ekalda commented on PR #94: URL: https://github.com/apache/tvm-rfcs/pull/94#issuecomment-1275917969
Thanks for your input and suggestions @tqchen, much appreciated! I added a paragraph about pattern matching TIR, see if it makes sense. Yes, this RFC propses A1 change. A2 style TIR intrinsic is in the plan further down the line, it would let us expose SVE capabilities to the core compiler, so we could explore a larger space of optimisations. The decision to enable it initially just in the TIR->LLVM boundary came from a realisation that we can generate perfectly valid SVE from just looking at the TIR, without having to modify it. I have spent some time playing around with the current LLVM codegen and I think you make a very good point with the robustness. I have been looking at simple vectorized loads and stores (simple meaning here that the stride is 1 and that the index expression is a Ramp node, not a complex non-linear calculation with Ramp as a leaf node), the main challenge I currently see is that while the index itself is 1D at the point of code generation, the loop nest necessarily isn't, so I have to figure out the right loop bound that needs changing from the base of the Ramp node. It seems to me that we have to do some sort of analysis pass just before the codegen to collect that info. It would have been nice to directly generate the SVE LLVM "as we go" during the LLVM codegen, but it seems that we generate LLVM with the loop bounds fixed before we visit the loop body (so before we discover the Ramp nodes) and we can't change the bound afterwards. I think doing an analysis pass would help with the robustness since we can gather as much information from the TIR graph as we need to. I haven't worked a lot with LLVM backends, so interested in hearing any thoughts/suggestions. -- This is an automated message from the Apache Git Service. To respond to the message, please log on to GitHub and use the URL above to go to the specific comment. To unsubscribe, e-mail: [email protected] For queries about this service, please contact Infrastructure at: [email protected]
