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Diffstat (limited to 'deps/v8/src/mark-compact.cc')
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diff --git a/deps/v8/src/mark-compact.cc b/deps/v8/src/mark-compact.cc new file mode 100644 index 0000000000..c55345dc10 --- /dev/null +++ b/deps/v8/src/mark-compact.cc @@ -0,0 +1,1765 @@ +// Copyright 2006-2008 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 "execution.h" +#include "global-handles.h" +#include "ic-inl.h" +#include "mark-compact.h" +#include "stub-cache.h" + +namespace v8 { namespace internal { + +// ------------------------------------------------------------------------- +// MarkCompactCollector + +bool MarkCompactCollector::compacting_collection_ = false; + +int MarkCompactCollector::previous_marked_count_ = 0; +GCTracer* MarkCompactCollector::tracer_ = NULL; + + +#ifdef DEBUG +MarkCompactCollector::CollectorState MarkCompactCollector::state_ = IDLE; + +// Counters used for debugging the marking phase of mark-compact or mark-sweep +// collection. +int MarkCompactCollector::live_bytes_ = 0; +int MarkCompactCollector::live_young_objects_ = 0; +int MarkCompactCollector::live_old_data_objects_ = 0; +int MarkCompactCollector::live_old_pointer_objects_ = 0; +int MarkCompactCollector::live_code_objects_ = 0; +int MarkCompactCollector::live_map_objects_ = 0; +int MarkCompactCollector::live_lo_objects_ = 0; +#endif + +void MarkCompactCollector::CollectGarbage() { + // Make sure that Prepare() has been called. The individual steps below will + // update the state as they proceed. + ASSERT(state_ == PREPARE_GC); + + // Prepare has selected whether to compact the old generation or not. + // Tell the tracer. + if (IsCompacting()) tracer_->set_is_compacting(); + + MarkLiveObjects(); + + if (FLAG_collect_maps) ClearNonLiveTransitions(); + + SweepLargeObjectSpace(); + + if (compacting_collection_) { + EncodeForwardingAddresses(); + + UpdatePointers(); + + RelocateObjects(); + + RebuildRSets(); + + } else { + SweepSpaces(); + } + + Finish(); + + // Save the count of marked objects remaining after the collection and + // null out the GC tracer. + previous_marked_count_ = tracer_->marked_count(); + ASSERT(previous_marked_count_ == 0); + tracer_ = NULL; +} + + +void MarkCompactCollector::Prepare(GCTracer* tracer) { + // Rather than passing the tracer around we stash it in a static member + // variable. + tracer_ = tracer; + + static const int kFragmentationLimit = 50; // Percent. +#ifdef DEBUG + ASSERT(state_ == IDLE); + state_ = PREPARE_GC; +#endif + ASSERT(!FLAG_always_compact || !FLAG_never_compact); + + compacting_collection_ = FLAG_always_compact; + + // We compact the old generation if it gets too fragmented (ie, we could + // recover an expected amount of space by reclaiming the waste and free + // list blocks). We always compact when the flag --gc-global is true + // because objects do not get promoted out of new space on non-compacting + // GCs. + if (!compacting_collection_) { + int old_gen_recoverable = 0; + int old_gen_used = 0; + + OldSpaces spaces; + while (OldSpace* space = spaces.next()) { + old_gen_recoverable += space->Waste() + space->AvailableFree(); + old_gen_used += space->Size(); + } + int old_gen_fragmentation = + static_cast<int>((old_gen_recoverable * 100.0) / old_gen_used); + if (old_gen_fragmentation > kFragmentationLimit) { + compacting_collection_ = true; + } + } + + if (FLAG_never_compact) compacting_collection_ = false; + if (FLAG_collect_maps) CreateBackPointers(); + +#ifdef DEBUG + if (compacting_collection_) { + // We will write bookkeeping information to the remembered set area + // starting now. + Page::set_rset_state(Page::NOT_IN_USE); + } +#endif + + PagedSpaces spaces; + while (PagedSpace* space = spaces.next()) { + space->PrepareForMarkCompact(compacting_collection_); + } + +#ifdef DEBUG + live_bytes_ = 0; + live_young_objects_ = 0; + live_old_pointer_objects_ = 0; + live_old_data_objects_ = 0; + live_code_objects_ = 0; + live_map_objects_ = 0; + live_lo_objects_ = 0; +#endif +} + + +void MarkCompactCollector::Finish() { +#ifdef DEBUG + ASSERT(state_ == SWEEP_SPACES || state_ == REBUILD_RSETS); + state_ = IDLE; +#endif + // The stub cache is not traversed during GC; clear the cache to + // force lazy re-initialization of it. This must be done after the + // GC, because it relies on the new address of certain old space + // objects (empty string, illegal builtin). + StubCache::Clear(); +} + + +// ------------------------------------------------------------------------- +// Phase 1: tracing and marking live objects. +// before: all objects are in normal state. +// after: a live object's map pointer is marked as '00'. + +// Marking all live objects in the heap as part of mark-sweep or mark-compact +// collection. Before marking, all objects are in their normal state. After +// marking, live objects' map pointers are marked indicating that the object +// has been found reachable. +// +// The marking algorithm is a (mostly) depth-first (because of possible stack +// overflow) traversal of the graph of objects reachable from the roots. It +// uses an explicit stack of pointers rather than recursion. The young +// generation's inactive ('from') space is used as a marking stack. The +// objects in the marking stack are the ones that have been reached and marked +// but their children have not yet been visited. +// +// The marking stack can overflow during traversal. In that case, we set an +// overflow flag. When the overflow flag is set, we continue marking objects +// reachable from the objects on the marking stack, but no longer push them on +// the marking stack. Instead, we mark them as both marked and overflowed. +// When the stack is in the overflowed state, objects marked as overflowed +// have been reached and marked but their children have not been visited yet. +// After emptying the marking stack, we clear the overflow flag and traverse +// the heap looking for objects marked as overflowed, push them on the stack, +// and continue with marking. This process repeats until all reachable +// objects have been marked. + +static MarkingStack marking_stack; + + +static inline HeapObject* ShortCircuitConsString(Object** p) { + // Optimization: If the heap object pointed to by p is a non-symbol + // cons string whose right substring is Heap::empty_string, update + // it in place to its left substring. Return the updated value. + // + // Here we assume that if we change *p, we replace it with a heap object + // (ie, the left substring of a cons string is always a heap object). + // + // The check performed is: + // object->IsConsString() && !object->IsSymbol() && + // (ConsString::cast(object)->second() == Heap::empty_string()) + // except the maps for the object and its possible substrings might be + // marked. + HeapObject* object = HeapObject::cast(*p); + MapWord map_word = object->map_word(); + map_word.ClearMark(); + InstanceType type = map_word.ToMap()->instance_type(); + if ((type & kShortcutTypeMask) != kShortcutTypeTag) return object; + + Object* second = reinterpret_cast<ConsString*>(object)->unchecked_second(); + if (reinterpret_cast<String*>(second) != Heap::empty_string()) return object; + + // Since we don't have the object's start, it is impossible to update the + // remembered set. Therefore, we only replace the string with its left + // substring when the remembered set does not change. + Object* first = reinterpret_cast<ConsString*>(object)->unchecked_first(); + if (!Heap::InNewSpace(object) && Heap::InNewSpace(first)) return object; + + *p = first; + return HeapObject::cast(first); +} + + +// Helper class for marking pointers in HeapObjects. +class MarkingVisitor : public ObjectVisitor { + public: + void VisitPointer(Object** p) { + MarkObjectByPointer(p); + } + + void VisitPointers(Object** start, Object** end) { + // Mark all objects pointed to in [start, end). + const int kMinRangeForMarkingRecursion = 64; + if (end - start >= kMinRangeForMarkingRecursion) { + if (VisitUnmarkedObjects(start, end)) return; + // We are close to a stack overflow, so just mark the objects. + } + for (Object** p = start; p < end; p++) MarkObjectByPointer(p); + } + + void BeginCodeIteration(Code* code) { + // When iterating over a code object during marking + // ic targets are derived pointers. + ASSERT(code->ic_flag() == Code::IC_TARGET_IS_ADDRESS); + } + + void EndCodeIteration(Code* code) { + // If this is a compacting collection, set ic targets + // are pointing to object headers. + if (IsCompacting()) code->set_ic_flag(Code::IC_TARGET_IS_OBJECT); + } + + void VisitCodeTarget(RelocInfo* rinfo) { + ASSERT(RelocInfo::IsCodeTarget(rinfo->rmode())); + Code* code = CodeFromDerivedPointer(rinfo->target_address()); + if (FLAG_cleanup_ics_at_gc && code->is_inline_cache_stub()) { + IC::Clear(rinfo->pc()); + // Please note targets for cleared inline cached do not have to be + // marked since they are contained in Heap::non_monomorphic_cache(). + } else { + MarkCompactCollector::MarkObject(code); + } + if (IsCompacting()) { + // When compacting we convert the target to a real object pointer. + code = CodeFromDerivedPointer(rinfo->target_address()); + rinfo->set_target_object(code); + } + } + + void VisitDebugTarget(RelocInfo* rinfo) { + ASSERT(RelocInfo::IsJSReturn(rinfo->rmode()) && + rinfo->IsCallInstruction()); + HeapObject* code = CodeFromDerivedPointer(rinfo->call_address()); + MarkCompactCollector::MarkObject(code); + // When compacting we convert the call to a real object pointer. + if (IsCompacting()) rinfo->set_call_object(code); + } + + private: + // Mark object pointed to by p. + void MarkObjectByPointer(Object** p) { + if (!(*p)->IsHeapObject()) return; + HeapObject* object = ShortCircuitConsString(p); + MarkCompactCollector::MarkObject(object); + } + + // Tells whether the mark sweep collection will perform compaction. + bool IsCompacting() { return MarkCompactCollector::IsCompacting(); } + + // Retrieves the Code pointer from derived code entry. + Code* CodeFromDerivedPointer(Address addr) { + ASSERT(addr != NULL); + return reinterpret_cast<Code*>( + HeapObject::FromAddress(addr - Code::kHeaderSize)); + } + + // Visit an unmarked object. + void VisitUnmarkedObject(HeapObject* obj) { +#ifdef DEBUG + ASSERT(Heap::Contains(obj)); + ASSERT(!obj->IsMarked()); +#endif + Map* map = obj->map(); + MarkCompactCollector::SetMark(obj); + // Mark the map pointer and the body. + MarkCompactCollector::MarkObject(map); + obj->IterateBody(map->instance_type(), obj->SizeFromMap(map), this); + } + + // Visit all unmarked objects pointed to by [start, end). + // Returns false if the operation fails (lack of stack space). + inline bool VisitUnmarkedObjects(Object** start, Object** end) { + // Return false is we are close to the stack limit. + StackLimitCheck check; + if (check.HasOverflowed()) return false; + + // Visit the unmarked objects. + for (Object** p = start; p < end; p++) { + if (!(*p)->IsHeapObject()) continue; + HeapObject* obj = HeapObject::cast(*p); + if (obj->IsMarked()) continue; + VisitUnmarkedObject(obj); + } + return true; + } +}; + + +// Visitor class for marking heap roots. +class RootMarkingVisitor : public ObjectVisitor { + public: + void VisitPointer(Object** p) { + MarkObjectByPointer(p); + } + + void VisitPointers(Object** start, Object** end) { + for (Object** p = start; p < end; p++) MarkObjectByPointer(p); + } + + MarkingVisitor* stack_visitor() { return &stack_visitor_; } + + private: + MarkingVisitor stack_visitor_; + + void MarkObjectByPointer(Object** p) { + if (!(*p)->IsHeapObject()) return; + + // Replace flat cons strings in place. + HeapObject* object = ShortCircuitConsString(p); + if (object->IsMarked()) return; + + Map* map = object->map(); + // Mark the object. + MarkCompactCollector::SetMark(object); + // Mark the map pointer and body, and push them on the marking stack. + MarkCompactCollector::MarkObject(map); + object->IterateBody(map->instance_type(), object->SizeFromMap(map), + &stack_visitor_); + + // Mark all the objects reachable from the map and body. May leave + // overflowed objects in the heap. + MarkCompactCollector::EmptyMarkingStack(&stack_visitor_); + } +}; + + +// Helper class for pruning the symbol table. +class SymbolTableCleaner : public ObjectVisitor { + public: + SymbolTableCleaner() : pointers_removed_(0) { } + void VisitPointers(Object** start, Object** end) { + // Visit all HeapObject pointers in [start, end). + for (Object** p = start; p < end; p++) { + if ((*p)->IsHeapObject() && !HeapObject::cast(*p)->IsMarked()) { + // Check if the symbol being pruned is an external symbol. We need to + // delete the associated external data as this symbol is going away. + + // Since the object is not marked we can access its map word safely + // without having to worry about marking bits in the object header. + Map* map = HeapObject::cast(*p)->map(); + // Since no objects have yet been moved we can safely access the map of + // the object. + uint32_t type = map->instance_type(); + bool is_external = (type & kStringRepresentationMask) == + kExternalStringTag; + if (is_external) { + bool is_two_byte = (type & kStringEncodingMask) == kTwoByteStringTag; + byte* resource_addr = reinterpret_cast<byte*>(*p) + + ExternalString::kResourceOffset - + kHeapObjectTag; + if (is_two_byte) { + v8::String::ExternalStringResource** resource = + reinterpret_cast<v8::String::ExternalStringResource**> + (resource_addr); + delete *resource; + // Clear the resource pointer in the symbol. + *resource = NULL; + } else { + v8::String::ExternalAsciiStringResource** resource = + reinterpret_cast<v8::String::ExternalAsciiStringResource**> + (resource_addr); + delete *resource; + // Clear the resource pointer in the symbol. + *resource = NULL; + } + } + // Set the entry to null_value (as deleted). + *p = Heap::null_value(); + pointers_removed_++; + } + } + } + + int PointersRemoved() { + return pointers_removed_; + } + private: + int pointers_removed_; +}; + + +void MarkCompactCollector::MarkUnmarkedObject(HeapObject* object) { + ASSERT(!object->IsMarked()); + ASSERT(Heap::Contains(object)); + if (object->IsMap()) { + Map* map = Map::cast(object); + if (FLAG_cleanup_caches_in_maps_at_gc) { + map->ClearCodeCache(); + } + SetMark(map); + if (FLAG_collect_maps && + map->instance_type() >= FIRST_JS_OBJECT_TYPE && + map->instance_type() <= JS_FUNCTION_TYPE) { + MarkMapContents(map); + } else { + marking_stack.Push(map); + } + } else { + SetMark(object); + marking_stack.Push(object); + } +} + + +void