https://gcc.gnu.org/g:5b85364a6dd0bbfd3e26d3346b075a0819be7cd4
commit r16-3353-g5b85364a6dd0bbfd3e26d3346b075a0819be7cd4
Author: Nathaniel Shead <nathanielosh...@gmail.com>
Date: Fri Aug 22 15:15:01 2025 +1000
c++/modules: Provide definitions of synthesized methods outside their
defining module [PR120499]
In the PR, we're getting a linker error from _Vector_impl's destructor
never getting emitted. This is because of a combination of factors:
1. in imp-member-4_a, the destructor is not used and so there is no
definition generated.
2. in imp-member-4_b, the destructor gets synthesized (as part of the
synthesis for Coll's destructor) but is not ODR-used and so does not
get emitted. Despite there being a definition provided in this TU,
the destructor is still considered imported and so isn't streamed
into the module body.
3. in imp-member-4_c, we need to ODR-use the destructor but we only got
a forward declaration from imp-member-4_b, so we cannot emit a body.
The point of failure here is step 2; this function has effectively been
declared in the imp-member-4_b module, and so we shouldn't treat it as
imported. This way we'll properly stream the body so that importers can
emit it.
PR c++/120499
gcc/cp/ChangeLog:
* method.cc (synthesize_method): Set the instantiating module.
gcc/testsuite/ChangeLog:
* g++.dg/modules/imp-member-4_a.C: New test.
* g++.dg/modules/imp-member-4_b.C: New test.
* g++.dg/modules/imp-member-4_c.C: New test.
Signed-off-by: Nathaniel Shead <nathanielosh...@gmail.com>
Diff:
---
gcc/cp/method.cc | 3 +++
gcc/testsuite/g++.dg/modules/imp-member-4_a.C | 25 +++++++++++++++++++++++++
gcc/testsuite/g++.dg/modules/imp-member-4_b.C | 17 +++++++++++++++++
gcc/testsuite/g++.dg/modules/imp-member-4_c.C | 14 ++++++++++++++
4 files changed, 59 insertions(+)
diff --git a/gcc/cp/method.cc b/gcc/cp/method.cc
index 397e496ed477..ef8370fac5b3 100644
--- a/gcc/cp/method.cc
+++ b/gcc/cp/method.cc
@@ -1851,6 +1851,9 @@ synthesize_method (tree fndecl)
finish_function_body (stmt);
finish_function (/*inline_p=*/false);
+ /* Remember that we were defined in this module. */
+ set_instantiating_module (fndecl);
+
if (!DECL_DELETED_FN (fndecl))
expand_or_defer_fn (fndecl);
diff --git a/gcc/testsuite/g++.dg/modules/imp-member-4_a.C
b/gcc/testsuite/g++.dg/modules/imp-member-4_a.C
new file mode 100644
index 000000000000..f0699eb314cf
--- /dev/null
+++ b/gcc/testsuite/g++.dg/modules/imp-member-4_a.C
@@ -0,0 +1,25 @@
+// PR c++/120499
+// { dg-additional-options "-fmodules -fdump-lang-module-blocks" }
+// { dg-module-cmi A }
+
+export module A;
+
+struct allocator {
+ ~allocator() {}
+};
+
+export template <typename _Tp>
+struct vector {
+ struct _Vector_impl : public allocator {};
+ _Vector_impl _M_impl;
+ vector() = default;
+};
+
+template <typename T>
+struct regex_token_iterator {
+ vector<int> _M_subs;
+};
+template struct regex_token_iterator<const char*>;
+
+// No definition of _Vector_impl::~_Vector_impl here (not synthesized)
+// { dg-final { scan-lang-dump-not
{'::vector@A:1<int>::_Vector_impl@A:1<int>::__dt '} module } }
diff --git a/gcc/testsuite/g++.dg/modules/imp-member-4_b.C
b/gcc/testsuite/g++.dg/modules/imp-member-4_b.C
new file mode 100644
index 000000000000..db485095e777
--- /dev/null
+++ b/gcc/testsuite/g++.dg/modules/imp-member-4_b.C
@@ -0,0 +1,17 @@
+// PR c++/120499
+// { dg-additional-options "-fmodules -fdump-lang-module-blocks" }
+// { dg-module-cmi B }
+
+export module B;
+import A;
+
+struct Coll {
+ vector<int> vals;
+};
+
+export Coll createColl() {
+ return Coll{};
+}
+
+// But the definition of _Vector_impl::~_Vector_impl has been synthesized here
+// { dg-final { scan-lang-dump-times {\[0\]=decl definition
'::vector@A:1<int>::_Vector_impl@A:1<int>::__dt '} 1 module } }
diff --git a/gcc/testsuite/g++.dg/modules/imp-member-4_c.C
b/gcc/testsuite/g++.dg/modules/imp-member-4_c.C
new file mode 100644
index 000000000000..d405ce28bf7a
--- /dev/null
+++ b/gcc/testsuite/g++.dg/modules/imp-member-4_c.C
@@ -0,0 +1,14 @@
+// PR c++/120499
+// { dg-module-do link }
+// { dg-additional-options "-fmodules -fdump-lang-module" }
+
+import B;
+
+int main() {
+ createColl();
+}
+
+// And we should use the definition of _Vector_impl::~_Vector_impl now.
+// In this case we got the seeded import from A of the declaration
+// so let's just ensure we stream the definition.
+// { dg-final { scan-lang-dump {Reading function definition
'::vector@A:1<int>::_Vector_impl@A:1<int>::__dt @A:1'} module } }
