/*
 * Copyright (c) 2008, 2012, 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 sun.misc.Unsafe;
import sun.reflect.CallerSensitive;
import sun.reflect.Reflection;
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/**
 * 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.
Params:
srcType – required call type
target – original method handle
level – which strength of conversion is allowed
Returns:
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/**
     * 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 MethodHandle cache;

        AsVarargsCollector(MethodHandle target, MethodType type, Class<?> arrayType) {
            super(type, reinvokerForm(type));
            this.target = target;
            this.arrayType = arrayType;
            this.cache = target.asCollector(arrayType, 0);
        }

        @Override MethodHandle reinvokerTarget() { return target; }

        @Override
        public boolean isVarargsCollector() {
            return true;
        }

        @Override
        public MethodHandle asFixedArity() {
            return target;
        }

        @Override
        public MethodHandle asType(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 asFixedArity().asType(newType);
            }
            // check cache
            if (cache.type().parameterCount() == newArity)
                return cache.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);
            }
            cache = collector;
            return collector.asType(newType);
        }

        @Override
        MethodHandle setVarargs(MemberName member) {
            if (member.isVarargs())  return this;
            return asFixedArity();
        }

        @Override
        MethodHandle viewAsType(MethodType newType) {
            MethodHandle mh = super.viewAsType(newType);
            // put back the varargs bit:
            MethodType type = mh.type();
            int arity = type.parameterCount();
            return mh.asVarargsCollector(type.parameterType(arity-1));
        }

        @Override
        MemberName internalMemberName() {
            return asFixedArity().internalMemberName();
        }


        @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. /** 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.
/**
     * 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). /** 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 {
            MethodHandle gtarget = makeSpreadArguments(target, Object[].class, 0, nargs);
            catcher = catcher.asType(ctype.changeParameterType(0, Throwable.class));
            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;
    static
    MethodHandle fakeMethodHandleInvoke(MemberName method) {
        MethodType type = method.getInvocationType();
        assert(type.equals(MethodType.methodType(Object.class, Object[].class)));
        MethodHandle mh = FAKE_METHOD_HANDLE_INVOKE;
        if (mh != null)  return mh;
        mh = throwException(type.insertParameterTypes(0, UnsupportedOperationException.class));
        mh = mh.bindTo(new UnsupportedOperationException("cannot reflectively invoke MethodHandle"));
        FAKE_METHOD_HANDLE_INVOKE = 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.
/**
     * 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());
        }

        private static final Unsafe UNSAFE = Unsafe.getUnsafe();

        private static MethodHandle makeInjectedInvoker(Class<?> hostClass) {
            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 newInternalError(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) {
            return vamh.asCollector(Object[].class, type.parameterCount()).asType(type);
        }

        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 newInternalError(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 newInternalError(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);
            }
        }
    }
}