DataFlowSanitizer; LLVM changes.

DataFlowSanitizer is a generalised dynamic data flow analysis.

Unlike other Sanitizer tools, this tool is not designed to detect a
specific class of bugs on its own.  Instead, it provides a generic
dynamic data flow analysis framework to be used by clients to help
detect application-specific issues within their own code.

Differential Revision: http://llvm-reviews.chandlerc.com/D965

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@187923 91177308-0d34-0410-b5e6-96231b3b80d8

3 files changed, 1008 insertions, 0 deletions

diff --git a/lib/Transforms/Instrumentation/CMakeLists.txt b/lib/Transforms/Instrumentation/CMakeLists.txt
index 5e348633ca..65d41f51fe 100644
--- a/lib/Transforms/Instrumentation/CMakeLists.txt
+++ b/lib/Transforms/Instrumentation/CMakeLists.txt
@@ -1,6 +1,7 @@
 add_llvm_library(LLVMInstrumentation
   AddressSanitizer.cpp
   BoundsChecking.cpp
+  DataFlowSanitizer.cpp
   DebugIR.cpp
   EdgeProfiling.cpp
   GCOVProfiling.cpp
diff --git a/lib/Transforms/Instrumentation/DataFlowSanitizer.cpp b/lib/Transforms/Instrumentation/DataFlowSanitizer.cpp
new file mode 100644
index 0000000000..1cfbba7199
--- /dev/null
+++ b/lib/Transforms/Instrumentation/DataFlowSanitizer.cpp
@@ -0,0 +1,1006 @@
+//===-- DataFlowSanitizer.cpp - dynamic data flow analysis ----------------===//
+//
+//                     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 DataFlowSanitizer, a generalised dynamic data flow
+/// analysis.
+///
+/// Unlike other Sanitizer tools, this tool is not designed to detect a specific
+/// class of bugs on its own.  Instead, it provides a generic dynamic data flow
+/// analysis framework to be used by clients to help detect application-specific
+/// issues within their own code.
+///
+/// The analysis is based on automatic propagation of data flow labels (also
+/// known as taint labels) through a program as it performs computation.  Each
+/// byte of application memory is backed by two bytes of shadow memory which
+/// hold the label.  On Linux/x86_64, memory is laid out as follows:
+///
+/// +--------------------+ 0x800000000000 (top of memory)
+/// | application memory |
+/// +--------------------+ 0x700000008000 (kAppAddr)
+/// |                    |
+/// |       unused       |
+/// |                    |
+/// +--------------------+ 0x200200000000 (kUnusedAddr)
+/// |    union table     |
+/// +--------------------+ 0x200000000000 (kUnionTableAddr)
+/// |   shadow memory    |
+/// +--------------------+ 0x000000010000 (kShadowAddr)
+/// | reserved by kernel |
+/// +--------------------+ 0x000000000000
+///
+/// To derive a shadow memory address from an application memory address,
+/// bits 44-46 are cleared to bring the address into the range
+/// [0x000000008000,0x100000000000).  Then the address is shifted left by 1 to
+/// account for the double byte representation of shadow labels and move the
+/// address into the shadow memory range.  See the function
+/// DataFlowSanitizer::getShadowAddress below.
+///
+/// For more information, please refer to the design document:
+/// http://clang.llvm.org/docs/DataFlowSanitizerDesign.html
+
+#include "llvm/Transforms/Instrumentation.h"
+#include "llvm/ADT/DenseMap.h"
+#include "llvm/ADT/DenseSet.h"
+#include "llvm/ADT/DepthFirstIterator.h"
+#include "llvm/Analysis/ValueTracking.h"
+#include "llvm/IR/InlineAsm.h"
+#include "llvm/IR/IRBuilder.h"
+#include "llvm/IR/LLVMContext.h"
+#include "llvm/IR/MDBuilder.h"
+#include "llvm/IR/Type.h"
+#include "llvm/IR/Value.h"
+#include "llvm/InstVisitor.h"
+#include "llvm/Pass.h"
+#include "llvm/Support/CommandLine.h"
+#include "llvm/Transforms/Utils/BasicBlockUtils.h"
+#include "llvm/Transforms/Utils/SpecialCaseList.h"
+#include <iterator>
+
+using namespace llvm;
+
+// The -dfsan-preserve-alignment flag controls whether this pass assumes that
+// alignment requirements provided by the input IR are correct.  For example,
+// if the input IR contains a load with alignment 8, this flag will cause
+// the shadow load to have alignment 16.  This flag is disabled by default as
+// we have unfortunately encountered too much code (including Clang itself;
+// see PR14291) which performs misaligned access.
+static cl::opt<bool> ClPreserveAlignment(
+    "dfsan-preserve-alignment",
+    cl::desc("respect alignment requirements provided by input IR"), cl::Hidden,
+    cl::init(false));
+
+// The greylist file controls how shadow parameters are passed.
+// The program acts as though every function in the greylist is passed
+// parameters with zero shadow and that its return value also has zero shadow.
+// This avoids the use of TLS or extra function parameters to pass shadow state
+// and essentially makes the function conform to the "native" (i.e. unsanitized)
+// ABI.
