/*
 * Copyright (c) 1999, 2018, 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 com.sun.tools.javac.jvm;

import com.sun.tools.javac.tree.TreeInfo.PosKind;
import com.sun.tools.javac.util.*;
import com.sun.tools.javac.util.JCDiagnostic.DiagnosticPosition;
import com.sun.tools.javac.util.List;
import com.sun.tools.javac.code.*;
import com.sun.tools.javac.code.Attribute.TypeCompound;
import com.sun.tools.javac.code.Symbol.VarSymbol;
import com.sun.tools.javac.comp.*;
import com.sun.tools.javac.tree.*;

import com.sun.tools.javac.code.Symbol.*;
import com.sun.tools.javac.code.Type.*;
import com.sun.tools.javac.jvm.Code.*;
import com.sun.tools.javac.jvm.Items.*;
import com.sun.tools.javac.resources.CompilerProperties.Errors;
import com.sun.tools.javac.tree.EndPosTable;
import com.sun.tools.javac.tree.JCTree.*;

import static com.sun.tools.javac.code.Flags.*;
import static com.sun.tools.javac.code.Kinds.Kind.*;
import static com.sun.tools.javac.code.TypeTag.*;
import static com.sun.tools.javac.jvm.ByteCodes.*;
import static com.sun.tools.javac.jvm.CRTFlags.*;
import static com.sun.tools.javac.main.Option.*;
import static com.sun.tools.javac.tree.JCTree.Tag.*;

This pass maps flat Java (i.e. without inner classes) to bytecodes.
 
This is NOT part of any supported API.
 If you write code that depends on this, you do so at your own risk.
 This code and its internal interfaces are subject to change or
 deletion without notice.
/** This pass maps flat Java (i.e. without inner classes) to bytecodes.
 *
 *  <p><b>This is NOT part of any supported API.
 *  If you write code that depends on this, you do so at your own risk.
 *  This code and its internal interfaces are subject to change or
 *  deletion without notice.</b>
 */
public class Gen extends JCTree.Visitor {
    protected static final Context.Key<Gen> genKey = new Context.Key<>();

    private final Log log;
    private final Symtab syms;
    private final Check chk;
    private final Resolve rs;
    private final TreeMaker make;
    private final Names names;
    private final Target target;
    private final Name accessDollar;
    private final Types types;
    private final Lower lower;
    private final Annotate annotate;
    private final StringConcat concat;

    
Format of stackmap tables to be generated. /** Format of stackmap tables to be generated. */
    private final Code.StackMapFormat stackMap;

    
A type that serves as the expected type for all method expressions.
/** A type that serves as the expected type for all method expressions.
     */
    private final Type methodType;

    public static Gen instance(Context context) {
        Gen instance = context.get(genKey);
        if (instance == null)
            instance = new Gen(context);
        return instance;
    }

    
Constant pool, reset by genClass.
/** Constant pool, reset by genClass.
     */
    private final Pool pool;

    protected Gen(Context context) {
        context.put(genKey, this);

        names = Names.instance(context);
        log = Log.instance(context);
        syms = Symtab.instance(context);
        chk = Check.instance(context);
        rs = Resolve.instance(context);
        make = TreeMaker.instance(context);
        target = Target.instance(context);
        types = Types.instance(context);
        concat = StringConcat.instance(context);

        methodType = new MethodType(null, null, null, syms.methodClass);
        accessDollar = names.
            fromString("access" + target.syntheticNameChar());
        lower = Lower.instance(context);

        Options options = Options.instance(context);
        lineDebugInfo =
            options.isUnset(G_CUSTOM) ||
            options.isSet(G_CUSTOM, "lines");
        varDebugInfo =
            options.isUnset(G_CUSTOM)
            ? options.isSet(G)
            : options.isSet(G_CUSTOM, "vars");
        genCrt = options.isSet(XJCOV);
        debugCode = options.isSet("debug.code");
        disableVirtualizedPrivateInvoke = options.isSet("disableVirtualizedPrivateInvoke");
        pool = new Pool(types);

        // ignore cldc because we cannot have both stackmap formats
        this.stackMap = StackMapFormat.JSR202;
        annotate = Annotate.instance(context);
    }

    
Switches
/** Switches
     */
    private final boolean lineDebugInfo;
    private final boolean varDebugInfo;
    private final boolean genCrt;
    private final boolean debugCode;
    private boolean disableVirtualizedPrivateInvoke;

    
Code buffer, set by genMethod.
/** Code buffer, set by genMethod.
     */
    private Code code;

    
Items structure, set by genMethod.
/** Items structure, set by genMethod.
     */
    private Items items;

    
Environment for symbol lookup, set by genClass
/** Environment for symbol lookup, set by genClass
     */
    private Env<AttrContext> attrEnv;

    
The top level tree.
/** The top level tree.
     */
    private JCCompilationUnit toplevel;

    
The number of code-gen errors in this class.
/** The number of code-gen errors in this class.
     */
    private int nerrs = 0;

    
An object containing mappings of syntax trees to their
 ending source positions.
/** An object containing mappings of syntax trees to their
     *  ending source positions.
     */
    EndPosTable endPosTable;

    boolean inCondSwitchExpression;
    Chain switchExpressionTrueChain;
    Chain switchExpressionFalseChain;
    List<LocalItem> stackBeforeSwitchExpression;

    
Generate code to load an integer constant.
 @param n     The integer to be loaded.
/** Generate code to load an integer constant.
     *  @param n     The integer to be loaded.
     */
    void loadIntConst(int n) {
        items.makeImmediateItem(syms.intType, n).load();
    }

    
The opcode that loads a zero constant of a given type code.
 @param tc   The given type code (@see ByteCode).
/** The opcode that loads a zero constant of a given type code.
     *  @param tc   The given type code (@see ByteCode).
     */
    public static int zero(int tc) {
        switch(tc) {
        case INTcode: case BYTEcode: case SHORTcode: case CHARcode:
            return iconst_0;
        case LONGcode:
            return lconst_0;
        case FLOATcode:
            return fconst_0;
        case DOUBLEcode:
            return dconst_0;
        default:
            throw new AssertionError("zero");
        }
    }

    
The opcode that loads a one constant of a given type code.
 @param tc   The given type code (@see ByteCode).
/** The opcode that loads a one constant of a given type code.
     *  @param tc   The given type code (@see ByteCode).
     */
    public static int one(int tc) {
        return zero(tc) + 1;
    }

    
Generate code to load -1 of the given type code (either int or long).
 @param tc   The given type code (@see ByteCode).
/** Generate code to load -1 of the given type code (either int or long).
     *  @param tc   The given type code (@see ByteCode).
     */
    void emitMinusOne(int tc) {
        if (tc == LONGcode) {
            items.makeImmediateItem(syms.longType, Long.valueOf(-1)).load();
        } else {
            code.emitop0(iconst_m1);
        }
    }

    
Construct a symbol to reflect the qualifying type that should appear in the byte code as per JLS 13.1. For target >= 1.2: Clone a method with the qualifier as owner (except for those cases where we need to work around VM bugs). For target <= 1.1: If qualified variable or method is defined in a non-accessible class, clone it with the qualifier class as owner. @param sym The accessed symbol @param site The qualifier's type. /** Construct a symbol to reflect the qualifying type that should
     *  appear in the byte code as per JLS 13.1.
     *
     *  For {@literal target >= 1.2}: Clone a method with the qualifier as owner (except
     *  for those cases where we need to work around VM bugs).
     *
     *  For {@literal target <= 1.1}: If qualified variable or method is defined in a
     *  non-accessible class, clone it with the qualifier class as owner.
     *
     *  @param sym    The accessed symbol
     *  @param site   The qualifier's type.
     */
    Symbol binaryQualifier(Symbol sym, Type site) {

        if (site.hasTag(ARRAY)) {
            if (sym == syms.lengthVar ||
                sym.owner != syms.arrayClass)
                return sym;
            // array clone can be qualified by the array type in later targets
            Symbol qualifier = new ClassSymbol(Flags.PUBLIC, site.tsym.name,
                                               site, syms.noSymbol);
            return sym.clone(qualifier);
        }

        if (sym.owner == site.tsym ||
            (sym.flags() & (STATIC | SYNTHETIC)) == (STATIC | SYNTHETIC)) {
            return sym;
        }

        // leave alone methods inherited from Object
        // JLS 13.1.
        if (sym.owner == syms.objectType.tsym)
            return sym;

        return sym.clone(site.tsym);
    }

    
Insert a reference to given type in the constant pool,
 checking for an array with too many dimensions;
 return the reference's index.
 @param type   The type for which a reference is inserted.
/** Insert a reference to given type in the constant pool,
     *  checking for an array with too many dimensions;
     *  return the reference's index.
     *  @param type   The type for which a reference is inserted.
     */
    int makeRef(DiagnosticPosition pos, Type type) {
        checkDimension(pos, type);
        if (type.isAnnotated()) {
            return pool.put((Object)type);
        } else {
            return pool.put(type.hasTag(CLASS) ? (Object)type.tsym : (Object)type);
        }
    }

    
Check if the given type is an array with too many dimensions.
/** Check if the given type is an array with too many dimensions.
     */
    private void checkDimension(DiagnosticPosition pos, Type t) {
        switch (t.getTag()) {
        case METHOD:
            checkDimension(pos, t.getReturnType());
            for (List<Type> args = t.getParameterTypes(); args.nonEmpty(); args = args.tail)
                checkDimension(pos, args.head);
            break;
        case ARRAY:
            if (types.dimensions(t) > ClassFile.MAX_DIMENSIONS) {
                log.error(pos, Errors.LimitDimensions);
                nerrs++;
            }
            break;
        default:
            break;
        }
    }

    
Create a tempory variable.
 @param type   The variable's type.
/** Create a tempory variable.
     *  @param type   The variable's type.
     */
    LocalItem makeTemp(Type type) {
        VarSymbol v = new VarSymbol(Flags.SYNTHETIC,
                                    names.empty,
                                    type,
                                    env.enclMethod.sym);
        code.newLocal(v);
        return items.makeLocalItem(v);
    }

    
Generate code to call a non-private method or constructor.
 @param pos         Position to be used for error reporting.
 @param site        The type of which the method is a member.
 @param name        The method's name.
 @param argtypes    The method's argument types.
 @param isStatic    A flag that indicates whether we call a
                    static or instance method.
/** Generate code to call a non-private method or constructor.
     *  @param pos         Position to be used for error reporting.
     *  @param site        The type of which the method is a member.
     *  @param name        The method's name.
     *  @param argtypes    The method's argument types.
     *  @param isStatic    A flag that indicates whether we call a
     *                     static or instance method.
     */
    void callMethod(DiagnosticPosition pos,
                    Type site, Name name, List<Type> argtypes,
                    boolean isStatic) {
        Symbol msym = rs.
            resolveInternalMethod(pos, attrEnv, site, name, argtypes, null);
        if (isStatic) items.makeStaticItem(msym).invoke();
        else items.makeMemberItem(msym, name == names.init).invoke();
    }

    
Is the given method definition an access method
 resulting from a qualified super? This is signified by an odd
 access code.
/** Is the given method definition an access method
     *  resulting from a qualified super? This is signified by an odd
     *  access code.
     */
    private boolean isAccessSuper(JCMethodDecl enclMethod) {
        return
            (enclMethod.mods.flags & SYNTHETIC) != 0 &&
            isOddAccessName(enclMethod.name);
    }

