Revert of Changed scavenge GC to collect unmodified references

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/base/bits.h"
 #include "src/base/once.h"
@@ skipping 1222 matching lines @@
   GCType gc_type =
       collector == MARK_COMPACTOR ? kGCTypeMarkSweepCompact : kGCTypeScavenge;
 
   {
     GCCallbacksScope scope(this);
     if (scope.CheckReenter()) {
       AllowHeapAllocation allow_allocation;
       GCTracer::Scope scope(tracer(), GCTracer::Scope::EXTERNAL);
       VMState<EXTERNAL> state(isolate_);
       HandleScope handle_scope(isolate_);
-      if (!(FLAG_scavenge_reclaim_unmodified_objects &&
-            (gc_type == kGCTypeScavenge))) {
-        CallGCPrologueCallbacks(gc_type, kNoGCCallbackFlags);
-      }
+      CallGCPrologueCallbacks(gc_type, kNoGCCallbackFlags);
     }
   }
 
   EnsureFromSpaceIsCommitted();
 
   int start_new_space_size = Heap::new_space()->SizeAsInt();
 
   if (IsHighSurvivalRate()) {
     // We speed up the incremental marker if it is running so that it
     // does not fall behind the rate of promotion, which would cause a
@@ skipping 64 matching lines @@
     DampenOldGenerationAllocationLimit(old_gen_size, gc_speed, mutator_speed);
   }
 
   {
     GCCallbacksScope scope(this);
     if (scope.CheckReenter()) {
       AllowHeapAllocation allow_allocation;
       GCTracer::Scope scope(tracer(), GCTracer::Scope::EXTERNAL);
       VMState<EXTERNAL> state(isolate_);
       HandleScope handle_scope(isolate_);
-      if (!(FLAG_scavenge_reclaim_unmodified_objects &&
-            (gc_type == kGCTypeScavenge))) {
-        CallGCEpilogueCallbacks(gc_type, gc_callback_flags);
-      }
+      CallGCEpilogueCallbacks(gc_type, gc_callback_flags);
     }
   }
 
 #ifdef VERIFY_HEAP
   if (FLAG_verify_heap) {
     VerifyStringTable(this);
   }
 #endif
 
   return freed_global_handles > 0;
@@ skipping 139 matching lines @@
   }
 }
 
 
 static bool IsUnscavengedHeapObject(Heap* heap, Object** p) {
   return heap->InNewSpace(*p) &&
          !HeapObject::cast(*p)->map_word().IsForwardingAddress();
 }
 
 
-static bool IsUnmodifiedHeapObject(Object** p) {
-  Object* object = *p;
-  DCHECK(object->IsHeapObject());
-  HeapObject* heap_object = HeapObject::cast(object);
-  if (!object->IsJSObject()) return false;
-  Object* obj_constructor = (JSObject::cast(object))->map()->GetConstructor();
-  if (!obj_constructor->IsJSFunction()) return false;
-  JSFunction* constructor = JSFunction::cast(obj_constructor);
-  if (constructor != nullptr &&
-      constructor->initial_map() == heap_object->map()) {
-    return true;
-  }
-  return false;
-}
-
-
 void Heap::ScavengeStoreBufferCallback(Heap* heap, MemoryChunk* page,
                                        StoreBufferEvent event) {
   heap->store_buffer_rebuilder_.Callback(page, event);
 }
 
 
 void PromotionQueue::Initialize() {
   // The last to-space page may be used for promotion queue. On promotion
   // conflict, we use the emergency stack.
   DCHECK((Page::kPageSize - MemoryChunk::kBodyOffset) % (2 * kPointerSize) ==
@@ skipping 98 matching lines @@
   // updated as a side effect of promoting an object.
   //
   // There is guaranteed to be enough room at the top of the to space
   // for the addresses of promoted objects: every object promoted
   // frees up its size in bytes from the top of the new space, and
   // objects are at least one pointer in size.
   Address new_space_front = new_space_.ToSpaceStart();
   promotion_queue_.Initialize();
 
   ScavengeVisitor scavenge_visitor(this);
-
-  if (FLAG_scavenge_reclaim_unmodified_objects) {
-    isolate()->global_handles()->IdentifyWeakUnmodifiedObjects(
-        &IsUnmodifiedHeapObject);
-  }
-
   {
     // Copy roots.
     GCTracer::Scope gc_scope(tracer(), GCTracer::Scope::SCAVENGER_ROOTS);
     IterateRoots(&scavenge_visitor, VISIT_ALL_IN_SCAVENGE);
   }
 
   {
     // Copy objects reachable from the old generation.
     GCTracer::Scope gc_scope(tracer(),
                              GCTracer::Scope::SCAVENGER_OLD_TO_NEW_POINTERS);
@@ skipping 18 matching lines @@
     if (collector->is_code_flushing_enabled()) {
       collector->code_flusher()->IteratePointersToFromSpace(&scavenge_visitor);
     }
   }
 
   {
     GCTracer::Scope gc_scope(tracer(), GCTracer::Scope::SCAVENGER_SEMISPACE);
     new_space_front = DoScavenge(&scavenge_visitor, new_space_front);
   }
 
-  if (FLAG_scavenge_reclaim_unmodified_objects) {
-    isolate()->global_handles()->MarkNewSpaceWeakUnmodifiedObjectsPending(
-        &IsUnscavengedHeapObject);
-
-    isolate()->global_handles()->IterateNewSpaceWeakUnmodifiedRoots(
-        &scavenge_visitor);
-    new_space_front = DoScavenge(&scavenge_visitor, new_space_front);
-  } else {
+  {
     GCTracer::Scope gc_scope(tracer(),
                              GCTracer::Scope::SCAVENGER_OBJECT_GROUPS);
     while (isolate()->global_handles()->IterateObjectGroups(
         &scavenge_visitor, &IsUnscavengedHeapObject)) {
       new_space_front = DoScavenge(&scavenge_visitor, new_space_front);
     }
     isolate()->global_handles()->RemoveObjectGroups();
     isolate()->global_handles()->RemoveImplicitRefGroups();
+  }
 
-    isolate()->global_handles()->IdentifyNewSpaceWeakIndependentHandles(
-        &IsUnscavengedHeapObject);
+  isolate()->global_handles()->IdentifyNewSpaceWeakIndependentHandles(
+      &IsUnscavengedHeapObject);
 
-    isolate()->global_handles()->IterateNewSpaceWeakIndependentRoots(
-        &scavenge_visitor);
-    new_space_front = DoScavenge(&scavenge_visitor, new_space_front);
-  }
+  isolate()->global_handles()->IterateNewSpaceWeakIndependentRoots(
+      &scavenge_visitor);
+  new_space_front = DoScavenge(&scavenge_visitor, new_space_front);
 
   UpdateNewSpaceReferencesInExternalStringTable(
       &UpdateNewSpaceReferenceInExternalStringTableEntry);
 
   promotion_queue_.Destroy();
 
   incremental_marking()->UpdateMarkingDequeAfterScavenge();
 
   ScavengeWeakObjectRetainer weak_object_retainer(this);
   ProcessYoungWeakReferences(&weak_object_retainer);
@@ skipping 4425 matching lines @@
 }
 
 
 // static
 int Heap::GetStaticVisitorIdForMap(Map* map) {
   return StaticVisitorBase::GetVisitorId(map);
 }
 
 }  // namespace internal
 }  // namespace v8