Arm backend: Add sign decomposition pass and test

backends/arm/_passes/__init__.py

@@ -41,6 +41,7 @@
 from .decompose_ne_pass import DecomposeNotEqualPass  # noqa
 from .decompose_round_pass import DecomposeRoundPass  # noqa
 from .decompose_select import DecomposeSelectPass  # noqa
+from .decompose_sign_pass import DecomposeSignPass  # noqa
 from .decompose_silu_pass import DecomposeSiluPass  # noqa
 from .decompose_sinh_pass import DecomposeSinhPass  # noqa
 from .decompose_softmax_pass import DecomposeSoftmaxPass  # noqa

backends/arm/_passes/arm_pass_manager.py

@@ -44,6 +44,7 @@
     DecomposeNotEqualPass,
     DecomposeRoundPass,
     DecomposeSelectPass,
+    DecomposeSignPass,
     DecomposeSiluPass,
     DecomposeSinhPass,
     DecomposeSoftmaxPass,
@@ -158,6 +159,7 @@ def _tosa_080_MI_pipeline(self, exported_program: ExportedProgram) -> GraphModul
         self.add_pass(ConvertIntPowToMuls())
         self.add_pass(CastBoolToInt8Pass())
         self.add_pass(DecomposeSinhPass())
+        self.add_pass(DecomposeSignPass())
         self.add_pass(ReplaceScalarWithTensorArgPassTOSAMI())
         self.add_pass(DecomposeEmbeddingPass())
         self.add_pass(FuseQuantizedActivationPass())
@@ -242,6 +244,7 @@ def transform_for_annotation_pipeline(self, graph_module: GraphModule):
         self.add_pass(DecomposeScaledDotProductAttention())
         self.add_pass(DecomposeRoundPass())
         self.add_pass(CastBoolToInt8Pass())
+        self.add_pass(DecomposeSignPass())
         self.add_pass(ReplaceScalarWithTensorArgPassTOSABI())
         self.add_pass(ScalarsToAttributePass())
         self.add_pass(DecomposeGroupNormPass())

backends/arm/_passes/decompose_sign_pass.py

@@ -0,0 +1,73 @@
+# 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.
+
+import torch
+
+from executorch.backends.arm._passes import ArmPass
+from executorch.exir.dialects._ops import ops as exir_ops
+
+
+# For MI case
+edge_sign = exir_ops.edge.aten.sign.default
+# For BI case
+aten_sign = torch.ops.aten.sign.default
+
+
+def get_ops(op):
+    """Returns the appropriate operator functions based on the input operator."""
+    if op == edge_sign:
+        return (
+            exir_ops.edge.aten.gt.Scalar,
+            exir_ops.edge.aten.lt.Scalar,
+            exir_ops.edge.aten.where.self,
+            exir_ops.edge.aten.neg.default,
+            exir_ops.edge.aten.mul.Scalar,
+            exir_ops.edge.aten.add.Scalar,
+        )
+    elif op == aten_sign:
+        return (
+            torch.ops.aten.gt.Scalar,
+            torch.ops.aten.lt.Scalar,
+            torch.ops.aten.where.self,
+            torch.ops.aten.neg.default,
+            torch.ops.aten.mul.Scalar,
+            torch.ops.aten.add.Scalar,
+        )
+    else:
+        raise ValueError(f"Unsupported operator: {op}")
+
+
+class DecomposeSignPass(ArmPass):
+    """Decomposes the sign operator into a sequence of operations that are supported by the Arm backend."""
+
+    def call_operator(self, op, args, kwargs, meta):
+        if op not in (edge_sign, aten_sign):
+            return super().call_operator(op, args, kwargs, meta)
+
+        gt_op, lt_op, where_op, neg_op, mul_op, add_op = get_ops(op)
+
+        x = args[0]
+
+        gt_mask = super().call_operator(gt_op, (x, 0.0), {}, meta, updated=True)
+        lt_mask = super().call_operator(lt_op, (x, 0.0), {}, meta, updated=True)
+
+        zeros = super().call_operator(mul_op, (x, 0.0), {}, meta, updated=True)
+        ones = super().call_operator(add_op, (zeros, 1.0), {}, meta, updated=True)
+        neg_ones = super().call_operator(neg_op, (ones,), {}, meta, updated=True)
+
+        negative_tensor = super().call_operator(
+            where_op, (lt_mask, neg_ones, zeros), {}, meta, updated=True
+        )
+        positive_tensor = super().call_operator(
+            where_op, (gt_mask, ones, zeros), {}, meta, updated=True
+        )
+
+        return super().call_operator(
+            where_op,
+            (lt_mask, negative_tensor, positive_tensor),
+            {},
+            meta,
+            updated=True,
+        )

