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 * Copyright (c) 2010, 2016, 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
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package jdk.nashorn.internal.codegen.types;

import static jdk.internal.org.objectweb.asm.Opcodes.DALOAD;
import static jdk.internal.org.objectweb.asm.Opcodes.DASTORE;
import static jdk.internal.org.objectweb.asm.Opcodes.DUP;
import static jdk.internal.org.objectweb.asm.Opcodes.DUP2;
import static jdk.internal.org.objectweb.asm.Opcodes.DUP2_X1;
import static jdk.internal.org.objectweb.asm.Opcodes.DUP2_X2;
import static jdk.internal.org.objectweb.asm.Opcodes.DUP_X1;
import static jdk.internal.org.objectweb.asm.Opcodes.DUP_X2;
import static jdk.internal.org.objectweb.asm.Opcodes.IALOAD;
import static jdk.internal.org.objectweb.asm.Opcodes.IASTORE;
import static jdk.internal.org.objectweb.asm.Opcodes.INVOKESTATIC;
import static jdk.internal.org.objectweb.asm.Opcodes.LALOAD;
import static jdk.internal.org.objectweb.asm.Opcodes.LASTORE;
import static jdk.internal.org.objectweb.asm.Opcodes.NEWARRAY;
import static jdk.internal.org.objectweb.asm.Opcodes.POP;
import static jdk.internal.org.objectweb.asm.Opcodes.POP2;
import static jdk.internal.org.objectweb.asm.Opcodes.SWAP;
import static jdk.internal.org.objectweb.asm.Opcodes.T_DOUBLE;
import static jdk.internal.org.objectweb.asm.Opcodes.T_INT;
import static jdk.internal.org.objectweb.asm.Opcodes.T_LONG;

import java.io.DataInput;
import java.io.DataOutput;
import java.io.IOException;
import java.io.Serializable;
import java.util.Collections;
import java.util.Map;
import java.util.TreeMap;
import java.util.WeakHashMap;
import java.util.concurrent.ConcurrentHashMap;
import java.util.concurrent.ConcurrentMap;
import jdk.internal.org.objectweb.asm.MethodVisitor;
import jdk.nashorn.internal.codegen.CompilerConstants.Call;
import jdk.nashorn.internal.runtime.Context;
import jdk.nashorn.internal.runtime.ScriptObject;
import jdk.nashorn.internal.runtime.Undefined;

This is the representation of a JavaScript type, disassociated from java
Classes, with the basis for conversion weight, mapping to ASM types
and implementing the ByteCodeOps interface which tells this type
how to generate code for various operations.
Except for ClassEmitter, this is the only class that has to know
about the underlying byte code generation system.
The different types know how to generate bytecode for the different
operations, inherited from BytecodeOps, that they support. This avoids
if/else chains depending on type in several cases and allows for
more readable and shorter code
The Type class also contains logic used by the type inference and
for comparing types against each other, as well as the concepts
of narrower to wider types. The widest type is an object. Ideally we
would like as narrow types as possible for code to be efficient, e.g
INTs rather than OBJECTs
/**
 * This is the representation of a JavaScript type, disassociated from java
 * Classes, with the basis for conversion weight, mapping to ASM types
 * and implementing the ByteCodeOps interface which tells this type
 * how to generate code for various operations.
 *
 * Except for ClassEmitter, this is the only class that has to know
 * about the underlying byte code generation system.
 *
 * The different types know how to generate bytecode for the different
 * operations, inherited from BytecodeOps, that they support. This avoids
 * if/else chains depending on type in several cases and allows for
 * more readable and shorter code
 *
 * The Type class also contains logic used by the type inference and
 * for comparing types against each other, as well as the concepts
 * of narrower to wider types. The widest type is an object. Ideally we
 * would like as narrow types as possible for code to be efficient, e.g
 * INTs rather than OBJECTs
 */

public abstract class Type implements Comparable<Type>, BytecodeOps, Serializable {
    private static final long serialVersionUID = 1L;

    
Human readable name for type /** Human readable name for type */
    private transient final String name;

    
Descriptor for type /** Descriptor for type */
    private transient final String descriptor;

    
The "weight" of the type. Used for picking widest/least specific common type /** The "weight" of the type. Used for picking widest/least specific common type */
    private transient final int weight;

    
How many bytecode slots does this type occupy /** How many bytecode slots does this type occupy */
    private transient final int slots;

    
The class for this type /** The class for this type */
    private final Class<?> clazz;

    
Cache for internal types - this is a query that requires complex stringbuilding inside
ASM and it saves startup time to cache the type mappings
/**
     * Cache for internal types - this is a query that requires complex stringbuilding inside
     * ASM and it saves startup time to cache the type mappings
     */
    private static final Map<Class<?>, jdk.internal.org.objectweb.asm.Type> INTERNAL_TYPE_CACHE =
            Collections.synchronizedMap(new WeakHashMap<Class<?>, jdk.internal.org.objectweb.asm.Type>());

    
Internal ASM type for this Type - computed once at construction /** Internal ASM type for this Type - computed once at construction */
    private transient final jdk.internal.org.objectweb.asm.Type internalType;

