Mercurial > jdk8-mips64-public > langtools / file revision

 /*

  * Copyright (c) 1999, 2012, 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.

  */

 //todo: one might eliminate uninits.andSets when monotonic

 package com.sun.tools.javac.comp;

 import java.util.HashMap;

 import com.sun.tools.javac.code.*;

 import com.sun.tools.javac.tree.*;

 import com.sun.tools.javac.util.*;

 import com.sun.tools.javac.util.JCDiagnostic.DiagnosticPosition;

 import com.sun.tools.javac.code.Symbol.*;

 import com.sun.tools.javac.tree.JCTree.*;

 import static com.sun.tools.javac.code.Flags.*;

 import static com.sun.tools.javac.code.Flags.BLOCK;

 import static com.sun.tools.javac.code.Kinds.*;

 import static com.sun.tools.javac.code.TypeTags.*;

 import static com.sun.tools.javac.tree.JCTree.Tag.*;

 /** This pass implements dataflow analysis for Java programs though

  *  different AST visitor steps. Liveness analysis (see AliveAlanyzer) checks that

  *  every statement is reachable. Exception analysis (see FlowAnalyzer) ensures that

  *  every checked exception that is thrown is declared or caught.  Definite assignment analysis

  *  (see AssignAnalyzer) ensures that each variable is assigned when used.  Definite

  *  unassignment analysis (see AssignAnalyzer) in ensures that no final variable

  *  is assigned more than once. Finally, local variable capture analysis (see CaptureAnalyzer)

  *  determines that local variables accessed within the scope of an inner class are

  *  either final or effectively-final.

  *

  *  <p>The JLS has a number of problems in the

  *  specification of these flow analysis problems. This implementation

  *  attempts to address those issues.

  *

  *  <p>First, there is no accommodation for a finally clause that cannot

  *  complete normally. For liveness analysis, an intervening finally

  *  clause can cause a break, continue, or return not to reach its

  *  target.  For exception analysis, an intervening finally clause can

  *  cause any exception to be "caught".  For DA/DU analysis, the finally

  *  clause can prevent a transfer of control from propagating DA/DU

  *  state to the target.  In addition, code in the finally clause can

  *  affect the DA/DU status of variables.

  *

  *  <p>For try statements, we introduce the idea of a variable being

  *  definitely unassigned "everywhere" in a block.  A variable V is

  *  "unassigned everywhere" in a block iff it is unassigned at the

  *  beginning of the block and there is no reachable assignment to V

  *  in the block.  An assignment V=e is reachable iff V is not DA

  *  after e.  Then we can say that V is DU at the beginning of the

  *  catch block iff V is DU everywhere in the try block.  Similarly, V

  *  is DU at the beginning of the finally block iff V is DU everywhere

  *  in the try block and in every catch block.  Specifically, the

  *  following bullet is added to 16.2.2

  *  <pre>

  *      V is <em>unassigned everywhere</em> in a block if it is

  *      unassigned before the block and there is no reachable

  *      assignment to V within the block.

  *  </pre>

  *  <p>In 16.2.15, the third bullet (and all of its sub-bullets) for all

  *  try blocks is changed to

  *  <pre>

  *      V is definitely unassigned before a catch block iff V is

  *      definitely unassigned everywhere in the try block.

  *  </pre>

  *  <p>The last bullet (and all of its sub-bullets) for try blocks that

  *  have a finally block is changed to

  *  <pre>

  *      V is definitely unassigned before the finally block iff

  *      V is definitely unassigned everywhere in the try block

  *      and everywhere in each catch block of the try statement.

  *  </pre>

  *  <p>In addition,

  *  <pre>

  *      V is definitely assigned at the end of a constructor iff

  *      V is definitely assigned after the block that is the body

  *      of the constructor and V is definitely assigned at every

  *      return that can return from the constructor.

  *  </pre>

  *  <p>In addition, each continue statement with the loop as its target

  *  is treated as a jump to the end of the loop body, and "intervening"

  *  finally clauses are treated as follows: V is DA "due to the

  *  continue" iff V is DA before the continue statement or V is DA at

  *  the end of any intervening finally block.  V is DU "due to the

  *  continue" iff any intervening finally cannot complete normally or V

  *  is DU at the end of every intervening finally block.  This "due to

  *  the continue" concept is then used in the spec for the loops.

  *

  *  <p>Similarly, break statements must consider intervening finally

  *  blocks.  For liveness analysis, a break statement for which any

  *  intervening finally cannot complete normally is not considered to

  *  cause the target statement to be able to complete normally. Then

  *  we say V is DA "due to the break" iff V is DA before the break or

  *  V is DA at the end of any intervening finally block.  V is DU "due

  *  to the break" iff any intervening finally cannot complete normally

  *  or V is DU at the break and at the end of every intervening

  *  finally block.  (I suspect this latter condition can be

  *  simplified.)  This "due to the break" is then used in the spec for

  *  all statements that can be "broken".

  *

  *  <p>The return statement is treated similarly.  V is DA "due to a

  *  return statement" iff V is DA before the return statement or V is

  *  DA at the end of any intervening finally block.  Note that we

  *  don't have to worry about the return expression because this

  *  concept is only used for construcrors.

  *

  *  <p>There is no spec in the JLS for when a variable is definitely

  *  assigned at the end of a constructor, which is needed for final

  *  fields (8.3.1.2).  We implement the rule that V is DA at the end

  *  of the constructor iff it is DA and the end of the body of the

  *  constructor and V is DA "due to" every return of the constructor.

  *

  *  <p>Intervening finally blocks similarly affect exception analysis.  An

  *  intervening finally that cannot complete normally allows us to ignore

  *  an otherwise uncaught exception.

  *

  *  <p>To implement the semantics of intervening finally clauses, all

  *  nonlocal transfers (break, continue, return, throw, method call that

  *  can throw a checked exception, and a constructor invocation that can

  *  thrown a checked exception) are recorded in a queue, and removed

  *  from the queue when we complete processing the target of the

  *  nonlocal transfer.  This allows us to modify the queue in accordance

  *  with the above rules when we encounter a finally clause.  The only

  *  exception to this [no pun intended] is that checked exceptions that

  *  are known to be caught or declared to be caught in the enclosing

  *  method are not recorded in the queue, but instead are recorded in a

  *  global variable "Set<Type> thrown" that records the type of all

  *  exceptions that can be thrown.

  *

  *  <p>Other minor issues the treatment of members of other classes

  *  (always considered DA except that within an anonymous class

  *  constructor, where DA status from the enclosing scope is

  *  preserved), treatment of the case expression (V is DA before the

  *  case expression iff V is DA after the switch expression),

  *  treatment of variables declared in a switch block (the implied

  *  DA/DU status after the switch expression is DU and not DA for

  *  variables defined in a switch block), the treatment of boolean ?:

  *  expressions (The JLS rules only handle b and c non-boolean; the

  *  new rule is that if b and c are boolean valued, then V is

  *  (un)assigned after a?b:c when true/false iff V is (un)assigned

  *  after b when true/false and V is (un)assigned after c when

  *  true/false).

  *

  *  <p>There is the remaining question of what syntactic forms constitute a

  *  reference to a variable.  It is conventional to allow this.x on the

  *  left-hand-side to initialize a final instance field named x, yet

  *  this.x isn't considered a "use" when appearing on a right-hand-side

  *  in most implementations.  Should parentheses affect what is

  *  considered a variable reference?  The simplest rule would be to

  *  allow unqualified forms only, parentheses optional, and phase out

  *  support for assigning to a final field via this.x.

  *

  *  <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 Flow {

     protected static final Context.Key<Flow> flowKey =

         new Context.Key<Flow>();

     private final Names names;

     private final Log log;

     private final Symtab syms;

     private final Types types;

     private final Check chk;

     private       TreeMaker make;

     private final Resolve rs;

     private final JCDiagnostic.Factory diags;

     private Env<AttrContext> attrEnv;

     private       Lint lint;

     private final boolean allowImprovedRethrowAnalysis;

     private final boolean allowImprovedCatchAnalysis;

     private final boolean allowEffectivelyFinalInInnerClasses;

     public static Flow instance(Context context) {

         Flow instance = context.get(flowKey);

         if (instance == null)

             instance = new Flow(context);

         return instance;

     }

     public void analyzeTree(Env<AttrContext> env, TreeMaker make) {

         new AliveAnalyzer().analyzeTree(env, make);

         new AssignAnalyzer().analyzeTree(env, make);

         new FlowAnalyzer().analyzeTree(env, make);

         new CaptureAnalyzer().analyzeTree(env, make);

     }

     /**

      * Definite assignment scan mode

      */

     enum FlowKind {

         /**

          * This is the normal DA/DU analysis mode

          */

         NORMAL("var.might.already.be.assigned", false),

         /**

          * This is the speculative DA/DU analysis mode used to speculatively

          * derive assertions within loop bodies

          */

         SPECULATIVE_LOOP("var.might.be.assigned.in.loop", true);

         String errKey;

         boolean isFinal;

         FlowKind(String errKey, boolean isFinal) {

             this.errKey = errKey;

             this.isFinal = isFinal;

         }

         boolean isFinal() {

             return isFinal;

         }

     }

     protected Flow(Context context) {

         context.put(flowKey, this);

         names = Names.instance(context);

         log = Log.instance(context);

         syms = Symtab.instance(context);

         types = Types.instance(context);

         chk = Check.instance(context);

         lint = Lint.instance(context);

         rs = Resolve.instance(context);

         diags = JCDiagnostic.Factory.instance(context);

         Source source = Source.instance(context);

         allowImprovedRethrowAnalysis = source.allowImprovedRethrowAnalysis();

         allowImprovedCatchAnalysis = source.allowImprovedCatchAnalysis();

         Options options = Options.instance(context);

         allowEffectivelyFinalInInnerClasses = source.allowEffectivelyFinalInInnerClasses() &&

                 options.isSet("allowEffectivelyFinalInInnerClasses"); //pre-lambda guard

     }

     /**

      * Base visitor class for all visitors implementing dataflow analysis logic.

