[WIP][M68k][Disassembler] Adopt the new variable length infrastructure in disassembler

[0x59616e]

Summary

We still have some problems that need discussion

• Arithmetic instructions with addressing mode dd & dr have decoding conflict. For example: ADD32dd & ADD32dr, SUB16dd & SUB16dr

• pc-relative decoder.

[0x59616e]

FYI, I've found some bugs in operand decoding. But that doesn't bother the discussion of the problems I listed.

[0x59616e]

OK, after fixing that bug, more decoding conflict show up. I don't know why. It may take some time.

[0x59616e]

Bug has been fixed, llvm/test/MC/M68k/Relaxations/branch.s is passed.

[0x59616e]

FYI, here are the instructions that have decoding conflict:

OR16dd / OR16dr
OR32dd/ OR32dr
SUB16dd / SUB16dr
SUB32dd / SUB32dr
AND16dd / AND16dr
AND32dd / AND32dr
ADD16dd / ADD16dr
ADD32dd / ADD32dr

I have two ideas:

• Decode these instruction manually and add a flag to suppress the "decode conflict" warning message in TableGen

or

• Refactor these instruction. For example, can ADD32dd be removed and only use ADD32dr ?

[0x59616e]

update diff. I forgot the context

[0x59616e]

More tests are needed, that's huge amount of work. I may be too hasty.

llvm/lib/Target/M68k/CMakeLists.txt

 add_llvm_component_group(M68k)
 
 set(LLVM_TARGET_DEFINITIONS M68k.td)
 
 tablegen(LLVM M68kGenGlobalISel.inc       -gen-global-isel)
 tablegen(LLVM M68kGenRegisterInfo.inc     -gen-register-info)
 tablegen(LLVM M68kGenRegisterBank.inc     -gen-register-bank)
 tablegen(LLVM M68kGenInstrInfo.inc        -gen-instr-info)
 tablegen(LLVM M68kGenSubtargetInfo.inc    -gen-subtarget)
 tablegen(LLVM M68kGenMCCodeBeads.inc      -gen-code-beads)
 tablegen(LLVM M68kGenMCCodeEmitter.inc    -gen-emitter)
 tablegen(LLVM M68kGenMCPseudoLowering.inc -gen-pseudo-lowering)
 tablegen(LLVM M68kGenDAGISel.inc          -gen-dag-isel)
 tablegen(LLVM M68kGenCallingConv.inc      -gen-callingconv)
 tablegen(LLVM M68kGenAsmWriter.inc        -gen-asm-writer)
 tablegen(LLVM M68kGenAsmMatcher.inc       -gen-asm-matcher)
+tablegen(LLVM M68kGenDisassemblerTable.inc -gen-disassembler)
 
 add_public_tablegen_target(M68kCommonTableGen)
 
 add_llvm_target(M68kCodeGen
   GISel/M68kCallLowering.cpp
   GISel/M68kInstructionSelector.cpp
   GISel/M68kLegalizerInfo.cpp
   GISel/M68kRegisterBankInfo.cpp

llvm/lib/Target/M68k/Disassembler/M68kDisassembler.cpp

 #include "M68kSubtarget.h"
 #include "MCTargetDesc/M68kMCCodeEmitter.h"
 #include "MCTargetDesc/M68kMCTargetDesc.h"
 #include "TargetInfo/M68kTargetInfo.h"
 
 #include "llvm/MC/MCAsmInfo.h"
 #include "llvm/MC/MCContext.h"
 #include "llvm/MC/MCDisassembler/MCDisassembler.h"
+#include "llvm/MC/MCFixedLenDisassembler.h"
 #include "llvm/MC/MCInst.h"
 #include "llvm/MC/TargetRegistry.h"
+#include "llvm/Support/Endian.h"
 
 using namespace llvm;
 
 #define DEBUG_TYPE "m68k-disassembler"
 
 typedef MCDisassembler::DecodeStatus DecodeStatus;
+const unsigned MaxInstrWord = 11;
 
