[Bug middle-end/69526] ivopts candidate strangeness

[amker at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=69526

--- Comment #6 from amker at gcc dot gnu.org ---
(In reply to rdapp from comment #5)
> I still don't quite get why the "n - 1" is needed. Do we need it to possibly
> have an exit condition like
> 
>  if (i != n-1) or 
>  if (i <= n-1)?
> 
> Am I missing something really obvious here?

The dump before ivopt is as below:

  <bb 2>:
  if (n_5(D) != 0)
    goto <bb 4>;
  else
    goto <bb 3>;

  <bb 3>:
  return;

  <bb 4>:

  <bb 5>:
  # i_18 = PHI <0(4), i_14(7)>
  _6 = (long unsigned int) i_18;
  _7 = _6 * 8;
  _9 = out_8(D) + _7;
  _11 = in_10(D) + _7;
  _12 = *_11;
  *_9 = _12;
  i_14 = i_18 + 1;
  i.0_4 = (unsigned int) i_14;
  if (i.0_4 < n_5(D))
    goto <bb 7>;
  else
    goto <bb 6>;

  <bb 6>:
  goto <bb 3>;

  <bb 7>:
  goto <bb 5>;


It comes from loop niter analysis, as in may_eliminate_iv, we have:

(gdb) call debug_generic_expr(desc->niter)
n_5(D) + 4294967295