      * This class define the shared logic for handling jumps (break/continue statements).

      */

     static abstract class BaseAnalyzer<P extends BaseAnalyzer.PendingExit> extends TreeScanner {

         enum JumpKind {

             BREAK(JCTree.Tag.BREAK) {

                 @Override

                 JCTree getTarget(JCTree tree) {

                     return ((JCBreak)tree).target;

                 }

             },

             CONTINUE(JCTree.Tag.CONTINUE) {

                 @Override

                 JCTree getTarget(JCTree tree) {

                     return ((JCContinue)tree).target;

                 }

             };

             JCTree.Tag treeTag;

             private JumpKind(Tag treeTag) {

                 this.treeTag = treeTag;

             }

             abstract JCTree getTarget(JCTree tree);

         }

         /** The currently pending exits that go from current inner blocks

          *  to an enclosing block, in source order.

          */

         ListBuffer<P> pendingExits;

         /** A pending exit.  These are the statements return, break, and

          *  continue.  In addition, exception-throwing expressions or

          *  statements are put here when not known to be caught.  This

          *  will typically result in an error unless it is within a

          *  try-finally whose finally block cannot complete normally.

          */

         static class PendingExit {

             JCTree tree;

             PendingExit(JCTree tree) {

                 this.tree = tree;

             }

             void resolveJump() {

                 //do nothing

             }

         }

         abstract void markDead();

         /** Record an outward transfer of control. */

         void recordExit(JCTree tree, P pe) {

             pendingExits.append(pe);

             markDead();

         }

         /** Resolve all jumps of this statement. */

         private boolean resolveJump(JCTree tree,

                         ListBuffer<P> oldPendingExits,

                         JumpKind jk) {

             boolean resolved = false;

             List<P> exits = pendingExits.toList();

             pendingExits = oldPendingExits;

             for (; exits.nonEmpty(); exits = exits.tail) {

                 P exit = exits.head;

                 if (exit.tree.hasTag(jk.treeTag) &&

                         jk.getTarget(exit.tree) == tree) {

                     exit.resolveJump();

                     resolved = true;

                 } else {

                     pendingExits.append(exit);

                 }

             }

             return resolved;

         }

         /** Resolve all breaks of this statement. */

         boolean resolveContinues(JCTree tree) {

             return resolveJump(tree, new ListBuffer<P>(), JumpKind.CONTINUE);

         }

         /** Resolve all continues of this statement. */

         boolean resolveBreaks(JCTree tree, ListBuffer<P> oldPendingExits) {

             return resolveJump(tree, oldPendingExits, JumpKind.BREAK);

         }

     }

     /**

      * This pass implements the first step of the dataflow analysis, namely

      * the liveness analysis check. This checks that every statement is reachable.

      * The output of this analysis pass are used by other analyzers. This analyzer

      * sets the 'finallyCanCompleteNormally' field in the JCTry class.

      */

     class AliveAnalyzer extends BaseAnalyzer<BaseAnalyzer.PendingExit> {

         /** A flag that indicates whether the last statement could

          *  complete normally.

          */

         private boolean alive;

         @Override

         void markDead() {

             alive = false;

         }

     /*************************************************************************

      * Visitor methods for statements and definitions

      *************************************************************************/

         /** Analyze a definition.

          */

         void scanDef(JCTree tree) {

             scanStat(tree);

             if (tree != null && tree.hasTag(JCTree.Tag.BLOCK) && !alive) {

                 log.error(tree.pos(),

                           "initializer.must.be.able.to.complete.normally");

             }

         }

         /** Analyze a statement. Check that statement is reachable.

          */

         void scanStat(JCTree tree) {

             if (!alive && tree != null) {

                 log.error(tree.pos(), "unreachable.stmt");

                 if (!tree.hasTag(SKIP)) alive = true;

             }

             scan(tree);

         }

         /** Analyze list of statements.

          */

         void scanStats(List<? extends JCStatement> trees) {

             if (trees != null)

                 for (List<? extends JCStatement> l = trees; l.nonEmpty(); l = l.tail)

                     scanStat(l.head);

         }

         /* ------------ Visitor methods for various sorts of trees -------------*/

         public void visitClassDef(JCClassDecl tree) {

             if (tree.sym == null) return;

             boolean alivePrev = alive;

             ListBuffer<PendingExit> pendingExitsPrev = pendingExits;

             Lint lintPrev = lint;

             pendingExits = new ListBuffer<PendingExit>();

             lint = lint.augment(tree.sym.attributes_field);

             try {

                 // process all the static initializers

                 for (List<JCTree> l = tree.defs; l.nonEmpty(); l = l.tail) {

                     if (!l.head.hasTag(METHODDEF) &&

                         (TreeInfo.flags(l.head) & STATIC) != 0) {

                         scanDef(l.head);

                     }

                 }

                 // process all the instance initializers

                 for (List<JCTree> l = tree.defs; l.nonEmpty(); l = l.tail) {

                     if (!l.head.hasTag(METHODDEF) &&

                         (TreeInfo.flags(l.head) & STATIC) == 0) {

                         scanDef(l.head);

                     }

                 }

                 // process all the methods

                 for (List<JCTree> l = tree.defs; l.nonEmpty(); l = l.tail) {

                     if (l.head.hasTag(METHODDEF)) {

                         scan(l.head);

                     }

                 }

             } finally {

                 pendingExits = pendingExitsPrev;

                 alive = alivePrev;

                 lint = lintPrev;

             }

         }

         public void visitMethodDef(JCMethodDecl tree) {

             if (tree.body == null) return;

             Lint lintPrev = lint;

             lint = lint.augment(tree.sym.attributes_field);

             Assert.check(pendingExits.isEmpty());

             try {

                 alive = true;

                 scanStat(tree.body);

                 if (alive && tree.sym.type.getReturnType().tag != VOID)

                     log.error(TreeInfo.diagEndPos(tree.body), "missing.ret.stmt");

                 List<PendingExit> exits = pendingExits.toList();

                 pendingExits = new ListBuffer<PendingExit>();

                 while (exits.nonEmpty()) {

                     PendingExit exit = exits.head;

                     exits = exits.tail;

                     Assert.check(exit.tree.hasTag(RETURN));

                 }

             } finally {

                 lint = lintPrev;

             }

         }

         public void visitVarDef(JCVariableDecl tree) {

             if (tree.init != null) {

                 Lint lintPrev = lint;

                 lint = lint.augment(tree.sym.attributes_field);

                 try{

                     scan(tree.init);

                 } finally {

                     lint = lintPrev;

                 }

             }

         }

         public void visitBlock(JCBlock tree) {

             scanStats(tree.stats);

         }

         public void visitDoLoop(JCDoWhileLoop tree) {

             ListBuffer<PendingExit> prevPendingExits = pendingExits;

             pendingExits = new ListBuffer<PendingExit>();

             scanStat(tree.body);

             alive |= resolveContinues(tree);

             scan(tree.cond);

             alive = alive && !tree.cond.type.isTrue();

             alive |= resolveBreaks(tree, prevPendingExits);

         }

         public void visitWhileLoop(JCWhileLoop tree) {

             ListBuffer<PendingExit> prevPendingExits = pendingExits;

             pendingExits = new ListBuffer<PendingExit>();

             scan(tree.cond);

             alive = !tree.cond.type.isFalse();

             scanStat(tree.body);

             alive |= resolveContinues(tree);

             alive = resolveBreaks(tree, prevPendingExits) ||

                 !tree.cond.type.isTrue();

         }

         public void visitForLoop(JCForLoop tree) {

             ListBuffer<PendingExit> prevPendingExits = pendingExits;

             scanStats(tree.init);

             pendingExits = new ListBuffer<PendingExit>();

             if (tree.cond != null) {

                 scan(tree.cond);

                 alive = !tree.cond.type.isFalse();

             } else {

                 alive = true;

             }

             scanStat(tree.body);

             alive |= resolveContinues(tree);

             scan(tree.step);

             alive = resolveBreaks(tree, prevPendingExits) ||

                 tree.cond != null && !tree.cond.type.isTrue();

         }

         public void visitForeachLoop(JCEnhancedForLoop tree) {

             visitVarDef(tree.var);

             ListBuffer<PendingExit> prevPendingExits = pendingExits;

             scan(tree.expr);

             pendingExits = new ListBuffer<PendingExit>();

             scanStat(tree.body);

             alive |= resolveContinues(tree);

             resolveBreaks(tree, prevPendingExits);

             alive = true;

         }

         public void visitLabelled(JCLabeledStatement tree) {

             ListBuffer<PendingExit> prevPendingExits = pendingExits;

             pendingExits = new ListBuffer<PendingExit>();

             scanStat(tree.body);

             alive |= resolveBreaks(tree, prevPendingExits);

         }

         public void visitSwitch(JCSwitch tree) {

             ListBuffer<PendingExit> prevPendingExits = pendingExits;

             pendingExits = new ListBuffer<PendingExit>();

             scan(tree.selector);

             boolean hasDefault = false;

             for (List<JCCase> l = tree.cases; l.nonEmpty(); l = l.tail) {

                 alive = true;

                 JCCase c = l.head;

                 if (c.pat == null)

                     hasDefault = true;

                 else

                     scan(c.pat);

                 scanStats(c.stats);

                 // Warn about fall-through if lint switch fallthrough enabled.

                 if (alive &&

                     lint.isEnabled(Lint.LintCategory.FALLTHROUGH) &&

                     c.stats.nonEmpty() && l.tail.nonEmpty())

                     log.warning(Lint.LintCategory.FALLTHROUGH,

                                 l.tail.head.pos(),

                                 "possible.fall-through.into.case");

             }

             if (!hasDefault) {

                 alive = true;

             }

             alive |= resolveBreaks(tree, prevPendingExits);