-namespace {
-constexpr unsigned MaxInstructionWords = 11;
-
-class M68kInstructionBuffer {
-  typedef SmallVector<uint16_t, MaxInstructionWords> BufferType;
-  BufferType Buffer;
-
-public:
-  M68kInstructionBuffer() {}
-
-  template <typename TIt>
-  M68kInstructionBuffer(TIt Start, TIt End) : Buffer(Start, End) {}
-
-  unsigned size() const { return Buffer.size(); }
-
-  BufferType::const_iterator begin() const { return Buffer.begin(); }
-  BufferType::const_iterator end() const { return Buffer.end(); }
-
-  uint16_t operator[](unsigned Index) const {
-    assert((Index < Buffer.size()) && "tried to read out of bounds word");
-    return Buffer[Index];
-  }
+static DecodeStatus DecodeRegisterClass(MCInst &Inst, uint64_t RegNo,
+                                        uint64_t Address, const void *Decoder,
+                                        uint64_t FirstReg) {
+  if (RegNo >= 8)
+    return DecodeStatus::Fail;
+  Inst.addOperand(MCOperand::createReg(FirstReg + RegNo));
+  return DecodeStatus::Success;
 
-  void truncate(unsigned NewLength) {
-    assert((NewLength <= Buffer.size()) &&
-           "instruction buffer too short to truncate");
-    Buffer.resize(NewLength);
-  }
+static DecodeStatus DecodeDR32RegisterClass(MCInst &Inst, uint64_t RegNo,
+                                            uint64_t Address,
+                                            const void *Decoder) {
+  return DecodeRegisterClass(Inst, RegNo, Address, Decoder, M68k::D0);
 
-  void dump() const;
-
-  static M68kInstructionBuffer fill(ArrayRef<uint8_t> Bytes);
-};
-
-class M68kInstructionReader {
-  M68kInstructionBuffer Buffer;
-  unsigned NumRead;
-
-public:
-  M68kInstructionReader(M68kInstructionBuffer Buf) : Buffer(Buf), NumRead(0) {}
-
-  unsigned size() const { return (Buffer.size() * 16) - NumRead; }
-
-  uint64_t readBits(unsigned NumBits);
-};
+static DecodeStatus DecodeDR16RegisterClass(MCInst &Inst, uint64_t RegNo,
+                                            uint64_t Address,
+                                            const void *Decoder) {
+  return DecodeRegisterClass(Inst, RegNo, Address, Decoder, M68k::WD0);
+}
 
-struct M68kInstructionLookup {
-  unsigned OpCode;
-  M68kInstructionBuffer Mask;
-  M68kInstructionBuffer Value;
-
-  unsigned size() const { return Mask.size(); }
-
-  // Check whether this instruction could possibly match the given bytes.
-  bool matches(const M68kInstructionBuffer &Test) const;
-  void dump() const;
-};
+static DecodeStatus DecodeDR8RegisterClass(MCInst &Inst, uint64_t RegNo,
+                                           uint64_t Address,
+                                           const void *Decoder) {
+  return DecodeRegisterClass(Inst, RegNo, Address, Decoder, M68k::BD0);
+}
 
-class M68kInstructionLookupBuilder {
-  std::array<uint16_t, MaxInstructionWords> Mask;
-  std::array<uint16_t, MaxInstructionWords> Value;
-  unsigned NumWritten;
+static DecodeStatus DecodeAR32RegisterClass(MCInst &Inst, uint64_t RegNo,
+                                            uint64_t Address,
+                                            const void *Decoder) {
+  return DecodeRegisterClass(Inst, RegNo, Address, Decoder, M68k::A0);
+}
 
-public:
-  M68kInstructionLookupBuilder() : NumWritten(0) {
-    Mask.fill(0);
-    Value.fill(0);
-  }
+static DecodeStatus DecodeXR32RegisterClass(MCInst &Inst, uint64_t RegNo,
+                                            uint64_t Address,
+                                            const void *Decoder) {
+  return DecodeRegisterClass(Inst, RegNo & 0x7ULL, Address, Decoder,
+                             (RegNo >> 3 ? M68k::A0 : M68k::D0));
 
