[Bug c++/71092] [6/7 Regression] ICE: in cxx_eval_call_expression, at cp/constexpr.c:1449; only with -Os

["trippels at gcc dot gnu.org" <gcc-bugzilla at gcc dot gnu dot org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=71092

--- Comment #5 from Markus Trippelsdorf <trippels at gcc dot gnu.org> ---
(In reply to schoko.teddy from comment #3)
> Created attachment 38494 [details]
> Preprocessed source
> 
> This Error occurs while compiling this motioncontrollayer.cpp file from a Qt
> project. Gzipped because of largeness.

Looks like a ICE on invalid and is probably unrelated to the original issue:

markus@x4 tmp % cat motioncontrollayer.ii
namespace std {
template <typename _Tp> struct A { static constexpr _Tp value = 0; };
typedef A<bool> false_type;
struct B : false_type {};
template <typename> struct is_floating_point : B {};
template <int, typename> struct enable_if { typedef int type; };
}
typedef int Value;
namespace detail {
template <typename T, std::enable_if<std::is_floating_point<Value>::value,
                                     bool>::type = false>
constexpr Value toValue(T) {}
}
struct Quantity {
  template <typename T> constexpr Quantity(T) : value(detail::toValue(0)) {}
  Value value;
};
struct Pose {
  int x;
  int y;
  Quantity phi;
  constexpr Pose() : x(), y(), phi(0) {}
};
struct C {
  Pose pose;
};
struct D {
  Pose route[1];
};
void fn1() { C obj; }
void fn2() { D obj; }

markus@x4 tmp % clang++ -std=c++14 -ferror-limit=1 -c motioncontrollayer.ii
motioncontrollayer.ii:12:17: error: no return statement in constexpr function
constexpr Value toValue(T) {}
                ^
fatal error: too many errors emitted, stopping now [-ferror-limit=]
2 errors generated.

markus@x4 tmp % icpc -std=c++14 -c motioncontrollayer.ii
motioncontrollayer.ii(12): error: missing return statement at end of non-void
function "detail::toValue(T)"
  constexpr Value toValue(T) {}
                              ^
          detected during instantiation of "Quantity::Quantity(T) [with T=int]"
at line 22

compilation aborted for motioncontrollayer.ii (code 2)

markus@x4 tmp % g++ -c motioncontrollayer.ii
motioncontrollayer.ii: In constructor âconstexpr D::D()â:
motioncontrollayer.ii:27:8:   in constexpr expansion of âPose()â
motioncontrollayer.ii:22:37:   in constexpr expansion of
â((Pose*)this)->Pose::phi.Quantity::Quantity<int>(0)â
motioncontrollayer.ii:15:70:   in constexpr expansion of âdetail::toValue<int,
0>(0)â
motioncontrollayer.ii:27:8: internal compiler error: in
cxx_eval_call_expression, at cp/constexpr.c:1449