RE: RPG IV Performance

["Richard Jackson" <richardjackson@xxxxxxxxxxxxxxxxxx>]

Jon:

Thanks for correcting me.

When I wrote that statement, I was thinking that it was true for the reason
that I stated - better optimizer.  When it posted, I read it again and it
struck me as suspect - and probably wrong - but I wasn't sure why.  I hadn't
thought about the difference between the high-level "copy bytes left
adjusted" and the lower-level W-code.  I did notice that other postings of
ILE program size looked roughly one-quarter to one-third larger than OPM
program size.

Expanding on your point, isn't this kind of optimization (replace one big
thing with lots of simple and quick instructions) called "reduction in
strength"?

Thanks again for setting me straight.

Richard Jackson
(speaking only for myself)

-----Original Message-----
From: owner-rpg400-l@midrange.com [mailto:owner-rpg400-l@midrange.com]On
Behalf Of Jon.Paris@hal.it
Sent: Saturday, January 20, 2001 1:43 PM
To: RPG400-L@midrange.com
Subject: RE: RPG IV Performance



 >> I assert that the code part of the rpg4 program is probably shorter
than the code part for rpg3 programs.

Barbara or Hans can supply a more definitive answer but I believe the
reverse of what you suggest is true.  MI instructions are as you know of
the "Move Universe from A to B type".  W-code are of the "Move atom from
area A to area B.  If more atoms remain at A repeat." type.  The result is
that the actual instruction stream is significantly longer.  This would
also explain why you see far less difference when observability is removed.


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