Java Code Examples for com.android.dx.rop.type.Type#isArray()

/**
 * Returns the required array type for an array load or store
 * instruction, based on a given implied type and an observed
 * actual array type.
 *
 * <p>The interesting cases here have to do with object arrays,
 * <code>byte[]</code>s, <code>boolean[]</code>s, and
 * known-nulls.</p>
 *
 * <p>In the case of arrays of objects, we want to narrow the type
 * to the actual array present on the stack, as long as what is
 * present is an object type. Similarly, due to a quirk of the
 * original bytecode representation, the instructions for dealing
 * with <code>byte[]</code> and <code>boolean[]</code> are
 * undifferentiated, and we aim here to return whichever one was
 * actually present on the stack.</p>
 *
 * <p>In the case where there is a known-null on the stack where
 * an array is expected, our behavior depends on the implied type
 * of the instruction. When the implied type is a reference, we
 * don't attempt to infer anything, as we don't know the dimension
 * of the null constant and thus any explicit inferred type could
 * be wrong. When the implied type is a primitive, we fall back to
 * the implied type of the instruction. Due to the quirk described
 * above, this means that source code that uses
 * <code>boolean[]</code> might get translated surprisingly -- but
 * correctly -- into an instruction that specifies a
 * <code>byte[]</code>. It will be correct, because should the
 * code actually execute, it will necessarily throw a
 * <code>NullPointerException</code>, and it won't matter what
 * opcode variant is used to achieve that result.</p>
 *
 * @param impliedType {@code non-null;} type implied by the
 * instruction; is <i>not</i> an array type
 * @param foundArrayType {@code non-null;} type found on the
 * stack; is either an array type or a known-null
 * @return {@code non-null;} the array type that should be
 * required in this context
 */
private static Type requiredArrayTypeFor(Type impliedType,
        Type foundArrayType) {
    if (foundArrayType == Type.KNOWN_NULL) {
        return impliedType.isReference()
            ? Type.KNOWN_NULL
            : impliedType.getArrayType();
    }

    if ((impliedType == Type.OBJECT)
            && foundArrayType.isArray()
            && foundArrayType.getComponentType().isReference()) {
        return foundArrayType;
    }

    if ((impliedType == Type.BYTE)
            && (foundArrayType == Type.BOOLEAN_ARRAY)) {
        /*
         * Per above, an instruction with implied byte[] is also
         * allowed to be used on boolean[].
         */
        return Type.BOOLEAN_ARRAY;
    }

    return impliedType.getArrayType();
}
 

/**
 * Merges two frame types.
 *
 * @param ft1 {@code non-null;} a frame type
 * @param ft2 {@code non-null;} another frame type
 * @return {@code non-null;} the result of merging the two types
 */
public static TypeBearer mergeType(TypeBearer ft1, TypeBearer ft2) {
    if ((ft1 == null) || ft1.equals(ft2)) {
        return ft1;
    } else if (ft2 == null) {
        return null;
    } else {
        Type type1 = ft1.getType();
        Type type2 = ft2.getType();

        if (type1 == type2) {
            return type1;
        } else if (type1.isReference() && type2.isReference()) {
            if (type1 == Type.KNOWN_NULL) {
                /*
                 * A known-null merges with any other reference type to
                 * be that reference type.
                 */
                return type2;
            } else if (type2 == Type.KNOWN_NULL) {
                /*
                 * The same as above, but this time it's type2 that's
                 * the known-null.
                 */
                return type1;
            } else if (type1.isArray() && type2.isArray()) {
                TypeBearer componentUnion =
                    mergeType(type1.getComponentType(),
                            type2.getComponentType());
                if (componentUnion == null) {
                    /*
                     * At least one of the types is a primitive type,
                     * so the merged result is just Object.
                     */
                    return Type.OBJECT;
                }
                return ((Type) componentUnion).getArrayType();
            } else {
                /*
                 * All other unequal reference types get merged to be
                 * Object in this phase. This is fine here, but it
                 * won't be the right thing to do in the verifier.
                 */
                return Type.OBJECT;
            }
        } else if (type1.isIntlike() && type2.isIntlike()) {
            /*
             * Merging two non-identical int-like types results in
             * the type int.
             */
            return Type.INT;
        } else {
            return null;
        }
    }
}
 

