[{"id":3673160,"web_url":"http://patchwork.ozlabs.org/comment/3673160/","msgid":"","list_archive_url":null,"date":"2026-04-03T14:55:24","subject":"Re: [PATCH] c++: Implement CWG3135 - constexpr structured bindings\n with prvalues from tuples","submitter":{"id":4337,"url":"http://patchwork.ozlabs.org/api/people/4337/","name":"Jason Merrill","email":"jason@redhat.com"},"content":"On 4/3/26 4:51 AM, Jakub Jelinek wrote:\n> Hi!\n> \n> The following patch implements another CWG issue, added e.g. for the\n> P1789R3 (Library Support for Expansion Statements) APIs where get returns\n> a prvalue rather than a reference.\n> \n> The gomp testcase was using get returning prvalue and the changes\n> cause some changes in lines on which stuff is reported.\n> \n> Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk?\n> \n> 2026-04-03 Jakub Jelinek \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> --- 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 (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\nHmm, indeed we said that this wasn't a DR, but I think that wasn't well \nconsidered. Is there significant breakage if we apply the change to all \nmodes?\n\nJason","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=TEaRnFpp;\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; helo=vm01.sourceware.org;\n envelope-from=gcc-patches-bounces~incoming=patchwork.ozlabs.org@gcc.gnu.org;\n receiver=patchwork.ozlabs.org)","sourceware.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=TEaRnFpp","sourceware.org; dmarc=pass (p=quarantine dis=none)\n header.from=redhat.com","sourceware.org; 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charset=UTF-8; format=flowed","Content-Transfer-Encoding":"7bit","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"}},{"id":3673265,"web_url":"http://patchwork.ozlabs.org/comment/3673265/","msgid":"","list_archive_url":null,"date":"2026-04-03T18:39:37","subject":"Re: [PATCH] c++: Implement CWG3135 - constexpr structured bindings\n with prvalues from tuples","submitter":{"id":671,"url":"http://patchwork.ozlabs.org/api/people/671/","name":"Jakub Jelinek","email":"jakub@redhat.com"},"content":"On Fri, Apr 03, 2026 at 10:55:24AM -0400, Jason Merrill wrote:\n> On 4/3/26 4:51 AM, Jakub Jelinek wrote:\n> > The following patch implements another CWG issue, added e.g. for the\n> > P1789R3 (Library Support for Expansion Statements) APIs where get returns\n> > a prvalue rather than a reference.\n> > \n> > The gomp testcase was using get returning prvalue and the changes\n> > cause some changes in lines on which stuff is reported.\n> > \n> > Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk?\n> > \n> > 2026-04-03 Jakub Jelinek \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> > --- 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 (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> \n> Hmm, indeed we said that this wasn't a DR, but I think that wasn't well\n> considered. Is there significant breakage if we apply the change to all\n> modes?\n\nThe pr108503.C testcase was the only one affected in the testsuite.\n\n\tJakub","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=cJfpjdNg;\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; helo=vm01.sourceware.org;\n envelope-from=gcc-patches-bounces~incoming=patchwork.ozlabs.org@gcc.gnu.org;\n receiver=patchwork.ozlabs.org)","sourceware.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=cJfpjdNg","sourceware.org; dmarc=pass (p=quarantine dis=none)\n header.from=redhat.com","sourceware.org; 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