MarkCompactCollector::MarkMapContents(Map* map) { + MarkDescriptorArray(reinterpret_cast<DescriptorArray*>( + *HeapObject::RawField(map, Map::kInstanceDescriptorsOffset))); + + // Mark the Object* fields of the Map. + // Since the descriptor array has been marked already, it is fine + // that one of these fields contains a pointer to it. + MarkingVisitor visitor; // Has no state or contents. + visitor.VisitPointers(HeapObject::RawField(map, Map::kPrototypeOffset), + HeapObject::RawField(map, Map::kSize)); +} + + +void MarkCompactCollector::MarkDescriptorArray( + DescriptorArray *descriptors) { + if (descriptors->IsMarked()) return; + // Empty descriptor array is marked as a root before any maps are marked. + ASSERT(descriptors != Heap::empty_descriptor_array()); + SetMark(descriptors); + + FixedArray* contents = reinterpret_cast<FixedArray*>( + descriptors->get(DescriptorArray::kContentArrayIndex)); + ASSERT(contents->IsHeapObject()); + ASSERT(!contents->IsMarked()); + ASSERT(contents->IsFixedArray()); + ASSERT(contents->length() >= 2); + SetMark(contents); + // Contents contains (value, details) pairs. If the details say + // that the type of descriptor is MAP_TRANSITION, CONSTANT_TRANSITION, + // or NULL_DESCRIPTOR, we don't mark the value as live. Only for + // type MAP_TRANSITION is the value a Object* (a Map*). + for (int i = 0; i < contents->length(); i += 2) { + // If the pair (value, details) at index i, i+1 is not + // a transition or null descriptor, mark the value. + PropertyDetails details(Smi::cast(contents->get(i + 1))); + if (details.type() < FIRST_PHANTOM_PROPERTY_TYPE) { + HeapObject* object = reinterpret_cast<HeapObject*>(contents->get(i)); + if (object->IsHeapObject() && !object->IsMarked()) { + SetMark(object); + marking_stack.Push(object); + } + } + } + // The DescriptorArray descriptors contains a pointer to its contents array, + // but the contents array is already marked. + marking_stack.Push(descriptors); +} + + +void MarkCompactCollector::CreateBackPointers() { + HeapObjectIterator iterator(Heap::map_space()); + while (iterator.has_next()) { + Object* next_object = iterator.next(); + if (next_object->IsMap()) { // Could also be ByteArray on free list. + Map* map = Map::cast(next_object); + if (map->instance_type() >= FIRST_JS_OBJECT_TYPE && + map->instance_type() <= JS_FUNCTION_TYPE) { + map->CreateBackPointers(); + } else { + ASSERT(map->instance_descriptors() == Heap::empty_descriptor_array()); + } + } + } +} + + +static int OverflowObjectSize(HeapObject* obj) { + // Recover the normal map pointer, it might be marked as live and + // overflowed. + MapWord map_word = obj->map_word(); + map_word.ClearMark(); + map_word.ClearOverflow(); + return obj->SizeFromMap(map_word.ToMap()); +} + + +// Fill the marking stack with overflowed objects returned by the given +// iterator. Stop when the marking stack is filled or the end of the space +// is reached, whichever comes first. +template<class T> +static void ScanOverflowedObjects(T* it) { + // The caller should ensure that the marking stack is initially not full, + // so that we don't waste effort pointlessly scanning for objects. + ASSERT(!marking_stack.is_full()); + + while (it->has_next()) { + HeapObject* object = it->next(); + if (object->IsOverflowed()) { + object->ClearOverflow(); + ASSERT(object->IsMarked()); + ASSERT(Heap::Contains(object)); + marking_stack.Push(object); + if (marking_stack.is_full()) return; + } + } +} + + +bool MarkCompactCollector::MustBeMarked(Object** p) { + // Check whether *p is a HeapObject pointer. + if (!(*p)->IsHeapObject()) return false; + return !HeapObject::cast(*p)->IsMarked(); +} + + +void MarkCompactCollector::ProcessRoots(RootMarkingVisitor* visitor) { + // Mark the heap roots gray, including global variables, stack variables, + // etc. + Heap::IterateStrongRoots(visitor); + + // Take care of the symbol table specially. + SymbolTable* symbol_table = SymbolTable::cast(Heap::symbol_table()); + // 1. Mark the prefix of the symbol table gray. + symbol_table->IteratePrefix(visitor); + // 2. Mark the symbol table black (ie, do not push it on the marking stack + // or mark it overflowed). + SetMark(symbol_table); + + // There may be overflowed objects in the heap. Visit them now. + while (marking_stack.overflowed()) { + RefillMarkingStack(); + EmptyMarkingStack(visitor->stack_visitor()); + } +} + + +void MarkCompactCollector::MarkObjectGroups() { + List<ObjectGroup*>* object_groups = GlobalHandles::ObjectGroups(); + + for (int i = 0; i < object_groups->length(); i++) { + ObjectGroup* entry = object_groups->at(i); + if (entry == NULL) continue; + + List<Object**>& objects = entry->objects_; + bool group_marked = false; + for (int j = 0; j < objects.length(); j++) { + Object* object = *objects[j]; + if (object->IsHeapObject() && HeapObject::cast(object)->IsMarked()) { + group_marked = true; + break; + } + } + + if (!group_marked) continue; + + // An object in the group is marked, so mark as gray all white heap + // objects in the group. + for (int j = 0; j < objects.length(); ++j) { + if ((*objects[j])->IsHeapObject()) { + MarkObject(HeapObject::cast(*objects[j])); + } + } + // Once the entire group has been colored gray, set the object group + // to NULL so it won't be processed again. + delete object_groups->at(i); + object_groups->at(i) = NULL; + } +} + + +// Mark all objects reachable from the objects on the marking stack. +// Before: the marking stack contains zero or more heap object pointers. +// After: the marking stack is empty, and all objects reachable from the +// marking stack have been marked, or are overflowed in the heap. +void MarkCompactCollector::EmptyMarkingStack(MarkingVisitor* visitor) { + while (!marking_stack.is_empty()) { + HeapObject* object = marking_stack.Pop(); + ASSERT(object->IsHeapObject()); + ASSERT(Heap::Contains(object)); + ASSERT(object->IsMarked()); + ASSERT(!object->IsOverflowed()); + + // Because the object is marked, we have to recover the original map + // pointer and use it to mark the object's body. + MapWord map_word = object->map_word(); + map_word.ClearMark(); + Map* map = map_word.ToMap(); + MarkObject(map); + object->IterateBody(map->instance_type(), object->SizeFromMap(map), + visitor); + } +} + + +// Sweep the heap for overflowed objects, clear their overflow bits, and +// push them on the marking stack. Stop early if the marking stack fills +// before sweeping completes. If sweeping completes, there are no remaining +// overflowed objects in the heap so the overflow flag on the markings stack +// is cleared. +void MarkCompactCollector::RefillMarkingStack() { + ASSERT(marking_stack.overflowed()); + + SemiSpaceIterator new_it(Heap::new_space(), &OverflowObjectSize); + ScanOverflowedObjects(&new_it); + if (marking_stack.is_full()) return; + + HeapObjectIterator old_pointer_it(Heap::old_pointer_space(), + &OverflowObjectSize); + ScanOverflowedObjects(&old_pointer_it); + if (marking_stack.is_full()) return; + + HeapObjectIterator old_data_it(Heap::old_data_space(), &OverflowObjectSize); + ScanOverflowedObjects(&old_data_it); + if (marking_stack.is_full()) return; + + HeapObjectIterator code_it(Heap::code_space(), &OverflowObjectSize); + ScanOverflowedObjects(&code_it); + if (marking_stack.is_full()) return; + + HeapObjectIterator map_it(Heap::map_space(), &OverflowObjectSize); + ScanOverflowedObjects(&map_it); + if (marking_stack.is_full()) return; + + LargeObjectIterator lo_it(Heap::lo_space(), &OverflowObjectSize); + ScanOverflowedObjects(&lo_it); + if (marking_stack.is_full()) return; + + marking_stack.clear_overflowed(); +} + + +// Mark all objects reachable (transitively) from objects on the marking +// stack. Before: the marking stack contains zero or more heap object +// pointers. After: the marking stack is empty and there are no overflowed +// objects in the heap. +void MarkCompactCollector::ProcessMarkingStack(MarkingVisitor* visitor) { + EmptyMarkingStack(visitor); + while (marking_stack.overflowed()) { + RefillMarkingStack(); + EmptyMarkingStack(visitor); + } +} + + +void MarkCompactCollector::ProcessObjectGroups(MarkingVisitor* visitor) { + bool work_to_do = true; + ASSERT(marking_stack.is_empty()); + while (work_to_do) { + MarkObjectGroups(); + work_to_do = !marking_stack.is_empty(); + ProcessMarkingStack(visitor); + } +} + + +void MarkCompactCollector::MarkLiveObjects() { +#ifdef DEBUG + ASSERT(state_ == PREPARE_GC); + state_ = MARK_LIVE_OBJECTS; +#endif + // The to space contains live objects, the from space is used as a marking + // stack. + marking_stack.Initialize(Heap::new_space()->FromSpaceLow(), + Heap::new_space()->FromSpaceHigh()); + + ASSERT(!marking_stack.overflowed()); + + RootMarkingVisitor root_visitor; + ProcessRoots(&root_visitor); + + // The objects reachable from the roots are marked black, unreachable + // objects are white. Mark objects reachable from object groups with at + // least one marked object, and continue until no new objects are + // reachable from the object groups. + ProcessObjectGroups(root_visitor.stack_visitor()); + + // The objects reachable from the roots or object groups are marked black, + // unreachable objects are white. Process objects reachable only from + // weak global handles. + // + // First we mark weak pointers not yet reachable. + GlobalHandles::MarkWeakRoots(&MustBeMarked); + // Then we process weak pointers and process the transitive closure. + GlobalHandles::IterateWeakRoots(&root_visitor); + while (marking_stack.overflowed()) { + RefillMarkingStack(); + EmptyMarkingStack(root_visitor.stack_visitor()); + } + + // Repeat the object groups to mark unmarked groups reachable from the + // weak roots. + ProcessObjectGroups(root_visitor.stack_visitor()); + + // Prune the symbol table removing all symbols only pointed to by the + // symbol table. Cannot use SymbolTable::cast here because the symbol + // table is marked. + SymbolTable* symbol_table = + reinterpret_cast<SymbolTable*>(Heap::symbol_table()); + SymbolTableCleaner v; + symbol_table->IterateElements(&v); + symbol_table->ElementsRemoved(v.PointersRemoved()); + + // Remove object groups after marking phase. + GlobalHandles::RemoveObjectGroups(); +} + + +static int CountMarkedCallback(HeapObject* obj) { + MapWord map_word = obj->map_word(); + map_word.ClearMark(); + return obj->SizeFromMap(map_word.ToMap()); +} + + +#ifdef DEBUG +void MarkCompactCollector::UpdateLiveObjectCount(HeapObject* obj) { + live_bytes_ += obj->Size(); + if (Heap::new_space()->Contains(obj)) { + live_young_objects_++; + } else if (Heap::map_space()->Contains(obj)) { + ASSERT(obj->IsMap()); + live_map_objects_++; + } else if (Heap::old_pointer_space()->Contains(obj)) { + live_old_pointer_objects_++; + } else if (Heap::old_data_space()->Contains(obj)) { + live_old_data_objects_++; + } else if (Heap::code_space()->Contains(obj)) { + live_code_objects_++; + } else if (Heap::lo_space()->Contains(obj)) { + live_lo_objects_++; + } else { + UNREACHABLE(); + } +} +#endif // DEBUG + + +void MarkCompactCollector::SweepLargeObjectSpace() { +#ifdef DEBUG + ASSERT(state_ == MARK_LIVE_OBJECTS); + state_ = + compacting_collection_ ? ENCODE_FORWARDING_ADDRESSES : SWEEP_SPACES; +#endif + // Deallocate unmarked objects and clear marked bits for marked objects. + Heap::lo_space()->FreeUnmarkedObjects(); +} + +// Safe to use during marking phase only. +bool MarkCompactCollector::SafeIsMap(HeapObject* object) { + MapWord metamap = object->map_word(); + metamap.ClearMark(); + return metamap.ToMap()->instance_type() == MAP_TYPE; +} + +void MarkCompactCollector::ClearNonLiveTransitions() { + HeapObjectIterator map_iterator(Heap::map_space(), &CountMarkedCallback); + // Iterate over the map space, setting map transitions that go from + // a marked map to an unmarked map to null transitions. At the same time, + // set all the prototype fields of maps back to their original value, + // dropping the back pointers temporarily stored in the prototype field. + // Setting the prototype field requires following the linked list of + // back pointers, reversing them all at once. This allows us to find + // those maps with map transitions that need to be nulled, and only + // scan the descriptor arrays of those maps, not all maps. + // All of these actions are carried out only on maps of JSObects + // and related subtypes. + while (map_iterator.has_next()) { + Map* map = reinterpret_cast<Map*>(map_iterator.next()); + if (!map->IsMarked() && map->IsByteArray()) continue; + + ASSERT(SafeIsMap(map)); + // Only JSObject and subtypes have map transitions and back pointers. + if (map->instance_type() < FIRST_JS_OBJECT_TYPE) continue; + if (map->instance_type() > JS_FUNCTION_TYPE) continue; + // Follow the chain of back pointers to find the prototype. + Map* current = map; + while (SafeIsMap(current)) { + current = reinterpret_cast<Map*>(current->prototype()); + ASSERT(current->IsHeapObject()); + } + Object* real_prototype = current; + + // Follow back pointers, setting them to prototype, + // clearing map transitions when necessary. + current = map; + bool on_dead_path = !current->IsMarked(); + Object *next; + while (SafeIsMap(current)) { + next = current->prototype(); + // There should never be a dead map above a live map. + ASSERT(on_dead_path || current->IsMarked()); + + // A live map above a dead map indicates a dead transition. + // This test will always be false on the first iteration. + if (on_dead_path && current->IsMarked()) { + on_dead_path = false; + current->ClearNonLiveTransitions(real_prototype); + } + *HeapObject::RawField(current, Map::kPrototypeOffset) = + real_prototype; + current = reinterpret_cast<Map*>(next); + } + } +} + +// ------------------------------------------------------------------------- +// Phase 2: Encode forwarding addresses. +// When compacting, forwarding addresses for objects in old space and map +// space are encoded in their map pointer word (along with an encoding of +// their map pointers). +// +// 31 21 20 10 9 0 +// +-----------------+------------------+-----------------+ +// |forwarding offset|page offset of map|page index of map| +// +-----------------+------------------+-----------------+ +// 11 bits 11 bits 10 bits +// +// An address range [start, end) can have both live and non-live objects. +// Maximal non-live regions are marked so they can be skipped on subsequent +// sweeps of the heap. A distinguished map-pointer encoding is used to mark +// free regions of one-word size (in which case the next word is the start +// of a live object). A second distinguished map-pointer encoding is used +// to mark free regions larger than one word, and the size of the