Use own implementation of _has_exclusive_writes

AssignmentCollection.has_exclusive_writes was not merged in pystencils core
since the check overlaps with pystencils own checks and is very specific

src/pystencils_autodiff/autodiff.py

@@ -20,6 +20,27 @@ class DiffModes(str, Enum):
     TF_MAD = 'transposed-forward'
 
 
+def _has_exclusive_writes(assignment_collection):
+    """
+    Simple check for exclusive (non-overlapping) writes.
+    I.e. AssignmentCollection can be executed safely in parallel without caring about race conditions.
+    No writes on same spatial location (considering all possible shifts).
+    """
+
+    assignments = assignment_collection.main_assignments
+    write_field_accesses = [a.lhs for a in assignments if isinstance(a.lhs, ps.Field.Access)]
+
+    exclusive_writes = set()
+    for a in write_field_accesses:
+
+        if (a.field, a.index) in exclusive_writes:
+            return False
+        else:
+            exclusive_writes.add((a.field, a.index))
+
+    return True
+
+
 def get_jacobian_of_assignments(assignments, diff_variables):
     """
     Calculates the Jacobian of iterable of assignments wrt. diff_variables
@@ -180,7 +201,7 @@ Backward:
         main_assignments = [a for a in backward_assignments if isinstance(a.lhs, ps.Field.Access)]
         subexpressions = [a for a in backward_assignments if not isinstance(a.lhs, ps.Field.Access)]
         backward_assignments = ps.AssignmentCollection(main_assignments, subexpressions)
-        assert backward_assignments.has_exclusive_writes, "Backward assignments don't have exclusive writes." + \
+        assert _has_exclusive_writes(backward_assignments), "Backward assignments don't have exclusive writes." + \
             " You should consider using 'transposed-forward' mode for resolving those conflicts"
 
         self._forward_assignments = forward_assignments
@@ -329,7 +350,7 @@ Backward:
         subexpressions = [a for a in backward_assignments if not isinstance(a.lhs, ps.Field.Access)]
         backward_assignments = ps.AssignmentCollection(main_assignments, subexpressions)
 
-        assert backward_assignments.has_exclusive_writes, "Backward assignments don't have exclusive writes!"
+        assert _has_exclusive_writes(backward_assignments), "Backward assignments don't have exclusive writes!"
 
         self._backward_assignments = backward_assignments
         self._backward_field_map = {**diff_read_fields, **diff_write_fields}