Re: [PATCH] libstdc++: Refactor implementation of operator+ for std::string
On Thu, 20 Oct 2022 at 01:06, Will Hawkins wrote:
>
> Sorry for the delay. Tested on x86-64 Linux.
>
> -->8--
>
> After consultation with Jonathan, it seemed like a good idea to create a
> single function that performed one-allocation string concatenation that
> could be used by various different version of operator+. This patch adds
> such a function and calls it from the relevant implementations.
>
> libstdc++-v3/ChangeLog:
>
> * include/bits/basic_string.h:
> Add common function that performs single-allocation string
> concatenation. (__str_cat)
> Use __str_cat to perform optimized operator+, where relevant.
> * include/bits/basic_string.tcc::
> Remove single-allocation implementation of operator+.
>
> Signed-off-by: Will Hawkins
I've pushed this patch to trunk now. I changed the commit message
significantly though:
libstdc++: Refactor implementation of operator+ for std::string
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.
After consultation with Jonathan, it seemed like a good idea to create a
single function that performed one-allocation string concatenation that
could be used by various different version of operator+. This patch adds
such a function and calls it from the relevant implementations.
Co-authored-by: Jonathan Wakely
libstdc++-v3/ChangeLog:
* include/bits/basic_string.h (__str_cat): Add common function
that performs single-allocation string concatenation.
(operator+): Use __str_cat.
* include/bits/basic_string.tcc (operator+): Move to .h and
define inline using __str_cat.
Signed-off-by: Will Hawkins
Specifically, I restored part of your earlier commit's message, which
gives the necessary context for the commit. Just starting with "After
consultation with Jonathan, ..." doesn't say anything about the patch
itself and is not very helpful without the earlier context from the
mailing list.
I added myself as Co-author, since the new patch was largely based on
a patch I sent in a private email.
And I changed the changelog part to better meet the format of GNU ChangeLogs.
https://www.gnu.org/prep/standards/html_node/Style-of-Change-Logs.html
The change is on trunk now (and I didn't see any libgomp test failures
this time).
> ---
> libstdc++-v3/include/bits/basic_string.h | 66 --
> libstdc++-v3/include/bits/basic_string.tcc | 41 --
> 2 files changed, 49 insertions(+), 58 deletions(-)
>
> diff --git a/libstdc++-v3/include/bits/basic_string.h
> b/libstdc++-v3/include/bits/basic_string.h
> index cd244191df4..9c2b57f5a1d 100644
> --- a/libstdc++-v3/include/bits/basic_string.h
> +++ b/libstdc++-v3/include/bits/basic_string.h
> @@ -3485,6 +3485,24 @@ _GLIBCXX_BEGIN_NAMESPACE_CXX11
> _GLIBCXX_END_NAMESPACE_CXX11
> #endif
>
> + template
> +_GLIBCXX20_CONSTEXPR
> +inline _Str
> +__str_concat(typename _Str::value_type const* __lhs,
> +typename _Str::size_type __lhs_len,
> +typename _Str::value_type const* __rhs,
> +typename _Str::size_type __rhs_len,
> +typename _Str::allocator_type const& __a)
> +{
> + typedef typename _Str::allocator_type allocator_type;
> + typedef __gnu_cxx::__alloc_traits _Alloc_traits;
> + _Str __str(_Alloc_traits::_S_select_on_copy(__a));
> + __str.reserve(__lhs_len + __rhs_len);
> + __str.append(__lhs, __lhs_len);
> + __str.append(__rhs, __rhs_len);
> + return __str;
> +}
> +
>// operator+
>/**
> * @brief Concatenate two strings.
