Path: utzoo!mnetor!uunet!husc6!cmcl2!brl-adm!brl-smoke!gwyn
From: gwyn@brl-smoke.ARPA (Doug Gwyn )
Newsgroups: comp.lang.c
Subject: Re: noalias; parens honored
Message-ID: <6860@brl-smoke.ARPA>
Date: 17 Dec 87 20:46:19 GMT
References: <6829@brl-smoke.ARPA> <2845@zeus.TEK.COM>
Reply-To: gwyn@brl.arpa (Doug Gwyn (VLD/VMB) <gwyn>)
Organization: Ballistic Research Lab (BRL), APG, MD.
Lines: 15
Keywords: ANSI C standard

In article <2845@zeus.TEK.COM> dant@tekla.UUCP (Dan Tilque) writes:
>It also seems pretty late in the process to be making major changes like
>adding keywords.  Is there any current compiler (i.e. prior art) which
>uses 'noalias'?  If so, how much better is the code generated by it?

The "noalias" keyword itself is new, but not the particular optimization
it permits.  The answer to the code efficiency question depends on the
particular implementation environment.  It can make a drastic difference
for some functions with parameters that are pointers to noalias objects.

>Also, how much worse will the code be when paren grouping must be honored?

I don't think it matters much.  If your environment is such that the
same result is obtained either way, which is true of many environments,
the optimzer can go ahead and rearrange integer expressions at least.