Avoid unnecessary cloning of regexp answer

src/regexp.js

Index: src/regexp.js
===================================================================
--- src/regexp.js	(revision 4357)
+++ src/regexp.js	(working copy)
@@ -126,6 +126,9 @@
   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;
 }
 
 
@@ -133,6 +136,7 @@
 
 
 function CloneRegexpAnswer(array) {
+  if (array == null) return null; 
   var len = array.length;
   var answer = new $Array(len);
   for (var i = 0; i < len; i++) {
@@ -151,17 +155,19 @@
   }
 
   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) {
@@ -196,6 +202,7 @@
     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.
   }
@@ -225,15 +232,18 @@
   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;
+
 }