From 1111135929860742483 X-Google-Thread: f78e5,174aa7b34b06a51 X-Google-Attributes: gidf78e5,public X-Google-Language: ENGLISH,ASCII-7-bit Path: g2news1.google.com!news1.google.com!proxad.net!newsfeed.stueberl.de!newsfeed.vmunix.org!peer-uk.news.demon.net!kibo.news.demon.net!news.demon.co.uk!demon!stump.algebra.com!devnull From: ben-public-nospam@decadentplace.org.uk (Ben Hutchings) Newsgroups: comp.std.c++ Subject: Re: Is this really unspecified behavior? Date: Sat, 24 Dec 2005 14:20:50 GMT Organization: private site Lines: 65 Sender: mail2news@demon.net Approved: fjh@cs.mu.oz.au (Fergus Henderson , moderator of comp.std.c++) Message-ID: References: <1132759176.368850.264850@g43g2000cwa.googlegroups.com> <1132933832.802917.153350@g14g2000cwa.googlegroups.com> <1133551647.532929.325730@z14g2000cwz.googlegroups.com> <1133583412.951239.208510@g49g2000cwa.googlegroups.com> <1133910546.716987.80030@g14g2000cwa.googlegroups.com> <0l5ep1ppfhdj5p1pcu7e4na4ub0vjajlq3@4ax.com> <87irtjy5sy.fsf@boost-consulting.com> NNTP-Posting-Host: news.news.demon.net X-Trace: news.demon.co.uk 1135434060 2883 158.152.254.254 (24 Dec 2005 14:21:00 GMT) X-Complaints-To: abuse@demon.net NNTP-Posting-Date: Sat, 24 Dec 2005 14:21:00 +0000 (UTC) X-Robomod: STUMP, ichudov@algebra.com (Igor Chudov) X-User-Agent: slrn/0.9.8.1 (Debian) X-Orig-X-Trace: individual.net jj4OX72M1hklzazeByusJwwxkTZdDwdh1+mwLL89Hi03DiAY8= X-Virus-Scanned: amavisd-new at cs.mu.OZ.AU X-Reply-To: Ben Hutchings X-Received: (from fjh@localhost) by mulga.cs.mu.OZ.AU (8.12.10+Sun/8.12.9/Submit) id jBOEKo85023277; Sun, 25 Dec 2005 01:20:50 +1100 (EST) X-Path: comp-std-cpp-robomod!not-for-mail X-Delivered-To: std-c++@ucar.edu X-Authentication-Warning: mulga.cs.mu.OZ.AU: fjh set sender to devnull@stump.algebra.com using -f X-Orig-Path: decadentplace.org.uk!news X-Newsgroups: comp.std.c++ Xref: g2news1.google.com comp.std.c++:2904 David Abrahams wrote: > hyrosen@mail.com (Hyman Rosen) writes: >> This hypothetical high-performance code and smart/stupid compiler is >> a myth anyway, but people confused by order of evaluation issues are >> all too real, ... > > Okay, maybe I'm one of them, and you can clear it up. Andrew Koenig > described why evaluation order might matter to a compiler > (http://groups.google.com/group/comp.std.c++/msg/54716a09f97cc000). > Do you have an argument against his post? It *might* matter, but Sethi-Ullman numbering is not the state of the art in code optimisation. > Also, it seems obvious to me that in some cases at least, evaluating > the arguments in the same order they need to be pushed onto the stack > could be important: > > g( f1(), f2(), f3() ) > > call f3 > push r0 > call f2 > push r0 > call f1 > push r0 > call g > > If you force an ordering that conflicts with the calling convention, > you end up with > > sub sp, #3 > call f1 > mv r0, sp+1 > call f2 > mv r0, sp+2 > call f3 > mv r0, sp+3 > call g > > What am I missing? First, AFAIK the only current architecture that has stack-based calling conventions even for small numbers of function parameters is x86, and for performance-sensitive code I suspect that will soon be obsoleted by x86-64, which has register-based calling conventions due to its larger register set. Second, "push" is relatively complex and expensive even on x86; certainly sufficiently so that current compilers already prefer sp-relative addressing to pushing in some cases when generating code for a function call. -- Ben Hutchings It is easier to write an incorrect program than to understand a correct one. --- [ 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://www.jamesd.demon.co.uk/csc/faq.html ]