         }

         public void visitTry(JCTry tree) {

             ListBuffer<PendingExit> prevPendingExits = pendingExits;

             pendingExits = new ListBuffer<PendingExit>();

             for (JCTree resource : tree.resources) {

                 if (resource instanceof JCVariableDecl) {

                     JCVariableDecl vdecl = (JCVariableDecl) resource;

                     visitVarDef(vdecl);

                 } else if (resource instanceof JCExpression) {

                     scan((JCExpression) resource);

                 } else {

                     throw new AssertionError(tree);  // parser error

                 }

             }

             scanStat(tree.body);

             boolean aliveEnd = alive;

             for (List<JCCatch> l = tree.catchers; l.nonEmpty(); l = l.tail) {

                 alive = true;

                 JCVariableDecl param = l.head.param;

                 scan(param);

                 scanStat(l.head.body);

                 aliveEnd |= alive;

             }

             if (tree.finalizer != null) {

                 ListBuffer<PendingExit> exits = pendingExits;

                 pendingExits = prevPendingExits;

                 alive = true;

                 scanStat(tree.finalizer);

                 tree.finallyCanCompleteNormally = alive;

                 if (!alive) {

                     if (lint.isEnabled(Lint.LintCategory.FINALLY)) {

                         log.warning(Lint.LintCategory.FINALLY,

                                 TreeInfo.diagEndPos(tree.finalizer),

                                 "finally.cannot.complete");

                     }

                 } else {

                     while (exits.nonEmpty()) {

                         pendingExits.append(exits.next());

                     }

                     alive = aliveEnd;

                 }

             } else {

                 alive = aliveEnd;

                 ListBuffer<PendingExit> exits = pendingExits;

                 pendingExits = prevPendingExits;

                 while (exits.nonEmpty()) pendingExits.append(exits.next());

             }

         }

         @Override

         public void visitIf(JCIf tree) {

             scan(tree.cond);

             scanStat(tree.thenpart);

             if (tree.elsepart != null) {

                 boolean aliveAfterThen = alive;

                 alive = true;

                 scanStat(tree.elsepart);

                 alive = alive | aliveAfterThen;

             } else {

                 alive = true;

             }

         }

         public void visitBreak(JCBreak tree) {

             recordExit(tree, new PendingExit(tree));

         }

         public void visitContinue(JCContinue tree) {

             recordExit(tree, new PendingExit(tree));

         }

         public void visitReturn(JCReturn tree) {

             scan(tree.expr);

             recordExit(tree, new PendingExit(tree));

         }

         public void visitThrow(JCThrow tree) {

             scan(tree.expr);

             markDead();

         }

         public void visitApply(JCMethodInvocation tree) {

             scan(tree.meth);

             scan(tree.args);

         }

         public void visitNewClass(JCNewClass tree) {

             scan(tree.encl);

             scan(tree.args);

             if (tree.def != null) {

                 scan(tree.def);

             }

         }

         public void visitTopLevel(JCCompilationUnit tree) {

             // Do nothing for TopLevel since each class is visited individually

         }

     /**************************************************************************

      * main method

      *************************************************************************/

         /** Perform definite assignment/unassignment analysis on a tree.

          */

         public void analyzeTree(Env<AttrContext> env, TreeMaker make) {

             try {

                 attrEnv = env;

                 Flow.this.make = make;

                 pendingExits = new ListBuffer<PendingExit>();

                 alive = true;

                 scan(env.tree);

             } finally {

                 pendingExits = null;

                 Flow.this.make = null;

             }

         }

     }

     /**

      * This pass implements the second step of the dataflow analysis, namely

      * the exception analysis. This is to ensure that every checked exception that is

      * thrown is declared or caught. The analyzer uses some info that has been set by

      * the liveliness analyzer.

      */

     class FlowAnalyzer extends BaseAnalyzer<FlowAnalyzer.FlowPendingExit> {

         /** A flag that indicates whether the last statement could

          *  complete normally.

          */

         HashMap<Symbol, List<Type>> preciseRethrowTypes;

         /** The current class being defined.

          */

         JCClassDecl classDef;

         /** The list of possibly thrown declarable exceptions.

          */

         List<Type> thrown;

         /** The list of exceptions that are either caught or declared to be

          *  thrown.

          */

         List<Type> caught;

         class FlowPendingExit extends BaseAnalyzer.PendingExit {

             Type thrown;

             FlowPendingExit(JCTree tree, Type thrown) {

                 super(tree);

                 this.thrown = thrown;

             }

         }

         @Override

         void markDead() {

             //do nothing

         }

         /*-------------------- Exceptions ----------------------*/

         /** Complain that pending exceptions are not caught.

          */

         void errorUncaught() {

             for (FlowPendingExit exit = pendingExits.next();

                  exit != null;

                  exit = pendingExits.next()) {

                 if (classDef != null &&

                     classDef.pos == exit.tree.pos) {

                     log.error(exit.tree.pos(),

                             "unreported.exception.default.constructor",

                             exit.thrown);

                 } else if (exit.tree.hasTag(VARDEF) &&

                         ((JCVariableDecl)exit.tree).sym.isResourceVariable()) {

                     log.error(exit.tree.pos(),

                             "unreported.exception.implicit.close",

                             exit.thrown,

                             ((JCVariableDecl)exit.tree).sym.name);

                 } else {

                     log.error(exit.tree.pos(),

                             "unreported.exception.need.to.catch.or.throw",

                             exit.thrown);

                 }

             }

         }

         /** Record that exception is potentially thrown and check that it

          *  is caught.

          */

         void markThrown(JCTree tree, Type exc) {

             if (!chk.isUnchecked(tree.pos(), exc)) {

                 if (!chk.isHandled(exc, caught))

                     pendingExits.append(new FlowPendingExit(tree, exc));

                     thrown = chk.incl(exc, thrown);

             }

         }

     /*************************************************************************

      * Visitor methods for statements and definitions

      *************************************************************************/

         /* ------------ Visitor methods for various sorts of trees -------------*/

         public void visitClassDef(JCClassDecl tree) {

             if (tree.sym == null) return;

             JCClassDecl classDefPrev = classDef;

             List<Type> thrownPrev = thrown;

             List<Type> caughtPrev = caught;

             ListBuffer<FlowPendingExit> pendingExitsPrev = pendingExits;

             Lint lintPrev = lint;

             pendingExits = new ListBuffer<FlowPendingExit>();

             if (tree.name != names.empty) {

                 caught = List.nil();

             }

             classDef = tree;

             thrown = List.nil();

             lint = lint.augment(tree.sym.attributes_field);

             try {

                 // process all the static initializers

                 for (List<JCTree> l = tree.defs; l.nonEmpty(); l = l.tail) {

                     if (!l.head.hasTag(METHODDEF) &&

                         (TreeInfo.flags(l.head) & STATIC) != 0) {

                         scan(l.head);

                         errorUncaught();

                     }

                 }

                 // add intersection of all thrown clauses of initial constructors

                 // to set of caught exceptions, unless class is anonymous.

                 if (tree.name != names.empty) {

                     boolean firstConstructor = true;

                     for (List<JCTree> l = tree.defs; l.nonEmpty(); l = l.tail) {

                         if (TreeInfo.isInitialConstructor(l.head)) {

                             List<Type> mthrown =

                                 ((JCMethodDecl) l.head).sym.type.getThrownTypes();

                             if (firstConstructor) {

                                 caught = mthrown;

                                 firstConstructor = false;

                             } else {

                                 caught = chk.intersect(mthrown, caught);

                             }

                         }

                     }

                 }

                 // process all the instance initializers

                 for (List<JCTree> l = tree.defs; l.nonEmpty(); l = l.tail) {

                     if (!l.head.hasTag(METHODDEF) &&

                         (TreeInfo.flags(l.head) & STATIC) == 0) {

                         scan(l.head);

                         errorUncaught();

                     }

                 }

                 // in an anonymous class, add the set of thrown exceptions to

                 // the throws clause of the synthetic constructor and propagate

                 // outwards.

                 // Changing the throws clause on the fly is okay here because

                 // the anonymous constructor can't be invoked anywhere else,

                 // and its type hasn't been cached.

                 if (tree.name == names.empty) {

                     for (List<JCTree> l = tree.defs; l.nonEmpty(); l = l.tail) {

                         if (TreeInfo.isInitialConstructor(l.head)) {

                             JCMethodDecl mdef = (JCMethodDecl)l.head;

                             mdef.thrown = make.Types(thrown);

                             mdef.sym.type = types.createMethodTypeWithThrown(mdef.sym.type, thrown);

                         }

                     }

                     thrownPrev = chk.union(thrown, thrownPrev);

                 }

                 // process all the methods

                 for (List<JCTree> l = tree.defs; l.nonEmpty(); l = l.tail) {

                     if (l.head.hasTag(METHODDEF)) {

                         scan(l.head);

                         errorUncaught();

                     }

                 }

                 thrown = thrownPrev;

             } finally {

                 pendingExits = pendingExitsPrev;

                 caught = caughtPrev;

                 classDef = classDefPrev;

                 lint = lintPrev;

             }

         }

         public void visitMethodDef(JCMethodDecl tree) {

             if (tree.body == null) return;

             List<Type> caughtPrev = caught;

             List<Type> mthrown = tree.sym.type.getThrownTypes();

             Lint lintPrev = lint;

             lint = lint.augment(tree.sym.attributes_field);

             Assert.check(pendingExits.isEmpty());

             try {

                 for (List<JCVariableDecl> l = tree.params; l.nonEmpty(); l = l.tail) {

                     JCVariableDecl def = l.head;

                     scan(def);

                 }

                 if (TreeInfo.isInitialConstructor(tree))

                     caught = chk.union(caught, mthrown);

                 else if ((tree.sym.flags() & (BLOCK | STATIC)) != BLOCK)

                     caught = mthrown;

                 // else we are in an instance initializer block;

                 // leave caught unchanged.

                 scan(tree.body);

                 List<FlowPendingExit> exits = pendingExits.toList();

                 pendingExits = new ListBuffer<FlowPendingExit>();

                 while (exits.nonEmpty()) {

                     FlowPendingExit exit = exits.head;

                     exits = exits.tail;

                     if (exit.thrown == null) {

                         Assert.check(exit.tree.hasTag(RETURN));

