[Bug c++/70111] New: Internal compiler error on constant enum access

["tomasz at tomaszklak dot pl" <gcc-bugzilla at gcc dot gnu dot org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=70111

            Bug ID: 70111
           Summary: Internal compiler error on constant enum access
           Product: gcc
           Version: 5.2.1
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: tomasz at tomaszklak dot pl
  Target Milestone: ---

Created attachment 37881
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=37881&action=edit
example

The following code fails to compile with "internal compiler error: Segmentation
fault (program cc1plus)" with command "g++ -std=c++11 -Wall -Wextra -pedantic
-ftemplate-depth=100000 gccbug.cc"

struct Zero { enum { value = 0 }; };

template <typename Nat>
struct Next { enum { value = 1 + Nat::value }; };

using One   = Next<Zero>;
using Two   = Next<One>;
using Three = Next<Two>;

template <typename Lhs, typename Rhs>
struct Add;

template <typename Rhs>
struct Add<Zero, Rhs>
{
    using type = Rhs;
};

template <typename Lhs, typename Rhs>
struct Add<Next<Lhs>, Rhs>
{
    using type = Next<typename Add<Lhs, Rhs>::type>;
};

using Five = typename Add<Three, Two>::type;
using Six = typename Add<Three, Three>::type;
using v12 = typename Add<Six, Six>::type;
using v18 = typename Add<v12, Six>::type;
using v23 = typename Add<v18, Five>::type;
using v24 = typename Add<v12, v12>::type;

template <typename N>
struct Fib;

template<>
struct Fib<One> { using type = One; };

template<>
struct Fib<Two> { using type = One; };

template<typename Prev>
struct Fib<Next<Next<Prev>>> {
    using type = typename Add<
        typename Fib<Next<Prev>>::type,
        typename Fib<Prev>::type>::type;
};

int main() {
    // This compiles:
    // using fib = typename Fib<v23>::type;
    using fib = typename Fib<v24>::type;
    (void) fib::value;
}

replacing fib assigment to Fib<v23> works fine. Similar behaviour is seen on
5.3.0 - https://goo.gl/rD2zy1