[PATCH] D53867: [libcxx] Implement http://wg21.link/p1006, constexpr in pointer_traits

[Louis Dionne via Phabricator]

ldionne created this revision.
ldionne added a reviewer: mclow.lists.
Herald added a reviewer: EricWF.
Herald added subscribers: libcxx-commits, dexonsmith, christof.

https://reviews.llvm.org/P1006 adds support for constexpr in the specialization of pointer_traits
for raw pointers. This is necessary in order to use pointer_traits in
the upcoming constexpr containers. We expect https://reviews.llvm.org/P1006 to be voted into the
working draft for C++20 at the San Diego meeting.


Repository:
  rCXX libc++

https://reviews.llvm.org/D53867

Files:
  libcxx/include/memory
  libcxx/test/std/utilities/memory/pointer.traits/pointer_to.pass.cpp


Index: libcxx/test/std/utilities/memory/pointer.traits/pointer_to.pass.cpp
===================================================================
--- libcxx/test/std/utilities/memory/pointer.traits/pointer_to.pass.cpp
+++ libcxx/test/std/utilities/memory/pointer.traits/pointer_to.pass.cpp
@@ -12,15 +12,18 @@
 // template <class T>
 // struct pointer_traits<T*>
 // {
-//     static pointer pointer_to(<details>);
+//     constexpr static pointer pointer_to(<details>);
 //     ...
 // };
 
 #include <memory>
 #include <cassert>
+#include "test_macros.h"
 
-int main()
-{
+#if TEST_STD_VER >= 20
+constexpr
+#endif
+bool check() {
     {
         int i = 0;
         static_assert((std::is_same<int *, decltype(std::pointer_traits<int*>::pointer_to(i))>::value), "");
@@ -30,4 +33,12 @@
     {
         (std::pointer_traits<void*>::element_type)0;
     }
+    return true;
+}
+
+int main() {
+    check();
+#if TEST_STD_VER >= 20
+    static_assert(check(), "");
+#endif
 }
Index: libcxx/include/memory
===================================================================
--- libcxx/include/memory
+++ libcxx/include/memory
@@ -43,7 +43,7 @@
 
     template <class U> using rebind = U*;
 
-    static pointer pointer_to(<details>) noexcept;
+    static constexpr pointer pointer_to(<details>) noexcept;
 };
 
 template <class T> constexpr T* to_address(T* p) noexcept; // C++20
@@ -984,7 +984,7 @@
 private:
     struct __nat {};
 public:
-    _LIBCPP_INLINE_VISIBILITY
+    _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX17
     static pointer pointer_to(typename conditional<is_void<element_type>::value,
                                       __nat, element_type>::type& __r) _NOEXCEPT
         {return _VSTD::addressof(__r);}


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