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

1 files changed, 644 insertions, 0 deletions

diff --git a/lib/Target/AArch64/AArch64FrameLowering.cpp b/lib/Target/AArch64/AArch64FrameLowering.cpp
new file mode 100644
index 0000000000..2301114219
--- /dev/null
+++ b/lib/Target/AArch64/AArch64FrameLowering.cpp
@@ -0,0 +1,644 @@
+//===- AArch64FrameLowering.cpp - AArch64 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 AArch64 implementation of TargetFrameLowering class.
+//
+//===----------------------------------------------------------------------===//
+
+#include "AArch64.h"
+#include "AArch64FrameLowering.h"
+#include "AArch64MachineFunctionInfo.h"
+#include "AArch64InstrInfo.h"
+#include "llvm/CodeGen/MachineFrameInfo.h"
+#include "llvm/CodeGen/MachineFunction.h"
+#include "llvm/CodeGen/MachineInstrBuilder.h"
+#include "llvm/CodeGen/MachineMemOperand.h"
+#include "llvm/CodeGen/MachineModuleInfo.h"
+#include "llvm/CodeGen/MachineRegisterInfo.h"
+#include "llvm/CodeGen/RegisterScavenging.h"
+#include "llvm/IR/Function.h"
+#include "llvm/MC/MachineLocation.h"
+#include "llvm/Support/Debug.h"
+#include "llvm/Support/ErrorHandling.h"
+
+using namespace llvm;
+
+void AArch64FrameLowering::splitSPAdjustments(uint64_t Total,
+                                              uint64_t &Initial,
+                                              uint64_t &Residual) const {
+  // 0x1f0 here is a pessimistic (i.e. realistic) boundary: x-register LDP
+  // instructions have a 7-bit signed immediate scaled by 8, giving a reach of
+  // 0x1f8, but stack adjustment should always be a multiple of 16.
+  if (Total <= 0x1f0) {
+    Initial = Total;
+    Residual = 0;
+  } else {
+    Initial = 0x1f0;
+    Residual = Total - Initial;
+  }
+}
+
+void AArch64FrameLowering::emitPrologue(MachineFunction &MF) const {
+  AArch64MachineFunctionInfo *FuncInfo =
+    MF.getInfo<AArch64MachineFunctionInfo>();
+  MachineBasicBlock &MBB = MF.front();
+  MachineBasicBlock::iterator MBBI = MBB.begin();
+  MachineFrameInfo *MFI = MF.getFrameInfo();
+  const TargetInstrInfo &TII = *MF.getTarget().getInstrInfo();
+  DebugLoc DL = MBBI != MBB.end() ? MBBI->getDebugLoc() : DebugLoc();
+
+  MachineModuleInfo &MMI = MF.getMMI();
+  std::vector<MachineMove> &Moves = MMI.getFrameMoves();
+  bool NeedsFrameMoves = MMI.hasDebugInfo()
+    || MF.getFunction()->needsUnwindTableEntry();
+
+  uint64_t NumInitialBytes, NumResidualBytes;
+
+  // Currently we expect the stack to be laid out by
+  //     sub sp, sp, #initial
+  //     stp x29, x30, [sp, #offset]
+  //     ...
+  //     str xxx, [sp, #offset]
+  //     sub sp, sp, #rest (possibly via extra instructions).
+  if (MFI->getCalleeSavedInfo().size()) {
+    // If there are callee-saved registers, we want to store them efficiently as
+    // a block, and virtual base assignment happens too early to do it for us so
+    // we adjust the stack in two phases: first just for callee-saved fiddling,
+    // then to allocate the rest of the frame.
+    splitSPAdjustments(MFI->getStackSize(), NumInitialBytes, NumResidualBytes);
+  } else {
+    // If there aren't any callee-saved registers, two-phase adjustment is
+    // inefficient. It's more efficient to adjust with NumInitialBytes too
+    // because when we're in a "callee pops argument space" situation, that pop
+    // must be tacked onto Initial for correctness.
+    NumInitialBytes = MFI->getStackSize();
+    NumResidualBytes = 0;
+  }
+
+  // Tell everyone else how much adjustment we're expecting them to use. In
+  // particular if an adjustment is required for a tail call the epilogue could
+  // have a different view of things.
