[llvm-bugs] [Bug 145398] Failure to recognize that `int` and `int[1]` cannot alias

[LLVM Bugs via llvm-bugs]

Issue	145398
Summary	Failure to recognize that `int` and `int[1]` cannot alias
Labels	missed-optimization, TBAA
Assignees
Reporter	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
```c
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;
}
```

```asm
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
```

_______________________________________________
llvm-bugs mailing list
llvm-bugs@lists.llvm.org
https://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-bugs