Index: include/llvm/InitializePasses.h
===================================================================
--- include/llvm/InitializePasses.h
+++ include/llvm/InitializePasses.h
@@ -109,6 +109,7 @@
 void initializeDataFlowSanitizerPass(PassRegistry&);
 void initializeDeadInstEliminationPass(PassRegistry&);
 void initializeDeadMachineInstructionElimPass(PassRegistry&);
+void initializeDebugIRPass(PassRegistry&);
 void initializeDelinearizationPass(PassRegistry&);
 void initializeDemandedBitsWrapperPassPass(PassRegistry&);
 void initializeDependenceAnalysisPass(PassRegistry&);
Index: include/llvm/LinkAllPasses.h
===================================================================
--- include/llvm/LinkAllPasses.h
+++ include/llvm/LinkAllPasses.h
@@ -44,6 +44,7 @@
 #include "llvm/Transforms/IPO/FunctionAttrs.h"
 #include "llvm/Transforms/Instrumentation.h"
 #include "llvm/Transforms/Instrumentation/BoundsChecking.h"
+#include "llvm/Transforms/DebugIR.h"
 #include "llvm/Transforms/ObjCARC.h"
 #include "llvm/Transforms/Scalar.h"
 #include "llvm/Transforms/Scalar/GVN.h"
@@ -84,6 +85,7 @@
       (void) llvm::createConstantMergePass();
       (void) llvm::createConstantPropagationPass();
       (void) llvm::createCostModelAnalysisPass();
+      (void) llvm::createDebugIRPass();
       (void) llvm::createDeadArgEliminationPass();
       (void) llvm::createDeadCodeEliminationPass();
       (void) llvm::createDeadInstEliminationPass();
Index: include/llvm/Transforms/DebugIR.h
===================================================================
--- /dev/null
+++ include/llvm/Transforms/DebugIR.h
@@ -0,0 +1,103 @@
+//===- llvm/Transforms/Instrumentation/DebugIR.h - Interface ----*- C++ -*-===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// This file defines the interface of the DebugIR pass. For most users,
+// including Instrumentation.h and calling createDebugIRPass() is sufficient and
+// there is no need to include this file.
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_LIB_TRANSFORMS_INSTRUMENTATION_DEBUGIR_H
+#define LLVM_LIB_TRANSFORMS_INSTRUMENTATION_DEBUGIR_H
+
+#include "llvm/Pass.h"
+
+namespace llvm {
+
+class DebugIR : public llvm::ModulePass {
+  /// If true, write a source file to disk.
+  bool WriteSourceToDisk;
+
+  /// Hide certain (non-essential) debug information (only relevant if
+  /// createSource is true.
+  bool HideDebugIntrinsics;
+  bool HideDebugMetadata;
+
+  /// The location of the source file.
+  std::string Directory;
+  std::string Filename;
+
+  /// True if a temporary file name was generated.
+  bool GeneratedPath;
+
+  /// True if the file name was read from the Module.
+  bool ParsedPath;
+
+public:
+  static char ID;
+
+  StringRef getPassName() const override { return "DebugIR"; }
+
+  /// Generate a file on disk to be displayed in a debugger. If Filename and
+  /// Directory are empty, a temporary path will be generated.
+  DebugIR(bool HideDebugIntrinsics, bool HideDebugMetadata,
+          llvm::StringRef Directory, llvm::StringRef Filename);
+//      : ModulePass(ID), WriteSourceToDisk(true),
+//        HideDebugIntrinsics(HideDebugIntrinsics),
+//        HideDebugMetadata(HideDebugMetadata), Directory(Directory),
+//        Filename(Filename), GeneratedPath(false), ParsedPath(false) {}
+
+  /// Modify input in-place; do not generate additional files, and do not hide
+  /// any debug intrinsics/metadata that might be present.
+  DebugIR();
+      //: ModulePass(ID), WriteSourceToDisk(false), HideDebugIntrinsics(false),
+      //  HideDebugMetadata(false), GeneratedPath(false), ParsedPath(false) {}
+
+  /// Run pass on M and set Path to the source file path in the output module.
+  bool runOnModule(llvm::Module &M, std::string &Path);
+  bool runOnModule(llvm::Module &M) override;
+
+private:
+
+  /// Returns the concatenated Directory + Filename, without error checking
+  std::string getPath();
+
+  /// Attempts to read source information from debug information in M, and if
+  /// that fails, from M's identifier. Returns true on success, false otherwise.
