[C11-atomic] Miscellaneous fixes 1/n

[Andrew MacLeod]

On 10/17/2013 05:50 PM, Joseph S. Myers wrote:
> I've applied this patch to the C11-atomic branch to fix various
> miscellaneous issues.

excellent!
>
> I put a hack in the C++ front end to disable checks on atomic
> qualifiers so that libstdc++ builds - I think that if you want other
> people to help on a development branch, it should be kept in a state
> where it builds and tests cleanly.  However, I'm aiming specifically
Yes, perhaps I should not have checked in the bit that uses the atomic 
attribute in the c++ templates... it was working fine until late in the 
game when I removed the incorrect "treat atomic as volatile" parts of 
the patches.. which then caused that failure. sorry.  I didn't know how 
to fix it "correctly"...  I figured it should be easy if you knew how 
:-P  but maybe not...

> to sort out the C front-end (and later stdatomic.h) issues, with a
> view to getting the actual C11 support in shape and with adequate
> testsuite coverage, so if that's ready on time I may propose it for
> mainline without the attribute or C++ changes - as I understand it,
> those are only needed for when targets start defining atomic types as
> larger or more-aligned than the corresponding non-atomic types, not to
> support the C11 features on the most common architectures.
>
right.  We may re-visit it when we finalize the ABI changes for c++...  
Use of the attribute in c++ will ensure that C and C++ both treat an 
atomic object the same...  My original discussions with lawrence and 
jeffrey over atomics concerned the desire to "upsize" an _Atomic object 
to the next highest size that supports lock-free operations. (ie, a 6 
byte object becomes an 8 byte atomic object). The __attribute__ is 
really to ensure we can share the code and get compatible behaviour 
between languages.  At the moment it is a nop. A better solution may 
show up, if we ever actually need it.

Thanks for picking this up... I for one really appreciate it.

Andrew