[Bug tree-optimization/101769] loop->finite_p is not always true for some loops even with -ffinite-loops being used

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101769

--- Comment #2 from Richard Biener <rguenth at gcc dot gnu.org> ---
free_all2_r loses it during CDDCE1 which elides the original while loop.  Then
tail-recursion discovers a new loop from the following IL

void free_all2_r (struct Node * n_)
{
  struct Node * t;
  struct Node * _1;

  <bb 2> :
  _1 = n__6(D)->right;
  if (_1 != 0B)
    goto <bb 3>; [INV]
  else
    goto <bb 4>; [INV]

  <bb 3> :
  free_all2_r (_1);

  <bb 4> :
  return;

which leaves loop fixup to discover the created loop which is then
not marked as finite (I don't think we can technically say it is?):

fix_loop_structure: fixing up loops for function
flow_loops_find: discovered new loop 2 with header 2

that then gets inlined into free_all2.  free_all suffers from exactly the
same issue.  The info doesn't get lost - it's simply that tail recursion
added loops are not marked finite.

I guess since it's recursion we know it will eventually terminate (blow
the stack).  But the tail-recursion pass doesn't bother to create the
loop structure where it could set ->finite_p.

  if (changed)
    {
      /* We may have created new loops.  Make them magically appear.  */
      loops_state_set (LOOPS_NEED_FIXUP);
      free_dominance_info (CDI_DOMINATORS);
    }

I have a patch that tries to fix that.  With this all functions end up empty.