/*

 * Copyright (c) 2008, 2013, Oracle and/or its affiliates. All rights reserved.

 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.

 *

 * This code is free software; you can redistribute it and/or modify it

 * 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.

 *

 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA

 * or visit www.oracle.com if you need additional information or have any

 * questions.

 */

package java.lang.invoke;

import java.security.AccessController;

import java.security.PrivilegedAction;

import java.util.ArrayList;

import java.util.Arrays;

import java.util.HashMap;

import sun.invoke.empty.Empty;

import sun.invoke.util.ValueConversions;

import sun.invoke.util.VerifyType;

import sun.invoke.util.Wrapper;

import static java.lang.invoke.LambdaForm.*;

import static java.lang.invoke.MethodHandleStatics.*;

import static java.lang.invoke.MethodHandles.Lookup.IMPL_LOOKUP;

/**

 * Trusted implementation code for MethodHandle.

 * @author jrose

 */

/*non-public*/ abstract class MethodHandleImpl {

    /// Factory methods to create method handles:

    static void initStatics() {

        // Trigger selected static initializations.

        MemberName.Factory.INSTANCE.getClass();

    }

    static MethodHandle makeArrayElementAccessor(Class<?> arrayClass, boolean isSetter) {

        if (!arrayClass.isArray())

            throw newIllegalArgumentException("not an array: "+arrayClass);

        MethodHandle accessor = ArrayAccessor.getAccessor(arrayClass, isSetter);

        MethodType srcType = accessor.type().erase();

        MethodType lambdaType = srcType.invokerType();

        Name[] names = arguments(1, lambdaType);

        Name[] args  = Arrays.copyOfRange(names, 1, 1 + srcType.parameterCount());

        names[names.length - 1] = new Name(accessor.asType(srcType), (Object[]) args);

        LambdaForm form = new LambdaForm("getElement", lambdaType.parameterCount(), names);

        MethodHandle mh = SimpleMethodHandle.make(srcType, form);

        if (ArrayAccessor.needCast(arrayClass)) {

            mh = mh.bindTo(arrayClass);

        }

        mh = mh.asType(ArrayAccessor.correctType(arrayClass, isSetter));

        return mh;

    }

    static final class ArrayAccessor {

        /// Support for array element access

        static final HashMap<Class<?>, MethodHandle> GETTER_CACHE = new HashMap<>();  // TODO use it

        static final HashMap<Class<?>, MethodHandle> SETTER_CACHE = new HashMap<>();  // TODO use it

        static int     getElementI(int[]     a, int i)            { return              a[i]; }

        static long    getElementJ(long[]    a, int i)            { return              a[i]; }

        static float   getElementF(float[]   a, int i)            { return              a[i]; }

        static double  getElementD(double[]  a, int i)            { return              a[i]; }

        static boolean getElementZ(boolean[] a, int i)            { return              a[i]; }

        static byte    getElementB(byte[]    a, int i)            { return              a[i]; }

        static short   getElementS(short[]   a, int i)            { return              a[i]; }

        static char    getElementC(char[]    a, int i)            { return              a[i]; }

        static Object  getElementL(Object[]  a, int i)            { return              a[i]; }

        static void    setElementI(int[]     a, int i, int     x) {              a[i] = x; }

        static void    setElementJ(long[]    a, int i, long    x) {              a[i] = x; }

        static void    setElementF(float[]   a, int i, float   x) {              a[i] = x; }

        static void    setElementD(double[]  a, int i, double  x) {              a[i] = x; }

        static void    setElementZ(boolean[] a, int i, boolean x) {              a[i] = x; }

        static void    setElementB(byte[]    a, int i, byte    x) {              a[i] = x; }

        static void    setElementS(short[]   a, int i, short   x) {              a[i] = x; }

        static void    setElementC(char[]    a, int i, char    x) {              a[i] = x; }

        static void    setElementL(Object[]  a, int i, Object  x) {              a[i] = x; }

        static Object  getElementL(Class<?> arrayClass, Object[] a, int i)           { arrayClass.cast(a); return a[i]; }

        static void    setElementL(Class<?> arrayClass, Object[] a, int i, Object x) { arrayClass.cast(a); a[i] = x; }

        // Weakly typed wrappers of Object[] accessors:

        static Object  getElementL(Object    a, int i)            { return getElementL((Object[])a, i); }

        static void    setElementL(Object    a, int i, Object  x) {        setElementL((Object[]) a, i, x); }

        static Object  getElementL(Object   arrayClass, Object a, int i)             { return getElementL((Class<?>) arrayClass, (Object[])a, i); }

        static void    setElementL(Object   arrayClass, Object a, int i, Object x)   {        setElementL((Class<?>) arrayClass, (Object[])a, i, x); }

        static boolean needCast(Class<?> arrayClass) {

            Class<?> elemClass = arrayClass.getComponentType();

            return !elemClass.isPrimitive() && elemClass != Object.class;

        }

        static String name(Class<?> arrayClass, boolean isSetter) {

            Class<?> elemClass = arrayClass.getComponentType();

            if (elemClass == null)  throw new IllegalArgumentException();

            return (!isSetter ? "getElement" : "setElement") + Wrapper.basicTypeChar(elemClass);

        }

        static final boolean USE_WEAKLY_TYPED_ARRAY_ACCESSORS = false;  // FIXME: decide

        static MethodType type(Class<?> arrayClass, boolean isSetter) {

            Class<?> elemClass = arrayClass.getComponentType();

            Class<?> arrayArgClass = arrayClass;

            if (!elemClass.isPrimitive()) {

                arrayArgClass = Object[].class;

                if (USE_WEAKLY_TYPED_ARRAY_ACCESSORS)

                    arrayArgClass = Object.class;

            }

            if (!needCast(arrayClass)) {

                return !isSetter ?

