[CMake] Disable building libomptarget and add CMake switch

[Hahnfeld]

Summary

Introduce OPENMP_ENABLE_LIBOMPTARGET which defaults to OFF at the moment.

libomptarget is not yet ready for prime time:

• Offloading to NVIDIA GPUs is not completed yet (compiler, device RTL)
• The generic ELF plugin for offloading to the host (meant for testing) uses a single instance of the OpenMP runtime (libomp). That is why omp_is_initial_device() returns 1 which makes the tests fail.

Because of these reasons, we want to disable building (and testing!) for release 5.0.

See https://bugs.llvm.org/show_bug.cgi?id=33859

[hans]

CMakeLists.txt

8 ↗

(On Diff #107634)

Since the tests fail by default, I think it should be disabled in the build by default.

trunk should always be in a working state.

[Hahnfeld]

CMakeLists.txt

8 ↗

(On Diff #107634)

Well, it's broken since January so nobody cared enough. @gtbercea, what do you think?

[hans]

CMakeLists.txt

8 ↗

(On Diff #107634)

Most people don't check out or build the openmp repo, and your buildbot doesn't run the tests -- which is another reason the code shouldn't be built by default.

[Hahnfeld]

Disable building by default.

[Hahnfeld]

CMakeLists.txt

8 ↗

(On Diff #107634)

Updated the patch. I'll let it sit for two days or so to give the others time to respond.

[hans]

Looks good to me. Thanks!

[Hahnfeld]

I've committed the patch without an explicit answer from the IBM guys to unblock the release

[hans]

In D35719#821451, @Hahnfeld wrote:

I've committed the patch without an explicit answer from the IBM guys to unblock the release

Thanks! Merged to 5.0 in r309126.

openmp/trunk/CMakeLists.txt

 cmake_minimum_required(VERSION 2.8 FATAL_ERROR)
 
 set(OPENMP_LLVM_TOOLS_DIR "" CACHE PATH "Path to LLVM tools for testing")
 
 add_subdirectory(runtime)
 
+
+# The tests currently don't pass if the generic ELF plugin is built.
+# TODO: Fix the tests and enable libomptarget by default on supported
+#       architectures and platforms.
+set(ENABLE_LIBOMPTARGET OFF)
 # Currently libomptarget cannot be compiled on Windows or MacOS X.
 # Since the device plugins are only supported on Linux anyway,
 # there is no point in trying to compile libomptarget on other OSes.
-if (NOT (WIN32 OR ${CMAKE_SYSTEM_NAME} MATCHES "Darwin"))
+if (WIN32 OR ${CMAKE_SYSTEM_NAME} MATCHES "Darwin")
+  set(ENABLE_LIBOMPTARGET OFF)
+endif()
+
+option(OPENMP_ENABLE_LIBOMPTARGET "Enable building libomptarget for offloading."
+       ${ENABLE_LIBOMPTARGET})
+if (OPENMP_ENABLE_LIBOMPTARGET)
   add_subdirectory(libomptarget)
 endif()