    
Does given name start with "access$" and end in an odd digit?
/** Does given name start with "access$" and end in an odd digit?
     */
    private boolean isOddAccessName(Name name) {
        return
            name.startsWith(accessDollar) &&
            (name.getByteAt(name.getByteLength() - 1) & 1) == 1;
    }

/* ************************************************************************
 * Non-local exits
 *************************************************************************/

    
Generate code to invoke the finalizer associated with given
 environment.
 Any calls to finalizers are appended to the environments `cont' chain.
 Mark beginning of gap in catch all range for finalizer.
/** Generate code to invoke the finalizer associated with given
     *  environment.
     *  Any calls to finalizers are appended to the environments `cont' chain.
     *  Mark beginning of gap in catch all range for finalizer.
     */
    void genFinalizer(Env<GenContext> env) {
        if (code.isAlive() && env.info.finalize != null)
            env.info.finalize.gen();
    }

    
Generate code to call all finalizers of structures aborted by
 a non-local
 exit.  Return target environment of the non-local exit.
 @param target      The tree representing the structure that's aborted
 @param env         The environment current at the non-local exit.
/** Generate code to call all finalizers of structures aborted by
     *  a non-local
     *  exit.  Return target environment of the non-local exit.
     *  @param target      The tree representing the structure that's aborted
     *  @param env         The environment current at the non-local exit.
     */
    Env<GenContext> unwind(JCTree target, Env<GenContext> env) {
        Env<GenContext> env1 = env;
        while (true) {
            genFinalizer(env1);
            if (env1.tree == target) break;
            env1 = env1.next;
        }
        return env1;
    }

    
Mark end of gap in catch-all range for finalizer.
 @param env   the environment which might contain the finalizer
              (if it does, env.info.gaps != null).
/** Mark end of gap in catch-all range for finalizer.
     *  @param env   the environment which might contain the finalizer
     *               (if it does, env.info.gaps != null).
     */
    void endFinalizerGap(Env<GenContext> env) {
        if (env.info.gaps != null && env.info.gaps.length() % 2 == 1)
            env.info.gaps.append(code.curCP());
    }

    
Mark end of all gaps in catch-all ranges for finalizers of environments
 lying between, and including to two environments.
 @param from    the most deeply nested environment to mark
 @param to      the least deeply nested environment to mark
/** Mark end of all gaps in catch-all ranges for finalizers of environments
     *  lying between, and including to two environments.
     *  @param from    the most deeply nested environment to mark
     *  @param to      the least deeply nested environment to mark
     */
    void endFinalizerGaps(Env<GenContext> from, Env<GenContext> to) {
        Env<GenContext> last = null;
        while (last != to) {
            endFinalizerGap(from);
            last = from;
            from = from.next;
        }
    }

    
Do any of the structures aborted by a non-local exit have
 finalizers that require an empty stack?
 @param target      The tree representing the structure that's aborted
 @param env         The environment current at the non-local exit.
/** Do any of the structures aborted by a non-local exit have
     *  finalizers that require an empty stack?
     *  @param target      The tree representing the structure that's aborted
     *  @param env         The environment current at the non-local exit.
     */
    boolean hasFinally(JCTree target, Env<GenContext> env) {
        while (env.tree != target) {
            if (env.tree.hasTag(TRY) && env.info.finalize.hasFinalizer())
                return true;
            env = env.next;
        }
        return false;
    }

/* ************************************************************************
 * Normalizing class-members.
 *************************************************************************/

    
Distribute member initializer code into constructors and <clinit> method. @param defs The list of class member declarations. @param c The enclosing class. /** Distribute member initializer code into constructors and {@code <clinit>}
     *  method.
     *  @param defs         The list of class member declarations.
     *  @param c            The enclosing class.
     */
    List<JCTree> normalizeDefs(List<JCTree> defs, ClassSymbol c) {
        ListBuffer<JCStatement> initCode = new ListBuffer<>();
        ListBuffer<Attribute.TypeCompound> initTAs = new ListBuffer<>();
        ListBuffer<JCStatement> clinitCode = new ListBuffer<>();
        ListBuffer<Attribute.TypeCompound> clinitTAs = new ListBuffer<>();
        ListBuffer<JCTree> methodDefs = new ListBuffer<>();
        // Sort definitions into three listbuffers:
        //  - initCode for instance initializers
        //  - clinitCode for class initializers
        //  - methodDefs for method definitions
        for (List<JCTree> l = defs; l.nonEmpty(); l = l.tail) {
            JCTree def = l.head;
            switch (def.getTag()) {
            case BLOCK:
                JCBlock block = (JCBlock)def;
                if ((block.flags & STATIC) != 0)
                    clinitCode.append(block);
                else if ((block.flags & SYNTHETIC) == 0)
                    initCode.append(block);
                break;
            case METHODDEF:
                methodDefs.append(def);
                break;
            case VARDEF:
                JCVariableDecl vdef = (JCVariableDecl) def;
                VarSymbol sym = vdef.sym;
                checkDimension(vdef.pos(), sym.type);
                if (vdef.init != null) {
                    if ((sym.flags() & STATIC) == 0) {
                        // Always initialize instance variables.
                        JCStatement init = make.at(vdef.pos()).
                            Assignment(sym, vdef.init);
                        initCode.append(init);
                        endPosTable.replaceTree(vdef, init);
                        initTAs.addAll(getAndRemoveNonFieldTAs(sym));
                    } else if (sym.getConstValue() == null) {
                        // Initialize class (static) variables only if
                        // they are not compile-time constants.
                        JCStatement init = make.at(vdef.pos).
                            Assignment(sym, vdef.init);
                        clinitCode.append(init);
                        endPosTable.replaceTree(vdef, init);
                        clinitTAs.addAll(getAndRemoveNonFieldTAs(sym));
                    } else {
                        checkStringConstant(vdef.init.pos(), sym.getConstValue());
                        /* if the init contains a reference to an external class, add it to the
                         * constant's pool
                         */
                        vdef.init.accept(classReferenceVisitor);
                    }
                }
                break;
            default:
                Assert.error();
            }
        }
        // Insert any instance initializers into all constructors.
        if (initCode.length() != 0) {
            List<JCStatement> inits = initCode.toList();
            initTAs.addAll(c.getInitTypeAttributes());
            List<Attribute.TypeCompound> initTAlist = initTAs.toList();
            for (JCTree t : methodDefs) {
                normalizeMethod((JCMethodDecl)t, inits, initTAlist);
            }
        }
        // If there are class initializers, create a <clinit> method
        // that contains them as its body.
        if (clinitCode.length() != 0) {
            MethodSymbol clinit = new MethodSymbol(
                STATIC | (c.flags() & STRICTFP),
                names.clinit,
                new MethodType(
                    List.nil(), syms.voidType,
                    List.nil(), syms.methodClass),
                c);
            c.members().enter(clinit);
            List<JCStatement> clinitStats = clinitCode.toList();
            JCBlock block = make.at(clinitStats.head.pos()).Block(0, clinitStats);
            block.endpos = TreeInfo.endPos(clinitStats.last());
            methodDefs.append(make.MethodDef(clinit, block));

            if (!clinitTAs.isEmpty())
                clinit.appendUniqueTypeAttributes(clinitTAs.toList());
            if (!c.getClassInitTypeAttributes().isEmpty())
                clinit.appendUniqueTypeAttributes(c.getClassInitTypeAttributes());
        }
        // Return all method definitions.
        return methodDefs.toList();
    }

    private List<Attribute.TypeCompound> getAndRemoveNonFieldTAs(VarSymbol sym) {
        List<TypeCompound> tas = sym.getRawTypeAttributes();
        ListBuffer<Attribute.TypeCompound> fieldTAs = new ListBuffer<>();
        ListBuffer<Attribute.TypeCompound> nonfieldTAs = new ListBuffer<>();
        for (TypeCompound ta : tas) {
            Assert.check(ta.getPosition().type != TargetType.UNKNOWN);
            if (ta.getPosition().type == TargetType.FIELD) {
                fieldTAs.add(ta);
            } else {
                nonfieldTAs.add(ta);
            }
        }
        sym.setTypeAttributes(fieldTAs.toList());
        return nonfieldTAs.toList();
    }

    
Check a constant value and report if it is a string that is
 too large.
/** Check a constant value and report if it is a string that is
     *  too large.
     */
    private void checkStringConstant(DiagnosticPosition pos, Object constValue) {
        if (nerrs != 0 || // only complain about a long string once
            constValue == null ||
            !(constValue instanceof String) ||
            ((String)constValue).length() < Pool.MAX_STRING_LENGTH)
            return;
        log.error(pos, Errors.LimitString);
        nerrs++;
    }

    
Insert instance initializer code into initial constructor.
 @param md        The tree potentially representing a
                  constructor's definition.
 @param initCode  The list of instance initializer statements.
 @param initTAs  Type annotations from the initializer expression.
/** Insert instance initializer code into initial constructor.
     *  @param md        The tree potentially representing a
     *                   constructor's definition.
     *  @param initCode  The list of instance initializer statements.
     *  @param initTAs  Type annotations from the initializer expression.
     */
    void normalizeMethod(JCMethodDecl md, List<JCStatement> initCode, List<TypeCompound> initTAs) {
        if (md.name == names.init && TreeInfo.isInitialConstructor(md)) {
            // We are seeing a constructor that does not call another
            // constructor of the same class.
            List<JCStatement> stats = md.body.stats;
            ListBuffer<JCStatement> newstats = new ListBuffer<>();

            if (stats.nonEmpty()) {
                // Copy initializers of synthetic variables generated in
                // the translation of inner classes.
                while (TreeInfo.isSyntheticInit(stats.head)) {
                    newstats.append(stats.head);
                    stats = stats.tail;
                }
                // Copy superclass constructor call
                newstats.append(stats.head);
                stats = stats.tail;
                // Copy remaining synthetic initializers.
                while (stats.nonEmpty() &&
                       TreeInfo.isSyntheticInit(stats.head)) {
                    newstats.append(stats.head);
                    stats = stats.tail;
                }
                // Now insert the initializer code.
                newstats.appendList(initCode);
                // And copy all remaining statements.
                while (stats.nonEmpty()) {
                    newstats.append(stats.head);
                    stats = stats.tail;
                }
            }
            md.body.stats = newstats.toList();
            if (md.body.endpos == Position.NOPOS)
                md.body.endpos = TreeInfo.endPos(md.body.stats.last());

            md.sym.appendUniqueTypeAttributes(initTAs);
        }
    }

/* ************************************************************************
 * Traversal methods
 *************************************************************************/

    
Visitor argument: The current environment.
/** Visitor argument: The current environment.
     */
    Env<GenContext> env;

    
Visitor argument: The expected type (prototype).
/** Visitor argument: The expected type (prototype).
     */
    Type pt;

    
Visitor result: The item representing the computed value.
/** Visitor result: The item representing the computed value.
     */
    Item result;

    
Visitor method: generate code for a definition, catching and reporting
 any completion failures.
 @param tree    The definition to be visited.
 @param env     The environment current at the definition.
/** Visitor method: generate code for a definition, catching and reporting
     *  any completion failures.
     *  @param tree    The definition to be visited.
     *  @param env     The environment current at the definition.
     */
    public void genDef(JCTree tree, Env<GenContext> env) {
        Env<GenContext> prevEnv = this.env;
        try {
            this.env = env;
            tree.accept(this);
        } catch (CompletionFailure ex) {
            chk.completionError(tree.pos(), ex);
        } finally {
            this.env = prevEnv;
        }
    }

