2.14 Using Additional Performance Improvement Techniques

After you have successfully run KAP on a working program by using either the protocol for small programs or that for large programs, you can try the following procedures to find additional opportunities for optimization within your program:

• If each COMMON block is laid out the same way everywhere that it is used or if no data is passed between different layouts, then try -aggressive=a or -aggressive=ab . In some cases, these actions can yield up to a 20% performance improvement.

• If you have successfully run KAP on some routines in a large program, then try running KAP on the whole program with the same switches.

• Try -save=manual . If the user-written SAVE statements are sufficient and correct for the compiler you are using, this action may reduce unneeded precautions that KAP ordinarily takes.

• Try lowering the settings on the Invariant-IF switches -eiifg and -miifg . These actions may reduce the total code space enough to make paging or caching the program code work better.

• You can try brute-force inlining. Set -inline_and_copy and -inll=2 . Inlining is usually more effective if you inline only a few carefully chosen routines rather than inlining everything and cluttering up the code with too much low-payoff inlining. However, the shotgun approach can sometimes produce good results.

• Experiment with each of the following switches to determine if they improve the run-time of your program.
  -fuse
  -fuselevel=1
  -ipa
  ipa_from_files=<file>,<file>
  -ipa_optimize=2

  However, the above switches may increase the amount of time and memory KAP needs to process your source files.

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