Target RegisterInfo: devirtualize TargetFrameLowering

[jfb]

Summary

The target frame lowering's concrete type is always known in RegisterInfo, yet it's only sometimes devirtualized through a static_cast. This change adds an auto-generated static function <Target>GenRegisterInfo::getFrameLowering(const MachineFunction &MF) which does this devirtualization, and uses this function in all targets which can.

This change was suggested by sunfish in D11070 for WebAssembly, I figure that I may as well improve the other targets while I'm here.

[mcrosier]

I'm not the person to sign off on this, but FWIW this LGTM.

[echristo]

Sure, this seems reasonable to me.

-eric

lib/Target/AArch64/AArch64RegisterInfo.cpp

AArch64RegisterInfo::getThisReturnPreservedMask(const MachineFunction &MF,
   // In case that the calling convention does not use the same register for
   // both, the function should return NULL (does not currently apply)
   assert(CC != CallingConv::GHC && "should not be GHC calling convention.");
   return CSR_AArch64_AAPCS_ThisReturn_RegMask;
 }
 
 BitVector
 AArch64RegisterInfo::getReservedRegs(const MachineFunction &MF) const {
-  const TargetFrameLowering *TFI = MF.getSubtarget().getFrameLowering();
+  const AArch64FrameLowering *TFI = getFrameLowering(MF);
 
   // FIXME: avoid re-calculating this every time.
   BitVector Reserved(getNumRegs());
   Reserved.set(AArch64::SP);
   Reserved.set(AArch64::XZR);
   Reserved.set(AArch64::WSP);
   Reserved.set(AArch64::WZR);
 
if (hasBasePointer(MF)) {
     Reserved.set(AArch64::W19);
   }
 
   return Reserved;
 }
 
 bool AArch64RegisterInfo::isReservedReg(const MachineFunction &MF,
                                       unsigned Reg) const {
-  const TargetFrameLowering *TFI = MF.getSubtarget().getFrameLowering();
+  const AArch64FrameLowering *TFI = getFrameLowering(MF);
 
   switch (Reg) {
   default:
     break;
   case AArch64::SP:
   case AArch64::XZR:
   case AArch64::WSP:
   case AArch64::WZR:
bool AArch64RegisterInfo::canRealignStack(const MachineFunction &MF) const {
 
   return true;
 }
 
 // FIXME: share this with other backends with identical implementation?
 bool
 AArch64RegisterInfo::needsStackRealignment(const MachineFunction &MF) const {
   const MachineFrameInfo *MFI = MF.getFrameInfo();
+  const AArch64FrameLowering *TFI = getFrameLowering(MF);
   const Function *F = MF.getFunction();
-  unsigned StackAlign = MF.getTarget()
-                            .getSubtargetImpl(*MF.getFunction())
-                            ->getFrameLowering()
-                            ->getStackAlignment();
+  unsigned StackAlign = TFI->getStackAlignment();
   bool requiresRealignment =
       ((MFI->getMaxAlignment() > StackAlign) ||
        F->getAttributes().hasAttribute(AttributeSet::FunctionIndex,
                                        Attribute::StackAlignment));
 
   return requiresRealignment && canRealignStack(MF);
 }
 
 unsigned
 AArch64RegisterInfo::getFrameRegister(const MachineFunction &MF) const {
-  const TargetFrameLowering *TFI = MF.getSubtarget().getFrameLowering();
-
+  const AArch64FrameLowering *TFI = getFrameLowering(MF);
   return TFI->hasFP(MF) ? AArch64::FP : AArch64::SP;
 }
 
 bool AArch64RegisterInfo::requiresRegisterScavenging(
     const MachineFunction &MF) const {
   return true;
 }
 
if (!MI->mayLoad() && !MI->mayStore())
     return false;
 
   // Without a virtual base register, if the function has variable sized
   // objects, all fixed-size local references will be via the frame pointer,
   // Approximate the offset and see if it's legal for the instruction.
   // Note that the incoming offset is based on the SP value at function entry,
   // so it'll be negative.
   MachineFunction &MF = *MI->getParent()->getParent();
-  const TargetFrameLowering *TFI = MF.getSubtarget().getFrameLowering();
+  const AArch64FrameLowering *TFI = getFrameLowering(MF);
   MachineFrameInfo *MFI = MF.getFrameInfo();
 
   // Estimate an offset from the frame pointer.
   // Conservatively assume all GPR callee-saved registers get pushed.
   // FP, LR, X19-X28, D8-D15. 64-bits each.
   int64_t FPOffset = Offset - 16 * 20;
   // Estimate an offset from the stack pointer.
   // The incoming offset is relating to the SP at the start of the function,
void AArch64RegisterInfo::eliminateFrameIndex(MachineBasicBlock::iterator II,
                                               RegScavenger *RS) const {
   assert(SPAdj == 0 && "Unexpected");
 
   MachineInstr &MI = *II;
   MachineBasicBlock &MBB = *MI.getParent();
   MachineFunction &MF = *MBB.getParent();
   const AArch64InstrInfo *TII =
       MF.getSubtarget<AArch64Subtarget>().getInstrInfo();
-  const AArch64FrameLowering *TFI = static_cast<const AArch64FrameLowering *>(
-      MF.getSubtarget().getFrameLowering());
+  const AArch64FrameLowering *TFI = getFrameLowering(MF);
 
   int FrameIndex = MI.getOperand(FIOperandNum).getIndex();
   unsigned FrameReg;
   int Offset;
 
