/*

 * Copyright (c) 2012, 2013, Oracle and/or its affiliates. All rights reserved.

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

 *

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

 * under the terms of the GNU General Public License version 2 only, as

 * published by the Free Software Foundation.  Oracle designates this

 * particular file as subject to the "Classpath" exception as provided

 * by Oracle in the LICENSE file that accompanied this code.

 *

 * This code is distributed in the hope that it will be useful, but WITHOUT

 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or

 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License

 * version 2 for more details (a copy is included in the LICENSE file that

 * accompanied this code).

 *

 * You should have received a copy of the GNU General Public License version

 * 2 along with this work; if not, write to the Free Software Foundation,

 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.

 *

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

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

 * questions.

 */

package java.lang.invoke;

import sun.invoke.util.VerifyAccess;

import java.lang.invoke.LambdaForm.Name;

import java.lang.invoke.MethodHandles.Lookup;

import sun.invoke.util.Wrapper;

import java.io.*;

import java.util.*;

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

import java.lang.reflect.*;

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

import static java.lang.invoke.MethodHandleNatives.Constants.*;

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

import sun.invoke.util.ValueConversions;

import sun.invoke.util.VerifyType;

/**

 * Code generation backend for LambdaForm.

 * <p>

 * @author John Rose, JSR 292 EG

 */

class InvokerBytecodeGenerator {

    /** Define class names for convenience. */

    private static final String MH      = "java/lang/invoke/MethodHandle";

    private static final String BMH     = "java/lang/invoke/BoundMethodHandle";

    private static final String LF      = "java/lang/invoke/LambdaForm";

    private static final String LFN     = "java/lang/invoke/LambdaForm$Name";

    private static final String CLS     = "java/lang/Class";

    private static final String OBJ     = "java/lang/Object";

    private static final String OBJARY  = "[Ljava/lang/Object;";

    private static final String LF_SIG  = "L" + LF + ";";

    private static final String LFN_SIG = "L" + LFN + ";";

    private static final String LL_SIG  = "(L" + OBJ + ";)L" + OBJ + ";";

    /** Name of its super class*/

    private static final String superName = LF;

    /** Name of new class */

    private final String className;

    /** Name of the source file (for stack trace printing). */

    private final String sourceFile;

    private final LambdaForm lambdaForm;

    private final String     invokerName;

    private final MethodType invokerType;

    private final int[] localsMap;

    /** ASM bytecode generation. */

    private ClassWriter cw;

    private MethodVisitor mv;

    private static final MemberName.Factory MEMBERNAME_FACTORY = MemberName.getFactory();

    private static final Class<?> HOST_CLASS = LambdaForm.class;

    private InvokerBytecodeGenerator(LambdaForm lambdaForm, int localsMapSize,

                                     String className, String invokerName, MethodType invokerType) {

        if (invokerName.contains(".")) {

            int p = invokerName.indexOf(".");

            className = invokerName.substring(0, p);

            invokerName = invokerName.substring(p+1);

        }

        if (DUMP_CLASS_FILES) {

            className = makeDumpableClassName(className);

        }

        this.className  = superName + "$" + className;

        this.sourceFile = "LambdaForm$" + className;

        this.lambdaForm = lambdaForm;

        this.invokerName = invokerName;

        this.invokerType = invokerType;

        this.localsMap = new int[localsMapSize];

    }

    private InvokerBytecodeGenerator(String className, String invokerName, MethodType invokerType) {

        this(null, invokerType.parameterCount(),

             className, invokerName, invokerType);

        // Create an array to map name indexes to locals indexes.

        for (int i = 0; i < localsMap.length; i++) {

            localsMap[i] = invokerType.parameterSlotCount() - invokerType.parameterSlotDepth(i);

        }

    }

    private InvokerBytecodeGenerator(String className, LambdaForm form, MethodType invokerType) {

        this(form, form.names.length,

             className, form.debugName, invokerType);

        // Create an array to map name indexes to locals indexes.

        Name[] names = form.names;

        for (int i = 0, index = 0; i < localsMap.length; i++) {

            localsMap[i] = index;

            index += Wrapper.forBasicType(names[i].type).stackSlots();

        }

    }

    /** instance counters for dumped classes */

    private final static HashMap<String,Integer> DUMP_CLASS_FILES_COUNTERS;

    /** debugging flag for saving generated class files */

    private final static File DUMP_CLASS_FILES_DIR;

    static {

        if (DUMP_CLASS_FILES) {

            DUMP_CLASS_FILES_COUNTERS = new HashMap<>();

            try {

                File dumpDir = new File("DUMP_CLASS_FILES");

                if (!dumpDir.exists()) {

                    dumpDir.mkdirs();

