[Libomptarget] Remove dependency on the DeviceRTL from the GPU plugins

[jhuber6]

Summary

The GPU plugins have a dependency on the device libraries. Sometimes we
cannot build the device libraries because the user does not have a valid
clang to use or it was explicitly disabled. Currently this leads to a
transitive failure because we cannot meet this dependency. This patch
simply removes that dependency.

Fixes https://github.com/llvm/llvm-project/issues/60457

[h-vetinari]

Thanks for this!

[tianshilei1992]

I don't understand why a host library depends on a device library?

[jhuber6]

In D143196#4101531, @tianshilei1992 wrote:

I don't understand why a host library depends on a device library?

Well, I guess it's possible to use OpenMP without the device runtime. We could potentially just keep them completely separate. My guess is that whoever wrote the code first didn't know how to make the dependency build so they put it on the plugins.

[tianshilei1992]

The build of plugins don't need device runtime right? We set dependences in CMake for build and test running only.

[jhuber6]

Updating to just remove the dependency. I think it should be fine to build these anyway. Not sure why we need to depend on the DeviceRTL.

[h-vetinari]

Just to confirm: I applied this patch to rc1 (& rc2) and then things build fine again. Thanks!

[tianshilei1992]

LGTM

openmp/libomptarget/plugins-nextgen/amdgpu/CMakeLists.txt

 
 ################################################################################
 set(LIBOMPTARGET_BUILD_AMDGPU_PLUGIN TRUE CACHE BOOL
   "Whether to build AMDGPU plugin")
 if (NOT LIBOMPTARGET_BUILD_AMDGPU_PLUGIN)
   libomptarget_say("Not building AMDGPU NextGen offloading plugin: LIBOMPTARGET_BUILD_AMDGPU_PLUGIN is false")
   return()
 endif()
+if (NOT TARGET omptarget.devicertl.amdgpu)
+  libomptarget_say("Not building AMDGPU NextGen offloading plugin: No AMDGPU device library built")
+  return()
+endif()
+
 
 # as of rocm-3.7, hsa is installed with cmake packages and kmt is found via hsa
 find_package(hsa-runtime64 QUIET 1.2.0 HINTS ${CMAKE_INSTALL_PREFIX} PATHS /opt/rocm)
 
 if(NOT CMAKE_SYSTEM_PROCESSOR MATCHES "(x86_64)|(ppc64le)|(aarch64)$" AND CMAKE_SYSTEM_NAME MATCHES "Linux")
   libomptarget_say("Not building AMDGPU NextGen plugin: only support AMDGPU in Linux x86_64, ppc64le, or aarch64 hosts")
   return()
 endif()

openmp/libomptarget/plugins-nextgen/cuda/CMakeLists.txt

 #
 ##===----------------------------------------------------------------------===##
 set(LIBOMPTARGET_BUILD_CUDA_PLUGIN TRUE CACHE BOOL
   "Whether to build CUDA plugin")
 if (NOT LIBOMPTARGET_BUILD_CUDA_PLUGIN)
   libomptarget_say("Not building CUDA NextGen offloading plugin: LIBOMPTARGET_BUILD_CUDA_PLUGIN is false")
   return()
 endif()
+if (NOT TARGET omptarget.devicertl.nvptx)
+  libomptarget_say("Not building CUDA NextGen offloading plugin: LIBOMPTARGET_BUILD_CUDA_PLUGIN is built")
+endif()
 
 if (NOT(CMAKE_SYSTEM_PROCESSOR MATCHES "(x86_64)|(ppc64le)|(aarch64)$" AND CMAKE_SYSTEM_NAME MATCHES "Linux"))
   libomptarget_say("Not building CUDA NextGen offloading plugin: only support CUDA in Linux x86_64, ppc64le, or aarch64 hosts.")
   return()
 endif()
 
 libomptarget_say("Building CUDA NextGen offloading plugin.")
 

openmp/libomptarget/plugins/amdgpu/CMakeLists.txt

 
 ################################################################################
 set(LIBOMPTARGET_BUILD_AMDGPU_PLUGIN TRUE CACHE BOOL
   "Whether to build AMDGPU plugin")
 if (NOT LIBOMPTARGET_BUILD_AMDGPU_PLUGIN)
   libomptarget_say("Not building AMDGPU offloading plugin: LIBOMPTARGET_BUILD_AMDGPU_PLUGIN is false")
   return()
 endif()
+if (NOT TARGET omptarget.devicertl.amdgpu)
+  libomptarget_say("Not building AMDGPU offloading plugin: No AMDGPU device library built")
+  return()
+endif()
 
 # as of rocm-3.7, hsa is installed with cmake packages and kmt is found via hsa
 find_package(hsa-runtime64 QUIET 1.2.0 HINTS ${CMAKE_INSTALL_PREFIX} PATHS /opt/rocm)
 
 if(NOT CMAKE_SYSTEM_PROCESSOR MATCHES "(x86_64)|(ppc64le)|(aarch64)$" AND CMAKE_SYSTEM_NAME MATCHES "Linux")
   libomptarget_say("Not building AMDGPU plugin: only support AMDGPU in Linux x86_64, ppc64le, or aarch64 hosts")
   return()
 endif()

openmp/libomptarget/plugins/cuda/CMakeLists.txt

 #
 ##===----------------------------------------------------------------------===##
 set(LIBOMPTARGET_BUILD_CUDA_PLUGIN TRUE CACHE BOOL
   "Whether to build CUDA plugin")
 if (NOT LIBOMPTARGET_BUILD_CUDA_PLUGIN)
   libomptarget_say("Not building CUDA offloading plugin: LIBOMPTARGET_BUILD_CUDA_PLUGIN is false")
   return()
 endif()
+if (NOT TARGET omptarget.devicertl.nvptx)
+  libomptarget_say("Not building CUDA offloading plugin: LIBOMPTARGET_BUILD_CUDA_PLUGIN is built")
+endif()
 
 if (NOT(CMAKE_SYSTEM_PROCESSOR MATCHES "(x86_64)|(ppc64le)|(aarch64)$" AND CMAKE_SYSTEM_NAME MATCHES "Linux"))
   libomptarget_say("Not building CUDA offloading plugin: only support CUDA in Linux x86_64, ppc64le, or aarch64 hosts.")
   return()
 endif()
 
 libomptarget_say("Building CUDA offloading plugin.")