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Implement sized deallocation for std::allocator and friends.

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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.

Reviewers: ldionne, mclow.lists

Reviewed By: ldionne

Subscribers: rsmith, ckennelly, libcxx-commits, christof

Differential Revision: https://reviews.llvm.org/D53120

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@345214 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Eric Fiselier
2018-10-24 22:44:01 +00:00
parent 842383f69c
commit 0cfdf55219
6 changed files with 378 additions and 56 deletions
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4
include/__sso_allocator
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@@ -57,12 +57,12 @@ public:
}
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);}