Stop reading a backend config field that no longer exists

examples/models/llama/export_llama_lib.py

@@ -1805,9 +1805,7 @@ def _export_llama(llm_config: LlmConfig) -> LLMEdgeManager:  # noqa: C901
             verbose=llm_config.debug.verbose,
         )
     elif llm_config.backend.coreml.enabled and not (
-        llm_config.backend.vulkan.enabled
-        or llm_config.backend.mps.enabled
-        or llm_config.backend.qnn.enabled
+        llm_config.backend.vulkan.enabled or llm_config.backend.qnn.enabled
     ):
         builder = _to_edge_and_lower_llama_coreml(
             builder_exported,

examples/models/llama/tests/test_export_llama_lib.py

@@ -6,6 +6,7 @@
 # LICENSE file in the root directory of this source tree.
 
 import unittest
+from unittest.mock import patch
 
 from executorch.devtools.backend_debug import get_delegation_info
 
@@ -41,6 +42,36 @@
 
 
 class ExportLlamaLibTest(unittest.TestCase):
+    def _assert_export_reaches(self, target, **backends):
+        """Run an export and assert which lowering it routes to."""
+        llm_config = LlmConfig()
+        llm_config.backend.coreml.enabled = True
+        for name, enabled in backends.items():
+            getattr(llm_config.backend, name).enabled = enabled
+        # Core ML and QNN reject dynamic shapes, and _validate_args runs before the lowering.
+        llm_config.model.enable_dynamic_shape = False
+
+        with patch(
+            f"executorch.examples.models.llama.export_llama_lib.{target}",
+            side_effect=RuntimeError("reached"),
+        ) as lowering:
+            with self.assertRaises(RuntimeError):
+                _export_llama(llm_config)
+        lowering.assert_called_once()
+
+    def test_core_ml_alone_reaches_the_core_ml_lowering(self):
+        """The guard used to read a backend config field that no longer existed, so this raised
+        AttributeError before reaching any lowering."""
+        self._assert_export_reaches("_to_edge_and_lower_llama_coreml")
+
+    def test_core_ml_with_qnn_reaches_the_combined_lowering(self):
+        """The other case the removed read broke, and the one that pins the exclusion clause.
+
+        Core ML with QNN must fall through to the combined lowering, which still lowers Core ML but
+        keeps the QNN partitioner. Without this, deleting the whole clause passes.
+        """
+        self._assert_export_reaches("_to_edge_and_lower_llama", qnn=True)
+
     def test_has_expected_ops_and_op_counts(self):
         """
         Checks the presence of unwanted expensive ops.