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Re: Is this really necessary

From Vir Campestris <vir.campestris@invalid.invalid>
Newsgroups comp.lang.c++
Subject Re: Is this really necessary
Date 2021-06-06 21:27 +0100
Organization A noiseless patient Spider
Message-ID <s9jb4b$rs9$1@dont-email.me> (permalink)
References <s9fl3f$ha7$1@dont-email.me>

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On 05/06/2021 11:53, Bonita Montero wrote:
> Consider the following code:
> 
> 
> size_t s( int *begin, int *end )
> {
>      return (end - begin) * sizeof(int);
> }
> 
> This is MSVC's disassembly:
> 
>      sub    rdx, rcx
>      and    rdx, -4
>      mov    rax, rdx
>      ret    0
> 
> This is gcc's disassembly:
> 
>      movq    %rsi, %rax
>      subq    %rdi, %rax
>      ret
> 
> It the masking really necessary or just an optimizer weakness;
> it seems to me MSVC sees that two bits are shifted out and "in"
> and replaces this with a mask.
> I think that the language-standard assumes equally aligned data
> among same types for the above code and gcc is corcect, but I'm
> not sure.
> 
I've gone through the whole thread, and nobody else has commented.

That GCC disassembly can't possibly be a correct and complete rendition 
of the function.

Maybe on entry begin is in eax, and end in rdi, which would explain the 
second instruction. But what's it doing with rsi?

Andy

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Thread

Is this really necessary Bonita Montero <Bonita.Montero@gmail.com> - 2021-06-05 12:53 +0200
  Re: Is this really necessary David Brown <david.brown@hesbynett.no> - 2021-06-05 14:19 +0200
    Re: Is this really necessary Bonita Montero <Bonita.Montero@gmail.com> - 2021-06-05 14:27 +0200
      Re: Is this really necessary David Brown <david.brown@hesbynett.no> - 2021-06-05 14:33 +0200
        Re: Is this really necessary Bonita Montero <Bonita.Montero@gmail.com> - 2021-06-05 15:06 +0200
          Re: Is this really necessary David Brown <david.brown@hesbynett.no> - 2021-06-05 15:29 +0200
            Re: Is this really necessary Bonita Montero <Bonita.Montero@gmail.com> - 2021-06-05 17:38 +0200
              Re: Is this really necessary David Brown <david.brown@hesbynett.no> - 2021-06-05 17:51 +0200
              Re: Is this really necessary Richard Damon <Richard@Damon-Family.org> - 2021-06-05 11:56 -0400
            Re: Is this really necessary James Kuyper <jameskuyper@alumni.caltech.edu> - 2021-06-05 19:08 -0400
              Re: Is this really necessary David Brown <david.brown@hesbynett.no> - 2021-06-06 11:24 +0200
              Re: Is this really necessary Chris Vine <chris@cvine--nospam--.freeserve.co.uk> - 2021-06-06 10:33 +0100
                Re: Is this really necessary Richard Damon <Richard@Damon-Family.org> - 2021-06-06 07:56 -0400
                Re: Is this really necessary Chris Vine <chris@cvine--nospam--.freeserve.co.uk> - 2021-06-06 15:00 +0100
                Re: Is this really necessary Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2021-06-06 16:20 -0700
                Re: Is this really necessary Tim Rentsch <tr.17687@z991.linuxsc.com> - 2021-06-07 00:44 -0700
                Re: Is this really necessary Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2021-06-07 12:13 -0700
                Re: Is this really necessary Bo Persson <bo@bo-persson.se> - 2021-06-07 21:58 +0200
                Re: Is this really necessary Tim Rentsch <tr.17687@z991.linuxsc.com> - 2021-08-07 10:25 -0700
                Re: Is this really necessary Bo Persson <bo@bo-persson.se> - 2021-08-07 21:21 +0200
