Track usage of "this" and "arguments" in Scope

src/preparser.h

Index: src/preparser.h
diff --git a/src/preparser.h b/src/preparser.h
index 87addfbb9e8e89ec27a0ec19187c7862e6774e38..d5b7f94da61c6338a370c6643e137b9bdb221c7f 100644
--- a/src/preparser.h
+++ b/src/preparser.h
@@ -610,7 +610,9 @@ class PreParserIdentifier {
     return PreParserIdentifier(kYieldIdentifier);
   }
   bool IsEval() const { return type_ == kEvalIdentifier; }
-  bool IsArguments() const { return type_ == kArgumentsIdentifier; }
+  bool IsArguments(const AstValueFactory*) const {

[rossberg, 2014/09/10 06:33:56]

Why is this change necessary when the argument isn't even used?

+    return type_ == kArgumentsIdentifier;
+  }
   bool IsEvalOrArguments() const { return type_ >= kEvalIdentifier; }
   bool IsYield() const { return type_ == kYieldIdentifier; }
   bool IsFutureReserved() const { return type_ == kFutureReservedIdentifier; }
@@ -826,7 +828,7 @@ class PreParserExpression {
       const PreParserIdentifier ident = AsIdentifier();
       // A valid identifier can be an arrow function parameter list
       // except for eval, arguments, yield, and reserved keywords.
-      if (ident.IsEval() || ident.IsArguments() || ident.IsYield() ||
+      if (ident.IsEval() || ident.IsArguments(nullptr) || ident.IsYield() ||

[rossberg, 2014/09/10 06:33:56]

Unfortunately, we can't use C++11 yet...

           ident.IsFutureStrictReserved())
         return 0;
       return kBinaryOperationArrowParamList;
@@ -934,6 +936,8 @@ class PreParserScope {
 
   bool IsDeclared(const PreParserIdentifier& identifier) const { return false; }
   void DeclareParameter(const PreParserIdentifier& identifier, VariableMode) {}
+  void RecordArgumentsUsage() {}
+  void RecordThisUsage() {}
 
   // Allow scope->Foo() to work.
   PreParserScope* operator->() { return this; }
@@ -1599,6 +1603,8 @@ typename ParserBase<Traits>::IdentifierT ParserBase<Traits>::ParseIdentifier(
       ReportMessage("strict_eval_arguments");
       *ok = false;
     }
+    if (name->IsArguments(this->ast_value_factory()))
+      scope_->RecordArgumentsUsage();
     return name;
   } else if (strict_mode() == SLOPPY &&
              (next == Token::FUTURE_STRICT_RESERVED_WORD ||
@@ -1629,7 +1635,11 @@ typename ParserBase<Traits>::IdentifierT ParserBase<
     *ok = false;
     return Traits::EmptyIdentifier();
   }
-  return this->GetSymbol(scanner());
+
+  IdentifierT name = this->GetSymbol(scanner());
+  if (name->IsArguments(this->ast_value_factory()))
+    scope_->RecordArgumentsUsage();
+  return name;
 }
 
 
@@ -1644,7 +1654,11 @@ ParserBase<Traits>::ParseIdentifierName(bool* ok) {
     *ok = false;
     return Traits::EmptyIdentifier();
   }
-  return this->GetSymbol(scanner());
+
+  IdentifierT name = this->GetSymbol(scanner());
+  if (name->IsArguments(this->ast_value_factory()))
+    scope_->RecordArgumentsUsage();
+  return name;
 }
 
 
@@ -1721,6 +1735,7 @@ ParserBase<Traits>::ParsePrimaryExpression(bool* ok) {
   switch (token) {
     case Token::THIS: {
       Consume(Token::THIS);
+      scope_->RecordThisUsage();
       result = this->ThisExpression(scope_, factory());
       break;
     }