Proof-of-concept RegExp-cache for exec, test, replace.

src/string.js

Index: src/string.js
diff --git a/src/string.js b/src/string.js
index 49f403de7da8140bb8aeebd9d87c00c329850a0d..4319560324d8cb249444d76d83f1d66c6c13f574 100644
--- a/src/string.js
+++ b/src/string.js
@@ -162,15 +162,36 @@ function StringLocaleCompare(other) {
 }
 
 
+var stringMatchCacheInput;
+var stringMatchCacheId;
+var stringMatchCacheResult;
+
 // ECMA-262 section 15.5.4.10
 function StringMatch(regexp) {
   if (!IS_REGEXP(regexp)) regexp = new ORIGINAL_REGEXP(regexp);
   var subject = TO_STRING_INLINE(this);
 
-  if (!regexp.global) return regexp.exec(subject);
+  if (!regexp.global) return RegExpExec.call(regexp, subject);
   %_Log('regexp', 'regexp-match,%0S,%1r', [subject, regexp]);
+  
+  var reid = %_RegExpId(regexp);
+  if (%_IsIdentical(reid, stringMatchCacheId) &&
+      %_IsIdentical(this, stringMatchCacheInput)) {
+    %_Log("regexp", "regexp-match-cache-hit", []);
+    var cachedResult = stringMatchCacheResult;
+    if (cachedResult) {
+      cachedResult = ArraySlice.call(cachedResult, 0, cachedResult.length);
+    }
+    return cachedResult;
+  }
+  %_Log("regexp", "regexp-match-cache-miss", []);
+  
   // lastMatchInfo is defined in regexp-delay.js.
-  return %StringMatch(subject, regexp, lastMatchInfo);
+  var result = %StringMatch(subject, regexp, lastMatchInfo);
+  stringMatchCacheInput = this;
+  stringMatchCacheId = reid;
+  stringMatchCacheResult = result;
+  return result;
 }
 
 
@@ -239,13 +260,33 @@ function StringReplace(search, replace) {
 }
 
 
+var stringReplaceRegExpCacheInput;
+var stringReplaceRegExpCacheId;
+var stringReplaceRegExpCacheIndex;
+var stringReplaceRegExpCacheReplace;
+var stringReplaceRegExpCacheResult;
 // Helper function for regular expressions in String.prototype.replace.
 function StringReplaceRegExp(subject, regexp, replace) {
+  if (%_IsIdentical(%_RegExpId(regexp), stringReplaceRegExpCacheId) &&
+      %_IsIdentical(subject, stringReplaceRegExpCacheInput) &&
+      %_IsIdentical(replace, stringReplaceRegExpCacheReplace) &&
+      (!regexp.global || 
+        %_IsIdentical(regexp.lastIndex, stringReplaceRegExpCacheIndex))) {
+    %_Log("regexp", "regexp-replace-cache-hit", []);
+    return stringReplaceRegExpCacheResult;
+  }
+  %_Log("regexp", "regexp-replace-cache-miss", []);
+  stringReplaceRegExpCacheId = %_RegExpId(regexp);
+  stringReplaceRegExpCacheInput = subject;
+  stringReplaceRegExpCacheIndex = regexp.lastIndex;
+  stringReplaceRegExpCacheReplace = replace;
   replace = TO_STRING_INLINE(replace);
-  return %StringReplaceRegExpWithString(subject,
-                                        regexp,
-                                        replace,
-                                        lastMatchInfo);
+  var result = %StringReplaceRegExpWithString(subject,
+                                              regexp,
+                                              replace,
+                                              lastMatchInfo);
+  stringReplaceRegExpCacheResult = result;
+  return result;
 };