Path: utzoo!attcan!utgpu!jarvis.csri.toronto.edu!mailrus!tut.cis.ohio-state.edu!cs.utexas.edu!uunet!mcvax!ukc!etive!aiai!richard
From: richard@aiai.ed.ac.uk (Richard Tobin)
Newsgroups: comp.arch
Subject: Re: 80486 vs. 68040 code size [really: how many regs]
Message-ID: <459@skye.ed.ac.uk>
Date: 19 May 89 16:06:23 GMT
References: <948@aber-cs.UUCP> <8125@killer.Dallas.TX.US>
Reply-To: richard@aiai.UUCP (Richard Tobin)
Distribution: eunet,world
Organization: AIAI, University of Edinburgh, Scotland
Lines: 31

In article <8125@killer.Dallas.TX.US> elg@killer.Dallas.TX.US (Eric Green) writes:
>But there's one problem: Types. On a 68000, shorts and ints are 16
>bits, longs are 32 bits. What this means is that if I declare a
>register int xyz, I can't put a long into it -- the "C" compiler
>generates a "move.w" instead of a "move.l". If I declare everything as
>register long xyz, the "C" compiler generates a "add.l" instead of an
>"add.w", i.e. I just lost all the time I'd saved. 

Often you can get reasonable code out of a dumb compiler with code like
this:

    {
        register long t1;
        .....
    }
    {
        register short t2;
        .....
    }

(I.e. the compiler will use the same register for variables in different
blocks.)

But perhaps you already knew this.

-- Richard

-- 
Richard Tobin,                       JANET: R.Tobin@uk.ac.ed             
AI Applications Institute,           ARPA:  R.Tobin%uk.ac.ed@nsfnet-relay.ac.uk
Edinburgh University.                UUCP:  ...!ukc!ed.ac.uk!R.Tobin