Can we test for the existence of posix_memalign and disable support for C++17 aligned allocation functions if it doesn't exist? I'm not suggesting we implement that internally to libcxx, but that would obviously be an option as well.

On Windows, posix_memalign wouldn't be available, but _aligned_malloc would.

@​Jeremy Can you be more specific about the platform causing issues? Is it just an older OS X version? If so do you know how to detect the availability of posix_memalign or Apple's libc version on that platform?

On Windows, posix_memalign wouldn't be available, but _aligned_malloc would.

Ack. I'll make that change right away.

Windows fix made in r290448.

posix_memalign was added in Snow Leopard, and we've (MacPorts) got some users still on Leopard that we try to support. Yes, that's a bit far back.

Something like this should do it in CMakeLists.txt:

CHECK_SYMBOL_EXISTS(posix_memalign "stdlib.h" HAVE_POSIX_MEMALIGN)
CHECK_SYMBOL_EXISTS(_aligned_malloc "malloc.h" HAVE_ALIGNED_MALLOC)

Then something like this in new.cpp:

#if defined(HAVE_POSIX_MEMALIGN) || defined(HAVE_ALIGNED_MALLOC)
#define SUPPORT_ALIGNED_ALLOCATION 1
#else
#define SUPPORT_ALIGNED_ALLOCATION 0
#endif

Using CMake to detect it doesn't work.

We need to be able to detect it inside so we know if we can offer the aligned new/delete overloads.

Oh, well you could do something like this in :

#if defined(APPLE)

include <Availability.h>

if __MAC_OS_X_VERSION_MIN_REQUIRED < 1060

define _LIBCPP_HAS_NO_ALIGNED_ALLOCATION

endif

#endif

Awesome thanks!

Can you point to the OS X documentation that specifies the min required version for posix_memalign? I can't seem to find it anywhere.

It's declared in stdlib.h as:

int posix_memalign(void **, size_t, size_t) __OSX_AVAILABLE_STARTING(__MAC_10_6, __IPHONE_3_0);

And I've also verified as such through nm.

Fix up for review in D28931. I'll backport it to Clang 4.0 as well.

https://reviews.llvm.org/D28931

Fixed in r292564 and merged into the 4.0 release branch.

Patch LGTM. Thanks.