backends/arm/operator_support/tosa_supported_operators.py

@@ -249,6 +249,7 @@ def is_node_supported(
             exir_ops.edge.aten.sinh.default,
             exir_ops.edge.aten.atan.default,
             exir_ops.edge.aten.acosh.default,
+            exir_ops.edge.aten.sign.default,
         ]
 
         return supported

backends/arm/quantizer/quantization_annotator.py

@@ -216,6 +216,7 @@ def _match_pattern(
     torch.ops.aten.sinh.default,
     torch.ops.aten.atan.default,
     torch.ops.aten.acosh.default,
+    torch.ops.aten.sign.default,
 ]
 
 _one_to_one_shared_input_qspec = [

backends/arm/test/ops/test_sign.py

@@ -0,0 +1,86 @@
+# 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 pytest
+import torch
+from executorch.backends.arm.test import common
+from executorch.backends.arm.test.tester.test_pipeline import (
+    EthosU55PipelineBI,
+    EthosU85PipelineBI,
+    TosaPipelineBI,
+    TosaPipelineMI,
+)
+
+aten_op = "torch.ops.aten.sign.default"
+exir_op = "executorch_exir_dialects_edge__ops_aten__sign_default"
+
+input_t1 = Tuple[torch.Tensor]
+
+test_data_suite = {
+    "zeros": torch.zeros(3, 5),
+    "ones": torch.ones(4, 4),
+    "neg_ones": -torch.ones(4, 4),
+    "mixed_signs": torch.tensor([[-2.0, -1.0, 0.0, 1.0, 2.0]]),
+    "positive_ramp": torch.arange(0.1, 1.1, 0.2),
+    "negative_ramp": torch.arange(-1.0, -0.1, 0.2),
+    "small_values": torch.tensor([-1e-7, 0.0, 1e-7]),
+    "rand": torch.rand(10, 10) - 0.5,
+    "rand_alt_shape": torch.rand(10, 3, 5) - 0.5,
+    "high_magnitude": torch.tensor([-1e6, -10.0, 0.0, 10.0, 1e6]),
+}
+
+
+class Sign(torch.nn.Module):
+    def forward(self, x: torch.Tensor):
+        return torch.sign(x)
+
+
+@common.parametrize("test_data", test_data_suite)
+def test_sign_tosa_MI(test_data: Tuple):
+    pipeline = TosaPipelineMI[input_t1](
+        Sign(),
+        (test_data,),
+        aten_op=aten_op,
+        exir_op=exir_op,
+    )
+    pipeline.run()
+
+
+@common.parametrize("test_data", test_data_suite)
+def test_sign_tosa_BI(test_data: Tuple):
+    pipeline = TosaPipelineBI[input_t1](
+        Sign(),
+        (test_data,),
+        aten_op=[],
+        exir_op=exir_op,
+    )
+    pipeline.run()
+
+
+@common.XfailIfNoCorstone300
+@common.parametrize("test_data", test_data_suite)
+@pytest.mark.xfail(reason="where.self not supported on U55")
+def test_sign_u55_BI(test_data: Tuple):
+    pipeline = EthosU55PipelineBI[input_t1](
+        Sign(),
+        (test_data,),
+        aten_ops=[],
+        exir_ops=exir_op,
+    )
+    pipeline.run()
+
+
+@common.XfailIfNoCorstone320
+@common.parametrize("test_data", test_data_suite)
+def test_sign_u85_BI(test_data: Tuple):
+    pipeline = EthosU85PipelineBI[input_t1](
+        Sign(),
+        (test_data,),
+        aten_ops=[],
+        exir_ops=exir_op,
+    )
+    pipeline.run()