text: // Copyright 2011 the V8 project authors. All rights reserved.
  // Redistribution and use in source and binary forms, with or without
  // modification, are permitted provided that the following conditions are
  // met:
  //
  //     * Redistributions of source code must retain the above copyright
  //       notice, this list of conditions and the following disclaimer.
  //     * Redistributions in binary form must reproduce the above
  //       copyright notice, this list of conditions and the following
  //       disclaimer in the documentation and/or other materials provided
  //       with the distribution.
  //     * Neither the name of Google Inc. nor the names of its
  //       contributors may be used to endorse or promote products derived
  //       from this software without specific prior written permission.
  //
  // THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
  // "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
  // LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
  // A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
  // OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
  // SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
  // LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
  // DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
  // THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
  // (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
  // OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  
  #include "v8.h"
  
  #include "accessors.h"
  #include "api.h"
  #include "bootstrapper.h"
  #include "codegen.h"
  #include "compilation-cache.h"
  #include "debug.h"
  #include "deoptimizer.h"
  #include "global-handles.h"
  #include "heap-profiler.h"
  #include "liveobjectlist-inl.h"
  #include "mark-compact.h"
  #include "natives.h"
  #include "objects-visiting.h"
  #include "runtime-profiler.h"
  #include "scopeinfo.h"
  #include "snapshot.h"
  #include "v8threads.h"
  #include "vm-state-inl.h"
  #if V8_TARGET_ARCH_ARM && !V8_INTERPRETED_REGEXP
  #include "regexp-macro-assembler.h"
  #include "arm/regexp-macro-assembler-arm.h"
  #endif
  #if V8_TARGET_ARCH_MIPS && !V8_INTERPRETED_REGEXP
  #include "regexp-macro-assembler.h"
  #include "mips/regexp-macro-assembler-mips.h"
  #endif
  
  namespace v8 {
  namespace internal {
  
  
  static const intptr_t kMinimumPromotionLimit = 2 * MB;
  static const intptr_t kMinimumAllocationLimit = 8 * MB;
  
  
  static Mutex* gc_initializer_mutex = OS::CreateMutex();
  
  
  Heap::Heap()
      : isolate_(NULL),
  // semispace_size_ should be a power of 2 and old_generation_size_ should be
  // a multiple of Page::kPageSize.
  #if defined(ANDROID)
        reserved_semispace_size_(2*MB),
        max_semispace_size_(2*MB),
        initial_semispace_size_(128*KB),
        max_old_generation_size_(192*MB),
        max_executable_size_(max_old_generation_size_),
        code_range_size_(0),
  #elif defined(V8_TARGET_ARCH_X64)
        reserved_semispace_size_(16*MB),
        max_semispace_size_(16*MB),
        initial_semispace_size_(1*MB),
        max_old_generation_size_(1400*MB),
        max_executable_size_(256*MB),
        code_range_size_(512*MB),
  #else
        reserved_semispace_size_(8*MB),
        max_semispace_size_(8*MB),
        initial_semispace_size_(512*KB),
        max_old_generation_size_(700*MB),
        max_executable_size_(128*MB),
        code_range_size_(0),
  #endif
  // Variables set based on semispace_size_ and old_generation_size_ in
  // ConfigureHeap (survived_since_last_expansion_, external_allocation_limit_)
  // Will be 4 * reserved_semispace_size_ to ensure that young
  // generation can be aligned to its size.
        survived_since_last_expansion_(0),
        sweep_generation_(0),
        always_allocate_scope_depth_(0),
        linear_allocation_scope_depth_(0),
        contexts_disposed_(0),
        new_space_(this),
        old_pointer_space_(NULL),
        old_data_space_(NULL),
        code_space_(NULL),
        map_space_(NULL),
        cell_space_(NULL),
        lo_space_(NULL),
        gc_state_(NOT_IN_GC),
        gc_post_processing_depth_(0),
        mc_count_(0),
        ms_count_(0),
        gc_count_(0),
        unflattened_strings_length_(0),
  #ifdef DEBUG
        allocation_allowed_(true),
        allocation_timeout_(0),
        disallow_allocation_failure_(false),
        debug_utils_(NULL),
  #endif  // DEBUG
        old_gen_promotion_limit_(kMinimumPromotionLimit),
        old_gen_allocation_limit_(kMinimumAllocationLimit),
        external_allocation_limit_(0),
        amount_of_external_allocated_memory_(0),
        amount_of_external_allocated_memory_at_last_global_gc_(0),
        old_gen_exhausted_(false),
        hidden_symbol_(NULL),
        global_gc_prologue_callback_(NULL),
        global_gc_epilogue_callback_(NULL),
        gc_safe_size_of_old_object_(NULL),
        total_regexp_code_generated_(0),
        tracer_(NULL),
        young_survivors_after_last_gc_(0),
        high_survival_rate_period_length_(0),
        survival_rate_(0),
        previous_survival_rate_trend_(Heap::STABLE),
        survival_rate_trend_(Heap::STABLE),
        max_gc_pause_(0),
        max_alive_after_gc_(0),
        min_in_mutator_(kMaxInt),
        alive_after_last_gc_(0),
        last_gc_end_timestamp_(0.0),
        page_watermark_invalidated_mark_(1 << Page::WATERMARK_INVALIDATED),
        number_idle_notifications_(0),
        last_idle_notification_gc_count_(0),
        last_idle_notification_gc_count_init_(false),
        configured_(false),
        is_safe_to_read_maps_(true) {
    // Allow build-time customization of the max semispace size. Building
    // V8 with snapshots and a non-default max semispace size is much
    // easier if you can define it as part of the build environment.
  #if defined(V8_MAX_SEMISPACE_SIZE)
    max_semispace_size_ = reserved_semispace_size_ = V8_MAX_SEMISPACE_SIZE;
  #endif
  
    intptr_t max_virtual = OS::MaxVirtualMemory();
  
    if (max_virtual > 0) {
      if (code_range_size_ > 0) {
        // Reserve no more than 1/8 of the memory for the code range.
        code_range_size_ = Min(code_range_size_, max_virtual >> 3);
      }
    }
  
    memset(roots_, 0, sizeof(roots_[0]) * kRootListLength);
    global_contexts_list_ = NULL;
    mark_compact_collector_.heap_ = this;
    external_string_table_.heap_ = this;
  }
  
  
  intptr_t Heap::Capacity() {
    if (!HasBeenSetup()) return 0;
  
    return new_space_.Capacity() +
        old_pointer_space_->Capacity() +
        old_data_space_->Capacity() +
        code_space_->Capacity() +
        map_space_->Capacity() +
        cell_space_->Capacity();
  }
  
  
  intptr_t Heap::CommittedMemory() {
    if (!HasBeenSetup()) return 0;
  
    return new_space_.CommittedMemory() +
        old_pointer_space_->CommittedMemory() +
        old_data_space_->CommittedMemory() +
        code_space_->CommittedMemory() +
        map_space_->CommittedMemory() +
        cell_space_->CommittedMemory() +
        lo_space_->Size();
  }
  
  intptr_t Heap::CommittedMemoryExecutable() {
    if (!HasBeenSetup()) return 0;
  
    return isolate()->memory_allocator()->SizeExecutable();
  }
  
  
  intptr_t Heap::Available() {
    if (!HasBeenSetup()) return 0;
  
    return new_space_.Available() +
        old_pointer_space_->Available() +
        old_data_space_->Available() +
        code_space_->Available() +
        map_space_->Available() +
        cell_space_->Available();
  }
  
  
  bool Heap::HasBeenSetup() {
    return old_pointer_space_ != NULL &&
           old_data_space_ != NULL &&
           code_space_ != NULL &&
           map_space_ != NULL &&
           cell_space_ != NULL &&
           lo_space_ != NULL;
  }
  
  
  int Heap::GcSafeSizeOfOldObject(HeapObject* object) {
    ASSERT(!HEAP->InNewSpace(object));  // Code only works for old objects.
    ASSERT(!HEAP->mark_compact_collector()->are_map_pointers_encoded());
    MapWord map_word = object->map_word();
    map_word.ClearMark();
    map_word.ClearOverflow();
    return object->SizeFromMap(map_word.ToMap());
  }
  
  
  int Heap::GcSafeSizeOfOldObjectWithEncodedMap(HeapObject* object) {
    ASSERT(!HEAP->InNewSpace(object));  // Code only works for old objects.
    ASSERT(HEAP->mark_compact_collector()->are_map_pointers_encoded());
    uint32_t marker = Memory::uint32_at(object->address());
    if (marker == MarkCompactCollector::kSingleFreeEncoding) {
      return kIntSize;
    } else if (marker == MarkCompactCollector::kMultiFreeEncoding) {
      return Memory::int_at(object->address() + kIntSize);
    } else {
      MapWord map_word = object->map_word();
      Address map_address = map_word.DecodeMapAddress(HEAP->map_space());
      Map* map = reinterpret_cast<Map*>(HeapObject::FromAddress(map_address));
      return object->SizeFromMap(map);
    }
  }
  
  
  GarbageCollector Heap::SelectGarbageCollector(AllocationSpace space) {
    // Is global GC requested?
    if (space != NEW_SPACE || FLAG_gc_global) {
      isolate_->counters()->gc_compactor_caused_by_request()->Increment();
      return MARK_COMPACTOR;
    }
  
    // Is enough data promoted to justify a global GC?
    if (OldGenerationPromotionLimitReached()) {
      isolate_->counters()->gc_compactor_caused_by_promoted_data()->Increment();
      return MARK_COMPACTOR;
    }
  
    // Have allocation in OLD and LO failed?
    if (old_gen_exhausted_) {
      isolate_->counters()->
          gc_compactor_caused_by_oldspace_exhaustion()->Increment();
      return MARK_COMPACTOR;
    }
  
    // Is there enough space left in OLD to guarantee that a scavenge can
    // succeed?
    //
    // Note that MemoryAllocator->MaxAvailable() undercounts the memory available
    // for object promotion. It counts only the bytes that the memory
    // allocator has not yet allocated from the OS and assigned to any space,
    // and does not count available bytes already in the old space or code
    // space.  Undercounting is safe---we may get an unrequested full GC when
    // a scavenge would have succeeded.
    if (isolate_->memory_allocator()->MaxAvailable() <= new_space_.Size()) {
      isolate_->counters()->
          gc_compactor_caused_by_oldspace_exhaustion()->Increment();
      return MARK_COMPACTOR;
    }
  
    // Default
    return SCAVENGER;
  }
  
  
  // TODO(1238405): Combine the infrastructure for --heap-stats and
  // --log-gc to avoid the complicated preprocessor and flag testing.
  void Heap::ReportStatisticsBeforeGC() {
    // Heap::ReportHeapStatistics will also log NewSpace statistics when
    // compiled --log-gc is set.  The following logic is used to avoid
    // double logging.
  #ifdef DEBUG
    if (FLAG_heap_stats || FLAG_log_gc) new_space_.CollectStatistics();
    if (FLAG_heap_stats) {
      ReportHeapStatistics("Before GC");
    } else if (FLAG_log_gc) {
      new_space_.ReportStatistics();
    }
    if (FLAG_heap_stats || FLAG_log_gc) new_space_.ClearHistograms();
  #else
    if (FLAG_log_gc) {
      new_space_.CollectStatistics();
      new_space_.ReportStatistics();
      new_space_.ClearHistograms();
    }
  #endif  // DEBUG
  }
  
  
  void Heap::PrintShortHeapStatistics() {
    if (!FLAG_trace_gc_verbose) return;
    PrintF("Memory allocator,   used: %8" V8_PTR_PREFIX "d"
               ", available: %8" V8_PTR_PREFIX "d\n",
           isolate_->memory_allocator()->Size(),
           isolate_->memory_allocator()->Available());
    PrintF("New space,          used: %8" V8_PTR_PREFIX "d"
               ", available: %8" V8_PTR_PREFIX "d\n",
           Heap::new_space_.Size(),
           new_space_.Available());
    PrintF("Old pointers,       used: %8" V8_PTR_PREFIX "d"
               ", available: %8" V8_PTR_PREFIX "d"
               ", waste: %8" V8_PTR_PREFIX "d\n",
           old_pointer_space_->Size(),
           old_pointer_space_->Available(),
           old_pointer_space_->Waste());
    PrintF("Old data space,     used: %8" V8_PTR_PREFIX "d"
               ", available: %8" V8_PTR_PREFIX "d"
               ", waste: %8" V8_PTR_PREFIX "d\n",
           old_data_space_->Size(),
           old_data_space_->Available(),
           old_data_space_->Waste());
    PrintF("Code space,         used: %8" V8_PTR_PREFIX "d"
               ", available: %8" V8_PTR_PREFIX "d"
               ", waste: %8" V8_PTR_PREFIX "d\n",
           code_space_->Size(),
           code_space_->Available(),
           code_space_->Waste());
    PrintF("Map space,          used: %8" V8_PTR_PREFIX "d"
               ", available: %8" V8_PTR_PREFIX "d"
               ", waste: %8" V8_PTR_PREFIX "d\n",
           map_space_->Size(),
           map_space_->Available(),
           map_space_->Waste());
    PrintF("Cell space,         used: %8" V8_PTR_PREFIX "d"
               ", available: %8" V8_PTR_PREFIX "d"
               ", waste: %8" V8_PTR_PREFIX "d\n",
           cell_space_->Size(),
           cell_space_->Available(),
           cell_space_->Waste());
    PrintF("Large object space, used: %8" V8_PTR_PREFIX "d"
               ", available: %8" V8_PTR_PREFIX "d\n",
           lo_space_->Size(),
           lo_space_->Available());
  }
  
  
  // TODO(1238405): Combine the infrastructure for --heap-stats and
  // --log-gc to avoid the complicated preprocessor and flag testing.
  void Heap::ReportStatisticsAfterGC() {
    // Similar to the before GC, we use some complicated logic to ensure that
    // NewSpace statistics are logged exactly once when --log-gc is turned on.
  #if defined(DEBUG)
    if (FLAG_heap_stats) {
      new_space_.CollectStatistics();
      ReportHeapStatistics("After GC");
    } else if (FLAG_log_gc) {
      new_space_.ReportStatistics();
    }
  #else
    if (FLAG_log_gc) new_space_.ReportStatistics();
  #endif  // DEBUG
  }
  
  
  void Heap::GarbageCollectionPrologue() {
    isolate_->transcendental_cache()->Clear();
    ClearJSFunctionResultCaches();
    gc_count_++;
    unflattened_strings_length_ = 0;
  #ifdef DEBUG
    ASSERT(allocation_allowed_ && gc_state_ == NOT_IN_GC);
    allow_allocation(false);
  
    if (FLAG_verify_heap) {
      Verify();
    }
  
    if (FLAG_gc_verbose) Print();
  #endif  // DEBUG
  
  #if defined(DEBUG)
    ReportStatisticsBeforeGC();
  #endif  // DEBUG
  
    LiveObjectList::GCPrologue();
  }
  
  intptr_t Heap::SizeOfObjects() {
    intptr_t total = 0;
    AllSpaces spaces;
    for (Space* space = spaces.next(); space != NULL; space = spaces.next()) {
      total += space->SizeOfObjects();
    }
    return total;
  }
  
  void Heap::GarbageCollectionEpilogue() {
    LiveObjectList::GCEpilogue();
  #ifdef DEBUG
    allow_allocation(true);
    ZapFromSpace();
  
    if (FLAG_verify_heap) {
      Verify();
    }
  
    if (FLAG_print_global_handles) isolate_->global_handles()->Print();
    if (FLAG_print_handles) PrintHandles();
    if (FLAG_gc_verbose) Print();
    if (FLAG_code_stats) ReportCodeStatistics("After GC");
  #endif
  
    isolate_->counters()->alive_after_last_gc()->Set(
        static_cast<int>(SizeOfObjects()));
  
    isolate_->counters()->symbol_table_capacity()->Set(
        symbol_table()->Capacity());
    isolate_->counters()->number_of_symbols()->Set(
        symbol_table()->NumberOfElements());
  #if defined(DEBUG)
    ReportStatisticsAfterGC();
  #endif  // DEBUG
  #ifdef ENABLE_DEBUGGER_SUPPORT
    isolate_->debug()->AfterGarbageCollection();
  #endif  // ENABLE_DEBUGGER_SUPPORT
  }
  
  
  void Heap::CollectAllGarbage(bool force_compaction) {
    // Since we are ignoring the return value, the exact choice of space does
    // not matter, so long as we do not specify NEW_SPACE, which would not
    // cause a full GC.
    mark_compact_collector_.SetForceCompaction(force_compaction);
    CollectGarbage(OLD_POINTER_SPACE);
    mark_compact_collector_.SetForceCompaction(false);
  }
  
  
  void Heap::CollectAllAvailableGarbage() {
    // Since we are ignoring the return value, the exact choice of space does
    // not matter, so long as we do not specify NEW_SPACE, which would not
    // cause a full GC.
    mark_compact_collector()->SetForceCompaction(true);
  
    // Major GC would invoke weak handle callbacks on weakly reachable
    // handles, but won't collect weakly reachable objects until next
    // major GC.  Therefore if we collect aggressively and weak handle callback
    // has been invoked, we rerun major GC to release objects which become
    // garbage.
    // Note: as weak callbacks can execute arbitrary code, we cannot
    // hope that eventually there will be no weak callbacks invocations.
    // Therefore stop recollecting after several attempts.
    const int kMaxNumberOfAttempts = 7;
    for (int attempt = 0; attempt < kMaxNumberOfAttempts; attempt++) {
      if (!CollectGarbage(OLD_POINTER_SPACE, MARK_COMPACTOR)) {
        break;
      }
    }
    mark_compact_collector()->SetForceCompaction(false);
  }
  
  
  bool Heap::CollectGarbage(AllocationSpace space, GarbageCollector collector) {
    // The VM is in the GC state until exiting this function.
    VMState state(isolate_, GC);
  
  #ifdef DEBUG
    // Reset the allocation timeout to the GC interval, but make sure to
    // allow at least a few allocations after a collection. The reason
    // for this is that we have a lot of allocation sequences and we
    // assume that a garbage collection will allow the subsequent
    // allocation attempts to go through.
    allocation_timeout_ = Max(6, FLAG_gc_interval);
  #endif
  
    bool next_gc_likely_to_collect_more = false;
  
    { GCTracer tracer(this);
      GarbageCollectionPrologue();
      // The GC count was incremented in the prologue.  Tell the tracer about
      // it.
      tracer.set_gc_count(gc_count_);
  
      // Tell the tracer which collector we've selected.
      tracer.set_collector(collector);
  
      HistogramTimer* rate = (collector == SCAVENGER)
          ? isolate_->counters()->gc_scavenger()
          : isolate_->counters()->gc_compactor();
      rate->Start();
      next_gc_likely_to_collect_more =
          PerformGarbageCollection(collector, &tracer);
      rate->Stop();
  
      GarbageCollectionEpilogue();
    }
  
    return next_gc_likely_to_collect_more;
  }
  
  
  void Heap::PerformScavenge() {
    GCTracer tracer(this);
    PerformGarbageCollection(SCAVENGER, &tracer);
  }
  
  
  #ifdef DEBUG
  // Helper class for verifying the symbol table.
  class SymbolTableVerifier : public ObjectVisitor {
   public:
    void VisitPointers(Object** start, Object** end) {
      // Visit all HeapObject pointers in [start, end).
      for (Object** p = start; p < end; p++) {
        if ((*p)->IsHeapObject()) {
          // Check that the symbol is actually a symbol.
          ASSERT((*p)->IsNull() || (*p)->IsUndefined() || (*p)->IsSymbol());
        }
      }
    }
  };
  #endif  // DEBUG
  
  
  static void VerifySymbolTable() {
  #ifdef DEBUG
    SymbolTableVerifier verifier;
    HEAP->symbol_table()->IterateElements(&verifier);
  #endif  // DEBUG
  }
  
  
  void Heap::ReserveSpace(
      int new_space_size,
      int pointer_space_size,
      int data_space_size,
      int code_space_size,
      int map_space_size,
      int cell_space_size,
      int large_object_size) {
    NewSpace* new_space = Heap::new_space();
    PagedSpace* old_pointer_space = Heap::old_pointer_space();
    PagedSpace* old_data_space = Heap::old_data_space();
    PagedSpace* code_space = Heap::code_space();
    PagedSpace* map_space = Heap::map_space();
    PagedSpace* cell_space = Heap::cell_space();
    LargeObjectSpace* lo_space = Heap::lo_space();
    bool gc_performed = true;
    int counter = 0;
    static const int kThreshold = 20;
    while (gc_performed && counter++ < kThreshold) {
      gc_performed = false;
      if (!new_space->ReserveSpace(new_space_size)) {
        Heap::CollectGarbage(NEW_SPACE);
        gc_performed = true;
      }
      if (!old_pointer_space->ReserveSpace(pointer_space_size)) {
        Heap::CollectGarbage(OLD_POINTER_SPACE);
        gc_performed = true;
      }
      if (!(old_data_space->ReserveSpace(data_space_size))) {
        Heap::CollectGarbage(OLD_DATA_SPACE);
        gc_performed = true;
      }
      if (!(code_space->ReserveSpace(code_space_size))) {
        Heap::CollectGarbage(CODE_SPACE);
        gc_performed = true;
      }
      if (!(map_space->ReserveSpace(map_space_size))) {
        Heap::CollectGarbage(MAP_SPACE);
        gc_performed = true;
      }
      if (!(cell_space->ReserveSpace(cell_space_size))) {
        Heap::CollectGarbage(CELL_SPACE);
        gc_performed = true;
      }
      // We add a slack-factor of 2 in order to have space for a series of
      // large-object allocations that are only just larger than the page size.
      large_object_size *= 2;
      // The ReserveSpace method on the large object space checks how much
      // we can expand the old generation.  This includes expansion caused by
      // allocation in the other spaces.
      large_object_size += cell_space_size + map_space_size + code_space_size +
          data_space_size + pointer_space_size;
      if (!(lo_space->ReserveSpace(large_object_size))) {
        Heap::CollectGarbage(LO_SPACE);
        gc_performed = true;
      }
    }
  
    if (gc_performed) {
      // Failed to reserve the space after several attempts.
      V8::FatalProcessOutOfMemory("Heap::ReserveSpace");
    }
  }
  
  
  void Heap::EnsureFromSpaceIsCommitted() {
    if (new_space_.CommitFromSpaceIfNeeded()) return;
  
    // Committing memory to from space failed.
    // Try shrinking and try again.
    PagedSpaces spaces;
    for (PagedSpace* space = spaces.next();
         space != NULL;
         space = spaces.next()) {
      space->RelinkPageListInChunkOrder(true);
    }
  
    Shrink();
    if (new_space_.CommitFromSpaceIfNeeded()) return;
  
    // Committing memory to from space failed again.
    // Memory is exhausted and we will die.
    V8::FatalProcessOutOfMemory("Committing semi space failed.");
  }
  
  
  void Heap::ClearJSFunctionResultCaches() {
    if (isolate_->bootstrapper()->IsActive()) return;
  
    Object* context = global_contexts_list_;
    while (!context->IsUndefined()) {
      // Get the caches for this context:
      FixedArray* caches =
        Context::cast(context)->jsfunction_result_caches();
      // Clear the caches:
      int length = caches->length();
      for (int i = 0; i < length; i++) {
        JSFunctionResultCache::cast(caches->get(i))->Clear();
      }
      // Get the next context:
      context = Context::cast(context)->get(Context::NEXT_CONTEXT_LINK);
    }
  }
  
  
  
  void Heap::ClearNormalizedMapCaches() {
    if (isolate_->bootstrapper()->IsActive()) return;
  
    Object* context = global_contexts_list_;
    while (!context->IsUndefined()) {
      Context::cast(context)->normalized_map_cache()->Clear();
      context = Context::cast(context)->get(Context::NEXT_CONTEXT_LINK);
    }
  }
  
  
  #ifdef DEBUG
  
  enum PageWatermarkValidity {
    ALL_VALID,
    ALL_INVALID
  };
  
  static void VerifyPageWatermarkValidity(PagedSpace* space,
                                          PageWatermarkValidity validity) {
    PageIterator it(space, PageIterator::PAGES_IN_USE);
    bool expected_value = (validity == ALL_VALID);
    while (it.has_next()) {
      Page* page = it.next();
      ASSERT(page->IsWatermarkValid() == expected_value);
    }
  }
  #endif
  
  void Heap::UpdateSurvivalRateTrend(int start_new_space_size) {
    double survival_rate =
        (static_cast<double>(young_survivors_after_last_gc_) * 100) /
        start_new_space_size;
  
    if (survival_rate > kYoungSurvivalRateThreshold) {
      high_survival_rate_period_length_++;
    } else {
      high_survival_rate_period_length_ = 0;
    }
  
    double survival_rate_diff = survival_rate_ - survival_rate;
  
    if (survival_rate_diff > kYoungSurvivalRateAllowedDeviation) {
      set_survival_rate_trend(DECREASING);
    } else if (survival_rate_diff < -kYoungSurvivalRateAllowedDeviation) {
      set_survival_rate_trend(INCREASING);
    } else {
      set_survival_rate_trend(STABLE);
    }
  
    survival_rate_ = survival_rate;
  }
  
  bool Heap::PerformGarbageCollection(GarbageCollector collector,
                                      GCTracer* tracer) {
    bool next_gc_likely_to_collect_more = false;
  
    if (collector != SCAVENGER) {
      PROFILE(isolate_, CodeMovingGCEvent());
    }
  
    VerifySymbolTable();
    if (collector == MARK_COMPACTOR && global_gc_prologue_callback_) {
      ASSERT(!allocation_allowed_);
      GCTracer::Scope scope(tracer, GCTracer::Scope::EXTERNAL);
      global_gc_prologue_callback_();
    }
  
    GCType gc_type =
        collector == MARK_COMPACTOR ? kGCTypeMarkSweepCompact : kGCTypeScavenge;
  
    for (int i = 0; i < gc_prologue_callbacks_.length(); ++i) {
      if (gc_type & gc_prologue_callbacks_[i].gc_type) {
        gc_prologue_callbacks_[i].callback(gc_type, kNoGCCallbackFlags);
      }
    }
  
    EnsureFromSpaceIsCommitted();
  
    int start_new_space_size = Heap::new_space()->SizeAsInt();
  
    if (collector == MARK_COMPACTOR) {
      // Perform mark-sweep with optional compaction.
      MarkCompact(tracer);
      sweep_generation_++;
      bool high_survival_rate_during_scavenges = IsHighSurvivalRate() &&
          IsStableOrIncreasingSurvivalTrend();
  
      UpdateSurvivalRateTrend(start_new_space_size);
  
      intptr_t old_gen_size = PromotedSpaceSize();
      old_gen_promotion_limit_ =
          old_gen_size + Max(kMinimumPromotionLimit, old_gen_size / 3);
      old_gen_allocation_limit_ =
          old_gen_size + Max(kMinimumAllocationLimit, old_gen_size / 2);
  
      if (high_survival_rate_during_scavenges &&
          IsStableOrIncreasingSurvivalTrend()) {
        // Stable high survival rates of young objects both during partial and
        // full collection indicate that mutator is either building or modifying
        // a structure with a long lifetime.
        // In this case we aggressively raise old generation memory limits to
        // postpone subsequent mark-sweep collection and thus trade memory
        // space for the mutation speed.
        old_gen_promotion_limit_ *= 2;
        old_gen_allocation_limit_ *= 2;
      }
  
      old_gen_exhausted_ = false;
    } else {
      tracer_ = tracer;
      Scavenge();
      tracer_ = NULL;
  
      UpdateSurvivalRateTrend(start_new_space_size);
    }
  
    isolate_->counters()->objs_since_last_young()->Set(0);
  
    gc_post_processing_depth_++;
    { DisableAssertNoAllocation allow_allocation;
      GCTracer::Scope scope(tracer, GCTracer::Scope::EXTERNAL);
      next_gc_likely_to_collect_more =
          isolate_->global_handles()->PostGarbageCollectionProcessing(collector);
    }
    gc_post_processing_depth_--;
  
    // Update relocatables.
    Relocatable::PostGarbageCollectionProcessing();
  
    if (collector == MARK_COMPACTOR) {
      // Register the amount of external allocated memory.
      amount_of_external_allocated_memory_at_last_global_gc_ =
          amount_of_external_allocated_memory_;
    }
  