+  bool getSourceInfo(const llvm::Module &M);
+
+  /// Replace the extension of Filename with NewExtension, and return true if
+  /// successful. Return false if extension could not be found or Filename is
+  /// empty.
+  bool updateExtension(llvm::StringRef NewExtension);
+
+  /// Generate a temporary filename and open an fd
+  void generateFilename(std::unique_ptr<int> &fd);
+
+  /// Creates DWARF CU/Subroutine metadata
+  void createDebugInfo(llvm::Module &M,
+                       std::unique_ptr<llvm::Module> &DisplayM);
+
+  /// Returns true if either Directory or Filename is missing, false otherwise.
+  bool isMissingPath();
+
+  /// Write M to disk, optionally passing in an fd to an open file which is
+  /// closed by this function after writing. If no fd is specified, a new file
+  /// is opened, written, and closed.
+  void writeDebugBitcode(const llvm::Module *M, int *fd = nullptr);
+};
+
+ModulePass *createDebugIRPass(bool HideDebugIntrinsics,
+                                    bool HideDebugMetadata, StringRef Directory,
+                                    StringRef Filename);
+
+ModulePass *createDebugIRPass();
+} // llvm namespace
+
+#endif
Index: lib/Transforms/Instrumentation/CMakeLists.txt
===================================================================
--- lib/Transforms/Instrumentation/CMakeLists.txt
+++ lib/Transforms/Instrumentation/CMakeLists.txt
@@ -12,6 +12,7 @@
   SanitizerCoverage.cpp
   ThreadSanitizer.cpp
   EfficiencySanitizer.cpp
+  DebugIR.cpp
 
   ADDITIONAL_HEADER_DIRS
   ${LLVM_MAIN_INCLUDE_DIR}/llvm/Transforms
Index: lib/Transforms/Instrumentation/DebugIR.cpp
===================================================================
--- /dev/null
+++ lib/Transforms/Instrumentation/DebugIR.cpp
@@ -0,0 +1,697 @@
+//===--- DebugIR.cpp - Transform debug metadata to allow debugging IR -----===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// A Module transform pass that emits a succinct version of the IR and replaces
+// the source file metadata to allow debuggers to step through the IR.
+//
+// FIXME: instead of replacing debug metadata, this pass should allow for
+// additional metadata to be used to point capable debuggers to the IR file
+// without destroying the mapping to the original source file.
+//
+//===----------------------------------------------------------------------===//
+
+#include "llvm/Transforms/DebugIR.h"
+#include "llvm/IR/AssemblyAnnotationWriter.h"
+#include "llvm/IR/DIBuilder.h"
+#include "llvm/IR/DataLayout.h"
+#include "llvm/IR/DebugInfo.h"
+#include "llvm/IR/InstVisitor.h"
+#include "llvm/IR/Instruction.h"
+#include "llvm/IR/LLVMContext.h"
+#include "llvm/IR/Module.h"
+#include "llvm/IR/ValueMap.h"
+#include "llvm/Support/Debug.h"
+#include "llvm/Support/FileSystem.h"
+#include "llvm/Support/FormattedStream.h"
+#include "llvm/Support/Path.h"
+#include "llvm/Support/ToolOutputFile.h"
+#include "llvm/Transforms/Instrumentation.h"
+#include "llvm/Transforms/Utils/Cloning.h"
+#include <string>
+
+#define STR_HELPER(x) #x
+#define STR(x) STR_HELPER(x)
+
+using namespace llvm;
+
+#define DEBUG_TYPE "debug-ir"
+
+namespace {
+
+/// Builds a map of Value* to line numbers on which the Value appears in a
+/// textual representation of the IR by plugging into the AssemblyWriter by
+/// masquerading as an AssemblyAnnotationWriter.
+class ValueToLineMap : public AssemblyAnnotationWriter {
+  ValueMap<const Value *, unsigned int> Lines;
+  typedef ValueMap<const Value *, unsigned int>::const_iterator LineIter;
+
+  void addEntry(const Value *V, formatted_raw_ostream &Out) {
+    Out.flush();
+    Lines.insert(std::make_pair(V, Out.getLine() + 1));
+  }
+
+public:
+  /// Prints Module to a null buffer in order to build the map of Value pointers
+  /// to line numbers.
