Path: utzoo!mnetor!uunet!husc6!think!ames!amdahl!pyramid!prls!mips!hansen
From: hansen@mips.UUCP (Craig Hansen)
Newsgroups: comp.lang.c
Subject: Re: noalias; parens honored
Message-ID: <1174@mips.UUCP>
Date: 18 Dec 87 05:42:42 GMT
References: <6829@brl-smoke.ARPA> <2845@zeus.TEK.COM>
Lines: 23
Keywords: ANSI C standard

Doug Gwyn writes (about the last ANSI C standards meeting):
>A new keyword, "noalias", was added; it's a type-qualifier like const
>and volatile.  Its only function is to permit tighter optimization,
>
>Parenthesis grouping is now honored.  

I am pleased to hear of the ruling on parenthesis grouping: people
will recall the acrimonious treatment the idea received in this
newsgroup some time ago, and for good reason.

"noalias" appears to be ill-conceived. Pointer aliasing happens _between_ a
_pair_ of pointers, and is not a particularly useful property of a single
pointer. Fortran 77 actually has this property specified in a different
form; that no two procedure parameters may yield references that alias to
the same location, and for vector operations, it can be responsible for
significant speed-ups. However, checking for its proper use is extremely
difficult, and I would conjecture, as difficult as the halting problem.

-- 
Craig Hansen
Manager, Architecture Development
MIPS Computer Systems, Inc.
...{ames,decwrl,prls}!mips!hansen or hansen@mips.com