diff --git a/Analysis/GRConstants.cpp b/Analysis/GRConstants.cpp
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+++ b/Analysis/GRConstants.cpp
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+//===-- GRConstants.cpp - Simple, Path-Sens. Constant Prop. ------*- C++ -*-==//
+//   
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+//               Constant Propagation via Graph Reachability
+//
+//  This files defines a simple analysis that performs path-sensitive
+//  constant propagation within a function.  An example use of this analysis
+//  is to perform simple checks for NULL dereferences.
+//
+//===----------------------------------------------------------------------===//
+
+#include "clang/Analysis/PathSensitive/GREngine.h"
+#include "clang/AST/Expr.h"
+#include "clang/Analysis/Analyses/LiveVariables.h"
+#include "clang/Analysis/Visitors/CFGStmtVisitor.h"
+
+#include "llvm/Support/Casting.h"
+#include "llvm/Support/DataTypes.h"
+#include "llvm/ADT/APSInt.h"
+#include "llvm/ADT/FoldingSet.h"
+#include "llvm/ADT/ImmutableMap.h"
+#include "llvm/Support/Compiler.h"
+
+using namespace clang;
+using llvm::APInt;
+using llvm::APFloat;
+using llvm::dyn_cast;
+using llvm::cast;
+
+//===----------------------------------------------------------------------===//
+/// DeclStmtPtr - A variant smart pointer that wraps either a Decl* or a
+///  Stmt*.  Use cast<> or dyn_cast<> to get actual pointer type
+//===----------------------------------------------------------------------===//
+namespace {
+class VISIBILITY_HIDDEN DeclStmtPtr {
+  const uintptr_t Raw;
+public:
+  enum  VariantKind { IsDecl=0x1, IsBlkLvl=0x2, IsSubExp=0x3, Flags=0x3 };
+  inline void* getPtr() const { return reinterpret_cast<void*>(Raw & ~Flags); }
+  inline VariantKind getKind() const { return (VariantKind) (Raw & Flags); }
+  
+  DeclStmtPtr(Decl* D) : Raw(reinterpret_cast<uintptr_t>(D) | IsDecl) {}
+  DeclStmtPtr(Stmt* S, bool isBlkLvl) 
+    : Raw(reinterpret_cast<uintptr_t>(S) | (isBlkLvl ? IsBlkLvl : IsSubExp)) {}
+  
+  bool isSubExpr() const { return getKind() == IsSubExp; }
+  
+  inline void Profile(llvm::FoldingSetNodeID& ID) const {
+    ID.AddPointer(getPtr());
+  }      
+  inline bool operator==(const DeclStmtPtr& X) const { return Raw == X.Raw; }  
+  inline bool operator!=(const DeclStmtPtr& X) const { return Raw != X.Raw; }
+  inline bool operator<(const DeclStmtPtr& X) const { return Raw < X.Raw; }  
+};
+} // end anonymous namespace
+
+// Machinery to get cast<> and dyn_cast<> working with DeclStmtPtr.
+namespace llvm {
+  template<> inline bool isa<Decl,DeclStmtPtr>(const DeclStmtPtr& V) {
+    return V.getKind() == DeclStmtPtr::IsDecl;
+  }
+  template<> inline bool isa<Stmt,DeclStmtPtr>(const DeclStmtPtr& V) {
+    return ((unsigned) V.getKind()) > DeclStmtPtr::IsDecl;
+  }
+  template<> struct VISIBILITY_HIDDEN cast_retty_impl<Decl,DeclStmtPtr> {
+    typedef const Decl* ret_type;
+  };
+  template<> struct VISIBILITY_HIDDEN cast_retty_impl<Stmt,DeclStmtPtr> {
+    typedef const Stmt* ret_type;
+  };
+  template<> struct VISIBILITY_HIDDEN simplify_type<DeclStmtPtr> {
+    typedef void* SimpleType;
+    static inline SimpleType getSimplifiedValue(const DeclStmtPtr &V) {
+      return V.getPtr();
+    }
+  };
+} // end llvm namespace
+
+//===----------------------------------------------------------------------===//
+// DeclStmtMapTy - A ImmutableMap type from Decl*/Stmt* to integers.
+//
+//  FIXME: We may eventually use APSInt, or a mixture of APSInt and
+//         integer primitives to do this right; this will handle both
+//         different bit-widths and allow us to detect integer overflows, etc.
+//
+//===----------------------------------------------------------------------===//
+
+typedef llvm::ImmutableMap<DeclStmtPtr,uint64_t> DeclStmtMapTy;
+
+namespace clang {
+template<>
+struct VISIBILITY_HIDDEN GRTrait<DeclStmtMapTy> {
+  static inline void* toPtr(DeclStmtMapTy M) {
+    return reinterpret_cast<void*>(M.getRoot());
+  }  
+  static inline DeclStmtMapTy toState(void* P) {
+    return DeclStmtMapTy(static_cast<DeclStmtMapTy::TreeTy*>(P));
+  }
+};
+}
+
+//===----------------------------------------------------------------------===//
+// The Checker!
+//===----------------------------------------------------------------------===//
+
+namespace {
+class VISIBILITY_HIDDEN ExprVariantTy {
+  const uint64_t val;
+  const bool isConstant;
+public:
+  ExprVariantTy() : val(0), isConstant(false) {}
+  ExprVariantTy(uint64_t v) : val(v), isConstant(true) {}
+  
+  operator bool() const { return isConstant; }
+  uint64_t getVal() const { assert (isConstant); return val; }
+  
+  ExprVariantTy operator+(const ExprVariantTy& X) const {
+    if (!isConstant || !X.isConstant) return ExprVariantTy();
+    else return ExprVariantTy(val+X.val);
+  }
+  
+  ExprVariantTy operator-(const ExprVariantTy& X) const {
+    if (!isConstant || !X.isConstant) return ExprVariantTy();
+    else return ExprVariantTy(val+X.val);
+  }    
+};
+} // end anonymous namespace
+
+//===----------------------------------------------------------------------===//
+// The Checker!
