[C++ PATCH, RFC] Implement new C++ intrinsics __is_assignable and __is_constructible.

[Jonathan Wakely]

On 17/05/17 15:15 +0300, Ville Voutilainen wrote:
>One more round. This patch doesn't change any of the compiler bits,
>but the llvm testsuite revealed
>that we didn't handle things like
>is_trivially_copy_constructible<void> properly, so I needed to adjust
>the library implementation of the triviality-traits. Now we pass the
>llvm testsuite for these traits,
>and this patch passes our full testsuite.
>
>Jonathan, ok for trunk?

Yes OK, thanks.

A few observations ...

>@@ -1405,45 +1185,95 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>   { };
>
>   /// is_trivially_copy_constructible
>+
>+  template<typename _Tp, bool = __is_referenceable<_Tp>::value>
>+    struct __is_trivially_copy_constructible_impl;
>+
>   template<typename _Tp>
>-    struct is_trivially_copy_constructible
>+    struct __is_trivially_copy_constructible_impl<_Tp, false>
>+    : public false_type { };
>+
>+  template<typename _Tp>
>+    struct __is_trivially_copy_constructible_impl<_Tp, true>
>     : public __and_<is_copy_constructible<_Tp>,
> 		    integral_constant<bool,
> 			__is_trivially_constructible(_Tp, const _Tp&)>>
>     { };

This could use __bool_constant, and there doesn't seem to be any
advantage to using __and_ here, because there's nothing to
short-circuit. So:

    : public __bool_constant<is_copy_constructible<_Tp>::value
		    && __is_trivially_constructible(_Tp, const _Tp&)>

But that was pre-existing, so let's deal with that
separately.

>+  template<typename _Tp>
>+    struct __is_trivially_move_constructible_impl<_Tp, true>
>     : public __and_<is_move_constructible<_Tp>,
> 		    integral_constant<bool,
> 			__is_trivially_constructible(_Tp, _Tp&&)>>
>     { };

Ditto.

>+  template<typename _Tp>
>+    struct __is_trivially_copy_assignable_impl<_Tp, true>
>     : public __and_<is_copy_assignable<_Tp>,
> 		    integral_constant<bool,
> 			__is_trivially_assignable(_Tp&, const _Tp&)>>
>     { };

Ditto.

>+  template<typename _Tp>
>+    struct __is_trivially_move_assignable_impl<_Tp, true>
>     : public __and_<is_move_assignable<_Tp>,
> 		    integral_constant<bool,
> 			__is_trivially_assignable(_Tp&, _Tp&&)>>

Ditto.