Implement sized deallocation for std::allocator and friends.

[EricWF]

Summary

C++14 sized deallocation is disabled by default due to ABI concerns. However, when a user manually enables it then libc++ should take advantage of it since sized deallocation can provide a significant performance win depending on the underlying malloc implementation. (Note that libc++'s definitions of sized delete don't do anything special yet, but users are free to provide their own).

This patch updates __libcpp_deallocate to selectively call sized operator delete when it's available. __libcpp_deallocate_unsized should be used when the size of the allocation is unknown.

On Apple this patch makes no attempt to determine if the sized operator delete is unavailable, only that the language feature is enabled. This could cause a compile error when using std::allocator, but the same compile error would occur whenever the user calls new, so I don't think it's a problem.

[ckennelly]

include/new

345

Should this be specialized for the "don't know" case, rather than passing the size as 0?

For the common case (std::allocator<T>::deallocate()), we don't need to pay the cost of the branch.

[EricWF]

• Address inline comments about using 0 as a sentinel value and the branches it requires.
• Convert <valarray> to use sized deallocation.

[rsmith]

include/new

298–300

Any reason why one of these is returned but the other is not?

308–310

Likewise

include/valarray

3732–3738

I think __size would be clearer as __capacity here.

[EricWF]

include/new

298–300

I prefer explicit returns when inside conditional compilation blocks. I'll add return's above as well.

345

Ack. I've fixed this by adding a __libcpp_deallocate_unsized.

[EricWF]

Address review comments.

[ldionne]

C++14 sized deallocation is disabled by default due to ABI concerns.

@EricWF Can you expand on those ABI concerns? Do you mean because support for those is not provided in the dylib shipped by Apple?

On Apple this patch makes no attempt to determine if the sized operator delete is unavailable, only that the language feature is enabled.

You mean there's no check like there is for aligned allocation? For example (in __config):

#if defined(__APPLE__)
#  if defined(__MAC_OS_X_VERSION_MIN_REQUIRED)
#    if __MAC_OS_X_VERSION_MIN_REQUIRED < 1060
#      define _LIBCPP_HAS_NO_LIBRARY_ALIGNED_ALLOCATION
#    endif
#  endif
#endif // defined(__APPLE__)

I think there should be one -- users won't expect calls to std::allocator::deallocate to suddenly start failing after this patch when they target an OS version that does not have sized deallocation. I think Apple started shipping support for sized deallocation in 10.12, so the check should be:

#if defined(__APPLE__)
#  if defined(__MAC_OS_X_VERSION_MIN_REQUIRED)
#    if __MAC_OS_X_VERSION_MIN_REQUIRED < 101200
#      define _LIBCPP_HAS_NO_LIBRARY_SIZED_DEALLOCATION
#    endif
#  endif
#endif // defined(__APPLE__)

include/new

295

I think you need _LIBCPP_INLINE_VISIBILITY here and on other private functions too.

src/experimental/memory_resource.cpp

37

Do you know why there's a FIXME here? (I know it was there before your patch, I'm just curious)

test/libcxx/language.support/support.dynamic/libcpp_deallocate.sh.cpp

11

typo: relevant

[ldionne]

After talking w/ Eric:

1. Can you please add a test that checks that std::allocator and new end up calling the same allocation/deallocation functions?
2. I'm fine with not checking for availability on Mac OS. The rationale is that std::allocator should do the same as new: if you decide to turn on support for sized deallocation but your deployment target does not support sized deallocation, you should get a compiler error (regardless of whether you use new directly or use an allocator).

[EricWF]

• Make the library behavior of std::allocator match the language behavior in the current dialect.

