/*

 * Copyright (c) 2008, 2021, 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 jdk.internal.access.JavaLangInvokeAccess;

import jdk.internal.access.SharedSecrets;

import jdk.internal.invoke.NativeEntryPoint;

import jdk.internal.org.objectweb.asm.ClassWriter;

import jdk.internal.org.objectweb.asm.MethodVisitor;

import jdk.internal.reflect.CallerSensitive;

import jdk.internal.reflect.Reflection;

import jdk.internal.vm.annotation.ForceInline;

import jdk.internal.vm.annotation.Hidden;

import jdk.internal.vm.annotation.Stable;

import sun.invoke.empty.Empty;

import sun.invoke.util.ValueConversions;

import sun.invoke.util.VerifyType;

import sun.invoke.util.Wrapper;

import java.lang.invoke.MethodHandles.Lookup;

import java.lang.reflect.Array;

import java.nio.ByteOrder;

import java.util.Arrays;

import java.util.Collections;

import java.util.HashMap;

import java.util.Iterator;

import java.util.List;

import java.util.Map;

import java.util.Objects;

import java.util.concurrent.ConcurrentHashMap;

import java.util.function.Function;

import java.util.stream.Stream;

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

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

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

import static jdk.internal.org.objectweb.asm.Opcodes.*;

/**

 * Trusted implementation code for MethodHandle.

 * @author jrose

 */

/*non-public*/

abstract class MethodHandleImpl {

    /// Factory methods to create method handles:

    static MethodHandle makeArrayElementAccessor(Class<?> arrayClass, ArrayAccess access) {

        if (arrayClass == Object[].class) {

            return ArrayAccess.objectAccessor(access);

        }

        if (!arrayClass.isArray())

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

        MethodHandle[] cache = ArrayAccessor.TYPED_ACCESSORS.get(arrayClass);

        int cacheIndex = ArrayAccess.cacheIndex(access);

        MethodHandle mh = cache[cacheIndex];

        if (mh != null)  return mh;

        mh = ArrayAccessor.getAccessor(arrayClass, access);

        MethodType correctType = ArrayAccessor.correctType(arrayClass, access);

        if (mh.type() != correctType) {

            assert(mh.type().parameterType(0) == Object[].class);

            /* if access == SET */ assert(access != ArrayAccess.SET || mh.type().parameterType(2) == Object.class);

            /* if access == GET */ assert(access != ArrayAccess.GET ||

                    (mh.type().returnType() == Object.class &&

                     correctType.parameterType(0).getComponentType() == correctType.returnType()));

            // safe to view non-strictly, because element type follows from array type

            mh = mh.viewAsType(correctType, false);

        }

        mh = makeIntrinsic(mh, ArrayAccess.intrinsic(access));

        // Atomically update accessor cache.

        synchronized(cache) {

            if (cache[cacheIndex] == null) {

                cache[cacheIndex] = mh;

            } else {

                // Throw away newly constructed accessor and use cached version.

                mh = cache[cacheIndex];

            }

        }

        return mh;

    }

    enum ArrayAccess {

        GET, SET, LENGTH;

        // As ArrayAccess and ArrayAccessor have a circular dependency, the ArrayAccess properties cannot be stored in

        // final fields.

        static String opName(ArrayAccess a) {

            return switch (a) {

                case GET    -> "getElement";

                case SET    -> "setElement";

                case LENGTH -> "length";

                default -> throw unmatchedArrayAccess(a);

            };

        }

        static MethodHandle objectAccessor(ArrayAccess a) {

            return switch (a) {

                case GET    -> ArrayAccessor.OBJECT_ARRAY_GETTER;

                case SET    -> ArrayAccessor.OBJECT_ARRAY_SETTER;

                case LENGTH -> ArrayAccessor.OBJECT_ARRAY_LENGTH;

                default -> throw unmatchedArrayAccess(a);

            };

        }

        static int cacheIndex(ArrayAccess a) {

            return switch (a) {

                case GET    -> ArrayAccessor.GETTER_INDEX;

                case SET    -> ArrayAccessor.SETTER_INDEX;

                case LENGTH -> ArrayAccessor.LENGTH_INDEX;

                default -> throw unmatchedArrayAccess(a);

            };

        }

        static Intrinsic intrinsic(ArrayAccess a) {

            return switch (a) {

                case GET    -> Intrinsic.ARRAY_LOAD;

                case SET    -> Intrinsic.ARRAY_STORE;

                case LENGTH -> Intrinsic.ARRAY_LENGTH;

                default -> throw unmatchedArrayAccess(a);

            };

        }

    }

    static InternalError unmatchedArrayAccess(ArrayAccess a) {

        return newInternalError("should not reach here (unmatched ArrayAccess: " + a + ")");

    }

    static final class ArrayAccessor {

        /// Support for array element and length access

        static final int GETTER_INDEX = 0, SETTER_INDEX = 1, LENGTH_INDEX = 2, INDEX_LIMIT = 3;

        static final ClassValue<MethodHandle[]> TYPED_ACCESSORS

                = new ClassValue<MethodHandle[]>() {

                    @Override

                    protected MethodHandle[] computeValue(Class<?> type) {

                        return new MethodHandle[INDEX_LIMIT];