+static cl::opt<std::string> ClGreylistFile(
+    "dfsan-greylist",
+    cl::desc("File containing the list of functions with a native ABI"),
+    cl::Hidden);
+
+static cl::opt<bool> ClArgsABI(
+    "dfsan-args-abi",
+    cl::desc("Use the argument ABI rather than the TLS ABI"),
+    cl::Hidden);
+
+namespace {
+
+class DataFlowSanitizer : public ModulePass {
+  friend struct DFSanFunction;
+  friend class DFSanVisitor;
+
+  enum {
+    ShadowWidth = 16
+  };
+
+  enum InstrumentedABI {
+    IA_None,
+    IA_MemOnly,
+    IA_Args,
+    IA_TLS
+  };
+
+  DataLayout *DL;
+  Module *Mod;
+  LLVMContext *Ctx;
+  IntegerType *ShadowTy;
+  PointerType *ShadowPtrTy;
+  IntegerType *IntptrTy;
+  ConstantInt *ZeroShadow;
+  ConstantInt *ShadowPtrMask;
+  ConstantInt *ShadowPtrMul;
+  Constant *ArgTLS;
+  Constant *RetvalTLS;
+  void *(*GetArgTLSPtr)();
+  void *(*GetRetvalTLSPtr)();
+  Constant *GetArgTLS;
+  Constant *GetRetvalTLS;
+  FunctionType *DFSanUnionFnTy;
+  FunctionType *DFSanUnionLoadFnTy;
+  Constant *DFSanUnionFn;
+  Constant *DFSanUnionLoadFn;
+  MDNode *ColdCallWeights;
+  SpecialCaseList Greylist;
+  DenseMap<Value *, Function *> UnwrappedFnMap;
+
+  Value *getShadowAddress(Value *Addr, Instruction *Pos);
+  Value *combineShadows(Value *V1, Value *V2, Instruction *Pos);
+  FunctionType *getInstrumentedFunctionType(FunctionType *T);
+  InstrumentedABI getInstrumentedABI(Function *F);
+  InstrumentedABI getDefaultInstrumentedABI();
+
+public:
+  DataFlowSanitizer(void *(*getArgTLS)() = 0, void *(*getRetValTLS)() = 0);
+  static char ID;
+  bool doInitialization(Module &M);
+  bool runOnModule(Module &M);
+};
+
+struct DFSanFunction {
+  DataFlowSanitizer &DFS;
+  Function *F;
+  DataFlowSanitizer::InstrumentedABI IA;
+  Value *ArgTLSPtr;
+  Value *RetvalTLSPtr;
+  DenseMap<Value *, Value *> ValShadowMap;
+  DenseMap<AllocaInst *, AllocaInst *> AllocaShadowMap;
+  std::vector<std::pair<PHINode *, PHINode *> > PHIFixups;
+  DenseSet<Instruction *> SkipInsts;
+
+  DFSanFunction(DataFlowSanitizer &DFS, Function *F)
+      : DFS(DFS), F(F), IA(DFS.getInstrumentedABI(F)), ArgTLSPtr(0),
+        RetvalTLSPtr(0) {}
+  Value *getArgTLSPtr();
+  Value *getArgTLS(unsigned Index, Instruction *Pos);
+  Value *getRetvalTLS();
+  Value *getShadow(Value *V);
+  void setShadow(Instruction *I, Value *Shadow);
+  Value *combineOperandShadows(Instruction *Inst);
+  Value *loadShadow(Value *ShadowAddr, uint64_t Size, uint64_t Align,
+                    Instruction *Pos);
+  void storeShadow(Value *Addr, uint64_t Size, uint64_t Align, Value *Shadow,
+                   Instruction *Pos);
+};
+
+class DFSanVisitor : public InstVisitor<DFSanVisitor> {
+public:
+  DFSanFunction &DFSF;
+  DFSanVisitor(DFSanFunction &DFSF) : DFSF(DFSF) {}
+
+  void visitOperandShadowInst(Instruction &I);
+
+  void visitBinaryOperator(BinaryOperator &BO);
+  void visitCastInst(CastInst &CI);
+  void visitCmpInst(CmpInst &CI);
+  void visitGetElementPtrInst(GetElementPtrInst &GEPI);
+  void visitLoadInst(LoadInst &LI);
+  void visitStoreInst(StoreInst &SI);
+  void visitReturnInst(ReturnInst &RI);
+  void visitCallSite(CallSite CS);
+  void visitPHINode(PHINode &PN);
+  void visitExtractElementInst(ExtractElementInst &I);
+  void visitInsertElementInst(InsertElementInst &I);
+  void visitShuffleVectorInst(ShuffleVectorInst &I);
+  void visitExtractValueInst(ExtractValueInst &I);
+  void visitInsertValueInst(InsertValueInst &I);
+  void visitAllocaInst(AllocaInst &I);
+  void visitSelectInst(SelectInst &I);
+  void visitMemTransferInst(MemTransferInst &I);
+};
+
+}
+
+char DataFlowSanitizer::ID;
+INITIALIZE_PASS(DataFlowSanitizer, "dfsan",
+                "DataFlowSanitizer: dynamic data flow analysis.", false, false)
+
+ModulePass *llvm::createDataFlowSanitizerPass(void *(*getArgTLS)(),
+                                              void *(*getRetValTLS)()) {
+  return new DataFlowSanitizer(getArgTLS, getRetValTLS);
+}
+
+DataFlowSanitizer::DataFlowSanitizer(void *(*getArgTLS)(),
+                                     void *(*getRetValTLS)())
+    : ModulePass(ID), GetArgTLSPtr(getArgTLS), GetRetvalTLSPtr(getRetValTLS),
+      Greylist(ClGreylistFile) {}
+
+FunctionType *DataFlowSanitizer::getInstrumentedFunctionType(FunctionType *T) {
+  llvm::SmallVector<Type *, 4> ArgTypes;
+  std::copy(T->param_begin(), T->param_end(), std::back_inserter(ArgTypes));
+  for (unsigned i = 0, e = T->getNumParams(); i != e; ++i)
+    ArgTypes.push_back(ShadowTy);
+  if (T->isVarArg())
+    ArgTypes.push_back(ShadowPtrTy);
+  Type *RetType = T->getReturnType();
+  if (!RetType->isVoidTy())
+    RetType = StructType::get(RetType, ShadowTy, (Type *)0);
+  return FunctionType::get(RetType, ArgTypes, T->isVarArg());
+}
+
+bool DataFlowSanitizer::doInitialization(Module &M) {
+  DL = getAnalysisIfAvailable<DataLayout>();
+  if (!DL)
+    return false;
+
+  Mod = &M;
+  Ctx = &M.getContext();
+  ShadowTy = IntegerType::get(*Ctx, ShadowWidth);
+  ShadowPtrTy = PointerType::getUnqual(ShadowTy);
+  IntptrTy = DL->getIntPtrType(*Ctx);
+  ZeroShadow = ConstantInt::getSigned(ShadowTy, 0);
+  ShadowPtrMask = ConstantInt::getSigned(IntptrTy, ~0x700000000000);
+  ShadowPtrMul = ConstantInt::getSigned(IntptrTy, ShadowWidth / 8);
+
+  Type *DFSanUnionArgs[2] = { ShadowTy, ShadowTy };
+  DFSanUnionFnTy =
+      FunctionType::get(ShadowTy, DFSanUnionArgs, /*isVarArg=*/ false);
+  Type *DFSanUnionLoadArgs[2] = { ShadowPtrTy, IntptrTy };
+  DFSanUnionLoadFnTy =
+      FunctionType::get(ShadowTy, DFSanUnionLoadArgs, /*isVarArg=*/ false);
+
+  if (GetArgTLSPtr) {
+    Type *ArgTLSTy = ArrayType::get(ShadowTy, 64);
+    ArgTLS = 0;
+    GetArgTLS = ConstantExpr::getIntToPtr(
+        ConstantInt::get(IntptrTy, uintptr_t(GetArgTLSPtr)),
+        PointerType::getUnqual(
+            FunctionType::get(PointerType::getUnqual(ArgTLSTy), (Type *)0)));
