Initial commit of MemorySanitizer.

Compiler pass only.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@168866 91177308-0d34-0410-b5e6-96231b3b80d8

3 files changed, 1421 insertions, 0 deletions

diff --git a/lib/Transforms/Instrumentation/CMakeLists.txt b/lib/Transforms/Instrumentation/CMakeLists.txt
index 058f68c7ce..1c9e053679 100644
--- a/lib/Transforms/Instrumentation/CMakeLists.txt
+++ b/lib/Transforms/Instrumentation/CMakeLists.txt
@@ -4,6 +4,7 @@ add_llvm_library(LLVMInstrumentation
   BoundsChecking.cpp
   EdgeProfiling.cpp
   GCOVProfiling.cpp
+  MemorySanitizer.cpp
   Instrumentation.cpp
   OptimalEdgeProfiling.cpp
   PathProfiling.cpp
diff --git a/lib/Transforms/Instrumentation/Instrumentation.cpp b/lib/Transforms/Instrumentation/Instrumentation.cpp
index 46394da856..8ba102559b 100644
--- a/lib/Transforms/Instrumentation/Instrumentation.cpp
+++ b/lib/Transforms/Instrumentation/Instrumentation.cpp
@@ -27,6 +27,7 @@ void llvm::initializeInstrumentation(PassRegistry &Registry) {
   initializeGCOVProfilerPass(Registry);
   initializeOptimalEdgeProfilerPass(Registry);
   initializePathProfilerPass(Registry);
+  initializeMemorySanitizerPass(Registry);
   initializeThreadSanitizerPass(Registry);
 }
 
diff --git a/lib/Transforms/Instrumentation/MemorySanitizer.cpp b/lib/Transforms/Instrumentation/MemorySanitizer.cpp
new file mode 100644
index 0000000000..57c5003085
--- /dev/null
+++ b/lib/Transforms/Instrumentation/MemorySanitizer.cpp
@@ -0,0 +1,1419 @@
+//===-- MemorySanitizer.cpp - detector of uninitialized reads -------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+/// \file
+/// This file is a part of MemorySanitizer, a detector of uninitialized
+/// reads.
+///
+/// Status: early prototype.
+///
+/// The algorithm of the tool is similar to Memcheck
+/// (http://goo.gl/QKbem). We associate a few shadow bits with every
+/// byte of the application memory, poison the shadow of the malloc-ed
+/// or alloca-ed memory, load the shadow bits on every memory read,
+/// propagate the shadow bits through some of the arithmetic
+/// instruction (including MOV), store the shadow bits on every memory
+/// write, report a bug on some other instructions (e.g. JMP) if the
+/// associated shadow is poisoned.
+///
+/// But there are differences too. The first and the major one:
+/// compiler instrumentation instead of binary instrumentation. This
+/// gives us much better register allocation, possible compiler
+/// optimizations and a fast start-up. But this brings the major issue
+/// as well: msan needs to see all program events, including system
+/// calls and reads/writes in system libraries, so we either need to
+/// compile *everything* with msan or use a binary translation
+/// component (e.g. DynamoRIO) to instrument pre-built libraries.
+/// Another difference from Memcheck is that we use 8 shadow bits per
+/// byte of application memory and use a direct shadow mapping. This
+/// greatly simplifies the instrumentation code and avoids races on
+/// shadow updates (Memcheck is single-threaded so races are not a
+/// concern there. Memcheck uses 2 shadow bits per byte with a slow
+/// path storage that uses 8 bits per byte).
+///
+/// The default value of shadow is 0, which means "clean" (not poisoned).
+///
+/// Every module initializer should call __msan_init to ensure that the
+/// shadow memory is ready. On error, __msan_warning is called. Since
+/// parameters and return values may be passed via registers, we have a
+/// specialized thread-local shadow for return values
+/// (__msan_retval_tls) and parameters (__msan_param_tls).
+//===----------------------------------------------------------------------===//
+
+#define DEBUG_TYPE "msan"
+
+#include "BlackList.h"
+#include "llvm/DataLayout.h"
+#include "llvm/Function.h"
+#include "llvm/InlineAsm.h"
+#include "llvm/IntrinsicInst.h"
+#include "llvm/IRBuilder.h"
+#include "llvm/LLVMContext.h"
+#include "llvm/MDBuilder.h"
+#include "llvm/Module.h"
+#include "llvm/Type.h"
+#include "llvm/ADT/DepthFirstIterator.h"
+#include "llvm/ADT/SmallString.h"
+#include "llvm/ADT/SmallVector.h"
+#include "llvm/ADT/ValueMap.h"
+#include "llvm/Transforms/Instrumentation.h"
+#include "llvm/Transforms/Utils/BasicBlockUtils.h"
+#include "llvm/Transforms/Utils/ModuleUtils.h"
+#include "llvm/Support/CommandLine.h"
+#include "llvm/Support/Compiler.h"
+#include "llvm/Support/Debug.h"
+#include "llvm/Support/InstVisitor.h"
+#include "llvm/Support/raw_ostream.h"
+#include "llvm/Transforms/Instrumentation.h"
+#include "llvm/Transforms/Utils/BasicBlockUtils.h"
+#include "llvm/Transforms/Utils/ModuleUtils.h"
+
+using namespace llvm;
+
+static const uint64_t kShadowMask32 = 1ULL << 31;
+static const uint64_t kShadowMask64 = 1ULL << 46;
+static const uint64_t kOriginOffset32 = 1ULL << 30;
+static const uint64_t kOriginOffset64 = 1ULL << 45;
+
+// This is an important flag that makes the reports much more
+// informative at the cost of greater slowdown. Not fully implemented
+// yet.
+// FIXME: this should be a top-level clang flag, e.g.
+// -fmemory-sanitizer-full.
+static cl::opt<bool> ClTrackOrigins("msan-track-origins",
+       cl::desc("Track origins (allocation sites) of poisoned memory"),
+       cl::Hidden, cl::init(false));
+static cl::opt<bool> ClKeepGoing("msan-keep-going",
+       cl::desc("keep going after reporting a UMR"),
+       cl::Hidden, cl::init(false));
+static cl::opt<bool> ClPoisonStack("msan-poison-stack",
+       cl::desc("poison uninitialized stack variables"),
+       cl::Hidden, cl::init(true));
+static cl::opt<bool> ClPoisonStackWithCall("msan-poison-stack-with-call",
+       cl::desc("poison uninitialized stack variables with a call"),
+       cl::Hidden, cl::init(false));
+static cl::opt<int> ClPoisonStackPattern("msan-poison-stack-pattern",
+       cl::desc("poison uninitialized stack variables with the given patter"),
+       cl::Hidden, cl::init(0xff));
+
+static cl::opt<bool> ClHandleICmp("msan-handle-icmp",
+       cl::desc("propagate shadow through ICmpEQ and ICmpNE"),
+       cl::Hidden, cl::init(true));
+
+// This flag controls whether we check the shadow of the address
+// operand of load or store. Such bugs are very rare, since load from
+// a garbage address typically results in SEGV, but still happen
+// (e.g. only lower bits of address are garbage, or the access happens
+// early at program startup where malloc-ed memory is more likely to
+// be zeroed. As of 2012-08-28 this flag adds 20% slowdown.
+static cl::opt<bool> ClCheckAccessAddress("msan-check-access-address",
+       cl::desc("report accesses through a pointer which has poisoned shadow"),
+       cl::Hidden, cl::init(true));
+
+static cl::opt<bool> ClDumpStrictInstructions("msan-dump-strict-instructions",
+       cl::desc("print out instructions with default strict semantics"),
+       cl::Hidden, cl::init(false));
+
+static cl::opt<std::string>  ClBlackListFile("msan-blacklist",
+       cl::desc("File containing the list of functions where MemorySanitizer "
+                "should not report bugs"), cl::Hidden);
+
+namespace {
+
+/// \brief An instrumentation pass implementing detection of uninitialized
+/// reads.
+///
+/// MemorySanitizer: instrument the code in module to find
+/// uninitialized reads.
+class MemorySanitizer : public FunctionPass {
+public:
+  MemorySanitizer() : FunctionPass(ID), TD(0) { }
+  const char *getPassName() const { return "MemorySanitizer"; }
+  bool runOnFunction(Function &F);
+  bool doInitialization(Module &M);
+  static char ID;  // Pass identification, replacement for typeid.
+
+private:
+  DataLayout *TD;
+  LLVMContext *C;
+  Type *IntptrTy;
+  Type *OriginTy;
+  /// \brief Thread-local shadow storage for function parameters.
+  GlobalVariable *ParamTLS;
+  /// \brief Thread-local origin storage for function parameters.
+  GlobalVariable *ParamOriginTLS;
+  /// \brief Thread-local shadow storage for function return value.
+  GlobalVariable *RetvalTLS;
+  /// \brief Thread-local origin storage for function return value.
+  GlobalVariable *RetvalOriginTLS;
+  /// \brief Thread-local shadow storage for in-register va_arg function
+  /// parameters (x86_64-specific).