/**
 * Returns whether the given supertype is possibly assignable from
 * the given subtype. This takes into account primitiveness,
 * int-likeness, known-nullness, and array dimensions, but does
 * not assume anything about class hierarchy other than that the
 * type {@code Object} is the supertype of all reference
 * types and all arrays are assignable to
 * {@code Serializable} and {@code Cloneable}.
 *
 * @param supertypeBearer {@code non-null;} the supertype
 * @param subtypeBearer {@code non-null;} the subtype
 */
public static boolean isPossiblyAssignableFrom(TypeBearer supertypeBearer,
        TypeBearer subtypeBearer) {
    Type supertype = supertypeBearer.getType();
    Type subtype = subtypeBearer.getType();

    if (supertype.equals(subtype)) {
        // Easy out.
        return true;
    }

    int superBt = supertype.getBasicType();
    int subBt = subtype.getBasicType();

    // Treat return types as Object for the purposes of this method.

    if (superBt == Type.BT_ADDR) {
        supertype = Type.OBJECT;
        superBt = Type.BT_OBJECT;
    }

    if (subBt == Type.BT_ADDR) {
        subtype = Type.OBJECT;
        subBt = Type.BT_OBJECT;
    }

    if ((superBt != Type.BT_OBJECT) || (subBt != Type.BT_OBJECT)) {
        /*
         * No two distinct primitive types are assignable in this sense,
         * unless they are both int-like.
         */
        return supertype.isIntlike() && subtype.isIntlike();
    }

    // At this point, we know both types are reference types.

    if (supertype == Type.KNOWN_NULL) {
        /*
         * A known-null supertype is only assignable from another
         * known-null (handled in the easy out at the top of the
         * method).
         */
        return false;
    } else if (subtype == Type.KNOWN_NULL) {
        /*
         * A known-null subtype is in fact assignable to any
         * reference type.
         */
        return true;
    } else if (supertype == Type.OBJECT) {
        /*
         * Object is assignable from any reference type.
         */
        return true;
    } else if (supertype.isArray()) {
        // The supertype is an array type.
        if (! subtype.isArray()) {
            // The subtype isn't an array, and so can't be assignable.
            return false;
        }

        /*
         * Strip off as many matched component types from both
         * types as possible, and check the assignability of the
         * results.
         */
        do {
            supertype = supertype.getComponentType();
            subtype = subtype.getComponentType();
        } while (supertype.isArray() && subtype.isArray());

        return isPossiblyAssignableFrom(supertype, subtype);
    } else if (subtype.isArray()) {
        /*
         * Other than Object (handled above), array types are
         * assignable only to Serializable and Cloneable.
         */
        return (supertype == Type.SERIALIZABLE) ||
            (supertype == Type.CLONEABLE);
    } else {
        /*
         * All other unequal reference types are considered at
         * least possibly assignable.
         */
        return true;
    }
}
 