+  }
+  if (GetRetvalTLSPtr) {
+    RetvalTLS = 0;
+    GetRetvalTLS = ConstantExpr::getIntToPtr(
+        ConstantInt::get(IntptrTy, uintptr_t(GetRetvalTLSPtr)),
+        PointerType::getUnqual(
+            FunctionType::get(PointerType::getUnqual(ShadowTy), (Type *)0)));
+  }
+
+  ColdCallWeights = MDBuilder(*Ctx).createBranchWeights(1, 1000);
+  return true;
+}
+
+DataFlowSanitizer::InstrumentedABI
+DataFlowSanitizer::getInstrumentedABI(Function *F) {
+  if (Greylist.isIn(*F))
+    return IA_MemOnly;
+  else
+    return getDefaultInstrumentedABI();
+}
+
+DataFlowSanitizer::InstrumentedABI
+DataFlowSanitizer::getDefaultInstrumentedABI() {
+  return ClArgsABI ? IA_Args : IA_TLS;
+}
+
+bool DataFlowSanitizer::runOnModule(Module &M) {
+  if (!DL)
+    return false;
+
+  if (!GetArgTLSPtr) {
+    Type *ArgTLSTy = ArrayType::get(ShadowTy, 64);
+    ArgTLS = Mod->getOrInsertGlobal("__dfsan_arg_tls", ArgTLSTy);
+    if (GlobalVariable *G = dyn_cast<GlobalVariable>(ArgTLS))
+      G->setThreadLocalMode(GlobalVariable::InitialExecTLSModel);
+  }
+  if (!GetRetvalTLSPtr) {
+    RetvalTLS = Mod->getOrInsertGlobal("__dfsan_retval_tls", ShadowTy);
+    if (GlobalVariable *G = dyn_cast<GlobalVariable>(RetvalTLS))
+      G->setThreadLocalMode(GlobalVariable::InitialExecTLSModel);
+  }
+
+  DFSanUnionFn = Mod->getOrInsertFunction("__dfsan_union", DFSanUnionFnTy);
+  if (Function *F = dyn_cast<Function>(DFSanUnionFn)) {
+    F->addAttribute(AttributeSet::FunctionIndex, Attribute::ReadNone);
+    F->addAttribute(AttributeSet::ReturnIndex, Attribute::ZExt);
+    F->addAttribute(1, Attribute::ZExt);
+    F->addAttribute(2, Attribute::ZExt);
+  }
+  DFSanUnionLoadFn =
+      Mod->getOrInsertFunction("__dfsan_union_load", DFSanUnionLoadFnTy);
+  if (Function *F = dyn_cast<Function>(DFSanUnionLoadFn)) {
+    F->addAttribute(AttributeSet::ReturnIndex, Attribute::ZExt);
+  }
+
+  std::vector<Function *> FnsToInstrument;
+  for (Module::iterator i = M.begin(), e = M.end(); i != e; ++i) {
+    if (!i->isIntrinsic() && i != DFSanUnionFn && i != DFSanUnionLoadFn)
+      FnsToInstrument.push_back(&*i);
+  }
+
+  // First, change the ABI of every function in the module.  Greylisted
+  // functions keep their original ABI and get a wrapper function.
+  for (std::vector<Function *>::iterator i = FnsToInstrument.begin(),
+                                         e = FnsToInstrument.end();
+       i != e; ++i) {
+    Function &F = **i;
+
+    FunctionType *FT = F.getFunctionType();
+    FunctionType *NewFT = getInstrumentedFunctionType(FT);
+    // If the function types are the same (i.e. void()), we don't need to do
+    // anything here.
+    if (FT != NewFT) {
+      switch (getInstrumentedABI(&F)) {
+      case IA_Args: {
+        Function *NewF = Function::Create(NewFT, F.getLinkage(), "", &M);
+        NewF->setCallingConv(F.getCallingConv());
+        NewF->setAttributes(F.getAttributes().removeAttributes(
+            *Ctx, AttributeSet::ReturnIndex,
+            AttributeFuncs::typeIncompatible(NewFT->getReturnType(),
+                                             AttributeSet::ReturnIndex)));
+        for (Function::arg_iterator FArg = F.arg_begin(),
+                                    NewFArg = NewF->arg_begin(),
+                                    FArgEnd = F.arg_end();
+             FArg != FArgEnd; ++FArg, ++NewFArg) {
+          FArg->replaceAllUsesWith(NewFArg);
+        }
+        NewF->getBasicBlockList().splice(NewF->begin(), F.getBasicBlockList());
+
+        for (Function::use_iterator ui = F.use_begin(), ue = F.use_end();
+             ui != ue;) {
+          BlockAddress *BA = dyn_cast<BlockAddress>(ui.getUse().getUser());
+          ++ui;
+          if (BA) {
+            BA->replaceAllUsesWith(
+                BlockAddress::get(NewF, BA->getBasicBlock()));
+            delete BA;
+          }
+        }
+        F.replaceAllUsesWith(
+            ConstantExpr::getBitCast(NewF, PointerType::getUnqual(FT)));
+        NewF->takeName(&F);
+        F.eraseFromParent();
+        *i = NewF;
+        break;
+      }
+      case IA_MemOnly: {
+        assert(!FT->isVarArg() && "varargs not handled here yet");
+        assert(getDefaultInstrumentedABI() == IA_Args);
+        Function *NewF =
+            Function::Create(NewFT, GlobalValue::LinkOnceODRLinkage,
+                             std::string("dfsw$") + F.getName(), &M);
+        NewF->setCallingConv(F.getCallingConv());
+        NewF->setAttributes(F.getAttributes());
+
+        BasicBlock *BB = BasicBlock::Create(*Ctx, "entry", NewF);
+        std::vector<Value *> Args;
+        unsigned n = FT->getNumParams();
+        for (Function::arg_iterator i = NewF->arg_begin(); n != 0; ++i, --n)
+          Args.push_back(&*i);
+        CallInst *CI = CallInst::Create(&F, Args, "", BB);
+        if (FT->getReturnType()->isVoidTy())
+          ReturnInst::Create(*Ctx, BB);
+        else {
+          Value *InsVal = InsertValueInst::Create(
+              UndefValue::get(NewFT->getReturnType()), CI, 0, "", BB);
+          Value *InsShadow =
+              InsertValueInst::Create(InsVal, ZeroShadow, 1, "", BB);
+          ReturnInst::Create(*Ctx, InsShadow, BB);
+        }
+
+        Value *WrappedFnCst =
+            ConstantExpr::getBitCast(NewF, PointerType::getUnqual(FT));
+        F.replaceAllUsesWith(WrappedFnCst);
+        UnwrappedFnMap[WrappedFnCst] = &F;
+        break;
+      }
+      default:
+        break;
+      }
+    }
+  }
+
+  for (std::vector<Function *>::iterator i = FnsToInstrument.begin(),
+                                         e = FnsToInstrument.end();
+       i != e; ++i) {
+    if ((*i)->isDeclaration())
+      continue;
+
+    DFSanFunction DFSF(*this, *i);
+
+    // DFSanVisitor may create new basic blocks, which confuses df_iterator.
