Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!wuarchive!cs.utexas.edu!uunet!mcsun!ukc!warwick!cudcv
From: cudcv@warwick.ac.uk (Rob McMahon)
Newsgroups: comp.lang.c
Subject: Re: pointer representation (was: Re: effect of free())
Message-ID: <206@titania.warwick.ac.uk>
Date: 14 Sep 89 21:55:08 GMT
References: <319@cubmol.BIO.COLUMBIA.EDU> <3756@buengc.BU.EDU> <29171@news.Think.COM> <2079@munnari.oz.au> <29250@news.Think.COM>
Reply-To: cudcv@warwick.ac.uk (Rob McMahon)
Organization: Computing Services, Warwick University, UK
Lines: 36

In article <29250@news.Think.COM> barmar@think.COM (Barry Margolin) writes:
>>Yes, it would.  But the compiler writer would have been _seduced_ into that
>>mistake by the standard.  People are encouraged to think of == as testing
>>for EQUALITY.  In dpANS C, it appears that == does *NOT* have the properties
>>of equality, and at the very least this needs to be said clearly and
>>explicitly in the Rationale.
>
>This is only true if there can actually be non-interchangeable
>representations for pointers to the same location.  I'd expect the compiler
>implementor for a system to know whether this is true, and implement the
>optimizer accordingly.

Who remembers the Burroughs B6700, which had (in Algol)

	POINTER A, B;
	IF A = B THEN ...
vs
	IF A IS B THEN ...

compiling to

	A
	B
	EQUL (sp?)
vs.
	A
	B
	SAME

Sigh.  Those were the days ...

Rob
-- 
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Rob McMahon, Computing Services, Warwick University, Coventry CV4 7AL, England