xref: /external/clang/lib/Analysis/CFG.cpp

//===--- CFG.cpp - Classes for representing and building CFGs----*- C++ -*-===//
//
//                     The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
//  This file defines the CFG and CFGBuilder classes for representing and
//  building Control-Flow Graphs (CFGs) from ASTs.
//
//===----------------------------------------------------------------------===//

#include "clang/Analysis/Support/SaveAndRestore.h"
#include "clang/Analysis/CFG.h"
#include "clang/AST/DeclCXX.h"
#include "clang/AST/StmtVisitor.h"
#include "clang/AST/PrettyPrinter.h"
#include "llvm/Support/GraphWriter.h"
#include "llvm/Support/Allocator.h"
#include "llvm/Support/Format.h"
#include "llvm/ADT/DenseMap.h"
#include "llvm/ADT/SmallPtrSet.h"
#include "llvm/ADT/OwningPtr.h"

using namespace clang;

namespace {

static SourceLocation GetEndLoc(Decl* D) {
  if (VarDecl* VD = dyn_cast<VarDecl>(D))
    if (Expr* Ex = VD->getInit())
      return Ex->getSourceRange().getEnd();

  return D->getLocation();
}

class AddStmtChoice {
public:
  enum Kind { NotAlwaysAdd = 0,
              AlwaysAdd = 1,
              AsLValueNotAlwaysAdd = 2,
              AlwaysAddAsLValue = 3 };

  AddStmtChoice(Kind kind) : k(kind) {}

  bool alwaysAdd() const { return (unsigned)k & 0x1; }
  bool asLValue() const { return k >= AsLValueNotAlwaysAdd; }

private:
  Kind k;
};

/// LocalScope - Node in tree of local scopes created for C++ implicit
/// destructor calls generation. It contains list of automatic variables
/// declared in the scope and link to position in previous scope this scope
/// began in.
///
/// The process of creating local scopes is as follows:
/// - Init CFGBuilder::ScopePos with invalid position (equivalent for null),
/// - Before processing statements in scope (e.g. CompoundStmt) create
///   LocalScope object using CFGBuilder::ScopePos as link to previous scope
///   and set CFGBuilder::ScopePos to the end of new scope,
/// - On every occurrence of VarDecl increase CFGBuilder::ScopePos if it points
///   at this VarDecl,
/// - For every normal (without jump) end of scope add to CFGBlock destructors
///   for objects in the current scope,
/// - For every jump add to CFGBlock destructors for objects
///   between CFGBuilder::ScopePos and local scope position saved for jump
///   target. Thanks to C++ restrictions on goto jumps we can be sure that
///   jump target position will be on the path to root from CFGBuilder::ScopePos
///   (adding any variable that doesn't need constructor to be called to
///   LocalScope can break this assumption),
///
class LocalScope {
public:
  typedef llvm::SmallVector<VarDecl*, 4> AutomaticVarsTy;

  /// const_iterator - Iterates local scope backwards and jumps to previous
  /// scope on reaching the beginning of currently iterated scope.
  class const_iterator {
    const LocalScope* Scope;

    /// VarIter is guaranteed to be greater then 0 for every valid iterator.
    /// Invalid iterator (with null Scope) has VarIter equal to 0.
    unsigned VarIter;

  public:
    /// Create invalid iterator. Dereferencing invalid iterator is not allowed.
    /// Incrementing invalid iterator is allowed and will result in invalid
    /// iterator.
    const_iterator()
        : Scope(NULL), VarIter(0) {}

    /// Create valid iterator. In case when S.Prev is an invalid iterator and
    /// I is equal to 0, this will create invalid iterator.
    const_iterator(const LocalScope& S, unsigned I)
        : Scope(&S), VarIter(I) {
      // Iterator to "end" of scope is not allowed. Handle it by going up
      // in scopes tree possibly up to invalid iterator in the root.
      if (VarIter == 0 && Scope)
        *this = Scope->Prev;
    }

    VarDecl* const* operator->() const {
      assert (Scope && "Dereferencing invalid iterator is not allowed");
      assert (VarIter != 0 && "Iterator has invalid value of VarIter member");
      return &Scope->Vars[VarIter - 1];
    }
    VarDecl* operator*() const {
      return *this->operator->();
    }

    const_iterator& operator++() {
      if (!Scope)
        return *this;

      assert (VarIter != 0 && "Iterator has invalid value of VarIter member");
      --VarIter;
      if (VarIter == 0)
        *this = Scope->Prev;
      return *this;
    }
    const_iterator operator++(int) {
      const_iterator P = *this;
      ++*this;
      return P;
    }

    bool operator==(const const_iterator& rhs) const {
      return Scope == rhs.Scope && VarIter == rhs.VarIter;
    }
    bool operator!=(const const_iterator& rhs) const {
      return !(*this == rhs);
    }

    operator bool() const {
      return *this != const_iterator();
    }

    int distance(const_iterator L);
  };

  friend class const_iterator;

private:
  /// Automatic variables in order of declaration.
  AutomaticVarsTy Vars;
  /// Iterator to variable in previous scope that was declared just before
  /// begin of this scope.
  const_iterator Prev;

public:
  /// Constructs empty scope linked to previous scope in specified place.
  LocalScope(const_iterator P)
      : Vars()
      , Prev(P) {}

  /// Begin of scope in direction of CFG building (backwards).
  const_iterator begin() const { return const_iterator(*this, Vars.size()); }

  void addVar(VarDecl* VD) {
    Vars.push_back(VD);
  }
};

/// distance - Calculates distance from this to L. L must be reachable from this
/// (with use of ++ operator). Cost of calculating the distance is linear w.r.t.
/// number of scopes between this and L.
int LocalScope::const_iterator::distance(LocalScope::const_iterator L) {
  int D = 0;
  const_iterator F = *this;
  while (F.Scope != L.Scope) {
    assert (F != const_iterator()
        && "L iterator is not reachable from F iterator.");
    D += F.VarIter;
    F = F.Scope->Prev;
  }
  D += F.VarIter - L.VarIter;
  return D;
}

/// BlockScopePosPair - Structure for specifying position in CFG during its
/// build process. It consists of CFGBlock that specifies position in CFG graph
/// and  LocalScope::const_iterator that specifies position in LocalScope graph.
struct BlockScopePosPair {
  BlockScopePosPair() {}
  BlockScopePosPair(CFGBlock* B, LocalScope::const_iterator S)
      : Block(B), ScopePos(S) {}

  CFGBlock*                   Block;
  LocalScope::const_iterator  ScopePos;
};

/// CFGBuilder - This class implements CFG construction from an AST.
///   The builder is stateful: an instance of the builder should be used to only
///   construct a single CFG.
///
///   Example usage:
///
///     CFGBuilder builder;
///     CFG* cfg = builder.BuildAST(stmt1);
///
///  CFG construction is done via a recursive walk of an AST.  We actually parse
///  the AST in reverse order so that the successor of a basic block is
///  constructed prior to its predecessor.  This allows us to nicely capture
///  implicit fall-throughs without extra basic blocks.
///
class CFGBuilder {
  typedef BlockScopePosPair JumpTarget;
  typedef BlockScopePosPair JumpSource;

  ASTContext *Context;
  llvm::OwningPtr<CFG> cfg;

  CFGBlock* Block;
  CFGBlock* Succ;
  JumpTarget ContinueJumpTarget;
  JumpTarget BreakJumpTarget;
  CFGBlock* SwitchTerminatedBlock;
  CFGBlock* DefaultCaseBlock;
  CFGBlock* TryTerminatedBlock;

  // Current position in local scope.
  LocalScope::const_iterator ScopePos;

  // LabelMap records the mapping from Label expressions to their jump targets.
  typedef llvm::DenseMap<LabelStmt*, JumpTarget> LabelMapTy;
  LabelMapTy LabelMap;

  // A list of blocks that end with a "goto" that must be backpatched to their
  // resolved targets upon completion of CFG construction.
  typedef std::vector<JumpSource> BackpatchBlocksTy;
  BackpatchBlocksTy BackpatchBlocks;

  // A list of labels whose address has been taken (for indirect gotos).
  typedef llvm::SmallPtrSet<LabelStmt*,5> LabelSetTy;
  LabelSetTy AddressTakenLabels;

  bool badCFG;
  CFG::BuildOptions BuildOpts;

public:
  explicit CFGBuilder() : cfg(new CFG()), // crew a new CFG
                          Block(NULL), Succ(NULL),
                          SwitchTerminatedBlock(NULL), DefaultCaseBlock(NULL),
                          TryTerminatedBlock(NULL), badCFG(false) {}

  // buildCFG - Used by external clients to construct the CFG.
  CFG* buildCFG(const Decl *D, Stmt *Statement, ASTContext *C,
      CFG::BuildOptions BO);

private:
  // Visitors to walk an AST and construct the CFG.
  CFGBlock *VisitAddrLabelExpr(AddrLabelExpr *A, AddStmtChoice asc);
  CFGBlock *VisitBinaryOperator(BinaryOperator *B, AddStmtChoice asc);
  CFGBlock *VisitBlockExpr(BlockExpr* E, AddStmtChoice asc);
  CFGBlock *VisitBreakStmt(BreakStmt *B);
  CFGBlock *VisitCXXCatchStmt(CXXCatchStmt *S);
  CFGBlock *VisitCXXThrowExpr(CXXThrowExpr *T);
  CFGBlock *VisitCXXTryStmt(CXXTryStmt *S);
  CFGBlock *VisitCXXMemberCallExpr(CXXMemberCallExpr *C, AddStmtChoice asc);
  CFGBlock *VisitCallExpr(CallExpr *C, AddStmtChoice asc);
  CFGBlock *VisitCaseStmt(CaseStmt *C);
  CFGBlock *VisitChooseExpr(ChooseExpr *C, AddStmtChoice asc);
  CFGBlock *VisitCompoundStmt(CompoundStmt *C);
  CFGBlock *VisitConditionalOperator(ConditionalOperator *C, AddStmtChoice asc);
  CFGBlock *VisitContinueStmt(ContinueStmt *C);
  CFGBlock *VisitDeclStmt(DeclStmt *DS);
  CFGBlock *VisitDeclSubExpr(Decl* D);
  CFGBlock *VisitDefaultStmt(DefaultStmt *D);
  CFGBlock *VisitDoStmt(DoStmt *D);
  CFGBlock *VisitForStmt(ForStmt *F);
  CFGBlock *VisitGotoStmt(GotoStmt* G);
  CFGBlock *VisitIfStmt(IfStmt *I);
  CFGBlock *VisitIndirectGotoStmt(IndirectGotoStmt *I);
  CFGBlock *VisitLabelStmt(LabelStmt *L);
  CFGBlock *VisitMemberExpr(MemberExpr *M, AddStmtChoice asc);
  CFGBlock *VisitObjCAtCatchStmt(ObjCAtCatchStmt *S);
  CFGBlock *VisitObjCAtSynchronizedStmt(ObjCAtSynchronizedStmt *S);
  CFGBlock *VisitObjCAtThrowStmt(ObjCAtThrowStmt *S);
  CFGBlock *VisitObjCAtTryStmt(ObjCAtTryStmt *S);
  CFGBlock *VisitObjCForCollectionStmt(ObjCForCollectionStmt *S);
  CFGBlock *VisitReturnStmt(ReturnStmt* R);
  CFGBlock *VisitSizeOfAlignOfExpr(SizeOfAlignOfExpr *E, AddStmtChoice asc);
  CFGBlock *VisitStmtExpr(StmtExpr *S, AddStmtChoice asc);
  CFGBlock *VisitSwitchStmt(SwitchStmt *S);
  CFGBlock *VisitWhileStmt(WhileStmt *W);

  CFGBlock *Visit(Stmt *S, AddStmtChoice asc = AddStmtChoice::NotAlwaysAdd);
  CFGBlock *VisitStmt(Stmt *S, AddStmtChoice asc);
  CFGBlock *VisitChildren(Stmt* S);

  // NYS == Not Yet Supported
  CFGBlock* NYS() {
    badCFG = true;
    return Block;
  }

  void autoCreateBlock() { if (!Block) Block = createBlock(); }
  CFGBlock *createBlock(bool add_successor = true);

  CFGBlock *addStmt(Stmt *S) {
    return Visit(S, AddStmtChoice::AlwaysAdd);
  }
  CFGBlock *addAutomaticObjDtors(LocalScope::const_iterator B,
      LocalScope::const_iterator E, Stmt* S);