    
Weights are used to decide which types are "wider" than other types /** Weights are used to decide which types are "wider" than other types */
    protected static final int MIN_WEIGHT = -1;

    
Set way below Integer.MAX_VALUE to prevent overflow when adding weights. Objects are still heaviest. /** Set way below Integer.MAX_VALUE to prevent overflow when adding weights. Objects are still heaviest. */
    protected static final int MAX_WEIGHT = 20;

    
Constructor
Params:
clazz –       class for type
weight –      weight - higher is more generic
slots –       how many bytecode slots the type takes up/**
     * Constructor
     *
     * @param clazz       class for type
     * @param weight      weight - higher is more generic
     * @param slots       how many bytecode slots the type takes up
     */
    Type(final String name, final Class<?> clazz, final int weight, final int slots) {
        this.name         = name;
        this.clazz        = clazz;
        this.descriptor   = jdk.internal.org.objectweb.asm.Type.getDescriptor(clazz);
        this.weight       = weight;
        assert weight >= MIN_WEIGHT && weight <= MAX_WEIGHT : "illegal type weight: " + weight;
        this.slots        = slots;
        this.internalType = getInternalType(clazz);
    }

    
Get the weight of this type - use this e.g. for sorting method descriptors
Returns:
the weight/**
     * Get the weight of this type - use this e.g. for sorting method descriptors
     * @return the weight
     */
    public int getWeight() {
        return weight;
    }

    
Get the Class representing this type
Returns:
the class for this type/**
     * Get the Class representing this type
     * @return the class for this type
     */
    public Class<?> getTypeClass() {
        return clazz;
    }

    
For specialization, return the next, slightly more difficulty, type
to test.
Returns:
the next Type/**
     * For specialization, return the next, slightly more difficulty, type
     * to test.
     *
     * @return the next Type
     */
    public Type nextWider() {
        return null;
    }

    
Get the boxed type for this class
Returns:
the boxed version of this type or null if N/A/**
     * Get the boxed type for this class
     * @return the boxed version of this type or null if N/A
     */
    public Class<?> getBoxedType() {
        assert !getTypeClass().isPrimitive();
        return null;
    }

    
Returns the character describing the bytecode type for this value on the stack or local variable, identical to what would be used as the prefix for a bytecode LOAD or STORE instruction, therefore it must be one of A, F, D, I, L. Also, the special value U is used for local variable slots that haven't been initialized yet (it can't appear for a value pushed to the operand stack, those always have known values). Note that while we allow all JVM internal types, Nashorn doesn't necessarily use them all - currently we don't have floats, only doubles, but that might change in the future. 
Returns:
the character describing the bytecode type for this value on the stack./**
     * Returns the character describing the bytecode type for this value on the stack or local variable, identical to
     * what would be used as the prefix for a bytecode {@code LOAD} or {@code STORE} instruction, therefore it must be
     * one of {@code A, F, D, I, L}. Also, the special value {@code U} is used for local variable slots that haven't
     * been initialized yet (it can't appear for a value pushed to the operand stack, those always have known values).
     * Note that while we allow all JVM internal types, Nashorn doesn't necessarily use them all - currently we don't
     * have floats, only doubles, but that might change in the future.
     * @return the character describing the bytecode type for this value on the stack.
     */
    public abstract char getBytecodeStackType();

    
Generate a method descriptor given a return type and a param array
Params:
returnType – return type
types –      parameters
Returns:
a descriptor string/**
     * Generate a method descriptor given a return type and a param array
     *
     * @param returnType return type
     * @param types      parameters
     *
     * @return a descriptor string
     */
    public static String getMethodDescriptor(final Type returnType, final Type... types) {
        final jdk.internal.org.objectweb.asm.Type[] itypes = new jdk.internal.org.objectweb.asm.Type[types.length];
        for (int i = 0; i < types.length; i++) {
            itypes[i] = types[i].getInternalType();
        }
        return jdk.internal.org.objectweb.asm.Type.getMethodDescriptor(returnType.getInternalType(), itypes);
    }

    
Generate a method descriptor given a return type and a param array
Params:
returnType – return type
types –      parameters
Returns:
a descriptor string/**
     * Generate a method descriptor given a return type and a param array
     *
     * @param returnType return type
     * @param types      parameters
     *
     * @return a descriptor string
     */
    public static String getMethodDescriptor(final Class<?> returnType, final Class<?>... types) {
        final jdk.internal.org.objectweb.asm.Type[] itypes = new jdk.internal.org.objectweb.asm.Type[types.length];
        for (int i = 0; i < types.length; i++) {
            itypes[i] = getInternalType(types[i]);
        }
        return jdk.internal.org.objectweb.asm.Type.getMethodDescriptor(getInternalType(returnType), itypes);
    }

    
Return a character representing type in a method signature. 
Params:
type – parameter type
Returns:
descriptor character/**
     * Return a character representing {@code type} in a method signature.
     *
     * @param type parameter type
     * @return descriptor character
     */
    public static char getShortSignatureDescriptor(final Type type) {
        // Use 'Z' for boolean parameters as we need to distinguish from int
        if (type instanceof BooleanType) {
            return 'Z';
        }
        return type.getBytecodeStackType();
    }