   // Special handling of dbg_value, stackmap and patchpoint instructions.
   if (MI.isDebugValue() || MI.getOpcode() == TargetOpcode::STACKMAP ||
       MI.getOpcode() == TargetOpcode::PATCHPOINT) {
void AArch64RegisterInfo::eliminateFrameIndex(MachineBasicBlock::iterator II,
   emitFrameOffset(MBB, II, MI.getDebugLoc(), ScratchReg, FrameReg, Offset, TII);
   MI.getOperand(FIOperandNum).ChangeToRegister(ScratchReg, false, false, true);
 }
 
 namespace llvm {
 
 unsigned AArch64RegisterInfo::getRegPressureLimit(const TargetRegisterClass *RC,
                                                   MachineFunction &MF) const {
-  const TargetFrameLowering *TFI = MF.getSubtarget().getFrameLowering();
+  const AArch64FrameLowering *TFI = getFrameLowering(MF);
 
   switch (RC->getID()) {
   default:
     return 0;
   case AArch64::GPR32RegClassID:
   case AArch64::GPR32spRegClassID:
   case AArch64::GPR32allRegClassID:
   case AArch64::GPR64spRegClassID:

lib/Target/ARM/ARMBaseRegisterInfo.cpp

if (CC == CallingConv::GHC)
     return nullptr;
   return STI.isTargetDarwin() ? CSR_iOS_ThisReturn_RegMask
                               : CSR_AAPCS_ThisReturn_RegMask;
 }
 
 BitVector ARMBaseRegisterInfo::
 getReservedRegs(const MachineFunction &MF) const {
   const ARMSubtarget &STI = MF.getSubtarget<ARMSubtarget>();
-  const TargetFrameLowering *TFI = STI.getFrameLowering();
+  const ARMFrameLowering *TFI = getFrameLowering(MF);
 
   // FIXME: avoid re-calculating this every time.
   BitVector Reserved(getNumRegs());
   Reserved.set(ARM::SP);
   Reserved.set(ARM::PC);
   Reserved.set(ARM::FPSCR);
   Reserved.set(ARM::APSR_NZCV);
   if (TFI->hasFP(MF))
if (RC == &ARM::CCRRegClass)
     return &ARM::rGPRRegClass;  // Can't copy CCR registers.
   return RC;
 }
 
 unsigned
 ARMBaseRegisterInfo::getRegPressureLimit(const TargetRegisterClass *RC,
                                          MachineFunction &MF) const {
   const ARMSubtarget &STI = MF.getSubtarget<ARMSubtarget>();
-  const TargetFrameLowering *TFI = STI.getFrameLowering();
+  const ARMFrameLowering *TFI = getFrameLowering(MF);
 
   switch (RC->getID()) {
   default:
     return 0;
   case ARM::tGPRRegClassID:
     return TFI->hasFP(MF) ? 4 : 5;
   case ARM::GPRRegClassID: {
     unsigned FP = TFI->hasFP(MF) ? 1 : 0;
if (Hint.second == Reg) {
             : ARMRI::RegPairOdd, OtherReg);
     }
   }
 }
 
 bool ARMBaseRegisterInfo::hasBasePointer(const MachineFunction &MF) const {
   const MachineFrameInfo *MFI = MF.getFrameInfo();
   const ARMFunctionInfo *AFI = MF.getInfo<ARMFunctionInfo>();
-  const TargetFrameLowering *TFI = MF.getSubtarget().getFrameLowering();
+  const ARMFrameLowering *TFI = getFrameLowering(MF);
 
   // When outgoing call frames are so large that we adjust the stack pointer
   // around the call, we can no longer use the stack pointer to reach the
   // emergency spill slot.
   if (needsStackRealignment(MF) && !TFI->hasReservedCallFrame(MF))
     return true;
 
   // Thumb has trouble with negative offsets from the FP. Thumb2 has a limited
bool ARMBaseRegisterInfo::hasBasePointer(const MachineFunction &MF) const {
   }
 
   return false;
 }
 
 bool ARMBaseRegisterInfo::canRealignStack(const MachineFunction &MF) const {
   const MachineRegisterInfo *MRI = &MF.getRegInfo();
   const ARMFunctionInfo *AFI = MF.getInfo<ARMFunctionInfo>();
+  const ARMFrameLowering *TFI = getFrameLowering(MF);
   // We can't realign the stack if:
   // 1. Dynamic stack realignment is explicitly disabled,
   // 2. This is a Thumb1 function (it's not useful, so we don't bother), or
   // 3. There are VLAs in the function and the base pointer is disabled.
   if (MF.getFunction()->hasFnAttribute("no-realign-stack"))
     return false;
   if (AFI->isThumb1OnlyFunction())
     return false;
   // Stack realignment requires a frame pointer.  If we already started
   // register allocation with frame pointer elimination, it is too late now.
   if (!MRI->canReserveReg(getFramePointerReg(MF.getSubtarget<ARMSubtarget>())))
     return false;
   // We may also need a base pointer if there are dynamic allocas or stack
   // pointer adjustments around calls.
-  if (MF.getSubtarget().getFrameLowering()->hasReservedCallFrame(MF))
+  if (TFI->hasReservedCallFrame(MF))
     return true;
   // A base pointer is required and allowed.  Check that it isn't too late to
   // reserve it.
   return MRI->canReserveReg(BasePtr);
 }
 
