From: scf16!bashford@ford-wdl1.arpa (Dave Bashford)
Subject: Re: and then
Date: 9 Apr 93 18:08:08 GMT [thread overview]
Message-ID: <1993Apr9.180808.19494@scf.loral.com> (raw)
In article <1q29bd$7d8@huon.itd.adelaide.edu.au> andrewd@cs.adelaide.edu.au wri
tes:
>From article <1993Apr7.162133.3564@nosc.mil>, by sampson@nosc.mil (Charles H.
Sampson):
>
>[ should we always use short-circuit boolean forms?]
>
>So, the compiler writers are correct in not attempting to cast
>non-short circuit forms to short-circuit evaluation.
>
>There could well be cases where evaluation of both operands is wanted
>(if evaluation of one or both has a desired side-effect). If so,
>"optimising" evaluation of one away is highly undesirable.
I can't believe my eyes - "desired side-effect" in Ada ? Several people
have mentioned side-effects as a reason not to optimize boolean
expressions. I thought one of the guiding principles of good s/w
engineering was to minimize or eliminate side-effects. The only reason
I can think of not to optimize to short circuit forms is to catch
undesired side-effects.
I would've thought that with the number of purists out there, as the
height of the flames on this news group would suggest, someone would've
mentioned this before ?
Are there "desired side-effects" ?
Should compilers optimize when, because of poor programming, the
behaviour of the program might change ? ("poor programming" is too
strong, read "less than ideal programming") Apparently, the LRM says
no. I don't remember the specific reference, but it says something
about "optimizing should never change the semantics of the program."
--
db
bashford@srs.loral.com (Dave Bashford, Sunnyvale, CA)
next reply other threads:[~1993-04-09 18:08 UTC|newest]
Thread overview: 20+ messages / expand[flat|nested] mbox.gz Atom feed top
1993-04-09 18:08 Dave Bashford [this message]
-- strict thread matches above, loose matches on Subject: below --
1993-04-12 18:38 and then Charles H. Sampson
1993-04-12 13:29 cis.ohio-state.edu!zaphod.mps.ohio-state.edu!howland.reston.ans.net!noc.n
1993-04-11 3:55 Michael Feldman
1993-04-10 19:52 Alex Blakemore
1993-04-10 15:43 Dik T. Winter
1993-04-10 15:36 Dik T. Winter
1993-04-10 9:39 munnari.oz.au!yoyo.aarnet.edu.au!news.adelaide.edu.au!usenet
1993-04-10 1:03 Charles H. Sampson
1993-04-09 14:06 Dan Rittersdorf
1993-04-08 22:35 Andrew Dunstan,,2285592,
1993-04-08 22:28 Alex Blakemore
1993-04-08 19:03 Art Duncan
1993-04-08 16:18 Charles H. Sampson
1993-04-08 15:34 Christopher J. Henrich
1993-04-08 12:21 enterpoop.mit.edu!usc!cs.utexas.edu!mars.tsd.arlut.utexas.edu!gardner
1993-04-07 22:58 Mark Lundquist
1993-04-07 21:07 Ray Harwood -- Data Basix: (602)721-1988
1993-04-07 16:21 Charles H. Sampson
1993-04-07 12:42 Robert Firth
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