[Bug c++/78488] New: ICE when building call to inherited default constructor.

["eric at efcs dot ca" <gcc-bugzilla at gcc dot gnu dot org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=78488

            Bug ID: 78488
           Summary: ICE when building call to inherited default
                    constructor.
           Product: gcc
           Version: 7.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: eric at efcs dot ca
  Target Milestone: ---

GCC ICE's when default initializing a type T when T's default constructor is an
inherited constructor. Note that this only happens when T doesn't define its
own default ctor, either implicitly or explicitly.

The below reproducer is rejected by GCC 5.3 and earlier. GCC 6 exits with
status 1 and without producing any diagnostics or an output file, and GCC 7
segfaults.

Reproducer: 

// g++ -std=c++1z test.cpp
struct Foo { Foo() {} };

struct Bar : Foo {
  using Foo::Foo;
  Bar(void*); // Define another constructor so Foo() isn't generated.
};

int main() {
 Bar f;
}