------- Additional Comments From dberlin at gcc dot gnu dot org 2005-02-27
02:09 -------
Subject: Re: [4.0/4.1 Regression] Simple loop
runs out of stack at -O1
On Sun, 2005-02-27 at 00:51 +0000, fjahanian at apple dot com wrote:
> ------- Additional Comments From fjahanian at apple dot com 2005-02-27 00:51
> -------
> (In reply to comment #6)
> > The first part of the patch seems fine.
> > We should make tree_fold_binomial non-recursive.
> You meant tree_fold_factorial? tree_fold_binomial is not recursive as is.
>
> > Note, however, that once you do that, the other part of the patch isn't
> > actually
> > doing anything (the change to chrec_apply).
> I agree. checking for 1024 is arbitrary and I did not propose it as a final
> solution.
> I think a better solution would be to compute the factorial of the array
> upper bound,
> as currently is done. If it cannot be evaluated, due to overflow,
> chrec_evaluate
> which depends on computation of tree_fold_binomial returns chrec_dont_know.
> In other words, we
> do this optimization only when factorial can be computed. This prevents
> setting an arbitrary limit and will let the implmentation limitations dicides
> feasibility
> of this optimization. What do you think on a patch along this line?
I believe Roger Sayle was considering simply rewriting this code to not
use fold at all, for starters, and then doing the smart thing about
evaluation of binomial.
Let's see what he has to say.
--
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=20216
