1 /*
2 * Copyright (c) 2011, 2018, 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 */
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41 package jdk.internal.vm.compiler.word;
42
43 // JaCoCo Exclude
44
45 /**
46 * Marker interface for location identities. A different location identity of two memory accesses
47 * guarantees that the two accesses do not interfere.
48 * <p>
49 * Clients of {@link LocationIdentity} must use {@link #equals(Object)}, not {@code ==}, when
50 * comparing two {@link LocationIdentity} values for equality. Likewise, they must not use
51 * {@link java.util.IdentityHashMap}s with {@link LocationIdentity} values as keys.
52 *
53 * @since 1.0
54 */
55 public abstract class LocationIdentity {
56
57 private static final class AnyLocationIdentity extends LocationIdentity {
58 @Override
59 public boolean isImmutable() {
60 return false;
61 }
62
63 @Override
64 public String toString() {
65 return "ANY_LOCATION";
66 }
67 }
68
69 private static final class InitLocationIdentity extends LocationIdentity {
70 @Override
71 public boolean isImmutable() {
72 return true;
73 }
74
75 @Override
76 public String toString() {
77 return "INIT_LOCATION";
78 }
79 }
80
81 /**
82 * Creates a new location identity. Subclasses are responsible to provide proper implementations
83 * of {@link #equals} and {@link #hashCode}.
84 *
85 * @since 1.0
86 */
87 protected LocationIdentity() {
88 }
89
90 /**
91 * Indicates that the given location is the union of all possible mutable locations. A write to
92 * such a location kill all reads from mutable locations and a read from this location is killed
93 * by any write (except for initialization writes).
94 *
95 * @since 1.0
96 */
97 public static final LocationIdentity ANY_LOCATION = new AnyLocationIdentity();
98
99 /**
100 * Location only allowed to be used for writes. Indicates that a completely new memory location
101 * is written. Kills no read. The previous value at the given location must be either
102 * uninitialized or null. Writes to this location do not need a GC pre-barrier.
103 *
104 * @since 1.0
105 */
106 public static final LocationIdentity INIT_LOCATION = new InitLocationIdentity();
107
108 /**
109 * Indicates that the given location is the union of all possible mutable locations. A write to
110 * such a location kill all reads from mutable locations and a read from this location is killed
111 * by any write (except for initialization writes).
112 *
113 * @since 1.0
114 */
115 public static LocationIdentity any() {
116 return ANY_LOCATION;
117 }
118
119 /**
120 * Location only allowed to be used for writes. Indicates that a completely new memory location
121 * is written. Kills no read. The previous value at the given location must be either
122 * uninitialized or null. Writes to this location do not need a GC pre-barrier.
123 *
124 * @since 1.0
125 */
126 public static LocationIdentity init() {
127 return INIT_LOCATION;
128 }
129
130 /**
131 * Denotes a location is unchanging in all cases. Not that this is different than the Java
132 * notion of final which only requires definite assignment.
133 *
134 * @since 1.0
135 */
136 public abstract boolean isImmutable();
137
138 /**
139 * The inversion of {@link #isImmutable}.
140 *
141 * @since 1.0
142 */
143 public final boolean isMutable() {
144 return !isImmutable();
145 }
146
147 /**
148 * Returns true if this location identity is {@link #any}.
149 *
150 * @since 1.0
151 */
152 public final boolean isAny() {
153 return this == ANY_LOCATION;
154 }
155
156 /**
157 * Returns true if this location identity is {@link #init}.
158 *
159 * @since 1.0
160 */
161 public final boolean isInit() {
162 return this == INIT_LOCATION;
163 }
164
165 /**
166 * Returns true if this location identity is not {@link #any}.
167 *
168 * @since 1.0
169 */
170 public final boolean isSingle() {
171 return this != ANY_LOCATION;
172 }
173
174 /**
175 * Returns true if the memory slice denoted by this location identity may overlap with the
176 * provided other location identity.
177 *
178 * @since 1.0
179 */
180 public final boolean overlaps(LocationIdentity other) {
181 return isAny() || other.isAny() || this.equals(other);
182 }
183 }