[Bug tree-optimization/68185] New: wrong code at -O3 on x86_64-linux-gnu (in 64-bit mode)

["su at cs dot ucdavis.edu" <gcc-bugzilla at gcc dot gnu dot org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=68185

            Bug ID: 68185
           Summary: wrong code at -O3 on x86_64-linux-gnu (in 64-bit mode)
           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 the 64-bit mode (but not in the 32-bit mode). 

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 20151101 (experimental) [trunk revision 229639] (GCC) 
$ 
$ gcc-trunk -m64 -O2 small.c; ./a.out
$ gcc-trunk -m32 -O3 small.c; ./a.out
$ gcc-5.2 -m64 -O3 small.c; ./a.out
$ 
$ gcc-trunk -m64 -O3 small.c
$ ./a.out
Aborted (core dumped)
$ 


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


int a, b, d = 1, e, f, o, u, w = 1, z;
short c, q, t; 

int
main ()
{
  char g;
  for (; d; d--)
    {
      while (o)
        for (; e;)
          {
            c = b;
            int h = o = z;
            for (; u;)
              for (; a;)
                ;
          }
      if (t < 1)
        g = w;
      f = g;
      g && (q = 1);
    }

  if (q != 1) 
    __builtin_abort (); 

  return 0;
}