[Bug rtl-optimization/68250] New: wrong code at -O2 and -O3 on x86_64-linux-gnu (in 64-bit mode)

[su at cs dot ucdavis.edu]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=68250

            Bug ID: 68250
           Summary: wrong code at -O2 and -O3 on x86_64-linux-gnu (in
                    64-bit mode)
           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-gnu at -O2
and -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 20151107 (experimental) [trunk revision 229937] (GCC) 
$ 
$ gcc-trunk -m64 -Os small.c; ./a.out
1
$ gcc-trunk -m32 -O2 small.c; ./a.out
1
$ gcc-5.2 -m64 -O2 small.c; ./a.out
1
$ 
$ gcc-trunk -m64 -O2 small.c
$ ./a.out
0
$ 


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


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

char a, b, h, k, l, m, o;
short c, d, n;
int e, f, g, j, q;

void
fn1 ()
{
  int p = b || a;
  n = o > 0 || d > 1 >> o ? d : d << o;
  for (; j; j++)
    m = c < 0 || m || c << p;
  l = f + 1;
  for (; f < 1; f = 1)
    k = h + 1;
}

int
main ()
{
  char i;
  for (; e < 1; e++)
    {
      fn1 ();
      if (k)
        i = k;
      if (i > q)
        g = 0;
    }
  printf ("%d\n", k);
  return 0;
}