  // Local scopes creation.
  LocalScope* createOrReuseLocalScope(LocalScope* Scope);

  LocalScope* addLocalScopeForStmt(Stmt* S, LocalScope* Scope = NULL);
  LocalScope* addLocalScopeForDeclStmt(DeclStmt* DS, LocalScope* Scope = NULL);
  LocalScope* addLocalScopeForVarDecl(VarDecl* VD, LocalScope* Scope = NULL);

  void addLocalScopeAndDtors(Stmt* S);

  // Interface to CFGBlock - adding CFGElements.
  void AppendStmt(CFGBlock *B, Stmt *S,
                  AddStmtChoice asc = AddStmtChoice::AlwaysAdd) {
    B->appendStmt(S, cfg->getBumpVectorContext(), asc.asLValue());
  }

  void insertAutomaticObjDtors(CFGBlock* Blk, CFGBlock::iterator I,
    LocalScope::const_iterator B, LocalScope::const_iterator E, Stmt* S);
  void appendAutomaticObjDtors(CFGBlock* Blk, LocalScope::const_iterator B,
      LocalScope::const_iterator E, Stmt* S);
  void prependAutomaticObjDtorsWithTerminator(CFGBlock* Blk,
      LocalScope::const_iterator B, LocalScope::const_iterator E);

  void AddSuccessor(CFGBlock *B, CFGBlock *S) {
    B->addSuccessor(S, cfg->getBumpVectorContext());
  }

  /// TryResult - a class representing a variant over the values
  ///  'true', 'false', or 'unknown'.  This is returned by TryEvaluateBool,
  ///  and is used by the CFGBuilder to decide if a branch condition
  ///  can be decided up front during CFG construction.
  class TryResult {
    int X;
  public:
    TryResult(bool b) : X(b ? 1 : 0) {}
    TryResult() : X(-1) {}

    bool isTrue() const { return X == 1; }
    bool isFalse() const { return X == 0; }
    bool isKnown() const { return X >= 0; }
    void negate() {
      assert(isKnown());
      X ^= 0x1;
    }
  };

  /// TryEvaluateBool - Try and evaluate the Stmt and return 0 or 1
  /// if we can evaluate to a known value, otherwise return -1.
  TryResult TryEvaluateBool(Expr *S) {
    if (!BuildOpts.PruneTriviallyFalseEdges)
      return TryResult();

    Expr::EvalResult Result;
    if (!S->isTypeDependent() && !S->isValueDependent() &&
        S->Evaluate(Result, *Context) && Result.Val.isInt())
      return Result.Val.getInt().getBoolValue();

    return TryResult();
  }
};

// FIXME: Add support for dependent-sized array types in C++?
// Does it even make sense to build a CFG for an uninstantiated template?
static VariableArrayType* FindVA(Type* t) {
  while (ArrayType* vt = dyn_cast<ArrayType>(t)) {
    if (VariableArrayType* vat = dyn_cast<VariableArrayType>(vt))
      if (vat->getSizeExpr())
        return vat;

    t = vt->getElementType().getTypePtr();
  }

  return 0;
}

/// BuildCFG - Constructs a CFG from an AST (a Stmt*).  The AST can represent an
///  arbitrary statement.  Examples include a single expression or a function
///  body (compound statement).  The ownership of the returned CFG is
///  transferred to the caller.  If CFG construction fails, this method returns
///  NULL.
CFG* CFGBuilder::buildCFG(const Decl *D, Stmt* Statement, ASTContext* C,
    CFG::BuildOptions BO) {

  Context = C;
  assert(cfg.get());
  if (!Statement)
    return NULL;

  BuildOpts = BO;
  if (!C->getLangOptions().CPlusPlus)
    BuildOpts.AddImplicitDtors = false;

  // Create an empty block that will serve as the exit block for the CFG.  Since
  // this is the first block added to the CFG, it will be implicitly registered
  // as the exit block.
  Succ = createBlock();
  assert(Succ == &cfg->getExit());
  Block = NULL;  // the EXIT block is empty.  Create all other blocks lazily.

  // Visit the statements and create the CFG.
  CFGBlock *B = addStmt(Statement);

  if (badCFG)
    return NULL;

  if (B)
    Succ = B;

  if (const CXXConstructorDecl *CD = dyn_cast_or_null<CXXConstructorDecl>(D)) {
    // FIXME: Add code for base initializers and member initializers.
    (void)CD;
  }

  // Backpatch the gotos whose label -> block mappings we didn't know when we
  // encountered them.
  for (BackpatchBlocksTy::iterator I = BackpatchBlocks.begin(),
                                   E = BackpatchBlocks.end(); I != E; ++I ) {

    CFGBlock* B = I->Block;
    GotoStmt* G = cast<GotoStmt>(B->getTerminator());
    LabelMapTy::iterator LI = LabelMap.find(G->getLabel());

    // If there is no target for the goto, then we are looking at an
    // incomplete AST.  Handle this by not registering a successor.
    if (LI == LabelMap.end()) continue;

    JumpTarget JT = LI->second;
    AddSuccessor(B, JT.Block);
  }

  // Add successors to the Indirect Goto Dispatch block (if we have one).
  if (CFGBlock* B = cfg->getIndirectGotoBlock())
    for (LabelSetTy::iterator I = AddressTakenLabels.begin(),
                              E = AddressTakenLabels.end(); I != E; ++I ) {

      // Lookup the target block.
      LabelMapTy::iterator LI = LabelMap.find(*I);

      // If there is no target block that contains label, then we are looking
      // at an incomplete AST.  Handle this by not registering a successor.
      if (LI == LabelMap.end()) continue;

      AddSuccessor(B, LI->second.Block);
    }

  // Create an empty entry block that has no predecessors.
  cfg->setEntry(createBlock());

  return cfg.take();
}

/// createBlock - Used to lazily create blocks that are connected
///  to the current (global) succcessor.
CFGBlock* CFGBuilder::createBlock(bool add_successor) {
  CFGBlock* B = cfg->createBlock();
  if (add_successor && Succ)
    AddSuccessor(B, Succ);
  return B;
}

/// addAutomaticObjDtors - Add to current block automatic objects destructors
/// for objects in range of local scope positions. Use S as trigger statement
/// for destructors.
CFGBlock* CFGBuilder::addAutomaticObjDtors(LocalScope::const_iterator B,
    LocalScope::const_iterator E, Stmt* S) {
  if (!BuildOpts.AddImplicitDtors)
    return Block;
  if (B == E)
    return Block;

  autoCreateBlock();
  appendAutomaticObjDtors(Block, B, E, S);
  return Block;
}

/// createOrReuseLocalScope - If Scope is NULL create new LocalScope. Either
/// way return valid LocalScope object.
LocalScope* CFGBuilder::createOrReuseLocalScope(LocalScope* Scope) {
  if (!Scope) {
    Scope = cfg->getAllocator().Allocate<LocalScope>();
    new (Scope) LocalScope(ScopePos);
  }
  return Scope;
}

/// addLocalScopeForStmt - Add LocalScope to local scopes tree for statement
/// that should create implicit scope (e.g. if/else substatements). Will reuse
/// Scope if not NULL.
LocalScope* CFGBuilder::addLocalScopeForStmt(Stmt* S, LocalScope* Scope) {
  if (!BuildOpts.AddImplicitDtors)
    return Scope;

  // For compound statement we will be creating explicit scope.
  if (CompoundStmt* CS = dyn_cast<CompoundStmt>(S)) {
    for (CompoundStmt::body_iterator BI = CS->body_begin(), BE = CS->body_end()
        ; BI != BE; ++BI) {
      Stmt* SI = *BI;
      if (LabelStmt* LS = dyn_cast<LabelStmt>(SI))
        SI = LS->getSubStmt();
      if (DeclStmt* DS = dyn_cast<DeclStmt>(SI))
        Scope = addLocalScopeForDeclStmt(DS, Scope);
    }
    return Scope;
  }

  // For any other statement scope will be implicit and as such will be
  // interesting only for DeclStmt.
  if (LabelStmt* LS = dyn_cast<LabelStmt>(S))
    S = LS->getSubStmt();
  if (DeclStmt* DS = dyn_cast<DeclStmt>(S))
    Scope = addLocalScopeForDeclStmt(DS, Scope);
  return Scope;
}

/// addLocalScopeForDeclStmt - Add LocalScope for declaration statement. Will
/// reuse Scope if not NULL.
LocalScope* CFGBuilder::addLocalScopeForDeclStmt(DeclStmt* DS,
    LocalScope* Scope) {
  if (!BuildOpts.AddImplicitDtors)
    return Scope;

  for (DeclStmt::decl_iterator DI = DS->decl_begin(), DE = DS->decl_end()
      ; DI != DE; ++DI) {
    if (VarDecl* VD = dyn_cast<VarDecl>(*DI))
      Scope = addLocalScopeForVarDecl(VD, Scope);
  }
  return Scope;
}

/// addLocalScopeForVarDecl - Add LocalScope for variable declaration. It will
/// create add scope for automatic objects and temporary objects bound to
/// const reference. Will reuse Scope if not NULL.
LocalScope* CFGBuilder::addLocalScopeForVarDecl(VarDecl* VD,
    LocalScope* Scope) {
  if (!BuildOpts.AddImplicitDtors)
    return Scope;

  // Check if variable is local.
  switch (VD->getStorageClass()) {
  case SC_None:
  case SC_Auto:
  case SC_Register:
    break;
  default: return Scope;
  }

  // Check for const references bound to temporary. Set type to pointee.
  QualType QT = VD->getType();
  if (const ReferenceType* RT = QT.getTypePtr()->getAs<ReferenceType>()) {
    QT = RT->getPointeeType();
    if (!QT.isConstQualified())
      return Scope;
    if (!VD->getInit() || !VD->getInit()->Classify(*Context).isRValue())
      return Scope;
  }

  // Check if type is a C++ class with non-trivial destructor.
  const RecordType* RT = QT.getTypePtr()->getAs<RecordType>();
  if (!RT || cast<CXXRecordDecl>(RT->getDecl())->hasTrivialDestructor())
    return Scope;

  // Add the variable to scope
  Scope = createOrReuseLocalScope(Scope);
  Scope->addVar(VD);
  ScopePos = Scope->begin();
  return Scope;
}

/// addLocalScopeAndDtors - For given statement add local scope for it and
/// add destructors that will cleanup the scope. Will reuse Scope if not NULL.
void CFGBuilder::addLocalScopeAndDtors(Stmt* S) {
  if (!BuildOpts.AddImplicitDtors)
    return;

  LocalScope::const_iterator scopeBeginPos = ScopePos;
  addLocalScopeForStmt(S, NULL);
  addAutomaticObjDtors(ScopePos, scopeBeginPos, S);
}

/// insertAutomaticObjDtors - Insert destructor CFGElements for variables with
/// automatic storage duration to CFGBlock's elements vector. Insertion will be
/// performed in place specified with iterator.
void CFGBuilder::insertAutomaticObjDtors(CFGBlock* Blk, CFGBlock::iterator I,
    LocalScope::const_iterator B, LocalScope::const_iterator E, Stmt* S) {
  BumpVectorContext& C = cfg->getBumpVectorContext();
  I = Blk->beginAutomaticObjDtorsInsert(I, B.distance(E), C);
  while (B != E)
    I = Blk->insertAutomaticObjDtor(I, *B++, S);
}

/// appendAutomaticObjDtors - Append destructor CFGElements for variables with
/// automatic storage duration to CFGBlock's elements vector. Elements will be
/// appended to physical end of the vector which happens to be logical
/// beginning.
void CFGBuilder::appendAutomaticObjDtors(CFGBlock* Blk,
    LocalScope::const_iterator B, LocalScope::const_iterator E, Stmt* S) {
  insertAutomaticObjDtors(Blk, Blk->begin(), B, E, S);
}

/// prependAutomaticObjDtorsWithTerminator - Prepend destructor CFGElements for
/// variables with automatic storage duration to CFGBlock's elements vector.
/// Elements will be prepended to physical beginning of the vector which
/// happens to be logical end. Use blocks terminator as statement that specifies
/// destructors call site.
void CFGBuilder::prependAutomaticObjDtorsWithTerminator(CFGBlock* Blk,
    LocalScope::const_iterator B, LocalScope::const_iterator E) {
  insertAutomaticObjDtors(Blk, Blk->end(), B, E, Blk->getTerminator());
}

