Avoid unnecessary cloning of regexp answer

src/regexp.js

 // Copyright 2006-2009 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 108 matching lines @@
 }
 
 
 function RegExpCache() {
   this.type = 'none';
   this.regExp = 0;
   this.subject = 0;
   this.replaceString = 0;
   this.lastIndex = 0;
   this.answer = 0;
+  // answerSaved marks whether the contents of answer is valid for a cache
+  // hit in RegExpExec, StringMatch and StringSplit.
+  this.answerSaved = false;
 }
 
 
 var regExpCache = new RegExpCache();
 
 
 function CloneRegexpAnswer(array) {
+  if (array == null) return null; 
   var len = array.length;
   var answer = new $Array(len);
   for (var i = 0; i < len; i++) {
     answer[i] = array[i];
   }
   answer.index = array.index;
   answer.input = array.input;
   return answer;
 }
 
 
 function RegExpExec(string) {
   if (!IS_REGEXP(this)) {
     throw MakeTypeError('incompatible_method_receiver',
                         ['RegExp.prototype.exec', this]);
   }
 
   var cache = regExpCache;
+  var saveAnswer = false;
 
   if (%_ObjectEquals(cache.type, 'exec') &&
       %_ObjectEquals(cache.lastIndex, this.lastIndex) &&
       %_ObjectEquals(cache.regExp, this) &&
       %_ObjectEquals(cache.subject, string)) {
-    var last = cache.answer;
-    if (last == null) {
-      return last;
+    if (cache.answerSaved) {
+      return CloneRegexpAnswer(cache.answer);
     } else {
-      return CloneRegexpAnswer(last);
+      saveAnswer = true;
     }
+  } else {
+    cache.answerSaved = false;

[Lasse Reichstein, 2010/04/08 14:50:52]

No need to set answerSaved here. Set it, unconditionally, to saveAnswer when
updating the cache values below.

Due to the call to ToString below, we can't trust the value set here to stick
anyway.

   }
 
   if (%_ArgumentsLength() == 0) {
     var regExpInput = LAST_INPUT(lastMatchInfo);
     if (IS_UNDEFINED(regExpInput)) {
       throw MakeError('no_input_to_regexp', [this]);
     }
     string = regExpInput;
   }
   var s;
@@ skipping 14 matching lines @@
   %_Log('regexp', 'regexp-exec,%0r,%1S,%2i', [this, s, lastIndex]);
   // matchIndices is either null or the lastMatchInfo array.
   var matchIndices = %_RegExpExec(this, s, i, lastMatchInfo);
 
   if (matchIndices == null) {
     if (this.global) this.lastIndex = 0;
     cache.lastIndex = lastIndex;
     cache.regExp = this;
     cache.subject = s;
     cache.answer = matchIndices;  // Null.
+    cache.answerSaved = true;     // Safe since no cloning is needed.
     cache.type = 'exec';
     return matchIndices;        // No match.
   }
 
   var numResults = NUMBER_OF_CAPTURES(lastMatchInfo) >> 1;
   var result;
   if (numResults === 1) {
     var matchStart = lastMatchInfo[CAPTURE(0)];
     var matchEnd = lastMatchInfo[CAPTURE(1)];
     result = [SubString(s, matchStart, matchEnd)];
   } else {
     result = new $Array(numResults);
     for (var i = 0; i < numResults; i++) {
       var matchStart = lastMatchInfo[CAPTURE(i << 1)];
       var matchEnd = lastMatchInfo[CAPTURE((i << 1) + 1)];
       if (matchStart != -1 && matchEnd != -1) {
         result[i] = SubString(s, matchStart, matchEnd);
       } else {
         // Make sure the element is present. Avoid reading the undefined
         // property from the global object since this may change.
         result[i] = void 0;
       }
     }
   }
 
   result.index = lastMatchInfo[CAPTURE0];
   result.input = s;
   if (this.global) {
     this.lastIndex = lastMatchInfo[CAPTURE1];
-    return result;
   } else {
     cache.regExp = this;
     cache.subject = s;
     cache.lastIndex = lastIndex;
-    cache.answer = result;
+    if (saveAnswer) {
+      cache.answer = CloneRegexpAnswer(result);
+      cache.answerSaved = true;

[Lasse Reichstein, 2010/04/08 14:50:52]

I.e., always set answerSaved to saveAnswer here.

+    }
     cache.type = 'exec';
-    return CloneRegexpAnswer(result);
   }
+  return result;
+
 }
 
 
 // Section 15.10.6.3 doesn't actually make sense, but the intention seems to be
 // that test is defined in terms of String.prototype.exec. However, it probably
 // means the original value of String.prototype.exec, which is what everybody
 // else implements.
 function RegExpTest(string) {
   if (!IS_REGEXP(this)) {
     throw MakeTypeError('incompatible_method_receiver',
@@ skipping 250 matching lines @@
   %DefineAccessor($RegExp, "$'", SETTER, NoOpSetter, DONT_ENUM | DONT_DELETE);
 
   for (var i = 1; i < 10; ++i) {
     %DefineAccessor($RegExp, '$' + i, GETTER, RegExpMakeCaptureGetter(i), DONT_DELETE);
     %DefineAccessor($RegExp, '$' + i, SETTER, NoOpSetter, DONT_DELETE);
   }
 }
 
 
 SetupRegExp();