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 0C349387541E for ; Fri, 29 Sep 2023 09:33:15 +0000 (GMT) DMARC-Filter: OpenDMARC Filter v1.4.2 sourceware.org 0C349387541E Authentication-Results: sourceware.org; dmarc=pass (p=none dis=none) header.from=redhat.com Authentication-Results: sourceware.org; spf=pass smtp.mailfrom=redhat.com DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1695979994; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=L+PJ5z8TnmPhhokTp/lcVNuCg2qHrEZr7tHzCPTdZf4=; b=hzjTUsUOk+8HFdvDPGc8U0JFu4xyGKkzyXserBFL8inqze26LUHe9MJcBNW/sdCS8vopYh aMseyaTnejIE6cHddkP8hPRWiHILy1NU9+PuXxapXTe+snBgWP+MEU6+ZGmrwh9vXeZinG rETus6Itf96iJWeO9EXDInBKCMLTbo4= Received: from mail-lj1-f200.google.com (mail-lj1-f200.google.com [209.85.208.200]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-484-V2zXB8zzMbCyIHlmE8CCBA-1; 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Fri, 29 Sep 2023 02:33:09 -0700 (PDT) X-Google-Smtp-Source: AGHT+IGvrJCfzMDvIBkb9zS/XdolGBCIPjXQ080sulkTKRtjPLwtQSfNXgSLe8rYhk/YdiIhnKxEH3/o2TxMRktQO/4= X-Received: by 2002:a2e:9ccd:0:b0:2c0:afd:e7f4 with SMTP id g13-20020a2e9ccd000000b002c00afde7f4mr2999089ljj.36.1695979988876; Fri, 29 Sep 2023 02:33:08 -0700 (PDT) MIME-Version: 1.0 References: <65160b60.170a0220.894a0.06bc@mx.google.com> In-Reply-To: <65160b60.170a0220.894a0.06bc@mx.google.com> From: Jonathan Wakely Date: Fri, 29 Sep 2023 10:32:57 +0100 Message-ID: Subject: Re: [PATCH] libstdc++: Ensure active union member is correctly set To: Nathaniel Shead Cc: Jonathan Wakely , Jason Merrill , "libstdc++" , gcc-patches X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset="UTF-8" X-Spam-Status: No, score=-12.2 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_NONE,RCVD_IN_MSPIKE_H3,RCVD_IN_MSPIKE_WL,SPF_HELO_NONE,SPF_NONE,TXREP 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: On Fri, 29 Sept 2023 at 00:25, Nathaniel Shead wrote: > > On Wed, Sep 27, 2023 at 03:13:35PM +0100, Jonathan Wakely wrote: > > On Sat, 23 Sept 2023 at 08:30, Nathaniel Shead via Libstdc++ > > wrote: > > > > > > On Sat, Sep 23, 2023 at 07:40:48AM +0100, Jonathan Wakely wrote: > > > > On Sat, 23 Sept 2023, 01:39 Nathaniel Shead via Libstdc++, < > > > > libstdc++@gcc.gnu.org> wrote: > > > > > > > > > Now that bootstrap has finished, I have gotten regressions in the > > > > > following libstdc++ tests: > > > > > > > > > > Running libstdc++:libstdc++-dg/conformance.exp ... > > > > > FAIL: 20_util/bitset/access/constexpr.cc -std=gnu++23 (test for excess > > > > > errors) > > > > > FAIL: 20_util/bitset/access/constexpr.cc -std=gnu++26 (test for excess > > > > > errors) > > > > > FAIL: 20_util/variant/constexpr.cc -std=gnu++20 (test for excess errors) > > > > > FAIL: 20_util/variant/constexpr.cc -std=gnu++26 (test for excess errors) > > > > > FAIL: 21_strings/basic_string/cons/char/constexpr.cc -std=gnu++20 (test > > > > > for excess errors) > > > > > FAIL: 21_strings/basic_string/cons/char/constexpr.cc -std=gnu++26 (test > > > > > for excess errors) > > > > > FAIL: 21_strings/basic_string/cons/wchar_t/constexpr.cc -std=gnu++20 (test > > > > > for excess errors) > > > > > FAIL: 21_strings/basic_string/cons/wchar_t/constexpr.cc -std=gnu++26 (test > > > > > for excess errors) > > > > > FAIL: 21_strings/basic_string/modifiers/swap/constexpr-wchar_t.cc > > > > > -std=gnu++20 (test for excess errors) > > > > > FAIL: 21_strings/basic_string/modifiers/swap/constexpr-wchar_t.cc > > > > > -std=gnu++26 (test for excess errors) > > > > > FAIL: 21_strings/basic_string/modifiers/swap/constexpr.cc -std=gnu++20 > > > > > (test for excess errors) > > > > > FAIL: 21_strings/basic_string/modifiers/swap/constexpr.cc -std=gnu++26 > > > > > (test for excess errors) > > > > > FAIL: std/ranges/adaptors/join_with/1.cc -std=gnu++23 (test for excess > > > > > errors) > > > > > UNRESOLVED: std/ranges/adaptors/join_with/1.cc -std=gnu++23 compilation > > > > > failed to produce executable > > > > > FAIL: std/ranges/adaptors/join_with/1.cc -std=gnu++26 (test for excess > > > > > errors) > > > > > UNRESOLVED: std/ranges/adaptors/join_with/1.cc -std=gnu++26 compilation > > > > > failed to produce executable > > > > > > > > > > On investigation though it looks like the issue might be with libstdc++ > > > > > rather than the patch itself; running the failing tests using clang with > > > > > libstdc++ also produces similar errors, and my reading of the code > > > > > suggests that this is correct. > > > > > > > > > > What's the way forward here? Should I look at creating a patch to fix > > > > > the libstdc++ issues before resubmitting this patch for the C++ > > > > > frontend? Or should I submit a version of this patch without the > > > > > `std::construct_at` changes and wait till libstdc++ gets fixed for that? > > > > > > > > > > > > > I think we should fix libstdc++. There are probably only a few places that > > > > need a fix, which cause all those failures. > > > > > > > > I can help with those fixes. I'll look into it after the weekend. > > > > > > > > > > Thanks. I did end up getting a chance to look at it earlier today, and > > > with the following patch I had no regressions when applying the frontend > > > changes. Bootstrapped and regtested on x86_64-pc-linux-gnu. > > > > > > -- >8 -- > > > > > > This patch ensures that the union members for std::string and > > > std::variant are always properly set when a change occurs. > > > > > > libstdc++-v3/ChangeLog: > > > > > > * include/bits/basic_string.h: (basic_string(basic_string&&)): > > > Activate _M_local_buf when needed. > > > (basic_string(basic_string&&, const _Alloc&)): Likewise. > > > * include/bits/basic_string.tcc: (basic_string::swap): Likewise. > > > * include/std/variant: (__detail::__variant::__construct_n): New. > > > (__detail::_variant::__emplace): Use __construct_n. > > > > > > Signed-off-by: Nathaniel Shead > > > --- > > > libstdc++-v3/include/bits/basic_string.h | 7 +++-- > > > libstdc++-v3/include/bits/basic_string.tcc | 8 +++--- > > > libstdc++-v3/include/std/variant | 32 ++++++++++++++++++++-- > > > 3 files changed, 38 insertions(+), 9 deletions(-) > > > > > > diff --git a/libstdc++-v3/include/bits/basic_string.h b/libstdc++-v3/include/bits/basic_string.h > > > index 09fd62afa66..7c342879827 100644 > > > --- a/libstdc++-v3/include/bits/basic_string.h > > > +++ b/libstdc++-v3/include/bits/basic_string.h > > > @@ -678,7 +678,7 @@ _GLIBCXX_BEGIN_NAMESPACE_CXX11 > > > { > > > if (__str._M_is_local()) > > > { > > > - traits_type::copy(_M_local_buf, __str._M_local_buf, > > > + traits_type::copy(_M_use_local_data(), __str._M_local_buf, > > > __str.length() + 1); > > > } > > > else > > > @@ -691,7 +691,7 @@ _GLIBCXX_BEGIN_NAMESPACE_CXX11 > > > // basic_stringbuf relies on writing into unallocated capacity so > > > // we mess up the contents if we put a '\0' in the string. > > > _M_length(__str.length()); > > > - __str._M_data(__str._M_local_data()); > > > + __str._M_data(__str._M_use_local_data()); > > > __str._M_set_length(0); > > > } > > > > > > @@ -717,6 +717,7 @@ _GLIBCXX_BEGIN_NAMESPACE_CXX11 > > > { > > > if (__str._M_is_local()) > > > { > > > + _M_use_local_data(); > > > > Lets