[Bug tree-optimization/59121] [4.8/4.9 Regression] endless loop with -O2 -floop-parallelize-all

["grosser at gcc dot gnu.org" <gcc-bugzilla at gcc dot gnu dot org>]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=59121

Tobias Grosser <grosser at gcc dot gnu.org> changed:

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                 CC|                            |grosser at gcc dot gnu.org

--- Comment #16 from Tobias Grosser <grosser at gcc dot gnu.org> ---
(In reply to Jeffrey A. Law from comment #15)
> Mircea, thanks.  I'm definitely looking forward to seeing Graphite in a
> better state!  With you on board at INRIA and working on Graphite, I will
> not be calling for Graphite's removal after the 4.9 release.
> 
> Thanks again,
> jeff

This bug is probably the perfect case to use isl's new compute out facility,
which allows us to give up after a certain number of compute iterations.
This will give us the assurance that we do not hang any more in the graphite
dependence analysis, but that we instead bail out smoothly.

We should probably also work on the efficiency of the analysis (and there is a
lot that could be done), but in my opinion the number one priority is that we
avoid unpredictable compile time. After this issue is fixed, we can address
cases where we bail out as missed optimizations. Something, that is a lot less
intrusive.