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

 /*

  * Copyright 1999-2008 Sun Microsystems, Inc.  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.  Sun designates this

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

  * by Sun 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 Sun Microsystems, Inc., 4150 Network Circle, Santa Clara,

  * CA 95054 USA or visit www.sun.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 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.Kinds.*;

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

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

  *  Liveness analysis checks that every statement is reachable.

  *  Exception analysis ensures that every checked exception that is

  *  thrown is declared or caught.  Definite assignment analysis

  *  ensures that each variable is assigned when used.  Definite

  *  unassignment analysis ensures that no final variable is assigned

  *  more than once.

  *

  *  <p>The second edition of 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 JLS2 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 API supported by Sun Microsystems.  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 extends TreeScanner {

     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       Lint lint;

     public static Flow instance(Context context) {

         Flow instance = context.get(flowKey);

         if (instance == null)

             instance = new Flow(context);

         return instance;

     }

     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);

     }

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

      *  complete normally.

      */

     private boolean alive;

     /** 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 possibly thrown declarable exceptions.

      */

     List<Type> thrown;

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

      *  thrown.

      */

     List<Type> caught;

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

     boolean loopPassTwo = false;

     /*-------------------- Environments ----------------------*/

     /** 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;

         Bits inits;

         Bits uninits;

         Type thrown;

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

             this.tree = tree;

             this.inits = inits.dup();

             this.uninits = uninits.dup();

         }

         PendingExit(JCTree tree, Type thrown) {

             this.tree = tree;

             this.thrown = thrown;

         }

     }

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

      *  to an enclosing block, in source order.

      */

     ListBuffer<PendingExit> pendingExits;

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

     /** Complain that pending exceptions are not caught.

      */

     void errorUncaught() {

         for (PendingExit exit = pendingExits.next();

              exit != null;

              exit = pendingExits.next()) {

             boolean synthetic = classDef != null &&

                 classDef.pos == exit.tree.pos;

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

                       synthetic

                       ? "unreported.exception.default.constructor"

                       : "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 PendingExit(tree, exc));

             thrown = chk.incl(exc, thrown);

         }

     }

     /*-------------- 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.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;

         }

         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() & FINAL) != 0) {

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

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

                               sym);

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

                     log.error(pos,

                               loopPassTwo

                               ? "var.might.be.assigned.in.loop"

                               : "var.might.already.be.assigned",

                               sym);

                 } else 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);

                 }

             }

             inits.incl(sym.adr);

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

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

         }

     }

     /** 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.getTag() == JCTree.IDENT || tree.getTag() == JCTree.SELECT) {

             Symbol sym = TreeInfo.symbol(tree);

             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);

         }

     }

     /*-------------------- Handling jumps ----------------------*/

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

     void recordExit(JCTree tree) {

         pendingExits.append(new PendingExit(tree, inits, uninits));

         markDead();

     }

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

     boolean resolveBreaks(JCTree tree,

                           ListBuffer<PendingExit> oldPendingExits) {

         boolean result = false;

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

         pendingExits = oldPendingExits;

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

             PendingExit exit = exits.head;

             if (exit.tree.getTag() == JCTree.BREAK &&

                 ((JCBreak) exit.tree).target == tree) {

                 inits.andSet(exit.inits);

                 uninits.andSet(exit.uninits);

                 result = true;

             } else {

                 pendingExits.append(exit);

             }

         }

         return result;

     }

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

     boolean resolveContinues(JCTree tree) {

         boolean result = false;

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

         pendingExits = new ListBuffer<PendingExit>();

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

             PendingExit exit = exits.head;

             if (exit.tree.getTag() == JCTree.CONTINUE &&

                 ((JCContinue) exit.tree).target == tree) {

                 inits.andSet(exit.inits);

                 uninits.andSet(exit.uninits);

                 result = true;

             } else {

                 pendingExits.append(exit);

             }

         }

         return result;

     }

     /** Record that statement is unreachable.

      */

     void markDead() {

         inits.inclRange(firstadr, nextadr);

         uninits.inclRange(firstadr, nextadr);

         alive = false;

     }

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

      */

     void split() {

         initsWhenFalse = inits.dup();

         uninitsWhenFalse = uninits.dup();

         initsWhenTrue = inits;

         uninitsWhenTrue = uninits;

         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 a definition.