          Re: Is this really necessary Öö Tiib <ootiib@hot.ee> - 2021-06-05 06:34 -0700
          Re: Is this really necessary Richard Damon <Richard@Damon-Family.org> - 2021-06-05 20:03 -0400
            Re: Is this really necessary Tim Rentsch <tr.17687@z991.linuxsc.com> - 2021-08-07 12:59 -0700
              Re: Is this really necessary MrSpud_85yGi2@1ahbfz.gov - 2021-08-08 09:18 +0000
                Re: Is this really necessary James Kuyper <jameskuyper@alumni.caltech.edu> - 2021-08-08 09:23 -0400
                Re: Is this really necessary Juha Nieminen <nospam@thanks.invalid> - 2021-08-08 15:04 +0000
                Re: Is this really necessary Richard Damon <Richard@Damon-Family.org> - 2021-08-08 13:14 -0400
                Re: Is this really necessary MrSpud_1dgrmf@dx58865qyrdw30lqllb.info - 2021-08-09 08:21 +0000
                Re: Is this really necessary Juha Nieminen <nospam@thanks.invalid> - 2021-08-09 08:53 +0000
                Re: Is this really necessary "Alf P. Steinbach" <alf.p.steinbach@gmail.com> - 2021-08-09 19:53 +0200
                Re: Is this really necessary Juha Nieminen <nospam@thanks.invalid> - 2021-08-10 05:22 +0000
                Re: Is this really necessary scott@slp53.sl.home (Scott Lurndal) - 2021-08-10 14:54 +0000
                Re: Is this really necessary Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2021-08-10 11:41 -0700
                Re: Is this really necessary Juha Nieminen <nospam@thanks.invalid> - 2021-08-11 05:39 +0000
                Re: Is this really necessary Chris Vine <chris@cvine--nospam--.freeserve.co.uk> - 2021-08-08 20:01 +0100
                Re: Is this really necessary MrSpud_ifhov@nldls6_1kg3nl2qnwv.biz - 2021-08-09 08:19 +0000
                Re: Is this really necessary Juha Nieminen <nospam@thanks.invalid> - 2021-08-09 08:55 +0000
                Re: Is this really necessary James Kuyper <jameskuyper@alumni.caltech.edu> - 2021-08-09 12:16 -0400
                Re: Is this really necessary MrSpud_HG@_0b772d8ha3yjo0xb.edu - 2021-08-09 16:23 +0000
                Re: Is this really necessary Vir Campestris <vir.campestris@invalid.invalid> - 2021-08-09 21:50 +0100
                Re: Is this really necessary Richard Damon <Richard@Damon-Family.org> - 2021-08-09 20:57 -0400
                Re: Is this really necessary scott@slp53.sl.home (Scott Lurndal) - 2021-08-10 01:12 +0000
                Re: Is this really necessary Richard Damon <Richard@Damon-Family.org> - 2021-08-09 21:21 -0400
                Re: Is this really necessary Tim Rentsch <tr.17687@z991.linuxsc.com> - 2021-08-10 07:13 -0700
                Re: Is this really necessary Juha Nieminen <nospam@thanks.invalid> - 2021-08-10 05:29 +0000
                Re: Is this really necessary MrSpud_12tus_Atff@bya886olr5o8dhu9.ac.uk - 2021-08-10 07:28 +0000
                Re: Is this really necessary Mike Terry <news.dead.person.stones@darjeeling.plus.com> - 2021-08-10 15:34 +0100
                Re: Is this really necessary scott@slp53.sl.home (Scott Lurndal) - 2021-08-10 14:59 +0000
                Re: Is this really necessary MrSpud_wPgnov999o@vv7a6.tv - 2021-08-10 15:54 +0000
                Re: Is this really necessary Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2021-08-10 11:29 -0700
                Re: Is this really necessary mickspud@downthefarm.com - 2021-08-11 08:45 +0000
                Re: Is this really necessary Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2021-08-11 07:05 -0700
                Re: Is this really necessary mickspud@downthefarm.com - 2021-08-11 14:18 +0000
                Re: Is this really necessary scott@slp53.sl.home (Scott Lurndal) - 2021-08-10 14:57 +0000
