[MPI3 Fortran] Proposed solution for the volatile buffer problem

[Bill Long]

Aleksandar Donev wrote:
>
>
>> Secondly, a compiler is allowed to assume that unreferenced parts of an
>> array are invariant, and so may copy more than it needs to - which can
>> sometimes be a lot faster.
> OK, that's a good point in argument of explicitly marking variables 
> that get changed behind the scenes instead of relying on some form of 
> implicit assumptions.
>

Keep in mind the problem we're trying to solve here.  It is to prevent 
computations involving the "marked" variables from being moved by the 
compiler across a CALL to the wait routine.  So, what is the proposal 
for marked variables (which don't appear as arguments to the relevant 
routines - the ultimate source of the problem)?  Are they temporarily 
volatile across every procedure reference?  How would the compiler deal 
with a pointer that is associated with one of the marked variables?  It 
seems like there will be a lot of text, in addition to a new 
attribute/statement to get this to work. 

Cheers,
Bill



-- 
Bill Long                                   longb at cray.com
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