Re: [PATCH] adjust object size computation for union accesses and PHIs (PR 92765)

[Martin Sebor <msebor@gmail.com>]

On 2/4/20 7:35 AM, Richard Biener wrote:
>>
...
>> Jakub/Richi, comments on this hunk?
> 
> +         tree ref = TREE_OPERAND (TREE_OPERAND (arg, 0), 0);
> +         tree off = TREE_OPERAND (arg, 1);
> +         if ((TREE_CODE (ref) == PARM_DECL || VAR_P (ref))
> +             && (!DECL_EXTERNAL (ref)
> +                 || !array_at_struct_end_p (arg)))
> +           {
> 
> I think you'd want decl_binds_to_current_def_p (ref) instead of !DECL_EXTERNAL.

I've made the change.

> Since 'arg' is originally a pointer array_at_struct_end_p is
> meaningless here since
> that's about the structure of a reference while the pointer is just a
> value.

array_at_struct_end_p handles MEM_REF by looking at the argument
(i.e., at the DECL when it is one), so its use here avoids DECLs
with flexible arrays but allows others.  In other words, I don't
want to exclude MEM_REFs to a in:

   extern char a[4];

just because a is extern.

> So if
> you're concerned the objects size might not be as it looks like then you have to
> rely on decl_binds_to_current_def_p only.

I'm only concerned about sizes of extern objects of struct types
with flexible array members.  I believe others are handled fine.

> You also shouldn't use 'off' natively
> in the code below but use mem_ref_offset to access the embedded offset
> which is to be interpreted as signed integer (it's a pointer as you use it).
> You compare it against an unsigned size...

I've changed it in the latest revision of the patch.

Martin