[Bug tree-optimization/61576] 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=61576

            Bug ID: 61576
           Summary: wrong code at -O3 on x86_64-linux-gnu
           Product: gcc
           Version: 4.10.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: su at cs dot ucdavis.edu

The current gcc trunk miscompiles the following testcase on x86_64-linux at -O3
in both 32-bit and 64-bit modes.  

This is a regression from 4.9.x.  

$ 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/4.10.0/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 4.10.0 20140620 (experimental) [trunk revision 211848] (GCC) 
$ 
$ gcc-trunk -O2 small.c; a.out
0
$ gcc-4.9.0 -O3 small.c; a.out
0
$ 
$ gcc-trunk -O3 small.c; a.out
1
$ 

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

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

volatile int a, b;
int c, d, e, f;

static int
fn1 ()
{
  if (b)
    {
      d++;
      e = c || f;
    }
  return 0;
}

int
main ()
{
  for (; a < 1; a++)
    {
      fn1 ();
      continue;
    }
  printf ("%d\n", d);
  return 0;
}