    
Derived visitor method: check whether CharacterRangeTable
 should be emitted, if so, put a new entry into CRTable
 and call method to generate bytecode.
 If not, just call method to generate bytecode.
 @see    #genStat(JCTree, Env)
 @param  tree     The tree to be visited.
 @param  env      The environment to use.
 @param  crtFlags The CharacterRangeTable flags
                  indicating type of the entry.
/** Derived visitor method: check whether CharacterRangeTable
     *  should be emitted, if so, put a new entry into CRTable
     *  and call method to generate bytecode.
     *  If not, just call method to generate bytecode.
     *  @see    #genStat(JCTree, Env)
     *
     *  @param  tree     The tree to be visited.
     *  @param  env      The environment to use.
     *  @param  crtFlags The CharacterRangeTable flags
     *                   indicating type of the entry.
     */
    public void genStat(JCTree tree, Env<GenContext> env, int crtFlags) {
        if (!genCrt) {
            genStat(tree, env);
            return;
        }
        int startpc = code.curCP();
        genStat(tree, env);
        if (tree.hasTag(Tag.BLOCK)) crtFlags |= CRT_BLOCK;
        code.crt.put(tree, crtFlags, startpc, code.curCP());
    }

    
Derived visitor method: generate code for a statement.
/** Derived visitor method: generate code for a statement.
     */
    public void genStat(JCTree tree, Env<GenContext> env) {
        if (code.isAlive()) {
            code.statBegin(tree.pos);
            genDef(tree, env);
        } else if (env.info.isSwitch && tree.hasTag(VARDEF)) {
            // variables whose declarations are in a switch
            // can be used even if the decl is unreachable.
            code.newLocal(((JCVariableDecl) tree).sym);
        }
    }

    
Derived visitor method: check whether CharacterRangeTable
 should be emitted, if so, put a new entry into CRTable
 and call method to generate bytecode.
 If not, just call method to generate bytecode.
 @see    #genStats(List, Env)
 @param  trees    The list of trees to be visited.
 @param  env      The environment to use.
 @param  crtFlags The CharacterRangeTable flags
                  indicating type of the entry.
/** Derived visitor method: check whether CharacterRangeTable
     *  should be emitted, if so, put a new entry into CRTable
     *  and call method to generate bytecode.
     *  If not, just call method to generate bytecode.
     *  @see    #genStats(List, Env)
     *
     *  @param  trees    The list of trees to be visited.
     *  @param  env      The environment to use.
     *  @param  crtFlags The CharacterRangeTable flags
     *                   indicating type of the entry.
     */
    public void genStats(List<JCStatement> trees, Env<GenContext> env, int crtFlags) {
        if (!genCrt) {
            genStats(trees, env);
            return;
        }
        if (trees.length() == 1) {        // mark one statement with the flags
            genStat(trees.head, env, crtFlags | CRT_STATEMENT);
        } else {
            int startpc = code.curCP();
            genStats(trees, env);
            code.crt.put(trees, crtFlags, startpc, code.curCP());
        }
    }

    
Derived visitor method: generate code for a list of statements.
/** Derived visitor method: generate code for a list of statements.
     */
    public void genStats(List<? extends JCTree> trees, Env<GenContext> env) {
        for (List<? extends JCTree> l = trees; l.nonEmpty(); l = l.tail)
            genStat(l.head, env, CRT_STATEMENT);
    }

    
Derived visitor method: check whether CharacterRangeTable
 should be emitted, if so, put a new entry into CRTable
 and call method to generate bytecode.
 If not, just call method to generate bytecode.
 @see    #genCond(JCTree,boolean)
 @param  tree     The tree to be visited.
 @param  crtFlags The CharacterRangeTable flags
                  indicating type of the entry.
/** Derived visitor method: check whether CharacterRangeTable
     *  should be emitted, if so, put a new entry into CRTable
     *  and call method to generate bytecode.
     *  If not, just call method to generate bytecode.
     *  @see    #genCond(JCTree,boolean)
     *
     *  @param  tree     The tree to be visited.
     *  @param  crtFlags The CharacterRangeTable flags
     *                   indicating type of the entry.
     */
    public CondItem genCond(JCTree tree, int crtFlags) {
        if (!genCrt) return genCond(tree, false);
        int startpc = code.curCP();
        CondItem item = genCond(tree, (crtFlags & CRT_FLOW_CONTROLLER) != 0);
        code.crt.put(tree, crtFlags, startpc, code.curCP());
        return item;
    }

    
Derived visitor method: generate code for a boolean
 expression in a control-flow context.
 @param _tree         The expression to be visited.
 @param markBranches The flag to indicate that the condition is
                     a flow controller so produced conditions
                     should contain a proper tree to generate
                     CharacterRangeTable branches for them.
/** Derived visitor method: generate code for a boolean
     *  expression in a control-flow context.
     *  @param _tree         The expression to be visited.
     *  @param markBranches The flag to indicate that the condition is
     *                      a flow controller so produced conditions
     *                      should contain a proper tree to generate
     *                      CharacterRangeTable branches for them.
     */
    public CondItem genCond(JCTree _tree, boolean markBranches) {
        JCTree inner_tree = TreeInfo.skipParens(_tree);
        if (inner_tree.hasTag(CONDEXPR)) {
            JCConditional tree = (JCConditional)inner_tree;
            CondItem cond = genCond(tree.cond, CRT_FLOW_CONTROLLER);
            if (cond.isTrue()) {
                code.resolve(cond.trueJumps);
                CondItem result = genCond(tree.truepart, CRT_FLOW_TARGET);
                if (markBranches) result.tree = tree.truepart;
                return result;
            }
            if (cond.isFalse()) {
                code.resolve(cond.falseJumps);
                CondItem result = genCond(tree.falsepart, CRT_FLOW_TARGET);
                if (markBranches) result.tree = tree.falsepart;
                return result;
            }
            Chain secondJumps = cond.jumpFalse();
            code.resolve(cond.trueJumps);
            CondItem first = genCond(tree.truepart, CRT_FLOW_TARGET);
            if (markBranches) first.tree = tree.truepart;
            Chain falseJumps = first.jumpFalse();
            code.resolve(first.trueJumps);
            Chain trueJumps = code.branch(goto_);
            code.resolve(secondJumps);
            CondItem second = genCond(tree.falsepart, CRT_FLOW_TARGET);
            CondItem result = items.makeCondItem(second.opcode,
                                      Code.mergeChains(trueJumps, second.trueJumps),
                                      Code.mergeChains(falseJumps, second.falseJumps));
            if (markBranches) result.tree = tree.falsepart;
            return result;
        } else if (inner_tree.hasTag(SWITCH_EXPRESSION)) {
            boolean prevInCondSwitchExpression = inCondSwitchExpression;
            Chain prevSwitchExpressionTrueChain = switchExpressionTrueChain;
            Chain prevSwitchExpressionFalseChain = switchExpressionFalseChain;
            try {
                inCondSwitchExpression = true;
                switchExpressionTrueChain = null;
                switchExpressionFalseChain = null;
                try {
                    doHandleSwitchExpression((JCSwitchExpression) inner_tree);
                } catch (CompletionFailure ex) {
                    chk.completionError(_tree.pos(), ex);
                    code.state.stacksize = 1;
                }
                CondItem result = items.makeCondItem(goto_,
                                                     switchExpressionTrueChain,
                                                     switchExpressionFalseChain);
                if (markBranches) result.tree = _tree;
                return result;
            } finally {
                inCondSwitchExpression = prevInCondSwitchExpression;
                switchExpressionTrueChain = prevSwitchExpressionTrueChain;
                switchExpressionFalseChain = prevSwitchExpressionFalseChain;
            }
        } else if (inner_tree.hasTag(LETEXPR) && ((LetExpr) inner_tree).needsCond) {
            LetExpr tree = (LetExpr) inner_tree;
            int limit = code.nextreg;
            int prevLetExprStart = code.setLetExprStackPos(code.state.stacksize);
            try {
                genStats(tree.defs, env);
            } finally {
                code.setLetExprStackPos(prevLetExprStart);
            }
            CondItem result = genCond(tree.expr, markBranches);
            code.endScopes(limit);
            return result;
        } else {
            CondItem result = genExpr(_tree, syms.booleanType).mkCond();
            if (markBranches) result.tree = _tree;
            return result;
        }
    }

    public Code getCode() {
        return code;
    }

    public Items getItems() {
        return items;
    }

    public Env<AttrContext> getAttrEnv() {
        return attrEnv;
    }

    
Visitor class for expressions which might be constant expressions.
 This class is a subset of TreeScanner. Intended to visit trees pruned by
 Lower as long as constant expressions looking for references to any
 ClassSymbol. Any such reference will be added to the constant pool so
 automated tools can detect class dependencies better.
/** Visitor class for expressions which might be constant expressions.
     *  This class is a subset of TreeScanner. Intended to visit trees pruned by
     *  Lower as long as constant expressions looking for references to any
     *  ClassSymbol. Any such reference will be added to the constant pool so
     *  automated tools can detect class dependencies better.
     */
    class ClassReferenceVisitor extends JCTree.Visitor {

        @Override
        public void visitTree(JCTree tree) {}

        @Override
        public void visitBinary(JCBinary tree) {
            tree.lhs.accept(this);
            tree.rhs.accept(this);
        }

        @Override
        public void visitSelect(JCFieldAccess tree) {
            if (tree.selected.type.hasTag(CLASS)) {
                makeRef(tree.selected.pos(), tree.selected.type);
            }
        }

        @Override
        public void visitIdent(JCIdent tree) {
            if (tree.sym.owner instanceof ClassSymbol) {
                pool.put(tree.sym.owner);
            }
        }

        @Override
        public void visitConditional(JCConditional tree) {
            tree.cond.accept(this);
            tree.truepart.accept(this);
            tree.falsepart.accept(this);
        }

        @Override
        public void visitUnary(JCUnary tree) {
            tree.arg.accept(this);
        }

        @Override
        public void visitParens(JCParens tree) {
            tree.expr.accept(this);
        }

        @Override
        public void visitTypeCast(JCTypeCast tree) {
            tree.expr.accept(this);
        }
    }

    private ClassReferenceVisitor classReferenceVisitor = new ClassReferenceVisitor();

    
Visitor method: generate code for an expression, catching and reporting
 any completion failures.
 @param tree    The expression to be visited.
 @param pt      The expression's expected type (proto-type).
/** Visitor method: generate code for an expression, catching and reporting
     *  any completion failures.
     *  @param tree    The expression to be visited.
     *  @param pt      The expression's expected type (proto-type).
     */
    public Item genExpr(JCTree tree, Type pt) {
        Type prevPt = this.pt;
        try {
            if (tree.type.constValue() != null) {
                // Short circuit any expressions which are constants
                tree.accept(classReferenceVisitor);
                checkStringConstant(tree.pos(), tree.type.constValue());
                result = items.makeImmediateItem(tree.type, tree.type.constValue());
            } else {
                this.pt = pt;
                tree.accept(this);
            }
            return result.coerce(pt);
        } catch (CompletionFailure ex) {
            chk.completionError(tree.pos(), ex);
            code.state.stacksize = 1;
            return items.makeStackItem(pt);
        } finally {
            this.pt = prevPt;
        }
    }

