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Groups > comp.lang.c++ > #83489
| From | Keith Thompson <Keith.S.Thompson+u@gmail.com> |
|---|---|
| Newsgroups | comp.lang.c++ |
| Subject | Re: GCC hasn't even gotten around to sequencing argument evaluation |
| Date | 2022-04-05 11:31 -0700 |
| Organization | None to speak of |
| Message-ID | <87y20jnzz5.fsf@nosuchdomain.example.com> (permalink) |
| References | (9 earlier) <t2f07d$2sp$1@gioia.aioe.org> <t2f6mr$i8c$1@dont-email.me> <t2hmte$1s3b$1@gioia.aioe.org> <t2hnp9$c47$2@dont-email.me> <t2hoea$n5m$1@gioia.aioe.org> |
Muttley@dastardlyhq.com writes:
> On Tue, 5 Apr 2022 08:38:16 -0700
> Andrey Tarasevich <andreytarasevich@hotmail.com> wrote:
>>On 4/5/2022 8:23 AM, Muttley@dastardlyhq.com wrote:
>>> On Mon, 4 Apr 2022 18:34:35 +0200
>>> David Brown <david.brown@hesbynett.no> wrote:
>>>> On 04/04/2022 16:43, Muttley@dastardlyhq.com wrote:
>>>>> On Mon, 4 Apr 2022 12:15:42 +0200
>>>>> David Brown <david.brown@hesbynett.no> wrote:
>>>>>> On 04/04/2022 10:23, Muttley@dastardlyhq.com wrote:
>>>>>>> On Sat, 2 Apr 2022 11:27:59 -0700
>>>>>>>> opportunity. An equivalent definition of undefined behavior says: the
>>>>>>>> compilers are allowed to translate the code under assumption that
>>>>>>>> undefined behavior never happens.
>>>>>>>
>>>>>>> Except if it can be written in code then at some point it will happen.
>>>>>>>
>>>>>>
>>>>>> That is not even /remotely/ true.
>>>>>>
>>>>>> gcc even has a way "__builtin_unreachable()" to specifically say that
>>>>>> code flow cannot reach a particular point, and this is handled
>>>>>> internally in /precisely/ the same way as undefined behaviour.
>>>>>
>>>>> What has unreachable code got to do with anything?
>>>>>
>>>>
>>>> As I wrote - gcc treats code marked explicitly as "unreachable" in the
>>>> same way as it treats undefined behaviour. (And I really mean that - it
>>>> uses the same node type in the internal tree representation of the
>>>> code.) In other words, when the compiler sees undefined behaviour, it
>>>> /knows/ that code flow never enters there. If your code has the line "i
>>>> = i++ + ++i;", the compiler can replace it with
>>>> "__builtin_unreachable()" and know it will not be executed.
>>>
>>> Except it clearly is executed as any short test program would demonstrate.
>>>
>>
>>"Test programs" don't demonstrate anything at all.
>
> So how would you demonstrate how a compiler treats some code then? Ask it?
>
> int main()
> {
> int i = 0;
> i = i++ + ++i;
> printf("%d\n",i);
> return 0;
> }
>
> The output with clang is 1, 2 with gcc. If what you said was correct the
> result would be 0, an abort or some kind of compilation error.
We're talking about what the standard *allows* compilers to do, whether
any actual compiler takes advantage of that permission or not.
The statement was that a compiler *can* replace `i = i++ + ++i;`
with `__builtin_unreachable()`, not that it *must*.
