MC CFG: Add YAML MCModule representation to enable MC CFG testing.

Like yaml ObjectFiles, this will be very useful for testing the MC CFG
implementation (mostly MCObjectDisassembler), by matching the output
with YAML, and for potential users of the MC CFG, by using it as an input.

There isn't much to the actual format, it is just a serialization of the
MCModule class. Of note:
  - Basic block references (pred/succ, ..) are represented by the BB's
    start address.
  - Just as in the MC CFG, instructions are MCInsts with a size.
  - Operands have a prefix representing the type (only register and
    immediate supported here).
  - Instruction opcodes are represented by their names; enum values aren't
    stable, enum names mostly are: usually, a change to a name would need
    lots of changes in the backend anyway.
    Same with registers.

All in all, an example is better than 1000 words, here goes:

A simple binary:

  Disassembly of section __TEXT,__text:
  _main:
  100000f9c:      48 8b 46 08             movq    8(%rsi), %rax
  100000fa0:      0f be 00                movsbl  (%rax), %eax
  100000fa3:      3b 04 25 48 00 00 00    cmpl    72, %eax
  100000faa:      0f 8c 07 00 00 00       jl      7 <.Lend>
  100000fb0:      2b 04 25 48 00 00 00    subl    72, %eax
  .Lend:
  100000fb7:      c3                      ret

And the (pretty verbose) generated YAML:

  ---
  Atoms:
    - StartAddress:    0x0000000100000F9C
      Size:            20
      Type:            Text
      Content:
        - Inst:            MOV64rm
          Size:            4
          Ops:             [ RRAX, RRSI, I1, R, I8, R ]
        - Inst:            MOVSX32rm8
          Size:            3
          Ops:             [ REAX, RRAX, I1, R, I0, R ]
        - Inst:            CMP32rm
          Size:            7
          Ops:             [ REAX, R, I1, R, I72, R ]
        - Inst:            JL_4
          Size:            6
          Ops:             [ I7 ]
    - StartAddress:    0x0000000100000FB0
      Size:            7
      Type:            Text
      Content:
        - Inst:            SUB32rm
          Size:            7
          Ops:             [ REAX, REAX, R, I1, R, I72, R ]
    - StartAddress:    0x0000000100000FB7
      Size:            1
      Type:            Text
      Content:
        - Inst:            RET
          Size:            1
          Ops:             [  ]
  Functions:
    - Name:            __text
      BasicBlocks:
        - Address:         0x0000000100000F9C
          Preds:           [  ]
          Succs:           [ 0x0000000100000FB7, 0x0000000100000FB0 ]
     <snip>
  ...

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@188890 91177308-0d34-0410-b5e6-96231b3b80d8

