On 02/02/2016 08:21 PM, Martin Sebor wrote:
On 02/02/2016 05:28 AM, Jason Merrill wrote:
On 01/25/2016 05:55 PM, Martin Sebor wrote:
The downside of this approach is that it prevents everything but
the front end from distinguishing flexible array members from
arrays of unspecified or unknown bounds. The immediate impact
is that prevents us from maintaining ABI compatibility with GCC
5 (with -fabi-version=9) and from diagnosing the mangling change.
This means should we decide to adopt this approach, the final
version of the patch for c++/69277 mentioned above that's still
pending approval will need to be tweaked to have the ABI checks
removed.
That's unfortunate, but I think acceptable.
* decl.c (compute_array_index_type): Return null for flexible array
members.
Instead of this, I would think we can remove the calls to
compute_array_index_type added by your earlier patch, as well as many
other changes from that patch to handle null TYPE_MAX_VALUE.
Yes, that's possible but it didn't seem essential at this stage.
I wanted to make only conservative changes to avoid any further
fallout. I also wasn't sure whether the ABI issue above would
make this approach unviable.
I guess my sense of conservatism is different from yours: I think
removing recent changes is conservative in that it minimizes the change
from previous versions of the compiler.
* tree.c (array_of_runtime_bound_p): Handle gracefully array types
with null TYPE_MAX_VALUE.
This seems unneeded.
(build_ctor_subob_ref): Loosen debug checking to handle flexible
array members.
And this shouldn't need the TYPE_MAX_VALUE check.
I went ahead and made the requested changes. They might seem
perfectly innocuous to you but the removal of the tests for
TYPE_MAX_VALUE(t) being null makes me nervous at this stage.
I'm not nearly comfortable enough with the code to be confident
that they're all 100% safe. I defer to your better judgment
on this.
It was impossible to have null TYPE_MAX_VALUE until you introduced that
in compute_array_index_type, and thus we didn't test for it; if we
aren't doing that anymore I can't imagine where it would come from now.
@@ -4120,9 +4120,8 @@ walk_subobject_offsets (tree type,
- || !domain
- /* Flexible array members have no upper bound. */
- || !TYPE_MAX_VALUE (domain))
+ /* Flexible array members have a null domain. */
+ || !domain)
With this patch flexible array members are a special case of array of
unknown bound, so I don't think we need to call them out in a comment here.
@@ -875,10 +875,11 @@ dump_type_suffix (cxx_pretty_printer *pp, tree t, int
flags)
- if (TYPE_DOMAIN (t) && TYPE_MAX_VALUE (TYPE_DOMAIN (t)))
+ /* C++ flexible array members have a null domain. */
+ if (tree dtype = TYPE_DOMAIN (t))
Likewise.
OK with these two comments removed.
Jason