                    }

                };

        static final MethodHandle OBJECT_ARRAY_GETTER, OBJECT_ARRAY_SETTER, OBJECT_ARRAY_LENGTH;

        static {

            MethodHandle[] cache = TYPED_ACCESSORS.get(Object[].class);

            cache[GETTER_INDEX] = OBJECT_ARRAY_GETTER = makeIntrinsic(getAccessor(Object[].class, ArrayAccess.GET),    Intrinsic.ARRAY_LOAD);

            cache[SETTER_INDEX] = OBJECT_ARRAY_SETTER = makeIntrinsic(getAccessor(Object[].class, ArrayAccess.SET),    Intrinsic.ARRAY_STORE);

            cache[LENGTH_INDEX] = OBJECT_ARRAY_LENGTH = makeIntrinsic(getAccessor(Object[].class, ArrayAccess.LENGTH), Intrinsic.ARRAY_LENGTH);

            assert(InvokerBytecodeGenerator.isStaticallyInvocable(ArrayAccessor.OBJECT_ARRAY_GETTER.internalMemberName()));

            assert(InvokerBytecodeGenerator.isStaticallyInvocable(ArrayAccessor.OBJECT_ARRAY_SETTER.internalMemberName()));

            assert(InvokerBytecodeGenerator.isStaticallyInvocable(ArrayAccessor.OBJECT_ARRAY_LENGTH.internalMemberName()));

        }

        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 int     lengthI(int[]     a)                       { return a.length; }

        static int     lengthJ(long[]    a)                       { return a.length; }

        static int     lengthF(float[]   a)                       { return a.length; }

        static int     lengthD(double[]  a)                       { return a.length; }

        static int     lengthZ(boolean[] a)                       { return a.length; }

        static int     lengthB(byte[]    a)                       { return a.length; }

        static int     lengthS(short[]   a)                       { return a.length; }

        static int     lengthC(char[]    a)                       { return a.length; }

        static int     lengthL(Object[]  a)                       { return a.length; }

        static String name(Class<?> arrayClass, ArrayAccess access) {

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

            if (elemClass == null)  throw newIllegalArgumentException("not an array", arrayClass);

            return ArrayAccess.opName(access) + Wrapper.basicTypeChar(elemClass);

        }

        static MethodType type(Class<?> arrayClass, ArrayAccess access) {

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

            Class<?> arrayArgClass = arrayClass;

            if (!elemClass.isPrimitive()) {

                arrayArgClass = Object[].class;

                elemClass = Object.class;

            }

            return switch (access) {

                case GET    -> MethodType.methodType(elemClass, arrayArgClass, int.class);

                case SET    -> MethodType.methodType(void.class, arrayArgClass, int.class, elemClass);

                case LENGTH -> MethodType.methodType(int.class, arrayArgClass);

                default -> throw unmatchedArrayAccess(access);

            };

        }

        static MethodType correctType(Class<?> arrayClass, ArrayAccess access) {

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

            return switch (access) {

                case GET    -> MethodType.methodType(elemClass, arrayClass, int.class);

                case SET    -> MethodType.methodType(void.class, arrayClass, int.class, elemClass);

                case LENGTH -> MethodType.methodType(int.class, arrayClass);

                default -> throw unmatchedArrayAccess(access);

            };

        }

        static MethodHandle getAccessor(Class<?> arrayClass, ArrayAccess access) {

            String     name = name(arrayClass, access);

            MethodType type = type(arrayClass, access);

            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 strict if true, only asType conversions are allowed; if false, explicitCastArguments conversions allowed

     * @param monobox if true, unboxing conversions are assumed to be exactly typed (Integer to int only, not long or double)

     * @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,

                                            boolean strict, boolean monobox) {

        MethodType dstType = target.type();

        if (srcType == dstType)

            return target;

        return makePairwiseConvertByEditor(target, srcType, strict, monobox);

    }

    private static int countNonNull(Object[] array) {

        int count = 0;

        if (array != null) {

            for (Object x : array) {

                if (x != null) ++count;

            }

        }

        return count;

    }

    static MethodHandle makePairwiseConvertByEditor(MethodHandle target, MethodType srcType,

                                                    boolean strict, boolean monobox) {

        // In method types arguments start at index 0, while the LF

        // editor have the MH receiver at position 0 - adjust appropriately.

        final int MH_RECEIVER_OFFSET = 1;

        Object[] convSpecs = computeValueConversions(srcType, target.type(), strict, monobox);

        int convCount = countNonNull(convSpecs);

        if (convCount == 0)

            return target.viewAsType(srcType, strict);

        MethodType basicSrcType = srcType.basicType();

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

        BoundMethodHandle mh = target.rebind();

        // Match each unique conversion to the positions at which it is to be applied

        var convSpecMap = new HashMap<Object, int[]>(((4 * convCount) / 3) + 1);

        for (int i = 0; i < convSpecs.length - MH_RECEIVER_OFFSET; i++) {

            Object convSpec = convSpecs[i];

            if (convSpec == null) continue;

            int[] positions = convSpecMap.get(convSpec);

            if (positions == null) {

                positions = new int[] { i + MH_RECEIVER_OFFSET };

            } else {

                positions = Arrays.copyOf(positions, positions.length + 1);

                positions[positions.length - 1] = i + MH_RECEIVER_OFFSET;

            }

            convSpecMap.put(convSpec, positions);

        }

        for (var entry : convSpecMap.entrySet()) {

            Object convSpec = entry.getKey();

            MethodHandle fn;

            if (convSpec instanceof Class) {

                fn = getConstantHandle(MH_cast).bindTo(convSpec);

            } else {

                fn = (MethodHandle) convSpec;

            }

            int[] positions = entry.getValue();

