[ExecuTorch][WebGPU] sigmoid op test suite (cases.py op-test framework) (#20391)

Stack from [ghstack](https://github.com/ezyang/ghstack/tree/0.15.0)
(oldest at bottom):
* #20465
* #20464
* #20463
* #20435
* #20399
* #20398
* #20397
* #20396
* #20395
* #20394
* #20393
* #20392
* __->__ #20391
* #20390
* #20363
* #20362
* #20361
* #20360
* #20359



Registers `aten.sigmoid.default` in the `cases.py` op-test framework: a
`_sigmoid_suite` (hard-coded shapes + a saturation case over a
`linspace(-12, 12)` input) that `generate_op_tests` exports and compares
to an fp64 torch golden on Dawn. Also adds
`test/ops/sigmoid/test_sigmoid.py` (`SigmoidModule` + `N` + `_det_input`
+ an export-delegation/eager smoke test) and the `aten.sigmoid.default`
partitioner-allowlist entry in `tester.py`.
@exported-using-ghexport

Differential Revision:
[D108793159](https://our.internmc.facebook.com/intern/diff/D108793159/)

Differential Revision:
[D108793159](https://our.internmc.facebook.com/intern/diff/D108793159)

Author: JCNTH

backends/webgpu/test/op_tests/cases.py

@@ -44,6 +44,11 @@
     CONFIGS as _SELECT_CONFIGS,
     SelectModule,
 )
+from executorch.backends.webgpu.test.ops.test_sigmoid import (
+    _det_input as _sigmoid_det_input,
+    N as _SIGMOID_N,
+    SigmoidModule,
+)
 from executorch.backends.webgpu.test.ops.test_view_copy import (
     CONFIGS as _VIEW_CONFIGS,
     ViewModule,
@@ -153,3 +158,29 @@ def _view_copy_suite() -> WebGPUTestSuite:
 @register_op_test("select")
 def _select_suite() -> WebGPUTestSuite:
     return _fn_config_suite(SelectModule, _SELECT_CONFIGS)
+
+
+def _sigmoid_full_range(_shape) -> torch.Tensor:
+    # Reuses the monolith's saturation-tail input (linspace(-12, 12)).
+    return _sigmoid_det_input()
+
+
+@register_op_test("sigmoid")
+def _sigmoid_suite() -> WebGPUTestSuite:
+    # sigmoid has no CONFIGS table; cover unary shapes directly (tol 1e-4).
+    return WebGPUTestSuite(
+        module_factory=lambda: SigmoidModule(),
+        cases=[
+            Case(name="vec", inputs=((M1,),)),
+            Case(name="mat", inputs=((M1, M2),)),
+            Case(name="rank3", inputs=((S1, M1, M2),)),
+            Case(name="rank4", inputs=((S1, S2, S2, M2),)),
+            # Saturation tails sigmoid(+-12) (~6e-6 / 0.999994) that randn shapes miss.
+            Case(
+                name="saturation",
+                inputs=(InputSpec(shape=(_SIGMOID_N,), gen=_sigmoid_full_range),),
+            ),
+        ],
+        atol=1e-4,
+        rtol=1e-4,
+    )

backends/webgpu/test/ops/test_sigmoid.py

@@ -0,0 +1,51 @@
+# Copyright (c) Meta Platforms, Inc. and affiliates.
+# All rights reserved.
+#
+# This source code is licensed under the BSD-style license found in the
+# LICENSE file in the root directory of this source tree.
+
+"""`aten.sigmoid.default` module + input for the WebGPU op-test framework.
+
+`SigmoidModule`, `N`, and `_det_input` are imported by `cases.py` to drive the
+declarative op-test suite. `SigmoidTest` is the export-delegation
+smoke test. Sigmoid is on the Llama critical path (`F.silu` -> `sigmoid` + `mul`); the
+deterministic input spans the saturation tails.
+"""
+
+import unittest
+
+import torch
+
+from executorch.backends.vulkan.partitioner.vulkan_partitioner import VulkanPartitioner
+from executorch.exir import to_edge_transform_and_lower
+
+# Input length; the deterministic input spans the saturation tails.
+N = 64
+
+
+class SigmoidModule(torch.nn.Module):
+    def forward(self, x: torch.Tensor) -> torch.Tensor:
+        return torch.sigmoid(x)
+
+
+def _det_input() -> torch.Tensor:
+    """Deterministic fp32 input spanning negatives, zero, and large magnitudes."""
+    return torch.linspace(-12.0, 12.0, N, dtype=torch.float32)
+
+
+def _export(m: torch.nn.Module, x: torch.Tensor):
+    ep = torch.export.export(m, (x,))
+    return to_edge_transform_and_lower(
+        ep, partitioner=[VulkanPartitioner()]
+    ).to_executorch()
+
+
+class SigmoidTest(unittest.TestCase):
+    def test_export_delegates(self) -> None:
+        et = _export(SigmoidModule().eval(), _det_input())
+        found = any(
+            d.id == "VulkanBackend"
+            for plan in et.executorch_program.execution_plan
+            for d in plan.delegates
+        )
+        self.assertTrue(found, "Expected a VulkanBackend delegate (sigmoid)")

backends/webgpu/test/tester.py

@@ -24,6 +24,7 @@
     exir_ops.edge.aten.mul.Tensor,
     exir_ops.edge.aten.view_copy.default,
     exir_ops.edge.aten.select_copy.int,
+    exir_ops.edge.aten.sigmoid.default,
 ]