[es6] allow any LeftHandSideExpression in for-of loops

Fix an earlier regression which forbid non-VariableProxy LHS from being
used in for-of loops. Like for-in loops, the spec allows any LHS to be used,
with the sole exception that ObjectLiterals and ArrayLiterals must be valid
AssignmentPatterns.

Also fixes a bug in TurboFan which resulted in incorrectly replacing a variable load with a constant value in some instances, due to the AstLoopAssignmentAnalyzer failing to record the assignment to ForOfStatement's value.

BUG=v8:4418, v8:2720
LOG=N
R=wingo@igalia.com, littledan@chromium.org, adamk@chromium.org, bmeurer@chromium.org

Review URL: https://codereview.chromium.org/1411873004

Cr-Commit-Position: refs/heads/master@{#31816}

src/compiler/ast-loop-assignment-analyzer.cc

@@ -261,7 +261,9 @@ void ALAA::VisitForInStatement(ForInStatement* loop) {
 
 
 void ALAA::VisitForOfStatement(ForOfStatement* loop) {
+  Visit(loop->assign_iterator());
   Enter(loop);
+  Visit(loop->assign_each());
   Visit(loop->each());
   Visit(loop->subject());
   Visit(loop->body());

src/parser.cc

@@ -3635,12 +3635,11 @@ Statement* Parser::ParseForStatement(ZoneList<const AstRawString*>* labels,
 
       int num_decl = parsing_result.declarations.length();
       bool accept_IN = num_decl >= 1;
-      bool accept_OF = true;
       ForEachStatement::VisitMode mode;
       int each_beg_pos = scanner()->location().beg_pos;
       int each_end_pos = scanner()->location().end_pos;
 
-      if (accept_IN && CheckInOrOf(accept_OF, &mode, ok)) {
+      if (accept_IN && CheckInOrOf(&mode, ok)) {
         if (!*ok) return nullptr;
         if (num_decl != 1) {
           const char* loop_type =
@@ -3798,13 +3797,12 @@ Statement* Parser::ParseForStatement(ZoneList<const AstRawString*>* labels,
       Expression* expression = ParseExpression(false, CHECK_OK);
       int lhs_end_pos = scanner()->location().end_pos;
       ForEachStatement::VisitMode mode;
-      bool accept_OF = expression->IsVariableProxy();
       is_let_identifier_expression =
           expression->IsVariableProxy() &&
           expression->AsVariableProxy()->raw_name() ==
               ast_value_factory()->let_string();
 
-      if (CheckInOrOf(accept_OF, &mode, ok)) {
+      if (CheckInOrOf(&mode, ok)) {
         if (!*ok) return nullptr;
         expression = this->CheckAndRewriteReferenceExpression(
             expression, lhs_beg_pos, lhs_end_pos,

src/preparser.cc

@@ -925,8 +925,7 @@ PreParser::Statement PreParser::ParseForStatement(bool* ok) {
                                 &first_initializer_loc, &bindings_loc,
                                 CHECK_OK);
       bool accept_IN = decl_count >= 1;
-      bool accept_OF = true;
-      if (accept_IN && CheckInOrOf(accept_OF, &mode, ok)) {
+      if (accept_IN && CheckInOrOf(&mode, ok)) {
         if (!*ok) return Statement::Default();
         if (decl_count != 1) {
           const char* loop_type =
@@ -961,7 +960,7 @@ PreParser::Statement PreParser::ParseForStatement(bool* ok) {
       int lhs_end_pos = scanner()->location().end_pos;
       is_let_identifier_expression =
           lhs.IsIdentifier() && lhs.AsIdentifier().IsLet();
-      if (CheckInOrOf(lhs.IsIdentifier(), &mode, ok)) {
+      if (CheckInOrOf(&mode, ok)) {
         if (!*ok) return Statement::Default();
         lhs = CheckAndRewriteReferenceExpression(
             lhs, lhs_beg_pos, lhs_end_pos, MessageTemplate::kInvalidLhsInFor,

src/preparser.h

@@ -421,8 +421,7 @@ class ParserBase : public Traits {
     }
   }
 
-  bool CheckInOrOf(
-      bool accept_OF, ForEachStatement::VisitMode* visit_mode, bool* ok) {
+  bool CheckInOrOf(ForEachStatement::VisitMode* visit_mode, bool* ok) {
     if (Check(Token::IN)) {
       if (is_strong(language_mode())) {
         ReportMessageAt(scanner()->location(), MessageTemplate::kStrongForIn);
@@ -431,7 +430,7 @@ class ParserBase : public Traits {
         *visit_mode = ForEachStatement::ENUMERATE;
       }
       return true;
-    } else if (accept_OF && CheckContextualKeyword(CStrVector("of"))) {
+    } else if (CheckContextualKeyword(CStrVector("of"))) {
       *visit_mode = ForEachStatement::ITERATE;
       return true;
     }

test/mjsunit/es6/for-of.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.
+
+(function TestForOfName() {
+  var result = 0;
+  var index;
+
+  for (index of [1, 2, 3, 4, 5]) result += index;
+
+  assertEquals(result, 15);
+  assertEquals(index, 5);
+})();
+
+
+(function TestForOfProperty() {
+  var O = {};
+  var result = 0;
+
+  for (O.index of [1, 2, 3, 4, 5]) result += O.index;
+
+  assertEquals(result, 15);
+  assertEquals(O.index, 5);
+})();