Cache result of ScriptNameOrSourceURL function

src/messages.js

 // 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 515 matching lines @@
  * for details on using //@ sourceURL comment to identify scritps that don't
  * have name.
  *
  * @return {?string} script name if present, value for //@ sourceURL comment
  * otherwise.
  */
 function ScriptNameOrSourceURL() {
   if (this.name) {
     return this.name;
   }
+
+  // The result is cached as on long scripts it takes noticable time to search
+  // for the sourceURL.
+  if (this.hasCachedNameOrSourceURL)
+      return this.cachedNameOrSourceURL;
+  this.hasCachedNameOrSourceURL = true;
+
   // TODO(608): the spaces in a regexp below had to be escaped as \040
   // because this file is being processed by js2c whose handling of spaces
   // in regexps is broken. Also, ['"] are excluded from allowed URLs to
   // avoid matches against sources that invoke evals with sourceURL.
   // A better solution would be to detect these special comments in
   // the scanner/parser.
   var source = ToString(this.source);
   var sourceUrlPos = %StringIndexOf(source, "sourceURL=", 0);
+  var sourceUrl;
   if (sourceUrlPos > 4) {
     var sourceUrlPattern =
         /\/\/@[\040\t]sourceURL=[\040\t]*([^\s\'\"]*)[\040\t]*$/gm;
     // Don't reuse lastMatchInfo here, so we create a new array with room
     // for four captures (array with length one longer than the index
     // of the fourth capture, where the numbering is zero-based).
     var matchInfo = new InternalArray(CAPTURE(3) + 1);
     var match =
         %_RegExpExec(sourceUrlPattern, source, sourceUrlPos - 4, matchInfo);
     if (match) {
-      return SubString(source, matchInfo[CAPTURE(2)], matchInfo[CAPTURE(3)]);
+      sourceUrl = SubString(source, matchInfo[CAPTURE(2)], matchInfo[CAPTURE(3)]);

[danno, 2012/03/02 12:06:32]

80 col

[yurys, 2012/03/02 12:22:20]

Done.

     }
   }
-  return this.name;
+  this.cachedNameOrSourceURL = sourceUrl || this.name;

[danno, 2012/03/02 12:06:32]

I think it's a bit more readable if you name the variable nameOrSourceURL and
initialize it to this.name. That obviates the need for the use of the ||
operator in this way.

[yurys, 2012/03/02 12:22:20]

Done.

+  return this.cachedNameOrSourceURL;
 }
 
 
 SetUpLockedPrototype(Script,
-  $Array("source", "name", "line_ends", "line_offset", "column_offset"),
+  $Array("source", "name", "line_ends", "line_offset", "column_offset",
+         "cachedNameOrSourceURL", "hasCachedNameOrSourceURL" ),
   $Array(
     "lineFromPosition", ScriptLineFromPosition,
     "locationFromPosition", ScriptLocationFromPosition,
     "locationFromLine", ScriptLocationFromLine,
     "sourceSlice", ScriptSourceSlice,
     "sourceLine", ScriptSourceLine,
     "lineCount", ScriptLineCount,
     "nameOrSourceURL", ScriptNameOrSourceURL
   )
 );
@@ skipping 633 matching lines @@
     throw e;
   }
 }
 
 
 InstallFunctions($Error.prototype, DONT_ENUM, ['toString', ErrorToString]);
 
 // Boilerplate for exceptions for stack overflows. Used from
 // Isolate::StackOverflow().
 var kStackOverflowBoilerplate = MakeRangeError('stack_overflow', []);