                    MethodType.methodType(elemClass,  arrayArgClass, int.class) :

                    MethodType.methodType(void.class, arrayArgClass, int.class, elemClass);

            } else {

                Class<?> classArgClass = Class.class;

                if (USE_WEAKLY_TYPED_ARRAY_ACCESSORS)

                    classArgClass = Object.class;

                return !isSetter ?

                    MethodType.methodType(Object.class, classArgClass, arrayArgClass, int.class) :

                    MethodType.methodType(void.class,   classArgClass, arrayArgClass, int.class, Object.class);

            }

        }

        static MethodType correctType(Class<?> arrayClass, boolean isSetter) {

            Class<?> elemClass = arrayClass.getComponentType();

            return !isSetter ?

                    MethodType.methodType(elemClass,  arrayClass, int.class) :

                    MethodType.methodType(void.class, arrayClass, int.class, elemClass);

        }

        static MethodHandle getAccessor(Class<?> arrayClass, boolean isSetter) {

            String     name = name(arrayClass, isSetter);

            MethodType type = type(arrayClass, isSetter);

            try {

                return IMPL_LOOKUP.findStatic(ArrayAccessor.class, name, type);

            } catch (ReflectiveOperationException ex) {

                throw uncaughtException(ex);

            }

        }

    }

    /**

     * Create a JVM-level adapter method handle to conform the given method

     * handle to the similar newType, using only pairwise argument conversions.

     * For each argument, convert incoming argument to the exact type needed.

     * The argument conversions allowed are casting, boxing and unboxing,

     * integral widening or narrowing, and floating point widening or narrowing.

     * @param srcType required call type

     * @param target original method handle

     * @param level which strength of conversion is allowed

     * @return an adapter to the original handle with the desired new type,

     *          or the original target if the types are already identical

     *          or null if the adaptation cannot be made

     */

    static MethodHandle makePairwiseConvert(MethodHandle target, MethodType srcType, int level) {

        assert(level >= 0 && level <= 2);

        MethodType dstType = target.type();

        assert(dstType.parameterCount() == target.type().parameterCount());

        if (srcType == dstType)

            return target;

        // Calculate extra arguments (temporaries) required in the names array.

        // FIXME: Use an ArrayList<Name>.  Some arguments require more than one conversion step.

        final int INARG_COUNT = srcType.parameterCount();

        int conversions = 0;

        boolean[] needConv = new boolean[1+INARG_COUNT];

        for (int i = 0; i <= INARG_COUNT; i++) {

            Class<?> src = (i == INARG_COUNT) ? dstType.returnType() : srcType.parameterType(i);

            Class<?> dst = (i == INARG_COUNT) ? srcType.returnType() : dstType.parameterType(i);

            if (!VerifyType.isNullConversion(src, dst) ||

                level <= 1 && dst.isInterface() && !dst.isAssignableFrom(src)) {

                needConv[i] = true;

                conversions++;

            }

        }

        boolean retConv = needConv[INARG_COUNT];

        final int IN_MH         = 0;

        final int INARG_BASE    = 1;

        final int INARG_LIMIT   = INARG_BASE + INARG_COUNT;

        final int NAME_LIMIT    = INARG_LIMIT + conversions + 1;

        final int RETURN_CONV   = (!retConv ? -1         : NAME_LIMIT - 1);

        final int OUT_CALL      = (!retConv ? NAME_LIMIT : RETURN_CONV) - 1;

        // Now build a LambdaForm.

        MethodType lambdaType = srcType.basicType().invokerType();

        Name[] names = arguments(NAME_LIMIT - INARG_LIMIT, lambdaType);

        // Collect the arguments to the outgoing call, maybe with conversions:

        final int OUTARG_BASE = 0;  // target MH is Name.function, name Name.arguments[0]

        Object[] outArgs = new Object[OUTARG_BASE + INARG_COUNT];

        int nameCursor = INARG_LIMIT;

        for (int i = 0; i < INARG_COUNT; i++) {

            Class<?> src = srcType.parameterType(i);

            Class<?> dst = dstType.parameterType(i);

            if (!needConv[i]) {

                // do nothing: difference is trivial

                outArgs[OUTARG_BASE + i] = names[INARG_BASE + i];

                continue;

            }

            // Tricky case analysis follows.

            MethodHandle fn = null;

            if (src.isPrimitive()) {

                if (dst.isPrimitive()) {

                    fn = ValueConversions.convertPrimitive(src, dst);

                } else {

                    Wrapper w = Wrapper.forPrimitiveType(src);

                    MethodHandle boxMethod = ValueConversions.box(w);

                    if (dst == w.wrapperType())

                        fn = boxMethod;

                    else

                        fn = boxMethod.asType(MethodType.methodType(dst, src));

                }

            } else {

                if (dst.isPrimitive()) {

                    // Caller has boxed a primitive.  Unbox it for the target.

