Writing a basic Conversion Pass

MLIR
1

I am exploring MLIR, and am looking at writing my own conversion pass for the Linalg dialect, replacing matmul calls with something else. I am still to add the implementation of the pass, however I would like to be sure that the pass works as a stub, before developing it further.

I am following how LinalgToSPIRV appears to be doing it, however when I try and compile I get an error (see below). I’ve got all my changes as a single commit on the dev/external_pass branch.

/app/llvm-project-public/mlir/lib/Conversion/LinalgToExternal/LinalgToExternal.cpp:75:27: error: use of undeclared identifier 'ConvertLinalgToExternalPass'; did you mean 'ConvertLinalgToExternalBase'?
  return std::make_unique<ConvertLinalgToExternalPass>();
                          ^~~~~~~~~~~~~~~~~~~~~~~~~~~
                          ConvertLinalgToExternalBase
tools/mlir/include/mlir/Conversion/Passes.h.inc:1012:7: note: 'ConvertLinalgToExternalBase' declared here
class ConvertLinalgToExternalBase : public ::mlir::OperationPass<ModuleOp> {

To me, this suggests that the code generation step in Passes.h is not registering my pass properly. Is there something I’m missing?

To explain a bit more of what I’ve done:

  1. I have created a directory for my pass in lib, and added the directory to CMakeLists.txt, as well as having a basic C++ file. external_pass/mlir/lib/Conversion/LinalgToExternal

  2. I have also added my pass to the include directory, adding the header to mlir/include/mlir/Conversion/Passes.h, as well as to the tablegen file mlir/include/mlir/Conversion/Passes.td. mlir/include/mlir/Conversion/LinalgToExternal

Is there anything else I need here? Is my intuition about there being an issue with the tablegen for Passes.h reasonable, or is it more likely to be something else?

2

Adding your pass to Passes.td will result in a base class being generated (ConvertLinalgToExternalBase). To actually define your pass you will need to create a new class that inherits from this base class, i.e. define ConvertLinalgToExternalPass that inherits from ConvertLinalgToExternalBase<ConvertLinalgToExternalPass>.

The docs are here: Pass Infrastructure - MLIR
And here is where that happens for LinalgToSPRIV: llvm-project/LinalgToSPIRVPass.cpp at main · llvm/llvm-project · GitHub

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