[regexp] Avoid unneeded accesses to lastIndex

src/js/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.
 
 (function(global, utils) {
 
 %CheckIsBootstrapping();
 
 // -------------------------------------------------------------------
 // Imports
@@ skipping 167 matching lines @@
 
 // ES#sec-regexp.prototype.exec
 // RegExp.prototype.exec ( string )
 function RegExpSubclassExecJS(string) {
   if (!IS_REGEXP(this)) {
     throw %make_type_error(kIncompatibleMethodReceiver,
                         'RegExp.prototype.exec', this);
   }
 
   string = TO_STRING(string);
-  var lastIndex = this.lastIndex;
 
-  // Conversion is required by the ES2015 specification (RegExpBuiltinExec
-  // algorithm, step 4) even if the value is discarded for non-global RegExps.
-  var i = TO_LENGTH(lastIndex);
-
+  var lastIndex;
   var global = TO_BOOLEAN(REGEXP_GLOBAL(this));
   var sticky = TO_BOOLEAN(REGEXP_STICKY(this));
   var updateLastIndex = global || sticky;
   if (updateLastIndex) {
-    if (i > string.length) {
+    lastIndex = TO_LENGTH(this.lastIndex);
+    if (lastIndex > string.length) {
       this.lastIndex = 0;
       return null;
     }
   } else {
-    i = 0;
+    lastIndex = 0;
   }
 
   // matchIndices is either null or the RegExpLastMatchInfo array.
-  var matchIndices = %_RegExpExec(this, string, i, RegExpLastMatchInfo);
+  var matchIndices = %_RegExpExec(this, string, lastIndex, RegExpLastMatchInfo);
 
   if (IS_NULL(matchIndices)) {
-    this.lastIndex = 0;
+    if (updateLastIndex) this.lastIndex = 0;
     return null;
   }
 
   // Successful match.
   if (updateLastIndex) {
     this.lastIndex = RegExpLastMatchInfo[CAPTURE1];
   }
   RETURN_NEW_RESULT_FROM_MATCH_INFO(matchIndices, string);
 }
 %FunctionRemovePrototype(RegExpSubclassExecJS);
@@ skipping 707 matching lines @@
 
 // ES#sec-regexp.prototype-@@search
 // RegExp.prototype [ @@search ] ( string )
 function RegExpSubclassSearch(string) {
   if (!IS_RECEIVER(this)) {
     throw %make_type_error(kIncompatibleMethodReceiver,
                         "RegExp.prototype.@@search", this);
   }
   string = TO_STRING(string);
   var previousLastIndex = this.lastIndex;
-  this.lastIndex = 0;
+  if (previousLastIndex != 0) this.lastIndex = 0;
   var result = RegExpSubclassExec(this, string);
-  this.lastIndex = previousLastIndex;
+  var currentLastIndex = this.lastIndex;
+  if (currentLastIndex != previousLastIndex) this.lastIndex = previousLastIndex;
   if (IS_NULL(result)) return -1;
   return result.index;
 }
 %FunctionRemovePrototype(RegExpSubclassSearch);
 
 
 // Getters for the static properties lastMatch, lastParen, leftContext, and
 // rightContext of the RegExp constructor.  The properties are computed based
 // on the captures array of the last successful match and the subject string
 // of the last successful match.
@@ skipping 271 matching lines @@
   to.InternalRegExpMatch = InternalRegExpMatch;
   to.InternalRegExpReplace = InternalRegExpReplace;
   to.IsRegExp = IsRegExp;
   to.RegExpExec = DoRegExpExec;
   to.RegExpInitialize = RegExpInitialize;
   to.RegExpLastMatchInfo = RegExpLastMatchInfo;
   to.RegExpTest = RegExpTest;
 });
 
 })