
1333 #ifdef DEBUG
1334     if (block_id == 0) {
1335       BitVector::Iterator iterator(live);
1336       bool found = false;
1337       while (!iterator.Done()) {
1338         found = true;
1339         int operand_index = iterator.Current();
1340         if (chunk_->info()->IsStub()) {
1341           CodeStub::Major major_key = chunk_->info()->code_stub()->MajorKey();
1342           PrintF("Function: %s\n", CodeStub::MajorName(major_key, false));
1343         } else {
1344           DCHECK(chunk_->info()->IsOptimizing());
1345           AllowHandleDereference allow_deref;
1346           PrintF("Function: %s\n",
1347                  chunk_->info()->function()->debug_name()->ToCString().get());
1348         }
1349         PrintF("Value %d used before first definition!\n", operand_index);
1350         LiveRange* range = LiveRangeFor(operand_index);
1351         PrintF("First use is at %d\n", range->first_pos()->pos().Value());
1352         iterator.Advance();
1353       }
1354       DCHECK(!found);
1355     }
1356 #endif
1357   }
1358
1359   for (int i = 0; i < live_ranges_.length(); ++i) {
1360     if (live_ranges_[i] != NULL) {
1361       live_ranges_[i]->kind_ = RequiredRegisterKind(live_ranges_[i]->id());
1362     }
1363   }
1364 }
1365
1366
1367 bool LAllocator::SafePointsAreInOrder() const {
1368   const ZoneList<LPointerMap*>* pointer_maps = chunk_->pointer_maps();
1369   int safe_point = 0;
1370   for (int i = 0; i < pointer_maps->length(); ++i) {
1371     LPointerMap* map = pointer_maps->at(i);
1372     if (safe_point > map->lithium_position()) return false;
1373     safe_point = map->lithium_position();
1374   }
1375   return true;
1376 }
1377
1378
1379 void LAllocator::PopulatePointerMaps() {
1380   LAllocatorPhase phase("L_Populate pointer maps", this);
1381   const ZoneList<LPointerMap*>* pointer_maps = chunk_->pointer_maps();
1382
1383   DCHECK(SafePointsAreInOrder());
1384
1385   // Iterate over all safe point positions and record a pointer
1386   // for all spilled live ranges at this point.
1387   int first_safe_point_index = 0;
1388   int last_range_start = 0;
1389   for (int range_idx = 0; range_idx < live_ranges()->length(); ++range_idx) {
1390     LiveRange* range = live_ranges()->at(range_idx);
1391     if (range == NULL) continue;
1392     // Iterate over the first parts of multi-part live ranges.
1393     if (range->parent() != NULL) continue;
1394     // Skip non-pointer values.
1395     if (!HasTaggedValue(range->id())) continue;
1396     // Skip empty live ranges.
1397     if (range->IsEmpty()) continue;
1398
1399     // Find the extent of the range and its children.
1400     int start = range->Start().InstructionIndex();
1401     int end = 0;
1402     for (LiveRange* cur = range; cur != NULL; cur = cur->next()) {
1403       LifetimePosition this_end = cur->End();
1404       if (this_end.InstructionIndex() > end) end = this_end.InstructionIndex();
1405       DCHECK(cur->Start().InstructionIndex() >= start);
1406     }
1407
1408     // Most of the ranges are in order, but not all.  Keep an eye on when
1409     // they step backwards and reset the first_safe_point_index so we don't
1410     // miss any safe points.
1411     if (start < last_range_start) {
1412       first_safe_point_index = 0;
1413     }
1414     last_range_start = start;
1415
1416     // Step across all the safe points that are before the start of this range,
1417     // recording how far we step in order to save doing this for the next range.
1418     while (first_safe_point_index < pointer_maps->length()) {
1419       LPointerMap* map = pointer_maps->at(first_safe_point_index);
1420       int safe_point = map->lithium_position();
1421       if (safe_point >= start) break;
1422       first_safe_point_index++;
1423     }
1424
1425     // Step through the safe points to see whether they are in the range.
1426     for (int safe_point_index = first_safe_point_index;
1427          safe_point_index < pointer_maps->length();
1428          ++safe_point_index) {
1429       LPointerMap* map = pointer_maps->at(safe_point_index);
1430       int safe_point = map->lithium_position();
1431
1432       // The safe points are sorted so we can stop searching here.
1433       if (safe_point - 1 > end) break;
1434
1435       // Advance to the next active range that covers the current
1436       // safe point position.
