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Groups > comp.lang.c++ > #70161
| Newsgroups | comp.lang.c++ |
|---|---|
| Date | 2019-11-29 17:15 -0800 |
| References | (1 earlier) <cone.1574898034.956666.129095.1004@monster.email-scan.com> <qro3p4$gd7$1@dont-email.me> <2f0c5b1c-897c-4de9-bd28-1e06b6128045@googlegroups.com> <afb846b3-3b3d-4660-912b-76c4e52a8134@googlegroups.com> <qrqldf$dbu$1@dont-email.me> |
| Message-ID | <4ba97dfb-e642-4f0d-a129-60fdcb4999ee@googlegroups.com> (permalink) |
| Subject | Re: A question about if constexpr |
| From | Öö Tiib <ootiib@hot.ee> |
On Friday, 29 November 2019 10:38:18 UTC+2, David Brown wrote: > On 29/11/2019 08:50, Öö Tiib wrote: > > On Friday, 29 November 2019 07:09:19 UTC+2, Daniel wrote: > >> On Thursday, November 28, 2019 at 4:25:03 AM UTC-5, David Brown wrote: > >>> > >>> If the compiler is not > >>> generating identical code for an "if constexpr" and an "if" where the > >>> expression happens to be known at compile time (whether it is > >>> technically a C++ constant or not), then the compiler is doing a poor > >>> job at optimising. > >>> > >> Which raises the question, what is the point of the constexpr if statement anyway? > > > > In template code it is like super #if but outside of templates it is > > basically only for to tell to readers, maintainers and compiler that > > the condition is supposed to be constant expression by original logic > > and something is perhaps gone bad when it is not anymore. > > > > <https://en.cppreference.com/w/cpp/language/if> > > One other point is that since the discarded part is discarded, any > identifiers it uses do not need to be defined or linked in with the code. I'm in doubt about that other point. I noticed it long time ago that the implementations do not link useless functions. It was like 2004 or maybe 2007. I did delete unused functions after refactoring and since there was tens of such I used impossibility to set breakpoints in those as heuristic that these are now unused. However my program became ill-formed since I had erased one that was optimized out but not because it wasn't called but because it was called only in branch that was impossible to take. So compilers did not need if constexpr back then for it ... why these suddenly started to need it now?
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A question about if constexpr Daniel <danielaparker@gmail.com> - 2019-11-27 05:45 -0800
Re: A question about if constexpr "Alf P. Steinbach" <alf.p.steinbach+usenet@gmail.com> - 2019-11-27 15:03 +0100
Re: A question about if constexpr Mr Flibble <flibbleREMOVETHISBIT@i42.co.uk> - 2019-11-29 16:33 +0000
Re: A question about if constexpr Öö Tiib <ootiib@hot.ee> - 2019-11-29 16:52 -0800
Re: A question about if constexpr David Brown <david.brown@hesbynett.no> - 2019-11-30 12:03 +0100
Re: A question about if constexpr Öö Tiib <ootiib@hot.ee> - 2019-11-30 03:47 -0800
Re: A question about if constexpr David Brown <david.brown@hesbynett.no> - 2019-11-30 15:08 +0100
Re: A question about if constexpr Sam <sam@email-scan.com> - 2019-11-27 18:40 -0500
Re: A question about if constexpr Öö Tiib <ootiib@hot.ee> - 2019-11-27 23:16 -0800
Re: A question about if constexpr Mr Flibble <flibbleREMOVETHISBIT@i42.co.uk> - 2019-11-29 16:35 +0000
Re: A question about if constexpr Öö Tiib <ootiib@hot.ee> - 2019-11-29 16:41 -0800
Re: A question about if constexpr David Brown <david.brown@hesbynett.no> - 2019-11-28 10:24 +0100
