diff --git a/llvm/include/llvm/CodeGen/MIRParser/MIRParser.h b/llvm/include/llvm/CodeGen/MIRParser/MIRParser.h
index dd0780397f42..b631a8c0122a 100644
--- a/llvm/include/llvm/CodeGen/MIRParser/MIRParser.h
+++ b/llvm/include/llvm/CodeGen/MIRParser/MIRParser.h
@@ -18,7 +18,6 @@
 #ifndef LLVM_CODEGEN_MIRPARSER_MIRPARSER_H
 #define LLVM_CODEGEN_MIRPARSER_MIRPARSER_H
 
-#include "llvm/CodeGen/MachineFunctionInitializer.h"
 #include "llvm/IR/Module.h"
 #include "llvm/Support/MemoryBuffer.h"
 #include <memory>
@@ -27,29 +26,30 @@ namespace llvm {
 
 class StringRef;
 class MIRParserImpl;
+class MachineModuleInfo;
 class SMDiagnostic;
 
 /// This class initializes machine functions by applying the state loaded from
 /// a MIR file.
-class MIRParser : public MachineFunctionInitializer {
+class MIRParser {
   std::unique_ptr<MIRParserImpl> Impl;
 
 public:
   MIRParser(std::unique_ptr<MIRParserImpl> Impl);
   MIRParser(const MIRParser &) = delete;
-  ~MIRParser() override;
+  ~MIRParser();
 
-  /// Parse the optional LLVM IR module that's embedded in the MIR file.
+  /// Parses the optional LLVM IR module in the MIR file.
   ///
   /// A new, empty module is created if the LLVM IR isn't present.
-  /// Returns null if a parsing error occurred.
-  std::unique_ptr<Module> parseLLVMModule();
+  /// \returns nullptr if a parsing error occurred.
+  std::unique_ptr<Module> parseIRModule();
 
-  /// Initialize the machine function to the state that's described in the MIR
-  /// file.
+  /// \brief Parses MachineFunctions in the MIR file and add them to the given
+  /// MachineModuleInfo \p MMI.
   ///
-  /// Return true if error occurred.
-  bool initializeMachineFunction(MachineFunction &MF) override;
+  /// \returns true if an error occurred.
+  bool parseMachineFunctions(Module &M, MachineModuleInfo &MMI);
 };
 
 /// This function is the main interface to the MIR serialization format parser.
diff --git a/llvm/include/llvm/CodeGen/MachineFunctionInitializer.h b/llvm/include/llvm/CodeGen/MachineFunctionInitializer.h
deleted file mode 100644
index 0fbcb480b1ab..000000000000
--- a/llvm/include/llvm/CodeGen/MachineFunctionInitializer.h
+++ /dev/null
@@ -1,38 +0,0 @@
-//=- MachineFunctionInitializer.h - machine function initializer --*- C++ -*-=//
-//
-//                     The LLVM Compiler Infrastructure
-//
-// This file is distributed under the University of Illinois Open Source
-// License. See LICENSE.TXT for details.
-//
-//===----------------------------------------------------------------------===//
-//
-// This file declares an interface that allows custom machine function
-// initialization.
-//
-//===----------------------------------------------------------------------===//
-
-#ifndef LLVM_CODEGEN_MACHINEFUNCTIONINITIALIZER_H
-#define LLVM_CODEGEN_MACHINEFUNCTIONINITIALIZER_H
-
-namespace llvm {
-
-class MachineFunction;
-
-/// This interface provides a way to initialize machine functions after they are
-/// created by the machine function analysis pass.
-class MachineFunctionInitializer {
-  virtual void anchor();
-
-public:
-  virtual ~MachineFunctionInitializer() = default;
-
-  /// Initialize the machine function.
-  ///
-  /// Return true if error occurred.
-  virtual bool initializeMachineFunction(MachineFunction &MF) = 0;
-};
-
-} // end namespace llvm
-
-#endif // LLVM_CODEGEN_MACHINEFUNCTIONINITIALIZER_H
diff --git a/llvm/include/llvm/CodeGen/MachineModuleInfo.h b/llvm/include/llvm/CodeGen/MachineModuleInfo.h
index d4ac58c3bd22..d64941a9e725 100644
--- a/llvm/include/llvm/CodeGen/MachineModuleInfo.h
+++ b/llvm/include/llvm/CodeGen/MachineModuleInfo.h
@@ -47,7 +47,6 @@ class BasicBlock;
 class CallInst;
 class Function;
 class MachineFunction;
-class MachineFunctionInitializer;
 class MMIAddrLabelMap;
 class Module;
 class TargetMachine;
@@ -126,7 +125,6 @@ class MachineModuleInfo : public ImmutablePass {
   /// comments in lib/Target/X86/X86FrameLowering.cpp for more details.
   bool UsesMorestackAddr;
 