+    // Build a copy of the list before iterating over it.
+    llvm::SmallVector<BasicBlock *, 4> BBList;
+    std::copy(df_begin(&(*i)->getEntryBlock()), df_end(&(*i)->getEntryBlock()),
+              std::back_inserter(BBList));
+
+    for (llvm::SmallVector<BasicBlock *, 4>::iterator i = BBList.begin(),
+                                                      e = BBList.end();
+         i != e; ++i) {
+      Instruction *Inst = &(*i)->front();
+      while (1) {
+        // DFSanVisitor may split the current basic block, changing the current
+        // instruction's next pointer and moving the next instruction to the
+        // tail block from which we should continue.
+        Instruction *Next = Inst->getNextNode();
+        if (!DFSF.SkipInsts.count(Inst))
+          DFSanVisitor(DFSF).visit(Inst);
+        if (isa<TerminatorInst>(Inst))
+          break;
+        Inst = Next;
+      }
+    }
+
+    for (std::vector<std::pair<PHINode *, PHINode *> >::iterator
+             i = DFSF.PHIFixups.begin(),
+             e = DFSF.PHIFixups.end();
+         i != e; ++i) {
+      for (unsigned val = 0, n = i->first->getNumIncomingValues(); val != n;
+           ++val) {
+        i->second->setIncomingValue(
+            val, DFSF.getShadow(i->first->getIncomingValue(val)));
+      }
+    }
+  }
+
+  return false;
+}
+
+Value *DFSanFunction::getArgTLSPtr() {
+  if (ArgTLSPtr)
+    return ArgTLSPtr;
+  if (DFS.ArgTLS)
+    return ArgTLSPtr = DFS.ArgTLS;
+
+  IRBuilder<> IRB(F->getEntryBlock().begin());
+  return ArgTLSPtr = IRB.CreateCall(DFS.GetArgTLS);
+}
+
+Value *DFSanFunction::getRetvalTLS() {
+  if (RetvalTLSPtr)
+    return RetvalTLSPtr;
+  if (DFS.RetvalTLS)
+    return RetvalTLSPtr = DFS.RetvalTLS;
+
+  IRBuilder<> IRB(F->getEntryBlock().begin());
+  return RetvalTLSPtr = IRB.CreateCall(DFS.GetRetvalTLS);
+}
+
+Value *DFSanFunction::getArgTLS(unsigned Idx, Instruction *Pos) {
+  IRBuilder<> IRB(Pos);
+  return IRB.CreateConstGEP2_64(getArgTLSPtr(), 0, Idx);
+}
+
+Value *DFSanFunction::getShadow(Value *V) {
+  if (!isa<Argument>(V) && !isa<Instruction>(V))
+    return DFS.ZeroShadow;
+  Value *&Shadow = ValShadowMap[V];
+  if (!Shadow) {
+    if (Argument *A = dyn_cast<Argument>(V)) {
+      switch (IA) {
+      case DataFlowSanitizer::IA_TLS: {
+        Value *ArgTLSPtr = getArgTLSPtr();
+        Instruction *ArgTLSPos =
+            DFS.ArgTLS ? &*F->getEntryBlock().begin()
+                       : cast<Instruction>(ArgTLSPtr)->getNextNode();
+        IRBuilder<> IRB(ArgTLSPos);
+        Shadow = IRB.CreateLoad(getArgTLS(A->getArgNo(), ArgTLSPos));
+        break;
+      }
+      case DataFlowSanitizer::IA_Args: {
+        unsigned ArgIdx = A->getArgNo() + F->getArgumentList().size() / 2;
+        Function::arg_iterator i = F->arg_begin();
+        while (ArgIdx--)
+          ++i;
+        Shadow = i;
+        break;
+      }
+      default:
+        Shadow = DFS.ZeroShadow;
+        break;
+      }
+    } else {
+      Shadow = DFS.ZeroShadow;
+    }
+  }
+  return Shadow;
+}
+
+void DFSanFunction::setShadow(Instruction *I, Value *Shadow) {
+  assert(!ValShadowMap.count(I));
+  assert(Shadow->getType() == DFS.ShadowTy);
+  ValShadowMap[I] = Shadow;
+}
+
+Value *DataFlowSanitizer::getShadowAddress(Value *Addr, Instruction *Pos) {
+  assert(Addr != RetvalTLS && "Reinstrumenting?");
+  IRBuilder<> IRB(Pos);
+  return IRB.CreateIntToPtr(
+      IRB.CreateMul(
+          IRB.CreateAnd(IRB.CreatePtrToInt(Addr, IntptrTy), ShadowPtrMask),
+          ShadowPtrMul),
+      ShadowPtrTy);
+}
+
+// Generates IR to compute the union of the two given shadows, inserting it
+// before Pos.  Returns the computed union Value.
