Speed up no-capture case for RegExp.exec().

src/regexp-delay.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
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@@ skipping 134 matching lines @@
     throw MakeTypeError('incompatible_method_receiver',
                         ['RegExp.prototype.exec', this]);
   }
   if (%_ArgumentsLength() == 0) {
     var regExpInput = LAST_INPUT(lastMatchInfo);
     if (IS_UNDEFINED(regExpInput)) {
       throw MakeError('no_input_to_regexp', [this]);
     }
     string = regExpInput;
   }
-  var s = ToString(string);
-  var length = s.length;
+  var s;
+  if (IS_STRING(string)) {
+    s = string;
+  } else {
+    s = ToString(string);
+  }
   var lastIndex = this.lastIndex;
   var i = this.global ? TO_INTEGER(lastIndex) : 0;
 
   if (i < 0 || i > s.length) {
     this.lastIndex = 0;
     return null;
   }
 
   %_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;
     return matchIndices; // no match
   }
 
   var numResults = NUMBER_OF_CAPTURES(lastMatchInfo) >> 1;
-  var 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;
+  if (numResults === 1) {
+    var result = new $Array(1);

[Kasper Lund, 2010/03/05 14:50:29]

I wonder if 

   result = [ SubString(s, matchStart, matchEnd) ];

would be faster? 

+    var matchStart = lastMatchInfo[CAPTURE(0)];
+    var matchEnd = lastMatchInfo[CAPTURE(1)];
+    result[0] = SubString(s, matchStart, matchEnd);
+  } else {
+    var 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;
+      }
     }
   }
 
   if (this.global)
     this.lastIndex = lastMatchInfo[CAPTURE1];
   result.index = lastMatchInfo[CAPTURE0];
   result.input = s;
   return result;
 }
 
@@ skipping 202 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();