Strict Aliasing Rule and Type Aliasing in C++
No, it's not legal and you have Undefined Behavior:
8.2.1 Value category [basic.lval]
11 If a program attempts to access the stored value of an object through a glvalue of other than one of the following types the behavior is undefined: 63
(11.1) — the dynamic type of the object,
(11.2) — a cv-qualified version of the dynamic type of the object,
(11.3) — a type similar (as defined in 7.5) to the dynamic type of the object,
(11.4) — a type that is the signed or unsigned type corresponding to the dynamic type of the object,
(11.5) — a type that is the signed or unsigned type corresponding to a cv-qualified version of the dynamic type of the object,
(11.6) — an aggregate or union type that includes one of the aforementioned types among its elements or nonstatic data members (including, recursively, an element or non-static data member of a subaggregate or contained union),
(11.7) — a type that is a (possibly cv-qualified) base class type of the dynamic type of the object,
(11.8) — a char, unsigned char, or std::byte type
63) The intent of this list is to specify those circumstances in which an object may or may not be aliased.