[es8] Initial set of changes to support syntactic tail calls.

src/parsing/parser-base.h

 // 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.
 
 #ifndef V8_PARSING_PARSER_BASE_H
 #define V8_PARSING_PARSER_BASE_H
 
 #include "src/ast/scopes.h"
 #include "src/bailout-reason.h"
 #include "src/hashmap.h"
@@ skipping 172 matching lines @@
 
   struct DestructuringAssignment {
    public:
     DestructuringAssignment(ExpressionT expression, Scope* scope)
         : assignment(expression), scope(scope) {}
 
     ExpressionT assignment;
     Scope* scope;
   };
 
+  struct TailCallExpression {
+    TailCallExpression(ExpressionT expression, int pos)
+        : expression(expression), pos(pos) {}
+
+    ExpressionT expression;
+    int pos;
+  };
+
   class FunctionState BASE_EMBEDDED {
    public:
     FunctionState(FunctionState** function_state_stack, Scope** scope_stack,
                   Scope* scope, FunctionKind kind,
                   typename Traits::Type::Factory* factory);
     ~FunctionState();
 
     int NextMaterializedLiteralIndex() {
       return next_materialized_literal_index_++;
     }
@@ skipping 37 matching lines @@
       return generator_object_variable_;
     }
 
     typename Traits::Type::Factory* factory() { return factory_; }
 
     const List<DestructuringAssignment>& destructuring_assignments_to_rewrite()
         const {
       return destructuring_assignments_to_rewrite_;
     }
 
-    List<ExpressionT>& expressions_in_tail_position() {
+    List<TailCallExpression>& expressions_in_tail_position() {
       return expressions_in_tail_position_;
     }
-    void AddExpressionInTailPosition(ExpressionT expression) {
+    void AddExpressionInTailPosition(ExpressionT expression, int pos) {
       if (collect_expressions_in_tail_position_) {
-        expressions_in_tail_position_.Add(expression);
+        expressions_in_tail_position_.Add(TailCallExpression(expression, pos));
       }
     }
 
     bool collect_expressions_in_tail_position() const {
       return collect_expressions_in_tail_position_;
     }
     void set_collect_expressions_in_tail_position(bool collect) {
       collect_expressions_in_tail_position_ = collect;
     }
 
@@ skipping 42 matching lines @@
     // is used by yield expressions and return statements. It is not necessary
     // for generator functions to have this variable set.
     Variable* generator_object_variable_;
 
     FunctionState** function_state_stack_;
     FunctionState* outer_function_state_;
     Scope** scope_stack_;
     Scope* outer_scope_;
 
     List<DestructuringAssignment> destructuring_assignments_to_rewrite_;
-    List<ExpressionT> expressions_in_tail_position_;
+    List<TailCallExpression> expressions_in_tail_position_;
     bool collect_expressions_in_tail_position_;
     ZoneList<ExpressionT> non_patterns_to_rewrite_;
 
     typename Traits::Type::Factory* factory_;
 
     // If true, the next (and immediately following) function literal is
     // preceded by a parenthesis.
     bool next_function_is_parenthesized_;
 
     // The value of the parents' next_function_is_parenthesized_, as it applies
     // to this function. Filled in by constructor.
     bool this_function_is_parenthesized_;
 
     friend class ParserTraits;
     friend class PreParserTraits;
     friend class Checkpoint;
   };
 