    
Derived visitor method: generate code for a list of method arguments.
 @param trees    The argument expressions to be visited.
 @param pts      The expression's expected types (i.e. the formal parameter
                 types of the invoked method).
/** Derived visitor method: generate code for a list of method arguments.
     *  @param trees    The argument expressions to be visited.
     *  @param pts      The expression's expected types (i.e. the formal parameter
     *                  types of the invoked method).
     */
    public void genArgs(List<JCExpression> trees, List<Type> pts) {
        for (List<JCExpression> l = trees; l.nonEmpty(); l = l.tail) {
            genExpr(l.head, pts.head).load();
            pts = pts.tail;
        }
        // require lists be of same length
        Assert.check(pts.isEmpty());
    }

/* ************************************************************************
 * Visitor methods for statements and definitions
 *************************************************************************/

    
Thrown when the byte code size exceeds limit.
/** Thrown when the byte code size exceeds limit.
     */
    public static class CodeSizeOverflow extends RuntimeException {
        private static final long serialVersionUID = 0;
        public CodeSizeOverflow() {}
    }

    public void visitMethodDef(JCMethodDecl tree) {
        // Create a new local environment that points pack at method
        // definition.
        Env<GenContext> localEnv = env.dup(tree);
        localEnv.enclMethod = tree;
        // The expected type of every return statement in this method
        // is the method's return type.
        this.pt = tree.sym.erasure(types).getReturnType();

        checkDimension(tree.pos(), tree.sym.erasure(types));
        genMethod(tree, localEnv, false);
    }
//where
        
Generate code for a method.
 @param tree     The tree representing the method definition.
 @param env      The environment current for the method body.
 @param fatcode  A flag that indicates whether all jumps are
                 within 32K.  We first invoke this method under
                 the assumption that fatcode == false, i.e. all
                 jumps are within 32K.  If this fails, fatcode
                 is set to true and we try again.
/** Generate code for a method.
         *  @param tree     The tree representing the method definition.
         *  @param env      The environment current for the method body.
         *  @param fatcode  A flag that indicates whether all jumps are
         *                  within 32K.  We first invoke this method under
         *                  the assumption that fatcode == false, i.e. all
         *                  jumps are within 32K.  If this fails, fatcode
         *                  is set to true and we try again.
         */
        void genMethod(JCMethodDecl tree, Env<GenContext> env, boolean fatcode) {
            MethodSymbol meth = tree.sym;
            int extras = 0;
            // Count up extra parameters
            if (meth.isConstructor()) {
                extras++;
                if (meth.enclClass().isInner() &&
                    !meth.enclClass().isStatic()) {
                    extras++;
                }
            } else if ((tree.mods.flags & STATIC) == 0) {
                extras++;
            }
            //      System.err.println("Generating " + meth + " in " + meth.owner); //DEBUG
            if (Code.width(types.erasure(env.enclMethod.sym.type).getParameterTypes()) + extras >
                ClassFile.MAX_PARAMETERS) {
                log.error(tree.pos(), Errors.LimitParameters);
                nerrs++;
            }

            else if (tree.body != null) {
                // Create a new code structure and initialize it.
                int startpcCrt = initCode(tree, env, fatcode);

                try {
                    genStat(tree.body, env);
                } catch (CodeSizeOverflow e) {
                    // Failed due to code limit, try again with jsr/ret
                    startpcCrt = initCode(tree, env, fatcode);
                    genStat(tree.body, env);
                }

                if (code.state.stacksize != 0) {
                    log.error(tree.body.pos(), Errors.StackSimError(tree.sym));
                    throw new AssertionError();
                }

                // If last statement could complete normally, insert a
                // return at the end.
                if (code.isAlive()) {
                    code.statBegin(TreeInfo.endPos(tree.body));
                    if (env.enclMethod == null ||
                        env.enclMethod.sym.type.getReturnType().hasTag(VOID)) {
                        code.emitop0(return_);
                    } else {
                        // sometime dead code seems alive (4415991);
                        // generate a small loop instead
                        int startpc = code.entryPoint();
                        CondItem c = items.makeCondItem(goto_);
                        code.resolve(c.jumpTrue(), startpc);
                    }
                }
                if (genCrt)
                    code.crt.put(tree.body,
                                 CRT_BLOCK,
                                 startpcCrt,
                                 code.curCP());

                code.endScopes(0);

                // If we exceeded limits, panic
                if (code.checkLimits(tree.pos(), log)) {
                    nerrs++;
                    return;
                }

                // If we generated short code but got a long jump, do it again
                // with fatCode = true.
                if (!fatcode && code.fatcode) genMethod(tree, env, true);

                // Clean up
                if(stackMap == StackMapFormat.JSR202) {
                    code.lastFrame = null;
                    code.frameBeforeLast = null;
                }

                // Compress exception table
                code.compressCatchTable();

                // Fill in type annotation positions for exception parameters
                code.fillExceptionParameterPositions();
            }
        }

        private int initCode(JCMethodDecl tree, Env<GenContext> env, boolean fatcode) {
            MethodSymbol meth = tree.sym;

            // Create a new code structure.
            meth.code = code = new Code(meth,
                                        fatcode,
                                        lineDebugInfo ? toplevel.lineMap : null,
                                        varDebugInfo,
                                        stackMap,
                                        debugCode,
                                        genCrt ? new CRTable(tree, env.toplevel.endPositions)
                                               : null,
                                        syms,
                                        types,
                                        pool);
            items = new Items(pool, code, syms, types);
            if (code.debugCode) {
                System.err.println(meth + " for body " + tree);
            }

            // If method is not static, create a new local variable address
            // for `this'.
            if ((tree.mods.flags & STATIC) == 0) {
                Type selfType = meth.owner.type;
                if (meth.isConstructor() && selfType != syms.objectType)
                    selfType = UninitializedType.uninitializedThis(selfType);
                code.setDefined(
                        code.newLocal(
                            new VarSymbol(FINAL, names._this, selfType, meth.owner)));
            }

            // Mark all parameters as defined from the beginning of
            // the method.
            for (List<JCVariableDecl> l = tree.params; l.nonEmpty(); l = l.tail) {
                checkDimension(l.head.pos(), l.head.sym.type);
                code.setDefined(code.newLocal(l.head.sym));
            }

            // Get ready to generate code for method body.
            int startpcCrt = genCrt ? code.curCP() : 0;
            code.entryPoint();

            // Suppress initial stackmap
            code.pendingStackMap = false;

            return startpcCrt;
        }

    public void visitVarDef(JCVariableDecl tree) {
        VarSymbol v = tree.sym;
        if (tree.init != null) {
            checkStringConstant(tree.init.pos(), v.getConstValue());
            if (v.getConstValue() == null || varDebugInfo) {
                Assert.check(code.isStatementStart());
                code.newLocal(v);
                genExpr(tree.init, v.erasure(types)).load();
                items.makeLocalItem(v).store();
                Assert.check(code.isStatementStart());
            }
        } else {
            code.newLocal(v);
        }
        checkDimension(tree.pos(), v.type);
    }

    public void visitSkip(JCSkip tree) {
    }

    public void visitBlock(JCBlock tree) {
        int limit = code.nextreg;
        Env<GenContext> localEnv = env.dup(tree, new GenContext());
        genStats(tree.stats, localEnv);
        // End the scope of all block-local variables in variable info.
        if (!env.tree.hasTag(METHODDEF)) {
            code.statBegin(tree.endpos);
            code.endScopes(limit);
            code.pendingStatPos = Position.NOPOS;
        }
    }

    public void visitDoLoop(JCDoWhileLoop tree) {
        genLoop(tree, tree.body, tree.cond, List.nil(), false);
    }

    public void visitWhileLoop(JCWhileLoop tree) {
        genLoop(tree, tree.body, tree.cond, List.nil(), true);
    }

    public void visitForLoop(JCForLoop tree) {
        int limit = code.nextreg;
        genStats(tree.init, env);
        genLoop(tree, tree.body, tree.cond, tree.step, true);
        code.endScopes(limit);
    }
    //where
        
Generate code for a loop.
 @param loop       The tree representing the loop.
 @param body       The loop's body.
 @param cond       The loop's controling condition.
 @param step       "Step" statements to be inserted at end of
                   each iteration.
 @param testFirst  True if the loop test belongs before the body.
/** Generate code for a loop.
         *  @param loop       The tree representing the loop.
         *  @param body       The loop's body.
         *  @param cond       The loop's controling condition.
         *  @param step       "Step" statements to be inserted at end of
         *                    each iteration.
         *  @param testFirst  True if the loop test belongs before the body.
         */
        private void genLoop(JCStatement loop,
                             JCStatement body,
                             JCExpression cond,
                             List<JCExpressionStatement> step,
                             boolean testFirst) {
            Env<GenContext> loopEnv = env.dup(loop, new GenContext());
            int startpc = code.entryPoint();
            if (testFirst) { //while or for loop
                CondItem c;
                if (cond != null) {
                    code.statBegin(cond.pos);
                    Assert.check(code.isStatementStart());
                    c = genCond(TreeInfo.skipParens(cond), CRT_FLOW_CONTROLLER);
                } else {
                    c = items.makeCondItem(goto_);
                }
                Chain loopDone = c.jumpFalse();
                code.resolve(c.trueJumps);
                Assert.check(code.isStatementStart());
                genStat(body, loopEnv, CRT_STATEMENT | CRT_FLOW_TARGET);
                code.resolve(loopEnv.info.cont);
                genStats(step, loopEnv);
                code.resolve(code.branch(goto_), startpc);
                code.resolve(loopDone);
            } else {
                genStat(body, loopEnv, CRT_STATEMENT | CRT_FLOW_TARGET);
                code.resolve(loopEnv.info.cont);
                genStats(step, loopEnv);
                if (code.isAlive()) {
                    CondItem c;
                    if (cond != null) {
                        code.statBegin(cond.pos);
                        Assert.check(code.isStatementStart());
                        c = genCond(TreeInfo.skipParens(cond), CRT_FLOW_CONTROLLER);
                    } else {
                        c = items.makeCondItem(goto_);
                    }
                    code.resolve(c.jumpTrue(), startpc);
                    Assert.check(code.isStatementStart());
                    code.resolve(c.falseJumps);
                }
            }
            Chain exit = loopEnv.info.exit;
            if (exit != null) {
                code.resolve(exit);
                exit.state.defined.excludeFrom(code.nextreg);
            }
        }

    public void visitForeachLoop(JCEnhancedForLoop tree) {
        throw new AssertionError(); // should have been removed by Lower.
    }

    public void visitLabelled(JCLabeledStatement tree) {
        Env<GenContext> localEnv = env.dup(tree, new GenContext());
        genStat(tree.body, localEnv, CRT_STATEMENT);
        Chain exit = localEnv.info.exit;
        if (exit != null) {
            code.resolve(exit);
            exit.state.defined.excludeFrom(code.nextreg);
        }
    }

    public void visitSwitch(JCSwitch tree) {
        handleSwitch(tree, tree.selector, tree.cases);
    }