+  ValueToLineMap(const Module *M) {
+    raw_null_ostream ThrowAway;
+    M->print(ThrowAway, this);
+  }
+
+  // This function is called after an Instruction, GlobalValue, or GlobalAlias
+  // is printed.
+  void printInfoComment(const Value &V, formatted_raw_ostream &Out) override {
+    addEntry(&V, Out);
+  }
+
+  void emitFunctionAnnot(const Function *F,
+                         formatted_raw_ostream &Out) override {
+    addEntry(F, Out);
+  }
+
+  /// If V appears on a line in the textual IR representation, sets Line to the
+  /// line number and returns true, otherwise returns false.
+  bool getLine(const Value *V, unsigned int &Line) const {
+    LineIter i = Lines.find(V);
+    if (i != Lines.end()) {
+      Line = i->second;
+      return true;
+    }
+    return false;
+  }
+};
+
+/// Removes debug intrisncs like llvm.dbg.declare and llvm.dbg.value.
+class DebugIntrinsicsRemover : public InstVisitor<DebugIntrinsicsRemover> {
+  void remove(Instruction &I) { I.eraseFromParent(); }
+
+public:
+  static void process(Module &M) {
+
+    DebugIntrinsicsRemover Remover;
+    Remover.visit(&M);
+  }
+  void visitDbgDeclareInst(DbgDeclareInst &I) { remove(I); }
+  void visitDbgValueInst(DbgValueInst &I) { remove(I); }
+  void visitDbgInfoIntrinsic(DbgInfoIntrinsic &I) { remove(I); }
+};
+
+/// Removes debug metadata (!dbg) nodes from all instructions, and optionally
+/// metadata named "llvm.dbg.cu" if RemoveNamedInfo is true.
+class DebugMetadataRemover : public InstVisitor<DebugMetadataRemover> {
+  bool RemoveNamedInfo;
+
+public:
+  static void process(Module &M, bool RemoveNamedInfo = true) {
+    if (NamedMDNode *ModuleFlags = M.getModuleFlagsMetadata()) {
+      SmallVector<MDNode *, 4> NewModuleFlags;
+
+      for (unsigned i = 0; i < ModuleFlags->getNumOperands(); i++) {
+        MDNode *Node = ModuleFlags->getOperand(i);
+        // is this assumption correct?
+        MDString *Name = cast<MDString>(Node->getOperand(1));
+
+        // we do not want to keep the `Debug Info Version` node.
+        if (Name->getString() == "Debug Info Version")
+          continue;
+        NewModuleFlags.push_back(Node);
+      }
+      ModuleFlags->clearOperands();
+      for (MDNode *M : NewModuleFlags) {
+        ModuleFlags->addOperand(M);
+      }
+    }
+
+    DebugMetadataRemover Remover(RemoveNamedInfo);
+    Remover.run(&M);
+  }
+
+  DebugMetadataRemover(bool RemoveNamedInfo)
+      : RemoveNamedInfo(RemoveNamedInfo) {}
+
+  void visitInstruction(Instruction &I) {
+    if (I.getMetadata(LLVMContext::MD_dbg))
+      I.setMetadata(LLVMContext::MD_dbg, nullptr);
+  }
+
+  void run(Module *M) {
+    // Remove debug metadata attached to instructions
+    visit(M);
+
+    if (RemoveNamedInfo) {
+      // Remove CU named metadata (and all children nodes)
+      NamedMDNode *Node = M->getNamedMetadata("llvm.dbg.cu");
+      if (Node)
+        M->eraseNamedMetadata(Node);
+    }
+  }
+};
+
+/// Updates debug metadata in a Module:
+///   - changes Filename/Directory to values provided on construction
+///   - adds/updates line number (DebugLoc) entries associated with each
+///     instruction to reflect the instruction's location in an LLVM IR file
+class DIUpdater : public InstVisitor<DIUpdater> {
+  /// Builder of debug information
+  DIBuilder Builder;
+
+  /// Helper for type attributes/sizes/etc
+  DataLayout Layout;
+
+  /// Map of Value* to line numbers
+  const ValueToLineMap LineTable;
+
+  /// Map of Value* (in original Module) to Value* (in optional cloned Module)
+  const ValueToValueMapTy *VMap;
+
+  /// Directory of debug metadata
+  DebugInfoFinder Finder;
+
+  /// Source filename and directory
+  StringRef Filename;
+  StringRef Directory;
+
+  // CU nodes needed when creating DI subprograms
+  DIFile *FileNode;
+  DILexicalBlockFile *LexicalBlockFileNode;
+
+  Module &M;
+
+  // CU nodes needed when creating DI subprograms
+  // DIFile *File;
+  // DIScope *Scope;
+
+  ValueMap<const Function *, DISubprogram *> SubprogramDescriptors;
+  DenseMap<const Type *, DIType *> TypeDescriptors;
+
+public:
+  DIUpdater(Module &M, StringRef Filename = StringRef(),
+            StringRef Directory = StringRef(), const Module *DisplayM = nullptr,
+            const ValueToValueMapTy *VMap = nullptr)
+      : Builder(M), Layout(&M), LineTable(DisplayM ? DisplayM : &M), VMap(VMap),
+        Finder(), Filename(Filename), Directory(Directory), FileNode(nullptr),
+        LexicalBlockFileNode(nullptr), M(M) {
+
+    // Even without finder, this screws up.
