Avoid re-installing if Tensorflow is already installed for WASI-NN (#2148)

Since the Tensorflow library is already installed in many cases(especially in the
case of the embedded system), move the installation code to find_package.

build-scripts/runtime_lib.cmake

@@ -101,26 +101,6 @@ if (WAMR_BUILD_LIB_PTHREAD_SEMAPHORE EQUAL 1)
 endif ()
 
 if (WAMR_BUILD_WASI_NN EQUAL 1)
-    if (NOT EXISTS "${WAMR_ROOT_DIR}/core/deps/tensorflow-src")
-        execute_process(COMMAND ${WAMR_ROOT_DIR}/core/deps/install_tensorflow.sh
-                        RESULT_VARIABLE TENSORFLOW_RESULT
-        )
-    else ()
-        message("Tensorflow is already downloaded.")
-    endif()
-    set(TENSORFLOW_SOURCE_DIR "${WAMR_ROOT_DIR}/core/deps/tensorflow-src")
-
-    if (WASI_NN_ENABLE_GPU EQUAL 1)
-        # Tensorflow specific:
-        # * https://www.tensorflow.org/lite/guide/build_cmake#available_options_to_build_tensorflow_lite
-        set (TFLITE_ENABLE_GPU ON)
-    endif ()
-
-    include_directories (${CMAKE_CURRENT_BINARY_DIR}/flatbuffers/include)
-    include_directories (${TENSORFLOW_SOURCE_DIR})
-    add_subdirectory(
-        "${TENSORFLOW_SOURCE_DIR}/tensorflow/lite"
-        "${CMAKE_CURRENT_BINARY_DIR}/tensorflow-lite" EXCLUDE_FROM_ALL)
     include (${IWASM_DIR}/libraries/wasi-nn/wasi_nn.cmake)
 endif ()
 

core/iwasm/libraries/wasi-nn/cmake/Findtensorflow_lite.cmake

@@ -0,0 +1,41 @@
+# Copyright (C) 2019 Intel Corporation. All rights reserved.
+# SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+
+
+find_library(TENSORFLOW_LITE 
+     NAMES tensorflow-lite
+)
+
+if(NOT EXISTS ${TENSORFLOW_LITE})
+    if (NOT EXISTS "${WAMR_ROOT_DIR}/core/deps/tensorflow-src")
+        execute_process(COMMAND ${WAMR_ROOT_DIR}/core/deps/install_tensorflow.sh
+                        RESULT_VARIABLE TENSORFLOW_RESULT
+        )
+    else ()
+        message("Tensorflow is already downloaded.")
+    endif()
+    set(TENSORFLOW_SOURCE_DIR "${WAMR_ROOT_DIR}/core/deps/tensorflow-src")
+
+    if (WASI_NN_ENABLE_GPU EQUAL 1)
+    # Tensorflow specific:
+    # * https://www.tensorflow.org/lite/guide/build_cmake#available_options_to_build_tensorflow_lite
+    set (TFLITE_ENABLE_GPU ON)
+    endif ()
+
+    include_directories (${CMAKE_CURRENT_BINARY_DIR}/flatbuffers/include)
+    include_directories (${TENSORFLOW_SOURCE_DIR})
+    add_subdirectory(
+        "${TENSORFLOW_SOURCE_DIR}/tensorflow/lite"
+        "${CMAKE_CURRENT_BINARY_DIR}/tensorflow-lite" EXCLUDE_FROM_ALL) 
+
+else()
+    find_path(TENSORFLOW_LITE_INCLUDE_DIR
+    NAMES tensorflow/lite/interpreter.h
+    )
+    find_path(FLATBUFFER_INCLUDE_DIR
+    NAMES flatbuffers/flatbuffers.h
+    )
+    include_directories (${TENSORFLOW_LITE_INCLUDE_DIR})
+    include_directories (${FLATBUFFER_INCLUDE_DIR})    
+endif()
+

core/iwasm/libraries/wasi-nn/wasi_nn.cmake

@@ -1,6 +1,11 @@
 # Copyright (C) 2019 Intel Corporation.  All rights reserved.
 # SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
+list(APPEND CMAKE_MODULE_PATH ${CMAKE_CURRENT_LIST_DIR}/cmake)
+
+# Find tensorflow-lite
+find_package(tensorflow_lite REQUIRED)
+
 set (WASI_NN_DIR ${CMAKE_CURRENT_LIST_DIR})
 
 include_directories (${WASI_NN_DIR})