[libcxx-commits] [PATCH] D155486: Optimize basic_string's memory usage
Martijn Vels via Phabricator via libcxx-commits
libcxx-commits at lists.llvm.org
Mon Jul 17 09:53:02 PDT 2023
mvels updated this revision to Diff 541106.
mvels added a comment.
Upload correct version this time
Repository:
rG LLVM Github Monorepo
CHANGES SINCE LAST ACTION
https://reviews.llvm.org/D155486/new/
https://reviews.llvm.org/D155486
Files:
libcxx/include/string
libcxx/test/libcxx/strings/basic.string/string.capacity/max_size.pass.cpp
Index: libcxx/test/libcxx/strings/basic.string/string.capacity/max_size.pass.cpp
===================================================================
--- libcxx/test/libcxx/strings/basic.string/string.capacity/max_size.pass.cpp
+++ libcxx/test/libcxx/strings/basic.string/string.capacity/max_size.pass.cpp
@@ -13,12 +13,9 @@
#include <algorithm>
#include <cassert>
#include <cstddef>
-#include <string>
-#include "test_macros.h"
-
-// alignment of the string heap buffer is hardcoded to 16
-static const std::size_t alignment = 16;
+// alignment of the string heap buffer is hard coded to 8.
+static const std::size_t alignment = 8;
template <class = int>
TEST_CONSTEXPR_CXX20 void full_size() {
Index: libcxx/include/string
===================================================================
--- libcxx/include/string
+++ libcxx/include/string
@@ -1872,7 +1872,7 @@
_LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20
size_type __align_it(size_type __s) _NOEXCEPT
{return (__s + (__a-1)) & ~(__a-1);}
- enum {__alignment = 16};
+ enum {__alignment = 8};
static _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20
size_type __recommend(size_type __s) _NOEXCEPT
{
@@ -2318,10 +2318,20 @@
size_type __ms = max_size();
if (__delta_cap > __ms - __old_cap - 1)
__throw_length_error();
- pointer __old_p = __get_pointer();
- size_type __cap = __old_cap < __ms / 2 - __alignment ?
- __recommend(std::max(__old_cap + __delta_cap, 2 * __old_cap)) :
- __ms - 1;
+ pointer __old_p;
+ size_type __cap;
+ if (__is_long()) {
+ __old_p = __get_long_pointer();
+ __cap = __old_cap < __ms / 2 - __alignment
+ ? __recommend(std::max(__old_cap + __delta_cap, 2 * __old_cap))
+ : __ms - 1;
+ } else {
+ // On first allocation SSO -> long, do not apply a minimum doubling
+ // of capacity/ This results in a minimum allocation size of 48 and we
+ // only need to guarantee amortized growth on subsequent growth.
+ __old_p = __get_short_pointer();
+ __cap = __recommend(__old_cap + __delta_cap);
+ }
auto __allocation = std::__allocate_at_least(__alloc(), __cap + 1);
pointer __p = __allocation.ptr;
__begin_lifetime(__p, __allocation.count);
@@ -2359,10 +2369,20 @@
size_type __ms = max_size();
if (__delta_cap > __ms - __old_cap)
__throw_length_error();
- pointer __old_p = __get_pointer();
- size_type __cap = __old_cap < __ms / 2 - __alignment ?
- __recommend(std::max(__old_cap + __delta_cap, 2 * __old_cap)) :
- __ms - 1;
+ pointer __old_p;
+ size_type __cap;
+ if (__is_long()) {
+ __old_p = __get_long_pointer();
+ __cap = __old_cap < __ms / 2 - __alignment
+ ? __recommend(std::max(__old_cap + __delta_cap, 2 * __old_cap))
+ : __ms - 1;
+ } else {
+ // On first allocation SSO -> long, do not apply a minimum doubling
+ // of capacity/ This results in a minimum allocation size of 48 and we
+ // only need to guarantee amortized growth on subsequent growth.
+ __old_p = __get_short_pointer();
+ __cap = __recommend(__old_cap + __delta_cap);
+ }
auto __allocation = std::__allocate_at_least(__alloc(), __cap + 1);
pointer __p = __allocation.ptr;
__begin_lifetime(__p, __allocation.count);
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