[heap] Black allocation.

src/heap/mark-compact-inl.h

 // Copyright 2012 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.
 
 #ifndef V8_HEAP_MARK_COMPACT_INL_H_
 #define V8_HEAP_MARK_COMPACT_INL_H_
 
 #include "src/heap/mark-compact.h"
 #include "src/heap/remembered-set.h"
 #include "src/isolate.h"
@@ skipping 125 matching lines @@
 
 void CodeFlusher::ClearNextCandidate(SharedFunctionInfo* candidate) {
   candidate->code()->set_gc_metadata(NULL, SKIP_WRITE_BARRIER);
 }
 
 
 template <LiveObjectIterationMode T>
 HeapObject* LiveObjectIterator<T>::Next() {
   while (!it_.Done()) {
     HeapObject* object = nullptr;
+    if (T == kGreyObjectsOnBlackPage) {
+      // Black objects will have most of the mark bits set to 1. If we invert
+      // the mark bits, grey objects will be left but the mark bit is moved by
+      // one position. We can just substract one word from the found location
+      // to obtain the grey object.
+      current_cell_ = ~current_cell_;
+    }
     while (current_cell_ != 0) {
       uint32_t trailing_zeros = base::bits::CountTrailingZeros32(current_cell_);
       Address addr = cell_base_ + trailing_zeros * kPointerSize;
 
+      if (T == kGreyObjectsOnBlackPage) {
+        addr -= kPointerSize;
+      }
+
       // Clear the first bit of the found object..
       current_cell_ &= ~(1u << trailing_zeros);
 
       uint32_t second_bit_index = 0;
       if (trailing_zeros < Bitmap::kBitIndexMask) {
         second_bit_index = 1u << (trailing_zeros + 1);
       } else {
         second_bit_index = 0x1;
         // The overlapping case; there has to exist a cell after the current
         // cell.
         DCHECK(!it_.Done());
         it_.Advance();
         cell_base_ = it_.CurrentCellBase();
         current_cell_ = *it_.CurrentCell();
       }
       if (T == kBlackObjects && (current_cell_ & second_bit_index)) {
         object = HeapObject::FromAddress(addr);
       } else if (T == kGreyObjects && !(current_cell_ & second_bit_index)) {
         object = HeapObject::FromAddress(addr);
       } else if (T == kAllLiveObjects) {
         object = HeapObject::FromAddress(addr);
+      } else if (T == kGreyObjectsOnBlackPage) {
+        object = HeapObject::FromAddress(addr);
       }
       // Clear the second bit of the found object.
       current_cell_ &= ~second_bit_index;
 
       // We found a live object.
       if (object != nullptr) break;
     }
     if (current_cell_ == 0) {
       if (!it_.Done()) {
         it_.Advance();
         cell_base_ = it_.CurrentCellBase();
         current_cell_ = *it_.CurrentCell();
       }
     }
     if (object != nullptr) return object;
   }
   return nullptr;
 }
 
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_HEAP_MARK_COMPACT_INL_H_