+Value *DataFlowSanitizer::combineShadows(Value *V1, Value *V2,
+                                         Instruction *Pos) {
+  if (V1 == ZeroShadow)
+    return V2;
+  if (V2 == ZeroShadow)
+    return V1;
+  if (V1 == V2)
+    return V1;
+  IRBuilder<> IRB(Pos);
+  BasicBlock *Head = Pos->getParent();
+  Value *Ne = IRB.CreateICmpNE(V1, V2);
+  Instruction *NeInst = dyn_cast<Instruction>(Ne);
+  if (NeInst) {
+    BranchInst *BI = cast<BranchInst>(SplitBlockAndInsertIfThen(
+        NeInst, /*Unreachable=*/ false, ColdCallWeights));
+    IRBuilder<> ThenIRB(BI);
+    CallInst *Call = ThenIRB.CreateCall2(DFSanUnionFn, V1, V2);
+    Call->addAttribute(AttributeSet::ReturnIndex, Attribute::ZExt);
+    Call->addAttribute(1, Attribute::ZExt);
+    Call->addAttribute(2, Attribute::ZExt);
+
+    BasicBlock *Tail = BI->getSuccessor(0);
+    PHINode *Phi = PHINode::Create(ShadowTy, 2, "", Tail->begin());
+    Phi->addIncoming(Call, Call->getParent());
+    Phi->addIncoming(ZeroShadow, Head);
+    Pos = Phi;
+    return Phi;
+  } else {
+    assert(0 && "todo");
+    return 0;
+  }
+}
+
+// A convenience function which folds the shadows of each of the operands
+// of the provided instruction Inst, inserting the IR before Inst.  Returns
+// the computed union Value.
+Value *DFSanFunction::combineOperandShadows(Instruction *Inst) {
+  if (Inst->getNumOperands() == 0)
+    return DFS.ZeroShadow;
+
+  Value *Shadow = getShadow(Inst->getOperand(0));
+  for (unsigned i = 1, n = Inst->getNumOperands(); i != n; ++i) {
+    Shadow = DFS.combineShadows(Shadow, getShadow(Inst->getOperand(i)), Inst);
+  }
+  return Shadow;
+}
+
+void DFSanVisitor::visitOperandShadowInst(Instruction &I) {
+  Value *CombinedShadow = DFSF.combineOperandShadows(&I);
+  DFSF.setShadow(&I, CombinedShadow);
+}
+
+// Generates IR to load shadow corresponding to bytes [Addr, Addr+Size), where
+// Addr has alignment Align, and take the union of each of those shadows.
+Value *DFSanFunction::loadShadow(Value *Addr, uint64_t Size, uint64_t Align,
+                                 Instruction *Pos) {
+  if (AllocaInst *AI = dyn_cast<AllocaInst>(Addr)) {
+    llvm::DenseMap<AllocaInst *, AllocaInst *>::iterator i =
+        AllocaShadowMap.find(AI);
+    if (i != AllocaShadowMap.end()) {
+      IRBuilder<> IRB(Pos);
+      return IRB.CreateLoad(i->second);
+    }
+  }
+
+  uint64_t ShadowAlign = Align * DFS.ShadowWidth / 8;
+  SmallVector<Value *, 2> Objs;
+  GetUnderlyingObjects(Addr, Objs, DFS.DL);
+  bool AllConstants = true;
+  for (SmallVector<Value *, 2>::iterator i = Objs.begin(), e = Objs.end();
+       i != e; ++i) {
+    if (isa<Function>(*i) || isa<BlockAddress>(*i))
+      continue;
+    if (isa<GlobalVariable>(*i) && cast<GlobalVariable>(*i)->isConstant())
+      continue;
+
+    AllConstants = false;
+    break;
+  }
+  if (AllConstants)
+    return DFS.ZeroShadow;
+
+  Value *ShadowAddr = DFS.getShadowAddress(Addr, Pos);
+  switch (Size) {
+  case 0:
+    return DFS.ZeroShadow;
+  case 1: {
+    LoadInst *LI = new LoadInst(ShadowAddr, "", Pos);
+    LI->setAlignment(ShadowAlign);
+    return LI;
+  }
+  case 2: {
+    IRBuilder<> IRB(Pos);
+    Value *ShadowAddr1 =
+        IRB.CreateGEP(ShadowAddr, ConstantInt::get(DFS.IntptrTy, 1));
+    return DFS.combineShadows(IRB.CreateAlignedLoad(ShadowAddr, ShadowAlign),
+                              IRB.CreateAlignedLoad(ShadowAddr1, ShadowAlign),
+                              Pos);
+  }
+  }
+  if (Size % (64 / DFS.ShadowWidth) == 0) {
+    // Fast path for the common case where each byte has identical shadow: load
+    // shadow 64 bits at a time, fall out to a __dfsan_union_load call if any
+    // shadow is non-equal.
+    BasicBlock *FallbackBB = BasicBlock::Create(*DFS.Ctx, "", F);
+    IRBuilder<> FallbackIRB(FallbackBB);
+    CallInst *FallbackCall = FallbackIRB.CreateCall2(
+        DFS.DFSanUnionLoadFn, ShadowAddr, ConstantInt::get(DFS.IntptrTy, Size));
+    FallbackCall->addAttribute(AttributeSet::ReturnIndex, Attribute::ZExt);
+
+    // Compare each of the shadows stored in the loaded 64 bits to each other,
+    // by computing (WideShadow rotl ShadowWidth) == WideShadow.
+    IRBuilder<> IRB(Pos);
+    Value *WideAddr =
+        IRB.CreateBitCast(ShadowAddr, Type::getInt64PtrTy(*DFS.Ctx));
+    Value *WideShadow = IRB.CreateAlignedLoad(WideAddr, ShadowAlign);
+    Value *TruncShadow = IRB.CreateTrunc(WideShadow, DFS.ShadowTy);
+    Value *ShlShadow = IRB.CreateShl(WideShadow, DFS.ShadowWidth);
+    Value *ShrShadow = IRB.CreateLShr(WideShadow, 64 - DFS.ShadowWidth);
+    Value *RotShadow = IRB.CreateOr(ShlShadow, ShrShadow);
+    Value *ShadowsEq = IRB.CreateICmpEQ(WideShadow, RotShadow);
+
+    BasicBlock *Head = Pos->getParent();
+    BasicBlock *Tail = Head->splitBasicBlock(Pos);
+    // In the following code LastBr will refer to the previous basic block's
+    // conditional branch instruction, whose true successor is fixed up to point
+    // to the next block during the loop below or to the tail after the final
+    // iteration.