                     } else {

                         // uncaught throws will be reported later

                         pendingExits.append(exit);

                     }

                 }

             } finally {

                 caught = caughtPrev;

                 lint = lintPrev;

             }

         }

         public void visitVarDef(JCVariableDecl tree) {

             if (tree.init != null) {

                 Lint lintPrev = lint;

                 lint = lint.augment(tree.sym.attributes_field);

                 try{

                     scan(tree.init);

                 } finally {

                     lint = lintPrev;

                 }

             }

         }

         public void visitBlock(JCBlock tree) {

             scan(tree.stats);

         }

         public void visitDoLoop(JCDoWhileLoop tree) {

             ListBuffer<FlowPendingExit> prevPendingExits = pendingExits;

             pendingExits = new ListBuffer<FlowPendingExit>();

             scan(tree.body);

             resolveContinues(tree);

             scan(tree.cond);

             resolveBreaks(tree, prevPendingExits);

         }

         public void visitWhileLoop(JCWhileLoop tree) {

             ListBuffer<FlowPendingExit> prevPendingExits = pendingExits;

             pendingExits = new ListBuffer<FlowPendingExit>();

             scan(tree.cond);

             scan(tree.body);

             resolveContinues(tree);

             resolveBreaks(tree, prevPendingExits);

         }

         public void visitForLoop(JCForLoop tree) {

             ListBuffer<FlowPendingExit> prevPendingExits = pendingExits;

             scan(tree.init);

             pendingExits = new ListBuffer<FlowPendingExit>();

             if (tree.cond != null) {

                 scan(tree.cond);

             }

             scan(tree.body);

             resolveContinues(tree);

             scan(tree.step);

             resolveBreaks(tree, prevPendingExits);

         }

         public void visitForeachLoop(JCEnhancedForLoop tree) {

             visitVarDef(tree.var);

             ListBuffer<FlowPendingExit> prevPendingExits = pendingExits;

             scan(tree.expr);

             pendingExits = new ListBuffer<FlowPendingExit>();

             scan(tree.body);

             resolveContinues(tree);

             resolveBreaks(tree, prevPendingExits);

         }

         public void visitLabelled(JCLabeledStatement tree) {

             ListBuffer<FlowPendingExit> prevPendingExits = pendingExits;

             pendingExits = new ListBuffer<FlowPendingExit>();

             scan(tree.body);

             resolveBreaks(tree, prevPendingExits);

         }

         public void visitSwitch(JCSwitch tree) {

             ListBuffer<FlowPendingExit> prevPendingExits = pendingExits;

             pendingExits = new ListBuffer<FlowPendingExit>();

             scan(tree.selector);

             for (List<JCCase> l = tree.cases; l.nonEmpty(); l = l.tail) {

                 JCCase c = l.head;

                 if (c.pat != null) {

                     scan(c.pat);

                 }

                 scan(c.stats);

             }

             resolveBreaks(tree, prevPendingExits);

         }

         public void visitTry(JCTry tree) {

             List<Type> caughtPrev = caught;

             List<Type> thrownPrev = thrown;

             thrown = List.nil();

             for (List<JCCatch> l = tree.catchers; l.nonEmpty(); l = l.tail) {

                 List<JCExpression> subClauses = TreeInfo.isMultiCatch(l.head) ?

                         ((JCTypeUnion)l.head.param.vartype).alternatives :

                         List.of(l.head.param.vartype);

                 for (JCExpression ct : subClauses) {

                     caught = chk.incl(ct.type, caught);

                 }

             }

             ListBuffer<FlowPendingExit> prevPendingExits = pendingExits;

             pendingExits = new ListBuffer<FlowPendingExit>();

             for (JCTree resource : tree.resources) {

                 if (resource instanceof JCVariableDecl) {

                     JCVariableDecl vdecl = (JCVariableDecl) resource;

                     visitVarDef(vdecl);

                 } else if (resource instanceof JCExpression) {

                     scan((JCExpression) resource);

                 } else {

                     throw new AssertionError(tree);  // parser error

                 }

             }

             for (JCTree resource : tree.resources) {

                 List<Type> closeableSupertypes = resource.type.isCompound() ?

                     types.interfaces(resource.type).prepend(types.supertype(resource.type)) :

                     List.of(resource.type);

                 for (Type sup : closeableSupertypes) {

                     if (types.asSuper(sup, syms.autoCloseableType.tsym) != null) {

                         Symbol closeMethod = rs.resolveQualifiedMethod(tree,

                                 attrEnv,

                                 sup,

                                 names.close,

                                 List.<Type>nil(),

                                 List.<Type>nil());

                         if (closeMethod.kind == MTH) {

                             for (Type t : ((MethodSymbol)closeMethod).getThrownTypes()) {

                                 markThrown(resource, t);

                             }

                         }

                     }

                 }

             }

             scan(tree.body);

             List<Type> thrownInTry = allowImprovedCatchAnalysis ?

                 chk.union(thrown, List.of(syms.runtimeExceptionType, syms.errorType)) :

                 thrown;

             thrown = thrownPrev;

             caught = caughtPrev;

             List<Type> caughtInTry = List.nil();

             for (List<JCCatch> l = tree.catchers; l.nonEmpty(); l = l.tail) {

                 JCVariableDecl param = l.head.param;

                 List<JCExpression> subClauses = TreeInfo.isMultiCatch(l.head) ?

                         ((JCTypeUnion)l.head.param.vartype).alternatives :

                         List.of(l.head.param.vartype);

                 List<Type> ctypes = List.nil();

                 List<Type> rethrownTypes = chk.diff(thrownInTry, caughtInTry);

                 for (JCExpression ct : subClauses) {

                     Type exc = ct.type;

                     if (exc != syms.unknownType) {

                         ctypes = ctypes.append(exc);

                         if (types.isSameType(exc, syms.objectType))

                             continue;

                         checkCaughtType(l.head.pos(), exc, thrownInTry, caughtInTry);

                         caughtInTry = chk.incl(exc, caughtInTry);

                     }

                 }

                 scan(param);

                 preciseRethrowTypes.put(param.sym, chk.intersect(ctypes, rethrownTypes));

                 scan(l.head.body);

                 preciseRethrowTypes.remove(param.sym);

             }

             if (tree.finalizer != null) {

                 List<Type> savedThrown = thrown;

                 thrown = List.nil();

                 ListBuffer<FlowPendingExit> exits = pendingExits;

                 pendingExits = prevPendingExits;

                 scan(tree.finalizer);

                 if (!tree.finallyCanCompleteNormally) {

                     // discard exits and exceptions from try and finally

                     thrown = chk.union(thrown, thrownPrev);

                 } else {

                     thrown = chk.union(thrown, chk.diff(thrownInTry, caughtInTry));

                     thrown = chk.union(thrown, savedThrown);

                     // FIX: this doesn't preserve source order of exits in catch

                     // versus finally!

                     while (exits.nonEmpty()) {

                         pendingExits.append(exits.next());

                     }

                 }

             } else {

                 thrown = chk.union(thrown, chk.diff(thrownInTry, caughtInTry));

                 ListBuffer<FlowPendingExit> exits = pendingExits;

                 pendingExits = prevPendingExits;

                 while (exits.nonEmpty()) pendingExits.append(exits.next());

             }

         }

         @Override

         public void visitIf(JCIf tree) {

             scan(tree.cond);

             scan(tree.thenpart);

             if (tree.elsepart != null) {

                 scan(tree.elsepart);

             }

         }

         void checkCaughtType(DiagnosticPosition pos, Type exc, List<Type> thrownInTry, List<Type> caughtInTry) {

             if (chk.subset(exc, caughtInTry)) {

                 log.error(pos, "except.already.caught", exc);

             } else if (!chk.isUnchecked(pos, exc) &&

                     !isExceptionOrThrowable(exc) &&

                     !chk.intersects(exc, thrownInTry)) {

                 log.error(pos, "except.never.thrown.in.try", exc);

             } else if (allowImprovedCatchAnalysis) {

                 List<Type> catchableThrownTypes = chk.intersect(List.of(exc), thrownInTry);

                 // 'catchableThrownTypes' cannnot possibly be empty - if 'exc' was an

                 // unchecked exception, the result list would not be empty, as the augmented

                 // thrown set includes { RuntimeException, Error }; if 'exc' was a checked

                 // exception, that would have been covered in the branch above

                 if (chk.diff(catchableThrownTypes, caughtInTry).isEmpty() &&

                         !isExceptionOrThrowable(exc)) {

                     String key = catchableThrownTypes.length() == 1 ?

                             "unreachable.catch" :

                             "unreachable.catch.1";

                     log.warning(pos, key, catchableThrownTypes);

                 }

             }

         }

         //where

             private boolean isExceptionOrThrowable(Type exc) {

                 return exc.tsym == syms.throwableType.tsym ||

                     exc.tsym == syms.exceptionType.tsym;

             }

         public void visitBreak(JCBreak tree) {

             recordExit(tree, new FlowPendingExit(tree, null));

         }

         public void visitContinue(JCContinue tree) {

             recordExit(tree, new FlowPendingExit(tree, null));

         }

         public void visitReturn(JCReturn tree) {

             scan(tree.expr);

             recordExit(tree, new FlowPendingExit(tree, null));

         }

         public void visitThrow(JCThrow tree) {

             scan(tree.expr);

             Symbol sym = TreeInfo.symbol(tree.expr);

             if (sym != null &&

                 sym.kind == VAR &&

                 (sym.flags() & (FINAL | EFFECTIVELY_FINAL)) != 0 &&

                 preciseRethrowTypes.get(sym) != null &&

                 allowImprovedRethrowAnalysis) {

                 for (Type t : preciseRethrowTypes.get(sym)) {

                     markThrown(tree, t);

                 }

             }

             else {

                 markThrown(tree, tree.expr.type);

             }

             markDead();

         }

         public void visitApply(JCMethodInvocation tree) {

             scan(tree.meth);

             scan(tree.args);

             for (List<Type> l = tree.meth.type.getThrownTypes(); l.nonEmpty(); l = l.tail)

                 markThrown(tree, l.head);

         }

         public void visitNewClass(JCNewClass tree) {

             scan(tree.encl);

             scan(tree.args);

            // scan(tree.def);

             for (List<Type> l = tree.constructorType.getThrownTypes();

                  l.nonEmpty();

                  l = l.tail) {

                 markThrown(tree, l.head);

             }

             List<Type> caughtPrev = caught;

             try {

                 // If the new class expression defines an anonymous class,

                 // analysis of the anonymous constructor may encounter thrown

                 // types which are unsubstituted type variables.

