[Bug tree-optimization/37242] missed FRE opportunity because of signedness of addition

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

------- Comment #3 from pinskia at gcc dot gnu dot org  2008-08-26 21:16 -------
>This could be due to array indexing lowered to POINTER_PLUS_EXPR.

Array indexing is never lowered using POINTER_PLUS_EXPR, only for pointers it
is.  Though it looks like
we are doing the math in unsigned in one case but signed in another but we
don't consider them the same for PRE.

Simple testcase:
int f(int a)
{
  unsigned b = a;
  b++;
  a++;
  return a + b;
}
We should just get return a*2 + 2; (which we do at the RTL level) but we get:
  b = (unsigned int) a;
  return (int) ((b + 1) + (unsigned int) (a + 1));


-- 

pinskia at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
     Ever Confirmed|0                           |1
   Last reconfirmed|0000-00-00 00:00:00         |2008-08-26 21:16:06
               date|                            |
            Summary|missed FRE opportunity      |missed FRE opportunity
                   |                            |because of signedness of
                   |                            |addition


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=37242