add a cast to void to make it clear we're intentionally > > discarding the return value here, and only calling it for its > > constexpr "side effects": > > > > (void) _M_use_local_data(); > > > > > > > traits_type::copy(_M_local_buf, __str._M_local_buf, > > > __str.length() + 1); > > > _M_length(__str.length()); > > > @@ -728,7 +729,7 @@ _GLIBCXX_BEGIN_NAMESPACE_CXX11 > > > _M_data(__str._M_data()); > > > _M_length(__str.length()); > > > _M_capacity(__str._M_allocated_capacity); > > > - __str._M_data(__str._M_local_buf); > > > + __str._M_data(__str._M_use_local_data()); > > > __str._M_set_length(0); > > > } > > > else > > > diff --git a/libstdc++-v3/include/bits/basic_string.tcc b/libstdc++-v3/include/bits/basic_string.tcc > > > index 104a517f794..ee6e57da555 100644 > > > --- a/libstdc++-v3/include/bits/basic_string.tcc > > > +++ b/libstdc++-v3/include/bits/basic_string.tcc > > > @@ -79,7 +79,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION > > > } > > > else if (__s.length()) > > > { > > > - traits_type::copy(_M_local_buf, __s._M_local_buf, > > > + traits_type::copy(_M_use_local_data(), __s._M_local_buf, > > > > I think we should call _M_use_local_data() before calling > > traits_type::copy, as you did for > > basic_string(basic_string&& __str, const _Alloc& __a) > > above. > > > > The problem is that _M_use_local_data() returns the allocator's > > pointer type, but traits_type::copy expects char_type*, and those > > might not be the same type. > > So: > > > > @@ -79,6 +79,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION > > } > > else if (__s.length()) > > { > > + (void) _M_use_local_data(); > > traits_type::copy(_M_local_buf, __s._M_local_buf, > > __s.length() + 1); > > _M_length(__s.length()); > > > > > > > > > __s.length() + 1); > > > _M_length(__s.length()); > > > __s._M_set_length(0); > > > @@ -87,7 +87,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION > > > } > > > else if (length()) > > > { > > > - traits_type::copy(__s._M_local_buf, _M_local_buf, > > > + traits_type::copy(__s._M_use_local_data(), _M_local_buf, > > > > Same here, for __s._M_use_local_data() > > > > > length() + 1); > > > __s._M_length(length()); > > > _M_set_length(0); > > > @@ -97,7 +97,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION > > > else > > > { > > > const size_type __tmp_capacity = __s._M_allocated_capacity; > > > - traits_type::copy(__s._M_local_buf, _M_local_buf, > > > + traits_type::copy(__s._M_use_local_data(), _M_local_buf, > > > > And again. > > > > > length() + 1); > > > _M_data(__s._M_data()); > > > __s._M_data(__s._M_local_buf); > > > @@ -108,7 +108,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION > > > const size_type __tmp_capacity = _M_allocated_capacity; > > > if (__s._M_is_local()) > > > { > > > - traits_type::copy(_M_local_buf, __s._M_local_buf, > > > + traits_type::copy(_M_use_local_data(), __s._M_local_buf, > > > > And again. > > > > > __s.length() + 1); > > > __s._M_data(_M_data()); > > > _M_data(_M_local_buf); > > > diff --git a/libstdc++-v3/include/std/variant b/libstdc++-v3/include/std/variant > > > index c0e41740dcf..7f24e760bb1 100644 > > > --- a/libstdc++-v3/include/std/variant > > > +++ b/libstdc++-v3/include/std/variant > > > @@ -320,6 +320,33 @@ namespace __variant > > > __get(_Variant&& __v) noexcept > > > { return __variant::__get_n<_Np>(std::forward<_Variant>(__v)._M_u); } > > > > > > + // Gets the _Uninitialized to construct into for __u. > > > + template > > > + constexpr decltype(auto) > > > + __construct_n(_Union& __u) noexcept > > > + { > > > + if constexpr (_Np == 0) > > > + return &__u._M_first; > > > + else if constexpr (_Np == 1) > > > + { > > > + std::_Construct(&__u._M_rest); > > > + return &__u._M_rest._M_first; > > > + } > > > + else if constexpr (_Np == 2) > > > + { > > > + std::_Construct(&__u._M_rest); > > > + std::_Construct(&__u._M_rest._M_rest); > > > + return &__u._M_rest._M_rest._M_first; > > > + } > > > + else > > > + { > > > + std::_Construct(&__u._M_rest); > > > + std::_Construct(&__u._M_rest._M_rest); > > > + std::_Construct(&__u._M_rest._M_rest._M_rest); > > > + return __variant::__construct_n<_Np - 3>(__u._M_rest._M_rest._M_rest); > > > + } > > > + } > > > > This is nice, thanks for optimizing it to reduce the recursion depth. > > > > > + > > > template > > > struct _Traits > > > { > > > @@ -536,8 +563,9 @@ namespace __variant > > > __emplace(_Variant_storage<_Triv, _Types...>& __v, _Args&&... __args) > > > { > > > __v._M_reset(); > > > - auto* __addr = std::__addressof(__variant::__get_n<_Np>(__v._M_u)); > > > - std::_Construct(__addr, std::forward<_Args>(__args)...); > > > + auto* __addr = __variant::__construct_n<_Np>(__v._M_u); > > > + std::_Construct(__addr, in_place_index<0>, > > > + std::forward<_Args>(__args)...); > > > // Construction didn't throw, so can set the new index now: > > > __v._M_index = _Np; > > > } > > > -- > > > 2.41.0 > > > > > > > Thanks for the comments, here's an updated version of the patch. > Bootstrapped and regtested on x86_64-pc-linux-gnu. Great, I'll get this committed today - thanks! > > I'll note that there are some existing calls to `_M_use_local_data()` > already used only for their side effects without a cast to void, e.g. > > /** > * @brief Default constructor creates an empty string. > */ > _GLIBCXX20_CONSTEXPR > basic_string() > _GLIBCXX_NOEXCEPT_IF(is_nothrow_default_constructible<_Alloc>::value) > : _M_dataplus(_M_local_data()) > { > _M_use_local_data(); > _M_set_length(0); > } > > I haven't updated these, but should this be changed for consistency? Yes, good idea. I can do that. Thanks again for fixing these. I think this might fix some bug reports about clang rejecting our std::string in constant expressions, so I'll check those. > > -- >8 -- > > This patch ensures that the union members for std::string and > std::variant are always properly set when a change occurs. > > libstdc++-v3/ChangeLog: > > * include/bits/basic_string.h: (basic_string(basic_string&&)): > Activate _M_local_buf when needed. > (basic_string(basic_string&&, const _Alloc&)): Likewise. > * include/bits/basic_string.tcc: (basic_string::swap): Likewise. > * include/std/variant: (__detail::__variant::__construct_n): New. > (__detail::__variant::__emplace): Use __construct_n. > > Signed-off-by: Nathaniel Shead > --- > libstdc++-v3/include/bits/basic_string.h | 6 ++-- > libstdc++-v3/include/bits/basic_string.tcc | 4 +++ > libstdc++-v3/include/std/variant | 32 ++++++++++++++++++++-- > 3 files changed, 38 insertions(+), 4 deletions(-) > > diff --git a/libstdc++-v3/include/bits/basic_string.h b/libstdc++-v3/include/bits/basic_string.h > index 09fd62afa66..4f94cd967cf 100644 > --- a/libstdc++-v3/include/bits/basic_string.h > +++ b/libstdc++-v3/include/bits/basic_string.h > @@ -678,6 +678,7 @@ _GLIBCXX_BEGIN_NAMESPACE_CXX11 > { > if (__str._M_is_local()) > { > + (void)_M_use_local_data(); > traits_type::copy(_M_local_buf, __str._M_local_buf, > __str.length() + 1); > } > @@ -691,7 +692,7 @@ _GLIBCXX_BEGIN_NAMESPACE_CXX11 > // basic_stringbuf relies on writing into unallocated capacity so > // we mess up the contents