From f2612aac2dad47f2ecd1b72a84016bfc5cc19a40 Mon Sep 17 00:00:00 2001
From: Andreas Beckmann <anbe@debian.org>
Date: Mon, 27 Jun 2022 14:04:28 +0200
Subject: [PATCH] [PATCH 3/3] check whether 64bit atomics require -latomic

Gbp-Pq: Name 1020-check-whether-64bit-atomics-require-latomic.patch
---
 CMakeLists.txt        | 31 +++++++++++++++++++++++++++++++
 lib/CL/CMakeLists.txt |  4 ++++
 2 files changed, 35 insertions(+)

diff --git a/CMakeLists.txt b/CMakeLists.txt
index 719b560..727b358 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -646,6 +646,37 @@ endif()
 
 ######################################################################################
 
+function(check_64bit_atomics varname)
+    check_c_source_compiles("
+#include <stdint.h>
+uint64_t x = 0;
+int main()
+{
+  __atomic_add_fetch(&x, 1, __ATOMIC_SEQ_CST);
+  __atomic_sub_fetch(&x, 1, __ATOMIC_SEQ_CST);
+  return x;
+}
+" ${varname})
+endfunction(check_64bit_atomics)
+
+# platforms w/o lockfree 64bit atomics need to link with -latomic
+if(UNIX)
+    check_64bit_atomics(HAVE_64BIT_ATOMICS_WITHOUT_LIB)
+    if(HAVE_64BIT_ATOMICS_WITHOUT_LIB)
+        set(HAVE_64BIT_ATOMICS_WITH_LIB FALSE)
+    else()
+        set(OLD_CMAKE_REQUIRED_LIBRARIES ${CMAKE_REQUIRED_LIBRARIES})
+        list(APPEND CMAKE_REQUIRED_LIBRARIES "atomic")
+        check_64bit_atomics(HAVE_64BIT_ATOMICS_WITH_LIB)
+        set(CMAKE_REQUIRED_LIBRARIES ${OLD_CMAKE_REQUIRED_LIBRARIES})
+        if(NOT HAVE_64BIT_ATOMICS_WITH_LIB)
+            message(SEND_ERROR "Missing 64-bit atomic increment")
+        endif()
+    endif()
+endif()
+
+######################################################################################
+
 if(UNIX AND ENABLE_LLVM AND HAVE_DLADDR)
     option(ENABLE_RELOCATION "make libpocl relocatable" ON)
 else()
diff --git a/lib/CL/CMakeLists.txt b/lib/CL/CMakeLists.txt
index 342cdac..ed57340 100644
--- a/lib/CL/CMakeLists.txt
+++ b/lib/CL/CMakeLists.txt
@@ -242,6 +242,10 @@ if(HAVE_CLOCK_GETTIME AND CMAKE_SYSTEM_NAME MATCHES "Linux")
   list(APPEND POCL_PRIVATE_LINK_LIST "rt")
 endif()
 
+if(HAVE_64BIT_ATOMICS_WITH_LIB)
+  list(APPEND POCL_PRIVATE_LINK_LIST "atomic")
+endif()
+
 list(APPEND POCL_PRIVATE_LINK_LIST ${LIBMATH} ${CMAKE_DL_LIBS} ${PTHREAD_LIBRARY})
 
 # see lib/CMakeLists.txt
-- 
2.30.2