1437       LifetimePosition safe_point_pos =
1438           LifetimePosition::FromInstructionIndex(safe_point);
1439       LiveRange* cur = range;
1440       while (cur != NULL && !cur->Covers(safe_point_pos)) {
1441         cur = cur->next();
1442       }
1443       if (cur == NULL) continue;
1444
1445       // Check if the live range is spilled and the safe point is after
1446       // the spill position.
1447       if (range->HasAllocatedSpillOperand() &&
1448           safe_point >= range->spill_start_index()) {
1449         TraceAlloc("Pointer for range %d (spilled at %d) at safe point %d\n",
1450                    range->id(), range->spill_start_index(), safe_point);
1451         map->RecordPointer(range->GetSpillOperand(), chunk()->zone());
1452       }
1453
1454       if (!cur->IsSpilled()) {
1455         TraceAlloc("Pointer in register for range %d (start at %d) "
1456                    "at safe point %d\n",
1457                    cur->id(), cur->Start().Value(), safe_point);
1458         LOperand* operand = cur->CreateAssignedOperand(chunk()->zone());
1459         DCHECK(!operand->IsStackSlot());
1460         map->RecordPointer(operand, chunk()->zone());
1461       }
1462     }
1463   }
1464 }
1465
1466
1467 void LAllocator::AllocateGeneralRegisters() {
1468   LAllocatorPhase phase("L_Allocate general registers", this);
1469   num_registers_ = Register::NumAllocatableRegisters();
1470   mode_ = GENERAL_REGISTERS;
1471   AllocateRegisters();
1472 }
1473
1474
1475 void LAllocator::AllocateDoubleRegisters() {
1476   LAllocatorPhase phase("L_Allocate double registers", this);
1477   num_registers_ = DoubleRegister::NumAllocatableRegisters();
1478   mode_ = DOUBLE_REGISTERS;
1479   AllocateRegisters();
1480 }
1481
1482
1483 void LAllocator::AllocateRegisters() {
1484   DCHECK(unhandled_live_ranges_.is_empty());
1485
1486   for (int i = 0; i < live_ranges_.length(); ++i) {
1487     if (live_ranges_[i] != NULL) {
1488       if (live_ranges_[i]->Kind() == mode_) {
1489         AddToUnhandledUnsorted(live_ranges_[i]);
1490       }
1491     }
1492   }
1493   SortUnhandled();
1494   DCHECK(UnhandledIsSorted());
1495
1496   DCHECK(reusable_slots_.is_empty());
1497   DCHECK(active_live_ranges_.is_empty());
1498   DCHECK(inactive_live_ranges_.is_empty());
1499
1500   if (mode_ == DOUBLE_REGISTERS) {
1501     for (int i = 0; i < DoubleRegister::NumAllocatableRegisters(); ++i) {
1502       LiveRange* current = fixed_double_live_ranges_.at(i);
1503       if (current != NULL) {
1504         AddToInactive(current);
1505       }
1506     }
1507   } else {
1508     DCHECK(mode_ == GENERAL_REGISTERS);
1509     for (int i = 0; i < fixed_live_ranges_.length(); ++i) {
1510       LiveRange* current = fixed_live_ranges_.at(i);
1511       if (current != NULL) {
1512         AddToInactive(current);
1513       }
1514     }
1515   }
1516
1517   while (!unhandled_live_ranges_.is_empty()) {
1518     DCHECK(UnhandledIsSorted());
1519     LiveRange* current = unhandled_live_ranges_.RemoveLast();
1520     DCHECK(UnhandledIsSorted());
1521     LifetimePosition position = current->Start();
1522 #ifdef DEBUG
1523     allocation_finger_ = position;
1524 #endif
1525     TraceAlloc("Processing interval %d start=%d\n",
1526                current->id(),
1527                position.Value());
1528
1529     if (current->HasAllocatedSpillOperand()) {
1530       TraceAlloc("Live range %d already has a spill operand\n", current->id());
1531       LifetimePosition next_pos = position;
1532       if (IsGapAt(next_pos.InstructionIndex())) {
1533         next_pos = next_pos.NextInstruction();
1534       }
1535       UsePosition* pos = current->NextUsePositionRegisterIsBeneficial(next_pos);
1536       // If the range already has a spill operand and it doesn't need a
1537       // register immediately, split it and spill the first part of the range.