/// Visit - Walk the subtree of a statement and add extra
///   blocks for ternary operators, &&, and ||.  We also process "," and
///   DeclStmts (which may contain nested control-flow).
CFGBlock* CFGBuilder::Visit(Stmt * S, AddStmtChoice asc) {
tryAgain:
  if (!S) {
    badCFG = true;
    return 0;
  }
  switch (S->getStmtClass()) {
    default:
      return VisitStmt(S, asc);

    case Stmt::AddrLabelExprClass:
      return VisitAddrLabelExpr(cast<AddrLabelExpr>(S), asc);

    case Stmt::BinaryOperatorClass:
      return VisitBinaryOperator(cast<BinaryOperator>(S), asc);

    case Stmt::BlockExprClass:
      return VisitBlockExpr(cast<BlockExpr>(S), asc);

    case Stmt::BreakStmtClass:
      return VisitBreakStmt(cast<BreakStmt>(S));

    case Stmt::CallExprClass:
    case Stmt::CXXOperatorCallExprClass:
      return VisitCallExpr(cast<CallExpr>(S), asc);

    case Stmt::CaseStmtClass:
      return VisitCaseStmt(cast<CaseStmt>(S));

    case Stmt::ChooseExprClass:
      return VisitChooseExpr(cast<ChooseExpr>(S), asc);

    case Stmt::CompoundStmtClass:
      return VisitCompoundStmt(cast<CompoundStmt>(S));

    case Stmt::ConditionalOperatorClass:
      return VisitConditionalOperator(cast<ConditionalOperator>(S), asc);

    case Stmt::ContinueStmtClass:
      return VisitContinueStmt(cast<ContinueStmt>(S));

    case Stmt::CXXCatchStmtClass:
      return VisitCXXCatchStmt(cast<CXXCatchStmt>(S));

    case Stmt::CXXExprWithTemporariesClass: {
      // FIXME: Handle temporaries.  For now, just visit the subexpression
      // so we don't artificially create extra blocks.
      return Visit(cast<CXXExprWithTemporaries>(S)->getSubExpr(), asc);
    }

    case Stmt::CXXMemberCallExprClass:
      return VisitCXXMemberCallExpr(cast<CXXMemberCallExpr>(S), asc);

    case Stmt::CXXThrowExprClass:
      return VisitCXXThrowExpr(cast<CXXThrowExpr>(S));

    case Stmt::CXXTryStmtClass:
      return VisitCXXTryStmt(cast<CXXTryStmt>(S));

    case Stmt::DeclStmtClass:
      return VisitDeclStmt(cast<DeclStmt>(S));

    case Stmt::DefaultStmtClass:
      return VisitDefaultStmt(cast<DefaultStmt>(S));

    case Stmt::DoStmtClass:
      return VisitDoStmt(cast<DoStmt>(S));

    case Stmt::ForStmtClass:
      return VisitForStmt(cast<ForStmt>(S));

    case Stmt::GotoStmtClass:
      return VisitGotoStmt(cast<GotoStmt>(S));

    case Stmt::IfStmtClass:
      return VisitIfStmt(cast<IfStmt>(S));

    case Stmt::IndirectGotoStmtClass:
      return VisitIndirectGotoStmt(cast<IndirectGotoStmt>(S));

    case Stmt::LabelStmtClass:
      return VisitLabelStmt(cast<LabelStmt>(S));

    case Stmt::MemberExprClass:
      return VisitMemberExpr(cast<MemberExpr>(S), asc);

    case Stmt::ObjCAtCatchStmtClass:
      return VisitObjCAtCatchStmt(cast<ObjCAtCatchStmt>(S));

    case Stmt::ObjCAtSynchronizedStmtClass:
      return VisitObjCAtSynchronizedStmt(cast<ObjCAtSynchronizedStmt>(S));

    case Stmt::ObjCAtThrowStmtClass:
      return VisitObjCAtThrowStmt(cast<ObjCAtThrowStmt>(S));

    case Stmt::ObjCAtTryStmtClass:
      return VisitObjCAtTryStmt(cast<ObjCAtTryStmt>(S));

    case Stmt::ObjCForCollectionStmtClass:
      return VisitObjCForCollectionStmt(cast<ObjCForCollectionStmt>(S));

    case Stmt::ParenExprClass:
      S = cast<ParenExpr>(S)->getSubExpr();
      goto tryAgain;

    case Stmt::NullStmtClass:
      return Block;

    case Stmt::ReturnStmtClass:
      return VisitReturnStmt(cast<ReturnStmt>(S));

    case Stmt::SizeOfAlignOfExprClass:
      return VisitSizeOfAlignOfExpr(cast<SizeOfAlignOfExpr>(S), asc);

    case Stmt::StmtExprClass:
      return VisitStmtExpr(cast<StmtExpr>(S), asc);

    case Stmt::SwitchStmtClass:
      return VisitSwitchStmt(cast<SwitchStmt>(S));

    case Stmt::WhileStmtClass:
      return VisitWhileStmt(cast<WhileStmt>(S));
  }
}

CFGBlock *CFGBuilder::VisitStmt(Stmt *S, AddStmtChoice asc) {
  if (asc.alwaysAdd()) {
    autoCreateBlock();
    AppendStmt(Block, S, asc);
  }

  return VisitChildren(S);
}

/// VisitChildren - Visit the children of a Stmt.
CFGBlock *CFGBuilder::VisitChildren(Stmt* Terminator) {
  CFGBlock *B = Block;
  for (Stmt::child_iterator I = Terminator->child_begin(),
         E = Terminator->child_end(); I != E; ++I) {
    if (*I) B = Visit(*I);
  }
  return B;
}

CFGBlock *CFGBuilder::VisitAddrLabelExpr(AddrLabelExpr *A,
                                         AddStmtChoice asc) {
  AddressTakenLabels.insert(A->getLabel());

  if (asc.alwaysAdd()) {
    autoCreateBlock();
    AppendStmt(Block, A, asc);
  }

  return Block;
}

CFGBlock *CFGBuilder::VisitBinaryOperator(BinaryOperator *B,
                                          AddStmtChoice asc) {
  if (B->isLogicalOp()) { // && or ||
    CFGBlock* ConfluenceBlock = Block ? Block : createBlock();
    AppendStmt(ConfluenceBlock, B, asc);

    if (badCFG)
      return 0;

    // create the block evaluating the LHS
    CFGBlock* LHSBlock = createBlock(false);
    LHSBlock->setTerminator(B);

    // create the block evaluating the RHS
    Succ = ConfluenceBlock;
    Block = NULL;
    CFGBlock* RHSBlock = addStmt(B->getRHS());

    if (RHSBlock) {
      if (badCFG)
        return 0;
    }
    else {
      // Create an empty block for cases where the RHS doesn't require
      // any explicit statements in the CFG.
      RHSBlock = createBlock();
    }

    // See if this is a known constant.
    TryResult KnownVal = TryEvaluateBool(B->getLHS());
    if (KnownVal.isKnown() && (B->getOpcode() == BO_LOr))
      KnownVal.negate();

    // Now link the LHSBlock with RHSBlock.
    if (B->getOpcode() == BO_LOr) {
      AddSuccessor(LHSBlock, KnownVal.isTrue() ? NULL : ConfluenceBlock);
      AddSuccessor(LHSBlock, KnownVal.isFalse() ? NULL : RHSBlock);
    } else {
      assert(B->getOpcode() == BO_LAnd);
      AddSuccessor(LHSBlock, KnownVal.isFalse() ? NULL : RHSBlock);
      AddSuccessor(LHSBlock, KnownVal.isTrue() ? NULL : ConfluenceBlock);
    }

    // Generate the blocks for evaluating the LHS.
    Block = LHSBlock;
    return addStmt(B->getLHS());
  }
  else if (B->getOpcode() == BO_Comma) { // ,
    autoCreateBlock();
    AppendStmt(Block, B, asc);
    addStmt(B->getRHS());
    return addStmt(B->getLHS());
  }
  else if (B->isAssignmentOp()) {
    if (asc.alwaysAdd()) {
      autoCreateBlock();
      AppendStmt(Block, B, asc);
    }

    // If visiting RHS causes us to finish 'Block' and the LHS doesn't
    // create a new block, then we should return RBlock.  Otherwise
    // we'll incorrectly return NULL.
    CFGBlock *RBlock = Visit(B->getRHS());
    CFGBlock *LBlock = Visit(B->getLHS(), AddStmtChoice::AsLValueNotAlwaysAdd);
    return LBlock ? LBlock : RBlock;
  }

  return VisitStmt(B, asc);
}

CFGBlock *CFGBuilder::VisitBlockExpr(BlockExpr *E, AddStmtChoice asc) {
  if (asc.alwaysAdd()) {
    autoCreateBlock();
    AppendStmt(Block, E, asc);
  }
  return Block;
}

CFGBlock *CFGBuilder::VisitBreakStmt(BreakStmt *B) {
  // "break" is a control-flow statement.  Thus we stop processing the current
  // block.
  if (badCFG)
    return 0;

  // Now create a new block that ends with the break statement.
  Block = createBlock(false);
  Block->setTerminator(B);

  // If there is no target for the break, then we are looking at an incomplete
  // AST.  This means that the CFG cannot be constructed.
  if (BreakJumpTarget.Block) {
    AddSuccessor(Block, BreakJumpTarget.Block);
  } else
    badCFG = true;


  return Block;
}

static bool CanThrow(Expr *E) {
  QualType Ty = E->getType();
  if (Ty->isFunctionPointerType())
    Ty = Ty->getAs<PointerType>()->getPointeeType();
  else if (Ty->isBlockPointerType())
    Ty = Ty->getAs<BlockPointerType>()->getPointeeType();

  const FunctionType *FT = Ty->getAs<FunctionType>();
  if (FT) {
    if (const FunctionProtoType *Proto = dyn_cast<FunctionProtoType>(FT))
      if (Proto->hasEmptyExceptionSpec())
        return false;
  }
  return true;
}

CFGBlock *CFGBuilder::VisitCallExpr(CallExpr *C, AddStmtChoice asc) {
  // If this is a call to a no-return function, this stops the block here.
  bool NoReturn = false;
  if (getFunctionExtInfo(*C->getCallee()->getType()).getNoReturn()) {
    NoReturn = true;
  }

  bool AddEHEdge = false;

  // Languages without exceptions are assumed to not throw.
  if (Context->getLangOptions().Exceptions) {
    if (BuildOpts.AddEHEdges)
      AddEHEdge = true;
  }

  if (FunctionDecl *FD = C->getDirectCallee()) {
    if (FD->hasAttr<NoReturnAttr>())
      NoReturn = true;
    if (FD->hasAttr<NoThrowAttr>())
      AddEHEdge = false;
  }

  if (!CanThrow(C->getCallee()))
    AddEHEdge = false;

  if (!NoReturn && !AddEHEdge) {
    if (asc.asLValue())
      return VisitStmt(C, AddStmtChoice::AlwaysAddAsLValue);
    else
      return VisitStmt(C, AddStmtChoice::AlwaysAdd);
  }

  if (Block) {
    Succ = Block;
    if (badCFG)
      return 0;
  }

  Block = createBlock(!NoReturn);
  AppendStmt(Block, C, asc);

  if (NoReturn) {
    // Wire this to the exit block directly.
    AddSuccessor(Block, &cfg->getExit());
  }
  if (AddEHEdge) {
    // Add exceptional edges.
    if (TryTerminatedBlock)
      AddSuccessor(Block, TryTerminatedBlock);
    else
      AddSuccessor(Block, &cfg->getExit());
  }

  return VisitChildren(C);
}

CFGBlock *CFGBuilder::VisitChooseExpr(ChooseExpr *C,
                                      AddStmtChoice asc) {
  CFGBlock* ConfluenceBlock = Block ? Block : createBlock();
  AppendStmt(ConfluenceBlock, C, asc);
  if (badCFG)
    return 0;

  asc = asc.asLValue() ? AddStmtChoice::AlwaysAddAsLValue
                       : AddStmtChoice::AlwaysAdd;

  Succ = ConfluenceBlock;
  Block = NULL;
  CFGBlock* LHSBlock = Visit(C->getLHS(), asc);
  if (badCFG)
    return 0;

  Succ = ConfluenceBlock;
  Block = NULL;
  CFGBlock* RHSBlock = Visit(C->getRHS(), asc);
  if (badCFG)
    return 0;

