Add AArch64 as an experimental target.

This patch adds support for AArch64 (ARM's 64-bit architecture) to
LLVM in the "experimental" category. Currently, it won't be built
unless requested explicitly.

This initial commit should have support for:
    + Assembly of all scalar (i.e. non-NEON, non-Crypto) instructions
      (except the late addition CRC instructions).
    + CodeGen features required for C++03 and C99.
    + Compilation for the "small" memory model: code+static data <
      4GB.
    + Absolute and position-independent code.
    + GNU-style (i.e. "__thread") TLS.
    + Debugging information.

The principal omission, currently, is performance tuning.

This patch excludes the NEON support also reviewed due to an outbreak of
batshit insanity in our legal department. That will be committed soon bringing
the changes to precisely what has been approved.

Further reviews would be gratefully received.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@174054 91177308-0d34-0410-b5e6-96231b3b80d8

4 files changed, 838 insertions, 0 deletions

diff --git a/lib/Target/AArch64/Disassembler/AArch64Disassembler.cpp b/lib/Target/AArch64/Disassembler/AArch64Disassembler.cpp
new file mode 100644
index 0000000000..e98285bc5c
--- /dev/null
+++ b/lib/Target/AArch64/Disassembler/AArch64Disassembler.cpp
@@ -0,0 +1,791 @@
+//===- AArch64Disassembler.cpp - Disassembler for AArch64/Thumb ISA -------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+
+#define DEBUG_TYPE "arm-disassembler"
+
+#include "AArch64.h"
+#include "AArch64RegisterInfo.h"
+#include "AArch64Subtarget.h"
+#include "MCTargetDesc/AArch64BaseInfo.h"
+#include "llvm/MC/MCInst.h"
+#include "llvm/MC/MCInstrDesc.h"
+#include "llvm/MC/MCExpr.h"
+#include "llvm/MC/MCContext.h"
+#include "llvm/MC/MCDisassembler.h"
+#include "llvm/MC/MCFixedLenDisassembler.h"
+#include "llvm/Support/Debug.h"
+#include "llvm/Support/MemoryObject.h"
+#include "llvm/Support/ErrorHandling.h"
+#include "llvm/Support/TargetRegistry.h"
+#include "llvm/Support/raw_ostream.h"
+
+using namespace llvm;
+
+typedef MCDisassembler::DecodeStatus DecodeStatus;
+
+namespace {
+/// AArch64 disassembler for all AArch64 platforms.
+class AArch64Disassembler : public MCDisassembler {
+  const MCRegisterInfo *RegInfo;
+public:
+  /// Initializes the disassembler.
+  ///
+  AArch64Disassembler(const MCSubtargetInfo &STI, const MCRegisterInfo *Info)
+    : MCDisassembler(STI), RegInfo(Info) {
+  }
+
+  ~AArch64Disassembler() {
+  }
+
+  /// See MCDisassembler.
+  DecodeStatus getInstruction(MCInst &instr,
+                              uint64_t &size,
+                              const MemoryObject &region,
+                              uint64_t address,
+                              raw_ostream &vStream,
+                              raw_ostream &cStream) const;
+
+  const MCRegisterInfo *getRegInfo() const { return RegInfo; }
+};
+
+}
+
+// Forward-declarations used in the auto-generated files.
+static DecodeStatus DecodeGPR64RegisterClass(llvm::MCInst &Inst, unsigned RegNo,
+                                         uint64_t Address, const void *Decoder);
+static DecodeStatus
+DecodeGPR64xspRegisterClass(llvm::MCInst &Inst, unsigned RegNo,
+                            uint64_t Address, const void *Decoder);
+
+static DecodeStatus DecodeGPR32RegisterClass(llvm::MCInst &Inst, unsigned RegNo,
+                                         uint64_t Address, const void *Decoder);
+static DecodeStatus
+DecodeGPR32wspRegisterClass(llvm::MCInst &Inst, unsigned RegNo,
+                            uint64_t Address, const void *Decoder);
+
+static DecodeStatus DecodeFPR8RegisterClass(llvm::MCInst &Inst, unsigned RegNo,
+                                         uint64_t Address, const void *Decoder);
+static DecodeStatus DecodeFPR16RegisterClass(llvm::MCInst &Inst, unsigned RegNo,
+                                         uint64_t Address, const void *Decoder);
+static DecodeStatus DecodeFPR32RegisterClass(llvm::MCInst &Inst, unsigned RegNo,
+                                         uint64_t Address, const void *Decoder);
+static DecodeStatus DecodeFPR64RegisterClass(llvm::MCInst &Inst, unsigned RegNo,
+                                         uint64_t Address, const void *Decoder);
+static DecodeStatus DecodeFPR128RegisterClass(llvm::MCInst &Inst, unsigned RegNo,
+                                         uint64_t Address, const void *Decoder);
+static DecodeStatus DecodeVPR64RegisterClass(llvm::MCInst &Inst, unsigned RegNo,
+                                              uint64_t Address, const void *Decoder);
+static DecodeStatus DecodeVPR128RegisterClass(llvm::MCInst &Inst, unsigned RegNo,
+                                              uint64_t Address, const void *Decoder);
+
+static DecodeStatus DecodeAddrRegExtendOperand(llvm::MCInst &Inst,
+                                               unsigned OptionHiS,
+                                               uint64_t Address,