            Class<?> newType = basicSrcType.parameterType(positions[0] - MH_RECEIVER_OFFSET);

            BasicType newBasicType = BasicType.basicType(newType);

            convCount -= positions.length;

            if (convCount == 0) {

                midType = srcType;

            } else {

                Class<?>[] ptypes = midType.ptypes().clone();

                for (int pos : positions) {

                    ptypes[pos - 1] = newType;

                }

                midType = MethodType.makeImpl(midType.rtype(), ptypes, true);

            }

            LambdaForm form2;

            if (positions.length > 1) {

                form2 = mh.editor().filterRepeatedArgumentForm(newBasicType, positions);

            } else {

                form2 = mh.editor().filterArgumentForm(positions[0], newBasicType);

            }

            mh = mh.copyWithExtendL(midType, form2, fn);

        }

        Object convSpec = convSpecs[convSpecs.length - 1];

        if (convSpec != null) {

            MethodHandle fn;

            if (convSpec instanceof Class) {

                if (convSpec == void.class)

                    fn = null;

                else

                    fn = getConstantHandle(MH_cast).bindTo(convSpec);

            } else {

                fn = (MethodHandle) convSpec;

            }

            Class<?> newType = basicSrcType.returnType();

            assert(--convCount == 0);

            midType = srcType;

            if (fn != null) {

                mh = mh.rebind();  // rebind if too complex

                LambdaForm form2 = mh.editor().filterReturnForm(BasicType.basicType(newType), false);

                mh = mh.copyWithExtendL(midType, form2, fn);

            } else {

                LambdaForm form2 = mh.editor().filterReturnForm(BasicType.basicType(newType), true);

                mh = mh.copyWith(midType, form2);

            }

        }

        assert(convCount == 0);

        assert(mh.type().equals(srcType));

        return mh;

    }

    static Object[] computeValueConversions(MethodType srcType, MethodType dstType,

                                            boolean strict, boolean monobox) {

        final int INARG_COUNT = srcType.parameterCount();

        Object[] convSpecs = null;

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

            boolean isRet = (i == INARG_COUNT);

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

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

            if (!VerifyType.isNullConversion(src, dst, /*keepInterfaces=*/ strict)) {

                if (convSpecs == null) {

                    convSpecs = new Object[INARG_COUNT + 1];

                }

                convSpecs[i] = valueConversion(src, dst, strict, monobox);

            }

        }

        return convSpecs;

    }

    static MethodHandle makePairwiseConvert(MethodHandle target, MethodType srcType,

                                            boolean strict) {

        return makePairwiseConvert(target, srcType, strict, /*monobox=*/ false);

    }

    /**

     * Find a conversion function from the given source to the given destination.

     * This conversion function will be used as a LF NamedFunction.

     * Return a Class object if a simple cast is needed.

     * Return void.class if void is involved.

     */

    static Object valueConversion(Class<?> src, Class<?> dst, boolean strict, boolean monobox) {

        assert(!VerifyType.isNullConversion(src, dst, /*keepInterfaces=*/ strict));  // caller responsibility

        if (dst == void.class)

            return dst;

        MethodHandle fn;

        if (src.isPrimitive()) {

            if (src == void.class) {

                return void.class;  // caller must recognize this specially

            } else if (dst.isPrimitive()) {

                // Examples: int->byte, byte->int, boolean->int (!strict)

                fn = ValueConversions.convertPrimitive(src, dst);

            } else {

                // Examples: int->Integer, boolean->Object, float->Number

                Wrapper wsrc = Wrapper.forPrimitiveType(src);

                fn = ValueConversions.boxExact(wsrc);

                assert(fn.type().parameterType(0) == wsrc.primitiveType());

                assert(fn.type().returnType() == wsrc.wrapperType());

                if (!VerifyType.isNullConversion(wsrc.wrapperType(), dst, strict)) {

                    // Corner case, such as int->Long, which will probably fail.

                    MethodType mt = MethodType.methodType(dst, src);

                    if (strict)

                        fn = fn.asType(mt);

                    else

                        fn = MethodHandleImpl.makePairwiseConvert(fn, mt, /*strict=*/ false);

                }

            }

        } else if (dst.isPrimitive()) {

            Wrapper wdst = Wrapper.forPrimitiveType(dst);

            if (monobox || src == wdst.wrapperType()) {

                // Use a strongly-typed unboxer, if possible.

                fn = ValueConversions.unboxExact(wdst, strict);

            } else {

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

                // must include additional conversions

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

                fn = (strict

                        ? ValueConversions.unboxWiden(wdst)

                        : ValueConversions.unboxCast(wdst));

            }

        } 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.

            return dst;

        }

        assert(fn.type().parameterCount() <= 1) : "pc"+Arrays.asList(src.getSimpleName(), dst.getSimpleName(), fn);

        return fn;

    }

    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, arrayType);

    }

    private static final class AsVarargsCollector extends DelegatingMethodHandle {

        private final MethodHandle target;

        private final Class<?> arrayType;

        private @Stable MethodHandle asCollectorCache;

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

            this(target.type(), target, arrayType);

        }

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

            super(type, target);

            this.target = target;

            this.arrayType = arrayType;

        }

        @Override

        public boolean isVarargsCollector() {

            return true;

        }

        @Override

        protected MethodHandle getTarget() {

            return target;

        }

        @Override

        public MethodHandle asFixedArity() {

            return target;

