Failure to recognize that `int` and `int[1]` cannot alias

[Kmeakin]

Thanks to C's strict aliasing rules, s->x and a->xs[0] cannot alias.
Therefore the second load of s->x in src is unnecessary.

https://godbolt.org/z/dcEPvE3ef

typedef struct Singleton {
    int x;
} Singleton;

typedef struct Array {
    int xs[1];
} Array;

int src(Singleton* s, Array* a) {
    s->x = 0;
    a->xs[0] = 1;
    return s->x;
}

int tgt(Singleton* s, Array* a) {
    s->x = 0;
    a->xs[0] = 1;
    return 0;
}

src:
        mov     w8, #1
        str     wzr, [x0]
        str     w8, [x1]
        ldr     w0, [x0]
        ret

tgt:
        mov     w8, #1
        str     wzr, [x0]
        mov     w0, wzr
        str     w8, [x1]
        ret

[Kmeakin]

Another example:

https://godbolt.org/z/osn99346v

struct Data2 {
    int i[1];
    char c;
};

struct Slice2 {
    struct Data2 *pData;
    int len;
};

// Optimized by GCC but not LLVM
int test2(struct Slice2 *slice) {
    int len_before = slice->len;

    slice->pData->i[0] = 0;

    int len_after = slice->len;

    return len_before == len_after;
}