+                                               const void *Decoder);
+
+
+static DecodeStatus DecodeBitfield32ImmOperand(llvm::MCInst &Inst,
+                                               unsigned Imm6Bits,
+                                               uint64_t Address,
+                                               const void *Decoder);
+
+static DecodeStatus DecodeCVT32FixedPosOperand(llvm::MCInst &Inst,
+                                               unsigned Imm6Bits,
+                                               uint64_t Address,
+                                               const void *Decoder);
+
+template<int RegWidth>
+static DecodeStatus DecodeMoveWideImmOperand(llvm::MCInst &Inst,
+                                             unsigned FullImm,
+                                             uint64_t Address,
+                                             const void *Decoder);
+
+template<int RegWidth>
+static DecodeStatus DecodeLogicalImmOperand(llvm::MCInst &Inst,
+                                            unsigned Bits,
+                                            uint64_t Address,
+                                            const void *Decoder);
+
+static DecodeStatus DecodeRegExtendOperand(llvm::MCInst &Inst,
+                                           unsigned ShiftAmount,
+                                           uint64_t Address,
+                                           const void *Decoder);
+
+static DecodeStatus Decode32BitShiftOperand(llvm::MCInst &Inst,
+                                            unsigned ShiftAmount,
+                                            uint64_t Address,
+                                            const void *Decoder);
+static DecodeStatus DecodeBitfieldInstruction(llvm::MCInst &Inst, unsigned Insn,
+                                              uint64_t Address,
+                                              const void *Decoder);
+
+static DecodeStatus DecodeFMOVLaneInstruction(llvm::MCInst &Inst, unsigned Insn,
+                                              uint64_t Address,
+                                              const void *Decoder);
+
+static DecodeStatus DecodeLDSTPairInstruction(llvm::MCInst &Inst,
+                                              unsigned Insn,
+                                              uint64_t Address,
+                                              const void *Decoder);
+
+static DecodeStatus DecodeLoadPairExclusiveInstruction(llvm::MCInst &Inst,
+                                                       unsigned Val,
+                                                       uint64_t Address,
+                                                       const void *Decoder);
+
+template<typename SomeNamedImmMapper>
+static DecodeStatus DecodeNamedImmOperand(llvm::MCInst &Inst,
+                                          unsigned Val,
+                                          uint64_t Address,
+                                          const void *Decoder);
+
+static DecodeStatus DecodeSysRegOperand(const A64SysReg::SysRegMapper &InstMapper,
+                                        llvm::MCInst &Inst,
+                                        unsigned Val,
+                                        uint64_t Address,
+                                        const void *Decoder);
+
+static DecodeStatus DecodeMRSOperand(llvm::MCInst &Inst,
+                                     unsigned Val,
+                                     uint64_t Address,
+                                     const void *Decoder);
+
+static DecodeStatus DecodeMSROperand(llvm::MCInst &Inst,
+                                     unsigned Val,
+                                     uint64_t Address,
+                                     const void *Decoder);
+
+
+static DecodeStatus DecodeSingleIndexedInstruction(llvm::MCInst &Inst,
+                                                   unsigned Val,
+                                                   uint64_t Address,
+                                                   const void *Decoder);
+
+
+static bool Check(DecodeStatus &Out, DecodeStatus In);
+
+#include "AArch64GenDisassemblerTables.inc"
+#include "AArch64GenInstrInfo.inc"
+
+static bool Check(DecodeStatus &Out, DecodeStatus In) {
+  switch (In) {
+    case MCDisassembler::Success:
+      // Out stays the same.
+      return true;
+    case MCDisassembler::SoftFail:
+      Out = In;
+      return true;
+    case MCDisassembler::Fail:
+      Out = In;
+      return false;
+  }
+  llvm_unreachable("Invalid DecodeStatus!");
+}
+
+DecodeStatus AArch64Disassembler::getInstruction(MCInst &MI, uint64_t &Size,
+                                                 const MemoryObject &Region,
+                                                 uint64_t Address,
+                                                 raw_ostream &os,
+                                                 raw_ostream &cs) const {
+  CommentStream = &cs;
+
+  uint8_t bytes[4];
+
+  // We want to read exactly 4 bytes of data.