  Block = createBlock(false);
  // See if this is a known constant.
  const TryResult& KnownVal = TryEvaluateBool(C->getCond());
  AddSuccessor(Block, KnownVal.isFalse() ? NULL : LHSBlock);
  AddSuccessor(Block, KnownVal.isTrue() ? NULL : RHSBlock);
  Block->setTerminator(C);
  return addStmt(C->getCond());
}


CFGBlock* CFGBuilder::VisitCompoundStmt(CompoundStmt* C) {
  CFGBlock* LastBlock = Block;

  for (CompoundStmt::reverse_body_iterator I=C->body_rbegin(), E=C->body_rend();
       I != E; ++I ) {
    // If we hit a segment of code just containing ';' (NullStmts), we can
    // get a null block back.  In such cases, just use the LastBlock
    if (CFGBlock *newBlock = addStmt(*I))
      LastBlock = newBlock;

    if (badCFG)
      return NULL;
  }

  return LastBlock;
}

CFGBlock *CFGBuilder::VisitConditionalOperator(ConditionalOperator *C,
                                               AddStmtChoice asc) {
  // Create the confluence block that will "merge" the results of the ternary
  // expression.
  CFGBlock* ConfluenceBlock = Block ? Block : createBlock();
  AppendStmt(ConfluenceBlock, C, asc);
  if (badCFG)
    return 0;

  asc = asc.asLValue() ? AddStmtChoice::AlwaysAddAsLValue
                       : AddStmtChoice::AlwaysAdd;

  // Create a block for the LHS expression if there is an LHS expression.  A
  // GCC extension allows LHS to be NULL, causing the condition to be the
  // value that is returned instead.
  //  e.g: x ?: y is shorthand for: x ? x : y;
  Succ = ConfluenceBlock;
  Block = NULL;
  CFGBlock* LHSBlock = NULL;
  if (C->getLHS()) {
    LHSBlock = Visit(C->getLHS(), asc);
    if (badCFG)
      return 0;
    Block = NULL;
  }

  // Create the block for the RHS expression.
  Succ = ConfluenceBlock;
  CFGBlock* RHSBlock = Visit(C->getRHS(), asc);
  if (badCFG)
    return 0;

  // Create the block that will contain the condition.
  Block = createBlock(false);

  // See if this is a known constant.
  const TryResult& KnownVal = TryEvaluateBool(C->getCond());
  if (LHSBlock) {
    AddSuccessor(Block, KnownVal.isFalse() ? NULL : LHSBlock);
  } else {
    if (KnownVal.isFalse()) {
      // If we know the condition is false, add NULL as the successor for
      // the block containing the condition.  In this case, the confluence
      // block will have just one predecessor.
      AddSuccessor(Block, 0);
      assert(ConfluenceBlock->pred_size() == 1);
    } else {
      // If we have no LHS expression, add the ConfluenceBlock as a direct
      // successor for the block containing the condition.  Moreover, we need to
      // reverse the order of the predecessors in the ConfluenceBlock because
      // the RHSBlock will have been added to the succcessors already, and we
      // want the first predecessor to the the block containing the expression
      // for the case when the ternary expression evaluates to true.
      AddSuccessor(Block, ConfluenceBlock);
      assert(ConfluenceBlock->pred_size() == 2);
      std::reverse(ConfluenceBlock->pred_begin(),
                   ConfluenceBlock->pred_end());
    }
  }

  AddSuccessor(Block, KnownVal.isTrue() ? NULL : RHSBlock);
  Block->setTerminator(C);
  return addStmt(C->getCond());
}

CFGBlock *CFGBuilder::VisitDeclStmt(DeclStmt *DS) {
  autoCreateBlock();

  if (DS->isSingleDecl()) {
    AppendStmt(Block, DS);
    return VisitDeclSubExpr(DS->getSingleDecl());
  }

  CFGBlock *B = 0;

  // FIXME: Add a reverse iterator for DeclStmt to avoid this extra copy.
  typedef llvm::SmallVector<Decl*,10> BufTy;
  BufTy Buf(DS->decl_begin(), DS->decl_end());

  for (BufTy::reverse_iterator I = Buf.rbegin(), E = Buf.rend(); I != E; ++I) {
    // Get the alignment of the new DeclStmt, padding out to >=8 bytes.
    unsigned A = llvm::AlignOf<DeclStmt>::Alignment < 8
               ? 8 : llvm::AlignOf<DeclStmt>::Alignment;

    // Allocate the DeclStmt using the BumpPtrAllocator.  It will get
    // automatically freed with the CFG.
    DeclGroupRef DG(*I);
    Decl *D = *I;
    void *Mem = cfg->getAllocator().Allocate(sizeof(DeclStmt), A);
    DeclStmt *DSNew = new (Mem) DeclStmt(DG, D->getLocation(), GetEndLoc(D));

    // Append the fake DeclStmt to block.
    AppendStmt(Block, DSNew);
    B = VisitDeclSubExpr(D);
  }

  return B;
}

/// VisitDeclSubExpr - Utility method to add block-level expressions for
///  initializers in Decls.
CFGBlock *CFGBuilder::VisitDeclSubExpr(Decl* D) {
  assert(Block);

  VarDecl *VD = dyn_cast<VarDecl>(D);

  if (!VD)
    return Block;

  Expr *Init = VD->getInit();

  if (Init) {
    AddStmtChoice::Kind k =
      VD->getType()->isReferenceType() ? AddStmtChoice::AsLValueNotAlwaysAdd
                                       : AddStmtChoice::NotAlwaysAdd;
    Visit(Init, AddStmtChoice(k));
  }

  // If the type of VD is a VLA, then we must process its size expressions.
  for (VariableArrayType* VA = FindVA(VD->getType().getTypePtr()); VA != 0;
       VA = FindVA(VA->getElementType().getTypePtr()))
    Block = addStmt(VA->getSizeExpr());

  return Block;
}

CFGBlock* CFGBuilder::VisitIfStmt(IfStmt* I) {
  // We may see an if statement in the middle of a basic block, or it may be the
  // first statement we are processing.  In either case, we create a new basic
  // block.  First, we create the blocks for the then...else statements, and
  // then we create the block containing the if statement.  If we were in the
  // middle of a block, we stop processing that block.  That block is then the
  // implicit successor for the "then" and "else" clauses.

  // The block we were proccessing is now finished.  Make it the successor
  // block.
  if (Block) {
    Succ = Block;
    if (badCFG)
      return 0;
  }

  // Process the false branch.
  CFGBlock* ElseBlock = Succ;

  if (Stmt* Else = I->getElse()) {
    SaveAndRestore<CFGBlock*> sv(Succ);

    // NULL out Block so that the recursive call to Visit will
    // create a new basic block.
    Block = NULL;
    ElseBlock = addStmt(Else);

    if (!ElseBlock) // Can occur when the Else body has all NullStmts.
      ElseBlock = sv.get();
    else if (Block) {
      if (badCFG)
        return 0;
    }
  }

  // Process the true branch.
  CFGBlock* ThenBlock;
  {
    Stmt* Then = I->getThen();
    assert(Then);
    SaveAndRestore<CFGBlock*> sv(Succ);
    Block = NULL;
    ThenBlock = addStmt(Then);

    if (!ThenBlock) {
      // We can reach here if the "then" body has all NullStmts.
      // Create an empty block so we can distinguish between true and false
      // branches in path-sensitive analyses.
      ThenBlock = createBlock(false);
      AddSuccessor(ThenBlock, sv.get());
    } else if (Block) {
      if (badCFG)
        return 0;
    }
  }

  // Now create a new block containing the if statement.
  Block = createBlock(false);

  // Set the terminator of the new block to the If statement.
  Block->setTerminator(I);

  // See if this is a known constant.
  const TryResult &KnownVal = TryEvaluateBool(I->getCond());

  // Now add the successors.
  AddSuccessor(Block, KnownVal.isFalse() ? NULL : ThenBlock);
  AddSuccessor(Block, KnownVal.isTrue()? NULL : ElseBlock);

  // Add the condition as the last statement in the new block.  This may create
  // new blocks as the condition may contain control-flow.  Any newly created
  // blocks will be pointed to be "Block".
  Block = addStmt(I->getCond());

  // Finally, if the IfStmt contains a condition variable, add both the IfStmt
  // and the condition variable initialization to the CFG.
  if (VarDecl *VD = I->getConditionVariable()) {
    if (Expr *Init = VD->getInit()) {
      autoCreateBlock();
      AppendStmt(Block, I, AddStmtChoice::AlwaysAdd);
      addStmt(Init);
    }
  }

  return Block;
}


CFGBlock* CFGBuilder::VisitReturnStmt(ReturnStmt* R) {
  // If we were in the middle of a block we stop processing that block.
  //
  // NOTE: If a "return" appears in the middle of a block, this means that the
  //       code afterwards is DEAD (unreachable).  We still keep a basic block
  //       for that code; a simple "mark-and-sweep" from the entry block will be
  //       able to report such dead blocks.

  // Create the new block.
  Block = createBlock(false);

  // The Exit block is the only successor.
  AddSuccessor(Block, &cfg->getExit());

  // Add the return statement to the block.  This may create new blocks if R
  // contains control-flow (short-circuit operations).
  return VisitStmt(R, AddStmtChoice::AlwaysAdd);
}

CFGBlock* CFGBuilder::VisitLabelStmt(LabelStmt* L) {
  // Get the block of the labeled statement.  Add it to our map.
  addStmt(L->getSubStmt());
  CFGBlock* LabelBlock = Block;

  if (!LabelBlock)              // This can happen when the body is empty, i.e.
    LabelBlock = createBlock(); // scopes that only contains NullStmts.

  assert(LabelMap.find(L) == LabelMap.end() && "label already in map");
  LabelMap[ L ] = JumpTarget(LabelBlock, ScopePos);

  // Labels partition blocks, so this is the end of the basic block we were
  // processing (L is the block's label).  Because this is label (and we have
  // already processed the substatement) there is no extra control-flow to worry
  // about.
  LabelBlock->setLabel(L);
  if (badCFG)
    return 0;

  // We set Block to NULL to allow lazy creation of a new block (if necessary);
  Block = NULL;

  // This block is now the implicit successor of other blocks.
  Succ = LabelBlock;

  return LabelBlock;
}

CFGBlock* CFGBuilder::VisitGotoStmt(GotoStmt* G) {
  // Goto is a control-flow statement.  Thus we stop processing the current
  // block and create a new one.

  Block = createBlock(false);
  Block->setTerminator(G);

  // If we already know the mapping to the label block add the successor now.
  LabelMapTy::iterator I = LabelMap.find(G->getLabel());

  if (I == LabelMap.end())
    // We will need to backpatch this block later.
    BackpatchBlocks.push_back(JumpSource(Block, ScopePos));
  else {
    JumpTarget JT = I->second;
    AddSuccessor(Block, JT.Block);
  }

  return Block;
}

CFGBlock* CFGBuilder::VisitForStmt(ForStmt* F) {
  CFGBlock* LoopSuccessor = NULL;

  LocalScope::const_iterator LoopBeginScopePos = ScopePos;

  // "for" is a control-flow statement.  Thus we stop processing the current
  // block.
  if (Block) {
    if (badCFG)
      return 0;
    LoopSuccessor = Block;
  } else
    LoopSuccessor = Succ;

  // Save the current value for the break targets.
  // All breaks should go to the code following the loop.
  SaveAndRestore<JumpTarget> save_break(BreakJumpTarget);
  BreakJumpTarget = JumpTarget(LoopSuccessor, LoopBeginScopePos);

  // Because of short-circuit evaluation, the condition of the loop can span
  // multiple basic blocks.  Thus we need the "Entry" and "Exit" blocks that
  // evaluate the condition.
  CFGBlock* ExitConditionBlock = createBlock(false);
  CFGBlock* EntryConditionBlock = ExitConditionBlock;

  // Set the terminator for the "exit" condition block.
  ExitConditionBlock->setTerminator(F);

  // Now add the actual condition to the condition block.  Because the condition
  // itself may contain control-flow, new blocks may be created.
  if (Stmt* C = F->getCond()) {
    Block = ExitConditionBlock;
    EntryConditionBlock = addStmt(C);
    assert(Block == EntryConditionBlock ||
           (Block == 0 && EntryConditionBlock == Succ));

