| Message ID | ZQ6UAFyty9z/Vuw+@Thaum.localdomain |
|---|---|
| State | New |
| Headers | show |
| Series | libstdc++: Ensure active union member is correctly set | expand |
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 > >
On Sat, 23 Sept 2023 at 08:30, Nathaniel Shead via Libstdc++ <libstdc++@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++, < > > 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 <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(); 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 >
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++ > <libstdc++@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++, < > > > 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 <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(); > > 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 <nathanieloshead@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; }
On Fri, 29 Sept 2023 at 00:25, Nathaniel Shead <nathanieloshead@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++ > > <libstdc++@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++, < > > > > 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 <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(); > > > > 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 <nathanieloshead@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 >
On Fri, 29 Sept 2023 at 10:32, Jonathan Wakely <jwakely@redhat.com> wrote: > > 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! That's done now. > > > > 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. I started to do that, and decided it made more sense to split out the constexpr loop from _M_use_local_data() into a separate function, _M_init_local_buf(). Then we can use that for all the places where we don't care about the return value. That avoids the overhead of using pointer_traits::pointer_to when we don't need the return value (which is admittedly only going to be an issue for -O0 code, but I think it's cleaner this way anyway). Please see the attached patch and let me know what you think. > 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. Your patch fixes https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110900 (so we should backport it to gcc-13 and gcc-12 too). commit 2668979d3206ff6c039ac0165aae29377a15666c Author: Jonathan Wakely <jwakely@redhat.com> Date: Fri Sep 29 12:12:22 2023 libstdc++: Split std::basic_string::_M_use_local_data into two functions This splits out the activate-the-union-member-for-constexpr logic from _M_use_local_data, so that it can be used separately in cases that don't need to use std::pointer_traits<pointer>::pointer_to to obtain the return value. This leaves only three uses of _M_use_local_data() which are all the same form: __s._M_data(_M_use_local_data()); __s._M_set_length(0); We could remove _M_use_local_data() and change those three places to use a new _M_reset() function that does: _M_init_local_buf(); _M_data(_M_local_data()); _M_set_length(0); This is left for a future change. libstdc++-v3/ChangeLog: * include/bits/basic_string.h (_M_init_local_buf()): New function. (_M_use_local_data()): Use _M_init_local_buf. (basic_string(), basic_string(const Alloc&)) (basic_string(basic_string&&)) (basic_string(basic_string&&, const Alloc&)): Use _M_init_local_buf instead of _M_use_local_data(). * include/bits/basic_string.tcc (swap(basic_string&)) (_M_construct(InIter, InIter, forward_iterator_tag)) (_M_construct(size_type, CharT), reserve()): Likewise. (_M_construct(InIter, InIter, input_iterator_tag)): Remove call to _M_use_local_data() and initialize the local buffer directly. diff --git a/libstdc++-v3/include/bits/basic_string.h b/libstdc++-v3/include/bits/basic_string.h index 4f94cd967cf..18a19b8dcbc 100644 --- a/libstdc++-v3/include/bits/basic_string.h +++ b/libstdc++-v3/include/bits/basic_string.h @@ -353,13 +353,23 @@ _GLIBCXX_BEGIN_NAMESPACE_CXX11 // Ensure that _M_local_buf is the active member of the union. __attribute__((__always_inline__)) _GLIBCXX14_CONSTEXPR - pointer - _M_use_local_data() _GLIBCXX_NOEXCEPT + void + _M_init_local_buf() _GLIBCXX_NOEXCEPT { #if __cpp_lib_is_constant_evaluated if (std::is_constant_evaluated()) for (size_type __i = 0; __i <= _S_local_capacity; ++__i) _M_local_buf[__i] = _CharT(); +#endif + } + + __attribute__((__always_inline__)) + _GLIBCXX14_CONSTEXPR + pointer + _M_use_local_data() _GLIBCXX_NOEXCEPT + { +#if __glibcxx_is_constant_evaluated + _M_init_local_buf(); #endif return _M_local_data(); } @@ -522,7 +532,7 @@ _GLIBCXX_BEGIN_NAMESPACE_CXX11 _GLIBCXX_NOEXCEPT_IF(is_nothrow_default_constructible<_Alloc>::value) : _M_dataplus(_M_local_data()) { - _M_use_local_data(); + _M_init_local_buf(); _M_set_length(0); } @@ -534,7 +544,7 @@ _GLIBCXX_BEGIN_NAMESPACE_CXX11 basic_string(const _Alloc& __a) _GLIBCXX_NOEXCEPT : _M_dataplus(_M_local_data(), __a) { - _M_use_local_data(); + _M_init_local_buf(); _M_set_length(0); } @@ -678,7 +688,7 @@ _GLIBCXX_BEGIN_NAMESPACE_CXX11 { if (__str._M_is_local()) { - (void)_M_use_local_data(); + _M_init_local_buf(); traits_type::copy(_M_local_buf, __str._M_local_buf, __str.length() + 