Hi, On Fri, 2008-10-10 at 23:31 +0200, Albert Cohen wrote: > Tobias Grosser wrote > > Hi graphities, > > > > graphite consists of four flags "-floop-block", "-floop-interchange", > > "-floop-stripmine" and "-fgraphite". > > > > If any of these flags is set, we enable the graphite pass and we search > > for SCoPs. > > For every SCoP we try to apply transformations specified with > > "-floop-block", "-floop-interchange" or "-floop-stripmine". But only if > > we could apply a transformation, we replace the SCoP with new code > > generated from the GRAPHITE data structures. Otherwise we do not touch > > the GIMPLE representation. > > If we only specify "-fgraphite", we never generate code for any SCoP, as > > we never tried any transformation. So just using "-fgraphite" is > > useless. > > > > What is missing is a way to make GRAPHITE always generate code, even if > > we did not apply any transformation. > > > > This has two benefits: > > - We can check the overhead the GIMPLE -> GRAPHITE -> GIMPLE > > transformation costs. > > - Wider test coverage, as we are able to run the code generator for > > every SCoP, not only the SCoPs, we are able to transform. > > > > > > Now: > > ---- > > > > -fgraphite: Do nothing. > > -floop-block, -floop-interchange, -floop-stripmine: Try these > > transformations. > > > > Only "-fgraphite": Do nothing > > Only "-floop-block": Only loop blocked SCoPs are changed. > > "-fgraphite -floop-block": Only loop blocked SCoPs are changed. > > > > One solution: Reuse -fgraphite > > ------------------------------ > > > > -fgraphite: Enable always code generation > > -floop-block, -floop-interchange, -floop-stripmine: Try these > > transformations. > > > > Only "-fgraphite": The identity transformation for all SCoPs. > > Only "-floop-block": Only loop blocked SCoPs are changed. > > "-fgraphite -floop-block": All SCoPs are are changed. Some SCoPs are > > loop blocked, others just the identity > > transformation. > > > > This allows us to get all the benefits but (mis)uses the -fgraphite > > flag. At the moment it has no other meaning, but I could think of it > > containing an automatic optimizer, that applies all available graphite > > transformations or selects them automatically. > > > > The other solution is: Use -fgraphite-identity > > ---------------------------------------------- > > > > -fgraphite: Enable always code generation > > -floop-block, -floop-interchange, -floop-stripmine, -fgraphite-identity: > > Try these transformations. > > > > Only "-fgraphite": Do nothing. Free for later use. > > Only "-floop-block": Only loop blocked SCoPs are changed. > > Only "-fgraphite-identity": The identity transformation for all SCoPs. > > "-fgraphite-identity > > -floop-block": All SCoPs are are changed. Some SCoPs are > > loop blocked, others just the identity > > transformation. > > > > This makes sense, as we only generate code for applied and enabled > > transformations. These are loop-blocking, interchange, stripmine and > > - may be - the new and very easy to write identity transformation, that > > does nothing, but enable code generation. > > > > What du you think about these different solutions? > > Hi Tobias, > > I am in favor of prefixing all transformation passes with -fgraphite- > leading to -fgraphite-block -fgraphite-stripmine -fgraphite-identity and > the new ones to come. These flags should probably disappear at some > point, as a more unified optimization heuristic should arise that > combines all transformations, with some parameters to influence the > profitability heuristic. > > I agree -fgraphite should be reserved for later use, but not mandatory > to use any of the new -fgraphite-xxx options. > > This is just a suggestion with a partial understanding of the option > naming scheme in GCC only!
I see what you mean. For me all the graphite flags seem to be like temporary flags, as the idea of the polyhedron model is to allow a lot of different optimizations, that can not be split up to loop blocking So in this case the current flags seem for me to just enable different demo/test optimizers in graphite, that are replaced later by a better general one. So I like your idea. I will submit a patch containing this idea. See you Tobias