    // If this block contains a condition variable, add both the condition
    // variable and initializer to the CFG.
    if (VarDecl *VD = F->getConditionVariable()) {
      if (Expr *Init = VD->getInit()) {
        autoCreateBlock();
        AppendStmt(Block, F, AddStmtChoice::AlwaysAdd);
        EntryConditionBlock = addStmt(Init);
        assert(Block == EntryConditionBlock);
      }
    }

    if (Block) {
      if (badCFG)
        return 0;
    }
  }

  // The condition block is the implicit successor for the loop body as well as
  // any code above the loop.
  Succ = EntryConditionBlock;

  // See if this is a known constant.
  TryResult KnownVal(true);

  if (F->getCond())
    KnownVal = TryEvaluateBool(F->getCond());

  // Now create the loop body.
  {
    assert(F->getBody());

   // Save the current values for Block, Succ, and continue targets.
   SaveAndRestore<CFGBlock*> save_Block(Block), save_Succ(Succ);
   SaveAndRestore<JumpTarget> save_continue(ContinueJumpTarget);

    // Create a new block to contain the (bottom) of the loop body.
    Block = NULL;

    if (Stmt* I = F->getInc()) {
      // Generate increment code in its own basic block.  This is the target of
      // continue statements.
      Succ = addStmt(I);
    } else {
      // No increment code.  Create a special, empty, block that is used as the
      // target block for "looping back" to the start of the loop.
      assert(Succ == EntryConditionBlock);
      Succ = createBlock();
    }

    // Finish up the increment (or empty) block if it hasn't been already.
    if (Block) {
      assert(Block == Succ);
      if (badCFG)
        return 0;
      Block = 0;
    }

    ContinueJumpTarget = JumpTarget(Succ, LoopBeginScopePos);

    // The starting block for the loop increment is the block that should
    // represent the 'loop target' for looping back to the start of the loop.
    ContinueJumpTarget.Block->setLoopTarget(F);

    // Now populate the body block, and in the process create new blocks as we
    // walk the body of the loop.
    CFGBlock* BodyBlock = addStmt(F->getBody());

    if (!BodyBlock)
      BodyBlock = ContinueJumpTarget.Block;//can happen for "for (...;...;...);"
    else if (badCFG)
      return 0;

    // This new body block is a successor to our "exit" condition block.
    AddSuccessor(ExitConditionBlock, KnownVal.isFalse() ? NULL : BodyBlock);
  }

  // Link up the condition block with the code that follows the loop.  (the
  // false branch).
  AddSuccessor(ExitConditionBlock, KnownVal.isTrue() ? NULL : LoopSuccessor);

  // If the loop contains initialization, create a new block for those
  // statements.  This block can also contain statements that precede the loop.
  if (Stmt* I = F->getInit()) {
    Block = createBlock();
    return addStmt(I);
  } else {
    // There is no loop initialization.  We are thus basically a while loop.
    // NULL out Block to force lazy block construction.
    Block = NULL;
    Succ = EntryConditionBlock;
    return EntryConditionBlock;
  }
}

CFGBlock *CFGBuilder::VisitMemberExpr(MemberExpr *M, AddStmtChoice asc) {
  if (asc.alwaysAdd()) {
    autoCreateBlock();
    AppendStmt(Block, M, asc);
  }
  return Visit(M->getBase(),
               M->isArrow() ? AddStmtChoice::NotAlwaysAdd
                            : AddStmtChoice::AsLValueNotAlwaysAdd);
}

CFGBlock* CFGBuilder::VisitObjCForCollectionStmt(ObjCForCollectionStmt* S) {
  // Objective-C fast enumeration 'for' statements:
  //  http://developer.apple.com/documentation/Cocoa/Conceptual/ObjectiveC
  //
  //  for ( Type newVariable in collection_expression ) { statements }
  //
  //  becomes:
  //
  //   prologue:
  //     1. collection_expression
  //     T. jump to loop_entry
  //   loop_entry:
  //     1. side-effects of element expression
  //     1. ObjCForCollectionStmt [performs binding to newVariable]
  //     T. ObjCForCollectionStmt  TB, FB  [jumps to TB if newVariable != nil]
  //   TB:
  //     statements
  //     T. jump to loop_entry
  //   FB:
  //     what comes after
  //
  //  and
  //
  //  Type existingItem;
  //  for ( existingItem in expression ) { statements }
  //
  //  becomes:
  //
  //   the same with newVariable replaced with existingItem; the binding works
  //   the same except that for one ObjCForCollectionStmt::getElement() returns
  //   a DeclStmt and the other returns a DeclRefExpr.
  //

  CFGBlock* LoopSuccessor = 0;

  if (Block) {
    if (badCFG)
      return 0;
    LoopSuccessor = Block;
    Block = 0;
  } else
    LoopSuccessor = Succ;

  // Build the condition blocks.
  CFGBlock* ExitConditionBlock = createBlock(false);
  CFGBlock* EntryConditionBlock = ExitConditionBlock;

  // Set the terminator for the "exit" condition block.
  ExitConditionBlock->setTerminator(S);

  // The last statement in the block should be the ObjCForCollectionStmt, which
  // performs the actual binding to 'element' and determines if there are any
  // more items in the collection.
  AppendStmt(ExitConditionBlock, S);
  Block = ExitConditionBlock;

  // Walk the 'element' expression to see if there are any side-effects.  We
  // generate new blocks as necesary.  We DON'T add the statement by default to
  // the CFG unless it contains control-flow.
  EntryConditionBlock = Visit(S->getElement(), AddStmtChoice::NotAlwaysAdd);
  if (Block) {
    if (badCFG)
      return 0;
    Block = 0;
  }

  // The condition block is the implicit successor for the loop body as well as
  // any code above the loop.
  Succ = EntryConditionBlock;

  // Now create the true branch.
  {
    // Save the current values for Succ, continue and break targets.
    SaveAndRestore<CFGBlock*> save_Succ(Succ);
    SaveAndRestore<JumpTarget> save_continue(ContinueJumpTarget),
        save_break(BreakJumpTarget);

    BreakJumpTarget = JumpTarget(LoopSuccessor, ScopePos);
    ContinueJumpTarget = JumpTarget(EntryConditionBlock, ScopePos);

    CFGBlock* BodyBlock = addStmt(S->getBody());

    if (!BodyBlock)
      BodyBlock = EntryConditionBlock; // can happen for "for (X in Y) ;"
    else if (Block) {
      if (badCFG)
        return 0;
    }

    // This new body block is a successor to our "exit" condition block.
    AddSuccessor(ExitConditionBlock, BodyBlock);
  }

  // Link up the condition block with the code that follows the loop.
  // (the false branch).
  AddSuccessor(ExitConditionBlock, LoopSuccessor);

  // Now create a prologue block to contain the collection expression.
  Block = createBlock();
  return addStmt(S->getCollection());
}

CFGBlock* CFGBuilder::VisitObjCAtSynchronizedStmt(ObjCAtSynchronizedStmt* S) {
  // FIXME: Add locking 'primitives' to CFG for @synchronized.

  // Inline the body.
  CFGBlock *SyncBlock = addStmt(S->getSynchBody());

  // The sync body starts its own basic block.  This makes it a little easier
  // for diagnostic clients.
  if (SyncBlock) {
    if (badCFG)
      return 0;

    Block = 0;
    Succ = SyncBlock;
  }

  // Add the @synchronized to the CFG.
  autoCreateBlock();
  AppendStmt(Block, S, AddStmtChoice::AlwaysAdd);

  // Inline the sync expression.
  return addStmt(S->getSynchExpr());
}

CFGBlock* CFGBuilder::VisitObjCAtTryStmt(ObjCAtTryStmt* S) {
  // FIXME
  return NYS();
}

CFGBlock* CFGBuilder::VisitWhileStmt(WhileStmt* W) {
  CFGBlock* LoopSuccessor = NULL;

  LocalScope::const_iterator LoopBeginScopePos = ScopePos;

  // "while" is a control-flow statement.  Thus we stop processing the current
  // block.
  if (Block) {
    if (badCFG)
      return 0;
    LoopSuccessor = Block;
  } else
    LoopSuccessor = Succ;

  // Because of short-circuit evaluation, the condition of the loop can span
  // multiple basic blocks.  Thus we need the "Entry" and "Exit" blocks that
  // evaluate the condition.
  CFGBlock* ExitConditionBlock = createBlock(false);
  CFGBlock* EntryConditionBlock = ExitConditionBlock;

  // Set the terminator for the "exit" condition block.
  ExitConditionBlock->setTerminator(W);

  // Now add the actual condition to the condition block.  Because the condition
  // itself may contain control-flow, new blocks may be created.  Thus we update
  // "Succ" after adding the condition.
  if (Stmt* C = W->getCond()) {
    Block = ExitConditionBlock;
    EntryConditionBlock = addStmt(C);
    assert(Block == EntryConditionBlock);

    // If this block contains a condition variable, add both the condition
    // variable and initializer to the CFG.
    if (VarDecl *VD = W->getConditionVariable()) {
      if (Expr *Init = VD->getInit()) {
        autoCreateBlock();
        AppendStmt(Block, W, AddStmtChoice::AlwaysAdd);
        EntryConditionBlock = addStmt(Init);
        assert(Block == EntryConditionBlock);
      }
    }

    if (Block) {
      if (badCFG)
        return 0;
    }
  }

  // The condition block is the implicit successor for the loop body as well as
  // any code above the loop.
  Succ = EntryConditionBlock;

  // See if this is a known constant.
  const TryResult& KnownVal = TryEvaluateBool(W->getCond());

  // Process the loop body.
  {
    assert(W->getBody());

    // Save the current values for Block, Succ, and continue and break targets
    SaveAndRestore<CFGBlock*> save_Block(Block), save_Succ(Succ);
    SaveAndRestore<JumpTarget> save_continue(ContinueJumpTarget),
        save_break(BreakJumpTarget);

    // Create an empty block to represent the transition block for looping back
    // to the head of the loop.
    Block = 0;
    assert(Succ == EntryConditionBlock);
    Succ = createBlock();
    Succ->setLoopTarget(W);
    ContinueJumpTarget = JumpTarget(Succ, LoopBeginScopePos);

    // All breaks should go to the code following the loop.
    BreakJumpTarget = JumpTarget(LoopSuccessor, LoopBeginScopePos);

    // NULL out Block to force lazy instantiation of blocks for the body.
    Block = NULL;

    // Create the body.  The returned block is the entry to the loop body.
    CFGBlock* BodyBlock = addStmt(W->getBody());

    if (!BodyBlock)
      BodyBlock = ContinueJumpTarget.Block; // can happen for "while(...) ;"
    else if (Block) {
      if (badCFG)
        return 0;
    }

    // Add the loop body entry as a successor to the condition.
    AddSuccessor(ExitConditionBlock, KnownVal.isFalse() ? NULL : BodyBlock);
  }

  // Link up the condition block with the code that follows the loop.  (the
  // false branch).
  AddSuccessor(ExitConditionBlock, KnownVal.isTrue() ? NULL : LoopSuccessor);

  // There can be no more statements in the condition block since we loop back
  // to this block.  NULL out Block to force lazy creation of another block.
  Block = NULL;

  // Return the condition block, which is the dominating block for the loop.
  Succ = EntryConditionBlock;
  return EntryConditionBlock;
}


CFGBlock *CFGBuilder::VisitObjCAtCatchStmt(ObjCAtCatchStmt* S) {
  // FIXME: For now we pretend that @catch and the code it contains does not
  //  exit.
  return Block;
}

CFGBlock* CFGBuilder::VisitObjCAtThrowStmt(ObjCAtThrowStmt* S) {
  // FIXME: This isn't complete.  We basically treat @throw like a return
  //  statement.