        }

        @Override

        MethodHandle setVarargs(MemberName member) {

            if (member.isVarargs())  return this;

            return asFixedArity();

        }

        @Override

        public MethodHandle withVarargs(boolean makeVarargs) {

            if (makeVarargs)  return this;

            return asFixedArity();

        }

        @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

        boolean viewAsTypeChecks(MethodType newType, boolean strict) {

            super.viewAsTypeChecks(newType, true);

            if (strict) return true;

            // extra assertion for non-strict checks:

            assert (type().lastParameterType().getComponentType()

                    .isAssignableFrom(

                            newType.lastParameterType().getComponentType()))

                    : Arrays.asList(this, newType);

            return true;

        }

        @Override

        public Object invokeWithArguments(Object... arguments) throws Throwable {

            MethodType type = this.type();

            int argc;

            final int MAX_SAFE = 127;  // 127 longs require 254 slots, which is safe to spread

            if (arguments == null

                    || (argc = arguments.length) <= MAX_SAFE

                    || argc < type.parameterCount()) {

                return super.invokeWithArguments(arguments);

            }

            // a jumbo invocation requires more explicit reboxing of the trailing arguments

            int uncollected = type.parameterCount() - 1;

            Class<?> elemType = arrayType.getComponentType();

            int collected = argc - uncollected;

            Object collArgs = (elemType == Object.class)

                ? new Object[collected] : Array.newInstance(elemType, collected);

            if (!elemType.isPrimitive()) {

                // simple cast:  just do some casting

                try {

                    System.arraycopy(arguments, uncollected, collArgs, 0, collected);

                } catch (ArrayStoreException ex) {

                    return super.invokeWithArguments(arguments);

                }

            } else {

                // corner case of flat array requires reflection (or specialized copy loop)

                MethodHandle arraySetter = MethodHandles.arrayElementSetter(arrayType);

                try {

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

                        arraySetter.invoke(collArgs, i, arguments[uncollected + i]);

                    }

                } catch (WrongMethodTypeException|ClassCastException ex) {

                    return super.invokeWithArguments(arguments);

                }

            }

            // chop the jumbo list down to size and call in non-varargs mode

            Object[] newArgs = new Object[uncollected + 1];

            System.arraycopy(arguments, 0, newArgs, 0, uncollected);

            newArgs[uncollected] = collArgs;

            return asFixedArity().invokeWithArguments(newArgs);

        }

    }

    static void checkSpreadArgument(Object av, int n) {

        if (av == null && n == 0) {

            return;

        } else if (av == null) {

            throw new NullPointerException("null array reference");

        } 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);

    }

    @Hidden

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

        if (testResult) {

            return target;

        } else {

            return fallback;

        }

    }

    // Intrinsified by C2. Counters are used during parsing to calculate branch frequencies.

    @Hidden

    @jdk.internal.vm.annotation.IntrinsicCandidate

    static boolean profileBoolean(boolean result, int[] counters) {

        // Profile is int[2] where [0] and [1] correspond to false and true occurrences respectively.

        int idx = result ? 1 : 0;

        try {

            counters[idx] = Math.addExact(counters[idx], 1);

        } catch (ArithmeticException e) {

            // Avoid continuous overflow by halving the problematic count.

            counters[idx] = counters[idx] / 2;

        }

        return result;

    }

    // Intrinsified by C2. Returns true if obj is a compile-time constant.

    @Hidden

    @jdk.internal.vm.annotation.IntrinsicCandidate

    static boolean isCompileConstant(Object obj) {

        return false;

    }

    static MethodHandle makeGuardWithTest(MethodHandle test,

                                   MethodHandle target,

                                   MethodHandle fallback) {

        MethodType type = target.type();

        assert(test.type().equals(type.changeReturnType(boolean.class)) && fallback.type().equals(type));

        MethodType basicType = type.basicType();

        LambdaForm form = makeGuardWithTestForm(basicType);

        BoundMethodHandle mh;

        try {

            if (PROFILE_GWT) {

                int[] counts = new int[2];

                mh = (BoundMethodHandle)

                        BoundMethodHandle.speciesData_LLLL().factory().invokeBasic(type, form,

                                (Object) test, (Object) profile(target), (Object) profile(fallback), counts);

            } else {

                mh = (BoundMethodHandle)

                        BoundMethodHandle.speciesData_LLL().factory().invokeBasic(type, form,

                                (Object) test, (Object) profile(target), (Object) profile(fallback));

            }

        } catch (Throwable ex) {

            throw uncaughtException(ex);

        }

        assert(mh.type() == type);

        return mh;

    }

    static MethodHandle profile(MethodHandle target) {

        if (DONT_INLINE_THRESHOLD >= 0) {

            return makeBlockInliningWrapper(target);

        } else {

            return target;

        }

    }

    /**

     * Block inlining during JIT-compilation of a target method handle if it hasn't been invoked enough times.

     * Corresponding LambdaForm has @DontInline when compiled into bytecode.

