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