[heap] Refactor evacuation for young and old gen into visitors.

src/heap/mark-compact.cc

Index: src/heap/mark-compact.cc
diff --git a/src/heap/mark-compact.cc b/src/heap/mark-compact.cc
index 884a8abc285cc183e349a474ee6bbf215c6bad15..980e4b3d373aeba23d242eec949edd1001a912b4 100644
--- a/src/heap/mark-compact.cc
+++ b/src/heap/mark-compact.cc
@@ -236,6 +236,11 @@ static void VerifyEvacuation(Heap* heap) {
 
 
 void MarkCompactCollector::SetUp() {
+  DCHECK(strcmp(Marking::kWhiteBitPattern, "00") == 0);
+  DCHECK(strcmp(Marking::kBlackBitPattern, "10") == 0);
+  DCHECK(strcmp(Marking::kGreyBitPattern, "11") == 0);
+  DCHECK(strcmp(Marking::kImpossibleBitPattern, "01") == 0);
+
   free_list_old_space_.Reset(new FreeList(heap_->old_space()));
   free_list_code_space_.Reset(new FreeList(heap_->code_space()));
   free_list_map_space_.Reset(new FreeList(heap_->map_space()));
@@ -1499,69 +1504,119 @@ void MarkCompactCollector::DiscoverGreyObjectsOnPage(MemoryChunk* p) {
 }
 
 
-int MarkCompactCollector::DiscoverAndEvacuateBlackObjectsOnPage(
-    NewSpace* new_space, NewSpacePage* p) {
-  DCHECK(strcmp(Marking::kWhiteBitPattern, "00") == 0);
-  DCHECK(strcmp(Marking::kBlackBitPattern, "10") == 0);
-  DCHECK(strcmp(Marking::kGreyBitPattern, "11") == 0);
-  DCHECK(strcmp(Marking::kImpossibleBitPattern, "01") == 0);
+class MarkCompactCollector::HeapObjectVisitor {
+ public:
+  virtual ~HeapObjectVisitor() {}
+  virtual bool Visit(HeapObject* object) = 0;
+};
 
-  MarkBit::CellType* cells = p->markbits()->cells();
-  int survivors_size = 0;
 
-  for (MarkBitCellIterator it(p); !it.Done(); it.Advance()) {
-    Address cell_base = it.CurrentCellBase();
-    MarkBit::CellType* cell = it.CurrentCell();
+class MarkCompactCollector::EvacuateNewSpaceVisitor
+    : public MarkCompactCollector::HeapObjectVisitor {
+ public:
+  explicit EvacuateNewSpaceVisitor(Heap* heap) : heap_(heap) {}
 
-    MarkBit::CellType current_cell = *cell;
-    if (current_cell == 0) continue;
+  virtual bool Visit(HeapObject* object) {
+    Heap::UpdateAllocationSiteFeedback(object, Heap::RECORD_SCRATCHPAD_SLOT);
+    int size = object->Size();
 
-    int offset = 0;
-    while (current_cell != 0) {
-      int trailing_zeros = base::bits::CountTrailingZeros32(current_cell);
-      current_cell >>= trailing_zeros;
-      offset += trailing_zeros;
-      Address address = cell_base + offset * kPointerSize;
-      HeapObject* object = HeapObject::FromAddress(address);
-      DCHECK(Marking::IsBlack(Marking::MarkBitFrom(object)));
+    // TODO(hpayer): Refactor EvacuateObject and call this function instead.
+    if (heap_->ShouldBePromoted(object->address(), size) &&
+        heap_->mark_compact_collector()->TryPromoteObject(object, size)) {
+      return true;
+    }
 
-      int size = object->Size();
-      survivors_size += size;
+    AllocationAlignment alignment = object->RequiredAlignment();
+    AllocationResult allocation =
+        heap_->new_space()->AllocateRaw(size, alignment);
+    if (allocation.IsRetry()) {
+      if (!heap_->new_space()->AddFreshPage()) {
+        // Shouldn't happen. We are sweeping linearly, and to-space
+        // has the same number of pages as from-space, so there is
+        // always room unless we are in an OOM situation.
+        FatalProcessOutOfMemory("MarkCompactCollector: semi-space copy\n");
+      }
+      allocation = heap_->new_space()->AllocateRaw(size, alignment);
+      DCHECK(!allocation.IsRetry());
+    }
+    Object* target = allocation.ToObjectChecked();
+
+    heap_->mark_compact_collector()->MigrateObject(
+        HeapObject::cast(target), object, size, NEW_SPACE, nullptr);
+    if (V8_UNLIKELY(target->IsJSArrayBuffer())) {
+      heap_->array_buffer_tracker()->MarkLive(JSArrayBuffer::cast(target));
+    }
+    heap_->IncrementSemiSpaceCopiedObjectSize(size);
+    return true;
+  }
 