     */

    static MethodHandle makeBlockInliningWrapper(MethodHandle target) {

        LambdaForm lform;

        if (DONT_INLINE_THRESHOLD > 0) {

            lform = Makers.PRODUCE_BLOCK_INLINING_FORM.apply(target);

        } else {

            lform = Makers.PRODUCE_REINVOKER_FORM.apply(target);

        }

        return new CountingWrapper(target, lform,

                Makers.PRODUCE_BLOCK_INLINING_FORM, Makers.PRODUCE_REINVOKER_FORM,

                                   DONT_INLINE_THRESHOLD);

    }

    private static final class Makers {

        /** Constructs reinvoker lambda form which block inlining during JIT-compilation for a particular method handle */

        static final Function<MethodHandle, LambdaForm> PRODUCE_BLOCK_INLINING_FORM = new Function<MethodHandle, LambdaForm>() {

            @Override

            public LambdaForm apply(MethodHandle target) {

                return DelegatingMethodHandle.makeReinvokerForm(target,

                                   MethodTypeForm.LF_DELEGATE_BLOCK_INLINING, CountingWrapper.class, false,

                                   DelegatingMethodHandle.NF_getTarget, CountingWrapper.NF_maybeStopCounting);

            }

        };

        /** Constructs simple reinvoker lambda form for a particular method handle */

        static final Function<MethodHandle, LambdaForm> PRODUCE_REINVOKER_FORM = new Function<MethodHandle, LambdaForm>() {

            @Override

            public LambdaForm apply(MethodHandle target) {

                return DelegatingMethodHandle.makeReinvokerForm(target,

                        MethodTypeForm.LF_DELEGATE, DelegatingMethodHandle.class, DelegatingMethodHandle.NF_getTarget);

            }

        };

        /** Maker of type-polymorphic varargs */

        static final ClassValue<MethodHandle[]> TYPED_COLLECTORS = new ClassValue<MethodHandle[]>() {

            @Override

            protected MethodHandle[] computeValue(Class<?> type) {

                return new MethodHandle[MAX_JVM_ARITY + 1];

            }

        };

    }

    /**

     * Counting method handle. It has 2 states: counting and non-counting.

     * It is in counting state for the first n invocations and then transitions to non-counting state.

     * Behavior in counting and non-counting states is determined by lambda forms produced by

     * countingFormProducer & nonCountingFormProducer respectively.

     */

    static class CountingWrapper extends DelegatingMethodHandle {

        private final MethodHandle target;

        private int count;

        private Function<MethodHandle, LambdaForm> countingFormProducer;

        private Function<MethodHandle, LambdaForm> nonCountingFormProducer;

        private volatile boolean isCounting;

        private CountingWrapper(MethodHandle target, LambdaForm lform,

                                Function<MethodHandle, LambdaForm> countingFromProducer,

                                Function<MethodHandle, LambdaForm> nonCountingFormProducer,

                                int count) {

            super(target.type(), lform);

            this.target = target;

            this.count = count;

            this.countingFormProducer = countingFromProducer;

            this.nonCountingFormProducer = nonCountingFormProducer;

            this.isCounting = (count > 0);

        }

        @Hidden

        @Override

        protected MethodHandle getTarget() {

            return target;

        }

        @Override

        public MethodHandle asTypeUncached(MethodType newType) {

            MethodHandle newTarget = target.asType(newType);

            MethodHandle wrapper;

            if (isCounting) {

                LambdaForm lform;

                lform = countingFormProducer.apply(newTarget);

                wrapper = new CountingWrapper(newTarget, lform, countingFormProducer, nonCountingFormProducer, DONT_INLINE_THRESHOLD);

            } else {

                wrapper = newTarget; // no need for a counting wrapper anymore

            }

            return (asTypeCache = wrapper);

        }

        boolean countDown() {

            int c = count;

            target.maybeCustomize(); // customize if counting happens for too long

            if (c <= 1) {

                // Try to limit number of updates. MethodHandle.updateForm() doesn't guarantee LF update visibility.

                if (isCounting) {

                    isCounting = false;

                    return true;

                } else {

                    return false;

                }

            } else {

                count = c - 1;

                return false;

            }

        }

        @Hidden

        static void maybeStopCounting(Object o1) {

             final CountingWrapper wrapper = (CountingWrapper) o1;

             if (wrapper.countDown()) {

                 // Reached invocation threshold. Replace counting behavior with a non-counting one.

                 wrapper.updateForm(new Function<>() {

                     public LambdaForm apply(LambdaForm oldForm) {

                         LambdaForm lform = wrapper.nonCountingFormProducer.apply(wrapper.target);

                         lform.compileToBytecode(); // speed up warmup by avoiding LF interpretation again after transition

                         return lform;

                     }});

             }

        }

        static final NamedFunction NF_maybeStopCounting;

        static {

            Class<?> THIS_CLASS = CountingWrapper.class;

            try {

                NF_maybeStopCounting = new NamedFunction(THIS_CLASS.getDeclaredMethod("maybeStopCounting", Object.class));

            } catch (ReflectiveOperationException ex) {

                throw newInternalError(ex);

            }

        }

    }

    static LambdaForm makeGuardWithTestForm(MethodType basicType) {

        LambdaForm lform = basicType.form().cachedLambdaForm(MethodTypeForm.LF_GWT);

        if (lform != null)  return lform;

        final int THIS_MH      = 0;  // the BMH_LLL

        final int ARG_BASE     = 1;  // start of incoming arguments

        final int ARG_LIMIT    = ARG_BASE + basicType.parameterCount();

        int nameCursor = ARG_LIMIT;

        final int GET_TEST     = nameCursor++;

        final int GET_TARGET   = nameCursor++;

        final int GET_FALLBACK = nameCursor++;

        final int GET_COUNTERS = PROFILE_GWT ? nameCursor++ : -1;

        final int CALL_TEST    = nameCursor++;

        final int PROFILE      = (GET_COUNTERS != -1) ? nameCursor++ : -1;

        final int TEST         = nameCursor-1; // previous statement: either PROFILE or CALL_TEST

        final int SELECT_ALT   = nameCursor++;

        final int CALL_TARGET  = nameCursor++;

        assert(CALL_TARGET == SELECT_ALT+1);  // must be true to trigger IBG.emitSelectAlternative

