1 /*
2 * Copyright (c) 2008, 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 sun.invoke.util;
27
28 import java.lang.invoke.MethodType;
29 import sun.invoke.empty.Empty;
30
31 /**
32 * This class centralizes information about the JVM verifier
33 * and its requirements about type correctness.
34 * @author jrose
35 */
36 public class VerifyType {
37
38 private VerifyType() { } // cannot instantiate
39
40 /**
41 * True if a value can be stacked as the source type and unstacked as the
42 * destination type, without violating the JVM's type consistency.
43 *
44 * @param src the type of a stacked value
45 * @param dst the type by which we'd like to treat it
46 * @return whether the retyping can be done without motion or reformatting
47 */
48 public static boolean isNullConversion(Class<?> src, Class<?> dst) {
49 if (src == dst) return true;
50 // Verifier allows any interface to be treated as Object:
51 if (dst.isInterface()) dst = Object.class;
52 if (src.isInterface()) src = Object.class;
53 if (src == dst) return true; // check again
54 if (dst == void.class) return true; // drop any return value
55 if (isNullType(src)) return !dst.isPrimitive();
56 if (!src.isPrimitive()) return dst.isAssignableFrom(src);
57 if (!dst.isPrimitive()) return false;
58 // Verifier allows an int to carry byte, short, char, or even boolean:
59 Wrapper sw = Wrapper.forPrimitiveType(src);
60 if (dst == int.class) return sw.isSubwordOrInt();
61 Wrapper dw = Wrapper.forPrimitiveType(dst);
62 if (!sw.isSubwordOrInt()) return false;
63 if (!dw.isSubwordOrInt()) return false;
64 if (!dw.isSigned() && sw.isSigned()) return false;
65 return dw.bitWidth() > sw.bitWidth();
66 }
67
68 /**
69 * Specialization of isNullConversion to reference types.
70 * @param src the type of a stacked value
71 * @param dst the reference type by which we'd like to treat it
72 * @return whether the retyping can be done without a cast
73 */
74 public static boolean isNullReferenceConversion(Class<?> src, Class<?> dst) {
75 assert(!dst.isPrimitive());
76 if (dst.isInterface()) return true; // verifier allows this
77 if (isNullType(src)) return true;
78 return dst.isAssignableFrom(src);
79 }
80
81 /**
82 * Is the given type java.lang.Null or an equivalent null-only type?
83 */
84 public static boolean isNullType(Class<?> type) {
85 if (type == null) return false;
86 return type == NULL_CLASS
87 // This one may also be used as a null type.
88 // TO DO: Decide if we really want to legitimize it here.
89 // Probably we do, unless java.lang.Null really makes it into Java 7
90 //|| type == Void.class
91 // Locally known null-only class:
92 || type == Empty.class
93 ;
94 }
95 private static final Class<?> NULL_CLASS;
96 static {
97 Class<?> nullClass = null;
98 try {
99 nullClass = Class.forName("java.lang.Null");
100 } catch (ClassNotFoundException ex) {
101 // OK, we'll cope
102 }
103 NULL_CLASS = nullClass;
104 }
105
106 /**
107 * True if a method handle can receive a call under a slightly different
108 * method type, without moving or reformatting any stack elements.
109 *
110 * @param call the type of call being made
111 * @param recv the type of the method handle receiving the call
112 * @return whether the retyping can be done without motion or reformatting
113 */
114 public static boolean isNullConversion(MethodType call, MethodType recv) {
115 if (call == recv) return true;
116 int len = call.parameterCount();
117 if (len != recv.parameterCount()) return false;
118 for (int i = 0; i < len; i++)
119 if (!isNullConversion(call.parameterType(i), recv.parameterType(i)))
120 return false;
121 return isNullConversion(recv.returnType(), call.returnType());
122 }
123
124 /**
125 * Determine if the JVM verifier allows a value of type call to be
126 * passed to a formal parameter (or return variable) of type recv.
127 * Returns 1 if the verifier allows the types to match without conversion.
128 * Returns -1 if the types can be made to match by a JVM-supported adapter.
129 * Cases supported are:
130 * <ul><li>checkcast
131 * </li><li>conversion between any two integral types (but not floats)
132 * </li><li>unboxing from a wrapper to its corresponding primitive type
133 * </li><li>conversion in either direction between float and double
134 * </li></ul>
135 * (Autoboxing is not supported here; it must be done via Java code.)
136 * Returns 0 otherwise.
137 */
138 public static int canPassUnchecked(Class<?> src, Class<?> dst) {
139 if (src == dst)
140 return 1;
141
142 if (dst.isPrimitive()) {
143 if (dst == void.class)
144 // Return anything to a caller expecting void.
145 // This is a property of the implementation, which links
146 // return values via a register rather than via a stack push.
147 // This makes it possible to ignore cleanly.
148 return 1;
149 if (src == void.class)
150 return 0; // void-to-something?
151 if (!src.isPrimitive())
152 // Cannot pass a reference to any primitive type (exc. void).
153 return 0;
154 Wrapper sw = Wrapper.forPrimitiveType(src);
155 Wrapper dw = Wrapper.forPrimitiveType(dst);
156 if (sw.isSubwordOrInt() && dw.isSubwordOrInt()) {
157 if (sw.bitWidth() >= dw.bitWidth())
158 return -1; // truncation may be required
159 if (!dw.isSigned() && sw.isSigned())
160 return -1; // sign elimination may be required
161 return 1;
162 }
163 if (src == float.class || dst == float.class) {
164 if (src == double.class || dst == double.class)
165 return -1; // floating conversion may be required
166 else
167 return 0; // other primitive conversions NYI
168 } else {
169 // all fixed-point conversions are supported
170 return 0;
171 }
172 } else if (src.isPrimitive()) {
173 // Cannot pass a primitive to any reference type.
174 // (Maybe allow null.class?)
175 return 0;
176 }
177
178 // Handle reference types in the rest of the block:
179
180 // The verifier treats interfaces exactly like Object.
181 if (isNullReferenceConversion(src, dst))
182 // pass any reference to object or an arb. interface
183 return 1;
184 // else it's a definite "maybe" (cast is required)
185 return -1;
186 }
187
188 public static boolean isSpreadArgType(Class<?> spreadArg) {
189 return spreadArg.isArray();
190 }
191 public static Class<?> spreadArgElementType(Class<?> spreadArg, int i) {
192 return spreadArg.getComponentType();
193 }
194 }