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Re: rhel 7 and kforth

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From "Rod Pemberton" <bork@lllljunkqwer.cpm>
Newsgroups comp.lang.forth
Subject Re: rhel 7 and kforth
Date Mon, 27 Apr 2015 18:21:26 -0400
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On Mon, 27 Apr 2015 05:19:48 -0400, Anton Ertl  
<anton@mips.complang.tuwien.ac.at> wrote:

> I'll try to explain it again:
>
> If you have
>
> i=5;
> if (i<16)
>   ...
>
> you know that "i<16" is true, so you can optimize it to true.
>
> If you have
>
> i=...
> if (i<16) {
>   ... \ no change in i
>   if (i<16)
>     ...
>
> In the second "i<16", you know that it is true, so you can optimize it
> to true.
>
> That's all fine and well.  Now consider:
>
> int a[16];
> i=...; \ too complex to determine the range of i
> r=a[i];
> if (i<16)
>   ...
>
> Here the compiler does not really know the range of i, but because it
> occurs in a[i], it assumes that i<16 (otherwise the access a[i] would
> be undefined behaviour),

So?  Who said undefined behavior is incorrect?  There is a difference.

AIR, the C specifications say that undefined behavior can be
defined for a platform, i.e., correct on a specific platform.
E.g., it's common for most C platforms to allow a value to be
assigned to a pointer.  That's undefined behavior which is
defined for the specific host.

It's not the compiler's job to correct undefined behavior.
Undefined behavior might be exactly what the coder wanted.
The compiler's job is to do exactly what it was told to do
without changing the end result as understood by people.
Clearly, it fails here.

> so it miscompiles the "i<16" to true (or at
> least the version that miscompiled the SPEC program did).

Logic error.  Why should it assume "i<16" is true from "a[i]"?
It could just as easily assume "a[i]" is incorrect, but "i<16" isn't.

> However, in real programs out-of-bounds accesses and other undefined
> behaviours do happen (not frequent for out-of-bounds accesses, but
> still), and "optimizing" based on the assumption that they don't is
> miscompilation.

Agreed.


Rod Pemberton

-- 
Cars kill more people than guns in the U.S.
Yet, no one is trying to take away your car.

