text: //===-- Mips16FrameLowering.cpp - Mips16 Frame Information ----------------===//
  //
  //                     The LLVM Compiler Infrastructure
  //
  // This file is distributed under the University of Illinois Open Source
  // License. See LICENSE.TXT for details.
  //
  //===----------------------------------------------------------------------===//
  //
  // This file contains the Mips16 implementation of TargetFrameLowering class.
  //
  //===----------------------------------------------------------------------===//
  
  #include "Mips16FrameLowering.h"
  #include "MCTargetDesc/MipsBaseInfo.h"
  #include "Mips16InstrInfo.h"
  #include "MipsInstrInfo.h"
  #include "MipsRegisterInfo.h"
  #include "MipsSubtarget.h"
  #include "llvm/CodeGen/MachineFrameInfo.h"
  #include "llvm/CodeGen/MachineFunction.h"
  #include "llvm/CodeGen/MachineInstrBuilder.h"
  #include "llvm/CodeGen/MachineModuleInfo.h"
  #include "llvm/CodeGen/MachineRegisterInfo.h"
  #include "llvm/IR/DataLayout.h"
  #include "llvm/IR/Function.h"
  #include "llvm/Support/CommandLine.h"
  #include "llvm/Target/TargetOptions.h"
  
  using namespace llvm;
  
  Mips16FrameLowering::Mips16FrameLowering(const MipsSubtarget &STI)
      : MipsFrameLowering(STI, STI.stackAlignment()) {}
  
  void Mips16FrameLowering::emitPrologue(MachineFunction &MF) const {
    MachineBasicBlock &MBB = MF.front();
    MachineFrameInfo *MFI = MF.getFrameInfo();
    const Mips16InstrInfo &TII =
      *static_cast<const Mips16InstrInfo*>(MF.getTarget().getInstrInfo());
    MachineBasicBlock::iterator MBBI = MBB.begin();
    DebugLoc dl = MBBI != MBB.end() ? MBBI->getDebugLoc() : DebugLoc();
    uint64_t StackSize = MFI->getStackSize();
  
    // No need to allocate space on the stack.
    if (StackSize == 0 && !MFI->adjustsStack()) return;
  
    MachineModuleInfo &MMI = MF.getMMI();
    const MCRegisterInfo *MRI = MMI.getContext().getRegisterInfo();
    MachineLocation DstML, SrcML;
  
    // Adjust stack.
    TII.makeFrame(Mips::SP, StackSize, MBB, MBBI);
  
    // emit ".cfi_def_cfa_offset StackSize"
    unsigned CFIIndex = MMI.addFrameInst(
        MCCFIInstruction::createDefCfaOffset(nullptr, -StackSize));
    BuildMI(MBB, MBBI, dl, TII.get(TargetOpcode::CFI_INSTRUCTION))
        .addCFIIndex(CFIIndex);
  
    const std::vector<CalleeSavedInfo> &CSI = MFI->getCalleeSavedInfo();
  
    if (CSI.size()) {
      const std::vector<CalleeSavedInfo> &CSI = MFI->getCalleeSavedInfo();
  
      for (std::vector<CalleeSavedInfo>::const_iterator I = CSI.begin(),
           E = CSI.end(); I != E; ++I) {
        int64_t Offset = MFI->getObjectOffset(I->getFrameIdx());
        unsigned Reg = I->getReg();
        unsigned DReg = MRI->getDwarfRegNum(Reg, true);
        unsigned CFIIndex = MMI.addFrameInst(
            MCCFIInstruction::createOffset(nullptr, DReg, Offset));
        BuildMI(MBB, MBBI, dl, TII.get(TargetOpcode::CFI_INSTRUCTION))
            .addCFIIndex(CFIIndex);
      }
    }
    if (hasFP(MF))
      BuildMI(MBB, MBBI, dl, TII.get(Mips::MoveR3216), Mips::S0)
        .addReg(Mips::SP).setMIFlag(MachineInstr::FrameSetup);
  
  }
  
  void Mips16FrameLowering::emitEpilogue(MachineFunction &MF,
                                   MachineBasicBlock &MBB) const {
    MachineBasicBlock::iterator MBBI = MBB.getLastNonDebugInstr();
    MachineFrameInfo *MFI = MF.getFrameInfo();
    const Mips16InstrInfo &TII =
      *static_cast<const Mips16InstrInfo*>(MF.getTarget().getInstrInfo());
    DebugLoc dl = MBBI->getDebugLoc();
    uint64_t StackSize = MFI->getStackSize();
  
    if (!StackSize)
      return;
  
    if (hasFP(MF))
      BuildMI(MBB, MBBI, dl, TII.get(Mips::Move32R16), Mips::SP)
        .addReg(Mips::S0);
  
