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Posted to commits@tvm.apache.org by "masahi (via GitHub)" <gi...@apache.org> on 2023/10/01 19:45:11 UTC

[GitHub] [tvm] masahi opened a new issue, #15851: [Bug][Unity] Legalization of cumsum op is broken

masahi opened a new issue, #15851:
URL: https://github.com/apache/tvm/issues/15851

   `R.cumsum` is legalized to `topi.cumsum` according to
   
   https://github.com/apache/tvm/blob/unity/python/tvm/relax/transform/legalize_ops/statistical.py#L90-L92
   
   But this is broken on GPU. `topi.cumsum` is one of topi ops that cannot be defined by `te.compute` and thus they are written using IR builder by hand, for CPU and GPU targets separately. Since `topi.cumsum` is meant to be used only for CPU targets, after legalization we get TIR that has a for loop with `parallel` kind, for example, even on GPU. Other common ops that would have the same issue include sorting etc. 
   
   So in this case, it would be more correct to use `topi.cuda.cumsum` for legalizing `relax.cumsum`, meaning the `LegalizeOp` pass needs to be target dependent. But I think that would break the original semantics of `LegalizeOp`. `DefaultGPUSchedule` pass also needs to ignore such legalized ops carefully since they are already scheduled for GPU by hand.
   
   I think we need to discuss what the Relax compilation story is going to be for such ops that were previously implemented using `te.extern`. 
   
   cc @tqchen @MasterJH5574 @Hzfengsy  


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Re: [I] [Bug][Unity] Legalization of cumsum op is broken [tvm]

Posted by "tqchen (via GitHub)" <gi...@apache.org>.
tqchen commented on issue #15851:
URL: https://github.com/apache/tvm/issues/15851#issuecomment-1742938886

   In this particular case, we should build up a tensor ir of cumsum, and then bring dlight schedule for them


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Re: [I] [Bug][Unity] Legalization of cumsum op is broken [tvm]

Posted by "tqchen (via GitHub)" <gi...@apache.org>.
tqchen commented on issue #15851:
URL: https://github.com/apache/tvm/issues/15851#issuecomment-1798618247

   opens up a discussion thread in https://discuss.tvm.apache.org/t/discuss-default-compilation-flow-for-scan-and-sort/15949


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