Add hello world codegen example (#2163)

This PR adds a codegen inference example for the hello world model to demonstrate how to invoke the code generator and build the generated source. For now, we're just checking the generated source into the repo to skip over building out the make rules and also ensuring the generated source complies with formatting rules.

This also fixes a minor formatting issue in the source templates, as clang-format now properly complained about it.

BUG=b/295390000

codegen/examples/hello_world/Makefile.inc

@@ -0,0 +1,10 @@
+CODEGEN_HELLO_WORLD_SRCS := \
+$(TENSORFLOW_ROOT)codegen/examples/hello_world/hello_world.cc \
+$(TENSORFLOW_ROOT)codegen/examples/hello_world/hello_world_model.cc
+
+CODEGEN_HELLO_WORLD_HDRS := \
+$(TENSORFLOW_ROOT)codegen/examples/hello_world/hello_world_model.h
+
+# Builds a standalone binary.
+$(eval $(call microlite_test,codegen_hello_world,\
+$(CODEGEN_HELLO_WORLD_SRCS),,))

codegen/examples/hello_world/README.md

@@ -0,0 +1,18 @@
+# Codegen Hello World Example
+
+This is a code-generated example of the hello world model.
+
+To generate the inference code at `codegen/example/hello_world_model.h/.cc`:
+
+```
+bazel run codegen:code_generator -- \
+  --model $(pwd)/tensorflow/lite/micro/examples/hello_world/models/hello_world_int8.tflite \
+  --output_dir $(pwd)/codegen/examples/hello_world \
+  --output_name hello_world_model
+```
+
+To compile the generated source, you can use the Makefile:
+
+```
+make -f tensorflow/lite/micro/tools/make/Makefile codegen_hello_world
+```

codegen/examples/hello_world/hello_world.cc

@@ -0,0 +1,22 @@
+/* Copyright 2023 The TensorFlow Authors. All Rights Reserved.
+
+Licensed 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.
+==============================================================================*/
+
+#include "hello_world_model.h"
+
+int main(int argc, char** argv) {
+  hello_world_model::Invoke();
+
+  return 0;
+}

codegen/examples/hello_world/hello_world_model.cc

@@ -0,0 +1,24 @@
+/* Copyright 2023 The TensorFlow Authors. All Rights Reserved.
+
+Licensed 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.
+==============================================================================*/
+
+/* AUTOMATICALLY GENERATED DO NOT MODIFY */
+
+#include "hello_world_model.h"
+
+namespace hello_world_model {
+
+void Invoke() {}
+
+}  // namespace hello_world_model

codegen/examples/hello_world/hello_world_model.h

@@ -0,0 +1,24 @@
+/* Copyright 2023 The TensorFlow Authors. All Rights Reserved.
+
+Licensed 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.
+==============================================================================*/
+
+/* AUTOMATICALLY GENERATED DO NOT MODIFY */
+
+#pragma once
+
+namespace hello_world_model {
+
+void Invoke();
+
+}  // namespace hello_world_model

codegen/templates/inference.cc.mako

@@ -21,4 +21,4 @@ namespace ${model_name} {
 
 void Invoke() {}
 
-} // ${model_name}
+}  // namespace ${model_name}

codegen/templates/inference.h.mako

@@ -21,4 +21,4 @@ namespace ${model_name} {
 
 void Invoke();
 
-} // ${model_name}
+}  // namespace ${model_name}

tensorflow/lite/micro/tools/make/Makefile

@@ -287,6 +287,8 @@ MICRO_LITE_BENCHMARKS := $(wildcard $(TENSORFLOW_ROOT)tensorflow/lite/micro/tool
 MICROLITE_BENCHMARK_SRCS := \
 $(wildcard $(TENSORFLOW_ROOT)tensorflow/lite/micro/tools/benchmarking/*benchmark.cc)
 
+MICRO_LITE_CODEGEN_EXAMPLES := $(shell find $(TENSORFLOW_ROOT)codegen/examples/ -name Makefile.inc)
+
 MICROLITE_TEST_SRCS := \
 $(TENSORFLOW_ROOT)tensorflow/lite/micro/fake_micro_context_test.cc \
 $(TENSORFLOW_ROOT)tensorflow/lite/micro/flatbuffer_utils_test.cc \
@@ -676,6 +678,9 @@ INCLUDES += -I$(GENERATED_SRCS_DIR)$(TENSORFLOW_ROOT)
 # Load the examples.
 include $(MICRO_LITE_EXAMPLE_TESTS)
 
+# Load codegen examples.
+include $(MICRO_LITE_CODEGEN_EXAMPLES)
+
 # Load the integration tests.
 include $(MICRO_LITE_INTEGRATION_TESTS)