[libc++] Temporarily not use compiler intrinsics for some type traits in Objective-C++ mode.

[var-const]

Summary

Currently, there are bugs in Clang's intrinsics for type traits when
handling Objective-C++ id (e.g. in add_pointer). As a temporary
workaround, don't use these intrinsics in the Objective-C++ mode.

[var-const]

Add __libcpp_is_referenceable test

[ldionne]

libcxx/include/__config

1265

You'll need to clang-format this bit

1265

Let's rename this to e.g. _LIBCPP_WORKAROUND_OBJCXX_COMPILER_INTRINSICS -- this is going to be really short lived until Clang is fixed.

libcxx/include/__type_traits/remove_volatile.h

20 ↗

(On Diff #501972)

All type traits that work fine with the intrinsics should keep using the intrinsics IMO. I think we only need to carve out __remove_pointer and` __add_pointer` for now.

libcxx/test/std/utilities/meta/meta.trans/objc_support.pass.mm

66

66–67

We should also test that !is_same<remove_ptr<id>::type, id>. Otherwise, people could get ambiguous overloads (for instance).

68

Let's also add a test like this:

static_assert(std::is_same<std::add_pointer<std::remove_pointer<id>::type>::type, id>::value, "");
static_assert(std::is_same<std::remove_pointer<std::add_pointer<id>::type>::type, id>::value, ""); // this one is kinda paranoid, but just to be sure

[var-const]

Only disable the known bad intrinsics.

[var-const]

Properly invert the condition.

[ldionne]

LGTM, thanks. Please land when the CI is green!

[philnik]

libcxx/include/__config

1262

FWIW I'd just drop the name from TODOs. If you want to know who wrote it you can just look at the git blame, so I don't really see an upside. They will just get out of date as people stop working on libc++. (We still have a few TODO(EricWF) in the code base and I have the feeling he won't resolve them.)

libcxx/test/std/utilities/meta/meta.trans/objc_support.pass.mm

101–103

Maybe make this a .compile.pass.mm instead? Or do we not have that?

[var-const]

libcxx/include/__config

1262

Personally, I find it useful. "TODO(name)" just means "'name' is the best person to ask about this issue", not "'name' is the person who will necessarily fix this issue". It's true that you can find it via blame, but a) it saves a context switch; and b) it's robust to copy-pasting, moving code between files, etc., all at essentially no cost. I find TODO(EricWF) useful regardless of whether Eric will work on those issues or not.

libcxx/test/std/utilities/meta/meta.trans/objc_support.pass.mm

101–103

It doesn't work -- the linker complains about missing _main.

[ldionne]

libcxx/test/std/utilities/meta/meta.trans/objc_support.pass.mm

101–103

See D145193. Once this lands and D145193 lands, I'll change it.

[var-const]

Fix the CI.

libcxx/include/__config

 #if _LIBCPP_STD_VER >= 17
 #    define _LIBCPP_CTAD_SUPPORTED_FOR_TYPE(_ClassName)                                                                \
       template <class ..._Tag>                                                                                         \
       _ClassName(typename _Tag::__allow_ctad...) -> _ClassName<_Tag...>
 #else
 #  define _LIBCPP_CTAD_SUPPORTED_FOR_TYPE(_ClassName) static_assert(true, "")
 #endif
 
+// TODO(varconst): currently, there are bugs in Clang's intrinsics when handling Objective-C++ `id`, so don't use
+// compiler intrinsics in the Objective-C++ mode.
+#  ifdef __OBJC__
+#    define _LIBCPP_WORKAROUND_OBJCXX_COMPILER_INTRINSICS
+#  endif
+
 #endif // __cplusplus
 
 #endif // _LIBCPP___CONFIG

libcxx/include/__type_traits/add_pointer.h

 #include <__type_traits/remove_reference.h>
 
 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
 #  pragma GCC system_header
 #endif
 
 _LIBCPP_BEGIN_NAMESPACE_STD
 
-#if __has_builtin(__add_pointer)
+#if !defined(_LIBCPP_WORKAROUND_OBJCXX_COMPILER_INTRINSICS) && __has_builtin(__add_pointer)
 
 template <class _Tp>
 using __add_pointer_t = __add_pointer(_Tp);
 
 #else
 template <class _Tp,
           bool = __libcpp_is_referenceable<_Tp>::value || is_void<_Tp>::value>
 struct __add_pointer_impl {
   typedef _LIBCPP_NODEBUG __libcpp_remove_reference_t<_Tp>* type;
 };
 template <class _Tp> struct __add_pointer_impl<_Tp, false>
     {typedef _LIBCPP_NODEBUG _Tp type;};
 
 template <class _Tp>
 using __add_pointer_t = typename __add_pointer_impl<_Tp>::type;
 
