[libcxx-commits] [libcxx] f87d30c - Partially inline basic_string::operator=(const basic_string&)
Martijn Vels via libcxx-commits
libcxx-commits at lists.llvm.org
Mon Mar 2 06:59:06 PST 2020
Author: Martijn Vels
Date: 2020-03-02T09:58:11-05:00
New Revision: f87d30cba2b54a9083a0b276ad97d645c4b8b16c
URL: https://github.com/llvm/llvm-project/commit/f87d30cba2b54a9083a0b276ad97d645c4b8b16c
DIFF: https://github.com/llvm/llvm-project/commit/f87d30cba2b54a9083a0b276ad97d645c4b8b16c.diff
LOG: Partially inline basic_string::operator=(const basic_string&)
Summary:
This change partially inlines operator=(const basic_string&) where both the input and current instance are short strings, making the assignment a fixed length inlined memcpy.
Assignments where either of the strings are long are delegate to __assign_no_alias<__is_short>(), which is templated for the long / short branch already observed in the caller.
Stable:
```
--------------------------------------------------------------------------------
Benchmark Time CPU Iterations
--------------------------------------------------------------------------------
BM_StringAssignStr_Empty_Opaque 2.65 ns 2.66 ns 263745536
BM_StringAssignStr_Empty_Transparent 2.95 ns 2.96 ns 236494848
BM_StringAssignStr_Small_Opaque 2.93 ns 2.94 ns 237301760
BM_StringAssignStr_Small_Transparent 2.69 ns 2.69 ns 265809920
BM_StringAssignStr_Large_Opaque 19.6 ns 19.6 ns 35573760
BM_StringAssignStr_Large_Transparent 19.1 ns 19.1 ns 36716544
BM_StringAssignStr_Huge_Opaque 1901 ns 1901 ns 364544
BM_StringAssignStr_Huge_Transparent 1889 ns 1889 ns 360448
```
Unstable
```
--------------------------------------------------------------------------------
Benchmark Time CPU Iterations
--------------------------------------------------------------------------------
BM_StringAssignStr_Empty_Opaque 1.29 ns 1.29 ns 540454912
BM_StringAssignStr_Empty_Transparent 1.11 ns 1.12 ns 628482048
BM_StringAssignStr_Small_Opaque 1.29 ns 1.29 ns 541216768
BM_StringAssignStr_Small_Transparent 1.11 ns 1.11 ns 629469184
BM_StringAssignStr_Large_Opaque 15.6 ns 15.6 ns 44945408
BM_StringAssignStr_Large_Transparent 14.9 ns 14.9 ns 46764032
BM_StringAssignStr_Huge_Opaque 1713 ns 1713 ns 401408
BM_StringAssignStr_Huge_Transparent 1704 ns 1704 ns 397312
```
Subscribers: libcxx-commits
Tags: #libc
Differential Revision: https://reviews.llvm.org/D75211
Added:
Modified:
libcxx/include/__string
libcxx/include/string
Removed:
################################################################################
diff --git a/libcxx/include/__string b/libcxx/include/__string
index 2aeaeb8aecdf..45060c282d59 100644
--- a/libcxx/include/__string
+++ b/libcxx/include/__string
@@ -165,6 +165,8 @@ _LIBCPP_BEGIN_NAMESPACE_STD
_Func(_LIBCPP_FUNC_VIS basic_string<_CharType>::size_type basic_string<_CharType>::find_last_of(value_type const*, size_type, size_type) const) \
_Func(_LIBCPP_FUNC_VIS void basic_string<_CharType>::__grow_by(size_type, size_type, size_type, size_type, size_type, size_type)) \
_Func(_LIBCPP_FUNC_VIS void basic_string<_CharType>::__grow_by_and_replace(size_type, size_type, size_type, size_type, size_type, size_type, value_type const*)) \
+ _Func(_LIBCPP_FUNC_VIS void basic_string<_CharType>::__assign_no_alias<false>(value_type const*, size_type)) \
+ _Func(_LIBCPP_FUNC_VIS void basic_string<_CharType>::__assign_no_alias<true>(value_type const*, size_type)) \
_Func(_LIBCPP_FUNC_VIS void basic_string<_CharType>::push_back(value_type)) \
_Func(_LIBCPP_FUNC_VIS basic_string<_CharType>& basic_string<_CharType>::append(size_type, value_type)) \