1); } @@ -718,7 +728,7 @@ _GLIBCXX_BEGIN_NAMESPACE_CXX11 { if (__str._M_is_local()) { - (void)_M_use_local_data(); + _M_init_local_buf(); traits_type::copy(_M_local_buf, __str._M_local_buf, __str.length() + 1); _M_length(__str.length()); diff --git a/libstdc++-v3/include/bits/basic_string.tcc b/libstdc++-v3/include/bits/basic_string.tcc index 4bc98f2aea7..052eeb9e846 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()) { - (void)_M_use_local_data(); + _M_init_local_buf(); traits_type::copy(_M_local_buf, __s._M_local_buf, __s.length() + 1); _M_length(__s.length()); @@ -88,7 +88,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION } else if (length()) { - (void)__s._M_use_local_data(); + __s._M_init_local_buf(); traits_type::copy(__s._M_local_buf, _M_local_buf, length() + 1); __s._M_length(length()); @@ -99,7 +99,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION else { const size_type __tmp_capacity = __s._M_allocated_capacity; - (void)__s._M_use_local_data(); + __s._M_init_local_buf(); traits_type::copy(__s._M_local_buf, _M_local_buf, length() + 1); _M_data(__s._M_data()); @@ -111,7 +111,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION const size_type __tmp_capacity = _M_allocated_capacity; if (__s._M_is_local()) { - (void)_M_use_local_data(); + _M_init_local_buf(); traits_type::copy(_M_local_buf, __s._M_local_buf, __s.length() + 1); __s._M_data(_M_data()); @@ -174,14 +174,18 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION size_type __len = 0; size_type __capacity = size_type(_S_local_capacity); - pointer __p = _M_use_local_data(); - while (__beg != __end && __len < __capacity) { - __p[__len++] = *__beg; + _M_local_buf[__len++] = *__beg; ++__beg; } +#if __glibcxx_is_constant_evaluated + if (std::is_constant_evaluated()) + for (size_type __i = __len; __i <= __capacity; ++__i) + _M_local_buf[__i] = _CharT(); +#endif + struct _Guard { _GLIBCXX20_CONSTEXPR @@ -230,7 +234,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION _M_capacity(__dnew); } else - _M_use_local_data(); + _M_init_local_buf(); // Check for out_of_range and length_error exceptions. struct _Guard @@ -263,7 +267,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION _M_capacity(__n); } else - _M_use_local_data(); + _M_init_local_buf(); if (__n) this->_S_assign(_M_data(), __n, __c); @@ -372,7 +376,8 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION if (__length <= size_type(_S_local_capacity)) { - this->_S_copy(_M_use_local_data(), _M_data(), __length + 1); + _M_init_local_buf(); + this->_S_copy(_M_local_buf, _M_data(), __length + 1); _M_destroy(__capacity); _M_data(_M_local_data()); }
On Fri, Sep 29, 2023 at 04:06:33PM +0100, Jonathan Wakely wrote: > On Fri, 29 Sept 2023 at 10:32, Jonathan Wakely <jwakely@redhat.com> wrote: > > > 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! > > That's done now. > 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. > > I started to do that, and decided it made more sense to split out the > constexpr loop from _M_use_local_data() into a separate function, > _M_init_local_buf(). Then we can use that for all the places where we > don't care about the return value. That avoids the overhead of using > pointer_traits::pointer_to when we don't need the return value (which > is admittedly only going to be an issue for -O0 code, but I think it's > cleaner this way anyway). > > Please see the attached patch and let me know what you think. I agree, and it also looks clearer to me what is happening. > > > 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. > > Your patch fixes https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110900 > (so we should backport it to gcc-13 and gcc-12 too). > commit 2668979d3206ff6c039ac0165aae29377a15666c > Author: Jonathan Wakely <jwakely@redhat.com> > Date: Fri Sep 29 12:12:22 2023 > > libstdc++: Split std::basic_string::_M_use_local_data into two functions > > This splits out the activate-the-union-member-for-constexpr logic from > _M_use_local_data, so that it can be used separately in cases that don't > need to use std::pointer_traits<pointer>::pointer_to to obtain the > return value. > > This leaves only three uses of _M_use_local_data() which are all the > same form: > > __s._M_data(_M_use_local_data()); > __s._M_set_length(0); > > We could remove _M_use_local_data() and change those three places to use > a new _M_reset() function that does: > > _M_init_local_buf(); > _M_data(_M_local_data()); > _M_set_length(0); > > This is left for a future change. > > libstdc++-v3/ChangeLog: > > * include/bits/basic_string.h (_M_init_local_buf()): New > function. > (_M_use_local_data()): Use _M_init_local_buf. > (basic_string(), basic_string(const Alloc&)) > (basic_string(basic_string&&)) > (basic_string(basic_string&&, const Alloc&)): Use > _M_init_local_buf instead of _M_use_local_data(). > * include/bits/basic_string.tcc (swap(basic_string&)) > (_M_construct(InIter, InIter, forward_iterator_tag)) > (_M_construct(size_type, CharT), reserve()): Likewise. > (_M_construct(InIter, InIter, input_iterator_tag)): Remove