[Bug tree-optimization/67916] 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=67916

            Bug ID: 67916
           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.


$ 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 20151009 (experimental) [trunk revision 228653] (GCC) 
$ 
$ gcc-trunk -O2 small.c; ./a.out
$ gcc-5.2 -O3 small.c; ./a.out
$ 
$ gcc-trunk -O3 small.c
$ ./a.out
Aborted (core dumped)
$ 


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


int a[6], b = 1, d, e;
long long c;
static int f = 1;

void
fn1 (int p1)
{
  b = (b >> 1) & (1 ^ a[(1 ^ p1) & 5]);
}

void
fn2 ()
{
  b = (b >> 1) & (1 ^ a[(b ^ 1) & 1]);
  fn1 (c >> 1 & 5);
  fn1 (c >> 2 & 5);
  fn1 (c >> 4 & 5);
  fn1 (c >> 8 & 5);
}

int
main ()
{
  int i, j;
  for (; d;)
    {
      for (; e;)
        fn2 ();
      f = 0;
    }
  for (i = 0; i < 8; i++)
    {
      if (f)
        i = 9;
      for (j = 0; j < 7; j++)
        fn2 ();
    }

  if (b != 0)
    __builtin_abort ();

  return 0;
}