-  MachineFunctionInitializer *MFInitializer;
   /// Maps IR Functions to their corresponding MachineFunctions.
   DenseMap<const Function*, std::unique_ptr<MachineFunction>> MachineFunctions;
   /// Next unique number available for a MachineFunction.
@@ -150,14 +148,13 @@ public:
   void setModule(const Module *M) { TheModule = M; }
   const Module *getModule() const { return TheModule; }
 
-  void setMachineFunctionInitializer(MachineFunctionInitializer *MFInit) {
-    MFInitializer = MFInit;
-  }
-
   /// Returns the MachineFunction constructed for the IR function \p F.
-  /// Creates a new MachineFunction and runs the MachineFunctionInitializer
-  /// if none exists yet.
-  MachineFunction &getMachineFunction(const Function &F);
+  /// Creates a new MachineFunction if none exists yet.
+  MachineFunction &getOrCreateMachineFunction(const Function &F);
+
+  /// \bried Returns the MachineFunction associated to IR function \p F if there
+  /// is one, otherwise nullptr.
+  MachineFunction *getMachineFunction(const Function &F) const;
 
   /// Delete the MachineFunction \p MF and reset the link in the IR Function to
   /// Machine Function map.
diff --git a/llvm/include/llvm/Target/TargetMachine.h b/llvm/include/llvm/Target/TargetMachine.h
index d68bd3543dd3..933c6c87b0be 100644
--- a/llvm/include/llvm/Target/TargetMachine.h
+++ b/llvm/include/llvm/Target/TargetMachine.h
@@ -25,7 +25,6 @@
 namespace llvm {
 
 class GlobalValue;
-class MachineFunctionInitializer;
 class Mangler;
 class MCAsmInfo;
 class MCContext;
@@ -227,8 +226,7 @@ public:
       PassManagerBase &, raw_pwrite_stream &, CodeGenFileType,
       bool /*DisableVerify*/ = true, AnalysisID /*StartBefore*/ = nullptr,
       AnalysisID /*StartAfter*/ = nullptr, AnalysisID /*StopBefore*/ = nullptr,
-      AnalysisID /*StopAfter*/ = nullptr,
-      MachineFunctionInitializer * /*MFInitializer*/ = nullptr) {
+      AnalysisID /*StopAfter*/ = nullptr) {
     return true;
   }
 
@@ -289,8 +287,7 @@ public:
       PassManagerBase &PM, raw_pwrite_stream &Out, CodeGenFileType FileType,
       bool DisableVerify = true, AnalysisID StartBefore = nullptr,
       AnalysisID StartAfter = nullptr, AnalysisID StopBefore = nullptr,
-      AnalysisID StopAfter = nullptr,
-      MachineFunctionInitializer *MFInitializer = nullptr) override;
+      AnalysisID StopAfter = nullptr) override;
 
   /// Add passes to the specified pass manager to get machine code emitted with
   /// the MCJIT. This method returns true if machine code is not supported. It
diff --git a/llvm/lib/CodeGen/LLVMTargetMachine.cpp b/llvm/lib/CodeGen/LLVMTargetMachine.cpp
index 66e6e7abc067..35c4dfae008f 100644
--- a/llvm/lib/CodeGen/LLVMTargetMachine.cpp
+++ b/llvm/lib/CodeGen/LLVMTargetMachine.cpp
@@ -95,9 +95,7 @@ static MCContext *
 addPassesToGenerateCode(LLVMTargetMachine *TM, PassManagerBase &PM,
                         bool DisableVerify, AnalysisID StartBefore,
                         AnalysisID StartAfter, AnalysisID StopBefore,
-                        AnalysisID StopAfter,
-                        MachineFunctionInitializer *MFInitializer = nullptr) {
-
+                        AnalysisID StopAfter) {
   // Targets may override createPassConfig to provide a target-specific
   // subclass.
   TargetPassConfig *PassConfig = TM->createPassConfig(PM);
@@ -107,7 +105,6 @@ addPassesToGenerateCode(LLVMTargetMachine *TM, PassManagerBase &PM,
   PassConfig->setDisableVerify(DisableVerify);
   PM.add(PassConfig);
   MachineModuleInfo *MMI = new MachineModuleInfo(TM);
-  MMI->setMachineFunctionInitializer(MFInitializer);
   PM.add(MMI);
 
