[Bug tree-optimization/80974] New: wrong code (generated code hangs) at -O2 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=80974

            Bug ID: 80974
           Summary: wrong code (generated code hangs) at -O2 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: ---

It seems to be a recent regression. 

$ 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 20170604 (experimental) [trunk revision 248860] (GCC) 
$ 
$ gcc-trunk -Os small.c; ./a.out
$ gcc-6.2 -O2 small.c; ./a.out
$ 
$ gcc-trunk -O2 small.c
$ timeout -s 9 5 ./a.out
Killed
$ 


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


int a, b, c, d, e, f, g[4];

static int fn1 ()
{
  int h, i;
  if (b)
    goto L1;
L2:;
  int m = a;
  while (1)
    {
      int n = 2;
      e = !f && (n = 5);
      if (e)
        for (h = 0; h < 9; h++)
          for (i = 0; i < 6; i++)
            if (a)
              g[h] = 4;
      if (d)
        goto L2;
      a & n || b;
    L1:
      if (a)
      L3:
        c = m;
      if (a)
        goto L3;
      if (b < 5)
        return 0;
    }
}

int main ()
{
  fn1 ();
  return 0; 
}