[Bug tree-optimization/116823] phiprop should ignore clobbers

[pinskia at gcc dot gnu.org via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=116823

--- Comment #3 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Here is a testcase for a well defined case:
```
void f(int *);

int g(int i, struct f *ff)
{
  const int t = 10;
  const int *a;
  {
    int b;
    f(&b);
    if (t < i)
      a = &t;
    else
      a = &i;
  }
  return *a;
}
```

Without the clobber, phiprop handles this.