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Subject: gcc optimizations (Re: off-topic - Nt vs Linux)
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From: David Moore <dmoore@ucsd.edu>
Date: 13 Mar 1997 12:35:00 -0800
In-Reply-To: Steven L Baur's message of 12 Mar 1997 22:42:55 -0800
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Steven L Baur <steve@miranova.com> writes:

> -m486 -O4 -fno-strength-reduce -malign-loops=2 -malign-jumps=2
> 	   -malign-functions=2 -fomit-frame-pointer

Btw, there is no -O4 (or anything above -O3) in gcc 2.7.2.1.  -O3 turns
is the highest level which turns on various generic -f optimizations,
and the only two machines with cpu specific optimizations (i960 and
pdp11) turn their extra optimization on at -O2 and -O3.  Has this
changed in 2.7.2.2?

And -fomit-frame-pointer will get turned on with -O1 on machines that
can debug w/o frame pointers (such as sparc).  Just in case anyone was
wondering. :) So this means that on any machine you'll either already
have this speedup with simple -O, or will basically be guaranteed no
ability to debug if you turn it on yourself.

Looking at toplev.c around line 3392 in the gcc dist should help you see
the generic affects of -O levels.  And you can look at `egrep
OPTIMIZATION_OPTIONS config/*/*' to see what cpus have specific other
optimizations.  Also try `egrep optimize config/i386/*', etc.

-- 
David Moore <dmoore@ucsd.edu>       | Computer Systems Lab      __o
UCSD Dept. Computer Science - 0114  | Work: (619) 534-8604    _ \<,_
La Jolla, CA 92093-0114             | Fax:  (619) 534-1445   (_)/ (_)
<URL:http://oj.egbt.org/dmoore/>    | In a cloud bones of steel.