                }

                DUMP_CLASS_FILES_DIR = dumpDir;

                System.out.println("Dumping class files to "+DUMP_CLASS_FILES_DIR+"/...");

            } catch (Exception e) {

                throw newInternalError(e);

            }

        } else {

            DUMP_CLASS_FILES_COUNTERS = null;

            DUMP_CLASS_FILES_DIR = null;

        }

    }

    static void maybeDump(final String className, final byte[] classFile) {

        if (DUMP_CLASS_FILES) {

            System.out.println("dump: " + className);

            java.security.AccessController.doPrivileged(

            new java.security.PrivilegedAction<Void>() {

                public Void run() {

                    try {

                        String dumpName = className;

                        //dumpName = dumpName.replace('/', '-');

                        File dumpFile = new File(DUMP_CLASS_FILES_DIR, dumpName+".class");

                        dumpFile.getParentFile().mkdirs();

                        FileOutputStream file = new FileOutputStream(dumpFile);

                        file.write(classFile);

                        file.close();

                        return null;

                    } catch (IOException ex) {

                        throw newInternalError(ex);

                    }

                }

            });

        }

    }

    private static String makeDumpableClassName(String className) {

        Integer ctr;

        synchronized (DUMP_CLASS_FILES_COUNTERS) {

            ctr = DUMP_CLASS_FILES_COUNTERS.get(className);

            if (ctr == null)  ctr = 0;

            DUMP_CLASS_FILES_COUNTERS.put(className, ctr+1);

        }

        String sfx = ctr.toString();

        while (sfx.length() < 3)

            sfx = "0"+sfx;

        className += sfx;

        return className;

    }

    class CpPatch {

        final int index;

        final String placeholder;

        final Object value;

        CpPatch(int index, String placeholder, Object value) {

            this.index = index;

            this.placeholder = placeholder;

            this.value = value;

        }

        public String toString() {

            return "CpPatch/index="+index+",placeholder="+placeholder+",value="+value;

        }

    }

    Map<Object, CpPatch> cpPatches = new HashMap<>();

    int cph = 0;  // for counting constant placeholders

    String constantPlaceholder(Object arg) {

        String cpPlaceholder = "CONSTANT_PLACEHOLDER_" + cph++;

        if (DUMP_CLASS_FILES) cpPlaceholder += " <<" + arg.toString() + ">>";  // debugging aid

        if (cpPatches.containsKey(cpPlaceholder)) {

            throw new InternalError("observed CP placeholder twice: " + cpPlaceholder);

        }

        // insert placeholder in CP and remember the patch

        int index = cw.newConst((Object) cpPlaceholder);  // TODO check if aready in the constant pool

        cpPatches.put(cpPlaceholder, new CpPatch(index, cpPlaceholder, arg));

        return cpPlaceholder;

    }

    Object[] cpPatches(byte[] classFile) {

        int size = getConstantPoolSize(classFile);

        Object[] res = new Object[size];

        for (CpPatch p : cpPatches.values()) {

            if (p.index >= size)

                throw new InternalError("in cpool["+size+"]: "+p+"\n"+Arrays.toString(Arrays.copyOf(classFile, 20)));

            res[p.index] = p.value;

        }

        return res;

    }

    /**

     * Extract the number of constant pool entries from a given class file.

     *

     * @param classFile the bytes of the class file in question.

     * @return the number of entries in the constant pool.

     */

    private static int getConstantPoolSize(byte[] classFile) {

        // The first few bytes:

        // u4 magic;

        // u2 minor_version;

        // u2 major_version;

        // u2 constant_pool_count;

        return ((classFile[8] & 0xFF) << 8) | (classFile[9] & 0xFF);

    }

    /**

     * Extract the MemberName of a newly-defined method.

     */

    private MemberName loadMethod(byte[] classFile) {

        Class<?> invokerClass = loadAndInitializeInvokerClass(classFile, cpPatches(classFile));

        return resolveInvokerMember(invokerClass, invokerName, invokerType);

    }

    /**

     * Define a given class as anonymous class in the runtime system.

     */

    private static Class<?> loadAndInitializeInvokerClass(byte[] classBytes, Object[] patches) {

        Class<?> invokerClass = UNSAFE.defineAnonymousClass(HOST_CLASS, classBytes, patches);

        UNSAFE.ensureClassInitialized(invokerClass);  // Make sure the class is initialized; VM might complain.

        return invokerClass;

    }

    private static MemberName resolveInvokerMember(Class<?> invokerClass, String name, MethodType type) {

        MemberName member = new MemberName(invokerClass, name, type, REF_invokeStatic);

        //System.out.println("resolveInvokerMember => "+member);

        //for (Method m : invokerClass.getDeclaredMethods())  System.out.println("  "+m);

        try {

            member = MEMBERNAME_FACTORY.resolveOrFail(REF_invokeStatic, member, HOST_CLASS, ReflectiveOperationException.class);

        } catch (ReflectiveOperationException e) {

            throw newInternalError(e);

        }

        //System.out.println("resolveInvokerMember => "+member);

        return member;

    }

    /**

     * Set up class file generation.

