[cpp-threads] C++ memory model

[Boehm, Hans]

> From: Lawrence Crowl [mailto:crowl at google.com] 
> Sent: Tuesday, September 22, 2009 12:44 AM
> 
> 8.7 section 29.3 paragraph 9
> 
> | Deleting "Implementations shall not ... out of an unbounded loop."
> | Adding "An atomic operation contained in a substatement of 
> one of the 
> | iteration statements specified in 6.5 must not be moved out of the 
> | substatement."
> 
> The added sentence is okay in direction, but the wording does 
> not reflect the fact that the standard likes "shall" and the 
> standard likes to specify whether requirements are on the 
> implementation or the program.  I would rewrite that statement as:
> 
>     The implementation shall not move an atomic side effect contained
>     in a substatement of one of the iteration statements specified in
>     6.5 out of the substatement.
I still have a general problem with all forms of this sentence, in that it doesn't seem to be a constraint on observable program behavior.  The program can't tell whether it was moved out of the loop or just held in a local store buffer indefinitely.  It seems to me that the most we can really properly state is precisely what's already said in the preceding sentence.  

I think this sentence should just disappear.

Does Clark have an opinion?

Hans