1 /*
2 * Copyright (c) 2010, 2013, 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. Oracle designates this
8 * particular file as subject to the "Classpath" exception as provided
9 * by Oracle in the LICENSE file that accompanied this code.
10 *
11 * This code is distributed in the hope that it will be useful, but WITHOUT
12 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
13 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
14 * version 2 for more details (a copy is included in the LICENSE file that
15 * accompanied this code).
16 *
17 * You should have received a copy of the GNU General Public License version
18 * 2 along with this work; if not, write to the Free Software Foundation,
19 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
20 *
21 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
22 * or visit www.oracle.com if you need additional information or have any
23 * questions.
24 */
25
26 package jdk.nashorn.internal.ir;
27
28 import jdk.nashorn.internal.codegen.types.Type;
29 import jdk.nashorn.internal.runtime.UnwarrantedOptimismException;
30
31 /**
32 * Common superclass for all expression nodes. Expression nodes can have
33 * an associated symbol as well as a type.
34 *
35 */
36 public abstract class Expression extends Node {
37 private static final long serialVersionUID = 1L;
38
39 static final String OPT_IDENTIFIER = "%";
40
41 protected Expression(final long token, final int start, final int finish) {
42 super(token, start, finish);
43 }
44
45 Expression(final long token, final int finish) {
46 super(token, finish);
47 }
48
49 Expression(final Expression expr) {
50 super(expr);
51 }
52
53 /**
54 * Returns the type of the expression.
55 *
56 * @return the type of the expression.
57 */
58 public abstract Type getType();
59
60 /**
61 * Returns {@code true} if this expression depends exclusively on state that is constant
62 * or local to the currently running function and thus inaccessible to other functions.
63 * This implies that a local expression must not call any other functions (neither directly
64 * nor implicitly through a getter, setter, or object-to-primitive type conversion).
65 *
66 * @return true if this expression does not depend on state shared with other functions.
67 */
68 public boolean isLocal() {
69 return false;
70 }
71
72 /**
73 * Is this a self modifying assignment?
74 * @return true if self modifying, e.g. a++, or a*= 17
75 */
76 public boolean isSelfModifying() {
77 return false;
78 }
79
80 /**
81 * Returns widest operation type of this operation.
82 *
83 * @return the widest type for this operation
84 */
85 public Type getWidestOperationType() {
86 return Type.OBJECT;
87 }
88
89 /**
90 * Returns true if the type of this expression is narrower than its widest operation type (thus, it is
91 * optimistically typed).
92 * @return true if this expression is optimistically typed.
93 */
94 public final boolean isOptimistic() {
95 return getType().narrowerThan(getWidestOperationType());
96 }
97
98 void optimisticTypeToString(final StringBuilder sb) {
99 optimisticTypeToString(sb, isOptimistic());
100 }
101
102 void optimisticTypeToString(final StringBuilder sb, final boolean optimistic) {
103 sb.append('{');
104 final Type type = getType();
105 final String desc = type == Type.UNDEFINED ? "U" : type.getDescriptor();
106
107 sb.append(desc.charAt(desc.length() - 1) == ';' ? "O" : desc);
108 if (isOptimistic() && optimistic) {
109 sb.append(OPT_IDENTIFIER);
110 final int pp = ((Optimistic)this).getProgramPoint();
111 if (UnwarrantedOptimismException.isValid(pp)) {
112 sb.append('_').append(pp);
113 }
114 }
115 sb.append('}');
116 }
117
118 /**
119 * Returns true if the runtime value of this expression is always false when converted to boolean as per ECMAScript
120 * ToBoolean conversion. Used in control flow calculations.
121 * @return true if this expression's runtime value converted to boolean is always false.
122 */
123 public boolean isAlwaysFalse() {
124 return false;
125 }
126
127 /**
128 * Returns true if the runtime value of this expression is always true when converted to boolean as per ECMAScript
129 * ToBoolean conversion. Used in control flow calculations.
130 * @return true if this expression's runtime value converted to boolean is always true.
131 */
132 public boolean isAlwaysTrue() {
133 return false;
134 }
135
136 /**
137 * Returns true if the expression is not null and {@link #isAlwaysFalse()}.
138 * @param test a test expression used as a predicate of a branch or a loop.
139 * @return true if the expression is not null and {@link #isAlwaysFalse()}.
140 */
141 public static boolean isAlwaysFalse(final Expression test) {
142 return test != null && test.isAlwaysFalse();
143 }
144
145
146 /**
147 * Returns true if the expression is null or {@link #isAlwaysTrue()}. Null is considered to be always true as a
148 * for loop with no test is equivalent to a for loop with always-true test.
149 * @param test a test expression used as a predicate of a branch or a loop.
150 * @return true if the expression is null or {@link #isAlwaysFalse()}.
151 */
152 public static boolean isAlwaysTrue(final Expression test) {
153 return test == null || test.isAlwaysTrue();
154 }
155 }