Adds Nip() function, makes UnloadReference() work without spilling

src/codegen-ia32.cc

 // Copyright 2006-2008 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 531 matching lines @@
     frame_->CallRuntime(Runtime::kThrowReferenceError, 1);
   }
 
   in_spilled_code_ = was_in_spilled_code;
 }
 
 
 void CodeGenerator::UnloadReference(Reference* ref) {
   // Pop a reference from the stack while preserving TOS.
   Comment cmnt(masm_, "[ UnloadReference");
-  int size = ref->size();
-  if (size == 1) {
-    VirtualFrame::SpilledScope spilled_scope(this);
-    frame_->EmitPop(eax);
-    __ mov(frame_->Top(), eax);
-  } else if (size > 1) {
-    VirtualFrame::SpilledScope spilled_scope(this);
-    frame_->EmitPop(eax);
-    frame_->Drop(size);
-    frame_->EmitPush(eax);
-  }
+  frame_->Nip(ref->size());
 }
 
 
 class ToBooleanStub: public CodeStub {
  public:
   ToBooleanStub() { }
 
   void Generate(MacroAssembler* masm);
 
  private:
@@ skipping 2534 matching lines @@
         LoadAndSpill(node->value());
         GenericBinaryOperation(node->binary_op(), node->type());
       }
     }
 
     Variable* var = node->target()->AsVariableProxy()->AsVariable();
     if (var != NULL &&
         var->mode() == Variable::CONST &&
         node->op() != Token::INIT_VAR && node->op() != Token::INIT_CONST) {
       // Assignment ignored - leave the value on the stack.
-  } else {
+    } else {
       CodeForSourcePosition(node->position());
       if (node->op() == Token::INIT_CONST) {
         // Dynamic constant initializations must use the function context
         // and initialize the actual constant declared. Dynamic variable
         // initializations are simply assignments and use SetValue.
         target.SetValue(CONST_INIT);
       } else {
         target.SetValue(NOT_CONST_INIT);
       }
     }
@@ skipping 2849 matching lines @@
 
   // Slow-case: Go through the JavaScript implementation.
   __ bind(&slow);
   __ InvokeBuiltin(Builtins::INSTANCE_OF, JUMP_FUNCTION);
 }
 
 
 #undef __
 
 } }  // namespace v8::internal