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Re: [graphite] Weekly phone call notes
On Wed, 2009-04-29 at 23:57 +0200, Richard Guenther wrote:
> On Wed, Apr 29, 2009 at 11:34 PM, Tobias Grosser
> <grosser@fim.uni-passau.de> wrote:
> > Hi gcc developers, hi graphities
> >
> > here are some notes from our weekly phone call. Unfortunately I missed
> > to send out the notes from the last two phone calls, but I hope to get
> > them out more regulary. Believe in me! ;-)
> >
> > http://gcc.gnu.org/wiki/Graphite_Phone_Call/2009_04_29
> >
> > Attendees: Li, Jan, Konrad, Sebastian, Tobias, David, Christophe
> >
> > * Reductions: Diego OK with going out of SSA.
>
> You will loose all points-to information. I think going out of SSA is
> a very bad idea.
It makes live a lot easier and it is just for reductions. ;-) But you
are right we should get SSA back.
The point was more if it is the right moment to try to regenerate SSA as
the polyhedral model is actually not single assignment. Or actually the
other way around. More single assignment than SSA.
We postponed this complication or silently hoped that a later pass might
clean up our mess. Actually Sebastian already looked at the output and
there seems to be a later gcc pass, that cleans it up and reintroduces
SSA. But we have to investigate this further or at least document it
correctly. The final goal has to be to get an optimized loop, that is
still in SSA. The way we take is not completely clear yet.
> > * Patch not yet ready. The higher code coverage exposes an
> > IVSTACK bug.
> > * IVStack: Sebastian is working on removing it
> > * Data dependence analysis: Committed to graphite branch.
> > * Not yet enabled, as the data reference still does not
> > bootstrap. The lexicographic smaller than constraint is
> > not yet added. This is not wrong but very conservative.
> > Dependence test should be enabled with
> > -fgraphite-identity.
> > * Loop transformations: We need some simple transformations to
> > check data dependency analysis.
> > * Pranav? We did not hear anything yet.
> > * Data reference: Last bugs have to be fixed.
> > * Not yet enabled. Blocks data dependence analysis.
> > * PCP:
> > * Jan Implemented simplification/canonicalization for
> > expressions. This will allow a systematic translation of
> > expressions to constraints. Jan will work on a reduced
> > polyhedral interface that is used in PCP. First PCP
> > integration in gcc - later extended by reductions.
> >
> > No good representation for reductions for the general
> > case. Like conditions and PHI nodes (Sebastian) Maybe
> > for a subset of the reductions we can add commutativaty
> > of operations.
> >
> > * Autopar: Li prepared some patches to trigger autopar by
> > graphite.
> > * Autopar failed in the graphite branch even without
> > graphite enabled. It seems we introduced a bug while
> > using some code of it for graphite. The breakage happens
> > in the reductions part.
> > * Merge from trunk:
> > * Sebastian wants to work on this Changes in vectorizer
> > Last merge 4 months ago Tried mid march but was
> > difficult. So stopped because of ENOTIME.
> > * Parts of graphite working well?: The polyhedral part of the
> > graphite architecture will be described
> > * in the Tobias' paper at the summit and the PCP part by
> > Jan.
> > * Worldwide interest: Cristianno Martins from Brazil showed some
> > interest
> > * http://gcc.gnu.org/ml/gcc/2009-04/msg00711.html
> >
> > * We already have people from the US, Europe and China
> > contributing.
> >
> >
> >
> >