[Bug tree-optimization/77605] 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=77605

            Bug ID: 77605
           Summary: wrong code at -O3 on x86_64-linux-gnu
           Product: gcc
           Version: 7.0
            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: ---

This seems to affect at least all versions 4.6.x and later. 

$ 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/7.0.0/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 7.0.0 20160915 (experimental) [trunk revision 240161] (GCC) 
$ 
$ gcc-trunk -O2 small.c; ./a.out
$ 
$ gcc-trunk -O3 small.c
$ ./a.out
Aborted (core dumped)
$ 


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


int a, b, c[2][8];

int main ()
{
  for (a = 0; a < 8; a++)
    for (b = 0; b < 2; b++)
      c[b][a] = c[b][b + 6] ^ 1;

  if (c[0][7] != 0) 
    __builtin_abort ();

  return 0; 
}