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Re: RFH: Impose code-movement restrictions and value assumption (for ASYNCHRONOUS/Coarrays)
On 07/13/2011 12:57 PM, Richard Guenther wrote:
On Wed, Jul 13, 2011 at 12:30 PM, Tobias Burnus<burnus@net-b.de> wrote:
Example 2: Coarray with sync. The SYNC is not directly called, but via a
wrapper function to increase the fun factor.
subroutine sub(coarray)
integer :: coarray[*]
coarray = 5
call SYNC_calling_proc()
! coarray is modified remotely
call SYNC_calling_proc()
if (coarray /= 5) ...
end subroutine sub
Here, the "if" may not be removed as the image could have been changed
remotely.
> From the last two examples it looks like a regular restrict qualified pointer
would work. At least I don't see how it would not.
Would it? How does the compiler know that between "call
SYNC_calling_proc()" the value of "coarray" could change? Hmm,
seemingly, that's indeed the case, looking at the optimized dump of the
example above:
sub (integer(kind=4) * restrict coarray)
{
integer(kind=4) D.1560;
*coarray_1(D) = 5;
sync_calling_proc ();
sync_calling_proc ();
D.1560_2 = *coarray_1(D);
if (D.1560_2 != 5)
Well, then I have a different question: How can one tell the middle end
to optimize the "if (...)" away in the following case? Seemingly having
an "integer(kind=4) & restrict non_aliasing_var" does not seem to be
sufficient to do so:
subroutine sub(non_aliasing_var)
interface
subroutine some_function()
end subroutine some_function
end interface
integer :: non_aliasing_var
non_aliasing_var = 5
call some_function()
if (non_aliasing_var /= 5) call foobar_()
end subroutine sub
That's an optimization, which other compiles do - such as NAG or
PathScale/Open64/sunf95.
Tobias