call > to _M_use_local_data() and initialize the local buffer directly. > > diff --git a/libstdc++-v3/include/bits/basic_string.h b/libstdc++-v3/include/bits/basic_string.h > index 4f94cd967cf..18a19b8dcbc 100644 > --- a/libstdc++-v3/include/bits/basic_string.h > +++ b/libstdc++-v3/include/bits/basic_string.h > @@ -353,13 +353,23 @@ _GLIBCXX_BEGIN_NAMESPACE_CXX11 > // Ensure that _M_local_buf is the active member of the union. > __attribute__((__always_inline__)) > _GLIBCXX14_CONSTEXPR > - pointer > - _M_use_local_data() _GLIBCXX_NOEXCEPT > + void > + _M_init_local_buf() _GLIBCXX_NOEXCEPT > { > #if __cpp_lib_is_constant_evaluated > if (std::is_constant_evaluated()) > for (size_type __i = 0; __i <= _S_local_capacity; ++__i) > _M_local_buf[__i] = _CharT(); > +#endif > + } > + > + __attribute__((__always_inline__)) > + _GLIBCXX14_CONSTEXPR > + pointer > + _M_use_local_data() _GLIBCXX_NOEXCEPT > + { > +#if __glibcxx_is_constant_evaluated > + _M_init_local_buf(); > #endif > return _M_local_data(); > } What's the difference between __cpp_lib_is_constant_evaluated and __glibcxx_is_constant_evaluated? Should these lines be using the same macro here? > @@ -522,7 +532,7 @@ _GLIBCXX_BEGIN_NAMESPACE_CXX11 > _GLIBCXX_NOEXCEPT_IF(is_nothrow_default_constructible<_Alloc>::value) > : _M_dataplus(_M_local_data()) > { > - _M_use_local_data(); > + _M_init_local_buf(); > _M_set_length(0); > } > > @@ -534,7 +544,7 @@ _GLIBCXX_BEGIN_NAMESPACE_CXX11 > basic_string(const _Alloc& __a) _GLIBCXX_NOEXCEPT > : _M_dataplus(_M_local_data(), __a) > { > - _M_use_local_data(); > + _M_init_local_buf(); > _M_set_length(0); > } > > @@ -678,7 +688,7 @@ _GLIBCXX_BEGIN_NAMESPACE_CXX11 > { > if (__str._M_is_local()) > { > - (void)_M_use_local_data(); > + _M_init_local_buf(); > traits_type::copy(_M_local_buf, __str._M_local_buf, > __str.length() + 1); > } > @@ -718,7 +728,7 @@ _GLIBCXX_BEGIN_NAMESPACE_CXX11 > { > if (__str._M_is_local()) > { > - (void)_M_use_local_data(); > + _M_init_local_buf(); > traits_type::copy(_M_local_buf, __str._M_local_buf, > __str.length() + 1); > _M_length(__str.length()); > diff --git a/libstdc++-v3/include/bits/basic_string.tcc b/libstdc++-v3/include/bits/basic_string.tcc > index 4bc98f2aea7..052eeb9e846 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()) > { > - (void)_M_use_local_data(); > + _M_init_local_buf(); > traits_type::copy(_M_local_buf, __s._M_local_buf, > __s.length() + 1); > _M_length(__s.length()); > @@ -88,7 +88,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION > } > else if (length()) > { > - (void)__s._M_use_local_data(); > + __s._M_init_local_buf(); > traits_type::copy(__s._M_local_buf, _M_local_buf, > length() + 1); > __s._M_length(length()); > @@ -99,7 +99,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION > else > { > const size_type __tmp_capacity = __s._M_allocated_capacity; > - (void)__s._M_use_local_data(); > + __s._M_init_local_buf(); > traits_type::copy(__s._M_local_buf, _M_local_buf, > length() + 1); > _M_data(__s._M_data()); > @@ -111,7 +111,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION > const size_type __tmp_capacity = _M_allocated_capacity; > if (__s._M_is_local()) > { > - (void)_M_use_local_data(); > + _M_init_local_buf(); > traits_type::copy(_M_local_buf, __s._M_local_buf, > __s.length() + 1); > __s._M_data(_M_data()); > @@ -174,14 +174,18 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION > size_type __len = 0; > size_type __capacity = size_type(_S_local_capacity); > > - pointer __p = _M_use_local_data(); > - > while (__beg != __end && __len < __capacity) > { > - __p[__len++] = *__beg; > + _M_local_buf[__len++] = *__beg; > ++__beg; > } > > +#if __glibcxx_is_constant_evaluated > + if (std::is_constant_evaluated()) > + for (size_type __i = __len; __i <= __capacity; ++__i) > + _M_local_buf[__i] = _CharT(); > +#endif > + I wonder if maybe this should still be a call to `_M_init_local_buf()` above, where the `_M_use_local_data()` used to be? That way the logic stays in one place, and I don't imagine the compile time savings of not immediately overwriting the first __len characters would be significant. > struct _Guard > { > _GLIBCXX20_CONSTEXPR > @@ -230,7 +234,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION > _M_capacity(__dnew); > } > else > - _M_use_local_data(); > + _M_init_local_buf(); > > // Check for out_of_range and length_error exceptions. > struct _Guard > @@ -263,7 +267,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION > _M_capacity(__n); > } > else > - _M_use_local_data(); > + _M_init_local_buf(); > > if (__n) > this->_S_assign(_M_data(), __n, __c); > @@ -372,7 +376,8 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION > > if (__length <= size_type(_S_local_capacity)) > { > - this->_S_copy(_M_use_local_data(), _M_data(), __length + 1); > + _M_init_local_buf(); > + this->_S_copy(_M_local_buf, _M_data(), __length + 1); > _M_destroy(__capacity); > _M_data(_M_local_data()); > } But looks good to me; I tried applying this on top of my frontend patch and it looks like everything still works correctly.
