[libcxx] r329167 - [libcxx][cmake] Remove libatomic temporarily from CMAKE_REQUIRED_LIBRARIES when configuring

[Simon Dardis via cfe-commits]

Author: sdardis
Date: Wed Apr  4 04:05:03 2018
New Revision: 329167

URL: http://llvm.org/viewvc/llvm-project?rev=329167&view=rev
Log:
[libcxx][cmake] Remove libatomic temporarily from CMAKE_REQUIRED_LIBRARIES when configuring

When libcxx is built in tree for a host which requires libatomic, LLVM's
configuration steps will determine it is required and add it to
CMAKE_REQUIRED_LIBRARIES. When libcxx is later configured, it tests if it
has C++ atomics without libatomic. The test erroneously passes as libatomic
is already part of the set of required libraries.

In turn, a number of the atomic tests will fail as they require libatomic
but the test suite is configured not to use libatomic.

Address this by always dropping libatomic from the set of required libraries
before determining if LIBCXX_HAVE_CXX_ATOMICS_WITHOUT_LIB is true,
then restoring the set of required libraries.

Reviewers: EricWF

Differential Revision: https://reviews.llvm.org/D43509

Modified:
    libcxx/trunk/cmake/Modules/CheckLibcxxAtomic.cmake

Modified: libcxx/trunk/cmake/Modules/CheckLibcxxAtomic.cmake
URL: http://llvm.org/viewvc/llvm-project/libcxx/trunk/cmake/Modules/CheckLibcxxAtomic.cmake?rev=329167&r1=329166&r2=329167&view=diff
==============================================================================
--- libcxx/trunk/cmake/Modules/CheckLibcxxAtomic.cmake (original)
+++ libcxx/trunk/cmake/Modules/CheckLibcxxAtomic.cmake Wed Apr  4 04:05:03 2018
@@ -31,7 +31,14 @@ int main() {
   set(CMAKE_REQUIRED_FLAGS ${OLD_CMAKE_REQUIRED_FLAGS})
 endfunction(check_cxx_atomics)
 
+# Perform the check for 64bit atomics without libatomic. It may have been
+# added to the required libraries during in the configuration of LLVM, which
+# would cause the check for CXX atomics without libatomic to incorrectly pass.
+set(OLD_CMAKE_REQUIRED_LIBRARIES ${CMAKE_REQUIRED_LIBRARIES})
+list(REMOVE_ITEM CMAKE_REQUIRED_LIBRARIES "atomic")
 check_cxx_atomics(LIBCXX_HAVE_CXX_ATOMICS_WITHOUT_LIB)
+set(CMAKE_REQUIRED_LIBRARIES ${OLD_CMAKE_REQUIRED_LIBRARIES})
+
 check_library_exists(atomic __atomic_fetch_add_8 "" LIBCXX_HAS_ATOMIC_LIB)
 # If not, check if the library exists, and atomics work with it.
 if(NOT LIBCXX_HAVE_CXX_ATOMICS_WITHOUT_LIB)