4 files changed, 532 insertions, 9 deletions

diff --git a/include/llvm/MC/MCModuleYAML.h b/include/llvm/MC/MCModuleYAML.h
new file mode 100644
index 0000000000..0ea29dafe4
--- /dev/null
+++ b/include/llvm/MC/MCModuleYAML.h
@@ -0,0 +1,41 @@
+//===- MCModuleYAML.h - MCModule YAMLIO implementation ----------*- C++ -*-===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+///
+/// \file
+/// \brief This file declares classes for handling the YAML representation
+/// of MCModule.
+///
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_OBJECT_MCMODULEYAML_H
+#define LLVM_OBJECT_MCMODULEYAML_H
+
+#include "llvm/ADT/OwningPtr.h"
+#include "llvm/ADT/StringRef.h"
+#include "llvm/MC/MCModule.h"
+#include "llvm/Support/raw_ostream.h"
+
+namespace llvm {
+
+class MCInstrInfo;
+class MCRegisterInfo;
+
+/// \brief Dump a YAML representation of the MCModule \p MCM to \p OS.
+/// \returns The empty string on success, an error message on failure.
+StringRef mcmodule2yaml(raw_ostream &OS, const MCModule &MCM,
+                        const MCInstrInfo &MII, const MCRegisterInfo &MRI);
+
+/// \brief Creates a new module and returns it in \p MCM.
+/// \returns The empty string on success, an error message on failure.
+StringRef yaml2mcmodule(OwningPtr<MCModule> &MCM, StringRef YamlContent,
+                        const MCInstrInfo &MII, const MCRegisterInfo &MRI);
+
+} // end namespace llvm
+
+#endif
diff --git a/lib/MC/CMakeLists.txt b/lib/MC/CMakeLists.txt
index 89e2aaf48b..fffe886a4a 100644
--- a/lib/MC/CMakeLists.txt
+++ b/lib/MC/CMakeLists.txt
@@ -25,6 +25,7 @@ add_llvm_library(LLVMMC
   MCMachOStreamer.cpp
   MCMachObjectTargetWriter.cpp
   MCModule.cpp
+  MCModuleYAML.cpp
   MCNullStreamer.cpp
   MCObjectFileInfo.cpp
   MCObjectDisassembler.cpp
diff --git a/lib/MC/MCModuleYAML.cpp b/lib/MC/MCModuleYAML.cpp
new file mode 100644
index 0000000000..e2de57849b
--- /dev/null
+++ b/lib/MC/MCModuleYAML.cpp
@@ -0,0 +1,461 @@
+//===- MCModuleYAML.cpp - MCModule YAMLIO implementation ------------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// This file defines classes for handling the YAML representation of MCModule.
+//
+//===----------------------------------------------------------------------===//
+
+#include "llvm/MC/MCModuleYAML.h"
+#include "llvm/ADT/StringMap.h"
+#include "llvm/MC/MCAtom.h"
+#include "llvm/MC/MCFunction.h"
+#include "llvm/MC/MCInstrInfo.h"
+#include "llvm/MC/MCRegisterInfo.h"
+#include "llvm/Object/YAML.h"
+#include "llvm/Support/Allocator.h"
+#include "llvm/Support/MathExtras.h"
+#include "llvm/Support/YAMLTraits.h"
+#include <vector>
+
+namespace llvm {
+
+namespace {
+
+// This class is used to map opcode and register names to enum values.
+//
+// There are at least 3 obvious ways to do this:
+// 1- Generate an MII/MRI method using a tablegen StringMatcher
+// 2- Write an MII/MRI method using std::lower_bound and the assumption that
+//    the enums are sorted (starting at a fixed value).
+// 3- Do the matching manually as is done here.
+//
+// Why 3?
+// 1- A StringMatcher function for thousands of entries would incur
+//    a non-negligible binary size overhead.
+// 2- The lower_bound comparators would be somewhat involved and aren't
+//    obviously reusable (see LessRecordRegister in llvm/TableGen/Record.h)
+// 3- This isn't actually something useful outside tests (but the same argument
+//    can be made against having {MII,MRI}::getName).
+//
+// If this becomes useful outside this specific situation, feel free to do
+// the Right Thing (tm) and move the functionality to MII/MRI.
+//
+class InstrRegInfoHolder {
