[Bug tree-optimization/67465] New: wrong code at -O3 on x86_64-linux-gnu

[su at cs dot ucdavis.edu]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67465

            Bug ID: 67465
           Summary: wrong code at -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 -O3
in both 32-bit and 64-bit modes. 

This is a regression from 5.2.x.

Different from PR 67464, -fno-tree-vectorize makes the bug disappear. 


$ 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 20150905 (experimental) [trunk revision 227508] (GCC) 
$ 
$ gcc-trunk -O2 small.c; ./a.out
$ gcc-trunk -O3 -fno-tree-vectorize small.c; ./a.out
$ gcc-5.2 -O3 small.c; ./a.out
$ 
$ gcc-trunk -O3 small.c
$ ./a.out
Aborted
$ 


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


int a, b, c, d, e, h;

int
fn1 (int p1)
{
  {
    int g[2];
    for (int i = 0; i < 1; i++)
      g[i] = 0;
    if (g[0] < c)
      {
        a = (unsigned) (1 ^ p1) % 2;
        return 0;
      }
  }
  return 0;
}

void
fn2 ()
{
  for (h = 0; h < 1; h++)
    {
      for (int j = 0; j < 2; j++)
        {
          for (b = 1; b; b = 0)
            a = 1;
          for (; b < 1; b++)
            ;
          if (e)
            continue;
          a = 2;
        }
      fn1 (h);
      short k = -16; 
      d = k > a;
    }
}

int
main ()
{
  fn2 ();

  if (a != 2) 
    __builtin_abort (); 

  return 0;
}