                Re: Is this really necessary MrSpud_pb9bpp7Ej@6urvt16b9fax.gov.uk - 2021-08-10 07:23 +0000
                Re: Is this really necessary scott@slp53.sl.home (Scott Lurndal) - 2021-08-10 15:02 +0000
                Re: Is this really necessary Tim Rentsch <tr.17687@z991.linuxsc.com> - 2021-08-10 06:11 -0700
                Re: Is this really necessary Bo Persson <bo@bo-persson.se> - 2021-08-10 16:13 +0200
                Re: Is this really necessary Tim Rentsch <tr.17687@z991.linuxsc.com> - 2021-08-11 12:40 -0700
                Re: Is this really necessary mickspud@downthefarm.com - 2021-08-12 08:20 +0000
                Re: Is this really necessary Tim Rentsch <tr.17687@z991.linuxsc.com> - 2021-08-12 03:50 -0700
                Re: Is this really necessary mickspud@downthefarm.com - 2021-08-12 14:58 +0000
                Re: Is this really necessary Tim Rentsch <tr.17687@z991.linuxsc.com> - 2021-08-12 08:29 -0700
                Re: Is this really necessary mickspud@downthefarm.com - 2021-08-12 15:39 +0000
                Re: Is this really necessary Paavo Helde <myfirstname@osa.pri.ee> - 2021-08-12 20:07 +0300
                Re: Is this really necessary Juha Nieminen <nospam@thanks.invalid> - 2021-08-13 07:16 +0000
                Re: Is this really necessary mickspud@downthefarm.com - 2021-08-13 09:26 +0000
                Re: Is this really necessary James Kuyper <jameskuyper@alumni.caltech.edu> - 2021-08-13 10:30 -0400
                Re: Is this really necessary mickspud@downthefarm.com - 2021-08-13 14:58 +0000
                Re: Is this really necessary Juha Nieminen <nospam@thanks.invalid> - 2021-08-14 08:07 +0000
                Re: Is this really necessary "james...@alumni.caltech.edu" <jameskuyper@alumni.caltech.edu> - 2021-08-14 10:40 -0700
                Re: Is this really necessary "james...@alumni.caltech.edu" <jameskuyper@alumni.caltech.edu> - 2021-08-14 10:38 -0700
                Re: Is this really necessary "Alf P. Steinbach" <alf.p.steinbach@gmail.com> - 2021-08-13 15:30 +0200
                Re: Is this really necessary Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2021-08-13 11:18 -0700
                Re: Is this really necessary Tim Rentsch <tr.17687@z991.linuxsc.com> - 2021-08-14 03:20 -0700
                Re: Is this really necessary Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2021-08-14 13:24 -0700
                Re: Is this really necessary Juha Nieminen <nospam@thanks.invalid> - 2021-08-14 20:33 +0000
                Re: Is this really necessary James Kuyper <jameskuyper@alumni.caltech.edu> - 2021-08-15 00:40 -0400
                Re: Is this really necessary Tim Rentsch <tr.17687@z991.linuxsc.com> - 2021-08-15 07:02 -0700
                Re: Is this really necessary "Alf P. Steinbach" <alf.p.steinbach@gmail.com> - 2021-08-15 21:19 +0200
                Re: Is this really necessary Richard Damon <Richard@Damon-Family.org> - 2021-08-15 15:42 -0400
                Re: Is this really necessary Tim Rentsch <tr.17687@z991.linuxsc.com> - 2021-08-21 12:38 -0700
                Re: Is this really necessary Juha Nieminen <nospam@thanks.invalid> - 2021-08-14 08:13 +0000
                Re: Is this really necessary Tim Rentsch <tr.17687@z991.linuxsc.com> - 2021-08-14 02:58 -0700
                Re: Is this really necessary scott@slp53.sl.home (Scott Lurndal) - 2021-08-13 14:32 +0000
                Re: Is this really necessary Tim Rentsch <tr.17687@z991.linuxsc.com> - 2021-08-14 02:28 -0700
                Re: Is this really necessary Tim Rentsch <tr.17687@z991.linuxsc.com> - 2021-08-14 03:00 -0700
