[Bug c++/93955] New: detect conversion from pointer type to arithmetic type in constexpr

[mpolacek at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=93955

            Bug ID: 93955
           Summary: detect conversion from pointer type to arithmetic type
                    in constexpr
           Product: gcc
           Version: 10.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: mpolacek at gcc dot gnu.org
  Target Milestone: ---

constexpr long int
foo ()
{
  return (long int) "foo"
#ifdef FOO
    - 1
#endif
    ;
}

constexpr long int l = foo ();

is currently accepted with -DFOO but rejected otherwise.  It should be rejected
even in the -DFOO case: converting a pointer to an integral type must be done
via a reinterpret_cast and that can't be part of a core constant expression.