NXP backend: added aten.split support (#16490)

### Summary

adds support for aten.split operator

### Test plan

tests can be manually run using `pytest -c /dev/null
backends/nxp/tests/`

cc @robert-kalmar @JakeStevens @digantdesai @MartinPavella

Author: novak-vaclav

backends/nxp/aten_passes/decompose_split_to_slices_pass.py

@@ -0,0 +1,193 @@
+# Copyright 2026 NXP
+#
+# This source code is licensed under the BSD-style license found in the
+# LICENSE file in the root directory of this source tree.
+from typing import Optional, TypeAlias
+
+import torch
+from torch._subclasses import FakeTensor, FakeTensorMode
+from torch.fx import GraphModule, Node
+from torch.fx.passes.infra.pass_base import PassBase, PassResult
+
+
+class DecomposeSplitToSlicesPass(PassBase):
+    """
+      The `split` operator returns multiple tensors by partitioning `x` along `dim`. Each partitioning can be done
+      using one `slice` operator. Replacing the `split` operator with multiple `slice` operators will yield the same results.
+
+
+                                  │
+                    ┌─────────────▼─────────────┐
+                    │             x             │
+                    └─────────────┬─────────────┘
+                                  │
+            ┌─────────────────────▼─────────────────────┐
+            │     aten.split / aten.split_with_sizes    │
+            └─────────────────────┬─────────────────────┘
+                                  │
+             ┌────────────────────┼─────────────────────────┐
+             │                    │                         │
+    ┌────────▼────────┐  ┌────────▼────────┐       ┌────────▼────────┐
+    │    getitem(0)   │  │    getitem(1)   │  ...  │   getitem(N-1)  │
+    └────────┬────────┘  └────────┬────────┘       └────────┬────────┘
+             │                    │                         │
+             ▼                    ▼                         ▼
+            out0                 out1                    out(N-1)
+
+
+                                  |
+                                  |
+                             replace with
+                                  |
+                                  |
+                                  ▼
+
+
+                                  │
+                    ┌─────────────▼─────────────┐
+                    │             x             │
+                    └─────────────┬─────────────┘
+                                  │
+             ┌────────────────────┼─────────────────────────┐
+             │                    │                         │
+    ┌────────▼────────┐  ┌────────▼────────┐       ┌────────▼────────┐
+    │  aten.slice(x,  │  │  aten.slice(x,  │  ...  │  (more slices)  │
+    │    dim,s0,e0    │  │   dim,s1,e1)    │  ...  │                 │
+    └────────┬────────┘  └────────┬────────┘       └────────┬────────┘
+             │                    │                         │
+             │                    │                         │
+             ▼                    ▼                         ▼
+            out0                 out1                     outN-1
+
+    """
+
+    graph_module: GraphModule
+
+    @staticmethod
+    def _is_split_with_sizes(node: Node) -> bool:
+        return (
+            node.op == "call_function"
+            and node.target == torch.ops.aten.split_with_sizes.default
+        )
+
+    @staticmethod
+    def _is_regular_split(node: Node) -> bool:
+        is_split_tensor = (
+            node.op == "call_function" and node.target == torch.ops.aten.split.Tensor
+        )
+
+        is_split_default = (
+            node.op == "call_function" and node.target == torch.ops.aten.split.default
+        )
+
+        return is_split_tensor or is_split_default
+
+    def _create_slice_node(self, *slice_args) -> Node:
+        slice_target = torch.ops.aten.slice.Tensor
+        slice_node = self.graph_module.graph.call_function(slice_target, slice_args)
+
+        slice_node.meta["source_fn_stack"] = [
+            (slice_node.name, torch.ops.aten.slice.Tensor)
+        ]
+
+        with FakeTensorMode() as mode:
+            input_ = slice_args[0].meta["val"]
+
+            fake_input = FakeTensor.from_tensor(
+                torch.empty(input_.shape, dtype=input_.dtype), mode
+            )
+            output = slice_target(fake_input, *slice_args[1:])
+            slice_node.meta["val"] = FakeTensor.from_tensor(
+                torch.empty(output.shape, dtype=output.dtype), mode
+            )
+
+        return slice_node
+
+    SlicesArgs: TypeAlias = tuple[list[int], list[int], int]
+
+    def _get_slices_args(self, split_node: Node) -> SlicesArgs:
+        split_nodes_chunks = split_node.meta["val"]
+        dim = 0 if len(split_node.args) < 3 else split_node.args[2]
+
+        # Sometimes chunks are in tuples
+        if isinstance(split_nodes_chunks, tuple):
+            split_nodes_chunks = list(split_nodes_chunks)
+
+        if not isinstance(split_nodes_chunks, list):
+            raise RuntimeError("Faulty split chunks")
+
+        # Get slices start, end params
+        starts = []
+        ends = []
+
+        curr_start = 0
+        for s in split_nodes_chunks:
+            starts.append(curr_start)
+            ends.append(curr_start + s.shape[dim])
+            curr_start += s.shape[dim]
+
+        return starts, ends, dim
+
+    def _replace_split_with_slices(self, input_node, split_node, starts, ends, dim):
+        # Replace getitem nodes after split with slices
+        getitem_nodes = list(split_node.users.keys())
+        slice_nodes = []
+        for i in range(len(starts)):
+            slice_arguments = (input_node, dim, starts[i], ends[i])
+            with self.graph_module.graph.inserting_after(split_node):
+                slice_node = self._create_slice_node(*slice_arguments)
+                slice_nodes.append(slice_node)
+
+                getitem_node = getitem_nodes[i]
+                getitem_node.replace_all_uses_with(slice_node)
+
+                self.graph_module.graph.erase_node(getitem_node)
+
+        # Wire split node correctly to the input node
+        split_node.replace_all_uses_with(input_node)
+        self.graph_module.graph.erase_node(split_node)
+
+    def call(self, graph_module: GraphModule) -> Optional[PassResult]:
+        self.graph_module = graph_module
+        made_changes = False
+
+        if not any(map(self._is_regular_split, graph_module.graph.nodes)) and not any(
+            map(self._is_split_with_sizes, graph_module.graph.nodes)
+        ):
+            return PassResult(graph_module, made_changes)
+
+        for node in graph_module.graph.nodes:
+            # Skip if not split
+            is_split_with_sizes = self._is_split_with_sizes(node)
+            is_regular_split = self._is_regular_split(node)
+
+            if not is_split_with_sizes and not is_regular_split:
+                continue
+
+            # Get split args
+            split_node = node
+            input_node = split_node.all_input_nodes[0]
+            split_nodes_chunks = split_node.meta["val"]
+
+            # Check if split is even necessary - if not, remove it
+            if len(split_nodes_chunks) == 1:
+                getitem_node = list(split_node.users)[0]
+                getitem_node.replace_all_uses_with(input_node)
+
+                self.graph_module.graph.erase_node(getitem_node)
+                self.graph_module.graph.erase_node(split_node)
+
+                made_changes = True
+                continue
+
+            # Get arguments for the new slices
+            starts, ends, dim = self._get_slices_args(split_node)
+
+            # Replace split with slices and restructure the graph
+            self._replace_split_with_slices(input_node, split_node, starts, ends, dim)
+            made_changes = True
+
+        self.graph_module.recompile()
+        self.graph_module.graph.eliminate_dead_code()
+
+        return PassResult(self.graph_module, made_changes)

