[libcxx-commits] [libcxx] [libc++] Support sorting consteval-only ranges (PR #134623)

[A. Jiang via libcxx-commits]

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@@ -912,30 +900,63 @@ using __sort_is_specialized_in_library _LIBCPP_NODEBUG = __is_any_of<
     long double>;
 
 template <class _AlgPolicy, class _Type, __enable_if_t<__sort_is_specialized_in_library<_Type>::value, int> = 0>
-_LIBCPP_HIDE_FROM_ABI void __sort_dispatch(_Type* __first, _Type* __last, __less<>&) {
-  __less<_Type> __comp;
-  std::__sort<__less<_Type>&, _Type*>(__first, __last, __comp);
+_LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 void __sort_dispatch(_Type* __first, _Type* __last, __less<>&) {
+#if _LIBCPP_STD_VER >= 20
+  if (std::is_constant_evaluated()) {
+    auto __depth_limit = static_cast<ptrdiff_t>(2 * std::__bit_log2(static_cast<size_t>(__last - __first)));
+    std::__introsort<_ClassicAlgPolicy, ranges::less, _Type*, __use_branchless_sort<ranges::less, _Type*>>(
+        __first, __last, ranges::less{}, __depth_limit);
+  } else
+#endif
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frederick-vs-ja wrote:

Hmm, I think the changes here "fix" an ironic inconsistency.

Some functions needs to be `constexpr` to make instantiation `sort` involving consteval-only operations well-formed, while without these changes they are not even called in constant evaluation. If we keep these functions not called in constant evaluation, maybe someone will get confused and attempt to remove `constexpr` in the future.

https://github.com/llvm/llvm-project/pull/134623