1. A method, for employing a stack register when a processor with a register stack executes a program, comprising the steps of: when a different procedure is called in a predetermined procedure, said predetermined procedure called before the different procedure, reallocating registers that are allocated for the execution of said predetermined procedure and are live when said different procedure is called, and calling said different procedure; and upon the return from said different procedure, restoring the register image to the state immediately before the reallocation.