--
Keith Thompson (The_Other_Keith) Keith.S.Thompson+u@gmail.com
Working, but not speaking, for Philips
void Void(void) { Void(); } /* The recursive call of the void */
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GCC hasn't even gotten around to sequencing argument evaluation yet??? Andrey Tarasevich <andreytarasevich@hotmail.com> - 2022-04-01 20:34 -0700
Re: GCC hasn't even gotten around to sequencing argument evaluation yet??? "Alf P. Steinbach" <alf.p.steinbach@gmail.com> - 2022-04-02 10:19 +0200
Re: GCC hasn't even gotten around to sequencing argument evaluation yet??? Bo Persson <bo@bo-persson.se> - 2022-04-02 12:19 +0200
Re: GCC hasn't even gotten around to sequencing argument evaluation yet??? Bonita Montero <Bonita.Montero@gmail.com> - 2022-04-02 14:18 +0200
Re: GCC hasn't even gotten around to sequencing argument evaluation yet??? Christian Gollwitzer <auriocus@gmx.de> - 2022-04-02 12:30 +0200
Re: GCC hasn't even gotten around to sequencing argument evaluation yet??? David Brown <david.brown@hesbynett.no> - 2022-04-02 14:12 +0200
Re: GCC hasn't even gotten around to sequencing argument evaluation yet??? Bonita Montero <Bonita.Montero@gmail.com> - 2022-04-02 14:20 +0200
Re: GCC hasn't even gotten around to sequencing argument evaluation Muttley@dastardlyhq.com - 2022-04-02 14:28 +0000
Re: GCC hasn't even gotten around to sequencing argument evaluation David Brown <david.brown@hesbynett.no> - 2022-04-02 17:27 +0200
Re: GCC hasn't even gotten around to sequencing argument evaluation Muttley@dastardlyhq.com - 2022-04-02 15:39 +0000
Re: GCC hasn't even gotten around to sequencing argument evaluation Barry Schwarz <schwarzb@delq.com> - 2022-04-02 09:15 -0700
Re: GCC hasn't even gotten around to sequencing argument evaluation Muttley@dastardlyhq.com - 2022-04-04 08:21 +0000
Re: GCC hasn't even gotten around to sequencing argument evaluation David Brown <david.brown@hesbynett.no> - 2022-04-04 12:02 +0200
Re: GCC hasn't even gotten around to sequencing argument evaluation Muttley@dastardlyhq.com - 2022-04-04 14:42 +0000
Re: GCC hasn't even gotten around to sequencing argument evaluation Andrey Tarasevich <andreytarasevich@hotmail.com> - 2022-04-04 08:49 -0700
Re: GCC hasn't even gotten around to sequencing argument evaluation Muttley@dastardlyhq.com - 2022-04-05 15:18 +0000
Re: GCC hasn't even gotten around to sequencing argument evaluation Andrey Tarasevich <andreytarasevich@hotmail.com> - 2022-04-05 08:37 -0700
Re: GCC hasn't even gotten around to sequencing argument evaluation Muttley@dastardlyhq.com - 2022-04-05 15:54 +0000
Re: GCC hasn't even gotten around to sequencing argument evaluation David Brown <david.brown@hesbynett.no> - 2022-04-06 11:24 +0200
Re: GCC hasn't even gotten around to sequencing argument evaluation Juha Nieminen <nospam@thanks.invalid> - 2022-04-06 10:49 +0000
Re: GCC hasn't even gotten around to sequencing argument evaluation David Brown <david.brown@hesbynett.no> - 2022-04-06 18:21 +0200
Re: GCC hasn't even gotten around to sequencing argument evaluation Chris Vine <chris@cvine--nospam--.freeserve.co.uk> - 2022-04-06 15:40 +0100
Re: GCC hasn't even gotten around to sequencing argument evaluation Muttley@dastardlyhq.com - 2022-04-06 15:00 +0000
Re: GCC hasn't even gotten around to sequencing argument evaluation Chris Vine <chris@cvine--nospam--.freeserve.co.uk> - 2022-04-06 17:03 +0100
