[v3] atomics

[David Daney]

Benjamin Kosnik wrote:
> This adds in experimental support for C++0x chapter 29, atomics. It is
> based on the sample implementation by Lawrence Crowl in N2427, who
> generously allowed libstdc++ use of this code. Thanks Lawrence!
> 

This patch badly breaks things on MIPS.

The problem is that MIPS only supports atomic operations on 32 bit wide 
locations (and 64 for mips64).  src/atomic.cc appears to be trying to 
generate code for operations on 8 bit wide locations thus generating 
calls to  __sync_lock_test_and_set_1 as the operation can not be 
expanded.  Since there is no __sync_lock_test_and_set_1 anything that 
links against libstdc++.so fails to link (most of the c++ and libstdc++ 
testsuite for example).


At this point I don't really have an opinion as to how to fix the 
problem.  One thought that comes to mind is to change the definition of 
atomic_flag so that the size of the atomic variable is appropriate for 
the target architecture (32 bits in the case of MIPS)

Thoughts?

Thanks,
David Daney