Add export_llama performance regression test using expected ops (#9158)

### Summary
Add a proxy for an `export_llama` performance regression test by
comparing the ops in the graph before and after the PR. The export
happens without loading a checkpoint or params file, which means that
all of the base `ModelArgs` values for `llama_transformer` will be used.

### Test plan
N/A

Author: jackzhxng

examples/models/llama/model.py

@@ -178,7 +178,7 @@ def __init__(self, **kwargs):
             if checkpoint:
                 self.model_.checkpoint_dtype = get_checkpoint_dtype(checkpoint)
             else:
-                self.model_.checkpoint_dtype = None
+                self.model_.checkpoint_dtype = torch.float32
 
         if "int8" in str(checkpoint_path):
             print("Using int8 weight-only quantization!")

examples/models/llama/model_args.py

@@ -5,7 +5,7 @@
 @dataclass
 class ModelArgs:
     dim: int = 4096
-    n_layers: int = 32
+    n_layers: int = 8
     n_heads: int = 32
     n_kv_heads: Optional[int] = None
     vocab_size: int = 512  # Arbitrary value, should be defined later by tokenizer.

examples/models/llama/tests/test_export_llama_lib.py

@@ -0,0 +1,48 @@
+# 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.
+
+import unittest
+
+from executorch.devtools.backend_debug import get_delegation_info
+from executorch.examples.models.llama.export_llama_lib import (
+    _export_llama,
+    build_args_parser,
+)
+
+UNWANTED_OPS = [
+    "aten_permute_copy_default",
+    "aten_transpose_copy_default",
+]
+
+
+class ExportLlamaLibTest(unittest.TestCase):
+    def test_has_expected_ops_and_op_counts(self):
+        """
+        Checks the presence of unwanted expensive ops.
+
+        Serves as a proxy for a performance regression test, as performance
+        is directly tied to which and how many of each ops are in the graph.
+
+        If this test breaks, please ensure that the difference in ops
+        is intentional before updating the expected ops.
+        """
+        # Since we aren't loading a checkpoint, it doesn't
+        # matter what model we specify. Note that
+        # we cannot test quantization args in this way
+        # since quantization requires promoting meta tensors
+        # to device=cpu, which requires real weights.
+        parser = build_args_parser()
+        args = parser.parse_args([])
+        args.use_sdpa_with_kv_cache = True
+        args.use_kv_cache = True
+        args.verbose = True
+
+        builder = _export_llama(args)
+        graph_module = builder.edge_manager.exported_program().graph_module
+        delegation_info = get_delegation_info(graph_module)
+
+        for op, _op_info in delegation_info.delegation_by_operator.items():
+            self.assertTrue(op not in UNWANTED_OPS)

examples/models/llava/model.py

@@ -56,6 +56,7 @@ def __init__(
         )
         self.text_model_args = ModelArgs(
             use_kv_cache=True,
+            n_layers=32,
             vocab_size=self.model_.config.text_config.vocab_size,
             hidden_dim=self.model_.config.text_config.intermediate_size,
             max_batch_size=1,  # doesn't work with default batch size 32