[libcxx-commits] [libcxx] [libc++] P3450R1: Extend `std::is_within_lifetime` (PR #201053)

[Hristo Hristov via libcxx-commits]

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@@ -18,9 +18,9 @@
 _LIBCPP_BEGIN_NAMESPACE_STD
 
 #if _LIBCPP_STD_VER >= 26 && __has_builtin(__builtin_is_within_lifetime)
-template <class _Tp>
+template <class _Up = void, class _Tp>
 [[nodiscard]] _LIBCPP_HIDE_FROM_ABI consteval bool is_within_lifetime(const _Tp* __p) noexcept {
-  return __builtin_is_within_lifetime(__p);
+  return __builtin_is_within_lifetime(__p) && __builtin_constant_p(static_cast<const volatile _Up*>(__p) && true);
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Zingam wrote:

Wouldn't it be better to use this implementation as a temporary workaround and to update the builtin itself to provide the updated functionality?
Are there any other uses for `__builtin_is_within_lifetime` that require just the initial functionality? I'd find it strange that the builtin with the same name as std::is_within_lifetime supports just some of it. Does my question make any sense or is it a stupid one?

https://github.com/llvm/llvm-project/pull/201053