  // If we were in the middle of a block we stop processing that block.
  if (badCFG)
    return 0;

  // Create the new block.
  Block = createBlock(false);

  // The Exit block is the only successor.
  AddSuccessor(Block, &cfg->getExit());

  // Add the statement to the block.  This may create new blocks if S contains
  // control-flow (short-circuit operations).
  return VisitStmt(S, AddStmtChoice::AlwaysAdd);
}

CFGBlock* CFGBuilder::VisitCXXThrowExpr(CXXThrowExpr* T) {
  // If we were in the middle of a block we stop processing that block.
  if (badCFG)
    return 0;

  // Create the new block.
  Block = createBlock(false);

  if (TryTerminatedBlock)
    // The current try statement is the only successor.
    AddSuccessor(Block, TryTerminatedBlock);
  else
    // otherwise the Exit block is the only successor.
    AddSuccessor(Block, &cfg->getExit());

  // Add the statement to the block.  This may create new blocks if S contains
  // control-flow (short-circuit operations).
  return VisitStmt(T, AddStmtChoice::AlwaysAdd);
}

CFGBlock *CFGBuilder::VisitDoStmt(DoStmt* D) {
  CFGBlock* LoopSuccessor = NULL;

  // "do...while" is a control-flow statement.  Thus we stop processing the
  // current block.
  if (Block) {
    if (badCFG)
      return 0;
    LoopSuccessor = Block;
  } else
    LoopSuccessor = Succ;

  // Because of short-circuit evaluation, the condition of the loop can span
  // multiple basic blocks.  Thus we need the "Entry" and "Exit" blocks that
  // evaluate the condition.
  CFGBlock* ExitConditionBlock = createBlock(false);
  CFGBlock* EntryConditionBlock = ExitConditionBlock;

  // Set the terminator for the "exit" condition block.
  ExitConditionBlock->setTerminator(D);

  // Now add the actual condition to the condition block.  Because the condition
  // itself may contain control-flow, new blocks may be created.
  if (Stmt* C = D->getCond()) {
    Block = ExitConditionBlock;
    EntryConditionBlock = addStmt(C);
    if (Block) {
      if (badCFG)
        return 0;
    }
  }

  // The condition block is the implicit successor for the loop body.
  Succ = EntryConditionBlock;

  // See if this is a known constant.
  const TryResult &KnownVal = TryEvaluateBool(D->getCond());

  // Process the loop body.
  CFGBlock* BodyBlock = NULL;
  {
    assert(D->getBody());

    // Save the current values for Block, Succ, and continue and break targets
    SaveAndRestore<CFGBlock*> save_Block(Block), save_Succ(Succ);
    SaveAndRestore<JumpTarget> save_continue(ContinueJumpTarget),
        save_break(BreakJumpTarget);

    // All continues within this loop should go to the condition block
    ContinueJumpTarget = JumpTarget(EntryConditionBlock, ScopePos);

    // All breaks should go to the code following the loop.
    BreakJumpTarget = JumpTarget(LoopSuccessor, ScopePos);

    // NULL out Block to force lazy instantiation of blocks for the body.
    Block = NULL;

    // Create the body.  The returned block is the entry to the loop body.
    BodyBlock = addStmt(D->getBody());

    if (!BodyBlock)
      BodyBlock = EntryConditionBlock; // can happen for "do ; while(...)"
    else if (Block) {
      if (badCFG)
        return 0;
    }

    if (!KnownVal.isFalse()) {
      // Add an intermediate block between the BodyBlock and the
      // ExitConditionBlock to represent the "loop back" transition.  Create an
      // empty block to represent the transition block for looping back to the
      // head of the loop.
      // FIXME: Can we do this more efficiently without adding another block?
      Block = NULL;
      Succ = BodyBlock;
      CFGBlock *LoopBackBlock = createBlock();
      LoopBackBlock->setLoopTarget(D);

      // Add the loop body entry as a successor to the condition.
      AddSuccessor(ExitConditionBlock, LoopBackBlock);
    }
    else
      AddSuccessor(ExitConditionBlock, NULL);
  }

  // Link up the condition block with the code that follows the loop.
  // (the false branch).
  AddSuccessor(ExitConditionBlock, KnownVal.isTrue() ? NULL : LoopSuccessor);

  // There can be no more statements in the body block(s) since we loop back to
  // the body.  NULL out Block to force lazy creation of another block.
  Block = NULL;

  // Return the loop body, which is the dominating block for the loop.
  Succ = BodyBlock;
  return BodyBlock;
}

CFGBlock* CFGBuilder::VisitContinueStmt(ContinueStmt* C) {
  // "continue" is a control-flow statement.  Thus we stop processing the
  // current block.
  if (badCFG)
    return 0;

  // Now create a new block that ends with the continue statement.
  Block = createBlock(false);
  Block->setTerminator(C);

  // If there is no target for the continue, then we are looking at an
  // incomplete AST.  This means the CFG cannot be constructed.
  if (ContinueJumpTarget.Block) {
    AddSuccessor(Block, ContinueJumpTarget.Block);
  } else
    badCFG = true;

  return Block;
}

CFGBlock *CFGBuilder::VisitSizeOfAlignOfExpr(SizeOfAlignOfExpr *E,
                                             AddStmtChoice asc) {

  if (asc.alwaysAdd()) {
    autoCreateBlock();
    AppendStmt(Block, E);
  }

  // VLA types have expressions that must be evaluated.
  if (E->isArgumentType()) {
    for (VariableArrayType* VA = FindVA(E->getArgumentType().getTypePtr());
         VA != 0; VA = FindVA(VA->getElementType().getTypePtr()))
      addStmt(VA->getSizeExpr());
  }

  return Block;
}

/// VisitStmtExpr - Utility method to handle (nested) statement
///  expressions (a GCC extension).
CFGBlock* CFGBuilder::VisitStmtExpr(StmtExpr *SE, AddStmtChoice asc) {
  if (asc.alwaysAdd()) {
    autoCreateBlock();
    AppendStmt(Block, SE);
  }
  return VisitCompoundStmt(SE->getSubStmt());
}

CFGBlock* CFGBuilder::VisitSwitchStmt(SwitchStmt* Terminator) {
  // "switch" is a control-flow statement.  Thus we stop processing the current
  // block.
  CFGBlock* SwitchSuccessor = NULL;

  if (Block) {
    if (badCFG)
      return 0;
    SwitchSuccessor = Block;
  } else SwitchSuccessor = Succ;

  // Save the current "switch" context.
  SaveAndRestore<CFGBlock*> save_switch(SwitchTerminatedBlock),
                            save_default(DefaultCaseBlock);
  SaveAndRestore<JumpTarget> save_break(BreakJumpTarget);

  // Set the "default" case to be the block after the switch statement.  If the
  // switch statement contains a "default:", this value will be overwritten with
  // the block for that code.
  DefaultCaseBlock = SwitchSuccessor;

  // Create a new block that will contain the switch statement.
  SwitchTerminatedBlock = createBlock(false);

  // Now process the switch body.  The code after the switch is the implicit
  // successor.
  Succ = SwitchSuccessor;
  BreakJumpTarget = JumpTarget(SwitchSuccessor, ScopePos);

  // When visiting the body, the case statements should automatically get linked
  // up to the switch.  We also don't keep a pointer to the body, since all
  // control-flow from the switch goes to case/default statements.
  assert(Terminator->getBody() && "switch must contain a non-NULL body");
  Block = NULL;
  addStmt(Terminator->getBody());
  if (Block) {
    if (badCFG)
      return 0;
  }

  // If we have no "default:" case, the default transition is to the code
  // following the switch body.
  AddSuccessor(SwitchTerminatedBlock, DefaultCaseBlock);

  // Add the terminator and condition in the switch block.
  SwitchTerminatedBlock->setTerminator(Terminator);
  assert(Terminator->getCond() && "switch condition must be non-NULL");
  Block = SwitchTerminatedBlock;
  Block = addStmt(Terminator->getCond());

  // Finally, if the SwitchStmt contains a condition variable, add both the
  // SwitchStmt and the condition variable initialization to the CFG.
  if (VarDecl *VD = Terminator->getConditionVariable()) {
    if (Expr *Init = VD->getInit()) {
      autoCreateBlock();
      AppendStmt(Block, Terminator, AddStmtChoice::AlwaysAdd);
      addStmt(Init);
    }
  }

  return Block;
}

CFGBlock* CFGBuilder::VisitCaseStmt(CaseStmt* CS) {
  // CaseStmts are essentially labels, so they are the first statement in a
  // block.
  CFGBlock *TopBlock = 0, *LastBlock = 0;

  if (Stmt *Sub = CS->getSubStmt()) {
    // For deeply nested chains of CaseStmts, instead of doing a recursion
    // (which can blow out the stack), manually unroll and create blocks
    // along the way.
    while (isa<CaseStmt>(Sub)) {
      CFGBlock *CurrentBlock = createBlock(false);
      CurrentBlock->setLabel(CS);

      if (TopBlock)
        AddSuccessor(LastBlock, CurrentBlock);
      else
        TopBlock = CurrentBlock;

      AddSuccessor(SwitchTerminatedBlock, CurrentBlock);
      LastBlock = CurrentBlock;

      CS = cast<CaseStmt>(Sub);
      Sub = CS->getSubStmt();
    }

    addStmt(Sub);
  }

  CFGBlock* CaseBlock = Block;
  if (!CaseBlock)
    CaseBlock = createBlock();

  // Cases statements partition blocks, so this is the top of the basic block we
  // were processing (the "case XXX:" is the label).
  CaseBlock->setLabel(CS);

  if (badCFG)
    return 0;

  // Add this block to the list of successors for the block with the switch
  // statement.
  assert(SwitchTerminatedBlock);
  AddSuccessor(SwitchTerminatedBlock, CaseBlock);

  // We set Block to NULL to allow lazy creation of a new block (if necessary)
  Block = NULL;

  if (TopBlock) {
    AddSuccessor(LastBlock, CaseBlock);
    Succ = TopBlock;
  }
  else {
    // This block is now the implicit successor of other blocks.
    Succ = CaseBlock;
  }

  return Succ;
}

CFGBlock* CFGBuilder::VisitDefaultStmt(DefaultStmt* Terminator) {
  if (Terminator->getSubStmt())
    addStmt(Terminator->getSubStmt());

  DefaultCaseBlock = Block;

  if (!DefaultCaseBlock)
    DefaultCaseBlock = createBlock();

  // Default statements partition blocks, so this is the top of the basic block
  // we were processing (the "default:" is the label).
  DefaultCaseBlock->setLabel(Terminator);

  if (badCFG)
    return 0;

  // Unlike case statements, we don't add the default block to the successors
  // for the switch statement immediately.  This is done when we finish
  // processing the switch statement.  This allows for the default case
  // (including a fall-through to the code after the switch statement) to always
  // be the last successor of a switch-terminated block.

  // We set Block to NULL to allow lazy creation of a new block (if necessary)
  Block = NULL;

  // This block is now the implicit successor of other blocks.
  Succ = DefaultCaseBlock;

  return DefaultCaseBlock;
}

CFGBlock *CFGBuilder::VisitCXXTryStmt(CXXTryStmt *Terminator) {
  // "try"/"catch" is a control-flow statement.  Thus we stop processing the
  // current block.
  CFGBlock* TrySuccessor = NULL;

  if (Block) {
    if (badCFG)
      return 0;
    TrySuccessor = Block;
  } else TrySuccessor = Succ;

  CFGBlock *PrevTryTerminatedBlock = TryTerminatedBlock;

  // Create a new block that will contain the try statement.
  CFGBlock *NewTryTerminatedBlock = createBlock(false);
  // Add the terminator in the try block.
  NewTryTerminatedBlock->setTerminator(Terminator);

  bool HasCatchAll = false;
  for (unsigned h = 0; h <Terminator->getNumHandlers(); ++h) {
    // The code after the try is the implicit successor.
    Succ = TrySuccessor;
    CXXCatchStmt *CS = Terminator->getHandler(h);
    if (CS->getExceptionDecl() == 0) {
      HasCatchAll = true;
    }
    Block = NULL;
    CFGBlock *CatchBlock = VisitCXXCatchStmt(CS);
    if (CatchBlock == 0)
      return 0;
    // Add this block to the list of successors for the block with the try
    // statement.
    AddSuccessor(NewTryTerminatedBlock, CatchBlock);
  }
  if (!HasCatchAll) {
    if (PrevTryTerminatedBlock)
      AddSuccessor(NewTryTerminatedBlock, PrevTryTerminatedBlock);
    else
      AddSuccessor(NewTryTerminatedBlock, &cfg->getExit());
  }

  // The code after the try is the implicit successor.
  Succ = TrySuccessor;

  // Save the current "try" context.
  SaveAndRestore<CFGBlock*> save_try(TryTerminatedBlock);
  TryTerminatedBlock = NewTryTerminatedBlock;

  assert(Terminator->getTryBlock() && "try must contain a non-NULL body");
  Block = NULL;
  Block = addStmt(Terminator->getTryBlock());
  return Block;
}

CFGBlock* CFGBuilder::VisitCXXCatchStmt(CXXCatchStmt* CS) {
  // CXXCatchStmt are treated like labels, so they are the first statement in a
  // block.

  if (CS->getHandlerBlock())
    addStmt(CS->getHandlerBlock());

  CFGBlock* CatchBlock = Block;
  if (!CatchBlock)
    CatchBlock = createBlock();