+  FuncInfo->setInitialStackAdjust(NumInitialBytes);
+
+  emitSPUpdate(MBB, MBBI, DL, TII, AArch64::X16, -NumInitialBytes,
+               MachineInstr::FrameSetup);
+
+  if (NeedsFrameMoves && NumInitialBytes) {
+    // We emit this update even if the CFA is set from a frame pointer later so
+    // that the CFA is valid in the interim.
+    MCSymbol *SPLabel = MMI.getContext().CreateTempSymbol();
+    BuildMI(MBB, MBBI, DL, TII.get(TargetOpcode::PROLOG_LABEL))
+      .addSym(SPLabel);
+
+    MachineLocation Dst(MachineLocation::VirtualFP);
+    MachineLocation Src(AArch64::XSP, NumInitialBytes);
+    Moves.push_back(MachineMove(SPLabel, Dst, Src));
+  }
+
+  // Otherwise we need to set the frame pointer and/or add a second stack
+  // adjustment.
+
+  bool FPNeedsSetting = hasFP(MF);
+  for (; MBBI != MBB.end(); ++MBBI) {
+    // Note that this search makes strong assumptions about the operation used
+    // to store the frame-pointer: it must be "STP x29, x30, ...". This could
+    // change in future, but until then there's no point in implementing
+    // untestable more generic cases.
+    if (FPNeedsSetting && MBBI->getOpcode() == AArch64::LSPair64_STR
+                       && MBBI->getOperand(0).getReg() == AArch64::X29) {
+      int64_t X29FrameIdx = MBBI->getOperand(2).getIndex();
+      FuncInfo->setFramePointerOffset(MFI->getObjectOffset(X29FrameIdx));
+
+      ++MBBI;
+      emitRegUpdate(MBB, MBBI, DL, TII, AArch64::X29, AArch64::XSP,
+                    AArch64::X29,
+                    NumInitialBytes + MFI->getObjectOffset(X29FrameIdx),
+                    MachineInstr::FrameSetup);
+
+      // The offset adjustment used when emitting debugging locations relative
+      // to whatever frame base is set. AArch64 uses the default frame base (FP
+      // or SP) and this adjusts the calculations to be correct.
+      MFI->setOffsetAdjustment(- MFI->getObjectOffset(X29FrameIdx)
+                               - MFI->getStackSize());
+
+      if (NeedsFrameMoves) {
+        MCSymbol *FPLabel = MMI.getContext().CreateTempSymbol();
+        BuildMI(MBB, MBBI, DL, TII.get(TargetOpcode::PROLOG_LABEL))
+          .addSym(FPLabel);
+        MachineLocation Dst(MachineLocation::VirtualFP);
+        MachineLocation Src(AArch64::X29, -MFI->getObjectOffset(X29FrameIdx));
+        Moves.push_back(MachineMove(FPLabel, Dst, Src));
+      }
+
+      FPNeedsSetting = false;
+    }
+
+    if (!MBBI->getFlag(MachineInstr::FrameSetup))
+      break;
+  }
+
+  assert(!FPNeedsSetting && "Frame pointer couldn't be set");
+
+  emitSPUpdate(MBB, MBBI, DL, TII, AArch64::X16, -NumResidualBytes,
+               MachineInstr::FrameSetup);
+
+  // Now we emit the rest of the frame setup information, if necessary: we've
+  // already noted the FP and initial SP moves so we're left with the prologue's
+  // final SP update and callee-saved register locations.
+  if (!NeedsFrameMoves)
+    return;
+
+  // Reuse the label if appropriate, so create it in this outer scope.
+  MCSymbol *CSLabel = 0;
+
+  // The rest of the stack adjustment
+  if (!hasFP(MF) && NumResidualBytes) {
+    CSLabel = MMI.getContext().CreateTempSymbol();
+    BuildMI(MBB, MBBI, DL, TII.get(TargetOpcode::PROLOG_LABEL))
+      .addSym(CSLabel);
+
+    MachineLocation Dst(MachineLocation::VirtualFP);
+    MachineLocation Src(AArch64::XSP, NumResidualBytes + NumInitialBytes);
+    Moves.push_back(MachineMove(CSLabel, Dst, Src));
+  }
+
+  // And any callee-saved registers (it's fine to leave them to the end here,
+  // because the old values are still valid at this point.