+    Finder.processModule(M);
+    visit(&M);
+  }
+
+  ~DIUpdater() { Builder.finalize(); }
+
+  void visitModule(Module &M) {
+    if (Finder.compile_unit_count() > 1)
+      report_fatal_error("DebugIR pass supports only a signle compile unit per "
+                         "Module.");
+    createCompileUnit(Finder.compile_unit_count() == 1
+                          ? (DICompileUnit *)*Finder.compile_units().begin()
+                          : nullptr);
+  }
+
+  void visitFunction(Function &F) {
+    if (F.isDeclaration() || findDISubprogram(&F))
+      return;
+
+    StringRef MangledName = F.getName();
+    DISubroutineType *Sig = createFunctionSignature(&F);
+
+    // find line of function declaration
+    unsigned Line = 0;
+    if (!findLine(&F, Line)) {
+      DEBUG(dbgs() << "WARNING: No line for Function " << F.getName().str()
+                   << "\n");
+      return;
+    }
+
+    Instruction *FirstInst = &*F.begin()->begin();
+    unsigned ScopeLine = 0;
+    if (!findLine(FirstInst, ScopeLine)) {
+      DEBUG(dbgs() << "WARNING: No line for 1st Instruction in Function "
+                   << F.getName().str() << "\n");
+      return;
+    }
+
+    bool Local = F.hasInternalLinkage();
+    bool IsDefinition = !F.isDeclaration();
+    bool IsOptimized = false;
+
+    DINode::DIFlags FuncFlags = llvm::DINode::FlagPrototyped;
+    DISubprogram *Sub = Builder.createFunction(
+        /*LexicalBlockFileNode*/ FileNode, F.getName(), MangledName, FileNode,
+        Line, Sig, /*InternalLinkage=*/Local, /*definition */ IsDefinition,
+        ScopeLine, FuncFlags, IsOptimized);
+    F.setSubprogram(Sub);
+    DEBUG(dbgs() << "create subprogram mdnode " << *Sub << ": "
+                 << "\n");
+
+    SubprogramDescriptors.insert(std::make_pair(&F, Sub));
+  }
+
+  void visitInstruction(Instruction &I) {
+    DebugLoc Loc(I.getDebugLoc());
+
+    /// If a ValueToValueMap is provided, use it to get the real instruction as
+    /// the line table was generated on a clone of the module on which we are
+    /// operating.
+    Value *RealInst = nullptr;
+    if (VMap)
+      RealInst = VMap->lookup(&I);
+
+    if (!RealInst)
+      RealInst = &I;
+
+    unsigned Col = 0; // FIXME: support columns
+    unsigned Line;
+    if (!LineTable.getLine(RealInst, Line)) {
+      // Instruction has no line, it may have been removed (in the module that
+      // will be passed to the debugger) so there is nothing to do here.
+      DEBUG(dbgs() << "WARNING: no LineTable entry for instruction " << RealInst
+                   << "\n");
+      DEBUG(RealInst->dump());
+      return;
+    }
+
+    DebugLoc NewLoc;
+    if (Loc) {
+      // I had a previous debug location: re-use the DebugLoc
+      NewLoc = DebugLoc::get(Line, Col,
+                             // Loc.getScope(RealInst->getContext()),
+                             Loc.getScope(),
+                             // Loc.getInlinedAt(RealInst->getContext()));
+                             Loc.getInlinedAt());
+    } else if (DINode *scope = findScope(&I)) {
+      NewLoc = DebugLoc::get(Line, Col, scope, nullptr);
+    } else {
+      DEBUG(dbgs() << "WARNING: no valid scope for instruction " << &I
+                   << ". no DebugLoc will be present."