        MethodType lambdaType = basicType.invokerType();

        Name[] names = arguments(nameCursor - ARG_LIMIT, lambdaType);

        BoundMethodHandle.SpeciesData data =

                (GET_COUNTERS != -1) ? BoundMethodHandle.speciesData_LLLL()

                                     : BoundMethodHandle.speciesData_LLL();

        names[THIS_MH] = names[THIS_MH].withConstraint(data);

        names[GET_TEST]     = new Name(data.getterFunction(0), names[THIS_MH]);

        names[GET_TARGET]   = new Name(data.getterFunction(1), names[THIS_MH]);

        names[GET_FALLBACK] = new Name(data.getterFunction(2), names[THIS_MH]);

        if (GET_COUNTERS != -1) {

            names[GET_COUNTERS] = new Name(data.getterFunction(3), names[THIS_MH]);

        }

        Object[] invokeArgs = Arrays.copyOfRange(names, 0, ARG_LIMIT, Object[].class);

        // call test

        MethodType testType = basicType.changeReturnType(boolean.class).basicType();

        invokeArgs[0] = names[GET_TEST];

        names[CALL_TEST] = new Name(testType, invokeArgs);

        // profile branch

        if (PROFILE != -1) {

            names[PROFILE] = new Name(getFunction(NF_profileBoolean), names[CALL_TEST], names[GET_COUNTERS]);

        }

        // call selectAlternative

        names[SELECT_ALT] = new Name(new NamedFunction(

                makeIntrinsic(getConstantHandle(MH_selectAlternative), Intrinsic.SELECT_ALTERNATIVE)),

                names[TEST], names[GET_TARGET], names[GET_FALLBACK]);

        // call target or fallback

        invokeArgs[0] = names[SELECT_ALT];

        names[CALL_TARGET] = new Name(basicType, invokeArgs);

        lform = new LambdaForm(lambdaType.parameterCount(), names, /*forceInline=*/true, Kind.GUARD);

        return basicType.form().setCachedLambdaForm(MethodTypeForm.LF_GWT, lform);

    }

    /**

     * The LambdaForm shape for catchException combinator is the following:

     * <blockquote><pre>{@code

     *  guardWithCatch=Lambda(a0:L,a1:L,a2:L)=>{

     *    t3:L=BoundMethodHandle$Species_LLLLL.argL0(a0:L);

     *    t4:L=BoundMethodHandle$Species_LLLLL.argL1(a0:L);

     *    t5:L=BoundMethodHandle$Species_LLLLL.argL2(a0:L);

     *    t6:L=BoundMethodHandle$Species_LLLLL.argL3(a0:L);

     *    t7:L=BoundMethodHandle$Species_LLLLL.argL4(a0:L);

     *    t8:L=MethodHandle.invokeBasic(t6:L,a1:L,a2:L);

     *    t9:L=MethodHandleImpl.guardWithCatch(t3:L,t4:L,t5:L,t8:L);

     *   t10:I=MethodHandle.invokeBasic(t7:L,t9:L);t10:I}

     * }</pre></blockquote>

     *

     * argL0 and argL2 are target and catcher method handles. argL1 is exception class.

     * argL3 and argL4 are auxiliary method handles: argL3 boxes arguments and wraps them into Object[]

     * (ValueConversions.array()) and argL4 unboxes result if necessary (ValueConversions.unbox()).

     *

     * Having t8 and t10 passed outside and not hardcoded into a lambda form allows to share lambda forms

     * among catchException combinators with the same basic type.

     */

    private static LambdaForm makeGuardWithCatchForm(MethodType basicType) {

        MethodType lambdaType = basicType.invokerType();

        LambdaForm lform = basicType.form().cachedLambdaForm(MethodTypeForm.LF_GWC);

        if (lform != null) {

            return lform;

        }

        final int THIS_MH      = 0;  // the BMH_LLLLL

        final int ARG_BASE     = 1;  // start of incoming arguments

        final int ARG_LIMIT    = ARG_BASE + basicType.parameterCount();

        int nameCursor = ARG_LIMIT;

        final int GET_TARGET       = nameCursor++;

        final int GET_CLASS        = nameCursor++;

        final int GET_CATCHER      = nameCursor++;

        final int GET_COLLECT_ARGS = nameCursor++;

        final int GET_UNBOX_RESULT = nameCursor++;

        final int BOXED_ARGS       = nameCursor++;

        final int TRY_CATCH        = nameCursor++;

        final int UNBOX_RESULT     = nameCursor++;

        Name[] names = arguments(nameCursor - ARG_LIMIT, lambdaType);

        BoundMethodHandle.SpeciesData data = BoundMethodHandle.speciesData_LLLLL();

        names[THIS_MH]          = names[THIS_MH].withConstraint(data);

        names[GET_TARGET]       = new Name(data.getterFunction(0), names[THIS_MH]);

        names[GET_CLASS]        = new Name(data.getterFunction(1), names[THIS_MH]);

        names[GET_CATCHER]      = new Name(data.getterFunction(2), names[THIS_MH]);

        names[GET_COLLECT_ARGS] = new Name(data.getterFunction(3), names[THIS_MH]);

        names[GET_UNBOX_RESULT] = new Name(data.getterFunction(4), names[THIS_MH]);