+  const std::vector<CalleeSavedInfo> &CSI = MFI->getCalleeSavedInfo();
+  if (CSI.size()) {
+    if (!CSLabel) {
+      CSLabel = MMI.getContext().CreateTempSymbol();
+      BuildMI(MBB, MBBI, DL, TII.get(TargetOpcode::PROLOG_LABEL))
+        .addSym(CSLabel);
+    }
+
+    for (std::vector<CalleeSavedInfo>::const_iterator I = CSI.begin(),
+           E = CSI.end(); I != E; ++I) {
+      MachineLocation Dst(MachineLocation::VirtualFP, MFI->getObjectOffset(I->getFrameIdx()));
+      MachineLocation Src(I->getReg());
+      Moves.push_back(MachineMove(CSLabel, Dst, Src));
+    }
+  }
+}
+
+void
+AArch64FrameLowering::emitEpilogue(MachineFunction &MF,
+                                   MachineBasicBlock &MBB) const {
+  AArch64MachineFunctionInfo *FuncInfo =
+    MF.getInfo<AArch64MachineFunctionInfo>();
+
+  MachineBasicBlock::iterator MBBI = MBB.getLastNonDebugInstr();
+  DebugLoc DL = MBBI->getDebugLoc();
+  const TargetInstrInfo &TII = *MF.getTarget().getInstrInfo();
+  MachineFrameInfo &MFI = *MF.getFrameInfo();
+  unsigned RetOpcode = MBBI->getOpcode();
+
+  // Initial and residual are named for consitency with the prologue. Note that
+  // in the epilogue, the residual adjustment is executed first.
+  uint64_t NumInitialBytes = FuncInfo->getInitialStackAdjust();
+  uint64_t NumResidualBytes = MFI.getStackSize() - NumInitialBytes;
+  uint64_t ArgumentPopSize = 0;
+  if (RetOpcode == AArch64::TC_RETURNdi ||
+      RetOpcode == AArch64::TC_RETURNxi) {
+    MachineOperand &JumpTarget = MBBI->getOperand(0);
+    MachineOperand &StackAdjust = MBBI->getOperand(1);
+
+    MachineInstrBuilder MIB;
+    if (RetOpcode == AArch64::TC_RETURNdi) {
+      MIB = BuildMI(MBB, MBBI, DL, TII.get(AArch64::TAIL_Bimm));
+      if (JumpTarget.isGlobal()) {
+        MIB.addGlobalAddress(JumpTarget.getGlobal(), JumpTarget.getOffset(),
+                             JumpTarget.getTargetFlags());
+      } else {
+        assert(JumpTarget.isSymbol() && "unexpected tail call destination");
+        MIB.addExternalSymbol(JumpTarget.getSymbolName(),
+                              JumpTarget.getTargetFlags());
+      }
+    } else {
+      assert(RetOpcode == AArch64::TC_RETURNxi && JumpTarget.isReg()
+             && "Unexpected tail call");
+
+      MIB = BuildMI(MBB, MBBI, DL, TII.get(AArch64::TAIL_BRx));
+      MIB.addReg(JumpTarget.getReg(), RegState::Kill);
+    }
+
+    // Add the extra operands onto the new tail call instruction even though
+    // they're not used directly (so that liveness is tracked properly etc).
+    for (unsigned i = 2, e = MBBI->getNumOperands(); i != e; ++i)
+        MIB->addOperand(MBBI->getOperand(i));
+
+
+    // Delete the pseudo instruction TC_RETURN.
+    MachineInstr *NewMI = prior(MBBI);
+    MBB.erase(MBBI);
+    MBBI = NewMI;
+
+    // For a tail-call in a callee-pops-arguments environment, some or all of
+    // the stack may actually be in use for the call's arguments, this is
+    // calculated during LowerCall and consumed here...
+    ArgumentPopSize = StackAdjust.getImm();
+  } else {
+    // ... otherwise the amount to pop is *all* of the argument space,
+    // conveniently stored in the MachineFunctionInfo by
+    // LowerFormalArguments. This will, of course, be zero for the C calling
+    // convention.
+    ArgumentPopSize = FuncInfo->getArgumentStackToRestore();
+  }
+
+  assert(NumInitialBytes % 16 == 0 && NumResidualBytes % 16 == 0
+         && "refusing to adjust stack by misaligned amt");
+
+  // We may need to address callee-saved registers differently, so find out the
+  // bound on the frame indices.
