[MLIR] Enable LIT testing in CMAKE (#3524)

* [MLIR] Enable LIT testing in CMAKE

This PR enables LIT testing in nGraph for MLIR Compiler, introduced in
PR3523. We can now do `make check-mlir-lit` to run LIT tests.

* Address feedback

* Revisit PR after cmake clean-up

test/CMakeLists.txt

@@ -24,6 +24,11 @@ endif()
 
 message(STATUS "unit tests enabled")
 
+if (NGRAPH_MLIR_ENABLE)
+    add_subdirectory(mlir)
+    message(STATUS "MLIR LIT tests enabled")
+endif()
+
 if(LINUX)
     set(CMAKE_BUILD_WITH_INSTALL_RPATH FALSE)
 endif()

test/mlir/CMakeLists.txt

+# ******************************************************************************
+# Copyright 2017-2019 Intel Corporation
+#
+# 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.
+# ******************************************************************************
+
+# Enable use of the lit tool that we build from MLIR repo.
+set(LLVM_DEFAULT_EXTERNAL_LIT ${MLIR_TOOLS_DIR}/llvm-lit)
+
+configure_lit_site_cfg(
+    ${CMAKE_CURRENT_SOURCE_DIR}/lit.site.cfg.py.in
+    ${CMAKE_CURRENT_BINARY_DIR}/lit.site.cfg.py
+    MAIN_CONFIG
+    ${CMAKE_CURRENT_SOURCE_DIR}/lit.cfg.py
+    )
+
+#set(NGRAPH_MLIR_TEST_DEPENDS
+#    ngraph-opt
+#    )
+
+add_lit_testsuite(check-mlir-lit "Running the nGraph MLIR regression tests"
+    ${CMAKE_CURRENT_BINARY_DIR}
+    DEPENDS ${NGRAPH_MLIR_TEST_DEPENDS}
+    )
+set_target_properties(check-mlir-lit PROPERTIES FOLDER "Tests")
+
+add_lit_testsuites(NGRAPH_MLIR ${CMAKE_CURRENT_SOURCE_DIR}
+    DEPENDS ${NGRAPH_MLIR_TEST_DEPS}
+    )