If `x` is a constant, `(x) * 0l` is a zero constant, so `(void*)((x) * 0l)` is a null pointer. When a null void pointer is one branch of a ternary conditional, the expression takes the (pointer) type of the other branch.

If `x` is not a constant, `(void*)((x) * 0l)` is a void pointer to address 0 (which may not even be a null pointer at runtime, since null may have a runtime address distinct from zero!). The ternary conditional then unifies the types of the branches, resulting in `void*`.

My understanding of how it works is, with constant value, the compiler replaces (x) with the constant 0 and converts (void *) into (int *) which makes the size equality to return true. But I am not entire sure :)