llvm-project

859c550e - [libc++] Require the exact assignment expression to be trivial in __uninitialized_allocator_copy_impl (#196648)

[libc++] Require the exact assignment expression to be trivial in __uninitialized_allocator_copy_impl (#196648) Fixes https://github.com/llvm/llvm-project/issues/196645 `__uninitialized_allocator_copy_impl` has an optimization that replaces `allocator_traits::construct` with `std::copy` for raw pointer ranges when the element type is trivially copy constructible and trivially copy assignable. The copy-assignment trait only checks whether assignment from `const T&` is trivial. That is weaker than the expression used by `std::copy`, which evaluates `*out = *in`. If overload resolution selects a different non-trivial assignment operator for that expression, `std::copy` can call that operator on uninitialized storage. Check `is_trivially_assignable<_Out&, _In&>` instead. This matches the assignment expression used by `std::copy`, preserves the optimized path when that assignment is actually trivial, and avoids making non-const raw pointer callers select the generic `allocator_traits::construct` overload due to a qualification conversion. Add a vector copy-constructor regression test with a type whose defaulted copy assignment is trivial but whose templated assignment operator is selected for non-const lvalue sources.