[GitHub] [tvm] FranckQC edited a comment on pull request #9482: Implementation of Common Subexpression Elimination for TIR

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FranckQC edited a comment on pull request #9482:
URL: https://github.com/apache/tvm/pull/9482#issuecomment-969151523


   > 
   > 
   > Hi @FranckQC, I wanted TIR-level CSE for a long time, so very excited to see this!
   > 
   > What I wanted to do is to eliminate common expressions that span across the host and GPU - for example, in GPU `sort` kernel, I need to make `log2(N)` GPU kernel calls from the host to sort the input bottom up. In principle, `log2(N)` needs to computed once by the host and pass to the GPU kernel, but since we cannot CSE `log2(N)` expression that appears both in the host and GPU kernel, right now the GPU sort kernel is littered with `log2(N)` compute like this (note a lot of calls to `call_spirv_pure_glsl450` which is totally unnecessary if we had TIR-level CSE) https://gist.github.com/masahi/7a755ef67009e1a836e3212c53cf496f
   > 
   > Is this PR going to solve my problem?
   
   Hi @masahi 
   Thanks a lot for the kind words! I'm happy to read that this new pass will be useful to you.
   Yes, in principle, every redundant subterms that are eligible for being commoned out (i.e, which does not contain function calls, etc) will be commoned out. There are also a few restrictions which are due to some specifics of TVM, but these are rare.
   Do you have a little snippet of the TIR code that you have which has some redundancies? I cant try to tell if the CSE pass will be able to optimize it.
   Also please do not hesitate to play with the pass and to let me know if it does what you would hope to obtain. I can help of course.
   
   Kind regards.


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