/**
 * Returns the required array type for an array load or store
 * instruction, based on a given implied type and an observed
 * actual array type.
 *
 * <p>The interesting cases here have to do with object arrays,
 * <code>byte[]</code>s, <code>boolean[]</code>s, and
 * known-nulls.</p>
 *
 * <p>In the case of arrays of objects, we want to narrow the type
 * to the actual array present on the stack, as long as what is
 * present is an object type. Similarly, due to a quirk of the
 * original bytecode representation, the instructions for dealing
 * with <code>byte[]</code> and <code>boolean[]</code> are
 * undifferentiated, and we aim here to return whichever one was
 * actually present on the stack.</p>
 *
 * <p>In the case where there is a known-null on the stack where
 * an array is expected, our behavior depends on the implied type
 * of the instruction. When the implied type is a reference, we
 * don't attempt to infer anything, as we don't know the dimension
 * of the null constant and thus any explicit inferred type could
 * be wrong. When the implied type is a primitive, we fall back to
 * the implied type of the instruction. Due to the quirk described
 * above, this means that source code that uses
 * <code>boolean[]</code> might get translated surprisingly -- but
 * correctly -- into an instruction that specifies a
 * <code>byte[]</code>. It will be correct, because should the
 * code actually execute, it will necessarily throw a
 * <code>NullPointerException</code>, and it won't matter what
 * opcode variant is used to achieve that result.</p>
 *
 * @param impliedType {@code non-null;} type implied by the
 * instruction; is <i>not</i> an array type
 * @param foundArrayType {@code non-null;} type found on the
 * stack; is either an array type or a known-null
 * @return {@code non-null;} the array type that should be
 * required in this context
 */
private static Type requiredArrayTypeFor(Type impliedType,
        Type foundArrayType) {
    if (foundArrayType == Type.KNOWN_NULL) {
        return impliedType.isReference()
            ? Type.KNOWN_NULL
            : impliedType.getArrayType();
    }

    if ((impliedType == Type.OBJECT)
            && foundArrayType.isArray()
            && foundArrayType.getComponentType().isReference()) {
        return foundArrayType;
    }

    if ((impliedType == Type.BYTE)
            && (foundArrayType == Type.BOOLEAN_ARRAY)) {
        /*
         * Per above, an instruction with implied byte[] is also
         * allowed to be used on boolean[].
         */
        return Type.BOOLEAN_ARRAY;
    }

    return impliedType.getArrayType();
}
 

/**
 * Merges two frame types.
 *
 * @param ft1 {@code non-null;} a frame type
 * @param ft2 {@code non-null;} another frame type
 * @return {@code non-null;} the result of merging the two types
 */
public static TypeBearer mergeType(TypeBearer ft1, TypeBearer ft2) {
    if ((ft1 == null) || ft1.equals(ft2)) {
        return ft1;
    } else if (ft2 == null) {
        return null;
    } else {
        Type type1 = ft1.getType();
        Type type2 = ft2.getType();

        if (type1 == type2) {
            return type1;
        } else if (type1.isReference() && type2.isReference()) {
            if (type1 == Type.KNOWN_NULL) {
                /*
                 * A known-null merges with any other reference type to
                 * be that reference type.
                 */
                return type2;
            } else if (type2 == Type.KNOWN_NULL) {
                /*
                 * The same as above, but this time it's type2 that's
                 * the known-null.
                 */
                return type1;
            } else if (type1.isArray() && type2.isArray()) {
                TypeBearer componentUnion =
                    mergeType(type1.getComponentType(),
                            type2.getComponentType());
                if (componentUnion == null) {
                    /*
                     * At least one of the types is a primitive type,
                     * so the merged result is just Object.
                     */
                    return Type.OBJECT;
                }
                return ((Type) componentUnion).getArrayType();
            } else {
                /*
                 * All other unequal reference types get merged to be
                 * Object in this phase. This is fine here, but it
                 * won't be the right thing to do in the verifier.
                 */
                return Type.OBJECT;
            }
        } else if (type1.isIntlike() && type2.isIntlike()) {
            /*
             * Merging two non-identical int-like types results in
             * the type int.
             */
            return Type.INT;
        } else {
            return null;
        }
    }
}
 

/**
 * Returns whether the given supertype is possibly assignable from
 * the given subtype. This takes into account primitiveness,
 * int-likeness, known-nullness, and array dimensions, but does
 * not assume anything about class hierarchy other than that the
 * type {@code Object} is the supertype of all reference
 * types and all arrays are assignable to
 * {@code Serializable} and {@code Cloneable}.
 *
 * @param supertypeBearer {@code non-null;} the supertype
 * @param subtypeBearer {@code non-null;} the subtype
 */
public static boolean isPossiblyAssignableFrom(TypeBearer supertypeBearer,
        TypeBearer subtypeBearer) {
    Type supertype = supertypeBearer.getType();
    Type subtype = subtypeBearer.getType();

    if (supertype.equals(subtype)) {
        // Easy out.
        return true;
    }

    int superBt = supertype.getBasicType();
    int subBt = subtype.getBasicType();

