mirror of https://github.com/llvm/torch-mlir
51902ec2dc
Resolves #3384. Many ONNX operators are defined by functions and therefore could be expanded into simpler ONNX operations during importing, avoiding the need for tools downstream to support these operators directly. This commit adds this capability to onnx_importer.py. When importing a node, the schema for the node's operator is retrieved. If the schema provides a function for the operator, a specialized version for the node's types and attributes will be created and imported as an MLIR function with private visibility. An MLIR function call will then be emitted, instead of a normal operator node. Caching is used to avoid generating redundant functions within the same module. In order to avoid a disruptive change to the importer output for a large number of operators that already have TorchOnnxToTorch support, an allowlist strategy is used by default. With this commit, only one operator is allowlisted for expansion, MeanVarianceNormalization. However, many other operators can be correctly expanded by the current code, so hopefully the allowlist can be gradually extended. It is possible to disable the allowlist in the configuration, in which case all functions are expanded (useful for testing). Tools downstream of the importer may now need to do inlining when consuming the output of the importer, e.g.: cat imported.mlir | torch-mlir-opt --inline --convert-onnx-to-torch Explanations for subtle code changes: - Looking up the correct schema and function for an operator requires knowing the opset version. NodeImporter retrieves this from the opset imports on the ModelProto retained by the GraphInfo. Previously, the model_proto field on GraphInfo was None when importing a subgraph in import_regions, but this conflicts with the new need for opset version info. Since the apparent purpose of setting it to None was to control how GraphInfo generates its input map, a new flag is added to GraphInfo (is_subgraph) to control this behavior, so that the actual ModelProto can now be provided without breaking this. This also turned out to be useful for getting the Config via ModelInfo via GraphInfo. - Some operators' functions are context-dependent, which means the function definition depends on the types of the inputs. Therefore node importing now needs to look up the types of a node's inputs, not just its outputs as was the case previously. Consequently the operand to find_type_proto_for_name() may now be a graph input or initializer in some cases, so it has to be updated. |
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