+  // This scope disables collecting of expressions at tail call position.
+  class DontCollectExpressionsInTailPositionScope {
+   public:
+    explicit DontCollectExpressionsInTailPositionScope(
+        FunctionState* function_state)
+        : function_state_(function_state),
+          old_value_(function_state->collect_expressions_in_tail_position()) {
+      function_state->set_collect_expressions_in_tail_position(false);
+    }
+    ~DontCollectExpressionsInTailPositionScope() {
+      function_state_->set_collect_expressions_in_tail_position(old_value_);
+    }
+
+   private:
+    FunctionState* function_state_;
+    bool old_value_;
+  };
+
+  // Collects all return expressions at tail call position in this scope
+  // to a separate list.
+  class CollectExpressionsInTailPositionToListScope {
+   public:
+    CollectExpressionsInTailPositionToListScope(FunctionState* function_state,
+                                                List<TailCallExpression>* list)
+        : function_state_(function_state), list_(list) {
+      function_state->expressions_in_tail_position().Swap(list_);
+    }
+    ~CollectExpressionsInTailPositionToListScope() {
+      function_state_->expressions_in_tail_position().Swap(list_);
+    }
+
+   private:
+    FunctionState* function_state_;
+    List<TailCallExpression>* list_;
+  };
+
   // Annoyingly, arrow functions first parse as comma expressions, then when we
   // see the => we have to go back and reinterpret the arguments as being formal
   // parameters.  To do so we need to reset some of the parser state back to
   // what it was before the arguments were first seen.
   class Checkpoint BASE_EMBEDDED {
    public:
     explicit Checkpoint(ParserBase* parser) {
       function_state_ = parser->function_state_;
       next_materialized_literal_index_ =
           function_state_->next_materialized_literal_index_;
@@ skipping 1538 matching lines @@
 template <class Traits>
 typename ParserBase<Traits>::ExpressionT
 ParserBase<Traits>::ParseAssignmentExpression(bool accept_IN,
                                               ExpressionClassifier* classifier,
                                               bool* ok) {
   // AssignmentExpression ::
   //   ConditionalExpression
   //   ArrowFunction
   //   YieldExpression
   //   LeftHandSideExpression AssignmentOperator AssignmentExpression
+  //   TailCallExpression
   bool is_destructuring_assignment = false;
   int lhs_beg_pos = peek_position();
 
   if (peek() == Token::YIELD && is_generator()) {
     return this->ParseYieldExpression(classifier, ok);
   }
 
   FuncNameInferrer::State fni_state(fni_);
   ParserBase<Traits>::Checkpoint checkpoint(this);
   ExpressionClassifier arrow_formals_classifier(this,
@@ skipping 946 matching lines @@
             this->EmptyIdentifier(), RelocInfo::kNoPosition, formal_parameters,
             kArrowFunction, FunctionLiteral::kAnonymousExpression, CHECK_OK);
         materialized_literal_count =
             function_state.materialized_literal_count();
         expected_property_count = function_state.expected_property_count();
       }
     } else {
       // Single-expression body
       int pos = position();
       ExpressionClassifier classifier(this);
+      bool is_tail_call_expression;
+      if (FLAG_harmony_explicit_tailcalls) {
+        // TODO(ishell): update chapter number.
+        // ES7 XX.YY.ZZ
+        if (peek() == Token::CONTINUE) {
+          Consume(Token::CONTINUE);
+          pos = position();
+          is_tail_call_expression = true;
+        } else {
+          is_tail_call_expression = false;
+        }
+      } else {
+        // ES6 14.6.1 Static Semantics: IsInTailPosition
+        is_tail_call_expression =
+            allow_tailcalls() && !is_sloppy(language_mode());
+      }
       ExpressionT expression =
           ParseAssignmentExpression(accept_IN, &classifier, CHECK_OK);
       Traits::RewriteNonPattern(&classifier, CHECK_OK);
       body = this->NewStatementList(1, zone());
       this->AddParameterInitializationBlock(formal_parameters, body, CHECK_OK);
       body->Add(factory()->NewReturnStatement(expression, pos), zone());
       materialized_literal_count = function_state.materialized_literal_count();
       expected_property_count = function_state.expected_property_count();
-      // ES6 14.6.1 Static Semantics: IsInTailPosition
-      if (allow_tailcalls() && !is_sloppy(language_mode())) {
+      if (is_tail_call_expression) {

[rossberg, 2016/04/26 14:56:57]

Nit: why separate this from the rest of the logic?

[Igor Sheludko, 2016/04/26 16:48:17]

I'll address this in a follow-up CL when I introduce ParseTailCallExpression. 

         this->MarkTailPosition(expression);
       }
     }
     super_loc = function_state.super_location();
 
     formal_parameters.scope->set_end_position(scanner()->location().end_pos);
 
     // Arrow function formal parameters are parsed as StrictFormalParameterList,
     // which is not the same as "parameters of a strict function"; it only means
     // that duplicates are not allowed.  Of course, the arrow function may
@@ skipping 238 matching lines @@
     has_seen_constructor_ = true;
     return;
   }
 }
 
 
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_PARSING_PARSER_BASE_H