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From: bright@nazgul.UUCP (Walter Bright)
Newsgroups: comp.lang.c
Subject: Re: Heroic constant folding (was micro-optimizing loops etc.)
Message-ID: <287@nazgul.UUCP>
Date: 23 Mar 91 11:28:48 GMT
References: <10191@dog.ee.lbl.gov> <14522@ganymede.inmos.co.uk> <10450@dog.ee.lbl.gov> <1991Mar2.010049.21044@grebyn.com> <RJOHNSON.91Mar11141459@olorin.shell.com>
Reply-To: bright@nazgul.UUCP (Walter Bright)
Organization: Zortech, Seattle
Lines: 16

In article <RJOHNSON.91Mar11141459@olorin.shell.com> rjohnson@shell.com (Roy Johnson) writes:
/>Of course, the best optimization for:
/>	for (i = 1; i < 100; i++)
/>		x += i;
/>is:
/>	x += 4950;
/This doesn't look to be such a bad thing to optimize away (speaking
/with all the authority of one who doesn't write compilers).

Actually, it is probably not worth the bother to attempt to optimize away.
In general, a program that needs to be optimized is one that is going to be
run many times. A loop that is determinate (doesn't change from run to run)
generally does not appear in a program that is to be run many times.

There are still lots of unexploited opportunities for optimizations in
code that *does* commonly appear in production programs.