Path: utzoo!mnetor!uunet!lll-winken!lll-tis!ames!nrl-cmf!cmcl2!brl-adm!brl-smoke!gwyn
From: gwyn@brl-smoke.ARPA (Doug Gwyn )
Newsgroups: comp.lang.c
Subject: Re: volatile isn't necessary, but it's there
Message-ID: <7642@brl-smoke.ARPA>
Date: 9 Apr 88 23:26:36 GMT
References: <7794@alice.UUCP> <10988@mimsy.UUCP>
Reply-To: gwyn@brl.arpa (Doug Gwyn (VLD/VMB) <gwyn>)
Organization: Ballistic Research Lab (BRL), APG, MD.
Lines: 17

In article <10988@mimsy.UUCP> mangoe@mimsy.umd.edu.UUCP (Charley Wingate) writes:
>>Volatile is of use only with optimizing compilers; those that don't
>>do some kind of data-flow analysis can ignore it.  More bluntly,
>>it is intended to be used in cases where your compiler will do something
>>other than what your program plainly asks it to do.
>These statements only acquire truth because the default understanding of
>what the compiler ought to do is very very conservative and tends to reflect
>the most simple-minded way of understanding the code.

A programmer who is at all concerned with portability will code for
a "virtual machine", not for the current accidental hardware.  It is
extremely important that this virtual machine HAVE simple properties;
otherwise it becomes practically impossible to write correct code for
it.  Matters are somewhat confused in C because its virtual machine
has some properties that have deliberately fuzzy specifications; this
was intended to permit more efficient realizations of the virtual
machine on actual hardware, but it causes trouble when programmers
don't clearly understand this issue.