PrependStructSlot prepends a struct onto the object at vtable slot `o`.
        Structs are stored inline, so nothing additional is being added.
        In generated code, `d` is always 0.

def PrependStructSlot(self, v, x, d):
        """
        PrependStructSlot prepends a struct onto the object at vtable slot `o`.
        Structs are stored inline, so nothing additional is being added.
        In generated code, `d` is always 0.
        """

        N.enforce_number(d, N.UOffsetTFlags)
        if x != d:
            self.assertStructIsInline(x)
            self.Slot(v)