On 5/21/25 10:14 PM, 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?
It seems like the only way to reach such a FIELD_DECL is through
DECL_BIT_FIELD_REPRESENTATIVE, so we ought to be able to use that
without adding another walk?
-- >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)