backends/nxp/aten_passes/neutron_aten_pass_manager.py

@@ -1,4 +1,4 @@
-# Copyright 2026 NXP
+# Copyright 2025-2026 NXP
 #
 # This source code is licensed under the BSD-style license found in the
 # LICENSE file in the root directory of this source tree.
@@ -10,6 +10,9 @@
 from executorch.backends.nxp.aten_passes.convert_unsqueeze_to_view import (
     ConvertUnsqueezeToViewPass,
 )
+from executorch.backends.nxp.aten_passes.decompose_split_to_slices_pass import (
+    DecomposeSplitToSlicesPass,
+)
 from executorch.backends.nxp.aten_passes.fuse_batch_norm_with_conv_pass import (
     FuseBatchNormWithConvPass,
 )
@@ -45,6 +48,7 @@ def __init__(
         self, neutron_target_spec: NeutronTargetSpec, passes: list[PassType] = None
     ):
         passes: list[PassType] = passes or [
+            DecomposeSplitToSlicesPass(),
             FuseBatchNormWithConvPass(),
             FuseBatchNormWithLinearPass(),
             SplitGroupConvolution(),

backends/nxp/tests/models.py

@@ -633,6 +633,38 @@ def forward(self, x):
         return self.activation(x)
 
 
+class GRUModel(nn.Module):
+    def __init__(self, num_layers=1):
+        super().__init__()
+        self.gru = torch.nn.GRU(8, 8, num_layers=num_layers)
+
+    def forward(self, input_):
+        # `input_` has shape [sequence_length, batch_size, input_size] ([8, 1, 8])
+        return self.gru(
+            input_, None
+        )  # The initial hidden is `None`, which will result in a `Zeros` node being added.
+
+
+class SplitWithSize(torch.nn.Module):
+    def __init__(self, split_size, dim):
+        super().__init__()
+        self.split_size = split_size
+        self.dim = dim
+
+    def forward(self, x: torch.Tensor) -> tuple[torch.Tensor]:
+        return torch.split(x, self.split_size, self.dim)
+
+
+class SplitWithSections(torch.nn.Module):
+    def __init__(self, sections, dim):
+        super().__init__()
+        self.sections = sections
+        self.dim = dim
+
+    def forward(self, x: torch.Tensor) -> tuple[torch.Tensor]:
+        return torch.split(x, self.sections, self.dim)
+
+
 class MiniConvNetWithRegressionHead(torch.nn.Module):
     def __init__(self):
         super().__init__()