                    Wrapper w = Wrapper.forPrimitiveType(dst);

                    if (level == 0 || VerifyType.isNullConversion(src, w.wrapperType())) {

                        fn = ValueConversions.unbox(dst);

                    } else if (src == Object.class || !Wrapper.isWrapperType(src)) {

                        // Examples:  Object->int, Number->int, Comparable->int; Byte->int, Character->int

                        // must include additional conversions

                        // src must be examined at runtime, to detect Byte, Character, etc.

                        MethodHandle unboxMethod = (level == 1

                                                    ? ValueConversions.unbox(dst)

                                                    : ValueConversions.unboxCast(dst));

                        fn = unboxMethod;

                    } else {

                        // Example: Byte->int

                        // Do this by reformulating the problem to Byte->byte.

                        Class<?> srcPrim = Wrapper.forWrapperType(src).primitiveType();

                        MethodHandle unbox = ValueConversions.unbox(srcPrim);

                        // Compose the two conversions.  FIXME:  should make two Names for this job

                        fn = unbox.asType(MethodType.methodType(dst, src));

                    }

                } else {

                    // Simple reference conversion.

                    // Note:  Do not check for a class hierarchy relation

                    // between src and dst.  In all cases a 'null' argument

                    // will pass the cast conversion.

                    fn = ValueConversions.cast(dst);

                }

            }

            Name conv = new Name(fn, names[INARG_BASE + i]);

            assert(names[nameCursor] == null);

            names[nameCursor++] = conv;

            assert(outArgs[OUTARG_BASE + i] == null);

            outArgs[OUTARG_BASE + i] = conv;

        }

        // Build argument array for the call.

        assert(nameCursor == OUT_CALL);

        names[OUT_CALL] = new Name(target, outArgs);

        if (RETURN_CONV < 0) {

            assert(OUT_CALL == names.length-1);

        } else {

            Class<?> needReturn = srcType.returnType();

            Class<?> haveReturn = dstType.returnType();

            MethodHandle fn;

            Object[] arg = { names[OUT_CALL] };

            if (haveReturn == void.class) {

                // synthesize a zero value for the given void

                Object zero = Wrapper.forBasicType(needReturn).zero();

                fn = MethodHandles.constant(needReturn, zero);

                arg = new Object[0];  // don't pass names[OUT_CALL] to conversion

            } else {

                MethodHandle identity = MethodHandles.identity(needReturn);

                MethodType needConversion = identity.type().changeParameterType(0, haveReturn);

                fn = makePairwiseConvert(identity, needConversion, level);

            }

            assert(names[RETURN_CONV] == null);

            names[RETURN_CONV] = new Name(fn, arg);

            assert(RETURN_CONV == names.length-1);

        }

        LambdaForm form = new LambdaForm("convert", lambdaType.parameterCount(), names);

        return SimpleMethodHandle.make(srcType, form);

    }

    static MethodHandle makeReferenceIdentity(Class<?> refType) {

        MethodType lambdaType = MethodType.genericMethodType(1).invokerType();

        Name[] names = arguments(1, lambdaType);

        names[names.length - 1] = new Name(ValueConversions.identity(), names[1]);

        LambdaForm form = new LambdaForm("identity", lambdaType.parameterCount(), names);

        return SimpleMethodHandle.make(MethodType.methodType(refType, refType), form);

    }

    static MethodHandle makeVarargsCollector(MethodHandle target, Class<?> arrayType) {

        MethodType type = target.type();

        int last = type.parameterCount() - 1;

        if (type.parameterType(last) != arrayType)

            target = target.asType(type.changeParameterType(last, arrayType));

        target = target.asFixedArity();  // make sure this attribute is turned off

        return new AsVarargsCollector(target, target.type(), arrayType);

    }

    static class AsVarargsCollector extends MethodHandle {

        private final MethodHandle target;

        private final Class<?> arrayType;

        private /*@Stable*/ MethodHandle asCollectorCache;

        AsVarargsCollector(MethodHandle target, MethodType type, Class<?> arrayType) {

            super(type, reinvokerForm(target));

            this.target = target;

            this.arrayType = arrayType;

            this.asCollectorCache = target.asCollector(arrayType, 0);

        }

        @Override MethodHandle reinvokerTarget() { return target; }

        @Override

        public boolean isVarargsCollector() {

            return true;

        }

        @Override

        public MethodHandle asFixedArity() {

            return target;

        }

        @Override

        public MethodHandle asTypeUncached(MethodType newType) {

            MethodType type = this.type();

            int collectArg = type.parameterCount() - 1;

            int newArity = newType.parameterCount();

            if (newArity == collectArg+1 &&

                type.parameterType(collectArg).isAssignableFrom(newType.parameterType(collectArg))) {

                // if arity and trailing parameter are compatible, do normal thing

                return asTypeCache = asFixedArity().asType(newType);

            }

            // check cache

            MethodHandle acc = asCollectorCache;

            if (acc != null && acc.type().parameterCount() == newArity)

                return asTypeCache = acc.asType(newType);

            // build and cache a collector

            int arrayLength = newArity - collectArg;

            MethodHandle collector;

            try {

                collector = asFixedArity().asCollector(arrayType, arrayLength);

                assert(collector.type().parameterCount() == newArity) : "newArity="+newArity+" but collector="+collector;

