Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP
Path: utzoo!mnetor!seismo!ll-xn!husc6!necntc!pec
From: pec@necntc.NEC.COM (Paul Cohen)
Newsgroups: comp.arch
Subject: Re: Japanese 32-bit CPUs ( NEC V70 ) [really 29K]
Message-ID: <4070@necntc.NEC.COM>
Date: Thu, 7-May-87 11:49:55 EDT
Article-I.D.: necntc.4070
Posted: Thu May  7 11:49:55 1987
Date-Received: Sat, 9-May-87 04:24:38 EDT
References: <3810030@nucsrl.UUCP> <491@necis.UUCP>
Reply-To: pec@necntc.UUCP (Paul Cohen)
Organization: NEC Electronics Inc.  Natick, MA 01760
Lines: 65
Keywords: V60, V70

In article <372@winchester.UUCP> mash@winchester.UUCP (John Mashey) writes:
>In article <16561@amdcad.AMD.COM> bcase@amdcad.UUCP (Brian Case) writes:
>>In article <4016@necntc.NEC.COM> pec@necntc.UUCP (Paul Cohen) writes:
>>>It depends on its objectives.  The 29K requires two separate
>>>paths to memory, one for code and another for data.  The memory must be
>>>extremely fast (read expensive) to service the CPU without wait states.

>2 paths are usually better than one, as any chips will discover when they
>keep pushing clock rates.

I very much agree if you mean better performance.  Do you also mean
better system cost?

>>optimizations *easier* not more difficult.  I believe that most of
>>the members of the compiler-writing and architecture community would
>>agree that a simple architecture with a predictable cost for instructions
>>(in both time and space) is the best match for automatic code generation.

There is no doubt that having fewer options makes decisions easier.

I agree that comments from compiler writers would be welcome here.

>If somebody says "20 addressing modes are good", to be convincing, they'd
>better be able to show tradeoffs, and show us the dynamic and static usages
>of those things, in real compiled code of substantial size.  

A quibble here: Why is the size of the code important?  

	I don't understand why the size of the code has any bearing on 
	use of addressing modes, though I do see that it would have some 
	bearing on the difficulty of determining usage statistics.  Even 
	if there is some connection, I suspect there are many machines 
	in active use that spend most of their time executing fairly 
	small programs.  

The C compiler that is currently available for the V60/V70 is based on 
the Unix Portable C Compiler.  This is admitedly not the best (in terms
of performance, disregarding cost) compiler technology around (there are 
two other C compilers under development for the V60/V70 by U.S. compiler 
companies), but this compiler does use all of the available addressing 
modes (and all of the V60/V70 non-privileged instructions except for 
some of the string instructions).  

I wish that I had the time to do a study of the sort suggested (though 
probably any results that I would get would be suspected of bias).
One question to ponder in this regard: suppose only 15 (or even only 5) 
of the addressing modes were found to be extensively used by SOME compiler.
Could you conclude that you would be better off with only one or two 
addressing modes?

If anyone (preferably someone with no axe to grind) would like to 
volunteer to do some research of this kind on V60/V70 code I'd be more 
than happy to cooperate.

On another note, in response to an earlier posting, I've had numerous 
requests for help in getting documentation on the V60/V70.  I earlier 
posted the telephone numbers:

		1-800-NEC-ELEC (California)
		1-800-NEC-ELE1 (During California working hours)

It did not occur to me that I would get requests from Europe as well.
If that is your general location, a better number would be:

		0049-211-6503-333 (Dusseldorf)