void lfort::runUninitializedVariablesAnalysis(
    const DeclContext &dc,
    const CFG &cfg,
    AnalysisDeclContext &ac,
    UninitVariablesHandler &handler,
    UninitVariablesAnalysisStats &stats) {
  CFGBlockValues vals(cfg);
  vals.computeSetOfDeclarations(dc);
  if (vals.hasNoDeclarations())
    return;

  stats.NumVariablesAnalyzed = vals.getNumEntries();

  // Precompute which expressions are uses and which are initializations.
  ClassifyRefs classification(ac);
  cfg.VisitBlockStmts(classification);

  // Mark all variables uninitialized at the entry.
  const CFGBlock &entry = cfg.getEntry();
  ValueVector &vec = vals.getValueVector(&entry);
  const unsigned n = vals.getNumEntries();
  for (unsigned j = 0; j < n ; ++j) {
    vec[j] = Uninitialized;
  }

  // Proceed with the workist.
  DataflowWorklist worklist(cfg, *ac.getAnalysis<PostOrderCFGView>());
  llvm::BitVector previouslyVisited(cfg.getNumBlockIDs());
  worklist.enqueueSuccessors(&cfg.getEntry());
  llvm::BitVector wasAnalyzed(cfg.getNumBlockIDs(), false);
  wasAnalyzed[cfg.getEntry().getBlockID()] = true;
  PruneBlocksHandler PBH(cfg.getNumBlockIDs());

  while (const CFGBlock *block = worklist.dequeue()) {
    PBH.currentBlock = block->getBlockID();

    // Did the block change?
    bool changed = runOnBlock(block, cfg, ac, vals,
                              classification, wasAnalyzed, PBH);
    ++stats.NumBlockVisits;
    if (changed || !previouslyVisited[block->getBlockID()])
      worklist.enqueueSuccessors(block);    
    previouslyVisited[block->getBlockID()] = true;
  }

  if (!PBH.hadAnyUse)
    return;

  // Run through the blocks one more time, and report uninitialized variabes.
  for (CFG::const_iterator BI = cfg.begin(), BE = cfg.end(); BI != BE; ++BI) {
    const CFGBlock *block = *BI;
    if (PBH.hadUse[block->getBlockID()]) {
      runOnBlock(block, cfg, ac, vals, classification, wasAnalyzed, handler);
      ++stats.NumBlockVisits;
    }
  }
}
Exemple #2
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void clang::runUninitializedVariablesAnalysis(
    const DeclContext &dc,
    const CFG &cfg,
    AnalysisDeclContext &ac,
    UninitVariablesHandler &handler,
    UninitVariablesAnalysisStats &stats) {
  CFGBlockValues vals(cfg);
  vals.computeSetOfDeclarations(dc);
  if (vals.hasNoDeclarations())
    return;

  stats.NumVariablesAnalyzed = vals.getNumEntries();

  // Mark all variables uninitialized at the entry.
  const CFGBlock &entry = cfg.getEntry();
  for (CFGBlock::const_succ_iterator i = entry.succ_begin(), 
        e = entry.succ_end(); i != e; ++i) {
    if (const CFGBlock *succ = *i) {
      ValueVector &vec = vals.getValueVector(&entry, succ);
      const unsigned n = vals.getNumEntries();
      for (unsigned j = 0; j < n ; ++j) {
        vec[j] = Uninitialized;
      }
    }
  }

  // Proceed with the workist.
  DataflowWorklist worklist(cfg);
  llvm::BitVector previouslyVisited(cfg.getNumBlockIDs());
  worklist.enqueueSuccessors(&cfg.getEntry());
  llvm::BitVector wasAnalyzed(cfg.getNumBlockIDs(), false);
  wasAnalyzed[cfg.getEntry().getBlockID()] = true;

  while (const CFGBlock *block = worklist.dequeue()) {
    // Did the block change?
    bool changed = runOnBlock(block, cfg, ac, vals, wasAnalyzed);
    ++stats.NumBlockVisits;
    if (changed || !previouslyVisited[block->getBlockID()])
      worklist.enqueueSuccessors(block);    
    previouslyVisited[block->getBlockID()] = true;
  }
  
