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Path: utzoo!dciem!nrcaer!cognos!roberts
From: roberts@cognos.uucp (Robert Stanley)
Newsgroups: comp.arch
Subject: Re: Wirth's "challenge" (was Re: RISC)
Message-ID: <1775@cognos.UUCP>
Date: Tue, 17-Nov-87 09:24:19 EST
Article-I.D.: cognos.1775
Posted: Tue Nov 17 09:24:19 1987
Date-Received: Fri, 20-Nov-87 22:16:25 EST
References: <902@mips.UUCP>
Reply-To: roberts@cognos.UUCP (Robert Stanley)
Organization: Cognos Inc., Ottawa, Canada
Lines: 33
Summary: RISC architecture and compiler design go hand in hand

In article <902@mips.UUCP> hansen@mips.UUCP writes:

>Enough of the details; Wirth's basic argument is that architectures and
>programming languages should support each other, and basically be designed
>together. In the abstract, this possition is unassailable; however, the need
>for compatibility with old, badly designed languages will require that
>compromises be made in architectures. 

It is interesting to reflect on IBM's Project 801, where the RISC instructions
were designed very much with the compiler writers in mind.  In fact, if memory
serves, it was the compiler writers who had the final say in a number of cases.
What made this project so particularly interesting was that not only was it a
PL/1 machine (in that PL/1 was the language for which the compiler was being 
developed in tandem with the hardware development), but that the compiler suite
included a 370 (uh, 360) compatability mode.  In the compatability mode, the
target architecture was System/360 and optimized run-time code generated
compared *extremely* favourably with output from the PL/1 Optimizer of the
day.  It is by no means obvious that the 801's architectural integrity had
to be compromised to achieve this, with the caveat that perhaps 10 (or so)
years ago there was less awareness.....

Perhaps of more relevance was the PL/1 Optimizer, which maintained backwards
compatability with the System/360 by steadfastly ignoring the System/370
extended instruction set.  I forget just how long that particular piece of
double-think was perpetuated.

Robert_S

-- 
Robert Stanley           Cognos Incorporated     S-mail: P.O. Box 9707
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