Created attachment 44129 [details]
(though not minimal) testcase

Compiling the attached program using `-std=c++11` with boost 1.66 results in an ICE:

```
E:\Desktop>g++ -std=c++11 test.cc
In file included from C:/MinGW/MSYS2/mingw32/include/boost/thread/detail/thread.hpp:23,
                 from C:/MinGW/MSYS2/mingw32/include/boost/thread/thread_only.hpp:22,
                 from C:/MinGW/MSYS2/mingw32/include/boost/thread/thread.hpp:12,
                 from C:/MinGW/MSYS2/mingw32/include/boost/thread.hpp:13,
                 from test.cc:1:
C:/MinGW/MSYS2/mingw32/include/boost/thread/detail/invoke.hpp: In function 'decltype (*(forward<A0>)(boost::detail::invoke::a0).*boost::detail::invoke::f) boost::detail::invoke(Fp&&, A0&&) [with Fp = void (A::*)(); A0 = A*]':
C:/MinGW/MSYS2/mingw32/include/boost/thread/detail/invoke.hpp:102:43: internal compiler error: in gimplify_expr, at gimplify.c:12188
         return (*boost::forward<A0>(a0)).*f;
                                           ^
Please submit a full bug report,
with preprocessed source if appropriate.
See <https://gcc-mcf.lhmouse.com/> for instructions.
```

This is confirmed to be the case on 5.4 (native and cross from Linux) and 8.1.1 (native).


Preprocessing the testcase results in such an enormous file (5+ MiB) that CReduce has been unable to reduce it at all (it resulted in a `}` only, which was apparently a bug).