            } catch (IllegalArgumentException ex) {

                throw new WrongMethodTypeException("cannot build collector", ex);

            }

            asCollectorCache = collector;

            return asTypeCache = collector.asType(newType);

        }

        @Override

        MethodHandle setVarargs(MemberName member) {

            if (member.isVarargs())  return this;

            return asFixedArity();

        }

        @Override

        MethodHandle viewAsType(MethodType newType) {

            if (newType.lastParameterType() != type().lastParameterType())

                throw new InternalError();

            MethodHandle newTarget = asFixedArity().viewAsType(newType);

            // put back the varargs bit:

            return new AsVarargsCollector(newTarget, newType, arrayType);

        }

        @Override

        MemberName internalMemberName() {

            return asFixedArity().internalMemberName();

        }

        @Override

        Class<?> internalCallerClass() {

            return asFixedArity().internalCallerClass();

        }

        /*non-public*/

        @Override

        boolean isInvokeSpecial() {

            return asFixedArity().isInvokeSpecial();

        }

        @Override

        MethodHandle bindArgument(int pos, char basicType, Object value) {

            return asFixedArity().bindArgument(pos, basicType, value);

        }

        @Override

        MethodHandle bindReceiver(Object receiver) {

            return asFixedArity().bindReceiver(receiver);

        }

        @Override

        MethodHandle dropArguments(MethodType srcType, int pos, int drops) {

            return asFixedArity().dropArguments(srcType, pos, drops);

        }

        @Override

        MethodHandle permuteArguments(MethodType newType, int[] reorder) {

            return asFixedArity().permuteArguments(newType, reorder);

        }

    }

    /** Factory method:  Spread selected argument. */

    static MethodHandle makeSpreadArguments(MethodHandle target,

                                            Class<?> spreadArgType, int spreadArgPos, int spreadArgCount) {

        MethodType targetType = target.type();

        for (int i = 0; i < spreadArgCount; i++) {

            Class<?> arg = VerifyType.spreadArgElementType(spreadArgType, i);

            if (arg == null)  arg = Object.class;

            targetType = targetType.changeParameterType(spreadArgPos + i, arg);

        }

        target = target.asType(targetType);

        MethodType srcType = targetType

                .replaceParameterTypes(spreadArgPos, spreadArgPos + spreadArgCount, spreadArgType);

        // Now build a LambdaForm.

        MethodType lambdaType = srcType.invokerType();

        Name[] names = arguments(spreadArgCount + 2, lambdaType);

        int nameCursor = lambdaType.parameterCount();

        int[] indexes = new int[targetType.parameterCount()];

        for (int i = 0, argIndex = 1; i < targetType.parameterCount() + 1; i++, argIndex++) {

            Class<?> src = lambdaType.parameterType(i);

            if (i == spreadArgPos) {

                // Spread the array.

                MethodHandle aload = MethodHandles.arrayElementGetter(spreadArgType);

                Name array = names[argIndex];

                names[nameCursor++] = new Name(Lazy.NF_checkSpreadArgument, array, spreadArgCount);

                for (int j = 0; j < spreadArgCount; i++, j++) {

                    indexes[i] = nameCursor;

                    names[nameCursor++] = new Name(aload, array, j);

                }

            } else if (i < indexes.length) {

                indexes[i] = argIndex;

            }

        }

        assert(nameCursor == names.length-1);  // leave room for the final call

        // Build argument array for the call.

        Name[] targetArgs = new Name[targetType.parameterCount()];

        for (int i = 0; i < targetType.parameterCount(); i++) {

            int idx = indexes[i];

            targetArgs[i] = names[idx];

        }

        names[names.length - 1] = new Name(target, (Object[]) targetArgs);

        LambdaForm form = new LambdaForm("spread", lambdaType.parameterCount(), names);

        return SimpleMethodHandle.make(srcType, form);

    }

    static void checkSpreadArgument(Object av, int n) {

        if (av == null) {

            if (n == 0)  return;

        } else if (av instanceof Object[]) {

            int len = ((Object[])av).length;

            if (len == n)  return;

        } else {

            int len = java.lang.reflect.Array.getLength(av);

            if (len == n)  return;

        }

        // fall through to error:

        throw newIllegalArgumentException("array is not of length "+n);

    }

    /**

     * Pre-initialized NamedFunctions for bootstrapping purposes.

     * Factored in an inner class to delay initialization until first usage.

     */

    private static class Lazy {

        static final NamedFunction NF_checkSpreadArgument;

        static {

            try {

                NF_checkSpreadArgument = new NamedFunction(MethodHandleImpl.class

                        .getDeclaredMethod("checkSpreadArgument", Object.class, int.class));

                NF_checkSpreadArgument.resolve();

            } catch (ReflectiveOperationException ex) {

                throw newInternalError(ex);

            }

        }

    }

    /** Factory method:  Collect or filter selected argument(s). */

    static MethodHandle makeCollectArguments(MethodHandle target,

                MethodHandle collector, int collectArgPos, boolean retainOriginalArgs) {

        MethodType targetType = target.type();          // (a..., c, [b...])=>r

        MethodType collectorType = collector.type();    // (b...)=>c

        int collectArgCount = collectorType.parameterCount();

        Class<?> collectValType = collectorType.returnType();

        int collectValCount = (collectValType == void.class ? 0 : 1);

        MethodType srcType = targetType                 // (a..., [b...])=>r

                .dropParameterTypes(collectArgPos, collectArgPos+collectValCount);

        if (!retainOriginalArgs) {                      // (a..., b...)=>r

            srcType = srcType.insertParameterTypes(collectArgPos, collectorType.parameterList());

        }

        // in  arglist: [0: ...keep1 | cpos: collect...  | cpos+cacount: keep2... ]

        // out arglist: [0: ...keep1 | cpos: collectVal? | cpos+cvcount: keep2... ]

        // out(retain): [0: ...keep1 | cpos: cV? coll... | cpos+cvc+cac: keep2... ]

        // Now build a LambdaForm.

