[Bug tree-optimization/55802] Various missed optimizations for a simple function in GCC itself

["rguenth at gcc dot gnu.org" <gcc-bugzilla at gcc dot gnu dot org>]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=55802

--- Comment #2 from Richard Biener <rguenth at gcc dot gnu.org> 2013-01-02 11:00:54 UTC ---
The sink issue is that we cannot sink PHI nodes:

  <bb 4>:
...
  if (_11 < _20)
    goto <bb 5>;
  else
    goto <bb 6>;

  <bb 5>:
  _26 = _19->block_info;
  _27 = (long unsigned int) _11;
  _28 = _27 * 8;
  _29 = _26 + _28;

  <bb 6>:
  # _30 = PHI <0B(4), _29(5)>
...
  if (_14 != 0)
    goto <bb 8>;
  else
    goto <bb 7>;

  <bb 7>:
  op2_12 = &_30->out;
...

to be able to sink the definition of _30 into basic-block 7 we'd have to
sink the whole control structure.  Similar to how we only (very) weakly
handle hoisting loop invaraint conditional code we cannot at all sink
conditional code.

-> more specific bug