https://gcc.gnu.org/bugzilla/show_bug.cgi?id=85244
Richard Biener <rguenth at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Status|NEW |ASSIGNED
Assignee|unassigned at gcc dot gnu.org |rguenth at gcc dot
gnu.org
--- Comment #3 from Richard Biener <rguenth at gcc dot gnu.org> ---
(In reply to Jakub Jelinek from comment #2)
> That said, it is get_ref_base_and_extent that for the variable index returns
> offset 96 bits and size == maxsize == 32, identical to the [0] case.
>
> Perhaps we shouldn't trust:
> 638 /* If maxsize is unknown adjust it according to the size of the
> 639 base decl. */
> 640 else if (!known_size_p (maxsize)
> 641 && DECL_SIZE (exp)
> 642 && poly_int_tree_p (DECL_SIZE (exp)))
> 643 maxsize = wi::to_poly_offset (DECL_SIZE (exp)) - bit_offset;
> if exp is DECL_EXTERNAL and the struct/union ends with flexible array member
> (or flexible array member-like array)? Perhaps we'd need to remember from
> the case where we set seen_variable_array_ref to true if it was
> array_at_end_of_struct_p and if yes and DECL_EXTERNAL, ignore this?
>
> Richard?
Hmm, what about
extern int a[];
or
extern int a[1];
?
so should we just treat structs with trailing flexible arrays in this way
(flexible as in [] or [0]?).
I think if we fix another case in get_ref_base_and_extent like with
Index: gcc/tree-dfa.c
===================================================================
--- gcc/tree-dfa.c (revision 259082)
+++ gcc/tree-dfa.c (working copy)
@@ -464,6 +464,11 @@ get_ref_base_and_extent (tree exp, poly_
maxsize += tem;
}
}
+ /* An component ref with an adjacent field up in the
+ structure hierarchy constrains the size of any variable
+ array ref lower in the access hierarchy. */
+ if (next)
+ seen_variable_array_ref = false;
}
}
else
then we can just do
@@ -622,7 +627,9 @@ get_ref_base_and_extent (tree exp, poly_
if (DECL_P (exp))
{
- if (flag_unconstrained_commons && VAR_P (exp) && DECL_COMMON (exp))
+ if (VAR_P (exp)
+ && ((flag_unconstrained_commons && DECL_COMMON (exp))
+ || (DECL_EXTERNAL (exp) && seen_variable_array_ref)))
{
tree sz_tree = TYPE_SIZE (TREE_TYPE (exp));
/* If size is unknown, or we have read to the end, assume there
and that way also handle plain arrays (very) conservatively.