    
Return the type for an internal type, package private - do not use
outside code gen
Params:
itype – internal type
Returns:
Nashorn type/**
     * Return the type for an internal type, package private - do not use
     * outside code gen
     *
     * @param itype internal type
     * @return Nashorn type
     */
    @SuppressWarnings("fallthrough")
    private static Type typeFor(final jdk.internal.org.objectweb.asm.Type itype) {
        switch (itype.getSort()) {
        case jdk.internal.org.objectweb.asm.Type.BOOLEAN:
            return BOOLEAN;
        case jdk.internal.org.objectweb.asm.Type.INT:
            return INT;
        case jdk.internal.org.objectweb.asm.Type.LONG:
            return LONG;
        case jdk.internal.org.objectweb.asm.Type.DOUBLE:
            return NUMBER;
        case jdk.internal.org.objectweb.asm.Type.OBJECT:
            if (Context.isStructureClass(itype.getClassName())) {
                return SCRIPT_OBJECT;
            }
            return cacheByName.computeIfAbsent(itype.getClassName(), (name) -> {
                try {
                    return Type.typeFor(Class.forName(name));
                } catch(final ClassNotFoundException e) {
                    throw new AssertionError(e);
                }
            });
        case jdk.internal.org.objectweb.asm.Type.VOID:
            return null;
        case jdk.internal.org.objectweb.asm.Type.ARRAY:
            switch (itype.getElementType().getSort()) {
            case jdk.internal.org.objectweb.asm.Type.DOUBLE:
                return NUMBER_ARRAY;
            case jdk.internal.org.objectweb.asm.Type.INT:
                return INT_ARRAY;
            case jdk.internal.org.objectweb.asm.Type.LONG:
                return LONG_ARRAY;
            default:
                assert false;
            case jdk.internal.org.objectweb.asm.Type.OBJECT:
                return OBJECT_ARRAY;
            }

        default:
            assert false : "Unknown itype : " + itype + " sort " + itype.getSort();
            break;
        }
        return null;
    }

    
Get the return type for a method
Params:
methodDescriptor – method descriptor
Returns:
return type/**
     * Get the return type for a method
     *
     * @param methodDescriptor method descriptor
     * @return return type
     */
    public static Type getMethodReturnType(final String methodDescriptor) {
        return Type.typeFor(jdk.internal.org.objectweb.asm.Type.getReturnType(methodDescriptor));
    }

    
Get type array representing arguments of a method in order
Params:
methodDescriptor – method descriptor
Returns:
parameter type array/**
     * Get type array representing arguments of a method in order
     *
     * @param methodDescriptor method descriptor
     * @return parameter type array
     */
    public static Type[] getMethodArguments(final String methodDescriptor) {
        final jdk.internal.org.objectweb.asm.Type itypes[] = jdk.internal.org.objectweb.asm.Type.getArgumentTypes(methodDescriptor);
        final Type types[] = new Type[itypes.length];
        for (int i = 0; i < itypes.length; i++) {
            types[i] = Type.typeFor(itypes[i]);
        }
        return types;
    }

    
Write a map of int to Type to an output stream. This is used to store deoptimization state. 
Params:
typeMap – the type map
output – data output
Throws:
IOException – if write cannot be completed/**
     * Write a map of {@code int} to {@code Type} to an output stream. This is used to store deoptimization state.
     *
     * @param typeMap the type map
     * @param output data output
     * @throws IOException if write cannot be completed
     */
    public static void writeTypeMap(final Map<Integer, Type> typeMap, final DataOutput output) throws IOException {
        if (typeMap == null) {
            output.writeInt(0);
        } else {
            output.writeInt(typeMap.size());
            for(final Map.Entry<Integer, Type> e: typeMap.entrySet()) {
                output.writeInt(e.getKey());
                final byte typeChar;
                final Type type = e.getValue();
                if(type == Type.OBJECT) {
                    typeChar = 'L';
                } else if (type == Type.NUMBER) {
                    typeChar = 'D';
                } else if (type == Type.LONG) {
                    typeChar = 'J';
                } else {
                    throw new AssertionError();
                }
                output.writeByte(typeChar);
            }
        }
    }

    
Read a map of int to Type from an input stream. This is used to store deoptimization state. 
Params:
input – data input
Throws:
IOException – if read cannot be completed
Returns:
type map/**
     * Read a map of {@code int} to {@code Type} from an input stream. This is used to store deoptimization state.
     *
     * @param input data input
     * @return type map
     * @throws IOException if read cannot be completed
     */
    public static Map<Integer, Type> readTypeMap(final DataInput input) throws IOException {
        final int size = input.readInt();
        if (size <= 0) {
            return null;
        }
        final Map<Integer, Type> map = new TreeMap<>();
        for(int i = 0; i < size; ++i) {
            final int pp = input.readInt();
            final int typeChar = input.readByte();
            final Type type;
            switch (typeChar) {
                case 'L': type = Type.OBJECT; break;
                case 'D': type = Type.NUMBER; break;
                case 'J': type = Type.LONG; break;
                default: continue;
            }
            map.put(pp, type);
        }
        return map;
    }

    static jdk.internal.org.objectweb.asm.Type getInternalType(final String className) {
        return jdk.internal.org.objectweb.asm.Type.getType(className);
    }

