diff --git a/lib/Checker/CallAndMessageChecker.cpp b/lib/Checker/CallAndMessageChecker.cpp
new file mode 100644
index 0000000..9013c38
--- /dev/null
+++ b/lib/Checker/CallAndMessageChecker.cpp
@@ -0,0 +1,252 @@
+//===--- CallAndMessageChecker.cpp ------------------------------*- C++ -*--==//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// This defines CallAndMessageChecker, a builtin checker that checks for various
+// errors of call and objc message expressions.
+//
+//===----------------------------------------------------------------------===//
+
+#include "clang/Basic/TargetInfo.h"
+#include "clang/Checker/PathSensitive/CheckerVisitor.h"
+#include "clang/Checker/BugReporter/BugReporter.h"
+#include "clang/AST/ParentMap.h"
+#include "GRExprEngineInternalChecks.h"
+
+using namespace clang;
+
+namespace {
+class CallAndMessageChecker
+  : public CheckerVisitor<CallAndMessageChecker> {
+  BugType *BT_call_null;
+  BugType *BT_call_undef;  
+  BugType *BT_call_arg;
+  BugType *BT_msg_undef;
+  BugType *BT_msg_arg;
+  BugType *BT_msg_ret;
+public:
+  CallAndMessageChecker() :
+    BT_call_null(0), BT_call_undef(0), BT_call_arg(0),
+    BT_msg_undef(0), BT_msg_arg(0), BT_msg_ret(0) {}
+
+  static void *getTag() {
+    static int x = 0;
+    return &x;
+  }
+
+  void PreVisitCallExpr(CheckerContext &C, const CallExpr *CE);
+  void PreVisitObjCMessageExpr(CheckerContext &C, const ObjCMessageExpr *ME);
+  bool EvalNilReceiver(CheckerContext &C, const ObjCMessageExpr *ME);
+
+private:
+  void EmitBadCall(BugType *BT, CheckerContext &C, const CallExpr *CE);
+  void EmitNilReceiverBug(CheckerContext &C, const ObjCMessageExpr *ME,
+                          ExplodedNode *N);
+    
+  void HandleNilReceiver(CheckerContext &C, const GRState *state,
+                         const ObjCMessageExpr *ME);    
+};
+} // end anonymous namespace
+
+void clang::RegisterCallAndMessageChecker(GRExprEngine &Eng) {
+  Eng.registerCheck(new CallAndMessageChecker());
+}
+
+void CallAndMessageChecker::EmitBadCall(BugType *BT, CheckerContext &C,
+                                        const CallExpr *CE) {
+  ExplodedNode *N = C.GenerateSink();
+  if (!N)
+    return;
+    
+  EnhancedBugReport *R = new EnhancedBugReport(*BT, BT->getName(), N);
+  R->addVisitorCreator(bugreporter::registerTrackNullOrUndefValue,
+                       bugreporter::GetCalleeExpr(N));
+  C.EmitReport(R);
+}
+
+void CallAndMessageChecker::PreVisitCallExpr(CheckerContext &C, 
+                                             const CallExpr *CE){
+  
+  const Expr *Callee = CE->getCallee()->IgnoreParens();
+  SVal L = C.getState()->getSVal(Callee);
+  
+  if (L.isUndef()) {
+    if (!BT_call_undef)
+      BT_call_undef =
+        new BuiltinBug("Called function pointer is an undefined pointer value");
+    EmitBadCall(BT_call_undef, C, CE);
+    return;
+  }
+  
+  if (isa<loc::ConcreteInt>(L)) {
+    if (!BT_call_null)
+      BT_call_null =
+        new BuiltinBug("Called function pointer is null (null dereference)");
+    EmitBadCall(BT_call_null, C, CE);
+  }  
+  
+  for (CallExpr::const_arg_iterator I = CE->arg_begin(), E = CE->arg_end();
+       I != E; ++I) {
+    if (C.getState()->getSVal(*I).isUndef()) {
+      if (ExplodedNode *N = C.GenerateSink()) {
+        if (!BT_call_arg)
+          BT_call_arg = new BuiltinBug("Pass-by-value argument in function call"
+                                       " is undefined");
+        // Generate a report for this bug.
+        EnhancedBugReport *R = new EnhancedBugReport(*BT_call_arg,
+                                                     BT_call_arg->getName(), N);
+        R->addRange((*I)->getSourceRange());
+        R->addVisitorCreator(bugreporter::registerTrackNullOrUndefValue, *I);
+        C.EmitReport(R);
+        return;
+      }
+    }
+  }
+}
+
+void CallAndMessageChecker::PreVisitObjCMessageExpr(CheckerContext &C,
+                                                    const ObjCMessageExpr *ME) {
+
+  const GRState *state = C.getState();
+
+  if (const Expr *receiver = ME->getReceiver())
+    if (state->getSVal(receiver).isUndef()) {
+      if (ExplodedNode *N = C.GenerateSink()) {
+        if (!BT_msg_undef)
+          BT_msg_undef =
+            new BuiltinBug("Receiver in message expression is a garbage value");
+        EnhancedBugReport *R =
+          new EnhancedBugReport(*BT_msg_undef, BT_msg_undef->getName(), N);
+        R->addRange(receiver->getSourceRange());
+        R->addVisitorCreator(bugreporter::registerTrackNullOrUndefValue,
+                             receiver);
+        C.EmitReport(R);
+      }
+      return;
+    }
+
+  // Check for any arguments that are uninitialized/undefined.
