Seeking Guidance on Resolving Issues with Custom MLIR Frontend and Dialect Registration

I’m working on developing a custom out-of-tree MLIR frontend for a specialized neural network model format. The current goal is to create a program that parses this custom model file and converts it into MLIR code using a custom dialect specific to the model format.

Here’s my current code snippet:

mlir::DialectRegistry registry;
MLIRContext ctx(registry);

mlir::ModuleOp moduleOp = readFromFile(ctx, inputFilename);
moduleOp->print(output->os(), OpPrintingFlags{}.printGenericOpForm(false));

The readFromFile function is responsible for reading the model format and converting it to MLIR. Inside the module, I want to use func.func to represent the model code, and I create it like this:

return builder.create<func::FuncOp>(loc, funcName, funcType);

However, I encountered an issue with the following error message:

LLVM ERROR: Building op `func.func` but it isn't registered in this MLIRContext: the dialect may not be loaded or this operation isn't registered by the dialect. See also

To address this error, I tried adding ctx.loadAllAvailableDialects(); to my code, which resolved the previous issue. However, I now face a new problem: despite specifying that I want non-generic operations, the output still includes generic operations. Here’s an example of the undesired behavior:

"builtin.module"() ({
  "func.func"() <{function_type = (tensor<784x1xf32>) -> (), sym_name = "mnist"}> ({
  }) : () -> ()
}) : () -> ()

I couldn’t find any loadAllAvailableDialects calls in MlirOptMain, so I suspect I might be doing something wrong initially, leading to the ICE. I’m seeking guidance on how to resolve this issue.

1 Like

Your func op failed verification and so was printed in generic format. Probably in your tool you are using you aren’t reporting errors. Try passing this output through mlir-opt and it will show

<stdin>:22:3: error: 'func.func' op symbol declaration cannot have public visibility
<stdin>:22:3: note: see current operation:
"func.func"() <{function_type = (tensor<784x1xf32>) -> (), sym_name = "mnist"}> ({
}) : () -> ()

Could you please tell how I can fix the problem? Or something to read on the symbol visibility and why functions can’t have the public one.

Indeed, you are correct. By adding the following line of code:


I was able to resolve the issue with the printing. Thank you for your assistance!

Now, I have a follow-up question: if I intend to create a JIT engine later and call the function from C++ code, how can I make the function public? Or is this not related to the linking attributes?

Regarding the ICE issue without using loadAllAvailableDialects, is this behavior expected?

Lastly, how can I print the errors effectively? I believe having error messages would be quite useful. Should I register a handler in the Diagnostics Engine to achieve this?


Here you can’t have it public because it does not have a body. If you define a function then you can have it public.

Yeah, I couldn’t see the solution staring me in the face. I need to read more carefully next time…

Oh, I see. Seems reasonable, thanks for the help!