[libcxx-commits] [libcxx] [libc++] Optimize vector::__move_range for trivially copyable types (PR #207384)

[Louis Dionne via libcxx-commits]

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@@ -1120,14 +1122,26 @@ _LIBCPP_CONSTEXPR_SINCE_CXX20 void
 vector<_Tp, _Allocator>::__move_range(pointer __from_s, pointer __from_e, pointer __to) {
   pointer __old_last  = __layout_.__end_ptr();
   difference_type __n = __old_last - __to;
+#ifndef _LIBCPP_CXX03_LANG
+  if constexpr (__allocator_has_trivial_move_construct_v<allocator_type, value_type> &&
+                is_trivially_copyable<value_type>::value) {
+    if (__libcpp_is_constant_evaluated()) // construct the new trailing objects
+      std::uninitialized_fill_n(__old_last, (__from_e - __from_s) - __n, *__from_s);
+    std::__constexpr_memmove(
+        std::__to_address(__to), std::__to_address(__from_s), __element_count(__from_e - __from_s));
+    __layout_.__set_bound_using_pointer(__to + (__from_e - __from_s));
+  } else
+#endif
   {
-    pointer __i = __from_s + __n;
-    _ConstructTransaction __tx(*this, __from_e - __i);
-    for (pointer __pos = __tx.__pos_; __i < __from_e; ++__i, (void)++__pos, __tx.__pos_ = __pos) {
-      __alloc_traits::construct(this->__layout_.__alloc(), std::__to_address(__pos), std::move(*__i));
+    {
+      pointer __i = __from_s + __n;
+      _ConstructTransaction __tx(*this, __from_e - __i);
+      for (pointer __pos = __tx.__pos_; __i < __from_e; ++__i, (void)++__pos, __tx.__pos_ = __pos) {
+        __alloc_traits::construct(this->__layout_.__alloc(), std::__to_address(__pos), std::move(*__i));
+      }
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ldionne wrote:

This could be `__uninitialized_allocator_move`, I think.

https://github.com/llvm/llvm-project/pull/207384