Filter invalid slots out from the SlotsBuffer after marking.

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 d7623cbec3f51970a978a3e83cd6aabe4ec58b5c..1e50fab3f9f994827caab898a6fa8720bd7a1f9f 100644
--- a/src/heap/mark-compact.cc
+++ b/src/heap/mark-compact.cc
@@ -287,6 +287,60 @@ bool MarkCompactCollector::StartCompaction(CompactionMode mode) {
 }
 
 
+void MarkCompactCollector::ClearInvalidSlotsBufferEntries(PagedSpace* space) {
+  PageIterator it(space);
+  while (it.has_next()) {
+    Page* p = it.next();
+    SlotsBuffer::RemoveInvalidSlots(heap_, p->slots_buffer());
+  }
+}
+
+
+void MarkCompactCollector::ClearInvalidStoreAndSlotsBufferEntries() {
+  heap_->store_buffer()->ClearInvalidStoreBufferEntries();
+
+  ClearInvalidSlotsBufferEntries(heap_->old_pointer_space());
+  ClearInvalidSlotsBufferEntries(heap_->old_data_space());
+  ClearInvalidSlotsBufferEntries(heap_->code_space());
+  ClearInvalidSlotsBufferEntries(heap_->cell_space());
+  ClearInvalidSlotsBufferEntries(heap_->map_space());
+
+  LargeObjectIterator it(heap_->lo_space());
+  for (HeapObject* object = it.Next(); object != NULL; object = it.Next()) {
+    MemoryChunk* chunk = MemoryChunk::FromAddress(object->address());
+    SlotsBuffer::RemoveInvalidSlots(heap_, chunk->slots_buffer());
+  }
+}
+
+
+#ifdef VERIFY_HEAP
+static void VerifyValidSlotsBufferEntries(Heap* heap, PagedSpace* space) {
+  PageIterator it(space);
+  while (it.has_next()) {
+    Page* p = it.next();
+    SlotsBuffer::VerifySlots(heap, p->slots_buffer());
+  }
+}
+
+
+static void VerifyValidStoreAndSlotsBufferEntries(Heap* heap) {
+  heap->store_buffer()->VerifyValidStoreBufferEntries();
+
+  VerifyValidSlotsBufferEntries(heap, heap->old_pointer_space());
+  VerifyValidSlotsBufferEntries(heap, heap->old_data_space());
+  VerifyValidSlotsBufferEntries(heap, heap->code_space());
+  VerifyValidSlotsBufferEntries(heap, heap->cell_space());
+  VerifyValidSlotsBufferEntries(heap, heap->map_space());
+
+  LargeObjectIterator it(heap->lo_space());
+  for (HeapObject* object = it.Next(); object != NULL; object = it.Next()) {
+    MemoryChunk* chunk = MemoryChunk::FromAddress(object->address());
+    SlotsBuffer::VerifySlots(heap, chunk->slots_buffer());
+  }
+}
+#endif
+
+
 void MarkCompactCollector::CollectGarbage() {
   // Make sure that Prepare() has been called. The individual steps below will
   // update the state as they proceed.
@@ -312,11 +366,11 @@ void MarkCompactCollector::CollectGarbage() {
   }
 #endif
 
-  heap_->store_buffer()->ClearInvalidStoreBufferEntries();
+  ClearInvalidStoreAndSlotsBufferEntries();
 
 #ifdef VERIFY_HEAP
   if (FLAG_verify_heap) {
-    heap_->store_buffer()->VerifyValidStoreBufferEntries();
+    VerifyValidStoreAndSlotsBufferEntries(heap_);
   }
 #endif
 
@@ -723,6 +777,7 @@ void MarkCompactCollector::CollectEvacuationCandidates(PagedSpace* space) {
 
   int count = 0;
   int fragmentation = 0;
+  int page_number = 0;
   Candidate* least = NULL;
 
