is_convertible with 16-byte aligned types causes errors on MSVC

[Mathias Gaunard]

This appears to be caused by passing those types by value to functions, as is done by "...". MSVC doesn't allow types with alignment higher than that of the stack to be passed by value to functions.

The fix would involve forcing everything to be references somehow.

Testcase:

#include <boost/type_traits/is_convertible.hpp>

struct A
{
    __declspec(align(16)) int value;
};

struct B
{
};

typedef boost::is_convertible<A, B>::type C;

[Mathias Gaunard]

It doesn't really seem fixable within the field of portable C++03, so I see three solutions:

• use std::is_convertible or std::tr1::is_convertible if either is available
• use the __is_convertible_to built-in on MSVC (available since 7.1)
• use SFINAE extended to expressions, if available, to implement this trait without passing by value to a function

Solution number 2 seems to be the easiest one for a quick fix, and the one most MSVC versions will be able to benefit from.

[John Maddock]

(In [69822]) Change is_convertible to use C++0x behaviour where possible. Change is_converible to use MSVC is_convertible intrinsic. Fixes #5271. Fixes #4530.