                Re: Is this really necessary Bart <bc@freeuk.com> - 2021-08-14 14:03 +0100
                Re: Is this really necessary mickspud@downthefarm.com - 2021-08-14 15:06 +0000
                Re: Is this really necessary "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2021-08-12 12:06 -0700
                Re: Is this really necessary mickspud@downthefarm.com - 2021-08-13 09:19 +0000
                Re: Is this really necessary scott@slp53.sl.home (Scott Lurndal) - 2021-08-13 14:35 +0000
                Re: Is this really necessary mickspud@downthefarm.com - 2021-08-13 14:58 +0000
                Re: Is this really necessary scott@slp53.sl.home (Scott Lurndal) - 2021-08-10 15:03 +0000
                Re: Is this really necessary Tim Rentsch <tr.17687@z991.linuxsc.com> - 2021-08-11 12:54 -0700
                Re: Is this really necessary scott@slp53.sl.home (Scott Lurndal) - 2021-08-11 20:20 +0000
                Re: Is this really necessary Tim Rentsch <tr.17687@z991.linuxsc.com> - 2021-08-12 03:42 -0700
                Re: Is this really necessary Juha Nieminen <nospam@thanks.invalid> - 2021-08-11 05:45 +0000
                Re: Is this really necessary Tim Rentsch <tr.17687@z991.linuxsc.com> - 2021-08-11 05:26 -0700
                Re: Is this really necessary scott@slp53.sl.home (Scott Lurndal) - 2021-08-11 14:06 +0000
                Re: Is this really necessary scott@slp53.sl.home (Scott Lurndal) - 2021-08-11 14:01 +0000
                Re: Is this really necessary James Kuyper <jameskuyper@alumni.caltech.edu> - 2021-08-09 23:20 -0400
                Re: Is this really necessary MrSpud_m7k7yilq_8@u6w.biz - 2021-08-10 07:26 +0000
                Re: Is this really necessary Juha Nieminen <nospam@thanks.invalid> - 2021-08-10 07:51 +0000
                Re: Is this really necessary MrSpud_ggBp1lq0@lxz.tv - 2021-08-10 07:59 +0000
                Re: Is this really necessary Juha Nieminen <nospam@thanks.invalid> - 2021-08-10 12:24 +0000
                Re: Is this really necessary MrSpud_u7lm@bxuc3wy1g3cxiqu5j2x1_7iu.com - 2021-08-10 15:51 +0000
                Re: Is this really necessary Juha Nieminen <nospam@thanks.invalid> - 2021-08-11 05:47 +0000
                Re: Is this really necessary mickspud@downthefarm.com - 2021-08-11 08:46 +0000
                Re: Is this really necessary David Brown <david.brown@hesbynett.no> - 2021-08-10 11:20 +0200
                Re: Is this really necessary James Kuyper <jameskuyper@alumni.caltech.edu> - 2021-08-10 10:27 -0400
                Re: Is this really necessary David Brown <david.brown@hesbynett.no> - 2021-08-10 17:44 +0200
                Re: Is this really necessary MrSpud_885p_dugji@l6zhsgj_v6t3dbj.tv - 2021-08-10 15:50 +0000
                Re: Is this really necessary David Brown <david.brown@hesbynett.no> - 2021-08-11 08:31 +0200
                Re: Is this really necessary James Kuyper <jameskuyper@alumni.caltech.edu> - 2021-08-10 10:27 -0400
                Re: Is this really necessary Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2021-08-10 11:27 -0700
                Re: Is this really necessary mickspud@downthefarm.com - 2021-08-11 08:44 +0000
                Re: Is this really necessary Paavo Helde <myfirstname@osa.pri.ee> - 2021-08-11 16:05 +0300
                Re: Is this really necessary Tim Rentsch <tr.17687@z991.linuxsc.com> - 2021-08-10 06:41 -0700
          Re: Is this really necessary Paavo Helde <myfirstname@osa.pri.ee> - 2021-06-06 18:48 +0300
            Re: Is this really necessary Richard Damon <Richard@Damon-Family.org> - 2021-06-06 14:26 -0400
