[{"id":3673801,"web_url":"http://patchwork.ozlabs.org/comment/3673801/","msgid":"","list_archive_url":null,"date":"2026-04-06T16:41:49","subject":"Re: [PATCH] c++/modules: Fix propagating noexcept for templates\n [PR124785]","submitter":{"id":4337,"url":"http://patchwork.ozlabs.org/api/people/4337/","name":"Jason Merrill","email":"jason@redhat.com"},"content":"On 4/5/26 10:56 AM, Nathaniel Shead wrote:\n> Bootstrapped and regtested on x86_64-pc-linux-gnu, OK for trunk/15?\n\nOK.\n\n> -- >8 --\n> \n> We triggered a checking assertion because when propagating deduced\n> noexcept, we were updating the type of the existing TEMPLATE_DECL but\n> not the type of its DECL_TEMPLATE_RESULT, violating assumptions made\n> later on during modules streaming.\n> \n> But actually there was nothing to propagate here anyway, these\n> declarations are identical, so this patch also fixes the condition for\n> checking whether we need to propagate anything. And so now I don't\n> think there is ever a case we should have a noexcept-spec to propagate\n> for a TEMPLATE_DECL, so add an assertion to validate this.\n> \n> \tPR c++/124785\n> \n> gcc/cp/ChangeLog:\n> \n> \t* module.cc (trees_in::is_matching_decl): Narrow condition for\n> \twhen noexcept propagation occurs; assert that we don't propagate\n> \tnoexcept-specs for TEMPLATE_DECLs.\n> \n> gcc/testsuite/ChangeLog:\n> \n> \t* g++.dg/modules/noexcept-5.h: New test.\n> \t* g++.dg/modules/noexcept-5_a.C: New test.\n> \t* g++.dg/modules/noexcept-5_b.C: New test.\n> \t* g++.dg/modules/noexcept-5_c.C: New test.\n> \n> Signed-off-by: Nathaniel Shead \n> ---\n> gcc/cp/module.cc | 4 +++-\n> gcc/testsuite/g++.dg/modules/noexcept-5.h | 4 ++++\n> gcc/testsuite/g++.dg/modules/noexcept-5_a.C | 7 +++++++\n> gcc/testsuite/g++.dg/modules/noexcept-5_b.C | 7 +++++++\n> gcc/testsuite/g++.dg/modules/noexcept-5_c.C | 11 +++++++++++\n> 5 files changed, 32 insertions(+), 1 deletion(-)\n> create mode 100644 gcc/testsuite/g++.dg/modules/noexcept-5.h\n> create mode 100644 gcc/testsuite/g++.dg/modules/noexcept-5_a.C\n> create mode 100644 gcc/testsuite/g++.dg/modules/noexcept-5_b.C\n> create mode 100644 gcc/testsuite/g++.dg/modules/noexcept-5_c.C\n> \n> diff --git a/gcc/cp/module.cc b/gcc/cp/module.cc\n> index a8517569a1b..8b820f97fee 100644\n> --- a/gcc/cp/module.cc\n> +++ b/gcc/cp/module.cc\n> @@ -12619,12 +12619,14 @@ trees_in::is_matching_decl (tree existing, tree decl, bool is_typedef)\n> tree d_spec = TYPE_RAISES_EXCEPTIONS (d_type);\n> if (DECL_MAYBE_DELETED (e_inner) || DEFERRED_NOEXCEPT_SPEC_P (e_spec))\n> \t{\n> -\t if (!DEFERRED_NOEXCEPT_SPEC_P (d_spec)\n> +\t if (!(DECL_MAYBE_DELETED (d_inner)\n> +\t\t|| DEFERRED_NOEXCEPT_SPEC_P (d_spec))\n> \t || (UNEVALUATED_NOEXCEPT_SPEC_P (e_spec)\n> \t\t && !UNEVALUATED_NOEXCEPT_SPEC_P (d_spec)))\n> \t {\n> \t dump (dumper::MERGE)\n> \t\t&& dump (\"Propagating instantiated noexcept to %N\", existing);\n> +\t gcc_checking_assert (existing == e_inner);\n> \t TREE_TYPE (existing) = d_type;\n> \n> \t /* Propagate to existing clones. */\n> diff --git a/gcc/testsuite/g++.dg/modules/noexcept-5.h b/gcc/testsuite/g++.dg/modules/noexcept-5.h\n> new file mode 100644\n> index 00000000000..78d91322a1a\n> --- /dev/null\n> +++ b/gcc/testsuite/g++.dg/modules/noexcept-5.h\n> @@ -0,0 +1,4 @@\n> +// PR c++/124785\n> +template struct Iterator {\n> + constexpr friend auto operator<=>(const Iterator&, const Iterator&) = default;\n> +};\n> diff --git a/gcc/testsuite/g++.dg/modules/noexcept-5_a.C b/gcc/testsuite/g++.dg/modules/noexcept-5_a.C\n> new file mode 100644\n> index 00000000000..72085717e60\n> --- /dev/null\n> +++ b/gcc/testsuite/g++.dg/modules/noexcept-5_a.C\n> @@ -0,0 +1,7 @@\n> +// PR c++/124785\n> +// { dg-do compile { target c++20 } }\n> +// { dg-additional-options \"-fmodules\" }\n> +// { dg-module-cmi M:A }\n> +\n> +export module M:A;\n> +#include \"noexcept-5.h\"\n> diff --git a/gcc/testsuite/g++.dg/modules/noexcept-5_b.C b/gcc/testsuite/g++.dg/modules/noexcept-5_b.C\n> new file mode 100644\n> index 00000000000..928980b6c1d\n> --- /dev/null\n> +++ b/gcc/testsuite/g++.dg/modules/noexcept-5_b.C\n> @@ -0,0 +1,7 @@\n> +// PR c++/124785\n> +// { dg-do compile { target c++20 } }\n> +// { dg-additional-options \"-fmodules\" }\n> +// { dg-module-cmi M:B }\n> +\n> +export module M:B;\n> +#include \"noexcept-5.h\"\n> diff --git a/gcc/testsuite/g++.dg/modules/noexcept-5_c.C b/gcc/testsuite/g++.dg/modules/noexcept-5_c.C\n> new file mode 100644\n> index 00000000000..d9349147766\n> --- /dev/null\n> +++ b/gcc/testsuite/g++.dg/modules/noexcept-5_c.C\n> @@ -0,0 +1,11 @@\n> +// PR c++/124785\n> +// { dg-do compile { target c++20 } }\n> +// { dg-additional-options \"-fmodules -fdump-lang-module-alias\" }\n> +// { dg-module-cmi M }\n> +\n> +export module M;\n> +export import :A;\n> +export import :B;\n> +\n> +// The noexcept-specifiers are equivalent, no need to merge.\n> +// { dg-final { scan-lang-dump-not {Propagating instantiated noexcept} module } }","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=ZRgzkSB2;\n\tdkim-atps=neutral","legolas.ozlabs.org;\n spf=pass (sender SPF authorized) smtp.mailfrom=gcc.gnu.org\n (client-ip=38.145.34.32; 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