Function parameter 'map' with unknown value cannot be used in a constant expression

[4465464]

#include <iostream>

namespace cuco{

    template<typename Key,typename Value>
    class static_multimap{
        public:
            static_multimap(std::size_t capacity);
            static constexpr uint32_t cg_size() noexpect{
                return 100;
            }
    };

    template<typename Key,typename Value>
    static_multimap<Key,Value>::static_multimap(std::size_t capicity){

    }

    template <typename Map>
    void test_non_shmem_pair_retrieve(Map& map){
        auto constexpr cg_size =map.cg_size();
    } 

    template<typename Key,typename Value>
    void test_cuco(){
        cuco::static_multimap<Key,Value>map{100};
        auto constexpr cg_size=map.cg_size();             //case1
        test_non_shmem_pair_retrieve(map);                //case2
    }
}

int main(){
    cuco::test_cuco<int64_t,int64_t>();
}

[4465464]

<source>:21:24: error: constexpr variable 'cg_size' must be initialized by a constant expression
        auto constexpr cg_size =map.cg_size();
                       ^        ~~~~~~~~~~~~~
<source>:28:9: note: in instantiation of function template specialization 'cuco::test_non_shmem_pair_retrieve<cuco::static_multimap<long, long>>' requested here
        test_non_shmem_pair_retrieve(map);    //case2
        ^
<source>:33:11: note: in instantiation of function template specialization 'cuco::test_cuco<long, long>' requested here
    cuco::test_cuco<int64_t,int64_t>();
          ^
<source>:21:33: note: function parameter 'map' with unknown value cannot be used in a constant expression
        auto constexpr cg_size =map.cg_size();
                                ^
<source>:20:44: note: declared here
    void test_non_shmem_pair_retrieve(Map& map){
                                           ^
1 error generated.

[4465464]

Call cg_size() function directly can be compiled, but the call in the template will fail

[llvmbot]

@llvm/issue-subscribers-clang-frontend

[shafik]

This is P2280R4 which we can see from the clang status page we don't implement yet.

I am working on this but no ETA yet.

[llvmbot]

@llvm/issue-subscribers-c-20