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rhel 7 and kforth krishna.myneni@ccreweb.org - 2015-04-15 11:20 -0700
  Re: rhel 7 and kforth krishna.myneni@ccreweb.org - 2015-04-15 19:09 -0700
  Re: rhel 7 and kforth krishna.myneni@ccreweb.org - 2015-04-16 04:13 -0700
    Re: rhel 7 and kforth krishna.myneni@ccreweb.org - 2015-04-16 04:55 -0700
      Re: rhel 7 and kforth anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2015-04-16 12:08 +0000
        Re: rhel 7 and kforth krishna.myneni@ccreweb.org - 2015-04-16 05:29 -0700
          Re: rhel 7 and kforth krishna.myneni@ccreweb.org - 2015-04-16 07:07 -0700
            Re: rhel 7 and kforth franck.bensusan@gmail.com - 2015-04-16 07:44 -0700
              Re: rhel 7 and kforth krishna.myneni@ccreweb.org - 2015-04-16 08:14 -0700
          Re: rhel 7 and kforth anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2015-04-16 14:02 +0000
            Re: rhel 7 and kforth krishna.myneni@ccreweb.org - 2015-04-16 08:12 -0700
      Re: rhel 7 and kforth krishna.myneni@ccreweb.org - 2015-04-16 12:25 -0700
        Re: rhel 7 and kforth krishna.myneni@ccreweb.org - 2015-04-16 17:02 -0700
          Re: rhel 7 and kforth krishna.myneni@ccreweb.org - 2015-04-16 17:06 -0700
            Re: rhel 7 and kforth foxaudioresearch@gmail.com - 2015-04-16 17:24 -0700
              Re: rhel 7 and kforth krishna.myneni@ccreweb.org - 2015-04-16 17:39 -0700
              Re: rhel 7 and kforth Paul Rubin <no.email@nospam.invalid> - 2015-04-16 17:47 -0700
                Re: rhel 7 and kforth krishna.myneni@ccreweb.org - 2015-04-16 18:44 -0700
                Re: rhel 7 and kforth krishna.myneni@ccreweb.org - 2015-04-16 18:50 -0700
                Re: rhel 7 and kforth Paul Rubin <no.email@nospam.invalid> - 2015-04-16 19:10 -0700
                Re: rhel 7 and kforth krishna.myneni@ccreweb.org - 2015-04-16 19:29 -0700
                Re: rhel 7 and kforth krishna.myneni@ccreweb.org - 2015-04-16 20:10 -0700
                Re: rhel 7 and kforth Paul Rubin <no.email@nospam.invalid> - 2015-04-16 20:27 -0700
                Re: rhel 7 and kforth krishna.myneni@ccreweb.org - 2015-04-17 02:04 -0700
                Re: rhel 7 and kforth anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2015-04-17 11:41 +0000
                Re: rhel 7 and kforth krishna.myneni@ccreweb.org - 2015-04-17 14:45 -0700
                Re: rhel 7 and kforth anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2015-04-18 14:01 +0000
                Re: rhel 7 and kforth Paul Rubin <no.email@nospam.invalid> - 2015-04-17 07:47 -0700
                Re: rhel 7 and kforth krishna.myneni@ccreweb.org - 2015-04-17 08:35 -0700
                Re: rhel 7 and kforth Paul Rubin <no.email@nospam.invalid> - 2015-04-17 10:33 -0700
                Re: rhel 7 and kforth krishna.myneni@ccreweb.org - 2015-04-17 11:15 -0700
                Re: rhel 7 and kforth Paul Rubin <no.email@nospam.invalid> - 2015-04-17 11:47 -0700
                Re: rhel 7 and kforth krishna.myneni@ccreweb.org - 2015-04-17 14:51 -0700
                Re: rhel 7 and kforth anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2015-04-18 14:41 +0000
                Re: rhel 7 and kforth Paul Rubin <no.email@nospam.invalid> - 2015-04-24 11:42 -0700
                Re: rhel 7 and kforth "Elizabeth D. Rather" <erather@forth.com> - 2015-04-24 09:02 -1000
                Re: rhel 7 and kforth anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2015-05-02 10:53 +0000
                Re: rhel 7 and kforth Paul Rubin <no.email@nospam.invalid> - 2015-05-03 17:22 -0700
                Re: rhel 7 and kforth anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2015-05-04 10:23 +0000
                Re: rhel 7 and kforth Bernd Paysan <bernd.paysan@gmx.de> - 2015-04-22 00:10 +0200
                Re: rhel 7 and kforth Paul Rubin <no.email@nospam.invalid> - 2015-04-21 17:45 -0700
                Re: rhel 7 and kforth anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2015-04-22 13:08 +0000
                Re: rhel 7 and kforth albert@spenarnc.xs4all.nl (Albert van der Horst) - 2015-04-17 20:27 +0000
                Re: rhel 7 and kforth krishna.myneni@ccreweb.org - 2015-04-17 14:41 -0700
                Re: rhel 7 and kforth anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2015-04-18 14:11 +0000
                Re: rhel 7 and kforth Paul Rubin <no.email@nospam.invalid> - 2015-04-17 15:47 -0700
                Re: rhel 7 and kforth anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2015-04-18 14:34 +0000
                Re: rhel 7 and kforth krishna.myneni@ccreweb.org - 2015-04-18 14:09 -0700
                Re: rhel 7 and kforth Paul Rubin <no.email@nospam.invalid> - 2015-04-19 20:31 -0700
                Re: rhel 7 and kforth anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2015-04-20 11:35 +0000
                Re: rhel 7 and kforth Paul Rubin <no.email@nospam.invalid> - 2015-04-21 18:07 -0700
