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Groups > comp.lang.forth > #38643
| From | anton@mips.complang.tuwien.ac.at (Anton Ertl) |
|---|---|
| Newsgroups | comp.lang.forth |
| Subject | Re: rhel 7 and kforth |
| Date | 2015-04-27 09:02 +0000 |
| Organization | Institut fuer Computersprachen, Technische Universitaet Wien |
| Message-ID | <2015Apr27.110253@mips.complang.tuwien.ac.at> (permalink) |
| References | (6 earlier) <mhejre$oim$1@dont-email.me> <2015Apr25.184119@mips.complang.tuwien.ac.at> <eaafbeec-dca2-44c0-8972-418739745abf@googlegroups.com> <2015Apr26.165622@mips.complang.tuwien.ac.at> <6f87de3d-bf50-4d21-814b-e106b29cd299@googlegroups.com> |
krishna.myneni@ccreweb.org writes:
>On Sunday, April 26, 2015 at 10:09:38 AM UTC-5, Anton Ertl wrote:
>> krishna.myneni@ccreweb.org writes:
>...
>> >The compiler knows when undefined behavior happens.
>>
>> Not in general. The "optimize into an endless loop" bug does not work
>> by the compiler seeing that something is undefined and then choosing
>> to do funny things, but it goes something like:
>>
>> Array a has indexes 0-15, and is indexed with a[i], so i can only have
>> values 0-15 at that point (everything else would be undefined
>> behaviour). So obviously i<16 is always true and we can "optimize" it
>> to true.
>>
>> The compiler is oblivious to the fact that i<16 controls a loop that
>> is "optimized" into an endless loop.
>>
>> The fun thing is that the resulting "optimized" program also does many
>> more out-of-bounds accesses than if it had been compiled as expected.
>> ...
>
>I was trying to reproduce the behavior described above with gcc (v. 4.9.x), but couldn't. Do you have a C code snippet which illustrates this (so I know how to avoid this)?
When they added this to gcc-4.8, it broke one of the few programs they
don't feel free to miscompile (a SPEC benchmark), so they made this
optimization less aggressive. Bernd Paysan wrote that it still occurs
with the original code from which the benchmark was derived; maybe he
can post the code. In the meantime, here's a variant not deriving
from "out-of-bounds is undefined behaviour":
extern void foo(int a[]);
int main(int argc, char *argv[]) {
int i, a[16];
int x=0;
do {
a[i++]=x;
x+=0x10000000;
} while (x!=0);
foo(a);
return 0;
}
gcc-4.8.2 miscompiles this into:
...
main:
.LFB24:
.cfi_startproc
.p2align 4,,10
.p2align 3
.L2:
jmp .L2
...
Do you see why it does this?
As for avoiding it, I think the way to go is to avoid this compiler
and any other where the developers have this mindset. I don't see any
other good way.
- anton
--
M. Anton Ertl http://www.complang.tuwien.ac.at/anton/home.html
comp.lang.forth FAQs: http://www.complang.tuwien.ac.at/forth/faq/toc.html
New standard: http://www.forth200x.org/forth200x.html
EuroForth 2014: http://www.euroforth.org/ef14/
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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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