PSA: GHC can now be built with Clang

[Manuel M T Chakravarty]

Austin,

Thank you very much for taking care of all these clang issues — that is very helpful!

Cheers,
Manuel

Austin Seipp <aseipp at pobox.com>:
> Hi all,
> 
> As of commit 5dc74f it should now be possible to build a working
> stage1 and stage2 compiler with (an extremely recent) Clang. With some
> caveats.
> 
> You can just do:
> 
> $ CC=/path/to/clang ./configure --with-gcc=/path/to/clang
> $ make
> 
> I have done this work on Linux. I don't expect much difficulty on Mac
> OS X, but it needs testing. Ditto with Windows, although Clang/mingw
> is considered experimental.
> 
> The current caveats are:
> 
> * The testsuite will probably fail everywhere, because of some
> warnings that happen during the linking phase when you invoke the
> built compiler. So the testsuite runner will probably be unhappy.
> Clang is very noisy about unused options, unlike GCC. That needs to be
> fixed somewhere in DriverPipeline I'd guess, but with some
> refactoring.
> * Some of the stage2 libraries don't build due to a Clang bug. These
> are vector/primitive/dph so far.
> * There is no buildbot or anything to cover it.
> 
> You will need a very recent Clang. Due to this bug (preventing
> primitive etc from building,) you'll preferably want to use an SVN
> checkout from about 6 hours ago at latest:
> 
> http://llvm.org/bugs/show_bug.cgi?id=16363
> 
> Hilariously, this bug was tripped on primitive's Data.Primitive.Types
> module due to some CPP weirdness. But even with a proper bugfix and no
> segfault, it still fails to correctly parse this same module with the
> same CPP declarations. I'm fairly certain this is another bug in
> Clang, but I might be wrong. I'm trying to isolate it. Unfortunately
> Clang/LLVM 3.3 was just released and it won't see bugfix releases. But
> it will *probably* work if we just get rid of the CPP tomfoolery in
> primitive. I'll be testing it in the next few days to see if we can
> get 3.3 supported. (I'm sort of kicking myself in the head for not
> doing this a week or two ago...)
> 
> Anyway, there are some rough edges but it should be in shape for 7.8 I
> hope. It should be especially welcome for Mac users. (I'm also hoping
> modern Macs could even go all-clang-all-the-time if my fix for #7602
> can go in soon...)
> 
> PS. If you use ASSERT, I just fixed a lot of instances of using that
> macro, involving whitespace between the name and arguments (commit
> d8ee2b.) Clang does not forgive you for this. Should I note this
> anywhere for the future in the wiki or something?
> 
> -- 
> Regards,
> Austin - PGP: 4096R/0x91384671
> 
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