[Bug libgcc/79982] New: Compiler crashes when using illegal concepts (nested requirements)

[gcc.bugzilla at cpockrandt dot de]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=79982

            Bug ID: 79982
           Summary: Compiler crashes when using illegal concepts (nested
                    requirements)
           Product: gcc
           Version: unknown
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: libgcc
          Assignee: unassigned at gcc dot gnu.org
          Reporter: gcc.bugzilla at cpockrandt dot de
  Target Milestone: ---

Created attachment 40939
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=40939&action=edit
output when compiler crashes

I'm using the latest snapshot of g++-7 (7-20170305) and compile with
"-fconcepts -std=c++17". When using nested requirements with "auto" or when the
type inside the requirements is not known, the compiler crashes.

template <typename T>
concept bool my_concept = requires(T t)
{
    requires requires (int val) { { t.serialize(val) } -> void; };
};

class my_class
{
    void serialize(int);
};

static_assert(my_concept<my_class>);

The compiler *also* crashes with this line of code (not sure whether it's
actually illegal code or not)

requires requires (T t, auto val) { { t.serialize(val) } -> void; };

Complete crash output and both code samples are attached.