Re: A question about if constexpr Bo Persson <bo@bo-persson.se> - 2019-11-28 11:58 +0100
Re: A question about if constexpr David Brown <david.brown@hesbynett.no> - 2019-11-28 12:37 +0100
Re: A question about if constexpr Robert Wessel <robertwessel2@yahoo.com> - 2019-11-28 14:04 -0600
Re: A question about if constexpr David Brown <david.brown@hesbynett.no> - 2019-11-29 09:23 +0100
Re: A question about if constexpr Robert Wessel <robertwessel2@yahoo.com> - 2019-11-29 14:42 -0600
Re: A question about if constexpr Daniel <danielaparker@gmail.com> - 2019-11-28 21:09 -0800
Re: A question about if constexpr "Alf P. Steinbach" <alf.p.steinbach+usenet@gmail.com> - 2019-11-29 07:41 +0100
Re: A question about if constexpr Öö Tiib <ootiib@hot.ee> - 2019-11-28 23:50 -0800
Re: A question about if constexpr David Brown <david.brown@hesbynett.no> - 2019-11-29 09:38 +0100
Re: A question about if constexpr Öö Tiib <ootiib@hot.ee> - 2019-11-29 17:15 -0800
Re: A question about if constexpr Paavo Helde <myfirstname@osa.pri.ee> - 2019-11-30 08:19 +0200
Re: A question about if constexpr Ned Latham <nedlatham@woden.valhalla.oz> - 2019-11-30 00:24 -0600
Re: A question about if constexpr Öö Tiib <ootiib@hot.ee> - 2019-11-30 02:13 -0800
Re: A question about if constexpr Ned Latham <nedlatham@woden.valhalla.oz> - 2019-11-30 04:56 -0600
Re: A question about if constexpr Öö Tiib <ootiib@hot.ee> - 2019-11-30 03:20 -0800
Re: A question about if constexpr Ned Latham <nedlatham@woden.valhalla.oz> - 2019-11-30 05:38 -0600
Re: A question about if constexpr Öö Tiib <ootiib@hot.ee> - 2019-11-30 04:57 -0800
Re: A question about if constexpr Ned Latham <nedlatham@woden.valhalla.oz> - 2019-11-30 09:46 -0600
Re: A question about if constexpr Öö Tiib <ootiib@hot.ee> - 2019-11-30 11:09 -0800
Re: A question about if constexpr Ned Latham <nedlatham@woden.valhalla.oz> - 2019-11-30 20:03 -0600
Re: A question about if constexpr Öö Tiib <ootiib@hot.ee> - 2019-11-30 23:43 -0800
Re: A question about if constexpr Ned Latham <nedlatham@woden.valhalla.oz> - 2019-12-01 04:56 -0600
Re: A question about if constexpr Christian Gollwitzer <auriocus@gmx.de> - 2019-12-01 18:33 +0100
Re: A question about if constexpr Ned Latham <nedlatham@woden.valhalla.oz> - 2019-12-01 19:27 -0600
Re: A question about if constexpr boltar@nowhere.co.uk - 2019-12-02 08:34 +0000
Re: A question about if constexpr Ned Latham <nedlatham@woden.valhalla.oz> - 2019-12-02 04:21 -0600
Re: A question about if constexpr boltar@nowhere.co.uk - 2019-12-02 08:33 +0000
Re: A question about if constexpr Mr Flibble <flibbleREMOVETHISBIT@i42.co.uk> - 2019-12-03 17:05 +0000
Re: A question about if constexpr boltar@nowhere.co.uk - 2019-12-03 17:09 +0000
Re: A question about if constexpr Mr Flibble <flibbleREMOVETHISBIT@i42.co.uk> - 2019-12-03 18:03 +0000
Re: A question about if constexpr boltar@nowhere.co.uk - 2019-12-04 16:49 +0000
Re: A question about if constexpr Mr Flibble <flibbleREMOVETHISBIT@i42.co.uk> - 2019-12-04 18:36 +0000
Re: A question about if constexpr boltar@nowhere.co.uk - 2019-12-05 12:51 +0000
Re: A question about if constexpr David Brown <david.brown@hesbynett.no> - 2019-11-29 09:30 +0100
Re: A question about if constexpr Paavo Helde <myfirstname@osa.pri.ee> - 2019-11-29 10:51 +0200
Re: A question about if constexpr Tim Rentsch <tr.17687@z991.linuxsc.com> - 2019-11-28 13:52 -0800
Re: A question about if constexpr Bonita Montero <Bonita.Montero@gmail.com> - 2019-12-01 14:42 +0100
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