[Bug tree-optimization/69720] 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=69720

            Bug ID: 69720
           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 5.3.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 20160207 (experimental) [trunk revision 233200] (GCC) 
$ 
$ gcc-trunk -O2 small.c; ./a.out
$ gcc-5.3 -O3 small.c; ./a.out
$ 
$ gcc-trunk -O3 small.c
$ ./a.out
Aborted (core dumped)
$ 


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


int a, b, c, e, f; 
long long d[32] = { 4, 0, 4, 4, 0, 4, 4, 0, 4, 4, 0, 4, 4 };

int
main ()
{
  for (; a < 6; a++)
    {
      b ^= e;
      for (c = 0; c < 2; c++)
        d[a * 6] |= 9;
    }

  if (d[12] != 13) 
    __builtin_abort (); 

  return 0;
}