+  typedef StringMap<unsigned, BumpPtrAllocator> EnumValByNameTy;
+  EnumValByNameTy InstEnumValueByName;
+  EnumValByNameTy RegEnumValueByName;
+
+public:
+  const MCInstrInfo &MII;
+  const MCRegisterInfo &MRI;
+  InstrRegInfoHolder(const MCInstrInfo &MII, const MCRegisterInfo &MRI)
+      : InstEnumValueByName(NextPowerOf2(MII.getNumOpcodes())),
+        RegEnumValueByName(NextPowerOf2(MRI.getNumRegs())), MII(MII), MRI(MRI) {
+    for (int i = 0, e = MII.getNumOpcodes(); i != e; ++i)
+      InstEnumValueByName[MII.getName(i)] = i;
+    for (int i = 0, e = MRI.getNumRegs(); i != e; ++i)
+      RegEnumValueByName[MRI.getName(i)] = i;
+  }
+
+  bool matchRegister(StringRef Name, unsigned &Reg) {
+    EnumValByNameTy::const_iterator It = RegEnumValueByName.find(Name);
+    if (It == RegEnumValueByName.end())
+      return false;
+    Reg = It->getValue();
+    return true;
+  }
+  bool matchOpcode(StringRef Name, unsigned &Opc) {
+    EnumValByNameTy::const_iterator It = InstEnumValueByName.find(Name);
+    if (It == InstEnumValueByName.end())
+      return false;
+    Opc = It->getValue();
+    return true;
+  }
+};
+
+} // end unnamed namespace
+
+namespace MCModuleYAML {
+
+LLVM_YAML_STRONG_TYPEDEF(unsigned, OpcodeEnum)
+
+struct Operand {
+  MCOperand MCOp;
+};
+
+struct Inst {
+  OpcodeEnum Opcode;
+  std::vector<Operand> Operands;
+  uint64_t Size;
+};
+
+struct Atom {
+  MCAtom::AtomKind Type;
+  yaml::Hex64 StartAddress;
+  uint64_t Size;
+
+  std::vector<Inst> Insts;
+  object::yaml::BinaryRef Data;
+};
+
+struct BasicBlock {
+  yaml::Hex64 Address;
+  std::vector<yaml::Hex64> Preds;
+  std::vector<yaml::Hex64> Succs;
+};
+
+struct Function {
+  StringRef Name;
+  std::vector<BasicBlock> BasicBlocks;
+};
+
+struct Module {
+  std::vector<Atom> Atoms;
+  std::vector<Function> Functions;
+};
+
+} // end namespace MCModuleYAML
+} // end namespace llvm
+
+LLVM_YAML_IS_FLOW_SEQUENCE_VECTOR(llvm::yaml::Hex64)
+LLVM_YAML_IS_FLOW_SEQUENCE_VECTOR(llvm::MCModuleYAML::Operand)
+LLVM_YAML_IS_SEQUENCE_VECTOR(llvm::MCModuleYAML::Inst)
+LLVM_YAML_IS_SEQUENCE_VECTOR(llvm::MCModuleYAML::Atom)
+LLVM_YAML_IS_SEQUENCE_VECTOR(llvm::MCModuleYAML::BasicBlock)
+LLVM_YAML_IS_SEQUENCE_VECTOR(llvm::MCModuleYAML::Function)
+
+namespace llvm {
+
+namespace yaml {
+
+template <> struct ScalarEnumerationTraits<MCAtom::AtomKind> {
+  static void enumeration(IO &IO, MCAtom::AtomKind &Kind);
+};
+
+template <> struct MappingTraits<MCModuleYAML::Atom> {
+  static void mapping(IO &IO, MCModuleYAML::Atom &A);
+};
+
+template <> struct MappingTraits<MCModuleYAML::Inst> {
+  static void mapping(IO &IO, MCModuleYAML::Inst &I);
+};
+
+template <> struct MappingTraits<MCModuleYAML::BasicBlock> {
+  static void mapping(IO &IO, MCModuleYAML::BasicBlock &BB);
+};
+
+template <> struct MappingTraits<MCModuleYAML::Function> {
+  static void mapping(IO &IO, MCModuleYAML::Function &Fn);
+};
+
+template <> struct MappingTraits<MCModuleYAML::Module> {
+  static void mapping(IO &IO, MCModuleYAML::Module &M);
+};
+
+template <> struct ScalarTraits<MCModuleYAML::Operand> {
+  static void output(const MCModuleYAML::Operand &, void *,
+                     llvm::raw_ostream &);
+  static StringRef input(StringRef, void *, MCModuleYAML::Operand &);
+};
+
+template <> struct ScalarTraits<MCModuleYAML::OpcodeEnum> {
+  static void output(const MCModuleYAML::OpcodeEnum &, void *,
+                     llvm::raw_ostream &);
+  static StringRef input(StringRef, void *, MCModuleYAML::OpcodeEnum &);
+};
+
+void ScalarEnumerationTraits<MCAtom::AtomKind>::enumeration(
+    IO &IO, MCAtom::AtomKind &Value) {
