[Bug c/80622] New: wrong code at -O1 and above in both 32-bit and 64-bit modes on x86_64-linux-gnu

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

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=80622

            Bug ID: 80622
           Summary: wrong code at -O1 and above in both 32-bit and 64-bit
                    modes on x86_64-linux-gnu
           Product: gcc
           Version: 7.0.1
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c
          Assignee: unassigned at gcc dot gnu.org
          Reporter: chengniansun at gmail dot com
  Target Milestone: ---

$ 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/8.0.0/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 8.0.0 20170503 (experimental) [trunk revision 247550] (GCC) 
$ gcc-trunk small.c -O3 ; ./a.out
0
$ gcc-trunk small.c -O3 -m32 ; ./a.out
0
$ gcc-trunk small.c -O1 -m32 ; ./a.out
0
$ gcc-trunk small.c -O0 -m32 ; ./a.out
4
$ 
$ cat small.c
int printf(const char *, ...);
struct S2 {
  int f2;
  char f4;
  int f5;
  char f6;
} a;
int main() {
  struct S2 b[][1] = {3, 0, 3, 4, 3, 0, 3, 4, 3, 0, 3, 4, 3, 0, 3, 4, 3,
                      0, 3, 4, 3, 0, 3, 4, 3, 0, 3, 4, 3, 0, 3, 4, 3, 0,
                      3, 4, 3, 4, 7, 7, 3, 5, 0, 3, 4, 7, 7, 3, 5, 0, 3,
                      4, 3, 4, 7, 7, 3, 5, 0, 3, 4, 7, 7, 3, 5, 0, 3, 4};
  a = b[4][0];
  b[4][0].f4 &printf("%d\n", a.f6);
  return 0;
}
$    
$ gcc-5.4 small.c -O3 -m32 ; ./a.out
4
$