[Bug tree-optimization/69615] 0 to limit signed range checks don't always use unsigned compare

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=69615

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|                            |2016-02-02
                 CC|                            |rguenth at gcc dot gnu.org
          Component|rtl-optimization            |tree-optimization
     Ever confirmed|0                           |1

--- Comment #1 from Richard Biener <rguenth at gcc dot gnu.org> ---
GCC relies on some fold() routine to do this and we end up with

;; Function r0_to_imax_2 (null)
;; enabled by -tree-original


{
  if ((unsigned int) x <= 2147483645)
    {
      ext ();
    }
}


;; Function r0_to_imax_1 (null)
;; enabled by -tree-original


{
  if (x >= 0 && x != 2147483647)
    {
      ext ();
    }
}

;; Function r0_to_imax (null)
;; enabled by -tree-original


{
  if (x >= 0)
    {
      ext ();
    }


so it seems we are confused by the trick that triggers first, replacing
the <= INT_MAX-1 compare with a != INT_MAX compare and that not being handled
in the range construction code.

Looks like ifcombine doesn't handle it either (maybe_fold_and_comparisons).

void ext(void);
void r0_to_imax_1(int x){ if (x>=0 && x<=(__INT_MAX__-1)) ext(); }