https://gcc.gnu.org/bugzilla/show_bug.cgi?id=81933
Bug ID: 81933
Summary: [7 Regression] Invalid "constexpr call flows off the
end of the function" error
Product: gcc
Version: 7.2.1
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: ldionne.2 at gmail dot com
Target Milestone: ---
The following code does not compile with GCC 7, std=c++14:
----------------------------------------------------------------------------
#include <tuple>
struct any_udt { };
template <typename ...Tuples>
constexpr auto flatten(Tuples ...tuples) {
auto all = std::make_tuple(tuples...);
auto flat = std::make_tuple(
std::get<0>(std::get<1>(all)),
std::get<0>(std::get<2>(all))
);
return flat;
}
constexpr auto fail = ::flatten(std::make_tuple(),
std::make_tuple(any_udt{}),
std::make_tuple(any_udt{}));
int main() { }
----------------------------------------------------------------------------
It triggers the following error:
foo.cpp:17:59: in constexpr expansion of 'flatten(Tuples ...)
[with Tuples = {std::tuple<>, std::tuple<any_udt>, std::tuple<any_udt>}]
(std::make_tuple(_Elements&& ...) [with _Elements = {any_udt}](),
std::make_tuple(_Elements&& ...) [with _Elements = {any_udt}]())'
foo.cpp:17:59: error: constexpr call flows off the end of the function
std::make_tuple(any_udt{}));
^
Note that the code compiles just fine with GCC 6 and all Clang versions I've
tried, so this looks like a 7 regression.
Working example (GCC 6.3.0, -std=c++14):
https://wandbox.org/permlink/5AjQ50OSxNjJPP8r
Working example (GCC 6.3.0, -std=c++1z):
https://wandbox.org/permlink/dKegxu0QeVXtzObB
Failing example (GCC 7.2.0, -std=c++14):
https://wandbox.org/permlink/hfbI0Ndg5UyCIF9W
Working example (GCC 7.2.0, -std=c++1z):
https://wandbox.org/permlink/Hz1gm6EipU5Ej5jy
Failing example (GCC 8.0.0, -std=c++14):
https://wandbox.org/permlink/jSHOPt8zXosccp8a
Working example (GCC 8.0.0, -std=c++1z):
https://wandbox.org/permlink/Nj7tNIYWu8Ueury7
