[PATCH] libstdc++: Ensure active union member is correctly set
Jonathan Wakely
jwakely.gcc@gmail.com
Sat Sep 23 10:52:10 GMT 2023
On Sat, 23 Sept 2023, 08:30 Nathaniel Shead, <nathanieloshead@gmail.com>
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.
>
Nice, thanks! This looks good at first glance, I'll review it properly ASAP.
> -- >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 <nathanieloshead@gmail.com>
> ---
> 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<size_t _Np, typename _Union>
> + 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<typename... _Types>
> 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
>
>
More information about the Libstdc++
mailing list