-  unsigned numWords() const {
-    assert(!(NumWritten & 0xf) && "instructions must be whole words");
-    return NumWritten >> 4;
-  }
+static DecodeStatus DecodeXR16RegisterClass(MCInst &Inst, uint64_t RegNo,
+                                            uint64_t Address,
+                                            const void *Decoder) {
+  return DecodeRegisterClass(Inst, RegNo & 07ULL, Address, Decoder,
+                             (RegNo >> 3 ? M68k::WA0 : M68k::WD0));
 
-  bool isValid() const;
-  M68kInstructionLookup build(unsigned OpCode);
-  void addBits(unsigned N, uint64_t Bits);
-  void skipBits(unsigned N);
-};
+#include "M68kGenDisassemblerTable.inc"
 
 /// A disassembler class for M68k.
 class M68kDisassembler : public MCDisassembler {
   MCInstrInfo *MCII;
-  std::vector<M68kInstructionLookup> Lookups;
 
 public:
   M68kDisassembler(const MCSubtargetInfo &STI, MCContext &Ctx,
                    MCInstrInfo *MCII)
-      : MCDisassembler(STI, Ctx), MCII(MCII) {
-    buildBeadTable();
-  }
+      : MCDisassembler(STI, Ctx), MCII(MCII) {}
   virtual ~M68kDisassembler() {}
 