    GCCallbackFlags callback_flags = tracer->is_compacting()
        ? kGCCallbackFlagCompacted
        : kNoGCCallbackFlags;
    for (int i = 0; i < gc_epilogue_callbacks_.length(); ++i) {
      if (gc_type & gc_epilogue_callbacks_[i].gc_type) {
        gc_epilogue_callbacks_[i].callback(gc_type, callback_flags);
      }
    }
  
    if (collector == MARK_COMPACTOR && global_gc_epilogue_callback_) {
      ASSERT(!allocation_allowed_);
      GCTracer::Scope scope(tracer, GCTracer::Scope::EXTERNAL);
      global_gc_epilogue_callback_();
    }
    VerifySymbolTable();
  
    return next_gc_likely_to_collect_more;
  }
  
  
  void Heap::MarkCompact(GCTracer* tracer) {
    gc_state_ = MARK_COMPACT;
    LOG(isolate_, ResourceEvent("markcompact", "begin"));
  
    mark_compact_collector_.Prepare(tracer);
  
    bool is_compacting = mark_compact_collector_.IsCompacting();
  
    if (is_compacting) {
      mc_count_++;
    } else {
      ms_count_++;
    }
    tracer->set_full_gc_count(mc_count_ + ms_count_);
  
    MarkCompactPrologue(is_compacting);
  
    is_safe_to_read_maps_ = false;
    mark_compact_collector_.CollectGarbage();
    is_safe_to_read_maps_ = true;
  
    LOG(isolate_, ResourceEvent("markcompact", "end"));
  
    gc_state_ = NOT_IN_GC;
  
    Shrink();
  
    isolate_->counters()->objs_since_last_full()->Set(0);
  
    contexts_disposed_ = 0;
  }
  
  
  void Heap::MarkCompactPrologue(bool is_compacting) {
    // At any old GC clear the keyed lookup cache to enable collection of unused
    // maps.
    isolate_->keyed_lookup_cache()->Clear();
    isolate_->context_slot_cache()->Clear();
    isolate_->descriptor_lookup_cache()->Clear();
    StringSplitCache::Clear(string_split_cache());
  
    isolate_->compilation_cache()->MarkCompactPrologue();
  
    CompletelyClearInstanceofCache();
  
    if (is_compacting) FlushNumberStringCache();
    if (FLAG_cleanup_code_caches_at_gc) {
      polymorphic_code_cache()->set_cache(undefined_value());
    }
  
    ClearNormalizedMapCaches();
  }
  
  
  Object* Heap::FindCodeObject(Address a) {
    Object* obj = NULL;  // Initialization to please compiler.
    { MaybeObject* maybe_obj = code_space_->FindObject(a);
      if (!maybe_obj->ToObject(&obj)) {
        obj = lo_space_->FindObject(a)->ToObjectUnchecked();
      }
    }
    return obj;
  }
  
  
  // Helper class for copying HeapObjects
  class ScavengeVisitor: public ObjectVisitor {
   public:
    explicit ScavengeVisitor(Heap* heap) : heap_(heap) {}
  
    void VisitPointer(Object** p) { ScavengePointer(p); }
  
    void VisitPointers(Object** start, Object** end) {
      // Copy all HeapObject pointers in [start, end)
      for (Object** p = start; p < end; p++) ScavengePointer(p);
    }
  
   private:
    void ScavengePointer(Object** p) {
      Object* object = *p;
      if (!heap_->InNewSpace(object)) return;
      Heap::ScavengeObject(reinterpret_cast<HeapObject**>(p),
                           reinterpret_cast<HeapObject*>(object));
    }
  
    Heap* heap_;
  };
  
  
  #ifdef DEBUG
  // Visitor class to verify pointers in code or data space do not point into
  // new space.
  class VerifyNonPointerSpacePointersVisitor: public ObjectVisitor {
   public:
    void VisitPointers(Object** start, Object**end) {
      for (Object** current = start; current < end; current++) {
        if ((*current)->IsHeapObject()) {
          ASSERT(!HEAP->InNewSpace(HeapObject::cast(*current)));
        }
      }
    }
  };
  
  
  static void VerifyNonPointerSpacePointers() {
    // Verify that there are no pointers to new space in spaces where we
    // do not expect them.
    VerifyNonPointerSpacePointersVisitor v;
    HeapObjectIterator code_it(HEAP->code_space());
    for (HeapObject* object = code_it.next();
         object != NULL; object = code_it.next())
      object->Iterate(&v);
  
    HeapObjectIterator data_it(HEAP->old_data_space());
    for (HeapObject* object = data_it.next();
         object != NULL; object = data_it.next())
      object->Iterate(&v);
  }
  #endif
  
  
  void Heap::CheckNewSpaceExpansionCriteria() {
    if (new_space_.Capacity() < new_space_.MaximumCapacity() &&
        survived_since_last_expansion_ > new_space_.Capacity()) {
      // Grow the size of new space if there is room to grow and enough
      // data has survived scavenge since the last expansion.
      new_space_.Grow();
      survived_since_last_expansion_ = 0;
    }
  }
  
  
  static bool IsUnscavengedHeapObject(Heap* heap, Object** p) {
    return heap->InNewSpace(*p) &&
        !HeapObject::cast(*p)->map_word().IsForwardingAddress();
  }
  
  
  void Heap::Scavenge() {
  #ifdef DEBUG
    if (FLAG_enable_slow_asserts) VerifyNonPointerSpacePointers();
  #endif
  
    gc_state_ = SCAVENGE;
  
    SwitchScavengingVisitorsTableIfProfilingWasEnabled();
  
    Page::FlipMeaningOfInvalidatedWatermarkFlag(this);
  #ifdef DEBUG
    VerifyPageWatermarkValidity(old_pointer_space_, ALL_VALID);
    VerifyPageWatermarkValidity(map_space_, ALL_VALID);
  #endif
  
    // We do not update an allocation watermark of the top page during linear
    // allocation to avoid overhead. So to maintain the watermark invariant
    // we have to manually cache the watermark and mark the top page as having an
    // invalid watermark. This guarantees that dirty regions iteration will use a
    // correct watermark even if a linear allocation happens.
    old_pointer_space_->FlushTopPageWatermark();
    map_space_->FlushTopPageWatermark();
  
    // Implements Cheney's copying algorithm
    LOG(isolate_, ResourceEvent("scavenge", "begin"));
  
    // Clear descriptor cache.
    isolate_->descriptor_lookup_cache()->Clear();
  
    // Used for updating survived_since_last_expansion_ at function end.
    intptr_t survived_watermark = PromotedSpaceSize();
  
    CheckNewSpaceExpansionCriteria();
  
    // Flip the semispaces.  After flipping, to space is empty, from space has
    // live objects.
    new_space_.Flip();
    new_space_.ResetAllocationInfo();
  
    // We need to sweep newly copied objects which can be either in the
    // to space or promoted to the old generation.  For to-space
    // objects, we treat the bottom of the to space as a queue.  Newly
    // copied and unswept objects lie between a 'front' mark and the
    // allocation pointer.
    //
    // Promoted objects can go into various old-generation spaces, and
    // can be allocated internally in the spaces (from the free list).
    // We treat the top of the to space as a queue of addresses of
    // promoted objects.  The addresses of newly promoted and unswept
    // objects lie between a 'front' mark and a 'rear' mark that is
    // updated as a side effect of promoting an object.
    //
    // There is guaranteed to be enough room at the top of the to space
    // for the addresses of promoted objects: every object promoted
    // frees up its size in bytes from the top of the new space, and
    // objects are at least one pointer in size.
    Address new_space_front = new_space_.ToSpaceLow();
    promotion_queue_.Initialize(new_space_.ToSpaceHigh());
  
    is_safe_to_read_maps_ = false;
    ScavengeVisitor scavenge_visitor(this);
    // Copy roots.
    IterateRoots(&scavenge_visitor, VISIT_ALL_IN_SCAVENGE);
  
    // Copy objects reachable from the old generation.  By definition,
    // there are no intergenerational pointers in code or data spaces.
    IterateDirtyRegions(old_pointer_space_,
                        &Heap::IteratePointersInDirtyRegion,
                        &ScavengePointer,
                        WATERMARK_CAN_BE_INVALID);
  
    IterateDirtyRegions(map_space_,
                        &IteratePointersInDirtyMapsRegion,
                        &ScavengePointer,
                        WATERMARK_CAN_BE_INVALID);
  
    lo_space_->IterateDirtyRegions(&ScavengePointer);
  
    // Copy objects reachable from cells by scavenging cell values directly.
    HeapObjectIterator cell_iterator(cell_space_);
    for (HeapObject* cell = cell_iterator.next();
         cell != NULL; cell = cell_iterator.next()) {
      if (cell->IsJSGlobalPropertyCell()) {
        Address value_address =
            reinterpret_cast<Address>(cell) +
            (JSGlobalPropertyCell::kValueOffset - kHeapObjectTag);
        scavenge_visitor.VisitPointer(reinterpret_cast<Object**>(value_address));
      }
    }
  
    // Scavenge object reachable from the global contexts list directly.
    scavenge_visitor.VisitPointer(BitCast<Object**>(&global_contexts_list_));
  
    new_space_front = DoScavenge(&scavenge_visitor, new_space_front);
    isolate_->global_handles()->IdentifyNewSpaceWeakIndependentHandles(
        &IsUnscavengedHeapObject);
    isolate_->global_handles()->IterateNewSpaceWeakIndependentRoots(
        &scavenge_visitor);
    new_space_front = DoScavenge(&scavenge_visitor, new_space_front);
  
  
    UpdateNewSpaceReferencesInExternalStringTable(
        &UpdateNewSpaceReferenceInExternalStringTableEntry);
  
    LiveObjectList::UpdateReferencesForScavengeGC();
    isolate()->runtime_profiler()->UpdateSamplesAfterScavenge();
  
    ASSERT(new_space_front == new_space_.top());
  
    is_safe_to_read_maps_ = true;
  
    // Set age mark.
    new_space_.set_age_mark(new_space_.top());
  
    // Update how much has survived scavenge.
    IncrementYoungSurvivorsCounter(static_cast<int>(
        (PromotedSpaceSize() - survived_watermark) + new_space_.Size()));
  
    LOG(isolate_, ResourceEvent("scavenge", "end"));
  
    gc_state_ = NOT_IN_GC;
  }
  
  
  String* Heap::UpdateNewSpaceReferenceInExternalStringTableEntry(Heap* heap,
                                                                  Object** p) {
    MapWord first_word = HeapObject::cast(*p)->map_word();
  
    if (!first_word.IsForwardingAddress()) {
      // Unreachable external string can be finalized.
      heap->FinalizeExternalString(String::cast(*p));
      return NULL;
    }
  
    // String is still reachable.
    return String::cast(first_word.ToForwardingAddress());
  }
  
  
  void Heap::UpdateNewSpaceReferencesInExternalStringTable(
      ExternalStringTableUpdaterCallback updater_func) {
    external_string_table_.Verify();
  
    if (external_string_table_.new_space_strings_.is_empty()) return;
  
    Object** start = &external_string_table_.new_space_strings_[0];
    Object** end = start + external_string_table_.new_space_strings_.length();
    Object** last = start;
  
    for (Object** p = start; p < end; ++p) {
      ASSERT(InFromSpace(*p));
      String* target = updater_func(this, p);
  
      if (target == NULL) continue;
  
      ASSERT(target->IsExternalString());
  
      if (InNewSpace(target)) {
        // String is still in new space.  Update the table entry.
        *last = target;
        ++last;
      } else {
        // String got promoted.  Move it to the old string list.
        external_string_table_.AddOldString(target);
      }
    }
  
    ASSERT(last <= end);
    external_string_table_.ShrinkNewStrings(static_cast<int>(last - start));
  }
  
  
  static Object* ProcessFunctionWeakReferences(Heap* heap,
                                               Object* function,
                                               WeakObjectRetainer* retainer) {
    Object* head = heap->undefined_value();
    JSFunction* tail = NULL;
    Object* candidate = function;
    while (candidate != heap->undefined_value()) {
      // Check whether to keep the candidate in the list.
      JSFunction* candidate_function = reinterpret_cast<JSFunction*>(candidate);
      Object* retain = retainer->RetainAs(candidate);
      if (retain != NULL) {
        if (head == heap->undefined_value()) {
          // First element in the list.
          head = candidate_function;
        } else {
          // Subsequent elements in the list.
          ASSERT(tail != NULL);
          tail->set_next_function_link(candidate_function);
        }
        // Retained function is new tail.
        tail = candidate_function;
      }
      // Move to next element in the list.
      candidate = candidate_function->next_function_link();
    }
  
    // Terminate the list if there is one or more elements.
    if (tail != NULL) {
      tail->set_next_function_link(heap->undefined_value());
    }
  
    return head;
  }
  
  
  void Heap::ProcessWeakReferences(WeakObjectRetainer* retainer) {
    Object* head = undefined_value();
    Context* tail = NULL;
    Object* candidate = global_contexts_list_;
    while (candidate != undefined_value()) {
      // Check whether to keep the candidate in the list.
      Context* candidate_context = reinterpret_cast<Context*>(candidate);
      Object* retain = retainer->RetainAs(candidate);
      if (retain != NULL) {
        if (head == undefined_value()) {
          // First element in the list.
          head = candidate_context;
        } else {
          // Subsequent elements in the list.
          ASSERT(tail != NULL);
          tail->set_unchecked(this,
                              Context::NEXT_CONTEXT_LINK,
                              candidate_context,
                              UPDATE_WRITE_BARRIER);
        }
        // Retained context is new tail.
        tail = candidate_context;
  
        // Process the weak list of optimized functions for the context.
        Object* function_list_head =
            ProcessFunctionWeakReferences(
                this,
                candidate_context->get(Context::OPTIMIZED_FUNCTIONS_LIST),
                retainer);
        candidate_context->set_unchecked(this,
                                         Context::OPTIMIZED_FUNCTIONS_LIST,
                                         function_list_head,
                                         UPDATE_WRITE_BARRIER);
      }
      // Move to next element in the list.
      candidate = candidate_context->get(Context::NEXT_CONTEXT_LINK);
    }
  
    // Terminate the list if there is one or more elements.
    if (tail != NULL) {
      tail->set_unchecked(this,
                          Context::NEXT_CONTEXT_LINK,
                          Heap::undefined_value(),
                          UPDATE_WRITE_BARRIER);
    }
  
    // Update the head of the list of contexts.
    global_contexts_list_ = head;
  }
  
  
  class NewSpaceScavenger : public StaticNewSpaceVisitor<NewSpaceScavenger> {
   public:
    static inline void VisitPointer(Heap* heap, Object** p) {
      Object* object = *p;
      if (!heap->InNewSpace(object)) return;
      Heap::ScavengeObject(reinterpret_cast<HeapObject**>(p),
                           reinterpret_cast<HeapObject*>(object));
    }
  };
  
  
  Address Heap::DoScavenge(ObjectVisitor* scavenge_visitor,
                           Address new_space_front) {
    do {
      ASSERT(new_space_front <= new_space_.top());
  
      // The addresses new_space_front and new_space_.top() define a
      // queue of unprocessed copied objects.  Process them until the
      // queue is empty.
      while (new_space_front < new_space_.top()) {
        HeapObject* object = HeapObject::FromAddress(new_space_front);
        new_space_front += NewSpaceScavenger::IterateBody(object->map(), object);
      }
  
      // Promote and process all the to-be-promoted objects.
      while (!promotion_queue_.is_empty()) {
        HeapObject* target;
        int size;
        promotion_queue_.remove(&target, &size);
  
        // Promoted object might be already partially visited
        // during dirty regions iteration. Thus we search specificly
        // for pointers to from semispace instead of looking for pointers
        // to new space.
        ASSERT(!target->IsMap());
        IterateAndMarkPointersToFromSpace(target->address(),
                                          target->address() + size,
                                          &ScavengePointer);
      }
  
      // Take another spin if there are now unswept objects in new space
      // (there are currently no more unswept promoted objects).
    } while (new_space_front < new_space_.top());
  
    return new_space_front;
  }
  
  
  enum LoggingAndProfiling {
    LOGGING_AND_PROFILING_ENABLED,
    LOGGING_AND_PROFILING_DISABLED
  };
  
  
  typedef void (*ScavengingCallback)(Map* map,
                                     HeapObject** slot,
                                     HeapObject* object);
  
  
  static Atomic32 scavenging_visitors_table_mode_;
  static VisitorDispatchTable<ScavengingCallback> scavenging_visitors_table_;
  
  
  INLINE(static void DoScavengeObject(Map* map,
                                      HeapObject** slot,
                                      HeapObject* obj));
  
  
  void DoScavengeObject(Map* map, HeapObject** slot, HeapObject* obj) {
    scavenging_visitors_table_.GetVisitor(map)(map, slot, obj);
  }
  
  
  template<LoggingAndProfiling logging_and_profiling_mode>
  class ScavengingVisitor : public StaticVisitorBase {
   public:
    static void Initialize() {
      table_.Register(kVisitSeqAsciiString, &EvacuateSeqAsciiString);
      table_.Register(kVisitSeqTwoByteString, &EvacuateSeqTwoByteString);
      table_.Register(kVisitShortcutCandidate, &EvacuateShortcutCandidate);
      table_.Register(kVisitByteArray, &EvacuateByteArray);
      table_.Register(kVisitFixedArray, &EvacuateFixedArray);
      table_.Register(kVisitFixedDoubleArray, &EvacuateFixedDoubleArray);
  
      table_.Register(kVisitGlobalContext,
                      &ObjectEvacuationStrategy<POINTER_OBJECT>::
                          template VisitSpecialized<Context::kSize>);
  
      table_.Register(kVisitConsString,
                      &ObjectEvacuationStrategy<POINTER_OBJECT>::
                          template VisitSpecialized<ConsString::kSize>);
  
      table_.Register(kVisitSlicedString,
                      &ObjectEvacuationStrategy<POINTER_OBJECT>::
                          template VisitSpecialized<SlicedString::kSize>);
  
      table_.Register(kVisitSharedFunctionInfo,
                      &ObjectEvacuationStrategy<POINTER_OBJECT>::
                          template VisitSpecialized<SharedFunctionInfo::kSize>);
  
      table_.Register(kVisitJSWeakMap,
                      &ObjectEvacuationStrategy<POINTER_OBJECT>::
                      Visit);
  
      table_.Register(kVisitJSRegExp,
                      &ObjectEvacuationStrategy<POINTER_OBJECT>::
                      Visit);
  
      table_.Register(kVisitJSFunction,
                      &ObjectEvacuationStrategy<POINTER_OBJECT>::
                          template VisitSpecialized<JSFunction::kSize>);
  
      table_.RegisterSpecializations<ObjectEvacuationStrategy<DATA_OBJECT>,
                                     kVisitDataObject,
                                     kVisitDataObjectGeneric>();
  
      table_.RegisterSpecializations<ObjectEvacuationStrategy<POINTER_OBJECT>,
                                     kVisitJSObject,
                                     kVisitJSObjectGeneric>();
  
      table_.RegisterSpecializations<ObjectEvacuationStrategy<POINTER_OBJECT>,
                                     kVisitStruct,
                                     kVisitStructGeneric>();
    }
  
    static VisitorDispatchTable<ScavengingCallback>* GetTable() {
      return &table_;
    }
  
   private:
    enum ObjectContents  { DATA_OBJECT, POINTER_OBJECT };
    enum SizeRestriction { SMALL, UNKNOWN_SIZE };
  
    static void RecordCopiedObject(Heap* heap, HeapObject* obj) {
      bool should_record = false;
  #ifdef DEBUG
      should_record = FLAG_heap_stats;
  #endif
      should_record = should_record || FLAG_log_gc;
      if (should_record) {
        if (heap->new_space()->Contains(obj)) {
          heap->new_space()->RecordAllocation(obj);
        } else {
          heap->new_space()->RecordPromotion(obj);
        }
      }
    }
  
    // Helper function used by CopyObject to copy a source object to an
    // allocated target object and update the forwarding pointer in the source
    // object.  Returns the target object.
    INLINE(static HeapObject* MigrateObject(Heap* heap,
                                            HeapObject* source,
                                            HeapObject* target,
                                            int size)) {
      // Copy the content of source to target.
      heap->CopyBlock(target->address(), source->address(), size);
  
      // Set the forwarding address.
      source->set_map_word(MapWord::FromForwardingAddress(target));
  
      if (logging_and_profiling_mode == LOGGING_AND_PROFILING_ENABLED) {
        // Update NewSpace stats if necessary.
        RecordCopiedObject(heap, target);
        HEAP_PROFILE(heap, ObjectMoveEvent(source->address(), target->address()));
        Isolate* isolate = heap->isolate();
        if (isolate->logger()->is_logging() ||
            CpuProfiler::is_profiling(isolate)) {
          if (target->IsSharedFunctionInfo()) {
            PROFILE(isolate, SharedFunctionInfoMoveEvent(
                source->address(), target->address()));
          }
        }
      }
  
      return target;
    }
  
  
    template<ObjectContents object_contents, SizeRestriction size_restriction>
    static inline void EvacuateObject(Map* map,
                                      HeapObject** slot,
                                      HeapObject* object,
                                      int object_size) {
      ASSERT((size_restriction != SMALL) ||
             (object_size <= Page::kMaxHeapObjectSize));
      ASSERT(object->Size() == object_size);
  
      Heap* heap = map->heap();
      if (heap->ShouldBePromoted(object->address(), object_size)) {
        MaybeObject* maybe_result;
  
        if ((size_restriction != SMALL) &&
            (object_size > Page::kMaxHeapObjectSize)) {
          maybe_result = heap->lo_space()->AllocateRawFixedArray(object_size);
        } else {
          if (object_contents == DATA_OBJECT) {
            maybe_result = heap->old_data_space()->AllocateRaw(object_size);
          } else {
            maybe_result = heap->old_pointer_space()->AllocateRaw(object_size);
          }
        }
  
        Object* result = NULL;  // Initialization to please compiler.
        if (maybe_result->ToObject(&result)) {
          HeapObject* target = HeapObject::cast(result);
          *slot = MigrateObject(heap, object , target, object_size);
  
          if (object_contents == POINTER_OBJECT) {
            heap->promotion_queue()->insert(target, object_size);
          }
  
          heap->tracer()->increment_promoted_objects_size(object_size);
          return;
        }
      }
      Object* result =
          heap->new_space()->AllocateRaw(object_size)->ToObjectUnchecked();
      *slot = MigrateObject(heap, object, HeapObject::cast(result), object_size);
      return;
    }
  
  
    static inline void EvacuateFixedArray(Map* map,
                                          HeapObject** slot,
                                          HeapObject* object) {
      int object_size = FixedArray::BodyDescriptor::SizeOf(map, object);
      EvacuateObject<POINTER_OBJECT, UNKNOWN_SIZE>(map,
                                                   slot,
                                                   object,
                                                   object_size);
    }
  
  
    static inline void EvacuateFixedDoubleArray(Map* map,
                                                HeapObject** slot,
                                                HeapObject* object) {
      int length = reinterpret_cast<FixedDoubleArray*>(object)->length();
      int object_size = FixedDoubleArray::SizeFor(length);
      EvacuateObject<DATA_OBJECT, UNKNOWN_SIZE>(map,
                                                slot,
                                                object,
                                                object_size);
    }
  
  
    static inline void EvacuateByteArray(Map* map,
                                         HeapObject** slot,
                                         HeapObject* object) {
      int object_size = reinterpret_cast<ByteArray*>(object)->ByteArraySize();
      EvacuateObject<DATA_OBJECT, UNKNOWN_SIZE>(map, slot, object, object_size);
    }
  
  
    static inline void EvacuateSeqAsciiString(Map* map,
                                              HeapObject** slot,
                                              HeapObject* object) {
      int object_size = SeqAsciiString::cast(object)->
          SeqAsciiStringSize(map->instance_type());
      EvacuateObject<DATA_OBJECT, UNKNOWN_SIZE>(map, slot, object, object_size);
    }
  
  
    static inline void EvacuateSeqTwoByteString(Map* map,
                                                HeapObject** slot,
                                                HeapObject* object) {
      int object_size = SeqTwoByteString::cast(object)->
          SeqTwoByteStringSize(map->instance_type());
      EvacuateObject<DATA_OBJECT, UNKNOWN_SIZE>(map, slot, object, object_size);
    }
  
  
    static inline bool IsShortcutCandidate(int type) {
      return ((type & kShortcutTypeMask) == kShortcutTypeTag);
    }
  
    static inline void EvacuateShortcutCandidate(Map* map,
                                                 HeapObject** slot,
                                                 HeapObject* object) {
      ASSERT(IsShortcutCandidate(map->instance_type()));
  
      if (ConsString::cast(object)->unchecked_second() ==
          map->heap()->empty_string()) {
        HeapObject* first =
            HeapObject::cast(ConsString::cast(object)->unchecked_first());
  
        *slot = first;
  
        if (!map->heap()->InNewSpace(first)) {
          object->set_map_word(MapWord::FromForwardingAddress(first));
          return;
        }
  
        MapWord first_word = first->map_word();
        if (first_word.IsForwardingAddress()) {
          HeapObject* target = first_word.ToForwardingAddress();
  
          *slot = target;
          object->set_map_word(MapWord::FromForwardingAddress(target));
          return;
        }
  
        DoScavengeObject(first->map(), slot, first);
        object->set_map_word(MapWord::FromForwardingAddress(*slot));
        return;
      }
  
      int object_size = ConsString::kSize;
      EvacuateObject<POINTER_OBJECT, SMALL>(map, slot, object, object_size);
    }
  
    template<ObjectContents object_contents>
    class ObjectEvacuationStrategy {
     public:
      template<int object_size>
      static inline void VisitSpecialized(Map* map,
                                          HeapObject** slot,
                                          HeapObject* object) {
        EvacuateObject<object_contents, SMALL>(map, slot, object, object_size);
      }
  
      static inline void Visit(Map* map,
                               HeapObject** slot,
                               HeapObject* object) {
        int object_size = map->instance_size();
        EvacuateObject<object_contents, SMALL>(map, slot, object, object_size);
      }
    };
  
    static VisitorDispatchTable<ScavengingCallback> table_;
  };
  
  
  template<LoggingAndProfiling logging_and_profiling_mode>
  VisitorDispatchTable<ScavengingCallback>
      ScavengingVisitor<logging_and_profiling_mode>::table_;
  
  
  static void InitializeScavengingVisitorsTables() {
    ScavengingVisitor<LOGGING_AND_PROFILING_DISABLED>::Initialize();
    ScavengingVisitor<LOGGING_AND_PROFILING_ENABLED>::Initialize();
    scavenging_visitors_table_.CopyFrom(
        ScavengingVisitor<LOGGING_AND_PROFILING_DISABLED>::GetTable());
    scavenging_visitors_table_mode_ = LOGGING_AND_PROFILING_DISABLED;
  }
  
  
  void Heap::SwitchScavengingVisitorsTableIfProfilingWasEnabled() {
    if (scavenging_visitors_table_mode_ == LOGGING_AND_PROFILING_ENABLED) {
      // Table was already updated by some isolate.
      return;
    }
  
    if (isolate()->logger()->is_logging() |
        CpuProfiler::is_profiling(isolate()) ||
        (isolate()->heap_profiler() != NULL &&
         isolate()->heap_profiler()->is_profiling())) {
      // If one of the isolates is doing scavenge at this moment of time
      // it might see this table in an inconsitent state when
      // some of the callbacks point to
      // ScavengingVisitor<LOGGING_AND_PROFILING_ENABLED> and others
      // to ScavengingVisitor<LOGGING_AND_PROFILING_DISABLED>.
      // However this does not lead to any bugs as such isolate does not have
      // profiling enabled and any isolate with enabled profiling is guaranteed
      // to see the table in the consistent state.
      scavenging_visitors_table_.CopyFrom(
          ScavengingVisitor<LOGGING_AND_PROFILING_ENABLED>::GetTable());
  
      // We use Release_Store to prevent reordering of this write before writes
      // to the table.
      Release_Store(&scavenging_visitors_table_mode_,
                    LOGGING_AND_PROFILING_ENABLED);
    }
  }
  
  
  void Heap::ScavengeObjectSlow(HeapObject** p, HeapObject* object) {
    ASSERT(HEAP->InFromSpace(object));
    MapWord first_word = object->map_word();
    ASSERT(!first_word.IsForwardingAddress());
    Map* map = first_word.ToMap();
    DoScavengeObject(map, p, object);
  }
  
