Internalize strings in-place

src/objects-inl.h

 // 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.
 //
 // Review notes:
 //
 // - The use of macros in these inline functions may seem superfluous
 // but it is absolutely needed to make sure gcc generates optimal
 // code. gcc is not happy when attempting to inline too deep.
 //
@@ skipping 257 matching lines @@
   STATIC_ASSERT(kNotInternalizedTag != 0);
   return (type & (kIsNotStringMask | kIsNotInternalizedMask)) ==
       (kStringTag | kInternalizedTag);
 }
 
 bool HeapObject::IsConsString() const {
   if (!IsString()) return false;
   return StringShape(String::cast(this)).IsCons();
 }
 
+bool HeapObject::IsThinString() const {
+  if (!IsString()) return false;
+  return StringShape(String::cast(this)).IsThin();
+}
+
 bool HeapObject::IsSlicedString() const {
   if (!IsString()) return false;
   return StringShape(String::cast(this)).IsSliced();
 }
 
 bool HeapObject::IsSeqString() const {
   if (!IsString()) return false;
   return StringShape(String::cast(this)).IsSequential();
 }
 
@@ skipping 403 matching lines @@
 CAST_ACCESSOR(SharedFunctionInfo)
 CAST_ACCESSOR(Simd128Value)
 CAST_ACCESSOR(SlicedString)
 CAST_ACCESSOR(Smi)
 CAST_ACCESSOR(String)
 CAST_ACCESSOR(StringSet)
 CAST_ACCESSOR(StringTable)
 CAST_ACCESSOR(Struct)
 CAST_ACCESSOR(Symbol)
 CAST_ACCESSOR(TemplateInfo)
+CAST_ACCESSOR(ThinString)
 CAST_ACCESSOR(Uint16x8)
 CAST_ACCESSOR(Uint32x4)
 CAST_ACCESSOR(Uint8x16)
 CAST_ACCESSOR(UnseededNumberDictionary)
 CAST_ACCESSOR(WeakCell)
 CAST_ACCESSOR(WeakFixedArray)
 CAST_ACCESSOR(WeakHashTable)
 
 #define MAKE_STRUCT_CAST(NAME, Name, name) CAST_ACCESSOR(Name)
 STRUCT_LIST(MAKE_STRUCT_CAST)
@@ skipping 123 matching lines @@
 bool String::HasOnlyOneByteChars() {
   uint32_t type = map()->instance_type();
   return (type & kOneByteDataHintMask) == kOneByteDataHintTag ||
          IsOneByteRepresentation();
 }
 
 bool StringShape::IsCons() {
   return (type_ & kStringRepresentationMask) == kConsStringTag;
 }
 
+bool StringShape::IsThin() {
+  return (type_ & kStringRepresentationMask) == kThinStringTag;
+}
+
 bool StringShape::IsSliced() {
   return (type_ & kStringRepresentationMask) == kSlicedStringTag;
 }
 
 bool StringShape::IsIndirect() {
   return (type_ & kIsIndirectStringMask) == kIsIndirectStringTag;
 }
 
 bool StringShape::IsExternal() {
   return (type_ & kStringRepresentationMask) == kExternalStringTag;
@@ skipping 2801 matching lines @@
 bool String::Equals(Handle<String> one, Handle<String> two) {
   if (one.is_identical_to(two)) return true;
   if (one->IsInternalizedString() && two->IsInternalizedString()) {
     return false;
   }
   return SlowEquals(one, two);
 }
 
 
 Handle<String> String::Flatten(Handle<String> string, PretenureFlag pretenure) {
-  if (!string->IsConsString()) return string;
-  Handle<ConsString> cons = Handle<ConsString>::cast(string);
-  if (cons->IsFlat()) return handle(cons->first());
-  return SlowFlatten(cons, pretenure);
+  if (string->IsConsString()) {
+    Handle<ConsString> cons = Handle<ConsString>::cast(string);
+    if (cons->IsFlat()) {
+      string = handle(cons->first());
+    } else {
+      return SlowFlatten(cons, pretenure);
+    }
+  }
+  if (string->IsThinString()) {
+    string = handle(Handle<ThinString>::cast(string)->actual());
+    DCHECK(!string->IsConsString());
+  }
+  return string;
 }
 