+  GlobalVariable *VAArgTLS;
+  /// \brief Thread-local shadow storage for va_arg overflow area
+  /// (x86_64-specific).
+  GlobalVariable *VAArgOverflowSizeTLS;
+  /// \brief Thread-local space used to pass origin value to the UMR reporting
+  /// function.
+  GlobalVariable *OriginTLS;
+
+  /// \brief The run-time callback to print a warning.
+  Value *WarningFn;
+  /// \brief Run-time helper that copies origin info for a memory range.
+  Value *MsanCopyOriginFn;
+  /// \brief Run-time helper that generates a new origin value for a stack
+  /// allocation.
+  Value *MsanSetAllocaOriginFn;
+  /// \brief Run-time helper that poisons stack on function entry.
+  Value *MsanPoisonStackFn;
+  /// \brief The actual "memmove" function.
+  Value *MemmoveFn;
+
+  /// \brief Address mask used in application-to-shadow address calculation.
+  /// ShadowAddr is computed as ApplicationAddr & ~ShadowMask.
+  uint64_t ShadowMask;
+  /// \brief Offset of the origin shadow from the "normal" shadow.
+  /// OriginAddr is computed as (ShadowAddr + OriginOffset) & ~3ULL
+  uint64_t OriginOffset;
+  /// \brief Branch weights for error reporting.
+  MDNode *ColdCallWeights;
+  /// \brief The blacklist.
+  OwningPtr<BlackList> BL;
+
+  friend class MemorySanitizerVisitor;
+  friend class VarArgAMD64Helper;
+};
+}  // namespace
+
+char MemorySanitizer::ID = 0;
+INITIALIZE_PASS(MemorySanitizer, "msan",
+                "MemorySanitizer: detects uninitialized reads.",
+                false, false)
+
+FunctionPass *llvm::createMemorySanitizerPass() {
+  return new MemorySanitizer();
+}
+
+/// \brief Create a non-const global initialized with the given string.
+///
+/// Creates a writable global for Str so that we can pass it to the
+/// run-time lib. Runtime uses first 4 bytes of the string to store the
+/// frame ID, so the string needs to be mutable.
+static GlobalVariable *createPrivateNonConstGlobalForString(Module &M,
+                                                            StringRef Str) {
+  Constant *StrConst = ConstantDataArray::getString(M.getContext(), Str);
+  return new GlobalVariable(M, StrConst->getType(), /*isConstant=*/false,
+                            GlobalValue::PrivateLinkage, StrConst, "");
+}
+
+/// \brief Module-level initialization.
+///
+/// Obtains pointers to the required runtime library functions, and
+/// inserts a call to __msan_init to the module's constructor list.
+bool MemorySanitizer::doInitialization(Module &M) {
+  TD = getAnalysisIfAvailable<DataLayout>();
+  if (!TD)
+    return false;
+  BL.reset(new BlackList(ClBlackListFile));
+  C = &(M.getContext());
+  unsigned PtrSize = TD->getPointerSizeInBits(/* AddressSpace */0);
+  switch (PtrSize) {
+    case 64:
+      ShadowMask = kShadowMask64;
+      OriginOffset = kOriginOffset64;
+      break;
+    case 32:
+      ShadowMask = kShadowMask32;
+      OriginOffset = kOriginOffset32;
+      break;
+    default:
+      report_fatal_error("unsupported pointer size");
+      break;
+  }
+
+  IRBuilder<> IRB(*C);
+  IntptrTy = IRB.getIntPtrTy(TD);
+  OriginTy = IRB.getInt32Ty();
+
+  ColdCallWeights = MDBuilder(*C).createBranchWeights(1, 1000);
+
+  // Insert a call to __msan_init/__msan_track_origins into the module's CTORs.
+  appendToGlobalCtors(M, cast<Function>(M.getOrInsertFunction(
+                      "__msan_init", IRB.getVoidTy(), NULL)), 0);
+
+  new GlobalVariable(M, IRB.getInt32Ty(), true, GlobalValue::LinkOnceODRLinkage,
+                     IRB.getInt32(ClTrackOrigins), "__msan_track_origins");
+
+  // Create the callback.
+  // FIXME: this function should have "Cold" calling conv,
+  // which is not yet implemented.
+  StringRef WarningFnName = ClKeepGoing ? "__msan_warning"
+                                        : "__msan_warning_noreturn";
+  WarningFn = M.getOrInsertFunction(WarningFnName, IRB.getVoidTy(), NULL);
+
+  MsanCopyOriginFn = M.getOrInsertFunction(
+    "__msan_copy_origin", IRB.getVoidTy(), IRB.getInt8PtrTy(),
+    IRB.getInt8PtrTy(), IntptrTy, NULL);
+  MsanSetAllocaOriginFn = M.getOrInsertFunction(
+    "__msan_set_alloca_origin", IRB.getVoidTy(), IRB.getInt8PtrTy(), IntptrTy,
+    IRB.getInt8PtrTy(), NULL);
+  MsanPoisonStackFn = M.getOrInsertFunction(
+    "__msan_poison_stack", IRB.getVoidTy(), IRB.getInt8PtrTy(), IntptrTy, NULL);
+  MemmoveFn = M.getOrInsertFunction(
+    "memmove", IRB.getInt8PtrTy(), IRB.getInt8PtrTy(), IRB.getInt8PtrTy(),
+    IntptrTy, NULL);
+
+  // Create globals.
+  RetvalTLS = new GlobalVariable(
+    M, ArrayType::get(IRB.getInt64Ty(), 8), false,
+    GlobalVariable::ExternalLinkage, 0, "__msan_retval_tls", 0,
+    GlobalVariable::GeneralDynamicTLSModel);
+  RetvalOriginTLS = new GlobalVariable(
+    M, OriginTy, false, GlobalVariable::ExternalLinkage, 0,
+    "__msan_retval_origin_tls", 0, GlobalVariable::GeneralDynamicTLSModel);
+
+  ParamTLS = new GlobalVariable(
+    M, ArrayType::get(IRB.getInt64Ty(), 1000), false,
+    GlobalVariable::ExternalLinkage, 0, "__msan_param_tls", 0,
+    GlobalVariable::GeneralDynamicTLSModel);
+  ParamOriginTLS = new GlobalVariable(
+    M, ArrayType::get(OriginTy, 1000), false, GlobalVariable::ExternalLinkage,
+    0, "__msan_param_origin_tls", 0, GlobalVariable::GeneralDynamicTLSModel);
+
+  VAArgTLS = new GlobalVariable(
+    M, ArrayType::get(IRB.getInt64Ty(), 1000), false,
+    GlobalVariable::ExternalLinkage, 0, "__msan_va_arg_tls", 0,
+    GlobalVariable::GeneralDynamicTLSModel);
+  VAArgOverflowSizeTLS = new GlobalVariable(
+    M, IRB.getInt64Ty(), false, GlobalVariable::ExternalLinkage, 0,
+    "__msan_va_arg_overflow_size_tls", 0,
+    GlobalVariable::GeneralDynamicTLSModel);
+  OriginTLS = new GlobalVariable(
+    M, IRB.getInt32Ty(), false, GlobalVariable::ExternalLinkage, 0,
+    "__msan_origin_tls", 0, GlobalVariable::GeneralDynamicTLSModel);
+  return true;
+}
+
+namespace {
+
+/// \brief A helper class that handles instrumentation of VarArg
+/// functions on a particular platform.
+///
+/// Implementations are expected to insert the instrumentation
+/// necessary to propagate argument shadow through VarArg function
+/// calls. Visit* methods are called during an InstVisitor pass over
+/// the function, and should avoid creating new basic blocks. A new
+/// instance of this class is created for each instrumented function.
+struct VarArgHelper {
+  /// \brief Visit a CallSite.
+  virtual void visitCallSite(CallSite &CS, IRBuilder<> &IRB) = 0;
+
+  /// \brief Visit a va_start call.
+  virtual void visitVAStartInst(VAStartInst &I) = 0;
+
+  /// \brief Visit a va_copy call.
+  virtual void visitVACopyInst(VACopyInst &I) = 0;
+
+  /// \brief Finalize function instrumentation.
+  ///
+  /// This method is called after visiting all interesting (see above)
+  /// instructions in a function.
+  virtual void finalizeInstrumentation() = 0;
+};
+
+struct MemorySanitizerVisitor;
+
+VarArgHelper*
+CreateVarArgHelper(Function &Func, MemorySanitizer &Msan,
+                   MemorySanitizerVisitor &Visitor);
+
+/// This class does all the work for a given function. Store and Load
+/// instructions store and load corresponding shadow and origin
+/// values. Most instructions propagate shadow from arguments to their
+/// return values. Certain instructions (most importantly, BranchInst)
+/// test their argument shadow and print reports (with a runtime call) if it's
+/// non-zero.
