Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP
Posting-Version: version B 2.10.2 9/18/84; site mcnc.mcnc.UUCP
Path: utzoo!watmath!clyde!burl!ulysses!allegra!mit-eddie!genrad!decvax!mcnc!jnw
From: jnw@mcnc.UUCP (John White)
Newsgroups: net.arch,net.micro.68k
Subject: Re: M680*0 "small model"
Message-ID: <587@mcnc.mcnc.UUCP>
Date: Mon, 17-Jun-85 22:30:40 EDT
Article-I.D.: mcnc.587
Posted: Mon Jun 17 22:30:40 1985
Date-Received: Wed, 19-Jun-85 04:53:34 EDT
References: <167@mot.UUCP> <1069@peora.UUCP>
Organization: Microelectronics Center of NC; RTP, NC
Lines: 22
Xref: watmath net.arch:1422 net.micro.68k:934

> >      The M680*0 small model is not generally supported in M680*0 systems
...
> It sounds to me like what the 68000 needs is an optimizing assembler.
...
> It seems to me that such an optimizer could be used as a post-processor
> for the compiler allowing all languages to use this technique.

    There is a problem in doing this. Since several files can be compiled
seperatly and then linked together, there is no way the compiler can
know what data can be fit into the area of memory accessed by "short"
instructions. Only the linker can know where each piece of data will be
put. I have seen a compiler (on a time-sharing system) that could be
given a "shortstatic=number" switch. All variables shorter than "number" bytes
whould be put in a seperate partition that the linker whould put within
the first 32k of memory. Now the compiler would be able to generate short
absolute addreses instead of long absolute addreses. Everything except
the biggest arrays could usually be fit in this short partition. In
fact, the savings from the shortstatic switch were about as large as from
the -O switch, only the shortstatic switch didn't slow the compiler down.
The -O and shortstatic switches were independant, so they could be used
together for even greater savings.
- John N. White   {duke, mcnc}!jnw