+++ This bug was initially created as a clone of Bug #46755 +++

PR46755#c8 is unrelated bug to the original one, so creating a separate PR for it:

Not sure if this is still useful, but here's a fairly small failure-inducing
testcase for this bug for today's GCC.

[regehr@gamow tmp437]$ current-gcc -O2 -c small.c

small.c: In function 'func':
small.c:32:1: internal compiler error: in calc_dfs_tree, at dominance.c:395
Please submit a full bug report,
with preprocessed source if appropriate.
See <http://gcc.gnu.org/bugs.html> for instructions.

[regehr@gamow tmp437]$ current-gcc -v

Using built-in specs.
COLLECT_GCC=current-gcc
COLLECT_LTO_WRAPPER=/uusoc/exports/scratch/regehr/z/compiler-install/gcc-r168402-install/bin/../libexec/gcc/x86_64-unknown-linux-gnu/4.6.0/lto-wrapper
Target: x86_64-unknown-linux-gnu
Configured with: ../configure --with-libelf=/usr/local --enable-lto
--prefix=/home/regehr/z/compiler-install/gcc-r168402-install
--program-prefix=r168402- --enable-languages=c,c++
Thread model: posix
gcc version 4.6.0 20110102 (experimental) (GCC) 

[regehr@gamow tmp437]$ cat small.c


static int
foo (int si1, short si2)
{
  return ((si1 ^ si2) & ((si1 ^ (si1 ^ si2) & ~2147483647) - si2 ^ si2)) <
    0 ? si1 : si1 - si2;
}

struct S0
{
  const unsigned f3:1;
  const unsigned f8:1;
};
struct S0 g_111 = {
  1
};

struct S0 g_139 = {
  1
};

unsigned long int g_22;

void safe (int);
int func_42 (void);

void func (void)
{
  safe (foo (func_42 () != (g_139.f3 | g_111.f8), -1L));
  for (g_22 = 0; g_22; g_22 = 1)
    {
    }
}

This is caused by revision 164431:

http://gcc.gnu.org/ml/gcc-cvs/2010-09/msg00727.html