[Bug rtl-optimization/77855] New: wrong code at -O3 on x86_64-linux-gnu (in both 32-bit and 64-bit modes)

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

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=77855

            Bug ID: 77855
           Summary: wrong code at -O3 on x86_64-linux-gnu (in both 32-bit
                    and 64-bit modes)
           Product: gcc
           Version: 7.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: rtl-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: su at cs dot ucdavis.edu
  Target Milestone: ---

It is a regression from 6.2.x.


$ 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/7.0.0/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 7.0.0 20161004 (experimental) [trunk revision 240755] (GCC) 
$ 
$ gcc-6.2 -O3 small.c; ./a.out
2
$ gcc-trunk -O2 small.c; ./a.out
2
$ 
$ gcc-trunk -O3 small.c; ./a.out
0
$ 


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


int a, b = 1, c, e, f, g, k, m, n, o;
char d, h, i, j, l; 

void fn1 ()
{
  if (e)
    j = 1;
  if (f)
  L1:
    k = j | (a & l);
  for (;;)
    {
      __builtin_printf ("%d\n", d);
      if (d)
        break;
      for (; o; o--)
        for (; n;)
          for (; m; m++)
            ;
      goto L1;
    }
}

void fn2 ()
{
  d = 2;
}

void fn3 ()
{
  for (;;)
    {
      for (; b; b--)
        {
          fn2 (8);  
          fn1 ();
        }
      g = h;
      c = i;
      break;
    }
}

int main ()
{
  fn3 ();
  return 0; 
}