{"id":2225228,"url":"http://patchwork.ozlabs.org/api/1.1/patches/2225228/?format=json","web_url":"http://patchwork.ozlabs.org/project/gcc/patch/20260420164552.1598895-1-jason@redhat.com/","project":{"id":17,"url":"http://patchwork.ozlabs.org/api/1.1/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},"msgid":"<20260420164552.1598895-1-jason@redhat.com>","date":"2026-04-20T16:45:36","name":"[pushed] c++: std::optional reset and constexpr [PR124910]","commit_ref":null,"pull_url":null,"state":"new","archived":false,"hash":"0a79478e25b2ea4d283b2761b833c10d58c1d28b","submitter":{"id":4337,"url":"http://patchwork.ozlabs.org/api/1.1/people/4337/?format=json","name":"Jason Merrill","email":"jason@redhat.com"},"delegate":null,"mbox":"http://patchwork.ozlabs.org/project/gcc/patch/20260420164552.1598895-1-jason@redhat.com/mbox/","series":[{"id":500638,"url":"http://patchwork.ozlabs.org/api/1.1/series/500638/?format=json","web_url":"http://patchwork.ozlabs.org/project/gcc/list/?series=500638","date":"2026-04-20T16:45:36","name":"[pushed] c++: std::optional reset and constexpr [PR124910]","version":1,"mbox":"http://patchwork.ozlabs.org/series/500638/mbox/"}],"comments":"http://patchwork.ozlabs.org/api/patches/2225228/comments/","check":"pending","checks":"http://patchwork.ozlabs.org/api/patches/2225228/checks/","tags":{},"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=GPn6shxv;\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=1776703565;\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=8Jf+HMVHf8dld6n71uA+QUMDzQLn1uJ/x79dD3Gan70=;\n b=GPn6shxvT517dw7i8IIgGb5wl3OQNrG/k/rl4GgMimhz6ZGQNZEn6qpSP0LYkJ9MVdBdvv\n MbRFz0562TYsSEAlU4ab6I+5hn213bLtlcjv6HuPZOwwjMEIWcuxnmJnDMuxbp1WL2DMGL\n NK2NFLVG7iyKmHiYh2Rmh05lsUBoj5I=","X-MC-Unique":"SXp4UEM-OPOR2LUHYtAIVg-1","X-Mimecast-MFC-AGG-ID":"SXp4UEM-OPOR2LUHYtAIVg_1776703554","From":"Jason Merrill ","To":"gcc-patches@gcc.gnu.org","Subject":"[pushed] c++: std::optional reset and constexpr [PR124910]","Date":"Mon, 20 Apr 2026 12:45:36 -0400","Message-ID":"<20260420164552.1598895-1-jason@redhat.com>","MIME-Version":"1.0","X-Scanned-By":"MIMEDefang 3.4.1 on 10.30.177.93","X-Mimecast-Spam-Score":"0","X-Mimecast-MFC-PROC-ID":"5y3H57iSPdSMYoeV8zm7xLgtnQUB9-68alb2PxxsvME_1776703554","X-Mimecast-Originator":"redhat.com","Content-Transfer-Encoding":"8bit","content-type":"text/plain; charset=\"US-ASCII\"; x-default=true","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":"Tested x86_64-pc-linux-gnu, applying to trunk.\n\n-- 8< --\n\nConstant evaluation didn't recognize that destroying _M_value made it no\nlonger the active member of the anonymous union, so we were treating the\nresult as containing an out-of-lifetime value. Instead we should treat the\nunion as no longer having an active member.\n\n\tPR c++/124910\n\ngcc/cp/ChangeLog:\n\n\t* constexpr.cc (cxx_eval_store_expression): Ending the\n\tlifetime of the active member means no active member.\n\ngcc/testsuite/ChangeLog:\n\n\t* g++.dg/cpp2a/constexpr-union11.C: New test.\n---\n gcc/cp/constexpr.cc | 10 +++++++\n .../g++.dg/cpp2a/constexpr-union11.C | 29 +++++++++++++++++++\n 2 files changed, 39 insertions(+)\n create mode 100644 gcc/testsuite/g++.dg/cpp2a/constexpr-union11.C\n\n\nbase-commit: b40bb34c3f5e9942d083efdee393c6e2d25e5981","diff":"diff --git a/gcc/cp/constexpr.cc b/gcc/cp/constexpr.cc\nindex 5b7d385fa97..a593b66dd41 100644\n--- a/gcc/cp/constexpr.cc\n+++ b/gcc/cp/constexpr.cc\n@@ -8207,6 +8207,16 @@ cxx_eval_store_expression (const constexpr_ctx *ctx, tree t,\n \t no_zero_init = true;\n \t}\n \n+ /* Ending the lifetime of the active union member means the union no\n+\t longer has an active member. */\n+ if (code == UNION_TYPE && refs->is_empty ()\n+\t && TREE_CLOBBER_P (init)\n+\t && CLOBBER_KIND (init) >= CLOBBER_OBJECT_END)\n+\t{\n+\t vec_safe_truncate (CONSTRUCTOR_ELTS (*valp), 0);\n+\t return void_node;\n+\t}\n+\n ctors.safe_push (valp);\n vec_safe_push (indexes, index);\n \ndiff --git a/gcc/testsuite/g++.dg/cpp2a/constexpr-union11.C b/gcc/testsuite/g++.dg/cpp2a/constexpr-union11.C\nnew file mode 100644\nindex 00000000000..56919715f55\n--- /dev/null\n+++ b/gcc/testsuite/g++.dg/cpp2a/constexpr-union11.C\n@@ -0,0 +1,29 @@\n+// PR c++/124910\n+// { dg-do compile { target c++20 } }\n+\n+struct nullopt_t { } nullopt;\n+using _Stored_type = int;\n+struct _Empty { };\n+struct _Optional_payload_base {\n+ union {\n+ int _M_value = 1;\n+ _Empty _M_empty;\n+ };\n+ constexpr void _M_reset() {\n+ _M_value.~_Stored_type();\n+ _M_empty = {};\n+ }\n+};\n+struct _Optional_payload : _Optional_payload_base {};\n+struct _Optional_base {\n+ _Optional_payload _M_payload;\n+};\n+struct optional : _Optional_base {\n+ constexpr void operator=(nullopt_t) { _M_payload._M_reset(); }\n+};\n+constexpr auto f() {\n+ optional result;\n+ result = nullopt;\n+ return result;\n+}\n+constexpr auto v = f();\n","prefixes":["pushed"]}