[llvm-dev] [RFC] Proposal for TLX: Tensor LLVM eXtensions

[Florian Hahn via llvm-dev]

Hi,

Thanks for sharing the proposal! I think the matrix extension has shown that it is feasible to use a ‘flat vector’ encoding to support more complex operations. Decoupling the shape information from the ‘operational’ intrinsics seems very neat!


Below some additional initial questions. 

* The proposal itself is very big, both in terms of text as well as in the code that will be required to implement it. Have you thought about how to bring up support in a way that allows using a (smaller) subset of intrinsics end-to-end? 

* What will the hardware specific lowering look like? I think you mentioned you are planning to support a set of different hardware architectures. Will this require a separate lowering pass for each of those?

* What’s the motivation for some intrinsics returning a vector and others returning a token type? Could all intrinsics return vector? This would be more consistent and the type info is associated to the value itself in any case.

* Will variable shapes/sizes be supported? IIRC you mentioned that the type intrinsic can take arbitrary values as arguments. But some intrinsics return vectors, so they would need a fixed size?

* You mentioned Julia and Halide as potential adopters. Do you know if there’s concrete interest to switch to using the new intrinsics by the maintainers ? What would the anticipated timeframe be? I think this could be a crucial argument for having this in LLVM directly, if we have people who are going to use this ASAP.

* What will Clang support for arbitrary tensors look like? If Clang won’t support arbitrary tensors, why not?

* AFAICT this should completely subsume the matrix extension and if we decide to add the more general extension the matrix extension should be removed. How will the transition from the current matrix intrinsics to the new tensor intrinsics work? Can existing IR be auto-upgraded?

Cheers,
Florian