free +// region (including the first word) is written to the second word of the +// region. +// +// Any valid map page offset must lie in the object area of the page, so map +// page offsets less than Page::kObjectStartOffset are invalid. We use a +// pair of distinguished invalid map encodings (for single word and multiple +// words) to indicate free regions in the page found during computation of +// forwarding addresses and skipped over in subsequent sweeps. +static const uint32_t kSingleFreeEncoding = 0; +static const uint32_t kMultiFreeEncoding = 1; + + +// Encode a free region, defined by the given start address and size, in the +// first word or two of the region. +void EncodeFreeRegion(Address free_start, int free_size) { + ASSERT(free_size >= kIntSize); + if (free_size == kIntSize) { + Memory::uint32_at(free_start) = kSingleFreeEncoding; + } else { + ASSERT(free_size >= 2 * kIntSize); + Memory::uint32_at(free_start) = kMultiFreeEncoding; + Memory::int_at(free_start + kIntSize) = free_size; + } + +#ifdef DEBUG + // Zap the body of the free region. + if (FLAG_enable_slow_asserts) { + for (int offset = 2 * kIntSize; + offset < free_size; + offset += kPointerSize) { + Memory::Address_at(free_start + offset) = kZapValue; + } + } +#endif +} + + +// Try to promote all objects in new space. Heap numbers and sequential +// strings are promoted to the code space, all others to the old space. +inline Object* MCAllocateFromNewSpace(HeapObject* object, int object_size) { + OldSpace* target_space = Heap::TargetSpace(object); + ASSERT(target_space == Heap::old_pointer_space() || + target_space == Heap::old_data_space()); + Object* forwarded = target_space->MCAllocateRaw(object_size); + + if (forwarded->IsFailure()) { + forwarded = Heap::new_space()->MCAllocateRaw(object_size); + } + return forwarded; +} + + +// Allocation functions for the paged spaces call the space's MCAllocateRaw. +inline Object* MCAllocateFromOldPointerSpace(HeapObject* object, + int object_size) { + return Heap::old_pointer_space()->MCAllocateRaw(object_size); +} + + +inline Object* MCAllocateFromOldDataSpace(HeapObject* object, int object_size) { + return Heap::old_data_space()->MCAllocateRaw(object_size); +} + + +inline Object* MCAllocateFromCodeSpace(HeapObject* object, int object_size) { + return Heap::code_space()->MCAllocateRaw(object_size); +} + + +inline Object* MCAllocateFromMapSpace(HeapObject* object, int object_size) { + return Heap::map_space()->MCAllocateRaw(object_size); +} + + +// The forwarding address is encoded at the same offset as the current +// to-space object, but in from space. +inline void EncodeForwardingAddressInNewSpace(HeapObject* old_object, + int object_size, + Object* new_object, + int* ignored) { + int offset = + Heap::new_space()->ToSpaceOffsetForAddress(old_object->address()); + Memory::Address_at(Heap::new_space()->FromSpaceLow() + offset) = + HeapObject::cast(new_object)->address(); +} + + +// The forwarding address is encoded in the map pointer of the object as an +// offset (in terms of live bytes) from the address of the first live object +// in the page. +inline void EncodeForwardingAddressInPagedSpace(HeapObject* old_object, + int object_size, + Object* new_object, + int* offset) { + // Record the forwarding address of the first live object if necessary. + if (*offset == 0) { + Page::FromAddress(old_object->address())->mc_first_forwarded = + HeapObject::cast(new_object)->address(); + } + + MapWord encoding = + MapWord::EncodeAddress(old_object->map()->address(), *offset); + old_object->set_map_word(encoding); + *offset += object_size; + ASSERT(*offset <= Page::kObjectAreaSize); +} + + +// Most non-live objects are ignored. +inline void IgnoreNonLiveObject(HeapObject* object) {} + + +// A code deletion event is logged for non-live code objects. +inline void LogNonLiveCodeObject(HeapObject* object) { + if (object->IsCode()) LOG(CodeDeleteEvent(object->address())); +} + + +// Function template that, given a range of addresses (eg, a semispace or a +// paged space page), iterates through the objects in the range to clear +// mark bits and compute and encode forwarding addresses. As a side effect, +// maximal free chunks are marked so that they can be skipped on subsequent +// sweeps. +// +// The template parameters are an allocation function, a forwarding address +// encoding function, and a function to process non-live objects. +template<MarkCompactCollector::AllocationFunction Alloc, + MarkCompactCollector::EncodingFunction Encode, + MarkCompactCollector::ProcessNonLiveFunction ProcessNonLive> +inline void EncodeForwardingAddressesInRange(Address start, + Address end, + int* offset) { + // The start address of the current free region while sweeping the space. + // This address is set when a transition from live to non-live objects is + // encountered. A value (an encoding of the 'next free region' pointer) + // is written to memory at this address when a transition from non-live to + // live objects is encountered. + Address free_start = NULL; + + // A flag giving the state of the previously swept object. Initially true + // to ensure that free_start is initialized to a proper address before + // trying to write to it. + bool is_prev_alive = true; + + int object_size; // Will be set on each iteration of the loop. + for (Address current = start; current < end; current += object_size) { + HeapObject* object = HeapObject::FromAddress(current); + if (object->IsMarked()) { + object->ClearMark(); + MarkCompactCollector::tracer()->decrement_marked_count(); + object_size = object->Size(); + + Object* forwarded = Alloc(object, object_size); + // Allocation cannot fail, because we are compacting the space. + ASSERT(!forwarded->IsFailure()); + Encode(object, object_size, forwarded, offset); + +#ifdef DEBUG + if (FLAG_gc_verbose) { + PrintF("forward %p -> %p.\n", object->address(), + HeapObject::cast(forwarded)->address()); + } +#endif + if (!is_prev_alive) { // Transition from non-live to live. + EncodeFreeRegion(free_start, current - free_start); + is_prev_alive = true; + } + } else { // Non-live object. + object_size = object->Size(); + ProcessNonLive(object); + if (is_prev_alive) { // Transition from live to non-live. + free_start = current; + is_prev_alive = false; + } + } + } + + // If we ended on a free region, mark it. + if (!is_prev_alive) EncodeFreeRegion(free_start, end - free_start); +} + + +// Functions to encode the forwarding pointers in each compactable space. +void MarkCompactCollector::EncodeForwardingAddressesInNewSpace() { + int ignored; + EncodeForwardingAddressesInRange<MCAllocateFromNewSpace, + EncodeForwardingAddressInNewSpace, + IgnoreNonLiveObject>( + Heap::new_space()->bottom(), + Heap::new_space()->top(), + &ignored); +} + + +template<MarkCompactCollector::AllocationFunction Alloc, + MarkCompactCollector::ProcessNonLiveFunction ProcessNonLive> +void MarkCompactCollector::EncodeForwardingAddressesInPagedSpace( + PagedSpace* space) { + PageIterator it(space, PageIterator::PAGES_IN_USE); + while (it.has_next()) { + Page* p = it.next(); + // The offset of each live object in the page from the first live object + // in the page. + int offset = 0; + EncodeForwardingAddressesInRange<Alloc, + EncodeForwardingAddressInPagedSpace, + ProcessNonLive>( + p->ObjectAreaStart(), + p->AllocationTop(), + &offset); + } +} + + +static