1538       if (pos == NULL) {
1539         Spill(current);
1540         continue;
1541       } else if (pos->pos().Value() >
1542                  current->Start().NextInstruction().Value()) {
1543         // Do not spill live range eagerly if use position that can benefit from
1544         // the register is too close to the start of live range.
1545         SpillBetween(current, current->Start(), pos->pos());
1546         if (!AllocationOk()) return;
1547         DCHECK(UnhandledIsSorted());
1548         continue;
1549       }
1550     }
1551
1552     for (int i = 0; i < active_live_ranges_.length(); ++i) {
1553       LiveRange* cur_active = active_live_ranges_.at(i);
1554       if (cur_active->End().Value() <= position.Value()) {
1555         ActiveToHandled(cur_active);
1556         --i;  // The live range was removed from the list of active live ranges.
1557       } else if (!cur_active->Covers(position)) {
1558         ActiveToInactive(cur_active);
1559         --i;  // The live range was removed from the list of active live ranges.
1560       }
1561     }
1562
1563     for (int i = 0; i < inactive_live_ranges_.length(); ++i) {
1564       LiveRange* cur_inactive = inactive_live_ranges_.at(i);
1565       if (cur_inactive->End().Value() <= position.Value()) {
1566         InactiveToHandled(cur_inactive);
1567         --i;  // Live range was removed from the list of inactive live ranges.
1568       } else if (cur_inactive->Covers(position)) {
1569         InactiveToActive(cur_inactive);
1570         --i;  // Live range was removed from the list of inactive live ranges.
1571       }
1572     }
1573
1574     DCHECK(!current->HasRegisterAssigned() && !current->IsSpilled());
1575
1576     bool result = TryAllocateFreeReg(current);
1577     if (!AllocationOk()) return;
1578
1579     if (!result) AllocateBlockedReg(current);
1580     if (!AllocationOk()) return;
1581
1582     if (current->HasRegisterAssigned()) {
1583       AddToActive(current);
1584     }
1585   }
1586
1587   reusable_slots_.Rewind(0);
1588   active_live_ranges_.Rewind(0);
1589   inactive_live_ranges_.Rewind(0);
1590 }
1591
1592
1593 const char* LAllocator::RegisterName(int allocation_index) {
1594   if (mode_ == GENERAL_REGISTERS) {
1595     return Register::AllocationIndexToString(allocation_index);
1596   } else {
1597     return DoubleRegister::AllocationIndexToString(allocation_index);
1598   }
1599 }
1600
1601
1602 void LAllocator::TraceAlloc(const char* msg, ...) {
1603   if (FLAG_trace_alloc) {
1604     va_list arguments;
1605     va_start(arguments, msg);
1606     base::OS::VPrint(msg, arguments);
1607     va_end(arguments);
1608   }
1609 }
1610
1611
1612 bool LAllocator::HasTaggedValue(int virtual_register) const {
1613   HValue* value = graph_->LookupValue(virtual_register);
1614   if (value == NULL) return false;
1615   return value->representation().IsTagged() && !value->type().IsSmi();
1616 }
1617
1618
1619 RegisterKind LAllocator::RequiredRegisterKind(int virtual_register) const {
1620   if (virtual_register < first_artificial_register_) {
1621     HValue* value = graph_->LookupValue(virtual_register);
1622     if (value != NULL && value->representation().IsDouble()) {
1623       return DOUBLE_REGISTERS;
1624     }
1625   } else if (double_artificial_registers_.Contains(
1626       virtual_register - first_artificial_register_)) {
1627     return DOUBLE_REGISTERS;
1628   }
1629
1630   return GENERAL_REGISTERS;
1631 }
1632
1633
1634 void LAllocator::AddToActive(LiveRange* range) {
1635   TraceAlloc("Add live range %d to active\n", range->id());
1636   active_live_ranges_.Add(range, zone());
1637 }
1638
1639
1640 void LAllocator::AddToInactive(LiveRange* range) {
1641   TraceAlloc("Add live range %d to inactive\n", range->id());
1642   inactive_live_ranges_.Add(range, zone());
1643 }
1644
1645
1646 void LAllocator::AddToUnhandledSorted(LiveRange* range) {
1647   if (range == NULL || range->IsEmpty()) return;
1648   DCHECK(!range->HasRegisterAssigned() && !range->IsSpilled());
1649   DCHECK(allocation_finger_.Value() <= range->Start().Value());