  
  MaybeObject* Heap::AllocatePartialMap(InstanceType instance_type,
                                        int instance_size) {
    Object* result;
    { MaybeObject* maybe_result = AllocateRawMap();
      if (!maybe_result->ToObject(&result)) return maybe_result;
    }
  
    // Map::cast cannot be used due to uninitialized map field.
    reinterpret_cast<Map*>(result)->set_map(raw_unchecked_meta_map());
    reinterpret_cast<Map*>(result)->set_instance_type(instance_type);
    reinterpret_cast<Map*>(result)->set_instance_size(instance_size);
    reinterpret_cast<Map*>(result)->set_visitor_id(
          StaticVisitorBase::GetVisitorId(instance_type, instance_size));
    reinterpret_cast<Map*>(result)->set_inobject_properties(0);
    reinterpret_cast<Map*>(result)->set_pre_allocated_property_fields(0);
    reinterpret_cast<Map*>(result)->set_unused_property_fields(0);
    reinterpret_cast<Map*>(result)->set_bit_field(0);
    reinterpret_cast<Map*>(result)->set_bit_field2(0);
    return result;
  }
  
  
  MaybeObject* Heap::AllocateMap(InstanceType instance_type, int instance_size) {
    Object* result;
    { MaybeObject* maybe_result = AllocateRawMap();
      if (!maybe_result->ToObject(&result)) return maybe_result;
    }
  
    Map* map = reinterpret_cast<Map*>(result);
    map->set_map(meta_map());
    map->set_instance_type(instance_type);
    map->set_visitor_id(
        StaticVisitorBase::GetVisitorId(instance_type, instance_size));
    map->set_prototype(null_value());
    map->set_constructor(null_value());
    map->set_instance_size(instance_size);
    map->set_inobject_properties(0);
    map->set_pre_allocated_property_fields(0);
    map->init_instance_descriptors();
    map->set_code_cache(empty_fixed_array());
    map->set_prototype_transitions(empty_fixed_array());
    map->set_unused_property_fields(0);
    map->set_bit_field(0);
    map->set_bit_field2(1 << Map::kIsExtensible);
    map->set_elements_kind(FAST_ELEMENTS);
  
    // If the map object is aligned fill the padding area with Smi 0 objects.
    if (Map::kPadStart < Map::kSize) {
      memset(reinterpret_cast<byte*>(map) + Map::kPadStart - kHeapObjectTag,
             0,
             Map::kSize - Map::kPadStart);
    }
    return map;
  }
  
  
  MaybeObject* Heap::AllocateCodeCache() {
    Object* result;
    { MaybeObject* maybe_result = AllocateStruct(CODE_CACHE_TYPE);
      if (!maybe_result->ToObject(&result)) return maybe_result;
    }
    CodeCache* code_cache = CodeCache::cast(result);
    code_cache->set_default_cache(empty_fixed_array());
    code_cache->set_normal_type_cache(undefined_value());
    return code_cache;
  }
  
  
  MaybeObject* Heap::AllocatePolymorphicCodeCache() {
    return AllocateStruct(POLYMORPHIC_CODE_CACHE_TYPE);
  }
  
  
  const Heap::StringTypeTable Heap::string_type_table[] = {
  #define STRING_TYPE_ELEMENT(type, size, name, camel_name)                      \
    {type, size, k##camel_name##MapRootIndex},
    STRING_TYPE_LIST(STRING_TYPE_ELEMENT)
  #undef STRING_TYPE_ELEMENT
  };
  
  
  const Heap::ConstantSymbolTable Heap::constant_symbol_table[] = {
  #define CONSTANT_SYMBOL_ELEMENT(name, contents)                                \
    {contents, k##name##RootIndex},
    SYMBOL_LIST(CONSTANT_SYMBOL_ELEMENT)
  #undef CONSTANT_SYMBOL_ELEMENT
  };
  
  
  const Heap::StructTable Heap::struct_table[] = {
  #define STRUCT_TABLE_ELEMENT(NAME, Name, name)                                 \
    { NAME##_TYPE, Name::kSize, k##Name##MapRootIndex },
    STRUCT_LIST(STRUCT_TABLE_ELEMENT)
  #undef STRUCT_TABLE_ELEMENT
  };
  
  
  bool Heap::CreateInitialMaps() {
    Object* obj;
    { MaybeObject* maybe_obj = AllocatePartialMap(MAP_TYPE, Map::kSize);
      if (!maybe_obj->ToObject(&obj)) return false;
    }
    // Map::cast cannot be used due to uninitialized map field.
    Map* new_meta_map = reinterpret_cast<Map*>(obj);
    set_meta_map(new_meta_map);
    new_meta_map->set_map(new_meta_map);
  
    { MaybeObject* maybe_obj =
          AllocatePartialMap(FIXED_ARRAY_TYPE, kVariableSizeSentinel);
      if (!maybe_obj->ToObject(&obj)) return false;
    }
    set_fixed_array_map(Map::cast(obj));
  
    { MaybeObject* maybe_obj = AllocatePartialMap(ODDBALL_TYPE, Oddball::kSize);
      if (!maybe_obj->ToObject(&obj)) return false;
    }
    set_oddball_map(Map::cast(obj));
  
    // Allocate the empty array.
    { MaybeObject* maybe_obj = AllocateEmptyFixedArray();
      if (!maybe_obj->ToObject(&obj)) return false;
    }
    set_empty_fixed_array(FixedArray::cast(obj));
  
    { MaybeObject* maybe_obj = Allocate(oddball_map(), OLD_DATA_SPACE);
      if (!maybe_obj->ToObject(&obj)) return false;
    }
    set_null_value(obj);
    Oddball::cast(obj)->set_kind(Oddball::kNull);
  
    // Allocate the empty descriptor array.
    { MaybeObject* maybe_obj = AllocateEmptyFixedArray();
      if (!maybe_obj->ToObject(&obj)) return false;
    }
    set_empty_descriptor_array(DescriptorArray::cast(obj));
  
    // Fix the instance_descriptors for the existing maps.
    meta_map()->init_instance_descriptors();
    meta_map()->set_code_cache(empty_fixed_array());
    meta_map()->set_prototype_transitions(empty_fixed_array());
  
    fixed_array_map()->init_instance_descriptors();
    fixed_array_map()->set_code_cache(empty_fixed_array());
    fixed_array_map()->set_prototype_transitions(empty_fixed_array());
  
    oddball_map()->init_instance_descriptors();
    oddball_map()->set_code_cache(empty_fixed_array());
    oddball_map()->set_prototype_transitions(empty_fixed_array());
  
    // Fix prototype object for existing maps.
    meta_map()->set_prototype(null_value());
    meta_map()->set_constructor(null_value());
  
    fixed_array_map()->set_prototype(null_value());
    fixed_array_map()->set_constructor(null_value());
  
    oddball_map()->set_prototype(null_value());
    oddball_map()->set_constructor(null_value());
  
    { MaybeObject* maybe_obj =
          AllocateMap(FIXED_ARRAY_TYPE, kVariableSizeSentinel);
      if (!maybe_obj->ToObject(&obj)) return false;
    }
    set_fixed_cow_array_map(Map::cast(obj));
    ASSERT(fixed_array_map() != fixed_cow_array_map());
  
    { MaybeObject* maybe_obj =
          AllocateMap(FIXED_ARRAY_TYPE, kVariableSizeSentinel);
      if (!maybe_obj->ToObject(&obj)) return false;
    }
    set_serialized_scope_info_map(Map::cast(obj));
  
    { MaybeObject* maybe_obj = AllocateMap(HEAP_NUMBER_TYPE, HeapNumber::kSize);
      if (!maybe_obj->ToObject(&obj)) return false;
    }
    set_heap_number_map(Map::cast(obj));
  
    { MaybeObject* maybe_obj = AllocateMap(FOREIGN_TYPE, Foreign::kSize);
      if (!maybe_obj->ToObject(&obj)) return false;
    }
    set_foreign_map(Map::cast(obj));
  
    for (unsigned i = 0; i < ARRAY_SIZE(string_type_table); i++) {
      const StringTypeTable& entry = string_type_table[i];
      { MaybeObject* maybe_obj = AllocateMap(entry.type, entry.size);
        if (!maybe_obj->ToObject(&obj)) return false;
      }
      roots_[entry.index] = Map::cast(obj);
    }
  
    { MaybeObject* maybe_obj = AllocateMap(STRING_TYPE, kVariableSizeSentinel);
      if (!maybe_obj->ToObject(&obj)) return false;
    }
    set_undetectable_string_map(Map::cast(obj));
    Map::cast(obj)->set_is_undetectable();
  
    { MaybeObject* maybe_obj =
          AllocateMap(ASCII_STRING_TYPE, kVariableSizeSentinel);
      if (!maybe_obj->ToObject(&obj)) return false;
    }
    set_undetectable_ascii_string_map(Map::cast(obj));
    Map::cast(obj)->set_is_undetectable();
  
    { MaybeObject* maybe_obj =
          AllocateMap(FIXED_DOUBLE_ARRAY_TYPE, kVariableSizeSentinel);
      if (!maybe_obj->ToObject(&obj)) return false;
    }
    set_fixed_double_array_map(Map::cast(obj));
  
    { MaybeObject* maybe_obj =
          AllocateMap(BYTE_ARRAY_TYPE, kVariableSizeSentinel);
      if (!maybe_obj->ToObject(&obj)) return false;
    }
    set_byte_array_map(Map::cast(obj));
  
    { MaybeObject* maybe_obj = AllocateByteArray(0, TENURED);
      if (!maybe_obj->ToObject(&obj)) return false;
    }
    set_empty_byte_array(ByteArray::cast(obj));
  
    { MaybeObject* maybe_obj =
          AllocateMap(EXTERNAL_PIXEL_ARRAY_TYPE, ExternalArray::kAlignedSize);
      if (!maybe_obj->ToObject(&obj)) return false;
    }
    set_external_pixel_array_map(Map::cast(obj));
  
    { MaybeObject* maybe_obj = AllocateMap(EXTERNAL_BYTE_ARRAY_TYPE,
                                           ExternalArray::kAlignedSize);
      if (!maybe_obj->ToObject(&obj)) return false;
    }
    set_external_byte_array_map(Map::cast(obj));
  
    { MaybeObject* maybe_obj = AllocateMap(EXTERNAL_UNSIGNED_BYTE_ARRAY_TYPE,
                                           ExternalArray::kAlignedSize);
      if (!maybe_obj->ToObject(&obj)) return false;
    }
    set_external_unsigned_byte_array_map(Map::cast(obj));
  
    { MaybeObject* maybe_obj = AllocateMap(EXTERNAL_SHORT_ARRAY_TYPE,
                                           ExternalArray::kAlignedSize);
      if (!maybe_obj->ToObject(&obj)) return false;
    }
    set_external_short_array_map(Map::cast(obj));
  
    { MaybeObject* maybe_obj = AllocateMap(EXTERNAL_UNSIGNED_SHORT_ARRAY_TYPE,
                                           ExternalArray::kAlignedSize);
      if (!maybe_obj->ToObject(&obj)) return false;
    }
    set_external_unsigned_short_array_map(Map::cast(obj));
  
    { MaybeObject* maybe_obj = AllocateMap(EXTERNAL_INT_ARRAY_TYPE,
                                           ExternalArray::kAlignedSize);
      if (!maybe_obj->ToObject(&obj)) return false;
    }
    set_external_int_array_map(Map::cast(obj));
  
    { MaybeObject* maybe_obj = AllocateMap(EXTERNAL_UNSIGNED_INT_ARRAY_TYPE,
                                           ExternalArray::kAlignedSize);
      if (!maybe_obj->ToObject(&obj)) return false;
    }
    set_external_unsigned_int_array_map(Map::cast(obj));
  
    { MaybeObject* maybe_obj = AllocateMap(EXTERNAL_FLOAT_ARRAY_TYPE,
                                           ExternalArray::kAlignedSize);
      if (!maybe_obj->ToObject(&obj)) return false;
    }
    set_external_float_array_map(Map::cast(obj));
  
    { MaybeObject* maybe_obj =
          AllocateMap(FIXED_ARRAY_TYPE, kVariableSizeSentinel);
      if (!maybe_obj->ToObject(&obj)) return false;
    }
    set_non_strict_arguments_elements_map(Map::cast(obj));
  
    { MaybeObject* maybe_obj = AllocateMap(EXTERNAL_DOUBLE_ARRAY_TYPE,
                                           ExternalArray::kAlignedSize);
      if (!maybe_obj->ToObject(&obj)) return false;
    }
    set_external_double_array_map(Map::cast(obj));
  
    { MaybeObject* maybe_obj = AllocateMap(CODE_TYPE, kVariableSizeSentinel);
      if (!maybe_obj->ToObject(&obj)) return false;
    }
    set_code_map(Map::cast(obj));
  
    { MaybeObject* maybe_obj = AllocateMap(JS_GLOBAL_PROPERTY_CELL_TYPE,
                                           JSGlobalPropertyCell::kSize);
      if (!maybe_obj->ToObject(&obj)) return false;
    }
    set_global_property_cell_map(Map::cast(obj));
  
    { MaybeObject* maybe_obj = AllocateMap(FILLER_TYPE, kPointerSize);
      if (!maybe_obj->ToObject(&obj)) return false;
    }
    set_one_pointer_filler_map(Map::cast(obj));
  
    { MaybeObject* maybe_obj = AllocateMap(FILLER_TYPE, 2 * kPointerSize);
      if (!maybe_obj->ToObject(&obj)) return false;
    }
    set_two_pointer_filler_map(Map::cast(obj));
  
    for (unsigned i = 0; i < ARRAY_SIZE(struct_table); i++) {
      const StructTable& entry = struct_table[i];
      { MaybeObject* maybe_obj = AllocateMap(entry.type, entry.size);
        if (!maybe_obj->ToObject(&obj)) return false;
      }
      roots_[entry.index] = Map::cast(obj);
    }
  
    { MaybeObject* maybe_obj =
          AllocateMap(FIXED_ARRAY_TYPE, kVariableSizeSentinel);
      if (!maybe_obj->ToObject(&obj)) return false;
    }
    set_hash_table_map(Map::cast(obj));
  
    { MaybeObject* maybe_obj =
          AllocateMap(FIXED_ARRAY_TYPE, kVariableSizeSentinel);
      if (!maybe_obj->ToObject(&obj)) return false;
    }
    set_function_context_map(Map::cast(obj));
  
    { MaybeObject* maybe_obj =
          AllocateMap(FIXED_ARRAY_TYPE, kVariableSizeSentinel);
      if (!maybe_obj->ToObject(&obj)) return false;
    }
    set_catch_context_map(Map::cast(obj));
  
    { MaybeObject* maybe_obj =
          AllocateMap(FIXED_ARRAY_TYPE, kVariableSizeSentinel);
      if (!maybe_obj->ToObject(&obj)) return false;
    }
    set_with_context_map(Map::cast(obj));
  
    { MaybeObject* maybe_obj =
          AllocateMap(FIXED_ARRAY_TYPE, kVariableSizeSentinel);
      if (!maybe_obj->ToObject(&obj)) return false;
    }
    set_block_context_map(Map::cast(obj));
  
    { MaybeObject* maybe_obj =
          AllocateMap(FIXED_ARRAY_TYPE, kVariableSizeSentinel);
      if (!maybe_obj->ToObject(&obj)) return false;
    }
    Map* global_context_map = Map::cast(obj);
    global_context_map->set_visitor_id(StaticVisitorBase::kVisitGlobalContext);
    set_global_context_map(global_context_map);
  
    { MaybeObject* maybe_obj = AllocateMap(SHARED_FUNCTION_INFO_TYPE,
                                           SharedFunctionInfo::kAlignedSize);
      if (!maybe_obj->ToObject(&obj)) return false;
    }
    set_shared_function_info_map(Map::cast(obj));
  
    { MaybeObject* maybe_obj = AllocateMap(JS_MESSAGE_OBJECT_TYPE,
                                           JSMessageObject::kSize);
      if (!maybe_obj->ToObject(&obj)) return false;
    }
    set_message_object_map(Map::cast(obj));
  
    ASSERT(!InNewSpace(empty_fixed_array()));
    return true;
  }
  
  
  MaybeObject* Heap::AllocateHeapNumber(double value, PretenureFlag pretenure) {
    // Statically ensure that it is safe to allocate heap numbers in paged
    // spaces.
    STATIC_ASSERT(HeapNumber::kSize <= Page::kMaxHeapObjectSize);
    AllocationSpace space = (pretenure == TENURED) ? OLD_DATA_SPACE : NEW_SPACE;
  
    Object* result;
    { MaybeObject* maybe_result =
          AllocateRaw(HeapNumber::kSize, space, OLD_DATA_SPACE);
      if (!maybe_result->ToObject(&result)) return maybe_result;
    }
  
    HeapObject::cast(result)->set_map(heap_number_map());
    HeapNumber::cast(result)->set_value(value);
    return result;
  }
  
  
  MaybeObject* Heap::AllocateHeapNumber(double value) {
    // Use general version, if we're forced to always allocate.
    if (always_allocate()) return AllocateHeapNumber(value, TENURED);
  
    // This version of AllocateHeapNumber is optimized for
    // allocation in new space.
    STATIC_ASSERT(HeapNumber::kSize <= Page::kMaxHeapObjectSize);
    ASSERT(allocation_allowed_ && gc_state_ == NOT_IN_GC);
    Object* result;
    { MaybeObject* maybe_result = new_space_.AllocateRaw(HeapNumber::kSize);
      if (!maybe_result->ToObject(&result)) return maybe_result;
    }
    HeapObject::cast(result)->set_map(heap_number_map());
    HeapNumber::cast(result)->set_value(value);
    return result;
  }
  
  
  MaybeObject* Heap::AllocateJSGlobalPropertyCell(Object* value) {
    Object* result;
    { MaybeObject* maybe_result = AllocateRawCell();
      if (!maybe_result->ToObject(&result)) return maybe_result;
    }
    HeapObject::cast(result)->set_map(global_property_cell_map());
    JSGlobalPropertyCell::cast(result)->set_value(value);
    return result;
  }
  
  
  MaybeObject* Heap::CreateOddball(const char* to_string,
                                   Object* to_number,
                                   byte kind) {
    Object* result;
    { MaybeObject* maybe_result = Allocate(oddball_map(), OLD_DATA_SPACE);
      if (!maybe_result->ToObject(&result)) return maybe_result;
    }
    return Oddball::cast(result)->Initialize(to_string, to_number, kind);
  }
  
  
  bool Heap::CreateApiObjects() {
    Object* obj;
  
    { MaybeObject* maybe_obj = AllocateMap(JS_OBJECT_TYPE, JSObject::kHeaderSize);
      if (!maybe_obj->ToObject(&obj)) return false;
    }
    set_neander_map(Map::cast(obj));
  
    { MaybeObject* maybe_obj = AllocateJSObjectFromMap(neander_map());
      if (!maybe_obj->ToObject(&obj)) return false;
    }
    Object* elements;
    { MaybeObject* maybe_elements = AllocateFixedArray(2);
      if (!maybe_elements->ToObject(&elements)) return false;
    }
    FixedArray::cast(elements)->set(0, Smi::FromInt(0));
    JSObject::cast(obj)->set_elements(FixedArray::cast(elements));
    set_message_listeners(JSObject::cast(obj));
  
    return true;
  }
  
  
  void Heap::CreateJSEntryStub() {
    JSEntryStub stub;
    set_js_entry_code(*stub.GetCode());
  }
  
  
  void Heap::CreateJSConstructEntryStub() {
    JSConstructEntryStub stub;
    set_js_construct_entry_code(*stub.GetCode());
  }
  
  
  void Heap::CreateFixedStubs() {
    // Here we create roots for fixed stubs. They are needed at GC
    // for cooking and uncooking (check out frames.cc).
    // The eliminates the need for doing dictionary lookup in the
    // stub cache for these stubs.
    HandleScope scope;
    // gcc-4.4 has problem generating correct code of following snippet:
    // {  JSEntryStub stub;
    //    js_entry_code_ = *stub.GetCode();
    // }
    // {  JSConstructEntryStub stub;
    //    js_construct_entry_code_ = *stub.GetCode();
    // }
    // To workaround the problem, make separate functions without inlining.
    Heap::CreateJSEntryStub();
    Heap::CreateJSConstructEntryStub();
  }
  
  
  bool Heap::CreateInitialObjects() {
    Object* obj;
  
    // The -0 value must be set before NumberFromDouble works.
    { MaybeObject* maybe_obj = AllocateHeapNumber(-0.0, TENURED);
      if (!maybe_obj->ToObject(&obj)) return false;
    }
    set_minus_zero_value(obj);
    ASSERT(signbit(minus_zero_value()->Number()) != 0);
  
    { MaybeObject* maybe_obj = AllocateHeapNumber(OS::nan_value(), TENURED);
      if (!maybe_obj->ToObject(&obj)) return false;
    }
    set_nan_value(obj);
  
    { MaybeObject* maybe_obj = Allocate(oddball_map(), OLD_DATA_SPACE);
      if (!maybe_obj->ToObject(&obj)) return false;
    }
    set_undefined_value(obj);
    Oddball::cast(obj)->set_kind(Oddball::kUndefined);
    ASSERT(!InNewSpace(undefined_value()));
  
    // Allocate initial symbol table.
    { MaybeObject* maybe_obj = SymbolTable::Allocate(kInitialSymbolTableSize);
      if (!maybe_obj->ToObject(&obj)) return false;
    }
    // Don't use set_symbol_table() due to asserts.
    roots_[kSymbolTableRootIndex] = obj;
  
    // Assign the print strings for oddballs after creating symboltable.
    Object* symbol;
    { MaybeObject* maybe_symbol = LookupAsciiSymbol("undefined");
      if (!maybe_symbol->ToObject(&symbol)) return false;
    }
    Oddball::cast(undefined_value())->set_to_string(String::cast(symbol));
    Oddball::cast(undefined_value())->set_to_number(nan_value());
  
    // Allocate the null_value
    { MaybeObject* maybe_obj =
          Oddball::cast(null_value())->Initialize("null",
                                                  Smi::FromInt(0),
                                                  Oddball::kNull);
      if (!maybe_obj->ToObject(&obj)) return false;
    }
  
    { MaybeObject* maybe_obj = CreateOddball("true",
                                             Smi::FromInt(1),
                                             Oddball::kTrue);
      if (!maybe_obj->ToObject(&obj)) return false;
    }
    set_true_value(obj);
  
    { MaybeObject* maybe_obj = CreateOddball("false",
                                             Smi::FromInt(0),
                                             Oddball::kFalse);
      if (!maybe_obj->ToObject(&obj)) return false;
    }
    set_false_value(obj);
  
    { MaybeObject* maybe_obj = CreateOddball("hole",
                                             Smi::FromInt(-1),
                                             Oddball::kTheHole);
      if (!maybe_obj->ToObject(&obj)) return false;
    }
    set_the_hole_value(obj);
  
    { MaybeObject* maybe_obj = CreateOddball("arguments_marker",
                                             Smi::FromInt(-4),
                                             Oddball::kArgumentMarker);
      if (!maybe_obj->ToObject(&obj)) return false;
    }
    set_arguments_marker(obj);
  
    { MaybeObject* maybe_obj = CreateOddball("no_interceptor_result_sentinel",
                                             Smi::FromInt(-2),
                                             Oddball::kOther);
      if (!maybe_obj->ToObject(&obj)) return false;
    }
    set_no_interceptor_result_sentinel(obj);
  
    { MaybeObject* maybe_obj = CreateOddball("termination_exception",
                                             Smi::FromInt(-3),
                                             Oddball::kOther);
      if (!maybe_obj->ToObject(&obj)) return false;
    }
    set_termination_exception(obj);
  
    // Allocate the empty string.
    { MaybeObject* maybe_obj = AllocateRawAsciiString(0, TENURED);
      if (!maybe_obj->ToObject(&obj)) return false;
    }
    set_empty_string(String::cast(obj));
  
    for (unsigned i = 0; i < ARRAY_SIZE(constant_symbol_table); i++) {
      { MaybeObject* maybe_obj =
            LookupAsciiSymbol(constant_symbol_table[i].contents);
        if (!maybe_obj->ToObject(&obj)) return false;
      }
      roots_[constant_symbol_table[i].index] = String::cast(obj);
    }
  
    // Allocate the hidden symbol which is used to identify the hidden properties
    // in JSObjects. The hash code has a special value so that it will not match
    // the empty string when searching for the property. It cannot be part of the
    // loop above because it needs to be allocated manually with the special
    // hash code in place. The hash code for the hidden_symbol is zero to ensure
    // that it will always be at the first entry in property descriptors.
    { MaybeObject* maybe_obj =
          AllocateSymbol(CStrVector(""), 0, String::kZeroHash);
      if (!maybe_obj->ToObject(&obj)) return false;
    }
    hidden_symbol_ = String::cast(obj);
  
    // Allocate the foreign for __proto__.
    { MaybeObject* maybe_obj =
          AllocateForeign((Address) &Accessors::ObjectPrototype);
      if (!maybe_obj->ToObject(&obj)) return false;
    }
    set_prototype_accessors(Foreign::cast(obj));
  
    // Allocate the code_stubs dictionary. The initial size is set to avoid
    // expanding the dictionary during bootstrapping.
    { MaybeObject* maybe_obj = UnseededNumberDictionary::Allocate(128);
      if (!maybe_obj->ToObject(&obj)) return false;
    }
    set_code_stubs(UnseededNumberDictionary::cast(obj));
  
    // Allocate the non_monomorphic_cache used in stub-cache.cc. The initial size
    // is set to avoid expanding the dictionary during bootstrapping.
    { MaybeObject* maybe_obj = UnseededNumberDictionary::Allocate(64);
      if (!maybe_obj->ToObject(&obj)) return false;
    }
    set_non_monomorphic_cache(UnseededNumberDictionary::cast(obj));
  
    { MaybeObject* maybe_obj = AllocatePolymorphicCodeCache();
      if (!maybe_obj->ToObject(&obj)) return false;
    }
    set_polymorphic_code_cache(PolymorphicCodeCache::cast(obj));
  
    set_instanceof_cache_function(Smi::FromInt(0));
    set_instanceof_cache_map(Smi::FromInt(0));
    set_instanceof_cache_answer(Smi::FromInt(0));
  
    CreateFixedStubs();
  
    // Allocate the dictionary of intrinsic function names.
    { MaybeObject* maybe_obj = StringDictionary::Allocate(Runtime::kNumFunctions);
      if (!maybe_obj->ToObject(&obj)) return false;
    }
    { MaybeObject* maybe_obj = Runtime::InitializeIntrinsicFunctionNames(this,
                                                                         obj);
      if (!maybe_obj->ToObject(&obj)) return false;
    }
    set_intrinsic_function_names(StringDictionary::cast(obj));
  
    if (InitializeNumberStringCache()->IsFailure()) return false;
  
    // Allocate cache for single character ASCII strings.
    { MaybeObject* maybe_obj =
          AllocateFixedArray(String::kMaxAsciiCharCode + 1, TENURED);
      if (!maybe_obj->ToObject(&obj)) return false;
    }
    set_single_character_string_cache(FixedArray::cast(obj));
  
    // Allocate cache for string split.
    { MaybeObject* maybe_obj =
          AllocateFixedArray(StringSplitCache::kStringSplitCacheSize, TENURED);
      if (!maybe_obj->ToObject(&obj)) return false;
    }
    set_string_split_cache(FixedArray::cast(obj));
  
    // Allocate cache for external strings pointing to native source code.
    { MaybeObject* maybe_obj = AllocateFixedArray(Natives::GetBuiltinsCount());
      if (!maybe_obj->ToObject(&obj)) return false;
    }
    set_natives_source_cache(FixedArray::cast(obj));
  
    // Handling of script id generation is in FACTORY->NewScript.
    set_last_script_id(undefined_value());
  
    // Initialize keyed lookup cache.
    isolate_->keyed_lookup_cache()->Clear();
  
    // Initialize context slot cache.
    isolate_->context_slot_cache()->Clear();
  
    // Initialize descriptor cache.
    isolate_->descriptor_lookup_cache()->Clear();
  
