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Partially inline basic_string copy constructor in UNSTABLE

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Summary:
    This is a recommit of https://reviews.llvm.org/D73223 where the added function accidentally ended up inside an idef block.

    This 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
    ```
    With this change
    ```
    ---------------------------------------------------------------
    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
    ```

    Subscribers: libcxx-commits

    Tags: #libc

    Differential Revision: https://reviews.llvm.org/D75639
This commit is contained in:
Martijn Vels 2020-03-04 17:52:46 -05:00
parent 45499f3801
commit b019c5c037
3 changed files with 85 additions and 4 deletions
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3
libcxx/include/__string
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@ -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) \

36
libcxx/include/string
View File

@ -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
@ -1861,7 +1871,9 @@ 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
@ -1875,12 +1887,32 @@ 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
}
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);
}
#ifndef _LIBCPP_CXX03_LANG
template <class _CharT, class _Traits, class _Allocator>

50
libcxx/test/libcxx/strings/basic.string/string.cons/copy_shrunk_long.pass.cpp Normal file
View File

@ -0,0 +1,50 @@
//===----------------------------------------------------------------------===//
//
// 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;
}