void SweepSpace(NewSpace* space) { + HeapObject* object; + for (Address current = space->bottom(); + current < space->top(); + current += object->Size()) { + object = HeapObject::FromAddress(current); + if (object->IsMarked()) { + object->ClearMark(); + MarkCompactCollector::tracer()->decrement_marked_count(); + } else { + // We give non-live objects a map that will correctly give their size, + // since their existing map might not be live after the collection. + int size = object->Size(); + if (size >= Array::kHeaderSize) { + object->set_map(Heap::byte_array_map()); + ByteArray::cast(object)->set_length(ByteArray::LengthFor(size)); + } else { + ASSERT(size == kPointerSize); + object->set_map(Heap::one_word_filler_map()); + } + ASSERT(object->Size() == size); + } + // The object is now unmarked for the call to Size() at the top of the + // loop. + } +} + + +static void SweepSpace(PagedSpace* space, DeallocateFunction dealloc) { + PageIterator it(space, PageIterator::PAGES_IN_USE); + while (it.has_next()) { + Page* p = it.next(); + + bool is_previous_alive = true; + Address free_start = NULL; + HeapObject* object; + + for (Address current = p->ObjectAreaStart(); + current < p->AllocationTop(); + current += object->Size()) { + object = HeapObject::FromAddress(current); + if (object->IsMarked()) { + object->ClearMark(); + MarkCompactCollector::tracer()->decrement_marked_count(); + if (MarkCompactCollector::IsCompacting() && object->IsCode()) { + // If this is compacting collection marked code objects have had + // their IC targets converted to objects. + // They need to be converted back to addresses. + Code::cast(object)->ConvertICTargetsFromObjectToAddress(); + } + if (!is_previous_alive) { // Transition from free to live. + dealloc(free_start, current - free_start); + is_previous_alive = true; + } + } else { + if (object->IsCode()) { + // Notify the logger that compiled code has been collected. + LOG(CodeDeleteEvent(Code::cast(object)->address())); + } + if (is_previous_alive) { // Transition from live to free. + free_start = current; + is_previous_alive = false; + } + } + // The object is now unmarked for the call to Size() at the top of the + // loop. + } + + // If the last region was not live we need to from free_start to the + // allocation top in the page. + if (!is_previous_alive) { + int free_size = p->AllocationTop() - free_start; + if (free_size > 0) { + dealloc(free_start, free_size); + } + } + } +} + + +void MarkCompactCollector::DeallocateOldPointerBlock(Address start, + int size_in_bytes) { + Heap::ClearRSetRange(start, size_in_bytes); + Heap::old_pointer_space()->Free(start, size_in_bytes); +} + + +void MarkCompactCollector::DeallocateOldDataBlock(Address start, + int size_in_bytes) { + Heap::old_data_space()->Free(start, size_in_bytes); +} + + +void MarkCompactCollector::DeallocateCodeBlock(Address start, + int size_in_bytes) { + Heap::code_space()->Free(start, size_in_bytes); +} + + +void MarkCompactCollector::DeallocateMapBlock(Address start, + int size_in_bytes) { + // Objects in map space are frequently assumed to have size Map::kSize and a + // valid map in their first word. Thus, we break the free block up into + // chunks and free them separately. + ASSERT(size_in_bytes % Map::kSize == 0); + Heap::ClearRSetRange(start, size_in_bytes); + Address end = start + size_in_bytes; + for (Address a = start; a < end; a += Map::kSize) { + Heap::map_space()->Free(a); + } +} + + +void MarkCompactCollector::EncodeForwardingAddresses() { + ASSERT(state_ == ENCODE_FORWARDING_ADDRESSES); + // Objects in the active semispace of the young generation may be + // relocated to the inactive semispace (if not promoted). Set the + // relocation info to the beginning of the inactive semispace. + Heap::new_space()->MCResetRelocationInfo(); + + // Compute the forwarding pointers in each space. + EncodeForwardingAddressesInPagedSpace<MCAllocateFromOldPointerSpace, + IgnoreNonLiveObject>( + Heap::old_pointer_space()); + + EncodeForwardingAddressesInPagedSpace<MCAllocateFromOldDataSpace, + IgnoreNonLiveObject>( + Heap::old_data_space()); + + EncodeForwardingAddressesInPagedSpace<MCAllocateFromCodeSpace, + LogNonLiveCodeObject>( + Heap::code_space()); + + // Compute new space next to last after the old and code spaces have been + // compacted. Objects in new space can be promoted to old or code space. + EncodeForwardingAddressesInNewSpace(); + + // Compute map space last because computing forwarding addresses + // overwrites non-live objects. Objects in the other spaces rely on + // non-live map pointers to get the sizes of non-live objects. + EncodeForwardingAddressesInPagedSpace<MCAllocateFromMapSpace, + IgnoreNonLiveObject>( + Heap::map_space()); + + // Write relocation info to the top page, so we can use it later. This is + // done after promoting objects from the new space so we get the correct + // allocation top. + Heap::old_pointer_space()->MCWriteRelocationInfoToPage(); + Heap::old_data_space()->MCWriteRelocationInfoToPage(); + Heap::code_space()->MCWriteRelocationInfoToPage(); + Heap::map_space()->MCWriteRelocationInfoToPage(); +} + + +void MarkCompactCollector::SweepSpaces() { + ASSERT(state_ == SWEEP_SPACES); + ASSERT(!IsCompacting()); + // Noncompacting collections simply sweep the spaces to clear the mark + // bits and free the nonlive blocks (for old and map spaces). We sweep + // the map space last because freeing non-live maps overwrites them and + // the other spaces rely on possibly non-live maps to get the sizes for + // non-live objects. + SweepSpace(Heap::old_pointer_space(), &DeallocateOldPointerBlock); + SweepSpace(Heap::old_data_space(), &DeallocateOldDataBlock); + SweepSpace(Heap::code_space(), &DeallocateCodeBlock); + SweepSpace(Heap::new_space()); + SweepSpace(Heap::map_space(), &DeallocateMapBlock); +} + + +// Iterate the live objects in a range of addresses (eg, a page or a +// semispace). The live regions of the range have been linked into a list. +// The first live region is [first_live_start, first_live_end), and the last +// address in the range is top. The callback function is used to get the +// size of each live object. +int MarkCompactCollector::IterateLiveObjectsInRange( + Address start, + Address end, + HeapObjectCallback size_func) { + int live_objects = 0; + Address current = start; + while (current < end) { + uint32_t encoded_map = Memory::uint32_at(current); + if (encoded_map == kSingleFreeEncoding) { + current += kPointerSize; + } else if (encoded_map == kMultiFreeEncoding) { + current += Memory::int_at(current + kIntSize); + } else { + live_objects++; + current += size_func(HeapObject::FromAddress(current)); + } + } + return live_objects; +} + + +int MarkCompactCollector::IterateLiveObjects(NewSpace* space, + HeapObjectCallback size_f) { + ASSERT(MARK_LIVE_OBJECTS < state_ && state_ <= RELOCATE_OBJECTS); + return IterateLiveObjectsInRange(space->bottom(), space->top(), size_f); +} + + +int MarkCompactCollector::IterateLiveObjects(PagedSpace* space, + HeapObjectCallback size_f) { + ASSERT(MARK_LIVE_OBJECTS < state_ && state_ <= RELOCATE_OBJECTS); + int total = 0; + PageIterator it(space, PageIterator::PAGES_IN_USE); + while (it.has_next()) { + Page* p = it.next(); + total += IterateLiveObjectsInRange(p->ObjectAreaStart(), + p->AllocationTop(), + size_f); + } + return total; +} + + +// ------------------------------------------------------------------------- +// Phase 3: Update pointers + +// Helper class for updating pointers in HeapObjects. +class UpdatingVisitor: public ObjectVisitor { + public: + void VisitPointer(Object** p) { + UpdatePointer(p); + } + + void VisitPointers(Object** start, Object** end) { + // Mark all HeapObject pointers in [start, end) + for (Object** p = start; p < end; p++) UpdatePointer(p); + } + + private: + void UpdatePointer(Object** p) { + if (!