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, prior to modification of the control flow graph, 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 wherein when zero is assigned to the edge v→w, no instruction to add a path value to the edge v→w is added; modifying, by one or more computer processors, the control flow graph according to one of the following steps: 1) inserting an instruction to add a path value in a successor basic block w′ other than the successor basic block w in a case where the successor basic block w′ other than the successor basic block w following the predecessor basic block v has no predecessor basic block other than the predecessor basic block v; 2) inserting a basic block m on an edge v→w′ between the predecessor basic block v and a successor basic block w′ other than the successor basic block w and inserting an instruction to add a path value in the basic block m in a case where the successor basic block w′ other than the successor basic block w following the predecessor basic block v has a predecessor basic block y other than the predecessor basic block v; or 3) modifying the control flow graph by taking out one successor basic block wi from three or more successor basic blocks {w 1 ,. .. , wn} if the three or more successor basic blocks {w 1 ,. .. , wn} exist subsequently to the predecessor basic block v, provided that the successor basic block wi has a predecessor basic block x other than the predecessor basic block v existing as a successor basic block following the predecessor basic block v and exists on a fall-through path from the predecessor basic block x, and by assigning zero to an edge v→wi between the predecessor basic block v and the successor basic block wi taken out; and obtaining, by one or more computer processors, the execution frequency information by using the control flow graph modified by the modifying step.