This example crashes DMD from Git master when invoked with -g or -gc:
---
struct Foo {
  const(Foo)* bar;
}
Foo foo;
---
(the global is just necessary to trigger debug info generation for Foo).

What happens is that that for emitting debug info for const types, a copy of the type is made at https://github.com/D-Programming-Language/dmd/blob/master/src/backend/dwarf.c#L1571, thus breaking the TYforward loop detection mechanism.