[Bug c++/81957] New: ICE decltype

["roland at rschulz dot eu" <gcc-bugzilla at gcc dot gnu dot org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=81957

            Bug ID: 81957
           Summary: ICE decltype
           Product: gcc
           Version: 7.2.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: roland at rschulz dot eu
  Target Milestone: ---

#include <type_traits>

struct f {
    template<bool b, typename Int>
    void operator()(std::integral_constant<bool,b>, Int i) {
    }
};

template<bool...Bs, typename F, typename ...T>
auto dispatch(F f, T...t) -> decltype(f(std::integral_constant<bool,Bs>()...,
t...)) {
    return f(std::integral_constant<bool,Bs>()..., t...);
}

template<bool...Bs, typename F, typename ...T>
auto dispatch(F f, bool b, T...t) -> decltype(dispatch<Bs..., true>(f, t...)) {
    if (b)
        return dispatch<Bs..., true>(f, t...);
    else
        return dispatch<Bs..., false>(f, t...);
}

int main() {
    dispatch(f(), true, 5);
    return 0;
}

gives:
Internal compiler error: Error reporting routines re-entered.

Without the 2nd decltype (either using void or no return type specification) it
compiles fine.

The problem is present in all supported GCC versions.