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

The {force_promotion} flag causes the scavenger to move an object to the
old generation instead of to the other semi-space. We use the flag to force
the promotion of objects which are referenced by code objects.

R=ulan@chromium.org

Committed: https://crrev.com/f2a7ba6449406d0b11a245aa1f5b4981265b6f20
Cr-Commit-Position: refs/heads/master@{#36443}

Review-Url: https://codereview.chromium.org/2002013002
Cr-Commit-Position: refs/heads/master@{#36462}

src/heap/heap.cc

@@ -1670,15 +1670,18 @@ 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(
         this, [this](SlotType type, Address addr) {
           return UpdateTypedSlotHelper::UpdateTypedSlot(
               isolate(), type, addr, [this](Object** addr) {
+                // 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.
                 return Scavenger::CheckAndScavengeObject(
-                    this, reinterpret_cast<Address>(addr));
+                    this, reinterpret_cast<Address>(addr), FORCE_PROMOTION);
               });
         });
   }
@@ -4666,8 +4669,8 @@ 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));

src/heap/heap.h

@@ -301,7 +301,10 @@ class Scavenger;
 class ScavengeJob;
 class WeakObjectRetainer;
 
-typedef void (*ObjectSlotCallback)(HeapObject** from, HeapObject* to);
+enum PromotionMode { FORCE_PROMOTION, DEFAULT_PROMOTION };
+
+typedef void (*ObjectSlotCallback)(HeapObject** from, HeapObject* to,
+                                   PromotionMode mode);
 
 // A queue of objects promoted during scavenge. Each object is accompanied
 // by it's size to avoid dereferencing a map pointer for scanning.

src/heap/scavenger-inl.h

@@ -10,7 +10,8 @@
 namespace v8 {
 namespace internal {
 
-void Scavenger::ScavengeObject(HeapObject** p, HeapObject* object) {
+void Scavenger::ScavengeObject(HeapObject** p, HeapObject* object,
+                               PromotionMode promotion_mode) {
   DCHECK(object->GetIsolate()->heap()->InFromSpace(object));
 
   // We use the first word (where the map pointer usually is) of a heap
@@ -34,18 +35,19 @@ void Scavenger::ScavengeObject(HeapObject** p, HeapObject* object) {
   // AllocationMementos are unrooted and shouldn't survive a scavenge
   DCHECK(object->map() != object->GetHeap()->allocation_memento_map());
   // Call the slow part of scavenge object.
-  return ScavengeObjectSlow(p, object);
+  return ScavengeObjectSlow(p, object, promotion_mode);
 }
 
-SlotCallbackResult Scavenger::CheckAndScavengeObject(Heap* heap,
-                                                     Address slot_address) {
+SlotCallbackResult Scavenger::CheckAndScavengeObject(
+    Heap* heap, Address slot_address, PromotionMode promotion_mode) {
   Object** slot = reinterpret_cast<Object**>(slot_address);
   Object* object = *slot;
   if (heap->InFromSpace(object)) {
     HeapObject* heap_object = reinterpret_cast<HeapObject*>(object);
     DCHECK(heap_object->IsHeapObject());
 
-    ScavengeObject(reinterpret_cast<HeapObject**>(slot), heap_object);
+    ScavengeObject(reinterpret_cast<HeapObject**>(slot), heap_object,
+                   promotion_mode);
 
     object = *slot;
     // If the object was in from space before and is after executing the
@@ -67,7 +69,8 @@ void StaticScavengeVisitor::VisitPointer(Heap* heap, HeapObject* obj,
   Object* object = *p;
   if (!heap->InNewSpace(object)) return;
   Scavenger::ScavengeObject(reinterpret_cast<HeapObject**>(p),
-                            reinterpret_cast<HeapObject*>(object));
+                            reinterpret_cast<HeapObject*>(object),
+                            DEFAULT_PROMOTION);
 }
 
 }  // namespace internal

src/heap/scavenger.h

@@ -12,7 +12,8 @@ namespace v8 {
 namespace internal {
 
 typedef void (*ScavengingCallback)(Map* map, HeapObject** slot,
-                                   HeapObject* object);
+                                   HeapObject* object,
+                                   PromotionMode promotion_mode);
 
 class Scavenger {
  public:
@@ -25,12 +26,15 @@ class Scavenger {
   // necessary, the object might be promoted to an old space.  The caller must
   // ensure the precondition that the object is (a) a heap object and (b) in
   // the heap's from space.
-  static inline void ScavengeObject(HeapObject** p, HeapObject* object);
-  static inline SlotCallbackResult CheckAndScavengeObject(Heap* heap,
-                                                          Address slot_address);
+  static inline void ScavengeObject(
+      HeapObject** p, HeapObject* object,
+      PromotionMode promotion_mode = DEFAULT_PROMOTION);
+  static inline SlotCallbackResult CheckAndScavengeObject(
+      Heap* heap, Address slot_address, PromotionMode promotion_mode);
 
   // Slow part of {ScavengeObject} above.
-  static void ScavengeObjectSlow(HeapObject** p, HeapObject* object);
+  static void ScavengeObjectSlow(HeapObject** p, HeapObject* object,
+                                 PromotionMode promotion_mode);
 
   // Chooses an appropriate static visitor table depending on the current state
   // of the heap (i.e. incremental marking, logging and profiling).