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From: "pinskia at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug middle-end/109990] [12/13/14 Regression] Bogus -Wuse-after-free
 warning after realloc
Date: Fri, 26 May 2023 14:31:47 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D109990

--- Comment #3 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
(In reply to Andrew Pinski from comment #1)
> ```
>=20
>                   char *new_pool =3D (char *) realloc (string_space, new_=
size);
>                   if (new_pool =3D=3D ((void *)0))
>                     goto out;
>                   if (__builtin_expect (string_space !=3D new_pool, 0))
>                     {
>                       size_t i;
>                       for (i =3D 0; i < nmap; i++)
>                         {
>                           map[i].alias +=3D new_pool - string_space;
>                           map[i].value +=3D new_pool - string_space;
>                         }
>                     }
>                   string_space =3D new_pool;
> ```
>=20
> Hmmm

Also I think `new_pool - string_space` is undefined really.  That is
subtracting two unrelated arrays is undefined. You can only compare equalit=
y on
them.=