   if (PassConfig->addISelPasses())
@@ -192,12 +189,11 @@ bool LLVMTargetMachine::addAsmPrinter(PassManagerBase &PM,
 bool LLVMTargetMachine::addPassesToEmitFile(
     PassManagerBase &PM, raw_pwrite_stream &Out, CodeGenFileType FileType,
     bool DisableVerify, AnalysisID StartBefore, AnalysisID StartAfter,
-    AnalysisID StopBefore, AnalysisID StopAfter,
-    MachineFunctionInitializer *MFInitializer) {
+    AnalysisID StopBefore, AnalysisID StopAfter) {
   // Add common CodeGen passes.
   MCContext *Context =
       addPassesToGenerateCode(this, PM, DisableVerify, StartBefore, StartAfter,
-                              StopBefore, StopAfter, MFInitializer);
+                              StopBefore, StopAfter);
   if (!Context)
     return true;
 
diff --git a/llvm/lib/CodeGen/MIRParser/MIRParser.cpp b/llvm/lib/CodeGen/MIRParser/MIRParser.cpp
index ff12297e3fc6..cdeba007458f 100644
--- a/llvm/lib/CodeGen/MIRParser/MIRParser.cpp
+++ b/llvm/lib/CodeGen/MIRParser/MIRParser.cpp
@@ -50,18 +50,24 @@ namespace llvm {
 /// file.
 class MIRParserImpl {
   SourceMgr SM;
+  yaml::Input In;
   StringRef Filename;
   LLVMContext &Context;
-  StringMap<std::unique_ptr<yaml::MachineFunction>> Functions;
   SlotMapping IRSlots;
   /// Maps from register class names to register classes.
   Name2RegClassMap Names2RegClasses;
   /// Maps from register bank names to register banks.
   Name2RegBankMap Names2RegBanks;
+  /// True when the MIR file doesn't have LLVM IR. Dummy IR functions are
+  /// created and inserted into the given module when this is true.
+  bool NoLLVMIR = false;
+  /// True when a well formed MIR file does not contain any MIR/machine function
+  /// parts.
+  bool NoMIRDocuments = false;
 
 public:
-  MIRParserImpl(std::unique_ptr<MemoryBuffer> Contents, StringRef Filename,
-                LLVMContext &Context);
+  MIRParserImpl(std::unique_ptr<MemoryBuffer> Contents,
+                StringRef Filename, LLVMContext &Context);
 
   void reportDiagnostic(const SMDiagnostic &Diag);
 
@@ -85,22 +91,22 @@ public:
   /// file.
   ///
   /// Return null if an error occurred.
-  std::unique_ptr<Module> parse();
+  std::unique_ptr<Module> parseIRModule();
+
+  bool parseMachineFunctions(Module &M, MachineModuleInfo &MMI);
 
   /// Parse the machine function in the current YAML document.
   ///
-  /// \param NoLLVMIR - set to true when the MIR file doesn't have LLVM IR.
-  /// A dummy IR function is created and inserted into the given module when
-  /// this parameter is true.
   ///
   /// Return true if an error occurred.
-  bool parseMachineFunction(yaml::Input &In, Module &M, bool NoLLVMIR);
+  bool parseMachineFunction(Module &M, MachineModuleInfo &MMI);
 
   /// Initialize the machine function to the state that's described in the MIR
   /// file.
   ///
   /// Return true if error occurred.
-  bool initializeMachineFunction(MachineFunction &MF);
+  bool initializeMachineFunction(const yaml::MachineFunction &YamlMF,
+                                 MachineFunction &MF);
 
   bool parseRegisterInfo(PerFunctionMIParsingState &PFS,
                          const yaml::MachineFunction &YamlMF);
@@ -144,9 +150,6 @@ private:
   SMDiagnostic diagFromBlockStringDiag(const SMDiagnostic &Error,
                                        SMRange SourceRange);
 
