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.invoke.VarHandle;
28 import java.lang.invoke.MethodHandles;
29 import java.lang.ref.Reference;
30 import java.lang.ref.ReferenceQueue;
31 import java.lang.ref.SoftReference;
32 import java.lang.ref.WeakReference;
33 import jdk.test.lib.Asserts;
34
35 /**
36 * @test
37 * @summary Test that implicit null checks are generated as expected for
38 different GC memory accesses.
39 * @library /test/lib /
40 * @run driver compiler.gcbarriers.TestImplicitNullChecks
41 */
42
43
44 public class TestImplicitNullChecks {
45
46 static class Outer {
47 Object f;
48 }
49
50 static class OuterWithVolatileField {
51 volatile Object f;
52 }
53
54 static final VarHandle fVarHandle;
55 static {
56 MethodHandles.Lookup l = MethodHandles.lookup();
57 try {
58 fVarHandle = l.findVarHandle(Outer.class, "f", Object.class);
59 } catch (Exception e) {
60 throw new Error(e);
61 }
62 }
63
64 public static void main(String[] args) {
65 TestFramework.runWithFlags("-XX:CompileCommand=inline,java.lang.ref.*::*",
66 "-XX:-TieredCompilation");
67 }
68
69 @Test
70 // On AIX, implicit null checks are limited because the zero page is
71 // readable (but not writable). See os::zero_page_read_protected().
72 @IR(applyIfPlatform = {"aix", "false"},
73 applyIfOr = {"UseZGC", "true", "UseG1GC", "true"},
74 counts = {IRNode.NULL_CHECK, "1"},
75 phase = CompilePhase.FINAL_CODE)
76 static Object testLoad(Outer o) {
77 return o.f;
78 }
79
80 @Test
81 // On aarch64, volatile loads always use indirect memory operands, which
82 // leads to a pattern that cannot be exploited by the current C2 analysis.
83 // On PPC64, volatile loads are preceded by membar_volatile instructions,
84 // which also inhibits the current C2 analysis.
85 @IR(applyIfPlatformAnd = {"aarch64", "false", "ppc", "false"},
86 applyIfOr = {"UseZGC", "true", "UseG1GC", "true"},
87 counts = {IRNode.NULL_CHECK, "1"},
88 phase = CompilePhase.FINAL_CODE)
89 static Object testLoadVolatile(OuterWithVolatileField o) {
90 return o.f;
91 }
92
93 @Run(test = {"testLoad",
94 "testLoadVolatile"},
95 mode = RunMode.STANDALONE)
96 static void runLoadTests() {
97 {
98 Outer o = new Outer();
99 // Trigger compilation with implicit null check.
100 for (int i = 0; i < 10_000; i++) {
101 testLoad(o);
102 }
103 // Trigger null pointer exception.
104 o = null;
105 boolean nullPointerException = false;
106 try {
107 testLoad(o);
108 } catch (NullPointerException e) { nullPointerException = true; }
109 Asserts.assertTrue(nullPointerException);
110 }
111 {
112 OuterWithVolatileField o = new OuterWithVolatileField();
113 // Trigger compilation with implicit null check.
114 for (int i = 0; i < 10_000; i++) {
115 testLoadVolatile(o);
116 }
117 // Trigger null pointer exception.
118 o = null;
119 boolean nullPointerException = false;
120 try {
121 testLoadVolatile(o);
122 } catch (NullPointerException e) { nullPointerException = true; }
123 Asserts.assertTrue(nullPointerException);
124 }
125 }
126
127 @Test
128 // G1 and ZGC stores cannot be currently used to implement implicit null
129 // checks, because they expand into multiple memory access instructions that
130 // are not necessarily located at the initial instruction start address.
131 @IR(applyIfOr = {"UseZGC", "true", "UseG1GC", "true"},
132 failOn = IRNode.NULL_CHECK,
133 phase = CompilePhase.FINAL_CODE)
134 static void testStore(Outer o, Object o1) {
135 o.f = o1;
136 }
137
138 @Run(test = {"testStore"})
139 static void runStoreTests() {
140 {
141 Outer o = new Outer();
142 Object o1 = new Object();
143 testStore(o, o1);
144 }
145 }
146
147 @Test
148 // G1 and ZGC compare-and-exchange operations cannot be currently used to
149 // implement implicit null checks, because they expand into multiple memory
150 // access instructions that are not necessarily located at the initial
151 // instruction start address. The same holds for testCompareAndSwap and
152 // testGetAndSet below.
153 @IR(applyIfOr = {"UseZGC", "true", "UseG1GC", "true"},
154 failOn = IRNode.NULL_CHECK,
155 phase = CompilePhase.FINAL_CODE)
156 static Object testCompareAndExchange(Outer o, Object oldVal, Object newVal) {
157 return fVarHandle.compareAndExchange(o, oldVal, newVal);
158 }
159
160 @Test
161 @IR(applyIfOr = {"UseZGC", "true", "UseG1GC", "true"},
162 failOn = IRNode.NULL_CHECK,
163 phase = CompilePhase.FINAL_CODE)
164 static boolean testCompareAndSwap(Outer o, Object oldVal, Object newVal) {
165 return fVarHandle.compareAndSet(o, oldVal, newVal);
166 }
167
168 @Test
169 @IR(applyIfOr = {"UseZGC", "true", "UseG1GC", "true"},
170 failOn = IRNode.NULL_CHECK,
171 phase = CompilePhase.FINAL_CODE)
172 static Object testGetAndSet(Outer o, Object newVal) {
173 return fVarHandle.getAndSet(o, newVal);
174 }
175
176 @Run(test = {"testCompareAndExchange",
177 "testCompareAndSwap",
178 "testGetAndSet"})
179 static void runAtomicTests() {
180 {
181 Outer o = new Outer();
182 Object oldVal = new Object();
183 Object newVal = new Object();
184 testCompareAndExchange(o, oldVal, newVal);
185 }
186 {
187 Outer o = new Outer();
188 Object oldVal = new Object();
189 Object newVal = new Object();
190 testCompareAndSwap(o, oldVal, newVal);
191 }
192 {
193 Outer o = new Outer();
194 Object oldVal = new Object();
195 Object newVal = new Object();
196 testGetAndSet(o, newVal);
197 }
198 }
199
200 @Test
201 // G1 reference loads use indirect memory operands, which leads to a pattern
202 // that cannot be exploited by the current C2 analysis. The same holds for
203 // testLoadWeakReference.
204 @IR(applyIf = {"UseZGC", "true"},
205 counts = {IRNode.NULL_CHECK, "1"},
206 phase = CompilePhase.FINAL_CODE)
207 static Object testLoadSoftReference(SoftReference<Object> ref) {
208 return ref.get();
209 }
210
211 @Test
212 @IR(applyIf = {"UseZGC", "true"},
213 counts = {IRNode.NULL_CHECK, "1"},
214 phase = CompilePhase.FINAL_CODE)
215 static Object testLoadWeakReference(WeakReference<Object> ref) {
216 return ref.get();
217 }
218
219 @Run(test = {"testLoadSoftReference",
220 "testLoadWeakReference"})
221 static void runReferenceTests() {
222 {
223 Object o1 = new Object();
224 SoftReference<Object> sref = new SoftReference<Object>(o1);
225 Object o2 = testLoadSoftReference(sref);
226 }
227 {
228 Object o1 = new Object();
229 WeakReference<Object> wref = new WeakReference<Object>(o1);
230 Object o2 = testLoadWeakReference(wref);
231 }
232 }
233
234 }