[runtime] Optimize and unify rest parameters.

src/parsing/parser.cc

 // 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.
 
 #include "src/parsing/parser.h"
 
 #include "src/api.h"
 #include "src/ast/ast.h"
 #include "src/ast/ast-expression-rewriter.h"
 #include "src/ast/ast-expression-visitor.h"
@@ skipping 4190 matching lines @@
     ParseFormalParameterList(&formals, &formals_classifier, CHECK_OK);
     arity = formals.Arity();
     Expect(Token::RPAREN, CHECK_OK);
     int formals_end_position = scanner()->location().end_pos;
 
     CheckArityRestrictions(arity, arity_restriction,
                            formals.has_rest, start_position,
                            formals_end_position, CHECK_OK);
     Expect(Token::LBRACE, CHECK_OK);
 
+    // Don't include the rest parameter into the function's formal parameter
+    // count (esp. the SharedFunctionInfo::internal_formal_parameter_count,
+    // which says whether we need to create an arguments adaptor frame).
+    if (formals.has_rest) arity--;
+
     // Determine if the function can be parsed lazily. Lazy parsing is different
     // from lazy compilation; we need to parse more eagerly than we compile.
 
     // We can only parse lazily if we also compile lazily. The heuristics for
     // lazy compilation are:
     // - It must not have been prohibited by the caller to Parse (some callers
     //   need a full AST).
     // - The outer scope must allow lazy compilation of inner functions.
     // - The function mustn't be a function expression with an open parenthesis
     //   before; we consider that a hint that the function will be called
@@ skipping 2104 matching lines @@
 
   statements->Add(get_return, zone);
   statements->Add(check_return, zone);
   statements->Add(call_return, zone);
   statements->Add(validate_output, zone);
 }
 
 
 }  // namespace internal
 }  // namespace v8