-      Heap::UpdateAllocationSiteFeedback(object, Heap::RECORD_SCRATCHPAD_SLOT);
+ private:
+  Heap* heap_;
+};
 
-      offset += 2;
-      current_cell >>= 2;
 
-      // TODO(hpayer): Refactor EvacuateObject and call this function instead.
-      if (heap()->ShouldBePromoted(object->address(), size) &&
-          TryPromoteObject(object, size)) {
-        continue;
-      }
+class MarkCompactCollector::EvacuateOldSpaceVisitor
+    : public MarkCompactCollector::HeapObjectVisitor {
+ public:
+  EvacuateOldSpaceVisitor(Heap* heap,
+                          CompactionSpaceCollection* compaction_spaces,
+                          SlotsBuffer** evacuation_slots_buffer)
+      : heap_(heap),
+        compaction_spaces_(compaction_spaces),
+        evacuation_slots_buffer_(evacuation_slots_buffer) {}
 
-      AllocationAlignment alignment = object->RequiredAlignment();
-      AllocationResult allocation = new_space->AllocateRaw(size, alignment);
-      if (allocation.IsRetry()) {
-        if (!new_space->AddFreshPage()) {
-          // Shouldn't happen. We are sweeping linearly, and to-space
-          // has the same number of pages as from-space, so there is
-          // always room unless we are in an OOM situation.
-          FatalProcessOutOfMemory("MarkCompactCollector: semi-space copy\n");
-        }
-        allocation = new_space->AllocateRaw(size, alignment);
-        DCHECK(!allocation.IsRetry());
-      }
-      Object* target = allocation.ToObjectChecked();
+  virtual bool Visit(HeapObject* object) {
+    int size = object->Size();
+    AllocationAlignment alignment = object->RequiredAlignment();
+    HeapObject* target_object = nullptr;
+    AllocationSpace id =
+        Page::FromAddress(object->address())->owner()->identity();
+    AllocationResult allocation =
+        compaction_spaces_->Get(id)->AllocateRaw(size, alignment);
+    if (!allocation.To(&target_object)) {
+      return false;
+    }
+    heap_->mark_compact_collector()->MigrateObject(
+        target_object, object, size, id, evacuation_slots_buffer_);
+    DCHECK(object->map_word().IsForwardingAddress());
+    return true;
+  }
+
+ private:
+  Heap* heap_;
+  CompactionSpaceCollection* compaction_spaces_;
+  SlotsBuffer** evacuation_slots_buffer_;
+};
+
+
+bool MarkCompactCollector::IterateLiveObjectsOnPage(MemoryChunk* page,
+                                                    HeapObjectVisitor* visitor,
+                                                    IterationMode mode) {
+  Address offsets[16];
+  for (MarkBitCellIterator it(page); !it.Done(); it.Advance()) {
+    Address cell_base = it.CurrentCellBase();
+    MarkBit::CellType* cell = it.CurrentCell();
+
+    if (*cell == 0) continue;
 
-      MigrateObject(HeapObject::cast(target), object, size, NEW_SPACE, nullptr);
-      if (V8_UNLIKELY(target->IsJSArrayBuffer())) {
-        heap()->array_buffer_tracker()->MarkLive(JSArrayBuffer::cast(target));
+    int live_objects = MarkWordToObjectStarts(*cell, cell_base, offsets);
+    for (int i = 0; i < live_objects; i++) {
+      HeapObject* object = HeapObject::FromAddress(offsets[i]);
+      DCHECK(Marking::IsBlack(Marking::MarkBitFrom(object)));
+      if (!visitor->Visit(object)) {
+        if ((mode == kClearMarkbits) && (i > 0)) {
+          page->markbits()->ClearRange(
+              page->AddressToMarkbitIndex(page->area_start()),
+              page->AddressToMarkbitIndex(offsets[i]));
+        }
+        return false;
       }
-      heap()->IncrementSemiSpaceCopiedObjectSize(size);
     }
-    *cells = 0;
+    if (mode == kClearMarkbits) {
+      *cell = 0;
+    }
   }
-  return survivors_size;
+  return true;
 }
 
