Jakub Jelinek <ja...@redhat.com> writes:
> Hi!
>
> On Tue, Apr 21, 2020 at 03:58:52PM +0100, Richard Sandiford wrote:
>> > if (TREE_CODE (field) != FIELD_DECL)
>> > continue;
>> >
>> > - sub_count = aapcs_vfp_sub_candidate (TREE_TYPE (field), modep);
>> > + /* Ignore C++17 empty base fields, while their type indicates
>> > + they do contain padding, they have zero size and thus don't
>> > + contain any padding. */
>> > + if (DECL_ARTIFICIAL (field)
>> > + && DECL_NAME (field) == NULL_TREE
>> > + && RECORD_OR_UNION_TYPE_P (TREE_TYPE (field))
>> > + && DECL_SIZE (field)
>> > + && integer_zerop (DECL_SIZE (field))
>> > + && (*avoid_c17empty_field & AVOID))
>> > + {
>
> As multiple targets are affected apparently, I believe at least
> aarch64, arm, powerpc64le, s390{,x} and ia64,
> I think we should have a middle-end predicate for this, so that if we need
> to tweak it, we can do it in one spot.
>
> So is the following ok (of course after testing)?
>
> 2020-04-22 Jakub Jelinek <ja...@redhat.com>
>
> PR target/94383
> * calls.h (cxx17_empty_base_field_p): Declare.
> * calls.c (cxx17_empty_base_field_p): Define.
>
> --- gcc/calls.h.jj 2020-01-12 11:54:36.214416411 +0100
> +++ gcc/calls.h 2020-04-22 11:44:09.037853379 +0200
> @@ -135,5 +135,6 @@ extern tree get_attr_nonstring_decl (tre
> extern void maybe_warn_nonstring_arg (tree, tree);
> extern bool get_size_range (tree, tree[2], bool = false);
> extern rtx rtx_for_static_chain (const_tree, bool);
> +extern bool cxx17_empty_base_field_p (const_tree);
>
> #endif // GCC_CALLS_H
> --- gcc/calls.c.jj 2020-03-27 22:27:09.615964438 +0100
> +++ gcc/calls.c 2020-04-22 11:44:17.621722376 +0200
> @@ -6261,5 +6261,22 @@ must_pass_va_arg_in_stack (tree type)
> return targetm.calls.must_pass_in_stack (arg);
> }
>
> +/* Return true if FIELD is the C++17 empty base field that should
> + be ignored for ABI calling convention decisions in order to
> + maintain ABI compatibility between C++14 and earlier, which doesn't
> + add this FIELD to classes with empty bases, and C++17 and later
> + which does. */
> +
> +bool
> +cxx17_empty_base_field_p (const_tree field)
> +{
> + return (TREE_CODE (field) == FIELD_DECL
> + && DECL_ARTIFICIAL (field)
> + && DECL_NAME (field) == NULL_TREE
Given what was said on irc about DECL_NAME not necessarily being
significant for DECL_ARTIFICIAL decls, would it be better to drop
this part of the check?
Thanks,
Richard
> + && RECORD_OR_UNION_TYPE_P (TREE_TYPE (field))
> + && DECL_SIZE (field)
> + && integer_zerop (DECL_SIZE (field)));
> +}
> +
> /* Tell the garbage collector about GTY markers in this source file. */
> #include "gt-calls.h"
>
>
> Jakub