        // FIXME: rework argument boxing/result unboxing logic for LF interpretation

        // t_{i}:L=MethodHandle.invokeBasic(collectArgs:L,a1:L,...);

        MethodType collectArgsType = basicType.changeReturnType(Object.class);

        MethodHandle invokeBasic = MethodHandles.basicInvoker(collectArgsType);

        Object[] args = new Object[invokeBasic.type().parameterCount()];

        args[0] = names[GET_COLLECT_ARGS];

        System.arraycopy(names, ARG_BASE, args, 1, ARG_LIMIT-ARG_BASE);

        names[BOXED_ARGS] = new Name(new NamedFunction(makeIntrinsic(invokeBasic, Intrinsic.GUARD_WITH_CATCH)), args);

        // t_{i+1}:L=MethodHandleImpl.guardWithCatch(target:L,exType:L,catcher:L,t_{i}:L);

        Object[] gwcArgs = new Object[] {names[GET_TARGET], names[GET_CLASS], names[GET_CATCHER], names[BOXED_ARGS]};

        names[TRY_CATCH] = new Name(getFunction(NF_guardWithCatch), gwcArgs);

        // t_{i+2}:I=MethodHandle.invokeBasic(unbox:L,t_{i+1}:L);

        MethodHandle invokeBasicUnbox = MethodHandles.basicInvoker(MethodType.methodType(basicType.rtype(), Object.class));

        Object[] unboxArgs  = new Object[] {names[GET_UNBOX_RESULT], names[TRY_CATCH]};

        names[UNBOX_RESULT] = new Name(invokeBasicUnbox, unboxArgs);

        lform = new LambdaForm(lambdaType.parameterCount(), names, Kind.GUARD_WITH_CATCH);

        return basicType.form().setCachedLambdaForm(MethodTypeForm.LF_GWC, lform);

    }

    static MethodHandle makeGuardWithCatch(MethodHandle target,

                                    Class<? extends Throwable> exType,

                                    MethodHandle catcher) {

        MethodType type = target.type();

        LambdaForm form = makeGuardWithCatchForm(type.basicType());

        // Prepare auxiliary method handles used during LambdaForm interpretation.

        // Box arguments and wrap them into Object[]: ValueConversions.array().

        MethodType varargsType = type.changeReturnType(Object[].class);

        MethodHandle collectArgs = varargsArray(type.parameterCount()).asType(varargsType);

        MethodHandle unboxResult = unboxResultHandle(type.returnType());

        BoundMethodHandle.SpeciesData data = BoundMethodHandle.speciesData_LLLLL();

        BoundMethodHandle mh;

        try {

            mh = (BoundMethodHandle) data.factory().invokeBasic(type, form, (Object) target, (Object) exType,

                    (Object) catcher, (Object) collectArgs, (Object) unboxResult);

        } catch (Throwable ex) {

            throw uncaughtException(ex);

        }

        assert(mh.type() == type);

        return mh;

    }

    /**

     * Intrinsified during LambdaForm compilation

     * (see {@link InvokerBytecodeGenerator#emitGuardWithCatch emitGuardWithCatch}).

     */

    @Hidden

    static Object guardWithCatch(MethodHandle target, Class<? extends Throwable> exType, MethodHandle catcher,

                                 Object... av) throws Throwable {

        // Use asFixedArity() to avoid unnecessary boxing of last argument for VarargsCollector case.

        try {

            return target.asFixedArity().invokeWithArguments(av);

        } catch (Throwable t) {

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

            return catcher.asFixedArity().invokeWithArguments(prepend(av, t));

        }

    }

    /** Prepend elements to an array. */

    @Hidden

    private static Object[] prepend(Object[] array, Object... elems) {

        int nArray = array.length;

        int nElems = elems.length;

        Object[] newArray = new Object[nArray + nElems];

        System.arraycopy(elems, 0, newArray, 0, nElems);

        System.arraycopy(array, 0, newArray, nElems, nArray);

        return newArray;

    }

    static MethodHandle throwException(MethodType type) {

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

        int arity = type.parameterCount();

        if (arity > 1) {

            MethodHandle mh = throwException(type.dropParameterTypes(1, arity));

            mh = MethodHandles.dropArguments(mh, 1, Arrays.copyOfRange(type.parameterArray(), 1, arity));

            return mh;

        }

        return makePairwiseConvert(getFunction(NF_throwException).resolvedHandle(), type, false, true);

    }

    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) {

        assert(method.isMethodHandleInvoke());

        int idx = switch (method.getName()) {

            case "invoke"      -> 0;

            case "invokeExact" -> 1;

            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, false);

        mh = mh.withVarargs(true);

        assert(method.isVarargs());

        FAKE_METHOD_HANDLE_INVOKE[idx] = mh;

        return mh;

    }

    static MethodHandle fakeVarHandleInvoke(MemberName method) {

        // TODO caching, is it necessary?

