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

src/heap/heap.cc

Index: src/heap/heap.cc
diff --git a/src/heap/heap.cc b/src/heap/heap.cc
index 3c8b876bf5d1e5b529001a985fe5ecabfdd92085..bdca5533f0c047ca66709e3b1deceb5e02b6a151 100644
--- a/src/heap/heap.cc
+++ b/src/heap/heap.cc
@@ -1668,7 +1668,7 @@ void Heap::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(
@@ -1676,7 +1676,7 @@ void Heap::Scavenge() {
           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.

               });
         });
   }
@@ -4665,8 +4665,8 @@ void Heap::IteratePromotedObjectPointers(HeapObject* object, Address start,
     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));