    // Initialize compilation cache.
    isolate_->compilation_cache()->Clear();
  
    return true;
  }
  
  
  Object* StringSplitCache::Lookup(
      FixedArray* cache, String* string, String* pattern) {
    if (!string->IsSymbol() || !pattern->IsSymbol()) return Smi::FromInt(0);
    uint32_t hash = string->Hash();
    uint32_t index = ((hash & (kStringSplitCacheSize - 1)) &
        ~(kArrayEntriesPerCacheEntry - 1));
    if (cache->get(index + kStringOffset) == string &&
        cache->get(index + kPatternOffset) == pattern) {
      return cache->get(index + kArrayOffset);
    }
    index = ((index + kArrayEntriesPerCacheEntry) & (kStringSplitCacheSize - 1));
    if (cache->get(index + kStringOffset) == string &&
        cache->get(index + kPatternOffset) == pattern) {
      return cache->get(index + kArrayOffset);
    }
    return Smi::FromInt(0);
  }
  
  
  void StringSplitCache::Enter(Heap* heap,
                               FixedArray* cache,
                               String* string,
                               String* pattern,
                               FixedArray* array) {
    if (!string->IsSymbol() || !pattern->IsSymbol()) return;
    uint32_t hash = string->Hash();
    uint32_t index = ((hash & (kStringSplitCacheSize - 1)) &
        ~(kArrayEntriesPerCacheEntry - 1));
    if (cache->get(index + kStringOffset) == Smi::FromInt(0)) {
      cache->set(index + kStringOffset, string);
      cache->set(index + kPatternOffset, pattern);
      cache->set(index + kArrayOffset, array);
    } else {
      uint32_t index2 =
          ((index + kArrayEntriesPerCacheEntry) & (kStringSplitCacheSize - 1));
      if (cache->get(index2 + kStringOffset) == Smi::FromInt(0)) {
        cache->set(index2 + kStringOffset, string);
        cache->set(index2 + kPatternOffset, pattern);
        cache->set(index2 + kArrayOffset, array);
      } else {
        cache->set(index2 + kStringOffset, Smi::FromInt(0));
        cache->set(index2 + kPatternOffset, Smi::FromInt(0));
        cache->set(index2 + kArrayOffset, Smi::FromInt(0));
        cache->set(index + kStringOffset, string);
        cache->set(index + kPatternOffset, pattern);
        cache->set(index + kArrayOffset, array);
      }
    }
    if (array->length() < 100) {  // Limit how many new symbols we want to make.
      for (int i = 0; i < array->length(); i++) {
        String* str = String::cast(array->get(i));
        Object* symbol;
        MaybeObject* maybe_symbol = heap->LookupSymbol(str);
        if (maybe_symbol->ToObject(&symbol)) {
          array->set(i, symbol);
        }
      }
    }
    array->set_map(heap->fixed_cow_array_map());
  }
  
  
  void StringSplitCache::Clear(FixedArray* cache) {
    for (int i = 0; i < kStringSplitCacheSize; i++) {
      cache->set(i, Smi::FromInt(0));
    }
  }
  
  
  MaybeObject* Heap::InitializeNumberStringCache() {
    // Compute the size of the number string cache based on the max heap size.
    // max_semispace_size_ == 512 KB => number_string_cache_size = 32.
    // max_semispace_size_ ==   8 MB => number_string_cache_size = 16KB.
    int number_string_cache_size = max_semispace_size_ / 512;
    number_string_cache_size = Max(32, Min(16*KB, number_string_cache_size));
    Object* obj;
    MaybeObject* maybe_obj =
        AllocateFixedArray(number_string_cache_size * 2, TENURED);
    if (maybe_obj->ToObject(&obj)) set_number_string_cache(FixedArray::cast(obj));
    return maybe_obj;
  }
  
  
  void Heap::FlushNumberStringCache() {
    // Flush the number to string cache.
    int len = number_string_cache()->length();
    for (int i = 0; i < len; i++) {
      number_string_cache()->set_undefined(this, i);
    }
  }
  
  
  static inline int double_get_hash(double d) {
    DoubleRepresentation rep(d);
    return static_cast<int>(rep.bits) ^ static_cast<int>(rep.bits >> 32);
  }
  
  
  static inline int smi_get_hash(Smi* smi) {
    return smi->value();
  }
  
  
  Object* Heap::GetNumberStringCache(Object* number) {
    int hash;
    int mask = (number_string_cache()->length() >> 1) - 1;
    if (number->IsSmi()) {
      hash = smi_get_hash(Smi::cast(number)) & mask;
    } else {
      hash = double_get_hash(number->Number()) & mask;
    }
    Object* key = number_string_cache()->get(hash * 2);
    if (key == number) {
      return String::cast(number_string_cache()->get(hash * 2 + 1));
    } else if (key->IsHeapNumber() &&
               number->IsHeapNumber() &&
               key->Number() == number->Number()) {
      return String::cast(number_string_cache()->get(hash * 2 + 1));
    }
    return undefined_value();
  }
  
  
  void Heap::SetNumberStringCache(Object* number, String* string) {
    int hash;
    int mask = (number_string_cache()->length() >> 1) - 1;
    if (number->IsSmi()) {
      hash = smi_get_hash(Smi::cast(number)) & mask;
      number_string_cache()->set(hash * 2, Smi::cast(number));
    } else {
      hash = double_get_hash(number->Number()) & mask;
      number_string_cache()->set(hash * 2, number);
    }
    number_string_cache()->set(hash * 2 + 1, string);
  }
  
  
  MaybeObject* Heap::NumberToString(Object* number,
                                    bool check_number_string_cache) {
    isolate_->counters()->number_to_string_runtime()->Increment();
    if (check_number_string_cache) {
      Object* cached = GetNumberStringCache(number);
      if (cached != undefined_value()) {
        return cached;
      }
    }
  
    char arr[100];
    Vector<char> buffer(arr, ARRAY_SIZE(arr));
    const char* str;
    if (number->IsSmi()) {
      int num = Smi::cast(number)->value();
      str = IntToCString(num, buffer);
    } else {
      double num = HeapNumber::cast(number)->value();
      str = DoubleToCString(num, buffer);
    }
  
    Object* js_string;
    MaybeObject* maybe_js_string = AllocateStringFromAscii(CStrVector(str));
    if (maybe_js_string->ToObject(&js_string)) {
      SetNumberStringCache(number, String::cast(js_string));
    }
    return maybe_js_string;
  }
  
  
  Map* Heap::MapForExternalArrayType(ExternalArrayType array_type) {
    return Map::cast(roots_[RootIndexForExternalArrayType(array_type)]);
  }
  
  
  Heap::RootListIndex Heap::RootIndexForExternalArrayType(
      ExternalArrayType array_type) {
    switch (array_type) {
      case kExternalByteArray:
        return kExternalByteArrayMapRootIndex;
      case kExternalUnsignedByteArray:
        return kExternalUnsignedByteArrayMapRootIndex;
      case kExternalShortArray:
        return kExternalShortArrayMapRootIndex;
      case kExternalUnsignedShortArray:
        return kExternalUnsignedShortArrayMapRootIndex;
      case kExternalIntArray:
        return kExternalIntArrayMapRootIndex;
      case kExternalUnsignedIntArray:
        return kExternalUnsignedIntArrayMapRootIndex;
      case kExternalFloatArray:
        return kExternalFloatArrayMapRootIndex;
      case kExternalDoubleArray:
        return kExternalDoubleArrayMapRootIndex;
      case kExternalPixelArray:
        return kExternalPixelArrayMapRootIndex;
      default:
        UNREACHABLE();
        return kUndefinedValueRootIndex;
    }
  }
  
  
  MaybeObject* Heap::NumberFromDouble(double value, PretenureFlag pretenure) {
    // We need to distinguish the minus zero value and this cannot be
    // done after conversion to int. Doing this by comparing bit
    // patterns is faster than using fpclassify() et al.
    static const DoubleRepresentation minus_zero(-0.0);
  
    DoubleRepresentation rep(value);
    if (rep.bits == minus_zero.bits) {
      return AllocateHeapNumber(-0.0, pretenure);
    }
  
    int int_value = FastD2I(value);
    if (value == int_value && Smi::IsValid(int_value)) {
      return Smi::FromInt(int_value);
    }
  
    // Materialize the value in the heap.
    return AllocateHeapNumber(value, pretenure);
  }
  
  
  MaybeObject* Heap::AllocateForeign(Address address, PretenureFlag pretenure) {
    // Statically ensure that it is safe to allocate foreigns in paged spaces.
    STATIC_ASSERT(Foreign::kSize <= Page::kMaxHeapObjectSize);
    AllocationSpace space = (pretenure == TENURED) ? OLD_DATA_SPACE : NEW_SPACE;
    Object* result;
    { MaybeObject* maybe_result = Allocate(foreign_map(), space);
      if (!maybe_result->ToObject(&result)) return maybe_result;
    }
  
    Foreign::cast(result)->set_address(address);
    return result;
  }
  
  
  MaybeObject* Heap::AllocateSharedFunctionInfo(Object* name) {
    SharedFunctionInfo* share;
    MaybeObject* maybe = Allocate(shared_function_info_map(), OLD_POINTER_SPACE);
    if (!maybe->To<SharedFunctionInfo>(&share)) return maybe;
  
    // Set pointer fields.
    share->set_name(name);
    Code* illegal = isolate_->builtins()->builtin(Builtins::kIllegal);
    share->set_code(illegal);
    share->set_scope_info(SerializedScopeInfo::Empty());
    Code* construct_stub =
        isolate_->builtins()->builtin(Builtins::kJSConstructStubGeneric);
    share->set_construct_stub(construct_stub);
    share->set_instance_class_name(Object_symbol());
    share->set_function_data(undefined_value());
    share->set_script(undefined_value());
    share->set_debug_info(undefined_value());
    share->set_inferred_name(empty_string());
    share->set_initial_map(undefined_value());
    share->set_this_property_assignments(undefined_value());
    share->set_deopt_counter(Smi::FromInt(FLAG_deopt_every_n_times));
  
    // Set integer fields (smi or int, depending on the architecture).
    share->set_length(0);
    share->set_formal_parameter_count(0);
    share->set_expected_nof_properties(0);
    share->set_num_literals(0);
    share->set_start_position_and_type(0);
    share->set_end_position(0);
    share->set_function_token_position(0);
    // All compiler hints default to false or 0.
    share->set_compiler_hints(0);
    share->set_this_property_assignments_count(0);
    share->set_opt_count(0);
  
    return share;
  }
  
  
  MaybeObject* Heap::AllocateJSMessageObject(String* type,
                                             JSArray* arguments,
                                             int start_position,
                                             int end_position,
                                             Object* script,
                                             Object* stack_trace,
                                             Object* stack_frames) {
    Object* result;
    { MaybeObject* maybe_result = Allocate(message_object_map(), NEW_SPACE);
      if (!maybe_result->ToObject(&result)) return maybe_result;
    }
    JSMessageObject* message = JSMessageObject::cast(result);
    message->set_properties(Heap::empty_fixed_array());
    message->set_elements(Heap::empty_fixed_array());
    message->set_type(type);
    message->set_arguments(arguments);
    message->set_start_position(start_position);
    message->set_end_position(end_position);
    message->set_script(script);
    message->set_stack_trace(stack_trace);
    message->set_stack_frames(stack_frames);
    return result;
  }
  
  
  
  // Returns true for a character in a range.  Both limits are inclusive.
  static inline bool Between(uint32_t character, uint32_t from, uint32_t to) {
    // This makes uses of the the unsigned wraparound.
    return character - from <= to - from;
  }
  
  
  MUST_USE_RESULT static inline MaybeObject* MakeOrFindTwoCharacterString(
      Heap* heap,
      uint32_t c1,
      uint32_t c2) {
    String* symbol;
    // Numeric strings have a different hash algorithm not known by
    // LookupTwoCharsSymbolIfExists, so we skip this step for such strings.
    if ((!Between(c1, '0', '9') || !Between(c2, '0', '9')) &&
        heap->symbol_table()->LookupTwoCharsSymbolIfExists(c1, c2, &symbol)) {
      return symbol;
    // Now we know the length is 2, we might as well make use of that fact
    // when building the new string.
    } else if ((c1 | c2) <= String::kMaxAsciiCharCodeU) {  // We can do this
      ASSERT(IsPowerOf2(String::kMaxAsciiCharCodeU + 1));  // because of this.
      Object* result;
      { MaybeObject* maybe_result = heap->AllocateRawAsciiString(2);
        if (!maybe_result->ToObject(&result)) return maybe_result;
      }
      char* dest = SeqAsciiString::cast(result)->GetChars();
      dest[0] = c1;
      dest[1] = c2;
      return result;
    } else {
      Object* result;
      { MaybeObject* maybe_result = heap->AllocateRawTwoByteString(2);
        if (!maybe_result->ToObject(&result)) return maybe_result;
      }
      uc16* dest = SeqTwoByteString::cast(result)->GetChars();
      dest[0] = c1;
      dest[1] = c2;
      return result;
    }
  }
  
  
  MaybeObject* Heap::AllocateConsString(String* first, String* second) {
    int first_length = first->length();
    if (first_length == 0) {
      return second;
    }
  
    int second_length = second->length();
    if (second_length == 0) {
      return first;
    }
  
    int length = first_length + second_length;
  
    // Optimization for 2-byte strings often used as keys in a decompression
    // dictionary.  Check whether we already have the string in the symbol
    // table to prevent creation of many unneccesary strings.
    if (length == 2) {
      unsigned c1 = first->Get(0);
      unsigned c2 = second->Get(0);
      return MakeOrFindTwoCharacterString(this, c1, c2);
    }
  
    bool first_is_ascii = first->IsAsciiRepresentation();
    bool second_is_ascii = second->IsAsciiRepresentation();
    bool is_ascii = first_is_ascii && second_is_ascii;
  
    // Make sure that an out of memory exception is thrown if the length
    // of the new cons string is too large.
    if (length > String::kMaxLength || length < 0) {
      isolate()->context()->mark_out_of_memory();
      return Failure::OutOfMemoryException();
    }
  
    bool is_ascii_data_in_two_byte_string = false;
    if (!is_ascii) {
      // At least one of the strings uses two-byte representation so we
      // can't use the fast case code for short ascii strings below, but
      // we can try to save memory if all chars actually fit in ascii.
      is_ascii_data_in_two_byte_string =
          first->HasOnlyAsciiChars() && second->HasOnlyAsciiChars();
      if (is_ascii_data_in_two_byte_string) {
        isolate_->counters()->string_add_runtime_ext_to_ascii()->Increment();
      }
    }
  
    // If the resulting string is small make a flat string.
    if (length < String::kMinNonFlatLength) {
      // Note that neither of the two inputs can be a slice because:
      STATIC_ASSERT(String::kMinNonFlatLength <= SlicedString::kMinLength);
      ASSERT(first->IsFlat());
      ASSERT(second->IsFlat());
      if (is_ascii) {
        Object* result;
        { MaybeObject* maybe_result = AllocateRawAsciiString(length);
          if (!maybe_result->ToObject(&result)) return maybe_result;
        }
        // Copy the characters into the new object.
        char* dest = SeqAsciiString::cast(result)->GetChars();
        // Copy first part.
        const char* src;
        if (first->IsExternalString()) {
          src = ExternalAsciiString::cast(first)->resource()->data();
        } else {
          src = SeqAsciiString::cast(first)->GetChars();
        }
        for (int i = 0; i < first_length; i++) *dest++ = src[i];
        // Copy second part.
        if (second->IsExternalString()) {
          src = ExternalAsciiString::cast(second)->resource()->data();
        } else {
          src = SeqAsciiString::cast(second)->GetChars();
        }
        for (int i = 0; i < second_length; i++) *dest++ = src[i];
        return result;
      } else {
        if (is_ascii_data_in_two_byte_string) {
          Object* result;
          { MaybeObject* maybe_result = AllocateRawAsciiString(length);
            if (!maybe_result->ToObject(&result)) return maybe_result;
          }
          // Copy the characters into the new object.
          char* dest = SeqAsciiString::cast(result)->GetChars();
          String::WriteToFlat(first, dest, 0, first_length);
          String::WriteToFlat(second, dest + first_length, 0, second_length);
          isolate_->counters()->string_add_runtime_ext_to_ascii()->Increment();
          return result;
        }
  
        Object* result;
        { MaybeObject* maybe_result = AllocateRawTwoByteString(length);
          if (!maybe_result->ToObject(&result)) return maybe_result;
        }
        // Copy the characters into the new object.
        uc16* dest = SeqTwoByteString::cast(result)->GetChars();
        String::WriteToFlat(first, dest, 0, first_length);
        String::WriteToFlat(second, dest + first_length, 0, second_length);
        return result;
      }
    }
  
    Map* map = (is_ascii || is_ascii_data_in_two_byte_string) ?
        cons_ascii_string_map() : cons_string_map();
  
    Object* result;
    { MaybeObject* maybe_result = Allocate(map, NEW_SPACE);
      if (!maybe_result->ToObject(&result)) return maybe_result;
    }
  
    AssertNoAllocation no_gc;
    ConsString* cons_string = ConsString::cast(result);
    WriteBarrierMode mode = cons_string->GetWriteBarrierMode(no_gc);
    cons_string->set_length(length);
    cons_string->set_hash_field(String::kEmptyHashField);
    cons_string->set_first(first, mode);
    cons_string->set_second(second, mode);
    return result;
  }
  
  
  MaybeObject* Heap::AllocateSubString(String* buffer,
                                       int start,
                                       int end,
                                       PretenureFlag pretenure) {
    int length = end - start;
    if (length == 0) {
      return empty_string();
    } else if (length == 1) {
      return LookupSingleCharacterStringFromCode(buffer->Get(start));
    } else if (length == 2) {
      // Optimization for 2-byte strings often used as keys in a decompression
      // dictionary.  Check whether we already have the string in the symbol
      // table to prevent creation of many unneccesary strings.
      unsigned c1 = buffer->Get(start);
      unsigned c2 = buffer->Get(start + 1);
      return MakeOrFindTwoCharacterString(this, c1, c2);
    }
  
    // Make an attempt to flatten the buffer to reduce access time.
    buffer = buffer->TryFlattenGetString();
  
    // TODO(1626): For now slicing external strings is not supported.  However,
    // a flat cons string can have an external string as first part in some cases.
    // Therefore we have to single out this case as well.
    if (!FLAG_string_slices ||
        (buffer->IsConsString() &&
          (!buffer->IsFlat() ||
           !ConsString::cast(buffer)->first()->IsSeqString())) ||
        buffer->IsExternalString() ||
        length < SlicedString::kMinLength ||
        pretenure == TENURED) {
      Object* result;
      { MaybeObject* maybe_result = buffer->IsAsciiRepresentation()
                       ? AllocateRawAsciiString(length, pretenure)
                       : AllocateRawTwoByteString(length, pretenure);
        if (!maybe_result->ToObject(&result)) return maybe_result;
      }
      String* string_result = String::cast(result);
      // Copy the characters into the new object.
      if (buffer->IsAsciiRepresentation()) {
        ASSERT(string_result->IsAsciiRepresentation());
        char* dest = SeqAsciiString::cast(string_result)->GetChars();
        String::WriteToFlat(buffer, dest, start, end);
      } else {
        ASSERT(string_result->IsTwoByteRepresentation());
        uc16* dest = SeqTwoByteString::cast(string_result)->GetChars();
        String::WriteToFlat(buffer, dest, start, end);
      }
      return result;
    }
  
    ASSERT(buffer->IsFlat());
    ASSERT(!buffer->IsExternalString());
  #if DEBUG
    buffer->StringVerify();
  #endif
  
    Object* result;
    { Map* map = buffer->IsAsciiRepresentation()
                   ? sliced_ascii_string_map()
                   : sliced_string_map();
      MaybeObject* maybe_result = Allocate(map, NEW_SPACE);
      if (!maybe_result->ToObject(&result)) return maybe_result;
    }
  
    AssertNoAllocation no_gc;
    SlicedString* sliced_string = SlicedString::cast(result);
    sliced_string->set_length(length);
    sliced_string->set_hash_field(String::kEmptyHashField);
    if (buffer->IsConsString()) {
      ConsString* cons = ConsString::cast(buffer);
      ASSERT(cons->second()->length() == 0);
      sliced_string->set_parent(cons->first());
      sliced_string->set_offset(start);
    } else if (buffer->IsSlicedString()) {
      // Prevent nesting sliced strings.
      SlicedString* parent_slice = SlicedString::cast(buffer);
      sliced_string->set_parent(parent_slice->parent());
      sliced_string->set_offset(start + parent_slice->offset());
    } else {
      sliced_string->set_parent(buffer);
      sliced_string->set_offset(start);
    }
    ASSERT(sliced_string->parent()->IsSeqString());
    return result;
  }
  
  
  MaybeObject* Heap::AllocateExternalStringFromAscii(
      ExternalAsciiString::Resource* resource) {
    size_t length = resource->length();
    if (length > static_cast<size_t>(String::kMaxLength)) {
      isolate()->context()->mark_out_of_memory();
      return Failure::OutOfMemoryException();
    }
  
    Map* map = external_ascii_string_map();
    Object* result;
    { MaybeObject* maybe_result = Allocate(map, NEW_SPACE);
      if (!maybe_result->ToObject(&result)) return maybe_result;
    }
  
    ExternalAsciiString* external_string = ExternalAsciiString::cast(result);
    external_string->set_length(static_cast<int>(length));
    external_string->set_hash_field(String::kEmptyHashField);
    external_string->set_resource(resource);
  
    return result;
  }
  
  
  MaybeObject* Heap::AllocateExternalStringFromTwoByte(
      ExternalTwoByteString::Resource* resource) {
    size_t length = resource->length();
    if (length > static_cast<size_t>(String::kMaxLength)) {
      isolate()->context()->mark_out_of_memory();
      return Failure::OutOfMemoryException();
    }
  
    // For small strings we check whether the resource contains only
    // ASCII characters.  If yes, we use a different string map.
    static const size_t kAsciiCheckLengthLimit = 32;
    bool is_ascii = length <= kAsciiCheckLengthLimit &&
        String::IsAscii(resource->data(), static_cast<int>(length));
    Map* map = is_ascii ?
        external_string_with_ascii_data_map() : external_string_map();
    Object* result;
    { MaybeObject* maybe_result = Allocate(map, NEW_SPACE);
      if (!maybe_result->ToObject(&result)) return maybe_result;
    }
  
    ExternalTwoByteString* external_string = ExternalTwoByteString::cast(result);
    external_string->set_length(static_cast<int>(length));
    external_string->set_hash_field(String::kEmptyHashField);
    external_string->set_resource(resource);
  
    return result;
  }
  
  
  MaybeObject* Heap::LookupSingleCharacterStringFromCode(uint16_t code) {
    if (code <= String::kMaxAsciiCharCode) {
      Object* value = single_character_string_cache()->get(code);
      if (value != undefined_value()) return value;
  
      char buffer[1];
      buffer[0] = static_cast<char>(code);
      Object* result;
      MaybeObject* maybe_result = LookupSymbol(Vector<const char>(buffer, 1));
  
      if (!maybe_result->ToObject(&result)) return maybe_result;
      single_character_string_cache()->set(code, result);
      return result;
    }
  
    Object* result;
    { MaybeObject* maybe_result = AllocateRawTwoByteString(1);
      if (!maybe_result->ToObject(&result)) return maybe_result;
    }
    String* answer = String::cast(result);
    answer->Set(0, code);
    return answer;
  }
  
  
  MaybeObject* Heap::AllocateByteArray(int length, PretenureFlag pretenure) {
    if (length < 0 || length > ByteArray::kMaxLength) {
      return Failure::OutOfMemoryException();
    }
    if (pretenure == NOT_TENURED) {
      return AllocateByteArray(length);
    }
    int size = ByteArray::SizeFor(length);
    Object* result;
    { MaybeObject* maybe_result = (size <= MaxObjectSizeInPagedSpace())
                     ? old_data_space_->AllocateRaw(size)
                     : lo_space_->AllocateRaw(size);
      if (!maybe_result->ToObject(&result)) return maybe_result;
    }
  
    reinterpret_cast<ByteArray*>(result)->set_map(byte_array_map());
    reinterpret_cast<ByteArray*>(result)->set_length(length);
    return result;
  }
  
  
  MaybeObject* Heap::AllocateByteArray(int length) {
    if (length < 0 || length > ByteArray::kMaxLength) {
      return Failure::OutOfMemoryException();
    }
    int size = ByteArray::SizeFor(length);
    AllocationSpace space =
        (size > MaxObjectSizeInPagedSpace()) ? LO_SPACE : NEW_SPACE;
    Object* result;
    { MaybeObject* maybe_result = AllocateRaw(size, space, OLD_DATA_SPACE);
      if (!maybe_result->ToObject(&result)) return maybe_result;
    }
  
    reinterpret_cast<ByteArray*>(result)->set_map(byte_array_map());
    reinterpret_cast<ByteArray*>(result)->set_length(length);
    return result;
  }
  
  
  void Heap::CreateFillerObjectAt(Address addr, int size) {
    if (size == 0) return;
    HeapObject* filler = HeapObject::FromAddress(addr);
    if (size == kPointerSize) {
      filler->set_map(one_pointer_filler_map());
    } else if (size == 2 * kPointerSize) {
      filler->set_map(two_pointer_filler_map());
    } else {
      filler->set_map(byte_array_map());
      ByteArray::cast(filler)->set_length(ByteArray::LengthFor(size));
    }
  }
  
  
  MaybeObject* Heap::AllocateExternalArray(int length,
                                           ExternalArrayType array_type,
                                           void* external_pointer,
                                           PretenureFlag pretenure) {
    AllocationSpace space = (pretenure == TENURED) ? OLD_DATA_SPACE : NEW_SPACE;
    Object* result;
    { MaybeObject* maybe_result = AllocateRaw(ExternalArray::kAlignedSize,
                                              space,
                                              OLD_DATA_SPACE);
      if (!maybe_result->ToObject(&result)) return maybe_result;
    }
  
    reinterpret_cast<ExternalArray*>(result)->set_map(
        MapForExternalArrayType(array_type));
    reinterpret_cast<ExternalArray*>(result)->set_length(length);
    reinterpret_cast<ExternalArray*>(result)->set_external_pointer(
        external_pointer);
  
    return result;
  }
  
  
  MaybeObject* Heap::CreateCode(const CodeDesc& desc,
                                Code::Flags flags,
                                Handle<Object> self_reference,
                                bool immovable) {
    // Allocate ByteArray before the Code object, so that we do not risk
    // leaving uninitialized Code object (and breaking the heap).
    Object* reloc_info;
    { MaybeObject* maybe_reloc_info = AllocateByteArray(desc.reloc_size, TENURED);
      if (!maybe_reloc_info->ToObject(&reloc_info)) return maybe_reloc_info;
    }
  
    // Compute size.
    int body_size = RoundUp(desc.instr_size, kObjectAlignment);
    int obj_size = Code::SizeFor(body_size);
    ASSERT(IsAligned(static_cast<intptr_t>(obj_size), kCodeAlignment));
    MaybeObject* maybe_result;
    // Large code objects and code objects which should stay at a fixed address
    // are allocated in large object space.
    if (obj_size > MaxObjectSizeInPagedSpace() || immovable) {
      maybe_result = lo_space_->AllocateRawCode(obj_size);
    } else {
      maybe_result = code_space_->AllocateRaw(obj_size);
    }
  
    Object* result;
    if (!maybe_result->ToObject(&result)) return maybe_result;
  
    // Initialize the object
    HeapObject::cast(result)->set_map(code_map());
    Code* code = Code::cast(result);
    ASSERT(!isolate_->code_range()->exists() ||
        isolate_->code_range()->contains(code->address()));
    code->set_instruction_size(desc.instr_size);
    code->set_relocation_info(ByteArray::cast(reloc_info));
    code->set_flags(flags);
    if (code->is_call_stub() || code->is_keyed_call_stub()) {
      code->set_check_type(RECEIVER_MAP_CHECK);
    }
    code->set_deoptimization_data(empty_fixed_array());
    code->set_next_code_flushing_candidate(undefined_value());
    // Allow self references to created code object by patching the handle to
    // point to the newly allocated Code object.
    if (!self_reference.is_null()) {
      *(self_reference.location()) = code;
    }
    // Migrate generated code.
    // The generated code can contain Object** values (typically from handles)
    // that are dereferenced during the copy to point directly to the actual heap
    // objects. These pointers can include references to the code object itself,
    // through the self_reference parameter.
    code->CopyFrom(desc);
  
