[Bug c++/89766] [8 Regression] ICE: canonical types differ for identical types, -std=c++17

[rimvydas.jas at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=89766

--- Comment #10 from Rimvydas (RJ) <rimvydas.jas at gmail dot com> ---
Using 9.0.1 20190319 as reference several ICE cases reduce down to the same
snippet (regression on trunk)?
$ cat trunk_accepts_invalid.ii
class a {
  constexpr a();
};
template <class> struct b { static constexpr a c{}; };


Using different tactics other two (hopefully valid) testcases:
$ cat vcontract.ii
template <template <class> class a> struct b {
  template <class> static int c;
  using d = decltype(c<a>);
};
template <typename> struct e {
  template <typename a, typename> bool f() const;
  template <typename, typename> bool f(int) const;
};
$ cat vdefault.ii
template <typename, template <typename, typename> class> struct a;
template <template <typename, typename> class b> struct a<int, b>;
template <typename> struct c {
  template <typename b, typename, typename> bool operator()();
  template <typename, typename, typename d> bool operator()(d);
};