https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105726
--- Comment #4 from Richard Biener <rguenth at gcc dot gnu.org> ---
(In reply to Richard Biener from comment #3)
> The following fixes the bogus diagnostic:
>
> diff --git a/gcc/gimple-ssa-warn-restrict.cc
> b/gcc/gimple-ssa-warn-restrict.cc
> index b678e806da3..25c63f99c61 100644
> --- a/gcc/gimple-ssa-warn-restrict.cc
> +++ b/gcc/gimple-ssa-warn-restrict.cc
> @@ -539,13 +559,6 @@ builtin_memref::set_base_and_offset (tree expr)
> offset_int off = tree_to_shwi (memrefoff);
> refoff += off;
> }
> -
> - if (!integer_zerop (memrefoff))
> - /* A non-zero offset into an array of struct with flexible array
> - members implies that the array is empty because there is no
> - way to initialize such a member when it belongs to an array.
> - This must be some sort of a bug. */
> - refsize = 0;
> }
>
> if (TREE_CODE (ref) == COMPONENT_REF)
It for example regresses gcc.dg/Warray-bounds-46.c which essentially does
struct X { char pad[4]; char ax[]; };
void foo (struct X *p, char *a)
{
__builtin_strcpy (p[1].ax, a);
}
and the intent was to detect that p[1] implies a zero-size 'ax'. That's
going to be interesting to distinguish from our case here with just
the MEM_REF - possibly the easiest heuristic is to trigger this only
for incomplete TREE_TYPE of the MEM_REF at least. That will still
trigger in too many cases, requiring the MEM_REF offset to be a multiple
of the size of the struct will trigger in not enough cases (if there's
also an embedded offset into the array). But maybe it's a good compromise:
diff --git a/gcc/gimple-ssa-warn-restrict.cc b/gcc/gimple-ssa-warn-restrict.cc
index b678e806da3..734cdd7f5b4 100644
--- a/gcc/gimple-ssa-warn-restrict.cc
+++ b/gcc/gimple-ssa-warn-restrict.cc
@@ -525,7 +525,6 @@ builtin_memref::set_base_and_offset (tree expr)
{
tree memrefoff = fold_convert (ptrdiff_type_node, TREE_OPERAND (base,
1));
extend_offset_range (memrefoff);
- base = TREE_OPERAND (base, 0);
if (refoff != HOST_WIDE_INT_MIN
&& TREE_CODE (expr) == COMPONENT_REF)
@@ -538,14 +537,19 @@ builtin_memref::set_base_and_offset (tree expr)
REFOFF is set to s[1].b - (char*)s. */
offset_int off = tree_to_shwi (memrefoff);
refoff += off;
- }
-
- if (!integer_zerop (memrefoff))
- /* A non-zero offset into an array of struct with flexible array
- members implies that the array is empty because there is no
- way to initialize such a member when it belongs to an array.
- This must be some sort of a bug. */
- refsize = 0;
+
+ if (!integer_zerop (memrefoff)
+ && !COMPLETE_TYPE_P (TREE_TYPE (expr))
+ && multiple_of_p (sizetype, memrefoff,
+ TYPE_SIZE_UNIT (TREE_TYPE (base)), true))
+ /* A non-zero offset into an array of struct with flexible array
+ members implies that the array is empty because there is no
+ way to initialize such a member when it belongs to an array.
+ This must be some sort of a bug. */
+ refsize = 0;
+ }
+
+ base = TREE_OPERAND (base, 0);
}
if (TREE_CODE (ref) == COMPONENT_REF)