  #ifdef DEBUG
    code->Verify();
  #endif
    return code;
  }
  
  
  MaybeObject* Heap::CopyCode(Code* code) {
    // Allocate an object the same size as the code object.
    int obj_size = code->Size();
    MaybeObject* maybe_result;
    if (obj_size > MaxObjectSizeInPagedSpace()) {
      maybe_result = lo_space_->AllocateRawCode(obj_size);
    } else {
      maybe_result = code_space_->AllocateRaw(obj_size);
    }
  
    Object* result;
    if (!maybe_result->ToObject(&result)) return maybe_result;
  
    // Copy code object.
    Address old_addr = code->address();
    Address new_addr = reinterpret_cast<HeapObject*>(result)->address();
    CopyBlock(new_addr, old_addr, obj_size);
    // Relocate the copy.
    Code* new_code = Code::cast(result);
    ASSERT(!isolate_->code_range()->exists() ||
        isolate_->code_range()->contains(code->address()));
    new_code->Relocate(new_addr - old_addr);
    return new_code;
  }
  
  
  MaybeObject* Heap::CopyCode(Code* code, Vector<byte> reloc_info) {
    // Allocate ByteArray before the Code object, so that we do not risk
    // leaving uninitialized Code object (and breaking the heap).
    Object* reloc_info_array;
    { MaybeObject* maybe_reloc_info_array =
          AllocateByteArray(reloc_info.length(), TENURED);
      if (!maybe_reloc_info_array->ToObject(&reloc_info_array)) {
        return maybe_reloc_info_array;
      }
    }
  
    int new_body_size = RoundUp(code->instruction_size(), kObjectAlignment);
  
    int new_obj_size = Code::SizeFor(new_body_size);
  
    Address old_addr = code->address();
  
    size_t relocation_offset =
        static_cast<size_t>(code->instruction_end() - old_addr);
  
    MaybeObject* maybe_result;
    if (new_obj_size > MaxObjectSizeInPagedSpace()) {
      maybe_result = lo_space_->AllocateRawCode(new_obj_size);
    } else {
      maybe_result = code_space_->AllocateRaw(new_obj_size);
    }
  
    Object* result;
    if (!maybe_result->ToObject(&result)) return maybe_result;
  
    // Copy code object.
    Address new_addr = reinterpret_cast<HeapObject*>(result)->address();
  
    // Copy header and instructions.
    memcpy(new_addr, old_addr, relocation_offset);
  
    Code* new_code = Code::cast(result);
    new_code->set_relocation_info(ByteArray::cast(reloc_info_array));
  
    // Copy patched rinfo.
    memcpy(new_code->relocation_start(), reloc_info.start(), reloc_info.length());
  
    // Relocate the copy.
    ASSERT(!isolate_->code_range()->exists() ||
        isolate_->code_range()->contains(code->address()));
    new_code->Relocate(new_addr - old_addr);
  
  #ifdef DEBUG
    code->Verify();
  #endif
    return new_code;
  }
  
  
  MaybeObject* Heap::Allocate(Map* map, AllocationSpace space) {
    ASSERT(gc_state_ == NOT_IN_GC);
    ASSERT(map->instance_type() != MAP_TYPE);
    // If allocation failures are disallowed, we may allocate in a different
    // space when new space is full and the object is not a large object.
    AllocationSpace retry_space =
        (space != NEW_SPACE) ? space : TargetSpaceId(map->instance_type());
    Object* result;
    { MaybeObject* maybe_result =
          AllocateRaw(map->instance_size(), space, retry_space);
      if (!maybe_result->ToObject(&result)) return maybe_result;
    }
    HeapObject::cast(result)->set_map(map);
    return result;
  }
  
  
  MaybeObject* Heap::InitializeFunction(JSFunction* function,
                                        SharedFunctionInfo* shared,
                                        Object* prototype) {
    ASSERT(!prototype->IsMap());
    function->initialize_properties();
    function->initialize_elements();
    function->set_shared(shared);
    function->set_code(shared->code());
    function->set_prototype_or_initial_map(prototype);
    function->set_context(undefined_value());
    function->set_literals(empty_fixed_array());
    function->set_next_function_link(undefined_value());
    return function;
  }
  
  
  MaybeObject* Heap::AllocateFunctionPrototype(JSFunction* function) {
    // Allocate the prototype.  Make sure to use the object function
    // from the function's context, since the function can be from a
    // different context.
    JSFunction* object_function =
        function->context()->global_context()->object_function();
    Object* prototype;
    { MaybeObject* maybe_prototype = AllocateJSObject(object_function);
      if (!maybe_prototype->ToObject(&prototype)) return maybe_prototype;
    }
    // When creating the prototype for the function we must set its
    // constructor to the function.
    Object* result;
    { MaybeObject* maybe_result =
          JSObject::cast(prototype)->SetLocalPropertyIgnoreAttributes(
              constructor_symbol(), function, DONT_ENUM);
      if (!maybe_result->ToObject(&result)) return maybe_result;
    }
    return prototype;
  }
  
  
  MaybeObject* Heap::AllocateFunction(Map* function_map,
                                      SharedFunctionInfo* shared,
                                      Object* prototype,
                                      PretenureFlag pretenure) {
    AllocationSpace space =
        (pretenure == TENURED) ? OLD_POINTER_SPACE : NEW_SPACE;
    Object* result;
    { MaybeObject* maybe_result = Allocate(function_map, space);
      if (!maybe_result->ToObject(&result)) return maybe_result;
    }
    return InitializeFunction(JSFunction::cast(result), shared, prototype);
  }
  
  
  MaybeObject* Heap::AllocateArgumentsObject(Object* callee, int length) {
    // To get fast allocation and map sharing for arguments objects we
    // allocate them based on an arguments boilerplate.
  
    JSObject* boilerplate;
    int arguments_object_size;
    bool strict_mode_callee = callee->IsJSFunction() &&
                              JSFunction::cast(callee)->shared()->strict_mode();
    if (strict_mode_callee) {
      boilerplate =
          isolate()->context()->global_context()->
              strict_mode_arguments_boilerplate();
      arguments_object_size = kArgumentsObjectSizeStrict;
    } else {
      boilerplate =
          isolate()->context()->global_context()->arguments_boilerplate();
      arguments_object_size = kArgumentsObjectSize;
    }
  
    // This calls Copy directly rather than using Heap::AllocateRaw so we
    // duplicate the check here.
    ASSERT(allocation_allowed_ && gc_state_ == NOT_IN_GC);
  
    // Check that the size of the boilerplate matches our
    // expectations. The ArgumentsAccessStub::GenerateNewObject relies
    // on the size being a known constant.
    ASSERT(arguments_object_size == boilerplate->map()->instance_size());
  
    // Do the allocation.
    Object* result;
    { MaybeObject* maybe_result =
          AllocateRaw(arguments_object_size, NEW_SPACE, OLD_POINTER_SPACE);
      if (!maybe_result->ToObject(&result)) return maybe_result;
    }
  
    // Copy the content. The arguments boilerplate doesn't have any
    // fields that point to new space so it's safe to skip the write
    // barrier here.
    CopyBlock(HeapObject::cast(result)->address(),
              boilerplate->address(),
              JSObject::kHeaderSize);
  
    // Set the length property.
    JSObject::cast(result)->InObjectPropertyAtPut(kArgumentsLengthIndex,
                                                  Smi::FromInt(length),
                                                  SKIP_WRITE_BARRIER);
    // Set the callee property for non-strict mode arguments object only.
    if (!strict_mode_callee) {
      JSObject::cast(result)->InObjectPropertyAtPut(kArgumentsCalleeIndex,
                                                    callee);
    }
  
    // Check the state of the object
    ASSERT(JSObject::cast(result)->HasFastProperties());
    ASSERT(JSObject::cast(result)->HasFastElements());
  
    return result;
  }
  
  
  static bool HasDuplicates(DescriptorArray* descriptors) {
    int count = descriptors->number_of_descriptors();
    if (count > 1) {
      String* prev_key = descriptors->GetKey(0);
      for (int i = 1; i != count; i++) {
        String* current_key = descriptors->GetKey(i);
        if (prev_key == current_key) return true;
        prev_key = current_key;
      }
    }
    return false;
  }
  
  
  MaybeObject* Heap::AllocateInitialMap(JSFunction* fun) {
    ASSERT(!fun->has_initial_map());
  
    // First create a new map with the size and number of in-object properties
    // suggested by the function.
    int instance_size = fun->shared()->CalculateInstanceSize();
    int in_object_properties = fun->shared()->CalculateInObjectProperties();
    Object* map_obj;
    { MaybeObject* maybe_map_obj = AllocateMap(JS_OBJECT_TYPE, instance_size);
      if (!maybe_map_obj->ToObject(&map_obj)) return maybe_map_obj;
    }
  
    // Fetch or allocate prototype.
    Object* prototype;
    if (fun->has_instance_prototype()) {
      prototype = fun->instance_prototype();
    } else {
      { MaybeObject* maybe_prototype = AllocateFunctionPrototype(fun);
        if (!maybe_prototype->ToObject(&prototype)) return maybe_prototype;
      }
    }
    Map* map = Map::cast(map_obj);
    map->set_inobject_properties(in_object_properties);
    map->set_unused_property_fields(in_object_properties);
    map->set_prototype(prototype);
    ASSERT(map->has_fast_elements());
  
    // If the function has only simple this property assignments add
    // field descriptors for these to the initial map as the object
    // cannot be constructed without having these properties.  Guard by
    // the inline_new flag so we only change the map if we generate a
    // specialized construct stub.
    ASSERT(in_object_properties <= Map::kMaxPreAllocatedPropertyFields);
    if (fun->shared()->CanGenerateInlineConstructor(prototype)) {
      int count = fun->shared()->this_property_assignments_count();
      if (count > in_object_properties) {
        // Inline constructor can only handle inobject properties.
        fun->shared()->ForbidInlineConstructor();
      } else {
        Object* descriptors_obj;
        { MaybeObject* maybe_descriptors_obj = DescriptorArray::Allocate(count);
          if (!maybe_descriptors_obj->ToObject(&descriptors_obj)) {
            return maybe_descriptors_obj;
          }
        }
        DescriptorArray* descriptors = DescriptorArray::cast(descriptors_obj);
        for (int i = 0; i < count; i++) {
          String* name = fun->shared()->GetThisPropertyAssignmentName(i);
          ASSERT(name->IsSymbol());
          FieldDescriptor field(name, i, NONE);
          field.SetEnumerationIndex(i);
          descriptors->Set(i, &field);
        }
        descriptors->SetNextEnumerationIndex(count);
        descriptors->SortUnchecked();
  
        // The descriptors may contain duplicates because the compiler does not
        // guarantee the uniqueness of property names (it would have required
        // quadratic time). Once the descriptors are sorted we can check for
        // duplicates in linear time.
        if (HasDuplicates(descriptors)) {
          fun->shared()->ForbidInlineConstructor();
        } else {
          map->set_instance_descriptors(descriptors);
          map->set_pre_allocated_property_fields(count);
          map->set_unused_property_fields(in_object_properties - count);
        }
      }
    }
  
    fun->shared()->StartInobjectSlackTracking(map);
  
    return map;
  }
  
  
  void Heap::InitializeJSObjectFromMap(JSObject* obj,
                                       FixedArray* properties,
                                       Map* map) {
    obj->set_properties(properties);
    obj->initialize_elements();
    // TODO(1240798): Initialize the object's body using valid initial values
    // according to the object's initial map.  For example, if the map's
    // instance type is JS_ARRAY_TYPE, the length field should be initialized
    // to a number (eg, Smi::FromInt(0)) and the elements initialized to a
    // fixed array (eg, Heap::empty_fixed_array()).  Currently, the object
    // verification code has to cope with (temporarily) invalid objects.  See
    // for example, JSArray::JSArrayVerify).
    Object* filler;
    // We cannot always fill with one_pointer_filler_map because objects
    // created from API functions expect their internal fields to be initialized
    // with undefined_value.
    if (map->constructor()->IsJSFunction() &&
        JSFunction::cast(map->constructor())->shared()->
            IsInobjectSlackTrackingInProgress()) {
      // We might want to shrink the object later.
      ASSERT(obj->GetInternalFieldCount() == 0);
      filler = Heap::one_pointer_filler_map();
    } else {
      filler = Heap::undefined_value();
    }
    obj->InitializeBody(map->instance_size(), filler);
  }
  
  
  MaybeObject* Heap::AllocateJSObjectFromMap(Map* map, PretenureFlag pretenure) {
    // JSFunctions should be allocated using AllocateFunction to be
    // properly initialized.
    ASSERT(map->instance_type() != JS_FUNCTION_TYPE);
  
    // Both types of global objects should be allocated using
    // AllocateGlobalObject to be properly initialized.
    ASSERT(map->instance_type() != JS_GLOBAL_OBJECT_TYPE);
    ASSERT(map->instance_type() != JS_BUILTINS_OBJECT_TYPE);
  
    // Allocate the backing storage for the properties.
    int prop_size =
        map->pre_allocated_property_fields() +
        map->unused_property_fields() -
        map->inobject_properties();
    ASSERT(prop_size >= 0);
    Object* properties;
    { MaybeObject* maybe_properties = AllocateFixedArray(prop_size, pretenure);
      if (!maybe_properties->ToObject(&properties)) return maybe_properties;
    }
  
    // Allocate the JSObject.
    AllocationSpace space =
        (pretenure == TENURED) ? OLD_POINTER_SPACE : NEW_SPACE;
    if (map->instance_size() > MaxObjectSizeInPagedSpace()) space = LO_SPACE;
    Object* obj;
    { MaybeObject* maybe_obj = Allocate(map, space);
      if (!maybe_obj->ToObject(&obj)) return maybe_obj;
    }
  
    // Initialize the JSObject.
    InitializeJSObjectFromMap(JSObject::cast(obj),
                              FixedArray::cast(properties),
                              map);
    ASSERT(JSObject::cast(obj)->HasFastElements());
    return obj;
  }
  
  
  MaybeObject* Heap::AllocateJSObject(JSFunction* constructor,
                                      PretenureFlag pretenure) {
    // Allocate the initial map if absent.
    if (!constructor->has_initial_map()) {
      Object* initial_map;
      { MaybeObject* maybe_initial_map = AllocateInitialMap(constructor);
        if (!maybe_initial_map->ToObject(&initial_map)) return maybe_initial_map;
      }
      constructor->set_initial_map(Map::cast(initial_map));
      Map::cast(initial_map)->set_constructor(constructor);
    }
    // Allocate the object based on the constructors initial map.
    MaybeObject* result =
        AllocateJSObjectFromMap(constructor->initial_map(), pretenure);
  #ifdef DEBUG
    // Make sure result is NOT a global object if valid.
    Object* non_failure;
    ASSERT(!result->ToObject(&non_failure) || !non_failure->IsGlobalObject());
  #endif
    return result;
  }
  
  
  MaybeObject* Heap::AllocateJSProxy(Object* handler, Object* prototype) {
    // Allocate map.
    // TODO(rossberg): Once we optimize proxies, think about a scheme to share
    // maps. Will probably depend on the identity of the handler object, too.
    Map* map;
    MaybeObject* maybe_map_obj = AllocateMap(JS_PROXY_TYPE, JSProxy::kSize);
    if (!maybe_map_obj->To<Map>(&map)) return maybe_map_obj;
    map->set_prototype(prototype);
  
    // Allocate the proxy object.
    JSProxy* result;
    MaybeObject* maybe_result = Allocate(map, NEW_SPACE);
    if (!maybe_result->To<JSProxy>(&result)) return maybe_result;
    result->InitializeBody(map->instance_size(), Smi::FromInt(0));
    result->set_handler(handler);
    return result;
  }
  
  
  MaybeObject* Heap::AllocateJSFunctionProxy(Object* handler,
                                             Object* call_trap,
                                             Object* construct_trap,
                                             Object* prototype) {
    // Allocate map.
    // TODO(rossberg): Once we optimize proxies, think about a scheme to share
    // maps. Will probably depend on the identity of the handler object, too.
    Map* map;
    MaybeObject* maybe_map_obj =
        AllocateMap(JS_FUNCTION_PROXY_TYPE, JSFunctionProxy::kSize);
    if (!maybe_map_obj->To<Map>(&map)) return maybe_map_obj;
    map->set_prototype(prototype);
  
    // Allocate the proxy object.
    JSFunctionProxy* result;
    MaybeObject* maybe_result = Allocate(map, NEW_SPACE);
    if (!maybe_result->To<JSFunctionProxy>(&result)) return maybe_result;
    result->InitializeBody(map->instance_size(), Smi::FromInt(0));
    result->set_handler(handler);
    result->set_call_trap(call_trap);
    result->set_construct_trap(construct_trap);
    return result;
  }
  
  
  MaybeObject* Heap::AllocateGlobalObject(JSFunction* constructor) {
    ASSERT(constructor->has_initial_map());
    Map* map = constructor->initial_map();
  
    // Make sure no field properties are described in the initial map.
    // This guarantees us that normalizing the properties does not
    // require us to change property values to JSGlobalPropertyCells.
    ASSERT(map->NextFreePropertyIndex() == 0);
  
    // Make sure we don't have a ton of pre-allocated slots in the
    // global objects. They will be unused once we normalize the object.
    ASSERT(map->unused_property_fields() == 0);
    ASSERT(map->inobject_properties() == 0);
  
    // Initial size of the backing store to avoid resize of the storage during
    // bootstrapping. The size differs between the JS global object ad the
    // builtins object.
    int initial_size = map->instance_type() == JS_GLOBAL_OBJECT_TYPE ? 64 : 512;
  
    // Allocate a dictionary object for backing storage.
    Object* obj;
    { MaybeObject* maybe_obj =
          StringDictionary::Allocate(
              map->NumberOfDescribedProperties() * 2 + initial_size);
      if (!maybe_obj->ToObject(&obj)) return maybe_obj;
    }
    StringDictionary* dictionary = StringDictionary::cast(obj);
  
    // The global object might be created from an object template with accessors.
    // Fill these accessors into the dictionary.
    DescriptorArray* descs = map->instance_descriptors();
    for (int i = 0; i < descs->number_of_descriptors(); i++) {
      PropertyDetails details(descs->GetDetails(i));
      ASSERT(details.type() == CALLBACKS);  // Only accessors are expected.
      PropertyDetails d =
          PropertyDetails(details.attributes(), CALLBACKS, details.index());
      Object* value = descs->GetCallbacksObject(i);
      { MaybeObject* maybe_value = AllocateJSGlobalPropertyCell(value);
        if (!maybe_value->ToObject(&value)) return maybe_value;
      }
  
      Object* result;
      { MaybeObject* maybe_result = dictionary->Add(descs->GetKey(i), value, d);
        if (!maybe_result->ToObject(&result)) return maybe_result;
      }
      dictionary = StringDictionary::cast(result);
    }
  
    // Allocate the global object and initialize it with the backing store.
    { MaybeObject* maybe_obj = Allocate(map, OLD_POINTER_SPACE);
      if (!maybe_obj->ToObject(&obj)) return maybe_obj;
    }
    JSObject* global = JSObject::cast(obj);
    InitializeJSObjectFromMap(global, dictionary, map);
  
    // Create a new map for the global object.
    { MaybeObject* maybe_obj = map->CopyDropDescriptors();
      if (!maybe_obj->ToObject(&obj)) return maybe_obj;
    }
    Map* new_map = Map::cast(obj);
  
    // Setup the global object as a normalized object.
    global->set_map(new_map);
    global->map()->clear_instance_descriptors();
    global->set_properties(dictionary);
  
    // Make sure result is a global object with properties in dictionary.
    ASSERT(global->IsGlobalObject());
    ASSERT(!global->HasFastProperties());
    return global;
  }
  
  
  MaybeObject* Heap::CopyJSObject(JSObject* source) {
    // Never used to copy functions.  If functions need to be copied we
    // have to be careful to clear the literals array.
    ASSERT(!source->IsJSFunction());
  
    // Make the clone.
    Map* map = source->map();
    int object_size = map->instance_size();
    Object* clone;
  
    // If we're forced to always allocate, we use the general allocation
    // functions which may leave us with an object in old space.
    if (always_allocate()) {
      { MaybeObject* maybe_clone =
            AllocateRaw(object_size, NEW_SPACE, OLD_POINTER_SPACE);
        if (!maybe_clone->ToObject(&clone)) return maybe_clone;
      }
      Address clone_address = HeapObject::cast(clone)->address();
      CopyBlock(clone_address,
                source->address(),
                object_size);
      // Update write barrier for all fields that lie beyond the header.
      RecordWrites(clone_address,
                   JSObject::kHeaderSize,
                   (object_size - JSObject::kHeaderSize) / kPointerSize);
    } else {
      { MaybeObject* maybe_clone = new_space_.AllocateRaw(object_size);
        if (!maybe_clone->ToObject(&clone)) return maybe_clone;
      }
      ASSERT(InNewSpace(clone));
      // Since we know the clone is allocated in new space, we can copy
      // the contents without worrying about updating the write barrier.
      CopyBlock(HeapObject::cast(clone)->address(),
                source->address(),
                object_size);
    }
  
    FixedArrayBase* elements = FixedArrayBase::cast(source->elements());
    FixedArray* properties = FixedArray::cast(source->properties());
    // Update elements if necessary.
    if (elements->length() > 0) {
      Object* elem;
      { MaybeObject* maybe_elem;
        if (elements->map() == fixed_cow_array_map()) {
          maybe_elem = FixedArray::cast(elements);
        } else if (source->HasFastDoubleElements()) {
          maybe_elem = CopyFixedDoubleArray(FixedDoubleArray::cast(elements));
        } else {
          maybe_elem = CopyFixedArray(FixedArray::cast(elements));
        }
        if (!maybe_elem->ToObject(&elem)) return maybe_elem;
      }
      JSObject::cast(clone)->set_elements(FixedArrayBase::cast(elem));
    }
    // Update properties if necessary.
    if (properties->length() > 0) {
      Object* prop;
      { MaybeObject* maybe_prop = CopyFixedArray(properties);
        if (!maybe_prop->ToObject(&prop)) return maybe_prop;
      }
      JSObject::cast(clone)->set_properties(FixedArray::cast(prop));
    }
    // Return the new clone.
    return clone;
  }
  
  
  MaybeObject* Heap::ReinitializeJSReceiver(
      JSReceiver* object, InstanceType type, int size) {
    ASSERT(type >= FIRST_JS_RECEIVER_TYPE);
  
    // Allocate fresh map.
    // TODO(rossberg): Once we optimize proxies, cache these maps.
    Map* map;
    MaybeObject* maybe_map_obj = AllocateMap(type, size);
    if (!maybe_map_obj->To<Map>(&map)) return maybe_map_obj;
  
    // Check that the receiver has at least the size of the fresh object.
    int size_difference = object->map()->instance_size() - map->instance_size();
    ASSERT(size_difference >= 0);
  
    map->set_prototype(object->map()->prototype());
  
    // Allocate the backing storage for the properties.
    int prop_size = map->unused_property_fields() - map->inobject_properties();
    Object* properties;
    { MaybeObject* maybe_properties = AllocateFixedArray(prop_size, TENURED);
      if (!maybe_properties->ToObject(&properties)) return maybe_properties;
    }
  
    // Reset the map for the object.
    object->set_map(map);
  
    // Reinitialize the object from the constructor map.
    InitializeJSObjectFromMap(JSObject::cast(object),
                              FixedArray::cast(properties), map);
  
    // Functions require some minimal initialization.
    if (type == JS_FUNCTION_TYPE) {
      String* name;
      MaybeObject* maybe_name = LookupAsciiSymbol("<freezing call trap>");
      if (!maybe_name->To<String>(&name)) return maybe_name;
      SharedFunctionInfo* shared;
      MaybeObject* maybe_shared = AllocateSharedFunctionInfo(name);
      if (!maybe_shared->To<SharedFunctionInfo>(&shared)) return maybe_shared;
      JSFunction* func;
      MaybeObject* maybe_func =
          InitializeFunction(JSFunction::cast(object), shared, the_hole_value());
      if (!maybe_func->To<JSFunction>(&func)) return maybe_func;
      func->set_context(isolate()->context()->global_context());
    }
  
    // Put in filler if the new object is smaller than the old.
    if (size_difference > 0) {
      CreateFillerObjectAt(
          object->address() + map->instance_size(), size_difference);
    }
  
    return object;
  }
  
  
  MaybeObject* Heap::ReinitializeJSGlobalProxy(JSFunction* constructor,
                                               JSGlobalProxy* object) {
    ASSERT(constructor->has_initial_map());
    Map* map = constructor->initial_map();
  
    // Check that the already allocated object has the same size and type as
    // objects allocated using the constructor.
    ASSERT(map->instance_size() == object->map()->instance_size());
    ASSERT(map->instance_type() == object->map()->instance_type());
  
    // Allocate the backing storage for the properties.
    int prop_size = map->unused_property_fields() - map->inobject_properties();
    Object* properties;
    { MaybeObject* maybe_properties = AllocateFixedArray(prop_size, TENURED);
      if (!maybe_properties->ToObject(&properties)) return maybe_properties;
    }
  
    // Reset the map for the object.
    object->set_map(constructor->initial_map());
  
    // Reinitialize the object from the constructor map.
    InitializeJSObjectFromMap(object, FixedArray::cast(properties), map);
    return object;
  }
  
  
  MaybeObject* Heap::AllocateStringFromAscii(Vector<const char> string,
                                             PretenureFlag pretenure) {
    if (string.length() == 1) {
      return Heap::LookupSingleCharacterStringFromCode(string[0]);
    }
    Object* result;
    { MaybeObject* maybe_result =
          AllocateRawAsciiString(string.length(), pretenure);
      if (!maybe_result->ToObject(&result)) return maybe_result;
    }
  
    // Copy the characters into the new object.
    SeqAsciiString* string_result = SeqAsciiString::cast(result);
    for (int i = 0; i < string.length(); i++) {
      string_result->SeqAsciiStringSet(i, string[i]);
    }
    return result;
  }
  
  
  MaybeObject* Heap::AllocateStringFromUtf8Slow(Vector<const char> string,
                                                PretenureFlag pretenure) {
    // V8 only supports characters in the Basic Multilingual Plane.
    const uc32 kMaxSupportedChar = 0xFFFF;
    // Count the number of characters in the UTF-8 string and check if
    // it is an ASCII string.
    Access<UnicodeCache::Utf8Decoder>
        decoder(isolate_->unicode_cache()->utf8_decoder());
    decoder->Reset(string.start(), string.length());
    int chars = 0;
    while (decoder->has_more()) {
      decoder->GetNext();
      chars++;
    }
  
    Object* result;
    { MaybeObject* maybe_result = AllocateRawTwoByteString(chars, pretenure);
      if (!maybe_result->ToObject(&result)) return maybe_result;
    }
  
    // Convert and copy the characters into the new object.
    String* string_result = String::cast(result);
    decoder->Reset(string.start(), string.length());
    for (int i = 0; i < chars; i++) {
      uc32 r = decoder->GetNext();
      if (r > kMaxSupportedChar) { r = unibrow::Utf8::kBadChar; }
      string_result->Set(i, r);
    }
    return result;
  }
  
  
  MaybeObject* Heap::AllocateStringFromTwoByte(Vector<const uc16> string,
                                               PretenureFlag pretenure) {
    // Check if the string is an ASCII string.
    MaybeObject* maybe_result;
    if (String::IsAscii(string.start(), string.length())) {
      maybe_result = AllocateRawAsciiString(string.length(), pretenure);
    } else {  // It's not an ASCII string.
      maybe_result = AllocateRawTwoByteString(string.length(), pretenure);
    }
    Object* result;
    if (!maybe_result->ToObject(&result)) return maybe_result;
  
    // Copy the characters into the new object, which may be either ASCII or
    // UTF-16.
    String* string_result = String::cast(result);
    for (int i = 0; i < string.length(); i++) {
      string_result->Set(i, string[i]);
    }
    return result;
  }
  
  
  Map* Heap::SymbolMapForString(String* string) {
    // If the string is in new space it cannot be used as a symbol.
    if (InNewSpace(string)) return NULL;
  