                 // However, since the constructor's actual thrown types have

                 // already been marked as thrown, it is safe to simply include

                 // each of the constructor's formal thrown types in the set of

                 // 'caught/declared to be thrown' types, for the duration of

                 // the class def analysis.

                 if (tree.def != null)

                     for (List<Type> l = tree.constructor.type.getThrownTypes();

                          l.nonEmpty();

                          l = l.tail) {

                         caught = chk.incl(l.head, caught);

                     }

                 scan(tree.def);

             }

             finally {

                 caught = caughtPrev;

             }

         }

         public void visitTopLevel(JCCompilationUnit tree) {

             // Do nothing for TopLevel since each class is visited individually

         }

     /**************************************************************************

      * main method

      *************************************************************************/

         /** Perform definite assignment/unassignment analysis on a tree.

          */

         public void analyzeTree(Env<AttrContext> env, TreeMaker make) {

             analyzeTree(env, env.tree, make);

         }

         public void analyzeTree(Env<AttrContext> env, JCTree tree, TreeMaker make) {

             try {

                 attrEnv = env;

                 Flow.this.make = make;

                 pendingExits = new ListBuffer<FlowPendingExit>();

                 preciseRethrowTypes = new HashMap<Symbol, List<Type>>();

                 this.thrown = this.caught = null;

                 this.classDef = null;

                 scan(tree);

             } finally {

                 pendingExits = null;

                 Flow.this.make = null;

                 this.thrown = this.caught = null;

                 this.classDef = null;

             }

         }

     }

     /**

      * This pass implements (i) definite assignment analysis, which ensures that

      * each variable is assigned when used and (ii) definite unassignment analysis,

      * which ensures that no final variable is assigned more than once. This visitor

      * depends on the results of the liveliness analyzer. This pass is also used to mark

      * effectively-final local variables/parameters.

      */

     class AssignAnalyzer extends BaseAnalyzer<AssignAnalyzer.AssignPendingExit> {

         /** The set of definitely assigned variables.

          */

         Bits inits;

         /** The set of definitely unassigned variables.

          */

         Bits uninits;

         /** The set of variables that are definitely unassigned everywhere

          *  in current try block. This variable is maintained lazily; it is

          *  updated only when something gets removed from uninits,

          *  typically by being assigned in reachable code.  To obtain the

          *  correct set of variables which are definitely unassigned

          *  anywhere in current try block, intersect uninitsTry and

          *  uninits.

          */

         Bits uninitsTry;

         /** When analyzing a condition, inits and uninits are null.

          *  Instead we have:

          */

         Bits initsWhenTrue;

         Bits initsWhenFalse;

         Bits uninitsWhenTrue;

         Bits uninitsWhenFalse;

         /** A mapping from addresses to variable symbols.

          */

         VarSymbol[] vars;

         /** The current class being defined.

          */

         JCClassDecl classDef;

         /** The first variable sequence number in this class definition.

          */

         int firstadr;

         /** The next available variable sequence number.

          */

         int nextadr;

         /** The list of unreferenced automatic resources.

          */

         Scope unrefdResources;

         /** Set when processing a loop body the second time for DU analysis. */

         FlowKind flowKind = FlowKind.NORMAL;

         /** The starting position of the analysed tree */

         int startPos;

         class AssignPendingExit extends BaseAnalyzer.PendingExit {

             Bits exit_inits;

             Bits exit_uninits;

             AssignPendingExit(JCTree tree, Bits inits, Bits uninits) {

                 super(tree);

                 this.exit_inits = inits.dup();

                 this.exit_uninits = uninits.dup();

             }

             void resolveJump() {

                 inits.andSet(exit_inits);

                 uninits.andSet(exit_uninits);

             }

         }

         @Override

         void markDead() {

             inits.inclRange(firstadr, nextadr);

             uninits.inclRange(firstadr, nextadr);

         }

         /*-------------- Processing variables ----------------------*/

         /** Do we need to track init/uninit state of this symbol?

          *  I.e. is symbol either a local or a blank final variable?

          */

         boolean trackable(VarSymbol sym) {

             return

                 sym.pos >= startPos &&

                 ((sym.owner.kind == MTH ||

                  ((sym.flags() & (FINAL | HASINIT | PARAMETER)) == FINAL &&

                   classDef.sym.isEnclosedBy((ClassSymbol)sym.owner))));

         }

         /** Initialize new trackable variable by setting its address field

          *  to the next available sequence number and entering it under that

          *  index into the vars array.

          */

         void newVar(VarSymbol sym) {

             if (nextadr == vars.length) {

                 VarSymbol[] newvars = new VarSymbol[nextadr * 2];

                 System.arraycopy(vars, 0, newvars, 0, nextadr);

                 vars = newvars;

             }

             if ((sym.flags() & FINAL) == 0) {

                 sym.flags_field |= EFFECTIVELY_FINAL;

             }

             sym.adr = nextadr;

             vars[nextadr] = sym;

             inits.excl(nextadr);

             uninits.incl(nextadr);

             nextadr++;

         }

         /** Record an initialization of a trackable variable.

          */

         void letInit(DiagnosticPosition pos, VarSymbol sym) {

             if (sym.adr >= firstadr && trackable(sym)) {

                 if ((sym.flags() & EFFECTIVELY_FINAL) != 0) {

                     if (!uninits.isMember(sym.adr)) {

                         //assignment targeting an effectively final variable

                         //makes the variable lose its status of effectively final

                         //if the variable is _not_ definitively unassigned

                         sym.flags_field &= ~EFFECTIVELY_FINAL;

                     } else {

                         uninit(sym);

                     }

                 }

                 else if ((sym.flags() & FINAL) != 0) {

                     if ((sym.flags() & PARAMETER) != 0) {

                         if ((sym.flags() & UNION) != 0) { //multi-catch parameter

                             log.error(pos, "multicatch.parameter.may.not.be.assigned",

                                       sym);

                         }

                         else {

                             log.error(pos, "final.parameter.may.not.be.assigned",

                                   sym);

                         }

                     } else if (!uninits.isMember(sym.adr)) {

                         log.error(pos, flowKind.errKey, sym);

                     } else {

                         uninit(sym);

                     }

                 }

                 inits.incl(sym.adr);

             } else if ((sym.flags() & FINAL) != 0) {

                 log.error(pos, "var.might.already.be.assigned", sym);

             }

         }

         //where

             void uninit(VarSymbol sym) {

                 if (!inits.isMember(sym.adr)) {

                     // reachable assignment

                     uninits.excl(sym.adr);

                     uninitsTry.excl(sym.adr);

                 } else {

                     //log.rawWarning(pos, "unreachable assignment");//DEBUG

                     uninits.excl(sym.adr);

                 }

             }

         /** If tree is either a simple name or of the form this.name or

          *  C.this.name, and tree represents a trackable variable,

          *  record an initialization of the variable.

          */

         void letInit(JCTree tree) {

             tree = TreeInfo.skipParens(tree);

             if (tree.hasTag(IDENT) || tree.hasTag(SELECT)) {

                 Symbol sym = TreeInfo.symbol(tree);

                 if (sym.kind == VAR) {

                     letInit(tree.pos(), (VarSymbol)sym);

                 }

             }

         }

         /** Check that trackable variable is initialized.

          */

         void checkInit(DiagnosticPosition pos, VarSymbol sym) {

             if ((sym.adr >= firstadr || sym.owner.kind != TYP) &&

                 trackable(sym) &&

                 !inits.isMember(sym.adr)) {

                 log.error(pos, "var.might.not.have.been.initialized",

                           sym);

                 inits.incl(sym.adr);

             }

         }

         /** Split (duplicate) inits/uninits into WhenTrue/WhenFalse sets

          */

         void split(boolean setToNull) {

             initsWhenFalse = inits.dup();

             uninitsWhenFalse = uninits.dup();

             initsWhenTrue = inits;

             uninitsWhenTrue = uninits;

             if (setToNull)

                 inits = uninits = null;

         }

         /** Merge (intersect) inits/uninits from WhenTrue/WhenFalse sets.

          */

         void merge() {

             inits = initsWhenFalse.andSet(initsWhenTrue);

             uninits = uninitsWhenFalse.andSet(uninitsWhenTrue);

         }

     /* ************************************************************************

      * Visitor methods for statements and definitions

      *************************************************************************/

         /** Analyze an expression. Make sure to set (un)inits rather than

          *  (un)initsWhenTrue(WhenFalse) on exit.

          */

         void scanExpr(JCTree tree) {

             if (tree != null) {

                 scan(tree);

                 if (inits == null) merge();

             }

         }

         /** Analyze a list of expressions.

          */

         void scanExprs(List<? extends JCExpression> trees) {

             if (trees != null)

                 for (List<? extends JCExpression> l = trees; l.nonEmpty(); l = l.tail)

                     scanExpr(l.head);

         }

         /** Analyze a condition. Make sure to set (un)initsWhenTrue(WhenFalse)

          *  rather than (un)inits on exit.