  // Run through the blocks one more time, and report uninitialized variabes.
  for (CFG::const_iterator BI = cfg.begin(), BE = cfg.end(); BI != BE; ++BI) {
    const CFGBlock *block = *BI;
    if (wasAnalyzed[block->getBlockID()]) {
      runOnBlock(block, cfg, ac, vals, wasAnalyzed, &handler);
      ++stats.NumBlockVisits;
    }
  }
}
Exemple #3
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void FindUnreachableCode(AnalysisDeclContext &AC, Preprocessor &PP,
                         Callback &CB) {

  CFG *cfg = AC.getCFG();
  if (!cfg)
    return;

  // Scan for reachable blocks from the entrance of the CFG.
  // If there are no unreachable blocks, we're done.
  llvm::BitVector reachable(cfg->getNumBlockIDs());
  unsigned numReachable =
    scanMaybeReachableFromBlock(&cfg->getEntry(), PP, reachable);
  if (numReachable == cfg->getNumBlockIDs())
    return;
  
  // If there aren't explicit EH edges, we should include the 'try' dispatch
  // blocks as roots.
  if (!AC.getCFGBuildOptions().AddEHEdges) {
    for (CFG::try_block_iterator I = cfg->try_blocks_begin(),
         E = cfg->try_blocks_end() ; I != E; ++I) {
      numReachable += scanMaybeReachableFromBlock(*I, PP, reachable);
    }
    if (numReachable == cfg->getNumBlockIDs())
      return;
  }

  // There are some unreachable blocks.  We need to find the root blocks that
  // contain code that should be considered unreachable.  
  for (CFG::iterator I = cfg->begin(), E = cfg->end(); I != E; ++I) {
    const CFGBlock *block = *I;
    // A block may have been marked reachable during this loop.
    if (reachable[block->getBlockID()])
      continue;
    
    DeadCodeScan DS(reachable, PP);
    numReachable += DS.scanBackwards(block, CB);
    
    if (numReachable == cfg->getNumBlockIDs())
      return;
  }
}
CFGReverseBlockReachabilityAnalysis::CFGReverseBlockReachabilityAnalysis(const CFG &cfg)
  : analyzed(cfg.getNumBlockIDs(), false) {}
Exemple #5
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/// CheckFallThrough - Check that we don't fall off the end of a
/// Statement that should return a value.
///
/// \returns AlwaysFallThrough iff we always fall off the end of the statement,
/// MaybeFallThrough iff we might or might not fall off the end,
/// NeverFallThroughOrReturn iff we never fall off the end of the statement or
/// return.  We assume NeverFallThrough iff we never fall off the end of the
/// statement but we may return.  We assume that functions not marked noreturn
/// will return.
static ControlFlowKind CheckFallThrough(AnalysisContext &AC) {
    CFG *cfg = AC.getCFG();
    if (cfg == 0) return UnknownFallThrough;

    // The CFG leaves in dead things, and we don't want the dead code paths to
    // confuse us, so we mark all live things first.
    llvm::BitVector live(cfg->getNumBlockIDs());
    unsigned count = reachable_code::ScanReachableFromBlock(cfg->getEntry(),
                     live);

    bool AddEHEdges = AC.getAddEHEdges();
    if (!AddEHEdges && count != cfg->getNumBlockIDs())
        // When there are things remaining dead, and we didn't add EH edges
        // from CallExprs to the catch clauses, we have to go back and
        // mark them as live.
        for (CFG::iterator I = cfg->begin(), E = cfg->end(); I != E; ++I) {
            CFGBlock &b = **I;
            if (!live[b.getBlockID()]) {
                if (b.pred_begin() == b.pred_end()) {
                    if (b.getTerminator() && isa<CXXTryStmt>(b.getTerminator()))
                        // When not adding EH edges from calls, catch clauses
                        // can otherwise seem dead.  Avoid noting them as dead.
                        count += reachable_code::ScanReachableFromBlock(b, live);
                    continue;
                }
            }
        }

    // Now we know what is live, we check the live precessors of the exit block
    // and look for fall through paths, being careful to ignore normal returns,
    // and exceptional paths.
    bool HasLiveReturn = false;
    bool HasFakeEdge = false;
    bool HasPlainEdge = false;
    bool HasAbnormalEdge = false;
    for (CFGBlock::pred_iterator I=cfg->getExit().pred_begin(),
            E = cfg->getExit().pred_end();
            I != E;
            ++I) {
        CFGBlock& B = **I;
        if (!live[B.getBlockID()])
            continue;
        if (B.size() == 0) {
            if (B.getTerminator() && isa<CXXTryStmt>(B.getTerminator())) {
                HasAbnormalEdge = true;
                continue;
            }