      */

     void scanDef(JCTree tree) {

         scanStat(tree);

         if (tree != null && tree.getTag() == JCTree.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.getTag() != JCTree.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);

     }

     /** 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();

         }

         inits = uninits = null;

     }

     /* ------------ 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;

         boolean alivePrev = alive;

         int firstadrPrev = firstadr;

         int nextadrPrev = nextadr;

         ListBuffer<PendingExit> pendingExitsPrev = pendingExits;

         Lint lintPrev = lint;

         pendingExits = new ListBuffer<PendingExit>();

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

             caught = List.nil();

             firstadr = nextadr;

         }

         classDef = tree;

         thrown = List.nil();

         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.getTag() == JCTree.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.getTag() != JCTree.METHODDEF &&

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

                     scanDef(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);

                         }

                     }

                 }

             }

             // define all the instance fields

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

                 if (l.head.getTag() == JCTree.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.getTag() != JCTree.METHODDEF &&

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

                     scanDef(l.head);

                     errorUncaught();

                 }

             }

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

             // the throws clause of the synthetic constructor and propagate

             // outwards.

             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.setThrown(thrown);

                     }

                 }

                 thrownPrev = chk.union(thrown, thrownPrev);

             }

             // process all the methods

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

                 if (l.head.getTag() == JCTree.METHODDEF) {

                     scan(l.head);

                     errorUncaught();

                 }

             }

             thrown = thrownPrev;

         } finally {

             pendingExits = pendingExitsPrev;

             alive = alivePrev;

             nextadr = nextadrPrev;

             firstadr = firstadrPrev;

             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();

         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 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);

             }

             if (isInitialConstructor)

                 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.

             alive = true;

             scanStat(tree.body);

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

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

             if (isInitialConstructor) {

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

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

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

             }

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

             pendingExits = new ListBuffer<PendingExit>();

             while (exits.nonEmpty()) {

                 PendingExit exit = exits.head;

                 exits = exits.tail;

                 if (exit.thrown == null) {

                     assert exit.tree.getTag() == JCTree.RETURN;

                     if (isInitialConstructor) {

                         inits = exit.inits;

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

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

                     }

                 } else {

                     // uncaught throws will be reported later

                     pendingExits.append(exit);

                 }

             }

         } finally {

             inits = initsPrev;

             uninits = uninitsPrev;

             nextadr = nextadrPrev;

             firstadr = firstadrPrev;

             caught = caughtPrev;

             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;

         scanStats(tree.stats);

         nextadr = nextadrPrev;

     }

     public void visitDoLoop(JCDoWhileLoop tree) {

         ListBuffer<PendingExit> prevPendingExits = pendingExits;

         boolean prevLoopPassTwo = loopPassTwo;

         pendingExits = new ListBuffer<PendingExit>();

         do {

             Bits uninitsEntry = uninits.dup();

             scanStat(tree.body);

             alive |= resolveContinues(tree);

             scanCond(tree.cond);

             if (log.nerrors != 0 ||

                 loopPassTwo ||

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

                 break;

             inits = initsWhenTrue;

             uninits = uninitsEntry.andSet(uninitsWhenTrue);

             loopPassTwo = true;

             alive = true;

         } while (true);

         loopPassTwo = prevLoopPassTwo;

         inits = initsWhenFalse;

         uninits = uninitsWhenFalse;

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

         alive |= resolveBreaks(tree, prevPendingExits);

     }

     public void visitWhileLoop(JCWhileLoop tree) {

         ListBuffer<PendingExit> prevPendingExits = pendingExits;

         boolean prevLoopPassTwo = loopPassTwo;

         Bits initsCond;

         Bits uninitsCond;

         pendingExits = new ListBuffer<PendingExit>();

         do {

             Bits uninitsEntry = uninits.dup();

             scanCond(tree.cond);

             initsCond = initsWhenFalse;

             uninitsCond = uninitsWhenFalse;

             inits = initsWhenTrue;

             uninits = uninitsWhenTrue;

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

             scanStat(tree.body);

             alive |= resolveContinues(tree);

             if (log.nerrors != 0 ||

                 loopPassTwo ||

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

                 break;

             uninits = uninitsEntry.andSet(uninits);

             loopPassTwo = true;

             alive = true;

         } while (true);

         loopPassTwo = prevLoopPassTwo;

         inits = initsCond;

         uninits = uninitsCond;

         alive = resolveBreaks(tree, prevPendingExits) ||

             !tree.cond.type.isTrue();

     }

     public void visitForLoop(JCForLoop tree) {

         ListBuffer<PendingExit> prevPendingExits = pendingExits;

         boolean prevLoopPassTwo = loopPassTwo;

         int nextadrPrev = nextadr;

         scanStats(tree.init);

