vstack.pushItem(v);
v.release(eContext);
    public final void visit_instanceof(VmConstClass classRef) {        //TODO: port to orp-style        vstack.push(eContext);        RefItem v = vstack.popRef();        vstack.pushItem(v);        /* Objectref is already on the stack */        writeResolveAndLoadClassToEAX(classRef, S0);        final Label trueLabel = new Label(this.curInstrLabel + "io-true");        final Label endLabel = new Label(this.curInstrLabel + "io-end");        /* Pop objectref */        helper.writePOP(Register.ECX);        /* Is instanceof? */        instanceOf(trueLabel);        /* Not instanceof */        os.writeXOR(T0, T0);        os.writeJMP(endLabel);        os.setObjectRef(trueLabel);        os.writeMOV_Const(T0, 1);        os.setObjectRef(endLabel);        os.writePUSH(T0);    }