[libcxx-commits] [PATCH] D75639: Partially inline basic_string copy constructor in UNSTABLE

[Martijn Vels via Phabricator via libcxx-commits]

mvels created this revision.
Herald added a project: libc++.
Herald added a subscriber: libcxx-commits.
mvels added a reviewer: EricWF.
Herald added a reviewer: mclow.lists.

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


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D75639

Files:
  libcxx/include/string


Index: libcxx/include/string
===================================================================
--- libcxx/include/string
+++ libcxx/include/string
@@ -1894,6 +1894,25 @@
 #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>
@@ -1914,25 +1933,6 @@
 #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)


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