[test] Add test for recursive real function

tests/python/test_function.py

@@ -199,3 +199,25 @@ def run():
             add(30, 2)
 
         run()
+
+
+@test_utils.test(arch=[ti.cpu, ti.gpu], cfg_optimization=False)
+def test_recursion():
+    @ti.experimental.real_func
+    def sum(f: ti.template(), l: ti.i32, r: ti.i32) -> ti.i32:
+        ret = 0
+        if l == r:
+            ret = f[l]
+        else:
+            ret = sum(f, l, (l + r) // 2) + sum(f, (l + r) // 2 + 1, r)
+        return ret
+
+    f = ti.field(ti.i32, shape=100)
+    for i in range(100):
+        f[i] = i
+
+    @ti.kernel
+    def get_sum() -> ti.i32:
+        return sum(f, 0, 99)
+
+    assert get_sum() == 99 * 50