https://gcc.gnu.org/g:e3db74150f5eee104b996cc6f69d3e721b8832b9
commit r16-1736-ge3db74150f5eee104b996cc6f69d3e721b8832b9
Author: Nathaniel Shead <nathanielosh...@gmail.com>
Date: Tue May 20 23:07:20 2025 +1000
c++/modules: Implement streaming of uncontexted TYPE_DECLs [PR98735]
Currently, most declarations must have a DECL_CONTEXT for modules
streaming to behave correctly, so that they can have an appropriate
merge key generated and be correctly deduplicated on import.
There are a few exceptions, however, for internally generated
declarations that will never be merged and don't necessarily have an
appropriate parent to key off for the context. One case that's come up
a few times is TYPE_DECLs, especially temporary RECORD_TYPEs used as
intermediaries within expressions.
Previously I've tried to give all such types a DECL_CONTEXT, but in some
cases that has ended up being infeasible, such as with the types
generated by UBSan (which are shared with the C frontend and don't know
their context, especially when created at global scope). Additionally,
these types often don't have many of the parts that a normal struct
declaration created via parsing user code would have, which confuses
module streaming.
Given that these types are typically intended to be one-off and unique
anyway, this patch instead adds support for by-value streaming of
uncontexted TYPE_DECLs. The patch only support streaming the bare
minimum amount of fields needed for the cases I've come across so far;
in general the preference should still be to ensure that DECL_CONTEXT is
set where possible.
PR c++/98735
PR c++/120040
gcc/cp/ChangeLog:
* module.cc (trees_out::tree_value): Write TYPE_DECLs.
(trees_in::tree_value): Read TYPE_DECLs.
(trees_out::tree_node): Support uncontexted TYPE_DECLs, and
ensure that all parts of a by-value decl are marked for
streaming.
(trees_out::get_merge_kind): Treat members of uncontexted types
as always unique.
Signed-off-by: Nathaniel Shead <nathanielosh...@gmail.com>
Reviewed-by: Jason Merrill <ja...@redhat.com>
Diff:
---
gcc/cp/module.cc | 102 ++++++++++++++++++++++++++++++++++++++++++++++++++++---
1 file changed, 97 insertions(+), 5 deletions(-)
diff --git a/gcc/cp/module.cc b/gcc/cp/module.cc
index c99988da05b8..3e77d6ffde52 100644
--- a/gcc/cp/module.cc
+++ b/gcc/cp/module.cc
@@ -9658,9 +9658,10 @@ trees_out::tree_value (tree t)
if (DECL_P (t))
/* No template, type, var or function, except anonymous
- non-context vars. */
+ non-context vars and types. */
gcc_checking_assert ((TREE_CODE (t) != TEMPLATE_DECL
- && TREE_CODE (t) != TYPE_DECL
+ && (TREE_CODE (t) != TYPE_DECL
+ || (DECL_ARTIFICIAL (t) && !DECL_CONTEXT (t)))
&& (TREE_CODE (t) != VAR_DECL
|| (!DECL_NAME (t) && !DECL_CONTEXT (t)))
&& TREE_CODE (t) != FUNCTION_DECL));
@@ -9674,7 +9675,7 @@ trees_out::tree_value (tree t)
tree_node_bools (t);
}
- if (TREE_CODE (t) == TREE_BINFO)
+ if (TREE_CODE (t) == TREE_BINFO)
/* Binfos are decl-like and need merging information. */
binfo_mergeable (t);
@@ -9683,8 +9684,49 @@ trees_out::tree_value (tree t)
dump (dumper::TREE)
