[OpenMP] Make `libomptarget` link against `libomp`

[tianshilei1992]

Summary

In libomptarget we use a couple of functions from libomp, but we didn't link
libomptarget against libomp. That will not work on some platforms such
as macOS. A linker error will be encountered because those symbols are not resolved
at link time when building libomptarget. This patch simply makes libomptarget
link agains libomp, makes it a "user" of libomp. I think this will not break
the policies between libomp and libomptarget.

[jdoerfert]

LG

[Dinistro]

We observed some change in CMake behaviour in the last 24 hours and we suspect that this revision might be the cause of it.
Originality, we used to enable openmp with the -DLLVM_ENABLE_PROJECTS="....;openmp" flag, but this now produces the following error:

CMake Error: install(EXPORT "LLVMExports" ...) includes target "omptarget" which requires target "omp" that is not in any export set.
CMake Error in cmake/modules/CMakeLists.txt:
   export called with target "omptarget" which requires target "omp" that is
   not in any export set.

Switching to use the -DLLVM_ENABLE_RUNTIMES="openmp" seem fix this issue.

I was just wondering if this is intended behaviour.

[aaron.ballman]

In D149617#4311697, @Dinistro wrote:

We observed some change in CMake behaviour in the last 24 hours and we suspect that this revision might be the cause of it.
Originality, we used to enable openmp with the -DLLVM_ENABLE_PROJECTS="....;openmp" flag, but this now produces the following error:

CMake Error: install(EXPORT "LLVMExports" ...) includes target "omptarget" which requires target "omp" that is not in any export set.
CMake Error in cmake/modules/CMakeLists.txt:
   export called with target "omptarget" which requires target "omp" that is
   not in any export set.

Switching to use the -DLLVM_ENABLE_RUNTIMES="openmp" seem fix this issue.

I was just wondering if this is intended behaviour.

This broke our ability to publish Sphinx documentation, it seems: https://lab.llvm.org/buildbot/#/builders/89/builds/40301 so hopefully we can get a quick fix or revert.

[tianshilei1992]

Thanks for the report. I have reverted it and will fix it accordingly.

[aaron.ballman]

In D149617#4312319, @tianshilei1992 wrote:

Thanks for the report. I have reverted it and will fix it accordingly.

Thank you! I can confirm we're publishing documentation again, so that's appreciated!

[tianshilei1992]

export omp as well

[tianshilei1992]

rebase

openmp/libomptarget/src/CMakeLists.txt

add_llvm_library(omptarget
 
   ADDITIONAL_HEADER_DIRS
   ${LIBOMPTARGET_INCLUDE_DIR}
 
   LINK_COMPONENTS
   Support
   Object
 
+  LINK_LIBS
+  PUBLIC
+  omp
+
   NO_INSTALL_RPATH
 )
 target_include_directories(omptarget PRIVATE ${LIBOMPTARGET_INCLUDE_DIR})
 
 if (LIBOMP_HAVE_VERSION_SCRIPT_FLAG)
   target_link_libraries(omptarget PRIVATE
     "-Wl,--version-script=${CMAKE_CURRENT_SOURCE_DIR}/exports")
 endif()
 
 # libomptarget.so needs to be aware of where the plugins live as they
 # are now separated in the build directory.
 set_target_properties(omptarget PROPERTIES INSTALL_RPATH "$ORIGIN" BUILD_RPATH "$ORIGIN:${CMAKE_CURRENT_BINARY_DIR}/..")
 install(TARGETS omptarget LIBRARY COMPONENT omptarget DESTINATION "${OPENMP_INSTALL_LIBDIR}")

openmp/runtime/src/CMakeLists.txt

 if(NOT WIN32 AND NOT APPLE)
   add_dependencies(libomp-micro-tests libomp-test-execstack)
 endif()
 if(${MIC})
   add_dependencies(libomp-micro-tests libomp-test-instr)
 endif()
 add_dependencies(libomp-micro-tests libomp-test-deps)
 
+# `omp` needs to be exported if in-tree build.
+set(export_to_llvmexports)
+if (NOT OPENMP_STANDALONE_BUILD)
+  get_target_export_arg(omp LLVM export_to_llvmexports)
+  set_property(GLOBAL APPEND PROPERTY LLVM_EXPORTS omp)
+endif()
+
 # Install rules
 # We want to install libomp in ${DESTDIR}/${CMAKE_INSTALL_FULL_LIBDIR}
 # We want to install headers in ${DESTDIR}/${CMAKE_INSTALL_FULL_INCLUDEDIR}
 if(WIN32)
-  install(TARGETS omp RUNTIME DESTINATION "${CMAKE_INSTALL_BINDIR}")
+  install(TARGETS omp ${export_to_llvmexports} RUNTIME DESTINATION "${CMAKE_INSTALL_BINDIR}")
   install(TARGETS ${LIBOMP_IMP_LIB_TARGET} ARCHIVE DESTINATION "${OPENMP_INSTALL_LIBDIR}")
   # Create aliases (regular copies) of the library for backwards compatibility
   set(LIBOMP_ALIASES "libiomp5md")
   foreach(alias IN LISTS LIBOMP_ALIASES)
     install(CODE "execute_process(COMMAND \"\${CMAKE_COMMAND}\" -E copy \"${LIBOMP_LIB_FILE}\"
       \"${alias}${LIBOMP_LIBRARY_SUFFIX}\" WORKING_DIRECTORY \"${CMAKE_INSTALL_FULL_BINDIR}\")")
     extend_path(outdir "${CMAKE_INSTALL_PREFIX}" "${OPENMP_INSTALL_LIBDIR}")
     install(CODE "execute_process(COMMAND \"\${CMAKE_COMMAND}\" -E copy \"${LIBOMP_IMP_LIB_FILE}\"
       \"${alias}${CMAKE_STATIC_LIBRARY_SUFFIX}\" WORKING_DIRECTORY \"${outdir}\")")
   endforeach()
 else()
 
-  install(TARGETS omp ${LIBOMP_INSTALL_KIND} DESTINATION "${OPENMP_INSTALL_LIBDIR}")
+  install(TARGETS omp ${export_to_llvmexports} ${LIBOMP_INSTALL_KIND} DESTINATION "${OPENMP_INSTALL_LIBDIR}")
 
   if(${LIBOMP_INSTALL_ALIASES})
     # Create aliases (symlinks) of the library for backwards compatibility
     set(LIBOMP_ALIASES "libgomp;libiomp5")
     foreach(alias IN LISTS LIBOMP_ALIASES)
       extend_path(outdir "${CMAKE_INSTALL_PREFIX}" "${OPENMP_INSTALL_LIBDIR}")
       install(CODE "execute_process(COMMAND \"\${CMAKE_COMMAND}\" -E create_symlink \"${LIBOMP_LIB_FILE}\"
         \"${alias}${LIBOMP_LIBRARY_SUFFIX}\" WORKING_DIRECTORY