[Bug middle-end/54571] Missed optimization converting between bit sets

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

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=54571

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|                            |2012-09-14
            Version|unknown                     |4.8.0
     Ever Confirmed|0                           |1

--- Comment #1 from Richard Guenther <rguenth at gcc dot gnu.org> 2012-09-14 08:39:42 UTC ---
Confirmed.  The natural place to optimize this is the tree level phiopt pass.

  <bb 2>:
  _3 = x_2(D) & 2;
  if (_3 != 0)
    goto <bb 3>;
  else
    goto <bb 4>;

  <bb 3>:
  y_5 = y_4(D) | 1;

  <bb 4>:
  # y_1 = PHI <y_4(D)(2), y_5(3)>

where we should handle

int f1(int x, int y, int d) { int tem; if ((tem = x & d)) y |= tem; return y; }

as well.  Yes, that's just y |= x & d, but it falls out naturally if the
transform is implemented in a generic enough way.