[clang] [CMake] Link libclangBasic against libatomic when necessary.

[thesamesam]

Summary

This is necessary at least on PPC32.

Depends on D136280.

Bug: https://bugs.gentoo.org/874024
Thanks-to: Arfrever Frehtes Taifersar Arahesis <[e-mail]>
Tested-by: [e-mail] <[e-mail]>

[mgorny]

clang/lib/Basic/CMakeLists.txt

114–117

Is this the right place? Grepping for std::atomic, I see lib/Frontend and a bunch of tools, plus a few places in clang-tools-extra.

[Arfrever]

clang/lib/Basic/CMakeLists.txt

114–117

clang-15.0.2:20221005-132622.log (from https://bugs.gentoo.org/874024) says that this is the place where linking is needed:

/usr/bin/powerpc-unknown-linux-gnu-ld: lib/libclangBasic.a(FileManager.cpp.o): undefined reference to symbol '__atomic_load_8@@LIBATOMIC_1.0'
/usr/bin/powerpc-unknown-linux-gnu-ld: /usr/lib/gcc/powerpc-unknown-linux-gnu/11.3.1/libatomic.so.1: error adding symbols: DSO missing from command line

There were no reportedly no other errors with missing linking.

[mgorny]

I suppose it comes indirectly then. I'd prefer that you tested it with git main, though.

[aaronpuchert]

clang/lib/Basic/CMakeLists.txt

114–117

FileManager.cpp has some uses of ALWAYS_ENABLED_STATISTIC, which translates into a variable declaration using a TrackingStatistic from llvm/ADT/Statistic.h, which in turn has some usage of atomic operations inline. I stumbled across the same issue in D132799.

As we discussed there, this isn't quite right. This isn't a (private) dependency of clangBasic, but a public dependency of LLVMSupport. But currently we don't cleanly separate the two concepts and just declare everything as private dependency.

clang/CMakeLists.txt

option(LLVM_FORCE_USE_OLD_HOST_TOOLCHAIN
     "Set to ON to force using an old, unsupported host toolchain." OFF)
   option(CLANG_ENABLE_BOOTSTRAP "Generate the clang bootstrap target" OFF)
   option(LLVM_ENABLE_LIBXML2 "Use libxml2 if available." ON)
 
   include(AddLLVM)
   include(TableGen)
   include(HandleLLVMOptions)
   include(VersionFromVCS)
+  include(CheckAtomic)
   include(GetErrcMessages)
   include(LLVMDistributionSupport)
 
   set(PACKAGE_VERSION "${LLVM_PACKAGE_VERSION}")
   set(BUG_REPORT_URL "${LLVM_PACKAGE_BUGREPORT}" CACHE STRING
     "Default URL where bug reports are to be submitted.")
 
   if (NOT DEFINED LLVM_INCLUDE_TESTS)

clang/lib/Basic/CMakeLists.txt

add_clang_library(clangBasic
   XRayInstr.cpp
   XRayLists.cpp
   ${version_inc}
 
   DEPENDS
   omp_gen
   )
 
+target_link_libraries(clangBasic
+  PRIVATE
+  ${LLVM_ATOMIC_LIB}
+)