https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94971
--- Comment #2 from Jonathan Wakely <redi at gcc dot gnu.org> --- Parallel mode is basically broken for any new C++ standard. All the tests for C++20 constexpr algorithms fail, because the std::__parallel versions are not constexpr: FAIL: 25_algorithms/replace_if/constexpr.cc (test for excess errors) Excess errors: /home/jwakely/src/gcc/libstdc++-v3/testsuite/25_algorithms/replace_if/constexpr.cc:29: error: call to non-'constexpr' function 'void std::__parallel::replace_if(_FIter, _FIter, _Predicate, const _Tp&) [with _FIter = int*; _Predicate = test()::<lambda(int)>; _Tp = int]' /home/jwakely/src/gcc/libstdc++-v3/testsuite/25_algorithms/replace_if/constexpr.cc:34: error: non-constant condition for static assertion /home/jwakely/src/gcc/libstdc++-v3/testsuite/25_algorithms/replace_if/constexpr.cc:34: error: 'constexpr bool test()' called in a constant expression I think that could be fixed by adding _GLIBCXX20_CONSTEXPR to them and then at the beginning of each function: #if __cpp_lib_is_constant_evaluated if (std::is_constant_evaluated()) return _GLIBCXX_STD_A::replace_if(...); #endif These fail to compile because the parallel algos don't support move semantics: FAIL: 25_algorithms/stable_sort/49559.cc (test for excess errors) FAIL: 25_algorithms/stable_sort/moveable.cc (test for excess errors) FAIL: 25_algorithms/stable_sort/moveable2.cc (test for excess errors) FAIL: 25_algorithms/partial_sort/moveable.cc (test for excess errors) FAIL: 25_algorithms/nth_element/moveable.cc (test for excess errors) FAIL: 25_algorithms/for_each/1.cc (test for excess errors) FAIL: 25_algorithms/for_each/for_each_n.cc (test for excess errors) These time out, I didn't check why: FAIL: 25_algorithms/move/deque_iterators/1.cc execution test FAIL: 25_algorithms/move_backward/deque_iterators/1.cc execution test FAIL: 25_algorithms/copy_backward/deque_iterators/1.cc execution test This fails because the new overload of std::search that takes a searcher isn't declared in std::__parallel: FAIL: 25_algorithms/search/searcher.cc (test for excess errors) Excess errors: /home/jwakely/src/gcc/libstdc++-v3/testsuite/25_algorithms/search/searcher.cc:39: error: no matching function for call to 'search(int [2], int*, nocopy)' These fail at runtime, because the parallel algos copy instead of moving: FAIL: 26_numerics/accumulate/lwg2055.cc execution test FAIL: 26_numerics/inner_product/lwg2055.cc execution test
