[Bug c/25692] New: Strange results with cast when using -O2 flag or not under Linux ppc64

["fm at 4js dot com" <gcc-bugzilla at gcc dot gnu dot org>]

Hello,

Here is a small sample to repeat the case:

------------
#include <stdio.h>

main()
{
   double d1, *pd1;
   char *c = (char*)&d1;

   pd1 = &d1;
   ((int*)pd1)[0] = -1;
   ((int*)pd1)[1] = -1;

   fprintf(stderr,">> d1 = %lf\n", d1);

   fprintf(stderr,">> int: %d %d\n", ((int*)pd1)[0], ((int*)pd1)[1]);

   fprintf(stderr,">> c1 = %02x\n", c[0]);
   fprintf(stderr,">> c2 = %02x\n", c[1]);
   fprintf(stderr,">> c3 = %02x\n", c[2]);
   fprintf(stderr,">> c4 = %02x\n", c[3]);
   fprintf(stderr,">> c5 = %02x\n", c[4]);
   fprintf(stderr,">> c6 = %02x\n", c[5]);
   fprintf(stderr,">> c7 = %02x\n", c[6]);
   fprintf(stderr,">> c8 = %02x\n", c[7]);
}

------------

When I compile with `gcc -m64 -o b64 b64.c`, the output is correct:

>> d1 = nan
>> int: -1 -1
>> c1 = ff
>> c2 = ff
>> c3 = ff
>> c4 = ff
>> c5 = ff
>> c6 = ff
>> c7 = ff
>> c8 = ff

But when I use the optimise flag, `gcc -O2 -m64 -o b64 b64.c`, and run again
the sample, there is a problem with the results. See bellow:

>> d1 = 0.000000
>> int: -1 -1
>> c1 = ff
>> c2 = ff
>> c3 = ff
>> c4 = ff
>> c5 = ff
>> c6 = ff
>> c7 = ff
>> c8 = ff

Gcc release:

Using built-in specs.
Target: ppc64-redhat-linux
Configured with: ../gcc-4.0.0/configure --prefix=/home/comp/gcctest4.0.0
--enable-shared --enable-threads=posix --disable-checking --with-system-zlib
--enable-__cxa_atexit --disable-libunwind-exceptions --host=ppc64-redhat-linux
--build=ppc64-redhat-linux --target=ppc64-redhat-linux --with-cpu=default32
--enable-languages=c,c++
Thread model: posix
gcc version 4.0.0

Environment:

Linux 2.6.9-11.EL #1 SMP Fri May 20 18:18:48 EDT 2005 ppc64 ppc64 ppc64
GNU/Linux

Best regards.


-- 
           Summary: Strange results with cast when using -O2 flag or not
                    under Linux ppc64
           Product: gcc
           Version: 3.4.4
            Status: UNCONFIRMED
          Severity: major
          Priority: P3
         Component: c
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: fm at 4js dot com
 GCC build triplet: powerpc64-linux RedHat 4.0
  GCC host triplet: powerpc64-ibm
GCC target triplet: powerpc64-linux


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=25692