Make RegExp use ToLength on lastIndex when flag is turned on

In the ES2015 spec, RegExp uses ToLength, not ToInteger, on lastIndex
to coerce it to an integer. This patch switches to ToLength when
the --harmony-tolength flag is on, and adds some tests to verify the
new behavior.

BUG=v8:4244
LOG=Y
R=adamk

Review URL: https://codereview.chromium.org/1394023005

Cr-Commit-Position: refs/heads/master@{#31306}

src/js/macros.py

@@ -148,6 +148,7 @@ macro TO_INT32(arg) = ((arg) | 0);
 macro TO_UINT32(arg) = ((arg) >>> 0);
 macro TO_LENGTH(arg) = (%ToLength(arg));
 macro TO_LENGTH_OR_UINT32(arg) = (harmony_tolength ? TO_LENGTH(arg) : TO_UINT32(arg));
+macro TO_LENGTH_OR_INTEGER(arg) = (harmony_tolength ? TO_LENGTH(arg) : TO_INTEGER(arg));
 macro TO_STRING(arg) = (%_ToString(arg));
 macro TO_NUMBER(arg) = (%_ToNumber(arg));
 macro TO_OBJECT(arg) = (%_ToObject(arg));

src/js/regexp.js

@@ -163,9 +163,9 @@ function RegExpExecJS(string) {
   string = TO_STRING(string);
   var lastIndex = this.lastIndex;
 
-  // Conversion is required by the ES5 specification (RegExp.prototype.exec
-  // algorithm, step 5) even if the value is discarded for non-global RegExps.
-  var i = TO_INTEGER(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_OR_INTEGER(lastIndex);
 
   var updateLastIndex = this.global || (FLAG_harmony_regexps && this.sticky);
   if (updateLastIndex) {
@@ -211,9 +211,9 @@ function RegExpTest(string) {
 
   var lastIndex = this.lastIndex;
 
-  // Conversion is required by the ES5 specification (RegExp.prototype.exec
-  // algorithm, step 5) even if the value is discarded for non-global RegExps.
-  var i = TO_INTEGER(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_OR_INTEGER(lastIndex);
 
   if (this.global || (FLAG_harmony_regexps && this.sticky)) {
     if (i < 0 || i > string.length) {

test/mjsunit/harmony/regexp-tolength.js

+// Copyright 2015 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.
+
+// Flags: --harmony-tolength
+
+'use strict';
+
+let regexp = /x/g;
+
+regexp.lastIndex = -1;
+
+assertTrue(regexp.test("axb"));
+assertEquals(2, regexp.lastIndex);
+
+regexp.lastIndex = -1;
+
+assertEquals("x", regexp.exec("axb")[0]);
+assertEquals(2, regexp.lastIndex);