    @Override
    public void visitSwitchExpression(JCSwitchExpression tree) {
        code.resolvePending();
        boolean prevInCondSwitchExpression = inCondSwitchExpression;
        try {
            inCondSwitchExpression = false;
            doHandleSwitchExpression(tree);
        } finally {
            inCondSwitchExpression = prevInCondSwitchExpression;
        }
        result = items.makeStackItem(pt);
    }

    private void doHandleSwitchExpression(JCSwitchExpression tree) {
        List<LocalItem> prevStackBeforeSwitchExpression = stackBeforeSwitchExpression;
        int limit = code.nextreg;
        try {
            stackBeforeSwitchExpression = List.nil();
            if (hasTry(tree)) {
                //if the switch expression contains try-catch, the catch handlers need to have
                //an empty stack. So stash whole stack to local variables, and restore it before
                //breaks:
                while (code.state.stacksize > 0) {
                    Type type = code.state.peek();
                    Name varName = names.fromString(target.syntheticNameChar() +
                                                    "stack" +
                                                    target.syntheticNameChar() +
                                                    tree.pos +
                                                    target.syntheticNameChar() +
                                                    code.state.stacksize);
                    VarSymbol var = new VarSymbol(Flags.SYNTHETIC, varName, type,
                                                  this.env.enclMethod.sym);
                    LocalItem item = items.new LocalItem(type, code.newLocal(var));
                    stackBeforeSwitchExpression = stackBeforeSwitchExpression.prepend(item);
                    item.store();
                }
            }
            int prevLetExprStart = code.setLetExprStackPos(code.state.stacksize);
            try {
                handleSwitch(tree, tree.selector, tree.cases);
            } finally {
                code.setLetExprStackPos(prevLetExprStart);
            }
        } finally {
            stackBeforeSwitchExpression = prevStackBeforeSwitchExpression;
            code.endScopes(limit);
        }
    }
    //where:
        private boolean hasTry(JCSwitchExpression tree) {
            boolean[] hasTry = new boolean[1];
            new TreeScanner() {
                @Override
                public void visitTry(JCTry tree) {
                    hasTry[0] = true;
                }

                @Override
                public void visitClassDef(JCClassDecl tree) {
                }

                @Override
                public void visitLambda(JCLambda tree) {
                }
            }.scan(tree);
            return hasTry[0];
        }

    private void handleSwitch(JCTree swtch, JCExpression selector, List<JCCase> cases) {
        int limit = code.nextreg;
        Assert.check(!selector.type.hasTag(CLASS));
        int startpcCrt = genCrt ? code.curCP() : 0;
        Assert.check(code.isStatementStart());
        Item sel = genExpr(selector, syms.intType);
        if (cases.isEmpty()) {
            // We are seeing:  switch <sel> {}
            sel.load().drop();
            if (genCrt)
                code.crt.put(TreeInfo.skipParens(selector),
                             CRT_FLOW_CONTROLLER, startpcCrt, code.curCP());
        } else {
            // We are seeing a nonempty switch.
            sel.load();
            if (genCrt)
                code.crt.put(TreeInfo.skipParens(selector),
                             CRT_FLOW_CONTROLLER, startpcCrt, code.curCP());
            Env<GenContext> switchEnv = env.dup(swtch, new GenContext());
            switchEnv.info.isSwitch = true;

            // Compute number of labels and minimum and maximum label values.
            // For each case, store its label in an array.
            int lo = Integer.MAX_VALUE;  // minimum label.
            int hi = Integer.MIN_VALUE;  // maximum label.
            int nlabels = 0;               // number of labels.

            int[] labels = new int[cases.length()];  // the label array.
            int defaultIndex = -1;     // the index of the default clause.

            List<JCCase> l = cases;
            for (int i = 0; i < labels.length; i++) {
                if (l.head.pats.nonEmpty()) {
                    Assert.check(l.head.pats.size() == 1);
                    int val = ((Number)l.head.pats.head.type.constValue()).intValue();
                    labels[i] = val;
                    if (val < lo) lo = val;
                    if (hi < val) hi = val;
                    nlabels++;
                } else {
                    Assert.check(defaultIndex == -1);
                    defaultIndex = i;
                }
                l = l.tail;
            }

            // Determine whether to issue a tableswitch or a lookupswitch
            // instruction.
            long table_space_cost = 4 + ((long) hi - lo + 1); // words
            long table_time_cost = 3; // comparisons
            long lookup_space_cost = 3 + 2 * (long) nlabels;
            long lookup_time_cost = nlabels;
            int opcode =
                nlabels > 0 &&
                table_space_cost + 3 * table_time_cost <=
                lookup_space_cost + 3 * lookup_time_cost
                ?
                tableswitch : lookupswitch;

            int startpc = code.curCP();    // the position of the selector operation
            code.emitop0(opcode);
            code.align(4);
            int tableBase = code.curCP();  // the start of the jump table
            int[] offsets = null;          // a table of offsets for a lookupswitch
            code.emit4(-1);                // leave space for default offset
            if (opcode == tableswitch) {
                code.emit4(lo);            // minimum label
                code.emit4(hi);            // maximum label
                for (long i = lo; i <= hi; i++) {  // leave space for jump table
                    code.emit4(-1);
                }
            } else {
                code.emit4(nlabels);    // number of labels
                for (int i = 0; i < nlabels; i++) {
                    code.emit4(-1); code.emit4(-1); // leave space for lookup table
                }
                offsets = new int[labels.length];
            }
            Code.State stateSwitch = code.state.dup();
            code.markDead();

            // For each case do:
            l = cases;
            for (int i = 0; i < labels.length; i++) {
                JCCase c = l.head;
                l = l.tail;

                int pc = code.entryPoint(stateSwitch);
                // Insert offset directly into code or else into the
                // offsets table.
                if (i != defaultIndex) {
                    if (opcode == tableswitch) {
                        code.put4(
                            tableBase + 4 * (labels[i] - lo + 3),
                            pc - startpc);
                    } else {
                        offsets[i] = pc - startpc;
                    }
                } else {
                    code.put4(tableBase, pc - startpc);
                }

                // Generate code for the statements in this case.
                genStats(c.stats, switchEnv, CRT_FLOW_TARGET);
            }

            // Resolve all breaks.
            Chain exit = switchEnv.info.exit;
            if  (exit != null) {
                code.resolve(exit);
                exit.state.defined.excludeFrom(limit);
            }

            // If we have not set the default offset, we do so now.
            if (code.get4(tableBase) == -1) {
                code.put4(tableBase, code.entryPoint(stateSwitch) - startpc);
            }

            if (opcode == tableswitch) {
                // Let any unfilled slots point to the default case.
                int defaultOffset = code.get4(tableBase);
                for (long i = lo; i <= hi; i++) {
                    int t = (int)(tableBase + 4 * (i - lo + 3));
                    if (code.get4(t) == -1)
                        code.put4(t, defaultOffset);
                }
            } else {
                // Sort non-default offsets and copy into lookup table.
                if (defaultIndex >= 0)
                    for (int i = defaultIndex; i < labels.length - 1; i++) {
                        labels[i] = labels[i+1];
                        offsets[i] = offsets[i+1];
                    }
                if (nlabels > 0)
                    qsort2(labels, offsets, 0, nlabels - 1);
                for (int i = 0; i < nlabels; i++) {
                    int caseidx = tableBase + 8 * (i + 1);
                    code.put4(caseidx, labels[i]);
                    code.put4(caseidx + 4, offsets[i]);
                }
            }
        }
        code.endScopes(limit);
    }
//where
        
Sort (int) arrays of keys and values
/** Sort (int) arrays of keys and values
         */
       static void qsort2(int[] keys, int[] values, int lo, int hi) {
            int i = lo;
            int j = hi;
            int pivot = keys[(i+j)/2];
            do {
                while (keys[i] < pivot) i++;
                while (pivot < keys[j]) j--;
                if (i <= j) {
                    int temp1 = keys[i];
                    keys[i] = keys[j];
                    keys[j] = temp1;
                    int temp2 = values[i];
                    values[i] = values[j];
                    values[j] = temp2;
                    i++;
                    j--;
                }
            } while (i <= j);
            if (lo < j) qsort2(keys, values, lo, j);
            if (i < hi) qsort2(keys, values, i, hi);
        }

    public void visitSynchronized(JCSynchronized tree) {
        int limit = code.nextreg;
        // Generate code to evaluate lock and save in temporary variable.
        final LocalItem lockVar = makeTemp(syms.objectType);
        Assert.check(code.isStatementStart());
        genExpr(tree.lock, tree.lock.type).load().duplicate();
        lockVar.store();

        // Generate code to enter monitor.
        code.emitop0(monitorenter);
        code.state.lock(lockVar.reg);

        // Generate code for a try statement with given body, no catch clauses
        // in a new environment with the "exit-monitor" operation as finalizer.
        final Env<GenContext> syncEnv = env.dup(tree, new GenContext());
        syncEnv.info.finalize = new GenFinalizer() {
            void gen() {
                genLast();
                Assert.check(syncEnv.info.gaps.length() % 2 == 0);
                syncEnv.info.gaps.append(code.curCP());
            }
            void genLast() {
                if (code.isAlive()) {
                    lockVar.load();
                    code.emitop0(monitorexit);
                    code.state.unlock(lockVar.reg);
                }
            }
        };
        syncEnv.info.gaps = new ListBuffer<>();
        genTry(tree.body, List.nil(), syncEnv);
        code.endScopes(limit);
    }

    public void visitTry(final JCTry tree) {
        // Generate code for a try statement with given body and catch clauses,
        // in a new environment which calls the finally block if there is one.
        final Env<GenContext> tryEnv = env.dup(tree, new GenContext());
        final Env<GenContext> oldEnv = env;
        tryEnv.info.finalize = new GenFinalizer() {
            void gen() {
                Assert.check(tryEnv.info.gaps.length() % 2 == 0);
                tryEnv.info.gaps.append(code.curCP());
                genLast();
            }
            void genLast() {
                if (tree.finalizer != null)
                    genStat(tree.finalizer, oldEnv, CRT_BLOCK);
            }
            boolean hasFinalizer() {
                return tree.finalizer != null;
            }

            @Override
            void afterBody() {
                if (tree.finalizer != null && (tree.finalizer.flags & BODY_ONLY_FINALIZE) != 0) {
                    //for body-only finally, remove the GenFinalizer after try body
                    //so that the finally is not generated to catch bodies:
                    tryEnv.info.finalize = null;
                }
            }

        };
        tryEnv.info.gaps = new ListBuffer<>();
        genTry(tree.body, tree.catchers, tryEnv);
    }
    //where
        
Generate code for a try or synchronized statement
 @param body      The body of the try or synchronized statement.
 @param catchers  The lis of catch clauses.
 @param env       the environment current for the body.
/** Generate code for a try or synchronized statement
         *  @param body      The body of the try or synchronized statement.
         *  @param catchers  The lis of catch clauses.
         *  @param env       the environment current for the body.
         */
        void genTry(JCTree body, List<JCCatch> catchers, Env<GenContext> env) {
            int limit = code.nextreg;
            int startpc = code.curCP();
            Code.State stateTry = code.state.dup();
            genStat(body, env, CRT_BLOCK);
            int endpc = code.curCP();
            List<Integer> gaps = env.info.gaps.toList();
            code.statBegin(TreeInfo.endPos(body));
            genFinalizer(env);
            code.statBegin(TreeInfo.endPos(env.tree));
            Chain exitChain = code.branch(goto_);
            endFinalizerGap(env);
            env.info.finalize.afterBody();
            boolean hasFinalizer =
                env.info.finalize != null &&
                env.info.finalize.hasFinalizer();
            if (startpc != endpc) for (List<JCCatch> l = catchers; l.nonEmpty(); l = l.tail) {
                // start off with exception on stack
                code.entryPoint(stateTry, l.head.param.sym.type);
                genCatch(l.head, env, startpc, endpc, gaps);
                genFinalizer(env);
                if (hasFinalizer || l.tail.nonEmpty()) {
                    code.statBegin(TreeInfo.endPos(env.tree));
                    exitChain = Code.mergeChains(exitChain,
                                                 code.branch(goto_));
                }
                endFinalizerGap(env);
            }
            if (hasFinalizer) {
                // Create a new register segement to avoid allocating
                // the same variables in finalizers and other statements.
                code.newRegSegment();

                // Add a catch-all clause.