+  IO.enumCase(Value, "Text", MCAtom::TextAtom);
+  IO.enumCase(Value, "Data", MCAtom::DataAtom);
+}
+
+void MappingTraits<MCModuleYAML::Atom>::mapping(IO &IO, MCModuleYAML::Atom &A) {
+  IO.mapRequired("StartAddress", A.StartAddress);
+  IO.mapRequired("Size", A.Size);
+  IO.mapRequired("Type", A.Type);
+  if (A.Type == MCAtom::TextAtom)
+    IO.mapRequired("Content", A.Insts);
+  else if (A.Type == MCAtom::DataAtom)
+    IO.mapRequired("Content", A.Data);
+}
+
+void MappingTraits<MCModuleYAML::Inst>::mapping(IO &IO, MCModuleYAML::Inst &I) {
+  IO.mapRequired("Inst", I.Opcode);
+  IO.mapRequired("Size", I.Size);
+  IO.mapRequired("Ops", I.Operands);
+}
+
+void
+MappingTraits<MCModuleYAML::BasicBlock>::mapping(IO &IO,
+                                                 MCModuleYAML::BasicBlock &BB) {
+  IO.mapRequired("Address", BB.Address);
+  IO.mapRequired("Preds", BB.Preds);
+  IO.mapRequired("Succs", BB.Succs);
+}
+
+void MappingTraits<MCModuleYAML::Function>::mapping(IO &IO,
+                                                    MCModuleYAML::Function &F) {
+  IO.mapRequired("Name", F.Name);
+  IO.mapRequired("BasicBlocks", F.BasicBlocks);
+}
+
+void MappingTraits<MCModuleYAML::Module>::mapping(IO &IO,
+                                                  MCModuleYAML::Module &M) {
+  IO.mapRequired("Atoms", M.Atoms);
+  IO.mapOptional("Functions", M.Functions);
+}
+
+void
+ScalarTraits<MCModuleYAML::Operand>::output(const MCModuleYAML::Operand &Val,
+                                            void *Ctx, raw_ostream &Out) {
+  InstrRegInfoHolder *IRI = (InstrRegInfoHolder *)Ctx;
+
+  // FIXME: Doesn't support FPImm and expr/inst, but do these make sense?
+  if (Val.MCOp.isImm())
+    Out << "I" << Val.MCOp.getImm();
+  else if (Val.MCOp.isReg())
+    Out << "R" << IRI->MRI.getName(Val.MCOp.getReg());
+  else
+    llvm_unreachable("Trying to output invalid MCOperand!");
+}
+
+StringRef
+ScalarTraits<MCModuleYAML::Operand>::input(StringRef Scalar, void *Ctx,
+                                           MCModuleYAML::Operand &Val) {
+  InstrRegInfoHolder *IRI = (InstrRegInfoHolder *)Ctx;
+  char Type = 0;
+  if (Scalar.size() >= 1)
+    Type = Scalar.front();
+  if (Type != 'R' && Type != 'I')
+    return "Operand must start with 'R' (register) or 'I' (immediate).";
+  if (Type == 'R') {
+    unsigned Reg;
+    if (!IRI->matchRegister(Scalar.substr(1), Reg))
+      return "Invalid register name.";
+    Val.MCOp = MCOperand::CreateReg(Reg);
+  } else if (Type == 'I') {
+    int64_t RIVal;
+    if (Scalar.substr(1).getAsInteger(10, RIVal))
+      return "Invalid immediate value.";
+    Val.MCOp = MCOperand::CreateImm(RIVal);
+  } else {
+    Val.MCOp = MCOperand();
+  }
+  return StringRef();
+}
+
+void ScalarTraits<MCModuleYAML::OpcodeEnum>::output(
+    const MCModuleYAML::OpcodeEnum &Val, void *Ctx, raw_ostream &Out) {
+  InstrRegInfoHolder *IRI = (InstrRegInfoHolder *)Ctx;
+  Out << IRI->MII.getName(Val);
+}
+
+StringRef
+ScalarTraits<MCModuleYAML::OpcodeEnum>::input(StringRef Scalar, void *Ctx,
+                                              MCModuleYAML::OpcodeEnum &Val) {
+  InstrRegInfoHolder *IRI = (InstrRegInfoHolder *)Ctx;
+  unsigned Opc;
+  if (!IRI->matchOpcode(Scalar, Opc))
+    return "Invalid instruction opcode.";
+  Val = Opc;
+  return "";
+}
+
+} // end namespace yaml
+
+namespace {
+
+class MCModule2YAML {
+  const MCModule &MCM;
+  MCModuleYAML::Module YAMLModule;
+  void dumpAtom(const MCAtom *MCA);
+  void dumpFunction(const MCFunction *MCF);
+  void dumpBasicBlock(const MCBasicBlock *MCBB);
+
+public:
