1 /*
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23 
24 /**
25  * @test TestMaybeNullUnsafeAccess
26  * @summary cast before unsafe access moved in dominating null check null path causes crash
27  * @requires vm.gc.Shenandoah
28  * @modules java.base/jdk.internal.misc:+open
29  *
30  * @run main/othervm -XX:-UseOnStackReplacement -XX:-BackgroundCompilation -XX:-TieredCompilation
31  *                   TestMaybeNullUnsafeAccess
32  *
33  * @run main/othervm -XX:-UseOnStackReplacement -XX:-BackgroundCompilation -XX:-TieredCompilation
34  *                   -XX:+UnlockExperimentalVMOptions -XX:+UseShenandoahGC
35  *                   TestMaybeNullUnsafeAccess
36  *
37  */
38 
39 import jdk.internal.misc.Unsafe;
40 
41 import java.lang.reflect.Field;
42 
43 public class TestMaybeNullUnsafeAccess {
44 
45     static final jdk.internal.misc.Unsafe UNSAFE = Unsafe.getUnsafe();
46     static final long F_OFFSET;
47 
48     static class A {
49         int f;
50     }
51 
52     static {
53         try {
54             Field fField = A.class.getDeclaredField("f");
55             F_OFFSET = UNSAFE.objectFieldOffset(fField);
56         } catch (Exception e) {
57             throw new RuntimeException(e);
58         }
59     }
60 
test_helper(Object o)61     static A test_helper(Object o) {
62         return (A) o;
63     }
64 
test(Object o)65     static int test(Object o) {
66         int f = 0;
67         for (int i = 0; i < 100; i++) {
68             A a = test_helper(o);
69             f = UNSAFE.getInt(a, F_OFFSET);
70         }
71         return f;
72     }
73 
main(String[] args)74     static public void main(String[] args) {
75         A a = new A();
76         for (int i = 0; i < 20000; i++) {
77             test_helper(null);
78             test_helper(a);
79             test(a);
80         }
81     }
82 
83 }
84