To fully support hydrogen code stubs which accept a variable number of arguments,

src/x64/lithium-x64.h

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 1320 matching lines @@
 
   virtual Opcode opcode() const { return LInstruction::kArithmeticT; }
   virtual void CompileToNative(LCodeGen* generator);
   virtual const char* Mnemonic() const;
 
  private:
   Token::Value op_;
 };
 
 
-class LReturn: public LTemplateInstruction<0, 1, 0> {
+class LReturn: public LTemplateInstruction<0, 2, 0> {
  public:
-  explicit LReturn(LOperand* value) {
+  explicit LReturn(LOperand* value, LOperand* parameter_count) {
     inputs_[0] = value;
+    inputs_[1] = parameter_count;
   }
 
   LOperand* value() { return inputs_[0]; }
 
+  bool has_constant_parameter_count() {
+    return parameter_count()->IsConstantOperand();
+  }
+  LConstantOperand* constant_parameter_count() {
+    ASSERT(has_constant_parameter_count());
+    return LConstantOperand::cast(parameter_count());
+  }
+  LOperand* parameter_count() { return inputs_[1]; }
+
   DECLARE_CONCRETE_INSTRUCTION(Return, "return")
 };
 
 
 class LLoadNamedField: public LTemplateInstruction<1, 1, 0> {
  public:
   explicit LLoadNamedField(LOperand* object) {
     inputs_[0] = object;
   }
 
@@ skipping 1261 matching lines @@
 
   DISALLOW_COPY_AND_ASSIGN(LChunkBuilder);
 };
 
 #undef DECLARE_HYDROGEN_ACCESSOR
 #undef DECLARE_CONCRETE_INSTRUCTION
 
 } }  // namespace v8::int
 
 #endif  // V8_X64_LITHIUM_X64_H_