On Fri, 29 Sept 2023 at 17:29, Nathaniel Shead <nathanieloshead@gmail.com> wrote: > > On Fri, Sep 29, 2023 at 04:06:33PM +0100, Jonathan Wakely wrote: > > On Fri, 29 Sept 2023 at 10:32, Jonathan Wakely <jwakely@redhat.com> wrote: > > > > 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! > > > > That's done now. > > > > 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. > > > > I started to do that, and decided it made more sense to split out the > > constexpr loop from _M_use_local_data() into a separate function, > > _M_init_local_buf(). Then we can use that for all the places where we > > don't care about the return value. That avoids the overhead of using > > pointer_traits::pointer_to when we don't need the return value (which > > is admittedly only going to be an issue for -O0 code, but I think it's > > cleaner this way anyway). > > > > Please see the attached patch and let me know what you think. > > I agree, and it also looks clearer to me what is happening. Good, I'll make this change next week then. > > > > > > 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. > > > > Your patch fixes https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110900 > > (so we should backport it to gcc-13 and gcc-12 too). > > > commit 2668979d3206ff6c039ac0165aae29377a15666c > > Author: Jonathan Wakely <jwakely@redhat.com> > > Date: Fri Sep 29 12:12:22 2023 > > > > libstdc++: Split std::basic_string::_M_use_local_data into two functions > > > > This splits out the activate-the-union-member-for-constexpr logic from > > _M_use_local_data, so that it can be used separately in cases that don't > > need to use std::pointer_traits<pointer>::pointer_to to obtain the > > return value. > > > > This leaves only three uses of _M_use_local_data() which are all the > > same form: > > > > __s._M_data(_M_use_local_data()); > > __s._M_set_length(0); > > > > We could remove _M_use_local_data() and change those three places to use > > a new _M_reset() function that does: > > > > _M_init_local_buf(); > > _M_data(_M_local_data()); > > _M_set_length(0); > > > > This is left for a future change. > > > > libstdc++-v3/ChangeLog: > > > > * include/bits/basic_string.h (_M_init_local_buf()): New > > function. > > (_M_use_local_data()): Use _M_init_local_buf. > > (basic_string(), basic_string(const Alloc&)) > > (basic_string(basic_string&&)) > > (basic_string(basic_string&&, const Alloc&)): Use > > _M_init_local_buf instead of _M_use_local_data(). > > * include/bits/basic_string.tcc (swap(basic_string&)) > > (_M_construct(InIter, InIter, forward_iterator_tag)) > > (_M_construct(size_type, CharT), reserve()): Likewise. > > (_M_construct(InIter, InIter, input_iterator_tag)): Remove call > > to _M_use_local_data() and initialize the local buffer directly. > > > > diff --git a/libstdc++-v3/include/bits/basic_string.h b/libstdc++-v3/include/bits/basic_string.h > > index 4f94cd967cf..18a19b8dcbc 100644 > > --- a/libstdc++-v3/include/bits/basic_string.h > > +++ b/libstdc++-v3/include/bits/basic_string.h > > @@ -353,13 +353,23 @@ _GLIBCXX_BEGIN_NAMESPACE_CXX11 > > // Ensure that _M_local_buf is the active member of the union. > > __attribute__((__always_inline__)) > > _GLIBCXX14_CONSTEXPR > > - pointer > > - _M_use_local_data() _GLIBCXX_NOEXCEPT > > + void > > + _M_init_local_buf() _GLIBCXX_NOEXCEPT > > { > > #if __cpp_lib_is_constant_evaluated > > if (std::is_constant_evaluated()) > > for (size_type __i = 0; __i <= _S_local_capacity; ++__i) > > _M_local_buf[__i] = _CharT(); > > +#endif > > + } > > + > > + __attribute__((__always_inline__)) > > + _GLIBCXX14_CONSTEXPR > > + pointer > > + _M_use_local_data() _GLIBCXX_NOEXCEPT > > + { > > +#if __glibcxx_is_constant_evaluated > > + _M_init_local_buf(); > > #endif > > return _M_local_data(); > > } > > What's the difference between __cpp_lib_is_constant_evaluated and > __glibcxx_is_constant_evaluated? Should these lines be using the same > macro here? Ah, yeah, they could be the same. The difference is that (for most feature test macros) the __glibcxx_ftm form is defined after including <bits/version.h>, but the __cpp_lib_ftm form is only defined only by headers that do: #define __glibcxx_want_ftm #include <bits/version.h> This means we can ensure that the __cpp_lib_ftm form is only