Index: lib/Target/AVR/AVRAsmPrinter.cpp
===================================================================
--- /dev/null
+++ lib/Target/AVR/AVRAsmPrinter.cpp
@@ -0,0 +1,182 @@
+//===-- AVRAsmPrinter.cpp - AVR LLVM assembly writer ----------------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// This file contains a printer that converts from our internal representation
+// of machine-dependent LLVM code to GAS-format AVR assembly language.
+//
+//===----------------------------------------------------------------------===//
+
+#include "AVR.h"
+#include "AVRMCInstLower.h"
+#include "AVRSubtarget.h"
+#include "InstPrinter/AVRInstPrinter.h"
+
+#include "llvm/CodeGen/AsmPrinter.h"
+#include "llvm/CodeGen/MachineInstr.h"
+#include "llvm/CodeGen/MachineFunction.h"
+#include "llvm/IR/Mangler.h"
+#include "llvm/MC/MCInst.h"
+#include "llvm/MC/MCStreamer.h"
+#include "llvm/MC/MCSymbol.h"
+#include "llvm/Support/ErrorHandling.h"
+#include "llvm/Support/TargetRegistry.h"
+#include "llvm/Support/raw_ostream.h"
+#include "llvm/Target/TargetRegisterInfo.h"
+#include "llvm/Target/TargetSubtargetInfo.h"
+
+#define DEBUG_TYPE "avr-asm-printer"
+
+namespace llvm {
+
+/// An AVR assembly code printer.
+class AVRAsmPrinter : public AsmPrinter {
+public:
+  AVRAsmPrinter(TargetMachine &TM,
+                std::unique_ptr<MCStreamer> Streamer)
+      : AsmPrinter(TM, std::move(Streamer)), MRI(*TM.getMCRegisterInfo()) { }
+
+  StringRef getPassName() const override { return "AVR Assembly Printer"; }
+
+  void printOperand(const MachineInstr *MI, unsigned OpNo, raw_ostream &O,
+                    const char *Modifier = 0);
+
+  bool PrintAsmOperand(const MachineInstr *MI, unsigned OpNum,
+                       unsigned AsmVariant, const char *ExtraCode,
+                       raw_ostream &O) override;
+
+  bool PrintAsmMemoryOperand(const MachineInstr *MI, unsigned OpNum,
+                             unsigned AsmVariant, const char *ExtraCode,
+                             raw_ostream &O) override;
+
+  void EmitInstruction(const MachineInstr *MI) override;
+
+private:
+  const MCRegisterInfo &MRI;
+};
+
+void AVRAsmPrinter::printOperand(const MachineInstr *MI, unsigned OpNo,
+                                 raw_ostream &O, const char *Modifier) {
+  const MachineOperand &MO = MI->getOperand(OpNo);
+
+  switch (MO.getType()) {
+  case MachineOperand::MO_Register:
+    O << AVRInstPrinter::getPrettyRegisterName(MO.getReg(), MRI);
+    break;
+  case MachineOperand::MO_Immediate:
+    O << MO.getImm();
+    break;
+  case MachineOperand::MO_GlobalAddress:
+    O << getSymbol(MO.getGlobal());
+    break;
+  case MachineOperand::MO_ExternalSymbol:
+    O << *GetExternalSymbolSymbol(MO.getSymbolName());
+    break;
+  case MachineOperand::MO_MachineBasicBlock:
+    O << *MO.getMBB()->getSymbol();
+    break;
+  default:
+    llvm_unreachable("Not implemented yet!");
+  }
+}
+
+bool AVRAsmPrinter::PrintAsmOperand(const MachineInstr *MI, unsigned OpNum,
+                                    unsigned AsmVariant, const char *ExtraCode,
+                                    raw_ostream &O) {
+  // Default asm printer can only deal with some extra codes,
+  // so try it first.
+  bool Error = AsmPrinter::PrintAsmOperand(MI, OpNum, AsmVariant, ExtraCode, O);
+
+  if (Error && ExtraCode && ExtraCode[0]) {
+    if (ExtraCode[1] != 0)
+      return true; // Unknown modifier.