+  if (Region.readBytes(Address, 4, (uint8_t*)bytes, NULL) == -1) {
+    Size = 0;
+    return MCDisassembler::Fail;
+  }
+
+  // Encoded as a small-endian 32-bit word in the stream.
+  uint32_t insn = (bytes[3] << 24) |
+    (bytes[2] << 16) |
+    (bytes[1] <<  8) |
+    (bytes[0] <<  0);
+
+  // Calling the auto-generated decoder function.
+  DecodeStatus result = decodeInstruction(DecoderTableA6432, MI, insn, Address,
+                                          this, STI);
+  if (result != MCDisassembler::Fail) {
+    Size = 4;
+    return result;
+  }
+
+  MI.clear();
+  Size = 0;
+  return MCDisassembler::Fail;
+}
+
+static unsigned getReg(const void *D, unsigned RC, unsigned RegNo) {
+  const AArch64Disassembler *Dis = static_cast<const AArch64Disassembler*>(D);
+  return Dis->getRegInfo()->getRegClass(RC).getRegister(RegNo);
+}
+
+static DecodeStatus DecodeGPR64RegisterClass(llvm::MCInst &Inst, unsigned RegNo,
+                                        uint64_t Address, const void *Decoder) {
+  if (RegNo > 31)
+    return MCDisassembler::Fail;
+
+  uint16_t Register = getReg(Decoder, AArch64::GPR64RegClassID, RegNo);
+  Inst.addOperand(MCOperand::CreateReg(Register));
+  return MCDisassembler::Success;
+}
+
+static DecodeStatus
+DecodeGPR64xspRegisterClass(llvm::MCInst &Inst, unsigned RegNo,
+                            uint64_t Address, const void *Decoder) {
+  if (RegNo > 31)
+    return MCDisassembler::Fail;
+
+  uint16_t Register = getReg(Decoder, AArch64::GPR64xspRegClassID, RegNo);
+  Inst.addOperand(MCOperand::CreateReg(Register));
+  return MCDisassembler::Success;
+}
+
+static DecodeStatus DecodeGPR32RegisterClass(llvm::MCInst &Inst, unsigned RegNo,
+                                             uint64_t Address, const void *Decoder) {
+  if (RegNo > 31)
+    return MCDisassembler::Fail;
+
+  uint16_t Register = getReg(Decoder, AArch64::GPR32RegClassID, RegNo);
+  Inst.addOperand(MCOperand::CreateReg(Register));
+  return MCDisassembler::Success;
+}
+
+static DecodeStatus
+DecodeGPR32wspRegisterClass(llvm::MCInst &Inst, unsigned RegNo,
+                            uint64_t Address, const void *Decoder) {
+  if (RegNo > 31)
+    return MCDisassembler::Fail;
+
+  uint16_t Register = getReg(Decoder, AArch64::GPR32wspRegClassID, RegNo);
+  Inst.addOperand(MCOperand::CreateReg(Register));
+  return MCDisassembler::Success;
+}
+
+static DecodeStatus
+DecodeFPR8RegisterClass(llvm::MCInst &Inst, unsigned RegNo,
+                            uint64_t Address, const void *Decoder) {
+  if (RegNo > 31)
+    return MCDisassembler::Fail;
+
+  uint16_t Register = getReg(Decoder, AArch64::FPR8RegClassID, RegNo);
+  Inst.addOperand(MCOperand::CreateReg(Register));
+  return MCDisassembler::Success;
+}
+
+static DecodeStatus
+DecodeFPR16RegisterClass(llvm::MCInst &Inst, unsigned RegNo,
+                            uint64_t Address, const void *Decoder) {
+  if (RegNo > 31)
+    return MCDisassembler::Fail;
+
+  uint16_t Register = getReg(Decoder, AArch64::FPR16RegClassID, RegNo);
+  Inst.addOperand(MCOperand::CreateReg(Register));
+  return MCDisassembler::Success;
+}
+
+
+static DecodeStatus
+DecodeFPR32RegisterClass(llvm::MCInst &Inst, unsigned RegNo,
+                            uint64_t Address, const void *Decoder) {
+  if (RegNo > 31)
+    return MCDisassembler::Fail;
+
+  uint16_t Register = getReg(Decoder, AArch64::FPR32RegClassID, RegNo);
+  Inst.addOperand(MCOperand::CreateReg(Register));
+  return MCDisassembler::Success;
+}
+
+static DecodeStatus
+DecodeFPR64RegisterClass(llvm::MCInst &Inst, unsigned RegNo,
+                            uint64_t Address, const void *Decoder) {
+  if (RegNo > 31)
+    return MCDisassembler::Fail;
+
+  uint16_t Register = getReg(Decoder, AArch64::FPR64RegClassID, RegNo);
+  Inst.addOperand(MCOperand::CreateReg(Register));
+  return MCDisassembler::Success;
+}
+
+
+static DecodeStatus
+DecodeFPR128RegisterClass(llvm::MCInst &Inst, unsigned RegNo,
+                            uint64_t Address, const void *Decoder) {
+  if (RegNo > 31)
+    return MCDisassembler::Fail;
+
+  uint16_t Register = getReg(Decoder, AArch64::FPR128RegClassID, RegNo);
+  Inst.addOperand(MCOperand::CreateReg(Register));
+  return MCDisassembler::Success;
+}
+
+
+static DecodeStatus
+DecodeVPR64RegisterClass(llvm::MCInst &Inst, unsigned RegNo,
+                         uint64_t Address, const void *Decoder) {
+  if (RegNo > 31)
+    return MCDisassembler::Fail;
+
+  uint16_t Register = getReg(Decoder, AArch64::VPR64RegClassID, RegNo);
+  Inst.addOperand(MCOperand::CreateReg(Register));
