https://gcc.gnu.org/bugzilla/show_bug.cgi?id=89106
--- Comment #4 from Alexander Monakov <amonakov at gcc dot gnu.org> --- My concern is that the cast does not "create a compound literal": what it creates is an object, more specifically, an unnamed temporary object in automatic storage with unspecified lifetime [1]. A compound literal in function scope similarly creates an unnamed object. Likewise, the "result" of a cast-to-union is that temporary object, taken as rvalue. So to explain it well to users, the documentation would have to say something like: A cast to a union creates a temporary object of the given union type, initialized via a member matching the type of the operand, and taken as rvalue (unlike a compound literal, which yields an lvalue). [1] gcc doesn't seem to emit any gimple clobber statements for such casts, so effectively the lifetime is "entire function scope", but that is likely not intentional
