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Repair cmake libatomic check.

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The cmake check for whether libatomic could be used had been
unconditionally setting the result to false. Which was somewhat
fortunate, because the prerequisite check for whether it was *needed*
was always claiming it was, even if it was not.

However, this made platforms where libatomic is actually necessary
fail to link.

Differential Revision: http://reviews.llvm.org/D10453

llvm-svn: 239819
This commit is contained in:
James Y Knight 2015-06-16 14:00:01 +00:00
parent 3469cb7a94
commit a72dd36d78
1 changed files with 36 additions and 6 deletions
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42
cmake/modules/CheckAtomic.cmake
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@ -2,15 +2,45 @@
INCLUDE(CheckCXXSourceCompiles)
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")
# Sometimes linking against libatomic is required for atomic ops, if
# the platform doesn't support lock-free atomics.
function(check_working_cxx_atomics varname)
set(OLD_CMAKE_REQUIRED_FLAGS ${CMAKE_REQUIRED_FLAGS})
set(CMAKE_REQUIRED_FLAGS "-std=c++11")
CHECK_CXX_SOURCE_COMPILES("
#include <atomic>
std::atomic<int> x;
int main() {
return x;
}
" ${varname})
set(CMAKE_REQUIRED_FLAGS ${OLD_CMAKE_REQUIRED_FLAGS})
endfunction(check_working_cxx_atomics)
# This isn't necessary on MSVC, so avoid command-line switch annoyance
# by only running on GCC-like hosts.
if (LLVM_COMPILER_IS_GCC_COMPATIBLE)
# First check if atomics work without the library.
check_working_cxx_atomics(HAVE_CXX_ATOMICS_WITHOUT_LIB)
# If not, check if the library exists, and atomics work with it.
if(NOT HAVE_CXX_ATOMICS_WITHOUT_LIB)
check_library_exists(atomic __atomic_fetch_add_4 "" HAVE_LIBATOMIC)
if( HAVE_LIBATOMIC )
list(APPEND CMAKE_REQUIRED_LIBRARIES "atomic")
check_working_cxx_atomics(HAVE_CXX_ATOMICS_WITH_LIB)
if (NOT HAVE_CXX_ATOMICS_WITH_LIB)
message(FATAL_ERROR "Host compiler must support std::atomic!")
endif()
else()
message(FATAL_ERROR "Host compiler appears to require libatomic, but cannot find it.")
endif()
endif()
endif()
## TODO: This define is only used for the legacy atomic operations in
## llvm's Atomic.h, which should be replaced. Other code simply
## assumes C++11 <atomic> works.
CHECK_CXX_SOURCE_COMPILES("
#ifdef _MSC_VER
#include <Intrin.h> /* Workaround for PR19898. */