-  void buildBeadTable();
   DecodeStatus getInstruction(MCInst &Instr, uint64_t &Size,
                               ArrayRef<uint8_t> Bytes, uint64_t Address,
                               raw_ostream &CStream) const override;
-  void decodeReg(MCInst &Instr, unsigned int Bead,
-                 M68kInstructionReader &Reader, unsigned &Scratch) const;
-  void decodeImm(MCInst &Instr, unsigned int Bead,
-                 M68kInstructionReader &Reader, unsigned &Scratch) const;
-  unsigned int getRegOperandIndex(MCInst &Instr, unsigned int Bead) const;
-  unsigned int getImmOperandIndex(MCInst &Instr, unsigned int Bead) const;
 };
-} // namespace
-
-static unsigned RegisterDecode[] = {
-    M68k::A0, M68k::A1, M68k::A2, M68k::A3, M68k::A4, M68k::A5,
-    M68k::A6, M68k::SP, M68k::D0, M68k::D1, M68k::D2, M68k::D3,
-    M68k::D4, M68k::D5, M68k::D6, M68k::D7,
-};
-
-#if !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP)
-LLVM_DUMP_METHOD
-void M68kInstructionBuffer::dump() const {
-  for (auto Word : Buffer) {
-    for (unsigned B = 0; B < 16; ++B) {
-      uint16_t Bit = (1 << (16 - B - 1));
-      unsigned IsClear = !(Word & Bit);
-
-      if (B == 8)
-        dbgs() << " ";
-
-      char Ch = IsClear ? '0' : '1';
-      dbgs() << Ch;
-    }
-
-    dbgs() << " ";
-  }
-
-  dbgs() << "\n";
-}
-#endif
-
-M68kInstructionBuffer M68kInstructionBuffer::fill(ArrayRef<uint8_t> Bytes) {
-  SmallVector<uint16_t, MaxInstructionWords> Buffer;
-  Buffer.resize(std::min(Bytes.size() / 2, Buffer.max_size()));
-
-  for (unsigned I = 0, E = Buffer.size(); I < E; ++I) {
-    unsigned Offset = I * 2;
-    uint64_t Hi = Bytes[Offset];
-    uint64_t Lo = Bytes[Offset + 1];
-    uint64_t Word = (Hi << 8) | Lo;
-    Buffer[I] = Word;
-
-    LLVM_DEBUG(
-        errs() << format("Read word %x (%d)\n", (unsigned)Word, Buffer.size()));
-  }
-
-  return M68kInstructionBuffer(Buffer.begin(), Buffer.end());
-}
-
-uint64_t M68kInstructionReader::readBits(unsigned NumBits) {
-  assert((size() >= NumBits) && "not enough bits to read");
-
-  // We have to read the bits in 16-bit chunks because we read them as
-  // 16-bit words but they're actually written in big-endian. If a read
-  // crosses a word boundary we have to be careful.
-
-  uint64_t Value = 0;
-  unsigned BitsRead = 0;
-
-  while (BitsRead < NumBits) {
-    unsigned AvailableThisWord = 16 - (NumRead & 0xf);
-    unsigned ToRead = std::min(NumBits, AvailableThisWord);
-
-    unsigned WordIndex = NumRead >> 4;
-    uint64_t ThisWord = Buffer[WordIndex] >> (NumRead & 0xf);
-    uint64_t Mask = (1 << ToRead) - 1;
-    Value |= (ThisWord & Mask) << BitsRead;
-    NumRead += ToRead;
-    BitsRead += ToRead;
-  }
-  return Value;
-}
-
-bool M68kInstructionLookup::matches(const M68kInstructionBuffer &Test) const {
-  if (Test.size() < Value.size())
-    return false;
-
-  for (unsigned I = 0, E = Value.size(); I < E; ++I) {
-    uint16_t Have = Test[I];
-    uint16_t Need = Value[I];
-    uint16_t WordMask = Mask[I];
-
-    if ((Have & WordMask) != Need)
-      return false;
-  }
-
-  return true;
-}
-
-#if !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP)
