NXP backend: Add support for depthwise and separable convolution.

The `group` attribute of the `aten.convolution` has an effect on how the weights are used in the computation of the convolution. To properly utilize Neutron, the convolution is sometimes converted to `DepthwiseConv2D`.

Author: MartinPavella

backends/nxp/backend/edge_helper.py

@@ -5,6 +5,7 @@
 
 import torch
 from torch.fx import Node
+from torch.nn import Parameter
 
 
 def input_tensor(node: Node, input_index: int) -> torch.Tensor:
@@ -38,3 +39,35 @@ def input_tensor_safe(node: Node, input_index: int) -> torch.Tensor | None:
         return None
 
     return input_tensor(node, input_index)
+
+
+def node_is_static_tensor(node: Node, parameters_mapping: dict[str, Parameter]) -> bool:
+    """Return `True` if the given `node` has static data in the `parameters_mapping` dict.
+    :param node: Tensor node to check for data.
+    :param parameters_mapping: Dict mapping tensor names to their static data. Should be inferred from the
+                                `state_dict` attribute of an edge program.
+    """
+    return node.name in parameters_mapping.keys()
+
+
+def node_is_effectively_static_tensor(
+    node: Node, parameters_mapping: dict[str, Parameter]
+) -> bool:
+    """Return `True` if the given `node` has static data, or follows after a `Dequantize` node with a static input.
+     In the IR, the `node` will be turned into a static quantized tensor.
+    :param node: Tensor node to check for data.
+    :param parameters_mapping: Dict mapping tensor names to their static data. Should be inferred from the
+                                `state_dict` attribute of an edge program.
+    """
+    if node_is_static_tensor(node, parameters_mapping):
+        return True
+
+    def _is_dequantize(node_: Node) -> bool:
+        return node_.target.__name__ in {
+            "quantized_decomposed.dequantize_per_tensor.default",
+            "quantized_decomposed.dequantize_per_channel.default",
+        }
+
+    return _is_dequantize(node) and node_is_static_tensor(
+        node.args[0], parameters_mapping
+    )

backends/nxp/backend/ir/converter/node_converters/ops_converters/convolution_converter.py

@@ -6,26 +6,36 @@
 import numpy as np
 import torch
 
-from executorch.backends.nxp.backend.edge_helper import input_tensor, input_tensor_safe
+from executorch.backends.nxp.backend.edge_helper import (
+    input_tensor,
+    input_tensor_safe,
+    node_is_effectively_static_tensor,
+)
 from executorch.backends.nxp.backend.ir.converter.conversion import (
     aten_translator,
     common,
 )
-from executorch.backends.nxp.backend.ir.converter.conversion.common import (
-    OpsList,
-    try_get_input,
-)
+from executorch.backends.nxp.backend.ir.converter.conversion.common import try_get_input
 from executorch.backends.nxp.backend.ir.converter.node_converter import (
     NodeConverter,
     Target,
 )
+from executorch.backends.nxp.backend.ir.converter.node_converters.shared import (
+    conv_utils,
+)
+from executorch.backends.nxp.backend.ir.converter.node_converters.shared.conv_utils import (
+    ConvConversionResult,
+    ConvParameters,
+)
 from executorch.backends.nxp.backend.ir.converter.quantization_utils import (
     set_quantization_parameters_to_tensor,
 )
+from executorch.backends.nxp.backend.ir.converter.tensor_utils import tensor_has_data
 from executorch.backends.nxp.backend.ir.lib.tflite.TensorType import TensorType
 from executorch.backends.nxp.backend.ir.tflite_generator import tflite_model
 from executorch.backends.nxp.backend.ir.tflite_generator.builtin_options import (
     conv_2d_options,
+    depthwise_conv_2d_options,
 )
 from torch.fx import Node
 from torch.nn import Parameter
@@ -48,7 +58,24 @@ def _is_supported_in_IR(
         if output_padding != [0, 0]:
             return False
 
