[LLVMdev] broken Atomic.cpp on Darwin

[Owen Anderson]

On May 23, 2009, at 9:41 PM, Xi Wang wrote:

> There is no __sync_synchronize or __sync_val_compare_and_swap on Mac
> OS X.  One might use OSMemoryBarrier or OSAtomicCompareAndSwap32
> instead.  The patch is attached.

Actually, __sync_synchronize and __sync_val_compare_and_swap DO exist  
on Darwin, but only if you use Apple's GCC 4.2 (or later), just as it  
is on Linux.  We always want to use these intrinsic versions if  
possible, because they're much lower overhead.

The policy Chris has proposed is that we simply do not support  
multithreaded LLVM with a host compiler pre-GCC 4.2.  If you need  
multithreaded LLVM on an unsupported platform, you can build a single  
threaded LLVM and LLVM-GCC, and then use that to build a multithreaded  
LLVM.

--Owen
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