Remove lazy sweeping of new space and corresponding complicated pointer updating logic.

src/heap/store-buffer.cc

 // Copyright 2011 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include <algorithm>
 
 #include "src/v8.h"
 
 #include "src/base/atomicops.h"
 #include "src/counters.h"
@@ skipping 361 matching lines @@
   during_gc_ = false;
 #ifdef VERIFY_HEAP
   if (FLAG_verify_heap) {
     Verify();
   }
 #endif
 }
 
 
 void StoreBuffer::ProcessOldToNewSlot(Address slot_address,
-                                      ObjectSlotCallback slot_callback,
-                                      bool clear_maps) {
+                                      ObjectSlotCallback slot_callback) {
   Object** slot = reinterpret_cast<Object**>(slot_address);
   Object* object = reinterpret_cast<Object*>(
       base::NoBarrier_Load(reinterpret_cast<base::AtomicWord*>(slot)));
 
   // If the object is not in from space, it must be a duplicate store buffer
   // entry and the slot was already updated.
   if (heap_->InFromSpace(object)) {
     HeapObject* heap_object = reinterpret_cast<HeapObject*>(object);
     DCHECK(heap_object->IsHeapObject());
-    // The new space object was not promoted if it still contains a map
-    // pointer. Clear the map field now lazily (during full GC).
-    if (clear_maps) ClearDeadObject(heap_object);
     slot_callback(reinterpret_cast<HeapObject**>(slot), heap_object);
     object = reinterpret_cast<Object*>(
         base::NoBarrier_Load(reinterpret_cast<base::AtomicWord*>(slot)));
     // If the object was in from space before and is after executing the
     // callback in to space, the object is still live.
     // Unfortunately, we do not know about the slot. It could be in a
     // just freed free space object.
     if (heap_->InToSpace(object)) {
       EnterDirectlyIntoStoreBuffer(reinterpret_cast<Address>(slot));
     }
   }
 }
 
 
 void StoreBuffer::FindPointersToNewSpaceInRegion(
-    Address start, Address end, ObjectSlotCallback slot_callback,
-    bool clear_maps) {
+    Address start, Address end, ObjectSlotCallback slot_callback) {
   for (Address slot_address = start; slot_address < end;
        slot_address += kPointerSize) {
-    ProcessOldToNewSlot(slot_address, slot_callback, clear_maps);
+    ProcessOldToNewSlot(slot_address, slot_callback);
   }
 }
 
 
-void StoreBuffer::IteratePointersInStoreBuffer(ObjectSlotCallback slot_callback,
-                                               bool clear_maps) {
+void StoreBuffer::IteratePointersInStoreBuffer(
+    ObjectSlotCallback slot_callback) {
   Address* limit = old_top_;
   old_top_ = old_start_;
   {
     DontMoveStoreBufferEntriesScope scope(this);
     for (Address* current = old_start_; current < limit; current++) {
 #ifdef DEBUG
       Address* saved_top = old_top_;
 #endif
-      ProcessOldToNewSlot(*current, slot_callback, clear_maps);
+      ProcessOldToNewSlot(*current, slot_callback);
       DCHECK(old_top_ == saved_top + 1 || old_top_ == saved_top);
     }
   }
 }
 
 
 void StoreBuffer::ClearInvalidStoreBufferEntries() {
   Compact();
   Address* new_top = old_start_;
   for (Address* current = old_start_; current < old_top_; current++) {
@@ skipping 30 matching lines @@
         base::NoBarrier_Load(reinterpret_cast<base::AtomicWord*>(slot)));
     CHECK(heap_->InNewSpace(object));
     heap_->mark_compact_collector()->VerifyIsSlotInLiveObject(
         reinterpret_cast<HeapObject**>(slot),
         reinterpret_cast<HeapObject*>(object));
   }
 }
 
 
 void StoreBuffer::IteratePointersToNewSpace(ObjectSlotCallback slot_callback) {
-  IteratePointersToNewSpace(slot_callback, false);
-}
-
-
-void StoreBuffer::IteratePointersToNewSpaceAndClearMaps(
-    ObjectSlotCallback slot_callback) {
-  IteratePointersToNewSpace(slot_callback, true);
-}
-
-
-void StoreBuffer::IteratePointersToNewSpace(ObjectSlotCallback slot_callback,
-                                            bool clear_maps) {
   // We do not sort or remove duplicated entries from the store buffer because
   // we expect that callback will rebuild the store buffer thus removing
   // all duplicates and pointers to old space.
   bool some_pages_to_scan = PrepareForIteration();
 
