[{"id":3677383,"web_url":"http://patchwork.ozlabs.org/comment/3677383/","msgid":"","list_archive_url":null,"date":"2026-04-14T20:04:49","subject":"Re: [PATCH] c++: Fix up constexpr EH handling of TARGET_EXPR\n temporaries [PR124755]","submitter":{"id":4337,"url":"http://patchwork.ozlabs.org/api/people/4337/","name":"Jason Merrill","email":"jason@redhat.com"},"content":"On 4/14/26 3:08 AM, Jakub Jelinek wrote:\n> Hi!\n> \n> The following testcase is incorrectly rejected with spurious error about\n> used outside of its lifetime.\n> We constant evaluate\n> < (void) (n = TARGET_EXPR , n + D.2693) >>>>>;\n> in a loop, D.2693 is integral TARGET_EXPR_SLOT and foo throws in the second\n> or later iteration. Because D.2693 is not is_complex nor has\n> aggregate/vector type, we don't ctx->global->put_value (slot, something)\n> until the TARGET_EXPR_INITIAL evaluation successfully finishes, at which\n> point we ctx->save_exprs->safe_push (slot); and\n> ctx->global->put_value (slot, r); Because of the save_exprs push, the\n> CLEANUP_POINT_EXPR handling then\n> /* Forget SAVE_EXPRs and TARGET_EXPRs created by this\n> full-expression. */\n> for (tree save_expr : save_exprs)\n> destroy_value_checked (ctx, save_expr, non_constant_p);\n> and that ctx->global->put_value (slot, void_node); (i.e. marks it out of\n> lifetime). In the second iteration, we again don't call put_value on the\n> slot early, notice TARGET_EXPR_INITIAL evaluation throws, still\n> ctx->save_exprs->safe_push (slot); but then return. That means\n> the remembered value is still void_node and so destroy_value_checked\n> complains.\n> \n> The following patch fixes that by calling put_value in the case where\n> we know we haven't changed it yet (i.e. it is not is_complex and it doesn't\n> have aggregate/vector type), so that destroy_value_checked doesn't complain.\n> \n> Boptstrapped/regtested on x86_64-linux and i686-linux, ok for trunk?\n\nIt seems simpler to remove the if (is_complex) from the earlier put(null)?\n\n> 2026-04-14 Jakub Jelinek \n> \n> \tPR c++/124755\n> \t* constexpr.cc (cxx_eval_constant_expression): If TARGET_EXPR_INITIAL\n> \tthrows and !is_complex and type is neither aggregate nor vector,\n> \tcall ctx->global->put_value (slot, NULL) before returning.\n> \n> \t* g++.dg/cpp26/constexpr-eh19.C: New test.\n> \n> --- gcc/cp/constexpr.cc.jj\t2026-04-03 20:46:22.849229712 +0200\n> +++ gcc/cp/constexpr.cc\t2026-04-13 16:17:30.760424372 +0200\n> @@ -9504,7 +9504,16 @@ cxx_eval_constant_expression (const cons\n> \tif (ctx->save_exprs)\n> \t ctx->save_exprs->safe_push (slot);\n> \tif (*jump_target)\n> -\t return NULL_TREE;\n> +\t {\n> +\t if (!is_complex\n> +\t\t&& !(AGGREGATE_TYPE_P (type) || VECTOR_TYPE_P (type)))\n> +\t /* If TARGET_EXPR_INITIAL throws exception and slot's value\n> +\t\t has not been changed yet, CLEANUP_POINT_EXPR handling\n> +\t\t could see there void_node from a previous evaluation\n> +\t\t and complain. */\n> +\t ctx->global->put_value (slot, NULL_TREE);\n> +\t return NULL_TREE;\n> +\t }\n> \tif (!is_complex)\n> \t {\n> \t r = unshare_constructor (r);\n> --- gcc/testsuite/g++.dg/cpp26/constexpr-eh19.C.jj\t2026-04-13 16:22:53.086944490 +0200\n> +++ gcc/testsuite/g++.dg/cpp26/constexpr-eh19.C\t2026-04-13 16:23:15.592561870 +0200\n> @@ -0,0 +1,33 @@\n> +// PR c++/124755\n> +// { dg-do compile { target c++26 } }\n> +\n> +constexpr int\n> +foo (int a)\n> +{\n> + return a ? throw 1 : 0;\n> +}\n> +\n> +consteval int\n> +bar ()\n> +{\n> + int n = 0;\n> + int a[] = { 0, 1 };\n> + for (int m : a)\n> + n += foo (m);\n> + return n;\n> +}\n> +\n> +consteval int\n> +baz ()\n> +{\n> + try\n> + {\n> + return bar ();\n> + }\n> + catch (...)\n> + {\n> + return -1;\n> + }\n> +}\n> +\n> +static_assert (baz () == -1);\n> \n> \tJakub\n>","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=RrMHHfvK;\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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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":3677394,"web_url":"http://patchwork.ozlabs.org/comment/3677394/","msgid":"","list_archive_url":null,"date":"2026-04-14T20:27:35","subject":"Re: [PATCH] c++: Fix up constexpr EH handling of TARGET_EXPR\n temporaries [PR124755]","submitter":{"id":671,"url":"http://patchwork.ozlabs.org/api/people/671/","name":"Jakub Jelinek","email":"jakub@redhat.com"},"content":"On Tue, Apr 14, 2026 at 04:04:49PM -0400, Jason Merrill wrote:\n> It seems simpler to remove the if (is_complex) from the earlier put(null)?\n\nWouldn't that break pretty much all the aggregate/vector TARGET_EXPR\nhandling?\n\nI mean, we have there:\n case TARGET_EXPR:\n...