On Fri, 29 Sept 2023 at 00:25, Nathaniel Shead
<nathanielosh...@gmail.com> 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++
> > <libstd...@gcc.gnu.org> 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++, <
> > > > libstd...@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 <nathanielosh...@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();
> >
> > 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<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);
> > > + }
> > > + }
> >
> > This is nice, thanks for optimizing it to reduce the recursion depth.
> >
> > > +
> > > 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
> > >
> >
>
> 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 <nathanielosh...@gmail.com>
> ---
> 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<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
>
