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
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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 * <p>
44 * If both types are references, we apply the verifier's subclass check
45 * (or subtyping, if keepInterfaces).
46 * If the src type is a type guaranteed to be null (Void) it can be converted
47 * to any other reference type.
48 * <p>
49 * If both types are primitives, we apply the verifier's primitive conversions.
50 * These do not include Java conversions such as long to double, since those
51 * require computation and (in general) stack depth changes.
52 * But very simple 32-bit viewing changes, such as byte to int,
53 * are null conversions, because they do not require any computation.
54 * These conversions are from any type to a wider type up to 32 bits,
55 * as long as the conversion is not signed to unsigned (byte to char).
56 * <p>
57 * The primitive type 'void' does not interconvert with any other type,
58 * even though it is legal to drop any type from the stack and "return void".
59 * The stack effects, though are difference between void and any other type,
60 * so it is safer to report a non-trivial conversion.
61 *
62 * @param src the type of a stacked value
63 * @param dst the type by which we'd like to treat it
64 * @param keepInterfaces if false, we treat any interface as if it were Object
65 * @return whether the retyping can be done without motion or reformatting
66 */
67 public static boolean isNullConversion(Class<?> src, Class<?> dst, boolean keepInterfaces) {
68 if (src == dst) return true;
69 // Verifier allows any interface to be treated as Object:
70 if (!keepInterfaces) {
71 if (dst.isInterface()) dst = Object.class;
72 if (src.isInterface()) src = Object.class;
73 if (src == dst) return true; // check again
74 }
75 if (isNullType(src)) return !dst.isPrimitive();
76 if (!src.isPrimitive()) return dst.isAssignableFrom(src);
77 if (!dst.isPrimitive()) return false;
78 // Verifier allows an int to carry byte, short, char, or even boolean:
79 Wrapper sw = Wrapper.forPrimitiveType(src);
80 if (dst == int.class) return sw.isSubwordOrInt();
81 Wrapper dw = Wrapper.forPrimitiveType(dst);
82 if (!sw.isSubwordOrInt()) return false;
83 if (!dw.isSubwordOrInt()) return false;
84 if (!dw.isSigned() && sw.isSigned()) return false;
85 return dw.bitWidth() > sw.bitWidth();
86 }
87
88 /**
89 * Specialization of isNullConversion to reference types.
90 * @param src the type of a stacked value
91 * @param dst the reference type by which we'd like to treat it
92 * @return whether the retyping can be done without a cast
93 */
94 public static boolean isNullReferenceConversion(Class<?> src, Class<?> dst) {
95 assert(!dst.isPrimitive());
96 if (dst.isInterface()) return true; // verifier allows this
97 if (isNullType(src)) return true;
98 return dst.isAssignableFrom(src);
99 }
100
101 /**
102 * Is the given type java.lang.Null or an equivalent null-only type?
103 */
104 public static boolean isNullType(Class<?> type) {
105 // Any reference statically typed as Void is guaranteed to be null.
106 // Therefore, it can be safely treated as a value of any
107 // other type that admits null, i.e., a reference type.
108 if (type == Void.class) return true;
109 // Locally known null-only class:
110 if (type == Empty.class) return true;
111 return false;
112 }
113
114 /**
115 * True if a method handle can receive a call under a slightly different
116 * method type, without moving or reformatting any stack elements.
117 *
118 * @param call the type of call being made
119 * @param recv the type of the method handle receiving the call
120 * @return whether the retyping can be done without motion or reformatting
121 */
122 public static boolean isNullConversion(MethodType call, MethodType recv, boolean keepInterfaces) {
123 if (call == recv) return true;
124 int len = call.parameterCount();
125 if (len != recv.parameterCount()) return false;
126 for (int i = 0; i < len; i++)
127 if (!isNullConversion(call.parameterType(i), recv.parameterType(i), keepInterfaces))
128 return false;
129 return isNullConversion(recv.returnType(), call.returnType(), keepInterfaces);
130 }
131
132 /**
133 * Determine if the JVM verifier allows a value of type call to be
134 * passed to a formal parameter (or return variable) of type recv.
135 * Returns 1 if the verifier allows the types to match without conversion.
136 * Returns -1 if the types can be made to match by a JVM-supported adapter.
137 * Cases supported are:
138 * <ul><li>checkcast
139 * </li><li>conversion between any two integral types (but not floats)
140 * </li><li>unboxing from a wrapper to its corresponding primitive type
141 * </li><li>conversion in either direction between float and double
142 * </li></ul>
143 * (Autoboxing is not supported here; it must be done via Java code.)
144 * Returns 0 otherwise.
145 */
146 public static int canPassUnchecked(Class<?> src, Class<?> dst) {
147 if (src == dst)
148 return 1;
149
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