Introduce short external strings without pointer cache.

src/objects.h

 // Copyright 2011 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 213 matching lines @@
 // NOTE: Everything following JS_VALUE_TYPE is considered a
 // JSObject for GC purposes. The first four entries here have typeof
 // 'object', whereas JS_FUNCTION_TYPE has typeof 'function'.
 #define INSTANCE_TYPE_LIST_ALL(V)                                              \
   V(SYMBOL_TYPE)                                                               \
   V(ASCII_SYMBOL_TYPE)                                                         \
   V(CONS_SYMBOL_TYPE)                                                          \
   V(CONS_ASCII_SYMBOL_TYPE)                                                    \
   V(EXTERNAL_SYMBOL_TYPE)                                                      \
   V(EXTERNAL_SYMBOL_WITH_ASCII_DATA_TYPE)                                      \
   V(EXTERNAL_ASCII_SYMBOL_TYPE)                                                \

[Lasse Reichstein, 2011/11/23 08:43:20]

No SHORT_EXTERNAL_SYMBOL_TYPE etc.?

[Yang, 2011/11/23 09:58:48]

Must have forgotten that. Included now.

   V(STRING_TYPE)                                                               \
   V(ASCII_STRING_TYPE)                                                         \
   V(CONS_STRING_TYPE)                                                          \
   V(CONS_ASCII_STRING_TYPE)                                                    \
   V(SLICED_STRING_TYPE)                                                        \
   V(EXTERNAL_STRING_TYPE)                                                      \
   V(EXTERNAL_STRING_WITH_ASCII_DATA_TYPE)                                      \
   V(EXTERNAL_ASCII_STRING_TYPE)                                                \
+  V(SHORT_EXTERNAL_STRING_TYPE)                                                \
+  V(SHORT_EXTERNAL_STRING_WITH_ASCII_DATA_TYPE)                                \
+  V(SHORT_EXTERNAL_ASCII_STRING_TYPE)                                          \
   V(PRIVATE_EXTERNAL_ASCII_STRING_TYPE)                                        \
                                                                                \
   V(MAP_TYPE)                                                                  \
   V(CODE_TYPE)                                                                 \
   V(ODDBALL_TYPE)                                                              \
   V(JS_GLOBAL_PROPERTY_CELL_TYPE)                                              \
                                                                                \
   V(HEAP_NUMBER_TYPE)                                                          \
   V(FOREIGN_TYPE)                                                              \
   V(BYTE_ARRAY_TYPE)                                                           \
@@ skipping 80 matching lines @@
     external_symbol,                                                           \
     ExternalSymbol)                                                            \
   V(EXTERNAL_SYMBOL_WITH_ASCII_DATA_TYPE,                                      \
     ExternalTwoByteString::kSize,                                              \
     external_symbol_with_ascii_data,                                           \
     ExternalSymbolWithAsciiData)                                               \
   V(EXTERNAL_ASCII_SYMBOL_TYPE,                                                \
     ExternalAsciiString::kSize,                                                \
     external_ascii_symbol,                                                     \
     ExternalAsciiSymbol)                                                       \
+  V(SHORT_EXTERNAL_SYMBOL_TYPE,                                                \
+    ExternalTwoByteString::kShortSize,                                         \
+    short_external_symbol,                                                     \
+    ShortExternalSymbol)                                                       \
+  V(SHORT_EXTERNAL_SYMBOL_WITH_ASCII_DATA_TYPE,                                \
+    ExternalTwoByteString::kShortSize,                                         \
+    short_external_symbol_with_ascii_data,                                     \
+    ShortExternalSymbolWithAsciiData)                                          \
+  V(SHORT_EXTERNAL_ASCII_SYMBOL_TYPE,                                          \
+    ExternalAsciiString::kShortSize,                                           \
+    short_external_ascii_symbol,                                               \
+    ShortExternalAsciiSymbol)                                                  \
   V(STRING_TYPE,                                                               \
     kVariableSizeSentinel,                                                     \
     string,                                                                    \
     String)                                                                    \
   V(ASCII_STRING_TYPE,                                                         \
     kVariableSizeSentinel,                                                     \
     ascii_string,                                                              \
     AsciiString)                                                               \
   V(CONS_STRING_TYPE,                                                          \
     ConsString::kSize,                                                         \
@@ skipping 15 matching lines @@
     ExternalTwoByteString::kSize,                                              \
     external_string,                                                           \
     ExternalString)                                                            \
   V(EXTERNAL_STRING_WITH_ASCII_DATA_TYPE,                                      \
     ExternalTwoByteString::kSize,                                              \
     external_string_with_ascii_data,                                           \
     ExternalStringWithAsciiData)                                               \
   V(EXTERNAL_ASCII_STRING_TYPE,                                                \
     ExternalAsciiString::kSize,                                                \
     external_ascii_string,                                                     \
-    ExternalAsciiString)
+    ExternalAsciiString)                                                       \
+  V(SHORT_EXTERNAL_STRING_TYPE,                                                \
+    ExternalTwoByteString::kShortSize,                                         \
+    short_external_string,                                                     \
+    ShortExternalString)                                                       \
+  V(SHORT_EXTERNAL_STRING_WITH_ASCII_DATA_TYPE,                                \
+    ExternalTwoByteString::kShortSize,                                         \
+    short_external_string_with_ascii_data,                                     \
+    ShortExternalStringWithAsciiData)                                          \
+  V(SHORT_EXTERNAL_ASCII_STRING_TYPE,                                          \
+    ExternalAsciiString::kShortSize,                                           \
+    short_external_ascii_string,                                               \
+    ShortExternalAsciiString)
 