[ldionne]

LGTM

[EricWF]

• Misc cleanup.
• Work around Clang bug in C++03.

include/__sso_allocator

public:
     {
         if (!__allocated_ && __n <= _Np)
         {
             __allocated_ = true;
             return (pointer)&buf_;
         }
         return static_cast<pointer>(_VSTD::__libcpp_allocate(__n * sizeof(_Tp), __alignof(_Tp)));
     }
-    _LIBCPP_INLINE_VISIBILITY void deallocate(pointer __p, size_type)
+    _LIBCPP_INLINE_VISIBILITY void deallocate(pointer __p, size_type __n)
     {
         if (__p == (pointer)&buf_)
             __allocated_ = false;
         else
-            _VSTD::__libcpp_deallocate(__p, __alignof(_Tp));
+            _VSTD::__libcpp_deallocate(__p, __n * sizeof(_Tp), __alignof(_Tp));
     }
     _LIBCPP_INLINE_VISIBILITY size_type max_size() const throw() {return size_type(~0) / sizeof(_Tp);}
 
     _LIBCPP_INLINE_VISIBILITY
     bool operator==(__sso_allocator& __a) const {return &buf_ == &__a.buf_;}
     _LIBCPP_INLINE_VISIBILITY
     bool operator!=(__sso_allocator& __a) const {return &buf_ != &__a.buf_;}
 };
 
 _LIBCPP_END_NAMESPACE_STD
 
 #endif  // _LIBCPP___SSO_ALLOCATOR

include/memory

     _LIBCPP_NODISCARD_AFTER_CXX17 _LIBCPP_INLINE_VISIBILITY
     pointer allocate(size_type __n, allocator<void>::const_pointer = 0)
         {
         if (__n > max_size())
             __throw_length_error("allocator<T>::allocate(size_t n)"
                                  " 'n' exceeds maximum supported size");
         return static_cast<pointer>(_VSTD::__libcpp_allocate(__n * sizeof(_Tp), __alignof(_Tp)));
         }
-    _LIBCPP_INLINE_VISIBILITY void deallocate(pointer __p, size_type) _NOEXCEPT
-        {_VSTD::__libcpp_deallocate((void*)__p, __alignof(_Tp));}
+    _LIBCPP_INLINE_VISIBILITY void deallocate(pointer __p, size_type __n) _NOEXCEPT
+        {_VSTD::__libcpp_deallocate((void*)__p, __n * sizeof(_Tp), __alignof(_Tp));}
     _LIBCPP_INLINE_VISIBILITY size_type max_size() const _NOEXCEPT
         {return size_type(~0) / sizeof(_Tp);}
 #if !defined(_LIBCPP_HAS_NO_RVALUE_REFERENCES) && !defined(_LIBCPP_HAS_NO_VARIADICS)
     template <class _Up, class... _Args>
         _LIBCPP_INLINE_VISIBILITY
         void
         construct(_Up* __p, _Args&&... __args)
         {

         {return _VSTD::addressof(__x);}
     _LIBCPP_INLINE_VISIBILITY pointer allocate(size_type __n, allocator<void>::const_pointer = 0)
     {
         if (__n > max_size())
             __throw_length_error("allocator<const T>::allocate(size_t n)"
                                  " 'n' exceeds maximum supported size");
         return static_cast<pointer>(_VSTD::__libcpp_allocate(__n * sizeof(_Tp), __alignof(_Tp)));
     }
-    _LIBCPP_INLINE_VISIBILITY void deallocate(pointer __p, size_type) _NOEXCEPT
-        {_VSTD::__libcpp_deallocate((void*) const_cast<_Tp *>(__p), __alignof(_Tp));}
+    _LIBCPP_INLINE_VISIBILITY void deallocate(pointer __p, size_type __n) _NOEXCEPT
+        {_VSTD::__libcpp_deallocate((void*) const_cast<_Tp *>(__p), __n * sizeof(_Tp), __alignof(_Tp));}
     _LIBCPP_INLINE_VISIBILITY size_type max_size() const _NOEXCEPT
         {return size_type(~0) / sizeof(_Tp);}
 #if !defined(_LIBCPP_HAS_NO_RVALUE_REFERENCES) && !defined(_LIBCPP_HAS_NO_VARIADICS)
     template <class _Up, class... _Args>
         _LIBCPP_INLINE_VISIBILITY
         void
         construct(_Up* __p, _Args&&... __args)
         {

     }
     return __r;
 }
 
 template <class _Tp>
 inline _LIBCPP_INLINE_VISIBILITY
 void return_temporary_buffer(_Tp* __p) _NOEXCEPT
 {
-  _VSTD::__libcpp_deallocate((void*)__p, __alignof(_Tp));
+  _VSTD::__libcpp_deallocate_unsized((void*)__p, __alignof(_Tp));
 }
 
