Re: Bounds checking, Optimization techniques and undefined behavior

From	Hans-Peter Diettrich <DrDiettrich1@netscape.net>
Newsgroups	comp.compilers
Subject	Re: Bounds checking, Optimization techniques and undefined behavior
Date	2019-05-06 10:15 +0200
Organization	Compilers Central
Message-ID	<19-05-034@comp.compilers> (permalink)
References	(10 earlier) <19-05-020@comp.compilers> <19-05-024@comp.compilers> <19-05-025@comp.compilers> <19-05-028@comp.compilers> <19-05-029@comp.compilers>

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Am 05.05.2019 um 20:44 schrieb Hans-Peter Diettrich:
> Am 05.05.2019 um 12:14 schrieb Bart:
>
>> But how do they get there? Take this:
>>
>>     int A[10], *p;
>>     p = &A[3];
>>
>> You intend p to refer to the 4-element slice A[3..6], but how does the
>> language know that? How can it stop code from writing to p[5]?
>
> Not pointers are bad, but pointer arithmetic is. It should be allowed
> only with objects of known bounds.
>
> DoDi
> [In this case the bounds look known to me. -John]

The bounds are known for the array, so that the pointer is guaranteed
valid by compile time check. But p[x] or p+x can not be guaranteed valid
without considerable runtime and bounds storage overhead. Also simple
p++ operation or the like requires an update of the bounds information.
That's what I consider pointer arithmetic, not above &A[3].

I learned to love the Pascal indexing instead of pointers, because a
loop like
   for i := 1 to 10 do sum := sum + A[i];
can be optimized safely by the Pascal/Delphi compiler into pointer and
auto increment, so that no speed penalty exists vs. explicit pointer
usage. But in a C for loop the index variable can be changed in code, so
that even above code would execute slower with bounds checks.