        MethodType lambdaType = srcType.invokerType();

        Name[] names = arguments(2, lambdaType);

        final int collectNamePos = names.length - 2;

        final int targetNamePos  = names.length - 1;

        Name[] collectorArgs = Arrays.copyOfRange(names, 1 + collectArgPos, 1 + collectArgPos + collectArgCount);

        names[collectNamePos] = new Name(collector, (Object[]) collectorArgs);

        // Build argument array for the target.

        // Incoming LF args to copy are: [ (mh) headArgs collectArgs tailArgs ].

        // Output argument array is [ headArgs (collectVal)? (collectArgs)? tailArgs ].

        Name[] targetArgs = new Name[targetType.parameterCount()];

        int inputArgPos  = 1;  // incoming LF args to copy to target

        int targetArgPos = 0;  // fill pointer for targetArgs

        int chunk = collectArgPos;  // |headArgs|

        System.arraycopy(names, inputArgPos, targetArgs, targetArgPos, chunk);

        inputArgPos  += chunk;

        targetArgPos += chunk;

        if (collectValType != void.class) {

            targetArgs[targetArgPos++] = names[collectNamePos];

        }

        chunk = collectArgCount;

        if (retainOriginalArgs) {

            System.arraycopy(names, inputArgPos, targetArgs, targetArgPos, chunk);

            targetArgPos += chunk;   // optionally pass on the collected chunk

        }

        inputArgPos += chunk;

        chunk = targetArgs.length - targetArgPos;  // all the rest

        System.arraycopy(names, inputArgPos, targetArgs, targetArgPos, chunk);

        assert(inputArgPos + chunk == collectNamePos);  // use of rest of input args also

        names[targetNamePos] = new Name(target, (Object[]) targetArgs);

        LambdaForm form = new LambdaForm("collect", lambdaType.parameterCount(), names);

        return SimpleMethodHandle.make(srcType, form);

    }

    static

    MethodHandle selectAlternative(boolean testResult, MethodHandle target, MethodHandle fallback) {

        return testResult ? target : fallback;

    }

    static MethodHandle SELECT_ALTERNATIVE;

    static MethodHandle selectAlternative() {

        if (SELECT_ALTERNATIVE != null)  return SELECT_ALTERNATIVE;

        try {

            SELECT_ALTERNATIVE

            = IMPL_LOOKUP.findStatic(MethodHandleImpl.class, "selectAlternative",

                    MethodType.methodType(MethodHandle.class, boolean.class, MethodHandle.class, MethodHandle.class));

        } catch (ReflectiveOperationException ex) {

            throw new RuntimeException(ex);

        }

        return SELECT_ALTERNATIVE;

    }

    static

    MethodHandle makeGuardWithTest(MethodHandle test,

                                   MethodHandle target,

                                   MethodHandle fallback) {

        MethodType basicType = target.type().basicType();

        MethodHandle invokeBasic = MethodHandles.basicInvoker(basicType);

        int arity = basicType.parameterCount();

        int extraNames = 3;

        MethodType lambdaType = basicType.invokerType();

        Name[] names = arguments(extraNames, lambdaType);

        Object[] testArgs   = Arrays.copyOfRange(names, 1, 1 + arity, Object[].class);

        Object[] targetArgs = Arrays.copyOfRange(names, 0, 1 + arity, Object[].class);

        // call test

        names[arity + 1] = new Name(test, testArgs);

        // call selectAlternative

        Object[] selectArgs = { names[arity + 1], target, fallback };

        names[arity + 2] = new Name(MethodHandleImpl.selectAlternative(), selectArgs);

        targetArgs[0] = names[arity + 2];

        // call target or fallback

        names[arity + 3] = new Name(new NamedFunction(invokeBasic), targetArgs);

        LambdaForm form = new LambdaForm("guard", lambdaType.parameterCount(), names);

        return SimpleMethodHandle.make(target.type(), form);

    }

    private static class GuardWithCatch {

        private final MethodHandle target;

        private final Class<? extends Throwable> exType;

        private final MethodHandle catcher;

        // FIXME: Build the control flow out of foldArguments.