     */

    private void classFilePrologue() {

        cw = new ClassWriter(ClassWriter.COMPUTE_MAXS + ClassWriter.COMPUTE_FRAMES);

        cw.visit(Opcodes.V1_8, Opcodes.ACC_PUBLIC + Opcodes.ACC_FINAL + Opcodes.ACC_SUPER, className, null, superName, null);

        cw.visitSource(sourceFile, null);

        String invokerDesc = invokerType.toMethodDescriptorString();

        mv = cw.visitMethod(Opcodes.ACC_STATIC, invokerName, invokerDesc, null, null);

    }

    /**

     * Tear down class file generation.

     */

    private void classFileEpilogue() {

        mv.visitMaxs(0, 0);

        mv.visitEnd();

    }

    /*

     * Low-level emit helpers.

     */

    private void emitConst(Object con) {

        if (con == null) {

            mv.visitInsn(Opcodes.ACONST_NULL);

            return;

        }

        if (con instanceof Integer) {

            emitIconstInsn((int) con);

            return;

        }

        if (con instanceof Long) {

            long x = (long) con;

            if (x == (short) x) {

                emitIconstInsn((int) x);

                mv.visitInsn(Opcodes.I2L);

                return;

            }

        }

        if (con instanceof Float) {

            float x = (float) con;

            if (x == (short) x) {

                emitIconstInsn((int) x);

                mv.visitInsn(Opcodes.I2F);

                return;

            }

        }

        if (con instanceof Double) {

            double x = (double) con;

            if (x == (short) x) {

                emitIconstInsn((int) x);

                mv.visitInsn(Opcodes.I2D);

                return;

            }

        }

        if (con instanceof Boolean) {

            emitIconstInsn((boolean) con ? 1 : 0);

            return;

        }

        // fall through:

        mv.visitLdcInsn(con);

    }

    private void emitIconstInsn(int i) {

        int opcode;

        switch (i) {

        case 0:  opcode = Opcodes.ICONST_0;  break;

        case 1:  opcode = Opcodes.ICONST_1;  break;

        case 2:  opcode = Opcodes.ICONST_2;  break;

        case 3:  opcode = Opcodes.ICONST_3;  break;

        case 4:  opcode = Opcodes.ICONST_4;  break;

        case 5:  opcode = Opcodes.ICONST_5;  break;

        default:

            if (i == (byte) i) {

                mv.visitIntInsn(Opcodes.BIPUSH, i & 0xFF);

            } else if (i == (short) i) {

                mv.visitIntInsn(Opcodes.SIPUSH, (char) i);

            } else {

                mv.visitLdcInsn(i);

            }

            return;

        }

        mv.visitInsn(opcode);

    }

    /*

     * NOTE: These load/store methods use the localsMap to find the correct index!

     */

    private void emitLoadInsn(char type, int index) {

        int opcode;

        switch (type) {

        case 'I':  opcode = Opcodes.ILOAD;  break;

        case 'J':  opcode = Opcodes.LLOAD;  break;

        case 'F':  opcode = Opcodes.FLOAD;  break;

        case 'D':  opcode = Opcodes.DLOAD;  break;

        case 'L':  opcode = Opcodes.ALOAD;  break;

        default:

            throw new InternalError("unknown type: " + type);

        }

        mv.visitVarInsn(opcode, localsMap[index]);

    }

    private void emitAloadInsn(int index) {

        emitLoadInsn('L', index);

    }

    private void emitStoreInsn(char type, int index) {

        int opcode;

        switch (type) {

        case 'I':  opcode = Opcodes.ISTORE;  break;

        case 'J':  opcode = Opcodes.LSTORE;  break;

        case 'F':  opcode = Opcodes.FSTORE;  break;

        case 'D':  opcode = Opcodes.DSTORE;  break;

        case 'L':  opcode = Opcodes.ASTORE;  break;

        default:

            throw new InternalError("unknown type: " + type);

        }

        mv.visitVarInsn(opcode, localsMap[index]);

    }

    private void emitAstoreInsn(int index) {

        emitStoreInsn('L', index);

    }

    /**

     * Emit a boxing call.

     *

     * @param type primitive type class to box.

