On Mon, May 19, 2025 at 04:56:38PM -0400, Jason Merrill wrote:
> On 5/19/25 8:27 AM, Nathaniel Shead wrote:
> > Bootstrapped and regtested on x86_64-pc-linux-gnu, OK for trunk?
> >
> > Alternatively could go back to always marking vtables as DECL_EXTERNAL
> > as well but that doesn't seem to be necessary that I can tell.
>
> DECL_NOT_REALLY_EXTERN doesn't make sense without DECL_EXTERNAL. The
> antiquated linkage handling in the front end marks everything that might or
> might not get emitted with those two flags (and DECL_DEFER_OUTPUT for
> functions). I'd like to simplify that, it's been excessive since the
> introduction of cgraph, but for now we should be marking vtables as
> DECL_EXTERNAL.
>
Right, that does make sense, thanks.
Here's an updated patch to just restore the old behaviour: bootstrapped
and regtested on x86_64-pc-linux-gnu, OK for trunk?
-- >8 --
I missed a testcase in r16-688-gc875748cdc468e for whether a GM vtable
should be emitted in an importer when it has no non-inline key function.
Before that patch the code worked because always we marked all vtables
as DECL_EXTERNAL, which then meant that reading the definition marked
them as DECL_NOT_REALLY_EXTERN.
This patch restores the old behaviour so that vtables are marked
DECL_EXTERNAL (and hence DECL_NOT_REALLY_EXTERN).
PR c++/120349
gcc/cp/ChangeLog:
* module.cc (trees_out::core_bools): Always mark vtables as
DECL_EXTERNAL.
gcc/testsuite/ChangeLog:
* g++.dg/modules/vtt-3_a.C: New test.
* g++.dg/modules/vtt-3_b.C: New test.
Signed-off-by: Nathaniel Shead <nathanielosh...@gmail.com>
Reviewed-by: Jason Merrill <ja...@redhat.com>
---
gcc/cp/module.cc | 8 +++++--
gcc/testsuite/g++.dg/modules/vtt-3_a.C | 29 ++++++++++++++++++++++++++
gcc/testsuite/g++.dg/modules/vtt-3_b.C | 14 +++++++++++++
3 files changed, 49 insertions(+), 2 deletions(-)
create mode 100644 gcc/testsuite/g++.dg/modules/vtt-3_a.C
create mode 100644 gcc/testsuite/g++.dg/modules/vtt-3_b.C
diff --git a/gcc/cp/module.cc b/gcc/cp/module.cc
index f728275612e..13f8770b7bd 100644
--- a/gcc/cp/module.cc
+++ b/gcc/cp/module.cc
@@ -5724,9 +5724,13 @@ trees_out::core_bools (tree t, bits_out& bits)
DECL_NOT_REALLY_EXTERN -> base.not_really_extern
== that was a lie, it is here */
- /* decl_flag_1 is DECL_EXTERNAL. Things we emit here, might
- well be external from the POV of an importer. */
bool is_external = t->decl_common.decl_flag_1;
+ /* maybe_emit_vtables relies on vtables being marked as
+ DECL_EXTERNAL and DECL_NOT_REALLY_EXTERN before processing. */
+ if (!is_external && VAR_P (t) && DECL_VTABLE_OR_VTT_P (t))
+ is_external = true;
+ /* Things we emit here might well be external from the POV of an
+ importer. */
if (!is_external
&& VAR_OR_FUNCTION_DECL_P (t)
&& get_importer_interface (t) == importer_interface::external)
diff --git a/gcc/testsuite/g++.dg/modules/vtt-3_a.C
b/gcc/testsuite/g++.dg/modules/vtt-3_a.C
new file mode 100644
index 00000000000..f38f024ba1f
--- /dev/null
+++ b/gcc/testsuite/g++.dg/modules/vtt-3_a.C
@@ -0,0 +1,29 @@
+// PR c++/120349
+// { dg-additional-options "-fmodules -Wno-global-module" }
+// { dg-module-cmi M }
+
+module;
+
+// GMF types; should have vtables emitted in importers
+struct BGG {
+ virtual inline ~BGG() {}
+};
+struct BGM {
+ virtual inline ~BGM() {}
+};
+struct DGG : BGG {};
+
+export module M;
+
+export using ::DGG;
+
+// Module-local types; should have vtables emitted here
+struct BM {
+ virtual inline ~BM() {}
+};
+export struct DGM : BGM {}; // note: this emits BGM's vtable here too
+export struct DM : BM {};
+
+// { dg-final { scan-assembler-not "_ZTV3BGG:" } }
+// { dg-final { scan-assembler "_ZTV3BGM:" } }
+// { dg-final { scan-assembler "_ZTVW1M2BM:" } }
diff --git a/gcc/testsuite/g++.dg/modules/vtt-3_b.C
b/gcc/testsuite/g++.dg/modules/vtt-3_b.C
new file mode 100644
index 00000000000..ef7ae6ca4e6
--- /dev/null
+++ b/gcc/testsuite/g++.dg/modules/vtt-3_b.C
@@ -0,0 +1,14 @@
+// PR c++/120349
+// { dg-additional-options "-fmodules -Wno-global-module" }
+
+import M;
+
+int main() {
+ DGG dgg;
+ DGM dgm;
+ DM dm;
+}
+
+// { dg-final { scan-assembler "_ZTV3BGG:" } }
+// { dg-final { scan-assembler "_ZTV3BGM:" } }
+// { dg-final { scan-assembler-not "_ZTVW1M2BM:" } }
--
2.47.0
