[libc++] Don't use std::allocator inside <any>

[philnik777]

There isn't much of a reason to use the allocator abstraction facilities inside <any>. We can improve compile times a bit by avoiding them and using __libcpp_{,de}allocate directly. IMO this also significantly improves readability here.

[llvmbot]

@llvm/pr-subscribers-libcxx

Author: Nikolas Klauser (philnik777)

Changes

There isn't much of a reason to use the allocator abstraction facilities inside <any>. We can improve compile times a bit by avoiding them and using __libcpp_{,de}allocate directly. IMO this also significantly improves readability here.

---

Full diff: https://github.com/llvm/llvm-project/pull/161061.diff

3 Files Affected:

• (modified) libcxx/include/any (+18-28)
• (modified) libcxx/test/libcxx/transitive_includes/cxx26.csv (-2)
• (modified) libcxx/test/libcxx/utilities/any/allocator.pass.cpp (+35-79)

diff --git a/libcxx/include/any b/libcxx/include/any
index 89bf3cf1f7df0..c1c45c151d281 100644
--- a/libcxx/include/any
+++ b/libcxx/include/any
@@ -84,10 +84,8 @@ namespace std {
 #  include <__cxx03/__config>
 #else
 #  include <__config>
-#  include <__memory/allocator.h>
-#  include <__memory/allocator_destructor.h>
-#  include <__memory/allocator_traits.h>
-#  include <__memory/unique_ptr.h>
+#  include <__memory/construct_at.h>
+#  include <__new/allocate.h>
 #  include <__type_traits/add_cv_quals.h>
 #  include <__type_traits/add_pointer.h>
 #  include <__type_traits/aligned_storage.h>
@@ -103,6 +101,7 @@ namespace std {
 #  include <__type_traits/remove_cv.h>
 #  include <__type_traits/remove_cvref.h>
 #  include <__type_traits/remove_reference.h>
+#  include <__utility/exception_guard.h>
 #  include <__utility/forward.h>
 #  include <__utility/in_place.h>
 #  include <__utility/move.h>
@@ -339,22 +338,14 @@ struct _SmallHandler {
 
   template <class... _Args>
   _LIBCPP_HIDE_FROM_ABI static _Tp& __create(any& __dest, _Args&&... __args) {
-    typedef allocator<_Tp> _Alloc;
-    typedef allocator_traits<_Alloc> _ATraits;
-    _Alloc __a;
-    _Tp* __ret = static_cast<_Tp*>(static_cast<void*>(&__dest.__s_.__buf));
-    _ATraits::construct(__a, __ret, std::forward<_Args>(__args)...);
+    auto __ret  = std::__construct_at(reinterpret_cast<_Tp*>(&__dest.__s_.__buf), std::forward<_Args>(__args)...);
     __dest.__h_ = &_SmallHandler::__handle;
     return *__ret;
   }
 
 private:
   _LIBCPP_HIDE_FROM_ABI static void __destroy(any& __this) {
-    typedef allocator<_Tp> _Alloc;
-    typedef allocator_traits<_Alloc> _ATraits;
-    _Alloc __a;
-    _Tp* __p = static_cast<_Tp*>(static_cast<void*>(&__this.__s_.__buf));
-    _ATraits::destroy(__a, __p);
+    std::__destroy_at(reinterpret_cast<_Tp*>(&__this.__s_.__buf));
     __this.__h_ = nullptr;
   }
 
@@ -406,26 +397,20 @@ struct _LargeHandler {
 
   template <class... _Args>
   _LIBCPP_HIDE_FROM_ABI static _Tp& __create(any& __dest, _Args&&... __args) {
-    typedef allocator<_Tp> _Alloc;
-    typedef allocator_traits<_Alloc> _ATraits;
-    typedef __allocator_destructor<_Alloc> _Dp;
-    _Alloc __a;
-    unique_ptr<_Tp, _Dp> __hold(_ATraits::allocate(__a, 1), _Dp(__a, 1));
-    _Tp* __ret = __hold.get();
-    _ATraits::construct(__a, __ret, std::forward<_Args>(__args)...);
-    __dest.__s_.__ptr = __hold.release();
+    _Tp* __ptr = static_cast<_Tp*>(std::__libcpp_allocate<_Tp>(__element_count(1)));
+    std::__exception_guard __guard([&] { std::__libcpp_deallocate<_Tp>(__ptr, __element_count(1)); });
+    std::__construct_at(__ptr, std::forward<_Args>(__args)...);
+    __guard.__complete();
+    __dest.__s_.__ptr = __ptr;
     __dest.__h_       = &_LargeHandler::__handle;
-    return *__ret;
+    return *__ptr;
   }
 
 private:
   _LIBCPP_HIDE_FROM_ABI static void __destroy(any& __this) {
-    typedef allocator<_Tp> _Alloc;
-    typedef allocator_traits<_Alloc> _ATraits;
-    _Alloc __a;
     _Tp* __p = static_cast<_Tp*>(__this.__s_.__ptr);
-    _ATraits::destroy(__a, __p);
-    _ATraits::deallocate(__a, __p, 1);
+    std::__destroy_at(__p);
+    std::__libcpp_deallocate<_Tp>(__p, __element_count(1));
     __this.__h_ = nullptr;
   }
 
