diff --git a/lib/Checker/MallocChecker.cpp b/lib/Checker/MallocChecker.cpp
new file mode 100644
index 0000000..3be2e02
--- /dev/null
+++ b/lib/Checker/MallocChecker.cpp
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+//=== MallocChecker.cpp - A malloc/free checker -------------------*- 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 malloc/free checker, which checks for potential memory
+// leaks, double free, and use-after-free problems.
+//
+//===----------------------------------------------------------------------===//
+
+#include "GRExprEngineExperimentalChecks.h"
+#include "clang/Checker/PathSensitive/CheckerVisitor.h"
+#include "clang/Checker/PathSensitive/GRState.h"
+#include "clang/Checker/PathSensitive/GRStateTrait.h"
+#include "clang/Checker/PathSensitive/SymbolManager.h"
+#include "llvm/ADT/ImmutableMap.h"
+using namespace clang;
+
+namespace {
+
+class RefState {
+  enum Kind { AllocateUnchecked, AllocateFailed, Released, Escaped } K;
+  const Stmt *S;
+
+public:
+  RefState(Kind k, const Stmt *s) : K(k), S(s) {}
+
+  bool isAllocated() const { return K == AllocateUnchecked; }
+  bool isReleased() const { return K == Released; }
+  bool isEscaped() const { return K == Escaped; }
+
+  bool operator==(const RefState &X) const {
+    return K == X.K && S == X.S;
+  }
+
+  static RefState getAllocateUnchecked(const Stmt *s) { 
+    return RefState(AllocateUnchecked, s); 
+  }
+  static RefState getAllocateFailed() {
+    return RefState(AllocateFailed, 0);
+  }
+  static RefState getReleased(const Stmt *s) { return RefState(Released, s); }
+  static RefState getEscaped(const Stmt *s) { return RefState(Escaped, s); }
+
+  void Profile(llvm::FoldingSetNodeID &ID) const {
+    ID.AddInteger(K);
+    ID.AddPointer(S);
+  }
+};
+
+class RegionState {};
+
+class MallocChecker : public CheckerVisitor<MallocChecker> {
+  BuiltinBug *BT_DoubleFree;
+  BuiltinBug *BT_Leak;
+  IdentifierInfo *II_malloc, *II_free, *II_realloc;
+
+public:
+  MallocChecker() 
+    : BT_DoubleFree(0), BT_Leak(0), II_malloc(0), II_free(0), II_realloc(0) {}
+  static void *getTag();
+  bool EvalCallExpr(CheckerContext &C, const CallExpr *CE);
+  void EvalDeadSymbols(CheckerContext &C,const Stmt *S,SymbolReaper &SymReaper);
+  void EvalEndPath(GREndPathNodeBuilder &B, void *tag, GRExprEngine &Eng);
+  void PreVisitReturnStmt(CheckerContext &C, const ReturnStmt *S);
+  const GRState *EvalAssume(const GRState *state, SVal Cond, bool Assumption);
+
+private:
+  void MallocMem(CheckerContext &C, const CallExpr *CE);
+  const GRState *MallocMemAux(CheckerContext &C, const CallExpr *CE,
+                              const Expr *SizeEx, const GRState *state);
+  void FreeMem(CheckerContext &C, const CallExpr *CE);
+  const GRState *FreeMemAux(CheckerContext &C, const CallExpr *CE,
+                            const GRState *state);
+
+  void ReallocMem(CheckerContext &C, const CallExpr *CE);
+};
+} // end anonymous namespace
+
+typedef llvm::ImmutableMap<SymbolRef, RefState> RegionStateTy;
+
+namespace clang {
+  template <>
+  struct GRStateTrait<RegionState> 
+    : public GRStatePartialTrait<llvm::ImmutableMap<SymbolRef, RefState> > {
+    static void *GDMIndex() { return MallocChecker::getTag(); }
+  };
+}
+
+void clang::RegisterMallocChecker(GRExprEngine &Eng) {
+  Eng.registerCheck(new MallocChecker());
+}
+
+void *MallocChecker::getTag() {
+  static int x;
+  return &x;
+}
+
+bool MallocChecker::EvalCallExpr(CheckerContext &C, const CallExpr *CE) {
+  const GRState *state = C.getState();
+  const Expr *Callee = CE->getCallee();
+  SVal L = state->getSVal(Callee);
+
+  const FunctionDecl *FD = L.getAsFunctionDecl();
+  if (!FD)