+  const std::vector<CalleeSavedInfo> &CSI = MFI.getCalleeSavedInfo();
+  int MinCSFI = 0;
+  int MaxCSFI = -1;
+
+  if (CSI.size()) {
+    MinCSFI = CSI[0].getFrameIdx();
+    MaxCSFI = CSI[CSI.size() - 1].getFrameIdx();
+  }
+
+  // The "residual" stack update comes first from this direction and guarantees
+  // that SP is NumInitialBytes below its value on function entry, either by a
+  // direct update or restoring it from the frame pointer.
+  if (NumInitialBytes + ArgumentPopSize != 0) {
+    emitSPUpdate(MBB, MBBI, DL, TII, AArch64::X16,
+                 NumInitialBytes + ArgumentPopSize);
+    --MBBI;
+  }
+
+
+  // MBBI now points to the instruction just past the last callee-saved
+  // restoration (either RET/B if NumInitialBytes == 0, or the "ADD sp, sp"
+  // otherwise).
+
+  // Now we need to find out where to put the bulk of the stack adjustment
+  MachineBasicBlock::iterator FirstEpilogue = MBBI;
+  while (MBBI != MBB.begin()) {
+    --MBBI;
+
+    unsigned FrameOp;
+    for (FrameOp = 0; FrameOp < MBBI->getNumOperands(); ++FrameOp) {
+      if (MBBI->getOperand(FrameOp).isFI())
+        break;
+    }
+
+    // If this instruction doesn't have a frame index we've reached the end of
+    // the callee-save restoration.
+    if (FrameOp == MBBI->getNumOperands())
+      break;
+
+    // Likewise if it *is* a local reference, but not to a callee-saved object.
+    int FrameIdx = MBBI->getOperand(FrameOp).getIndex();
+    if (FrameIdx < MinCSFI || FrameIdx > MaxCSFI)
+      break;
+
+    FirstEpilogue = MBBI;
+  }
+
+  if (MF.getFrameInfo()->hasVarSizedObjects()) {
+    int64_t StaticFrameBase;
+    StaticFrameBase = -(NumInitialBytes + FuncInfo->getFramePointerOffset());
+    emitRegUpdate(MBB, FirstEpilogue, DL, TII,
+                  AArch64::XSP, AArch64::X29, AArch64::NoRegister,
+                  StaticFrameBase);
+  } else {
+    emitSPUpdate(MBB, FirstEpilogue, DL,TII, AArch64::X16, NumResidualBytes);
+  }
+}
+
+int64_t
+AArch64FrameLowering::resolveFrameIndexReference(MachineFunction &MF,
+                                                 int FrameIndex,
+                                                 unsigned &FrameReg,
+                                                 int SPAdj,
+                                                 bool IsCalleeSaveOp) const {
+  AArch64MachineFunctionInfo *FuncInfo =
+    MF.getInfo<AArch64MachineFunctionInfo>();
+  MachineFrameInfo *MFI = MF.getFrameInfo();
+
+  int64_t TopOfFrameOffset = MFI->getObjectOffset(FrameIndex);
+
+  assert(!(IsCalleeSaveOp && FuncInfo->getInitialStackAdjust() == 0)
+         && "callee-saved register in unexpected place");
+
+  // If the frame for this function is particularly large, we adjust the stack
+  // in two phases which means the callee-save related operations see a
+  // different (intermediate) stack size.
+  int64_t FrameRegPos;
+  if (IsCalleeSaveOp) {
+    FrameReg = AArch64::XSP;
+    FrameRegPos = -static_cast<int64_t>(FuncInfo->getInitialStackAdjust());
+  } else if (useFPForAddressing(MF)) {
+    // Have to use the frame pointer since we have no idea where SP is.
+    FrameReg = AArch64::X29;
+    FrameRegPos = FuncInfo->getFramePointerOffset();
+  } else {
+    FrameReg = AArch64::XSP;
+    FrameRegPos = -static_cast<int64_t>(MFI->getStackSize()) + SPAdj;
+  }
+
+  return TopOfFrameOffset - FrameRegPos;
+}
+
+/// Estimate and return the size of the frame.
+static unsigned estimateStackSize(MachineFunction &MF) {
+  // FIXME: Make generic? Really consider after upstreaming.  This code is now
+  // shared between PEI, ARM *and* here.
+  const MachineFrameInfo *MFI = MF.getFrameInfo();
+  const TargetFrameLowering *TFI = MF.getTarget().getFrameLowering();
+  const TargetRegisterInfo *RegInfo = MF.getTarget().getRegisterInfo();
+  unsigned MaxAlign = MFI->getMaxAlignment();
+  int Offset = 0;
+
+  // This code is very, very similar to PEI::calculateFrameObjectOffsets().
