Alias analysis and C++. Was: Re: [BusyBox] Re: Long term code...

[Paolo Carlini <pcarlini at unitus dot it>]

Jan Hubicka wrote:

> > Have you binary searched the changes and identified the change that
> > blew performance?  If not, that would be a big help in identifying
> > what went wrong.  If you have, it helps to name the patch that blew
> > performance in this type of email.
> The slowdown appears to come from the fact that Richard Kenner has fixed
> a bug that caused alias code to be bit more aggresive than it can be.
>
> Honza

... more aggressive than it can be... right now! :-)

Seriously, Jan has already made some good progress (excellent!) and I'm
still hoping that this alias analysis issue with C++ will be satisfactorily
solved in time for 3.1: it seems to me that it is not just a matter of
improving the optimization of a short testcase, but something from which
many common loop patterns may appreciably benefit.

What I cannot understand at all at this point is how *much* work is needed,
that is how much infrastructure is already present and only in need of
debugging and refinements, and how much has to be written from scratch...

Cheers,
Paolo Carlini.