[libcxx-commits] [libcxx] [libc++] Optimize vector growing of trivially relocatable types (PR #76657)

[Mark de Wever via libcxx-commits]

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@@ -646,6 +647,25 @@ __uninitialized_allocator_move_if_noexcept(_Alloc&, _Iter1 __first1, _Iter1 __la
 }
 #endif // _LIBCPP_COMPILER_GCC
 
+template <class _Alloc, class _Tp>
+struct __allocator_has_trivial_destroy : _Not<__has_destroy<_Alloc, _Tp*>> {};
+
+template <class _Tp, class _Up>
+struct __allocator_has_trivial_destroy<allocator<_Tp>, _Up> : true_type {};
+
+template <class _Alloc, class _Tp>
+_LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14 void
+__uninitialized_allocator_relocate(_Alloc& __alloc, _Tp* __first, _Tp* __last, _Tp* __out) {
+  if (__libcpp_is_constant_evaluated() || !__libcpp_is_trivially_relocatable<_Tp>::value ||
+      !__allocator_has_trivial_move_construct<_Alloc, _Tp>::value ||
+      !__allocator_has_trivial_destroy<_Alloc, _Tp>::value) {
+    std::__uninitialized_allocator_move_if_noexcept(__alloc, __first, __last, __out);
+    std::__allocator_destroy(__alloc, __first, __last);
+  } else {
+    __builtin_memcpy(__out, __first, sizeof(_Tp) * (__last - __first));
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mordante wrote:

doesn't `std::copy` do the same.

Note: I'm quite sure `__out` is a nasty macro.

https://github.com/llvm/llvm-project/pull/76657