defined by headers where we actually want to define it, e.g. in the headers that [version.syn] in the standard says should define the macro. So for our own internal uses, we should generally rely on the __glibcxx_ftm one. Users should rely on __cpp_lib_ftm after including the correct header. For example, __glibcxx_atomic_wait is defined after including <bits/atomic_wait.h> and so is available for our own uses, but __cpp_lib_atomic_wait is only defined after including <atomic>, not just <bits/atomic_wait.h>. Or at least, that's the plan - I have a pending patch to make everything I just said true :-) Currently we "leak" the __cpp_lib_ftm forms into lots of <bits/xxx.h> internal headers. That will change next week. In this specific case, it doesn't matter, because __cpp_lib_is_constant_evaluated is defined by <type_traits>, and every header includes that. So it doesn't really matter whether our internal uses are __cpp_lib_is_constant_evaluated or __glibcxx_is_constant_evaluated. But it would be good to be consistent. > > > @@ -522,7 +532,7 @@ _GLIBCXX_BEGIN_NAMESPACE_CXX11 > > _GLIBCXX_NOEXCEPT_IF(is_nothrow_default_constructible<_Alloc>::value) > > : _M_dataplus(_M_local_data()) > > { > > - _M_use_local_data(); > > + _M_init_local_buf(); > > _M_set_length(0); > > } > > > > @@ -534,7 +544,7 @@ _GLIBCXX_BEGIN_NAMESPACE_CXX11 > > basic_string(const _Alloc& __a) _GLIBCXX_NOEXCEPT > > : _M_dataplus(_M_local_data(), __a) > > { > > - _M_use_local_data(); > > + _M_init_local_buf(); > > _M_set_length(0); > > } > > > > @@ -678,7 +688,7 @@ _GLIBCXX_BEGIN_NAMESPACE_CXX11 > > { > > if (__str._M_is_local()) > > { > > - (void)_M_use_local_data(); > > + _M_init_local_buf(); > > traits_type::copy(_M_local_buf, __str._M_local_buf, > > __str.length() + 1); > > } > > @@ -718,7 +728,7 @@ _GLIBCXX_BEGIN_NAMESPACE_CXX11 > > { > > if (__str._M_is_local()) > > { > > - (void)_M_use_local_data(); > > + _M_init_local_buf(); > > traits_type::copy(_M_local_buf, __str._M_local_buf, > > __str.length() + 1); > > _M_length(__str.length()); > > diff --git a/libstdc++-v3/include/bits/basic_string.tcc b/libstdc++-v3/include/bits/basic_string.tcc > > index 4bc98f2aea7..052eeb9e846 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()) > > { > > - (void)_M_use_local_data(); > > + _M_init_local_buf(); > > traits_type::copy(_M_local_buf, __s._M_local_buf, > > __s.length() + 1); > > _M_length(__s.length()); > > @@ -88,7 +88,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION > > } > > else if (length()) > > { > > - (void)__s._M_use_local_data(); > > + __s._M_init_local_buf(); > > traits_type::copy(__s._M_local_buf, _M_local_buf, > > length() + 1); > > __s._M_length(length()); > > @@ -99,7 +99,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION > > else > > { > > const size_type __tmp_capacity = __s._M_allocated_capacity; > > - (void)__s._M_use_local_data(); > > + __s._M_init_local_buf(); > > traits_type::copy(__s._M_local_buf, _M_local_buf, > > length() + 1); > > _M_data(__s._M_data()); > > @@ -111,7 +111,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION > > const size_type __tmp_capacity = _M_allocated_capacity; > > if (__s._M_is_local()) > > { > > - (void)_M_use_local_data(); > > + _M_init_local_buf(); > > traits_type::copy(_M_local_buf, __s._M_local_buf, > > __s.length() + 1); > > __s._M_data(_M_data()); > > @@ -174,14 +174,18 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION > > size_type __len = 0; > > size_type __capacity = size_type(_S_local_capacity); > > > > - pointer __p = _M_use_local_data(); > > - > > while (__beg != __end && __len < __capacity) > > { > > - __p[__len++] = *__beg; > > + _M_local_buf[__len++] = *__beg; > > ++__beg; > > } > > > > +#if __glibcxx_is_constant_evaluated > > + if (std::is_constant_evaluated()) > > + for (size_type __i = __len; __i <= __capacity; ++__i) > > + _M_local_buf[__i] = _CharT(); > > +#endif > > + > > I wonder if maybe this should still be a call to `_M_init_local_buf()` > above, where the `_M_use_local_data()` used to be? That way the logic > stays in one place, and I don't imagine the compile time savings of not > immediately overwriting the first __len characters would be significant. Yeah, I went back and forth on that, but you're probably right. I'll do as you suggested.
