[Bug c++/47300] New: [C++0x] ICE: in decl_constant_var_p, at cp/decl2.c:3564 when using incomplete type as constexpr

["zsojka at seznam dot cz" <gcc-bugzilla at gcc dot gnu dot org>]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=47300

           Summary: [C++0x] ICE: in decl_constant_var_p, at
                    cp/decl2.c:3564 when using incomplete type as
                    constexpr
           Product: gcc
           Version: 4.6.0
            Status: UNCONFIRMED
          Severity: minor
          Priority: P3
         Component: c++
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: zsojka@seznam.cz
              Host: x86_64-pc-linux-gnu
            Target: x86_64-pc-linux-gnu


Created attachment 22968
  --> http://gcc.gnu.org/bugzilla/attachment.cgi?id=22968
reduced testcase

Compiler output:
$ gcc -std=c++0x testcase.C 
testcase.C:6:30: error: invalid use of incomplete type 'struct A'
testcase.C:1:8: error: forward declaration of 'struct A'
testcase.C:6:30: error: 'A::B<<anonymous> >::a' has incomplete type
testcase.C:7:12: internal compiler error: in decl_constant_var_p, at
cp/decl2.c:3564
Please submit a full bug report,
with preprocessed source if appropriate.
See <http://gcc.gnu.org/bugs.html> for instructions.

Tested revisions:
r168785 - crash