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Groups > comp.lang.c > #107168
| From | BartC <bc@freeuk.com> |
|---|---|
| Newsgroups | comp.lang.c |
| Subject | Re: C Compilers QoI |
| Date | 2017-03-27 17:01 +0100 |
| Organization | A noiseless patient Spider |
| Message-ID | <obbcro$foh$1@dont-email.me> (permalink) |
| References | (17 earlier) <a0f7bfaa-b646-4b76-93eb-1ed345ef417f@googlegroups.com> <obapbh$8mh$1@dont-email.me> <62d9295b-5304-4e92-af79-07493227f240@googlegroups.com> <obbak6$78i$1@dont-email.me> <cbf27b86-671f-4d30-aa68-9063b58daa1e@googlegroups.com> |
On 27/03/2017 16:55, supercat@casperkitty.com wrote: > On Monday, March 27, 2017 at 10:23:42 AM UTC-5, Bart wrote: >>> If the same machine code would be usable for the in-place and disjoint- >>> destination scenarios, would it make sense to require that the code for >>> the three-operand form check whether the destination matches one of the >>> sources and call a separate function that runs at just the same speed as >>> the three-operand form? >> >> I don't get you. Why would x=x+y be undefined behaviour? > > A compiler could not achieve efficient vectorization unless either the > pointers were declared "restrict", or the compiler generated separate > code to handle cases where some objects that are written in the loop get > read in a later iteration. If the pointers were declared "restrict", > then accessing a location via the source pointer and then writing that > same location via the destination pointer would invoke UB. > > I recognize that it can be beneficial to be able to say "add the contents > of x to y" in addition to being able to say "store the sum of x and y into > z", but it is less than helpful to have a three-operand form *require* > that all three operands be distinct. OK. Although I have plenty of functions that take pointers such as (x,y,z), of which perhaps z is a destination, and I have to specify in the docs that x and z for example could be the same. But this is to help in writing the right code within the function (don't write to *z before it's done reading from *x) rather than any language issues. -- bartc
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C Compilers QoI BartC <bc@freeuk.com> - 2017-03-14 13:01 +0000
Re: C Compilers QoI mark.bluemel@gmail.com - 2017-03-14 06:16 -0700
Re: C Compilers QoI already5chosen@yahoo.com - 2017-03-14 06:42 -0700
Re: C Compilers QoI "Rick C. Hodgin" <rick.c.hodgin@gmail.com> - 2017-03-14 06:56 -0700
Re: C Compilers QoI BartC <bc@freeuk.com> - 2017-03-14 15:58 +0000
Re: C Compilers QoI "Rick C. Hodgin" <rick.c.hodgin@gmail.com> - 2017-03-14 09:22 -0700
Re: C Compilers QoI scott@slp53.sl.home (Scott Lurndal) - 2017-03-14 16:54 +0000
Re: C Compilers QoI supercat@casperkitty.com - 2017-03-14 10:24 -0700
Re: C Compilers QoI scott@slp53.sl.home (Scott Lurndal) - 2017-03-14 17:58 +0000
Re: C Compilers QoI supercat@casperkitty.com - 2017-03-14 14:12 -0700
Re: C Compilers QoI Robert Wessel <robertwessel2@yahoo.com> - 2017-03-14 16:34 -0500
Re: C Compilers QoI Robert Wessel <robertwessel2@yahoo.com> - 2017-03-14 17:36 -0500
Re: C Compilers QoI BartC <bc@freeuk.com> - 2017-03-14 23:06 +0000
Re: C Compilers QoI supercat@casperkitty.com - 2017-03-14 16:20 -0700
Re: C Compilers QoI antispam@math.uni.wroc.pl - 2017-03-15 02:32 +0000
Re: C Compilers QoI BartC <bc@freeuk.com> - 2017-03-15 12:49 +0000
Re: C Compilers QoI supercat@casperkitty.com - 2017-03-15 11:56 -0700
Re: C Compilers QoI BartC <bc@freeuk.com> - 2017-03-15 23:09 +0000
Re: C Compilers QoI scott@slp53.sl.home (Scott Lurndal) - 2017-03-16 18:17 +0000