+  for (ObjCMessageExpr::const_arg_iterator I = ME->arg_begin(),
+         E = ME->arg_end(); I != E; ++I) {
+    if (state->getSVal(*I).isUndef()) {
+      if (ExplodedNode *N = C.GenerateSink()) {
+        if (!BT_msg_arg)
+          BT_msg_arg =
+            new BuiltinBug("Pass-by-value argument in message expression"
+                           " is undefined");      
+        // Generate a report for this bug.
+        EnhancedBugReport *R = new EnhancedBugReport(*BT_msg_arg,
+                                                     BT_msg_arg->getName(), N);
+        R->addRange((*I)->getSourceRange());
+        R->addVisitorCreator(bugreporter::registerTrackNullOrUndefValue, *I);
+        C.EmitReport(R);
+        return;
+      }
+    }
+  }
+}
+
+bool CallAndMessageChecker::EvalNilReceiver(CheckerContext &C,
+                                            const ObjCMessageExpr *ME) {
+  HandleNilReceiver(C, C.getState(), ME);
+  return true; // Nil receiver is not handled elsewhere.
+}
+
+void CallAndMessageChecker::EmitNilReceiverBug(CheckerContext &C,
+                                               const ObjCMessageExpr *ME,
+                                               ExplodedNode *N) {
+  
+  if (!BT_msg_ret)
+    BT_msg_ret =
+      new BuiltinBug("Receiver in message expression is "
+                     "'nil' and returns a garbage value");
+  
+  llvm::SmallString<200> buf;
+  llvm::raw_svector_ostream os(buf);
+  os << "The receiver of message '" << ME->getSelector().getAsString()
+     << "' is nil and returns a value of type '"
+     << ME->getType().getAsString() << "' that will be garbage";
+  
+  EnhancedBugReport *report = new EnhancedBugReport(*BT_msg_ret, os.str(), N);
+  const Expr *receiver = ME->getReceiver();
+  report->addRange(receiver->getSourceRange());
+  report->addVisitorCreator(bugreporter::registerTrackNullOrUndefValue, 
+                            receiver);
+  C.EmitReport(report);  
+}
+
+static bool SupportsNilWithFloatRet(const llvm::Triple &triple) {
+  return triple.getVendor() == llvm::Triple::Apple &&
+         triple.getDarwinMajorNumber() >= 9;
+}
+
+void CallAndMessageChecker::HandleNilReceiver(CheckerContext &C,
+                                              const GRState *state,
+                                              const ObjCMessageExpr *ME) {
+  
+  // Check the return type of the message expression.  A message to nil will
+  // return different values depending on the return type and the architecture.
+  QualType RetTy = ME->getType();
+  
+  ASTContext &Ctx = C.getASTContext();
+  CanQualType CanRetTy = Ctx.getCanonicalType(RetTy);
+
+  if (CanRetTy->isStructureType()) {
+    // FIXME: At some point we shouldn't rely on isConsumedExpr(), but instead
+    // have the "use of undefined value" be smarter about where the
+    // undefined value came from.
+    if (C.getPredecessor()->getParentMap().isConsumedExpr(ME)) {
+      if (ExplodedNode* N = C.GenerateSink(state))
+        EmitNilReceiverBug(C, ME, N);
+      return;
+    }
+
+    // The result is not consumed by a surrounding expression.  Just propagate
+    // the current state.
+    C.addTransition(state);
+    return;
+  }
+
+  // Other cases: check if the return type is smaller than void*.
+  if (CanRetTy != Ctx.VoidTy &&
+      C.getPredecessor()->getParentMap().isConsumedExpr(ME)) {
+    // Compute: sizeof(void *) and sizeof(return type)
+    const uint64_t voidPtrSize = Ctx.getTypeSize(Ctx.VoidPtrTy);    
+    const uint64_t returnTypeSize = Ctx.getTypeSize(CanRetTy);
+
+    if (voidPtrSize < returnTypeSize &&
+        !(SupportsNilWithFloatRet(Ctx.Target.getTriple()) &&
+          (Ctx.FloatTy == CanRetTy ||
+           Ctx.DoubleTy == CanRetTy ||
+           Ctx.LongDoubleTy == CanRetTy ||
+           Ctx.LongLongTy == CanRetTy))) {
+      if (ExplodedNode* N = C.GenerateSink(state))
+        EmitNilReceiverBug(C, ME, N);
+      return;
+    }
+
+    // Handle the safe cases where the return value is 0 if the
+    // receiver is nil.
+    //
+    // FIXME: For now take the conservative approach that we only
+    // return null values if we *know* that the receiver is nil.
+    // This is because we can have surprises like:
+    //
+    //   ... = [[NSScreens screens] objectAtIndex:0];
+    //
+    // What can happen is that [... screens] could return nil, but
+    // it most likely isn't nil.  We should assume the semantics
+    // of this case unless we have *a lot* more knowledge.
+    //
+    SVal V = C.getValueManager().makeZeroVal(ME->getType());
+    C.GenerateNode(state->BindExpr(ME, V));
+    return;
+  }
+  
+  C.addTransition(state);
+}