        GuardWithCatch(MethodHandle target, Class<? extends Throwable> exType, MethodHandle catcher) {

            this.target = target;

            this.exType = exType;

            this.catcher = catcher;

        }

        @LambdaForm.Hidden

        private Object invoke_V(Object... av) throws Throwable {

            try {

                return target.invokeExact(av);

            } catch (Throwable t) {

                if (!exType.isInstance(t))  throw t;

                return catcher.invokeExact(t, av);

            }

        }

        @LambdaForm.Hidden

        private Object invoke_L0() throws Throwable {

            try {

                return target.invokeExact();

            } catch (Throwable t) {

                if (!exType.isInstance(t))  throw t;

                return catcher.invokeExact(t);

            }

        }

        @LambdaForm.Hidden

        private Object invoke_L1(Object a0) throws Throwable {

            try {

                return target.invokeExact(a0);

            } catch (Throwable t) {

                if (!exType.isInstance(t))  throw t;

                return catcher.invokeExact(t, a0);

            }

        }

        @LambdaForm.Hidden

        private Object invoke_L2(Object a0, Object a1) throws Throwable {

            try {

                return target.invokeExact(a0, a1);

            } catch (Throwable t) {

                if (!exType.isInstance(t))  throw t;

                return catcher.invokeExact(t, a0, a1);

            }

        }

        @LambdaForm.Hidden

        private Object invoke_L3(Object a0, Object a1, Object a2) throws Throwable {

            try {

                return target.invokeExact(a0, a1, a2);

            } catch (Throwable t) {

                if (!exType.isInstance(t))  throw t;

                return catcher.invokeExact(t, a0, a1, a2);

            }

        }

        @LambdaForm.Hidden

        private Object invoke_L4(Object a0, Object a1, Object a2, Object a3) throws Throwable {

            try {

                return target.invokeExact(a0, a1, a2, a3);

            } catch (Throwable t) {

                if (!exType.isInstance(t))  throw t;

                return catcher.invokeExact(t, a0, a1, a2, a3);

            }

        }

        @LambdaForm.Hidden

        private Object invoke_L5(Object a0, Object a1, Object a2, Object a3, Object a4) throws Throwable {

            try {

                return target.invokeExact(a0, a1, a2, a3, a4);

            } catch (Throwable t) {

                if (!exType.isInstance(t))  throw t;

                return catcher.invokeExact(t, a0, a1, a2, a3, a4);

            }

        }

        @LambdaForm.Hidden

        private Object invoke_L6(Object a0, Object a1, Object a2, Object a3, Object a4, Object a5) throws Throwable {

            try {

                return target.invokeExact(a0, a1, a2, a3, a4, a5);

            } catch (Throwable t) {

                if (!exType.isInstance(t))  throw t;

                return catcher.invokeExact(t, a0, a1, a2, a3, a4, a5);

            }

        }

        @LambdaForm.Hidden

        private Object invoke_L7(Object a0, Object a1, Object a2, Object a3, Object a4, Object a5, Object a6) throws Throwable {

            try {

                return target.invokeExact(a0, a1, a2, a3, a4, a5, a6);

            } catch (Throwable t) {

                if (!exType.isInstance(t))  throw t;

                return catcher.invokeExact(t, a0, a1, a2, a3, a4, a5, a6);

            }

        }

        @LambdaForm.Hidden

        private Object invoke_L8(Object a0, Object a1, Object a2, Object a3, Object a4, Object a5, Object a6, Object a7) throws Throwable {

            try {

                return target.invokeExact(a0, a1, a2, a3, a4, a5, a6, a7);

            } catch (Throwable t) {

                if (!exType.isInstance(t))  throw t;

                return catcher.invokeExact(t, a0, a1, a2, a3, a4, a5, a6, a7);

            }

        }

        static MethodHandle[] makeInvokes() {

            ArrayList<MethodHandle> invokes = new ArrayList<>();

            MethodHandles.Lookup lookup = IMPL_LOOKUP;

            for (;;) {

                int nargs = invokes.size();

                String name = "invoke_L"+nargs;

                MethodHandle invoke = null;

                try {

                    invoke = lookup.findVirtual(GuardWithCatch.class, name, MethodType.genericMethodType(nargs));

                } catch (ReflectiveOperationException ex) {

                }

                if (invoke == null)  break;

                invokes.add(invoke);

            }

            assert(invokes.size() == 9);  // current number of methods

            return invokes.toArray(new MethodHandle[0]);

        };

        static final MethodHandle[] INVOKES = makeInvokes();

        // For testing use this:

        //static final MethodHandle[] INVOKES = Arrays.copyOf(makeInvokes(), 2);

        static final MethodHandle VARARGS_INVOKE;

        static {

            try {

                VARARGS_INVOKE = IMPL_LOOKUP.findVirtual(GuardWithCatch.class, "invoke_V", MethodType.genericMethodType(0, true));

            } catch (ReflectiveOperationException ex) {

                throw uncaughtException(ex);

            }

        }

    }

    static

    MethodHandle makeGuardWithCatch(MethodHandle target,

                                    Class<? extends Throwable> exType,

                                    MethodHandle catcher) {

        MethodType type = target.type();

        MethodType ctype = catcher.type();

        int nargs = type.parameterCount();

        if (nargs < GuardWithCatch.INVOKES.length) {

            MethodType gtype = type.generic();

            MethodType gcatchType = gtype.insertParameterTypes(0, Throwable.class);

            // Note: convertArguments(...2) avoids interface casts present in convertArguments(...0)

            MethodHandle gtarget = makePairwiseConvert(target, gtype, 2);

            MethodHandle gcatcher = makePairwiseConvert(catcher, gcatchType, 2);

            GuardWithCatch gguard = new GuardWithCatch(gtarget, exType, gcatcher);

            if (gtarget == null || gcatcher == null)  throw new InternalError();

