[libc++] Enable aligned allocation based on feature test macro, irrespective of standard

[ldionne]

Summary

The current code enables aligned allocation functions when compiling in C++17
and later. This is a problem because aligned allocation functions might not
be supported on the target platform, which leads to an error at link time.

Since r338934, Clang knows not to define __cpp_aligned_new when it's not
available on the target platform -- this commit takes advantage of that to
only use aligned allocation functions when they are available.

[vsapsai]

libcxx/include/__config

993

I think I'd rather keep __cpp_aligned_new >= 201606 check. I don't know about cases where the smaller value is possible, Clang always had 201606 as far as I (and SVN) know. But it seems to be safer and more correct.

Don't have objective arguments for keeping the check, so if you think it's not worth it, I trust your judgement.

libcxx/include/new

111–116

Maybe move this to __config too? This way we'll have __cpp_aligned_new-related macros together.

libcxx/test/libcxx/memory/aligned_allocation_macro.pass.cpp

12

Initially with_system_cxx_lib made me suspicious because macro _LIBCPP_HAS_NO_ALIGNED_ALLOCATION doesn't need specific dylib. And XFAIL: availability=macosx10.12 seems to be working.

Documentation describes which feature should be used in different cases but in this case I cannot definitely say if test uses unavailable feature. I think it is acceptable to stick with with_system_cxx_lib but I decided to brought to your attention the alternative.

[ldionne]

Address vsapsai's comments

[ldionne]

libcxx/include/new

111–116

The big difference is that _LIBCPP_HAS_NO_BUILTIN_ALIGNED_OPERATOR_NEW_DELETE is only used in <new>, whereas _LIBCPP_HAS_NO_ALIGNED_ALLOCATION was used in other files as well. Hence, I feel like it makes more sense to lift _LIBCPP_HAS_NO_ALIGNED_ALLOCATION into <__config>, but not _LIBCPP_HAS_NO_BUILTIN_ALIGNED_OPERATOR_NEW_DELETE .

[ldionne]

libcxx/test/libcxx/memory/aligned_allocation_macro.pass.cpp

12

My understanding is that the availability feature may not be there if we're not using availability macros, since they can be disabled entirely.

[vsapsai]

libcxx/include/new

111–116

Agree with your reasoning.

libcxx/test/libcxx/memory/aligned_allocation_macro.pass.cpp

12

availability feature will be present when tests are invoked with use_system_cxx_lib. I suspect in this case both with_system_cxx_lib and availability will work, so let's keep with_system_cxx_lib.

libcxx/include/__config

 #  endif
 #  if defined(__MAC_OS_X_VERSION_MIN_REQUIRED)
 #    if __MAC_OS_X_VERSION_MIN_REQUIRED < 1060
 #      define _LIBCPP_HAS_NO_ALIGNED_ALLOCATION
 #    endif
 #  endif
 #endif // defined(__APPLE__)
 
+#if !defined(_LIBCPP_HAS_NO_ALIGNED_ALLOCATION) && \
+    !defined(_LIBCPP_BUILDING_LIBRARY) && \
+    (!defined(__cpp_aligned_new) || __cpp_aligned_new < 201606)
+#  define _LIBCPP_HAS_NO_ALIGNED_ALLOCATION
+#endif
 
 #if defined(__APPLE__) || defined(__FreeBSD__)
 #define _LIBCPP_HAS_DEFAULTRUNELOCALE
 #endif
 
 #if defined(__APPLE__) || defined(__FreeBSD__) || defined(__sun__)
 #define _LIBCPP_WCTYPE_IS_MASK
 #endif

libcxx/include/new

 #pragma GCC system_header
 #endif
 
 #if !(defined(_LIBCPP_BUILDING_LIBRARY) || _LIBCPP_STD_VER >= 14 || \
     (defined(__cpp_sized_deallocation) && __cpp_sized_deallocation >= 201309))
 # define _LIBCPP_HAS_NO_SIZED_DEALLOCATION
 #endif
 
-#if !defined(_LIBCPP_HAS_NO_ALIGNED_ALLOCATION) && \
-    (!(defined(_LIBCPP_BUILDING_LIBRARY) || _LIBCPP_STD_VER > 14 || \
-    (defined(__cpp_aligned_new) && __cpp_aligned_new >= 201606)))
-# define _LIBCPP_HAS_NO_ALIGNED_ALLOCATION
-#endif
-
-
 #if !__has_builtin(__builtin_operator_new) || \
    __has_builtin(__builtin_operator_new) < 201802L || \
    defined(_LIBCPP_HAS_NO_ALIGNED_ALLOCATION) || \
    !defined(__cpp_aligned_new) || __cpp_aligned_new < 201606
 #define _LIBCPP_HAS_NO_BUILTIN_ALIGNED_OPERATOR_NEW_DELETE
 #endif
 
 namespace std  // purposefully not using versioning namespace
 {
 
 #if !defined(_LIBCPP_ABI_MICROSOFT) || defined(_LIBCPP_NO_VCRUNTIME)
 struct _LIBCPP_TYPE_VIS nothrow_t {};
 extern _LIBCPP_FUNC_VIS const nothrow_t nothrow;
 

libcxx/test/libcxx/memory/aligned_allocation_macro.pass.cpp

+//===----------------------------------------------------------------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is dual licensed under the MIT and the University of Illinois Open
+// Source Licenses. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+
+// UNSUPPORTED: c++98, c++03, c++11, c++14
+// XFAIL: with_system_cxx_lib=macosx10.12
+// XFAIL: with_system_cxx_lib=macosx10.11
+// XFAIL: with_system_cxx_lib=macosx10.10
+// XFAIL: with_system_cxx_lib=macosx10.9
+// XFAIL: with_system_cxx_lib=macosx10.8
+// XFAIL: with_system_cxx_lib=macosx10.7
+
+#include <new>
+
+
+#ifdef _LIBCPP_HAS_NO_ALIGNED_ALLOCATION
+#   error "libc++ should have aligned allocation in C++17 and up when targeting a platform that supports it"
+#endif
+
+int main() { }