On 10/28/25 12:06 AM, Nathaniel Shead wrote:
On Mon, Oct 27, 2025 at 05:04:18PM +0200, Jason Merrill wrote:
On 10/26/25 2:40 PM, Nathaniel Shead wrote:
Bootstrapped and regtested on x86_64-pc-linux-gnu, OK for trunk/15?
-- >8 --
The linker error in the PR is caused because when a static is defined
out of the class body, it doesn't yet have a definition and so
read_var_def (which would otherwise have noted it) never gets called.
I don't object to this change, but there's certainly a definition in
inst6_a, why wouldn't we call read_var_def? I imagine it's because we never
write_var_def for some reason?
Right. We've instantiated Type<int> so a declaration exists for
Type<int>::var, but because of this hunk in instantiate_class_template
no definition has been instantiated yet, so DECL_INITIAL is null, and so
has_definition returns false and we never call write_var_def.
Makes sense, but how is that different from a variable template
specialization that we've instantiated the declaration of, but not the
definition, e.g.
template <class T> T v = T();
decltype(v<int>) v2 = 0;
?
if (VAR_P (r))
{
/* In [temp.inst]:
[t]he initialization (and any associated
side-effects) of a static data member does
not occur unless the static data member is
itself used in a way that requires the
definition of the static data member to
exist.
Therefore, we do not substitute into the
initialized for the static data member here. */
finish_static_data_member_decl
(r,
/*init=*/NULL_TREE,
/*init_const_expr_p=*/false,
/*asmspec_tree=*/NULL_TREE,
/*flags=*/0);
/* Instantiate members marked with attribute used. */
if (r != error_mark_node && DECL_PRESERVE_P (r))
used.safe_push (r);
}
Nathaniel
This instead moves the responsibility for noting class-scope variables
to read_class_def.
PR c++/122421
gcc/cp/ChangeLog:
* module.cc (trees_in::read_var_def): Don't handle class-scope
variables anymore.
(trees_in::read_class_def): Handle them here instead.
gcc/testsuite/ChangeLog:
* g++.dg/modules/inst-6_a.C: New test.
* g++.dg/modules/inst-6_b.C: New test.
Signed-off-by: Nathaniel Shead <[email protected]>
---
gcc/cp/module.cc | 15 +++++++++------
gcc/testsuite/g++.dg/modules/inst-6_a.C | 14 ++++++++++++++
gcc/testsuite/g++.dg/modules/inst-6_b.C | 12 ++++++++++++
3 files changed, 35 insertions(+), 6 deletions(-)
create mode 100644 gcc/testsuite/g++.dg/modules/inst-6_a.C
create mode 100644 gcc/testsuite/g++.dg/modules/inst-6_b.C
diff --git a/gcc/cp/module.cc b/gcc/cp/module.cc
index ed0d69cead4..048aec598dd 100644
--- a/gcc/cp/module.cc
+++ b/gcc/cp/module.cc
@@ -13059,12 +13059,11 @@ trees_in::read_var_def (tree decl, tree
maybe_template)
if (DECL_EXPLICIT_INSTANTIATION (decl)
&& !DECL_EXTERNAL (decl))
setup_explicit_instantiation_definition_linkage (decl);
- if (DECL_IMPLICIT_INSTANTIATION (decl)
- || (DECL_EXPLICIT_INSTANTIATION (decl)
- && !DECL_EXTERNAL (decl))
- || (DECL_CLASS_SCOPE_P (decl)
- && !DECL_VTABLE_OR_VTT_P (decl)
- && !DECL_TEMPLATE_INFO (decl)))
+ /* Class static data members are handled in read_class_def. */
+ if (!DECL_CLASS_SCOPE_P (decl)
+ && (DECL_IMPLICIT_INSTANTIATION (decl)
+ || (DECL_EXPLICIT_INSTANTIATION (decl)
+ && !DECL_EXTERNAL (decl))))
note_vague_linkage_variable (decl);
}
if (!dyn_init)
@@ -13478,6 +13477,10 @@ trees_in::read_class_def (tree defn, tree
maybe_template)
DECL_ACCESS (d) = tree_cons (type, access, list);
}
}
+
+ if (TREE_CODE (decl) == VAR_DECL
+ && TREE_CODE (maybe_template) != TEMPLATE_DECL)
+ note_vague_linkage_variable (decl);
}
}
diff --git a/gcc/testsuite/g++.dg/modules/inst-6_a.C
b/gcc/testsuite/g++.dg/modules/inst-6_a.C
new file mode 100644
index 00000000000..7f35cc161bf
--- /dev/null
+++ b/gcc/testsuite/g++.dg/modules/inst-6_a.C
@@ -0,0 +1,14 @@
+// PR c++/122421
+// { dg-additional-options "-fmodules" }
+// { dg-module-cmi M }
+
+export module M;
+
+export template <typename T> struct Type {
+ static const int arr[3];
+};
+
+extern template const int Type<double>::arr[3];
+template <typename T> const int Type<T>::arr[] = { 42, 43, 44 };
+
+export Type<int> ti;
diff --git a/gcc/testsuite/g++.dg/modules/inst-6_b.C
b/gcc/testsuite/g++.dg/modules/inst-6_b.C
new file mode 100644
index 00000000000..5a8092ccb14
--- /dev/null
+++ b/gcc/testsuite/g++.dg/modules/inst-6_b.C
@@ -0,0 +1,12 @@
+// PR c++/122421
+// { dg-additional-options "-fmodules" }
+
+import M;
+
+int main() {
+ const int& a = Type<int>::arr[0];
+ const int& b = Type<double>::arr[0];
+}
+
+// { dg-final { scan-assembler {_ZNW1M4TypeIiE3arrE:} } }
+// { dg-final { scan-assembler-not {_ZNW1M4TypeIdE3arrE:} } }