DoDi

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Re: Optimization techniques David Brown <david.brown@hesbynett.no> - 2019-04-25 21:58 +0200
  Re: Optimization techniques Kaz Kylheku <847-115-0292@kylheku.com> - 2019-04-26 00:18 +0000
    Re: Optimization techniques David Brown <david.brown@hesbynett.no> - 2019-04-28 23:49 +0200
      Re: Optimization techniques and undefined behavior Bart <bc@freeuk.com> - 2019-04-29 00:31 +0100
        Re: Optimization techniques and undefined behavior David Brown <david.brown@hesbynett.no> - 2019-04-29 17:08 +0200
          Re: Optimization techniques and undefined behavior Christian Gollwitzer <auriocus@gmx.de> - 2019-04-29 18:10 +0200
            Re: Optimization techniques and undefined behavior David Brown <david.brown@hesbynett.no> - 2019-04-30 14:46 +0200
              Re: Optimization techniques and undefined behavior Bart <bc@freeuk.com> - 2019-05-01 13:53 +0100
                Re: Optimization techniques and undefined behavior Andy Walker <anw@cuboid.co.uk> - 2019-05-02 11:29 +0100
                Re: Optimization techniques and undefined behavior Bart <bc@freeuk.com> - 2019-05-03 00:48 +0100
                Re: Optimization techniques and undefined behavior Martin Ward <martin@gkc.org.uk> - 2019-05-03 10:52 +0100
                Re: Optimization techniques and undefined behavior George Neuner <gneuner2@comcast.net> - 2019-05-04 17:44 -0400
                Re: Bounds checking, Optimization techniques and undefined behavior George Neuner <gneuner2@comcast.net> - 2019-05-05 17:10 -0400
                Re: Optimization techniques and undefined behavior David Brown <david.brown@hesbynett.no> - 2019-05-06 08:14 +0200
                Re: Optimization techniques and undefined behavior Gene Wirchenko <genew@telus.net> - 2019-05-11 22:25 -0700
                Re: not a lot of memory, was Optimization techniques and undefined behavior Bart <bc@freeuk.com> - 2019-05-03 12:45 +0100
                Re: Optimization techniques and undefined behavior Andy Walker <anw@cuboid.co.uk> - 2019-05-03 13:29 +0100
                Re: Optimization techniques and undefined behavior Bart <bc@freeuk.com> - 2019-05-03 23:10 +0100
                Re: Optimization techniques and undefined behavior Andy Walker <anw@cuboid.co.uk> - 2019-05-04 10:45 +0100
                Re: Bounds checking, Optimization techniques and undefined behavior Bart <bc@freeuk.com> - 2019-05-05 11:14 +0100
                Re: Bounds checking, Optimization techniques and undefined behavior Hans-Peter Diettrich <DrDiettrich1@netscape.net> - 2019-05-05 20:44 +0200
                Re: Bounds checking, Optimization techniques and undefined behavior Hans-Peter Diettrich <DrDiettrich1@netscape.net> - 2019-05-06 10:15 +0200
                Re: Bounds checking, Optimization techniques and undefined behavior David Brown <david.brown@hesbynett.no> - 2019-05-07 11:04 +0200
                Re: Bounds checking, Optimization techniques and undefined behavior "Nuno Lopes" <nuno.lopes@ist.utl.pt> - 2019-05-07 22:38 +0100
                Re: Bounds checking, Optimization techniques and undefined behavior Bart <bc@freeuk.com> - 2019-05-08 01:14 +0100
                Re: Bounds checking, Optimization techniques and undefined behavior David Brown <david.brown@hesbynett.no> - 2019-05-08 09:55 +0200
                Re: Bounds checking, Optimization techniques and undefined behavior "Derek M. Jones" <derek@_NOSPAM_knosof.co.uk> - 2019-05-08 19:08 +0100
                Re: Bounds checking, Optimization techniques and undefined behavior Andy Walker <anw@cuboid.co.uk> - 2019-05-08 01:42 +0100
                Re: Bounds checking, Optimization techniques and undefined behavior David Brown <david.brown@hesbynett.no> - 2019-05-08 10:16 +0200
                Re: Bounds checking, Optimization techniques and undefined behavior Bart <bc@freeuk.com> - 2019-05-09 01:15 +0100
                Re: Bounds checking, Optimization techniques and undefined behavior David Brown <david.brown@hesbynett.no> - 2019-05-09 21:56 +0200
                Re: Bounds checking, Optimization techniques and undefined behavior David Brown <david.brown@hesbynett.no> - 2019-05-08 10:03 +0200
                Re: Bounds checking, Optimization techniques and undefined behavior David Brown <david.brown@hesbynett.no> - 2019-05-09 09:19 +0200
                Re: Bounds checking, Optimization techniques and undefined behavior Kaz Kylheku <847-115-0292@kylheku.com> - 2019-05-10 03:38 +0000
                Re: Bounds checking, Optimization techniques and undefined behavior Bart <bc@freeuk.com> - 2019-05-08 14:37 +0100
                Re: Bounds checking, Optimization techniques and undefined behavior Christopher F Clark <christopher.f.clark@compiler-resources.com> - 2019-05-06 05:05 -0400
                Re: Bounds checking, Optimization techniques and undefined behavior George Neuner <gneuner2@comcast.net> - 2019-05-05 17:38 -0400
                Re: Bounds checking, Optimization techniques and undefined behavior Bart <bc@freeuk.com> - 2019-05-06 13:07 +0100
                Re: Bounds checking, Optimization techniques and undefined behavior David Brown <david.brown@hesbynett.no> - 2019-05-07 14:01 +0200
                Re: Bounds checking, Optimization techniques and undefined behavior Andy Walker <anw@cuboid.co.uk> - 2019-05-06 01:15 +0100
                Re: Bounds checking, Optimization techniques and undefined behavior Andy Walker <anw@cuboid.co.uk> - 2019-05-06 14:40 +0100
                Re: Bounds checking, Optimization techniques and undefined behavior David Brown <david.brown@hesbynett.no> - 2019-05-07 15:05 +0200
