[Bug c++/85438] New: [8 Regression] invalid "a reinterpret_cast is not a constant expression" diagnostics since r249088

[jakub at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=85438

            Bug ID: 85438
           Summary: [8 Regression] invalid "a reinterpret_cast is not a
                    constant expression" diagnostics since r249088
           Product: gcc
           Version: 8.0
            Status: UNCONFIRMED
          Keywords: accepts-invalid
          Severity: minor
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: jakub at gcc dot gnu.org
                CC: daniel.kruegler at googlemail dot com, jakub at gcc dot 
gnu.org,
                    jason at gcc dot gnu.org, msebor at gcc dot gnu.org,
                    unassigned at gcc dot gnu.org, webrown.cpp at gmail dot com
        Depends on: 70248
            Blocks: 55004
  Target Milestone: ---

+++ This bug was initially created as a clone of Bug #70248 +++

struct A {};
struct B : A { int x; };
constexpr int A::*bx = (int(A::*))&B::x;

is rejected since r249088 with:
pr70248-2.C:3:24: error: a reinterpret_cast is not a constant expression
 constexpr int A::*bx = (int(A::*))&B::x;
                        ^~~~~~~~~~~~~


Referenced Bugs:

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=55004
[Bug 55004] [meta-bug] constexpr issues
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=70248
[Bug 70248] constexpr initialization with unspecified equality expression
accepted