Depend clause in openmp is not respecting dependence declared

Question

I am trying to use openmp tasks to schedule a tiled execution of basic jacobi2d computation. In jacobi2d there is a dependence on A(i,j) from

A(i, j)
A(i-1, j)
A(i+1, j)
A(i, j-1)
A(i, j+1).

To my understanding of the depend clause I am declaring the dependences correctly, but they are not being respected while executing the code. I have copied the simplified code piece below. Initially my guess was that the out of bounds ranges for some tiles might be causing this issue, so I corrected that but the issue persists.(I have not copied the longer code with corrected tile ranges as that part is just a bunch of ifs + max)

int n=8,tsteps=2,b=4;         //n - size of matrix, tsteps - time iterations, b - tile size or block size

#pragma omp parallel
{
#pragma omp master
for (t=0; t<tsteps; ++t)
  {
    for (i=0; i<n; i+=b)
      for (j=0; j<n; j+=b)
      {
        #pragma omp task firstprivate(t,i,j) depend(in:A[i-1:b+2][j-1:b+2]) depend(out:B[i:b][j:b])
        { 
          #pragma omp critical  
          printf("t-%d i-%d j-%d --A",t,i,j);     //Prints out time loop, i,j 
        }
      } 
    for (i=0; i<n; i+=b)
      for (j=0; j<n; j+=b)
      {
        #pragma omp task firstprivate(t,i,j) depend(in:B[i-1:b+2][j-1:b+2]) depend(out:A[i:b][j:b])
        {
          #pragma omp critical  
          printf("t-%d i-%d j-%d --B",t,i,j);     //Prints out time loop, i,j 
        }
      }
  }
}
}

So the idea with declaring dependence starting from i-1 and j-1 and the range being (b+2) is that the neighbouring tiles also affect your current tiles calculations. And similarly for the second set of loop where values in A should only be overwritten once the neighbouring tiles have used the values.

Code is being compiled using gcc 5.3 which supports openmp 4.0.

ps: the way array range is declared above denotes the starting position and the number of indices to be considered while creating the dependence graph.

edit (based on Zulan's comment) - changed the inner code to a simple print statement as this will suffice to check order of task execution. Ideally for the above values(since there are only 4 tiles) all tiles should complete the first printf and then only execute the second. But if you execute the code it will mix the order.

Answer 1

So I finally figured out the issue, even though OpenMP specs say that depend clause is supposed to be implemented with a starting point and range, it has not been implemented yet in gcc. So currently it only compares the starting point from the depend clause (depend(in:A[i-1:b+2][j-1:b+2])) A[i-1][j-1] in this case.

Initially I was comparing elements in different relative tile positions. Eg comparing (0,0) element with the last element of the tile, which was giving a no conflicts with dependence and hence the random order of execution of various tasks.

Current gcc implementation does not care about the range provided in the clause at all.