-LLVM_DUMP_METHOD
-void M68kInstructionLookup::dump() const {
-  dbgs() << "M68kInstructionLookup " << OpCode << " ";
-
-  for (unsigned I = 0, E = Mask.size(); I < E; ++I) {
-    uint16_t WordMask = Mask[I];
-    uint16_t WordValue = Value[I];
-
-    for (unsigned B = 0; B < 16; ++B) {
-      uint16_t Bit = (1 << (15 - B));
-      unsigned IsMasked = !(WordMask & Bit);
-      unsigned IsClear = !(WordValue & Bit);
-
-      if (B == 8)
-        dbgs() << " ";
-
-      char Ch = IsMasked ? '?' : (IsClear ? '0' : '1');
-      dbgs() << Ch;
-    }
-
-    dbgs() << " ";
-  }
-
-  dbgs() << "\n";
-}
-#endif
-
-bool M68kInstructionLookupBuilder::isValid() const {
-  for (unsigned I = 0, E = numWords(); I < E; ++I)
-    if (Mask[I])
-      return true;
-
-  return false;
-}
-
-M68kInstructionLookup M68kInstructionLookupBuilder::build(unsigned OpCode) {
-  unsigned NumWords = numWords();
-  M68kInstructionBuffer MaskBuffer(Mask.begin(), Mask.begin() + NumWords);
-  M68kInstructionBuffer ValueBuffer(Value.begin(), Value.begin() + NumWords);
-  M68kInstructionLookup Ret;
-  Ret.OpCode = OpCode;
-  Ret.Mask = MaskBuffer;
-  Ret.Value = ValueBuffer;
-  return Ret;
-}
-
-void M68kInstructionLookupBuilder::addBits(unsigned N, uint64_t Bits) {
-  while (N > 0) {
-    unsigned WordIndex = NumWritten >> 4;
-    unsigned WordOffset = NumWritten & 0xf;
-    unsigned AvailableThisWord = 16 - WordOffset;
-    unsigned ToWrite = std::min(AvailableThisWord, N);
-
-    uint16_t WordMask = (1 << ToWrite) - 1;
-    uint16_t BitsToWrite = Bits & WordMask;
-
-    Value[WordIndex] |= (BitsToWrite << WordOffset);
-    Mask[WordIndex] |= (WordMask << WordOffset);
-
-    Bits >>= ToWrite;
-    N -= ToWrite;
-    NumWritten += ToWrite;
-  }
-}
-
-void M68kInstructionLookupBuilder::skipBits(unsigned N) { NumWritten += N; }
-
-// This is a bit of a hack: we can't generate this table at table-gen time
-// because some of the definitions are in our platform.
-void M68kDisassembler::buildBeadTable() {
-  const unsigned NumInstr = M68k::INSTRUCTION_LIST_END;
-  Lookups.reserve(NumInstr);
-
-  for (unsigned I = 0; I < NumInstr; ++I) {
-    M68kInstructionLookupBuilder Builder;
-
-    for (const uint8_t *PartPtr = M68k::getMCInstrBeads(I); *PartPtr;
-         ++PartPtr) {
-      uint8_t Bead = *PartPtr;
-      unsigned Ext = Bead >> 4;
-      unsigned Op = Bead & 0xf;
-
-      switch (Op) {
-      case M68kBeads::Ctrl:
-        // Term will have already been skipped by the loop.
-        assert((Ext == M68kBeads::Ignore) && "unexpected command bead");
-        break;
-
-      case M68kBeads::Bits1:
-        Builder.addBits(1, Ext);
-        break;
-
-      case M68kBeads::Bits2:
-        Builder.addBits(2, Ext);
-        break;
-
-      case M68kBeads::Bits3:
-        Builder.addBits(3, Ext);
-        break;
-
-      case M68kBeads::Bits4:
-        Builder.addBits(4, Ext);
-        break;
-
-      case M68kBeads::DAReg:
-      case M68kBeads::DA:
-      case M68kBeads::DReg:
-      case M68kBeads::Reg:
-        if (Op != M68kBeads::DA)
-          Builder.skipBits(3);
-
-        if (Op != M68kBeads::Reg && Op != M68kBeads::DReg)
-          Builder.skipBits(1);