On Fri, 29 Sept 2023 at 17:46, Jonathan Wakely <jwakely.gcc@gmail.com> wrote: > > On Fri, 29 Sept 2023 at 17:29, Nathaniel Shead > <nathanieloshead@gmail.com> wrote: > > > > On Fri, Sep 29, 2023 at 04:06:33PM +0100, Jonathan Wakely wrote: > > > On Fri, 29 Sept 2023 at 10:32, Jonathan Wakely <jwakely@redhat.com> wrote: > > > > > 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! > > > > > > That's done now. > > > > > > > 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. > > > > > > I started to do that, and decided it made more sense to split out the > > > constexpr loop from _M_use_local_data() into a separate function, > > > _M_init_local_buf(). Then we can use that for all the places where we > > > don't care about the return value. That avoids the overhead of using > > > pointer_traits::pointer_to when we don't need the return value (which > > > is admittedly only going to be an issue for -O0 code, but I think it's > > > cleaner this way anyway). > > > > > > Please see the attached patch and let me know what you think. > > > > I agree, and it also looks clearer to me what is happening. > > Good, I'll make this change next week then. > > > > > > > > > > > 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. > > > > > > Your patch fixes https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110900 > > > (so we should backport it to gcc-13 and gcc-12 too). > > > > > commit 2668979d3206ff6c039ac0165aae29377a15666c > > > Author: Jonathan Wakely <jwakely@redhat.com> > > > Date: Fri Sep 29 12:12:22 2023 > > > > > > libstdc++: Split std::basic_string::_M_use_local_data into two functions > > > > > > This splits out the activate-the-union-member-for-constexpr logic from > > > _M_use_local_data, so that it can be used separately in cases that don't > > > need to use std::pointer_traits<pointer>::pointer_to to obtain the > > > return value. > > > > > > This leaves only three uses of _M_use_local_data() which are all the > > > same form: > > > > > > __s._M_data(_M_use_local_data()); > > > __s._M_set_length(0); > > > > > > We could remove _M_use_local_data() and change those three places to use > > > a new _M_reset() function that does: > > > > > > _M_init_local_buf(); > > > _M_data(_M_local_data()); > > > _M_set_length(0); > > > > > > This is left for a future change. > > > > > > libstdc++-v3/ChangeLog: > > > > > > * include/bits/basic_string.h (_M_init_local_buf()): New > > > function. > > > (_M_use_local_data()): Use _M_init_local_buf. > > > (basic_string(), basic_string(const Alloc&)) > > > (basic_string(basic_string&&)) > > > (basic_string(basic_string&&, const Alloc&)): Use > > > _M_init_local_buf instead of _M_use_local_data(). > > > * include/bits/basic_string.tcc (swap(basic_string&)) > > > (_M_construct(InIter, InIter, forward_iterator_tag)) > > > (_M_construct(size_type, CharT), reserve()): Likewise. > > > (_M_construct(InIter, InIter, input_iterator_tag)): Remove call > > > to _M_use_local_data() and initialize the local buffer directly. > > > > > > diff --git a/libstdc++-v3/include/bits/basic_string.h b/libstdc++-v3/include/bits/basic_string.h > > > index 4f94cd967cf..18a19b8dcbc 100644 > > > --- a/libstdc++-v3/include/bits/basic_string.h > > > +++ b/libstdc++-v3/include/bits/basic_string.h > > > @@ -353,13 +353,23 @@ _GLIBCXX_BEGIN_NAMESPACE_CXX11 > > > // Ensure that _M_local_buf is the active member of the union. > > > __attribute__((__always_inline__)) > > > _GLIBCXX14_CONSTEXPR > > > - pointer > > > - _M_use_local_data() _GLIBCXX_NOEXCEPT > > > + void > > > + _M_init_local_buf() _GLIBCXX_NOEXCEPT > > > { > > > #if __cpp_lib_is_constant_evaluated > > > if (std::is_constant_evaluated()) > > > for (size_type __i = 0; __i <= _S_local_capacity; ++__i) > > > _M_local_buf[__i] = _CharT(); > > > +#endif > > > + } > > > + > > > + __attribute__((__always_inline__)) > > > + _GLIBCXX14_CONSTEXPR > > > + pointer > > > + _M_use_local_data() _GLIBCXX_NOEXCEPT > > > + { > > > +#if __glibcxx_is_constant_evaluated > > > + _M_init_local_buf(); > > > #endif > > > return _M_local_data(); > > > } > > > > What's the difference between __cpp_lib_is_constant_evaluated and > > __glibcxx_is_constant_evaluated? Should these lines be using the same > > macro here? > > Ah, yeah, they could be the same. > > The difference is that (for most feature test macros) the > __glibcxx_ftm form is defined after including <bits/version.h>, but > the __cpp_lib_ftm form is only defined only by headers that do: > > #define __glibcxx_want_ftm > #include <bits/version.h> > > This means we can ensure that the __cpp_lib_ftm form is only defined > by headers where we actually want to define it, e.g. in the headers > that [version.syn] in the standard says should define the macro. So > for our own internal uses, we should generally rely on the > __glibcxx_ftm one. Users should