     */

    private void emitBoxing(Class<?> type) {

        Wrapper wrapper = Wrapper.forPrimitiveType(type);

        String owner = "java/lang/" + wrapper.wrapperType().getSimpleName();

        String name  = "valueOf";

        String desc  = "(" + wrapper.basicTypeChar() + ")L" + owner + ";";

        mv.visitMethodInsn(Opcodes.INVOKESTATIC, owner, name, desc);

    }

    /**

     * Emit an unboxing call (plus preceding checkcast).

     *

     * @param type wrapper type class to unbox.

     */

    private void emitUnboxing(Class<?> type) {

        Wrapper wrapper = Wrapper.forWrapperType(type);

        String owner = "java/lang/" + wrapper.wrapperType().getSimpleName();

        String name  = wrapper.primitiveSimpleName() + "Value";

        String desc  = "()" + wrapper.basicTypeChar();

        mv.visitTypeInsn(Opcodes.CHECKCAST, owner);

        mv.visitMethodInsn(Opcodes.INVOKEVIRTUAL, owner, name, desc);

    }

    /**

     * Emit an implicit conversion.

     *

     * @param ptype type of value present on stack

     * @param pclass type of value required on stack

     */

    private void emitImplicitConversion(char ptype, Class<?> pclass) {

        switch (ptype) {

        case 'L':

            if (VerifyType.isNullConversion(Object.class, pclass))

                return;

            if (isStaticallyNameable(pclass)) {

                mv.visitTypeInsn(Opcodes.CHECKCAST, getInternalName(pclass));

            } else {

                mv.visitLdcInsn(constantPlaceholder(pclass));

                mv.visitTypeInsn(Opcodes.CHECKCAST, CLS);

                mv.visitInsn(Opcodes.SWAP);

                mv.visitMethodInsn(Opcodes.INVOKEVIRTUAL, CLS, "cast", LL_SIG);

                if (pclass.isArray())

                    mv.visitTypeInsn(Opcodes.CHECKCAST, OBJARY);

            }

            return;

        case 'I':

            if (!VerifyType.isNullConversion(int.class, pclass))

                emitPrimCast(ptype, Wrapper.basicTypeChar(pclass));

            return;

        case 'J':

            assert(pclass == long.class);

            return;

        case 'F':

            assert(pclass == float.class);

            return;

        case 'D':

            assert(pclass == double.class);

            return;

        }

        throw new InternalError("bad implicit conversion: tc="+ptype+": "+pclass);

    }

    /**

     * Emits an actual return instruction conforming to the given return type.

     */

    private void emitReturnInsn(Class<?> type) {

        int opcode;

        switch (Wrapper.basicTypeChar(type)) {

        case 'I':  opcode = Opcodes.IRETURN;  break;

        case 'J':  opcode = Opcodes.LRETURN;  break;

        case 'F':  opcode = Opcodes.FRETURN;  break;

        case 'D':  opcode = Opcodes.DRETURN;  break;

        case 'L':  opcode = Opcodes.ARETURN;  break;

        case 'V':  opcode = Opcodes.RETURN;   break;

        default:

            throw new InternalError("unknown return type: " + type);

        }

        mv.visitInsn(opcode);

    }

    private static String getInternalName(Class<?> c) {

        assert(VerifyAccess.isTypeVisible(c, Object.class));

        return c.getName().replace('.', '/');

    }

    /**

     * Generate customized bytecode for a given LambdaForm.

     */

    static MemberName generateCustomizedCode(LambdaForm form, MethodType invokerType) {

        InvokerBytecodeGenerator g = new InvokerBytecodeGenerator("MH", form, invokerType);

        return g.loadMethod(g.generateCustomizedCodeBytes());

    }

    /**

     * Generate an invoker method for the passed {@link LambdaForm}.

     */

    private byte[] generateCustomizedCodeBytes() {

        classFilePrologue();

        // Suppress this method in backtraces displayed to the user.

        mv.visitAnnotation("Ljava/lang/invoke/LambdaForm$Hidden;", true);

        // Mark this method as a compiled LambdaForm

        mv.visitAnnotation("Ljava/lang/invoke/LambdaForm$Compiled;", true);

        // Force inlining of this invoker method.

        mv.visitAnnotation("Ljava/lang/invoke/ForceInline;", true);

        // iterate over the form's names, generating bytecode instructions for each

        // start iterating at the first name following the arguments

        for (int i = lambdaForm.arity; i < lambdaForm.names.length; i++) {

            Name name = lambdaForm.names[i];

            MemberName member = name.function.member();

            if (isSelectAlternative(member)) {

                // selectAlternative idiom

                // FIXME: make sure this idiom is really present!

                emitSelectAlternative(name, lambdaForm.names[i + 1]);

                i++;  // skip MH.invokeBasic of the selectAlternative result

            } else if (isStaticallyInvocable(member)) {

                emitStaticInvoke(member, name);

