[Bug c++/122671] New: GCC fails to compile-time valid C++26 code using both constexpr placement new (P2747R2) and constexpr exceptions (P3068R6).

[mte.zych at gmail dot com via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=122671

            Bug ID: 122671
           Summary: GCC fails to compile-time valid C++26 code using both
                    constexpr placement new (P2747R2) and constexpr
                    exceptions (P3068R6).
           Product: gcc
           Version: 16.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: mte.zych at gmail dot com
  Target Milestone: ---

Hello!

GCC-16 does not compile the following C++26 code, which AFAIK is valid:

  #include <new>
  #include <memory>

  consteval auto func ()
  {
      struct error { };

      struct object
      {
          constexpr explicit object (int value)
          {
              if (value < 0) { throw error { }; }
          }
      };

      try
      {
          struct storage
          {
              object* ptr;

              constexpr storage ()
              : ptr { std::allocator<object> { }.allocate(1) } { }

              constexpr ~storage ()
              { std::allocator<object> { }.deallocate(ptr, 1); }
          };

          auto object_storage = storage { };

          ::new(object_storage.ptr) object { -1 };
      }
      catch (error&) { }

      return true;
  }

  static_assert(func());

Compiler Explorer link: https://godbolt.org/z/K5K86qWvM

To me this looks like a bug in GCC, which is occurring when
an object is being created at compile-time via placement new,
inside a try & catch block, and its constructor throws an exception.

Thank you, Mateusz Zych