[Bug c++/94470] New: Constexpr variable initialization with self-modifying constructor incorrectly rejected since r7-6728

["ppalka at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94470

            Bug ID: 94470
           Summary: Constexpr variable initialization with self-modifying
                    constructor incorrectly rejected since r7-6728
           Product: gcc
           Version: 10.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: ppalka at gcc dot gnu.org
  Target Milestone: ---

$ cat testcase.C
struct X
{
  int b = 0;
  int c = ((this->b=1), 1);
};

constexpr X o = { };

static_assert(o.b == 1);

$ g++ -std=c++17 testcase.C
testcase.C:7:19: error: modification of ‘o’ is not a constant expression
 constexpr X o = { };
                   ^
testcase.C:9:19: error: non-constant condition for static assertion
 static_assert(o.b == 1);
               ~~~~^~~~