            } else {

                emitInvoke(name);

            }

            // store the result from evaluating to the target name in a local if required

            // (if this is the last value, i.e., the one that is going to be returned,

            // avoid store/load/return and just return)

            if (i == lambdaForm.names.length - 1 && i == lambdaForm.result) {

                // return value - do nothing

            } else if (name.type != 'V') {

                // non-void: actually assign

                emitStoreInsn(name.type, name.index());

            }

        }

        // return statement

        emitReturn();

        classFileEpilogue();

        bogusMethod(lambdaForm);

        final byte[] classFile = cw.toByteArray();

        maybeDump(className, classFile);

        return classFile;

    }

    /**

     * Emit an invoke for the given name.

     */

    void emitInvoke(Name name) {

        if (true) {

            // push receiver

            MethodHandle target = name.function.resolvedHandle;

            assert(target != null) : name.exprString();

            mv.visitLdcInsn(constantPlaceholder(target));

            mv.visitTypeInsn(Opcodes.CHECKCAST, MH);

        } else {

            // load receiver

            emitAloadInsn(0);

            mv.visitTypeInsn(Opcodes.CHECKCAST, MH);

            mv.visitFieldInsn(Opcodes.GETFIELD, MH, "form", LF_SIG);

            mv.visitFieldInsn(Opcodes.GETFIELD, LF, "names", LFN_SIG);

            // TODO more to come

        }

        // push arguments

        for (int i = 0; i < name.arguments.length; i++) {

            emitPushArgument(name, i);

        }

        // invocation

        MethodType type = name.function.methodType();

        mv.visitMethodInsn(Opcodes.INVOKEVIRTUAL, MH, "invokeBasic", type.basicType().toMethodDescriptorString());

    }

    static private Class<?>[] STATICALLY_INVOCABLE_PACKAGES = {

        // Sample classes from each package we are willing to bind to statically:

        java.lang.Object.class,

        java.util.Arrays.class,

        sun.misc.Unsafe.class

        //MethodHandle.class already covered

    };

    static boolean isStaticallyInvocable(MemberName member) {

        if (member == null)  return false;

        if (member.isConstructor())  return false;

        Class<?> cls = member.getDeclaringClass();

        if (cls.isArray() || cls.isPrimitive())

            return false;  // FIXME

        if (cls.isAnonymousClass() || cls.isLocalClass())

            return false;  // inner class of some sort

        if (cls.getClassLoader() != MethodHandle.class.getClassLoader())

            return false;  // not on BCP

        MethodType mtype = member.getMethodOrFieldType();

        if (!isStaticallyNameable(mtype.returnType()))

            return false;

        for (Class<?> ptype : mtype.parameterArray())

            if (!isStaticallyNameable(ptype))

                return false;

        if (!member.isPrivate() && VerifyAccess.isSamePackage(MethodHandle.class, cls))

            return true;   // in java.lang.invoke package

        if (member.isPublic() && isStaticallyNameable(cls))

            return true;

        return false;

    }

    static boolean isStaticallyNameable(Class<?> cls) {

        while (cls.isArray())

            cls = cls.getComponentType();

        if (cls.isPrimitive())

            return true;  // int[].class, for example

        // could use VerifyAccess.isClassAccessible but the following is a safe approximation

        if (cls.getClassLoader() != Object.class.getClassLoader())

            return false;

        if (VerifyAccess.isSamePackage(MethodHandle.class, cls))

            return true;

        if (!Modifier.isPublic(cls.getModifiers()))

            return false;

        for (Class<?> pkgcls : STATICALLY_INVOCABLE_PACKAGES) {

            if (VerifyAccess.isSamePackage(pkgcls, cls))

                return true;

        }

        return false;

    }

    /**

     * Emit an invoke for the given name, using the MemberName directly.

     */

    void emitStaticInvoke(MemberName member, Name name) {

        assert(member.equals(name.function.member()));

        String cname = getInternalName(member.getDeclaringClass());

        String mname = member.getName();

        String mtype;

        byte refKind = member.getReferenceKind();

        if (refKind == REF_invokeSpecial) {

            // in order to pass the verifier, we need to convert this to invokevirtual in all cases

            assert(member.canBeStaticallyBound()) : member;

            refKind = REF_invokeVirtual;

        }

        if (member.getDeclaringClass().isInterface() && refKind == REF_invokeVirtual) {

            // Methods from Object declared in an interface can be resolved by JVM to invokevirtual kind.