                Re: Bounds checking, Optimization techniques and undefined behavior David Brown <david.brown@hesbynett.no> - 2019-05-08 10:18 +0200
                Re: Bounds checking, Optimization techniques and undefined behavior Jan Ziak <0xe2.0x9a.0x9b@gmail.com> - 2019-05-06 05:39 -0700
                Re: Bounds checking, Optimization techniques and undefined behavior David Brown <david.brown@hesbynett.no> - 2019-05-07 15:42 +0200
                Re: Bounds checking, Optimization techniques and undefined behavior David Brown <david.brown@hesbynett.no> - 2019-05-06 16:32 +0200
                Re: Optimization techniques and undefined behavior George Neuner <gneuner2@comcast.net> - 2019-05-04 17:59 -0400
                Re: Optimization techniques and undefined behavior David Brown <david.brown@hesbynett.no> - 2019-05-02 16:51 +0200
                Re: Optimization techniques and undefined behavior Bart <bc@freeuk.com> - 2019-05-02 20:04 +0100
                Re: Optimization techniques and undefined behavior David Brown <david.brown@hesbynett.no> - 2019-05-03 17:23 +0200
                Re: Optimization techniques and undefined behavior Bart <bc@freeuk.com> - 2019-05-03 21:10 +0100
                Re: Optimization techniques and undefined behavior Martin Ward <martin@gkc.org.uk> - 2019-05-06 13:25 +0100
                Re: Optimization techniques and undefined behavior "Derek M. Jones" <derek@_NOSPAM_knosof.co.uk> - 2019-05-06 16:32 +0100
                Re: Optimization techniques and undefined behavior David Brown <david.brown@hesbynett.no> - 2019-05-07 16:03 +0200
                Re: Optimization techniques and undefined behavior Martin Ward <martin@gkc.org.uk> - 2019-05-08 13:16 +0100
                Re: Optimization techniques and undefined behavior George Neuner <gneuner2@comcast.net> - 2019-05-08 15:13 -0400
                Re: Optimization techniques and undefined behavior "Robin Vowels" <robin51@dodo.com.au> - 2019-05-07 01:22 +1000
                Re: Optimization techniques and undefined behavior David Brown <david.brown@hesbynett.no> - 2019-05-07 16:05 +0200
                Re: Optimization techniques and undefined behavior Christian Gollwitzer <auriocus@gmx.de> - 2019-05-02 22:22 +0200
          Re: Optimization techniques and undefined behavior Bart <bc@freeuk.com> - 2019-04-29 18:15 +0100
            Re: Optimization techniques and undefined behavior David Brown <david.brown@hesbynett.no> - 2019-04-30 15:48 +0200
              Re: Optimization techniques and undefined behavior Bart <bc@freeuk.com> - 2019-05-01 12:40 +0100
                Re: Optimization techniques and undefined behavior David Brown <david.brown@hesbynett.no> - 2019-05-02 17:27 +0200
                Re: Optimization techniques and undefined behavior Bart <bc@freeuk.com> - 2019-05-02 18:59 +0100
                Re: Optimization techniques and undefined behavior David Brown <david.brown@hesbynett.no> - 2019-05-07 16:16 +0200
              Re: Optimization techniques and undefined behavior Martin Ward <martin@gkc.org.uk> - 2019-05-02 14:54 +0100
      Re: Optimization techniques and runtime checks Hans-Peter Diettrich <DrDiettrich1@netscape.net> - 2019-04-29 22:36 +0200
        Re: Optimization techniques and runtime checks David Brown <david.brown@hesbynett.no> - 2019-05-07 16:29 +0200
          Re: Optimization techniques and runtime checks Hans-Peter Diettrich <DrDiettrich1@netscape.net> - 2019-05-08 02:27 +0200
            Re: Optimization techniques and runtime checks David Brown <david.brown@hesbynett.no> - 2019-05-08 10:31 +0200
              Re: Optimization techniques and runtime checks Hans-Peter Diettrich <DrDiettrich1@netscape.net> - 2019-05-08 22:50 +0200
              Re: Optimization techniques and runtime checks "Robin Vowels" <robin51@dodo.com.au> - 2019-05-11 19:26 +1000
              Re: Optimization techniques and runtime checks Gene Wirchenko <genew@telus.net> - 2019-05-11 22:43 -0700
                Re: Optimization techniques and runtime checks David Brown <david.brown@hesbynett.no> - 2019-05-12 20:17 +0200
          Re: Optimization techniques and runtime checks Bart <bc@freeuk.com> - 2019-05-08 14:58 +0100
            Re: Optimization techniques and runtime checks David Brown <david.brown@hesbynett.no> - 2019-05-08 23:02 +0200
              Re: Optimization techniques and runtime checks Bart <bc@freeuk.com> - 2019-05-09 18:28 +0100
                Re: Optimization techniques and runtime checks David Brown <david.brown@hesbynett.no> - 2019-05-09 22:07 +0200
      Re: Optimization techniques Gene Wirchenko <genew@telus.net> - 2019-04-30 18:24 -0700
        Re: Optimization techniques David Brown <david.brown@hesbynett.no> - 2019-05-01 09:20 +0200
          Re: Optimization techniques Kaz Kylheku <847-115-0292@kylheku.com> - 2019-05-02 17:40 +0000
          Re: Optimization techniques and error detection Gene Wirchenko <genew@telus.net> - 2019-05-03 10:16 -0700
          Re: Optimization techniques "Robin Vowels" <robin51@dodo.com.au> - 2019-05-07 01:42 +1000
  Re: Optimization techniques Kaz Kylheku <847-115-0292@kylheku.com> - 2019-04-26 02:26 +0000
    Re: Optimization techniques and undefined behavior David Brown <david.brown@hesbynett.no> - 2019-04-29 00:12 +0200
      Re: Optimization techniques and undefined behavior Kaz Kylheku <847-115-0292@kylheku.com> - 2019-05-02 17:18 +0000
        Re: Optimization techniques and undefined behavior David Brown <david.brown@hesbynett.no> - 2019-05-07 16:38 +0200

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