[libc] Ensure that the required clang tools are up-to-date for libc GPU

[jhuber6]

Summary

The clang-offload-packager. nvptx-arch, and amdgpu-arch tools are
required for building the GPU target of libc. This patch ensures that
we build this tool when directly building libc via ninja libc or similar.

[jhuber6]

Adding nvptx-arch and amdgpu-arch as well.

[tra]

llvm/runtimes/CMakeLists.txt

403

Do these tools depend on something that may not be present on a build machine w/o GPU?

I think nvptx-arch currently links with libcuda.so, which means that it will not build on machine w/o a NVIDIA GPU. Ideally the app needs to dlopen(libcuda.so.1) and gracefully fail if it's not found.

I think the dependency on nvptx-arch tools may need to be conditional on whether its build prerequisites are found.

[jhuber6]

llvm/runtimes/CMakeLists.txt

403

Yes, nvptx-arch will attempt to dynamically open CUDA if it wasn't found beforehand. Otherwise they just depend on ClangBasic and other LLVM libraries that should be supported.

[tra]

llvm/runtimes/CMakeLists.txt

403

If we already can dlopen it, then we should always do it. Linking with it explicitly just makes the binary unusable on machines w/o GPUs. E.g. you can just pack and ship it with the release build of clang. That a matter for a separate patch though.

[jhuber6]

llvm/runtimes/CMakeLists.txt

403

So right now it just dlopens if it's not found on the machine. Honestly it probably would be best if we just always dlopened it since it would guarantee any build configuration would work somewhat. Honestly the only reason I haven't done that is because linking it directly makes it easier to use within an IDE since it has access to the header files.

llvm/runtimes/CMakeLists.txt

if(TARGET libc-hdrgen)
       list(APPEND extra_deps ${libc_tools})
     else()
       # We want to build the libc build tools before we can build the libc
       # itself. So, the libc project should be included in LLVM_ENABLE_PROJECTS.
       # This should have been done in llvm/CMakeLists.txt automatically when
       # "libc" is detected in LLVM_ENABLE_RUNTIMES.
       message(FATAL_ERROR "libc-hdrgen target missing unexpectedly")
     endif()
+    if(LIBC_GPU_BUILD OR LIBC_GPU_ARCHITECTURES)
+      list(APPEND extra_deps clang-offload-packager nvptx-arch amdgpu-arch)
+    endif()
   endif()
   if(NOT LLVM_RUNTIME_TARGETS)
     runtime_default_target(
       DEPENDS ${builtins_dep} ${extra_deps}
       CMAKE_ARGS ${libc_cmake_args}
       PREFIXES ${prefixes})
     set(test_targets check-runtimes)
   else()