Is a non-constant zero integer cast to `void *` still a null pointer?

The expresssion (void *)0 is called a null pointer. But how about the following:

int i = 0;
void *s = (void *)i;

Is s also a null-pointer? The C-language standard says:

6.3.2.3 Pointers

3 An integer constant expression with the value 0, such an expression cast to type void *, or the predefined constant nullptr is called a null pointer constant⁷⁰⁾. If a null pointer constant or a value of the type nullptr_t (which is necessarily the value nullptr) is converted to a pointer type, the resulting pointer, called a null pointer, is guaranteed to compare unequal to a pointer to any object or function.

4 Conversion of a null pointer to another pointer type yields a null pointer of that type. Any two null pointers shall compare equal.

5 An integer may be converted to any pointer type. Except as previously specified, the result is implementation-defined, might not be correctly aligned, might not point to an entity of the referenced type, and might produce an indeterminate representation when stored into an object.⁷¹⁾

According to this s would not be a null pointer?

It will be on any typical modern system, but it doesn't have to be. Nothing in the standard requires pointer casts to behave the same for constant expressions and non-constant expressions.

The standard rationale document makes this explicit. From the C99 Rationale, Revision 5.10, 6.3.2.3:

Since pointers and integers are now considered incommensurate, the only integer value that can be safely converted to a pointer is a constant expression with the value 0. The result of converting any other integer value, including a non-constant expression with the value 0, to a pointer is implementation-defined.