Not pulling out obvious non-aliasing global from the loop

[Andrew Pinski <pinskia at physics dot uc dot edu>]

While working on a loop pass, I noticed that we were not pulling out 
the load
from a global variable from a loop where it obviously cannot alias 
anything in
the loop.  This seems like it would hurt the vectorizer also.

This example comes from bzip2:
unsigned short *q;
#define NOSB 10
void h1(int last)
{
  int i;
  for (i=0;i<last+NOSB;i++)
    q[i] = 0;
}

Tree after lim:

h1 (last)
{
  int i;
  int T.16;
  short unsigned int * T.15;
  short unsigned int * q.14;
  short unsigned int * T.13;
  unsigned int T.12;
  unsigned int i.11;

<bb 0>:
  T.16_16 = last_3 + 10;
  if (T.16_16 > 0) goto <L4>; else goto <L5>;

<L5>:;
  goto <bb 2> (<L2>);

<L4>:;

  # i_18 = PHI <0(3), i_11(6)>;
<L0>:;
  i.11_5 = (unsigned int)i_18;
  T.12_6 = i.11_5 * 2;
  T.13_7 = (short unsigned int *)T.12_6;
  q.14_9 = q;  <--- why is this here and not above the loop
  T.15_10 = T.13_7 + q.14_9;
  *T.15_10 = 0;
  i_11 = i_18 + 1;
  if (i_11 < T.16_16) goto <L7>; else goto <L6>;

<L7>:;
  goto <bb 1> (<L0>);

<L6>:;

<L2>:;
  return;

}