    // Find the corresponding symbol map for strings.
    Map* map = string->map();
    if (map == ascii_string_map()) {
      return ascii_symbol_map();
    }
    if (map == string_map()) {
      return symbol_map();
    }
    if (map == cons_string_map()) {
      return cons_symbol_map();
    }
    if (map == cons_ascii_string_map()) {
      return cons_ascii_symbol_map();
    }
    if (map == external_string_map()) {
      return external_symbol_map();
    }
    if (map == external_ascii_string_map()) {
      return external_ascii_symbol_map();
    }
    if (map == external_string_with_ascii_data_map()) {
      return external_symbol_with_ascii_data_map();
    }
  
    // No match found.
    return NULL;
  }
  
  
  MaybeObject* Heap::AllocateInternalSymbol(unibrow::CharacterStream* buffer,
                                            int chars,
                                            uint32_t hash_field) {
    ASSERT(chars >= 0);
    // Ensure the chars matches the number of characters in the buffer.
    ASSERT(static_cast<unsigned>(chars) == buffer->Length());
    // Determine whether the string is ascii.
    bool is_ascii = true;
    while (buffer->has_more()) {
      if (buffer->GetNext() > unibrow::Utf8::kMaxOneByteChar) {
        is_ascii = false;
        break;
      }
    }
    buffer->Rewind();
  
    // Compute map and object size.
    int size;
    Map* map;
  
    if (is_ascii) {
      if (chars > SeqAsciiString::kMaxLength) {
        return Failure::OutOfMemoryException();
      }
      map = ascii_symbol_map();
      size = SeqAsciiString::SizeFor(chars);
    } else {
      if (chars > SeqTwoByteString::kMaxLength) {
        return Failure::OutOfMemoryException();
      }
      map = symbol_map();
      size = SeqTwoByteString::SizeFor(chars);
    }
  
    // Allocate string.
    Object* result;
    { MaybeObject* maybe_result = (size > MaxObjectSizeInPagedSpace())
                     ? lo_space_->AllocateRaw(size)
                     : old_data_space_->AllocateRaw(size);
      if (!maybe_result->ToObject(&result)) return maybe_result;
    }
  
    reinterpret_cast<HeapObject*>(result)->set_map(map);
    // Set length and hash fields of the allocated string.
    String* answer = String::cast(result);
    answer->set_length(chars);
    answer->set_hash_field(hash_field);
  
    ASSERT_EQ(size, answer->Size());
  
    // Fill in the characters.
    for (int i = 0; i < chars; i++) {
      answer->Set(i, buffer->GetNext());
    }
    return answer;
  }
  
  
  MaybeObject* Heap::AllocateRawAsciiString(int length, PretenureFlag pretenure) {
    if (length < 0 || length > SeqAsciiString::kMaxLength) {
      return Failure::OutOfMemoryException();
    }
  
    int size = SeqAsciiString::SizeFor(length);
    ASSERT(size <= SeqAsciiString::kMaxSize);
  
    AllocationSpace space = (pretenure == TENURED) ? OLD_DATA_SPACE : NEW_SPACE;
    AllocationSpace retry_space = OLD_DATA_SPACE;
  
    if (space == NEW_SPACE) {
      if (size > kMaxObjectSizeInNewSpace) {
        // Allocate in large object space, retry space will be ignored.
        space = LO_SPACE;
      } else if (size > MaxObjectSizeInPagedSpace()) {
        // Allocate in new space, retry in large object space.
        retry_space = LO_SPACE;
      }
    } else if (space == OLD_DATA_SPACE && size > MaxObjectSizeInPagedSpace()) {
      space = LO_SPACE;
    }
    Object* result;
    { MaybeObject* maybe_result = AllocateRaw(size, space, retry_space);
      if (!maybe_result->ToObject(&result)) return maybe_result;
    }
  
    // Partially initialize the object.
    HeapObject::cast(result)->set_map(ascii_string_map());
    String::cast(result)->set_length(length);
    String::cast(result)->set_hash_field(String::kEmptyHashField);
    ASSERT_EQ(size, HeapObject::cast(result)->Size());
    return result;
  }
  
  
  MaybeObject* Heap::AllocateRawTwoByteString(int length,
                                              PretenureFlag pretenure) {
    if (length < 0 || length > SeqTwoByteString::kMaxLength) {
      return Failure::OutOfMemoryException();
    }
    int size = SeqTwoByteString::SizeFor(length);
    ASSERT(size <= SeqTwoByteString::kMaxSize);
    AllocationSpace space = (pretenure == TENURED) ? OLD_DATA_SPACE : NEW_SPACE;
    AllocationSpace retry_space = OLD_DATA_SPACE;
  
    if (space == NEW_SPACE) {
      if (size > kMaxObjectSizeInNewSpace) {
        // Allocate in large object space, retry space will be ignored.
        space = LO_SPACE;
      } else if (size > MaxObjectSizeInPagedSpace()) {
        // Allocate in new space, retry in large object space.
        retry_space = LO_SPACE;
      }
    } else if (space == OLD_DATA_SPACE && size > MaxObjectSizeInPagedSpace()) {
      space = LO_SPACE;
    }
    Object* result;
    { MaybeObject* maybe_result = AllocateRaw(size, space, retry_space);
      if (!maybe_result->ToObject(&result)) return maybe_result;
    }
  
    // Partially initialize the object.
    HeapObject::cast(result)->set_map(string_map());
    String::cast(result)->set_length(length);
    String::cast(result)->set_hash_field(String::kEmptyHashField);
    ASSERT_EQ(size, HeapObject::cast(result)->Size());
    return result;
  }
  
  
  MaybeObject* Heap::AllocateEmptyFixedArray() {
    int size = FixedArray::SizeFor(0);
    Object* result;
    { MaybeObject* maybe_result =
          AllocateRaw(size, OLD_DATA_SPACE, OLD_DATA_SPACE);
      if (!maybe_result->ToObject(&result)) return maybe_result;
    }
    // Initialize the object.
    reinterpret_cast<FixedArray*>(result)->set_map(fixed_array_map());
    reinterpret_cast<FixedArray*>(result)->set_length(0);
    return result;
  }
  
  
  MaybeObject* Heap::AllocateRawFixedArray(int length) {
    if (length < 0 || length > FixedArray::kMaxLength) {
      return Failure::OutOfMemoryException();
    }
    ASSERT(length > 0);
    // Use the general function if we're forced to always allocate.
    if (always_allocate()) return AllocateFixedArray(length, TENURED);
    // Allocate the raw data for a fixed array.
    int size = FixedArray::SizeFor(length);
    return size <= kMaxObjectSizeInNewSpace
        ? new_space_.AllocateRaw(size)
        : lo_space_->AllocateRawFixedArray(size);
  }
  
  
  MaybeObject* Heap::CopyFixedArrayWithMap(FixedArray* src, Map* map) {
    int len = src->length();
    Object* obj;
    { MaybeObject* maybe_obj = AllocateRawFixedArray(len);
      if (!maybe_obj->ToObject(&obj)) return maybe_obj;
    }
    if (InNewSpace(obj)) {
      HeapObject* dst = HeapObject::cast(obj);
      dst->set_map(map);
      CopyBlock(dst->address() + kPointerSize,
                src->address() + kPointerSize,
                FixedArray::SizeFor(len) - kPointerSize);
      return obj;
    }
    HeapObject::cast(obj)->set_map(map);
    FixedArray* result = FixedArray::cast(obj);
    result->set_length(len);
  
    // Copy the content
    AssertNoAllocation no_gc;
    WriteBarrierMode mode = result->GetWriteBarrierMode(no_gc);
    for (int i = 0; i < len; i++) result->set(i, src->get(i), mode);
    return result;
  }
  
  
  MaybeObject* Heap::CopyFixedDoubleArrayWithMap(FixedDoubleArray* src,
                                                 Map* map) {
    int len = src->length();
    Object* obj;
    { MaybeObject* maybe_obj = AllocateRawFixedDoubleArray(len, NOT_TENURED);
      if (!maybe_obj->ToObject(&obj)) return maybe_obj;
    }
    HeapObject* dst = HeapObject::cast(obj);
    dst->set_map(map);
    CopyBlock(
        dst->address() + FixedDoubleArray::kLengthOffset,
        src->address() + FixedDoubleArray::kLengthOffset,
        FixedDoubleArray::SizeFor(len) - FixedDoubleArray::kLengthOffset);
    return obj;
  }
  
  
  MaybeObject* Heap::AllocateFixedArray(int length) {
    ASSERT(length >= 0);
    if (length == 0) return empty_fixed_array();
    Object* result;
    { MaybeObject* maybe_result = AllocateRawFixedArray(length);
      if (!maybe_result->ToObject(&result)) return maybe_result;
    }
    // Initialize header.
    FixedArray* array = reinterpret_cast<FixedArray*>(result);
    array->set_map(fixed_array_map());
    array->set_length(length);
    // Initialize body.
    ASSERT(!InNewSpace(undefined_value()));
    MemsetPointer(array->data_start(), undefined_value(), length);
    return result;
  }
  
  
  MaybeObject* Heap::AllocateRawFixedArray(int length, PretenureFlag pretenure) {
    if (length < 0 || length > FixedArray::kMaxLength) {
      return Failure::OutOfMemoryException();
    }
  
    AllocationSpace space =
        (pretenure == TENURED) ? OLD_POINTER_SPACE : NEW_SPACE;
    int size = FixedArray::SizeFor(length);
    if (space == NEW_SPACE && size > kMaxObjectSizeInNewSpace) {
      // Too big for new space.
      space = LO_SPACE;
    } else if (space == OLD_POINTER_SPACE &&
               size > MaxObjectSizeInPagedSpace()) {
      // Too big for old pointer space.
      space = LO_SPACE;
    }
  
    AllocationSpace retry_space =
        (size <= MaxObjectSizeInPagedSpace()) ? OLD_POINTER_SPACE : LO_SPACE;
  
    return AllocateRaw(size, space, retry_space);
  }
  
  
  MUST_USE_RESULT static MaybeObject* AllocateFixedArrayWithFiller(
      Heap* heap,
      int length,
      PretenureFlag pretenure,
      Object* filler) {
    ASSERT(length >= 0);
    ASSERT(heap->empty_fixed_array()->IsFixedArray());
    if (length == 0) return heap->empty_fixed_array();
  
    ASSERT(!heap->InNewSpace(filler));
    Object* result;
    { MaybeObject* maybe_result = heap->AllocateRawFixedArray(length, pretenure);
      if (!maybe_result->ToObject(&result)) return maybe_result;
    }
  
    HeapObject::cast(result)->set_map(heap->fixed_array_map());
    FixedArray* array = FixedArray::cast(result);
    array->set_length(length);
    MemsetPointer(array->data_start(), filler, length);
    return array;
  }
  
  
  MaybeObject* Heap::AllocateFixedArray(int length, PretenureFlag pretenure) {
    return AllocateFixedArrayWithFiller(this,
                                        length,
                                        pretenure,
                                        undefined_value());
  }
  
  
  MaybeObject* Heap::AllocateFixedArrayWithHoles(int length,
                                                 PretenureFlag pretenure) {
    return AllocateFixedArrayWithFiller(this,
                                        length,
                                        pretenure,
                                        the_hole_value());
  }
  
  
  MaybeObject* Heap::AllocateUninitializedFixedArray(int length) {
    if (length == 0) return empty_fixed_array();
  
    Object* obj;
    { MaybeObject* maybe_obj = AllocateRawFixedArray(length);
      if (!maybe_obj->ToObject(&obj)) return maybe_obj;
    }
  
    reinterpret_cast<FixedArray*>(obj)->set_map(fixed_array_map());
    FixedArray::cast(obj)->set_length(length);
    return obj;
  }
  
  
  MaybeObject* Heap::AllocateEmptyFixedDoubleArray() {
    int size = FixedDoubleArray::SizeFor(0);
    Object* result;
    { MaybeObject* maybe_result =
          AllocateRaw(size, OLD_DATA_SPACE, OLD_DATA_SPACE);
      if (!maybe_result->ToObject(&result)) return maybe_result;
    }
    // Initialize the object.
    reinterpret_cast<FixedDoubleArray*>(result)->set_map(
        fixed_double_array_map());
    reinterpret_cast<FixedDoubleArray*>(result)->set_length(0);
    return result;
  }
  
  
  MaybeObject* Heap::AllocateUninitializedFixedDoubleArray(
      int length,
      PretenureFlag pretenure) {
    if (length == 0) return empty_fixed_double_array();
  
    Object* obj;
    { MaybeObject* maybe_obj = AllocateRawFixedDoubleArray(length, pretenure);
      if (!maybe_obj->ToObject(&obj)) return maybe_obj;
    }
  
    reinterpret_cast<FixedDoubleArray*>(obj)->set_map(fixed_double_array_map());
    FixedDoubleArray::cast(obj)->set_length(length);
    return obj;
  }
  
  
  MaybeObject* Heap::AllocateRawFixedDoubleArray(int length,
                                                 PretenureFlag pretenure) {
    if (length < 0 || length > FixedDoubleArray::kMaxLength) {
      return Failure::OutOfMemoryException();
    }
  
    AllocationSpace space =
        (pretenure == TENURED) ? OLD_DATA_SPACE : NEW_SPACE;
    int size = FixedDoubleArray::SizeFor(length);
    if (space == NEW_SPACE && size > kMaxObjectSizeInNewSpace) {
      // Too big for new space.
      space = LO_SPACE;
    } else if (space == OLD_DATA_SPACE &&
               size > MaxObjectSizeInPagedSpace()) {
      // Too big for old data space.
      space = LO_SPACE;
    }
  
    AllocationSpace retry_space =
        (size <= MaxObjectSizeInPagedSpace()) ? OLD_DATA_SPACE : LO_SPACE;
  
    return AllocateRaw(size, space, retry_space);
  }
  
  
  MaybeObject* Heap::AllocateHashTable(int length, PretenureFlag pretenure) {
    Object* result;
    { MaybeObject* maybe_result = AllocateFixedArray(length, pretenure);
      if (!maybe_result->ToObject(&result)) return maybe_result;
    }
    reinterpret_cast<HeapObject*>(result)->set_map(hash_table_map());
    ASSERT(result->IsHashTable());
    return result;
  }
  
  
  MaybeObject* Heap::AllocateGlobalContext() {
    Object* result;
    { MaybeObject* maybe_result =
          AllocateFixedArray(Context::GLOBAL_CONTEXT_SLOTS);
      if (!maybe_result->ToObject(&result)) return maybe_result;
    }
    Context* context = reinterpret_cast<Context*>(result);
    context->set_map(global_context_map());
    ASSERT(context->IsGlobalContext());
    ASSERT(result->IsContext());
    return result;
  }
  
  
  MaybeObject* Heap::AllocateFunctionContext(int length, JSFunction* function) {
    ASSERT(length >= Context::MIN_CONTEXT_SLOTS);
    Object* result;
    { MaybeObject* maybe_result = AllocateFixedArray(length);
      if (!maybe_result->ToObject(&result)) return maybe_result;
    }
    Context* context = reinterpret_cast<Context*>(result);
    context->set_map(function_context_map());
    context->set_closure(function);
    context->set_previous(function->context());
    context->set_extension(NULL);
    context->set_global(function->context()->global());
    return context;
  }
  
  
  MaybeObject* Heap::AllocateCatchContext(JSFunction* function,
                                          Context* previous,
                                          String* name,
                                          Object* thrown_object) {
    STATIC_ASSERT(Context::MIN_CONTEXT_SLOTS == Context::THROWN_OBJECT_INDEX);
    Object* result;
    { MaybeObject* maybe_result =
          AllocateFixedArray(Context::MIN_CONTEXT_SLOTS + 1);
      if (!maybe_result->ToObject(&result)) return maybe_result;
    }
    Context* context = reinterpret_cast<Context*>(result);
    context->set_map(catch_context_map());
    context->set_closure(function);
    context->set_previous(previous);
    context->set_extension(name);
    context->set_global(previous->global());
    context->set(Context::THROWN_OBJECT_INDEX, thrown_object);
    return context;
  }
  
  
  MaybeObject* Heap::AllocateWithContext(JSFunction* function,
                                         Context* previous,
                                         JSObject* extension) {
    Object* result;
    { MaybeObject* maybe_result = AllocateFixedArray(Context::MIN_CONTEXT_SLOTS);
      if (!maybe_result->ToObject(&result)) return maybe_result;
    }
    Context* context = reinterpret_cast<Context*>(result);
    context->set_map(with_context_map());
    context->set_closure(function);
    context->set_previous(previous);
    context->set_extension(extension);
    context->set_global(previous->global());
    return context;
  }
  
  
  MaybeObject* Heap::AllocateBlockContext(JSFunction* function,
                                          Context* previous,
                                          SerializedScopeInfo* scope_info) {
    Object* result;
    { MaybeObject* maybe_result =
          AllocateFixedArrayWithHoles(scope_info->NumberOfContextSlots());
      if (!maybe_result->ToObject(&result)) return maybe_result;
    }
    Context* context = reinterpret_cast<Context*>(result);
    context->set_map(block_context_map());
    context->set_closure(function);
    context->set_previous(previous);
    context->set_extension(scope_info);
    context->set_global(previous->global());
    return context;
  }
  
  
  MaybeObject* Heap::AllocateSerializedScopeInfo(int length) {
    Object* result;
    { MaybeObject* maybe_result = AllocateFixedArray(length, TENURED);
      if (!maybe_result->ToObject(&result)) return maybe_result;
    }
    SerializedScopeInfo* scope_info =
        reinterpret_cast<SerializedScopeInfo*>(result);
    scope_info->set_map(serialized_scope_info_map());
    return scope_info;
  }
  
  
  MaybeObject* Heap::AllocateStruct(InstanceType type) {
    Map* map;
    switch (type) {
  #define MAKE_CASE(NAME, Name, name) \
      case NAME##_TYPE: map = name##_map(); break;
  STRUCT_LIST(MAKE_CASE)
  #undef MAKE_CASE
      default:
        UNREACHABLE();
        return Failure::InternalError();
    }
    int size = map->instance_size();
    AllocationSpace space =
        (size > MaxObjectSizeInPagedSpace()) ? LO_SPACE : OLD_POINTER_SPACE;
    Object* result;
    { MaybeObject* maybe_result = Allocate(map, space);
      if (!maybe_result->ToObject(&result)) return maybe_result;
    }
    Struct::cast(result)->InitializeBody(size);
    return result;
  }
  
  
  bool Heap::IdleNotification() {
    static const int kIdlesBeforeScavenge = 4;
    static const int kIdlesBeforeMarkSweep = 7;
    static const int kIdlesBeforeMarkCompact = 8;
    static const int kMaxIdleCount = kIdlesBeforeMarkCompact + 1;
    static const unsigned int kGCsBetweenCleanup = 4;
  
    if (!last_idle_notification_gc_count_init_) {
      last_idle_notification_gc_count_ = gc_count_;
      last_idle_notification_gc_count_init_ = true;
    }
  
    bool uncommit = true;
    bool finished = false;
  
    // Reset the number of idle notifications received when a number of
    // GCs have taken place. This allows another round of cleanup based
    // on idle notifications if enough work has been carried out to
    // provoke a number of garbage collections.
    if (gc_count_ - last_idle_notification_gc_count_ < kGCsBetweenCleanup) {
      number_idle_notifications_ =
          Min(number_idle_notifications_ + 1, kMaxIdleCount);
    } else {
      number_idle_notifications_ = 0;
      last_idle_notification_gc_count_ = gc_count_;
    }
  
    if (number_idle_notifications_ == kIdlesBeforeScavenge) {
      if (contexts_disposed_ > 0) {
        HistogramTimerScope scope(isolate_->counters()->gc_context());
        CollectAllGarbage(false);
      } else {
        CollectGarbage(NEW_SPACE);
      }
      new_space_.Shrink();
      last_idle_notification_gc_count_ = gc_count_;
    } else if (number_idle_notifications_ == kIdlesBeforeMarkSweep) {
      // Before doing the mark-sweep collections we clear the
      // compilation cache to avoid hanging on to source code and
      // generated code for cached functions.
      isolate_->compilation_cache()->Clear();
  
      CollectAllGarbage(false);
      new_space_.Shrink();
      last_idle_notification_gc_count_ = gc_count_;
  
    } else if (number_idle_notifications_ == kIdlesBeforeMarkCompact) {
      CollectAllGarbage(true);
      new_space_.Shrink();
      last_idle_notification_gc_count_ = gc_count_;
      number_idle_notifications_ = 0;
      finished = true;
    } else if (contexts_disposed_ > 0) {
      if (FLAG_expose_gc) {
        contexts_disposed_ = 0;
      } else {
        HistogramTimerScope scope(isolate_->counters()->gc_context());
        CollectAllGarbage(false);
        last_idle_notification_gc_count_ = gc_count_;
      }
      // If this is the first idle notification, we reset the
      // notification count to avoid letting idle notifications for
      // context disposal garbage collections start a potentially too
      // aggressive idle GC cycle.
      if (number_idle_notifications_ <= 1) {
        number_idle_notifications_ = 0;
        uncommit = false;
      }
    } else if (number_idle_notifications_ > kIdlesBeforeMarkCompact) {
      // If we have received more than kIdlesBeforeMarkCompact idle
      // notifications we do not perform any cleanup because we don't
      // expect to gain much by doing so.
      finished = true;
    }
  
    // Make sure that we have no pending context disposals and
    // conditionally uncommit from space.
    ASSERT(contexts_disposed_ == 0);
    if (uncommit) UncommitFromSpace();
    return finished;
  }
  
  
  #ifdef DEBUG
  
  void Heap::Print() {
    if (!HasBeenSetup()) return;
    isolate()->PrintStack();
    AllSpaces spaces;
    for (Space* space = spaces.next(); space != NULL; space = spaces.next())
      space->Print();
  }
  
  
  void Heap::ReportCodeStatistics(const char* title) {
    PrintF(">>>>>> Code Stats (%s) >>>>>>\n", title);
    PagedSpace::ResetCodeStatistics();
    // We do not look for code in new space, map space, or old space.  If code
    // somehow ends up in those spaces, we would miss it here.
    code_space_->CollectCodeStatistics();
    lo_space_->CollectCodeStatistics();
    PagedSpace::ReportCodeStatistics();
  }
  
  
  // This function expects that NewSpace's allocated objects histogram is
  // populated (via a call to CollectStatistics or else as a side effect of a
  // just-completed scavenge collection).
  void Heap::ReportHeapStatistics(const char* title) {
    USE(title);
    PrintF(">>>>>> =============== %s (%d) =============== >>>>>>\n",
           title, gc_count_);
    PrintF("mark-compact GC : %d\n", mc_count_);
    PrintF("old_gen_promotion_limit_ %" V8_PTR_PREFIX "d\n",
           old_gen_promotion_limit_);
    PrintF("old_gen_allocation_limit_ %" V8_PTR_PREFIX "d\n",
           old_gen_allocation_limit_);
  
    PrintF("\n");
    PrintF("Number of handles : %d\n", HandleScope::NumberOfHandles());
    isolate_->global_handles()->PrintStats();
    PrintF("\n");
  
    PrintF("Heap statistics : ");
    isolate_->memory_allocator()->ReportStatistics();
    PrintF("To space : ");
    new_space_.ReportStatistics();
    PrintF("Old pointer space : ");
    old_pointer_space_->ReportStatistics();
    PrintF("Old data space : ");
    old_data_space_->ReportStatistics();
    PrintF("Code space : ");
    code_space_->ReportStatistics();
    PrintF("Map space : ");
    map_space_->ReportStatistics();
    PrintF("Cell space : ");
    cell_space_->ReportStatistics();
    PrintF("Large object space : ");
    lo_space_->ReportStatistics();
    PrintF(">>>>>> ========================================= >>>>>>\n");
  }
  
  #endif  // DEBUG
  
  bool Heap::Contains(HeapObject* value) {
    return Contains(value->address());
  }
  
  
  bool Heap::Contains(Address addr) {
    if (OS::IsOutsideAllocatedSpace(addr)) return false;
    return HasBeenSetup() &&
      (new_space_.ToSpaceContains(addr) ||
       old_pointer_space_->Contains(addr) ||
       old_data_space_->Contains(addr) ||
       code_space_->Contains(addr) ||
       map_space_->Contains(addr) ||
       cell_space_->Contains(addr) ||
       lo_space_->SlowContains(addr));
  }
  
  
  bool Heap::InSpace(HeapObject* value, AllocationSpace space) {
    return InSpace(value->address(), space);
  }
  
  
  bool Heap::InSpace(Address addr, AllocationSpace space) {
    if (OS::IsOutsideAllocatedSpace(addr)) return false;
    if (!HasBeenSetup()) return false;
  
    switch (space) {
      case NEW_SPACE:
        return new_space_.ToSpaceContains(addr);
      case OLD_POINTER_SPACE:
        return old_pointer_space_->Contains(addr);
      case OLD_DATA_SPACE:
        return old_data_space_->Contains(addr);
      case CODE_SPACE:
        return code_space_->Contains(addr);
      case MAP_SPACE:
        return map_space_->Contains(addr);
      case CELL_SPACE:
        return cell_space_->Contains(addr);
      case LO_SPACE:
        return lo_space_->SlowContains(addr);
    }
  
    return false;
  }
  
  
  #ifdef DEBUG
  static void DummyScavengePointer(HeapObject** p) {
  }
  
  
  static void VerifyPointersUnderWatermark(
      PagedSpace* space,
      DirtyRegionCallback visit_dirty_region) {
    PageIterator it(space, PageIterator::PAGES_IN_USE);
  
    while (it.has_next()) {
      Page* page = it.next();
      Address start = page->ObjectAreaStart();
      Address end = page->AllocationWatermark();
  
      HEAP->IterateDirtyRegions(Page::kAllRegionsDirtyMarks,
                                start,
                                end,
                                visit_dirty_region,
                                &DummyScavengePointer);
    }
  }
  
  
  static void VerifyPointersUnderWatermark(LargeObjectSpace* space) {
    LargeObjectIterator it(space);
    for (HeapObject* object = it.next(); object != NULL; object = it.next()) {
      if (object->IsFixedArray()) {
        Address slot_address = object->address();
        Address end = object->address() + object->Size();
  
        while (slot_address < end) {
          HeapObject** slot = reinterpret_cast<HeapObject**>(slot_address);
          // When we are not in GC the Heap::InNewSpace() predicate
          // checks that pointers which satisfy predicate point into
          // the active semispace.
          HEAP->InNewSpace(*slot);
          slot_address += kPointerSize;
        }
      }
    }
  }
  
  
  void Heap::Verify() {
    ASSERT(HasBeenSetup());
  
    VerifyPointersVisitor visitor;
    IterateRoots(&visitor, VISIT_ONLY_STRONG);
  
    new_space_.Verify();
  
    VerifyPointersAndDirtyRegionsVisitor dirty_regions_visitor;
    old_pointer_space_->Verify(&dirty_regions_visitor);
    map_space_->Verify(&dirty_regions_visitor);
  
    VerifyPointersUnderWatermark(old_pointer_space_,
                                 &IteratePointersInDirtyRegion);
    VerifyPointersUnderWatermark(map_space_,
                                 &IteratePointersInDirtyMapsRegion);
    VerifyPointersUnderWatermark(lo_space_);
  
    VerifyPageWatermarkValidity(old_pointer_space_, ALL_INVALID);
    VerifyPageWatermarkValidity(map_space_, ALL_INVALID);
  
    VerifyPointersVisitor no_dirty_regions_visitor;
    old_data_space_->Verify(&no_dirty_regions_visitor);
    code_space_->Verify(&no_dirty_regions_visitor);
    cell_space_->Verify(&no_dirty_regions_visitor);
  
    lo_space_->Verify();
  }
  #endif  // DEBUG
  
  
  MaybeObject* Heap::LookupSymbol(Vector<const char> string) {
    Object* symbol = NULL;
    Object* new_table;
    { MaybeObject* maybe_new_table =
          symbol_table()->LookupSymbol(string, &symbol);
      if (!maybe_new_table->ToObject(&new_table)) return maybe_new_table;
    }
    // Can't use set_symbol_table because SymbolTable::cast knows that
    // SymbolTable is a singleton and checks for identity.
    roots_[kSymbolTableRootIndex] = new_table;
    ASSERT(symbol != NULL);
    return symbol;
  }
  
