> On Oct 20, 2023, at 3:10 PM, Siddhesh Poyarekar <siddh...@gotplt.org> wrote:
>
> On 2023-10-20 14:38, Qing Zhao wrote:
>> How about the following:
>> Add one more parameter to __builtin_dynamic_object_size(), i.e
>> __builtin_dynamic_object_size (_1,1,array_annotated->foo)?
>> When we see the structure field has counted_by attribute.
>
> Or maybe add a barrier preventing any assignments to array_annotated->foo
> from being reordered below the __bdos call? Basically an __asm__ with
> array_annotated->foo in the clobber list ought to do it I think.
Maybe just adding the array_annotated->foo to the use list of the call to
__builtin_dynamic_object_size should be enough?
But I am not sure how to implement this in the TREE level, is there a
USE_LIST/CLOBBER_LIST for each call? Then I can just simply add the counted_by
field “array_annotated->foo” to the USE_LIST of the call to __bdos?
This might be the simplest solution?
Qing
>
> It may not work for something like this though:
>
> static size_t
> get_size_of (void *ptr)
> {
> return __bdos (ptr, 1);
> }
>
> void
> foo (size_t sz)
> {
> array_annotated = __builtin_malloc (sz);
> array_annotated = sz;
>
> ...
> __builtin_printf ("%zu\n", get_size_of (array_annotated->foo));
> ...
> }
>
> because the call to get_size_of () may not have been inlined that early.
>
> The more fool-proof alternative may be to put a compile time barrier right
> below the assignment to array_annotated->foo; I reckon you could do that
> early in the front end by marking the size identifier and then tracking
> assignments to that identifier. That may have a slight runtime performance
> overhead since it may prevent even legitimate reordering. I can't think of
> another alternative at the moment...
>
> Sid
