Re: Vector assignment semantics (was Re: latest trends in compiler optimization research?)

glen herrmannsfeldt <gah@ugcs.caltech.edu>
Wed, 15 Aug 2007 12:13:51 -0800

          From comp.compilers

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From: glen herrmannsfeldt <gah@ugcs.caltech.edu>
Newsgroups: comp.compilers,comp.lang.pl1
Date: Wed, 15 Aug 2007 12:13:51 -0800
Organization: Compilers Central
References: 07-08-01607-08-021 07-08-024 07-08-034 07-08-037
Keywords: PL/I, parallel

Anton Lokhmotov wrote:


> All the papers on Fortran 8x I read so far mention the parallel
> semantics. But I decided to check on the PL/I semantics. In "The
> early history and characteristics of PL/I" (HOPL-I, 1978,
> pp. 570-571), George Radin wrote that he original PL/I semantics was
> serial but was changed to parallel in the ANSI-1976 standard. Radin
> claims that the parallel semantics seems more natural to
> programmers, while the sequential semantics does not require
> temporaries (as Glen Herrmannsfeldt has noted), possibly leading to
> more efficient code on machines of the time. Today, few would argue
> against supporting "naturalness" (even if at the expense of space).


http://publibfp.boulder.ibm.com/cgi-bin/bookmgr/BOOKS/ibmol004/3.1.4.2.1


It seems that IBM doesn't follow the ANSI-1976 standard, and this is
one more example. (The manual is copyright 1964, 1990, and I believe
applies to current IBM compilers.)


In most other cases, PL/I does support what I would have called
"naturalness" at the expense of space and/or time. This may have been
more "natural" to programmers used to using DO loops for array
assignment.


I have added comp.lang.pl1. Implementors of other PL/I compilers
might comment on their support of array expressions.


-- glen


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