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.
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 <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