    private jdk.internal.org.objectweb.asm.Type getInternalType() {
        return internalType;
    }

    private static jdk.internal.org.objectweb.asm.Type lookupInternalType(final Class<?> type) {
        final Map<Class<?>, jdk.internal.org.objectweb.asm.Type> c = INTERNAL_TYPE_CACHE;
        jdk.internal.org.objectweb.asm.Type itype = c.get(type);
        if (itype != null) {
            return itype;
        }
        itype = jdk.internal.org.objectweb.asm.Type.getType(type);
        c.put(type, itype);
        return itype;
    }

    private static jdk.internal.org.objectweb.asm.Type getInternalType(final Class<?> type) {
        return lookupInternalType(type);
    }

    static void invokestatic(final MethodVisitor method, final Call call) {
        method.visitMethodInsn(INVOKESTATIC, call.className(), call.name(), call.descriptor(), false);
    }

    
Get the internal JVM name of a type
Returns:
the internal name/**
     * Get the internal JVM name of a type
     * @return the internal name
     */
    public String getInternalName() {
        return jdk.internal.org.objectweb.asm.Type.getInternalName(getTypeClass());
    }

    
Get the internal JVM name of type type represented by a given Java class
Params:
clazz – the class
Returns:
the internal name/**
     * Get the internal JVM name of type type represented by a given Java class
     * @param clazz the class
     * @return the internal name
     */
    public static String getInternalName(final Class<?> clazz) {
        return jdk.internal.org.objectweb.asm.Type.getInternalName(clazz);
    }

    
Determines whether a type is the UNKNOWN type, i.e. not set yet
Used for type inference.
Returns:
true if UNKNOWN, false otherwise/**
     * Determines whether a type is the UNKNOWN type, i.e. not set yet
     * Used for type inference.
     *
     * @return true if UNKNOWN, false otherwise
     */
    public boolean isUnknown() {
        return this.equals(Type.UNKNOWN);
    }

    
Determines whether this type represents an primitive type according to the ECMAScript specification,
which includes Boolean, Number, and String.
Returns:
true if a JavaScript primitive type, false otherwise./**
     * Determines whether this type represents an primitive type according to the ECMAScript specification,
     * which includes Boolean, Number, and String.
     *
     * @return true if a JavaScript primitive type, false otherwise.
     */
    public boolean isJSPrimitive() {
        return !isObject() || isString();
    }

    
Determines whether a type is the BOOLEAN type
Returns:
true if BOOLEAN, false otherwise/**
     * Determines whether a type is the BOOLEAN type
     * @return true if BOOLEAN, false otherwise
     */
    public boolean isBoolean() {
        return this.equals(Type.BOOLEAN);
    }

    
Determines whether a type is the INT type
Returns:
true if INTEGER, false otherwise/**
     * Determines whether a type is the INT type
     * @return true if INTEGER, false otherwise
     */
    public boolean isInteger() {
        return this.equals(Type.INT);
    }

    
Determines whether a type is the LONG type
Returns:
true if LONG, false otherwise/**
     * Determines whether a type is the LONG type
     * @return true if LONG, false otherwise
     */
    public boolean isLong() {
        return this.equals(Type.LONG);
    }

    
Determines whether a type is the NUMBER type
Returns:
true if NUMBER, false otherwise/**
     * Determines whether a type is the NUMBER type
     * @return true if NUMBER, false otherwise
     */
    public boolean isNumber() {
        return this.equals(Type.NUMBER);
    }

    
Determines whether a type is numeric, i.e. NUMBER,
INT, LONG.
Returns:
true if numeric, false otherwise/**
     * Determines whether a type is numeric, i.e. NUMBER,
     * INT, LONG.
     *
     * @return true if numeric, false otherwise
     */
    public boolean isNumeric() {
        return this instanceof NumericType;
    }

    
Determines whether a type is an array type, i.e.
OBJECT_ARRAY or NUMBER_ARRAY (for now)
Returns:
true if an array type, false otherwise/**
     * Determines whether a type is an array type, i.e.
     * OBJECT_ARRAY or NUMBER_ARRAY (for now)
     *
     * @return true if an array type, false otherwise
     */
    public boolean isArray() {
        return this instanceof ArrayType;
    }

    
Determines if a type takes up two bytecode slots or not
Returns:
true if type takes up two bytecode slots rather than one/**
     * Determines if a type takes up two bytecode slots or not
     *
     * @return true if type takes up two bytecode slots rather than one
     */
    public boolean isCategory2() {
        return getSlots() == 2;
    }

    
Determines whether a type is an OBJECT type, e.g. OBJECT, STRING,
NUMBER_ARRAY etc.
Returns:
true if object type, false otherwise/**
     * Determines whether a type is an OBJECT type, e.g. OBJECT, STRING,
     * NUMBER_ARRAY etc.
     *
     * @return true if object type, false otherwise
     */
    public boolean isObject() {
        return this instanceof ObjectType;
    }

    
Is this a primitive type (e.g int, long, double, boolean)
Returns:
true if primitive/**
     * Is this a primitive type (e.g int, long, double, boolean)
     * @return true if primitive
     */
    public boolean isPrimitive() {
        return !isObject();
    }

