[clang] [libc] [llvm] [openmp] [libc] Rework the GPU build to be a regular target (PR #81921)

[Jan Patrick Lehr via cfe-commits]

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@@ -102,6 +80,121 @@ function(add_entrypoint_library target_name)
     list(APPEND all_deps ${entrypoint_target})
   endforeach(dep)
   list(REMOVE_DUPLICATES all_deps)
+  set(${result} ${all_deps} PARENT_SCOPE)
+endfunction()
+
+# A rule to build a library from a collection of entrypoint objects and bundle
+# it into a GPU fatbinary. Usage is the same as 'add_entrypoint_library'.
+# Usage:
+#     add_gpu_entrypoint_library(
+#       DEPENDS <list of add_entrypoint_object targets>
+#     )
+function(add_gpu_entrypoint_library target_name)
+  cmake_parse_arguments(
+    "ENTRYPOINT_LIBRARY"
+    "" # No optional arguments
+    "" # No single value arguments
+    "DEPENDS" # Multi-value arguments
+    ${ARGN}
+  )
+  if(NOT ENTRYPOINT_LIBRARY_DEPENDS)
+    message(FATAL_ERROR "'add_entrypoint_library' target requires a DEPENDS list "
+                        "of 'add_entrypoint_object' targets.")
+  endif()
+
+  get_fq_deps_list(fq_deps_list ${ENTRYPOINT_LIBRARY_DEPENDS})
+  get_all_object_file_deps(all_deps "${fq_deps_list}")
+
+  # The GPU 'libc' needs to be exported in a format that can be linked with
+  # offloading langauges like OpenMP or CUDA. This wraps every GPU object into a
+  # fat binary and adds them to a static library.
+  set(objects "")
+  foreach(dep IN LISTS all_deps)
+    set(object $<$<STREQUAL:$<TARGET_NAME_IF_EXISTS:${dep}>,${dep}>:$<TARGET_OBJECTS:${dep}>>)
+    string(FIND ${dep} "." last_dot_loc REVERSE)
+    math(EXPR name_loc "${last_dot_loc} + 1")
+    string(SUBSTRING ${dep} ${name_loc} -1 name)
+    if(LIBC_TARGET_ARCHITECTURE_IS_NVPTX)
+      set(prefix --image=arch=generic,triple=nvptx64-nvidia-cuda,feature=+ptx63)
+    else()
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jplehr wrote:

Other places do `elseif(LIBC_TARGET_ARCHITECTURE_IS_AMDGPU)`. Maybe here as well for consistency?

https://github.com/llvm/llvm-project/pull/81921