{"id":2226100,"url":"http://patchwork.ozlabs.org/api/patches/2226100/?format=json","web_url":"http://patchwork.ozlabs.org/project/gcc/patch/bmm.hhu8qqul0c.gcc.gcc-TEST.redi.3.1.1@forge-stage.sourceware.org/","project":{"id":17,"url":"http://patchwork.ozlabs.org/api/projects/17/?format=json","name":"GNU Compiler Collection","link_name":"gcc","list_id":"gcc-patches.gcc.gnu.org","list_email":"gcc-patches@gcc.gnu.org","web_url":null,"scm_url":null,"webscm_url":null,"list_archive_url":"","list_archive_url_format":"","commit_url_format":""},"msgid":"","list_archive_url":null,"date":"2026-04-22T08:54:47","name":"[v1,1/1] libstdc++: Simplify std::__throw_bad_variant_access","commit_ref":null,"pull_url":null,"state":"new","archived":false,"hash":"9436999e9f71a2cc0bfa3af6d4a476657531b526","submitter":{"id":93210,"url":"http://patchwork.ozlabs.org/api/people/93210/?format=json","name":"Jonathan Wakely via Sourceware Forge","email":"forge-bot+redi@forge-stage.sourceware.org"},"delegate":null,"mbox":"http://patchwork.ozlabs.org/project/gcc/patch/bmm.hhu8qqul0c.gcc.gcc-TEST.redi.3.1.1@forge-stage.sourceware.org/mbox/","series":[{"id":500949,"url":"http://patchwork.ozlabs.org/api/series/500949/?format=json","web_url":"http://patchwork.ozlabs.org/project/gcc/list/?series=500949","date":"2026-04-22T08:54:46","name":"libstdc++: Simplify std::__throw_bad_variant_access","version":1,"mbox":"http://patchwork.ozlabs.org/series/500949/mbox/"}],"comments":"http://patchwork.ozlabs.org/api/patches/2226100/comments/","check":"pending","checks":"http://patchwork.ozlabs.org/api/patches/2226100/checks/","tags":{},"related":[],"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 spf=pass (sender SPF authorized) smtp.mailfrom=gcc.gnu.org\n (client-ip=2620:52:6:3111::32; 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server2.sourceware.org","From":"Jonathan Wakely via Sourceware Forge\n ","Date":"Wed, 22 Apr 2026 08:54:47 +0000","Subject":"[PATCH v1 1/1] libstdc++: Simplify std::__throw_bad_variant_access","To":"gcc-patches mailing list ","Message-ID":"\n ","X-Mailer":"batrachomyomachia","X-Requested-Reviewer":"ppalka","X-Pull-Request-Organization":"gcc","X-Pull-Request-Repository":"gcc-TEST","X-Pull-Request":"https://forge.sourceware.org/gcc/gcc-TEST/pulls/3","References":"\n ","In-Reply-To":"\n ","X-Patch-URL":"\n https://forge.sourceware.org/redi/gcc/commit/f9cdc7e69f3aa30fb19aec0ee30d31bb43601515","X-BeenThere":"gcc-patches@gcc.gnu.org","X-Mailman-Version":"2.1.30","Precedence":"list","List-Id":"Gcc-patches mailing list ","List-Unsubscribe":",\n ","List-Archive":"","List-Post":"","List-Help":"","List-Subscribe":",\n ","Reply-To":"gcc-patches mailing list , redi@gcc.gnu.org","Errors-To":"gcc-patches-bounces~incoming=patchwork.ozlabs.org@gcc.gnu.org"},"content":"From: Jonathan Wakely \n\nThis removes the overload of __throw_bad_variant_access that must be\ncalled with a string literal. This avoids a potential source of\nundefined behaviour if that function got misused. The other overload\nthat takes a bool parameter can be adjusted to take an integer index\nselecting one of the four possible string literals to use, ensuring\nthat the std::bad_variant_access constructor is only called with those\nliterals.