From 5285c120086265bfaca69c3a95e3e8e3a61b291d Mon Sep 17 00:00:00 2001
From: Saleem Abdulrasool <compnerd@compnerd.org>
Date: Wed, 25 Feb 2015 02:38:03 +0000
Subject: [PATCH] build: check if atomic routines are implicitly provided

It is possible for the atomic routines to be provided by the compiler without
requiring any additional libraries.  Check if that is the case before checking
for a library.

Patch by Matt Glazar!

llvm-svn: 230452
---
 llvm/cmake/modules/CheckAtomic.cmake | 10 +++++++---
 1 file changed, 7 insertions(+), 3 deletions(-)

diff --git a/llvm/cmake/modules/CheckAtomic.cmake b/llvm/cmake/modules/CheckAtomic.cmake
index 2ed48197728b..30a5e3112927 100644
--- a/llvm/cmake/modules/CheckAtomic.cmake
+++ b/llvm/cmake/modules/CheckAtomic.cmake
@@ -2,9 +2,13 @@
 
 INCLUDE(CheckCXXSourceCompiles)
 
-check_library_exists(atomic __atomic_fetch_add_4 "" HAVE_LIBATOMIC)
-if (HAVE_LIBATOMIC)
-  list(APPEND CMAKE_REQUIRED_LIBRARIES "atomic")
+check_function_exists(__atomic_fetch_add_4 HAVE___ATOMIC_FETCH_ADD_4)
+if( NOT HAVE___ATOMIC_FETCH_ADD_4 )
+  check_library_exists(atomic __atomic_fetch_add_4 "" HAVE_LIBATOMIC)
+  set(HAVE_LIBATOMIC False)
+  if( HAVE_LIBATOMIC )
+    list(APPEND CMAKE_REQUIRED_LIBRARIES "atomic")
+  endif()
 endif()
 
 CHECK_CXX_SOURCE_COMPILES("