            // A labeled empty statement, or the entry block...
            HasPlainEdge = true;
            continue;
        }
        Stmt *S = B[B.size()-1];
        if (isa<ReturnStmt>(S)) {
            HasLiveReturn = true;
            continue;
        }
        if (isa<ObjCAtThrowStmt>(S)) {
            HasFakeEdge = true;
            continue;
        }
        if (isa<CXXThrowExpr>(S)) {
            HasFakeEdge = true;
            continue;
        }
        if (const AsmStmt *AS = dyn_cast<AsmStmt>(S)) {
            if (AS->isMSAsm()) {
                HasFakeEdge = true;
                HasLiveReturn = true;
                continue;
            }
        }
        if (isa<CXXTryStmt>(S)) {
            HasAbnormalEdge = true;
            continue;
        }

        bool NoReturnEdge = false;
        if (CallExpr *C = dyn_cast<CallExpr>(S)) {
            if (std::find(B.succ_begin(), B.succ_end(), &cfg->getExit())
                    == B.succ_end()) {
                HasAbnormalEdge = true;
                continue;
            }
            Expr *CEE = C->getCallee()->IgnoreParenCasts();
            if (getFunctionExtInfo(CEE->getType()).getNoReturn()) {
                NoReturnEdge = true;
                HasFakeEdge = true;
            } else if (DeclRefExpr *DRE = dyn_cast<DeclRefExpr>(CEE)) {
                ValueDecl *VD = DRE->getDecl();
                if (VD->hasAttr<NoReturnAttr>()) {
                    NoReturnEdge = true;
                    HasFakeEdge = true;
                }
            }
        }
        // FIXME: Remove this hack once temporaries and their destructors are
        // modeled correctly by the CFG.
        if (CXXExprWithTemporaries *E = dyn_cast<CXXExprWithTemporaries>(S)) {
            for (unsigned I = 0, N = E->getNumTemporaries(); I != N; ++I) {
                const FunctionDecl *FD = E->getTemporary(I)->getDestructor();
                if (FD->hasAttr<NoReturnAttr>() ||
                        FD->getType()->getAs<FunctionType>()->getNoReturnAttr()) {
                    NoReturnEdge = true;
                    HasFakeEdge = true;
                    break;
                }
            }
        }
        // FIXME: Add noreturn message sends.
        if (NoReturnEdge == false)
            HasPlainEdge = true;
    }
    if (!HasPlainEdge) {
        if (HasLiveReturn)
            return NeverFallThrough;
        return NeverFallThroughOrReturn;
    }
    if (HasAbnormalEdge || HasFakeEdge || HasLiveReturn)
        return MaybeFallThrough;
    // This says AlwaysFallThrough for calls to functions that are not marked
    // noreturn, that don't return.  If people would like this warning to be more
    // accurate, such functions should be marked as noreturn.
    return AlwaysFallThrough;
}
/// \brief Check a function's CFG for thread-safety violations.
///
/// We traverse the blocks in the CFG, compute the set of mutexes that are held
/// at the end of each block, and issue warnings for thread safety violations.
/// Each block in the CFG is traversed exactly once.
void runThreadSafetyAnalysis(AnalysisContext &AC,
                             ThreadSafetyHandler &Handler) {
  CFG *CFGraph = AC.getCFG();
  if (!CFGraph) return;
  const NamedDecl *D = dyn_cast_or_null<NamedDecl>(AC.getDecl());

  if (!D)
    return;  // Ignore anonymous functions for now.
  if (D->getAttr<NoThreadSafetyAnalysisAttr>())
    return;

  Lockset::Factory LocksetFactory;

  // FIXME: Swith to SmallVector? Otherwise improve performance impact?
  std::vector<Lockset> EntryLocksets(CFGraph->getNumBlockIDs(),
                                     LocksetFactory.getEmptyMap());
  std::vector<Lockset> ExitLocksets(CFGraph->getNumBlockIDs(),
                                    LocksetFactory.getEmptyMap());

