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      1 // Copyright 2015 the V8 project authors. All rights reserved.
      2 // Use of this source code is governed by a BSD-style license that can be
      3 // found in the LICENSE file.
      4 
      5 #ifndef V8_HEAP_SCAVENGER_INL_H_
      6 #define V8_HEAP_SCAVENGER_INL_H_
      7 
      8 #include "src/heap/scavenger.h"
      9 
     10 namespace v8 {
     11 namespace internal {
     12 
     13 void Scavenger::ScavengeObject(HeapObject** p, HeapObject* object) {
     14   DCHECK(object->GetIsolate()->heap()->InFromSpace(object));
     15 
     16   // We use the first word (where the map pointer usually is) of a heap
     17   // object to record the forwarding pointer.  A forwarding pointer can
     18   // point to an old space, the code space, or the to space of the new
     19   // generation.
     20   MapWord first_word = object->map_word();
     21 
     22   // If the first word is a forwarding address, the object has already been
     23   // copied.
     24   if (first_word.IsForwardingAddress()) {
     25     HeapObject* dest = first_word.ToForwardingAddress();
     26     DCHECK(object->GetIsolate()->heap()->InFromSpace(*p));
     27     *p = dest;
     28     return;
     29   }
     30 
     31   object->GetHeap()->UpdateAllocationSite<Heap::kGlobal>(
     32       object, object->GetHeap()->global_pretenuring_feedback_);
     33 
     34   // AllocationMementos are unrooted and shouldn't survive a scavenge
     35   DCHECK(object->map() != object->GetHeap()->allocation_memento_map());
     36   // Call the slow part of scavenge object.
     37   return ScavengeObjectSlow(p, object);
     38 }
     39 
     40 SlotCallbackResult Scavenger::CheckAndScavengeObject(Heap* heap,
     41                                                      Address slot_address) {
     42   Object** slot = reinterpret_cast<Object**>(slot_address);
     43   Object* object = *slot;
     44   if (heap->InFromSpace(object)) {
     45     HeapObject* heap_object = reinterpret_cast<HeapObject*>(object);
     46     DCHECK(heap_object->IsHeapObject());
     47 
     48     ScavengeObject(reinterpret_cast<HeapObject**>(slot), heap_object);
     49 
     50     object = *slot;
     51     // If the object was in from space before and is after executing the
     52     // callback in to space, the object is still live.
     53     // Unfortunately, we do not know about the slot. It could be in a
     54     // just freed free space object.
     55     if (heap->InToSpace(object)) {
     56       return KEEP_SLOT;
     57     }
     58   }
     59   // Slots can point to "to" space if the slot has been recorded multiple
     60   // times in the remembered set. We remove the redundant slot now.
     61   return REMOVE_SLOT;
     62 }
     63 
     64 // static
     65 void StaticScavengeVisitor::VisitPointer(Heap* heap, HeapObject* obj,
     66                                          Object** p) {
     67   Object* object = *p;
     68   if (!heap->InNewSpace(object)) return;
     69   Scavenger::ScavengeObject(reinterpret_cast<HeapObject**>(p),
     70                             reinterpret_cast<HeapObject*>(object));
     71 }
     72 
     73 }  // namespace internal
     74 }  // namespace v8
     75 
     76 #endif  // V8_HEAP_SCAVENGER_INL_H_
     77