 // A struct is a simple object a set of object-valued fields.  Including an
 // object type in this causes the compiler to generate most of the boilerplate
 // code for the class including allocation and garbage collection routines,
 // casts and predicates.  All you need to define is the class, methods and
 // object verification routines.  Easy, no?
 //
 // Note that for subtle reasons related to the ordering or numerical values of
 // type tags, elements in this list have to be added to the INSTANCE_TYPE_LIST
 // manually.
@@ skipping 63 matching lines @@
 // Use this mask to distinguish between cons and slice only after making
 // sure that the string is one of the two (an indirect string).
 const uint32_t kSlicedNotConsMask = kSlicedStringTag & ~kConsStringTag;
 STATIC_ASSERT(IS_POWER_OF_TWO(kSlicedNotConsMask) && kSlicedNotConsMask != 0);
 
 // If bit 7 is clear, then bit 3 indicates whether this two-byte
 // string actually contains ascii data.
 const uint32_t kAsciiDataHintMask = 0x08;
 const uint32_t kAsciiDataHintTag = 0x08;
 
+// If bit 7 is clear and string representation indicates an external string,
+// then bit 4 indicates whether the data pointer is cached.
+const uint32_t kShortExternalStringMask = 0x10;
+const uint32_t kShortExternalStringTag = 0x10;
+
 
 // A ConsString with an empty string as the right side is a candidate
 // for being shortcut by the garbage collector unless it is a
 // symbol. It's not common to have non-flat symbols, so we do not
 // shortcut them thereby avoiding turning symbols into strings. See
 // heap.cc and mark-compact.cc.
 const uint32_t kShortcutTypeMask =
     kIsNotStringMask |
     kIsSymbolMask |
     kStringRepresentationMask;
 const uint32_t kShortcutTypeTag = kConsStringTag;
 
 
 enum InstanceType {
   // String types.
   SYMBOL_TYPE = kTwoByteStringTag | kSymbolTag | kSeqStringTag,
   ASCII_SYMBOL_TYPE = kAsciiStringTag | kSymbolTag | kSeqStringTag,
   CONS_SYMBOL_TYPE = kTwoByteStringTag | kSymbolTag | kConsStringTag,
   CONS_ASCII_SYMBOL_TYPE = kAsciiStringTag | kSymbolTag | kConsStringTag,
+  SHORT_EXTERNAL_SYMBOL_TYPE = kTwoByteStringTag | kSymbolTag |
+                               kExternalStringTag | kShortExternalStringTag,
+  SHORT_EXTERNAL_SYMBOL_WITH_ASCII_DATA_TYPE =
+      kTwoByteStringTag | kSymbolTag | kExternalStringTag |
+      kAsciiDataHintTag | kShortExternalStringTag,
+  SHORT_EXTERNAL_ASCII_SYMBOL_TYPE = kAsciiStringTag | kExternalStringTag |
+                                     kSymbolTag | kShortExternalStringTag,
   EXTERNAL_SYMBOL_TYPE = kTwoByteStringTag | kSymbolTag | kExternalStringTag,
   EXTERNAL_SYMBOL_WITH_ASCII_DATA_TYPE =
       kTwoByteStringTag | kSymbolTag | kExternalStringTag | kAsciiDataHintTag,
   EXTERNAL_ASCII_SYMBOL_TYPE =
       kAsciiStringTag | kSymbolTag | kExternalStringTag,
   STRING_TYPE = kTwoByteStringTag | kSeqStringTag,
   ASCII_STRING_TYPE = kAsciiStringTag | kSeqStringTag,
   CONS_STRING_TYPE = kTwoByteStringTag | kConsStringTag,
   CONS_ASCII_STRING_TYPE = kAsciiStringTag | kConsStringTag,
   SLICED_STRING_TYPE = kTwoByteStringTag | kSlicedStringTag,
   SLICED_ASCII_STRING_TYPE = kAsciiStringTag | kSlicedStringTag,
+  SHORT_EXTERNAL_STRING_TYPE =
+      kTwoByteStringTag | kExternalStringTag | kShortExternalStringTag,
+  SHORT_EXTERNAL_STRING_WITH_ASCII_DATA_TYPE =
+      kTwoByteStringTag | kExternalStringTag |
+      kAsciiDataHintTag | kShortExternalStringTag,
+  SHORT_EXTERNAL_ASCII_STRING_TYPE =
+      kAsciiStringTag | kExternalStringTag | kShortExternalStringTag,
   EXTERNAL_STRING_TYPE = kTwoByteStringTag | kExternalStringTag,
   EXTERNAL_STRING_WITH_ASCII_DATA_TYPE =
       kTwoByteStringTag | kExternalStringTag | kAsciiDataHintTag,
   // LAST_STRING_TYPE
   EXTERNAL_ASCII_STRING_TYPE = kAsciiStringTag | kExternalStringTag,
   PRIVATE_EXTERNAL_ASCII_STRING_TYPE = EXTERNAL_ASCII_STRING_TYPE,
 