    // Treat return types as Object for the purposes of this method.

    if (superBt == Type.BT_ADDR) {
        supertype = Type.OBJECT;
        superBt = Type.BT_OBJECT;
    }

    if (subBt == Type.BT_ADDR) {
        subtype = Type.OBJECT;
        subBt = Type.BT_OBJECT;
    }

    if ((superBt != Type.BT_OBJECT) || (subBt != Type.BT_OBJECT)) {
        /*
         * No two distinct primitive types are assignable in this sense,
         * unless they are both int-like.
         */
        return supertype.isIntlike() && subtype.isIntlike();
    }

    // At this point, we know both types are reference types.

    if (supertype == Type.KNOWN_NULL) {
        /*
         * A known-null supertype is only assignable from another
         * known-null (handled in the easy out at the top of the
         * method).
         */
        return false;
    } else if (subtype == Type.KNOWN_NULL) {
        /*
         * A known-null subtype is in fact assignable to any
         * reference type.
         */
        return true;
    } else if (supertype == Type.OBJECT) {
        /*
         * Object is assignable from any reference type.
         */
        return true;
    } else if (supertype.isArray()) {
        // The supertype is an array type.
        if (! subtype.isArray()) {
            // The subtype isn't an array, and so can't be assignable.
            return false;
        }

        /*
         * Strip off as many matched component types from both
         * types as possible, and check the assignability of the
         * results.
         */
        do {
            supertype = supertype.getComponentType();
            subtype = subtype.getComponentType();
        } while (supertype.isArray() && subtype.isArray());

        return isPossiblyAssignableFrom(supertype, subtype);
    } else if (subtype.isArray()) {
        /*
         * Other than Object (handled above), array types are
         * assignable only to Serializable and Cloneable.
         */
        return (supertype == Type.SERIALIZABLE) ||
            (supertype == Type.CLONEABLE);
    } else {
        /*
         * All other unequal reference types are considered at
         * least possibly assignable.
         */
        return true;
    }
}
 

/**
 * Returns the required array type for an array load or store
 * instruction, based on a given implied type and an observed
 * actual array type.
 *
 * <p>The interesting cases here have to do with object arrays,
 * <code>byte[]</code>s, <code>boolean[]</code>s, and
 * known-nulls.</p>
 *
 * <p>In the case of arrays of objects, we want to narrow the type
 * to the actual array present on the stack, as long as what is
 * present is an object type. Similarly, due to a quirk of the
 * original bytecode representation, the instructions for dealing
 * with <code>byte[]</code> and <code>boolean[]</code> are
 * undifferentiated, and we aim here to return whichever one was
 * actually present on the stack.</p>
 *
 * <p>In the case where there is a known-null on the stack where
 * an array is expected, our behavior depends on the implied type
 * of the instruction. When the implied type is a reference, we
 * don't attempt to infer anything, as we don't know the dimension
 * of the null constant and thus any explicit inferred type could
 * be wrong. When the implied type is a primitive, we fall back to
 * the implied type of the instruction. Due to the quirk described
 * above, this means that source code that uses
 * <code>boolean[]</code> might get translated surprisingly -- but
 * correctly -- into an instruction that specifies a
 * <code>byte[]</code>. It will be correct, because should the
 * code actually execute, it will necessarily throw a
 * <code>NullPointerException</code>, and it won't matter what
 * opcode variant is used to achieve that result.</p>
 *
 * @param impliedType {@code non-null;} type implied by the
 * instruction; is <i>not</i> an array type
 * @param foundArrayType {@code non-null;} type found on the
 * stack; is either an array type or a known-null
 * @return {@code non-null;} the array type that should be
 * required in this context
 */
private static Type requiredArrayTypeFor(Type impliedType,
        Type foundArrayType) {
    if (foundArrayType == Type.KNOWN_NULL) {
        return impliedType.isReference()
            ? Type.KNOWN_NULL
            : impliedType.getArrayType();
    }

