Optimizing BuildResultFromMatchInfo, StringReplace and StringSplit.

src/regexp.js

Index: src/regexp.js
===================================================================
--- src/regexp.js	(revision 5973)
+++ src/regexp.js	(working copy)
@@ -120,22 +120,28 @@
 
 function BuildResultFromMatchInfo(lastMatchInfo, s) {
   var numResults = NUMBER_OF_CAPTURES(lastMatchInfo) >> 1;
-  var result = %_RegExpConstructResult(numResults, lastMatchInfo[CAPTURE0], s);
-  if (numResults === 1) {
-    var matchStart = lastMatchInfo[CAPTURE(0)];
-    var matchEnd = lastMatchInfo[CAPTURE(1)];
-    result[0] = SubString(s, matchStart, matchEnd);
+  var start = lastMatchInfo[CAPTURE0];
+  var end = lastMatchInfo[CAPTURE1];
+  var result = %_RegExpConstructResult(numResults, start, s);
+  if (start + 1 == end) {
+    result[0] = %_StringCharAt(s, start);
   } else {
-    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);
+    result[0] = %_SubString(s, start, end);
+  }
+  var j = REGEXP_FIRST_CAPTURE + 2;
+  for (var i = 1; i < numResults; i++) {
+    start = lastMatchInfo[j++];
+    end = lastMatchInfo[j++];
+    if (end != -1) {
+      if (start + 1 == end) {
+        result[i] = %_StringCharAt(s, start);
       } 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[i] = %_SubString(s, start, end);
       }
+    } else {
+      // Make sure the element is present. Avoid reading the undefined
+      // property from the global object since this may change.
+      result[i] = void 0;
     }
   }
   return result;