[llvm] r217666 - Add CMake check for libatomic.

[Evgeniy Stepanov]

I understand that since gcc-4.8 they've moved atomics implementation
to libatomic.a, and it's supposed to be linked whenever atomics are
used. It's definitely needed on ARM in general, not just on Android.

Does this change break anything?


On Sun, Sep 14, 2014 at 6:33 PM, İsmail Dönmez <ismail at donmez.ws> wrote:
> Hi,
>
> On Fri, Sep 12, 2014 at 2:09 PM, Evgeniy Stepanov
> <eugeni.stepanov at gmail.com> wrote:
>> Author: eugenis
>> Date: Fri Sep 12 06:08:59 2014
>> New Revision: 217666
>>
>> URL: http://llvm.org/viewvc/llvm-project?rev=217666&view=rev
>> Log:
>> Add CMake check for libatomic.
>>
>>
>> Modified:
>>     llvm/trunk/cmake/modules/CheckAtomic.cmake
>>     llvm/trunk/cmake/modules/HandleLLVMOptions.cmake
>>     llvm/trunk/lib/Support/CMakeLists.txt
>>
>> Modified: llvm/trunk/cmake/modules/CheckAtomic.cmake
>> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/cmake/modules/CheckAtomic.cmake?rev=217666&r1=217665&r2=217666&view=diff
>> ==============================================================================
>> --- llvm/trunk/cmake/modules/CheckAtomic.cmake (original)
>> +++ llvm/trunk/cmake/modules/CheckAtomic.cmake Fri Sep 12 06:08:59 2014
>> @@ -2,6 +2,11 @@
>>
>>  INCLUDE(CheckCXXSourceCompiles)
>>
>> +check_library_exists(atomic __atomic_fetch_add_4 "" HAVE_LIBATOMIC)
>> +if (HAVE_LIBATOMIC)
>> +  list(APPEND CMAKE_REQUIRED_LIBRARIES "atomic")
>> +endif()
>> +
>>  CHECK_CXX_SOURCE_COMPILES("
>>  #ifdef _MSC_VER
>>  #include <windows.h>
>>
>> Modified: llvm/trunk/cmake/modules/HandleLLVMOptions.cmake
>> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/cmake/modules/HandleLLVMOptions.cmake?rev=217666&r1=217665&r2=217666&view=diff
>> ==============================================================================
>> --- llvm/trunk/cmake/modules/HandleLLVMOptions.cmake (original)
>> +++ llvm/trunk/cmake/modules/HandleLLVMOptions.cmake Fri Sep 12 06:08:59 2014
>> @@ -25,9 +25,6 @@ if(NOT LLVM_FORCE_USE_OLD_TOOLCHAIN)
>>        set(OLD_CMAKE_REQUIRED_FLAGS ${CMAKE_REQUIRED_FLAGS})
>>        set(OLD_CMAKE_REQUIRED_LIBRARIES ${CMAKE_REQUIRED_LIBRARIES})
>>        set(CMAKE_REQUIRED_FLAGS "-std=c++0x")
>> -      if (ANDROID)
>> -        set(CMAKE_REQUIRED_LIBRARIES "atomic")
>> -      endif()
>>        check_cxx_source_compiles("
>>  #include <atomic>
>>  std::atomic<float> x(0.0f);
>
> This used to be an Android only link library.
>
>> Modified: llvm/trunk/lib/Support/CMakeLists.txt
>> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Support/CMakeLists.txt?rev=217666&r1=217665&r2=217666&view=diff
>> ==============================================================================
>> --- llvm/trunk/lib/Support/CMakeLists.txt (original)
>> +++ llvm/trunk/lib/Support/CMakeLists.txt Fri Sep 12 06:08:59 2014
>> @@ -132,6 +132,9 @@ if( NOT MSVC )
>>          set(system_libs ${system_libs} ${TERMINFO_LIBS})
>>        endif()
>>      endif()
>> +    if( LLVM_ENABLE_THREADS AND HAVE_LIBATOMIC )
>> +      set(system_libs ${system_libs} atomic)
>> +    endif()
>>      if( LLVM_ENABLE_THREADS AND HAVE_LIBPTHREAD )
>>        set(system_libs ${system_libs} pthread)
>>      endif()
>
> Now everyone links to it if available, that looks wrong.