+                   << "\n");
+      return;
+    }
+
+    addDebugLocation(I, NewLoc);
+  }
+
+private:
+  void createCompileUnit(DICompileUnit *CUToReplace) {
+    std::string Flags;
+    bool IsOptimized = false;
+    StringRef Producer;
+    unsigned RuntimeVersion(0);
+    StringRef SplitName;
+
+    if (CUToReplace) {
+      // save fields from existing CU to re-use in the new CU
+      // unique_ptr<DICompileUnit> ExistingCU = CUToReplace->clone();
+      Producer = CUToReplace->getProducer();
+      IsOptimized = CUToReplace->isOptimized();
+      Flags = CUToReplace->getFlags();
+      RuntimeVersion = CUToReplace->getRuntimeVersion();
+      SplitName = CUToReplace->getSplitDebugFilename();
+    } else {
+      Producer =
+          "LLVM Version " STR(LLVM_VERSION_MAJOR) "." STR(LLVM_VERSION_MINOR);
+    }
+
+    FileNode = Builder.createFile(Filename, Directory);
+    DICompileUnit *CU =
+        Builder.createCompileUnit(dwarf::DW_LANG_C99, FileNode, Producer,
+                                  IsOptimized, Flags, RuntimeVersion);
+
+    NamedMDNode *NMD = M.getOrInsertNamedMetadata("llvm.dbg.cu");
+    NMD->clearOperands();
+    NMD->addOperand(CU);
+
+    // if (CUToReplace) {
+    //    errs() << "CUToReplace: " << *CUToReplace << "\n";
+    //    errs() << "CU: " << *CU << "\n";
+    //  // CUToReplace->replaceAllUsesWith(CU);
+    //};
+
+    // LexicalBlockFileNode = FileNode; // Builder.createLexicalBlockFile(CU,
+    // FileNode);
+  }
+
+  /// Returns the MDNode* that represents the DI scope to associate with I
+  DIScope *findScope(const Instruction *I) {
+    const Function *F = I->getParent()->getParent();
+    if (DISubprogram *ret = findDISubprogram(F))
+      return ret;
+
+    DEBUG(dbgs() << "WARNING: Using fallback lexical block file scope "
+                 << LexicalBlockFileNode << " as scope for instruction " << I
+                 << "\n");
+    return LexicalBlockFileNode;
+  }
+
+  /// Returns the MDNode* that is the descriptor for F
+  DISubprogram *findDISubprogram(const Function *F) {
+    typedef ValueMap<const Function *, DISubprogram *>::const_iterator
+        FuncNodeIter;
+    FuncNodeIter i = SubprogramDescriptors.find(F);
+    if (i != SubprogramDescriptors.end())
+      return i->second;
+
+    DEBUG(dbgs() << "searching for DI scope node for Function " << F
+                 << " in a list of " << Finder.subprogram_count()
+                 << " subprogram nodes"
+                 << "\n");
+
+    // TODO: When would this even be reached?
+    for (DISubprogram *S : Finder.subprograms()) {
+      // TODO: Is describes correct?
+      if (S->describes(F)) {
+        DEBUG(dbgs() << "Found DISubprogram " << S << " for function "
+                     << F->getName() << "\n");
+        return S;
+      }
+    }
+    DEBUG(dbgs() << "unable to find DISubprogram node for function "
+                 << F->getName().str() << "\n");
+    return nullptr;
+  }
+
+  /// Sets Line to the line number on which V appears and returns true. If a
+  /// line location for V is not found, returns false.
+  bool findLine(const Value *V, unsigned &Line) {
+    if (LineTable.getLine(V, Line))
+      return true;
+
+    if (VMap) {
+      Value *mapped = VMap->lookup(V);
+      if (mapped && LineTable.getLine(mapped, Line))
+        return true;
+    }
+    return false;
+  }
+
+  std::string getTypeName(Type *T) {
+    std::string TypeName;
+    raw_string_ostream TypeStream(TypeName);
+    if (T)
+      T->print(TypeStream);
+    else
+      TypeStream << "Printing <null> Type";
+    TypeStream.flush();
+    return TypeName;
+  }
+
+  /// Returns the MDNode that represents type T if it is already created, or 0
+  /// if it is not.