if we put a '\0' in the string. > _M_length(__str.length()); > - __str._M_data(__str._M_local_data()); > + __str._M_data(__str._M_use_local_data()); > __str._M_set_length(0); > } > > @@ -717,6 +718,7 @@ _GLIBCXX_BEGIN_NAMESPACE_CXX11 > { > if (__str._M_is_local()) > { > + (void)_M_use_local_data(); > traits_type::copy(_M_local_buf, __str._M_local_buf, > __str.length() + 1); > _M_length(__str.length()); > @@ -728,7 +730,7 @@ _GLIBCXX_BEGIN_NAMESPACE_CXX11 > _M_data(__str._M_data()); > _M_length(__str.length()); > _M_capacity(__str._M_allocated_capacity); > - __str._M_data(__str._M_local_buf); > + __str._M_data(__str._M_use_local_data()); > __str._M_set_length(0); > } > else > diff --git a/libstdc++-v3/include/bits/basic_string.tcc b/libstdc++-v3/include/bits/basic_string.tcc > index 104a517f794..4bc98f2aea7 100644 > --- a/libstdc++-v3/include/bits/basic_string.tcc > +++ b/libstdc++-v3/include/bits/basic_string.tcc > @@ -79,6 +79,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION > } > else if (__s.length()) > { > + (void)_M_use_local_data(); > traits_type::copy(_M_local_buf, __s._M_local_buf, > __s.length() + 1); > _M_length(__s.length()); > @@ -87,6 +88,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION > } > else if (length()) > { > + (void)__s._M_use_local_data(); > traits_type::copy(__s._M_local_buf, _M_local_buf, > length() + 1); > __s._M_length(length()); > @@ -97,6 +99,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION > else > { > const size_type __tmp_capacity = __s._M_allocated_capacity; > + (void)__s._M_use_local_data(); > traits_type::copy(__s._M_local_buf, _M_local_buf, > length() + 1); > _M_data(__s._M_data()); > @@ -108,6 +111,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION > const size_type __tmp_capacity = _M_allocated_capacity; > if (__s._M_is_local()) > { > + (void)_M_use_local_data(); > traits_type::copy(_M_local_buf, __s._M_local_buf, > __s.length() + 1); > __s._M_data(_M_data()); > diff --git a/libstdc++-v3/include/std/variant b/libstdc++-v3/include/std/variant > index c0e41740dcf..7f24e760bb1 100644 > --- a/libstdc++-v3/include/std/variant > +++ b/libstdc++-v3/include/std/variant > @@ -320,6 +320,33 @@ namespace __variant > __get(_Variant&& __v) noexcept > { return __variant::__get_n<_Np>(std::forward<_Variant>(__v)._M_u); } > > + // Gets the _Uninitialized to construct into for __u. > + template > + constexpr decltype(auto) > + __construct_n(_Union& __u) noexcept > + { > + if constexpr (_Np == 0) > + return &__u._M_first; > + else if constexpr (_Np == 1) > + { > + std::_Construct(&__u._M_rest); > + return &__u._M_rest._M_first; > + } > + else if constexpr (_Np == 2) > + { > + std::_Construct(&__u._M_rest); > + std::_Construct(&__u._M_rest._M_rest); > + return &__u._M_rest._M_rest._M_first; > + } > + else > + { > + std::_Construct(&__u._M_rest); > + std::_Construct(&__u._M_rest._M_rest); > + std::_Construct(&__u._M_rest._M_rest._M_rest); > + return __variant::__construct_n<_Np - 3>(__u._M_rest._M_rest._M_rest); > + } > + } > + > template > struct _Traits > { > @@ -536,8 +563,9 @@ namespace __variant > __emplace(_Variant_storage<_Triv, _Types...>& __v, _Args&&... __args) > { > __v._M_reset(); > - auto* __addr = std::__addressof(__variant::__get_n<_Np>(__v._M_u)); > - std::_Construct(__addr, std::forward<_Args>(__args)...); > + auto* __addr = __variant::__construct_n<_Np>(__v._M_u); > + std::_Construct(__addr, in_place_index<0>, > + std::forward<_Args>(__args)...); > // Construction didn't throw, so can set the new index now: > __v._M_index = _Np; > } > -- > 2.41.0 >