Arm Backend: Add tests for stack.default (#14623)

Stack is not in the list of core ATen ops and is decomposed
automatically when lowering the graph
(https://docs.pytorch.org/docs/main/export.html#export-ir-decompositions),
so only the tests need to be added.

stack is in this decomp table:
https://github.com/pytorch/pytorch/blob/5d749ceb92c2c28bcfbdf918b4ab99b1a91fcb50/torch/_decomp/__init__.py#L466


Signed-off-by: Agrima Khare <[email protected]>

Author: agrima1304

backends/arm/test/ops/test_stack.py

@@ -0,0 +1,150 @@
+# Copyright 2025 Arm Limited and/or its affiliates.
+#
+# 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 Tuple
+
+import torch
+import torch.nn as nn
+
+from executorch.backends.arm.test import common
+from executorch.backends.arm.test.tester.test_pipeline import (
+    EthosU55PipelineINT,
+    EthosU85PipelineINT,
+    TosaPipelineFP,
+    TosaPipelineINT,
+    VgfPipeline,
+)
+
+test_data_suite = {
+    # (test_name, test_data)
+    "ones_two_tensors": lambda: ((torch.ones(1), torch.ones(1)), 0),
+    "ones_and_rand_three_tensors": lambda: (
+        (torch.ones(1, 2), torch.randn(1, 2), torch.randn(1, 2)),
+        1,
+    ),
+    "ones_and_rand_four_tensors": lambda: (
+        (
+            torch.ones(1, 2, 5),
+            torch.randn(1, 2, 5),
+            torch.randn(1, 2, 5),
+            torch.randn(1, 2, 5),
+        ),
+        -1,
+    ),
+    "rand_two_tensors": lambda: (
+        (torch.randn(2, 2, 4), torch.randn(2, 2, 4)),
+        2,
+    ),
+    "rand_two_tensors_dim_0": lambda: (
+        (torch.randn(1, 2, 4, 4), torch.randn(1, 2, 4, 4)),
+    ),
+    "rand_two_tensors_dim_2": lambda: (
+        (torch.randn(2, 2, 3, 5), torch.randn(2, 2, 3, 5)),
+        2,
+    ),
+    "rand_large": lambda: (
+        (
+            10000 * torch.randn(2, 3, 1, 4),
+            torch.randn(2, 3, 1, 4),
+            torch.randn(2, 3, 1, 4),
+        ),
+        -3,
+    ),
+}
+
+
+class Stack(nn.Module):
+    aten_op = "torch.ops.aten.stack.default"
+    exir_op = "executorch_exir_dialects_edge__ops_aten_cat_default"
+
+    def forward(self, n: tuple[torch.Tensor, ...], dim: int = 0):
+        return torch.stack(n, dim)
+
+
+input_t1 = Tuple[torch.Tensor]
+
+
+@common.parametrize("test_module", test_data_suite)
+def test_stack_tosa_FP(test_module: input_t1):
+    test_data = test_module()
+    pipeline = TosaPipelineFP[input_t1](
+        Stack(),
+        test_data,
+        aten_op=Stack.aten_op,
+        exir_op=Stack.exir_op,
+        use_to_edge_transform_and_lower=False,
+    )
+    pipeline.run()
+
+
+@common.parametrize("test_module", test_data_suite)
+def test_stack_tosa_INT(test_module: input_t1):
+    test_data = test_module()
+    pipeline = TosaPipelineINT[input_t1](
+        Stack(),
+        test_data,
+        aten_op=Stack.aten_op,
+        exir_op=Stack.exir_op,
+        use_to_edge_transform_and_lower=False,
+    )
+    pipeline.run()
+
+
+@common.XfailIfNoCorstone300
+@common.parametrize("test_module", test_data_suite)
+def test_stack_u55_INT(test_module: input_t1):
+    test_data = test_module()
+    pipeline = EthosU55PipelineINT[input_t1](
+        Stack(),
+        test_data,
+        aten_ops=Stack.aten_op,
+        exir_ops=Stack.exir_op,
+        use_to_edge_transform_and_lower=False,
+    )
+    pipeline.run()
+
+
+@common.XfailIfNoCorstone320
+@common.parametrize("test_module", test_data_suite)
+def test_stack_u85_INT(test_module: input_t1):
+    test_data = test_module()
+    pipeline = EthosU85PipelineINT[input_t1](
+        Stack(),
+        test_data,
+        aten_ops=Stack.aten_op,
+        exir_ops=Stack.exir_op,
+        use_to_edge_transform_and_lower=False,
+    )
+    pipeline.run()
+
+
+@common.SkipIfNoModelConverter
+@common.parametrize("test_module", test_data_suite)
+def test_stack_vgf_FP(test_module: input_t1):
+    test_data = test_module()
+    pipeline = VgfPipeline[input_t1](
+        Stack(),
+        test_data,
+        aten_op=Stack.aten_op,
+        exir_op=Stack.exir_op,
+        tosa_version="TOSA-1.0+FP",
+        use_to_edge_transform_and_lower=False,
+    )
+    pipeline.run()
+
+
+@common.SkipIfNoModelConverter
+@common.parametrize("test_module", test_data_suite)
+def test_stack_vgf_INT(test_module: input_t1):
+    test_data = test_module()
+    pipeline = VgfPipeline[input_t1](
+        Stack(),
+        test_data,
+        aten_op=Stack.aten_op,
+        exir_op=Stack.exir_op,
+        tosa_version="TOSA-1.0+INT",
+        use_to_edge_transform_and_lower=False,
+    )
+    pipeline.run()