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From: "muecker at gwdg dot de" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug lto/112716] New: LTO optimization with struct of variable ssize
Date: Sun, 26 Nov 2023 17:46:53 +0000
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X-Bugzilla-Type: new
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X-Bugzilla-Product: gcc
X-Bugzilla-Component: lto
X-Bugzilla-Version: 14.0
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X-Bugzilla-Severity: normal
X-Bugzilla-Who: muecker at gwdg dot de
X-Bugzilla-Status: UNCONFIRMED
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X-Bugzilla-Priority: P3
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D112716

            Bug ID: 112716
           Summary: LTO optimization with struct of variable ssize
           Product: gcc
           Version: 14.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: lto
          Assignee: unassigned at gcc dot gnu.org
          Reporter: muecker at gwdg dot de
                CC: marxin at gcc dot gnu.org
  Target Milestone: ---

The following code using a GNU extension gets miscompiled due to incorrect
aliasing assumptions with -flto and -O2:=20

gcc -flto -O2 y.c y2.c  -DT1=3D"int[n]" -DT2=3D"int[n]"
// y.c
void bar(void*);

[[gnu::noinline,gnu::noipa]]
int foo(void *p, void *q)
{
        int n =3D 5;
        struct foo { int x; typeof(T1) y; } *p2 =3D p;
        p2->x =3D 1;
        bar(q);
        return p2->x;
}

int main()
{
        int n =3D 5;
        void *p =3D __builtin_malloc(sizeof(struct foo { int x; typeof(T1) =
y;
}));

        if (!p)
                return 0;

        if (2 !=3D foo(p, p))
                __builtin_abort();

        return 0;
}
// y2
void bar(void* q)
{=20=20=20=20=20=20=20
        int n =3D 5;
        struct foo { int x; typeof(T2) y; } *q2 =3D q;
        q2->x =3D 2;
}=