  // We need to explore the CFG via a "topological" ordering.
  // That way, we will be guaranteed to have information about required
  // predecessor locksets when exploring a new block.
  TopologicallySortedCFG SortedGraph(CFGraph);
  CFGBlockSet VisitedBlocks(CFGraph);

  if (!SortedGraph.empty() && D->hasAttrs()) {
    const CFGBlock *FirstBlock = *SortedGraph.begin();
    Lockset &InitialLockset = EntryLocksets[FirstBlock->getBlockID()];
    const AttrVec &ArgAttrs = D->getAttrs();
    for(unsigned i = 0; i < ArgAttrs.size(); ++i) {
      Attr *Attr = ArgAttrs[i];
      SourceLocation AttrLoc = Attr->getLocation();
      if (SharedLocksRequiredAttr *SLRAttr
            = dyn_cast<SharedLocksRequiredAttr>(Attr)) {
        for (SharedLocksRequiredAttr::args_iterator
            SLRIter = SLRAttr->args_begin(),
            SLREnd = SLRAttr->args_end(); SLRIter != SLREnd; ++SLRIter)
          InitialLockset = addLock(Handler, LocksetFactory, InitialLockset,
                                   *SLRIter, D, LK_Shared,
                                   AttrLoc);
      } else if (ExclusiveLocksRequiredAttr *ELRAttr
                   = dyn_cast<ExclusiveLocksRequiredAttr>(Attr)) {
        for (ExclusiveLocksRequiredAttr::args_iterator
            ELRIter = ELRAttr->args_begin(),
            ELREnd = ELRAttr->args_end(); ELRIter != ELREnd; ++ELRIter)
          InitialLockset = addLock(Handler, LocksetFactory, InitialLockset,
                                   *ELRIter, D, LK_Exclusive,
                                   AttrLoc);
      }
    }
  }

  for (TopologicallySortedCFG::iterator I = SortedGraph.begin(),
       E = SortedGraph.end(); I!= E; ++I) {
    const CFGBlock *CurrBlock = *I;
    int CurrBlockID = CurrBlock->getBlockID();

    VisitedBlocks.insert(CurrBlock);

    // Use the default initial lockset in case there are no predecessors.
    Lockset &Entryset = EntryLocksets[CurrBlockID];
    Lockset &Exitset = ExitLocksets[CurrBlockID];

    // Iterate through the predecessor blocks and warn if the lockset for all
    // predecessors is not the same. We take the entry lockset of the current
    // block to be the intersection of all previous locksets.
    // FIXME: By keeping the intersection, we may output more errors in future
    // for a lock which is not in the intersection, but was in the union. We
    // may want to also keep the union in future. As an example, let's say
    // the intersection contains Mutex L, and the union contains L and M.
    // Later we unlock M. At this point, we would output an error because we
    // never locked M; although the real error is probably that we forgot to
    // lock M on all code paths. Conversely, let's say that later we lock M.
    // In this case, we should compare against the intersection instead of the
    // union because the real error is probably that we forgot to unlock M on
    // all code paths.
    bool LocksetInitialized = false;
    for (CFGBlock::const_pred_iterator PI = CurrBlock->pred_begin(),
         PE  = CurrBlock->pred_end(); PI != PE; ++PI) {

      // if *PI -> CurrBlock is a back edge
      if (*PI == 0 || !VisitedBlocks.alreadySet(*PI))
        continue;

      int PrevBlockID = (*PI)->getBlockID();
      if (!LocksetInitialized) {
        Entryset = ExitLocksets[PrevBlockID];
        LocksetInitialized = true;
      } else {
        Entryset = intersectAndWarn(Handler, Entryset,
                                    ExitLocksets[PrevBlockID], LocksetFactory,
                                    LEK_LockedSomePredecessors);
      }
    }

    BuildLockset LocksetBuilder(Handler, Entryset, LocksetFactory);
    for (CFGBlock::const_iterator BI = CurrBlock->begin(),
         BE = CurrBlock->end(); BI != BE; ++BI) {
      if (const CFGStmt *CfgStmt = dyn_cast<CFGStmt>(&*BI))
        LocksetBuilder.Visit(const_cast<Stmt*>(CfgStmt->getStmt()));
    }
    Exitset = LocksetBuilder.getLockset();