 bool ARMBaseRegisterInfo::
 needsStackRealignment(const MachineFunction &MF) const {
   const MachineFrameInfo *MFI = MF.getFrameInfo();
+  const ARMFrameLowering *TFI = getFrameLowering(MF);
   const Function *F = MF.getFunction();
-  unsigned StackAlign =
-      MF.getSubtarget().getFrameLowering()->getStackAlignment();
+  unsigned StackAlign = TFI->getStackAlignment();
   bool requiresRealignment = ((MFI->getMaxAlignment() > StackAlign) ||
                               F->hasFnAttribute(Attribute::StackAlignment));
 
   return requiresRealignment && canRealignStack(MF);
 }
 
 bool ARMBaseRegisterInfo::
 cannotEliminateFrame(const MachineFunction &MF) const {
   const MachineFrameInfo *MFI = MF.getFrameInfo();
   if (MF.getTarget().Options.DisableFramePointerElim(MF) && MFI->adjustsStack())
     return true;
   return MFI->hasVarSizedObjects() || MFI->isFrameAddressTaken()
     || needsStackRealignment(MF);
 }
 
 unsigned
 ARMBaseRegisterInfo::getFrameRegister(const MachineFunction &MF) const {
   const ARMSubtarget &STI = MF.getSubtarget<ARMSubtarget>();
-  const TargetFrameLowering *TFI = STI.getFrameLowering();
+  const ARMFrameLowering *TFI = getFrameLowering(MF);
 
   if (TFI->hasFP(MF))
     return getFramePointerReg(STI);
   return ARM::SP;
 }
 
 /// emitLoadConstPool - Emits a load from constpool to materialize the
 /// specified immediate.
needsFrameBaseReg(MachineInstr *MI, int64_t Offset) const {
   }
 
   // Without a virtual base register, if the function has variable sized
   // objects, all fixed-size local references will be via the frame pointer,
   // Approximate the offset and see if it's legal for the instruction.
   // Note that the incoming offset is based on the SP value at function entry,
   // so it'll be negative.
   MachineFunction &MF = *MI->getParent()->getParent();
-  const TargetFrameLowering *TFI = MF.getSubtarget().getFrameLowering();
+  const ARMFrameLowering *TFI = getFrameLowering(MF);
   MachineFrameInfo *MFI = MF.getFrameInfo();
   ARMFunctionInfo *AFI = MF.getInfo<ARMFunctionInfo>();
 
   // Estimate an offset from the frame pointer.
   // Conservatively assume all callee-saved registers get pushed. R4-R6
   // will be earlier than the FP, so we ignore those.
   // R7, LR
   int64_t FPOffset = Offset - 8;

 ARMBaseRegisterInfo::eliminateFrameIndex(MachineBasicBlock::iterator II,
                                          int SPAdj, unsigned FIOperandNum,
                                          RegScavenger *RS) const {
   MachineInstr &MI = *II;
   MachineBasicBlock &MBB = *MI.getParent();
   MachineFunction &MF = *MBB.getParent();
   const ARMBaseInstrInfo &TII =
       *static_cast<const ARMBaseInstrInfo *>(MF.getSubtarget().getInstrInfo());
-  const ARMFrameLowering *TFI = static_cast<const ARMFrameLowering *>(
-      MF.getSubtarget().getFrameLowering());
+  const ARMFrameLowering *TFI = getFrameLowering(MF);
   ARMFunctionInfo *AFI = MF.getInfo<ARMFunctionInfo>();
   assert(!AFI->isThumb1OnlyFunction() &&
          "This eliminateFrameIndex does not support Thumb1!");
   int FrameIndex = MI.getOperand(FIOperandNum).getIndex();
   unsigned FrameReg;
 
   int Offset = TFI->ResolveFrameIndexReference(MF, FrameIndex, FrameReg, SPAdj);
 

lib/Target/Hexagon/HexagonRegisterInfo.cpp

 
 unsigned HexagonRegisterInfo::getRARegister() const {
   return Hexagon::R31;
 }
 
 
 unsigned HexagonRegisterInfo::getFrameRegister(const MachineFunction
                                                &MF) const {
-  const TargetFrameLowering *TFI = MF.getSubtarget().getFrameLowering();
+  const HexagonFrameLowering *TFI = getFrameLowering(MF);
   if (TFI->hasFP(MF))
     return Hexagon::R30;
   return Hexagon::R29;
 }
 
 
 unsigned HexagonRegisterInfo::getFrameRegister() const {
   return Hexagon::R30;
 }
 
 
 unsigned HexagonRegisterInfo::getStackRegister() const {
   return Hexagon::R29;
 }
 
 
 bool
 HexagonRegisterInfo::useFPForScavengingIndex(const MachineFunction &MF) const {
-  return MF.getSubtarget().getFrameLowering()->hasFP(MF);
+  const HexagonFrameLowering *TFI = getFrameLowering(MF);
+  return TFI->hasFP(MF);
 }
 
 
 bool
 HexagonRegisterInfo::needsStackRealignment(const MachineFunction &MF) const {
   const MachineFrameInfo *MFI = MF.getFrameInfo();
   return MFI->getMaxAlignment() > 8;
 }

lib/Target/MSP430/MSP430RegisterInfo.cpp

 #include "MSP430GenRegisterInfo.inc"
 