(*p)->IsHeapObject()) return; + + HeapObject* obj = HeapObject::cast(*p); + Address old_addr = obj->address(); + Address new_addr; + ASSERT(!Heap::InFromSpace(obj)); + + if (Heap::new_space()->Contains(obj)) { + Address f_addr = Heap::new_space()->FromSpaceLow() + + Heap::new_space()->ToSpaceOffsetForAddress(old_addr); + new_addr = Memory::Address_at(f_addr); + +#ifdef DEBUG + ASSERT(Heap::old_pointer_space()->Contains(new_addr) || + Heap::old_data_space()->Contains(new_addr) || + Heap::code_space()->Contains(new_addr) || + Heap::new_space()->FromSpaceContains(new_addr)); + + if (Heap::new_space()->FromSpaceContains(new_addr)) { + ASSERT(Heap::new_space()->FromSpaceOffsetForAddress(new_addr) <= + Heap::new_space()->ToSpaceOffsetForAddress(old_addr)); + } +#endif + + } else if (Heap::lo_space()->Contains(obj)) { + // Don't move objects in the large object space. + return; + + } else { + ASSERT(Heap::old_pointer_space()->Contains(obj) || + Heap::old_data_space()->Contains(obj) || + Heap::code_space()->Contains(obj) || + Heap::map_space()->Contains(obj)); + + new_addr = MarkCompactCollector::GetForwardingAddressInOldSpace(obj); + ASSERT(Heap::old_pointer_space()->Contains(new_addr) || + Heap::old_data_space()->Contains(new_addr) || + Heap::code_space()->Contains(new_addr) || + Heap::map_space()->Contains(new_addr)); + +#ifdef DEBUG + if (Heap::old_pointer_space()->Contains(obj)) { + ASSERT(Heap::old_pointer_space()->MCSpaceOffsetForAddress(new_addr) <= + Heap::old_pointer_space()->MCSpaceOffsetForAddress(old_addr)); + } else if (Heap::old_data_space()->Contains(obj)) { + ASSERT(Heap::old_data_space()->MCSpaceOffsetForAddress(new_addr) <= + Heap::old_data_space()->MCSpaceOffsetForAddress(old_addr)); + } else if (Heap::code_space()->Contains(obj)) { + ASSERT(Heap::code_space()->MCSpaceOffsetForAddress(new_addr) <= + Heap::code_space()->MCSpaceOffsetForAddress(old_addr)); + } else { + ASSERT(Heap::map_space()->MCSpaceOffsetForAddress(new_addr) <= + Heap::map_space()->MCSpaceOffsetForAddress(old_addr)); + } +#endif + } + + *p = HeapObject::FromAddress(new_addr); + +#ifdef DEBUG + if (FLAG_gc_verbose) { + PrintF("update %p : %p -> %p\n", + reinterpret_cast<Address>(p), old_addr, new_addr); + } +#endif + } +}; + + +void MarkCompactCollector::UpdatePointers() { +#ifdef DEBUG + ASSERT(state_ == ENCODE_FORWARDING_ADDRESSES); + state_ = UPDATE_POINTERS; +#endif + UpdatingVisitor updating_visitor; + Heap::IterateRoots(&updating_visitor); + GlobalHandles::IterateWeakRoots(&updating_visitor); + + int live_maps = IterateLiveObjects(Heap::map_space(), + &UpdatePointersInOldObject); + int live_pointer_olds = IterateLiveObjects(Heap::old_pointer_space(), + &UpdatePointersInOldObject); + int live_data_olds = IterateLiveObjects(Heap::old_data_space(), + &UpdatePointersInOldObject); + int live_codes = IterateLiveObjects(Heap::code_space(), + &UpdatePointersInOldObject); + int live_news = IterateLiveObjects(Heap::new_space(), + &UpdatePointersInNewObject); + + // Large objects do not move, the map word can be updated directly. + LargeObjectIterator it(Heap::lo_space()); + while (it.has_next()) UpdatePointersInNewObject(it.next()); + + USE(live_maps); + USE(live_pointer_olds); + USE(live_data_olds); + USE(live_codes); + USE(live_news); + +#ifdef DEBUG + ASSERT(live_maps == live_map_objects_); + ASSERT(live_data_olds == live_old_data_objects_); + ASSERT(live_pointer_olds == live_old_pointer_objects_); + ASSERT(live_codes == live_code_objects_); + ASSERT(live_news == live_young_objects_); +#endif +} + + +int MarkCompactCollector::UpdatePointersInNewObject(HeapObject* obj) { + // Keep old map pointers + Map* old_map = obj->map(); + ASSERT(old_map->IsHeapObject()); + + Address forwarded = GetForwardingAddressInOldSpace(old_map); + + ASSERT(Heap::map_space()->Contains(old_map)); + ASSERT(Heap::map_space()->Contains(forwarded)); +#ifdef DEBUG + if (FLAG_gc_verbose) { + PrintF("update %p : %p -> %p\n", obj->address(), old_map->address(), + forwarded); + } +#endif + // Update the map pointer. + obj->set_map(reinterpret_cast<Map*>(HeapObject::FromAddress(forwarded))); + + // We have to compute the object size relying on the old map because + // map objects are not relocated yet. + int obj_size = obj->SizeFromMap(old_map); + + // Update pointers in the object body. + UpdatingVisitor updating_visitor; + obj->IterateBody(old_map->instance_type(), obj_size, &updating_visitor); + return obj_size; +} + + +int MarkCompactCollector::UpdatePointersInOldObject(HeapObject* obj) { + // Decode the map pointer. + MapWord encoding = obj->map_word(); + Address map_addr = encoding.DecodeMapAddress(Heap::map_space()); + ASSERT(Heap::map_space()->Contains(HeapObject::FromAddress(map_addr))); + + // At this point, the first word of map_addr is also encoded, cannot + // cast it to Map* using Map::cast. + Map* map = reinterpret_cast<Map*>(HeapObject::FromAddress(map_addr)); + int obj_size = obj->SizeFromMap(map); + InstanceType type = map->instance_type(); + + // Update map pointer. + Address new_map_addr = GetForwardingAddressInOldSpace(map); + int offset = encoding.DecodeOffset(); + obj->set_map_word(MapWord::EncodeAddress(new_map_addr, offset)); + +#ifdef DEBUG + if (FLAG_gc_verbose) { + PrintF("update %p : %p -> %p\n", obj->address(), + map_addr, new_map_addr); + } +#endif + + // Update pointers in the object body. + UpdatingVisitor updating_visitor; + obj->IterateBody(type, obj_size, &updating_visitor); + return obj_size; +} + + +Address MarkCompactCollector::GetForwardingAddressInOldSpace(HeapObject* obj) { + // Object should either in old or map space. + MapWord encoding = obj->map_word(); + + // Offset to the first live object's forwarding address. + int offset = encoding.DecodeOffset(); + Address obj_addr = obj->address(); + + // Find the first live object's forwarding address. + Page* p = Page::FromAddress(obj_addr); + Address first_forwarded = p->mc_first_forwarded; + + // Page start address of forwarded address. + Page* forwarded_page = Page::FromAddress(first_forwarded); + int forwarded_offset = forwarded_page->Offset(first_forwarded); + + // Find end of allocation of in the page of first_forwarded. + Address mc_top = forwarded_page->mc_relocation_top; + int mc_top_offset = forwarded_page->Offset(mc_top); + + // Check if current object's forward pointer is in the same page + // as the first live object's forwarding pointer + if (forwarded_offset + offset < mc_top_offset) { + // In the same page. + return first_forwarded + offset; + } + + // Must be in the next page, NOTE: this may cross chunks. + Page* next_page = forwarded_page->next_page(); + ASSERT(next_page->is_valid()); + + offset -= (mc_top_offset - forwarded_offset); + offset += Page::kObjectStartOffset; + + ASSERT_PAGE_OFFSET(offset); + ASSERT(next_page->OffsetToAddress(offset) < next_page->mc_relocation_top); + + return next_page->OffsetToAddress(offset); +} + + +// ------------------------------------------------------------------------- +// Phase 4: Relocate objects + +void MarkCompactCollector::RelocateObjects() { +#ifdef DEBUG + ASSERT(state_ == UPDATE_POINTERS); + state_ = RELOCATE_OBJECTS; +#endif + // Relocates objects, always relocate map objects first. Relocating + // objects in other space relies on map objects to get object size. + int live_maps = IterateLiveObjects(Heap::map_space(), &RelocateMapObject); + int live_pointer_olds = IterateLiveObjects(Heap::old_pointer_space(), + &RelocateOldPointerObject); + int live_data_olds = IterateLiveObjects(Heap::old_data_space(), + &RelocateOldDataObject); + int live_codes = IterateLiveObjects(Heap::code_space(), &RelocateCodeObject); + int live_news = IterateLiveObjects(Heap::new_space(), &RelocateNewObject); + + USE(live_maps); + USE(live_data_olds); + USE(live_pointer_olds); + USE(live_codes); + USE(live_news); +#ifdef DEBUG + ASSERT(live_maps == live_map_objects_); + ASSERT(live_data_olds == live_old_data_objects_); + ASSERT(live_pointer_olds == live_old_pointer_objects_); + ASSERT(live_codes == live_code_objects_); + ASSERT(live_news == live_young_objects_); +#endif + + // Notify code object in LO to convert IC target to address + // This must happen after lo_space_->Compact + LargeObjectIterator it(Heap::lo_space()); + while (it.has_next()) { ConvertCodeICTargetToAddress(it.next()); } + + // Flips from and to spaces + Heap::new_space()->Flip(); + + // Sets age_mark to bottom in to space + Address mark = Heap::new_space()->bottom(); + Heap::new_space()->set_age_mark(mark); + + Heap::new_space()->MCCommitRelocationInfo(); +#ifdef DEBUG + // It is safe to write to the remembered sets as remembered sets on a + // page-by-page basis after committing the m-c forwarding pointer. + Page::set_rset_state(Page::IN_USE); +#endif + PagedSpaces spaces; + while (PagedSpace* space = spaces.next()) space->MCCommitRelocationInfo(); +} + + +int MarkCompactCollector::ConvertCodeICTargetToAddress(HeapObject* obj) { + if (obj->IsCode()) { + Code::cast(obj)->ConvertICTargetsFromObjectToAddress(); + } + return obj->Size(); +} + + +int MarkCompactCollector::RelocateMapObject(HeapObject* obj) { + // decode map pointer (forwarded address) + MapWord encoding = obj->map_word(); + Address map_addr = encoding.DecodeMapAddress(Heap::map_space()); + ASSERT(Heap::map_space()->Contains(HeapObject::FromAddress(map_addr))); + + // Get forwarding address before resetting map pointer + Address new_addr = GetForwardingAddressInOldSpace(obj); + + // recover map pointer + obj->set_map(reinterpret_cast<Map*>(HeapObject::FromAddress(map_addr))); + + // The meta map object may not be copied yet. + Address old_addr = obj->address(); + + if (new_addr != old_addr) { + memmove(new_addr, old_addr, Map::kSize); // copy contents + } + +#ifdef DEBUG + if (FLAG_gc_verbose) { + PrintF("relocate %p -> %p\n", old_addr, new_addr); + } +#endif + + return Map::kSize; +} + + +static inline int RelocateOldObject(HeapObject* obj, + OldSpace* space, + Address new_addr, + Address map_addr) { + // recover map pointer + obj->set_map(reinterpret_cast<Map*>(HeapObject::FromAddress(map_addr))); + + // This is a non-map object, it relies on the assumption that the Map space + // is compacted before the Old space (see RelocateObjects). + int obj_size = obj->Size(); + ASSERT_OBJECT_SIZE(obj_size); + + ASSERT(space->MCSpaceOffsetForAddress(new_addr) <= + space->MCSpaceOffsetForAddress(obj->address())); + + space->MCAdjustRelocationEnd(new_addr, obj_size); + +#ifdef DEBUG + if (FLAG_gc_verbose) { + PrintF("relocate %p -> %p\n", obj->address(), new_addr); + } +#endif + + return obj_size; +} + + +int MarkCompactCollector::RelocateOldNonCodeObject(HeapObject* obj, + OldSpace* space) { + // decode map pointer (forwarded address) + MapWord encoding = obj->map_word(); + Address map_addr = encoding.DecodeMapAddress(Heap::map_space()); + ASSERT(Heap::map_space()->Contains(map_addr)); + + // Get forwarding address before resetting map pointer + Address new_addr = GetForwardingAddressInOldSpace(obj); + + int obj_size = RelocateOldObject(obj, space, new_addr, map_addr); + + Address old_addr = obj->address(); + + if (new_addr != old_addr) { + memmove(new_addr, old_addr, obj_size); // copy contents + } + + ASSERT(!HeapObject::FromAddress(new_addr)->IsCode()); + + return obj_size; +} + + +int MarkCompactCollector::RelocateOldPointerObject(HeapObject* obj) { + return RelocateOldNonCodeObject(obj, Heap::old_pointer_space()); +} + + +int MarkCompactCollector::RelocateOldDataObject(HeapObject* obj) { + return RelocateOldNonCodeObject(obj, Heap::old_data_space()); +} + + +int MarkCompactCollector::RelocateCodeObject(HeapObject* obj) { + // decode map pointer (forwarded address) + MapWord encoding = obj->map_word(); + Address map_addr = encoding.DecodeMapAddress(Heap::map_space()); + ASSERT(Heap::map_space()->Contains(HeapObject::FromAddress(map_addr))); + + // Get forwarding address before resetting map pointer + Address new_addr = GetForwardingAddressInOldSpace(obj); + + int obj_size = RelocateOldObject(obj, Heap::code_space(), new_addr, map_addr); + + // convert inline cache target to address using old address + if (obj->IsCode()) { + // convert target to address first related to old_address + Code::cast(obj)->ConvertICTargetsFromObjectToAddress(); + } + + Address old_addr = obj->address(); + + if (new_addr != old_addr) { + memmove(new_addr, old_addr, obj_size); // copy contents + } + + HeapObject* copied_to = HeapObject::FromAddress(new_addr); + if (copied_to->IsCode()) { + // may also update inline cache target. + Code::cast(copied_to)->Relocate(new_addr - old_addr); + // Notify the logger that compiled code has moved. + LOG(CodeMoveEvent(old_addr, new_addr)); + } + + return obj_size; +} + + +int MarkCompactCollector::RelocateNewObject(HeapObject* obj) { + int obj_size = obj->Size(); + + // Get forwarding address + Address old_addr = obj->address(); + int offset = Heap::new_space()->ToSpaceOffsetForAddress(old_addr); + + Address new_addr = + Memory::Address_at(Heap::new_space()->FromSpaceLow() + offset); + + if (Heap::new_space()->FromSpaceContains(new_addr)) { + ASSERT(Heap::new_space()->FromSpaceOffsetForAddress(new_addr) <= + Heap::new_space()->ToSpaceOffsetForAddress(old_addr)); + } else { + OldSpace* target_space = Heap::TargetSpace(obj); + ASSERT(target_space == Heap::old_pointer_space() || + target_space == Heap::old_data_space()); + target_space->MCAdjustRelocationEnd(new_addr, obj_size); + } + + // New and old addresses cannot overlap. + memcpy(reinterpret_cast<void*>(new_addr), + reinterpret_cast<void*>(old_addr), + obj_size); + +#ifdef DEBUG + if (FLAG_gc_verbose) { + PrintF("relocate %p -> %p\n", old_addr, new_addr); + } +#endif + + return obj_size; +} + + +// ------------------------------------------------------------------------- +// Phase 5: rebuild remembered sets + +void MarkCompactCollector::RebuildRSets() { +#ifdef DEBUG + ASSERT(state_ == RELOCATE_OBJECTS); + state_ = REBUILD_RSETS; +#endif + Heap::RebuildRSets(); +} + +} } // namespace v8::internal |