[Bug tree-optimization/87177] New: wrong code at -O2 and -O3 on x86-64-linux-gnu

[su at cs dot ucdavis.edu]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=87177

            Bug ID: 87177
           Summary: wrong code at -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: ---

It is 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/9.0.0/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 9.0.0 20180831 (experimental) [trunk revision 264021] (GCC) 
$ 
$ gcctk -Os small.c; ./a.out
$ gcc-8.1.0 -O2 small.c; ./a.out
$ 
$ gcctk -O2 small.c
$ timeout -s 9 5 ./a.out
Killed
$ 


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


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

int a, b, c, e, f, g, h, i, j, k, l;
unsigned d;

static void p ()
{
  while (1)
    {
      int n = h;
      h = 8;
      if (!e)
        break;
      h = n;
      while (1)
        ;
    }
  for (; c != 4; c++)
    {
      int o = g = 1;
      for (; g; g--)
        {
          while (d < b)
            e--;
          a = g;
          int q = o;
          if (q)
          L1:
            j = f;
          if (l)
            {
              printf ("%d", g);
              goto L1;
            }
          o = l;
          k = q;
        }
    }
}

void s ()
{
  int m = 0;
L2:
  if (i && g)
    goto L2;
  for (; m < 2; m++)
    p ();
}

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