 // FIXME: Provide proper call frame setup / destroy opcodes.
 MSP430RegisterInfo::MSP430RegisterInfo()
   : MSP430GenRegisterInfo(MSP430::PC) {}
 
 const MCPhysReg*
 MSP430RegisterInfo::getCalleeSavedRegs(const MachineFunction *MF) const {
-  const TargetFrameLowering *TFI = MF->getSubtarget().getFrameLowering();
+  const MSP430FrameLowering *TFI = getFrameLowering(*MF);
   const Function* F = MF->getFunction();
   static const MCPhysReg CalleeSavedRegs[] = {
     MSP430::FP, MSP430::R5, MSP430::R6, MSP430::R7,
     MSP430::R8, MSP430::R9, MSP430::R10, MSP430::R11,
     0
   };
   static const MCPhysReg CalleeSavedRegsFP[] = {
     MSP430::R5, MSP430::R6, MSP430::R7,
MSP430RegisterInfo::getCalleeSavedRegs(const MachineFunction *MF) const {
   else
     return (F->getCallingConv() == CallingConv::MSP430_INTR ?
             CalleeSavedRegsIntr : CalleeSavedRegs);
 
 }
 
 BitVector MSP430RegisterInfo::getReservedRegs(const MachineFunction &MF) const {
   BitVector Reserved(getNumRegs());
-  const TargetFrameLowering *TFI = MF.getSubtarget().getFrameLowering();
+  const MSP430FrameLowering *TFI = getFrameLowering(MF);
 
   // Mark 4 special registers with subregisters as reserved.
   Reserved.set(MSP430::PCB);
   Reserved.set(MSP430::SPB);
   Reserved.set(MSP430::SRB);
   Reserved.set(MSP430::CGB);
   Reserved.set(MSP430::PC);
   Reserved.set(MSP430::SP);

 MSP430RegisterInfo::eliminateFrameIndex(MachineBasicBlock::iterator II,
                                         int SPAdj, unsigned FIOperandNum,
                                         RegScavenger *RS) const {
   assert(SPAdj == 0 && "Unexpected");
 
   MachineInstr &MI = *II;
   MachineBasicBlock &MBB = *MI.getParent();
   MachineFunction &MF = *MBB.getParent();
-  const TargetFrameLowering *TFI = MF.getSubtarget().getFrameLowering();
+  const MSP430FrameLowering *TFI = getFrameLowering(MF);
   DebugLoc dl = MI.getDebugLoc();
   int FrameIndex = MI.getOperand(FIOperandNum).getIndex();
 
   unsigned BasePtr = (TFI->hasFP(MF) ? MSP430::FP : MSP430::SP);
   int Offset = MF.getFrameInfo()->getObjectOffset(FrameIndex);
 
   // Skip the saved PC
   Offset += 2;
if (MI.getOpcode() == MSP430::ADD16ri) {
     return;
   }
 
   MI.getOperand(FIOperandNum).ChangeToRegister(BasePtr, false);
   MI.getOperand(FIOperandNum + 1).ChangeToImmediate(Offset);
 }
 
 unsigned MSP430RegisterInfo::getFrameRegister(const MachineFunction &MF) const {
-  const TargetFrameLowering *TFI = MF.getSubtarget().getFrameLowering();
-
+  const MSP430FrameLowering *TFI = getFrameLowering(MF);
   return TFI->hasFP(MF) ? MSP430::FP : MSP430::SP;
 }

lib/Target/PowerPC/PPCRegisterInfo.cpp

 void PPCRegisterInfo::adjustStackMapLiveOutMask(uint32_t *Mask) const {
   for (unsigned PseudoReg : {PPC::ZERO, PPC::ZERO8, PPC::RM})
     Mask[PseudoReg / 32] &= ~(1u << (PseudoReg % 32));
 }
 
 BitVector PPCRegisterInfo::getReservedRegs(const MachineFunction &MF) const {
   BitVector Reserved(getNumRegs());
   const PPCSubtarget &Subtarget = MF.getSubtarget<PPCSubtarget>();
-  const PPCFrameLowering *PPCFI =
-      static_cast<const PPCFrameLowering *>(Subtarget.getFrameLowering());
+  const PPCFrameLowering *TFI = getFrameLowering(MF);
 
   // The ZERO register is not really a register, but the representation of r0
   // when used in instructions that treat r0 as the constant 0.
   Reserved.set(PPC::ZERO);
   Reserved.set(PPC::ZERO8);
 
   // The FP register is also not really a register, but is the representation
   // of the frame pointer register used by ISD::FRAMEADDR.
BitVector PPCRegisterInfo::getReservedRegs(const MachineFunction &MF) const {
   
   // On PPC64, r13 is the thread pointer. Never allocate this register.
   if (TM.isPPC64()) {
     Reserved.set(PPC::R13);
 
     Reserved.set(PPC::X1);
     Reserved.set(PPC::X13);
 
-    if (PPCFI->needsFP(MF))
+    if (TFI->needsFP(MF))
       Reserved.set(PPC::X31);
 
     if (hasBasePointer(MF))
       Reserved.set(PPC::X30);
 