    if ((impliedType == Type.OBJECT)
            && foundArrayType.isArray()
            && foundArrayType.getComponentType().isReference()) {
        return foundArrayType;
    }

    if ((impliedType == Type.BYTE)
            && (foundArrayType == Type.BOOLEAN_ARRAY)) {
        /*
         * Per above, an instruction with implied byte[] is also
         * allowed to be used on boolean[].
         */
        return Type.BOOLEAN_ARRAY;
    }

    return impliedType.getArrayType();
}
 

/**
 * Merges two frame types.
 *
 * @param ft1 {@code non-null;} a frame type
 * @param ft2 {@code non-null;} another frame type
 * @return {@code non-null;} the result of merging the two types
 */
public static TypeBearer mergeType(TypeBearer ft1, TypeBearer ft2) {
    if ((ft1 == null) || ft1.equals(ft2)) {
        return ft1;
    } else if (ft2 == null) {
        return null;
    } else {
        Type type1 = ft1.getType();
        Type type2 = ft2.getType();

        if (type1 == type2) {
            return type1;
        } else if (type1.isReference() && type2.isReference()) {
            if (type1 == Type.KNOWN_NULL) {
                /*
                 * A known-null merges with any other reference type to
                 * be that reference type.
                 */
                return type2;
            } else if (type2 == Type.KNOWN_NULL) {
                /*
                 * The same as above, but this time it's type2 that's
                 * the known-null.
                 */
                return type1;
            } else if (type1.isArray() && type2.isArray()) {
                TypeBearer componentUnion =
                    mergeType(type1.getComponentType(),
                            type2.getComponentType());
                if (componentUnion == null) {
                    /*
                     * At least one of the types is a primitive type,
                     * so the merged result is just Object.
                     */
                    return Type.OBJECT;
                }
                return ((Type) componentUnion).getArrayType();
            } else {
                /*
                 * All other unequal reference types get merged to be
                 * Object in this phase. This is fine here, but it
                 * won't be the right thing to do in the verifier.
                 */
                return Type.OBJECT;
            }
        } else if (type1.isIntlike() && type2.isIntlike()) {
            /*
             * Merging two non-identical int-like types results in
             * the type int.
             */
            return Type.INT;
        } else {
            return null;
        }
    }
}
 

/**
 * Returns whether the given supertype is possibly assignable from
 * the given subtype. This takes into account primitiveness,
 * int-likeness, known-nullness, and array dimensions, but does
 * not assume anything about class hierarchy other than that the
 * type {@code Object} is the supertype of all reference
 * types and all arrays are assignable to
 * {@code Serializable} and {@code Cloneable}.
 *
 * @param supertypeBearer {@code non-null;} the supertype
 * @param subtypeBearer {@code non-null;} the subtype
 */
public static boolean isPossiblyAssignableFrom(TypeBearer supertypeBearer,
        TypeBearer subtypeBearer) {
    Type supertype = supertypeBearer.getType();
    Type subtype = subtypeBearer.getType();

    if (supertype.equals(subtype)) {
        // Easy out.
        return true;
    }

    int superBt = supertype.getBasicType();
    int subBt = subtype.getBasicType();

    // Treat return types as Object for the purposes of this method.

    if (superBt == Type.BT_ADDR) {
        supertype = Type.OBJECT;
        superBt = Type.BT_OBJECT;
    }

    if (subBt == Type.BT_ADDR) {
        subtype = Type.OBJECT;
        subBt = Type.BT_OBJECT;
    }

    if ((superBt != Type.BT_OBJECT) || (subBt != Type.BT_OBJECT)) {
        /*
         * No two distinct primitive types are assignable in this sense,
         * unless they are both int-like.
         */
        return supertype.isIntlike() && subtype.isIntlike();
    }

    // At this point, we know both types are reference types.