Re: GCC hasn't even gotten around to sequencing argument evaluation Chris Vine <chris@cvine--nospam--.freeserve.co.uk> - 2022-04-06 17:18 +0100
Re: GCC hasn't even gotten around to sequencing argument evaluation Muttley@dastardlyhq.com - 2022-04-07 08:58 +0000
Re: GCC hasn't even gotten around to sequencing argument evaluation James Kuyper <jameskuyper@alumni.caltech.edu> - 2022-04-07 11:01 -0400
Re: GCC hasn't even gotten around to sequencing argument evaluation "Alf P. Steinbach" <alf.p.steinbach@gmail.com> - 2022-04-06 23:13 +0200
Re: GCC hasn't even gotten around to sequencing argument evaluation David Brown <david.brown@hesbynett.no> - 2022-04-07 09:11 +0200
Re: GCC hasn't even gotten around to sequencing argument evaluation Andrey Tarasevich <andreytarasevich@hotmail.com> - 2022-04-06 10:53 -0700
Re: GCC hasn't even gotten around to sequencing argument evaluation James Kuyper <jameskuyper@alumni.caltech.edu> - 2022-04-06 14:50 -0400
Re: GCC hasn't even gotten around to sequencing argument evaluation Sams Lara <samlara622@gmail.com> - 2022-04-06 22:27 +0100
Re: GCC hasn't even gotten around to sequencing argument evaluation Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2022-04-06 14:51 -0700
Re: GCC hasn't even gotten around to sequencing argument evaluation Sams Lara <samlara622@gmail.com> - 2022-04-06 22:59 +0100
Re: GCC hasn't even gotten around to sequencing argument evaluation Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2022-04-06 15:54 -0700
Re: GCC hasn't even gotten around to sequencing argument evaluation Öö Tiib <ootiib@hot.ee> - 2022-04-06 15:11 -0700
Re: GCC hasn't even gotten around to sequencing argument evaluation Tim Rentsch <tr.17687@z991.linuxsc.com> - 2022-04-09 09:38 -0700
Re: GCC hasn't even gotten around to sequencing argument evaluation James Kuyper <jameskuyper@alumni.caltech.edu> - 2022-04-06 23:48 -0400
Re: GCC hasn't even gotten around to sequencing argument evaluation Andrey Tarasevich <andreytarasevich@hotmail.com> - 2022-04-06 18:39 -0700
Re: GCC hasn't even gotten around to sequencing argument evaluation James Kuyper <jameskuyper@alumni.caltech.edu> - 2022-04-06 23:49 -0400
Re: GCC hasn't even gotten around to sequencing argument evaluation Malcolm McLean <malcolm.arthur.mclean@gmail.com> - 2022-04-05 08:55 -0700
Re: GCC hasn't even gotten around to sequencing argument evaluation Andrey Tarasevich <andreytarasevich@hotmail.com> - 2022-04-05 10:23 -0700
Re: GCC hasn't even gotten around to sequencing argument evaluation James Kuyper <jameskuyper@alumni.caltech.edu> - 2022-04-05 14:36 -0400
Re: GCC hasn't even gotten around to sequencing argument evaluation James Kuyper <jameskuyper@alumni.caltech.edu> - 2022-04-04 12:27 -0400
Re: GCC hasn't even gotten around to sequencing argument evaluation Muttley@dastardlyhq.com - 2022-04-05 15:21 +0000
Re: GCC hasn't even gotten around to sequencing argument evaluation Andrey Tarasevich <andreytarasevich@hotmail.com> - 2022-04-05 08:41 -0700
Re: GCC hasn't even gotten around to sequencing argument evaluation Muttley@dastardlyhq.com - 2022-04-05 15:50 +0000
Re: GCC hasn't even gotten around to sequencing argument evaluation Andrey Tarasevich <andreytarasevich@hotmail.com> - 2022-04-05 10:19 -0700