rely on __cpp_lib_ftm after including > the correct header. For example, __glibcxx_atomic_wait is defined > after including <bits/atomic_wait.h> and so is available for our own > uses, but __cpp_lib_atomic_wait is only defined after including > <atomic>, not just <bits/atomic_wait.h>. Or at least, that's the plan > - I have a pending patch to make everything I just said true :-) > Currently we "leak" the __cpp_lib_ftm forms into lots of <bits/xxx.h> > internal headers. That will change next week. > > In this specific case, it doesn't matter, because > __cpp_lib_is_constant_evaluated is defined by <type_traits>, and every > header includes that. So it doesn't really matter whether our internal > uses are __cpp_lib_is_constant_evaluated or > __glibcxx_is_constant_evaluated. But it would be good to be > consistent. > > > > > > @@ -522,7 +532,7 @@ _GLIBCXX_BEGIN_NAMESPACE_CXX11 > > > _GLIBCXX_NOEXCEPT_IF(is_nothrow_default_constructible<_Alloc>::value) > > > : _M_dataplus(_M_local_data()) > > > { > > > - _M_use_local_data(); > > > + _M_init_local_buf(); > > > _M_set_length(0); > > > } > > > > > > @@ -534,7 +544,7 @@ _GLIBCXX_BEGIN_NAMESPACE_CXX11 > > > basic_string(const _Alloc& __a) _GLIBCXX_NOEXCEPT > > > : _M_dataplus(_M_local_data(), __a) > > > { > > > - _M_use_local_data(); > > > + _M_init_local_buf(); > > > _M_set_length(0); > > > } > > > > > > @@ -678,7 +688,7 @@ _GLIBCXX_BEGIN_NAMESPACE_CXX11 > > > { > > > if (__str._M_is_local()) > > > { > > > - (void)_M_use_local_data(); > > > + _M_init_local_buf(); > > > traits_type::copy(_M_local_buf, __str._M_local_buf, > > > __str.length() + 1); > > > } > > > @@ -718,7 +728,7 @@ _GLIBCXX_BEGIN_NAMESPACE_CXX11 > > > { > > > if (__str._M_is_local()) > > > { > > > - (void)_M_use_local_data(); > > > + _M_init_local_buf(); > > > traits_type::copy(_M_local_buf, __str._M_local_buf, > > > __str.length() + 1); > > > _M_length(__str.length()); > > > diff --git a/libstdc++-v3/include/bits/basic_string.tcc b/libstdc++-v3/include/bits/basic_string.tcc > > > index 4bc98f2aea7..052eeb9e846 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()) > > > { > > > - (void)_M_use_local_data(); > > > + _M_init_local_buf(); > > > traits_type::copy(_M_local_buf, __s._M_local_buf, > > > __s.length() + 1); > > > _M_length(__s.length()); > > > @@ -88,7 +88,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION > > > } > > > else if (length()) > > > { > > > - (void)__s._M_use_local_data(); > > > + __s._M_init_local_buf(); > > > traits_type::copy(__s._M_local_buf, _M_local_buf, > > > length() + 1); > > > __s._M_length(length()); > > > @@ -99,7 +99,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION > > > else > > > { > > > const size_type __tmp_capacity = __s._M_allocated_capacity; > > > - (void)__s._M_use_local_data(); > > > + __s._M_init_local_buf(); > > > traits_type::copy(__s._M_local_buf, _M_local_buf, > > > length() + 1); > > > _M_data(__s._M_data()); > > > @@ -111,7 +111,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION > > > const size_type __tmp_capacity = _M_allocated_capacity; > > > if (__s._M_is_local()) > > > { > > > - (void)_M_use_local_data(); > > > + _M_init_local_buf(); > > > traits_type::copy(_M_local_buf, __s._M_local_buf, > > > __s.length() + 1); > > > __s._M_data(_M_data()); > > > @@ -174,14 +174,18 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION > > > size_type __len = 0; > > > size_type __capacity = size_type(_S_local_capacity); > > > > > > - pointer __p = _M_use_local_data(); > > > - > > > while (__beg != __end && __len < __capacity) > > > { > > > - __p[__len++] = *__beg; > > > + _M_local_buf[__len++] = *__beg; > > > ++__beg; > > > } > > > > > > +#if __glibcxx_is_constant_evaluated > > > + if (std::is_constant_evaluated()) > > > + for (size_type __i = __len; __i <= __capacity; ++__i) > > > + _M_local_buf[__i] = _CharT(); > > > +#endif > > > + > > > > I wonder if maybe this should still be a call to `_M_init_local_buf()` > > above, where the `_M_use_local_data()` used to be? That way the logic > > stays in one place, and I don't imagine the compile time savings of not > > immediately overwriting the first __len characters would be significant. > > > Yeah, I went back and forth on that, but you're probably right. I'll > do as you suggested. Here's what I've pushed to trunk after testing on x86_64-linux. Thanks again for the fixes. commit 405a4140fc30bce86b1ec885a98bb17704e0c8c6 Author: Jonathan Wakely <jwakely@redhat.com> Date: Fri Sep 29 12:12:22 2023 libstdc++: Split std::basic_string::_M_use_local_data into two functions This splits out the activate-the-union-member-for-constexpr logic from _M_use_local_data, so that it can be used separately in cases that don't need to use std::pointer_traits<pointer>::pointer_to to obtain the return value. This leaves only three uses of _M_use_local_data() which