+  // It really should be refactored to share code. Until then, changes
+  // should keep in mind that there's tight coupling between the two.
+
+  for (int i = MFI->getObjectIndexBegin(); i != 0; ++i) {
+    int FixedOff = -MFI->getObjectOffset(i);
+    if (FixedOff > Offset) Offset = FixedOff;
+  }
+  for (unsigned i = 0, e = MFI->getObjectIndexEnd(); i != e; ++i) {
+    if (MFI->isDeadObjectIndex(i))
+      continue;
+    Offset += MFI->getObjectSize(i);
+    unsigned Align = MFI->getObjectAlignment(i);
+    // Adjust to alignment boundary
+    Offset = (Offset+Align-1)/Align*Align;
+
+    MaxAlign = std::max(Align, MaxAlign);
+  }
+
+  if (MFI->adjustsStack() && TFI->hasReservedCallFrame(MF))
+    Offset += MFI->getMaxCallFrameSize();
+
+  // Round up the size to a multiple of the alignment.  If the function has
+  // any calls or alloca's, align to the target's StackAlignment value to
+  // ensure that the callee's frame or the alloca data is suitably aligned;
+  // otherwise, for leaf functions, align to the TransientStackAlignment
+  // value.
+  unsigned StackAlign;
+  if (MFI->adjustsStack() || MFI->hasVarSizedObjects() ||
+      (RegInfo->needsStackRealignment(MF) && MFI->getObjectIndexEnd() != 0))
+    StackAlign = TFI->getStackAlignment();
+  else
+    StackAlign = TFI->getTransientStackAlignment();
+
+  // If the frame pointer is eliminated, all frame offsets will be relative to
+  // SP not FP. Align to MaxAlign so this works.
+  StackAlign = std::max(StackAlign, MaxAlign);
+  unsigned AlignMask = StackAlign - 1;
+  Offset = (Offset + AlignMask) & ~uint64_t(AlignMask);
+
+  return (unsigned)Offset;
+}
+
+void
+AArch64FrameLowering::processFunctionBeforeCalleeSavedScan(MachineFunction &MF,
+                                                       RegScavenger *RS) const {
+  const AArch64RegisterInfo *RegInfo =
+    static_cast<const AArch64RegisterInfo *>(MF.getTarget().getRegisterInfo());
+  MachineFrameInfo *MFI = MF.getFrameInfo();
+  const AArch64InstrInfo &TII =
+    *static_cast<const AArch64InstrInfo *>(MF.getTarget().getInstrInfo());
+
+  if (hasFP(MF)) {
+    MF.getRegInfo().setPhysRegUsed(AArch64::X29);
+    MF.getRegInfo().setPhysRegUsed(AArch64::X30);
+  }
+
+  // If addressing of local variables is going to be more complicated than
+  // shoving a base register and an offset into the instruction then we may well
+  // need to scavenge registers. We should either specifically add an
+  // callee-save register for this purpose or allocate an extra spill slot.
+
+  bool BigStack =
+    (RS && estimateStackSize(MF) >= TII.estimateRSStackLimit(MF))
+    || MFI->hasVarSizedObjects() // Access will be from X29: messes things up
+    || (MFI->adjustsStack() && !hasReservedCallFrame(MF));
+
+  if (!BigStack)
+    return;
+
+  // We certainly need some slack space for the scavenger, preferably an extra
+  // register.
+  const uint16_t *CSRegs = RegInfo->getCalleeSavedRegs();
+  uint16_t ExtraReg = AArch64::NoRegister;
+
+  for (unsigned i = 0; CSRegs[i]; ++i) {
+    if (AArch64::GPR64RegClass.contains(CSRegs[i]) &&
+        !MF.getRegInfo().isPhysRegUsed(CSRegs[i])) {
+      ExtraReg = CSRegs[i];
+      break;
+    }
+  }
+
+  if (ExtraReg != 0) {
+    MF.getRegInfo().setPhysRegUsed(ExtraReg);
+  } else {
+    // Create a stack slot for scavenging purposes. PrologEpilogInserter
+    // helpfully places it near either SP or FP for us to avoid
+    // infinitely-regression during scavenging.
