rapidsna wrote:
> With this PR I get:
>
> ```
> $ clang -O2 ~/llvm/bdos.c
> $ ./a.out
> 400
> 400
> 404
> ```
Oh I see.
> I think the first two `printf` s in your code seem correct with 40, because
> they're both looking at only the FAM, not the entire struct.
Interesting. So this sounds different from non-fam array cases. When the struct
is not a flexible array member, e.g., `struct s {int a; int arr[3]; int b;};`
`__bdos(&p->arr[0], 0)` would return the whole object size instead of the
array-only size (12). https://godbolt.org/z/1e9nKPYb4 Was this difference part
of the specification?
> struct flex *p = (struct flex *)malloc(sizeof(struct flex) + sizeof(int) *
> 10);
I just wanted to call out that this case is interesting because the size
derived from malloc and __counted_by compete each other. And __counted_by
always wins. This conforms to how `-fbounds-safety` will see the size of
objects, so sounds like we are all happy with it.
Similarly, this will also mean that , when we support `__counted_by` for
pointers, the following will be the case.
```
int arr[10];
int *__counted_by(4) p = arr;
__bdos(arr, 0); // returns 4 * sizeof(int) instead of 10 * sizeof(int)
```
https://github.com/llvm/llvm-project/pull/70606
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