    // For every back edge from CurrBlock (the end of the loop) to another block
    // (FirstLoopBlock) we need to check that the Lockset of Block is equal to
    // the one held at the beginning of FirstLoopBlock. We can look up the
    // Lockset held at the beginning of FirstLoopBlock in the EntryLockSets map.
    for (CFGBlock::const_succ_iterator SI = CurrBlock->succ_begin(),
         SE  = CurrBlock->succ_end(); SI != SE; ++SI) {

      // if CurrBlock -> *SI is *not* a back edge
      if (*SI == 0 || !VisitedBlocks.alreadySet(*SI))
        continue;

      CFGBlock *FirstLoopBlock = *SI;
      Lockset PreLoop = EntryLocksets[FirstLoopBlock->getBlockID()];
      Lockset LoopEnd = ExitLocksets[CurrBlockID];
      intersectAndWarn(Handler, LoopEnd, PreLoop, LocksetFactory,
                       LEK_LockedSomeLoopIterations);
    }
  }

  Lockset InitialLockset = EntryLocksets[CFGraph->getEntry().getBlockID()];
  Lockset FinalLockset = ExitLocksets[CFGraph->getExit().getBlockID()];

  // FIXME: Should we call this function for all blocks which exit the function?
  intersectAndWarn(Handler, InitialLockset, FinalLockset, LocksetFactory,
                   LEK_LockedAtEndOfFunction);
}
LiveVariables *
LiveVariables::computeLiveness(AnalysisDeclContext &AC,
                                 bool killAtAssign) {

  // No CFG?  Bail out.
  CFG *cfg = AC.getCFG();
  if (!cfg)
    return nullptr;

  // The analysis currently has scalability issues for very large CFGs.
  // Bail out if it looks too large.
  if (cfg->getNumBlockIDs() > 300000)
    return nullptr;

  LiveVariablesImpl *LV = new LiveVariablesImpl(AC, killAtAssign);

  // Construct the dataflow worklist.  Enqueue the exit block as the
  // start of the analysis.
  DataflowWorklist worklist(*cfg, AC);
  llvm::BitVector everAnalyzedBlock(cfg->getNumBlockIDs());

  // FIXME: we should enqueue using post order.
  for (CFG::const_iterator it = cfg->begin(), ei = cfg->end(); it != ei; ++it) {
    const CFGBlock *block = *it;
    worklist.enqueueBlock(block);
    
    // FIXME: Scan for DeclRefExprs using in the LHS of an assignment.
    // We need to do this because we lack context in the reverse analysis
    // to determine if a DeclRefExpr appears in such a context, and thus
    // doesn't constitute a "use".
    if (killAtAssign)
      for (CFGBlock::const_iterator bi = block->begin(), be = block->end();
           bi != be; ++bi) {
        if (Optional<CFGStmt> cs = bi->getAs<CFGStmt>()) {
          if (const BinaryOperator *BO =
                  dyn_cast<BinaryOperator>(cs->getStmt())) {
            if (BO->getOpcode() == BO_Assign) {
              if (const DeclRefExpr *DR =
                    dyn_cast<DeclRefExpr>(BO->getLHS()->IgnoreParens())) {
                LV->inAssignment[DR] = 1;
              }
            }
          }
        }
      }
  }
  
  while (const CFGBlock *block = worklist.dequeue()) {
    // Determine if the block's end value has changed.  If not, we
    // have nothing left to do for this block.
    LivenessValues &prevVal = LV->blocksEndToLiveness[block];
    
    // Merge the values of all successor blocks.
    LivenessValues val;
    for (CFGBlock::const_succ_iterator it = block->succ_begin(),
                                       ei = block->succ_end(); it != ei; ++it) {
      if (const CFGBlock *succ = *it) {     
        val = LV->merge(val, LV->blocksBeginToLiveness[succ]);
      }
    }
    
    if (!everAnalyzedBlock[block->getBlockID()])
      everAnalyzedBlock[block->getBlockID()] = true;
    else if (prevVal.equals(val))
      continue;

    prevVal = val;
    
    // Update the dataflow value for the start of this block.
    LV->blocksBeginToLiveness[block] = LV->runOnBlock(block, val);
    
