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-rw-r--r--cmake/modules/CheckCxxAtomic.cmake70
1 files changed, 70 insertions, 0 deletions
diff --git a/cmake/modules/CheckCxxAtomic.cmake b/cmake/modules/CheckCxxAtomic.cmake
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+++ b/cmake/modules/CheckCxxAtomic.cmake
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+# some platforms do not offer support for atomic primitive for all integer
+# types, in that case we need to link against libatomic
+
+include(CheckCXXSourceCompiles)
+include(CMakePushCheckState)
+
+
+function(check_cxx_atomics var)
+ set(CMAKE_REQUIRED_FLAGS "${CMAKE_REQUIRED_FLAGS} -std=c++11")
+ check_cxx_source_compiles("
+#include <atomic>
+#include <cstdint>
+#include <cstddef>
+
+#if defined(__SIZEOF_INT128__)
+// Boost needs 16-byte atomics for tagged pointers.
+// These are implemented via inline instructions on the platform
+// if 16-byte alignment can be proven, and are delegated to libatomic
+// library routines otherwise. Whether or not alignment is provably
+// OK for a std::atomic unfortunately depends on compiler version and
+// optimization levels, and also on the details of the expression.
+// We specifically test access via an otherwise unknown pointer here
+// to ensure we get the most complex case. If this access can be
+// done without libatomic, then all accesses can be done.
+struct tagged_ptr {
+ int* ptr;
+ std::size_t tag;
+};
+
+void atomic16(std::atomic<tagged_ptr> *ptr) __attribute__ ((used));
+void atomic16(std::atomic<tagged_ptr> *ptr)
+{
+ tagged_ptr p{nullptr, 1};
+ ptr->store(p);
+ tagged_ptr f = ptr->load();
+ tagged_ptr new_tag{nullptr, 0};
+ ptr->compare_exchange_strong(f, new_tag);
+}
+#endif
+
+int main() {
+#if defined(__SIZEOF_INT128__)
+ std::atomic<tagged_ptr> ptr;
+ atomic16(&ptr);
+#endif
+ std::atomic<uint8_t> w1;
+ std::atomic<uint16_t> w2;
+ std::atomic<uint32_t> w4;
+ std::atomic<uint64_t> w8;
+ return w1 + w2 + w4 + w8;
+}
+" ${var})
+endfunction(check_cxx_atomics)
+
+cmake_push_check_state()
+check_cxx_atomics(HAVE_CXX11_ATOMIC)
+cmake_pop_check_state()
+
+if(NOT HAVE_CXX11_ATOMIC)
+ cmake_push_check_state()
+ set(CMAKE_REQUIRED_LIBRARIES "atomic")
+ check_cxx_atomics(HAVE_LIBATOMIC)
+ cmake_pop_check_state()
+ if(HAVE_LIBATOMIC)
+ set(LIBATOMIC_LINK_FLAGS "-Wl,--as-needed -latomic")
+ else()
+ message(FATAL_ERROR
+ "Host compiler ${CMAKE_CXX_COMPILER} requires libatomic, but it is not found")
+ endif()
+endif()