[Bug c++/71368] New: [concepts] ICE on constrained compound requirement

["lucdanton at free dot fr" <gcc-bugzilla at gcc dot gnu dot org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=71368

            Bug ID: 71368
           Summary: [concepts] ICE on constrained compound requirement
           Product: gcc
           Version: 6.1.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: lucdanton at free dot fr
  Target Milestone: ---

The following produces an ICE on both GCC 6.1 and trunk (rev. 236974):

$ cat main.cpp
struct inner;

template<typename X> concept bool CompoundReq = requires {
    // fine with concrete type in trailing type, i.e. inner& instead of X&
    { X::inner_member() } -> X&;
};

template<typename X> concept bool Concept = requires {
    { X::outer_member() } -> CompoundReq;
};

struct inner { static inner& inner_member(); };
struct outer { static inner outer_member(); };

int main()
{
    // fine
    static_assert( CompoundReq<inner> );
    static_assert( CompoundReq<decltype( outer::outer_member() )> );

    // ICE
    static_assert( Concept<outer> );
}
$ g++-trunk -std=c++1z -fconcepts main.cpp
g++-trunk: internal compiler error: Segmentation fault (program cc1plus)