A computer-implemented method for comparing the results on a plurality of target machines of modification of a region of original code , the method comprising: at a local machine , allowing a user to annotate a region of original code in a program to be extracted with a compiler directive; distributing the annotated program from the local machine to the target machines; at each target machine and at the local machine , compiling the annotated program code including the original code and the compiler directive, and during compilation the compiler directive causing the annotated region of the original code to be extracted to generate extracted code , which is then linked to a function call located at a position in the original code from which the extracted region was extracted, instrumenting the remaining original code of the program to save starting and ending working sets required to execute the extracted code region in the form of the value or state of the variables and data structures used, and generating executable code comprising the extracted code and instrumented code ; allowing modification by a user of the extracted code at the local machine and sending the modification to the target machines, the modification triggering re-compilation of the modified extracted code at each target machine ; at the local machine , allowing selection by a user of one or more options that are sent to the target machines in the form of any of a particular invocation of the extracted code, a modification of the starting working set, and a change of the initial dataset of the program; at each target machine , generating a new executable version of the extracted code for dynamic loading into the instrumented code ; and at each target machine , executing the instrumented code and dynamically loading and executing the new executable version of the extracted code and sending the results of each individual execution to the local machine , where the results are received and displayed for comparison. at a local machine , allowing a user to annotate a region of original code in a program to be extracted with a compiler directive; distributing the annotated program from the local machine to the target machines; at each target machine and at the local machine , compiling the annotated program code including the original code and the compiler directive, and during compilation the compiler directive causing the annotated region of the original code to be extracted to generate extracted code , which is then linked to a function call located at a position in the original code from which the extracted region was extracted, instrumenting the remaining original code of the program to save starting and ending working sets required to execute the extracted code region in the form of the value or state of the variables and data structures used, and generating executable code comprising the extracted code and instrumented code ; allowing modification by a user of the extracted code at the local machine and sending the modification to the target machines, the modification triggering re-compilation of the modified extracted code at each target machine ; at the local machine , allowing selection by a user of one or more options that are sent to the target machines in the form of any of a particular invocation of the extracted code, a modification of the starting working set, and a change of the initial dataset of the program; at each target machine , generating a new executable version of the extracted code for dynamic loading into the instrumented code ; and at each target machine , executing the instrumented code and dynamically loading and executing the new executable version of the extracted code and sending the results of each individual execution to the local machine , where the results are received and displayed for comparison. <EOS>