\n\nPassing an index outside the range [0,3] is bogus, but will still select\na valid string literal and avoid undefined behaviour.\n\nlibstdc++-v3/ChangeLog:\n\n\t* include/std/variant (__throw_bad_variant_access(unsigned)):\n\tDefine new function as inline friend, with namespace-scope\n\tdeclaration using noreturn attribute.\n\t(__throw_bad_variant_access(const char*)): Remove.\n\t(__throw_bad_variant_access(bool)): Remove.\n\t(visit, visit): Adjust calls to __throw_bad_variant_access.\n---\n libstdc++-v3/include/std/variant | 32 +++++++++++++++-----------------\n 1 file changed, 15 insertions(+), 17 deletions(-)","diff":"diff --git a/libstdc++-v3/include/std/variant b/libstdc++-v3/include/std/variant\nindex cf532126d798..6d768e10bf95 100644\n--- a/libstdc++-v3/include/std/variant\n+++ b/libstdc++-v3/include/std/variant\n@@ -1402,6 +1402,8 @@ namespace __detail::__variant\n \t\t && (is_swappable_v<_Types> && ...))>\n swap(variant<_Types...>&, variant<_Types...>&) = delete;\n \n+ [[noreturn]] void __throw_bad_variant_access(unsigned);\n+\n class bad_variant_access : public exception\n {\n public:\n@@ -1411,28 +1413,24 @@ namespace __detail::__variant\n { return _M_reason; }\n \n private:\n+ // Must only be called with a string literal\n bad_variant_access(const char* __reason) noexcept : _M_reason(__reason) { }\n \n // Must point to a string with static storage duration:\n const char* _M_reason = \"bad variant access\";\n \n- friend void __throw_bad_variant_access(const char* __what);\n+ friend void __throw_bad_variant_access(unsigned __n)\n+ {\n+ [[maybe_unused]] static constexpr const char* __reasons[] = {\n+\t\"std::get: wrong index for variant\",\n+\t\"std::get: variant is valueless\",\n+\t\"std::visit: variant is valueless\",\n+\t\"std::visit: variant is valueless\",\n+ };\n+ _GLIBCXX_THROW_OR_ABORT(bad_variant_access(__reasons[__n % 4u]));\n+ }\n };\n \n- // Must only be called with a string literal\n- inline void\n- __throw_bad_variant_access(const char* __what)\n- { _GLIBCXX_THROW_OR_ABORT(bad_variant_access(__what)); }\n-\n- inline void\n- __throw_bad_variant_access(bool __valueless)\n- {\n- if (__valueless) [[__unlikely__]]\n- __throw_bad_variant_access(\"std::get: variant is valueless\");\n- else\n- __throw_bad_variant_access(\"std::get: wrong index for variant\");\n- }\n-\n template\n class variant\n : private __detail::__variant::_Variant_base<_Types...>,\n@@ -1941,7 +1939,7 @@ namespace __detail::__variant\n namespace __variant = std::__detail::__variant;\n \n if ((__variant::__as(__variants).valueless_by_exception() || ...))\n-\t__throw_bad_variant_access(\"std::visit: variant is valueless\");\n+\t__throw_bad_variant_access(2);\n \n using _Result_type\n \t= __detail::__variant::__visit_result_t<_Visitor, _Variants...>;\n@@ -1981,7 +1979,7 @@ namespace __detail::__variant\n namespace __variant = std::__detail::__variant;\n \n if ((__variant::__as(__variants).valueless_by_exception() || ...))\n-\t__throw_bad_variant_access(\"std::visit: variant is valueless\");\n+\t__throw_bad_variant_access(3);\n \n return std::__do_visit<_Res>(std::forward<_Visitor>(__visitor),\n \t __variant::__as(std::forward<_Variants>(__variants))...);\n","prefixes":["v1","1/1"]}