[Bug lto/112716] New: LTO optimization with struct of variable ssize

[muecker at gwdg dot de via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=112716

            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: 

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

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

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

        if (!p)
                return 0;

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

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