[Bug rtl-optimization/72855] Long compile time due to integrity checking during dataflow analysis per loop

["rguenther at suse dot de" <gcc-bugzilla at gcc dot gnu dot org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=72855

--- Comment #11 from rguenther at suse dot de <rguenther at suse dot de> ---
On Wed, 10 Aug 2016, wschmidt at gcc dot gnu.org wrote:

> https://gcc.gnu.org/bugzilla/show_bug.cgi?id=72855
> 
> --- Comment #10 from Bill Schmidt <wschmidt at gcc dot gnu.org> ---
> Some experiments on trunk:
> 
> - Using Bin's patch, I see compile time reduced to ~14 minutes.
> - Using Richi's patch, I see compile time reduced to ~9 minutes.
> 
> So both are quite helpful compared to somewhere around 2 hours.
> 
> I'll plan to implement the pre-approved patch, but first I want to try to dig
> into why flag_checking appears to have an unexpected value.

Yes, that's very much appreciated.  As the issue also appears on older
branches w/o flag_checking there may be a stray memory write to
df->changeable_flags somewhere?  As it is a global maybe put a watchpoint
to it ...