+  return MCDisassembler::Success;
+}
+
+static DecodeStatus
+DecodeVPR128RegisterClass(llvm::MCInst &Inst, unsigned RegNo,
+                         uint64_t Address, const void *Decoder) {
+  if (RegNo > 31)
+    return MCDisassembler::Fail;
+
+  uint16_t Register = getReg(Decoder, AArch64::VPR128RegClassID, RegNo);
+  Inst.addOperand(MCOperand::CreateReg(Register));
+  return MCDisassembler::Success;
+}
+
+static DecodeStatus DecodeAddrRegExtendOperand(llvm::MCInst &Inst,
+                                               unsigned OptionHiS,
+                                               uint64_t Address,
+                                               const void *Decoder) {
+  // Option{1} must be 1. OptionHiS is made up of {Option{2}, Option{1},
+  // S}. Hence we want to check bit 1.
+  if (!(OptionHiS & 2))
+    return MCDisassembler::Fail;
+
+  Inst.addOperand(MCOperand::CreateImm(OptionHiS));
+  return MCDisassembler::Success;
+}
+
+static DecodeStatus DecodeBitfield32ImmOperand(llvm::MCInst &Inst,
+                                               unsigned Imm6Bits,
+                                               uint64_t Address,
+                                               const void *Decoder) {
+  // In the 32-bit variant, bit 6 must be zero. I.e. the immediate must be
+  // between 0 and 31.
+  if (Imm6Bits > 31)
+    return MCDisassembler::Fail;
+
+  Inst.addOperand(MCOperand::CreateImm(Imm6Bits));
+  return MCDisassembler::Success;
+}
+
+static DecodeStatus DecodeCVT32FixedPosOperand(llvm::MCInst &Inst,
+                                               unsigned Imm6Bits,
+                                               uint64_t Address,
+                                               const void *Decoder) {
+  // 1 <= Imm <= 32. Encoded as 64 - Imm so: 63 >= Encoded >= 32.
+  if (Imm6Bits < 32)
+    return MCDisassembler::Fail;
+
+  Inst.addOperand(MCOperand::CreateImm(Imm6Bits));
+  return MCDisassembler::Success;
+}
+
+
+template<int RegWidth>
+static DecodeStatus DecodeMoveWideImmOperand(llvm::MCInst &Inst,
+                                             unsigned FullImm,
+                                             uint64_t Address,
+                                             const void *Decoder) {
+  unsigned Imm16 = FullImm & 0xffff;
+  unsigned Shift = FullImm >> 16;
+
+  if (RegWidth == 32 && Shift > 1) return MCDisassembler::Fail;
+
+  Inst.addOperand(MCOperand::CreateImm(Imm16));
+  Inst.addOperand(MCOperand::CreateImm(Shift));
+  return MCDisassembler::Success;
+}
+
+template<int RegWidth>
+static DecodeStatus DecodeLogicalImmOperand(llvm::MCInst &Inst,
+                                            unsigned Bits,
+                                            uint64_t Address,
+                                            const void *Decoder) {
+  uint64_t Imm;
+  if (!A64Imms::isLogicalImmBits(RegWidth, Bits, Imm))
+    return MCDisassembler::Fail;
+
+  Inst.addOperand(MCOperand::CreateImm(Bits));
+  return MCDisassembler::Success;
+}
+
+
+static DecodeStatus DecodeRegExtendOperand(llvm::MCInst &Inst,
+                                           unsigned ShiftAmount,
+                                           uint64_t Address,
+                                           const void *Decoder) {
+  // Only values 0-4 are valid for this 3-bit field
+  if (ShiftAmount > 4)
+    return MCDisassembler::Fail;
+
+  Inst.addOperand(MCOperand::CreateImm(ShiftAmount));
+  return MCDisassembler::Success;
+}
+
+static DecodeStatus Decode32BitShiftOperand(llvm::MCInst &Inst,
+                                            unsigned ShiftAmount,
+                                            uint64_t Address,
+                                            const void *Decoder) {
+  // Only values below 32 are valid for a 32-bit register
+  if (ShiftAmount > 31)
+    return MCDisassembler::Fail;
+
+  Inst.addOperand(MCOperand::CreateImm(ShiftAmount));
+  return MCDisassembler::Success;
+}
+
+static DecodeStatus DecodeBitfieldInstruction(llvm::MCInst &Inst, unsigned Insn,
+                                              uint64_t Address,
+                                              const void *Decoder) {
+  unsigned Rd = fieldFromInstruction(Insn, 0, 5);
+  unsigned Rn = fieldFromInstruction(Insn, 5, 5);
+  unsigned ImmS = fieldFromInstruction(Insn, 10, 6);
+  unsigned ImmR = fieldFromInstruction(Insn, 16, 6);
+  unsigned SF = fieldFromInstruction(Insn, 31, 1);
+
+  // Undef for 0b11 just in case it occurs. Don't want the compiler to optimise
+  // out assertions that it thinks should never be hit.
