They are problem in the sense that the address of the pointer gets exposed. After you lose track of who has it and who might do what with it, you can't track the aliasing information of the pointer, so you have to suppress some optimizations. But you are correct in the sense that if int2ptr never happens, it's all good.
About side effects: we are not talking about having side effects on hardware level, we are talking about side effects from the compiler's viewpoint. Again, the compiler might track aliasing information for optimizations, and casting has the side effect of "exposing" the pointer.
About side effects: we are not talking about having side effects on hardware level, we are talking about side effects from the compiler's viewpoint. Again, the compiler might track aliasing information for optimizations, and casting has the side effect of "exposing" the pointer.