-#endif // __has_builtin(__add_pointer)
+#endif // !defined(_LIBCPP_WORKAROUND_OBJCXX_COMPILER_INTRINSICS) && __has_builtin(__add_pointer)
 
 template <class _Tp>
 struct add_pointer {
   using type _LIBCPP_NODEBUG = __add_pointer_t<_Tp>;
 };
 
 #if _LIBCPP_STD_VER >= 14
 template <class _Tp> using add_pointer_t = __add_pointer_t<_Tp>;
 #endif
 
 _LIBCPP_END_NAMESPACE_STD
 
 #endif // _LIBCPP___TYPE_TRAITS_ADD_POINTER_H

libcxx/include/__type_traits/remove_pointer.h

 #include <__config>
 
 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
 #  pragma GCC system_header
 #endif
 
 _LIBCPP_BEGIN_NAMESPACE_STD
 
-#if __has_builtin(__remove_pointer)
+#if !defined(_LIBCPP_WORKAROUND_OBJCXX_COMPILER_INTRINSICS) && __has_builtin(__remove_pointer)
 template <class _Tp>
 struct remove_pointer {
   using type _LIBCPP_NODEBUG = __remove_pointer(_Tp);
 };
 
 template <class _Tp>
 using __remove_pointer_t = __remove_pointer(_Tp);
 #else
 template <class _Tp> struct _LIBCPP_TEMPLATE_VIS remove_pointer                      {typedef _LIBCPP_NODEBUG _Tp type;};
 template <class _Tp> struct _LIBCPP_TEMPLATE_VIS remove_pointer<_Tp*>                {typedef _LIBCPP_NODEBUG _Tp type;};
 template <class _Tp> struct _LIBCPP_TEMPLATE_VIS remove_pointer<_Tp* const>          {typedef _LIBCPP_NODEBUG _Tp type;};
 template <class _Tp> struct _LIBCPP_TEMPLATE_VIS remove_pointer<_Tp* volatile>       {typedef _LIBCPP_NODEBUG _Tp type;};
 template <class _Tp> struct _LIBCPP_TEMPLATE_VIS remove_pointer<_Tp* const volatile> {typedef _LIBCPP_NODEBUG _Tp type;};
 
 template <class _Tp>
 using __remove_pointer_t = typename remove_pointer<_Tp>::type;
-#endif // __has_builtin(__remove_pointer)
+#endif // !defined(_LIBCPP_WORKAROUND_OBJCXX_COMPILER_INTRINSICS) && __has_builtin(__remove_pointer)
 
 #if _LIBCPP_STD_VER >= 14
 template <class _Tp> using remove_pointer_t = __remove_pointer_t<_Tp>;
 #endif
 