   // Objects allocated in their own spaces (never in new space).
   MAP_TYPE = kNotStringTag,  // FIRST_NONSTRING_TYPE
   CODE_TYPE,
@@ skipping 6246 matching lines @@
 //
 // The API expects that all ExternalStrings are created through the
 // API.  Therefore, ExternalStrings should not be used internally.
 class ExternalString: public String {
  public:
   // Casting
   static inline ExternalString* cast(Object* obj);
 
   // Layout description.
   static const int kResourceOffset = POINTER_SIZE_ALIGN(String::kSize);
+  static const int kShortSize = kResourceOffset + kPointerSize;
   static const int kResourceDataOffset = kResourceOffset + kPointerSize;
   static const int kSize = kResourceDataOffset + kPointerSize;
 
-  // Clear the cached pointer to the character array provided by the resource.
-  // This cache is updated the first time the character array is accessed.
-  inline void clear_data_cache();
+  // Return whether external string is short (data pointer is not cached).
+  inline bool is_short();
 
   STATIC_CHECK(kResourceOffset == Internals::kStringResourceOffset);
 
  private:
   DISALLOW_IMPLICIT_CONSTRUCTORS(ExternalString);
 };
 
 
 // The ExternalAsciiString class is an external string backed by an
 // ASCII string.
 class ExternalAsciiString: public ExternalString {
  public:
   static const bool kHasAsciiEncoding = true;
 
   typedef v8::String::ExternalAsciiStringResource Resource;
 
   // The underlying resource.
   inline const Resource* resource();
   inline void set_resource(const Resource* buffer);
+  inline void update_data_cache();

[Lasse Reichstein, 2011/11/23 08:43:20]

Put a comment saying that this function is only used by deserialization, and
that the data cache is otherwise always set correctly 

[Yang, 2011/11/23 09:58:48]

Done.

 
   inline const char* GetChars();
 
   // Dispatched behavior.
   inline uint16_t ExternalAsciiStringGet(int index);
 
   // Casting.
   static inline ExternalAsciiString* cast(Object* obj);
 
   // Garbage collection support.
@@ skipping 19 matching lines @@
 // encoded string.
 class ExternalTwoByteString: public ExternalString {
  public:
   static const bool kHasAsciiEncoding = false;
 
   typedef v8::String::ExternalStringResource Resource;
 
   // The underlying string resource.
   inline const Resource* resource();
   inline void set_resource(const Resource* buffer);
+  inline void update_data_cache();
 
   inline const uint16_t* GetChars();
 
   // Dispatched behavior.
   inline uint16_t ExternalTwoByteStringGet(int index);
 
   // For regexp code.
   inline const uint16_t* ExternalTwoByteStringGetData(unsigned start);
 
   // Casting.
@@ skipping 1052 matching lines @@
     } else {
       value &= ~(1 << bit_position);
     }
     return value;
   }
 };
 
 } }  // namespace v8::internal
 
 #endif  // V8_OBJECTS_H_