[Bug c++/115744] [C++26] P2747R2 - constexpr placement new

[jakub at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=115744

Jakub Jelinek <jakub at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
  Attachment #58563|0                           |1
        is obsolete|                            |
             Status|NEW                         |ASSIGNED
           Assignee|unassigned at gcc dot gnu.org      |jakub at gcc dot gnu.org

--- Comment #3 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
Created attachment 58580
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=58580&action=edit
gcc15-pr115744.patch

With the PR115754 change in, this seems mostly about the FTMs and making
placement new constexpr.
The only thing that doesn't work is the
new (p + 1) int[]{2, 3};      // error (in this paper)
case from the paper xfailed in the last testcase, the IL has there
<<< Unknown tree: expr_stmt
  (void) (TARGET_EXPR <D.2640, (void *) TARGET_EXPR <D.2641,
VIEW_CONVERT_EXPR<int *>(b) + 4>>, TARGET_EXPR <D.2642, operator new [] (8,
NON_LVALUE_EXPR <D.2640>)>,   int * D.2643;
  <<< Unknown tree: expr_stmt
    (void) (D.2643 = (int *) D.2642) >>>;
and so there is nothing that would trigger some error during constexpr
evaluation.
Shouldn't build_new_1 for maybe_constexpr_fn (current_function_decl) in the
array_p case add some extra cast to the array type it is looking for rather
than just the ultimate element type?