         Bits initsCond;

         Bits uninitsCond;

         pendingExits = new ListBuffer<PendingExit>();

         do {

             Bits uninitsEntry = uninits.dup();

             if (tree.cond != null) {

                 scanCond(tree.cond);

                 initsCond = initsWhenFalse;

                 uninitsCond = uninitsWhenFalse;

                 inits = initsWhenTrue;

                 uninits = uninitsWhenTrue;

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

             } else {

                 initsCond = inits.dup();

                 initsCond.inclRange(firstadr, nextadr);

                 uninitsCond = uninits.dup();

                 uninitsCond.inclRange(firstadr, nextadr);

                 alive = true;

             }

             scanStat(tree.body);

             alive |= resolveContinues(tree);

             scan(tree.step);

             if (log.nerrors != 0 ||

                 loopPassTwo ||

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

                 break;

             uninits = uninitsEntry.andSet(uninits);

             loopPassTwo = true;

             alive = true;

         } while (true);

         loopPassTwo = prevLoopPassTwo;

         inits = initsCond;

         uninits = uninitsCond;

         alive = resolveBreaks(tree, prevPendingExits) ||

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

         nextadr = nextadrPrev;

     }

     public void visitForeachLoop(JCEnhancedForLoop tree) {

         visitVarDef(tree.var);

         ListBuffer<PendingExit> prevPendingExits = pendingExits;

         boolean prevLoopPassTwo = loopPassTwo;

         int nextadrPrev = nextadr;

         scan(tree.expr);

         Bits initsStart = inits.dup();

         Bits uninitsStart = uninits.dup();

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

         pendingExits = new ListBuffer<PendingExit>();

         do {

             Bits uninitsEntry = uninits.dup();

             scanStat(tree.body);

             alive |= resolveContinues(tree);

             if (log.nerrors != 0 ||

                 loopPassTwo ||

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

                 break;

             uninits = uninitsEntry.andSet(uninits);

             loopPassTwo = true;

             alive = true;

         } while (true);

         loopPassTwo = prevLoopPassTwo;

         inits = initsStart;

         uninits = uninitsStart.andSet(uninits);

         resolveBreaks(tree, prevPendingExits);

         alive = true;

         nextadr = nextadrPrev;

     }

     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>();

         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) {

             alive = true;

             inits = initsSwitch.dup();

             uninits = uninits.andSet(uninitsSwitch);

             JCCase c = l.head;

             if (c.pat == null)

                 hasDefault = true;

             else

                 scanExpr(c.pat);

             scanStats(c.stats);

             addVars(c.stats, initsSwitch, uninitsSwitch);

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

             if (!loopPassTwo &&

                 alive &&

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

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

                 log.warning(l.tail.head.pos(),

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

         }

         if (!hasDefault) {

             inits.andSet(initsSwitch);

             alive = true;

         }

         alive |= resolveBreaks(tree, prevPendingExits);

         nextadr = nextadrPrev;

     }

     // where

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

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

                                     Bits uninits) {

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

                 JCTree stat = stats.head;

                 if (stat.getTag() == JCTree.VARDEF) {

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

                     inits.excl(adr);

                     uninits.incl(adr);

                 }

             }

         }

     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)

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

         Bits uninitsTryPrev = uninitsTry;

         ListBuffer<PendingExit> prevPendingExits = pendingExits;

         pendingExits = new ListBuffer<PendingExit>();

         Bits initsTry = inits.dup();

         uninitsTry = uninits.dup();

         scanStat(tree.body);

         List<Type> thrownInTry = thrown;

         thrown = thrownPrev;

         caught = caughtPrev;

         boolean aliveEnd = alive;

         uninitsTry.andSet(uninits);

         Bits initsEnd = inits;

         Bits uninitsEnd = uninits;

         int nextadrCatch = nextadr;

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

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

             alive = true;

             JCVariableDecl param = l.head.param;

             Type exc = param.type;

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

                 log.error(l.head.pos(),

                           "except.already.caught", exc);

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

                        exc.tsym != syms.throwableType.tsym &&

                        exc.tsym != syms.exceptionType.tsym &&

                        !chk.intersects(exc, thrownInTry)) {

                 log.error(l.head.pos(),

                           "except.never.thrown.in.try", exc);

