Path: utzoo!utgpu!news-server.csri.toronto.edu!clyde.concordia.ca!uunet!cs.utexas.edu!usc!apple!baum
From: baum@Apple.COM (Allen J. Baum)
Newsgroups: comp.arch
Subject: Re: Why The Move To RISC Architectures?  ('386 vs. RISC)
Message-ID: <39747@apple.Apple.COM>
Date: 22 Mar 90 23:44:19 GMT
References: <28012@cup.portal.com> <289@emdeng.Dayton.NCR.COM> <1990Mar22.190941.1184@esegue.segue.boston.ma.us>
Reply-To: baum@apple.UUCP (Allen Baum)
Organization: Apple Computer, Inc.
Lines: 24

[]
>In article <1990Mar22.190941.1184@esegue.segue.boston.ma.us> johnl@esegue.segue.boston.ma.us (John R. Levine) writes:
>In article <289@emdeng.Dayton.NCR.COM> hrich@emdeng.UUCP (George.H.Harry.Rich) writes:
>>It might even be true that a complex instruction set designed ideally for
>>compiler code generation might beat RISC. ...
>
>I doubt it.  The IBM 801 project included some of the best compiler people
>around and they came up with the original RISC machine which was quite
>stripped down, and an extremely fancy compiler named PL.8 which generates
>fantastic code for it.

I'm afraid I no longer buy arguments of the form "x didn't do it, and x
is omnipotent, so it can't/shouldn't be done." That work was done 10+ years ago
and the state of the art has improved, and will continue to improve. In fact,
the IBM patent suite includes one patent that describes how to optimally 
choose instruction forms including mem->reg insts. For example, if something
was to be added to a register, and nothing else was done with it, then the
"Add mem to Reg" form would be selected, not "Load Mem to Reg",
"Add reg to reg". The latter might be used if the value was going to be used
again shortly, or be modified, etc.

--
		  baum@apple.com		(408)974-3385
{decwrl,hplabs}!amdahl!apple!baum