+struct MemorySanitizerVisitor : public InstVisitor<MemorySanitizerVisitor> {
+  Function &F;
+  MemorySanitizer &MS;
+  SmallVector<PHINode *, 16> ShadowPHINodes, OriginPHINodes;
+  ValueMap<Value*, Value*> ShadowMap, OriginMap;
+  bool InsertChecks;
+  OwningPtr<VarArgHelper> VAHelper;
+
+  // An unfortunate workaround for asymmetric lowering of va_arg stuff.
+  // See a comment in visitCallSite for more details.
+  static const unsigned AMD64GpEndOffset = 48; // AMD64 ABI Draft 0.99.6 p3.5.7
+  static const unsigned AMD64FpEndOffset = 176;
+
+  struct ShadowOriginAndInsertPoint {
+    Instruction *Shadow;
+    Instruction *Origin;
+    Instruction *OrigIns;
+    ShadowOriginAndInsertPoint(Instruction *S, Instruction *O, Instruction *I)
+      : Shadow(S), Origin(O), OrigIns(I) { }
+    ShadowOriginAndInsertPoint() : Shadow(0), Origin(0), OrigIns(0) { }
+  };
+  SmallVector<ShadowOriginAndInsertPoint, 16> InstrumentationList;
+
+  MemorySanitizerVisitor(Function &F, MemorySanitizer &MS)
+    : F(F), MS(MS), VAHelper(CreateVarArgHelper(F, MS, *this)) {
+    InsertChecks = !MS.BL->isIn(F);
+    DEBUG(if (!InsertChecks)
+            dbgs() << "MemorySanitizer is not inserting checks into '"
+                   << F.getName() << "'\n");
+  }
+
+  void materializeChecks() {
+    for (size_t i = 0, n = InstrumentationList.size(); i < n; i++) {
+      Instruction *Shadow = InstrumentationList[i].Shadow;
+      Instruction *OrigIns = InstrumentationList[i].OrigIns;
+      IRBuilder<> IRB(OrigIns);
+      DEBUG(dbgs() << "  SHAD0 : " << *Shadow << "\n");
+      Value *ConvertedShadow = convertToShadowTyNoVec(Shadow, IRB);
+      DEBUG(dbgs() << "  SHAD1 : " << *ConvertedShadow << "\n");
+      Value *Cmp = IRB.CreateICmpNE(ConvertedShadow,
+                                    getCleanShadow(ConvertedShadow), "_mscmp");
+      Instruction *CheckTerm =
+        SplitBlockAndInsertIfThen(cast<Instruction>(Cmp),
+                                  /* Unreachable */ !ClKeepGoing,
+                                  MS.ColdCallWeights);
+
+      IRB.SetInsertPoint(CheckTerm);
+      if (ClTrackOrigins) {
+        Instruction *Origin = InstrumentationList[i].Origin;
+        IRB.CreateStore(Origin ? (Value*)Origin : (Value*)IRB.getInt32(0),
+                        MS.OriginTLS);
+      }
+      CallInst *Call = IRB.CreateCall(MS.WarningFn);
+      Call->setDebugLoc(OrigIns->getDebugLoc());
+      DEBUG(dbgs() << "  CHECK: " << *Cmp << "\n");
+    }
+    DEBUG(dbgs() << "DONE:\n" << F);
+  }
+
+  /// \brief Add MemorySanitizer instrumentation to a function.
+  bool runOnFunction() {
+    if (!MS.TD) return false;
+    // Iterate all BBs in depth-first order and create shadow instructions
+    // for all instructions (where applicable).
+    // For PHI nodes we create dummy shadow PHIs which will be finalized later.
+    for (df_iterator<BasicBlock*> DI = df_begin(&F.getEntryBlock()),
+         DE = df_end(&F.getEntryBlock()); DI != DE; ++DI) {
+      BasicBlock *BB = *DI;
+      visit(*BB);
+    }
+
+    // Finalize PHI nodes.
+    for (size_t i = 0, n = ShadowPHINodes.size(); i < n; i++) {
+      PHINode *PN = ShadowPHINodes[i];
+      PHINode *PNS = cast<PHINode>(getShadow(PN));
+      PHINode *PNO = ClTrackOrigins ? cast<PHINode>(getOrigin(PN)) : 0;
+      size_t NumValues = PN->getNumIncomingValues();
+      for (size_t v = 0; v < NumValues; v++) {
+        PNS->addIncoming(getShadow(PN, v), PN->getIncomingBlock(v));
+        if (PNO)
+          PNO->addIncoming(getOrigin(PN, v), PN->getIncomingBlock(v));
+      }
+    }
+
+    VAHelper->finalizeInstrumentation();
+
+    materializeChecks();
+
+    return true;
+  }
+
+  /// \brief Compute the shadow type that corresponds to a given Value.
+  Type *getShadowTy(Value *V) {
+    return getShadowTy(V->getType());
+  }
+
+  /// \brief Compute the shadow type that corresponds to a given Type.
+  Type *getShadowTy(Type *OrigTy) {
+    if (!OrigTy->isSized()) {
+      return 0;
+    }
+    // For integer type, shadow is the same as the original type.
+    // This may return weird-sized types like i1.
+    if (IntegerType *IT = dyn_cast<IntegerType>(OrigTy))
+      return IT;
+    if (VectorType *VT = dyn_cast<VectorType>(OrigTy))
+      return VectorType::getInteger(VT);
+    if (StructType *ST = dyn_cast<StructType>(OrigTy)) {
+      SmallVector<Type*, 4> Elements;
+      for (unsigned i = 0, n = ST->getNumElements(); i < n; i++)
+        Elements.push_back(getShadowTy(ST->getElementType(i)));
+      StructType *Res = StructType::get(*MS.C, Elements, ST->isPacked());
+      DEBUG(dbgs() << "getShadowTy: " << *ST << " ===> " << *Res << "\n");
+      return Res;
+    }
+    uint32_t TypeSize = MS.TD->getTypeStoreSizeInBits(OrigTy);
+    return IntegerType::get(*MS.C, TypeSize);
+  }
+
+  /// \brief Flatten a vector type.
+  Type *getShadowTyNoVec(Type *ty) {
+    if (VectorType *vt = dyn_cast<VectorType>(ty))
+      return IntegerType::get(*MS.C, vt->getBitWidth());
+    return ty;
+  }
+
+  /// \brief Convert a shadow value to it's flattened variant.
+  Value *convertToShadowTyNoVec(Value *V, IRBuilder<> &IRB) {
+    Type *Ty = V->getType();
+    Type *NoVecTy = getShadowTyNoVec(Ty);
+    if (Ty == NoVecTy) return V;
+    return IRB.CreateBitCast(V, NoVecTy);
+  }
+
+  /// \brief Compute the shadow address that corresponds to a given application
+  /// address.
+  ///
+  /// Shadow = Addr & ~ShadowMask.
+  Value *getShadowPtr(Value *Addr, Type *ShadowTy,
+                      IRBuilder<> &IRB) {
+    Value *ShadowLong =
+      IRB.CreateAnd(IRB.CreatePointerCast(Addr, MS.IntptrTy),
+                    ConstantInt::get(MS.IntptrTy, ~MS.ShadowMask));
+    return IRB.CreateIntToPtr(ShadowLong, PointerType::get(ShadowTy, 0));
+  }
+
+  /// \brief Compute the origin address that corresponds to a given application
+  /// address.
+  ///
+  /// OriginAddr = (ShadowAddr + OriginOffset) & ~3ULL
+  ///            = Addr & (~ShadowMask & ~3ULL) + OriginOffset
+  Value *getOriginPtr(Value *Addr, IRBuilder<> &IRB) {
+    Value *ShadowLong =
+      IRB.CreateAnd(IRB.CreatePointerCast(Addr, MS.IntptrTy),
+                    ConstantInt::get(MS.IntptrTy, ~MS.ShadowMask & ~3ULL));
+    Value *Add =
+      IRB.CreateAdd(ShadowLong,
+                    ConstantInt::get(MS.IntptrTy, MS.OriginOffset));
+    return IRB.CreateIntToPtr(Add, PointerType::get(IRB.getInt32Ty(), 0));
+  }
+
+  /// \brief Compute the shadow address for a given function argument.
+  ///
+  /// Shadow = ParamTLS+ArgOffset.
+  Value *getShadowPtrForArgument(Value *A, IRBuilder<> &IRB,
+                                 int ArgOffset) {
+    Value *Base = IRB.CreatePointerCast(MS.ParamTLS, MS.IntptrTy);
+    Base = IRB.CreateAdd(Base, ConstantInt::get(MS.IntptrTy, ArgOffset));
+    return IRB.CreateIntToPtr(Base, PointerType::get(getShadowTy(A), 0),
+                              "_msarg");
+  }
+
+  /// \brief Compute the origin address for a given function argument.
+  Value *getOriginPtrForArgument(Value *A, IRBuilder<> &IRB,
+                                 int ArgOffset) {
+    if (!ClTrackOrigins) return 0;
+    Value *Base = IRB.CreatePointerCast(MS.ParamOriginTLS, MS.IntptrTy);
+    Base = IRB.CreateAdd(Base, ConstantInt::get(MS.IntptrTy, ArgOffset));
+    return IRB.CreateIntToPtr(Base, PointerType::get(MS.OriginTy, 0),
+                              "_msarg_o");
+  }
+
+  /// \brief Compute the shadow address for a retval.
