> > +static void
> > +maybe_lower_iteration_bound (struct loop *loop)
> > +{
> > + pointer_set_t *not_executed_last_iteration = pointer_set_create ();
> > + pointer_set_t *visited;
> > + struct nb_iter_bound *elt;
> > + bool found = false;
> > + VEC (basic_block, heap) *queue = NULL;
> > +
> > + for (elt = loop->bounds; elt; elt = elt->next)
> > + {
> > + if (!elt->is_exit
> > + && elt->bound.ult (loop->nb_iterations_upper_bound))
> > + {
> > + found = true;
> > + pointer_set_insert (not_executed_last_iteration, elt->stmt);
> > + }
> > + }
>
> So you are looking for all stmts a bound was derived from.
Yes, with bound smaller than the current estimate.
>
> > + if (!found)
> > + {
> > + pointer_set_destroy (not_executed_last_iteration);
>
> create this on-demand in the above loop?
Will do.
>
> > + return;
> > + }
> > + visited = pointer_set_create ();
> > + VEC_safe_push (basic_block, heap, queue, loop->header);
> > + pointer_set_insert (visited, loop->header);
>
> pointer-set for BB visited? In most other places we use a
> [s]bitmap with block numbers.
Will switch to bitmap though I think it is mostly because this tradition was
invented before pointer-set. bitmap has liner walk in it, pointer-set should
scale better.
>
> if we didn't find an exit we reduce count. double_int_one looks magic
> here, but with the assertion that each queued 'stmt_found' upper
> bound was less than loop->nb_iterations_upper_bound, subtracting one
> is certainly conservative. But why not use the maximum estimate from
> all stmts_found?
Because it is always nb_iterations_upper_bound-1, see logic in record_estimate.
I plan to change this - basically we can change record_esitmate to record all
statements, not only those dominating exit and do Dijkstra's algorithm in this
walk looking for largest upper bound we can reach loopback with.
But as I wrote in the email, I would like to do this incrementally - fix the
bug first (possibly for 4.7, too - the bug is there I am not sure if it can
lead to wrong code) and change this next. It means some further changes
thorough niter.c, but little challenge to implement Dijkstra with double-int
based queue.
>
> Thus, please add some comments, use a bitmap for visited and
> rename variables to be more descriptive.
Will do, and need to analyze the bounds fortran failures :)
Thanks,
Honza
