1. A computer-readable storage medium storing a computer program for generating, from a first code, a specific instruction for performing a same type of operation on different data in parallel by combining two or more instructions included in the first code, and generating a second code including the specific instruction, the computer program causing a computer to perform a procedure comprising: generating first and second operation trees representing a dependency relationship among instructions included in the first code, computing a first operation sequence by arranging operations specified by instructions of the first operation tree in an order that matches a structure of the first operation tree, and computing a second operation sequence by arranging operations specified by instructions of the second operation tree in an order that matches a structure of the second operation tree; computing one or more longest operation subsequences of operation subsequences common to the first and second operation sequences; and evaluating, for each of two or more longest operation subsequences, when computed, utilization of computing resources used for executing combinations of instructions of the first and second operation trees corresponding to operations included in said each longest operation subsequence, and selecting a combination pattern of instructions indicated by one of the two or more longest operation subsequences based on results of the evaluating.