  CatchBlock->setLabel(CS);

  if (badCFG)
    return 0;

  // We set Block to NULL to allow lazy creation of a new block (if necessary)
  Block = NULL;

  return CatchBlock;
}

CFGBlock *CFGBuilder::VisitCXXMemberCallExpr(CXXMemberCallExpr *C,
                                             AddStmtChoice asc) {
  AddStmtChoice::Kind K = asc.asLValue() ? AddStmtChoice::AlwaysAddAsLValue
                                         : AddStmtChoice::AlwaysAdd;
  autoCreateBlock();
  AppendStmt(Block, C, AddStmtChoice(K));
  return VisitChildren(C);
}

CFGBlock* CFGBuilder::VisitIndirectGotoStmt(IndirectGotoStmt* I) {
  // Lazily create the indirect-goto dispatch block if there isn't one already.
  CFGBlock* IBlock = cfg->getIndirectGotoBlock();

  if (!IBlock) {
    IBlock = createBlock(false);
    cfg->setIndirectGotoBlock(IBlock);
  }

  // IndirectGoto is a control-flow statement.  Thus we stop processing the
  // current block and create a new one.
  if (badCFG)
    return 0;

  Block = createBlock(false);
  Block->setTerminator(I);
  AddSuccessor(Block, IBlock);
  return addStmt(I->getTarget());
}

} // end anonymous namespace

/// createBlock - Constructs and adds a new CFGBlock to the CFG.  The block has
///  no successors or predecessors.  If this is the first block created in the
///  CFG, it is automatically set to be the Entry and Exit of the CFG.
CFGBlock* CFG::createBlock() {
  bool first_block = begin() == end();

  // Create the block.
  CFGBlock *Mem = getAllocator().Allocate<CFGBlock>();
  new (Mem) CFGBlock(NumBlockIDs++, BlkBVC);
  Blocks.push_back(Mem, BlkBVC);

  // If this is the first block, set it as the Entry and Exit.
  if (first_block)
    Entry = Exit = &back();

  // Return the block.
  return &back();
}

/// buildCFG - Constructs a CFG from an AST.  Ownership of the returned
///  CFG is returned to the caller.
CFG* CFG::buildCFG(const Decl *D, Stmt* Statement, ASTContext *C,
    BuildOptions BO) {
  CFGBuilder Builder;
  return Builder.buildCFG(D, Statement, C, BO);
}

//===----------------------------------------------------------------------===//
// CFG: Queries for BlkExprs.
//===----------------------------------------------------------------------===//

namespace {
  typedef llvm::DenseMap<const Stmt*,unsigned> BlkExprMapTy;
}

static void FindSubExprAssignments(Stmt *S,
                                   llvm::SmallPtrSet<Expr*,50>& Set) {
  if (!S)
    return;

  for (Stmt::child_iterator I=S->child_begin(), E=S->child_end(); I!=E; ++I) {
    Stmt *child = *I;
    if (!child)
      continue;

    if (BinaryOperator* B = dyn_cast<BinaryOperator>(child))
      if (B->isAssignmentOp()) Set.insert(B);

    FindSubExprAssignments(child, Set);
  }
}

static BlkExprMapTy* PopulateBlkExprMap(CFG& cfg) {
  BlkExprMapTy* M = new BlkExprMapTy();

  // Look for assignments that are used as subexpressions.  These are the only
  // assignments that we want to *possibly* register as a block-level
  // expression.  Basically, if an assignment occurs both in a subexpression and
  // at the block-level, it is a block-level expression.
  llvm::SmallPtrSet<Expr*,50> SubExprAssignments;

  for (CFG::iterator I=cfg.begin(), E=cfg.end(); I != E; ++I)
    for (CFGBlock::iterator BI=(*I)->begin(), EI=(*I)->end(); BI != EI; ++BI)
      if (CFGStmt S = BI->getAs<CFGStmt>())
        FindSubExprAssignments(S, SubExprAssignments);

  for (CFG::iterator I=cfg.begin(), E=cfg.end(); I != E; ++I) {

    // Iterate over the statements again on identify the Expr* and Stmt* at the
    // block-level that are block-level expressions.

    for (CFGBlock::iterator BI=(*I)->begin(), EI=(*I)->end(); BI != EI; ++BI) {
      CFGStmt CS = BI->getAs<CFGStmt>();
      if (!CS.isValid())
        continue;
      if (Expr* Exp = dyn_cast<Expr>(CS.getStmt())) {

        if (BinaryOperator* B = dyn_cast<BinaryOperator>(Exp)) {
          // Assignment expressions that are not nested within another
          // expression are really "statements" whose value is never used by
          // another expression.
          if (B->isAssignmentOp() && !SubExprAssignments.count(Exp))
            continue;
        } else if (const StmtExpr* Terminator = dyn_cast<StmtExpr>(Exp)) {
          // Special handling for statement expressions.  The last statement in
          // the statement expression is also a block-level expr.
          const CompoundStmt* C = Terminator->getSubStmt();
          if (!C->body_empty()) {
            unsigned x = M->size();
            (*M)[C->body_back()] = x;
          }
        }

        unsigned x = M->size();
        (*M)[Exp] = x;
      }
    }

    // Look at terminators.  The condition is a block-level expression.

    Stmt* S = (*I)->getTerminatorCondition();

    if (S && M->find(S) == M->end()) {
        unsigned x = M->size();
        (*M)[S] = x;
    }
  }

  return M;
}

CFG::BlkExprNumTy CFG::getBlkExprNum(const Stmt* S) {
  assert(S != NULL);
  if (!BlkExprMap) { BlkExprMap = (void*) PopulateBlkExprMap(*this); }

  BlkExprMapTy* M = reinterpret_cast<BlkExprMapTy*>(BlkExprMap);
  BlkExprMapTy::iterator I = M->find(S);
  return (I == M->end()) ? CFG::BlkExprNumTy() : CFG::BlkExprNumTy(I->second);
}

unsigned CFG::getNumBlkExprs() {
  if (const BlkExprMapTy* M = reinterpret_cast<const BlkExprMapTy*>(BlkExprMap))
    return M->size();
  else {
    // We assume callers interested in the number of BlkExprs will want
    // the map constructed if it doesn't already exist.
    BlkExprMap = (void*) PopulateBlkExprMap(*this);
    return reinterpret_cast<BlkExprMapTy*>(BlkExprMap)->size();
  }
}

//===----------------------------------------------------------------------===//
// Filtered walking of the CFG.
//===----------------------------------------------------------------------===//

bool CFGBlock::FilterEdge(const CFGBlock::FilterOptions &F,
        const CFGBlock *From, const CFGBlock *To) {

  if (F.IgnoreDefaultsWithCoveredEnums) {
    // If the 'To' has no label or is labeled but the label isn't a
    // CaseStmt then filter this edge.
    if (const SwitchStmt *S =
  dyn_cast_or_null<SwitchStmt>(From->getTerminator())) {
      if (S->isAllEnumCasesCovered()) {
  const Stmt *L = To->getLabel();
  if (!L || !isa<CaseStmt>(L))
    return true;
      }
    }
  }

  return false;
}

//===----------------------------------------------------------------------===//
// Cleanup: CFG dstor.
//===----------------------------------------------------------------------===//

CFG::~CFG() {
  delete reinterpret_cast<const BlkExprMapTy*>(BlkExprMap);
}

//===----------------------------------------------------------------------===//
// CFG pretty printing
//===----------------------------------------------------------------------===//

namespace {

class StmtPrinterHelper : public PrinterHelper  {
  typedef llvm::DenseMap<Stmt*,std::pair<unsigned,unsigned> > StmtMapTy;
  typedef llvm::DenseMap<Decl*,std::pair<unsigned,unsigned> > DeclMapTy;
  StmtMapTy StmtMap;
  DeclMapTy DeclMap;
  signed CurrentBlock;
  unsigned CurrentStmt;
  const LangOptions &LangOpts;
public:

  StmtPrinterHelper(const CFG* cfg, const LangOptions &LO)
    : CurrentBlock(0), CurrentStmt(0), LangOpts(LO) {
    for (CFG::const_iterator I = cfg->begin(), E = cfg->end(); I != E; ++I ) {
      unsigned j = 1;
      for (CFGBlock::const_iterator BI = (*I)->begin(), BEnd = (*I)->end() ;
           BI != BEnd; ++BI, ++j ) {
        if (CFGStmt SE = BI->getAs<CFGStmt>()) {
          std::pair<unsigned, unsigned> P((*I)->getBlockID(), j);
          StmtMap[SE] = P;

          if (DeclStmt* DS = dyn_cast<DeclStmt>(SE.getStmt())) {
              DeclMap[DS->getSingleDecl()] = P;

          } else if (IfStmt* IS = dyn_cast<IfStmt>(SE.getStmt())) {
            if (VarDecl* VD = IS->getConditionVariable())
              DeclMap[VD] = P;

          } else if (ForStmt* FS = dyn_cast<ForStmt>(SE.getStmt())) {
            if (VarDecl* VD = FS->getConditionVariable())
              DeclMap[VD] = P;

          } else if (WhileStmt* WS = dyn_cast<WhileStmt>(SE.getStmt())) {
            if (VarDecl* VD = WS->getConditionVariable())
              DeclMap[VD] = P;

          } else if (SwitchStmt* SS = dyn_cast<SwitchStmt>(SE.getStmt())) {
            if (VarDecl* VD = SS->getConditionVariable())
              DeclMap[VD] = P;

          } else if (CXXCatchStmt* CS = dyn_cast<CXXCatchStmt>(SE.getStmt())) {
            if (VarDecl* VD = CS->getExceptionDecl())
              DeclMap[VD] = P;
          }
        }
      }
    }
  }

  virtual ~StmtPrinterHelper() {}

  const LangOptions &getLangOpts() const { return LangOpts; }
  void setBlockID(signed i) { CurrentBlock = i; }
  void setStmtID(unsigned i) { CurrentStmt = i; }

  virtual bool handledStmt(Stmt* S, llvm::raw_ostream& OS) {
    StmtMapTy::iterator I = StmtMap.find(S);

    if (I == StmtMap.end())
      return false;

    if (CurrentBlock >= 0 && I->second.first == (unsigned) CurrentBlock
                          && I->second.second == CurrentStmt) {
      return false;
    }

    OS << "[B" << I->second.first << "." << I->second.second << "]";
    return true;
  }

  bool handleDecl(Decl* D, llvm::raw_ostream& OS) {
    DeclMapTy::iterator I = DeclMap.find(D);

    if (I == DeclMap.end())
      return false;

    if (CurrentBlock >= 0 && I->second.first == (unsigned) CurrentBlock
                          && I->second.second == CurrentStmt) {
      return false;
    }

    OS << "[B" << I->second.first << "." << I->second.second << "]";
    return true;
  }
};
} // end anonymous namespace


namespace {
class CFGBlockTerminatorPrint
  : public StmtVisitor<CFGBlockTerminatorPrint,void> {

  llvm::raw_ostream& OS;
  StmtPrinterHelper* Helper;
  PrintingPolicy Policy;
public:
  CFGBlockTerminatorPrint(llvm::raw_ostream& os, StmtPrinterHelper* helper,
                          const PrintingPolicy &Policy)
    : OS(os), Helper(helper), Policy(Policy) {}

  void VisitIfStmt(IfStmt* I) {
    OS << "if ";
    I->getCond()->printPretty(OS,Helper,Policy);
  }

  // Default case.
  void VisitStmt(Stmt* Terminator) {
    Terminator->printPretty(OS, Helper, Policy);
  }

  void VisitForStmt(ForStmt* F) {
    OS << "for (" ;
    if (F->getInit())
      OS << "...";
    OS << "; ";
    if (Stmt* C = F->getCond())
      C->printPretty(OS, Helper, Policy);
    OS << "; ";
    if (F->getInc())
      OS << "...";
    OS << ")";
  }

  void VisitWhileStmt(WhileStmt* W) {
    OS << "while " ;
    if (Stmt* C = W->getCond())
      C->printPretty(OS, Helper, Policy);
  }

  void VisitDoStmt(DoStmt* D) {
    OS << "do ... while ";
    if (Stmt* C = D->getCond())
      C->printPretty(OS, Helper, Policy);
  }

  void VisitSwitchStmt(SwitchStmt* Terminator) {
    OS << "switch ";
    Terminator->getCond()->printPretty(OS, Helper, Policy);
  }

  void VisitCXXTryStmt(CXXTryStmt* CS) {
    OS << "try ...";
  }

  void VisitConditionalOperator(ConditionalOperator* C) {
    C->getCond()->printPretty(OS, Helper, Policy);
    OS << " ? ... : ...";
  }

  void VisitChooseExpr(ChooseExpr* C) {
    OS << "__builtin_choose_expr( ";
    C->getCond()->printPretty(OS, Helper, Policy);
    OS << " )";
  }

  void VisitIndirectGotoStmt(IndirectGotoStmt* I) {
    OS << "goto *";
    I->getTarget()->printPretty(OS, Helper, Policy);
  }

  void VisitBinaryOperator(BinaryOperator* B) {
    if (!B->isLogicalOp()) {
      VisitExpr(B);
      return;
    }