    if (supertype == Type.KNOWN_NULL) {
        /*
         * A known-null supertype is only assignable from another
         * known-null (handled in the easy out at the top of the
         * method).
         */
        return false;
    } else if (subtype == Type.KNOWN_NULL) {
        /*
         * A known-null subtype is in fact assignable to any
         * reference type.
         */
        return true;
    } else if (supertype == Type.OBJECT) {
        /*
         * Object is assignable from any reference type.
         */
        return true;
    } else if (supertype.isArray()) {
        // The supertype is an array type.
        if (! subtype.isArray()) {
            // The subtype isn't an array, and so can't be assignable.
            return false;
        }

        /*
         * Strip off as many matched component types from both
         * types as possible, and check the assignability of the
         * results.
         */
        do {
            supertype = supertype.getComponentType();
            subtype = subtype.getComponentType();
        } while (supertype.isArray() && subtype.isArray());

        return isPossiblyAssignableFrom(supertype, subtype);
    } else if (subtype.isArray()) {
        /*
         * Other than Object (handled above), array types are
         * assignable only to Serializable and Cloneable.
         */
        return (supertype == Type.SERIALIZABLE) ||
            (supertype == Type.CLONEABLE);
    } else {
        /*
         * All other unequal reference types are considered at
         * least possibly assignable.
         */
        return true;
    }
}
 

/**
 * Returns the required array type for an array load or store
 * instruction, based on a given implied type and an observed
 * actual array type.
 *
 * <p>The interesting cases here have to do with object arrays,
 * <code>byte[]</code>s, <code>boolean[]</code>s, and
 * known-nulls.</p>
 *
 * <p>In the case of arrays of objects, we want to narrow the type
 * to the actual array present on the stack, as long as what is
 * present is an object type. Similarly, due to a quirk of the
 * original bytecode representation, the instructions for dealing
 * with <code>byte[]</code> and <code>boolean[]</code> are
 * undifferentiated, and we aim here to return whichever one was
 * actually present on the stack.</p>
 *
 * <p>In the case where there is a known-null on the stack where
 * an array is expected, our behavior depends on the implied type
 * of the instruction. When the implied type is a reference, we
 * don't attempt to infer anything, as we don't know the dimension
 * of the null constant and thus any explicit inferred type could
 * be wrong. When the implied type is a primitive, we fall back to
 * the implied type of the instruction. Due to the quirk described
 * above, this means that source code that uses
 * <code>boolean[]</code> might get translated surprisingly -- but
 * correctly -- into an instruction that specifies a
 * <code>byte[]</code>. It will be correct, because should the
 * code actually execute, it will necessarily throw a
 * <code>NullPointerException</code>, and it won't matter what
 * opcode variant is used to achieve that result.</p>
 *
 * @param impliedType {@code non-null;} type implied by the
 * instruction; is <i>not</i> an array type
 * @param foundArrayType {@code non-null;} type found on the
 * stack; is either an array type or a known-null
 * @return {@code non-null;} the array type that should be
 * required in this context
 */
private static Type requiredArrayTypeFor(Type impliedType,
        Type foundArrayType) {
    if (foundArrayType == Type.KNOWN_NULL) {
        return impliedType.isReference()
            ? Type.KNOWN_NULL
            : impliedType.getArrayType();
    }

    if ((impliedType == Type.OBJECT)
            && foundArrayType.isArray()
            && foundArrayType.getComponentType().isReference()) {
        return foundArrayType;
    }

    if ((impliedType == Type.BYTE)
            && (foundArrayType == Type.BOOLEAN_ARRAY)) {
        /*
         * Per above, an instruction with implied byte[] is also
         * allowed to be used on boolean[].
         */
        return Type.BOOLEAN_ARRAY;
    }

    return impliedType.getArrayType();
}
 

/**
 * Merges two frame types.
 *
 * @param ft1 {@code non-null;} a frame type
 * @param ft2 {@code non-null;} another frame type
 * @return {@code non-null;} the result of merging the two types
 */
public static TypeBearer mergeType(TypeBearer ft1, TypeBearer ft2) {
    if ((ft1 == null) || ft1.equals(ft2)) {
        return ft1;
    } else if (ft2 == null) {
        return null;
    } else {
        Type type1 = ft1.getType();
        Type type2 = ft2.getType();

