--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/lib/Target/AVR/AVRRelaxMemOperations.cpp	Fri Oct 27 17:07:41 2017 +0900
@@ -0,0 +1,149 @@
+//===-- AVRRelaxMemOperations.cpp - Relax out of range loads/stores -------===//
+//
+//                     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 pass which relaxes out of range memory operations into
+// equivalent operations which handle bigger addresses.
+//
+//===----------------------------------------------------------------------===//
+
+#include "AVR.h"
+#include "AVRInstrInfo.h"
+#include "AVRTargetMachine.h"
+#include "MCTargetDesc/AVRMCTargetDesc.h"
+
+#include "llvm/CodeGen/MachineFunctionPass.h"
+#include "llvm/CodeGen/MachineInstrBuilder.h"
+#include "llvm/CodeGen/MachineRegisterInfo.h"
+#include "llvm/Target/TargetRegisterInfo.h"
+
+using namespace llvm;
+
+#define AVR_RELAX_MEM_OPS_NAME "AVR memory operation relaxation pass"
+
+namespace {
+
+class AVRRelaxMem : public MachineFunctionPass {
+public:
+  static char ID;
+
+  AVRRelaxMem() : MachineFunctionPass(ID) {
+    initializeAVRRelaxMemPass(*PassRegistry::getPassRegistry());
+  }
+
+  bool runOnMachineFunction(MachineFunction &MF) override;
+
+  StringRef getPassName() const override { return AVR_RELAX_MEM_OPS_NAME; }
+
+private:
+  typedef MachineBasicBlock Block;
+  typedef Block::iterator BlockIt;
+
+  const TargetInstrInfo *TII;
+
+  template <unsigned OP> bool relax(Block &MBB, BlockIt MBBI);
+
+  bool runOnBasicBlock(Block &MBB);
+  bool runOnInstruction(Block &MBB, BlockIt MBBI);
+
+  MachineInstrBuilder buildMI(Block &MBB, BlockIt MBBI, unsigned Opcode) {
+    return BuildMI(MBB, MBBI, MBBI->getDebugLoc(), TII->get(Opcode));
+  }
+};
+
+char AVRRelaxMem::ID = 0;
+
+bool AVRRelaxMem::runOnMachineFunction(MachineFunction &MF) {
+  bool Modified = false;
+
+  const AVRSubtarget &STI = MF.getSubtarget<AVRSubtarget>();
+  TII = STI.getInstrInfo();
+
+  for (Block &MBB : MF) {
+    bool BlockModified = runOnBasicBlock(MBB);
+    Modified |= BlockModified;
+  }
+
+  return Modified;
+}
+
+bool AVRRelaxMem::runOnBasicBlock(Block &MBB) {
+  bool Modified = false;
+
+  BlockIt MBBI = MBB.begin(), E = MBB.end();
+  while (MBBI != E) {
+    BlockIt NMBBI = std::next(MBBI);
+    Modified |= runOnInstruction(MBB, MBBI);
+    MBBI = NMBBI;
+  }
+
+  return Modified;
+}
+
+template <>
+bool AVRRelaxMem::relax<AVR::STDWPtrQRr>(Block &MBB, BlockIt MBBI) {
+  MachineInstr &MI = *MBBI;
+
+  MachineOperand &Ptr = MI.getOperand(0);
+  MachineOperand &Src = MI.getOperand(2);
+  int64_t Imm = MI.getOperand(1).getImm();
+
+  // We can definitely optimise this better.
+  if (Imm > 63) {
+    // Push the previous state of the pointer register.
+    // This instruction must preserve the value.
+    buildMI(MBB, MBBI, AVR::PUSHWRr)
+      .addReg(Ptr.getReg());
+
+    // Add the immediate to the pointer register.
+    buildMI(MBB, MBBI, AVR::SBCIWRdK)
+      .addReg(Ptr.getReg(), RegState::Define)
+      .addReg(Ptr.getReg())
+      .addImm(-Imm);
+
+    // Store the value in the source register to the address
+    // pointed to by the pointer register.
+    buildMI(MBB, MBBI, AVR::STWPtrRr)
+      .addReg(Ptr.getReg())
+      .addReg(Src.getReg(), getKillRegState(Src.isKill()));
+
+    // Pop the original state of the pointer register.
+    buildMI(MBB, MBBI, AVR::POPWRd)
+      .addReg(Ptr.getReg(), getKillRegState(Ptr.isKill()));
+
+    MI.removeFromParent();
+  }
+
+  return false;
+}
+
+bool AVRRelaxMem::runOnInstruction(Block &MBB, BlockIt MBBI) {
+  MachineInstr &MI = *MBBI;
+  int Opcode = MBBI->getOpcode();
+
+#define RELAX(Op)                \
+  case Op:                       \
+    return relax<Op>(MBB, MI)
+
+  switch (Opcode) {
+    RELAX(AVR::STDWPtrQRr);
+  }
+#undef RELAX
+  return false;
+}
+
+} // end of anonymous namespace
+
+INITIALIZE_PASS(AVRRelaxMem, "avr-relax-mem",
+                AVR_RELAX_MEM_OPS_NAME, false, false)
+
+namespace llvm {
+
+FunctionPass *createAVRRelaxMemPass() { return new AVRRelaxMem(); }
+
+} // end of namespace llvm