[Bug tree-optimization/98598] Missed opportunity to optimize dependent loads in loops

["jiangning.liu at amperecomputing dot com" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98598

--- Comment #7 from Jiangning Liu <jiangning.liu at amperecomputing dot com> ---
(In reply to rguenther@suse.de from comment #6)
> On January 9, 2021 4:17:17 AM GMT+01:00, "jiangning.liu at amperecomputing
> dot com" <gcc-bugzilla@gcc.gnu.org> wrote:
> >https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98598
> >
> >--- Comment #5 from Jiangning Liu <jiangning.liu at amperecomputing dot
> >com> ---
> >> It has to be done with care of course, cost modeling is difficult
> >> (we need to have a good estimate of n and m or need to version
> >> the whole nest).  That said, usually we attempt the reverse
> >transform.
> >
> >Before tuning the cost model good enough, we may implement this
> >optimization by
> >adding a new optimization command line option. This won't hurt gcc,
> >right?
> 
> New options not enabled by default tend to bitrot, be broken from the start
> and won't be used by the lazy user. So I see no point in doing that. 
> 

Understand. I mean we can enable it by default eventually, but we need to
implement and tune it step by step. It is unrealistic to work out the best cost
model at the very beginning.