[Bug tree-optimization/68189] New: wrong code at -Os and above on x86_64-linux-gnu

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

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=68189

            Bug ID: 68189
           Summary: wrong code at -Os and above 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 mis-compiles the following code on x86_64-linux-gnu at
-Os and above in the 64-bit mode (and at -Os in the 32-bit mode). 

It also affects 4.9.x and later releases, making it a regression from 4.8.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 -O1 small.c; ./a.out
$ gcc-4.8.4 -Os small.c; ./a.out
$  
$ gcc-trunk -Os small.c  
$ ./a.out
Aborted (core dumped)
$ 


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


int printf (const char *, ...); 

int a, e, f, j;
char c, d = 1;

int
main ()
{
  char g;
  c = 1;
  for (; c >= 0; c--)
    {
      e = d;
      for (;;)
        {
          if (!a)
            break;
          if (j)
            printf ("%d", 0);
        }
      if (c < 2)
        g = c;
      f = g;
      d = 0;
    }

  if (e != 0) 
    __builtin_abort (); 

  return 0;
}