                // start off with exception on stack
                int catchallpc = code.entryPoint(stateTry, syms.throwableType);

                // Register all exception ranges for catch all clause.
                // The range of the catch all clause is from the beginning
                // of the try or synchronized block until the present
                // code pointer excluding all gaps in the current
                // environment's GenContext.
                int startseg = startpc;
                while (env.info.gaps.nonEmpty()) {
                    int endseg = env.info.gaps.next().intValue();
                    registerCatch(body.pos(), startseg, endseg,
                                  catchallpc, 0);
                    startseg = env.info.gaps.next().intValue();
                }
                code.statBegin(TreeInfo.finalizerPos(env.tree, PosKind.FIRST_STAT_POS));
                code.markStatBegin();

                Item excVar = makeTemp(syms.throwableType);
                excVar.store();
                genFinalizer(env);
                code.resolvePending();
                code.statBegin(TreeInfo.finalizerPos(env.tree, PosKind.END_POS));
                code.markStatBegin();

                excVar.load();
                registerCatch(body.pos(), startseg,
                              env.info.gaps.next().intValue(),
                              catchallpc, 0);
                code.emitop0(athrow);
                code.markDead();

                // If there are jsr's to this finalizer, ...
                if (env.info.cont != null) {
                    // Resolve all jsr's.
                    code.resolve(env.info.cont);

                    // Mark statement line number
                    code.statBegin(TreeInfo.finalizerPos(env.tree, PosKind.FIRST_STAT_POS));
                    code.markStatBegin();

                    // Save return address.
                    LocalItem retVar = makeTemp(syms.throwableType);
                    retVar.store();

                    // Generate finalizer code.
                    env.info.finalize.genLast();

                    // Return.
                    code.emitop1w(ret, retVar.reg);
                    code.markDead();
                }
            }
            // Resolve all breaks.
            code.resolve(exitChain);

            code.endScopes(limit);
        }

        
Generate code for a catch clause.
 @param tree     The catch clause.
 @param env      The environment current in the enclosing try.
 @param startpc  Start pc of try-block.
 @param endpc    End pc of try-block.
/** Generate code for a catch clause.
         *  @param tree     The catch clause.
         *  @param env      The environment current in the enclosing try.
         *  @param startpc  Start pc of try-block.
         *  @param endpc    End pc of try-block.
         */
        void genCatch(JCCatch tree,
                      Env<GenContext> env,
                      int startpc, int endpc,
                      List<Integer> gaps) {
            if (startpc != endpc) {
                List<Pair<List<Attribute.TypeCompound>, JCExpression>> catchTypeExprs
                        = catchTypesWithAnnotations(tree);
                while (gaps.nonEmpty()) {
                    for (Pair<List<Attribute.TypeCompound>, JCExpression> subCatch1 : catchTypeExprs) {
                        JCExpression subCatch = subCatch1.snd;
                        int catchType = makeRef(tree.pos(), subCatch.type);
                        int end = gaps.head.intValue();
                        registerCatch(tree.pos(),
                                      startpc,  end, code.curCP(),
                                      catchType);
                        for (Attribute.TypeCompound tc :  subCatch1.fst) {
                                tc.position.setCatchInfo(catchType, startpc);
                        }
                    }
                    gaps = gaps.tail;
                    startpc = gaps.head.intValue();
                    gaps = gaps.tail;
                }
                if (startpc < endpc) {
                    for (Pair<List<Attribute.TypeCompound>, JCExpression> subCatch1 : catchTypeExprs) {
                        JCExpression subCatch = subCatch1.snd;
                        int catchType = makeRef(tree.pos(), subCatch.type);
                        registerCatch(tree.pos(),
                                      startpc, endpc, code.curCP(),
                                      catchType);
                        for (Attribute.TypeCompound tc :  subCatch1.fst) {
                            tc.position.setCatchInfo(catchType, startpc);
                        }
                    }
                }
                VarSymbol exparam = tree.param.sym;
                code.statBegin(tree.pos);
                code.markStatBegin();
                int limit = code.nextreg;
                code.newLocal(exparam);
                items.makeLocalItem(exparam).store();
                code.statBegin(TreeInfo.firstStatPos(tree.body));
                genStat(tree.body, env, CRT_BLOCK);
                code.endScopes(limit);
                code.statBegin(TreeInfo.endPos(tree.body));
            }
        }
        // where
        List<Pair<List<Attribute.TypeCompound>, JCExpression>> catchTypesWithAnnotations(JCCatch tree) {
            return TreeInfo.isMultiCatch(tree) ?
                    catchTypesWithAnnotationsFromMulticatch((JCTypeUnion)tree.param.vartype, tree.param.sym.getRawTypeAttributes()) :
                    List.of(new Pair<>(tree.param.sym.getRawTypeAttributes(), tree.param.vartype));
        }
        // where
        List<Pair<List<Attribute.TypeCompound>, JCExpression>> catchTypesWithAnnotationsFromMulticatch(JCTypeUnion tree, List<TypeCompound> first) {
            List<JCExpression> alts = tree.alternatives;
            List<Pair<List<TypeCompound>, JCExpression>> res = List.of(new Pair<>(first, alts.head));
            alts = alts.tail;

            while(alts != null && alts.head != null) {
                JCExpression alt = alts.head;
                if (alt instanceof JCAnnotatedType) {
                    JCAnnotatedType a = (JCAnnotatedType)alt;
                    res = res.prepend(new Pair<>(annotate.fromAnnotations(a.annotations), alt));
                } else {
                    res = res.prepend(new Pair<>(List.nil(), alt));
                }
                alts = alts.tail;
            }
            return res.reverse();
        }

        
Register a catch clause in the "Exceptions" code-attribute.
/** Register a catch clause in the "Exceptions" code-attribute.
         */
        void registerCatch(DiagnosticPosition pos,
                           int startpc, int endpc,
                           int handler_pc, int catch_type) {
            char startpc1 = (char)startpc;
            char endpc1 = (char)endpc;
            char handler_pc1 = (char)handler_pc;
            if (startpc1 == startpc &&
                endpc1 == endpc &&
                handler_pc1 == handler_pc) {
                code.addCatch(startpc1, endpc1, handler_pc1,
                              (char)catch_type);
            } else {
                log.error(pos, Errors.LimitCodeTooLargeForTryStmt);
                nerrs++;
            }
        }

    public void visitIf(JCIf tree) {
        int limit = code.nextreg;
        Chain thenExit = null;
        Assert.check(code.isStatementStart());
        CondItem c = genCond(TreeInfo.skipParens(tree.cond),
                             CRT_FLOW_CONTROLLER);
        Chain elseChain = c.jumpFalse();
        Assert.check(code.isStatementStart());
        if (!c.isFalse()) {
            code.resolve(c.trueJumps);
            genStat(tree.thenpart, env, CRT_STATEMENT | CRT_FLOW_TARGET);
            thenExit = code.branch(goto_);
        }
        if (elseChain != null) {
            code.resolve(elseChain);
            if (tree.elsepart != null) {
                genStat(tree.elsepart, env,CRT_STATEMENT | CRT_FLOW_TARGET);
            }
        }
        code.resolve(thenExit);
        code.endScopes(limit);
        Assert.check(code.isStatementStart());
    }

    public void visitExec(JCExpressionStatement tree) {
        // Optimize x++ to ++x and x-- to --x.
        JCExpression e = tree.expr;
        switch (e.getTag()) {
            case POSTINC:
                ((JCUnary) e).setTag(PREINC);
                break;
            case POSTDEC:
                ((JCUnary) e).setTag(PREDEC);
                break;
        }
        Assert.check(code.isStatementStart());
        genExpr(tree.expr, tree.expr.type).drop();
        Assert.check(code.isStatementStart());
    }

    public void visitBreak(JCBreak tree) {
        Assert.check(code.isStatementStart());
        final Env<GenContext> targetEnv;
        if (tree.isValueBreak()) {
            //restore stack as it was before the switch expression:
            for (LocalItem li : stackBeforeSwitchExpression) {
                li.load();
            }
            if (inCondSwitchExpression) {
                CondItem value = genCond(tree.value, CRT_FLOW_TARGET);
                Chain falseJumps = value.jumpFalse();
                targetEnv = unwindBreak(tree);
                code.resolve(value.trueJumps);
                Chain trueJumps = code.branch(goto_);
                if (switchExpressionTrueChain == null) {
                    switchExpressionTrueChain = trueJumps;
                } else {
                    switchExpressionTrueChain =
                            Code.mergeChains(switchExpressionTrueChain, trueJumps);
                }
                if (switchExpressionFalseChain == null) {
                    switchExpressionFalseChain = falseJumps;
                } else {
                    switchExpressionFalseChain =
                            Code.mergeChains(switchExpressionFalseChain, falseJumps);
                }
            } else {
                genExpr(tree.value, pt).load();
                code.state.forceStackTop(tree.target.type);
                targetEnv = unwindBreak(tree);
                targetEnv.info.addExit(code.branch(goto_));
            }
        } else {
            targetEnv = unwindBreak(tree);
            targetEnv.info.addExit(code.branch(goto_));
        }
        endFinalizerGaps(env, targetEnv);
    }
    //where:
        private Env<GenContext> unwindBreak(JCBreak tree) {
            int tmpPos = code.pendingStatPos;
            Env<GenContext> targetEnv = unwind(tree.target, env);
            code.pendingStatPos = tmpPos;
            return targetEnv;
        }

    public void visitContinue(JCContinue tree) {
        int tmpPos = code.pendingStatPos;
        Env<GenContext> targetEnv = unwind(tree.target, env);
        code.pendingStatPos = tmpPos;
        Assert.check(code.isStatementStart());
        targetEnv.info.addCont(code.branch(goto_));
        endFinalizerGaps(env, targetEnv);
    }

    public void visitReturn(JCReturn tree) {
        int limit = code.nextreg;
        final Env<GenContext> targetEnv;

        /* Save and then restore the location of the return in case a finally
         * is expanded (with unwind()) in the middle of our bytecodes.
         */
        int tmpPos = code.pendingStatPos;
        if (tree.expr != null) {
            Assert.check(code.isStatementStart());
            Item r = genExpr(tree.expr, pt).load();
            if (hasFinally(env.enclMethod, env)) {
                r = makeTemp(pt);
                r.store();
            }
            targetEnv = unwind(env.enclMethod, env);
            code.pendingStatPos = tmpPos;
            r.load();
            code.emitop0(ireturn + Code.truncate(Code.typecode(pt)));
        } else {
            targetEnv = unwind(env.enclMethod, env);
            code.pendingStatPos = tmpPos;
            code.emitop0(return_);
        }
        endFinalizerGaps(env, targetEnv);
        code.endScopes(limit);
    }

    public void visitThrow(JCThrow tree) {
        Assert.check(code.isStatementStart());
        genExpr(tree.expr, tree.expr.type).load();
        code.emitop0(athrow);
        Assert.check(code.isStatementStart());
    }

