class PEI : public MachineFunctionPass {
  public:
    static char ID;
    PEI() : MachineFunctionPass(ID) {
      initializePEIPass(*PassRegistry::getPassRegistry());
    }

    void calculateSets(MachineFunction &Fn);
    void calculateCallsInformation(MachineFunction &Fn);
    void calculateCalleeSavedRegisters(MachineFunction &Fn);
    void insertCSRSpillsAndRestores(MachineFunction &Fn);
    void calculateFrameObjectOffsets(MachineFunction &Fn);
    void replaceFrameIndices(MachineFunction &Fn);
    void replaceFrameIndices(MachineBasicBlock *BB, MachineFunction &Fn,
                             int &SPAdj);
    void scavengeFrameVirtualRegs(MachineFunction &Fn);

    void insertPrologEpilogCode(MachineFunction &Fn);

bool PEI::runOnMachineFunction(MachineFunction &Fn) {
  const Function* F = Fn.getFunction();
  const TargetRegisterInfo *TRI = Fn.getSubtarget().getRegisterInfo();
  const TargetFrameLowering *TFI = Fn.getSubtarget().getFrameLowering();

  assert(!Fn.getRegInfo().getNumVirtRegs() && "Regalloc must assign all vregs");

  RS = TRI->requiresRegisterScavenging(Fn) ? new RegScavenger() : nullptr;
  FrameIndexVirtualScavenging = TRI->requiresFrameIndexScavenging(Fn);

  // Calculate the MaxCallFrameSize and AdjustsStack variables for the
  // function's frame information. Also eliminates call frame pseudo
  // instructions.
  calculateCallsInformation(Fn);

  // Allow the target machine to make some adjustments to the function
  // e.g. UsedPhysRegs before calculateCalleeSavedRegisters.
  TFI->processFunctionBeforeCalleeSavedScan(Fn, RS);

  // Scan the function for modified callee saved registers and insert spill code
  // for any callee saved registers that are modified.
  calculateCalleeSavedRegisters(Fn);

  // Determine placement of CSR spill/restore code:
  // place all spills in the entry block, all restores in return blocks.
  calculateSets(Fn);

  // Add the code to save and restore the callee saved registers
  if (!F->hasFnAttribute(Attribute::Naked))
    insertCSRSpillsAndRestores(Fn);

  // Allow the target machine to make final modifications to the function
  // before the frame layout is finalized.
  TFI->processFunctionBeforeFrameFinalized(Fn, RS);

  // Calculate actual frame offsets for all abstract stack objects...
  calculateFrameObjectOffsets(Fn);

  // Add prolog and epilog code to the function.  This function is required
  // to align the stack frame as necessary for any stack variables or
  // called functions.  Because of this, calculateCalleeSavedRegisters()
  // must be called before this function in order to set the AdjustsStack
  // and MaxCallFrameSize variables.
  if (!F->hasFnAttribute(Attribute::Naked))
    insertPrologEpilogCode(Fn);

  // Replace all MO_FrameIndex operands with physical register references
  // and actual offsets.
  replaceFrameIndices(Fn);

  // If register scavenging is needed, as we've enabled doing it as a
  // post-pass, scavenge the virtual registers that frame index elimination
  // inserted.
  if (TRI->requiresRegisterScavenging(Fn) && FrameIndexVirtualScavenging)
    scavengeFrameVirtualRegs(Fn);

  // Clear any vregs created by virtual scavenging.
  Fn.getRegInfo().clearVirtRegs();

  // Warn on stack size when we exceeds the given limit.
  MachineFrameInfo *MFI = Fn.getFrameInfo();
  uint64_t StackSize = MFI->getStackSize();
  if (WarnStackSize.getNumOccurrences() > 0 && WarnStackSize < StackSize) {
    DiagnosticInfoStackSize DiagStackSize(*F, StackSize);
    F->getContext().diagnose(DiagStackSize);
  }
  delete RS;
  ReturnBlocks.clear();
  return true;
}

void PEI::insertPrologEpilogCode(MachineFunction &Fn) {
  const TargetFrameLowering &TFI = *Fn.getSubtarget().getFrameLowering();

  // Add prologue to the function.
  TFI.emitPrologue(Fn);

  // Add epilogue to restore the callee-save registers in each exiting block
  for (MachineFunction::iterator I = Fn.begin(), E = Fn.end(); I != E; ++I) {
    // If last instruction is a return instruction, add an epilogue
    if (!I->empty() && I->back().isReturn())
      TFI.emitEpilogue(Fn, *I);
  }

  // Emit additional code that is required to support segmented stacks, if
  // we've been asked for it.  This, when linked with a runtime with support
  // for segmented stacks (libgcc is one), will result in allocating stack
  // space in small chunks instead of one large contiguous block.
  if (Fn.shouldSplitStack())
    TFI.adjustForSegmentedStacks(Fn);

  // Emit additional code that is required to explicitly handle the stack in
  // HiPE native code (if needed) when loaded in the Erlang/OTP runtime. The
  // approach is rather similar to that of Segmented Stacks, but it uses a
  // different conditional check and another BIF for allocating more stack
  // space.
  if (Fn.getFunction()->getCallingConv() == CallingConv::HiPE)
    TFI.adjustForHiPEPrologue(Fn);
}