+  Value *getShadowPtrForRetval(Value *A, IRBuilder<> &IRB) {
+    Value *Base = IRB.CreatePointerCast(MS.RetvalTLS, MS.IntptrTy);
+    return IRB.CreateIntToPtr(Base, PointerType::get(getShadowTy(A), 0),
+                              "_msret");
+  }
+
+  /// \brief Compute the origin address for a retval.
+  Value *getOriginPtrForRetval(IRBuilder<> &IRB) {
+    // We keep a single origin for the entire retval. Might be too optimistic.
+    return MS.RetvalOriginTLS;
+  }
+
+  /// \brief Set SV to be the shadow value for V.
+  void setShadow(Value *V, Value *SV) {
+    assert(!ShadowMap.count(V) && "Values may only have one shadow");
+    ShadowMap[V] = SV;
+  }
+
+  /// \brief Set Origin to be the origin value for V.
+  void setOrigin(Value *V, Value *Origin) {
+    if (!ClTrackOrigins) return;
+    assert(!OriginMap.count(V) && "Values may only have one origin");
+    DEBUG(dbgs() << "ORIGIN: " << *V << "  ==> " << *Origin << "\n");
+    OriginMap[V] = Origin;
+  }
+
+  /// \brief Create a clean shadow value for a given value.
+  ///
+  /// Clean shadow (all zeroes) means all bits of the value are defined
+  /// (initialized).
+  Value *getCleanShadow(Value *V) {
+    Type *ShadowTy = getShadowTy(V);
+    if (!ShadowTy)
+      return 0;
+    return Constant::getNullValue(ShadowTy);
+  }
+
+  /// \brief Create a dirty shadow of a given shadow type.
+  Constant *getPoisonedShadow(Type *ShadowTy) {
+    assert(ShadowTy);
+    if (isa<IntegerType>(ShadowTy) || isa<VectorType>(ShadowTy))
+      return Constant::getAllOnesValue(ShadowTy);
+    StructType *ST = cast<StructType>(ShadowTy);
+    SmallVector<Constant *, 4> Vals;
+    for (unsigned i = 0, n = ST->getNumElements(); i < n; i++)
+      Vals.push_back(getPoisonedShadow(ST->getElementType(i)));
+    return ConstantStruct::get(ST, Vals);
+  }
+
+  /// \brief Create a clean (zero) origin.
+  Value *getCleanOrigin() {
+    return Constant::getNullValue(MS.OriginTy);
+  }
+
+  /// \brief Get the shadow value for a given Value.
+  ///
+  /// This function either returns the value set earlier with setShadow,
+  /// or extracts if from ParamTLS (for function arguments).
+  Value *getShadow(Value *V) {
+    if (Instruction *I = dyn_cast<Instruction>(V)) {
+      // For instructions the shadow is already stored in the map.
+      Value *Shadow = ShadowMap[V];
+      if (!Shadow) {
+        DEBUG(dbgs() << "No shadow: " << *V << "\n" << *(I->getParent()));
+        assert(Shadow && "No shadow for a value");
+      }
+      return Shadow;
+    }
+    if (UndefValue *U = dyn_cast<UndefValue>(V)) {
+      Value *AllOnes = getPoisonedShadow(getShadowTy(V));
+      DEBUG(dbgs() << "Undef: " << *U << " ==> " << *AllOnes << "\n");
+      return AllOnes;
+    }
+    if (Argument *A = dyn_cast<Argument>(V)) {
+      // For arguments we compute the shadow on demand and store it in the map.
+      Value **ShadowPtr = &ShadowMap[V];
+      if (*ShadowPtr)
+        return *ShadowPtr;
+      Function *F = A->getParent();
+      IRBuilder<> EntryIRB(F->getEntryBlock().getFirstNonPHI());
+      unsigned ArgOffset = 0;
+      for (Function::arg_iterator AI = F->arg_begin(), AE = F->arg_end();
+           AI != AE; ++AI) {
+        if (!AI->getType()->isSized()) {
+          DEBUG(dbgs() << "Arg is not sized\n");
+          continue;
+        }
+        unsigned Size = AI->hasByValAttr()
+          ? MS.TD->getTypeAllocSize(AI->getType()->getPointerElementType())
+          : MS.TD->getTypeAllocSize(AI->getType());
+        if (A == AI) {
+          Value *Base = getShadowPtrForArgument(AI, EntryIRB, ArgOffset);
+          if (AI->hasByValAttr()) {
+            // ByVal pointer itself has clean shadow. We copy the actual
+            // argument shadow to the underlying memory.
+            Value *Cpy = EntryIRB.CreateMemCpy(
+              getShadowPtr(V, EntryIRB.getInt8Ty(), EntryIRB),
+              Base, Size, AI->getParamAlignment());
+            DEBUG(dbgs() << "  ByValCpy: " << *Cpy << "\n");
+            *ShadowPtr = getCleanShadow(V);
+          } else {
+            *ShadowPtr = EntryIRB.CreateLoad(Base);
+          }
+          DEBUG(dbgs() << "  ARG:    "  << *AI << " ==> " <<
+                **ShadowPtr << "\n");
+          if (ClTrackOrigins) {
+            Value* OriginPtr = getOriginPtrForArgument(AI, EntryIRB, ArgOffset);
+            setOrigin(A, EntryIRB.CreateLoad(OriginPtr));
+          }
+        }
+        ArgOffset += DataLayout::RoundUpAlignment(Size, 8);
+      }
+      assert(*ShadowPtr && "Could not find shadow for an argument");
+      return *ShadowPtr;
+    }
+    // For everything else the shadow is zero.
+    return getCleanShadow(V);
+  }
+
+  /// \brief Get the shadow for i-th argument of the instruction I.
+  Value *getShadow(Instruction *I, int i) {
+    return getShadow(I->getOperand(i));
+  }
+
+  /// \brief Get the origin for a value.
+  Value *getOrigin(Value *V) {
+    if (!ClTrackOrigins) return 0;
+    if (isa<Instruction>(V) || isa<Argument>(V)) {
+      Value *Origin = OriginMap[V];
+      if (!Origin) {
+        DEBUG(dbgs() << "NO ORIGIN: " << *V << "\n");
+        Origin = getCleanOrigin();
+      }
+      return Origin;
+    }
+    return getCleanOrigin();
+  }
+
+  /// \brief Get the origin for i-th argument of the instruction I.
+  Value *getOrigin(Instruction *I, int i) {
+    return getOrigin(I->getOperand(i));
+  }
+
+  /// \brief Remember the place where a shadow check should be inserted.
+  ///
+  /// This location will be later instrumented with a check that will print a
+  /// UMR warning in runtime if the value is not fully defined.
+  void insertCheck(Value *Val, Instruction *OrigIns) {
+    assert(Val);
+    if (!InsertChecks) return;
+    Instruction *Shadow = dyn_cast_or_null<Instruction>(getShadow(Val));
+    if (!Shadow) return;
+    Type *ShadowTy = Shadow->getType();
+    assert((isa<IntegerType>(ShadowTy) || isa<VectorType>(ShadowTy)) &&
+           "Can only insert checks for integer and vector shadow types");
+    Instruction *Origin = dyn_cast_or_null<Instruction>(getOrigin(Val));
+    InstrumentationList.push_back(
+      ShadowOriginAndInsertPoint(Shadow, Origin, OrigIns));
+  }
+
+  //------------------- Visitors.
+
+  /// \brief Instrument LoadInst
+  ///
+  /// Loads the corresponding shadow and (optionally) origin.
+  /// Optionally, checks that the load address is fully defined.
+  void visitLoadInst(LoadInst &I) {
+    Type *LoadTy = I.getType();
+    assert(LoadTy->isSized() && "Load type must have size");
+    IRBuilder<> IRB(&I);
+    Type *ShadowTy = getShadowTy(&I);
+    Value *Addr = I.getPointerOperand();
+    Value *ShadowPtr = getShadowPtr(Addr, ShadowTy, IRB);
+    setShadow(&I, IRB.CreateLoad(ShadowPtr, "_msld"));
+
+    if (ClCheckAccessAddress)
+      insertCheck(I.getPointerOperand(), &I);
+
+    if (ClTrackOrigins)
+      setOrigin(&I, IRB.CreateLoad(getOriginPtr(Addr, IRB)));
+  }
+
+  /// \brief Instrument StoreInst
+  ///
+  /// Stores the corresponding shadow and (optionally) origin.
+  /// Optionally, checks that the store address is fully defined.
+  /// Volatile stores check that the value being stored is fully defined.
+  void visitStoreInst(StoreInst &I) {
+    IRBuilder<> IRB(&I);
+    Value *Val = I.getValueOperand();
+    Value *Addr = I.getPointerOperand();
+    Value *Shadow = getShadow(Val);
+    Value *ShadowPtr = getShadowPtr(Addr, Shadow->getType(), IRB);
+
+    StoreInst *NewSI = IRB.CreateStore(Shadow, ShadowPtr);
+    DEBUG(dbgs() << "  STORE: " << *NewSI << "\n");
+    // If the store is volatile, add a check.