    B->getLHS()->printPretty(OS, Helper, Policy);

    switch (B->getOpcode()) {
      case BO_LOr:
        OS << " || ...";
        return;
      case BO_LAnd:
        OS << " && ...";
        return;
      default:
        assert(false && "Invalid logical operator.");
    }
  }

  void VisitExpr(Expr* E) {
    E->printPretty(OS, Helper, Policy);
  }
};
} // end anonymous namespace

static void print_elem(llvm::raw_ostream &OS, StmtPrinterHelper* Helper,
                       const CFGElement &E) {
  if (CFGStmt CS = E.getAs<CFGStmt>()) {
    Stmt *S = CS;

    if (Helper) {

      // special printing for statement-expressions.
      if (StmtExpr* SE = dyn_cast<StmtExpr>(S)) {
        CompoundStmt* Sub = SE->getSubStmt();

        if (Sub->child_begin() != Sub->child_end()) {
          OS << "({ ... ; ";
          Helper->handledStmt(*SE->getSubStmt()->body_rbegin(),OS);
          OS << " })\n";
          return;
        }
      }
      // special printing for comma expressions.
      if (BinaryOperator* B = dyn_cast<BinaryOperator>(S)) {
        if (B->getOpcode() == BO_Comma) {
          OS << "... , ";
          Helper->handledStmt(B->getRHS(),OS);
          OS << '\n';
          return;
        }
      }
    }
    S->printPretty(OS, Helper, PrintingPolicy(Helper->getLangOpts()));

    if (isa<CXXOperatorCallExpr>(S)) {
      OS << " (OperatorCall)";
    }
    else if (isa<CXXBindTemporaryExpr>(S)) {
      OS << " (BindTemporary)";
    }

    // Expressions need a newline.
    if (isa<Expr>(S))
      OS << '\n';

  } else if (CFGInitializer IE = E.getAs<CFGInitializer>()) {
    CXXBaseOrMemberInitializer* I = IE;
    if (I->isBaseInitializer())
      OS << I->getBaseClass()->getAsCXXRecordDecl()->getName();
    else OS << I->getMember()->getName();

    OS << "(";
    if (Expr* IE = I->getInit())
      IE->printPretty(OS, Helper, PrintingPolicy(Helper->getLangOpts()));
    OS << ")";

    if (I->isBaseInitializer())
      OS << " (Base initializer)\n";
    else OS << " (Member initializer)\n";

  } else if (CFGAutomaticObjDtor DE = E.getAs<CFGAutomaticObjDtor>()){
    VarDecl* VD = DE.getVarDecl();
    Helper->handleDecl(VD, OS);

    Type* T = VD->getType().getTypePtr();
    if (const ReferenceType* RT = T->getAs<ReferenceType>())
      T = RT->getPointeeType().getTypePtr();

    OS << ".~" << T->getAsCXXRecordDecl()->getName().str() << "()";
    OS << " (Implicit destructor)\n";
  }
 }

static void print_block(llvm::raw_ostream& OS, const CFG* cfg,
                        const CFGBlock& B,
                        StmtPrinterHelper* Helper, bool print_edges) {

  if (Helper) Helper->setBlockID(B.getBlockID());

  // Print the header.
  OS << "\n [ B" << B.getBlockID();

  if (&B == &cfg->getEntry())
    OS << " (ENTRY) ]\n";
  else if (&B == &cfg->getExit())
    OS << " (EXIT) ]\n";
  else if (&B == cfg->getIndirectGotoBlock())
    OS << " (INDIRECT GOTO DISPATCH) ]\n";
  else
    OS << " ]\n";

  // Print the label of this block.
  if (Stmt* Label = const_cast<Stmt*>(B.getLabel())) {

    if (print_edges)
      OS << "    ";

    if (LabelStmt* L = dyn_cast<LabelStmt>(Label))
      OS << L->getName();
    else if (CaseStmt* C = dyn_cast<CaseStmt>(Label)) {
      OS << "case ";
      C->getLHS()->printPretty(OS, Helper,
                               PrintingPolicy(Helper->getLangOpts()));
      if (C->getRHS()) {
        OS << " ... ";
        C->getRHS()->printPretty(OS, Helper,
                                 PrintingPolicy(Helper->getLangOpts()));
      }
    } else if (isa<DefaultStmt>(Label))
      OS << "default";
    else if (CXXCatchStmt *CS = dyn_cast<CXXCatchStmt>(Label)) {
      OS << "catch (";
      if (CS->getExceptionDecl())
        CS->getExceptionDecl()->print(OS, PrintingPolicy(Helper->getLangOpts()),
                                      0);
      else
        OS << "...";
      OS << ")";

    } else
      assert(false && "Invalid label statement in CFGBlock.");

    OS << ":\n";
  }

  // Iterate through the statements in the block and print them.
  unsigned j = 1;

  for (CFGBlock::const_iterator I = B.begin(), E = B.end() ;
       I != E ; ++I, ++j ) {

    // Print the statement # in the basic block and the statement itself.
    if (print_edges)
      OS << "    ";

    OS << llvm::format("%3d", j) << ": ";

    if (Helper)
      Helper->setStmtID(j);

    print_elem(OS,Helper,*I);
  }

  // Print the terminator of this block.
  if (B.getTerminator()) {
    if (print_edges)
      OS << "    ";

    OS << "  T: ";

    if (Helper) Helper->setBlockID(-1);

    CFGBlockTerminatorPrint TPrinter(OS, Helper,
                                     PrintingPolicy(Helper->getLangOpts()));
    TPrinter.Visit(const_cast<Stmt*>(B.getTerminator()));
    OS << '\n';
  }

  if (print_edges) {
    // Print the predecessors of this block.
    OS << "    Predecessors (" << B.pred_size() << "):";
    unsigned i = 0;

    for (CFGBlock::const_pred_iterator I = B.pred_begin(), E = B.pred_end();
         I != E; ++I, ++i) {

      if (i == 8 || (i-8) == 0)
        OS << "\n     ";

      OS << " B" << (*I)->getBlockID();
    }

    OS << '\n';

    // Print the successors of this block.
    OS << "    Successors (" << B.succ_size() << "):";
    i = 0;

    for (CFGBlock::const_succ_iterator I = B.succ_begin(), E = B.succ_end();
         I != E; ++I, ++i) {

      if (i == 8 || (i-8) % 10 == 0)
        OS << "\n    ";

      if (*I)
        OS << " B" << (*I)->getBlockID();
      else
        OS  << " NULL";
    }

    OS << '\n';
  }
}


/// dump - A simple pretty printer of a CFG that outputs to stderr.
void CFG::dump(const LangOptions &LO) const { print(llvm::errs(), LO); }

/// print - A simple pretty printer of a CFG that outputs to an ostream.
void CFG::print(llvm::raw_ostream &OS, const LangOptions &LO) const {
  StmtPrinterHelper Helper(this, LO);

  // Print the entry block.
  print_block(OS, this, getEntry(), &Helper, true);

  // Iterate through the CFGBlocks and print them one by one.
  for (const_iterator I = Blocks.begin(), E = Blocks.end() ; I != E ; ++I) {
    // Skip the entry block, because we already printed it.
    if (&(**I) == &getEntry() || &(**I) == &getExit())
      continue;

    print_block(OS, this, **I, &Helper, true);
  }

  // Print the exit block.
  print_block(OS, this, getExit(), &Helper, true);
  OS.flush();
}

/// dump - A simply pretty printer of a CFGBlock that outputs to stderr.
void CFGBlock::dump(const CFG* cfg, const LangOptions &LO) const {
  print(llvm::errs(), cfg, LO);
}

/// print - A simple pretty printer of a CFGBlock that outputs to an ostream.
///   Generally this will only be called from CFG::print.
void CFGBlock::print(llvm::raw_ostream& OS, const CFG* cfg,
                     const LangOptions &LO) const {
  StmtPrinterHelper Helper(cfg, LO);
  print_block(OS, cfg, *this, &Helper, true);
}

/// printTerminator - A simple pretty printer of the terminator of a CFGBlock.
void CFGBlock::printTerminator(llvm::raw_ostream &OS,
                               const LangOptions &LO) const {
  CFGBlockTerminatorPrint TPrinter(OS, NULL, PrintingPolicy(LO));
  TPrinter.Visit(const_cast<Stmt*>(getTerminator()));
}

Stmt* CFGBlock::getTerminatorCondition() {

  if (!Terminator)
    return NULL;

  Expr* E = NULL;

  switch (Terminator->getStmtClass()) {
    default:
      break;

    case Stmt::ForStmtClass:
      E = cast<ForStmt>(Terminator)->getCond();
      break;

    case Stmt::WhileStmtClass:
      E = cast<WhileStmt>(Terminator)->getCond();
      break;

    case Stmt::DoStmtClass:
      E = cast<DoStmt>(Terminator)->getCond();
      break;

    case Stmt::IfStmtClass:
      E = cast<IfStmt>(Terminator)->getCond();
      break;

    case Stmt::ChooseExprClass:
      E = cast<ChooseExpr>(Terminator)->getCond();
      break;

    case Stmt::IndirectGotoStmtClass:
      E = cast<IndirectGotoStmt>(Terminator)->getTarget();
      break;

    case Stmt::SwitchStmtClass:
      E = cast<SwitchStmt>(Terminator)->getCond();
      break;

    case Stmt::ConditionalOperatorClass:
      E = cast<ConditionalOperator>(Terminator)->getCond();
      break;

    case Stmt::BinaryOperatorClass: // '&&' and '||'
      E = cast<BinaryOperator>(Terminator)->getLHS();
      break;

    case Stmt::ObjCForCollectionStmtClass:
      return Terminator;
  }

  return E ? E->IgnoreParens() : NULL;
}

bool CFGBlock::hasBinaryBranchTerminator() const {

  if (!Terminator)
    return false;

  Expr* E = NULL;

  switch (Terminator->getStmtClass()) {
    default:
      return false;

    case Stmt::ForStmtClass:
    case Stmt::WhileStmtClass:
    case Stmt::DoStmtClass:
    case Stmt::IfStmtClass:
    case Stmt::ChooseExprClass:
    case Stmt::ConditionalOperatorClass:
    case Stmt::BinaryOperatorClass:
      return true;
  }

  return E ? E->IgnoreParens() : NULL;
}


//===----------------------------------------------------------------------===//
// CFG Graphviz Visualization
//===----------------------------------------------------------------------===//


#ifndef NDEBUG
static StmtPrinterHelper* GraphHelper;
#endif

void CFG::viewCFG(const LangOptions &LO) const {
#ifndef NDEBUG
  StmtPrinterHelper H(this, LO);
  GraphHelper = &H;
  llvm::ViewGraph(this,"CFG");
  GraphHelper = NULL;
#endif
}

namespace llvm {
template<>
struct DOTGraphTraits<const CFG*> : public DefaultDOTGraphTraits {

  DOTGraphTraits (bool isSimple=false) : DefaultDOTGraphTraits(isSimple) {}

  static std::string getNodeLabel(const CFGBlock* Node, const CFG* Graph) {

#ifndef NDEBUG
    std::string OutSStr;
    llvm::raw_string_ostream Out(OutSStr);
    print_block(Out,Graph, *Node, GraphHelper, false);
    std::string& OutStr = Out.str();

    if (OutStr[0] == '\n') OutStr.erase(OutStr.begin());

    // Process string output to make it nicer...
    for (unsigned i = 0; i != OutStr.length(); ++i)
      if (OutStr[i] == '\n') {                            // Left justify
        OutStr[i] = '\\';
        OutStr.insert(OutStr.begin()+i+1, 'l');
      }

    return OutStr;
#else
    return "";
#endif
  }
};
} // end namespace llvm