are all of the same form: __s._M_data(_M_use_local_data()); __s._M_set_length(0); We could remove _M_use_local_data() and change those three places to use a new _M_reset() function that does: _M_init_local_buf(); _M_data(_M_local_data()); _M_set_length(0); This is left for a future change. libstdc++-v3/ChangeLog: * include/bits/basic_string.h (_M_init_local_buf()): New function. (_M_use_local_data()): Use _M_init_local_buf. (basic_string(), basic_string(const Alloc&)) (basic_string(basic_string&&)) (basic_string(basic_string&&, const Alloc&)): Use _M_init_local_buf instead of _M_use_local_data(). * include/bits/basic_string.tcc (swap(basic_string&)) (_M_construct(InIter, InIter, input_iterator_tag)) (_M_construct(InIter, InIter, forward_iterator_tag)) (_M_construct(size_type, CharT), reserve()): Likewise. diff --git a/libstdc++-v3/include/bits/basic_string.h b/libstdc++-v3/include/bits/basic_string.h index 4f94cd967cf..0fa32afeb84 100644 --- a/libstdc++-v3/include/bits/basic_string.h +++ b/libstdc++-v3/include/bits/basic_string.h @@ -353,13 +353,23 @@ _GLIBCXX_BEGIN_NAMESPACE_CXX11 // Ensure that _M_local_buf is the active member of the union. __attribute__((__always_inline__)) _GLIBCXX14_CONSTEXPR - pointer - _M_use_local_data() _GLIBCXX_NOEXCEPT + void + _M_init_local_buf() _GLIBCXX_NOEXCEPT { #if __cpp_lib_is_constant_evaluated if (std::is_constant_evaluated()) for (size_type __i = 0; __i <= _S_local_capacity; ++__i) _M_local_buf[__i] = _CharT(); +#endif + } + + __attribute__((__always_inline__)) + _GLIBCXX14_CONSTEXPR + pointer + _M_use_local_data() _GLIBCXX_NOEXCEPT + { +#if __cpp_lib_is_constant_evaluated + _M_init_local_buf(); #endif return _M_local_data(); } @@ -522,7 +532,7 @@ _GLIBCXX_BEGIN_NAMESPACE_CXX11 _GLIBCXX_NOEXCEPT_IF(is_nothrow_default_constructible<_Alloc>::value) : _M_dataplus(_M_local_data()) { - _M_use_local_data(); + _M_init_local_buf(); _M_set_length(0); } @@ -534,7 +544,7 @@ _GLIBCXX_BEGIN_NAMESPACE_CXX11 basic_string(const _Alloc& __a) _GLIBCXX_NOEXCEPT : _M_dataplus(_M_local_data(), __a) { - _M_use_local_data(); + _M_init_local_buf(); _M_set_length(0); } @@ -678,7 +688,7 @@ _GLIBCXX_BEGIN_NAMESPACE_CXX11 { if (__str._M_is_local()) { - (void)_M_use_local_data(); + _M_init_local_buf(); traits_type::copy(_M_local_buf, __str._M_local_buf, __str.length() + 1); } @@ -718,7 +728,7 @@ _GLIBCXX_BEGIN_NAMESPACE_CXX11 { if (__str._M_is_local()) { - (void)_M_use_local_data(); + _M_init_local_buf(); traits_type::copy(_M_local_buf, __str._M_local_buf, __str.length() + 1); _M_length(__str.length()); diff --git a/libstdc++-v3/include/bits/basic_string.tcc b/libstdc++-v3/include/bits/basic_string.tcc index 4bc98f2aea7..f0a44e5e881 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()) { - (void)_M_use_local_data(); + _M_init_local_buf(); traits_type::copy(_M_local_buf, __s._M_local_buf, __s.length() + 1); _M_length(__s.length()); @@ -88,7 +88,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION } else if (length()) { - (void)__s._M_use_local_data(); + __s._M_init_local_buf(); traits_type::copy(__s._M_local_buf, _M_local_buf, length() + 1); __s._M_length(length()); @@ -99,7 +99,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION else { const size_type __tmp_capacity = __s._M_allocated_capacity; - (void)__s._M_use_local_data(); + __s._M_init_local_buf(); traits_type::copy(__s._M_local_buf, _M_local_buf, length() + 1); _M_data(__s._M_data()); @@ -111,7 +111,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION const size_type __tmp_capacity = _M_allocated_capacity; if (__s._M_is_local()) { - (void)_M_use_local_data(); + _M_init_local_buf(); traits_type::copy(_M_local_buf, __s._M_local_buf, __s.length() + 1); __s._M_data(_M_data()); @@ -174,11 +174,11 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION size_type __len = 0; size_type __capacity = size_type(_S_local_capacity); - pointer __p = _M_use_local_data(); + _M_init_local_buf(); while (__beg != __end && __len < __capacity) { - __p[__len++] = *__beg; + _M_local_buf[__len++] = *__beg; ++__beg; } @@ -230,7 +230,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION _M_capacity(__dnew); } else - _M_use_local_data(); + _M_init_local_buf(); // Check for out_of_range and length_error exceptions. struct _Guard @@ -263,7 +263,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION _M_capacity(__n); } else - _M_use_local_data(); + _M_init_local_buf(); if (__n) this->_S_assign(_M_data(), __n, __c); @@ -372,7 +372,8 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION if (__length <= size_type(_S_local_capacity)) { - this->_S_copy(_M_use_local_data(), _M_data(), __length + 1); + _M_init_local_buf(); + this->_S_copy(_M_local_buf, _M_data(), __length + 1); _M_destroy(__capacity); _M_data(_M_local_data()); }
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; }