[Bug tree-optimization/53791] Branches not re-ordered using profile-information

[rguenth at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=53791

Richard Guenther <rguenth at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|                            |2012-06-28
     Ever Confirmed|0                           |1

--- Comment #1 from Richard Guenther <rguenth at gcc dot gnu.org> 2012-06-28 09:51:48 UTC ---
Confirmed.  tree-ssa-ifcombine.c deals with two-comparison CFG patterns, so
it could handle transforming

  # BLOCK 4 freq:9688 count:93
  # PRED: 3 [96.9%]  count:93 (false,exec)
  if (xD.1241_2(D) == 2)
    goto <bb 7>;
  else
    goto <bb 5>;
  # SUCC: 7 [3.2%]  count:3 (true,exec) 5 [96.8%]  count:90 (false,exec)

  # BLOCK 5 freq:9375 count:90
  # PRED: 4 [96.8%]  count:90 (false,exec)
  if (xD.1241_2(D) == 3)
    goto <bb 7>;
  else
    goto <bb 6>;

at least (and by iterating would then catch the 2nd opportunity).  That's
of course somewhat ad-hoc (but the easiest place to implement).

The other trivially obvious possibility is to pattern-match this open-coded
switch/case and transform it back to switch/case early.