[heap] Pass a force_promotion flag to the evacuation routine in the scavenger.

src/heap/heap.cc

 // 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.
 
 #include "src/heap/heap.h"
 
 #include "src/accessors.h"
 #include "src/api.h"
 #include "src/ast/scopeinfo.h"
 #include "src/base/bits.h"
@@ skipping 1650 matching lines @@
   {
     // Copy roots.
     TRACE_GC(tracer(), GCTracer::Scope::SCAVENGER_ROOTS);
     IterateRoots(&scavenge_visitor, VISIT_ALL_IN_SCAVENGE);
   }
 
   {
     // Copy objects reachable from the old generation.
     TRACE_GC(tracer(), GCTracer::Scope::SCAVENGER_OLD_TO_NEW_POINTERS);
     RememberedSet<OLD_TO_NEW>::Iterate(this, [this](Address addr) {
-      return Scavenger::CheckAndScavengeObject(this, addr);
+      return Scavenger::CheckAndScavengeObject(this, addr, DEFAULT_PROMOTION);
     });
 
     RememberedSet<OLD_TO_NEW>::IterateTyped(
         this, [this](SlotType type, Address addr) {
           return UpdateTypedSlotHelper::UpdateTypedSlot(
               isolate(), type, addr, [this](Object** addr) {
                 return Scavenger::CheckAndScavengeObject(
-                    this, reinterpret_cast<Address>(addr));
+                    this, reinterpret_cast<Address>(addr), FORCE_PROMOTION);

[ulan, 2016/05/23 13:04:22]

Please add a comment why we force promotion here.
We expect that objects referenced by code are long living.
If we do not force promotion then we need to clear old_to_new slots in dead code
objects after mark-compact.

[ahaas, 2016/05/23 13:31:48]

Done.

               });
         });
   }
 
   {
     TRACE_GC(tracer(), GCTracer::Scope::SCAVENGER_WEAK);
     // Copy objects reachable from the encountered weak collections list.
     scavenge_visitor.VisitPointer(&encountered_weak_collections_);
     // Copy objects reachable from the encountered weak cells.
     scavenge_visitor.VisitPointer(&encountered_weak_cells_);
@@ skipping 2968 matching lines @@
                                          Address end, bool record_slots,
                                          ObjectSlotCallback callback) {
   Address slot_address = start;
   Page* page = Page::FromAddress(start);
 
   while (slot_address < end) {
     Object** slot = reinterpret_cast<Object**>(slot_address);
     Object* target = *slot;
     if (target->IsHeapObject()) {
       if (Heap::InFromSpace(target)) {
-        callback(reinterpret_cast<HeapObject**>(slot),
-                 HeapObject::cast(target));
+        callback(reinterpret_cast<HeapObject**>(slot), HeapObject::cast(target),
+                 DEFAULT_PROMOTION);
         Object* new_target = *slot;
         if (InNewSpace(new_target)) {
           SLOW_DCHECK(Heap::InToSpace(new_target));
           SLOW_DCHECK(new_target->IsHeapObject());
           RememberedSet<OLD_TO_NEW>::Insert(page, slot_address);
         }
         SLOW_DCHECK(!MarkCompactCollector::IsOnEvacuationCandidate(new_target));
       } else if (record_slots &&
                  MarkCompactCollector::IsOnEvacuationCandidate(target)) {
         mark_compact_collector()->RecordSlot(object, slot, target);
@@ skipping 1687 matching lines @@
 }
 
 
 // static
 int Heap::GetStaticVisitorIdForMap(Map* map) {
   return StaticVisitorBase::GetVisitorId(map);
 }
 
 }  // namespace internal
 }  // namespace v8