   // TODO(gc): we want to skip slots on evacuation candidates
   // but we can't simply figure that out from slot address
   // because slot can belong to a large object.
-  IteratePointersInStoreBuffer(slot_callback, clear_maps);
+  IteratePointersInStoreBuffer(slot_callback);
 
   // We are done scanning all the pointers that were in the store buffer, but
   // there may be some pages marked scan_on_scavenge that have pointers to new
   // space that are not in the store buffer.  We must scan them now.  As we
   // scan, the surviving pointers to new space will be added to the store
   // buffer.  If there are still a lot of pointers to new space then we will
   // keep the scan_on_scavenge flag on the page and discard the pointers that
   // were added to the store buffer.  If there are not many pointers to new
   // space left on the page we will keep the pointers in the store buffer and
   // remove the flag from the page.
   if (some_pages_to_scan) {
     if (callback_ != NULL) {
       (*callback_)(heap_, NULL, kStoreBufferStartScanningPagesEvent);
     }
     PointerChunkIterator it(heap_);
     MemoryChunk* chunk;
     while ((chunk = it.next()) != NULL) {
       if (chunk->scan_on_scavenge()) {
         chunk->set_scan_on_scavenge(false);
         if (callback_ != NULL) {
           (*callback_)(heap_, chunk, kStoreBufferScanningPageEvent);
         }
         if (chunk->owner() == heap_->lo_space()) {
           LargePage* large_page = reinterpret_cast<LargePage*>(chunk);
           HeapObject* array = large_page->GetObject();
           DCHECK(array->IsFixedArray());
           Address start = array->address();
           Address end = start + array->Size();
-          FindPointersToNewSpaceInRegion(start, end, slot_callback, clear_maps);
+          FindPointersToNewSpaceInRegion(start, end, slot_callback);
         } else {
           Page* page = reinterpret_cast<Page*>(chunk);
           PagedSpace* owner = reinterpret_cast<PagedSpace*>(page->owner());
           if (owner == heap_->map_space()) {
             DCHECK(page->WasSwept());
             HeapObjectIterator iterator(page, NULL);
             for (HeapObject* heap_object = iterator.Next(); heap_object != NULL;
                  heap_object = iterator.Next()) {
               // We skip free space objects.
               if (!heap_object->IsFiller()) {
                 DCHECK(heap_object->IsMap());
                 FindPointersToNewSpaceInRegion(
                     heap_object->address() + Map::kPointerFieldsBeginOffset,
                     heap_object->address() + Map::kPointerFieldsEndOffset,
-                    slot_callback, clear_maps);
+                    slot_callback);
               }
             }
           } else {
             if (!page->SweepingCompleted()) {
               heap_->mark_compact_collector()->SweepInParallel(page, owner);
               if (!page->SweepingCompleted()) {
                 // We were not able to sweep that page, i.e., a concurrent
                 // sweeper thread currently owns this page.
                 // TODO(hpayer): This may introduce a huge pause here. We
                 // just care about finish sweeping of the scan on scavenge page.
@@ skipping 14 matching lines @@
                 LayoutDescriptorHelper helper(heap_object->map());
                 bool has_only_tagged_fields = helper.all_fields_tagged();
 
                 if (!has_only_tagged_fields) {
                   for (int offset = start_offset; offset < end_offset;) {
                     int end_of_region_offset;
                     if (helper.IsTagged(offset, end_offset,
                                         &end_of_region_offset)) {
                       FindPointersToNewSpaceInRegion(
                           obj_address + offset,
-                          obj_address + end_of_region_offset, slot_callback,
-                          clear_maps);
+                          obj_address + end_of_region_offset, slot_callback);
                     }
                     offset = end_of_region_offset;
                   }
                 } else {
 #endif
                   Address start_address = obj_address + start_offset;
                   Address end_address = obj_address + end_offset;
                   // Object has only tagged fields.
                   FindPointersToNewSpaceInRegion(start_address, end_address,
-                                                 slot_callback, clear_maps);
+                                                 slot_callback);
 #if V8_DOUBLE_FIELDS_UNBOXING
                 }
 #endif
               }
             }
           }
         }
       }
     }
     if (callback_ != NULL) {
@@ skipping 53 matching lines @@
     }
     old_buffer_is_sorted_ = false;
     old_buffer_is_filtered_ = false;
     *old_top_++ = reinterpret_cast<Address>(int_addr << kPointerSizeLog2);
     DCHECK(old_top_ <= old_limit_);
   }
   heap_->isolate()->counters()->store_buffer_compactions()->Increment();
 }
 }
 }  // namespace v8::internal