[Patch, fortran] PR 50690 Disable common function elimination in WORKSHAREs

[Jakub Jelinek]

On Sun, Dec 04, 2011 at 02:07:49PM +0100, Thomas Koenig wrote:
> I worked out a patch which does this.  However, in testing it, I came
> across some very strange behavior (even without my patch):
> 
> With the program
> 
> program foo
>   implicit none
>   integer, parameter :: n = 100000000
>   real, parameter :: eps = 3e-7
>   integer :: i,j
>   real :: A(n), B(5), C(n)
>   real :: tmp
>   B(1) = 3.344
>   tmp = B(1)
>   do i=1,10
>      call random_number(a)
>      c = a
>      !$omp parallel default(shared)
>      A(:) = A(:)*cos(B(1))+A(:)*cos(B(1))
>      !$omp end parallel

The above contains data races, so anything can happen.
As A is shared, you can't write into all elements of
that array in all threads at once.
Either only one thread can write it ($omp critical,
$omp master, $omp single), or different threads need to write
different elements.

	Jakub