Heads up: New C++ stack

Hi,

I've just imported libc++[1] and libcxxrt[2] to head.  libc++ is UUIC =
licensed, libcxxrt is 2-clause BSDL.  The former implements the C++ =
standard template library, and provides all of the programmer-visible =
parts.  The latter provides an implementation of the ARM and Itanium ABI =
specifications providing the dynamic parts of the language (RTTI, =
exceptions, and so on).

This combination working out-of-tree and passing almost all of the test =
suite (the failing parts are related to missing C1x functionality in =
libc and missing C++11 / C1x atomic intrinsics in clang). =20

The goal of this is to have a working, permissively licensed, C++11 =
stack.  libc++abi would be an alternative to libcxxrt, but I would =
prefer to use libcxxrt because:

- I am totally biased towards libcxxrt because I wrote it.

- libcxxrt is already shipping in PathScale's C++ stack and has been =
fairly well tested.

- The demangler in libc++abi is bigger than the whole of libcxxrt and =
allocates a lot of memory in code that is called to generate helpful =
errors for out-of-memory conditions.

- libc++abi seems to be completely missing the exception personality =
function.  This was the hardest thing to get right in libcxxrt =
(debugging code that destroys the stack as it runs is not fun), so at =
this point it's basically uninteresting - more code, less functionality.

libcxxrt and libc++ are now in contrib and building with the base =
system, but are not used by anything (and are only built if you set =
WITH_LIBCPLUSPLUS=3Dyes when building world, not by default).  If you =
want to test some code with the new stack, you need to build it and then =
specify -stdlib=3Dlibc++ to clang++ (both when compiling and linking).

I'd like to see if we can persuade libstdc++ to link against libcxxrt =
instead of libsupc++ (In theory this should be easy, but I've never =
tried it.  Apple ships both linked against libsupc++).  This means that =
code can link against libraries that use libc++ and libstdc++ without =
things like exceptions breaking. =20

Eventually (FreeBSD 10 timeframe), I'd like to see the libstdc++ =
currently in base moved into a port so that we can ship a GNU-free C++ =
stack.

Any complaints / comments / contradictions / opinions?

David

P.S.  libcxxrt does support the weird GNU variant of the weird ARM =
variant of the C++ ABI, but I only finished that support very recently =
and it's not nearly as well tested as the ABI used on... everything =
else.  It also only supports DWARF 'zero-cost' unwinding, not setjmp / =
longjmp unwinding, so it can't be used until we finish moveing ARM to =
EABI. =20

[1] http://libcxx.llvm.org/
[2] https://github.com/pathscale/libcxxrt=
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