[Bug c++/70377] New: "unexpected AST" and "confused by earlier errors, bailing out" from throw in simple constexpr fn

[TonyELewis at hotmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=70377

            Bug ID: 70377
           Summary: "unexpected AST" and "confused by earlier errors,
                    bailing out" from throw in simple constexpr fn
           Product: gcc
           Version: unknown
            Status: UNCONFIRMED
          Severity: major
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: TonyELewis at hotmail dot com
  Target Milestone: ---

Compiling this code:


#include <array>
#include <cstddef>
#include <exception>

template <std::size_t N>
constexpr size_t simple_find(const std::array<int, N> &arg_array,
                             const int                &arg_value
                             ) {
        for (size_t ctr = 0; ctr != N; ++ctr) {
                if ( arg_array[ ctr ] == arg_value ) {
                        return ctr;
                }
        }
        throw std::out_of_range( "" );
}

static constexpr std::array<int, 3> some_ints { { 10, 11 } };

static_assert( simple_find( some_ints, 10 ) == static_cast<size_t>( 0 ), "" );
static_assert( simple_find( some_ints, 11 ) == static_cast<size_t>( 1 ), "" );

int main() { }


...under -std=c++14 gives:


a.cpp:19:1: error: non-constant condition for static assertion
 static_assert( simple_find( some_ints, 10 ) == static_cast<size_t>( 0 ), "" );
 ^
a.cpp:19:27: error: ‘constexpr size_t simple_find(const std::array<int, N>&,
const int&) [with long unsigned int N = 3ul; size_t = long unsigned int]’
called in a constant expression
 static_assert( simple_find( some_ints, 10 ) == static_cast<size_t>( 0 ), "" );
                           ^
a.cpp:6:18: note: ‘constexpr size_t simple_find(const std::array<int, N>&,
const int&) [with long unsigned int N = 3ul; size_t = long unsigned int]’ is
not usable as a constexpr function because:
 constexpr size_t simple_find(const std::array<int, N> &arg_array,
                  ^
a.cpp:6:18: sorry, unimplemented: unexpected AST of kind loop_expr
a.cpp:6: confused by earlier errors, bailing out


I think the code is valid C++14. Even if not, I doubt you want the errors seen
above.

The code compiles cleanly if the throw statement is replaced with 'return 0;'.

I'm seeing this issue on g++ (Ubuntu 5.2.1-22ubuntu2) 5.2.1 20151010. I've also
tried it on http://melpon.org/wandbox and I think the issue is still there on a
recent 6.0.0 HEAD.

Thanks very much.