_Func(_LIBCPP_FUNC_VIS basic_string<_CharType>::size_type basic_string<_CharType>::rfind(value_type, size_type) const) \
@@ -179,7 +181,6 @@ _LIBCPP_BEGIN_NAMESPACE_STD
_Func(_LIBCPP_FUNC_VIS basic_string<_CharType>::size_type basic_string<_CharType>::find(value_type const*, size_type, size_type) const) \
_Func(_LIBCPP_FUNC_VIS int basic_string<_CharType>::compare(size_type, size_type, basic_string const&, size_type, size_type) const) \
_Func(_LIBCPP_FUNC_VIS int basic_string<_CharType>::compare(size_type, size_type, value_type const*, size_type) const) \
- _Func(_LIBCPP_FUNC_VIS basic_string<_CharType>& basic_string<_CharType>::operator=(basic_string const&)) \
_Func(_LIBCPP_FUNC_VIS basic_string<_CharType>& basic_string<_CharType>::append(value_type const*)) \
_Func(_LIBCPP_FUNC_VIS basic_string<_CharType>& basic_string<_CharType>::replace(size_type, size_type, basic_string const&, size_type, size_type)) \
_Func(_LIBCPP_FUNC_VIS basic_string<_CharType>::iterator basic_string<_CharType>::insert(basic_string::const_iterator, value_type)) \
diff --git a/libcxx/include/string b/libcxx/include/string
index 2c90dae2f735..7688d3ff29ec 100644
--- a/libcxx/include/string
+++ b/libcxx/include/string
@@ -1571,6 +1571,12 @@ private:
size_type __n_copy, size_type __n_del,
size_type __n_add, const value_type* __p_new_stuff);
+ // __assign_no_alias is invoked for assignment operations where we
+ // have proof that the input does not alias the current instance.
+ // For example, operator=(basic_string) performs a 'self' check.
+ template <bool __is_short>
+ void __assign_no_alias(const value_type* __s, size_type __n);
+
_LIBCPP_INLINE_VISIBILITY
void __erase_to_end(size_type __pos);
@@ -2202,6 +2208,23 @@ basic_string<_CharT, _Traits, _Allocator>::__grow_by(size_type __old_cap, size_t
// assign
+template <class _CharT, class _Traits, class _Allocator>
+template <bool __is_short>
+void basic_string<_CharT, _Traits, _Allocator>::__assign_no_alias(
+ const value_type* __s, size_type __n) {
+ size_type __cap = __is_short ? __min_cap : __get_long_cap();
+ if (__n < __cap) {
+ pointer __p = __is_short ? __get_short_pointer() : __get_long_pointer();
+ __is_short ? __set_short_size(__n) : __set_long_size(__n);
+ traits_type::copy(_VSTD::__to_address(__p), __s, __n);
+ traits_type::assign(__p[__n], value_type());
+ __invalidate_iterators_past(__n);
+ } else {
+ size_type __sz = __is_short ? __get_short_size() : __get_long_size();
+ __grow_by_and_replace(__cap - 1, __n - __cap + 1, __sz, 0, __sz, __n, __s);
+ }
+}
+
template <class _CharT, class _Traits, class _Allocator>
basic_string<_CharT, _Traits, _Allocator>&
basic_string<_CharT, _Traits, _Allocator>::assign(const value_type* __s, size_type __n)
@@ -2268,16 +2291,19 @@ template <class _CharT, class _Traits, class _Allocator>
basic_string<_CharT, _Traits, _Allocator>&
basic_string<_CharT, _Traits, _Allocator>::operator=(const basic_string& __str)
{
- if (this != &__str)
- {
- __copy_assign_alloc(__str);
- const bool __str_is_long = __str.__is_long(); // Force single branch
- if (__is_long() || __str_is_long) {
- return assign(__str.data(), __str.size());
- }
+ if (this != &__str) {
+ __copy_assign_alloc(__str);
+ if (!__is_long()) {
+ if (!__str.__is_long()) {
__r_.first().__r = __str.__r_.first().__r;
+ } else {
+ __assign_no_alias<true>(__str.data(), __str.size());
+ }
+ } else {
+ __assign_no_alias<false>(__str.data(), __str.size());
}
- return *this;
+ }
+ return *this;
}
#ifndef _LIBCPP_CXX03_LANG
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