From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [216.205.24.124]) by sourceware.org (Postfix) with ESMTP id 189A73896C19 for ; Tue, 5 Jan 2021 15:26:31 +0000 (GMT) DMARC-Filter: OpenDMARC Filter v1.3.2 sourceware.org 189A73896C19 Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-317-muei8O_BNfKMFJyv3v0l_g-1; Tue, 05 Jan 2021 10:26:29 -0500 X-MC-Unique: muei8O_BNfKMFJyv3v0l_g-1 Received: from smtp.corp.redhat.com (int-mx06.intmail.prod.int.phx2.redhat.com [10.5.11.16]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 06102107ACE6 for ; Tue, 5 Jan 2021 15:26:28 +0000 (UTC) Received: from tucnak.zalov.cz (ovpn-112-11.ams2.redhat.com [10.36.112.11]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 926DD5F9B8; Tue, 5 Jan 2021 15:26:27 +0000 (UTC) Received: from tucnak.zalov.cz (localhost [127.0.0.1]) by tucnak.zalov.cz (8.16.1/8.16.1) with ESMTPS id 105FQOHq3979521 (version=TLSv1.3 cipher=TLS_AES_256_GCM_SHA384 bits=256 verify=NOT); Tue, 5 Jan 2021 16:26:25 +0100 Received: (from jakub@localhost) by tucnak.zalov.cz (8.16.1/8.16.1/Submit) id 105FQOa33979520; Tue, 5 Jan 2021 16:26:24 +0100 Date: Tue, 5 Jan 2021 16:26:24 +0100 From: Jakub Jelinek To: Jason Merrill Cc: gcc-patches@gcc.gnu.org Subject: [PATCH] c++, v2: Fix ICE with __builtin_bit_cast [PR98469] Message-ID: <20210105152624.GR725145@tucnak> Reply-To: Jakub Jelinek References: <20201230091343.GU3788@tucnak> <20210104204820.GB725145@tucnak> <989b7d53-25fe-dc11-63a1-deaf18df615c@redhat.com> MIME-Version: 1.0 In-Reply-To: <989b7d53-25fe-dc11-63a1-deaf18df615c@redhat.com> X-Scanned-By: MIMEDefang 2.79 on 10.5.11.16 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=us-ascii Content-Disposition: inline X-Spam-Status: No, score=-6.1 required=5.0 tests=BAYES_00, DKIMWL_WL_HIGH, DKIM_SIGNED, DKIM_VALID, DKIM_VALID_AU, DKIM_VALID_EF, RCVD_IN_DNSWL_LOW, RCVD_IN_MSPIKE_H3, RCVD_IN_MSPIKE_WL, SPF_HELO_NONE, SPF_PASS, TXREP autolearn=ham autolearn_force=no version=3.4.2 X-Spam-Checker-Version: SpamAssassin 3.4.2 (2018-09-13) on server2.sourceware.org X-BeenThere: gcc-patches@gcc.gnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Gcc-patches mailing list List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Tue, 05 Jan 2021 15:26:32 -0000 On Mon, Jan 04, 2021 at 04:01:25PM -0500, Jason Merrill via Gcc-patches wrote: > On 1/4/21 3:48 PM, Jakub Jelinek wrote: > > On Mon, Jan 04, 2021 at 03:44:46PM -0500, Jason Merrill wrote: > > > This change is OK, but part of the problem is that we're trying to do > > > overload resolution for an S copy/move constructor, which we shouldn't be > > > because bit_cast is a prvalue, so in C++17 and up we should use it to > > > directly initialize the target without any implied constructor call. > > > > > > It seems we're mishandling this because the code in > > > build_special_member_call specifically looks for TARGET_EXPR or CONSTRUCTOR, > > > and BIT_CAST_EXPR is neither of those. > > > > > > Wrapping a BIT_CAST_EXPR of aggregate type in a TARGET_EXPR would address > > > this, and any other places that expect a class prvalue to come in the form > > > of a TARGET_EXPR. > > > > I can try that tomorrow. Won't that cause copying through extra temporary > > in some cases though, or is that guaranteed to be optimized? > > It won't cause any extra copying when it's used to initialize another object > (like the return value of std::bit_cast). Class prvalues are always > expressed with a TARGET_EXPR in the front end; the TARGET_EXPR melts away > when used as an initializer, it only creates a temporary when it's used in > another way. Ok, this version wraps it into a TARGET_EXPR then, it alone fixes the bug, but I've kept the constexpr.c change too. Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk? 2021-01-05 Jakub Jelinek PR c++/98469 * constexpr.c (cxx_eval_constant_expression) : Punt if lval is true. * semantics.c (cp_build_bit_cast): Call get_target_expr_sfinae on the result if it has a class type. * g++.dg/cpp2a/bit-cast8.C: New test. * g++.dg/cpp2a/bit-cast9.C: New test. --- gcc/cp/constexpr.c.jj 2021-01-04 10:25:48.750121531 +0100 +++ gcc/cp/constexpr.c 2021-01-05 11:41:38.315032636 +0100 @@ -6900,6 +6900,15 @@ cxx_eval_constant_expression (const cons return t; case BIT_CAST_EXPR: + if (lval) + { + if (!ctx->quiet) + error_at (EXPR_LOCATION (t), + "address of a call to %qs is not a constant expression", + "__builtin_bit_cast"); + *non_constant_p = true; + return t; + } r = cxx_eval_bit_cast (ctx, t, non_constant_p, overflow_p); break; --- gcc/cp/semantics.c.jj 2021-01-04 10:25:48.489124486 +0100 +++ gcc/cp/semantics.c 2021-01-05 11:27:49.327372582 +0100 @@ -10761,6 +10761,10 @@ cp_build_bit_cast (location_t loc, tree tree ret = build_min (BIT_CAST_EXPR, type, arg); SET_EXPR_LOCATION (ret, loc); + + if (!processing_template_decl && CLASS_TYPE_P (type)) + ret = get_target_expr_sfinae (ret, complain); + return ret; } --- gcc/testsuite/g++.dg/cpp2a/bit-cast8.C.jj 2021-01-05 11:41:38.315032636 +0100 +++ gcc/testsuite/g++.dg/cpp2a/bit-cast8.C 2021-01-05 11:41:38.315032636 +0100 @@ -0,0 +1,11 @@ +// PR c++/98469 +// { dg-do compile { target c++20 } } +// { dg-options "-Wall" } + +struct S { int s; }; + +S +foo () +{ + return __builtin_bit_cast (S, 0); +} --- gcc/testsuite/g++.dg/cpp2a/bit-cast9.C.jj 2021-01-05 11:41:38.315032636 +0100 +++ gcc/testsuite/g++.dg/cpp2a/bit-cast9.C 2021-01-05 11:41:38.315032636 +0100 @@ -0,0 +1,15 @@ +// PR c++/98469 +// { dg-do compile { target c++20 } } +// { dg-options "-Wall" } + +template +constexpr T +bit_cast (const F &f) noexcept +{ + return __builtin_bit_cast (T, f); +} +struct S { int s; }; +constexpr int foo (const S &x) { return x.s; } +constexpr int bar () { return foo (bit_cast (0)); } +constexpr int x = bar (); +static_assert (!x); Jakub