Consider the following example that compiles with clang but is rejected by clang,gcc and msvc. Demo

#include <initializer_list>

struct C
{ 
    C(){}
    C(std::initializer_list<int> i = {3})
    {
    }  
};

int main()
{
    C d{};   //clang:Ok, gcc:No, MSVC: No, EDG: No
}

As we can see clang accepts the code while gcc and others reject it. GCC says:

<source>: In function 'int main()':
<source>:20:9: error: call of overloaded 'C(<brace-enclosed initializer list>)' is ambiguous
   20 |     C d{};   //clang:Ok, gcc:No, MSVC: No, EDG: No
      |         ^
<source>:10:5: note: candidate: 'C::C(std::initializer_list<int>)'
   10 |     C(std::initializer_list<int> i = {3})
      |     ^
<source>:6:5: note: candidate: 'C::C()'
    6 |     C()
      |     ^

I want to know which compiler is correct here as per the latest standard.