Add more fusion test-cases (part 1) (#2896)

Add more unit test cases for fusion rules. (Currently, these are tested
via real-world models in the benchmark-suite elsewhere, but unit tests
are missing for various fusions.)

* Erfgelu fusion
* MHA-Bias fusion
* MHA-Scale fusion
* RmsNormalization fusion
* MHA fusion
* Rotary Embedding
* Skip Norm
* Layer Norm

---------

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: gramalingam

onnxscript/rewriter/ort_fusions/erfgelu_test.py

@@ -0,0 +1,143 @@
+# Copyright (c) Microsoft Corporation.
+# Licensed under the MIT License.
+
+import math
+import unittest
+
+import numpy as np
+import onnx_ir as ir
+
+import onnxscript.rewriter.ort_fusions._test_utils as test_utils
+from onnxscript import FLOAT, script
+from onnxscript import opset18 as op
+from onnxscript.optimizer import optimize, remove_unused_nodes
+from onnxscript.rewriter.ort_fusions.erfgelu import fuse_erfgelu
+
+_SQRT_TWO = math.sqrt(2.0)
+
+
+class ErfGeluFusionTest(unittest.TestCase):
+    """Tests for erf-based GELU fusion patterns in erfgelu.py.
+
+    Pattern 1: 0.5 * (x * (erf(x / sqrt(2)) + 1))
+    Pattern 2: x * (0.5 * (erf(x / sqrt(2)) + 1))
+    """
+
+    def _check_fusion(self, model, input):
+        original_output = test_utils.ort_run("Original", model, input)
+        fuse_erfgelu(model)
+        remove_unused_nodes(model)
+        self.assertEqual(len(model.graph), 1)
+        self.assertEqual(model.graph.node(0).op_type, "Gelu")
+        self.assertEqual(model.graph.node(0).domain, "com.microsoft")
+        optimized_output = test_utils.ort_run("Optimized", model, input)
+        test_utils.assert_allclose(original_output, optimized_output)
+
+    def _check_no_fusion(self, model):
+        node_count_before = len(model.graph)
+        fuse_erfgelu(model)
+        remove_unused_nodes(model)
+        self.assertEqual(len(model.graph), node_count_before)
+        self.assertTrue(
+            all(node.op_type != "Gelu" for node in model.graph),
+            "Gelu node should not be present after failed fusion",
+        )
+
+    def _build_model(self, script_fn, shape):
+        model_proto = script_fn.to_model_proto(
+            input_types=[FLOAT[shape]], output_types=[FLOAT[shape]]
+        )
+        model = ir.serde.deserialize_model(model_proto)
+        optimize(model)
+        return model
+
+    def test_pattern1_half_times_x_times_erf_plus_one(self):
+        """Pattern 1: 0.5 * (x * (erf(x / sqrt(2)) + 1))"""
+
+        @script()
+        def erf_gelu_p1(x):
+            t1 = op.Div(x, _SQRT_TWO)
+            t2 = op.Erf(t1)
+            t3 = op.Add(t2, 1.0)
+            t4 = op.Mul(x, t3)
+            return op.Mul(0.5, t4)
+
+        model = self._build_model(erf_gelu_p1, 10)
+        input = {"x": np.random.randn(10).astype(np.float32)}
+        self._check_fusion(model, input)
+
+    def test_pattern2_x_times_half_times_erf_plus_one(self):
+        """Pattern 2: x * (0.5 * (erf(x / sqrt(2)) + 1))"""
+
+        @script()
+        def erf_gelu_p2(x):
+            t1 = op.Div(x, _SQRT_TWO)
+            t2 = op.Erf(t1)
+            t3 = op.Add(t2, 1.0)
+            t4 = op.Mul(0.5, t3)
+            return op.Mul(x, t4)
+
+        model = self._build_model(erf_gelu_p2, 10)
+        input = {"x": np.random.randn(10).astype(np.float32)}
+        self._check_fusion(model, input)
+
+    def test_multidimensional_input(self):
+        """Verify fusion works with 3D inputs (batch, seq, hidden)."""
+
+        @script()
+        def erf_gelu_3d(x):
+            t1 = op.Div(x, _SQRT_TWO)
+            t2 = op.Erf(t1)
+            t3 = op.Add(t2, 1.0)
+            t4 = op.Mul(x, t3)
+            return op.Mul(0.5, t4)
+
+        model = self._build_model(erf_gelu_3d, (2, 4, 8))
+        input = {"x": np.random.randn(2, 4, 8).astype(np.float32)}
+        self._check_fusion(model, input)
+
+    def test_no_fusion_without_erf(self):
+        """Replacing Erf with Tanh should not match the erf-gelu pattern."""
+
+        @script()
+        def not_erf_gelu(x):
+            t1 = op.Div(x, _SQRT_TWO)
+            t2 = op.Tanh(t1)
+            t3 = op.Add(t2, 1.0)
+            t4 = op.Mul(x, t3)
+            return op.Mul(0.5, t4)
+
+        model = self._build_model(not_erf_gelu, 10)
+        self._check_no_fusion(model)
+
+    def test_no_fusion_wrong_divisor(self):
+        """Using a divisor other than sqrt(2) should not match."""
+
+        @script()
+        def wrong_divisor(x):
+            t1 = op.Div(x, 2.0)
+            t2 = op.Erf(t1)
+            t3 = op.Add(t2, 1.0)
+            t4 = op.Mul(x, t3)
+            return op.Mul(0.5, t4)
+
+        model = self._build_model(wrong_divisor, 10)
+        self._check_no_fusion(model)
+
+    def test_no_fusion_wrong_scale(self):
+        """Using 0.3 instead of 0.5 should not match."""
+
+        @script()
+        def wrong_scale(x):
+            t1 = op.Div(x, _SQRT_TWO)
+            t2 = op.Erf(t1)
+            t3 = op.Add(t2, 1.0)
+            t4 = op.Mul(x, t3)
+            return op.Mul(0.3, t4)
+
+        model = self._build_model(wrong_scale, 10)
+        self._check_no_fusion(model)
+
+
+if __name__ == "__main__":
+    unittest.main()