1650   for (int i = unhandled_live_ranges_.length() - 1; i >= 0; --i) {
1651     LiveRange* cur_range = unhandled_live_ranges_.at(i);
1652     if (range->ShouldBeAllocatedBefore(cur_range)) {
1653       TraceAlloc("Add live range %d to unhandled at %d\n", range->id(), i + 1);
1654       unhandled_live_ranges_.InsertAt(i + 1, range, zone());
1655       DCHECK(UnhandledIsSorted());
1656       return;
1657     }
1658   }
1659   TraceAlloc("Add live range %d to unhandled at start\n", range->id());
1660   unhandled_live_ranges_.InsertAt(0, range, zone());
1661   DCHECK(UnhandledIsSorted());
1662 }
1663
1664
1665 void LAllocator::AddToUnhandledUnsorted(LiveRange* range) {
1666   if (range == NULL || range->IsEmpty()) return;
1667   DCHECK(!range->HasRegisterAssigned() && !range->IsSpilled());
1668   TraceAlloc("Add live range %d to unhandled unsorted at end\n", range->id());
1669   unhandled_live_ranges_.Add(range, zone());
1670 }
1671
1672
1673 static int UnhandledSortHelper(LiveRange* const* a, LiveRange* const* b) {
1674   DCHECK(!(*a)->ShouldBeAllocatedBefore(*b) ||
1675          !(*b)->ShouldBeAllocatedBefore(*a));
1676   if ((*a)->ShouldBeAllocatedBefore(*b)) return 1;
1677   if ((*b)->ShouldBeAllocatedBefore(*a)) return -1;
1678   return (*a)->id() - (*b)->id();
1679 }
1680
1681
1682 // Sort the unhandled live ranges so that the ranges to be processed first are
1683 // at the end of the array list.  This is convenient for the register allocation
1684 // algorithm because it is efficient to remove elements from the end.
1685 void LAllocator::SortUnhandled() {
1686   TraceAlloc("Sort unhandled\n");
1687   unhandled_live_ranges_.Sort(&UnhandledSortHelper);
1688 }
1689
1690
1691 bool LAllocator::UnhandledIsSorted() {
1692   int len = unhandled_live_ranges_.length();
1693   for (int i = 1; i < len; i++) {
1694     LiveRange* a = unhandled_live_ranges_.at(i - 1);
1695     LiveRange* b = unhandled_live_ranges_.at(i);
1696     if (a->Start().Value() < b->Start().Value()) return false;
1697   }
1698   return true;
1699 }
1700
1701
1702 void LAllocator::FreeSpillSlot(LiveRange* range) {
1703   // Check that we are the last range.
1704   if (range->next() != NULL) return;
1705
1706   if (!range->TopLevel()->HasAllocatedSpillOperand()) return;
1707
1708   int index = range->TopLevel()->GetSpillOperand()->index();
1709   if (index >= 0) {
1710     reusable_slots_.Add(range, zone());
1711   }
1712 }
1713
1714
1715 LOperand* LAllocator::TryReuseSpillSlot(LiveRange* range) {
1716   if (reusable_slots_.is_empty()) return NULL;
1717   if (reusable_slots_.first()->End().Value() >
1718       range->TopLevel()->Start().Value()) {
1719     return NULL;
1720   }
1721   LOperand* result = reusable_slots_.first()->TopLevel()->GetSpillOperand();
1722   reusable_slots_.Remove(0);
1723   return result;
1724 }
1725
1726
1727 void LAllocator::ActiveToHandled(LiveRange* range) {
1728   DCHECK(active_live_ranges_.Contains(range));
1729   active_live_ranges_.RemoveElement(range);
1730   TraceAlloc("Moving live range %d from active to handled\n", range->id());
1731   FreeSpillSlot(range);
1732 }
1733
1734
1735 void LAllocator::ActiveToInactive(LiveRange* range) {
1736   DCHECK(active_live_ranges_.Contains(range));
1737   active_live_ranges_.RemoveElement(range);
1738   inactive_live_ranges_.Add(range, zone());
1739   TraceAlloc("Moving live range %d from active to inactive\n", range->id());
1740 }
1741
1742
1743 void LAllocator::InactiveToHandled(LiveRange* range) {
1744   DCHECK(inactive_live_ranges_.Contains(range));
1745   inactive_live_ranges_.RemoveElement(range);
1746   TraceAlloc("Moving live range %d from inactive to handled\n", range->id());
1747   FreeSpillSlot(range);
1748 }
1749
1750
1751 void LAllocator::InactiveToActive(LiveRange* range) {
1752   DCHECK(inactive_live_ranges_.Contains(range));
1753   inactive_live_ranges_.RemoveElement(range);
1754   active_live_ranges_.Add(range, zone());
1755   TraceAlloc("Moving live range %d from inactive to active\n", range->id());
1756 }
1757
1758
1759 // TryAllocateFreeReg and AllocateBlockedReg assume this
1760 // when allocating local arrays.