+
+    if (ExtraCode[0] >= 'A' && ExtraCode[0] <= 'Z') {
+      const MachineOperand &RegOp = MI->getOperand(OpNum);
+
+      assert(RegOp.isReg() && "Operand must be a register when you're"
+                              "using 'A'..'Z' operand extracodes.");
+      unsigned Reg = RegOp.getReg();
+
+      unsigned ByteNumber = ExtraCode[0] - 'A';
+
+      unsigned OpFlags = MI->getOperand(OpNum - 1).getImm();
+      unsigned NumOpRegs = InlineAsm::getNumOperandRegisters(OpFlags);
+
+      const AVRSubtarget &STI = MF->getSubtarget<AVRSubtarget>();
+      const TargetRegisterInfo &TRI = *STI.getRegisterInfo();
+
+      unsigned BytesPerReg = TRI.getMinimalPhysRegClass(Reg)->getSize();
+      assert(BytesPerReg <= 2 && "Only 8 and 16 bit regs are supported.");
+
+      unsigned RegIdx = ByteNumber / BytesPerReg;
+      assert(RegIdx < NumOpRegs && "Multibyte index out of range.");
+
+      Reg = MI->getOperand(OpNum + RegIdx).getReg();
+
+      if (BytesPerReg == 2) {
+        Reg = TRI.getSubReg(Reg, ByteNumber % BytesPerReg ? AVR::sub_hi
+                                                          : AVR::sub_lo);
+      }
+
+      O << AVRInstPrinter::getPrettyRegisterName(Reg, MRI);
+      return false;
+    }
+  }
+
+  printOperand(MI, OpNum, O);
+
+  return false;
+}
+
+bool AVRAsmPrinter::PrintAsmMemoryOperand(const MachineInstr *MI,
+                                          unsigned OpNum, unsigned AsmVariant,
+                                          const char *ExtraCode,
+                                          raw_ostream &O) {
+  if (ExtraCode && ExtraCode[0]) {
+    llvm_unreachable("This branch is not implemented yet");
+  }
+
+  const MachineOperand &MO = MI->getOperand(OpNum);
+  assert(MO.isReg() && "Unexpected inline asm memory operand");
+
+  // TODO: We can look up the alternative name for the register if it's given.
+  if (MI->getOperand(OpNum).getReg() == AVR::R31R30) {
+    O << "Z";
+  } else {
+    assert(MI->getOperand(OpNum).getReg() == AVR::R29R28 &&
+           "Wrong register class for memory operand.");
+    O << "Y";
+  }
+
+  // If NumOpRegs == 2, then we assume it is product of a FrameIndex expansion
+  // and the second operand is an Imm.
+  unsigned OpFlags = MI->getOperand(OpNum - 1).getImm();
+  unsigned NumOpRegs = InlineAsm::getNumOperandRegisters(OpFlags);
+
+  if (NumOpRegs == 2) {
+    O << '+' << MI->getOperand(OpNum + 1).getImm();
+  }
+
+  return false;
+}
+
+void AVRAsmPrinter::EmitInstruction(const MachineInstr *MI) {
+  AVRMCInstLower MCInstLowering(OutContext, *this);
+
+  MCInst I;
+  MCInstLowering.lowerInstruction(*MI, I);
+  EmitToStreamer(*OutStreamer, I);
+}
+
+} // end of namespace llvm
+
+extern "C" void LLVMInitializeAVRAsmPrinter() {
+  llvm::RegisterAsmPrinter<llvm::AVRAsmPrinter> X(llvm::TheAVRTarget);
+}
+
Index: lib/Target/AVR/CMakeLists.txt
===================================================================
--- lib/Target/AVR/CMakeLists.txt
+++ lib/Target/AVR/CMakeLists.txt
@@ -8,6 +8,7 @@
 add_public_tablegen_target(AVRCommonTableGen)
 
 add_llvm_target(AVRCodeGen
+  AVRAsmPrinter.cpp
   AVRInstrInfo.cpp
   AVRRegisterInfo.cpp
   AVRSubtarget.cpp