            MethodHandle ginvoker = GuardWithCatch.INVOKES[nargs].bindReceiver(gguard);

            return makePairwiseConvert(ginvoker, type, 2);

        } else {

            target = target.asType(type.changeReturnType(Object.class));

            MethodHandle gtarget = makeSpreadArguments(target, Object[].class, 0, nargs);

            MethodType catcherType = ctype.changeParameterType(0, Throwable.class)

                                          .changeReturnType(Object.class);

            catcher = catcher.asType(catcherType);

            MethodHandle gcatcher = makeSpreadArguments(catcher, Object[].class, 1, nargs);

            GuardWithCatch gguard = new GuardWithCatch(gtarget, exType, gcatcher);

            if (gtarget == null || gcatcher == null)  throw new InternalError();

            MethodHandle ginvoker = GuardWithCatch.VARARGS_INVOKE.bindReceiver(gguard);

            MethodHandle gcollect = makeCollectArguments(ginvoker, ValueConversions.varargsArray(nargs), 0, false);

            return makePairwiseConvert(gcollect, type, 2);

        }

    }

    static

    MethodHandle throwException(MethodType type) {

        assert(Throwable.class.isAssignableFrom(type.parameterType(0)));

        int arity = type.parameterCount();

        if (arity > 1) {

            return throwException(type.dropParameterTypes(1, arity)).dropArguments(type, 1, arity-1);

        }

        return makePairwiseConvert(throwException(), type, 2);

    }

    static MethodHandle THROW_EXCEPTION;

    static MethodHandle throwException() {

        MethodHandle mh = THROW_EXCEPTION;

        if (mh != null)  return mh;

        try {

            mh

            = IMPL_LOOKUP.findStatic(MethodHandleImpl.class, "throwException",

                    MethodType.methodType(Empty.class, Throwable.class));

        } catch (ReflectiveOperationException ex) {

            throw new RuntimeException(ex);

        }

        THROW_EXCEPTION = mh;

        return mh;

    }

    static <T extends Throwable> Empty throwException(T t) throws T { throw t; }

    static MethodHandle[] FAKE_METHOD_HANDLE_INVOKE = new MethodHandle[2];

    static MethodHandle fakeMethodHandleInvoke(MemberName method) {

        int idx;

        assert(method.isMethodHandleInvoke());

        switch (method.getName()) {

        case "invoke":       idx = 0; break;

        case "invokeExact":  idx = 1; break;

        default:             throw new InternalError(method.getName());

        }

        MethodHandle mh = FAKE_METHOD_HANDLE_INVOKE[idx];

        if (mh != null)  return mh;

        MethodType type = MethodType.methodType(Object.class, UnsupportedOperationException.class,

                                                MethodHandle.class, Object[].class);

        mh = throwException(type);

        mh = mh.bindTo(new UnsupportedOperationException("cannot reflectively invoke MethodHandle"));

        if (!method.getInvocationType().equals(mh.type()))

            throw new InternalError(method.toString());

        mh = mh.withInternalMemberName(method);

        mh = mh.asVarargsCollector(Object[].class);

        assert(method.isVarargs());

        FAKE_METHOD_HANDLE_INVOKE[idx] = mh;

        return mh;

    }

    /**

     * Create an alias for the method handle which, when called,

     * appears to be called from the same class loader and protection domain

     * as hostClass.

     * This is an expensive no-op unless the method which is called

     * is sensitive to its caller.  A small number of system methods

     * are in this category, including Class.forName and Method.invoke.

     */

    static

    MethodHandle bindCaller(MethodHandle mh, Class<?> hostClass) {

        return BindCaller.bindCaller(mh, hostClass);

    }

    // Put the whole mess into its own nested class.

    // That way we can lazily load the code and set up the constants.

    private static class BindCaller {

        static

        MethodHandle bindCaller(MethodHandle mh, Class<?> hostClass) {

            // Do not use this function to inject calls into system classes.

            if (hostClass == null

                ||    (hostClass.isArray() ||

                       hostClass.isPrimitive() ||

                       hostClass.getName().startsWith("java.") ||

                       hostClass.getName().startsWith("sun."))) {

                throw new InternalError();  // does not happen, and should not anyway

            }

            // For simplicity, convert mh to a varargs-like method.

            MethodHandle vamh = prepareForInvoker(mh);

            // Cache the result of makeInjectedInvoker once per argument class.

            MethodHandle bccInvoker = CV_makeInjectedInvoker.get(hostClass);

            return restoreToType(bccInvoker.bindTo(vamh), mh.type(), mh.internalMemberName(), hostClass);

        }

        private static MethodHandle makeInjectedInvoker(Class<?> hostClass) {

            throw new IllegalStateException("Implement me too!");

            /*

            Class<?> bcc = UNSAFE.defineAnonymousClass(hostClass, T_BYTES, null);

            if (hostClass.getClassLoader() != bcc.getClassLoader())

                throw new InternalError(hostClass.getName()+" (CL)");

            try {

                if (hostClass.getProtectionDomain() != bcc.getProtectionDomain())

                    throw new InternalError(hostClass.getName()+" (PD)");

            } catch (SecurityException ex) {

                // Self-check was blocked by security manager.  This is OK.

                // In fact the whole try body could be turned into an assertion.