     // The 64-bit SVR4 ABI reserves r2 for the TOC pointer.
     if (Subtarget.isSVR4ABI()) {
       // We only reserve r2 if we need to use the TOC pointer. If we have no
       // explicit uses of the TOC pointer (meaning we're a leaf function with
       // no constant-pool loads, etc.) and we have no potential uses inside an
       // inline asm block, then we can treat r2 has an ordinary callee-saved
       // register.
       const PPCFunctionInfo *FuncInfo = MF.getInfo<PPCFunctionInfo>();
       if (FuncInfo->usesTOCBasePtr() || MF.hasInlineAsm())
         Reserved.set(PPC::X2);
       else
         Reserved.reset(PPC::R2);
     }
   }
 
-  if (PPCFI->needsFP(MF))
+  if (TFI->needsFP(MF))
     Reserved.set(PPC::R31);
 
   if (hasBasePointer(MF)) {
     if (Subtarget.isSVR4ABI() && !TM.isPPC64() &&
         TM.getRelocationModel() == Reloc::PIC_)
       Reserved.set(PPC::R29);
     else
       Reserved.set(PPC::R30);
for (TargetRegisterClass::iterator I = PPC::VRRCRegClass.begin(),
          IE = PPC::VRRCRegClass.end(); I != IE; ++I)
       Reserved.set(*I);
 
   return Reserved;
 }
 
 unsigned PPCRegisterInfo::getRegPressureLimit(const TargetRegisterClass *RC,
                                               MachineFunction &MF) const {
-  const PPCSubtarget &Subtarget = MF.getSubtarget<PPCSubtarget>();
-  const TargetFrameLowering *TFI = Subtarget.getFrameLowering();
+  const PPCFrameLowering *TFI = getFrameLowering(MF);
   const unsigned DefaultSafety = 1;
 
   switch (RC->getID()) {
   default:
     return 0;
   case PPC::G8RC_NOX0RegClassID:
   case PPC::GPRC_NOR0RegClassID: 
   case PPC::G8RCRegClassID:
void PPCRegisterInfo::lowerDynamicAlloc(MachineBasicBlock::iterator II) const {
   DebugLoc dl = MI.getDebugLoc();
 
   // Get the maximum call stack size.
   unsigned maxCallFrameSize = MFI->getMaxCallFrameSize();
   // Get the total frame size.
   unsigned FrameSize = MFI->getStackSize();
   
   // Get stack alignments.
-  unsigned TargetAlign = Subtarget.getFrameLowering()->getStackAlignment();
+  const PPCFrameLowering *TFI = getFrameLowering(MF);
+  unsigned TargetAlign = TFI->getStackAlignment();
   unsigned MaxAlign = MFI->getMaxAlignment();
   assert((maxCallFrameSize & (MaxAlign-1)) == 0 &&
          "Maximum call-frame size not sufficiently aligned");
 
   // Determine the previous frame's address.  If FrameSize can't be
   // represented as 16 bits or we need special alignment, then we load the
   // previous frame's address from 0(SP).  Why not do an addis of the hi? 
   // Because R0 is our only safe tmp register and addi/addis treat R0 as zero. 
PPCRegisterInfo::eliminateFrameIndex(MachineBasicBlock::iterator II,
   }
 
   unsigned StackReg = MI.getOperand(FIOperandNum).getReg();
   MI.getOperand(OperandBase).ChangeToRegister(StackReg, false);
   MI.getOperand(OperandBase + 1).ChangeToRegister(SReg, false, false, true);
 }
 
 unsigned PPCRegisterInfo::getFrameRegister(const MachineFunction &MF) const {
-  const PPCSubtarget &Subtarget = MF.getSubtarget<PPCSubtarget>();
-  const TargetFrameLowering *TFI = Subtarget.getFrameLowering();
+  const PPCFrameLowering *TFI = getFrameLowering(MF);
 
   if (!TM.isPPC64())
     return TFI->hasFP(MF) ? PPC::R31 : PPC::R1;
   else
     return TFI->hasFP(MF) ? PPC::X31 : PPC::X1;
 }
 
 unsigned PPCRegisterInfo::getBaseRegister(const MachineFunction &MF) const {

 bool PPCRegisterInfo::canRealignStack(const MachineFunction &MF) const {
   if (MF.getFunction()->hasFnAttribute("no-realign-stack"))
     return false;
 
   return true;
 }
 
 bool PPCRegisterInfo::needsStackRealignment(const MachineFunction &MF) const {
-  const PPCSubtarget &Subtarget = MF.getSubtarget<PPCSubtarget>();
+  const PPCFrameLowering *TFI = getFrameLowering(MF);
   const MachineFrameInfo *MFI = MF.getFrameInfo();
   const Function *F = MF.getFunction();
-  unsigned StackAlign = Subtarget.getFrameLowering()->getStackAlignment();
+  unsigned StackAlign = TFI->getStackAlignment();
   bool requiresRealignment = ((MFI->getMaxAlignment() > StackAlign) ||
                               F->hasFnAttribute(Attribute::StackAlignment));
 
   return requiresRealignment && canRealignStack(MF);
 }
 
 /// Returns true if the instruction's frame index
 /// reference would be better served by a base register other than FP
needsFrameBaseReg(MachineInstr *MI, int64_t Offset) const {
 
   // Don't generate a new virtual base register just to add zero to it.
   if ((OpC == PPC::ADDI || OpC == PPC::ADDI8) &&
       MI->getOperand(2).getImm() == 0)
     return false;
 
