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

src/ia32/lithium-ia32.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 1373 matching lines @@
   virtual void CompileToNative(LCodeGen* generator);
   virtual const char* Mnemonic() const;
 
   Token::Value op() const { return op_; }
 
  private:
   Token::Value op_;
 };
 
 
-class LReturn: public LTemplateInstruction<0, 2, 0> {
+class LReturn: public LTemplateInstruction<0, 3, 0> {
  public:
-  explicit LReturn(LOperand* value, LOperand* context) {
+  explicit LReturn(LOperand* value, LOperand* context,
+                   LOperand* parameter_count) {
     inputs_[0] = value;
     inputs_[1] = context;
+    inputs_[2] = parameter_count;
+  }
+
+  bool has_constant_parameter_count() const {
+    return hydrogen()->has_constant_parameter_count();

[danno, 2013/03/07 15:11:14]

You can implement these in terms of calls on the parameter_count LOperand*,
maybe allowing you to keep some of the
has_constant_parameter_count/constant_parameter_count abstraction that you count
on in lithium-codegen-ia32.cc

[mvstanton, 2013/03/07 16:48:49]

Done.

+  }
+  int constant_parameter_count() const {
+    return hydrogen()->constant_parameter_count();
+  }
+  LOperand* parameter_count() {
+    ASSERT(!has_constant_parameter_count());
+    return inputs_[2];
   }
 
   DECLARE_CONCRETE_INSTRUCTION(Return, "return")
+  DECLARE_HYDROGEN_ACCESSOR(Return)
 };
 
 
 class LLoadNamedField: public LTemplateInstruction<1, 1, 0> {
  public:
   explicit LLoadNamedField(LOperand* object) {
     inputs_[0] = object;
   }
 
   LOperand* object() { return inputs_[0]; }
@@ skipping 1417 matching lines @@
 
   DISALLOW_COPY_AND_ASSIGN(LChunkBuilder);
 };
 
 #undef DECLARE_HYDROGEN_ACCESSOR
 #undef DECLARE_CONCRETE_INSTRUCTION
 
 } }  // namespace v8::internal
 
 #endif  // V8_IA32_LITHIUM_IA32_H_