From -512036382495802943 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: 2000/01/11 Message-ID: #1/1 X-Deja-AN: 571116101 Content-Transfer-Encoding: 7bit Approved: Fergus Henderson , moderator of comp.std.c++ References: <3876254a.30903561@news.csrlink.net> <3879ca08.3142429@news.csrlink.net> X-Authentication-Warning: mulga.cs.mu.OZ.AU: fjh set sender to devnull@stump.algebra.com 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 947584293 mail2news:15675 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: 11 Jan 2000 04:37:25 GMT Newsgroups: comp.std.c++ In article <3879ca08.3142429@news.csrlink.net>, jpotter@falcon.lhup.edu (John Potter) wrote: >On Mon, 10 Jan 2000 08:28:54 CST, Anthony DeRobertis > wrote: > >: In article <3876254a.30903561@news.csrlink.net>, >: jpotter@falcon.lhup.edu (John Potter) wrote: >: >: >: >could someone give an example of translation which would produce >: >something other than expected? >: > >: > (i1 = i2) += i3; >: >: Well, on my PowerPC this would generate (unoptimized): >: -- sequence point -- >: or i1,i2,i2 >: add i1,i1,i3 >: -- sequence point -- >: >: Which could legally be re-arranged: >: add i1,i1,i3 >: or i1, i2, i2 > >I don't think so. The standard, by saying that a value can't be modified twice between sequencing points, has disallowed this dependency. The compiler need not check if a new value for an variables depends on another new value inside the same sequencing point, and there is no reason to expect that it does check. One could concieve a compiler that would decide 'ok, the final destination is i1' and then add three too it. Then manage the assign i1=i2 after it. Since there can be no more than one assignment to a single variable in a sequencing point, there's nothing wrong with this implementation, either. -- 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 ]