Add 1-element caches to RegExp.exec and String.replace. We...

src/regexp-delay.js

Index: src/regexp-delay.js
===================================================================
--- src/regexp-delay.js	(revision 4060)
+++ src/regexp-delay.js	(working copy)
@@ -140,7 +140,36 @@
 }
 
 
+var cachedRegexp;
+var cachedSubject;
+var cachedLastIndex;
+var cachedAnswer;
+
+
+function CloneRegexpAnswer(array) {
+  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 (cachedLastIndex === this.lastIndex &&

[Lasse Reichstein, 2010/03/10 08:53:24]

lastIndex is only relevant if the regexp is global.

+      cachedRegexp === this &&

[Lasse Reichstein, 2010/03/10 08:53:24]

Checking the regexp itself is unsafe. Its behavior can be overwritten by
RegExp.prototype.compile.
You should check the underlying FixedArray instead (which is good, because
that's what the RegExp compile cache reuses too).

+      cachedSubject === string) {

[Mads Ager (chromium), 2010/03/10 08:12:22]

I would use %_ObjectEquals for the string and regexp comparisons here.

+    var last = cachedAnswer;
+    if (last == null) {

[Lasse Reichstein, 2010/03/10 08:53:24]

Use ===?

+      return last;
+    } else {
+      return CloneRegexpAnswer(last);
+    }
+  }
+
   if (!IS_REGEXP(this)) {
     throw MakeTypeError('incompatible_method_receiver',
                         ['RegExp.prototype.exec', this]);
@@ -159,6 +188,7 @@
     s = ToString(string);
   }
   var lastIndex = this.lastIndex;
+
   var i = this.global ? TO_INTEGER(lastIndex) : 0;
 
   if (i < 0 || i > s.length) {
@@ -172,7 +202,11 @@
 
   if (matchIndices == null) {
     if (this.global) this.lastIndex = 0;
-    return matchIndices; // no match
+    cachedLastIndex = lastIndex;
+    cachedRegexp = this;
+    cachedSubject = s;
+    cachedAnswer = matchIndices;  // Null.
+    return matchIndices;        // No match.
   }
 
   var numResults = NUMBER_OF_CAPTURES(lastMatchInfo) >> 1;
@@ -196,11 +230,18 @@
     }
   }
 
-  if (this.global)
-    this.lastIndex = lastMatchInfo[CAPTURE1];
   result.index = lastMatchInfo[CAPTURE0];
   result.input = s;
-  return result;
+  if (this.global) {
+    this.lastIndex = lastMatchInfo[CAPTURE1];
+    return result;
+  } else {
+    cachedRegexp = this;
+    cachedSubject = s;
+    cachedLastIndex = lastIndex;
+    cachedAnswer = result;
+    return CloneRegexpAnswer(result);
+  }
 }