+  DIType *getType(const Type *T) {
+    typedef DenseMap<const Type *, DIType *>::const_iterator TypeNodeIter;
+    TypeNodeIter i = TypeDescriptors.find(T);
+    if (i != TypeDescriptors.end())
+      return i->second;
+    return nullptr;
+  }
+
+  /// Returns a DebugInfo type from an LLVM type T.
+  DIType *getOrCreateType(Type *T) {
+    DIType *N = getType(T);
+    if (N)
+      return N;
+    else if (T->isVoidTy())
+      return Builder.createUnspecifiedType("void");
+    else if (T->isStructTy()) {
+      // NOTE: where does DINodeArray come from?
+      DICompositeType *S = Builder.createStructType(
+          LexicalBlockFileNode, T->getStructName(), FileNode,
+          /*LineNumber=*/0, Layout.getTypeSizeInBits(T),
+          Layout.getABITypeAlignment(T), /*DIFlags=*/llvm::DINode::FlagZero,
+          /*DerivedFrom=*/nullptr, llvm::DINodeArray()); // filled in later
+      N = S; // the Node _is_ the struct type.
+
+      // N is added to the map (early) so that element search below can find it,
+      // so as to avoid infinite recursion for structs that contain pointers to
+      // their own type.
+      TypeDescriptors[T] = N;
+
+      SmallVector<Metadata *, 4>
+          Elements; // unfortunately, SmallVector<Type *> does not decay to
+                    // SmallVector<Metadata *>
+
+      for (unsigned i = 0; i < T->getStructNumElements(); ++i)
+        Elements.push_back(getOrCreateType(T->getStructElementType(i)));
+
+      Builder.replaceArrays(S, Builder.getOrCreateArray(Elements));
+    } else if (T->isPointerTy()) {
+      Type *PointeeTy = T->getPointerElementType();
+      if (!(N = getType(PointeeTy)))
+        N = Builder.createPointerType(
+            getOrCreateType(PointeeTy), Layout.getPointerTypeSizeInBits(T),
+            Layout.getPrefTypeAlignment(T), /*DWARFAddressSpace=*/None,
+            getTypeName(T));
+    } else if (T->isArrayTy()) {
+      // assert(false && "unimplemented arrayty lowering.");
+      SmallVector<Metadata *, 4>
+          Subscripts; // unfortunately, SmallVector<Type *> does not decay to
+                      // SmallVector<Metadata *>
+
+      Subscripts.push_back(
+          Builder.getOrCreateSubrange(0, T->getArrayNumElements() - 1));
+
+      N = Builder.createArrayType(Layout.getTypeSizeInBits(T),
+                                  Layout.getPrefTypeAlignment(T),
+                                  getOrCreateType(T->getArrayElementType()),
+                                  Builder.getOrCreateArray(Subscripts));
+    } else {
+      // assert(false && "unimplemented lowering for other types.");
+      int encoding = llvm::dwarf::DW_ATE_signed;
+      if (T->isIntegerTy())
+        encoding = llvm::dwarf::DW_ATE_unsigned;
+      else if (T->isFloatingPointTy())
+        encoding = llvm::dwarf::DW_ATE_float;
+
+      N = Builder.createBasicType(getTypeName(T), T->getPrimitiveSizeInBits(),
+                                  encoding);
+    }
+    TypeDescriptors[T] = N;
+    return N;
+  }
+
+  /// Returns a DebugInfo type that represents a function signature for Func.
+  DISubroutineType *createFunctionSignature(const Function *Func) {
+    SmallVector<Metadata *, 4> Params; // SmallVector<DIType *> does not
+                                       // auto-case to SmallVector<Metadata *>
+    DIType *ReturnType = getOrCreateType(Func->getReturnType());
+    Params.push_back(ReturnType);
+
+    for (const Argument &Arg : Func->args()) {
+      Type *T = Arg.getType();
+      Params.push_back(getOrCreateType(T));
+    }
+
+    DITypeRefArray ParamArray = Builder.getOrCreateTypeArray(Params);
+    return Builder.createSubroutineType(ParamArray);
+  }
+
+  /// Associates Instruction I with debug location Loc.