1761 STATIC_ASSERT(DoubleRegister::kMaxNumAllocatableRegisters >=
1762               Register::kMaxNumAllocatableRegisters);
1763
1764
1765 bool LAllocator::TryAllocateFreeReg(LiveRange* current) {
1766   LifetimePosition free_until_pos[DoubleRegister::kMaxNumAllocatableRegisters];
1767
1768   for (int i = 0; i < num_registers_; i++) {
1769     free_until_pos[i] = LifetimePosition::MaxPosition();
1770   }
1771
1772   for (int i = 0; i < active_live_ranges_.length(); ++i) {
1773     LiveRange* cur_active = active_live_ranges_.at(i);
1774     free_until_pos[cur_active->assigned_register()] =
1775         LifetimePosition::FromInstructionIndex(0);
1776   }
1777
1778   for (int i = 0; i < inactive_live_ranges_.length(); ++i) {
1779     LiveRange* cur_inactive = inactive_live_ranges_.at(i);
1780     DCHECK(cur_inactive->End().Value() > current->Start().Value());
1781     LifetimePosition next_intersection =
1782         cur_inactive->FirstIntersection(current);
1783     if (!next_intersection.IsValid()) continue;
1784     int cur_reg = cur_inactive->assigned_register();
1785     free_until_pos[cur_reg] = Min(free_until_pos[cur_reg], next_intersection);
1786   }
1787
1788   LOperand* hint = current->FirstHint();
1789   if (hint != NULL && (hint->IsRegister() || hint->IsDoubleRegister())) {
1790     int register_index = hint->index();
1791     TraceAlloc(
1792         "Found reg hint %s (free until [%d) for live range %d (end %d[).\n",
1793         RegisterName(register_index),
1794         free_until_pos[register_index].Value(),
1795         current->id(),
1796         current->End().Value());
1797
1798     // The desired register is free until the end of the current live range.
1799     if (free_until_pos[register_index].Value() >= current->End().Value()) {
1800       TraceAlloc("Assigning preferred reg %s to live range %d\n",
1801                  RegisterName(register_index),
1802                  current->id());
1803       SetLiveRangeAssignedRegister(current, register_index);
1804       return true;
1805     }
1806   }
1807
1808   // Find the register which stays free for the longest time.
1809   int reg = 0;
1810   for (int i = 1; i < RegisterCount(); ++i) {
1811     if (free_until_pos[i].Value() > free_until_pos[reg].Value()) {
1812       reg = i;
1813     }
1814   }
1815
1816   LifetimePosition pos = free_until_pos[reg];
1817
1818   if (pos.Value() <= current->Start().Value()) {
1819     // All registers are blocked.
1820     return false;
1821   }
1822
1823   if (pos.Value() < current->End().Value()) {
1824     // Register reg is available at the range start but becomes blocked before
1825     // the range end. Split current at position where it becomes blocked.
1826     LiveRange* tail = SplitRangeAt(current, pos);
1827     if (!AllocationOk()) return false;
1828     AddToUnhandledSorted(tail);
1829   }
1830
1831
1832   // Register reg is available at the range start and is free until
1833   // the range end.
1834   DCHECK(pos.Value() >= current->End().Value());
1835   TraceAlloc("Assigning free reg %s to live range %d\n",
1836              RegisterName(reg),
1837              current->id());
1838   SetLiveRangeAssignedRegister(current, reg);
1839
1840   return true;
1841 }
1842
1843
1844 void LAllocator::AllocateBlockedReg(LiveRange* current) {
1845   UsePosition* register_use = current->NextRegisterPosition(current->Start());
1846   if (register_use == NULL) {
1847     // There is no use in the current live range that requires a register.
1848     // We can just spill it.
