[Bug c++/56991] New: constexpr std::initializer_list crashes on too complex initialization

[morwenn29 at hotmail dot fr]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56991



             Bug #: 56991

           Summary: constexpr std::initializer_list crashes on too complex

                    initialization

    Classification: Unclassified

           Product: gcc

           Version: 4.8.0

            Status: UNCONFIRMED

          Severity: normal

          Priority: P3

         Component: c++

        AssignedTo: unassig...@gcc.gnu.org

        ReportedBy: morwen...@hotmail.fr





I found some strange behaviour that, after a discussion on StackOverflow, seems

to be a bug (discussion here:

http://stackoverflow.com/questions/16057690/confusion-about-constant-expressions/16068953?noredirect=1#16068953).



It seems that GCC implements N3471 which means that every function of an

std::initializer_list are constexpr. When trying to pass simple constexpr

things in the initializer_list, it works fine:



#include <array>

#include <initializer_list>



int main()

{

    constexpr std::array<int, 3> a = {{ 1, 2, 3 }};

    constexpr int a0 = a[0];

    constexpr int a1 = a[1];

    constexpr int a2 = a[2];

    constexpr std::initializer_list<int> b = { a0, a1, a2 };



    return 0;

}



However, without the intermediate variables a0, a1 and a2, the example above

crashes:



#include <array>

#include <initializer_list>



int main()

{

    constexpr std::array<int, 3> a = {{ 1, 2, 3 }};

    constexpr std::initializer_list<int> b = { a[0], a[1], a[2] };



    return 0;

}



The error is the following one:



error: 'const std::initializer_list<int>{((const int*)(&<anonymous>)), 3u}' is

not a constant expression



This last example works fine if I remove the constexpr qualifier at the

beginning of the line or if I replace the initializer_list by a std::array. It

seems that the bug is only triggered when using std::initializer_list with

constexpr.