 
@@ -3082,9 +3137,13 @@ void MarkCompactCollector::EvacuateNewSpace() {
   // new entries in the store buffer and may cause some pages to be marked
   // scan-on-scavenge.
   NewSpacePageIterator it(from_bottom, from_top);
+  EvacuateNewSpaceVisitor new_space_visitor(heap());
   while (it.has_next()) {
     NewSpacePage* p = it.next();
-    survivors_size += DiscoverAndEvacuateBlackObjectsOnPage(new_space, p);
+    survivors_size += p->LiveBytes();
+    bool ok = IterateLiveObjectsOnPage(p, &new_space_visitor, kClearMarkbits);
+    USE(ok);
+    DCHECK(ok);
   }
 
   heap_->IncrementYoungSurvivorsCounter(survivors_size);
@@ -3099,50 +3158,6 @@ void MarkCompactCollector::AddEvacuationSlotsBufferSynchronized(
 }
 
 
-bool MarkCompactCollector::EvacuateLiveObjectsFromPage(
-    Page* p, PagedSpace* target_space, SlotsBuffer** evacuation_slots_buffer) {
-  AlwaysAllocateScope always_allocate(isolate());
-  DCHECK(p->IsEvacuationCandidate() && !p->WasSwept());
-
-  Address starts[16];
-  for (MarkBitCellIterator it(p); !it.Done(); it.Advance()) {
-    Address cell_base = it.CurrentCellBase();
-    MarkBit::CellType* cell = it.CurrentCell();
-
-    if (*cell == 0) continue;
-
-    int live_objects = MarkWordToObjectStarts(*cell, cell_base, starts);
-    for (int i = 0; i < live_objects; i++) {
-      HeapObject* object = HeapObject::FromAddress(starts[i]);
-      DCHECK(Marking::IsBlack(Marking::MarkBitFrom(object)));
-
-      int size = object->Size();
-      AllocationAlignment alignment = object->RequiredAlignment();
-      HeapObject* target_object = nullptr;
-      AllocationResult allocation = target_space->AllocateRaw(size, alignment);
-      if (!allocation.To(&target_object)) {
-        // We need to abort compaction for this page. Make sure that we reset
-        // the mark bits for objects that have already been migrated.
-        if (i > 0) {
-          p->markbits()->ClearRange(p->AddressToMarkbitIndex(p->area_start()),
-                                    p->AddressToMarkbitIndex(starts[i]));
-        }
-        return false;
-      }
-
-      MigrateObject(target_object, object, size, target_space->identity(),
-                    evacuation_slots_buffer);
-      DCHECK(object->map_word().IsForwardingAddress());
-    }
-
-    // Clear marking bits for current cell.
-    *cell = 0;
-  }
-  p->ResetLiveBytes();
-  return true;
-}
-
-
 int MarkCompactCollector::NumberOfParallelCompactionTasks() {
   if (!FLAG_parallel_compaction) return 1;
   // Compute the number of needed tasks based on a target compaction time, the
@@ -3307,6 +3322,8 @@ void MarkCompactCollector::WaitUntilCompactionCompleted(uint32_t* task_ids,
 void MarkCompactCollector::EvacuatePages(
     CompactionSpaceCollection* compaction_spaces,
     SlotsBuffer** evacuation_slots_buffer) {
+  EvacuateOldSpaceVisitor visitor(heap(), compaction_spaces,
+                                  evacuation_slots_buffer);
   for (int i = 0; i < evacuation_candidates_.length(); i++) {
     Page* p = evacuation_candidates_[i];
     DCHECK(p->IsEvacuationCandidate() ||
@@ -3320,9 +3337,8 @@ void MarkCompactCollector::EvacuatePages(
                   MemoryChunk::kCompactingInProgress);
         double start = heap()->MonotonicallyIncreasingTimeInMs();
         intptr_t live_bytes = p->LiveBytes();
-        if (EvacuateLiveObjectsFromPage(
-                p, compaction_spaces->Get(p->owner()->identity()),
-                evacuation_slots_buffer)) {
+        if (IterateLiveObjectsOnPage(p, &visitor, kClearMarkbits)) {
+          p->ResetLiveBytes();
           p->parallel_compaction_state().SetValue(
               MemoryChunk::kCompactingFinalize);
           compaction_spaces->ReportCompactionProgress(