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Sat, 23 Sep 2023 00:30:14 -0700 (PDT) Date: Sat, 23 Sep 2023 17:30:08 +1000 From: Nathaniel Shead To: Jonathan Wakely Cc: Jason Merrill , libstdc++ , gcc-patches Subject: [PATCH] libstdc++: Ensure active union member is correctly set Message-ID: References: <053faf76-f918-7527-4a41-755a18d0018a@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Spam-Status: No, score=-11.7 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 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(); 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, __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, 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, 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, __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); + } + } + 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