CoreML Execution Provider
Core ML is a machine learning framework introduced by Apple. It is designed to seamlessly take advantage of powerful hardware technology including CPU, GPU, and Neural Engine, in the most efficient way in order to maximize performance while minimizing memory and power consumption.
Contents
Requirements
The CoreML Execution Provider (EP) requires iOS devices with iOS 13 or higher, or Mac computers with macOS 10.15 or higher.
It is recommended to use Apple devices equipped with Apple Neural Engine to achieve optimal performance.
Install
Pre-built binaries of ONNX Runtime with CoreML EP for iOS are published to CocoaPods.
See here for installation instructions.
Build
For build instructions for iOS devices, please see Build for iOS.
Usage
The ONNX Runtime API details are here.
The CoreML EP can be used via the C, C++, Objective-C, C# and Java APIs.
The CoreML EP must be explicitly registered when creating the inference session. For example:
Ort::Env env = Ort::Env{ORT_LOGGING_LEVEL_ERROR, "Default"};
Ort::SessionOptions so;
uint32_t coreml_flags = 0;
Ort::ThrowOnError(OrtSessionOptionsAppendExecutionProvider_CoreML(so, coreml_flags));
Ort::Session session(env, model_path, so);
Configuration Options
There are several run time options available for the CoreML EP.
To use the CoreML EP run time options, create an unsigned integer representing the options, and set each individual option by using the bitwise OR operator.
uint32_t coreml_flags = 0;
coreml_flags |= COREML_FLAG_ONLY_ENABLE_DEVICE_WITH_ANE;
Available Options
COREML_FLAG_USE_CPU_ONLY
Limit CoreML to running on CPU only.
This decreases performance but provides reference output value without precision loss, which is useful for validation.
Intended for developer usage only.
COREML_FLAG_ENABLE_ON_SUBGRAPH
Enable CoreML EP to run on a subgraph in the body of a control flow operator (i.e. a Loop, Scan or If operator).
COREML_FLAG_ONLY_ENABLE_DEVICE_WITH_ANE
By default the CoreML EP will be enabled for all compatible Apple devices.
Setting this option will only enable CoreML EP for Apple devices with a compatible Apple Neural Engine (ANE). Note, enabling this option does not guarantee the entire model to be executed using ANE only.
For more information, see Which devices have an ANE?
COREML_FLAG_ONLY_ALLOW_STATIC_INPUT_SHAPES
Only allow the CoreML EP to take nodes with inputs that have static shapes. By default the CoreML EP will also allow inputs with dynamic shapes, however performance may be negatively impacted by inputs with dynamic shapes.
COREML_FLAG_CREATE_MLPROGRAM
Create an MLProgram format model. Requires Core ML 5 or later (iOS 15+ or macOS 12+). The default is for a NeuralNetwork model to be created as that requires Core ML 3 or later (iOS 13+ or macOS 10.15+).
Supported operators
NeuralNetwork
Operators that are supported by the CoreML Execution Provider when a NeuralNetwork model (the default) is created:
| Operator | Note |
|---|---|
| ai.onnx:Add | |
| ai.onnx:ArgMax | |
| ai.onnx:AveragePool | Only 2D Pool is supported. |
| ai.onnx:BatchNormalization | |
| ai.onnx:Cast | |
| ai.onnx:Clip | |
| ai.onnx:Concat | |
| ai.onnx:Conv | Only 1D/2D Conv is supported. Weights and bias should be constant. |
| ai.onnx:DepthToSpace | Only DCR mode DepthToSpace is supported. |
| ai.onnx:Div | |
| ai.onnx:Flatten | |
| ai.onnx:Gather | Input indices with scalar value is not supported. |
| ai.onnx:Gemm | Input B should be constant. |
| ai.onnx:GlobalAveragePool | Only 2D Pool is supported. |
| ai.onnx:GlobalMaxPool | Only 2D Pool is supported. |
| ai.onnx:LeakyRelu | |
| ai.onnx:LRN | |
| ai.onnx:MatMul | Input B should be constant. |
| ai.onnx:MaxPool | Only 2D Pool is supported. |
| ai.onnx:Mul | |
| ai.onnx:Pad | Only constant mode and last two dim padding is supported. Input pads and constant_value should be constant. If provided, axes should be constant. |
| ai.onnx:Pow | Only supports cases when both inputs are fp32. |
| ai.onnx:PRelu | Input slope should be constant. Input slope should either have shape [C, 1, 1] or have 1 element. |
| ai.onnx:Reciprocal | |
| ai.onnx.ReduceSum | |
| ai.onnx:Relu | |
| ai.onnx:Reshape | |
| ai.onnx:Resize | 4D input.coordinate_transformation_mode == asymmetric.mode == linear or nearest.nearest_mode == floor.exclude_outside == falsescales or sizes must be constant. |
| ai.onnx:Shape | Attribute start with non-default value is not supported.Attribute end is not supported. |
| ai.onnx:Sigmoid | |
| ai.onnx:Slice | Inputs starts, ends, axes, and steps should be constant. Empty slice is not supported. |
| ai.onnx:Softmax | |
| ai.onnx:Split | If provided, splits must be constant. |
| ai.onnx:Squeeze | |
| ai.onnx:Sqrt | |
| ai.onnx:Sub | |
| ai.onnx:Tanh | |
| ai.onnx:Transpose |
MLProgram
Operators that are supported by the CoreML Execution Provider when a MLProgram model (COREML_FLAG_CREATE_MLPROGRAM flag is set) is created:
| Operator | Note |
|---|---|
| ai.onnx:Add | |
| ai.onnx:AveragePool | Only 2D Pool is supported currently. 3D and 5D support can be added if needed. |
| ai.onnx:Clip | |
| ai.onnx:Concat | |
| ai.onnx:Conv | Only 1D/2D Conv is supported. Bias if provided must be constant. |
| ai.onnx:ConvTranspose | Weight and bias must be constant. padding_type of SAME_UPPER/SAME_LOWER is not supported. kernel_shape must have default values. output_shape is not supported. output_padding must have default values. |
| ai.onnx.DepthToSpace | If ‘mode’ is ‘CRD’ the input must have a fixed shape. |
| ai.onnx:Div | |
| ai.onnx:Gemm | Input B must be constant. |
| ai.onnx:GlobalAveragePool | Only 2D Pool is supported currently. 3D and 5D support can be added if needed. |
| ai.onnx:GlobalMaxPool | Only 2D Pool is supported currently. 3D and 5D support can be added if needed. |
| ai.onnx:GridSample | 4D input. ‘mode’ of ‘linear’ or ‘zeros’. (mode==linear && padding_mode==reflection && align_corners==0) is not supported. |
| ai.onnx.LeakyRelu | |
| ai.onnx:MatMul | Only support for transA == 0, alpha == 1.0 and beta == 1.0 is currently implemented. |
| ai.onnx:MaxPool | Only 2D Pool is supported currently. 3D and 5D support can be added if needed. |
| ai.onnx:Mul | |
| ai.onnx:Pow | Only supports cases when both inputs are fp32. |
| ai.onnx:Relu | |
| ai.onnx:Reshape | |
| ai.onnx:Resize | See resize_op_builder.cc implementation. There are too many permutations to describe the valid combinations. |
| ai.onnx.Slice | starts/ends/axes/steps must be constant initializers. |
| ai.onnx.Split | If provided, splits must be constant. |
| ai.onnx:Sub | |
| ai.onnx:Sigmoid | |
| ai.onnx:Tanh | |
| ai.onnx:Transpose |