[libomptarget][amdcgn] Only add opt/llvm-link dependency if TARGET is available

[protze.joachim]

Summary

In some build configurations, the target we depend on is not available for declaring the build dependency.
We only need to declare the build dependency, if the build target is available in the same build.

Should fix the issue raised in https://reviews.llvm.org/D107156#2969862
This patch should go into release/13 together with D108404

If the patch is accepted, please go ahead and commit - I might not be available for the next week.

[JonChesterfield]

Looks reasonable to me, thanks for the patch!

[tianshilei1992]

From my understanding, we probably want a more precise way. When building with LLVM_ENABLE_RUNTIMES, opt and llvm-link have to be targets, and they have to be added into dependences. For standalone build, opt and llvm-link have to be paths to two binaries.

[raj.khem]

I verified both patches together on latest 13.x branch and it fixes the issue I was seeing. So please apply both the fixes suggested in description to 13.x branch.

llvm/runtimes/CMakeLists.txt

llvm_ExternalProject_Add(runtimes-${name}
                            TARGET_TRIPLE ${target}
                            ${EXTRA_ARGS})
 endfunction()
 
 if(runtimes)
   # Create a runtimes target that uses this file as its top-level CMake file.
   # The runtimes target is a configuration of all the runtime libraries
   # together in a single CMake invocaiton.
+  set(extra_deps "")
   if("openmp" IN_LIST LLVM_ENABLE_RUNTIMES)
-    message(STATUS "Adding dependencies opt llvm-link")
-    set(extra_deps opt llvm-link)
+    if(TARGET opt)
+      list(APPEND extra_deps opt)
+    endif()
+    if(TARGET llvm-link)
+      list(APPEND extra_deps llvm-link)
+    endif()
   endif()
   if(NOT LLVM_RUNTIME_TARGETS)
     runtime_default_target(
       DEPENDS ${deps} ${extra_deps}
       PREFIXES ${prefixes})
     set(test_targets check-runtimes)
   else()
     if("default" IN_LIST LLVM_RUNTIME_TARGETS)

openmp/libomptarget/deviceRTLs/amdgcn/CMakeLists.txt

add_custom_command(
     COMMAND ${LINK_TOOL} ${bc1_files} -o linkout.cuda.${mcpu}.bc
     DEPENDS ${bc1_files})
 
   list(APPEND bc_files linkout.cuda.${mcpu}.bc)
 endmacro()
 
 set(libname "omptarget-amdgcn")
 
+set(toolchain_deps "")
+if(TARGET llvm-link)
+  list(APPEND toolchain_deps llvm-link)
+endif()
+if(TARGET opt)
+  list(APPEND toolchain_deps opt)
+endif()
+
 foreach(mcpu ${mcpus})
   set(bc_files)
   add_cuda_bc_library(${cuda_sources})
 
   set(bc_libname lib${libname}-${mcpu}.bc)
   add_custom_command(
     OUTPUT ${bc_libname}
     COMMAND ${LINK_TOOL} ${bc_files} | ${OPT_TOOL} --always-inline -o ${OUTPUTDIR}/${bc_libname}
-    DEPENDS ${bc_files} llvm-link opt)
+    DEPENDS ${bc_files} ${toolchain_deps})
 
   add_custom_target(lib${libname}-${mcpu} ALL DEPENDS ${bc_libname})
 
   install(FILES ${OUTPUTDIR}/${bc_libname}
      DESTINATION "${OPENMP_INSTALL_LIBDIR}"
   )
 endforeach()