1. A method for obtaining execution frequency information on execution paths in a control flow graph, the method comprising causing a computer to execute the steps of: reading, by one or more computer processors, into a memory a source code to be complied; preparing, by one or more computer processors, a control flow graph from the source code read into the memory, the preparing step including a step of modifying the control flow graph by assigning zero to an edge v→w between a basic block v in a precedent position (hereinafter referred to as “predecessor basic block”) and a basic block w following the predecessor basic block v (hereinafter referred to as “successor basic block”) in a case where the successor basic block w has a predecessor basic block x other than the predecessor basic block v, and where the successor basic block w exists on a fall-through path from the predecessor basic block x; and obtaining, by one or more computer processors, the execution frequency information by using the control flow graph modified by the modifying step.