   MachineBasicBlock &MBB = *MI->getParent();
   MachineFunction &MF = *MBB.getParent();
-  const PPCSubtarget &Subtarget = MF.getSubtarget<PPCSubtarget>();
-  const PPCFrameLowering *PPCFI =
-      static_cast<const PPCFrameLowering *>(Subtarget.getFrameLowering());
-  unsigned StackEst =
-    PPCFI->determineFrameLayout(MF, false, true);
+  const PPCFrameLowering *TFI = getFrameLowering(MF);
+  unsigned StackEst = TFI->determineFrameLayout(MF, false, true);
 
   // If we likely don't need a stack frame, then we probably don't need a
   // virtual base register either.
   if (!StackEst)
     return false;
 
   // Estimate an offset from the stack pointer.
   // The incoming offset is relating to the SP at the start of the function,
bool PPCRegisterInfo::isFrameOffsetLegal(const MachineInstr *MI,
   unsigned OffsetOperandNo = getOffsetONFromFION(*MI, FIOperandNum);
   Offset += MI->getOperand(OffsetOperandNo).getImm();
 
   return MI->getOpcode() == PPC::DBG_VALUE || // DBG_VALUE is always Reg+Imm
          MI->getOpcode() == TargetOpcode::STACKMAP ||
          MI->getOpcode() == TargetOpcode::PATCHPOINT ||
          (isInt<16>(Offset) && (!usesIXAddr(*MI) || (Offset & 3) == 0));
 }
-

lib/Target/SystemZ/SystemZRegisterInfo.cpp

 SystemZRegisterInfo::getCallPreservedMask(const MachineFunction &MF,
                                           CallingConv::ID CC) const {
   return CSR_SystemZ_RegMask;
 }
 
 BitVector
 SystemZRegisterInfo::getReservedRegs(const MachineFunction &MF) const {
   BitVector Reserved(getNumRegs());
-  const TargetFrameLowering *TFI = MF.getSubtarget().getFrameLowering();
+  const SystemZFrameLowering *TFI = getFrameLowering(MF);
 
   if (TFI->hasFP(MF)) {
     // R11D is the frame pointer.  Reserve all aliases.
     Reserved.set(SystemZ::R11D);
     Reserved.set(SystemZ::R11L);
     Reserved.set(SystemZ::R11H);
     Reserved.set(SystemZ::R10Q);
   }
SystemZRegisterInfo::eliminateFrameIndex(MachineBasicBlock::iterator MI,
                                          int SPAdj, unsigned FIOperandNum,
                                          RegScavenger *RS) const {
   assert(SPAdj == 0 && "Outgoing arguments should be part of the frame");
 
   MachineBasicBlock &MBB = *MI->getParent();
   MachineFunction &MF = *MBB.getParent();
   auto *TII =
       static_cast<const SystemZInstrInfo *>(MF.getSubtarget().getInstrInfo());
-  const TargetFrameLowering *TFI = MF.getSubtarget().getFrameLowering();
+  const SystemZFrameLowering *TFI = getFrameLowering(MF);
   DebugLoc DL = MI->getDebugLoc();
 
   // Decompose the frame index into a base and offset.
   int FrameIndex = MI->getOperand(FIOperandNum).getIndex();
   unsigned BasePtr = getFrameRegister(MF);
   int64_t Offset = (TFI->getFrameIndexOffset(MF, FrameIndex) +
                     MI->getOperand(FIOperandNum + 1).getImm());
 
else {
     }
   }
   MI->setDesc(TII->get(OpcodeForOffset));
   MI->getOperand(FIOperandNum + 1).ChangeToImmediate(Offset);
 }
 
 unsigned
 SystemZRegisterInfo::getFrameRegister(const MachineFunction &MF) const {
-  const TargetFrameLowering *TFI = MF.getSubtarget().getFrameLowering();
+  const SystemZFrameLowering *TFI = getFrameLowering(MF);
   return TFI->hasFP(MF) ? SystemZ::R11D : SystemZ::R15D;
 }

lib/Target/X86/X86RegisterInfo.cpp

else
       return &X86::GR32RegClass;
   }
   return RC;
 }
 
 unsigned
 X86RegisterInfo::getRegPressureLimit(const TargetRegisterClass *RC,
                                      MachineFunction &MF) const {
-  const TargetFrameLowering *TFI = MF.getSubtarget().getFrameLowering();
+  const X86FrameLowering *TFI = getFrameLowering(MF);
 
   unsigned FPDiff = TFI->hasFP(MF) ? 1 : 0;
   switch (RC->getID()) {
   default:
     return 0;
   case X86::GR32RegClassID:
     return 4 - FPDiff;
   case X86::GR64RegClassID:

 
 const uint32_t*
 X86RegisterInfo::getNoPreservedMask() const {
   return CSR_NoRegs_RegMask;
 }
 
 BitVector X86RegisterInfo::getReservedRegs(const MachineFunction &MF) const {
   BitVector Reserved(getNumRegs());
-  const TargetFrameLowering *TFI = MF.getSubtarget().getFrameLowering();
+  const X86FrameLowering *TFI = getFrameLowering(MF);
 
   // Set the stack-pointer register and its aliases as reserved.
   for (MCSubRegIterator I(X86::RSP, this, /*IncludeSelf=*/true); I.isValid();
        ++I)
     Reserved.set(*I);
 
