From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-ed1-x52a.google.com (mail-ed1-x52a.google.com [IPv6:2a00:1450:4864:20::52a]) by sourceware.org (Postfix) with ESMTPS id F0B983858D39; Sat, 20 Jan 2024 07:47:09 +0000 (GMT) DMARC-Filter: OpenDMARC Filter v1.4.2 sourceware.org F0B983858D39 Authentication-Results: sourceware.org; dmarc=pass (p=none dis=none) header.from=gmail.com Authentication-Results: sourceware.org; spf=pass smtp.mailfrom=gmail.com ARC-Filter: OpenARC Filter v1.0.0 sourceware.org F0B983858D39 Authentication-Results: server2.sourceware.org; arc=none smtp.remote-ip=2a00:1450:4864:20::52a ARC-Seal: i=1; a=rsa-sha256; d=sourceware.org; s=key; t=1705736832; cv=none; b=BG56Wk+7/32j0aId21j632imrZt1mRI6MKfRaW6DGq71D+jTto3yq9K3sh+KDkH+YgFzp1qdJvEqIzbnpMG1C0t9R6aJil/1fYM5QwRYSFF/enrY6KeD6iVnv9R9Q+dv3UvP2SMTkMukgzKb5+BpQwyc+aLCnoJk7nei10hlUho= ARC-Message-Signature: i=1; a=rsa-sha256; d=sourceware.org; s=key; t=1705736832; c=relaxed/simple; bh=wCevynAWf7DNsmOYANUCvtPhldx99knIPAKCww2e10s=; h=DKIM-Signature:MIME-Version:From:Date:Message-ID:Subject:To; b=iEllTsGZWrufxBIC7Iwe9PsfNhsef2oZt3nxPygXEX9A9t7QmbkIJH3PHSxb60wyzPHyY5TQqUkoA31hdPG+rZNoitJaNJC2ZMus+C65usFgX3e0Wq3LHZ3O/CqkeiY/zbovJvGSE4eju8EjR3cFG19W3R3QDWtB4ocNGxPgXLM= ARC-Authentication-Results: i=1; server2.sourceware.org Received: by mail-ed1-x52a.google.com with SMTP id 4fb4d7f45d1cf-55a356f8440so1789621a12.2; Fri, 19 Jan 2024 23:47:09 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20230601; t=1705736829; x=1706341629; darn=gcc.gnu.org; h=cc:to:subject:message-id:date:from:in-reply-to:references :mime-version:from:to:cc:subject:date:message-id:reply-to; bh=ForFzQ4jwEmY5lhSix9CFKgVigVOL2v9q0Lqde3JpK0=; b=PZn3cCRGAIjQ+mTMIJA+IahbUkGAUtteNY+d1WXsLKLeA7OXdbX0A6o6IBampnYI19 EqcFVfKmPW92L+3j77pvUGbxnkLIcmp1E3tzHZHTVqiE+0/pFEJ7lWDgdeFXJR/mHbL2 yhVaDVQgPHWLHjYWk/yuQMmrkMTlUpJcBij5RAm82fKPJVpMRy1bCKWAmetig5j3Y6mZ BYHOxbNYnV+i5UqzmwDliTcGk5XRXFNgukQLXbGqTpQ+thHRifNw3aAFR689qxmMEmh3 S2zFnAqSiRzJ4kayrEv4ubwpR2e7bvh6t78jeN4tX/tTcQWV0XSAzWR085ohxBo2qqrU iLMg== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1705736829; x=1706341629; h=cc:to:subject:message-id:date:from:in-reply-to:references :mime-version:x-gm-message-state:from:to:cc:subject:date:message-id :reply-to; bh=ForFzQ4jwEmY5lhSix9CFKgVigVOL2v9q0Lqde3JpK0=; b=n7QpmonATTOr8P/urLME32QNL5dH5hk9fsbSgWNpWgAwe7TisMRlqSD6iVCtu10RNh jMnMBoVpQX+ynwQlJVt9XScKvTfxNLHJXTKBLkUNg1ATEvQ6Y2WqovhYR4Ttlk5YqVXG 3RWW0AHtPJlZ2FRma6JIsq7e0WiSC9LkE/dOacl62rEKfboWA3hOow9Os6Ugg0vfCGoS ehuCAxHdEl6xy7FVXSEqjcliUCkqysY/C0oAsTlQrTxVfs4VlFnc+OBLMqPCJApDAFNM xff4hRT5EfB/7IPCUXDmU1BAYXlGzvtwlKPvksJchTw0VVTMLxuT+lLxJAyppzJ7m864 9gGw== X-Gm-Message-State: AOJu0Yz7OXtCWdwpIQ9U/Xe9vEYSx9IM392wECntXCGopRDQH66CVr0a AA730a933RnWuIVfu8pSEurCrO2CJP56/3fuLpvQ/CPcwqaT5DxFhh+Lb5sqkOQPaDGVkTVdd+J loBRcGkymLckziQm5kP8raeOSnyA= X-Google-Smtp-Source: AGHT+IGStegvlFZmvUlqdS02fDWJeWV9jqcZDshH619DmdkLd5Ju9rzgrQ1VTV+pEfeY8fv5uugzLDMmPIptXlbyEIo= X-Received: by 2002:a17:906:b052:b0:a2d:1dff:8be5 with SMTP id bj18-20020a170906b05200b00a2d1dff8be5mr530096ejb.78.1705736828446; Fri, 19 Jan 2024 23:47:08 -0800 (PST) MIME-Version: 1.0 References: <20240120021751.81798-1-polacek@redhat.com> In-Reply-To: <20240120021751.81798-1-polacek@redhat.com> From: Jonathan Wakely Date: Sat, 20 Jan 2024 07:46:55 +0000 Message-ID: Subject: Re: [PATCH] libstdc++: suppress -Wdangling-reference with operator| [PR111410] To: Marek Polacek Cc: GCC Patches , "libstdc++" , Jonathan Wakely , Jason Merrill Content-Type: multipart/alternative; boundary="000000000000bd6e3e060f5bcde4" X-Spam-Status: No, score=-6.7 required=5.0 tests=BAYES_00,DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,DKIM_VALID_EF,FREEMAIL_FROM,GIT_PATCH_0,HTML_MESSAGE,RCVD_IN_DNSWL_NONE,SPF_HELO_NONE,SPF_PASS,TXREP,T_SCC_BODY_TEXT_LINE autolearn=ham autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on server2.sourceware.org List-Id: --000000000000bd6e3e060f5bcde4 Content-Type: text/plain; charset="UTF-8" On Sat, 20 Jan 2024, 03:47 Marek Polacek, wrote: > Bootstrapped/regtested on x86_64-pc-linux-gnu, ok for trunk? > OK, thanks. The standard ranges have their own protection against dangling via the opt-in borrowed_range concept, and algorithms that don't allow returning iterators into rvalue ranges, and the automatic use of ref_view or owning_view as needed. So I think it's reasonable to assume they are less prone to the bugs this warning detects, at least when used idiomatically. > -- >8 -- > It seems to me that we should exclude > std::ranges::views::__adaptor::operator| > from the -Wdangling-reference warning. It's commonly used when handling > ranges. > > PR c++/111410 > > libstdc++-v3/ChangeLog: > > * include/std/ranges: Add #pragma to disable -Wdangling-reference > with > std::ranges::views::__adaptor::operator|. > > gcc/testsuite/ChangeLog: > > * g++.dg/warn/Wdangling-reference17.C: New test. > --- > gcc/testsuite/g++.dg/warn/Wdangling-reference17.C | 15 +++++++++++++++ > libstdc++-v3/include/std/ranges | 3 +++ > 2 files changed, 18 insertions(+) > create mode 100644 gcc/testsuite/g++.dg/warn/Wdangling-reference17.C > > diff --git a/gcc/testsuite/g++.dg/warn/Wdangling-reference17.C > b/gcc/testsuite/g++.dg/warn/Wdangling-reference17.C > new file mode 100644 > index 00000000000..223698422c2 > --- /dev/null > +++ b/gcc/testsuite/g++.dg/warn/Wdangling-reference17.C > @@ -0,0 +1,15 @@ > +// PR c++/111410 > +// { dg-do compile { target c++20 } } > +// { dg-options "-Wdangling-reference" } > + > +#include > +#include > + > +int main() > +{ > + std::vector v{1, 2, 3, 4, 5}; > + for (auto i : std::span{v} | std::views::take(1)) > + { > + (void) i; > + } > +} > diff --git a/libstdc++-v3/include/std/ranges > b/libstdc++-v3/include/std/ranges > index 7ef835f486a..f2413badd9c 100644 > --- a/libstdc++-v3/include/std/ranges > +++ b/libstdc++-v3/include/std/ranges > @@ -942,6 +942,8 @@ namespace views::__adaptor > concept __is_range_adaptor_closure > = requires (_Tp __t) { > __adaptor::__is_range_adaptor_closure_fn(__t, __t); }; > > +#pragma GCC diagnostic push > +#pragma GCC diagnostic ignored "-Wdangling-reference" > // range | adaptor is equivalent to adaptor(range). > template > requires __is_range_adaptor_closure<_Self> > @@ -961,6 +963,7 @@ namespace views::__adaptor > return _Pipe, > decay_t<_Rhs>>{std::forward<_Lhs>(__lhs), > > std::forward<_Rhs>(__rhs)}; > } > +#pragma GCC diagnostic pop > > // The base class of every range adaptor non-closure. > // > > base-commit: 615e25c82de97acc17ab438f88d6788cf7ffe1d6 > -- > 2.43.0 > > --000000000000bd6e3e060f5bcde4--