1849     Spill(current);
1850     return;
1851   }
1852
1853
1854   LifetimePosition use_pos[DoubleRegister::kMaxNumAllocatableRegisters];
1855   LifetimePosition block_pos[DoubleRegister::kMaxNumAllocatableRegisters];
1856
1857   for (int i = 0; i < num_registers_; i++) {
1858     use_pos[i] = block_pos[i] = LifetimePosition::MaxPosition();
1859   }
1860
1861   for (int i = 0; i < active_live_ranges_.length(); ++i) {
1862     LiveRange* range = active_live_ranges_[i];
1863     int cur_reg = range->assigned_register();
1864     if (range->IsFixed() || !range->CanBeSpilled(current->Start())) {
1865       block_pos[cur_reg] = use_pos[cur_reg] =
1866           LifetimePosition::FromInstructionIndex(0);
1867     } else {
1868       UsePosition* next_use = range->NextUsePositionRegisterIsBeneficial(
1869           current->Start());
1870       if (next_use == NULL) {
1871         use_pos[cur_reg] = range->End();
1872       } else {
1873         use_pos[cur_reg] = next_use->pos();
1874       }
1875     }
1876   }
1877
1878   for (int i = 0; i < inactive_live_ranges_.length(); ++i) {
1879     LiveRange* range = inactive_live_ranges_.at(i);
1880     DCHECK(range->End().Value() > current->Start().Value());
1881     LifetimePosition next_intersection = range->FirstIntersection(current);
1882     if (!next_intersection.IsValid()) continue;
1883     int cur_reg = range->assigned_register();
1884     if (range->IsFixed()) {
1885       block_pos[cur_reg] = Min(block_pos[cur_reg], next_intersection);
1886       use_pos[cur_reg] = Min(block_pos[cur_reg], use_pos[cur_reg]);
1887     } else {
1888       use_pos[cur_reg] = Min(use_pos[cur_reg], next_intersection);
1889     }
1890   }
1891
1892   int reg = 0;
1893   for (int i = 1; i < RegisterCount(); ++i) {
1894     if (use_pos[i].Value() > use_pos[reg].Value()) {
1895       reg = i;
1896     }
1897   }
1898
1899   LifetimePosition pos = use_pos[reg];
1900
1901   if (pos.Value() < register_use->pos().Value()) {
1902     // All registers are blocked before the first use that requires a register.
1903     // Spill starting part of live range up to that use.
1904     SpillBetween(current, current->Start(), register_use->pos());
1905     return;
1906   }
1907
1908   if (block_pos[reg].Value() < current->End().Value()) {
1909     // Register becomes blocked before the current range end. Split before that
1910     // position.
1911     LiveRange* tail = SplitBetween(current,
1912                                    current->Start(),
1913                                    block_pos[reg].InstructionStart());
1914     if (!AllocationOk()) return;
1915     AddToUnhandledSorted(tail);
1916   }
1917
1918   // Register reg is not blocked for the whole range.
1919   DCHECK(block_pos[reg].Value() >= current->End().Value());
1920   TraceAlloc("Assigning blocked reg %s to live range %d\n",
1921              RegisterName(reg),
1922              current->id());
1923   SetLiveRangeAssignedRegister(current, reg);
1924
1925   // This register was not free. Thus we need to find and spill
1926   // parts of active and inactive live regions that use the same register
1927   // at the same lifetime positions as current.
1928   SplitAndSpillIntersecting(current);
1929 }
1930
1931
1932 LifetimePosition LAllocator::FindOptimalSpillingPos(LiveRange* range,
1933                                                     LifetimePosition pos) {
1934   HBasicBlock* block = GetBlock(pos.InstructionStart());
1935   HBasicBlock* loop_header =
1936       block->IsLoopHeader() ? block : block->parent_loop_header();
1937
1938   if (loop_header == NULL) return pos;
1939
1940   UsePosition* prev_use =
1941     range->PreviousUsePositionRegisterIsBeneficial(pos);
1942
1943   while (loop_header != NULL) {
1944     // We are going to spill live range inside the loop.
1945     // If possible try to move spilling position backwards to loop header.
1946     // This will reduce number of memory moves on the back edge.
1947     LifetimePosition loop_start = LifetimePosition::FromInstructionIndex(
1948         loop_header->first_instruction_index());
1949
1950     if (range->Covers(loop_start)) {
1951       if (prev_use == NULL || prev_use->pos().Value() < loop_start.Value()) {
1952         // No register beneficial use inside the loop before the pos.
1953         pos = loop_start;
1954       }
1955     }
1956
1957     // Try hoisting out to an outer loop.