 #if _LIBCPP_STD_VER <= 14 || defined(_LIBCPP_ENABLE_CXX17_REMOVED_AUTO_PTR)
 template <class _Tp>
 struct _LIBCPP_DEPRECATED_IN_CXX11 auto_ptr_ref
 {
     _Tp* __ptr_;
 };

include/new

 #if defined(_LIBCPP_ABI_MICROSOFT) && !defined(_LIBCPP_NO_VCRUNTIME)
 #include <new.h>
 #endif
 
 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
 #pragma GCC system_header
 #endif
 
-#if !defined(_LIBCPP_BUILDING_LIBRARY) && _LIBCPP_STD_VER < 14
+#if !defined(__cpp_sized_deallocation) || __cpp_sized_deallocation  < 201309L
+#define _LIBCPP_HAS_NO_LANGUAGE_SIZED_DEALLOCATION
+#endif
+
+#if !defined(_LIBCPP_BUILDING_LIBRARY) && _LIBCPP_STD_VER < 14 && \
+    defined(_LIBCPP_HAS_NO_LANGUAGE_SIZED_DEALLOCATION)
 # define _LIBCPP_HAS_NO_LIBRARY_SIZED_DEALLOCATION
 #endif
 
 #if defined(_LIBCPP_HAS_NO_LIBRARY_SIZED_DEALLOCATION) || \
-    !defined(__cpp_sized_deallocation) || __cpp_sized_deallocation < 201309
+    defined(_LIBCPP_HAS_NO_LANGUAGE_SIZED_DEALLOCATION)
 # define _LIBCPP_HAS_NO_SIZED_DEALLOCATION
 #endif
 
 #if !__has_builtin(__builtin_operator_new) || \
    __has_builtin(__builtin_operator_new) < 201802L
 #define _LIBCPP_HAS_NO_BUILTIN_OVERLOADED_OPERATOR_NEW_DELETE
 #endif
 

 #endif
 #ifdef _LIBCPP_HAS_NO_BUILTIN_OPERATOR_NEW_DELETE
   return ::operator new(__size);
 #else
   return __builtin_operator_new(__size);
 #endif
 }
 