+  void addDebugLocation(Instruction &I, DebugLoc Loc) {
+    I.setDebugLoc(Loc);
+    // MDNode *MD = Loc.getAsMDNode();
+    // I.setMetadata(LLVMContext::MD_dbg, MD);
+  }
+};
+
+/// Sets Filename/Directory from the Module identifier and returns true, or
+/// false if source information is not present.
+bool getSourceInfoFromModule(const Module &M, std::string &Directory,
+                             std::string &Filename) {
+  std::string PathStr(M.getModuleIdentifier());
+  if (PathStr.length() == 0 || PathStr == "<stdin>")
+    return false;
+
+  Filename = sys::path::filename(PathStr);
+  SmallVector<char, 16> Path(PathStr.begin(), PathStr.end());
+  sys::path::remove_filename(Path);
+  Directory = StringRef(Path.data(), Path.size());
+  return true;
+}
+
+// Sets Filename/Directory from debug information in M and returns true, or
+// false if no debug information available, or cannot be parsed.
+bool getSourceInfoFromDI(const Module &M, std::string &Directory,
+                         std::string &Filename) {
+  NamedMDNode *CUNode = M.getNamedMetadata("llvm.dbg.cu");
+  if (!CUNode || CUNode->getNumOperands() == 0)
+    return false;
+
+  DICompileUnit *CU = cast<DICompileUnit>(CUNode->getOperand(0));
+
+  // Verify no longer exists?
+  // if (!CU->Verify())
+  //  return false;
+
+  Filename = CU->getFilename();
+  Directory = CU->getDirectory();
+  return true;
+}
+
+} // anonymous namespace
+
+namespace llvm {
+
+DebugIR::DebugIR(bool HideDebugIntrinsics, bool HideDebugMetadata,
+                 llvm::StringRef Directory, llvm::StringRef Filename)
+    : ModulePass(ID), WriteSourceToDisk(true),
+      HideDebugIntrinsics(HideDebugIntrinsics),
+      HideDebugMetadata(HideDebugMetadata), Directory(Directory),
+      Filename(Filename), GeneratedPath(false), ParsedPath(false) {
+  llvm::initializeDebugIRPass(*PassRegistry::getPassRegistry());
+}
+
+/// Modify input in-place; do not generate additional files, and do not hide
+/// any debug intrinsics/metadata that might be present.
+DebugIR::DebugIR()
+    : ModulePass(ID), WriteSourceToDisk(false), HideDebugIntrinsics(false),
+      HideDebugMetadata(false), GeneratedPath(false), ParsedPath(false) {
+  llvm::initializeDebugIRPass(*PassRegistry::getPassRegistry());
+}
+
+bool DebugIR::getSourceInfo(const Module &M) {
+  ParsedPath = getSourceInfoFromDI(M, Directory, Filename) ||
+               getSourceInfoFromModule(M, Directory, Filename);
+  return ParsedPath;
+}
+
+bool DebugIR::updateExtension(StringRef NewExtension) {
+  size_t dot = Filename.find_last_of(".");
+  if (dot == std::string::npos)
+    return false;
+
+  Filename.erase(dot);
+  Filename += NewExtension.str();
+  return true;
+}
+
+void DebugIR::generateFilename(std::unique_ptr<int> &fd) {
+  SmallVector<char, 16> PathVec;
+  fd.reset(new int);
+  sys::fs::createTemporaryFile("debug-ir", "ll", *fd, PathVec);
+  StringRef Path(PathVec.data(), PathVec.size());
+  Filename = sys::path::filename(Path);
+  sys::path::remove_filename(PathVec);
+  Directory = StringRef(PathVec.data(), PathVec.size());
+
+  GeneratedPath = true;
+}
+
+std::string DebugIR::getPath() {
+  SmallVector<char, 16> Path;
+  sys::path::append(Path, Directory, Filename);
+  Path.resize(Filename.size() + Directory.size() + 2);
+  Path[Filename.size() + Directory.size() + 1] = '\0';
+  return std::string(Path.data());
+}
+
+void DebugIR::writeDebugBitcode(const Module *M, int *fd) {
+  std::unique_ptr<raw_fd_ostream> Out;
+  std::error_code EC;
+
+  if (!fd) {
+    std::string Path = getPath();
+    Out.reset(new raw_fd_ostream(Path, EC, sys::fs::F_Text));