-  /// Create an empty function with the given name.
-  void createDummyFunction(StringRef Name, Module &M);
-
   void initNames2RegClasses(const MachineFunction &MF);
   void initNames2RegBanks(const MachineFunction &MF);
 
@@ -166,10 +169,19 @@ private:
 
 } // end namespace llvm
 
+static void handleYAMLDiag(const SMDiagnostic &Diag, void *Context) {
+  reinterpret_cast<MIRParserImpl *>(Context)->reportDiagnostic(Diag);
+}
+
 MIRParserImpl::MIRParserImpl(std::unique_ptr<MemoryBuffer> Contents,
                              StringRef Filename, LLVMContext &Context)
-    : SM(), Filename(Filename), Context(Context) {
-  SM.AddNewSourceBuffer(std::move(Contents), SMLoc());
+    : SM(),
+      In(SM.getMemoryBuffer(
+            SM.AddNewSourceBuffer(std::move(Contents), SMLoc()))->getBuffer(),
+            nullptr, handleYAMLDiag, this),
+      Filename(Filename),
+      Context(Context) {
+  In.setContext(&In);
 }
 
 bool MIRParserImpl::error(const Twine &Message) {
@@ -206,24 +218,16 @@ void MIRParserImpl::reportDiagnostic(const SMDiagnostic &Diag) {
   Context.diagnose(DiagnosticInfoMIRParser(Kind, Diag));
 }
 
-static void handleYAMLDiag(const SMDiagnostic &Diag, void *Context) {
-  reinterpret_cast<MIRParserImpl *>(Context)->reportDiagnostic(Diag);
-}
-
-std::unique_ptr<Module> MIRParserImpl::parse() {
-  yaml::Input In(SM.getMemoryBuffer(SM.getMainFileID())->getBuffer(),
-                 /*Ctxt=*/nullptr, handleYAMLDiag, this);
-  In.setContext(&In);
-
+std::unique_ptr<Module> MIRParserImpl::parseIRModule() {
   if (!In.setCurrentDocument()) {
     if (In.error())
       return nullptr;
     // Create an empty module when the MIR file is empty.
+    NoMIRDocuments = true;
     return llvm::make_unique<Module>(Filename, Context);
   }
 
   std::unique_ptr<Module> M;
-  bool NoLLVMIR = false;
   // Parse the block scalar manually so that we can return unique pointer
   // without having to go trough YAML traits.
   if (const auto *BSN =
@@ -237,49 +241,68 @@ std::unique_ptr<Module> MIRParserImpl::parse() {
     }
     In.nextDocument();
     if (!In.setCurrentDocument())
-      return M;
+      NoMIRDocuments = true;
   } else {
     // Create an new, empty module.
     M = llvm::make_unique<Module>(Filename, Context);
     NoLLVMIR = true;
   }
-
-  // Parse the machine functions.
-  do {
-    if (parseMachineFunction(In, *M, NoLLVMIR))
-      return nullptr;
-    In.nextDocument();
-  } while (In.setCurrentDocument());
-
   return M;
 }
 
-bool MIRParserImpl::parseMachineFunction(yaml::Input &In, Module &M,
-                                         bool NoLLVMIR) {
-  auto MF = llvm::make_unique<yaml::MachineFunction>();
-  yaml::EmptyContext Ctx;
-  yaml::yamlize(In, *MF, false, Ctx);
-  if (In.error())
-    return true;
-  auto FunctionName = MF->Name;
-  if (Functions.find(FunctionName) != Functions.end())
-    return error(Twine("redefinition of machine function '") + FunctionName +
-                 "'");
-  Functions.insert(std::make_pair(FunctionName, std::move(MF)));
-  if (NoLLVMIR)
-    createDummyFunction(FunctionName, M);
-  else if (!M.getFunction(FunctionName))
-    return error(Twine("function '") + FunctionName +
-                 "' isn't defined in the provided LLVM IR");
+bool MIRParserImpl::parseMachineFunctions(Module &M, MachineModuleInfo &MMI) {
+  if (NoMIRDocuments)
+    return false;
+
+  // Parse the machine functions.
+  do {
+    if (parseMachineFunction(M, MMI))
+      return true;
+    In.nextDocument();
+  } while (In.setCurrentDocument());
+
   return false;
 }
 