    
Determines whether a type is a STRING type
Returns:
true if object type, false otherwise/**
     * Determines whether a type is a STRING type
     *
     * @return true if object type, false otherwise
     */
    public boolean isString() {
        return this.equals(Type.STRING);
    }

    
Determines whether a type is a CHARSEQUENCE type used internally strings
Returns:
true if CharSequence (internal string) type, false otherwise/**
     * Determines whether a type is a CHARSEQUENCE type used internally strings
     *
     * @return true if CharSequence (internal string) type, false otherwise
     */
    public boolean isCharSequence() {
        return this.equals(Type.CHARSEQUENCE);
    }

    
Determine if two types are equivalent, i.e. need no conversion
Params:
type – the second type to check
Returns:
true if types are equivalent, false otherwise/**
     * Determine if two types are equivalent, i.e. need no conversion
     *
     * @param type the second type to check
     *
     * @return true if types are equivalent, false otherwise
     */
    public boolean isEquivalentTo(final Type type) {
        return this.weight() == type.weight() || isObject() && type.isObject();
    }

    
Determine if a type can be assigned to from another
Params:
type0 – the first type to check
type1 – the second type to check
Returns:
true if type1 can be written to type2, false otherwise/**
     * Determine if a type can be assigned to from another
     *
     * @param type0 the first type to check
     * @param type1 the second type to check
     *
     * @return true if type1 can be written to type2, false otherwise
     */
    public static boolean isAssignableFrom(final Type type0, final Type type1) {
        if (type0.isObject() && type1.isObject()) {
            return type0.weight() >= type1.weight();
        }

        return type0.weight() == type1.weight();
    }

    
Determine if this type is assignable from another type
Params:
type – the type to check against
Returns:
true if "type" can be written to this type, false otherwise/**
     * Determine if this type is assignable from another type
     * @param type the type to check against
     *
     * @return true if "type" can be written to this type, false otherwise
     */
    public boolean isAssignableFrom(final Type type) {
        return Type.isAssignableFrom(this, type);
    }

    
Determines is this type is equivalent to another, i.e. needs no conversion
to be assigned to it.
Params:
type0 – the first type to check
type1 – the second type to check
Returns:
true if this type is equivalent to type, false otherwise/**
     * Determines is this type is equivalent to another, i.e. needs no conversion
     * to be assigned to it.
     *
     * @param type0 the first type to check
     * @param type1 the second type to check
     *
     * @return true if this type is equivalent to type, false otherwise
     */
    public static boolean areEquivalent(final Type type0, final Type type1) {
        return type0.isEquivalentTo(type1);
    }

    
Determine the number of bytecode slots a type takes up
Returns:
the number of slots for this type, 1 or 2./**
     * Determine the number of bytecode slots a type takes up
     *
     * @return the number of slots for this type, 1 or 2.
     */
    public int getSlots() {
        return slots;
    }

    
Returns the widest or most common of two types
Params:
type0 – type one
type1 – type two
Returns:
the widest type/**
     * Returns the widest or most common of two types
     *
     * @param type0 type one
     * @param type1 type two
     *
     * @return the widest type
     */
    public static Type widest(final Type type0, final Type type1) {
        if (type0.isArray() && type1.isArray()) {
            return ((ArrayType)type0).getElementType() == ((ArrayType)type1).getElementType() ? type0 : Type.OBJECT;
        } else if (type0.isArray() != type1.isArray()) {
            //array and non array is always object, widest(Object[], int) NEVER returns Object[], which has most weight. that does not make sense
            return Type.OBJECT;
        } else if (type0.isObject() && type1.isObject() && type0.getTypeClass() != type1.getTypeClass()) {
            // Object<type=String> and Object<type=ScriptFunction> will produce Object
            // TODO: maybe find most specific common superclass?
            return Type.OBJECT;
        }
        return type0.weight() > type1.weight() ? type0 : type1;
    }

    
Returns the widest or most common of two types, given as classes
Params:
type0 – type one
type1 – type two
Returns:
the widest type/**
     * Returns the widest or most common of two types, given as classes
     *
     * @param type0 type one
     * @param type1 type two
     *
     * @return the widest type
     */
    public static Class<?> widest(final Class<?> type0, final Class<?> type1) {
        return widest(Type.typeFor(type0), Type.typeFor(type1)).getTypeClass();
    }

    
When doing widening for return types of a function or a ternary operator, it is not valid to widen a boolean to anything other than object. Note that this wouldn't be necessary if Type.widest did not allow boolean-to-number widening. Eventually, we should address it there, but it affects too many other parts of the system and is sometimes legitimate (e.g. whenever a boolean value would undergo ToNumber conversion anyway). 
Params:
t1 – type 1
t2 – type 2
Returns:
wider of t1 and t2, except if one is boolean and the other is neither boolean nor unknown, in which case Type.OBJECT is returned./**
     * When doing widening for return types of a function or a ternary operator, it is not valid to widen a boolean to
     * anything other than object. Note that this wouldn't be necessary if {@code Type.widest} did not allow
     * boolean-to-number widening. Eventually, we should address it there, but it affects too many other parts of the
     * system and is sometimes legitimate (e.g. whenever a boolean value would undergo ToNumber conversion anyway).
     * @param t1 type 1
     * @param t2 type 2
     * @return wider of t1 and t2, except if one is boolean and the other is neither boolean nor unknown, in which case
     * {@code Type.OBJECT} is returned.
     */
    public static Type widestReturnType(final Type t1, final Type t2) {
        if (t1.isUnknown()) {
            return t2;
        } else if (t2.isUnknown()) {
            return t1;
        } else if(t1.isBoolean() != t2.isBoolean() || t1.isNumeric() != t2.isNumeric()) {
            return Type.OBJECT;
        }
        return Type.widest(t1, t2);
    }

