Local parallel reduction lowering fails for reduction size of 1

$ PYOPENCL_TEST=port python test_reduction.py "test_local_parallel_reduction(cl._csc, 1)"
No protocol specified
Traceback (most recent call last):
  File "test_reduction.py", line 410, in <module>
    exec(sys.argv[1])
  File "<string>", line 1, in <module>
  File "test_reduction.py", line 214, in test_local_parallel_reduction
    lp.auto_test_vs_ref(ref_knl, ctx, knl)
  File "/home/matt/src/loopy/loopy/auto_test.py", line 524, in auto_test_vs_ref
    test_knl = lp.preprocess_kernel(test_knl)
  File "/home/matt/src/loopy/loopy/preprocess.py", line 924, in preprocess_kernel
    kernel = realize_reduction(kernel, unknown_types_ok=False)
  File "/home/matt/src/loopy/loopy/preprocess.py", line 670, in realize_reduction
    new_expressions = (cb_mapper(insn.expression),)
  File "/home/matt/src/pymbolic/pymbolic/mapper/__init__.py", line 134, in __call__
    return method(expr, *args, **kwargs)
  File "/home/matt/src/loopy/loopy/symbolic.py", line 1352, in map_reduction
    result = self.callback(expr, self.rec, **kwargs)
  File "/home/matt/src/loopy/loopy/preprocess.py", line 628, in map_reduction
    reduction_dtypes)
  File "/home/matt/src/loopy/loopy/preprocess.py", line 542, in map_reduction_local
    new_insn_add_within_inames.add(stage_exec_iname or base_exec_iname)
UnboundLocalError: local variable 'stage_exec_iname' referenced before assignment