[openmp] 12 tests are failing w/ standalone build if libomp-14.x is installed system-wide

[mgorny]

It seems that there is some leakage of system libraries into the test suite. If libomp-14.0.6 is installed system-wide, running check-openmp from a standalone build of libomp-15.x (tip of release/15.x branch) yields the following test failures:

Failed Tests (12):
  libomp :: affinity/kmp-affinity-reset.c
  libomp :: api/omp_in_explicit_task.c
  libomp :: ompt/parallel/nested_thread_num.c
  libomp :: ompt/parallel/normal.c
  libomp :: ompt/parallel/not_enough_threads.c
  libomp :: ompt/tasks/serialized.c
  libomp :: ompt/tasks/taskloop_dispatch.c
  libomp :: ompt/teams/distribute_dispatch.c
  libomp :: ompt/worksharing/for/loop_dispatch.c
  libomp :: ompt/worksharing/sections_dispatch.c
  libomp :: tasking/hidden_helper_task/single_helper_thread.c
  libomp :: teams/teams-distr-on-host.c

openmp was configured with the following cmake flags:

cmake
 -C /tmp/portage/sys-libs/libomp-15.0.0.9999/work/openmp_build-abi_x86_64.amd64/gentoo_common_config.cmake
 -G Ninja
 -DCMAKE_INSTALL_PREFIX=/usr
 -DOPENMP_LIBDIR_SUFFIX=64
 -DLIBOMP_USE_HWLOC=yes
 -DLIBOMP_OMPT_SUPPORT=yes
 -DOPENMP_ENABLE_LIBOMPTARGET=yes
 -DLIBOMP_INSTALL_ALIASES=OFF
 -DLIBOMP_COPY_EXPORTS=OFF
 -DLIBOMPTARGET_BUILD_AMDGPU_PLUGIN=yes
 -DLIBOMPTARGET_BUILD_CUDA_PLUGIN=yes
 -DOPENMP_LLVM_LIT_EXECUTABLE=/usr/bin/lit
 -DOPENMP_LIT_ARGS="-vv;-j;12"
 -DOPENMP_TEST_C_COMPILER=/usr/lib/ccache/bin/x86_64-pc-linux-gnu-clang
 -DOPENMP_TEST_CXX_COMPILER=/usr/lib/ccache/bin/x86_64-pc-linux-gnu-clang++
 -DCMAKE_BUILD_TYPE=RelWithDebInfo
 -DCMAKE_TOOLCHAIN_FILE=/tmp/portage/sys-libs/libomp-15.0.0.9999/work/openmp_build-abi_x86_64.amd64/gentoo_toolchain.cmake
 /tmp/portage/sys-libs/libomp-15.0.0.9999/work/openmp

Full build and test log:
sys-libs:libomp-15.0.0.9999:20220730-183131.log

[llvmbot]

@llvm/issue-subscribers-openmp

[mgorny]

Ok, found the problem:

# Setup environment to find dynamic library at runtime
append_dynamic_library_path(config.library_dir)
if config.using_hwloc:
    append_dynamic_library_path(config.hwloc_library_dir)
    config.available_features.add('hwloc')

If hwloc is installed into /usr/lib64, then this path is prepended before the build directory, and openmp libraries are used from there.

To be honest, I don't really like the idea of adding system paths into LD_LIBRARY_PATH but if you feel like that hwloc path needs to be added implicitly, I suppose the simplest solution would be to reverse the call order, i.e. to "append" ("prepend" in reality) config.library_dir last.

CC @jpeyton52

[mgorny]

Proposed https://reviews.llvm.org/D130825 for it.

[jpeyton52]

I approve backporting to 15.x

[mgorny]

/cherry-pick eb4612c

[llvmbot]

/branch llvm/llvm-project-release-prs/issue56821

[llvmbot]

/pull-request llvm/llvm-project-release-prs#38