+    if (I.isVolatile())
+      insertCheck(Val, &I);
+    if (ClCheckAccessAddress)
+      insertCheck(Addr, &I);
+
+    if (ClTrackOrigins)
+      IRB.CreateStore(getOrigin(Val), getOriginPtr(Addr, IRB));
+  }
+
+  // Casts.
+  void visitSExtInst(SExtInst &I) {
+    IRBuilder<> IRB(&I);
+    setShadow(&I, IRB.CreateSExt(getShadow(&I, 0), I.getType(), "_msprop"));
+    setOrigin(&I, getOrigin(&I, 0));
+  }
+
+  void visitZExtInst(ZExtInst &I) {
+    IRBuilder<> IRB(&I);
+    setShadow(&I, IRB.CreateZExt(getShadow(&I, 0), I.getType(), "_msprop"));
+    setOrigin(&I, getOrigin(&I, 0));
+  }
+
+  void visitTruncInst(TruncInst &I) {
+    IRBuilder<> IRB(&I);
+    setShadow(&I, IRB.CreateTrunc(getShadow(&I, 0), I.getType(), "_msprop"));
+    setOrigin(&I, getOrigin(&I, 0));
+  }
+
+  void visitBitCastInst(BitCastInst &I) {
+    IRBuilder<> IRB(&I);
+    setShadow(&I, IRB.CreateBitCast(getShadow(&I, 0), getShadowTy(&I)));
+    setOrigin(&I, getOrigin(&I, 0));
+  }
+
+  void visitPtrToIntInst(PtrToIntInst &I) {
+    IRBuilder<> IRB(&I);
+    setShadow(&I, IRB.CreateIntCast(getShadow(&I, 0), getShadowTy(&I), false,
+             "_msprop_ptrtoint"));
+    setOrigin(&I, getOrigin(&I, 0));
+  }
+
+  void visitIntToPtrInst(IntToPtrInst &I) {
+    IRBuilder<> IRB(&I);
+    setShadow(&I, IRB.CreateIntCast(getShadow(&I, 0), getShadowTy(&I), false,
+             "_msprop_inttoptr"));
+    setOrigin(&I, getOrigin(&I, 0));
+  }
+
+  void visitFPToSIInst(CastInst& I) { handleShadowOr(I); }
+  void visitFPToUIInst(CastInst& I) { handleShadowOr(I); }
+  void visitSIToFPInst(CastInst& I) { handleShadowOr(I); }
+  void visitUIToFPInst(CastInst& I) { handleShadowOr(I); }
+  void visitFPExtInst(CastInst& I) { handleShadowOr(I); }
+  void visitFPTruncInst(CastInst& I) { handleShadowOr(I); }
+
+  /// \brief Propagate shadow for bitwise AND.
+  ///
+  /// This code is exact, i.e. if, for example, a bit in the left argument
+  /// is defined and 0, then neither the value not definedness of the
+  /// corresponding bit in B don't affect the resulting shadow.
+  void visitAnd(BinaryOperator &I) {
+    IRBuilder<> IRB(&I);
+    //  "And" of 0 and a poisoned value results in unpoisoned value.
+    //  1&1 => 1;     0&1 => 0;     p&1 => p;
+    //  1&0 => 0;     0&0 => 0;     p&0 => 0;
+    //  1&p => p;     0&p => 0;     p&p => p;
+    //  S = (S1 & S2) | (V1 & S2) | (S1 & V2)
+    Value *S1 = getShadow(&I, 0);
+    Value *S2 = getShadow(&I, 1);
+    Value *V1 = I.getOperand(0);
+    Value *V2 = I.getOperand(1);
+    if (V1->getType() != S1->getType()) {
+      V1 = IRB.CreateIntCast(V1, S1->getType(), false);
+      V2 = IRB.CreateIntCast(V2, S2->getType(), false);
+    }
+    Value *S1S2 = IRB.CreateAnd(S1, S2);
+    Value *V1S2 = IRB.CreateAnd(V1, S2);
+    Value *S1V2 = IRB.CreateAnd(S1, V2);
+    setShadow(&I, IRB.CreateOr(S1S2, IRB.CreateOr(V1S2, S1V2)));
+    setOriginForNaryOp(I);
+  }
+
+  void visitOr(BinaryOperator &I) {
+    IRBuilder<> IRB(&I);
+    //  "Or" of 1 and a poisoned value results in unpoisoned value.
+    //  1|1 => 1;     0|1 => 1;     p|1 => 1;
+    //  1|0 => 1;     0|0 => 0;     p|0 => p;
+    //  1|p => 1;     0|p => p;     p|p => p;
+    //  S = (S1 & S2) | (~V1 & S2) | (S1 & ~V2)
+    Value *S1 = getShadow(&I, 0);
+    Value *S2 = getShadow(&I, 1);
+    Value *V1 = IRB.CreateNot(I.getOperand(0));
+    Value *V2 = IRB.CreateNot(I.getOperand(1));
+    if (V1->getType() != S1->getType()) {
+      V1 = IRB.CreateIntCast(V1, S1->getType(), false);
+      V2 = IRB.CreateIntCast(V2, S2->getType(), false);
+    }
+    Value *S1S2 = IRB.CreateAnd(S1, S2);
+    Value *V1S2 = IRB.CreateAnd(V1, S2);
+    Value *S1V2 = IRB.CreateAnd(S1, V2);
+    setShadow(&I, IRB.CreateOr(S1S2, IRB.CreateOr(V1S2, S1V2)));
+    setOriginForNaryOp(I);
+  }
+
+  /// \brief Propagate origin for an instruction.
+  ///
+  /// This is a general case of origin propagation. For an Nary operation,
+  /// is set to the origin of an argument that is not entirely initialized.
+  /// It does not matter which one is picked if all arguments are initialized.
+  void setOriginForNaryOp(Instruction &I) {
+    if (!ClTrackOrigins) return;
+    IRBuilder<> IRB(&I);
+    Value *Origin = getOrigin(&I, 0);
+    for (unsigned Op = 1, n = I.getNumOperands(); Op < n; ++Op) {
+      Value *S = convertToShadowTyNoVec(getShadow(&I, Op - 1), IRB);
+      Origin = IRB.CreateSelect(IRB.CreateICmpNE(S, getCleanShadow(S)),
+                                Origin, getOrigin(&I, Op));
+    }
+    setOrigin(&I, Origin);
+  }
+
+  /// \brief Propagate shadow for a binary operation.
+  ///
+  /// Shadow = Shadow0 | Shadow1, all 3 must have the same type.
+  /// Bitwise OR is selected as an operation that will never lose even a bit of
+  /// poison.
+  void handleShadowOrBinary(Instruction &I) {
+    IRBuilder<> IRB(&I);
+    Value *Shadow0 = getShadow(&I, 0);
+    Value *Shadow1 = getShadow(&I, 1);
+    setShadow(&I, IRB.CreateOr(Shadow0, Shadow1, "_msprop"));
+    setOriginForNaryOp(I);
+  }
+
+  /// \brief Propagate shadow for arbitrary operation.
+  ///
+  /// This is a general case of shadow propagation, used in all cases where we
+  /// don't know and/or care about what the operation actually does.
+  /// It converts all input shadow values to a common type (extending or
+  /// truncating as necessary), and bitwise OR's them.
+  ///
+  /// This is much cheaper than inserting checks (i.e. requiring inputs to be
+  /// fully initialized), and less prone to false positives.
+  // FIXME: is the casting actually correct?
+  // FIXME: merge this with handleShadowOrBinary.
+  void handleShadowOr(Instruction &I) {
+    IRBuilder<> IRB(&I);
+    Value *Shadow = getShadow(&I, 0);
+    for (unsigned Op = 1, n = I.getNumOperands(); Op < n; ++Op)
+      Shadow = IRB.CreateOr(
+        Shadow, IRB.CreateIntCast(getShadow(&I, Op), Shadow->getType(), false),
+        "_msprop");
+    Shadow = IRB.CreateIntCast(Shadow, getShadowTy(&I), false);
+    setShadow(&I, Shadow);
+    setOriginForNaryOp(I);
+  }
+
+  void visitFAdd(BinaryOperator &I) { handleShadowOrBinary(I); }
+  void visitFSub(BinaryOperator &I) { handleShadowOrBinary(I); }
+  void visitFMul(BinaryOperator &I) { handleShadowOrBinary(I); }
+  void visitAdd(BinaryOperator &I) { handleShadowOrBinary(I); }
+  void visitSub(BinaryOperator &I) { handleShadowOrBinary(I); }
+  void visitXor(BinaryOperator &I) { handleShadowOrBinary(I); }
+  void visitMul(BinaryOperator &I) { handleShadowOrBinary(I); }
+
+  void handleDiv(Instruction &I) {
+    IRBuilder<> IRB(&I);
+    // Strict on the second argument.
