[heap] Move {hidden_string} into the root list.

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 78 matching lines @@
       gc_count_(0),
       remembered_unmapped_pages_index_(0),
 #ifdef DEBUG
       allocation_timeout_(0),
 #endif  // DEBUG
       old_generation_allocation_limit_(initial_old_generation_size_),
       old_gen_exhausted_(false),
       optimize_for_memory_usage_(false),
       inline_allocation_disabled_(false),
       store_buffer_rebuilder_(store_buffer()),
-      hidden_string_(NULL),
       total_regexp_code_generated_(0),
       tracer_(this),
       high_survival_rate_period_length_(0),
       promoted_objects_size_(0),
       promotion_ratio_(0),
       semi_space_copied_object_size_(0),
       previous_semi_space_copied_object_size_(0),
       semi_space_copied_rate_(0),
       nodes_died_in_new_space_(0),
       nodes_copied_in_new_space_(0),
@@ skipping 3110 matching lines @@
   set_exception(*factory->NewOddball(factory->exception_map(), "exception",
                                      handle(Smi::FromInt(-5), isolate()),
                                      "undefined", Oddball::kException));
 
   for (unsigned i = 0; i < arraysize(constant_string_table); i++) {
     Handle<String> str =
         factory->InternalizeUtf8String(constant_string_table[i].contents);
     roots_[constant_string_table[i].index] = *str;
   }
 
+  // The {hidden_string} is special because it is an empty string, but does not
+  // match any string (even the {empty_string}) when looked up in properties.
   // Allocate the hidden string which is used to identify the hidden properties
   // in JSObjects. The hash code has a special value so that it will not match
   // the empty string when searching for the property. It cannot be part of the
   // loop above because it needs to be allocated manually with the special
   // hash code in place. The hash code for the hidden_string is zero to ensure
   // that it will always be at the first entry in property descriptors.
-  hidden_string_ = *factory->NewOneByteInternalizedString(
-      OneByteVector("", 0), String::kEmptyStringHash);
+  set_hidden_string(*factory->NewOneByteInternalizedString(
+      OneByteVector("", 0), String::kEmptyStringHash));
 
   // Create the code_stubs dictionary. The initial size is set to avoid
   // expanding the dictionary during bootstrapping.
   set_code_stubs(*UnseededNumberDictionary::New(isolate(), 128));
 
   // Create the non_monomorphic_cache used in stub-cache.cc. The initial size
   // is set to avoid expanding the dictionary during bootstrapping.
   set_non_monomorphic_cache(*UnseededNumberDictionary::New(isolate(), 64));
 
   set_polymorphic_code_cache(PolymorphicCodeCache::cast(
@@ skipping 2000 matching lines @@
   ExecutionAccess access(isolate());
   v->VisitPointers(&roots_[kSmiRootsStart], &roots_[kRootListLength]);
   v->Synchronize(VisitorSynchronization::kSmiRootList);
 }
 
 
 void Heap::IterateStrongRoots(ObjectVisitor* v, VisitMode mode) {
   v->VisitPointers(&roots_[0], &roots_[kStrongRootListLength]);
   v->Synchronize(VisitorSynchronization::kStrongRootList);
 
-  v->VisitPointer(bit_cast<Object**>(&hidden_string_));
-  v->Synchronize(VisitorSynchronization::kInternalizedString);
-
   isolate_->bootstrapper()->Iterate(v);
   v->Synchronize(VisitorSynchronization::kBootstrapper);
   isolate_->Iterate(v);
   v->Synchronize(VisitorSynchronization::kTop);
   Relocatable::Iterate(isolate_, v);
   v->Synchronize(VisitorSynchronization::kRelocatable);
 
   if (isolate_->deoptimizer_data() != NULL) {
     isolate_->deoptimizer_data()->Iterate(v);
   }
@@ skipping 1634 matching lines @@
     *object_type = "CODE_TYPE";                                                \
     *object_sub_type = "CODE_AGE/" #name;                                      \
     return true;
     CODE_AGE_LIST_COMPLETE(COMPARE_AND_RETURN_NAME)
 #undef COMPARE_AND_RETURN_NAME
   }
   return false;
 }
 }  // namespace internal
 }  // namespace v8