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From: henry@utzoo.UUCP (Henry Spencer)
Newsgroups: comp.lang.c
Subject: Re: short circuit evaluation
Message-ID: <7588@utzoo.UUCP>
Date: Fri, 30-Jan-87 17:08:26 EST
Article-I.D.: utzoo.7588
Posted: Fri Jan 30 17:08:26 1987
Date-Received: Fri, 30-Jan-87 17:08:26 EST
References: <425@bobkat.UUCP> <102600001@datacube> <34@umich.UUCP> <5178@mimsy.UUCP>, <484@bobkat.UUCP>
Organization: U of Toronto Zoology
Lines: 19

>     x = f1(something) * f2(something) * f3(something) ...
> 
> Shouldn't I expect all the multiplications to be performed, even if one
> function returns zero?
> I don't think I've ever used a compiler that does such optimizations...
> ...  Has anyone else?

Yeah, some variants of the V7 pdp11 C compiler did, in cases where one of
the operands was a compile-time constant known to be 0.  (This can arise
legitimately when doing arithmetic on configuration-dependent #defined
constants, for example.)  Never bothered me, since I view side effects
inside expressions as being unjustifiable pornography except for some very
specific cases.  I did ask Dennis about it at one point, since strict
reading of K&R suggested it was a bug.  His reply, as I recall it, was
roughly "I think it is defensible in principle, but it caused so many
complaints that newer versions of the compiler don't do it".
-- 
Legalize			Henry Spencer @ U of Toronto Zoology
freedom!			{allegra,ihnp4,decvax,pyramid}!utzoo!henry