-void MIRParserImpl::createDummyFunction(StringRef Name, Module &M) {
+/// Create an empty function with the given name.
+static Function *createDummyFunction(StringRef Name, Module &M) {
   auto &Context = M.getContext();
   Function *F = cast<Function>(M.getOrInsertFunction(
       Name, FunctionType::get(Type::getVoidTy(Context), false)));
   BasicBlock *BB = BasicBlock::Create(Context, "entry", F);
   new UnreachableInst(Context, BB);
+  return F;
+}
+
+bool MIRParserImpl::parseMachineFunction(Module &M, MachineModuleInfo &MMI) {
+  // Parse the yaml.
+  yaml::MachineFunction YamlMF;
+  yaml::EmptyContext Ctx;
+  yaml::yamlize(In, YamlMF, false, Ctx);
+  if (In.error())
+    return true;
+
+  // Search for the corresponding IR function.
+  StringRef FunctionName = YamlMF.Name;
+  Function *F = M.getFunction(FunctionName);
+  if (!F) {
+    if (NoLLVMIR) {
+      F = createDummyFunction(FunctionName, M);
+    } else {
+      return error(Twine("function '") + FunctionName +
+                   "' isn't defined in the provided LLVM IR");
+    }
+  }
+  if (MMI.getMachineFunction(*F) != nullptr)
+    return error(Twine("redefinition of machine function '") + FunctionName +
+                 "'");
+
+  // Create the MachineFunction.
+  MachineFunction &MF = MMI.getOrCreateMachineFunction(*F);
+  if (initializeMachineFunction(YamlMF, MF))
+    return true;
+
+  return false;
 }
 
 static bool isSSA(const MachineFunction &MF) {
@@ -319,15 +342,12 @@ void MIRParserImpl::computeFunctionProperties(MachineFunction &MF) {
     Properties.set(MachineFunctionProperties::Property::NoVRegs);
 }
 
-bool MIRParserImpl::initializeMachineFunction(MachineFunction &MF) {
-  auto It = Functions.find(MF.getName());
-  if (It == Functions.end())
-    return error(Twine("no machine function information for function '") +
-                 MF.getName() + "' in the MIR file");
+bool
+MIRParserImpl::initializeMachineFunction(const yaml::MachineFunction &YamlMF,
+                                         MachineFunction &MF) {
   // TODO: Recreate the machine function.
   initNames2RegClasses(MF);
   initNames2RegBanks(MF);
-  const yaml::MachineFunction &YamlMF = *It->getValue();
   if (YamlMF.Alignment)
     MF.setAlignment(YamlMF.Alignment);
   MF.setExposesReturnsTwice(YamlMF.ExposesReturnsTwice);
@@ -838,10 +858,12 @@ MIRParser::MIRParser(std::unique_ptr<MIRParserImpl> Impl)
 
 MIRParser::~MIRParser() {}
 
-std::unique_ptr<Module> MIRParser::parseLLVMModule() { return Impl->parse(); }
+std::unique_ptr<Module> MIRParser::parseIRModule() {
+  return Impl->parseIRModule();
+}
 
-bool MIRParser::initializeMachineFunction(MachineFunction &MF) {
-  return Impl->initializeMachineFunction(MF);
+bool MIRParser::parseMachineFunctions(Module &M, MachineModuleInfo &MMI) {
+  return Impl->parseMachineFunctions(M, MMI);
 }
 
 std::unique_ptr<MIRParser> llvm::createMIRParserFromFile(StringRef Filename,
diff --git a/llvm/lib/CodeGen/MachineFunction.cpp b/llvm/lib/CodeGen/MachineFunction.cpp
index ac4ccb81b884..bbdae6e1a49e 100644
--- a/llvm/lib/CodeGen/MachineFunction.cpp
+++ b/llvm/lib/CodeGen/MachineFunction.cpp
@@ -20,7 +20,6 @@
 #include "llvm/Analysis/EHPersonalities.h"
 #include "llvm/CodeGen/MachineConstantPool.h"
 #include "llvm/CodeGen/MachineFrameInfo.h"
-#include "llvm/CodeGen/MachineFunctionInitializer.h"
 #include "llvm/CodeGen/MachineFunctionPass.h"
 #include "llvm/CodeGen/MachineInstr.h"
 #include "llvm/CodeGen/MachineJumpTableInfo.h"
@@ -52,8 +51,6 @@ static cl::opt<unsigned>
                       cl::desc("Force the alignment of all functions."),
                       cl::init(0), cl::Hidden);
 