1958     loop_header = loop_header->parent_loop_header();
1959   }
1960
1961   return pos;
1962 }
1963
1964
1965 void LAllocator::SplitAndSpillIntersecting(LiveRange* current) {
1966   DCHECK(current->HasRegisterAssigned());
1967   int reg = current->assigned_register();
1968   LifetimePosition split_pos = current->Start();
1969   for (int i = 0; i < active_live_ranges_.length(); ++i) {
1970     LiveRange* range = active_live_ranges_[i];
1971     if (range->assigned_register() == reg) {
1972       UsePosition* next_pos = range->NextRegisterPosition(current->Start());
1973       LifetimePosition spill_pos = FindOptimalSpillingPos(range, split_pos);
1974       if (next_pos == NULL) {
1975         SpillAfter(range, spill_pos);
1976       } else {
1977         // When spilling between spill_pos and next_pos ensure that the range
1978         // remains spilled at least until the start of the current live range.
1979         // This guarantees that we will not introduce new unhandled ranges that
1980         // start before the current range as this violates allocation invariant
1981         // and will lead to an inconsistent state of active and inactive
1982         // live-ranges: ranges are allocated in order of their start positions,
1983         // ranges are retired from active/inactive when the start of the
1984         // current live-range is larger than their end.
1985         SpillBetweenUntil(range, spill_pos, current->Start(), next_pos->pos());
1986       }
1987       if (!AllocationOk()) return;
1988       ActiveToHandled(range);
1989       --i;
1990     }
1991   }
1992
1993   for (int i = 0; i < inactive_live_ranges_.length(); ++i) {
1994     LiveRange* range = inactive_live_ranges_[i];
1995     DCHECK(range->End().Value() > current->Start().Value());
1996     if (range->assigned_register() == reg && !range->IsFixed()) {
1997       LifetimePosition next_intersection = range->FirstIntersection(current);
1998       if (next_intersection.IsValid()) {
1999         UsePosition* next_pos = range->NextRegisterPosition(current->Start());
2000         if (next_pos == NULL) {
2001           SpillAfter(range, split_pos);
2002         } else {
2003           next_intersection = Min(next_intersection, next_pos->pos());
2004           SpillBetween(range, split_pos, next_intersection);
2005         }
2006         if (!AllocationOk()) return;
2007         InactiveToHandled(range);
2008         --i;
2009       }
2010     }
2011   }
2012 }
2013
2014
2015 bool LAllocator::IsBlockBoundary(LifetimePosition pos) {
2016   return pos.IsInstructionStart() &&
2017       InstructionAt(pos.InstructionIndex())->IsLabel();
2018 }
2019
2020
2021 LiveRange* LAllocator::SplitRangeAt(LiveRange* range, LifetimePosition pos) {
2022   DCHECK(!range->IsFixed());
2023   TraceAlloc("Splitting live range %d at %d\n", range->id(), pos.Value());
2024
2025   if (pos.Value() <= range->Start().Value()) return range;
2026
2027   // We can't properly connect liveranges if split occured at the end
2028   // of control instruction.
2029   DCHECK(pos.IsInstructionStart() ||
2030          !chunk_->instructions()->at(pos.InstructionIndex())->IsControl());
2031
2032   int vreg = GetVirtualRegister();
2033   if (!AllocationOk()) return NULL;
2034   LiveRange* result = LiveRangeFor(vreg);
2035   range->SplitAt(pos, result, zone());
2036   return result;
2037 }
2038
2039
2040 LiveRange* LAllocator::SplitBetween(LiveRange* range,
2041                                     LifetimePosition start,
2042                                     LifetimePosition end) {
2043   DCHECK(!range->IsFixed());
2044   TraceAlloc("Splitting live range %d in position between [%d, %d]\n",
2045              range->id(),
2046              start.Value(),
2047              end.Value());
2048
2049   LifetimePosition split_pos = FindOptimalSplitPos(start, end);
2050   DCHECK(split_pos.Value() >= start.Value());
2051   return SplitRangeAt(range, split_pos);
2052 }
2053
2054
2055 LifetimePosition LAllocator::FindOptimalSplitPos(LifetimePosition start,
2056                                                  LifetimePosition end) {
2057   int start_instr = start.InstructionIndex();
2058   int end_instr = end.InstructionIndex();
2059   DCHECK(start_instr <= end_instr);
2060
2061   // We have no choice
2062   if (start_instr == end_instr) return end;
2063
2064   HBasicBlock* start_block = GetBlock(start);
2065   HBasicBlock* end_block = GetBlock(end);
2066
2067   if (end_block == start_block) {
2068     // The interval is split in the same basic block. Split at the latest
2069     // possible position.
