llvm dev - Jul 2016 - [RFC] One or many git repositories?

On 28 July 2016 at 09:42, David Chisnall <david.chisnall at cl.cam.ac.uk>
wrote:
> I think it’s important to differentiate between ‘needs’ as in ‘requires a
precisely matched version’ and ‘needs’ as in ‘requires something to provide this
functionality’.  Clang needs something equivalent to libc++ and something
equivalent to libunwind, but it doesn’t (or, at least, shouldn’t) need a
specific version of LLVM’s implementations of these.  In contrast, clang needs a
bunch of LLVM libraries and depends on precise versions.
Absolutely!

> In FreeBSD, we used to ship libsupc++, libstdc++ and GCC’s libunwind.  We
then switched to shipping libcxxrt, libstdc++, and GCC’s libunwind, then to
shipping libcxxrt, libc++, and GCC’s libunwind, and are now switching to
shipping libcxxrt, libc++, and LLVM’s libunwind.  We build all of these with
clang and gcc.  When we import a new lldb and clang (and, soon, when we start to
import lld), we need to do a complete import of LLVM, clang, lld, and lldb at
the same time, or things will break.  We can update libunwind and libc++ on a
different schedule.  We’ll probably want to keep roughly the same versions of
these for an entire major release series (modulo bug fixes) for stability and we
will want a new clang, lld, and lldb to work with the old ones.
My problem, and I'll be quick not to digress too much, is that
--rtlib=compiler-rt is slightly broken. I can't assume libunwind or
libc++abi are there, so for rtlib=RT, I don't add -lunwind and
-lc++abi "as needed" like we do for libgcc's counterparts.

This breaks expectations more than implementations. To use compiler-rt
I need to also add -lgcc_s or -lunwind, and that's not obvious. A
warning here would be weird.

Again, I totally agree it's not a hard requirement, nor version locked
or anything, but it would be good to "assume" the'd be there for
the
*default* case, and let people mix and match by using other advanced
flags.

cheers,
--renato

On 28 Jul 2016, at 15:30, Renato Golin <renato.golin at linaro.org>
wrote:
> 
> My problem, and I'll be quick not to digress too much, is that
> --rtlib=compiler-rt is slightly broken. I can't assume libunwind or
> libc++abi are there, so for rtlib=RT, I don't add -lunwind and
> -lc++abi "as needed" like we do for libgcc's counterparts.
> 
> This breaks expectations more than implementations. To use compiler-rt
> I need to also add -lgcc_s or -lunwind, and that's not obvious. A
> warning here would be weird.
> 
> Again, I totally agree it's not a hard requirement, nor version locked
> or anything, but it would be good to "assume" the'd be there
for the
> *default* case, and let people mix and match by using other advanced
> flags.
This seems to be more an issue with the clang toolchain definition than anything
to do with repository organisation.

David

On 28 July 2016 at 15:49, David Chisnall <David.Chisnall at cl.cam.ac.uk>
wrote:
> This seems to be more an issue with the clang toolchain definition than
anything to do with repository organisation.
Indeed. But since we're collecting "user stories"... :)

cheers,
--renato