1 /*
2 * Copyright (c) 2025, Oracle and/or its affiliates. All rights reserved.
3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
4 *
5 * This code is free software; you can redistribute it and/or modify it
6 * under the terms of the GNU General Public License version 2 only, as
7 * published by the Free Software Foundation.
8 *
9 * This code is distributed in the hope that it will be useful, but WITHOUT
10 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
11 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
12 * version 2 for more details (a copy is included in the LICENSE file that
13 * accompanied this code).
14 *
15 * You should have received a copy of the GNU General Public License version
16 * 2 along with this work; if not, write to the Free Software Foundation,
17 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
18 *
19 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
20 * or visit www.oracle.com if you need additional information or have any
21 * questions.
22 */
23
24 package compiler.gcbarriers;
25
26 import compiler.lib.ir_framework.*;
27 import java.lang.ref.SoftReference;
28 import java.lang.ref.WeakReference;
29 import jdk.test.lib.Asserts;
30 import jdk.internal.misc.Unsafe;
31
32 /**
33 * @test
34 * @summary Test that implicit null checks are generated as expected for
35 different GC memory accesses.
36 * @library /test/lib /
37 * @modules java.base/jdk.internal.misc
38 * @run driver compiler.gcbarriers.TestImplicitNullChecks
39 */
40
41
42 public class TestImplicitNullChecks {
43
44 static class Outer {
45 Object f;
46 }
47
48 static class OuterWithVolatileField {
49 volatile Object f;
50 }
51
52 static final Unsafe UNSAFE = Unsafe.getUnsafe();
53 static final long F_OFFSET;
54 static {
55 try {
56 F_OFFSET = UNSAFE.objectFieldOffset(Outer.class.getDeclaredField("f"));
57 } catch (Exception e) {
58 throw new Error(e);
59 }
60 }
61
62 public static void main(String[] args) {
63 TestFramework.runWithFlags("--add-exports", "java.base/jdk.internal.misc=ALL-UNNAMED",
64 "-XX:CompileCommand=inline,java.lang.ref.*::*",
65 "-XX:-TieredCompilation");
66 TestFramework.runWithFlags("--add-exports", "java.base/jdk.internal.misc=ALL-UNNAMED",
67 "-XX:CompileCommand=inline,java.lang.ref.*::*",
68 "-XX:+TieredCompilation", "-XX:TieredStopAtLevel=1");
69 }
70
71 @Test
72 // On AIX, implicit null checks are limited because the zero page is
73 // readable (but not writable). See os::zero_page_read_protected().
74 @IR(applyIfPlatform = {"aix", "false"},
75 applyIfOr = {"UseZGC", "true", "UseG1GC", "true"},
76 counts = {IRNode.NULL_CHECK, "1"},
77 phase = CompilePhase.FINAL_CODE)
78 static Object testLoad(Outer o) {
79 return o.f;
80 }
81
82 @Test
83 // On aarch64, volatile loads always use indirect memory operands, which
84 // leads to a pattern that cannot be exploited by the current C2 analysis.
85 // On PPC64, volatile loads are preceded by membar_volatile instructions,
86 // which also inhibits the current C2 analysis.
87 @IR(applyIfPlatformAnd = {"aarch64", "false", "ppc", "false"},
88 applyIfOr = {"UseZGC", "true", "UseG1GC", "true"},
89 counts = {IRNode.NULL_CHECK, "1"},
90 phase = CompilePhase.FINAL_CODE)
91 static Object testLoadVolatile(OuterWithVolatileField o) {
92 return o.f;
93 }
94
95 @Run(test = {"testLoad",
96 "testLoadVolatile"},
97 mode = RunMode.STANDALONE)
98 static void runLoadTests() {
99 {
100 Outer o = new Outer();
101 // Trigger compilation with implicit null check.
102 for (int i = 0; i < 10_000; i++) {
103 testLoad(o);
104 }
105 // Trigger null pointer exception.
106 o = null;
107 boolean nullPointerException = false;
108 try {
109 testLoad(o);
110 } catch (NullPointerException e) { nullPointerException = true; }
111 Asserts.assertTrue(nullPointerException);
112 }
113 {
114 OuterWithVolatileField o = new OuterWithVolatileField();
115 // Trigger compilation with implicit null check.
116 for (int i = 0; i < 10_000; i++) {
117 testLoadVolatile(o);
118 }
119 // Trigger null pointer exception.
