[clang] [llvm] [OpenMP] Remove 'libomptarget.devicertl.a' fatbinary and use static library (PR #126143)

[Ye Luo via cfe-commits]

================
@@ -142,99 +125,40 @@ function(compileDeviceRTLLibrary target_name target_triple)
     endif()
     set_property(DIRECTORY APPEND PROPERTY ADDITIONAL_MAKE_CLEAN_FILES ${outfile})
 
-    list(APPEND bc_files ${outfile})
+    list(APPEND obj_files ${CMAKE_CURRENT_BINARY_DIR}/${outfile})
   endforeach()
-
-  set(bclib_name "libomptarget-${target_name}.bc")
-
-  # Link to a bitcode library.
-  add_custom_command(OUTPUT ${CMAKE_CURRENT_BINARY_DIR}/linked_${bclib_name}
-      COMMAND ${LINK_TOOL}
-        -o ${CMAKE_CURRENT_BINARY_DIR}/linked_${bclib_name} ${bc_files}
-      DEPENDS ${bc_files}
-      COMMENT "Linking LLVM bitcode ${bclib_name}"
-  )
-
-  if(TARGET llvm-link)
-    add_custom_command(OUTPUT ${CMAKE_CURRENT_BINARY_DIR}/linked_${bclib_name}
-      DEPENDS llvm-link
-      APPEND)
-  endif()
-
-  add_custom_command(OUTPUT ${CMAKE_CURRENT_BINARY_DIR}/internalized_${bclib_name}
-      COMMAND ${OPT_TOOL} ${link_export_flag} ${CMAKE_CURRENT_BINARY_DIR}/linked_${bclib_name}
-                      -o ${CMAKE_CURRENT_BINARY_DIR}/internalized_${bclib_name}
-      DEPENDS ${source_directory}/exports ${CMAKE_CURRENT_BINARY_DIR}/linked_${bclib_name}
-      COMMENT "Internalizing LLVM bitcode ${bclib_name}"
-  )
-  if(TARGET opt)
-    add_custom_command(OUTPUT ${CMAKE_CURRENT_BINARY_DIR}/internalized_${bclib_name}
-      DEPENDS opt
-      APPEND)
-  endif()
-
-  add_custom_command(OUTPUT ${CMAKE_CURRENT_BINARY_DIR}/${bclib_name}
-      COMMAND ${OPT_TOOL} ${link_opt_flags} ${CMAKE_CURRENT_BINARY_DIR}/internalized_${bclib_name}
-                      -o ${CMAKE_CURRENT_BINARY_DIR}/${bclib_name}
-      DEPENDS ${CMAKE_CURRENT_BINARY_DIR}/internalized_${bclib_name}
-      COMMENT "Optimizing LLVM bitcode ${bclib_name}"
-  )
-  if(TARGET opt)
-    add_custom_command(OUTPUT ${CMAKE_CURRENT_BINARY_DIR}/${bclib_name}
-      DEPENDS opt
-      APPEND)
-  endif()
-
-  set(bclib_target_name "omptarget-${target_name}-bc")
-  add_custom_target(${bclib_target_name} DEPENDS ${CMAKE_CURRENT_BINARY_DIR}/${bclib_name})
-
-  # Copy library to destination.
-  add_custom_command(TARGET ${bclib_target_name} POST_BUILD
-                    COMMAND ${CMAKE_COMMAND} -E copy ${CMAKE_CURRENT_BINARY_DIR}/${bclib_name}
-                    ${LIBOMPTARGET_LIBRARY_DIR})
-  add_dependencies(omptarget.devicertl.${target_name} ${bclib_target_name})
-
-  set_property(DIRECTORY APPEND PROPERTY ADDITIONAL_MAKE_CLEAN_FILES ${bclib_name} ${LIBOMPTARGET_LIBRARY_DIR}/${bclib_name})
-
-  # Install bitcode library under the lib destination folder.
-  install(FILES ${CMAKE_CURRENT_BINARY_DIR}/${bclib_name} DESTINATION "${OFFLOAD_INSTALL_LIBDIR}")
-
-  set(target_feature "")
-  if("${target_triple}" STREQUAL "nvptx64-nvidia-cuda")
-    set(target_feature "feature=+ptx63")
-  endif()
-
-  # Package the bitcode in the bitcode and embed it in an ELF for the static library