    
Returns a generic version of the type. Basically, if the type isObject(), returns OBJECT, otherwise returns the type unchanged. 
Params:
type – the type to generify
Returns:
the generified type/**
     * Returns a generic version of the type. Basically, if the type {@link #isObject()}, returns {@link #OBJECT},
     * otherwise returns the type unchanged.
     * @param type the type to generify
     * @return the generified type
     */
    public static Type generic(final Type type) {
        return type.isObject() ? Type.OBJECT : type;
    }

    
Returns the narrowest or least common of two types
Params:
type0 – type one
type1 – type two
Returns:
the widest type/**
     * Returns the narrowest or least common of two types
     *
     * @param type0 type one
     * @param type1 type two
     *
     * @return the widest type
     */
    public static Type narrowest(final Type type0, final Type type1) {
        return type0.narrowerThan(type1) ? type0 : type1;
    }

    
Check whether this type is strictly narrower than another one
Params:
type – type to check against
Returns:
true if this type is strictly narrower/**
     * Check whether this type is strictly narrower than another one
     * @param type type to check against
     * @return true if this type is strictly narrower
     */
    public boolean narrowerThan(final Type type) {
        return weight() < type.weight();
    }

    
Check whether this type is strictly wider than another one
Params:
type – type to check against
Returns:
true if this type is strictly wider/**
     * Check whether this type is strictly wider than another one
     * @param type type to check against
     * @return true if this type is strictly wider
     */
    public boolean widerThan(final Type type) {
        return weight() > type.weight();
    }

    
Returns the widest or most common of two types, but no wider than "limit"
Params:
type0 – type one
type1 – type two
limit – limiting type
Returns:
the widest type, but no wider than limit/**
     * Returns the widest or most common of two types, but no wider than "limit"
     *
     * @param type0 type one
     * @param type1 type two
     * @param limit limiting type
     *
     * @return the widest type, but no wider than limit
     */
    public static Type widest(final Type type0, final Type type1, final Type limit) {
        final Type type = Type.widest(type0,  type1);
        if (type.weight() > limit.weight()) {
            return limit;
        }
        return type;
    }

    
Returns the widest or most common of two types, but no narrower than "limit"
Params:
type0 – type one
type1 – type two
limit – limiting type
Returns:
the widest type, but no wider than limit/**
     * Returns the widest or most common of two types, but no narrower than "limit"
     *
     * @param type0 type one
     * @param type1 type two
     * @param limit limiting type
     *
     * @return the widest type, but no wider than limit
     */
    public static Type narrowest(final Type type0, final Type type1, final Type limit) {
        final Type type = type0.weight() < type1.weight() ? type0 : type1;
        if (type.weight() < limit.weight()) {
            return limit;
        }
        return type;
    }

    
Returns the narrowest of this type and another
Params:
other – type to compare against
Returns:
the widest type/**
     * Returns the narrowest of this type and another
     *
     * @param  other type to compare against
     *
     * @return the widest type
     */
    public Type narrowest(final Type other) {
        return Type.narrowest(this, other);
    }

    
Returns the widest of this type and another
Params:
other – type to compare against
Returns:
the widest type/**
     * Returns the widest of this type and another
     *
     * @param  other type to compare against
     *
     * @return the widest type
     */
    public Type widest(final Type other) {
        return Type.widest(this, other);
    }

    
Returns the weight of a type, used for type comparison
between wider and narrower types
Returns:
the weight/**
     * Returns the weight of a type, used for type comparison
     * between wider and narrower types
     *
     * @return the weight
     */
    int weight() {
        return weight;
    }

    
Return the descriptor of a type, used for e.g. signature
generation
Returns:
the descriptor/**
     * Return the descriptor of a type, used for e.g. signature
     * generation
     *
     * @return the descriptor
     */
    public String getDescriptor() {
        return descriptor;
    }

    
Return the descriptor of a type, short version
Used mainly for debugging purposes
Returns:
the short descriptor/**
     * Return the descriptor of a type, short version
     * Used mainly for debugging purposes
     *
     * @return the short descriptor
     */
    public String getShortDescriptor() {
        return descriptor;
    }

    @Override
    public String toString() {
        return name;
    }

    
Return the (possibly cached) Type object for this class
Params:
clazz – the class to check
Returns:
the Type representing this class/**
     * Return the (possibly cached) Type object for this class
     *
     * @param clazz the class to check
     *
     * @return the Type representing this class
     */
    public static Type typeFor(final Class<?> clazz) {
        return cache.computeIfAbsent(clazz, (keyClass) -> {
            assert !keyClass.isPrimitive() || keyClass == void.class;
            return keyClass.isArray() ? new ArrayType(keyClass) : new ObjectType(keyClass);
        });
    }