-inline _LIBCPP_INLINE_VISIBILITY void __libcpp_deallocate(void* __ptr, size_t __align) {
-#ifndef _LIBCPP_HAS_NO_ALIGNED_ALLOCATION
+struct _DeallocateCaller {
+  static inline _LIBCPP_INLINE_VISIBILITY
+  void __do_deallocate_handle_size_align(void *__ptr, size_t __size, size_t __align) {
+#if defined(_LIBCPP_HAS_NO_ALIGNED_ALLOCATION)
+    ((void)__align);
+    return __do_deallocate_handle_size(__ptr, __size);
+#else
     if (__is_overaligned_for_new(__align)) {
       const align_val_t __align_val = static_cast<align_val_t>(__align);
-# ifdef _LIBCPP_HAS_NO_BUILTIN_OVERLOADED_OPERATOR_NEW_DELETE
-    return ::operator delete(__ptr, __align_val);
-# else
-    return __builtin_operator_delete(__ptr, __align_val);
-# endif
+      return __do_deallocate_handle_size(__ptr, __size, __align_val);
+    } else {
+      return __do_deallocate_handle_size(__ptr, __size);
+    }
+#endif
+  }
+
+  static inline _LIBCPP_INLINE_VISIBILITY
+  void __do_deallocate_handle_align(void *__ptr, size_t __align) {
+#if defined(_LIBCPP_HAS_NO_ALIGNED_ALLOCATION)
+    ((void)__align);
+    return __do_call(__ptr);
+#else
+    if (__is_overaligned_for_new(__align)) {
+      const align_val_t __align_val = static_cast<align_val_t>(__align);
+      return __do_call(__ptr, __align_val);
+    } else {
+      return __do_call(__ptr);
+    }
+#endif
   }
+
+ private:
+  static inline void __do_deallocate_handle_size(void *__ptr, size_t __size) {
+#ifdef _LIBCPP_HAS_NO_SIZED_DEALLOCATION
+    ((void)__size);
+    return __do_call(__ptr);
 #else
-  ((void)__align);
+    return __do_call(__ptr, __size);
 #endif
+  }
+
+#ifndef _LIBCPP_HAS_NO_ALIGNED_ALLOCATION
+  static inline void __do_deallocate_handle_size(void *__ptr, size_t __size, align_val_t __align) {
+#ifdef _LIBCPP_HAS_NO_SIZED_DEALLOCATION
+    ((void)__size);
+    return __do_call(__ptr, __align);
+#else
+    return __do_call(__ptr, __size, __align);
+#endif
+  }
+#endif
+
+private:
+  template <class _A1, class _A2>
+  static inline void __do_call(void *__ptr, _A1 __a1, _A2 __a2) {
+#if defined(_LIBCPP_HAS_NO_BUILTIN_OPERATOR_NEW_DELETE) || \
+    defined(_LIBCPP_HAS_NO_BUILTIN_OVERLOADED_OPERATOR_NEW_DELETE)
+    return ::operator delete(__ptr, __a1, __a2);
+#else
+    return __builtin_operator_delete(__ptr, __a1, __a2);
+#endif
+  }
+
+  template <class _A1>
+  static inline void __do_call(void *__ptr, _A1 __a1) {
+#if defined(_LIBCPP_HAS_NO_BUILTIN_OPERATOR_NEW_DELETE) || \
+    defined(_LIBCPP_HAS_NO_BUILTIN_OVERLOADED_OPERATOR_NEW_DELETE)
+    return ::operator delete(__ptr, __a1);
+#else
+    return __builtin_operator_delete(__ptr, __a1);
+#endif
+  }
+
+  static inline void __do_call(void *__ptr) {
 #ifdef _LIBCPP_HAS_NO_BUILTIN_OPERATOR_NEW_DELETE
     return ::operator delete(__ptr);
 #else
     return __builtin_operator_delete(__ptr);
 #endif
   }
+};
+
+inline _LIBCPP_INLINE_VISIBILITY void __libcpp_deallocate(void* __ptr, size_t __size, size_t __align) {
+  _DeallocateCaller::__do_deallocate_handle_size_align(__ptr, __size, __align);
+}
+
+inline _LIBCPP_INLINE_VISIBILITY void __libcpp_deallocate_unsized(void* __ptr, size_t __align) {
+  _DeallocateCaller::__do_deallocate_handle_align(__ptr, __align);
+}
 
 #ifdef _LIBCPP_BAD_ARRAY_LENGTH_DEFINED
 _LIBCPP_NORETURN inline _LIBCPP_INLINE_VISIBILITY
 #ifndef _LIBCPP_NO_EXCEPTIONS
 _LIBCPP_AVAILABILITY_BAD_ARRAY_LENGTH
 #endif
 void __throw_bad_array_length()
 {

include/valarray

     _Up*
     end(valarray<_Up>& __v);
 
     template <class _Up>
     friend
     const _Up*
     end(const valarray<_Up>& __v);
 
-    void __clear();
+    void __clear(size_t __capacity);
     valarray& __assign_range(const value_type* __f, const value_type* __l);
 };
 
 _LIBCPP_EXTERN_TEMPLATE(_LIBCPP_FUNC_VIS valarray<size_t>::valarray(size_t))
 _LIBCPP_EXTERN_TEMPLATE(_LIBCPP_FUNC_VIS valarray<size_t>::~valarray())
 _LIBCPP_EXTERN_TEMPLATE(_LIBCPP_FUNC_VIS void valarray<size_t>::resize(size_t, size_t))
 
 template <class _Op, class _Tp>

     if (__n)
     {
         __begin_ = __end_ = static_cast<value_type*>(
             _VSTD::__libcpp_allocate(__n * sizeof(value_type), __alignof(value_type)));
 #ifndef _LIBCPP_NO_EXCEPTIONS
         try
         {
 #endif  // _LIBCPP_NO_EXCEPTIONS
-            for (; __n; --__n, ++__end_)
+            for (size_t __n_left = __n; __n_left; --__n_left, ++__end_)
                 ::new (__end_) value_type();
 #ifndef _LIBCPP_NO_EXCEPTIONS
         }
         catch (...)
         {
-            __clear();
+            __clear(__n);
             throw;
         }
 #endif  // _LIBCPP_NO_EXCEPTIONS
     }
 }
 
