Add latomic when needed. (#427)

CMakeLists.txt

@@ -110,6 +110,12 @@ add_executable(tilemaker vector_tile.pb.cc osmformat.pb.cc ${tilemaker_src_files
 target_link_libraries(tilemaker ${PROTOBUF_LIBRARY} ${LIBSHP_LIBRARIES} ${SQLITE3_LIBRARIES} ${LUAJIT_LIBRARY} ${LUA_LIBRARIES} ${ZLIB_LIBRARY} ${THREAD_LIB} ${CMAKE_DL_LIBS}
 	Boost::system Boost::filesystem Boost::program_options Boost::iostreams)
 
+include(CheckCxxAtomic)
+if(NOT HAVE_CXX11_ATOMIC)
+	string(APPEND CMAKE_CXX_STANDARD_LIBRARIES
+	" ${LIBATOMIC_LINK_FLAGS}")
+endif()
+
 if(MSVC)
     target_link_libraries(tilemaker unofficial::sqlite3::sqlite3)
 endif()

cmake/CheckCxxAtomic.cmake

@@ -0,0 +1,66 @@
+# some platforms do not offer support for atomic primitive for all integer
+# types, in that case we need to link against libatomic
+
+include(CheckCXXSourceCompiles)
+include(CMakePushCheckState)
+
+
+function(check_cxx_atomics var)
+  set(CMAKE_REQUIRED_FLAGS "${CMAKE_REQUIRED_FLAGS} -std=c++11")
+    check_cxx_source_compiles("
+#include <atomic>
+#include <cstdint>
+#include <cstddef>
+#if defined(__SIZEOF_INT128__)
+// Boost needs 16-byte atomics for tagged pointers.
+// These are implemented via inline instructions on the platform
+// if 16-byte alignment can be proven, and are delegated to libatomic
+// library routines otherwise.  Whether or not alignment is provably
+// OK for a std::atomic unfortunately depends on compiler version and
+// optimization levels, and also on the details of the expression.
+// We specifically test access via an otherwise unknown pointer here
+// to ensure we get the most complex case.  If this access can be
+// done without libatomic, then all accesses can be done.
+struct tagged_ptr {
+  int* ptr;
+  std::size_t tag;
+};
+void atomic16(std::atomic<tagged_ptr> *ptr)
+{
+  tagged_ptr p{nullptr, 1};
+  ptr->store(p);
+  tagged_ptr f = ptr->load();
+  tagged_ptr new_tag{nullptr, 0};
+  ptr->compare_exchange_strong(f, new_tag);
+}
+#endif
+int main() {
+#if defined(__SIZEOF_INT128__)
+  std::atomic<tagged_ptr> ptr;
+  atomic16(&ptr);
+#endif
+  std::atomic<uint8_t> w1;
+  std::atomic<uint16_t> w2;
+  std::atomic<uint32_t> w4;
+  std::atomic<uint64_t> w8;
+  return w1 + w2 + w4 + w8;
+}
+" ${var})
+endfunction(check_cxx_atomics)
+
+cmake_push_check_state()
+check_cxx_atomics(HAVE_CXX11_ATOMIC)
+cmake_pop_check_state()
+
+if(NOT HAVE_CXX11_ATOMIC)
+  cmake_push_check_state()
+  set(CMAKE_REQUIRED_LIBRARIES "atomic")
+  check_cxx_atomics(HAVE_LIBATOMIC)
+  cmake_pop_check_state()
+  if(HAVE_LIBATOMIC)
+    set(LIBATOMIC_LINK_FLAGS "-latomic")
+  else()
+    message(FATAL_ERROR
+      "Host compiler ${CMAKE_CXX_COMPILER} requires libatomic, but it is not found")
+  endif()
+endif()