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GET /api/patches/2219522/?format=api
{ "id": 2219522, "url": "http://patchwork.ozlabs.org/api/patches/2219522/?format=api", "web_url": "http://patchwork.ozlabs.org/project/gcc/patch/ac9_k-LZ0JWy7Dwc@tucnak/", "project": { "id": 17, "url": "http://patchwork.ozlabs.org/api/projects/17/?format=api", "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": "<ac9_k-LZ0JWy7Dwc@tucnak>", "list_archive_url": null, "date": "2026-04-03T08:51:31", "name": "c++: Implement CWG3135 - constexpr structured bindings with prvalues from tuples", "commit_ref": null, "pull_url": null, "state": "new", "archived": false, "hash": "26096aa0f8b1fcb2c6753b462845f8dbc6e7e19d", "submitter": { "id": 671, "url": "http://patchwork.ozlabs.org/api/people/671/?format=api", "name": "Jakub Jelinek", "email": "jakub@redhat.com" }, "delegate": null, "mbox": "http://patchwork.ozlabs.org/project/gcc/patch/ac9_k-LZ0JWy7Dwc@tucnak/mbox/", "series": [ { "id": 498605, "url": "http://patchwork.ozlabs.org/api/series/498605/?format=api", "web_url": "http://patchwork.ozlabs.org/project/gcc/list/?series=498605", "date": "2026-04-03T08:51:31", "name": "c++: Implement CWG3135 - constexpr structured bindings with prvalues from tuples", "version": 1, "mbox": "http://patchwork.ozlabs.org/series/498605/mbox/" } ], "comments": "http://patchwork.ozlabs.org/api/patches/2219522/comments/", "check": "pending", "checks": "http://patchwork.ozlabs.org/api/patches/2219522/checks/", "tags": {}, "related": [], "headers": { "Return-Path": "<gcc-patches-bounces~incoming=patchwork.ozlabs.org@gcc.gnu.org>", "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=Y4K6j+p7;\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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Fri, 3 Apr 2026 08:51:35 +0000 (UTC)", "from tucnak.zalov.cz (unknown [10.44.32.9])\n by mx-prod-int-08.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with\n ESMTPS\n id A861E180035F; Fri, 3 Apr 2026 08:51:34 +0000 (UTC)", "from tucnak.zalov.cz (localhost [127.0.0.1])\n by tucnak.zalov.cz (8.18.1/8.18.1) with ESMTPS id 6338pVBi3680583\n (version=TLSv1.3 cipher=TLS_AES_256_GCM_SHA384 bits=256 verify=NOT);\n Fri, 3 Apr 2026 10:51:31 +0200", "(from jakub@localhost)\n by tucnak.zalov.cz (8.18.1/8.18.1/Submit) id 6338pVAA3680582;\n Fri, 3 Apr 2026 10:51:31 +0200" ], "DKIM-Filter": [ "OpenDKIM Filter v2.11.0 sourceware.org AB6C64BA2E06", "OpenDKIM Filter v2.11.0 sourceware.org DCBCE4BA23D3" ], "DMARC-Filter": "OpenDMARC Filter v1.4.2 sourceware.org DCBCE4BA23D3", "ARC-Filter": "OpenARC Filter v1.0.0 sourceware.org DCBCE4BA23D3", "ARC-Seal": "i=1; a=rsa-sha256; d=sourceware.org; s=key; t=1775206298; cv=none;\n b=S98jJUIF9y/Hk7fA+ZJIfNXVT+ZnDBTafx2wo6HhVQ4KFzX0sSzZ62MENGZTEY1aj5CMquCNWMPJRc2o5R8bJhlJ8orfmIQQONnr2csBJojaZQ6com0QLzqXfUI1Fk3neY1MZlbxqU5ygaBbt005N4DoGJNjhnrvEvzmypq8vcE=", "ARC-Message-Signature": "i=1; a=rsa-sha256; d=sourceware.org; s=key;\n t=1775206298; c=relaxed/simple;\n bh=/eL6zvmJ3AbQ/Hm3s5zxtgIGG/y6tSeFfFS7t+x9LF4=;\n h=DKIM-Signature:Date:From:To:Subject:Message-ID:MIME-Version;\n b=M1IkUZzbiLVlm6DOBcbQVzhmRarsdk8o8ubQkmVTDuuh5mo9pMF7qDTveLN0VKUZNU4WCsL6S+dvBve5r/f9SOza+cs/kSfggsaYLAt9brn5n8F2VJJvbcBVaTVgPnAoPAg9xfNX2dKGknjDp4AlBZczVRwFos2K9srmIi/W75s=", "ARC-Authentication-Results": "i=1; server2.sourceware.org", "DKIM-Signature": "v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com;\n