+    DEBUG(dbgs() << "WRITING debug bitcode from Module " << M << " to file "
+                 << Path << "\n");
+  } else {
+    DEBUG(dbgs() << "WRITING debug bitcode from Module " << M << " to fd "
+                 << *fd << "\n");
+    Out.reset(new raw_fd_ostream(*fd, true));
+  }
+
+  M->print(*Out, nullptr);
+  Out->close();
+}
+
+void DebugIR::createDebugInfo(Module &M, std::unique_ptr<Module> &DisplayM) {
+  if (M.getFunctionList().size() == 0)
+    // no functions -- no debug info needed
+    return;
+
+  std::unique_ptr<ValueToValueMapTy> VMap;
+
+  if (WriteSourceToDisk && (HideDebugIntrinsics || HideDebugMetadata)) {
+    VMap.reset(new ValueToValueMapTy);
+    DisplayM = CloneModule(&M, *VMap);
+
+    if (HideDebugIntrinsics)
+      DebugIntrinsicsRemover::process(*DisplayM);
+
+    if (HideDebugMetadata)
+      DebugMetadataRemover::process(*DisplayM);
+  }
+
+  DIUpdater R(M, Filename, Directory, DisplayM.get(), VMap.get());
+}
+
+bool DebugIR::isMissingPath() { return Filename.empty() || Directory.empty(); }
+
+bool DebugIR::runOnModule(Module &M) {
+  std::unique_ptr<int> fd;
+
+  if (isMissingPath() && !getSourceInfo(M)) {
+    if (!WriteSourceToDisk) {
+      errs() << "DebugIR unable to determine file name in input. "
+                "Ensure Module contains an identifier, a valid "
+                "DICompileUnit, or construct DebugIR with "
+                "non-empty Filename/Directory parameters.";
+      return false;
+
+    } else {
+      generateFilename(fd);
+    }
+  }
+
+  // assert(Filename != "");
+  // assert(Directory != "");
+
+  if (!GeneratedPath && WriteSourceToDisk)
+    updateExtension(".debug-ll");
+
+  DEBUG(dbgs() << "- Filename: " << Filename << " | Directory: " << Directory
+               << "\n");
+
+  // Clear line numbers. Keep debug info (if any) if we were able to read the
+  // file name from the DICompileUnit descriptor.
+  DebugMetadataRemover::process(M, !ParsedPath);
+
+  // Add the current debug info version into the module.
+  M.addModuleFlag(Module::Warning, "Debug Info Version",
+                  DEBUG_METADATA_VERSION);
+
+  std::unique_ptr<Module> DisplayM;
+  createDebugInfo(M, DisplayM) if (WriteSourceToDisk) {
+    Module *OutputM = DisplayM.get() ? DisplayM.get() : &M;
+    writeDebugBitcode(OutputM, fd.get());
+  }
+
+  return true;
+}
+
+bool DebugIR::runOnModule(Module &M, std::string &Path) {
+  bool result = runOnModule(M);
+  Path = getPath();
+  return result;
+}
+
+char DebugIR::ID = 0;
+
+} // namespace llvm
+
+INITIALIZE_PASS_BEGIN(DebugIR, "debugir", "Enable debugging IR", false, false)
+INITIALIZE_PASS_END(DebugIR, "debugir", "Enable debugging IR", false, false)
+
+ModulePass *llvm::createDebugIRPass(bool HideDebugIntrinsics,
+                                    bool HideDebugMetadata, StringRef Directory,
+                                    StringRef Filename) {
+  return new DebugIR(HideDebugIntrinsics, HideDebugMetadata, Directory,
+                     Filename);
+}
+
+ModulePass *llvm::createDebugIRPass() { return new DebugIR(); }
Index: lib/Transforms/Instrumentation/Instrumentation.cpp
===================================================================
--- lib/Transforms/Instrumentation/Instrumentation.cpp
+++ lib/Transforms/Instrumentation/Instrumentation.cpp
@@ -59,6 +59,7 @@
   initializeAddressSanitizerPass(Registry);
   initializeAddressSanitizerModulePass(Registry);
   initializeBoundsCheckingLegacyPassPass(Registry);
+  initializeDebugIRPass(Registry);
   initializeGCOVProfilerLegacyPassPass(Registry);
   initializePGOInstrumentationGenLegacyPassPass(Registry);
   initializePGOInstrumentationUseLegacyPassPass(Registry);