We've started using `_LIBCPP_BEGIN_NAMESPACE_STD` and
`_LIBCPP_END_NAMESPACE_STD` for more than just the namespace for a while
now. For example, we're using it to add visibility annotations to types.
This works very well and avoids a bunch of annotations, but doesn't work
for the few places where we have an unversioned namespace. This adds
`_LIBCPP_BEGIN_UNVERSIONED_NAMESPACE_STD` and
`_LIBCPP_END_UNVERSIONED_NAMESPACE_STD` to make it simpler to add new
annotations consistently across the library as well as making it more
explicit that the unversioned namespace is indeed intended.
There doesn't seem to be much benefit in always providing declarations
for the sized deallocations from C++14 onwards if the user explicitly
passed `-fno-sized-deallocation` to disable them. This patch simplifies
the declarations to be available exactly when the compiler expects sized
deallocation functions to be available.
Currently, places where we call __libcpp_allocate must drop type
information on the ground even when they actually have such information
available. That is unfortunate since some toolchains and system
allocators are able to provide improved security when they know what
type is being allocated.
This is the purpose of http://wg21.link/p2719, where we introduce a new
variant of `operator new` which takes a type in its interface. A
different but related issue is that `std::allocator` does not honor any
in-class `T::operator new` since it is specified to call the global
`::operator new` instead.
This patch closes the gap to make it trivial for implementations that
provide typed memory allocators to actually benefit from that
information in more contexts, and also makes libc++ forward-compatible
with future proposals that would fix the existing defects in
`std::allocator`. It also makes the internal allocation API higher level
by operating on objects instead of operating on bytes of memory.
Since this is a widely-used function and making this a template could
have an impact on debug info sizes, I tried minimizing the number of
templated layers by removing `__do_deallocate_handle_size`, which was
easy to replace with a macro (and IMO this leads to cleaner code).
This disentangles the code which previously had a mix of many #ifdefs, a
non-versioned namespace and a versioned namespace. It also makes it
clearer which parts of <new> are implemented on Windows by including <new.h>.