-
-        break;
-
-      case M68kBeads::Disp8:
-        Builder.skipBits(8);
-        break;
-
-      case M68kBeads::Imm8:
-      case M68kBeads::Imm16:
-        Builder.skipBits(16);
-        break;
-
-      case M68kBeads::Imm32:
-        Builder.skipBits(32);
-        break;
-
-      case M68kBeads::Imm3:
-        Builder.skipBits(3);
-        break;
-
-      default:
-        llvm_unreachable("unhandled bead type");
-      }
-    }
-
-    // Ignore instructions which are unmatchable (usually pseudo instructions).
-    if (!Builder.isValid())
-      continue;
-
-    Lookups.push_back(Builder.build(I));
-  }
-}
-
-unsigned M68kDisassembler::getRegOperandIndex(MCInst &Instr,
-                                              unsigned Bead) const {
-  unsigned Ext = Bead >> 4;
-
-  const MCInstrDesc &Desc = MCII->get(Instr.getOpcode());
-  auto MIOpIdx = M68k::getLogicalOperandIdx(Instr.getOpcode(), Ext & 7);
-
-  if (M68kII::hasMultiMIOperands(Instr.getOpcode(), Ext & 7)) {
-    bool IsPCRel = Desc.OpInfo[MIOpIdx].OperandType == MCOI::OPERAND_PCREL;
-    if (IsPCRel)
-      MIOpIdx += M68k::PCRelIndex;
-    else if (Ext & 8)
-      MIOpIdx += M68k::MemIndex;
-    else
-      MIOpIdx += M68k::MemBase;
-  }
-
-  return MIOpIdx;
-}
-
-unsigned M68kDisassembler::getImmOperandIndex(MCInst &Instr,
-                                              unsigned Bead) const {
-  unsigned Ext = Bead >> 4;
-
-  const MCInstrDesc &Desc = MCII->get(Instr.getOpcode());
-  auto MIOpIdx = M68k::getLogicalOperandIdx(Instr.getOpcode(), Ext & 7);
-
-  if (M68kII::hasMultiMIOperands(Instr.getOpcode(), Ext & 7)) {
-    bool IsPCRel = Desc.OpInfo[MIOpIdx].OperandType == MCOI::OPERAND_PCREL;
-    if (IsPCRel)
-      MIOpIdx += M68k::PCRelDisp;
-    else if (Ext & 8)
-      MIOpIdx += M68k::MemOuter;
-    else
-      MIOpIdx += M68k::MemDisp;
-  }
-
-  return MIOpIdx;
-}
-
-void M68kDisassembler::decodeReg(MCInst &Instr, unsigned Bead,
-                                 M68kInstructionReader &Reader,
-                                 unsigned &Scratch) const {
-  unsigned Op = Bead & 0xf;
-  LLVM_DEBUG(errs() << format("decodeReg %x\n", Bead));
-
-  if (Op != M68kBeads::DA)
-    Scratch = (Scratch & ~7) | Reader.readBits(3);
-
-  if (Op != M68kBeads::Reg) {
-    bool DA = (Op != M68kBeads::DReg) && Reader.readBits(1);
-    if (!DA)
-      Scratch |= 8;
-    else
-      Scratch &= ~8;
-  }
-}
-
-void M68kDisassembler::decodeImm(MCInst &Instr, unsigned Bead,
-                                 M68kInstructionReader &Reader,
-                                 unsigned &Scratch) const {
-  unsigned Op = Bead & 0xf;
-  LLVM_DEBUG(errs() << format("decodeImm %x\n", Bead));
-
-  unsigned NumToRead;
-  switch (Op) {
-  case M68kBeads::Disp8:
-    NumToRead = 8;
-    break;
-  case M68kBeads::Imm8:
-  case M68kBeads::Imm16:
-    NumToRead = 16;
-    break;
-  case M68kBeads::Imm32:
-    NumToRead = 32;
-    break;
-  case M68kBeads::Imm3:
-    NumToRead = 3;
-    break;
-  default:
-    llvm_unreachable("invalid imm");
-  }
-
-  Scratch = (NumToRead < 32) ? (Scratch << NumToRead) : 0;
-  Scratch |= Reader.readBits(NumToRead);
-}
 
