From 780bac671f45ab2c5ef15c9e7d6dff0031673e28 Mon Sep 17 00:00:00 2001
From: David Adam <zanchey@ucc.gu.uwa.edu.au>
Date: Fri, 20 Dec 2019 23:00:06 +0800
Subject: [PATCH] cmake: add -latomic on platforms that need it for 64-bit
 atomic operations

Closes #5865.
---
 CMakeLists.txt              |  2 +-
 cmake/ConfigureChecks.cmake | 13 +++++++++++++
 2 files changed, 14 insertions(+), 1 deletion(-)

diff --git a/CMakeLists.txt b/CMakeLists.txt
index 32cf3ac17..2f1560ecf 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -172,7 +172,7 @@ ADD_LIBRARY(fishlib STATIC ${FISH_SRCS})
 TARGET_SOURCES(fishlib PRIVATE ${FISH_HEADERS})
 TARGET_LINK_LIBRARIES(fishlib
   ${CURSES_LIBRARY} ${CURSES_EXTRA_LIBRARY} Threads::Threads ${CMAKE_DL_LIBS}
-  ${PCRE2_LIB} ${Intl_LIBRARIES})
+  ${PCRE2_LIB} ${Intl_LIBRARIES} ${ATOMIC_LIBRARY})
 
 # Define fish.
 ADD_EXECUTABLE(fish src/fish.cpp)
diff --git a/cmake/ConfigureChecks.cmake b/cmake/ConfigureChecks.cmake
index 3bc0f41c3..69dbb17b0 100644
--- a/cmake/ConfigureChecks.cmake
+++ b/cmake/ConfigureChecks.cmake
@@ -187,3 +187,16 @@ int main () {
 )
 
 FIND_PROGRAM(SED sed)
+
+# https://github.com/fish-shell/fish-shell/issues/5865
+CHECK_CXX_SOURCE_COMPILES("
+#include <atomic>
+struct big { int foo[64]; };
+std::atomic<big> x;
+int main() {
+   return x.load().foo[13];
+}"
+LIBATOMIC_NOT_NEEDED)
+IF (NOT LIBATOMIC_NOT_NEEDED)
+    SET(ATOMIC_LIBRARY "atomic")
+ENDIF()