[TIR] Regression test for PrettyPrint/IterMapExpr bugfix

Follow-up from apache#11412, adding a
regression test for the bugfix.

Author: Lunderberg

tests/python/unittest/test_arith_intset.py

@@ -322,6 +322,23 @@ def do_test_point_access(point, predicates, var_dom, expect):
     )
 
 
+def test_region_lower_bound_unfusable():
+    # This test is designed to trigger an error in DetectIterMap,
+    # resulting from a numerator which required multiple input
+    # variables.  The bug resulted in an exception being thrown,
+    # rather than a return value of None.
+    var_dom = {
+        tvm.tir.Var("i", "int32"): tvm.ir.Range(8),
+        tvm.tir.Var("j", "int32"): tvm.ir.Range(4),
+    }
+    i, j = var_dom
+    region = [
+        tvm.ir.Range.from_min_extent((i + j) // 2, 1),
+    ]
+    result = tvm.arith.estimate_region_lower_bound(region, var_dom, predicate=True)
+    assert result is None
+
+
 def test_union_lower_bound():
     neg_inf = tvm.arith.int_set.neg_inf()
     pos_inf = tvm.arith.int_set.pos_inf()