+  enum OpcTypes { SBFM = 0, BFM, UBFM, Undef } Opc;
+  Opc = (OpcTypes)fieldFromInstruction(Insn, 29, 2);
+
+  if (!SF) {
+    // ImmR and ImmS must be between 0 and 31 for 32-bit instructions.
+    if (ImmR > 31 || ImmS > 31)
+      return MCDisassembler::Fail;
+  }
+
+  if (SF) {
+    DecodeGPR64RegisterClass(Inst, Rd, Address, Decoder);
+    // BFM MCInsts use Rd as a source too.
+    if (Opc == BFM) DecodeGPR64RegisterClass(Inst, Rd, Address, Decoder);
+    DecodeGPR64RegisterClass(Inst, Rn, Address, Decoder);
+  } else {
+    DecodeGPR32RegisterClass(Inst, Rd, Address, Decoder);
+    // BFM MCInsts use Rd as a source too.
+    if (Opc == BFM) DecodeGPR32RegisterClass(Inst, Rd, Address, Decoder);
+    DecodeGPR32RegisterClass(Inst, Rn, Address, Decoder);
+  }
+
+  // ASR and LSR have more specific patterns so they won't get here:
+  assert(!(ImmS == 31 && !SF && Opc != BFM) && "shift should have used auto decode");
+  assert(!(ImmS == 63 && SF && Opc != BFM) && "shift should have used auto decode");
+
+  // Extension instructions similarly:
+  if (Opc == SBFM && ImmR == 0) {
+    assert((ImmS != 7 && ImmS != 15) && "extension got here");
+    assert((ImmS != 31 || SF == 0) && "extension got here");
+  } else if (Opc == UBFM && ImmR == 0) {
+    assert((SF != 0 || (ImmS != 7 && ImmS != 15)) && "extension got here");
+  }
+
+  if (Opc == UBFM) {
+    // It might be a LSL instruction, which actually takes the shift amount
+    // itself as an MCInst operand.
+    if (SF && (ImmS + 1) % 64 == ImmR) {
+      Inst.setOpcode(AArch64::LSLxxi);
+      Inst.addOperand(MCOperand::CreateImm(63 - ImmS));
+      return MCDisassembler::Success;
+    } else if (!SF && (ImmS + 1) % 32 == ImmR) {
+      Inst.setOpcode(AArch64::LSLwwi);
+      Inst.addOperand(MCOperand::CreateImm(31 - ImmS));
+      return MCDisassembler::Success;
+    }
+  }
+
+  // Otherwise it's definitely either an extract or an insert depending on which
+  // of ImmR or ImmS is larger.
+  unsigned ExtractOp, InsertOp;
+  switch (Opc) {
+  default: llvm_unreachable("unexpected instruction trying to decode bitfield");
+  case SBFM:
+    ExtractOp = SF ? AArch64::SBFXxxii : AArch64::SBFXwwii;
+    InsertOp = SF ? AArch64::SBFIZxxii : AArch64::SBFIZwwii;
+    break;
+  case BFM:
+    ExtractOp = SF ? AArch64::BFXILxxii : AArch64::BFXILwwii;
+    InsertOp = SF ? AArch64::BFIxxii : AArch64::BFIwwii;
+    break;
+  case UBFM:
+    ExtractOp = SF ? AArch64::UBFXxxii : AArch64::UBFXwwii;
+    InsertOp = SF ? AArch64::UBFIZxxii : AArch64::UBFIZwwii;
+    break;
+  }
+
+  // Otherwise it's a boring insert or extract
+  Inst.addOperand(MCOperand::CreateImm(ImmR));
+  Inst.addOperand(MCOperand::CreateImm(ImmS));
+
+
+  if (ImmS < ImmR)
+    Inst.setOpcode(InsertOp);
+  else
+    Inst.setOpcode(ExtractOp);
+
+  return MCDisassembler::Success;
+}
+
+static DecodeStatus DecodeFMOVLaneInstruction(llvm::MCInst &Inst, unsigned Insn,
+                                              uint64_t Address,
+                                              const void *Decoder) {
+  // This decoder exists to add the dummy Lane operand to the MCInst, which must
+  // be 1 in assembly but has no other real manifestation.