 template <class _Tp>
 inline

     if (__n)
     {
         __begin_ = __end_ = static_cast<value_type*>(
             _VSTD::__libcpp_allocate(__n * sizeof(value_type), __alignof(value_type)));
 #ifndef _LIBCPP_NO_EXCEPTIONS
         try
         {
 #endif  // _LIBCPP_NO_EXCEPTIONS
-            for (; __n; ++__end_, ++__p, --__n)
+            for (size_t __n_left = __n; __n_left; ++__end_, ++__p, --__n_left)
                 ::new (__end_) value_type(*__p);
 #ifndef _LIBCPP_NO_EXCEPTIONS
         }
         catch (...)
         {
-            __clear();
+            __clear(__n);
             throw;
         }
 #endif  // _LIBCPP_NO_EXCEPTIONS
     }
 }
 
 template <class _Tp>
 valarray<_Tp>::valarray(const valarray& __v)

         {
 #endif  // _LIBCPP_NO_EXCEPTIONS
             for (value_type* __p = __v.__begin_; __p != __v.__end_; ++__end_, ++__p)
                 ::new (__end_) value_type(*__p);
 #ifndef _LIBCPP_NO_EXCEPTIONS
         }
         catch (...)
         {
-            __clear();
+            __clear(__v.size());
             throw;
         }
 #endif  // _LIBCPP_NO_EXCEPTIONS
     }
 }
 
 #ifndef _LIBCPP_CXX03_LANG
 
 template <class _Tp>
 inline
 valarray<_Tp>::valarray(valarray&& __v) _NOEXCEPT
     : __begin_(__v.__begin_),
       __end_(__v.__end_)
 {
     __v.__begin_ = __v.__end_ = nullptr;
 }
 
 template <class _Tp>
 valarray<_Tp>::valarray(initializer_list<value_type> __il)
     : __begin_(0),
       __end_(0)
 {
-    size_t __n = __il.size();
+    const size_t __n = __il.size();
     if (__n)
     {
         __begin_ = __end_ = static_cast<value_type*>(
 _VSTD::__libcpp_allocate(__n * sizeof(value_type), __alignof(value_type)));
 #ifndef _LIBCPP_NO_EXCEPTIONS
         try
         {
 #endif  // _LIBCPP_NO_EXCEPTIONS
-            for (const value_type* __p = __il.begin(); __n; ++__end_, ++__p, --__n)
+            size_t __n_left = __n;
+            for (const value_type* __p = __il.begin(); __n_left; ++__end_, ++__p, --__n_left)
                 ::new (__end_) value_type(*__p);
 #ifndef _LIBCPP_NO_EXCEPTIONS
         }
         catch (...)
         {
-            __clear();
+            __clear(__n);
             throw;
         }
 #endif  // _LIBCPP_NO_EXCEPTIONS
     }
 }
 
 #endif  // _LIBCPP_CXX03_LANG
 
 template <class _Tp>
 valarray<_Tp>::valarray(const slice_array<value_type>& __sa)
     : __begin_(0),
       __end_(0)
 {
-    size_t __n = __sa.__size_;
+    const size_t __n = __sa.__size_;
     if (__n)
     {
         __begin_ = __end_ = static_cast<value_type*>(
           _VSTD::__libcpp_allocate(__n * sizeof(value_type), __alignof(value_type)));
 #ifndef _LIBCPP_NO_EXCEPTIONS
         try
         {
 #endif  // _LIBCPP_NO_EXCEPTIONS
-            for (const value_type* __p = __sa.__vp_; __n; ++__end_, __p += __sa.__stride_, --__n)
+            size_t __n_left = __n;
+            for (const value_type* __p = __sa.__vp_; __n_left; ++__end_, __p += __sa.__stride_, --__n_left)
                 ::new (__end_) value_type(*__p);
 #ifndef _LIBCPP_NO_EXCEPTIONS
         }
         catch (...)
         {
-            __clear();
+            __clear(__n);
             throw;
         }
 #endif  // _LIBCPP_NO_EXCEPTIONS
     }
 }
 