-void MachineFunctionInitializer::anchor() {}
-
 static const char *getPropertyName(MachineFunctionProperties::Property Prop) {
   typedef MachineFunctionProperties::Property P;
   switch(Prop) {
diff --git a/llvm/lib/CodeGen/MachineFunctionPass.cpp b/llvm/lib/CodeGen/MachineFunctionPass.cpp
index 2265676ff8b1..5ffe33006131 100644
--- a/llvm/lib/CodeGen/MachineFunctionPass.cpp
+++ b/llvm/lib/CodeGen/MachineFunctionPass.cpp
@@ -42,7 +42,7 @@ bool MachineFunctionPass::runOnFunction(Function &F) {
     return false;
 
   MachineModuleInfo &MMI = getAnalysis<MachineModuleInfo>();
-  MachineFunction &MF = MMI.getMachineFunction(F);
+  MachineFunction &MF = MMI.getOrCreateMachineFunction(F);
 
   MachineFunctionProperties &MFProps = MF.getProperties();
 
diff --git a/llvm/lib/CodeGen/MachineModuleInfo.cpp b/llvm/lib/CodeGen/MachineModuleInfo.cpp
index c1b72430e605..62fa1f9444f7 100644
--- a/llvm/lib/CodeGen/MachineModuleInfo.cpp
+++ b/llvm/lib/CodeGen/MachineModuleInfo.cpp
@@ -13,7 +13,6 @@
 #include "llvm/ADT/StringRef.h"
 #include "llvm/ADT/TinyPtrVector.h"
 #include "llvm/CodeGen/MachineFunction.h"
-#include "llvm/CodeGen/MachineFunctionInitializer.h"
 #include "llvm/CodeGen/MachineModuleInfo.h"
 #include "llvm/CodeGen/Passes.h"
 #include "llvm/IR/BasicBlock.h"
@@ -259,7 +258,14 @@ void MachineModuleInfo::addPersonality(const Function *Personality) {
 
 /// \}
 
-MachineFunction &MachineModuleInfo::getMachineFunction(const Function &F) {
+MachineFunction *
+MachineModuleInfo::getMachineFunction(const Function &F) const {
+  auto I = MachineFunctions.find(&F);
+  return I != MachineFunctions.end() ? I->second.get() : nullptr;
+}
+
+MachineFunction &
+MachineModuleInfo::getOrCreateMachineFunction(const Function &F) {
   // Shortcut for the common case where a sequence of MachineFunctionPasses
   // all query for the same Function.
   if (LastRequest == &F)
@@ -273,10 +279,6 @@ MachineFunction &MachineModuleInfo::getMachineFunction(const Function &F) {
     MF = new MachineFunction(&F, TM, NextFnNum++, *this);
     // Update the set entry.
     I.first->second.reset(MF);
-
-    if (MFInitializer)
-      if (MFInitializer->initializeMachineFunction(*MF))
-        report_fatal_error("Unable to initialize machine function");
   } else {
     MF = I.first->second.get();
   }
diff --git a/llvm/lib/CodeGen/MachineOutliner.cpp b/llvm/lib/CodeGen/MachineOutliner.cpp
index 9ea3c00a2fc4..fd6b2427891d 100644
--- a/llvm/lib/CodeGen/MachineOutliner.cpp
+++ b/llvm/lib/CodeGen/MachineOutliner.cpp
@@ -1111,7 +1111,7 @@ MachineOutliner::createOutlinedFunction(Module &M, const OutlinedFunction &OF,
   Builder.CreateRetVoid();
 
   MachineModuleInfo &MMI = getAnalysis<MachineModuleInfo>();
-  MachineFunction &MF = MMI.getMachineFunction(*F);
+  MachineFunction &MF = MMI.getOrCreateMachineFunction(*F);
   MachineBasicBlock &MBB = *MF.CreateMachineBasicBlock();
   const TargetSubtargetInfo &STI = MF.getSubtarget();
   const TargetInstrInfo &TII = *STI.getInstrInfo();
@@ -1207,7 +1207,7 @@ bool MachineOutliner::runOnModule(Module &M) {
     return false;
 
   MachineModuleInfo &MMI = getAnalysis<MachineModuleInfo>();
-  const TargetSubtargetInfo &STI = MMI.getMachineFunction(*M.begin())
+  const TargetSubtargetInfo &STI = MMI.getOrCreateMachineFunction(*M.begin())
                                       .getSubtarget();
   const TargetRegisterInfo *TRI = STI.getRegisterInfo();
   const TargetInstrInfo *TII = STI.getInstrInfo();
@@ -1216,7 +1216,7 @@ bool MachineOutliner::runOnModule(Module &M) {
 
