[Bug tree-optimization/33498] [4.2/4.3 Regression] Optimizer (-O2) may convert a normal loop to infinite

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

------- Comment #1 from rguenth at gcc dot gnu dot org  2007-09-19 15:53 -------
Confirmed.  IVOPTs chooses to replace the exit test by one that is true
only after signed overflow.  SCEV/VRP happily optimizes this away.

<bb 2>:
  ivtmp.52_2 = (long unsigned int) value_8;

  # ivtmp.52_16 = PHI <ivtmp.52_12(4), ivtmp.52_2(2)>;
  # val_18 = PHI <val_10(4), 50462976(2)>;
<L0>:;
  MEM[index: ivtmp.52_16]{*D.1961} = val_18;
  val_10 = val_18 + 67372036;
  ivtmp.52_12 = ivtmp.52_16 + 4;
  if (val_10 != 67305984) goto <L5>; else goto <L2>;

<L5>:;
  goto <bb 3> (<L0>);

<L2>:;
  return;

The same happens with trunk.  Zdenek?


-- 

rguenth at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |rguenth at gcc dot gnu dot
                   |                            |org, rakdver at gcc dot gnu
                   |                            |dot org
             Status|UNCONFIRMED                 |NEW
          Component|c                           |tree-optimization
     Ever Confirmed|0                           |1
           Keywords|                            |wrong-code
   Last reconfirmed|0000-00-00 00:00:00         |2007-09-19 15:53:13
               date|                            |
            Summary|Optimizer (-O2) may convert |[4.2/4.3 Regression]
                   |a normal loop to infinite   |Optimizer (-O2) may convert
                   |                            |a normal loop to infinite
   Target Milestone|---                         |4.2.2


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=33498