Internalize strings in-place

src/runtime/runtime-object.cc

 // Copyright 2014 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/runtime/runtime-utils.h"
 
 #include "src/arguments.h"
 #include "src/bootstrapper.h"
 #include "src/debug/debug.h"
 #include "src/isolate-inl.h"
@@ skipping 38 matching lines @@
   // prototype including own lookups.
   //
   // Additionally, we need to make sure that we do not cache results
   // for objects that require access checks.
   if (receiver_obj->IsJSObject()) {
     if (!receiver_obj->IsJSGlobalProxy() &&
         !receiver_obj->IsAccessCheckNeeded() && key_obj->IsName()) {
       DisallowHeapAllocation no_allocation;
       Handle<JSObject> receiver = Handle<JSObject>::cast(receiver_obj);
       Handle<Name> key = Handle<Name>::cast(key_obj);
+      // Get to a ThinString's referenced internalized string, but don't
+      // otherwise force internalization. We assume that internalization
+      // (which is a dictionary lookup with a non-internalized key) is
+      // about as expensive as doing the property dictionary lookup with
+      // the non-internalized key directly.
+      if (key->IsThinString()) {
+        key = handle(Handle<ThinString>::cast(key)->actual(), isolate);
+      }
       if (receiver->IsJSGlobalObject()) {
         // Attempt dictionary lookup.
         GlobalDictionary* dictionary = receiver->global_dictionary();
         int entry = dictionary->FindEntry(key);
         if (entry != GlobalDictionary::kNotFound) {
           DCHECK(dictionary->ValueAt(entry)->IsPropertyCell());
           PropertyCell* cell = PropertyCell::cast(dictionary->ValueAt(entry));
           if (cell->property_details().kind() == kData) {
             Object* value = cell->value();
             if (!value->IsTheHole(isolate)) {
@@ skipping 895 matching lines @@
   if (!success) return isolate->heap()->exception();
   MAYBE_RETURN(
       JSReceiver::CreateDataProperty(&it, value, Object::THROW_ON_ERROR),
       isolate->heap()->exception());
   return *value;
 }
 
 
 }  // namespace internal
 }  // namespace v8