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 [170.10.133.124]) by sourceware.org (Postfix) with ESMTPS id C63913858427 for ; Fri, 11 Feb 2022 13:36:48 +0000 (GMT) DMARC-Filter: OpenDMARC Filter v1.4.1 sourceware.org C63913858427 Received: from mail-yb1-f199.google.com (mail-yb1-f199.google.com [209.85.219.199]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-652-UOQF73MwOxShSW4w3Seg3A-1; Fri, 11 Feb 2022 08:36:47 -0500 X-MC-Unique: UOQF73MwOxShSW4w3Seg3A-1 Received: by mail-yb1-f199.google.com with SMTP id g205-20020a2552d6000000b0061e1843b8edso17674722ybb.18 for ; Fri, 11 Feb 2022 05:36:47 -0800 (PST) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=5/y3rBrgM6igoyS4p43MxonWSznnAmr0hn43IyyukWQ=; b=IiXQ6l0T64gAQVCzBgF2Uk5CCrFzhhc27grcsGU2CUb7IntX5ecYyKzYrOTat0vLQ0 hjBlYK3q2afjzLMmvC9ZObkiURY55wzVhFN3f+9m+XynuE8OR5p/T1k5GVR70x+0iMuB 63CRBA0/sWqSMnesgiKdsVExDd2LFfC9Sc96VAZgNHPyTqCGBxvcoCqtbPjGzTy9D8Vo YrHT8EmHjvyYlMXn1+JBSCRZ0ojCBoR/LxvRDVqUkAxZ/RuNOHWcHzpVA2zEa6T2zvoD BbjpC0D1F6fpAr14sRN+4jP5wAzjixcCAtaX2100Noz98O7dP2puqfZhmUsancEl/Hgs 9DKA== X-Gm-Message-State: AOAM5307baBMK/JW7PrfjOEgfp77I3ZDzGB9fOmDbrO+1tlDqK7tmtaX Mu5kz1InHuz2wwPHarS0lYIYqAXUVl3OYN7GBviO1RNS3DfPS/kNX1lCP0NBVnNXYF2Zr6KYDy0 vbZL4bQ5utSliYIzN48I6pDP5k4caSkg= X-Received: by 2002:a05:6902:344:: with SMTP id e4mr1447951ybs.316.1644586607130; Fri, 11 Feb 2022 05:36:47 -0800 (PST) X-Google-Smtp-Source: ABdhPJwyIN9BkexfPEnYDGwNzk/pR7FmnGxAa+1DU51hQF0UwYucuOpAnrjfpd4oxHG7dMQaW20X0tJ9JVyXmZujwNA= X-Received: by 2002:a05:6902:344:: with SMTP id e4mr1447925ybs.316.1644586606893; Fri, 11 Feb 2022 05:36:46 -0800 (PST) MIME-Version: 1.0 References: <20220210165624.2953676-1-ppalka@redhat.com> <20220210165624.2953676-3-ppalka@redhat.com> In-Reply-To: <20220210165624.2953676-3-ppalka@redhat.com> From: Jonathan Wakely Date: Fri, 11 Feb 2022 13:36:35 +0000 Message-ID: Subject: Re: [PATCH 3/3, 11 backport] libstdc++: invalid default init in _CachedPosition [PR101231] To: Patrick Palka Cc: gcc Patches , "libstdc++" X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset="UTF-8" X-Spam-Status: No, score=-12.7 required=5.0 tests=BAYES_00, DKIMWL_WL_HIGH, DKIM_SIGNED, DKIM_VALID, DKIM_VALID_AU, DKIM_VALID_EF, GIT_PATCH_0, RCVD_IN_DNSWL_LOW, SPF_HELO_NONE, SPF_NONE, TXREP, T_SCC_BODY_TEXT_LINE autolearn=ham autolearn_force=no version=3.4.4 X-Spam-Checker-Version: SpamAssassin 3.4.4 (2020-01-24) on server2.sourceware.org X-BeenThere: libstdc++@gcc.gnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Libstdc++ mailing list List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Fri, 11 Feb 2022 13:36:50 -0000 On Thu, 10 Feb 2022 at 16:58, Patrick Palka via Libstdc++ wrote: > > The primary template for _CachedPosition is a dummy implementation for > non-forward ranges, the iterators for which generally can't be cached. > Because this implementation doesn't actually cache anything, _M_has_value > is defined to be false and so calls to _M_get (which are always guarded > by _M_has_value) are unreachable. > > Still, to suppress a "control reaches end of non-void function" warning > I made _M_get return {}, but after P2325 input iterators are no longer > necessarily default constructible so this workaround now breaks valid > programs. > > This patch fixes this by instead using __builtin_unreachable to squelch > the warning. OK > > PR libstdc++/103904 > PR libstdc++/101231 > > libstdc++-v3/ChangeLog: > > * include/std/ranges (_CachedPosition::_M_get): For non-forward > ranges, just call __builtin_unreachable. > * testsuite/std/ranges/istream_view.cc (test05): New test. > > (cherry picked from commit 1af937eb6246ad7f63ebff03590e9eede33aca81) > --- > libstdc++-v3/include/std/ranges | 2 +- > libstdc++-v3/testsuite/std/ranges/istream_view.cc | 12 ++++++++++++ > 2 files changed, 13 insertions(+), 1 deletion(-) > > diff --git a/libstdc++-v3/include/std/ranges b/libstdc++-v3/include/std/ranges > index bf6cfae2a6e..a4228ba9aa0 100644 > --- a/libstdc++-v3/include/std/ranges > +++ b/libstdc++-v3/include/std/ranges > @@ -1221,7 +1221,7 @@ namespace views::__adaptor > _M_get(const _Range&) const > { > __glibcxx_assert(false); > - return {}; > + __builtin_unreachable(); > } > > constexpr void > diff --git a/libstdc++-v3/testsuite/std/ranges/istream_view.cc b/libstdc++-v3/testsuite/std/ranges/istream_view.cc > index af76a1ab39e..f5c0c2a6bb0 100644 > --- a/libstdc++-v3/testsuite/std/ranges/istream_view.cc > +++ b/libstdc++-v3/testsuite/std/ranges/istream_view.cc > @@ -83,6 +83,17 @@ test04() > static_assert(!std::forward_iterator); > } > > +void > +test05() > +{ > + // PR libstdc++/101231 > + auto words = std::istringstream{"42"}; > + auto is = ranges::istream_view(words); > + auto r = is | views::filter([](auto) { return true; }); > + for (auto x : r) > + ; > +} > + > void > test06() > { > @@ -99,5 +110,6 @@ main() > test02(); > test03(); > test04(); > + test05(); > test06(); > } > -- > 2.35.1.102.g2b9c120970 >