[AOT] Add AOTLowerMain pass to lower a Relay main into TIR

This is a pass refactored out of the AOTExecutorCodegen. Instead of
combining all of the functionality of the AOTExecutorCodegen into a
single monolithic pass, this pass only handles the lowering of the
Relay main function into TIR. Tests for the pass are included.

CMakeLists.txt

@@ -305,6 +305,7 @@ tvm_file_glob(GLOB_RECURSE RELAY_PASS_SRCS
 tvm_file_glob(GLOB RELAY_BACKEND_SRCS
     src/relay/backend/*.cc
     src/relay/backend/vm/*.cc
+    src/relay/backend/aot/*.cc
     )
 tvm_file_glob(GLOB_RECURSE RELAY_IR_SRCS
     src/relay/ir/*.cc

python/tvm/relay/backend/_aot.py

@@ -0,0 +1,21 @@
+# Licensed to the Apache Software Foundation (ASF) under one
+# or more contributor license agreements.  See the NOTICE file
+# distributed with this work for additional information
+# regarding copyright ownership.  The ASF licenses this file
+# to you under the Apache License, Version 2.0 (the
+# "License"); you may not use this file except in compliance
+# with the License.  You may obtain a copy of the License at
+#
+#   http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing,
+# software distributed under the License is distributed on an
+# "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+# KIND, either express or implied.  See the License for the
+# specific language governing permissions and limitations
+# under the License.
+"""The AOT FFI namespace.
+"""
+import tvm._ffi
+
+tvm._ffi._init_api("relay.backend.aot", __name__)

python/tvm/relay/backend/aot.py

@@ -0,0 +1,43 @@
+# Licensed to the Apache Software Foundation (ASF) under one
+# or more contributor license agreements.  See the NOTICE file
+# distributed with this work for additional information
+# regarding copyright ownership.  The ASF licenses this file
+# to you under the Apache License, Version 2.0 (the
+# "License"); you may not use this file except in compliance
+# with the License.  You may obtain a copy of the License at
+#
+#   http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing,
+# software distributed under the License is distributed on an
+# "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+# KIND, either express or implied.  See the License for the
+# specific language governing permissions and limitations
+# under the License.
+# pylint: disable=invalid-name
+"""AOT passes"""
+from tvm.ir.transform import Pass
+from .utils import CallType
+
+from . import _aot
+
+
+def AOTLowerMain(mod_name: str, config: object, call_type: CallType) -> Pass:
+    """Lower a Relay main function into an AOT TIR main function.
+
+    Parameters
+    ----------
+    mod_name: str
+        The name of the module.
+    config : CompilationConfig
+        The compilation configuration.
+    call_type : CallType
+        The calling convention to use.
+
+    Returns
+    -------
+    Pass
+        The AOTLowerMain pass.
+
+    """
+    return _aot.AOTLowerMain(mod_name, config, call_type.value)

python/tvm/relay/backend/utils.py

@@ -15,6 +15,13 @@
 # specific language governing permissions and limitations
 # under the License.
 """Utility backend functions."""
+from enum import Enum
+
+
+class CallType(Enum):
+    Packed = 0
+    CPacked = 1
+    Unpacked = 2
 
 
 def _is_valid_modname(mod_name):