[{"id":3681479,"web_url":"http://patchwork.ozlabs.org/comment/3681479/","msgid":"","list_archive_url":null,"date":"2026-04-23T13:54:48","subject":"Re: [PATCH] c++/modules: PTRMEM_CST member considered unused\n [PR124981]","submitter":{"id":4337,"url":"http://patchwork.ozlabs.org/api/people/4337/","name":"Jason Merrill","email":"jason@redhat.com"},"content":"On 4/22/26 4:19 PM, Patrick Palka wrote:\n> Tested on x86_64-pc-linux-gnu, does this look OK for 17/16.2?\n\nOK.\n\n> -- >8 --\n> \n> Here from the importer side the specialization A has already\n> been instantiated in module M, so we stream it in rather than\n> instantiate it. We then proceed to instantiate A::f() whose\n> definition invokes the pointer-to-member &B::g, clearly a use, but it\n> turns out that nothing has marked B::g as used in _b.C and we complain\n> at link time about an undefined reference.\n> \n> Without modules we would have marked B::g as used during instantiation\n> of A via mark_template_arguments_used. But this instantiaton\n> happens in module M, not the importer.\n> \n> This patch fixes this by force setting TREE_USED on PTRMEM_CST_MEMBER\n> during stream-in, via the RTU macro, which seems sufficient to ensure\n> B::g gets emitted. I don't fully understand the reason for this RTU macro\n> but it's already used for streaming in operands of tcc_expression nodes\n> and BASELINK_FUNCTIONS so using it for PTRMEM_CST_MEMBER doesn't seem too\n> out of place.\n> \n> \tPR c++/124981\n> \n> gcc/cp/ChangeLog:\n> \n> \t* module.cc (trees_in::core_vals) : Use RTU\n> \tinstead of RT to stream PTRMEM_CST_MEMBER.\n> \n> gcc/testsuite/ChangeLog:\n> \n> \t* g++.dg/modules/ptrmem-1_a.C: New test.\n> \t* g++.dg/modules/ptrmem-1_b.C: New test.\n> ---\n> gcc/cp/module.cc | 2 +-\n> gcc/testsuite/g++.dg/modules/ptrmem-1_a.C | 21 +++++++++++++++++++++\n> gcc/testsuite/g++.dg/modules/ptrmem-1_b.C | 10 ++++++++++\n> 3 files changed, 32 insertions(+), 1 deletion(-)\n> create mode 100644 gcc/testsuite/g++.dg/modules/ptrmem-1_a.C\n> create mode 100644 gcc/testsuite/g++.dg/modules/ptrmem-1_b.C\n> \n> diff --git a/gcc/cp/module.cc b/gcc/cp/module.cc\n> index e5547f7d029f..61e9e70936bd 100644\n> --- a/gcc/cp/module.cc\n> +++ b/gcc/cp/module.cc\n> @@ -7443,7 +7443,7 @@ trees_in::core_vals (tree t)\n> break;\n> \n> case PTRMEM_CST:\n> - RT (((lang_tree_node *)t)->ptrmem.member);\n> + RTU (((lang_tree_node *)t)->ptrmem.member);\n> break;\n> \n> case STATIC_ASSERT:\n> diff --git a/gcc/testsuite/g++.dg/modules/ptrmem-1_a.C b/gcc/testsuite/g++.dg/modules/ptrmem-1_a.C\n> new file mode 100644\n> index 000000000000..ca16c39bea3b\n> --- /dev/null\n> +++ b/gcc/testsuite/g++.dg/modules/ptrmem-1_a.C\n> @@ -0,0 +1,21 @@\n> +// PR c++/124981\n> +// { dg-additional-options \"-fmodules\" }\n> +// { dg-module-cmi M }\n> +\n> +export module M;\n> +\n> +template\n> +struct A {\n> + void f(const T& t) {\n> + (t.*F)();\n> + }\n> +};\n> +\n> +export\n> +template\n> +struct B {\n> + void g() const { }\n> + A m;\n> +};\n> +\n> +B b;\n> diff --git a/gcc/testsuite/g++.dg/modules/ptrmem-1_b.C b/gcc/testsuite/g++.dg/modules/ptrmem-1_b.C\n> new file mode 100644\n> index 000000000000..5c65bfc1fb10\n> --- /dev/null\n> +++ b/gcc/testsuite/g++.dg/modules/ptrmem-1_b.C\n> @@ -0,0 +1,10 @@\n> +// PR c++/124981\n> +// { dg-additional-options \"-fmodules\" }\n> +// { dg-module-do link }\n> +\n> +import M;\n> +\n> +int main() {\n> + B b;\n> + b.m.f(b);\n> +}","headers":{"Return-Path":"","X-Original-To":["incoming@patchwork.ozlabs.org","gcc-patches@gcc.gnu.org"],"Delivered-To":["patchwork-incoming@legolas.ozlabs.org","gcc-patches@gcc.gnu.org"],"Authentication-Results":["legolas.ozlabs.org;\n\tdkim=pass (1024-bit key;\n unprotected) header.d=redhat.com header.i=@redhat.com header.a=rsa-sha256\n header.s=mimecast20190719 header.b=g16TPBMd;\n\tdkim-atps=neutral","legolas.ozlabs.org;\n spf=pass (sender SPF authorized) smtp.mailfrom=gcc.gnu.org\n (client-ip=2620:52:6:3111::32; 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