&& dump ("Writing tree:%d %C:%N", tag, TREE_CODE (t), t);
+ int type_tag = 0;
+ tree type = NULL_TREE;
+ if (TREE_CODE (t) == TYPE_DECL)
+ {
+ type = TREE_TYPE (t);
+
+ /* We only support a limited set of features for uncontexted types;
+ these are typically types created in the language-independent
+ parts of the frontend (such as ubsan). */
+ gcc_checking_assert (RECORD_OR_UNION_TYPE_P (type)
+ && TYPE_MAIN_VARIANT (type) == type
+ && TYPE_NAME (type) == t
+ && TYPE_STUB_DECL (type) == t
+ && !TYPE_VFIELD (type)
+ && !TYPE_BINFO (type)
+ && !CLASS_TYPE_P (type));
+
+ if (streaming_p ())
+ {
+ start (type);
+ tree_node_bools (type);
+ }
+
+ type_tag = insert (type, WK_value);
+ if (streaming_p ())
+ dump (dumper::TREE)
+ && dump ("Writing type: %d %C:%N", type_tag,
+ TREE_CODE (type), type);
+ }
+
tree_node_vals (t);
+ if (type)
+ {
+ tree_node_vals (type);
+ tree_node (TYPE_SIZE (type));
+ tree_node (TYPE_SIZE_UNIT (type));
+ chained_decls (TYPE_FIELDS (type));
+ if (streaming_p ())
+ dump (dumper::TREE)
+ && dump ("Written type:%d %C:%N", type_tag, TREE_CODE (type), type);
+ }
+
if (streaming_p ())
dump (dumper::TREE) && dump ("Written tree:%d %C:%N", tag, TREE_CODE (t),
t);
}
@@ -9723,14 +9765,48 @@ trees_in::tree_value ()
dump (dumper::TREE)
&& dump ("Reading tree:%d %C", tag, TREE_CODE (t));
- if (!tree_node_vals (t))
+ int type_tag = 0;
+ tree type = NULL_TREE;
+ if (TREE_CODE (t) == TYPE_DECL)
+ {
+ type = start ();
+ if (!type || !tree_node_bools (type))
+ t = NULL_TREE;
+
+ type_tag = insert (type);
+ if (t)
+ dump (dumper::TREE)
+ && dump ("Reading type:%d %C", type_tag, TREE_CODE (type));
+ }
+
+ if (!t)
{
+bail:
back_refs[~tag] = NULL_TREE;
+ if (type_tag)
+ back_refs[~type_tag] = NULL_TREE;
set_overrun ();
- /* Bail. */
return NULL_TREE;
}
+ if (!tree_node_vals (t))
+ goto bail;
+
+ if (type)
+ {
+ if (!tree_node_vals (type))
+ goto bail;
+
+ TYPE_SIZE (type) = tree_node ();
+ TYPE_SIZE_UNIT (type) = tree_node ();
+ TYPE_FIELDS (type) = chained_decls ();
+ if (get_overrun ())
+ goto bail;
+
+ dump (dumper::TREE)
+ && dump ("Read type:%d %C:%N", type_tag, TREE_CODE (type), type);
+ }
+
if (TREE_CODE (t) == LAMBDA_EXPR
&& CLASSTYPE_LAMBDA_EXPR (TREE_TYPE (t)))
{
@@ -9984,7 +10060,18 @@ trees_out::tree_node (tree t)
PARM_DECLS. It'd be nice if they had a
distinguishing flag to double check. */
break;
+
+ case TYPE_DECL:
+ /* Some parts of the compiler need internal struct types;
+ these types may not have an appropriate context to use.
+ Walk the whole type (including its definition) by value. */
+ gcc_checking_assert (DECL_ARTIFICIAL (t)
+ && TYPE_ARTIFICIAL (TREE_TYPE (t))
+ && RECORD_OR_UNION_TYPE_P (TREE_TYPE (t))
+ && !CLASS_TYPE_P (TREE_TYPE (t)));
+ break;
}
+ mark_declaration (t, has_definition (t));
goto by_value;
}
}
@@ -11124,6 +11211,11 @@ trees_out::get_merge_kind (tree decl, depset *dep)
return MK_local_friend;
gcc_checking_assert (TYPE_P (ctx));
+
+ /* Internal-only types will not need to dedup their members. */
+ if (!DECL_CONTEXT (TYPE_NAME (ctx)))
+ return MK_unique;
+
if (TREE_CODE (decl) == USING_DECL)
return MK_field;
