[Bug tree-optimization/123113] factor_out_conditional_operation could be improved to handle `EDGE_COUNT (merge->preds) != 2`

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

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=123113

--- Comment #2 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
```
void f(int a, int b, int c, int d, int *e)
{
  if (a)
  {
    if (b){
      c = c > d ? c : d;
      *e = c;
    }
    else {
      c = c > d ? c : d;
      *e = c;
    }
  }
}
```

cs_elim/cs_elim_limited does not handle the above case either.
It has:
```
          /* Only handle sinking of store from 2 bbs only,
             The middle bbs don't need to come from the
             if always since we are sinking rather than
             hoisting. */
          if (EDGE_COUNT (bb3->preds) != 2)
            return;
...
      /* bb1 is the middle block, bb2 the join block, bb the split block,
         e1 the fallthrough edge from bb1 to bb2.  We can't do the
         optimization if the join block has more than two predecessors.  */
      if (EDGE_COUNT (bb2->preds) > 2)
        return;
```

But basically we need to do the split here too.

This is definitely stage 1 material.