One instead of two runtime calls when initializing regexp.

src/regexp.js

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 // This file relies on the fact that the following declaration has been made
 // in runtime.js:
 // var $Object = global.Object;
 // var $Array = global.Array;
 
 var $RegExp = global.RegExp;
@@ skipping 12 matching lines @@
         + (pattern.ignoreCase ? 'i' : '')
         + (pattern.multiline ? 'm' : '');
     if (harmony_regexps)
         flags += (pattern.sticky ? 'y' : '');
     pattern = pattern.source;
   }
 
   pattern = IS_UNDEFINED(pattern) ? '' : ToString(pattern);
   flags = IS_UNDEFINED(flags) ? '' : ToString(flags);
 
-  var global = false;
-  var ignoreCase = false;
-  var multiline = false;
-  var sticky = false;
-  for (var i = 0; i < flags.length; i++) {
-    var c = %_CallFunction(flags, i, StringCharAt);
-    switch (c) {
-      case 'g':
-        if (global) {
-          throw MakeSyntaxError("invalid_regexp_flags", [flags]);
-        }
-        global = true;
-        break;
-      case 'i':
-        if (ignoreCase) {
-          throw MakeSyntaxError("invalid_regexp_flags", [flags]);
-        }
-        ignoreCase = true;
-        break;
-      case 'm':
-        if (multiline) {
-          throw MakeSyntaxError("invalid_regexp_flags", [flags]);
-        }
-        multiline = true;
-        break;
-      case 'y':
-        if (!harmony_regexps || sticky) {
-          throw MakeSyntaxError("invalid_regexp_flags", [flags]);
-        }
-        sticky = true;
-        break;
-      default:
-        throw MakeSyntaxError("invalid_regexp_flags", [flags]);
-    }
-  }
-
-  %RegExpInitializeObject(object, pattern, global, ignoreCase, multiline, sticky);
-
-  // Call internal function to compile the pattern.
-  %RegExpCompile(object, pattern, flags);
+  %RegExpInitializeAndCompile(object, pattern, flags);
 }
 
 
 function RegExpConstructor(pattern, flags) {
   if (%_IsConstructCall()) {
     DoConstructRegExp(this, pattern, flags);
   } else {
     // RegExp : Called as function; see ECMA-262, section 15.10.3.1.
     if (IS_REGEXP(pattern) && IS_UNDEFINED(flags)) {
       return pattern;
@@ skipping 383 matching lines @@
 
   for (var i = 1; i < 10; ++i) {
     %DefineAccessorPropertyUnchecked($RegExp, '$' + i,
                                      RegExpMakeCaptureGetter(i), NoOpSetter,
                                      DONT_DELETE);
   }
   %ToFastProperties($RegExp);
 }
 
 SetUpRegExp();