        MethodType type = MethodType.methodType(method.getReturnType(), UnsupportedOperationException.class,

                                                VarHandle.class, Object[].class);

        MethodHandle mh = throwException(type);

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

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

            throw new InternalError(method.toString());

        mh = mh.withInternalMemberName(method, false);

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

        assert(method.isVarargs());

        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 {

        private static MethodType INVOKER_MT = MethodType.methodType(Object.class, MethodHandle.class, Object[].class);

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

            // Code in the boot layer should now be careful while creating method handles or

            // functional interface instances created from method references to @CallerSensitive  methods,

            // it needs to be ensured the handles or interface instances are kept safe and are not passed

            // from the boot layer to untrusted code.

            if (hostClass == null

                ||    (hostClass.isArray() ||

                       hostClass.isPrimitive() ||

                       hostClass.getName().startsWith("java.lang.invoke."))) {

                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, hostClass);

        }

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

            try {

                /*

                 * The invoker class defined to the same class loader as the lookup class

                 * but in an unnamed package so that the class bytes can be cached and

                 * reused for any @CSM.

                 *

                 * @CSM must be public and exported if called by any module.

                 */

                String name = targetClass.getName() + "$$InjectedInvoker";

                if (targetClass.isHidden()) {

                    // use the original class name

                    name = name.replace('/', '_');

                }

                Class<?> invokerClass = new Lookup(targetClass)

                        .makeHiddenClassDefiner(name, INJECTED_INVOKER_TEMPLATE)

                        .defineClass(true);

                assert checkInjectedInvoker(targetClass, invokerClass);

                return IMPL_LOOKUP.findStatic(invokerClass, "invoke_V", INVOKER_MT);

            } catch (ReflectiveOperationException ex) {

                throw uncaughtException(ex);

            }

        }

        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,

                                                  MethodHandle original,

                                                  Class<?> hostClass) {

            MethodType type = original.type();

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

            MemberName member = original.internalMemberName();

            mh = mh.asType(type);

            mh = new WrappedMember(mh, type, member, original.isInvokeSpecial(), hostClass);

            return mh;

        }

        private static boolean checkInjectedInvoker(Class<?> hostClass, Class<?> invokerClass) {

            assert (hostClass.getClassLoader() == invokerClass.getClassLoader()) : hostClass.getName()+" (CL)";

            try {

                assert (hostClass.getProtectionDomain() == invokerClass.getProtectionDomain()) : hostClass.getName()+" (PD)";

            } catch (SecurityException ex) {

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

            }

            try {

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

                MethodHandle invoker = IMPL_LOOKUP.findStatic(invokerClass, "invoke_V", INVOKER_MT);

                MethodHandle vamh = prepareForInvoker(MH_checkCallerClass);

                return (boolean)invoker.invoke(vamh, new Object[]{ invokerClass });

            } catch (Throwable ex) {

                throw new InternalError(ex);

            }

        }

        private static final MethodHandle MH_checkCallerClass;

        static {

            final Class<?> THIS_CLASS = BindCaller.class;

            assert(checkCallerClass(THIS_CLASS));

            try {

                MH_checkCallerClass = IMPL_LOOKUP

                    .findStatic(THIS_CLASS, "checkCallerClass",

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

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

            } catch (Throwable ex) {

                throw new InternalError(ex);

            }

        }

        @CallerSensitive

        @ForceInline // to ensure Reflection.getCallerClass optimization

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

            // 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)

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

            return true;

        }

        private static final byte[] INJECTED_INVOKER_TEMPLATE = generateInvokerTemplate();

        /** Produces byte code for a class that is used as an injected invoker. */

        private static byte[] generateInvokerTemplate() {

            ClassWriter cw = new ClassWriter(0);

            // private static class InjectedInvoker {

            //     @Hidden

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

            //        return vamh.invokeExact(args);

            //     }

            // }

            cw.visit(52, ACC_PRIVATE | ACC_SUPER, "InjectedInvoker", null, "java/lang/Object", null);

            MethodVisitor mv = cw.visitMethod(ACC_STATIC, "invoke_V",

                          "(Ljava/lang/invoke/MethodHandle;[Ljava/lang/Object;)Ljava/lang/Object;",

                          null, null);

            mv.visitCode();

            mv.visitVarInsn(ALOAD, 0);

            mv.visitVarInsn(ALOAD, 1);

            mv.visitMethodInsn(INVOKEVIRTUAL, "java/lang/invoke/MethodHandle", "invokeExact",

                               "([Ljava/lang/Object;)Ljava/lang/Object;", false);

            mv.visitInsn(ARETURN);

            mv.visitMaxs(2, 2);

            mv.visitEnd();

            cw.visitEnd();

            return cw.toByteArray();

        }

    }

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

    private static final class WrappedMember extends DelegatingMethodHandle {

        private final MethodHandle target;

        private final MemberName member;

        private final Class<?> callerClass;

        private final boolean isInvokeSpecial;

        private WrappedMember(MethodHandle target, MethodType type,

                              MemberName member, boolean isInvokeSpecial,

                              Class<?> callerClass) {

            super(type, target);

            this.target = target;

            this.member = member;

            this.callerClass = callerClass;

            this.isInvokeSpecial = isInvokeSpecial;

        }

        @Override

        MemberName internalMemberName() {

            return member;

        }

        @Override

        Class<?> internalCallerClass() {

            return callerClass;

        }

        @Override

        boolean isInvokeSpecial() {

            return isInvokeSpecial;

        }

        @Override

        protected MethodHandle getTarget() {

            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);

        }

    }

    static MethodHandle makeWrappedMember(MethodHandle target, MemberName member, boolean isInvokeSpecial) {

        if (member.equals(target.internalMemberName()) && isInvokeSpecial == target.isInvokeSpecial())

            return target;

        return new WrappedMember(target, target.type(), member, isInvokeSpecial, null);

    }

    /** Intrinsic IDs */

    /*non-public*/