+    BranchInst *LastBr = BranchInst::Create(FallbackBB, FallbackBB, ShadowsEq);
+    ReplaceInstWithInst(Head->getTerminator(), LastBr);
+
+    for (uint64_t Ofs = 64 / DFS.ShadowWidth; Ofs != Size;
+         Ofs += 64 / DFS.ShadowWidth) {
+      BasicBlock *NextBB = BasicBlock::Create(*DFS.Ctx, "", F);
+      IRBuilder<> NextIRB(NextBB);
+      WideAddr = NextIRB.CreateGEP(WideAddr, ConstantInt::get(DFS.IntptrTy, 1));
+      Value *NextWideShadow = NextIRB.CreateAlignedLoad(WideAddr, ShadowAlign);
+      ShadowsEq = NextIRB.CreateICmpEQ(WideShadow, NextWideShadow);
+      LastBr->setSuccessor(0, NextBB);
+      LastBr = NextIRB.CreateCondBr(ShadowsEq, FallbackBB, FallbackBB);
+    }
+
+    LastBr->setSuccessor(0, Tail);
+    FallbackIRB.CreateBr(Tail);
+    PHINode *Shadow = PHINode::Create(DFS.ShadowTy, 2, "", &Tail->front());
+    Shadow->addIncoming(FallbackCall, FallbackBB);
+    Shadow->addIncoming(TruncShadow, LastBr->getParent());
+    return Shadow;
+  }
+
+  IRBuilder<> IRB(Pos);
+  CallInst *FallbackCall = IRB.CreateCall2(
+      DFS.DFSanUnionLoadFn, ShadowAddr, ConstantInt::get(DFS.IntptrTy, Size));
+  FallbackCall->addAttribute(AttributeSet::ReturnIndex, Attribute::ZExt);
+  return FallbackCall;
+}
+
+void DFSanVisitor::visitLoadInst(LoadInst &LI) {
+  uint64_t Size = DFSF.DFS.DL->getTypeStoreSize(LI.getType());
+  uint64_t Align;
+  if (ClPreserveAlignment) {
+    Align = LI.getAlignment();
+    if (Align == 0)
+      Align = DFSF.DFS.DL->getABITypeAlignment(LI.getType());
+  } else {
+    Align = 1;
+  }
+  IRBuilder<> IRB(&LI);
+  Value *LoadedShadow =
+      DFSF.loadShadow(LI.getPointerOperand(), Size, Align, &LI);
+  Value *PtrShadow = DFSF.getShadow(LI.getPointerOperand());
+  DFSF.setShadow(&LI, DFSF.DFS.combineShadows(LoadedShadow, PtrShadow, &LI));
+}
+
+void DFSanFunction::storeShadow(Value *Addr, uint64_t Size, uint64_t Align,
+                                Value *Shadow, Instruction *Pos) {
+  if (AllocaInst *AI = dyn_cast<AllocaInst>(Addr)) {
+    llvm::DenseMap<AllocaInst *, AllocaInst *>::iterator i =
+        AllocaShadowMap.find(AI);
+    if (i != AllocaShadowMap.end()) {
+      IRBuilder<> IRB(Pos);
+      IRB.CreateStore(Shadow, i->second);
+      return;
+    }
+  }
+
+  uint64_t ShadowAlign = Align * DFS.ShadowWidth / 8;
+  IRBuilder<> IRB(Pos);
+  Value *ShadowAddr = DFS.getShadowAddress(Addr, Pos);
+  if (Shadow == DFS.ZeroShadow) {
+    IntegerType *ShadowTy = IntegerType::get(*DFS.Ctx, Size * DFS.ShadowWidth);
+    Value *ExtZeroShadow = ConstantInt::get(ShadowTy, 0);
+    Value *ExtShadowAddr =
+        IRB.CreateBitCast(ShadowAddr, PointerType::getUnqual(ShadowTy));
+    IRB.CreateAlignedStore(ExtZeroShadow, ExtShadowAddr, ShadowAlign);
+    return;
+  }
+
+  const unsigned ShadowVecSize = 128 / DFS.ShadowWidth;
+  uint64_t Offset = 0;
+  if (Size >= ShadowVecSize) {
+    VectorType *ShadowVecTy = VectorType::get(DFS.ShadowTy, ShadowVecSize);
+    Value *ShadowVec = UndefValue::get(ShadowVecTy);
+    for (unsigned i = 0; i != ShadowVecSize; ++i) {
+      ShadowVec = IRB.CreateInsertElement(
+          ShadowVec, Shadow, ConstantInt::get(Type::getInt32Ty(*DFS.Ctx), i));
+    }
+    Value *ShadowVecAddr =
+        IRB.CreateBitCast(ShadowAddr, PointerType::getUnqual(ShadowVecTy));
+    do {
+      Value *CurShadowVecAddr = IRB.CreateConstGEP1_32(ShadowVecAddr, Offset);
+      IRB.CreateAlignedStore(ShadowVec, CurShadowVecAddr, ShadowAlign);
+      Size -= ShadowVecSize;
+      ++Offset;
+    } while (Size >= ShadowVecSize);
+    Offset *= ShadowVecSize;
+  }
+  while (Size > 0) {
+    Value *CurShadowAddr = IRB.CreateConstGEP1_32(ShadowAddr, Offset);
+    IRB.CreateAlignedStore(Shadow, CurShadowAddr, ShadowAlign);
+    --Size;
+    ++Offset;
+  }
+}
+
+void DFSanVisitor::visitStoreInst(StoreInst &SI) {
+  uint64_t Size =
+      DFSF.DFS.DL->getTypeStoreSize(SI.getValueOperand()->getType());
+  uint64_t Align;
+  if (ClPreserveAlignment) {
+    Align = SI.getAlignment();
+    if (Align == 0)
+      Align = DFSF.DFS.DL->getABITypeAlignment(SI.getValueOperand()->getType());
+  } else {
+    Align = 1;
+  }
+  DFSF.storeShadow(SI.getPointerOperand(), Size, Align,
+                   DFSF.getShadow(SI.getValueOperand()), &SI);
+}
+
+void DFSanVisitor::visitBinaryOperator(BinaryOperator &BO) {
+  visitOperandShadowInst(BO);
+}
+
+void DFSanVisitor::visitCastInst(CastInst &CI) { visitOperandShadowInst(CI); }
+
