[Bug middle-end/109557] __builtin_dynamic_object_size() does not work for simple testing case

[siddhesh at gcc dot gnu.org via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109557

--- Comment #2 from Siddhesh Poyarekar <siddhesh at gcc dot gnu.org> ---
(In reply to qinzhao from comment #0)
> I am wondering for 
> p.3_1 = p;
> _2 = __builtin_object_size (p.3_1, 0);
> 
> why the size of p.3_1 cannot use the TYPE_SIZE of the pointee of p when its
> size can be determined (i.e, not a structure with a flexible array member,
> etc)?

To answer this specific question, it's because the compiler can't see in main()
if p is pointing to any actual storage.