Retire StringTracker.

BUG=

Review URL: https://codereview.chromium.org/1269343002

Cr-Commit-Position: refs/heads/master@{#30031}

src/api.cc

@@ -5133,7 +5133,6 @@ static inline int WriteHelper(const String* string,
   ENTER_V8(isolate);
   DCHECK(start >= 0 && length >= -1);
   i::Handle<i::String> str = Utils::OpenHandle(string);
-  isolate->string_tracker()->RecordWrite(str);
   if (options & String::HINT_MANY_WRITES_EXPECTED) {
     // Flatten the string for efficiency.  This applies whether we are
     // using StringCharacterStream or Get(i) to access the characters.
@@ -5845,9 +5844,6 @@ bool v8::String::MakeExternal(v8::String::ExternalStringResource* resource) {
     return false;  // Already an external string.
   }
   ENTER_V8(isolate);
-  if (isolate->string_tracker()->IsFreshUnusedString(obj)) {
-    return false;
-  }
   if (isolate->heap()->IsInGCPostProcessing()) {
     return false;
   }
@@ -5872,9 +5868,6 @@ bool v8::String::MakeExternal(
     return false;  // Already an external string.
   }
   ENTER_V8(isolate);
-  if (isolate->string_tracker()->IsFreshUnusedString(obj)) {
-    return false;
-  }
   if (isolate->heap()->IsInGCPostProcessing()) {
     return false;
   }
@@ -5895,9 +5888,10 @@ bool v8::String::CanMakeExternal() {
   i::Handle<i::String> obj = Utils::OpenHandle(this);
   i::Isolate* isolate = obj->GetIsolate();
 
-  if (isolate->string_tracker()->IsFreshUnusedString(obj)) return false;
+  // Old space strings should be externalized.
+  if (!isolate->heap()->new_space()->Contains(*obj)) return true;
   int size = obj->Size();  // Byte size of the original string.
-  if (size < i::ExternalString::kShortSize) return false;
+  if (size <= i::ExternalString::kShortSize) return false;
   i::StringShape shape(*obj);
   return !shape.IsExternal();
 }

src/api.h

@@ -406,72 +406,6 @@ OPEN_HANDLE_LIST(MAKE_OPEN_HANDLE)
 
 namespace internal {
 
-// Tracks string usage to help make better decisions when
-// externalizing strings.
-//
-// Implementation note: internally this class only tracks fresh
-// strings and keeps a single use counter for them.
-class StringTracker {
- public:
-  // Records that the given string's characters were copied to some
-  // external buffer. If this happens often we should honor
-  // externalization requests for the string.
-  void RecordWrite(Handle<String> string) {
-    Address address = reinterpret_cast<Address>(*string);
-    Address top = isolate_->heap()->NewSpaceTop();
-    if (IsFreshString(address, top)) {
-      IncrementUseCount(top);
-    }
-  }
-
-  // Estimates freshness and use frequency of the given string based
-  // on how close it is to the new space top and the recorded usage
-  // history.
-  inline bool IsFreshUnusedString(Handle<String> string) {
-    Address address = reinterpret_cast<Address>(*string);
-    Address top = isolate_->heap()->NewSpaceTop();
-    return IsFreshString(address, top) && IsUseCountLow(top);
-  }
-
- private:
-  StringTracker() : use_count_(0), last_top_(NULL), isolate_(NULL) { }
-
-  static inline bool IsFreshString(Address string, Address top) {
-    return top - kFreshnessLimit <= string && string <= top;
-  }
-
-  inline bool IsUseCountLow(Address top) {
-    if (last_top_ != top) return true;
-    return use_count_ < kUseLimit;
-  }
-
-  inline void IncrementUseCount(Address top) {
-    if (last_top_ != top) {
-      use_count_ = 0;
-      last_top_ = top;
-    }
-    ++use_count_;
-  }
-
-  // Single use counter shared by all fresh strings.
-  int use_count_;
-
-  // Last new space top when the use count above was valid.
-  Address last_top_;
-
-  Isolate* isolate_;
-
-  // How close to the new space top a fresh string has to be.
-  static const int kFreshnessLimit = 1024;
-
-  // The number of uses required to consider a string useful.
-  static const int kUseLimit = 32;
-
-  friend class Isolate;
-
-  DISALLOW_COPY_AND_ASSIGN(StringTracker);
-};
-
 
 class DeferredHandles {
  public:

src/isolate.cc

@@ -1760,7 +1760,6 @@ Isolate::Isolate(bool enable_serializer)
       eternal_handles_(NULL),
       thread_manager_(NULL),
       has_installed_extensions_(false),
-      string_tracker_(NULL),
       regexp_stack_(NULL),
       date_cache_(NULL),
       call_descriptor_data_(NULL),
@@ -1995,9 +1994,6 @@ Isolate::~Isolate() {
   delete thread_manager_;
   thread_manager_ = NULL;
 
