Internalize strings in-place

src/heap/scavenger.cc

Index: src/heap/scavenger.cc
diff --git a/src/heap/scavenger.cc b/src/heap/scavenger.cc
index f2722e81de5e27a1d415991b955ce3f91cc1e38f..d4e191ade48f36f4c136b82c4147fc63c0d5ce04 100644
--- a/src/heap/scavenger.cc
+++ b/src/heap/scavenger.cc
@@ -30,6 +30,7 @@ class ScavengingVisitor : public StaticVisitorBase {
     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);
@@ -89,6 +90,12 @@ class ScavengingVisitor : public StaticVisitorBase {
     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 };
 
@@ -339,6 +346,22 @@ class ScavengingVisitor : public StaticVisitorBase {
                                                  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:
@@ -423,6 +446,10 @@ void Scavenger::SelectScavengingVisitorsTable() {
           StaticVisitorBase::kVisitShortcutCandidate,
           scavenging_visitors_table_.GetVisitorById(
               StaticVisitorBase::kVisitConsString));
+      scavenging_visitors_table_.Register(
+          StaticVisitorBase::kVisitThinString,
+          &ScavengingVisitor<TRANSFER_MARKS, LOGGING_AND_PROFILING_DISABLED>::
+              EvacuateThinStringNoShortcut);
     }
   }
 }