   // Set the instruction pointer register and its aliases as reserved.
   for (MCSubRegIterator I(X86::RIP, this, /*IncludeSelf=*/true); I.isValid();
bool X86RegisterInfo::canRealignStack(const MachineFunction &MF) const {
   // it.
   if (MFI->hasVarSizedObjects())
     return MRI->canReserveReg(BasePtr);
   return true;
 }
 
 bool X86RegisterInfo::needsStackRealignment(const MachineFunction &MF) const {
   const MachineFrameInfo *MFI = MF.getFrameInfo();
+  const X86FrameLowering *TFI = getFrameLowering(MF);
   const Function *F = MF.getFunction();
-  unsigned StackAlign =
-    MF.getSubtarget().getFrameLowering()->getStackAlignment();
+  unsigned StackAlign = TFI->getStackAlignment();
   bool requiresRealignment = ((MFI->getMaxAlignment() > StackAlign) ||
                               F->hasFnAttribute(Attribute::StackAlignment));
 
   // If we've requested that we force align the stack do so now.
   if (ForceStackAlign)
     return canRealignStack(MF);
 
   return requiresRealignment && canRealignStack(MF);
 }
 
 bool X86RegisterInfo::hasReservedSpillSlot(const MachineFunction &MF,
                                            unsigned Reg, int &FrameIdx) const {
   // Since X86 defines assignCalleeSavedSpillSlots which always return true
   // this function neither used nor tested.
   llvm_unreachable("Unused function on X86. Otherwise need a test case.");
 }
 
 void
 X86RegisterInfo::eliminateFrameIndex(MachineBasicBlock::iterator II,
                                      int SPAdj, unsigned FIOperandNum,
                                      RegScavenger *RS) const {
   MachineInstr &MI = *II;
   MachineFunction &MF = *MI.getParent()->getParent();
-  const TargetFrameLowering *TFI = MF.getSubtarget().getFrameLowering();
+  const X86FrameLowering *TFI = getFrameLowering(MF);
   int FrameIndex = MI.getOperand(FIOperandNum).getIndex();
   unsigned BasePtr;
 
   unsigned Opc = MI.getOpcode();
   bool AfterFPPop = Opc == X86::TAILJMPm64 || Opc == X86::TAILJMPm ||
                     Opc == X86::TCRETURNmi || Opc == X86::TCRETURNmi64;
   if (hasBasePointer(MF))
     BasePtr = (FrameIndex < 0 ? FramePtr : getBaseRegister());
X86RegisterInfo::eliminateFrameIndex(MachineBasicBlock::iterator II,
   // offset is from the traditional base pointer location.  On 64-bit, the
   // offset is from the SP at the end of the prologue, not the FP location. This
   // matches the behavior of llvm.frameaddress.
   if (Opc == TargetOpcode::LOCAL_ESCAPE) {
     MachineOperand &FI = MI.getOperand(FIOperandNum);
     bool IsWinEH = MF.getTarget().getMCAsmInfo()->usesWindowsCFI();
     int Offset;
     if (IsWinEH)
-      Offset = static_cast<const X86FrameLowering *>(TFI)
-                     ->getFrameIndexOffsetFromSP(MF, FrameIndex);
+      Offset = TFI->getFrameIndexOffsetFromSP(MF, FrameIndex);
     else
       Offset = TFI->getFrameIndexOffset(MF, FrameIndex);
     FI.ChangeToImmediate(Offset);
     return;
   }
 
   // For LEA64_32r when BasePtr is 32-bits (X32) we can use full-size 64-bit
   // register as source operand, semantic is the same and destination is
if (MI.getOperand(FIOperandNum+3).isImm()) {
     // Offset is symbolic. This is extremely rare.
     uint64_t Offset = FIOffset +
       (uint64_t)MI.getOperand(FIOperandNum+3).getOffset();
     MI.getOperand(FIOperandNum + 3).setOffset(Offset);
   }
 }
 
 unsigned X86RegisterInfo::getFrameRegister(const MachineFunction &MF) const {
-  const TargetFrameLowering *TFI = MF.getSubtarget().getFrameLowering();
+  const X86FrameLowering *TFI = getFrameLowering(MF);
   return TFI->hasFP(MF) ? FramePtr : StackPtr;
 }
 
 unsigned
 X86RegisterInfo::getPtrSizedFrameRegister(const MachineFunction &MF) const {
   const X86Subtarget &Subtarget = MF.getSubtarget<X86Subtarget>();
   unsigned FrameReg = getFrameRegister(MF);
   if (Subtarget.isTarget64BitILP32())

lib/Target/XCore/XCoreRegisterInfo.cpp

static const MCPhysReg CalleeSavedRegs[] = {
     XCore::R8, XCore::R9, XCore::R10,
     0
   };
   static const MCPhysReg CalleeSavedRegsFP[] = {
     XCore::R4, XCore::R5, XCore::R6, XCore::R7,
     XCore::R8, XCore::R9,
     0
   };
-  const TargetFrameLowering *TFI = MF->getSubtarget().getFrameLowering();
+  const XCoreFrameLowering *TFI = getFrameLowering(*MF);
   if (TFI->hasFP(*MF))
     return CalleeSavedRegsFP;
   return CalleeSavedRegs;
 }
 
