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From: "lsof at mailbox dot org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug c/110402] New: Bogus -Waddress warning that pointer comparison
 is always true
Date: Sun, 25 Jun 2023 09:58:39 +0000
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X-Bugzilla-Version: 13.1.1
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D110402

            Bug ID: 110402
           Summary: Bogus -Waddress warning that pointer comparison is
                    always true
           Product: gcc
           Version: 13.1.1
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c
          Assignee: unassigned at gcc dot gnu.org
          Reporter: lsof at mailbox dot org
  Target Milestone: ---

Created attachment 55398
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=3D55398&action=3Dedit
testcase

In the following testcase:


struct m { float *v; int t; };

_Bool chk(struct m *m, int key) {
    return (m->t =3D key) < 0 ? 0 : &m->v[key];
}

/* a comma expression can suppress it */
_Bool chk2(struct m *m, int key) {
    return (m->t =3D key, m->t < 0 ? 0 : &m->v[key]);
}

/* however, this does NOT warn */
_Bool chk3(struct m *m, int key) {
    return (m->t =3D key) < 0 ? &m->v[key] : &m->v[key];
}


gcc -Waddress gives this warning:

x.c: In function =E2=80=98chk=E2=80=99:
x.c:4:5: warning: the comparison will always evaluate as =E2=80=98true=E2=
=80=99 for the pointer
operand in =E2=80=98m->v + (sizetype)((long unsigned int)key * 4)=E2=80=99 =
must not be NULL
[-Waddress]
    4 |     return key < 0 ? 0 : &m->v[key];
      |     ^~~~~~

In particular the second function does not produce the warning (correctly),=
 but
the third function for which the warning actually applies does not give a
warning.=