Rewrite FindAtomics.cmake.

CMake/FindAtomics.cmake

@@ -7,50 +7,53 @@
 # riscv64 specific:
 # * https://lists.debian.org/debian-riscv/2022/01/msg00009.html
 #
-# ATOMICS_FOUND         - system has c++ atomics
-# ATOMICS_LIBRARIES     - libraries needed to use c++ atomics
-# ATOMICS_LIBRARY_FLAGS - flags required to link with c++ atomics library
+# ATOMICS_FOUND         - system has C++ atomics
+# ATOMICS_LIBRARIES     - libraries needed to use C++ atomics
+
+if (ATOMICS_FOUND)
+  return()
+endif()
 
 include(CheckCXXSourceCompiles)
 
 # RISC-V only has 32-bit and 64-bit atomic instructions. GCC is supposed
 # to convert smaller atomics to those larger ones via masking and
 # shifting like LLVM, but it’s a known bug that it does not. This means
 # anything that wants to use atomics on 1-byte or 2-byte types needs
-# -latomic, but not 4-byte or 8-byte (though it does no harm).
-set(atomic_code
+# to link atomic library, but not 4-byte or 8-byte (though it does no harm).
+set(ATOMIC_CODE
     "
      #include <atomic>
      #include <cstdint>
-     std::atomic<uint8_t> n8 (0); // riscv64
-     std::atomic<uint64_t> n64 (0); // armel, mipsel, powerpc
+     std::atomic<std::uint8_t> n8(0); // riscv64
+     std::atomic<std::uint64_t> n64(0); // armel, mipsel, powerpc
      int main() {
        ++n8;
        ++n64;
-       return 0;
      }")
 
-check_cxx_source_compiles("${atomic_code}" ATOMICS_LOCK_FREE_INSTRUCTIONS)
+set(ATOMICS_LIBS " " "-latomic")
 
-if (ATOMICS_LOCK_FREE_INSTRUCTIONS)
-  set(ATOMICS_FOUND TRUE)
-  set(ATOMICS_LIBRARIES)
-  set(ATOMICS_LIBRARY_FLAGS)
-else()
-  set(CMAKE_REQUIRED_LIBRARIES "-latomic")
-  check_cxx_source_compiles("${atomic_code}" ATOMICS_IN_LIBRARY)
-  set(CMAKE_REQUIRED_LIBRARIES)
-  if (ATOMICS_IN_LIBRARY)
-    set(ATOMICS_LIBRARY atomic)
-    include(FindPackageHandleStandardArgs)
-    find_package_handle_standard_args(Atomics DEFAULT_MSG ATOMICS_LIBRARY)
-    set(ATOMICS_LIBRARIES ${ATOMICS_LIBRARY})
-    set(ATOMICS_LIBRARY_FLAGS "-latomic")
-    unset(ATOMICS_LIBRARY)
-  else()
-    if (Atomics_FIND_REQUIRED)
-      message(FATAL_ERROR "Neither lock free instructions nor -latomic found.")
+foreach (ATOMICS_LIBRARY ${ATOMICS_LIBS})
+  unset(ATOMICS_FOUND CACHE)
+  set(CMAKE_REQUIRED_LIBRARIES "${ATOMICS_LIBRARY}")
+  check_cxx_source_compiles("${ATOMIC_CODE}" ATOMICS_FOUND)
+  unset(CMAKE_REQUIRED_LIBRARIES)
+  if (ATOMICS_FOUND)
+    if (NOT ATOMICS_LIBRARY STREQUAL " ")
+      include(FindPackageHandleStandardArgs)
+      find_package_handle_standard_args(Atomics DEFAULT_MSG ATOMICS_LIBRARY)
+      set(ATOMICS_LIBRARIES "${ATOMICS_LIBRARY}" CACHE STRING "Atomic library" FORCE)
+    else()
+      set(ATOMICS_LIBRARIES "" CACHE STRING "Atomic operations library" FORCE)
     endif()
+    break()
   endif()
+endforeach()
+if (Atomics_FIND_REQUIRED AND NOT ATOMICS_FOUND)
+  message(FATAL_ERROR "Atomic operations library isn't found.")
 endif()
-unset(atomic_code)
+
+unset(ATOMICS_LIBRARY)
+unset(ATOMICS_LIBS)
+unset(ATOMIC_CODE)

CMakeLists.txt

@@ -133,8 +133,8 @@ include(TdSetUpCompiler)
 td_set_up_compiler()
 
 find_package(Atomics REQUIRED)
-if (ATOMICS_LIBRARY_FLAGS)
-  set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} ${ATOMICS_LIBRARY_FLAGS}")
+if (ATOMICS_LIBRARIES)
+  set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} ${ATOMICS_LIBRARIES}")
 endif()
 
 if (MSVC)