 
 uint16_t String::Get(int index) {
   DCHECK(index >= 0 && index < length());
   switch (StringShape(this).full_representation_tag()) {
     case kSeqStringTag | kOneByteStringTag:
       return SeqOneByteString::cast(this)->SeqOneByteStringGet(index);
     case kSeqStringTag | kTwoByteStringTag:
       return SeqTwoByteString::cast(this)->SeqTwoByteStringGet(index);
     case kConsStringTag | kOneByteStringTag:
     case kConsStringTag | kTwoByteStringTag:
       return ConsString::cast(this)->ConsStringGet(index);
     case kExternalStringTag | kOneByteStringTag:
       return ExternalOneByteString::cast(this)->ExternalOneByteStringGet(index);
     case kExternalStringTag | kTwoByteStringTag:
       return ExternalTwoByteString::cast(this)->ExternalTwoByteStringGet(index);
     case kSlicedStringTag | kOneByteStringTag:
     case kSlicedStringTag | kTwoByteStringTag:
       return SlicedString::cast(this)->SlicedStringGet(index);
+    case kThinStringTag | kOneByteStringTag:
+    case kThinStringTag | kTwoByteStringTag:
+      return ThinString::cast(this)->ThinStringGet(index);
     default:
       break;
   }
 
   UNREACHABLE();
   return 0;
 }
 
 
 void String::Set(int index, uint16_t value) {
@@ skipping 11 matching lines @@
   return ConsString::cast(this)->second()->length() == 0;
 }
 
 
 String* String::GetUnderlying() {
   // Giving direct access to underlying string only makes sense if the
   // wrapping string is already flattened.
   DCHECK(this->IsFlat());
   DCHECK(StringShape(this).IsIndirect());
   STATIC_ASSERT(ConsString::kFirstOffset == SlicedString::kParentOffset);
+  STATIC_ASSERT(ConsString::kFirstOffset == ThinString::kActualOffset);
   const int kUnderlyingOffset = SlicedString::kParentOffset;
   return String::cast(READ_FIELD(this, kUnderlyingOffset));
 }
 
 
 template<class Visitor>
 ConsString* String::VisitFlat(Visitor* visitor,
                               String* string,
                               const int offset) {
   int slice_offset = offset;
@@ skipping 31 matching lines @@
         SlicedString* slicedString = SlicedString::cast(string);
         slice_offset += slicedString->offset();
         string = slicedString->parent();
         continue;
       }
 
       case kConsStringTag | kOneByteStringTag:
       case kConsStringTag | kTwoByteStringTag:
         return ConsString::cast(string);
 
+      case kThinStringTag | kOneByteStringTag:
+      case kThinStringTag | kTwoByteStringTag:
+        string = ThinString::cast(string)->actual();
+        continue;
+
       default:
         UNREACHABLE();
         return NULL;
     }
   }
 }
 
 
 template <>
 inline Vector<const uint8_t> String::GetCharVector() {
@@ skipping 111 matching lines @@
 Object* ConsString::unchecked_second() {
   return READ_FIELD(this, kSecondOffset);
 }
 
 
 void ConsString::set_second(String* value, WriteBarrierMode mode) {
   WRITE_FIELD(this, kSecondOffset, value);
   CONDITIONAL_WRITE_BARRIER(GetHeap(), this, kSecondOffset, value, mode);
 }
 
+ACCESSORS(ThinString, actual, String, kActualOffset);
 
 bool ExternalString::is_short() {
   InstanceType type = map()->instance_type();
   return (type & kShortExternalStringMask) == kShortExternalStringTag;
 }
 
 
 const ExternalOneByteString::Resource* ExternalOneByteString::resource() {
   return *reinterpret_cast<Resource**>(FIELD_ADDR(this, kResourceOffset));
 }
@@ skipping 4489 matching lines @@
 #undef WRITE_INT64_FIELD
 #undef READ_BYTE_FIELD
 #undef WRITE_BYTE_FIELD
 #undef NOBARRIER_READ_BYTE_FIELD
 #undef NOBARRIER_WRITE_BYTE_FIELD
 
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_OBJECTS_INL_H_