Re: [OpenCoarrays] RFC patch: Dependency/alias analysis wir same-image coarray access

[Tobias Burnus <burnus at net-b dot de>]

Alessandro Fanfarillo wrote:
> The compiler participation could be useful for performance purposes.
> The idea is:
>
> 1) the library checks if source and destination are the same and if
> the compiler finds an aliasing.

I assume you mean: source and target are on the same image. (Which for 
caf_sendget might be not the executing one.)

> 2) If the compiler does not find anything, the library just applies memmove.

Ditto if memory source and destination are contiguous. That's in line 
with the current compiler check but can in general only be done at run 
time - and, for performance reasons, this check is already done. (One 
could also check more as the compiler cannot do all checks at compile 
time; one could also support walking the array in reverse order etc. 
However, I don't think that's worthwhile.)

> 3) If the compiler find an aliasing, the library does not do anything.

I do not understand your 3: If the library doesn't do anything, you get 
wrong results for
  a(5:1:-1)[1] = a(1:5:1)

I think what one wants is the following: The library creates a temporary 
array and first assigns to it - before assigning from the temporary to 
the target variable.

Tobias