Newsgroups: comp.arch
Path: utzoo!henry
From: henry@utzoo.uucp (Henry Spencer)
Subject: Re: RISC is NOT micro-code (was Re: Compiling - RISC vs. CISC
Message-ID: <1989Jul17.035238.6497@utzoo.uucp>
Organization: U of Toronto Zoology
References: <28471@ames.arc.nasa.gov> <200@dg.dg.com> <12233@pur-ee.UUCP> <753@bnr-fos.UUCP>
Date: Mon, 17 Jul 89 03:52:38 GMT

In article <753@bnr-fos.UUCP> schow%BNR.CA.bitnet@relay.cs.net (Stanley Chow) writes:
>  4) RISC has more opportunaty for optimizations ... This means
>     the compiler is much harder to get right...

No, it means it is harder to get optimal.  There's a difference between
generating suboptimal code and generating wrong code.  Truly well-built
compilers (obviously the semantics of "well-built" here are somewhat a
matter of opinion) do much optimization by applying transformations that
are *hoped* to improve the code but are *known* to preserve semantics.
Such compilers may not always generate the fastest code but will seldom
generate wrong code.

Incidentally, do you really think the greater complexity of CISC
instruction sets makes CISC compilers *easier* to get right?  The
compiler, if nobody else, has to know all the gory details of the
machine if it's really pushing for good code quality.
-- 
$10 million equals 18 PM       |     Henry Spencer at U of Toronto Zoology
(Pentagon-Minutes). -Tom Neff  | uunet!attcan!utzoo!henry henry@zoo.toronto.edu