From b072c44c08beb00fdcb510e1f2cbb9e73d88327a Mon Sep 17 00:00:00 2001
From: yangfl <yangfl@users.noreply.github.com>
Date: Sat, 1 Jan 2022 15:25:35 +0800
Subject: [PATCH] Add CheckAtomic.cmake

Sometimes linking against libatomic is required for atomic ops, if
the platform doesn't support lock-free atomics.

This is a fixup for #4556, which does not work as intended.
---
 CMakeLists.txt          |  1 +
 cmake/CheckAtomic.cmake | 52 +++++++++++++++++++++++++++++++++++++++++
 2 files changed, 53 insertions(+)
 create mode 100644 cmake/CheckAtomic.cmake

diff --git a/CMakeLists.txt b/CMakeLists.txt
index 075913ae6..932f8bb69 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -83,6 +83,7 @@ endif()
 include(CheckCCompilerFlag)
 include(CheckCXXCompilerFlag)
 include(CheckSymbolExists)
+include(CheckAtomic)
 
 check_symbol_exists(__i386 "" TARGET_ARCH_X86_i386)
 if(TARGET_ARCH_X86_i386)
diff --git a/cmake/CheckAtomic.cmake b/cmake/CheckAtomic.cmake
new file mode 100644
index 000000000..78c725708
--- /dev/null
+++ b/cmake/CheckAtomic.cmake
@@ -0,0 +1,52 @@
+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>
+#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_atomics)
+
+if(NOT DEFINED COMPILER_IS_GCC_COMPATIBLE)
+  if(MSVC OR APPLE)
+    set(COMPILER_IS_GCC_COMPATIBLE OFF)
+  else()
+    set(COMPILER_IS_GCC_COMPATIBLE ON)
+  endif()
+endif()
+
+if(NOT COMPILER_IS_GCC_COMPATIBLE)
+  set(HAVE_ATOMICS_WITHOUT_LIB ON)
+else()
+  # Check for 64 bit atomic operations.
+  # First check if atomics work without the library.
+  check_working_cxx_atomics(HAVE_ATOMICS_WITHOUT_LIB)
+  # If not, check if the library exists, and atomics work with it.
+  if(NOT HAVE_ATOMICS_WITHOUT_LIB)
+    check_library_exists(atomic __atomic_load_8 "" HAVE_LIBATOMICS)
+    mark_as_advanced(HAVE_LIBATOMICS)
+    if(NOT HAVE_LIBATOMICS)
+      message(FATAL_ERROR "Host compiler appears to require libatomic, but cannot find it.")
+    endif()
+    list(APPEND CMAKE_REQUIRED_LIBRARIES "atomic")
+    check_working_cxx_atomics(HAVE_ATOMICS_WITH_LIB)
+    if(NOT HAVE_ATOMICS_WITH_LIB)
+      message(FATAL_ERROR "Host compiler must support std::atomic!")
+    endif()
+    list(APPEND CMAKE_C_STANDARD_LIBRARIES "-latomic")
+    list(APPEND CMAKE_CXX_STANDARD_LIBRARIES "-latomic")
+  endif()
+endif()