          */

         void scanCond(JCTree tree) {

             if (tree.type.isFalse()) {

                 if (inits == null) merge();

                 initsWhenTrue = inits.dup();

                 initsWhenTrue.inclRange(firstadr, nextadr);

                 uninitsWhenTrue = uninits.dup();

                 uninitsWhenTrue.inclRange(firstadr, nextadr);

                 initsWhenFalse = inits;

                 uninitsWhenFalse = uninits;

             } else if (tree.type.isTrue()) {

                 if (inits == null) merge();

                 initsWhenFalse = inits.dup();

                 initsWhenFalse.inclRange(firstadr, nextadr);

                 uninitsWhenFalse = uninits.dup();

                 uninitsWhenFalse.inclRange(firstadr, nextadr);

                 initsWhenTrue = inits;

                 uninitsWhenTrue = uninits;

             } else {

                 scan(tree);

                 if (inits != null)

                     split(tree.type != syms.unknownType);

             }

             if (tree.type != syms.unknownType)

                 inits = uninits = null;

         }

         /* ------------ Visitor methods for various sorts of trees -------------*/

         public void visitClassDef(JCClassDecl tree) {

             if (tree.sym == null) return;

             JCClassDecl classDefPrev = classDef;

             int firstadrPrev = firstadr;

             int nextadrPrev = nextadr;

             ListBuffer<AssignPendingExit> pendingExitsPrev = pendingExits;

             Lint lintPrev = lint;

             pendingExits = new ListBuffer<AssignPendingExit>();

             if (tree.name != names.empty) {

                 firstadr = nextadr;

             }

             classDef = tree;

             lint = lint.augment(tree.sym.attributes_field);

             try {

                 // define all the static fields

                 for (List<JCTree> l = tree.defs; l.nonEmpty(); l = l.tail) {

                     if (l.head.hasTag(VARDEF)) {

                         JCVariableDecl def = (JCVariableDecl)l.head;

                         if ((def.mods.flags & STATIC) != 0) {

                             VarSymbol sym = def.sym;

                             if (trackable(sym))

                                 newVar(sym);

                         }

                     }

                 }

                 // process all the static initializers

                 for (List<JCTree> l = tree.defs; l.nonEmpty(); l = l.tail) {

                     if (!l.head.hasTag(METHODDEF) &&

                         (TreeInfo.flags(l.head) & STATIC) != 0) {

                         scan(l.head);

                     }

                 }

                 // define all the instance fields

                 for (List<JCTree> l = tree.defs; l.nonEmpty(); l = l.tail) {

                     if (l.head.hasTag(VARDEF)) {

                         JCVariableDecl def = (JCVariableDecl)l.head;

                         if ((def.mods.flags & STATIC) == 0) {

                             VarSymbol sym = def.sym;

                             if (trackable(sym))

                                 newVar(sym);

                         }

                     }

                 }

                 // process all the instance initializers

                 for (List<JCTree> l = tree.defs; l.nonEmpty(); l = l.tail) {

                     if (!l.head.hasTag(METHODDEF) &&

                         (TreeInfo.flags(l.head) & STATIC) == 0) {

                         scan(l.head);

                     }

                 }

                 // process all the methods

                 for (List<JCTree> l = tree.defs; l.nonEmpty(); l = l.tail) {

                     if (l.head.hasTag(METHODDEF)) {

                         scan(l.head);

                     }

                 }

             } finally {

                 pendingExits = pendingExitsPrev;

                 nextadr = nextadrPrev;

                 firstadr = firstadrPrev;

                 classDef = classDefPrev;

                 lint = lintPrev;

             }

         }

         public void visitMethodDef(JCMethodDecl tree) {

             if (tree.body == null) return;

             Bits initsPrev = inits.dup();

             Bits uninitsPrev = uninits.dup();

             int nextadrPrev = nextadr;

             int firstadrPrev = firstadr;

             Lint lintPrev = lint;

             lint = lint.augment(tree.sym.attributes_field);

             Assert.check(pendingExits.isEmpty());

             try {

                 boolean isInitialConstructor =

                     TreeInfo.isInitialConstructor(tree);

                 if (!isInitialConstructor)

                     firstadr = nextadr;

                 for (List<JCVariableDecl> l = tree.params; l.nonEmpty(); l = l.tail) {

                     JCVariableDecl def = l.head;

                     scan(def);

                     inits.incl(def.sym.adr);

                     uninits.excl(def.sym.adr);

                 }

                 // else we are in an instance initializer block;

                 // leave caught unchanged.

                 scan(tree.body);

                 if (isInitialConstructor) {

                     for (int i = firstadr; i < nextadr; i++)

                         if (vars[i].owner == classDef.sym)

                             checkInit(TreeInfo.diagEndPos(tree.body), vars[i]);

                 }

                 List<AssignPendingExit> exits = pendingExits.toList();

                 pendingExits = new ListBuffer<AssignPendingExit>();

                 while (exits.nonEmpty()) {

                     AssignPendingExit exit = exits.head;

                     exits = exits.tail;

                     Assert.check(exit.tree.hasTag(RETURN), exit.tree);

                     if (isInitialConstructor) {

                         inits = exit.exit_inits;

                         for (int i = firstadr; i < nextadr; i++)

                             checkInit(exit.tree.pos(), vars[i]);

                     }

                 }

             } finally {

                 inits = initsPrev;

                 uninits = uninitsPrev;

                 nextadr = nextadrPrev;

                 firstadr = firstadrPrev;

                 lint = lintPrev;

             }

         }

         public void visitVarDef(JCVariableDecl tree) {

             boolean track = trackable(tree.sym);

             if (track && tree.sym.owner.kind == MTH) newVar(tree.sym);

             if (tree.init != null) {

                 Lint lintPrev = lint;

                 lint = lint.augment(tree.sym.attributes_field);

                 try{

                     scanExpr(tree.init);

                     if (track) letInit(tree.pos(), tree.sym);

                 } finally {

                     lint = lintPrev;

                 }

             }

         }

         public void visitBlock(JCBlock tree) {

             int nextadrPrev = nextadr;

             scan(tree.stats);

             nextadr = nextadrPrev;

         }

         public void visitDoLoop(JCDoWhileLoop tree) {

             ListBuffer<AssignPendingExit> prevPendingExits = pendingExits;

             FlowKind prevFlowKind = flowKind;

             flowKind = FlowKind.NORMAL;

             Bits initsSkip = null;

             Bits uninitsSkip = null;

             pendingExits = new ListBuffer<AssignPendingExit>();

             int prevErrors = log.nerrors;

             do {

                 Bits uninitsEntry = uninits.dup();

                 uninitsEntry.excludeFrom(nextadr);

                 scan(tree.body);

                 resolveContinues(tree);

                 scanCond(tree.cond);

                 if (!flowKind.isFinal()) {

                     initsSkip = initsWhenFalse;

                     uninitsSkip = uninitsWhenFalse;

                 }

                 if (log.nerrors !=  prevErrors ||

                     flowKind.isFinal() ||

                     uninitsEntry.dup().diffSet(uninitsWhenTrue).nextBit(firstadr)==-1)

                     break;

                 inits = initsWhenTrue;

                 uninits = uninitsEntry.andSet(uninitsWhenTrue);

                 flowKind = FlowKind.SPECULATIVE_LOOP;

             } while (true);

             flowKind = prevFlowKind;

             inits = initsSkip;

             uninits = uninitsSkip;

             resolveBreaks(tree, prevPendingExits);

         }

         public void visitWhileLoop(JCWhileLoop tree) {

             ListBuffer<AssignPendingExit> prevPendingExits = pendingExits;

             FlowKind prevFlowKind = flowKind;

             flowKind = FlowKind.NORMAL;

             Bits initsSkip = null;

             Bits uninitsSkip = null;

             pendingExits = new ListBuffer<AssignPendingExit>();

             int prevErrors = log.nerrors;

             Bits uninitsEntry = uninits.dup();

             uninitsEntry.excludeFrom(nextadr);

             do {

                 scanCond(tree.cond);

                 if (!flowKind.isFinal()) {

                     initsSkip = initsWhenFalse;

                     uninitsSkip = uninitsWhenFalse;

                 }

                 inits = initsWhenTrue;

                 uninits = uninitsWhenTrue;

                 scan(tree.body);

                 resolveContinues(tree);

                 if (log.nerrors != prevErrors ||

                     flowKind.isFinal() ||

                     uninitsEntry.dup().diffSet(uninits).nextBit(firstadr) == -1)

                     break;

                 uninits = uninitsEntry.andSet(uninits);

                 flowKind = FlowKind.SPECULATIVE_LOOP;

             } while (true);

             flowKind = prevFlowKind;

             //a variable is DA/DU after the while statement, if it's DA/DU assuming the

             //branch is not taken AND if it's DA/DU before any break statement

             inits = initsSkip;

             uninits = uninitsSkip;

             resolveBreaks(tree, prevPendingExits);

         }

         public void visitForLoop(JCForLoop tree) {

             ListBuffer<AssignPendingExit> prevPendingExits = pendingExits;

             FlowKind prevFlowKind = flowKind;

             flowKind = FlowKind.NORMAL;

             int nextadrPrev = nextadr;

             scan(tree.init);

             Bits initsSkip = null;

             Bits uninitsSkip = null;

             pendingExits = new ListBuffer<AssignPendingExit>();

             int prevErrors = log.nerrors;

             do {

                 Bits uninitsEntry = uninits.dup();

                 uninitsEntry.excludeFrom(nextadr);

                 if (tree.cond != null) {

                     scanCond(tree.cond);

                     if (!flowKind.isFinal()) {

                         initsSkip = initsWhenFalse;

                         uninitsSkip = uninitsWhenFalse;

                     }

                     inits = initsWhenTrue;

                     uninits = uninitsWhenTrue;

                 } else if (!flowKind.isFinal()) {

                     initsSkip = inits.dup();

                     initsSkip.inclRange(firstadr, nextadr);

                     uninitsSkip = uninits.dup();

                     uninitsSkip.inclRange(firstadr, nextadr);