> @@ -3494,13 +3512,14 @@ _GLIBCXX_END_NAMESPACE_CXX11
> */
>template
> _GLIBCXX_NODISCARD _GLIBCXX20_CONSTEXPR
> -basic_string<_CharT, _Traits, _Alloc>
> +inline basic_string<_CharT, _Traits, _Alloc>
> operator+(const basic_string<_CharT, _Traits, _Alloc>& __lhs,
> const basic_string<_CharT, _Traits, _Alloc>& __rhs)
> {
> - basic_string<_CharT, _Traits, _Alloc> __str(__lhs);
> - __str.append(__rhs);
> - return __str;
> + typedef basic_string<_CharT, _Traits, _Alloc> _Str;
> + return std::__str_concat<_Str>(__lhs.c_str(), __lhs.size(),
> +__rhs.c_str(), __rhs.size(),
> +__lhs.get_allocator());
> }
>
>/**
> @@ -3511,9 +3530,16 @@ _GLIBCXX_END_NAMESPACE_CXX11
> */
>template
> _GLIBCXX_NODISCARD _GLIBCXX20_CONSTEXPR
> -basic_string<_CharT,_Traits,_Alloc>
> +inline basic_string<_CharT,_Traits,_Alloc>
> operator+(const _CharT* __lhs,
> - const basic_string<_CharT,_Traits,_Alloc>& __rhs);
> + const basic_string<_CharT,_Traits,_Alloc>& __rhs)
> +{
> +
Re: [PATCH] libstdc++: Refactor implementation of operator+ for std::string
Just wanted to see if there was anything else I can do to help move
this over the finish line! Thanks for all the work that you all do!
Sincerely,
Will
On Wed, Oct 19, 2022 at 8:06 PM Will Hawkins wrote:
>
> Sorry for the delay. Tested on x86-64 Linux.
>
> -->8--
>
> After consultation with Jonathan, it seemed like a good idea to create a
> single function that performed one-allocation string concatenation that
> could be used by various different version of operator+. This patch adds
> such a function and calls it from the relevant implementations.
>
> libstdc++-v3/ChangeLog:
>
> * include/bits/basic_string.h:
> Add common function that performs single-allocation string
> concatenation. (__str_cat)
> Use __str_cat to perform optimized operator+, where relevant.
> * include/bits/basic_string.tcc::
> Remove single-allocation implementation of operator+.
>
> Signed-off-by: Will Hawkins
> ---
> libstdc++-v3/include/bits/basic_string.h | 66 --
> libstdc++-v3/include/bits/basic_string.tcc | 41 --
> 2 files changed, 49 insertions(+), 58 deletions(-)
>
> diff --git a/libstdc++-v3/include/bits/basic_string.h
> b/libstdc++-v3/include/bits/basic_string.h
> index cd244191df4..9c2b57f5a1d 100644
> --- a/libstdc++-v3/include/bits/basic_string.h
> +++ b/libstdc++-v3/include/bits/basic_string.h
> @@ -3485,6 +3485,24 @@ _GLIBCXX_BEGIN_NAMESPACE_CXX11
> _GLIBCXX_END_NAMESPACE_CXX11
> #endif
>
> + template
> +_GLIBCXX20_CONSTEXPR
> +inline _Str
> +__str_concat(typename _Str::value_type const* __lhs,
> +typename _Str::size_type __lhs_len,
> +typename _Str::value_type const* __rhs,
> +typename _Str::size_type __rhs_len,
> +typename _Str::allocator_type const& __a)
> +{
> + typedef typename _Str::allocator_type allocator_type;
> + typedef __gnu_cxx::__alloc_traits _Alloc_traits;
> + _Str __str(_Alloc_traits::_S_select_on_copy(__a));
> + __str.reserve(__lhs_len + __rhs_len);
> + __str.append(__lhs, __lhs_len);
> + __str.append(__rhs, __rhs_len);
> + return __str;
> +}
> +
>// operator+
>/**
> * @brief Concatenate two strings.
