bench: Patch autotuner after ParallelIteration revamp

devito/core/autotuning.py

@@ -258,7 +258,12 @@ def finalize_time_bounds(stepper, at_args, args, mode):
 def calculate_nblocks(tree, blockable):
     block_indices = [n for n, i in enumerate(tree) if i.dim in blockable]
     index = block_indices[0]
-    collapsed = tree[index:index + (tree[index].ncollapsed or index+1)]
+    try:
+        ncollapsed = tree[index].ncollapsed
+    except AttributeError:
+        # Not using OpenMP
+        ncollapsed = 0
+    collapsed = tree[index:index + (ncollapsed or index+1)]
     blocked = [i.dim for i in collapsed if i.dim in blockable]
     remainders = [(d.root.symbolic_max-d.root.symbolic_min+1) % d.step for d in blocked]
     niters = [d.root.symbolic_max - i for d, i in zip(blocked, remainders)]