                 }

                 scan(tree.body);

                 resolveContinues(tree);

                 scan(tree.step);

                 if (log.nerrors != prevErrors ||

                     flowKind.isFinal() ||

                     uninitsEntry.dup().diffSet(uninits).nextBit(firstadr) == -1)

                     break;

                 uninits = uninitsEntry.andSet(uninits);

                 flowKind = FlowKind.SPECULATIVE_LOOP;

             } while (true);

             flowKind = prevFlowKind;

             //a variable is DA/DU after a for loop, if it's DA/DU assuming the

             //branch is not taken AND if it's DA/DU before any break statement

             inits = initsSkip;

             uninits = uninitsSkip;

             resolveBreaks(tree, prevPendingExits);

             nextadr = nextadrPrev;

         }

         public void visitForeachLoop(JCEnhancedForLoop tree) {

             visitVarDef(tree.var);

             ListBuffer<AssignPendingExit> prevPendingExits = pendingExits;

             FlowKind prevFlowKind = flowKind;

             flowKind = FlowKind.NORMAL;

             int nextadrPrev = nextadr;

             scan(tree.expr);

             Bits initsStart = inits.dup();

             Bits uninitsStart = uninits.dup();

             letInit(tree.pos(), tree.var.sym);

             pendingExits = new ListBuffer<AssignPendingExit>();

             int prevErrors = log.nerrors;

             do {

                 Bits uninitsEntry = uninits.dup();

                 uninitsEntry.excludeFrom(nextadr);

                 scan(tree.body);

                 resolveContinues(tree);

                 if (log.nerrors != prevErrors ||

                     flowKind.isFinal() ||

                     uninitsEntry.dup().diffSet(uninits).nextBit(firstadr) == -1)

                     break;

                 uninits = uninitsEntry.andSet(uninits);

                 flowKind = FlowKind.SPECULATIVE_LOOP;

             } while (true);

             flowKind = prevFlowKind;

             inits = initsStart;

             uninits = uninitsStart.andSet(uninits);

             resolveBreaks(tree, prevPendingExits);

             nextadr = nextadrPrev;

         }

         public void visitLabelled(JCLabeledStatement tree) {

             ListBuffer<AssignPendingExit> prevPendingExits = pendingExits;

             pendingExits = new ListBuffer<AssignPendingExit>();

             scan(tree.body);

             resolveBreaks(tree, prevPendingExits);

         }

         public void visitSwitch(JCSwitch tree) {

             ListBuffer<AssignPendingExit> prevPendingExits = pendingExits;

             pendingExits = new ListBuffer<AssignPendingExit>();

             int nextadrPrev = nextadr;

             scanExpr(tree.selector);

             Bits initsSwitch = inits;

             Bits uninitsSwitch = uninits.dup();

             boolean hasDefault = false;

             for (List<JCCase> l = tree.cases; l.nonEmpty(); l = l.tail) {

                 inits = initsSwitch.dup();

                 uninits = uninits.andSet(uninitsSwitch);

                 JCCase c = l.head;

                 if (c.pat == null)

                     hasDefault = true;

                 else

                     scanExpr(c.pat);

                 scan(c.stats);

                 addVars(c.stats, initsSwitch, uninitsSwitch);

                 // Warn about fall-through if lint switch fallthrough enabled.

             }

             if (!hasDefault) {

                 inits.andSet(initsSwitch);

             }

             resolveBreaks(tree, prevPendingExits);

             nextadr = nextadrPrev;

         }

         // where

             /** Add any variables defined in stats to inits and uninits. */

             private void addVars(List<JCStatement> stats, Bits inits,

                                         Bits uninits) {

                 for (;stats.nonEmpty(); stats = stats.tail) {

                     JCTree stat = stats.head;

                     if (stat.hasTag(VARDEF)) {

                         int adr = ((JCVariableDecl) stat).sym.adr;

                         inits.excl(adr);

                         uninits.incl(adr);

                     }

                 }

             }

         public void visitTry(JCTry tree) {

             ListBuffer<JCVariableDecl> resourceVarDecls = ListBuffer.lb();

             Bits uninitsTryPrev = uninitsTry;

             ListBuffer<AssignPendingExit> prevPendingExits = pendingExits;

             pendingExits = new ListBuffer<AssignPendingExit>();

             Bits initsTry = inits.dup();

             uninitsTry = uninits.dup();

             for (JCTree resource : tree.resources) {

                 if (resource instanceof JCVariableDecl) {

                     JCVariableDecl vdecl = (JCVariableDecl) resource;

                     visitVarDef(vdecl);

                     unrefdResources.enter(vdecl.sym);

                     resourceVarDecls.append(vdecl);

                 } else if (resource instanceof JCExpression) {

                     scanExpr((JCExpression) resource);

                 } else {

                     throw new AssertionError(tree);  // parser error

                 }

             }

             scan(tree.body);

             uninitsTry.andSet(uninits);

             Bits initsEnd = inits;

             Bits uninitsEnd = uninits;

             int nextadrCatch = nextadr;

             if (!resourceVarDecls.isEmpty() &&

                     lint.isEnabled(Lint.LintCategory.TRY)) {

                 for (JCVariableDecl resVar : resourceVarDecls) {

                     if (unrefdResources.includes(resVar.sym)) {

                         log.warning(Lint.LintCategory.TRY, resVar.pos(),

                                     "try.resource.not.referenced", resVar.sym);

                         unrefdResources.remove(resVar.sym);

                     }

                 }

             }

             for (List<JCCatch> l = tree.catchers; l.nonEmpty(); l = l.tail) {

                 JCVariableDecl param = l.head.param;

                 inits = initsTry.dup();

                 uninits = uninitsTry.dup();

                 scan(param);

                 inits.incl(param.sym.adr);

                 uninits.excl(param.sym.adr);

                 scan(l.head.body);

                 initsEnd.andSet(inits);

                 uninitsEnd.andSet(uninits);

                 nextadr = nextadrCatch;

             }

             if (tree.finalizer != null) {

                 inits = initsTry.dup();

                 uninits = uninitsTry.dup();

                 ListBuffer<AssignPendingExit> exits = pendingExits;

                 pendingExits = prevPendingExits;

                 scan(tree.finalizer);

                 if (!tree.finallyCanCompleteNormally) {

                     // discard exits and exceptions from try and finally

                 } else {

                     uninits.andSet(uninitsEnd);

                     // FIX: this doesn't preserve source order of exits in catch

                     // versus finally!

                     while (exits.nonEmpty()) {

                         AssignPendingExit exit = exits.next();

                         if (exit.exit_inits != null) {

                             exit.exit_inits.orSet(inits);

                             exit.exit_uninits.andSet(uninits);

                         }

                         pendingExits.append(exit);

                     }

                     inits.orSet(initsEnd);

                 }

             } else {

                 inits = initsEnd;

                 uninits = uninitsEnd;

                 ListBuffer<AssignPendingExit> exits = pendingExits;

                 pendingExits = prevPendingExits;

                 while (exits.nonEmpty()) pendingExits.append(exits.next());

             }

             uninitsTry.andSet(uninitsTryPrev).andSet(uninits);

         }

         public void visitConditional(JCConditional tree) {

             scanCond(tree.cond);

             Bits initsBeforeElse = initsWhenFalse;

             Bits uninitsBeforeElse = uninitsWhenFalse;

             inits = initsWhenTrue;

             uninits = uninitsWhenTrue;

             if (tree.truepart.type.tag == BOOLEAN &&

                 tree.falsepart.type.tag == BOOLEAN) {

                 // if b and c are boolean valued, then

                 // v is (un)assigned after a?b:c when true iff

                 //    v is (un)assigned after b when true and

                 //    v is (un)assigned after c when true

                 scanCond(tree.truepart);

                 Bits initsAfterThenWhenTrue = initsWhenTrue.dup();

                 Bits initsAfterThenWhenFalse = initsWhenFalse.dup();

                 Bits uninitsAfterThenWhenTrue = uninitsWhenTrue.dup();

                 Bits uninitsAfterThenWhenFalse = uninitsWhenFalse.dup();

                 inits = initsBeforeElse;

                 uninits = uninitsBeforeElse;

                 scanCond(tree.falsepart);

                 initsWhenTrue.andSet(initsAfterThenWhenTrue);

                 initsWhenFalse.andSet(initsAfterThenWhenFalse);

                 uninitsWhenTrue.andSet(uninitsAfterThenWhenTrue);

                 uninitsWhenFalse.andSet(uninitsAfterThenWhenFalse);

             } else {

                 scanExpr(tree.truepart);

                 Bits initsAfterThen = inits.dup();

                 Bits uninitsAfterThen = uninits.dup();

                 inits = initsBeforeElse;

                 uninits = uninitsBeforeElse;

                 scanExpr(tree.falsepart);

                 inits.andSet(initsAfterThen);

                 uninits.andSet(uninitsAfterThen);

             }

         }

         public void visitIf(JCIf tree) {

             scanCond(tree.cond);

             Bits initsBeforeElse = initsWhenFalse;

             Bits uninitsBeforeElse = uninitsWhenFalse;

             inits = initsWhenTrue;

             uninits = uninitsWhenTrue;

             scan(tree.thenpart);

             if (tree.elsepart != null) {

                 Bits initsAfterThen = inits.dup();

                 Bits uninitsAfterThen = uninits.dup();

                 inits = initsBeforeElse;

                 uninits = uninitsBeforeElse;

                 scan(tree.elsepart);

                 inits.andSet(initsAfterThen);

                 uninits.andSet(uninitsAfterThen);

             } else {

                 inits.andSet(initsBeforeElse);

                 uninits.andSet(uninitsBeforeElse);

             }

         }

         public void visitBreak(JCBreak tree) {

             recordExit(tree, new AssignPendingExit(tree, inits, uninits));

         }

         public void visitContinue(JCContinue tree) {

             recordExit(tree, new AssignPendingExit(tree, inits, uninits));

         }

         public void visitReturn(JCReturn tree) {

             scanExpr(tree.expr);

             recordExit(tree, new AssignPendingExit(tree, inits, uninits));