> @@ -3494,13 +3512,14 @@ _GLIBCXX_END_NAMESPACE_CXX11
> */
>template
> _GLIBCXX_NODISCARD _GLIBCXX20_CONSTEXPR
> -basic_string<_CharT, _Traits, _Alloc>
> +inline basic_string<_CharT, _Traits, _Alloc>
> operator+(const basic_string<_CharT, _Traits, _Alloc>& __lhs,
> const basic_string<_CharT, _Traits, _Alloc>& __rhs)
> {
> - basic_string<_CharT, _Traits, _Alloc> __str(__lhs);
> - __str.append(__rhs);
> - return __str;
> + typedef basic_string<_CharT, _Traits, _Alloc> _Str;
> + return std::__str_concat<_Str>(__lhs.c_str(), __lhs.size(),
> +__rhs.c_str(), __rhs.size(),
> +__lhs.get_allocator());
> }
>
>/**
> @@ -3511,9 +3530,16 @@ _GLIBCXX_END_NAMESPACE_CXX11
> */
>template
> _GLIBCXX_NODISCARD _GLIBCXX20_CONSTEXPR
> -basic_string<_CharT,_Traits,_Alloc>
> +inline basic_string<_CharT,_Traits,_Alloc>
> operator+(const _CharT* __lhs,
> - const basic_string<_CharT,_Traits,_Alloc>& __rhs);
> + const basic_string<_CharT,_Traits,_Alloc>& __rhs)
> +{
> + __glibcxx_requires_string(__lhs);
> + typedef basic_string<_CharT, _Traits, _Alloc> _Str;
> + return std::__str_concat<_Str>(__lhs, _Traits::length(__lhs),
> +__rhs.c_str(), __rhs.size(),
> +__rhs.get_allocator());
> +}
>
>/**
> * @brief Concatenate character and string.
> @@ -3523,8 +3549,14 @@ _GLIBCXX_END_NAMESPACE_CXX11
> */
>template
> _GLIBCXX_NODISCARD _GLIBCXX20_CONSTEXPR
> -basic_string<_CharT,_Traits,_Alloc>
> -operator+(_CharT __lhs, const basic_string<_CharT,_Traits,_Alloc>&
> __rhs);
> +inline basic_string<_CharT,_Traits,_Alloc>
> +operator+(_CharT __lhs, const basic_string<_CharT,_Traits,_Alloc>& __rhs)
> +{
> + typedef basic_string<_CharT, _Traits, _Alloc> _Str;
> + return std::__str_concat<_Str>(__builtin_addressof(__lhs), 1,
> +__rhs.c_str(), __rhs.size(),
> +__rhs.get_allocator());
> +}
>
>/**
> * @brief Concatenate string and C string.
> @@ -3538,11 +3570,12 @@ _GLIBCXX_END_NAMESPACE_CXX11
> operator+(const basic_string<_CharT, _Traits, _Alloc>& __lhs,
> const _CharT* __rhs)
> {
> - basic_string<_CharT, _Traits, _Alloc> __str(__lhs);
> - __str.append(__rhs);
> - return __str;
> + __glibcxx_requires_string(__rhs);
> + typedef basic_string<_CharT, _Traits, _Alloc> _Str;
> + return std::__str_concat<_Str>(__lhs.c_str(), __lhs.size(),
> +
Re: [PATCH] libstdc++: Refactor implementation of operator+ for std::string
On Thu, 8 Sept 2022 at 18:51, François Dumont via Libstdc++
wrote:
>
> On 05/09/22 20:30, Will Hawkins wrote:
> > Based on Jonathan's work, here is a patch for the implementation of
> > operator+
> > on std::string that makes sure we always use the best allocation strategy.
> >
> > I have attempted to learn from all the feedback that I got on a previous
> > submission -- I hope I did the right thing.
> >
> > Passes abi and conformance testing on x86-64 trunk.
> >
> > Sincerely,
> > Will
> >
> > -- >8 --
> >
> > Create a single function that performs one-allocation string concatenation
> > that can be used by various different version of operator+.
> >
> > libstdc++-v3/ChangeLog:
> >
> > * include/bits/basic_string.h:
> > Add common function that performs single-allocation string
> > concatenation. (__str_cat)
> > Use __str_cat to perform optimized operator+, where relevant.
> > * include/bits/basic_string.tcc::
> > Remove single-allocation implementation of operator+.