\n if ((AGGREGATE_TYPE_P (type) || VECTOR_TYPE_P (type)))\n\t {\n...\n new_ctx.object = slot;\n ctx->global->put_value (new_ctx.object, new_ctx.ctor);\n ctx = &new_ctx;\n\t }\n\n /* If the initializer is complex, evaluate it to initialize slot. */\n bool is_complex = target_expr_needs_replace (t);\n if (is_complex)\n /* In case no initialization actually happens, clear out any\n void_node from a previous evaluation. */\n ctx->global->put_value (slot, NULL_TREE);\n\nExcept for one rare case (0.01%, g++.dg/cpp0x/constexpr-prvalue5.C (X::X))\nwhen AGGREGATE_TYPE_P (type) || VECTOR_TYPE_P (type) is true, is_complex\nis false, so removing if (is_complex) would make the\nctx->global->put_value (new_ctx.object, new_ctx.ctor); earlier completely\nuseless. I don't know how it works if it works for the\nconstexpr-prvalue5.C (X::X) case where it is aggregate and is_complex.\n\nIf you mean I should\n- if (is_complex)\n+ if (is_complex || !(AGGREGATE_TYPE_P (type) || VECTOR_TYPE_P (type)))\nI can certainly do it, but thought the posted version is faster (doesn''t\nput a value in the usual case when it is overwritten soon after) and safer\n(because it clearly can't affect anything but C++26 constexpr exceptions\ncode).\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=TvhDtDCb;\n\tdkim-atps=neutral","legolas.ozlabs.org;\n spf=pass (sender SPF authorized) smtp.mailfrom=gcc.gnu.org\n (client-ip=38.145.34.32; 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=TvhDtDCb","sourceware.org; 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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 ","List-Unsubscribe":",\n ","List-Archive":"","List-Post":"","List-Help":"","List-Subscribe":",\n ","Reply-To":"Jakub Jelinek ","Errors-To":"gcc-patches-bounces~incoming=patchwork.ozlabs.org@gcc.gnu.org"}},{"id":3677733,"web_url":"http://patchwork.ozlabs.org/comment/3677733/","msgid":"","list_archive_url":null,"date":"2026-04-15T15:23:53","subject":"Re: [PATCH] c++: Fix up constexpr EH handling of TARGET_EXPR\n temporaries [PR124755]","submitter":{"id":4337,"url":"http://patchwork.ozlabs.org/api/people/4337/","name":"Jason Merrill","email":"jason@redhat.com"},"content":"On 4/14/26 4:27 PM, Jakub Jelinek wrote:\n> On Tue, Apr 14, 2026 at 04:04:49PM -0400, Jason Merrill wrote:\n>> It seems simpler to remove the if (is_complex) from the earlier put(null)?\n> \n> Wouldn't that break pretty much all the aggregate/vector TARGET_EXPR\n> handling?\n> \n> I mean, we have there:\n> case TARGET_EXPR:\n> ...\n> if ((AGGREGATE_TYPE_P (type) || VECTOR_TYPE_P (type)))\n> \t {\n> ...\n> new_ctx.object = slot;\n> ctx->global->put_value (new_ctx.object, new_ctx.ctor);\n> ctx = &new_ctx;\n> \t }\n\nGood point, it would need to be an else to this if.\n\n> /* If the initializer is complex, evaluate it to initialize slot. */\n> bool is_complex = target_expr_needs_replace (t);\n> if (is_complex)\n> /* In case no initialization actually happens, clear out any\n> void_node from a previous evaluation. */\n> ctx->global->put_value (slot, NULL_TREE);\n> \n> Except for one rare case (0.01%, g++.dg/cpp0x/constexpr-prvalue5.C (X::X))\n> when AGGREGATE_TYPE_P (type) || VECTOR_TYPE_P (type) is true, is_complex\n> is false, so removing if (is_complex) would make the\n> ctx->global->put_value (new_ctx.object, new_ctx.ctor); earlier completely\n> useless. I don't know how it works if it works for the\n> constexpr-prvalue5.C (X::X) case where it is aggregate and is_complex.\n> \n> If you mean I should\n> - if (is_complex)\n> + if (is_complex || !(AGGREGATE_TYPE_P (type) || VECTOR_TYPE_P (type)))\n> I can certainly do it, but thought the posted version is faster (doesn''t\n> put a value in the usual case when it is overwritten soon after) and safer\n> (because it clearly can't affect anything but C++26 constexpr exceptions\n> code).\nBut more complicated in terms of keeping conditions in sync. Well, OK \neither way.\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=MAZFZ+b3;\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=MAZFZ+b3","sourceware.org; dmarc=pass (p=quarantine dis=none)\n header.from=redhat.com","sourceware.org; spf=pass smtp.mailfrom=redhat.com","server2.sourceware.org;\n arc=none smtp.remote-ip=170.10.129.124"],"Received":["from vm01.sourceware.org (vm01.sourceware.org\n [IPv6:2620:52:6:3111::32])\n\t(using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits)\n\t key-exchange x25519 server-signature ECDSA (secp384r1) server-digest SHA384)\n\t(No client certificate requested)\n\tby legolas.ozlabs.org (Postfix) with ESMTPS id 4fwlLg117Pz1yHc\n\tfor ; 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