    // Enqueue the value to the predecessors.
    worklist.enqueuePredecessors(block);
  }
  
  return new LiveVariables(LV);
}
Exemple #8
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/// CheckFallThrough - Check that we don't fall off the end of a
/// Statement that should return a value.
///
/// \returns AlwaysFallThrough iff we always fall off the end of the statement,
/// MaybeFallThrough iff we might or might not fall off the end,
/// NeverFallThroughOrReturn iff we never fall off the end of the statement or
/// return.  We assume NeverFallThrough iff we never fall off the end of the
/// statement but we may return.  We assume that functions not marked noreturn
/// will return.
static ControlFlowKind CheckFallThrough(AnalysisContext &AC) {
  CFG *cfg = AC.getCFG();
  if (cfg == 0) return UnknownFallThrough;

  // The CFG leaves in dead things, and we don't want the dead code paths to
  // confuse us, so we mark all live things first.
  llvm::BitVector live(cfg->getNumBlockIDs());
  unsigned count = reachable_code::ScanReachableFromBlock(cfg->getEntry(),
                                                          live);

  bool AddEHEdges = AC.getAddEHEdges();
  if (!AddEHEdges && count != cfg->getNumBlockIDs())
    // When there are things remaining dead, and we didn't add EH edges
    // from CallExprs to the catch clauses, we have to go back and
    // mark them as live.
    for (CFG::iterator I = cfg->begin(), E = cfg->end(); I != E; ++I) {
      CFGBlock &b = **I;
      if (!live[b.getBlockID()]) {
        if (b.pred_begin() == b.pred_end()) {
          if (b.getTerminator() && isa<CXXTryStmt>(b.getTerminator()))
            // When not adding EH edges from calls, catch clauses
            // can otherwise seem dead.  Avoid noting them as dead.
            count += reachable_code::ScanReachableFromBlock(b, live);
          continue;
        }
      }
    }

  // Now we know what is live, we check the live precessors of the exit block
  // and look for fall through paths, being careful to ignore normal returns,
  // and exceptional paths.
  bool HasLiveReturn = false;
  bool HasFakeEdge = false;
  bool HasPlainEdge = false;
  bool HasAbnormalEdge = false;

  // Ignore default cases that aren't likely to be reachable because all
  // enums in a switch(X) have explicit case statements.
  CFGBlock::FilterOptions FO;
  FO.IgnoreDefaultsWithCoveredEnums = 1;

  for (CFGBlock::filtered_pred_iterator
	 I = cfg->getExit().filtered_pred_start_end(FO); I.hasMore(); ++I) {
    const CFGBlock& B = **I;
    if (!live[B.getBlockID()])
      continue;

    // Destructors can appear after the 'return' in the CFG.  This is
    // normal.  We need to look pass the destructors for the return
    // statement (if it exists).
    CFGBlock::const_reverse_iterator ri = B.rbegin(), re = B.rend();
    bool hasNoReturnDtor = false;
    
    for ( ; ri != re ; ++ri) {
      CFGElement CE = *ri;

      // FIXME: The right solution is to just sever the edges in the
      // CFG itself.
      if (const CFGImplicitDtor *iDtor = ri->getAs<CFGImplicitDtor>())
        if (iDtor->isNoReturn(AC.getASTContext())) {
          hasNoReturnDtor = true;
          HasFakeEdge = true;
          break;
        }
      
      if (isa<CFGStmt>(CE))
        break;
    }
    
    if (hasNoReturnDtor)
      continue;
    
    // No more CFGElements in the block?
    if (ri == re) {
      if (B.getTerminator() && isa<CXXTryStmt>(B.getTerminator())) {
        HasAbnormalEdge = true;
        continue;
      }
      // A labeled empty statement, or the entry block...
      HasPlainEdge = true;
      continue;
    }

    CFGStmt CS = cast<CFGStmt>(*ri);
    Stmt *S = CS.getStmt();
    if (isa<ReturnStmt>(S)) {
      HasLiveReturn = true;
      continue;
    }
    if (isa<ObjCAtThrowStmt>(S)) {
      HasFakeEdge = true;
      continue;
    }
    if (isa<CXXThrowExpr>(S)) {
      HasFakeEdge = true;
      continue;
    }
    if (const AsmStmt *AS = dyn_cast<AsmStmt>(S)) {
      if (AS->isMSAsm()) {
        HasFakeEdge = true;
        HasLiveReturn = true;
        continue;
      }
    }
    if (isa<CXXTryStmt>(S)) {
      HasAbnormalEdge = true;
      continue;
    }

