1. A method, executed by a computer, comprising: identifying one or more regions of COBOL source code having an entry point; selecting a PERFORM instruction associated with the entry point to analyze; determining a PERFORM range for the selected PERFORM instruction; identifying an instruction that changes control flow in execution of the COBOL source code subsequent to the selected PERFORM instruction; determining flow-affected code resulting from the instruction; determining reachable regions from the one or more regions of the COBOL source code for the selected PERFORM instruction; and forming an adjusted PERFORM range for the selected PERFORM instruction based on the determined reachable regions.