   // Build instruction mappings for each function in the module.
   for (Function &F : M) {
-    MachineFunction &MF = MMI.getMachineFunction(F);
+    MachineFunction &MF = MMI.getOrCreateMachineFunction(F);
 
     // Is the function empty? Safe to outline from?
     if (F.empty() || !TII->isFunctionSafeToOutlineFrom(MF))
diff --git a/llvm/test/CodeGen/MIR/AArch64/generic-virtual-registers-error.mir b/llvm/test/CodeGen/MIR/AArch64/generic-virtual-registers-error.mir
index d63c2ef6e871..af785bcb10a9 100644
--- a/llvm/test/CodeGen/MIR/AArch64/generic-virtual-registers-error.mir
+++ b/llvm/test/CodeGen/MIR/AArch64/generic-virtual-registers-error.mir
@@ -17,6 +17,5 @@ body: |
     liveins: %w0
     ; ERR: generic virtual registers must have a type
     ; ERR-NEXT: %0
-    ; ERR: Unable to initialize machine function
     %0 = G_ADD i32 %w0, %w0
 ...
diff --git a/llvm/test/CodeGen/MIR/AArch64/generic-virtual-registers-with-regbank-error.mir b/llvm/test/CodeGen/MIR/AArch64/generic-virtual-registers-with-regbank-error.mir
index e331179773d6..f177b91da559 100644
--- a/llvm/test/CodeGen/MIR/AArch64/generic-virtual-registers-with-regbank-error.mir
+++ b/llvm/test/CodeGen/MIR/AArch64/generic-virtual-registers-with-regbank-error.mir
@@ -18,6 +18,5 @@ body: |
     liveins: %w0
     ; ERR: generic virtual registers must have a type
     ; ERR-NEXT: %0
-    ; ERR: Unable to initialize machine function
     %0 = G_ADD i32 %w0, %w0
 ...
diff --git a/llvm/test/CodeGen/MIR/Generic/function-missing-machine-function.mir b/llvm/test/CodeGen/MIR/Generic/function-missing-machine-function.mir
deleted file mode 100644
index f3a834801671..000000000000
--- a/llvm/test/CodeGen/MIR/Generic/function-missing-machine-function.mir
+++ /dev/null
@@ -1,13 +0,0 @@
-# RUN: not llc -run-pass none -o /dev/null %s 2>&1 | FileCheck %s
-# This test verifies that an error is reported when a MIR file has some
-# function but is missing a corresponding machine function.
-
-# CHECK: no machine function information for function 'foo' in the MIR file
-
---- |
-
-  define i32 @foo() {
-    ret i32 0
-  }
-
-...
diff --git a/llvm/test/CodeGen/MIR/X86/empty0.mir b/llvm/test/CodeGen/MIR/X86/empty0.mir
new file mode 100644
index 000000000000..4431af7c6a99
--- /dev/null
+++ b/llvm/test/CodeGen/MIR/X86/empty0.mir
@@ -0,0 +1,6 @@
+# RUN: llc -run-pass none -o - %s | FileCheck %s
+# Make sure empty files don't crash us
+# CHECK: --- |
+# ... moduleid, sourcefilename stuff here ..
+# CHECK: target datalayout =
+# CHECK: ...
diff --git a/llvm/test/CodeGen/MIR/X86/empty1.mir b/llvm/test/CodeGen/MIR/X86/empty1.mir
new file mode 100644
index 000000000000..d80b0cd30231
--- /dev/null
+++ b/llvm/test/CodeGen/MIR/X86/empty1.mir
@@ -0,0 +1,8 @@
+# RUN: llc -run-pass none -o - %s | FileCheck %s
+# Make sure empty files don't crash us
+--- |
+...
+# CHECK: --- |
+# ... moduleid, sourcefilename stuff here ..
+# CHECK: target datalayout =
+# CHECK: ...
diff --git a/llvm/test/CodeGen/MIR/X86/empty2.mir b/llvm/test/CodeGen/MIR/X86/empty2.mir
new file mode 100644
index 000000000000..7495807cd4d6
--- /dev/null
+++ b/llvm/test/CodeGen/MIR/X86/empty2.mir
@@ -0,0 +1,8 @@
+# RUN: llc -run-pass none -o - %s | FileCheck %s
+# Make sure empty files don't crash us
+---
+...
+# CHECK: --- |
+# ... moduleid, sourcefilename stuff here ..
+# CHECK: target datalayout =
+# CHECK: ...
diff --git a/llvm/tools/llc/llc.cpp b/llvm/tools/llc/llc.cpp
index 9c42f66b8931..10fb9f623325 100644
--- a/llvm/tools/llc/llc.cpp
+++ b/llvm/tools/llc/llc.cpp
@@ -401,7 +401,7 @@ static int compileModule(char **argv, LLVMContext &Context) {
     if (StringRef(InputFilename).endswith_lower(".mir")) {
       MIR = createMIRParserFromFile(InputFilename, Err, Context);
       if (MIR)
-        M = MIR->parseLLVMModule();
+        M = MIR->parseIRModule();
     } else
       M = parseIRFile(InputFilename, Err, Context);
     if (!M) {
@@ -540,7 +540,8 @@ static int compileModule(char **argv, LLVMContext &Context) {
       TPC.setDisableVerify(NoVerify);
       PM.add(&TPC);
       MachineModuleInfo *MMI = new MachineModuleInfo(&LLVMTM);
-      MMI->setMachineFunctionInitializer(MIR.get());
+      if (MIR->parseMachineFunctions(*M, *MMI))
+        return 1;
       PM.add(MMI);
       TPC.printAndVerify("");
 