/* ************************************************************************
 * Visitor methods for expressions
 *************************************************************************/

    public void visitApply(JCMethodInvocation tree) {
        setTypeAnnotationPositions(tree.pos);
        // Generate code for method.
        Item m = genExpr(tree.meth, methodType);
        // Generate code for all arguments, where the expected types are
        // the parameters of the method's external type (that is, any implicit
        // outer instance of a super(...) call appears as first parameter).
        MethodSymbol msym = (MethodSymbol)TreeInfo.symbol(tree.meth);
        genArgs(tree.args,
                msym.externalType(types).getParameterTypes());
        if (!msym.isDynamic()) {
            code.statBegin(tree.pos);
        }
        result = m.invoke();
    }

    public void visitConditional(JCConditional tree) {
        Chain thenExit = null;
        code.statBegin(tree.cond.pos);
        CondItem c = genCond(tree.cond, CRT_FLOW_CONTROLLER);
        Chain elseChain = c.jumpFalse();
        if (!c.isFalse()) {
            code.resolve(c.trueJumps);
            int startpc = genCrt ? code.curCP() : 0;
            code.statBegin(tree.truepart.pos);
            genExpr(tree.truepart, pt).load();
            code.state.forceStackTop(tree.type);
            if (genCrt) code.crt.put(tree.truepart, CRT_FLOW_TARGET,
                                     startpc, code.curCP());
            thenExit = code.branch(goto_);
        }
        if (elseChain != null) {
            code.resolve(elseChain);
            int startpc = genCrt ? code.curCP() : 0;
            code.statBegin(tree.falsepart.pos);
            genExpr(tree.falsepart, pt).load();
            code.state.forceStackTop(tree.type);
            if (genCrt) code.crt.put(tree.falsepart, CRT_FLOW_TARGET,
                                     startpc, code.curCP());
        }
        code.resolve(thenExit);
        result = items.makeStackItem(pt);
    }

    private void setTypeAnnotationPositions(int treePos) {
        MethodSymbol meth = code.meth;
        boolean initOrClinit = code.meth.getKind() == javax.lang.model.element.ElementKind.CONSTRUCTOR
                || code.meth.getKind() == javax.lang.model.element.ElementKind.STATIC_INIT;

        for (Attribute.TypeCompound ta : meth.getRawTypeAttributes()) {
            if (ta.hasUnknownPosition())
                ta.tryFixPosition();

            if (ta.position.matchesPos(treePos))
                ta.position.updatePosOffset(code.cp);
        }

        if (!initOrClinit)
            return;

        for (Attribute.TypeCompound ta : meth.owner.getRawTypeAttributes()) {
            if (ta.hasUnknownPosition())
                ta.tryFixPosition();

            if (ta.position.matchesPos(treePos))
                ta.position.updatePosOffset(code.cp);
        }

        ClassSymbol clazz = meth.enclClass();
        for (Symbol s : new com.sun.tools.javac.model.FilteredMemberList(clazz.members())) {
            if (!s.getKind().isField())
                continue;

            for (Attribute.TypeCompound ta : s.getRawTypeAttributes()) {
                if (ta.hasUnknownPosition())
                    ta.tryFixPosition();

                if (ta.position.matchesPos(treePos))
                    ta.position.updatePosOffset(code.cp);
            }
        }
    }

    public void visitNewClass(JCNewClass tree) {
        // Enclosing instances or anonymous classes should have been eliminated
        // by now.
        Assert.check(tree.encl == null && tree.def == null);
        setTypeAnnotationPositions(tree.pos);

        code.emitop2(new_, makeRef(tree.pos(), tree.type));
        code.emitop0(dup);

        // Generate code for all arguments, where the expected types are
        // the parameters of the constructor's external type (that is,
        // any implicit outer instance appears as first parameter).
        genArgs(tree.args, tree.constructor.externalType(types).getParameterTypes());

        items.makeMemberItem(tree.constructor, true).invoke();
        result = items.makeStackItem(tree.type);
    }

    public void visitNewArray(JCNewArray tree) {
        setTypeAnnotationPositions(tree.pos);

        if (tree.elems != null) {
            Type elemtype = types.elemtype(tree.type);
            loadIntConst(tree.elems.length());
            Item arr = makeNewArray(tree.pos(), tree.type, 1);
            int i = 0;
            for (List<JCExpression> l = tree.elems; l.nonEmpty(); l = l.tail) {
                arr.duplicate();
                loadIntConst(i);
                i++;
                genExpr(l.head, elemtype).load();
                items.makeIndexedItem(elemtype).store();
            }
            result = arr;
        } else {
            for (List<JCExpression> l = tree.dims; l.nonEmpty(); l = l.tail) {
                genExpr(l.head, syms.intType).load();
            }
            result = makeNewArray(tree.pos(), tree.type, tree.dims.length());
        }
    }
//where
        
Generate code to create an array with given element type and number
 of dimensions.
/** Generate code to create an array with given element type and number
         *  of dimensions.
         */
        Item makeNewArray(DiagnosticPosition pos, Type type, int ndims) {
            Type elemtype = types.elemtype(type);
            if (types.dimensions(type) > ClassFile.MAX_DIMENSIONS) {
                log.error(pos, Errors.LimitDimensions);
                nerrs++;
            }
            int elemcode = Code.arraycode(elemtype);
            if (elemcode == 0 || (elemcode == 1 && ndims == 1)) {
                code.emitAnewarray(makeRef(pos, elemtype), type);
            } else if (elemcode == 1) {
                code.emitMultianewarray(ndims, makeRef(pos, type), type);
            } else {
                code.emitNewarray(elemcode, type);
            }
            return items.makeStackItem(type);
        }

    public void visitParens(JCParens tree) {
        result = genExpr(tree.expr, tree.expr.type);
    }

    public void visitAssign(JCAssign tree) {
        Item l = genExpr(tree.lhs, tree.lhs.type);
        genExpr(tree.rhs, tree.lhs.type).load();
        if (tree.rhs.type.hasTag(BOT)) {
            /* This is just a case of widening reference conversion that per 5.1.5 simply calls
               for "regarding a reference as having some other type in a manner that can be proved
               correct at compile time."
            */
            code.state.forceStackTop(tree.lhs.type);
        }
        result = items.makeAssignItem(l);
    }

    public void visitAssignop(JCAssignOp tree) {
        OperatorSymbol operator = tree.operator;
        Item l;
        if (operator.opcode == string_add) {
            l = concat.makeConcat(tree);
        } else {
            // Generate code for first expression
            l = genExpr(tree.lhs, tree.lhs.type);

            // If we have an increment of -32768 to +32767 of a local
            // int variable we can use an incr instruction instead of
            // proceeding further.
            if ((tree.hasTag(PLUS_ASG) || tree.hasTag(MINUS_ASG)) &&
                l instanceof LocalItem &&
                tree.lhs.type.getTag().isSubRangeOf(INT) &&
                tree.rhs.type.getTag().isSubRangeOf(INT) &&
                tree.rhs.type.constValue() != null) {
                int ival = ((Number) tree.rhs.type.constValue()).intValue();
                if (tree.hasTag(MINUS_ASG)) ival = -ival;
                ((LocalItem)l).incr(ival);
                result = l;
                return;
            }
            // Otherwise, duplicate expression, load one copy
            // and complete binary operation.
            l.duplicate();
            l.coerce(operator.type.getParameterTypes().head).load();
            completeBinop(tree.lhs, tree.rhs, operator).coerce(tree.lhs.type);
        }
        result = items.makeAssignItem(l);
    }

    public void visitUnary(JCUnary tree) {
        OperatorSymbol operator = tree.operator;
        if (tree.hasTag(NOT)) {
            CondItem od = genCond(tree.arg, false);
            result = od.negate();
        } else {
            Item od = genExpr(tree.arg, operator.type.getParameterTypes().head);
            switch (tree.getTag()) {
            case POS:
                result = od.load();
                break;
            case NEG:
                result = od.load();
                code.emitop0(operator.opcode);
                break;
            case COMPL:
                result = od.load();
                emitMinusOne(od.typecode);
                code.emitop0(operator.opcode);
                break;
            case PREINC: case PREDEC:
                od.duplicate();
                if (od instanceof LocalItem &&
                    (operator.opcode == iadd || operator.opcode == isub)) {
                    ((LocalItem)od).incr(tree.hasTag(PREINC) ? 1 : -1);
                    result = od;
                } else {
                    od.load();
                    code.emitop0(one(od.typecode));
                    code.emitop0(operator.opcode);
                    // Perform narrowing primitive conversion if byte,
                    // char, or short.  Fix for 4304655.
                    if (od.typecode != INTcode &&
                        Code.truncate(od.typecode) == INTcode)
                      code.emitop0(int2byte + od.typecode - BYTEcode);
                    result = items.makeAssignItem(od);
                }
                break;
            case POSTINC: case POSTDEC:
                od.duplicate();
                if (od instanceof LocalItem &&
                    (operator.opcode == iadd || operator.opcode == isub)) {
                    Item res = od.load();
                    ((LocalItem)od).incr(tree.hasTag(POSTINC) ? 1 : -1);
                    result = res;
                } else {
                    Item res = od.load();
                    od.stash(od.typecode);
                    code.emitop0(one(od.typecode));
                    code.emitop0(operator.opcode);
                    // Perform narrowing primitive conversion if byte,
                    // char, or short.  Fix for 4304655.
                    if (od.typecode != INTcode &&
                        Code.truncate(od.typecode) == INTcode)
                      code.emitop0(int2byte + od.typecode - BYTEcode);
                    od.store();
                    result = res;
                }
                break;
            case NULLCHK:
                result = od.load();
                code.emitop0(dup);
                genNullCheck(tree);
                break;
            default:
                Assert.error();
            }
        }
    }

    
Generate a null check from the object value at stack top. /** Generate a null check from the object value at stack top. */
    private void genNullCheck(JCTree tree) {
        code.statBegin(tree.pos);
        callMethod(tree.pos(), syms.objectsType, names.requireNonNull,
                   List.of(syms.objectType), true);
        code.emitop0(pop);
    }

    public void visitBinary(JCBinary tree) {
        OperatorSymbol operator = tree.operator;
        if (operator.opcode == string_add) {
            result = concat.makeConcat(tree);
        } else if (tree.hasTag(AND)) {
            CondItem lcond = genCond(tree.lhs, CRT_FLOW_CONTROLLER);
            if (!lcond.isFalse()) {
                Chain falseJumps = lcond.jumpFalse();
                code.resolve(lcond.trueJumps);
                CondItem rcond = genCond(tree.rhs, CRT_FLOW_TARGET);
                result = items.
                    makeCondItem(rcond.opcode,
                                 rcond.trueJumps,
                                 Code.mergeChains(falseJumps,
                                                  rcond.falseJumps));
            } else {
                result = lcond;
            }
        } else if (tree.hasTag(OR)) {
            CondItem lcond = genCond(tree.lhs, CRT_FLOW_CONTROLLER);
            if (!lcond.isTrue()) {
                Chain trueJumps = lcond.jumpTrue();
                code.resolve(lcond.falseJumps);
                CondItem rcond = genCond(tree.rhs, CRT_FLOW_TARGET);
                result = items.
                    makeCondItem(rcond.opcode,
                                 Code.mergeChains(trueJumps, rcond.trueJumps),
                                 rcond.falseJumps);
            } else {
                result = lcond;
            }
        } else {
            Item od = genExpr(tree.lhs, operator.type.getParameterTypes().head);
            od.load();
            result = completeBinop(tree.lhs, tree.rhs, operator);
        }
    }