 DecodeStatus M68kDisassembler::getInstruction(MCInst &Instr, uint64_t &Size,
                                               ArrayRef<uint8_t> Bytes,
                                               uint64_t Address,
                                               raw_ostream &CStream) const {
-  // Read and shift the input (fetch as much as we can for now).
-  auto Buffer = M68kInstructionBuffer::fill(Bytes);
-  if (Buffer.size() == 0)
-    return Fail;
-
-  // Check through our lookup table.
-  bool Found = false;
-  for (unsigned I = 0, E = Lookups.size(); I < E; ++I) {
-    const M68kInstructionLookup &Lookup = Lookups[I];
-    if (!Lookup.matches(Buffer))
-      continue;
-
-    Found = true;
-    Size = Lookup.size() * 2;
-    Buffer.truncate(Lookup.size());
-    Instr.setOpcode(Lookup.OpCode);
-    LLVM_DEBUG(errs() << "decoding instruction " << MCII->getName(Lookup.OpCode)
-                      << "\n");
-    break;
-  }
-
-  if (!Found)
-    return Fail;
-
-  M68kInstructionReader Reader(Buffer);
-  const MCInstrDesc &Desc = MCII->get(Instr.getOpcode());
-  unsigned NumOperands = Desc.NumOperands;
-
-  // Now use the beads to decode the operands.
-  enum class OperandType {
-    Invalid,
-    Reg,
-    Imm,
-  };
-
-  SmallVector<OperandType, 6> OpType(NumOperands, OperandType::Invalid);
-  SmallVector<unsigned, 6> Scratch(NumOperands, 0);
-  for (const uint8_t *PartPtr = M68k::getMCInstrBeads(Instr.getOpcode());
-       *PartPtr; ++PartPtr) {
-    uint8_t Bead = *PartPtr;
-    unsigned Ext = Bead >> 4;
-    unsigned Op = Bead & 0xf;
-    unsigned MIOpIdx;
-
-    switch (Op) {
-    case M68kBeads::Ctrl:
-      // Term will have already been skipped by the loop.
-      assert((Ext == M68kBeads::Ignore) && "unexpected command bead");
-      break;
-
-      // These bits are constant - if we're here we've already matched them.
-    case M68kBeads::Bits1:
-      Reader.readBits(1);
-      break;
-    case M68kBeads::Bits2:
-      Reader.readBits(2);
-      break;
-    case M68kBeads::Bits3:
-      Reader.readBits(3);
-      break;
-    case M68kBeads::Bits4:
-      Reader.readBits(4);
-      break;
-
-    case M68kBeads::DAReg:
-    case M68kBeads::DA:
-    case M68kBeads::DReg:
-    case M68kBeads::Reg:
-      MIOpIdx = getRegOperandIndex(Instr, Bead);
-      assert(((OpType[MIOpIdx] == OperandType::Invalid) ||
-              (OpType[MIOpIdx] == OperandType::Reg)) &&
-             "operands cannot change type");
-      OpType[MIOpIdx] = OperandType::Reg;
-      decodeReg(Instr, Bead, Reader, Scratch[MIOpIdx]);
-      break;
-
-    case M68kBeads::Disp8:
-    case M68kBeads::Imm8:
-    case M68kBeads::Imm16:
-    case M68kBeads::Imm32:
-    case M68kBeads::Imm3:
-      MIOpIdx = getImmOperandIndex(Instr, Bead);
-      assert(((OpType[MIOpIdx] == OperandType::Invalid) ||
-              (OpType[MIOpIdx] == OperandType::Imm)) &&
-             "operands cannot change type");
-      OpType[MIOpIdx] = OperandType::Imm;
-      decodeImm(Instr, Bead, Reader, Scratch[MIOpIdx]);
-      break;
-
-    default:
-      llvm_unreachable("unhandled bead type");
-    }
-  }
-
-  // Copy constrained operands.
-  for (unsigned DstMIOpIdx = 0; DstMIOpIdx < NumOperands; ++DstMIOpIdx) {
-    int TiedTo = Desc.getOperandConstraint(DstMIOpIdx, MCOI::TIED_TO);
-    if (TiedTo < 0)
-      continue;
-
-    unsigned SrcMIOpIdx = TiedTo;
-
-    unsigned OpCount = 0;
-    for (unsigned I = 0;; ++I) {
-      unsigned Offset = M68k::getLogicalOperandIdx(Instr.getOpcode(), I);
-      assert(Offset <= SrcMIOpIdx && "missing logical operand");
-      if (Offset == SrcMIOpIdx) {
-        OpCount = M68k::getLogicalOperandSize(Instr.getOpcode(), I);
-        break;
-      }
-    }
-    assert(OpCount != 0 && "operand count not found");
-
-    for (unsigned I = 0; I < OpCount; ++I) {
-      assert(OpType[DstMIOpIdx + I] == OperandType::Invalid &&
-             "tried to stomp over operand whilst applying constraints");
-      OpType[DstMIOpIdx + I] = OpType[SrcMIOpIdx + I];
-      Scratch[DstMIOpIdx + I] = Scratch[SrcMIOpIdx + I];
-    }
-  }
-
-  // Create the operands from our scratch space.
-  for (unsigned O = 0; O < NumOperands; ++O) {
-    switch (OpType[O]) {
-    case OperandType::Invalid:
-      assert(false && "operand not parsed");
-
-    case OperandType::Imm:
-      Instr.addOperand(MCOperand::createImm(Scratch[O]));
-      break;
-
-    case OperandType::Reg:
-      Instr.addOperand(MCOperand::createReg(RegisterDecode[Scratch[O]]));
-      break;
-    }
+  uint64_t insn = support::endian::read16be(Bytes.data());
+  DecodeStatus Result;
+  Result = decodeInstruction(
+      DecoderTable80, Instr, insn, Address, this, STI,
+      [&](APInt &insn, unsigned InstrBits) {
+        assert(!(InstrBits & 0x7) && "Instruction bits is not multiple of 8");
+        Size = InstrBits >> 3;
+        for (unsigned i = 2U; i < Size; i += 2) {
+          uint64_t tmp = support::endian::read16be(&Bytes[i]);
+          insn.insertBits(tmp, i * 8, 16);
         }
-
-  assert((Reader.size() == 0) && "wrong number of bits consumed");
-  return Success;
+      });
+  return Result;
 }
 
