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From: "Rod Pemberton" <bork@lllljunkqwer.cpm>
Newsgroups: comp.lang.forth
Subject: Re: rhel 7 and kforth
Date: Tue, 28 Apr 2015 02:03:15 -0400
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On Mon, 27 Apr 2015 22:30:43 -0400, <krishna.myneni@ccreweb.org> wrote:
> On Monday, April 27, 2015 at 4:15:37 AM UTC-5, Anton Ertl wrote:

>> 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?
>>
> ...
>
> I'm having trouble understanding why the compiler does this. To avoid  
> issues of initialization and such, I modified the example as follows:
>
> int main()
> {
>         int i=0, a[16];
>         int x=0;
>         do {
>           a[i++] = x;
>           x += 1;
>         } while (x != 0 );
>         printf("%d\n", a[0]);
>         return 0;
> }
>
>
> gcc v 4.9.x generates the following, with -S -Wall -O3 :
> :
> main:
> .LFB0:
>         .cfi_startproc
>         .p2align 4,,10
>         .p2align 3
> .L2:
>         jmp     .L2
>         .cfi_endproc
> :
>

Anton said "gcc-4.8.2" introduced this error, but I'm seeing it for
much older GCC versions too.  GCC 3.4.1 (DOS 32-bit) does not generate
an infinite loop for any optimization level.  GCC 4.1.0 (DOS 32-bit)
and GCC 4.7.2 (Linux 64-bit) generate an infinite loop for -O2 and
-O3 levels.  So, the issue is likely with the entire GCC 4.x series
with -O2 optimization or higher.


Rod Pemberton

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