             }

             caughtInTry = chk.incl(exc, caughtInTry);

             inits = initsTry.dup();

             uninits = uninitsTry.dup();

             scan(param);

             inits.incl(param.sym.adr);

             uninits.excl(param.sym.adr);

             scanStat(l.head.body);

             initsEnd.andSet(inits);

             uninitsEnd.andSet(uninits);

             nextadr = nextadrCatch;

             aliveEnd |= alive;

         }

         if (tree.finalizer != null) {

             List<Type> savedThrown = thrown;

             thrown = List.nil();

             inits = initsTry.dup();

             uninits = uninitsTry.dup();

             ListBuffer<PendingExit> exits = pendingExits;

             pendingExits = prevPendingExits;

             alive = true;

             scanStat(tree.finalizer);

             if (!alive) {

                 // discard exits and exceptions from try and finally

                 thrown = chk.union(thrown, thrownPrev);

                 if (!loopPassTwo &&

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

                     log.warning(TreeInfo.diagEndPos(tree.finalizer),

                                 "finally.cannot.complete");

                 }

             } else {

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

                 thrown = chk.union(thrown, savedThrown);

                 uninits.andSet(uninitsEnd);

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

                 // versus finally!

                 while (exits.nonEmpty()) {

                     PendingExit exit = exits.next();

                     if (exit.inits != null) {

                         exit.inits.orSet(inits);

                         exit.uninits.andSet(uninits);

                     }

                     pendingExits.append(exit);

                 }

                 inits.orSet(initsEnd);

                 alive = aliveEnd;

             }

         } else {

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

             inits = initsEnd;

             uninits = uninitsEnd;

             alive = aliveEnd;

             ListBuffer<PendingExit> 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;

         scanStat(tree.thenpart);

         if (tree.elsepart != null) {

             boolean aliveAfterThen = alive;

             alive = true;

             Bits initsAfterThen = inits.dup();

             Bits uninitsAfterThen = uninits.dup();

             inits = initsBeforeElse;

             uninits = uninitsBeforeElse;

             scanStat(tree.elsepart);

             inits.andSet(initsAfterThen);

             uninits.andSet(uninitsAfterThen);

             alive = alive | aliveAfterThen;

         } else {

             inits.andSet(initsBeforeElse);

             uninits.andSet(uninitsBeforeElse);

             alive = true;

         }

     }

     public void visitBreak(JCBreak tree) {

         recordExit(tree);

     }

     public void visitContinue(JCContinue tree) {

         recordExit(tree);

     }

     public void visitReturn(JCReturn tree) {

         scanExpr(tree.expr);

         // if not initial constructor, should markDead instead of recordExit

         recordExit(tree);

     }

     public void visitThrow(JCThrow tree) {

         scanExpr(tree.expr);

         markThrown(tree, tree.expr.type);

         markDead();

     }

     public void visitApply(JCMethodInvocation tree) {

         scanExpr(tree.meth);

         scanExprs(tree.args);

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

             markThrown(tree, l.head);

     }

     public void visitNewClass(JCNewClass tree) {

         scanExpr(tree.encl);

         scanExprs(tree.args);

        // scan(tree.def);

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

              l.nonEmpty();

              l = l.tail)

             markThrown(tree, l.head);

         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 JCTree.NOT:

             scanCond(tree.arg);

             Bits t = initsWhenFalse;

             initsWhenFalse = initsWhenTrue;

             initsWhenTrue = t;

             t = uninitsWhenFalse;

             uninitsWhenFalse = uninitsWhenTrue;

             uninitsWhenTrue = t;

             break;

         case JCTree.PREINC: case JCTree.POSTINC:

         case JCTree.PREDEC: case JCTree.POSTDEC:

             scanExpr(tree.arg);

             letInit(tree.arg);

             break;

         default:

             scanExpr(tree.arg);

         }

     }

     public void visitBinary(JCBinary tree) {

         switch (tree.getTag()) {

         case JCTree.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 JCTree.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);

     }

     public void visitTypeCast(JCTypeCast tree) {

         super.visitTypeCast(tree);

         if (!tree.type.isErroneous()

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

             && types.isSameType(tree.expr.type, tree.clazz.type)) {

             log.warning(tree.pos(), "redundant.cast", tree.expr.type);

         }

     }

     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(JCTree tree, TreeMaker make) {

         try {

             this.make = make;

             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<PendingExit>();

             alive = true;

             this.thrown = this.caught = null;

             this.classDef = null;

             scan(tree);

         } finally {

             // note that recursive invocations of this method fail hard

             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;

             this.make = null;

             this.thrown = this.caught = null;

             this.classDef = null;

         }

     }

 }