module_ m makes every function referenced by ref.func inside a function body declared as referenceable, so the module passes strict reference validation. Functions already referenced in an element-segment or global initialiser are already declared and left alone; the rest are added to an existing declarative element segment (extending it) or, if there is none, a fresh one appended to the module.

A module containing conditional ((@if ...)) fields is returned unchanged: a referenced function may be defined only under some configuration, so a single declarative segment cannot name it safely (and such a module cannot be emitted to the binary format anyway).