From 38d79de10da65d234c70cbb36c24c58d189f76db Mon Sep 17 00:00:00 2001
From: mrambacher <mrambach@gmail.com>
Date: Mon, 12 Apr 2021 20:06:57 -0400
Subject: [PATCH 1/3] Add check to cmake to see if we need to link against
 -latomic

For some compilers/environments (e.g. Clang, riscv64), we need to link against -latomic.  Check if this is a requirement and add the library to the third-party libs if it is.
---
 CMakeLists.txt | 21 ++++++++++++++++++++-
 1 file changed, 20 insertions(+), 1 deletion(-)

diff --git a/CMakeLists.txt b/CMakeLists.txt
index 984c6197cb..460d350054 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -312,7 +312,6 @@ int main() {
   auto d = _mm_cvtsi128_si64(c);
 }
 " HAVE_SSE42)
-unset(CMAKE_REQUIRED_FLAGS)
 if(HAVE_SSE42)
   add_definitions(-DHAVE_SSE42)
   add_definitions(-DHAVE_PCLMUL)
@@ -320,6 +319,26 @@ elseif(FORCE_SSE42)
   message(FATAL_ERROR "FORCE_SSE42=ON but unable to compile with SSE4.2 enabled")
 endif()
 
+# Check if -latomic is required or not
+if (NOT MSVC)
+  set(CMAKE_REQUIRED_FLAGS "--std=c++11")
+  CHECK_CXX_SOURCE_COMPILES("
+#include <atomic>
+std::atomic<uint64_t> x(0);
+int main() {
+  uint64_t i = x.load(std::memory_order_relaxed);
+  bool b = x.is_lock_free();
+  return 0;
+}
+" BUILTIN_ATOMIC)
+if (NOT BUILTIN_ATOMIC)
+  #TODO: Check if -latomic exists 
+  list(APPEND THIRDPARTY_LIBS atomic)
+endif()
+endif()
+
+unset(CMAKE_REQUIRED_FLAGS)
+
 CHECK_CXX_SOURCE_COMPILES("
 #if defined(_MSC_VER) && !defined(__thread)
 #define __thread __declspec(thread)

From df7fdd69ac19f26601a80e35f70ec51913838a6e Mon Sep 17 00:00:00 2001
From: mrambacher <mrambach@gmail.com>
Date: Wed, 14 Apr 2021 10:33:47 -0400
Subject: [PATCH 2/3] Reset CMAKE_REQUIRED_FLAGS after compilation checks

---
 CMakeLists.txt | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/CMakeLists.txt b/CMakeLists.txt
index 460d350054..5d167855a7 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -296,6 +296,7 @@ else()
 endif()
 
 include(CheckCXXSourceCompiles)
+set(OLD_CMAKE_REQUIRED_FLAGS ${CMAKE_REQUIRED_FLAGS})
 if(NOT MSVC)
   set(CMAKE_REQUIRED_FLAGS "-msse4.2 -mpclmul")
 endif()
@@ -337,7 +338,8 @@ if (NOT BUILTIN_ATOMIC)
 endif()
 endif()
 
-unset(CMAKE_REQUIRED_FLAGS)
+# Reset the required flags
+set(CMAKE_REQUIRED_FLAGS ${OLD_CMAKE_REQUIRED_FLAGS})
 
 CHECK_CXX_SOURCE_COMPILES("
 #if defined(_MSC_VER) && !defined(__thread)

From 4793c5c75351d5d7c609c27d0243c2138729c7b0 Mon Sep 17 00:00:00 2001
From: mrambacher <mrambach@gmail.com>
Date: Fri, 16 Apr 2021 08:53:48 -0400
Subject: [PATCH 3/3] Fix lint warning

---
 CMakeLists.txt | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/CMakeLists.txt b/CMakeLists.txt
index 5d167855a7..558b985073 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -333,7 +333,7 @@ int main() {
 }
 " BUILTIN_ATOMIC)
 if (NOT BUILTIN_ATOMIC)
-  #TODO: Check if -latomic exists 
+  #TODO: Check if -latomic exists
   list(APPEND THIRDPARTY_LIBS atomic)
 endif()
 endif()