-        if groups != 1:
+        if groups == 1:
+            # Regular convolution.
+            pass
+
+        elif conv_utils.group_conv_convertible_as_depthwise(
+            node, groups
+        ) and node_is_effectively_static_tensor(node.args[1], parameters_mapping):
+            # Depthwise convolution.
+            # Only supported if the weights are static, because TFLite `DepthwiseConv2D` uses permuted weights. In case
+            #  the weights are dynamic, a Transpose operator would have to be added, which is not supported on Neutron.
+            pass
+
+        elif conv_utils.group_conv_convertible_into_multiple_convolutions(node, groups):
+            # Separable convolution. Currently not supported.
+            return False
+
+        else:
+            # All conversion options related to the `group` attribute have been checked and none of them can be used.
             return False
 
         if input_tensor_safe(node, 2) is None:
@@ -59,69 +86,144 @@ def _is_supported_in_IR(
 
         return True
 
-    def _convert_2d_conv(
-        self, stride, padding, dilation, t_op: tflite_model.Operator
-    ) -> list[tflite_model.Operator]:
-        ops = OpsList(middle_op=t_op)
-        t_op.builtin_options = conv_2d_options.Conv2D()
-        common.assign_2d_strides(t_op.builtin_options, stride)
-        common.assign_2d_dilations(t_op.builtin_options, dilation)
-        t_op.builtin_options.padding, explicit_padding = (
-            aten_translator.convert_padding(padding)
-        )
+    Stride = Padding = Dilation = OutPadding = list[int]
+    Transposed = bool
+    Groups = int
 
-        if explicit_padding is not None:
-            # Need to prepend a 'Pad' operator, which adds 0s. But these will be included in the computation!
-            ops.add_pre(
-                self.builder.create_pad_operator_before(t_op, 0, explicit_padding)
-            )
-
-        input_tensor: tflite_model.Tensor = t_op.tmp_inputs[0]
-        weight_tensor: tflite_model.Tensor = t_op.tmp_inputs[1]
-        output_tensor: tflite_model.Tensor = t_op.tmp_outputs[0]
-
-        if (bias_tensor := try_get_input(t_op, 2)) is None:
+    @staticmethod
+    def _get_convolution_arguments(
+        conv_node: Node,
+    ) -> (Stride, Padding, Dilation, Transposed, OutPadding, Groups):
+        # The arguments of the conv are:
+        # [x, w, b, stride, padding, dilation, transposed, output padding, groups]
+        # https://github.com/pytorch/pytorch/blob/v2.6.0/aten/src/ATen/native/Convolution.cpp#L286-L291
+        _, _, _, stride, padding, dilation, transposed, out_padding, groups = (
+            conv_node.args
+        )
+        return stride, padding, dilation, transposed, out_padding, groups
+
+    # noinspection PyPep8Naming
+    def _convert_unpadded_2D(
+        self, t_op: tflite_model.Operator, conv_params: ConvParameters
+    ) -> conv_utils.ConvConversionResult:
+        """Convert the `aten.convolution` into TFLite. The `padding` and `builtin_options` must be converter by the
+        caller.
+        """
+        common.assign_2d_strides(t_op.builtin_options, conv_params.stride)
+        common.assign_2d_dilations(t_op.builtin_options, conv_params.dilation)
+
+        x: tflite_model.Tensor = t_op.tmp_inputs[0]
+        w: tflite_model.Tensor = t_op.tmp_inputs[1]
+        y: tflite_model.Tensor = t_op.tmp_outputs[0]
+
+        if (b := try_get_input(t_op, 2)) is None:
             # Operator has no bias. Convolution aten op can omit it, TFLite can't.
-            output_channels = weight_tensor.shape.vector[0]
+            output_channels = w.shape.vector[0]
 
-            if weight_tensor.type == TensorType.FLOAT32:
+            if w.type == TensorType.FLOAT32:
                 bias_type = np.dtype(np.float32)
-            elif weight_tensor.type in [TensorType.INT8, TensorType.UINT8]:
+            elif w.type in [TensorType.INT8, TensorType.UINT8]:
                 bias_type = np.dtype(np.int32)
             else:
                 # Should never happen.
                 raise NotImplementedError(
-                    f"Convolution node with unsupported weight type: {weight_tensor.type}"
+                    f"Convolution node with unsupported weight type: {w.type}"
                 )
 
-            bias_tensor = self.builder.create_zeros_tensor(
+            b = self.builder.create_zeros_tensor(
                 [output_channels], "zero_bias", bias_type, True
             )
 