        
Complete generating code for operation, with left operand
 already on stack.
 @param lhs       The tree representing the left operand.
 @param rhs       The tree representing the right operand.
 @param operator  The operator symbol.
/** Complete generating code for operation, with left operand
         *  already on stack.
         *  @param lhs       The tree representing the left operand.
         *  @param rhs       The tree representing the right operand.
         *  @param operator  The operator symbol.
         */
        Item completeBinop(JCTree lhs, JCTree rhs, OperatorSymbol operator) {
            MethodType optype = (MethodType)operator.type;
            int opcode = operator.opcode;
            if (opcode >= if_icmpeq && opcode <= if_icmple &&
                rhs.type.constValue() instanceof Number &&
                ((Number) rhs.type.constValue()).intValue() == 0) {
                opcode = opcode + (ifeq - if_icmpeq);
            } else if (opcode >= if_acmpeq && opcode <= if_acmpne &&
                       TreeInfo.isNull(rhs)) {
                opcode = opcode + (if_acmp_null - if_acmpeq);
            } else {
                // The expected type of the right operand is
                // the second parameter type of the operator, except for
                // shifts with long shiftcount, where we convert the opcode
                // to a short shift and the expected type to int.
                Type rtype = operator.erasure(types).getParameterTypes().tail.head;
                if (opcode >= ishll && opcode <= lushrl) {
                    opcode = opcode + (ishl - ishll);
                    rtype = syms.intType;
                }
                // Generate code for right operand and load.
                genExpr(rhs, rtype).load();
                // If there are two consecutive opcode instructions,
                // emit the first now.
                if (opcode >= (1 << preShift)) {
                    code.emitop0(opcode >> preShift);
                    opcode = opcode & 0xFF;
                }
            }
            if (opcode >= ifeq && opcode <= if_acmpne ||
                opcode == if_acmp_null || opcode == if_acmp_nonnull) {
                return items.makeCondItem(opcode);
            } else {
                code.emitop0(opcode);
                return items.makeStackItem(optype.restype);
            }
        }

    public void visitTypeCast(JCTypeCast tree) {
        result = genExpr(tree.expr, tree.clazz.type).load();
        setTypeAnnotationPositions(tree.pos);
        // Additional code is only needed if we cast to a reference type
        // which is not statically a supertype of the expression's type.
        // For basic types, the coerce(...) in genExpr(...) will do
        // the conversion.
        if (!tree.clazz.type.isPrimitive() &&
           !types.isSameType(tree.expr.type, tree.clazz.type) &&
           types.asSuper(tree.expr.type, tree.clazz.type.tsym) == null) {
            code.emitop2(checkcast, makeRef(tree.pos(), tree.clazz.type));
        }
    }

    public void visitWildcard(JCWildcard tree) {
        throw new AssertionError(this.getClass().getName());
    }

    public void visitTypeTest(JCInstanceOf tree) {
        genExpr(tree.expr, tree.expr.type).load();
        setTypeAnnotationPositions(tree.pos);
        code.emitop2(instanceof_, makeRef(tree.pos(), tree.clazz.type));
        result = items.makeStackItem(syms.booleanType);
    }

    public void visitIndexed(JCArrayAccess tree) {
        genExpr(tree.indexed, tree.indexed.type).load();
        genExpr(tree.index, syms.intType).load();
        result = items.makeIndexedItem(tree.type);
    }

    public void visitIdent(JCIdent tree) {
        Symbol sym = tree.sym;
        if (tree.name == names._this || tree.name == names._super) {
            Item res = tree.name == names._this
                ? items.makeThisItem()
                : items.makeSuperItem();
            if (sym.kind == MTH) {
                // Generate code to address the constructor.
                res.load();
                res = items.makeMemberItem(sym, true);
            }
            result = res;
        } else if (sym.kind == VAR && (sym.owner.kind == MTH || sym.owner.kind == VAR)) {
            result = items.makeLocalItem((VarSymbol)sym);
        } else if (isInvokeDynamic(sym)) {
            result = items.makeDynamicItem(sym);
        } else if ((sym.flags() & STATIC) != 0) {
            if (!isAccessSuper(env.enclMethod))
                sym = binaryQualifier(sym, env.enclClass.type);
            result = items.makeStaticItem(sym);
        } else {
            items.makeThisItem().load();
            sym = binaryQualifier(sym, env.enclClass.type);
            result = items.makeMemberItem(sym, nonVirtualForPrivateAccess(sym));
        }
    }

    //where
    private boolean nonVirtualForPrivateAccess(Symbol sym) {
        boolean useVirtual = target.hasVirtualPrivateInvoke() &&
                             !disableVirtualizedPrivateInvoke;
        return !useVirtual && ((sym.flags() & PRIVATE) != 0);
    }

    public void visitSelect(JCFieldAccess tree) {
        Symbol sym = tree.sym;

        if (tree.name == names._class) {
            code.emitLdc(makeRef(tree.pos(), tree.selected.type));
            result = items.makeStackItem(pt);
            return;
       }

        Symbol ssym = TreeInfo.symbol(tree.selected);

        // Are we selecting via super?
        boolean selectSuper =
            ssym != null && (ssym.kind == TYP || ssym.name == names._super);

        // Are we accessing a member of the superclass in an access method
        // resulting from a qualified super?
        boolean accessSuper = isAccessSuper(env.enclMethod);

        Item base = (selectSuper)
            ? items.makeSuperItem()
            : genExpr(tree.selected, tree.selected.type);

        if (sym.kind == VAR && ((VarSymbol) sym).getConstValue() != null) {
            // We are seeing a variable that is constant but its selecting
            // expression is not.
            if ((sym.flags() & STATIC) != 0) {
                if (!selectSuper && (ssym == null || ssym.kind != TYP))
                    base = base.load();
                base.drop();
            } else {
                base.load();
                genNullCheck(tree.selected);
            }
            result = items.
                makeImmediateItem(sym.type, ((VarSymbol) sym).getConstValue());
        } else {
            if (isInvokeDynamic(sym)) {
                result = items.makeDynamicItem(sym);
                return;
            } else {
                sym = binaryQualifier(sym, tree.selected.type);
            }
            if ((sym.flags() & STATIC) != 0) {
                if (!selectSuper && (ssym == null || ssym.kind != TYP))
                    base = base.load();
                base.drop();
                result = items.makeStaticItem(sym);
            } else {
                base.load();
                if (sym == syms.lengthVar) {
                    code.emitop0(arraylength);
                    result = items.makeStackItem(syms.intType);
                } else {
                    result = items.
                        makeMemberItem(sym,
                                       nonVirtualForPrivateAccess(sym) ||
                                       selectSuper || accessSuper);
                }
            }
        }
    }

    public boolean isInvokeDynamic(Symbol sym) {
        return sym.kind == MTH && ((MethodSymbol)sym).isDynamic();
    }

    public void visitLiteral(JCLiteral tree) {
        if (tree.type.hasTag(BOT)) {
            code.emitop0(aconst_null);
            result = items.makeStackItem(tree.type);
        }
        else
            result = items.makeImmediateItem(tree.type, tree.value);
    }

    public void visitLetExpr(LetExpr tree) {
        int limit = code.nextreg;
        int prevLetExprStart = code.setLetExprStackPos(code.state.stacksize);
        try {
            genStats(tree.defs, env);
        } finally {
            code.setLetExprStackPos(prevLetExprStart);
        }
        result = genExpr(tree.expr, tree.expr.type).load();
        code.endScopes(limit);
    }

    private void generateReferencesToPrunedTree(ClassSymbol classSymbol, Pool pool) {
        List<JCTree> prunedInfo = lower.prunedTree.get(classSymbol);
        if (prunedInfo != null) {
            for (JCTree prunedTree: prunedInfo) {
                prunedTree.accept(classReferenceVisitor);
            }
        }
    }

/* ************************************************************************
 * main method
 *************************************************************************/

    
Generate code for a class definition.
 @param env   The attribution environment that belongs to the
              outermost class containing this class definition.
              We need this for resolving some additional symbols.
 @param cdef  The tree representing the class definition.
 @return      True if code is generated with no errors.
/** Generate code for a class definition.
     *  @param env   The attribution environment that belongs to the
     *               outermost class containing this class definition.
     *               We need this for resolving some additional symbols.
     *  @param cdef  The tree representing the class definition.
     *  @return      True if code is generated with no errors.
     */
    public boolean genClass(Env<AttrContext> env, JCClassDecl cdef) {
        try {
            attrEnv = env;
            ClassSymbol c = cdef.sym;
            this.toplevel = env.toplevel;
            this.endPosTable = toplevel.endPositions;
            c.pool = pool;
            pool.reset();
            /* method normalizeDefs() can add references to external classes into the constant pool
             */
            cdef.defs = normalizeDefs(cdef.defs, c);
            generateReferencesToPrunedTree(c, pool);
            Env<GenContext> localEnv = new Env<>(cdef, new GenContext());
            localEnv.toplevel = env.toplevel;
            localEnv.enclClass = cdef;

            for (List<JCTree> l = cdef.defs; l.nonEmpty(); l = l.tail) {
                genDef(l.head, localEnv);
            }
            if (pool.numEntries() > Pool.MAX_ENTRIES) {
                log.error(cdef.pos(), Errors.LimitPool);
                nerrs++;
            }
            if (nerrs != 0) {
                // if errors, discard code
                for (List<JCTree> l = cdef.defs; l.nonEmpty(); l = l.tail) {
                    if (l.head.hasTag(METHODDEF))
                        ((JCMethodDecl) l.head).sym.code = null;
                }
            }
            cdef.defs = List.nil(); // discard trees
            return nerrs == 0;
        } finally {
            // note: this method does NOT support recursion.
            attrEnv = null;
            this.env = null;
            toplevel = null;
            endPosTable = null;
            nerrs = 0;
        }
    }

/* ************************************************************************
 * Auxiliary classes
 *************************************************************************/

    
An abstract class for finalizer generation.
/** An abstract class for finalizer generation.
     */
    abstract class GenFinalizer {
        
Generate code to clean up when unwinding. /** Generate code to clean up when unwinding. */
        abstract void gen();

        
Generate code to clean up at last. /** Generate code to clean up at last. */
        abstract void genLast();

        
Does this finalizer have some nontrivial cleanup to perform? /** Does this finalizer have some nontrivial cleanup to perform? */
        boolean hasFinalizer() { return true; }

        
Should be invoked after the try's body has been visited. /** Should be invoked after the try's body has been visited. */
        void afterBody() {}
    }

    
code generation contexts,
 to be used as type parameter for environments.
/** code generation contexts,
     *  to be used as type parameter for environments.
     */
    static class GenContext {

        
A chain for all unresolved jumps that exit the current environment.
/** A chain for all unresolved jumps that exit the current environment.
         */
        Chain exit = null;

        
A chain for all unresolved jumps that continue in the
 current environment.
/** A chain for all unresolved jumps that continue in the
         *  current environment.
         */
        Chain cont = null;

        
A closure that generates the finalizer of the current environment.
 Only set for Synchronized and Try contexts.
/** A closure that generates the finalizer of the current environment.
         *  Only set for Synchronized and Try contexts.
         */
        GenFinalizer finalize = null;

        
Is this a switch statement?  If so, allocate registers
even when the variable declaration is unreachable.
/** Is this a switch statement?  If so, allocate registers
         * even when the variable declaration is unreachable.
         */
        boolean isSwitch = false;

        
A list buffer containing all gaps in the finalizer range,
 where a catch all exception should not apply.
/** A list buffer containing all gaps in the finalizer range,
         *  where a catch all exception should not apply.
         */
        ListBuffer<Integer> gaps = null;

        
Add given chain to exit chain.
/** Add given chain to exit chain.
         */
        void addExit(Chain c)  {
            exit = Code.mergeChains(c, exit);
        }

        
Add given chain to cont chain.
/** Add given chain to cont chain.
         */
        void addCont(Chain c) {
            cont = Code.mergeChains(c, cont);
        }
    }

}