1 files changed, 125 insertions, 0 deletions
diff --git a/rcc/cmake/modules/CheckAtomic.cmake b/rcc/cmake/modules/CheckAtomic.cmake
new file mode 100644
index 0000000..b9ec06e
--- /dev/null
+++ b/rcc/cmake/modules/CheckAtomic.cmake
@@ -0,0 +1,125 @@
+# atomic builtins are required for threading support.
+
+INCLUDE(CheckCXXSourceCompiles)
+INCLUDE(CheckLibraryExists)
+
+# Sometimes linking against libatomic is required for atomic ops, if
+# the platform doesn't support lock-free atomics.
+
+function(check_working_cxx_atomics varname)
+  set(OLD_CMAKE_REQUIRED_FLAGS ${CMAKE_REQUIRED_FLAGS})
+  set(CMAKE_REQUIRED_FLAGS "${CMAKE_REQUIRED_FLAGS} -std=c++11")
+  CHECK_CXX_SOURCE_COMPILES("
+#include <atomic>
+std::atomic<int> x;
+std::atomic<short> y;
+std::atomic<char> z;
+int main() {
+  ++z;
+  ++y;
+  return ++x;
+}
+" ${varname})
+  set(CMAKE_REQUIRED_FLAGS ${OLD_CMAKE_REQUIRED_FLAGS})
+endfunction(check_working_cxx_atomics)
+
+function(check_working_cxx_atomics64 varname)
+  set(OLD_CMAKE_REQUIRED_FLAGS ${CMAKE_REQUIRED_FLAGS})
+  set(CMAKE_REQUIRED_FLAGS "-std=c++11 ${CMAKE_REQUIRED_FLAGS}")
+  CHECK_CXX_SOURCE_COMPILES("
+#include <atomic>
+#include <cstdint>
+std::atomic<uint64_t> x (0);
+int main() {
+  uint64_t i = x.load(std::memory_order_relaxed);
+  (void)i;
+  return 0;
+}
+" ${varname})
+  set(CMAKE_REQUIRED_FLAGS ${OLD_CMAKE_REQUIRED_FLAGS})
+endfunction(check_working_cxx_atomics64)
+
+
+# Check for (non-64-bit) atomic operations.
+if(MSVC)
+  set(HAVE_CXX_ATOMICS_WITHOUT_LIB True)
+elseif(RCC_COMPILER_IS_GCC_COMPATIBLE OR CMAKE_CXX_COMPILER_ID MATCHES "XL")
+  # First check if atomics work without the library.
+  check_working_cxx_atomics(HAVE_CXX_ATOMICS_WITHOUT_LIB)
+  # If not, check if the library exists, and atomics work with it.
+  if(NOT HAVE_CXX_ATOMICS_WITHOUT_LIB)
+    check_library_exists(atomic __atomic_fetch_add_4 "" HAVE_LIBATOMIC)
+    if(HAVE_LIBATOMIC)
+      list(APPEND CMAKE_REQUIRED_LIBRARIES "atomic")
+      check_working_cxx_atomics(HAVE_CXX_ATOMICS_WITH_LIB)
+      if (NOT HAVE_CXX_ATOMICS_WITH_LIB)
+        message(FATAL_ERROR "Host compiler must support std::atomic!")
+      endif()
+    else()
+      message(FATAL_ERROR "Host compiler appears to require libatomic, but cannot find it.")
+    endif()
+  endif()
+endif()
+
+# Check for 64 bit atomic operations.
+if(MSVC)
+  set(HAVE_CXX_ATOMICS64_WITHOUT_LIB True)
+elseif(RCC_COMPILER_IS_GCC_COMPATIBLE OR CMAKE_CXX_COMPILER_ID MATCHES "XL")
+  # First check if atomics work without the library.
+  check_working_cxx_atomics64(HAVE_CXX_ATOMICS64_WITHOUT_LIB)
+  # If not, check if the library exists, and atomics work with it.
+  if(NOT HAVE_CXX_ATOMICS64_WITHOUT_LIB)
+    check_library_exists(atomic __atomic_load_8 "" HAVE_CXX_LIBATOMICS64)
+    if(HAVE_CXX_LIBATOMICS64)
+      list(APPEND CMAKE_REQUIRED_LIBRARIES "atomic")
+      check_working_cxx_atomics64(HAVE_CXX_ATOMICS64_WITH_LIB)
+      if (NOT HAVE_CXX_ATOMICS64_WITH_LIB)
+        message(FATAL_ERROR "Host compiler must support 64-bit std::atomic!")
+      endif()
+    else()
+      message(FATAL_ERROR "Host compiler appears to require libatomic for 64-bit operations, but cannot find it.")
+    endif()
+  endif()
+endif()
+
+# Set variable RCC_ATOMIC_LIB specifying flags for linking against libatomic.
+if(HAVE_CXX_ATOMICS_WITH_LIB OR HAVE_CXX_ATOMICS64_WITH_LIB)
+  # Use options --push-state, --as-needed and --pop-state if linker is known to support them.
+  # Use single option -Wl of compiler driver to avoid incorrect re-ordering of options by CMake.
+  if(RCC_LINKER_IS_GNULD OR RCC_LINKER_IS_GOLD OR RCC_LINKER_IS_LLD OR RCC_LINKER_IS_MOLD)
+    set(RCC_ATOMIC_LIB "-Wl,--push-state,--as-needed,-latomic,--pop-state")
+  else()
+    set(RCC_ATOMIC_LIB "-latomic")
+  endif()
+else()
+  set(RCC_ATOMIC_LIB)
+endif()
+
+## TODO: This define is only used for the legacy atomic operations in
+## rcc's Atomic.h, which should be replaced.  Other code simply
+## assumes C++11 <atomic> works.
+CHECK_CXX_SOURCE_COMPILES("
+#ifdef _MSC_VER
+#include <windows.h>
+#endif
+int main() {
+#ifdef _MSC_VER
+        volatile LONG val = 1;
+        MemoryBarrier();
+        InterlockedCompareExchange(&val, 0, 1);
+        InterlockedIncrement(&val);
+        InterlockedDecrement(&val);
+#else
+        volatile unsigned long val = 1;
+        __sync_synchronize();
+        __sync_val_compare_and_swap(&val, 1, 0);
+        __sync_add_and_fetch(&val, 1);
+        __sync_sub_and_fetch(&val, 1);
+#endif
+        return 0;
+      }
+" RCC_HAS_ATOMICS)
+
+if( NOT RCC_HAS_ATOMICS )
+  message(STATUS "Warning: RCC will be built thread-unsafe because atomic builtins are missing")
+endif()