             # Compute scale and zero point for bias tensor
-            input_scale = np.array(input_tensor.quantization.scale.vector)
-            weight_scale = np.array(weight_tensor.quantization.scale.vector)
+            input_scale = np.array(x.quantization.scale.vector)
+            weight_scale = np.array(w.quantization.scale.vector)
             bias_scale = input_scale * weight_scale
             bias_zero_point = np.zeros(weight_scale.shape, dtype=np.int64)
 
             set_quantization_parameters_to_tensor(
-                bias_tensor, bias_scale, bias_zero_point, quantized_dimension=0
+                b, bias_scale, bias_zero_point, quantized_dimension=0
             )
 
         # Assign the operator its TFLite inputs and outputs
-        t_op.tmp_inputs = [input_tensor, weight_tensor, bias_tensor]
-        t_op.tmp_outputs = [output_tensor]
+        t_op.tmp_inputs = [x, w, b]
+        t_op.tmp_outputs = [y]
+
+        conversion_result = ConvConversionResult(x, w, b, y)
+        conversion_result.ops_list.middle_op = t_op
+
+        return conversion_result
+
+    def _convert_2d_conv(
+        self, t_op: tflite_model.Operator, conv_params: ConvParameters
+    ) -> list[tflite_model.Operator]:
+        if conv_utils.group_conv_convertible_as_depthwise(
+            t_op, conv_params.groups
+        ):  # Convert to `DepthwiseConv2D`.
+            t_op.builtin_options = depthwise_conv_2d_options.DepthwiseConv2D()
+
+            conversion_result = self._convert_unpadded_2D(t_op, conv_params)
+            t_op.builtin_options.padding, explicit_padding = (
+                aten_translator.convert_padding(conv_params.padding)
+            )
+            if explicit_padding is not None:
+                # Need to prepend a 'Pad' operator, which adds 0s.
+                conversion_result.ops_list.add_pre(
+                    self.builder.create_pad_operator_before(t_op, 0, explicit_padding)
+                )
+
+            # DepthwiseConv2D expects weights in format [kernel_channels, kernel_height, kernel_width, output_channels]
+            perm = [3, 1, 2, 0]
+            weight_tensor = conversion_result.conv_weight_tensor
+            if tensor_has_data(weight_tensor):
+                # Transpose cloned tensor statically
+                t_op.tmp_inputs[1] = self.builder.create_transposed_tensor(
+                    weight_tensor, perm
+                )
+            else:
+                raise NotImplementedError("Dynamic Depthwise Conv weights.")
+
+        elif conv_utils.group_conv_convertible_into_multiple_convolutions(
+            t_op, conv_params.groups
+        ):
+            t_op.builtin_options = conv_2d_options.Conv2D()
+
+            return conv_utils.create_separated_convolutions_based_on_group(
+                t_op,
+                conv_params,
+                self.builder,
+                self._convert_unpadded_2D,
+                conv_utils.conv_op_factory,
+            )
+
+        else:
+            # Convert to regular `Conv2D`.
+            t_op.builtin_options = conv_2d_options.Conv2D()
+            conversion_result = self._convert_unpadded_2D(t_op, conv_params)
+            t_op.builtin_options.padding, explicit_padding = (
+                aten_translator.convert_padding(conv_params.padding)
+            )
+            if explicit_padding is not None:
+                # Need to prepend a 'Pad' operator, which adds 0s.
+                conversion_result.ops_list.add_pre(
+                    self.builder.create_pad_operator_before(t_op, 0, explicit_padding)
+                )
 
-        return ops.flatten()
+        return conversion_result.ops_list.flatten()
 
     def convert(self, node: Node):
         self.assert_convertible(node)
 
-        stride = node.args[3]
-        padding = node.args[4]
-        dilation = node.args[5]
+        stride, padding, dilation, _, _, groups = self._get_convolution_arguments(node)
 
         t_op = self._create_tflite_op_with_io_tensors(node)
-        ops_to_add = self._convert_2d_conv(stride, padding, dilation, t_op)
+        conv_params = ConvParameters(stride, padding, dilation, groups)
+
+        rank = t_op.tmp_inputs[1].shape.len()
+        if rank == 4:  # Conv2D
+            ops_to_add = self._convert_2d_conv(t_op, conv_params)
+        else:
+            raise NotImplementedError(
+                f"{rank - 2}D convolution is not supported."
+            )  # Should never get here.
 
         self.builder.append_operators(ops_to_add)