+  MCModule2YAML(const MCModule &MCM);
+  MCModuleYAML::Module &getYAMLModule();
+};
+
+class YAML2MCModule {
+  MCModule &MCM;
+
+public:
+  YAML2MCModule(MCModule &MCM);
+  StringRef parse(const MCModuleYAML::Module &YAMLModule);
+};
+
+} // end unnamed namespace
+
+MCModule2YAML::MCModule2YAML(const MCModule &MCM) : MCM(MCM), YAMLModule() {
+  for (MCModule::const_atom_iterator AI = MCM.atom_begin(), AE = MCM.atom_end();
+       AI != AE; ++AI)
+    dumpAtom(*AI);
+  for (MCModule::const_func_iterator FI = MCM.func_begin(), FE = MCM.func_end();
+       FI != FE; ++FI)
+    dumpFunction(*FI);
+}
+
+void MCModule2YAML::dumpAtom(const MCAtom *MCA) {
+  YAMLModule.Atoms.resize(YAMLModule.Atoms.size() + 1);
+  MCModuleYAML::Atom &A = YAMLModule.Atoms.back();
+  A.Type = MCA->getKind();
+  A.StartAddress = MCA->getBeginAddr();
+  A.Size = MCA->getEndAddr() - MCA->getBeginAddr() + 1;
+  if (const MCTextAtom *TA = dyn_cast<MCTextAtom>(MCA)) {
+    const size_t InstCount = TA->size();
+    A.Insts.resize(InstCount);
+    for (size_t i = 0; i != InstCount; ++i) {
+      const MCDecodedInst &MCDI = TA->at(i);
+      A.Insts[i].Opcode = MCDI.Inst.getOpcode();
+      A.Insts[i].Size = MCDI.Size;
+      const unsigned OpCount = MCDI.Inst.getNumOperands();
+      A.Insts[i].Operands.resize(OpCount);
+      for (unsigned oi = 0; oi != OpCount; ++oi)
+        A.Insts[i].Operands[oi].MCOp = MCDI.Inst.getOperand(oi);
+    }
+  } else if (const MCDataAtom *DA = dyn_cast<MCDataAtom>(MCA)) {
+    A.Data = DA->getData();
+  } else {
+    llvm_unreachable("Unknown atom type.");
+  }
+}
+
+void MCModule2YAML::dumpFunction(const MCFunction *MCF) {
+  YAMLModule.Functions.resize(YAMLModule.Functions.size() + 1);
+  MCModuleYAML::Function &F = YAMLModule.Functions.back();
+  F.Name = MCF->getName();
+  for (MCFunction::const_iterator BBI = MCF->begin(), BBE = MCF->end();
+       BBI != BBE; ++BBI) {
+    const MCBasicBlock *MCBB = *BBI;
+    F.BasicBlocks.resize(F.BasicBlocks.size() + 1);
+    MCModuleYAML::BasicBlock &BB = F.BasicBlocks.back();
+    BB.Address = MCBB->getInsts()->getBeginAddr();
+    for (MCBasicBlock::pred_const_iterator PI = MCBB->pred_begin(),
+                                           PE = MCBB->pred_end();
+         PI != PE; ++PI)
+      BB.Preds.push_back((*PI)->getInsts()->getBeginAddr());
+    for (MCBasicBlock::succ_const_iterator SI = MCBB->succ_begin(),
+                                           SE = MCBB->succ_end();
+         SI != SE; ++SI)
+      BB.Succs.push_back((*SI)->getInsts()->getBeginAddr());
+  }
+}
+
+MCModuleYAML::Module &MCModule2YAML::getYAMLModule() { return YAMLModule; }
+
+YAML2MCModule::YAML2MCModule(MCModule &MCM) : MCM(MCM) {}
+
+StringRef YAML2MCModule::parse(const MCModuleYAML::Module &YAMLModule) {
+  typedef std::vector<MCModuleYAML::Atom>::const_iterator AtomIt;
+  typedef std::vector<MCModuleYAML::Inst>::const_iterator InstIt;
+  typedef std::vector<MCModuleYAML::Operand>::const_iterator OpIt;
+
+  typedef DenseMap<uint64_t, MCTextAtom *> AddrToTextAtomTy;
+  AddrToTextAtomTy TAByAddr;
+
+  for (AtomIt AI = YAMLModule.Atoms.begin(), AE = YAMLModule.Atoms.end();
+       AI != AE; ++AI) {
+    uint64_t StartAddress = AI->StartAddress;
+    if (AI->Size == 0)
+      return "Atoms can't be empty!";
+    uint64_t EndAddress = StartAddress + AI->Size - 1;
+    switch (AI->Type) {
+    case MCAtom::TextAtom: {
+      MCTextAtom *TA = MCM.createTextAtom(StartAddress, EndAddress);
+      TAByAddr[StartAddress] = TA;
+      for (InstIt II = AI->Insts.begin(), IE = AI->Insts.end(); II != IE;
+           ++II) {