+  unsigned Rd = fieldFromInstruction(Insn, 0, 5);
+  unsigned Rn = fieldFromInstruction(Insn, 5, 5);
+  unsigned IsToVec = fieldFromInstruction(Insn, 16, 1);
+
+  if (IsToVec) {
+    DecodeVPR128RegisterClass(Inst, Rd, Address, Decoder);
+    DecodeGPR64RegisterClass(Inst, Rn, Address, Decoder);
+  } else {
+    DecodeGPR64RegisterClass(Inst, Rd, Address, Decoder);
+    DecodeVPR128RegisterClass(Inst, Rn, Address, Decoder);
+  }
+
+  // Add the lane
+  Inst.addOperand(MCOperand::CreateImm(1));
+
+  return MCDisassembler::Success;
+}
+
+
+static DecodeStatus DecodeLDSTPairInstruction(llvm::MCInst &Inst,
+                                              unsigned Insn,
+                                              uint64_t Address,
+                                              const void *Decoder) {
+  DecodeStatus Result = MCDisassembler::Success;
+  unsigned Rt = fieldFromInstruction(Insn, 0, 5);
+  unsigned Rn = fieldFromInstruction(Insn, 5, 5);
+  unsigned Rt2 = fieldFromInstruction(Insn, 10, 5);
+  unsigned SImm7 = fieldFromInstruction(Insn, 15, 7);
+  unsigned L = fieldFromInstruction(Insn, 22, 1);
+  unsigned V = fieldFromInstruction(Insn, 26, 1);
+  unsigned Opc = fieldFromInstruction(Insn, 30, 2);
+
+  // Not an official name, but it turns out that bit 23 distinguishes indexed
+  // from non-indexed operations.
+  unsigned Indexed = fieldFromInstruction(Insn, 23, 1);
+
+  if (Indexed && L == 0) {
+    // The MCInst for an indexed store has an out operand and 4 ins:
+    //    Rn_wb, Rt, Rt2, Rn, Imm
+    DecodeGPR64xspRegisterClass(Inst, Rn, Address, Decoder);
+  }
+
+  // You shouldn't load to the same register twice in an instruction...
+  if (L && Rt == Rt2)
+    Result = MCDisassembler::SoftFail;
+
+  // ... or do any operation that writes-back to a transfer register. But note
+  // that "stp xzr, xzr, [sp], #4" is fine because xzr and sp are different.
+  if (Indexed && V == 0 && Rn != 31 && (Rt == Rn || Rt2 == Rn))
+    Result = MCDisassembler::SoftFail;
+
+  // Exactly how we decode the MCInst's registers depends on the Opc and V
+  // fields of the instruction. These also obviously determine the size of the
+  // operation so we can fill in that information while we're at it.
+  if (V) {
+    // The instruction operates on the FP/SIMD registers
+    switch (Opc) {
+    default: return MCDisassembler::Fail;
+    case 0:
+      DecodeFPR32RegisterClass(Inst, Rt, Address, Decoder);
+      DecodeFPR32RegisterClass(Inst, Rt2, Address, Decoder);
+      break;
+    case 1:
+      DecodeFPR64RegisterClass(Inst, Rt, Address, Decoder);
+      DecodeFPR64RegisterClass(Inst, Rt2, Address, Decoder);
+      break;
+    case 2:
+      DecodeFPR128RegisterClass(Inst, Rt, Address, Decoder);
+      DecodeFPR128RegisterClass(Inst, Rt2, Address, Decoder);
+      break;
+    }
+  } else {
+    switch (Opc) {
+    default: return MCDisassembler::Fail;
+    case 0:
+      DecodeGPR32RegisterClass(Inst, Rt, Address, Decoder);
+      DecodeGPR32RegisterClass(Inst, Rt2, Address, Decoder);
+      break;
+    case 1:
+      assert(L && "unexpected \"store signed\" attempt");
+      DecodeGPR64RegisterClass(Inst, Rt, Address, Decoder);
+      DecodeGPR64RegisterClass(Inst, Rt2, Address, Decoder);
+      break;
+    case 2:
+      DecodeGPR64RegisterClass(Inst, Rt, Address, Decoder);
+      DecodeGPR64RegisterClass(Inst, Rt2, Address, Decoder);
+      break;
+    }
+  }
+
+  if (Indexed && L == 1) {
+    // The MCInst for an indexed load has 3 out operands and an 3 ins:
+    //    Rt, Rt2, Rn_wb, Rt2, Rn, Imm
+    DecodeGPR64xspRegisterClass(Inst, Rn, Address, Decoder);
+  }
+
+
+  DecodeGPR64xspRegisterClass(Inst, Rn, Address, Decoder);
+  Inst.addOperand(MCOperand::CreateImm(SImm7));
+
+  return Result;
+}
+
+static DecodeStatus DecodeLoadPairExclusiveInstruction(llvm::MCInst &Inst,
+                                                       uint32_t Val,
+                                                       uint64_t Address,
+                                                       const void *Decoder) {
+  unsigned Rt = fieldFromInstruction(Val, 0, 5);
+  unsigned Rn = fieldFromInstruction(Val, 5, 5);
+  unsigned Rt2 = fieldFromInstruction(Val, 10, 5);
+  unsigned MemSize = fieldFromInstruction(Val, 30, 2);
+
+  DecodeStatus S = MCDisassembler::Success;
+  if (Rt == Rt2) S = MCDisassembler::SoftFail;
+
+  switch (MemSize) {
+    case 2:
