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C++ Interface

The standalone library exports the IR/ONNX API consumed by Python bindings through include/mlx/ir.hpp under mlx::onnx:

  • export_ir_json
  • export_onnx_compatibility_report_json
  • export_onnx_json
  • export_onnx
  • ir_to_onnx_json
  • ir_to_onnx
  • ir_compatibility_report_json
  • build_onnx_binary_artifact_from_onnx_json
  • write_onnx_binary_artifact_to_path
  • ir_is_unsupported_error_message

namespace: mlx::onnx in include/mlx/ir.hpp

Shared types:

  • using IrCaptureFunction = std::function<std::vector<mlx::core::array>(const mlx::core::Args&, const mlx::core::Kwargs&)>;
  • struct OnnxBinaryWriteOptions { bool external_data; std::string external_data_file; int64_t external_data_size_threshold; }; Defaults: external_data=false, external_data_file="weights.bin", external_data_size_threshold=1024.
  • struct OnnxBinaryArtifact { std::string model_bytes; std::string external_data_bytes; bool has_external_data; };

Function signatures and semantics:

  • std::string ir_to_onnx_json(const std::string& ir_json, int64_t opset, const std::string& model_name) Input: IR JSON payload as string, ONNX opset (must be positive), model name (must be non-empty). Returns ONNX JSON string.

  • std::string ir_to_onnx(const std::string& target_path, const std::string& ir_json, int64_t opset, const std::string& model_name, const OnnxBinaryWriteOptions& options) Same IR/metadata inputs as above plus output path and write options. Returns the written ONNX artifact path.

  • std::string ir_compatibility_report_json(const std::string& ir_json) Input: IR JSON string. Returns compatibility report JSON string.

  • std::string export_ir_json(const IrCaptureFunction& fun, const mlx::core::Args& args, const mlx::core::Kwargs& kwargs, bool shapeless) Inputs: captured function and concrete positional/keyword tracing inputs. shapeless=true allows shape-agnostic tracing behavior in supported paths. Returns traced MLX IR JSON string.

  • std::string export_onnx_compatibility_report_json(const IrCaptureFunction& fun, const mlx::core::Args& args, const mlx::core::Kwargs& kwargs, bool shapeless) Same function/input contract as export_ir_json. Returns compatibility report JSON string.

  • std::string export_onnx_json(const IrCaptureFunction& fun, const mlx::core::Args& args, const mlx::core::Kwargs& kwargs, bool shapeless, int64_t opset, const std::string& model_name) Traces and directly emits ONNX JSON. Returns ONNX JSON string.

  • std::string export_onnx(const std::string& target_path, const IrCaptureFunction& fun, const mlx::core::Args& args, const mlx::core::Kwargs& kwargs, bool shapeless, int64_t opset, const std::string& model_name, const OnnxBinaryWriteOptions& options) Same tracing and conversion inputs as above plus output path and write options. Returns the written ONNX artifact path.

  • OnnxBinaryArtifact build_onnx_binary_artifact_from_onnx_json(const std::string& onnx_json, const OnnxBinaryWriteOptions& options) Input: ONNX JSON text and write options. Returns OnnxBinaryArtifact containing serialized model bytes and optional external tensor bytes.

  • std::string write_onnx_binary_artifact_to_path(const std::string& target_path, const OnnxBinaryArtifact& artifact, const OnnxBinaryWriteOptions& options) Writes a binary ONNX artifact plus optional external tensor file(s) as configured. Returns final written ONNX path.

  • bool ir_is_unsupported_error_message(const std::string& message) Returns true when message represents an unsupported-operator IR export error.