+    const TargetRegisterClass *RC = &AArch64::GPR64RegClass;
+    RS->setScavengingFrameIndex(MFI->CreateStackObject(RC->getSize(),
+                                                       RC->getAlignment(),
+                                                       false));
+  }
+}
+
+bool AArch64FrameLowering::determinePrologueDeath(MachineBasicBlock &MBB,
+                                                  unsigned Reg) const {
+  // If @llvm.returnaddress is called then it will refer to X30 by some means;
+  // the prologue store does not kill the register.
+  if (Reg == AArch64::X30) {
+    if (MBB.getParent()->getFrameInfo()->isReturnAddressTaken()
+        && MBB.getParent()->getRegInfo().isLiveIn(Reg))
+    return false;
+  }
+
+  // In all other cases, physical registers are dead after they've been saved
+  // but live at the beginning of the prologue block.
+  MBB.addLiveIn(Reg);
+  return true;
+}
+
+void
+AArch64FrameLowering::emitFrameMemOps(bool isPrologue, MachineBasicBlock &MBB,
+                                      MachineBasicBlock::iterator MBBI,
+                                      const std::vector<CalleeSavedInfo> &CSI,
+                                      const TargetRegisterInfo *TRI,
+                                      LoadStoreMethod PossClasses[],
+                                      unsigned NumClasses) const {
+  DebugLoc DL = MBB.findDebugLoc(MBBI);
+  MachineFunction &MF = *MBB.getParent();
+  MachineFrameInfo &MFI = *MF.getFrameInfo();
+  const TargetInstrInfo &TII = *MF.getTarget().getInstrInfo();
+
+  // A certain amount of implicit contract is present here. The actual stack
+  // offsets haven't been allocated officially yet, so for strictly correct code
+  // we rely on the fact that the elements of CSI are allocated in order
+  // starting at SP, purely as dictated by size and alignment. In practice since
+  // this function handles the only accesses to those slots it's not quite so
+  // important.
+  //
+  // We have also ordered the Callee-saved register list in AArch64CallingConv
+  // so that the above scheme puts registers in order: in particular we want
+  // &X30 to be &X29+8 for an ABI-correct frame record (PCS 5.2.2)
+  for (unsigned i = 0, e = CSI.size(); i < e; ++i) {
+    unsigned Reg = CSI[i].getReg();
+
+    // First we need to find out which register class the register belongs to so
+    // that we can use the correct load/store instrucitons.
+    unsigned ClassIdx;
+    for (ClassIdx = 0; ClassIdx < NumClasses; ++ClassIdx) {
+      if (PossClasses[ClassIdx].RegClass->contains(Reg))
+        break;
+    }
+    assert(ClassIdx != NumClasses
+           && "Asked to store register in unexpected class");
+    const TargetRegisterClass &TheClass = *PossClasses[ClassIdx].RegClass;
+
+    // Now we need to decide whether it's possible to emit a paired instruction:
+    // for this we want the next register to be in the same class.
+    MachineInstrBuilder NewMI;
+    bool Pair = false;
+    if (i + 1 < CSI.size() && TheClass.contains(CSI[i+1].getReg())) {
+      Pair = true;
+      unsigned StLow = 0, StHigh = 0;
+      if (isPrologue) {
+        // Most of these registers will be live-in to the MBB and killed by our
+        // store, though there are exceptions (see determinePrologueDeath).
+        StLow = getKillRegState(determinePrologueDeath(MBB, CSI[i+1].getReg()));
+        StHigh = getKillRegState(determinePrologueDeath(MBB, CSI[i].getReg()));
+      } else {
+        StLow = RegState::Define;
+        StHigh = RegState::Define;
+      }
+
+      NewMI = BuildMI(MBB, MBBI, DL, TII.get(PossClasses[ClassIdx].PairOpcode))
+                .addReg(CSI[i+1].getReg(), StLow)
+                .addReg(CSI[i].getReg(), StHigh);
+
+      // If it's a paired op, we've consumed two registers
+      ++i;
+    } else {
+      unsigned State;
+      if (isPrologue) {
+        State = getKillRegState(determinePrologueDeath(MBB, CSI[i].getReg()));
+      } else {
+        State = RegState::Define;
+      }
+
+      NewMI = BuildMI(MBB, MBBI, DL, TII.get(PossClasses[ClassIdx].SingleOpcode))
+                .addReg(CSI[i].getReg(), State);
+    }
+
+    // Note that the FrameIdx refers to the second register in a pair: it will
+    // be allocated the smaller numeric address and so is the one an LDP/STP
+    // address must use.