            // Need to convert it back to invokeinterface to pass verification and make the invocation works as expected.

            refKind = REF_invokeInterface;

        }

        // push arguments

        for (int i = 0; i < name.arguments.length; i++) {

            emitPushArgument(name, i);

        }

        // invocation

        if (member.isMethod()) {

            mtype = member.getMethodType().toMethodDescriptorString();

            mv.visitMethodInsn(refKindOpcode(refKind), cname, mname, mtype,

                               member.getDeclaringClass().isInterface());

        } else {

            mtype = MethodType.toFieldDescriptorString(member.getFieldType());

            mv.visitFieldInsn(refKindOpcode(refKind), cname, mname, mtype);

        }

    }

    int refKindOpcode(byte refKind) {

        switch (refKind) {

        case REF_invokeVirtual:      return Opcodes.INVOKEVIRTUAL;

        case REF_invokeStatic:       return Opcodes.INVOKESTATIC;

        case REF_invokeSpecial:      return Opcodes.INVOKESPECIAL;

        case REF_invokeInterface:    return Opcodes.INVOKEINTERFACE;

        case REF_getField:           return Opcodes.GETFIELD;

        case REF_putField:           return Opcodes.PUTFIELD;

        case REF_getStatic:          return Opcodes.GETSTATIC;

        case REF_putStatic:          return Opcodes.PUTSTATIC;

        }

        throw new InternalError("refKind="+refKind);

    }

    /**

     * Check if MemberName is a call to MethodHandleImpl.selectAlternative.

     */

    private boolean isSelectAlternative(MemberName member) {

        return member != null &&

               member.getDeclaringClass() == MethodHandleImpl.class &&

               member.getName().equals("selectAlternative");

    }

    /**

     * Emit bytecode for the selectAlternative idiom.

     *

     * The pattern looks like (Cf. MethodHandleImpl.makeGuardWithTest):

     * <blockquote><pre>{@code

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

     *     t2:I=foo.test(a1:I);

     *     t3:L=MethodHandleImpl.selectAlternative(t2:I,(MethodHandle(int)int),(MethodHandle(int)int));

     *     t4:I=MethodHandle.invokeBasic(t3:L,a1:I);t4:I}

     * }</pre></blockquote>

     */

    private void emitSelectAlternative(Name selectAlternativeName, Name invokeBasicName) {

        MethodType type = selectAlternativeName.function.methodType();

        Name receiver = (Name) invokeBasicName.arguments[0];

        Label L_fallback = new Label();

        Label L_done     = new Label();

        // load test result

        emitPushArgument(selectAlternativeName, 0);

        mv.visitInsn(Opcodes.ICONST_1);

        // if_icmpne L_fallback

        mv.visitJumpInsn(Opcodes.IF_ICMPNE, L_fallback);

        // invoke selectAlternativeName.arguments[1]

        MethodHandle target = (MethodHandle) selectAlternativeName.arguments[1];

        emitPushArgument(selectAlternativeName, 1);  // get 2nd argument of selectAlternative

        emitAstoreInsn(receiver.index());  // store the MH in the receiver slot

        emitInvoke(invokeBasicName);

        // goto L_done

        mv.visitJumpInsn(Opcodes.GOTO, L_done);

        // L_fallback:

        mv.visitLabel(L_fallback);

        // invoke selectAlternativeName.arguments[2]

        MethodHandle fallback = (MethodHandle) selectAlternativeName.arguments[2];

        emitPushArgument(selectAlternativeName, 2);  // get 3rd argument of selectAlternative

        emitAstoreInsn(receiver.index());  // store the MH in the receiver slot

        emitInvoke(invokeBasicName);

        // L_done:

        mv.visitLabel(L_done);

    }

    private void emitPushArgument(Name name, int paramIndex) {

        Object arg = name.arguments[paramIndex];

        char ptype = name.function.parameterType(paramIndex);

        MethodType mtype = name.function.methodType();

        if (arg instanceof Name) {

            Name n = (Name) arg;

            emitLoadInsn(n.type, n.index());

            emitImplicitConversion(n.type, mtype.parameterType(paramIndex));

        } else if ((arg == null || arg instanceof String) && ptype == 'L') {

            emitConst(arg);

        } else {

            if (Wrapper.isWrapperType(arg.getClass()) && ptype != 'L') {

                emitConst(arg);

            } else {

                mv.visitLdcInsn(constantPlaceholder(arg));

                emitImplicitConversion('L', mtype.parameterType(paramIndex));

            }

        }

    }

    /**

     * Emits a return statement from a LF invoker. If required, the result type is cast to the correct return type.

