[clang++ Bug] subobject of type 'unsigned int' is not initialized

[AFN4096]

The following code compiled successfully with MSVC, GCC(C++11), but failed with CLANG(C++11)

#include <iostream>
#include <stdexcept>
 
int main()
{
    union Reg{
        struct {
            unsigned int A1                           :  8;
            unsigned int                                : 24;
        } bits, bitfields;
    
        unsigned int u32All;
        signed int   i32All;
        float        f32All;
    };

    constexpr uint MaxTargets = 8;

    constexpr struct
    {
        Reg a[MaxTargets];
        Reg b[MaxTargets];
        Reg c[MaxTargets];
        Reg d[MaxTargets];
    } base = {};

    std::cout << base.a[0].f32All << std::endl;
}

Error Information:

main.cpp:25:7: error: constexpr variable 'base' must be initialized by a constant expression
    } base = {};
      ^      ~~
main.cpp:25:7: note: subobject of type 'unsigned int' is not initialized
1 error generated.

Could be workaround by following modification code

#include <iostream>
#include <stdexcept>
 
int main()
{
    union Reg{
        struct {
            unsigned int  A1                           :  8;
            unsigned int  A2                              : 24;
        } bits, bitfields;
    
        unsigned int u32All;
        signed int   i32All;
        float        f32All;
    };

    constexpr uint MaxTargets = 8;

    constexpr struct
    {
        Reg a[MaxTargets];
        Reg b[MaxTargets];
        Reg c[MaxTargets];
        Reg d[MaxTargets];
    } base = {};

    std::cout << base.a[0].f32All << std::endl;
}

and

#include <iostream>
#include <stdexcept>
 
int main()
{
    union Reg{
        unsigned int u32All;
        signed int   i32All;
        float        f32All;

        struct {
            unsigned int  A1                           :  8;
            unsigned int  A2                            : 24;
        } bits, bitfields;

    };

    constexpr uint MaxTargets = 8;

    constexpr struct
    {
        Reg a[MaxTargets];
        Reg b[MaxTargets];
        Reg c[MaxTargets];
        Reg d[MaxTargets];
    } base = {};

    std::cout << base.a[0].f32All << std::endl;
}

Could someone look into this issue? The problem exists in c++11/14/17.

[AFN4096]

Ok, find the issue has been solved in >= clang 6.0.