[Bug rtl-optimization/66166] New: wrong code at -O1 and above on x86_64-linux-gnu

[su at cs dot ucdavis.edu]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=66166

            Bug ID: 66166
           Summary: wrong code at -O1 and above on x86_64-linux-gnu
           Product: gcc
           Version: 6.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: rtl-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 at -O1 and
above in both 32-bit and 64-bit modes. 

It also affects all earlier versions of GCC since at least 4.6. 


$ gcc-trunk -v
Using built-in specs.
COLLECT_GCC=gcc-trunk
COLLECT_LTO_WRAPPER=/usr/local/gcc-trunk/libexec/gcc/x86_64-unknown-linux-gnu/6.0.0/lto-wrapper
Target: x86_64-unknown-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 20150515 (experimental) [trunk revision 223211] (GCC) 
$ 
$ gcc-trunk -O0 small.c; ./a.out
$ 
$ gcc-trunk -O1 small.c
$ ./a.out
Aborted (core dumped)
$ 


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


int a, b, e, c = 1;
const int d = 0;

int
fn1 (int p)
{
  if (a)
    c = 0;
  for (; e < 2; e++)
    {
      b = p;
      if (c)
        p = 0;
    }
  return 0;
}

int
main ()
{
  (a = 1) < ((fn1 (8) > 0) >= d);

  if (b != 8)
    __builtin_abort ();

  return 0;
}