+void DFSanVisitor::visitCmpInst(CmpInst &CI) { visitOperandShadowInst(CI); }
+
+void DFSanVisitor::visitGetElementPtrInst(GetElementPtrInst &GEPI) {
+  visitOperandShadowInst(GEPI);
+}
+
+void DFSanVisitor::visitExtractElementInst(ExtractElementInst &I) {
+  visitOperandShadowInst(I);
+}
+
+void DFSanVisitor::visitInsertElementInst(InsertElementInst &I) {
+  visitOperandShadowInst(I);
+}
+
+void DFSanVisitor::visitShuffleVectorInst(ShuffleVectorInst &I) {
+  visitOperandShadowInst(I);
+}
+
+void DFSanVisitor::visitExtractValueInst(ExtractValueInst &I) {
+  visitOperandShadowInst(I);
+}
+
+void DFSanVisitor::visitInsertValueInst(InsertValueInst &I) {
+  visitOperandShadowInst(I);
+}
+
+void DFSanVisitor::visitAllocaInst(AllocaInst &I) {
+  bool AllLoadsStores = true;
+  for (Instruction::use_iterator i = I.use_begin(), e = I.use_end(); i != e;
+       ++i) {
+    if (isa<LoadInst>(*i))
+      continue;
+
+    if (StoreInst *SI = dyn_cast<StoreInst>(*i)) {
+      if (SI->getPointerOperand() == &I)
+        continue;
+    }
+
+    AllLoadsStores = false;
+    break;
+  }
+  if (AllLoadsStores) {
+    IRBuilder<> IRB(&I);
+    DFSF.AllocaShadowMap[&I] = IRB.CreateAlloca(DFSF.DFS.ShadowTy);
+  }
+  DFSF.setShadow(&I, DFSF.DFS.ZeroShadow);
+}
+
+void DFSanVisitor::visitSelectInst(SelectInst &I) {
+  Value *CondShadow = DFSF.getShadow(I.getCondition());
+  Value *TrueShadow = DFSF.getShadow(I.getTrueValue());
+  Value *FalseShadow = DFSF.getShadow(I.getFalseValue());
+
+  if (isa<VectorType>(I.getCondition()->getType())) {
+    DFSF.setShadow(
+        &I, DFSF.DFS.combineShadows(
+                CondShadow,
+                DFSF.DFS.combineShadows(TrueShadow, FalseShadow, &I), &I));
+  } else {
+    Value *ShadowSel;
+    if (TrueShadow == FalseShadow) {
+      ShadowSel = TrueShadow;
+    } else {
+      ShadowSel =
+          SelectInst::Create(I.getCondition(), TrueShadow, FalseShadow, "", &I);
+    }
+    DFSF.setShadow(&I, DFSF.DFS.combineShadows(CondShadow, ShadowSel, &I));
+  }
+}
+
+void DFSanVisitor::visitMemTransferInst(MemTransferInst &I) {
+  IRBuilder<> IRB(&I);
+  Value *DestShadow = DFSF.DFS.getShadowAddress(I.getDest(), &I);
+  Value *SrcShadow = DFSF.DFS.getShadowAddress(I.getSource(), &I);
+  Value *LenShadow = IRB.CreateMul(
+      I.getLength(),
+      ConstantInt::get(I.getLength()->getType(), DFSF.DFS.ShadowWidth / 8));
+  Value *AlignShadow;
+  if (ClPreserveAlignment) {
+    AlignShadow = IRB.CreateMul(I.getAlignmentCst(),
+                                ConstantInt::get(I.getAlignmentCst()->getType(),
+                                                 DFSF.DFS.ShadowWidth / 8));
+  } else {
+    AlignShadow = ConstantInt::get(I.getAlignmentCst()->getType(),
+                                   DFSF.DFS.ShadowWidth / 8);
+  }
+  Type *Int8Ptr = Type::getInt8PtrTy(*DFSF.DFS.Ctx);
+  DestShadow = IRB.CreateBitCast(DestShadow, Int8Ptr);
+  SrcShadow = IRB.CreateBitCast(SrcShadow, Int8Ptr);
+  IRB.CreateCall5(I.getCalledValue(), DestShadow, SrcShadow, LenShadow,
+                  AlignShadow, I.getVolatileCst());
+}
+
+void DFSanVisitor::visitReturnInst(ReturnInst &RI) {
+  if (RI.getReturnValue()) {
+    switch (DFSF.IA) {
+    case DataFlowSanitizer::IA_TLS: {
+      Value *S = DFSF.getShadow(RI.getReturnValue());
+      IRBuilder<> IRB(&RI);
+      IRB.CreateStore(S, DFSF.getRetvalTLS());
+      break;
+    }
+    case DataFlowSanitizer::IA_Args: {
+      IRBuilder<> IRB(&RI);
+      Type *RT = DFSF.F->getFunctionType()->getReturnType();
+      Value *InsVal =
+          IRB.CreateInsertValue(UndefValue::get(RT), RI.getReturnValue(), 0);
+      Value *InsShadow =
+          IRB.CreateInsertValue(InsVal, DFSF.getShadow(RI.getReturnValue()), 1);
+      RI.setOperand(0, InsShadow);
+      break;
+    }
+    default:
+      break;
+    }
+  }
+}
+
+void DFSanVisitor::visitCallSite(CallSite CS) {
+  Function *F = CS.getCalledFunction();
+  if ((F && F->isIntrinsic()) || isa<InlineAsm>(CS.getCalledValue())) {
+    visitOperandShadowInst(*CS.getInstruction());
+    return;
+  }
+
+  DenseMap<Value *, Function *>::iterator i =
+      DFSF.DFS.UnwrappedFnMap.find(CS.getCalledValue());
+  if (i != DFSF.DFS.UnwrappedFnMap.end()) {
+    CS.setCalledFunction(i->second);
+    DFSF.setShadow(CS.getInstruction(), DFSF.DFS.ZeroShadow);
+    return;
+  }
+
+  IRBuilder<> IRB(CS.getInstruction());
+
+  FunctionType *FT = cast<FunctionType>(
+      CS.getCalledValue()->getType()->getPointerElementType());