Re: GCC hasn't even gotten around to sequencing argument evaluation James Kuyper <jameskuyper@alumni.caltech.edu> - 2022-04-05 14:33 -0400
Re: GCC hasn't even gotten around to sequencing argument evaluation James Kuyper <jameskuyper@alumni.caltech.edu> - 2022-04-05 14:28 -0400
Re: GCC hasn't even gotten around to sequencing argument evaluation David Brown <david.brown@hesbynett.no> - 2022-04-04 18:29 +0200
Re: GCC hasn't even gotten around to sequencing argument evaluation Andrey Tarasevich <andreytarasevich@hotmail.com> - 2022-04-02 11:27 -0700
Re: GCC hasn't even gotten around to sequencing argument evaluation Muttley@dastardlyhq.com - 2022-04-04 08:23 +0000
Re: GCC hasn't even gotten around to sequencing argument evaluation David Brown <david.brown@hesbynett.no> - 2022-04-04 12:15 +0200
Re: GCC hasn't even gotten around to sequencing argument evaluation Muttley@dastardlyhq.com - 2022-04-04 14:43 +0000
Re: GCC hasn't even gotten around to sequencing argument evaluation David Brown <david.brown@hesbynett.no> - 2022-04-04 18:34 +0200
Re: GCC hasn't even gotten around to sequencing argument evaluation Muttley@dastardlyhq.com - 2022-04-05 15:23 +0000
Re: GCC hasn't even gotten around to sequencing argument evaluation Andrey Tarasevich <andreytarasevich@hotmail.com> - 2022-04-05 08:38 -0700
Re: GCC hasn't even gotten around to sequencing argument evaluation Muttley@dastardlyhq.com - 2022-04-05 15:49 +0000
Re: GCC hasn't even gotten around to sequencing argument evaluation Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2022-04-05 11:31 -0700
Re: GCC hasn't even gotten around to sequencing argument evaluation scott@slp53.sl.home (Scott Lurndal) - 2022-04-05 22:45 +0000
Re: GCC hasn't even gotten around to sequencing argument evaluation James Kuyper <jameskuyper@alumni.caltech.edu> - 2022-04-02 23:34 -0400
Re: GCC hasn't even gotten around to sequencing argument evaluation Manfred <noname@add.invalid> - 2022-04-03 17:43 +0200
Re: GCC hasn't even gotten around to sequencing argument evaluation James Kuyper <jameskuyper@alumni.caltech.edu> - 2022-04-03 15:40 -0400
Re: GCC hasn't even gotten around to sequencing argument evaluation Muttley@dastardlyhq.com - 2022-04-04 08:24 +0000
Re: GCC hasn't even gotten around to sequencing argument evaluation James Kuyper <jameskuyper@alumni.caltech.edu> - 2022-04-04 12:01 -0400
Re: GCC hasn't even gotten around to sequencing argument evaluation David Brown <david.brown@hesbynett.no> - 2022-04-03 13:02 +0200
Re: GCC hasn't even gotten around to sequencing argument evaluation Malcolm McLean <malcolm.arthur.mclean@gmail.com> - 2022-04-03 04:46 -0700
Re: GCC hasn't even gotten around to sequencing argument evaluation Öö Tiib <ootiib@hot.ee> - 2022-04-03 07:02 -0700
Re: GCC hasn't even gotten around to sequencing argument evaluation Malcolm McLean <malcolm.arthur.mclean@gmail.com> - 2022-04-03 11:30 -0700
Re: GCC hasn't even gotten around to sequencing argument evaluation David Brown <david.brown@hesbynett.no> - 2022-04-03 21:20 +0200
Re: GCC hasn't even gotten around to sequencing argument evaluation Malcolm McLean <malcolm.arthur.mclean@gmail.com> - 2022-04-03 12:49 -0700
Re: GCC hasn't even gotten around to sequencing argument evaluation Paavo Helde <eesnimi@osa.pri.ee> - 2022-04-04 00:40 +0300
Re: GCC hasn't even gotten around to sequencing argument evaluation Malcolm McLean <malcolm.arthur.mclean@gmail.com> - 2022-04-03 15:40 -0700