     */

    private void emitReturn() {

        // return statement

        if (lambdaForm.result == -1) {

            // void

            mv.visitInsn(Opcodes.RETURN);

        } else {

            LambdaForm.Name rn = lambdaForm.names[lambdaForm.result];

            char rtype = Wrapper.basicTypeChar(invokerType.returnType());

            // put return value on the stack if it is not already there

            if (lambdaForm.result != lambdaForm.names.length - 1) {

                emitLoadInsn(rn.type, lambdaForm.result);

            }

            // potentially generate cast

            // rtype is the return type of the invoker - generated code must conform to this

            // rn.type is the type of the result Name in the LF

            if (rtype != rn.type) {

                // need cast

                if (rtype == 'L') {

                    // possibly cast the primitive to the correct type for boxing

                    char boxedType = Wrapper.forWrapperType(invokerType.returnType()).basicTypeChar();

                    if (boxedType != rn.type) {

                        emitPrimCast(rn.type, boxedType);

                    }

                    // cast primitive to reference ("boxing")

                    emitBoxing(invokerType.returnType());

                } else {

                    // to-primitive cast

                    if (rn.type != 'L') {

                        // prim-to-prim cast

                        emitPrimCast(rn.type, rtype);

                    } else {

                        // ref-to-prim cast ("unboxing")

                        throw new InternalError("no ref-to-prim (unboxing) casts supported right now");

                    }

                }

            }

            // generate actual return statement

            emitReturnInsn(invokerType.returnType());

        }

    }

    /**

     * Emit a type conversion bytecode casting from "from" to "to".

     */

    private void emitPrimCast(char from, char to) {

        // Here's how.

        // -   indicates forbidden

        // <-> indicates implicit

        //      to ----> boolean  byte     short    char     int      long     float    double

        // from boolean    <->        -        -        -        -        -        -        -

        //      byte        -       <->       i2s      i2c      <->      i2l      i2f      i2d

        //      short       -       i2b       <->      i2c      <->      i2l      i2f      i2d

        //      char        -       i2b       i2s      <->      <->      i2l      i2f      i2d

        //      int         -       i2b       i2s      i2c      <->      i2l      i2f      i2d

        //      long        -     l2i,i2b   l2i,i2s  l2i,i2c    l2i      <->      l2f      l2d

        //      float       -     f2i,i2b   f2i,i2s  f2i,i2c    f2i      f2l      <->      f2d

        //      double      -     d2i,i2b   d2i,i2s  d2i,i2c    d2i      d2l      d2f      <->

        if (from == to) {

            // no cast required, should be dead code anyway

            return;

        }

        Wrapper wfrom = Wrapper.forBasicType(from);

        Wrapper wto   = Wrapper.forBasicType(to);

        if (wfrom.isSubwordOrInt()) {

            // cast from {byte,short,char,int} to anything

            emitI2X(to);

        } else {

            // cast from {long,float,double} to anything

            if (wto.isSubwordOrInt()) {

                // cast to {byte,short,char,int}

                emitX2I(from);

                if (wto.bitWidth() < 32) {

                    // targets other than int require another conversion

                    emitI2X(to);

                }

            } else {

                // cast to {long,float,double} - this is verbose

                boolean error = false;

                switch (from) {

                case 'J':

                         if (to == 'F') { mv.visitInsn(Opcodes.L2F); }

                    else if (to == 'D') { mv.visitInsn(Opcodes.L2D); }

                    else error = true;

                    break;

                case 'F':

                         if (to == 'J') { mv.visitInsn(Opcodes.F2L); }

                    else if (to == 'D') { mv.visitInsn(Opcodes.F2D); }

                    else error = true;

                    break;

                case 'D':

                         if (to == 'J') { mv.visitInsn(Opcodes.D2L); }

                    else if (to == 'F') { mv.visitInsn(Opcodes.D2F); }

                    else error = true;

                    break;

                default:

                    error = true;

                    break;

                }

                if (error) {

                    throw new IllegalStateException("unhandled prim cast: " + from + "2" + to);

                }

            }

        }

    }

    private void emitI2X(char type) {

        switch (type) {

        case 'B':  mv.visitInsn(Opcodes.I2B);  break;

        case 'S':  mv.visitInsn(Opcodes.I2S);  break;

        case 'C':  mv.visitInsn(Opcodes.I2C);  break;

        case 'I':  /* naught */                break;

        case 'J':  mv.visitInsn(Opcodes.I2L);  break;

        case 'F':  mv.visitInsn(Opcodes.I2F);  break;

        case 'D':  mv.visitInsn(Opcodes.I2D);  break;

        case 'Z':

            // For compatibility with ValueConversions and explicitCastArguments:

            mv.visitInsn(Opcodes.ICONST_1);

            mv.visitInsn(Opcodes.IAND);

            break;

        default:   throw new InternalError("unknown type: " + type);