+        MCInst MI;
+        MI.setOpcode(II->Opcode);
+        for (OpIt OI = II->Operands.begin(), OE = II->Operands.end(); OI != OE;
+             ++OI)
+          MI.addOperand(OI->MCOp);
+        TA->addInst(MI, II->Size);
+      }
+      break;
+    }
+    case MCAtom::DataAtom: {
+      MCDataAtom *DA = MCM.createDataAtom(StartAddress, EndAddress);
+      SmallVector<char, 64> Data;
+      raw_svector_ostream OS(Data);
+      AI->Data.writeAsBinary(OS);
+      OS.flush();
+      for (size_t i = 0, e = Data.size(); i != e; ++i)
+        DA->addData((uint8_t)Data[i]);
+      break;
+    }
+    }
+  }
+
+  typedef std::vector<MCModuleYAML::Function>::const_iterator FuncIt;
+  typedef std::vector<MCModuleYAML::BasicBlock>::const_iterator BBIt;
+  typedef std::vector<yaml::Hex64>::const_iterator AddrIt;
+  for (FuncIt FI = YAMLModule.Functions.begin(),
+              FE = YAMLModule.Functions.end();
+       FI != FE; ++FI) {
+    MCFunction *MCFN = MCM.createFunction(FI->Name);
+    for (BBIt BBI = FI->BasicBlocks.begin(), BBE = FI->BasicBlocks.end();
+         BBI != BBE; ++BBI) {
+      AddrToTextAtomTy::const_iterator It = TAByAddr.find(BBI->Address);
+      if (It == TAByAddr.end())
+        return "Basic block start address doesn't match any text atom!";
+      MCFN->createBlock(*It->second);
+    }
+    for (BBIt BBI = FI->BasicBlocks.begin(), BBE = FI->BasicBlocks.end();
+         BBI != BBE; ++BBI) {
+      MCBasicBlock *MCBB = MCFN->find(BBI->Address);
+      if (!MCBB)
+        return "Couldn't find matching basic block in function.";
+      for (AddrIt PI = BBI->Preds.begin(), PE = BBI->Preds.end(); PI != PE;
+           ++PI) {
+        MCBasicBlock *Pred = MCFN->find(*PI);
+        if (!Pred)
+          return "Couldn't find predecessor basic block.";
+        MCBB->addPredecessor(Pred);
+      }
+      for (AddrIt SI = BBI->Succs.begin(), SE = BBI->Succs.end(); SI != SE;
+           ++SI) {
+        MCBasicBlock *Succ = MCFN->find(*SI);
+        if (!Succ)
+          return "Couldn't find predecessor basic block.";
+        MCBB->addSuccessor(Succ);
+      }
+    }
+  }
+  return "";
+}
+
+StringRef mcmodule2yaml(raw_ostream &OS, const MCModule &MCM,
+                        const MCInstrInfo &MII, const MCRegisterInfo &MRI) {
+  MCModule2YAML Dumper(MCM);
+  InstrRegInfoHolder IRI(MII, MRI);
+  yaml::Output YOut(OS, (void *)&IRI);
+  YOut << Dumper.getYAMLModule();
+  return "";
+}
+
+StringRef yaml2mcmodule(OwningPtr<MCModule> &MCM, StringRef YamlContent,
+                        const MCInstrInfo &MII, const MCRegisterInfo &MRI) {
+  MCM.reset(new MCModule);
+  YAML2MCModule Parser(*MCM);
+  MCModuleYAML::Module YAMLModule;
+  InstrRegInfoHolder IRI(MII, MRI);
+  yaml::Input YIn(YamlContent, (void *)&IRI);
+  YIn >> YAMLModule;
+  if (error_code ec = YIn.error())
+    return ec.message();
+  StringRef err = Parser.parse(YAMLModule);
+  if (!err.empty())
+    return err;
+  return "";
+}
+
+} // end namespace llvm
diff --git a/tools/llvm-objdump/llvm-objdump.cpp b/tools/llvm-objdump/llvm-objdump.cpp
index 122ac83398..a4cd6a2f73 100644
--- a/tools/llvm-objdump/llvm-objdump.cpp
+++ b/tools/llvm-objdump/llvm-objdump.cpp
@@ -31,6 +31,7 @@
 #include "llvm/MC/MCInstrAnalysis.h"
 #include "llvm/MC/MCInstrInfo.h"
 #include "llvm/MC/MCModule.h"
+#include "llvm/MC/MCModuleYAML.h"
 #include "llvm/MC/MCObjectDisassembler.h"
 #include "llvm/MC/MCObjectFileInfo.h"
 #include "llvm/MC/MCObjectSymbolizer.h"
@@ -61,6 +62,7 @@
 #include <algorithm>
 #include <cctype>
 #include <cstring>
+
 using namespace llvm;
 using namespace object;
 