 template <class _Tp>
 valarray<_Tp>::valarray(const gslice_array<value_type>& __ga)
     : __begin_(0),
       __end_(0)
 {
-    size_t __n = __ga.__1d_.size();
+    const size_t __n = __ga.__1d_.size();
     if (__n)
     {
         __begin_ = __end_ = static_cast<value_type*>(
            _VSTD::__libcpp_allocate(__n * sizeof(value_type), __alignof(value_type)));
 #ifndef _LIBCPP_NO_EXCEPTIONS
         try
         {
 #endif  // _LIBCPP_NO_EXCEPTIONS
             typedef const size_t* _Ip;
             const value_type* __s = __ga.__vp_;
             for (_Ip __i = __ga.__1d_.__begin_, __e = __ga.__1d_.__end_;
                     __i != __e; ++__i, ++__end_)
                 ::new (__end_) value_type(__s[*__i]);
 #ifndef _LIBCPP_NO_EXCEPTIONS
         }
         catch (...)
         {
-            __clear();
+            __clear(__n);
             throw;
         }
 #endif  // _LIBCPP_NO_EXCEPTIONS
     }
 }
 
 template <class _Tp>
 valarray<_Tp>::valarray(const mask_array<value_type>& __ma)
     : __begin_(0),
       __end_(0)
 {
-    size_t __n = __ma.__1d_.size();
+    const size_t __n = __ma.__1d_.size();
     if (__n)
     {
         __begin_ = __end_ = static_cast<value_type*>(
            _VSTD::__libcpp_allocate(__n * sizeof(value_type), __alignof(value_type)));
 #ifndef _LIBCPP_NO_EXCEPTIONS
         try
         {
 #endif  // _LIBCPP_NO_EXCEPTIONS
             typedef const size_t* _Ip;
             const value_type* __s = __ma.__vp_;
             for (_Ip __i = __ma.__1d_.__begin_, __e = __ma.__1d_.__end_;
                     __i != __e; ++__i, ++__end_)
                 ::new (__end_) value_type(__s[*__i]);
 #ifndef _LIBCPP_NO_EXCEPTIONS
         }
         catch (...)
         {
-            __clear();
+            __clear(__n);
             throw;
         }
 #endif  // _LIBCPP_NO_EXCEPTIONS
     }
 }
 
 template <class _Tp>
 valarray<_Tp>::valarray(const indirect_array<value_type>& __ia)
     : __begin_(0),
       __end_(0)
 {
-    size_t __n = __ia.__1d_.size();
+    const size_t __n = __ia.__1d_.size();
     if (__n)
     {
         __begin_ = __end_ = static_cast<value_type*>(
            _VSTD::__libcpp_allocate(__n * sizeof(value_type), __alignof(value_type)));
 #ifndef _LIBCPP_NO_EXCEPTIONS
         try
         {
 #endif  // _LIBCPP_NO_EXCEPTIONS
             typedef const size_t* _Ip;
             const value_type* __s = __ia.__vp_;
             for (_Ip __i = __ia.__1d_.__begin_, __e = __ia.__1d_.__end_;
                     __i != __e; ++__i, ++__end_)
                 ::new (__end_) value_type(__s[*__i]);
 #ifndef _LIBCPP_NO_EXCEPTIONS
         }
         catch (...)
         {
-            __clear();
+            __clear(__n);
             throw;
         }
 #endif  // _LIBCPP_NO_EXCEPTIONS
     }
 }
 
 template <class _Tp>
 inline
 valarray<_Tp>::~valarray()
 {
-    __clear();
+    __clear(size());
 }
 
 template <class _Tp>
 valarray<_Tp>&
 valarray<_Tp>::__assign_range(const value_type* __f, const value_type* __l)
 {
     size_t __n = __l - __f;
     if (size() != __n)
     {
-        __clear();
+        __clear(size());
         __begin_ = static_cast<value_type*>(
            _VSTD::__libcpp_allocate(__n * sizeof(value_type), __alignof(value_type)));
         __end_ = __begin_ + __n;
         _VSTD::uninitialized_copy(__f, __l, __begin_);
     } else {
         _VSTD::copy(__f, __l, __begin_);
     }
     return *this;