    // Adjust stack.
    // assumes stacksize multiple of 8
    TII.restoreFrame(Mips::SP, StackSize, MBB, MBBI);
  }
  
  bool Mips16FrameLowering::
  spillCalleeSavedRegisters(MachineBasicBlock &MBB,
                            MachineBasicBlock::iterator MI,
                            const std::vector<CalleeSavedInfo> &CSI,
                            const TargetRegisterInfo *TRI) const {
    MachineFunction *MF = MBB.getParent();
    MachineBasicBlock *EntryBlock = MF->begin();
  
    //
    // Registers RA, S0,S1 are the callee saved registers and they
    // will be saved with the "save" instruction
    // during emitPrologue
    //
    for (unsigned i = 0, e = CSI.size(); i != e; ++i) {
      // Add the callee-saved register as live-in. Do not add if the register is
      // RA and return address is taken, because it has already been added in
      // method MipsTargetLowering::LowerRETURNADDR.
      // It's killed at the spill, unless the register is RA and return address
      // is taken.
      unsigned Reg = CSI[i].getReg();
      bool IsRAAndRetAddrIsTaken = (Reg == Mips::RA)
        && MF->getFrameInfo()->isReturnAddressTaken();
      if (!IsRAAndRetAddrIsTaken)
        EntryBlock->addLiveIn(Reg);
    }
  
    return true;
  }
  
  bool Mips16FrameLowering::restoreCalleeSavedRegisters(MachineBasicBlock &MBB,
                                            MachineBasicBlock::iterator MI,
                                         const std::vector<CalleeSavedInfo> &CSI,
                                         const TargetRegisterInfo *TRI) const {
    //
    // Registers RA,S0,S1 are the callee saved registers and they will be restored
    // with the restore instruction during emitEpilogue.
    // We need to override this virtual function, otherwise llvm will try and
    // restore the registers on it's on from the stack.
    //
  
    return true;
  }
  
  // Eliminate ADJCALLSTACKDOWN, ADJCALLSTACKUP pseudo instructions
  void Mips16FrameLowering::
  eliminateCallFramePseudoInstr(MachineFunction &MF, MachineBasicBlock &MBB,
                                MachineBasicBlock::iterator I) const {
    if (!hasReservedCallFrame(MF)) {
      int64_t Amount = I->getOperand(0).getImm();
  
      if (I->getOpcode() == Mips::ADJCALLSTACKDOWN)
        Amount = -Amount;
  
      const Mips16InstrInfo &TII =
        *static_cast<const Mips16InstrInfo*>(MF.getTarget().getInstrInfo());
  
      TII.adjustStackPtr(Mips::SP, Amount, MBB, I);
    }
  
    MBB.erase(I);
  }
  
  bool
  Mips16FrameLowering::hasReservedCallFrame(const MachineFunction &MF) const {
    const MachineFrameInfo *MFI = MF.getFrameInfo();
    // Reserve call frame if the size of the maximum call frame fits into 15-bit
    // immediate field and there are no variable sized objects on the stack.
    return isInt<15>(MFI->getMaxCallFrameSize()) && !MFI->hasVarSizedObjects();
  }
  
  void Mips16FrameLowering::
  processFunctionBeforeCalleeSavedScan(MachineFunction &MF,
                                       RegScavenger *RS) const {
    const Mips16InstrInfo &TII =
      *static_cast<const Mips16InstrInfo*>(MF.getTarget().getInstrInfo());
    const MipsRegisterInfo &RI = TII.getRegisterInfo();
    const BitVector Reserved = RI.getReservedRegs(MF);
    bool SaveS2 = Reserved[Mips::S2];
    if (SaveS2)
      MF.getRegInfo().setPhysRegUsed(Mips::S2);
    if (hasFP(MF))
      MF.getRegInfo().setPhysRegUsed(Mips::S0);
  }
  
  const MipsFrameLowering *
  llvm::createMips16FrameLowering(const MipsSubtarget &ST) {
    return new Mips16FrameLowering(ST);
  }
  