https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109990
--- Comment #4 from Bruno Haible <bruno at clisp dot org> ---
> >
> > char *new_pool = (char *) realloc (string_space,
> > new_size);
> > if (new_pool == ((void *)0))
> > goto out;
> > if (__builtin_expect (string_space != new_pool, 0))
> > {
> > size_t i;
> > for (i = 0; i < nmap; i++)
> > {
> > map[i].alias += new_pool - string_space;
> > map[i].value += new_pool - string_space;
> > }
> > }
> > string_space = new_pool;
> Also I think `new_pool - string_space` is undefined really. That is
> subtracting two unrelated arrays is undefined. You can only compare equality
> on them.
That is the only way of keeping track of pointers _into_ the string_space area,
when it is reallocated. How else would you want to do it?
