Add one-char string table for faster String.charAt to the VM.

runtime/vm/symbols.h

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #ifndef VM_SYMBOLS_H_
 #define VM_SYMBOLS_H_
 
 #include "vm/object.h"
 #include "vm/snapshot_ids.h"
 
@@ skipping 128 matching lines @@
   V(_ExternalFloat64Array, "_ExternalFloat64Array")                            \
   V(_WeakProperty, "_WeakProperty")                                            \
   V(InvocationMirror, "_InvocationMirror")                                     \
   V(AllocateInvocationMirror, "_allocateInvocationMirror")                     \
 
 // Contains a list of frequently used strings in a canonicalized form. This
 // list is kept in the vm_isolate in order to share the copy across isolates
 // without having to maintain copies in each isolate.
 class Symbols : public AllStatic {
  public:
+  static const uint32_t kMaxOneByteCharCode = 0x7F;

[Ivan Posva, 2012/11/15 09:07:10]

There is no reason to limit this to the maximum one byte char code. How about
just calling it kMaxCharCode and setting it to 255 to get all Latin-1 characters
out of the way.

[Florian Schneider, 2012/11/15 21:54:42]

For now I only want to deal with OneByteStrings in the VM isolate. We can extend
it to more characters if needed.

+
   // List of strings that are pre created in the vm isolate.
-  enum {
+  enum SymbolId {
     kIllegal = 0,
 
 #define DEFINE_SYMBOL_INDEX(symbol, literal)                                   \
     k##symbol,
 PREDEFINED_SYMBOLS_LIST(DEFINE_SYMBOL_INDEX)
 #undef DEFINE_SYMBOL_INDEX
-
-    kMaxId,
+    kMaxPredefinedId,

[Ivan Posva, 2012/11/15 09:07:10]

This causes us to have a hole in the used strings. How about this or something
similar?
#undef DEFINE_SYMBOL_INDEX
    kNullCharId,
    // Further ids for single char code symbols.
    kMaxId = kNullCharId + kMaxCharCode + 1,
    kMaxPredefinedId = kNullCharId,
  };

[Florian Schneider, 2012/11/15 21:54:42]

Done. kNullCharId is an alias for kMaxPredefinedId.

+    kMaxId = kMaxPredefinedId + kMaxOneByteCharCode + 1,
   };
 
   // Access methods for symbols stored in the vm isolate.
 #define DEFINE_SYMBOL_ACCESSOR(symbol, literal)                                \
   static RawString* symbol() { return predefined_[k##symbol]; }
 PREDEFINED_SYMBOLS_LIST(DEFINE_SYMBOL_ACCESSOR)
 #undef DEFINE_SYMBOL_ACCESSOR
 
   // Initialize frequently used symbols in the vm isolate.
   static void InitOnce(Isolate* isolate);
 
   // Initialize and setup a symbol table for the isolate.
   static void SetupSymbolTable(Isolate* isolate);
 
   // Get number of symbols in an isolate's symbol table.
   static intptr_t Size(Isolate* isolate);
 
   // Helper functions to create a symbol given a string or set of characters.
   static RawString* New(const char* str);
   template<typename T>
   static RawString* New(const T* characters, intptr_t len);
   static RawString* New(const String& str);
   static RawString* New(const String& str,
                         intptr_t begin_index,
                         intptr_t length);
 
   // Returns char* of predefined symbol.
-  static const char* Name(intptr_t symbol);
+  static const char* Name(SymbolId symbol);
+
+  static RawString* FromCharCode(uint32_t char_code);
 
  private:
   enum {
     kInitialVMIsolateSymtabSize = ((Symbols::kMaxId + 15) & -16),
     kInitialSymtabSize = 256
   };
 
   // Add the string into the VM isolate symbol table.
   static void Add(const Array& symbol_table, const String& str);
 
@@ skipping 30 matching lines @@
   friend class SnapshotReader;
   friend class SnapshotWriter;
   friend class ApiMessageReader;
 
   DISALLOW_COPY_AND_ASSIGN(Symbols);
 };
 
 }  // namespace dart
 
 #endif  // VM_SYMBOLS_H_