[Bug tree-optimization/82363] New: wrong code at -O1, -O2 and -O3 on x86_64-linux-gnu

["su at cs dot ucdavis.edu" <gcc-bugzilla at gcc dot gnu dot org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=82363

            Bug ID: 82363
           Summary: wrong code at -O1, -O2 and -O3 on x86_64-linux-gnu
           Product: gcc
           Version: unknown
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: su at cs dot ucdavis.edu
  Target Milestone: ---

This seems to be a recent regression. 

$ gcctk -v
Using built-in specs.
COLLECT_GCC=gcctk
COLLECT_LTO_WRAPPER=/home/su/software/tmp/gcc/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=/home/su/software/tmp/gcc/gcc-trunk --disable-bootstrap
Thread model: posix
gcc version 8.0.0 20170929 (experimental) [trunk revision 253283] (GCC)
$
$ gcc-7.2.0 -O1 small.c; ./a.out
1
$ gcctk -O0 small.c; ./a.out
1
$
$ gcctk -O1 small.c; ./a.out
0
$


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


int printf (const char *, ...);

struct A
{ 
  int b;
  int c;
  int d;
};

struct E
{ 
  int f;
  int g:18;
  struct A h;
};

struct I
{ 
  int b;
  int j;
  struct E k;
};

int l, *m = &l;

struct A n;
struct I o;

int main ()
{ 
  while (1)
    { 
      struct I q = { 0, 0, {0, 0, {1, 1, 1}}}, p = q, r = p, *s = &q;
      if (p.k.h.c)
        o = p;
      *m = r.k.h.d;
      n = (*s).k.h;
      break;
    }
  printf ("%d\n", l);
  return 0;
}