> >
> > Signed-off-by: Will Hawkins
> > ---
> > libstdc++-v3/include/bits/basic_string.h | 66 --
> > libstdc++-v3/include/bits/basic_string.tcc | 41 --
> > 2 files changed, 49 insertions(+), 58 deletions(-)
> >
> > diff --git a/libstdc++-v3/include/bits/basic_string.h
> > b/libstdc++-v3/include/bits/basic_string.h
> > index 0df64ea98ca..4078651fadb 100644
> > --- a/libstdc++-v3/include/bits/basic_string.h
> > +++ b/libstdc++-v3/include/bits/basic_string.h
> > @@ -3481,6 +3481,24 @@ _GLIBCXX_BEGIN_NAMESPACE_CXX11
> > _GLIBCXX_END_NAMESPACE_CXX11
> > #endif
> >
> > + template
> > +_GLIBCXX20_CONSTEXPR
> > +inline _Str
> > +__str_concat(typename _Str::value_type const* __lhs,
> > + typename _Str::size_type __lhs_len,
> > + typename _Str::value_type const* __rhs,
> > + typename _Str::size_type __rhs_len,
> > + typename _Str::allocator_type const& __a)
> > +{
> > + typedef typename _Str::allocator_type allocator_type;
> > + typedef __gnu_cxx::__alloc_traits _Alloc_traits;
> > + _Str __str(_Alloc_traits::_S_select_on_copy(__a));
> > + __str.reserve(__lhs_len + __rhs_len);
> > + __str.append(__lhs, __lhs_len);
> > + __str.append(__rhs, __rhs_len);
> > + return __str;
> > +}
> > +
> > // operator+
> > /**
> > * @brief Concatenate two strings.
> > @@ -3490,13 +3508,14 @@ _GLIBCXX_END_NAMESPACE_CXX11
> > */
> > template
> > _GLIBCXX_NODISCARD _GLIBCXX20_CONSTEXPR
> > -basic_string<_CharT, _Traits, _Alloc>
> > +inline basic_string<_CharT, _Traits, _Alloc>
> > operator+(const basic_string<_CharT, _Traits, _Alloc>& __lhs,
> > const basic_string<_CharT, _Traits, _Alloc>& __rhs)
> > {
> > - basic_string<_CharT, _Traits, _Alloc> __str(__lhs);
> > - __str.append(__rhs);
> > - return __str;
> > + typedef basic_string<_CharT, _Traits, _Alloc> _Str;
> > + return std::__str_concat<_Str>(__lhs.c_str(), __lhs.size(),
> > + __rhs.c_str(), __rhs.size(),
>
> You should use data() rather than c_str() here and all other operators.
>
> It is currently the same but is more accurate in your context. Maybe one
> day it will make a difference.
As I said, it will never make a difference, so there's no technical
reason to change it. I suppose data() is a little more expressive
here, in that we only care about the characters, not the null
terminator that c_str() implies (even though data() has the null
terminator too, as it's the same pointer returned).
>
> > + __lhs.get_allocator());
> > }
> >
> > /**
> > @@ -3507,9 +3526,16 @@ _GLIBCXX_END_NAMESPACE_CXX11
> > */
> > template
> > _GLIBCXX_NODISCARD _GLIBCXX20_CONSTEXPR
> > -basic_string<_CharT,_Traits,_Alloc>
> > +inline basic_string<_CharT,_Traits,_Alloc>
>
> Why inlining ?
Because it's a one line function that just calls another function.
That's an ideal candidate for being inline.
Re: [PATCH] libstdc++: Refactor implementation of operator+ for std::string
On Thu, Sep 8, 2022 at 2:05 PM Jonathan Wakely wrote:
>
>
>
> On Thu, 8 Sep 2022, 18:51 François Dumont via Libstdc++,
> wrote:
>>
>> On 05/09/22 20:30, Will Hawkins wrote:
>> > Based on Jonathan's work, here is a patch for the implementation of
>> > operator+
>> > on std::string that makes sure we always use the best allocation strategy.
>> >
>> > I have attempted to learn from all the feedback that I got on a previous
>> > submission -- I hope I did the right thing.
>> >
>> > Passes abi and conformance testing on x86-64 trunk.
>> >
>> > Sincerely,
>> > Will
>> >
>> > -- >8 --
>> >
>> > Create a single function that performs one-allocation string concatenation
>> > that can be used by various different version of operator+.
>> >
>> > libstdc++-v3/ChangeLog:
>> >
>> > * include/bits/basic_string.h:
>> > Add common function that performs single-allocation string
>> > concatenation. (__str_cat)
>> > Use __str_cat to perform optimized operator+, where relevant.
>> > * include/bits/basic_string.tcc::
>> > Remove single-allocation implementation of operator+.
>> >
>> > Signed-off-by: Will Hawkins
>> > ---
>> > libstdc++-v3/include/bits/basic_string.h | 66 --
>> > libstdc++-v3/include/bits/basic_string.tcc | 41 --
>> > 2 files changed, 49 insertions(+), 58 deletions(-)
>> >
>> > diff --git a/libstdc++-v3/include/bits/basic_string.h
>> > b/libstdc++-v3/include/bits/basic_string.h
>> > index 0df64ea98ca..4078651fadb 100644
>> > --- a/libstdc++-v3/include/bits/basic_string.h
>> > +++ b/libstdc++-v3/include/bits/basic_string.h
>> > @@ -3481,6 +3481,24 @@ _GLIBCXX_BEGIN_NAMESPACE_CXX11
>> > _GLIBCXX_END_NAMESPACE_CXX11
>> > #endif
>> >
>> > + template
>> > +_GLIBCXX20_CONSTEXPR
>> > +inline _Str
>> > +__str_concat(typename _Str::value_type const* __lhs,
>> > + typename _Str::size_type __lhs_len,
>> > + typename _Str::value_type const* __rhs,
>> > + typename _Str::size_type __rhs_len,
>> > + typename _Str::allocator_type const& __a)
>> > +{
>> > + typedef typename _Str::allocator_type allocator_type;
>> > + typedef __gnu_cxx::__alloc_traits _Alloc_traits;
>> > + _Str __str(_Alloc_traits::_S_select_on_copy(__a));
>> > + __str.reserve(__lhs_len + __rhs_len);
>> > + __str.append(__lhs, __lhs_len);
>> > + __str.append(__rhs, __rhs_len);
>> > + return __str;
>> > +}
>> > +
>> > // operator+
>> > /**
>> > * @brief Concatenate two strings.
>> > @@ -3490,13 +3508,14 @@ _GLIBCXX_END_NAMESPACE_CXX11
>> > */
>> > template
>> > _GLIBCXX_NODISCARD _GLIBCXX20_CONSTEXPR
>> > -basic_string<_CharT, _Traits, _Alloc>
>> > +inline basic_string<_CharT, _Traits, _Alloc>
>> > operator+(const basic_string<_CharT, _Traits, _Alloc>& __lhs,
>> > const basic_string<_CharT, _Traits, _Alloc>& __rhs)
>> > {
>> > - basic_string<_CharT, _Traits, _Alloc> __str(__lhs);
>> > - __str.append(__rhs);
>> > - return __str;
>> > + typedef basic_string<_CharT, _Traits, _Alloc> _Str;
>> > + return std::__str_concat<_Str>(__lhs.c_str(), __lhs.size(),
>> > + __rhs.c_str(), __rhs.size(),
>>
>> You should use data() rather than c_str() here and all other operators.
>>
>> It is currently the same but is more accurate in your context. Maybe one
>> day it will make a difference.
>
>
>
> I don't think so, that would be a major breaking change, for no benefit. I
> think it's safe to assume they will always stay equivalent now.
Happy to make any changes to the patch that the group thinks are necessary!
Will
>
>
>>
>> > + __lhs.get_allocator());
>> > }
>> >
>> > /**
>> > @@ -3507,9 +3526,16 @@ _GLIBCXX_END_NAMESPACE_CXX11
>> > */
>> > template
>> > _GLIBCXX_NODISCARD _GLIBCXX20_CONSTEXPR
>> > -basic_string<_CharT,_Traits,_Alloc>
>> > +inline basic_string<_CharT,_Traits,_Alloc>
>>
>> Why inlining ?
>>
>> I guess it is done this way to limit code bloat.
>>
>> > operator+(const _CharT* __lhs,
>> > - const basic_string<_CharT,_Traits,_Alloc>& __rhs);
>> > + const basic_string<_CharT,_Traits,_Alloc>& __rhs)
>> > +{
>> > + __glibcxx_requires_string(__lhs);
>> > + typedef basic_string<_CharT, _Traits, _Alloc> _Str;
>> > + return std::__str_concat<_Str>(__lhs, _Traits::length(__lhs),
>> > + __rhs.c_str(), __rhs.size(),
>> > + __rhs.get_allocator());
>> > +}
>> >
>> > /**
>> > * @brief Concatenate character and string.
>> > @@ -3519,8 +3545,14 @@ _GLIBCXX_END_NAMESPACE_CXX11
>> > */
>> > template
>> > _GLIBCXX_NODISCARD _GLIBCXX20_CONSTEXPR
>> > -basic_string<_CharT,_Traits,_Alloc>
>> > -operator+(_CharT __lhs, const basic_string<_CharT,_Traits,_Alloc>&
Re: [PATCH] libstdc++: Refactor implementation of operator+ for std::string
On Thu, 8 Sep 2022, 18:51 François Dumont via Libstdc++, <
libstd...@gcc.gnu.org> wrote:
> On 05/09/22 20:30, Will Hawkins wrote:
> > Based on Jonathan's work, here is a patch for the implementation of
> operator+
> > on std::string that makes sure we always use the best allocation
> strategy.
> >
> > I have attempted to learn from all the feedback that I got on a previous
> > submission -- I hope I did the right thing.
> >
> > Passes abi and conformance testing on x86-64 trunk.
> >
> > Sincerely,
> > Will
> >
> > -- >8 --
> >
> > Create a single function that performs one-allocation string
> concatenation
> > that can be used by various different version of operator+.
> >
> > libstdc++-v3/ChangeLog:
> >
> > * include/bits/basic_string.h:
> > Add common function that performs single-allocation string
> > concatenation. (__str_cat)
> > Use __str_cat to perform optimized operator+, where relevant.
> > * include/bits/basic_string.tcc::
> > Remove single-allocation implementation of operator+.
> >
> > Signed-off-by: Will Hawkins
> > ---
> > libstdc++-v3/include/bits/basic_string.h | 66 --
> > libstdc++-v3/include/bits/basic_string.tcc | 41 --
> > 2 files changed, 49 insertions(+), 58 deletions(-)
> >
> > diff --git a/libstdc++-v3/include/bits/basic_string.h
> b/libstdc++-v3/include/bits/basic_string.h
> > index 0df64ea98ca..4078651fadb 100644
> > --- a/libstdc++-v3/include/bits/basic_string.h
> > +++ b/libstdc++-v3/include/bits/basic_string.h
> > @@ -3481,6 +3481,24 @@ _GLIBCXX_BEGIN_NAMESPACE_CXX11
> > _GLIBCXX_END_NAMESPACE_CXX11
> > #endif
> >
> > + template
> > +_GLIBCXX20_CONSTEXPR
> > +inline _Str
> > +__str_concat(typename _Str::value_type const* __lhs,
> > + typename _Str::size_type __lhs_len,
> > + typename _Str::value_type const* __rhs,
> > + typename _Str::size_type __rhs_len,
> > + typename _Str::allocator_type const& __a)
> > +{
> > + typedef typename _Str::allocator_type allocator_type;
> > + typedef __gnu_cxx::__alloc_traits _Alloc_traits;
> > + _Str __str(_Alloc_traits::_S_select_on_copy(__a));
> > + __str.reserve(__lhs_len + __rhs_len);
> > + __str.append(__lhs, __lhs_len);
> > + __str.append(__rhs, __rhs_len);
> > + return __str;
> > +}
> > +
> > // operator+
> > /**
> > * @brief Concatenate two strings.
> > @@ -3490,13 +3508,14 @@ _GLIBCXX_END_NAMESPACE_CXX11
> > */
> > template
> > _GLIBCXX_NODISCARD _GLIBCXX20_CONSTEXPR
> > -basic_string<_CharT, _Traits, _Alloc>
> > +inline basic_string<_CharT, _Traits, _Alloc>
> > operator+(const basic_string<_CharT, _Traits, _Alloc>& __lhs,
> > const basic_string<_CharT, _Traits, _Alloc>& __rhs)
> > {
> > - basic_string<_CharT, _Traits, _Alloc> __str(__lhs);
> > - __str.append(__rhs);
> > - return __str;
> > + typedef basic_string<_CharT, _Traits, _Alloc> _Str;
> > + return std::__str_concat<_Str>(__lhs.c_str(), __lhs.size(),
> > + __rhs.c_str(), __rhs.size(),
>
> You should use data() rather than c_str() here and all other operators.
>
> It is currently the same but is more accurate in your context. Maybe one
> day it will make a difference.
>
I don't think so, that would be a major breaking change, for no benefit. I
think it's safe to assume they will always stay equivalent now.
> > + __lhs.get_allocator());
> > }
> >
> > /**
> > @@ -3507,9 +3526,16 @@ _GLIBCXX_END_NAMESPACE_CXX11
> > */
> > template
> > _GLIBCXX_NODISCARD _GLIBCXX20_CONSTEXPR
> > -basic_string<_CharT,_Traits,_Alloc>
> > +inline basic_string<_CharT,_Traits,_Alloc>
>
> Why inlining ?
>
> I guess it is done this way to limit code bloat.
>
> > operator+(const _CharT* __lhs,
> > - const basic_string<_CharT,_Traits,_Alloc>& __rhs);
> > + const basic_string<_CharT,_Traits,_Alloc>& __rhs)
> > +{
> > + __glibcxx_requires_string(__lhs);
> > + typedef basic_string<_CharT, _Traits, _Alloc> _Str;
> > + return std::__str_concat<_Str>(__lhs, _Traits::length(__lhs),
> > + __rhs.c_str(), __rhs.size(),
> > + __rhs.get_allocator());
> > +}
> >
> > /**
> > * @brief Concatenate character and string.
> > @@ -3519,8 +3545,14 @@ _GLIBCXX_END_NAMESPACE_CXX11
> > */
> > template
> > _GLIBCXX_NODISCARD _GLIBCXX20_CONSTEXPR
> > -basic_string<_CharT,_Traits,_Alloc>
> > -operator+(_CharT __lhs, const basic_string<_CharT,_Traits,_Alloc>&
> __rhs);
> > +inline basic_string<_CharT,_Traits,_Alloc>
> > +operator+(_CharT __lhs, const basic_string<_CharT,_Traits,_Alloc>&
> __rhs)
> > +{
> > + typedef basic_string<_CharT, _Traits, _Alloc> _Str;
> > + return
Re: [PATCH] libstdc++: Refactor implementation of operator+ for std::string
On 05/09/22 20:30, Will Hawkins wrote:
Based on Jonathan's work, here is a patch for the implementation of operator+
on std::string that makes sure we always use the best allocation strategy.
I have attempted to learn from all the feedback that I got on a previous
submission -- I hope I did the right thing.
Passes abi and conformance testing on x86-64 trunk.
Sincerely,
Will
-- >8 --
Create a single function that performs one-allocation string concatenation
that can be used by various different version of operator+.
libstdc++-v3/ChangeLog:
* include/bits/basic_string.h:
Add common function that performs single-allocation string
concatenation. (__str_cat)
Use __str_cat to perform optimized operator+, where relevant.
* include/bits/basic_string.tcc::
Remove single-allocation implementation of operator+.
Signed-off-by: Will Hawkins
---
libstdc++-v3/include/bits/basic_string.h | 66 --
libstdc++-v3/include/bits/basic_string.tcc | 41 --
2 files changed, 49 insertions(+), 58 deletions(-)
diff --git a/libstdc++-v3/include/bits/basic_string.h
b/libstdc++-v3/include/bits/basic_string.h
index 0df64ea98ca..4078651fadb 100644
--- a/libstdc++-v3/include/bits/basic_string.h
+++ b/libstdc++-v3/include/bits/basic_string.h
@@ -3481,6 +3481,24 @@ _GLIBCXX_BEGIN_NAMESPACE_CXX11
_GLIBCXX_END_NAMESPACE_CXX11
#endif
+ template
+_GLIBCXX20_CONSTEXPR
+inline _Str
+__str_concat(typename _Str::value_type const* __lhs,
+typename _Str::size_type __lhs_len,
+typename _Str::value_type const* __rhs,
+typename _Str::size_type __rhs_len,
+typename _Str::allocator_type const& __a)
+{
+ typedef typename _Str::allocator_type allocator_type;
+ typedef __gnu_cxx::__alloc_traits _Alloc_traits;
+ _Str __str(_Alloc_traits::_S_select_on_copy(__a));
+ __str.reserve(__lhs_len + __rhs_len);
+ __str.append(__lhs, __lhs_len);
+ __str.append(__rhs, __rhs_len);
+ return __str;
+}
+
// operator+
/**
* @brief Concatenate two strings.
@@ -3490,13 +3508,14 @@ _GLIBCXX_END_NAMESPACE_CXX11
*/
template
_GLIBCXX_NODISCARD _GLIBCXX20_CONSTEXPR
-basic_string<_CharT, _Traits, _Alloc>
+inline basic_string<_CharT, _Traits, _Alloc>
operator+(const basic_string<_CharT, _Traits, _Alloc>& __lhs,
const basic_string<_CharT, _Traits, _Alloc>& __rhs)
{
- basic_string<_CharT, _Traits, _Alloc> __str(__lhs);
- __str.append(__rhs);
- return __str;
+ typedef basic_string<_CharT, _Traits, _Alloc> _Str;
+ return std::__str_concat<_Str>(__lhs.c_str(), __lhs.size(),
+__rhs.c_str(), __rhs.size(),
You should use data() rather than c_str() here and all other operators.
It is currently the same but is more accurate in your context. Maybe one
day it will make a difference.
+__lhs.get_allocator());
}
/**
@@ -3507,9 +3526,16 @@ _GLIBCXX_END_NAMESPACE_CXX11
*/
template
_GLIBCXX_NODISCARD _GLIBCXX20_CONSTEXPR
-basic_string<_CharT,_Traits,_Alloc>
+inline basic_string<_CharT,_Traits,_Alloc>
Why inlining ?
I guess it is done this way to limit code bloat.
operator+(const _CharT* __lhs,
- const basic_string<_CharT,_Traits,_Alloc>& __rhs);
+ const basic_string<_CharT,_Traits,_Alloc>& __rhs)
+{
+ __glibcxx_requires_string(__lhs);
+ typedef basic_string<_CharT, _Traits, _Alloc> _Str;
+ return std::__str_concat<_Str>(__lhs, _Traits::length(__lhs),
+__rhs.c_str(), __rhs.size(),
+__rhs.get_allocator());
+}
/**
* @brief Concatenate character and string.
@@ -3519,8 +3545,14 @@ _GLIBCXX_END_NAMESPACE_CXX11
*/
template
_GLIBCXX_NODISCARD _GLIBCXX20_CONSTEXPR
-basic_string<_CharT,_Traits,_Alloc>
-operator+(_CharT __lhs, const basic_string<_CharT,_Traits,_Alloc>& __rhs);
+inline basic_string<_CharT,_Traits,_Alloc>
+operator+(_CharT __lhs, const basic_string<_CharT,_Traits,_Alloc>& __rhs)
+{
+ typedef basic_string<_CharT, _Traits, _Alloc> _Str;
+ return std::__str_concat<_Str>(__builtin_addressof(__lhs), 1,
+__rhs.c_str(), __rhs.size(),
+__rhs.get_allocator());
+}
/**
* @brief Concatenate string and C string.
@@ -3534,11 +3566,12 @@ _GLIBCXX_END_NAMESPACE_CXX11
operator+(const basic_string<_CharT, _Traits, _Alloc>& __lhs,
const _CharT* __rhs)
{
- basic_string<_CharT, _Traits, _Alloc> __str(__lhs);
- __str.append(__rhs);
- return __str;
+ __glibcxx_requires_string(__rhs);
+ typedef basic_string<_CharT, _Traits, _Alloc> _Str;
+ return