                Re: rhel 7 and kforth anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2015-04-22 11:21 +0000
                Re: rhel 7 and kforth Paul Rubin <no.email@nospam.invalid> - 2015-04-24 19:34 -0700
                Re: rhel 7 and kforth anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2015-04-25 08:36 +0000
                Re: rhel 7 and kforth albert@spenarnc.xs4all.nl (Albert van der Horst) - 2015-04-25 11:36 +0000
                Re: rhel 7 and kforth anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2015-04-25 16:29 +0000
                Re: rhel 7 and kforth albert@spenarnc.xs4all.nl (Albert van der Horst) - 2015-04-19 10:08 +0000
                Re: rhel 7 and kforth krishna.myneni@ccreweb.org - 2015-04-19 20:11 -0700
                Re: rhel 7 and kforth anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2015-04-20 12:05 +0000
                Re: rhel 7 and kforth Bernd Paysan <bernd.paysan@gmx.de> - 2015-04-22 01:27 +0200
                Re: rhel 7 and kforth Paul Rubin <no.email@nospam.invalid> - 2015-04-21 18:18 -0700
                Re: rhel 7 and kforth anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2015-04-22 11:00 +0000
                Re: rhel 7 and kforth Paul Rubin <no.email@nospam.invalid> - 2015-04-24 11:28 -0700
                Re: rhel 7 and kforth Bernd Paysan <bernd.paysan@gmx.de> - 2015-04-25 01:34 +0200
                Re: rhel 7 and kforth Paul Rubin <no.email@nospam.invalid> - 2015-04-24 21:07 -0700
                Re: rhel 7 and kforth anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2015-04-25 16:41 +0000
                Re: rhel 7 and kforth krishna.myneni@ccreweb.org - 2015-04-25 10:06 -0700
                Re: rhel 7 and kforth anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2015-04-26 14:56 +0000
                Re: rhel 7 and kforth krishna.myneni@ccreweb.org - 2015-04-26 20:22 -0700
                Re: rhel 7 and kforth anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2015-04-27 09:02 +0000
                Re: rhel 7 and kforth mhx@iae.nl - 2015-04-27 03:59 -0700
                Re: rhel 7 and kforth albert@spenarnc.xs4all.nl (Albert van der Horst) - 2015-04-27 15:45 +0000
                Re: rhel 7 and kforth "Rod Pemberton" <bork@lllljunkqwer.cpm> - 2015-04-27 18:09 -0400
                Re: rhel 7 and kforth Bernd Paysan <bernd.paysan@gmx.de> - 2015-04-28 03:55 +0200
                Re: rhel 7 and kforth krishna.myneni@ccreweb.org - 2015-04-27 19:30 -0700
                Re: rhel 7 and kforth krishna.myneni@ccreweb.org - 2015-04-27 19:44 -0700
                Re: rhel 7 and kforth "Rod Pemberton" <bork@lllljunkqwer.cpm> - 2015-04-28 02:03 -0400
                Re: rhel 7 and kforth krishna.myneni@ccreweb.org - 2015-04-28 01:44 -0700
                Re: rhel 7 and kforth Mark Wills <markwills1970@gmail.com> - 2015-04-28 02:44 -0700
                Re: rhel 7 and kforth Paul Rubin <no.email@nospam.invalid> - 2015-04-28 16:47 -0700
                Re: rhel 7 and kforth krishna.myneni@ccreweb.org - 2015-04-28 17:00 -0700
                Re: rhel 7 and kforth Paul Rubin <no.email@nospam.invalid> - 2015-04-28 17:14 -0700
                Re: rhel 7 and kforth krishna.myneni@ccreweb.org - 2015-04-28 17:59 -0700
                Re: rhel 7 and kforth Paul Rubin <no.email@nospam.invalid> - 2015-04-28 21:41 -0700
                Re: rhel 7 and kforth Bernd Paysan <bernd.paysan@gmx.de> - 2015-04-29 03:07 +0200
                Re: rhel 7 and kforth krishna.myneni@ccreweb.org - 2015-04-28 18:13 -0700
                Re: rhel 7 and kforth albert@spenarnc.xs4all.nl (Albert van der Horst) - 2015-04-29 00:07 +0000
                Re: rhel 7 and kforth Bernd Paysan <bernd.paysan@gmx.de> - 2015-04-28 22:22 +0200
                Re: rhel 7 and kforth krishna.myneni@ccreweb.org - 2015-04-28 14:23 -0700
                Re: rhel 7 and kforth Bernd Paysan <bernd.paysan@gmx.de> - 2015-04-28 23:51 +0200
                Re: rhel 7 and kforth krishna.myneni@ccreweb.org - 2015-04-28 16:50 -0700
                Re: rhel 7 and kforth David Thompson <dave.thompson2@verizon.net> - 2015-05-10 12:24 -0400
                Re: rhel 7 and kforth mhx@iae.nl - 2015-04-26 22:16 -0700
                Re: rhel 7 and kforth anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2015-04-27 09:19 +0000
                Re: rhel 7 and kforth mhx@iae.nl - 2015-04-27 04:03 -0700
                Re: rhel 7 and kforth "Rod Pemberton" <bork@lllljunkqwer.cpm> - 2015-04-27 18:21 -0400
                Re: rhel 7 and kforth anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2015-05-01 14:46 +0000
                Re: rhel 7 and kforth Bernd Paysan <bernd.paysan@gmx.de> - 2015-04-23 16:46 +0200
                Re: rhel 7 and kforth albert@spenarnc.xs4all.nl (Albert van der Horst) - 2015-04-17 10:35 +0000
                Re: rhel 7 and kforth krishna.myneni@ccreweb.org - 2015-04-17 08:43 -0700
  Re: rhel 7 and kforth krishna.myneni@ccreweb.org - 2015-04-17 08:41 -0700

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