Author: Gokturk Yuksek Date: 2020-02-20T15:22:06+01:00 New Revision: a572a8a147c76b9d31585c2d4257a5db566c9a9d
URL: https://github.com/llvm/llvm-project/commit/a572a8a147c76b9d31585c2d4257a5db566c9a9d DIFF: https://github.com/llvm/llvm-project/commit/a572a8a147c76b9d31585c2d4257a5db566c9a9d.diff LOG: [CMake] CheckAtomic.cmake: catch false positives in RISC-V The check for 'HAVE_CXX_ATOMICS_WITHOUT_LIB' may create false positives in RISC-V. This is reproducible when compiling LLVM natively using GCC on a rv64gc (rv64imafdgc) host. Due to the 'A' (atomic) extension, g++ replaces calls to libatomic operations on the std::atomic<int> type with the native hardware instructions. As a result, the compilation succeeds and the build system thinks it doesn't need to pass '-latomic'. Improve the reliability of the 'HAVE_CXX_ATOMICS_WITHOUT_LIB' test in two steps: 1. Force a pre-increment on x (++x), which should force a call to a libatomic function; 2. Because step 1 would resolve the increment to 'amoadd.w.aq' under the 'A' extension, force the same operation on sub-word types, for which there is no hardware support. Reviewers: jfb, hintonda, smeenai, mgorny, JDevlieghere, jyknight Reviewed By: jfb Tags: #llvm Differential Revision: https://reviews.llvm.org/D68964 (cherry picked from commit cef85193b2cc1817ca43199a0ae9c6f25723997d) Added: Modified: llvm/cmake/modules/CheckAtomic.cmake Removed: ################################################################################ diff --git a/llvm/cmake/modules/CheckAtomic.cmake b/llvm/cmake/modules/CheckAtomic.cmake index 29f3bdd57f03..34ab8e98de42 100644 --- a/llvm/cmake/modules/CheckAtomic.cmake +++ b/llvm/cmake/modules/CheckAtomic.cmake @@ -12,8 +12,12 @@ function(check_working_cxx_atomics varname) CHECK_CXX_SOURCE_COMPILES(" #include <atomic> std::atomic<int> x; +std::atomic<short> y; +std::atomic<char> z; int main() { - return x; + ++z; + ++y; + return ++x; } " ${varname}) set(CMAKE_REQUIRED_FLAGS ${OLD_CMAKE_REQUIRED_FLAGS}) _______________________________________________ llvm-branch-commits mailing list llvm-branch-commits@lists.llvm.org https://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-branch-commits