         }

         public void visitThrow(JCThrow tree) {

             scanExpr(tree.expr);

             markDead();

         }

         public void visitApply(JCMethodInvocation tree) {

             scanExpr(tree.meth);

             scanExprs(tree.args);

         }

         public void visitNewClass(JCNewClass tree) {

             scanExpr(tree.encl);

             scanExprs(tree.args);

             scan(tree.def);

         }

         public void visitNewArray(JCNewArray tree) {

             scanExprs(tree.dims);

             scanExprs(tree.elems);

         }

         public void visitAssert(JCAssert tree) {

             Bits initsExit = inits.dup();

             Bits uninitsExit = uninits.dup();

             scanCond(tree.cond);

             uninitsExit.andSet(uninitsWhenTrue);

             if (tree.detail != null) {

                 inits = initsWhenFalse;

                 uninits = uninitsWhenFalse;

                 scanExpr(tree.detail);

             }

             inits = initsExit;

             uninits = uninitsExit;

         }

         public void visitAssign(JCAssign tree) {

             JCTree lhs = TreeInfo.skipParens(tree.lhs);

             if (!(lhs instanceof JCIdent)) {

                 scanExpr(lhs);

             }

             scanExpr(tree.rhs);

             letInit(lhs);

         }

         public void visitAssignop(JCAssignOp tree) {

             scanExpr(tree.lhs);

             scanExpr(tree.rhs);

             letInit(tree.lhs);

         }

         public void visitUnary(JCUnary tree) {

             switch (tree.getTag()) {

             case NOT:

                 scanCond(tree.arg);

                 Bits t = initsWhenFalse;

                 initsWhenFalse = initsWhenTrue;

                 initsWhenTrue = t;

                 t = uninitsWhenFalse;

                 uninitsWhenFalse = uninitsWhenTrue;

                 uninitsWhenTrue = t;

                 break;

             case PREINC: case POSTINC:

             case PREDEC: case POSTDEC:

                 scanExpr(tree.arg);

                 letInit(tree.arg);

                 break;

             default:

                 scanExpr(tree.arg);

             }

         }

         public void visitBinary(JCBinary tree) {

             switch (tree.getTag()) {

             case AND:

                 scanCond(tree.lhs);

                 Bits initsWhenFalseLeft = initsWhenFalse;

                 Bits uninitsWhenFalseLeft = uninitsWhenFalse;

                 inits = initsWhenTrue;

                 uninits = uninitsWhenTrue;

                 scanCond(tree.rhs);

                 initsWhenFalse.andSet(initsWhenFalseLeft);

                 uninitsWhenFalse.andSet(uninitsWhenFalseLeft);

                 break;

             case OR:

                 scanCond(tree.lhs);

                 Bits initsWhenTrueLeft = initsWhenTrue;

                 Bits uninitsWhenTrueLeft = uninitsWhenTrue;

                 inits = initsWhenFalse;

                 uninits = uninitsWhenFalse;

                 scanCond(tree.rhs);

                 initsWhenTrue.andSet(initsWhenTrueLeft);

                 uninitsWhenTrue.andSet(uninitsWhenTrueLeft);

                 break;

             default:

                 scanExpr(tree.lhs);

                 scanExpr(tree.rhs);

             }

         }

         public void visitIdent(JCIdent tree) {

             if (tree.sym.kind == VAR) {

                 checkInit(tree.pos(), (VarSymbol)tree.sym);

                 referenced(tree.sym);

             }

         }

         void referenced(Symbol sym) {

             unrefdResources.remove(sym);

         }

         public void visitTopLevel(JCCompilationUnit tree) {

             // Do nothing for TopLevel since each class is visited individually

         }

     /**************************************************************************

      * main method

      *************************************************************************/

         /** Perform definite assignment/unassignment analysis on a tree.

          */

         public void analyzeTree(Env<AttrContext> env, TreeMaker make) {

             analyzeTree(env, env.tree, make);

         }

         public void analyzeTree(Env<AttrContext> env, JCTree tree, TreeMaker make) {

             try {

                 attrEnv = env;

                 Flow.this.make = make;

                 startPos = tree.pos().getStartPosition();

                 inits = new Bits();

                 uninits = new Bits();

                 uninitsTry = new Bits();

                 initsWhenTrue = initsWhenFalse =

                     uninitsWhenTrue = uninitsWhenFalse = null;

                 if (vars == null)

                     vars = new VarSymbol[32];

                 else

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

                         vars[i] = null;

                 firstadr = 0;

                 nextadr = 0;

                 pendingExits = new ListBuffer<AssignPendingExit>();

                 this.classDef = null;

                 unrefdResources = new Scope(env.enclClass.sym);

                 scan(tree);

             } finally {

                 // note that recursive invocations of this method fail hard

                 startPos = -1;

                 inits = uninits = uninitsTry = null;

                 initsWhenTrue = initsWhenFalse =

                     uninitsWhenTrue = uninitsWhenFalse = null;

                 if (vars != null) for (int i=0; i<vars.length; i++)

                     vars[i] = null;

                 firstadr = 0;

                 nextadr = 0;

                 pendingExits = null;

                 Flow.this.make = null;

                 this.classDef = null;

                 unrefdResources = null;

             }

         }

     }

     /**

      * This pass implements the last step of the dataflow analysis, namely

      * the effectively-final analysis check. This checks that every local variable

      * reference from a lambda body/local inner class is either final or effectively final.

      * As effectively final variables are marked as such during DA/DU, this pass must run after

      * AssignAnalyzer.

      */

     class CaptureAnalyzer extends BaseAnalyzer<BaseAnalyzer.PendingExit> {

         JCTree currentTree; //local class or lambda

         @Override

         void markDead() {

             //do nothing

         }

         @SuppressWarnings("fallthrough")

         void checkEffectivelyFinal(DiagnosticPosition pos, VarSymbol sym) {

             if (currentTree != null &&

                     sym.owner.kind == MTH &&

                     sym.pos < currentTree.getStartPosition()) {

                 switch (currentTree.getTag()) {

                     case CLASSDEF:

                         if (!allowEffectivelyFinalInInnerClasses) {

                             if ((sym.flags() & FINAL) == 0) {

                                 reportInnerClsNeedsFinalError(pos, sym);

                             }

                             break;

                         }

                     case LAMBDA:

                         if ((sym.flags() & (EFFECTIVELY_FINAL | FINAL)) == 0) {

                            reportEffectivelyFinalError(pos, sym);

                         }

                 }

             }

         }

         @SuppressWarnings("fallthrough")

         void letInit(JCTree tree) {

             tree = TreeInfo.skipParens(tree);

             if (tree.hasTag(IDENT) || tree.hasTag(SELECT)) {

                 Symbol sym = TreeInfo.symbol(tree);

                 if (currentTree != null &&

                         sym.kind == VAR &&

                         sym.owner.kind == MTH &&

                         ((VarSymbol)sym).pos < currentTree.getStartPosition()) {

                     switch (currentTree.getTag()) {

                         case CLASSDEF:

                             if (!allowEffectivelyFinalInInnerClasses) {

                                 reportInnerClsNeedsFinalError(tree, sym);

                                 break;

                             }

                         case LAMBDA:

                             reportEffectivelyFinalError(tree, sym);

                     }

                 }

             }

         }

         void reportEffectivelyFinalError(DiagnosticPosition pos, Symbol sym) {

             String subKey = currentTree.hasTag(LAMBDA) ?

                   "lambda"  : "inner.cls";

             log.error(pos, "cant.ref.non.effectively.final.var", sym, diags.fragment(subKey));

         }

         void reportInnerClsNeedsFinalError(DiagnosticPosition pos, Symbol sym) {

             log.error(pos,

                     "local.var.accessed.from.icls.needs.final",

                     sym);

         }

     /*************************************************************************

      * Visitor methods for statements and definitions

      *************************************************************************/

         /* ------------ Visitor methods for various sorts of trees -------------*/

         public void visitClassDef(JCClassDecl tree) {

             JCTree prevTree = currentTree;

             try {

                 currentTree = tree.sym.isLocal() ? tree : null;

                 super.visitClassDef(tree);

             } finally {

                 currentTree = prevTree;

             }

         }

         @Override

         public void visitLambda(JCLambda tree) {

             JCTree prevTree = currentTree;

             try {

                 currentTree = tree;

                 super.visitLambda(tree);

             } finally {

                 currentTree = prevTree;

             }

         }

         @Override

         public void visitIdent(JCIdent tree) {

             if (tree.sym.kind == VAR) {

                 checkEffectivelyFinal(tree, (VarSymbol)tree.sym);

             }

         }

         public void visitAssign(JCAssign tree) {

             JCTree lhs = TreeInfo.skipParens(tree.lhs);

             if (!(lhs instanceof JCIdent)) {

                 scan(lhs);

             }

             scan(tree.rhs);

             letInit(lhs);

         }

         public void visitAssignop(JCAssignOp tree) {

             scan(tree.lhs);

             scan(tree.rhs);

             letInit(tree.lhs);

         }

         public void visitUnary(JCUnary tree) {

             switch (tree.getTag()) {

                 case PREINC: case POSTINC:

                 case PREDEC: case POSTDEC:

                     scan(tree.arg);

                     letInit(tree.arg);

                     break;

                 default:

                     scan(tree.arg);

             }

         }

         public void visitTopLevel(JCCompilationUnit tree) {

             // Do nothing for TopLevel since each class is visited individually

         }

     /**************************************************************************

      * main method

      *************************************************************************/

         /** Perform definite assignment/unassignment analysis on a tree.

          */

         public void analyzeTree(Env<AttrContext> env, TreeMaker make) {

             analyzeTree(env, env.tree, make);

         }

         public void analyzeTree(Env<AttrContext> env, JCTree tree, TreeMaker make) {

             try {

                 attrEnv = env;

                 Flow.this.make = make;

                 pendingExits = new ListBuffer<PendingExit>();

                 scan(tree);

             } finally {

                 pendingExits = null;

                 Flow.this.make = null;

             }

         }

     }

 }