@@ -139,6 +141,12 @@ static cl::opt<bool>
 CFG("cfg", cl::desc("Create a CFG for every function found in the object"
                       " and write it to a graphviz file"));
 
+// FIXME: Does it make sense to have a dedicated tool for yaml cfg output?
+static cl::opt<std::string>
+YAMLCFG("yaml-cfg",
+        cl::desc("Create a CFG and write it as a YAML MCModule."),
+        cl::value_desc("yaml output file"));
+
 static StringRef ToolName;
 
 bool llvm::error(error_code ec) {
@@ -178,6 +186,7 @@ static const Target *getTarget(const ObjectFile *Obj = NULL) {
 }
 
 // Write a graphviz file for the CFG inside an MCFunction.
+// FIXME: Use GraphWriter
 static void emitDOTFile(const char *FileName, const MCFunction &f,
                         MCInstPrinter *IP) {
   // Start a new dot file.
@@ -333,7 +342,7 @@ static void DisassembleObject(const ObjectFile *Obj, bool InlineRelocs) {
     return;
   }
 
-  if (CFG) {
+  if (CFG || !YAMLCFG.empty()) {
     OwningPtr<MCObjectDisassembler> OD(
       new MCObjectDisassembler(*Obj, *DisAsm, *MIA));
     OwningPtr<MCModule> Mod(OD->buildModule(/* withCFG */ true));
@@ -350,14 +359,25 @@ static void DisassembleObject(const ObjectFile *Obj, bool InlineRelocs) {
         }
       }
     }
-    for (MCModule::const_func_iterator FI = Mod->func_begin(),
-                                       FE = Mod->func_end();
-                                       FI != FE; ++FI) {
-      static int filenum = 0;
-      emitDOTFile((Twine((*FI)->getName()) + "_" +
-                   utostr(filenum) + ".dot").str().c_str(),
-                    **FI, IP.get());
-      ++filenum;
+    if (CFG) {
+      for (MCModule::const_func_iterator FI = Mod->func_begin(),
+                                         FE = Mod->func_end();
+                                         FI != FE; ++FI) {
+        static int filenum = 0;
+        emitDOTFile((Twine((*FI)->getName()) + "_" +
+                     utostr(filenum) + ".dot").str().c_str(),
+                      **FI, IP.get());
+        ++filenum;
+      }
+    }
+    if (!YAMLCFG.empty()) {
+      std::string Error;
+      raw_fd_ostream YAMLOut(YAMLCFG.c_str(), Error);
+      if (!Error.empty()) {
+        errs() << "llvm-objdump: warning: " << Error << '\n';
+        return;
+      }
+      mcmodule2yaml(YAMLOut, *Mod, *MII, *MRI);
     }
   }