[LLVMdev] RFC: Atomics.h

[Owen Anderson]

On May 17, 2009, at 12:32 PM, Chris Lattner wrote:
> Owen, I would really rather that you didn't take this path.  Threading
> support in LLVM should always be optional: it should be possible to
> use LLVM on systems where we don't have support for threading
> operations.  Indeed, some systems don't support threads!

I'm not trying to make it required.  I had provided threads-disabled  
versions of all the operations.

> Given that, I think it makes sense to start  out the atomics
> operations very simple: just make them work for compilers that support
> GCC 4.2's atomics.  Since things will be changing quickly initially,
> this makes it easy to prototype and build things out, and this also
> avoids pulling in an external library with a (compatible but)
> different license.
>
> In practice, I think a huge chunk of the community will be served when
> LLVM supports GCC 4.2 atomics + a windows implementation.  I don't see
> a reason to make things any more complex than that.  Since llvm-gcc
> supports atomics, someone doing development on a supported
> architecture can just build llvm-gcc single threaded, which provides
> them with a compiler that supports atomics on their platform.

After thinking about this some more, I think you're right.  Trying to  
support every platform anyone cares about is rapidly becoming a  
nightmare.  Setting GCC4.2 as a baseline requirement (and presumably  
providing a Windows implementation as well) is probably a good way to  
get this back to a sane amount of stuff to support.

--Owen
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