s=mimecast20190719; t=1775206297;\n h=from:from:reply-to:reply-to:subject:subject:date:date:\n message-id:message-id:to:to:cc:cc:mime-version:mime-version:\n content-type:content-type; bh=Ho7r0h63uWW+99Ht45MYMpE777vSt7oXfIbV5Llp9Z0=;\n b=Y4K6j+p7VfDRhwAupofQbo6Kw0OZpFcmU83ypxqWcTCGM919uzw6irjj8KpHAA56e9VYbm\n olNvHKBQljWbrbb0Fn476RsF3a1C2D7MssaQIINh8vvMpfMVpOhpwpxoxBZH+Vq5LTP3cj\n /qA9XO4QhD3Y8ZI7G6fQw7IPwUkA2J8=", "X-MC-Unique": "Qq5wBdWGPbKVeMH-Lgm-xQ-1", "X-Mimecast-MFC-AGG-ID": "Qq5wBdWGPbKVeMH-Lgm-xQ_1775206295", "Date": "Fri, 3 Apr 2026 10:51:31 +0200", "From": "Jakub Jelinek <jakub@redhat.com>", "To": "Jason Merrill <jason@redhat.com>", "Cc": "gcc-patches@gcc.gnu.org", "Subject": "[PATCH] c++: Implement CWG3135 - constexpr structured bindings with\n prvalues from tuples", "Message-ID": "<ac9_k-LZ0JWy7Dwc@tucnak>", "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": "FmF8SawnaylKzPpkzTG-CNNE4NFhV9tbVVbE0KvuTvA_1775206295", "X-Mimecast-Originator": "redhat.com", "Content-Type": "text/plain; charset=us-ascii", "Content-Disposition": "inline", "X-BeenThere": "gcc-patches@gcc.gnu.org", "X-Mailman-Version": "2.1.30", "Precedence": "list", "List-Id": "Gcc-patches mailing list <gcc-patches.gcc.gnu.org>", "List-Unsubscribe": "<https://gcc.gnu.org/mailman/options/gcc-patches>,\n <mailto:gcc-patches-request@gcc.gnu.org?subject=unsubscribe>", "List-Archive": "<https://gcc.gnu.org/pipermail/gcc-patches/>", "List-Post": "<mailto:gcc-patches@gcc.gnu.org>", "List-Help": "<mailto:gcc-patches-request@gcc.gnu.org?subject=help>", "List-Subscribe": "<https://gcc.gnu.org/mailman/listinfo/gcc-patches>,\n <mailto:gcc-patches-request@gcc.gnu.org?subject=subscribe>", "Reply-To": "Jakub Jelinek <jakub@redhat.com>", "Errors-To": "gcc-patches-bounces~incoming=patchwork.ozlabs.org@gcc.gnu.org" }, "content": "Hi!\n\nThe following patch implements another CWG issue, added e.g. for the\nP1789R3 (Library Support for Expansion Statements) APIs where get returns\na prvalue rather than a reference.\n\nThe gomp testcase was using get returning prvalue and the changes\ncause some changes in lines on which stuff is reported.\n\nBootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk?\n\n2026-04-03 Jakub Jelinek <jakub@redhat.com>\n\n\t* decl.cc (cp_finish_decomp): Implement CWG3135 - constexpr structured\n\tbindings with prvalues from tuples. Don't call cp_build_reference_type\n\tif init is prvalue for C++26.\n\n\t* g++.dg/cpp26/decomp30.C: New test.\n\t* g++.dg/gomp/pr108503.C: Expect diagnostics in C++26 on a different\n\tline.\n\n\n\tJakub", "diff": "--- gcc/cp/decl.cc.jj\t2026-04-01 20:10:43.899063964 +0200\n+++ gcc/cp/decl.cc\t2026-04-02 16:26:49.865791353 +0200\n@@ -11011,7 +11011,8 @@ cp_finish_decomp (tree decl, cp_decomp *\n \t\t maybe_push_decl (t);\n \t\t /* Save the decltype away before reference collapse. */\n \t\t hash_map_safe_put<hm_ggc> (decomp_type_table, t, eltype);\n-\t\t eltype = cp_build_reference_type (eltype, !lvalue_p (init));\n+\t\t if (cxx_dialect < cxx26 || glvalue_p (init))\n+\t\t eltype = cp_build_reference_type (eltype, !lvalue_p (init));\n \t\t TREE_TYPE (t) = eltype;\n \t\t layout_decl (t, 0);\n \t\t DECL_HAS_VALUE_EXPR_P (t) = 0;\n@@ -11056,7 +11057,8 @@ cp_finish_decomp (tree decl, cp_decomp *\n \t }\n \t /* Save the decltype away before reference collapse. */\n \t hash_map_safe_put<hm_ggc> (decomp_type_table, v[i], eltype);\n-\t eltype = cp_build_reference_type (eltype, !lvalue_p (init));\n+\t if (cxx_dialect < cxx26 || glvalue_p (init))\n+\t eltype = cp_build_reference_type (eltype, !lvalue_p (init));\n \t TREE_TYPE (v[i]) = eltype;\n \t layout_decl (v[i], 0);\n \t if (DECL_HAS_VALUE_EXPR_P (v[i]))\n--- gcc/testsuite/g++.dg/cpp26/decomp30.C.jj\t2026-04-02 16:55:02.549367082 +0200\n+++ gcc/testsuite/g++.dg/cpp26/decomp30.C\t2026-04-02 16:54:45.142659067 +0200\n@@ -0,0 +1,37 @@\n+// CWG3135 - constexpr structured bindings with prvalues from tuples\n+// { dg-do compile { target c++11 } }\n+// { dg-options \"\" }\n+\n+namespace std {\n+ template <typename T> struct tuple_size;\n+ template <int, typename> struct tuple_element;\n+}\n+\n+struct A {\n+ template <int I> constexpr int get () const { return I + 6; }\n+};\n+\n+template <> struct std::tuple_size <A> { static const int value = 2; };\n+template <int I> struct std::tuple_element <I, A> { using type = int; };\n+template <> struct std::tuple_size <const A> { static const int value = 2; };\n+template <int I> struct std::tuple_element <I, const A> { using type = const int; };\n+\n+constexpr A\n+bar ()\n+{\n+ return A {};\n+}\n+\n+template <int N>\n+constexpr int\n+foo ()\n+{\n+ constexpr auto [...i] = bar ();\t// { dg-warning \"structured binding packs only available with\" \"\" { target { c++17 && c++23_down } } }\n+\t\t\t\t\t// { dg-warning \"structured binding declaration can be 'constexpr' only with\" \"\" { target c++23_down } .-1 }\n+\t\t\t\t\t// { dg-warning \"structured bindings only available with\" \"\" { target c++14_down } .-2 }\n+\t\t\t\t\t// { dg-error \"'<anonymous>' is not a constant expression\" \"\" { target c++23_down } .-3 }\n+ return i...[0] + i...[1];\t\t// { dg-warning \"pack indexing only available with\" \"\" { target c++23_down } }\n+}\n+\n+static_assert (foo <42> () == 13);\t// { dg-error \"non-constant condition for static assertion\" \"\" { target c++23_down } }\n+\t\t\t\t\t// { dg-error \"called in a constant expression\" \"\" { target c++23_down } .-1 }\n--- gcc/testsuite/g++.dg/gomp/pr108503.C.jj\t2023-01-26 14:11:48.505599103 +0100\n+++ gcc/testsuite/g++.dg/gomp/pr108503.C\t2026-04-03 10:33:02.591824046 +0200\n@@ -20,8 +20,8 @@ struct B {\n void\n foo (B a)\n {\n- #pragma omp for collapse(2)\n- for (auto [i, j, k] : a)\n- for (int l = i; l < j; l += k)\t// { dg-error \"initializer expression refers to iteration variable 'i'\" }\n+ #pragma omp for collapse(2)\t\t// { dg-error \"increment expression refers to iteration variable 'k'\" \"\" { target c++26 } .+1 }\n+ for (auto [i, j, k] : a)\t\t// { dg-error \"initializer expression refers to iteration variable 'i'\" \"\" { target c++26 } }\n+ for (int l = i; l < j; l += k)\t// { dg-error \"initializer expression refers to iteration variable 'i'\" \"\" { target c++23_down } }\n ;\t\t\t\t\t// { dg-error \"condition expression refers to iteration variable 'j'\" \"\" { target *-*-* } .-1 }\n-}\t\t\t\t\t// { dg-error \"increment expression refers to iteration variable 'k'\" \"\" { target *-*-* } .-2 }\n+}\t\t\t\t\t// { dg-error \"increment expression refers to iteration variable 'k'\" \"\" { target c++23_down } .-2 }\n", "prefixes": [] }