Re: C Compilers QoI supercat@casperkitty.com - 2017-03-16 11:47 -0700
Re: C Compilers QoI Ian Collins <ian-news@hotmail.com> - 2017-03-17 07:50 +1300
Re: C Compilers QoI supercat@casperkitty.com - 2017-03-16 12:59 -0700
Re: C Compilers QoI David Brown <david.brown@hesbynett.no> - 2017-03-16 21:24 +0100
Re: C Compilers QoI supercat@casperkitty.com - 2017-03-16 14:23 -0700
Re: C Compilers QoI Ian Collins <ian-news@hotmail.com> - 2017-03-17 11:30 +1300
Re: C Compilers QoI Ian Collins <ian-news@hotmail.com> - 2017-03-17 11:38 +1300
Re: C Compilers QoI Gareth Owen <gwowen@gmail.com> - 2017-03-17 05:07 +0000
Re: C Compilers QoI Ian Collins <ian-news@hotmail.com> - 2017-03-17 20:26 +1300
Re: C Compilers QoI Gareth Owen <gwowen@gmail.com> - 2017-03-17 07:59 +0000
Re: C Compilers QoI supercat@casperkitty.com - 2017-03-16 16:14 -0700
Re: C Compilers QoI Robert Wessel <robertwessel2@yahoo.com> - 2017-03-16 22:54 -0500
Re: C Compilers QoI supercat@casperkitty.com - 2017-03-17 09:01 -0700
Re: C Compilers QoI Ian Collins <ian-news@hotmail.com> - 2017-03-26 14:16 +1300
Re: C Compilers QoI supercat@casperkitty.com - 2017-03-26 14:19 -0700
Re: C Compilers QoI BartC <bc@freeuk.com> - 2017-03-26 22:43 +0100
Re: C Compilers QoI GOTHIER Nathan <nathan.gothier@gmail.com> - 2017-03-27 01:28 +0200
Re: C Compilers QoI supercat@casperkitty.com - 2017-03-26 22:07 -0700
Re: C Compilers QoI BartC <bc@freeuk.com> - 2017-03-27 11:28 +0100
Re: C Compilers QoI supercat@casperkitty.com - 2017-03-27 07:38 -0700
Re: C Compilers QoI BartC <bc@freeuk.com> - 2017-03-27 16:23 +0100
Re: C Compilers QoI supercat@casperkitty.com - 2017-03-27 08:55 -0700
Re: C Compilers QoI BartC <bc@freeuk.com> - 2017-03-27 17:01 +0100
Re: C Compilers QoI supercat@casperkitty.com - 2017-03-27 10:03 -0700
Re: C Compilers QoI GOTHIER Nathan <nathan.gothier@gmail.com> - 2017-03-27 17:58 +0200
Re: C Compilers QoI already5chosen@yahoo.com - 2017-03-27 03:54 -0700
Re: C Compilers QoI supercat@casperkitty.com - 2017-03-27 08:46 -0700
Re: C Compilers QoI scott@slp53.sl.home (Scott Lurndal) - 2017-03-27 17:47 +0000
Re: C Compilers QoI supercat@casperkitty.com - 2017-03-27 11:48 -0700
Re: C Compilers QoI Robert Wessel <robertwessel2@yahoo.com> - 2017-03-27 15:37 -0500
Re: C Compilers QoI supercat@casperkitty.com - 2017-03-27 14:46 -0700
Re: C Compilers QoI Robert Wessel <robertwessel2@yahoo.com> - 2017-03-27 20:28 -0500
Re: C Compilers QoI supercat@casperkitty.com - 2017-03-28 01:18 -0700
Re: C Compilers QoI Robert Wessel <robertwessel2@yahoo.com> - 2017-03-28 18:24 -0500
Re: C Compilers QoI supercat@casperkitty.com - 2017-03-29 07:40 -0700
Re: C Compilers QoI David Brown <david.brown@hesbynett.no> - 2017-03-29 17:05 +0200
Re: C Compilers QoI supercat@casperkitty.com - 2017-03-29 11:07 -0700
Re: C Compilers QoI antispam@math.uni.wroc.pl - 2017-03-31 04:04 +0000
Re: C Compilers QoI bartc <bc@freeuk.com> - 2017-03-31 10:53 +0100
Re: C Compilers QoI Malcolm McLean <malcolm.mclean5@btinternet.com> - 2017-03-31 07:35 -0700
Re: C Compilers QoI supercat@casperkitty.com - 2017-03-31 08:07 -0700
Re: C Compilers QoI supercat@casperkitty.com - 2017-03-31 07:54 -0700
Re: C Compilers QoI supercat@casperkitty.com - 2017-03-31 07:43 -0700
Re: C Compilers QoI Ian Collins <ian-news@hotmail.com> - 2017-03-17 11:21 +1300
Re: C Compilers QoI Ian Collins <ian-news@hotmail.com> - 2017-03-17 11:24 +1300
Re: C Compilers QoI BartC <bc@freeuk.com> - 2017-03-16 22:15 +0000
Re: C Compilers QoI scott@slp53.sl.home (Scott Lurndal) - 2017-03-17 12:31 +0000
Re: C Compilers QoI already5chosen@yahoo.com - 2017-03-16 15:24 -0700
