Why do I get "use of undeclared identifier" even when using constexr if?

play with the code.

template<typename T>
T f() {
    if constexpr (std::is_same<T, int>::value) {
        T t = 10;
    }else {
        T t;
    }
    return t;
}

My understanding of the above code is that the body of f will either be

int t = 10; 
return t;

or

T t = // some default value for T 
return t;

depending on T. In both there will be an identifier called t. Why does the compiler still complain about use of undeclared identifier 't'?.

Does the compiler check for undeclared identifiers before it resolves constexpr statements?