    @Override
    public int compareTo(final Type o) {
        return o.weight() - weight();
    }

    
Common logic for implementing dup for all types
Params:
method – method visitor
depth – dup depth
Returns:
the type at the top of the stack afterwards/**
     * Common logic for implementing dup for all types
     *
     * @param method method visitor
     * @param depth dup depth
     *
     * @return the type at the top of the stack afterwards
     */
    @Override
    public Type dup(final MethodVisitor method, final int depth) {
        return Type.dup(method, this, depth);
    }

    
Common logic for implementing swap for all types
Params:
method – method visitor
other –  the type to swap with
Returns:
the type at the top of the stack afterwards, i.e. other/**
     * Common logic for implementing swap for all types
     *
     * @param method method visitor
     * @param other  the type to swap with
     *
     * @return the type at the top of the stack afterwards, i.e. other
     */
    @Override
    public Type swap(final MethodVisitor method, final Type other) {
        Type.swap(method, this, other);
        return other;
    }

    
Common logic for implementing pop for all types
Params:
method – method visitor
Returns:
the type that was popped/**
     * Common logic for implementing pop for all types
     *
     * @param method method visitor
     *
     * @return the type that was popped
     */
    @Override
    public Type pop(final MethodVisitor method) {
        Type.pop(method, this);
        return this;
    }

    @Override
    public Type loadEmpty(final MethodVisitor method) {
        assert false : "unsupported operation";
        return null;
    }

    
Superclass logic for pop for all types
Params:
method – method emitter
type –   type to pop/**
     * Superclass logic for pop for all types
     *
     * @param method method emitter
     * @param type   type to pop
     */
    protected static void pop(final MethodVisitor method, final Type type) {
        method.visitInsn(type.isCategory2() ? POP2 : POP);
    }

    private static Type dup(final MethodVisitor method, final Type type, final int depth) {
        final boolean       cat2 = type.isCategory2();

        switch (depth) {
        case 0:
            method.visitInsn(cat2 ? DUP2 : DUP);
            break;
        case 1:
            method.visitInsn(cat2 ? DUP2_X1 : DUP_X1);
            break;
        case 2:
            method.visitInsn(cat2 ? DUP2_X2 : DUP_X2);
            break;
        default:
            return null; //invalid depth
        }

        return type;
    }

    private static void swap(final MethodVisitor method, final Type above, final Type below) {
        if (below.isCategory2()) {
            if (above.isCategory2()) {
                method.visitInsn(DUP2_X2);
                method.visitInsn(POP2);
            } else {
                method.visitInsn(DUP_X2);
                method.visitInsn(POP);
            }
        } else {
            if (above.isCategory2()) {
                method.visitInsn(DUP2_X1);
                method.visitInsn(POP2);
            } else {
                method.visitInsn(SWAP);
            }
        }
    }

    
Mappings between java classes and their Type singletons /** Mappings between java classes and their Type singletons */
    private static final ConcurrentMap<Class<?>, Type> cache = new ConcurrentHashMap<>();
    private static final ConcurrentMap<String, Type> cacheByName = new ConcurrentHashMap<>();

    
This is the boolean singleton, used for all boolean types
/**
     * This is the boolean singleton, used for all boolean types
     */
    public static final Type BOOLEAN = putInCache(new BooleanType());

    
This is an integer type, i.e INT, INT32.
/**
     * This is an integer type, i.e INT, INT32.
     */
    public static final BitwiseType INT = putInCache(new IntType());

    
This is the number singleton, used for all number types
/**
     * This is the number singleton, used for all number types
     */
    public static final NumericType NUMBER = putInCache(new NumberType());

    
This is the long singleton, used for all long types
/**
     * This is the long singleton, used for all long types
     */
    public static final Type LONG = putInCache(new LongType());

    
A string singleton
/**
     * A string singleton
     */
    public static final Type STRING = putInCache(new ObjectType(String.class));

    
This is the CharSequence singleton used to represent JS strings internally (either a java.lang.String or jdk.nashorn.internal.runtime.ConsString. /**
     * This is the CharSequence singleton used to represent JS strings internally
     * (either a {@code java.lang.String} or {@code jdk.nashorn.internal.runtime.ConsString}.
     */
    public static final Type CHARSEQUENCE = putInCache(new ObjectType(CharSequence.class));


    
This is the object singleton, used for all object types
/**
     * This is the object singleton, used for all object types
     */
    public static final Type OBJECT = putInCache(new ObjectType());

    
A undefined singleton
/**
     * A undefined singleton
     */
    public static final Type UNDEFINED = putInCache(new ObjectType(Undefined.class));

    
This is the singleton for ScriptObjects
/**
     * This is the singleton for ScriptObjects
     */
    public static final Type SCRIPT_OBJECT = putInCache(new ObjectType(ScriptObject.class));

    
This is the singleton for integer arrays
/**
     * This is the singleton for integer arrays
     */
    public static final ArrayType INT_ARRAY = putInCache(new ArrayType(int[].class) {
        private static final long serialVersionUID = 1L;