-  add_custom_command(OUTPUT ${CMAKE_CURRENT_BINARY_DIR}/packaged_${bclib_name}
-      COMMAND ${PACKAGER_TOOL} -o ${CMAKE_CURRENT_BINARY_DIR}/packaged_${bclib_name}
-        "--image=file=${CMAKE_CURRENT_BINARY_DIR}/${bclib_name},${target_feature},triple=${target_triple},arch=generic,kind=openmp"
-      DEPENDS ${CMAKE_CURRENT_BINARY_DIR}/${bclib_name}
-      COMMENT "Packaging LLVM offloading binary ${bclib_name}.out"
-  )
-  if(TARGET clang-offload-packager)
-    add_custom_command(OUTPUT ${CMAKE_CURRENT_BINARY_DIR}/packaged_${bclib_name}
-      DEPENDS clang-offload-packager
-      APPEND)
-  endif()
-
-  set(output_name "${CMAKE_CURRENT_BINARY_DIR}/devicertl-${target_name}.o")
-  add_custom_command(OUTPUT ${output_name}
-    COMMAND ${CLANG_TOOL} --std=c++17 -c -nostdlib
-            -Xclang -fembed-offload-object=${CMAKE_CURRENT_BINARY_DIR}/packaged_${bclib_name}
-            -o ${output_name}
-            ${source_directory}/Stub.cpp
-    DEPENDS ${CMAKE_CURRENT_BINARY_DIR}/packaged_${bclib_name} ${source_directory}/Stub.cpp
-    COMMENT "Embedding LLVM offloading binary in devicertl-${target_name}.o"
-    VERBATIM
+  # Trick to combine these into a bitcode file via the linker's LTO pass. This
+  # is used to provide the legacy `libomptarget-<name>.bc` files. Hack this
+  # through as an executable to get it to use the relocatable link.
+  add_executable(libomptarget-${target_name} ${obj_files})
+  set_target_properties(libomptarget-${target_name} PROPERTIES
+    RUNTIME_OUTPUT_DIRECTORY ${LIBOMPTARGET_LLVM_LIBRARY_INTDIR}
+    LINKER_LANGUAGE CXX
+    BUILD_RPATH ""
+    INSTALL_RPATH ""
+    RUNTIME_OUTPUT_NAME libomptarget-${target_name}.bc)
+  target_compile_options(libomptarget-${target_name} PRIVATE "--target=${target_triple}")
+  target_link_options(libomptarget-${target_name} PRIVATE "--target=${target_triple}"
+                      "-r" "-nostdlib" "-flto" "-Wl,--lto-emit-llvm")
+  install(TARGETS libomptarget-${target_name}
+          PERMISSIONS OWNER_WRITE OWNER_READ GROUP_READ WORLD_READ
+          DESTINATION ${OFFLOAD_INSTALL_LIBDIR})
+
+  add_library(omptarget.${target_name}.all_objs OBJECT IMPORTED)
+  set_property(TARGET omptarget.${target_name}.all_objs APPEND PROPERTY IMPORTED_OBJECTS
+               ${LIBOMPTARGET_LLVM_LIBRARY_INTDIR}/libomptarget-${target_name}.bc)
----------------
ye-luo wrote:

Getting
```
make[5]: *** No rule to make target '/vast/users/yeluo/opt/llvm-clang/build_mirror_offload_nightly/lib/libomptarget-amdgpu.bc', needed by '/vast/users/yeluo/opt/llvm-clang/build_mirror_offload_nightly/lib/amdgcn-amd-amdhsa/libompdevice.a'.  Stop.
make[4]: *** [CMakeFiles/Makefile2:17388: offload/DeviceRTL/CMakeFiles/omptarget.amdgpu.dir/all] Error 2
```
target files produced within the project, libomptarget-amdgpu.bc in this case, cannot be used as imported because such files may not exist when it is needed, in this case by `omptarget.amdgpu` target.

https://github.com/llvm/llvm-project/pull/126143