Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP
Path: utzoo!mnetor!seismo!rutgers!clyde!cbosgd!ihnp4!occrsh!uokmax!rmtodd
From: rmtodd@uokmax.UUCP (Richard Michael Todd)
Newsgroups: comp.os.minix
Subject: Re: minix C compiler performance
Message-ID: <582@uokmax.UUCP>
Date: Sun, 31-May-87 23:44:13 EDT
Article-I.D.: uokmax.582
Posted: Sun May 31 23:44:13 1987
Date-Received: Tue, 2-Jun-87 07:10:52 EDT
References: <1131@rocksvax.UUCP>
Organization: University of Oklahoma, Norman, OK
Lines: 40
Summary: main difference may be register variables

In article <1131@rocksvax.UUCP>, martyl@rocksvax.UUCP (Marty Leisner) writes:
> Under Minix, dhrystone (at least the copy I got from netlib) turned about
> 250 dhrystones/second.  Under Aztec C/MS-DOS on the same hardware, dhrystone
> turned 1200+ dhrystones/second.
Well, what little testing I've done doesn't show that drastic a difference
between the two compilers, but there is a difference in execution times.
I'm not familiar with the Dhrystone benchmark--does it use register variables
heavily?  You see, the Minix compiler apparently ignores register
declarations, whereas Aztec C (I have the developer's system, v3.40a), seems
to handle up to two int-sized register vars, one in si, one in di.  It makes
a good bit of difference.  I just recently did a slightly modified sieve,
(I upped the number of iterations to 100 from 10) compiling both with and
without register declarations, and linking with the Minix library and
running them through dos2out, so that the two Aztec-compiled versions
(with & without register declarations) would run under Minix.  This
ensures that we aren't accidentally including any differences arising
from the different operating environments (DOS and Minix). Timing them
and the sieve compiled under Minix's compiler gave these results
(all results are user time given by /usr/bin/time, CPU is 8088 at 4.77MHz)
Aztec cc with register declarations:       96.5 sec.
Aztec cc without register declarations:   132.4 sec.
Minix cc                                  141.0 sec.
You can see that without register declarations, Aztec's code gives
performance slightly better than the Minix cc.  The register variables
make a huge difference.  
Of course, the sieve is a rather limited benchmark; other benchmarks like
Dhrystone will get different improvements by addition/subtraction of
register variables.
> A few questions about the Minix C compiler and the distribution disks:
> 	1) which compiler was the AT kernel/utilities compiled with?
> 	   When I recompiled the kernel, the sizes of the linked files
> 	   didn't agree with the distribution versions.
Apparently it was the PC/IX compiler.  The Minix compiler produces somewhat
larger code.  From my limited experimentation with Aztec C -- recompiling
the shell and fs -- the code size produced is roughly comparable to the
PC/IX output.
--------------------------------------------------------------------------
Richard Todd
USSnail:820 Annie Court,Norman OK 73069
UUCP: {allegra!cbosgd|ihnp4}!okstate!uokmax!rmtodd