On Thu, May 22, 2025 at 12:14:34PM +1000, Nathaniel Shead wrote:
> This patch isn't currently necessary with how I've currently done the
> follow-up patches, but is needed for avoiding any potential issues in
> the future with DECL_CONTEXT'ful types getting created in the compiler
> with no names on the fields. (For instance, this change would make much
> of r15-7342-gd3627c78be116e unnecessary.)
>
> It does take up another flag though in the frontend though. Another
> possible approach would be to instead do a walk through all the fields
> first to see if this is the target of a DECL_BIT_FIELD_REPRESENTATIVE;
> thoughts? Or would you prefer to skip this patch entirely?
>
Ping.
> -- >8 --
>
> Modules streaming needs to handle these differently from other unnamed
> FIELD_DECLs that are streamed for internal RECORD_DECLs, and there
> doesn't seem to be a good way to detect this case otherwise.
>
> gcc/cp/ChangeLog:
>
> * module.cc (trees_out::get_merge_kind): Use new flag.
>
> gcc/ChangeLog:
>
> * stor-layout.cc (start_bitfield_representative): Mark with
> DECL_BIT_FIELD_UNDERLYING_REPR_P.
> * tree-core.h (struct tree_decl_common): Add comment.
> * tree.h (DECL_BIT_FIELD_UNDERLYING_REPR_P): New accessor.
>
> Signed-off-by: Nathaniel Shead <nathanielosh...@gmail.com>
> ---
> gcc/cp/module.cc | 4 +---
> gcc/stor-layout.cc | 1 +
> gcc/tree-core.h | 1 +
> gcc/tree.h | 5 +++++
> 4 files changed, 8 insertions(+), 3 deletions(-)
>
> diff --git a/gcc/cp/module.cc b/gcc/cp/module.cc
> index 13f8770b7bd..99cbfdbf01d 100644
> --- a/gcc/cp/module.cc
> +++ b/gcc/cp/module.cc
> @@ -11131,9 +11131,7 @@ trees_out::get_merge_kind (tree decl, depset *dep)
> return MK_named;
> }
>
> - if (!DECL_NAME (decl)
> - && !RECORD_OR_UNION_TYPE_P (TREE_TYPE (decl))
> - && !DECL_BIT_FIELD_REPRESENTATIVE (decl))
> + if (!DECL_NAME (decl) && DECL_BIT_FIELD_UNDERLYING_REPR_P (decl))
> {
> /* The underlying storage unit for a bitfield. We do not
> need to dedup it, because it's only reachable through
> diff --git a/gcc/stor-layout.cc b/gcc/stor-layout.cc
> index 12071c96ca7..1f37a130e24 100644
> --- a/gcc/stor-layout.cc
> +++ b/gcc/stor-layout.cc
> @@ -2067,6 +2067,7 @@ static tree
> start_bitfield_representative (tree field)
> {
> tree repr = make_node (FIELD_DECL);
> + DECL_BIT_FIELD_UNDERLYING_REPR_P (repr) = 1;
> DECL_FIELD_OFFSET (repr) = DECL_FIELD_OFFSET (field);
> /* Force the representative to begin at a BITS_PER_UNIT aligned
> boundary - C++ may use tail-padding of a base object to
> diff --git a/gcc/tree-core.h b/gcc/tree-core.h
> index bd19c99d326..2e773d7bf83 100644
> --- a/gcc/tree-core.h
> +++ b/gcc/tree-core.h
> @@ -1911,6 +1911,7 @@ struct GTY(()) tree_decl_common {
> unsigned decl_read_flag : 1;
> /* In a VAR_DECL or RESULT_DECL, this is DECL_NONSHAREABLE. */
> /* In a PARM_DECL, this is DECL_HIDDEN_STRING_LENGTH. */
> + /* In a FIELD_DECL, this is DECL_BIT_FIELD_UNDERLYING_REPR_P. */
> unsigned decl_nonshareable_flag : 1;
>
> /* DECL_OFFSET_ALIGN, used only for FIELD_DECLs. */
> diff --git a/gcc/tree.h b/gcc/tree.h
> index 99f26177628..0d876234824 100644
> --- a/gcc/tree.h
> +++ b/gcc/tree.h
> @@ -3085,6 +3085,11 @@ extern void decl_value_expr_insert (tree, tree);
> #define DECL_BIT_FIELD_REPRESENTATIVE(NODE) \
> (FIELD_DECL_CHECK (NODE)->field_decl.qualifier)
>
> +/* In a FIELD_DECL of a RECORD_TYPE, this indicates whether the field
> + is used as the underlying storage unit for a bitfield. */
> +#define DECL_BIT_FIELD_UNDERLYING_REPR_P(NODE) \
> + (FIELD_DECL_CHECK (NODE)->decl_common.decl_nonshareable_flag)
> +
> /* For a FIELD_DECL in a QUAL_UNION_TYPE, records the expression, which
> if nonzero, indicates that the field occupies the type. */
> #define DECL_QUALIFIER(NODE) (FIELD_DECL_CHECK (NODE)->field_decl.qualifier)
> --
> 2.47.0
>