+    insertCheck(I.getOperand(1), &I);
+    setShadow(&I, getShadow(&I, 0));
+    setOrigin(&I, getOrigin(&I, 0));
+  }
+
+  void visitUDiv(BinaryOperator &I) { handleDiv(I); }
+  void visitSDiv(BinaryOperator &I) { handleDiv(I); }
+  void visitFDiv(BinaryOperator &I) { handleDiv(I); }
+  void visitURem(BinaryOperator &I) { handleDiv(I); }
+  void visitSRem(BinaryOperator &I) { handleDiv(I); }
+  void visitFRem(BinaryOperator &I) { handleDiv(I); }
+
+  /// \brief Instrument == and != comparisons.
+  ///
+  /// Sometimes the comparison result is known even if some of the bits of the
+  /// arguments are not.
+  void handleEqualityComparison(ICmpInst &I) {
+    IRBuilder<> IRB(&I);
+    Value *A = I.getOperand(0);
+    Value *B = I.getOperand(1);
+    Value *Sa = getShadow(A);
+    Value *Sb = getShadow(B);
+    if (A->getType()->isPointerTy())
+      A = IRB.CreatePointerCast(A, MS.IntptrTy);
+    if (B->getType()->isPointerTy())
+      B = IRB.CreatePointerCast(B, MS.IntptrTy);
+    // A == B  <==>  (C = A^B) == 0
+    // A != B  <==>  (C = A^B) != 0
+    // Sc = Sa | Sb
+    Value *C = IRB.CreateXor(A, B);
+    Value *Sc = IRB.CreateOr(Sa, Sb);
+    // Now dealing with i = (C == 0) comparison (or C != 0, does not matter now)
+    // Result is defined if one of the following is true
+    // * there is a defined 1 bit in C
+    // * C is fully defined
+    // Si = !(C & ~Sc) && Sc
+    Value *Zero = Constant::getNullValue(Sc->getType());
+    Value *MinusOne = Constant::getAllOnesValue(Sc->getType());
+    Value *Si =
+      IRB.CreateAnd(IRB.CreateICmpNE(Sc, Zero),
+                    IRB.CreateICmpEQ(
+                      IRB.CreateAnd(IRB.CreateXor(Sc, MinusOne), C), Zero));
+    Si->setName("_msprop_icmp");
+    setShadow(&I, Si);
+    setOriginForNaryOp(I);
+  }
+
+  void visitICmpInst(ICmpInst &I) {
+    if (ClHandleICmp && I.isEquality())
+      handleEqualityComparison(I);
+    else
+      handleShadowOr(I);
+  }
+
+  void visitFCmpInst(FCmpInst &I) {
+    handleShadowOr(I);
+  }
+
+  void handleShift(BinaryOperator &I) {
+    IRBuilder<> IRB(&I);
+    // If any of the S2 bits are poisoned, the whole thing is poisoned.
+    // Otherwise perform the same shift on S1.
+    Value *S1 = getShadow(&I, 0);
+    Value *S2 = getShadow(&I, 1);
+    Value *S2Conv = IRB.CreateSExt(IRB.CreateICmpNE(S2, getCleanShadow(S2)),
+                                   S2->getType());
+    Value *V2 = I.getOperand(1);
+    Value *Shift = IRB.CreateBinOp(I.getOpcode(), S1, V2);
+    setShadow(&I, IRB.CreateOr(Shift, S2Conv));
+    setOriginForNaryOp(I);
+  }
+
+  void visitShl(BinaryOperator &I) { handleShift(I); }
+  void visitAShr(BinaryOperator &I) { handleShift(I); }
+  void visitLShr(BinaryOperator &I) { handleShift(I); }
+
+  void visitMemSetInst(MemSetInst &I) {
+    IRBuilder<> IRB(&I);
+    Value *Ptr = I.getArgOperand(0);
+    Value *Val = I.getArgOperand(1);
+    Value *ShadowPtr = getShadowPtr(Ptr, Val->getType(), IRB);
+    Value *ShadowVal = getCleanShadow(Val);
+    Value *Size = I.getArgOperand(2);
+    unsigned Align = I.getAlignment();
+    bool isVolatile = I.isVolatile();
+
+    IRB.CreateMemSet(ShadowPtr, ShadowVal, Size, Align, isVolatile);
+  }
+
+  void visitMemCpyInst(MemCpyInst &I) {
+    IRBuilder<> IRB(&I);
+    Value *Dst = I.getArgOperand(0);
+    Value *Src = I.getArgOperand(1);
+    Type *ElementType = dyn_cast<PointerType>(Dst->getType())->getElementType();
+    Value *ShadowDst = getShadowPtr(Dst, ElementType, IRB);
+    Value *ShadowSrc = getShadowPtr(Src, ElementType, IRB);
+    Value *Size = I.getArgOperand(2);
+    unsigned Align = I.getAlignment();
+    bool isVolatile = I.isVolatile();
+
+    IRB.CreateMemCpy(ShadowDst, ShadowSrc, Size, Align, isVolatile);
+    if (ClTrackOrigins)
+      IRB.CreateCall3(MS.MsanCopyOriginFn, Dst, Src, Size);
+  }
+
+  /// \brief Instrument llvm.memmove
+  ///
+  /// At this point we don't know if llvm.memmove will be inlined or not.
+  /// If we don't instrument it and it gets inlined,
+  /// our interceptor will not kick in and we will lose the memmove.
+  /// If we instrument the call here, but it does not get inlined,
+  /// we will memove the shadow twice: which is bad in case
+  /// of overlapping regions. So, we simply lower the intrinsic to a call.
+  ///
+  /// Similar situation exists for memcpy and memset, but for those functions
+  /// calling instrumentation twice does not lead to incorrect results.
+  void visitMemMoveInst(MemMoveInst &I) {
+    IRBuilder<> IRB(&I);
+    IRB.CreateCall3(
+      MS.MemmoveFn,
+      IRB.CreatePointerCast(I.getArgOperand(0), IRB.getInt8PtrTy()),
+      IRB.CreatePointerCast(I.getArgOperand(1), IRB.getInt8PtrTy()),
+      IRB.CreateIntCast(I.getArgOperand(2), MS.IntptrTy, false));
+    I.eraseFromParent();
+  }
+
+  void visitVAStartInst(VAStartInst &I) {
+    VAHelper->visitVAStartInst(I);
+  }
+
+  void visitVACopyInst(VACopyInst &I) {
+    VAHelper->visitVACopyInst(I);
+  }
+
+  void visitCallSite(CallSite CS) {
+    Instruction &I = *CS.getInstruction();
+    assert((CS.isCall() || CS.isInvoke()) && "Unknown type of CallSite");
+    if (CS.isCall()) {
+      // Allow only tail calls with the same types, otherwise
+      // we may have a false positive: shadow for a non-void RetVal
+      // will get propagated to a void RetVal.
+      CallInst *Call = cast<CallInst>(&I);
+      if (Call->isTailCall() && Call->getType() != Call->getParent()->getType())
+        Call->setTailCall(false);
+      if (isa<IntrinsicInst>(&I)) {
+        // All intrinsics we care about are handled in corresponding visit*
+        // methods. Add checks for the arguments, mark retval as clean.
+        visitInstruction(I);
+        return;
+      }
+    }
+    IRBuilder<> IRB(&I);
+    unsigned ArgOffset = 0;
+    DEBUG(dbgs() << "  CallSite: " << I << "\n");
+    for (CallSite::arg_iterator ArgIt = CS.arg_begin(), End = CS.arg_end();
+         ArgIt != End; ++ArgIt) {
+      Value *A = *ArgIt;
+      unsigned i = ArgIt - CS.arg_begin();
+      if (!A->getType()->isSized()) {
+        DEBUG(dbgs() << "Arg " << i << " is not sized: " << I << "\n");
+        continue;
+      }
+      unsigned Size = 0;
+      Value *Store = 0;
+      // Compute the Shadow for arg even if it is ByVal, because
+      // in that case getShadow() will copy the actual arg shadow to
+      // __msan_param_tls.
+      Value *ArgShadow = getShadow(A);
+      Value *ArgShadowBase = getShadowPtrForArgument(A, IRB, ArgOffset);
+      DEBUG(dbgs() << "  Arg#" << i << ": " << *A <<
+            " Shadow: " << *ArgShadow << "\n");
+      if (CS.paramHasAttr(i + 1, Attributes::ByVal)) {
+        assert(A->getType()->isPointerTy() &&
+               "ByVal argument is not a pointer!");
+        Size = MS.TD->getTypeAllocSize(A->getType()->getPointerElementType());
+        unsigned Alignment = CS.getParamAlignment(i + 1);
+        Store = IRB.CreateMemCpy(ArgShadowBase,
+                                 getShadowPtr(A, Type::getInt8Ty(*MS.C), IRB),
+                                 Size, Alignment);
+      } else {
+        Size = MS.TD->getTypeAllocSize(A->getType());
+        Store = IRB.CreateStore(ArgShadow, ArgShadowBase);
+      }
+      if (ClTrackOrigins)
+        IRB.CreateStore(getOrigin(A),
+                        getOriginPtrForArgument(A, IRB, ArgOffset));
+      assert(Size != 0 && Store != 0);
+      DEBUG(dbgs() << "  Param:" << *Store << "\n");
+      ArgOffset += DataLayout::RoundUpAlignment(Size, 8);
+    }
+    DEBUG(dbgs() << "  done with call args\n");
+
+    FunctionType *FT =
+      cast<FunctionType>(CS.getCalledValue()->getType()-> getContainedType(0));
+    if (FT->isVarArg()) {
+      VAHelper->visitCallSite(CS, IRB);
+    }
+
+    // Now, get the shadow for the RetVal.
