{"id":2222777,"url":"http://patchwork.ozlabs.org/api/patches/2222777/?format=json","web_url":"http://patchwork.ozlabs.org/project/gcc/patch/20260413164814.90675-1-jwakely@redhat.com/","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":"<20260413164814.90675-1-jwakely@redhat.com>","list_archive_url":null,"date":"2026-04-13T16:47:58","name":"c++tools: Use std::map::try_emplace to avoid use-after-move","commit_ref":null,"pull_url":null,"state":"new","archived":false,"hash":"fdb812622edca4ab30f9f407f5c23aec660f65f0","submitter":{"id":48004,"url":"http://patchwork.ozlabs.org/api/people/48004/?format=json","name":"Jonathan Wakely","email":"jwakely@redhat.com"},"delegate":null,"mbox":"http://patchwork.ozlabs.org/project/gcc/patch/20260413164814.90675-1-jwakely@redhat.com/mbox/","series":[{"id":499729,"url":"http://patchwork.ozlabs.org/api/series/499729/?format=json","web_url":"http://patchwork.ozlabs.org/project/gcc/list/?series=499729","date":"2026-04-13T16:47:58","name":"c++tools: Use std::map::try_emplace to avoid use-after-move","version":1,"mbox":"http://patchwork.ozlabs.org/series/499729/mbox/"}],"comments":"http://patchwork.ozlabs.org/api/patches/2222777/comments/","check":"pending","checks":"http://patchwork.ozlabs.org/api/patches/2222777/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\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=YaPN/VRN;\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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a=rsa-sha256; c=relaxed/relaxed; d=redhat.com;\n s=mimecast20190719; t=1776098902;\n h=from:from:reply-to:subject:subject:date:date:message-id:message-id:\n to:to:cc:mime-version:mime-version:content-type:content-type:\n content-transfer-encoding:content-transfer-encoding;\n bh=VXjWulI69pcAg2iY1PuG15K9kNHMBEqsX9Y829tB4tI=;\n b=YaPN/VRNeUh966D2xinuNPF280PbendPpSV5eyheo9y6TGkIyf3WzR5xHaB4TGJavAeCri\n c74blYZKu1zVfG7ehMr4Nsd3DJyQj9uXAX2pWbPTpq2XayqtNVWPQPdeM4Ovj4f7pV7pNF\n B1MHfVwCfWusZwtQt9c5b338ZVOULvQ=","X-MC-Unique":"lhJrkKiqOQuIKIgs0BgCNQ-1","X-Mimecast-MFC-AGG-ID":"lhJrkKiqOQuIKIgs0BgCNQ_1776098897","From":"Jonathan Wakely ","To":"gcc-patches@gcc.gnu.org","Subject":"[PATCH] c++tools: Use std::map::try_emplace to avoid use-after-move","Date":"Mon, 13 Apr 2026 17:47:58 +0100","Message-ID":"<20260413164814.90675-1-jwakely@redhat.com>","MIME-Version":"1.0","X-Scanned-By":"MIMEDefang 3.4.1 on 10.30.177.111","X-Mimecast-Spam-Score":"0","X-Mimecast-MFC-PROC-ID":"WAK4uIr0LthSjLiE8MMpncM-BzTsszv_rjA7qcpr8vE_1776098897","X-Mimecast-Originator":"redhat.com","Content-Type":"text/plain","Content-Transfer-Encoding":"8bit","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 ","Errors-To":"gcc-patches-bounces~incoming=patchwork.ozlabs.org@gcc.gnu.org"},"content":"With std::map in libstdc++, std::map::emplace always forwards its\nparameters and constructs a node from them. This means that the file\nparameter will have been moved-from and so might be empty when it is\nused again in the assignment.\n\nUse the C++17 try_emplace member (supported since GCC 6.1.0), which\nguarantees to have no effects on the parameters if no insertion happens.\nFor C++14 and GCC 5.x, pass the file parameter to emplace as an lvalue\nso it isn't moved.\n\nc++tools/ChangeLog:\n\n\t* resolver.cc (module_resolver::add_mapping): Use try_emplace\n\twhen available and avoid use-after-move otherwise.\n---\n c++tools/resolver.cc | 6 +++++-\n 1 file changed, 5 insertions(+), 1 deletion(-)","diff":"diff --git a/c++tools/resolver.cc b/c++tools/resolver.cc\nindex 53c48b4fc6a8..f4d8029b43af 100644\n--- a/c++tools/resolver.cc\n+++ b/c++tools/resolver.cc\n@@ -88,9 +88,13 @@ module_resolver::set_repo (std::string &&r, bool force)\n bool\n module_resolver::add_mapping (std::string &&module, std::string &&file,\n \t\t\t bool force)\n {\n- auto res = map.emplace (std::move (module), std::move (file));\n+#ifdef __cpp_lib_map_try_emplace\n+ auto res = map.try_emplace (std::move (module), std::move (file));\n+#else\n+ auto res = map.emplace (std::move (module), file);\n+#endif\n if (res.second)\n force = true;\n else if (force)\n res.first->second = std::move (file);\n","prefixes":[]}