Path: utzoo!yunexus!geac!syntron!jtsv16!uunet!mcvax!enea!kth!sics!uplog!lynx!grzm
From: grzm@zyx.SE (Gunnar Blomberg)
Newsgroups: comp.arch
Subject: Re: RISC v. CISC (was The NeXT problem)
Message-ID: <310@lynx.zyx.SE>
Date: 20 Oct 88 15:24:52 GMT
Article-I.D.: lynx.310
References: <156@gloom.UUCP>
Reply-To: grzm@lynx.zyx.SE (Gunnar Blomberg)
Organization: ZYX Sweden AB, Stockholm, Sweden
Lines: 42

In article <156@gloom.UUCP> cory@gloom.UUCP (Cory Kempf) writes:
>[...]
>
>Second, to perform a complex task, a RISC chip will need more
>instructions than a CISC chip.
>
>[...]

   Is this really the widely accepted truth?  It seems to me that a typical
well-designed RISC chip should actually need *fewer* instructions
(statically and dynamically) to perform most tasks than your typical CISC
chip, for the following reasons:

   * The RISC chip has more registers.

   * The RISC chip has a more orthogonal instruction set.

   * The RISC chip has three-operand instructions.

   I am assuming something like a 680x0 or an 80386 as the CISC here, ie
something that suffers heavily from non-orthogonality and lack of
registers.  A memory-to-memory CISC with a really orthogonal instruction
set is quite a different animal.

   What this boils down to is that a well-designed orthogonal instruction
set should give fewer instructions for most tasks than your typical Complex
Instruction Set, even taking into account all the strange instructions for
function calls and other things.  I would *much* rather program an HP-PA
RISC than any CISC I have ever seen (with the possible exception of the
PDP-10), and the same is true for the SPARC chip, though less emphatically
so.  Thank heaven chip designers (finally) realized the value of a clean,
orthogonal instruction set!

   On the other hand, since most RISC encodings use a fixed instruction
size, the program will probably be bigger.  Maybe this is what is meant
above?

-- 
Disguised as a Dutch mathematician, | Gunnar Blomberg
Brow [the alien] had advanced the   | ZYX Sweden AB, Bangardsg 13,
destructive mathematical philosophy | S-753 20  Uppsala, Sweden
called intuitionsism --Rudy Rucker  | email: grzm@zyx.SE