            Re: Is this really necessary Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2021-06-06 16:10 -0700
              Re: Is this really necessary Richard Damon <Richard@Damon-Family.org> - 2021-06-06 21:30 -0400
                Re: Is this really necessary Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2021-06-06 18:49 -0700
                Re: Is this really necessary Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2021-06-06 18:51 -0700
                Re: Is this really necessary Richard Damon <Richard@Damon-Family.org> - 2021-06-06 22:57 -0400
                Re: Is this really necessary Tim Rentsch <tr.17687@z991.linuxsc.com> - 2021-06-07 09:43 -0700
                Re: Is this really necessary Öö Tiib <ootiib@hot.ee> - 2021-06-07 09:51 -0700
                Re: Is this really necessary Tim Rentsch <tr.17687@z991.linuxsc.com> - 2021-08-07 10:22 -0700
                Re: Is this really necessary "james...@alumni.caltech.edu" <jameskuyper@alumni.caltech.edu> - 2021-06-07 10:13 -0700
                Re: Is this really necessary Tim Rentsch <tr.17687@z991.linuxsc.com> - 2021-08-07 10:22 -0700
                Re: Is this really necessary "james...@alumni.caltech.edu" <jameskuyper@alumni.caltech.edu> - 2021-08-07 12:40 -0700
                Re: Is this really necessary Tim Rentsch <tr.17687@z991.linuxsc.com> - 2021-08-07 12:54 -0700
              Re: Is this really necessary Öö Tiib <ootiib@hot.ee> - 2021-06-06 23:17 -0700
            Re: Is this really necessary Tim Rentsch <tr.17687@z991.linuxsc.com> - 2021-06-07 09:19 -0700
              Re: Is this really necessary Paavo Helde <myfirstname@osa.pri.ee> - 2021-06-07 21:58 +0300
                Re: Is this really necessary Tim Rentsch <tr.17687@z991.linuxsc.com> - 2021-06-10 11:29 -0700
    Re: Is this really necessary Öö Tiib <ootiib@hot.ee> - 2021-06-05 05:38 -0700
      Re: Is this really necessary David Brown <david.brown@hesbynett.no> - 2021-06-05 15:41 +0200
        Re: Is this really necessary Öö Tiib <ootiib@hot.ee> - 2021-06-05 08:18 -0700
          Re: Is this really necessary Richard Damon <Richard@Damon-Family.org> - 2021-06-05 11:58 -0400
    Re: Is this really necessary MrSpook_rs7x@4hhtozmpj299zx.tv - 2021-06-05 16:00 +0000
      Re: Is this really necessary David Brown <david.brown@hesbynett.no> - 2021-06-05 18:16 +0200
        Re: Is this really necessary David Brown <david.brown@hesbynett.no> - 2021-06-06 17:34 +0200
        Re: Is this really necessary MrSpook_ie@q67rq6_2ly9ut44j.org - 2021-06-06 13:55 +0000
      Re: Is this really necessary Bo Persson <bo@bo-persson.se> - 2021-06-05 19:50 +0200
        Re: Is this really necessary MrSpook_zn7@4tzq7j92.gov - 2021-06-06 13:59 +0000
    Re: Is this really necessary James Kuyper <jameskuyper@alumni.caltech.edu> - 2021-06-05 17:42 -0400
      Re: Is this really necessary David Brown <david.brown@hesbynett.no> - 2021-06-06 11:05 +0200
      Re: Is this really necessary Tim Rentsch <tr.17687@z991.linuxsc.com> - 2021-06-07 00:27 -0700
  Re: Is this really necessary Vir Campestris <vir.campestris@invalid.invalid> - 2021-06-06 21:27 +0100
    Re: Is this really necessary "Alf P. Steinbach" <alf.p.steinbach@gmail.com> - 2021-06-07 00:22 +0200
      Re: Is this really necessary scott@slp53.sl.home (Scott Lurndal) - 2021-06-07 14:53 +0000
        Re: Is this really necessary Bonita Montero <Bonita.Montero@gmail.com> - 2021-06-07 18:02 +0200
      Re: Is this really necessary Vir Campestris <vir.campestris@invalid.invalid> - 2021-06-16 21:38 +0100
    Re: Is this really necessary scott@slp53.sl.home (Scott Lurndal) - 2021-06-07 14:52 +0000

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