Path: utzoo!mnetor!uunet!husc6!necntc!celtics!roger
From: roger@celtics.UUCP (Roger B.A. Klorese)
Newsgroups: comp.lang.c
Subject: Re: some objections to 'noalias'
Message-ID: <1912@celtics.UUCP>
Date: 28 Dec 87 20:21:58 GMT
References: <485@cresswell.quintus.UUCP> <1453@cuuxb.ATT.COM> <492@cresswell.quintus.UUCP>
Reply-To: roger@celtics.UUCP (Roger B.A. Klorese)
Organization: CELERITY (Northeast Area), Framingham, MA
Lines: 28

In article <492@cresswell.quintus.UUCP> ok@quintus.UUCP (Richard A. O'Keefe) writes:
>I would claim that aliasing is a worse problem in Fortran than in C.

Probably true.

>So my question: if people care about optimising Fortran (and they DO)
>and they care about writing correct programs in Fortran (and they DO)
>and if aliasing is a problem in Fortran (and I've just shown that it
>IS), what is so special about C that it needs a 'noalias' declaration?

Because many people have *already* extended their FORTRAN compilers
to handle aliasing properly.  Quoting from the Celerity Computing
Tools and Applications Reference Manual, Volume III, Book 2 (Languages,
Kernel), which is Copyright 1986 Celerity Computing, on page 1-14:

"However, even programs that contain hidden aliasing can be safely
optimized if the optimization control '-Oc s' is specified.  It causes
the optimizer to refrain from placing in registers any expressions
that depend on common-block variables or incoming parameters."

When parameters and common block allocations are eliminated from
consideration, and proper subscripting is observed, FORTRAN aliases
should all be detectable.  (Any cases left out?)
-- 
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