std::tuple chokes on final

[llvmbot]

Bugzilla Link	11461
Resolution	FIXED
Resolved on	Dec 11, 2011 14:31
Version	unspecified
OS	All
Reporter	LLVM Bugzilla Contributor

Extended Description

The following code does not compile:

#include

struct A final {};
struct B { virtual ~B() final; };

int main()
{
std::tuple x; // #​1
std::tuple y; // #​2
}

This currently happens because of a problem in std::is_empty<> that has been reported as bug #​11459. However even if we fix std::is_empty<>, only line #​2 will compile. Line #​1 will still trigger an error, because std::tuple will attempt to derive from the empty class type A, which is forbidden.

In order to fix the problem we should disable the empty base optimization for final classes. To achieve that, we need either an __is_final intrinsic or a (possibly library-only) trait to check if derivation from a type T is actually possible.

[llvmbot]

Suggested a possibile implementation of the __is_final intrinsic as bug #​11462.

[llvmbot]

Patch to tuple using the __is_final intrinsic

[llvmbot]

Fix Committed revision 146345.