Fortran's DO CONCURRENT - make use of it middle-end-wise

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

Hi,

Fortran 2008 has a do concurrent construct, where the programmer 
guarantees that the result is independent of the order; e.g.
  do concurrent (i = 1:10:2)  ! from, to, step/stride
     A(i) = sin(B(i))
  end do
can be run as i = 1, 3, 5, 7, 9; in any permutation or in parallel.

The plan is to translate it as normal loop; however, it would be useful 
if this non-order-dependence could be used by the middle end (general 
optimization or at least for -floop-parallelize-all / 
-ftree-parallelize-loops). Is there a way to tell the middle-end about 
this property?

Tobias

PS: By default, do concurrent loops will run consecutively, but I was 
thinking of optionally using OpenMP parallelization for those by 
explicitly adding an OMP directive. The do-concurrent parsing/resolving 
patch is at http://gcc.gnu.org/ml/fortran/2011-09/msg00002.html. The 
tree-generating part still needs to be written, but should be simple 
(for the serial case).