+  if (DFSF.DFS.getDefaultInstrumentedABI() == DataFlowSanitizer::IA_TLS) {
+    for (unsigned i = 0, n = FT->getNumParams(); i != n; ++i) {
+      IRB.CreateStore(DFSF.getShadow(CS.getArgument(i)),
+                      DFSF.getArgTLS(i, CS.getInstruction()));
+    }
+  }
+
+  Instruction *Next = 0;
+  if (!CS.getType()->isVoidTy()) {
+    if (InvokeInst *II = dyn_cast<InvokeInst>(CS.getInstruction())) {
+      if (II->getNormalDest()->getSinglePredecessor()) {
+        Next = II->getNormalDest()->begin();
+      } else {
+        BasicBlock *NewBB =
+            SplitEdge(II->getParent(), II->getNormalDest(), &DFSF.DFS);
+        Next = NewBB->begin();
+      }
+    } else {
+      Next = CS->getNextNode();
+    }
+
+    if (DFSF.DFS.getDefaultInstrumentedABI() == DataFlowSanitizer::IA_TLS) {
+      IRBuilder<> NextIRB(Next);
+      LoadInst *LI = NextIRB.CreateLoad(DFSF.getRetvalTLS());
+      DFSF.SkipInsts.insert(LI);
+      DFSF.setShadow(CS.getInstruction(), LI);
+    }
+  }
+
+  // Do all instrumentation for IA_Args down here to defer tampering with the
+  // CFG in a way that SplitEdge may be able to detect.
+  if (DFSF.DFS.getDefaultInstrumentedABI() == DataFlowSanitizer::IA_Args) {
+    FunctionType *NewFT = DFSF.DFS.getInstrumentedFunctionType(FT);
+    Value *Func =
+        IRB.CreateBitCast(CS.getCalledValue(), PointerType::getUnqual(NewFT));
+    std::vector<Value *> Args;
+
+    CallSite::arg_iterator i = CS.arg_begin(), e = CS.arg_end();
+    for (unsigned n = FT->getNumParams(); n != 0; ++i, --n)
+      Args.push_back(*i);
+
+    i = CS.arg_begin();
+    for (unsigned n = FT->getNumParams(); n != 0; ++i, --n)
+      Args.push_back(DFSF.getShadow(*i));
+
+    if (FT->isVarArg()) {
+      unsigned VarArgSize = CS.arg_size() - FT->getNumParams();
+      ArrayType *VarArgArrayTy = ArrayType::get(DFSF.DFS.ShadowTy, VarArgSize);
+      AllocaInst *VarArgShadow =
+          new AllocaInst(VarArgArrayTy, "", DFSF.F->getEntryBlock().begin());
+      Args.push_back(IRB.CreateConstGEP2_32(VarArgShadow, 0, 0));
+      for (unsigned n = 0; i != e; ++i, ++n) {
+        IRB.CreateStore(DFSF.getShadow(*i),
+                        IRB.CreateConstGEP2_32(VarArgShadow, 0, n));
+        Args.push_back(*i);
+      }
+    }
+
+    CallSite NewCS;
+    if (InvokeInst *II = dyn_cast<InvokeInst>(CS.getInstruction())) {
+      NewCS = IRB.CreateInvoke(Func, II->getNormalDest(), II->getUnwindDest(),
+                               Args);
+    } else {
+      NewCS = IRB.CreateCall(Func, Args);
+    }
+    NewCS.setCallingConv(CS.getCallingConv());
+    NewCS.setAttributes(CS.getAttributes().removeAttributes(
+        *DFSF.DFS.Ctx, AttributeSet::ReturnIndex,
+        AttributeFuncs::typeIncompatible(NewCS.getInstruction()->getType(),
+                                         AttributeSet::ReturnIndex)));
+
+    if (Next) {
+      ExtractValueInst *ExVal =
+          ExtractValueInst::Create(NewCS.getInstruction(), 0, "", Next);
+      DFSF.SkipInsts.insert(ExVal);
+      ExtractValueInst *ExShadow =
+          ExtractValueInst::Create(NewCS.getInstruction(), 1, "", Next);
+      DFSF.SkipInsts.insert(ExShadow);
+      DFSF.setShadow(ExVal, ExShadow);
+
+      CS.getInstruction()->replaceAllUsesWith(ExVal);
+    }
+
+    CS.getInstruction()->eraseFromParent();
+  }
+}
+
+void DFSanVisitor::visitPHINode(PHINode &PN) {
+  PHINode *ShadowPN =
+      PHINode::Create(DFSF.DFS.ShadowTy, PN.getNumIncomingValues(), "", &PN);
+
+  // Give the shadow phi node valid predecessors to fool SplitEdge into working.
+  Value *UndefShadow = UndefValue::get(DFSF.DFS.ShadowTy);
+  for (PHINode::block_iterator i = PN.block_begin(), e = PN.block_end(); i != e;
+       ++i) {
+    ShadowPN->addIncoming(UndefShadow, *i);
+  }
+
+  DFSF.PHIFixups.push_back(std::make_pair(&PN, ShadowPN));
+  DFSF.setShadow(&PN, ShadowPN);
+}
diff --git a/lib/Transforms/Instrumentation/Instrumentation.cpp b/lib/Transforms/Instrumentation/Instrumentation.cpp
index 9f353967f3..94f7901fb9 100644
--- a/lib/Transforms/Instrumentation/Instrumentation.cpp
+++ b/lib/Transforms/Instrumentation/Instrumentation.cpp
@@ -30,6 +30,7 @@ void llvm::initializeInstrumentation(PassRegistry &Registry) {
   initializePathProfilerPass(Registry);
   initializeMemorySanitizerPass(Registry);
   initializeThreadSanitizerPass(Registry);
+  initializeDataFlowSanitizerPass(Registry);
 }
 
 /// LLVMInitializeInstrumentation - C binding for