@@ -613,6 +598,11 @@ _LIBCPP_POP_MACROS
 #    include <type_traits>
 #    include <variant>
 #  endif
+
+#  if !defined(_LIBCPP_REMOVE_TRANSITIVE_INCLUDES) & _LIBCPP_STD_VER <= 23
+#    include <cstring>
+#    include <limits>
+#  endif
 #endif // __cplusplus < 201103L && defined(_LIBCPP_USE_FROZEN_CXX03_HEADERS)
 
 #endif // _LIBCPP_ANY
diff --git a/libcxx/test/libcxx/transitive_includes/cxx26.csv b/libcxx/test/libcxx/transitive_includes/cxx26.csv
index 81c8c41d88756..d047b29b63cc6 100644
--- a/libcxx/test/libcxx/transitive_includes/cxx26.csv
+++ b/libcxx/test/libcxx/transitive_includes/cxx26.csv
@@ -14,9 +14,7 @@ algorithm ratio
 algorithm tuple
 algorithm version
 any cstdint
-any cstring
 any initializer_list
-any limits
 any typeinfo
 any version
 array cctype
diff --git a/libcxx/test/libcxx/utilities/any/allocator.pass.cpp b/libcxx/test/libcxx/utilities/any/allocator.pass.cpp
index eab3ca8826493..34827ff7acb32 100644
--- a/libcxx/test/libcxx/utilities/any/allocator.pass.cpp
+++ b/libcxx/test/libcxx/utilities/any/allocator.pass.cpp
@@ -17,111 +17,67 @@
 #include <any>
 #include <cassert>
 #include <cstddef>
-#include <memory>
 #include <new>
-#include <type_traits>
-#include <utility>
 
-#include "test_macros.h"
+// Make sure we don't fit in std::any's SBO
+int allocated_count   = 0;
+int constructed_count = 0;
 
+struct Large {
+  Large() { ++constructed_count; }
 
-// Make sure we don't fit in std::any's SBO
-struct Large { char big[sizeof(std::any) + 1]; };
+  Large(const Large&) { ++constructed_count; }
 
-// Make sure we fit in std::any's SBO
-struct Small { };
-
-bool Large_was_allocated = false;
-bool Large_was_constructed = false;
-bool Large_was_destroyed = false;
-bool Large_was_deallocated = false;
-
-bool Small_was_constructed = false;
-bool Small_was_destroyed = false;
-
-template <>
-struct std::allocator<Large> {
-  using value_type                             = Large;
-  using size_type                              = std::size_t;
-  using difference_type                        = std::ptrdiff_t;
-  using propagate_on_container_move_assignment = std::true_type;
-  using is_always_equal                        = std::true_type;
-
-  Large* allocate(std::size_t n) {
-    Large_was_allocated = true;
-    return static_cast<Large*>(::operator new(n * sizeof(Large)));
-  }
+  ~Large() { --constructed_count; }
 
-  template <typename... Args>
-  void construct(Large* p, Args&&... args) {
-    new (p) Large(std::forward<Args>(args)...);
-    Large_was_constructed = true;
-  }
+  char big[sizeof(std::any) + 1];
 
-  void destroy(Large* p) {
-    p->~Large();
-    Large_was_destroyed = true;
+  static void* operator new(size_t n) {
+    ++allocated_count;
+    return ::operator new(n);
   }
 
-  void deallocate(Large* p, std::size_t) {
-    Large_was_deallocated = true;
-    return ::operator delete(p);
+  static void operator delete(void* ptr) {
+    --allocated_count;
+    ::operator delete(ptr);
   }
 };
 
-template <>
-struct std::allocator<Small> {
-  using value_type                             = Small;
-  using size_type                              = std::size_t;
-  using difference_type                        = std::ptrdiff_t;
-  using propagate_on_container_move_assignment = std::true_type;
-  using is_always_equal                        = std::true_type;
-
-  Small* allocate(std::size_t) {
-    assert(false);
-    return nullptr;
-  }
+// Make sure we fit in std::any's SBO
+struct Small {
+  Small() { ++constructed_count; }
 
-  template <typename... Args>
-  void construct(Small* p, Args&&... args) {
-    new (p) Small(std::forward<Args>(args)...);
-    Small_was_constructed = true;
-  }
+  Small(const Small&) { ++constructed_count; }
+
+  ~Small() { --constructed_count; }
 
-  void destroy(Small* p) {
-    p->~Small();
-    Small_was_destroyed = true;
+  static void* operator new(size_t n) {
+    ++allocated_count;
+    return ::operator new(n);
   }
 
-  void deallocate(Small*, std::size_t) { assert(false); }
+  static void operator delete(void* ptr) {
+    --allocated_count;
+    ::operator delete(ptr);
+  }
 };
 
 int main(int, char**) {
   // Test large types
   {
-    {
-      std::any a = Large();
-      (void)a;
-
-      assert(Large_was_allocated);
-      assert(Large_was_constructed);
-    }
-
-    assert(Large_was_destroyed);
-    assert(Large_was_deallocated);
+    [[maybe_unused]] std::any a = Large();
+    assert(constructed_count == 1);
   }
+  assert(allocated_count == 0);
+  assert(constructed_count == 0);
 
   // Test small types
   {
-    {
-      std::any a = Small();
-      (void)a;
-
-      assert(Small_was_constructed);
-    }
-
-    assert(Small_was_destroyed);
+    [[maybe_unused]] std::any a = Small();
+    assert(constructed_count == 1);
   }
+  assert(allocated_count == 0);
+  assert(constructed_count == 0);
 
   return 0;
 }

[ldionne]

LGTM with comments. Thanks for fixing this!