Path: utzoo!attcan!uunet!ncrlnk!ncr-sd!hp-sdd!hplabs!decwrl!purdue!haven!ncifcrf!nlm-mcs!adm!smoke!gwyn
From: gwyn@smoke.BRL.MIL (Doug Gwyn )
Newsgroups: comp.lang.c
Subject: Re: const, volatile, etc
Message-ID: <9141@smoke.BRL.MIL>
Date: 11 Dec 88 06:00:37 GMT
References: <674@quintus.UUCP> <117@halcdc.UUCP> <468@auspex.UUCP> <1526@micomvax.UUCP> <10988@ulysses.homer.nj.att.com>
Reply-To: gwyn@brl.arpa (Doug Gwyn (VLD/VMB) <gwyn>)
Organization: Ballistic Research Lab (BRL), APG, MD.
Lines: 18

In article <10988@ulysses.homer.nj.att.com> cjc@ulysses.homer.nj.att.com (Chris Calabrese[mav]) writes:
>If the variables
>can all be optimized out of loops, etc, how come the machine
>I'm working on, which has a memory bit-mapped screen,
>memory mapped keyboard, etc - whith all the drivers written
>in Classic C - possibly work?

Well, first of all you're probably using a compiler that doesn't
optimize very highly, and possibly when compiling the kernel the
cc -O option is NOT used, to further restrict the amount of
optimization.

If it's a PDP-11 or VAX PCC, then there is an explicit check for
*(pointer_cast)(device_space_address) usage, and certain optimizations
are disabled if it can be determined that the I/O page may be accessed.
I don't know whether something similar is done for other architectures.

"volatile" would have been a much better solution..