            }

            try {

                MethodHandle init = IMPL_LOOKUP.findStatic(bcc, "init", MethodType.methodType(void.class));

                init.invokeExact();  // force initialization of the class

            } catch (Throwable ex) {

                throw uncaughtException(ex);

            }

            MethodHandle bccInvoker;

            try {

                MethodType invokerMT = MethodType.methodType(Object.class, MethodHandle.class, Object[].class);

                bccInvoker = IMPL_LOOKUP.findStatic(bcc, "invoke_V", invokerMT);

            } catch (ReflectiveOperationException ex) {

                throw uncaughtException(ex);

            }

            // Test the invoker, to ensure that it really injects into the right place.

            try {

                MethodHandle vamh = prepareForInvoker(MH_checkCallerClass);

                Object ok = bccInvoker.invokeExact(vamh, new Object[]{hostClass, bcc});

            } catch (Throwable ex) {

                throw new InternalError(ex);

            }

            return bccInvoker;

            */

        }

        private static ClassValue<MethodHandle> CV_makeInjectedInvoker = new ClassValue<MethodHandle>() {

            @Override protected MethodHandle computeValue(Class<?> hostClass) {

                return makeInjectedInvoker(hostClass);

            }

        };

        // Adapt mh so that it can be called directly from an injected invoker:

        private static MethodHandle prepareForInvoker(MethodHandle mh) {

            mh = mh.asFixedArity();

            MethodType mt = mh.type();

            int arity = mt.parameterCount();

            MethodHandle vamh = mh.asType(mt.generic());

            vamh.internalForm().compileToBytecode();  // eliminate LFI stack frames

            vamh = vamh.asSpreader(Object[].class, arity);

            vamh.internalForm().compileToBytecode();  // eliminate LFI stack frames

            return vamh;

        }

        // Undo the adapter effect of prepareForInvoker:

        private static MethodHandle restoreToType(MethodHandle vamh, MethodType type,

                                                  MemberName member,

                                                  Class<?> hostClass) {

            MethodHandle mh = vamh.asCollector(Object[].class, type.parameterCount());

            mh = mh.asType(type);

            mh = new WrappedMember(mh, type, member, hostClass);

            return mh;

        }

        private static final MethodHandle MH_checkCallerClass;

        static {

            final Class<?> THIS_CLASS = BindCaller.class;

//            assert(checkCallerClass(THIS_CLASS, THIS_CLASS));

            try {

                MH_checkCallerClass = IMPL_LOOKUP

                    .findStatic(THIS_CLASS, "checkCallerClass",

                                MethodType.methodType(boolean.class, Class.class, Class.class));

                assert((boolean) MH_checkCallerClass.invokeExact(THIS_CLASS, THIS_CLASS));

            } catch (Throwable ex) {

                throw new InternalError(ex);

            }

        }

//        @CallerSensitive

//        private static boolean checkCallerClass(Class<?> expected, Class<?> expected2) {

//            // This method is called via MH_checkCallerClass and so it's

//            // correct to ask for the immediate caller here.

//            Class<?> actual = Reflection.getCallerClass();

//            if (actual != expected && actual != expected2)

//                throw new InternalError("found "+actual.getName()+", expected "+expected.getName()

//                                        +(expected == expected2 ? "" : ", or else "+expected2.getName()));

//            return true;

//        }

        private static final byte[] T_BYTES;

        static {

            final Object[] values = {null};

            AccessController.doPrivileged(new PrivilegedAction<Void>() {

                    public Void run() {

                        try {

                            Class<T> tClass = T.class;

                            String tName = tClass.getName();

                            String tResource = tName.substring(tName.lastIndexOf('.')+1)+".class";

                            java.net.URLConnection uconn = tClass.getResource(tResource).openConnection();

                            int len = uconn.getContentLength();

                            byte[] bytes = new byte[len];

                            try (java.io.InputStream str = uconn.getInputStream()) {

                                int nr = str.read(bytes);

                                if (nr != len)  throw new java.io.IOException(tResource);

                            }

                            values[0] = bytes;

                        } catch (java.io.IOException ex) {

                            throw new InternalError(ex);

                        }

                        return null;

                    }

                });

            T_BYTES = (byte[]) values[0];

        }

        // The following class is used as a template for Unsafe.defineAnonymousClass:

        private static class T {

            static void init() { }  // side effect: initializes this class

            static Object invoke_V(MethodHandle vamh, Object[] args) throws Throwable {

                return vamh.invokeExact(args);

            }

        }

    }

    /** This subclass allows a wrapped method handle to be re-associated with an arbitrary member name. */

    static class WrappedMember extends MethodHandle {

        private final MethodHandle target;

        private final MemberName member;

        private final Class<?> callerClass;

        private WrappedMember(MethodHandle target, MethodType type, MemberName member, Class<?> callerClass) {

            super(type, reinvokerForm(target));

            this.target = target;

            this.member = member;

            this.callerClass = callerClass;

        }

        @Override

        MethodHandle reinvokerTarget() {

            return target;

        }

        @Override

        public MethodHandle asTypeUncached(MethodType newType) {

            // This MH is an alias for target, except for the MemberName

            // Drop the MemberName if there is any conversion.

            return asTypeCache = target.asType(newType);

        }

        @Override

        MemberName internalMemberName() {

            return member;

        }