[Bug tree-optimization/61681] New: wrong code at -Os and above on x86_64-linux-gnu

[su at cs dot ucdavis.edu]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=61681

            Bug ID: 61681
           Summary: wrong code at -Os and above 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 and 4.9 miscompiles the following code on x86_64-linux at
-Os and above in both 32-bit and 64-bit modes.

This is 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-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 20140702 (experimental) [trunk revision 212218] (GCC) 
$ 
$ gcc-trunk -O1 small.c; a.out
0
$ gcc-4.8 -Os small.c; a.out
0
$ 
$ gcc-trunk -Os small.c; a.out
1
$ gcc-4.9 -Os small.c; a.out
1
$ 


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


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

int a = 1, *e = &a, **f = &e, *l, *p, j;
static int b;
long d;
short g;

void
fn1 (int *p)
{
  int m;
  if (!(*p & j))
    {
      int *n = &m;
      for (d = 6; d; d--)
    {
      for (g = 0; g < 1; g++)
        {
          n = l = *f;
          b = *p;
        }
      *n = 0;
    }
    }
}

int
main ()
{
  p = *f;
  fn1 (p);
  printf ("%d\n", b);
  return 0;
}