2070     return end;
2071   }
2072
2073   HBasicBlock* block = end_block;
2074   // Find header of outermost loop.
2075   while (block->parent_loop_header() != NULL &&
2076       block->parent_loop_header()->block_id() > start_block->block_id()) {
2077     block = block->parent_loop_header();
2078   }
2079
2080   // We did not find any suitable outer loop. Split at the latest possible
2081   // position unless end_block is a loop header itself.
2082   if (block == end_block && !end_block->IsLoopHeader()) return end;
2083
2084   return LifetimePosition::FromInstructionIndex(
2085       block->first_instruction_index());
2086 }
2087
2088
2089 void LAllocator::SpillAfter(LiveRange* range, LifetimePosition pos) {
2090   LiveRange* second_part = SplitRangeAt(range, pos);
2091   if (!AllocationOk()) return;
2092   Spill(second_part);
2093 }
2094
2095
2096 void LAllocator::SpillBetween(LiveRange* range,
2097                               LifetimePosition start,
2098                               LifetimePosition end) {
2099   SpillBetweenUntil(range, start, start, end);
2100 }
2101
2102
2103 void LAllocator::SpillBetweenUntil(LiveRange* range,
2104                                    LifetimePosition start,
2105                                    LifetimePosition until,
2106                                    LifetimePosition end) {
2107   CHECK(start.Value() < end.Value());
2108   LiveRange* second_part = SplitRangeAt(range, start);
2109   if (!AllocationOk()) return;
2110
2111   if (second_part->Start().Value() < end.Value()) {
2112     // The split result intersects with [start, end[.
2113     // Split it at position between ]start+1, end[, spill the middle part
2114     // and put the rest to unhandled.
2115     LiveRange* third_part = SplitBetween(
2116         second_part,
2117         Max(second_part->Start().InstructionEnd(), until),
2118         end.PrevInstruction().InstructionEnd());
2119     if (!AllocationOk()) return;
2120
2121     DCHECK(third_part != second_part);
2122
2123     Spill(second_part);
2124     AddToUnhandledSorted(third_part);
2125   } else {
2126     // The split result does not intersect with [start, end[.
2127     // Nothing to spill. Just put it to unhandled as whole.
2128     AddToUnhandledSorted(second_part);
2129   }
2130 }
2131
2132
2133 void LAllocator::Spill(LiveRange* range) {
2134   DCHECK(!range->IsSpilled());
2135   TraceAlloc("Spilling live range %d\n", range->id());
2136   LiveRange* first = range->TopLevel();
2137
2138   if (!first->HasAllocatedSpillOperand()) {
2139     LOperand* op = TryReuseSpillSlot(range);
2140     if (op == NULL) op = chunk_->GetNextSpillSlot(range->Kind());
2141     first->SetSpillOperand(op);
2142   }
2143   range->MakeSpilled(chunk()->zone());
2144 }
2145
2146
2147 int LAllocator::RegisterCount() const {
2148   return num_registers_;
2149 }
2150
2151
2152 #ifdef DEBUG
2153
2154
2155 void LAllocator::Verify() const {
2156   for (int i = 0; i < live_ranges()->length(); ++i) {
2157     LiveRange* current = live_ranges()->at(i);
2158     if (current != NULL) current->Verify();
2159   }
2160 }
2161
2162
2163 #endif
2164
2165
2166 LAllocatorPhase::LAllocatorPhase(const char* name, LAllocator* allocator)
2167     : CompilationPhase(name, allocator->graph()->info()),
2168       allocator_(allocator) {
2169   if (FLAG_hydrogen_stats) {
2170     allocator_zone_start_allocation_size_ =
2171         allocator->zone()->allocation_size();
2172   }
2173 }
2174
2175
2176 LAllocatorPhase::~LAllocatorPhase() {
2177   if (FLAG_hydrogen_stats) {
2178     unsigned size = allocator_->zone()->allocation_size() -
2179                     allocator_zone_start_allocation_size_;
2180     isolate()->GetHStatistics()->SaveTiming(name(), base::TimeDelta(), size);
2181   }
2182
2183   if (ShouldProduceTraceOutput()) {
2184     isolate()->GetHTracer()->TraceLithium(name(), allocator_->chunk());
2185     isolate()->GetHTracer()->TraceLiveRanges(name(), allocator_);
2186   }
2187
2188 #ifdef DEBUG
2189   if (allocator_ != NULL) allocator_->Verify();
2190 #endif
2191 }
2192
2193
2194 } }  // namespace v8::internal