 _LIBCPP_END_NAMESPACE_STD
 
 #endif // _LIBCPP___TYPE_TRAITS_REMOVE_POINTER_H

libcxx/test/std/utilities/meta/meta.trans/objc_support.pass.mm

+//===----------------------------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+// REQUIRES: objective-c++
+
+// Simple test to check that type traits support Objective-C types.
+
+#include <type_traits>
+#include "test_macros.h"
+
+@interface I;
+@end
+
+// add_pointer
+static_assert(std::is_same<std::add_pointer<id>::type, id*>::value, "");
+static_assert(std::is_same<std::add_pointer<I>::type, I*>::value, "");
+
+// add_lvalue_reference
+static_assert(std::is_same<std::add_lvalue_reference<id>::type, id&>::value, "");
+static_assert(std::is_same<std::add_lvalue_reference<I>::type, I&>::value, "");
+
+// add_rvalue_reference
+static_assert(std::is_same<std::add_rvalue_reference<id>::type, id&&>::value, "");
+static_assert(std::is_same<std::add_rvalue_reference<I>::type, I&&>::value, "");
+
+// decay
+static_assert(std::is_same<std::decay<id>::type, id>::value, "");
+static_assert(std::is_same<std::decay<I>::type, I>::value, "");
+static_assert(std::is_same<std::decay<id(&)[5]>::type, id*>::value, "");
+
+// __libcpp_is_referenceable
+LIBCPP_STATIC_ASSERT(std::__libcpp_is_referenceable<id>::value, "");
+LIBCPP_STATIC_ASSERT(std::__libcpp_is_referenceable<id*>::value, "");
+LIBCPP_STATIC_ASSERT(std::__libcpp_is_referenceable<id&>::value, "");
+LIBCPP_STATIC_ASSERT(std::__libcpp_is_referenceable<id&&>::value, "");
+LIBCPP_STATIC_ASSERT(std::__libcpp_is_referenceable<I>::value, "");
+LIBCPP_STATIC_ASSERT(std::__libcpp_is_referenceable<I*>::value, "");
+LIBCPP_STATIC_ASSERT(std::__libcpp_is_referenceable<I&>::value, "");
+LIBCPP_STATIC_ASSERT(std::__libcpp_is_referenceable<I&&>::value, "");
+
+// remove_all_extents
+static_assert(std::is_same<std::remove_all_extents<id>::type, id>::value, "");
+static_assert(std::is_same<std::remove_all_extents<id[5]>::type, id>::value, "");
+static_assert(std::is_same<std::remove_all_extents<id[5][10]>::type, id>::value, "");
+static_assert(std::is_same<std::remove_all_extents<I>::type, I>::value, "");
+
+// remove_const
+static_assert(std::is_same<std::remove_const<id>::type, id>::value, "");
+static_assert(std::is_same<std::remove_const<const id>::type, id>::value, "");
+static_assert(std::is_same<std::remove_const<I>::type, I>::value, "");
+static_assert(std::is_same<std::remove_const<const I>::type, I>::value, "");
+
+// remove_cv
+static_assert(std::is_same<std::remove_cv<id>::type, id>::value, "");
+static_assert(std::is_same<std::remove_cv<const volatile id>::type, id>::value, "");
+static_assert(std::is_same<std::remove_cv<I>::type, I>::value, "");
+static_assert(std::is_same<std::remove_cv<const volatile I>::type, I>::value, "");
+
+#if TEST_STD_VER >= 20
+// remove_cvref
+static_assert(std::is_same<std::remove_cvref<id>::type, id>::value, "");
+static_assert(std::is_same<std::remove_cvref<const volatile id&>::type, id>::value, "");
+static_assert(std::is_same<std::remove_cvref<const volatile id&&>::type, id>::value, "");
+static_assert(std::is_same<std::remove_cvref<I>::type, I>::value, "");
+static_assert(std::is_same<std::remove_cvref<const volatile I&>::type, I>::value, "");
+static_assert(std::is_same<std::remove_cvref<const volatile I&&>::type, I>::value, "");
+#endif
+
+// remove_extent
+static_assert(std::is_same<std::remove_all_extents<id>::type, id>::value, "");
+static_assert(std::is_same<std::remove_all_extents<id[5]>::type, id>::value, "");
+static_assert(std::is_same<std::remove_all_extents<I>::type, I>::value, "");
+
+// remove_pointer
+static_assert(!std::is_same<std::remove_pointer<id>::type, id>::value, "");
+// The result of removing and re-adding pointer to `id` should be still `id`.
+static_assert(std::is_same<std::remove_pointer<id>::type*, id>::value, "");
+static_assert(std::is_same<std::add_pointer<std::remove_pointer<id>::type>::type, id>::value, "");
+static_assert(std::is_same<std::remove_pointer<std::add_pointer<id>::type>::type, id>::value, "");
+
+// remove_reference
+static_assert(std::is_same<std::remove_reference<id>::type, id>::value, "");
+static_assert(std::is_same<std::remove_reference<id&>::type, id>::value, "");
+static_assert(std::is_same<std::remove_reference<const id&>::type, const id>::value, "");
+static_assert(std::is_same<std::remove_reference<id&&>::type, id>::value, "");
+static_assert(std::is_same<std::remove_reference<const id&&>::type, const id>::value, "");
+static_assert(std::is_same<std::remove_reference<I>::type, I>::value, "");
+static_assert(std::is_same<std::remove_reference<I&>::type, I>::value, "");
+static_assert(std::is_same<std::remove_reference<const I&>::type, const I>::value, "");
+static_assert(std::is_same<std::remove_reference<I&&>::type, I>::value, "");
+static_assert(std::is_same<std::remove_reference<const I&&>::type, const I>::value, "");
+
+// remove_volatile
+static_assert(std::is_same<std::remove_volatile<id>::type, id>::value, "");
+static_assert(std::is_same<std::remove_volatile<volatile id>::type, id>::value, "");
+static_assert(std::is_same<std::remove_volatile<I>::type, I>::value, "");
+static_assert(std::is_same<std::remove_volatile<volatile I>::type, I>::value, "");
+
+int main(int, char**) {
+  return 0;
+}