To save and restore the contents of registers efficiently and enhance the execution efficiency of compilation. For a predetermined variable in an executable program, a determination is made whether or not the variable lives across invoking of a predetermined function, and if so, the kind of invoking of the function is determined. The variable is allocated to any of volatile registers, non-volatile registers, and semi-volatile registers, based on this determination. Also, it is determined to which register the variable living across invoking of the function is allocated, based on an execution frequency of the function when the executable program is run.