+    if (!I.getType()->isSized()) return;
+    IRBuilder<> IRBBefore(&I);
+    // Untill we have full dynamic coverage, make sure the retval shadow is 0.
+    Value *Base = getShadowPtrForRetval(&I, IRBBefore);
+    IRBBefore.CreateStore(getCleanShadow(&I), Base);
+    Instruction *NextInsn = 0;
+    if (CS.isCall()) {
+      NextInsn = I.getNextNode();
+    } else {
+      BasicBlock *NormalDest = cast<InvokeInst>(&I)->getNormalDest();
+      if (!NormalDest->getSinglePredecessor()) {
+        // FIXME: this case is tricky, so we are just conservative here.
+        // Perhaps we need to split the edge between this BB and NormalDest,
+        // but a naive attempt to use SplitEdge leads to a crash.
+        setShadow(&I, getCleanShadow(&I));
+        setOrigin(&I, getCleanOrigin());
+        return;
+      }
+      NextInsn = NormalDest->getFirstInsertionPt();
+      assert(NextInsn &&
+             "Could not find insertion point for retval shadow load");
+    }
+    IRBuilder<> IRBAfter(NextInsn);
+    setShadow(&I, IRBAfter.CreateLoad(getShadowPtrForRetval(&I, IRBAfter),
+                                      "_msret"));
+    if (ClTrackOrigins)
+      setOrigin(&I, IRBAfter.CreateLoad(getOriginPtrForRetval(IRBAfter)));
+  }
+
+  void visitReturnInst(ReturnInst &I) {
+    IRBuilder<> IRB(&I);
+    if (Value *RetVal = I.getReturnValue()) {
+      // Set the shadow for the RetVal.
+      Value *Shadow = getShadow(RetVal);
+      Value *ShadowPtr = getShadowPtrForRetval(RetVal, IRB);
+      DEBUG(dbgs() << "Return: " << *Shadow << "\n" << *ShadowPtr << "\n");
+      IRB.CreateStore(Shadow, ShadowPtr);
+      if (ClTrackOrigins)
+        IRB.CreateStore(getOrigin(RetVal), getOriginPtrForRetval(IRB));
+    }
+  }
+
+  void visitPHINode(PHINode &I) {
+    IRBuilder<> IRB(&I);
+    ShadowPHINodes.push_back(&I);
+    setShadow(&I, IRB.CreatePHI(getShadowTy(&I), I.getNumIncomingValues(),
+                                "_msphi_s"));
+    if (ClTrackOrigins)
+      setOrigin(&I, IRB.CreatePHI(MS.OriginTy, I.getNumIncomingValues(),
+                                  "_msphi_o"));
+  }
+
+  void visitAllocaInst(AllocaInst &I) {
+    setShadow(&I, getCleanShadow(&I));
+    if (!ClPoisonStack) return;
+    IRBuilder<> IRB(I.getNextNode());
+    uint64_t Size = MS.TD->getTypeAllocSize(I.getAllocatedType());
+    if (ClPoisonStackWithCall) {
+      IRB.CreateCall2(MS.MsanPoisonStackFn,
+                      IRB.CreatePointerCast(&I, IRB.getInt8PtrTy()),
+                      ConstantInt::get(MS.IntptrTy, Size));
+    } else {
+      Value *ShadowBase = getShadowPtr(&I, Type::getInt8PtrTy(*MS.C), IRB);
+      IRB.CreateMemSet(ShadowBase, IRB.getInt8(ClPoisonStackPattern),
+                       Size, I.getAlignment());
+    }
+
+    if (ClTrackOrigins) {
+      setOrigin(&I, getCleanOrigin());
+      SmallString<2048> StackDescriptionStorage;
+      raw_svector_ostream StackDescription(StackDescriptionStorage);
+      // We create a string with a description of the stack allocation and
+      // pass it into __msan_set_alloca_origin.
+      // It will be printed by the run-time if stack-originated UMR is found.
+      // The first 4 bytes of the string are set to '----' and will be replaced
+      // by __msan_va_arg_overflow_size_tls at the first call.
+      StackDescription << "----" << I.getName() << "@" << F.getName();
+      Value *Descr =
+          createPrivateNonConstGlobalForString(*F.getParent(),
+                                               StackDescription.str());
+      IRB.CreateCall3(MS.MsanSetAllocaOriginFn,
+                      IRB.CreatePointerCast(&I, IRB.getInt8PtrTy()),
+                      ConstantInt::get(MS.IntptrTy, Size),
+                      IRB.CreatePointerCast(Descr, IRB.getInt8PtrTy()));
+    }
+  }
+
+  void visitSelectInst(SelectInst& I) {
+    IRBuilder<> IRB(&I);
+    setShadow(&I,  IRB.CreateSelect(I.getCondition(),
+              getShadow(I.getTrueValue()), getShadow(I.getFalseValue()),
+              "_msprop"));
+    if (ClTrackOrigins)
+      setOrigin(&I, IRB.CreateSelect(I.getCondition(),
+                getOrigin(I.getTrueValue()), getOrigin(I.getFalseValue())));
+  }
+
+  void visitLandingPadInst(LandingPadInst &I) {
+    // Do nothing.
+    // See http://code.google.com/p/memory-sanitizer/issues/detail?id=1
+    setShadow(&I, getCleanShadow(&I));
+    setOrigin(&I, getCleanOrigin());
+  }
+
+  void visitGetElementPtrInst(GetElementPtrInst &I) {
+    handleShadowOr(I);
+  }
+
+  void visitExtractValueInst(ExtractValueInst &I) {
+    IRBuilder<> IRB(&I);
+    Value *Agg = I.getAggregateOperand();
+    DEBUG(dbgs() << "ExtractValue:  " << I << "\n");
+    Value *AggShadow = getShadow(Agg);
+    DEBUG(dbgs() << "   AggShadow:  " << *AggShadow << "\n");
+    Value *ResShadow = IRB.CreateExtractValue(AggShadow, I.getIndices());
+    DEBUG(dbgs() << "   ResShadow:  " << *ResShadow << "\n");
+    setShadow(&I, ResShadow);
+    setOrigin(&I, getCleanOrigin());
+  }
+
+  void visitInsertValueInst(InsertValueInst &I) {
+    IRBuilder<> IRB(&I);
+    DEBUG(dbgs() << "InsertValue:  " << I << "\n");
+    Value *AggShadow = getShadow(I.getAggregateOperand());
+    Value *InsShadow = getShadow(I.getInsertedValueOperand());
+    DEBUG(dbgs() << "   AggShadow:  " << *AggShadow << "\n");
+    DEBUG(dbgs() << "   InsShadow:  " << *InsShadow << "\n");
+    Value *Res = IRB.CreateInsertValue(AggShadow, InsShadow, I.getIndices());
+    DEBUG(dbgs() << "   Res:        " << *Res << "\n");
+    setShadow(&I, Res);
+    setOrigin(&I, getCleanOrigin());
+  }
+
+  void dumpInst(Instruction &I) {
+    if (CallInst *CI = dyn_cast<CallInst>(&I)) {
+      errs() << "ZZZ call " << CI->getCalledFunction()->getName() << "\n";
+    } else {
+      errs() << "ZZZ " << I.getOpcodeName() << "\n";
+    }
+    errs() << "QQQ " << I << "\n";
+  }
+
+  void visitResumeInst(ResumeInst &I) {
+    DEBUG(dbgs() << "Resume: " << I << "\n");
+    // Nothing to do here.
+  }
+
+  void visitInstruction(Instruction &I) {
+    // Everything else: stop propagating and check for poisoned shadow.
+    if (ClDumpStrictInstructions)
+      dumpInst(I);
+    DEBUG(dbgs() << "DEFAULT: " << I << "\n");
+    for (size_t i = 0, n = I.getNumOperands(); i < n; i++)
+      insertCheck(I.getOperand(i), &I);
+    setShadow(&I, getCleanShadow(&I));
+    setOrigin(&I, getCleanOrigin());
+  }
+};
+
+/// \brief AMD64-specific implementation of VarArgHelper.
+struct VarArgAMD64Helper : public VarArgHelper {
+  // An unfortunate workaround for asymmetric lowering of va_arg stuff.
+  // See a comment in visitCallSite for more details.