diff --git a/llvm/unittests/MI/LiveIntervalTest.cpp b/llvm/unittests/MI/LiveIntervalTest.cpp
index 026fb42d345f..a37d6ed8f630 100644
--- a/llvm/unittests/MI/LiveIntervalTest.cpp
+++ b/llvm/unittests/MI/LiveIntervalTest.cpp
@@ -59,18 +59,15 @@ std::unique_ptr<Module> parseMIR(LLVMContext &Context,
   if (!MIR)
     return nullptr;
 
-  std::unique_ptr<Module> M = MIR->parseLLVMModule();
+  std::unique_ptr<Module> M = MIR->parseIRModule();
   if (!M)
     return nullptr;
 
   M->setDataLayout(TM.createDataLayout());
 
-  Function *F = M->getFunction(FuncName);
-  if (!F)
-    return nullptr;
-
   MachineModuleInfo *MMI = new MachineModuleInfo(&TM);
-  MMI->setMachineFunctionInitializer(MIR.get());
+  if (MIR->parseMachineFunctions(*M, *MMI))
+    return nullptr;
   PM.add(MMI);
 
   return M;
@@ -154,6 +151,7 @@ body: |
   std::unique_ptr<MIRParser> MIR;
   std::unique_ptr<Module> M = parseMIR(Context, PM, MIR, *TM, MIRString,
                                        "func");
+  assert(M && "MIR parsing successfull");
 
   PM.add(new TestPass(T));
 
diff --git a/llvm/unittests/Target/AArch64/InstSizes.cpp b/llvm/unittests/Target/AArch64/InstSizes.cpp
index 22b47c6852ab..5ee5e9c048ac 100644
--- a/llvm/unittests/Target/AArch64/InstSizes.cpp
+++ b/llvm/unittests/Target/AArch64/InstSizes.cpp
@@ -60,18 +60,19 @@ void runChecks(
       createMIRParser(std::move(MBuffer), Context);
   assert(MParser && "Couldn't create MIR parser");
 
-  std::unique_ptr<Module> M = MParser->parseLLVMModule();
+  std::unique_ptr<Module> M = MParser->parseIRModule();
   assert(M && "Couldn't parse module");
 
   M->setTargetTriple(TM->getTargetTriple().getTriple());
   M->setDataLayout(TM->createDataLayout());
 
+  MachineModuleInfo MMI(TM);
+  bool Res = MParser->parseMachineFunctions(*M, MMI);
+  assert(!Res && "Couldn't parse MIR functions");
+
   auto F = M->getFunction("sizes");
   assert(F && "Couldn't find intended function");
-
-  MachineModuleInfo MMI(TM);
-  MMI.setMachineFunctionInitializer(MParser.get());
-  auto &MF = MMI.getMachineFunction(*F);
+  auto &MF = MMI.getOrCreateMachineFunction(*F);
 
   Checks(*II, MF);
 }