Calling base function through wrong pointer

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Putting aside all the good practices against writing code like below, just from the language lawyer perspective, is the following snippet legal?

struct Base {
  int f() { return 42; }
};
struct D1 : Base {};
struct D2 : Base {};

int main() {
  D2 d2;
  D1* ouch = reinterpret_cast<D1*>(&D2);
  return ouch->f();
}

It seems to me that [class.mfct.non.static] is the most relevant clause and that it suggests it is ok, as we are calling a non-static member function for an object of a derived class.

Should it happen that the non-virtual case is indeed legal, does anything change if f or the inheritance is virtual?

c++20 c++17 language-lawyer inheritance c++
1 Answers

CWG 2535 underlines that, unlike for unions (where common initial sequences of standard layout types can be reused), accessing class members through a pointer of distinct class type is undefined.

For an instance of practical relevance: if you used the created pointer to modify a member of d2, that could be rearranged with other accesses to that member during optimization, as a result of alias analysis.

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