Use direct copy and templates to speed up flattening of strings.

src/objects.h

 // Copyright 2006-2008 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 2947 matching lines @@
 
   // Specialization of this function from Object that skips the
   // string check.
   inline bool IsSeqAsciiString();
 
   // Fast testing routines that assume the receiver is a string and
   // just check whether it is a certain kind of string.
   inline bool StringIsSlicedString();
   inline bool StringIsConsString();
 
-  Vector<const char> ToAsciiVector();
+  Vector<const byte> ToAsciiVector();
   Vector<const uc16> ToUC16Vector();
 
   // Mark the string as an undetectable object. It only applies to
   // ascii and two byte string types.
   bool MarkAsUndetectable();
 
   // Slice the string and return a substring.
   Object* Slice(int from, int to);
 
   // String equality operations.
@@ skipping 57 matching lines @@
   // True if the string is a symbol.
   inline bool is_symbol();
   static inline bool is_symbol_map(Map* map);
 
   // True if the string is ASCII.
   inline bool is_ascii_representation();
   static inline bool is_ascii_representation_map(Map* map);
 
   // Get the representation tag.
   inline StringRepresentationTag representation_tag();
+  // Get the representation and ASCII tag.
+  inline int full_representation_tag();
   static inline StringRepresentationTag map_representation_tag(Map* map);
 
   // For use during stack traces.  Performs rudimentary sanity check.
   bool LooksValid();
 
   // Dispatched behavior.
   void StringShortPrint(StringStream* accumulator);
 #ifdef DEBUG
   void StringPrint();
   void StringVerify();
 #endif
   inline bool IsFlat();
 
   // Layout description.
   static const int kLengthOffset = HeapObject::kHeaderSize;
   static const int kSize = kLengthOffset + kIntSize;
 
   // Limits on sizes of different types of strings.
   static const int kMaxShortStringSize = 255;
   static const int kMaxMediumStringSize = 65535;
 
   static const int kMaxArrayIndexSize = 10;
 
   // Max ascii char code.
   static const int kMaxAsciiCharCode = 127;
 
+  // Minimum lenth for a cons or sliced string.
+  static const int kMinNonFlatLength = 13;
+
   // Mask constant for checking if a string has a computed hash code
   // and if it is an array index.  The least significant bit indicates
   // whether a hash code has been computed.  If the hash code has been
   // computed the 2nd bit tells whether the string can be used as an
   // array index.
   static const int kHashComputedMask = 1;
   static const int kIsArrayIndexMask = 1 << 1;
   static const int kNofLengthBitFields = 2;
 
   // Shift constants for retriving length and hash code from
@@ skipping 17 matching lines @@
                                         unsigned capacity,
                                         unsigned* remaining,
                                         unsigned* offset);
   static const unibrow::byte* ReadBlock(String** input,
                                         unibrow::byte* util_buffer,
                                         unsigned capacity,
                                         unsigned* remaining,
                                         unsigned* offset);
 
   // Helper function for flattening strings.
-  static void Flatten(String* source,
-                      String* sink,
-                      int from,
-                      int to,
-                      int sink_offset);
+  template <typename sinkchar>
+  static void WriteToFlat(String* source,
+                          sinkchar* sink,
+                          int from,
+                          int to);
 
  protected:
   class ReadBlockBuffer {
    public:
     ReadBlockBuffer(unibrow::byte* util_buffer_,
                     unsigned cursor_,
                     unsigned capacity_,
                     unsigned remaining_) :
       util_buffer(util_buffer_),
       cursor(cursor_),
@@ skipping 170 matching lines @@
 
   // Support for StringInputBuffer.
   inline const unibrow::byte* ConsStringReadBlock(ReadBlockBuffer* buffer,
                                                   unsigned* offset_ptr,
                                                   unsigned chars);
   inline void ConsStringReadBlockIntoBuffer(ReadBlockBuffer* buffer,
                                             unsigned* offset_ptr,
                                             unsigned chars);
 
 
-  // Minimum lenth for a cons string.
-  static const int kMinLength = 13;
 
  private:
   DISALLOW_IMPLICIT_CONSTRUCTORS(ConsString);
 };
 
 
 // The SlicedString class describes string values that are slices of
 // some other string.  SlicedStrings consist of a reference to an
 // underlying heap-allocated string value, a start index, and the
 // length field common to all strings.
@@ skipping 25 matching lines @@
   static const int kSize = kStartOffset + kIntSize;
 
   // Support for StringInputBuffer.
   inline const unibrow::byte* SlicedStringReadBlock(ReadBlockBuffer* buffer,
                                                     unsigned* offset_ptr,
                                                     unsigned chars);
   inline void SlicedStringReadBlockIntoBuffer(ReadBlockBuffer* buffer,
                                               unsigned* offset_ptr,
                                               unsigned chars);
 
-  // Minimum lenth for a sliced string.
-  static const int kMinLength = 13;
-
  private:
   DISALLOW_IMPLICIT_CONSTRUCTORS(SlicedString);
 };
 
 
 // The ExternalString class describes string values that are backed by
 // a string resource that lies outside the V8 heap.  ExternalStrings
 // consist of the length field common to all strings, a pointer to the
 // external resource.  It is important to ensure (externally) that the
 // resource is not deallocated while the ExternalString is live in the
@@ skipping 656 matching lines @@
     } else {
       value &= ~(1 << bit_position);
     }
     return value;
   }
 };
 
 } }  // namespace v8::internal
 
 #endif  // V8_OBJECTS_H_