On Mon, 22 Aug 2022 at 19:15, Will Hawkins wrote: > > Until now operator+(char*, string) and operator+(string, char*) had > different performance characteristics. The former required a single > memory allocation and the latter required two. This patch makes the > performance equal.
If you don't have a GCC copyright assignment on file with the FSF then please follow the procedure described at https://gcc.gnu.org/dco.html > libstdc++-v3/ChangeLog: > * libstdc++-v3/include/bits/basic_string.h (operator+(string, char*)): > Remove naive implementation. > * libstdc++-v3/include/bits/basic_string.tcc (operator+(string, > char*)): > Add single-allocation implementation. > --- > libstdc++-v3/include/bits/basic_string.h | 7 +------ > libstdc++-v3/include/bits/basic_string.tcc | 21 +++++++++++++++++++++ > 2 files changed, 22 insertions(+), 6 deletions(-) > > diff --git a/libstdc++-v3/include/bits/basic_string.h > b/libstdc++-v3/include/bits/basic_string.h > index b04fba95678..bc048fc0689 100644 > --- a/libstdc++-v3/include/bits/basic_string.h > +++ b/libstdc++-v3/include/bits/basic_string.h > @@ -3523,12 +3523,7 @@ _GLIBCXX_END_NAMESPACE_CXX11 > _GLIBCXX20_CONSTEXPR > inline basic_string<_CharT, _Traits, _Alloc> Please remove the 'inline' specifier here, since you're moving the definition into the non-inline .tcc file. There's a separate discussion to be had about whether these operator+ overloads *should* be inline. But for the purposes of this change, we want these two operator+ overloads to be consistent, and so they should both be non-inline. > operator+(const basic_string<_CharT, _Traits, _Alloc>& __lhs, > - const _CharT* __rhs) > - { > - basic_string<_CharT, _Traits, _Alloc> __str(__lhs); > - __str.append(__rhs); > - return __str; > - } > + const _CharT* __rhs); > > /** > * @brief Concatenate string and character. > diff --git a/libstdc++-v3/include/bits/basic_string.tcc > b/libstdc++-v3/include/bits/basic_string.tcc > index 4563c61429a..95ba8e503e9 100644 > --- a/libstdc++-v3/include/bits/basic_string.tcc > +++ b/libstdc++-v3/include/bits/basic_string.tcc > @@ -640,6 +640,27 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION > return __str; > } > > + template<typename _CharT, typename _Traits, typename _Alloc> > + _GLIBCXX20_CONSTEXPR > + basic_string<_CharT, _Traits, _Alloc> > + operator+(const basic_string<_CharT, _Traits, _Alloc>& __lhs, > + const _CharT* __rhs) > + { > + __glibcxx_requires_string(__rhs); > + typedef basic_string<_CharT, _Traits, _Alloc> __string_type; > + typedef typename __string_type::size_type __size_type; > + typedef typename __gnu_cxx::__alloc_traits<_Alloc>::template > + rebind<_CharT>::other _Char_alloc_type; > + typedef __gnu_cxx::__alloc_traits<_Char_alloc_type> _Alloc_traits; > + const __size_type __len = _Traits::length(__rhs); > + __string_type __str(_Alloc_traits::_S_select_on_copy( > + __lhs.get_allocator())); > + __str.reserve(__len + __lhs.size()); > + __str.append(__lhs); > + __str.append(__rhs, __len); > + return __str; > + } > + > template<typename _CharT, typename _Traits, typename _Alloc> > _GLIBCXX_STRING_CONSTEXPR > typename basic_string<_CharT, _Traits, _Alloc>::size_type > -- > 2.34.1 >