        }

    }

    private void emitX2I(char type) {

        switch (type) {

        case 'J':  mv.visitInsn(Opcodes.L2I);  break;

        case 'F':  mv.visitInsn(Opcodes.F2I);  break;

        case 'D':  mv.visitInsn(Opcodes.D2I);  break;

        default:   throw new InternalError("unknown type: " + type);

        }

    }

    private static String basicTypeCharSignature(String prefix, MethodType type) {

        StringBuilder buf = new StringBuilder(prefix);

        for (Class<?> ptype : type.parameterList())

            buf.append(Wrapper.forBasicType(ptype).basicTypeChar());

        buf.append('_').append(Wrapper.forBasicType(type.returnType()).basicTypeChar());

        return buf.toString();

    }

    /**

     * Generate bytecode for a LambdaForm.vmentry which calls interpretWithArguments.

     */

    static MemberName generateLambdaFormInterpreterEntryPoint(String sig) {

        assert(LambdaForm.isValidSignature(sig));

        //System.out.println("generateExactInvoker "+sig);

        // compute method type

        // first parameter and return type

        char tret = LambdaForm.signatureReturn(sig);

        MethodType type = MethodType.methodType(LambdaForm.typeClass(tret), MethodHandle.class);

        // other parameter types

        int arity = LambdaForm.signatureArity(sig);

        for (int i = 1; i < arity; i++) {

            type = type.appendParameterTypes(LambdaForm.typeClass(sig.charAt(i)));

        }

        InvokerBytecodeGenerator g = new InvokerBytecodeGenerator("LFI", "interpret_"+tret, type);

        return g.loadMethod(g.generateLambdaFormInterpreterEntryPointBytes());

    }

    private byte[] generateLambdaFormInterpreterEntryPointBytes() {

        classFilePrologue();

        // Suppress this method in backtraces displayed to the user.

        mv.visitAnnotation("Ljava/lang/invoke/LambdaForm$Hidden;", true);

        // Don't inline the interpreter entry.

        mv.visitAnnotation("Ljava/lang/invoke/DontInline;", true);

        // create parameter array

        emitIconstInsn(invokerType.parameterCount());

        mv.visitTypeInsn(Opcodes.ANEWARRAY, "java/lang/Object");

        // fill parameter array

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

            Class<?> ptype = invokerType.parameterType(i);

            mv.visitInsn(Opcodes.DUP);

            emitIconstInsn(i);

            emitLoadInsn(Wrapper.basicTypeChar(ptype), i);

            // box if primitive type

            if (ptype.isPrimitive()) {

                emitBoxing(ptype);

            }

            mv.visitInsn(Opcodes.AASTORE);

        }

        // invoke

        emitAloadInsn(0);

        mv.visitFieldInsn(Opcodes.GETFIELD, MH, "form", "Ljava/lang/invoke/LambdaForm;");

        mv.visitInsn(Opcodes.SWAP);  // swap form and array; avoid local variable

        mv.visitMethodInsn(Opcodes.INVOKEVIRTUAL, LF, "interpretWithArguments", "([Ljava/lang/Object;)Ljava/lang/Object;");

        // maybe unbox

        Class<?> rtype = invokerType.returnType();

        if (rtype.isPrimitive() && rtype != void.class) {

            emitUnboxing(Wrapper.asWrapperType(rtype));

        }

        // return statement

        emitReturnInsn(rtype);

        classFileEpilogue();

        bogusMethod(invokerType);

        final byte[] classFile = cw.toByteArray();

        maybeDump(className, classFile);

        return classFile;

    }

    /**

     * Generate bytecode for a NamedFunction invoker.

     */

    static MemberName generateNamedFunctionInvoker(MethodTypeForm typeForm) {

        MethodType invokerType = LambdaForm.NamedFunction.INVOKER_METHOD_TYPE;

        String invokerName = basicTypeCharSignature("invoke_", typeForm.erasedType());

        InvokerBytecodeGenerator g = new InvokerBytecodeGenerator("NFI", invokerName, invokerType);

        return g.loadMethod(g.generateNamedFunctionInvokerImpl(typeForm));

    }

    static int nfi = 0;

    private byte[] generateNamedFunctionInvokerImpl(MethodTypeForm typeForm) {

        MethodType dstType = typeForm.erasedType();

        classFilePrologue();

        // Suppress this method in backtraces displayed to the user.

        mv.visitAnnotation("Ljava/lang/invoke/LambdaForm$Hidden;", true);

        // Force inlining of this invoker method.

        mv.visitAnnotation("Ljava/lang/invoke/ForceInline;", true);

        // Load receiver

        emitAloadInsn(0);

        // Load arguments from array

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

            emitAloadInsn(1);

            emitIconstInsn(i);