   PageIterator it(space);
@@ -737,9 +792,16 @@ void MarkCompactCollector::CollectEvacuationCandidates(PagedSpace* space) {
     CHECK(p->slots_buffer() == NULL);
 
     if (FLAG_stress_compaction) {
-      unsigned int counter = space->heap()->ms_count();
-      uintptr_t page_number = reinterpret_cast<uintptr_t>(p) >> kPageSizeBits;
-      if ((counter & 1) == (page_number & 1)) fragmentation = 1;
+      if (FLAG_manual_evacuation_candidates_selection) {
+        if (p->IsFlagSet(MemoryChunk::FORCE_EVACUATION_CANDIDATE_FOR_TESTING)) {
+          p->ClearFlag(MemoryChunk::FORCE_EVACUATION_CANDIDATE_FOR_TESTING);
+          fragmentation = 1;
+        }
+      } else {
+        unsigned int counter = space->heap()->ms_count();
+        if ((counter & 1) == (page_number & 1)) fragmentation = 1;
+        page_number++;
+      }
     } else if (mode == REDUCE_MEMORY_FOOTPRINT && !FLAG_always_compact) {
       // Don't try to release too many pages.
       if (estimated_release >= over_reserved) {
@@ -3036,10 +3098,14 @@ bool MarkCompactCollector::TryPromoteObject(HeapObject* object,
 }
 
 
-bool MarkCompactCollector::IsSlotInBlackObject(Page* p, Address slot) {
+bool MarkCompactCollector::IsSlotInBlackObject(Page* p, Address slot,
+                                               HeapObject** out_object) {
   // This function does not support large objects right now.
   Space* owner = p->owner();
-  if (owner == heap_->lo_space() || owner == NULL) return true;
+  if (owner == heap_->lo_space() || owner == NULL) {
+    *out_object = NULL;
+    return true;
+  }
 
   uint32_t mark_bit_index = p->AddressToMarkbitIndex(slot);
   unsigned int start_index = mark_bit_index >> Bitmap::kBitsPerCellLog2;
@@ -3093,6 +3159,7 @@ bool MarkCompactCollector::IsSlotInBlackObject(Page* p, Address slot) {
       (object->address() + object->Size()) > slot) {
     // If the slot is within the last found object in the cell, the slot is
     // in a live object.
+    *out_object = object;
     return true;
   }
   return false;
@@ -3134,28 +3201,38 @@ bool MarkCompactCollector::IsSlotInBlackObjectSlow(Page* p, Address slot) {
 }
 
 
-bool MarkCompactCollector::IsSlotInLiveObject(HeapObject** address,
-                                              HeapObject* object) {
-  // If the target object is not black, the source slot must be part
-  // of a non-black (dead) object.
-  if (!Marking::IsBlack(Marking::MarkBitFrom(object))) {
-    return false;
-  }
-
+bool MarkCompactCollector::IsSlotInLiveObject(Address slot) {
+  HeapObject* object = NULL;
   // The target object is black but we don't know if the source slot is black.
   // The source object could have died and the slot could be part of a free
   // space. Find out based on mark bits if the slot is part of a live object.
-  if (!IsSlotInBlackObject(
-          Page::FromAddress(reinterpret_cast<Address>(address)),
-          reinterpret_cast<Address>(address))) {
+  if (!IsSlotInBlackObject(Page::FromAddress(slot), slot, &object)) {
     return false;
   }
 
+#if V8_DOUBLE_FIELDS_UNBOXING
+  // |object| is NULL only when the slot belongs to large object space.
+  DCHECK(object != NULL ||
+         Page::FromAnyPointerAddress(heap_, slot)->owner() ==
+             heap_->lo_space());
+  // We don't need to check large objects' layout descriptor since it can't
+  // contain in-object fields anyway.
+  if (object != NULL) {
+    // Filter out slots that happens to point to unboxed double fields.
+    LayoutDescriptorHelper helper(object->map());
+    bool has_only_tagged_fields = helper.all_fields_tagged();
+    if (!has_only_tagged_fields &&
+        !helper.IsTagged(static_cast<int>(slot - object->address()))) {
+      return false;
+    }
+  }
+#endif
+
   return true;
 }
 
