Hi Tobias, > >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. > >
I think this is a good idea in the long run (in the 4.5 timeframe). My only issue with it is that we have several bugs today even without generating code unless a transformation is picked. Of cpu2006 benchmarks, all but 4 fail to build. We have memory leak issues, we have not tried to bootstrap gcc with graphite enabled. I think that expanding the coverage or overhead testing only makes sense after we have fixed the existing bugs. I personally like the "-fgraphite-identity" approach the best. Thanks, Harsha >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? > >See you >Tobi >