  
  MaybeObject* Heap::LookupAsciiSymbol(Vector<const char> string) {
    Object* symbol = NULL;
    Object* new_table;
    { MaybeObject* maybe_new_table =
          symbol_table()->LookupAsciiSymbol(string, &symbol);
      if (!maybe_new_table->ToObject(&new_table)) return maybe_new_table;
    }
    // Can't use set_symbol_table because SymbolTable::cast knows that
    // SymbolTable is a singleton and checks for identity.
    roots_[kSymbolTableRootIndex] = new_table;
    ASSERT(symbol != NULL);
    return symbol;
  }
  
  
  MaybeObject* Heap::LookupAsciiSymbol(Handle<SeqAsciiString> string,
                                       int from,
                                       int length) {
    Object* symbol = NULL;
    Object* new_table;
    { MaybeObject* maybe_new_table =
          symbol_table()->LookupSubStringAsciiSymbol(string,
                                                     from,
                                                     length,
                                                     &symbol);
      if (!maybe_new_table->ToObject(&new_table)) return maybe_new_table;
    }
    // Can't use set_symbol_table because SymbolTable::cast knows that
    // SymbolTable is a singleton and checks for identity.
    roots_[kSymbolTableRootIndex] = new_table;
    ASSERT(symbol != NULL);
    return symbol;
  }
  
  
  MaybeObject* Heap::LookupTwoByteSymbol(Vector<const uc16> string) {
    Object* symbol = NULL;
    Object* new_table;
    { MaybeObject* maybe_new_table =
          symbol_table()->LookupTwoByteSymbol(string, &symbol);
      if (!maybe_new_table->ToObject(&new_table)) return maybe_new_table;
    }
    // Can't use set_symbol_table because SymbolTable::cast knows that
    // SymbolTable is a singleton and checks for identity.
    roots_[kSymbolTableRootIndex] = new_table;
    ASSERT(symbol != NULL);
    return symbol;
  }
  
  
  MaybeObject* Heap::LookupSymbol(String* string) {
    if (string->IsSymbol()) return string;
    Object* symbol = NULL;
    Object* new_table;
    { MaybeObject* maybe_new_table =
          symbol_table()->LookupString(string, &symbol);
      if (!maybe_new_table->ToObject(&new_table)) return maybe_new_table;
    }
    // Can't use set_symbol_table because SymbolTable::cast knows that
    // SymbolTable is a singleton and checks for identity.
    roots_[kSymbolTableRootIndex] = new_table;
    ASSERT(symbol != NULL);
    return symbol;
  }
  
  
  bool Heap::LookupSymbolIfExists(String* string, String** symbol) {
    if (string->IsSymbol()) {
      *symbol = string;
      return true;
    }
    return symbol_table()->LookupSymbolIfExists(string, symbol);
  }
  
  
  #ifdef DEBUG
  void Heap::ZapFromSpace() {
    ASSERT(reinterpret_cast<Object*>(kFromSpaceZapValue)->IsFailure());
    for (Address a = new_space_.FromSpaceLow();
         a < new_space_.FromSpaceHigh();
         a += kPointerSize) {
      Memory::Address_at(a) = kFromSpaceZapValue;
    }
  }
  #endif  // DEBUG
  
  
  bool Heap::IteratePointersInDirtyRegion(Heap* heap,
                                          Address start,
                                          Address end,
                                          ObjectSlotCallback copy_object_func) {
    Address slot_address = start;
    bool pointers_to_new_space_found = false;
  
    while (slot_address < end) {
      Object** slot = reinterpret_cast<Object**>(slot_address);
      if (heap->InNewSpace(*slot)) {
        ASSERT((*slot)->IsHeapObject());
        copy_object_func(reinterpret_cast<HeapObject**>(slot));
        if (heap->InNewSpace(*slot)) {
          ASSERT((*slot)->IsHeapObject());
          pointers_to_new_space_found = true;
        }
      }
      slot_address += kPointerSize;
    }
    return pointers_to_new_space_found;
  }
  
  
  // Compute start address of the first map following given addr.
  static inline Address MapStartAlign(Address addr) {
    Address page = Page::FromAddress(addr)->ObjectAreaStart();
    return page + (((addr - page) + (Map::kSize - 1)) / Map::kSize * Map::kSize);
  }
  
  
  // Compute end address of the first map preceding given addr.
  static inline Address MapEndAlign(Address addr) {
    Address page = Page::FromAllocationTop(addr)->ObjectAreaStart();
    return page + ((addr - page) / Map::kSize * Map::kSize);
  }
  
  
  static bool IteratePointersInDirtyMaps(Address start,
                                         Address end,
                                         ObjectSlotCallback copy_object_func) {
    ASSERT(MapStartAlign(start) == start);
    ASSERT(MapEndAlign(end) == end);
  
    Address map_address = start;
    bool pointers_to_new_space_found = false;
  
    Heap* heap = HEAP;
    while (map_address < end) {
      ASSERT(!heap->InNewSpace(Memory::Object_at(map_address)));
      ASSERT(Memory::Object_at(map_address)->IsMap());
  
      Address pointer_fields_start = map_address + Map::kPointerFieldsBeginOffset;
      Address pointer_fields_end = map_address + Map::kPointerFieldsEndOffset;
  
      if (Heap::IteratePointersInDirtyRegion(heap,
                                             pointer_fields_start,
                                             pointer_fields_end,
                                             copy_object_func)) {
        pointers_to_new_space_found = true;
      }
  
      map_address += Map::kSize;
    }
  
    return pointers_to_new_space_found;
  }
  
  
  bool Heap::IteratePointersInDirtyMapsRegion(
      Heap* heap,
      Address start,
      Address end,
      ObjectSlotCallback copy_object_func) {
    Address map_aligned_start = MapStartAlign(start);
    Address map_aligned_end   = MapEndAlign(end);
  
    bool contains_pointers_to_new_space = false;
  
    if (map_aligned_start != start) {
      Address prev_map = map_aligned_start - Map::kSize;
      ASSERT(Memory::Object_at(prev_map)->IsMap());
  
      Address pointer_fields_start =
          Max(start, prev_map + Map::kPointerFieldsBeginOffset);
  
      Address pointer_fields_end =
          Min(prev_map + Map::kPointerFieldsEndOffset, end);
  
      contains_pointers_to_new_space =
        IteratePointersInDirtyRegion(heap,
                                     pointer_fields_start,
                                     pointer_fields_end,
                                     copy_object_func)
          || contains_pointers_to_new_space;
    }
  
    contains_pointers_to_new_space =
      IteratePointersInDirtyMaps(map_aligned_start,
                                 map_aligned_end,
                                 copy_object_func)
        || contains_pointers_to_new_space;
  
    if (map_aligned_end != end) {
      ASSERT(Memory::Object_at(map_aligned_end)->IsMap());
  
      Address pointer_fields_start =
          map_aligned_end + Map::kPointerFieldsBeginOffset;
  
      Address pointer_fields_end =
          Min(end, map_aligned_end + Map::kPointerFieldsEndOffset);
  
      contains_pointers_to_new_space =
        IteratePointersInDirtyRegion(heap,
                                     pointer_fields_start,
                                     pointer_fields_end,
                                     copy_object_func)
          || contains_pointers_to_new_space;
    }
  
    return contains_pointers_to_new_space;
  }
  
  
  void Heap::IterateAndMarkPointersToFromSpace(Address start,
                                               Address end,
                                               ObjectSlotCallback callback) {
    Address slot_address = start;
    Page* page = Page::FromAddress(start);
  
    uint32_t marks = page->GetRegionMarks();
  
    while (slot_address < end) {
      Object** slot = reinterpret_cast<Object**>(slot_address);
      if (InFromSpace(*slot)) {
        ASSERT((*slot)->IsHeapObject());
        callback(reinterpret_cast<HeapObject**>(slot));
        if (InNewSpace(*slot)) {
          ASSERT((*slot)->IsHeapObject());
          marks |= page->GetRegionMaskForAddress(slot_address);
        }
      }
      slot_address += kPointerSize;
    }
  
    page->SetRegionMarks(marks);
  }
  
  
  uint32_t Heap::IterateDirtyRegions(
      uint32_t marks,
      Address area_start,
      Address area_end,
      DirtyRegionCallback visit_dirty_region,
      ObjectSlotCallback copy_object_func) {
    uint32_t newmarks = 0;
    uint32_t mask = 1;
  
    if (area_start >= area_end) {
      return newmarks;
    }
  
    Address region_start = area_start;
  
    // area_start does not necessarily coincide with start of the first region.
    // Thus to calculate the beginning of the next region we have to align
    // area_start by Page::kRegionSize.
    Address second_region =
        reinterpret_cast<Address>(
            reinterpret_cast<intptr_t>(area_start + Page::kRegionSize) &
            ~Page::kRegionAlignmentMask);
  
    // Next region might be beyond area_end.
    Address region_end = Min(second_region, area_end);
  
    if (marks & mask) {
      if (visit_dirty_region(this, region_start, region_end, copy_object_func)) {
        newmarks |= mask;
      }
    }
    mask <<= 1;
  
    // Iterate subsequent regions which fully lay inside [area_start, area_end[.
    region_start = region_end;
    region_end = region_start + Page::kRegionSize;
  
    while (region_end <= area_end) {
      if (marks & mask) {
        if (visit_dirty_region(this,
                               region_start,
                               region_end,
                               copy_object_func)) {
          newmarks |= mask;
        }
      }
  
      region_start = region_end;
      region_end = region_start + Page::kRegionSize;
  
      mask <<= 1;
    }
  
    if (region_start != area_end) {
      // A small piece of area left uniterated because area_end does not coincide
      // with region end. Check whether region covering last part of area is
      // dirty.
      if (marks & mask) {
        if (visit_dirty_region(this, region_start, area_end, copy_object_func)) {
          newmarks |= mask;
        }
      }
    }
  
    return newmarks;
  }
  
  
  
  void Heap::IterateDirtyRegions(
      PagedSpace* space,
      DirtyRegionCallback visit_dirty_region,
      ObjectSlotCallback copy_object_func,
      ExpectedPageWatermarkState expected_page_watermark_state) {
  
    PageIterator it(space, PageIterator::PAGES_IN_USE);
  
    while (it.has_next()) {
      Page* page = it.next();
      uint32_t marks = page->GetRegionMarks();
  
      if (marks != Page::kAllRegionsCleanMarks) {
        Address start = page->ObjectAreaStart();
  
        // Do not try to visit pointers beyond page allocation watermark.
        // Page can contain garbage pointers there.
        Address end;
  
        if ((expected_page_watermark_state == WATERMARK_SHOULD_BE_VALID) ||
            page->IsWatermarkValid()) {
          end = page->AllocationWatermark();
        } else {
          end = page->CachedAllocationWatermark();
        }
  
        ASSERT(space == old_pointer_space_ ||
               (space == map_space_ &&
                ((page->ObjectAreaStart() - end) % Map::kSize == 0)));
  
        page->SetRegionMarks(IterateDirtyRegions(marks,
                                                 start,
                                                 end,
                                                 visit_dirty_region,
                                                 copy_object_func));
      }
  
      // Mark page watermark as invalid to maintain watermark validity invariant.
      // See Page::FlipMeaningOfInvalidatedWatermarkFlag() for details.
      page->InvalidateWatermark(true);
    }
  }
  
  
  void Heap::IterateRoots(ObjectVisitor* v, VisitMode mode) {
    IterateStrongRoots(v, mode);
    IterateWeakRoots(v, mode);
  }
  
  
  void Heap::IterateWeakRoots(ObjectVisitor* v, VisitMode mode) {
    v->VisitPointer(reinterpret_cast<Object**>(&roots_[kSymbolTableRootIndex]));
    v->Synchronize("symbol_table");
    if (mode != VISIT_ALL_IN_SCAVENGE &&
        mode != VISIT_ALL_IN_SWEEP_NEWSPACE) {
      // Scavenge collections have special processing for this.
      external_string_table_.Iterate(v);
    }
    v->Synchronize("external_string_table");
  }
  
  
  void Heap::IterateStrongRoots(ObjectVisitor* v, VisitMode mode) {
    v->VisitPointers(&roots_[0], &roots_[kStrongRootListLength]);
    v->Synchronize("strong_root_list");
  
    v->VisitPointer(BitCast<Object**>(&hidden_symbol_));
    v->Synchronize("symbol");
  
    isolate_->bootstrapper()->Iterate(v);
    v->Synchronize("bootstrapper");
    isolate_->Iterate(v);
    v->Synchronize("top");
    Relocatable::Iterate(v);
    v->Synchronize("relocatable");
  
  #ifdef ENABLE_DEBUGGER_SUPPORT
    isolate_->debug()->Iterate(v);
    if (isolate_->deoptimizer_data() != NULL) {
      isolate_->deoptimizer_data()->Iterate(v);
    }
  #endif
    v->Synchronize("debug");
    isolate_->compilation_cache()->Iterate(v);
    v->Synchronize("compilationcache");
  
    // Iterate over local handles in handle scopes.
    isolate_->handle_scope_implementer()->Iterate(v);
    v->Synchronize("handlescope");
  
    // Iterate over the builtin code objects and code stubs in the
    // heap. Note that it is not necessary to iterate over code objects
    // on scavenge collections.
    if (mode != VISIT_ALL_IN_SCAVENGE &&
        mode != VISIT_ALL_IN_SWEEP_NEWSPACE) {
      isolate_->builtins()->IterateBuiltins(v);
    }
    v->Synchronize("builtins");
  
    // Iterate over global handles.
    switch (mode) {
      case VISIT_ONLY_STRONG:
        isolate_->global_handles()->IterateStrongRoots(v);
        break;
      case VISIT_ALL_IN_SCAVENGE:
        isolate_->global_handles()->IterateNewSpaceStrongAndDependentRoots(v);
        break;
      case VISIT_ALL_IN_SWEEP_NEWSPACE:
      case VISIT_ALL:
        isolate_->global_handles()->IterateAllRoots(v);
        break;
    }
    v->Synchronize("globalhandles");
  
    // Iterate over pointers being held by inactive threads.
    isolate_->thread_manager()->Iterate(v);
    v->Synchronize("threadmanager");
  
    // Iterate over the pointers the Serialization/Deserialization code is
    // holding.
    // During garbage collection this keeps the partial snapshot cache alive.
    // During deserialization of the startup snapshot this creates the partial
    // snapshot cache and deserializes the objects it refers to.  During
    // serialization this does nothing, since the partial snapshot cache is
    // empty.  However the next thing we do is create the partial snapshot,
    // filling up the partial snapshot cache with objects it needs as we go.
    SerializerDeserializer::Iterate(v);
    // We don't do a v->Synchronize call here, because in debug mode that will
    // output a flag to the snapshot.  However at this point the serializer and
    // deserializer are deliberately a little unsynchronized (see above) so the
    // checking of the sync flag in the snapshot would fail.
  }
  
  
  // TODO(1236194): Since the heap size is configurable on the command line
  // and through the API, we should gracefully handle the case that the heap
  // size is not big enough to fit all the initial objects.
  bool Heap::ConfigureHeap(int max_semispace_size,
                           int max_old_gen_size,
                           int max_executable_size) {
    if (HasBeenSetup()) return false;
  
    if (max_semispace_size > 0) max_semispace_size_ = max_semispace_size;
  
    if (Snapshot::IsEnabled()) {
      // If we are using a snapshot we always reserve the default amount
      // of memory for each semispace because code in the snapshot has
      // write-barrier code that relies on the size and alignment of new
      // space.  We therefore cannot use a larger max semispace size
      // than the default reserved semispace size.
      if (max_semispace_size_ > reserved_semispace_size_) {
        max_semispace_size_ = reserved_semispace_size_;
      }
    } else {
      // If we are not using snapshots we reserve space for the actual
      // max semispace size.
      reserved_semispace_size_ = max_semispace_size_;
    }
  
    if (max_old_gen_size > 0) max_old_generation_size_ = max_old_gen_size;
    if (max_executable_size > 0) {
      max_executable_size_ = RoundUp(max_executable_size, Page::kPageSize);
    }
  
    // The max executable size must be less than or equal to the max old
    // generation size.
    if (max_executable_size_ > max_old_generation_size_) {
      max_executable_size_ = max_old_generation_size_;
    }
  
    // The new space size must be a power of two to support single-bit testing
    // for containment.
    max_semispace_size_ = RoundUpToPowerOf2(max_semispace_size_);
    reserved_semispace_size_ = RoundUpToPowerOf2(reserved_semispace_size_);
    initial_semispace_size_ = Min(initial_semispace_size_, max_semispace_size_);
    external_allocation_limit_ = 10 * max_semispace_size_;
  
    // The old generation is paged.
    max_old_generation_size_ = RoundUp(max_old_generation_size_, Page::kPageSize);
  
    configured_ = true;
    return true;
  }
  
  
  bool Heap::ConfigureHeapDefault() {
    return ConfigureHeap(FLAG_max_new_space_size / 2 * KB,
                         FLAG_max_old_space_size * MB,
                         FLAG_max_executable_size * MB);
  }
  
  
  void Heap::RecordStats(HeapStats* stats, bool take_snapshot) {
    *stats->start_marker = HeapStats::kStartMarker;
    *stats->end_marker = HeapStats::kEndMarker;
    *stats->new_space_size = new_space_.SizeAsInt();
    *stats->new_space_capacity = static_cast<int>(new_space_.Capacity());
    *stats->old_pointer_space_size = old_pointer_space_->Size();
    *stats->old_pointer_space_capacity = old_pointer_space_->Capacity();
    *stats->old_data_space_size = old_data_space_->Size();
    *stats->old_data_space_capacity = old_data_space_->Capacity();
    *stats->code_space_size = code_space_->Size();
    *stats->code_space_capacity = code_space_->Capacity();
    *stats->map_space_size = map_space_->Size();
    *stats->map_space_capacity = map_space_->Capacity();
    *stats->cell_space_size = cell_space_->Size();
    *stats->cell_space_capacity = cell_space_->Capacity();
    *stats->lo_space_size = lo_space_->Size();
    isolate_->global_handles()->RecordStats(stats);
    *stats->memory_allocator_size = isolate()->memory_allocator()->Size();
    *stats->memory_allocator_capacity =
        isolate()->memory_allocator()->Size() +
        isolate()->memory_allocator()->Available();
    *stats->os_error = OS::GetLastError();
        isolate()->memory_allocator()->Available();
    if (take_snapshot) {
      HeapIterator iterator(HeapIterator::kFilterFreeListNodes);
      for (HeapObject* obj = iterator.next();
           obj != NULL;
           obj = iterator.next()) {
        InstanceType type = obj->map()->instance_type();
        ASSERT(0 <= type && type <= LAST_TYPE);
        stats->objects_per_type[type]++;
        stats->size_per_type[type] += obj->Size();
      }
    }
  }
  
  
  intptr_t Heap::PromotedSpaceSize() {
    return old_pointer_space_->Size()
        + old_data_space_->Size()
        + code_space_->Size()
        + map_space_->Size()
        + cell_space_->Size()
        + lo_space_->Size();
  }
  
  
  int Heap::PromotedExternalMemorySize() {
    if (amount_of_external_allocated_memory_
        <= amount_of_external_allocated_memory_at_last_global_gc_) return 0;
    return amount_of_external_allocated_memory_
        - amount_of_external_allocated_memory_at_last_global_gc_;
  }
  
  #ifdef DEBUG
  
  // Tags 0, 1, and 3 are used. Use 2 for marking visited HeapObject.
  static const int kMarkTag = 2;
  
  
  class HeapDebugUtils {
   public:
    explicit HeapDebugUtils(Heap* heap)
      : search_for_any_global_(false),
        search_target_(NULL),
        found_target_(false),
        object_stack_(20),
        heap_(heap) {
    }
  
    class MarkObjectVisitor : public ObjectVisitor {
     public:
      explicit MarkObjectVisitor(HeapDebugUtils* utils) : utils_(utils) { }
  
      void VisitPointers(Object** start, Object** end) {
        // Copy all HeapObject pointers in [start, end)
        for (Object** p = start; p < end; p++) {
          if ((*p)->IsHeapObject())
            utils_->MarkObjectRecursively(p);
        }
      }
  
      HeapDebugUtils* utils_;
    };
  
    void MarkObjectRecursively(Object** p) {
      if (!(*p)->IsHeapObject()) return;
  
      HeapObject* obj = HeapObject::cast(*p);
  
      Object* map = obj->map();
  
      if (!map->IsHeapObject()) return;  // visited before
  
      if (found_target_) return;  // stop if target found
      object_stack_.Add(obj);
      if ((search_for_any_global_ && obj->IsJSGlobalObject()) ||
          (!search_for_any_global_ && (obj == search_target_))) {
        found_target_ = true;
        return;
      }
  
      // not visited yet
      Map* map_p = reinterpret_cast<Map*>(HeapObject::cast(map));
  
      Address map_addr = map_p->address();
  
      obj->set_map(reinterpret_cast<Map*>(map_addr + kMarkTag));
  
      MarkObjectRecursively(&map);
  
      MarkObjectVisitor mark_visitor(this);
  
      obj->IterateBody(map_p->instance_type(), obj->SizeFromMap(map_p),
                       &mark_visitor);
  
      if (!found_target_)  // don't pop if found the target
        object_stack_.RemoveLast();
    }
  
  
    class UnmarkObjectVisitor : public ObjectVisitor {
     public:
      explicit UnmarkObjectVisitor(HeapDebugUtils* utils) : utils_(utils) { }
  
      void VisitPointers(Object** start, Object** end) {
        // Copy all HeapObject pointers in [start, end)
        for (Object** p = start; p < end; p++) {
          if ((*p)->IsHeapObject())
            utils_->UnmarkObjectRecursively(p);
        }
      }
  
      HeapDebugUtils* utils_;
    };
  
  
    void UnmarkObjectRecursively(Object** p) {
      if (!(*p)->IsHeapObject()) return;
  
      HeapObject* obj = HeapObject::cast(*p);
  
      Object* map = obj->map();
  
      if (map->IsHeapObject()) return;  // unmarked already
  
      Address map_addr = reinterpret_cast<Address>(map);
  
      map_addr -= kMarkTag;
  
      ASSERT_TAG_ALIGNED(map_addr);
  
      HeapObject* map_p = HeapObject::FromAddress(map_addr);
  
      obj->set_map(reinterpret_cast<Map*>(map_p));
  
      UnmarkObjectRecursively(reinterpret_cast<Object**>(&map_p));
  
      UnmarkObjectVisitor unmark_visitor(this);
  
      obj->IterateBody(Map::cast(map_p)->instance_type(),
                       obj->SizeFromMap(Map::cast(map_p)),
                       &unmark_visitor);
    }
  
  
    void MarkRootObjectRecursively(Object** root) {
      if (search_for_any_global_) {
        ASSERT(search_target_ == NULL);
      } else {
        ASSERT(search_target_->IsHeapObject());
      }
      found_target_ = false;
      object_stack_.Clear();
  
      MarkObjectRecursively(root);
      UnmarkObjectRecursively(root);
  
      if (found_target_) {
        PrintF("=====================================\n");
        PrintF("====        Path to object       ====\n");
        PrintF("=====================================\n\n");
  
        ASSERT(!object_stack_.is_empty());
        for (int i = 0; i < object_stack_.length(); i++) {
          if (i > 0) PrintF("\n     |\n     |\n     V\n\n");
          Object* obj = object_stack_[i];
          obj->Print();
        }
        PrintF("=====================================\n");
      }
    }
  
    // Helper class for visiting HeapObjects recursively.
    class MarkRootVisitor: public ObjectVisitor {
     public:
      explicit MarkRootVisitor(HeapDebugUtils* utils) : utils_(utils) { }
  
      void VisitPointers(Object** start, Object** end) {
        // Visit all HeapObject pointers in [start, end)
        for (Object** p = start; p < end; p++) {
          if ((*p)->IsHeapObject())
            utils_->MarkRootObjectRecursively(p);
        }
      }
  
      HeapDebugUtils* utils_;
    };
  
    bool search_for_any_global_;
    Object* search_target_;
    bool found_target_;
    List<Object*> object_stack_;
    Heap* heap_;
  
    friend class Heap;
  };
  
  #endif
  
  bool Heap::Setup(bool create_heap_objects) {
  #ifdef DEBUG
    debug_utils_ = new HeapDebugUtils(this);
  #endif
  
    // Initialize heap spaces and initial maps and objects. Whenever something
    // goes wrong, just return false. The caller should check the results and
    // call Heap::TearDown() to release allocated memory.
    //
    // If the heap is not yet configured (eg, through the API), configure it.
    // Configuration is based on the flags new-space-size (really the semispace
    // size) and old-space-size if set or the initial values of semispace_size_
    // and old_generation_size_ otherwise.
    if (!configured_) {
      if (!ConfigureHeapDefault()) return false;
    }
  
    gc_initializer_mutex->Lock();
    static bool initialized_gc = false;
    if (!initialized_gc) {
      initialized_gc = true;
      InitializeScavengingVisitorsTables();
      NewSpaceScavenger::Initialize();
      MarkCompactCollector::Initialize();
    }
    gc_initializer_mutex->Unlock();
  
    MarkMapPointersAsEncoded(false);
  
    // Setup memory allocator and reserve a chunk of memory for new
    // space.  The chunk is double the size of the requested reserved
    // new space size to ensure that we can find a pair of semispaces that
    // are contiguous and aligned to their size.
    if (!isolate_->memory_allocator()->Setup(MaxReserved(), MaxExecutableSize()))
        return false;
    void* chunk =
        isolate_->memory_allocator()->ReserveInitialChunk(
            4 * reserved_semispace_size_);
    if (chunk == NULL) return false;
  
    // Align the pair of semispaces to their size, which must be a power
    // of 2.
    Address new_space_start =
        RoundUp(reinterpret_cast<byte*>(chunk), 2 * reserved_semispace_size_);
    if (!new_space_.Setup(new_space_start, 2 * reserved_semispace_size_)) {
      return false;
    }
  
    // Initialize old pointer space.
    old_pointer_space_ =
        new OldSpace(this,
                     max_old_generation_size_,
                     OLD_POINTER_SPACE,
                     NOT_EXECUTABLE);
    if (old_pointer_space_ == NULL) return false;
    if (!old_pointer_space_->Setup(NULL, 0)) return false;
  
    // Initialize old data space.
    old_data_space_ =
        new OldSpace(this,
                     max_old_generation_size_,
                     OLD_DATA_SPACE,
                     NOT_EXECUTABLE);
    if (old_data_space_ == NULL) return false;
    if (!old_data_space_->Setup(NULL, 0)) return false;
  
    // Initialize the code space, set its maximum capacity to the old
    // generation size. It needs executable memory.
    // On 64-bit platform(s), we put all code objects in a 2 GB range of
    // virtual address space, so that they can call each other with near calls.
    if (code_range_size_ > 0) {
      if (!isolate_->code_range()->Setup(code_range_size_)) {
        return false;
      }
    }
  
    code_space_ =
        new OldSpace(this, max_old_generation_size_, CODE_SPACE, EXECUTABLE);
    if (code_space_ == NULL) return false;
    if (!code_space_->Setup(NULL, 0)) return false;
  
    // Initialize map space.
    map_space_ = new MapSpace(this, FLAG_use_big_map_space
        ? max_old_generation_size_
        : MapSpace::kMaxMapPageIndex * Page::kPageSize,
        FLAG_max_map_space_pages,
        MAP_SPACE);
    if (map_space_ == NULL) return false;
    if (!map_space_->Setup(NULL, 0)) return false;
  
    // Initialize global property cell space.
    cell_space_ = new CellSpace(this, max_old_generation_size_, CELL_SPACE);
    if (cell_space_ == NULL) return false;
    if (!cell_space_->Setup(NULL, 0)) return false;
  
    // The large object code space may contain code or data.  We set the memory
    // to be non-executable here for safety, but this means we need to enable it
    // explicitly when allocating large code objects.
    lo_space_ = new LargeObjectSpace(this, LO_SPACE);
    if (lo_space_ == NULL) return false;
    if (!lo_space_->Setup()) return false;
  
    // Setup the seed that is used to randomize the string hash function.
    ASSERT(hash_seed() == 0);
    if (FLAG_randomize_hashes) {
      if (FLAG_hash_seed == 0) {
        set_hash_seed(
            Smi::FromInt(V8::RandomPrivate(isolate()) & 0x3fffffff));
      } else {
        set_hash_seed(Smi::FromInt(FLAG_hash_seed));
      }
    }
  
    if (create_heap_objects) {
      // Create initial maps.
      if (!CreateInitialMaps()) return false;
      if (!CreateApiObjects()) return false;
  
      // Create initial objects
      if (!CreateInitialObjects()) return false;
  
      global_contexts_list_ = undefined_value();
    }
  
    LOG(isolate_, IntPtrTEvent("heap-capacity", Capacity()));
    LOG(isolate_, IntPtrTEvent("heap-available", Available()));
  
    return true;
  }
  
  
  void Heap::SetStackLimits() {
    ASSERT(isolate_ != NULL);
    ASSERT(isolate_ == isolate());
    // On 64 bit machines, pointers are generally out of range of Smis.  We write
    // something that looks like an out of range Smi to the GC.
  