+    return false;
+
+  ASTContext &Ctx = C.getASTContext();
+  if (!II_malloc)
+    II_malloc = &Ctx.Idents.get("malloc");
+  if (!II_free)
+    II_free = &Ctx.Idents.get("free");
+  if (!II_realloc)
+    II_realloc = &Ctx.Idents.get("realloc");
+
+  if (FD->getIdentifier() == II_malloc) {
+    MallocMem(C, CE);
+    return true;
+  }
+
+  if (FD->getIdentifier() == II_free) {
+    FreeMem(C, CE);
+    return true;
+  }
+
+  if (FD->getIdentifier() == II_realloc) {
+    ReallocMem(C, CE);
+    return true;
+  }
+
+  return false;
+}
+
+void MallocChecker::MallocMem(CheckerContext &C, const CallExpr *CE) {
+  const GRState *state = MallocMemAux(C, CE, CE->getArg(0), C.getState());
+  C.addTransition(state);
+}
+
+const GRState *MallocChecker::MallocMemAux(CheckerContext &C,  
+                                           const CallExpr *CE,
+                                           const Expr *SizeEx,
+                                           const GRState *state) {
+  unsigned Count = C.getNodeBuilder().getCurrentBlockCount();
+  ValueManager &ValMgr = C.getValueManager();
+
+  SVal RetVal = ValMgr.getConjuredSymbolVal(NULL, CE, CE->getType(), Count);
+
+  SVal Size = state->getSVal(SizeEx);
+
+  state = C.getEngine().getStoreManager().setExtent(state, RetVal.getAsRegion(),
+                                                    Size);
+
+  state = state->BindExpr(CE, RetVal);
+  
+  SymbolRef Sym = RetVal.getAsLocSymbol();
+  assert(Sym);
+  // Set the symbol's state to Allocated.
+  return state->set<RegionState>(Sym, RefState::getAllocateUnchecked(CE));
+}
+
+void MallocChecker::FreeMem(CheckerContext &C, const CallExpr *CE) {
+  const GRState *state = FreeMemAux(C, CE, C.getState());
+
+  if (state)
+    C.addTransition(state);
+}
+
+const GRState *MallocChecker::FreeMemAux(CheckerContext &C, const CallExpr *CE,
+                                         const GRState *state) {
+  SVal ArgVal = state->getSVal(CE->getArg(0));
+  SymbolRef Sym = ArgVal.getAsLocSymbol();
+  assert(Sym);
+
+  const RefState *RS = state->get<RegionState>(Sym);
+
+  // If the symbol has not been tracked, return. This is possible when free() is
+  // called on a pointer that does not get its pointee directly from malloc(). 
+  // Full support of this requires inter-procedural analysis.
+  if (!RS)
+    return state;
+
+  // Check double free.
+  if (RS->isReleased()) {
+    ExplodedNode *N = C.GenerateSink();
+    if (N) {
+      if (!BT_DoubleFree)
+        BT_DoubleFree = new BuiltinBug("Double free",
+                         "Try to free a memory block that has been released");
+      // FIXME: should find where it's freed last time.
+      BugReport *R = new BugReport(*BT_DoubleFree, 
+                                   BT_DoubleFree->getDescription(), N);
+      C.EmitReport(R);
+    }
+    return NULL;
+  }
+
+  // Normal free.
+  return state->set<RegionState>(Sym, RefState::getReleased(CE));
+}
+
+void MallocChecker::ReallocMem(CheckerContext &C, const CallExpr *CE) {
+  const GRState *state = C.getState();
+  const Expr *Arg0 = CE->getArg(0);
+  DefinedOrUnknownSVal Arg0Val=cast<DefinedOrUnknownSVal>(state->getSVal(Arg0));
+
+  ValueManager &ValMgr = C.getValueManager();
+  SValuator &SVator = C.getSValuator();
+
+  DefinedOrUnknownSVal PtrEQ = SVator.EvalEQ(state, Arg0Val, ValMgr.makeNull());
+
+  // If the ptr is NULL, the call is equivalent to malloc(size).
+  if (const GRState *stateEqual = state->Assume(PtrEQ, true)) {
+    // Hack: set the NULL symbolic region to released to suppress false warning.
+    // In the future we should add more states for allocated regions, e.g., 
+    // CheckedNull, CheckedNonNull.