 
 #ifndef _LIBCPP_CXX03_LANG
 
 template <class _Tp>
 inline
 valarray<_Tp>&
 valarray<_Tp>::operator=(valarray&& __v) _NOEXCEPT
 {
-    __clear();
+    __clear(size());
     __begin_ = __v.__begin_;
     __end_ = __v.__end_;
     __v.__begin_ = nullptr;
     __v.__end_ = nullptr;
     return *this;
 }
 
 template <class _Tp>

            _VSTD::__libcpp_allocate(__n * sizeof(value_type), __alignof(value_type)));
         for (const value_type* __p = __begin_; __n; ++__r.__end_, ++__p, --__n)
             ::new (__r.__end_) value_type(__f(*__p));
     }
     return __r;
 }
 
 template <class _Tp>
-void
-valarray<_Tp>::__clear()
+inline _LIBCPP_INLINE_VISIBILITY
+void valarray<_Tp>::__clear(size_t __capacity)
 {
-    if (__begin_ != nullptr)
-    {
-        while (__end_ != __begin_)
-            (--__end_)->~value_type();
-        _VSTD::__libcpp_deallocate(__begin_, __alignof(value_type));
-        __begin_ = __end_ = nullptr;
-    }
+    _VSTD::__libcpp_deallocate(__begin_, __capacity * sizeof(value_type), __alignof(value_type));
 }
 
 template <class _Tp>
 void
 valarray<_Tp>::resize(size_t __n, value_type __x)
 {
-    __clear();
+    __clear(size());
     if (__n)
     {
         __begin_ = __end_ = static_cast<value_type*>(
            _VSTD::__libcpp_allocate(__n * sizeof(value_type), __alignof(value_type)));
 #ifndef _LIBCPP_NO_EXCEPTIONS
         try
         {
 #endif  // _LIBCPP_NO_EXCEPTIONS
-            for (; __n; --__n, ++__end_)
+            for (size_t __n_left = __n; __n_left; --__n_left, ++__end_)
                 ::new (__end_) value_type(__x);
 #ifndef _LIBCPP_NO_EXCEPTIONS
         }
         catch (...)
         {
-            __clear();
+            __clear(__n);
             throw;
         }
 #endif  // _LIBCPP_NO_EXCEPTIONS
     }
 }
 
 template<class _Tp>
 inline _LIBCPP_INLINE_VISIBILITY

src/experimental/memory_resource.cpp

 {
 public:
     ~__new_delete_memory_resource_imp() = default;
 
 protected:
     virtual void* do_allocate(size_t __size, size_t __align)
         { return _VSTD::__libcpp_allocate(__size, __align); /* FIXME */}
 
-    virtual void do_deallocate(void * __p, size_t, size_t __align)
-        { _VSTD::__libcpp_deallocate(__p, __align); /* FIXME */ }
+    virtual void do_deallocate(void * __p, size_t __n, size_t __align)
+        { _VSTD::__libcpp_deallocate(__p, __n, __align); /* FIXME */ }
 
     virtual bool do_is_equal(memory_resource const & __other) const _NOEXCEPT
         { return &__other == this; }
 };
 
 // null_memory_resource()
 
