[libcxx-commits] [libcxx] [libc++][C++26] P2562R1: `constexpr` Stable Sorting (PR #110320)

[A. Jiang via libcxx-commits]

================
@@ -83,30 +106,35 @@ _LIBCPP_HIDE_FROM_ABI void __merge_move_construct(
   for (; true; ++__result) {
     if (__first1 == __last1) {
       for (; __first2 != __last2; ++__first2, (void)++__result, __d.template __incr<value_type>())
-        ::new ((void*)__result) value_type(_Ops::__iter_move(__first2));
+        __STABLE_SORT_NEW(__result, value_type, _Ops::__iter_move, __first2);
       __h.release();
       return;
     }
     if (__first2 == __last2) {
       for (; __first1 != __last1; ++__first1, (void)++__result, __d.template __incr<value_type>())
-        ::new ((void*)__result) value_type(_Ops::__iter_move(__first1));
+        __STABLE_SORT_NEW(__result, value_type, _Ops::__iter_move, __first1);
       __h.release();
       return;
     }
     if (__comp(*__first2, *__first1)) {
-      ::new ((void*)__result) value_type(_Ops::__iter_move(__first2));
+      __STABLE_SORT_NEW(__result, value_type, _Ops::__iter_move, __first2);
       __d.template __incr<value_type>();
       ++__first2;
     } else {
-      ::new ((void*)__result) value_type(_Ops::__iter_move(__first1));
+// __STABLE_SORT_NEW(__result, value_type, _Ops::__iter_move, __first1);
+#if !defined(__clang__) && defined(__GNUC__) && (__GNUC__ * 10000 + __GNUC_MINOR__ * 100 <= 140100)
+      [__result, &__first1] { ::new (__result) value_type(_Ops::__iter_move(__first1)); }();
+#else
+      ::new (__result) value_type(_Ops::__iter_move(__first1));
----------------
frederick-vs-ja wrote:

We still need to cast to `void*` to select the correct `operator new` overload.

```suggestion
      [__result, &__first1] { ::new ((void*)__result) value_type(_Ops::__iter_move(__first1)); }();
#else
      ::new ((void*)__result) value_type(_Ops::__iter_move(__first1));
```

Or perhaps we might need to use `std::construct` as the fallback. (I hope this is not the case, because `std::construct` breaks guaranteed copy elision.)

https://github.com/llvm/llvm-project/pull/110320