+    
+    SymbolRef Sym = Arg0Val.getAsLocSymbol();
+    if (Sym)
+      stateEqual = stateEqual->set<RegionState>(Sym, RefState::getReleased(CE));
+
+    const GRState *stateMalloc = MallocMemAux(C, CE, CE->getArg(1), stateEqual);
+    C.addTransition(stateMalloc);
+  }
+
+  if (const GRState *stateNotEqual = state->Assume(PtrEQ, false)) {
+    const Expr *Arg1 = CE->getArg(1);
+    DefinedOrUnknownSVal Arg1Val = 
+      cast<DefinedOrUnknownSVal>(stateNotEqual->getSVal(Arg1));
+    DefinedOrUnknownSVal SizeZero = SVator.EvalEQ(stateNotEqual, Arg1Val,
+                                      ValMgr.makeIntValWithPtrWidth(0, false));
+
+    if (const GRState *stateSizeZero = stateNotEqual->Assume(SizeZero, true)) {
+      const GRState *stateFree = FreeMemAux(C, CE, stateSizeZero);
+      if (stateFree)
+        C.addTransition(stateFree->BindExpr(CE, UndefinedVal(), true));
+    }
+
+    if (const GRState *stateSizeNotZero=stateNotEqual->Assume(SizeZero,false)) {
+      const GRState *stateFree = FreeMemAux(C, CE, stateSizeNotZero);
+      if (stateFree) {
+        // FIXME: We should copy the content of the original buffer.
+        const GRState *stateRealloc = MallocMemAux(C, CE, CE->getArg(1), 
+                                                   stateFree);
+        C.addTransition(stateRealloc);
+      }
+    }
+  }
+}
+
+void MallocChecker::EvalDeadSymbols(CheckerContext &C, const Stmt *S,
+                                    SymbolReaper &SymReaper) {
+  for (SymbolReaper::dead_iterator I = SymReaper.dead_begin(),
+         E = SymReaper.dead_end(); I != E; ++I) {
+    SymbolRef Sym = *I;
+    const GRState *state = C.getState();
+    const RefState *RS = state->get<RegionState>(Sym);
+    if (!RS)
+      return;
+
+    if (RS->isAllocated()) {
+      ExplodedNode *N = C.GenerateSink();
+      if (N) {
+        if (!BT_Leak)
+          BT_Leak = new BuiltinBug("Memory leak",
+                     "Allocated memory never released. Potential memory leak.");
+        // FIXME: where it is allocated.
+        BugReport *R = new BugReport(*BT_Leak, BT_Leak->getDescription(), N);
+        C.EmitReport(R);
+      }
+    }
+  }
+}
+
+void MallocChecker::EvalEndPath(GREndPathNodeBuilder &B, void *tag,
+                                GRExprEngine &Eng) {
+  SaveAndRestore<bool> OldHasGen(B.HasGeneratedNode);
+  const GRState *state = B.getState();
+  typedef llvm::ImmutableMap<SymbolRef, RefState> SymMap;
+  SymMap M = state->get<RegionState>();
+
+  for (SymMap::iterator I = M.begin(), E = M.end(); I != E; ++I) {
+    RefState RS = I->second;
+    if (RS.isAllocated()) {
+      ExplodedNode *N = B.generateNode(state, tag, B.getPredecessor());
+      if (N) {
+        if (!BT_Leak)
+          BT_Leak = new BuiltinBug("Memory leak",
+                     "Allocated memory never released. Potential memory leak.");
+        BugReport *R = new BugReport(*BT_Leak, BT_Leak->getDescription(), N);
+        Eng.getBugReporter().EmitReport(R);
+      }
+    }
+  }
+}
+
+void MallocChecker::PreVisitReturnStmt(CheckerContext &C, const ReturnStmt *S) {
+  const Expr *RetE = S->getRetValue();
+  if (!RetE)
+    return;
+
+  const GRState *state = C.getState();
+
+  SymbolRef Sym = state->getSVal(RetE).getAsSymbol();
+
+  if (!Sym)
+    return;
+
+  const RefState *RS = state->get<RegionState>(Sym);
+  if (!RS)
+    return;
+
+  // FIXME: check other cases.
+  if (RS->isAllocated())
+    state = state->set<RegionState>(Sym, RefState::getEscaped(S));
+
+  C.addTransition(state);
+}
+
+const GRState *MallocChecker::EvalAssume(const GRState *state, SVal Cond, 
+                                         bool Assumption) {
+  // If a symblic region is assumed to NULL, set its state to AllocateFailed.
+  // FIXME: should also check symbols assumed to non-null.
+
+  RegionStateTy RS = state->get<RegionState>();
+
+  for (RegionStateTy::iterator I = RS.begin(), E = RS.end(); I != E; ++I) {
+    if (state->getSymVal(I.getKey()))
+      state = state->set<RegionState>(I.getKey(),RefState::getAllocateFailed());
+  }
+
+  return state;
+}