TR : Possible GCC bug on m68k

[etienne.fortin at sensio.tv]

Hi Chris,
I may be mystaken, but your example is not valid since char and short
varargs are promoted to int. This is from the opengroup web site on
varargs.h:

"
C language converts type char and short arguments to int and converts type
float arguments to double before passing them to a function.
"

So the promotion to int, in your example, is not from the ~ operator but
from the fact that varargs are promoted to int.

Etienne Fortin
Sensio


> Thomas Doerfler wrote:
>>
>> I tried Joels test with a gcc-2.8.1. It also generated code with
>> a "long" (32 bit) compare. My idea about that: Wouldn't the "~"
>> operator generate an "int" result, forcing the comparision to be
>> done with "int" (=32 bit) size? This does not make sense in that
>> situation, but this is an issue for the programmer (Etienne) not
>> the compiler. Am I totally wrogn with this?
>>
>
> I think you are correct. Here is another example that shows this:
>
> /* m68k-rtems-gcc -g -c -o comp.o comp.c */
> #include <stdio.h>
> int main ()
> {
>          unsigned char v = 0;
>          printf ("v = %i (0x%08x)\n", ~v, ~v);
>          return 0;
> }
>
> The code is:
>
> #include <stdio.h>
> int main ()
> {
>          unsigned char v = 0;
>     0:   4e56 fffc       linkw %fp,#-4
> comp.c:6
>          printf ("v = %i (0x%08x)\n", ~v, ~v);
>     4:   422e ffff       clrb %fp@(-1)      <--- correct size
> comp.c:7
>          return 0;
>     8:   4280            clrl %d0           <--- changed type
>     a:   102e ffff       moveb %fp@(-1),%d0 <--- geting the value
>     e:   4680            notl %d0
>    10:   2f00            movel %d0,%sp at -
>    12:   4280            clrl %d0
>    14:   102e ffff       moveb %fp@(-1),%d0
>    18:   4680            notl %d0
>    1a:   2f00            movel %d0,%sp at -
>    1c:   4879 0000 0000  pea 0 <main>
>    22:   61ff 0000 0000  bsrl 24 <main+0x24>
>    28:   4fef 000c       lea %sp@(12),%sp
> comp.c:8
> }
>    2c:   4280            clrl %d0
> comp.c:9
>    2e:   4e5e            unlk %fp
>    30:   4e75            rts
>
> I compiled the code on Linux and the result is:
>
> $ ./comp
> v = -1 (0xffffffff)
>
> --
>   Chris Johns
>