Re: GCC hasn't even gotten around to sequencing argument evaluation David Brown <david.brown@hesbynett.no> - 2022-04-04 09:13 +0200
Re: GCC hasn't even gotten around to sequencing argument evaluation David Brown <david.brown@hesbynett.no> - 2022-04-04 09:02 +0200
Re: GCC hasn't even gotten around to sequencing argument evaluation Malcolm McLean <malcolm.arthur.mclean@gmail.com> - 2022-04-04 02:07 -0700
Re: GCC hasn't even gotten around to sequencing argument evaluation David Brown <david.brown@hesbynett.no> - 2022-04-04 13:28 +0200
Re: GCC hasn't even gotten around to sequencing argument evaluation Malcolm McLean <malcolm.arthur.mclean@gmail.com> - 2022-04-04 06:01 -0700
Re: GCC hasn't even gotten around to sequencing argument evaluation David Brown <david.brown@hesbynett.no> - 2022-04-04 19:11 +0200
Re: GCC hasn't even gotten around to sequencing argument evaluation scott@slp53.sl.home (Scott Lurndal) - 2022-04-04 17:59 +0000
Re: GCC hasn't even gotten around to sequencing argument evaluation Malcolm McLean <malcolm.arthur.mclean@gmail.com> - 2022-04-05 06:55 -0700
Re: GCC hasn't even gotten around to sequencing argument evaluation Manfred <noname@add.invalid> - 2022-04-03 18:39 +0200
Re: GCC hasn't even gotten around to sequencing argument evaluation Paavo Helde <eesnimi@osa.pri.ee> - 2022-04-03 09:09 +0300
Re: GCC hasn't even gotten around to sequencing argument evaluation yet??? Manfred <noname@add.invalid> - 2022-04-02 19:53 +0200
Re: GCC hasn't even gotten around to sequencing argument evaluation yet??? David Brown <david.brown@hesbynett.no> - 2022-04-03 13:45 +0200
Re: GCC hasn't even gotten around to sequencing argument evaluation yet??? Manfred <noname@add.invalid> - 2022-04-03 17:27 +0200
Re: GCC hasn't even gotten around to sequencing argument evaluation yet??? Ben Bacarisse <ben.usenet@bsb.me.uk> - 2022-04-02 21:17 +0100
Re: GCC hasn't even gotten around to sequencing argument evaluation yet??? Manfred <noname@invalid.add> - 2022-04-02 23:04 +0200
Re: GCC hasn't even gotten around to sequencing argument evaluation yet??? Ben Bacarisse <ben.usenet@bsb.me.uk> - 2022-04-03 00:22 +0100
Re: GCC hasn't even gotten around to sequencing argument evaluation yet??? Andrey Tarasevich <andreytarasevich@hotmail.com> - 2022-04-02 17:33 -0700
Re: GCC hasn't even gotten around to sequencing argument evaluation yet??? Ben Bacarisse <ben.usenet@bsb.me.uk> - 2022-04-03 14:23 +0100
Re: GCC hasn't even gotten around to sequencing argument evaluation yet??? Tim Rentsch <tr.17687@z991.linuxsc.com> - 2022-04-06 08:31 -0700
Re: GCC hasn't even gotten around to sequencing argument evaluation yet??? Andrey Tarasevich <andreytarasevich@hotmail.com> - 2022-04-06 11:05 -0700
Re: GCC hasn't even gotten around to sequencing argument evaluation yet??? Tim Rentsch <tr.17687@z991.linuxsc.com> - 2022-04-25 03:32 -0700
Re: GCC hasn't even gotten around to sequencing argument evaluation yet??? Andrey Tarasevich <andreytarasevich@hotmail.com> - 2022-04-02 11:18 -0700
Re: GCC hasn't even gotten around to sequencing argument evaluation yet??? David Brown <david.brown@hesbynett.no> - 2022-04-02 13:11 +0200
Re: GCC hasn't even gotten around to sequencing argument evaluation yet??? Manu Raju <MR@invalid.invalid> - 2022-04-02 18:26 +0100