+  static const unsigned AMD64GpEndOffset = 48; // AMD64 ABI Draft 0.99.6 p3.5.7
+  static const unsigned AMD64FpEndOffset = 176;
+
+  Function &F;
+  MemorySanitizer &MS;
+  MemorySanitizerVisitor &MSV;
+  Value *VAArgTLSCopy;
+  Value *VAArgOverflowSize;
+
+  SmallVector<CallInst*, 16> VAStartInstrumentationList;
+
+  VarArgAMD64Helper(Function &F, MemorySanitizer &MS,
+                    MemorySanitizerVisitor &MSV)
+    : F(F), MS(MS), MSV(MSV), VAArgTLSCopy(0), VAArgOverflowSize(0) { }
+
+  enum ArgKind { AK_GeneralPurpose, AK_FloatingPoint, AK_Memory };
+
+  ArgKind classifyArgument(Value* arg) {
+    // A very rough approximation of X86_64 argument classification rules.
+    Type *T = arg->getType();
+    if (T->isFPOrFPVectorTy() || T->isX86_MMXTy())
+      return AK_FloatingPoint;
+    if (T->isIntegerTy() && T->getPrimitiveSizeInBits() <= 64)
+      return AK_GeneralPurpose;
+    if (T->isPointerTy())
+      return AK_GeneralPurpose;
+    return AK_Memory;
+  }
+
+  // For VarArg functions, store the argument shadow in an ABI-specific format
+  // that corresponds to va_list layout.
+  // We do this because Clang lowers va_arg in the frontend, and this pass
+  // only sees the low level code that deals with va_list internals.
+  // A much easier alternative (provided that Clang emits va_arg instructions)
+  // would have been to associate each live instance of va_list with a copy of
+  // MSanParamTLS, and extract shadow on va_arg() call in the argument list
+  // order.
+  void visitCallSite(CallSite &CS, IRBuilder<> &IRB) {
+    unsigned GpOffset = 0;
+    unsigned FpOffset = AMD64GpEndOffset;
+    unsigned OverflowOffset = AMD64FpEndOffset;
+    for (CallSite::arg_iterator ArgIt = CS.arg_begin(), End = CS.arg_end();
+         ArgIt != End; ++ArgIt) {
+      Value *A = *ArgIt;
+      ArgKind AK = classifyArgument(A);
+      if (AK == AK_GeneralPurpose && GpOffset >= AMD64GpEndOffset)
+        AK = AK_Memory;
+      if (AK == AK_FloatingPoint && FpOffset >= AMD64FpEndOffset)
+        AK = AK_Memory;
+      Value *Base;
+      switch (AK) {
+      case AK_GeneralPurpose:
+        Base = getShadowPtrForVAArgument(A, IRB, GpOffset);
+        GpOffset += 8;
+        break;
+      case AK_FloatingPoint:
+        Base = getShadowPtrForVAArgument(A, IRB, FpOffset);
+        FpOffset += 16;
+        break;
+      case AK_Memory:
+        uint64_t ArgSize = MS.TD->getTypeAllocSize(A->getType());
+        Base = getShadowPtrForVAArgument(A, IRB, OverflowOffset);
+        OverflowOffset += DataLayout::RoundUpAlignment(ArgSize, 8);
+      }
+      IRB.CreateStore(MSV.getShadow(A), Base);
+    }
+    Constant *OverflowSize =
+      ConstantInt::get(IRB.getInt64Ty(), OverflowOffset - AMD64FpEndOffset);
+    IRB.CreateStore(OverflowSize, MS.VAArgOverflowSizeTLS);
+  }
+
+  /// \brief Compute the shadow address for a given va_arg.
+  Value *getShadowPtrForVAArgument(Value *A, IRBuilder<> &IRB,
+                                   int ArgOffset) {
+    Value *Base = IRB.CreatePointerCast(MS.VAArgTLS, MS.IntptrTy);
+    Base = IRB.CreateAdd(Base, ConstantInt::get(MS.IntptrTy, ArgOffset));
+    return IRB.CreateIntToPtr(Base, PointerType::get(MSV.getShadowTy(A), 0),
+                              "_msarg");
+  }
+
+  void visitVAStartInst(VAStartInst &I) {
+    IRBuilder<> IRB(&I);
+    VAStartInstrumentationList.push_back(&I);
+    Value *VAListTag = I.getArgOperand(0);
+    Value *ShadowPtr = MSV.getShadowPtr(VAListTag, IRB.getInt8Ty(), IRB);
+
+    // Unpoison the whole __va_list_tag.
+    // FIXME: magic ABI constants.
+    IRB.CreateMemSet(ShadowPtr, Constant::getNullValue(IRB.getInt8Ty()),
+                     /* size */24, /* alignment */16, false);
+  }
+
+  void visitVACopyInst(VACopyInst &I) {
+    IRBuilder<> IRB(&I);
+    Value *VAListTag = I.getArgOperand(0);
+    Value *ShadowPtr = MSV.getShadowPtr(VAListTag, IRB.getInt8Ty(), IRB);
+
+    // Unpoison the whole __va_list_tag.
+    // FIXME: magic ABI constants.
+    IRB.CreateMemSet(ShadowPtr, Constant::getNullValue(IRB.getInt8Ty()),
+                     /* size */ 24, /* alignment */ 16, false);
+  }
+
+  void finalizeInstrumentation() {
+    assert(!VAArgOverflowSize && !VAArgTLSCopy &&
+           "finalizeInstrumentation called twice");
+    if (!VAStartInstrumentationList.empty()) {
+      // If there is a va_start in this function, make a backup copy of
+      // va_arg_tls somewhere in the function entry block.
+      IRBuilder<> IRB(F.getEntryBlock().getFirstNonPHI());
+      VAArgOverflowSize = IRB.CreateLoad(MS.VAArgOverflowSizeTLS);
+      Value *CopySize =
+        IRB.CreateAdd(ConstantInt::get(MS.IntptrTy, AMD64FpEndOffset),
+                      VAArgOverflowSize);
+      VAArgTLSCopy = IRB.CreateAlloca(Type::getInt8Ty(*MS.C), CopySize);
+      IRB.CreateMemCpy(VAArgTLSCopy, MS.VAArgTLS, CopySize, 8);
+    }
+
+    // Instrument va_start.
+    // Copy va_list shadow from the backup copy of the TLS contents.
+    for (size_t i = 0, n = VAStartInstrumentationList.size(); i < n; i++) {
+      CallInst *OrigInst = VAStartInstrumentationList[i];
+      IRBuilder<> IRB(OrigInst->getNextNode());
+      Value *VAListTag = OrigInst->getArgOperand(0);
+
+      Value *RegSaveAreaPtrPtr =
+        IRB.CreateIntToPtr(
+          IRB.CreateAdd(IRB.CreatePtrToInt(VAListTag, MS.IntptrTy),
+                        ConstantInt::get(MS.IntptrTy, 16)),
+          Type::getInt64PtrTy(*MS.C));
+      Value *RegSaveAreaPtr = IRB.CreateLoad(RegSaveAreaPtrPtr);
+      Value *RegSaveAreaShadowPtr =
+        MSV.getShadowPtr(RegSaveAreaPtr, IRB.getInt8Ty(), IRB);
+      IRB.CreateMemCpy(RegSaveAreaShadowPtr, VAArgTLSCopy,
+                       AMD64FpEndOffset, 16);
+
+      Value *OverflowArgAreaPtrPtr =
+        IRB.CreateIntToPtr(
+          IRB.CreateAdd(IRB.CreatePtrToInt(VAListTag, MS.IntptrTy),
+                        ConstantInt::get(MS.IntptrTy, 8)),
+          Type::getInt64PtrTy(*MS.C));
+      Value *OverflowArgAreaPtr = IRB.CreateLoad(OverflowArgAreaPtrPtr);
+      Value *OverflowArgAreaShadowPtr =
+        MSV.getShadowPtr(OverflowArgAreaPtr, IRB.getInt8Ty(), IRB);
+      Value *SrcPtr =
+        getShadowPtrForVAArgument(VAArgTLSCopy, IRB, AMD64FpEndOffset);
+      IRB.CreateMemCpy(OverflowArgAreaShadowPtr, SrcPtr, VAArgOverflowSize, 16);
+    }
+  }
+};
+
+VarArgHelper* CreateVarArgHelper(Function &Func, MemorySanitizer &Msan,
+                                 MemorySanitizerVisitor &Visitor) {
+  return new VarArgAMD64Helper(Func, Msan, Visitor);
+}
+
+}  // namespace
+
+bool MemorySanitizer::runOnFunction(Function &F) {
+  MemorySanitizerVisitor Visitor(F, *this);
+
+  // Clear out readonly/readnone attributes.
+  AttrBuilder B;
+  B.addAttribute(Attributes::ReadOnly)
+    .addAttribute(Attributes::ReadNone);
+  F.removeAttribute(AttrListPtr::FunctionIndex,
+                    Attributes::get(F.getContext(), B));
+
+  return Visitor.runOnFunction();
+}