Re: C Compilers QoI supercat@casperkitty.com - 2017-03-16 16:03 -0700
Re: C Compilers QoI scott@slp53.sl.home (Scott Lurndal) - 2017-03-17 12:39 +0000
Re: C Compilers QoI already5chosen@yahoo.com - 2017-03-17 08:27 -0700
Re: C Compilers QoI antispam@math.uni.wroc.pl - 2017-03-16 01:35 +0000
Re: C Compilers QoI BartC <bc@freeuk.com> - 2017-03-16 02:18 +0000
Re: C Compilers QoI antispam@math.uni.wroc.pl - 2017-03-18 00:45 +0000
Re: C Compilers QoI BartC <bc@freeuk.com> - 2017-03-18 13:12 +0000
Re: C Compilers QoI antispam@math.uni.wroc.pl - 2017-03-18 20:31 +0000
Re: C Compilers QoI supercat@casperkitty.com - 2017-03-18 17:31 -0700
Re: C Compilers QoI supercat@casperkitty.com - 2017-03-16 09:22 -0700
Re: C Compilers QoI Nick Bowler <nbowler@draconx.ca> - 2017-03-24 16:13 +0000
Re: C Compilers QoI supercat@casperkitty.com - 2017-03-24 12:32 -0700
Re: C Compilers QoI Robert Wessel <robertwessel2@yahoo.com> - 2017-03-24 22:13 -0500
Re: C Compilers QoI supercat@casperkitty.com - 2017-03-25 13:05 -0700
Re: C Compilers QoI Robert Wessel <robertwessel2@yahoo.com> - 2017-03-27 15:44 -0500
Re: C Compilers QoI supercat@casperkitty.com - 2017-03-27 14:51 -0700
Re: C Compilers QoI Robert Wessel <robertwessel2@yahoo.com> - 2017-03-27 20:31 -0500
Re: C Compilers QoI BartC <bc@freeuk.com> - 2017-03-14 17:26 +0000
Re: C Compilers QoI Andrew Haley <andrew29@littlepinkcloud.invalid> - 2017-03-15 12:02 -0500
Re: C Compilers QoI David Brown <david.brown@hesbynett.no> - 2017-03-14 15:00 +0100
Re: C Compilers QoI already5chosen@yahoo.com - 2017-03-14 07:36 -0700
Re: C Compilers QoI David Brown <david.brown@hesbynett.no> - 2017-03-14 15:57 +0100
Re: C Compilers QoI Andrey Tarasevich <andreytarasevich@hotmail.com> - 2017-03-14 08:11 -0700
Re: C Compilers QoI BGB <cr88192@hotmail.com> - 2017-03-29 23:51 -0500
Re: C Compilers QoI BartC <bc@freeuk.com> - 2017-03-14 15:28 +0000
Re: C Compilers QoI David Brown <david.brown@hesbynett.no> - 2017-03-14 21:41 +0100
Re: C Compilers QoI Keith Thompson <kst-u@mib.org> - 2017-03-14 09:26 -0700
Re: C Compilers QoI BartC <bc@freeuk.com> - 2017-03-14 18:23 +0000
Re: C Compilers QoI Keith Thompson <kst-u@mib.org> - 2017-03-14 12:05 -0700
Re: C Compilers QoI already5chosen@yahoo.com - 2017-03-14 09:35 -0700
Re: C Compilers QoI BartC <bc@freeuk.com> - 2017-03-14 17:08 +0000
Re: C Compilers QoI already5chosen@yahoo.com - 2017-03-14 10:24 -0700
Re: C Compilers QoI BartC <bc@freeuk.com> - 2017-03-14 17:34 +0000
Re: C Compilers QoI already5chosen@yahoo.com - 2017-03-14 11:55 -0700
Re: C Compilers QoI BartC <bc@freeuk.com> - 2017-03-14 19:03 +0000
Re: C Compilers QoI BartC <bc@freeuk.com> - 2017-03-14 19:06 +0000
Re: C Compilers QoI already5chosen@yahoo.com - 2017-03-14 12:10 -0700
Re: C Compilers QoI BartC <bc@freeuk.com> - 2017-03-14 21:14 +0000
Re: C Compilers QoI already5chosen@yahoo.com - 2017-03-14 14:42 -0700
Re: C Compilers QoI supercat@casperkitty.com - 2017-03-14 14:53 -0700
Re: C Compilers QoI BartC <bc@freeuk.com> - 2017-03-14 23:20 +0000
Re: C Compilers QoI antispam@math.uni.wroc.pl - 2017-03-15 02:43 +0000
Re: C Compilers QoI jacobnavia <jacob@jacob.remcomp.fr> - 2017-03-14 19:39 +0100
Re: C Compilers QoI BartC <bc@freeuk.com> - 2017-03-14 19:10 +0000
Re: C Compilers QoI antispam@math.uni.wroc.pl - 2017-03-14 19:29 +0000
Re: C Compilers QoI Noob <root@127.0.0.1> - 2017-03-15 09:27 +0100
Re: C Compilers QoI ed_davis2@yahoo.com - 2017-03-16 15:10 -0700
Re: C Compilers QoI BartC <bc@freeuk.com> - 2017-03-16 23:19 +0000
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