 BitVector XCoreRegisterInfo::getReservedRegs(const MachineFunction &MF) const {
   BitVector Reserved(getNumRegs());
-  const TargetFrameLowering *TFI = MF.getSubtarget().getFrameLowering();
+  const XCoreFrameLowering *TFI = getFrameLowering(MF);
 
   Reserved.set(XCore::CP);
   Reserved.set(XCore::DP);
   Reserved.set(XCore::SP);
   Reserved.set(XCore::LR);
   if (TFI->hasFP(MF)) {
     Reserved.set(XCore::R10);
   }
XCoreRegisterInfo::eliminateFrameIndex(MachineBasicBlock::iterator II,
   MachineInstr &MI = *II;
   MachineOperand &FrameOp = MI.getOperand(FIOperandNum);
   int FrameIndex = FrameOp.getIndex();
 
   MachineFunction &MF = *MI.getParent()->getParent();
   const XCoreInstrInfo &TII =
       *static_cast<const XCoreInstrInfo *>(MF.getSubtarget().getInstrInfo());
 
-  const TargetFrameLowering *TFI = MF.getSubtarget().getFrameLowering();
+  const XCoreFrameLowering *TFI = getFrameLowering(MF);
   int Offset = MF.getFrameInfo()->getObjectOffset(FrameIndex);
   int StackSize = MF.getFrameInfo()->getStackSize();
 
   #ifndef NDEBUG
   DEBUG(errs() << "\nFunction         : " 
         << MF.getName() << "\n");
   DEBUG(errs() << "<--------->\n");
   DEBUG(MI.print(errs()));
XCoreRegisterInfo::eliminateFrameIndex(MachineBasicBlock::iterator II,
   }
   // Erase old instruction.
   MachineBasicBlock &MBB = *MI.getParent();
   MBB.erase(II);
 }
 
 
 unsigned XCoreRegisterInfo::getFrameRegister(const MachineFunction &MF) const {
-  const TargetFrameLowering *TFI = MF.getSubtarget().getFrameLowering();
+  const XCoreFrameLowering *TFI = getFrameLowering(MF);
 
   return TFI->hasFP(MF) ? XCore::R10 : XCore::SP;
 }

utils/TableGen/RegisterInfoEmitter.cpp

RegisterInfoEmitter::runTargetHeader(raw_ostream &OS, CodeGenTarget &Target,
 
   const std::string &TargetName = Target.getName();
   std::string ClassName = TargetName + "GenRegisterInfo";
 
   OS << "#include \"llvm/Target/TargetRegisterInfo.h\"\n\n";
 
   OS << "namespace llvm {\n\n";
 
+  OS << "class " << TargetName << "FrameLowering;\n\n";
+
   OS << "struct " << ClassName << " : public TargetRegisterInfo {\n"
      << "  explicit " << ClassName
      << "(unsigned RA, unsigned D = 0, unsigned E = 0, unsigned PC = 0);\n"
      << "  bool needsStackRealignment(const MachineFunction &) const override\n"
      << "     { return false; }\n";
   if (!RegBank.getSubRegIndices().empty()) {
     OS << "  unsigned composeSubRegIndicesImpl"
        << "(unsigned, unsigned) const override;\n"
OS << "  const RegClassWeight &getRegClassWeight("
      << "  unsigned getRegPressureSetLimit(const MachineFunction &MF, unsigned "
         "Idx) const override;\n"
      << "  const int *getRegClassPressureSets("
      << "const TargetRegisterClass *RC) const override;\n"
      << "  const int *getRegUnitPressureSets("
      << "unsigned RegUnit) const override;\n"
      << "  ArrayRef<const char *> getRegMaskNames() const override;\n"
      << "  ArrayRef<const uint32_t *> getRegMasks() const override;\n"
+     << "  /// Devirtualized TargetFrameLowering.\n"
+     << "  static const " << TargetName << "FrameLowering *getFrameLowering(\n"
+     << "      const MachineFunction &MF);\n"
      << "};\n\n";
 
   const auto &RegisterClasses = RegBank.getRegClasses();
 
   if (!RegisterClasses.empty()) {
     OS << "namespace " << RegisterClasses.front().Namespace
        << " { // Register classes\n";
 
RegisterInfoEmitter::runTargetDesc(raw_ostream &OS, CodeGenTarget &Target,
   OS << "  static const char *Names[] = {\n";
   for (Record *CSRSet : CSRSets)
     OS << "    " << '"' << CSRSet->getName() << '"' << ",\n";
   OS << "    nullptr\n  };\n";
   OS << "  return ArrayRef<const char *>(Names, (size_t)" << CSRSets.size()
      << ");\n";
   OS << "}\n\n";
 
+  OS << "const " << TargetName << "FrameLowering *"
+     << TargetName << "GenRegisterInfo::\n"
+     << "    getFrameLowering(const MachineFunction &MF) {\n"
+     << "  return static_cast<const " << TargetName << "FrameLowering *>(\n"
+     << "      MF.getSubtarget().getFrameLowering());\n"
+     << "}\n\n";
+
   OS << "} // End llvm namespace\n";
   OS << "#endif // GET_REGINFO_TARGET_DESC\n\n";
 }
 
 void RegisterInfoEmitter::run(raw_ostream &OS) {
   CodeGenTarget Target(Records);
   CodeGenRegBank &RegBank = Target.getRegBank();
   RegBank.computeDerivedInfo();