ABO should be useful for sites not going to V5/V6 "anytime soon"
The following presumes a "12" or "13" system, and z/OS 2.1 or higher.
1. Staying with pre-V4.2, bimbling along with out-of-service compilers
Pre-Enterprise COBOL programs, would need recompile with Enterprise COBOL to
allow ABO. For any already Enterprise COBOL executables, the ABO will operate
and give benefit.
2. Migrating to V4.2
Even after recompiling with V4.2, ABO would give benefits, access to "new"
instructions, and advanced optimisation techniques.
ABO could be useful to sites migrating to V5/V6
1. Really rapid migration, probably no point in ABO ("Really rapid" is
subjective).
2. Long process of migration, ABO would be useful for heavy CPU-users which are
scheduled to migrate a year or more down the track ("Long" is subjective).
An interesting question is whether, or to what extent, you "test" optimised
programs.
That may depend on how you take this claim: "[ABO] ... produces a functionally
equivalent executable program".
I know that there are some people/sites who don't "trust" the existing
optimisation in the compilers. Obviously they are not going to be ABO-users
anyway.
IBM's advice for the use of OPT (even prior to V5) is to "whack it on just
before you go into Production". I've never liked that, but not because I don't
trust the optimiser. I don't trust the application code :-) Anyone who has ever
encountered an accidental overlay of executable code is probably aware that
"incidental" overwriting can also be occurring. And it can be so incidental as
to "work to specification" until something changes in the code and
now-significant code gets overwritten.
I don't want a program to go through N stages of "testing" and then have the
object code changed (so that something may become significant) just before
tossing it into Production. So I recommend OPT after initial program-testing.
So, should programs after ABOing be "tested", to partially test ABO? Should ABO
be "tested" in isolation (a wider coverage of things in a shorter period of
time) or - perhaps taking ABO-stability into account (no "program doesn't work"
fixes yet for ABO) - just go with the flow?
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