operator domain com.microsoft.nchwc

[jchia]

From the main goal of productionizing a model's inference by building an inference .so to be called from a C++ program, I ran into operator-related errors while running onnx-mlir on an .onnx file I got from offline optimization done in the approach described here.

Then I noticed that the optimized .onnx has ops from the domain com.microsoft.nchwc, among which there is a ReorderOutput op that onnx-mlir does not recognize.

From here I have some questions about operator domains:

• What are domains? Are they analogous to programming language namespaces? Are there or can there be 2 operators with the same name from different domains that behave differently so that identifying an op not just by the name but also by the domain is necessary?
• What is the status of the com.microsoft.nchwc domain in the ONNX project? Is it considered third-party so that tools in the ONNX project (e.g. onnx-mlir) will not try to understand or process them? (onnx.defs.get_all_schemas_with_history() also has no op from com.microsoft.nchwc.)
• In general how do you know which tools will support which op domains? In the case of onnx-mlir, I think the errors I got were ultimately due to unsupported operator/domain but the error message was a cryptic error: not ranked that led me to dig into the code.