curiosity about constexpr

While thinking about how to implement constexpr in Cake for structs/unions, a question came to mind.
Do they emulated "shared" storage in unions?
So, I decided to test it using GCC and Clang.
https://godbolt.org/z/dqz9jcx13
union X
{
     int i;
     bool b;
};
constexpr union X x = { .i = 1 };
static_assert(x.i == 1);
static_assert(x.b == 1); //error
The answer seems NO, constexpr don't emulate what happens in runtime.
I also checked in C++.
https://godbolt.org/z/6qosY4xbK
union X {
     int i;
     bool b;
};
consteval int f(int i)
{
   union X x={0};
   x.i = i;
   return x.b;
}
int main()
{
     constexpr int i = f(2);
}