+//===----------------------------------------------------------------------===//
+
+namespace {
+class VISIBILITY_HIDDEN GRConstants : public CFGStmtVisitor<GRConstants> {
+    
+public:
+  typedef DeclStmtMapTy StateTy;
+  typedef GRNodeBuilder<GRConstants> NodeBuilder;
+  typedef ExplodedNode<StateTy> NodeTy;
+                                                              
+protected:
+  // Liveness - live-variables information the Decl* and Expr* (block-level)
+  //  in the CFG.  Used to prune out dead state.
+  LiveVariables* Liveness;
+
+  // Builder - The current GRNodeBuilder which is used when building the nodes
+  //  for a given statement.
+  NodeBuilder* Builder;
+
+  DeclStmtMapTy::Factory StateFactory;
+  
+  // cfg - the current CFG.
+  CFG* cfg;
+
+  typedef llvm::SmallPtrSet<NodeTy*,16> NodeSetTy;
+  NodeSetTy NodeSetA;
+  NodeSetTy NodeSetB;
+  NodeSetTy* Nodes;
+  NodeSetTy* OldNodes;
+  NodeTy* Pred;
+  
+  bool DoNotSwitch;
+      
+public:
+  GRConstants() : Liveness(NULL), Builder(NULL), cfg(NULL), 
+    Nodes(&NodeSetA), OldNodes(&NodeSetB), Pred(NULL), DoNotSwitch(false) {}    
+    
+  ~GRConstants() { delete Liveness; }
+  
+  CFG& getCFG() { assert (cfg); return *cfg; }
+      
+  void Initialize(CFG& c) {
+    cfg = &c;    
+    Liveness = new LiveVariables(c);
+    Liveness->runOnCFG(c);
+  }
+  
+  StateTy getInitialState() {
+    return StateFactory.GetEmptyMap();
+  }
+    
+  void ProcessStmt(Stmt* S, NodeBuilder& builder);    
+  void SwitchNodeSets();  
+  void DoStmt(Stmt* S);
+
+  void AddBinding(Expr* E, ExprVariantTy V, bool isBlkLvl = false);
+  ExprVariantTy GetBinding(Expr* E);
+  
+  void BlockStmt_VisitStmt(Stmt* S) { DoStmt(S); }
+  void VisitStmt(Stmt* S) { DoNotSwitch = true; }
+  
+  void VisitAssign(BinaryOperator* O);
+  void VisitIntegerLiteral(IntegerLiteral* L);
+  void VisitBinAdd(BinaryOperator* O);
+  void VisitBinSub(BinaryOperator* O);
+};
+} // end anonymous namespace
+
+void GRConstants::ProcessStmt(Stmt* S, NodeBuilder& builder) {
+  Builder = &builder;
+  Nodes->clear();
+  OldNodes->clear();
+  NodeTy* N = Builder->getLastNode();
+  assert (N);
+  OldNodes->insert(N);
+  DoNotSwitch = true;
+  BlockStmt_Visit(S);
+  Builder = NULL;  
+}
+
+ExprVariantTy GRConstants::GetBinding(Expr* E) {
+  DeclStmtPtr P(E, getCFG().isBlkExpr(E));
+  StateTy M = Pred->getState();
+  StateTy::iterator I = M.find(P);
+
+  if (I == M.end())
+    return ExprVariantTy();
+  
+  return (*I).second;
+}
+
+void GRConstants::AddBinding(Expr* E, ExprVariantTy V, bool isBlkLvl) {
+  if (!V) {
+    Nodes->insert(Pred);
+    return;
+  }
+  
+  StateTy M = Pred->getState();
+  StateTy MNew = StateFactory.Add(M, DeclStmtPtr(E,isBlkLvl), V.getVal());
+  NodeTy* N = Builder->generateNode(E, MNew, Pred);
+  if (N) Nodes->insert(N);
+}
+
+void GRConstants::SwitchNodeSets() {
+  NodeSetTy* Tmp = OldNodes;
+  OldNodes = Nodes;
+  Nodes = Tmp;
+  Nodes->clear(); 
+}
+
+
+void GRConstants::DoStmt(Stmt* S) {  
+  for (Stmt::child_iterator I=S->child_begin(), E=S->child_end(); I!=E; ++I)
+    DoStmt(*I);
+  
+  if (!DoNotSwitch) SwitchNodeSets();
+  DoNotSwitch = false;
+  
+  for (NodeSetTy::iterator I=OldNodes->begin(), E=OldNodes->end(); I!=E; ++I) {
+    Pred = *I;    
+    Visit(S);
+    Pred = NULL;
+  }
+}
+
+void GRConstants::VisitIntegerLiteral(IntegerLiteral* L) {
+  AddBinding(L, L->getValue().getZExtValue());
+}
+
+void GRConstants::VisitBinAdd(BinaryOperator* B) {
+  AddBinding(B, GetBinding(B->getLHS()) + GetBinding(B->getRHS()));
+}
+
+void GRConstants::VisitBinSub(BinaryOperator* B) {
+  AddBinding(B, GetBinding(B->getLHS()) - GetBinding(B->getRHS()));
+}
+    
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