Path: utzoo!mnetor!uunet!husc6!cmcl2!phri!dasys1!jsb
From: jsb@dasys1.UUCP (Jim Baumbach)
Newsgroups: comp.lang.c
Subject: Re: `noalias' vs `register'
Message-ID: <2270@dasys1.UUCP>
Date: 19 Dec 87 17:49:56 GMT
References: <8712170057.AA17035@decwrl.dec.com> <6858@brl-smoke.ARPA>
Reply-To: jsb@dasys1.UUCP (Jim Baumbach)
Organization: The Big Electric Cat
Lines: 23
Keywords: noalias ANSI

In article <6858@brl-smoke.ARPA> gwyn@brl.arpa (Doug Gwyn (VLD/VMB) <gwyn>) writes:
-In article <8712170057.AA17035@decwrl.dec.com> devine@cookie.dec.com (Bob Devine) writes:
->In article <6833@brl-smoke.ARPA> gwyn@brl.arpa (Doug Gwyn (VLD/VMB) <gwyn>) writes:
->  A better way, in hindsight, would have been to have a 'alias' keyword
->that designates those cases where multiple handles are used; all other
->cases could then be assumed to be optimizable.  Too late.
-
-It was always too late for that!
-The default has to be "safe" behavior to agree with current C.

Sort of true, but the opposite decision was made vis a vis 'volatile'.
Before the invention of volatile, all variables were potentially volatile
and optimizers which treated them otherwise were WRONG.  I had to use a
work around to get my routine which checked for the ready bit to be set
on my disc controller not to have the check removed by the optimizing
compiler.  In actuality, few cases of troublesome aliasing occur but a lot
fewer cases of 'volatile' occur so it was safe to break one but not the other.
				-jim
-- 
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