[Bug tree-optimization/68249] 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=68249

            Bug ID: 68249
           Summary: wrong code at -O2 and -O3 on x86_64-linux-gnu
           Product: gcc
           Version: 6.0
            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: ---

The current gcc trunk miscompiles the following code on x86_64-linux-gnu at -O2
and -O3 in both 32-bit and 64-bit modes. 

It also affects 4.9.x and later, and is a regression from 4.8.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/6.0.0/lto-wrapper
Target: x86_64-pc-linux-gnu
Configured with: ../gcc-trunk/configure --prefix=/usr/local/gcc-trunk
--enable-languages=c,c++ --disable-werror --enable-multilib
Thread model: posix
gcc version 6.0.0 20151107 (experimental) [trunk revision 229937] (GCC) 
$ 
$ gcc-trunk -Os small.c; ./a.out
$ gcc-4.8 -O2 small.c; ./a.out
$ 
$ gcc-trunk -O2 small.c
$ ./a.out
Aborted (core dumped)
$ 
$ gcc-4.9 -O2 small.c  
$ ./a.out
Aborted (core dumped)
$ 


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


int a, b, c, g, k, l, m, n;
char h;

void
fn1 ()
{
  for (; k; k++)
    {
      m = b || c < 0 || c > 1 ? : c;
      g = l = n || m < 0 || (m > 1) > 1 >> m ? : 1 << m;
    }
  l = b + 1;
  for (; b < 1; b++)
    h = a + 1;
}

int
main ()
{
  char j; 
  for (; a < 1; a++)
    {
      fn1 ();
      if (h)
        j = h;
      if (j > c)
        g = 0;
    }

  if (h != 1) 
    __builtin_abort (); 

  return 0;
}