/*

  * 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);

             mv.visitInsn(Opcodes.AALOAD);

             // Maybe unbox

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

             if (dptype.isPrimitive()) {

                 Class<?> sptype = dstType.basicType().wrap().parameterType(i);

                 Wrapper dstWrapper = Wrapper.forBasicType(dptype);

                 Wrapper srcWrapper = dstWrapper.isSubwordOrInt() ? Wrapper.INT : dstWrapper;  // narrow subword from int

                 emitUnboxing(srcWrapper.wrapperType());

                 emitPrimCast(srcWrapper.basicTypeChar(), dstWrapper.basicTypeChar());

             }

         }

         // Invoke

         String targetDesc = dstType.basicType().toMethodDescriptorString();

         mv.visitMethodInsn(Opcodes.INVOKEVIRTUAL, MH, "invokeBasic", targetDesc);

         // Box primitive types

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

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

             Wrapper srcWrapper = Wrapper.forBasicType(rtype);

             Wrapper dstWrapper = srcWrapper.isSubwordOrInt() ? Wrapper.INT : srcWrapper;  // widen subword to int

             // boolean casts not allowed

             emitPrimCast(srcWrapper.basicTypeChar(), dstWrapper.basicTypeChar());

             emitBoxing(dstWrapper.primitiveType());

         }

         // If the return type is void we return a null reference.

         if (rtype == void.class) {

             mv.visitInsn(Opcodes.ACONST_NULL);

         }

         emitReturnInsn(Object.class);  // NOTE: NamedFunction invokers always return a reference value.

         classFileEpilogue();

         bogusMethod(dstType);

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

         maybeDump(className, classFile);

         return classFile;

     }

     /**

      * Emit a bogus method that just loads some string constants. This is to get the constants into the constant pool

      * for debugging purposes.

      */

     private void bogusMethod(Object... os) {

         if (DUMP_CLASS_FILES) {

             mv = cw.visitMethod(Opcodes.ACC_STATIC, "dummy", "()V", null, null);

             for (Object o : os) {

                 mv.visitLdcInsn(o.toString());

                 mv.visitInsn(Opcodes.POP);

             }

             mv.visitInsn(Opcodes.RETURN);

             mv.visitMaxs(0, 0);

             mv.visitEnd();

         }

     }

 }