        @Override
        public void astore(final MethodVisitor method) {
            method.visitInsn(IASTORE);
        }

        @Override
        public Type aload(final MethodVisitor method) {
            method.visitInsn(IALOAD);
            return INT;
        }

        @Override
        public Type newarray(final MethodVisitor method) {
            method.visitIntInsn(NEWARRAY, T_INT);
            return this;
        }

        @Override
        public Type getElementType() {
            return INT;
        }
    });

    
This is the singleton for long arrays
/**
     * This is the singleton for long arrays
     */
    public static final ArrayType LONG_ARRAY = putInCache(new ArrayType(long[].class) {
        private static final long serialVersionUID = 1L;

        @Override
        public void astore(final MethodVisitor method) {
            method.visitInsn(LASTORE);
        }

        @Override
        public Type aload(final MethodVisitor method) {
            method.visitInsn(LALOAD);
            return LONG;
        }

        @Override
        public Type newarray(final MethodVisitor method) {
            method.visitIntInsn(NEWARRAY, T_LONG);
            return this;
        }

        @Override
        public Type getElementType() {
            return LONG;
        }
    });

    
This is the singleton for numeric arrays
/**
     * This is the singleton for numeric arrays
     */
    public static final ArrayType NUMBER_ARRAY = putInCache(new ArrayType(double[].class) {
        private static final long serialVersionUID = 1L;

        @Override
        public void astore(final MethodVisitor method) {
            method.visitInsn(DASTORE);
        }

        @Override
        public Type aload(final MethodVisitor method) {
            method.visitInsn(DALOAD);
            return NUMBER;
        }

        @Override
        public Type newarray(final MethodVisitor method) {
            method.visitIntInsn(NEWARRAY, T_DOUBLE);
            return this;
        }

        @Override
        public Type getElementType() {
            return NUMBER;
        }
    });

    
This is the singleton for object arrays /** This is the singleton for object arrays */
    public static final ArrayType OBJECT_ARRAY = putInCache(new ArrayType(Object[].class));

    
This type, always an object type, just a toString override /** This type, always an object type, just a toString override */
    public static final Type THIS = new ObjectType() {
        private static final long serialVersionUID = 1L;

        @Override
        public String toString() {
            return "this";
        }
    };

    
Scope type, always an object type, just a toString override /** Scope type, always an object type, just a toString override */
    public static final Type SCOPE = new ObjectType() {
        private static final long serialVersionUID = 1L;

        @Override
        public String toString() {
            return "scope";
        }
    };

    private static interface Unknown {
        // EMPTY - used as a class that is absolutely not compatible with a type to represent "unknown"
    }

    private abstract static class ValueLessType extends Type {
        private static final long serialVersionUID = 1L;

        ValueLessType(final String name) {
            super(name, Unknown.class, MIN_WEIGHT, 1);
        }

        @Override
        public Type load(final MethodVisitor method, final int slot) {
            throw new UnsupportedOperationException("load " + slot);
        }

        @Override
        public void store(final MethodVisitor method, final int slot) {
            throw new UnsupportedOperationException("store " + slot);
        }

        @Override
        public Type ldc(final MethodVisitor method, final Object c) {
            throw new UnsupportedOperationException("ldc " + c);
        }

        @Override
        public Type loadUndefined(final MethodVisitor method) {
            throw new UnsupportedOperationException("load undefined");
        }

        @Override
        public Type loadForcedInitializer(final MethodVisitor method) {
            throw new UnsupportedOperationException("load forced initializer");
        }

        @Override
        public Type convert(final MethodVisitor method, final Type to) {
            throw new UnsupportedOperationException("convert => " + to);
        }

        @Override
        public void _return(final MethodVisitor method) {
            throw new UnsupportedOperationException("return");
       }

        @Override
        public Type add(final MethodVisitor method, final int programPoint) {
            throw new UnsupportedOperationException("add");
        }
    }

    
This is the unknown type which is used as initial type for type
inference. It has the minimum type width
/**
     * This is the unknown type which is used as initial type for type
     * inference. It has the minimum type width
     */
    public static final Type UNKNOWN = new ValueLessType("<unknown>") {
        private static final long serialVersionUID = 1L;

        @Override
        public String getDescriptor() {
            return "<unknown>";
        }

        @Override
        public char getBytecodeStackType() {
            return 'U';
        }
    };

    
This is the unknown type which is used as initial type for type
inference. It has the minimum type width
/**
     * This is the unknown type which is used as initial type for type
     * inference. It has the minimum type width
     */
    public static final Type SLOT_2 = new ValueLessType("<slot_2>") {
        private static final long serialVersionUID = 1L;

        @Override
        public String getDescriptor() {
            return "<slot_2>";
        }

        @Override
        public char getBytecodeStackType() {
            throw new UnsupportedOperationException("getBytecodeStackType");
        }
    };

    private static <T extends Type> T putInCache(final T type) {
        cache.put(type.getTypeClass(), type);
        return type;
    }

    
Read resolve
Returns:
resolved type/**
     * Read resolve
     * @return resolved type
     */
    protected final Object readResolve() {
        return Type.typeFor(clazz);
    }
}