Internalize strings in-place

src/heap/scavenger.cc

 // Copyright 2015 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/scavenger.h"
 
 #include "src/contexts.h"
 #include "src/heap/heap.h"
 #include "src/heap/objects-visiting-inl.h"
 #include "src/heap/scavenger-inl.h"
@@ skipping 12 matching lines @@
 enum MarksHandling { TRANSFER_MARKS, IGNORE_MARKS };
 
 template <MarksHandling marks_handling,
           LoggingAndProfiling logging_and_profiling_mode>
 class ScavengingVisitor : public StaticVisitorBase {
  public:
   static void Initialize() {
     table_.Register(kVisitSeqOneByteString, &EvacuateSeqOneByteString);
     table_.Register(kVisitSeqTwoByteString, &EvacuateSeqTwoByteString);
     table_.Register(kVisitShortcutCandidate, &EvacuateShortcutCandidate);
+    table_.Register(kVisitThinString, &EvacuateThinString);
     table_.Register(kVisitByteArray, &EvacuateByteArray);
     table_.Register(kVisitFixedArray, &EvacuateFixedArray);
     table_.Register(kVisitFixedDoubleArray, &EvacuateFixedDoubleArray);
     table_.Register(kVisitFixedTypedArray, &EvacuateFixedTypedArray);
     table_.Register(kVisitFixedFloat64Array, &EvacuateFixedFloat64Array);
     table_.Register(kVisitJSArrayBuffer,
                     &ObjectEvacuationStrategy<POINTER_OBJECT>::Visit);
 
     table_.Register(
         kVisitNativeContext,
@@ skipping 39 matching lines @@
                                  kVisitJSApiObject, kVisitJSApiObjectGeneric>();
 
     table_.RegisterSpecializations<ObjectEvacuationStrategy<POINTER_OBJECT>,
                                    kVisitStruct, kVisitStructGeneric>();
   }
 
   static VisitorDispatchTable<ScavengingCallback>* GetTable() {
     return &table_;
   }
 
+  static void EvacuateThinStringNoShortcut(Map* map, HeapObject** slot,
+                                           HeapObject* object) {
+    EvacuateObject<POINTER_OBJECT, kWordAligned>(map, slot, object,
+                                                 ThinString::kSize);
+  }
+
  private:
   enum ObjectContents { DATA_OBJECT, POINTER_OBJECT };
 
   static void RecordCopiedObject(Heap* heap, HeapObject* obj) {
     bool should_record = false;
 #ifdef DEBUG
     should_record = FLAG_heap_stats;
 #endif
     should_record = should_record || FLAG_log_gc;
     if (should_record) {
@@ skipping 230 matching lines @@
       Scavenger::ScavengeObjectSlow(slot, first);
       object->set_map_word(MapWord::FromForwardingAddress(*slot));
       return;
     }
 
     int object_size = ConsString::kSize;
     EvacuateObject<POINTER_OBJECT, kWordAligned>(map, slot, object,
                                                  object_size);
   }
 
+  static inline void EvacuateThinString(Map* map, HeapObject** slot,
+                                        HeapObject* object) {
+    if (marks_handling == IGNORE_MARKS) {
+      HeapObject* actual = ThinString::cast(object)->actual();
+      *slot = actual;
+      // ThinStrings always refer to internalized strings, which are
+      // always in old space.
+      DCHECK(!map->GetHeap()->InNewSpace(actual));
+      object->set_map_word(MapWord::FromForwardingAddress(actual));
+      return;
+    }
+
+    EvacuateObject<POINTER_OBJECT, kWordAligned>(map, slot, object,
+                                                 ThinString::kSize);
+  }
+
   template <ObjectContents object_contents>
   class ObjectEvacuationStrategy {
    public:
     template <int object_size>
     static inline void VisitSpecialized(Map* map, HeapObject** slot,
                                         HeapObject* object) {
       EvacuateObject<object_contents, kWordAligned>(map, slot, object,
                                                     object_size);
     }
 
@@ skipping 64 matching lines @@
 
     if (heap()->incremental_marking()->IsCompacting()) {
       // When compacting forbid short-circuiting of cons-strings.
       // Scavenging code relies on the fact that new space object
       // can't be evacuated into evacuation candidate but
       // short-circuiting violates this assumption.
       scavenging_visitors_table_.Register(
           StaticVisitorBase::kVisitShortcutCandidate,
           scavenging_visitors_table_.GetVisitorById(
               StaticVisitorBase::kVisitConsString));
+      scavenging_visitors_table_.Register(
+          StaticVisitorBase::kVisitThinString,
+          &ScavengingVisitor<TRANSFER_MARKS, LOGGING_AND_PROFILING_DISABLED>::
+              EvacuateThinStringNoShortcut);
     }
   }
 }
 
 
 Isolate* Scavenger::isolate() { return heap()->isolate(); }
 
 
 void ScavengeVisitor::VisitPointer(Object** p) { ScavengePointer(p); }
 
 
 void ScavengeVisitor::VisitPointers(Object** start, Object** end) {
   // Copy all HeapObject pointers in [start, end)
   for (Object** p = start; p < end; p++) ScavengePointer(p);
 }
 
 
 void ScavengeVisitor::ScavengePointer(Object** p) {
   Object* object = *p;
   if (!heap_->InNewSpace(object)) return;
 
   Scavenger::ScavengeObject(reinterpret_cast<HeapObject**>(p),
                             reinterpret_cast<HeapObject*>(object));
 }
 
 }  // namespace internal
 }  // namespace v8