 static MCDisassembler *createM68kDisassembler(const Target &T,
                                               const MCSubtargetInfo &STI,
                                               MCContext &Ctx) {
   return new M68kDisassembler(STI, Ctx, T.createMCInstrInfo());
 }
 
 extern "C" LLVM_EXTERNAL_VISIBILITY void LLVMInitializeM68kDisassembler() {
   // Register the disassembler.
   TargetRegistry::RegisterMCDisassembler(getTheM68kTarget(),
                                          createM68kDisassembler);
 }

llvm/lib/Target/M68k/M68kInstrFormats.td

class MxInst<dag outs, dag ins,
   let InOperandList  = ins;
   let AsmString      = asmStr;
   let Pattern        = pattern;
   let Itinerary      = itin;
 
   // Byte stream
   field bits<192> Beads = beads.Value;
   dag Inst = (ascend);
-
+  bit isVarLenInst = 1;
   // Number of bytes
   let Size = 0;
 
   let UseLogicalOperandMappings = 1;
 }
 
 // M68k PSEUDO INSTRUCTION
 class MxPseudo<dag outs, dag ins, list<dag> pattern = []>
     : MxInst<outs, ins, "; error: this should not be emitted", pattern> {
   let isPseudo = 1;
 }

llvm/test/MC/Disassembler/M68k/bits.txt

 # RUN: llvm-mc -disassemble -triple m68k %s | FileCheck %s
-# Disable this particular test until migration to the new code emitter is
-# finished.
-# XFAIL: *
 
-# CHECK: btst #0, %d3
-0x08 0x03 0x00 0x00
+# CHECK: btst #20, %d3
+0x08 0x03 0x00 0x14

llvm/test/MC/Disassembler/M68k/control.txt

 # RUN: llvm-mc -disassemble -triple m68k %s | FileCheck %s
-# XFAIL: *
 
 # CHECK: bra $0
 0x60 0x00 0x00 0x00
 # CHECK: jsr $0
 0x4e 0xb9 0x00 0x00 0x00 0x00
 # CHECK: rts
 0x4e 0x75
 # CHECK: seq %d0
 0x57 0xc0
 # CHECK: sgt %d0
 0x5e 0xc0
 # CHECK: nop
 0x4e 0x71

llvm/test/MC/Disassembler/M68k/data.txt

 # RUN: llvm-mc -disassemble -triple m68k %s | FileCheck %s
+# XFAIL: *
 
 # CHECK: move.l %a1, %a0
 0x20 0x49
 # CHECK: lea (50,%a0), %a1
 0x43 0xe8 0x00 0x32

llvm/test/MC/Disassembler/M68k/shift-rotate.txt

 # RUN: llvm-mc -disassemble -triple m68k %s | FileCheck %s
+# XFAIL: *
 
 # CHECK: lsl.l #5, %d1
 0xeb 0x89
 # CHECK: lsr.l #5, %d1
 0xea 0x89
 # CHECK: asr.l #5, %d1
 0xea 0x81
 # CHECK: rol.l #5, %d1
 0xeb 0x99
 # CHECK: ror.l #5, %d1
 0xea 0x99

llvm/test/MC/M68k/Relaxations/branch.s

 ; RUN: llvm-mc -triple=m68k -motorola-integers -filetype=obj < %s \
 ; RUN:     | llvm-objdump -d - | FileCheck %s
-; XFAIL: *
 
 ; CHECK-LABEL: <TIGHT>:
 TIGHT:
         ; CHECK: bra  $78
   bra .LBB0_2
   move.l  $0, $0
   move.l  $0, $0
   move.l  $0, $0