[libcxx-commits] [libcxx] [libc++] Make forward_list constexpr as part of P3372R3 (PR #129435)

[Peng Liu via libcxx-commits]

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@@ -295,9 +295,12 @@ struct __forward_node_traits {
                 "the _LIBCPP_ABI_FORWARD_LIST_REMOVE_NODE_POINTER_UB macro to silence this diagnostic.");
 #  endif
 
-  _LIBCPP_HIDE_FROM_ABI static __begin_node_pointer __as_iter_node(__begin_node_pointer __p) { return __p; }
-  _LIBCPP_HIDE_FROM_ABI static __begin_node_pointer __as_iter_node(__node_pointer __p) {
-    return static_cast<__begin_node_pointer>(static_cast<__void_pointer>(__p));
+  _LIBCPP_CONSTEXPR_SINCE_CXX26 _LIBCPP_HIDE_FROM_ABI static __begin_node_pointer
+  __as_iter_node(__begin_node_pointer __p) {
+    return __p;
+  }
+  _LIBCPP_CONSTEXPR_SINCE_CXX26 _LIBCPP_HIDE_FROM_ABI static __begin_node_pointer __as_iter_node(__node_pointer __p) {
+    return std::__static_fancy_pointer_cast<__begin_node_pointer>(__p);
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winner245 wrote:

The old version fails in constant evaluation. I fixed it without resorting to the `void*` pointer. Given that the redundant `__as_iter_node` identity cast has already been fixed for `forward_list`, is there anything else that needs to be addressed before this patch is landed? I've just rebased the patch to resolve conflicts due to the removal of `__as_iter_node`.

https://github.com/llvm/llvm-project/pull/129435