        if (type1 == type2) {
            return type1;
        } else if (type1.isReference() && type2.isReference()) {
            if (type1 == Type.KNOWN_NULL) {
                /*
                 * A known-null merges with any other reference type to
                 * be that reference type.
                 */
                return type2;
            } else if (type2 == Type.KNOWN_NULL) {
                /*
                 * The same as above, but this time it's type2 that's
                 * the known-null.
                 */
                return type1;
            } else if (type1.isArray() && type2.isArray()) {
                TypeBearer componentUnion =
                    mergeType(type1.getComponentType(),
                            type2.getComponentType());
                if (componentUnion == null) {
                    /*
                     * At least one of the types is a primitive type,
                     * so the merged result is just Object.
                     */
                    return Type.OBJECT;
                }
                return ((Type) componentUnion).getArrayType();
            } else {
                /*
                 * All other unequal reference types get merged to be
                 * Object in this phase. This is fine here, but it
                 * won't be the right thing to do in the verifier.
                 */
                return Type.OBJECT;
            }
        } else if (type1.isIntlike() && type2.isIntlike()) {
            /*
             * Merging two non-identical int-like types results in
             * the type int.
             */
            return Type.INT;
        } else {
            return null;
        }
    }
}
 

/**
 * Returns whether the given supertype is possibly assignable from
 * the given subtype. This takes into account primitiveness,
 * int-likeness, known-nullness, and array dimensions, but does
 * not assume anything about class hierarchy other than that the
 * type {@code Object} is the supertype of all reference
 * types and all arrays are assignable to
 * {@code Serializable} and {@code Cloneable}.
 *
 * @param supertypeBearer {@code non-null;} the supertype
 * @param subtypeBearer {@code non-null;} the subtype
 */
public static boolean isPossiblyAssignableFrom(TypeBearer supertypeBearer,
        TypeBearer subtypeBearer) {
    Type supertype = supertypeBearer.getType();
    Type subtype = subtypeBearer.getType();

    if (supertype.equals(subtype)) {
        // Easy out.
        return true;
    }

    int superBt = supertype.getBasicType();
    int subBt = subtype.getBasicType();

    // Treat return types as Object for the purposes of this method.

    if (superBt == Type.BT_ADDR) {
        supertype = Type.OBJECT;
        superBt = Type.BT_OBJECT;
    }

    if (subBt == Type.BT_ADDR) {
        subtype = Type.OBJECT;
        subBt = Type.BT_OBJECT;
    }

    if ((superBt != Type.BT_OBJECT) || (subBt != Type.BT_OBJECT)) {
        /*
         * No two distinct primitive types are assignable in this sense,
         * unless they are both int-like.
         */
        return supertype.isIntlike() && subtype.isIntlike();
    }

    // At this point, we know both types are reference types.

    if (supertype == Type.KNOWN_NULL) {
        /*
         * A known-null supertype is only assignable from another
         * known-null (handled in the easy out at the top of the
         * method).
         */
        return false;
    } else if (subtype == Type.KNOWN_NULL) {
        /*
         * A known-null subtype is in fact assignable to any
         * reference type.
         */
        return true;
    } else if (supertype == Type.OBJECT) {
        /*
         * Object is assignable from any reference type.
         */
        return true;
    } else if (supertype.isArray()) {
        // The supertype is an array type.
        if (! subtype.isArray()) {
            // The subtype isn't an array, and so can't be assignable.
            return false;
        }

        /*
         * Strip off as many matched component types from both
         * types as possible, and check the assignability of the
         * results.
         */
        do {
            supertype = supertype.getComponentType();
            subtype = subtype.getComponentType();
        } while (supertype.isArray() && subtype.isArray());

        return isPossiblyAssignableFrom(supertype, subtype);
    } else if (subtype.isArray()) {
        /*
         * Other than Object (handled above), array types are
         * assignable only to Serializable and Cloneable.
         */
        return (supertype == Type.SERIALIZABLE) ||
            (supertype == Type.CLONEABLE);
    } else {
        /*
         * All other unequal reference types are considered at
         * least possibly assignable.
         */
        return true;
    }
}