    bool NoReturnEdge = false;
    if (CallExpr *C = dyn_cast<CallExpr>(S)) {
      if (std::find(B.succ_begin(), B.succ_end(), &cfg->getExit())
            == B.succ_end()) {
        HasAbnormalEdge = true;
        continue;
      }
      Expr *CEE = C->getCallee()->IgnoreParenCasts();
      QualType calleeType = CEE->getType();
      if (calleeType == AC.getASTContext().BoundMemberTy) {
        calleeType = Expr::findBoundMemberType(CEE);
        assert(!calleeType.isNull() && "analyzing unresolved call?");
      }
      if (getFunctionExtInfo(calleeType).getNoReturn()) {
        NoReturnEdge = true;
        HasFakeEdge = true;
      } else if (DeclRefExpr *DRE = dyn_cast<DeclRefExpr>(CEE)) {
        ValueDecl *VD = DRE->getDecl();
        if (VD->hasAttr<NoReturnAttr>()) {
          NoReturnEdge = true;
          HasFakeEdge = true;
        }
      }
    }
    // FIXME: Add noreturn message sends.
    if (NoReturnEdge == false)
      HasPlainEdge = true;
  }
  if (!HasPlainEdge) {
    if (HasLiveReturn)
      return NeverFallThrough;
    return NeverFallThroughOrReturn;
  }
  if (HasAbnormalEdge || HasFakeEdge || HasLiveReturn)
    return MaybeFallThrough;
  // This says AlwaysFallThrough for calls to functions that are not marked
  // noreturn, that don't return.  If people would like this warning to be more
  // accurate, such functions should be marked as noreturn.
  return AlwaysFallThrough;
}
void FindUnreachableCode(AnalysisContext &AC, Callback &CB) {
  CFG *cfg = AC.getCFG();
  if (!cfg)
    return;

  // Scan for reachable blocks.
  llvm::BitVector reachable(cfg->getNumBlockIDs());
  unsigned numReachable = ScanReachableFromBlock(cfg->getEntry(), reachable);

    // If there are no unreachable blocks, we're done.
  if (numReachable == cfg->getNumBlockIDs())
    return;

  SourceRange R1, R2;

  llvm::SmallVector<ErrLoc, 24> lines;
  bool AddEHEdges = AC.getAddEHEdges();

  // First, give warnings for blocks with no predecessors, as they
  // can't be part of a loop.
  for (CFG::iterator I = cfg->begin(), E = cfg->end(); I != E; ++I) {
    CFGBlock &b = **I;
    if (!reachable[b.getBlockID()]) {
      if (b.pred_empty()) {
        if (!AddEHEdges
        && dyn_cast_or_null<CXXTryStmt>(b.getTerminator().getStmt())) {
            // When not adding EH edges from calls, catch clauses
            // can otherwise seem dead.  Avoid noting them as dead.
          numReachable += ScanReachableFromBlock(b, reachable);
          continue;
        }
        SourceLocation c = GetUnreachableLoc(b, R1, R2);
        if (!c.isValid()) {
            // Blocks without a location can't produce a warning, so don't mark
            // reachable blocks from here as live.
          reachable.set(b.getBlockID());
          ++numReachable;
          continue;
        }
        lines.push_back(ErrLoc(c, R1, R2));
          // Avoid excessive errors by marking everything reachable from here
        numReachable += ScanReachableFromBlock(b, reachable);
      }
    }
  }

  if (numReachable < cfg->getNumBlockIDs()) {
      // And then give warnings for the tops of loops.
    for (CFG::iterator I = cfg->begin(), E = cfg->end(); I != E; ++I) {
      CFGBlock &b = **I;
      if (!reachable[b.getBlockID()])
          // Avoid excessive errors by marking everything reachable from here
        lines.push_back(ErrLoc(MarkLiveTop(&b, reachable,
                                         AC.getASTContext().getSourceManager()),
                               SourceRange(), SourceRange()));
    }
  }

  llvm::array_pod_sort(lines.begin(), lines.end(), LineCmp);

  for (llvm::SmallVectorImpl<ErrLoc>::iterator I=lines.begin(), E=lines.end();
       I != E; ++I)
    if (I->Loc.isValid())
      CB.HandleUnreachable(I->Loc, I->R1, I->R2);
}