 
-void MarkCompactCollector::VerifyIsSlotInLiveObject(HeapObject** address,
+void MarkCompactCollector::VerifyIsSlotInLiveObject(Address slot,
                                                     HeapObject* object) {
   // The target object has to be black.
   CHECK(Marking::IsBlack(Marking::MarkBitFrom(object)));
@@ -3163,9 +3240,7 @@ void MarkCompactCollector::VerifyIsSlotInLiveObject(HeapObject** address,
   // The target object is black but we don't know if the source slot is black.
   // The source object could have died and the slot could be part of a free
   // space. Use the mark bit iterator to find out about liveness of the slot.
-  CHECK(IsSlotInBlackObjectSlow(
-      Page::FromAddress(reinterpret_cast<Address>(address)),
-      reinterpret_cast<Address>(address)));
+  CHECK(IsSlotInBlackObjectSlow(Page::FromAddress(slot), slot));
 }
 
 
@@ -4484,6 +4559,66 @@ bool SlotsBuffer::AddTo(SlotsBufferAllocator* allocator,
 }
 
 
+static Object* g_smi_slot = NULL;
+
+
+void SlotsBuffer::RemoveInvalidSlots(Heap* heap, SlotsBuffer* buffer) {
+  DCHECK_EQ(Smi::FromInt(0), g_smi_slot);
+
+  // Remove entries by replacing them with a dummy slot containing a smi.
+  const ObjectSlot kRemovedEntry = &g_smi_slot;
+
+  while (buffer != NULL) {
+    SlotsBuffer::ObjectSlot* slots = buffer->slots_;
+    intptr_t slots_count = buffer->idx_;
+
+    for (int slot_idx = 0; slot_idx < slots_count; ++slot_idx) {
+      ObjectSlot slot = slots[slot_idx];
+      if (!IsTypedSlot(slot)) {
+        Object* object = *slot;
+        if (object->IsHeapObject()) {
+          if (heap->InNewSpace(object) ||
+              !heap->mark_compact_collector()->IsSlotInLiveObject(
+                  reinterpret_cast<Address>(slot))) {
+            slots[slot_idx] = kRemovedEntry;
+          }
+        }
+      } else {
+        ++slot_idx;
+        DCHECK(slot_idx < slots_count);
+      }
+    }
+    buffer = buffer->next();
+  }
+}
+
+
+void SlotsBuffer::VerifySlots(Heap* heap, SlotsBuffer* buffer) {
+  DCHECK_EQ(Smi::FromInt(0), g_smi_slot);
+
+  while (buffer != NULL) {
+    SlotsBuffer::ObjectSlot* slots = buffer->slots_;
+    intptr_t slots_count = buffer->idx_;
+
+    for (int slot_idx = 0; slot_idx < slots_count; ++slot_idx) {
+      ObjectSlot slot = slots[slot_idx];
+      if (!IsTypedSlot(slot)) {
+        Object* object = *slot;
+        if (object->IsHeapObject()) {
+          CHECK(!heap->InNewSpace(object));
+          CHECK(heap->mark_compact_collector()->IsSlotInLiveObject(
+              reinterpret_cast<Address>(slot)));
+        }
+      } else {
+        ++slot_idx;
+        DCHECK(slot_idx < slots_count);
+      }
+    }
+    buffer = buffer->next();
+  }
+}
+
+
 static inline SlotsBuffer::SlotType SlotTypeForRMode(RelocInfo::Mode rmode) {
   if (RelocInfo::IsCodeTarget(rmode)) {
     return SlotsBuffer::CODE_TARGET_SLOT;