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From: ags@pucc-i (Seaman)
Newsgroups: net.arch
Subject: Re: Cray-XMP v/s VP-200 - (nf)
Message-ID: <290@pucc-i>
Date: Tue, 22-May-84 11:16:34 EDT
Article-I.D.: pucc-i.290
Posted: Tue May 22 11:16:34 1984
Date-Received: Sat, 26-May-84 10:03:14 EDT
References: <3200004@uicsg.UUCP> <2600001@uicsl.UUCP>
Organization: Purdue University Computing Center
Lines: 26

>  The task of vectorizing a Fortran Program is not as difficult as you may 
>  imagine. Systems have been developed that can do the job quite well.
>  In some cases these programs are claimed to be better then even 
>  hand-coded versions. In general, however, they are able to extract 
>  upto about 70-80 percent of the maximum parallelism attainable for 
>  the program. 

There is much more to vectorization than you think.  I have seen code
generated by two of these programs:  the Vector and Array Syntax
Translator (VAST) and the Kuck Analyzer Program (KAP) for the CYBER 205.
Both programs are reasonably good at SYNTACTIC VECTORIZATION (recognizing
and translating vectorizable DO loops), although the resulting vector
code can be further improved by any competent programmer.

Neither program can do SEMANTIC VECTORIZATION (transforming or replacing
entire algorithms to make parallel computation possible).  I have seen
cases where semantic vectorization improved program performance by two
orders of magnitude, which is far beyond what can be achieved by vectorizing
preprocessors.
-- 

Dave Seaman
..!pur-ee!pucc-i:ags

"Against people who give vent to their loquacity 
by extraneous bombastic circumlocution."