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[124.150.88.161]) by smtp.gmail.com with ESMTPSA id b1-20020a17090a800100b002777001ee76sm92346pjn.18.2023.09.28.16.25.18 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 28 Sep 2023 16:25:20 -0700 (PDT) Message-ID: <65160b60.170a0220.894a0.06bc@mx.google.com> X-Google-Original-Message-ID: Date: Fri, 29 Sep 2023 09:25:15 +1000 From: Nathaniel Shead To: Jonathan Wakely Cc: Jonathan Wakely , Jason Merrill , libstdc++ , gcc-patches Subject: Re: [PATCH] libstdc++: Ensure active union member is correctly set References: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Spam-Status: No, score=-11.9 required=5.0 tests=BAYES_00,DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,DKIM_VALID_EF,FREEMAIL_FROM,GIT_PATCH_0,RCVD_IN_DNSWL_NONE,SPF_HELO_NONE,SPF_PASS,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 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. 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? -- >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