    // Set up the special root array entries containing the stack limits.
    // These are actually addresses, but the tag makes the GC ignore it.
    roots_[kStackLimitRootIndex] =
        reinterpret_cast<Object*>(
            (isolate_->stack_guard()->jslimit() & ~kSmiTagMask) | kSmiTag);
    roots_[kRealStackLimitRootIndex] =
        reinterpret_cast<Object*>(
            (isolate_->stack_guard()->real_jslimit() & ~kSmiTagMask) | kSmiTag);
  }
  
  
  void Heap::TearDown() {
    if (FLAG_print_cumulative_gc_stat) {
      PrintF("\n\n");
      PrintF("gc_count=%d ", gc_count_);
      PrintF("mark_sweep_count=%d ", ms_count_);
      PrintF("mark_compact_count=%d ", mc_count_);
      PrintF("max_gc_pause=%d ", get_max_gc_pause());
      PrintF("min_in_mutator=%d ", get_min_in_mutator());
      PrintF("max_alive_after_gc=%" V8_PTR_PREFIX "d ",
             get_max_alive_after_gc());
      PrintF("\n\n");
    }
  
    isolate_->global_handles()->TearDown();
  
    external_string_table_.TearDown();
  
    new_space_.TearDown();
  
    if (old_pointer_space_ != NULL) {
      old_pointer_space_->TearDown();
      delete old_pointer_space_;
      old_pointer_space_ = NULL;
    }
  
    if (old_data_space_ != NULL) {
      old_data_space_->TearDown();
      delete old_data_space_;
      old_data_space_ = NULL;
    }
  
    if (code_space_ != NULL) {
      code_space_->TearDown();
      delete code_space_;
      code_space_ = NULL;
    }
  
    if (map_space_ != NULL) {
      map_space_->TearDown();
      delete map_space_;
      map_space_ = NULL;
    }
  
    if (cell_space_ != NULL) {
      cell_space_->TearDown();
      delete cell_space_;
      cell_space_ = NULL;
    }
  
    if (lo_space_ != NULL) {
      lo_space_->TearDown();
      delete lo_space_;
      lo_space_ = NULL;
    }
  
    isolate_->memory_allocator()->TearDown();
  
  #ifdef DEBUG
    delete debug_utils_;
    debug_utils_ = NULL;
  #endif
  }
  
  
  void Heap::Shrink() {
    // Try to shrink all paged spaces.
    PagedSpaces spaces;
    for (PagedSpace* space = spaces.next(); space != NULL; space = spaces.next())
      space->Shrink();
  }
  
  
  void Heap::AddGCPrologueCallback(GCPrologueCallback callback, GCType gc_type) {
    ASSERT(callback != NULL);
    GCPrologueCallbackPair pair(callback, gc_type);
    ASSERT(!gc_prologue_callbacks_.Contains(pair));
    return gc_prologue_callbacks_.Add(pair);
  }
  
  
  void Heap::RemoveGCPrologueCallback(GCPrologueCallback callback) {
    ASSERT(callback != NULL);
    for (int i = 0; i < gc_prologue_callbacks_.length(); ++i) {
      if (gc_prologue_callbacks_[i].callback == callback) {
        gc_prologue_callbacks_.Remove(i);
        return;
      }
    }
    UNREACHABLE();
  }
  
  
  void Heap::AddGCEpilogueCallback(GCEpilogueCallback callback, GCType gc_type) {
    ASSERT(callback != NULL);
    GCEpilogueCallbackPair pair(callback, gc_type);
    ASSERT(!gc_epilogue_callbacks_.Contains(pair));
    return gc_epilogue_callbacks_.Add(pair);
  }
  
  
  void Heap::RemoveGCEpilogueCallback(GCEpilogueCallback callback) {
    ASSERT(callback != NULL);
    for (int i = 0; i < gc_epilogue_callbacks_.length(); ++i) {
      if (gc_epilogue_callbacks_[i].callback == callback) {
        gc_epilogue_callbacks_.Remove(i);
        return;
      }
    }
    UNREACHABLE();
  }
  
  
  #ifdef DEBUG
  
  class PrintHandleVisitor: public ObjectVisitor {
   public:
    void VisitPointers(Object** start, Object** end) {
      for (Object** p = start; p < end; p++)
        PrintF("  handle %p to %p\n",
               reinterpret_cast<void*>(p),
               reinterpret_cast<void*>(*p));
    }
  };
  
  void Heap::PrintHandles() {
    PrintF("Handles:\n");
    PrintHandleVisitor v;
    isolate_->handle_scope_implementer()->Iterate(&v);
  }
  
  #endif
  
  
  Space* AllSpaces::next() {
    switch (counter_++) {
      case NEW_SPACE:
        return HEAP->new_space();
      case OLD_POINTER_SPACE:
        return HEAP->old_pointer_space();
      case OLD_DATA_SPACE:
        return HEAP->old_data_space();
      case CODE_SPACE:
        return HEAP->code_space();
      case MAP_SPACE:
        return HEAP->map_space();
      case CELL_SPACE:
        return HEAP->cell_space();
      case LO_SPACE:
        return HEAP->lo_space();
      default:
        return NULL;
    }
  }
  
  
  PagedSpace* PagedSpaces::next() {
    switch (counter_++) {
      case OLD_POINTER_SPACE:
        return HEAP->old_pointer_space();
      case OLD_DATA_SPACE:
        return HEAP->old_data_space();
      case CODE_SPACE:
        return HEAP->code_space();
      case MAP_SPACE:
        return HEAP->map_space();
      case CELL_SPACE:
        return HEAP->cell_space();
      default:
        return NULL;
    }
  }
  
  
  
  OldSpace* OldSpaces::next() {
    switch (counter_++) {
      case OLD_POINTER_SPACE:
        return HEAP->old_pointer_space();
      case OLD_DATA_SPACE:
        return HEAP->old_data_space();
      case CODE_SPACE:
        return HEAP->code_space();
      default:
        return NULL;
    }
  }
  
  
  SpaceIterator::SpaceIterator()
      : current_space_(FIRST_SPACE),
        iterator_(NULL),
        size_func_(NULL) {
  }
  
  
  SpaceIterator::SpaceIterator(HeapObjectCallback size_func)
      : current_space_(FIRST_SPACE),
        iterator_(NULL),
        size_func_(size_func) {
  }
  
  
  SpaceIterator::~SpaceIterator() {
    // Delete active iterator if any.
    delete iterator_;
  }
  
  
  bool SpaceIterator::has_next() {
    // Iterate until no more spaces.
    return current_space_ != LAST_SPACE;
  }
  
  
  ObjectIterator* SpaceIterator::next() {
    if (iterator_ != NULL) {
      delete iterator_;
      iterator_ = NULL;
      // Move to the next space
      current_space_++;
      if (current_space_ > LAST_SPACE) {
        return NULL;
      }
    }
  
    // Return iterator for the new current space.
    return CreateIterator();
  }
  
  
  // Create an iterator for the space to iterate.
  ObjectIterator* SpaceIterator::CreateIterator() {
    ASSERT(iterator_ == NULL);
  
    switch (current_space_) {
      case NEW_SPACE:
        iterator_ = new SemiSpaceIterator(HEAP->new_space(), size_func_);
        break;
      case OLD_POINTER_SPACE:
        iterator_ = new HeapObjectIterator(HEAP->old_pointer_space(), size_func_);
        break;
      case OLD_DATA_SPACE:
        iterator_ = new HeapObjectIterator(HEAP->old_data_space(), size_func_);
        break;
      case CODE_SPACE:
        iterator_ = new HeapObjectIterator(HEAP->code_space(), size_func_);
        break;
      case MAP_SPACE:
        iterator_ = new HeapObjectIterator(HEAP->map_space(), size_func_);
        break;
      case CELL_SPACE:
        iterator_ = new HeapObjectIterator(HEAP->cell_space(), size_func_);
        break;
      case LO_SPACE:
        iterator_ = new LargeObjectIterator(HEAP->lo_space(), size_func_);
        break;
    }
  
    // Return the newly allocated iterator;
    ASSERT(iterator_ != NULL);
    return iterator_;
  }
  
  
  class HeapObjectsFilter {
   public:
    virtual ~HeapObjectsFilter() {}
    virtual bool SkipObject(HeapObject* object) = 0;
  };
  
  
  class FreeListNodesFilter : public HeapObjectsFilter {
   public:
    FreeListNodesFilter() {
      MarkFreeListNodes();
    }
  
    bool SkipObject(HeapObject* object) {
      if (object->IsMarked()) {
        object->ClearMark();
        return true;
      } else {
        return false;
      }
    }
  
   private:
    void MarkFreeListNodes() {
      Heap* heap = HEAP;
      heap->old_pointer_space()->MarkFreeListNodes();
      heap->old_data_space()->MarkFreeListNodes();
      MarkCodeSpaceFreeListNodes(heap);
      heap->map_space()->MarkFreeListNodes();
      heap->cell_space()->MarkFreeListNodes();
    }
  
    void MarkCodeSpaceFreeListNodes(Heap* heap) {
      // For code space, using FreeListNode::IsFreeListNode is OK.
      HeapObjectIterator iter(heap->code_space());
      for (HeapObject* obj = iter.next_object();
           obj != NULL;
           obj = iter.next_object()) {
        if (FreeListNode::IsFreeListNode(obj)) obj->SetMark();
      }
    }
  
    AssertNoAllocation no_alloc;
  };
  
  
  class UnreachableObjectsFilter : public HeapObjectsFilter {
   public:
    UnreachableObjectsFilter() {
      MarkUnreachableObjects();
    }
  
    bool SkipObject(HeapObject* object) {
      if (object->IsMarked()) {
        object->ClearMark();
        return true;
      } else {
        return false;
      }
    }
  
   private:
    class UnmarkingVisitor : public ObjectVisitor {
     public:
      UnmarkingVisitor() : list_(10) {}
  
      void VisitPointers(Object** start, Object** end) {
        for (Object** p = start; p < end; p++) {
          if (!(*p)->IsHeapObject()) continue;
          HeapObject* obj = HeapObject::cast(*p);
          if (obj->IsMarked()) {
            obj->ClearMark();
            list_.Add(obj);
          }
        }
      }
  
      bool can_process() { return !list_.is_empty(); }
  
      void ProcessNext() {
        HeapObject* obj = list_.RemoveLast();
        obj->Iterate(this);
      }
  
     private:
      List<HeapObject*> list_;
    };
  
    void MarkUnreachableObjects() {
      HeapIterator iterator;
      for (HeapObject* obj = iterator.next();
           obj != NULL;
           obj = iterator.next()) {
        obj->SetMark();
      }
      UnmarkingVisitor visitor;
      HEAP->IterateRoots(&visitor, VISIT_ALL);
      while (visitor.can_process())
        visitor.ProcessNext();
    }
  
    AssertNoAllocation no_alloc;
  };
  
  
  HeapIterator::HeapIterator()
      : filtering_(HeapIterator::kNoFiltering),
        filter_(NULL) {
    Init();
  }
  
  
  HeapIterator::HeapIterator(HeapIterator::HeapObjectsFiltering filtering)
      : filtering_(filtering),
        filter_(NULL) {
    Init();
  }
  
  
  HeapIterator::~HeapIterator() {
    Shutdown();
  }
  
  
  void HeapIterator::Init() {
    // Start the iteration.
    space_iterator_ = filtering_ == kNoFiltering ? new SpaceIterator :
        new SpaceIterator(MarkCompactCollector::SizeOfMarkedObject);
    switch (filtering_) {
      case kFilterFreeListNodes:
        filter_ = new FreeListNodesFilter;
        break;
      case kFilterUnreachable:
        filter_ = new UnreachableObjectsFilter;
        break;
      default:
        break;
    }
    object_iterator_ = space_iterator_->next();
  }
  
  
  void HeapIterator::Shutdown() {
  #ifdef DEBUG
    // Assert that in filtering mode we have iterated through all
    // objects. Otherwise, heap will be left in an inconsistent state.
    if (filtering_ != kNoFiltering) {
      ASSERT(object_iterator_ == NULL);
    }
  #endif
    // Make sure the last iterator is deallocated.
    delete space_iterator_;
    space_iterator_ = NULL;
    object_iterator_ = NULL;
    delete filter_;
    filter_ = NULL;
  }
  
  
  HeapObject* HeapIterator::next() {
    if (filter_ == NULL) return NextObject();
  
    HeapObject* obj = NextObject();
    while (obj != NULL && filter_->SkipObject(obj)) obj = NextObject();
    return obj;
  }
  
  
  HeapObject* HeapIterator::NextObject() {
    // No iterator means we are done.
    if (object_iterator_ == NULL) return NULL;
  
    if (HeapObject* obj = object_iterator_->next_object()) {
      // If the current iterator has more objects we are fine.
      return obj;
    } else {
      // Go though the spaces looking for one that has objects.
      while (space_iterator_->has_next()) {
        object_iterator_ = space_iterator_->next();
        if (HeapObject* obj = object_iterator_->next_object()) {
          return obj;
        }
      }
    }
    // Done with the last space.
    object_iterator_ = NULL;
    return NULL;
  }
  
  
  void HeapIterator::reset() {
    // Restart the iterator.
    Shutdown();
    Init();
  }
  
  
  #if defined(DEBUG) || defined(LIVE_OBJECT_LIST)
  
  Object* const PathTracer::kAnyGlobalObject = reinterpret_cast<Object*>(NULL);
  
  class PathTracer::MarkVisitor: public ObjectVisitor {
   public:
    explicit MarkVisitor(PathTracer* tracer) : tracer_(tracer) {}
    void VisitPointers(Object** start, Object** end) {
      // Scan all HeapObject pointers in [start, end)
      for (Object** p = start; !tracer_->found() && (p < end); p++) {
        if ((*p)->IsHeapObject())
          tracer_->MarkRecursively(p, this);
      }
    }
  
   private:
    PathTracer* tracer_;
  };
  
  
  class PathTracer::UnmarkVisitor: public ObjectVisitor {
   public:
    explicit UnmarkVisitor(PathTracer* tracer) : tracer_(tracer) {}
    void VisitPointers(Object** start, Object** end) {
      // Scan all HeapObject pointers in [start, end)
      for (Object** p = start; p < end; p++) {
        if ((*p)->IsHeapObject())
          tracer_->UnmarkRecursively(p, this);
      }
    }
  
   private:
    PathTracer* tracer_;
  };
  
  
  void PathTracer::VisitPointers(Object** start, Object** end) {
    bool done = ((what_to_find_ == FIND_FIRST) && found_target_);
    // Visit all HeapObject pointers in [start, end)
    for (Object** p = start; !done && (p < end); p++) {
      if ((*p)->IsHeapObject()) {
        TracePathFrom(p);
        done = ((what_to_find_ == FIND_FIRST) && found_target_);
      }
    }
  }
  
  
  void PathTracer::Reset() {
    found_target_ = false;
    object_stack_.Clear();
  }
  
  
  void PathTracer::TracePathFrom(Object** root) {
    ASSERT((search_target_ == kAnyGlobalObject) ||
           search_target_->IsHeapObject());
    found_target_in_trace_ = false;
    object_stack_.Clear();
  
    MarkVisitor mark_visitor(this);
    MarkRecursively(root, &mark_visitor);
  
    UnmarkVisitor unmark_visitor(this);
    UnmarkRecursively(root, &unmark_visitor);
  
    ProcessResults();
  }
  
  
  void PathTracer::MarkRecursively(Object** p, MarkVisitor* mark_visitor) {
    if (!(*p)->IsHeapObject()) return;
  
    HeapObject* obj = HeapObject::cast(*p);
  
    Object* map = obj->map();
  
    if (!map->IsHeapObject()) return;  // visited before
  
    if (found_target_in_trace_) return;  // stop if target found
    object_stack_.Add(obj);
    if (((search_target_ == kAnyGlobalObject) && obj->IsJSGlobalObject()) ||
        (obj == search_target_)) {
      found_target_in_trace_ = true;
      found_target_ = true;
      return;
    }
  
    bool is_global_context = obj->IsGlobalContext();
  
    // not visited yet
    Map* map_p = reinterpret_cast<Map*>(HeapObject::cast(map));
  
    Address map_addr = map_p->address();
  
    obj->set_map(reinterpret_cast<Map*>(map_addr + kMarkTag));
  
    // Scan the object body.
    if (is_global_context && (visit_mode_ == VISIT_ONLY_STRONG)) {
      // This is specialized to scan Context's properly.
      Object** start = reinterpret_cast<Object**>(obj->address() +
                                                  Context::kHeaderSize);
      Object** end = reinterpret_cast<Object**>(obj->address() +
          Context::kHeaderSize + Context::FIRST_WEAK_SLOT * kPointerSize);
      mark_visitor->VisitPointers(start, end);
    } else {
      obj->IterateBody(map_p->instance_type(),
                       obj->SizeFromMap(map_p),
                       mark_visitor);
    }
  
    // Scan the map after the body because the body is a lot more interesting
    // when doing leak detection.
    MarkRecursively(&map, mark_visitor);
  
    if (!found_target_in_trace_)  // don't pop if found the target
      object_stack_.RemoveLast();
  }
  
  
  void PathTracer::UnmarkRecursively(Object** p, UnmarkVisitor* unmark_visitor) {
    if (!(*p)->IsHeapObject()) return;
  
    HeapObject* obj = HeapObject::cast(*p);
  
    Object* map = obj->map();
  
    if (map->IsHeapObject()) return;  // unmarked already
  
    Address map_addr = reinterpret_cast<Address>(map);
  
    map_addr -= kMarkTag;
  
    ASSERT_TAG_ALIGNED(map_addr);
  
    HeapObject* map_p = HeapObject::FromAddress(map_addr);
  
    obj->set_map(reinterpret_cast<Map*>(map_p));
  
    UnmarkRecursively(reinterpret_cast<Object**>(&map_p), unmark_visitor);
  
    obj->IterateBody(Map::cast(map_p)->instance_type(),
                     obj->SizeFromMap(Map::cast(map_p)),
                     unmark_visitor);
  }
  
  
  void PathTracer::ProcessResults() {
    if (found_target_) {
      PrintF("=====================================\n");
      PrintF("====        Path to object       ====\n");
      PrintF("=====================================\n\n");
  
      ASSERT(!object_stack_.is_empty());
      for (int i = 0; i < object_stack_.length(); i++) {
        if (i > 0) PrintF("\n     |\n     |\n     V\n\n");
        Object* obj = object_stack_[i];
  #ifdef OBJECT_PRINT
        obj->Print();
  #else
        obj->ShortPrint();
  #endif
      }
      PrintF("=====================================\n");
    }
  }
  #endif  // DEBUG || LIVE_OBJECT_LIST
  
  
  #ifdef DEBUG
  // Triggers a depth-first traversal of reachable objects from roots
  // and finds a path to a specific heap object and prints it.
  void Heap::TracePathToObject(Object* target) {
    PathTracer tracer(target, PathTracer::FIND_ALL, VISIT_ALL);
    IterateRoots(&tracer, VISIT_ONLY_STRONG);
  }
  
  
  // Triggers a depth-first traversal of reachable objects from roots
  // and finds a path to any global object and prints it. Useful for
  // determining the source for leaks of global objects.
  void Heap::TracePathToGlobal() {
    PathTracer tracer(PathTracer::kAnyGlobalObject,
                      PathTracer::FIND_ALL,
                      VISIT_ALL);
    IterateRoots(&tracer, VISIT_ONLY_STRONG);
  }
  #endif
  
  
  static intptr_t CountTotalHolesSize() {
    intptr_t holes_size = 0;
    OldSpaces spaces;
    for (OldSpace* space = spaces.next();
         space != NULL;
         space = spaces.next()) {
      holes_size += space->Waste() + space->AvailableFree();
    }
    return holes_size;
  }
  
  
  GCTracer::GCTracer(Heap* heap)
      : start_time_(0.0),
        start_size_(0),
        gc_count_(0),
        full_gc_count_(0),
        is_compacting_(false),
        marked_count_(0),
        allocated_since_last_gc_(0),
        spent_in_mutator_(0),
        promoted_objects_size_(0),
        heap_(heap) {
    // These two fields reflect the state of the previous full collection.
    // Set them before they are changed by the collector.
    previous_has_compacted_ = heap_->mark_compact_collector_.HasCompacted();
    previous_marked_count_ =
        heap_->mark_compact_collector_.previous_marked_count();
    if (!FLAG_trace_gc && !FLAG_print_cumulative_gc_stat) return;
    start_time_ = OS::TimeCurrentMillis();
    start_size_ = heap_->SizeOfObjects();
  
    for (int i = 0; i < Scope::kNumberOfScopes; i++) {
      scopes_[i] = 0;
    }
  
    in_free_list_or_wasted_before_gc_ = CountTotalHolesSize();
  
    allocated_since_last_gc_ =
        heap_->SizeOfObjects() - heap_->alive_after_last_gc_;
  
    if (heap_->last_gc_end_timestamp_ > 0) {
      spent_in_mutator_ = Max(start_time_ - heap_->last_gc_end_timestamp_, 0.0);
    }
  }
  
  
  GCTracer::~GCTracer() {
    // Printf ONE line iff flag is set.
    if (!FLAG_trace_gc && !FLAG_print_cumulative_gc_stat) return;
  
    bool first_gc = (heap_->last_gc_end_timestamp_ == 0);
  
    heap_->alive_after_last_gc_ = heap_->SizeOfObjects();
    heap_->last_gc_end_timestamp_ = OS::TimeCurrentMillis();
  
    int time = static_cast<int>(heap_->last_gc_end_timestamp_ - start_time_);
  
    // Update cumulative GC statistics if required.
    if (FLAG_print_cumulative_gc_stat) {
      heap_->max_gc_pause_ = Max(heap_->max_gc_pause_, time);
      heap_->max_alive_after_gc_ = Max(heap_->max_alive_after_gc_,
                                       heap_->alive_after_last_gc_);
      if (!first_gc) {
        heap_->min_in_mutator_ = Min(heap_->min_in_mutator_,
                                     static_cast<int>(spent_in_mutator_));
      }
    }
  
    if (!FLAG_trace_gc_nvp) {
      int external_time = static_cast<int>(scopes_[Scope::EXTERNAL]);
  
      PrintF("%s %.1f -> %.1f MB, ",
             CollectorString(),
             static_cast<double>(start_size_) / MB,
             SizeOfHeapObjects());
  
      if (external_time > 0) PrintF("%d / ", external_time);
      PrintF("%d ms.\n", time);
    } else {
      PrintF("pause=%d ", time);
      PrintF("mutator=%d ",
             static_cast<int>(spent_in_mutator_));
  
      PrintF("gc=");
      switch (collector_) {
        case SCAVENGER:
          PrintF("s");
          break;
        case MARK_COMPACTOR:
          PrintF("%s",
                 heap_->mark_compact_collector_.HasCompacted() ? "mc" : "ms");
          break;
        default:
          UNREACHABLE();
      }
      PrintF(" ");
  
      PrintF("external=%d ", static_cast<int>(scopes_[Scope::EXTERNAL]));
      PrintF("mark=%d ", static_cast<int>(scopes_[Scope::MC_MARK]));
      PrintF("sweep=%d ", static_cast<int>(scopes_[Scope::MC_SWEEP]));
      PrintF("sweepns=%d ", static_cast<int>(scopes_[Scope::MC_SWEEP_NEWSPACE]));
      PrintF("compact=%d ", static_cast<int>(scopes_[Scope::MC_COMPACT]));
  
      PrintF("total_size_before=%" V8_PTR_PREFIX "d ", start_size_);
      PrintF("total_size_after=%" V8_PTR_PREFIX "d ", heap_->SizeOfObjects());
      PrintF("holes_size_before=%" V8_PTR_PREFIX "d ",
             in_free_list_or_wasted_before_gc_);
      PrintF("holes_size_after=%" V8_PTR_PREFIX "d ", CountTotalHolesSize());
  
      PrintF("allocated=%" V8_PTR_PREFIX "d ", allocated_since_last_gc_);
      PrintF("promoted=%" V8_PTR_PREFIX "d ", promoted_objects_size_);
  
      PrintF("\n");
    }
  
    heap_->PrintShortHeapStatistics();
  }
  
  
  const char* GCTracer::CollectorString() {
    switch (collector_) {
      case SCAVENGER:
        return "Scavenge";
      case MARK_COMPACTOR:
        return heap_->mark_compact_collector_.HasCompacted() ? "Mark-compact"
                                                             : "Mark-sweep";
    }
    return "Unknown GC";
  }
  
  
  int KeyedLookupCache::Hash(Map* map, String* name) {
    // Uses only lower 32 bits if pointers are larger.
    uintptr_t addr_hash =
        static_cast<uint32_t>(reinterpret_cast<uintptr_t>(map)) >> kMapHashShift;
    return static_cast<uint32_t>((addr_hash ^ name->Hash()) & kCapacityMask);
  }
  
  
  int KeyedLookupCache::Lookup(Map* map, String* name) {
    int index = Hash(map, name);
    Key& key = keys_[index];
    if ((key.map == map) && key.name->Equals(name)) {
      return field_offsets_[index];
    }
    return kNotFound;
  }
  
  
  void KeyedLookupCache::Update(Map* map, String* name, int field_offset) {
    String* symbol;
    if (HEAP->LookupSymbolIfExists(name, &symbol)) {
      int index = Hash(map, symbol);
      Key& key = keys_[index];
      key.map = map;
      key.name = symbol;
      field_offsets_[index] = field_offset;
    }
  }
  
  
  void KeyedLookupCache::Clear() {
    for (int index = 0; index < kLength; index++) keys_[index].map = NULL;
  }
  
  
  void DescriptorLookupCache::Clear() {
    for (int index = 0; index < kLength; index++) keys_[index].array = NULL;
  }
  
  
  #ifdef DEBUG
  void Heap::GarbageCollectionGreedyCheck() {
    ASSERT(FLAG_gc_greedy);
    if (isolate_->bootstrapper()->IsActive()) return;
    if (disallow_allocation_failure()) return;
    CollectGarbage(NEW_SPACE);
  }
  #endif
  
  
  TranscendentalCache::SubCache::SubCache(Type t)
    : type_(t),
      isolate_(Isolate::Current()) {
    uint32_t in0 = 0xffffffffu;  // Bit-pattern for a NaN that isn't
    uint32_t in1 = 0xffffffffu;  // generated by the FPU.
    for (int i = 0; i < kCacheSize; i++) {
      elements_[i].in[0] = in0;
      elements_[i].in[1] = in1;
      elements_[i].output = NULL;
    }
  }
  
  
  void TranscendentalCache::Clear() {
    for (int i = 0; i < kNumberOfCaches; i++) {
      if (caches_[i] != NULL) {
        delete caches_[i];
        caches_[i] = NULL;
      }
    }
  }
  
  
  void ExternalStringTable::CleanUp() {
    int last = 0;
    for (int i = 0; i < new_space_strings_.length(); ++i) {
      if (new_space_strings_[i] == heap_->raw_unchecked_null_value()) continue;
      if (heap_->InNewSpace(new_space_strings_[i])) {
        new_space_strings_[last++] = new_space_strings_[i];
      } else {
        old_space_strings_.Add(new_space_strings_[i]);
      }
    }
    new_space_strings_.Rewind(last);
    last = 0;
    for (int i = 0; i < old_space_strings_.length(); ++i) {
      if (old_space_strings_[i] == heap_->raw_unchecked_null_value()) continue;
      ASSERT(!heap_->InNewSpace(old_space_strings_[i]));
      old_space_strings_[last++] = old_space_strings_[i];
    }
    old_space_strings_.Rewind(last);
    Verify();
  }
  
  
  void ExternalStringTable::TearDown() {
    new_space_strings_.Free();
    old_space_strings_.Free();
  }
  
  
  } }  // namespace v8::internal
  