+      if (!Check(S, DecodeGPR32RegisterClass(Inst, Rt, Address, Decoder)))
+        return MCDisassembler::Fail;
+      if (!Check(S, DecodeGPR32RegisterClass(Inst, Rt2, Address, Decoder)))
+        return MCDisassembler::Fail;
+      break;
+    case 3:
+      if (!Check(S, DecodeGPR64RegisterClass(Inst, Rt, Address, Decoder)))
+        return MCDisassembler::Fail;
+      if (!Check(S, DecodeGPR64RegisterClass(Inst, Rt2, Address, Decoder)))
+        return MCDisassembler::Fail;
+      break;
+    default:
+      llvm_unreachable("Invalid MemSize in DecodeLoadPairExclusiveInstruction");
+  }
+
+  if (!Check(S, DecodeGPR64xspRegisterClass(Inst, Rn, Address, Decoder)))
+    return MCDisassembler::Fail;
+
+  return S;
+}
+
+template<typename SomeNamedImmMapper>
+static DecodeStatus DecodeNamedImmOperand(llvm::MCInst &Inst,
+                                          unsigned Val,
+                                          uint64_t Address,
+                                          const void *Decoder) {
+  SomeNamedImmMapper Mapper;
+  bool ValidNamed;
+  Mapper.toString(Val, ValidNamed);
+  if (ValidNamed || Mapper.validImm(Val)) {
+    Inst.addOperand(MCOperand::CreateImm(Val));
+    return MCDisassembler::Success;
+  }
+
+  return MCDisassembler::Fail;
+}
+
+static DecodeStatus DecodeSysRegOperand(const A64SysReg::SysRegMapper &Mapper,
+                                        llvm::MCInst &Inst,
+                                        unsigned Val,
+                                        uint64_t Address,
+                                        const void *Decoder) {
+  bool ValidNamed;
+  Mapper.toString(Val, ValidNamed);
+
+  Inst.addOperand(MCOperand::CreateImm(Val));
+
+  return ValidNamed ? MCDisassembler::Success : MCDisassembler::Fail;
+}
+
+static DecodeStatus DecodeMRSOperand(llvm::MCInst &Inst,
+                                     unsigned Val,
+                                     uint64_t Address,
+                                     const void *Decoder) {
+  return DecodeSysRegOperand(A64SysReg::MRSMapper(), Inst, Val, Address,
+                             Decoder);
+}
+
+static DecodeStatus DecodeMSROperand(llvm::MCInst &Inst,
+                                     unsigned Val,
+                                     uint64_t Address,
+                                     const void *Decoder) {
+  return DecodeSysRegOperand(A64SysReg::MSRMapper(), Inst, Val, Address,
+                             Decoder);
+}
+
+static DecodeStatus DecodeSingleIndexedInstruction(llvm::MCInst &Inst,
+                                                   unsigned Insn,
+                                                   uint64_t Address,
+                                                   const void *Decoder) {
+  unsigned Rt = fieldFromInstruction(Insn, 0, 5);
+  unsigned Rn = fieldFromInstruction(Insn, 5, 5);
+  unsigned Imm9 = fieldFromInstruction(Insn, 12, 9);
+
+  unsigned Opc = fieldFromInstruction(Insn, 22, 2);
+  unsigned V = fieldFromInstruction(Insn, 26, 1);
+  unsigned Size = fieldFromInstruction(Insn, 30, 2);
+
+  if (Opc == 0 || (V == 1 && Opc == 2)) {
+    // It's a store, the MCInst gets: Rn_wb, Rt, Rn, Imm
+    DecodeGPR64xspRegisterClass(Inst, Rn, Address, Decoder);
+  }
+
+  if (V == 0 && (Opc == 2 || Size == 3)) {
+    DecodeGPR64RegisterClass(Inst, Rt, Address, Decoder);
+  } else if (V == 0) {
+    DecodeGPR32RegisterClass(Inst, Rt, Address, Decoder);
+  } else if (V == 1 && (Opc & 2)) {
+    DecodeFPR128RegisterClass(Inst, Rt, Address, Decoder);
+  } else {
+    switch (Size) {
+    case 0:
+      DecodeFPR8RegisterClass(Inst, Rt, Address, Decoder);
+      break;
+    case 1:
+      DecodeFPR16RegisterClass(Inst, Rt, Address, Decoder);
+      break;
+    case 2:
+      DecodeFPR32RegisterClass(Inst, Rt, Address, Decoder);
+      break;
+    case 3:
+      DecodeFPR64RegisterClass(Inst, Rt, Address, Decoder);
+      break;
+    }
+  }
+
+  if (Opc != 0 && (V != 1 || Opc != 2)) {
+    // It's a load, the MCInst gets: Rt, Rn_wb, Rn, Imm
+    DecodeGPR64xspRegisterClass(Inst, Rn, Address, Decoder);
+  }
+
+  DecodeGPR64xspRegisterClass(Inst, Rn, Address, Decoder);
+
+  Inst.addOperand(MCOperand::CreateImm(Imm9));
+
+  // N.b. The official documentation says undpredictable if Rt == Rn, but this
+  // takes place at the architectural rather than encoding level:
+  //
+  // "STR xzr, [sp], #4" is perfectly valid.
