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# Original issue:
# * https://gitlab.kitware.com/cmake/cmake/-/issues/23021#note_1098733
#
# For reference:
# * https://gcc.gnu.org/wiki/Atomic/GCCMM
#
# riscv64 specific:
# * https://lists.debian.org/debian-riscv/2022/01/msg00009.html
#
# ATOMICS_FOUND - system has C++ atomics
# ATOMICS_LIBRARIES - libraries needed to use C++ atomics
if (ATOMICS_FOUND)
return()
endif()
include(CheckCXXSourceCompiles)
# RISC-V only has 32-bit and 64-bit atomic instructions. GCC is supposed
# to convert smaller atomics to those larger ones via masking and
# shifting like LLVM, but it's a known bug that it does not. This means
# anything that wants to use atomics on 1-byte or 2-byte types needs
# to link atomic library, but not 4-byte or 8-byte (though it does no harm).
set(ATOMIC_CODE
"
#include <atomic>
#include <cstdint>
std::atomic<std::uint8_t> n8{0}; // riscv64
std::atomic<std::uint64_t> n64{0}; // armel, mipsel, powerpc
int main() {
++n8;
++n64;
}")
set(ATOMICS_LIBS " " "-latomic")
if (CMAKE_SYSTEM_NAME MATCHES "NetBSD")
set(ATOMICS_LIBS "${ATOMICS_LIBS}" /usr/pkg/gcc12/x86_64--netbsd/lib/libatomic.so /usr/pkg/gcc12/i486--netbsdelf/lib/libatomic.so)
endif()
foreach (ATOMICS_LIBRARY ${ATOMICS_LIBS})
unset(ATOMICS_FOUND CACHE)
set(CMAKE_REQUIRED_LIBRARIES "${ATOMICS_LIBRARY}")
check_cxx_source_compiles("${ATOMIC_CODE}" ATOMICS_FOUND)
unset(CMAKE_REQUIRED_LIBRARIES)
if (ATOMICS_FOUND)
if (NOT ATOMICS_LIBRARY STREQUAL " ")
include(FindPackageHandleStandardArgs)
find_package_handle_standard_args(Atomics DEFAULT_MSG ATOMICS_LIBRARY)
set(ATOMICS_LIBRARIES "${ATOMICS_LIBRARY}" CACHE STRING "Atomic library" FORCE)
else()
set(ATOMICS_LIBRARIES "" CACHE STRING "Atomic operations library" FORCE)
endif()
break()
endif()
endforeach()
if (Atomics_FIND_REQUIRED AND NOT ATOMICS_FOUND)
message(FATAL_ERROR "Atomic operations library isn't found.")
endif()
unset(ATOMICS_LIBRARY)
unset(ATOMICS_LIBS)
unset(ATOMIC_CODE)
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