Memory ordering in C2

[Andrew Haley]

On 02/26/2014 04:32 AM, David Holmes wrote:
> On 26/02/2014 1:41 AM, Lindenmaier, Goetz wrote:
>> Hi,
>>
>>>  From what I've seen, C2 is enthusiastically emitting barrier nodes
>>> around CompareAndSwap, so I'm not quite sure what this means.
>> Yes, you are right ... that's again because we implement MemBArAcquire empty,
>> but after the CompareAndSwap we need one, so we had to add it in the node ;)
>> So same issue, distinguishing nodes would help!  The bad thing is that MemBarAcquire
>> is implemented empty, that spoils the other uses.  If there is a way to avoid MemBarAcquire
>> where it needs to be empty (after volatile load), then it can be implemented
>> properly ...
> 
> I'm unclear what you mean by "needs to be empty" ??

"Does not need to be emitted," I think.

Andrew.