+  if (V == 0 && Rt == Rn && Rn != 31)
+    return MCDisassembler::SoftFail;
+  else
+    return MCDisassembler::Success;
+}
+
+static MCDisassembler *createAArch64Disassembler(const Target &T,
+                                                 const MCSubtargetInfo &STI) {
+  return new AArch64Disassembler(STI, T.createMCRegInfo(""));
+}
+
+extern "C" void LLVMInitializeAArch64Disassembler() {
+  TargetRegistry::RegisterMCDisassembler(TheAArch64Target,
+                                         createAArch64Disassembler);
+}
+
+
diff --git a/lib/Target/AArch64/Disassembler/CMakeLists.txt b/lib/Target/AArch64/Disassembler/CMakeLists.txt
new file mode 100644
index 0000000000..d4bd163dad
--- /dev/null
+++ b/lib/Target/AArch64/Disassembler/CMakeLists.txt
@@ -0,0 +1,7 @@
+include_directories( ${CMAKE_CURRENT_BINARY_DIR}/.. ${CMAKE_CURRENT_SOURCE_DIR}/.. )
+
+add_llvm_library(LLVMAArch64Disassembler
+  AArch64Disassembler.cpp
+  )
+
+add_dependencies(LLVMAArch64Disassembler AArch64CommonTableGen)
diff --git a/lib/Target/AArch64/Disassembler/LLVMBuild.txt b/lib/Target/AArch64/Disassembler/LLVMBuild.txt
new file mode 100644
index 0000000000..123eb3e504
--- /dev/null
+++ b/lib/Target/AArch64/Disassembler/LLVMBuild.txt
@@ -0,0 +1,24 @@
+;===- ./lib/Target/AArch64/Disassembler/LLVMBuild.txt ----------*- Conf -*--===;
+;
+;                     The LLVM Compiler Infrastructure
+;
+; This file is distributed under the University of Illinois Open Source
+; License. See LICENSE.TXT for details.
+;
+;===------------------------------------------------------------------------===;
+;
+; This is an LLVMBuild description file for the components in this subdirectory.
+;
+; For more information on the LLVMBuild system, please see:
+;
+;   http://llvm.org/docs/LLVMBuild.html
+;
+;===------------------------------------------------------------------------===;
+
+[component_0]
+type = Library
+name = AArch64Disassembler
+parent = AArch64
+required_libraries = AArch64CodeGen AArch64Desc AArch64Info MC Support
+add_to_library_groups = AArch64
+
diff --git a/lib/Target/AArch64/Disassembler/Makefile b/lib/Target/AArch64/Disassembler/Makefile
new file mode 100644
index 0000000000..5c861207f8
--- /dev/null
+++ b/lib/Target/AArch64/Disassembler/Makefile
@@ -0,0 +1,16 @@
+##===- lib/Target/AArch64/Disassembler/Makefile ------------*- Makefile -*-===##
+#
+#                     The LLVM Compiler Infrastructure
+#
+# This file is distributed under the University of Illinois Open Source
+# License. See LICENSE.TXT for details.
+#
+##===----------------------------------------------------------------------===##
+
+LEVEL = ../../../..
+LIBRARYNAME = LLVMAArch64Disassembler
+
+# Hack: we need to include 'main' target directory to grab private headers
+CPPFLAGS = -I$(PROJ_OBJ_DIR)/.. -I$(PROJ_SRC_DIR)/..
+
+include $(LEVEL)/Makefile.common