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: [email protected]
ReportedBy: [email protected]
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.
