From 7223127598623931354 X-Google-Language: ENGLISH,ASCII-7-bit X-Google-Thread: f78e5,7522e5259f7267d6 X-Google-Attributes: gidf78e5,public From: Anthony DeRobertis Subject: Re: x = y = z; Undefined? Date: 2000/01/17 Message-ID: #1/1 X-Deja-AN: 573681430 Content-Transfer-Encoding: 7bit Approved: Fergus Henderson , moderator of comp.std.c++ References: <3876254a.30903561@news.csrlink.net> <3879ca08.3142429@news.csrlink.net> <387b3c32.7816532@news.csrlink.net> <387bc96e.43976982@news.csrlink.net> <387dc78f.4864697@news.csrlink.net> X-Authentication-Warning: backdraft.briar.org: smap set sender to using -f Content-Type: text/plain; charset=ISO-8859-1 X-Complaints-To: abuse@demon.net X-Mail2News-Path: news.demon.net!mulga.cs.mu.oz.au X-Trace: mail2news.demon.co.uk 948103052 mail2news:1624 mail2news mail2news.demon.co.uk Organization: - X-Robomod: STUMP, ichudov@algebra.com (Igor Chudov) User-Agent: MT-NewsWatcher/3.0 (PPC) Mime-Version: 1.0 Nntp-Posting-Date: 17 Jan 2000 06:46:23 GMT Newsgroups: comp.std.c++ In article <387dc78f.4864697@news.csrlink.net>, jpotter@falcon.lhup.edu (John Potter) wrote: >On Thu, 13 Jan 2000 22:45:28 CST, Hyman Rosen >wrote: > >: jpotter@falcon.lhup.edu (John Potter) writes: >: > The only way that the mentioned reordering of the instructions is >: > valid is if the compiler detects the undefined behavior. Thus, the >: > reordering is not valid. >: >: You are presuming to omnisciently know the behavior of all compilers >: and optimizers, on into the future? > >For the given two machine instructions, I think I am safe in that. They >both modify the same variable with the second using the result of the >first. Without knowing that there is no sequence point, the >instructions may not be reversed. Correct. But if a compiler were to actually use the sequence points to determine how it can schedule instructions, it would not notice that dependency. There is no reason to expect a compiler to check for a store conflict like that inside of one sequence point. -- Windows 95 (win-DOH-z), n. A thirty-two bit extension and graphical shell to a sixteen bit patch to an eight bit operating system originally coded for a four bit microprocessor which was used in a PC built by a formerly two bit company that couldn't stand one bit of competition. --- [ comp.std.c++ is moderated. To submit articles, try just posting with ] [ your news-reader. If that fails, use mailto:std-c++@ncar.ucar.edu ] [ --- Please see the FAQ before posting. --- ] [ FAQ: http://reality.sgi.com/austern_mti/std-c++/faq.html ]