[Bug c++/44260] New: Strange behavior on bit fields sructures.

["dennis at conus dot info" <gcc-bugzilla at gcc dot gnu dot org>]

If compiled without -O3 option, this code snippet works fine (running
executable will print "i=11223344, bswap=44332211")
If compiled with -O3 option, executable will print "i=11223344,
bswap=00000000".
Checked on 4.4.1 x86 and 4.4.3 x64.

#include <stdio.h>

struct int32_bytes
{
        int byte1:8;
        int byte2:8;
        int byte3:8;
        int byte4:8;
};

unsigned int bswap (unsigned int in)
{
        struct int32_bytes *tmp_in;
        struct int32_bytes *tmp_out;
        unsigned int rt;

        tmp_in=(struct int32_bytes *)&in;
        tmp_out=(struct int32_bytes *)&rt;

        tmp_out->byte1 = tmp_in->byte4;
        tmp_out->byte2 = tmp_in->byte3;
        tmp_out->byte3 = tmp_in->byte2;
        tmp_out->byte4 = tmp_in->byte1;

        return rt;
};

int main()
{
        for (int i=0x11223344; i<=0x112233FF; i++)
        {
                if (i==0x11223344)
                        printf ("i=%08X, bswap=%08X\n", i, bswap (i));
        };
};


-- 
           Summary: Strange behavior on bit fields sructures.
           Product: gcc
           Version: 4.4.3
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: dennis at conus dot info
 GCC build triplet: 4.4.3
  GCC host triplet: 4.4.3
GCC target triplet: 4.4.3


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=44260