Re: GCC hasn't even gotten around to sequencing argument evaluation yet??? Manu Raju <MR@invalid.invalid> - 2022-04-02 21:46 +0100
Re: GCC hasn't even gotten around to sequencing argument evaluation yet??? Andrey Tarasevich <andreytarasevich@hotmail.com> - 2022-04-02 17:35 -0700
Re: GCC hasn't even gotten around to sequencing argument evaluation yet??? Language Lawyer <language.lawyer@gmail.com> - 2022-04-04 02:28 -0700
Re: GCC hasn't even gotten around to sequencing argument evaluation yet??? Andrey Tarasevich <andreytarasevich@hotmail.com> - 2022-04-04 05:52 -0700
Re: GCC hasn't even gotten around to sequencing argument evaluation yet??? Language Lawyer <language.lawyer@gmail.com> - 2022-06-21 03:36 -0700
Re: GCC hasn't even gotten around to sequencing argument evaluation yet??? Juha Nieminen <nospam@thanks.invalid> - 2022-04-04 10:48 +0000
Re: GCC hasn't even gotten around to sequencing argument evaluation yet??? Andrey Tarasevich <andreytarasevich@hotmail.com> - 2022-04-04 05:49 -0700
Re: GCC hasn't even gotten around to sequencing argument evaluation yet??? Juha Nieminen <nospam@thanks.invalid> - 2022-04-05 06:34 +0000
Re: GCC hasn't even gotten around to sequencing argument evaluation yet??? Ben Bacarisse <ben.usenet@bsb.me.uk> - 2022-04-05 10:20 +0100
Re: GCC hasn't even gotten around to sequencing argument evaluation yet??? Andrey Tarasevich <andreytarasevich@hotmail.com> - 2022-04-05 07:51 -0700
Re: GCC hasn't even gotten around to sequencing argument evaluation yet??? Manfred <noname@add.invalid> - 2022-04-05 17:53 +0200
Re: GCC hasn't even gotten around to sequencing argument evaluation yet??? Christian Hanné <the.hanne@gmail.com> - 2022-04-10 06:06 +0200
Re: GCC hasn't even gotten around to sequencing argument evaluation yet??? Andrey Tarasevich <andreytarasevich@hotmail.com> - 2022-04-09 21:20 -0700
Re: GCC hasn't even gotten around to sequencing argument evaluation yet??? "james...@alumni.caltech.edu" <jameskuyper@alumni.caltech.edu> - 2022-04-09 21:39 -0700
Re: GCC hasn't even gotten around to sequencing argument evaluation yet??? Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2022-04-09 22:34 -0700
Re: GCC hasn't even gotten around to sequencing argument evaluation yet??? Christian Hanné <the.hanne@gmail.com> - 2022-04-10 09:19 +0200
Re: GCC hasn't even gotten around to sequencing argument evaluation yet??? David Brown <david.brown@hesbynett.no> - 2022-04-10 12:21 +0200
Re: GCC hasn't even gotten around to sequencing argument evaluation yet??? Christian Hanné <the.hanne@gmail.com> - 2022-04-10 12:47 +0200
Re: GCC hasn't even gotten around to sequencing argument evaluation yet??? "james...@alumni.caltech.edu" <jameskuyper@alumni.caltech.edu> - 2022-04-11 12:18 -0700
Re: GCC hasn't even gotten around to sequencing argument evaluation yet??? Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2022-04-11 12:33 -0700
Re: GCC hasn't even gotten around to sequencing argument evaluation yet??? Christian Hanné <the.hanne@gmail.com> - 2022-04-10 09:20 +0200
Re: GCC hasn't even gotten around to sequencing argument evaluation yet??? "james...@alumni.caltech.edu" <jameskuyper@alumni.caltech.edu> - 2022-04-11 12:32 -0700
Re: GCC hasn't even gotten around to sequencing argument evaluation yet??? Andrey Tarasevich <andreytarasevich@hotmail.com> - 2022-04-11 15:11 -0700
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