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* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
*
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* under the terms of the GNU General Public License version 2 only, as
* published by the Free Software Foundation. Oracle designates this
* particular file as subject to the "Classpath" exception as provided
* by Oracle in the LICENSE file that accompanied this code.
*
* This code is distributed in the hope that it will be useful, but WITHOUT
* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
* version 2 for more details (a copy is included in the LICENSE file that
* accompanied this code).
*
* You should have received a copy of the GNU General Public License version
* 2 along with this work; if not, write to the Free Software Foundation,
* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
*
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package sun.invoke.util;
import java.lang.invoke.MethodType;
import sun.invoke.empty.Empty;
/**
* This class centralizes information about the JVM verifier
* and its requirements about type correctness.
* @author jrose
*/
public class VerifyType {
private VerifyType() { } // cannot instantiate
/**
* True if a value can be stacked as the source type and unstacked as the
* destination type, without violating the JVM's type consistency.
*
* If both types are references, we apply the verifier's subclass check
* (or subtyping, if keepInterfaces).
* If the src type is a type guaranteed to be null (Void) it can be converted
* to any other reference type.
*
* If both types are primitives, we apply the verifier's primitive conversions.
* These do not include Java conversions such as long to double, since those
* require computation and (in general) stack depth changes.
* But very simple 32-bit viewing changes, such as byte to int,
* are null conversions, because they do not require any computation.
* These conversions are from any type to a wider type up to 32 bits,
* as long as the conversion is not signed to unsigned (byte to char).
*
* The primitive type 'void' does not interconvert with any other type,
* even though it is legal to drop any type from the stack and "return void".
* The stack effects, though are different between void and any other type,
* so it is safer to report a non-trivial conversion.
*
* @param src the type of a stacked value
* @param dst the type by which we'd like to treat it
* @param keepInterfaces if false, we treat any interface as if it were Object
* @return whether the retyping can be done without motion or reformatting
*/
public static boolean isNullConversion(Class src, Class dst, boolean keepInterfaces) {
if (src == dst) return true;
// Verifier allows any interface to be treated as Object:
if (!keepInterfaces) {
if (dst.isInterface()) dst = Object.class;
if (src.isInterface()) src = Object.class;
if (src == dst) return true; // check again
}
if (isNullType(src)) return !dst.isPrimitive();
if (!src.isPrimitive()) return dst.isAssignableFrom(src);
if (!dst.isPrimitive()) return false;
// Verifier allows an int to carry byte, short, char, or even boolean:
Wrapper sw = Wrapper.forPrimitiveType(src);
if (dst == int.class) return sw.isSubwordOrInt();
Wrapper dw = Wrapper.forPrimitiveType(dst);
if (!sw.isSubwordOrInt()) return false;
if (!dw.isSubwordOrInt()) return false;
if (!dw.isSigned() && sw.isSigned()) return false;
return dw.bitWidth() > sw.bitWidth();
}
/**
* Specialization of isNullConversion to reference types.
* @param src the type of a stacked value
* @param dst the reference type by which we'd like to treat it
* @return whether the retyping can be done without a cast
*/
public static boolean isNullReferenceConversion(Class src, Class dst) {
assert(!dst.isPrimitive());
if (dst.isInterface()) return true; // verifier allows this
if (isNullType(src)) return true;
return dst.isAssignableFrom(src);
}
/**
* Is the given type java.lang.Null or an equivalent null-only type?
*/
public static boolean isNullType(Class type) {
// Any reference statically typed as Void is guaranteed to be null.
// Therefore, it can be safely treated as a value of any
// other type that admits null, i.e., a reference type.
if (type == Void.class) return true;
// Locally known null-only class:
if (type == Empty.class) return true;
return false;
}
/**
* True if a method handle can receive a call under a slightly different
* method type, without moving or reformatting any stack elements.
*
* @param call the type of call being made
* @param recv the type of the method handle receiving the call
* @return whether the retyping can be done without motion or reformatting
*/
public static boolean isNullConversion(MethodType call, MethodType recv, boolean keepInterfaces) {
if (call == recv) return true;
int len = call.parameterCount();
if (len != recv.parameterCount()) return false;
for (int i = 0; i < len; i++)
if (!isNullConversion(call.parameterType(i), recv.parameterType(i), keepInterfaces))
return false;
return isNullConversion(recv.returnType(), call.returnType(), keepInterfaces);
}
/**
* Determine if the JVM verifier allows a value of type call to be
* passed to a formal parameter (or return variable) of type recv.
* Returns 1 if the verifier allows the types to match without conversion.
* Returns -1 if the types can be made to match by a JVM-supported adapter.
* Cases supported are:
*
- checkcast
*
- conversion between any two integral types (but not floats)
*
- unboxing from a wrapper to its corresponding primitive type
*
- conversion in either direction between float and double
*
* (Autoboxing is not supported here; it must be done via Java code.)
* Returns 0 otherwise.
*/
public static int canPassUnchecked(Class src, Class dst) {
if (src == dst)
return 1;
if (dst.isPrimitive()) {
if (dst == void.class)
// Return anything to a caller expecting void.
// This is a property of the implementation, which links
// return values via a register rather than via a stack push.
// This makes it possible to ignore cleanly.
return 1;
if (src == void.class)
return 0; // void-to-something?
if (!src.isPrimitive())
// Cannot pass a reference to any primitive type (exc. void).
return 0;
Wrapper sw = Wrapper.forPrimitiveType(src);
Wrapper dw = Wrapper.forPrimitiveType(dst);
if (sw.isSubwordOrInt() && dw.isSubwordOrInt()) {
if (sw.bitWidth() >= dw.bitWidth())
return -1; // truncation may be required
if (!dw.isSigned() && sw.isSigned())
return -1; // sign elimination may be required
return 1;
}
if (src == float.class || dst == float.class) {
if (src == double.class || dst == double.class)
return -1; // floating conversion may be required
else
return 0; // other primitive conversions NYI
} else {
// all fixed-point conversions are supported
return 0;
}
} else if (src.isPrimitive()) {
// Cannot pass a primitive to any reference type.
// (Maybe allow null.class?)
return 0;
}
// Handle reference types in the rest of the block:
// The verifier treats interfaces exactly like Object.
if (isNullReferenceConversion(src, dst))
// pass any reference to object or an arb. interface
return 1;
// else it's a definite "maybe" (cast is required)
return -1;
}
public static boolean isSpreadArgType(Class spreadArg) {
return spreadArg.isArray();
}
public static Class spreadArgElementType(Class spreadArg, int i) {
return spreadArg.getComponentType();
}
}