 class _LIBCPP_TYPE_VIS __null_memory_resource_imp

test/libcxx/language.support/support.dynamic/libcpp_deallocate.sh.cpp

+//===----------------------------------------------------------------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is dual licensed under the MIT and the University of Illinois Open
+// Source Licenses. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+
+// test libc++'s implementation of align_val_t, and the relevent new/delete
+// overloads in all dialects when -faligned-allocation is present.
+
+// Libc++ defers to the underlying MSVC library to provide the new/delete
+// definitions, which does not yet provide aligned allocation
+// XFAIL: LIBCXX-WINDOWS-FIXME
+
+// XFAIL: with_system_cxx_lib=macosx10.12
+// XFAIL: with_system_cxx_lib=macosx10.11
+// XFAIL: with_system_cxx_lib=macosx10.10
+// XFAIL: with_system_cxx_lib=macosx10.9
+// XFAIL: with_system_cxx_lib=macosx10.7
+// XFAIL: with_system_cxx_lib=macosx10.8
+
+// RUN: %build -faligned-allocation -fsized-deallocation
+// RUN: %run
+// RUN: %build -faligned-allocation -fno-sized-deallocation -DNO_SIZE
+// RUN: %run
+// RUN: %build -fno-aligned-allocation -fsized-deallocation -DNO_ALIGN
+// RUN: %run
+// RUN: %build -fno-aligned-allocation -fno-sized-deallocation -DNO_ALIGN -DNO_SIZE
+// RUN: %run
+
+
+#include <new>
+#include <typeinfo>
+#include <string>
+#include <cassert>
+
+#include "test_macros.h"
+
+int aligned_sized_called = 0;
+int aligned_called = 0;
+int sized_called = 0;
+int plain_called = 0;
+int last_size = -1;
+int last_align = -1;
+
+void reset_state() {
+  aligned_sized_called = aligned_called = sized_called = plain_called = 0;
+  last_size = last_align = -1;
+}
+
+void operator delete(void *p) TEST_NOEXCEPT {
+  ::free(p);
+  ++plain_called;
+  last_size = last_align = -1;
+}
+
+void operator delete(void *p, size_t n) TEST_NOEXCEPT {
+  ::free(p);
+  ++sized_called;
+  last_size = n;
+  last_align = -1;
+}
+
+#ifndef NO_ALIGN
+void operator delete(void *p, std::align_val_t a) TEST_NOEXCEPT {
+  ::free(p);
+  ++aligned_called;
+  last_align = static_cast<int>(a);
+  last_size = -1;
+}
+
+void operator delete(void * p, size_t n, std::align_val_t a) TEST_NOEXCEPT {
+  ::free(p);
+  ++aligned_sized_called;
+  last_align = static_cast<int>(a);
+  last_size = n;
+}
+#endif
+
+bool expect_plain() {
+  assert(aligned_sized_called == 0);
+  assert(aligned_called == 0);
+  assert(sized_called == 0);
+  assert(last_size == -1);
+  assert(last_align == -1);
+  return plain_called == 1;
+}
+
+bool expect_size(int n) {
+  assert(plain_called == 0);
+  assert(aligned_sized_called == 0);
+  assert(aligned_called == 0);
+  assert(last_size == n);
+  assert(last_align == -1);
+  return sized_called == 1;
+}
+
+bool expect_align(int a) {
+  assert(plain_called == 0);
+  assert(aligned_sized_called == 0);
+  assert(sized_called == 0);
+  assert(last_size == -1);
+  assert(last_align == a);
+  return aligned_called == 1;
+}
+
+bool expect_size_align(int n, int a) {
+  assert(plain_called == 0);
+  assert(sized_called == 0);
+  assert(aligned_called == 0);
+  assert(last_size == n);
+  assert(last_align == a);
+  return aligned_sized_called == 1;
+}
+
+int main() {
+  void *p = nullptr;
+  size_t over_align_val = TEST_ALIGNOF(std::max_align_t) * 2;
+  size_t under_align_val = TEST_ALIGNOF(int);
+  size_t with_size_val = 2;
+
+  {
+    std::__libcpp_deallocate_unsized(p, under_align_val);
+    assert(expect_plain());
+  }
+  reset_state();
+
+#if defined(NO_SIZE) && defined(NO_ALIGN)
+  {
+    std::__libcpp_deallocate(p, with_size_val, over_align_val);
+    assert(expect_plain());
+  }
+  reset_state();
+#elif defined(NO_SIZE)
+  {
+    std::__libcpp_deallocate(p, with_size_val, over_align_val);
+    assert(expect_align(over_align_val));
+  }
+  reset_state();
+#elif defined(NO_ALIGN)
+  {
+    std::__libcpp_deallocate(p, with_size_val, over_align_val);
+    assert(expect_size(with_size_val));
+  }
+  reset_state();
+#else
+  {
+    std::__libcpp_deallocate(p, with_size_val, over_align_val);
+    assert(expect_size_align(with_size_val, over_align_val));
+  }
+  reset_state();
+  {
+    std::__libcpp_deallocate_unsized(p, over_align_val);
+    assert(expect_align(over_align_val));
+  }
+  reset_state();
+  {
+    std::__libcpp_deallocate(p, with_size_val, under_align_val);
+    assert(expect_size(with_size_val));
+  }
+  reset_state();
+#endif
+}