On Tue, Jan 22, 2019 at 06:18:28PM -0700, Martin Sebor wrote:
> PS In GCC 10, unless there is an important use case that escapes
> me, I think GCC should warn for zero-length non-member array
> objects, or perhaps even for internal struct members (those followed
> by another member). Not to avoid these sorts of bugs but because
> they seem too dangerous to use safely.
No, we shouldn't warn.
> --- gcc/gimple-fold.c (revision 268086)
> +++ gcc/gimple-fold.c (working copy)
> @@ -6715,12 +6715,14 @@ fold_array_ctor_reference (tree type, tree ctor,
> elt_size = wi::to_offset (TYPE_SIZE_UNIT (TREE_TYPE (TREE_TYPE (ctor))));
>
> /* When TYPE is non-null, verify that it specifies a constant-sized
> - accessed not larger than size of array element. */
> - if (type
> - && (!TYPE_SIZE_UNIT (type)
> - || TREE_CODE (TYPE_SIZE_UNIT (type)) != INTEGER_CST
> - || elt_size < wi::to_offset (TYPE_SIZE_UNIT (type))
> - || elt_size == 0))
> + accessed not larger than size of array element. Avoid using zero
> + ELT_SIZE, the result of an empty initializer for a zero-length
> + array. */
The comment is misleading, there are many reasons why you could have
zero elt_size, C struct S {}, or int x[10][0], etc. Just don't change
anything in the comment at all, or say
Punt if element size is zero to avoid division by zero.
or something similar.
> + if (elt_size == 0
> + || (type
> + && (!TYPE_SIZE_UNIT (type)
> + || TREE_CODE (TYPE_SIZE_UNIT (type)) != INTEGER_CST
> + || elt_size < wi::to_offset (TYPE_SIZE_UNIT (type)))))
> return NULL_TREE;
Otherwise LGTM.
If you could fix also the two comments a few lines above this:
/* Static constructors for variably sized objects makes no sense. */
to
/* Static constructors for variably sized objects make no sense. */
it would be appreciated.
Jakub
