[Bug web/70127] New: wrong code on x86_64-linux-gnu at -O3 in 32-bit and 64-bit modes

["chengniansun at gmail dot com" <gcc-bugzilla at gcc dot gnu dot org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=70127

            Bug ID: 70127
           Summary: wrong code on x86_64-linux-gnu at -O3 in 32-bit and
                    64-bit modes
           Product: gcc
           Version: 6.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: web
          Assignee: unassigned at gcc dot gnu.org
          Reporter: chengniansun at gmail dot com
  Target Milestone: ---

The following code is miscompiled by the trunk, gcc-4.7 and gcc-4.8 at -O3 in
both 32-bit and 64-bit modes on x86_64-linux-gnu. 


$: gcc-trunk -v
Using built-in specs.
COLLECT_GCC=gcc-trunk
COLLECT_LTO_WRAPPER=/usr/local/gcc-trunk/libexec/gcc/x86_64-pc-linux-gnu/6.0.0/lto-wrapper
Target: x86_64-pc-linux-gnu
Configured with: ../gcc-source-trunk/configure --enable-languages=c,c++,lto
--prefix=/usr/local/gcc-trunk --disable-bootstrap
Thread model: posix
gcc version 6.0.0 20160307 (experimental) [trunk revision 234022] (GCC) 
$: 
$: gcc-trunk -O3 small.c ; ./a.out
0
$: gcc-4.7 -O3 small.c ; ./a.out
0
$: gcc-4.8 -O3 small.c ; ./a.out
0
$: gcc-trunk -O0 small.c ; ./a.out
1
$: cat small.c
int printf(const char *, ...);
struct S0 {
    int f0;
    signed f1 : 2;
} a[1], c = {5, 1}, d;
short b;
int main() {
    for (; b <= 0; b++) {
        struct S0 e = {1, 1};
        d = e = a[0] = c;
    }
    printf("%d\n", a[0].f1);
    return 0;
}
$: