Commit 8cf76e91 authored by Martijn Vels's avatar Martijn Vels
Browse files

Partially inline basic_string copy constructor in UNSTABLE 

his change splits the copy constructor up inlining short initialization, and explicitly outlining long initialization into __init_copy_ctor_external() which is the externally instantiated slow path.

For unstable ABI, this has the following changes:

remove basic_string(const basic_string&)
remove basic_string(const basic_string&, const Allocator&)
add __init_copy_ctor_external(const value_type*, size_type)
Quick local benchmark for Copy:

Master
```
---------------------------------------------------------------
Benchmark                    Time             CPU   Iterations
---------------------------------------------------------------
BM_StringCopy_Empty       3.50 ns         3.51 ns    199326720
BM_StringCopy_Small       3.50 ns         3.51 ns    199510016
BM_StringCopy_Large       15.7 ns         15.7 ns     45230080
BM_StringCopy_Huge        1503 ns         1503 ns       464896
```

```
---------------------------------------------------------------
Benchmark                    Time             CPU   Iterations
---------------------------------------------------------------
BM_StringCopy_Empty       1.99 ns         2.00 ns    356471808
BM_StringCopy_Small       3.29 ns         3.30 ns    203425792
BM_StringCopy_Large       13.3 ns         13.3 ns     52948992
BM_StringCopy_Huge        1472 ns         1472 ns       475136
```

Author: Martijn Vels <martijn.vels@gmail.com>

Reviewers: EricWF, mclow.list

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D73223
parent 14ac84e5

libcxx/include/__string

+1 −2
Original line number Diff line number Diff line
@@ -140,15 +140,14 @@ _LIBCPP_BEGIN_NAMESPACE_STD 
  _Func(_LIBCPP_FUNC_VIS basic_string<_CharType>& basic_string<_CharType>::replace(size_type, size_type, value_type const*, size_type)) \

  _Func(_LIBCPP_FUNC_VIS basic_string<_CharType>::size_type basic_string<_CharType>::rfind(value_type const*, size_type, size_type) const) \

  _Func(_LIBCPP_FUNC_VIS void basic_string<_CharType>::__init(value_type const*, size_type, size_type)) \

  _Func(_LIBCPP_FUNC_VIS basic_string<_CharType>::basic_string(basic_string const&)) \

  _Func(_LIBCPP_FUNC_VIS basic_string<_CharType>& basic_string<_CharType>::replace(size_type, size_type, value_type const*)) \

  _Func(_LIBCPP_FUNC_VIS basic_string<_CharType>::basic_string(basic_string const&, std::allocator<_CharType> const&)) \

  _Func(_LIBCPP_FUNC_VIS basic_string<_CharType>::size_type basic_string<_CharType>::find_last_not_of(value_type const*, size_type, size_type) const) \

  _Func(_LIBCPP_FUNC_VIS basic_string<_CharType>::~basic_string()) \

  _Func(_LIBCPP_FUNC_VIS basic_string<_CharType>::size_type basic_string<_CharType>::find_first_not_of(value_type const*, size_type, size_type) const) \

  _Func(_LIBCPP_FUNC_VIS basic_string<_CharType>& basic_string<_CharType>::insert(size_type, size_type, value_type)) \

  _Func(_LIBCPP_FUNC_VIS basic_string<_CharType>& basic_string<_CharType>::operator=(value_type)) \

  _Func(_LIBCPP_FUNC_VIS void basic_string<_CharType>::__init(value_type const*, size_type)) \

  _Func(_LIBCPP_FUNC_VIS void basic_string<_CharType>::__init_copy_ctor_external(value_type const*, size_type)) \

  _Func(_LIBCPP_FUNC_VIS const _CharType& basic_string<_CharType>::at(size_type) const) \

  _Func(_LIBCPP_FUNC_VIS basic_string<_CharType>& basic_string<_CharType>::insert(size_type, value_type const*, size_type)) \

  _Func(_LIBCPP_FUNC_VIS basic_string<_CharType>::size_type basic_string<_CharType>::find_first_of(value_type const*, size_type, size_type) const) \

libcxx/include/string

+34 −2
Original line number Diff line number Diff line
@@ -1549,6 +1549,16 @@ private: 
    inline

    void __init(size_type __n, value_type __c);



    // Slow path for the (inlined) copy constructor for 'long' strings.

    // Always externally instantiated and not inlined.

    // Requires that __s is zero terminated.

    // The main reason for this function to exist is because for unstable, we

    // want to allow inlining of the copy constructor. However, we don't want

    // to call the __init() functions as those are marked as inline which may

    // result in over-aggressive inlining by the compiler, where our aim is

    // to only inline the fast path code directly in the ctor.

    void __init_copy_ctor_external(const value_type* __s, size_type __sz);



    template <class _InputIterator>

    inline

    _EnableIf
@@ -1850,7 +1860,9 @@ basic_string<_CharT, _Traits, _Allocator>::basic_string(const basic_string& __st 
    if (!__str.__is_long())

        __r_.first().__r = __str.__r_.first().__r;

    else

        __init(_VSTD::__to_address(__str.__get_long_pointer()), __str.__get_long_size());

        __init_copy_ctor_external(_VSTD::__to_address(__str.__get_long_pointer()),

                                  __str.__get_long_size());



#if _LIBCPP_DEBUG_LEVEL >= 2

    __get_db()->__insert_c(this);

#endif
@@ -1864,7 +1876,8 @@ basic_string<_CharT, _Traits, _Allocator>::basic_string( 
    if (!__str.__is_long())

        __r_.first().__r = __str.__r_.first().__r;

    else

        __init(_VSTD::__to_address(__str.__get_long_pointer()), __str.__get_long_size());

        __init_copy_ctor_external(_VSTD::__to_address(__str.__get_long_pointer()),

                                  __str.__get_long_size());

#if _LIBCPP_DEBUG_LEVEL >= 2

    __get_db()->__insert_c(this);

#endif
@@ -1890,6 +1903,25 @@ basic_string<_CharT, _Traits, _Allocator>::basic_string(basic_string&& __str) 
#endif

}



template <class _CharT, class _Traits, class _Allocator>

void basic_string<_CharT, _Traits, _Allocator>::__init_copy_ctor_external(

    const value_type* __s, size_type __sz) {

  pointer __p;

  if (__sz < __min_cap) {

    __p = __get_short_pointer();

    __set_short_size(__sz);

  } else {

    if (__sz > max_size())

      this->__throw_length_error();

    size_t __cap = __recommend(__sz);

    __p = __alloc_traits::allocate(__alloc(), __cap + 1);

    __set_long_pointer(__p);

    __set_long_cap(__cap + 1);

    __set_long_size(__sz);

  }

  traits_type::copy(_VSTD::__to_address(__p), __s, __sz + 1);

}



template <class _CharT, class _Traits, class _Allocator>

inline

basic_string<_CharT, _Traits, _Allocator>::basic_string(basic_string&& __str, const allocator_type& __a)

libcxx/test/libcxx/strings/basic.string/string.cons/copy_shrunk_long.pass.cpp

0 → 100644
+50 −0
Original line number Diff line number Diff line 
//===----------------------------------------------------------------------===//

//

// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.

// See https://llvm.org/LICENSE.txt for license information.

// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception

//

//===----------------------------------------------------------------------===//



// <string>



// basic_string(const basic_string<charT,traits,Allocator>& str);



#include <string>

#include <cassert>



#include "test_macros.h"

#include "test_allocator.h"

#include "min_allocator.h"



template <class S>

void

test()

{

  // Tests that a long string holding a SSO size string results in

  // an SSO copy constructed value.

  S s1("1234567890123456789012345678901234567890123456789012345678901234567890");

  s1.resize(7);

  S s2(s1);

  LIBCPP_ASSERT(s2.__invariants());

  assert(s2 == s1);

  assert(s2.capacity() < sizeof(S));

}



int main(int, char**)

{

    {

    typedef test_allocator<char> A;

    typedef std::basic_string<char, std::char_traits<char>, A> S;

    test<S>();

    }

#if TEST_STD_VER >= 11

    {

    typedef min_allocator<char> A;

    typedef std::basic_string<char, std::char_traits<char>, A> S;

    test<S>();

    }

#endif



  return 0;

}