[Bug tree-optimization/31521] / conversion to >> is not done when the divisor can be zero

[pinskia at gcc dot gnu dot org]

------- Comment #1 from pinskia at gcc dot gnu dot org  2007-04-10 08:39 -------
  i_5 = ASSERT_EXPR <i_1, i_1 < x_10>;
  D.1607_6 = i_5 / 4;

i_5: [0, 2147483646]  EQUIVALENCES: { i_1 } (1 elements)


We don't do the shifting if i's range includes 0 which is wrong as 0>>n is
always 0 so the reduced testcase is:

int f(int x)
{
  if (x<0) return 0;
  return x/4;
}

We should be able to convert the / into a >> without any issue.  Mine I have a
simple patch.


-- 

pinskia at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |pinskia at gcc dot gnu dot
                   |                            |org
         AssignedTo|unassigned at gcc dot gnu   |pinskia at gcc dot gnu dot
                   |dot org                     |org
           Severity|normal                      |enhancement
             Status|UNCONFIRMED                 |ASSIGNED
          Component|pending                     |tree-optimization
     Ever Confirmed|0                           |1
  GCC build triplet|x86_64-unknown-linux-gnu    |
   GCC host triplet|x86_64-unknown-linux-gnu    |
 GCC target triplet|x86_64-unknown-linux-gnu    |
           Keywords|                            |missed-optimization
   Last reconfirmed|0000-00-00 00:00:00         |2007-04-10 08:39:22
               date|                            |
            Summary|strength-reduce idiv given  |/ conversion to >> is not
                   |assertion numerator is      |done when the divisor can be
                   |positive                    |zero


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=31521