[Bug c++/87904] New: [9 Regression] ICE in lookup_mark, at cp/tree.c:2322 since r265679

[marxin at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=87904

            Bug ID: 87904
           Summary: [9 Regression] ICE in lookup_mark, at cp/tree.c:2322
                    since r265679
           Product: gcc
           Version: 9.0
            Status: UNCONFIRMED
          Keywords: ice-on-valid-code
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: marxin at gcc dot gnu.org
                CC: nathan at gcc dot gnu.org
  Target Milestone: ---

Reduced test-case:

$ cat filer.ii
struct a {};
namespace {
void operator<<(a, int) {};
}
struct b {
  friend a &operator<<(a &, const b &);
};
using ::operator<<;
void operator<<(a, b);

a &operator<<(a &c, const b &) {
  c << 123;
}