-  delete string_tracker_;
-  string_tracker_ = NULL;
-
   delete memory_allocator_;
   memory_allocator_ = NULL;
   delete code_range_;
@@ -2104,8 +2100,6 @@ bool Isolate::Init(Deserializer* des) {
   FOR_EACH_ISOLATE_ADDRESS_NAME(ASSIGN_ELEMENT)
 #undef ASSIGN_ELEMENT
 
-  string_tracker_ = new StringTracker();
-  string_tracker_->isolate_ = this;
   compilation_cache_ = new CompilationCache(this);
   keyed_lookup_cache_ = new KeyedLookupCache();
   context_slot_cache_ = new ContextSlotCache();

src/isolate.h

@@ -907,8 +907,6 @@ class Isolate {
 
   ThreadManager* thread_manager() { return thread_manager_; }
 
-  StringTracker* string_tracker() { return string_tracker_; }
-
   unibrow::Mapping<unibrow::Ecma262UnCanonicalize>* jsregexp_uncanonicalize() {
     return &jsregexp_uncanonicalize_;
   }
@@ -1290,7 +1288,6 @@ class Isolate {
   RuntimeState runtime_state_;
   Builtins builtins_;
   bool has_installed_extensions_;
-  StringTracker* string_tracker_;
   unibrow::Mapping<unibrow::Ecma262UnCanonicalize> jsregexp_uncanonicalize_;
   unibrow::Mapping<unibrow::CanonicalizationRange> jsregexp_canonrange_;
   unibrow::Mapping<unibrow::Ecma262Canonicalize>

test/cctest/test-api.cc

@@ -523,7 +523,7 @@ TEST(MakingExternalStringConditions) {
       String::NewFromTwoByte(env->GetIsolate(), two_byte_string);
   i::DeleteArray(two_byte_string);
 
-  // We should refuse to externalize newly created small string.
+  // We should refuse to externalize small strings.
   CHECK(!small_string->CanMakeExternal());
   // Trigger GCs so that the newly allocated string moves to old gen.
   CcTest::heap()->CollectGarbage(i::NEW_SPACE);  // in survivor space now
@@ -535,14 +535,6 @@ TEST(MakingExternalStringConditions) {
   small_string = String::NewFromTwoByte(env->GetIsolate(), two_byte_string);
   i::DeleteArray(two_byte_string);
 
-  // We should refuse externalizing newly created small string.
-  CHECK(!small_string->CanMakeExternal());
-  for (int i = 0; i < 100; i++) {
-    String::Value value(small_string);
-  }
-  // Frequently used strings should be accepted.
-  CHECK(small_string->CanMakeExternal());
-
   const int buf_size = 10 * 1024;
   char* buf = i::NewArray<char>(buf_size);
   memset(buf, 'a', buf_size);
@@ -567,7 +559,7 @@ TEST(MakingExternalOneByteStringConditions) {
   CcTest::heap()->CollectGarbage(i::NEW_SPACE);
 
   Local<String> small_string = String::NewFromUtf8(env->GetIsolate(), "s1");
-  // We should refuse to externalize newly created small string.
+  // We should refuse to externalize small strings.
   CHECK(!small_string->CanMakeExternal());
   // Trigger GCs so that the newly allocated string moves to old gen.
   CcTest::heap()->CollectGarbage(i::NEW_SPACE);  // in survivor space now
@@ -575,15 +567,6 @@ TEST(MakingExternalOneByteStringConditions) {
   // Old space strings should be accepted.
   CHECK(small_string->CanMakeExternal());
 
-  small_string = String::NewFromUtf8(env->GetIsolate(), "small string 2");
-  // We should refuse externalizing newly created small string.
-  CHECK(!small_string->CanMakeExternal());
-  for (int i = 0; i < 100; i++) {
-    String::Value value(small_string);
-  }
-  // Frequently used strings should be accepted.
-  CHECK(small_string->CanMakeExternal());
-
   const int buf_size = 10 * 1024;
   char* buf = i::NewArray<char>(buf_size);
   memset(buf, 'a', buf_size);