+    int FrameIdx = CSI[i].getFrameIdx();
+    MachineMemOperand::MemOperandFlags Flags;
+    Flags = isPrologue ? MachineMemOperand::MOStore : MachineMemOperand::MOLoad;
+    MachineMemOperand *MMO =
+      MF.getMachineMemOperand(MachinePointerInfo::getFixedStack(FrameIdx),
+                              Flags,
+                              Pair ? TheClass.getSize() * 2 : TheClass.getSize(),
+                              MFI.getObjectAlignment(FrameIdx));
+
+    NewMI.addFrameIndex(FrameIdx)
+      .addImm(0)                  // address-register offset
+      .addMemOperand(MMO);
+
+    if (isPrologue)
+      NewMI.setMIFlags(MachineInstr::FrameSetup);
+
+    // For aesthetic reasons, during an epilogue we want to emit complementary
+    // operations to the prologue, but in the opposite order. So we still
+    // iterate through the CalleeSavedInfo list in order, but we put the
+    // instructions successively earlier in the MBB.
+    if (!isPrologue)
+      --MBBI;
+  }
+}
+
+bool
+AArch64FrameLowering::spillCalleeSavedRegisters(MachineBasicBlock &MBB,
+                                        MachineBasicBlock::iterator MBBI,
+                                        const std::vector<CalleeSavedInfo> &CSI,
+                                        const TargetRegisterInfo *TRI) const {
+  if (CSI.empty())
+    return false;
+
+  static LoadStoreMethod PossibleClasses[] = {
+    {&AArch64::GPR64RegClass, AArch64::LSPair64_STR, AArch64::LS64_STR},
+    {&AArch64::FPR64RegClass, AArch64::LSFPPair64_STR, AArch64::LSFP64_STR},
+  };
+  unsigned NumClasses = llvm::array_lengthof(PossibleClasses);
+
+  emitFrameMemOps(/* isPrologue = */ true, MBB, MBBI, CSI, TRI,
+                  PossibleClasses, NumClasses);
+
+  return true;
+}
+
+bool
+AArch64FrameLowering::restoreCalleeSavedRegisters(MachineBasicBlock &MBB,
+                                        MachineBasicBlock::iterator MBBI,
+                                        const std::vector<CalleeSavedInfo> &CSI,
+                                        const TargetRegisterInfo *TRI) const {
+
+  if (CSI.empty())
+    return false;
+
+  static LoadStoreMethod PossibleClasses[] = {
+    {&AArch64::GPR64RegClass, AArch64::LSPair64_LDR, AArch64::LS64_LDR},
+    {&AArch64::FPR64RegClass, AArch64::LSFPPair64_LDR, AArch64::LSFP64_LDR},
+  };
+  unsigned NumClasses = llvm::array_lengthof(PossibleClasses);
+
+  emitFrameMemOps(/* isPrologue = */ false, MBB, MBBI, CSI, TRI,
+                  PossibleClasses, NumClasses);
+
+  return true;
+}
+
+bool
+AArch64FrameLowering::hasFP(const MachineFunction &MF) const {
+  const MachineFrameInfo *MFI = MF.getFrameInfo();
+  const TargetRegisterInfo *RI = MF.getTarget().getRegisterInfo();
+
+  // This is a decision of ABI compliance. The AArch64 PCS gives various options
+  // for conformance, and even at the most stringent level more or less permits
+  // elimination for leaf functions because there's no loss of functionality
+  // (for debugging etc)..
+  if (MF.getTarget().Options.DisableFramePointerElim(MF) && MFI->hasCalls())
+    return true;
+
+  // The following are hard-limits: incorrect code will be generated if we try
+  // to omit the frame.
+  return (RI->needsStackRealignment(MF) ||
+          MFI->hasVarSizedObjects() ||
+          MFI->isFrameAddressTaken());
+}
+
+bool
+AArch64FrameLowering::useFPForAddressing(const MachineFunction &MF) const {
+  return MF.getFrameInfo()->hasVarSizedObjects();
+}
+
+bool
+AArch64FrameLowering::hasReservedCallFrame(const MachineFunction &MF) const {
+  const MachineFrameInfo *MFI = MF.getFrameInfo();
+
+  // Of the various reasons for having a frame pointer, it's actually only
+  // variable-sized objects that prevent reservation of a call frame.
+  return !(hasFP(MF) && MFI->hasVarSizedObjects());
+}