120 o = null;
121 boolean nullPointerException = false;
122 try {
123 testLoadVolatile(o);
124 } catch (NullPointerException e) { nullPointerException = true; }
125 Asserts.assertTrue(nullPointerException);
126 }
127 }
128
129 @Test
130 // G1 and ZGC stores cannot be currently used to implement implicit null
131 // checks, because they expand into multiple memory access instructions that
132 // are not necessarily located at the initial instruction start address.
133 @IR(applyIfOr = {"UseZGC", "true", "UseG1GC", "true"},
134 failOn = IRNode.NULL_CHECK,
135 phase = CompilePhase.FINAL_CODE)
136 static void testStore(Outer o, Object o1) {
137 o.f = o1;
138 }
139
140 @Run(test = {"testStore"})
141 static void runStoreTests() {
142 {
143 Outer o = new Outer();
144 Object o1 = new Object();
145 testStore(o, o1);
146 }
147 }
148
149 @Test
150 // G1 and ZGC compare-and-exchange operations cannot be currently used to
151 // implement implicit null checks, because they expand into multiple memory
152 // access instructions that are not necessarily located at the initial
153 // instruction start address. The same holds for testCompareAndSwap and
154 // testGetAndSet below.
155 @IR(applyIfOr = {"UseZGC", "true", "UseG1GC", "true"},
156 failOn = IRNode.NULL_CHECK,
157 phase = CompilePhase.FINAL_CODE)
158 static Object testCompareAndExchange(Outer o, Object oldVal, Object newVal) {
159 return UNSAFE.compareAndExchangeReference(o, F_OFFSET, oldVal, newVal);
160 }
161
162 @Test
163 @IR(applyIfOr = {"UseZGC", "true", "UseG1GC", "true"},
164 failOn = IRNode.NULL_CHECK,
165 phase = CompilePhase.FINAL_CODE)
166 static boolean testCompareAndSwap(Outer o, Object oldVal, Object newVal) {
167 return UNSAFE.compareAndSetReference(o, F_OFFSET, oldVal, newVal);
168 }
169
170 @Test
171 @IR(applyIfOr = {"UseZGC", "true", "UseG1GC", "true"},
172 failOn = IRNode.NULL_CHECK,
173 phase = CompilePhase.FINAL_CODE)
174 static Object testGetAndSet(Outer o, Object newVal) {
175 return UNSAFE.getAndSetReference(o, F_OFFSET, newVal);
176 }
177
178 @Run(test = {"testCompareAndExchange",
179 "testCompareAndSwap",
180 "testGetAndSet"})
181 static void runAtomicTests() {
182 {
183 Outer o = new Outer();
184 Object oldVal = new Object();
185 Object newVal = new Object();
186 testCompareAndExchange(o, oldVal, newVal);
187 }
188 {
189 Outer o = new Outer();
190 Object oldVal = new Object();
191 Object newVal = new Object();
192 testCompareAndSwap(o, oldVal, newVal);
193 }
194 {
195 Outer o = new Outer();
196 Object oldVal = new Object();
197 Object newVal = new Object();
198 testGetAndSet(o, newVal);
199 }
200 }
201
202 @Test
203 // G1 reference loads use indirect memory operands, which leads to a pattern
204 // that cannot be exploited by the current C2 analysis. The same holds for
205 // testLoadWeakReference.
206 @IR(applyIf = {"UseZGC", "true"},
207 counts = {IRNode.NULL_CHECK, "1"},
208 phase = CompilePhase.FINAL_CODE)
209 static Object testLoadSoftReference(SoftReference<Object> ref) {
210 return ref.get();
211 }
212
213 @Test
214 @IR(applyIf = {"UseZGC", "true"},
215 counts = {IRNode.NULL_CHECK, "1"},
216 phase = CompilePhase.FINAL_CODE)
217 static Object testLoadWeakReference(WeakReference<Object> ref) {
218 return ref.get();
219 }
220
221 @Run(test = {"testLoadSoftReference",
222 "testLoadWeakReference"})
223 static void runReferenceTests() {
224 {
225 Object o1 = new Object();
226 SoftReference<Object> sref = new SoftReference<Object>(o1);
227 Object o2 = testLoadSoftReference(sref);
228 }
229 {
230 Object o1 = new Object();
231 WeakReference<Object> wref = new WeakReference<Object>(o1);
232 Object o2 = testLoadWeakReference(wref);
233 }
234 }
235
236 }